US20180058449A1

US20180058449A1 - Variable displacement hydraulic pump with electromechanical actuator and method thereof

Info

Publication number: US20180058449A1
Application number: US15/683,826
Authority: US
Inventors: Joseph Johnson; Jonathan Richards
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2016-08-29
Filing date: 2017-08-23
Publication date: 2018-03-01

Abstract

A pump, including: inlet port and outlet ports; a cylinder block including a piston disposed in a through-bore; a swash plate engaged with the piston; a drive shaft non-rotatably connected to the drive shaft, arranged to rotate the cylinder block to draw fluid through the inlet port into the through-bore and to expel the fluid from the through-bore and through the outlet port and including an axis of rotation; an axis transverse to the axis of rotation; and an actuator including a roller screw; a nut disposed about the roller screw and in threaded contact with the roller screw; an actuator pin; and an electric motor arranged to rotate the roller screw or the nut to axially displace the actuator pin to pivot the swash plate or the cylinder block about the axis and control an amount of the fluid expelled from the through-bore.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 62/380,769, filed Aug. 29, 2016, which application is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a variable displacement hydraulic pump with torque sensing and a method thereof, in particular, a variable displacement hydraulic pump using torque sensing to attain or maintain a desired flow rate correlated to a known torque level on a drive shaft for the pump.

BACKGROUND

Known variable flow hydraulic pumps use an auxiliary hydraulic control piston or an electromechanical controller to control the flow rate for the pump. Feedback for control of the piston is typically provided by down-stream (of the pump outlet) measurements of pressure or flow. However, pressure in the control piston is affected by the overall pressure in the hydraulic system, for example to due to activation of various hydraulic components. Changes in the overall pressure cause deviations in the position of the piston, which in turn affects the flow rate of the pump. The control piston can be made more precise by using an electromechanical actuator, but the control loop still has errors and lag induced by the down-stream measurement of pressure or flow. Thus, it is difficult to quickly and accurately attain or maintain a desired flow rate for known variable flow hydraulic pumps.

SUMMARY

According to aspects illustrated herein, there is provided a variable displacement axial pump, including: an inlet port; an outlet port; a cylinder block including a first piston disposed in a first through-bore; a swash plate engaged with the first piston; a drive shaft non-rotatably connected to the drive shaft, arranged to rotate the cylinder block to draw fluid through the inlet port into the first through-bore and to expel the fluid from the first through-bore and through the outlet port, and including an axis of rotation; an axis transverse to the axis of rotation; and an actuator including a roller screw, a nut disposed about the roller screw and in threaded contact with the roller screw, an actuator pin engaged with the roller screw, and an electric motor arranged to rotate the roller screw or the nut to axially displace the actuator pin to pivot the swash plate about the axis and control an amount of the fluid expelled from the first through-bore or pivot the cylinder block about the axis and control an amount of the fluid expelled from the first through-bore.
According to aspects illustrated herein, there is provided a variable displacement hydraulic pump, including: an inlet port; an outlet port; a cylinder block including a through-bore and a piston at least partially disposed in the through-bore; a drive shaft non-rotatably connected to the drive shaft, arranged to rotate the cylinder block to displace the piston to draw fluid through the inlet port into the through-bore and expel the fluid from the through-bore and through the outlet port, and including an axis of rotation; an axis transverse to the axis of rotation; an actuator including a roller screw, a nut disposed about and in contact with the roller screw, an actuator pin engaged with the roller screw and the swash plate and an electric motor arranged to rotate the roller screw to axially displace the actuator pin to pivot the swash plate about the axis and control an amount of the fluid expelled from the through-bore or pivot the cylinder block about the axis and control an amount of the fluid expelled from the through-bore.
According to aspects illustrated herein, there is provided a variable displacement hydraulic pump, including: an inlet port; an outlet port; a cylinder block including a through-bore and a piston at least partially disposed in the through-bore; a drive shaft non-rotatably connected to the drive shaft, arranged to rotate the cylinder block to displace the piston to draw fluid through the inlet port into the through-bore and expel the fluid from the through-bore and through the outlet port, and including an axis of rotation; an axis transverse to the axis of rotation; an actuator including a roller screw, a nut disposed about and in contact with the roller screw, an actuator pin engaged with the roller screw and the swash plate and an electric motor arranged to rotate the nut to axially displace the actuator pin to pivot the swash plate about the axis and control an amount of the fluid expelled from the through-bore or pivot the cylinder block about the axis and control an amount of the fluid expelled from the through-bore.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are disclosed, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which:

FIG. 1 is a cross-sectional view of an electromechanical actuator for a variable displacement pump with a driven nut;

FIG. 2 is a cross-sectional view of an electromechanical actuator for a variable displacement pump with a roller screw;

FIG. 3 is a schematic representation of a variable displacement pump with a pivotable swash plate and including the actuator of FIG. 1 or the actuator of FIG. 2;

FIG. 4 is a schematic representation of the variable displacement pump of FIG. 3 with the swash plate pivoted;

FIG. 5 is a schematic representation of a variable displacement bent-axis pump including the actuator of FIG. 1 or the actuator of FIG. 2; and,

FIG. 6 is a schematic representation of the variable displacement bent-axis pump of FIG. 5 with a cylinder block pivoted.

DETAILED DESCRIPTION

At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects.
Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure.
FIG. 1 is a cross-sectional view of electromechanical actuator 100 for a variable displacement pump, with a driven nut. Actuator 100 includes housing 102, electric motor 104, roller screw 106, nut 108 and actuator pin 110. Pin 110 is engaged with screw 106, for example is axially fixed to screw 106 such that pin 110 axially displaces with screw 106. In an example embodiment, motor 104 includes stator 112 and rotor 114. Nut 108 is disposed about screw 106 and is in threaded engagement with screw 106. For example, nut 108 includes threads 116 in contact with threads 118 of screw 106. In an example embodiment, screw 106 is a differential roller screw.
Electric motor 104 rotates nut 108 about axis of rotation AR1 for nut 108 in opposite circumferential directions CD1 and CD2. In the example of FIG. 1, nut 108 is axially fixed and rotating nut 108 about axis of rotation AR1 in opposite circumferential directions CD1 and CD2 displaces screw 106 and pin 110 in opposite axial directions AD1 and AD2, respectively. In an example embodiment, rotating nut 108 about axis of rotation AR1 in opposite circumferential directions CD1 and CD2 displaces screw 106 and pin 110 in axial directions AD2 and AD1, respectively. The discussion that follows is directed to rotation of nut 108 about axis of rotation AR1 in circumferential directions CD1 and CD2 displacing screw 106 and pin 110 in axial directions AD1 and AD2, respectively. However, it should be understood that the discuss that follows is applicable to rotation of nut 108 about axis of rotation AR1 in circumferential directions CD1 and CD2 displacing screw 106 and pin 110 in axial directions AD2 and AD1, respectively.
In an example embodiment, pump 100 includes resilient element 120. Element 120 reacts against housing 102 to urge screw 106 in direction AD2 to prevent back-driving of screw 106 in direction AD2. Thus, pump 100 is self-locking. For example, when motor 104 is de-energized, element 120 frictionally engages threads 116 and 118 to prevent screw 106 from rotating in direction CD2 and displacing in direction AD2. Element 120 can be any resilient element known in the art, including but not limited to a wrap spring (shown in FIG. 1) or a spring-pressurized friction pad. In an example embodiment (not shown), pump 100 includes an electromechanical brake to prevent back-driving of screw 106.
FIG. 2 is a cross-sectional view of electromechanical actuator 200 for a variable displacement pump, with a driven nut. Actuator 200 includes housing 202, electric motor 204, roller screw 206, nut 208 and actuator pin 210. Pin 210 is engaged with screw 206, for example is axially fixed to screw 206 such that pin 210 axially displaces with screw 206. In the example of FIG. 2, screw 206 is an actuating pin as further described below. In an example embodiment, motor 204 includes stator 212 and rotor 214. Nut 208 is disposed about screw 206 and is in threaded engagement with screw 206. For example, nut 208 includes threads 216 in contact with threads 218 of screw 206. In an example embodiment, screw 206 is a differential roller screw.
Electric motor 204 rotates screw 206 about axis of rotation AR2 for screw 206 in opposite circumferential directions CD1 and CD2. In the example of FIG. 2, nut 208 is rotationally fixed and rotating screw 206 about axis of rotation AR2 in opposite circumferential directions CD1 and CD2 displaces screw 206 and pin 210 in opposite axial directions AD1 and AD2, respectively. In an example embodiment, nut 208 is rotationally fixed and rotating screw 206 about axis of rotation AR1 in opposite circumferential directions CD1 and CD2 displaces screw 206 and pin 210 in axial directions AD2 and AD1, respectively. The discussion that follows is directed to rotation of screw 206 about axis of rotation AR1 in circumferential directions CD1 and CD2 displacing screw 206 and pin 210 in axial directions AD1 and AD2, respectively. However, it should be understood that the discuss that follows is applicable to rotation of screw 206 about axis of rotation AR2 in circumferential directions CD1 and CD2 displacing screw 206 and pin 210 in axial directions AD2 and AD1, respectively.
