Hydraulically actuated, electrically controlled linear motor

Abstract

A hydraulically actuated, electrically controlled linear motor includes a trigger that is electrically controllable. A hydraulic cartridge has a needle and a piston, the needle being operably coupled to the trigger and the piston being operably fluidly in communication with a source of high pressure actuation fluid, translation of the needle effected by the trigger acting to selectively port high pressure actuation fluid to the piston and to vent actuation fluid from the piston. A method of linear actuation is also included.

Description

TECHNICAL FIELD

[0002] The present application is related to motors. More particularly, the present application relates to a linear motor adaptable for linear actuation of diverse devices.

BACKGROUND OF THE INVENTION

[0003] There is a need for linear motors in many industries. This need is felt in the automotive industry in particular. There is increasing sophistication in microprocessor control of major automotive components in order to enhance vehicle control and safety. Many of these components have been previously controlled by cables and direct hydraulic actuation. With the shift to microprocessor control, there is a growing need for linear motors, particularly, hydraulically-actuated, electrically-controlled linear motors.

[0004] For example, it is usual to provide each vehicle wheel with a brake having a disk or drum shaped friction surface as well as a friction element and an actuator. The actuator presses the friction element against the friction surface when the brake is operated. In a motor vehicle, the service and parking brake system generally employ a common brake. Commonly, the parking brake system is operated manually, by hand or foot, and maintained in the operating condition by mechanical means, typically a cable or direct hydraulic control. There is a need in the industry for the more sophisticated control afforded by a linear motor.

[0005] Additionally, the service brake system may have brake slip control and automatic brake management for active brake operations such as traction control and driving dynamics control. Such traction control systems are commonly known as ABS, antilock brake system. Driving dynamics control devices have been marketed under a number of acronyms. There is a need in the industry for more sophisticated actuation of such brakes, such as could be afforded by a linear motor.

[0006] In another application, small internal combustion engines are an attractive choice for portable electric generators. These generators are commonly used to provide electric power in places without access to the national electric grid, and are particularly popular for use on construction sites, and recreational vehicles in remote areas, and during power outages.

[0007] One problem with the use of internal combustion engines in portable generators is that many electrical appliances require alternating current at almost exactly 60 hertz. Operating the IC engine to maintain 60 hertz requires that the speed of the IC engine be very accurately controlled. There is a need in the industry for sophisticated governance of such IC engines, and a linear motor could prove effective in providing such governance.

[0008] In another application, in compression ignition engines it is desirable to have both a positive power mode of operation and a braking mode of power operation. A highly effective way of operating an engine in braking mode is to cut off the fuel supply to the engine and then to open the exhaust valves in the engine near top dead center of the compression strokes of the engine cylinders. This causes air that the engine has compressed in its cylinders to escape to the exhaust system of the engine before the engine can recover the work of compressing the air during the subsequent “power” stroke of the engine piston. There is a need in the industry for a means of opening the exhaust valves to effect the compression release engine braking. The linear motor could be effective in opening the valves as described, either directly or through a rocker arm device.

[0009] In a further application, there has been a continual problem of how to successfully bring two rotatable gears selectively into and out of gear meshing engagement, such that both gears when engaged will then rotate together to do some form of useful work. One environment in which this problem exists is in the area of power take off devices (PTO). PTO's have found commercial uses in a wide variety of vehicular areas such as where the PTO is attached to the transmission of the vehicle for translating the power of the engine into the rotation of a shaft for doing useful work. Such work may be for example operating a hydraulic pump, compacting a garbage compactor, operating a separate attachable implement such as a snow blower, operating a separate non-attachable implement such as a grain auger, and the like. There is a need in the industry for a linear motor effective in engaging and disengaging the gears to effect the rotation of the PTO. A linear motor could be effective in making the gear engagement and disengagement as noted above.

SUMMARY OF THE INVENTION

[0010] The linear motor of the present invention substantially meets the aforementioned actuation needs set forth above. The mechanical components needed to effect the actuation by the linear motor are relatively simple, thereby minimizing the additional components required. The linear motor of the present invention is designed to provide for uniform actuation over a wide range of hydraulic fluid temperatures.

