DEVICE FOR REDUCTION OF PULSATIONS
TECHNICAL FIELD
The present invention relates to a device for reducing pressure pulsations, the device being
connectible between a pressure chamber of a slave cylinder and a pressure chamber of a
master cylinder of a hydraulic force transmission system and being constantly open to the
pressure medium, according to the preamble portion of patent claim 1 In particular, the
invention relates to such devices to reducing pressure pulsations, such as are used on a large
scale in hydraulic clutch actuating means for motor vehicles.
PRIOR ART
Fig. 23 shows a conventional hydraulic clutch actuating means 10 for motor vehicles in a
simplified illustration. The hydraulic clutch actuating means 10 comprises a master
cylinder 12, which is mounted on a pedal block 11 of the motor vehicle, and a slave
cylinder mounted in the motor vehicle in the vicinity of a transmission, the cylinders being
hydraulically interconnected by way of a hydraulic line 16 which in this case consists,
starting from the master cylinder 12, of a first pipe section 18, a hose section 20 and a
second pipe section 22. The piston (not illustrated) of the master cylinder 12 hydraulically
connected with a fluid reservoir 24 is operatively connected with a clutch pedal 28 by way
of a piston rod 26 so that the master cylinder 12 can be actuated by pressing down the
clutch pedal 28, which produces displacement of the piston in the master cylinder 12. In
this connection, a fluid column hydraulically loading the slave cylinder 14 is displaced
through the hydraulic line 16 in the direction of the slave cylinder 14.
The slave cylinder 14, more precisely the piston (not shown here) thereof, is disposed in
operative connection with a release mechanism 36 of a friction clutch 38 by means of a
piston rod 30 via a release lever 32 and a release bearing 34. If the slave cylinder 14 is
hydraulically loaded for release of the friction clutch 38, then by means of the release
mechanism 36 a clutch pressure plate 40 is separated from a clutch drive disc 44, which is
seated on a transmission shaft 42 and which co-operates with a flywheel 43 carried by the
crankshaft of the internal combustion engine (not illustrated), of the friction clutch 38 and
thus the internal combustion engine is also separated from the transmission (similarly not
shown in more detail) of the motor vehicle.

If the clutch pedal 28 is released in order to re-engage the friction clutch 38 the slave
cylinder 14, specifically the piston thereof, is returned to its basic or initial setting as a
consequence of, inter alia, the spring forces of the friction clutch 38, in which case the
above-mentioned fluid column is displaced through the hydraulic line 16 back again in the
direction of the master cylinder 12.
In such a hydraulic clutch actuating means 10 - which is to be regarded as a quasi-static
hydraulic force transmission system in which a continuous flow of hydraulic fluid is not
present - vibrations of the internal combustion engine, particularly the crankshaft thereof,
are transmitted by way of the components of the friction clutch 38, the release bearing 34,
the release lever 32 and the slave cylinder 14 to the liquid column, which is present in the
hydraulic line 16, between the slave cylinder 14 and the master cylinder 12, the vibrations
propagating in the column as pressure pulsations. It was already regarded as
disadvantageous that the pressure pulsations are tracked by the driver at the clutch pedal
28 as vibrations particularly when the driver's foot rests on the clutch pedal in typical city
driving - so-called "rest tingling" - or the depressed clutch pedal 28 is held, for example
during a stop in front of traffic lights.
There is no lack of proposa^in the prior art for counteracting this problem, for example DE 36
31 507 C2 "Square helix", DE 40 03 521 C2 "Double line with line branches of different length ",
DE 195 40 753 C1 "Auxiliary oscillator" , DE 101 12 674 C1 "Diaphragm damper cell" ,
DE 100 06 542 A1 or DE103 51907AI "Damping device with labyrinth body".
It is common to these proposals that inserted into or arranged parallel to the hydraulic line
between master cylinder and slave cylinder is a separate subassembly, which does not
interrupt the fluid column between master cylinder and slave cylinder, for vibration
damping, the subassembly being capable in general of also satisfactorily damping the
pressure pulsations. However, the previously known solutions partially claim a relatively
large amount of installation space, which is not always available in the engine
compartment of the motor vehicle to a sufficient extent, and/or give rise to a comparatively
complex and accordingly expensive construction of the device, which is not desirable for
mass production.
"Double-acting" valve mechanisms connected between master cylinder and slave cylinder
(for example, JP 59-89833 A, EP 1 719 921 A2) will not be considered in more detail in

this connection, which mechanisms open when each displacement of the liquid column
occurs, i.e. not only in the case of displacement in the direction of the slave cylinder, but
also in the case of a displacement in the direction of the master cylinder, and close when
the liquid column is not moving, so as to screen or decouple in terms of vibration the
master cylinder from the slave cylinder, since these valve mechanisms (a) are usually of
even considerably more complicated construction than damping devices which are
constantly "open to the pressure medium" and do not require spring-biased valve bodies
or the like, (b) require specific opening and closing pressures which often undesirably
increase the return times and the system hysteresis, and finally (c) are provided with
bypasses susceptible to contaminations and thus accompanying losses in performance.
OBJECT
The invention has the object, starting from document DE 36 31 507 C2 forming the preamble
portion of patent claim 1, of providing a device for reducing pressure pulsations, which device is
connective between a pressure chamber of a slave cylinder and a pressure chamber of a
master cylinder of a hydraulic force transmission system, particularly a hydraulic clutch
actuating means for motor vehicles, and constantly open to the pressure medium, and
which device in conjunction with bsst possible vibration-damping characteristics by
comparison with the prior art is of compact and economic construction.
ILLUSTRATION OF THE INVENTION
This object is fulfilled by the features indicated in patent claim 1. Advantageous or
expedient developments of the invention are the subject of patent claims 2 to 2.1.
According to the invention a device, which is connective between a pressure chamber of a
slave cylinder and a pressure chamber of a master cylinder of a hydraulic force
transmission system, particularly a hydraulic clutch actuating means for motor vehicles,
and which is constantly open to the pressure medium, for reducing pressure pulsations
comprises, in combination, an additional conduit in the form of a channel having a helix
section defining an opening at the slave cylinder side and an opening at the master
cylinder side and having a channel length which is multiple of the direct spacing between
the two openings, and a volume receiving means which is resiliently deformable under

pressure, the channel and the volume receiving means being combined into a subassembly in a
housing in such a way that the helix section, which extends in the manner of a screw thread,
and the volume receiving means are arranged in the housing in a mutual coaxial positional
relationship with one substantially surrounding the other.
Investigations by the applicant have firstly led to the unexpected result that the two afore-
described measures for vibration damping - namely an additional conduit in the form of a
channel on the one hand and a volume receiving means on the other hand - are in
combination capable of reducing pressure pulsations to an extent going well beyond the
vibration damping effect of the respective measures individually, so that the vibration
damping characteristics of the device according to the invention can be categorized as
highly effective. Since, in addition, the channel and the volume receiving means are
combined into a subassembly in one and the same housing, wherein in addition the
channel length is a multiple of the direct spacing between the two channel openings, the
device according to the invention is on the one hand of very compact construction and on
the other hand the channel and the volume receiving means can be disposed in fluid
connection with very little outlay on sealing and connection, thus very economically. A
further advantage of the device according to the invention consists in that in the case of
use of the device in a hydraulic clutch actuating means according to Fig. 23, which is
otherwise conventional, the second pipe, section, which is near the slave cylinder, of the
hydraulic line which was usually constructed with a cross-section narrowed relative to the
first pipe section for the purpose of reduction in vibrations, can be eliminated, i.e. the hose
section of the hydraulic line can now be directly connected with the pressure connection of
the slave cylinder, in which case the second pipe section according to Fig 23 can be quasi
integrated into the device according to the invention in simple and very space-saving
manner. Further, from production aspects it is of advantage that the helix section extends in the
manner of a screw thead. Finally, since the helix section and the volume receiving means are
arranged in the housing in the housing in a mutually coaxial positional relationship with one
substantially surrounding the other, the device is of particularly short and compact construction.
In this connection, the helix section of the channel can surround the volume receiving means at
least partly coaxially. However, alternatively thereto the volume receiving means can also at
least partly coaxially surround the helix section of the channel.
It has proved to be particularly effective in terms of damping or reducing vibration if the
volume receiving means is hydraulically connected upstream of the channel, which forms

the additional conduit, as seen in a direction from the slave cylinder to the master cylinder,
so that the pressure pulsations propagating from the pressure chamber of the slave
cylinder do not have to firstly pass through the additional conduit in order to reach the
volume receiving means.
In an embodiment of the device according to the invention with particular cost advantages
an insert member can be inserted in the housing and bounds, at least partly together with
the housing, the channel, which also facilitates assembly of the device.
In this regard, the helix section of the channel can be formed at the outer
circumference of the insert member as a groove which is covered radially outwardly by an
inner circumferential surface of the housing, which on the one hand can be produced
particularly simply and economically - for example, by injection-molding of the insert
member, the radially outwardly open groove of which is "completed" in extremely simple
manner to form the channel, only on insertion of the insert member into the housing, by the
housing wall which is present there in any case, and, in particular, without use of sealing
elements or the like - and on the other hand produces a deflection of the fluid column,
which has proved advantageous with respect to good vibration damping with smallest
possible throughflow resistance. In addition, the helix section can have a helix reversal
dividing the helix section into a subsection running in righthanded direction and a
subsection running in lefthanded direction, whereby, in particular, the axial installation
space requirement for the helix section is reduced.
In a compact embodiment which is particularly simple in terms of production the insert
member can be of substantially pot-shaped construction with a casing section and a base.
Advantageously, in this regard the helix section, which is formed at the outer