FIG. 3 is a schematic representation of variable displacement pump 300 with a pivotable swash plate and including actuator 100 of FIG. 1 or actuator 200 of FIG. 2. Pump 300 includes housing 302, inlet port 304, outlet port 306, drive shaft 308, cylinder block 310 non-rotatably connected to shaft 308, swash plate 312, actuator 100 or actuator 200, axis of rotation AR3 for shaft 308, and axis of rotation AR4 for block 310. Cylinder block 310 includes through- bores 318 and 320 and pistons 322 and 324 at least partially disposed in through- bores 318 and 320, respectively. The discussion that follows assumes actuator 100 is included in pump 300; however, it should be understood that the discussion for actuator 100 in pump 300 is applicable to actuator 200 in pump 300.
By “non-rotatably connected” elements, we mean that: the elements are connected so that whenever one of the elements rotates, all the elements rotate; and relative rotation between the elements is not possible. Radial and/or axial movement of non-rotatably connected elements with respect to each other is possible, but not required.
Pump 300 is located in device D (for example, a bulldozer, tractor, or construction equipment). Shaft 308 is rotated by engine E of device D. Actuator 100 is arranged to receive, from processor P, control signal 328. Actuator 100 is arranged to: pivot swash plate 312 about axis A1, transverse to axis of rotation AR3, according control signal 328; or maintain a circumferential position of swash plate 312, about axis AR3, according to control signal 328.
Pistons 322 and 324 are engaged with plate 312. Pistons 322 and 324 remain engaged to plate 312 as is known in the art. In an example embodiment, each of pistons 322 and 324 is connected to swash plate 312 via a respective retention assembly 330, as is known in the art. In an example embodiment (not shown) fluids at ports 304 and 306 are pressurized to force pistons 322 and 324 into contact with plate 312 during rotation of block 310 about axis AR3/AR4. For example, assemblies 330 are not used to maintain connection between the pistons and plate 312.
As cylinder block 310 rotates about axis AR3 and AR4: when piston 322 or 324 is aligned with port 304, plate 312 has displaced piston 322 or 324 in direction AD1, within through- bores 318 or 320, respectively, to create suction and draw fluid F into through- bore 318 or 320 through port 304; and when piston 322 or 324 is aligned with port 306, plate 312 has displaced piston 322 or 324 in direction AD2, within through- bores 318 or 320, respectively, to expel fluid F from through- bore 318 or 320 into port 306 at a flow rate. In FIG. 3, the flow rate is flow rate 332.
A flow rate at which fluid F is drawn into and expelled from pump 300 is dependent upon the speed of rotation of block 310 and the displacement of pistons 322 and 324, by plate 312, within through- bores 318 and 320, respectively. The speed of rotation of block 310 is a function of engine E, which is determined by operations other than those for pump 300. That is, the speed of rotation is not controllable by pump 300. For a given position of plate 312 about axis A1, increasing and decreasing the speed of rotation of block 310 increases and decreases rate 332, respectively.
A flow rate for pump 300 is also governed by the circumferential position of plate 312 with respect to axis A1. The circumferential position of plate 312 determines the distance that pistons 322 and 324 are displaced by plate 312 within through- bores 318 and 320, respectively. In the example of FIG. 3, pistons 322 and 324 are displaced distance 334 by plate 312 within through- bores 318 and 320, respectively. Thus, pistons 322 and 324 displace distance 334 to draw fluid F into through- bores 318 and 320, respectively, and pistons 322 and 324 displace distance 334 to expel fluid F from through- bores 318 and 320, respectively.
As discussed below, changing the extent of the axial displacement of pistons 322 and 324 (for example, distance 334) changes the amount of fluid F drawn into and expelled by block 310 and hence changes flow rate 332.
