PILOT OPERATED IMPLEMENT CONTROL SYSTEM

Abstract: A pilot operated control system (10) which eliminates the problems of excessive cost, system complexity, reduced operator visibility, operator fatigue and controllability of fluid operated motors (30, 36, 40, 44) from a single location or a plurality of spaced apart locations. The pilot operated control system (10) has first and second pilot valves (48, 50) connected to a pilot operated control valve (52). The pilot valves (48, 50) are each actuatable between first (56) and second (58) fluid directing positions for shifting the pilot operated control valve (52) between first (86) and second (88) fluid directing positions. Thus, the pilot operated control system (10) provides a less complex, lower cost control system with improved visibility and accurate controllability of the fluid operated motors from a single location or spaced apart locations. The pilot operated control system (10) is particularly useful in controlling a lift mast (14) of a lift truck (16).

Description: Description Pilot Operated Implement Control System Technical Field This invention relates to a pilot operated control system and more particularly to a pilot operated control system having first and second pilot valves and a pilot operated control valve actuatable to first and second fluid directing positions in response to either of the first and second pilot valves being at a respective first and a second pilot position. Background Art Pilot operated control systems have frequently been μsed in controlling fluid powered implements, such as used on material handling and earthmoving equipment and the like. Typically, these pilot operated control systems require a pilot valve and a pilot operated control valve for each implement function. This, however, is expensive, requires a significant amount of space, requires a control lever for actuating each pilot valve and requires a large number of conduits. Subsequently, with the improved reliability of solenoid operated valves, the pilot valve and pilot operated control valves have been replaced in part with solenoid operated selector valves to the extent that a single pilot valve, a single pilot operated control valve and a plurality of solenoid valves now do the job previously requiring a plurality of pilot valves and pilot operated control valves. Since good to excellent modulation of fluid flow delivered to the fluid operated motors is a prerequisite of any pilot operated implement control system and solenoid valves do not offer this capability, it is necessary to provide at r least one pilot valve and an associated matched pilot operated control valve. This has been very successful in reducing the numbers of fluid conduits required since the solenoid operated selector valves may be mounted adjacent their respective implement and thus only a pair of conduits are necessary to pass fluid flow between the control valve and each solenoid operated selector valve. However, controlability of such a system is confusing to the operator since only one pilot valve is provided. Since an electrical switch of some sort is normally provided for controlling each solenoid selector valve, applications where many solenoid valves are utilized the number of switches becomes excessive. The optimum location for these switches, according to user feedback, is on the manual control lever which actuates the pilot valve. Whenever three or more switches are provided on the control lever, the user has difficulty operating the system. This reduces the efficiency in operation of the system and often fatigues the operator. Locating all but two of the switches elsewhere on the vehicle has been tried but offers substantially little improvement. Multiple mechanical lever arrangements, each having two switches thereon, have been provided to actuate a single pilot valve. However, the complexity of the linkage, the cost and the reliability thereof has not been satisfactory. The present invention is directed to overcoming one or more of the problems as set forth above. Disclosure of the Invention In one aspect of the present invention, a pilot operated control system is provided which - ~ ΕE OMPI includes a first pilot valve, a second pilot valve and a pilot operated control valve. The first and second pilot valves are each connected to and in fluid communication with the pilot operated control valve and the first and second pilot valves and the pilot operated control valve are each actuatable between first and second fluid directing positions. The pilot operated control valve is actuatable to the first fluid directing position in response to either of the first and second pilot valves being at the first fluid directing position and actuatable to the second fluid directing position in response to either of the first and second pilot valves being at the second fluid directing position. In another aspect of the present invention, a pilot operated control system