COUNTER ROTATING MASS SYSTEM CONFIGURED TO BE APPLIED TO AN
INLINE-FOUR INTERNAL COMBUSTION ENGINE TO BALANCE THE
VIBRATIONS PRODUCED BY SAID ENGINE, AND INLINE-FOUR ENGINE
COMPRISING SAID SYSTEM
Application field of the invention
The present invention refers to a counter rotating mass
system configured to be applied to an inline-four internal
combustion engine to balance the vibrations produced by
said engine, and an inline-four engine comprising said
system.
Description of the prior art
The application of a counter rotating mass system to an
engine is known in the art for balancing the vibrations and
the inertias produced by the drive shaft in order to
eliminate or at least to considerably reduce them. Said
system is usually fixed to the crankcase or to the
crankcase sump under the engine, anyway to a point where
the balancing is necessary, and where it is possible to
take the control of the mass rotation from the drive shaft.
Balancing the vibrations produced by •an inline-four engine
presents, however, different problems with respect to other
cylinder alignment configurations.
For example, an inline-three engine is described in the
following, whose behavior is similar to an inline-five
engine, both having an odd number of cylinders.
In an inline-three engine, the explosion occurs at each
240° of rotation the driving shaft {120° / = 240°). The
driving shaft is schematized in figure 1 , with ignition
order: 3.1 - 3.3 - 3.2.
At a first analysis, it may seem that, during its rotation,
the center of gravity of the three pistons and their
respective connecting rods is always at the center of the
engine, thus they do not generate any vibration. The
analysis may also lead to believe there are no spurious
forces, both vertically and transversally generated.
This, however, is not correct, because it implies the
assumption that the engine is a single point and the forces
are acting on a single plane. The forces have, on the
contrary, a different collocation along the shaft itself
and, instead of being reciprocally cancelled out, they
generate resultants that make the driving shaft vibrate at
the two ends, generating first-order free moments, of the
type "pitching".
Figure 1 clearly shows that when piston 3.1 is at its upper
dead center and inverts its motion downwards, it generates
an upward force at the front end of the engine; piston 3.2
moves downwards and it generates an upward force positioned
at the center of the engine; on the contrary, piston 3.3,
which moves upwards, generates a downward force positioned
at the rear end of the engine.
Since the axial center of gravity of the engine is
positioned over the middle cylinder 3.2, a longitudinal
"clockwise" moment is generated on the driving shaft, due
to the fact that cylinder 3.1 pushes upwards and cylinder
3.3 pushes downwards. After a rotation of 180°, the
situation is completely reversed, and the moment generated
by pistons 3.1, 3.3 is inverted and becomes
"counterclockwise" .
The solution usually provided to counterbalance such
moments on an- inline-three engine is to apply a balance
shaft driven by the driving shaft with two eccentric masses
at the two ends of the shaft. The two masses move in a
direction opposite to the piston's direction. Thus the
"pitching" moment is balanced by an equal and opposite
moment .
In an inline-five engine occur the same phenomena as in the
inline-three engine.
An inline-five engine, the explosion occurs at each 720°/5=
144° of the driving shaft rotation. A s shown in figure 2 ,
the ignition order is 5.1-5.3-5.5-5.4-5.2.
The resultants of the first-order alternate forces are
balanced.
The resultants of the second-order alternate forces are
balanced as well.
On the contrary, an inline-five engine generates "pitching"
longitudinal moments similar to the ones of an inline-three
engine. This happens because piston 5.1 is not in the same
position as piston 5.5 and piston 5.2 is not in the same
position as piston 5.4.
For this reason, the two ends of the engine vibrate with
respect to the center of the engine.
A solution that is usually provided to counterbalance such
moments on an inline-five engine is to apply, as in the
case of the inline-three engine, a balance shaft which
rotates in a direction opposite to the driving shaft, has
the same length as the engine and two counterweights moving
in a direction opposite to that of the pistons. The shaft
is driven by the engine at the same speed as the driving
shaft .
Or, as described in EP-462411, pairs of counter rotating
masses may be applied at the two ends of the driving shaft.
The solutions provided in the aforementioned cases,
however, cannot be applied in case of an inline-four
engine, where the generated vibrations are of a completely
different type.
Figure 3.1 shows the diagram of an inline-four engine,
whose ignition order is: cylinder 1 (4.1) - cylinder 3
(4.3) - cylinder 4 (4.4) - cylinder 2 (4.2).
The ignition occurs each 720°/4=180° of the driving shaft
rotation, thus the pairs of pistons 4.1-4.4 and 4.2-4.3 are
exactly in the same position and always move according to
the same direction. In order to avoid the pitching
phenomenon, cylinders are arranged as in the figure, thus
piston 4.1 is perfectly balanced by 4.4, and piston 4.2 is
balanced by 4.3.
