Variable Valve Timing Motor Current Control for Engine Startability
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Solution Overview
Problem
Existing methods for controlling camshaft orientation in engines with start-stop capabilities are inefficient in quickly advancing the phasing of the camshaft during engine re-start, leading to increased torque requirements and reduced startability.
Innovation Solution
A method that determines operational motor current limits based on predetermined conditions such as motor temperature and age, allowing for elevated current usage during engine interruptions and reduced current usage upon resumption, enabling efficient camshaft re-phasing using an electric motor in the variable valve timing mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the electric motor operates with standard current limits during engine re-start, then the motor performance is maintained within safe operating parameters, but the camshaft phasing advancement is slow and torque requirements increase
Solution Approach 1:
The patent changes the electrical parameter (current limit) of the electric motor from its standard operational value to an elevated startup value during engine re-start conditions. This parameter change allows the motor to deliver higher torque and advance camshaft phasing more quickly, directly resolving the contradiction between advancement speed and torque requirement.
2Loss of time
If the electric motor uses elevated current during engine re-start, then the camshaft is re-positioned quickly with reduced torque requirements, but the motor may overheat or sustain damage
Solution Approach 1:
The patent implements dynamic current limiting that adapts the motor's current threshold based on real-time motor temperature conditions. When the motor is cold, elevated current limits are permitted to enable quick camshaft re-positioning. When the motor approaches thermal limits, the current limit is reduced to prevent overheating. This dynamic adjustment resolves the contradiction between reducing re-start time and maintaining motor reliability.
Solution Approach 2:
The system continuously monitors motor temperature and uses this feedback to adjust the current limit accordingly. The controller modifies the allowable current based on thermal conditions, ensuring the motor operates safely during elevated current periods. This feedback mechanism allows the system to exploit higher performance when safe and protects reliability when thermal limits are approached.
3Ease of operation
If the camshaft phasing is advanced gradually, then the motor operates within safe current limits, but the engine startability is reduced due to insufficient torque reduction
Solution Approach 1:
The patent temporarily changes the motor's current limit parameter from its standard operational value to an elevated startup value specifically during engine re-start conditions. This allows the motor to consume higher current briefly to achieve rapid camshaft phasing advancement, which reduces the torque needed to start the engine. The elevated current is only permitted when the engine is stopped and about to restart, resolving the contradiction between ease of operation and energy consumption.
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 improves engine startability by quickly and efficiently re-positioning the camshaft, reducing torque requirements and emissions, while maintaining optimal motor performance.
Implementation Method 1
The VVT mechanisms typically adjust the phase of the opening of the intake and/or exhaust valves by rotating a camshaft that is employed to control the opening and closing of the valves. It is common for such VVT mechanisms to rotate the camshaft with an electric motor.
Data Source
AI summary
A method includes determining a value of an operational motor current limit and setting a value of a startup current limit equal to a predetermined value in excess of the value of the operational motor current limit if a set of predetermined conditions is satisfied. The method includes determining that operation of the engine has been interrupted, operating the electric motor of the variable valve timing mechanism with a current having a magnitude that is less than or equal to the startup current limit after determining that operation of the engine has been interrupted, determining that operation of the engine has resumed, and operating the electric motor of the variable valve timing mechanism with a current having a magnitude that is less than or equal to the operational motor current limit after determining that operation of the engine has resumed.