Vane Phaser Hydraulic Detent Valve for Cranking Position Control
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Solution Overview
Problem
Existing variable camshaft timing (VCT) systems, particularly oil pressure actuated (OPA) and torsional assist (TA) systems, are limited in their ability to control the vane phaser during engine start-up when oil pressure is low, often defaulting to one extreme position and unable to move to intermediate positions, which is inadequate for hot start conditions.
Innovation Solution
A VCT phaser with three start positions (full advance, full retard, and intermediate) that can be controlled during cranking, utilizing a hydraulic detent circuit and a spool valve pump to unlock the lock pin and allow movement to these positions, even at low oil pressure, based on factors like fuel type, oil temperature, and altitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lock pin is used to lock the vane phaser at extreme positions during engine shutdown, then the phaser can be held in a fixed position, but the phaser cannot move to intermediate positions during engine start-up when oil pressure is low
Solution Approach 1:
A hydraulic detent circuit is introduced as an intermediary mechanism between the lock pin and the vane phaser. This circuit includes a detent valve that can hold the phaser at intermediate positions by providing hydraulic locking, while allowing the lock pin to remain engaged for extreme position stability. The detent circuit acts as a mediator that enables partial movement without compromising overall position stability.
Solution Approach 2:
The system transitions from a static locking mechanism (lock pin only) to a dynamic system where the hydraulic detent circuit can selectively engage or disengage based on operating conditions. During engine start-up, the detent valve can be activated to allow intermediate positioning, while during normal operation, the lock pin provides fixed positioning. This dynamic behavior enables the system to adapt between stability and flexibility requirements.
2Device complexity
If the control valve exhausts oil from working chambers to default the vane phaser to one direction, then the system simplifies control, but the phaser is limited to moving in one direction only during engine shutdown
Solution Approach 1:
The control system is segmented into two independent pathways: the main control valve that handles extreme position control by exhausting oil, and the hydraulic detent circuit that handles intermediate position control by maintaining oil pressure. This segmentation allows each subsystem to specialize in its function, with the detent circuit providing the additional degree of freedom for intermediate positioning without complicating the main control valve operation.
Solution Approach 2:
The hydraulic detent circuit serves as an intermediary system that supplements the main control valve. While the control valve provides simplified binary control (advance/retard extremes), the detent circuit mediates by providing incremental positioning capability through controlled oil pressure maintenance, enabling the phaser to stop at intermediate positions during engine start-up.
3Reliability
If the phaser is commanded to lock at extreme travel limits during engine shutdown, then the system ensures proper starting position, but it cannot accommodate hot start conditions requiring intermediate positions
Solution Approach 1:
The system dynamically adapts its locking behavior based on engine conditions. During cold starts, the lock pin engages at extreme positions for reliable starting. During hot starts, the hydraulic detent circuit activates to allow intermediate positioning while maintaining sufficient oil pressure. This dynamic adaptation enables the system to optimize for different starting conditions without compromising reliability.
Solution Approach 2:
The system changes the operational parameters of the locking mechanism based on engine temperature and oil pressure conditions. When oil pressure is sufficient (hot start), the detent valve maintains pressure to enable intermediate positioning. When oil pressure is low (cold start), the system defaults to extreme position locking. This parameter-based control allows the system to adjust its behavior to match environmental conditions.
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 solution provides increased flexibility in camshaft positioning at start-up, enabling the phaser to reach optimal positions quickly and efficiently, improving engine restart performance across various conditions.
Implementation Method 1
A hydraulic detent circuit can be activated to direct the vane phaser in either direction, advance or retard, via detent valve to specific positions
Implementation Method 2
The lock pin can be controlled by a spool valve pump to build hydraulic pressure to unlock the lock pin during cranking
Data Source
AI summary
A phaser which has three camshaft start positions at start-up during cranking before the engine can fire. By having three possible start positions of the phaser, there is an increase in flexibility of the cam position at startup during cranking. The three start positions can also be achieved in open loop, reducing the complexity of the control system needed at cranking.