GB2281757A

GB2281757A - Proportional control hydraulic valves

Info

Publication number: GB2281757A
Application number: GB9415133A
Authority: GB
Inventors: Peter William Pridham
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-07-30
Filing date: 1994-07-27
Publication date: 1995-03-15
Also published as: GB9315778D0; GB9415133D0

Abstract

An hydraulic valve assembly comprising an inlet (31) for connection to a source of pressure fluid, a number of subsidiary valves (43, 44) supplied from the inlet (31) and an outlet (32) for the return of fluid from the assembly to tank, and a pair of electro-hydraulic proportional load and pressure compensated cartridge valves (36, 37) to enable proportional control of fluid entering and leaving the assembly. The invention enables increased levels of control to actuators connected to the subsidiary valves, at reduced cost and in a more compact assembly when compared with conventional valve assemblies in which separate proportional control valves are required for each subsidiary valve and each requires a separate electronic channel for its operation. A valve (47) enables a float condition to be achieved on an actuator connected to service ports (41) and (42). <IMAGE>

Description

PROPORTIONAL CONTROL HYDRAULIC VALVES THIS INVENTION concerns an hydraulic valve assembly and electrical control system enabling proportional control of, for example rotary or linear actuators. Hydraulic valve assemblies commonly include an inlet for connection to a source of pressure fluid, one or more valves supplied from the inlet and adapted for connection to a rotary or linear actuator, and an outlet for the return of fluid from the assembly to tank.

Where proportional, or variable, flow control to a particular actuator is required it is usually achieved by incorporating an electro-hydraulic proportional control valve as the valve assembly, and if several such actuators are to be individually proportionally controlled with hydraulic fluid, it is necessary to take the expensive and cumbersome measure of providing a number of proportionally controlled electro-hydraulic valves, all mounted together on a single manifold block, arranged on a single monoblock or in a sectional or stacking format.

An electronic control system to operate such an assembly requires separate electronic channels, one or more for each electrohydraulic proportional control valve.

An object of the present invention is to enable increased levels of actuator control to be available at reduced cost and in a more compact assembly. A control valve assembly may include any number of separate sections and the present invention is designed to provide proportional control to the inlet and outlet of a valve assembly thus in turn providing proportional control for the whole assembly.

According to the present invention there is provided an hydraulic valve assembly comprising an inlet for connection to a source of pressure fluid, one or more subsidiary valves supplied from the inlet, and an outlet for the return of fluid from the assembly to tank; characterised in that the inlet and outlet are controlled by at least one proportional control valve.

Preferably, said at least one proportional control valve is an electro-hydraulic proportional load and pressure compensated cartridge valve. The term "valve assembly" is to be construed throughout as including those items commonly referred to as valve blocks, manifold blocks, and manifold assemblies.

Embodiments of the invention will now be described, by way of example only, with reference to Figs. 1 to 4 of the accompanying drawings being hydraulic circuit diagrams illustrating the components of a plurality of valve assemblies incorporating the invention.

An hydraulic valve assembly made in accordance with the invention comprises an inlet port for connection to a source of pressure fluid and at least one outlet port for the fluid, a first valve to control a flow of fluid into the valve assembly by means of electro-hydraulic proportional control, one or more subsidiary valves for distributing the fluid from the first valve to various actuators such as the operating cylinders of an earth moving machine, and a final valve similar to the first valve and also controlled by electrohydraulic proportional control to determine the flow of fluid out of the valve assembly. The first and final valves are preferably electrohydraulic proportional load and pressure compensated cartridge valves known by the registered trade mark VALVISTOR.Where such cartridge valves are used the first or inlet valve will accept the supply of pressure fluid into the assembly on the "nose" or front port of the cartridge and the final or outlet valve will accept the supply of return fluid to pass out of the assembly on the "side" port of the cartridge. Alternatively the first and final valves may be two separate halves of one proportional valve known as Cetop in which case a different electrical control switching sequence than described hereafter will be required to effect the invention. The subsidiary valves may be selected from those known as Cetop, cartridge, poppet and spool. The first and final valves may be installed in a manifold block or they may be provided as a separate principal proportional valve assembly.In each case, there should be a check valve after the first valve to permit pressure fluid to flow from the first valve to any subsidiary valve or valve assembly whilst protecting the first valve from any downstream reactive forces. In each case there should also be a check valve after the final valve to permit return fluid to flow from the subsidiary valve or valve assembly whilst protecting the final valve from any downstream reactive forces or back pressure.

