Individual active torsional springs

A suspension system for a vehicle includes at least two torsion bars, each of which are connected on their first end to respective wheel suspensions that are arranged on opposite lateral sides of the vehicle. Movement of the wheel suspensions produces torque in the respective torsion bars. Each of the torsion bars are connected on their second ends to a frame of the vehicle through a damper system. Movement of the wheel suspensions produces torque in the respective torsion bar. The damper system selectively applies resistance to the torque in the torsion bars to selectively provide active variable spring rates to the wheel suspension, which application of resistance may be coordinated amongst the various torsion bars to inhibit roll of the vehicle during a turning maneuver or to increase occupant comfort when the vehicle encounters a bump or hole.

BACKGROUND

Stabilizer bars are one of the most common methods for combating vehicle roll when performing a turning maneuver. Automobiles and off road vehicles will generally use a single torsional bar that will connect both left and right suspensions systems together. The stabilizing bar can be included in either of the longitudinal front or rear axles of the vehicles.

Current torsional sway bars can help reduce vehicle roll, but they also limit individual wheel articulation. This can greatly reduce the overall comfort of an occupant of the vehicle when the vehicle experiences a single wheel suspension event, because such an event will cause both wheels to move together, limiting the overall articulation a single wheel can experience. This in turn can cause the suspension and vehicle dynamics to become upset and reduce overall suspension performance. This also limits the maximum allowable sway bar stiffness, and will generally lead to a compromise in both the control of vehicle roll versus handling performance.

Additionally, suspensions that are expected to carry heavy loads or those used in performance applications will often include heavier/stiffer springs to compensate for the extreme conditions experienced so that the vehicle does not move to the bottom of its suspension stroke. This requires a spring with a proper stiffness to be used for the expected use of the vehicle. However, this use of the vehicle is not always constant, and the vehicle may be used in other varying applications with higher or lower loading conditions. In these cases, springs that are too hard or too soft provide a suspension that fails to properly isolate the vehicle from the road. There is currently no way to manipulate the vehicles spring rate, which causes the required use of stiffer springs to account for the most extreme use. This stiffer spring causes increased movement of the frame when the wheel encounters a bump or hole, and thus causes a reduction of overall comfort to an occupant of the vehicle. There can also be suspension events that can occur where a stiffer spring rate is desired but cannot be realized due to a compromise in performance of the suspension if a stiffer spring were used.

BRIEF DESCRIPTION

According to one aspect, a suspension system for a vehicle includes a first torsion bar, a second torsion bar, and a damper system. A first end of the first torsion bar is connected to a first wheel suspension of the vehicle, such that movement of the first wheel suspension in a first wheel suspension stroke produces torque in the first torsion bar. A second end of the first torsion bar is connected to the damper system. A first end of the second torsion bar is connected to a second wheel suspension of the vehicle, such that movement of the second wheel suspension in a second wheel suspension stroke produces torque in the second torsion bar. A second end of the second torsion bar is connected to the damper system. The damper system selectively applies resistance to the torque in the first and second torsion bars to selectively provide active variable spring rates to the first and second wheel suspensions.

According to another aspect, a vehicle includes a frame, a first wheel suspension arrange on a first lateral side of the frame, a second wheel suspension arranged on a second lateral side of the frame opposite from the first lateral side, and a suspension system connecting the first wheel suspension and the second wheel suspension to the frame. The suspension system includes a first torsion bar, a second torsion bar, and a damper system. A first end of the first torsion bar is connected to the first wheel suspension of the vehicle, such that movement of the first wheel suspension in a first wheel suspension stroke produces torque in the first torsion bar. A second end of the first torsion bar is connected to the damper system. A first end of the second torsion bar is connected to the second wheel suspension of the vehicle, such that movement of the second wheel suspension in a second wheel suspension stroke produces torque in the second torsion bar. A second end of the second torsion bar is connected to the damper system. The damper system selectively applies resistance to the torque in the first and second torsion bars to provide active variable spring rates to the first and second wheel suspensions.

