Patent Publication Number: US-2023151800-A1

Title: Assistive torque electro-hydraulic piston pump system

Description:
TECHNICAL FIELD 
     The present invention relates generally to the field of electro-hydraulic pump systems, and more particularly to an improved assistive torque electro-hydraulic piston pump system. 
     BACKGROUND ART 
     Hydrostatic radial piston pumps are generally known in the prior art. The drive torque of a shaft is transmitted to a radial piston cylinder block rotationally mounted on a control stud or journal with pistons arranged radially in the cylinder block and supported at their outer end by a thrust or stroke ring via slide shoes in the thrust ring. When the cylinder block rotates, the pistons exert a stroke movement as a result of an eccentric position of the thrust ring. The pump flow is routed into and out of the housing and control stud via channels and is controlled by means of suction and pressure windows in the control stud. If a differential cylinder is to be actuated by means of a hydrostatic radial piston motor, proportional or control valves are interposed. Differential cylinders comprise two working spaces, each with its own working connection, a first working connection leading to the working space on the piston-end and a second working connection leading to the working space on the rod-end of the differential cylinder. The volume flow of the hydraulic fluid supplied by the hydrostatic radial piston motor can be routed to the particular working connection and thereby the particular working space via the valves. 
     BRIEF SUMMARY 
     With parenthetical reference to corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, an electro-hydraulic pump system ( 15 ,  115 ,  215 ,  315 ) is provided comprising: an electric motor ( 16 ) adapted to be supplied with a current and having a drive shaft ( 18 ,  18 A,  18 B,  18 C,  23 ,  123 ,  318 ,  323 ); a first hydraulic piston pump ( 30 ,  330 ) comprising a first fluid control journal ( 31 ,  331 ), a plurality of pistons ( 32 ,  332 ) in a first cylinder block ( 33 ,  333 ) adapted to rotate relative to the first fluid control journal ( 31 ,  331 ) about a first block axis ( 34 ,  334 ) with rotation of the drive shaft ( 18 ,  318 ), and a first displacement drive ( 35 ,  335 ) having a first displacement axis ( 38 ,  338 ); the first displacement drive ( 35 ,  335 ) adapted to move in a first positive displacement range ( 40 ,  340 ) between a first neutral position between the first displacement axis ( 38 ,  338 ) and the first block axis ( 34 ,  334 ) and a first maximum positive displacement position between the first displacement axis ( 38 ,  338 ) and the first block axis ( 34 ,  334 ); the first displacement drive ( 35 ,  335 ) adapted to move in a first negative displacement range ( 44 ,  344 ) between the first neutral position and a first maximum negative displacement position between the first displacement axis ( 38 ,  338 ) and the first block axis ( 34 ,  334 ); the first fluid control journal ( 31 ,  331 ) comprising a first pump port ( 48 ,  348 ) and a second pump port ( 49 ,  349 ), wherein rotation of the drive shaft ( 18 ,  318 ) when the first displacement drive ( 35 ,  335 ) is in the first positive displacement range ( 40 ,  340 ) provides higher pressure to the first pump port ( 48 ,  348 ) relative to the second pump port ( 49 ,  349 ), and wherein rotation of the drive shaft ( 18 ,  318 ) when the first displacement drive ( 35 ,  335 ) is in the first negative displacement range ( 44 ,  344 ) provides higher pressure to the second pump port ( 49 ,  349 ) relative to the first pump port ( 48 ,  348 ); a second hydraulic piston pump ( 60 ,  360 ) comprising a second fluid control journal ( 61 ,  361 ), a plurality of pistons ( 62 ,  362 ) in a second cylinder block ( 63 ,  363 ) adapted to rotate relative to the second fluid control journal ( 61 ,  361 ) about a second block axis ( 64 ,  364 ) with rotation of the drive shaft ( 18 ,  318 ), and a second displacement drive ( 65 ,  365 ) having a second displacement axis ( 68 ,  368 ); the second displacement drive ( 65 ,  365 ) adapted to move in a second positive displacement range ( 70 ,  370 ) between a second neutral position between the second displacement axis ( 68 ,  368 ) and the second block axis ( 64 ,  364 ) and a second maximum positive displacement position between the second displacement axis ( 68 ,  368 ) and the second block axis ( 64 ,  364 ); the second displacement drive ( 65 ,  365 ) adapted to move in a second negative displacement range ( 74 ,  374 ) between the second neutral position between the second displacement axis ( 68 ,  368 ) and the second block axis ( 64 ,  364 ) and a second maximum negative displacement position between the second displacement axis ( 68 ,  368 ) and the second block axis ( 64 ,  364 ); the second fluid control journal ( 61 ,  361 ) comprising a third pump port ( 78 ,  378 ) and a fourth pump port ( 79 ,  379 ), wherein rotation of the drive shaft ( 18 ,  318 ) when the second displacement drive ( 65 ,  365 ) is in the second positive displacement range ( 70 ,  370 ) provides higher pressure to the third pump port ( 78 ,  378 ) relative to the fourth pump port ( 79 ,  379 ), and wherein rotation of the drive shaft ( 18 ,  318 ) when the second displacement drive ( 65 ,  365 ) is in the second negative displacement range ( 74 ,  374 ) provides higher pressure to the fourth pump port ( 79 ,  379 ) relative to the third pump port ( 78 ,  378 ); a first hydraulic actuator ( 90 ,  390 ) having a first working port ( 93 ,  393 ) hydraulically connected ( 52 ,  352 ) to the first pump port ( 48 ,  348 ) of the first piston pump ( 30 ,  330 ); the first hydraulic actuator ( 90 ,  390 ) having a second working port ( 94 ,  394 ) hydraulically connected ( 53 ,  353 ) to the second pump port ( 49 ,  349 ) of the first piston pump ( 30 ,  330 ); a second hydraulic actuator ( 100 ,  400 ) having a third working port ( 103 ,  403 ) hydraulically connected ( 82 ,  382 ) to the third pump port ( 78 ,  378 ) of the second piston pump ( 60 ,  360 ); the second hydraulic actuator ( 100 ,  400 ) having a fourth working port ( 104 ,  404 ) hydraulically connected ( 83 ,  383 ) to the fourth pump port ( 79 ,  379 ) of the second piston pump ( 60 ,  360 ); wherein an external force (F 1 ) applied to the first hydraulic actuator ( 90 ,  390 ) that provides higher pressure ( 51 ) to the second pump port ( 49 ,  349 ) relative to the first pump port ( 48 ,  348 ) when the first displacement drive ( 35 ,  335 ) is in the first positive displacement range ( 40 ,  340 ) applies an assistive torque to the drive shaft ( 18 ,  318 ); and wherein an external force (F 2 ) applied to the first hydraulic actuator ( 90 ,  390 ) that provides higher pressure ( 51 ) to the first pump port ( 48 ,  348 ) relative to the second pump port ( 49 ,  349 ) when the first displacement drive ( 35 ,  335 ) is in the first negative displacement range ( 44 ,  344 ) applies an assistive torque to the drive shaft ( 18 ,  318 ). 
     An external force (F 3 ) applied to the second hydraulic actuator ( 100 ,  400 ) that provides higher pressure ( 81 ) to the fourth pump port ( 79 ,  379 ) relative to the third pump port ( 78 ,  378 ) when the second displacement drive ( 65 ,  365 ) is in the second positive displacement range ( 70 ,  370 ) may apply an assistive torque to the drive shaft ( 18 ,  318 ); and an external force (F 4 ) applied to the second hydraulic actuator ( 100 ,  400 ) that provides higher pressure ( 81 ) to the third pump port ( 78 ,  378 ) relative to the fourth pump port ( 79 ,  379 ) when the second displacement drive ( 65 ,  365 ) is in the second negative displacement range ( 74 ,  374 ) may apply an assistive torque to the drive shaft ( 18 ,  318 ). 
     The electro-hydraulic pump system may comprise a battery ( 21 ) supplying the current to the electric motor ( 16 ). The motor ( 16 ) may be configured to selectively supply a current to the battery ( 21 ) in a regeneration mode when: an external force (F 1 ) applied to the first hydraulic actuator ( 90 ,  390 ) provides higher pressure to the second pump port ( 49 ,  349 ) relative to the first pump port ( 48 ,  348 ) when the first displacement drive ( 35 ,  335 ) is in the first positive displacement range ( 40 ,  340 ) or an external force (F 2 ) applied to the first hydraulic actuator ( 90 ,  390 ) provides higher pressure ( 51 ) to the first pump port ( 48 ,  348 ) relative to the second pump port ( 49 ,  349 ) when the first displacement drive ( 35 ,  335 ) is in the first negative displacement range ( 44 ,  344 ); and an external force (F 3 ) applied to the second hydraulic actuator ( 100 ,  400 ) provides higher pressure ( 81 ) to the fourth pump port ( 79 ,  379 ) relative to the third pump port ( 78 ,  378 ) when the second displacement drive ( 65 ,  365 ) is in the second positive displacement range ( 70 ,  370 ) or an external force (F 4 ) applied to the second hydraulic actuator ( 100 ,  400 ) provides higher pressure ( 81 ) to the third pump port ( 78 ,  378 ) relative to the fourth pump port ( 79 ,  379 ) when the second displacement drive ( 65 ,  365 ) is in the second negative displacement range ( 74 ,  374 ). 
     The first hydraulic actuator ( 90 ,  390 ) may be configured to actuate a first object ( 118 ) of an electrically powered vehicle ( 116 ) and the second hydraulic actuator ( 100 ,  400 ) may be configured to actuate a second object of the electrically powered vehicle ( 116 ). The electric motor may be selected from a group consisting of a brushless DC servo-motor, a stepper motor, a brush motor and an induction motor. The first hydraulic actuator may comprise a linear hydraulic actuator or a rotary hydraulic actuator. The first hydraulic actuator may comprise a linear hydraulic actuator having a first chamber ( 91 ,  241 ,  391 ), a second chamber ( 92 ,  242 ,  392 ) and a piston ( 95 ,  245 ,  395 ) separating the first and second chambers. The first hydraulic actuator may comprise a cylinder ( 98 ,  248 ,  398 ) having a first end wall ( 98 A,  248 A), the piston ( 95 ,  245 ,  395 ) disposed in the cylinder ( 98 ,  248 ,  348 ) for sealed sliding movement therein, and the piston ( 95 ,  245 ,  395 ) may comprise a first actuator rod ( 96 ,  246 ,  396 ) having a portion sealingly penetrating the first end wall ( 98 A,  248 A). The cylinder ( 98 ) may have a second end wall ( 98 B) and the piston ( 95 ) may comprise a second actuator rod ( 97 ) having a portion sealingly penetrating the second end wall ( 98 B). The electro-hydraulic pump system may comprise a position sensor configured to sense the position of the piston ( 95 ,  245 ,  395 ). The electro-hydraulic pump system may comprise a pressure sensor configured to sense pressure in the first and second chambers ( 91 ,  92 ,  141 ,  142 ,  391 ,  392 ). 
     The electro-hydraulic pump system may comprise a third hydraulic piston pump ( 130 ) comprising a third fluid control journal ( 131 ), a plurality of pistons ( 132 ) in a third cylinder block ( 133 ) adapted to rotate relative to the third fluid control journal ( 131 ) about a third block axis ( 134 ) with rotation of the drive shaft ( 18 ), and a third displacement drive ( 135 ) having a third displacement axis ( 138 ); the third displacement drive ( 135 ) adapted to move in a third positive displacement range ( 140 ) between a third neutral position between the third displacement axis ( 138 ) and the third block axis ( 134 ) and a third maximum positive displacement position between the third displacement axis ( 138 ) and the third block axis ( 134 ); the third displacement drive ( 135 ) adapted to move in a third negative displacement range ( 144 ) between the third neutral position between the third displacement axis ( 138 ) and the third block axis ( 134 ) and a third maximum negative displacement position between the third displacement axis ( 138 ) and the third block axis ( 134 ); the third fluid control journal ( 131 ) comprising a fifth pump port ( 148 ) and a sixth pump port ( 149 ), wherein rotation of the drive shaft ( 18 ) when the third displacement drive ( 135 ) is in the third positive displacement range ( 140 ) provides higher pressure to the fifth pump port ( 148 ) relative to the sixth pump port ( 149 ), and wherein rotation of the drive shaft ( 18 ) when the third displacement drive ( 135 ) is in the third negative displacement range ( 144 ) provides higher pressure to the sixth pump port ( 149 ) relative to the fifth pump port ( 148 ); a third hydraulic actuator ( 190 ) having a fifth working port ( 193 ) hydraulically connected ( 152 ) to the fifth pump port ( 148 ) of the third piston pump ( 130 ); the third hydraulic actuator ( 190 ) having a sixth working port ( 194 ) hydraulically connected ( 153 ) to the sixth pump port ( 149 ) of the third piston pump ( 130 ); wherein an external force applied to the third hydraulic actuator ( 190 ) that provides higher pressure to the sixth pump port ( 149 ) relative to the fifth pump port ( 148 ) when the third displacement drive ( 135 ) is in the third positive displacement range ( 140 ) applies an assistive torque to the drive shaft ( 18 ); and an external force applied to the third hydraulic actuator ( 190 ) that provides higher pressure to the fifth pump port ( 148 ) relative to the sixth pump port ( 149 ) when the third displacement drive ( 135 ) is in the third negative displacement range ( 144 ) applies an assistive torque to the drive shaft ( 18 ). The shaft may comprise a first portion ( 18 A) mechanically connected to the first cylinder block ( 33 ), a second portion ( 23 ,  18 B) mechanically connected to the second cylinder block ( 63 ), and a third portion ( 123 ) mechanically connected to the third cylinder block ( 133 ). 
