GB2354058A - Control valve - Google Patents

Abstract

A control valve comprises a spool 24 moveable within a housing 22 under the action of fluid pressure applied thereto. The spool 24 is moveable such that between first and second modes of operation. In the first mode it is moveable through a first range of positions to control the fluid pressure applied to a first pair of outlets 29a, 29b, and which of the outlets is connected to which of low pressure inlet 28 and a high pressure inlet 27. In the second mode the spool is moveable through a second range of positions to control the fluid pressure applied to a second pair of outlets 30a, 30b and which of those is connected to inlets 27, 28. When operating in the first mode, the second pair of outlets 30a, 30b is isolated, and when operating in the second mode, the first pair of outlets 29a, 29b is isolated. A third mode may be provided in which a third pair of outlets 31a, 31b is connected to inlets 28, 27. A third stage valve (33, figure 1) may be provided in a system incorporating the control valve as a second stage valve. Preferably the first pair of outlets controls an auxiliary proportional device, and the second pair of outlets control third stage valve (33), the third pair of outlets being connected to inlets of valve (33). The valve is used for hydraulic control in aerospace applications.

Description

2354058 CONTROL VALVE This invention relates to a control valve suitable

for use in the control system for a plurality of hydraulically controlled devices.

A known control system for controlling hydraulically controlled devices for use in aerospace applications comprises an electrohydraulic first stage valve, the output of which is used to control a second stage valve. The second stage valve is typically a spool valve, the first stage valve being used to control the fluid pressures applied to the control chambers of the second stage valve to control the position of the spool of the second stage valve. The second stage valve has first and second outputs connected to the control chambers of a third stage multiplexing valve to control the position occupied by the valve member of the third stage valve, and third and fourth, low and high pressure outputs connected to respective inlets of the third stage valve.

The third stage valve has a plurality of outlet ports, the valve member be' g moveable under the control of the second stage valve between a plurality of discrete positions in each of which one or other of the inlets is connected to a selected one of the outlet ports, the other outlet ports being closed by the valve member. Once a selected position has been reached, appropriate control of the second stage valve allows either a low- or a high-pressure fluid source to be connected to the appropriate inlet to control the operation of a hydraulically controlled device, for example a bistable latched valve, connected to the selected outlet port.

A system of this type is described in US 5570718.

2 Where it is required to use the control system to control the operation of a hydraulic device in the form of a proportional device, for example a variable stator vane actuator device, then it is known to use two of the outputs of the third stage to control the operation of the proportional device. Clearly, if two of the outputs are used in this way, then the number of devices which can be controlled by the control system is reduced. In order to maintain the number of devices which can be controlled, the third stage valve would have to be of increased length and complexity, and this is undesirable.

According to the present invention there is provided a control valve comprising a spool moveable within a housing under the action of fluid pressure applied thereto, the spool being moveable such that, in a first mode of operation it is moveable through a first range of positions to control the fluid pressure applied to a first pair of outlets, and in a second mode of operation it is moveable through a second range of positions to control the fluid pressure applied to a second pair of outlets, and wherein when operating in the first mode the second pair of outlets is isolated, and when operating in the second mode, the first pair of outlets is isolated, and wherein the first and second pairs of outlets are arranged such that, when fluid under high pressure is applied to one of the outlets of one of the pairs, the other outlet of that pair has low pressure fluid applied thereto.

Preferably the spool of the control valve is further arranged such that in a third mode of operation fluid is permitted to flow through a third pair of outlets, and wherein when operating in the first and second modes, the third pair of outlets is isolated, and when operating in the third mode, the first and second pairs of outlets are isolated.

3 The control valve may be used as a second stage valve of a control system, the first pair of outlets being used to control the operation of an auxiliary proportional device, the second pair of outlets being used to control the movement of a valve member of a third stage valve and the third pair of outlets being connected to the inlets of the third stage valve. Alternatively, the control valve may be used to control the operation of two auxiliary proportional devices, in which case it may not be necessary to provide the third mode of operation. The invention also relates to a control system including such a control valve.

