Abstract:
A method for adjusting the camber of a vehicle&#39;s axle comprising attaching collars ( 30, 30′, 32, 32′, 44 ) to the axle ( 12 ) of the vehicle attaching links ( 38, 38′ ) to the collars, introducing a deflection in the axle in a concave downward direction and modifying the length

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to vehicle axles and more specifically to trailer axles. 
         [0003]    2. Background 
         [0004]    A vehicle&#39;s axle supports the weight of the vehicle and load and also provides a shaft upon which the wheels revolve. Truck rigs carrying heavy loads over long distances provide substantial forces to the axles. The allowable axle loads are restricted by law, but typically tandem truck trailer axles are expected to carry loads of up to 34,000 pounds per tandem. In fact, the camber of the wheels on these loaded axles can be altered by these forces such that the wheels are closer together at the top then at the bottom. This condition is known as negative camber. 
         [0005]    Most trailer axles are manufactured with no intentional camber but with an acceptance that when in use, there will be some degree of camber deflection attributable to load. On a new trailer axle, manufacturers typically accept a camber alignment tolerance of about one quarter of a degree, positive or negative. This tolerance applies to the axle beam itself with no load applied and with no consideration for additional camber deflection that may be experienced by components of the hub and the wheel. On a typical truck semi-trailer, even with the minimal load applied by the weight of the empty trailer, each axle end may have a load of approximately 2000 pounds. This load is sufficient to cause the wheels to exhibit a negative camber orientation. 
         [0006]    A fully loaded trailer may support a load of about 8500 pounds to each axle end and typically causes as much as one half degree or more of negative camber at the tire. This negative camber indicates that the contact surface of the tires is not parallel to the road surface. Consequently, the tread may wear unevenly, with the inner shoulder wearing most rapidly. When the truck is driven with a reduced load, the inner shoulder may not make firm contact with the ground, which allows slipping. 
         [0007]    One solution to the problem above is to remove the axle and deflect it mechanically, or by other means, in the opposite direction. An example of one known technique for effecting a camber change to an axle is by applying heat to the axle to accomplish a plastic deformation. However, manufacturers frequently disapprove of such practices because the variables of the necessary plastic deformation are difficult to control and often explicitly void the warranty. Furthermore, this practice is time consuming and it is difficult to achieve the precise camber required without iterative trials. 
       SUMMARY OF THE INVENTION 
       [0008]    A method is provided for adjusting the camber of a truck&#39;s trailer axle comprising attaching a first collar to the trailer axle of the truck, proximate to a first wheel of the truck, the said first collar having an offset link attachment; attaching a second collar to the trailer axle, opposite from the first wheel, proximate to a second wheel of the truck, the said second collar having an offset link attachment; attaching a third collar to the trailer axle, therebetween the first and second collars, the said third collar having an offset link attachment; attaching a first link between the offset link attachment of the first collar and the offset link attachment of the third collar; attaching a second link between the offset link attachment of the third collar and the offset link attachment of the second collar; introducing a deflection in the trailer axle in a concave downward direction; and modifying the length of the first and second links. 
         [0009]    A method is provided for adjusting the camber of a truck&#39;s trailer axle comprising attaching a first collar, with an offset link attachment, to the trailer axle of the truck, proximate to a first wheel of the truck; attaching a second collar, with an offset link attachment, to the axle, opposite from the first wheel, proximate to a second wheel of the truck; attaching a third collar, with an offset link attachment, to the axle, therebetween the first and second collars and proximate to the first collar; attaching a fourth collar, with an offset link attachment, to the axle, therebetween the first and second collars and proximate to the second collar; attaching a fifth collar, with an extension, to the axle, therebetween the third and fourth collars; attaching a first link between the offset link attachment of the first collar and the offset link attachment of the third collar; attaching a second link between the offset link attachment of the third collar and the offset link attachment of the fourth collar; attaching a third link between the offset link attachment of the fourth collar and the offset link attachment of the second collar; introducing a deflection in the trailer axle in a concave downward direction; and modifying the length of the first, second and third links. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a rear view of a truck&#39;s trailer axle. 
           [0011]      FIG. 2  is a simplified force diagram showing the forces applied to the trailer axle while under load. 
