Anti-roll bars are used in sprung vehicle suspensions in order to reduce body roll during cornering by adding to the roll resistance of the suspension components such as springs and torsion bars. Springs and torsion bars (referred to hereinafter collectively as “torsion bars”) in a vehicle suspension are provided to allow the wheels to maintain maximum contact with the road surface when the vehicle travels over imperfections in the roadway. The presence of the torsion bars in the suspension, however, also allow the vehicle to roll from side to side under cornering, which has many undesirable consequences for vehicle handling, such as reduced cornering traction caused by the changing suspension geometry no longer keeping the bottom of the tire parallel with the road surface. This lifts the edges of the tire, reducing the contact patch size. The use of stiffer torsion bars will reduce the amount of body roll, but at the expense of maintaining maximum road surface tire contact. Therefore, anti-roll bars have been developed in order to increase roll resistance without resorting to overly stiff torsion bars.
Anti-roll bars couple the left and right wheels at one end of the car together while allowing for semi-independent movement of each wheel. When cornering, the bar will twist and form a torsion spring, with the outside end being pushed down and the inside end being lifted. These forces counteract the roll of the vehicle, pushing down on the outside tire and lifting up on the inside tire. On the outside tire, this downward force helps to increase traction. On the inside tire, the bar is lifting up against the suspension torsion bar that is trying to keep the tire on the ground. Therefore, too stiff of an anti-roll bar can actually cause the inside tire to lift off of the ground, which is obviously an undesirable result. It is therefore important to have the appropriate torsion bar rate in the anti-roll bar in order to ensure the appropriate amount of traction for each wheel.
Anti-roll bars are also used to tune the roll coupling of the chassis. Roll coupling is the relationship of the roll resistance of the front of the car and the roll resistance of the rear of the car. The balance of the roll coupling, because of its effect on traction, influences whether the car has a tendency to understeer or oversteer. Increasing the traction of the outside wheel on one end of the car may leave the other end of the car with too little traction to match the performance of the first end. With such an imbalance of traction, one end of the car will lose traction before the other end. If the front end loses traction before the rear end, the car is said to understeer or “push” (i.e. the front of the car moves to the outside of the turning direction as the front tires lose grip). If the rear end loses traction before the front end, the car is said to oversteer or “pull” (i.e. the front of the car moves to the inside of the turning direction as the rear tires lose grip and the rear of the car begins to swing around). Because an adjustable anti-roll bar can adjust the traction of the tires during a turn, it can therefore be used to adjust not only the amount of roll resistance, but also the amount of understeer and oversteer exhibited by the vehicle.
Adjustable anti-roll bars are used in many race cars to adjust the handling of the car for different track conditions, for changing track conditions, and for changing (wearing) tire conditions. A common prior art adjustable anti-roll bar blade component 10 used in race cars is shown in FIGS. 1A-C. The blade 10 is used as a coupling member between the vehicle suspension 12 (only partially illustrated) and the torsion bar 14. The blade 10 and the torsion bar 14 act as two springs in series. When a load is applied to one, the same load is applied simultaneously to the other and both will have some deflection at the same time. By varying the spring rate of the blade 10, the effective spring rate of the series combination will therefore be varied.
In the position shown in FIG. 1A, the suspension 12 may move with respect to the vehicle chassis (not shown), and the suspension 12 acts upon the end of the flexible blade 10 in a direction 16 perpendicular to the wide flat surface of the blade 10. In this position, the blade 10 has maximum flexibility, therefore it produces the lowest spring rate of the blade 10/torsion bar 14 combination. In FIG. 1B, the blade 10 has been rotated 45 degrees from the position shown in FIG. 1A by movement of a member 18 operating on a tab 20 coupled to the blade 10. Rotation of the blade 10 is facilitated by rotary couplings 22 and 24. In this position, the blade 10 is considerably stiffer than in the position of FIG. 1A (i.e. it resists movement in the direction 16 to a greater extent), therefore it produces a higher spring rate of the blade 10/torsion bar 14 combination than the position shown in FIG. 1A. Finally in FIG. 1C, the blade 10 has been rotated a full 90 degrees from the position in FIG. 1A (again, by movement of the member 18) such that the suspension 12 acts upon the end of the flexible blade 10 in a direction parallel to the wide flat surface of the blade 10. In this position, the blade 10 has maximum stiffness, and therefore it produces the highest spring rate of the blade 10/torsion bar 14 combination.
Although the anti-roll bar of FIGS. 1A-C is adjustable, the range of adjustability is fairly limited. Therefore, there remains a need in the art for an improved adjustable anti-roll bar.