Electric Power Steering Motor Control for Torque Sensor Failure
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Solution Overview
Problem
Existing electric power steering systems cannot provide appropriate steering assistance when the torque sensor fails, especially on vehicles without a steering angle sensor, leading to a loss of assistive force and increased steering effort for the driver.
Innovation Solution
An electric power steering apparatus that includes a torque detector, vehicle speed detector, rotational angle detector, motor controller, and abnormality detector, which allows the system to generate assistive torque based on rotational angle and vehicle speed even if the torque sensor fails, using stored characteristics to control the motor current and reduce excessive turning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the torque sensor fails, then the steering assistive force is canceled, but the driver experiences increased steering effort and loss of assistance
Solution Approach 1:
The patent introduces a steering angle sensor as an intermediary device to detect steering wheel angle and convert it into assistive torque control signals. When the torque sensor fails, the steering angle sensor serves as a mediator to maintain steering assistance by calculating torque based on the relationship between steering angle and vehicle dynamics, thus preventing complete loss of assistive force while reducing driver steering effort
Solution Approach 2:
The patent replaces the mechanical torque sensing mechanism with an electronic control system that uses steering angle detection and computational algorithms. Instead of directly measuring torque mechanically, the system substitutes a sensor-based electronic approach that calculates assistive torque from steering angle, vehicle speed, and stored characteristic data, thereby maintaining assistance functionality during torque sensor failure
2Reliability
If the torque sensor fails on vehicles without a steering angle sensor, then all steering assistance is lost, but adding a steering angle sensor increases device complexity
Solution Approach 1:
The patent makes the steering angle sensor multi-functional by using it for both normal operating conditions and failure mode compensation. The same sensor that normally works alongside the torque sensor now serves as the primary input for maintaining steering assistance when the torque sensor fails, eliminating the need for separate backup systems and reducing overall device complexity
Solution Approach 2:
The patent changes the control parameter from direct torque measurement to steering angle measurement. By switching from torque-based control to steering angle-based control, the system can maintain assistance functionality using different sensor data, thereby ensuring continuity of steering assistance without requiring duplicate sensor hardware
3Reliability
If the motor is continuously energized at high current during torque sensor failure, then steering assistance is maintained, but excessive current causes harmful effects on the motor and system
Solution Approach 1:
The patent implements dynamic current control by continuously adjusting motor current based on real-time steering angle detection and vehicle speed data. Instead of maintaining constant high current, the system dynamically modulates current levels according to actual steering conditions, preventing motor overheating and excessive turning while maintaining necessary steering assistance during torque sensor failure
Solution Approach 2:
The patent introduces feedback control by using the steering angle sensor to continuously monitor actual steering wheel position and feed this information back to the controller. The controller compares feedback steering angle data with intended steering commands and adjusts motor current accordingly, preventing excessive current application and harmful effects while maintaining appropriate steering assistance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Ensures continued appropriate assistive force to the driver during torque sensor failures, reducing steering effort and preventing excessive turning, even in the absence of a steering angle sensor, by using rotational angle and vehicle speed data to control motor current.
Implementation Method 1
a motor for applying an assistive torque to a rotational shaft of the steering system
Implementation Method 2
a torque detector for detecting a torque generated by a steering system of the vehicle
Implementation Method 3
a rotational angle detector for detecting a rotational angle of the steering system
Data Source
AI summary
An electric power steering device provides an appropriate power assist from the motor even when torque sensors have failed and the steering torque is no longer detected. If an error is detected in a torque sensor, the motor is driven based on the rotor rotation angle detected by a resolver and assist characteristics. When the absolute value of the rotor turning angle velocity calculated based on the rotor rotation angle falls to or below a prescribed value, a process is started for reducing the current driving the motor, and if the state in which the absolute value of the rotor turning angle velocity has fallen to or below the prescribed value continues over a prescribed length of time, the process for reducing the current is interrupted and, because an assist current was flowing at said time of interruption, an appropriate power assist can be given during a steering retention period.