DETAILED DESCRIPTION

The present subject matter provides a suspension system including individual active torsional springs that collectively act as a sway bar for a vehicle, as well as work to provide an active variable spring rate to the vehicle suspension. Each torsional spring may operate physically independent from the other(s), but may work in conjunction with all other torsional springs to control vehicle dynamics through control logic.

The suspension system includes at least two torsion bars, each operatively connected at a first end to a wheel suspension on only one lateral side of the vehicle. The opposite second end of each torsion bar may be connected to the vehicle frame through a damper system. Movement of the wheel suspensions in their respective suspension strokes (i.e. the distance between maximum compression and full extension of the wheel suspensions) produced torque in the torsion bars. The damper system selectively applies resistance to this torque produced in the torsion bars. The suspension mechanisms on the lateral sides (i.e. left and right sides) of the vehicle may have their own torsion bar operatively associated therewith, and the suspension system may gather measurement data taken from each of the torsion bars. This gathering of measurement data may be accomplished using angle encoders that take measurements of angular positions of the torsion bars in order to determine the location of the suspension in a suspension stroke, as well as the overall torque being applied to the torsion bars. The system may use these measurements to control the damper system via a control logic to provide a coordinated resistance to the torque in the torsion bars. The system may be used in conjunction with conventional suspension components, including for example for example, tires, wheels, linkages, springs, shocks, and struts, and may apply the resistance to inhibit vehicle roll and/or to provide an active variable spring rate to the suspension, which may result in improve vehicle dynamics.

The control logic may cause the damper system to selectively apply resistance to torque in the torsion bars to thereby manipulate the torsion bar index and the amount that the torsion bar is allowed to move. This selectively applied resistance may inhibit movement of the torsion bars, and therefore allow the torsion bars to collectively function as a very stiff sway bar to inhibit vehicle roll, e.g. during a turning event. When no resistance is applied to the torque in the torsion bars, the torsion bars may be allowed to move freely to allow for full wheel suspension articulation within a suspension stroke and thus improving overall comfort, e.g. during straight line movement of the vehicle.

The system may be used to apply resistance to torque in the torsion bars when the suspension is subjected to a large impact, for example when a vehicle tire encounters a bump or hole in the ground during travel. This functioning may allow the suspension system to assist the primary shocks/struts to create a variable suspension rate for the vehicle, wherein the system may apply no resistance to torque in the torsion bar to allow for a softer primary spring rate, but may apply a supplemental resistance to help absorb large impacts. This operation of the suspension system via operation of the control logic may help to improve both occupant comfort and performance of the vehicle.

Referring now to the figures, a vehicle2includes a frame4, wheels6, and a suspension system connecting the wheels6to the frame4. The suspension system includes a first torsion bar10, a second torsion bar12, and a damper system14.

The first and second torsion bars10,12are operatively associated with a pair of rear wheels6A,6B of the vehicle2, which wheels may be arranged on respective opposite lateral sides of the vehicle2(e.g. a driver's and passenger's sides of the vehicle2) and may be longitudinally aligned with one another (i.e. rear axle).

The first torsion bar10has a first end16and a second end18distal from the first end16. The first end16of the first torsion bar10may be attached to a first wheel suspension20on a first lateral side22(e.g. driver's side) of the vehicle2, such that movement of the first wheel suspension20in a first wheel suspension stroke produces torque in the first torsion bar10.

The second torsion bar12has a first end24and a second end26distal from the first end24. The first end24of the second torsion bar12may be attached to a second wheel suspension28on a second lateral side30(e.g. passenger's side) of the vehicle2opposite from the first lateral side22, such that movement of the second wheel suspension28in a second wheel suspension stroke produces torque in the second torsion bar12.

The first torsion bar10may have a general L-shape including a short section32including the first end16, and a long section34including the second end18. The first torsion bar10may be connect to the first wheel suspension20at the first end16, such that movement of the first wheel suspension20in a first wheel suspension stroke (e.g. the up and down movement indicated by arrows inFIGS. 4,5,8,9) produces the torque in the first torsion bar10, and specifically in the long section34of the first torsion bar10.

