ON THE ROCKS – Rock Crawler Axle

Votes: 2
Views: 451

The illustrated rock crawler axle is a simple mechanism that combines articulation and side shift to provide adjustable on-the-go variable caster and camber angles throughout the range of steering.

Rock crawling/bouncing introduces significant forces on the tires of a vehicle. Independent wheel braking has been used to control tire contact forces. Imagine, however, if it were also possible to position the tire so that the ground forces would assist propulsion and keep side-loads of the tires from rolling themselves off the rim, enabling the vehicle to maneuver in even tighter spots.

Land-based traction vehicles with independent wheel suspension could use a simultaneous side-shift and articulate mechanism to reach even tighter spots and more quickly complete a driving course. This design would provide modification of the wheelbase, suspension height, and kingpin camber, caster, and inclination angles throughout the maneuver, allowing for better handling performance.

The steering knuckle is attached to the axle using a pinned (non-rotating along the axle axis) spherical joint. Three actuators control the caster, camber, and steer angle simultaneously. The tire contact geometry is controlled by these three actuators working together, while the general steer angle is constrained by a tie rod in the common sense of a steering axle.
For those interested in more information, the design is explained in detail within US Patent 11,666,126 B2.

There have been similar mechanisms with two swashplates; however, they have yet to implement a fixed planar separation distance between them to provide a truly articulating and side-shifting mechanism. For various reasons, the distance between the two swashplates has been variable. The new mechanism would allow the vehicle more flexible maneuvering to position the tire to provide best clearance and traction.

The idea could be applied to various land-traction vehicles with tires or tread. High-speed racing and crawler/bouncer vehicles would appreciate the ability to vary caster and camber on the go.

Those who appreciate a more comfortable ride and/or better tire contact might be interested in this new development in suspension and steering.

The product could use conventional casting, welding, and machining methods; additionally, some software controller logic would enhance the operation for the general user.

The number of components is relatively equivalent to the conventional axle today. There would be a slight increase in the number of actuators required. The educational component for mechanics may, however, be steeper. There would need to be a paradigm shift to establish confidence in a different way that technicians are used to thinking about kingpin geometry.

A prototype has been developed to validate the concept. An illustration of the prototype is also included in the reference US Patent. The prototype provides for the steer angles with four actuators. It does not have the steering tie rod feature shown in the rock crawler axle illustration. Regardless, one can identify that the variable caster, camber, and steer are all possible outcomes from these four actuators.




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  • Name:
    Daniel Cowley
  • Type of entry:
  • Software used for this entry:
    Alibre Design Expert, DST SimWise Motion