Abstract:
A vehicle roll control system for a vehicle having a hydraulic actuator attached to a torsion bar, and means for controlling the operation thereof on detection of a predetermined vehicle condition to either extend or compress the hydraulic actuator, the control means including pressure control valves that are actuated to control the fluid pressure within the hydraulic actuator.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a roll control system for a motor vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002]     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 a hydraulic actuator. During a change in cornering (left to right turn or vice versa), the switching of the directional valves has to be controlled in such a manner that roll control of the vehicle is discontinuous.  
       SUMMARY OF THE INVENTION  
       [0003]     The aim of the present invention is to provide a roll control system, which is an improvement to the above-mentioned arrangement.  
         [0004]     A vehicle roll control system in accordance with the present invention for a vehicle having a pair of wheels each rotatable on an axle includes a torsion bar; a first arm attached to the torsion bar at one end of the first arm and being connectable to one of the axles at the other end of the first arm; a hydraulic actuator attached to the torsion bar; and control means connected to the hydraulic actuator and controlling the operation thereof on detection of a predetermined vehicle condition; wherein the hydraulic actuator includes 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 either to apply fluid pressure to the first and second fluid chambers with a substantially fixed pressure differential when the piston tends to move in a first direction to extend the hydraulic actuator, or to apply a fluid pressure to the second fluid chamber above the fluid pressure in the first fluid chamber whilst maintaining the fluid pressure in the first fluid chamber substantially constant when the piston tends to move in a second direction to compress the hydraulic actuator; and wherein the control means includes a source of fluid pressure, a fluid reservoir, first and second pressure control valves fluidly connected in series between the pressure source and the reservoir, and a directional valve fluidly connected between the pressure control valves and the hydraulic actuator, wherein the pressure control valves are actuated to control the fluid pressure in the first and second fluid chambers.  
         [0005]     The present invention provides active roll control in which roll control can be substantially continuous during a change in cornering. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0007]      FIG. 1  is a schematic presentation of a vehicle incorporating a vehicle roll control system in accordance with the present invention;  
         [0008]      FIG. 2  is an enlarged view of the front and rear portions of the vehicle roll control system shown in  FIG. 1 ;  
         [0009]      FIG. 3  is a side view of the first arm of the vehicle roll control system shown in  FIG. 2 ;  
         [0010]      FIG. 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  FIG. 2 ;  
         [0011]      FIG. 5  is a schematic diagram of the hydraulic and electrical control circuit of the vehicle roll control system shown in  FIG. 1  when the directional valve is de-energized;  
         [0012]      FIG. 6  is a schematic diagram of the hydraulic and electrical control circuit of  FIG. 5  when the directional valve is actuated;  
         [0013]      FIG. 7  is a schematic diagram of a first alternative arrangement for the hydraulic circuit of a vehicle roll control system in accordance with the present invention when the directional valve is de-energized;  
         [0014]      FIG. 8  is a schematic diagram of a second alternative arrangement for the hydraulic circuit of a vehicle roll control system in accordance with the present invention when the directional valve is de-energized;  
         [0015]      FIG. 9  is a view of a portion of a vehicle roll control system in accordance with a second embodiment of the present invention;  
         [0016]      FIG. 10  is a view of a vehicle roll control system in accordance with a third embodiment of the present invention;  
         [0017]      FIG. 11  is a cross-section view of the hydraulic actuator of the vehicle roll control system of  FIG. 10 ;  
         [0018]      FIG. 12  is a cross-sectional view of an alternative embodiment of hydraulic actuator for the vehicle roll control system of  FIG. 10 ;  
         [0019]      FIG. 13  is a cross-sectional view of a further alternative embodiment of hydraulic actuator for the vehicle roll control system of  FIG. 10 ; and  
         [0020]      FIG. 14  is a graph of fluid pressure against actuator force. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     Referring to  FIG. 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 .  
         [0022]     Referring in more detail to FIGS.  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  ( FIG. 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  ( FIG. 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 the 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 .  
         [0023]     The lever arm  32  ( FIG. 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 hydraulic actuator  34  ( FIG. 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 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  FIG. 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  34  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.  
         [0024]     The hydraulic and electrical control circuit of the vehicle roll control system is shown in  FIGS. 5 and 6 . The hydraulic circuit includes a fluid pump  80 , a fluid reservoir  82 , a directional valve  84 , a first pressure control valve  86 , and a second pressure control valve  88 . The first pressure control valve  86  has an input fluidly connected to the output of the pump  80  and an output fluidly connected to the input to the second pressure control valve  88 . The second pressure control valve  88  has an output fluidly connected to the input to the reservoir  82 .  