for a lift mast assembly having first and second pumps, a pilot operated control valve and an extensible hydraulic jack is provided. The pilot operated control valve is connected to the second pump and the hydraulic jack and actuatable between a first position, at which hydraulic fluid is directed from the second pump to extend the hydraulic jack, and a second position, at which hydraulic flow is directed from said second pump to retract said hydraulic jack. A first pilot valve is connected to the first pump and the pilot operated control valve and actuatable between a first position, at which hydraulic fluid is directed from the first pump to the pilot operated control valve to actuate the pilot operated control valve to the first position thereof, and a second position, at which hydraulic fluid is directed from the first pump to the pilot operated control valve to actuate the pilot operated control valve to the second position thereof. A second pilot valve is connected to the first pump and the pilot operated OMPI control valve and actuatable between a first position, at which hydraulic fluid is directed from the first pump to the pilot operated control valve to actuate the pilot operated control to the first position thereof, and a second position, at which hydraulic fluid is directed from the first pump to the pilot operated control valve to actuate the pilot operated control valve to the second position thereof. A first pressure responsive shuttle valve is connected to and between the first and second pilot valves and the pilot operated control valve. The first shuttle valve is responsive to pressurized hydraulic fluid flow passed by the first and second pilot valves, at the first position thereof, to prevent hydraulic fluid flow from passing between the first and second pilot valves. A second pressure responsive shuttle valve is connected to and between the first and second pilot valves and the pilot operated control valve. The second shuttle valve is responsive to pressurized hydraulic fluid flow passed by the first and second pilot valves, at the second position thereof, to prevent hydraulic fluid flow from passing between the first and second pilot valves. Therefore, the pilot operated control system eliminates the previously required plurality of pilot operated control valves, maintains good to excellent fluid flow modulation by utilizing pilot valves and a pilot operated control valve, permits actuation of a single pilot operated control valve to at least two fluid directing positions by a plurality of pilot valves, eliminates the need for more than two fluid motor conduits, offers excellent operator control by limiting the number of switches for actuating the solenoid valves to two on each control lever, reduces the space required to mount the pilot operated control valve and reduces the overall cost of the system. The pilot operated control system of the subject invention is also useful in applications wherein a single pilot operated control valve is controllably responsive to a pair of pilot valves located at two remote or separate locations to direct fluid flow in at least two directions to actuate a double acting fluid operated motor in two directions. Brief Description of the Drawings Fig. 1 is a diagrammatic side elevational view of an embodiment of the present invention showing a lift truck having a lift mast assembly mounted thereon and the pilot operated control system for controlling the mast assembly connected thereto; Fig. 2 is a diagrammatic front elevational view of Fig. 1 showing the lift mast and associated fluid operated motors of the pilot operated control system in greater detail; and Fig. 3 depicts schematically the pilot operated control system of Fig. 1 in which first and second pilot valves are each connected to actuate a pilot operated control valve between first and second fluid directing positions. Best Mode for Carrying Out the Invention ■ With reference to the drawings, a pilot operated control system 10 for controlling the position of an implement 12, such as a lift mast assembly 14 of a vehicle such as a lift truck 16 is shown. The lift mast assembly 14 has at least a pair of spaced apart uprights 18, a carriage assembly 20 and a container handling assembly 22. The carriage assembly assembly 20 has a guide frame 24 mounted on the spaced apart uprights 18 and a lift jack 26 connected thereto for elevationally moving the guide frame 24 along the uprights 18. The carriage assembly 20 also has a support frame 28 movably mounted on the guide frame 24 and a side shift jack 30 connected to the support frame 28 and the guide frame 24 for shifting the support frame 28 along the guide frame 24, transversely of the uprights 18 and sideways relative to the lift truck 16. The support frame 28 includes an upper frame portion 32 to which the container handling assembly 22 is connected. A plurality of telescopic suspension link members 34 connect the container