EP1747106A1

EP1747106A1 - Vehicle roll control system

Info

Publication number: EP1747106A1
Application number: EP05736186A
Authority: EP
Inventors: Christophe Cardon; Philippe Germain; Frederic Sauvage; Bruno Perree
Original assignee: Delphi Technologies Inc
Current assignee: BWI Co Ltd SA
Priority date: 2004-05-10
Filing date: 2005-04-27
Publication date: 2007-01-31
Also published as: GB0410357D0; WO2005108127A1

Abstract

A vehicle roll control system comprising a front torsion bar; a front hydraulic actuator (34) attached to the front torsion bar; a rear torsion bar; a rear hydraulic actuator (34’) attached to the rear torsion bar; and control means (70-87) connected to the front and rear hydraulic actuators and controlling the operation thereof on detection of a determined vehicle condition; wherein each front and rear hydraulic actuator comprises a housing, a piston (62, 62’) making a seal sliding fit inside the housing to define a first fluid chamber (58, 58’) and a second fluid chamber (60, 60’), and a piston rod (64, 64’) connected to the piston hand extending through the second fluid chamber and out of the housing; wherein the control means acts on detection of the predetermined vehicle condition to apply a fluid pressure to the first fluid pressure to the first fluid chamber of the front hydraulic actuator which is different from the fluid pressure applied to the first fluid chamber of the rear hydraulic actuator and/or apply a fluid pressure to the second fluid chamber of the front hydraulic actuator which is different from the fluid pressure applied to the second fluid chamber of the rear hydraulic actuator, and wherein the control means comprises a source of the fluid (80), a fluid reservoir (81), a fluid flow path divider (87) fluidly connected to the pressure source and having a first output (88) and a second output (89), a first pressure control valve (85) fluidly connected between the first output of the flow divider and the reservoir to control the fluid pressure in the first or second fluid chamber of the front actuator, a second pressure control valve (86) connected between the second output of the flow divider and the reservoir to control the fluid pressure in the first or second fluid chamber of the rear actuator; wherein the pressure control valves are actuated to create the pressure differential between the first fluid chamber and/or to create the pressure differential between the second fluid chambers.

Description

DP-312207A VEHICLE ROLL CONTROL SYSTEM

Technical Field The present invention relates to a roll control system for a motor vehicle.

Background of the Invention EP-A-1103395 discloses a vehicle roll control system in which a pair of directional valves and a pressure control valve are used to control the movement of the piston of hydraulic actuators associated with the front and rear axles of a motor vehicle. WO-A-03/093041 discloses a vehicle roll control system in which a pair of pressure control valves and a directional valve are used to control the movement of the piston of hydraulic actuators associated with the front and rear axles of a motor vehicle. In both cases, each hydraulic actuator has a first fluid chamber positioned on one side of the piston, and a second fluid chamber positioned on the other side of the piston. The first fluid chambers of the front and rear hydraulic actuators receive hydraulic fluid at substantially the same pressure; and the second fluid chambers of the front and rear hydraulic actuators receive hydraulic fluid at substantially the same pressure.

Summary of the Invention The aim of the present invention is to provide a roll control system which is an improvement to the above mentioned arrangements. A vehicle roll control system in accordance with the present invention is characterised by the features specified in claim 1. In the present invention, the control means for the hydraulic circuit is capable of providing fluid pressure to the first fluid chamber of the front hydraulic actuator which is different from the fluid pressure provided to the first fluid chamber of the rear hydraulic actuator; and/or is capable of providing fluid pressure to the second fluid chamber of the front hydraulic actuator which is different from the fluid pressure provided to second fluid chamber of the rear hydraulic actuator. The present invention provides a system which allows an aggressive roll control strategy and balance strategy which leads to improvements in motion, turning, and stability (braking in turn at high speed).

Brief Description of the Drawings The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: - Figure 1 is a schematic presentation of a vehicle incorporating a vehicle roll control system in accordance with the present invention; Figure 2 is an enlarged view of the front and rear portions of the vehicle roll control system shown in Figure 1 ; Figure 3 is a side view of the first arm of the vehicle roll control system shown in Figure 2; Figure 4 is a side view of the second arm, hydraulic actuator (shown in cross-section) and lever arm of the vehicle roll control system shown in Figure 2; Figure 5 is a schematic diagram of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figure 1 when the directional valves are de-actuated or in their fail-safe mode; Figures 5B and 5C is a schematic diagram of the circuit of

Figure 5 during compression and extension respectively of the actuators; Figure 6 is a schematic diagram of a first alternative hydraulic and electrical control circuit of the vehicle roll control system shown in Figure 1 when the directional valves are de-actuated or in their fail-safe mode; Figure 6A is a schematic diagram of a modification to the circuit shown in Figure 6; Figure 7 is a schematic diagram of a second alternative hydraulic and electrical control circuit of the vehicle roll control system shown in Figure 1 when the directional valves are de-actuated or in their fail safe mode; Figure 8 is a schematic diagram of a third alternative hydraulic and electrical control circuit of the vehicle roll control system shown in Figure 1 when the directional valves are de-actuated or in their fail safe mode; Figure 8A is a schematic diagram of a modification to the circuit of Figure 8; Figure 9 is a schematic diagram of a fourth alternative hydraulic and electrical circuit of the vehicle roll control system shown in Figure 1 in which four pressure control valves and no directional valves are used; Figure 10 is a schematic diagram of a fifth alternative hydraulic and electrical circuit of the vehicle roll control system shown in Figure 1 in which four pressure control valves and two directional valves are used, with the directional valves being in their de-actuated state or fail-safe mode; Figure 11 is a schematic diagram of a sixth alternative hydraulic and electrical circuit of the vehicle roll control system shown in Figure 1 in which four pressure control valves and two directional valves are used, with the directional valves being in their de-actuated state or fail-safe mode; Figure 12 is a schematic diagram of a seventh alternative hydraulic and electrical circuit of the vehicle roll control system shown in Figure 1 in which four pressure control valves and one directional valve are used, with the directional valves being in their de-actuated state or fail-safe mode; Figure 13 is a schematic diagram of an eighth alternative hydraulic and electrical circuit of the vehicle roll control system shown in Figure 1 in which four pressure control valves and one directional valve are used, with the directional valves being in their de-actuated state or fail-safe mode; Figure 14 is a view of a portion of a vehicle roll control system in accordance with a second embodiment of the present invention; Figure 15 is a view of a portion of a vehicle roll control system in accordance with a third embodiment of the present invention; Figure 16 is a cross-section view of the hydraulic actuator of the vehicle roll control system of Figure 15; Figure 17 is a cross-sectional view of an alternative embodiment of hydraulic actuator for the vehicle roll control system of Figure 15; and Figure 18 is a cross-sectional view of a further alternative embodiment of hydraulic actuator for the vehicle roll control system of Figure 15.

