Electric Motor Torque Monitoring via Power Characteristic Curves
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Solution Overview
Problem
Existing methods for monitoring the torque of electric motors in hybrid vehicles are unreliable at low speeds due to large measurement errors, making it impossible to check the torque's plausibility and potentially leading to unwanted vehicle acceleration.
Innovation Solution
A method using a characteristic curve that links electrical power and torque, allowing for condition monitoring with redundancy, especially at low speeds, by recording consumed electrical power and cross-currents flowing through the motor's coils, enabling a more precise plausibility check without inaccuracies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque is monitored using the formula T=P/(n*η) at low speeds, then torque can be calculated, but measurement errors are greatly amplified leading to unreliable monitoring
Solution Approach 1:
The patent introduces a characteristic curve as an intermediary element that links electrical power and torque. Instead of directly calculating torque from power and speed measurements (which amplifies errors at low speeds), the characteristic curve serves as a mediator that provides expected torque values based on measured power, avoiding the mathematical operations that cause error amplification.
Solution Approach 2:
The patent changes the monitoring approach from direct torque calculation using physical measurements to comparing measured power against expected power derived from characteristic curves. This parameter transformation allows monitoring to be performed in a way that is not sensitive to the speed-dependent error amplification inherent in direct torque calculation.
2Reliability
If direct torque monitoring is performed at low speeds, then torque plausibility can be checked, but large measurement errors make every torque appear reliable
Solution Approach 1:
The patent creates a copy of the expected torque-power relationship through characteristic curves that were empirically determined at higher speeds. Instead of relying on direct low-speed measurements with poor precision, the system uses these pre-established characteristic curves to represent what the torque-power relationship should be, allowing plausibility checks without direct low-speed torque measurement.
Solution Approach 2:
The characteristic curves are determined in advance through empirical measurements at various operating conditions. This preliminary action of establishing the expected relationships before actual monitoring allows the system to perform plausibility checks by comparing against pre-established expectations rather than relying on real-time measurements that are prone to error.
3Power
If torque monitoring is performed using power and speed measurements, then torque can be determined, but the error window widens significantly at low speeds
Solution Approach 1:
The patent transitions from a direct calculation approach in the torque-speed-power measurement space to a comparative approach using characteristic curves. By introducing the dimension of expected versus measured values and using graphical/curve-based representation, the system avoids the mathematical operations that cause error amplification while maintaining the ability to monitor the same physical relationships.
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 reliable state plausibility checks at low speeds, preventing system errors and ensuring vehicle safety by accurately monitoring torque and power, even at low speeds up to 1,000 rpm, and enabling immediate error reactions.
Implementation Method 1
an actual torque generated by the electric motor of a hybrid vehicle... The relationship P = U*I applies to the electrical power... where η denotes an efficiency of the conversion of electrical energy into mechanical energy from the high-voltage battery to the electric motor
Data Source
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AI summary
The invention relates to a method for examining the state of an electric motor, comprising the step (101) of capturing a measured first physical variable of the electric motor by way of measurement, the first physical variable being indicative of an actual state of the electric motor, a step (103) of providing a second physical variable of the electric motor, said variable being indicative of a desired state of the electric motor, a step (105) of determining a first physical variable to be expected based on the second physical variable and a characteristic line of the electric motor, said characteristic line linking the first physical variable to be expected and the second physical variable, and a step (107) of examining the state using a comparison between the measured first physical variable and the first physical variable to be expected.