handling assembly 22 to the upper frame portion 32. This permits a limited amount of movement of the container handling assembly 22 relative to the support frame 28 for positioning the container handling assembly 22 on a container (not shown) to be lifted. A pair of extension jacks 36 are connected to an extensible frame 38 of the container handling assembly 22 to extend and retract the extensible frame to accommodate different sized containers. A pair of slewing cylinders 40 (one shown) are connected to the support frame and the extensible frame 38 of the container handling assembly 22 to slew the container handling assembly 22 relative to the lift truck 16 and the upper frame portion 32 and thereby align the container handling assembly 22 and the extensible frame 38 thereof for engagement with the container to be lifted. A plurality of twist locks 42 are provided, one at each corner of the extensible frame 38, for selectively connecting the container handling assembly to the container to be lifted. Each twist lock 42 is powered by a twist lock jack 44 associated therewith for rotating the twist lock between locking and unlocking positions with respect to the container to be lifted. The lift mast assembly 14 is preferably pivotally mounted at a lower end portion thereof to the lift truck 16. A pair of tilt jacks 46 (one shown) are provided for tilting the lift mast assembly 14 in directions towards and away from the lift truck 16. The pilot operated control system 10 is suitable for controlling all or predetermined ones of the jacks 26,30,36,40,44 heretofore described. The pilot operated control system 10 has first and second pilot valves 48,50, a pilot operated control valve 52 and a plurality of selector valves 54. The number of selector valves provided is in part determined by the number of jacks and implement functions to be controlled. The- pilot valves 48,50 are preferably mounted on the lift truck 16 at a location thereon convenient for operator control, and the pilot operated control valve 52 is located on the lift truck 16 at another location spaced from the pilot valves 48,52. The selector valves 54 are preferably mounted on the implemen (s) to be controlled or at a location in close proximity thereto. In the embodiment shown in Fig. 1, the selector valves are mounted on the support frame 28 of the carriage assembly 20. The importance of the locations of valves 48, 50 and 52 will become apparent during subsequent discussion. Referring to Fig. 3, the first and second pilot valves 48,50 are manually actuatable, 3 position, infinitely variable valves each having a spool 70 shiftable between first and second fluid directing positions 56 and 58 from a neutral position 60. Each of the pilot valves 48,50 have first and second ports 62,64, an inlet port 66 and a reservoir port 68. Each pilot valve spool 70 is normally biased to the neutral position 60 via a pair of centering springs 72. A "gURE , first source of pressurized fluid flow 74, such as a hydraulic pump, is connected to the inlet port 66 of the pilot valves 48 and 50 by conduit 76 which supplies pressurized fluid flow to the pilot valves. A reservoir conduit 78 connects the reservoir port 68 of each pilot valve 48 and 50 to a reservoir 80 and passes fluid flow therebetween. At the neutral position 60 of the spools 70 pressurized fluid flow from the first source is blocked at the pilot valves 48 and 50 and the first and second ports 62 and 64 thereof are in communication with tank. At the first position 56 of spools 70, the pressurized fluid flow delivered from the first source 74 is passed by the spools from the inlet port 66 to the first port 62 and the second port 64 is in communication with the reservoir port 68. Similarly, at the second position 58 of spools 70, pressurized fluid flow delivered from the first source 74 is passed by the spools from the inlet port 66 to the second port 64 and the first port 62 is in communication with the reservoir port 68. It should be noted that the spools 70 of the first and second pilot valves 48 and 50 are independently manually actuatable by a respective control lever 82. Pilot operated control valve 52, which is infinitely variable, has a valve spool 84 which is shiftable between a first fluid directing position 86 and a second fluid directing position 88 from a neutral position 90. The control valve 52 has first and second signal ports 92 and 94, an inlet port 96, first and second control ports 98 and 100 and a reservoir port 102. Valve spool 84 is normally biased to the neutral position 90 via a pair of centering springs 104 and shiftable to the first and second fluid directing positions 86 and 88 in response to fluid pressure being applied to the valve spool 84 at ports 92 and 94. A second source 106 of pressurized fluid flow, such as a hydraulic pump, is connected by a conduit 108 to the inlet port 96 of the pilot operated control valve 52 and the reservoir port 102 is connected