Hydraulic Phaser Mid-Position Lock for Cold Start Optimization
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Solution Overview
Problem
Existing variable cam timing (VCT) systems in internal combustion engines face challenges in managing camshaft timing during engine start cycles, particularly in stop-start modes, where hot starts require different valve timing settings than cold starts, and current systems are limited to extreme positions, leading to inefficient engine restarts and emissions issues.
Innovation Solution
A hybrid phaser with a hydraulic lock in an intermediate position is introduced, featuring an offset or remote pilot valve to manage hydraulic detent switching, allowing for mid-position locking during cold starts, optimizing camshaft positioning for efficient engine restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the phaser defaults to extreme positions (full advance or full retard) using existing OPA or TA systems, then the system is simple to operate, but the engine cannot achieve optimal compression ratio for cold starts, resulting in poor starting performance and high emissions
Solution Approach 1:
The system pre-positions the phaser at an intermediate position during the shutdown phase before engine restart, rather than waiting until start occurs. This preliminary positioning ensures optimal compression ratio is ready before ignition, improving cold start reliability and reducing emissions without requiring complex real-time control during the actual start cycle
2Ease of operation
If the oil control valve directs oil to extreme positions only, then the hydraulic system is simple to control, but the phaser cannot be positioned at intermediate angles needed for optimal cold start compression ratio
Solution Approach 1:
The system dynamically adjusts phaser positioning based on engine state (shutdown vs. start). During shutdown, the control valve directs oil to position the phaser at an intermediate angle optimal for cold starts. During normal operation, the system reverts to extreme position control. This dynamic adaptation allows both simple control logic and versatile positioning capability
3Reliability
If the system uses a mid-position lock with hydraulic detent circuit, then cold start performance is improved, but the device complexity increases due to additional valves and circuits
Solution Approach 1:
The control valve is designed to perform multiple functions: it controls both the main hydraulic pressure to the phaser and pilots the detent circuit for mid-position locking. The detent circuit itself serves dual purposes by providing both positioning control and mechanical locking. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in overall system complexity
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
The solution enables the phaser to default to an intermediate phase angle position without electronic controls, ensuring reliable engine starting and improved fuel efficiency by optimizing compression ratios, even in the absence of active control signals, thus addressing the limitations of existing VCT systems.
Implementation Method 1
the fluid supplied to the pilot valve directs the pilot valve to a position that opens a hydraulic detent circuit
Implementation Method 2
hydraulic detent circuit to actuate a lock pin that locks the rotor assembly in the mid-position
Data Source
AI summary
A phaser which has an offset or remote pilot valve added to the hydraulic circuit to manage a hydraulic detent switching function, in order to provide a mid-position lock for cold starts of the engine, either during cranking or prior to complete engine shutdown. The mid-position locking of the phaser positions the cam at an optimum position for cold restarts of the engine.