US20100119393A1

US20100119393A1 - Hydraulic pump assembly

Info

Publication number: US20100119393A1
Application number: US12/269,251
Authority: US
Inventors: Adam M. Osswald; David F. Reuter
Original assignee: Delphi Technologies Inc
Current assignee: BWI Co Ltd SA
Priority date: 2008-11-12
Filing date: 2008-11-12
Publication date: 2010-05-13

Abstract

A hydraulic pump assembly including a fluid reservoir, a body defining a fluid inlet and a fluid outlet, the fluid inlet being in fluid communication with the fluid reservoir, and a radially opposed piston pump assembly at least partially housed within the body and including a first piston pump mechanism and a second piston pump mechanism, the first piston pump mechanism being in fluid communication with the fluid inlet and having a first pump outlet, the second piston pump mechanism being in fluid communication with the fluid inlet and having a second pump outlet, wherein the first pump outlet and the second pump outlet are both in fluid communication with the fluid outlet.

Description

FIELD

The present patent application is directed to pump assemblies and, more particularly, to hydraulic pump assemblies configured to supply a pressurized fluid line to various auxiliary applications.

BACKGROUND

Anti-lock braking systems typically include wheel speed sensors, an electronic control unit and a hydraulic control unit. The electronic control unit is integrated with the hydraulic control unit to form a hydraulic modulator or electro-hydraulic control unit. The hydraulic control unit may include a motor for pumping hydraulic fluid through various channels, accumulators for storing accumulated hydraulic fluid and valves having internal components for directing hydraulic fluid to the brakes. The electronic control unit may include a processor for receiving signals from the speed sensors and solenoid coils corresponding to each valve stem for actuating the valves according to command signals generated by the processor. The electronic control unit may be integrated with the hydraulic control unit such that the coils contact the valve stems, thereby forming the electro-hydraulic control unit.
Advances in electro-hydraulic control unit technology and, in particular, advances in the manufacture of electro-hydraulic control units, including the machining of the associated hydraulic control units, have resulted in efficiencies and economies of scale that led to mass production of electro-hydraulic control unit. As a result, anti-lock braking systems have become standard features of modern automobiles.
Elsewhere in the art, hydraulic pumps such as gear pumps and vane pumps are used to supply hydraulic fluid to various auxiliary applications, such as positioning applications (e.g., hydraulic door operators, conveyor belt tensioners and medical chairs and beds), recreational vehicle applications (e.g., leveling, slideouts and tent trailers), clamping applications (e.g., tool fixtures and jigs, hydraulic brakes, crimping tools, arbor presses and truck restraints), cycling applications (e.g., garbage compactors, valve operators, press controls, packing equipment and indexing tables), and lifting applications (e.g., handicap lifts, scissor lift tables and pellet movers).
It has been discovered that electro-hydraulic control unit technology may be used to supply a highly pressurized fluid line to various auxiliary applications, thereby providing a low-cost alternative to traditional hydraulic pumps for auxiliary applications.

SUMMARY

In one aspect, the disclosed hydraulic pump assembly may include a fluid reservoir, a body defining a fluid inlet and a fluid outlet, the fluid inlet being in fluid communication with the fluid reservoir, and a radially opposed piston pump assembly at least partially housed within the body and including a first piston pump mechanism and a second piston pump mechanism, the first piston pump mechanism being in fluid communication with the fluid inlet and having a first pump outlet, the second piston pump mechanism being in fluid communication with the fluid inlet and having a second pump outlet, wherein the first pump outlet and the second pump outlet are both in fluid communication with the fluid outlet.
In another aspect, the disclosed hydraulic pump assembly may include a fluid reservoir, a body defining a fluid inlet and a fluid outlet, the fluid inlet being in fluid communication with the fluid reservoir, a radially opposed piston pump assembly at least partially housed within the body and including a first piston pump mechanism, a second piston pump mechanism and an electric motor, the electric motor including an eccentric that engages the first and second piston pump mechanisms, the first piston pump mechanism being in fluid communication with the fluid inlet and having a first pump outlet, the second piston pump mechanism being in fluid communication with the fluid inlet and having a second pump outlet, wherein the first pump outlet and the second pump outlet are both in fluid communication with the fluid outlet, a first pump inlet check valve positioned in a first inlet fluid path within the body between the fluid reservoir and the first piston pump mechanism, a second pump inlet check valve positioned in a second inlet fluid path within the body between the fluid reservoir and the second piston pump mechanism, a first pump outlet check valve positioned in a first outlet fluid path within the body between the first piston pump mechanism and the first pump outlet, a second pump outlet check valve positioned in a second outlet fluid path within the body between the second piston pump mechanism and the second pump outlet, and a pressure relief valve in fluid communication with the fluid outlet.
Other aspects of the disclosed hydraulic pump assembly will become apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of one aspect of the disclosed hydraulic pump assembly connected to an auxiliary application;