circumference of the casing section of the insert member, of the channel can communicate
with the opening of the channel at the master cylinder side by way of a connecting section
of the channel extending in the base of the insert member.
The volume receiving means is preferably mounted at the inner circumference of the
sleeve section of the insert member, which on the one hand is required for a compact
construction of the device and on the other hand enables a simple plug mounting of the
volume receiving means. It is in addition preferred if the volume receiving means is a
rubber-elastic bobbin-shaped element with a passage bore and, at the outer
circumferential side, an annular recess which together with the inner circumference of the
sleeve section of the insert member bounds an annular air chamber. With such a design
of the volume receiving means, if a pressure amplitude runs into the passage bore the
bobbin-shaped element deforms against the spring effect of the rubber-elastic material, in
which case the air volume in the annular air chamber is compressed so that the bobbin-
shaped element - as the term "volume receiving means" already implies - experiences a
defined expansion in the region of the passage bore, which leads to a specific "relieving"
of the pressure amplitude. In this connection, the spring effect of the rubber-elastic
material and the compressed air volume ensures automatic return of the bobbin-shaped
element to its original form when the pressure, which is present in the region of the
passage bore of the bobbin-shaped element, of the pressure medium drops below a
predetermined value.
In an alternative embodiment of the voiume receiving means this can moreover be a
tubular element of a resilient plastics material which separates a radially inner pressure
medium chamber from a radially outer air chamber in the housing. The volume receiving
means is thus advantageously capable of injection molding, in which case the length and
cross-sectional profile can be formed to be relatively simple. In this embodiment of the
volume receiving means, if a pressure amplitude runs into the inner pressure medium
chamber the tubular element slightly deforms against the spring effect of the plastics
material, whereby the air volume in the radially outer air chamber is compressed so that
the tubular element experiences a predetermined expansion which in turn leads to
"relieving" of the pressure amplitude. In that case, the spring effect of the plastics material
and - to a far smaller extent - the compressed air volume in the radially outer air chamber
ensure automatic return of the tubular element to its original form when the pressure,
which is present in the inner pressure medium chamber, of the pressure medium drops

below a defined value. In this alternative of the device the substantially pin-shaped insert
member can advantageously be inserted into a central bore, which communicates with the
pressure medium chamber, in the housing.
Alternatively thereto, the volume receiving means can be a substantially hose-shaped
element of a rubber-elastic material which bounds a radially inner pressure medium
chamber in the housing and bears by its outer circumferential surface against an inner
circumferential surface of the housing, in which case the outer circumferential surface of
the volume receiving means is provided with a profiling for formation of cavities between
the volume receiving means and housing. Thus, in particular, the volume take-up of the
system can advantageously be limited in defined manner.
However, as a further alternative for the volume receiving means an embodiment is also
conceivable in which there is formed in the housing or insert member a smaller cylinder
space in which a spring-biased small piston is accommodated to be longitudinally
dispiaceable in such a manner that in the case of a pressure amplitude the piston is
displaced against its spring bias and through the thus-produced volume take-up a
"relieving" of the pressure amplitude is again produced. The automatic return of the piston
when a predetermined pressure of the pressure medium is fallen below would, in the case
of such an embodiment, be produced by the spring operatively connected vrth the piston,
for example a metallic helical compression spring, the characteristic and bias of which
could in a given case also be settable in correspondence with the respective constructional
conditions or requirements, but in each instance would be clearly defined and in addition
advantageously substantially independent of the ambient temperature
In one possible variant of the device it is provided that the housing is a separate housing
which, provided with a slave connection and a master connection, is connective into a
hydraulic line between slave cylinder and master cylinder so that the slave connection and
the master connection communicate with the pressure medium chamber formed in the
interior space of the housing. This variant enables a substantially free placing, or a placing
adapted to the respective constructional requirements or preconditions, of the device in the
hydraulic line between slave cylinder and master cylinder. In this regard, the separate
housing preferably consists of two parts, which, when fastened to one another, bound the
interior space in which the insert member and the volume receiving means are arranged.
However, an embodiment is also conceivable in which the insert member and/or - in the

case of the tubular element - the volume receiving means is or are formed integrally with
one of the housing halves so as to further reduce the parts count. The volume receiving
means preferably separates the pressure medium chamber from an air chamber in the
interior space of the separate housing. The insert member is preferably axially clamped in
place between the two parts of the separate housing so that there is no need for additional
measures for fastening of the insert member. In analogous manner the tubular or hose-
shaped element can also be clamped in place between the two parts of the separate
housing.
In another variant of the device the housing is a cylinder housing of the slave cylinder
(more preferred) or the master cylinder (less preferred), which has a pressure connection.
Through arrangement of the device in the cylinder housing, particularly in the pressure
chamber of the slave cylinder - where for this purpose no additional installation space has
to be provided, since the cylinder dead space present here in any case can be utilized, so
that the axial constructional length of the slave cylinder compared with conventional
constructions does not change - the integration of the vibration-damping measures in the
hydraulic force transmission system is similarly undertaken in very space-saving manner,
wherein in a given case even an existing slave cylinder such as known from, for example,
EP 1 666 752 A2 of the applicant can be adopted unchanged for integration of the device
according to the invention. Through the arrangement of the device according to the
invention in the pressure chamber of the slave cylinder, i.e. in the immediate vicinity of the
location of the introduction of vibrations into the liquid column, it is in addition
advantageously ensured that the pressure pulsations cannot propagate at maximum
amplitude in or through the hydraulic line between slave cylinder and master cylinder, so
that there is also minimization of the risk that the hydraulic line due to vibration detaches
from its fastening points at, for example, the bodywork of a motor vehicle or shakes loose
at these.
In an alternative, which is particularly favorable in terms of maintenance, to the
arrangement of the device in the pressure chamber of the cylinder housing, the channel
and volume receiving means of the device can be contained in a pressure connecting
section of the cylinder housing. In an advantageous embodiment the insert member is
then inserted into the pressure connecting section and held there by means of a
connecting member. With respect to, in particular, simple mounting and capability of
exchange it is in that regard advantageous if the insert member and the connecting

member are constructed integrally.
With respect to a best possible damping effect it has also proved advantageous if the helix
section of the channel has a cross-section which is smaller than or equal to the minimum
cross-section of the slave and/or master connection of the separate housing or of the
pressure connection of the cylinder housing, whereby a specific throttling effect is also
provided.
In principle, the insert member and/or the housing of the device can be made of a metallic
material, for example an aluminum alloy, such as by machining. However, is beneficial
particularly for creation of an economic device if the insert member and preferably also the
housing are injection-molded, as already mentioned, from a plastics material.
In a further variant of the device, finally, an additional path section can branch off the
channel and open into a closed chamber in order to further influence the damping
characteristics. In this regard, the afore-mentioned volume receiving means or an
additional volume receiving means can be accommodated in the closed chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in more detail in the following on the basis of preferred
exemplifying embodiments with reference to the accompanying, partly schematic
drawings, in which the same reference numerals denote the same or corresponding parts
and elastomeric parts are, for simplification of illustration, mostly shown in undeformed
state and in which:
Fig. 1 shows a longitudinal sectional view of a slave cylinder for a hydraulic clutch
actuating means for motor vehicles, into the pressure chamber of which is
inserted an insert member equipped with a device for reducing pressure
pulsations, the device being constantly open to the pressure medium and
comprising in combination an additional conduit in the form of a channel
and a volume receiving means, as a first embodiment of the device
according to the invention,
Fig. 2 shows a perspective individual illustration, obliquely from the front, of the

pot-shaped insert member fastened, in the case of the slave cylinder
according to Fig. 1, in the pressure connection,
Fig. 3 shows a side view of the insert member according to Fig 2,
Fig. 4 shows a front view of the insert member according to Fig 2, from the left in
Fig. 3,
Fig. 5 shows a back view of the insert member according to Fig 2, from the right
in Fig. 3,
Fig. 6 shows a sectional view of the insert member according to Fig. 2 in
correspondence with the section line VI-VI in Fig. 5,
Fig. 7 shows an illustration, to enlarged scale, of the detail VII in Fig. 6,
Fig. 8 shows a perspective individual illustration, obliquely from the front, of the
elastomeric volume receiving means mounted at the insert member in the
case of the slave cylinder according to Fig. 1,
Fig. 9 shows a longitudinal sectional view of the volume receiving means
according to Fig. 8,
Fig. 10 shows a diagram in which for (1) a hydraulic clutch actuating means without
the device according to the invention for reducing pressure pulsations
(marked by triangles) and (2) a hydraulic clutch actuating means with a
slave cylinder equipped in correspondence with Fig. 1 (marked by blank
squares) the ratio of the acceleration measured at a piston rod of the
master cylinder to the acceleration measured at a piston rod of the slave
cylinder is recorded against frequency, as a result of a test in which a
sinusoidal vibration with variable frequency and an amplitude of 1 g (9.81
m/s2) was applied to the piston rod of the slave cylinder.
Fig. 11 shows a side view of a device according to the invention for reducing
pressure pulsations in accordance with a second embodiment, which has

an own housing, i.e. separate from the cylinder housing, but is otherwise
similar to the first embodiment,
Fig. 12 shows a longitudinal sectional view of the device according to Fig. 11,
Fig. 13 shows a side view of a device according to the invention for reducing
pressure pulsations in accordance with a third embodiment, which similarly
has an own housing, i.e. separate from the cylinder housing, but differs
from the second embodiment with respect to the construction and physical
arrangement of the additional conduit and volume receiving means,
Fig. 14 shows a longitudinal sectional view of the device according to Fig. 13,
Fig. 15 shows a perspective individual illustration, obliquely from the front, of a pin-
shaped insert member inserted into the device according to Figs. 13 and
14, particularly for illustration of a groove helically extending at the outer
circumference of the insert part and forming a helix section of a channel,
which is provided as an additional conduit of the device,
Fig. 16 shows a diagram analogous to that of Fig. 10 in which for (1) a hydraulic
clutch actuating means without a device according to the invention for
reducing pressure pulsations (marked by triangles) and (2) a hydraulic
clutch actuating means into which a device corresponding with Figs. 13 to
15 is connected into the hydraulic line between master cylinder and slave
cylinder (marked by blank squares), the ratio of the acceleration measured
at a piston rod of the master cylinder to the acceleration measured at a
piston rod of the slave cylinder is recorded against frequency, as the result
of a test in which a sinusoidal vibration at a variable frequency and an
amplitude of 1 g (9.81 mis2) was applied to the piston rod of the slave
cylinder,
Fig. 17 shows a longitudinal sectional view of a device according to the invention
for reducing pressure pulsations in accordance with a variant of the third
embodiment, in which - by comparison with Fig. 14 - in particular the
volume receiving means is of different construction,

