Spline reduction extension for auxilliary drive component

A gerotor motor is disclosed of the type including a stationary, internally-toothed ring member (21;221) and an externally-toothed star member (23;223) orbiting and rotating within the ring member. The motor is of the type utilizing a valving member (53;253) of the "low-speed" type, which rotates at the speed of rotation of the star member. The star member defines internal splines (43;243) and in engagement therewith is an insert member (79;279) which is, in turn, in splined engagement with a valve drive shaft (47;247). The insert member (79;279) extends axially beyond the star member and is received within an adjacent annular recess (85;285), thus maximizing the spline length available for engagement with the main drive shaft (39;239), and maximizing the torque capacity of the motor.

BACKGROUND OF THE DISCLOSURE 
The present invention relates to low-speed, high-torque gerotor motors, and 
more particularly, to such motors of the type having a separate valve 
drive shaft driving the valve member. 
A typical gerotor motor of the type to which the present invention relates 
includes a housing defining inlet and outlet ports, and a gerotor gear 
set. The typical motor further includes valve means to provide fluid 
communication between the ports and the volume chambers of the gerotor 
gear set. The invention is especially advantageous when used in a device 
wherein the gerotor set includes an orbiting and rotating 
externally-toothed star member, and will be described in connection 
therewith. 
In most gerotor motors, an externally-splined main drive shaft (dogbone) is 
used to transmit torque from the orbiting and rotating star member to the 
rotating output shaft. A gerotor motor having a "separate" or "two-piece" 
valve drive is one in which the valve member is disposed "behind" the 
gerotor, i.e., at the end of the motor opposite the output shaft, with the 
output shaft typically being considered the "forward" end of the motor. 
Conventionally, in such motors, the valve is driven at the speed of 
rotation of the gerotor star member by means of a valve drive shaft which 
is in splined engagement with both the valve member and the gerotor star 
member. See for example, U.S. Pat. No. 4,992,034, assigned to the assignee 
of the present invention. 
In most gerotor motors, the limitation on the torque-transmitting 
capability of the motor is the strength of the spline connection between 
the star member and the dogbone. In motors using two-piece valve drives, a 
portion of the axial length of the splines defined by the gerotor star 
member is required, merely to drive the valve drive shaft. Driving the 
valve member, whether it be a disk valve or a spool valve, requires a very 
small percentage of the total torque output of the motor, but typically, 
the spline connection between the star member and the orbiting and 
rotating valve drive shaft has taken up a significant portion of the 
gerotor star splines. This becomes a more serious problem in the case of 
relatively small displacement motors, in which the axial length of the 
gerotor may be on the order of one-half inch. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
improved valve drive arrangement for a gerotor motor which permits an 
increase in the overall torque capacity of the motor. 
It is a more specific object of the present invention to provide an 
improved valve drive arrangement which utilizes less of the axial length 
of the star splines, thus leaving more of the axial length of the star 
splines for engagement with the main drive shaft. 
It is another object of the present invention to provide an improved valve 
drive arrangement wherein the central opening in the valve member can have 
a smaller diameter, such that the various ports and passages in the valve 
member can be larger, especially in the radial dimension. 
The above and other objects of the invention are accomplished by the 
provision of an improved rotary fluid pressure device of the type 
including housing means having fluid inlet means and fluid outlet means. A 
fluid energy translating displacement means is associated with the housing 
means and includes a stationary, internally-toothed member, and an 
externally-toothed member eccentrically disposed within the 
internally-toothed member, and having orbital and rotational movement 
relative to the internally-toothed member, to define expanding and 
contracting fluid volume chambers, in response to the orbital and 
rotational movement. Valve means cooperates with the housing means to 
provide fluid communication between the inlet means and the expanding 
fluid volume chambers and between the contracting fluid volume chambers 
and the outlet means. Input-output shaft means are provided, and means for 
transmitting torque between the externally-toothed member and the 
input-output shaft means. The valve means comprises a generally 
cylindrical valve member defining valving passages and being rotated at 
the same speed of rotation of the externally-toothed member. A valve drive 
shaft operable to translate the orbital and rotational movement of the 
externally-toothed member into rotational movement of the valve member is 
provided. 