FIG. 2 is a side elevational view of the hydraulic pump assembly of FIG. 1;

FIG. 3 is a front elevational view, shown in section, of the hydraulic pump assembly of FIG. 2;

FIG. 4 is a schematic illustration of a second aspect of the disclosed hydraulic pump assembly;

FIG. 5 is a front elevational view, shown in section, of the hydraulic pump assembly of FIG. 4;

FIG. 6 is a schematic illustration of a third aspect of the disclosed hydraulic pump assembly; and

FIG. 7 is a front elevational view, shown in section, of the hydraulic pump assembly of FIG. 6.

DETAILED DESCRIPTION

Referring to FIG. 1, one aspect of the disclosed hydraulic pump assembly, generally designated 6, may include a radially opposed piston pump assembly 8, a pressure relief valve 10, and a fluid reservoir 12. The radially opposed piston pump assembly 8 may include a first piston pump mechanism 7 and a second piston pump mechanism 9, wherein the outputs of the first and second piston pump mechanisms 7, 9 may be combined to provide a single hydraulic fluid outlet 11. The fluid outlet 11 of the radially opposed piston pump assembly 8 may be in fluid communication with an auxiliary application 18 by way of a pressurized fluid line 20. The pressurized fluid line 20 may supply high pressure hydraulic fluid to the auxiliary application 18 and a return fluid line 22 may return hydraulic fluid from the auxiliary application 18 to the fluid reservoir 12 at atmospheric pressure.
In particular, as shown in FIG. 2, the hydraulic pump assembly 6 may include the fluid reservoir 12, a hydraulic control unit body 14, and a pump motor 16. The hydraulic control unit body 14 may house the radially opposed piston pump assembly 8 and the pressure relief valve 10, and, in response to rotational power supplied by the pump motor 16, may operate to draw hydraulic fluid from the fluid reservoir 12, pressurize the hydraulic fluid, communicate the hydraulic fluid to the auxiliary application 18 by way of fluid line 20, and then return the hydraulic fluid to the fluid reservoir 12 by way of fluid line 22.
The fluid reservoir 12 may be any vessel capable of storing a hydraulic fluid. For example, as shown in FIGS. 2 and 3, the fluid reservoir 12 may include a bottle 24 (e.g., a plastic bottle) and a cap 26 for securing hydraulic fluid within the bottle 24. In one aspect, the fluid reservoir 12 may be connected to the body 14 to form an integral reservoir/body/motor assembly. In an alternative aspect, the fluid reservoir 12 may be physically separated from the body 14, but in fluid communication with the body 14 by way of external fluid lines (not shown).
The pump motor 16 may be any appropriate motor having a motor shaft 28 (FIG. 3) with an eccentric 30 (FIG. 3) extending therefrom. In one example, the pump motor 16 may be a 12-volt electric motor with an eccentric 30 of about 0.85 mm to about 1.20 mm. In another example, the pump motor 16 may be a 24-volt motor. In another example, the pump motor 16 may be 10-volt motor. However, those skilled in the art will appreciate that the size of the pump motor 16, the shaft 28 and the eccentric 30 will be dictated by design considerations.
As shown in FIG. 2, the pump motor 16 may be connected to the body 14 such that, as shown in FIG. 3, the motor shaft 28 and associated eccentric 30 extend into the shaft chamber 38 (discussed below) defined in the body 14 for engagement with the first and second pistons 66, 76 (discussed below). Therefore, rotational power from the pump motor 16 may be translated into flow and pressurization of hydraulic fluid within the body 14.
Referring to FIG. 3, the body 14 may be a block of rigid material, such as aluminum, and may define a first fluid inlet bore 30, a second fluid inlet bore 32, a first piston bore 34, a second piston bore 36, a shaft chamber 38, a first fluid outlet bore 40, a second fluid outlet bore 42, a connecting bore 44, a pressure relief bore 46 and a fluid return bore 48. The bores 30, 32, 34, 36, 40, 42, 44, 46, 48 and chamber 38 may be machined into the body 14 using any available technique (e.g., drilling). Plugs (discussed in greater detail below), such as ball plugs, may be inserted into the bores to seal the bores as appropriate.