Fig. 18 shows an illustration, to enlarged scale, of the detail XVIII in Fig. 17,
Fig. 19 shows a longitudinal section view of a device according to the invention for
reducing pressure pulsations in accordance with a variant of the second
embodiment, which differs from Fig. 12 particularly in the respect that a
further path section branches off the additional conduit and opens into a
closed chamber in which a second volume receiving means can be
arranged,
Fig. 20 shows a broken-away longitudinal sectional view of a slave cylinder for a
hydraulic clutch actuating means for motor vehicles, in the pressure
connecting section of which a volume receiving means and an insert
member with an additional duct in the form of a channel are inserted, which
in combination form a device - which is always open to the pressure
medium - for reducing pressure pulsations and which are held in the
pressure connecting section by means of a connecting member, similar
toas a first variant of the first embodiments of the devioebut not according to
the invention,
Fig. 21 shows a perspective individual illustration, obliquely from the front, of the
insert member inserted into the pressure connecting section in the case of
the slave cylinder according to Fig. 20,
Fig. 22 shows a broken-away longitudinal sectional view of a slave cylinder for a
hydraulic clutch actuating means for motor vehicles, in which - similarly to
Fig. 20 - the device, which consists of volume receiving means and an
additional conduit in the form of a channel, for reducing pressure pulsations
is accommodated in the pressure connecting section, wherein by contrast
to Fig. 20 the insert member and connecting member are constructed
integrally, as a second variant ofagain similar to the first embodiment, of the
devicebut not according to the invention, and
Fig. 23 shows a basic illustration of a hydraulic clutch actuating means according to
the prior art.

DETAILED DESCRIPTION OF THE EMBODIMENTS
Fig. 1 shows a slave cylinder 50 for a vibration-damped hydraulic force transmission
system, namely a vibration-damped hydraulic clutch actuating means for motor vehicles.
The slave cylinder 50 has a cylinder housing which is denoted in general by 52 and in
which a piston subassembly 54 is received to be longitudinally displaceable, the
subassembly comprising a piston 56 and a piston rod 58 which is connected at least
tension-resistantly and compression-resistantly, thus effective in terms of actuation, with
the piston 56. Disposed in the cylinder housing 52 is a pressure chamber 60 which is
variably bounded on the side on the left in Fig. 1 by the piston 56, fixedly bounded on the
side on the right in Fig. 1 by a housing base 62 of the cylinder housing 52 and fixedly
bounded radially outwardly by a circumferential wall 64 of the cylinder housing 52. The
pressure chamber 60 is selectably loadable by way of a pressure connection 66 - which is
provided at the housing base 62 and which in the mounted state of the slave cylinder 50 is
connected in a manner known per se (cf. Fig. 23) by way of a pressure line (which by
comparison with Fig. 23 can also be of different construction) with a clutch master cylinder
- by a pressure medium, for example brake fluid, in order to displace the piston 56 in the
cylinder housing 52. As will be described in more detail in the following, inserted into the
pressure chamber 60 adjoining the housing base 62 is an insert member 68 which is
secured in the pressure connection 66 and in the first exemplifying embodiment illustrated
here advantageously fulfils a plurality of functions. In this regard, the insert member 68
serves, in particular, as a support for a device 70, which is constantly open to the pressure
medium, for reducing pressure pulsations or is equipped with this.
As is similarly explained in detail further below, the device 70, which in the mounted state
of the slave cylinder 50 is therefore connected between the pressure chamber 60 of the
slave cylinder 50 and a pressure chamber of the master cylinder (cf. again Fig. 23) for
reducing pressure pulsations comprises on the one hand an additional conduit in the form
of a channel 72, which has an opening 74 at the pressure chamber side or slave cylinder
side, an opening 76 at the pressure connection side or master cylinder side and
therebetween a channel length amounting to a multiple of the direct spacing, i.e. the
"straight line spacing", between the two openings 74, 76, and on the other hand a volume
receiving means 78 which is mounted at the insert member 68 and which is resiliency
deformable under pressure. As a result, the channel 72 and the volume receiving means

78 of the device 70 for reducing pressure pulsations are combined in the cylinder housing
52 with the highest degree of compactness to form a subassembly, in which case the
insert member 68 at least partly together with the cylinder housing 52 bounds the channel
72.
According to Fig. 1 the cylinder housing 52 comprises a base body 80. which is preferably
injection-molded from plastics material and which is provided at the outer circumferential
side with a fastening flange 82 for mounting the slave cylinder 50 in the motor vehicle.
The fastening flange 82 has two fastening bores 84, which are reinforced by means of
slotted steel bushes 86. Extending through the fastening bores 84 lined by the steel
bushes 86 are, in the mounted state of the slave cylinder 50, for example, screws (not
shown) which serve for fastening the slave cylinder 50 to, for example, a transmission wall
(not illustrated) in the motor vehicle. In Fig. 1 on the left of the fastening flange 82 the
base body 80 of the cylinder housing 52 moreover has at the outer circumferential side a
radial groove 88 into which an elastomeric protective cap 92, which has a bellows section
90 surrounding the piston rod 58, is clipped by an annular collar 94 at the inner
circumferential side. The bellows section 90 of the protective cap 92 additionally encloses
a spring element in the form of a helical compression spring 96, which is provided on the
side of the piston 56 remote from the pressure chamber 60 and which is supported at its
end on *he right in Fig. 1 at the cylinder housing 52 and engages at its end at..the left in
Fig. 1 the piston rod 58, so that the helical compression spring 96 biases the piston
subassembly 54 in a direction away from the housing base 62 so as to keep the piston rod
58 in contact with a clutch lever (not shown) in the mounted state of the slave cylinder.
At the inner circumferential side the base body 80 of the cylinder housing 52 has a
stepped bore 98 which is open towards the left in Fig. 1 and into which a preferably
metallic guide sleeve 100 as a further component of the cylinder housing 52 is inserted.
The guide sleeve 100 has two hollow-cylindrical sleeve sections 102, 104 of different
diameter which are connected together at the housing base 62 of the cylinder housing 52
by way of an annular section 106. Starting from the side at the left in Fig 1 the stepped
bore 98 of the base body 80 now has four bore sections 108, 110, 112 and 114 which are
of different diameter reducing in Fig. 1 from the left to the right.
The first bore section 108 of the stepped bore 98 in the base body 80 has at its open end
an undercut 116 which serves for the fixing at the cylinder housing 52 of an annular

securing element 118 preferably of plastics material, which is slotted for mounting and
which bears against the end face of the guide sleeve 100 at the left in Fig 1 and thus
secures the guide sleeve 100 in the base body 80 of the cylinder housing 52. The larger-
diameter sleeve section 102 of the guide sleeve 100 is tightly received in the second bore
section 110 of the stepped bore 98 of the base body 80 and forms by its inner
circumferential surface the circumferential wall 64 bounding the pressure chamber 60.
The third bore section 112 of the stepped bore 98 is connected with the second bore
section 110 by way of an annular shoulder 120 against which the annular section 116 of
the guide sleeve 100 bears. The smaller-diameter sleeve section 104 of the guide sleeve
100 is tightly received in the third bore section 112 of the stepped bore 98 in the base body
80. in that case the sleeve section 104 is provided at the outer circumferential side with a
radial groove 122 for reception of an O-ring 124, which ensures static sealing between the
third bore section 112 with the base body 80 and the sleeve section 104 of the guide
sleeve 100. The fourth bore section 114 of the base body 80 is connected with the third
bore section 112 by way of a further annular shoulder 126, wherein the dimensions of the
smaller diameter sleeve section 104 of the guide sleeve 100 on the one hand and the third
and fourth bore sections 112, 114 of the stepped bore 98 on the other hand are so
matched to one another that an annular end surface 128 of the sleeve section 104 of the
guide sleeve 100 has a small axial spacing from the annular shoulder 126 of the base
body 80 and protrudes radially inwardly beyond this for fastening, which will be described -
in more detail in the following, of the insert member 68 in the pressure connection 66. The
fourth bore section 114 of the stepped bore 98 in the base body 80 is additionally provided
at the inner circumferential side with a plurality - here for example four - of longitudinal ribs
(not able to be seen in Fig. 1) which extend in axial direction of the cylinder housing 52
and which protrude radially inwardly and are non-uniformly or asymmetrically distributed
over the circumference of the fourth bore section 114, the ribs serving for rotational angle
orientation of the insert member 68 in the pressure connection 66 as will be similarly
explained in more detail in the following. Finally, a smaller-diameter pressure connection
bore 130, which is formed in the base body 80, in the fourth bore section 114 opens at the
end, which is at the right in Fig. 1, of the fourth bore section 114 of the stepped bore 98.
It is evident from the above description that the pressure connection bore 130, the fourth
bore section 114 of the stepped bore 98 and the sleeve section 104, which is received in
the third bore section 112 thereof, of the guide sleeve 100 are a component of the
pressure connection 66, by way of which the pressure chamber 60 of the slave cylinder 50

