Heave-Based Wheel Slip Control for Deformable Terrain
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Solution Overview
Problem
Off-road vehicles experience wheel spin and subsequent axle or skid plate contact with terrain when traversing deformable surfaces, leading to slowing or stopping, as existing traction control systems drastically reduce torque, which is not effective in maintaining forward motion.
Innovation Solution
A controller programmed for an electric machine in an electrified vehicle to limit wheel slip based on vehicle vertical acceleration and wheel angular acceleration, allowing for higher torque control on deformable surfaces by adjusting wheel slip speed targets and reducing overshoot thresholds during heave events, thereby preventing wheel spin and maintaining forward motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional traction control systems drastically reduce torque to limit wheel slip, then wheel spin is reduced, but forward motion is lost and vehicle productivity decreases
Solution Approach 1:
The system dynamically adjusts wheel slip limits based on detected heave events. During heave events (vertical acceleration exceeding threshold), the controller allows higher wheel slip speeds to maintain forward motion, while during normal conditions it enforces stricter slip limits to prevent wheel spin. This dynamic adaptation resolves the contradiction by making the control strategy context-dependent rather than static.
Solution Approach 2:
The controller changes the target wheel slip speed parameter based on vehicle vertical acceleration state. When heave is detected, the target slip speed is increased from a first value (during heave) to a second value (during normal conditions). This parameter change allows the system to maintain forward momentum during terrain transitions while preventing excessive wheel spin during stable operation.
2Productivity
If wheel slip is allowed to maintain forward momentum on deformable terrain, then vehicle mobility is improved, but uncontrolled wheel spin removes soil beneath the wheel and causes axle contact
Solution Approach 1:
The system uses feedback from vertical acceleration sensors and wheel speed sensors to continuously monitor vehicle state. When heave events are detected (indicating potential axle burial risk), the controller adjusts wheel slip limits in real-time. This feedback mechanism allows the system to permit beneficial wheel slip for forward motion while preventing excessive slip that would cause axle contact.
Solution Approach 2:
The controller detects heave events before complete wheel spin occurs by monitoring vertical acceleration thresholds. Upon detecting the onset of heave, the system proactively adjusts wheel slip limits to prevent the development of uncontrolled wheel spin and soil removal, rather than reacting after the problem has fully developed.
3Measurement precision
If wheel speed controller overshoot threshold is reduced during heave events, then wheel speed control precision is improved, but control responsiveness may be affected
Solution Approach 1:
The overshoot threshold parameter is dynamically adjusted based on heave detection. During heave events, a lower overshoot threshold is applied to improve control precision and prevent excessive wheel speed fluctuations. During normal conditions, the threshold can be relaxed to maintain responsive control. This dynamic parameter adjustment resolves the contradiction between precision and responsiveness.
Data Source
AI summary
An electrified vehicle, system, and method include an electric machine, a traction battery coupled to the electric machine, and a controller programmed to control wheel slip to provide high wheel slip to traverse deformable terrain, such as sand or loose soil, and lower wheel slip to avoid excessive soil removal beneath the wheels after detecting a vertical acceleration or heave event, such as after landing when driving over a jump or bump. When vehicle vertical acceleration exceeds a first threshold, and a ratio of a wheel angular acceleration to vehicle longitudinal acceleration exceeds a second threshold, the electric machine is controlled to limit wheel slip to a lower value that provides sufficient tractive force to maintain some forward motion. Otherwise, the electric machine is controlled to limit wheel slip to a higher value to accommodate higher vehicle speeds over the deformable terrain.