         [0025]     The directional valve  84  has a first port  90  fluidly connected to the output of pump  80 ; a second port  92  fluidly connected to fluid line  87  connecting the first and second pressure control valves  86 , 88 ; a third port  94  fluidly connected to the fluid line  66  and the first fluid chamber  58  of each hydraulic actuator  34 , 34 ′; and a fourth port  96  fluidly connected to the fluid line  68  and the second fluid chamber  60  of each hydraulic actuator. The directional valve  84  is solenoid actuated, and has a de-energized state ( FIG. 5 ) in which the first and second ports  90 ,  92  are fluidly connected, and the third and fourth ports  94 , 96  are isolated from one another and from the other ports, and an energized or actuated state ( FIG. 6 ) in which the first port  90  is fluidly connected with the fourth port  96 , and in which the second port  92  is fluidly connected with the third port  94 .  
         [0026]     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  86 , 88  are actuated to adjust the fluid pressure in the hydraulic system between a predetermined minimum pressure and a predetermined maximum pressure, and to adjust the pressure differential between the first and second chambers  58 , 60  of each hydraulic actuator  34 , 34 ′ (when the directional valve  84  is actuated).  
         [0027]     The electrical control circuit includes an electronic and/or computerized control module  70 . The control module  70  operates the fluid pump  80 , the directional valve  84 , and the pressure control valves  86 , 88 , when required. The control module  70  actuates the valves  84 , 86 , 88  dependent on predetermined vehicle conditions which are determined by signals from one or more sensors, such as a pressure sensor  76  (which detects the presence of fluid pressure in the hydraulic circuit), a pressure sensor  77  (which detects the fluid pressure in line  87 ), 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.  
         [0028]     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 which acts on the piston rod  64  to extend the actuators  34 , 34 ′, or to compress the actuators, in an axial direction. For extension, the control module  70  actuates the pressure control valves  86 , 88  to provide a predetermined fluid pressure in each of the first and second fluid chambers  58 , 60 , which correlates with the force F, and sets the directional valve  84  in the actuated position as shown in  FIG. 6 . In this case, the pressure differential between the first and second chambers  58 , 60  is maintained substantially constant as the level of the fluid pressure increases or decreases as required. For compression, the control module  70  actuates the pressure control valves  86 , 88  to provide a substantially constant fluid pressure in the first chamber  58  and a predetermined fluid pressure in the second chamber  60  (which is greater than the fluid pressure in the first chamber) which correlates with the force F, and again sets the directional valve  84  in the actuated position as shown in  FIG. 6 . In this case, the pressure differential between the first and second chambers  58 , 60  varies as the fluid pressure in the second chamber increases or decreases. A graph illustrating the fluid pressure in the first and second chambers  58 , 60  when the actuator  34 , 34 ′ is subjected to a compression force or an extension force is shown in  FIG. 14 .  
         [0029]     If the control module  70  detects, for example, that the vehicle is travelling in a straight line, the control module actuates the pressure control valves  86 , 88  and the directional valve  84 , and generates fluid pressure in the first and second chambers  58 , 60  such that the actuators  34 , 34 ′ neither extend nor compress in the axial direction.  
         [0030]     By suitable dimensions for the actuators  34 , 34 ′, the output force from the actuators can be made substantially the same irrespective of the direction of motion of the piston  62 .  
         [0031]     In the failure mode, or during certain diagnostics, the directional valve  84  is de-energized (as shown in  FIGS. 5 ) such that the hydraulic actuators  34 , 34 ′ are locked. Fluid can freely flow within the hydraulic system between the pump  80  and the reservoir  82  by way of the first and second ports  90 , 92  of the directional valve  84 , and the second pressure control valve  88  (which may include a pressure relief valve). As the third and fourth ports  94 , 96  of the directional valve  84  are closed and isolated, the actuators  34 , 34 ′ are effectively locked.  
         [0032]      FIG. 7  shows a first alternative arrangement for the hydraulic circuit in which (in comparison to  FIGS. 5 and 6 ) like parts have been given the same reference numeral. In this first alternative, the directional valve  184  has a fifth port  97  fluidly connected to the input of the fluid reservoir  82 . In the de-energized state of the directional valve  184 , the first, second and fifth ports  90 , 92 , 97  are fluidly connected with each other and to the fluid reservoir  82 . In the energized or actuated state of the directional valve  184 , the fifth port  97  is fluidly isolated from the other ports  90 - 96 . The presence of the fifth port  97  removes the need for actuation of the second pressure control valve  88  (when the directional valve  184  is de-energized), or the presence of a pressure relief for the second pressure control valve. Other features and operation of this first alternative hydraulic circuit in a vehicle roll control system in accordance with the present invention are as described above in respect of FIGS.  1  to  6 , and  14 .  