to the reservoir 80 via conduit 110. At the neutral position 90 of spool 84, the inlet port 96 and reservoir port 102 are in fluid communication with one another and the first and second control ports 98 and 100 are blocked. At the first position 86 of the valve spool 84, fluid is passed by valve spool 84 from the second source 106 to the first control port 98 and the reservoir port 102 is in fluid communication with the second control port 100. At the second position 88 of the valve spool 84, the inlet port 96 is in fluid communication with the second control port 100 and the first control port 98 is in fluid communication with the reservoir port 102. A first shuttle valve 112 having a pair of. inlet passages 114 and 116 and an outlet passage 118, is provided to tee the first port 62 of the first and second pilot valves 48 and 50 to the first signal port 92 of the control valve 52. A second shuttle valve 120 having a pair of inlet passages 122 and 124 and an outlet passage 126 is provided to tee the second port 64 of the first and second pilot valves 48 and 50 to the second signal port 94 of the control valve 52. In addition, the first shuttle valve 112 has a ball check 127 operatively associated with the pair of inlet passages 114 and 116 and a pair of seats 131 associated therewith and the second shuttle valve 120 has a ball check 129 operatively associated with the pair of inlet passages 122 and 124 and a pair of seats 133 associated therewith to prevent fluid flow from passing between the first port 62 of the first and second pilot valves 48,50 and the second port 64 of the first and second pilot valves 48 and 50. It should be noted that the ball checks 127,129 are pressure responsive. In the event that both inlet passages 114, 116, 122, and 124 of either shuttle valve are pressurized the shuttle valve will only pass the fluid at the highest pressure to the respective outlet passage 118,126. The first port 62 of the first pilot valve 48 is connected to one inlet passage 114 of the first shuttle valve 112 via conduit 128, and .the first port 62 of the second pilot valve 50 is connected to the other inlet passage 116 of the first shuttle valve 112 via conduit 130. The outlet passage 118 of the first shuttle valve.112 is connected to the first signal port 92 of the pilot operated control valve 52 via conduit 132. Similarly, the second port 62 of the first pilot valve 48 is connected to one inlet passage 122 of the second shuttle valve 120 via conduit 134 and the second port 64 of the second pilot valve 50 is connected to the other inlet passage 124 of the second shuttle valve 120 via conduit 136. The outlet passage 126 of the second shuttle valve 120 is connected to he second signal port 94 of control valves 52 via conduit 138. The plurality of selector valves 54 previously mentioned are connected in parallel to the first and second control ports 98 and 100 of the pilot operated control valve 52 via conduits 140 and 142 respectively. Since the selector valves are mounted close to the implement to be controlled and only a single control valve is used to modulate fluid flow only conduits 140 and 142 are required. Each selector valve provided is a two position solenoid operated valve having a fluid flow passing position 144 and a fluid flow blocking position 146 and a shiftable therebetween via a solenoid 148. In the embodiment shown, the plurality of selector valves 54 includes; a side shift selector valve 150, a twist lock selector valve 152, a spread selector valve 154 and a slewing selector valve 156. Each of these selector valves 150, 152, 154, and 156 are connected to their respective hydraulic jacks 30,44,36,40. A pair of electrical switches 158 are connected to each control lever 82. The switches 158 are connected to a source 160 of electric power and a respective one of the solenoids 148. Therefore, each selector valve is independently selected to pass fluid delivered from the control valve 52 to its respective hydraulic jack. It should be noted that the selector valves do not modulate fluid flow or determine the direction of fluid flow. This is determined by the condition established at the control valve 52. Industrial Applicability With reference to the drawings, the operator of the lift truck has control of the implements 12 mounted thereon by actuating a selected one of the first and second pilot valves 48 and 50 and a selected one of the plurality of selector valves 54 by simply actuating the proper one of the switches 158 and the control lever 82 upon which the proper switche is mounted. Thus, for given implement function to be controlled, only that lever 82 upon which the proper switch to be actuated is mounted is utilized. Thus, operator confusion, excessive operator motions and the like are eliminated with this system 10. Due to the capability each of the pilot valves 48 and 50 being able to controllably shift the single pilot operated control valve 52 between the first