Steering Control Slip Angle Limiting Algorithm
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Solution Overview
Problem
Existing steering control systems fail to accurately account for the nonlinear relationship between tire lateral force and slip angle, leading to excessive understeer or oversteer, particularly on slippery surfaces or during emergency maneuvers, and require multiple costly sensors, increasing vehicle weight and reducing fuel efficiency.
Innovation Solution
A method that calculates a steering augmentation angle based on vehicle speed and handwheel angle, sets upper and lower bound angle limits for tire slip angle, and adjusts the steering actuator command to maintain the tire slip angle within these bounds, thereby preventing excessive tire slip angles and improving vehicle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If steering control systems use control algorithms that do not fully comprehend the tire force-slip relationship, then the system complexity is reduced, but vehicle steering performance deteriorates due to tire lateral force saturation
Solution Approach 1:
The system changes the control parameter from direct steering angle control to slip angle-based control. By calculating the slip angle (difference between tire contact patch direction and road wheel direction) and using this to determine the steering actuator command, the system adapts to the nonlinear tire force-slip relationship and prevents force saturation, thereby improving steering performance without requiring overly complex algorithms
Solution Approach 2:
The system implements feedback by continuously monitoring the slip angle and adjusting the steering actuator command accordingly. The slip angle is calculated from sensor inputs (steering angle, vehicle speed, yaw rate) and used to generate a corrective command that maintains optimal tire operation within the linear region of the force-slip curve
2Reliability
If steering control systems attempt to control tire slip angle based on an assumed relationship with peak or knee values, then steering performance improves, but the system becomes less adaptable when no knee or peak exists in the tire force-slip curve
Solution Approach 1:
Instead of relying on assumed peak or knee values in the tire force-slip curve, the system changes its approach to directly control the slip angle within a defined range. This parameter-based control approach works universally regardless of whether a knee or peak exists in the specific tire force-slip curve, greatly enhancing adaptability to different tire characteristics and road conditions
Solution Approach 2:
The system dynamically adjusts the steering actuator command based on real-time slip angle calculations and vehicle operating conditions. This dynamic control allows the system to adapt to varying tire force-slip characteristics without requiring pre-programmed assumptions about peak or knee values, making it versatile across different tire types and road surfaces
3Reliability
If steering control systems include steering control system augmentation offsets, then vehicle stability is improved, but the order of limiting calculations becomes critically important and system complexity increases
Solution Approach 1:
The system performs preliminary calculations by first determining the slip angle and then using this to calculate the steering actuator command. By establishing the correct calculation order beforehand (slip angle calculation → steering actuator command → augmentation offset application), the system manages complexity while ensuring stability control effectiveness
Solution Approach 2:
The system uses feedback from vehicle stability sensors (yaw rate, lateral acceleration) to continuously monitor and adjust the steering control. This feedback mechanism allows the system to handle the complexity of multiple calculation steps automatically, as the control algorithm adapts to current vehicle conditions and corrects any potential over- or under-correction from augmentation offsets
4Measurement precision
If steering control systems use multiple sensors (yaw rate sensors, speed sensors, lateral acceleration sensors, etc.), then measurement precision improves, but system cost and vehicle weight increase substantially
Solution Approach 1:
The system makes existing sensors multi-functional by using them for both stability control and slip angle calculation purposes. Yaw rate sensors, speed sensors, and lateral acceleration sensors that are already required for stability control algorithms are also utilized to calculate the slip angle, eliminating the need for additional dedicated sensors while maintaining measurement precision
Solution Approach 2:
The system merges the slip angle calculation function with the existing stability control algorithm. By combining these two functions into a unified control approach that uses the same sensor inputs, the system reduces the total number of sensors required while maintaining the precision needed for effective vehicle control
Data Source
AI summary
A method, system, and computer program product for tire slip angle limiting in a steering control system for a vehicle are provided. The method includes calculating a first steering augmentation angle from a vehicle speed and a handwheel angle. The method further includes calculating an upper bound angle limit and a lower bound angle limit as functions of a vehicle slip angle and a tire slip angle limit. The method also includes bounding the sum of the handwheel angle plus the first steering augmentation angle between the upper bound angle limit and the lower bound angle limit to produce a first bounded angle. The method additionally includes subtracting the sum of the handwheel angle plus the first steering augmentation angle from the first bounded angle to produce a first limiting function, and producing a motor angle command by adding the first limiting function plus the first steering augmentation angle.