Multi-mode Variable Camshaft Timing with Dual Lock Pins
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Solution Overview
Problem
Existing variable camshaft timing (VCT) mechanisms, such as oil pressure actuated (OPA) and torsional assist (TA) systems, are limited in their ability to control the camshaft position during engine start and shut down, particularly in stop-start modes, as they default to extreme positions and cannot move the phaser during engine start cycles without oil pressure, and are not optimized for hot starts.
Innovation Solution
A variable camshaft timing system with two lock pins and a control valve configuration that includes a recirculation check valve and an inlet check valve, allowing for multi-mode operation, including a mid-lock position for cold starts and full retard position during automatic engine stop, enabling precise control and engagement of the camshaft position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If oil pressure actuated (OPA) or torsional assist (TA) systems are used for variable camshaft timing, then the phaser can be controlled during normal engine operation, but the system defaults to extreme positions during engine start and shut down and cannot move the phaser during engine start cycles without oil pressure
Solution Approach 1:
The system is divided into two independent locking mechanisms: a first lock pin for intermediate phase angle positioning and a second lock pin for full retard positioning. This segmentation allows the phaser to be controlled at different positions during engine start and shut down cycles, enabling mid-lock position for cold starts and full retard for hot starts in stop-start mode.
Solution Approach 2:
A control valve with a recirculation check valve and an inlet check valve is introduced as an intermediary mechanism. The recirculation check valve allows oil to recirculate between working chambers during engine cranking, enabling the first lock pin to engage at intermediate positions. The inlet check valve controls oil flow during normal operation and stop-start mode, enabling the second lock pin to engage at full retard position.
2Ease of manufacture
If the phaser is commanded to lock at extreme travel limits during engine shut down, then the system is simple to control, but the system is not optimized for hot starts where intermediate positions are needed
Solution Approach 1:
The control system dynamically selects between two locking positions based on engine operating conditions. During normal operation, the system can command extreme positions as before. During stop-start mode, the recirculation check valve enables the first lock pin to position the phaser at intermediate phase angles for cold starts, while the inlet check valve enables the second lock pin to position at full retard for hot starts, optimizing restart performance.
3Device complexity
If a single lock pin system is used, then the device complexity is reduced, but the system cannot provide both intermediate position locking for cold starts and full retard locking for hot starts
Solution Approach 1:
The locking mechanism is segmented into two independent lock pins: the first lock pin engages with a recess in the housing assembly to lock at intermediate phase angle positions during cold starts, while the second lock pin engages with another recess to lock at full retard positions during hot starts in stop-start mode. This segmentation provides the necessary adaptability without excessive complexity.
Solution Approach 2:
The dual lock pin system with recirculation check valve and inlet check valve creates a multi-functional locking mechanism that can accommodate both cold start and hot start requirements within a single VCT assembly, making the system universal for different operating 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
The system allows for improved engine performance and reduced emissions by enabling precise control of the camshaft timing, including mid-lock positions during engine cranking and hot starts, ensuring efficient engine restarts and operation in stop-start modes.
Implementation Method 1
The control valve includes a recirculation check valve and an inlet check valve
Implementation Method 2
The first and second locks pins having a locked position where they engage a recess in the housing assembly and an unlocked position in which they do not engage the housing assembly
Implementation Method 3
This creates a pressure differential across one or more of the vanes to hydraulically push the VCT phaser in one direction or the other
Data Source
AI summary
A system including a phaser with a first lock pin and a second lock pin in the rotor assembly. The first and second locks pins having a locked position where they engage a recess in the housing assembly and an unlocked position in which they do not engage the housing assembly. The first lock pin locks the rotor assembly to the housing assembly when the phaser is in an intermediate phase angle position. The second lock pin locks the rotor assembly to the housing assembly when the phaser is at a full retard position. The control valve includes a recirculation check valve and an inlet check valve.