Fluid device having interchangeable displacement control means

A fluid device of the axial piston type having high and low pressure operating passages, one of which may be an inlet and the other an outlet depending upon the pumping or motoring function of the device and the direction of rotation. The fluid device, which is of the variable displacement type, has a rotatable cylinder barrel with one end of each of a plurality of pistons disposed for reciprocation within cylinder bores at one end of the cylinder barrel, and cylinder ports successively communicating each of the cylinder bores with arcuate inlet and outlet passages formed in a valving face disposed at the opposite end of the cylinder barrel. The other ends of the pistons engage a pivotably mounted thrust plate adapted to impart a reciprocal movement to the pistons within the cylinder bores as the cylinder barrel is rotated. In one example of the invention, the thrust plate is provided with a coupling mechanism adapted to be operated by any one of a plurality of interchangeable displacement control mechanisms which vary the inclination of the thrust plate with respect to the axis of rotation of the cylinder barrel and thus the amount of reciprocal movement of the pistons within the cylinder barrel. The device is adapted to be converted into a manifold system adapted to accommodate a plurality of valves with a minimum of external fluid conduits.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to fluid devices and particularly to those of 
the variable displacement axial piston type which may function either as a 
fluid pump or as a fluid motor. 
2. Description of the Prior Art 
Heretofore, fluid pumping or motoring devices of the axial piston type have 
been constructed of a metallic housing having a revolving cylinder barrel 
with a plurality of parallel cylinder bores therein, within which pistons 
are reciprocated by means of a thrust plate assembly or the like. A rotary 
valve mechanism in the form of cylinder ports at one end of the cylinder 
barrel alternately connects each cylinder bore with an inlet and an outlet 
passage of the device as the cylinder barrel is rotated. 
The thrust plate assembly in fluid devices of the variable displacement 
type normally takes the form of a yoke having transversely extending 
pintles rotatably carried in bearings suitably mounted to the wall of the 
housing. Suitable means are provided to pivot the thrust plate with 
respect to the longitudinal axis of the drive shaft on which the cylinder 
barrel is rotated so as to vary the amount of reciprocal stroking movement 
imparted to the pistons within the cylinder bores and thereby permit a 
selected variation in the fluid displaced by the axial piston fluid 
devices. 
In such previously constructed axial piston fluid devices, the displacement 
control mechanism used to control the inclination of the thrust plate 
assembly with respect to the longitudinal axis of the drive shaft has 
necessitated a different design for the fixed displacement device and the 
variable displacement pump as the displacement control mechanism is 
normally constructed as an integral part of the housing in variable 
displacement devices, and thus a variable displacement device requires a 
larger housing than a fixed displacement device. Heretofore, the same 
housing could not be used for both variable and fixed displacement 
devices, as a larger housing is required for the variable displacement 
device since a portion of the housing is needed to mount the displacement 
control mechanism. The use of a variable displacement housing in a fixed 
displacement device results in an unduly large unit in proportion to its 
displacement. It would therefore be desirable to provide a housing having 
a construction adapted to accommodate both variable displacement and fixed 
displacement devices without requiring a larger housing for the variable 
displacement design. 
It has also been a conventional practice to construct such previously used 
devices with only one type of displacement control mechanism, that is, a 
different application requiring a different type of displacement control 
mechanism, such as a manual control or a pressure compensated control, 
would require a major disassembly of the device to convert from one type 
displacement control mechanism to another or would require a different 
housing construction for each type of displacement control mechanism. It 
would therefore be desirable to provide a construction which permits an 
easy interchangeable use of different types of displacement control 
mechanisms. 
SUMMARY OF THE INVENTION 
The present invention, which will be described subsequently in greater 
detail, comprises a fluid pumping or motoring device of the axial piston 
type having a pivotably mounted thrust plate and means adapted to 
operatively couple the thrust plate to any one of several types of 
displacement control mechanisms. 
It is therefore an object of the present invention to provide a rotary 
fluid device of the axial piston type having an improved construction 
which is readily adapted to low cost manufacturing. 
It is also an object of the present invention to provide a rotary fluid 
device of the axial piston type having an improved thrust plate 
construction. 
It is also an object of the present invention to provide a rotary fluid 
device of the axial piston type having means for varying the displacement 
thereof, and a housing construction adaptable to accommodate different 
types of displacement control mechanisms. 
It is a further object of the present invention to provide a fluid device 
adapted to be converted into a manifold system. 
Other objects, advantages, and applications of the present invention will 
become apparent to those skilled in the art of such fluid devices when the 
accompanying description of several examples of the present invention is 
read in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings and particularly to FIG. 1, there is illustrated 
a fluid device in the form of an axial piston pump 10 comprising a housing 
12 having a body section 14 with a longitudinally disposed bore 18 
enclosed by a cap 20 secured to the body section by any suitable fastening 
means, such as screws 19, extending axially through the cap 20 and into 
the threaded bores in the body section 14. An O-ring 24 insures a fluid 
tight seal between the juncture of the body section 14 and the cap 20. The 
body section 14 includes a pilot portion (not shown) forming a mounting 
flange to permit the mounting of the pump 10 at a desired location. 
