Motor Control Unit Capacitor Discharge via Dynamic Clutch
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Solution Overview
Problem
Existing motor control units face challenges in safely discharging capacitor energy while minimizing resistance heating and preventing excessive burden on motors and their components, particularly in vehicles where torque transmission is interrupted.
Innovation Solution
A motor control unit that includes a control circuit, driving circuit, and capacitor, where electric power is supplied to the motor to generate torque after the power supply line is switched off, with the control circuit controlling the motor's angular velocity to be less than or equal to a prescribed value, even when torque transmission is interrupted by a clutch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If electric power is supplied to the motor such that torque is generated during capacitor discharge, then resistance heating is suppressed, but the motor may rotate at excessively high angular velocity placing excessive burden on the motor and its components
Solution Approach 1:
The patent applies dynamics by making the load condition on the motor dynamic rather than static. During capacitor discharge, the clutch is controlled to connect the motor to the driven body only when the motor angular velocity is below a threshold value, and to disconnect when the angular velocity exceeds the threshold. This dynamic control of the clutch engagement state allows the motor to operate with load at low speeds (suppressing resistance heating) while preventing excessive speed and burden at high speeds.
Solution Approach 2:
The patent changes the parameter of motor angular velocity from an uncontrolled variable to a controlled parameter with a defined threshold value. By setting and monitoring the angular velocity threshold, the system determines when to engage or disconnect the clutch, thereby controlling the load condition on the motor during capacitor discharge. This parameter-based control resolves the contradiction between suppressing resistance heating and preventing excessive motor burden.
2Reliability
If a discharge circuit is provided to discharge electric charges from the capacitor, then safety is improved, but the size of the motor control unit increases
Solution Approach 1:
The patent applies multi-functionality by making the motor serve dual purposes: both as the driven load during normal operation and as the discharge path for the capacitor. Instead of adding a separate discharge circuit, the motor is utilized to consume the stored energy in the capacitor by generating torque and rotating. This eliminates the need for additional discharge circuit components, maintaining safety while avoiding increased device size.
Solution Approach 2:
The system applies self-service by using the motor itself to discharge the capacitor rather than requiring an external discharge circuit. The motor's own operation during capacitor discharge allows it to consume the stored energy, and the system leverages the existing motor structure and control capabilities to achieve the discharge function without adding separate dedicated discharge components.
3Speed
If electric power is supplied to the motor such that torque is not generated during capacitor discharge, then the motor does not rotate, but resistance heating increases
Solution Approach 1:
The patent applies dynamics by controlling the clutch engagement state dynamically based on motor angular velocity. Rather than maintaining a fixed state (either always connected or always disconnected), the clutch is connected when angular velocity is below the threshold to allow torque generation and suppress resistance heating, and disconnected when angular velocity exceeds the threshold to prevent excessive speed. This dynamic control resolves the contradiction between preventing motor rotation and suppressing resistance heating.
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 approach allows for safe capacitor discharge while suppressing resistance heating and preventing excessive motor and component stress by controlling the motor's angular velocity during discharge.
Implementation Method 1
a capacitor (C) provided at an intermediate portion of a power supply line (Lp) that connects the driving circuit (12) and an external power supply (15) to each other
Implementation Method 2
supplying electric power generated by electric charges stored in the capacitor (C) to the motor (2) such that torque is generated
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A motor control unit (1) controls an operation of a motor (2) connected to a wheel (4) via a clutch (3) that allows or interrupts torque transmission between the motor (2) and the wheel (4). The motor control unit (1) includes: a microcomputer (11) that outputs a motor control signal S_m; a driving circuit (12) that supplies driving electric power to the motor (2) based on the motor control signal S_m; and a capacitor (C) provided at an intermediate portion of a power supply line (Lp) that connects the driving circuit (12) and a driving power supply (15) to each other. The microcomputer (11) carries out electric discharge from the capacitor (C) by supplying electric power generated by electric charges stored in the capacitor (C) to the motor (2) such that torque is generated by the motor (2) and an angular velocity of the motor (2) becomes less than or equal to a prescribed angular velocity, with torque transmission between the motor (2) and the wheel (4) interrupted by the clutch (3), after a driving relay (16) is turned off.