US3700356A

US3700356A - Fluid system

Info

Publication number: US3700356A
Application number: US67177A
Authority: US
Inventors: Philip A Kubik
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-08-26
Filing date: 1970-08-26
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24

Abstract

A fluid system having a variable displacement fluid pump connected in a closed loop circuit to a fluid cylinder having a piston and a pair of connecting rods extending from opposite sides of the piston externally of the fluid cylinder. A directional control valve disposed in the closed circuit between the inlet and outlet of the fluid pump is adapted to selectively direct fluid to one side of the piston within the fluid cylinder, while exhausting fluid from the other side of the piston, to selectively move the piston within the fluid cylinder. The rate of movement of the piston in either direction of movement is controlled by the amount of fluid displaced by the fluid pump. A second directional control valve is adapted to direct fluid from a second source of fluid to a pressure responsive displacement control mechanism to selectively vary the displacement of the fluid pump between a maximum and a minimum flow position. The rate of fluid flow to the pressure responsive displacement control mechanism is selectively varied to control the rate of displacement of the fluid pump and to thereby selectively control the rate of movement of the cylinder piston, while the maximum flow position may be varied between defined limits by an electrically operated remote control.

Description

United States Patent Kllbik Oct. 24, 1972 [54] FLUID SYSTEM 72 Inventor: Philip A. Kubik, 6809 Spruce Drive, [57] ABSTRACT Birmi gh MiCh- A fluid system having a variable displacement fluid [22] Filed: 26, 1970 pump connected in a closed loop circuit to a fluid Appl. No.: 67,177

Related US. Application Data Primary Examiner-William L. Freeh Attorney-Andrew R. Basile cylinder having a piston and a pair of connecting rods extending from opposite sides of "the piston externally of the fluid cylinder. A directional control valve disposed in the closed circuit between the inlet and outlet of the fluid pump is adapted to selectively direct fluid to one side of the piston within the fluid cylinder, while exhausting fluid from the other side of the piston, to selectively move the piston within the fluid cylinder. The rate of movement of the piston in either direction of movement is controlled by the amount of fluid displaced by the fluid pump.

17 Claims, 12 Drawing Figures PATENTED act 24 m2 SHEET 1 OF 3 INIVENTOR PHILIP A. KUBIK l //%zm 1 I WW ATTORN EYS PATENTEDHBI 24 1912 '3. 700 35s SHEET 2 OF 3 FIGS INVENTOR PHILIP A. KUBIK BY ,fiM /fW @12445 ATTORNEYS FIGIO PATENTEDUCT 24 I972 3,700,356

SHEET 3 0F 3 FIG.6

FIG 7 F|G.9 [MW/Q l INVENTOR I PHILIP A- KUBIK 24v 202 BY %ae,

ATTORNEYS FLUID SYSTEM CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 50,093, filed June 26, 1970 and now US. Pat. No. 3,653,208.

BACKGROUND OF THE INVENTION ployed for controlling the rate of movement of a hydraulic motor and, particularly, such fluid systems have found extensive use in hydraulic machine tool drive transfer systems and the like. Such fluid systems are used to accelerate and decelerate a fluid cylinder respectively at the beginning and the end of its stroke prior to a feed movement. Such previously used fluid systems have normally consisted of a reservoir and a fluid pump for drawing fluid from the reservoir to supply the fluid cylinder and drive the same at some selected rate of movement. Suitable valving means are employed between the pump and the fluid cylinder to control the rate of movement of the fluid cylinder. The rate of movement of the fluid cylinder is a significant factor which must be considered in all but the simplest of circuits. When a variable rate control of the fluid cylinder is desired, it is customary to employ a meterin, meter-out, or a bleed-off system. Such systems generally include a deceleration valve connected in series with the pump; the deceleration valve being actuated by the movement of the fluid cylinder to variably restrict or stop the fluid flow between the outlet of the pump and the inlet of the fluid cylinder. When a finer rate control isdesired, a feed control valve connected in parallel with the deceleration valve is utilized. The feed control valve, which may be of the meter-in or meter-out type, controls the rate of flow to or from the fluid cylinder and may either be a fine or coarse feed, depending on the desired application. If the feed control is of the meter-in type, the rate of fluid flow supplied to the fluid cylinder is controlled. If the fluid flow from thedevice is controlled, the circuit is known as a meter-out circuit. When a portion of the fluid supply is diverted to a reservoir, the circuit is known as a bleedoff circuit. 7

Thus, in the previously used systems, fluid flows directly from the pump through a deceleration valve, a feed control valve and to the fluid cylinder. In such systems, if the load greatly varies, the feed control valves require pressure compensation.

Such systems, although commonly used, are difficult to adjust and control and, because of the pressune compensation required for variable loads, they have a lower efflciency than is desirable. Since acceleration and deceleration of the fluid cylinder is accomplished by means of a deceleration valve, such acceleration and deceleration is not smooth as the deceleration valves tend to generate pulsations in the fluid system which can damage the fluid cylinder and/or the fluid pump. Further, braking of the fluid cylinder is not obtainable as such previously used fluid systems are not a closedloop system. In addition, such systems are not capable of having a controlled acceleration, deceleration, start and stop at present rates, while having a means for changing the maximum output speed from a remote control position.

It would therefore be desirable to provide a fluid system which has all the advantages of the heretofore previously used systems without any of the aforementioned disadvantages.

SUMMARY OF THE INVENTION The present invention, which will be described subsequently in greater detail, comprises a fluid system having a closed-loop fluid circuit for selectively connecting the inlet and outlet of a main fluid motor to the inlet and outlet of a fluid pump. The main fluid motor may be a fluid cylinder of the type having a piston with connecting rods extending from the opposite sides thereof and externally of the main fluid cylinder, whereby the effective pressure responsive areas on the opposite sides of the main cylinder piston are equal. The pump has means for varying its displacement between minimum and maximum flow positions and is controlled by a fluid circuit having a secondary fluid cylinder which is operatively connected to the displacement varying means of the pump. The piston in the secondary fluid cylinder has its opposite sides selectively connected to a source of fluid through a pair of feed control valves and a conventional directional control valve. The acceleration and deceleration of the piston in the main fluid cylinder is controlled by varying the displacement of the fluid pump, which, in turn, is controlled by the feed circuit. An electrically operated remote control means is provided for varying the maximum flow position of the pump within preset limits to enable a change in the maximum output speed of the fluid motor without affecting preset rates of starting,

acceleration, deceleration, and stopping of the fluid motor.

It is therefore an object of the present invention to provide a fluid system for controlling the rate of movement of a fluid motor which is easily adjustable from a remote location and controlled more efficiently than previously used control circuits.

It is also an object of the present invention to provide a fluid system for controlling the rate of movement of a fluid pump control circuit in which the acceleration and deceleration forces exerted on a fluid motor are smooth.