An assembly made in accordance with the invention provides full electro-hydraulic proportional control over a source of pressure fluid entering and leaving the assembly and permitting any individual open or closed subsidiary valve to be controlled by the electro-hydraulic proportional control of the first and final valves.

Referring now to Fig. 1, in a first example, a valve block or manifold is illustrated at 30 having inlet and outlet ports 31 and 32 respectively. In this example VALVISTOR electro-hydraulic proportional control valves illustrated at 36 and 37 are respectively the first and final valves of the assembly. The manifold block 30 includes a load or dump valve at 33 making it suitable for open centred hydraulic circuits, a manifold block relief valve at 34, a check valve downstream of the first valve at 38 and a similar check valve downstream of the final valve at 35. The load or dump valve 33 and relief valve 34 can be removed and the resulting cavities plugged if a closed centre type of hydraulic circuit is required.

Subsidiary directional Cetop control valves at 43 and 44 respectively control the service ports 39-40 and 41-42. Each of the subsidiary valves 43 and 44 have an in-line check valve shown at 45 and 46 respectively on the pressure line to provide load control protection.

The subsidiary valves 43 and 44 are shown as standard spring centre directional control valves with all ports blocked in the centre position, and if so desired, other types of valve can be fitted in place of those illustrated to suit the particular hydraulic circuit requirements.

The assembly illustrated in Fig. 1 becomes operative when a source of pressure fluid is pumped to inlet port 31, and an operator or electronic controller selects one or other of the outlet subsidiary valves 43 and 44 or both. The valves 43 and 44 are electrically connected, for simultaneous control, to the first and final valves 36 and 37 respectively and to valve 33 where the manifold block is being used as part of or in conjunction with an open centred hydraulic circuit, whereby selection of either or both subsidiary valves causes simultaneous operation of valves 36, 37 and 33 by direct electrical switching or signalling.

An important part of this example of the invention is the sequence in which the load, first, final and subsidiary valves are electrically switched. The electrical control switching sequence for an open centred hydraulic circuit is first the load or dump valve 33 followed by the first valve 36, the final valve 37 and then one or more subsidiary valves 43 and 44 as required, and the electrical switching sequence for a closed centre hydraulic circuit commences with the first valve followed by the final valve and the subsidiary valve or valves. The electrical switching sequence for a load sensing hydraulic circuit is firstly the sensing line directional valve followed by the first and final valves and then one or more subsidiary valves.

A further innovative part of this invention concerns the system of operator control provided for use with operator or electronic control systems. The electronic control switching sequence and 'latching' facility has been developed specifically for use with this invention. The same electrical control system can be used in other control situations elsewhere to control equipment compatible with the instructions it transmits by any means whatsoever. The operator controls the subsidiary valve or valves and thus the electrical switching sequence by means of a control lever or joystick fitted with a number of electrical switches or buttons, with at least one or more buttons for each subsidiary valve and other functions.The operator operates a subsidiary valve by touching one of the buttons on the control lever, which action starts the electrical control switching sequence thus 'latching' that function. The system can be supplied to 'latch' one or more functions at once, as required by the machine operator or controller. In an electronic controller operator system the buttons are replaced by electronic signals and the control lever function is replaced by overriding electronic control from a digital processor. For this example the following detail of operation refers to an operator controlled system with one subsidiary valve selected or 'latched' at one time. The operator and machine is rendered safe from accidental operation by means of the remote control lever remaining electrically dead until a function is selected preventing accidental system operation.Once the operator or controller has opened a subsidiary valve in whatever type of hydraulic circuit, then the latter, in this example, remains open or 'latched' until the operator or controller de-selects the same by returning the remote control lever to the dead position whereupon the electrical switching system sequence de-activates the valves in the reverse order to that in which it selected them. The de-selection switching sequence can be timed to begin at an adjustable period from half a second after the control lever has been returned to the dead position. One significant benefit of this system of 'latching' control is that it enables an operator rapidly to select subsidiary valves, moving from one to another before the de-selection switching sequence begins.

