Motor Controller Overload Detection via Current Sensing
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Solution Overview
Problem
Existing motor controllers face challenges in quickly and accurately determining an overloaded state, particularly when the air intake system filter is removed, leading to frequent overload protection activation and potential overheating, which disrupts the smooth operation of vehicle air conditioners.
Innovation Solution
A motor controller that includes current detection means, overload determination means, and rotation speed control means to quickly and accurately determine motor overload without stopping rotation, utilizing a thermistor and resistor configuration to refine overload determination and prevent overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If overload protection control stops motor rotation to prevent overheating, then circuit safety is improved, but smooth operation of vehicle air conditioner deteriorates due to frequent activation when filter is removed
Solution Approach 1:
The patent changes the detection parameter from temperature-based (thermistor) to current-based (amplifier detecting current between inverter circuit and battery). This allows the system to detect overload conditions more accurately and respond appropriately without unnecessary shutdowns, improving both circuit safety and operational smoothness.
Solution Approach 2:
The patent replaces the mechanical/thermal detection method (thermistor measuring heat from shunt resistor) with an electrical detection method (amplifier directly measuring current). This substitution enables faster, more accurate overload detection that doesn't suffer from thermal lag or interference from motor coil heating, thereby preventing false overload protection activation while maintaining circuit safety.
2Reliability
If thermistor is used to detect heat from shunt resistor, then overload detection is performed, but quick and accurate determination deteriorates due to temperature changes from motor coil current
Solution Approach 1:
The patent replaces thermal detection (thermistor) with direct electrical current detection (amplifier). The amplifier measures current directly between the inverter circuit and battery, eliminating the thermal lag and measurement errors caused by thermistor heating from motor coil current. This provides quick and accurate overload determination without interference from temperature changes.
Solution Approach 2:
The patent extracts the overload detection function from the thermal measurement system (thermistor on shunt resistor) and places it in the electrical measurement system (amplifier detecting current between inverter circuit and battery). This separation removes the thermistor from the high-current path, eliminating the source of measurement error while maintaining overload detection capability.
3Productivity
If air intake system filter is removed to increase airflow, then air conditioner performance is improved, but motor overload increases leading to frequent protection activation
Solution Approach 1:
The patent changes the detection parameter from temperature (which lags and is inaccurate) to current (which responds immediately to load changes). This allows the system to distinguish between normal high-current operation (when filter is removed for high airflow) and actual overload conditions, preventing false protection activation and maintaining motor operation stability during high-performance modes.
Data Source
AI summary
The motor controller includes: a current detection section that detects a current between a battery and an inverter circuit generating a voltage applied to a coil of a motor; an overload determination value output section that outputs an overload determination value used to determine whether or not the motor is overloaded; an overload determination section that compares a current value detected by the current detection section against the overload determination value, and that determines the motor to be overloaded in a case in which the current value detected by the current detection section is the overload determination value or greater; and a forced 500 rpm instruction section that controls the motor rotation speed to 500 rpm, this being a specific speed, in a case in which the overload determination section has determined the motor to be overloaded.