It is also an object of the present invention to provide a fluid system in which the maximum output speed may be varied remotely between preset limits without affecting other control characteristics of the system.

It is also an object of the present invention to provide means for varying the maximum and/or minimum displacement of a variable displacement fluid pump between preset limits.

Other objects, advantages, and applications of the present invention will become apparent to those skilled in the art of fluid systems and fluid pumps when the accompanying description of several examples of the best modes contemplated for practicing the invention is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The description herein makes reference to the accompanying drawings in which like reference numerals refer to like parts throughout the several Figures, and in which:

FIG. 1 represents a schematic illustration of the present invention in the form of a fluid system;

FIG. 2 is a schematic illustration of a modification of a fluid pump illustrated in FIG. 1;

FIG. 2A is a rear elevational view of the fluid pump illustrated in'FIG. 2 as seen from line 2A-2A;

FIG. 3 is an enlarged fragmentary, partially sectioned top plane view of the fluid pump illustrated in FIG. 2 as seen from line 3-3;

FIG. 4 is a schematic illustration of another modification of the fluid pump illustrated in FIG. 1 taken in cross-section along line 4-4 of FIG. 4A;

FIG. 4A is a front elevational view of the fluid pump illustrated in FIG. 4 as seen from line 4A4A;

FIG. 5 is an enlarged fragmentary cross-sectional view of the fluid pump illustrated in FIG. 4;

FIG. 6 is an enlarged fragmentary cross-sectional view of the fluid pump illustrated in FIG. 4A and taken on line 6-6;

FIG. 7 is a fragmentary cross-sectional view of FIG. 6 taken generally along line 77 thereof;

FIG. 8 is a schematic illustration of a third modification of the fluid pump illustrated in FIG. 1;

FIG. 9 is an enlarged fragmentary cross-sectional view of FIG. 8; and,

FIG. 10 is a schematic diagram of one example of an electrically operated remote control circuit incorporating features of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, there is illustrated a fluid system 10 comprising a control circuit 12 and a main circuit 14. The main circuit 14 comprises a variable displacement pump 16 connected in closed-loop manner by

conduits

18, 20, 22 and 24 to a main fluid cylinder 26. Incorporated in the main circuit 14 is a conventional directional control valve 28 which is adapted to connect the conduits l8 and 20 selectively to the

conduits

22 and 24 or be positioned tandem-center so as to allow communication between conduits 18 and 20, but prevent fluid communication between

conduits

22 and 24.

The pump 16 may be of the well known axial piston type, comprising a housing 30 having a cylindrical barrel 32 rotatably mounted therein and suitably connected to a drive shaft 34. The cylinder barrel 32 is formed with a plurality of axial cylinder bores each housing a piston reciprocal therein; only two of the bores and pistons being shown and respectively indicated by the numerals 36 and 38. Each piston 38 has a spherical outer end portion 40 carrying a bearing shoe 42 that engages a swash plate 44 which is operatively coupled to a secondary fluid cylinder 46 by a connecting arm 48 for movement about a pivot 50 from a neutral, minimum displacement position 52 to a maximum or full flow position 54. A prime mover, such as an electric motor schematically illustrated at 56, is mechanically connected through a suitable coupling to the drive shaft 34 which, in turn, is supported within the pump housing 30 by bearings 58 and 60.

As is conventional in pumps of the type illustrated, each cylinder bore 36 in the cylinder barrel 32 is provided with a cylinder port 62 adapted to alternately register with the inlet and outlet ports 64 and 66 respectively as the cylinder barrel 32 rotates. The inlet and outlet ports 64 and 66 respectively communicate with the conduits l8 and 20.

The cylinder barrel 32, pistons 38, swash plate 44, and the input shaft 34 are immersed in fluid in a filled cavity normally referred to as a pump case 68. The pump 30 communicates with a reservoir 70 through a charge pump 92 and valving 100 or 102 and a conduit 94 on inlet and a conduit 72 on drain, all of which will be described hereinafter.

The main fluid cylinder 26 has a cylindrical housing 74 with an internal bore 76 in which a cylindrical piston 78 is reciprocally mounted, dividing the internal bore 76 into two pressure chambers 80 and 82 respectively on the opposite sides of the piston 78. The opposite sides of the piston 78 have

cylinder rods

84 and 86 which extend through the opposite endwalls and externally of the main fluid cylinder 26. The pressure chambers 80 and 82 of the cylinder 26 respectively have a fluid port 88 and 90 which, in turn, are respectively connected to the

fluid conduits

22 and 24. Since the connecting

rods

84 and 86 are of an equal diameter, the eflective pressure responsive areas on the opposite sides of the piston 78 are also equal. The cylinder 26 operates in a well known manner to move the piston 78 in opposite directions within the cylinder bore 76 when one of the pressure chambers 80 or 82 is pressurized, while the other pressure chamber is exhausted.

The fluid system 10 is provided with a positive fixed displacement replenishing pump 92, such as a gear pump, which is also driven by the prime mover 56 through the drive shaft 34. The replenishing pump 92 is in communication with the reservoir 70 through a supply conduit 94 and a filter 96 for supplying the replenishing fluid to the main circuit 14 by means of a delivery conduit 98. Spring biased check valves 100 and 102 are in communication with the delivery conduit 98 and the closed-loop main circuit conduits 18 and 20, respectively, for supplying replenishing fluid to whichever of the conduits 18 and 20 is the low pressure side of the closed main circuit through one of the check valves, which pressure on the high pressure side of the main circuit maintains the other check valve closed.

A spring biased relief valve 104 is provided for the replenishing pump 92 for relieving excessive fluid pressure in the replenishing delivery conduit 98 for exhausting fluid to the reservoir 70 by means of a fluid conduit 106 connected to the pump case 68 and the conduit 72.

Downstream of the directional control valve 28, the

conduits

22 and 24 are respectively connected to the inlets of high pressure relief valves 108 and l 10 which,

at a predetermined pressure, eg: 3,000 psi, will exhaust the fluid pressure from one of the conduits to the other conduit so as to prevent damage to the main circuit in the event of over pressurization.

Referring to the control circuit 12 for a description of the method of controlling the displacement of the fluid pump 16, there is illustrated a directional control valve 112 adapted to selectively connect fluid from the replenish pump 92 to either of a pair of feed control valves 114 and 116 by conduits 118 and 120 respectively. The feed valves 114 and 116 are respectively connected to the

ports

122 and 124 of the secondary cylinder 46 bymeans of

conduits

126 and 128 respectively. The fluid cylinder 46 is similar in construction to the main cylinder 26 and comprises a tubular housing 130 having an interior bore 132 divided into two

pressure chambers

134 and 136 by means of a reciprocally mounted piston l38,which, in turn, carries a connecting rod 140. Connecting rod 140 extends externally of the housing 130 and is operatively coupled at 142 to the swash plate connecting arm 48 of pump 16. The

pressure chambers

134 and 136 are respectively connected to the

conduits

126 and 128.