Another major advantage for all types of system is that an accidental movement of the control lever will not start a machine function.

Once the operator has selected a process of operation in this example by touching a button on the control lever then operation of valve 36 and valve 37 may be effected proportionally to control the fluid flow. A major feature of this innovation is that different flow values can be given to both the first and final valves 36 and 37 respectively at the same time to produce different control effects.

For example if the subsidiary valve selected is, by means of the invention, proportionally controlling a hydraulic cylinder or actuator with an annulus side volume half that of the full bore side then when such a cylinder is retracted the volume of oil coming from the full bore side will be greater than that entering the annulus side. To ensure the flow of fluid coming from such a cylinder is controlled both as to volume, and pressure due to any load on the cylinder, it is possible with this invention to give different electrical control values to valves 36 and 37 so that the first valve opens less than the final valve or vice versa as the case may be.

Any such different control values for valves 36 and 37 can be selected remotely by an operator or programmed into the electrical control system in such a way as to ensure the electrical state of control required, that is the required respective control values are automatically applied in the required proportions to valves 36 and 37 to provide electro-hydraulic proportional control over any pressure fluid within the assembly at any time.

A practical example of the use of this facility is in controlling a load which is being lowered or lifted by a machine controlled all or in part by the invention. In such a case a 'fine' or 'very slow' setting may be desirable to provide the operator or controller with the benefit of great accuracy in lifting or lowering a load attached to a machine controlled by the invention as aforesaid.

A setting for 'fine', 'very slow' or any such similar control state will take use of the facility to provide valves 36 and 37 with special values to ensure any pressure fluid entering or return fluid leaving the manifold can be metered down to zero flow.

A distinct innovation within the scope of this invention and in this example is in the specification of the valves selected for valves 36 and 37. For equipment or machines which involve lifting and lowering it will be advantageous to use a VALVISTOR type of valve at 36 with pressure flow entering on the nose of the valve, and to use a similar valve at 37 with return flow entering on the side of the valve. The reason for this important detail is that the valve at 36 electro-hydraulically proportionally controls flow into the valve assembly, whereas, the valve at 37 electro-hydraulically prdportionally controls flow out of the assembly.Valve 37 will often experience load induced pressure flow from upstream, and whereas valve 36 is protected from reactive forces downstream by check valve 38 and subsequently check valves 45 and 46, valve 37 has no such facility available to protect it from any load induced pressures and flow upstream. Therefore valve 37 is selected with return pressure flow and other return flows entering on the side of the valve, and it has its own internal check valve, thus proving a fail-safe load holding device on the return side of the manifold or valve block which is a unique facility.

A useful benefit of this facility is that if a machine fitted with the invention lifted a load and then suffered a hydraulic pressure flow failure, the precision of the invention is such that a load can be safely lowered with the benefit of full electro-hydraulic proportional control even without a pressure flow to the manifold, and because valve 37 has its own internal check valve, the load can be safely stopped at any desired position on its way down to a safe position or the ground.

In this manner electro-hydraulic proportional control is provided by means of the first and final valves to any one or more of the subsidiary valves at any one time. If an individual machine's control specification and use of the invention should permit the operator to select more than one subsidiary valve function simultaneously then the first and final valves will still provide electro-hydraulic proportional control over any pressure fluid passing through the same to said subsidiary valves, and any resultant pressure fluid force will be distributed between the subsidiary valves selected according to the individual loads on each actuator controlled by the selected subsidiary valves.

Referring now to Fig. 2 in which like parts have like reference numerals to those used in Fig. 1 the single valve assembly 30 has an extra valve 47 mounted under the subsidiary valve 44 to enable a float condition to be achieved on an actuator connected to service ports 41 and 42.

An actuator float condition is the state achieved when the two sides of an actuator are connected together and to tank simultaneously. This state permits an actuator or actuators connected for example to service ports 41 and 42 to move freely in and out without hindrance or restriction, and consequentially to push fluid down the outlet line and to draw fluid back up again as required so long as the float condition is allowed to remain in force. This condition may be required, for example, when an earth moving machine is driven across the ground with the bucket or blade in contact therewith.When a hump or hollow or other object is encountered the bucket or blade is free to rise or fall owing to the free state of the actuator or actuators which control it, and as long as the float condition is allowed to remain in force the bucket or blade will rise and fall to follow the contours of the ground.