The first fluid inlet bore 30 may be in fluid communication with the fluid reservoir 12 at a first end thereof and the first piston bore 34 at a second end thereof, and may define a valve seat 50 therein. A spring-loaded ball 52 may be received in the first fluid inlet bore 30 and may be biased into engagement with the valve seat 50, thereby defining a first pump inlet check valve 54 between the first fluid inlet bore 30 and the first piston bore 34. The first pump inlet check valve 54 may allow hydraulic fluid to flow from the fluid reservoir 12 to the first piston pump mechanism 7, but not in the reverse direction.
The second fluid inlet bore 32 may be in fluid communication with the fluid reservoir 12 at a first end thereof and the second piston bore 36 at a second end thereof, and may define a valve seat 56 therein. A spring-loaded ball 58 may be received in the second fluid inlet bore 32 and may be biased into engagement with the valve seat 56, thereby defining a second pump inlet check valve 60 between the second fluid inlet bore 32 and the second piston bore 36. The second pump inlet check valve 60 may allow hydraulic fluid to flow from the fluid reservoir 12 to the second piston pump mechanism 9, but not in the reverse direction.
The first piston bore 34 may include a plug 62 sealing a first end thereof and may connect with the shaft chamber 38 at a second end thereof. The first piston bore 34 may fluidly couple the first fluid inlet bore 30 with the first fluid outlet bore 40 (i.e., the outlet of the first piston pump mechanism 7) and may include a first pump outlet check valve 64 positioned between the first fluid inlet bore 30 and the first fluid outlet bore 40. The first pump outlet check valve 64 may allow hydraulic fluid to flow from the first piston bore 34 to the first fluid outlet bore 40, but not in the reverse direction.
A first piston 66 may be closely and sideably received in the first piston bore 34. A seal 68 may create a fluid-tight seal across the first piston 66 such that hydraulic fluid does not pass across the first piston 66 from the first piston bore 34 and into the shaft chamber 38. A biasing element 70, such as a coil spring, may bias the first piston 66 out of the first piston bore 34 and in the direction of the shaft chamber 38 for engagement with the eccentric 30 of the shaft 28 of the pump motor 16.
The second piston bore 36 may include a plug 72 sealing a first end thereof and may connect with the shaft chamber 38 at a second end thereof. The second piston bore 36 may fluidly couple the second fluid inlet bore 32 with the second fluid outlet bore 42 (i.e., the outlet of the second piston pump mechanism 9) and may include a second pump outlet check valve 74 positioned between the second fluid inlet bore 32 and the second fluid outlet bore 42. The second pump outlet check valve 74 may allow hydraulic fluid to flow from the second piston bore 36 to the second fluid outlet bore 42, but not in the reverse direction.
A second piston 76 may be closely and sideably received in the second piston bore 36. A seal 78 may create a fluid-tight seal across the second piston 76 such that hydraulic fluid does not pass across the second piston 76 from the second piston bore 36 and into the shaft chamber 38. A biasing element 80, such as a coil spring, may bias the second piston 76 out of the second piston bore 36 and in the direction of the shaft chamber 38 for engagement with the eccentric 30 of the shaft 28 of the pump motor 16 (FIG. 2).
As the pump motor 16 rotates the shaft 28 and associated eccentric 30, the eccentric 30 alternately acts on the first and second pistons 66, 76 such that the pistons 66, 76 are urged into the associated first and second piston bores 34, 36. Then, when the eccentric 30 passes, the biasing elements 70, 80 urge the associated pistons 66, 76 out of the associated piston bores 66, 76.