The housing bore 18 forms a chamber 32 in which a rotating group 33 is 
positioned. The rotating group 33 includes a cylinder barrel 34 which is 
provided with a plurality of arcuately spaced and longitudinally disposed 
cylinder bores 36, each having one end of a piston 38 axially slidable 
therein. A plurality of cylinder ports 40 axially aligned with each 
cylinder bore 36 communicate each of the cylinder bores 36 with a front 
face 42 of the cylinder barrel 34. Each of the pistons 38 have spherical 
ends 44 on which are swagged socketed shoes 46. The cylinder barrel 34 is 
positioned axially between a valving face 48 formed on the inner face of 
the cap 20 and an inclined thrust plate assembly 50. The valving face 48 
serves in a well known manner to provide a properly phased connection 
between the cylinder ports 40 and a pair of arcuate ports 52 and 54, such 
that the cylinder ports 40 communicate successively with the arcuate ports 
52 and 54 as the cylinder barrel 34 rotates. The arcuate ports 52 and 54 
are, respectively, connected to the external outlet and inlet connection 
ports 53 and 55 of the pump 10. 
The piston shoes 46 have outwardly extending flanges 56 which are contacted 
by an annular cage 58 with holes corresponding to each piston 38. The 
annular cage 58 has a centrally disposed conical bore 62 adapted to 
contact a spherical outer surface 64 of a collar 66 which is, in turn, 
carried on a drive shaft 68 that extends longitudinally through the 
housing bore 18. A spring 70 disposed between the piston end of the 
cylinder barrel 34 and the collar 66 exerts a force urging the face 42 of 
the cylinder barrel 34 into engagement with the valving face 48, while at 
the same time biases the shoes 46 by means of the collar 66 and the 
annular cage 58 into engagement with the thrust plate assembly 50. 
The drive shaft 68 is rotatably supported between bearings 72 and 74. The 
bearing 72 is carried in a bore 75 of a decreased diameter at the thrust 
plate assembly end of the housing bore 18, while the bearing 74 is carried 
in a centrally disposed bore 76 within the inner face of the cap 20. The 
drive shaft 68 is effective to transmit torque from a prime mover (not 
shown) to the cylinder barrel 34 through a splined driving connection 78 
in a conventional manner. A conventional shaft seal 80 is provided in the 
decreased diameter bore 75 and retained in position by a snap ring 82. 
The cylinder barrel 34 has a skirt portion 84 snugly fitted in an annular 
recess 86 at the piston end of the cylinder barrel 34 to form an inner 
race 88 for roller bearings 90, the outer race 92 of which is carried by 
the body section 14 in abutment with the thrust plate assembly in a manner 
which will be described in greater detail hereinafter. The skirted portion 
84 has an annular inclined inner surface 96 extending upwardly from the 
cylinder barrel 34 and terminating in such a manner that the thrust plate 
assembly end 98 of the inner race 88 is flush with the thrust plate 
assembly end 100 of the roller bearings 90 to provide an increased volume 
for accommodating the thrust plate assembly 50, resulting in an increased 
displacement capacity of the pump 10 by as much as 15 percent as compared 
to fluid devices heretofore constructed. 
Still referring to FIG. 1, as the cylinder barrel 34 rotates a 
reciprocating stroking motion is imparted to the pistons 38 due to the 
inclination of the thrust plate assembly 50, thus a relative reciprocating 
motion between the cylinder barrel 34 and the pistons 38 results as the 
cylinder barrel 34 rotates, wherein the cylinder bores 36 are alternately 
compressed and expanded, resulting in fluid being drawn into and expelled 
from the cylinder bores 36 through the cylinder ports 40. 
From the foregoing it can be seen that when a rotary movement is imparted 
to the outer end 112 of the drive shaft 68, the cylinder barrel 34 will be 
rotated to alternately register the cylinder bores 36 with the arcuate 
ports 52 and 54 of the valving face 48 by means of the cylinder ports 40. 
Referring to FIGS. 1, 4 and 5, the thrust plate assembly 50 is shown as 
comprising a movable yoke 55 and a fixed yoke support 57. The fixed yoke 
support 57 has a U-shaped configuration, the bottom wall 59 of which has 
an aperture 61 through which the drive shaft 68 extends. The bore 61 has 
an annular recessed portion 63 of an inner diameter closely fitting the 
outer diameter of the drive shaft support bearing 72, and thus the yoke 
support 57 is axially aligned with respect to the drive shaft 68 when 
positioned on the outer periphery of the bearing 72. 