The electrical control switching sequence for the float condition is different from that described before and can be effected in two ways. The first is for a float to be achieved on actuator or actuators connected to the service ports 41 and 42 without any other subsidiary valve activity. The electrical control switching sequence is initiated, in this example, by the operator touching the float button whereupon the final valve 37 opens to a pre-set value followed by valve 47 and then valve 44 moving to one side. This permits a state of float at ports 41 and 42 which remains in force until either an adjustable time out device interrupts the float facility returning the electrical control status to an inoperative state, or alternatively, another subsidiary valve function is selected by the operator whereupon the new control state takes priority.

The second electrical control switching sequence for the float condition is again different from that described immediately above and permits the float state to be achieved at one subsidiary valve while operating a second subsidiary valve provided the said second subsidiary valve is not being used as a lifting or load lowering device. This condition may be required where the blade of an earth moving machine as described before is moving over undulating ground and requires to be simultaneously angled by another actuator at the same time as it is in a float condition in relation to its rise and fall.

The electrical control switching sequence for the second float condition with the simultaneous float and angling by a second actuator will, in this example be initiated by the operator selecting the float function and pressing the float button twice in quick succession or similar signal upon which the final valve will open to a pre-set value followed by valves 47 and latterly 44 moving to one side as described before. However the electrical control system will now accept a second command signal from the operator to initiate a second subsidiary valve without de-selecting the float condition from valves 37, 47 and 44.Upon receiving an electrical control signal for the second subsidiary valve the float condition or state remains in force in relation to service port outlets 41 and 42, while in this example the load valve 33 followed by the first valve 36 and subsidiary valve 43 would as before be electrically sequentially switched into operation with the final valve 37 opening to a larger flow value for the duration of the operation of the two separate subsidiary operations as described before.

By providing an equivalent of valve 47 for each or any number of subsidiary valves in a system using this invention, and by modifying the electrical control switching sequence to take account of the additional float valve requirements, the operator may select the float condition on any subsidiary valve with the same float facility independently or simultaneously as the situation may require.

Referring now to the example illustrated in Fig. 3, a single valve assembly 50 contains the first and final valve and subsidiary valves 43 and 44, as described in relation to Figs. 1 and 2.

However, in this example the first, final and subsidiary valves are operated in conjunction with a load sensing hydraulic pump, and in the said invention an additional valve is included in this example to provide pressure and flow signals via a sensing line outlet at 49 to the pumps compensator. Such a valve is shown at 48, which can be any of Cetop, cartridge, poppet or spool types of valve.

The electrical control switching sequence for this example will be that when the operator or controller initiates a subsidiary valve function the order of switching sequence will be firstly the sensing line valve 48 followed by the first valve 36, the final valve 37 and the subsidiary valve or valves as selected. The operation of the valve block or manifold and the electrical control switching sequence will, other than the detail expressed earlier in this paragraph, be the same as described for Figs. 1 and 3.

In a further development of this invention reference is now made to the example illustrated in Fig. 4, where two separate valve blocks or manifold assemblies 51 and 52 are provided. The assembly 51 incorporates the first valve 36, the final valve 37, the check valves 35 and 38, the relief valve 34 and the load or dump valve 33.

A first manifold block 51 is connected to a second manifold block or valve assembly 52 via ports 53 and 54, 55 and 56 respectively which thus enables it to be located remotely therefrom.

In this example the assembly 52 is shown including two subsidiary valves 43 and 44.

As in other embodiments, one or more of the subsidiary valves in the valve assembly 52 may be operated thus to be under proportional control from the first and final valves 36 and 37 which provide overall proportional control for the functions of the or each subsidiary valve.

Also in this example and as in each example and embodiment considered heretofore a float condition can be achieved by fitting an extra valve such as valve 47 illustrated in Fig. 2 in conjunction with any subsidiary valve and by including the electrical control switching sequence appropriate to the control requirements of the equipment to be operated.

Whichever system is used and with whatever combination of subsidiary valves the invention will provide electro-hydraulic proportional control to actuators connected to it.