     The electro-hydraulic pump system may comprise a first displacement drive actuator ( 54 ,  354 ) mechanically connected to the first displacement drive ( 35 ,  335 ) and configured to selectively move the first displacement drive ( 35 ,  335 ) in the first positive displacement range ( 40 ,  340 ) and to selectively move the first displacement drive ( 35 ,  335 ) in the first negative displacement range ( 44 ,  344 ). The electro-hydraulic pump system may comprise a second displacement drive actuator ( 84 ,  384 ) mechanically connected to the second displacement drive ( 65 ,  365 ) and configured to selectively move the second displacement drive ( 65 ,  365 ) in the second positive displacement range ( 70 ,  370 ) and to selectively move the second displacement drive ( 65 ,  365 ) in the second negative displacement range ( 74 ,  374 ). 
     The first fluid control journal may comprise a first central control journal ( 31 ); the first displacement drive may comprise a first stroke ring ( 35 ) orientated about the first displacement axis ( 38 ); the first neutral position between the first displacement axis ( 38 ) and the first block axis ( 34 ) may comprise a position in which the first displacement axis ( 38 ) and the first block axis ( 34 ) are coaxial; the first stroke ring ( 35 ) may be adapted to move radially relative to the first neutral position; the first maximum positive displacement position between the first displacement axis ( 38 ) and the first block axis ( 34 ) may comprise a first positive eccentric position wherein the first displacement axis ( 38 ) is radially offset from the first block axis ( 34 ) in a first positive direction ( 41 ) relative the first neutral position a first positive maximum eccentric distance ( 42 ); the first positive displacement range may comprise a first positive eccentric range ( 40 ) between the first neutral position and a first positive eccentric position; the first maximum negative displacement position between the first displacement axis ( 38 ) and the first block axis ( 34 ) may comprise a first negative eccentric position wherein the first displacement axis ( 38 ) is radially offset from the first block axis ( 34 ) in a first negative direction ( 45 ) relative the first neutral position a first negative maximum eccentric distance ( 46 ); the first negative displacement range may comprise a first negative eccentric range ( 44 ) between the first neutral position and a first negative eccentric position; rotation of the drive shaft ( 18 ) when the first stroke ring ( 35 ) is in the first positive eccentric range ( 40 ) may provide higher pressure ( 51 ) to the first pump port ( 48 ) relative to the second pump port ( 49 ), and rotation of the drive shaft ( 18 ) when the first stroke ring ( 35 ) is in the first negative eccentric range ( 44 ) may provide higher pressure ( 51 ) to the second pump port ( 49 ) relative to the first pump port ( 48 ); the second fluid control journal may comprise a second central control journal ( 61 ); the second displacement drive may comprise a second stroke ring ( 65 ) orientated about the second displacement axis ( 68 ); the second neutral position between the second displacement axis ( 68 ) and the second block axis ( 64 ) may comprise a position in which the second displacement axis ( 68 ) and the second block axis ( 64 ) are coaxial; the second stroke ring ( 65 ) may be adapted to move radially relative to the second neutral position; the second maximum positive displacement position between the second displacement axis ( 68 ) and the second block axis ( 64 ) may comprise a second positive eccentric position wherein the second displacement axis ( 68 ) is offset from the second block axis ( 64 ) in a second positive direction ( 71 ) relative the second neutral position a second positive maximum eccentric distance ( 72 ); the second positive displacement range may comprise a second positive eccentric range ( 70 ) between the second neutral position and a second positive eccentric position; the second maximum negative displacement position between the second displacement axis ( 68 ) and the second block axis ( 64 ) may comprise a second negative eccentric position wherein the second displacement axis ( 68 ) is radially offset from the second block axis ( 64 ) in a second negative direction ( 75 ) relative the second neutral position a second negative maximum eccentric distance ( 76 ); the second negative displacement range may comprise a second negative eccentric range ( 74 ) between the second neutral position and a second negative eccentric position; rotation of the drive shaft ( 18 ) when the second stroke ring ( 65 ) is in the second positive eccentric range ( 70 ) may provide higher pressure to the third pump port ( 78 ) relative to the fourth pump port ( 79 ), and rotation of the drive shaft ( 18 ) when the second stroke ring ( 65 ) is in the second negative eccentric range ( 74 ) may provide higher pressure to the fourth pump port ( 79 ) relative to the third pump port ( 78 ); an external force (F 1 ) applied to the first hydraulic actuator ( 90 ) that provides higher pressure ( 51 ) to the second pump port ( 49 ) relative to the first pump port ( 48 ) when the first stroke ring ( 35 ) is in the first positive eccentric range ( 40 ) may apply an assistive torque to the drive shaft ( 18 ); and an external force (F 2 ) applied to the first hydraulic actuator ( 90 ) that provides higher pressure ( 51 ) to the first pump port ( 48 ) relative to the second pump port ( 49 ) when the first stroke ring ( 35 ) is in the first negative eccentric range ( 44 ) may apply an assistive torque to the drive shaft ( 18 ). 
     The electro-hydraulic pump system may comprise a third hydraulic piston pump ( 130 ) comprising a third central control journal ( 131 ), a plurality of pistons ( 132 ) in a third cylinder block ( 133 ) adapted to rotate relative to the third central control journal ( 131 ) about a third block axis ( 134 ) with rotation of the drive shaft ( 18 ), and a third stroke ring ( 135 ) orientated about a third stroke axis ( 138 ) and adapted to move radially relative to a third center position in which the third stroke axis ( 138 ) and the third block axis ( 134 ) are coaxial; the third stroke ring ( 135 ) adapted to move linearly in a third positive eccentric range ( 140 ) between the third center position and a third positive eccentric position, wherein the third stroke axis ( 138 ) is offset from the third block axis ( 134 ) in a third positive direction relative the third center position a third positive maximum eccentric distance; the third stroke ring ( 135 ) adapted to move linearly in a third negative eccentric range ( 144 ) between the third center position and a third negative eccentric position, wherein the third stroke axis ( 138 ) is offset from the third block axis ( 134 ) in a third negative direction opposite to the third positive direction relative to the third center position a third negative maximum eccentric distance; the third control journal ( 131 ) comprising a fifth pump port ( 148 ) and a sixth pump port ( 149 ), wherein rotation of the drive shaft ( 18 ) when the third stroke ring ( 135 ) is in the third positive eccentric range ( 140 ) provides higher pressure to the fifth pump port ( 148 ) relative to the sixth pump port ( 149 ), and wherein rotation of the drive shaft ( 18 ) when the third stroke ring ( 135 ) is in the third negative eccentric range ( 144 ) provides higher pressure to the sixth pump port ( 149 ) relative to the fifth pump port ( 148 ); a third hydraulic actuator ( 190 ) having a fifth working port ( 193 ) hydraulically connected ( 152 ) directly to the fifth pump port ( 148 ) of the third piston pump ( 130 ); the third hydraulic actuator ( 190 ) having a sixth working port ( 194 ) hydraulically connected ( 153 ) directly to the sixth pump port ( 149 ) of the third piston pump ( 130 ); wherein an external force applied to the third hydraulic actuator ( 190 ) that provides higher pressure to the sixth pump port ( 149 ) relative to the fifth pump port ( 148 ) when the third stroke ring ( 135 ) is in the third positive eccentric range ( 140 ) applies an assistive torque to the drive shaft ( 18 ); and an external force applied to the third hydraulic actuator ( 190 ) that provides higher pressure to the fifth pump port ( 148 ) relative to the sixth pump port ( 149 ) when the third stroke ring ( 135 ) is in the third negative eccentric range ( 144 ) applies an assistive torque to the drive shaft ( 18 B). The shaft may comprise a first portion ( 18 A) mechanically connected to the first cylinder block ( 33 ), a second portion ( 23 ,  18 B) mechanically connected to the second cylinder block ( 63 ), and a third portion ( 123 ) mechanically connected to the third cylinder block ( 133 ). 
     The electro-hydraulic pump system may comprise a first hydraulic ring actuator ( 54 ) mechanically connected to the first stroke ring ( 35 ) and configured to selectively move the first stroke ring ( 35 ) linearly in the first positive eccentric range ( 40 ) between the first center position and the first positive eccentric position and to selectively move the first stroke ring ( 35 ) linearly in the first negative eccentric range ( 44 ) between the first center position and the first negative eccentric position. The electro-hydraulic pump system may comprise a second hydraulic ring actuator ( 84 ) mechanically connected to the second stroke ring ( 65 ) and configured to selectively move the second stroke ring ( 65 ) linearly in the second positive eccentric range ( 70 ) between the second center position and the second positive eccentric position and to selectively move the second stroke ring ( 65 ) linearly in the second negative eccentric range ( 74 ) between the second center position and the second negative eccentric position. 
     The first fluid control journal may comprise a first port plate ( 331 ); the first displacement drive may comprise a first swash plate ( 335 ) orientated about the first displacement axis ( 338 ); the first neutral position between the first displacement axis ( 338 ) and the first block axis ( 334 ) may comprise a position in which the first displacement axis ( 338 ) and the first block axis ( 334 ) are coaxial; the first swash plate ( 335 ) may be adapted to move angularly relative to the first neutral position; the first maximum positive displacement position between the first displacement axis ( 338 ) and the first block axis ( 334 ) may comprise a first positive angular position wherein the first displacement axis ( 338 ) is offset from the first block axis ( 334 ) in a first positive angular direction relative the first neutral position a first positive maximum cam angle ( 340 ); the first positive displacement range may comprise a first positive angular range ( 340 ) between the first neutral position and a first positive angular position; the first maximum negative displacement position between the first displacement axis ( 338 ) and the first block axis ( 334 ) may comprise a first negative angular position wherein the first displacement axis ( 338 ) is offset from the first block axis ( 334 ) in a first negative angular direction relative the first neutral position a first negative maximum cam angle ( 346 ); the first negative displacement range may comprise a first negative angular range ( 344 ) between the first neutral position and a first negative angular position; rotation of the drive shaft ( 318 ) when the first swash plate ( 335 ) is in the first positive angular range ( 340 ) may provide higher pressure to the first pump port ( 348 ) relative to the second pump port ( 349 ), and rotation of the drive shaft ( 318 ) when the first swash plate ( 335 ) is in the first negative angular range ( 344 ) may provide higher pressure to the second pump port ( 349 ) relative to the first pump port ( 348 ); the second fluid control journal may comprise a second port plate ( 361 ); the second displacement drive may comprise a second swash plate orientated about the second displacement axis ( 368 ); the second neutral position between the second displacement axis ( 368 ) and the second block axis ( 364 ) may comprise a position in which the second displacement axis ( 368 ) and the second block axis ( 364 ) are coaxial; the second swash plate ( 365 ) may be adapted to move angularly relative to the second neutral position; the second maximum positive displacement position between the second displacement axis ( 368 ) and the second block axis ( 364 ) may comprise a second positive angular position wherein the second displacement axis ( 368 ) is offset from the second block axis ( 364 ) in a second positive angular direction relative the second neutral position a second positive maximum cam angle ( 372 ); the second positive displacement range may comprise a second positive angular range ( 370 ) between the second neutral position and a second positive angular position; the second maximum negative displacement position between the second displacement axis ( 368 ) and the second block axis ( 364 ) comprises a second negative angular position wherein the second displacement axis ( 368 ) is offset from the second block axis ( 364 ) in a second negative angular direction relative the second neutral position a second negative maximum cam angle ( 376 ); the second negative displacement range may comprise a second negative angular range ( 374 ) between the second neutral position and a second negative angular position; rotation of the drive shaft ( 318 ) when the second swash plate ( 365 ) is in the second positive angular range ( 370 ) may provide higher pressure to the third pump port ( 378 ) relative to the fourth pump port ( 379 ), and rotation of the drive shaft ( 318 ) when the second swash plate ( 365 ) is in the second negative angular range ( 374 ) may provide higher pressure to the fourth pump port ( 379 ) relative to the third pump port ( 378 ); an external force applied to the first hydraulic actuator ( 390 ) that provides higher pressure to the second pump port ( 349 ) relative to the first pump port ( 348 ) when the first swash plate ( 335 ) is in the first positive angular range ( 340 ) may apply an assistive torque to the drive shaft ( 318 ); and an external force applied to the first hydraulic actuator ( 390 ) that provides higher pressure to the first pump port ( 348 ) relative to the second pump port ( 349 ) when the first swash plate ( 335 ) is in the first negative angular range ( 344 ) may apply an assistive torque to the drive shaft ( 318 ). 