The feed control valves 114 and 116 may be of the conventional type and have restricted passages 144 and 146 which are adjustable such that each of the feed control valves may be pre-set to supply any desired flow rate over a wide range. Each of the feed control valves 114 and 116 includes a

check valve

148 and 150, respectively, which permits fluid to bypass the restricted passages 144 and 146 in one direction. Thus, when the directional control valve 112 is in the position indicated, fluid flow is directed from the fixed displacement pump 92 through the conduit 120 to the feed control valve 1 16, bypassing the same through check valve 150, and is then directed to the pressure chamber 136 on one side of the cylinder piston 140 to move the same leftwardly within the cylinder bore 132 to displace the fluid pump 16 toward its full flow position 54. Fluid on the opposite side of the piston cylinder 138 within the pressure chamber 124 will be exhausted through the cylinder port 122 and directed through conduit 126 to the feed control valve 114 at a rate of flow which is determined by the setting of the restricted passage 144. Fluid returns to the reservoir 70 through the directional control valve 112 and a conduit 152. When the directional control valve 1 12 is reversed so as to direct fluid flow through the check valve 148 of the feed control valve 1 14 to the pressure chamber 134 to move the piston 138 rightwardly, fluid is exhausted through the restricted passage 146 of the feed control valve 116 which, in turn, controls the rate of movement of the piston 138. As the piston 138 movesrightwardly, the swash plate connecting arm 48 is moved to the minimum displacement position 52.

The type of feed control illustrated is known as a meter-out control, that is, the rate of movement of the piston 138 within the secondary cylinder 46 is determined by the rate of the fluid being exhausted from the

pressure chamber

134 or 136, which, in turn, is controlled by the feed control valves 114 and 116. A detailed description of the

feed control valves

114 and 1 16 is not necessary as such feed control valves are well known and commercially available.

It can thus be seen that the rate of change in the displacement of the fluid pump 16 is controlled by the feed control valves 114 and 116, thus, if the restricted passages 144 and 146 of the feed control valves are set to permit a high rate of flow to pass therethrough, the

6 cylinder piston 138 will be displaced rapidly causing a rapid change in the displacement of the fluid pump 16 which, in turn, when communicated to the main fluid cylinder 26 will generate a rapid acceleration and/or deceleration of the cylinder piston 78 therein.

The connecting rod carries a stop member 154 which is adapted to abut axially adjustable

mechanical stops

156 and 158 to permit a variation in the displacement of the fluid pump 16 at predetermined intermediate displacements respectively below the maximum displacement of the fluid pump 16 and above the minimum displacement of the pump 16. The maximum displacement of the pump 16 occurs when the swash plate 44 abuts the wall 160 of the pump housing, while the minimum displacement of the pump 16 occurs when the swash plate 44 is disposed in a plane which is substantially perpendicular to the longitudinal axis of the drive shaft r In operation, when it is desired to direct fluid from the fluid pump 10 through the conduit 18, the directional control valve 28 and the conduit 24 to ac celerate the piston 78 in the main cylinder 26 forwardly (to the right as viewed in the drawings) at a rapid rate, the directional control valve 112 of the control circuit 12 is actuated by switching means 162 to direct fluid from the fixed pump 92 into the pressure chamber 136 of the fluid cylinder 46 to drive the piston therein rearwardly to stroke the swash plate 44 of the fluid pump 16 to the maximum displacement 54 or some other intermediate displacement as determined by the setting of the adjustable stop 156. Fluid from the secondary cylinder 46 is exhausted through the adjustable restricted passage 146 of the feed control valve 116 which is set to permit a high rate of fluid flow therethrough, thus permitting a rapid stroking of the pump 16 which, in turn, will displace a maximum amount of fluid into the conduit 18. The directional control valves 112 and 28 in the control and main circuits, respectively, are simultaneously actuated so that as the secondary cylinder 46 is actuated, fluid from the variable displacement pump 16 will be directed to the main fluid cylinder 26 to accelerate the piston 78 thereinrapidly to the right as viewed in the drawings. After the piston is displaced at a rapid rate of acceleration and strikes a limit switch Ll, the directional control valve 112 in the control circuit 12 is actuated, to direct fluid to the pressure chamber 136 on the opposite side of the piston 138 in the secondary fluid cylinder 46. Fluid entering the secondary cylinder 46 will move the piston 138 rightwardly to stroke swash plate 44 toward the minimum flow position 52 or some intermediate displacement position determined by the adjustable stop 158. The fluid in the pressure chamber 134 of cylinder 46 will be exhausted through the feed control valve restricted passage 1414 at some predetermined rate which will control the rate at which the piston 138 of the fluid cylinder 46 strokes the pump 16 back towards a lower displacement. As the pump 16 is stroked toward a lower displacement, the rate at which fluid is directed to the main cylinder 26 is decreased,

thereby decelerating the movement of the piston 78.

within the main fluid cylinder 26. When the pump 16 is stroked to a minimum, the forward movement of the piston 78 of the main cylinder 26 will be brought to a minimum creep speed to seek a final stop position, at

which time valve 28 will be centered and the piston will stop. A positive stop 166 may be provided to insure that the cylinder piston 78 stops at a desired position. The valve 28 may be actuated to a centered position by means of limit switch L2.

Acceleration and deceleration of the piston 78 within the main cylinder 26 in an opposite direction (to the right as viewed in the drawings) may be had by reversing the flow from the conduits 18 and 20 to the

conduits

22 and 24 by means of the directional control valve 28 without requiring any change in the setting of the feed control valves 114 and 116 as the volume of fluid required to move the piston in either direction at some predetermined rate is equal.

Moving the directional control valve 28 to a tandemcenter or no-flow condition will prevent fluid flow either to or from the cylinder chambers 80 and 82, quickly stopping the piston 78. Such a quick stop may be utilized in the event of an emergency when it is necessary to prevent damage to the machine tool or transfer mechanism which the connecting rod 86 and/or 84 is driving.

Referring to FIG. 2, the pump 16 is illustrated in a modified form with the swash plate 44 having a pair of diametrically

opposed pintle shafts

162 and 164 which are mounted to interior walls of the housing 30 by means of pintle bearings 166. The swash plate connecting arm 48 is in the form of an L-shaped handle having a lower end extending through the wall of the pump housing 30 and operatively coupled to the pintle shaft 164, as can be best seen in FIG. 2A. The upper end of the swash plate connecting arm 48 extends through an elongated slot 167 (FIG. 3) formed in a bracket assembly 168 and is coupled to the connecting rod 140 of the secondary cylinder 46 at 142 in the same manner as described hereinbefore. The adjustable

mechanical stops

156 and 158 are illustrated in FIGS. 2 and 2A as being carried on the bracket assembly 168 which, in turn, is attached to the housing of the pump 16. The mechanical stops 156 and 158 are disposed on opposite sides of the swash plate connecting arm 48 within its path of movement across the slot 167 as the inclination of the swash plate 44 is varied. The mechanical stop 158 may take the form of an adjusting screw 169 extending through a mounting block 171 which is, in turn, fixedly attached to the bracket 168. The screw 169 may be manually adjusted at a predetermined intermediate position above the minimum displacement of the pump 16 such that when the secondary cylinder 46 is actuated to rotate the swash plate 44 to a minimum displacement position, the swash plate connecting arm 48 will abut the mechanical stop 158 at the desired minimum displacement position. Likewise, the mechanical stop member 156 may be remotely adjusted, in a manner which will be described hereinafter, to a predetermined intermediate position below the maximum displacement of the fluid pump 16 such that the swash plate connecting arm 48 will abut the mechanical stop 156 at the desired maximum displacement position.

