TITLE OF INVENTION
[0001] Rotary Fluid Pressure Device And Improved Parking Lock Assembly
Therefor.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] This application claims priority to U.S. Provisional application Serial
No. 60/761, 021, filed January 20, 2006, in the name of Michio Kurokawa, Shoji
Nakazawa, and Hisatoshi Sakurai for a "Rotary Fluid Pressure Device and
Improved Parking Lock Assembly Therefor".
BACKGROUND
1. FIELD OF THE INVENTION
[0003] The present invention relates to rotary fluid pressure devices, and
more particularly, to a parking lock for such devices.
2. DESCRIPTION OF THE RELATED ART
[0004] In many vehicle applications for low-speed, high-torque gerotor
motors, it is desirable for the motor to have some sort of parking brake or
parking lock, the term "lock" being preferred because it is intended that the
parking lock be engaged only after the vehicle is stopped. In other words, such
parking lock devices are not intended to be dynamic brakes, which would be
engaged while the vehicle is moving, to bring the vehicle to a stop.
[0005] For many years, those skilled in the art have attempted to incorporate
brake and lock devices into gerotor motors, as opposed to merely adding a
brake package on the motor output shaft. Examples of such devices are
illustrated and described in U.S. Pat. Nos. 3,616,882 and 4,981,423. In the
device of U.S. Pat. No. 3,616,882, a braking element is disposed adjacent the
forward end of the gerotor star, and is biased by fluid pressure into frictional
engagement therewith. Such an arrangement involves a certain degree of

unpredictability of performance, in view of variations in clearances, etc. Such
an arrangement also requires a substantial redesign of the wear plate and
forward bearing housing of the motor. In the device of U.S. Pat. No. 4,981,423,
there is a multi-disc brake assembly which is of the "spring-applied, pressure-
released" type. The arrangement of the '423 patent also requires almost total
redesign of the forward bearing housing, and also results in a much larger
bearing housing. In addition, the disc pack is in splined engagement with the
output shaft and, therefore, must be able to brake or hold the full output torque
of the motor, thus necessitating that the discs, the spring, and the apply/release
piston all be relatively larger.
[0006] Another example of the incorporation of brake and lock devices into
gerotor motors is illustrated and described in U.S. Pat. No. 6,062,835, assigned
to the assignee of the present invention and incorporated herein by reference.
In the device of the '835 patent, a lock piston is disposed in an internal chamber
of an end cap assembly, located immediately adjacent to the gerotor gear set.
A spring biases the lock piston into engagement with the gerotor gear set when
hydraulic pressure is not supplied to the device. When hydraulic pressure is
supplied to the device, this hydraulic pressure acts against the lock piston to
disengage the piston from the gerotor gear set. Although the device in the '835
patent is compact and would function successfully in many hydraulic
applications, some current manufacturers of hydraulic applications, including
but not limited to mini-excavator manufacturers, have placed greater size
restrictions on gerotor motors while still requiring a parking brake or parking
lock feature.
BRIEF SUMMARY
[0007] The present invention provides a rotary fluid pressure device
comprising a housing member and a valve member, which provides fluid
communication between the housing member and a gerotor displacement
member. A central opening is defined by a member selected from the
group consisting of the housing member, the valve member, and any

combinations thereof. A release piston member, which is moveable
between a first position and a second position, is disposed in the central
opening. An end cap is disposed adjacent the gerotor displacement
mechanism and defines a piston cavity. A lock piston member, which is
moveable between a first position and a second position, is disposed in
the piston cavity. A drive shaft is disposed between the release piston
member and the lock piston member. The drive shaft defines an axial
bore, in which is disposed a pin member. The pin member defines a first
axial end, which is operably associated with the release piston member,
and a second axial end, which is operably associated with the lock piston
member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The accompanying drawings are included to provide a further
understanding of the present invention and are incorporated in and constitute
part of this specification. The drawings.illustrate exemplary embodiments of the
present invention and together with the description serve to further explain the
principles of the invention, wherein;
[0009] FIG. 1 is an axial cross section of a rotary fluid pressure device of the
type which may embody the present invention and includes a fragmentary
section taken on a different plane.
[0010] FIG. 2 is a transverse cross-section of the gerotor displacement
mechanism of the subject embodiment taken on line 2-2 in FIG. 1.
[0011] FIG. 3 is an enlarged, fragmentary axial cross section of the valve
ring assembly of the subject embodiment.
[0012] FIG. 4 is an enlarged, fragmentary axial cross section, similar to FIG.
1, of a rotary fluid pressure device illustrating the parking lock mechanism of the
present invention in the first position. .
[0013] FIG. 5 is an enlarged fragmentary axial cross section, similar to FIG.
1, of a rotary fluid pressure device illustrating the parking lock mechanism of the
present invention in the second position.

