Variable Cam Timing Phaser Control via Spool Valve Mid-Lock Position
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Solution Overview
Problem
Conventional variable cam timing (VCT) systems face delays in cam phaser response times, especially during low oil temperature conditions, leading to errors in engine performance due to asynchronous engine speed-load conditions and prolonged locking/unlocking times of the cam phaser.
Innovation Solution
A method involving moving a spool valve to lock the cam torque actuated VCT phaser without engaging a locking pin for a duration, then engaging it only during specific conditions, allowing for improved response times by holding the cam phaser at a mid-lock position with the locking pin engaged during unsuitable oil pressure or temperature conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the locking pin is engaged to hold the cam phaser at a fixed position, then the cam phaser position stability is improved, but the response time for phaser adjustment increases
Solution Approach 1:
The system pre-positions the cam phaser at a mid-lock position and temporarily holds it there without engaging the locking pin when rapid response is needed. This preliminary holding action allows the phaser to be ready for quick engagement or disengagement based on subsequent conditions, reducing the time penalty associated with locking pin operations.
Solution Approach 2:
The system dynamically decides whether to engage or disengage the locking pin based on real-time operating conditions such as oil temperature and pressure. By making the locking pin engagement state variable rather than fixed, the system can adapt between stability (engaged) and responsiveness (disengaged) modes as needed.
2Loss of time
If the locking pin is disengaged to improve response time, then the cam phaser can adjust quickly, but the position stability deteriorates
Solution Approach 1:
The mid-lock position serves as an intermediary state between fully locked and fully unlocked positions. By using this intermediate position as a temporary holding state, the system provides a stable enough position for quick response while avoiding the full stability commitment of the engaged locking pin, thus balancing response time and position stability.
3Reliability
If the spool valve travels to the detent region to engage the locking pin, then the cam phaser is securely locked, but the duty cycle change required increases the complexity of control
Solution Approach 1:
The system uses partial action by temporarily holding the phaser at the mid-lock position without completing the full locking sequence (i.e., without traveling to the detent region and engaging the locking pin). This partial holding action provides sufficient reliability for the specific operating condition while avoiding the excessive control complexity of full locking engagement.
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 enhances cam phaser response times by maintaining the cam phaser at a fixed target position without engaging the locking pin during low oil temperature conditions, reducing errors and improving engine performance by optimizing phaser control.
Implementation Method 1
The spool valve may direct flow of a hydraulic fluid, such as oil, from one side of the vane to the other, such as from a retard side to an advance side
Implementation Method 2
the phaser may be cam torque actuated wherein the actuation of the phaser is dependent on torque generated during cam actuation
Data Source
AI summary
Methods and systems are described for an engine with a cam torque actuated variable cam timing phaser. Phaser positioning control is improved by reducing inaccuracies resulting from inadvertent spool valve and/or phaser movement when the spool valve is commanded between regions. In addition, improved spool valve mapping is used to render phaser commands more consistent and robust.