Vehicle Dynamic Control Using Dual Understeer Gradients
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Solution Overview
Problem
Existing methods for generating yaw rate commands for torque-vectoring differentials in motor vehicles are empirical, require extensive testing, and produce nonlinear responses, failing to consider driver objectives and being actuator-dependent.
Innovation Solution
A method using measured vehicle road wheel angle, velocity, yaw rate, and empirically determined understeer gradients to dynamically generate desired yaw rates and accelerations, employing a first understeer gradient for low to moderate lateral accelerations and a second for high accelerations, avoiding discontinuities and actuator limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an empirical dual look-up table method is used to generate desired yaw rate commands, then the method can produce yaw rates observed in test regime, but it requires extensive vehicle testing with physical hardware and extended development time
Solution Approach 1:
The patent replaces extensive physical vehicle testing with a mathematical model that copies and simulates vehicle dynamics behavior. The desired yaw rate command is generated through equations (1) and (2) that model the relationship between steering angle, vehicle speed, and yaw rate, eliminating the need for repeated physical prototyping and testing while maintaining accuracy.
Solution Approach 2:
The patent substitutes the mechanical testing process with a computational mathematical model. Instead of physically testing the vehicle to generate lookup tables, the system uses equations involving understeer gradient, vehicle speed, and steering angle to directly calculate desired yaw rate commands, replacing the mechanical testing apparatus with mathematical computation.
2Adaptability or versatility
If a continuous variation of understeer gradient is attempted, then the method can adapt to different driving conditions, but it generates a nonlinear vehicle response
Solution Approach 1:
The patent implements a dynamic understeer gradient that varies continuously based on vehicle operating conditions. Equation (2) shows the understeer gradient is calculated as a function of vehicle speed and steering angle, allowing the system to adapt to different driving conditions while maintaining predictable linear vehicle response characteristics through the structured mathematical relationship.
3Ease of operation
If the prior art method is used, then yaw rate commands can be generated, but it is dependent on actuator limitations and does not consider true driver objectives
Solution Approach 1:
The patent extracts the actuator limitations from the control algorithm by calculating the desired yaw rate command independently of actuator capabilities. The mathematical model in equations (1) and (2) computes the ideal yaw rate based solely on driver input (steering angle) and vehicle state (speed), separating the control objective from the actuator implementation details.
Data Source
AI summary
A method for closed loop vehicle dynamic control with a yaw rate controller, such as for example a TVD, utilizing a first understeer gradient for vehicle lateral accelerations at or below a vehicle lateral acceleration threshold and a second understeer gradient for vehicle lateral accelerations thereabove, wherein the vehicle lateral acceleration threshold defines a vehicle lateral acceleration transition point. A first desired vehicle yaw rate per the first understeer gradient is determined, and a second desired vehicle yaw rate per the second understeer gradient is determined, wherein the second desired vehicle yaw rate at the predetermined vehicle lateral acceleration transition point is calibrated to equal the first desired vehicle yaw rate at the predetermined vehicle lateral acceleration transition point so as to avoid any discontinuity therebetween.