Electric Oil Pump Light Load Abnormality Detection
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Solution Overview
Problem
Conventional cooling systems for electric oil pumps face challenges in accurately determining light load abnormalities without relying on pressure sensors, leading to potential erroneous determinations, especially at varying temperatures and oil viscosities, which affects the accuracy of flow rate control and motor current differences.
Innovation Solution
A method that calculates a piping resistance equivalent value or its reciprocal based on detected motor current, voltage, and rotation speed to evaluate load abnormalities, allowing for determination without a pressure sensor, with threshold values set to prevent erroneous light load abnormality detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If motor current is used for light load abnormality determination, then the determination can be performed without a pressure sensor, but the difference in motor current between normal and idle states is reduced at low temperatures, making determination difficult
Solution Approach 1:
The patent changes the parameter used for abnormality determination from motor current alone to a composite parameter called 'piping resistance equivalent value' that incorporates motor current, motor rotation speed, and oil temperature. This parameter transformation allows accurate determination across varying temperature conditions by normalizing the effects of temperature-dependent viscosity changes on the measurement.
2Measurement precision
If rotation speed is increased to increase motor current difference for abnormality determination, then the difference becomes larger for better determination, but at low temperatures high viscosity prevents rotation speed increase
Solution Approach 1:
Instead of changing motor rotation speed to improve detectability, the patent transforms the measurement parameter to 'piping resistance equivalent value' which accounts for temperature effects. This allows accurate determination at any rotation speed, eliminating the need to increase speed even when viscosity is high.
Solution Approach 2:
The patent introduces oil temperature as an intermediary parameter that mediates between motor current and the determination of light load abnormality. By incorporating temperature into the calculation of piping resistance equivalent value, the system compensates for viscosity effects without requiring changes to motor operation.
3Measurement precision
If drive duty is varied to increase current difference for abnormality determination, then determination accuracy improves, but the system becomes dependent on drive duty variations
Solution Approach 1:
The patent creates a new parameter 'piping resistance equivalent value' that combines multiple measurements (current, speed, temperature) into a single metric that reflects system resistance. This parameter can be calculated under any drive duty condition, making the determination method adaptable to various operating modes without requiring specific duty cycle variations.
Data Source
AI summary
A light load abnormality determination method for an electric oil pump (3) that circulates oil to an object to be cooled by the electric oil pump driven by a motor (11), the method comprising: a detection step (41) to detect a current flowing through the motor, a voltage supplied to the motor, and a rotation speed of the motor; a calculation step (42) to calculate a piping resistance equivalent value or a reciprocal value of the piping resistance equivalent value, as a load evaluation value for light load abnormality determination, based on the current, the voltage and the rotation speed detected by the detection step; and a light load abnormality determination step (44) to determine a light load abnormality of the electric oil pump based on the load evaluation value.