Description of the Preferred Embodiment Referring to Figure 1, a vehicle 10 is shown schematically and comprises a pair of front wheels 12 each rotatably mounted on an axle 14, a pair of rear wheels 16 each rotatably mounted on an axle 18, and a shock absorbing system 20 associated with each wheel. A portion 22 of a vehicle roll control system in accordance with the present invention is associated with the front wheels 12, and a portion 24 of the vehicle roll control system in accordance with the present invention is associated with the rear wheels 16. The portions 22, 24 are substantially the same but with modifications made solely to allow fitting to the vehicle 10. Referring in more detail to Figures 2 to 4, the portion 22 of the vehicle roll control system for the front of the vehicle comprises a torsion bar 26, a first arm 28, a second arm 30, a lever arm 32, and a hydraulic actuator 34. The torsion bar 26 is mounted on the vehicle by a pair of resilient mounts 36 in conventional manner to extend longitudinally between the wheels 12. The first arm 28 (Figure 3) is fixed at one end 38 by a splined connection 40 to the torsion bar 26. The other end 42 of the first arm 28 is connected to the axle 14 of one of the front wheels 12 by a tie rod 43. The second arm 30 (Figure 4) is rotatably mounted at one end 44 on the torsion bar 26 by way of a bearing 46. The other end 48 of the second arm 30 is connected to ihe axle 14 of the other front wheel 12 by a tie rod 49. The first and second arms 28,30 extend substantially parallel to one another when the vehicle is stationary, and substantially perpendicular to the torsion bar 26. The lever arm 32 (Figure 4) is fixed at one end 50 to the torsion bar 26 by a splined connection 52 substantially adjacent the one end 44 of the second arm 30 and the bearing 46. The lever arm 32 extends substantially perpendicular to the torsion bar 26 to a free end 54. The front hydraulic actuator 34 (Figure 4) extends between, and is connected to, the free end 54 of the lever arm 32 and the other end 48 of the second arm 30. The front hydraulic actuator 34 comprises a housing 56 which defines first and second fluid chambers 58,60 separated by a piston 62 which makes a sealing sliding fit with the housing. As shown in Figure 4, the housing 56 is connected to the other end 48 of the second arm 30, and the piston 62 is connected to the free end 54 of the lever arm 32 by a piston rod 64 which extends through the second fluid chamber 60. It will be appreciated that these connections may be reversed. The fluid chambers 58,60 contain hydraulic fluid and are fluidly connected to fluid lines 66, 68 respectively. The portion 24 of the vehicle roll control for the rear of the vehicle is substantially the same, but with the components (which are primed) having a different layout. The rear hydraulic actuator 34' is substantially the same as the front hydraulic actuator 34. The hydraulic and electrical control circuit of the vehicle roll control system of Figures 1 to 4 is shown in Figure 5. The hydraulic circuit includes a fluid pump 80, a fluid reservoir 81, a first directional valve 82, a second direction valve 83, a third directional valve 84, a first pressure control valve 85, a second pressure control valve 86, and a fluid flow divider 87. The fluid flow divider 87 has an input fluidly connected to the pump 80, a first outlet 88 fluidly connected to the input of the first pressure control valve 85, and a second output 89 fluidly connected to the input of the second pressure control valve 86. Fluid filters may be positioned after the pump 80 and/or before the reservoir 81. The first directional valve 82 has a first port 90 fluidly connected to the first output 88 of the flow divider 87; a second port 91 fluidly connected to the second output 89 of the flow divider; a third port 92 fluidly connected to the second chamber 60'(by way of fluid line 68') of the rear hydraulic actuator 34'; and a fourth port 93 fluidly connected to the second chamber 60 (by way of fluid line 68) of the front hydraulic actuator 34. The first directional valve 82 is solenoid actuated, and has a deactuated state (shown in Figure 5) in which the first and second ports 90,91 are fluidly connected, and the third and fourth ports 92,93 are isolated from one another and from the first and second ports. In the actuated state of the first directional valve 82, the first and fourth ports 90,93 are fluidly connected, and the second and third ports 91,92 are fluidly connected. The second directional valve 83 has a first port 94 fluidly connected to the first output 88 of the flow divider 87; a second port 95 fluidly connected to the second output 89 of the flow divider; a third port 96 fluidly connected to the first chamber 58 '(by way of fluid line 66') of the rear hydraulic actuator 34'; and a fourth port 97 fluidly connected to the first chamber 58 (by way of fluid line 66) of the front hydraulic actuator 34. The second directional valve 83 is solenoid actuated, and has a de-actuated state (shown in Figure 5) in which the ports 94,95,96,97 are fluidly isolated from one another. In the actuated state of the second directional valve 83, the first and fourth ports 94,97 are fluidly connected, and the second and third ports 95,96 are fluidly connected. The third directional valve 84 has a first port 98 fluidly connected to reservoir 81; a second port 99 fluidly connected to the first chamber 58'(by way of fluid line 66') of the rear hydraulic actuator 34'; and a third port 100 fluidly connected to the first chamber 58 (by way of fluid line 66) of the front hydraulic actuator 34. The third directional valve 84 is solenoid actuated, and has a de-actuated state (shown in Figure 5) in which the ports 98,99,100 are isolated from one another. In the actuated state of the third directional valve 84, the first, second and third ports 98,99,100 are fluidly connected. As can be seen in Figure 5, ports 97 and 100 are fluidly connected; ports 96 and 99 are fluidly connected; ports 90 and 94 are fluidly connected; and ports 91 and 95 are fluidly connected. The pump 80 may be driven by the vehicle engine and hence continuously actuated. Alternatively, the pump 80 may be driven by an electric motor or any other suitable means, either continuously, or variably. The pressure control valves 85,86 are actuated to adjust the fluid pressure in the hydraulic system between a predetermined minimum pressure and a predetermined maximum pressure. The first pressure control valve 85 is also actuated to adjust the pressure differential between the first and second chambers 58,60 of the front hydraulic actuator 34 (when the directional valves 82,83,84 are also actuated as required). The second pressure control valve 86 is also actuated to adjust the pressure differential between the first and second chambers 58', 60' of the rear hydraulic actuator 34' (when the directional valves 82,83,84 are also actuated as required). The electrical control circuit includes an electronic and/or computerised control module 70. The control module 70 operates the directional valves 82-84, and the pressure control valves 85,86, when required, and may operate the pump 80. The control module 70 actuates the valves 82-86 dependent on predetermined vehicle conditions which are determined by signals from one or more sensors, such as a first pressure sensor 76 (which detects the fluid pressure associated with the front hydraulic actuator 34), a second pressure sensor 77 (which detects the fluid pressure associated with the rear hydraulic actuator 34'), a lateral g sensor 74 (which monitors the sideways acceleration of the vehicle), a steering sensor 72 (which monitors the steering angle of the front wheels 12), a vehicle speed sensor 78, and/or any other relevant parameter. If the control module 70 detects that roll control is required

