Engine Decompression Weight Asymmetry for Startability
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Solution Overview
Problem
The decompression mechanism in existing engines fails to improve startability due to the weight being in an open state when the engine is starting, attributed to the weakness of the return spring's force, which is reduced by the decompression mechanism's placement between the cam shaft ends, leading to insufficient centrifugal force and increased noise when trying to increase the spring force.
Innovation Solution
The engine design includes a weight with a unique shape and placement of the decompression pin, where the center of gravity is positioned further away from the cam shaft's center, increasing centrifugal force and reducing gravitational force, allowing the weight to remain closed during engine start-up without increasing the set rotation speed, thus enhancing startability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the decompression mechanism is disposed between both ends of the cam shaft, then the cam shaft can be made more compact in the axial direction, but the return spring force becomes weaker causing the weight to remain in an open state during starting
Solution Approach 1:
The weight is designed with an asymmetric mass distribution where the center of gravity is positioned offset from the rotational center. Specifically, the weight includes an asymmetric protrusion that extends in a specific direction, creating an unequal mass distribution. This asymmetric design generates a gravitational moment that assists the return spring in closing the weight during engine starting, compensating for the reduced spring force due to the compact cam shaft arrangement.
2Reliability
If the return spring force is increased to keep the weight closed during starting, then startability improves, but the set rotation speed must be increased causing noise
Solution Approach 1:
The asymmetric weight design creates a gravitational moment that acts as a counterbalancing force against the centrifugal force attempting to open the weight. During engine starting at low rotation speeds, the gravitational moment from the offset center of gravity works in conjunction with the return spring force to maintain the weight in a closed state, eliminating the need to increase the return spring force and its associated set rotation speed and noise.
3Force
If the weight is designed with larger mass to increase centrifugal force, then the weight can be kept closed during starting, but the device complexity and space requirements increase
Solution Approach 1:
Rather than uniformly increasing the entire weight's mass, the invention applies mass asymmetry locally through an asymmetric protrusion. This localized mass addition creates the necessary gravitational moment while minimizing overall weight increase and avoiding the need for a completely restructured weight design. The asymmetric protrusion is positioned to optimize the gravitational moment arm length, achieving the desired effect with minimal additional mass and structural 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
This design improves engine startability by maintaining the weight in a closed state during engine start-up, reducing noise and interference, and allowing easier return to the closed state, thereby enhancing the engine's starting performance.
Implementation Method 1
a return spring (45) which urges the weight (42) from the open state to the closed state
Implementation Method 2
increasing centrifugal force and reducing gravitational force, allowing the weight to remain closed during engine start-up
Implementation Method 3
increasing centrifugal force and reducing gravitational force
Data Source
Figure 1
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Figure 3
AI summary
The center of gravity of the weight (42) is disposed in a first region (A1) as seen from the axial direction of the cam shaft (26). The first region (A1) is located in the first vertical (Y1) direction from the horizontal axis and in the first horizontal direction (x1) from the vertical axis. A circumferential direction end portion of a first weight (47) portion is located in the first horizontal direction (x1) from the vertical axis. A circumferential direction end portion (481) of a second weight portion (48) is located in the second horizontal direction (x2) from the vertical axis. The first weight portion (47) is longer than the second weight portion (48) in the circumferential direction of the cam shaft (26). The decompression pin (44) is connected to the first weight portion (47).