The mechanical stop 156 is carried at the end of an arm member 170 of an actuator 172 and is adapted to vary the position of the mechanical stop 156 within a predetermined maximum displacement range. The end of the arm member 170 associated with the stop 156 has a threaded surface 173 which is received in a threaded bore 175 in the stop 156. Since the stop 156 is restrained from rotation, relative rotary motion between the arm member 170 and the stop 156 will cause axial movement of the stop 156. When the arm member 170 is actuated to shift the mechanical stop 156 leftwardly, as viewed in FIGS. 2 and 3, the displacement of the pump 16 will be increased as the swash plate 44 is rotated a greater amount from its neutral position, resulting in an increased output of the pump 16 and ultimately an increase in the speed of the fluid cylinder. If the arm member 170 is actuated to drive the mechanical stop 156 rightwardly, as viewed in FIGS. 2 and 3, the maximum displacement of the unit will be decreased accordingly, as the swash plate connecting arm 48 will abut the mechanical stop 156 after rotating a lesser amount from its neutral position.

The actuator 172 is driven by an electric motor 174 (FIG. 2A) through a pulley and belt arrangement 176 in a manner to be described in detail hereinafter.

The actuator 172 comprises a housing 178 (FIG. 3) having an internal bore 180 in which a hollow sleeve member 182 is rotatably mounted. One end of the sleeve member 182 projects outwardly from the rear of the housing 178 and has a pulley 184 coupled thereon by a pin 186 extending through both the pulley 184 and the projecting end of the sleeve 182. The interior of the sleeve member 182 has a threaded surface 188 which receives a mating threaded section 190 formed on the inner end of the arm member 170. Thrust bearing 189 provides a suitable bearing support for the rotating sleeve member 182.

It can thus be seen that when the electric motor 174 is actuated, the pulley and belt arrangement 176 will rotate the sleeve member 182. Since the arm member 170 is attached to sleeve 182, the arm member 170 will rotate and drive stop 156 along threaded surface 175 in an axial direction. As the sleeve member 182 is rotated in a first direction, the arm member 170 will move the mechanical stop 156 to the left as viewed in FIG. 3, thereby increasing the maximum displacement of the pump 16. When the electric motor 174 is actuated to rotate the sleeve member 182 in a second, opposite direction, the arm member 170 will move in an opposite axial direction, driving the mechanical stop member 156 rightwardly, as viewed in FIG. 3, decreasing the maximum displacement of the pump 16.

The amount of movement of the adjustable mechanical stop 156, and thus the amount of variation in the maximum displacement of the pump 16 is determined by the engagement of the pair of cam surfaces 198 and 199 (FIG. 3) formed at the opposite ends of the stop 156, respectively, with a pair of

limit switches

200 and 202 carried by the bracket assembly 168 adjacent the stop member 156. The relative position of the

limit switches

200 and 202 with respect to the mechanical stop 156 may be preset manually by set screws 203 extending through the switches and into the bracket assembly 168. As the stop 156 moves in a direction which increases the maximum displacement position of the pump 16, the cam surface 198 will engage the limit switch 200 and deactivate the electric motor 174, and when the stop 156 is moved in a direction which decreases the maximum displacement position, the cam surface 199 will engage the limit switch 202 to deactivate the electric motor 174.

Limit switches

200 and 202 form a portion of the electrical circuit 204, which is illustrated in FIG. 10 and used by an operator of the system 10 for remotely controlling the electric motor 174 to selectively vary the maximum displacement of the pump 10 and thus the speed of the fluid cylinder 26.

The circuit 204 comprises a manually operated reversing drum switch 206 having three portions; decrease,,off, and increase; the switch 206 being used by the operator to selectively connect the electric motor 174 to an electrical power supply 208. When the switch 206 is in the increase position, the electric motor 174 is activated in such a manner as to rotate the arm member 170 to drive the stop 156 to increase the maximum displacement position. Engagement of the cam surface 198 with the limit switch 200 deactivates the electric motor 174, thus limiting the maximum displacement of the pump 16 to a preset maximum limit. Thus the operator of the fluid system 10 may increase the output speed of the system without affecting its acceleration or deceleration characteristics and ,without exceeding a predetermined maximum output speed. Likewise, if the operator of the system 10 wishes to decrease the maximum displacement position, the switch 206 is turned to the decrease position, wherein the power supply 208 is connected to the electric motor 174 in such a manner so as to reverse its rotation and cause the arm member 170 to drive the stop 156 in an opposite direction to decrease the maximum displacement position. Engagement of the cam surface 199 of the stop 156 with the limit switch 202 breaks the electrical connection between the electric motor 174 and the power supply 208, thus limiting the maximum displacement position of the pump 16 to a preset minimum limit. This variation in the maximum displacement of the pump 16 between maximum and minimum limits is determined by the spacing between the

limit switches

200 and 202 and the spacing between the cam surfaces 198 and 199, which is preset in any desired manner depending on the particular application of the fluid system 10. It should be noted that the minimum limit of the maximum displacement position of the pump 16 cannot be less than the maximum preset minimum displacement position as determined by the mechanical stop 158.

Referring now to FIGS. 4-7, there is schematically illustrated a second modification of the pump 16 in which the secondary cylinder 46, the connecting rod 140, the swash plate connecting arm 48, and the adjustable

mechanical stops

156 and 158 are replaced by an internal displacement control mechanism generally indicated by the numeral 209.

