A Land Vehicle Suspension System

The present invention relates to a land vehicle suspension system.

It is well known to use in conventional suspension systems devices called 'anti-roll bars' which act between a pair of wheels located on opposite sides of the vehicle and act to lessen rolling of the vehicle as it corners, therefore improving its driving characteristics. However, such devices often have the undesired effect of adding stiffness to the suspension when the vehicle is travelling in a straight line, thereby degrading the 'ride' characteristics of the vehicle and exposing the driver to a greater degree of ride harshness as the vehicle passes over a rough surface in a straight line.

The present invention provides in a first aspect a road vehicle with a suspension system comprising: a pair of wheels spaced transversely apart across the vehicle; for each wheel a suspension arm connecting the wheel to the vehicle; and an anti-roll bar extending across the vehicle to interconnect the pair of wheels, wherein: the anti-roll bar has a first part connected to a first of the pair of wheels and a second part connected to a second of the pair of wheels; an electrically-controlled actuator interconnects the first and second parts of the anti-roll bar and is operable to control how much torque is transmitted from one part of the anti-roll bar to the other part of the anti-roll bar; and an electronic controller controls operation of the actuator; wherein

the actuator is a hydraulic actuator which has at least first and second chambers; the vehicle comprises a source of pressurised hydraulic fluid and a return for hydraulic fluid; for the actuator a first electrically-controlled valve is provided to control connection of the actuator to the source and the return ; for the actuator a second electrically-controlled valve is provided which has a first operating condition in which the first and second actuator chambers are connected to each other by the second electrically-controlled valve and a second operating condition in which the first and second actuator chambers are disconnected from each other by the second electrically-controlled valve and the electronic controller controls operation of the first and second electrically-controlled valves.

The present invention provides in a second aspect a road vehicle with a suspension system comprising: a pair of front wheels spaced transversely apart across the vehicle; a pair of rear wheels spaced transversely apart across the vehicle; for each wheel a suspension arm connecting the wheel to the vehicle; a front anti-roll bar extending across the vehicle to interconnect the pair of front wheels; a rear anti-roll bar extending across the vehicle to interconnect the pair of rear wheels; wherein: the front anti-roll bar has a first part connected to a first of the pair of front wheels and a second part connected to a second of the pair of front wheels; the rear anti-roll bar has a first part connected to a first of the pair of rear wheels and a second part connected to a second of the pair of rear wheels; an

electrically controlled front actuator connects the first and second parts of the front anti-roll bar and controls how much torque is transmitted from one part of the front anti- roll bar to the other part of the front anti-roll bar; an electrically controlled rear actuator interconnects the first and second parts of the rear anti-roll bar and controls how much torque is transmitted from one part of the rear anti-roll bar to the other part of the rear anti-roll bar; and an electronic controller controls operation of the front and rear actuators; wherein each actuator is a hydraulic actuator which has at least first and second chambers; the vehicle comprises a source of pressurised hydraulic fluid and a return for hydraulic fluid; for each actuator a first electrically-controlled valve is provided to control connection of the actuator to the source and the return ; for each actuator a second electrically-controlled valve is provided which has a first operating condition in which the first and second actuator chambers are connected to each other by the second electrically-controlled valve and a second operating condition in which the first and second actuator chambers are disconnected from each other by the second electrically-controlled valve; and the electronic controller controls operation of the first and second electrically-controlled valves.

The present invention enables a vehicle to benefit from the action of an anti-roll bar during cornering without suffering from undesired increased stiffness of the suspension while the vehicle is travelling in a straight line.

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A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a hydraulic schematic diagram of a land vehicle suspension system according to the present invention;

Figure 2 is a schematic drawing of an anti-roll bar arrangement for a single pair of wheels of a vehicle in the land vehicle suspension system of figure 1;

Figure 3 is an illustration of an anti-roll bar of the arrangement of figure 2;

Figure 4 is an illustration of a rotary actuator of the arrangement of figure 3; and Figure 5 is a hydraulic circuit diagram of the land vehicle suspension system of figure 1.

Figure 6 is a schematic representation of part of a second embodiment of a land vehicle suspension system according to the present invention; Figure 7 is a schematic representation of part of a third embodiment of land vehicle suspension system according to the present invention; and

Figure 8 is a schematic representation of part of a fourth embodiment of land vehicle suspension system according to the present invention.

