Steering Control Circuit End-Abutting Relaxation Overshoot
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Solution Overview
Problem
In electric power steering systems, overshoot of the electric current supplied to the motor occurs during end-abutting relaxation control, leading to insufficient relaxation of impact and increased load on component parts, especially on low-friction roads at high speeds.
Innovation Solution
A steering control device with a control circuit that detects absolute steer angles and computes current command values, performing end-abutting relaxation control by adjusting the control gain and limiting current command values to prevent overshoot, using a steer angle limit value and feedback computation to ensure the actual current value follows the command value closely.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If end-abutting relaxation control is executed by limiting current command value, then impact relaxation is improved, but overshoot of actual current value occurs
Solution Approach 1:
The control circuit executes preliminary action by detecting the approach to end position before actual end abutting occurs. When the absolute steer angle approaches the end position correspondence angle, the control circuit starts limiting the current command value in advance, and continues this limitation even after end abutting occurs, thereby preventing overshoot while maintaining impact relaxation.
Solution Approach 2:
The control circuit implements feedback by continuously monitoring the absolute steer angle and comparing it with the end position correspondence angle stored in memory. Based on this feedback, the control circuit dynamically adjusts the current command value limitation, ensuring that overshoot is prevented while maintaining effective end-abutting relaxation control.
2Reliability
If motor stops suddenly at high speed, then end abutting is prevented, but reverse voltage decreases rapidly causing overshoot
Solution Approach 1:
The control circuit executes preliminary action by detecting the approach to end position before actual end abutting occurs. When the absolute steer angle approaches the end position correspondence angle, the control circuit starts limiting the current command value in advance, and continues this limitation even after end abutting occurs, thereby preventing overshoot while maintaining impact relaxation.
Solution Approach 2:
The control circuit applies preliminary anti-action by preemptively limiting the current command value before the motor stops suddenly. This preliminary limitation counteracts the harmful effect of rapid reverse voltage decrease that would otherwise cause overshoot, while still allowing the motor to stop sufficiently to prevent end abutting.
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
The solution effectively restrains overshoot of the electric current, reducing the impact on steering device components and maintaining optimal responsiveness, thereby preventing vibration and abnormal noise.
Implementation Method 1
an actuator configured to give motor torque by which the turning shaft reciprocates using a motor as a drive source
Implementation Method 2
the reverse voltage generated in the motor decreases rapidly
Data Source
AI summary
A steering control device includes a control circuit and a drive circuit. The control circuit is configured to perform a current feedback computation by which the actual current value of electric current to be supplied to a motor follows a current command value. The control circuit is configured to execute an end-abutting relaxation control to correct the current command value such that decrease in an end interval angle is restricted, when the end interval angle is equal to or smaller than a predetermined angle, the end interval angle indicating the distance of the absolute steer angle from the end position correspondence angle. The control circuit is configured to adjust a control gain to be used in the current feedback computation, such that the control gain increases, when overshoot of the actual current value occurs during the execution of the end-abutting relaxation control.