The internal displacement control mechanism 209 comprises a pair of diametrically

opposed piston members

210 and 212 respectively slidably mounted in intemal housing bores 214 and 216. The outer projecting ends of the

pistons

210 and 212 are connected to the outer portions of the swash plate 44 by a suitable linkage 213 and rotate the swash plate 44 in opposite directions about the axis 50 which is defined by the longitudinal axes of trunnions 219 (FIG. 4A) on which the swash plate 44 is rotatably mounted. The interior of the housing bores 214 and 216 respectively form expansible pressure chambers 215 (FIG. 4) and 217 (FIG. 5), which, in turn, are respectively connected to the

conduits

126 and 128, such that when fluid pressure is admitted into the pressure chamber 215 from the conduit 128,' the pressure therein generates a force acting against the piston 210 to cause the swash plate 44 to rotate toward a maximum displacement position; while, at the same time, the swash plate 44 displaces the piston 212 into the pressure chamber 217 until the inner end of piston 212 abuts a mechanical stop 218. The position of the mechanical stop 218 determines the maximum displacement of the pump 16 in a manner similar to the mechanical stop 156 described hereinbe fore. When it is desired to decrease the displacement of the pump 16, that is, when it is desired to rotate the swash plate 44 toward a minimum displacement position, fluid from the conduit 126 is directed intothe pressure chamber 217, wherein the pressure therewithin generates a force acting against the piston 212 to cause the swash plate 44 to rotate about the trunnions 219. The swash plate 44 will rotate towards s minimum displacement position driving the piston 210 into the bore 214 until the inner end of the piston 210 abuts a manually adjustable mechanical stop 220. The manually adjustable stop 220 may take the form of a screw extending through the face of a pump 16 and into the pressure chamber 215, and is normally preset at any desired position and functions in a manner similar to the mechanical stop 158 described herebefore. Suitable sealing means (not shown) prevents the passage of fluid from the bore 214 y the stop 220 and externally of the pump 16. t

The mechanical stop 218, which controls the range of the maximum displacement of the pump 16 may be varied by an arm member 222 of an actuator 224 between a minimum and maximum limit. The actuator 224 is substantially similar in function and structure to the actuator 172 described hereinbefore, and is carried at the face of the pump 16 in axial alignment with the bore 216. The arm member 222 of the actuator 224 differs from the arm member in that the arm member 222 has a shear pin 192 with one end fixedly mounted in a bore 194 within the actuator housing 178, while the other end of the shear pin 192 is received in a longitudinal slot 196 that extends axially through the threaded section of the arm member 222. The shear pin 192, in addition to preventing damage to the actuator 224 in the event the electric motor 174 is not deactivated at the proper time, prevents relative rotary motion between the arm member 222 and the sleeve 182 such that rotation of the sleeve 182 produces axial movement of the arm member 222, which, in turn, produces axial movement of the stop 218 into the pres sure chamber 217. Suitable sealing means, such as an O-ring 234 within a peripheral recess 235 in stop 218 prevents the passage of fluid thereby and into the actuator 224. I

It can thus be seen that when the electric motor 174 is activated in a first direction by switch 206, the mechanical stop 218 will be driven from the bore 216 (rightwardly as viewed in FIGS. 4 and 5) to increase the maximum displacement position of the pump 16. By reversing the rotation of the electric motor 174, the actuator 224 will drive the mechanical stop 218 in an opposite direction, that is, into the bore 216 to decrease the maximum displacement position of the pump 16 and thus decreasing the output of the pump 16.

Since the

limit switches

200 and 202 in the circuit 204 may not be positioned proximate the stop 218, a feedback mechanism 236 (FIGS. 5, 6 and 7) is provided to sense the position of the swash plate 44 and engage the

limit switches

200 and 202, to control the rotation of the electric motor 174 and define the limits in the variation of the maximum displacement position of pump 16. The feedback mechanism system 236 is illustrated in FIGS. 6 and 7 as comprising an outer housing 238 attached to the pump 16 and including a longitudinal bore 239 in which a connecting rod 240 is slidably mounted. One end of the connecting rod 240 has a pair of

cams

242 and 244 carried thereby, both cams having set screws 247 for locking the cams to the connecting rod 240 to permit their initial adjustment with respect to the

limit switches

200 and 202. The other end of the connecting rod 240 is attached to a portion of the swash plate 44 by a pivotal linkage 248 such that as the swash plate 44 is rotated about its trunnions 219 the linkage 248 will drive the connecting rod 240 and thus the

cams

242 and 244 relative to the

limit switches

200 and 202. Thus, when the pump 16 is at an intermediate maximum displacement position and the operator of the fluid system 10 desires to increase the displacement of the pump 16 and the speed of the fluid motor 26, the switch 206 is activated to cause the electric motor 174 to drive the actuator 224 which, in turn,

causes the stop 218 to be moved from the bore 216 (rightwardly as viewed in FIGS. 4 and and thus permitting the piston 212 to move further into the pressure chamber 217 under the force of the piston 210 acting against the opposite portion of the swash plate 44. The swash plate 44 will rotate to increase the displacement of the pump 16 until the piston 212 abuts the mechanical stop 218 which, in turn, is positioned when the electric motor 174 is stopped by the limit switch 200 being engaged by the cam 242 thereby positioning the stop 218 at a predetermined maximum limit in a manner similar to that hereinbefore described in the description of the operation of the embodiment of FIG. 2. In a like manner, when the operator of the system wishes to decrease the maximum displacement of the pump 16 and the speed of the fluid motor 26, the electric motor 174 is activated by the switch 206 to rotate the actuator 224 to drive the stop 218 into the bore 216 (leftwardly as viewed in FIGS. 4 and 5), causing the piston 212 to rotate the swash plate 44 to decrease the pump displacement. As the swash plate 44 is moving toward a decrease displacement, the cam 244 will engage the limit switch 202 to deactivate the electric motor 174, thereby positioning the stop 218 at a predetermined minimum limit. Thus, the maximum displacement of the pump 16 may be varied by remote control within preset limits by varying the position of the stop 218; those limits, in turn, being remotely controlled by en gagement of the

cams

242 and 244 with the

limit switches

200 and 202, respectively, without having to change the rate of acceleration or deceleration of the pump 16 and thus without having to change the rate of acceleration or deceleration of the fluid motor 26.

Referring now to FIGS. 8 and 9 wherein there is schematically illustrated a third embodiment of the present invention in which the pump 16 of FIG. 2 is modified in a manner similar to the embodiment illustrated in FIG. 4, that is, an internal means 249 is provided for varying the inclination of the swash plate 44 and thus the displacement of the pump 16. In the embodiment illustrated in FIG. 8, the swash plate 44 rotates about a pair of

pintle shafts

166 and 164 in the same manner as disclosed in FIG. 2, such that the pintle shaft 164 is easily accessible through the wall of the pump housing 30. As can best be seen in FIG. 9, a pair of

cams

250 and 252 are attached by set screw 253 to the end of the pintle shaft 164 and rotate therewith as the swash plate 44 is rotated by the internal displacement control mechanism 249. A plate 254 is attached to the end of the pintle shaft 164 below the

cams

250 and 252 and provides a means of initially adjusting the cams with respect to the

limit switches

200 and 202. The adjustment of the position of the earn 250 and 252 may taken the form of set screws 256 extending through elongated slots 258 in each cam and into threaded bores (not shown) formed in the plate 254. The limit switches 200 and 202, mounted on

plates

260 and 262, respectively, adjacent the

cams

252 and 250, are actuated by engagement with the

cams

252 and 250 to break the connection between the electric motor 174 and the power supply 208 when the swash plate 44 is rotated past defined limits in the same manner as described hereinbefore. Initial adjustment of the position of the

limit switches

200 and 202 is obtained by the relative positioning of elongated slots 264 in

plates

260 and 262 with respect to screws 266 passing through slots 264 into the wall of the pump housing 30.