Turning first to figure 1 there can be seen a hydraulic schematic of a land vehicle suspension system according to the present invention. The system is for a vehicle having four wheels: a pair of front wheels (not shown in figure 1) located spaced laterally apart on opposite sides of the vehicle (assuming that the longitudinal direction of the

vehicle runs fore and aft and the lateral direction perpendicular to this, from side to side) ; and a pair of rear wheels (not shown in figure 1) again located spaced laterally apart on opposite sides of the vehicle.

The system has a front hydraulic rotary actuator 11 associated with the front pair of wheels and a rear hydraulic rotary actuator 12 associated with the rear pair of wheels. Figure 4 shows one of the rotary actuators 11,12 - both will be identical to each other. Each is of a compact design and allows a significant degree of wheel travel. Each has two chambers and operates to apply a torque in a first sense (e.g. clockwise) if one chamber is connected to receive fluid pressure and the other to a fluid return, and operates to apply a torque in an opposite sense (e.g. anticlockwise) if the chamber connections are reversed. Rotary actuators are commercially available products.

Figure 2 shows an anti-roll bar 50 for a pair of rear wheels 40,41 (the anti-roll bar for the front wheels will be identical) . The rear rotary actuator 12 provides the connection between two parts 51,52 of the anti-roll bar 50. It controls the torque transmitted from the wheel 40 on one side on the vehicle to the wheel 41 on the other side of the vehicle. Figure 3 is a simplified view of this arrangement showing that the two parts 51,52 of the anti-roll bar 50 are connected via the rotary actuator 12. Figure 2 also shows conventional spring-and-damper assemblies 80 and 81 respectively for the wheels 40, 41. The roll bar arrangement acts in parallel with the spring-and-damper assemblies to provide suspension for the wheels 40, 41. Three articulated suspension arms 82, 83, 84 are provided

for the wheel 41. Each is pivotally connected at one end to part of a body of the vehicle and at the other end to a suspension upright on which the wheel is rotatably mounted. A similar arrangement is provided for the wheel 40; articulated suspension arms 85, 86 can be seen with pivot joints 87, 88 by which the arms 85, 86 are rotatably connected to a vehicle body. Additionally seen in Figure 2 are supports 89, 90 which are part of the vehicle body and which support the anti-roll bar 50, the anti-roll bar 50 being mounted on the supports 89, 90 by joints shown which allow the anti-roll bar to rotate relative to the supports 89, 90. The rotary actuator 12 will also be secured to the vehicle body.

As seen in Figure 1, the suspension system has a pump 13 common to both actuators 11,12, which is mechanically- driven by a belt 14 relaying power from an internal combustion engine 15. The pump 13 draws hydraulic fluid from a sump 16, which also provides the fluid return for the actuators 11,12. An electrically controlled throttle valve 17 is used both to disconnect the pump 13 from the sump 16 and also to control the rate of flow of fluid to the pump 13 when the pump 13 is connected to sump 16. A spring-loaded pressure relief valve 18 is included in the hydraulic circuit for safety and at a preset pressure opens to allow fluid to flow directly from the pump 13 to the sump 16 to prevent excessive build up of pressure in the hydraulic circuit. The valve 18 is a spring-loaded valve which operates automatically once a threshold pressure is reached. An electrically controlled dump valve 19 is also provided which can be opened to allow flow of fluid directly from pump 13 to sump 16 when the rotary actuators 11 and 12 are

isolated (see later) . Two expansion chambers 20, 21 are provided to allow for storage of hydraulic fluid under pressure for release at times of high demand for fluid flow.

A front servo-valve 22 is provided to control operation of the front actuator 11. It is a three position valve, having: a first position in which fluid supplied to the rotary actuator 11 causes the actuator 11 to apply a torque in a first (e.g. clockwise) rotational sense; a second position in which fluid supplied to the rotary actuator 11 causes the actuator 11 to apply a torque in a second (e.g. anti-clockwise) rotational sense opposite to the first rotational sense; and a third position in which the actuator 11 is isolated by the valve 22 from the pump 13 and sump 16.

A rear servo-valve 23 is provided to control operation of the rear actuator 12. It is a three position valve, having: a first position in which fluid supplied to the rotary actuator 12 causes the actuator 12 to apply a torque in a first (e.g. clockwise) rotational sense; a second position in which fluid supplied to the rotary actuator 12 causes the actuator 12 to apply a torque in a second (e.g. anti-clockwise) rotational sense opposite to the first rotational sense; and a third position in which the actuator 12 is isolated by the valve 23 from the pump 13 and sump 16.