(due, for example, to cornering of the motor vehicle 10), the control module determines if the module has to generate a force F, F' which acts on the piston rods 64,64' respectively to extend the front and rear actuators 34,34', or to compress the front and rear actuators, in an axial direction. In the present invention, the force F on the front actuator 34 may be different from the force F' on the rear actuator 34'. Figure 5B illustrates the circuit of Figure 5 when the actuators 34,34' are subject to compression. In this case, the first and third directional valves 82 and 84 are actuated, whilst the second directional valve 83 is de actuated. In this mode of operation, the first fluid chambers 58, 58' are at substantially the same pressure, whereas the second fluid chambers 60, 60' are (or may be) at different pressures dependent on the actuation of the pressure control valves 85, 86. Figure 5C illustrates the circuit of Figure 5 when the actuators 34, 34' are subject to extension. In this case, the first and second directional valves 82, 83 are actuated, whilst the third directional valve 84 is de-actuated. In this mode of operation, the first and second fluid chambers 58, 60 of the front actuator 34 are at substantially the same pressure, and the first and second fluid chambers 58', 60' of the rear actuator 34' are at substantially the same pressure, but the pressures in the front and rear actuators are (or may be) different dependent on the actuation of the pressure control valves 85, 86. Figure 6 illustrates a first alternative of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figures 1 to 4. Figure 6 is a modification of the hydraulic circuit shown in Figure 5, in which changes have been made to the first and second directional valves 82,83. In this alternative, in the de-actuated state of the first directional valve 82, the first and second ports 90,91 are fluidly connected; and the third and fourth ports 92,93 are fluidly connected, but isolated from the first and second ports. Also, in the de-actuated state of the second directional valve 83, the first and second ports 94,95 are fluidly isolated from one another and from the third and fourth ports 96,97; but the third and fourth ports are fluidly connected. The operation of this first alternative is substantially the same as the operation of the arrangement shown in Figure 5. Figure 6 A illustrates a modification to the circuit of Figure 6. In Figure 6A, only two directional valves 882 and 883 are required. The first directional valve 882 has five ports 90-94. The second directional valve 883 has five ports 95-99. The first port 90 of the first directional valve 882 is fluidly connected to the first output 88 of the flow divider 87 and to the second chamber 60 of the front actuator 34; the second port 91 is fluidly connected to the second output 89 of the flow divider and to the second chamber 60' of the rear actuator 34'; the third port 92 is fluidly connected to the fourth port 98 of the second directional valve 883; the fourth port 93 is fluidly connected to the first chamber 58' of the rear actuator 34'; and the fifth port 94 is fluidly connected to the first chamber 58 of the front actuator 34. In the de-actuated state of the first directional valve 882 (as shown in Figure 6A), the first and second ports 90,91 are fluidly isolated, and the third, fourth and fifth ports 92-93 are fluidly connected. In the actuated state of the first directional valve 882, the first and fifth ports 90,94 are fluidly connected, the second and fourth ports 91,93 are fluidly connected, and the third port 92 is fluidly isolated. The first port 95 of the second directional valve 883 is fluidly connected to the reservoir 81; the second port 96 is fluidly connected to the pump 80; the third port 97 is fluidly connected to the input of the flow divider 87; the fourth port 98 is fluidly connected to the third port 92 of the first directional valve 882; and the fifth port 99 is fluidly connected to the outputs from the first and second pressure control valves 85,86. In the de-actuated state of the second directional valve 883 (as shown in Figure 6A), the first and second ports 95,96 are fluidly connected, and the third, fourth and fifth ports 97-99 are fluidly isolated. In the actuated state of the second directional valve 883, the first, fourth and fifth ports 95,98,99 are fluidly connected, and the second and third ports 96,97 are fluidly connected. Figure 7 illustrates a second alternative of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figures 1 to 4. Figure 7 is a modification of the hydraulic circuit shown in Figure 5, in which changes have been made to the first and second directional valves 82,83, and in which the third directional valve 84 has been split into two separate valves 84 ',84". In this alternative, in the de-actuated state of the first directional valve 82, the first and second ports 90,91 are fluidly isolated from one another and from the third and fourth ports 92,93; and the third and fourth ports are fluidly connected. Also, in the de-actuated state of the second directional valve 83, the first and second ports 94,95 are fluidly isolated from one another and from the third and fourth ports 96,97; but the third and fourth ports are fluidly connected. The two valves 84', 84" of the third directional valve 84 are substantially identical. Each valve 84 ',84" has first and second ports 98, 99. The first ports 98 are fluidly connected to the reservoir 81. The second port 99 of the first valve 84' is fluidly connected to the second chamber 60 of the front actuator 34. The second port 99 of the second valve 84" is fluidly connected to the first chamber 58' of the rear actuator 34'. The valves 84 ',84" have a de-actuated state as shown in Figure 7 is which the first and second ports 98,99 are fluidly isolated; and an actuated state in which the first and second ports are fluidly connected. This second alternative essentially has two actuation modes. In a first mode, the directional valves 82, 84" are actuated, and directional valves 83, 84' are de-actuate, to provide an arrangement substantially the same as in Figure 5B. In a second mode, the directional valves 83, 84' are actuated, and directional valves 82, 84" are de actuated, such that the second fluid chambers 60, 60' are at substantially the same pressure, whereas the first fluid chambers 58, 58' are (or may be) at different pressures dependent on the actuation of the pressure control valves 85, 86. There is an optional third mode in which the directional valves 82,83 are actuated, and the directional valves 84', 84" are de-actuated, but this mode is unlikely to be used. Figure 8 illustrates a third alternative of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figures 1 to 4. Figure 8 is a modification of the hydraulic circuit shown in Figure 5, in which changes have been made to the three directional valves have been replaced by first and second directional valves 82 ',83' fluidly connected in series. The first directional valve 82' has eight ports 90-97. The first port 90 is fluidly connected to the first output 88 of the flow divider 87. The second port 91 is fluidly connected to the fluid reservoir 81. The third port 92 is fluidly connected to the second output 89 of the flow divider 87. The fourth port 93 is fluidly connected to the fluid reservoir 81. The second directional valve 83' has eight ports 98-105. The first port 98 is fluidly connected to the eighth port 97 of the first directional valve 82'. The second port 99 is fluidly connected to the seventh port 96 of the first directional valve 82'. The third port 100 is fluidly connected to the sixth port 95 of the first directional valve 82'. The fourth port 101 is fluidly connected to the fifth port 94 of the first directional valve 82' . The fifth port 102 is fluidly connected (via fluid line 66') to the first chamber 58' of the rear actuator 34'. The sixth port 103 is fluidly connected (via fluid line 68') to the second chamber 60' of the rear actuator 34'. The seventh port 104 is fluidly connected (via fluid line 66) to the first chamber 58 of the front actuator 34. The eighth port 105 is fluidly connected (via fluid line 68) to the second chamber 60 of the front actuator 34. In this alternative, in the de-actuated state of the first directional valve 82', the first and eighth ports 90,97 are fluidly connected; the second and seventh ports 92,96 are fluidly connected; the third and sixth ports 92,95 are fluidly connected; and the fourth and fifth ports 93,94 are fluidly connected. In the actuated state of the first directional valve 82', the first, seventh and eighth ports 90, 96, 97 are fluidly connected; the third, fifth and sixth ports 92,94,95 are fluidly connected; and the second and fourth ports 91,93 are closed. Also, in the de-actuated state of the second directional valve 83', the first and second ports 98,99 are fluidly connected; the third and fourth ports 100,101 are fluidly connected; the fifth and seventh ports 102,104 are fluidly connected; and the sixth and eighth ports 103,105 are fluidly connected. In the actuated state of the second directional valve 83', the first and eighth ports 98,105 are fluidly connected; the second and seventh ports 99,104 are fluidly connected; the third and sixth ports 100,103 are fluidly connected; and the fourth and fifth ports 101,102 are fluidly connected. The operation of this third alternative is substantially the same as the operation of the arrangement shown in Figure 5. Figure 8A illustrates a modification to the arrangement of