The yoke support 57 includes a pair of axially projecting side walls 64, 
each of which has arcuately shaped bearing surface 67 supporting the 
movable yoke 55 on which the piston shoes 46 slidably engage as the 
cylinder barrel 34 is rotated so as to impart a reciprocal stroking 
movement to the pistons 38. The movable yoke 55 has a pair of transversely 
extending aligned support pins 69 and 71 (FIG. 5), each of which has 
arcuately shaped bearing surfaces 73 contoured to meet with the arcuately 
shaped bearing surfaces 67 of the projecting side walls 65, such that the 
yoke 55 is adapted to pivot within the side wall bearing surfaces 67 about 
an axis 75 (FIG. 1) defined by the transversely extending support pins 69 
and 71 in a manner which will be described in greater detail hereinafter. 
The yoke support pin 71 includes a L-shaped arm 77 integrally formed 
therewith and projecting rearwardly away from the support pin 71. The 
projecting arm 77 carries a U-shaped member 79 having a slot 81. The outer 
face and side walls of the arm 77 are received in the U-shaped member 
slots 81 in such a manner that the U-shaped member 79 is adapted to 
reciprocate along a portion of the length of the arm 77. The base portion 
83 of the U-shaped member 79 has a bore 85 which carries a coupling pin 87 
which, in turn, extends through an opening 89 (FIG. 1) formed in the side 
wall of the body section 14 and is adapted to be coupled to any one of 
several displacement varying mechanisms which will be described in greater 
detail hereinafter. 
As can best be seen in FIG. 4, the opening 89 is so sized to enable the 
U-shaped member 79 to be inserted therethrough and onto the arm 77 during 
assembly of the pump 10. The connecting pin 87 extends through the housing 
body section 14 and moves along a linear path as the U-shaped member 79 
and arm 77 pivot about the axis 75 defined by the supporting pins 69 and 
71 without interference with the side wall of the housing body section 14. 
As can be seen in FIG. 1, the preferred axis of rotation of the yoke arm 
77, and for purposes of description the longitudinal axis of the support 
pins 69 and 71, is an axis passing through the center point about which 
each of the arcuate bearing surfaces 67 is formed. The axis 75 should 
intersect the plane at which the centers of the spherical piston ends 44 
lie and may also intersect the longitudinal axis of the drive shaft 68. 
However, the axis 75 may be vertically offset from the drive shaft axis, 
in a well known manner, depending upon the desired results. 
The arcuately shaped bearing surfaces 67 formed on the side walls of the 
yoke support 57 are in the form of a plastic bearing 87 (FIG. 1), such as 
a teflon-lead bearing or the like, which provides the necessary support to 
withstand the load transmitted through the pistons 38 and the movable yoke 
55, while at the same time offering the least amount of frictional 
resistance to the pivotal movement of the yoke 55 therewithin. The plastic 
bearings 87 have a central aperture adapted to receive a boss formed in 
each side wall 65 so as to securely retain the bearing 87 on its 
associated side wall 65. 
The yoke 55 has a circular thrust bearing face 93 with which the shoes 46 
cooperate and a hemispherical cross section with an elliptical, centrally 
disposed bore 97 through which the drive shaft 68 extends. The elliptical 
shape of the bore 97 permits the yoke 55 to rotate about the axis 75 with 
respect to the shaft 68 without interference therewith. The yoke 55 and 
the yoke support 57 are both preferably constructed of a sintered 
material, with the thickness of support pins 69 and 71, as measured from 
the bearing face 93 to the bottom of the support pin bearing surface 73, 
being at least 40 percent of the total thickness of the yoke 55 as 
measured from the bearing face 93 to the bottom thereof. This assures that 
the yoke 55 will withstand the loads to which it is subjected. The 
L-shaped arm 77 extending from the support pin 71 should have a length 
which is at least equal to the yoke thickness in order to provide good 
fill characteristics when the same is manufactured. 
The amount of friction between the bearing surfaces of the yoke 55 and the 
yoke support 57 will be directly proportional to the load exerted thereon, 
while the frictional torque is in direct proportion to the radius of the 
arcuate bearing surfaces 67. In the present design the radius of the 
bearing surfaces is kept to a minimum consistent with producibility and 
strength, and thus the frictional torque is minimized. It should also be 
noted that present construction of the yoke 55 and the yoke support 57 
results in the length and thickness of the yoke 55 being respectively 
shorter and greater than comparable components of presently used devices. 
The shorter length and increased thickness of the yoke 55 reduces unit 
deflections under load and the resulting vibrations which results in an 
extremely quiet pump compared to such presently used designs. 