           [0012]      FIG. 3  is a rear view of a truck&#39;s trailer axle showing a 3-collar camber truss assembly. 
           [0013]      FIG. 4  is a simplified force diagram showing the forces applied to the trailer axle while the trailer is supported by an inner offset link attachment. 
           [0014]      FIG. 5  is a rear view of a truck&#39;s trailer axle showing a 3-collar camber truss assembly with a pair of spacer collars. 
           [0015]      FIG. 6  is a rear view of a truck&#39;s trailer axle showing a 4-collar camber truss assembly. 
           [0016]      FIG. 7  is a perspective view of a removable jacking fixture. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Advantageously, particular embodiments of the present invention provide a method that adjusts the camber of a truck&#39;s trailer axle. Other embodiments provide a method that modifies an introduced negative camber of the truck&#39;s trailer wheels when a load is applied. The technology has particular applicability to the trailer axles of a semi-truck rig. However, the invention could be applied to other vehicles as well as any axle bearing a load. 
         [0018]    Referring now to the drawings,  FIG. 1  illustrates a rear view of a truck&#39;s trailer axle  12 . As illustrated in  FIG. 1 , the truck is supported for travel over ground by wheels with attached pneumatic tires. The left wheel  14  and right wheel  14 ′ are attached to an axle  12 . The trailer has a pair of frame members  18  which support the weight of the trailer. The frame members  18  are separated from the axle  12  by a pair of springs  20 . The springs  20  shown in  FIG. 1  are metal leaf springs, although composite leaf springs and air springs are also commonly known in the art. Air springs are airtight units and are connected to a source of compressed air on board the truck. The springs  20  are attached to the axle  12  by means of a spring hanger  22 . Also shown attached to the wheels  14  and  14 ′ is a brake backing plate  24 . 
         [0019]    With the trailer axle configuration shown in  FIG. 1 , the ground supplies an upward force to the tire and wheel combinations, while the weight of the trailer is translated to the axle  12 , inboard of the wheels  14  and  14 ′, via the air springs  20 .  FIG. 2  shows a simplified depiction of the forces applied to the axle  12 . As shown in  FIG. 2 , the forces cause the axle  12  to be deflected in a concave downward direction. 
         [0020]    Referring to  FIG. 3 , a first collar  30  is attached to the axle  12  proximate to the left wheel, and a second collar  30 ′ is attached to the axle  12  proximate to the right wheel. The collars  30  and  30 ′ may be attached in the space between the spring hanger  22  and the brake backing plate  24 . In a preferred embodiment, the collar should take up all the space between the spring hanger  22  and the brake backing plate  24  in order to increase the deflection resistance of the axle  12 . Attached to the underside of the collars  30  and  30 ′ are offset link attachments  34  and  34 ′. Between the collars  30  and  30 ′ is a third, inner collar  32 , also attached to the axle  12 . Attached to the underside of the inner collar  32  is an inner offset link attachment  36 . The inner collar  32  is attached to collar  30  by a link  38  and to collar  30 ′ by a link  38 ′. The links  38  and  38 ′ are connected to the offset link attachments  34 ,  34 ′ and  36  of their respective collars  30 ,  30 ′ and  32 , for example, by means of a clevis pin. The clevis attachment point for the inner collar  32  should be as long in the vertical direction from the axle  12  as possible, taking into consideration ground clearance considerations. Conversely, the clevis attachment point for the collars  30  and  30 ′ should be as short a vertical distance as practical to the axle  12 . The offset link attachments  34 ,  34 ′ and  36  may each have more than one attachment point in order to provide for adjustable geometry. In the figure, the links  38  and  38 ′ are shown as a turnbuckle, but any threaded adjustable device can be used. The axle, links  38  and  38 ′, collars  30  and  30 ′, inner collar  32 , offset link attachments  34  and  34 ′, and inner offset link attachment  36 , constitute a camber truss assembly. Also shown below the inner offset link attachment  36  in  FIG. 3  is a standard 20 ton shop jack  40 . 