Figure 8, and in particular a modification to the second directional valve 83' in which, during de-energisation (as shown), the fifth, sixth, seventh and eighth ports 102-105 are fluidly isolated from one another and from the other ports 98-101. The above-described embodiments all operate in substantially the same way, but provide different hydraulic circuit arrangements for their respective fail-safe modes, as illustrated in the drawings. Also, the selection is dependent on the type of hydraulic actuator that is used. Figure 9 illustrates a fourth alternative of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figures 1 to 4. In this fourth alternative, the hydraulic circuit includes a fluid pump 480, a fluid reservoir 481, a first pair of pressure control valves 485, 485' associated with the front hydraulic actuator 34, a second pair of pressure control valves 486, 486' associated with the rear hydraulic actuator 34', and a fluid flow divider 487. The fluid flow divider 487 has an input fluidly connected to the pump 480, a first outlet 488 fluidly connected to the input of the first pressure control valve 485 associated with the front actuator 34, and a second output 489 fluidly connected to the input of the first pressure control valve 485' associated with the rear actuator 34'. The first pair of pressure control valves 485,485' associated with the front actuator 34 are fluidly connected in series, with the output of one valve 485 fluidly connected to the input of the other valve 485'. The output of the other valve 485' is fluidly connected to the reservoir 481. The second chamber 60 of the front actuator 34 is fluidly connected to the input of the one valve 485 by way of fluid line 68. The first chamber 58 of the front actuator 34 is fluidly connected to the output of the one valve 485 by way of fluid line 66. The second pair of pressure control valves 486, 486' associated with the rear actuator 34' are fluidly connected in series, with the output of the one valve 486 fluidly connected to the input of the other valve 486' . The output of the other valve 486' is fluidly connected to the reservoir 481. The second chamber 60' of the rear actuator 34' is fluidly connected to the input of the one valve 486 by way of fluid line 68'. The first chamber 58' of the rear actuator 34' is fluidly connected to the output of the one valve 486 by way of fluid line 66' . The pump 480 may be driven by the vehicle engine and hence continuously actuated. Alternatively, the pump 480 may be driven by an electric motor or any other suitable means, either continuously, or variably. The first pair of pressure control valves 485, 485' are actuated to adjust the pressure differential between the first and second chambers 58,60 of the front hydraulic actuator 34. The second pair of pressure control valves 486, 486' are actuated to adjust the pressure differential between the first and second chambers 58', 60' of the rear hydraulic actuator 34'. The pressure control valves 485, 485', 486, 486' are also actuated to adjust the fluid pressure in the hydraulic system for the front actuator 34 and the rear actuator 34' between a predetermined -minimum pressure and a predetermined maximum pressure, and to adjust the pressure differential between the front and rear actuators. The electrical control circuit includes an electronic and/or computerised control module 70. The control module 70 operates the fluid pump 480, and the pressure control valves 485, 485', 486, 486' when required. The control module 70 actuates the valves 485, 485', 486, 486' dependent on predetermined vehicle conditions which are determined by signals from one or more sensors, such as a first pressure sensor 76 (which detects the fluid pressure associated with the front hydraulic actuator 34), a second pressure sensor 77 (which detects the fluid pressure associated with the rear hydraulic actuator 34'), a lateral g sensor 74 (which monitors the sideways acceleration of the vehicle), a steering sensor 72 (which monitors the steering angle of the front wheels 12), a vehicle speed sensor 78, and/or any other relevant parameter. If the control module 70 detects that roll control is required