can be loaded with the pressure medium. As a consequence of the static sealing, which is
produced by the O-ring 124, at the outer circumference of the smaller-diameter sleeve
section 104 of the guide sleeve 100 this experiences, in the case of a pressure loading of
the pressure chamber 60 by way of the pressure connection 66 in which the hydraulic
pressure on the one hand acts on the annular end surface 128 of the sleeve section 104
and on the other hand on the larger-area end surface - which is opposite thereto and faces
the pressure chamber 60 - of the annular section 106 of the guide sleeve 100, a resulting
force to the right in Fig. 1 which endeavors to keep the guide sleeve 100 in the stepped
bore 98 of the base body 80, thus relieves of load the fastening of the guide sleeve 100 in
the base body 80 by means of the securing element 118.
As can be further inferred from Fig. 1, the piston 56, which is guided with a small radial
play in the larger-diameter sleeve section 102 of the guide sleeve 100 of the cylinder
housing 52 and in the illustrated embodiment is metallic, has at the outer circumference a
radial groove 132 for reception of a groove ring 134. The elastomeric groove ring 134
bears, in a manner known per se, by its outer circumferential sealing lip under a defined
bias against the circumferential wall 64 of the cylinder housing 52 and thus ensures
dynamic sealing of the pressure chamber 60 towards the left in Fig. 1.
The piston 56 is additionally provided on the side at the left in Fig. 1 with a central recess
136 in which a ball head 138, which is formed at the end of the piston rod 58 at the right in
Fig. 1, is pivotably retained by means of a securing element 140 so that the piston rod 58
has a defined capability of angular movement with respect to the piston 56. Instead of the
form of the piston subassembly 54 shown in Fig. 1 this could also be of integral
construction with a piston outer surface, which decreases conically or spherically towards
the piston rod, for ensuring the capability of angular movement, as is known in principle
from DE 43 22 969 A1 or DE 43 31 241 A1.
The piston rod 58 which is metallic in the illustrated embodiment has on the side at the left
in Fig. 1 a profiled end 142 onto which an end member 144 of plastics matenal is injection-
molded, the end member having a substantially spherical end surface 146 by way of which
the piston rod 58 engages the clutch lever (not shown) to be effective in terms of actuation.
At the end of the end member 144 at the right in Fig. 1 this forms an annular collar 148 of
the piston rod 58 which serves on the one hand for coupling the protective cap 92 to the
piston rod 58, wherein the annular collar 148 is mechanically positively engaged in an

annular recess 150 of substantially complementary form in a fastening section 152 of the
protective cap 92, which is connected on the side of the protective cap 92 remote from the
pressure chamber 60 with the bellows section 90 of the protective cap 92 On the other
hand, the annular collar 148 of the piston rod 58 forms by its end face towards the
pressure chamber 60 a counter-bearing for the helical compression spring 96, wherein a
defined radial centering effect, which is of advantage when mounting the slave cylinder 50
in the motor vehicle, also derives from the end of the biased helical compression spring 96
facing the annular collar 148.
It is additionally evident from Fig. 1 that the securing element 118 for retaining the guide
sleeve 100 in the cylinder housing 52 is provided on its side remote from the pressure
chamber 60 with an axial groove 154 which serves as a further counter-bearing and for
centering of the end, which faces the pressure chamber 60 and is at the right in Fig. 1, of
the helical compression spring 96, which starting from the annular collar 148 of the piston
rod 58 substantially conically widens in diameter towards the axial groove 154, thus is of
frusto-conical construction. Through this "outward redisposition" of the helical
compression spring from the pressure chamber 60 and the guide sleeve 100 to the
illustrated setting between securing element 118 and annular collar 148 at the piston rod
58 it is possible to advantageously reduce by comparison with previously known
constructions the ratio of stroke vslume to dead-space volume - or actual volume in the
illustrated (installed) basic setting of the piston rod 56 - of the pressure chamber 60, which
ultimately produces a very short axial constructional length of the actual cylinder housing
52. Moreover, since the pressure chamber 60 does not have to receive a piston restoring
spring at which air bubbles could 'settle', the pressure chamber 60 on return of the piston
rod 56 from an actuating setting to a basic setting thereof is effectively flushed or
evacuated by the pressure medium, which contributes to very good ventilation of the slave
cylinder 50.
Further details of the device 70 for reducing pressure pulsations are evident from Figs. 2 to
9, in particular with respect to the insert member 68 (Figs. 2 to 7) injection-molded from a
suitable plastics material, for example from a glass-fiber-reinforced polyamide 66, and the
elastomeric volume receiving means 78 (Figs. 8 and 9) contained therein.
According to, in particular, Figs. 1 and 6, the insert member 68 is of substantially pot-
shaped construction, with a casing section 156, the outer diameter of which substantially

corresponds with the inner diameter of the circumferential wall 64 of the cylinder housing
52, and a base 158 with which a substantially hollow-cylindrical projection 160 is
connected, the projection being inserted into the pressure connection 66 of the cylinder
housing 52.
More precisely, the insert member 68 is axially mechanically positively fastened in the
pressure connection 66 of the cylinder housing 52, namely by means of a snap
connection. For this purpose the projection 160 of the insert member 68 is provided, going
out from its free end at the outer circumference, with a segmented annular collar 162 and
has multiple longitudinal slotting for formation of a plurality of spring arms 164 (see, in
particular, Figs. 2, 3, 5 and 6), wherein a counter-bearing surface 165, which is formed by
the annular collar 162 of the projection 160 and faces towards the pressure chamber 60,
according to Fig. 1 engages in the pressure connection 66 of the cylinder housing 52 in the
manner of a snap hook behind the annular end surface 128, which protrudes radially
inwardly into the base body 80 beyond the fourth bore section 114 of the stepped bore 98
and is formed by the smaller-diameter sleeve section 104 of the guide sleeve 100.
According to, in particular, Fig. 5, there are four slots 166, which extend in longitudinal
direction of the projection 160 and which in the illustrated embodiment interrupt the
projection 160 of the insert member 68 and the asymmetrical distribution of which over the
circumference of the projection 160 corresponds with the distribution of the above-
mentioned longitudinal ribs (not shown) in the fourth bore section 114 of the stepped bore
98 in the base body 80 of the cylinder housing 52. In this regard, the slots 166 in the
projection 160 of the insert member 68 on the one hand and the longitudinal ribs in the
base body 80 of the cylinder housing 52 on the other hand are so matched to one another
in terms of dimensions that in the mounted state of the insert member 68 the longitudinal
ribs at the housing side engage with a small circumferential play in the slots 166, but in
that case do not protrude radially inwardly beyond the spring aims 164. The
asymmetrical, mutually matched circumferential distribution of the longitudinal ribs and
slots 166 ensures in simple manner a unique rotational angle orientation of the mounted
insert member 68 in the slave cylinder 50, in particular in such a manner that the opening
74, which is at the pressure chamber side, of the channel 72 of the device 70 for reducing
pressure pulsations is, in the installed position of the slave cylinder 50, disposed at the top
near the inner circumferential surface of the cylinder housing 52 formed by the
circumferential wall 64, as shown in Fig. 1.

For preferably automatic production of the afore-described snap connection between the
cylinder housing 52 and the insert member 68, which is oriented in terms of angle with
respect to the cylinder housing 52, the insert member is pushed, starting from the open
end of the cylinder housing 52 lined with the guide sleeve 100, into the guide sleeve 100
until the spring arms 164 of the projection 160 come into contact with a small chamfer
between the annular section 106 and the inner circumference of the smaller-diameter
sleeve section 104 of the guide sleeve 100. On further axial relative displacement of the
insert member 68 with respect to the cylinder housing 52 the spring arms 164 spring
radially inwardly. As a consequence, the longitudinal ribs (not shown) in the fourth bore
section 114 of the base body 80 of the cylinder housing 52 enter the slots 166 of the
projection 160 of the insert member 68 before the spring arms spring radially outwardly
again and detent by their segmented counter-bearing surface 165 behind the annular end
surface 128 of the sleeve section 104. At substantially the same time trie base 158 of the
insert member 168 comes into contact by its end face towards the pressure connection 66
with the end surface, which faces the pressure chamber 60, of the annular section 106 of
the guide sleeve 100. Since not only the transition from the end surface, which faces the
pressure connection 56, of the spring arms 164 to the outer circumferential surface
thereof, but also the transition of the end surface, which faces the pressure chamber 60, of
the longitudinal ribs (not illustrated) to the inner circumferential surface thereof is formed to
be right-angular only with a broken edge,- i.e. without a chamfer, the insert member 68 can
be joined to the cylinder housing 52 only in the case of correct angular orientation of these
parts relative to one another. In the event of an attempt to join the insert member 68
without angular orientation or with incorrect angular orientation to the cylinder housing 52
the mutually facing end surfaces at the spring arms 164 on the one hand and at the
longitudinal ribs (not shown) on the other hand hit one another substantially by an area
and thus prevent further axial displacement of the insert member 68 with respect to the
cylinder housing 52. Since, moreover, the angular orientation of the insert member 68 with
respect to the cylinder housing 52 takes place at the base body 80 thereof, a fixing, which
acts in circumferential direction, of the guide sleeve 100 in the base body 80 is not
necessary.
As evident particularly from Figs. 1 and 6, the channel 72 in the insert member 68 has a
helically extending helix section 168, which is connected by way of a connecting section
170, which extends in radial direction in the base 158 of the insert member 68, with an end
section 172 formed by the projection 160 of the insert member 68 and extending in radial

direction, so that the helix section 168 communicates not only with the opening 74 at the
slave cylinder side, but also with the opening 76 at the master cylinder side, of the channel
72. In that case the helix section 168 of the channel 72 is formed at the outer
circumference of the casing section 156 of the insert member 68, preferably by injection
molding, as a groove which in the mounted state of the insert member 68 is covered
radially outwardly by the inner circumferential surface of the cylinder housing 52 formed by
the circumferential wall 64. In the illustrated embodiment, the helix section 168 has five
complete turns; however, it will be evident that the helix section can have also more or less
turns in correspondence with the respective functional requirements, which - just as other
cross-sectional shapes of the helix section departing from the illustrated substantially
rectangular cross-sectional shape - can be easily managed by injection molding. The
cross-section or the cross-sectional area of the helix section 168 of the channel 72 is
preferably to be selected so that it is smaller than or equal to the minimum cross-section of
the pressure connection 66, which in the illustrated embodiment is defined by the pressure
connecting bore 130.
According to, in particular, Figs. 1, 6 and 7 the insert member 68 additionally has at its end
at the pressure chamber side a captive section 174 which co-operates with a projection
176 of the piston 56 at the pressure chamber side in such a manner that the piston 56
prior to pressure-medium filling or first actuation of the slave cylinder 50 is fixed in a
predetermined stroke setting with respect to the cylinder housing 52 and is releasable
relative to the cylinder housing 52 by the pressure-medium filling or first actuation of the
slave cylinder 50. More precisely, the captive section 174 of the insert member 68
comprises a hollow cylinder 178, which is connected at the left in Fig. 1 with the casing
section 156 of the member and is axially aligned with respect to a centre axis of the
pressure chamber 60, with a radially inwardly projecting annular bead 180 which extends
at the inner circumferential side and which is shown in Fig. 7 to enlarged scale, whilst the
central projection 176 at the piston 56 is provided at the outer circumferential side with an
annular collar 182 (see Fig. 1) which has an outer surface slightly tapering in direction
towards the pressure connection 66 and mechanically positively engages behind the
annular bead 180 in the fixed state of the piston 56 at the insert member 68. For this
purpose, the annular bead 180, which according to, in particular, Fig. 7 is radiused towards
the pressure chamber 60, on the one hand and the annular collar 182 on the other hand
are so matched to one another in terms of dimensions that the clear inner diameter of the
annular bead 180 is slightly smaller than the largest outer diameter of the annular collar