     An external force (F 3 ) applied to the second hydraulic actuator ( 400 ) that provides higher pressure to the fourth pump port ( 379 ) relative to the third pump port ( 378 ) when the second swash plate ( 365 ) is in the second positive angular range ( 374 ) may apply an assistive torque to the drive shaft ( 318 ); and an external force (F 4 ) applied to the second hydraulic actuator ( 400 ) that provides higher pressure to the third pump port ( 378 ) relative to the fourth pump port ( 379 ) when the second swash plate ( 365 ) is in the second negative angular range ( 374 ) may apply an assistive torque to the drive shaft ( 318 ). 
     The electro-hydraulic pump system may comprise a battery ( 21 ) supplying the current to the electric motor ( 16 ) and the motor ( 16 ) may be configured to selectively supply a current to the battery ( 21 ) in a regeneration mode when: an external force (F 1 ) applied to the first hydraulic actuator ( 390 ) provides higher pressure to the second pump port ( 349 ) relative to the first pump port ( 348 ) when the first swash plate ( 335 ) is in the first positive angular range ( 340 ) or an external force (F 2 ) applied to the first hydraulic actuator ( 390 ) provides higher pressure to the first pump port ( 348 ) relative to the second pump port ( 349 ) when the first swash plate ( 335 ) is in the first negative angular range ( 344 ); and an external force (F 3 ) applied to the second hydraulic actuator ( 400 ) provides higher pressure to the fourth pump port ( 379 ) relative to the third pump port ( 378 ) when the second swash plate ( 365 ) is in the second positive angular range ( 370 ) or an external force (F 4 ) applied to the second hydraulic actuator ( 400 ) provides higher pressure to the third pump port ( 378 ) relative to the fourth pump port ( 379 ) when the second swash plate ( 365 ) is in the second negative angular range ( 374 ). 
     The electro-hydraulic pump system may comprise a third hydraulic piston pump comprising a third port plate, a plurality of pistons in a third cylinder block adapted to rotate relative to the third port plate about a third block axis with rotation of the drive shaft, and a third swash plate orientated about a third swash plate axis and adapted to move angularly relative to a third neutral position in which the third swash plate axis and the third block axis are coaxial; the third swash plate adapted to move angularly in a third positive angular range between the third neutral position and a third positive angular position, wherein the third swash plate axis is offset from the third block axis in a third positive angular direction relative the third neutral position a third positive maximum cam angle; the third swash plate adapted to move angularly in a third negative angular range between the third neutral position and a third negative angular position, wherein the third swash plate axis is offset from the third block axis in a third negative angular direction opposite to the third positive angular direction relative to the third neutral position a third negative maximum cam angle; the third port plate comprising a fifth pump port and a sixth pump port, wherein rotation of the drive shaft when the third swash plate is in the third positive angular range provides higher pressure to the fifth pump port relative to the sixth pump port, and wherein rotation of the drive shaft when the third swash plate is in the third negative angular range provides higher pressure to the sixth pump port relative to the fifth pump port; a third hydraulic actuator having a fifth working port hydraulically connected to the fifth pump port of the third piston pump; the third hydraulic actuator having a sixth working port hydraulically connected to the sixth pump port of the third piston pump; wherein an external force applied to the third hydraulic actuator that provides higher pressure to the sixth pump port relative to the fifth pump port when the third swash plate is in the third positive angular range applies an assistive torque to the drive shaft; and wherein an external force applied to the third hydraulic actuator that provides higher pressure to the fifth pump port relative to the sixth pump port when the third swash plate is in the third negative angular range applies an assistive torque to the drive shaft. The shaft may comprise a first portion connected to the first cylinder block, a second portion connected to the second cylinder block, and a third portion connected to the third cylinder block. 
     The electro-hydraulic pump system may comprise a first hydraulic swash plate actuator ( 354 ) connected to the first swash plate ( 335 ) and configured to selectively move the first swash plate ( 335 ) in the first positive angular range ( 340 ) between the first neutral position and the first positive angular position and to selectively move the first swash plate ( 335 ) in the first negative angular range ( 344 ) between the first neutral position and the first negative angular position. The electro-hydraulic pump system may comprise a second hydraulic swash plate actuator ( 384 ) connected to the second swash plate ( 365 ) and configured to selectively move the second swash plate ( 365 ) in the second positive angular range ( 370 ) between the second neutral position and the second positive angular position and to selectively move the second swash plate ( 365 ) in the second negative angular range ( 374 ) between the second neutral position and the second negative angular position. 
     The first fluid control journal may comprise a first central control journal ( 31 ); the first displacement drive may comprise a first stroke ring ( 35 ) orientated about the first displacement axis ( 38 ); the first neutral position between the first displacement axis ( 38 ) and the first block axis ( 34 ) may comprise a position in which the first displacement axis and the first block axis are coaxial; the first stroke ring ( 35 ) may be adapted to move radially relative to the first neutral position; the first maximum positive displacement position between the first displacement axis ( 38 ) and the first block axis ( 34 ) may comprise a first positive eccentric position wherein the first displacement axis ( 38 ) is offset from the first block axis ( 34 ) in a first positive direction ( 41 ) relative the first neutral position a first positive maximum eccentric distance ( 42 ); the first positive displacement range may comprise a first positive eccentric range ( 40 ) between the first neutral position and a first positive eccentric position; the first maximum negative displacement position between the first displacement axis ( 38 ) and the first block axis ( 34 ) may comprise a first negative eccentric position wherein the first displacement axis ( 38 ) is offset from the first block axis ( 34 ) in a first negative direction ( 45 ) relative the first neutral position a first negative maximum eccentric distance ( 46 ); the first negative displacement range may comprise a first negative eccentric range ( 44 ) between the first neutral position and a first negative eccentric position; rotation of the drive shaft when the first stroke ring ( 35 ) is in the first positive eccentric range ( 40 ) may provide higher pressure to the first pump port ( 48 ) relative to the second pump port ( 49 ), and rotation of the drive shaft when the first stroke ring is in the first negative eccentric range ( 44 ) may provide higher pressure to the second pump port ( 49 ) relative to the first pump port ( 48 ); the second fluid control journal may comprise a first port plate ( 361 ); the second displacement drive may comprise a first swash plate ( 365 ) orientated about the second displacement axis ( 368 ); the second neutral position between the second displacement axis ( 368 ) and the second block axis ( 364 ) may comprise a position in which the second displacement axis ( 368 ) and the second block axis ( 364 ) are coaxial; the first swash plate ( 365 ) may be adapted to move angularly relative to the second neutral position; the second maximum positive displacement position between the second displacement axis ( 368 ) and the second block axis ( 364 ) may comprise a first positive angular position wherein the second displacement axis ( 368 ) is offset from the second block axis ( 364 ) in a first positive angular direction relative the second neutral position a first positive maximum cam angle ( 372 ); the second positive displacement range may comprise a first positive angular range ( 370 ) between the second neutral position and a first positive angular position; the second maximum negative displacement position between the second displacement axis ( 368 ) and the second block axis ( 364 ) may comprise a first negative angular position wherein the second displacement axis ( 368 ) is offset from the second block axis ( 364 ) in a first negative angular direction relative the second neutral position a first negative maximum cam angle ( 376 ); the second negative displacement range may comprise a first negative angular range ( 374 ) between the second neutral position and a first negative angular position; rotation of the drive shaft when the first swash plate ( 365 ) is in the first positive angular range ( 370 ) may provide higher pressure to the third pump port ( 378 ) relative to the fourth pump port ( 379 ), and rotation of the drive shaft when the second swash plate ( 365 ) is in the first negative angular range ( 374 ) may provide higher pressure to the fourth pump port ( 379 ) relative to the third pump port ( 378 ); an external force applied to the first hydraulic actuator ( 90 ) that provides higher pressure to the second pump port ( 49 ) relative to the first pump port ( 48 ) when the first stroke ring ( 35 ) is in the first positive eccentric range ( 40 ) may apply an assistive torque to the drive shaft; and an external force applied to the first hydraulic actuator ( 90 ) that provides higher pressure to the first pump port ( 48 ) relative to the second pump port ( 49 ) when the first stroke ring is in the first negative eccentric range ( 44 ) may apply an assistive torque to the drive shaft. 
     An external force applied to the second hydraulic actuator ( 400 ) that provides higher pressure to the fourth pump port ( 379 ) relative to the third pump port ( 378 ) when the first swash plate ( 365 ) is in the first positive angular range ( 370 ) may apply an assistive torque to the drive shaft; and an external force applied to the second hydraulic actuator ( 400 ) that provides higher pressure to the third pump port ( 378 ) relative to the fourth pump port ( 379 ) when the first swash plate ( 365 ) is in the first negative angular range ( 374 ) may apply an assistive torque to the drive shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view of a first radial embodiment of an assistive torque electro-hydraulic piston pump system. 
         FIG.  2    is a transverse cross-sectional view of the radial piston pumps shown in  FIG.  1    and  FIG.  27   . 
         FIG.  3    is a partial longitudinal cross-sectional view and partial schematic view of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1    in a first drive-drive configuration. 
         FIG.  4 A  is a transverse cross-section view of the first radial piston pump shown in  FIG.  3   . 
         FIG.  4 B  is a transverse cross-section view of the second radial piston pump shown in  FIG.  3   . 
         FIG.  5 A  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  4 A . 
         FIG.  5 B  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  4 B . 
         FIG.  6    is a partial longitudinal cross-sectional view and partial schematic view of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1    in a second drive-drive configuration. 
         FIG.  7 A  is a transverse cross-section view of the first radial piston pump shown in  FIG.  6   . 
         FIG.  7 B  is a transverse cross-section view of the second radial piston pump shown in  FIG.  6   . 
         FIG.  8 A  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  7 A . 
         FIG.  8 B  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  7 B . 
         FIG.  9    is a partial longitudinal cross-sectional view and partial schematic view of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1    in a first regen-drive configuration. 
         FIG.  10 A  is a transverse cross-section view of the first radial piston pump shown in  FIG.  9   . 
         FIG.  10 B  is a transverse cross-section view of the second radial piston pump shown in  FIG.  9   . 
         FIG.  11 A  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  10 A . 
         FIG.  11 B  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  10 B . 
         FIG.  12    is a partial longitudinal cross-sectional view and partial schematic view of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1    in a second regen-drive configuration. 
         FIG.  13 A  is a transverse cross-section view of the first radial piston pump shown in  FIG.  12   . 
         FIG.  13 B  is a transverse cross-section view of the second radial piston pump shown in  FIG.  12   . 
         FIG.  14 A  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  13 A . 
         FIG.  14 B  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  13 B . 
         FIG.  15    is a partial longitudinal cross-sectional view and partial schematic view of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1    in a first drive-regen configuration. 
         FIG.  16 A  is a transverse cross-section view of the first radial piston pump shown in  FIG.  15   . 
         FIG.  16 B  is a transverse cross-section view of the second radial piston pump shown in  FIG.  15   . 
         FIG.  17 A  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  16 A . 
         FIG.  17 B  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  16 B . 
         FIG.  18    is a partial longitudinal cross-sectional view and partial schematic view of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1    in a second drive-regen configuration. 
         FIG.  19 A  is a transverse cross-section view of the first radial piston pump shown in  FIG.  18   . 
         FIG.  19 B  is a transverse cross-section view of the second radial piston pump shown in  FIG.  18   . 
         FIG.  20 A  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  19 A . 
         FIG.  20 B  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  19 B . 
         FIG.  21    is a partial longitudinal cross-sectional view and partial schematic view of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1    in a first regen-regen configuration. 