Accordingly, due to the reciprocating action of the pistons 66, 76 caused by the pump motor 16 and the biasing elements 70, 80, hydraulic fluid is drawn from the fluid reservoir 12, through the first and second pump inlet check valves 54, 60, and into the first and second piston bores 34, 36 when the pistons 66, 76 are urged out of the associated piston bores 34, 36 by the biasing elements 70, 80. Then, when the pistons 66, 76 are urged into the associated piston bores 34, 36 by the eccentric 30, the hydraulic fluid in the piston bores 34, 36 is urged through the first and second pump outlet check valves 64, 74 and into the first and second fluid outlet bores 40, 42, thereby operating as the radially opposed piston pump assembly 8.
The first fluid outlet bore 40 may include a first end 82 and a second end 84. The first end 82 of the first fluid outlet bore 40 may be connected to the first piston bore 34 and a first end 86 of the connecting bore 44. The second end 84 of the first fluid outlet bore may include a plug 88, such as a ball plug, received therein to form an external seal.
The second fluid outlet bore 42 may include a first end 90 and a second end 92. The first end 90 of the second fluid outlet bore 42 may be connected to the second piston bore 36 and a second end 94 of the connecting bore 44. (A plug 96, such as a ball plug, may be used to seal the external portion of the second end 94 of the connecting bore 44.) The second end 92 of the second fluid outlet bore 42 may be connected to an outlet port 93, which may be connected to the pressurized fluid line 20 for directing hydraulic fluid to the auxiliary application 18 (FIG. 2).
Thus, the connecting bore 44 may combine the first and second fluid outlet bores 40, 42 (i.e., both outputs of the radially opposed piston pump assembly 8) into a single fluid outlet port 93.
Still referring to FIG. 3, the pressure relief bore 46 may define a valve seat 98 therein and may include a first end 100 in fluid communication with the connecting bore 44 and a second end 102 having threads formed therein. A spring-loaded ball 104 or the like may be positioned in the pressure relief bore 46 to engage the valve seat 98 and form a pressure sensitive seal therebetween, thereby operating as the pressure relief valve 10. A return bore 106 extending between the fluid reservoir 12 and the pressure relief bore 46 may fluidly couple the pressure relief bore 46 with the fluid reservoir 12. The return bore 106 may be connected to the pressure relief bore 46 at a point between the valve seat 98 and the second end 102 of the pressure relief bore 46.
A pressure relief control screw 108 may engage the threads at the second end 102 of the pressure relief bore 46 and a seal 110 may provide a fluid tight seal between the pressure relief bore 46 and the pressure relief control screw 108. Rotation of the pressure relief control screw 108 about the threads may compress the spring-loaded ball 104, thereby urging the spring-loaded ball 104 against the valve seat 98 with greater force, thereby increasing the amount of fluid pressure that may be resisted by the spring-loaded ball 104 before the spring-loaded ball 104 is displaced from the valve seat 98 to release hydraulic fluid to the fluid reservoir 12 through the return bore 106.
The fluid return bore 48 may include a first end 112 and a second end 114. The first end 112 of the fluid return bore 48 may be in fluid communication with the fluid reservoir 12. The second end 114 of the fluid return bore 48 may be connected to a return port 116. The return port 116 may be connected to the return fluid line 22 for directing return fluid to the fluid reservoir 12.
At this point, those skilled in the art will appreciate that the body 14 of the hydraulic pump assembly 6 may be formed by machining a solid block of material (e.g., aluminum) to form a plurality of bores having the desired configuration and geometry, and inserting the necessary plugs and components (e.g., pistons, check valves and biasing elements) into the bores to form the radially opposed piston pump assembly 8 that delivers a single, high pressure fluid outlet and the pressure relief valve 10 that controls excess fluid pressure within the hydraulic pump assembly 6.
Accordingly, those skilled in the art will appreciate that the disclosed hydraulic pump assembly 6 may provide a low-cost, high-volume radial two piston pump and motor assembly with an integral pressure relief valve, and, optionally, an integral plastic fluid reservoir.