Thus it is possible to say that an inline-four engine does
not need to balance the first-order free moments, due to
the opposed reciprocal movements of the four cylinders.
As for the vertical forces, it may be seen that piston 4.1
is balanced by piston 4.2 and piston 4.3 by piston 4.4.
This, however, is valid only for first-order alternate
forces. Second-order alternate forces are much smaller
than first-order ones and rotate at twice the frequency of
the first-order ones and their application point coincides
with the center of the engine. If said forces intensify so
as to provoke a resonance phenomenon, they may even break
the driving shaft.
The phenomenon may be explained with reference t o figure
3.2.
In an inline-four engine, both the linear movement of the
pistons and the angular movement of the connecting rods are
such that the piston which is moving in the upper part of
the cylinder (towards the upper dead center) has a
displacement (b) along the cylinder axis higher than the
displacement (a) of the piston moving in the lower part
(towards the lower dead center) , being the angular
displacement the same.
Such difference of displacement is such that the piston
moving in the upper part generates a force along the
cylinder axis higher than the force, having opposite
direction, generated by the piston moving in the lower
part. The resultant force is, as said above, a second-order
force which rotates at twice the speed of the driving
shaft .
The longer is the stroke, d the heavier are the piston
and the connecting rod, the more important are the secondorder
alternate forces to be balanced.
This occurs in particular on engines that are part of the
load bearing structure of the vehicle, as for example in a
tractor or in earthworks machines. Indeed in such cases the
engine produces strong vibrations that need to be balanced.
Solutions suitable for dampening the vibrations induced by
second-order alternate forces in an inline-four engine are
known in the art, applying eccentric masses so that their
center of gravity is as near as possible to the center of
the engine.
In an example of known solution (figure 4), two counter
rotating shafts are applied, driven by the driving shaft
and rotating at twice its speed, of the type "distributed"
along the whole length of the engine. Such solution has
problems deriving from its weight and its bulk.
In another example of known solution, a system of the type
shown in figures 5.1 and 5.2 is applied.
The system is provided with a sump having a closed rigid
body 1 , for example made of cast iron, which contains two
shafts 2 , 3 pivoted to the two ends of the sump supporting
them. Two eccentric masses 4 , 5 , with their respective gear
wheels , 7 engaging with each other and thus determining
the counter "rotation, are mounted on the shafts by means of
appropriate bearings or bushes. Generally the motion of the
drive shaft is transmitted to one of the two gear wheels,
for example by means of gears. Moreover, an internal
canalization system is usually present in order to bring
oil for lubricating the two counter rotating masses which
rotate at high speed, typically twice the RPM of the
engine. The whole system is fixed to the engine by screws.
Also a system of this type known in the art has problems
deriving from its weight and its bulk. For example, the
sump is a rigid body made of cast iron, thus very heavy and
bulky. The pre-assembling of such a system takes long time,
and consequently has high production costs.
Summary of the invention
Therefore the aim of the present invention is to
overcome all the aforementioned drawbacks and to provide a
counter rotating mass system configured to be applied to an
inline-four internal combustion engine for balancing the
second-order alternate forces generated on the driving
shaft of said engine, having a lower weight, bulk, costs.
The idea at the basis of the present invention is to
realize a counter rotating eccentric mass system projecting
from the opposite sides of a central support.
The system is preferably applied in the middle, under the
driving shaft.
This system is considerably simpler than the systems known
in the art, since the eccentric masses project from the two
sides of a central support that is very simple and compact.
The present invention refers in particular to a counter
rotating mass system configured to be applied to an inlinefour
internal combustion engine to balance the vibrations
produced by said engine, and inline-four engine comprising
said system, as described more fully in the claims, that
are an integral part of the present description.
Brief description of the Figures
Further purposes and advantages of . the present
invention will become clear from the following detailed
description of a preferred embodiment (and its alternative
embodiments) and the drawings that are attached hereto,
which are merely illustrative and non-limitative, in which:
figures 1 and 2 show a schematization of, respectively,
inline-three and inline-five engines;
figures 3.1 shows a schematization of an inline-four
engine;
figures 3.2 shows a schematization of the movement of a
piston in the inline-four engine;
figure 4 shows a schematization of a balancing system
of the type known in the art, described above, that can be
applied to an inline-four engine;
figures 5.1 and 5.2 show a further balancing system of
the type known in the art, as described above, that can be
applied to an inline-four engine, respectively according to
an assembled and an exploded view;
figures 6 and 7 show a first embodiment of a counter
rotating mass system according to the present invention,
that can be applied to an inline-four engine, respectively
according to an assembled and an exploded view;
figures 8 , 9 , and 10 show further views of the system
of figures 6 and 7 , respectively according to a
longitudinal section on the plane of the masses, according
to a cross section in correspondence of middle of the
support, and according to a view in a plan;
figures 11 and 12 show a second embodiment of a counter
rotating mass system according to the present invention,
that can be applied to an inline-four engine, with rolling
bearings replacing sliding bushes, respectively according
to an exploded view and a cross section view.
figure 13 shows an example of collocation of the system
that is object of the invention on an inline-four four
engine.