         FIG.  22 A  is a transverse cross-section view of the first radial piston pump shown in  FIG.  21   . 
         FIG.  22 B  is a transverse cross-section view of the second radial piston pump shown in  FIG.  21   . 
         FIG.  23 A  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  22 A . 
         FIG.  23 B  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  22 B . 
         FIG.  24    is a partial longitudinal cross-sectional view and partial schematic view of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1    in a second regen-regen configuration. 
         FIG.  25 A  is a transverse cross-section view of the first radial piston pump shown in  FIG.  24   . 
         FIG.  25 B  is a transverse cross-section view of the second radial piston pump shown in  FIG.  24   . 
         FIG.  26 A  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  25 A . 
         FIG.  26 B  is a schematic view of the eccentric and resulting port pressure profile of the radial piston pump shown in  FIG.  25 B . 
         FIG.  27    is a schematic view of a second embodiment of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1   , this view showing three radial piston pumps and hydraulic actuators in the system. 
         FIGS.  28  and  29    are schematic views of the assistive torque electro-hydraulic radial piston pump system shown in  FIG.  27    employed on an electric vehicle. 
         FIG.  30    is a schematic view of a third embodiment of an assistive torque electro-hydraulic radial piston pump system shown in  FIG.  1   , this view showing an unequal piston area and single actuating rod form. 
         FIG.  31    is a schematic view of a fourth axial embodiment of an assistive torque electro-hydraulic piston pump system. 
         FIG.  32    is a cross-section view of the first axial piston pump shown in  FIG.  31   . 
         FIG.  33    is a cross-section view of the second axial piston pump shown in  FIG.  31   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
     Referring now to the drawings, and more particularly to  FIG.  1    thereof, the present invention broadly provides an assistive torque electro-hydraulic piston pump system, of which a first embodiment is indicated at  15 . As shown in  FIG.  1   , system  15  is adapted to actuate at least two objects and generally includes electrical power source  21 , motor controller  22 , variable speed electric motor  16 , shaft  18  driven to rotate about axis  20  by motor  16 , first radial piston pump  30  mechanically connected to shaft  18 , first hydraulic actuator  90  hydraulically connected to first radial piston pump  30 , second radial piston pump  60  mechanically connected to shaft  18 , and second hydraulic actuator  100  hydraulically connected to second radial piston pump  60 . 
     In this embodiment, motor  16  is a brushless DC variable-speed servo-motor that is supplied with a current. Motor  16  has an inner rotor with permanent magnets and a fixed non-rotating stator with coil windings. When current is appropriately applied through the coils of the stator, a magnetic field is induced. The magnetic field interaction between the stator and the rotor generates torque which may rotate output shaft  18 . There are no mechanical brushes that commutate the stator fields in this embodiment of the motor. In this embodiment, motor  16  rotates shaft  18  in only one direction about axis  20 . Accordingly, motor  16  will selectively apply a torque on shaft  18  in one direction about axis  20  at varying speeds. Other motors may be used as alternatives. For example, a variable speed stepper motor, brush motor or induction motor may be used. 
     Motor controller  22  includes drive electronics that, based on a resolver angular position feedback, generate and commutate the stator fields to vary the speed of motor  16 . Controller  22  receives drive commands and feedback from sensors in system  15  and controls motor  16  accordingly. For example, pressure transducers and position transducers in system  15  may be fed back to motor controller  22 . 
     In this embodiment, power source  21  comprises a battery and includes a regenerative power circuit to take advantage of the regenerative mode described below in which motor  16  is controlled to operate as a generator in a power generation mode when external regenerative forces F 1 , F 2 , F 3  and/or F 4 , such as gravity loads, on hydraulic actuators  90  and  100  exceed a threshold drive pressure differential of pumps  30  and  60  and drive torque of motor  16 . 
     As shown in  FIGS.  1 - 8 B , radial piston pump  30  generally comprises central control journal  31 , a plurality of pistons  32  in cylinder block  33  adapted to rotate relative to control journal  31  about block axis  34  with rotation of drive shaft  18 , stroke ring  35  orientated about stroke axis  38  and adapted to move radially relative to the neutral or center position N 1  in which stroke axis  38  and block axis  34  are coaxial and stroke ring  35  and cylinder block  33  are concentric. Stroke ring  35  does not rotate with rotation of cylinder block  33 . As shown, hydraulic ring actuator  54  is controlled to move stroke ring  35  linearly, or radially from the center position N 1 , to positions in positive eccentric range  40  between the center position N 1  and the positive eccentric position shown in  FIG.  5 A  in which stroke axis  38  is offset from block axis  34  in positive direction  41  relative the center position N 1  a maximum positive eccentric distance  42 . Hydraulic ring actuator  54  is also controlled to move stroke ring  35  linearly, or radially from the center position N 1 , to positions in negative eccentric range  44  between the center position N 1  and the negative eccentric position shown in  FIG.  8 A  in which stroke axis  38  is offset from block axis  34  in negative direction  45  opposite to positive direction  41  relative to the center position N 1  a maximum negative eccentric distance  46 . 
     As shown, drive torque from motor  16  is transferred from shaft  18  to cylinder block  33  by cross-key coupling  18 A. Cylinder block  33  rotates on central journal  31  and central journal  31  is shrunk fit into housing  17 . Pistons  32  are arranged radially in cylinder block  33  and are held in contact with stroke ring  35  by slipper pads  36 , with each piston  32  and slipper pad  36  connected to each other by a ball-and-socket joint. Slipper pads  36  are held in stroke ring  35  by overlapping retainer rings and pressed against stroke ring  35  during operation by centrifugal force and oil pressure. With rotation of cylinder block  33  by shaft  18 , pistons  32  execute a radial stroking motion due to the eccentricity of stroke ring  35 . 
     The pressure flow from and suction flow into the cylinder chamber is controlled by control journal  31 . Control journal  31  includes pump port  48  and pump port  49 . Rotation  19  of drive shaft  18  when stroke ring  35  is in positive eccentric range  40  provides higher pressure  51  to pump port  48  relative to pump port  49 . Alternatively, rotation of drive shaft  18  when stroke ring  35  is in negative eccentric range  44  provides higher pressure  51  to pump port  49  relative to pump port  48 . Thus, for positive eccentric range  40 , the normal drive pressure differential is P 48 /P 49  and it is positive (P 48 /P 49 &gt;0) in normal drive, and for negative eccentric range  44 , the normal drive pressure differential is P 49 /P 48  and it is positive (P 49 /P 48 &gt;0) in normal drive. In this embodiment, piston stroke “h” equals double the eccentricity “e” of stroke ring  35 . 
     Hydraulic ring actuator  54  is connected to stroke ring  35  and selectively moves stroke ring  35  in both positive eccentric range  40 , between the center position N 1  and the positive eccentric position, shown in  FIG.  5 A , and negative eccentric range  44 , between the center position N 1  and the negative eccentric position, shown in  FIG.  8 A . Thus, hydraulic servo-valve  54  varies the radial eccentricity of stroke ring  35 . In this embodiment, the normal flow direction, whether from port  48  or from port  49 , is determined by the direction of the eccentricity from the neutral center position, with positive eccentricity  40  providing flow out of port  48  and negative eccentricity  44  providing flow out of port  49 . So in this embodiment, motor  16  rotates shaft  18  in only one direction about axis  20  and the direction of flow is not determined by the direction of rotation of shaft  18 . 
     As shown in  FIG.  2   , hydraulic ring control actuator  54  includes hydraulic control pistons  55  and  56  in opposed alignment on axis  54 A that vary the eccentricity of stroke ring  35 . The effective areas of pistons  55  and  56  differ, with the effective area of piston  56  being greater than the effective area of piston  55 . Hydraulic pressure is constantly applied to small area control piston  55  to press stroke ring  35  against large area control piston  56 . Large area control piston  56  is selectively pressurized to maintain stroke ring  35  in a neutral center position with equal pressure, to move stroke ring  35  into positive eccentric range  40  towards maximum positive eccentric distance  42  with greater pressure, or to move stroke ring  35  into negative eccentric range  44  towards maximum negative eccentric distance  46  with less pressure. Thus, hydraulic ring actuator  54  controls the position of stroke ring  35  and thereby the flow rate, flow direction and system pressure. 
     As shown in  FIGS.  1 ,  3  and  6   , hydraulic actuator assembly  90  includes piston  95  slidably disposed within cylindrical housing  98  orientated about axis  99 . In this embodiment, rod  96  is mounted to one side of piston  95  for movement with piston  95  and extends to the right and sealably penetrates right end wall  98 A of housing  98 . Rod  97  is mounted to the other side of piston  95  for movement with piston  95  and extends to the left and sealably penetrates left end wall  98 B of housing  98 . Piston  95  is slidably disposed within cylinder  98 , and sealingly separates left chamber  91  from right chamber  92 . In this embodiment, the leftwardly-facing annular vertical end surface of piston  95  faces into left chamber  91  and the rightwardly-facing annular vertical end surface of piston  95  faces into right chamber  92 , creating an equal piston area configuration. Left chamber  91  has fluid port  93  and right chamber  92  has fluid port  94 . Thus, hydraulic actuator  90  comprises chamber  91 , chamber  92  and piston  95  separating the first and second chambers  91 ,  92 . The hydraulic actuator may include a position sensor configured to sense the position of piston  95 . While in this embodiment actuator  90  is shown as a linear hydraulic actuator, a rotary hydraulic actuator that imparts a rotary output may be used as an alternative. 
     As shown in  FIG.  1   , port  48  of pump  30  is hydraulically connected directly with left chamber  93  via fluid line  52 , and the opposite side or port  49  of pump  30  is hydraulically connected directly with right chamber  93  via fluid line  53 . With such direct hydraulic connection  52 , no one way check valves or proportional valves are provided in line  52  between pump port  48  and actuator chamber port  93 . With such direct hydraulic connection  53 , no one way check valves or proportional valves are provided in line  53  between pump port  49  and actuator chamber port  94 . 
     Piston  95  will move to the right when motor  16  is rotated and pump  30  is in positive eccentric range  40 , thereby pressurizing port  48  relative to port  49  and driving fluid out port  48  through conduit  52  and into chamber  91  and drawing fluid from chamber  92  in through port  94 , conduit  53  and port  49 , and thereby creating a differential pressure on piston  55  and causing it to extend rod  96  to the right. Piston  95  will move to the left when motor  16  is rotated and pump  30  is in negative eccentric range  44 , thereby pressurizing port  49  relative to port  48  and driving fluid out port  49  through conduit  53  and into chamber  92  and drawing fluid from chamber  91  in through port  93 , conduit  52  and port  48 , and thereby creating a differential pressure on piston  55  and causing it to extend rod  97  to the left. Thus, in a normal drive mode rotation of drive shaft  18  when stroke ring  35  is in positive eccentric range  40  provides higher pressure  51  to pump port  48  relative to pump port  49 , and rotation of shaft  18  when stroke ring  35  is in negative eccentric range  44  provides higher pressure  51  to pump port  49  relative to pump port  48 . 
     As shown in  FIG.  3   , central control journal  31  includes a cylindrical center bore orientated on central axis  20  and configured to receive through-shaft  23  of drive shaft  18 . Through-shaft  23  of drive shaft  18  extends through and rotates in such center bore in central journal  31 . Through-shaft  23  therefore rotates with rotation of shaft  18 . 
     As shown in  FIGS.  1 - 8 B , radial piston pump  60  is configured and functions in substantially the same manner as radial piston pump  30 . Radial piston pump  60  generally comprises central control journal  61 , a plurality of pistons  62  in cylinder block  63  adapted to rotate relative to control journal  61  about block axis  64  with rotation of drive shaft  18 , stroke ring  65  orientated about stroke axis  68  and adapted to move radially relative to the neutral or center position N 2  in which stroke axis  68  and block axis  64  are coaxial and stroke ring  65  and cylinder block  63  are concentric. Stroke ring  65  does not rotate with rotation of cylinder block  63 . As shown, hydraulic ring actuator  84  is controlled to move stroke ring  65  linearly, or radially from the center position N 2 , to positions in positive eccentric range  70  between the center position N 2  and the positive eccentric position shown in  FIG.  5 B  in which stroke axis  68  is offset from block axis  64  in positive direction  71  relative the center position N 2  a maximum positive eccentric distance  72 . Hydraulic ring actuator  84  is also controlled to move stroke ring  65  linearly, or radially from the center position N 2 , to positions in negative eccentric range  74  between the center position N 2  and the negative eccentric position shown in  FIG.  8 B  in which stroke axis  68  is offset from block axis  64  in negative direction  75  opposite to positive direction  71  relative to the center position N 2  a maximum negative eccentric distance  76 . 
