CONTROL VALVE AND HYDRAULIC DAMPER

Abstract: A control valve (13) for modulating the flow of a conventional oil- or water-based working liquid, comprises a valve member (2A, 2B) movable with respect to an orifice (19) through which the working fluid is adapted to flow, with the force on the valve member (2A, 2B), due to the pressure of the working liquid, being reduced by the provision of a fixed element (3, 5) on or in which the valve member (2A, 2B) is adapted to slide.

Description: Title of the Invention Control valve and hydraulic damper Field of the Invention This invention relates to a control valve for the modulation of the flow of an oil or water- based working fluid, and to a hydraulic damper incorporating such a valve. Background of the Invention Electro-rheological (ER) fluids are concentrated suspensions of finely divided solid particles in a base liquid which show large reversible increases in flow resistance when they are exposed to electric fields. Since their response is proportional to the applied field, and virtually instantaneous, and their consumption of electrical power is relatively small, ER fluids have been proposed as an interface between electrical control signals and many forms of mechanical device, including linear dampers. Several workers have proposed a conventional single-ended damper filled with ER fluid, with an "ER valve" between the chambers above and below the piston. An ER valve is basically a pair of parallel fixed electrodes electrically insulated from each other, so that a voltage can be applied between them. This voltage controls the flow resistance of the ER fluid, and hence the pressure drop across the valve. ER valves can take many forms:- they can be a stack of parallel flat plates, an array of concentric cylinders or even a simple rod mounted concentrically in a tube. The simple ER damper described above has several serious disadvantages: - 1. Using present ER fluids, the ER valves must be quite long to generate the maximum pressures achieved in normal dampers. Similarly, these ER valves must be quite wide, with large gaps between the electrodes, to keep the no-field pressure drop down to acceptable levels at maximum flow rates. The overall result is that the ER valve required to achieve realistic performance using the ER fluids currently available must be very large. Such valves require large, heavy, dangerous and costly high voltage power supplies. 2. Any damper converts mechanical energy into heat, so temperature rises are unavoidable. At present, there are no ER fluids available which can maintain satisfactory performance in all essential aspects over the normal operating temperature range of an automotive damper, for example. 3. Most conventional single-ended dampers have an extra chamber, such as a concentric tube outside the main cylinder, to take up the fluid displaced by the piston rod and thermal expansion. Access to this chamber is controlled by a separate valve. An ER damper using this system would require two ER valves, which would be bulky and complex, but a simple spring-loaded valve would sacrifice most of the control. 4. Modern ER fluids are relatively costly, since they are made up from specially-made liquids and solids. It is uneconomic to use such sophisticated materials merely to transmit pressure, where a standard oil is perfectly satisfactory. Reported in "Eureka", July 1997, page 25, Brooks D, is described a damper filled with ER fluid in which the application of a voltage to a relatively small electrode generates a small pressure which is applied to a diaphragm, which controls an orifice valve through which the main flow of ER fluid passes. This addresses disadvantage 2 above very successfully, but the published design does not deal with any of the other problems. Furthermore, a small orifice is likely to be clogged by the particles in the ER fluid. Object of the Invention A basic object of the present invention is the provision of an improved control valve and hydraulic damper incorporating such a valve. Summary of a First Aspect of the Invention According to a first aspect of the invention, there is provided a control valve for modulating the flow of a conventional oil- or water-based working liquid, the valve comprising an element movable with respect to an orifice through which the working fluid is adapted to flow, with the force on the movable element, due to the pressure of the working liquid, being reduced by the provision of a fixed element on or in which the movable element is adapted to slide. Preferred features of the valve are defined in sub-Claims 2 - 12. Summary of a Second Aspect of the Invention According to a second aspect of the invention there is provided a hydraulic damper controlled by a valve in accordance with the first aspect. Preferred features of the damper are defined in Claims 14 - 20. Advantage(s) of the Invention The invention provides a variable orifice valve which is itself controlled preferably by an ER device, which, by the presence of the fixed element and the slidable relationship reduces the force necessary to displace the movable element against the pressure and flow of the working fluid so that, when applied to a hydraulic damper, it is possible to fill the main body of the damper with conventional hydraulic liquid, thus reducing the amount of ER