Referring to FIGS. 4 and 5, a second aspect of the disclosed hydraulic pump assembly, generally designated 200, may include a hydraulic control unit body 201 (FIG. 5), a pump motor 203 (FIG. 4), a pressure relief valve 204, a fluid reservoir 206 and a manual control valve 208. The hydraulic control unit body 201 and the pump motor 203 may combine to form a radially opposed piston pump assembly 202. The radially opposed piston pump assembly 202, the pressure relief valve 204 and the fluid reservoir 206 may be configured in the manner described above in connection with the hydraulic pump assembly 6. However, those skilled in the art will appreciate that the radially opposed piston pump assembly 202, the pressure relief valve 204 and the fluid reservoir 206 may be configured in various ways.
The manual control valve 208 may be a three-position, two-way bi-direction spool valve having a moveable spool 213 received in a bore 209 defined in the body 201 of the assembly 200. The manual control valve 208 may be in communication with the combined fluid output 211 of the radially opposed piston pump assembly 202 by way of a first fluid channel 210, the fluid reservoir 206 by way of a second fluid channel 212, a first bi-directional input/output port 214 and a second bi-directional input/output port 216. Those skilled in the art will appreciate that the combined fluid output 211, the first and second fluid channels 210, 212 and the first and second input/ output ports 214, 216 may be formed as bores machined into the body 201 of the assembly 200.
As shown in FIG. 4, the first and second input/ output ports 214, 216 may be in fluid communication with an auxiliary application 218 by way of first and second fluid lines 220, 222. The auxiliary application 218 is shown in FIG. 4 as a hydraulic cylinder; however, those skilled in the art will appreciate that the auxiliary application 218 may be any auxiliary device that can be manipulated by the application of pressurized hydraulic fluid.
In the first (e.g., left) position (not shown), the spool 213 may be shifted in the direction of arrow C (FIG. 5) such that the manual control valve 208 may connect the first input/output port 214 with the first fluid channel 210 (i.e., the pressurized fluid) by way of a first valve bore 230 and the second input/output port 216 with the second fluid channel 212 (i.e., the reservoir) by way of a second valve bore 232. In the first position, the first input/output port 214 may be pressurized while the second input/output port 216 may be depressurized, thereby pressurizing the piston chamber 224 of the auxiliary application 218 and depressurizing the rod chamber 226 of the auxiliary application 218.
In the second (e.g., middle) position (shown in FIG. 4), the spool 213 may be centered in the bore 209 such that the first fluid channel 210 (i.e., the pressurized fluid) is in fluid communication with a third valve bore 234, which is not in fluid communication with either the first input/output port 214 or the second input/output port 216, and the second fluid channel 212 (i.e., the reservoir) is in fluid communication with a fourth valve bore 236, which is not in fluid communication with either the first input/output port 214 or the second input/output port 216. Therefore, in the second position, the manual control valve 208 locks hydraulic fluid in the first and second input/ output ports 214, 216, thereby locking the auxiliary application 218 in a fixed position.
In the third (e.g., right) position (not shown), the spool 213 may be shifted in the direction of arrow D (FIG. 5) such that the manual control valve 208 may connect the first input/output port 214 with the second fluid channel 212 (i.e., the reservoir) by way of a fifth valve bore 238 and the second input/output port 216 with the first fluid channel 210 (i.e., the pressurized fluid) by way of a sixth valve bore 240. In the third position, the first input/output port 214 may be depressurized while the second input/output port 216 may be pressurized, thereby depressurizing the piston chamber 224 of the auxiliary application 218 and pressurizing the rod chamber 226 of the auxiliary application 218.
