Variable Compression Ratio Mechanism Wave Gear Reducer
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Solution Overview
Problem
Conventional variable compression ratio mechanisms for internal combustion engines face challenges in achieving lightweight, high durability, low noise/vibration characteristics, and efficient gear tooth durability within limited vehicle space, particularly due to gear strength deterioration and surface wear issues.
Innovation Solution
The mechanism employs a double-link piston-crank mechanism with a wave gear reducer, featuring a larger number of teeth on the output-side gear portion to distribute stress and reduce load per gear tooth, combined with a low-rigidity flange part to minimize local loads and prevent surface wear, and utilizes an electric motor to control the compression ratio by shifting the control shaft's rotational position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional gear reducer is used in the variable compression ratio mechanism, then the mechanism can achieve compression ratio control, but gear strength deterioration and surface wear occur due to high load concentration on gear teeth
Solution Approach 1:
The patent changes the fundamental parameter of gear tooth configuration by using a wave gear mechanism instead of conventional spur gears. This alters the load distribution pattern from concentrated point contact to distributed line contact across multiple teeth simultaneously, resolving the strength deterioration issue through parameter transformation rather than incremental modification
Solution Approach 2:
The patent replaces the conventional gear reducer mechanical system with a wave gear mechanism that operates on different mechanical principles. The wave gear uses elastic deformation and sequential tooth engagement to achieve reduction, substituting the traditional meshing gear system and thereby eliminating the surface wear problems associated with conventional gear teeth contact
2Weight of moving object
If the gear module size is decreased to reduce weight, then the mechanism becomes lighter, but surface wear and strength deterioration of gear teeth increase
Solution Approach 1:
The patent fundamentally changes the gear engagement parameter from single-tooth contact to multi-tooth simultaneous contact through the wave mechanism. This parameter change allows the use of smaller module sizes while maintaining or improving durability, as the load is distributed across multiple teeth rather than concentrated on individual teeth
Solution Approach 2:
The wave gear mechanism segments the load transmission function across multiple gear teeth that engage simultaneously. Instead of one tooth pair bearing the entire load, the mechanism divides the load among several teeth in sequence and parallel, enabling weight reduction without sacrificing durability
3Measurement precision
If a high reduction ratio is achieved in the gear reducer, then the compression ratio control precision improves, but the gear tooth load increases causing surface wear
Solution Approach 1:
The patent changes the mechanical advantage generation method from direct gear meshing to wave-induced sequential engagement. This parameter change enables high reduction ratios to be achieved through the amplification effect of the wave mechanism rather than through multiple stages of conventional gears, thereby maintaining tooth load capacity while achieving precise control
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 configuration enhances gear tooth durability by reducing surface wear and breakage, while maintaining a high reduction ratio and efficient compression ratio control, thereby improving the overall performance and reliability of the variable compression ratio mechanism.
Implementation Method 1
wave gear reducer... a larger number of teeth on the output-side gear portion to distribute stress and reduce load per gear tooth
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Disclosed is a variable compression ration mechanism (5) in which a control shaft (10) is rotated and driven by an electric motor (21) through a wave gear reducer (22). The wave gear reducer (22) includes: a first internal gear member (31); an external gear member (32) arranged concentrically inside the internal gear member (31); a wave generator (33) having an oval outer shape and arranged inside the external gear member (32); and a second internal gear member (34), wherein a ratio of the number of teeth of a fixed gear portion (35) of the first internal gear member (31) to the number of teeth of a first gear portion (37) of the external gear member (32) is set greater than a ratio of the number of teeth of an output-side gear portion (42) of the second internal gear member (34) to the number of teeth of a second gear portion (38) of the external gear member (32).