Variable Valve Timing Controller Thermal Management
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Solution Overview
Problem
Variable valve timing controllers for internal combustion engines face challenges in changing valve timing after engine stop due to gear individual differences, leading to lock states and temperature-related motor torque issues, which can result in incomplete phase changes and potential motor drive circuit failures.
Innovation Solution
A variable valve timing controller with a first power supply control for setting target rotational phases, a lock detecting mechanism to identify lock states, a cooling control to lower motor device temperature, and a second power supply control to eliminate lock states by reversing motor power supply direction and increasing torque, ensuring successful phase changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If power supply is continued to the motor to change valve timing after engine stop, then the cam shaft can be rotated from stop state, but the motor or motor drive circuit temperature rises causing potential failure
Solution Approach 1:
The control unit performs preliminary cooling of the motor device before attempting to change valve timing after engine stop. The cooling period is determined based on the elapsed time since engine operation, ensuring the motor temperature is reduced to a safe level before power supply is applied, thus preventing temperature rise and potential failure
Solution Approach 2:
The system dynamically adjusts the cooling requirement based on the elapsed time since engine operation. The control unit determines whether cooling is required by comparing the current elapsed time against predetermined time thresholds, allowing the system to adapt the cooling strategy to the actual thermal state of the motor device
2Reliability
If motor operates at high temperature to eliminate lock state, then lock state can be released, but motor torque decreases leading to potential control failure
Solution Approach 1:
The control unit performs preliminary cooling of the motor device before attempting to eliminate the lock state. By ensuring the motor temperature is reduced to an appropriate level through the cooling period, the system guarantees sufficient motor torque availability when power supply is applied to release the lock state, preventing torque deficiency and control failure
3Adaptability or versatility
If gear rotation is attempted after engine stop, then valve timing can be changed, but individual gear dimension differences cause lock state occurrence
Solution Approach 1:
The control unit performs preliminary cooling of the motor device before attempting phase change after engine stop. This preliminary cooling action ensures the motor operates at optimal temperature for reliable torque delivery, which is crucial for overcoming the lock state caused by gear dimension differences and ensuring complete phase change
Solution Approach 2:
The system changes the temperature parameter of the motor device through the cooling period, transforming the motor into an optimal operating state. This parameter change (temperature reduction) enables the motor to deliver sufficient torque to handle the increased resistance from gear engagement differences, ensuring reliable phase change completion
Data Source
AI summary
An engine is provided with a variable valve timing device which transmits a rotational force generated by a motor via a motor drive circuit to a cam shaft so as to change a rotational phase of the cam shaft relative to a crank shaft. An ECU cools a motor and a motor drive circuit when the change of the rotational phase stops during the changing of the rotational phase of the cam shaft to a target value is detected. In addition, the lock state is eliminated by driving the motor by the motor drive circuit after cooling the motor device.