The internal displacement mechanism 249 illustrated in FIG. 8 differs from the displacement mechanism 209 illustrated in FIG. 4 in that the displacement mechanism 249 comprises a pair of

pistons

268 and 270 each having one end respectively disposed in housing bores 272 and 274, with the piston 270 having approximately twice the effective pressure responsive areas as the piston 268, while the other ends of the

pistons

268 and 270 abut the swash plate in diametrically opposed locations. Stop 218 abuts the inner end of piston 270 and functions in the same manner as hereinbefore described. The system 10 is also modified to accommodate the displacement control mechanism 249 in that the bore 272 is in constant communication with fluid pressure generating a force on piston 268 urging the swash plate 44 toward a maximum displacement position. When it is desired to stroke the swash plate 44 to maximum displacement position, fluid is metered-out from the bore 274 and when it is desired to stroke the swash plate 44 to a minimum displacement position fluid is metered-in to the bore 274. Since the area of the piston 270 is approximately twice that of the piston 268, the swash plate 44 will be stroked to a minimum displacement position.

Further, in the embodiment disclosed in FIG. 4, the trunnions 219 are so constructed that they are not accessible from the wall of the pump housing 30, therefore it is necessary to have the pivot linkage 248 and the connecting rod 240 to provide the feedback means 236 for controlling the position of the stop 218; however, since the pintle shaft 164 in the embodiment illustrated in FIGS. 8 and 9 is easily accessible, such a pivot linkage 248 and the connecting rod 240 is not required.

It can thus be seen that an improved fluid system has been provided for selectively starting, accelerating,.

decelerating, and stopping a fluid motor in which the maximum output speed of the fluid motor may be remotely selectively varied between preset limits independent of the operating characteristics of the system.

While the forms of the embodiments of the present invention disclosed herein constitute preferred forms, it is to be understood that other forms might be adopted all coming within the spirit of the invention and the scope of the appended claims which follow.

What is claimed is as follows:

1. A fluid pressure energy translating device, comprising:

a housing having an inlet and an outlet port;

a cylinder barrel rotatably mounted within said housing, said cylinder barrel having a plurality of arcuately spaced cylinder bores;

a plurality of pistons with inner ends disposed for reciprocal stroking movement within said cylinder bores;

means for successively communicating said cylinder bores with said inlet and outlet ports;

an inclined swash plate mounted in said housing in a driving relationship with the other end of said pistons for imparting said reciprocal stroking movement to said pistons within said cylinder barrel bores as said cylinder barrel rotates, the amount of fluid flowing from said inlet port to said outlet port being a function of the amount of said reciprocal stroking movement of said pistons;

means for varying the inclination of said swash plate between selected maximum and minimum inclination positions to vary the amount of said reciprocal stroking movement of said pistons such that the fluid flowing from said inlet port to said outlet port is increased as said swash plate inclination increases and said fluid flow between said inlet and outlet ports decreases as said swash plate inclination is decreased;

a pair of stop means defining said maximum and minimum inclination positions;

electrically actuated means for selectively varying the position of one of said stop means to vary one of said inclination positions between preset limits;

a pair of spaced limit switch means electrically coupled to said electrically actuated means;

a pair of cam means respectively movable relative to said spaced limit switch means for engagement therewith to terminate said electrically actuated means when said one stop means has been moved to either of said preset limits. 4

2. The fluid pressure energy translating device defined in claim 1 wherein said electrically actuated means is remotely controlled.

3. The fluid pressure energy translating device as defined in claim 1 wherein said maximum inclination position as defined by one of said stop means is selectively varied between a higher preset limit and a lower preset limit by said electrically actuated means.

4. The fluid pressure energy translating device defined in claim 3 wherein said lower limit of said maximum inclination position defined by said one stop means is greater than said minimum inclination position defined by said other stop means.

5. The fluid pressure energy translating device defined in claim 1 wherein the means for varying the inclination of said swash plate comprises a connecting arm attached to said swash plate and extending externally of said housing, actuating means operatively coupled to said connecting arm and adapted to rotate said swash plate about a predetermined axis; said pair of stop means comprising a pair of mechanical stops, one of which limits the amount of movement of said swash plate in a first direction and defines said minimum inclination position, while the other of said mechanical stops limits the amount of movement of said swash plate in a second, opposite direction and defines said maximum inclination position, one of said mechanical stops being selectively varied between a higher preset limit and a lower preset limit.

6. The fluid pressure energy translating device defined in claim 5 wherein said cam means are carried by said one mechanical stop and adapted to engage said limit switch means to terminate said electrically actuated means when said one mechanical stop is moved to either of said preset limits.

7. The fluid pressure energy translating device defined in claim 1 wherein said swash plate is rotatable about a predetermined axis, a first pressure responsive means carried within said housing adapted to engage said swash plate to rotate said swash plate about said axis to vary the inclination of said swash plate and thus the amount of reciprocal stroking movement of said pistons within said cylinder bores, said first pressure responsive means tending to increase the inclination of said swash plate; second pressure responsive means carried within said housing and adapted to engage said swash plate to rotate said swash plate about said axis in an opposite direction to thereby decrease the inclination of said swash plate.

8. The fluid pressurev energy translating device defined in claim 7 wherein said first pressure responsive means comprises a first piston slidably mounted in a first pressure chamber in said housing and having an extended end engaging said swash plate and adapted to extend under pressure from said pressure chamber to rotate said swash plate about said predetermined axis toward said maximum inclination position; said second pressure responsive means comprising a second piston slidably mounted in a second pressure chamber, said second piston having an extended end engaging said swash plate and adapted to extend under pressure from said second pressure chamber to rotate said swash plate toward said minimum inclination position, said second pressure chamber having a movable mechanical stop disposed therein; and electrically actuated means adapted to selectively move said mechanical stop toward and away from said second piston to limit the amount of inward movement of said second piston into said second pressure chamber, the movement of said movable mechanical stop being defined by said preset limits.

9. The fluid pressure energy translating device defined in claim 8 further comprising a movable rod member, said cams being carried on said movable rod member, and means connecting said rod member to said swash plate such that movement of said rod member isa function of the rotational movement of said swash plate between said preset limits.

10. The fluid pressure energy translating device defined in claim 8 wherein said swash plate is rotatably mounted on a pair of trunnions extending from opposite sides of said swash plate and carried by said housing, one end of one of said trunnions being accessible through a bore in said housing; said cam means being carried by said one end of said one trunnion; said limit switch means being adapted to be engaged by said cam means when said swash plate is inclined to said limits such that said limit switch means terminates said electrically actuated means.