Since the periphery of the yoke support 57 is rectangular and the periphery 
of the yoke 55 is circular, each corner 117 of the yoke support 57 will 
project radially outwardly beyond the yoke 55. Although not shown, the 
longitudinal center of the rollers of bearing 90 are axially positioned 
with respect to the center of a plane passing through the center of each 
piston ball 44 by the abutment of the thrust plate facing side of outer 
race 90 against the corners of the yoke support 57. This arrangement 
provides a simple construction which insures proper axial alignment which 
is essential for a smooth, efficient and accurate operation of the pump 
10. 
The amount of reciprocal motion of the pistons 38 within their respective 
bores 36 and thus the amount of fluid displaced by the pump 10 is 
controlled by the angle of inclination of the thrust plate face 93 with 
respect to the axis of rotation of the cylinder barrel 34. In the position 
illustrated, the face 93 of the movable yoke 55 is perpendicular to the 
axis of rotation of the cylinder barrel 34 and thus there will be a 
minimum amount of reciprocal movement of the pistons within their 
respective bores and thus a minimum or no-flow condition will exist. As 
the movable yoke 55 is tilted or inclined with respect to the longitudinal 
axis of rotation of the cylinder barrel 34, the amount of reciprocal 
movement between the pistons 38 and their respective bores will increase 
until the movable yoke 55 has been inclined, with respect to the axis or 
rotation of the cylinder barrel 34, to a maximum amount. The tilting of 
the movable yoke 55 to impart a reciprocal motion to the pistons 38 with 
respect to their cylinder bores 36 is well known to those skilled in the 
art of axial piston pumps and motors and a further detailed description is 
not deemed necessary. 
The movement of the yoke 55 to various positions with respect to the 
rotating axis of the cylinder barrel 34 is accomplished by means of the 
yoke arm 77, the U-shaped member 79, the coupling pin 87 and any suitable 
displacement control mechanism, such as the interchangeable mechanism to 
be described hereinafter. 
Referring to FIG. 4, it can be seen that when a suitable displacement 
control mechanism is actuated to move the coupling pin 87, the same moves 
along a linear path 120, while the arm 77 will follow an arcuate path 122. 
The relative rotational movement of the pin 87 within the bore 85 of the 
U-shaped member 79 and the reciprocal movement of the U-shaped member 79 
on the arm 77 permits the U-shaped member to transfer the linear motion of 
the pin 87 into an arcuate motion of the arm 77 and thus to the movable 
yoke 55. It can thus be seen that when the pin 87 is moved upwardly (as 
viewed in FIG. 4) along the linear path 120 to incline the face 93 of the 
yoke 55 to a maximum condition, the U-shaped member 79 will move 
rightwardly along the arm 77 to the position 124 as the arm 77 follows the 
arcuate path 122. When it is desired to incline the face 93 of the yoke 55 
to a maximum inclination in an opposite direction, that is, to reverse the 
direction of flow from the pump 10, the displacement control mechanism 
actuates the coupling pin 87 to move it downwardly (as viewed in FIG. 4) 
along the linear path 120 to the position 126 wherein the U-shaped member 
79 will reciprocate along a portion of the arm 77 as the U-shaped member 
79 and pin 87 move along the linear path 120 and the arm 77 follows the 
arcuate path 122. 
In FIGS. 1 and 2, the pump 10 is illustrated as having a displacement 
control mechanism 134 of the pressure compensated type and comprising a 
coupling plate 136 having an elongated aperture 138 through which pin 87 
extends and which aperture 138 defines the linear path 120 (FIG. 5). The 
pressure compensated displacement control mechanism 134 further comprises 
an upper housing portion 140 which, together with the plate 136, is 
fastened to the body section 14 adjacent the opening 89 by any suitable 
fastening means, such as elongated screws 142 extending through the upper 
housing 140, the coupling plate 136 and into threaded bores (not shown) in 
the body section 14 of the pump 10. 
It should be noted that the plate 136 need not be a separate element, but 
may be an integral part of the upper housing 140. 
The upper housing 140 includes two parallel bores, one bore 150 having a 
pressure compensator valve 152 carried therein, while the other bore 154 
has a pressure responsive piston member 156 slidably mounted therein 
which, in turn, is attached to the yoke 55 by the connecting pin 87 
extending through the elongated slot 138 in the coupling plate 136 and the 
opening 89 in the wall of the housing section 14. Each of the bores 150 
and 154 are enclosed at their open ends by closure plates 164 and 165 
secured to the upper housing 140 by screws 166 or the like. The piston 
carrying bore 154 has a spring 168 disposed between the closure plate 164 
and the one side of the pressure responsive piston 156 to bias the piston 
156 toward the other end of the bore 154. The pressure responsive piston 
156 is so attached to the yoke 55 that the yoke 55 is normally pivoted 
toward a maximum inclination or maximum flow position when piston 156 is 
nearest the closure plate 165 as illustrated in FIG. 2. The inner end 170 
of the piston 156 and the associated end of the bore 154 form a pressure 
chamber 172 adapted to be selectively communicated to a source of fluid 
pressure generating a force acting on the piston 156 to move the same 
against the bias of the spring 168 and move the coupling pin 87 along the 
linear path 120 and thus stroke the yoke 55 toward a minimum displacement 
position. The pressure chamber 172 is supplied with fluid pressure through 
a passageway 174 in communication with the high pressure port of the 
device 10. The bore 154 is enlarged at the pressure chamber end to provide 
a path between the passageway 174 and the pressure chamber 172, which 
permits a construction having a minimum amount of passageways, while at 
the same time allowing for a compact construction of the mechanism 134. 
