LOCK VALVE

Abstract: A lock valve (20) for preventing fluid swapping between separate fluid ram ends (18a, 19a and 18b, 19b) which are fluidly connected in parallel. The lock valve (20) includes a first control port (30) which is fluidly joined by a first conduit (38) to a first (34) and a second (36) distribution ports which are fluidly connected in parallel. A second control port (32) is fluidly connected to a third (40) and a fourth (42) distribution port through a second conduit (44). A first (54) and a second (56) pilot operated check valve regulates the fluid communication between the first (34) and second (36) distribution ports. The check valves (54, 56) permit fluid flow from the first control port (30) to the first (34) and second (36) distribution ports, but obstruct fluid flow in the opposite direction unless actuated to a fluid transmitting mode by a pilot signal communicated thereto from the second conduit (44). A relief valve (60) provides fluid flow from the check valves (54, 56) to the first control port (30) only when both the check valves (54, 56) have opened. A third pilot operated check valve (62) regulates fluid communication through the second conduit (44) and is actuated by fluid passing from the second control port (32) to the third (40) and fourth (42) distribution ports and by a pilot signal communicated thereto from the first fluid conduit (38). A bypass check valve (66) fluidly connected in parallel relationship with the relief valve (60) provides fluid flow from the first control port (30) to the first (34) and second (36) distribution ports. Movement of the hydraulic rams (18, 19) is thereby precluded unless high pressure fluid is transmitted to the first or the second control port.

Description: • -i- Description Lock Valve Technical Field This invention relates to zero leakage lock valves and, more particularly, to lock valves for preventing fluid swapping between multiple apparatus connected in parallel flow relation therewith. Background Art In some applications requiring hydraulic tilt power it has been found desirable to have two or more hydraulic cylinders rather than a single, large hydraulic cylinder. Multiple cylinders connected at separated points on a load support device provides greater rigidity and more stable .load carrying capability than using a single hydraulic cylinder. In • applications such as lift trucks where loads of substantial size must be precisely maneuvered and positioned by the lift truck such load carrying rigidity has been found to be a desirable characteristic. A problem encountered, however, with using multiple (hereafter two shall be described) cylinders connected in a parallel flow relationship occurs when an external force acts on one of the cylinders. As a result of such force application, fluid from the cylinder portion which is diminished in size by the external force is transmitted into the corresponding, interconnected portion on the other hydraulic cylinder. That response is, of course, undesirable because the load support device carried by the cylinders can tilt and twist and cause bending of the cylinders so as to adversely affect the performance of the lift truck. One technique used for preventing fluid swapping between interconnected hydraulic cylinders is to interconnect them in a cross connected series flow relationship such that only two fluid conduits extend between the hydraulic cylinders, the pump, and reservoir. Opposite ends of the hydraulic cylinders are typically interconnected to form a series relationship such that fluid supplied by the pump to a first hydraulic cylinder's rod end causes the rod to move and expel fluid from that cylinder's head end into an interconnected rod end of a second interconnected hydraulic cylinder. Fluid transmitted to the rod end of the second hydraulic cylinder causes displacement of the rod and diminishes the size of the second cylinder's head end so as to expel fluid therefrom to the fluid reservoir. Examples of such serially interconnected hydraulic cylinders a 1 the systems with which they are associated are illustrated in U.S. Patent 3,184,920 which issued May 25, 1965 and U.S. Patent 4,086,843 which issued May 2, 1978. While such systems have performed admirably, greater pump pressures are required than where the cooperating hydraulic cylinders are interconnected in parallel flow relationship such that the head ends are interconnected and the rod ends are interconnected. U.S. Patent 4,114,516 which issued September 19, 1978, illustrates a directional control valve which insures fluid transmission to the desired cylinder end and which modulates the fluid flow rate from the other cylinder end. Such directional control valve will not, however, prevent fluid swapping between corresponding ends of hydraulic cylinders fluidly connected in parallel. The present invention is directed toward solving one or more of the problems encountered by the prior art. Disclosure of the Invention In one aspect of the present invention a lock valve is provided which has a first and a second distribution port each connected in series flow relationship through a first conduit with a first control port and a third and a fourth distribution port