1. Field of the Invention
The invention relates generally to land vehicles of the wheeled type. Specifically, the invention relates to fluid suspension and independent suspension systems. A tandem axle suspension system is disclosed that is especially well suited for use on a towed trailer for damping road vibration.
2. Description of the Prior Art
Tandem axle suspension is known in trailers, trucks, busses, and like vehicles. Often the front and rear transversely extending axles of such a system are mounted at opposite ends of a longitudinally extending "rocker arm" or "walking beam", which provides a firm mechanical link between the front and rear axles on each side of the chassis. The walking beam is typically connected to the chassis by a trunnion bearing near its longitudinal center. This arrangement transmits shock between axles and often disturbs the rotational stability of other wheels in the tandem suspension system. Walking beam suspension is known to employ springs and air bags to absorb shock and selective pressure adjustment in air bags is known for the purpose of adjusting the bag characteristics to fit the load.
A variation of the usual walking beam suspension employs a leaf spring supported live forward axle and a walking beam supported rear dead axle, wherein the walking beam has the dead axle at its rear end and an air bag at its forward end such that the air bag may be inflated to pivot the dead axle into a non-load bearing position. This arrangement is for the purpose of reducing vibrations transmitted to the vehicle frame when the load is sufficiently light that the dead axle is not needed.
In any of the described arrangements, the gyroscopic forces generated by a spinning wheel are disrupted when a wheel encounters irregularities in the road. Front and rear wheels often share an unequal portion of the load with the result that one of the tandem axles transmits a stronger vibration to the vehicle chassis than is necessary if the load were equally shared between the tandem axles.
These problems are resolved by providing for equal load sharing between tandem axles under all circumstances and for independent wheel suspension on each axle.