[0014] FIG. 6 is a hydraulic schematic of a housing member made in
accordance with the present invention.
[0015] FIG. 7 is a hydraulic schematic of an alternate embodiment of a
housing member made in accordance with the present invention.
DETAILED DESCRIPTION
[0016] Although the present invention may be included in a gerotor type
device being utilized as a pump, it is especially adapted for use in a low-speed
high-torque gerotor motor, and will be described in connection therewith.
[0017] Referring now to the drawings, which are not intended to limit the
invention, FIG. 1 illustrates an axial cross-section of a rotary fluid pressure
device of the type with which the parking lock mechanism of the present
invention is especially advantageous. The rotary fluid pressure device,
generally designated 11, includes a housing member 13, a valve housing 15, a
mounting plate 17, a valve plate 19, a gerotor displacement mechanism,
generally designated 21, and an end cap 23. The valve housing 15 includes a
flange 15a that defines a plurality of mounting holes 16 for rigidly mounting the
rotary fluid pressure device 11 to a hydraulic application. The mounting plate
17 also includes a flange 17a that defines a plurality of mounting holes 18 for
mounting the rotary fluid pressure device 11 to a rotating component (such as a
wheel or sprocket) of the hydraulic application. The end cap 23, the gerotor
displacement mechanism 21, the valve plate 19, and the mounting plate 17 are
held together in tight sealing engagement by means of a plurality of bolts 25 in
threaded engagement with the mounting plate 17. The end cap 23, the gerotor
displacement mechanism 21 and the valve plate 19 are further held in tight
sealing engagement by a plurality of bolts 27 in threaded engagement with the
valve plate 19. The housing member 13 and the valve housing 15 are held in
tight sealing engagement by a plurality of bolts 29 in threaded engagement with
the valve housing 15. As a result of this tight sealing engagement between the
housing member 13 and the valve housing 15, the term "housing member" in
the appended claims may refer to the housing member 13 and valve housing 15

individually or in combination. The valve housing 15 and the mounting plate 17
are held in engagement by a bearing assembly, generally designated 31. The
bearing assembly 31 includes an inner race 33 and an outer race 36. The inner
race 33 of the bearing assembly 31 is in a press fit engagement with the valve
housing 15, while the outer race 35 of the bearing assembly 31 is in a press fit
engagement with the mounting plate 17. The engagement of the inner race 33
of the bearing assembly 31 and the valve housing 15 is retained by a retainer
member 37. The engagement of the outer race 35 of the bearing assembly 31
and the mounting plate 17 is retained by a retainer member 39.
[0018] Referring now to FIGS. 1 and 2, the gerotor displacement mechanism
21 is well known in the art and will therefore be described only briefly herein.
More specifically, in the subject embodiment, the gerotor displacement
mechanism 21 is a Geroler ® displacement mechanism comprising an internally
toothed assembly 41. The internally toothed assembly 41 comprises a ring
member 43 which defines a plurality of generally semi-cylindrical openings 45.
Rotatably disposed within each of the semi-cylindrical openings 45 is a
cylindrical member 47, as is now well known in the art. Eccentrically disposed
within the internally toothed assembly 41 is a rotationally stationary externally
toothed rotor member 49, typically having one less external tooth than the
number of cylindrical members 47, thus permitting the externally toothed rotor
member 49 to orbit relative to the internally toothed assembly 41 and the
internally toothed assembly 41 to rotate relative to the externally toothed rotor
member 49. The relative orbital and rotational movement between the
internally toothed assembly 41 and the externally toothed rotor member 49
defines a plurality of expanding and contracting fluid volume chambers 51. The
externally toothed rotor member 49 defines a set of internal splines 53 formed
at the inside diameter of the rotor member 49. The internal splines 53 of the
rotor member 49 are in engagement with a set of external, crowned splines 55
on a main drive shaft 57. Disposed at the opposite end of the main drive shaft
57 is another set of external, crowned splines 59, for engagement with a set of
internal splines 61 in a stationary valve member 63.