and second fluid directing positions, the pilot operated control system 10 is applicable for use in applications wherein the implement 12 is controlled from two or more separate spaced apart locations on the vehicle 16. In operation, to power a selected implement, for example, to side shift the carriage support frame 28 the operator must actuate the side shift selector valve 150 to the fluid flow passing position 144 thereof. This is accomplished by actuating the proper one of the switches 158 on the control lever 82 of the second pilot valve 50 to pass electrical current from the electrical energy source 160 to the solenoid 148 of side shift selector valve 150. Upon completion of this operation, the jack 30 now connected is to receive pressurized fluid flow from directed by control valve 52 from the second source 106. In order to pass fluid flow from the second source 106, the operator must determine which direction to shift the second pilot valve 50. To extend jack 30, the operator must shift the pilot valve spool 70 toward the first position 56 and to retract jack 30 the spool 70 should be shifted to the second position 58. Assuming the operator requires extension of side shift jack 30, he will progressively shift the second pilot valve spool 70 toward the second position 58. Due to the fine modulating characteristics of the pilot valves 48 and 50 and the pilot operated control valve 52, the speed of actuation of the jack 30 is proportional to the amount of movement of the second pilot valve 50 spool 70. Pressurized fluid from source 74 at the inlet port 66 of the second pilot valve 50 is directed by the valve spool 70 at a selected modulated pressure and flow level to the first port 62. Conduit 136 will carry this fluid flow to the inlet passage 116 of the first shuttle valve 112. The ball check 127 will respond to this pressurized fluid flow by shifting toward inlet passage 114 thereof and against adjacent seat 131. This check action will block passage 116 from passage 114 and open inlet passage 116 to outlet passage 118. The fluid will then pass through the first shuttle valve 112 and exit outlet passage 118. Conduit 132 will deliver this fluid flow to the first signal port 92 of control valve 52. The valve spools 84 of the control valve 52 will respond to the pressure of this fluid acting thereon and shift toward the first fluid directing position 86. The exact resulting position of the spool 84 is a function of the pressure of the fluid at the signal port 92 and the force of springs 104. Subsequently, pressurized fluid flow will be directed from pump 106 through conduit 108 through inlet port 96 and past the first control port 98. Since the control valve 52 is of the infinitely variable type, the fluid exiting control port 98 will be passed at a flow rate established by the position of the spool 84. This fluid will be passed by conduit 140 to selector valve 150 and by selector valve to jack 30 resulting in extension thereof. The exhaust fluid from jack 30 will D< ≥ returned to the reservoir 80 via selector valve 150, conduit 142 and control valve 52. To actuate the other jacks 44,36,40, to extend or retract a similar procedure is followed by the vehicle operator. Thus, the pilot operated control system heretofore described provides excellent controllability of the jacks and thus the implement connected thereto, reduces operator fatigue, is simple in operation, low in cost, reduces the number of conduits required and permits a single pilot operated control valve to be actuated to two different fluid directing positions from either one of a first and second pilot valve. Other aspects, objects and advantages of the invention can be obtained from a study of the drawings, the disclosure and appended claims. O PI

Claims: Clai s 1. A pilot operated control system (10) comprising: a first source of pressurized fluid flow (74) ; a first pilot valve (48) having a first and a second port (62,64) and being connected to said first source of pressurized fluid flow (74) , said pilot valve having first and second positions (56,58) and being actuatable between the first position (56) , at which pressurized fluid flow is passed from said first source (74) to said first port (62) , and the second position (58) at which pressurized fluid flow is passed from said first source (74) to said second port (64) ; a second pilot valve (50) having a first and second port (62,64) and being connected to said first source of pressurized fluid flow (74) , said second pilot valve having first and second positions (56,58) and being actuatable between the first position (56) , at which pressurized fluid flow is passed from said first source (74) to said first port (62) , and the second position (58) , at which pressurized fluid flow is passed from said first source (74) to said second port (64) ; and a pilot operated control valve (52) having first and second signal ports (92,94) and first and second fluid directing