Control Valve Unit for Hydraulic Linear Actuator

This invention relates to a control valve unit for controlling the supply of hydraulic fluid to a hydraulic linear actuator that is alternately movable in opposite directions to provide movement in such directions for whatever purpose is required.

Hydraulic actuators are utilized in various industrial and other applications to provide movement in opposite directions under the control of hydraulic fluid supplied by a control valve unit. For example, material handling systems, conveyors, various metal removal machines, cold and hot forming machines, indexers, automatic loaders, and door positioners, etc. utilize hydraulic actuators to control positioning of components during operation.

Most hydraulic actuators are of the linear type and thus provide linear movement and positioning; however, some hydraulic actuators are of the rotary type and provide rotary motion and positioning. Hydraulic linear actuators are most often embodied by cylinders which include a housing and a piston that is received within the housing and has a connecting rod extending outwardly therefrom in order to provide connection of the cylinder for actuating movement. A bore within the cylinder housing receives the piston in a sealingly slidable relationship such that hydraulic fluid supplied to one or the other sides of the piston provides piston movement and accompanying driving of the associated connecting rod. Some hydraulic cylinders have two connecting rods extending from the piston thereof so as to have equal amounts of fluid supplied to the cylinder on one side of the piston thereof and ejected from the cylinder on the other side of the piston. However, the more conventional cylinder has only a single connecting rod and thus has a different area on the side thereof having the connecting rod than the area of the side thereof without any connecting rod. As such, different amounts of fluid are supplied to and ejected from such a cylinder during hydraulically actuated movement of its piston. One of the most common constructions of hydraulic cylinders incorporates a tubular housing and square end caps that are held in position against ends of the housing by through-bolts extending alongside the housing and through the corners of the end caps.

The U.S. patent of Barlow U.S. Pat. No. 3,954,045 is assigned to the assignee of the present invention and discloses a control unit for a hydraulic rotary actuator. This control unit includes a valve that supplies hydraulic fluid to the rotary actuator under the control of a solenoid assembly and a cam mechanism in order to control actuator rotation. The solenoid assembly opens the supply valve to initiate the hydraulically actuated rotation. Cams of the cam mechanism are contoured to close the supply valve and thereby terminate the actuator movement with a feedback action.

U.S. patent application Ser. No. 014,175, filed Feb. 22, 1979, is assigned to the assignee of the present invention and discloses a control valve unit for a hydraulic actuator of either the linear or the rotary type. This control valve unit includes a supply valve that is opened at a predetermined rate to control acceleration and closed by cams to provide deceleration of the actuator movement by a feedback action.

Other hydraulic control valves are disclosed by U.S. Pat. Nos. Re. 29,392; 2,879,644; 3,640,069; 3,693,385; 3,779,136; and 3,780,623.

An object of the present invention is to provide an improved control valve unit for use with a hydraulic linear actuator in order to provide operation of the actuator with a feedback action.

In carrying out the above object, the control valve unit includes a slide mechanism mounted on a base of the unit and having a pair of movable slides that are spring biased away from each other. A control member of the unit is driven by a hydraulic linear actuator with which the unit is used to respectively engage and move the pair of slides adjacent the limits of actuator movement. A control valve of the unit feeds hydraulic fluid to the actuator and has a deactivator that is operated by the slide movement in order to terminate the driving of the actuator.

Preferably, the slide mechanism includes a slideway on the base and a pair of fixed stops between which the movable slides are supported on the slideway and biased by a helical spring against the stops. The helical spring has ends engaged with the slides and is aligned with openings through the slides, and the control member extends through the spring and the slide openings. Lugs on the control member engage and move the slides and are preferably embodied as collars including adjustable mounts so as to permit adjustment of the locations at which driving of the linear actuator is terminated.

During use of the mounted unit, an adjustable cam on each slide engages and moves the deactivator of the control valve adjacent the associated limit of actuator movement. This engagement takes place at cam surfaces of the cams which are movable toward the deactivator from opposite directions and on opposite sides. Cam actuated movement of the deactivator to a central position from either direction terminates the supply of pressurized hydraulic fluid to the actuator from the control valve so as to terminate the actuator movement.