The spool of the control valve and the housing conveniently define first and second control chambers, the fluid pressure within which controls the position occupied by and movement of the spool. A position sensor may be associated with the spool.

It will be appreciated that the control valve is advantageous in that it permits the control of one or more auxiliary proportional devices in a relatively simple and convenient form.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: - Figure 1 is a diagrammatic view illustrating a control system including a control valve in accordance with an embodiment of the invention; Figure 2 is a diagrammatic sectional view illustrating the control valve operating in a first mode; and 4 Figures 3 and 4 are diagrams illustrating the control valve operating in its second and third modes, respectively.

The control system illustrated in Figure 1 comprises an electromechanical servo valve 10 to which fluid under pressure is supplied as denoted by arrow 11. The valve 10 typically includes a jet pipe 12 which is moveable upon energization of coils 13, 14 to direct a flow of fluid at a relatively high pressure to first and second outlets 15, 16. The outlets 15, 16 are connected through passages 17, 18 to inlets 19, 20 of a second stage control valve 21.

As illustrated most clearly in Figure 2, the second stage control valve 21 comprises a housing 22 within which a bore 23 is formed, a spool 24 being slidable within the bore 23. Although the housing 22 is illustrated as a single component in Figure 2, it will, in practice, be of multi-part construction. The spool 24 and bore 23 of the housing 22 together define first and second control chambers 25, 26 which communicate, respectively, with the inlets 19, 20. It will be appreciated that the spool 24 is moveable within the bore 23 under the action of the fluid pressures within the control chambers 25, 26, and that these pressures are controlled by the first stage valve 10. By appropriate control of the currents applied to the coils 13, 14, the spool 24 can be moved within the housing 22 to desired positions.

The housing 22 further includes high and low pressure ports 27, 28, respectively which are connected, in use, to appropriate high and low pressure fluid sources (not shown). As will be described herein, the spool 24 is moveable to control the fluid pressure applied to a first pair of outlet ports 29a, 29b, a second pair of outlet ports 30a, 30b, and a third pair of outlet ports 31a, 31b. The first pair of outlet ports 29a, 29b is used to control the operation of an auxiliary proportional device, for example a variable stator vane actuator.

The control system further comprises a third stage multiplexing valve 32 which comprises a valve member 33 moveable within a bore 34. The valve member 33 and bore 34 together define first and second control chambers 35, 36, the fluid pressures within which act upon the valve member 33 to move the valve member 33 within the bore 34 to desired positions. The control chambers 35, 36 are connected, respectively, through passages 37, 38 to the second pair of outlet ports 30a, 30b. The valve member 33 is moveable between positions in which a selected one of a pair of inlets 39a, 39b, connected, respectively, to the outlet ports forming the third pair of outlet ports 3 1 a, 3 1 b, is connected to a selected one of a plurality of outlet ports 40. The outlet ports 40 are connected to respective hydraulically controlled devices, for example in the form of bistable latched switches - The nature and operation of the second stage valve will now be described with reference to Figures 2, 3 and 4. With reference to Figure 2, the spool 24 is provided with nine lands denoted by reference numerals 41 to 49 which define, therebetween, eight annular chambers which can be regarded as constituting two groups 50, 51.

Figure 2 illustrates the second stage control valve 21 in a first mode of operation. In this mode of operation, the second and third pairs of outlet ports 30a, 30b, 3 1 a, 3 1 b are isolated from one another and from the low and high pressure ports 27, 28. As a result, provided the spool 24 forms a substantially fluid tight seal within the bore 23, the fluid pressure applied to 6 these outlet ports will not alter whilst the control valve 21 operates in its first mode of operation.