positions (86,88) and being actuable between said first and the second fluid directing positions (86,88) , said first signal port (98) being connected to and in fluid communication with the first port (62) of said first and second pilot valves (48,50) and said second signal port (94) being connected to and in fluid communication with the second port (64) of said first and second pilot valves (48,50) , said pilot operated control valve (52) being 5 JRE T OMPI actuatable to said first fluid directing position (86) in response to either one of said first and second pilot valves (48,50) being at said first position (56) and actuatable to said second fluid directing position (88) in response to either one of said first and second pilot valves (48,50) being at said second position (58). 2. The pilot operated control system (10) as set forth in claim 1 wherein said pilot operated control valve (52) includes a spool (84) , said spool (84) being fluid pressure responsive and shiftable to said first position (86) in response to fluid pressure being at said first signal port (92) and shiftable to said second position (88) in response to fluid pressure being at said second signal port (94) . 3. The pilot operated control system (10) as set forth in claim 1 including; a first shuttle valve (112) connected between and in fluid communication with the first port (62) of said first and second pilot valves (48,50) and the first pilot port (92) of said pilot operated control valve (52) ; a second shuttle valve (120) connected between and in fluid communication with the second port (64) of said first and second pilot valves (48,50) and the second pilot port (94) of said pilot operated control valve (52) ; said first shuttle valve (112) being actuatable to pass fluid flow between the first port (62) of one of said first and second pilot valves (48,50) and the first signal port (92) of said pilot operated control valve (52) and prevent pressurized fluid flow from passing between the first port (62) of the other one of said first and second pilot valves (48,50) and the first signal port (92) of the pilot operated control valve (52) ; and said second shuttle valve (120) being actuatable to pass fluid flow between the second port (64) of one of said first and second pilot valves (48,50) and the second signal port (94) of the pilot operated control valve (52) and prevent pressurized fluid flow from passing between the second port (64) of the other of said first and second pilot valves (48,50) and the second signal port (94) of the pilot operated control valve (52) . 4. The pilot operated control system (10) as set forth in claim 2 wherein the first shuttle valve (112) is actuatable in response to the pressurized fluid flow delivered from the first port (62) of either of the first and second pilot valves (48,50) to block fluid flow between said first ports (62) , and the second shuttle valve (120) is actuatable in response to the pressurized fluid flow delivered from the second port (64) of either of the first and second pilot valves (48,50) to block fluid flow between said second ports (64) . 5. The pilot operated control system (10) as set forth in claim 1 including; first and second shuttle valves (112,120) each having a pair of inlet passages (114,116,122,124), an outlet passage (118,126) and a check (127,129) operatively associated with each of said pair of inlet passages (114,116,122,124); ^tJREl O PΓ said inlet passages (114,116) of the first shuttle valve (112) being connected to and in fluid communication with a respective one of the first ports (62) of the first and second pilot valves (48,50) and the outlet passage (118) of the first shuttle valve (112) being connected to and in fluid communication with the first pilot port (92) of the control valve (52) ; said inlet passages (122,124) of the second shuttle valve (120) being connected to and in fluid communication with a respective one of the second ports (64) of the first and second pilot valves (48,50), and the outlet passage (126) of the second shuttle valve (120) being connected to and in fluid communication with the second pilot port (94) of the control valve (52); said check (127) of the first shuttle valve (112) being actuatable, in response to fluid pressure of the highest magnitude at one of the pair of inlet passages (114,116) of said first shuttle valve (112) acting thereon, to pass fluid flow at the highest pressure from said one inlet passage (114,116) of the first shuttle valve (112) to said outlet passage (118) of the first shuttle valve (112) , block fluid flow from passing between said inlet passages (114,116) of the first shuttle valve (112) and block fluid flow from passing between the other inlet passage (114,116) and the outlet passage (118) of said first shuttle valve (112) ; and said check (129) of the second shuttle valve (120) being actuatable, in response to fluid pressure of the highest magnitude at one of the pair of inlet passages (122,124) of said second shuttle valve (120) acting thereon, to pass fluid flow at the highest pressure from said one inlet passage (122,124) of the second shuttle valve (120) to said outlet passage (126) of the second shuttle valve (120) , block fluid flow from passing between said inlet passages (122,124) of the second shuttle valve (120) and block fluid flow from passing between the other inlet passage (122,124) and outlet passage (126) of the second shuttle valve (120) . 