[0019] Referring again to FIG. 1, the housing member 13 defines a fluid port
65 which is in fluid communication with a fluid passage 67. The valve housing
15 defines a fluid passage 69 which is in open fluid communication with the
fluid passage 67 in the housing member 13. Disposed within the valve housing
15 in an interference fit engagement is the stationary valve member 63. The
stationary valve member 63 defines an annular groove 71 which is in open fluid
communication with the fluid passage 69 in the valve housing 15. The
stationary valve member 63 further defines a plurality of fluid passages 73
which are in open fluid communication with the annular groove 71. In the
subject embodiment and by way of example only, there are six fluid passages
73 which are in open fluid communication with the annular groove 71, the
passages 73 being alternately arranged in the stationary valve member 63 with
six fluid passages (not shown) which are in open fluid communication with an
annular groove 75.
[0020] Referring now to FIGS. 1 and 3, a valve ring assembly, generally
designated 77, is disposed adjacent to the stationary valve member 63. The
valve ring assembly 77 includes a valve ring 79, a plurality of valve pistons 81,
and a plurality of springs 83. The valve ring 79 defines a plurality of valve
cavities 85. One of the plurality of valve pistons 81 is disposed in each valve
cavity 85. Each valve piston 81 defines a fluid passage 87, which is in open
fluid communication with the adjacent fluid passage in the stationary valve
member 63. One of the plurality of springs 83 is also disposed in each valve
cavity 85 between the valve ring 79 and the valve piston 81. Each spring 83
biases its respective valve piston 81 into the stationary valve member 63 to
provide sealing engagement between the valve piston 81 and the stationary
valve member 63. The valve ring 79 further defines a plurality of fluid passages
89 which are in commutating fluid communication with a plurality of valve
passages 91 in the valve plate 19. Each valve passage 91 is in open fluid
communication with one of the plurality of expanding or contracting fluid volume
chambers 51.

[0021] Referring now primarily to FIG. 3, the valve ring 79 further defines a
plurality of constraint holes 93, and each of the constraint holes 93 has
associated therewith a pin member 95 including a first axial end 97 and a
second axial end 99. The second axial ends 99 are disposed in a plurality of
constraint holes 101 defined by the stationary valve member 63. The pin
members 95 are disposed in the constraint holes 93 of the valve ring 79 and
constraint holes 101 of the stationary valve member 63 in order to prevent
rotation of the valve ring 79 with respect to the stationary valve member 63.
[0022] Referring now to FIGS. 1, 2 and 3, pressurized fluid entering the
rotary fluid pressure device 11 through the fluid port 65 in the housing member
13 will flow through the fluid passage 67 and into the fluid passage 69 in the
valve housing 15. The pressurized fluid will then flow through the annular
groove 71 and into the fluid passage 73 in the stationary valve member 63. The
pressurized fluid enters the valve cavity 85 through the fluid passage 87 in the
valve piston 81. From the valve cavity 85, the pressurized fluid flows through
the fluid passage 89 in the valve ring 79 and into the valve passages 91 in the
valve plate 19 which are in commutating fluid communication with the fluid
passage 89. The pressurized fluid will then enter the expanding fluid volume
chambers 51 in the gerotor displacement mechanism 21 through the adjacent
valve passages.91 in the valve' plate 19. As is well known to those skilled in the
art, the previously described flow will result in orbital movement of the externally
toothed rotor member 49 and rotational movement of the internally toothed
assembly 41.
[0023] Exhaust fluid will flow from the contracting fluid volume chambers 51
along a path similar to that previously described to the annular groove 75 in the
stationary valve member 63 and out a fluid port 102 (not shown in FIG. 1, but
shown schematically in FIG. 4) in the housing member 13.
[0024] Referring now to FIG. 4, with reference made to elements introduced
in FIGS. 1, 2 and 3, the parking lock mechanism will now be described. The
end cap 23 defines a piston cavity 103, which in the subject embodiment is
generally cylindrical. While the figures show the piston cavity 103 in the end