Both of the valves 22 and 23 are metering valves which can control the rate of flow of fluid through them.

Connected between the valve 22 and the front actuator 11 is a 'soft system ¹ 24, which is shown in greater detail in Figure 5. This comprises an electrically-controlled valve

26 which either connects the two chambers of the actuator 11 together or disconnects them from each other. In Figure 5 can also be seen that the valve 22 is connected in parallel with the valve 26 to the actuator 11 via the soft system 24. The valve 26 is a proportional valve which not only connects together the two chambers of the actuator 11 but can also control a rate of flow of fluid from one chamber to the other when they are connected.

Connected between the valve 23 and the front actuator 12 is a 'soft system ¹ 25. This comprises an electrically- controlled valve 27 which either connects the two chambers of the actuator 12 together or disconnects them from each other. This can be seen in figure 5, where it can also be seen that the valve 23 is connected in parallel with the valve 27 to the actuator 12 via the soft system 25. The valve 27 is a proportional valve which not only connects together the two chambers of the actuator 12, but can also control a rate of flow of fluid from one chamber to the other when they are connected.

The valves 22 and 23 and the valves 26,27 are all controlled by a common electronic controller (not shown) . The electronic controller is connected to sensors around the vehicle (e.g. a lateral accelerometer, yaw rate gyrometer, steer angle sensor, wheel hub accelerometers and force and/or position sensors associated with the wheels) which together enable the controller to ascertain whether the vehicle is travelling in a straight line or whether the vehicle is cornering.

When the vehicle is travelling in straight line (e.g. when the controller determines that lateral acceleration is below a chosen threshold value) the controller will control the valves 22 and 23 to isolate the actuators 11,12 from the pump 13 and sump 16. At the same time the valves 26,27 are controlled to connect together the two chambers of each rotary actuator. The rate of flow of fluid between the two chambers of each actuator is also controlled. The rotary actuators are thus controlled to offer a variable degree of damping to relative rotation between the two halves of each anti-roll bar. Any damping provided by the actuators when operating with their chambers interconnected will be additional to and in parallel with the damping provided by the spring-and-damper assemblies (e.g.80, 81) . The actuators can be controlled, if desired, to offer minimal damping when the vehicle is travelling in a straight line in which case little or no torque will be transmitted through each anti- roll bar and each wheel will move independently controlled by its own spring and damper assembly.

When the vehicle is cornering then the electronic controller will control the valves 25 and 26 so that they disconnect the two chambers of each actuator 11,12. The valves 22 and 23 will then be controlled to connect one chamber of each actuator to fluid pressure and the other to fluid return so that the actuators apply torques between the halves of the anti-roll bars which resist rolling of the vehicle while cornering. The sense of torque applied (clockwise or anticlockwise) will depend on whether the vehicle is cornering through a left hand or a right hand corner. The metering capability of the valves 22,23 will be used by the electronic controller to control the amount of

rotation and/or torque transmitted from one half of each ant-roll bar to the other and thereby control the rolling of the vehicle through corners. The controller will use the signals it receives form the vehicle's sensors (e.g. a lateral accelerometer, yaw rate gyrometer, steer angle sensor, wheel hub accelerometers and force and/or position sensors associated with the wheels) to determine the right level of torque to be applied. The pressure in the control line will also be monitored and controlled because the torque applied will vary with line pressure available.

In a failsafe mode the rotary actuators will be locked so that each anti-roll effectively functions as a conventional anti-roll bar. It may be desirable to allow some leakage through each control valve to provide the overall system with some compliance.

As shown above, the valves 26 and 27 are pilot-operated valves, in other words they have spools moved by the application of hydraulic pressure, the application of hydraulic pressure being controlled by a pair of electrically-operated valves 60,61 - one for each valve 26,27. The valves 60,61 are electrically controlled by the electronic controller. However, the valves 26,27 could themselves be directly electrically controlled by the electronic controller and the need for the valves 60,61 avoided.

The operation of the system is energy efficient since there is little power required to power the pump when the vehicle is travelling in a straight line and the valves

26,27 connect together the two chambers of the rotary actuators .

The electronic controller operates to effectively decouple the anti-roll bars when the vehicle is travelling in a straight line to ensure that the vehicle has good ride characteristics in such circumstances; however, if desired the actuator can provide some controlled damping of wheel movement. The electronic controller then couples in the anti-roll bars during cornering and controls the functioning of the roll bars to provide the vehicle with good cornering characteristics .