fluid required. Since the main energy dissipation takes place in the conventional liquid rather than the ER fluid, the latter can be isolated from the resultant increases in temperature. Brief Description of the Drawings Figure 1 illustrates the basic principle of a variable orifice control valve; Figure 2 is a diagrammatic sectional view through a first embodiment of control valve in accordance with the first aspect; Figures 3 and 4 correspond to Figure 2 but show second and third embodiments; Figure 5 is a diagrammatic sectional view through a first embodiment of hydraulic damper in accordance with the second aspect. Figures 6 and 7 correspond to Figure 5 but show second and third embodiments. Referring to the control valve 13 shown in Figure 1 , the working liquid, under pressure, flows upwardly through an orifice 18 in a fixed position valve seat 1, as indicated by the arrow 19, and enters a movable valve member 2 in the form of an inverted cup, whose radius is R. The valve member 2 is displaceable towards or away from the valve seat 1 along an axis 20, so as to vary the flow of working fluid through the orifice, so that the gap h between rim 21 of the valve member 2 and the valve seat 1 increases or decreases. When this gap h is wide enough to accommodate the whole incoming flow, if P is the difference in pressure between the inside and outside of the valve member 2, Q is the volume flow rate through the valve and p is the density of the working liquid: P = '/ 2 p[Q/2πRh] 2 However, the value of P is set by the area of the cup (πR 2 ), and the downward force upon it. If for instance the latter is generated by an ER device, it can be controlled independent of h the latter will vary in response to changes in flow rate, but this need not directly affect the pressure. Thus, the pressure drop across the control valve, and hence the force exerted by the damper as a whole, is determined purely by eg the ER system and can be varied as required. In practice, it is desirable to restrict the movement of the control valve 13, in order to minimise mechanical difficulties and the effects of inertia. This could be done by increasing the diameter of the valve member 2, increasing its circumference so the same flow can be accommodated by a smaller value of h. However, this also increases the area, and hence the force that must be exerted by eg the ER device to achieve a given pressure. As shown firstly in Figure 2, this force is reduced in accordance with the first aspect of the invention by slidably locating the valve member 2 within an element 3 that is fixed in position with respect to the valve seat 1 and hence orifice 18. In Figure 2, the valve member 2A is a short length tube, and a top 21 is perforated to become a "spider". The valve member 2A slides in a fixed position element 3 in which there is a sliding seal for an operating rod 4. The valve member 2A experiences a net downward force, since its annulus side 22 is at full supply pressure, whereas its inside 23, which forms the control orifice, is at roughly half this pressure. However, this force can be balanced out by the effect of the supply pressure on the operating rod 4, which acts as a plunger. By choosing the cross-sectional area of the operating rod 4 to suit the valve member 2A, a good force balance can be achieved. In the embodiment of Figure 3 is shown another way in which the force on the valve member 2B can be reduced. In this case, the valve member 2B, in the form of a sleeve, is adapted to slide over a fixed rod 24 with an enlarged head 5 retained in a position by the rod 24 passing through the valve seat 1. Providing the two are a good sliding fit, only a negligible amount of working liquid will escape through the annular gap between the external periphery of the enlarged head 5 and the internal periphery of the valve member 2B, and this can be reduced by grooving the enlarged head 5 to form a labyrinth seal. Working liquid which escapes in this way will leave through the vents 25 in the top of the sleeve, but the majority will pass through the gap between the rim 21 of valve member 2B and the valve seat 1 as previously discussed. The embodiment of Figure 4 is essentially the same as Figure 3, except that fixed rod 24 A passes through an opening 26 in the valve member 2B and is attached above it (not shown). The arrangements shown in Figures 3 and 4 cannot completely balance the upward force due to the pressure on the bottom end of the valve member 2B. This is, in practice, an advantage, because the pressure drop through the control valve 13 can be set purely by the force on the valve, and position control is not required. The control valve 13 described above can be made quite light, to reduce inertia, and the hydrostatic forces upon it will be small. Furthermore, since the flow rate varies as the square of the gap (h), the required travel is small. The resulting low power requirement of the valves of Figures 2 - 4 will be reflected in the size of the eg ER actuator, and its power supply. Several workers have described bi-directional ER actuators based on a four-arm bridge, and in PCT/GB97/01679 is described one which requires only two ER valves. Either of these could be used to operate the control valve. Alternatively, the control valve 13 can be arranged to be biassed in one direction and a