Quick Disconnect Control for Windscreen Wiper Motor Transients
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Solution Overview
Problem
Motor vehicle windshield wiper motors generate transient switching voltages during power disconnection due to their permanent magnet and inertia, causing electromagnetic compatibility issues and requiring costly doubling of switching components to mitigate these voltages.
Innovation Solution
A power supply connection/disconnection control device with a quick disconnect switching circuit, comprising a PMOS field-effect transistor or an electromechanical relay, controlled by a motor operation signaling signal, is inserted between the motor supply voltage and the power switch, reducing switching voltage magnitude to less than 1 volt and decay time to less than 10 ms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a quick disconnect switching circuit is inserted to reduce switching voltage, then electromagnetic compatibility is improved, but device complexity increases
Solution Approach 1:
A quick disconnect switching circuit is inserted as an intermediary component between the motor supply voltage and the power switch. This circuit includes a controlled switching transistor (PMOS or NPN) that acts as a mediator to rapidly disconnect the motor from the power supply, reducing the switching voltage magnitude to less than 1 volt and decay time to less than 10 ms.
Solution Approach 2:
The patent replaces mechanical relay-based switching with electronic transistor-based switching. The controlled switching transistor (PMOS or NPN) provides electronic control of the disconnect operation, eliminating the need for mechanical contacts and reducing both the switching voltage transient and the physical complexity of the switching mechanism.
2Object-affected harmful factors
If alternate conduction of PNP and NPN transistors is used to reduce switching voltage, then electromagnetic compatibility is improved, but manufacturing cost increases due to doubling of switching components
Solution Approach 1:
The patent uses an asymmetric switching configuration where only one transistor (either PNP or NPN, but not both in alternate conduction) is employed in the quick disconnect circuit. This asymmetric approach achieves the required voltage suppression while avoiding the cost penalty of doubling the switching components.
Solution Approach 2:
The invention extracts the essential function of voltage suppression by using a single controlled switching transistor that performs both the connection and disconnection functions. The unnecessary complexity of alternate conduction with two transistors is removed, keeping only the minimal component required to achieve the technical goal.
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 solution effectively eliminates parasitic voltages generated by the wiper motor during disconnection, improving electromagnetic compatibility and reducing manufacturing costs by minimizing the need for additional switching components.
Implementation Method 1
the quick disconnection switching circuit is constituted by a transistor of controlled switching, piloted by a motor operation signaling signal
Implementation Method 2
the quick disconnect switching circuit is constituted by an electromechanical relay controlled, piloted by an engine operation signaling signal
Implementation Method 3
When the motor power supply is cut off, the wiper motor being in operation, a cut-off voltage appears due to the operation of the windscreen wiper motor as a generator, during this cut-off, due to the presence of the permanent magnet fitted to this type of motor and its inertia
Data Source
Figure 1~2a
Figure 2b~3
AI summary
The invention relates to a device for controlling the connection/disconnection of the power supply of a windscreen wiper motor (WM) of a motor vehicle. This device comprises at least one quick disconnect switching circuit (1) inserted between the terminal (P+) of the line delivering the supply voltage to the motor and the terminal of the motor power supply switch (2). Application in building and fitting out motor vehicles of all kinds.