IMPROVEMENTS IN FLUID FLOW CONTROL VALVE MEANS

Abstract: Fluid flow control valve means for servo systems operate in response to an input load to control fluid flow to a fluid pressure operated device, which produces an output load. A valve means typically comprises inlet and exhaust valves 10 and 15 operated by the input load and a feedback from the output load, which may be too slow to operate the valves 10, 15 successfully. The valve (eg. 15) therefore has a valve member 6 responsive to the input load, which is biassed by resilient means 16 towards a valve seat 8, which is movable in response to the pressure differential across it such that for at least one mode of operation of the valve, the seat 8 moves in response to a change in the pressure differential to counter the effect of a change in input load. This effect is known as negative feedback. The valve means is preferably arranged so that the effect operates for opening of both inlet and exhaust valves 10, 15. The resilient means 13 may comprise a spring, or a flexible diaphragm 12, 18.

Description: IMPROVEMENTS IN FLUID FLOW CONTROL VALVE MEANS This invention relates to fluid flow control valve means of the kind which operate in response to an input load to control fluid flow to a fluid pressure operated device, such that the device produces a given output load. In servo systems such as vehicle brake and clutch systems, fluid flow control valve means of the kind set forth may control pressurisation of a servo, which provides an augmented output load for operating the brakes or the clutch, in response to the input load applied to it. Alternatively, the valve means may control pressurisation of the braking system directly. Typically, a valve means of the kind set forth has inlet and exhaust valves for controlling communication between the fluid pressure operated device and a fluid pressure source or a fluid reservoir respectively. When the device -is inoperative, it is connected to the reservoir through the open exhaust valve, while the inlet valve is closed. When the input load is applied the exhaust valve closes and the inlet valve opens to allow pressure fluid into the device. Feedback from the device, preferably from the output load, is used to control closure of the inlet valve when the required output load is reached, and is also used to provide 'feel' for the operator. When the input load is removed the inlet valve closes and the exhaust valve opens, and if necessary is controlled by the output load. In some servo systems, the feedback from the device may not reach the valves quickly enough to control them successfully, although the feedback to the operator may be adequate. According to our invention, a fluid flow control valve means of the kind set forth includes a valve comprising a valve member movable in response to an input load, a valve seat co-operating with the valve member, and resilient means biassing the valve member towards the valve seat, the valve seat also being movable in response to the pressure differential acting across it, the arrangement being such that, for at least one mode of operation of the valve, the valve seat moves in response to a change in the pressure differential to counter the effect on the valve of a change in input load. Thus, for example, if the input load operates to open the valve, the pressure differential across the valve seat changes, altering the force acting on the valve seat and moving it to close the valve again. This effect is known as negative feedback, and provides a rapid way of stabilising operation of the valve in response to a given input load, without requiring feedback from the device. However, the feedback from the device can still operate to provide feel for the operator. The arrangement may be such that the negative feedback effect operates for opening and closing of the valve. The valve may comprise an inlet valve for controlling communication between the device and a source of fluid pressure or an exhaust valve for controlling communication between the device and a fluid reservoir. The resilient means biassing the valve member towards the seat preferably comprises a spring of any suitable type, or an elastomeric member. The valve seat may be carried by a flexible diaphragm, which allows it the necessary movement. The diaphragm may also act to bias the valve seat to its retracted position. Alternatively, separate biassing means may be incorporated to bias the valve seat to its retracted position. Where the valve means comprises an inlet valve and an exhaust valve, both valves may be constructed and arranged in accordance with the invention. In this case, the valve means conveniently has a single valve member movable in response to the input load, first and second valve seats co-operating with the valve member to form first and second valves, which operate as the inlet and exhaust valves, and resilient means biassing the valve member towards the second valve seat, which is movable in response to the pressure differential acting across