The improved device is characterized by a generally cylindrical insert 
member defining a set of external, straight splines in engagement with a 
mating set of internal, straight splines defined by the externally-toothed 
member, at least a substantial portion of the insert member extending 
axially beyond the externally-toothed member, toward the valve member. The 
insert member defines a set of internal, straight splines in engagement 
with a mating first set of external, crown splines defined by the valve 
drive shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, which are not intended to limit the 
invention, FIG. 1 illustrates a low-speed, high-torque gerotor motor of 
the general type illustrated and described in detail in U.S. Pat. No. 
4,992,034, assigned to the assignee of the present invention and 
incorporated herein by reference. The motor, generally designated 11, 
comprises a plurality of sections secured together, such as by a plurality 
of bolts B, only one of which is shown in FIG. 1, and then, only 
fragmentarily. 
The motor 11 includes a shaft support casing 13, including an enlarged 
portion 15. The motor further includes a gerotor displacement mechanism 
17, and a valve housing section 19. The gerotor displacement mechanism 17 
is well known in the art, is shown and described in U.S. Pat. No. 
4,533,302, assigned to the assignee of the present invention, and will be 
described only briefly herein. More specifically, the gerotor mechanism 17 
comprises an internally-toothed ring member 21, and an externally-toothed 
star member 23, eccentrically disposed within the ring member 21, and 
having one less tooth than the ring member 21. In the subject embodiment, 
the star member 23 orbits and rotates relative to the ring member 21, and 
this orbital and rotational movement defines a plurality of expanding and 
contracting fluid volume chambers 25. 
Referring still to FIG. 1, the motor includes an output shaft 27 positioned 
within the shaft support casing 13, and rotatably supported therein by 
suitable bearing sets 29 and 31. Disposed adjacent the forward end of the 
bearing set 29 is a bearing retainer and snap ring assembly, generally 
designated 33. The output shaft 27 includes a set of internal, straight 
splines 35, and in engagement therewith is a set of external, crowned 
splines 37, formed on a forward end of a main drive shaft 39. Disposed 
toward a rearward end of the main drive shaft 39 is another set of 
external, crowned splines 41, in engagement with a set of internal, 
straight splines 43, formed on the inside diameter of the star member 23. 
In the subject embodiment, the ring member 21 includes nine internal 
teeth, and the star member 23 includes eight external teeth. Therefore, 
eight orbits of the star 23 result in one complete rotation thereof, and 
one complete rotation of the main drive shaft 39, and of the output shaft 
27. It should be understood by those skilled in the art that "input-output 
shaft means", as used hereinafter in the claims, may refer to either the 
output shaft 27 (which may comprise an input shaft if the motor is being 
used as a pump), and/or the main drive shaft 39. 
Also in engagement, but only indirectly, with the internal splines 43 of 
the star member 23 is a set of external, crowned splines 45, formed about 
one end of a valve drive shaft 47 which has, at its opposite end, another 
set of external, crowned splines 49 in engagement with a set of internal, 
straight splines 51 formed about the inner periphery of a central opening 
52 of a valve spool, generally designated 53. The details of the indirect 
connection between the internal splines 43 and the external splines 45, 
which comprises an important aspect of the present invention, will be 
described in detail subsequently. The valve spool 53 is rotatably disposed 
within the valve housing section 19, and more particularly, is rotatably 
disposed within a valve bore 55. The valve housing section 19 also defines 
a plurality of fluid passages 57 (only one of which is shown in FIG. 1, 
and in dashed lines), each of which is disposed to be in continuous fluid 
communication with an adjacent fluid volume chamber 25. In the subject 
embodiment, there are nine of the fluid passages 57, because the ring 
member 21 has nine internal teeth, and therefore, defines nine of the 
volume chambers 25. 