cap, it will be understood by those skilled in the art that the piston cavity 103
could also be defined by a plate member (not shown) that is adjacent the
gerotor displacement mechanism 21. Therefore, it will be understood that the
term "end cap" as used in the appended claims would include a plate member
that is adjacent to the gerotor displacement mechanism 21. Disposed within the
piston cavity 103 in the end cap 23 is a lock piston 105, which in the subject
embodiment is also generally cylindrical. The lock piston 105 includes a
forward portion 107 and a rearward portion 109. In the subject embodiment, the
forward portion 107 of the lock piston 105 has a larger diameter than the
rearward portion 109 of the lock piston 105. However, it will be understood by
those skilled in the art that the scope of the present invention is not limited to
the forward portion 107 having a larger diameter than the rearward portion 109.
The diameter of the forward portion 107 of the lock piston 105 is slightly
smaller than the diameter of the piston cavity 103 in the end cap 23. This
diametrical clearance between the lock piston 105 and the piston cavity 103
allows for axial movement of the lock piston 105 relative to the piston cavity
103. In the subject embodiment, the lock piston 105 further defines at least one
hole 111 that maintains substantially equal fluid pressure around the lock piston
105. However, it will be understood by those skilled in the art that the scope of
the present invention is not limited to the lock piston 105 containing the hole
111. Disposed rearwardly of the lock piston 105 in a spring cavity 113 is a
spring 115. In the subject embodiment, there is a cover plate 117 which is held
in tight sealing engagement with the end cap 23 by a plurality of bolts 119. The
cover plate 117 cooperates with the lock piston 105 to define the spring cavity
113. It should be understood by those skilled in the art, however, that the
spring cavity 113 could alternatively be disposed in the end cap 23.
[0025] The externally toothed rotor member 49 defines a central opening
121 at the axial end of the rotor member 49 which is adjacent to the end cap 23.
Disposed in the central opening 121 of the rotor member 49 is a lock collar
123. The inner diameter of the lock collar 115 is slightly larger than the
diameter of the forward portion 107 of the lock piston 105.

[0026] Referring still to FIG. 4, the stationary valve member 63 of the subject
embodiment defines a central opening 125 in which is disposed a release
piston ring 127. Although the central opening 125 is shown in the stationary
valve member 63 in the subject embodiment, those skilled in the art will
recognize that the central opening 125 could alternatively be disposed in the
housing member 13, as that term has been defined above, or a plate member
(not shown) that is adjacent to the housing member 13. Therefore, it will be
understood by those skilled in the art that the term "housing member" as used
in the appended claims may further refer to the plate member (not shown). The
release piston ring 127 includes a forward portion 129 and a rearward portion
131. The forward portion 129 of the release piston ring 127 defines a release
piston cavity 133. The rearward portion 131 of the release piston ring 127
defines a bore 135, the diameter of which is smaller than the diameter of the
release piston cavity 133. Disposed in sliding engagement with the release
piston cavity 133 of the release piston ring 127 is a release piston 137. In the
subject embodiment, the diametral clearance between the release piston 137
and the release piston cavity 133 is small enough to prevent or reduce fluid
leakage around the release piston while still allowing axial movement of the
release piston 137 relative to the release piston ring 127. It should be
understood, however, that fluid leakage around the release piston 137 could
also be prevented or reduced by the use of a sealing member (not shown), such
as an o-ring or a reciprocating seal, between the release piston 137 and the
release piston cavity 133.
[0027] Disposed between the lock piston 105 and the release piston 137 is
the main drive shaft 57. The main drive shaft 57 defines a pin bore 139 which
extends along the entire axial length of the main drive shaft 57. A brake pin
141, which includes a first axial end 143 and a second axial end 145, is
disposed in sliding engagement in the pin bore 139 in the main drive shaft 57.
The axial length of the brake pin 141 is longer than the axial length of the main
drive shaft 57. The first axial end 143 of the brake pin 141 extends through the
bore 135 in the rearward portion 131 of the release piston ring 127 and is