[0011] The foregoing advantages of the present invention are effected by the use of fine needle control. The fine needle control provides for modulation of the device being actuated as needed and provides for aggressive or less aggressive actuation as needed. Further, the device being actuated very closely follows the input of the linear motor. Therefore, the linear motor of the present invention does not require the added complexity requiring a sensor to measure the position of the device being the actuated for feedback control. The accurate control of the device being actuated is attained by accurate control of the needle at the end of needle stroke.

[0012] The present invention is a hydraulically actuated, electrically controlled, linear motor and includes a trigger that is electrically controlled. A hydraulic cartridge has a needle and a piston, the needle being operably coupled to the trigger and the piston being operably fluidly in communication with a source of high pressure actuation fluid, translation of the needle effected by the trigger acting to selectively port high pressure actuation fluid to the piston and to vent actuation fluid from the piston. The present invention is further a method of linear actuation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a sectional side perspective view of a further embodiment of a linear motor of the present invention and a device to be actuated (an engine valve);

[0014] FIG. 2 is a sectional side perspective view of the embodiment of the linear motor of FIG. 1 and engine valve, the engine valve being in the closed disposition;

[0015] FIG. 3 is a sectional side perspective view of the embodiment of the linear motor of FIG. 1 and engine valve, the engine valve being in the open disposition;

[0016] FIG. 4 is a sectional view of a further embodiment of the linear motor of the present invention;

[0017] FIG. 5 is a sectional view of the embodiment of FIG. 4 depicting actuating fluid flow;

[0018] FIG. 6 is a sectional view of the embodiment of FIG. 4 depicting overlap and opening dimensions; and

[0019] FIG. 7 is an enlarged sectional view of the embodiment of FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS

[0020] The use of the linear motor in the application noted below is but one of a myriad of uses of the linear motor of the present invention. With this point in mind, the present invention is detailed below.

[0021] A preferred embodiment of the linear motor 10 is presented in FIGS. 1-3. In this embodiment of the linear motor 10, the linear motor is employed to act on a rocker arm 14 to effect the opening and closing of an engine valve 16. Engine valve 16 has a valve stem 18, a keeper 20 and a return spring 22. The return spring 22 typically biases the engine valve 16 in the closed disposition and opposes the action of the linear motor 10. Valve 16 has a valve longitudinal axis 23.

[0022] The rocker arm 14 has an elongate arm member 64. The arm member 64 is pivotable about a pivot point 68. A first arm portion 70 extends leftward in the depiction of FIG. 3 from the pivot point 68 to the proximal end 72 of the arm member 64. A ball bearing 74 is disposed proximate the proximal end 72 for coupling to the drive piston 26. The first arm portion 70 has a length L1, defined between the pivot point 68 and the point of contact of the ball bearing 74 with the piston 26.

[0023] A second arm portion 76 of the arm member 64 extends rightward from the pivot point 68 to the distal end 78 of the arm member 64. A bearing surface 80 is presented proximate the distal end 78. The bearing surface 80 bears upon the stem upper margin 82 of the engine valve 16. The second arm portion 76 has a length, L2, defined between the pivot point 68 and the point of contact of the bearing surface 80 with the stem upper margin 82. L1 is preferably less than L2 to provide stroke amplification as discussed in more detail below.

[0024] The linear motor 10 has two major subcomponents: the actuator valve 24 and drive piston 26. The actuator valve 24 is an elongate piston comprising a spool valve 28 at a first end and including a spool groove 29. The actuator valve 24 is translatably disposed in part in spool bore 30. A solenoid 32 is disposed proximate a second end of the actuator valve 24. A return spring 33 bears on the end of the actuator valve 24 (top margin) that is disposed proximate the spool groove 29.

[0025] An inlet port 34 is fluidly coupled to the source of high pressure actuating fluid 36. This source may be a high pressure rail 36. The rail 36 may convey any suitable high pressure fluid. Preferably, the fluid in the rail 36 is engine oil at approximately 450-3,500 psi. The rail 36 provides for hydraulic actuation of the linear motor 10. The inlet port 34 is defined in the drive piston 26 and is in fluid communication with the spool bore 30 via the bore 49, described in greater detail below. A vent port 38 is also in fluid communication with the spool bore 30 and is further fluidly coupled to a ambient reservoir 40. The ambient reservoir 40 may be at substantially ambient pressure of 0 to 100 psi.