1 l. A fluid system comprising:

a variable displacement pressure energy translating device having an inlet and an outlet;

pressure responsive means for varying the fluid displacement of said device between selected minimum and maximum flow positions;

a pair of stop means defining said maximum and minimum flow positions;

. electrically actuated means for selectively varying the position of one of said stop means to vary one of said flow positions between minimum and maximum limits;

a pair of cam means respectively movable relative to said spaced limit switch means for engagement therewith to terminate said electrically actuated means when said one stop means has been moved to either of said preset limits;

fluid motor means operable in response to fluid pressure from said device;

valve means for selectively connecting the inlet and the outlet of said device to said fluid motor means;

a second source of fluid pressure; and

means for communicating said second source of fluid pressure to said pressure responsive displacement varying means at a selected raTe to thereby vary the rate of change of the displacement of said fluid pressure energy translating device selectively between said maximum and minimum flow positlons.

12. The fluid system defined in claim 1 1 wherein said electrically actuated means is remotely controlled.

13. The fluid system defined in claim 1 1 wherein said electrically actuated means varies said maximum flow positions between said minimum and maximum limits.

14. The fluid system defined in claim 13 wherein said minimum limit of said maximum flow position is greater than said selected minimum flow position.

15. A fluid pressure energy translating device, comprising:

a housing having an inlet and an outlet port;

a plurality of pistons with inner ends disposed for reciprocal stroking movement within said cylinder I bores;

an inclined swash plate mounted in said housing in a driving relationship with the other end of said pistons for imparting said reciprocal stroking movement to said pistons within said cylinder barrel bores as said cylinder barrel rotates, the amount of fluid flowing from said inlet port to said outlet port beinga function of the amount of said reciprocal stroking movement of said pistons;

means for varying the inclination of said swash plate between selected maximum and minimum inclination positions to vary the amount of said reciprocal stroking movement of said pistons such that the fluid flowing from said inlet port to said outlet port is increased as said swash plate inclination increases and said fluid flow between said inlet and outlet ports decreases as said swash plate inclination is decreased, said means for varying the inclination of said swash plate comprising a connecting arm attached to said swash plate and extending externally of said housing;

actuating means operatively coupled to said conne cting arm and adapted to rotate said swash plate about a predetermined axis;

a pair of mechanical stops, one of which limits the amount of movement of said swash plate in a first direction and defines said minimum inclination position, while the other of said mechanical stops limits the amount of movement of said swash plate in a second, opposite direction and defines said maximum inclination position, one of said mechanical stops being selectively varied between a higher preset limit and a lower preset limit, said maximum inclination position being selectively variable between said higher and lower preset limits;

means for selectively varying said maximum inclination position between said limits comprising electrically actuated means for moving said one mechanical stop;

limit switch means carried proximate said one mechanical stop; and

cam means carried by said one mechanical stop and adapted to engage said limit switch means to terminate said electrically actuated means when said one mechanical stop is moved to either of said preset limits.

16. A fluid pressure energy translating device, comprising:

a housing having an inlet and an outlet port;

a cylinder barrel rotatably mounted within said he using, said cylinder barrel having a plurality of arcuately spaced cylinder bores;

means for varying the inclination of said swash plate between selected maximum and minimum inclination positions to vary the amount of said reciprocal stroking movement of said pistons such that the fluid flowing from said inlet to said outlet port is increased as said swash plate inclination increases and said fluid flow between said inlet and outlet ports decreases as said swash plate inclination is decreased, said swash plate being rotatable about a predetermined axis;

a first pressure responsive means carried within said housing adapted to engage said swash plate to rotate said swash plate about said axis to vary the inclination of said swash plate and thus the amount of reciprocal stroking movement of said pistons within said cylinder bores, said first pressure 7 responsive means tending to increase the inclination of said swash plate, said first pressure responsive means comprising a first piston slidably mounted in a first pressure chamber in said housingand having-an extended end engaging said swash plate and adapted to extend under pressure from said pressure chamber to rotate said swash plate about said predetermined axis toward said maximum inclination position;

second pressure responsive means carried within said Electrically actuated means adapted to selectively move said mechanical stop toward and away from said second position to limit the amount of inward movement of said second piston into said second pressure chamber, the movement of said movable mechanical stop being defined by preset limits;

a pair of spaced limit switches; a

a pair of cams respectively adapted to engage said spaced limit switches when said swash plate has been moved to said preset limits toterminate said electrically actuated means, said cams being carried on a movable rod member; and

means connecting said rod member to said swash plate such that movement of said rod member is a function of the rotational movement of said swash plate between said preset 17. A fluid pressure energy translating device, comprising:

a housing having an inlet and an outlet port;

means in said housing for displacing fluid between said ports;

means for varying the amount of fluid displaced by said device between selected minimum and maximum flow conditions;

a pair of stop means cooperating with said last mentioned means and defining said maximum and minimum flow positions;

electrically actuated means for selectively varying the position of one of said stop means to vary one of said flow positions between minimum and maximum limits;

a pair of spaced limit switch means electrically coupled to said electrically actuating means; and

a pair of cams respectively movable relative to said spaced limit switch means for engagement therewith to terminate said electrically actuated means when said one stop means has been moved to either of said preset limits.

Claims

1. A fluid pressure energy translating device, comprising: a housing having an inlet and an outlet port; a cylinder barrel rotatably mounted within said housing, said cylinder barrel having a plurality of arcuately spaced cylinder bores; a plurality of pistons with inner ends disposed for reciprocal stroking movement within said cylinder bores; means for successively communicating said cylinder bores with said inlet and outlet ports; an inclined swash plate mounted in said housing in a driving relationship with the other end of said pistons for imparting said reciprocal stroking movement to said pistons within said cylinder barrel bores as said cylinder barrel rotates, the amount of fluid flowing from said inlet port to said outlet port being a function of the amount of said reciprocal stroking movement of said pistons; means for varying the inclination of said swash plate between selected maximum and minimum inclination positions to vary the amount of said reciprocal stroking movement of said pistons such that the fluid flowing from said inlet port to said outlet port is increased as said swash plate inclination increases and said fluid flow between said inlet and outlet ports decreases as said swash plate inclination is decreased; a pair of stop means defining said maximum and minimum inclination positions; electrically actuated means for selectively varying the position of one of said stop means to vary one of said iNclination positions between preset limits; a pair of spaced limit switch means electrically coupled to said electrically actuated means; a pair of cam means respectively movable relative to said spaced limit switch means for engagement therewith to terminate said electrically actuated means when said one stop means has been moved to either of said preset limits.