The second torsion bar12may have a general L-shape including a short section36including the first end24, and a long section38including the second end18. The second torsion bar12may be connect to the second wheel suspension28at the first end24, such that movement of the second wheel suspension28in a second wheel suspension stroke (e.g. the up and down movement indicated by arrows inFIGS. 4-9) produces the torque in the second torsion bar12, and specifically in the long section38of the second torsion bar12.

The damper system14may include a first resistive device40and a second resistive device42, each of which may be mounted on the frame4of the vehicle2. The first and second resistive devices40,42may each include an electronic motor, a hydraulic damper, valving, or a clutch pack that provides resistance to torque in the first and second torsion bars10,12. The second end18of the first torsion bar10may be connected to the frame4of the vehicle2through the first resistive device40. The second end26of the second torsion bar12may be connected to the frame4through the second resistive device42. The first torsion bar10may be attached to the frame4by a first bearing44(e.g. bushing), which may be arranged on the first torsion bar10between the first and second ends16,18of the first torsion bar10. The second torsion bar12may be attached to the frame4by a second bearing46(e.g. bushing), which may be arranged on the second torsion bar12between the first and second ends24,26of the second torsion bar12.

The first torsion bar10is depicted inFIG. 1to be connected to the first wheel suspension20, where the first torsion bar10is connected via a first link rod48to a first control arm50of a first wheel6A. The first wheel suspension20is further depicted to include a first strut54including a first spring56. The second torsion bar12is depicted to be connected to the second wheel suspension28, where the second torsion bar12is connected via a second link rod58to a second control arm60of a second wheel6B. The second wheel suspension28is further depicted to include a second strut64including a second spring66.

The suspension system may include other torsion bars operatively connected with other wheel suspensions of the vehicle2. As depicted inFIG. 2, the suspension system may include a third torsion bar68and a fourth torsion bar70that are operatively connected with the respective two front wheels6C,6D of the vehicle2, which wheels may be arranged on respective opposite lateral sides of the vehicle2(e.g. a driver's and passenger's sides of the vehicle2) and may be longitudinally aligned with one another (i.e. front axles).

In particular, the third torsion bar68has a first end72and a second end74distal from the first end72. The first end72of the third torsion bar68may be attached to a third wheel suspension76on the second lateral side30(e.g. passenger's side) of the vehicle2, such that movement of the third wheel suspension76in a third wheel suspension stroke produces torque in the third torsion bar68.

The fourth torsion bar70has a first end80and a second end82distal from the first end80. The first end80of the fourth torsion bar70may be attached to a fourth wheel suspension84on the first lateral side22(e.g. driver's side) of the vehicle2, such that movement of the fourth wheel suspension84in a fourth wheel suspension stroke produces torque in the fourth torsion bar70.

The third torsion bar68may have a general L-shape including a short section86including the first end72, and a long section88including the second end74. The third torsion bar68may be connect to the third wheel suspension76at the first end72, such that movement of the third wheel suspension76in a third wheel suspension stroke produces the torque in the third torsion bar68, and specifically in the long section88of the third torsion bar68.

The fourth torsion bar70may have a general L-shape including a short section90including the first end80, and a long section92including the second end82. The fourth torsion bar70may be connect to the fourth wheel suspension84at the first end80, such that movement of the fourth wheel suspension84in a fourth wheel suspension stroke produces the torque in the fourth torsion bar70, and specifically in the long section92of the fourth torsion bar70.

The damper system14may include a third resistive device94and a fourth resistive device96, each of which may be mounted on the frame4of the vehicle2. The third and fourth resistive devices94,96may each include an electronic motor, a hydraulic damper, valving, or a clutch pack that provides resistance to torque in the third and fourth torsion bars68,70. The second end74of the third torsion bar68may be connected to the frame4of the vehicle2through the third resistive device94. The second end82of the fourth torsion bar70may be connected to the frame4through the fourth resistive device96. The third torsion bar68may be attached to the frame4by a third bearing98(e.g. bushing), which may be arranged on the third torsion bar68between the first and second ends72,74of the third torsion bar68. The fourth torsion bar70may be attached to the frame4by a fourth bearing100(e.g. bushing), which may be arranged on the fourth torsion bar70between the first and second ends80,82of the fourth torsion bar70.