     As shown, drive torque from motor  16  is transferred via through-shaft  23  of drive shaft  18  to cylinder block  63  by cross-key coupling  18 B. Cylinder block  63  rotates on central journal  61  and central journal  61  is shrunk fit into housing  17 . Pistons  62  are arranged radially in cylinder block  63  and are held in contact with stroke ring  65  by slipper pads  66 , with each piston  62  and slipper pad  66  connected to each other by a ball-and-socket joint. Slipper pads  66  are held in stroke ring  65  by overlapping retainer rings and pressed against stroke ring  65  during operation by centrifugal force and oil pressure. With rotation of cylinder block  63  by shaft  23  of drive shaft  18 , pistons  62  execute a radial stroking motion due to the eccentricity of stroke ring  65 . 
     The pressure flow from and suction flow into the cylinder chamber is controlled by control journal  61 . Control journal  61  includes pump port  78  and pump port  79 . Rotation  19  of drive shaft  18  when stroke ring  75  is in positive eccentric range  70  provides higher pressure  71  to pump port  78  relative to pump port  79 . Alternatively, rotation of drive shaft  18  when stroke ring  65  is in negative eccentric range  74  provides higher pressure  71  to pump port  79  relative to pump port  78 . Thus, for positive eccentric range  70 , the normal drive pressure differential is P 78 /P 79  and it is positive (P 78 /P 79 &gt;0) in normal drive, and for negative eccentric range  74 , the normal drive pressure differential is P 79 /P 78  and it is also positive (P 79 /P 78 &gt;0) in normal drive. In this embodiment, piston stroke “h” equals double the eccentricity “e” of stroke ring  65 . 
     Hydraulic ring actuator  84  is connected to stroke ring  65  and selectively moves stroke ring  65  in both positive eccentric range  70 , between the center position N 2  and the positive eccentric position, shown in  FIG.  5 B , and negative eccentric range  74 , between the first center position N 2  and the first negative eccentric position, shown in  FIG.  8 B . Thus, hydraulic servo-valve  84  varies the radial eccentricity of stroke ring  65 . In this embodiment, the normal flow direction, whether from port  78  or from port  79 , is determined by the direction of the eccentricity from the neutral center position, with positive eccentricity  70  providing flow out of port  78  and negative eccentricity  74  providing flow out of port  79 . 
     As shown in  FIG.  2   , hydraulic ring control actuator  84  includes hydraulic control pistons  85  and  86  in opposed alignment on axis  84 A that vary the eccentricity of stroke ring  65 . The effective areas of pistons  85  and  86  differ, with the effective area of piston  86  being greater than the effective area of piston  85 . Hydraulic pressure is constantly applied to small area control piston  85  to press stroke ring  65  against large area control piston  86 . Large area control piston  86  is selectively pressurized to maintain stroke ring  65  in a neutral center position with equal pressure, to move stroke ring  65  into positive eccentric range  70  towards maximum positive eccentric distance  72  with greater pressure, or to move stroke ring  65  into negative eccentric range  74  towards maximum negative eccentric distance  76  with less pressure. Thus, hydraulic ring actuator  84  controls the position of stroke ring  75  and thereby the flow rate, flow direction and system pressure. 
     As shown in  FIGS.  1 ,  3  and  6   , hydraulic actuator assembly  100  includes piston  105  slidably disposed within cylindrical housing  108  orientated about axis  109 . In this embodiment, rod  106  is mounted to one side of piston  105  for movement with piston  105  and extends to the right and sealably penetrates right end wall  108 A of housing  108 . Rod  107  is mounted to the other side of piston  105  for movement with piston  105  and extends to the left and sealably penetrates left end wall  108 B of housing  108 . Piston  105  is slidably disposed within cylinder  108 , and sealingly separates left chamber  101  from right chamber  102 . In this embodiment, the leftwardly-facing annular vertical end surface of piston  105  faces into left chamber  101  and the rightwardly-facing annular vertical end surface of piston  105  faces into right chamber  102 , creating an equal piston area configuration. Left chamber  101  has fluid port  103  and right chamber  102  has fluid port  104 . Thus, hydraulic actuator  100  comprises chamber  101 , chamber  102  and piston  105  separating the first and second chambers  101 ,  102 . The hydraulic actuator may include a position sensor configured to sense the position of piston  105 . While in this embodiment actuator  100  is shown as a linear hydraulic actuator, a rotary hydraulic actuator that imparts a rotary output may be used as an alternative. 
     As shown in  FIG.  1   , port  78  of pump  60  is hydraulically connected directly with left chamber  101  via fluid line  82 , and the opposite side or port  79  of pump  60  is hydraulically connected directly with right chamber  102  via fluid line  83 . With such direct hydraulic connection  82 , no one way check valves or proportional valves are provided in line  82  between pump port  78  and actuator chamber port  103 . With such direct hydraulic connection  83 , no one way check valves or proportional valves are provided in line  83  between pump port  79  and actuator chamber port  104 . 
     Piston  105  will move to the right when motor  16  is rotated and pump  60  is in positive eccentric range  70 , thereby pressurizing port  78  relative to port  79  and driving fluid out port  78  through conduit  82  and into chamber  101  and drawing fluid from chamber  102  in through port  104 , conduit  83  and port  79 , and thereby creating a differential pressure on piston  85  and causing it to extend rod  106  to the right. Piston  105  will move to the left when motor  16  is rotated and pump  60  is in negative eccentric range  74 , thereby pressurizing port  79  relative to port  78  and driving fluid out port  79  through conduit  83  and into chamber  102  and drawing fluid from chamber  101  in through port  103 , conduit  82  and port  78 , and thereby creating a differential pressure on piston  85  and causing it to extend rod  107  to the left. Thus, in a normal drive mode rotation of drive shaft  18  when stroke ring  65  is in positive eccentric range  70  provides higher pressure  81  to pump port  78  relative to pump port  79 , and rotation of shaft  18  when stroke ring  65  is in negative eccentric range  74  provides higher pressure  81  to pump port  79  relative to pump port  78 . 
       FIGS.  3 - 8 B  show assistive torque electro-hydraulic rotary pump system  15  in different example normal drive modes.  FIGS.  3 - 5 B  show a normal drive mode in which the desired drive direction D 1  of actuator  90  is down and the desired drive direction D 3  of actuator  100  is down. In this configuration, ring actuator  54  is commanded so stroke ring  35  is in positive eccentric range  40 . As shown, rotation of shaft  18  provides greater pressure  51  to pump port  48  and therefore chamber  91  of actuator  90  relative to pump port  49  and chamber  92 , driving actuator rod  96  in direction D 1 . In this configuration, ring actuator  84  is commanded so stroke ring  65  is in positive eccentric range  70 . As shown, rotation of shaft  18  provides greater pressure  81  to pump port  78  and therefore chamber  101  of actuator  100  relative to pump port  79  and chamber  102 , driving actuator rod  106  in direction D 3 . 
       FIGS.  6 - 8 B  show a normal drive mode in which the desired drive direction D 2  of actuator  90  is up and the desired drive direction D 4  of actuator  100  is up. In this configuration, ring actuator  54  is commanded so stroke ring  35  is in negative eccentric range  44 . As shown, rotation of shaft  18  provides greater pressure  51  to pump port  49  and therefore chamber  92  of actuator  90  relative to pump port  49  and chamber  91 , driving actuator rod  97  in direction D 2 . In this configuration, ring actuator  84  is commanded so stroke ring  65  is in negative eccentric range  74 . As shown, rotation of shaft  18  provides greater pressure  81  to pump port  79  and therefore chamber  102  of actuator  100  relative to pump port  78  and chamber  101 , driving actuator rod  107  in direction D 4 . Other combinations of actuator directions, such as D 1 /D 4  or D 2 /D 3  with a  40 / 74  or  44 / 70  stroke ring eccentric range, respectively, may also be commanded. 
       FIGS.  9 - 26 B  show assistive torque electro-hydraulic rotary pump system  15  in different example regenerative modes.  FIGS.  9 - 20 B  showing mechanical torque assist regenerative modes in which one of either pump/actuator combinations  30 / 90  or  60 / 100  provides an assistive torque applied through shaft  18  to the other of either pump/actuator combination  30 / 90  or  60 / 100 .  FIGS.  21 - 26 B  show electrical generation regenerative modes in which the pump/actuator combinations  30 / 90  and  60 / 100  provide a net regenerative torque on shaft  18  that is used by motor  16  and drive electronics  22  to charge battery  21 . 
       FIGS.  9 - 11 B  show a first example mechanical regenerative mode. As show, the commanded drive direction of actuator  90  is D 1  with resulting commanded stroke ring eccentric range  40 , and the commanded drive direction of actuator  100  is D 3  with resulting commanded stroke ring eccentric range  70 . However, as shown, an external force having a force component F 1  in direction D 1  is applied to actuator  90 . This results in higher pressure in chamber  92  relative to chamber  91  and, because of direct hydraulic connection  53 , higher pressure at port  49  relative to port  48 . Such negative pressure differential P 48 /P 49 , given the commanded positive pressure differential, provides added torque on cylinder block  33  that is transferred forward, via shaft connection  18   a,  through-shaft  23  and shaft connection  18 B, to cylinder block  63  of pump  60  to assist in driving actuator  100 . Thus, when an external force F 1  is applied to hydraulic actuator  90  that provides higher pressure  51  to pump port  49  relative to pump port  48  (P 48 /P 49 &lt;0) when stroke ring  35  is in positive eccentric range  40 , then an assistive torque is applied to drive shaft  18 . As a result, less power is needed from motor  16 . 
       FIGS.  12 - 14 B  show a second example mechanical regenerative mode. As show, the commanded drive direction of actuator  90  is D 2  with resulting commanded stroke ring eccentric range  44 , and the commanded drive direction of actuator  100  is D 4  with resulting commanded stroke ring eccentric range  74 . However, as shown, an external force having a force component F 2  in direction D 2  is applied to actuator  90 . This results in higher pressure in chamber  91  relative to chamber  92  and, because of direct hydraulic connection  52 , higher pressure at port  48  relative to port  49 . Such negative pressure differential (P 49 /P 48 ), given the commanded positive pressure differential, again provides added torque on cylinder block  33  that is transferred, via shaft connection  18 A, through-shaft  23  and shaft connection  18 B, to cylinder block  63  of pump  60  to assist in driving actuator  100 . Thus, when an external force F 2  is applied to hydraulic actuator  90  that provides higher pressure  51  to pump port  48  relative to pump port  49  (P 49 /P 48 &lt;0) when stroke ring  35  is in negative eccentric range  44 , then an assistive torque is applied to drive shaft  18 . As a result, less power is needed from motor  16 . 
       FIGS.  15 - 17 B  show a third example mechanical regenerative mode. As show, the commanded drive direction of actuator  90  is D 1  with resulting commanded stroke ring eccentric range  40 , and the commanded drive direction of actuator  100  is D 3  with resulting commanded stroke ring eccentric range  70 . However, as shown, an external force having a force component F 3  in direction D 3  is applied to actuator  100 . This results in higher pressure in chamber  102  relative to chamber  101  and, because of direct hydraulic connection  83 , higher pressure at port  79  relative to port  78 . Such negative pressure differential, given the commanded positive pressure differential, provides added torque on cylinder block  63  that is transferred back, via shaft connection  18 B, through-shaft  23  and shaft connection  18 A, to cylinder block  33  of pump  30  to assist in driving actuator  90 . Thus, when an external force F 3  is applied to hydraulic actuator  100  that provides higher pressure  81  to pump port  79  relative to pump port  78  (P 78 /P 79 &lt;0) when stroke ring  65  is in positive eccentric range  70 , then an assistive torque is applied to drive shaft  18 . As a result, less power is needed from motor  16 . 
       FIGS.  18 - 20 B  show a fourth example mechanical regenerative mode. As show, the commanded drive direction of actuator  90  is D 2  with resulting commanded stroke ring eccentric range  44 , and the commanded drive direction of actuator  100  is D 4  with resulting commanded stroke ring eccentric range  74 . However, as shown, an external force having a force component F 4  in direction D 4  is applied to actuator  100 . This results in higher pressure in chamber  101  relative to chamber  102  and, because of direct hydraulic connection  82 , higher pressure at port  78  relative to port  79 . Such negative pressure differential, given the commanded positive pressure differential, again provides added torque on cylinder block  63  that is transferred, via shaft connection  18 B, through-shaft  23  and shaft connection  18 A, to cylinder block  33  of pump  30  to assist in driving actuator  90 . Thus, when an external force F 4  is applied to hydraulic actuator  100  that provides higher pressure  81  to pump port  78  relative to pump port  79  (P 79 /P 78 &lt;0) when stroke ring  65  is in negative eccentric range  74 , then an assistive torque is applied to drive shaft  18 . As a result, less power is needed from motor  16 . 
