Zero-Slip Steering Differential for both Automotive and Track-Steered Vehicles

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Modern traction control systems typically rely on friction in the form of brakes, clutches, or built-in torque bias ratios in order to mitigate wheel slip. However, under certain conditions, traction control systems may not be able to apply sufficient friction to control a suddenly slipping wheel. In addition, they may not respond fast enough to prevent the vehicle from losing its forward momentum. For these reasons, locking differentials, or lockers are generally preferred by off-roading enthusiasts. However, the operation of lockers requires special knowledge and can lead to rapid tire wear or driveline damage if left engaged.

The SPARC DRIVE™ differential system presented here solves all of the above issues by precisely governing an allowable differential rate at all times. It accomplishes this by using an algorithm called Steering Fusion™ to calculate the ideal differential rate range that the vehicle should experience for a given steering angle and wheel speed. This ideal differential range is then fed to a small low-speed servo or stepper motor which in turn ensures that the prescribed range is adhered to. Any external forces acting outside of the prescribed range would result in wheel slip and would not be allowed. For example, during straight-line acceleration, we would expect a vehicle to have little if any differential rotation between its wheels and so in this scenario, the servo motor is commanded to remain stationary. Any forces acting against this command, such as torque steer or wheel slip, are thereby prevented.

Like a fully locked differential, SPARC Drive™ delivers complete and uninterrupted power to the wheels regardless of traction conditions, but it does this while simultaneously preserving the full steering agility of an open differential. With SPARC Drive™, there are no lockers to engage, no traction modes to toggle between, and no brakes, clutches, or other friction parts to wear out.

When installed in track-steered/differentially-steered vehicles, SPARC Drive™ represents an extremely compact and efficient steering differential. The design is fully regenerative to provide full-powered turns (including neutral turns). In addition, SPARC Drive™ features more direct and efficient power delivery to the tracks when compared to a double-differential as it does not use any intermediate gears along its power path.


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    Shaun Chu
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