EPS Motor Temperature Estimation Under Sensor Circuit Failure
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Solution Overview
Problem
Existing motor temperature estimation systems inaccurately limit motor current when an abnormality occurs in the temperature detection circuit, leading to excessive limitations despite the actual motor temperature being below the threshold.
Innovation Solution
A motor control device with a temperature detection circuit, a rise value estimation unit, and an abnormality determination unit that gradually adjusts the estimated temperature value when the detection circuit is abnormal, allowing for controlled motor current limitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor temperature is estimated by adding a comparatively high set value in place of detected temperature and a rise value estimated from the motor current when an abnormality occurs in the temperature detection circuit, then the motor can be protected from overheating, but the estimated value of the motor temperature immediately exceeds the threshold value and the motor current is excessively limited even though the actual motor temperature is less than the threshold value
Solution Approach 1:
The patent applies dynamics by making the temperature increase rate adjustable based on motor current conditions. When motor current is below a predetermined threshold, the temperature increase rate is set to a first (lower) value; when motor current exceeds the threshold, the rate is set to a second (higher) value. This dynamic adjustment prevents excessive current limitation while maintaining adequate motor protection.
Solution Approach 2:
The patent changes the parameter of temperature increase rate based on motor current levels. By setting different increase rates (first value vs. second value) according to whether motor current is below or above a threshold, the system adapts the temperature estimation behavior to actual operating conditions, avoiding unnecessary current limitation during low-load operations.
2Reliability
If the motor current is limited when the estimated motor temperature exceeds the threshold value, then the motor is protected from overheating, but the motor current is excessively limited immediately after an abnormality in the temperature detection circuit even though the actual motor temperature is below the threshold
Solution Approach 1:
The system dynamically adjusts the temperature increase rate based on motor current conditions. When motor current is low (below threshold), a slower temperature increase rate is applied, allowing the estimated temperature to rise more gradually and avoid triggering unnecessary current limitation. When motor current is high, a faster increase rate ensures adequate protection.
Solution Approach 2:
The patent changes the temperature estimation parameter (increase rate) based on operating conditions. By setting the increase rate to a first value when motor current is below threshold and a second value when above threshold, the system optimizes the balance between protection and operational smoothness.
Data Source
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AI summary
A motor control device includes: an abnormality determination unit (51) configured to determine whether or not a temperature detection circuit is abnormal; a first temperature estimation unit (52) configured to, when the temperature detection circuit is determined to be abnormal, output a value gradually increasing from a detected temperature detected by the temperature detection circuit to a predetermined set value at a constant increase rate as a first temperature estimated value; and a second temperature estimation unit (54) configured to calculate a value obtained by adding a rise value of temperature estimated based on motor current to the first temperature estimated value as a second temperature estimated value.