As mentioned hereinbefore, the spool 24 defines first and second groups of annular chambers 50, 51. The chambers 50 forming the first group are denoted herein using reference numerals 50a, 50b, 50c, 50d. The low pressure port 28 is in constant communication with the chamber 50d. The low pressure port 28 further communicates through a passage 28a such that when the control valve 21 is operating in its first mode of operation, the chamber 50a is also in constant communication with the low pressure port 28. The remaining annular chambers 50b, 50c of the first group 50 are in constant communication with the high pressure port 27 when the control valve 21 is operating in its first mode of operation. Figure 2 illustrates the spool 24 in an equilibrium position in which the outlet ports 29a, 29b are closed, respectively, by the lands 42, 44. If it is determined that the outlet port 29a should be connected to the low pressure port 28 and the outlet port 29b connected to the high pressure port 27, then the spool 24 is moved to the right, as illustrated in Figure 2 by a small distance by operating the first stage valve 10 to increase the fluid pressure within the first control chamber 25 and allowing the fluid to escape from the second control chamber 26. Such movement results in the land 42 being moved to the right to connect the outlet port 29a to the chamber 50a which is in constant communication through the passage 28a with the low pressure port 28. The movement also causes the land 44 to move to connect the outlet port 29b through the chamber 50c to the high pressure port 27. When it is determined that the connection between the outlet ports 29a, 29b and the ports 27, 28 should be broken, the spool 24 is returned to the position illustrated to isolate the outlet ports 29a, 29b. In the event that the fluid pressure at the outlet port 29a should be increased and that 7 at the outlet port 29a decreased, then the spool 24 is moved to the left in the orientation illustrated to comect the outlet port 29a through the chamber 50b to the high pressure port 27 and to connect the outlet port 29b through the chamber 50d to the low pressure port 28. As described hereinbefore, the ports 29a, 29b are connected to an auxiliary proportional device, and it will be appreciated that by appropriate control of the position occupied by the spool 24, the pressures applied to the proportional device can be controlled in a relatively simple and convenient manner.

The range of movement through which the spool 24 is able to move when operating in its first mode is relatively small.

Figure 3 illustrates the control valve 21 operating in a second mode. In this mode of operation, the first and third pairs of outlet ports 29a, 29b, 3 1 a, 3 1 b are isolated from one another and from the high and low pressure ports 27, 28, thus the fluid pressures at the first and third pairs of outlets 29a, 29b, 3 1 a, 3 lb are held substantially constant. In this mode of operation, the land 45 is moved to a position in which the chamber 50d is in constant communication with a passage 52 provided in the housing 22. The spool 24 is provided with drillings forming a passage 53 which connects the exterior of the land 43 to the exterior of the land 47 and the exterior of the land 49. The land 47 is positioned such that, when the valve 21 is operating in its second mode of operation, the part of the passage 53 which opens to the surface of the land 47 communicates, constantly, with an annular recess 54 formed in the housing 22.

As mentioned hereinbefore, the lands of the spool 24 define a second group of annular chambers which are denoted herein by the reference numerals 5 1 a, 8 51b, 51c and 51d. When operating in its second mode of operation, the chamber 5 1 a is in constant communication with the passage 52. Similarly the chamber 51d is in constant communication with the passage 52. As the passage 52 is also in constant communication with the chamber 50d which in tum communicates with the low pressure port 28, the chambers 5 la, 5 1 d are held at low pressure when the spool 24 is positioned for operation in the second mode of operation. The chambers 51b, 51c are in constant communication with the annular recess 54 which, as described hereinbefore, communicates through the passage 53 with the high pressure port 27. The chambers 5 1 b, 5 1 c are therefore held at relatively high pressure during this mode of operation. The second pair of outlet ports 30a, 30b are closed by the lands 46, 48 when the spool 24 occupies an equilibrium position in the second mode of operation. As the second pair of outlet ports 30a, 30b are isolated from both the low and high pressure fluid sources in the equilibrium position by the lands 46, 48, it will be appreciated that the fluid pressures applied to these outlet ports is held at a substantially constant level.