Each cam is mounted on the associated slide about a pivotal support axis and includes a positioner for providing positioning thereof about its support axis so as to control the deactivator movement in relationship to the linear actuator movement and thereby control the deceleration rate of the linear actuator. The deactivator includes a round cam surface of a radius r.sub.1 and each adjustable cam has its cam surface provided with a limit cam surface positioned therealong at a location spaced from the associated pivotal support axis by a radius r.sub.2 which is equal to r.sub.1 so that the locations at which the linear actuator movement terminates are not affected by the adjusted positions of the cams.

A preferred construction of the slideway includes a pair of slide rods mounted on the base of the unit extending between the stops. Each slide has opposed slide surfaces that slidably engage the slide rods and one or more springs bias one of the slide rods against the associated slide surfaces in order to provide the slidable mounting of the slides for movement toward and away from the stops under the action of the helical spring and the lugs of the control member that is moved by the linear actuator.

An L-shaped construction of the base facilitates mounting of the unit on a hydraulic linear actuator of the through-bolt cylinder type. A right angle junction of the L-shaped base engages one of the through-bolts on an associated cylinder of this type and cooperative pairs of clamps engage the through-bolts on each side of the one through-bolt at the base junction so as to provide a secured mounting of the unit on the cylinder.

A check valve and a pressure relief valve arrangement of the control valve unit accommodates for the different amounts of hydraulic fluid that must be supplied to and ejected from a hydraulic linear actuator of the single connecting rod type as inertial or other forced piston movement takes place subsequent to operation of the control valve by the deactivator movement. A first conduit including the check valve feeds hydraulic fluid from a reservoir to the piston bore on the large area side thereof opposite its connecting rod side in order to accommodate for the increased fluid volume required as a result of any forced piston movement subsequent to termination of the control valve operation that moves the piston in a direction from its large area side toward its small area side at which the connecting rod is located. A second conduit including the pressure relief valve dumps hydraulic fluid from the large area side of the piston bore in order to accommodate for the decreased volume of hydraulic fluid permitted during any forced piston movement subsequent to termination of control valve operation that moves the piston in a direction from its small area side where the connecting rod is located toward its large area side.

The objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.

FIG. 1 is a perspective view of a control valve unit shown mounted on a hydraulic linear actuator and constructed in accordance with this invention to control operation of the actuator;

FIG. 2 is a side view of the control valve unit and the actuator;

FIG. 3 is a top plan view of the control valve unit and the actuator taken along line 3--3 of FIG. 2;

FIG. 4 is an end view of the control valve unit and the actuator taken along line 4--4 of FIG. 2;

FIG. 5 is a partially sectioned view of the control valve unit taken along line 5--5 of FIG. 2;

FIG. 6 is a partial plan view of the control valve unit taken along line 6--6 of FIG. 2; and

FIG. 7 is a schematic view illustrating a control valve of the unit and the manner in which operation thereof controls movement of the associated hydraulic linear actuator.

Referring to FIG. 1 of the drawings, a control valve unit constructed in accordance with the present invention is indicated generally by reference numeral 10 and is shown mounted on an associated hydraulic linear actuator embodied by a hydraulic cylinder 12 of the through-bolt type. A slide mechanism 14 of control valve unit 10 includes a pair of slides 16a,b that are moved by a control member 18 under the driving impetus of a piston rod 20 of cylinder 12 in order to control operation of the cylinder. A control valve 22 of the unit includes a deactivator 24 that is engaged and moved by the movement of the slides 16a,b under the impetus of the control member 18 in order to provide termination of the flow of hydraulic fluid to and from the cylinder 12 so as to terminate the movement of the piston connecting rod 20 toward the left and the right as is hereinafter more fully described.

Cylinder 12 includes an elongated tubular housing 26 (FIG. 1) defining a piston bore 28 (FIG. 7) in which a piston 30 connected to the inner end of rod 20 is movable to the left and the right in a sealingly slidable relationship. Opposite ends of the tubular housing 26 are sealed within round grooves in square end caps 32 and 33 which are held in position by four through-bolts 34 (FIGS. 1 and 4) extending through the corners of the end caps. Attachment lugs 35 (FIGS. 1, 2 and 3) are provided on end caps 32 and 33 for use in mounting of the cylinder, and a suitable seal within a central opening in end cap 33 slidably seals with the piston rod 20. Suitable fittings 36a,b are respectively threaded onto the end caps 32 and 33 and feed hydraulic fluid to and from the hydraulic cylinder 12 through suitable hose conduits 38a,b in order to control movement of the piston 30 shown in FIG. 7 by operation of the control valve 22. Such piston movement is accompanied by extension or retraction of rod 20 such that the cylinder can be used to provide driving movement or positioning for whatever purpose required.

