Motor Temperature Estimation via Dynamic Radiating Coefficients
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Solution Overview
Problem
Existing motor protective devices for electrically-operated power steering systems, particularly in all-terrain vehicles, fail to accurately estimate motor temperature due to a fixed radiating value correction term, leading to excessive cumulative heating values and premature shutdown of the motor, even when it is not overheating, especially in conditions with varying ambient temperatures and frequent power usage.
Innovation Solution
A motor protective device that estimates motor temperature by cumulating the difference between heating and radiating values, using adjustable heating and radiating coefficients to accurately reflect the motor's temperature, and sets ambient temperature as a fixed value to simplify calculations, allowing for effective overheat protection without unnecessary shutdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed radiating value correction term is used in temperature estimation, then the calculation is simple, but the temperature estimation becomes inaccurate under varying ambient temperatures and frequent power usage
Solution Approach 1:
The patent applies dynamics by making the radiating value correction term variable rather than fixed. The correction term is dynamically adjusted based on the cumulative heating value, allowing the temperature estimation to adapt to varying operating conditions such as frequent power usage and changing ambient temperatures, thereby resolving the contradiction between calculation simplicity and estimation accuracy.
Solution Approach 2:
The patent changes the parameter of the radiating value correction term from a constant to a variable that depends on the cumulative heating value. This parameter change allows the temperature estimation formula to accurately reflect the motor's thermal state under different operating conditions, improving measurement precision without significantly increasing calculation complexity.
2Reliability
If the radiating value correction term is set to an extremely small value to ensure high temperature protection, then motor protection is enhanced, but the cumulative heating value becomes excessive leading to premature shutdown
Solution Approach 1:
The patent uses dynamics by making the radiating value correction term variable based on cumulative heating value. This dynamic adjustment prevents the correction term from being excessively small throughout operation, allowing the motor to operate continuously without premature shutdown while still providing reliable protection when actual overheating occurs.
Solution Approach 2:
The patent implements feedback by using the cumulative heating value to dynamically adjust the radiating value correction term. This feedback mechanism ensures that the temperature estimation accurately reflects the motor's actual thermal state, preventing both premature shutdown and false protection, thereby maintaining both reliability and productivity.
3Device complexity
If the cumulative heating value is used to estimate temperature, then temperature can be estimated without temperature sensors, but the estimation becomes excessive under frequent power supply conditions
Solution Approach 1:
The patent changes the parameter of the radiating value correction term from fixed to variable based on cumulative heating value. This parameter change allows the estimation formula to accurately reflect temperature under frequent power supply conditions, maintaining measurement precision while avoiding the need for additional temperature sensors.
Solution Approach 2:
The patent uses feedback by continuously updating the radiating value correction term based on the cumulative heating value. This feedback mechanism ensures that the temperature estimation remains accurate even under frequent power supply conditions, resolving the contradiction between sensor-less operation 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 solution enables accurate motor temperature estimation and prevention of overheating in electrically-operated power steering systems, even under varying load conditions, by using adjustable coefficients and a fixed ambient temperature, ensuring the motor is protected without unnecessary power interruptions.
Implementation Method 1
an electrically-operated power steering system is known which eases the steering by imparting a rotational auxiliary force to the steering shaft by using an electrically-operated motor
Implementation Method 2
In general, in estimating the wiring temperature of the motor, a current value which flows in the wiring and a resistance value of the wiring are used in accordance with Joule's Law. More specifically, assuming the current value is I, the resistance value is R and an electricity supply time is t, a heating value Q can be estimated by a following formula (1). Q=I×I×R×t
Data Source
AI summary
A heating value calculation part obtains a substantial heating value based on the difference between a heating value and a radiating value attributed to a motor supply current. The radiating value is obtained by a difference between a motor estimation temperature Td and an ambient temperature Tm. The heating value is cumulated in the heating value calculation part and the cumulated value is inputted to a cumulated buffer. A cumulated value TS which is obtained by adding an initial temperature T0 to the cumulated value Td is inputted to a target current value ratio map and a target current value upper limit map. One of the target current values is selected and the selected target current value is inputted to a current feedback control part. The current feedback control part controls a motor output part such that the motor supply current is converged to the target current value.