(due, for example, to cornering of the motor vehicle 10), the control module determines if the module has to generate a force F, F' which acts on the piston rods 64,64' respectively to extend the front and rear actuators 34,34' , or to compress the front and rear actuators, in an axial direction. In the present invention, the force F on the front actuator 34 may be different from the force F' on the rear actuator 34'. Figure 10 illustrates a fifth alternative of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figures 1 to 4. Figure 10 is a modification of the hydraulic circuit shown in Figure 9 in which a first directional valve 482 is positioned in the fluid lines 66, 68, and in which a second directional valve 483 is positioned in the fluid lines 66', 68'. The first directional valve 482 has a first port 490 fluidly connected to the first output 488 of the flow divider 487; a second port 491 fluidly connected to the output of the one pressure control valve 485 of the first pair; a third port 492 fluidly connected to the first chamber 58 (by way of fluid line 66) of the front hydraulic actuator 34; and a fourth port 493 fluidly connected to the second chamber 60 (by way of fluid line 68) of the front hydraulic actuator 34. The first directional valve 482 is solenoid actuated, and has a de actuated state (shown in Figure 10) in which the first and second ports 490, 491 are fluidly connected, and the third and fourth ports 492, 493 are isolated from one another and from the first and second ports. In the actuated state of the first directional valve 482, the first and fourth ports 490, 493 are fluidly connected, and the second and third ports 491, 492 are fluidly connected. The second directional valve 483 has a first port 494 fluidly connected to the second output 489 of the flow divider 487; a second port 495 fluidly connected to the output of the one pressure control valve 486 of the second pair; a third port 496 fluidly connected to the first chamber 58' (by way of fluid line 66') of the rear hydraulic actuator 34'; and a fourth port 497 fluidly connected to the second chamber 60' (by way of fluid line 68') of the rear hydraulic actuator 34'. The second directional valve 483 is solenoid actuated, and has a de-actuated state (shown in Figure 10) in which the first and second ports 494, 495 are fluidly connected, and the third and fourth ports 496, 497 are isolated from one another and from the first and second ports. In the actuated state of the second directional valve 483, the first and fourth ports 494, 497 are fluidly connected, and the second and third ports 495, 496 are fluidly connected. The control module 70 is connected to, and actuates, the directional valves 482, 483 dependent on the predetermined vehicle conditions. In this alternative, when the directional valves 482, 483 are actuated, the pressure control valves 485, 485', 486, 486' are actuated and the operation of this fifth alternative is substantially the same as the operation of the arrangement shown in Figure 9. Figure 11 illustrates a sixth alternative of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figures 1 to 4. Figure 11 is a modification of the hydraulic circuit shown in Figure 9 in which a first directional valve 582 is positioned in the fluid lines 68,68', and in which a second directional valve 583 is positioned in the fluid lines 66,66'. The first directional valve 582 has a first port 590 fluidly connected to the first output 488 of the flow divider 487; a second port 591 fluidly connected to the second output 489 of the flow divider 487; a third port 592 fluidly connected to the second chamber 60' (by way of fluid line 68') of the rear hydraulic actuator 34'; and a fourth port 593 fluidly connected to the second chamber 60 (by way of fluid line 68) of the front hydraulic actuator 34. The first directional valve 582 is solenoid actuated, and has a de-actuated state (shown in Figure 11) in which the first and second ports 590, 591 are fluidly connected, and the third and fourth ports 592, 593 are fluidly connected but isolated from the first and second ports. In the actuated state of the first directional valve 582, the first and fourth ports 590, 593 are fluidly connected, and the second and third ports 591, 592 are fluidly connected. The second directional valve 583 has a first port 594 fluidly connected to the output of the one pressure control valve 485 of the first pair; a second port 595 fluidly connected to the output of the one pressure control valve 486 of the second pair; a third port 596 fluidly connected to the first chamber 58' (by way of fluid line 66') of the rear hydraulic actuator 34'; and a fourth port 597 fluid connected to the first chamber 58 (by way of fluid line 66) of the front hydraulic actuator 34. The second directional valve 583 is solenoid actuated, and has a de-actuated state (shown in Figure 11) in which the first and second ports 594, 595 are fluidly connected, and the third and fourth ports 596,597 are fluidly connected but isolated from the first and second ports. In the actuated state of the second directional valve 583, the first and fourth ports 594, 597 are fluidly connected, and the second and third ports 595, 596 are fluidly connected. The control module 70 is connected to, and actuates, the directional valves 582, 583 dependent on the predetermined vehicle conditions. The operation of this sixth alternative is substantially the same as the operation of the arrangement shown in Figure 10. Figure 12 illustrates a seventh alternative of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figures 1 to 4. Figure 12 is a modification of the hydraulic circuit shown in Figure 10 in which the first and second directional valves have been combined into a single directional valve 682 is positioned in the fluid lines 66,66', 68,68'. The directional valve 682 has a first port 690 fluidly connected to the first output 488 of the flow divider 487; a second port 691 fluidly connected to the output of the one pressure control valve 485 of the first pair; a third port 692 fluidly connected to the first chamber 58 (by way of fluid line 66) of the front hydraulic actuator 34; and a fourth port 693 fluidly connected to the second chamber 60 (by way of fluid line 68) of the front hydraulic actuator 34. The directional valve 682 has a fourth port 694 fluidly connected to the second output 489 of the flow divider 487; a fifth port 695 fluidly connected to the output of the one pressure control valve 486 of the second pair; a seventh port 696 fluidly connected to the first chamber 58' (by way of fluid line 66') of the rear hydraulic actuator 34'; and an eighth port 697 fluidly connected to the second chamber 60' (by way of fluid line 68') of the rear hydraulic actuator 34'. The directional valve 682 is solenoid actuated, and has a de-actuated state (shown in Figure 12) in which the first and second ports 690, 691 are fluidly connected, the third and fourth ports 692, 693 are isolated from one another and from the other ports, the fifth and sixth ports 694, 695 are fluidly connected, and the seventh and eighth ports 696, 697 are isolated from one another and from the other ports. In the actuated state of the directional valve 682, the first and fourth ports 690, 693 are fluidly connected, the second and third ports 691, 692 are fluidly connected, the fifth and eighth ports 694, 697 are fluidly connected, and the sixth and seventh ports 695, 696 are fluidly connected. The control module 70 is connected to, and actuates, the directional valve 682 dependent on the predetermined vehicle conditions. The operation of this seventh alternative is substantially the same as the operation of the arrangement shown in Figure 10. Figure 13 illustrates an eighth alternative of the hydraulic and electrical control circuit of the vehicle roll control system shown in Figures 1 to 4. Figure 13 is a modification of the hydraulic circuit shown in Figure 12. The directional valve 782 has a first port 790 fluidly connected to the first output 488 of the flow divider 487; a second port 791 fluidly connected to the output of the one pressure control valve 485 of the first pair; a third port 792 fluidly connected to the first chamber 58 (by way of fluid line 66) of the front hydraulic actuator 34; and a fourth port 793 fluidly connected to the second chamber 60 (by way of fluid line 68) of the front hydraulic actuator 34. The directional valve 782 has a fourth port 794 fluidly connected to the second output 489 of the flow divider 487; a fifth port 795 fluidly connected to the output of the one pressure control valve 486 of the second pair; a seventh port 796 fluidly connected to the first chamber 58' (by way of fluid line 66') of the rear hydraulic actuator 34'; and an eighth port 797 fluidly connected to the second chamber 60' (by way of fluid line 68') of the rear hydraulic actuator 34' . The directional valve 782 is solenoid actuated, and has a de-actuated state (shown in Figure 13) in which the first and second ports 790, 791 are fluidly connected, the fifth and sixth ports 794, 795 are fluidly connected, the third and seventh ports 792, 796 are fluidly connected, and the fourth and eighth ports 793, 797 are fluidly connected. In the actuated state of the directional valve 782, the first and fourth ports 790, 793 are fluidly connected, the second and third ports 791, 792 are fluidly connected, the fifth and eighth ports 794, 797 are fluidly connected, and the sixth and seventh