     This also applies with other combinations of actuator directions, such as when a D 1 /D 4  or D 2 /D 3  with a  40 / 74  or  44 / 70  stroke ring eccentric range, respectively, are commanded and the subject pressure differentials are negative. Thus, a regenerative mode is employed when the commanded pump port pressure differential is positive for the subject eccentricity and the resulting operational pump port pressure differential is negative. 
       FIGS.  21 - 23 B  show a first example electrical generator regenerative mode. As show, the commanded drive direction of actuator  90  is D 1  with resulting commanded stroke ring eccentric range  40 , and the commanded drive direction of actuator  100  is D 3  with resulting commanded stroke ring eccentric range  70 . However, as shown, an external force having a force component F 1  in direction D 1  is applied to actuator  90  and an external force having a force component F 3  in direction D 3  is applied to actuator  100 . This results in higher pressure in chamber  92  relative to chamber  91  and, because of direct hydraulic connection  53 , higher pressure at port  49  relative to port  48 . This also results in higher pressure in chamber  102  relative to chamber  101  and, because of direct hydraulic connection  83 , higher pressure at port  79  relative to port  78 . Such summed negative pressure differential, given the commanded positive pressure differentials, provides added torque on cylinder block  33  that is transferred, via shaft connection  18   a,  to shaft  18  and motor  16 , and provides added torque on cylinder block  63  that is transferred, via shaft connection  18 B and through-shaft  23 , to shaft  18  and motor  16 . Motor  16  functions as a generator and converts such regenerative torque into electrical current that is stored in battery  21 . Thus, when external forces F 1  and F 3  are applied to hydraulic actuators  90  and  100  that provide a combined higher pressure to pump ports  49  and  79  relative to pump ports  48  and  78  (Σ(P 48 /P 49 +P 78 /P 79 )&lt;0) when stroke rings  35  and  65  are in positive eccentric ranges  40  and  70 , respectively, then such torque is used to charge battery  21 . 
       FIGS.  24 - 26 B  show a second example electrical generator regenerative mode. As show, the commanded drive direction of actuator  90  is D 2  with resulting commanded stroke ring eccentric range  44 , and the commanded drive direction of actuator  100  is D 4  with resulting commanded stroke ring eccentric range  74 . However, as shown, an external force having a force component F 2  in direction D 2  is applied to actuator  90  and an external force having a force component F 4  in direction D 4  is applied to actuator  100 . This results in higher pressure in chamber  91  relative to chamber  92  and, because of direct hydraulic connection  52 , higher pressure at port  48  relative to port  49 . This also results in higher pressure in chamber  101  relative to chamber  102  and, because of direct hydraulic connection  82 , higher pressure at port  78  relative to port  79 . Such summed negative pressure differential, given the commanded positive pressure differentials, again provides added torque on cylinder block  33  that is transferred, via shaft connection  18 A, to shaft  18  and motor  16 , and provides added torque on cylinder block  63  that is transferred, via shaft connection  18 B and through-shaft  23 , to shaft  18  and motor  16 . Motor  16  functions as a generator and converts such regenerative torque into electrical current that is stored in battery  21 . Thus, when external forces F 2  and F 4  are applied to hydraulic actuators  90  and  100  that provide a combined higher pressure to pump ports  48  and  78  relative to pump ports  49  and  79  (Σ(P 49 /P 48 +P 79 /P 78 )&lt;0) when stroke rings  35  and  65  are in negative eccentric ranges  44  and  74 , respectively, then such torque is used to charge battery  21 . 
     This also applies with other combinations of actuator directions, such as when a D 1 /D 4  or D 2 /D 3  with a  40 / 74  or  44 / 70  stroke ring eccentric range, respectively, are commanded and the subject pressure differentials are negative. Thus, a regenerative mode is employed when the commanded pump port pressure differentials are positive for the subject eccentricities and the sum of the resulting operational pump port pressure differentials is negative. 
     Controller  22  controls the current to motor  16  at the appropriate magnitude. The position of pistons  95  and  105  are monitored via position transducers, and the position signals are then fed back to motor controller  22 . In addition, or alternatively, the pressure in lines  52 ,  53 ,  82  and  83  to and from chambers  91 ,  92 ,  101  and  102 , respectively, are monitored with pressure transducers and the pressure signals are fed back to controller  22 . Variable speed motor  16  and ring actuators  54  and  84  of pumps  30  and  60  control the direction, speed and force of pistons  95  and  105 , and in turn rods  96 ,  97 ,  106  and  107 , by changing the flow and pressure acting on pistons  95  and  105 , respectively. This is accomplished by looking at the feedback of the position transducer and/or the pressure transducers and then closing the control loop by adjusting the motor  16  speed and the eccentricity of stroke rings  35  and  65  accordingly. 
     Referring now to  FIG.  27   , a second embodiment  115  of an assistive torque electro-hydraulic pump system is shown. As shown, system  115  is adapted to actuate at least three objects and generally includes electrical power source  21 , motor controller  22 , variable speed electric motor  16 , shaft  18  driven to rotate about axis  20  by motor  16 , first radial piston pump  30  mechanically connected to shaft  18 , first hydraulic actuator  90  hydraulically connected to first radial piston pump  30 , second radial piston pump  60  mechanically connected to shaft  18 , second hydraulic actuator  100  hydraulically connected to second radial piston pump  60 , third radial piston pump  130  mechanically connected to shaft  18 , and third hydraulic actuator  190  hydraulically connected to third radial piston pump  130 . 
     Electrical power source  21 , motor controller  22 , variable speed electric motor  16 , first radial piston pump  30  mechanically connected to shaft  18 , first hydraulic actuator  90  hydraulically connected to first radial piston pump  30 , second radial piston pump  60  mechanically connected to shaft  18 , and second hydraulic actuator  100  hydraulically connected to second radial piston pump  60  are configured substantially the same as in embodiment  15 . However, in this embodiment a third pump and hydraulic actuator combination  130 / 190  has been added in series with pump and hydraulic actuator combinations  30 / 90  and  60 / 100 . 
     Radial piston pump  130  is substantially the same as radial piston pump  60 . Accordingly and with reference to  FIG.  2   , radial piston pump  130  generally comprises central control journal  131 , a plurality of pistons  132  in cylinder block  133  adapted to rotate relative to control journal  131  about block axis  134  with rotation of drive shaft  18 , stroke ring  135  orientated about stroke axis  138  and adapted to move radially relative to the neutral or center position in which stroke axis  138  and block axis  134  are coaxial and stroke ring  135  and cylinder block  133  are concentric. Stroke ring  135  does not rotate with rotation of cylinder block  133 . As shown, hydraulic ring actuator  154  is controlled to move stroke ring  135  linearly, or radially from the center position, to positions in positive eccentric range  140  between the center position and the positive eccentric position in which stroke axis  138  is offset from block axis  134  in a positive direction relative the center position a maximum positive eccentric distance. Hydraulic ring actuator  154  is also controlled to move stroke ring  135  linearly, or radially from the center position, to positions in negative eccentric range  144  between the center position and the negative eccentric position in which stroke axis  138  is offset from block axis  134  in a negative direction opposite to the positive direction relative to the center position a maximum negative eccentric distance. 
     In this embodiment, central control journal  61  of radial piston pump  60  includes a cylindrical center bore orientated on central axis  20  and configured to receive through-shaft  123  of drive shaft  18 . Through-shaft  123  of drive shaft  18  extends through and rotates in such center bore in central journal  61 . Through-shaft  123  therefore rotates with rotation of shaft  18 . 
     Drive torque from motor  16  is transferred from shaft  18  via through-shafts  23  and  123  of drive shaft  18  to cylinder block  133 . Cylinder block  133  rotates on central journal  131  and central journal  131  is shrunk fit into housing  117 . Pistons  132  are arranged radially in cylinder block  133  and are held in contact with stroke ring  135  by slipper pads  136 , with each piston  132  and slipper pad  136  connected to each other by ball-and-socket joints. Slipper pads  136  are held in stroke ring  135  by overlapping retainer rings and pressed against stroke ring  135  during operation by centrifugal force and oil pressure. With rotation of cylinder block  133  by shaft  18 , pistons  132  execute a radial stroking motion due to the eccentricity of stroke ring  135 . 
     The pressure flow from and suction flow into the cylinder chamber is controlled by control journal  131 . Control journal  131  includes pump port  148  and pump port  149 . Rotation  19  of drive shaft  18  when stroke ring  135  is in positive eccentric range  140  provides higher pressure to pump port  148  relative to pump port  149 . Alternatively, rotation of drive shaft  18  when stroke ring  135  is in negative eccentric range  144  provides higher pressure to pump port  149  relative to pump port  148 . Thus, for positive eccentric range  140 , the normal drive pressure differential is P 148 /P 149  and it is positive (P 148 /P 149 &gt;0) in normal drive, and for negative eccentric range  144 , the normal drive pressure differential is P 149 /P 148  and it is positive (P 149 /P 148 &gt;0) in normal drive. In this embodiment, the piston stroke equals double the eccentricity of stroke ring  135 . 
     Hydraulic ring actuator  154  is connected to stroke ring  135  and selectively moves stroke ring  135  in both positive eccentric range  140  and negative eccentric range  144 . Thus, hydraulic servo-valve  154  varies the radial eccentricity of stroke ring  135 . In this embodiment, the normal flow direction, whether from port  148  or from port  149 , is determined by the direction of the eccentricity from the neutral center position, with positive eccentricity  140  providing flow out of port  148  and negative eccentricity  144  providing flow out of port  149 . 
     As shown in  FIG.  2   , hydraulic ring control actuator  154  includes hydraulic control pistons  155  and  156  in opposed alignment on the same axis that vary the eccentricity of stroke ring  135 . The effective areas of pistons  155  and  156  differ, with the effective area of piston  156  being greater than the effective area of piston  155 . Hydraulic pressure is constantly applied to small area control piston  155  to press stroke ring  135  against large area control piston  156 . Large area control piston  156  is selectively pressurized to maintain stroke ring  135  in a neutral center position with equal pressure, to move stroke ring  135  into positive eccentric range  140  towards the maximum positive eccentric distance with greater pressure, or to move stroke ring  135  into negative eccentric range  144  towards the maximum negative eccentric distance with less pressure. Thus, hydraulic ring actuator  154  controls the position of stroke ring  135  and thereby the flow rate, flow direction and system pressure. 
     As shown in  FIG.  27   , hydraulic actuator assembly  190  includes piston  195  slidably disposed within cylindrical housing  198  orientated about axis  199 . In this embodiment, rod  196  is mounted to one side of piston  195  for movement with piston  195  and extends to the right and sealably penetrates the right end wall of housing  198 . Rod  197  is mounted to the other side of piston  195  for movement with piston  195  and extends to the left and sealably penetrates the left end wall of housing  198 . Piston  195  is slidably disposed within cylinder  198 , and sealingly separates left chamber  191  from right chamber  192 . In this embodiment, the leftwardly-facing annular vertical end surface of piston  195  faces into left chamber  191  and the rightwardly-facing annular vertical end surface of piston  195  faces into right chamber  192 , creating an equal piston area configuration. Left chamber  191  has fluid port  193  and right chamber  192  has fluid port  194 . Thus, hydraulic actuator  190  comprises chamber  191 , chamber  192  and piston  195  separating the first and second chambers  191 ,  192 . The hydraulic actuator may include a position sensor configured to sense the position of piston  195 . While in this embodiment actuator  190  is shown as a linear hydraulic actuator, a rotary hydraulic actuator that imparts a rotary output may be used as an alternative. 
     As shown in  FIG.  27   , port  148  of pump  130  is hydraulically connected directly with left chamber  191  via fluid line  152 , and the opposite side or port  149  of pump  130  is hydraulically connected directly with right chamber  192  via fluid line  153 . With such direct hydraulic connection  152 , no one way check valves or proportional valves are provided in line  152  between pump port  148  and actuator chamber port  193 . With such direct hydraulic connection  153 , no one way check valves or proportional valves are provided in line  153  between pump port  149  and actuator chamber port  194 . 