182, whilst the spacing thereof from the end surface of the piston 56 is slightly larger than
the axial length of the annular bead 180.
For rendering the piston subassembly 54 captive at the insert member 68 when the slave
cylinder 50 is assembled the piston subassembly 54 is pushed against the force of the
helical compression spring 96 into the cylinder housing 58 in the sense of reduction of the
pressure chamber 60 until the projection 176 at the piston 56 comes into contact by its
annular collar 182, which is chamfered towards the insert member 68, with the radiused
annular bead 180 facing the pressure chamber 60. On further axial relative displacement
of the piston subassembly 54 with respect to the cylinder housing 52 in the direction of the
pressure connection 68 the annular collar 182 at the piston projection 176 resiliently
widens the annular bead 180 of the captive section 174 in radially outward direction. After
pressing beyond the annular bead 180 this snaps behind the annular collar 182 as a
consequence of the resilient characteristics of the material of the insert member 68, thus
into the annular gap between the annular collar 182 and the end surface of the piston 56
facing the pressure chamber 60. The piston subassembly 54 is now mechanically
positively fixed to the captive section 174 of the insert member 68.
Since the piston subassembly 54 is thus captive in a setting in which it is pushed as far as
possible into the cylinder housing 52, the slave cylinder 50 requires only a small amount of
space for storage, transport and mounting in the motor vehicle. Moreover, the slave
cylinder 50 can be mounted substantially free of force in the motor vehicle, because the
helical compression spring 96 does not have to be compressed, but is kept in a biased
setting by means of the capture of the piston subassembly 54 produced by the insert
member 68.
For the first actuation of the slave cylinder 50 mounted in the motor vehicle the pressure
medium is fed to the pressure chamber 60 by way of the pressure connection 66. As a
consequence of the pressure which thereby builds up in the pressure chamber 60 and acts
on the effective area of the piston 56, the piston 56 experiences a force which is directed
to the left in Fig. 1 and which adds to the force of the helical compression spring 96. If the
sum of these forces exceeds the holding force of the connection between the projection
176 of the piston 56 and the captive section 174 of the insert member 68 the annular bead
180 at the captive section 174 is further expanded beyond the annular collar 182 at the
projection 176, whereupon the piston subassembly 54 is released from the insert member

68. Further capturing of the piston subassembly 54 in operation of the slave cylinder 50 is
not intended and also cannot take place, since the axial spacing, which is shown in Fig. 1,
between the projection 176 of the piston 56 and the captive section 174 at the insert
member 68 is, in operation of the slave cylinder 50, no longer fallen below.
It is apparent from the above description that the holding force of the connection between
the projection 176 of the piston 56 and the captive section 174 of the insert member 68 is
constructionally designed in such a manner that it is on the one hand sufficiently larger
than the spring force of the helical compression spring 96 so as to prevent unintended
release of the captivation of the piston subassembly 54, but on the other hand sufficiently
smaller than the holding force of the connection between the insert member 68 and the
cylinder housing 52 so that the insert member 68 on first actuation of the slave cylinder 50
is not pulled out of the pressure connection 66.
As is further evident from Figure 1, the volume receiving means 78 is mounted at the inner
circumference of the casing section 156 of the insert member 68 so that the helix section
168 of the channel 72 coaxially surrounds the volume receiving means 78. For this
purpose the insert member 68 has a cylindrical blind bore 184 with which at the left in Figs.
1 and 6 a conically widening joining section 186 for the volume receiving means 78, which
ends with a small step at the hollow cylinder 178, is connected.
The volume receiving means 78 shown in more detail in Figs. 8 and 9 is a rubber-elastic
substantially bobbin-shaped element which has a passage bore 188 with a central cylinder
section 190 and opening funnels 192 disposed on either side of the cylinder section 190.
At the outer circumferential side the volume receiving means 78, which is rotationally
symmetrical with respect to its longitudinal axis and which is formed with mirror symmetry
with respect to a notional plane perpendicular to the longitudinal axis, is provided with a
channel-shaped annular recess 194 which according to Fig. 1 bounds, in the region of the
blind bore 184 and together with the inner circumference of the casing section 156 of the
insert member 68, an annular air chamber 196. The air chamber 196 is sealed at both
sides, i.e. to the right and left in Fig. 1, by annular sealing beads 198 (see Figs. 8 and 9) of
the volume receiving means 78. The function of this volume receiving means 78 was
already explained in more detail in the introduction, so that further explanations with
respect thereto at this point appear redundant. In this connection it is finally still to be
mentioned that the illustrated arrangement or positioning of channel 72 and volume

receiving means 78, in which the volume receiving means 78 is upstream in hydraulic
terms of the channel 72 - which forms the additional conduit - as seen from the pressure
chamber 60, has proved particularly effective in terms of damping vibrations.
The vibration-damping characteristics of the afore-described device 70 for reducing
pressure pulsations can be readily seen in Fig. 10, which illustrates by way of example the
result of tests in which (1) a sinusoidal vibration with variable frequency and an amplitude
of 1 g was applied to the piston rod 58 of the slave cylinder 50, (2) the accelerations of the
piston rod (not shown) of the master cylinder (not illustrated) hydraulically connected with
the slave cylinder 50 and of the piston rod 58 were measured and (3) were, for the test
evaluation, recorded in a diagram placed in relationship to one another against excitation
frequency. In this regard use was made of a slave cylinder 50 with an effective piston
effective diameter of 22.20 mm and a master cylinder with an effective piston effective
diameter of 19.05 mm, which were hydraulically interconnected by way of, starting from
the slave cylinder 50, (a) an elastomeric coupling hose section (inner diameter: approx. 6
mm; outer diameter: approx. 12 mm; length: approx. 250 mm, one fabric layer) and (b) a
metallic coupling pipe section (inner diameter: approx. 4.75 mm; wall thickness: approx.
0.7 mm; length: approx. 610 mm) of an existing pressure line arrangement. The length of
the helix section 168 of the channel 72 of the device 70 for reducing pressure pulsations
was approximately 200 mm with an open cross-section of approx 6 mm2. As volume
receiving means 78 use was made of a rubber sealing plug in correspondence with Figs. 8
and 9 with an overall length of approx. 7.3 mm, a maximum outer diameter of approx. 9.6
mm in the region of the sealing bead 198 and an inner diameter of approx. 3 mm in the
region of the cylinder section 190.
The vibration-damping capability of the tested device 70 for reduction of pressure
pulsations (marked by blank squares) by comparison with the arrangement without a
device for reducing pressure pulsations (marked by triangles) is clearly apparent in Fig. 10:
a substantial reduction in and displacement of the first maximum (at approx. 65 Hz)
towards lower frequencies occurred; in addition, the further vibration maxima are strongly
'depressed', by at least approx. 50%. It is clear to the expert that these results are to be
understood as only by way of example and the device 70 for reduction of pressure
pulsations can obviously be optimized as desired with respect to its vibration-damping
action for the respective installation situation such as in respect of the amplitude behavior
or the frequency range to be damped, whether through change in the shape/dimensions of

the channel 72 or volume receiving means 78 or selection of a different material for the
volume receiving means 78.
The second and third embodiments shall be described in the following with reference to
Figs. 11 to 16 only to the extent that they differ from the afore-described first embodiment.
In these figures the same or corresponding parts were provided with the same reference
numerals supplemented by an apostrophe (') for the second embodiment or two
apostrophes (") for the third embodiment (not listed in the Reference Numeral List at the
end).
The second embodiment illustrated in Figs. 11 and 12 differs from the first embodiment
principally in that the housing for receiving the channel 72' and the volume receiving
means 78' is a separate housing 200', i.e. a housing separate from the cylinder housing of
the slave or master cylinder, which, provided with a slave connection 202' and a master
connection 204', is connectible into the hydraulic line (not illustrated) between slave
cylinder and master cylinder so that the slave connection 202' and the master connection
204' (the latter by way of the channel 72') communicate with a pressure medium chamber
208' formed in an interior space 206' of the housing 200'. In the illustrated embodiment
the separate housing 200" consists of two parts 210', 212', which are injection-molded from
a suitable plastics material and which when fastened to one another bound the interior
space 206', in which the modified insert member 68', similarly injection-molded from a
suitable plastics material, corresponding with Fig. 12 and the volume receiving means 78'
according to Figs. 8 and 9 of the first embodiment are arranged. The latter separates,
analogously to the first embodiment, the pressure medium chamber 208' from an annular
air chamber 196' in the interior space 206' of the housing 200'.
At the housing part 210' at the left in Fig. 12 the slave connection 202' is executed as a
plug part with a plug geometry known per se, comprising a central passage bore 214' for
the pressure medium chamber 208' and two axially spaced-apart radial grooves 216', 218',
of which the outer radial groove 216' serves for reception of an O-ring 220" for sealing with
respect to the (receiving) counter-part (not shown), whilst the second radial groove 218' in
the mounted state of the device 70' receives a securing element (not illustrated), which is
fastened to the (receiving) counter-part, of spring steel wire. At the housing part 212' on
the right in Fig. 12, thereagainst, the master connection 204' is constructed as a receiving
part with a receiving geometry known per se, comprising a recess 222* into which the

