Steering Control System Torque Sensor Abnormality Handling
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Solution Overview
Problem
Existing electric power steering systems face difficulties in maintaining steering assist response when the steering torque sensor is abnormal, leading to aliasing issues and unpleasant self-excited vibrations due to external disturbances like road noise, which affect the driver's experience.
Innovation Solution
A steering control system that includes an electric motor, a torque sensor, an angular velocity sensor, and a control unit that computes assist control amounts using angular velocity to damp vibrations and stabilize steering assistance, even when the torque sensor is abnormal, by increasing the damping control amount and reducing the derivative control amount, and setting a dead zone to prevent unintended assistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the sensing interval for estimating steering torque is made longer than the normal sensor interval, then the update cycle of estimated steering torque shortens and response speed increases, but aliasing occurs when torque vibrations from external forces are input
Solution Approach 1:
The patent changes the control gain parameter dynamically based on the operational state. When the steering torque sensor is abnormal, the system switches to a larger control gain value that compensates for the longer sensing interval and prevents aliasing effects, thereby maintaining both response speed and torque estimation accuracy
Solution Approach 2:
The patent implements dynamic adjustment of control parameters based on system state. The control gain is not fixed but varies according to whether the torque sensor is normal or abnormal, allowing the system to adapt to changing conditions and resolve the contradiction between response speed and accuracy
2Speed
If the control gain based on derivative value of estimated steering torque is set to be larger than normal, then the response of steering assistance is maintained, but self-excited vibrations occur due to aliasing from external forces
Solution Approach 1:
The patent converts the harmful aliasing effect into a beneficial damping effect. By setting a dead zone in the control characteristic and using angular velocity information, the system transforms the spurious signals from aliasing into a mechanism that suppresses self-excited vibrations and stabilizes steering assistance
Solution Approach 2:
The patent introduces angular velocity as an intermediary parameter to mediate between the torque estimation and the control output. This intermediary helps filter out aliasing effects while maintaining the beneficial response characteristics, preventing self-excited vibrations
Data Source
AI summary
A steering control system for a vehicle includes an electric motor, a torque sensor, an angular velocity sensor, and a control unit. The electric motor applies assist force to a turning operation of a steering wheel. The torque sensor detects a torque generated in a steering system including the steering wheel and varying with the turning operation. The angular velocity sensor detects an angular velocity generated in the steering system and varying with the turning operation. The control unit computes an assist control amount for the turning operation by using the torque and the angular velocity, and, when an abnormality occurs in a torque detection operation, increases a control amount computed by using the angular velocity among control amounts that constitute the assist control amount as compared to that when torque sensor operation is normal and executes drive control over the electric motor based on the assist control amount.