Skid Steer Drive Torque Allocation Control
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Solution Overview
Problem
In skid-steered vehicles with electric drive transmissions, the torque required for steering increases rapidly at lower vehicle speeds, leading to high power demands on the steer motor, which can be inefficient and limit the propulsion motors' ability to contribute to steering, especially at higher speeds.
Innovation Solution
A control system that dynamically allocates differential torque between propulsion and steer motors based on vehicle speed, allowing propulsion motors to contribute significantly at lower speeds and steer motors at higher speeds, thereby optimizing torque distribution and reducing the power rating requirements of the steer motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the steer motor provides all steering torque through the differential gear mechanism, then steering is achieved, but the power rating required for the steer motor increases rapidly as vehicle speed reduces
Solution Approach 1:
The patent combines the steering function with the propulsion motors by enabling them to provide differential torque in addition to their primary propulsion function. The propulsion motors are controlled to contribute to steering torque through differential adjustment of their output, merging two functions (propulsion and steering) into a single integrated system that reduces the burden on the steer motor.
Solution Approach 2:
The propulsion motors are designed to perform multiple functions: primary propulsion and secondary steering assistance. By controlling the propulsion motors to provide differential torque, the system makes these motors universal components that can operate in both propulsion mode and steering assistance mode, depending on operational requirements.
2Speed
If the propulsion motors are designed for high torque at low speed for mobility, then mobility is improved, but the torque output is limited by power rating at higher speeds
Solution Approach 1:
The system dynamically adjusts the torque contribution from propulsion motors based on vehicle speed. At low speeds, propulsion motors provide high torque for both propulsion and steering assistance. At higher speeds, the system modulates their torque output to remain within power rating limits while still contributing to steering, creating a dynamic, adaptive torque distribution strategy.
3Ease of operation
If the steer motor is sized for high power to provide all steering torque, then steering is achieved at all speeds, but the size and cost of the steer motor increases
Solution Approach 1:
The steering function is merged with the propulsion system, allowing propulsion motors to share the steering torque burden. This integration enables a smaller, more compact steer motor to be used since it only needs to provide supplemental steering torque rather than all steering torque across the entire operating range.
4Loss of energy
If electrical regeneration is used to transfer power from slower to faster running shaft, then energy efficiency is improved, but the complexity of the control system increases
Solution Approach 1:
The system replaces complex electrical regeneration control with a simpler mechanical power transfer through the differential gear mechanism. The mechanical differential naturally facilitates power transfer from the slower-running propulsion motor to the faster-running one, eliminating the need for complex electrical regeneration control systems while maintaining energy efficiency.
Data Source
AI summary
A drive configuration for a skid steered vehicle comprises a pair of electric motors for propulsion of the vehicle, one each coupled to drive a respective track on a respective side of the vehicle, and one or more electric steer motors coupled through a differential gear mechanism to impose a speed difference between the tracks. An associated control system controls the current to each motor so that substantial contributions to the differential torque to turn the vehicle are made both by the steer motors and by the propulsion motors, in variable proportions preferably as a function of the vehicle speed.