FIG. 4 shows variable displacement axial pump 300 of FIG. 3 with swash plate 312 pivoted. In the example of FIG. 4, swash plate 312 has been rotated in direction CD3 about axis A1 from the position shown in FIG. 3. The alignment of through- bores 318 and 320 with ports 304 and 306 remains the same. The rotation and subsequent tilting of swash plate 312 in FIG. 4 changes the axial displacement of pistons 322 and 322. As a result: pistons 322 and 324 are displaced distance 336 by plate 312. In the example of FIGS. 3 and 4: distance 336 is less than distance 334.
Assuming a constant speed of rotation of shaft 308 in FIGS. 3 and 4, and since distance 336 is less than distance 334, the amount of fluid F drawn into and expelled from through- bores 318 and 320 in FIG. 4 decreases in comparison to the amount of fluid F drawn into through- bores 318 and 320 in FIG. 3. Thus flow rate 338 in FIG. 4 is less than rate 332 in FIG. 3.
The following discussion is directed to a transition from FIG. 4 to FIG. 3. To transition from FIG. 4 to FIG. 3, swash plate 312 is pivoted by actuator 100 about axis A1 in direction CD4. Assuming a constant speed of rotation of shaft 308 in FIGS. 3 and 4, and since distance 336 is less than distance 334, the amount of fluid F drawn into and expelled from through- bores 318 and 320 in FIG. 3 increases in comparison to the amount of fluid F drawn into through- bores 318 and 320 in FIG. 4. Thus rate 332 in FIG. 3 is greater than rate 338 in FIG. 4.
FIG. 5 is a schematic representation of variable displacement bent-axis pump 400 including actuator 100 of FIG. 1 or actuator 200 of FIG. 2. Pump 400 includes: housing 402; inlet port 404, outlet port 406; shaft 408 with axis of rotation AR3; cylinder block 410 with axis of rotation AR4; universal joint 411 connecting block 410 to shaft 408; swash plate 412 non-rotatably connected to shaft 408; and electromechanical actuator 100. The discussion that follows assumes actuator 100 is included in pump 400; however, it should be understood that the discussion for actuator 100 in pump 400 is applicable to actuator 200 in pump 400.
Block 410 includes: through- bores 418 and 420; and pistons 422 and 424 engaged with swash plate 412 and at least partly disposed in through- bores 418 and 420, respectively. Cylinder block 410 rotates with shaft 408 and about axis AR4 due to the action of joint 411. Axis AR4 is displaceable in directions CD3 and CD4 with respect to axis AR3.
Swash plate 412 is arranged to displace pistons 422 and 424 within through- bores 418 and 420, respectively, to draw fluid F through port 404 into through- bores 418 and 420 and to expel fluid F from through- bores 418 and 420 into port 406.
Swash plate 412 rotates about axis AR3 with shaft 408. Pistons 422 and 424 remain engaged to plate 412 as is known in the art. Block 410 rotates about axis AR4 with shaft 408 and plate 412. As cylinder block 410 rotates about axis AR4: when piston 422 or 424 is aligned with port 404, plate 412 displaces piston 422 or 424 in direction AD3, within through- bores 418 or 420, respectively, to draw fluid F into through- bore 418 or 420 through port 404 (the displacement creates suction at port 404); and when piston 422 or 424 is aligned with port 406, plate 412 displaces piston 422 or 424 in direction AD4, within through- bores 418 or 420, respectively, to expel fluid F from through- bore 418 or 420 into port 406 at a flow rate. In FIG. 5, the flow rate is flow rate 432.
Pump 400 is located in device D (for example, a bulldozer, tractor, or construction equipment). Shaft 408 is rotated by engine E of device D. Actuator 100 is arranged to receive, from processor P, control signal 428. Actuator 100 is arranged to: pivot cylinder block 410 about axis A2, transverse to axis of rotation AR3 and AR4 according control signal 428; or maintain a circumferential position of cylinder block 410, about axis A2, according to control signal 428.
A flow rate at which fluid is drawn into and expelled from pump 400 is dependent upon the speed of rotation of shaft 408 and the displacement of pistons 422 and 424, by plate 412, within through- bores 418 and 420, respectively. The speed of rotation of block 410 is a function of engine E, which is determined by operations other than those for pump 400. That is, the speed of rotation is not controllable by pump 400. For a given position of block 410 about axis A2, increasing or decreasing the speed of rotation of block 410 increases or decreases flow rate 432, respectively.