Whilst above the actuators used are rotary actuators, and this is preferred for reasons of packaging, it would be possible to use linear actuators each connecting the two halves of a roll bar through suitable linkages. This possibility is illustrated in Figures 6, 7, and 8.

In Figure 6, a pair of wheels 100, 101 are shown connected to a vehicle body (not shown) by articulated suspension arms 102, 103. An anti-roll bar 104 extends transversely across the vehicle and is secured to the vehicle by a pair of mounts 105, 106 which allow rotation of the anti-roll bar 104 relative to the vehicle. The anti- roll bar 104 has a central section 104A having an axis lying on an axis of rotation of the anti-roll bar 104 and two level arms 104B, 104C extending radially out from the central section 104A. A distal end of the arm 104B, spaced from the axis of rotation of the anti-roll bar, is connected to the suspension arm 102 via a linear actuator 107, the linear actuator also forming part of the anti-roll bar 104.

The linear actuator 107 comprises a piston 108 connected by a rod 109 and an articulating joint 110 to the suspension arm 102. The piston 108 slides in a cylinder 114 which is connected by a rod 111 and articulating joint 112 to the distal end of the lever arm 104B. A distal end of the arm 104C, spaced from the axis of rotation of the anti-roll bar, is connected to the suspension arm 103 via a linear actuator 115, the linear actuator also forming part of the anti-roll bar 104. The linear actuator 115 has a piston 116 connected by a rod 117 and an articulating joint 118 to the suspension arm 103. The linear actuator 115 has a cylinder 119 in which the piston 116 slides, the cylinder 119 being connected via a rod 120 and an articulating joint 121 to the distal end of the leaver arm 104C.

Each of the actuators has an upper chamber 107A, 115A and a lower chamber 107B, 115B and a soft system , having a pair of valves, of the kind described above, so that the upper 107A, 115A and lower 107B, 115B chambers can be: a) . connected to each other whilst being disconnected from the source of hydraulic pressure and the fluid return, with fluid either being allowed to flow freely between the chambers on passing through a passive or actively controlled restriction to provide damping of wheel motion; b) . disconnected from each other and disconnected from fluid pressure and return lines, to "lock" the actuator; and c) . disconnected from each other and selectively connected to hydraulic fluid pressure and return lines to provide actively controlled torque.

Figure 7 shows a variant of the Figure 6 embodiment, with the actuator 115 removed, so that only one actuator 107

is incorporated in the anti-roll bar; otherwise the operation is the same as described above.

Figure 8 shows a further embodiment of the invention in which an anti-roll bar 300 extends across a vehicle to connect a wheel 301 on one side of the vehicle with a wheel 302 on the other side of the vehicle. The anti-roll bar 300 is formed of two parts 303, 304 and a linear actuator 305 interconnecting the two parts 303, 304.

The part 303 comprises: a section 306 which lies along the axis of rotation of the anti-roll bar; a lever arm 307 which extends radially out from an outboard end of the section 306; a rod 308 connected by a first articulated joint 309 to a distal end of lever arm 307, spaced from the axis of rotation, and connected by a second articulated joint 310 to a suspension arm 311 by which the wheel 301 is connected to the vehicle; and a lever arm 312 which extends radially out from an inboard end of the section 306 and which is connected at a distal end thereof, spaced from the axis of rotation, by an articulating joint 313 to the linear actuator 305. The anti-roll bar part 304 is similarly- constructed.

The actuator 305 has a piston 314 slidable in a cylinder 315 and dividing the cylinder 315 into two chambers 316, 317. The chambers 316, 317 are interconnected by a soft system as previously described, in which a first valve of a pair of valves selectively connects the chamber 316, 317 to a fluid pressure line and a fluid return line and in which a second valve of the pair of valves can connect the chambers 316, 317 together so that fluid can flow between

them. In a first operating condition the first valve disconnects the chambers 316, 317 from fluid pressure and return lines while the second valve connect the chambers 316, 317 together; fluid can either be allowed to flow freely between the chambers or the fluid can pass through a restriction so that the motion of the piston 314 is damped, the restriction can be actively controlled by the electronic controller to provide a variable degree of damping. In a second operating conditions the second valve disconnects the chambers 316, 317 from each other and the first valve selectively connects the chambers to the fluid pressure and return lines so that the actuator can apply a torque on the anti-roll bar parts 303, 304. In a third operating condition the first valve disconnects the chambers 316, 317 from the fluid pressure and return lines and the second valve disconnects the chambers 316, 371 from each other so that the actuator is "locked".