operably associated with the release piston 137. The second axial end 145 of
the brake pin 141 is operably associated with the lock piston 105.
[0028] Referring still to FIG. 4, when the release piston cavity 133 is
subjected to pressurized fluid from the housing member 13 through a fluid
passage 147, in a manner which will be described in greater detail
subsequently, the release piston 137 moves to the rearward portion 131 of the
release piston ring 127, hereinafter referred to in the appended claims as the
"first position." While the release piston 137 moves towards the rearward
portion 131 of the release piston ring 127, the release piston 137 engages the
first axial end 143 of the brake pin 141. The force exerted on the release piston
137 by the pressurized fluid from the housing member 13 causes the brake pin
141 to slide in the pin bore 139 of the main drive shaft 57 toward the lock piston
105 causing the second axial end 145 of the brake pin 139 to engage the lock
piston 105. If the force exerted on the release piston 137 is greater than the
force exerted on the lock piston 105 by the spring 115 disposed in the spring
cavity 113, the lock piston 105 will disengage from the lock collar 123 and move
axially toward the spring cavity 103 in the cover plate 117, thereby allowing the
rotor member 49 to orbit relative to the internally toothed assembly 41 and the
internally toothed assembly 41 to rotate relative to the rotor member 49. This
position of the lock piston 105, as shown in FIG. 4, will be referred to
hereinafter in the appended claims as the "first position."
[0029] Referring now to FIG. 5, when the pressurized fluid in the fluid
passage 147 in the housing member 13 is vented or relieved, the spring 115 in
the spring cavity 113 biases the lock piston 105 into sliding engagement with
the rearward face of the rotor member 49. After the rotor member 49 has
orbited a sufficient amount such that the central opening 121 of the rotor
member 49 is coaxial with the cavity 103 in the end cap 23 (which occurs once
per orbit of the rotor 49), the spring 115 biases the lock piston 105 into the
engaged position (as shown in FIG. 5) with the lock piston collar 123 in the
central opening 121 of the rotor member 49, thereby prohibiting the relative
rotation and orbit of the internally toothed assembly 41 and the externally

toothed rotor member 49. This position of the lock piston 105, as shown in FIG.
5, will be referred to hereinafter in the appended claims as the "second
position." As the lock piston 105 moves into engagement with the lock piston
collar 121, the lock piston 105 engages the second axial end 145 of the brake
pin 141. The force exerted by the spring 115 on the lock piston 105 is
transmitted through the brake pin 141 and acts on the release piston 137
through the engagement of the first axial end 143 of the brake pin 141 with the
release piston 137. With the spring force acting on the release piston 137
through the brake pin 141 and the pressurized fluid in the fluid passage 147 in
the housing member 13 relieved, the release piston 137 moves to the forward
portion 129 of the release piston ring 127, hereinafter referred to in the
appended claims as the "second position."
[0030] Referring now to FIG. 6, the housing member 13 is shown
schematically to illustrate how pressurized fluid is supplied to the fluid passage
147 in the housing member 13. In the'subject embodiment, but by way of
example only, pressurized fluid is supplied to the fluid passage 147 through a
3-position, 5-way valve assembly, generally designated 149. As the operation
of this type of valve is well known to those skilled in the art, a detailed
description, beyond the schematic, will not be provided herein.
[0031] Referring now to FIG. 7, an alternate embodiment of the housing
member 13 is shown schematically to illustrate how pressurized fluid is supplied
to the fluid passage 147 in the housing member 13. In the alternate
embodiment illustrated in FIG. 6, pressurized fluid is supplied to the fluid
passage 147 through a shuttle valve assembly, generally designated 151. As is
well known to those skilled in the art, the shuttle valve assembly 151 allows
pressurized fluid from fluid port 65 or fluid port 102 to flow to the fluid passage
147 while prohibiting direct fluid communication between fluid port 65 and fluid
port 102.
[0032] In addition to the three-position, five-way valve assembly 149 shown
in FIG. 6 and the shuttle valve assembly 151 shown in FIG. 7, an alternate
embodiment of the housing member 13 could allow pressurized fluid to be