[0026] A controller 42 is in communication with the solenoid 32 for energizing and deenergizing the solenoid 32. The controller 42 effects electric control of the linear motor 10. The controller 42 may be a microprocessor that is in communication with a sensor or sensors for sensing parameters or other inputs, some of which may be manually inputted, necessary to exert control over the particular device to which linear actuation (in this case, valve 16) is to be imparted by the linear motor 10. For example, in an ABS application, the sensors might sense a certain difference in rotational speed of two or more vehicle wheels and the controller 42 would then command the linear motor coupled to at least on wheel brake to linearly actuate the brake with a single stroke or a modulated stroke to effect a single brake actuation or a pulsed brake actuation, as desired.

[0027] The second subcomponent of the actuator 12 is the drive piston 26. The drive piston 26 includes a cylinder housing 46 having a cylinder 48 defined therein. The drive piston 26 is translatably disposed in the cylinder 48. In the depiction of FIGS. 3-5, the drive piston 26 is depicted as having two components, a cylinder capped by a cap. It should be noted that the drive piston 26 could as well be a single unitary component.

[0028] An axial central actuator piston bore 49 is defined in the drive piston 26. The actuator piston bore 49 is an extension of the spool bore 30. The actuator valve 24 projects into the actuator piston bore 49, the actuator piston bore 49 accommodating, in cooperation with the spool bore 30, the translation of the actuator valve 24. Additionally, the return spring 33 is housed within the actuator piston bore 49, bearing on the top margin of the actuator valve 24 and a spring stop 47 and being compressed therebetween.

[0029] A fluid chamber 50 is defined beneath the lower margin of the drive piston 26. The fluid chamber 50 is selectively in communication with the inlet port 34 as a function of the disposition of the spool groove 29 relative to both the fluid chamber 50 and the inlet port 34. The fluid chamber 50 is a variable volume chamber defined in part by the actuating surface 52, the actuating surface 52 defining the lower margin of the drive piston 26.

[0030] A bearing surface 54 is presented proximate the upper margin of the drive piston 26. The bearing surface could be an elongate rod operably coupled to the device to which linear motion is to be applied by the linear motor.

[0031] The actuator valve 24 is electromagnetically actuated by a solenoid 32. The actuator valve 24 is constrained to move linearly between a lower and an upper limit. Motion of the actuator valve 24 relative to the hydraulically actuated drive piston 26 sequentially opens and closes orifices (the groove 29 of spool 28) that control hydraulic fluid in fluid chamber 50 acting on the actuating surface 52 of the drive piston 26. In the closed disposition, depicted in FIG. 2, the vent port 38 and L.P. reservoir 40 are in fluid communication with fluid chamber 50. In the open disposition, depicted in FIG. 3, the inlet port 34 is in fluid communication with the fluid chamber 50 by means of the spool groove 29.

[0032] The function of this system is described below. The actuator valve 24 is actuated from rest (see FIGS. 1 and 2) to the open valve disposition (see FIG. 3) by the controller 42 applying voltage to the solenoid 32. The actuator valve 24 then moves upward against its return spring 33 due to the magnetic force generated at the solenoid 32 responsive to the input signal from the controller 42. Displacement of the actuator valve 24 relative to the drive piston 26 sequentially closes the vent 38 connected to tank 40 and opens the inlet port 34 that allows high-pressure fluid to flow from the rail 36 through the spool groove 29 into the actuating chamber 50. The resulting hydraulic force acting on the actuating surface 52 displaces the drive piston 26 upward against the rocker arm 14. It should be noted that actuator valve 24 moves upward in concert with the drive piston 26 after moving independently the small distance necessary to effect porting of the high pressure actuating fluid to the actuating chamber 50.

[0033] Motion of the drive piston 26 displaces the rocker arm 14 about its pivot point 68. The linear motion of the drive piston 26 is amplified and transmitted to the poppet valve 16 according to: 1$x_{\mathrm{poppetvalve}}=x_{\mathrm{drivepiston}}\left(\frac{L_2}{L_1}\right),$

[0034] where L2>L1. See FIGS. 2 and 3.

