Abstract:
Vehicle suspension movements are transmitted to an anti-roll mechanism which is pivotally mounted on the vehicle for movement about the pitch axis thereof to accommodate normal ride motion of the vehicle in which wheels on opposite sides of the vehicle move equally. Vehicle roll is controlled by an anti-roll mechanism includes a torsion bar which is loaded by the suspension movement. Roll stiffness is controlled by adjusting the lever arm through which suspension movement is transmitted to the torsion bar by a lever arrangement commonly referred to as a Watt&#39;s link to assure that the change in the length of the lever arm is directly proportional to the change in the control in the cockpit. Accordingly, linear control is assured, and the torsion bar and lever arms do not appreciable deflect during cornering.

Description:
TECHNICAL FIELD 
     This invention relates to an adjustable anti-roll mechanism which is particularly suited for an open wheel style racing car. 
     BACKGROUND OF THE INVENTION 
     Racing cars are regularly subjected to harsh cornering maneuvers which tend to roll the vehicle about the roll or longitudinal axis thereof. Accordingly, the vehicle suspension system must exhibit roll stiffness, or resistance to roll around the roll axis of the vehicle. These types of vehicles have suspension systems which include an anti-roll mechanism, which resists this tendency of the vehicle to roll during cornering, while still accommodating normal vehicle riding motions in which wheels on opposite sides of the vehicle move substantially equally and all significant vehicle suspension movement is about the pitch axis of the vehicle. Race cars may have two separate anti-roll mechanisms, one of which controls the roll stiffness of the rear wheel suspension and the other controlling the roll stiffness of the front wheel suspension. Conventionally, the driver may adjust the roll stiffness of the vehicle suspension during racing by operating a control in the cockpit. 
     Drivers commonly complain that existing adjustable roll control mechanisms are “non-linear”, that is, that a given adjustment of the control in the cockpit does not always result in a corresponding change in roll stiffness. Drivers also complain that the roll stiffness does not feel constant during cornering, so that the handling characteristics of the car change during cornering, making the car unstable. Both of these complaints are the result of deflections inherent in prior anti-roll mechanisms. 
     SUMMARY OF THE INVENTION 
     According to the present invention, vehicle suspension movements are transmitted to an anti-roll mechanism which is pivotally mounted on the vehicle for movement about the pitch axis thereof to accommodate normal ride motion of the vehicle in which wheels on opposite sides of the vehicle move equally. The anti-roll mechanism includes a torsion bar which is loaded by suspension movement. Roll stiffness is controlled by adjusting the lever arm through which suspension movement is transmitted to the torsion bar by a lever arrangement commonly referred to as a Watt&#39;s link to assure that the change in the length of the lever arm is directly proportional to the change in the control in the cockpit. Accordingly, linear control is assured, and the torsion bar and lever arms to not appreciable deflect during cornering. While the invention is particularly described as being used in a racing car, other vehicles, such as passenger cars and similar vehicles may also benefit from the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration, taken from above, of a racing car upon which the anti-roll mechanism of the present invention is typically used; 
     FIG. 2 is a rear view of the racing car illustrated in FIG. 1; 
     FIG. 3 is a view similar to FIG. 2, but illustrating the racing car during a severe cornering maneuver; and 
     FIG. 4 is a perspective view of an anti-roll mechanism made pursuant to the present invention that is adapted to be used in the racing car illustrated in FIGS.  1 - 3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, a typical, open cockpit racing car upon which an anti-roll mechanism of the present invention is typically used is illustrated generally by the numeral  10 . The racing car  10  includes a body  12 , which is supported by rear wheels  14 ,  16  and front wheels  18 ,  20  in the conventional manner, so that the front wheel are steered by operation of a steering wheel  22  in the cockpit  24  of the racing car  10 . Each of the rear wheels  14 , 16  are supported on the body  12  by a conventional suspension system, which includes rocker arms  28 , which extend into the body  12 . The cockpit  24  includes a seat  26  for the driver, as well as other standard vehicle controls (brake pedal, clutch pedal, gearshift, etc.) well known to those skilled in the art. The cockpit also includes a lever (not shown) which is easily accessable to the driver for controlling the anti-roll mechanism of the present invention, as will be hereinafter described. For reference, the vehicle roll axis, which extends longitudinally in the vehicle direction of travel, is indicated at  30 , and the vehicle pitch axis, which extends transversely with respect to the vehicle, is indicated at  32 . 