6. The pilot operated control system (10) as set forth in claim 1, including; a reservoir (80) connected to said first and second pilot valves (48,50), said first and second pilot valves (48,50) each having a neutral position (60) and being actuatable between said neutral position (60) and a selected one of the first and second positions (56,58), said first and second ports (62,64) of the first pilot valve (48) being in fluid communication with said reservoir (80) at the neutral position (60) of said first valve (48) and said first and second ports (62,64) of the second pilot valve (50) being in fluid communication with the reservoir (80) at the neutral position (60) of said second pilot valve (50). 7. The pilot operated control system (10) as set forth in claim 6 wherein pressurized fluid flow delivered from said first source (74) to the first and second ports (62,64) of said first pilot valve (48) is blocked at the neutral position (60) of the first valve (48) and pressurized fluid flow from the first source (74) to the first and second ports (62,64) of said second pilot valve (50) is blocked at the neutral position (60) of said second pilot valve (50) . 8. The pilot operated control system (10) as set forth in claim 2, including; a second source of pressurized fluid flow (106) , said pilot operated control valve (52) having a first and second control port (98,100) and an inlet port (96) , said second source (106) being connected to and in fluid communication with the inlet port (96) and said inlet port (96) being in fluid communication with the first control port (98) at the first fluid directing position (86) of said pilot operated control valve (52) and said inlet port (96) being in fluid communication with the second control port (100) at the second fluid directing position (88) of said pilot operated control valve (52) . 9. The pilot operated control system (10) as set forth in claim 8 including; a reservoir (80) connected to said pilot operated control valve (52) , said pilot operated control valve (52) having a neutral position (90) and being actuatable between the neutral position (90) and the first and second fluid directing positions (86,88) , said second source (106) being connected to the reservoir (80) at the neutral position (90) of said pilot operated control valve (52) . 10. The pilot operated control system (10) as set forth in claim 1, including; a plurality of selector valves (54) and a plurality of fluid operated motors (30,36,40,44), said selector valves (54) each being connected to and in fluid communication with said pilot operated control valve (52) and a respective one of said plurality of fluid operated motors (30,36,44,40), said selector valves (54) each being actuatable between a first position (146) at which pressurized fluid flow directed from said pilot operated control valve (52) to said respective fluid operated motor (30,36,40,44) is blocked and a second position (144) at which pressurized fluid flow from said pilot operated control valve (52) is passed to said respective fluid operated motor (30,36,40,44), and means (158,148,160) for selectively shifting each of said selector valves (54) between said first and second positions (146,144) . 11. The pilot operated control system (10) as set forth in claim 10 wherein said first and second pilot valves (48,50) each have a lever (82) connected thereto, said levers (82) being manually movable to actuate said pilot valves (48,50) between the first and second positions (52,58), and said means (158,148) for selectively shifting includes, a plurality of electrical switches (158) and a plurality of solenoids (148) , said switches (158) being mounted on said levers (82) and said solenoids (148) being connected to said selector valves (54) , said switches (158) being connected to said solenoids (148) and selectively actuatable to actuate selected ones of said solenoids (148) to shift selected ones of said selector valves (54) . 12. The pilot operated control system (10) as set forth in claim 10 wherein said fluid operated motors (30,36,40,44) are hydraulic jacks. 