SUSPENSION CONTROL DEVICE

Abstract: A suspension control device for hydropneumatic suspensions of the active type for a vehicle. This suspension control device provides proportional flow control irrespective of changes of pressure in the strut (5). Each device comprises an electrical actuator, preferably a linear motor, driving a primary valve (3) which is used in fluid flow connection with a bump and rebound valve (2).

Description: SUSPENSION CONTROL DEVICE TECHNICAL FIELD This invention relates to a suspension control system of vehicles, particularly of motor vehicles. BACKGROUND ART Suspension systems that use hydropneumatically operated suspension struts and provide positive response to the dynamic condition of the vehicle, rather than merely absorbing the shocks from the roadwheels caused by the road surface, are often referred to in the art as active suspensions or semi-active suspensions or active ride systems, which terms are used interchangably in the art. Such systems are described in more detail in "Motor", October 31 , 1987, pages 66 to 69, entitled "Active Ride" by Anthony Curtis. The electronically controlled system in the aforesaid article is said to include "... valves that ... are high cost aircraft-style components", and the article states that the system is both complex and costly. The suspension control device, as hereinafter defined is suitable for use in the aforesaid active suspension system. DISCLOSURE OF THE INVENTION We have now devised a suspension control device which provides control of movement of the hydraulic fluid into and out of the struts and the associated components, e. g. gas springs, sometimes known in the art as accumulators, used to control the movement of the roadwheels in relation to the vehicle's chassis. The controlled rate of flow tends to remain constant even wdth changes in hydraulic pressure in the strut. This control, inter alia provides the opportunity of a reduction of the complexity of the electronic controls used for input ι signals for the suspension control device. The suspension control device includes an electrical actuator, and is controlled by electrical input signals from an appropriate source, e. g. a micro-processor. The device provides a high degree of control of the movement of hydraulic fluid in the suspension system, and tends to avoid the use of high cost aircraft- style components thus enabling the device to be manufactured at economic cost levels. Furthermore, we have found that the use of an electrical actuator which is capable of providing a force in both directions of movement, gives certain further improvements. These further improvments include inter alia a reduction in the power consumed in the null position, and the capability that the spool can return to the null position in the case of electrical power failure. The spool returning to null with the power off allows the valve to substantially stop the flow of hydraulic fluid from the vehicle strut, which will tend to hold the vehicle at the ride height applicable at the time the power is switched off. Preferably the electrical actuator which is capable of providing force in both directions of movement is a linear motor. According to the present invention there is provided a suspension control device characterised in that it provides proportional flow control for semi-active suspensions of vehicles, irrespective of changes of pressure in the strut. According to a preferred aspect of the present invention there is provided a suspension control device comprising :- (A) a valve operated by an electrical actuator (hereinafter referred to for convenience as a "primary valve"), and (B) a valve in operational connection with valve ( A ) , used in controlling the bump and rebound movements of the strut (hereinafter referred to as the "bump and rebound valve"). Whereas we do not exclude the ' possibility that the electrical actuator may be a unidirectional actuating device, e. g. a proportional solenoid, preferably the electrical actuator is capable of providing a force in both directions of movement. However, we do not exclude the possibility that a plurality of electrical actuators may be used in the primary valve, but this is not preferred. The electrical actuator in the suspension control device according to the present invention is preferably a constituent part of the primary valve. However, we do not exclude the possibility that it may be mounted in an alternative position which can be readily determined by a man skilled in the art. For example, the electrical actuators for all the vehicle's suspension control devices could be mounted in a central location of the vehicle. According to a more preferred aspect of the present invention, there is provided a suspension control device comprising:- (A) a bidirectional primary valve, and (B) a bump and rebound valve. By "bidirectional primary valve" we mean a device in which a spool is moved within a valve body in two directions by an actuator, and is returned to the null or neutral position by the spring mechanism, and/or, where the actuator is a linear motor, the magnetic forces within the linear motor. As hereinafter described in more detail at Figure 3, SUBSTITUTE SHEET flow is directed from the pressure port (37) to the strut via port (38 ), or from port (38) to reservoir via port (39). In this manner, the bidirectional primary valve is used to provide directional control of the fluid proportional to the signal to the electrical actuator, by varying the control orifices therein. The description of the linear motor hereinafter refers to a moving magnet type of motor, and this is preferred. However, we do not exclude the possibility of 'the use of an alternative type of linear motor, e. g. a moving coil type. The "bump and rebound" valve typically comprises a valve body in which two poppets are disposed and movable within a valve body, such that the pressure drop across the control orifice in the primary valve is controlled, and the appropriate performance characteristics are obtained for the strut movement in the bump and in the rebound directions . Furthermore, the suspension control device according to the present invention provides two flow gains which may be the same or different, a first operational flow gain for bump, and a second operational flow gain for rebound. The suspension control device according to the present invention provides different characteristics for the bump and for the rebound direction. In order to introduce the maximum usable energy into the strut in the rebound direction, it will be appreciated that the loss of hydraulic energy through the suspension control device should be minimised. Therefore the differential pressure setting for the rebound poppet valve would typically be set as low " as is practical . Also the maximum opening of the primary valve ports may be maximised to reduce the loss of hydraulic energy. A person skilled in the art would select a suitable pressure setting for the rebound poppet valve, typically between 2.5 and 10 bar pressure differential. The pressure loss through the suspension control device according to the present invention in the bump direction would typically be greater than the pressure loss in the rebound direction. This will cause increased resistance to movement in the bump direction, and the hydraulic energy dissipated will be converted into heat energy. This heat will be carried away in the fluid, from the suspension control device and the strut towards the reservoir. However, we do not exclude the possibility that the aforesaid pressure losses may be the same, or that the pressure loss in the rebound direction may be greater than that in the bump direction. Furthermore, the bump and rebound valve provides a means of regulating the flow according to the pressure differential between the ports of the primary valve. Thereby, for any one position of the spool in the primary valve, there will be a flow which will remain constant irrespective of the changing pressure in the strut, caused by varying loads. It will be appreciated that the pressure in the strut can change due to a number of different causes or combinations thereof:- inter alia change in vehicle weight, the change in pressure due to damping and weight transfer. Certain embodiments of the suspension control device according to the present invention allow an increase in the internal volume of the spring enclosure by reducing the wall thickness thereof. For example, this may be achieved by the use of an annular spring clip to hold the valve body to a spring enclosure which is a constituent part of the electrical actuator. This allows more space to be made available for the spring mechanism within a specific space envelope for the primary valve. When the primary valve is mounted, for example screwed, into the cartridge housing, the aforsaid method of construction allows the valve body to "float" in relation to the spring enclosure thereby tending to reduce the problems of mounting due inter alia to manufacturing tolerances of the mating parts. The suspension control device according to the present invention is preferably in cartridge valve format, more preferably utilising two cartridges per device. We do not exclude the possibility that the suspension control device may be in an alternative format, such as manifold mounted unit or units. Furthermore, the suspension control device according to the present invention may be mounted in any suitable position in the vehicle as will be readily determined by the skilled man. Typically, the suspension control device according to the present invention is mounted adjacent to the damper orifices, and may be mounted in the strut used - " to control the position of the roadwheel relative to the vehicle chassis. It will be appreciated that the suspension control device may be disposed such that the hydraulic fluid flow connection between the primary valve and the strut may be upstream or downstream of the damper orifices. Typically there will be one suspension control device for each roadwheel, but we do not exclude the possibility that the number of suspension control devices could differ therefrom, e. g. be less than, the number of roadwheels. Typically, there is one pump or one source of hydraulic power for the suspension system in a vehicle, but we do not exclude the possibility that there could be more than one source of such hydraulic power. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be further described by reference to the accompanying drawings which show, by way of example only, a preferred embodiment of a suspension control device according to the present invention and in which: Figure 1 illustrates, in a simple schematic manner (with the system with the primary valve in the null position), components of the suspension control device and the fluid flow lines therebetween; Figure 2 illustrates the bump and rebound valve, which is a constituent part of the suspension control device, partly in longitudinal section; Figure 3 illustrates the bidirectional primary valve, which is a constituent part of the suspension control device, partly in longitudinal section ; Figures 4, 5 and 6 illustrate the bidirectional primary valve in the three different working states, partly in longitudinal section. Referring firstly to Figure 1 , full flow connections are shown in full lines, and the pilot connections by broken lines, following the standard practice in the art. The supply of hydraulic pressure is from the pump (1), which is a discrete device, and is fed into the rebound poppet of the bump and rebound valve (2). When the rebound poppet ((23) in Figure 2) is in the open position, fluid flows through the valve to the inlet port (3a) of the primary valve (3). The primary valve has three control states, which are selected according to the input signal to the electrical actuator such as a linear motor; which are (a) rebound, (b) null, often referred to in the art as neutral, and (c) bump. When in the rebound control state, the inlet port (3a) is connected to the strut port (3b) and the pressure from the pump is used to drive the strut (5) and roadwheel (6) in the rebound direction. By "rebound direction" we mean pushing the roadwheel down in relation to the vehicle chassis, extending the strut towards the rebound stop position. In the null position, the three ports (3a), (3b) and (3c) are closed, and the strut is only interconnected to the gas spring (4), but is neither being hydraulically driven in the rebound direction, nor is the suspension control device allowing fluid from the strut to return to reservoir (7). In the null position, movement of the strut will cause flow into and out of the gas spring (4), via the damper orifice (8). In the bump state, hydraulic fluid from the strut is allowed to return to the reservoir (7) by the opening of the strut port (3b) to the reservoir port (3c). Hydraulic fluid flow from the reservoir port (3c ) of the primary valve to the reservoir (7), is controlled by the bump valve poppet (27). This poppet is spring loaded (by spring (29)) towards the open position, but as the fluid passes through the primary valve (3). the pressure differential which is generated will effect a change in the bump poppet (27) position when the pressure differential is greater than the pressure equivalent to the force generated by the bump poppet valve spring (29); hereinafter described in more detail. It will be appreciated that the strut (5), damper orifice (8) and the gas spring (4) remain in fluid flow connection in the aforsaid three control states, thereby providing the springing for the roadwheel movement in relation to the vehicle chassis with damping of the said movement. Referring now to Figure 2, which illustrates the bump and rebound valve (2). The valve comprises a valve body (18), in which are disposed two poppets (23) and (27). The poppets may slide along the bore of the valve body according to the hydraulic pressures they are subjected to and the forces applied by the springs (22) and (29). Spring pin (19) is used to provide (a) the stop to limit the travel of poppet (27), (b) support for spring (22), and (c) through the hollow centre of the pin provides the hydraulic pressure feed to gallery (25). The spring (29) used for control in the bump direction of flow is of significantly greater strength than the spring (22) used for rebound. The different strength springs provide different pressure differentials for each of the two directions of flow. A person skilled in the art will, by simple experimentation, determine a suitable ratio between the spring strengths, e. g. the strength of the spring for the bump poppet valve could be double that of the spring for the rebound poppet valve. In operation, fluid from the hydraulic pump (1 ) enters the valve at port (21 ). Spring (22) holds the rebound poppet (23) in the "open" position, allowing hydraulic fluid flow through gallery (23a) to port (24). From port (24) the fluid passes onto the primary valve. Gallery (25) is in fluid flow connection with the strut (5). When the fluid flow through the primary valve is such that the pressure differential between hydraulic pump pressure and the strut pressure is greater than the pressure equating to the spring setting of the rebound poppet, then the excess pressure differential will tend to move the poppet towards the closed position, by moving the poppet (23) against the spring (22). When the suspension control device is controlling the strut moving in the bump direction, then fluid will enter the bump and rebound valve (2) at port (26). The bump poppet (27 ) will be held in the open position by spring (29), allowing fluid flow .connection through gallery (27a) to port (28). When the fluid flow through the primary valve is such that the pressure differential between