Electric Power Steering Current Limits for Parking Assistance
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Solution Overview
Problem
Existing methods for preventing overheating in electric power steering systems during automatic parking fail to prevent steering disablement and cancellation of parking assistance, leading to increased steering angles and potential motor overheating, which can interrupt parking control.
Innovation Solution
An electric power steering device with route generation, calculation command, automatic steering control, overheat protection current limit, and statically-steerable number determination units to manage steering loads and prevent overheating, ensuring continuous parking assistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If static steering is performed during automatic parking, then parking assistance function is provided, but the EPS motor may overheat and cause steering disablement
Solution Approach 1:
The system performs preliminary estimation of the number of static steering operations required for parking before actually executing them. Based on this estimation, the system determines in advance whether the EPS motor can complete the parking maneuver without overheating, and only enables parking assistance when the estimated static steering count is within the safe operating range.
Solution Approach 2:
The system continuously monitors the actual number of static steering operations performed during parking and compares it against the estimated value. If the actual count exceeds the estimated safe range, the system provides feedback by notifying the driver and disabling further parking assistance to prevent motor overheating.
2Temperature
If the steering angle is reduced to prevent overheat, then motor temperature is controlled, but the number of turnabouts increases and parking time extends
Solution Approach 1:
The system dynamically adjusts the steering control strategy based on real-time monitoring of static steering operations. When the number of static steering operations approaches the estimated safe limit, the system transitions from enabling full parking assistance to requiring driver intervention, thereby preventing overheating while minimizing unnecessary time extension.
3Reliability
If overheat protection is activated early to prevent motor damage, then motor safety is improved, but parking assistance is canceled and steering function is disabled
Solution Approach 1:
The system performs preliminary estimation of the number of static steering operations before executing parking assistance. This allows the system to determine in advance whether the motor can safely complete the required steering without exceeding thermal limits, enabling parking assistance only when safe and preventing premature activation of overheat protection that would cancel the function.
Data Source
AI summary
This electric power steering device is provided with a function for: notifying a parking assistance device of a statically-steerable upper limit number obtained from an estimated motor current when static steering is performed in turnabout and a current limit value for the purpose of overheat protection of an electric power steering; and notifying the parking assistance device of whether the electric power steering can perform steering according to a target steering angle command, from a target steering angle and a target vehicle speed from the start of parking to the completion thereof, thus preventing interruption due to overheat of the electric power steering during parking assistance.