each connected in series flow relationship through a second conduit with a second control port. The first and second distribution ports are connected in parallel flow relationship and the third and fourth distribution ports are connected in parallel flow relationship wherein fluid flow between the parallel flow connected distribution ports is obstructed and fluid swapping therebetween is prevented. The lock valve generally includes a flow regulating apparatus associated with each of the first and second distribution ports which * transmit flow therethrough in one direction and obstruct flow in the other direction except when actuated to a flow transmission mode by a signal • . generated in the second conduit. Another flow regulating device obstructs flow in the other direction until all flow regulating apparatus are in the flow transmission mode. A further flow regulating apparatus permits fluid transmission through the second conduit in one direction and obstructs flow in the other direction except when actuated to a flow transmission mode by a signal generated in the first conduit. The present invention lock valve is particularly useful when the distribution ports associated with one of the control ports are fluidly interconnected with cooperating ends of two hydraulic cylinders. Of course, the remaining distribution ports which are associated with the remaining control port are fluidly connected to the remaining ends of the hydraulic cylinders, respectively. Brief Description of the Drawing The sole figure is a schematic view of the present invention lock valve incorporated into a hydraulic system. Best Mode for Carrying Out the Invention The present invention is concerned primarily with ensuring fluid segreation between any number of fluid motors such as hydraulic cylinders or rams fluidly connected in parallel flow relationship. Such fluid segregation prevents fluid swapping between the fluid rams to advantageously preclude relative movement therebetween. In the description which follows the invention is shown embodied in a hydraulic system 10 utilizing two hydraulic cylinders. It is to be understood, however, that the invention may be extended to cover three or more hydraulic cylinders. Referring now to the drawing detail the hydraulic system 10 includes a source of pressurized fluid such as pump 12, a reservoir 14, a control valve 16, a first hydraulic cylinder 18, a second hydraulic cylinder 19 and a lock valve 20. Pressurized hydraulic fluid is supplied to the control valve 16 from the pump 12 through a transmission line 22 while a drain line 24 transmits hydraulic fluid from the control valve 16 to the reservoir 14. A pair of actuation lines 26 and 28 provide fluid communication between the control valve 16 and the lock valve 20 through a first and a second control port 30 and 32, respectively. The control ports 30 and 32 constitute portions of the lock valve 20 and are joined to the actuation lines 26 and 28, respectively. The lock valve 20 further includes a first and a second distribution port 34 and 36, respectively, which are connected in parallel flow relationship through a conduit 38 to the first control port 30. A third and a fourth distribution port 40 and 42, respectively, constitute a portion of the lock valve 20 and are, likewise, fluidly connected in parallel flow relationship through a second conduit 44 to the second control port 32. The hydraulic cylinder 18 has a first or rod end 18a and a second or head end 18b while the hydraulic cylinder 19 has a third or rod end 19a and a fourth or head end 19b. The first and third cylinder ends 18a and 19a, respectively, are connected to the distribution ports 34 and 36 by a pair of cylinder lines 46 and 48 while the second and fourth cylinder ends 18b and 19b, respectively, are joined to the distribution ports 40 and 42 by another pair of cylinder lines 50 and 52, respectively. The lock valve's fluid conduit 38 includes a bifurcated portion which constitutes.distribution conduits 38a and 38b which respectively extend to the distribution ports 34 and 36. First means for regulating fluid communication between the distribution ports 34 and 36 preferably constitute a first and a second pilot operated check valve 54 and 56, respectively, which are operable in a fluid obstructing and a fluid transmitting mode. The check valves 54 and 56 are connected into distribution conduits 38a and 38b, respectively. Means for providing fluid communication between the second conduit 44 and the pilot actuation system (not illustrated) of the check valves 54 and 56 constitutes a pilot line 58. A relief valve 60, which is operable in a fluid obstructing and fluid transmitting mode, regulates fluid communication through the first conduit 38 between both of the pilot operated check valves 54 and 56 and the control port 30 by permitting fluid flow only in a direction toward the control port 30. The relief valve 60 transmits fluid flow only when the fluid pressure between the pilot operated check valves 54,56 and the relief valve 60 is greater than a predetermined value which is sufficient to ensure that the check valves 54 and 56 are both in their fluid transmission mode. Preferably, the pressure required to