As best seen in FIG. 4, a base 40 of the unit has an L shape including a pair of plates 42 and 44 that are secured to each other by bolts 46 as shown also in FIG. 6. Plates 42 and 44 respectively support the slide mechanism 14 and the control valve 22 and have an inside right angle junction that engages the upper left through-bolt 34 of cylinder 12 with the control unit 10 mounted on the cylinder as shown in FIG. 4. Cooperative pairs of through-bolt clamps 48 are secured to the plates 42 and 44 by associated bolts 50 (only one shown in FIG. 4) and engage the lower left and upper right through-bolts 34 on opposite sides of the upper left through-bolt engaged by the inside junction of the plates. Threading of the bolts 50 to edges of the plates 42 and 44 with the clamps 48 engaged with the through-bolts 34 provides mounting of the base 40 on the hydraulic cylinder 12 in a secured relationship.

As seen in FIG. 5, slide mechanism 14 includes a plate 52 that is secured to the base plate 42 by bolts 53 (only one shown) so as to provide a slideway on which the slides 16a,b are movable. Upper and lower edges of the plate 52 define V-shaped grooves 54 that respectively receive a pair of slide rods 56 also received by opposed slide surfaces defined on the slides 16a,b by V-shaped grooves 58. One or more springs 60 (only one shown) are respectively received within associated spring holes 61 and are compressed so that the lower ends thereof engage the lower slide rod 56 in order to provide a downward biasing that engages both of the slide rods 56 with the opposed slide surfaces defined by the grooves 54 and 58 on the slides 16a,b. Such a resilient mounting of the slide rods 56 provides an economical manner of mounting the slides 16a,b without requiring extensive machining normally required to provide a slideway. At the ends of the slideway plate 52, stops 62a,b (FIG. 2) are secured to this plate by associated bolts 64 with the slides 16a,b positioned therebetween such that the stops limit the movement of the slides to the left and the right.

With reference to FIG. 2, each of the slides 16a,b includes an opening 66 through which the control member 18 extends so as to be supported thereby for movement toward the right and the left under the driving impetus of the rod 20 connected to the piston of the cylinder. A spring 68 of the helical type also has the control member 18 extending therethrough and has opposite ends received within the slide openings 66. Each slide 16a,b includes a collar plate 70 secured thereto by recessed bolts with an annular rib 72 of the collar plate received within a complementary groove at the outer end of the associated slide opening 66 so as to seat the adjacent end of the spring 68. Spring 68 thus normally biases the slides 16a,b in opposite directions away from each other and into engagement with the stops 62a,b while permitting movement of the slides away from the stops under the action of the control member 18.

As previously mentioned in connection with FIG. 1, movement of the slides 16a,b under the impetus of the control member 18 moves the control valve deactivator 24 in order to terminate driving operation of the hydraulic cylinder 12. Control member 18 has its right end secured as shown in FIG. 3 by a spring and bolt connection 74 to one end of an arm 75 whose other end is secured by a suitable connection to the piston rod 20. Spring and bolt connection 74 prevents backlash as the driving of the piston rod 20 moves arm 75 and the control member 18 in order to operate the control valve 22. Lugs on the control member 18 are embodied by a pair of adjustable collars 76a,b that respectively engage and move the slides 16a,b adjacent the limits of movement of the cylinder rod 20 so as to terminate such driving movement under the operation of control valve 22. Each collar 76a,b is made up of complementary half collars with bolts 78 extending therebetween so as to thereby provide adjustable mounts for positioning the collars along the control member 18 in a manner that allows adjustment of the extent of driving movement of the cylinder.