     Piston  195  will move to the right when motor  16  is rotated and pump  130  is in positive eccentric range  140 , thereby pressurizing port  148  relative to port  149  and driving fluid out port  148  through conduit  152  and into chamber  191  and drawing fluid from chamber  192  in through port  194 , conduit  153  and port  149 , and thereby creating a differential pressure on piston  155  and causing it to extend rod  196  to the right. Piston  195  will move to the left when motor  16  is rotated and pump  130  is in negative eccentric range  144 , thereby pressurizing port  149  relative to port  148  and driving fluid out port  149  through conduit  153  and into chamber  192  and drawing fluid from chamber  191  in through port  193 , conduit  152  and port  148 , and thereby creating a differential pressure on piston  155  and causing it to extend rod  197  to the left. Thus, in a normal drive mode rotation of drive shaft  18  when stroke ring  135  is in positive eccentric range  140  provides higher pressure to pump port  148  relative to pump port  149 , and rotation of shaft  18  when stroke ring  135  is in negative eccentric range  144  provides higher pressure to pump port  149  relative to pump port  148 . 
     As with embodiment  15 , all three actuators  90 ,  100  and  190  may be driven in either direction with rotation of shaft  18  as a function of the eccentricity of stroke ring centers  38 ,  68 , and  138  relative to block axes  34 ,  64 , and  134 , respectively. Thus, various combinations of actuator directions may be commanded, such as for example and without limitation: directions D 1 /D 3 /D 5  with stroke ring eccentric ranges  40 / 70 / 140 , respectively; directions D 2 /D 4 /D 6  with stroke ring eccentric ranges  44 / 74 / 144 , respectively; directions D 1 /D 4 /D 5  with stroke ring eccentric ranges  40 / 74 / 140 , respectively; directions D 2 /D 4 /D 5  with stroke ring eccentric ranges  44 / 74 / 140 , respectively; and directions D 2 /D 3 /D 5  with stroke ring eccentric ranges  44 / 70 / 140 , respectively. In normal drive, eccentric ranges  40 ,  70  and  140  generate pressure differentials P 48 /P 49 , P 78 /P 79  and P 148 /P 149  that are positive, and eccentric ranges  44 ,  74  and  144  generate pressure differentials P 49 /P 48 , P 79 /P 78  and P 149 /P 148  that are positive. 
     Similar to pump actuator combinations  30 / 60  and  60 / 100 , an external force having a force component in direction D 5  applied to actuator  190  may result in higher pressure in chamber  192  relative to chamber  191  and, because of direct hydraulic connection  153 , higher pressure at port  149  relative to port  148 . Such negative pressure differential P 148 /P 149 , given the commanded positive pressure differential, provides added torque on cylinder block  133  that is transferred, via through-shaft  123  and shaft connection  18 B, to cylinder block  63  of pump  60  to assist in driving actuator  100 . And an external force having a force component in direction D 6  applied to actuator  190  may result in higher pressure in chamber  191  relative to chamber  192  and, because of direct hydraulic connection  152 , higher pressure at port  148  relative to port  149 . Such negative pressure differential (P 149 /P 148 ), given the commanded positive pressure differential, again provides added torque on cylinder block  133  that is transferred, via though-shaft  123  and shaft connection  18 B, to cylinder block  63  of pump  60  to assist in driving actuator  100 . Thus, when an external force is applied to hydraulic actuator  190  that provides higher pressure to pump port  149  relative to pump port  148  (P 148 /P 149 &lt;0) when stroke ring  135  is in positive eccentric range  140 , then an assistive torque is applied to drive shaft  18 . And when an external force is applied to hydraulic actuator  190  that provides higher pressure to pump port  148  relative to pump port  149  (P 149 /P 148 &lt;0) when stroke ring  135  is in negative eccentric range  144 , then an assistive torque is applied to drive shaft  18 . 
     Similar to embodiment  15 , one or more of pump/actuator combinations  30 / 90 ,  60 / 100  and  130 / 190  may provide an assistive torque applied through shaft  18  to the other of pump/actuator combination  30 / 90 ,  60 / 100 ,  130 / 190  when any of pressure differentials P 48 /P 49 , P 78 /P 79  and P 148 /P 149  for eccentric ranges  40 ,  70  and  140  or P 49 /P 48 , P 79 /P 78  and P 149 /P 148  for eccentric ranges  44 ,  74  and  144  are negative. Thus, a regenerative mode is employed when the commanded pump port pressure differential is positive for the subject eccentricity and the resulting operational pump port pressure differential is negative. 
     Pump/actuator combinations  30 / 90 ,  60 / 100  and  130 / 160  may also provide a net regenerative torque on shaft  18  that is used by motor  16  and drive electronics  22  to charge battery  21 . For example, and without limitation, when external forces are applied to hydraulic actuators  90 ,  100  and/or  190  that provide a combined higher pressure to pump ports  49 ,  79  and  149  relative to pump ports  48 ,  78  and  148  (Σ(P 48 /P 49 +P 78 /P 79 +P 148 /P 149 )&lt;0) when stroke rings  35 ,  75  and  135  are in positive eccentric ranges  40 ,  70  and  140 , respectively, then such torque is used to charge battery  21 . Motor  16  functions as a generator and converts such regenerative torque into electrical current that is stored in battery  21 . Also, for example, and without limitation, when external forces are applied to hydraulic actuators  90 ,  100  and/or  190  that provide a combined higher pressure to pump ports  48 ,  78  and  148  relative to pump ports  49 ,  79  and  149  (Σ(P 49 /P 48 +P 79 /P 78 +P 149 /P 148 )&lt;0) when stroke rings  35 ,  75  and  135  are in negative eccentric ranges  44 ,  74  and  144 , respectively, then such torque is used to charge battery  21 . Thus, a regenerative mode is employed when the commanded pump port pressure differentials are positive for the subject eccentricities and the sum of the resulting operational pump port pressure differentials is negative. 
     Again, controller  22  controls the current to motor  16  and ring actuators  54 ,  84  and  154  of pumps  30 ,  60  and  130  to control the direction, speed and force of pistons  95 ,  105  and  195 , and in turn rods  96 ,  97 ,  106 ,  107 ,  196  and  197 , by changing the flow and pressure acting on pistons  95 ,  105  and  195 , respectively, and closing the control loop by adjusting the motor  16  speed and the eccentricity of stroke rings  35 ,  65  and  135  accordingly. 
       FIGS.  28  and  29    show system  115  actuating the tilt cylinder, lift cylinder and accessory implements cylinder of skid steer  116 . Direct hydraulic lines run from housing  117  of the motor and pumps assembly to the respective hydraulic cylinders, with lines  52  and  53  feeding accessory implements cylinder  98  from pump  30 , lines  82  and  83  feeding bucket  119  tilt cylinder  108  from pump  130 , and lines  152  and  153  feeding bucket  119  lift cylinder  198  from pump  60 . System  15  may be employed in a variety of other applications, including without limitation in applications in which diesel engines are replaced with electrical systems. For example, and without limitation, the system may be employed in excavators, wheel loaders and in other mobile equipment that requires multiple actuation. 
     Referring now to  FIG.  30   , a third embodiment  215  of an assistive torque electro-hydraulic pump system is shown. Electrical power source  21 , motor controller  22 , variable speed electric motor  16 , first radial piston pump  30  mechanically connected to shaft  18 , second radial piston pump  60  mechanically connected to shaft  18 , and third radial piston pump  130  mechanically connected to shaft  18  are configured substantially the same as in embodiment  115 . However, in this embodiment dual piston rod and equal piston area actuators  90 ,  100 , and  190  have been replaced with single rod and unequal piston area actuators  220 ,  230  and  240 . With reference to actuator  240 , each of actuators  220 ,  230  and  240  include piston  245  slidably disposed within cylindrical housing  248  orientated about an axis  249 . In this embodiment, a single rod  246  is mounted to one side of piston  245  for movement with piston  245  and extends to the right and sealably penetrates the right end wall  248 A of housing  248 . Piston  245  is slidably disposed within cylinder  248 , and sealingly separates left chamber  241  from right chamber  242 . In this embodiment, the leftwardly-facing circular vertical end surface  245 B of piston  245  faces into left chamber  241  and the rightwardly-facing annular vertical end surface  245 A of piston  245  faces into right chamber  242 , creating an unequal piston area configuration. Thus, almost all of leftwardly-facing circular vertical end surface  245 B of piston  245  faces into left chamber  241 . However, only annular rightwardly-facing vertical end surface  245 A of piston  245  faces rightwardly into right chamber  242  due to the addition of rod  246  through chamber  242  and outside housing  248 . This creates an unequal piston area configuration, with the surface area of face  245 B being greater than the surface area of face  245 A. 
     Referring now to  FIG.  31   , a fourth embodiment  315  of an assistive torque electro-hydraulic pump system is shown. Electrical power source  21 , motor controller  22 , and variable speed electric motor  16  are configured substantially the same as in embodiment  15  In addition, hydraulic actuator  390  in system  315  is configured substantially the same as actuator  90  in embodiment  15  and hydraulic actuator  400  in system  315  is configured substantially the same as actuator  100  in embodiment  15 . However, in this embodiment radial piston pumps  30  and  60  have been replaced with axial piston pumps  330  and  360 . 
     As shown in  FIG.  32   , axial piston pump  330  generally comprises fluid control journal plate  331 , a plurality of pistons  332  in cylinder block  333  adapted to rotate relative to plate  331  about block axis  334  with rotation of drive shaft  318 , swash plate  335  positioned axially adjacent one end face of cylinder block  333  and orientated about swash plate axis  338  and adapted to move angularly relative to a neutral or center position in which swash plate axis  338  and block axis  334  are coaxial and the cam surface of swash plate  335  is perpendicular to cylinder block axis  334 . Swash plate  335  does not rotate with rotation of cylinder block  333 . Hydraulic plate actuator  354  is controlled to adjust the tilt or cam angle of swash plate  335  relative to cylinder block  333  from the center position, to positions in positive angular range  340  between the center position and a positive angular position in which swash plate axis  338  is angularly offset from block axis  334  in a positive angular direction relative to the center position a maximum positive angle  342 . Hydraulic plate actuator  354  is also controlled to adjust the tilt or cam angle of swash plate  335  relative to cylinder block  333  from the center position to positions in negative angular range  344  between the center position and a negative angular position in which swash plate axis  338  is angularly offset from block axis  334  in a negative angular direction, opposite to the positive angular direction, relative to the center position a maximum negative angle  346 . 
     Drive torque from motor  16  is transferred from shaft  318  to cylinder block  333  and cylinder block  333  rotates with shaft  318 . Pistons  332  are arranged axially in cylinder block  333  and are held in contact with swash plate  335  by slipper pads  336 , with each piston  332  and slipper pad  336  connected to each other by ball-and-socket joints. With rotation of cylinder block  333  by shaft  318 , pistons  332  execute an axial stroking motion due to the tilt angle of swash plate  335 . 
     Port plate  331 , on the opposite side of cylinder block  333  to swash plate  335 , includes pump port  348  and pump port  349 . Rotation  19  of drive shaft  318  when swash plate  335  is in positive angular range  340  provides higher pressure to pump port  348  relative to pump port  349 . Alternatively, rotation of drive shaft  318  when swash plate  335  is in negative angular range  344  provides higher pressure to pump port  349  relative to pump port  348 . Thus, for positive angular range  340 , the normal drive pressure differential is P 348 /P 349  and it is positive (P 348 /P 349 &gt;0) in normal drive, and for negative angular range  344 , the normal drive pressure differential is P 349 /P 348  and it is positive (P 349 /P 348 &gt;0) in normal drive. 
     Hydraulic swash plate actuator  354  is connected to swash plate  335  and selectively moves swash plate  335  in both positive angular range  340  and negative angular range  344 . Thus, hydraulic servo-valve  354  varies the angularity or cam angle of swash plate  335 . In this embodiment, the normal flow direction, whether from port  448  or from port  449 , is determined by the direction of the angularity from the neutral center position, with positive angularity  440  providing flow out of port  448  and negative angularity  444  providing flow out of port  449 . 
     As shown in  FIG.  31   , hydraulic actuator assembly  390  includes piston  395  slidably disposed within cylindrical housing  398  orientated about axis  399 . In this embodiment, rod  396  is mounted to one side of piston  395  for movement with piston  395  and extends to the right and sealably penetrates the right end wall of housing  398 . Rod  397  is mounted to the other side of piston  395  for movement with piston  395  and extends to the left and sealably penetrates the left end wall of housing  398 . Piston  395  is slidably disposed within cylinder  398 , and sealingly separates left chamber  391  from right chamber  392 . Left chamber  391  has fluid port  393  and right chamber  392  has fluid port  394 . Thus, hydraulic actuator  390  comprises chamber  391 , chamber  392  and piston  395  separating the first and second chambers  391 ,  392 . The hydraulic actuator may include a position sensor configured to sense the position of piston  395 . 
