Cam Timing Locking Pin Backlash Control
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Solution Overview
Problem
Variable cam timing (VCT) systems face issues with component wear and noise, vibration, and harshness (NVH) due to excessive backlash and overtravel in locking mechanisms, which complicate assembly and reduce system longevity.
Innovation Solution
A phase control apparatus is designed with a locking pin backlash maintained only between the locking pin and a recess, eliminating the gap between the vane and housing, allowing for easier assembly and reduced wear by ensuring face-sharing contact between the vane and housing during locking, thereby reducing NVH issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backlash is controlled to tight specifications during assembly, then sticking and binding issues are prevented, but assembly time and cost increase due to precise measurement techniques and frequent re-calibration
Solution Approach 1:
The locking pin recess is pre-formed with a specific width that automatically defines the backlash gap when the locking pin is installed. This preliminary preparation of the recess geometry eliminates the need for post-assembly measurement and adjustment, allowing workers to simply install the locking pin without requiring precise measurement techniques or frequent re-calibration, thus reducing assembly time while maintaining reliable backlash control
Solution Approach 2:
The locking pin and recess are designed with self-aligning features where the locking pin automatically positions itself within the recess during installation. The recess width is engineered to provide the correct backlash clearance without requiring external measurement or adjustment tools, enabling the assembly process to be self-servicing and eliminating the need for worker expertise in precise measurement and frequent re-calibration
2Ease of manufacture
If VCT overtravel gap is included between vane and housing, then assembly is simplified, but component wear increases and NVH issues arise due to excessive travel distance
Solution Approach 1:
The VCT overtravel gap is extracted and eliminated from the design by positioning the locking pin recess such that when the locking pin engages, the vane is already in or near its final position against the housing. This removes the unnecessary travel distance that causes wear and NVH issues, while the locking mechanism itself provides the required assembly flexibility
Solution Approach 2:
The locking pin recess is pre-positioned at a specific location that accounts for the vane's final position against the housing. This preliminary positioning ensures that when the locking pin is installed, there is no excessive overtravel, thereby preventing component wear and reducing NVH issues while maintaining ease of assembly
3Reliability
If locking pin extends deeply into locking pin recess to ensure locking, then locking reliability improves, but wear between locking pin and recess increases
Solution Approach 1:
The locking pin recess is designed with non-uniform geometry, featuring a wider entrance portion and a narrower base portion. This local quality variation allows the locking pin to engage deeply for reliable locking at the base while minimizing contact area and wear at the entrance region. The varying width distribution optimizes both locking reliability and component longevity by concentrating engagement forces in a controlled manner
Data Source
AI summary
Methods and systems are provided for a phase control apparatus in a variable cam timing (VCT) system of an engine, the phase control apparatus having a locking pin coupled to a rotor vane and engageable with a locking pin recess in the phase control apparatus cover plate. In one example, a method for assembling the phase control apparatus may include positioning respective retarded side surfaces of the rotor vane and the housing in face-sharing contact while positioning respective retarded side surfaces of the locking pin and the locking pin recess in face-sharing contact and maintaining a backlash gap between only the advanced side surfaces of the locking pin recess.