Electric Power Steering Skid Detection Torque Adjustment
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Solution Overview
Problem
Conventional electric power steering systems cause driver discomfort during counter steering on low friction roads due to assist torque reactions that counteract the driver's steering input, leading to an unstable steering feel.
Innovation Solution
An electric power steering system with a control mechanism that detects vehicle skid and adjusts the assist torque components to reduce the absolute value of the second assist component during skidding, thereby minimizing the sense of discomfort and maintaining optimal steering stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If steered-angle feedback control is performed to maintain target steered angle, then steering stability is improved, but driver discomfort increases during counter steering on low friction roads
Solution Approach 1:
The system dynamically adjusts the gain of steered-angle feedback control based on detected vehicle skid conditions. During normal operation, full feedback control maintains steering stability. When a skid is detected, the gain is reduced to allow counter steering operations without generating excessive assist torque that would cause driver discomfort.
Solution Approach 2:
The control system changes the parameter (gain) of the steered-angle feedback control based on vehicle state. By detecting skid conditions and adjusting the feedback gain parameter, the system adapts to different operating conditions, reducing the assist torque magnitude during skids while maintaining it during normal conditions.
2Stability of the object's composition
If assist torque is increased to stabilize steered wheels during skid, then vehicle stability is improved, but steering feel deteriorates due to counteracting driver input
Solution Approach 1:
The system extracts or removes the steered-angle feedback control component during detected skid conditions. By taking out this specific control function that generates counteracting assist torque, the system allows the driver's counter steering input to act directly on the steering mechanism without being opposed by automated assist torque.
3Measurement precision
If steered-angle feedback control is applied to cancel reverse input vibration, then steering precision is improved, but reaction force on driver increases during counter steering
Solution Approach 1:
The system dynamically modifies the steered-angle feedback control based on vehicle state. During normal conditions, the feedback control operates at full gain to cancel reverse input vibration and improve steering precision. During detected skids, the gain is reduced to minimize the reaction force on the driver during counter steering operations.
Data Source
AI summary
An electric power steering system includes a motor control device that controls, based on an assist command value, driving of a motor that gives an assist torque to a steering mechanism. The motor control device computes a first assist component based on a steering torque and a vehicle speed. A steered-angle command value is computed based on the steering torque and the first assist component, and a second assist component is computed by performing a feedback control that matches the steered angle with the steered-angle command value. The motor control device adds the second assist component to the first assist component so as to compute an assist command value. The motor control device includes a road information compensation portion that decreases an absolute value of the second assist component included in the assist command value when a skid is detected by a vehicle state detecting portion.