MDPS Motor Temperature Estimation Using Vehicle Speed Thermal Resistance
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Solution Overview
Problem
Existing motor-driven power steering (MDPS) systems face challenges in precisely estimating motor temperatures due to the use of a single temperature sensor, leading to potential overheating and degradation in performance, as different components within the power pack have distinct thermal characteristics.
Innovation Solution
The MDPS system incorporates a vehicle speed sensor, temperature sensor, current sensor, and a control unit that calculates an estimated motor temperature using a thermal resistance value based on vehicle speed, applied current, and stored thermal resistance values, adjusting torque gain and current limits to prevent overheating and enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single temperature sensor is used to estimate motor temperature, then production cost is reduced, but temperature estimation precision deteriorates
Solution Approach 1:
The patent introduces thermal resistance as an intermediary parameter to bridge the gap between the single temperature sensor measurement and the actual motor temperature. By using thermal resistance values that account for heat transfer characteristics between different components (motor, ECU, temperature sensor), the system can estimate individual component temperatures without requiring separate sensors for each, thus maintaining cost effectiveness while improving estimation precision.
Solution Approach 2:
The patent changes the parameter used for temperature estimation from direct sensor measurement to a calculated value based on thermal resistance models. The system dynamically adjusts thermal resistance values based on operating conditions (vehicle speed, current, duty cycle), allowing accurate temperature estimation of different components using a single temperature sensor reading combined with these variable parameters.
2Measurement precision
If thermal resistance value is constantly updated based on vehicle speed and operating conditions, then temperature estimation precision is improved, but computational complexity increases
Solution Approach 1:
The patent pre-calculates and stores thermal resistance values in lookup tables before system operation. These pre-computed values are organized based on different vehicle speed ranges and operating conditions. During real-time operation, the control unit simply retrieves the appropriate thermal resistance value from the stored tables based on current conditions, avoiding complex real-time calculations while maintaining high estimation precision.
Solution Approach 2:
The patent implements dynamic selection of thermal resistance values based on real-time operating conditions such as vehicle speed and current duty cycle. The system dynamically switches between different pre-stored thermal resistance values corresponding to different operating ranges, allowing the temperature estimation to adapt to changing conditions without requiring complex continuous computation.
3Reliability
If current limit is reduced to prevent overheating, then motor protection is improved, but steering performance deteriorates
Solution Approach 1:
The patent applies partial current limiting based on the actual thermal state of the motor. Instead of applying a fixed conservative current limit that would degrade performance, the system monitors the estimated motor temperature and applies current limits only when and to the extent necessary to prevent overheating. When the motor is within safe temperature ranges, full current is permitted, maintaining optimal steering performance.
Solution Approach 2:
The patent implements a feedback control mechanism where the estimated motor temperature continuously informs current limit decisions. The control unit monitors the calculated motor temperature and dynamically adjusts the current limit accordingly - reducing current when temperature approaches critical thresholds and allowing higher current when temperatures are safe, thus balancing motor protection with steering performance.
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 more precise temperature estimation and improved performance by controlling current application, enhancing steering stability and reliability, especially at high speeds, while reducing production costs by enabling the use of smaller motors and maintaining assist functionality over extended periods.
Implementation Method 1
a storage unit configured to store a thermal resistance value based on the vehicle speed with respect to the temperature of the power pack; and a control unit configured to calculate an estimated temperature by reflecting the thermal resistance value based on the vehicle speed with respect to the temperature of the power pack and the current amount applied to the MDPS into a temperature estimation function
Data Source
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AI summary
A motor driven power steering (MOPS) may include: a vehicle speed sensor (10) configured to sense vehicle speed; a temperature sensor (40) configured to sense a temperature of a power pack; a current sensor (50) configured to sense an amount of current applied to the MDPS; a storage unit (60) configured to store a thermal resistance value based on the vehicle speed with respect to the temperature of the power pack; and a control unit (70) configured to calculate an estimated temperature by reflecting the thermal resistance value based on the vehicle speed with respect to the temperature of the power pack and the current amount applied to the MDPS into a temperature estimation function, and drive a motor (80) according to the calculated estimated temperature.