     Referring now to FIGS. 2 and 3, during normal forward movement of the vehicle when the vehicle suspension system accommodates only vehicle ride motions and lateral forces acting on the vehicle  10  are not significant, both of the rear wheels  14 ,  16  move substantially the same amount. However, during cornering, lateral forces acting on the vehicle cause the vehicle to pivot about the roll axis  30  or the vehicle, as illustrated in FIG.  3 . As illustrated in FIG. 3, during sever cornering, one of the rear wheels may lift off of the pavement surface S, causing the vehicle to become unstable. Accordingly, it is necessary to resist vehicle roll about the roll axis to maintain stability of the vehicle. The relative roll stiffness of the front and rear suspensions along with the placement of the roll axis determines how much weight transfer takes place from the inside to outside tires (front and rear ). The relative amount of weight transfer front to rear is what is used to tune the limit handling characteristics (and stability) of the vehicle. When the vehicle rotates around the roll axis, instability may result even if a wheel does not lift off of the pavement surface. The anti-roll mechanism of the present invention indicated generally at  34  (FIG. 4) provides such roll resistance, the roll stiffness being adjustable by the driver. 
     The anti-roll mechanism  34  is mounted in the vehicle body  10  in any appropriate location. Although the anti-roll mechanism  34  is illustrated in controlling the rear wheels of the vehicle and would normally be mounted behind the cockpit  24 , a similar mechanism may be used to control the front wheels of the vehicle. Anti-roll mechanism  34  includes a mounting member  36  which terminates in substantially cylindrical end portions  38  that are attached to pillow block bearings (not shown) mounted on the vehicle to permit the mounting member  36  to rotate freely about the pitch axis of the vehicle. Accordingly, during the normal ride motions of the vehicle (substantially the same movement of the left and right wheels), the anti-roll mechanism  34  rotates freely relative to the vehicle. Midway between the end portions  38 , the mounting member  36  defines a downwardly tapering (viewing FIG. 4) receiver socket  40  having a square cross section that receives a tapered, similarly shaped tongue  42  of a torsion bar  44  so that relative rotation between the tongue  42  and the mounting member  36  is prevented. Of course, instead of a square cross section, the socket  40  and tongue  42  may have a polygonal cross section other than square. 
     The other end of the torsion bar  44  also terminates in a tongue (not shown) similar to the tongue  42  which is received in a socket (not shown) similar to the socket  40  at substantially the midpoint of a crossbar  46  which includes portions  48 , 50  which extend laterally in opposite directions from the torsion bar  44 . Portions  48 , 50  define cylindrical sliding surfaces  52 , 54  which slidably support end pieces  56 , 58  for sliding movement toward and away from the torsion bar  44 . Each of the end pieces  56 , 58  extend from corresponding equalizer links  60  and  62 , which are a part of the vehicle suspension system. Link  60  is connected to rocker arms  28  supporting rear wheel  14 , and transmits deflection of the rocker arms  28  supporting rear wheel  14  to the end piece  58 . Similarly, link  62  is connected to the rocker arms  28  supporting rear wheel  16 , and transmits deflection of the rocker arms  28  supporting rear wheel  16  to the end piece  60 , Each of the end pieces  56 , 58  are supported by spherical bearing assemblies  64 , 66 , which allow the corresponding end pieces to pivot relative to the cross bar  46 . Each bearing assembly  64 , 66  include an inner race  68 , 70  to permit the end pieces  56 , 58  to slide along the cylindrical sliding surfaces  50 , 52 . 