[0035] At the appropriate time, dictated by engine performance and emissions constraints, the poppet valve 16 is returned to its seat as follows. Return motion of the actuator valve 24 to its initial position is initiated by the controller 42 removing the applied solenoid 32 voltage. The return spring 33 overcomes any residual magnetic force and returns the actuator valve 24 to its seat, as depicted in FIG. 2. The initial motion of the actuator valve 24 relative to the drive piston 26 sequentially closes the inlet port 34 connected to the high-pressure rail 36 and opens the vent orifice 38 connected to the tank 40. Hydraulic pressure is thus removed from the drive piston 26, which is then forced to return to its seat by the return spring 22 connected to the poppet valve 16. A second return spring acting only on the drive piston could also be used where the device being actuated by the linear motor 10 does not have its own closing or return bias. Such a return spring could be disposed to act on the upper margin 55 of the drive piston 26. It should be noted that actuator valve 24 moves downward in concert with the drive piston 26 after moving independently the small distance necessary to effect venting of the high pressure actuating fluid from the actuating chamber 50. Further, a second solenoid could be utilized to oppose the solenoid 32 by generating an opposing linear motion of the drive piston 26 when actuated. Such second solenoid would be disposed external to the drive piston 26 in a manner similar to the disposition of the solenoid 32 relative to the actuator valve 24 and exert an electromagnetic force thereon when activated.

[0036] A constraint on the hydraulic surfaces of the second drive piston 26 is as follows: 2$F_{\mathrm{hydraulic}}=F_{\mathrm{returnspring}}\left(\frac{L_2}{L_1}\right)$

[0037] In other words, the hydraulic force supplied to the drive piston 26 must overcome the “amplified” return spring force exerted by the return spring 22. This force requirement may be accommodated by a larger area actuation surface 52 on the drive piston 26, or by supplying higher pressure actuating fluid from the rail 36.

[0038] A further preferred embodiment of the linear motor 10 is presented in FIGS. 4-77. The first component of the linear motor 10 is the solenoid 140. The solenoid 140 includes an armature 148 that is translatably disposed within an armature guide 150. The armature guide 150 provides a cylindrical surface that is coincident with at least a portion of the outside margin of the armature 148 and constrains the armature 148 during translation thereof. Accordingly, the cylindrical surface of the armature guide 150 comprises a guide bore 152.

[0039] A needle bearing surface 154 comprises a portion of the bottom margin of the armature 148. The needle bearing surface 154 resides within a recess 156 defined in the bottom surface margin of the armature 148.

[0040] The upper margin 158 of the armature 148 comprises an armature stop. The upper margin 158 is stopped by a shim 160 when the armature 148 is in the retracted disposition. The shim 160 has a selected depth dimension B, as will be described in greater detail below with reference to FIG. 6.

[0041] A hydraulic vent 162 is defined in the shim 160. The hydraulic vent 162 is preferably in registry with a hydraulic vent 164 defined in the cover 166. The underside margin 168 of the top of the cover 166 constrains the shim 160 between the cover 166 and the upper margin 158 of the armature 148.

[0042] The cover 166 further has retaining groove 170 that is formed proximate the lower margin of the cover 166. The retaining groove 170 bears on a peripheral margin of the cartridge 142. A bore 172 is defined in a flange 174 that projects to the side of the cover 166. A bolt 176 may be passed through the bore 172 and threaded into a threaded bore defined in the rail 20. By such means, the cover 1166 secures both the solenoid 140 and the cartridge 142 in the integral receiver 130 defined in the rail 120 and holds the shim 160 in place.

[0043] The cover 166 additionally provides a retaining element for the coil 178 that is associated with the armature 148. The coil 178 is generally cylindrical in shape and resides outward of the armature 148. The armature guide 150 is preferably disposed between the coil 178 and the armature 148. Suitable electrical leads (not shown) couple the coil 178 to an external controller (not shown) for providing actuation commands to the linear motor 10.

[0044] The second component of the linear motor 10 is the hydraulic cartridge 142. The hydraulic cartridge 142 includes a cartridge body 180. An actuator bore 182 is centrally defined within the cartridge body 180. The actuator bore 82 extends all the way through the cartridge body 180 and has a number of varying diameters. Commencing at the top margin of the cartridge body 180, the first such diameter defines an armature receiver 184. When the armature 48 is in the actuated, extended disposition, the armature 148 translates downward from a retracted disposition to a extended disposition and is encompassed in part by the armature receiver 184.

[0045] The portion of the actuator bore 182 immediately below the armature receiver 184 has a lesser diameter than the armature receiver 184 and comprises a spring cage 186. A step formed at the bottom margin of the spring cage 186 comprises a spring seat 188.