the strut pressure and the pressure at the reservoir port (3c) of .the primary valve (3) is greater than the pressure equating to the spring force, then the excess of pressure differential will tend to move the poppet (27 ) against the spring (29 ). thereby moving poppet (27) towards the closed position. Referring now to Figure 3, which shows the primary valve (3) in the null position. A linear motor, comprising housing (31 ) and moving magnet (32), w r hich is activated by a micro-processor (not shown) is mechanically linked to the valve body (34). The moving magnet (32) is in driving engagement with spool (33 ) which is disposed in. and moveable within, the bore of the valve body (34 ). The spool (33) is hollow to allow both ends of the spool to be subject to the same pressure (thereby tending to reduce or eliminate imbalance forces on the spool). The fluid in gallery (36 ) is in fluid flow connection with the reservoir through aperture (41), which allows gallery (36) to remain at low pressure. The moving magnet (3) drives the spool in a first direction and against spring (35), and in a second direction against spring (40). It will be appreciated that the primary valve port (39) can be subjected to a pressure approaching that of the pressure from the pump, and that there is a separate connection, aperture (41 ) from the primary valve (3) direct to the reservoir (7), suitable for internal leakage and for lower pressures . In Figures 4, 5 and 6, parts corresponding to those in Figure 3 are indicated by the same numbering. When the spool (33) is in the position shown in Figure 4, the strut port (38) is in hydraulic fluid flow connection with the reservoir port (39 ) and allows hydraulic fluid flow from the strut to the reservoir port (39 ). This is hereinbefore described as the bump control state. From port (39j the hydraulic fluid returns to the reservoir (7), via the bump and rebound valve (3). To move from the bump control state, the current to the electrical actuator is reduced, the force therefrom decreases, and the spool (33 ) moves towards the null position. The null position is shown in Figure 5. The spool position for the rebound control state is shown in Figure 6, wherein the flow of hydraulic fluid is from pressure port (37) to strut port (38). The suspension control device according to the present invention may be mounted adjacent to the damper orifices, as mentioned hereinbefore. The nearer the suspension control device is mounted to the damper orifices, the greater the opportunity of dissipating the heat from the strut. It will be appreciated that the problems of changes in fluid viscosity may be alleviated by the elimination of pipes and/or hoses from between the suspension control device and the strut. This would have the advantage of maintaining a more consistent performance of the suspension system as the fluid in the said system changes temperature. We have now found that the present device affords such an alleviation. The disposition of the suspension control device according to the present invention adjacent to the strut tends to improve the responsiveness of the control. This improvement is, we believe, due inter alia to the reduction of mass of fluid between the suspension control device and the strut. INDUSTRIAL APPLICABILITY The suspension control device according to the present invention provides control of hydraulic fluid into and out of the struts and the associated components, e. g. gas springs, sometimes known in the art as accumulators, used to control the movement of the roadwheels in relation to the vehicle's chassis. The controlled rate of flow tends to remain constant even with changes in hydraulic pressure in the strut. This control, inter alia provides the opportunity of a reduction of the complexity of the electronic controls used for input signals for the suspension control device, and enables the device to be manufactured at economic cost levels. It will be appreciated that whereas the foregoing description refers to motor vehicles, the suspension control device may also be used for inter alia commercial vehicles, rail vehicles and for track laying vehicles.

Claims: CLAIMS 1 . A suspension control device characterised in that it provides proportional flow control for semi-active suspensions of vehicles, irrespective of changes of pressure in the strut. 2. A suspension control device as claimed in claim 1 , further characterised in that:- (A) a valve operated by an electrical actuator, and (B ) a valve in operational connection with valve (A) , used in controlling the bump and rebound movements of the strut. 3. A suspension control device as claimed in claim 2 further characterised in that the electrical actuator is capable of providing a force in both directions of movement. 4. A suspension control device as claimed in claims 2 wherein the primary valve is activatable by an electrical actuator which is not a constituent part of the primary valve. 5. A suspension control device as claimed in claims 2 or 3 or 4 wherein the electrical actuator is a linear motor.

Inventors: JENNINS WILLIAM STUART, JENNINS, WILLIAM, STUART
Applicants: ELECTRO HYDRAULIC TECHNOLOGY L, ELECTRO HYDRAULIC TECHNOLOGY LTD.
Application year: 1989
Main classification: B60G17
IPC codes: B60G17