The pressure compensator valve 152 comprises a piston member 178 having the 
sealing land 180 adapted to control the amount of fluid through the 
passageway 174 to the pressure chamber 252. The piston member 178 is 
normally biased to a closed position by a spring 182 disposed between one 
end 184 of the piston member 178 and a second movable wall member 186 
which, in turn, is axially adjustable within the bore 150 by a threaded 
member 188 extending through the wall of the housing 140 and externally 
thereof. By adjusting the position of wall member 186 with respect to the 
piston end wall 184, the compression force of the spring 182 may be varied 
to thereby vary the amount of force necessary to move the piston 178. The 
inner piston end of the valve 152 is connected directly to high pressure 
generating a force against the piston 178, urging it against the bias of 
the spring 182. When the pressure of the pump 10 exceeds a predetermined 
value, the sealing land 180 is moved toward an opened position, permitting 
fluid pressure to pass thereby and into the pressure chamber 172, 
generating the aforementioned force for urging the piston member 156 to 
move against the bias of the spring 168. A pressure between 200 psi and 
300 psi acting against the piston member 156 will move the same a 
sufficient distance to stroke the yoke 55 from a full flow or maximum 
displacement to a near zero flow or minimum displacement, that is, the 
U-shaped member 79 will move from the position 126 (FIGS. 2 and 4) to the 
position 127 (FIG. 4). 
Referring now to FIG. 3, there is illustrated, on a reduced scale, a 
servo-operated displacement control mechanism 200 for varying the 
inclination of the face 93 of the movable yoke 55 to selectively control 
the displacement or flow output of the pump 10. In order to use the 
servo-operated displacement control mechanism 200 on the pump 10, the 
pressure compensated displacement control mechanism 134 is first removed 
by removing the screws 142. The plate 136 is adapted for use with the 
servo mechanism 200 as well as the pressure compensated mechanism 134. The 
servo mechanism 200 is positioned on top of the coupling plate 136 and 
screws 142 extend through the upper housing 202 of the servo mechanism 200 
into the aforementioned threaded bores in the pump housing section 14. 
Upon placement of the servo housing 202 in position on the coupling plate 
135, the coupling pin 87 will extend into a bore 206 in an actuating 
piston 208 reciprocally mounted within a longitudinal bore 210 within the 
servo mechanism 200. As the servo-actuating mechanism piston 208 is 
reciprocated in a pressure bore 210 in a manner which will be described 
hereinafter, the coupling pin 87 is moved along the linear path 120 and 
thus the movable yoke 55 may be inclined with respect to the rotating axis 
of the cylinder barrel 34 in the same manner as hereinbefore described 
with respect to the pressure compensated displacement control mechanism 
134. The housing 202 of the servo-operated displacement control mechanism 
200 further comprises two parallel, spaced bores, the larger of which is 
the pressure bore 210, while the second bore 212 has a plurality of 
axially spaced ports 214, 216 and 218. The port 214 communicates via a 
passageway 220 with a pressure chamber 222 formed at one end 224 of the 
piston 208, while the port 218 communicates via a second passageway 226 
with a second pressure chamber 228 formed on the opposite end 230 of the 
piston 208. The intermediate port 216 of the bore 212 is connected to a 
source of pressure, such as the high pressure output port of the pump 10 
or a second pump operated in tandem with the main pump which supplies 
control pressure and is adapted to be selectively communicated to the 
ports 214 and 218. When pressure fluid is communicated through the port 
214, the fluid within chamber 222 acts against the top end 224 of the 
piston 208 to move the same downwardly, whereby the coupling pin 87 
carried by the actuating piston 208 is moved along the linear path 120 
from the position 127 (FIG. 4) to the position 126, thereby changing the 
displacement of the pump 10 from a minimum or zero flow displacement to a 
maximum or full flow displacement. At the same time, the U-shaped member 
79 will reciprocably move along a portion of the arm 77 in the manner 
hereinbefore described to move the arm 77 along the arcuate path 122. 
