Frame steered construction vehicles, Articulated Dump Trucks (ADT), Wheeled Loaders, are known to be unstable at elevated speeds presenting safety/productivity concerns. Literature on this issue deals only with measures such as control systems to reduce instability.
The cause of instability, rear wheel steer, is not addressed. Instability can be controlled by the driver at lower speeds but control is beyond the reaction speeds of most drivers at elevated speeds, as shown in high speed maneuvering of fork lifts or high speed reversing of automobiles.
In a frame steer vehicle when the wheel is turned right the front chassis turns to the right but the rear chassis initially turns to the left. This is a cause of instability. At elevated speeds attempts by the driver to "correct" the opposite turn of the rear causes an opposite effect thus developing an increasing amplitude snaking motion ending in loss of control. Instability can be induced by road perturbations.
Timoney VPS removes/reduces the instability issues (snaking, jacknifing, trailer swing, rollover) of the conventional frame steer articulated chassis increasing safety, improving handling and productivity.
The Timoney Steering System replaces the conventional frame pivot bearing by a linkage which effectively moves the instantaneous steering pivot point to the center of the front axle. This eliminates the "rear steering" effect.
Illustration 1. To remove the rear wheel steering effect a Virtual Pivot Point located on the front axle center is kinematically established. The conventional pivot is replaced by a four bar linkage - an isosceles trapezoid in which the parallel links are formed by the front and rear chassis elements “AD” and “BC” in the illustration below. The arms “AB” and “CD” form the other part of the trapezoid. It can be seen that the pivot center remains on the axle centerline.
Illustration 2 shows that the lateral offset of the bucket is reduced by a factor of 1.6.
Illustration 3 compares ADT models.
Timoney Steering has the potential to transform the articulated construction vehicle market.
Benefits include improved safety, productivity, reduced whole body vibration(reduced pitching/lateral acceleration.Market is the whole construction vehicle sector. System would be produced as a integrated element . Production costs are more or less the same but reduced suspension weights due to reduced steering forces offer potential for overall cost reduction.
The public good is served by improved operator conditions, preventing injuries, saving lives, improving safety improving productivity, enabling other product improvements, reducing consumption of natural resources (by improved speeds and productivity).