Electric Power Steering Torque Sensor Fallback Control
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Solution Overview
Problem
Electric power steering control systems become unstable when the torque sensor malfunctions, leading to increased vibration due to a longer detection cycle of the estimated steering torque, which cannot be sufficiently suppressed by damping torque alone.
Innovation Solution
An electric power steering control apparatus that includes a target torque calculation unit, an assist torque calculation unit, a motor drive unit, and a followability change unit. When a torque sensor abnormality is detected, the followability of the actual steering torque to the target torque is degraded to reduce vibration and stabilize the control system by adjusting the control gains and using filters for phase compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the detection cycle of the steering torque is extended when the torque sensor malfunctions, then the system can operate without the torque sensor, but the torque oscillation increases and the control system becomes unstable
Solution Approach 1:
The control apparatus dynamically adjusts the followability of the assist torque calculation based on the detection cycle. When the detection cycle is long (torque sensor malfunction), the system reduces the followability to prevent torque oscillation, while when the detection cycle is short (normal operation), the system increases followability for responsive steering assistance. This dynamic adjustment resolves the contradiction between maintaining reliability during sensor malfunction and preserving control system stability.
Solution Approach 2:
The system changes the control parameter (followability) based on the detection cycle conditions. By monitoring whether the detection cycle exceeds a predetermined threshold, the system switches between different followability levels, effectively adapting to the changed operational state and preventing instability while tolerating sensor malfunctions.
2Speed
If the followability of the actual steering torque to the target steering torque is increased, then the steering response is more responsive, but the vibration increases when the detection cycle is long
Solution Approach 1:
The followability is dynamically adjusted based on the detection cycle length. During normal operation with short detection cycles, high followability provides responsive steering assistance. When the detection cycle extends due to sensor malfunction, the system automatically reduces followability to eliminate vibration, thus dynamically balancing responsiveness and vibration suppression.
Solution Approach 2:
The system takes preliminary action by detecting the detection cycle length before vibration occurs. When a long detection cycle is detected, the system proactively reduces followability to prevent torque oscillation and vibration, rather than reacting after the vibration has already occurred.
Data Source
AI summary
An electric power steering control apparatus that assists a steering operation made by a driver with a motor includes: a target torque calculation unit calculating a target steering torque; an assist torque calculation unit calculating an assist torque which enables an actual steering torque follows close to the target steering torque according to a difference therebetween; a motor drive unit driving a motor acting on a steering system mechanism so that a steering angle of vehicle is changed according to the assist torque; and a followability change unit that detects an abnormality of a torque sensor for detecting the actual steering torque. When abnormality is detected in the torque sensor, a followability of the actual steering torque to the target steering torque controlled by the assist torque is degraded compared with a case where no abnormality is detected in the torque sensor.