actuate the relief valve 60 to its transmitting mode is greater than such predetermined pressure by a selected difference to account for cases where one check valve (54 or 56) is open and the other (54 or 56) is closed. Such case can occur as a result of the pilot opening pressures of the check valves 54 and 56 differing from their ideal (identical) design opening pressure due to practical tolerances in manufacturing and materials. Means for regulating fluid communication through the second conduit 44 referably constitutes a third pilot operated check valve 62 which is actuatable from a closed, flow obstructing mode to an open, fluid transmitting mode by fluid flowing from the control port 32 to the distribution ports 40 and 42 or by pilot pressure transmitted through a pilot line 64 from the first conduit 38 to the pilot mechanism (not illustrated) of the pilot operated check valve 62. A bypass check valve 66 arranged in parallel flow relationship with the relief valve 60 is actuatable to its fluid transmitting mode by a positive pressure differential from the control port 30 to the check valves 54 and 56. Suitable actuation of the control valve 16 (either left or right of the position illustrated) enables transmission of hydraulic fluid to the appropriate cylinder ends to either extend or retract the hydraulic cylinders 18 and 19. Control valves, by their nature, are usually spool type valves or other mechanisms which cannot seal to zero flow and typically per it a small, albeit significant, fluid leakage therethrough. Fluid leakage of any amount is sometimes unacceptable such as in applications where loads must be supported at a selected attitude for an extended time. The lock valve 20 preferably utilizes components such as the check valves 54,56,62, and 66 which seal to substantially zero flow and thus are customarily used in combination with control valves such as control valve 16. Actual operation of the hereinbefore described hydraulic system 10 will be provided in the following section. Industrial Applicability If extension of the hydraulic cylinders or rams 18 and 19 is desired, the control valve 16 is shifted to the left whereby pressurized fluid is transmitted from the fluid transmission line 22, through the fluid actuation line 28, and to the control port 32. Fluid entering the control port 32 passes through the conduit 44 and actuates the pilot operated check valve 62 to its fluid transmitting mode. Fluid passing through the pilot operated check valve 62 divides into parallel flow paths and exits the lock valve 20 through the distribution ports 40 and 42 from whence it enters the hydraulic cylinder ends 18b and 19b so as to bias the cylinders 18 and 19 to their extended positions. Fluid pressure along the fluid flow path previously described subsequently increases since the hydraulic fluid resident in the cylinder ends 18a and 19a cannot be expelled due to the pilot operated check valves 54 and 56 operating in their fluid flow obstructing mode. The increasing fluid pressure is transmitted through the pilot line 58 to the pilot mechanisms of pilot operated check valves 54 and 5-6 and subsequently actuate them to their fluid transmitting mode. The relief valve 60 remains in the fluid obstructing mode until the pressure in the conduit 38 exceeds the pressure (by a predetermined differential) necessary to pilotably open the check valves 54 and 56 so as to ensure the open, fluid transmitting mode for both check valves 54 and 56 prior to actually permitting any fluid flow to the control port 30. Such predetermined pressure differential is necessary to account for pilot opening pressure tolerances and the typically unsynchronized opening of the check valves 54 and 56 resulting therefrom. Subsequent to the opening of the relief valve 60, hydraulic fluid previously resident in the cylinder ends 18a and 19a is serially transmitted through the relief valve 60, through the control port 30, through the actuation line 26, and through the drain line 24 to the fluid reservoir 14. If it is desired to retract the hydraulic cylinders 18 and 19, the control valve 16 is shifted to the right whereupon hydraulic fluid from the transmission line 22 is transmitted through the actuation line 26 to the control port 30. Since the relief valve 60 will transmit flow only toward the control port 30, the pressurized fluid opens the bypass check valve 66 and passes around the relief valve 60 in parallel flow relationship therewith. Such transmitted hydraulic fluid actuates the pilot operated check valves 54 and 56 to their fluid transmitting mode and permits fluid communication therefrom to the cylinder ends 18a and 19a. The fluid pressure in the hydraulic circuit immediately hereinbefore described increases in magnitude since the hydraulic fluid in the cylinder ends 18b and 19b cannot escape therefrom due to encountering the pilot operated check valve 62. The pressure in the fluid conduit 38 is transmitted through the pilot line 64 to the pilot operated check valve 62 and actuates the same to its fluid transmitting mode when the pressure in the fluid conduit 38 exceeds a predetermined minimum. Subsequent to the opening of the pilot operated check valve 62, the