Steering Control Device End Contact Relaxation
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Solution Overview
Problem
Existing electric power steering systems (EPS) face a deterioration in small-turn performance due to end contact relaxation control, which limits the rack shaft movement at a virtual position closer to the neutral steering position, resulting in a larger minimum turning radius and discomfort for drivers during turns.
Innovation Solution
A steering control device with an electronic control unit that performs partial release control by decreasing the correction value of the current command value based on steering torque, allowing the turning shaft to move to the actual end position, thereby increasing the current command value and preventing discomfort, while maintaining the steering angle limit value within a preset threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If end contact relaxation control is performed to limit rack shaft movement at a virtual end position, then impact of end contact is relaxed, but minimum turning radius increases and small-turn performance deteriorates
Solution Approach 1:
The patent applies dynamics by making the end-position-corresponding angle variable rather than fixed. The virtual end position is dynamically adjusted based on vehicle speed: at low speeds, the virtual end position is set closer to the actual end position to improve small-turn performance, while at high speeds, it is set farther away to reduce end contact impact. This dynamic adjustment resolves the contradiction between impact relaxation and small-turn performance.
2Reliability
If end contact relaxation control is performed by decreasing target motor torque, then end contact impact is reduced, but steering feel deteriorates and driver discomfort increases
Solution Approach 1:
The patent changes the parameter of end-position-corresponding angle based on vehicle speed. By adjusting this angle parameter dynamically, the system achieves both end contact impact reduction and maintained steering feel. The parameter change allows the control system to adapt to different operating conditions, resolving the contradiction between impact reduction and steering quality.
3Reliability
If virtual rack end position is set closer to neutral steering position, then end contact relaxation is improved, but minimum turning radius increases
Solution Approach 1:
The patent makes the virtual end position dynamic by correlating it with vehicle speed. At low speeds where small turning radius is needed, the virtual end position is set closer to the actual end position. At high speeds where end contact impact is the concern, the virtual end position is set farther away. This dynamic positioning resolves the contradiction between end contact relaxation and minimum turning radius.
Data Source
AI summary
A steering control device includes an electronic control unit. The electronic control unit is configured to perform end contact relaxation control for correcting a current command value such that a decrease of an end separation angle indicating a distance of an absolute steering angle from an end-position-corresponding angle is limited when the end separation angle is equal to or less than a predetermined angle and to perform partial release control for decreasing a correction value of the current command value due to execution of the end contact relaxation control based on a steering torque which is input to a steering system when a vehicle is intended to travel while turning at the time of execution of the end contact relaxation control.