(plug) counter-part (not shown) is insertable, and a securing element 224' of spring steel
wire, which is arranged at the outer circumferential side and which passes through a plug
slot 226', which extends transversely to the longitudinal axis of the master connection 204',
in order in the mounted state of the device 70' to secure the (plug) counter-part in the
recess 222' in a manner known per se.
The righthand housing part 212', which is connected with the master connection 204' at
the left in Fig. 12, is of substantially pot-shaped construction, with a base 228' through
which the end section 172" of the channel 72' extends in order to ensure a central
hydraulic connection between the connecting section 170' in the base 158' of the insert
member 68' and the recess 222' of the housing part 212', and a casing section 230', which
at the inner circumferential side forms the circumferential wall 64' radially outwardly
covering the helix section 168' of the channel 72'. By contrast to the first embodiment, the
insert member 68' in the second embodiment does not have at the base 158' any
projection for fastening in the housing 200', but instead is axially clamped between the two
housing parts 210', 212'. In that case the insert member 68' in Fig. 12 at the right bears by
its base 158' over an area against the base 228' of the housing part 212\ whilst the insert
member 68' is retained on the side at the left in Fig. 12 in the interior space 206' of the
housing 200' by means of a projection 232' - which is centrally hollowed in hollow-
cylindrical manner and plugged into the casing section 230' of the righthand housing part
212' and which bears against the insert member 68' - of the lefthand housing part 210'. In
the region of the projection 232' the two housing parts 210', 212', which here tightly
engage one in the other, are preferably glued together or ultrasonically welded together;
alternatively thereto, however, a screw connection could also be provided.
As already mentioned in the introduction, the thus-constructed device 70' for reducing
pressure pulsations can be arranged largely freely in the hydraulic line between slave
cylinder and master cylinder, for example between a hose section, which is at the slave
cylinder side, and a pipe section which is at the master cylinder side, of the hydraulic line.
The function or manner of effect of the device 70' in this regard corresponds with that of
the device 70 according to the first embodiment.
In the case of the third embodiment illustrated in Figs. 13 to 15 firstly the slave connection
202" and the master connection 204" of the two-part housing 200" are constructed
differently from the case of the second embodiment, namely mutually reversed so that the

slave connection 202" is formed as receiving part whilst the slave connection 204" is
constructed as plug part. In this regard the recess 222" of the slave connection 202" is in
fluid connection with the pressure medium chamber 208" via a passage 234" in the
housing part 210" at the left in Fig. 14.
The central passage bore 214", which communicates with the pressure medium chamber
208" by way of the channel 72", thereagainst has in the housing part 212" on the right in
Fig. 14 a stepped bore section 236" into which the substantially pin-shaped insert member
68" is inserted. As a result, the helix section 168" - which again is formed at the outer
circumference of the insert member 68" as a groove in accordance with, in particular, Fig.
15 - of the channel 72" is covered radially outwardly by an inner circumferential surface
64" of the bore section 236" of the housing 200". The ends 238" of the insert member 68"
injection-molded from a suitable plastics material are respectively planoparallelly flattened
in order to ensure a free passage to the pressure medium chamber 208" or to the end, at
the right in Fig. 14, of the passage bore 214". The insert member 68" can, for example, be
dimensioned/matched in, for example, outer diameter with respect to the inner diameter at
the circumferential wall 64" in such a manner that it is fixed by pressing into the passage
bore 214". Transverse bores with very small cross-section can be provided (indicated in
Fig. 14 by dashed lines) in order to ensure better ventilation of the channel 72" with
respect to the pressure medium channel 208" particularly in the case of filling of the device
70" with hydraulic fluid. In the case of this embodiment as well, the helix section 168" of
the channel 72" has a cross-section - here substantially rectangular - smaller than the
minimum free cross-section of the master connection 204" (in the end of the passage bore
214" at the right in Fig. 14).
According to Fig. 14 the two housing parts 210", 212" are additionally provided at 240"
with annular structures of complementary construction, which mechanically positively
interengage and at which the two housing parts 210", 212" are welded or glued for
formation of the housing 200'. The righthand housing part 210" and the lefthand housing
part 212" are formed with an annular recess 242" and 244", respectively, which together
receive the volume receiving means 78" so that the volume receiving means 78" is
clamped between the two housing parts 210", 212".
The volume receiving means 78" itself is a tubular element of a resilient plastics material,
for example injection-molded polyamide 66 without glass-fiber reinforcement, which

separates the radially inner pressure medium chamber 208" from the radially outer air
chamber 196" in the somewhat spherically formed housing 200". O-rings 246" at the end
and between the volume receiving means 78" and the respective housing part 210", 212"
in that regard seal the pressure medium chamber 208" relative to the air chamber 196". In
the case of this embodiment as well the helix section 168" of the channel 72" and the
volume receiving means 78" in the housing 200" are arranged in a mutual coaxial
positional relationship with one substantially surrounding the other, so that the housing
200" is of relative short construction, but here designed so that the volume receiving
means 78" at least partly coaxially surrounds the helix section 168" of the channel 72".
It will be apparent to the expert that the volume take-up of a volume receiving means 78"
designed in that manner can easily be appropriately matched to the respective installation
and functional requirements by suitable selection of the parameters of material, wall
thickness, diameter and/or length of the hollow-cylindrical pipe section so as to take into
account, for example, the respective operating pressure of an actuating path. The function
or manner of effect of the device 70" overall was already explained in more detail in the
introduction so that further explanations with respect thereto at this point appear
superfluous.
Tests were also carried out with respect to the third-embodiment, the result of which is
illustrated in Fig. 16 by way of example. The actual performance of the test corresponded
with that which was already described further above with reference to Fig. 10. However, in
the present case use was made of a slave cylinder with an effective piston effective
diameter of 19.05 mm and a master cylinder with an effective piston effective diameter of
15.87 mm, which - analogously to Fig. 23 - were hydraulically connected together by way
of, starting from the slave cylinder, (a) a metallic clutch pipe section (inner diameter:
approx. 4.75 mm; wall thickness: approx. 0.7 mm; length: approx. 300 mm), (b) an
elastomeric clutch hose section (inner diameter: approx. 6 mm; outer diameter: approx. 12
mm; length: approx. 250 mm, one fabric layer) and (c) a metallic clutch pipe section (inner
diameter: approx. 6 mm, wall thickness: approx. 0.7 mm; length: approx 400 mm) of an
existing pressure line arrangement. The (developed) length of the helix section 168" of the
channel 72" of the device 70" for reducing pressure pulsations, which was arranged
between the clutch hose section and the clutch pipe section at the master cylinder side,
again amounted to approx. 200 mm, with a free cross-section of approx. 3.6 mm2. As
volume receiving means 78" use was made of a pipe section of an unreinforced polyamide

66 with an overall length of approx. 40 mm, an outer diameter of approx. 18 mm and an
inner diameter of approx. 15.4 mm.
The vibration damping capability of the tested device 70" for reducing pressure pulsations
(marked by blank squares) by comparison with the arrangement without a device for
reduction of pressure pulsations (marked by triangles) is clearly evident from Fig. 16: there
is a substantial reduction particularly of the first maximum (at approx. 60 Hz), but without
displacement in the frequency range. It is also to be noted that these results are to be
understood as only by way of example: the device 70" for reducing pressure pulsations
can be optimized as desired with respect to its vibration-damping effect for the respective
installation situation such as in respect of the amplitude behavior or the frequency range to
be damped, whether by changing the shape/dimensions of channel 72" or volume
receiving means 78" and/or the selection of a different material for the volume receiving
means 78".
Figs. 17 and 18 show a variant of the third embodiment according to Figs 13 to 15, which
will be described in the following only to the extent that it differs from the third embodiment.
In the first instance, in Fig. 17 - by comparison with Fig. 14 - the insert member 68" is
turned through 90° about its longitudinal axis so that the free passages to the pressure
medium chamber 208" or to the passage bore 214" are not visible. Moreover, the housing
200" is not of spherical construction in correspondence with Fig. 14, but such that the inner
circumferential surface 248", which is formed by the housing parts 210", 212" and
surrounds the volume receiving means 78", of the housing 200" is substantially cylindrical.
Moreover, an air chamber corresponding with Fig. 14 (there reference number 196") is not
present between the outer circumferential surface 250" of the volume receiving means
78", which for simplification of the illustration is shown in undeformed state, and the inner
circumferential surface 248" of the housing 200". Instead, the volume receiving means
78" bears by its outer circumferential surface 250" against the inner circumferential surface
248" of the housing 200". For that purpose, the substantially hose-shaped volume
receiving means 78", here consisting of a rubber-elastic material such as EPDM
(elastomer on the basis ethylene-propylene-diene rubber), is profiled (profiling 251") at its
outer circumferential surface 250" so that it does not bear over the whole area against the
inner circumferential surface 248" of the housing 200", but only so as to leave