[0046] A portion of the actuator bore 182 that comprises a piston neck receiver 190 is beneath the spring cage 186 and has a diameter that is greater than the step forming the spring seat 188. A hydraulic vent 192 extends radially outward from the piston neck receiver 190 and fluidly connects the piston neck receiver 190 to ambient conditions exterior to the hydraulic cartridge 142 (see in particular FIG. 5). A piston stop 194 is formed at the upper margin of the piston neck receiver 190. Preferably, the piston stop 194 is formed by the step that also forms the spring seat 188, the stop 194 being the lower margin of the step and the seat 188 being the upper margin of the step.

[0047] The greatest diameter of the actuator bore 182 comprises the lowermost portion of the actuator bore 182. This portion defines a power section receiver 198. A hydraulic inlet 200 extends through the cartridge body 180 and fluidly couples the power section receiver 198 to actuating fluid under pressure provided by the rail 20. See in particular FIG. 5. A retainer groove 202 is defined in the power section receiver 198 proximate the lower margin of the cartridge body 180. A retainer 204, preferably a snap ring, may be disposed in the retainer groove 202.

[0048] A piston 206 and a needle (sometimes referred to as a spool) 108 reside within the actuator bore 182 and are retained in place by the retainer 204.

[0049] The piston 206 is preferably a unitary device having a generally cylindrical outside margin of varying diameters. The piston 206 has, in descending order as depicted, a neck 210, a power section 214, and an actuator rod 238. A blind needle bore 211 is centrally defined within the piston 206 and extends downward to approximately the juncture of the power section 214 and the actuator rod 238. The needle bore 211, being blind, is closed at the bottom 224. The needle bore 211 is open at a top opening 226 formed by an upper margin 212.

[0050] The neck 210 of the piston 206 preferably translatably resides within the piston neck receiver 190 of the cartridge body 180. When the piston 206 is in the retracted, venting disposition, the upper margin 212 of the neck 210 is stopped by the piston stop 194 defined in the actuator bore 182 of the cartridge body 180.

[0051] The power section 214 of the piston 206 has an annular groove 216 defined between a pair of spaced apart lands 217. The annular groove 216 is preferably in registry with the hydraulic inlet 200 and, accordingly, is in fluid communication with actuating fluid provided by the rail 20. An annulus 218 is defined in the needle bore 211 substantially in registry with the annular groove 216. A fluid passageway 222 fluidly connects the annular groove 216 to the annulus 218. As noted in more detail below, the upper margin 220 of the annulus 218 becomes a critical interface in the operation of the piston 206 and needle 208.

[0052] A second critical interface of the piston 206 and needle 208 is the sealing shoulder 228. Sealing shoulder 228 is formed by a step increase in the diameter of the needle bore 211. The increase in diameter of the needle bore 211 forms an annulus 229 that is at least in part in registry with the hydraulic vent 192 defined in the cartridge body 180.

[0053] A high pressure fluid passageway 232 extends between the needle bore 211 and a piston head 234. A vent passageway 236 extends between the annulus 229 formed by the increased diameter of the needle bore 211 upward up the step 228 and the vent 192.

[0054] The actuator rod 238 depends from the power section 214. The distal end of the actuator rod 138 bears on the device to which linear motion is to be imparted.

[0055] The needle (spool) 208 is operably coupled to the armature 148 of the solenoid 140 and is translatably disposed within the needle bore 211 of the piston 206. The needle 208 has a head 242 that bears on the needle bearing surface 154 defined within the recess 156 of the armature 148. The underside margin of the head 242 comprises a spring seat 244. A coil return spring 245 is captured between the spring seat 244 and the spring seat 188 formed at the bottom of the spring cage 186 defined in the cartridge body 180. The return spring 245 is generally always in a state of compression and exerts an upward bias on the needle 208.

[0056] The return spring 245 is disposed concentric with a shank 246 that depends from the head 242. The shank 246 has a spool groove 252 defined between an upper land 248 and a lower land 250. As described in greater detail below, the positional interaction between the lower margin 249 of the upper land 248 and the sealing shoulder 228 and upper margin 251 of the lower land 250 with the upper margin 220 of the annulus 218 is critical to the operation of the piston 206 and needle 208.