     A bolt  72  extends axially through the torsion bar  44  and through the cross bar  46  and mounting member  36  to hold the cross bar, the torsion bar, and the mounting member together. Accordingly, the anti-roll mechanism  34  may be disassembled and the torsion bar  44  replaced with a torsion bar having a different torsional stiffness. Accordingly, a library of torsion bars  44  may be provided to enable a mechanic to provide a suitable range of torsional stiffness for the suspension system. 
     A pivot member  74  circumscribes the end of the bolt  72  and mounts an intermediate lever  76  for pivoting about the axis of the torsion bar  44 . Lever arms  78 , 80  are pivotally mounted on opposite ends of the intermediate lever  76  by pivot connections  82 , 84 . Each of a pair of rings  86 , 88  extend through slots  90 , 92  of a corresponding end piece  56 , 58  and wrap around the outer races (not shown) of the bearing assemblies  64 , 66  which support the end pieces  56 , 58  on the cross bar  46 . Each of the rings  86 , 88  terminate in a post  94 , 96  which pivotally engages an aperture in a corresponding one of the lever arms  78 , 80 . A cable  98  is pivotally mounted to the lever arm  78  by a pivot connection  100 . The cable  98  extends through a cable guide  102  that is supported by a bracket  104  pivotally mounted on the lever arm  80 . Accordingly, when the cable  98  is pulled so that the pivot connection is moved toward the bracket  104 , both of the end pieces  56 , 58  and moved toward the torsion bar  44  by an identical distance. Conversely, when the cable is operated in the opposite direction pushing the connection  100  away from the bracket  104 , each of the end pieces  56 ,  58  are pushed away from the torsion bar  44  by an identical amount. It will be noted that the pivoting of the levers  78 , 80  is transmitted to the end pieces  56 , 58  by the rings  86 , 88  to slide the end pieces  56 , 58  along the cross bar  46 . The arrangement of the lever arms  78 , 80 , and the intermediate lever  76  is commonly referred to by those skilled in the art as a Watt&#39;s link adjustment mechanism. 
     In operation, when the vehicle is operated on a straight, flat road segment, vehicle suspension movements of the rear wheels  14 , 16  are substantially equal. The anti-roll mechanism rotates freely about the bearings (not shown) connecting the mounting member  36  to the vehicle and the torsion bar  44  is unaffected because suspension forces acting across the vehicle are equal. During a more severe vehicle cornering maneuver, when vehicle roll forces are a factor, suspension forces are unequal across the vehicle (as can be seen in FIG.  3 ); accordingly, the suspension forces applied to the cross bar  46  through the end pieces  56 , 58  will also be unequal, thereby tending to twist the torsion bar, which resists such twisting thereby causing resistance to the suspension movement which increases as the degree of suspension movement increases, thereby providing resistance to rolling of the vehicle. Since the magnitude of the twisting motion applied to the torsion bar  44  is a function of the length of the lever arm along the cross bar  46  between the end pieces  56 , 58  and the torsion bar  44 , movement of the end pieces  56 , 58  along the cross bar  46  by operation of the cable  98  changes the magnitude of the moment applied to the torsion bar  44  for a given magnitude of suspension movement. Accordingly, the magnitude of the roll resistance provided by the anti-roll mechanism  34  may be changed by the driver by operation of the aforementioned lever in the cockpit. As explained above, both of the end pieces  56 , 58  will be moved the same amount for a given movement of the lever, and the change in roll resistance changes linearly by movement of the lever since a given movement of the lever always moves each of the end pieces  56 , 58  the same proportional distance. Accordingly, the roll resistance of the vehicle will remain constant during cornering (unless the position of the lever is changed) and all changes in roll resistance will be linear, will be the same across the vehicle, and will be in proportion to lever movement.