In the event that it is determined that the fluid pressure at the outlet port 30a should be reduced and that at the outlet port 30b increased, to cause the valve member 33 of the third stage valve to move to the left as illustrated in Figure 1, then the spool 24 is moved by a small distance to the right, from the position illustrated in Figure 3. The movement of the spool 24 is achieved by appropriate control of the first stage valve 10 to increase the fluid pressure within the first control chamber 25, the movement of the spool 24 displacing fluid from the second control chamber 26. The movement of the spool 24 is by a sufficiently small distance that the chamber 5 1 c. remains in communication with the recess 54, but is sufficiently large to move the land 48 to a position in which the chamber 51 communicates with the outlet port 9 30b. It will be appreciated that in this position, the outlet port 30b communicates through the chamber 5 1 c with the recess 54 and through the passage 53 to the high pressure port 27. The movement of the spool 24 further results in the land 46 moving to bring the outlet port 30a into communication with the chamber 5 1 a which, as described hereinbefore, communicates with the low pressure port 28. Once the valve member 33 has been moved by an appropriate distance, the spool 24 is returned to the position illustrated to isolate the outlet ports 30a, 30b from the low and high pressure fluid sources, thereby isolating the control chambers 35, 36 and holding the valve member 33 in its new position. As described hereinbefore, movement of the spool 24 by a small distance to the left in the orientation illustrated results in the outlet port 30a being supplied with fluid under relatively high pressure, the outlet port 30b being connected to the low pressure fluid source.

The distance through which the spool 24 is moved whilst operating in its second mode is small, the spool 24 being moved through a relatively large distance when switching between the various operating modes.

Figure 4 illustrates the spool 24 in a third mode of operation. In the position illustrated in Figure 4, the first and second pairs of outlet ports 29a, 29b, 30a, 30b are isolated from one another and from the low and high pressure ports 27, 28. Further, in this position, the chamber 51d communicates both with the passage 52 and with the port 3 1 a of the third pair of outlet ports. As the passage 52 communicates through the chamber 50d with the low pressure port 28, it will be appreciated that the outlet port 3 1 a is connected to the low pressure fluid source. The movement of the spool 24 further brings the part of the passage 53 which opens to the surface of the land 49 into communication with the outlet port 31b. As the passage 53 communicates with the high pressure port 27, it will be appreciated that fluid under high pressure is applied to the outlet port 31b.

It will be appreciated from the description hereinbefore that by appropriate control of the first stage valve 10, the spool 24 of the second stage control valve 21 can be moved through a range of positions when the control valve 21 is operating in its first mode of operation to control the fluid pressures at the first pair of outlet ports 29a, 29b, through a second range of positions when the control valve 21 is operating in a second mode to control the fluid pressures applied to the second pair of outlet ports 30a, 30b, and to apply fluid under low and high pressures to the outlet ports 3 1 a, 3 1 b forming the third pair of outlet ports when the control valve 21 is operating in a third mode. In the control system illustrated in Figure 1, operation of the control valve 21 in its second mode is used to control the position occupied by the valve member 33 of the third stage valve, and once the valve member 33 has been moved to a desired position to connect one or other of the inlet ports 39a, 39b to a selected one of the outlet ports 40, the control valve 21 is moved to its third mode of operation to connect the third pair of outlet ports 3 1 a, 3 lb to the high and low pressure fluid sources, respectively. Once the control valve 21 is operating in its third mode, depending upon the position occupied by the valve member 33 of the third stage 32, either low or high pressure fluid will be applied to one of the outlet ports 40 and the associated hydraulically controlled device. Where the hydraulically controlled devices. connected to the outlet ports 40 take the form of latched switches, then after a predetermined time or after it has been sensed that the chosen device has been adjusted, the control valve 21 can be returned to its second mode of operation, isolating the third pair of outlet ports 31a, 31b from the low and

11 high pressure fluid sources, the operation of the control valve 21 in its second mode being used to move the valve member 33 of the third stage 32 to an alternative position to permit control of the operation of another of the devices connected to the outlet ports 40. Alternatively, should it be determined that the pressures applied to the auxiliary proportional device require alteration, then the control valve 21 is returned to its first mode of operation to adjust the pressures applied to the first pair of outlet ports 29a, 29b.