Claims

1. An hydraulic valve assembly comprising an inlet for connection to a source of pressure fluid, one or more valves supplied from the inlet, and an outlet for the return of fluid from the assembly to the tank; characterised in that the inlet and outlet are controlled by at least one proportional control valve.

2. An hydraulic valve assembly according to Claim 1, wherein the inlet and outlet are controlled each by a separate proportional control valve.

3. An hydraulic valve assembly according to Claim 1 or Claim 2, wherein the or each proportional control valve is an electrohydraulic proportional control valve.

4. An hydraulic valve assembly according to any preceding claim, wherein the or each proportional control valve is an electrohydraulic proportional load and pressure compensated cartridge valve.

5. An hydraulic valve assembly according to Claim 4, wherein separate electro-hydraulic proportional load and pressure compensated cartridge valves are connected respectively to the inlet and outlet of the assembly in such a way that the inlet cartridge valve is connected to receive the supply of pressure fluid on the nose" or front port of the cartridge, and the outlet cartridge valve is connected to accept a supply of return fluid on the "side" port of the cartridge.

6. An hydraulic valve assembly according to any preceding claim, wherein the or each subsidiary valve may be selected from those known respectively as Cetop, cartridge, poppet and spool valves.

7. An hydraulic valve assembly according to Claim 2, wherein the inlet and outlet control valves are installed in a common manifold or valve block.

8. An hydraulic valve assembly according to Claim 2, wherein the inlet and outlet control valves are provided in a separate principal proportional valve assembly.

9. An hydraulic valve assembly according to Claim 2, including an in-line check valve after the inlet proportional control valve and a further in-line check valve after the outlet proportional control valve, the check valves being adapted to protect the proportional control valves from any reactive forces or back pressure.

10. An hydraulic valve assembly according to any preceding claim, and including a load or dump valve connected directly between the inlet and the outlet whereby the assembly shall be suitable for open centred hydraulic circuits.

11. An hydraulic valve assembly according to any preceding claim, including a relief valve connected directly between the inlet and the outlet.

12. An hydraulic valve assembly according to any preceding claim, wherein the or each subsidiary valve is connected to an in-line check valve on its pressure side.

13. An hydraulic valve assembly according to any preceding claim, wherein the or each subsidiary valve is a spring centred directional control valve with all ports blocked in the centre position.

14. An hydraulic valve assembly according to any preceding claim, wherein the or each proportional control valve is electrically connected to the or each subsidiary valve such that actuation of the latter causes simultaneous actuation of the or each proportional control valve by direct electrical switching or signalling.

15. An hydraulic valve assembly according to any one of Claims 1 to 13, including electrical control means to actuate sequentially the inlet control valve, the outlet control valve and then one or more subsidiary valves.

16. An hydraulic valve assembly according to Claim 15, wherein said electrical control means includes a control lever having a plurality of electrical switches with at least one electrical switch for the or each subsidiary valve, the electrical control means being adapted to effect a predetermined switching sequence by actuation of any said electrical switch.

17. An hydraulic valve assembly according to Claim 15, wherein said electrical control means is adapted to effect valve operation by receiving signals generated from a digital processor.

18. An hydraulic valve assembly according to Claim 15, wherein said electrical control means includes means to effect a deselection switching sequence for a number of valves, arranged to commence at a predetermined time after a control level or button has been released by an operator, whereby the operator subsequently may select operation of a different subsidiary valve without waiting for de-selection of the previously operating subsidiary valve.

19. An hydraulic valve assembly according to Claim 1, including electro-hydraulic proportional control valves connected both to the inlet and to the outlet and wherein different flow values may be selected for the two control valves simultaneously.

20. An hydraulic valve assembly according to Claim 2, wherein the proportional control valve connected to the outlet includes its own internal check valve thus providing a failsafe load holding facility on the return side of the assembly.

21. An hydraulic valve assembly according to any preceding claim, wherein at least one subsidiary valve is connected to a further valve to enable a float condition to be achieved on the subsidiary valve such that any actuator connected thereto may operate freely in both directions.

22. An hydraulic valve assembly according to any preceding claim, wherein the or each proportional control valve and the or each subsidiary valve is connected to a load sensing hydraulic pump and there is included an additional valve to provide pressure and flow signals via a sensing line output to the pump.

23. An hydraulic valve assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.