Accordingly, those skilled in the art will appreciate that the disclosed hydraulic pump assembly 200 may provide a low-cost, high-volume radial two piston pump and motor assembly with an integral pressure relief valve, an integral plastic fluid reservoir, and an integral three-position, bi-directional spool valve for manual pressure control.
Referring to FIGS. 6 and 7, a third aspect of the disclosed hydraulic pump assembly, generally designated 300, may include a hydraulic control unit body 301, a pump motor 303, a pressure relief valve 304, a fluid reservoir 306, a first normally closed solenoid actuated poppet valve 308 (actuated by electric switch 314), and a second normally closed solenoid actuated poppet valve 310 (actuated by electric switch 316). The hydraulic control unit body 301 and the pump motor 303 may combine to form a radially opposed piston pump assembly 302 (actuated by electric switch 312), The radially opposed piston pump assembly 302, the pressure relief valve 304 and the fluid reservoir 306 may be configured in the manner described above in connection with the hydraulic pump assembly 6. However, those skilled in the art will appreciate that the radially opposed piston pump assembly 302, the pressure relief valve 304 and the fluid reservoir 306 may be configured in various ways.
Furthermore, the hydraulic pump assembly 300 may include a first, constant high pressure outlet port 318 and a second, variable pressure outlet port 320. The first outlet port 318 may be in fluid communication with the radially opposed piston pump assembly 302 by way of a first bore 322 and a rod chamber 324 of a hydraulic cylinder 326 by way of a first fluid line 328 (FIG. 6). The second outlet port 320 may be in fluid communication with the radially opposed piston pump assembly 302 by way of a second bore 330, the fluid reservoir 306 by way of a third bore 332, and a rod chamber 334 of the hydraulic cylinder 326 by way of a second fluid line 336 (FIG. 6). The second bore 330 may be interrupted by the first normally closed solenoid actuated poppet valve 308 and the third bore 332 may be interrupted by the second normally closed solenoid actuated poppet valve 310.
In a first configuration of the disclosed hydraulic pump assembly 300, the radially opposed piston pump assembly 302 may be actuated by the switch 312, but the first and second solenoid actuated poppet valves 308, 310 may not actuated, thereby locking the hydraulic cylinder 326. In a second configuration of the disclosed hydraulic pump assembly 300, the radially opposed piston pump assembly 302 may be actuated by the switch 312, the first solenoid actuated poppet valve 308 may be actuated by the switch 314, and the second solenoid actuated poppet valve 310 may not be actuated, thereby pressurizing the piston chamber 334 and driving the piston 335 in the direction shown by arrow A. (Equal pressures in the piston and rod chambers 334, 324, but the rod chamber 324 has less surface area due to the rod.) In a third configuration of the disclosed hydraulic pump assembly 300, the radially opposed piston pump assembly 302 may be actuated by the switch 312, the second solenoid actuated poppet valve 310 may be actuated by the switch 316, and the first solenoid actuated poppet valve 308 may not be actuated, thereby pressurizing the rod chamber 324 and driving the piston 335 in the direction shown by arrow B. In a fourth configuration of the disclosed hydraulic pump assembly 300, the radially opposed piston pump assembly 302 may be actuated by the switch 312, the first solenoid actuated poppet valve 308 may be actuated by the switch 314, and the second solenoid actuated poppet valve 310 may be actuated by the switch 316, thereby freeing the hydraulic cylinder 326 and removing the load from the radially opposed piston pump assembly 302.
Accordingly, those skilled in the art will appreciate that the disclosed hydraulic pump assembly 300 may provide a low-cost, high-volume radial two piston pump and motor assembly with an integral pressure relief valve, an integral plastic fluid reservoir, and integral solenoid actuated poppet valves allowing for remote operation and full pressure control using electric switches.
Although various aspects of the disclosed hydraulic pump assembly have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.