The third torsion bar68is depicted inFIG. 2to be connected to the third wheel suspension76, where the third torsion bar68is connected via a third link rod102to a third strut104of a third wheel6C. The third wheel suspension76is further depicted to include a third spring108as part of the third strut104. The fourth torsion bar70is depicted to be connected to the fourth wheel suspension84, where the fourth torsion bar70is connected via a fourth link rod110to a fourth strut112of a fourth wheel6D. The fourth wheel suspension84is further depicted to include a fourth spring116as part of the fourth strut112.

The suspension system may include, and may therefore operate to improve vehicle dynamics utilizing, only the first and second torsion bars10,12; only the third and fourth torsion bars,68,70; or all of the first, second, third, and fourth torsion bars10,12,68,70.

The suspension system may include an electronic control unit (ECU)118in communication with the damper system14as shown inFIG. 10, and configured to control operation of the damper system14to selectively apply resistance to torque in the individual torsion bars10,12,68,70that are included in the suspension system8.

The suspension system may include one or more sensors in communication with the ECU118as shown inFIG. 10for providing sensor data to the ECU118relative to the vehicle2, the frame4, the wheels6, and the suspension system8. This sensor data may be utilized by the ECU118, along with the level of resistance being applied by the damper system14to the individual torsion bars, for controlling operation of the damper system14to selectively apply resistance to the torque in the individual torsion bars produced by movement of the wheel suspensions in their suspensions strokes. In other words, the ECU may apply the resistance to each of the individual torsion bars10,12,68,70in a variable amount, and the variable amount may be determined as a function of this sensor data and the level of resistance being applied by the damper system14to the other of the individual torsion bars. The sensor data may include any of an angular position of each of the torsion bars10,12,68,70as well as the overall torque/torsion in each of the torsion bars; a position of the wheel suspensions20,28,76,84in each of their respective suspension strokes; a steering input to the vehicle2; an angular velocity of the vehicle2; or other sensor data.

The sensors may include two angle encoders120,122on each torsion bar for determining the angular position of each of the torsion bars. As depicted inFIGS. 1-2, each torsion bar includes a first angle encoder120A-D positioned at or near the resistive devices40,42,94,96, and a second angle encoder122A-D positioned between the first end and the second end of each torsion bar. The angle encoders120,122may be in communication with the ECU118to provide to the ECU118an angular position of the torsion bar at the two location where the angle encoder are arranged on the torsion bar. A difference between the two angular positions of the two locations on the torsion bar may indicate the overall torque/torsion of each torsion bar.

The sensors may include suspension sensors124A-D for determining the position of the wheel suspensions20,28,76,84in each of their respective suspension strokes.

The sensors may include a steering input sensor126for determining the steering input to the vehicle2, e.g. the input generated by an operator of the vehicle2and which causes the wheels of the vehicle2to change their travel direction. This sensed steering input may be used to determine that the vehicle is traveling in a straight line or is performing a turning maneuver. Resistance applied to the torsion bars10,12,68,70by the damper system14may be dependent in part, on the steering input being over or under a steering input threshold. The steering input threshold may be preselected by a vehicle manufacturer in the control logic, or may be user selected, or may change based on a speed of the vehicle2. If the steering input is above the steering input threshold, thus indicating a turning maneuver, the damper system14may apply resistance to torque in one or more of the torsion bars1,012,68,70based on the control logic, or may apply no resistance if the steering input is below the steering input threshold.

The sensors may include a gyrometer128for determining the angular velocity of the vehicle2as gyrometer measurement, and specifically for an angular velocity around a vertical axis of the vehicle2. This sensed gyrometer measurement may be used to determine that the vehicle2is traveling in a straight line or is performing a turning maneuver, or for determining that the vehicle2is on an inclined surface. Resistance applied to the torsion bars10,12,68,70by the damper system14may be dependent in part, on the gyrometer measurement being over or under a gyrometer measurement threshold. The gyrometer measurement threshold may be preselected by a vehicle manufacturer in the control logic, or may be user selected, or may change based on a speed of the vehicle2. If the gyrometer measurement is above the gyrometer measurement threshold, thus indicating a turning maneuver, the damper system14may apply resistance to torque in one or more of the torsion bars10,12,68,70based on the control logic, or may apply no resistance if the gyrometer measurement is below the gyrometer measurement threshold.