ports 795, 796 are fluidly connected. The control module 70 is connected to, and actuates, the directional valve 782 dependent on the predetermined vehicle conditions. The operation of this eighth alternative is substantially the same as the operation of the arrangement shown in Figure 10. The above-described embodiments of Figures 9 to 13 all operate in substantially the same way, but provide different hydraulic circuit arrangements for their respective fail-safe modes, as illustrated in the drawings. Also, the selection is dependent on the type of hydraulic actuator that is used. In the present invention, in all of the above embodiments, the valves of the hydraulic circuit are actuable to provide fluid pressure to the first fluid chamber of the front hydraulic actuator which is different from the fluid pressure provided to the first fluid chamber of the rear hydraulic actuator; and/or actuable to provide fluid pressure to the second fluid chamber of the front hydraulic actuator which is different from the fluid pressure provided to second fluid chamber of the rear hydraulic actuator. In all of the above embodiments, the directional valves are solenoid actuated. In an alternative arrangement, the directional valves may be hydraulically actuated by first and second pilot (on/off) valves, which pilot valves are controlled by the control module 70. The present invention is also applicable for use with a vehicle roll control system, the front portion 122 of which is as shown in Figure 14 and the rear portion of which is substantially identical to the front portion. In this embodiment in accordance with the present invention, the front portion 122 comprises a torsion bar 126, a first arm 128, and a hydraulic actuator 134. The first arm 128 is fixed at one end 138 to one end 140 of the torsion bar 126. The other end 142 of the first arm 128 is connected to one of the shock absorbers 120. The hydraulic actuator 134 has a piston rod 164 which is fixed to the other end 187 of the torsion bar 126. The housing 156 of the actuator 134 is connected to the other shock absorber 120. The hydraulic actuator 134 is substantially the same as the actuator 34 described above with reference to Figures 1 to 5, and has a fluid line 166 connected to a first fluid chamber inside the housing, and another fluid line 168 connected to a second fluid chamber inside the housing. The first and second fluid chambers inside the housing 156 are separated by a piston secured to the piston rod 164. The fluid lines 166,168 for each hydraulic actuator are connected to a hydraulic circuit as shown in Figure 5, which is controlled by a control circuit as shown in Figure 5, or any one of the arrangements shown in Figures 6 to 13. The roll control system is operated in substantially the same manner as that described above with reference to Figures 1 to5, or any one of Figures 6 to 13. The present invention is also applicable for use with a vehicle roll control system as shown in Figure 15. In this third embodiment in accordance with the present invention, the front portion 222 of the system comprises a torsion bar 226, a first arm 228, a second arm 228', and a hydraulic actuator 234. The rear portion of the system is substantially identical. The first arm 228 is fixed at one end 238 to one end 240 of the torsion bar 226. The other end 242 of the first arm 228 is connected to one of the shock absorbers 220. The second arm 228' is fixed at one end 238' to the other end 287 of the torsion bar 226. The other end 242' of the second arm 228' is connected to the other shock absorber 220'. The torsion bar 226 is split into first and second parts 290,292, respectively. The first and second parts 290,292 of the torsion bar 226 have portions 294,296, respectively, which are axially aligned. The axially aligned portions 294,296 are connected by a hydraulic actuator 234. The hydraulic actuator 234, as shown in Figure 16, comprises a cylindrical housing 256 which is connected at one end 239 to the portion 294 of the first part 290 of the torsion bar 226. The actuator 234 further comprises a rod 241 positioned inside the housing 256, extending out of the other end 243 of the housing, and connectable to the portion 296 of the second part 292 of the torsion bar 226. The rod 241 has an external screw thread 249 adjacent the housing 256. Balls 251 are rotatably positioned in hemispherical indentations 253 in the inner surface 255 of the housing 256 adjacent the screw thread 249. The balls 251 extend into the screw thread 249. The rod 241 is slidably and rotatably mounted in the housing 256 at the other end 243 by way of a bearing 259 positioned in the other end 243. This arrangement allows the rod 241 to rotate about its longitudinal axis relative to the housing 256, and to slide in an axial direction A relative to the housing. A piston chamber 261 is defined inside the housing 256. The rod 241 sealing extends into the piston chamber 261 to define a piston rod 264, and a piston 262 is secured to the end of the piston rod inside the piston chamber. The piston 262 makes a sealing sliding fit with the housing 256 and divides the chamber 261 into a first fluid chamber 258 and a second fluid chamber 260. The first fluid chamber 258 is fluidly connected to fluid line 266, and the second fluid chamber 260 is fluidly connected to fluid line 268. The fluid lines 266,268 are connected to a hydraulic circuit as shown in Figure 5, which is controlled by a control circuit as shown in Figure 5, or any one of the arrangements shown in Figures 6 to 13. The roll control system 222 is operated in substantially the same manner as that described above with reference to Figures 1 to 5, or any one of Figures 6 to 13 An alternative arrangement for the hydraulic actuator of Figure 16 is shown in Figure 17. In this alternative embodiment, the actuator 334 comprises a cylindrical housing 356 which is connected at one end 339 to the portion 294 of the first part 290 of the torsion bar 226. The actuator 334 further comprises a rod 341 positioned inside the housing 356, extending out of the other end 343 of the housing, and connectable to the portion 296 of the second part 292 of the torsion bar 226. The rod 341 has an external screw thread 349 adjacent the housing 356. Balls 351 are rotatably positioned in hemispherical indentations 353 in the inner surface 355 of the housing 356 adjacent the screw thread 349. The balls 351 extend into the screw thread 349. The rod 341 is slidably and rotatably mounted in the housing 356 at the other end 343 of the housing by way of a bearing 359 positioned in the other end. The rod 341 makes a sliding guiding fit with the inner surface 355 of the housing 356 at its end 341' remote from the second part 292 of the torsion bar 226. This arrangement allows the rod 341 to rotate about its longitudinal axis relative to the housing 356, and to slide in an axial direction A relative to the housing. First and second fluid chambers 358,360 are defined inside the housing 356. The rod 341 makes a sealing fit with the inner surface 355 of the housing 356 by way of seal 371 to define a piston 362. The first fluid chamber 358 is positioned on one side of the piston 362, and the second fluid chamber 360 is positioned on the other side of the piston. A seal 369 is positioned adjacent the bearing 359. A portion 364 of the rod 341 defines a piston rod which extends through the second fluid chamber 360. The first fluid chamber 358 is fluidly connected to fluid line 366, and the second fluid chamber 360 is fluidly connected to fluid line 368. The fluid lines 366,368 are fluidly connected with one of the hydraulic circuits shown in Figures 5 to 8 to actuate the actuator 334. A further alternative arrangement of hydraulic actuator 334' is shown in Figure 18. In this further alternative embodiment, the actuator 334' is substantially the same as the actuator 334 shown in Figure 17, but without the sliding guiding fit of the free end 341' of the rod 341 with the housing 356. In a preferred arrangement, the cross-sectional area of the first fluid chamber of each hydraulic actuator described above is substantially double the cross-sectional area of the piston rod of the hydraulic actuator, when considered on a radial basis. Such an arrangement provides the same output force from the hydraulic actuator in either direction. In the preferred arrangement described above, a hydraulic actuator is provided for both the front of the vehicle and the rear of the vehicle, and these hydraulic actuators are substantially the same. In an alternative arrangement, the hydraulic actuator for the front of the vehicle may be a different type to the hydraulic actuator for the rear of the vehicle. In any of the roll control systems described above, the hydraulic actuator may include a check valve (not shown, but preferably mounted in the piston) which allows flow of hydraulic fluid from the first fluid chamber to the second fluid chamber only when the fluid pressure in the first fluid chamber is greater than the fluid pressure in the second fluid chamber. With such an arrangement, the second fluid chamber can be connected to a reservoir during servicing of the actuator to bleed air from the hydraulic fluid. Also, the presence of the check valve reduces the risk of air being sucked into the second fluid chamber should the fluid pressure in the second fluid chamber fall below the fluid pressure in the first fluid chamber, and provides further improvements in ride comfort.