In the figures the same reference numbers and letters
identify the same elements or components.
Detailed description of preferred embodiments of the
invention
A s said above, the idea at the basis of the present
invention is to realize a central support having low weight
and small bulk, with counter rotating eccentric masses
projecting from the two sides of the support.
With reference to figures from 6 to 13, a central
support 21 is shown, suitable for supporting two pairs of
counter rotating eccentric masses 22, 23 and 24, 25, being
at the .two opposite sides of the support.
The eccentric masses 22 and 23 on one side of the
support are held by the respective hubs 26, 27, on which
the driving means of the mass rotation are fixed. In this
example they comprise wheel gears 28 and 29, suitable to
engage with each other in order to determine the counter
rotation of the masses.
The eccentric masses 2 4 and 25 from the other side of
the support are held by the respective shafts 30, 31.
The support 21 is provided with two through cross holes
32 and 33, which allow the shafts 30 and 31 to pass
through, such shafts being coaxially fixed to the hubs 26,
27 of the respective masses on the opposite side, for
example by means of tightening screws 34, 35.
In order to ensure the correct rotation and to avoid
friction, an appropriate backlash is realized between the
lateral sides of the support and the sides of the hubs and
of the shafts that face them. Moreover, appropriate
shoulders 30', 31' are present on the edges of the shafts.
In order to guarantee the correct rotation phase,
centering pins 38, 39 are preferably present and fit in
appropriate blind holes on the terminal sides of the shafts
30, 31 and in corresponding contact points of the hubs 26,
27.
Bushes 36, 37 are preferably present and are inserted
in the holes 32, 33 in order to facilitate the rotation of
the shafts 30, 31 and to minimize the friction.
The support comprising the elements described above is
fixed to the engine by screws 40, and an appropriate gear
of the drive shaft (not shown in the figures), connected to
one of the gear wheels, drives the rotation of the masses.
A lower protection sump 41 is fixed to the support 21
for example by means of screws 42.
With reference to figure 9 , a canalization 43 internal
to the support 21 may be present in order to bring
lubricating oil to the bushes 36, 37, which are preferably
provided with a groove placed in correspondence of the
canalization in order to facilitate the introduction of the
oil. A plug 44 may be applied from the outside in order to
close the external access to the canalization. A hole 45
may also be present on the upper side of the support 21, in
order to connect the oil canalization 43 to an appropriate
oil delivery on the crankcase of the engine, interfacing
with the mass unit.
In a possible alternative embodiment shown with
reference to the figures 11 and 12, roller bearings 71, 72
may be present instead of the bushes. In this case
lubrication may be unnecessary and therefore it is possible
to avoid the internal canalization of the support.
Moreover, in order to ensure the transmission of a
higher torque, if necessary, and to ensure the correct
rotation phase of the masses, raised parts 73, 74 may be
present, for example on the terminal side of the shafts 30,
31, fitting in corresponding recesses 75, 7 in the hubs
supporting the masses. Of course, the opposite arrangement
of raised parts and recesses is also possible.
Figure 13 shows an example of collocation of the system
that is object of the invention on an inline-four four
engine. The system, globally indicated by the reference 131
is placed in the middle under the driving shaft 132. The
support 21 is fixed by screws 40 to the fixed wall of the
engine (not shown in the figures) under the central support
bank 133. A specially provided gear 135 is present on the
driving shaft and generates the rotation of the gear wheel
28 of the system, so that the masses rotate at twice the
frequency of the driving shaft.
Number 134 indicates the profile of the oil sump, which
contains also the system 131. The lower protection sump 41
may be not present, as in this case.
The central position of the system is preferred, since it
simplifies design, manufacturing and installation of the
system, since the eccentric masses may have the same
magnitude on the two opposite sides of the support. The
system may also be installed in a decentralized position,
nearer to a side of the driving shaft. In this case it is
necessary to recalculate the balancing of the rotating
masses, proportionally to the magnitude of the lateral
displacement .