As seen in FIG. 6, deactivator 24 of the control valve is movable in opposite directions, as illustrated by arrow 80, by a pair of adjustable cams 82a,b which are respectively mounted on the slides 16a,b. Each adjustable cam 82a,b includes a base portion 84 which is secured to the associated slide by a pintle bolt 86 for adjustment about an associated pivotal support axis A. Bolts 88 secure a cam member 90 of each cam 82a,b to the associated base portion 84 thereof such that cam surfaces 92a,b of the cam members are aligned with the deactivator 24 in order to engage a round cam surface 94 thereof upon movement of the associated cam away from its stop under the impetus of the collars on the control member 18 as previously described. Positioners 96 respectively associated with the cams 82a,b each include a clamp member 98 that is secured by a bolt 100 to the associated slide 16a,b with a rounded nose 102 of the clamp member engaged with the base portion 84 of the cam 82a,b on the slide. Tightening of the bolt 100 pivotally locates the associated cam 82a,b on the slide so as to fix the angular relationship of the cam surface 92a,b thereof with respect to the direction of slide movement parallel with the direction of movement of the control member 18. As will be more fully hereinafter described, the control valve of the unit continues to drive the hydraulic cylinder until the deactivator 24 is moved toward the central position shown in FIG. 6 whereupon the driving movement of the cylinder is decelerated in a controlled manner and ultimately terminated upon reaching the central position. Appropriate adjustment of the cam surfaces 92a,b with respect to the slides 16a,b controls the rate at which the deactivator 24 is moved to the central position in relationship to the rate of slide movement in order to provide the controlled rate of deceleration.

With continuing reference to FIG. 6, one of the bolts 88 of each adjustable cam 82a,b secures a round cam member with a limit cam surface 104a,b as well as securing the associated cam member 90. Limit cam surfaces 104a,b engage the cam surface 94 on the deactivator 24 from opposite axial directions with respect to the axis of cylinder movement and from opposite sides. This engagement provides the final extent of deactivator movement to the central position and termination of the cylinder operation at precise positions without any creeping movement that could result in uncontrolled final positions. Cam surface 94 on the deactivator has a radius r.sub.1 which is equal to the spacing r.sub.2 of the limit cam surfaces 104a,b from their associated support axes A of pivotal adjustment. As such, adjustment of the cams 82a,b about the axes A to control the rate of deceleration does not change the final positions at which the limit cam surfaces 104a,b move the deactivator 24 to the central position to terminate the driving of the hydraulic cylinder in the associated direction.

With reference to FIG. 4, control valve 22 includes a manifold block 106 that is secured to the plate 44 of base 40 by a plurality of bolts 108, only one of which is shown. Manifold block 106 is in turn secured as shown in FIGS. 1 and 2, to a valve block 110 by bolts 112. A cross line relief valve assembly 114 is also secured to the manifold block 106 by bolts 116 so as to relieve any excessive pressure that may occur in either conduit 38a or 38b, as is hereinafter more fully described. Operation of the control valve 22 is controlled by a directional valve 118 that is secured in any suitable manner such as by bolts to the valve block 110 on the opposite side thereof as the manifold block 106.

Referring to FIGS. 1, 2, and 3, operation of the control valve 22 is controlled by a cradle 120 which includes a connecting portion 122 (FIG. 3) and upwardly extending legs 124 connected to opposite ends of the connecting portion. Connecting portion 122 of the cradle 120 extends below the lower side of the valve block 110 and the legs 124 are located on opposite sides of this valve block supported thereon by slide screws 126 for movement in opposite directions as shown by arrow 128 in FIG. 3. Control cradle 120 has a central position at which driving operation of the hydraulic cylinder is terminated as will be more fully hereinafter described. Movement of the cradle 120 from this central position in either direction under operation of the directional valve 118 commences driving of the hydraulic cylinder from a rest position in which the rod 20 is located to the opposite limit of travel whereupon the cradle is then moved to the central position to terminate the driving cylinder movement.

Referring now to FIGS. 2 and 3, a support block 130 is secured to the valve block 110 of the control valve by bolts 132 and has a lower side at which a deactivator lever 134 is pivotally secured by a bolt 136. Deactivator lever 134 is thus pivotal about a vertical axis B. One end of lever 134 receives a vertically extending threaded bolt connection 138 that mounts the deactivator 24. The other end of lever 134 is bifurcated and includes spaced legs 140 (FIG. 7) positioned on opposite sides of a downwardly extending projection 142 on the connecting portion 122 of cradle 120. Locking nut-studs 144 of each lever leg 140 engage the projection 142 in order to provide movement of the cradle 120 as the lever is pivoted by movement of deactivator 24 under the impetus of the slide mechanism.