         [0021]    In certain embodiments where the trailer&#39;s air spring configuration does not permit placing the collars  30  and  30 ′ outboard of the spring hangers  22 , the collars may be placed inboard of the spring hangers  22 .  FIG. 5  shows this configuration. To prevent the collars  30  and  30 ′ from slipping towards the inner collar  32  once tension is applied to the links  38  and  38 ′, a pair of spacer devices  42  may be placed between the collars  30  and  30 ′, and the inner collar  32 . The spacer devices may take the form of a rod, beam, or a collar as is shown in  FIG. 5 . 
         [0022]    In a particular embodiment of the invention, the loaded trailer is lifted off the ground by contacting a shop jack  40  with the inner offset link attachment  36 . However, any means of lifting the trailer off the ground such as a standard lift may be used.  FIG. 4  shows a simplified depiction of the forces applied to the axle  12  with the trailer supported by the inner offset link attachment  36 , rather than the tire and wheel combination as shown in  FIG. 2 . The weight of the truck applied to the axle  12  via the spring hangers  22 , while the axle  12  is supported proximate to its center, causes the axle  12  to deflect in a concave downward direction. In the instances where the trailer utilizes air springs, it is preferable to release the air from both the front and rear air springs prior to lifting the trailer. This is done to assist in lifting the tires and wheel combination off the ground so that all the weight of the truck is applied to the inner offset link attachment  36 . 
         [0023]    After lifting the loaded trailer off the ground, the length of the links  38  and  38 ′ are reduced, causing them to come into tension. Once the shop jack  40  is subsequently removed, the load of the trailer is once again supported by the tire and wheel combination. However, the camber truss assembly now supplies sufficient rigidity to the axle  12  to resist much of the bending moment. The camber truss assembly thus preserves most of the current axle camber correction. If too much deflection is introduced in the axle  12  by supporting the load of the trailer at the inner offset link attachment  36 , the tension in the links  38  and  38 ′ may be reduced until a desired setting is reached. Although this setting might be zero camber, other settings are possible. If the links  38  and  38 ′ are later removed from the axle  12 , the axle  12  returns to its original deflection, because there is no significant plastic deformation. 
         [0024]      FIG. 6  shows an alternative embodiment of the invention. In certain cases where it is not possible to fit the 3-collar design onto the axle because of constraints imposed by the suspension and braking configurations, a 4-collar design may be utilized. In  FIG. 6 , a pair of collars  30  and  30 ′ are attached to the axle  12  proximate to the left and right wheels  14  and  14 ′ respectively. Attached to the underside of the collars  30  and  30 ′ are offset link attachments  34  and  34 ′. Between the collars  30  and  30 ′, an inner collar  32  is attached to the axle  12  proximate to collar  30  and an inner collar  32 ′ is attached to the axle  12  proximate to collar  30 ′. Attached to the underside of the inner collars  32  and  32 ′ are inner offset link attachments  36  and  36 ′. Between the inner collars  32  and  32 ′ a fifth collar  44  is attached to the axle. Attached to the underside of the fifth collar  44  is an extension  46 . The extension  46  contains an opening  48  through which a link may extend. 
         [0025]    The utilization of the 4-collar design is similar to the 3-collar design with the following exceptions. Collar  30  is attached to inner collar  32  with link  38 . Collar  30 ′ is attached to inner collar  32 ′ with link  38 ′. The inner collars  32  and  32 ′ are then connected to each other by a link  38 ″ which passes through the opening  48  in the extension  46 . The loaded trailer is lifted off the ground by contacting the shop jack  40  with the extension  46  of the fifth collar  44 . Once the loaded trailer is off the ground, the lengths of each of the links are reduced, causing the links to come into tension. The fifth collar  44  may be removed after the desired camber correction has been made, but it should be removed without disturbing the links. To facilitate this, the extension  46  should have a removable rod  50  or, in an alternative embodiment, a hinge portion which retains the structural integrity of the extension  46  during loading. 
         [0026]      FIG. 7  shows a closer view of the fifth collar  44  and extension  46  with a removable rod  50 . The removable rod  50  can be moved in and out of the extension opening by hand until sufficient force is applied to the extension  46 ; for example, by contacting the extension  46  with a floor jack. At that point, the extension  46  is temporarily deformed, clamping the rod  50  into place.