Compared to the systems known in the art, a heavy and
bulky sump having a rigid body is no longer necessary for
supporting the masses, instead there is only a central
support 21, which may be made of a lighter material, for
example aluminium, which is fixed to the crankcase.
The possibly present lower sump 41 does not have any
load bearing function, but it only has a protection
function, and therefore it may be made of a lighter
material as well, such as metal plate or plastic. Moreover
the hermetic seal of the sump is not necessary, while in
the system known in the art the rigid body sump is
hermetically sealed.
The rotation drive of the masses by means of gears and
wheel gears, may be replaced by a different drive, for
example by means of belts and pulleys or chain.
The counter rotating masses on one side of the support
are in phase with the ones on the other side, and they do
not necessarily have the same shape, but they may be
different .
The masses have to be made of a material which resists
to high RPM, for example high-duty cast iron or pressed
steel .
It will be apparent to the person skilled in the art
that other alternative and equivalent embodiments of the
invention can be conceived and reduced to practice without
departing from the scope of the invention.
The advantages deriving from the use of this invention
are evident, with respect to the solutions known in the
art .
The new solution is compact and simple, with a
monolithic support and simple machining replacing a complex
case; thus the overall weight is remarkably reduced, even
by 50%, and the longitudinal bulk is also reduced, even by
20%.
Assembling is easier, with a considerable reduction of
the costs. Masses are mounted from the outside of the
support by means of simple procedures and a reduced number
of operations; on the contrary in the systems known in the
art, masses, shafts and bushes have to be mounted from the
inside of the sump by using complex and time-consuming
assembling procedures.
Since the system is so compact, it is possible to
easily integrate additional functions to the system, such
as: oil pump, suction rose, oil delivery canalization to
the crankcase.
More standardization opportunities are possible.
From the description set forth above it will be
possible for the person skilled in the art to embody the
invention with no need of describing further construction
details .
CLAIMS
1 . Counter rotating mass system configured to be
applied to an inline-four internal combustion engine, with
cylinder ignition sequence 1-3-4-2 (4.1, 4.3, 4.4, 4.2), to
balance second-order alternate forces produced on the
driving shaft of said engine, the system comprising a
central support (21) and counter rotating eccentric masses
(22, 23, 24, 25) projecting from the two opposite sides of
the support.
2 . Counter rotating mass system as in claim 1 ,
centrally positioned under the driving shaft (132), inside
an engine oil sump (134), and whose rotation is driven by
said shaft with twice its frequency of rotation.
3 . Counter rotating mass system as in claim 2 ,
wherein said counter rotating masses have equal value on
said two opposite sides of the support.
4 . Counter rotating mass system as in claim 1 ,
wherein :
- the eccentric masses (22, 23) on one side of the support
are held by respective hubs (26, 27), on which the driving
means of the mass rotation are fixed, suitable to engage
with each other in order to determine the counter rotation
of said masses;
- the eccentric masses (24, 25) on the other side of the
support are held by their respective shafts (30, 31);
- the support (21) is provided with through cross holes
(32, 33), which allow the passage of said shafts (30, 31)
coaxially fixed to the hubs (26, 27) of the respective
masses on the opposite side.
5 . Counter rotating mass system as in claim 4 ,
wherein said driving means of the mass rotation are gear
wheels (28, 29) or pulleys.
6 . Counter rotating mass system as in claim 4 ,
wherein in order to ensure the correct rotation phase of
the masses, centering pins (38, 39) are present and fit in
appropriate blind holes on the terminal sides of the shafts
(30, 31) and in corresponding contact points of the hubs
(26, 27) .
7 . Counter rotating mass system as in claim 4 ,
wherein in order to ensure the correct rotation phase of
the masses, raised parts (73, 74) are present on the
terminal sides of the shafts (30, 31) or of the hubs (26,
27) and fit in appropriate recesses (75, 76) on the hubs or
on the shafts.
8 . Counter rotating mass system as in claim 1 ,
further comprising a lower protection sump (41) fixed to
the support (21) .
9 . Counter rotating mass system as in claim 4 ,
further comprising bushes (36, 37) or roller bearings (71,
72) inserted in the holes (32, 33) of the support, in order
to facilitate the rotation of the shafts (30, 31) .
10. Counter rotating mass system as in claim 9 ,
further comprising a canalization (43) internal to the
support (21) in order to bring lubricating oil to said
bushes (36, 37) or roller bearings (71, 72).
11. Inline-four internal combustion engine, with
cylinder ignition sequence 1-3-4-2 (4.1, 4.3, 4.4, 4.2),
comprising a counter rotating mass system to balance
second-order alternate forces produced on the driving shaft
of said engine, as in any of the previous claims.