uni-directional ER actuator used to oppose this bias. Such an arrangement is much simpler than a bi-directional actuator. It consists of two ER valves in series with a piston or diaphragm at the mid point. The two ER valves operate like a potential divider chain, so that the pressure at the mid-point can be set to any value virtually up to the supply pressure. Against this, the system relies on the out of balance force on the control valve 13 to return it and may be sluggish if used in conjunction with a hydraulic damper having low stroking speeds. A return spring improves this aspect, but the power of an ER actuator must be increased to overcome it. The mechanical power to drive an ER actuator can be provided externally, for example by a small motor-driven pump. However, when the control valves in accordance with the invention are applied to a hydraulic damper, then in a preferred arrangement, this power is derived from the movement of the hydraulic damper itself. The simplest way of doing this is to provide a second piston and cylinder, in parallel with the main hydraulic damper, which acts as a double- acting pump, taking ER fluid from a low pressure reservoir, and driving it through the actuator back to the reservoir. This is clumsy, and the flow rate will be very variable, since it will be directly linked to the stroking speed of the hydraulic damper. An alternative arrangement which makes use of the flow of the working liquid within the hydraulic damper itself, is described below. With regard to the embodiments of hydraulic damper 31 illustrated in Figures 5 to 7, although the damper itself is conventional, it must meet certain requirements if it is to take full advantage of incorporation of a control valve 13 of Figures 2 to 4. It must have provision for the piston rod volume and thermal expansion without introducing any compliance, which would degrade the control available. Similarly, the system should not expose the working liquid to sub- atmospheric pressures since this would lead to cavitation which would also degrade the control. An ideal system would also use a single valve to control both compression and extension. Several systems meet these criteria: the one illustrated in Figure 5 is well known and is provided purely by way of example. In this, the piston rod 7 passes through a sliding seal 27 and is attached to the piston 8 which moves inside the cylinder 9, which is filled with the working liquid. The piston has one-way valves 10 set into it, and there is a further one-way valve 11 in the base of the cylinder. An external pipe 28 connects this one-way valve to a port 12, and the control valve 13 is connected into the pipe 28. A side-branch 29 between the one way valve 11 and the control valve 13 connects to a compliant reservoir 14. The cross-sectional area of the piston rod 7 is roughly half that of the piston 8. When the damper 31 is compressed, valves 10 open and valve 1 1 closes, so that the piston rod 7 acts as a plunger, expelling liquid through the port 12 and the control valve 13 into the reservoir 14. When the damper is extended, valves 10 close, so that the liquid contained in annulus 35 around the piston rod is expelled through the port 12 and the control valve 13. At the same time, valve 11 opens, allowing the working liquid in the reservoir 14 to return to the cylinder 9. This arrangement meets the requirements outlined and is therefore entirely suitable to be used in conjunction with the control valve 13. Figure 6 shows a variant in which the one-way valves are flaps (10A and 11A) of spring steel, and the low pressure reservoir is connected to a pneumatic spring 30. This allows the damper 31 and spring to be combined into a single unit. If it is required to have greater damping on the extension stroke than in compression - this is usually required in vehicle suspension systems - this can be achieved by adjusting the ratio of the cross-sectional area of the piston rod 7 to that of the piston itself. The flow of working liquid into and out of the low pressure reservoir can be used to operate a pump to provide the energy for the ER actuator. If such a pump is sized to provide sufficient flow from the small movements of the damper 31 running on a smooth surface, the flow provided during large excursions of the damper 31 on rough terrain will be excessive and lead to an undesirable temperature rise in the ER fluid. Figure 7, which is provided by way of example, shows one way in which this problem can be overcome. In the diagram, the flow of working liquid passes into and out of the compliant reservoir 14 in Figure 6 through connections A and B. As it does so, it drives the piston 15 up and down. This piston is lightly loaded by springs 32 towards the centre and is connected via light piston rods 33 to the rolling diaphragms 16 and 17. These diaphragms, together with four one-way valves 34, act as a double acting pump and generate a flow of ER fluid out of connection D, C being the return. For very large excursions of the main damper 31, piston 15 is driven beyond A or B, so the excess working liquid passes through without increasing the flow of ER fluid. The system is thus self-limiting. Those skilled in the art will recognise that the pulsations in the flow of ER fluid can be largely removed by hydraulic accumulators attached at A and B.