comparatively small cavities. In the illustrated embodiment (see Fig. 18) these cavities are
formed by a plurality of annular grooves 252" which are separated from one another by
encircling webs 254". As a consequence of this design, the volume receiving means 78"
can, in the case of pressure loading by the housing 200", more specifically the inner
circumferential surface 248" thereof, be compressed, with comparatively small volume
take-up in the pressure medium chamber 208. Through suitable selection of the geometry
- groove or grooves with rounded or polygonal cross-section, other recesses serving to
leave nubs, etc. - and/or the dimensions - depth, width and/or number of grooves or
recesses, etc. - of the profiling 251', the volume take-up of the device 70" can be limited in
defined manner in correspondence with the respective use requirements and the damping
characteristics of the device 70" influenced.
As can, moreover, be seen particularly in Fig. 18, the pressure medium chamber 208" is
sealed by sealing means between the ends of the volume receiving means 78" and the
housing 200". More precisely in the illustrated embodiment the volume receiving means
78" is integrally formed at its end, which is at the right in Fig. 18, at the inner
circumferential side with a sealing bead 256" which is received in an associated annular
groove 258" of the housing part 212". Thereagainst, at the end, which is at the left in Fig.
18, of the volume receiving means 78" there is provided an O-ring 260" which bears
against the substantially cylindrical inner circumference of the volume receiving means 78"
and is in turn received in an associated annular groove 262" of the housing part 210". In
principle, however, also both ends of the volume receiving means can be provided at the
inner circumference with a respective sealing bead or be provided at both ends of the
volume receiving means at the inner circumference with a respective O-ring
Fig. 19 shows a device variant with respect to the second embodiment according to Figs.
11 and 12, such as can in principle also be used in the first embodiment according to Figs.
1 to 10 and which in the following will be described only to the extent that it differs from the
afore-described embodiments.
According to Fig. 19 the housing parts 210', 212' of the housing 200' are firstly formed to
be axially prolonged by comparison with Figs. 11 and 12 so as to create space in the
housing part 210' for a receiving space 264', which is connected with the passage bore
214' and has a larger diameter by comparison therewith, for reception of the volume
receiving means 78'. The receiving space 264' is terminated in Fig 19 at the left by a

radially inwardly protruding annular bead 266' which ensures that the volume receiving
means 78' cannot, in operation, migrate out of the receiving space 264'.
Moreover, inserted into the insert member 68' arranged in the housing part 212' is a
substantially pot-shaped inner insert 268' with a closed base 270', which faces the housing
part 210', and a casing section 272' bearing at the end against the base 158' of the insert
member 68'. The base 270' and the casing section 272' of the inner insert 268' bound
together with the base 158' of the insert part 68' a closed chamber 274' having a single
step in diameter. A further volume receiving means 278' can be provided, as illustrated, in
the larger diameter chamber section 276' of the chamber 274' in addition to the afore-
described volume receiving means 278'. However, alternatively thereto also only the
volume receiving means 78' can be provided in the receiving space 264', whilst no volume
receiving means is arranged in the chamber 274', or the volume receiving means 278' can
be provided in the chamber 274' instead of the volume receiving means 78' in the
receiving chamber 264'.
The smaller-diameter chamber section 280' of the chamber 274' is disposed in fluid
connection by way of a connecting bore 282' with a helix section 284' which is formed at
the outer circumference of the inner insert 268", more precisely the casing section 272'
thereof, analogously to the helix section 168', which is at the outer circumference, of the
insert member 68'. The helix section 284' is in turn hydraulically connected by way of a
further connecting bore 286' with the helix section 168' of the insert member 68'. As a
result, the connecting bore 286' in the insert member 68', the helix section 284' formed
between insert member 68' and inner insert 268' and the connecting bore 282' in the inner
insert 268' form a further path section 288', which branches off the additional conduit or the
channel 72', of the device 70' for reducing pressure pulsations, which path section has a
length which is a multiple of the direct spacing between the connecting bores 282' and
286' and which path section opens in the manner of a dead end in the closed chamber
274' with or without volume receiving means 278'. This represents a further possibility of
appropriately adapting the device 70' with respect to its damping characteristics to the
respective use requirements.
It remains to be mentioned with respect to this variant that the inner insert 286' is held in
the insert member 68' with the help of annularly segmental webs 290' which in integral
construction with the housing part 210' or the inner insert 268' and distnbuted uniformly

over the circumference follow the annular bead 266' on the left in Fig 19
Figs. 20 to 22 finally show two variants with respect similar to the first embodiment which
was described above with reference to Figs. 1 to 10 and which will be described in the
following only to the extent that they differ from the first embodiment.
It is common to these variants that the device 70 for reducing pressure pulsations is again
integrated in the cylinder housing 52 of the slave cylinder 50; however this time it is not in
the pressure chamber 60, but in a pressure connection section 292, which is physically
separate or spaced from the pressure chamber 60, of the cylinder housing 52, which in the
illustrated embodiments variants extends, starting from the housing base 62 of the cylinder
housing 52, away from the housing base 62 at approx. 40° to the housing longitudinal axis.
In this regard, the pressure connecting section 292 is provided, .starting from its upper end
at the right in Figs. 20 and 22, with a stepped bore 294 which ultimately opens into the
pressure connecting bore 130 of the pressure connection 66 to the pressure chamber 60.
More precisely, the stepped bore 294, starting from the pressure connecting bore 130, has
a plurality of bore sections with increasing diameter from section to section, namely:
a connecting section 296 to the pressure connecting bore 130,
- a first receiving section 298 for reception of the volume receiving means 78 (cf., for
details of the latter, Figs. 8 and 9 with associated description) and a tubular projection 300
of the insert member 68,
a second, optionally again slightly stepped (see Fig. 22), second receiving section
302 for the main part of the insert member 68 and a plug end or plug section 304 of a
connecting member 306, by means of which the insert member 68 is retained in the
pressure connecting section 292,
a fastening section 308 for fastening the connecting member 306 in the pressure
connecting section 292, provided - in Fig. 20 - with an internal thread which co-operates
with an external thread 310 at the connecting member 306; in Fig. 22, thereagainst,
provided with an annular groove 312 into which a slotted plastics material ring 314 is
inserted for formation of a snap connection with an associated annular groove 315 in the
connection member 306, and
optionally a joining chamfer 316 (see Fig. 20) for the connecting member 306.
The connecting member 306 itself has, analogously to the second embodiment described

in the foregoing with reference to, in particular, Fig. 12, a master connection 204 with
receiving geometry known per se, comprising the recess 222 ending at the opening 76 of
the channel 72 at the master cylinder side, the securing element 224 and the insertion slot
226 for that purpose. In addition, the plug end or plug section 304 is provided with an
annular groove for reception of an O-ring 318 which seals relative to the second receiving
section 302 of the stepped bore 294.
The insert member 68 bearing against the annular shoulder 320 formed between the first
receiving section 298 and the second receiving section 302 of the stepped bore 294
similarly has at the outer circumference of the projection 300 an annular groove 322 (cf.
Fig. 21) in which a further O-ring 324 is received, which seals relative to the first receiving
section 298 of the stepped bore 294. Finally, the insert member 68, starting from the free
end of the projection 300, is provided with a blind bore 326 which as a component of the
channel 72 forms at one end thereof the opening 74 at the slave cylinder side and at the
other end thereof is hydraulically connected with the helix section 168 of the insert
member 68 by way of a connecting bore 328 to be regarded as similar to the channel 72
and extending transversely to the insert member 68.
The helix section 168 of the insert member 68 additionally has, in this variant according to
Fig. 21, the feature that at 330 it possesses a helix reversal having the effect that the
hydraulic fluid, which on actuation of the hydraulic clutch actuating means comes from the
opening 76 at the master cylinder side and which initially flows with respect to the
longitudinal axis of the insert member 68 in clockwise sense through the helix section 168
of the channel 72, changes its direction of movement at the helix reversal 330, which is
formed in the manner of a switchback turn, and flows from the helix reversal 330 through
the helix section 168 in counter-clockwise sense. In other words, the helix reversal 330
divides the helix section 168 into a subsection 332 running in the manner of a righthand
thread and a subsection 334 running in the manner of a lefthand thread. As a result, by
comparison with the helix section without helix reversal, on the one hand a slightly larger
throughflow resistance increasing the damping effect of the device 70 arises and on the
other hand the axial space requirement of the thus-formed helix section 168 is smaller. A
helix reversal of that kind can obviously also be provided in the other embodiments.
Otherwise, the variants according to Figs. 20 and 22 additionally differ - apart from the
different material for the cylinder housing 52 (light metal in Fig. 20; plastics material in Fig.

22) - in that in the case of the variant according to Fig. 22 the insert member 68 and the
connection member 306 are of integral construction, preferably by means of injection
molding from plastics material.
A device, which is connectible between a pressure chamber of a slave cylinder and a
pressure chamber of a master cylinder of a hydraulic force transmission system,
particularly a hydraulic clutch actuating means for motor vehicles, and which is constantly
open to the pressure medium, for reducing pressure pulsations is disclosed. This device
comprises an additional conduit in the form of a channel, which has a helix section, an
opening at the slave cylinder side, an opening at the master cylinder side and a channel
length which is a multiple of the direct spacing between the two openings, and a volume
receiving means which is resiliency deformable under pressure, wherein the channel and
the volume receiving means are combined in a housing to form a subassembly in such a way
that the helix section, which extends in the manner of a screw thread, and the volume receiving
means are arranged in the housing in a mutual coaxial positional relationship with one
substantially surrounding the other. As a result, a device is created which not only has very
good vibration damping characteristics, but is also constructed very compactly and has an
economic construction.