Claims

Claims 1. A vehicle roll control system for a vehicle having a pair of front wheels and a pair of rear wheels each rotatable on an axle, comprising a front torsion bar; a front first arm attached to the front torsion bar at one end of the front first arm and being connectable to one of the axles of the front wheels at the other end of the front first arm; a front hydraulic actuator attached to the front torsion bar; a rear torsion bar; a rear first arm attached to the rear torsion bar at one end of the rear first arm and being connectable to one of the axles of the rear wheels at the other end of the rear first arm; a rear hydraulic actuator attached to the rear torsion bar; and control means connected to the front and rear hydraulic actuators and controlling the operation thereof on detection of a predetermined vehicle condition; wherein each front and rear hydraulic actuator comprises a housing, a piston making a sealing sliding fit inside the housing to define a first fluid chamber and a second fluid chamber, and a piston rod connected to the piston and extending through the second fluid chamber and out of the housing; wherein the control means acts on detection of the predetermined vehicle condition to apply a fluid pressure to the first fluid chamber of the front hydraulic actuator which is different from the fluid pressure applied to the first fluid chamber of the rear hydraulic actuator and/or apply a fluid pressure to the second fluid chamber of the front hydraulic actuator which is different from the fluid pressure applied to the second fluid chamber of the rear hydraulic actuator; and wherein the control means comprises a source of fluid pressure, a fluid reservoir, a fluid flow path divider fluidly connected to the pressure source and having a first output and a second output, a first pressure control valve fluidly connected between the first output of the flow divider and the reservoir to control the fluid pressure in the first or second fluid chamber of the front actuator, a second pressure control valve connected between the second output of the flow divider and the reservoir to control the fluid pressure in the first or second fluid chamber of the rear actuator; wherein the pressure control valves are actuated to create the pressure differential between the first fluid chambers and/or to create the pressure differential between the second fluid chambers.

2. A vehicle roll control system as claimed in Claim 1, wherein the first pressure control valves comprises a pair of pressure control valves fluidly connected in series in which one of the valves controls the pressure differential between the first and second fluid chambers of the front actuator and the other valve controls the pressure differential between the first fluid chamber of the front actuator and the reservoir; and wherein the second pressure control valve comprises a pair of pressure control valves fluidly connected in series in which one of the valves controls the pressure differential between the first and second fluid chambers of the rear actuator and the other valve controls the pressure differential between the first fluid chamber of the rear actuator and the reservoir.