In the arrangement illustrated in Figure 1, a position sensor is associated with the third stage valve 32 to monitor movement of the valve member 33 thereof such that accurate control of the third stage valve 32 can be achieved. If desired, a position sensor may also be associated with the control valve 2 1. Alternatively, operation of the control valve 21 may be achieved by monitoring the operation of the third stage valve 32, possibly also monitoring operation of the auxiliary proportional device. Provided the third stage valve 32 and the auxiliary proportional device are operating correctly, then it can be assumed that the control valve 21 is operating correctly, and the information from the position sensors associated with the third stage valve 32 and the auxiliary proportional device can be used in controlling the positioning of the spool 24 in a closed loop manner.

It will be appreciated that when the spool 24 is being moved between the positions occupied when operating in its various modes of operation, there will be short periods during which the first and second pairs of outlet ports 29a, 29b, 30a, 30b may be connected to either the low or high pressure fluid sources at points in the operation during which such connection is undesirable. The movement of the spool 24 between the various operating 12 modes occurs rapidly, thus the time periods during which such unwanted connection occurs are very small. It is thought that the quantity of fluid which is able to flow through the control valve 21 during such short intervals will be sufficiently small that the operation of the devices connected to the control valve 21 will not be significantly impaired. If desired, prior to switching between operating modes, the control valve 21 may be moved to slightly raise or lower the pressures of the ports in such a manner that the subsequent switching returns the pressures to their desired levels.

Although in the description hereinbefore, the control valve 21 is described as being used to control the operation of one auxiliary proportional device and a third stage valve, it will be appreciated that if desired, the control valve 21 may be modified to permit control of two or more auxiliary proportional devices. Further, if desired, the third stage valve 32 may be omitted and, if desired, the second pair of outlet ports 30a, 30b may be used in controlling the operation of an auxiliary proportional device.

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Claims (7)

1. A control valve comprising a spool moveable within a housing under the action of fluid pressure applied thereto, the spool being moveable such that, in a first mode of operation it is moveable through a first range of positions to control the fluid pressure applied to a first pair of outlets, and in a second mode of operation it is moveable through a second range of positions to control the fluid pressure applied to a second pair of outlets, and wherein when operating in the first mode the second pair of outlets is isolated, and when operating in the second mode, the first pair of outlets is isolated, and wherein the first and second pairs of outlets are arranged such that, when fluid under high pressure is applied to one of the outlets of one of the pairs, the other outlet of that pair has low pressure fluid applied thereto.

2. The control valve as claimed in Claim 1, wherein the spool of the control valve is further arranged such that in a third mode of operation fluid is permitted to flow through a third pair of outlets, and wherein when operating in the first and second modes, the third pair of outlets is isolated, and when operating in the third mode, the first and second pairs of outlets are isolated.

3. The control valve as claimed in Claim 2, for use as a second stage valve of a control system, the first pair of outlets being used to control the operation of an auxiliary proportional device, the second pair of outlets be' used to control the movement of a valve member of a third stage valve and the third pair of outlets being connected to the inlets of the third stage valve.

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4. The control valve as claimed in any of Claims I to 3, wherein the spool of the control valve and the housing define first and second control chambers, the fluid pressure within which controls the position occupied by, and movement of, the spool.

5. The control valve as claimed in Claim 4, wherein the spool is provided with an associated position sensor.

6. A control system for an auxiliary proportional device comprising a control valve as claimed in any of Claims I to 5.

7. A control valve substantially as hereindescribed with reference to the accompanying Figures 1 to 4.