Other sensors may be included in the suspension system for providing other sensor data to the ECU118for use by the ECU118in controlling the damper system14. The sensors may include an accelerometer130for measuring the acceleration of the vehicle2as an accelerometer measurement. This sensed accelerometer measurement may be used to determine that the vehicle2is accelerating, decelerating, or keeping a constant speed, and may be utilized by the ECU as part of the control logic for determining if resistance will be applied to one or more of the torsion bars1,012,68,70.

The ECU118may coordinate the operation of the individual resistive devices40,42,94,96for selectively applying a variable amount of resistance to the individual torsion bars10,12,68,70. Such coordination may be accomplished by controlling the amount of resistance applied to one of the torsion bars as a function of the amount of resistance being applied to the other torsion bars. In this way, the functioning of the resistive devices40,42,94,96and the effect on the torsion bars10,12,68,70can be coordinated to provide improved vehicle performance and improved occupant riding comfort. The individual resistive devices40,42,94,96are operated in conjunction with one another, which may mean that the amount of resistance applied to one of the torsion bars10,12,68,70is coordinated with the amount of resistance applied to the other torsion bars, by taking into account the sensor data and the amount of resistance that is applied to the other torsion bars. This operation of the individual resistive devices40,42,94,96may cause the individual resistive devices40,42,94,96to provide an independent suspension effect on the vehicle2, or may cause the resistive devices40,42,94,96to provide a collective suspension effect on the vehicle2.

The selectively applied resistance may allow the first pair of torsion bars10,12and the second pair of torsion bars68,70to collectively provide similar forces to the vehicle2as would a conventional sway bar, or may operate to provide an independent and active variable spring rate for each of the wheel suspension20,28,76,84.

The coordination of the operation of the resistive devices will be explained further with references toFIGS. 3-9, which depict the rear axle of the vehicle2including the first and second resistive devices40,42. It will be appreciated that the described operation of the suspension system for the rear axle can be similarly applied to the front axles including the third and fourth resistive devices94,96, and in conjunction with operation of the suspension system for the front axle including the first and second resistive devices40,42.

As depicted inFIG. 3, two wheel suspensions20,28are positioned near a midpoint in their suspension strokes. This arrangement may be realized when the vehicle2is parked or is traveling at a relatively constant speed in a straight line direction. In this scenario, the first and second resistive devices40,42may apply no resistance or only a minimal amount of resistance to the respective torsion bars10,12because the wheel suspensions20,28are not moving in their suspension strokes, and thus do not produce torque in the torsion bars10,12. The resistive devices40,42may not apply resistance to the torsion bars10,12because of the stationary position of the first and second wheel suspensions20,28, and because of the straight line travel of the vehicle2.

InFIG. 4, both wheel suspensions20,28have moved up from their midpoint and towards a top of their suspension strokes as indicated by the up arrows. This movement may occur during a straight line travel of the vehicle2and as a result of both wheels6A,6B hitting a bump, and may produce a torque in the torsion bars10,12. In this scenario, the first and second resistive devices40,42may apply no resistance or only a minimal amount of resistance to the torque produced in the respective torsion bars10,12. The resistive devices40,42may not apply resistance to their respective torsion bars10,12because of the corresponding upward movement of both of the wheel suspensions20,28, and because of the straight line travel of the vehicle2. This operation of the resistive devices40,42may allow the wheel suspensions20,28to freely move all the way up in their suspension strokes and thereby more fully absorb the impact forces acting upon the wheels suspensions20,28from the bump. This operation of the wheel suspensions20,28may minimize the effect of the bump on moving the frame4, which minimized movement of the frame4may provide increased comfort for occupants of the vehicle2because the occupants experience minimum effects from the bump. In this scenario, the spring rates of the wheel suspensions20,28may correspond to the spring rates of the springs56,66, and may be independent from the effects of the resistive devices40,42.