A flow rate for pump 400 is also governed by the circumferential position of block 410 with respect to axis A2. The circumferential position of block 410 determines the distance that pistons 422 and 424 are displaced by plate 412 within through- bores 418 and 420, respectively. In the example of FIG. 5, pistons 422 and 424 are displaced distance 434 by plate 412 within through- bores 418 and 420, respectively. Thus, pistons 422 and 424 displace distance 434 to draw fluid F into through- bores 418 and 420, respectively, and pistons 422 and 424 displace distance 434 to expel fluid F from through- bores 418 and 420, respectively.
As discussed below, changing the extent of the axial displacement of pistons 422 and 424 (for example, distance 434) changes the amount of fluid F drawn into and expelled by block 410 and hence changes flow rate 432.
FIG. 6 shows variable displacement bent-axis pump 400 of FIG. 5 with block 410 pivoted. In the example of FIG. 6, block 410 has been rotated in direction CD4 about axis A2 from the position shown in FIG. 5. The alignment of through- bores 418 and 420 with ports 404 and 406 remains the same. The rotation and subsequent tilting of swash plate 412 in FIG. 6 changes the axial displacement of pistons 422 and 422 by plate 412. As a result: pistons 422 and 424 are displaced distance 436 by plate 412. In the example of FIGS. 5 and 6: distance 436 is less than distance 434.
Assuming a constant speed of rotation of shaft 408 in FIGS. 5 and 6, and since distance 436 is less than distance 434, the amount of fluid F drawn into and expelled from through- bores 418 and 120 in FIG. 6 decreases in comparison to the amount of fluid F drawn into through- bores 418 and 420 in FIG. 5. Thus flow rate 438 in FIG. 6 is less than rate 432 in FIG. 5.
The following discussion is directed to a transition from FIG. 6 to FIG. 5. To transition from FIG. 6 to FIG. 5, block 410 is pivoted about axis A2 in direction CD3. Assuming the constant speed of rotation of shaft 408 in FIGS. 5 and 6, and since distance 436 is less than distance 434, the amount of fluid F drawn into and expelled from through- bores 418 and 420 in FIG. 5 increases in comparison to the amount of fluid F drawn into through- bores 418 and 420 in FIG. 6. Thus rate 432 in FIG. 5 is greater than rate 438 in FIG. 6.
The following should be viewed in light of FIGS. 1 through 6. The following describes a method of operating variable displacement hydraulic pump 300 or 400. Although the method is presented as a sequence of steps for clarity, no order should be inferred from the sequence unless explicitly stated. It should be understood that the method is applicable to pump 300 or pump 400 including actuator 100 or 200 unless indicated otherwise. This conflation of applicability is shown by designating respective elements included in the method with the nomenclature “3xx/4xx.” For example, the first step cites drive shaft 308/408. A first step rotates, with drive shaft 308/408, cylinder block 310/410. A second step draws fluid F through inlet port 304/404 and into through-bore 318/418. A third step expels fluid F from through-bore 318/418 and through outlet port 306/406 at flow rate 332/432. A fourth step rotates, with electric motor 104/204, roller screw 106 or nut 208. A fifth step axially displaces actuator pin 110/210. A sixth step: pivots, with actuator pin 110/210, swash plate 312/412 about axis A1/A2 and controls an amount of fluid expelled from through-bore 318/418. In an example embodiment, a seventh step blocks, with resilient element 120 in actuator 100, axial displacement of actuating pin 110.
In an example embodiment, the fourth step rotates roller screw 106 and an eighth step: rotates, with electric motor 104, roller screw 106 in circumferential direction CD1; displaces, with roller screw 106, actuator pin 110 in axial direction AD1; pivots, with actuator pin 110, swash plate 312/412 about axis A1/A2 in circumferential direction CD3; generates flow rate 338/438; rotates, with electric motor 104, roller screw 106 in circumferential direction CD2; displaces, with roller screw 106, actuator pin 110 in axial direction AD2; pivots, with actuator pin 110, swash plate 312/412 about axis A1 in circumferential direction CD4; and generates flow rate 332/432.
In an example embodiment, the fourth step rotates nut 208 and an eighth step: rotates, with electric motor 204, nut 208 in circumferential direction CD1; displaces, with roller screw 206, actuator pin 210 in axial direction AD1; pivots, with actuator pin 210, swash plate 312/412 about axis A1/A2 in circumferential direction CD3; generates flow rate 338/438; rotates, with electric motor 104, nut 208 in circumferential direction CD2; displaces, with roller screw 206, actuator pin 210 in axial direction AD2; pivots, with actuator pin 210, swash plate 312/412 about axis A1 in circumferential direction CD4; and generates flow rate 332/432.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