Claims: CLAIMS 1. A control valve for modulating the flow of a conventional oil- or water-based working liquid, the valve comprising a valve member with respect to an orifice through which the working fluid is adapted to flown, with the force on the valve member, due to the pressure of the working liquid, being reduced by the provision of a fixed element (3, 5) on or in which the valve member 2A, 2B is adapted to slide. 2. A control valve, as in Claim 1, in which the force on the valve member due to the pressure of the working liquid is opposed by the force generated by an electromagnetic device. 3. A control valve, as in Claim 1, in which the force on the valve member due to the pressure of the working liquid is opposed by the force generated by a pneumatic device. 4. A control valve, as in Claim 1, in which the force on the valve member due to the pressure of the working liquid is opposed by the force generated by a hydraulic device. 5. A control valve, as in Claim 1, in which the force on the valve member due to the pressure of the working liquid is opposed by the force generated by a piezoelectric device. 6. A control valve, as in Claim 1, in which the force on the valve member due to the pressure of the working liquid is opposed by the force generated by a magnetostrictive device. 7. A control valve, as in Claim 1, in which the force on the valve member due to the pressure of the working liquid is opposed by the force generated by a magneto-rheological (MR) device.. 8. A control valve, as in Claim 1, in which the force on the valve member due to the pressure of the working liquid is opposed by the force generated by an electro-rheological (ER) device. 9. A control valve, as in Claim 8, in which the ER device is a bi-directional actuator based on a four-arm bridge. 10. A control valve, as in Claim 8, in which the ER device is a bi-directional actuator based on two ER valves in series. 11. A control valve, as in Claim 8, in which the ER device is a uni-directional actuator based on two ER valves in series. 12. A control valve, as in Claims 1 and 8 to 11 inclusive, in which the flow of ER fluid to operate the ER device is provided by an external pump. 13. A hydraulic damper, controlled by a control valve as defined in any preceding Claim. 14. A hydraulic damper, controlled by a control valve as in Claims 1 and 8 to 11 inclusive, in which the flow of ER fluid to operate the ER device is generated by the movement of the damper itself. 15. A hydraulic damper, as in Claim 14, in which the flow of ER fluid is generated by a piston and cylinder assembly working in parallel with a main damper. 16. A hydraulic damper, as in Claim 14, in which the flow of ER fluid is generated by the flow of the working liquid within the damper itself 17. A hydraulic damper, as in Claim 16, in which the mechanism generating the flow of ER fluid has provision to minimise the effects of large displacements of the main damper. 18. A hydraulic damper, as in Claims 14 to 17 inclusive, in which pulsations in the flow of ER fluid are reduced by one or more hydraulic accumulators. 19. A hydraulic damper, as in any preceding Claim, in which the performance of the damper in both compression and extension is controlled by the same valve. 20. A hydraulic damper, as in any preceding Claim, in which the damper is combined with a gas spring to form a complete suspension strut, for a vehicle.

Inventors: KERMODE PETER RICHARD, STANGROOM JAMES EDWARD, KERMODE, PETER, RICHARD, STANGROOM, JAMES, EDWARD
Applicants: ER FLUID DEV, KERMODE PETER RICHARD, STANGROOM JAMES EDWARD, ER FLUID DEVELOPMENTS LIMITED, KERMODE, PETER, RICHARD, STANGROOM, JAMES, EDWARD
Application year: 2000
Main classification: F16F9
IPC codes: F16F9, F16F15