Variable Cam Timing Phaser Control via Detent Circuit
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Solution Overview
Problem
Conventional variable cam timing (VCT) systems with cam torque actuated phasers face issues such as inadvertent engagement and locking of the detent circuit due to low oil pressure, leading to engine performance degradation and unpredictable phaser responses.
Innovation Solution
Implementing a method where the spool valve is commanded to the detent region in response to low system oil pressure, preventing inadvertent engagement of the detent circuit, and allowing oil flow only through the detent circuit until oil pressure returns to a threshold, ensuring accurate VCT position control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the spool valve is commanded to move into the retard or advance region, then the VCT position control is improved, but the detent circuit may inadvertently engage and lock the phaser due to low system oil pressure, causing unpredictable phaser responses
Solution Approach 1:
The patent introduces a detent circuit as an intermediary mechanism that provides a predetermined mechanical stopping position for the phaser. This detent circuit acts as a mediator between the hydraulic control system and the phaser mechanism, ensuring that when system oil pressure is insufficient, the phaser still has a defined fallback position rather than exhibiting unpredictable behavior. The detent circuit includes a detent piston and detent spring that mechanically engage to provide this predetermined position.
Solution Approach 2:
The patent implements dynamic monitoring of system oil pressure and adjusts the operational parameters of the spool valve based on pressure conditions. When oil pressure falls below a threshold, the system changes the spool valve's commanded position to prevent inadvertent detent circuit engagement. This parameter adjustment ensures that VCT position control commands are modified adaptively based on the actual hydraulic conditions, maintaining reliability while preserving control accuracy when conditions permit.
2Reliability
If the spool valve is commanded to the detent region to prevent inadvertent engagement, then the reliability of phaser control is improved, but the ability to adjust VCT position via phasing circuit lines is restricted
Solution Approach 1:
The patent implements a dynamic control strategy where the spool valve's operational mode switches between detent region and phasing region based on real-time oil pressure conditions. The system is not statically restricted to one mode but dynamically adapts: when oil pressure is sufficient, the spool valve operates in the phasing region to allow full VCT position adjustment capability; when oil pressure drops below the threshold, the system transitions to the detent region to ensure stability and prevent inadvertent engagement. This dynamic switching resolves the contradiction by making the system adaptable to changing conditions.
Solution Approach 2:
The patent employs a feedback mechanism that continuously monitors system oil pressure and uses this information to adjust the spool valve's commanded position. The control system receives feedback about oil pressure conditions and automatically modifies the spool valve operation accordingly. When low oil pressure is detected, the feedback loop triggers a command to move the spool valve to the detent region, preventing unreliable operation. When pressure恢复正常, the feedback allows return to normal phasing operation, thus maintaining both reliability and adaptability.
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 performance by preventing conflicts between VCT position control and hydraulic control, maintaining engine efficiency, and reducing erratic actuation issues caused by low oil pressure.
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 chamber to an advance chamber
Implementation Method 2
When the piloted valve is in the second position, hydraulic fluid is allowed to flow between a detent line from the advance chamber and a detent line from the retard chamber through the piloted valve and a common line, such that the rotor assembly is moved to and held in the intermediate phase angle position relative to the housing assembly
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.