Wiper Motor Advance-Angle Control to Prevent Low-Speed Overcurrent
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Solution Overview
Problem
Conventional motor devices used in wiper systems may experience overcurrent issues even when the output is suppressed by an upper limit value of the output duty during wide-angle energization.
Innovation Solution
A motor device with a three-phase motor, a rotation speed detector, a drive signal generator that controls the duty ratio and energization angle, and an inverter that supplies alternating current to the motor windings. The drive signal generator includes an advance angle/energization angle controller that adjusts the energization angle to 120 degrees or less when the duty ratio exceeds the upper limit and the motor rotation speed is below a predetermined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If wide-angle energization is performed to improve motor output, then the motor output is improved, but an overcurrent may occur even though the output is suppressed by the upper limit value of the output duty
Solution Approach 1:
The patent applies dynamics by making the energization angle variable rather than fixed. The control device dynamically adjusts the energization angle based on motor rotation speed: using a first energization angle for high speeds and a second energization angle for low speeds. This dynamic adjustment resolves the contradiction by optimizing motor output at high speeds while preventing overcurrent at low speeds where wide-angle energization causes harmful effects.
Solution Approach 2:
The patent applies parameter changes by modifying the energization angle parameter according to operating conditions. By changing the energization angle from a wide angle (greater than 120 degrees) at high rotation speeds to a narrower angle (120 degrees or less) at low rotation speeds, the system achieves high output when needed while preventing overcurrent conditions that occur with wide-angle energization at low speeds.
2Power
If the energization angle is increased to improve output, then the motor output increases, but the current consumption increases causing overcurrent
Solution Approach 1:
The system dynamically adjusts the energization angle based on rotation speed conditions. At high rotation speeds where wide-angle energization improves output without causing overcurrent, the system uses a first energization angle greater than 120 degrees. At low rotation speeds where wide-angle energization causes overcurrent, the system switches to a second energization angle of 120 degrees or less, thus optimizing the balance between output and current consumption across different operating conditions.
Solution Approach 2:
The patent changes the energization angle parameter based on motor rotation speed to optimize the relationship between output and current consumption. By setting the energization angle to a first value (greater than 120 degrees) at high speeds and a second value (120 degrees or less) at low speeds, the system achieves efficient energy utilization while preventing overcurrent 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
This solution effectively reduces the occurrence of overcurrents, preventing demagnetization of the motor's permanent magnets and ensuring stable operation of the wiper system.
Implementation Method 1
a motor (2) that has armature coils of three phases (21u, 21v, and 21w) and is rotationally driven
Data Source
AI summary
A motor device includes a motor having three-phase windings; a rotation speed detector detecting a rotation speed of the motor; a drive signal generator controlling a duty ratio not to exceed a duty ratio upper limit value, and performing control for an energization angle of each phase and performing advance angle control shifting the phase from a reference position to generate a drive signal corresponding to the duty ratio; and an inverter supplying alternating current to the windings based on the drive signal. The drive signal generator includes an advance angle/energization angle controller changing the energization angle to 120 degrees or less while performing advance angle control when the duty ratio is equal to or greater than the duty ratio upper limit value and the rotation speed is equal to or less than a predetermined threshold value in a state where the energization angle is greater than 120 degrees.