When pressure fluid is communicated to the other port 218 and thus to the 
pressure chamber 228, the fluid acts against the piston bottom side 230 to 
move the piston upwardly and thus move the coupling pin 87 and the 
U-shaped member 79 upwardly along the linear path 120 from the maximum or 
full flow displacement position 126 back to the minimum or zero flow 
displacement position 127 or beyond to the maximum reverse flow position 
124 hereinbefore described. The bore 212 is further provided with a pair 
of exhaust ports 232 which communicate one of the ports 214 or 216 with a 
reservoir (not shown) when the other port 218 or 214 is in communication 
with the pressure port 216. Communication between the pressure inlet port 
216 and the two outlet ports 214 and 218 is controlled by a reciprocally 
mounted spool 234 having a pair of spaced lands 236 and 238, which are 
adapted to cooperate with the ports 214, 216 and 218 to control 
communication therebetween, the operation of which is conventional. One 
end of the spool 234 is attached to an armature 240 of a torque motor 242 
and in response to a predetermined electrical signal from a source 244 the 
spool 234 will be moved leftwardly or rightwardly to communicate pressure 
to the appropriate port depending upon the type of actuation desired, i.e. 
whether the pump is desired to be stroked toward a minimum or a maximum 
flow condition. The opposite end of the spool forms a seat 246 for one end 
of a spring 248, while the other end of the spring 248 is seated on a 
reciprocally mounted feedback member 250 in bore 212. The feedback member 
250, in turn, carries a feedback linkage 252 connected to the actuating 
piston 208. The feedback linkage 252, which extends through an elongated 
slot 253 in the housing 204 connecting the bores 210 and 212, connects the 
feedback member 250 to the actuating piston such that the two components 
move together as a unit. Thus, when the servo torque motor 242 is actuated 
to move the spool 234 downwardly to communicate fluid pressure to the 
lower port 218 and thus to the pressure chamber 228 to shift the actuating 
piston 208 upwardly and stroke the pump 10 in a minimum flow condition or 
at some intermediate point therebetween, the spring 248 will be further 
compressed by the upward movement of the piston 208 because of its 
feedback linkage 252, all of which exerts a greater force on the spool 234 
to return it to its original position against the force of the torque 
motor 242. The spool 234 will move to a position corresponding to the 
proper movement of the piston 208, which is a function of the electrical 
signal fed to the torque motor 242. The greater the electrical input 
signal into the torque motor 242, the further the actuating piston 208 
will move before the spring 248 overcomes the force of the torque motor 
242. 
Referring now to FIG. 6 wherein there is illustrated a displacement control 
mechanism 254 for varying the inclination of the face 93 of the movable 
yoke 55 with respect to the axis of rotation of the cylinder barrel 34 to 
vary the flow output of the pump 10. The displacement control mechanism 
254 comprises an upper housing 256 positioned on the coupling plate 136 
and attached to the pump 10 by the screws 142 extending through the 
housing 256 and into threaded bores in the pump housing section 14 in the 
same manner as hereinbefore described with respect to the mechanisms 
illustrated in FIGS. 1, 2 and 3. Upon placement of the housing 256 in 
position on the coupling plate 136, the coupling pin 87 extending through 
the slot 138 will be received in a bore 258 of an actuating piston 260 
reciprocably mounted in a longitudinal bore 262 of the upper housing 256. 
The inner end 264 of the piston 260 and the inner end of the bore 262 
define a pressure chamber 266 which, when communicated to pressure fluid, 
exerts a force against the end 264 of the piston 260 to shift the same 
upwardly as viewed in FIG. 6. As the piston 260 moves upwardly under the 
force of pressure communicated to the pressure chamber 266, the pin 87 
will be moved within the slot 138 along the linear path 120 to shift the 
movable yoke 55 from a full flow position toward the zero flow position in 
the same manner as hereinbefore described. 
The opposite end of the bore 262 defines a chamber 268 which is normally 
vented to a reservoir (not shown) via passageway 269 and has a spring 270 
with one end bearing against the piston 260, while the other end of the 
spring 270 bears against a cover plate 272 which in turn encloses the 
housing bore 262. The spring 270 exerts a predetermined force against the 
piston 260 to bias the same downwardly to normally maintain the pump 10 in 
a full flow condition. The spring 270 functions in a manner similar to the 
spring 168 hereinbefore described in respect to the pressure compensated 
displacement control mechanism 134 illustrated in FIG. 2. 
The pressure is communicated to the pressure chamber 266 at the end of the 
longitudinal bore 262 from the high pressure outlet port of the pump 10 
through a passageway 271 and a valving spool 273 having a land 276 which 
controls the amount of fluid pressure communicated to the chamber. The 
piston 260 has an annular groove 274 which is always in constant 
communication with the high pressure passageway 271 as the piston 260 is 
reciprocated within the bore 262. 
