Wiper Motor Control to Prevent Magnet Demagnetization
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Solution Overview
Problem
The existing wiper devices face demagnetization issues due to field weakening control, especially when magnets are at high temperatures, leading to torque shortages and increased current values, which degrade motor performance.
Innovation Solution
A wiper device with a temperature sensor and protection units that control the duty ratio, advance angle, and energization angle to prevent demagnetization by prohibiting boost control when temperature thresholds are exceeded, thereby maintaining motor performance without structural changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If field weakening control is performed to increase rotation speed and torque, then motor speed and torque are improved, but demagnetization occurs when magnets are at high temperature
Solution Approach 1:
The control device performs preliminary detection of motor temperature and predicts the risk of demagnetization before it occurs. When the temperature exceeds a predetermined threshold, the control device preemptively restricts field weakening control, preventing demagnetization from happening in the first place
Solution Approach 2:
The control device creates a virtual model of the motor's magnetic field state by calculating the magnitude of the magnetic field vector based on armature reaction flux and rotor flux. This virtual representation allows the system to monitor and predict demagnetization risk without physically measuring the magnetic field directly
2Speed
If field weakening control is applied to achieve high-speed operation, then rotation speed increases, but current value increases due to torque shortage
Solution Approach 1:
The control device continuously monitors motor temperature and uses this feedback to dynamically adjust the field weakening control strategy. When temperature is high, the system reduces or prohibits field weakening, maintaining a balance between speed and current consumption while preventing demagnetization
Solution Approach 2:
The control device changes the operating parameters of the motor by adjusting the magnetic field strength through field weakening control. By dynamically modifying the advance angle and energization angle, the system optimizes the balance between rotation speed and current consumption based on temperature conditions
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
Prevents demagnetization, avoids torque shortages, and reduces current values, ensuring stable motor operation and improved wiping efficiency without altering the motor structure.
Implementation Method 1
a temperature sensor which detects a temperature of the motor
Implementation Method 2
a motor for causing the wiper member to swing. When an operator turns on a wiper switch provided in a vehicle interior, a motor is driven to rotate
Implementation Method 3
an external magnetic field in a direction opposite to a magnetic field of the rotor is applied to magnets of the rotor
Data Source
Figure 1
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AI summary
The objective of the present invention is to provide a wiper device with which motor demagnetization can be prevented. For this purpose, a boost control unit 87, if a duty ratio has reached an upper limit value that is determined in advance, and if the rotational speed of a motor is less than a target rotational speed, varies an advance angle and an energization angle associated with the energization of the motor in accordance with the target rotational speed. An overtemperature protection unit 81 monitors a load state of the motor, and, upon detecting a high-load state, performs a first protection control for decreasing the rotational speed of the motor. A demagnetization protection unit, upon receipt of an operating signal from a wiper switch 70 when the temperature detected by means of a temperature sensor 45 exceeds a first threshold and the first protection control is being performed, performs a second protection control for fixing the advance angle and energization angle of the motor by prohibiting the operation of the boost control unit 87.