it, the arrangement being such that on opening of each valve the second valve seat moves in response to a change in pressure differential to counter the effect on that valve of a change in input load. In a first type of valve means, both valve seats may be movable, the first valve seat being responsive to the input load, and the second valve seat being responsive to the pressure differential. Alternatively, in a second type of valve means the first valve seat may be fixed, with the second valve seat being movable in response to the input load and the pressure differential. The first valve may comprise the exhaust valve and the second valve the inlet valve, but this has the disadvantage that the second valve seat is subjected to a pressure differential when the valve means is inoperative. To overcome this, it is preferable therefore for the first valve to be the inlet valve, and the second valve the exhaust valve. The resilient means biassing the valve member towards the seat preferably comprises a spring of any suitable type, but may be an elastomeric member. The second valve seat may be carried by a flexible diaphragm which allows it the necessary movement. The diaphragm may be of metal, or an elastomeric material such as rubber. In a valve means of the first type a metal diaphragm may also act as means biassing the second seat to its retracted position. If an elastomeric diaphragm is used, it may also act as the biassing means, but only in constructions where the second valve seat is not subjected to a pressure differential when the valve means is inoperative. If the second valve seat is subjected to such a pressure differential, it tends to produce a permanent set in the diaphragm, which means that it is not suitable to act as a biassing means as well. In that case therefore, the second valve seat is biassed by a spring. In a valve means of the second type, where the second valve seat is not subjected to a pressure differential when the valve means is inoperative, the second valve seat may be carried by a rolling diaphragm of elastomeric material, with a spring biassing the seat to its retracted position. Some embodiments of our invention are illustrated in the accompanying drawings, in which: Figure 1 is a schematic cross-section of a valve means in accordance with the invention; Figure 2 is a cross-section through a modified valve means; Figure 3 is a cross-section through a further modified valve means; and Figure 4 is a cross-section through another valve means in accordance with the invention. Figure 1 shows a fluid control valve means 1 for a servo system, the valve means operating in response to an input load to control fluid flow between a fluid pressure operated device 2 and a fluid pressure source 3 or a fluid reservoir 4, so that the device produces a given output load. The valve means 1 has a housing 5, in which is located a valve member 6, which co-operates with first and second valve seats 7, 8 respectively. The first valve seat 7 is carried by an input member 9 in the form of a tube connected to the reservoir 4, the input load being applied to the valve means 1 by the input member 9. The valve member 6 and the first valve seat 7 form a first valve 10, which is an exhaust valve controlling communication between the reservoir 4 and a control pressure space 11 connected to the device 2. The second valve seat 8 surrounds the first valve seat 7, and is carried by an annular rubber diaphragm 12, which allows it axial movement, and also seals between the housing 1 and the seat 8. The second valve seat 8 is biassed into a retracted position by a spring 13, which abuts a shoulder 14 in the housing. The seat 8 forms with the valve member 6 a second valve 15, which is an inlet valve controlling communication between the pressure space 11 and the source 3. The valve member 6 is movable in response to the input load applied by the input member 9, against the force in a resilient means in the form of a compression spring 16. The second valve seat 8 is movable in response to the pressure differential across it, and the force in the spring 13. In the inoperative position shown the inlet valve is closed, with the force in the spring 13 balancing the pressure differential acting across the second valve seat 8 and the valve member 6, and the force in the spring 16; the exhaust valve is open, so that the device 2 is in communication with the reservoir 4. When the input load is applied the input member 9 is moved towards the valve member 6, so that the first valve seat 7 comes into contact with the valve member 6 to close the exhaust valve, isolating the device 2 from the reservoir 4. Further movement of the input member 9 moves the valve member 6 against the spring 16, and away from the second valve seat 8. This opens the inlet valve, allowing fluid from the source 3 to control pressure space 11, and to the device 2. The control pressure therefore rises, increasing the force acting in the input direction on the second valve seat 8, which is urged towards the valve