hydraulic cylinders 18 and 19 retract and fluid is expelled from the cylinder ends 18b and 19b through the cylinder lines 50 and 52, through the pilot operated check valve 62, through the actuation line 28, through the control valve 16, and through the drain line 24 to the reservoir 14. When the desired degree of cylinder retraction or extension has been achieved, the control valve 16 is moved to a closed position as illustrated wherein fluid supplied by the pump 12 through the transmission line 22 is shunted back to the reservoir 14 through the drain line 24. The position of the hydraulic cylinders 18 and 19 is then locked by the lock valve 20 and fluid swapping between the cylinders 18 and 19 is prevented. In analyzing fluid swapping between the cylinders first consider an application of a force on the cylinder 18 tending to retract it. Such transmitted force will increase the pressure in the cylinder lines 50 and 52 and tend to extend the hydraulic cylinder 19. However, for the hydraulic cylinder 19 to extend, fluid must flow out of the cylinder end 19a. Although pressure in the cylinder line 48 will increase, fluid flow therethrough is obstructed by the pilot operated check valve 56 which is in a fluid flow obstructing mode. Thus, the cylinder 18 resists retraction and the cylinder 19 resists extension. Of course the same result obtains by applying a retractive force on the cylinder 19 since fluid flow from cylinder end 19b is obstructed by the pilot operated check valve 62 and fluid flow from the cylinder end 18a is obstructed by the pilot operated check valve 54 being in the flow obstructing mode. Secondly consider an extension force on the cylinder 18. Fluid within the cylinder end 18a cannot be transmitted through the distribution port 34 since the pilot operated check valve 54 is in its flow obstructing mode. The same results obtain when an extending force is applied to the cylinder 19 since fluid in the cylinder end 19a cannot flow due to the pilot operated check valve 56 being in its flow obstructing mode. While several conduits and lines have been described hereinbefore, it is to be understood that the same could be eliminated or replaced by suitable passages in a single body for purposes of the present invention and are only included to illustrate a practical arrangement of components rather than one in which the components are directly connected to each other. It will now be apparent that a lock valve has been provided which prevents fluid swapping between hydraulic cylinders fluidly connected in parallel when an external force is unevenly applied to the cylinders. Preventing- such fluid swapping between the hydraulic cylinders 18 and 19 to maintain a constant relationship between the hydraulic cylinders is often necessary to hold a load supported thereby in a fixed position. In the case of a lift truck using the lock valve 20 with hydraulic cylinders for tilting its mast, forces applied unevenly to the hydraulic cylinders are distributed among the cylinders to maintain the born load at a constant tilt attitude, prevent relative displacement of the hydraulic tilt cylinders, and preclude tilt cylinder binding resulting therefrom.

Claims: Claims 1. A lock valve (20) comprising: a first (30) and a second (32) fluid control port; a first (34) and a second (36) fluid distribution port; a first fluid transmission conduit (38) providing fluid communication between said first control port (30) , and said first (34) and second distribution port (36); a third (40) and a fourth (42) fluid distribution port; a second fluid transmission conduit (44) providing fluid communication between said second control port (32) and said third (40) and fourth (42) distribution ports; first means (54,56) for regulating fluid communication through said first conduit (38) between said first (34) and second (36) fluid distribution ports, said regulating means (54,56) being actuatable between a fluid transmitting mode and a fluid obstructing mode; second means (60) for regulating fluid communication through said first conduit (38) between both said first (34) and second (36) fluid distribution ports and said first control port (30) when said first fluid communication regulating means (54,56) is in said fluid transmitting mode; means (58) for actuating said first regulating means to said fluid transmitting mode in response to fluid pressure in said second conduit (44) greater than a first predetermined minimum; O FI third means (62) for regulating fluid communication through said second conduit (44) among said third (40) and fourth (42) distribution ports and said second control port (32) , said third fluid regulating means (62) being actuatable between a flow transmitting mode and an obstructing mode; and means (64) for actuating said third regulating means (62) to said flow transmitting mode in response to fluid pressure in said first conduit (38) greater than a second predetermined minimum. 2. The lock valve (20) of claim 1, said first fluid communication regulating means (54,56) comprising: a first (54) and a second (56) pilot operated check valve respectively connected to said first (34) and second (36) distribution ports, said first (54) and second (56) check valves being actuatable to said fluid transmitting mode by fluid pressure directed from said first control port (30) to said first (34) and second (36) distribution ports. 