LIST OF REFERENCE CHARACTERS

A1 axis transverse to axis AR1 and AR2
A2 axis transverse to axis AR1 and AR2
AD1 axial direction
AD2 axial direction
AR1 axis of rotation for nut 108
AR2 axis of rotation for roller screw 206
AR3 axis of rotation for shafts 308 and 408
AR4 axis of rotation for cylinder blocks 310 and 410
CD1 circumferential direction about axis AR1
CD2 circumferential direction about axis AR1
CD3 circumferential direction about axis A1 and A2
CD4 circumferential direction about axis A1 and A2
100 axial pump
102 housing
104 electric motor
106 roller screw
108 nut
110 actuator pin
112 stator
114 rotor
116 threads
118 threads
120 resilient element
200 axial pump
202 housing
204 electric motor
206 roller screw
208 nut
210 actuator pin
212 stator
214 rotor
216 threads
218 threads
220 resilient element
300 axial pump
302 housing
304 port
306 port
308 shaft
310 cylinder block
312 swash plate
318 through-bore
320 through-bore
322 piston
324 piston
330 retention assembly
332 flow rate
334 axial displacement distance
336 axial displacement distance
338 flow rate
400 axial pump
402 housing
404 port
406 port
408 shaft
410 cylinder block
412 swash plate
418 through-bore
420 through-bore
422 piston
424 piston
430 retention assembly
432 flow rate
434 axial displacement distance
436 axial displacement distance
438 flow rate

Claims

1. A variable displacement hydraulic pump, comprising:

an inlet port;

an outlet port;

a cylinder block including a first piston disposed in a first through-bore;

a swash plate engaged with the first piston;

a drive shaft:

non-rotatably connected to the cylinder block;

arranged to rotate the cylinder block to draw fluid through the inlet port into the first through-bore and to expel the fluid from the first through-bore and through the outlet port; and,

including an axis of rotation;

an axis transverse to the axis of rotation; and,

an actuator including:

a roller screw;

a nut disposed about the roller screw and in threaded contact with the roller screw;

an actuator pin engaged with the roller screw; and,

an electric motor arranged to rotate the roller screw or the nut to axially displace the actuator pin to:

pivot the swash plate about the axis and control an amount of the fluid expelled from the first through-bore; or,

pivot the cylinder block about the axis and control an amount of the fluid expelled from the first through-bore.