Claims

1. A hydraulic pump assembly comprising:

a fluid reservoir;

a body defining a fluid inlet and a fluid outlet, said fluid inlet being in fluid communication with said fluid reservoir; and

a radially opposed piston pump assembly at least partially housed within said body and including a first piston pump mechanism and a second piston pump mechanism, said first piston pump mechanism being in fluid communication with said fluid inlet and having a first pump outlet, said second piston pump mechanism being in fluid communication with said fluid inlet and having a second pump outlet, wherein said first pump outlet and said second pump outlet are both in fluid communication with said fluid outlet.

2. The hydraulic pump assembly of claim 1 further comprising a pressure relief valve in fluid communication with said fluid outlet.

3. The hydraulic pump assembly of claim 2 wherein said pressure relief valve includes a biasing element that urges a ball into engagement with a valve seat.

4. The hydraulic pump assembly of claim 3 wherein said pressure relief valve further includes a pressure relief control screw, said biasing element being positioned between said ball and said pressure relief control screw.

5. The hydraulic pump assembly of claim 1 wherein said fluid reservoir includes a bottle and a cap, said cap sealingly engaging said bottle.

6. The hydraulic pump assembly of claim 1 wherein said radially opposed piston pump assembly includes a motor connected to said body, said motor having a shaft with an eccentric.

7. The hydraulic pump assembly of claim 6 wherein said eccentric operatively engages said first and said second piston pump mechanisms.

8. The hydraulic pump assembly of claim 6 wherein said motor is an electric motor.

9. The hydraulic pump assembly of claim 6 wherein said first piston pump mechanism includes a first piston biased into engagement with said eccentric and said second piston pump mechanism includes a second piston biased into engagement with said eccentric.

10. The hydraulic pump assembly of claim 1 further comprising a first pump inlet check valve positioned in a first fluid path within said body between said fluid reservoir and said first piston pump mechanism and a second pump inlet check valve positioned in a second fluid path within said body between said fluid reservoir and said second piston pump mechanism.

11. The hydraulic pump assembly of claim 1 further comprising a first pump outlet check valve positioned in a first fluid path within said body between said first piston pump mechanism and said first pump outlet and a second pump outlet check valve positioned in a second fluid path within said body between said second piston pump mechanism and said second pump outlet.

12. The hydraulic pump assembly of claim 1 further comprising a spool valve received within said body, said spool valve being disposed in a fluid channel between said fluid outlet and said first and second pump outlets.

13. The hydraulic pump assembly of claim 12 wherein said spool valve includes a first input/output and a second input/output, and wherein said spool valve is configurable between a first position, wherein said first input/output is in fluid communication with said fluid output, a second position, wherein said fluid output is decoupled from said first input/output and said second input/output, and a third position, wherein said second input/output is in fluid communication with said fluid output.

14. The hydraulic pump assembly of claim 1 wherein said first pump outlet and said second pump outlet are combined to form a combined pump outlet, said combined pump outlet being in fluid communication with a constant pressure outlet port and a variable pressure outlet port, and wherein a first normally closed solenoid actuated poppet valve is disposed in a first fluid line between said variable pressure outlet port and said combined pump outlet, said first normally closed solenoid actuated poppet valve being received, at least partially, within said body.

15. The hydraulic pump assembly of claim 14 further comprising a second normally closed solenoid actuated poppet valve disposed in a second fluid line between said variable pressure outlet port and said fluid reservoir, said second normally closed solenoid actuated poppet valve being received, at least partially, within said body.

16. A hydraulic pump assembly comprising:

a fluid reservoir;

a body defining a fluid inlet and a fluid outlet, said fluid inlet being in fluid communication with said fluid reservoir;

a radially opposed piston pump assembly at least partially housed within said body and including a first piston pump mechanism, a second piston pump mechanism and an electric motor, said electric motor including an eccentric that engages said first and said second piston pump mechanisms, said first piston pump mechanism being in fluid communication with said fluid inlet and having a first pump outlet, said second piston pump mechanism being in fluid communication with said fluid inlet and having a second pump outlet, wherein said first pump outlet and said second pump outlet are both in fluid communication with said fluid outlet;

a first pump inlet check valve positioned in a first inlet fluid path within said body between said fluid reservoir and said first piston pump mechanism;

a second pump inlet check valve positioned in a second inlet fluid path within said body between said fluid reservoir and said second piston pump mechanism;

a first pump outlet check valve positioned in a first outlet fluid path within said body between said first piston pump mechanism and said first pump outlet;

a second pump outlet check valve positioned in a second outlet fluid path within said body between said second piston pump mechanism and said second pump outlet; and

a pressure relief valve in fluid communication with said fluid outlet.

17. The hydraulic pump assembly of claim 16 wherein said pressure relief valve includes a biasing element that urges a ball into engagement with a valve seat, and a pressure relief control screw, said biasing element being positioned between said ball and said pressure relief control screw.

18. The hydraulic pump assembly of claim 16 wherein said fluid reservoir includes a bottle and a cap sealing engaged with said bottle.

19. The hydraulic pump assembly of claim 16 further comprising a three-position, bi-directional spool valve at least partially received in said body, said spool valve being in fluid communication with said fluid outlet.

20. The hydraulic pump assembly of claim 16 further comprising a normally closed solenoid actuated poppet valve at least partially received in said body, said solenoid actuated poppet valve being in fluid communication with said fluid outlet.