         [0033]      FIG. 8  shows a second alternative arrangement for the hydraulic circuit in which (in comparison to  FIGS. 5 and 6 ) like parts have been given the same reference numeral. In this second alternative, the directional valve  284  has been split into two parts, a first part  284 ′ and a second part  284 ″. The two parts  284 ′, 284 ″ of the direction valve  284  are actuated separately, but in unison. The first part  284 ′ of the directional valve  284  incorporates the first port  90 , and the fourth port  96  which is fluidly connected with the second fluid chambers  60  of the hydraulic actuators  34 , 34 ′. The second part  284 ″ of the directional valve  284  incorporates the second port  92 , and the third port  94  which is fluidly connected with the first fluid chambers  58  of the hydraulic actuators  34 , 34 ′. The first part  284 ′ of the directional valve  284  has an additional port  92 ′ which is fluidly connected with the second port  92  of the second part  284 ″. The second part  284 ″ of the directional valve  284  has an additional port  97  which is fluidly connected with the input of the fluid reservoir  82 . In the de-energized state of the first and second parts  284 ′, 284 ″ of the directional valve  284 , the first port  90  is fluidly connected with the fluid reservoir  82  by way of ports  92 ′, 92  and  97  as shown in  FIG. 8 . In the energized state of the first and second parts  284 ′, 284 ″ of the directional valve  284 , the ports  92 ′ and  97 ′ are fluidly isolated from the other ports in the same part. The presence of the ports  92 ′, 97  removes the need for actuation of the second pressure control valve  88  (when the directional valve  284  is de-energized), or the presence of a pressure relief for the second pressure control valve. Other features and operation of this second alternative hydraulic circuit in a vehicle roll control system in accordance with the present invention are as described above in respect of FIGS.  1  to  6 , and  14 .  
         [0034]     In the present invention, the directional valve  84 ,  184 ,  284  is energized when roll control is required, irrespective of the direction of turn of the vehicle. The fluid pressure in the first and second fluid chambers  58 , 60  of the hydraulic actuators  34 , 34 ′ is controlled by the actuation of the first and second pressure control valves  86 , 88 . By adjusting the actuation of the first and second pressure control valves  86 , 88 , the hydraulic actuators  34 , 34 ′ are actuated for compression or extension dependent on the direction of turn of the vehicle. Consequently, the roll control system of the present invention controls vehicle roll during a change in the direction of turn of the vehicle by adjusting the operation of the first and second pressure control valves  86 , 88 . Such an arrangement provides a smooth transition between left and right turns.  
         [0035]     The present invention is also applicable for use with a vehicle roll control system, the front portion  122  of which is as shown in  FIG. 9  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 FIGS.  1  to  6 , 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  FIGS. 5 and 6 , which is controlled by a control circuit as shown in  FIGS. 5 and 6 , or any one of the arrangements shown in  FIGS. 7 and 8 . The roll control system is operated in substantially the same manner as that described above with reference to FIGS.  1  to  6 , and  14 , or either one of  FIGS. 7 and 8 .  
         [0036]     The present invention is also applicable for use with a vehicle roll control system as shown in  FIG. 10 . In this third embodiment in accordance with the present invention, the system  222  comprises a torsion bar  226 , a first arm  228 , a second arm  228 ′, and a hydraulic actuator  234 . 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 .  
         [0037]     The hydraulic actuator  234 , as shown in  FIG. 11 , 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 .  
         [0038]     The fluid lines  266 , 268  are connected to a hydraulic circuit as shown in  FIGS. 5 and 6 , which is controlled by a control circuit as shown in  FIGS. 5 and 6 , or any one of the arrangements shown in  FIGS. 7 and 8 . The roll control system  222  is operated in substantially the same manner as that described above with reference to FIGS.  1  to  6 , and  14 , or any one of  FIGS. 7 and 8 .  
         [0039]     An alternative arrangement for the hydraulic actuator of  FIG. 11  is shown in  FIG. 12 . 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 FIGS.  5  to  8  to actuate the actuator  334 .  
         [0040]     A further alternative arrangement of hydraulic actuator  334 ′ is shown in  FIG. 13 . In this further alternative embodiment, the actuator  334 ′ is substantially the same as the actuator  334  shown in  FIG. 12 , but without the sliding guiding fit of the free end  341 ′ of the rod  341  with the housing  356 .  
         [0041]     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, using the same fluid pressure and equal amounts of fluid.  
         [0042]     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 controlled in unison. It will be appreciated that the hydraulic actuators may be controlled individually, and in certain cases the portion of the roll control system at the rear of the vehicle may be omitted. Also, the hydraulic actuator for the front of the vehicle may be a different type to the hydraulic actuator for the rear of the vehicle.  
         [0043]     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.