Electric Power Steering Stroke End Detection Using Current Change Rates
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Solution Overview
Problem
Existing electric power steering devices face challenges in detecting the stroke end quickly and accurately, leading to excessive torque generation and false detections, which result in reduced assist torque during steering operations.
Innovation Solution
The electric power steering device incorporates actual current change detection and motor control amount change detection to judge the stroke end based on the state of change of the actual current value and control amount, setting an upper limit for the target current value to prevent overcurrent and maintain necessary assist torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the stroke end is detected by monitoring motor current overshoot, then the detection timing is delayed, but excessively large torque occurs
Solution Approach 1:
The system performs preliminary action by detecting the tendency of current to increase and control amount to decrease before actual overshoot occurs. By monitoring the rates of change (derivatives) of these parameters, the system identifies stroke end conditions in advance, preventing excessive torque generation while maintaining accurate detection timing.
Solution Approach 2:
The system uses feedback by continuously monitoring both the actual current and control amount, comparing their rates of change against predetermined thresholds. This feedback mechanism enables real-time detection of stroke end conditions and allows the system to respond by restricting target current values, thereby preventing torque overshoot while maintaining precise detection.
2Reliability
If the stroke end is detected by steering rotation speed, then false detections occur during steering-held state, but detection timing is delayed
Solution Approach 1:
The system introduces an intermediary approach by combining multiple parameters (current rate of change and control amount rate of change) rather than relying on a single parameter like steering rotation speed. This multi-parameter intermediary mechanism distinguishes between genuine stroke end events and steering-held states, improving detection reliability without significant timing delay.
Solution Approach 2:
The system applies parameter changes by monitoring the rates of change of current and control amount rather than their absolute values. This transformation of parameters allows the system to detect stroke end conditions based on dynamic changes, improving reliability by distinguishing between different operational states while maintaining timely detection.
3Object-affected harmful factors
If the target current is restricted to prevent overshoot, then overcurrent is prevented, but assist torque is reduced during normal steering
Solution Approach 1:
The system applies dynamics by making the target current restriction dynamic rather than static. The restriction is applied selectively based on real-time detection of stroke end conditions through monitoring current and control amount changes. During normal steering operations, no restriction is applied and full assist torque is maintained, while during detected stroke end events, restriction is dynamically imposed to prevent overcurrent.
Solution Approach 2:
The system performs preliminary anti-action by restricting the target current value before actual overshoot can occur. By detecting the tendency toward overshoot through monitoring parameter changes and applying restriction in advance, the system prevents harmful overcurrent while maintaining normal assist torque during regular steering operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for early detection of the stroke end, preventing excessive torque generation and ensuring a minimum needed assist torque without unnecessary restrictions, improving precision and reducing false determinations.
Implementation Method 1
a motor for providing a steering assist torque
Implementation Method 2
feedback control means for determining a control amount that drives and controls the motor by feeding back a deviation between the target current value determined by the target current determination means and the actual current value detected by the actual current detection means
Data Source
AI summary
An actual detected current value and a target voltage value of an electric motor are subjected to a low-pass filter process, and amounts of change per time in the filtered actual current value and the filtered target voltage value are calculated. If the amount of change in the actual current value on the increase side is greater than a criterion value and the amount of change in the target voltage value on the decrease side is greater than a criterion value, it is judged that the stroke end has been reached. Then, the upper limit value of the target current value is set at the actual current value obtained in the immediately previous cycle of the feedback control, so as to prevent generation of unnecessary torque.