Variable Cam Timing Phaser Control via Spool Valve Segmentation
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Solution Overview
Problem
Conventional variable cam timing (VCT) systems with cam torque actuated mid-lock phasers face issues such as unpredictable phaser control due to simultaneous engagement of detent and phasing circuits, leading to engine performance degradation, especially when hydraulic pressure is insufficient or leaked, causing unintended cam phaser positions and erratic actuation.
Innovation Solution
A method is implemented to detect and mitigate situations where both detent and phasing circuits are engaged by monitoring cam torsion magnitudes and engine speed, commanding the spool valve to the auto-lock region to prevent competition for phaser control, and adaptively learning the boundaries of the overlap region to prevent further unintended commands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the spool valve is commanded to move into the retard or advance region, then the cam phaser position can be adjusted, but the detent circuit may engage and compete with the phasing circuit for hydraulic control, causing unpredictable phaser control
Solution Approach 1:
The spool valve operation is divided into distinct regions (detent region, retard region, advance region, no-fly zone) with clear boundaries. The controller segments the control space to prevent simultaneous engagement of detent and phasing circuits by ensuring the spool valve operates exclusively in either detent or retard/advance regions, never in overlapping zones.
Solution Approach 2:
The spool valve acts as an intermediary component that mediates between the controller commands and the hydraulic circuits. By positioning the spool valve in specific regions, it controls which hydraulic circuit (detent or phasing) is active, preventing competition between circuits through proper intermediary positioning.
2Stability of the object's composition
If the detent circuit is engaged to auto-lock the cam phaser, then the phaser position is held stable, but the phasing circuit cannot adjust the position, limiting operational flexibility
Solution Approach 1:
The system dynamically switches between detent circuit engagement (for stability/holding position) and phasing circuit engagement (for position adjustment). The spool valve transitions between detent region (engaging detent circuit) and retard/advance regions (engaging phasing circuit), allowing the system to adapt between stable holding and flexible adjustment modes as needed.
Solution Approach 2:
The system periodically alternates between auto-lock mode (detent circuit active) and adjustment mode (phasing circuit active) based on operational requirements. The controller commands the spool valve to move between detent and retard/advance regions in a periodic manner, enabling the cam phaser to be held stable when needed and adjusted when needed.
3Reliability
If hydraulic pressure is insufficient or leaked, then the spool valve may not maintain proper positioning, but increasing pressure may cause other system issues
Solution Approach 1:
The controller monitors spool valve position and cam phaser position feedback to detect when the spool valve is in the no-fly zone or when improper circuit engagement occurs. Based on this feedback, the controller adjusts spool valve commands to keep the valve in proper regions, compensating for hydraulic pressure issues by using active control rather than relying solely on passive pressure positioning.
Solution Approach 2:
The controller proactively commands the spool valve to avoid the no-fly zone and overlap regions before hydraulic pressure issues can cause problems. By taking preliminary action to position the spool valve in safe regions with clear circuit separation, the system prevents unpredictable behavior before it occurs, rather than reacting after pressure problems manifest.
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 allows for timely detection and mitigation of simultaneous circuit engagement, reducing unpredictable phaser control and improving engine performance and emissions by ensuring accurate cam phaser positioning and operation.
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 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.