InFIG. 5, both wheel suspensions20,28have moved down from their midpoint and towards a bottom of their suspension strokes as indicated by the down arrows. This movement may occur during a straight line travel of the vehicle2and as a result of both wheels6A,6B encountering a hole, and may produce a torque in the torsion bars10,12. In this scenario, the first and second resistive devices40,42may apply no resistance or only a minimal amount of resistance to the torque produced in the respective torsion bars10,12. The resistive devices40,42may not apply resistance to their respective torsion bars10,12because of the corresponding downward movement of both of the wheel suspensions20,28, and because of the straight line travel of the vehicle2. This operation of the resistive devices40,42may allow the wheel suspensions20,28to freely move all the way down in their suspension strokes and thereby fully engage the wheels6A,6B to the hole. This operation of the wheel suspensions20,28may minimize the effect of the hole on moving the frame4, which minimized movement of the frame4may provide increased comfort for occupants of the vehicle2because the occupants experience minimum effects from the hole. In this scenario, the spring rates of the wheel suspensions20,28may correspond to the spring rates of the springs56,66, and may be independent from the effects of the resistive devices40,42.

InFIG. 6, only the second wheel suspensions28has moved up from its midpoint and towards a top of its suspension stroke as indicated by the up arrow; while the first wheel suspension20has remained near the midpoint of its suspension stroke. This movement of the second wheel suspensions28and the lack of movement in the first wheel suspension20may occur during a straight line travel of the vehicle2and as a result of only the second wheel6B hitting a bump, which movement may produce a torque in the second torsion bars12. The first wheel suspension20is not moving in its suspension stroke, and thus does not produce torque in the first torsion bars10. In this scenario, the second resistive device42may apply no resistance or only a minimal amount of resistance to the torque produced in the second torsion bar12, and the first resistive device40may also apply no resistance or only a minimal amount of resistance to the first torsion bar10. This functioning may allow the wheel suspensions20,28to freely move in their suspension strokes and independently from one another, such that the second wheel suspension28can thereby freely move all the way up in its suspension stroke to fully absorb the impact forces acting upon the second wheels suspension28from the bump. The second resistive device42may not apply resistance to the second torsion bar12because of the stationary position of the first wheel suspension20, and because of the straight line travel of the vehicle2. This functioning can be similarly applicable in the opposite scenario, where the first wheel6A encounters a bump while the second wheel6B does not. This operation of the wheel suspensions20,28may minimize the effect of the bump on moving the frame4, which minimized movement of the frame4may provide increased comfort for occupants of the vehicle2because the occupants experience minimum effects from the bump. In this scenario, the spring rates of the wheel suspensions20,28may correspond to the spring rates of the springs56,66, and may be independent from the effects of the resistive devices40,42.

InFIG. 7, only the second wheel suspensions28has moved down from its midpoint and towards a bottom of its suspension stroke as indicated by the down arrow; while the first wheel suspension20has remained near the midpoint of its suspension stroke. This movement of the second wheel suspensions28and the lack of movement in the first wheel suspension20may occur during a straight line travel of the vehicle2and as result of only the second wheel6B encountering a hole, which movement may produce a torque in the second torsion bars12. The first wheel suspension20is not moving in its suspension stroke, and thus does not produce torque in the first torsion bars10. In this scenario, the second resistive device42may apply no resistance or only a minimal amount of resistance to the torque produced in the second torsion bar12, and the first resistive device40may also apply no resistance or only a minimal amount of resistance to the first torsion bar10. This functioning may allow the wheel suspensions20,28to freely move in their suspension strokes and independently from one another, such that the second wheel suspension28can thereby freely move all the way down to thereby fully engage the second wheel6B to the hole. The second resistive device42may not apply resistance to the second torsion bar12because of the stationary position of the first wheel suspension20, and because of the straight line travel of the vehicle2. This functioning can be similarly applicable in the opposite scenario, where the first wheel6A encounters a hole while the second wheel6B does not. This operation of the resistive devices40,42may allow the wheel suspensions20,28to freely move all the way up in their suspension strokes and thereby more fully absorb the impact forces acting upon the wheels suspensions20,28from the bump. This operation of the wheel suspensions20,28may minimize the effect of the hole on moving the frame4, which minimized movement of the frame4may provide increased comfort for occupants of the vehicle2because the occupants experience minimum effects from the bump. In this scenario, the spring rates of the wheel suspensions20,28may correspond to the spring rates of the springs56,66, and may be independent from the effects of the resistive devices40,42.