Referring still to FIG. 1, the enlarged portion 15 of the shaft support 
casing 13 defines an inlet port 59 and an outlet port 61. The inlet port 
59 communicates through an axial fluid passage 63 which extends through 
the casing 13, the ring member 21, and the valve housing section 19, 
terminating in a cored portion 65. Similarly, the outlet port communicates 
through an axial fluid passage 67 with a cored portion 69. The passage 63 
and cored portion 65 communicate pressurized, inlet fluid into an annular 
groove 71 defined by the valve spool 53. Similarly, low pressure, return 
fluid is communicated from an annular groove 73 by the cored portion 69 
and passage 67 to the outlet port 61. In open communication with the 
annular groove 71 is a plurality of timing slots 75, and in open 
communication with the annular groove 73 is a plurality of timing slots 
77. As is well known to those skilled in the art of low-speed, commutating 
valving, the timing slots 75 and 77 provide commutating fluid 
communication with the fluid passages 57, thereby providing, in the fluid 
volume chambers 25 of the gerotor 17, a rotating pattern of high-pressure 
and low-pressure, wherein the pattern rotates at the rotational speed of 
the star member 23. This type of valving is referred to as "low speed" 
valving, in contrast to "high speed" valving, wherein the pattern rotates 
at the faster, orbiting speed of the star member 23. Therefore, in the 
subject embodiment, there are eight of the timing slots 75 and eight of 
the timing slots 77, as is now well known to those skilled in the art. 
Referring now to FIG. 2, the indirect drive connection between the star 23 
and the valve drive shaft 47 will be described in detail. Disposed 
adjacent the rearward end (right end in FIG. 2) of the main drive shaft 39 
is an insert member 79. The insert member 79 defines a set of external, 
straight splines 81, which are in engagement with the straight splines 43 
defined by the star member 23. In addition, the insert member 79 defines a 
set of internal, straight splines 83, which are in engagement with the 
crowned splines 45 at the forward end of the valve drive shaft 47. 
It is one important advantage of the present invention that only a portion 
of the insert member 79 may be disposed within the star member 23, i.e., 
only a portion of the axial length of the external splines 81 is in 
engagement with the internal splines 43. In the embodiment of FIGS. 1 
through 3, the valve spool 53 is disposed immediately adjacent the star 
member 23 and defines a generally annular recess 85. As is well known to 
those skilled in the art, the orbital and rotational movement of the star 
member 23, relative to the ring member 21 results in the total area 
traversed by the insert member 79 being larger than the member 79. 
Specifically, the diameter of the annular recess 85 must be equal to at 
least the overall diameter of the insert member 79, plus twice the 
eccentricity of the star member 23. Furthermore, the annular recess 85 is 
concentric with the axis of rotation A of the motor 11. 
The amount of torque required to rotate the valve spool 53 is a relatively 
small percentage of the total torque output of the gerotor mechanism 17. 
The spline connection between the internal splines 83 and the external, 
crowned splines 45 is designed to transmit whatever torque is required to 
rotate the valve spool 53 (plus and appropriate design safety factor), and 
the axial length of engagement between the external splines 81 and the 
internal splines 43 may be selected to provide approximately the same 
torque transmission capability as that between the splines 45 and 83. As 
is well known to those skilled in the art, a substantially greater axial 
length of crowned spline-to-straight spline engagement is required to 
provide the same torque capacity as a straight spline-to-straight spline 
connection. 
As a result of the use of the insert member 79, and the decreased axial 
length of engagement required with the splines 43, there may now be, as 
shown in FIG. 2, an increase in the length of engagement between the 
crowned splines 41 and the internal splines 43. As was mentioned in the 
Background of the Disclosure, the connection between the gerotor star 23 
and the dogbone or main drive shaft 39 is typically the limiting factor on 
the output torque of a gerotor motor. Therefore, being able to increase 
the axial length of spline engagement between the star member 23 and the 
drive shaft 39 typically results in a proportional increase in the torque 
capacity of the motor. 