member 6 until the inlet valve is balanced. If a further increase of the control pressure is required, the inlet valve must be opened again by further movement of the input member 9 and valve member 6. The increase in pressure will again move the second valve seat 8 to balance the inlet valve. If the input load is reduced, but not removed altogether, the input member 9 moves away from the valve member 6. This allows the inlet valve to close fully, due to spring 16, and then opens the outlet valve, connecting the pressure space 11 and the device 2 to the reservoir 4. The reduction in control pressure reduces the force acting on the second valve seat 8, so that the second valve seat 8 and the valve member 6 move towards the first valve seat 7 to balance the exhaust valve in a new position. When the input load is removed altogether, the exhaust valve is opened, and the reduction in control pressure enables the second valve seat 8 and the valve member 6 to return to their original positions. The valve means of Figure 1 provides a negative feedback effect on opening of the inlet valve, that is, in this mode of operation the effect on the valve of a change in input load is countered by movement of the second valve seat 8 in -response to the change in the pressure differential across it. A similar negative feedback effect is provided on opening of the exhaust valve, as the effect on the exhaust valve of a change in input load is countered by movement of the valve member 6 in response to the change in pressure differential across the valve seat 8 and the valve member 6. Figure 2 shows a practical design of the valve means of Figure 1, for controlling the pressure in an air brake system. The valve means of Figure 2 is a modified version of Figure 1, and corresponding reference numerals have been applied to corresponding parts. In Figure 2 the valve member 6 is in the form of a spool while the input member 9 carries the first valve seat 7 in the form of a rubber diaphragm 17. The second valve seat 8 is carried by a flexible metal plate 18 rather than the rubber diaphragm 12. The plate 18 is sealed in the housing by a seal 19, and has sufficient resilience to act as the biassing means, so that the spring 13 is omitted. Operation of the valve means of Figure 2 is the same as that of Figure 1. In a modification of the valve means 1 of Figure 1 (not shown) the spring 13 could be omitted, and the resilient force required to balance the second valve seat against the pressure differential would then be provided by the resilience in the diaphragm 12. With this arrangement it is possible for the second valve seat 8 to contact the shoulder 14 when the valve means is in its inoperative position. This does not affect the operation, as described, of the inlet valve, as movement of the second valve seat 8 away from the shoulder 14 is not restricted. However, operation of the exhaust valve is affected, since movement of the second valve seat 8 towards the shoulder 14 as a result of the changing pressure differential will cease once the seat 8 contacts the shoulder 14, so that the negative feedback effect will no longer operate. The loss of the negative feedback effect at this point may not be important, or may be outweighed by the simpler construction of the valve means. However, the use of the rubber diaphragm 12 as the biassing means in the arrangement shown in Figure 1 has the disadvantage that when the valve means is in its inoperative position, the diaphragm 12 is subjected to a pressure differential, which will cause it to take a permanent 'set'. This will affect its resilience characteristics, so that the valve means may not operate reliably. Figure 3 shows a further modified valve means which overcomes this disadvantage. Corresponding reference numerals have again been applied to corresponding parts. The valve means of Figure 3 is a servo control valve means for a vacuum-operated servo, so that the pressure source 3 is at atmospheric pressure, while the reservoir 4 is connected to a vacuum source. The valve member 6 is again in the form of a plate, and has a rubber seating portion 20. The first valve seat 7 is carried by the input member 9, which comprises a piston working in the housing 5, with a seal 21 between the seat 7 and the member 9. The input member 9 works against a spring 22 located in the housing 1 between the seat 7 and an abutment 23, which also forms a guide for the seat 7. In this embodiment the first valve 10 formed by the first seat 7 and the valve member 6 is the inlet valve. The second valve seat 8 is carried by the resilient rubber diaphragm 12, which provides a seal between the seat 8 and the housing 1, and biasses the seat 8 to its retracted position. As the second valve 15 comprises the exhaust valve, the rubber diaphragm 12 is not subjected to a pressure differential when the valve means is in the inoperative position shown. The spring 16, which biasses the valve member 6 towards the seats 7, 8, acts between the valve member 6 and the input member 9. In