Wheel Torque Control via Slip-Adhesion Gradient
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Solution Overview
Problem
Precise regulation of wheel torques in vehicles, especially during anti-lock braking or anti-slip conditions, is challenging due to the complexity of determining reference velocity and desired slip on various surfaces, particularly in all-wheel drive vehicles.
Innovation Solution
The method sets wheel torques by defining a slip-adhesion coefficient gradient, allowing for precise torque control using a recursive algorithm with low-precision reference velocity, where the gradient is adjusted to match the surface conditions, and torque distribution between axles to maintain stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference velocity is determined with high precision to achieve accurate slip regulation, then wheel torque control precision is improved, but system complexity and measurement difficulty increase significantly
Solution Approach 1:
The patent changes the control parameter from direct slip regulation (requiring precise reference velocity) to slip-adhesion coefficient gradient regulation. By controlling the gradient dλ/ds instead of the absolute slip value, the system achieves accurate wheel torque control using only low-precision reference velocity measurements, thereby reducing system complexity while maintaining control precision
Solution Approach 2:
Instead of determining the desired slip value directly from reference velocity and then calculating torque, the patent inverts the approach: it defines the desired gradient on the slip-adhesion curve and derives the torque setting from this gradient. This inversion allows the use of recursive algorithms that are computationally efficient and tolerant of measurement imprecision
2Manufacturing precision
If desired setpoint slip is determined for various undersurfaces to achieve optimal traction, then wheel torque control accuracy is improved, but the complexity of determining setpoint slip increases
Solution Approach 1:
The patent replaces the complex task of determining desired setpoint slip for different surfaces with a simpler gradient-based approach. By defining a target gradient value on the slip-adhesion coefficient curve that is applicable across various surface conditions, the system achieves adaptive torque control without requiring complex surface classification and setpoint lookup tables
Solution Approach 2:
The gradient-based control parameter serves as a universal control strategy that works across different surface conditions (ice, snow, dry asphalt, wet surfaces). A single gradient setpoint can be applied universally, eliminating the need for separate control strategies for each surface type and simplifying the overall control system
3Reliability
If reference velocity is determined with high precision during anti-lock braking in all-wheel drive vehicles, then anti-slip regulation accuracy is improved, but the error-proneness and complexity of the system increase
Solution Approach 1:
The patent changes the control objective from maintaining a specific slip value to maintaining a specific slip-adhesion coefficient gradient. This gradient-based parameter is less sensitive to errors in reference velocity measurement, particularly during dynamic braking events in all-wheel drive vehicles, thereby improving reliability without increasing system complexity
Solution Approach 2:
The patent implements a feedback mechanism where the actual slip-adhesion coefficient gradient is continuously calculated from measured wheel torques and wheel speeds, compared to the desired gradient setpoint, and used to adjust the torque application. This feedback loop naturally compensates for measurement errors and disturbances, reducing the system's error-proneness
Data Source
AI summary
In a method for setting a wheel torque in a vehicle, a setpoint value for a slip-adhesion coefficient gradient for one wheel of one vehicle axle is ascertained, and the wheel torque is set in such a way that the actual value of the gradient is approximated to the setpoint value.