     As shown in  FIG.  31   , port  348  of pump  330  is hydraulically connected directly with left chamber  391  via fluid line  352 , and the opposite side or port  349  of pump  330  is hydraulically connected directly with right chamber  392  via fluid line  353 . With such direct hydraulic connection  352 , no one way check valves or proportional valves are provided in line  352  between pump port  348  and actuator chamber port  393 . With such direct hydraulic connection  353 , no one way check valves or proportional valves are provided in line  353  between pump port  349  and actuator chamber port  394 . 
     Piston  395  will move to the right when motor  16  is rotated and pump  330  is in positive angular range  340 , thereby pressurizing port  348  relative to port  349  and driving fluid out port  348  through conduit  352  and into chamber  391  and drawing fluid from chamber  392  in through port  394 , conduit  353  and port  349 , and thereby creating a differential pressure on piston  355  and causing it to extend rod  396  to the right. Piston  395  will move to the left when motor  16  is rotated and pump  330  is in negative angular range  344 , thereby pressurizing port  349  relative to port  348  and driving fluid out port  349  through conduit  353  and into chamber  392  and drawing fluid from chamber  391  in through port  393 , conduit  352  and port  348 , and thereby creating a differential pressure on piston  355  and causing it to extend rod  397  to the left. Thus, in a normal drive mode rotation of drive shaft  318  when swash plate  335  is in positive angular range  340  provides higher pressure to pump port  348  relative to pump port  349 , and rotation of shaft  318  when swash plate  335  is in negative angular range  344  provides higher pressure to pump port  349  relative to pump port  348 . 
     In this embodiment, through-shaft  323  of drive shaft  318  extends through swash plate  335  and rotates with rotation of shaft  318 . Through shaft  323  is connected to swash plate  365  of axial piston pump  360 . 
     As shown in  FIG.  33   , axial piston pump  360  generally comprises fluid control journal plate  361 , a plurality of pistons  362  in cylinder block  363  adapted to rotate relative to plate  361  about block axis  364  with rotation of drive shaft  318 , swash plate  365  positioned axially adjacent one end face of cylinder block  363  and orientated about swash plate axis  368  and adapted to move angularly relative to a neutral or center position in which swash plate axis  368  and block axis  364  are coaxial and the cam surface of swash plate  365  is perpendicular to cylinder block axis  364 . Swash plate  365  does not rotate with rotation of cylinder block  363 . Hydraulic plate actuator  384  is controlled to adjust the tilt or cam angle of swash plate  365  relative to cylinder block  363  from the center position, to positions in positive angular range  370  between the center position and a positive angular position in which swash plate axis  368  is angularly offset from block axis  364  in a positive angular direction relative to the center position a maximum positive angle  372 . Hydraulic plate actuator  384  is also controlled to adjust the tilt or cam angle of swash plate  365  relative to cylinder block  363  from the center position to positions in negative angular range  374  between the center position and a negative angular position in which swash plate axis  368  is angularly offset from block axis  364  in a negative angular direction, opposite to the positive angular direction, relative to the center position a maximum negative angle  376 . 
     Drive torque from motor  16  is transferred from shaft  318  via through-shaft  323  to cylinder block  363  and cylinder block  363  rotates with shaft  318 . Pistons  362  are arranged axially in cylinder block  363  and are held in contact with swash plate  365  by slipper pads  366 , with each piston  362  and slipper pad  366  connected to each other by ball-and-socket joints. With rotation of cylinder block  363  by shaft  318 , pistons  362  execute an axial stroking motion due to the tilt angle of swash plate  365 . 
     Port plate  361 , on the opposite side of cylinder block  363  to swash plate  365 , includes pump port  378  and pump port  379 . Rotation  19  of drive shaft  318  when swash plate  365  is in positive angular range  370  provides higher pressure to pump port  378  relative to pump port  379 . Alternatively, rotation of drive shaft  318  when swash plate  365  is in negative angular range  374  provides higher pressure to pump port  379  relative to pump port  378 . Thus, for positive angular range  370 , the normal drive pressure differential is P 378 /P 379  and it is positive (P 378 /P 379 &gt;0) in normal drive, and for negative angular range  374 , the normal drive pressure differential is P 379 /P 378  and it is positive (P 379 /P 378 &gt;0) in normal drive. 
     Hydraulic swash plate actuator  384  is connected to swash plate  365  and selectively moves swash plate  365  in both positive angular range  370  and negative angular range  374 . Thus, hydraulic servo-valve  384  varies the angularity or cam angle of swash plate  365 . In this embodiment, the normal flow direction, whether from port  448  or from port  449 , is determined by the direction of the angularity from the neutral center position, with positive angularity  440  providing flow out of port  448  and negative angularity  444  providing flow out of port  449 . 
     As shown in  FIG.  31   , hydraulic actuator assembly  400  includes piston  405  slidably disposed within cylindrical housing  408  orientated about axis  409 . In this embodiment, rod  406  is mounted to one side of piston  405  for movement with piston  405  and extends to the right and sealably penetrates the right end wall of housing  408 . Rod  407  is mounted to the other side of piston  405  for movement with piston  405  and extends to the left and sealably penetrates the left end wall of housing  408 . Piston  405  is slidably disposed within cylinder  408 , and sealingly separates left chamber  401  from right chamber  402 . Left chamber  401  has fluid port  403  and right chamber  402  has fluid port  404 . Thus, hydraulic actuator  400  comprises chamber  401 , chamber  402  and piston  405  separating the first and second chambers  401 ,  402 . The hydraulic actuator may include a position sensor configured to sense the position of piston  405 . 
     As shown in  FIG.  31   , port  378  of pump  360  is hydraulically connected directly with left chamber  401  via fluid line  382 , and the opposite side or port  379  of pump  360  is hydraulically connected directly with right chamber  402  via fluid line  383 . With such direct hydraulic connection  382 , no one way check valves or proportional valves are provided in line  382  between pump port  378  and actuator chamber port  403 . With such direct hydraulic connection  383 , no one way check valves or proportional valves are provided in line  383  between pump port  379  and actuator chamber port  404 . 
     Piston  405  will move to the right when motor  16  is rotated and pump  360  is in positive angular range  370 , thereby pressurizing port  378  relative to port  379  and driving fluid out port  378  through conduit  382  and into chamber  401  and drawing fluid from chamber  402  in through port  404 , conduit  383  and port  379 , and thereby creating a differential pressure on piston  385  and causing it to extend rod  406  to the right. Piston  405  will move to the left when motor  16  is rotated and pump  360  is in negative angular range  374 , thereby pressurizing port  379  relative to port  378  and driving fluid out port  379  through conduit  383  and into chamber  402  and drawing fluid from chamber  401  in through port  403 , conduit  382  and port  378 , and thereby creating a differential pressure on piston  385  and causing it to extend rod  407  to the left. Thus, in a normal drive mode rotation of drive shaft  318  when swash plate  365  is in positive angular range  370  provides higher pressure to pump port  378  relative to pump port  379 , and rotation of shaft  318  when swash plate  365  is in negative angular range  374  provides higher pressure to pump port  379  relative to pump port  378 . 
     As with embodiment  15 , both actuators  390  and  400  may be driven in either direction with rotation of shaft  318  as a function of the angularity of swash plates axes  338  and  378  relative to block axes  334  and  364 , respectively. Thus, various combinations of actuator directions may be commanded, such as for example and without limitation: directions D 1 /D 3  with swash plate angular ranges  340 / 370 , respectively; directions D 2 /D 4  with swash plate angular ranges  344 / 374 , respectively; directions D 1 /D 4  with swash plate angular ranges  340 / 374 , respectively; and directions D 2 /D 3  with swash plate angular ranges  344 / 370 , respectively. In normal drive, angular ranges  340  and  370  generate pressure differentials P 348 /P 349 , and P 378 /P 379  that are positive, and angular ranges  344  and  374  generate pressure differentials P 349 /P 348  and P 379 /P 378  that are positive. 
     Similar to pump actuator combinations  30 / 60  and  60 / 100 , an external force having a force component in direction D 1  applied to actuator  390  may result in higher pressure in chamber  392  relative to chamber  391  and, because of direct hydraulic connection  353 , higher pressure at port  349  relative to port  348 . Such negative pressure differential P 348 /P 349 , given a commanded positive pressure differential, provides added torque on cylinder block  333  that is transferred, via through-shaft  323  to cylinder block  363  of pump  360  to assist in driving actuator  400 . And an external force having a force component in direction D 2  applied to actuator  390  may result in higher pressure in chamber  391  relative to chamber  392  and, because of direct hydraulic connection  352 , higher pressure at port  348  relative to port  349 . Such negative pressure differential (P 349 /P 348 ), given a commanded positive pressure differential, again provides added torque on cylinder block  333  that is transferred, via though-shaft  323 , to cylinder block  363  of pump  360  to assist in driving actuator  400 . Thus, when an external force is applied to hydraulic actuator  390  that provides higher pressure to pump port  349  relative to pump port  348  (P 348 /P 349 &lt;0) when swash plate  335  is in positive angular range  340 , then an assistive torque is applied to drive shaft  318 . And when an external force is applied to hydraulic actuator  390  that provides higher pressure to pump port  348  relative to pump port  349  (P 349 /P 348 &lt;0) when swash plate  335  is in negative angular range  344 , then an assistive torque is applied to drive shaft  318 . 
     Similar to embodiment  15 , one or more of pump/actuator combinations  330 / 390  and  360 / 400  may provide an assistive torque applied through shaft  318  to the other of pump/actuator combinations  330 / 390  and  360 / 400  when any of pressure differentials P 348 /P 349  and P 378 /P 379  for angular ranges  340  and  370  or P 349 /P 348  and P 379 /P 378  for angular ranges  344  and  374  are negative. Thus, a regenerative mode is employed when the commanded pump port pressure differential is positive for the subject angularity and the resulting operational pump port pressure differential is negative. 
     Pump/actuator combinations  330 / 390  and  360 / 400  may also provide a net regenerative torque on shaft  318  that is used by motor  16  and drive electronics  22  to charge battery  21 . For example, and without limitation, when external forces are applied to hydraulic actuators  390  and/or  400  that provide a combined higher pressure to pump ports  349  and  379  relative to pump ports  348  and  378  (Σ(P 348 /P 349 +P 378 /P 379 )&lt;0) when swash plates  335  and  375  are in positive angular ranges  340  and  370 , respectively, then such torque is used to charge battery  21 . Motor  16  functions as a generator and converts such regenerative torque into electrical current that is stored in battery  21 . Also, for example, and without limitation, when external forces are applied to hydraulic actuators  390  and/or  400  that provide a combined higher pressure to pump ports  348  and  378  relative to pump ports  349  and  379  (Σ(P 349 /P 348 +P 379 /P 378 )&lt;0) when swash plates  335  and  375  are in negative angular ranges  344  and  374 , respectively, then such torque is used to charge battery  21 . Thus, a regenerative mode is employed when the commanded pump port pressure differentials are positive for the subject angularities and the sum of the resulting operational pump port pressure differentials is negative. 
     Again, controller  22  controls the current to motor  16  and swash plate actuators  354  and  384  of pumps  330  and  360  to control the direction, speed and force of pistons  395  and  405 , and in turn rods  396 ,  397 ,  406  and  407 , by changing the flow and pressure acting on pistons  395  and  405 , respectively, and closing the control loop by adjusting the motor  16  speed and the angularity of swash plates  335  and  365  accordingly. 
     Assistive torque electro-hydraulic piston pump systems  15 ,  115 ,  215  and  315  provide a number of benefits. Unexpectedly, the systems provide actuating forces that are high enough to meet the rigorous demands of mobile equipment. The systems allow for variable speed actuation and full control of the location of the actuator within its range of motion. The system can operate in a closed system with self-contained hydraulic supply and return porting and limited fluid contamination and leakage concerns. The systems do not use proportional valves to meter flow between the pumps and the hydraulic actuators, and instead the pumps control the direct flow to the respective actuators. The systems are battery powered and extremely efficient, are robust for harsh impacts, are compact, and are low cost. Regenerative power from gravity loads are transferred directly on the pump and motor shaft instead of going to a battery first and then back. The systems can handle extreme impact, do not require sensitive electromechanical solutions, and the actuator cylinders in the systems are easy to replace. And the increased energy efficiency of the systems minimizes the battery pack size, lowering costs. 
     Many changes and modifications may be made. Therefore, while an embodiment of an improved assistive torque electro-hydraulic piston pump system has been shown and described, and a number of alternatives discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the scope of the invention, as defined and differentiated by the following claims.