The structure of the control valve 22 and the operation of the control valve unit 10 can best be understood by reference to FIG. 7 which illustrates the unit in a condition with the hydraulic cylinder 12 at rest in its retracted position. Operation of the hydraulic cylinder 12 is controlled by a supply valve 146 whose spool 148 is movable to the left and the right by movement of cradle 120. Hydraulic fluid from a reservior 150 is pressurized by a pump 152 and fed through a conduit 154 to a high pressure supply passage 156 of the valve block 110. Operation of the valve 146 controls the supply of the pressurized fluid from passage 156 to the ports 158a,b which respectively feed the conduits 38a,b to provide extending or retracting movement of the hydraulic cylinder 12. A return passage 160 of valve block 110 feeds hydraulic fluid returned from the cylinder 12 under the control of the supply valve 146 back through a conduit 162 to the reservoir 150. In addition to supply valve 146, control valve 22 includes a pair of pilot pistons 164a,b which cooperate with the directional valve 118 to control movement of the cradle 120 in order to operate the supply valve in a manner which is more fully hereinafter described.

With continuing reference to FIG. 7, valve block 110 includes a bore 166 extending between the opposite sides thereof with the spool 148 of the supply valve 146 received within this bore. Left and right end lands 168 of valve spool 148 have associated seals 170 that provide a sealingly slidable relationship thereof within the bore 166. Adjustable nut studs 172 on the cradle legs 124 engage the spool end lands 168 in order to provide movement and positioning of the spool 148 and consequent control of the supply valve operation. It will be noted that the right end land 168 includes an axial bore which receives a spring 174 whose outer end is engaged by the nut stud 172 on the right cradle leg 124 in order to prevent any backlash during operation. Between its end lands, spool 148 includes central lands 176 that control communication of the supply valve bore 166 with a branch 178 of the high pressure passage 156. Right and left intermediate lands 180 of spool 148 are spaced from the end lands 168 and the central lands 176 by reduced diameter portions of the spool and cooperate therewith to control the flow of hydraulic fluid from cylinder 12 back through branches 182 of the return passage 160.

Movement of the cradle 120 to the left as viewed in FIG. 7 moves the valve spool 148 of the supply valve to the left so that pressurized hydraulic fluid from passage 156 flows through its branch 178 to the port 158a and whence through the conduit 38a to the cylinder bore 28 on the large area side of the piston 30 in order to provide extending movement of the rod 20. As this extending movement proceeds, hydraulic fluid is returned from the cylinder bore 28 on the small area side of the piston 30 to the port 158b through conduit 38b and whence to the left branch 182 of the return passage 160 for flow to the conduit 162 back into the reservoir 150. Similarly, movement of the cradle 120 to the right feeds pressurized hydraulic fluid from the branch 178 of the high pressure passage 156 to the port 158b for flow through the conduit 38b to the hydraulic cylinder bore 28 on the small area side of the piston 30 in order to provide retracting movement of rod 20. During the retracting movement, hydraulic fluid is returned from the cylinder bore 28 on the larger area side of piston 30 through conduit 38a to port 158a for flow through the right branch 182 of the return passage 160 back through the conduit 162 to the reservoir. In both directions of cradle movement, adjustable nut studs 184 on the cradle legs 124 engage the adjacent sides of the valve block 110 in order to limit the extent of such movement in either the left or right direction so as to control the opening movement of the supply valve 146 and hence the speed at which the cylinder 12 is extended or retracted by any selected level of fluid pressure. Movement of the cradle 120 back to the central position shown by operation of the slide mechanism previously described closes the supply valve 146 in order to terminate the movement of the hydraulic cylinder.

Pilot pistons 164a,b illustrated in FIG. 7 initiate movement of the cradle 120 from its central position in order to commence movement of the hydraulic cylinder in either direction. Each pilot piston 164a,b includes a piston end 184a,b having a O-ring seal so as to be sealingly slidable within its associated valve block bore 186a,b. Plunger ends 188a,b of the pilot pistons are slidable within associated block bores and respectively engaged with adjustable nut studs 190 on the cradle legs 124 in order to provide cradle positioning by the pilot piston operation. Connecting rods 192 of the pilot pistons have first ends respectively fixed to the piston ends 184a,b and second ends that slidably extend through central apertures in discs 194 of the plunger ends. A spring 196 of each pilot piston 164a,b extends between its piston end 184a,b and the disc 194 on its plunger end 188a,b to provide a bias that normally moves the pilot piston ends away from each other.