8. The fluid pressure energy translating device defined in claim 7 wherein said first pressure responsive means comprises a first piston slidably mounted in a first pressure chamber in said housing and having an extended end engaging said swash plate and adapted to extend under pressure from said pressure chamber to rotate said swash plate about said predetermined axis toward said maximum inclination position; said second pressure responsive means comprising a second piston slidably mounted in a second pressure chamber, said second piston having an extended end engaging said swash plate and adapted to extend under pressure from said second pressure chamber to rotate said swash plate toward said minimum inclination position, said second pressure chamber having a movable mechanical stop disposed therein; and electrically actuated means adapted to selectively move said mechanical stop toward and away from said second piston to limit the amount of inward movement of said second piston into said second pressure chamber, the movement of said movable mechanical stop being defined by said preset limits.

9. The fluid pressure enerGy translating device defined in claim 8 further comprising a movable rod member, said cams being carried on said movable rod member, and means connecting said rod member to said swash plate such that movement of said rod member is a function of the rotational movement of said swash plate between said preset limits.

11. A fluid system comprising: a variable displacement pressure energy translating device having an inlet and an outlet; pressure responsive means for varying the fluid displacement of said device between selected minimum and maximum flow positions; a pair of stop means defining said maximum and minimum flow positions; electrically actuated means for selectively varying the position of one of said stop means to vary one of said flow positions between minimum and maximum limits; a pair of spaced limit switch means electrically coupled to said electrically actuated means; a pair of cam means respectively movable relative to said spaced limit switch means for engagement therewith to terminate said electrically actuated means when said one stop means has been moved to either of said preset limits; fluid motor means operable in response to fluid pressure from said device; valve means for selectively connecting the inlet and the outlet of said device to said fluid motor means; a second source of fluid pressure; and means for communicating said second source of fluid pressure to said pressure responsive displacement varying means at a selected raTe to thereby vary the rate of change of the displacement of said fluid pressure energy translating device selectively between said maximum and minimum flow positions.

12. The fluid system defined in claim 11 wherein said electrically actuated means is remotely controlled.

13. The fluid system defined in claim 11 wherein said electrically actuated means varies said maximum flow positions between said minimum and maximum limits.

15. A fluid pressure energy translating device, comprising: a housing having an inlet and an outlet port; a cylinder barrel rotatably mounted within said housing, said cylinder barrel having a plurality of arcuately spaced cylinder bores; a plurality of pistons with inner ends disposed for reciprocal stroking movement within said cylinder bores; means for successively communicating said cylinder bores with said inlet and outlet ports; an inclined swash plate mounted in said housing in a driving relationship with the other end of said pistons for imparting said reciprocal stroking movement to said pistons within said cylinder barrel bores as said cylinder barrel rotates, the amount of fluid flowing from said inlet port to said outlet port being a function of the amount of said reciprocal stroking movement of said pistons; means for varying the inclination of said swash plate between selected maximum and minimum inclination positions to vary the amount of said reciprocal stroking movement of said pistons such that the fluid flowing from said inlet port to said outlet port is increased as said swash plate inclination increases and said fluid flow between said inlet and outlet ports decreases as said swash plate inclination is decreased, said means for varying the inclination of said swash plate comprisiNg a connecting arm attached to said swash plate and extending externally of said housing; actuating means operatively coupled to said connecting arm and adapted to rotate said swash plate about a predetermined axis; a pair of mechanical stops, one of which limits the amount of movement of said swash plate in a first direction and defines said minimum inclination position, while the other of said mechanical stops limits the amount of movement of said swash plate in a second, opposite direction and defines said maximum inclination position, one of said mechanical stops being selectively varied between a higher preset limit and a lower preset limit, said maximum inclination position being selectively variable between said higher and lower preset limits; means for selectively varying said maximum inclination position between said limits comprising electrically actuated means for moving said one mechanical stop; limit switch means carried proximate said one mechanical stop; and cam means carried by said one mechanical stop and adapted to engage said limit switch means to terminate said electrically actuated means when said one mechanical stop is moved to either of said preset limits.

16. A fluid pressure energy translating device, comprising: a housing having an inlet and an outlet port; a cylinder barrel rotatably mounted within said housing, said cylinder barrel having a plurality of arcuately spaced cylinder bores; a plurality of pistons with inner ends disposed for reciprocal stroking movement within said cylinder bores; means for successively communicating said cylinder bores with said inlet and outlet ports; an inclined swash plate mounted in said housing in a driving relationship with the other end of said pistons for imparting said reciprocal stroking movement to said pistons within said cylinder barrel bores as said cylinder barrel rotates, the amount of fluid flowing from said inlet port to said outlet port being a function of the amount of said reciprocal stroking movement of said pistons; means for varying the inclination of said swash plate between selected maximum and minimum inclination positions to vary the amount of said reciprocal stroking movement of said pistons such that the fluid flowing from said inlet to said outlet port is increased as said swash plate inclination increases and said fluid flow between said inlet and outlet ports decreases as said swash plate inclination is decreased, said swash plate being rotatable about a predetermined axis; a first pressure responsive means carried within said housing adapted to engage said swash plate to rotate said swash plate about said axis to vary the inclination of said swash plate and thus the amount of reciprocal stroking movement of said pistons within said cylinder bores, said first pressure responsive means tending to increase the inclination of said swash plate, said first pressure responsive means comprising a first piston slidably mounted in a first pressure chamber in said housing and having an extended end engaging said swash plate and adapted to extend under pressure from said pressure chamber to rotate said swash plate about said predetermined axis toward said maximum inclination position; second pressure responsive means carried within said housing and adapted to engage said swash plate to rotate said swash plate about said axis in an opposite direction to thereby decrease the inclination of said swash plate, said second pressure responsive means comprising a second piston slidably mounted in a second pressure chamber, said second piston having an extended end engaging said swash plate and adapted to extend under pressure from said second pressure chamber to rotate said swash plate toward said minimum inclination position, said second pressure chamber having a movable mechanical stop disposed therein; Electrically actuated means adapted to selectively move said mechanical stop toward and away from said second position to limit the aMount of inward movement of said second piston into said second pressure chamber, the movement of said movable mechanical stop being defined by preset limits; a pair of spaced limit switches; a pair of cams respectively adapted to engage said spaced limit switches when said swash plate has been moved to said preset limits to terminate said electrically actuated means, said cams being carried on a movable rod member; and means connecting said rod member to said swash plate such that movement of said rod member is a function of the rotational movement of said swash plate between said preset limits.

17. A fluid pressure energy translating device, comprising: a housing having an inlet and an outlet port; means in said housing for displacing fluid between said ports; means for varying the amount of fluid displaced by said device between selected minimum and maximum flow conditions; a pair of stop means cooperating with said last mentioned means and defining said maximum and minimum flow positions; electrically actuated means for selectively varying the position of one of said stop means to vary one of said flow positions between minimum and maximum limits; a pair of spaced limit switch means electrically coupled to said electrically actuating means; and a pair of cams respectively movable relative to said spaced limit switch means for engagement therewith to terminate said electrically actuated means when said one stop means has been moved to either of said preset limits.