Variable Valve Timing Control Using Feedforward and Feedback
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Solution Overview
Problem
Existing variable valve timing control systems face delays in starting feedback-control when the engine is stopped, leading to significant deviations in valve timing due to cam torque, which affects engine start performance and fuel efficiency.
Innovation Solution
A sensor-based control system that detects the changing amount of valve timing and converges it to a target value by adjusting the actuator's output, ensuring precise control even after engine stoppage and during engine start-up, using an electronic controller and VTC angle sensor to manage the electric motor's manipulated variables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If feedback-control is started on detecting rotation of the crank shaft, then the control system can respond to engine start, but the valve timing significantly deviates from target angle due to delay in starting feedback-control
Solution Approach 1:
The control system performs preliminary action by detecting crank shaft rotation and immediately executing feedforward control based on predetermined map data before feedback control is fully established. This preliminary feedforward action compensates for the delay in feedback response, preventing significant valve timing deviation during engine start-up.
Solution Approach 2:
The system implements feedback control by continuously monitoring the actual valve timing angle via sensor and comparing it with the target angle from map data. The controller adjusts the actuator output based on the deviation between actual and target angles, ensuring accurate valve timing control after the initial feedforward phase.
2Device complexity
If VTC cannot change valve timing when engine is stopped, then the system remains simple, but engine-start performance is affected due to cam torque causing timing deviation
Solution Approach 1:
The system stores predetermined valve timing angles in map data corresponding to various engine operating conditions. When engine start is detected, the controller immediately retrieves and applies the appropriate target angle from the map, enabling proactive compensation for cam torque effects without requiring complex real-time calculations during the critical start-up phase.
Solution Approach 2:
The system replaces purely mechanical valve timing control with an electronically controlled actuator that can be precisely driven by the controller. This substitution enables the valve timing to be actively adjusted during engine start-up through electrical signals, overcoming the limitation of mechanical systems that cannot change timing when the engine is stopped.
3Productivity
If feedforward control is executed based on map data, then valve timing can be proactively controlled, but the system requires additional memory and control logic
Solution Approach 1:
The system pre-calculates and stores optimal valve timing angles for various engine operating conditions in map data during the development phase. This preliminary preparation eliminates the need for complex real-time calculations during operation, allowing the controller to simply retrieve and apply predetermined values, thereby maintaining control efficiency without excessive computational complexity.
Data Source
AI summary
An apparatus for controlling a variable valve timing mechanism includes an electronic controller which includes a microcomputer converges a valve timing of a variable valve timing mechanism to a target changing amount based on a deviation between the target changing amount and an output of a sensor for detecting a changing amount of the valve timing.