As previously mentioned, directional valve 118 shown in FIG. 7 is operated to initiate driving movement of the hydraulic cylinder 12 in either direction. A housing 198 of this valve is mounted on the valve block 110 in any suitable manner and defines a bore 200 having a valve spool 202 received thereby in a sealingly slidable relationship for movement to the left and the right. A central land 204 of spool 202 is connected to right and left end lands 206 and 208 by reduced diameter portions of the spool. End lands 206 and 208 of spool 202 are respectively engaged by the output plungers of solenoids 210a,b which are actuated to respectively move the spool 202 to the left and the right in order to initiate driving of the hydraulic cylinder 12 in the extending and retracting directions.

A supply passage 212 of the valve block 110 shown in FIG. 7 feeds high pressure fluid from passage 156 to the directional valve 118 and the positioning of the spool 202 of this valve selectively feeds the pressurized fluid to either passage 214a or b in order to pressurize one of the pilot piston bores 186a or b. Hydraulic fluid pressure within the pilot piston bores moves the associated pilot piston end 184a or b out of engagement with a cooperative stop 216a or b and thereby retracts the plunger and piston ends thereof so that the spring 196 of the retracted pilot piston biases the cradle 120 in the associated direction. A drain passage 218 for the directional valve 118 has right and left branch passages 220 that are respectively communicated with the ends of valve bore 200 in order to convey hydraulic fluid from the pilot piston bores to a drain passage 221 that feeds a conduit 222 for dumping into the reservoir 150. It will be noted that drain passage 221 also has branches 221' that communicate with the supply valve bore 166 at grooves 168' in the end lands of the spool therein so as to lessen the fluid pressure at the seals 170 and thereby lengthen the effective seal lifetime.

Operation of the hydraulic control unit 10 during an extending movement of the hydraulic cylinder 12 will now be described in connection with FIG. 7 wherein the control valve 22 is shown with the cylinder at rest subsequent to a driving cycle to the retracted position shown. In this condition, the pilot piston bore 186b is filled with pressurized hydraulic fluid so that pilot piston end 184b is positioned to the right against the bias of its associated spring 196 and the plunger 188b thus biases the cradle 120 to the right. However, the cam 82b of slide mechanism 14 engages the deactivator 24 as shown in FIG. 6 so that pivotal bias of the lever supporting the deactivator biases the right nut stud 144 shown in FIG. 7 toward the left to force the projection 142 of the cradle toward the left and thereby counteract the spring bias by pilot piston 164b. These counteracting forces thus position the cradle 120 in its central position so that supply valve 146 remains closed and the cylinder thus remains retracted.

Driving actuation of the hydraulic cylinder 12 from the retracted position of FIG. 7 toward the extended position is initiated by operation of the solenoid 210a of directional valve 118 in order to move the spool 202 toward the left so that the supply passage 212 is moved out of communication with the passage 214b and into communication with the passage 214a. Just before the high pressure fluid is switched from passage 214b to passage 214a, the movement of the valve spool 202 to the left moves the right end land 206 thereof to the left past the right drain passage 220 so that passage 214a is moved out of communication therewith and the left end land 208 of the spool moves to the left of the left drain passage 220 in order to communicate the passage 214b with the drain passage 218. Thus, spring 196 of the pilot piston 164b is allowed to extend the piston end 184b to the left and thereby force the hydraulic fluid in bore 186b through passage 214b and directional valve 118 to the drain passage 218 and whence to drain passage 221 for flow through conduit 222 to the reservoir. Simultaneously, pressurized fluid from the supply passage 212 is communicated through the directional valve 118 to the passage 214a in order to pressurize the bore 186a and move the piston end 184a therein toward the left as the rod 192 thereof slides through the plunger disc 194 in order to provide a retracted condition of pilot piston 164a which biases its plunger end 188a toward the left. Cradle 120 is thus relieved of the rightward bias by pilot piston 164b but is subjected to a leftward bias by the pilot piston 164a so as to move toward the left and thereby move the spool 148 of the supply valve 146 toward the left. Pressurized hydraulic fluid thus flows from the supply passage 156 through the supply valve 146 and to the port 158a for flow through conduit 38a to the cylinder bore 28 on the large area side of the piston 30 in order to provide piston movement toward the left and extension of rod 20. At the same time, hydraulic fluid in the cylinder bore 28 on the small area side of the piston 30 is forced through the conduit 38b and to the port 158b for flow through the left branch 182 of return passage 160 back through conduit 162 to the reservoir 150. Such extending movement of the cylinder 12 continues until the movement of the slide 16a on which the cam 82a is supported engages this cam with the deactivator 24 and thereby moves the cradle 120 back toward the right against the bias of pilot piston 164a to the central closed position of the supply valve 146 in order to terminate the driving operation of the cylinder.