directly supplied to the fluid passage 147 from a source of pressurized fluid
(such as a charge pump) located elsewhere on the hydraulic application
through a fluid port (not shown) in the housing member 13.
[0033] The invention has been described in great detail in the foregoing
specification, and it is believed that various alterations and modifications of the
invention will become apparent to those skilled in the art from a reading and
understanding of the specification. It is intended that all such alterations and
modifications are included in the invention, insofar as they come within the
scope of the appended claims.

What is claimed is:
1. A rotary fluid pressure device comprising
a housing member;
a valve member, which provides fluid communication between the
housing member and a gerotor displacement mechanism;
a central opening being defined by a member selected from the group
consisting of the housing member, the valve member, and any
combinations thereof;
an end cap being disposed adjacent the gerotor displacement
mechanism, wherein the end cap defines a piston cavity;
a release piston, which is moveable between a first position and a
second position, being disposed in the central opening;
a lock piston, which is moveable between a first position and a second
position, being disposed in the piston cavity;
a drive shaft disposed between the release piston and the lock piston,
wherein the drive shaft defines an axial bore; and
a brake pin, which is disposed in the axial bore of the drive shaft,
defining a first axial end and a second axial end, wherein the
first axial end is operably associated with the release piston and
the second axial end is operably associated with the lock piston
2. A rotary fluid pressure device as claimed in claim 1, further comprising
a lock collar, which is disposed in a central opening of the gerotor
displacement mechanism.
3. A rotary fluid pressure device as claimed in claim 1, wherein the piston
cavity in the end cap assembly is of a cylindrical shape.
4. A rotary fluid pressure device as claimed in claim 1 wherein the piston
cavity is in substantial alignment with a central opening of the gerotor
displacement mechanism during at least one point in the orbital

movement of the gerotor displacement mechanism.
5. A rotary fluid pressure device as claimed in claim 1, further comprising
a spring disposed in the piston cavity and operably associated with the
lock piston.
6. A rotary fluid pressure device as claimed in claim 1, further comprising
a release piston ring disposed in the central opening.
7. A rotary fluid pressure device as claimed in claim 1 wherein the lock
piston defines at least one hole.
8. A rotary fluid pressure device as claimed in claim 1 further comprising
a fluid passage that provides fluid communication between a source of
fluid pressure and a release piston cavity.
9. A rotary fluid pressure device as claimed in claim 8 further comprising
a valve assembly that provides fluid communication between the fluid
passage and the source of fluid pressure.
10. A rotary fluid pressure device as claimed in claim 9 wherein the valve
assembly is a 3-position, 5-way valve assembly.
11. A rotary fluid pressure device as claimed in claim 9 wherein the valve
assembly is a shuttle valve assembly.

A rotary fluid pressure device (11) includes an end cap (23) which is disposed rearwardly of, and adjacent, the fluid displacement mechanism (21). The end cap defines a piston cavity (103) in which is disposed a lock piston (105), which is moveable between a first position and a second position, in which the forward portion (107) of the lock piston extends within a
central opening (121) of a rotor member (49) to prevent movement. A release piston (137) is disposed in a central opening (125) of one of the housing member (13) and stationary valve member (63). A brake pin (141) is disposed in a bore (139) of a drive shaft (57), with a
first axial end of the brake pin being operably
associated with release piston and a second axial end being operably associated with the lock piston.