Steering Control Device End Contact Relaxation
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Solution Overview
Problem
In electric power steering systems, end contact relaxation control often results in insufficient motor torque during return steering near the rack end position, leading to a 'hooked feeling' and degradation of steering quality due to the lack of consideration for steering direction in setting current command values.
Innovation Solution
A steering control device that includes an electronic control unit to detect absolute steering angles, calculate current command values, and perform end contact relaxation control by adjusting the current command value based on the end separation angle, ensuring sufficient motor torque is maintained during return steering by limiting the current command value only when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If end contact relaxation control is performed by limiting current command value based on steering angle, then impact of end contact is relaxed, but motor torque becomes insufficient during return steering causing hooked feeling
Solution Approach 1:
The control method applies different current limiting strategies based on the local condition of steering direction. When return steering is detected (current command value has opposite sign to previous value), no limiting is applied. When turning steering is detected (current command value has same sign as previous value), limiting is applied. This local differentiation resolves the contradiction by tailoring the control action to the specific operational context.
Solution Approach 2:
The control system dynamically adjusts the current command value limiting based on real-time detection of steering direction and comparison with previous values. The limiting threshold is not fixed but changes dynamically according to whether the system is in return steering or turning steering mode, allowing optimal performance across different operating conditions.
2Object-affected harmful factors
If current command value is limited to relax end contact impact, then rack end contact impact is reduced, but steering torque is insufficient near rack end position
Solution Approach 1:
The control method applies different torque strategies based on the local condition of steering operation. During return steering operations near the rack end, full torque is permitted without limiting. During turning steering operations, torque limiting is applied to prevent excessive impact. This spatial and operational differentiation resolves the contradiction between impact reduction and torque sufficiency.
Solution Approach 2:
The control system performs preliminary detection of steering direction and anticipates the need for full torque during return steering operations. By detecting the change in current command value sign before the end contact impact occurs, the system prepares to provide sufficient torque in advance, preventing the hooked feeling while still protecting against excessive impact during turning operations.
3Object-affected harmful factors
If steering angle-based current limiting is applied, then end contact protection is achieved, but steering direction sensitivity is lost
Solution Approach 1:
The control method enhances adaptability by applying different control strategies based on the local condition of steering direction. The system detects whether the operation is return steering or turning steering and applies corresponding current limiting or no-limiting strategies. This directional sensitivity allows the system to adapt its behavior to match the driver's intent and operational context.
Solution Approach 2:
The control system uses feedback from the current command value and its previous value to determine steering direction. By continuously monitoring the sign relationship between current and previous current command values, the system adapts its torque output in real-time, maintaining high adaptability to steering direction while still providing end contact protection when needed.
Data Source
AI summary
A steering control device includes an electronic control unit. The electronic control unit is configured to detect an absolute steering angle, to calculate a current command value, to control driving of a motor such that an actual current value which is supplied to the motor reaches the current command value, to store an end-position-corresponding angle which is correlated with the absolute steering angle, to perform end contact relaxation control for correcting the current command value such that a decrease of an end separation angle is regulated when the end separation angle is equal to or less than a predetermined angle, and to calculate the current command value such that an increase of the end separation angle is not regulated by the end contact relaxation control when the end separation angle is equal to or less than the predetermined angle.