An annular groove 274 communicates fluid pressure through a passageway 275 
in the actuating piston 260 to a longitudinally disposed bore 277 within 
which is reciprocably mounted the valving spool 273. The bore 277 has a 
pair of pressure ports 278 and 279 which respectively communicate with the 
pressure chamber 266 and the vented chamber 268 at the opposite ends of 
the piston 260. The spool land 276 is adapted to control communication 
through the pressure port 278 between the pressure chamber 266 and the 
bore 277 as relative movement takes place between the actuating piston 260 
and the spool 273. When the inner end of the spool 273 abuts the blind end 
of the bore 277, communication between the chamber 266 and bore 277 is 
closed. 
The opposite end of the spool 273 is rounded and engages a spring seat 280 
mounted on one end of a second spring 281, the other end of which is 
carried by a movable spring seat 282, the position of which is controlled 
by an adjusting screw 283 extending through the cover 272. Suitable O-ring 
seals 284 around the seat 282 prevent the leakage of fluid from the 
chamber 268. 
It can thus be seen that when high pressure fluid enters the inner end of 
the spool bore 277, a force is exerted against the spool 273 to move the 
same upwardly against the bias of the spring 281 to open the pressure port 
278 and communicate fluid to the pressure chamber 266 at the inner end of 
the actuating piston 260 to exert a force against the piston 260 and to 
move the same upwardly against the bias of the spring 270. The actuating 
piston 260 following the movement of the spool 273 in a master-slave 
relationship will move to a location depending upon the relative spring 
forces exerted on the piston 280 and spool 273, at which time the flow to 
the pressure chamber 266 is cut off and the pump 10 will be positioned at 
some output level corresponding to the positioning of the yoke 55 by the 
piston 260. By adjusting the amount of precompression of the spring 281 by 
adjusting the position of the movable seat 282, the pressure level 
necessary to move the spool 273 upwardly in order to communicate fluid to 
the pressure chamber 260 can be selectively controlled. 
Referring to FIG. 7, there is illustrated flow versus pressure curves for 
various setting on the inner spring 281, for example, curve A illustrates 
the spring 281 with a small amount of precompression, while curve B 
illustrates the spring 281 with a greater amount of precompression and 
thus a greater pressure is necessary to overcome the spring 281 before 
pressure is communicated to the chamber 266 to move the piston 260 and 
change the displacement of the pump 10. As illustrated in FIG. 7, at lower 
pressures a high flow is available, while as the pressure increases the 
rate of flow decreases and thus the mechanism 254 approximates a constant 
horsepower output. It can thus be seen that the displacement control 
mechanism illustrated in FIG. 7 provides a very simple, compact and 
accurate means for providing a constant horsepower variable displacement 
pump. 
Referring now to FIGS. 8 and 9 wherein there is illustrated a manifold 300 
adapted to be mounted to the pump 10 for converting the same into a 
manifold system that is adapted to accommodate a plurality of sub-plate 
mounted valves with a minimum of external plumbing as will be described in 
greater detail hereinafter. The manifold 300 comprises a generally 
rectangularly shaped housing 302 having an L-shaped bore 304 which is 
enclosed at one end by a plug 306, while the other end of the L-shaped 
bore 304 communicates through an enlarged recess 308 with the high 
pressure outlet port 53 of the pump 10. The recessed portion 308 formed on 
the outer face of the housing 302 adjacent the port 300 accommodates a 
suitable seal such as O-ring 310. The manifold housing 302 is secured to 
the flat outer face 312 of the pump 10 by a plurality of strategically 
located screws 314 which extend through bores 316 in the housing 302 into 
threaded bores in the cover 20 of the pump 10. In addition to mounting the 
manifold 300 to the device 10, the screws 314 are also adapted to mount a 
flow control valve, such as a directional control valve, to the manifold 
300 as will be described hereinafter. 
The internal passageway 304 communicates the pressure fluid to each of a 
plurality of spaced passageways 317, 318, 320 and 322, each of which 
terminates in the outer face 324 of the housing 302. 
As can best be seen in FIG. 8, the outer face 324 of the manifold 300 is 
provided with a plurality of sets of threaded bores respectively indicated 
by numerals 326, 328 and 330, which threaded bores are adapted to receive 
the mounting screws of a plurality of any one of a number of sub-plate 
mounted valves, as for example, directional control valves, sequence 
valves, pressure relief valves and the like, all of which will be 
explained hereinafter. 
A pair of intersecting bores 332 and 331 form a passage extending the full 
length of the housing 302 and are respectively enclosed at their ends by 
plugs 334 and 333. The mid-portion of the bore 331 is intersected by a 
bore 335 threaded at 336 to receive a suitable line to communicate the 
bores 332, 331 and 335 back to a reservoir (not shown), such that the 
bores 332, 331 and 335 are normally at a low or return pressure. The 
return pressure bores 332, 331 communicate with the face 324 of the 
housing through a plurality of inclined passageways 337, 338, 340 and 342 
which, as can best be seen in FIG. 8, are spaced just below the pressure 
ports 317, 318, 320 and 322, respectively. Still referring to FIG. 8, it 
can be seen that the housing 302 has a plurality of L-shaped passageways 
opening to the face 324 at strategic locations between the high pressure 
passageways and the return passageways. At the upper end of the housing, 
the L-shaped passageways 344 and 346 open to the face 324 on opposite 
sides and between the pressure opening 318 and the return passageway 338. 