13. The pilot operated control system (10) as set forth in claim 11 wherein two electrical switches (158) are mounted on each control lever (82) . OMPI 14. In a pilot operated control system (10) for a lift mast assembly (12) having first and second pumps (74,106) , a pilot operated control valve (52) and an extensible hydraulic jack (30) , said pilot operated control valve (52) being connected to said second pump (106) and said hydraulic jack (30) and actuatable between a first position (86) at which hydraulic fluid is directed from said second pump (106) to extend said hydraulic jack (30) and a second position (88) at which hydraulic flow is directed from said second pump (106) to retract said hydraulic jack (30) ; the improvement comprising: a first pilot valve (48) connected to said first pump (74) and said pilot operated control valve (52) and actuatable between a first position (56) , at which hydraulic fluid is directed from said first pump (74) to said pilot operated control valve (52) to actuate said pilot operated control valve (52) to the first position (86) and. a second position (58) , at which hydraulic fluid is directed from said first pump (74) to said pilot operated control valve (52) to actuate said pilot operated control valve (52) to the second position (88) ; a second pilot valve (50) connected to said first pump (74) and said pilot operated control valve (52) and actuatable between first position (56) , at which hydraulic fluid is directed from said first pump (74) to said pilot operated control valve (52) to actuate said pilot operated control valve (52) to the first position (86) , and a second position (52) , at which hydraulic fluid is directed from aid first pump (74) to said pilot operated control valve (52) to actuate said pilot operated control valve (52) to the second position (88) ; ξfRE i OMPI a first pressure responsive shuttle valve (112) connected to said first and second pilot valves (48,50) and said pilot operated control valve (52) , said first shuttle valve (112) being responsive to pressurized hydraulic fluid flow passed by the first and second pilot valves (48,50) , at the first position (56) thereof, to prevent hydraulic fluid flow from passing between said first and second pilot valves (48,50) ; and a second pressure responsive shuttle valve (120) connected to said first and second pilot valves (48,50) and said pilot operated control valve (52) , said second shuttle valve (120) being responsive to pressurized hydraulic fluid flow passed by the first and second pilot valves (48,50) at the second position (58) thereof, to prevent hydraulic fluid flow from passing between said first and second pilot valves (48,50) . 15. In a lift truck (16) having a lift mast assembly (14) mounted thereon and a plurality of hydraulic jacks (30,36,40,44) operatively connected to said lift mast assembly (14) , a plurality of solenoid operated selector valves (54) connected to said lift mast assembly (14) , said selector valves (54) each being in fluid communication with a respective one of said hydraulic jacks (30,36,40,44), a pilot operated control valve (52) mounted on said lift truck (16) and a pair of conduits (140,142) connecting said pilot operated control valve (52) to said selector valves (54) , the improvement comprising: first and second pilot valves (48,50) each having a manual control lever (82) and first and second fluid directing positions (56,58) , said pilot valves (48,50) each being independently actuatable by said respective control lever (82) between said first and second fluid directing positions (56,58) , said first and second pilot valves (48,50) each being in fluid communication with said pilot operated control valve (52) , said pilot operated control valve (52) having a valve spool (70) , said valve spool (70) being fluid pressure responsive and shiftable between first and second fluid directing positions (86,88) at which pressurized fluid flow is passed by said pair of conduits (140,142) between said pilot operated control valve (52) and said selector valves (54) , said valve spool (70) being shiftable to said first fluid directing position (86) in response to pressurized fluid flow, delivered from one of the first and second pilot valves (48,50) at the first position (56) thereof, acting thereon, and shiftable to said second fluid directing position (88) in response to pressurized fluid flow, delivered from one of the first and second pilot valves (48,50) at the second position (58) thereof, acting thereon; a plurality of electrical switches (158) each being connected to actuate a respective solenoid operated selector valve (54) and mounted on said control lever (82) , said selector valves (54) each being actuatable by a respective one of said switches (158) between a fluid blocking and fluid passing position (146,144) . 16. The lift truck (16) as set forth in claim 15 wherein said first and second pilot valves (48,50) are mounted on said lift truck (16) at spaced apart locations thereon. 17. The lift truck (16) as set forth in claim 15 wherein two electrical switches (158) are mounted on each control lever (82) . O PI V/IIPPOO .N lO

Inventors: FIELD JESSE L JR, FIELD, JESSE, L., JR.
Applicants: TOWMOTOR CORP, TOWMOTOR CORPORATION
Application year: 1983
Main classification: F15B11
IPC codes: B66F9, E02F9, F15B13