3. The lock valve (20) of claim 2, said first and second check valves' actuating means (58) comprising: means (58) for providing fluid communication between said second conduit (44) and both said check valves (54,56) . 4. The lock valve (20) of claim 2, said second fluid communication regulating means (60) comprising: a relief valve (60) having an upstream side in fluid communication with said pilot operated check valves (54,56) and a downstream side in fluid communication with said first control port (30) , said relief valve (60) providing fluid flow between said upstream and downstream sides when the pressure differential between the upstream fluid pressure and said first predetermined minimum is greater than a selected amount. 5. The lock valve (20) of claim 4 wherein said selected amount is sufficiently great to ensure actuation of both check valves (54,56) to their fluid transmitting mode. 6. The lock valve (20) of claim 4, further comprising: a bypass check valve (66) in parallel flow relationship with said relief valve (60) , said bypass check valve (66) having an upstream and a downstream side in respective fluid communication with said first control port (30) and said pilot operated check valves (54,56), said bypass check valve (66) providing fluid flow through said first conduit (38) only from said upstream side to said downstream side. 7. The lock valve (20) of claim 1, said third fluid communication regulating means (62) comprising: a third pilot operated check valve (62) having a first side and a second side in respective fluid communication with said second control port (32) and both of said third (40) and fourth (42) distribution ports, said third pilot operated check valve (62) being actuatable to a fluid transmitting mode by a pilot pressure and by a pressure exerted on its first side which is greater than a pressure exerted on its second side by a predetermined differential. 8. The lock valve (20) of claim 1 , said third fluid communication regulating means' actuating means (64) comprising: means (64) for providing said pilot pressure to said third pilot operated check valve (62) from said first fluid conduit (38) . 9. A fluid system (10) comprising: a first (18) and a second (19) fluid ram, said first ram (18) having a first end (18a) and a second end (18b) , said second ram (19) having a third end (19a) and a fourth end (19b) ; means (12) for supplying pressurized fluid; a reservoir (14) ; a lock valve (20) having a first (34) and a second (36) fluid distribution port in respective fluid communication with said first (18a) and third (19a) ram ends, a third (40) and a fourth (42) fluid distribution port in respective fluid communication with said second (18b) and fourth (19b) ram ends, and a first (30) and a second (32) fluid control port;, and a control valve (16) for selectively providing fluid flow between said pressurized fluid supply means (12) and a desired one of said control ports (30,32) and between said reservoir (14) and the remaining control port (30,32), said lock valve (20) further including a first conduit (38) fluidly connecting said first control port (30) to said first (34) and second (36) distribution ports, a second conduit (44) fluidly connecting said second control port (32) to said third (40) and fourth (42) distribution ports, first means (54,56) for regulating fluid communication between said first (34) and second (36) distribution ports to prevent fluid transfer between said first (18a) and third (19a) ram ends, said regulating means (54,.56) being actuatable between a transmitting mode and an obstructing mode, first means (58) for actuating said first regulating means (54,56) to said transmitting mode in response to fluid pressure in said second conduit (44) greater than a first predetermined minimum, second means (60) for regulating fluid communication between said first regulating means (54,56) and said first control port (30) , said second regulating means (60) being actuatable to a transmitting mode when said first regulating means (54,56) is in a transmitting mode, third means (62) for regulating fluid communication between said second control port (32) and both of said third (40) and fourth (42) distribution ports, said third regulating means (62) being actuatable between a transmitting mode and an obstructing mode, and means (64) for actuating said third regulating means (62) to said transmitting mode in response to fluid pressure in said first conduit (38) being greater than a second predetermined minimum. - 10. The fluid system (10) of claim 9 further comprising: fourth means (66) for regulating fluid communication between said first control port (30) and said first regulating means (54,56) , said fourth regulating means (66) being actuatable between a transmitting mode and an obstructing mode and being independent of said first regulating means' actuation mode.

Inventors: REEVES JAMES L, REEVES, JAMES, L.
Applicants: TOWMOTOR CORP, TOWMOTOR CORPORATION
Application year: 1981
Main classification: F15B11
IPC codes: F15B11