In FIG. 2, there is a slight axial clearance shown between the insert 
member 79 and the annular recess 85, for clarity of illustration. It will 
be apparent to those skilled in the art that, typically, the transverse 
end surface of the insert member 79 could be in sliding engagement with 
the adjacent surface of the recess 85, thus limiting or restraining axial 
movement of the insert member 79, relative to the star member 23. However, 
the insert member 79 would probably be freely floating within the recess 
85, and it is not anticipated that the drive shaft 39 would apply any 
axial load to the insert member 79, which in turn, would be transferred to 
the valve spool 53. Referring again to both FIGS. 1 and 2, one beneficial 
result of the insert member 79 engaging the recess 85 is that the insert 
member 79 is able to limit the rearward axial motion (i.e., to the right 
in FIGS. 1 and 2) of the main drive shaft 39. It has long been recognized 
in the gerotor motor art that a crowned spline-to-straight spline 
connection exhibits a better wear pattern, and longer life, if relative 
axial movement therebetween is substantially prevented. 
Alternative Embodiment 
Additional benefits which can result from the use of the present invention 
will now be described by means of an alternative embodiment. In order to 
illustrate and describe various other benefits of the present invention, 
FIGS. 4 and 5 provide a comparison of a disc valve motor utilizing a valve 
drive arrangement made in accordance with the "PRIOR ART", and a disc 
valve motor utilizing the valve drive arrangement of the present 
invention. 
In the embodiment of FIGS. 1 and 3, the valve member was the valve spool 
53, the term "spool" in reference to the valve 53 indicating that the 
valve passages (the timing slots 75 and 77) are disposed on the outer 
cylindrical surface of the valve spool 53. By way of contrast, in a disc 
valve motor, the valving action occurs on a flat, transverse surface. A 
motor of the "disc valve" type is shown and described in greater detail in 
the above-cited U.S. Pat. No. 4,533,302. However, it will be understood 
that the term "generally cylindrical" in reference to a valve member, 
hereinafter and in the claims, includes either a spool valve or a disc 
valve. 
Referring first to FIG. 4, those elements which are the structural and/or 
functional equivalent of elements in the embodiment of FIGS. 1 through 3 
will bear the same reference numeral, plus "100". New elements bear 
reference numerals in excess of "190". 
Disposed between the gerotor ring member 121 and the valve housing section 
119 is a stationary valve plate 191, which defines a plurality of fluid 
ports 157, each of which is in fluid communication with one of the 
expanding or contracting fluid volume chambers 125. 
Referring still to FIG. 4, there are designated certain dimensions of the 
"PRIOR ART" device which are relevant to the subsequent explanation of 
additional benefits of the present invention. The pitch diameter of the 
internal splines 143, of the star member 123, is designated as "d", while 
the overall axial length of the external, crowned splines 141 is 
designated as "1". Those dimensions both relate to the torque-transmitting 
capability of the main drive shaft 139. The diameter of the central 
opening of the valve member 153 is designated as "v", while the radial 
dimension of the fluid passages 177 defined by the valve member 153 are 
designated as "r". In engagement with the internal splines 143 are the 
external splines 145 of the valve drive shaft 147. The external splines 
149 of the shaft 147 are in engagement with the internal splines 151 of 
the valve member 151. 
Referring now to FIG. 5, there is illustrated the application of the 
present invention to a disc valve motor of the general type shown in FIG. 
4. In FIG. 5 elements which are the same, or substantially the same, as in 
the embodiment of FIGS. 1 through 3, bear the same reference numerals, 
plus "200". New elements bear reference numerals in excess of "290". 
In comparing FIG. 5 to FIG. 4, it may be seen that the axial dimension of 
the ring member 221 and star member 223 are identical to that of the ring 
member 121 and star member 123 of the FIG. 4 "PRIOR ART" device. Adjacent 
the ring member 221 is a stationary valve plate 291 which has 
substantially less axial thickness than the valve plate 191 shown in FIG. 