REFERENCE NUMERAL LIST
10 hydraulic clutch actuating means
11 pedal block
12 master cylinder
14 slave cylinder
16 hydraulic line
18 first pipe section
20 hose section
22 second pipe section
24 fluid reservoir
26 piston rod
28 clutch pedal
30 piston rod
32 release lever
34 release bearing
36 release mechanism
38 friction clutch
40 clutch pressure plate
42 transmission shaft
43 flywheel
44 clutch drive disc
50 slave cylinder
52 cylinder housing
54 piston subassembly
56 piston
58 piston rod
60 pressure chamber
62 housing base
64 circumferential wall
66 pressure connection
68 insert member
70 device for reducing pressure pulsations
72 channel

74 opening at slave cylinder side
76 opening at master cylinder side
78 volume receiving means
80 base body
82 fastening flange
84 fastening bore
86 steel bush
88 radial groove
90 bellows section
92 protective cap
94 annular collar
96 helical compression spring
98 stepped bore
100 guide sleeve
102 sleeve section
104 sleeve section
106 annular section
108 bore section
110 bore section
112 bore section
114 bore section
116 undercut
118 securing element
120 annular shoulder
122 radial groove
124 O-ring
126 annular shoulder
128 end surface
130 pressure connecting bore
132 radial groove
134 groove ring
136 recess
138 ball head
140 securing element
142 end

144 end member
146 end surface
148 annular collar
150 annular recess
152 fastening section
154 axial groove
156 casing section
158 base
160 projection
162 annular collar
164 spring arm
165 counter-bearing surface
166 slot
168 helix section
170 connecting section
172 end section
174 captive section
176 projection
178 hollow cylinder
180 annular bead
182 annular collar
184 blind bore
186 joining section
188 passage bore
190 cylinder section
192 opening funnel
194 annular recess
196 air chamber
198 sealing bead
200 housing
202 slave connection
204 master connection
206 interior space
208 pressure medium chamber
210 housing part

212 housing part
214 passage bore
216 radial groove
218 radial groove
220 O-ring
222 recess
224 securing element
226 plug slot
228 base
230 casing section
232 projection
234 passage
236 bore section
238 end
240 annular structure
242 annular recess
244 annular recess
246 O-ring
248 inner circumferential surface
250 outer circumferential surface
251 profiling
252 annular groove
254 web
256 sealing bead
258 annular groove
260 O-ring
262 annular groove
264 receiving space
266 annular bead
268 inner insert
270 base
272 casing section
274 chamber
276 larger-diameter chamber section
278 (further) volume receiving means

280 smaller-diameter chamber section
282 connecting bore
284 helix section
286 connecting bore
288 path section
290 web
292 pressure connecting section
294 stepped bore
296 connecting section
298 first receiving section
300 projection
302 second receiving section
304 plug end or plug section
306 connection member
308 fastening section
310 external thread
312 annular groove
314 plastics material ring
315 annular groove
316 joining chamfer
318 O-ring
320 annular shoulder
322 annular groove
324 O-ring
326 blind bore
328 connecting bore
330 helix reversal
332 subsection extending in the manner of a righthand thread
334 subsection extending in the manner of a lefthand thread

We claim:
1. Device (70, 70 ', 70") for reducing pressure pulsations, the device being
connectible between a pressure chamber (60) of a slaves cylinder (50) and a pressure
chamber of a master cylinder of a hydraulic force transmission system, particularly
hydraulic clutch actuating means for motor vehicles, and constantly open to the
pressure medium, comprising
an additional conduit in the form of a channel (72, 72 ', 72") having a helix
section (168, 168', 168"), defining an opening (74, 74', 74") at the slave cylinder side
and an opening (76, 76', 76") at the master cylinder side, and having a channel length
equal to a multiple of the direct spacing of the two openings (74,76; 74', 76'; 74", 76"),
and
a volume receiving means (78, 78', 78") resiliency deformable under pressure,
characterized in that the channel (72, 72', 72") and the volume receiving means
(78, 78', 78") are combined in a housing (52, 200', 200") to form a subassembly in such
a way that the helix section (168,168', 168"), which extends in the manner of a screw
thread, and the volume receiving means (78, 78', 78") are arranged in the housing (52,
200', 200") in a mutual coaxial positional relationship with one substantially surrounding
the other.
2. Device (70, 70 ', 70') according to claim 1, characterized in that the volume
receiving means (78, 78 ', 78') is hydraulically connected upstream of the channel (72,
72 ', 72") forming the additional conduit as seen in the direction from the slave cylinder
(50) to the master cylinder. .
3. Device (70, 70 ', 70") according to claim 1 or 2, characterized in that an insert
member (68, 68', 68") which at least partly together with the housing (52, 200 ', 200")
bounds the channel ( 72, 72', 72") is inserted into the housing (52, 200'. 200").

4. Device (70, 70 ', 70") according to claims 3 , characterized in that the helix
section (168, 168', 168") of the channel (72, 72', 72") is formed at the outer
circumference of the insert member (68, 68', 68") as a groove, the groove being
covered radially outwardly by an inner circumferential surface (64, 64', 64") of the
housing (52, 200'. 200").
5. Device (70, 70 ') according to the claim 3, characterized in that the insert member
(68, 68') is of substantially pot-shaped construction with a casing section (156. 156')
and a base (158, 158).
6. Device (70, 70') according to claim 5, characterized in that the helix section (168,
168') of the channel (72, 72') formed at the outer circumference of the casing section
(156,156') of the insert member (68, 68') communicates with the opening (76, 76') of
the channel (72, 72') at the master cylinder side by way of a connecting section (170,
170') of the channel (72, 72') extending in the base (158, 158') of the insert member
(68, 68').
7. Device (70, 70') according to claim 5 or 6 characterized in that the volume
receiving means (78, 78') is mounted at the inner circumference of the casing section
(156, 156') of the insert member (68, 68').
8. Device (70, 70') according to claim 7, characterized in that the volume receiving
means (78, 78') is a rubber-elastic bobbin-shaped element with a passage bore (188,
188') and at the outer circumferential side an annular recess (194, 194) bounding
together with the inner circumference of the casing section (156,156') of the insert
member (68, 68') an annular air chamber (196, 196').
9. Device (70, 70') according to at least claim 1, characterized in that the helix
section (168, 168') of the channel (72, 72') at least partly coaxially surrounds the volume
receiving means (78, 78').

10. Device (70") according to any one of claims 1 to 4, characterized in (hat the
volume receiving means (78") is a tubular element of a resilient plastics material
separating a radially inner pressure medium chamber (208") from a radially outer air
chamber (196") in the housing (200").
11. Device (70") according to any one of claims 1 to 4, characterized in that the
volume receiving means (78") is a substantially hose-shaped element of a rubber-
elastic material bounding a radially inner pressure chamber (208") in the housing (200")
and bearing by its outer circumferential surface (250") against an inner circumferential
surface (248") of the housing (200"), the outer circumferential surface (250") of the
volume receiving means (78") being provided with a profiling (251") for formation of
cavities between the volume receiving means (78") and the housing (200").
12. Device (70") according to at lease claims 3 and 10 or at least claim 3 and 11,
characterized in that the substantially pin-shaped insert member (68") is inserted into a
central bore (214") in the housing (200"), the bore communicating with the pressure
medium chamber (208").
13. Device (70") according to at least claim 10 and 12 or at least claim 11 and 12,
characterized in that the volume receiving means (78") at least partly coaxially
surrounds the helix section (168") of the channel (72").
14. Device (70', 70") according to any one of the preceding claims, characterized in
that the housing is a separate housing (200', 200") provided with a slave connection
(202', 202") and a master connection (204', 204") and connectible into a hydraulic line
between slave cylinder and master cylinder so that the slave connection (202 , 202")
and the master connection (204', 204") communicate with the pressure medium
chamber (208, 208") formed in the interior space (206', 206") of the housing (200',
200").

15. Device (70' 70") according to claim 3 and 14, characterized in that the separate
housing (200', 200") consists of two parts (210', 212'; 210", 212") which when fastened
to one another bound the interior space (206', 206") in which the insert member (68',
68") and the volume receiving means (78', 78") are arranged.
16. Device (70', 70") according to claim 14 to 15, characterized in that the volume
receiving means (78', 78") in the interior space (206', 206") of the housing (200', 200")
separates the pressure medium chamber (208', 208") from an air chamber (196, 196").
17. Device (70) according to at least claim 15 characterized in that the insert member
(68') is axially clamped between the two parts (210', 212') of the housing (200').
18. Device (70") according to at least claim 10 and 15 or at least claims 11 and 15,
characterized in that the tubular or hose-shaped element (78") is clamped between the
two parts (210", 212") of the housing (200").
19. Device (70) according to any one of claims 1 to 13, characterized in that the
housing is a cylinder housing (52) of the slave cylinder (50) or the master cylinder and
has a pressure connection (66).
20. Device (70, 70', 70") according to at least claim 14 or at least claim 19
characterized in that the helix section (168, 168', 168") of the channel (72, 72', 72") has
a cross-section smaller than or equal to the minimum cross-section of the slave
connection and/or master connection (202', 204'; 202", 204") or of the pressure
connection (66).
21. Device (70, 70'. 70") according to at least claim 3, characterized in that the insert
member (68, 68', 68") and preferably also the housing (52, 200', 200") are injection-
molded at least partly from a plastics material.
22. Device (70') according to at least claim 1, characterized in that an additional path
section (288') opening into a closed chamber (274') branches off the channel (72').

23. Device (70') according to claim 22, characterized in that the volume receiving
means (78') or an additional volume receiving means (278') is received in the closed
chamber (274').
24. Device (70) according to at least claim 19, characterized in that the cylinder
housing (52) has a pressure connection section (292) containing the channel (72) and
the volume receiving means (78).
25. Device (70) according to at least claim 3 and 19, characterized in that the insert
member (68) is inserted into the pressure connection section (292) and held there by
means of a connecting member (306).
26. Device (70) according to claim 25, characterized in that the insert member (68)
and the connecting member (306) are constructed integrally.
27. Device (70) according to at least claim 1, characterized in that the helix section
(168) has a helix reversal (330) dividing the helix section (168) into a subsection (332)
extending in righthanded direction and a subsection (334) extending in lefthanded
direction.

The invention relates to a device (70) that is always
open for the pressure medium for reducing pressure
pulsations and that can be switched between a pressure
chamber (60) of a slave cylinder (50) and a pressure
chamber of a master cylinder of a hydraulic force
transmission system, in particular a hydraulic clutch
actuator for motor vehicles. Said device comprises an
additional line section in the form of a channel (72)
having an opening (74) on the slave cylinder side, an
opening (76) on the master cylinder side, and a channel
length equaling a multiple of the direct distance
between the two openings, and a volume receiver (78)
that can be elastically deformed under pressure,
wherein the channel and the volume receiver are
combined into an assembly in a housing (52). The result
according to the invention is a device that not only
has very good vibration dampening properties, but is
also very compact and has a cost-effective design.