Driving operation of the hydraulic cylinder 12 in a retracting direction is initiated by operation of the solenoid 210b of directional valve 118 which moves the valve spool 202 from the left toward the right to the position shown in FIG. 7. Pilot piston 164a is then allowed to extend under the bias of its spring 196 and pilot piston 164b is moved to a retracted position against the bias of its spring 196 as the directional valve 118 switches the supply and drain passages communicated with the associated piston end bores 186a and b of the pilot pistons. As such, the cradle 120 is moved toward the right in order to move the spool 148 of supply valve 146 toward the right and allow pressurized hydraulic fluid to flow to port 158b and through conduit 38b to the cylinder bore 28 on the small area side of the piston 30 in order to move the rod 20 to the right in a retracting direction. At the same time, hydraulic fluid is forced from the cylinder bore 28 on the large area side of the piston 30 through the conduit 38a to port 158a for flow through the right branch passage 182 of return passage 160 for passage through the conduit 162 to the reservoir 150. Such retracting movement of the hydraulic cylinder continues until the slide mechanism previously described moves the cradle 120 back toward the left to the central position where the supply valve 146 is closed in order to terminate the driving operation of the cylinder.

Cross line relief valve assembly 114 shown in FIG. 7 includes a pair of high pressure relief valves 222a,b for respectively relieving any excessive pressure that may build up on either side of the piston 30 during driving operation of the cylinder 12. Bores 224a,b provide for fluid communication between the ports 158a and b and respectively receive ends 226 on valve spool housings 228 of valves 222a,b. Each valve spool housing end 226 includes a seal 230 that closes the associated bore 224a,b in a sealed relationship. Springs 232 bias unshown spools within the spool housings 228 to closed positions so as to block fluid communication between the ports 158a and 158b which are respectively communicated with the large and small area sides of the piston 30 within the bore 28 of the hydraulic cylinder 12. An excessive hydraulic pressure on either side of the piston 30 within the cylinder 12, such as would result if the driving of the connecting rod 20 were blocked mechanically in either direction, will result in a pressure buildup at one of the ports 158a and b and will move the unshown spool of either valve 222a or b against the bias of its associated spring 232 in order to provide flow between the ports 158a and 158b in the appropriate direction to relieve the pressure buildup. Thus, the pressurized fluid from supply passage 156 flows through valve 146 and the opened valve 222a or b or the return passage 160 in order to relieve the pressure buildup.

In certain applications, the relatively large inertial load that is driven by the piston connecting rod 20 of the hydraulic cylinder 12 can cause continued piston movement even after the control valve 22 has terminated the supply of pressurized hydraulic fluid for such driving. In such instances, the unequal area relationship on opposite sides of the piston 30 with its single connecting rod 90 can generate either a vacuum or pressure buildup. In the extending direction of movement, to the left as shown in FIG. 7, inertial or other forced movement to the left after closing of the supply valve 146 results in an increased amount of fluid required within the hydraulic cylinder 12 and control valve 22 as well as the associated fluid circuitry. To prevent a vacuum from being generated on the large area side of the piston 30, a conduit 234 is provided extending between the conduit 38a and the return conduit 162 and includes a check valve 236 that opens to permit the flow of the required fluid from the reservoir 150 to the cylinder bore 28 on the large area side of the piston 30. As such, no vacuum is generated as a result of inertial or other forced piston movement subsequent to closing of the supply valve 146 of control valve 22.

Inertial or other forced driving of the piston 30 of hydraulic cylinder 12 in a retracting direction, toward the right as in FIG. 7, after closing of the supply valve 146 of control valve 22 results in an excessive amount of hydraulic fluid in the hydraulic cylinder 12 and the control valve 22 as well as the associated fluid circuitry. To prevent a pressure buildup of the hydraulic fluid during this condition, a conduit 238 is provided extending between the conduit 38a and the return conduit 162 and includes an adjustable pressure relief valve 242 for dumping excessive hydraulic fluid from the large area side of piston 30 to the reservoir 150 through this conduit. As such, pressure buildup is relieved from inertial or other forced movement of piston 30 in a retracting direction subsequent to closing of the supply valve 146 of control valve 22.

While the best mode for carrying out the invention has herein been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.