3. A vehicle roll control system as claimed in Claim 2, wherein the control means further comprises first and second directional valves, the first directional valve being fluidly connected in parallel with said one pressure control valve of the first pair between said one pressure control valve and the front actuator, and the second directional valve being fluidly connected in parallel with said one pressure control valve of the second pair between said one pressure control valve and the rear actuator.

4. A vehicle roll control system as claimed in Claim 3, wherein the first directional valve, in its de-actuated state, fluidly isolates the first and second fluid chambers of the front actuator, and wherein the second directional valve, in its de-actuated state, fluidly isolates the first and second fluid chambers of the rear actuator.

5. A vehicle roll control system as claimed in Claim 3, wherein the first directional valve, in its de-actuated state, fluidly connects the first and second fluid chambers of the front actuator, and wherein the second directional valve, in its de-actuated state, fluidly connects the first and second fluid chambers of the rear actuator.

6. A vehicle roll control system as claimed in Claim 2, wherein the control means further comprises a directional valve, the directional valve being fluidly connected in parallel with said one pressure control valve of the first pair between said one pressure control valve and the front actuator, and being fluidly connected in parallel with said one pressure control valve of the second pair between said one pressure control valve and the rear actuator.

7. A vehicle roll control system as claimed in Claim 6, wherein the directional valve, in its de-actuated state, fluidly isolates the first and second fluid chambers of the front actuator, and fluidly isolates the first and second fluid chambers of the rear actuator.

8. A vehicle roll control system as claimed in Claim 6, wherein the directional valve, in its de-actuated state, fluidly connects the first fluid chambers of the actuators, and fluidly connects the second fluid chambers of the actuators.

9. A vehicle roll control system as claimed in Claim 1, wherein the control means further comprises first, second and third directional valves, the first directional valves being fluidly connected between the outputs of the flow divider and the second fluid chambers of the actuators, the second directional valve being fluidly connected between the outputs of the flow divider and the first fluid chambers of the actuators, and the third directional valve being fluidly connected between the first fluid chambers and the reservoir.

10. A vehicle roll control system as claimed in Claim 9, wherein the first directional valve, in its de-actuated state, fluidly isolates the second fluid chambers of the actuators, and wherein the second directional valve, in its de-actuated state, fluidly isolates the first fluid chambers of the actuators.

11. A vehicle roll control system as claimed in Claim 9, wherein the first directional valve, in its de-actuated state, fluidly connects the second fluid chambers of the actuators, and wherein the second directional valve, in its de-actuated state, fluidly connects the first fluid chambers of the actuators.

12. A vehicle roll control system as claimed in Claim 1, wherein the control means further comprises first, second, third and fourth directional valves, the first directional valves being fluidly connected between the outputs of the flow divider and the second fluid chambers of the actuators, the second directional valve being fluidly connected between the outputs of the flow divider and the first fluid chambers of the actuators, the third directional valve being fluidly connected between the first fluid chamber of the rear actuator and the reservoir, and the fourth directional valve being fluidly connected between the second fluid chamber of the front actuator and the reservoir.

13. A vehicle roll control system as claimed in Claim 12, wherein the first directional valve, in its de-actuated state, fluidly connects the second fluid chambers of the actuators, and wherein the second directional valve, in its de-actuated state, fluidly connects the first fluid chambers of the actuators.

14. A vehicle roll control system as claimed in Claim 1, wherein the control means further comprises first and second directional valves, the first directional valve being fluidly connected between the outputs of the flow divider and the fluid chambers of the actuators, and the second directional valve being fluidly connected between the pressure source and the flow divider, and between the pressure control valves and the reservoir.

15. A vehicle roll control system as claimed in Claim 1, wherein the control means further comprises first and second directional valves, the directional valves being fluidly connected in series between the outputs of the flow divider and the fluid chambers of the actuators.

16. A vehicle roll control system as claimed in any one of Claims 3 to 15, wherein the or each directional valve is actuated by a solenoid.

17. A vehicle roll control system as claimed in any one of Claims 1 to 16, wherein the control means further comprises an electronic control module which receives signals dependent on the predetermined vehicle condition, and which controls the position of the first and second directional valves.

18. A vehicle roll control system as claimed in any one of Claims 1 to 17, wherein the cross-sectional area of the first fluid chamber of each actuator is substantially double the cross-sectional area of the piston rod of each actuator.

19. A vehicle roll control system as claimed in any one of Claims 1 to 18, wherein the front hydraulic actuator is attached to the front torsion bar at one end of the front hydraulic actuator and is connectable to the other axle of the front wheels at the other end of the front hydraulic actuator; and wherein the rear hydraulic actuator is attached to the rear torsion bar at one end of the rear hydraulic actuator and is connectable to the other axle of the rear wheels at the other end of the rear hydraulic actuator.

20. A vehicle roll control system as claimed in Claim 19; further comprising a second front arm rotatably mounted on the front torsion bar at one end of the second front arm and being connectable to the other axle of the front wheels at the other end of the second front arm; wherein the front hydraulic actuator controls the rotation of the second front arm relative to the front torsion bar; and further comprising a second rear arm rotatably mounted on the rear torsion bar at one end of the second rear arm and being connectable to the other axle of the rear wheels at the other end of the second rear arm; wherein the rear hydraulic actuator controls the rotation of the second rear arm relative to the rear torsion bar.

21. A vehicle roll control system as claimed in any one of Claims 1 to 18, wherein each hydraulic actuator is attached directly to its associated torsion bar at one end of the hydraulic actuator.

22. A vehicle roll control system as claimed in any one of Claims 1 to 18, wherein each hydraulic actuator is attached to its associated torsion bar between axially aligned portions of first and second parts of the torsion bar.

23. A vehicle roll control system as claimed in any one of Claims 1 to 22, wherein each hydraulic actuator includes a check valve which allows fluid to flow from the first fluid chamber to the second fluid chamber when the fluid pressure in the first fluid chamber exceeds the fluid pressure in the second fluid chamber.

24. A vehicle roll control system as claimed in Claim 23, wherein the check valve is mounted in the piston.