the inoperative position shown, the exhaust valve is open, and the inlet valve closed. When the input load is applied to the input member 9, the input member 9 and the first valve seat 7 move against the force in the spring 22, while the spring 16 ensures that the valve member 6 stays in contact with the seat 7. The valve member 6 then contacts the second valve seat 8 to close the exhaust valve. On further movement of the input member 9, the second valve seat 8 and the valve member 6 remain stationary, as the resilient force applied to the seat 8 by the diaphragm 12 is greater than the force acting on the valve member 6 in the opposite direction. The spring 16 is therefore compressed, and the seat 7 is lifted clear of the valve member 6 to open the inlet valve. The subsequent increase in pressure in the control space 11 moves the seat 8, and the valve member 6 (due to spring 16), thus balancing the inlet valve. If the input load is reduced, but not removed altogether, the force in the spring 22 moves the valve seat 7, valve member 6 and input member 9 away from the valve seat 8, first closing the inlet valve fully, and then opening the exhaust valve. The decrease in pressure in the control space 11 causes the second valve seat 8 to move towards the valve member 6, balancing the exhaust valve in a new position. When the input load is removed altogether the exhaust valve is opened, and the par-ts return to their original positions. The valve means of Figure 3 also exhibits a negative feedback effect for opening of the inlet and exhaust valves. Such a valve means may be particularly useful in a clutch servo system, where the feedback in a clutch system is through a clutch cable, which does not give a rapid response. The valve means of Figures 1 to 3 are all of a first type in which the valve member 6 and the valve seats 7, 8 are all movable, with the first seat 7 movable in response to the input load, and the second seat 8 movable in response to the pressure differential. With this type of valve, it will be noted that in the balanced position, the position of the member 6 and seats 7, 8 relative to the housing 5 varies in accordance with the input load. Figure 4 shows a second type of valve means, in which the first seat 7 is fixed, and the second seat 8 is movable both in response to the input load and the pressure differential. This simplifies construction of the valve means. Like that of Figure 3, the valve means of Figure 4 is a servo control valve for a vacuum-operated servo, and corresponding reference numerals have been applied to corresponding parts. The valve member 6 is again in the form of a plate, with an elastomeric seating portion 25, and is carried from the housing 5 by the spring 16, which comprises a blade spring. The first valve seat 7 is fixed relative to the housing 5, and includes an axial extension 26. The second valve seat 8 is carried from the input member 9, and by an elastomeric rolling diaphragm 12, which extends round the axial extension 26, and is fixed to the housing 5 to form a seal. The second valve seat 8 is guided for movement by tags 27 projecting inwardly from the first seat 7, and a light spring 28 acting between the seats biasses the second seat 8 into its retracted position. The first valve 10 is the inlet valve, and the second valve 15 is not subjected to a pressure differential when the valve means is inoperative, as shown. In operation, an input load applied to the input member 9 moves the second seat 8 to overcome the force in the spring 28, and then to engage the valve member 6 to close the exhaust valve. Further movement of the second seat 8 then moves the valve member 6 against the spring 16 away from the fixed seat 7 to open the inlet valve. The consequent increase of pressure in the control pressure space 11 acts on the diaphragm 12, producing a reaction force on the second valve seat 8 which opposes the input load. At a given control pressure, the reaction force and the force in the spring 16 will move the valve seat 8 and the valve member 6 against the input load, to balance the inlet valve. On reduction of the input load, the reaction force moves the second valve seat 8 away from the valve member 6 to close the inlet valve fully, and to open the exhaust valve. This reduces the reaction force, allowing the second valve seat 8 to move towards the valve member 6 again, until the exhaust valve is balanced. When the input load is removed altogether, the exhaust valve is opened, and the parts return to their original positions. In a modification, not shown, the valve means may be mounted on a servo diaphragm rather than on the housing. In this case, the first valve seat 7 is fixed relative to the servo diaphragm, while the second valve seat 8 is carried from the servo diaphragm by the rolling diaphragm 12. The valve member 6 is mounted on the servo diaphragm by a rubber, or elastomeric mount, rather than the blade spring 16 of Figure 4. The operation of such a modified valve means is exactly the same as that of Figure 4.

