Wiper Motor Control Circuit Braking Current Overrun
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Solution Overview
Problem
Existing wiper control devices struggle to effectively suppress overrun and maintain target wiping speed, leading to increased deviation and potential issues like sudden acceleration and hunting due to continuous PI control after the wiper blade reaches the return position.
Innovation Solution
A wiper control device that includes a drive circuit, rotation angle detection sensor, and control circuit, which applies a braking current when the wiper blade has overrun, halting PI control during braking and resuming it once the rotation speed reaches a threshold or zero, to prevent sudden acceleration and hunting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PI control is continued after the wiper blade reaches the return position to eliminate speed deviation, then the target speed and wiper speed deviation is reduced, but overrun suppression becomes difficult and sudden acceleration or hunting may occur
Solution Approach 1:
The control circuit detects when the wiper blade reaches the return position in advance and applies a braking current before the blade actually overruns. This preliminary braking action prevents overrun from occurring in the first place, allowing PI control to be stopped early without causing speed deviations. The braking current is applied proactively based on position detection rather than reactively after overrun detection.
Solution Approach 2:
The control circuit continuously monitors both the rotation angle (position) and rotation speed of the wiper motor. When the blade reaches the return position, the system provides feedback to stop PI control and apply braking current. This feedback mechanism ensures that control actions are taken at the correct moment to prevent overrun while maintaining speed accuracy.
2Reliability
If the rotation speed of the wiper motor is reduced rapidly to suppress overrun, then the wiper blade can be stopped before passing the return position, but the wiping speed may become too slow or cause hunting
Solution Approach 1:
Braking current is applied in advance when the wiper blade reaches the return position, preventing overrun before it occurs. This approach avoids the need for rapid speed reduction after overrun detection, thereby maintaining smooth wiping speed without causing hunting or excessive slowdown.
Solution Approach 2:
The braking current, which inherently slows down the motor, is applied at a precise moment (when the blade reaches the return position) to convert the potentially harmful effect of speed reduction into a beneficial outcome. Instead of causing unwanted slowdown during normal operation, the braking current prevents overrun while maintaining overall wiping speed performance.
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 suppresses overrun by decelerating the wiper speed through braking current application, ensuring smooth speed changes and preventing hunting, thereby maintaining accurate wiping speed and reducing motor load.
Implementation Method 1
a rotation angle detection section that detects a rotation angle of an output shaft of the wiper motor
Implementation Method 2
controls the drive circuit so as to apply a braking current in the wiper motor when the wiper blade has reached a return position of the wiper blade as determined according to the rotation angle and the rotation speed of the wiper motor has exceeded a threshold value
Data Source
AI summary
A wiper motor control circuit controls a drive circuit such that an actual speed of a wiper speed computed based on change in a rotation angle of an output shaft of the wiper motor detected by a rotation angle sensor that detects the rotation angle becomes a target speed corresponding to a position of a wiper blade indicated by the rotation angle detected by the rotation angle sensor. The wiper motor control circuit also controls the drive circuit so as to apply a braking current in the wiper motor when the actual speed has exceeded a threshold value when the rotation angle detected by the rotation angle sensor indicates a return position of the wiper blade.