Integrated Shaft-Lifter Decompression Mechanism for Compact Engine Design
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Solution Overview
Problem
Existing decompression devices for internal combustion engines are bulky, restrict component placement, and require a large number of components, increasing manufacturing and assembly complexity and cost.
Innovation Solution
A camshaft with a decompression device featuring a shaft with eccentric portions that radially extend and retract lifters, allowing dual valve activation, reducing component count, and enabling easier assembly and manufacturing, while also allowing for adjustable cam timing without affecting decompression functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a traditional decompression device with multiple separate components is used, then the decompression function is achieved, but the device size increases and component placement is restricted
Solution Approach 1:
The patent combines the shaft and lifter into a single integrated component where the lifter is formed as an extension of the shaft itself. This merging eliminates the need for separate lifter components and reduces the overall number of parts in the decompression device, thereby reducing manufacturing and assembly complexity while minimizing the space required in the cylinder head portion.
Solution Approach 2:
The shaft is designed to serve multiple functions: it acts as both the rotating component driven by the cam lobe and as the lifter that directly contacts the valve stem. This multi-functionality eliminates the need for separate components and reduces the overall device size, allowing for more flexible component placement in the cylinder head.
2Device complexity
If a decompression device with multiple separate components is used, then the decompression function is achieved, but the number of components increases and assembly complexity increases
Solution Approach 1:
The patent merges the shaft and lifter into a single integrated component, reducing the total number of parts in the decompression device. This integration eliminates the need for separate lifter components and their associated mounting structures, thereby simplifying both manufacturing and assembly processes.
Solution Approach 2:
The decompression device is segmented into functional zones within the integrated shaft-lifter component, with the shaft portion driven by the cam lobe and the lifter portion contacting the valve stem. This functional segmentation within a unified structure maintains the necessary mechanical functions while reducing overall component count.
3Length of moving object
If a traditional decompression device is used, then decompression function is provided, but the engine width increases and mass increases
Solution Approach 1:
The integration of the shaft and lifter into a single component reduces the overall footprint of the decompression device, allowing for more compact engine packaging and reduced engine width while maintaining the necessary decompression functionality.
Solution Approach 2:
The shaft-lifter component is designed to operate within the existing three-dimensional space of the cylinder head, utilizing the radial and axial dimensions efficiently. The lifter extends radially from the shaft to contact the valve stem, optimizing space utilization and reducing the overall envelope of the decompression device.
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 provides improved starting capability, reduced engine width, and lower mass and cost by simplifying the decompression mechanism, allowing for more efficient pressure relief in cylinders and improved spark plug packaging.
Implementation Method 1
The shaft has an eccentric portion, axially extending from an end of the shaft nearest the lifter. The eccentric portion locates in a transverse slot in the lifter such that the lifter is extended or retracted due to the eccentric rotation of the eccentric portion.
Data Source
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AI summary
A camshaft (2) comprising a decompression device (1) to reduce pressure in a cylinder when an engine starts, the camshaft (2) having first and second lobes (14, 15) for actuating cylinder valves (62). The decompression device (1) has a shaft (10) located axially within the camshaft (2), and rotatable relative to the camshaft (2) to extend or retract a first and a second lifter (12, 13) radially. The first and second lifters (12, 13) are respectively provided inwardly of lobe faces of the first and second lobes (14, 15) on the camshaft (2) in a radial direction of the camshaft (2) such that the first lifter and the second lifter (12, 13) can extend outwardly or retract inwardly in the radial direction from the lobe faces. The shaft (10) has first and second eccentric portions (10A, 10B) located in transverse slots (12B, 13B) in the first and second lifters (12, 13) to extend or retract the first and second lifters (12, 13) respectively. The second lifter (13) has a longitudinal cut-out (13C) extending to the transverse slot (13B) of the second lifter (13) to allow the second eccentric portion (10B) to enter the transverse slot (13B).