[0057] When the trigger (solenoid 140) actuates the spool (needle 208) in the linear motor 10, the device to be actuated is also shifted linearly. The only delay in actuation of the device to be actuated between the time of actuation of the solenoid 140 and movement of the device to be actuated is the amount time the it takes the needle 208 to translate through the dimension A, A′ noted in FIG. 6.

[0058] Prior to actuation of the solenoid 140, the piston 206 and needle 208 are in their retracted dispositions as indicated in FIG. 6. The incoming high-pressure actuation fluid is sealed off where the overlap is indicated by the dimension A′. The spool 252 is opened as indicated by the dimension A and actuating fluid is free to flow from the spool 252 upward through the vent passageway 236 and out the hydraulic vent 192. See also FIG. 5.

[0059] Upon actuation of the solenoid 140, the armature 148 is drawn downward by the magnetic force generated in the coil 178, overcoming the bias of the return spring 245. The armature 148 carries with it the needle 208. The needle 208 translates downward relative to the piston 206. Such motion closes the opening indicated by dimension A, thereby sealing off the venting of actuating fluid. Simultaneously, the overlap indicated by dimension A′ is eliminated, thereby opening the spool 252 to the annulus 218 and causing the flow of high pressure actuating fluid into the spool 252, as depicted in FIG. 7. The high pressure actuating fluid flows radially outward through high-pressure fluid passageway 232 to bear downward on the piston head 234.

[0060] The force generated by the high pressure actuating fluid acting on the piston head 234 drives the piston 206 downward (in conjunction with the continued downward travel of the spool 208). This downward translation of the piston 206 exerts a downward pressure and linear translational motion on the device to be actuated.

[0061] Retraction or closing of the device to be actuated occurs when the actuation command to the solenoid 140 is withdrawn. The magnetic field collapses and the return spring 245 shifts the needle 208 upward relative to the piston 208 to the retracted venting disposition depicted in FIG. 4. The accumulator 268 of rail 20 is sealed off from the hydraulic cartridge 142 by the overlap A′ of FIG. 4. Hydraulic fluid in the hydraulic cartridge 142 escapes through opening A and out hydraulic vent 192, as depicted in FIG. 5.

[0062] It will be obvious to those skilled in the art that other embodiments in addition to the ones described herein are indicated to be within the scope and breadth of the present application. Accordingly, the applicant intends to be limited only by the claims appended hereto.

Claims

1. A hydraulically-assisted linear motor for imparting linear actuation to a device, comprising: an actuator piston being operably coupled to the device; and a translatable needle valve being in fluid communication with a source of hydraulic fluid under pressure and with the actuator piston and further being operably coupled to a needle positioning mechanism, the needle valve being translatable at a desired rate and effecting the metering of hydraulic fluid under pressure to and from the actuator piston in response to translational control inputs from the needle positioning mechanism, the metered hydraulic fluid at least partially effecting translational motion of the actuator piston to follow the translation of the needle valve to effect a desired profile of linear translational motion of the device.

2. The hydraulically-assisted linear motor of claim 1 wherein the needle valve has a generally elongate cylindrical shape and has a first end defining a first end groove and a second end opposed thereto, the second end being operably coupled to the needle positioning mechanism.

3. The hydraulically-assisted linear motor of claim 1 wherein the needle positioning mechanism is selected from mechanisms consisting of a solenoid and a stepper motor.

4. The hydraulically-assisted linear motor of claim 1 wherein the actuator piston has a generally cylindrical shape and has a first end operably coupled to the device and a second end opposed thereto, an axial bore being defined in the actuator piston extending from the second end at least a portion of a longitudinal dimension of the actuator piston.

5. The hydraulically-assisted linear motor of claim 1 further including an actuator housing, the actuator housing having an axial housing cylinder bore defined therein, the actuator piston having a piston head, the piston head being translatably disposed in the housing cylinder bore.

6. The hydraulically-assisted linear motor of claim 5 wherein the actuator housing is fluidly coupled to a source of relatively high pressure hydraulic fluid.

7. The hydraulically-assisted linear motor of claim 5, wherein the needle valve has a generally elongate cylindrical shape and has a first end defining a first end groove and a second end opposed thereto, the second end being operably coupled to the needle positioning mechanism, the needle valve being translatably disposed in an axial bore defined in the actuator piston.

8. The hydraulically-assisted linear motor of claim 7 wherein the needle valve first end groove acts to meter hydraulic fluid to and from the actuator piston head responsive to translation of the needle valve relative to the actuator piston.

