Steer-by-Wire Reaction Force Control During Motor Failure
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Solution Overview
Problem
The existing steer-by-wire steering system is vulnerable to excessive steering operations when a reaction force motor fails, leading to unintended vehicle steering due to a sudden loss of reaction force.
Innovation Solution
The system incorporates at least two reaction force motors and a control unit with a failure detection unit. Upon detecting a failure of all but one reaction force motor, the control unit progressively reduces the output of the remaining motor to a prescribed limit value, preventing abrupt loss of steering reaction force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If one reaction force motor fails in a steer-by-wire steering system, then the system continues to operate with the remaining motor, but the reaction force suddenly decreases causing excessive steering by the driver
Solution Approach 1:
The system dynamically adjusts the output of the remaining reaction force motor based on real-time failure detection. When one motor fails, the control unit progressively increases the output of the remaining motor to compensate for the loss, maintaining stable reaction force characteristics and preventing sudden steering changes that would affect driver control precision.
Solution Approach 2:
The control unit changes the operational parameters of the remaining reaction force motor in response to failure. By detecting the failure state and adjusting the motor's output torque and speed parameters, the system maintains adequate reaction force to prevent excessive steering while ensuring the vehicle can still be controlled safely.
2Force
If the output of the remaining reaction force motor is increased to compensate for failure, then the reaction force is maintained, but the driver may still turn the steering wheel excessively if the remaining motor also fails during cornering
Solution Approach 1:
The control unit performs preliminary detection of motor failure conditions and proactively adjusts the output of the remaining reaction force motor before a second failure can occur. By monitoring the operational status of both motors and preparing compensation strategies in advance, the system ensures that if one motor fails, the remaining motor is already operating at adjusted levels to maintain stable reaction force and prevent excessive steering.
Solution Approach 2:
The system implements continuous feedback monitoring of the reaction force and motor operational status. When a failure is detected, the control unit uses feedback from sensors to adjust the remaining motor's output in real-time, ensuring the reaction force remains within safe limits and preventing the driver from excessively turning the steering wheel even during cornering maneuvers.
3Speed
If the reaction force motor output is suddenly reduced to a limit value upon failure, then the system responds quickly to failure, but the driver cannot adapt to the change causing unintended vehicle steering
Solution Approach 1:
Instead of immediately reducing the reaction force motor output to a limit value upon failure detection, the control unit implements periodic or gradual reduction over a predetermined time period. This allows the driver to progressively adapt to the changing steering characteristics while the system maintains adequate reaction force, preventing unintended vehicle steering during the transition.
Data Source
AI summary
In a steer-by-wire steering system for a vehicle, a control unit (16) controls an operation of a steering actuator to cause the steered angle of wheels to be in a prescribed relationship to a steering angle, and an operation of the reaction force actuator (15) including a pair of reaction force motors (14) to cause the reaction force to be a value (Tt) corresponding to a steered state of the wheels, wherein the control unit is provided with a failure detection unit (36) configured to detect failures of the reaction force motors, and upon detecting a failure of one of the reaction force motors, progressively reduce an output (Tta) of the other reaction motor to a prescribed limit value (TL).