4, for reasons to be described subsequently. 
The star member 223 defines the internal straight splines 243, which are in 
engagement with the external crowned splines 241 of the main drive shaft 
239. Also in engagement with the internal splines 243 is a set of external 
splines 281, formed about the outer periphery of the insert member 279. 
About its inner periphery, the insert member 279 defines a set of straight 
splines 283, in engagement with the external, crowned splines 245 defined 
at the forward end of the valve drive shaft 247. At the rearward end of 
the valve drive shaft 247 is a set of external, crowned splines 249, in 
engagement with a set of internal, straight splines 251 defined by the 
disc valve member 253. The valve member 253 defines a plurality of fluid 
passages 277, each of which communicates through a fluid port 257 with one 
of the expanding or contracting fluid volume chambers 225. 
The stationary valve plate 291 also defines the annular recess 285, which 
receives the portion of the insert member 279, which extends axially 
beyond (to the right in FIG. 5) the end of the star member 223. The 
stationary valve plate 291 also defines a stationary valve surface 292, 
and in sliding engagement therewith is a rotatable valve surface 294, 
defined by the valve member 253. 
The internal splines 243 defined by the star member 223 have a pitch 
diameter designated as "D", and the overall length of the external, 
crowned splines 241 is designated "L". By comparing FIG. 5 to FIG. 4, it 
may be seen that the use of the present invention facilitates the use of a 
larger drive (i.e., "D" is larger than "d"), and permits a greater length 
of spline engagement in the main drive area (i.e., "L" is longer than 
"1"). These two factors contribute to a substantial increase in the 
torque-transmitting capability of the device shown in FIG. 5. 
Referring still to FIG. 5, the central opening 252 defined by the valve 
member 253 has a diameter designated "V", and the radial dimension of the 
fluid passages 277 is designated as "R". The use of the valve drive 
arrangement of the present invention makes it possible for the internal 
splines 251 and central opening 252 of the valve member 253 to be much 
smaller than the internal splines 151 of the valve member 153 ("V" is 
smaller than "v"). As a result, it is possible for the fluid passages 277 
in the valve member 253 to have a substantially greater radial dimension 
than the fluid passages 177 in the valve member 153 ("R" is larger than 
"r"). In turn, the greater radial dimension of the fluid passages 277 
eliminates the need for the fluid ports 257 to undergo a "transition" 
within the axial length of the valve plate 291, as is required for the 
fluid ports 157 of the FIG. 4 "PRIOR ART" device. By "transition", it is 
meant that the fluid ports 257 can have the same flow area and 
cross-sectional configuration throughout their entire axial extent, 
whereas the fluid ports 157 are required to change flow area and 
cross-sectional configuration over their axial extent, thus requiring the 
valve plate 191 to be thicker axially, with the machining of the valve 
plate 191 being much more complicated and expensive. By way of contrast, 
the valve plate 291 can, because of the present invention, be much 
thinner, and the fluid ports 257 can be formed by any number of relatively 
less expensive operations, such as by "piercing", or "punching". 
Thus, it may be seen that the present invention makes it possible, for any 
given size of gerotor ring and star, to increase the torque-transmitting 
capability of the gerotor drive while, at the same time, providing a 
smaller valve drive shaft, which makes it possible to improve certain 
dimensional aspects of the valving system. 
Although the present invention has been illustrated and described in 
connection with an embodiment in which the insert member 79 is splined to 
the star member 23, it should be understood that the invention is not so 
limited. Instead of being splined to the star member 23, the insert member 
79 could have a shape such as square or hexagonal, and be received within 
a mating recess defined by the star. Alternatively, if the star member 23 
were formed from powdered metal, the insert member 79 could be formed 
integrally with the star, with the star and insert member still having the 
overall configuration illustrated in the drawings. Both of the above are 
considered to be included within the scope of the appended claims, except 
as specifically recited in greater detail. 
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.