9. A method of linear actuation of a device, comprising: translating an actuator valve responsive to control inputs by a pilot valve positioning system; metering hydraulic fluid under pressure to and from a servo piston by means of translation of the pilot valve relative to the servo piston; operably coupling the servo piston to the device; and translating the servo piston and the device by means of a force exerted on the servo piston by the hydraulic fluid under pressure, the hydraulic fluid under pressure causing the servo piston to closely follow the translation of the pilot valve to effect a desired profile of linear translational motion of the device.

10. The method of claim 9 including biasing the servo piston by a return spring, the force exerted on the servo piston by the hydraulic fluid under pressure acting in opposition to the bias exerted by the return spring.

11. The method of claim 9, including actuating the actuator valve by at least one solenoid.

12. The method of claim 9, including actuating the actuator valve by a first solenoid and an opposed spring.

13. The method of claim 9, including shifting a spool valve to selectively port actuating fluid to the servo piston and to selectively vent actuating fluid from the servo piston.

14. A hydraulically actuated, electrically controlled linear motor, comprising: a trigger being electrically controllable; a hydraulic cartridge having a needle and a piston, the needle being operably coupled to the trigger and the piston being operably fluidly in communication with a source of high pressure actuation fluid, translation of the needle effected by the trigger acting to selectively port high pressure actuation fluid to the piston and to vent actuation fluid from the piston for effecting linear translation of the piston.

15. The linear motor of claim 14, the needle having a spool, the spool selectively being in fluid communication with the source of high pressure actuation fluid and being vented by translatory motion of the needle relative to the piston.

16. The linear motor of claim 14 being an open loop system.

17. A linear motor for actuating a device, comprising: an electrohydraulic actuator having a piston, the piston being operably couplable to the device and being translatable responsive to an actuating fluid bearing on a piston surface, the piston surface being in fluid communication with an actuator valve, the actuator valve being in selective fluid communication with a source of actuating fluid under pressure, the actuator valve being selectively shiftable relative to the piston to selectively port and vent actuating fluid to and from the piston surface to effect at least in part linear translatory motion of the piston and the device as desired.

18. The linear motor of claim 17, a return spring being operably coupled to the actuator valve and exerting a bias on the actuator valve.

19. The linear motor of claim 17, the actuator valve being actuated by at least one solenoid.

20. The linear motor of claim 19, the actuator valve being actuated by a first solenoid and a second opposed solenoid.

21. The linear motor of claim 20, the actuator valve being actuated by a first solenoid and by a bias exerted by an opposed spring.

22. The linear motor of claim 17, the source of actuating fluid under pressure being a high pressure rail.

23. The linear motor of claim 17, the actuating fluid being engine lubricating oil.

24. The linear motor of claim 17, the actuator valve being a spool valve translatably disposed at least in part in a bore defined in the piston.

25. The linear motor of claim 17, the actuator valve being in selective fluid communication with a reservoir at substantially ambient pressure.

26. A linear motor for actuating a device, comprising: a hydraulically actuated, electrically controlled servomechanism having an actuator valve and a drive piston, motion of the actuator valve relative to the drive piston acting to open and close certain orifices for controlling fluid acting on the drive piston, the drive piston being operably coupled to the device for imparting linear motion in at least one direction to the device.

27. The linear motor of claim 26, a return spring being operably coupled to the actuator valve and exerting a bias on the actuator valve.

28. The linear motor of claim 26, the actuator valve being actuated by at least one solenoid.

29. The linear motor of claim 28, the actuator valve being actuated by a first solenoid and an opposed spring.

30. The linear motor of claim 26, the actuator valve including a spool valve, the spool valve being shiftable to selectively port actuating fluid to the drive piston and to selectively vent actuating fluid from the drive piston.

31. The linear motor of claim 26, the source of actuating fluid under pressure being a high pressure rail.

32. The linear motor of claim 26, the actuator valve being a spool valve translatably disposed at least in part in a bore defined in the piston.

33. The linear motor of claim 26, the actuator valve being translatable through a known stroke, a first portion of the stroke being relative to the drive piston and a second portion of the stroke being in concert with the translation of the drive piston.

34. The linear motor of claim 33, the first portion of the stroke of the actuator valve selectively effecting porting actuating fluid to the power piston and venting actuating fluid from the power piston.