2. The variable displacement hydraulic pump of claim 1, wherein the actuator includes a resilient element urging the roller screw in a first axial direction.

3. The variable displacement hydraulic pump of claim 1, wherein:

the electric motor is arranged to rotate the roller screw or the nut to axially displace the actuator pin to pivot the swash plate about the axis;

the cylinder block includes:

a second through-bore; and,

a second piston disposed in the second through-bore and engaged with the swash plate; and,

rotation of the cylinder block is arranged to:

displace the first piston within the first through-bore;

displace the second piston within the second through-bore;

draw the fluid through the inlet port into the second through-bore; and,

expel the fluid from the second through-bore and through the outlet port.

4. The variable displacement hydraulic pump of claim 1, wherein:

the electric motor is arranged to rotate the roller screw or the nut to pivot the cylinder block about the axis;

the cylinder block includes:

a second through-bore; and,

rotation of the cylinder block is arranged to:

displace the first piston within the first through-bore;

displace the second piston within the second through-bore;

draw the fluid through the inlet port into the second through-bore; and,

expel the fluid from the second through-bore and through the outlet port.

5. The variable displacement hydraulic pump of claim 1, wherein:

the electric motor is arranged to rotate the roller screw to axially displace the actuator pin to pivot the swash plate about the axis;

the electric motor is arranged to rotate the roller screw in a first circumferential direction about the axis of rotation to displace the actuator pin in a first axial direction;

the actuator pin is arranged to pivot the swash plate about the axis in a second circumferential direction to increase the amount of fluid expelled from the first through-bore;

the electric motor is arranged to rotate the roller screw in a third circumferential direction, opposite the first circumferential direction, about the axis of rotation to displace the actuator pin in a second axial direction, opposite the first axial direction; and,

the actuator pin is arranged to pivot the swash plate about the axis in a fourth circumferential direction, opposite the second circumferential direction to decrease the amount of fluid expelled from the first through-bore.

6. The variable displacement hydraulic pump of claim 1, wherein:

the electric motor is arranged to rotate the nut to axially displace the actuator pin to pivot the swash plate about the axis;

the electric motor is arranged to rotate the nut in a first circumferential direction about the axis of rotation to displace the actuator pin in a first axial direction;

the electric motor is arranged to rotate the nut in a third circumferential direction, opposite the first circumferential direction, about the axis of rotation to displace the actuator pin in a second axial direction, opposite the first axial direction; and,

7. The variable displacement hydraulic pump of claim 1, wherein:

the electric motor is arranged to rotate the roller screw to axially displace the actuator pin to pivot the cylinder block about the axis;

the actuator pin is arranged to pivot the cylinder block about the axis in a second circumferential direction to increase the amount of fluid expelled from the first through-bore;

8. The variable displacement hydraulic pump of claim 1, wherein:

the electric motor is arranged to rotate the nut to axially displace the actuator pin to pivot the cylinder block about the axis;

the actuator pin is arranged to pivot the cylinder block about the axis in a fourth circumferential direction, opposite the second circumferential direction to decrease the amount of fluid expelled from the first through-bore.

9. The variable displacement hydraulic pump of claim 1, wherein:

the actuator pin is arranged to pivot the swash plate about the axis; and,

the actuator pin is arranged to pivot the swash plate about the axis to control an extent of displacement of the first piston within the first through-bore.

10. The variable displacement hydraulic pump of claim 1, wherein:

the actuator pin is arranged to pivot the cylinder block about the axis; and,

the actuator pin is arranged to pivot the cylinder block about the axis to control an extent of displacement of the first piston within the first through-bore.

