Motor Overheat Protection via Dynamic Thermal Calculation
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Solution Overview
Problem
Existing overheat protection systems for electric power steering systems lack precision in estimating motor temperatures, leading to potential overheating of motors and peripheral components due to simplified heat generation and radiation calculations, which can result in premature current limitation and reduced system performance, especially in varying operating conditions.
Innovation Solution
An overheat protection apparatus that calculates a heat generation amount using a formula incorporating both heat generation and radiation correction terms, with a selection mechanism to adjust the calculation based on ambient temperature, allowing for dynamic current limitation to prevent overheating, and includes a current upper limit map and ratio map to determine optimal current limitation values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a simplified heat generation calculation (Q=I²×R×t) is used, then the calculation is simple, but the temperature estimation accuracy is insufficient leading to premature current limitation
Solution Approach 1:
The patent applies dynamics by making the heat radiation correction term dynamic rather than static. The correction term varies based on the integrated temperature value, with different coefficients applied at different temperature ranges. This allows the calculation to adapt to changing thermal conditions, improving accuracy without requiring a completely complex model.
Solution Approach 2:
The patent changes parameters by introducing temperature-dependent coefficients for heat radiation correction. Instead of using a fixed simple model or a constantly complex model, the parameters (coefficients) change based on the operating temperature, providing accuracy when needed while maintaining simplicity when temperatures are low.
2Reliability
If heat radiation correction term is always applied, then temperature estimation accuracy improves, but current limitation occurs prematurely during high ambient temperature operations
Solution Approach 1:
The patent applies local quality by differentiating the calculation approach based on local conditions (ambient temperature and integrated temperature levels). In high ambient temperature regions, the heat radiation correction term is reduced or eliminated. In normal operating regions, the full correction is applied. This localized adjustment ensures reliability where needed while maintaining productivity in high-temperature environments.
Solution Approach 2:
The patent makes the heat radiation correction dynamic by adjusting it based on real-time temperature conditions. When the integrated temperature exceeds certain thresholds or ambient temperature is high, the correction term is dynamically reduced or set to zero, preventing premature current limitation while maintaining accurate temperature estimation during normal operations.
3Loss of time
If the constant a (heat radiation amount) is set high, then the cumulative value T returns to zero faster, but the winding temperature is estimated lower reducing protection effectiveness
Solution Approach 1:
The patent changes the parameter (heat radiation correction coefficient) based on the operating state. During cooling periods when accuracy is less critical, a higher effective radiation coefficient is used to speed up the return to zero. During active heating and protection-critical periods, the appropriate coefficient is applied to maintain accurate temperature estimation. This parameter adaptation resolves the contradiction between cooling speed and estimation accuracy.
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 provides more accurate temperature estimation and efficient current limitation, preventing overheating of motors and controllers by considering the heat generation and radiation characteristics of different components, thereby enhancing the reliability and performance of electric power steering systems, especially in demanding conditions like off-road travel.
Implementation Method 1
a value I of current flowing through the winding and a resistance value R of the winding are utilized in accordance with the Joule's law. In particular, the heat generation amount Q accumulated within energization time t is calculated in accordance with the following: Q=I2×R×t
Implementation Method 2
an integration section configured to integrate the heat generation amount to obtain an integrated temperature
Data Source
AI summary
An apparatus which estimates the temperatures of a motor without using a temperature sensor can achieve overheat protection by proper control. In an example, a heat generation amount calculation section calculates a heat generation amount of a motor. A current upper limit map has a current upper limit value corresponding to a temperature estimated value and a ratio map has a ratio corresponding to the temperature estimated value. A lower one of limited current values, determined using the two maps, controls energization of the motor. The heat generation amount calculation section includes a heat generation correction term, and a heat radiation correction term for calculating a function of the difference between the integrated value of the heat generation amount and a motor ambient temperature. If the ambient temperature becomes equal to or higher than a comparison temperature, then the heat generation amount is calculated without the heat radiation correction present.