The L-shaped passageways 344 and 346 respectively extend downwardly into 
the housing and out the sides thereof for communication with appropriate 
hose couplings. Likewise, the L-shaped passageways 348 and 350 are grouped 
between and to the side of the openings 320 and 340, while L-shaped 
passageways 352 and 354 are associated with the high pressure passageway 
322 and return passageway 342 and L-shaped passageways 355 and 357 are 
associated with the high pressure passageway 317 and return passageway 
331. The passageways 348-357 similarly extend downwardly into the housing 
302 and outwardly to the sides for communication with hose couplings 
adapted to carry the pressure fluid to a fluid user. 
It can thus be seen that the mounting manifold 300 provides a very simple 
means for attaching any one of a plurality of valves to the pump 10 with a 
minimum of external plumbing. As for example, a conventional directional 
control valve could be mounted to the upper portion of the housing 302 
with the mounting screws of the directional control valve extending into 
threaded engagement with the mounting bores 326, such that the pressure 
passageway 318 communicates with the pressure inlet of the directional 
control valve while the return passageway 338 of the manifold 300 
communicates with the return port of the directional control valve and the 
outlet ports 344 and 346 would respectively communicate with the 
conventional A and B ports of the directional control valve, such that 
when the directional control valve is shifted in the conventional manner 
high pressure fluid may be selectively communicated from the pressure port 
318 of the manifold 300 to either the outlet port 344 or 346 or 
alternately the pressure can be dumped back to the reservoir via port 338. 
Such a directional control valve could be mounted to the face 324 of the 
manifold 300 by the mounting screws 314 when the same are used to mount 
the manifold 300 to the device 10. 
Similarly, a high pressure relief valve can be mounted to the intermediate 
portion of the manifold block 300 by having the mounting screws of the 
pressure relief valve extend into threaded engagement with the mounting 
bores 328 of the manifold, such that the high pressure passageway 320 
communicates with the high pressure inlet of the pressure relief valve, 
while the outlet of the pressure relief valve communicates with the return 
port 340 of the manifold 300 such that when pressure of the pump 10 
exceeds some predetermined value, the high pressure relief valve will 
function in the conventional manner to dump pressure from the high 
pressure port 320 back to the reservoir via the tank port 340. When the 
pressure relief valve is used on the intermediate portion of the manifold 
300, the manifold outlets ports 348 and 350 would not be in communication 
with any fluid. 
Similarly, the next lower portion of the manifold 300 can be adapted to 
mount any other type valve needed for the particular application, such as 
a sequence valve or another directional control valve. 
It can also be seen that the manifold 300 may be of any desired length and 
adapted to accommodate any number of a plurality of valves, all of which 
will be dependent upon the particular application. 
It can thus be seen that the present invention provides a manifold system 
which is easily attached to a conventional flow generating device, such as 
the pump 10, and which provides a simple and easy manner of attaching a 
plurality of different types of flow control devices, such as directional 
control valves and the like, and with a minimum of external plumbing. 
It can also be seen that the present invention provides a means in which 
the movable yoke 55 may be moved from a minimum or no-flow condition to a 
maximum or full-flow condition simply by the movement of the coupling pin 
87 along the linear path 120, all of which is due to the simple and unique 
arrangement of U-shaped member 79 reciprocally mounted on the arm 77. It 
can also be seen that the U-shaped member 79 and coupling pin 87 permit 
the interchangeable use of any type of displacement control mechanism 
simply by coupling the mechanism to the outer face of the pump housing and 
connecting the actuating portion of the displacement control mechanism to 
the coupling pin 87. 
Although it has been heretofore indicated that the pin 87 is fixedly 
attached to the U-shaped member bore 85, it should be noted that the pin 
87 may be rotatably carried within the bore 85 of the U-shaped member 79 
and fixedly attached to the actuating piston of whichever type of 
displacement control mechanism is used. 
It can thus be seen that the present invention provides a new, rugged, 
compact, and low cost fluid device of the axial piston type which may 
function as either a motor or a pump, which has a new, simple, and 
improved means for controlling the displacement of the pump, and which 
provides for the interchangeability of various types of displacement 
control mechanisms without any internal modification of the basic pump 
design. 
While the form of the present invention as disclosed herein constitutes a 
preferred form, it is to be understood that other forms may be adopted, 
all coming within the spirit of the invention and the scope of the 
appended claims.