11. A variable displacement hydraulic pump, comprising:

an inlet port;

an outlet port;

a cylinder block including:

a through-bore; and,

a piston at least partially disposed in the through-bore;

a drive shaft:

non-rotatably connected to the cylinder block;

arranged to rotate the cylinder block to displace the piston to draw fluid through the inlet port into the through-bore and expel the fluid from the through-bore and through the outlet port; and,

including an axis of rotation;

an axis transverse to the axis of rotation;

an actuator including:

a roller screw;

a nut disposed about and in contact with the roller screw;

an actuator pin engaged with the roller screw and the swash plate; and,

an electric motor arranged to rotate the roller screw to axially displace the actuator pin to:

pivot the swash plate about the axis and control an amount of the fluid expelled from the through-bore; or,

pivot the cylinder block about the axis and control an amount of the fluid expelled from the through-bore.

12. A variable displacement hydraulic pump, comprising:

an inlet port;

an outlet port;

a cylinder block including:

a through-bore; and,

a piston at least partially disposed in the through-bore;

a drive shaft:

non-rotatably connected to the drive shaft;

including an axis of rotation;

an axis transverse to the axis of rotation;

an actuator including:

a roller screw;

a nut disposed about and in contact with the roller screw;

an actuator pin engaged with the roller screw and the swash plate; and,

an electric motor arranged to rotate the nut to axially displace the actuator pin to:

13. A method of operating the variable displacement hydraulic pump of claim 1, comprising:

rotating, with the drive shaft, the cylinder block;

drawing the fluid through the inlet port and into the first through-bore;

expelling the fluid from the first through-bore and through the outlet port;

rotating, with the electric motor, the roller screw or the nut;

axially displacing the actuator pin; and,

pivoting, with the actuator pin:

the swash plate about the axis and controlling an amount of the fluid expelled from the first through-bore; or,

the cylinder block about the axis and controlling an amount of the fluid expelled from the first through-bore.

14. The method of claim 13, further comprising:

blocking, with a resilient element in the actuator, axial displacement of the actuating pin.

15. The method of claim 13, further comprising:

pivoting, with the actuator pin, the swash plate about the axis;

rotating, with the electric motor, the roller screw in a first circumferential direction about the axis of rotation;

displacing, with the roller screw, the actuator pin in a first axial direction;

pivoting, with the actuator pin, the swash plate about the axis in a second circumferential direction;

increasing the amount of fluid expelled from the first through-bore;

rotating, with the electric motor, the roller screw in a third circumferential direction, opposite the first circumferential direction, about the axis of rotation;

displacing, with the roller screw, the actuator pin in a second axial direction, opposite the first axial direction;

pivoting, with the actuator pin, the swash plate about the axis in a fourth circumferential direction, opposite the second circumferential direction; and,

decreasing the amount of fluid expelled from the first through-bore.

16. The method of claim 13, further comprising:

pivoting, with the actuator pin, the cylinder block about the axis;

displacing, with the roller screw, the actuator pin in a first axial direction;

pivoting, with the actuator pin, the cylinder block about the axis in a second circumferential direction;

increasing the amount of fluid expelled from the first through-bore;

pivoting, with the actuator pin, the cylinder block about the axis in a fourth circumferential direction, opposite the second circumferential direction; and,

decreasing the amount of fluid expelled from the first through-bore.

17. The method of claim 13, further comprising:

pivoting, with the actuator pin, the swash plate about the axis;

rotating, with the electric motor, the nut in a first circumferential direction about the axis of rotation;

displacing, with the roller screw, the actuator pin in a first axial direction;

increasing the amount of fluid expelled from the first through-bore;

rotating, with the electric motor, the nut in a third circumferential direction, opposite the first circumferential direction, about the axis of rotation;

decreasing the amount of fluid expelled from the first through-bore.

18. The method of claim 13, further comprising:

pivoting, with the actuator pin, the cylinder block about the axis;

displacing, with the roller screw, the actuator pin in a first axial direction;

increasing the amount of fluid expelled from the first through-bore;

decreasing the amount of fluid expelled from the first through-bore.

19. The method of claim 13, further comprising:

pivoting, with the actuator pin, the swash plate about the axis; and,

controlling, with the swash plate, an extent of displacement of the first piston within the first through-bore.

20. The method of claim 12, further comprising:

pivoting, with the actuator pin, the cylinder block about the axis; and,