InFIG. 8, the second wheel suspensions28has moved up from its midpoint and towards a top of its suspension stroke as indicated by the up arrow; while the first wheel suspension20has moved down from its midpoint and towards a bottom of its suspension stroke as indicated by the down arrow. This opposite movement of the wheel suspensions20,28may be as a result of the vehicle2executing a turning maneuver, resulting in a shifting of the weight of the vehicle (i.e. “vehicle roll”) onto the second wheel suspension28to compress it, and off of the first wheel suspension20to expand it, and may produce torque in both of the first and second torsion bars10,12. In this scenario, the first resistive device40may apply resistance to the torque in the first torsion bar10, and the second resistive device42may apply resistance to the torque in the second torsion bar12. The resistance applied to the first and second torsion bars10,12may counter the vehicle roll by inhibiting the second wheel suspensions28from moving up in its suspension stroke toward maximum compression, and by inhibiting the first wheel suspension20from moving down in its suspension stroke toward full rebound. The amount of resistance applied to the first torsion bar10may be varied by gradually increasing the resistance as the first wheel suspension20moves further down in its suspension stroke and further away from its midpoint, and gradually decreasing the resistance as the first wheel suspension20moves closer to its midpoint in the suspension stroke. The amount of resistance applied to the second torsion bar12may be varied by gradually increasing the resistance as the second wheel suspension28moves further up in its suspension stroke and further away from its midpoint, and gradually decreasing the resistance as the first wheel suspension20moves closer to its midpoint in the suspension stroke. The amount of resistance applied to the first and second torsion bars10,12may also be gradually increased as the vehicle2accelerates and decreased as the vehicle2decelerates. This gradual increase or decrease in the resistance applied to the torsion bars10,12may provide progressive resistance to movement of the wheel suspensions, and may provide an active spring rate for the springs in the wheel suspensions. The resistive devices40,42may apply resistance to the respective torsion bars10,12because of the opposite movement of the first and second wheel suspensions20,28and because of the turning maneuver performed by the vehicle2. This functioning can be similarly applicable in the opposite scenario as depicted inFIG. 9, where the first wheel suspension20is compressed and the second wheel suspension28is expanded from vehicle roll.

This opposite movement of the wheel suspensions20,28as depicted inFIG. 8, may also occur during straight line travel of the vehicle2, and as a result of the second wheel6B hitting a bump while the first wheel6A encounters a hole. In this scenario, the first and second resistive devices40,42may apply no resistance or only a minimal amount of resistance to the torque produced in the respective torsion bars10,12in order to allow the wheel suspensions20,28to freely move up and down, respectively, in their suspension strokes, and to thereby allow the second wheel suspension28to fully absorb the impact forces from the bump and to allow the first wheel6A to fully engage the hole. The resistive devices40,42may not apply resistance to their respective torsion bars10,12because of the opposite movement of the wheel suspensions20,28, and because of the straight line travel of the vehicle2. This functioning can be similarly applicable in the opposite scenario as depicted inFIG. 9, where the first wheel6A encounters a bump while the second wheel6B encounters a hole.

This operation of the wheel suspensions20,28as described forFIGS. 8 and 9may affect the spring rates of the wheel suspensions20,28, whereby operation of the resistive devices40,42may effectively increase the spring rates of the wheel suspensions20,28. This may cause the spring rates of the wheel suspensions20,28to be dependent on the spring rates of the springs56,66and on the operation of the resistive devices40,42. This operation of the resistive devices40,42may allow the first and second torsion bars10,12to collectively act, as would a conventional sway bar, to inhibit roll of the frame4and vehicle2during movement of the vehicle2in the turning maneuver. By selectively varying the amount of resistance applied to torque in each of the torsion bars10,12,68,70, the suspension system effectively provides an active variable spring rate to each of the wheel suspensions20,28,76,84, thus providing improved vehicle performance, occupant comfort, and inhibition to vehicle roll.