Rear Wheel Steering Control for Vehicle Stability
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Solution Overview
Problem
Existing rear wheel steering systems face challenges in ensuring safe operation by accurately limiting the steering angle based on vehicle speed, particularly at high speeds, and in achieving the highest Automotive Safety Integrity Level (ASIL) ratings due to uncertainties in vehicle speed estimation and fault tolerant time calculations.
Innovation Solution
A rear wheel steering system that includes a controller, rear wheel steering actuator, and vehicle speed sensor, which determines the vehicle's speed and maximum yaw rate to set a limited steering angle, using a combination of wheel speed sensors and additional sensors like lateral and longitudinal acceleration sensors to enhance accuracy, and adjusts the steering angle dynamically based on vehicle conditions and fault tolerant time to meet ASIL D ratings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the rear wheel steering angle is increased to improve vehicle maneuverability, then the vehicle's turning capability is enhanced, but the vehicle stability at high speeds deteriorates
Solution Approach 1:
The patent implements dynamic steering angle limits that adjust based on vehicle speed. At low speeds, larger steering angles are permitted to enhance maneuverability. At high speeds, the controller automatically reduces the maximum steering angle to maintain vehicle stability. This dynamic adjustment resolves the contradiction by adapting the steering capability to the current operating conditions rather than using fixed limits.
2Reliability
If the steering angle limit is reduced to ensure safety at high speeds, then vehicle stability is improved, but the vehicle's responsiveness to steering inputs deteriorates
Solution Approach 1:
The patent changes the steering angle parameter dynamically based on vehicle speed conditions. The controller monitors vehicle speed and adjusts the maximum steering angle parameter accordingly - allowing larger angles at low speeds for responsive handling, and reducing the parameter at high speeds for safety. This parameter adaptation resolves the contradiction by optimizing the steering response characteristics for each operating regime.
3Measurement precision
If multiple sensors are added to improve vehicle speed determination accuracy, then the ASIL rating is enhanced, but the device complexity increases
Solution Approach 1:
The patent combines multiple existing sensor systems (wheel speed sensors, lateral acceleration sensors, longitudinal acceleration sensors) that are already present in the vehicle for other functions. By merging the data from these sensors, the system achieves high measurement precision for vehicle speed determination and ASIL D rating without adding dedicated new hardware. This approach resolves the contradiction by utilizing existing resources rather than increasing device complexity.
Data Source
AI summary
A rear wheel steering system in a vehicle. The system includes a rear wheel steering actuator, a vehicle speed sensor, and an electronic control unit. The rear wheel steering actuator is coupled to a rear wheel of the vehicle and controls a steering angle of the rear wheel. The electronic control unit is coupled to the rear wheel steering actuator and the vehicle speed sensor and is configured to determine a speed of the vehicle and to limit the steering angle of the rear wheel based on the speed of the vehicle and a fault tolerant time of the rear wheel steering system.