Claims: CLAIMS 1. A fluid flow control valve means of the kind operating, in response to an input load, to control fluid flow to a fluid pressure operated device (2), such that the device produces a given output load, the valve means (1) include a valve (15) comprising a valve member (6) movable in response to an input load, a valve seat (8) co-operating with the valve member (6) and resilient means (16) biassing the valve member (6) towards the valve seat (8), characterised in that the valve seat (8) is also movable in response to the pressure differential acting across it, the arrangement being such that for at least one mode of operation of the valve (15) the valve seat (8) moves- in response to a change in the pressure differential to counter the effect on the valve of a change in input load. 2. A fluid flow control valve means according to claim 1, characterised in that the valve seat (8) is movable in response to a change in pressure differential for both modes of operation, that is opening and closing, of the valve. 3. A fluid flow control valve means according to claim 1 or claim 2, characterised in that the valve (15) comprises an inlet valve controlling communication between the device ( 2) and a source of fluid pressure (3). 4. A fluid flow control valve means according to claim 1 or claim 2, characterised in that the valve (15) comprises an exhaust valve controlling communication between the device (2) and a fluid reservoir (4). 5. A fluid flow control valve means according to any preceding claim, characterised in that the resilient means (16) comprises a spring. 6. A fluid flow control valve means according to any preceding claim, characterised in that the valve seat (8) is carried by a flexible diaphragm (12, 18). 7. A fluid flow control valve means according to claim 6, characterised in that the diaphragm (12, 18) also acts to bias the valve seat (8) to its retracted position. 8. A fluid flow control valve means according to claim 6, characterised in that the valve seat (8) is biassed to its retracted position by biassing means (13, 28) separate from the diaphragm (12). 9. A fluid flow control valve means of the kind operating, in response to an input load, to control fluid flow to a fluid pressure operated device (2), such that the device produces a given output load, the valve means (1) comprising a single valve member (6) movable in response to an input load, first and second valve seats (7, 8) co-operating with the valve member (6) to form first and second valves (10, 15) one of which operates as an inlet valve controlling communication between the device (2) and a source of fluid pressure (3), and the other of which operates as an exhaust valve controlling communication between the device (2) and a fluid reservoir (4), and resilient means (16) biassing the valve member (8) towards the second valve seat (8), characterised in that the second valve seat (8) is movable in response to the pressure differential acting across it, the arrangement being such that on opening of each valve (10, 15) the second valve seat (8) moves in response to a change in pressure differential to counter the effect on that valve of a change in input load. 10. A fluid flow control valve means according to claim 9, characterised in that the first valve (10) comprises the inlet valve and the second valve (15) is the exhaust valve. 11. A fluid flow control valve means according to claim 9, characterised in that the first valve (10) is the exhaust valve, and the second valve (15) is the inlet valve. 12. A fluid flow control valve means according to any of claims 9 to 11, characterised in that the resilient means (16) comprises a spring. 13. A fluid flow control valve means according to any of claims 9 to 12, characterised in that the second valve seat (8) is carried by a flexible diaphragm (12, 18). 14. A fluid flow control valve means according to any of claims 9 to 13, characterised in that the first valve seat (7) is movable in response to the input load. 15. A fluid flow control valve means according to claim 10 and claim 14, characterised in that the second valve seat (8) is carried by a flexible diaphragm (12) of elastomeric material, which also acts to bias the second valve seat (8) to its retracted position. 16. A fluid flow control valve means according to claim 11 and claim 14, characterised in that the second valve seat (8) is carried by a flexible diaphragm (12) of elastomeric material, and a bias spring (13) is incorporated to bias the second valve seat to its retracted position. 17. A fluid flow control valve means according to claim 11 and claim 14, characterised in that the second valve seat (8) is carried by a flexible metal diaphragm (18) which also acts to bias the second valve seat (8) to its retracted position. 18. A fluid flow control valve means according to any of claims 9 to 13, in which the first valve seat (7) is fixed, and the second valve seat (8) is movable in response to the input load and- the pressure differential. 19. A fluid flow control valve means according to claim 10 and claim 18, characterised in that the second valve seat (8) is carried by a rolling diaphragm (12) of elastomeric material, and a bias spring is (28) incorporated to bias the second valve seat (8) into its retracted position.

Inventors: HARRISON, ANTHONY WILLIAM
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1985
Main classification: F16K37
IPC codes: B60T13