Elastic Piston Fixing Element for Variable Compression Ratio Engine
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Solution Overview
Problem
Existing solutions for variable compression ratio engines fail to ensure consistent clamping prestress and rotational indexing of the piston with respect to the transmission member, leading to potential loosening and collision risks, which complicates mass production and engine reliability.
Innovation Solution
An elastic mounting system using a metal rod held in tension between the piston and transmission member, applying high contact pressure and allowing for rotational indexing without significant increase in prestress, utilizing a stud and sleeve configuration with opposing threads to maintain assembly height consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a threaded pin is used to fix the piston to the transmission member, then clamping prestress can be applied, but rotational indexing becomes difficult to control and maintain
Solution Approach 1:
A stepped pin with a shoulder acts as an intermediary element between the piston and transmission member. The shoulder provides a precise stopping point that enables rotational indexing, while the threaded portion maintains clamping prestress. This mediator component separates the functions of positioning and clamping.
Solution Approach 2:
The fixing mechanism is segmented into distinct functional zones: a threaded portion for applying clamping prestress and a stepped portion with a shoulder for rotational indexing. This segmentation allows each zone to optimize its specific function without interfering with the other.
2Reliability
If thread indexing is implemented to ensure both clamping force and rotational positioning, then reliability improves, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The stepped pin with its shoulder serves as a mechanical intermediary that provides rotational indexing without requiring indexed threads. The shoulder physically limits rotation to a precise position, achieving reliable indexing through geometry rather than thread configuration.
Solution Approach 2:
The solution changes the parameter of rotational control from thread angle indexing to shoulder-based mechanical stopping. This parameter change simplifies manufacturing by eliminating the need for precisely indexed threads while maintaining reliable rotational positioning.
3Weight of moving object
If aluminum alloy is used for the piston to reduce weight and improve thermal conductivity, then engine efficiency improves, but the piston becomes prone to loosening and plastic deformation
Solution Approach 1:
The threaded bore in the aluminum piston is designed with beforehand cushioning features including relief grooves and controlled thread engagement zones. These features prevent stress concentration and plastic deformation by distributing loads before they reach critical levels.
Solution Approach 2:
The material parameters of the aluminum alloy are optimized and the threaded bore geometry is specifically designed to compensate for aluminum's lower strength. The thread profile, bore depth, and surrounding structural parameters are adjusted to prevent loosening and deformation despite using lightweight aluminum material.
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 elastic mounting system prevents piston loosening, eliminates thread indexing needs, simplifies manufacturing and assembly, reduces compression ratio dispersion, and ensures consistent engine performance by maintaining a constant assembly height.
Implementation Method 1
at least one metal rod held in tension between said piston and said transmission member... said pin offering a reserve of elasticity making it possible to eliminate any risk of loosening of said assembly
Implementation Method 2
said pin offering a reserve of plasticity making it possible, when the piston is tightened on its transmission member, to index said piston in rotation
Data Source
Figure 1
Figure 2~3
Figure 4~7
AI summary
The invention relates to an elastic fixing element for a piston (2) of a variable compression ratio engine (10), said fixing element consisting of at least one metal rod (15) held under tension between the piston (2) and the transmission member (2) and applying a strong contact pressure between the base of the piston (2) and the upper face of the transmission member (3), said piston (2) being tightened according to a previously calculated angle enabling the metal rod (15) formed by a dowel (16) to be subjected to a desired tension strain and enabling the tightening pre-stress to be reached between the piston (2) and the transmission member (3), and indexed in rotation in relation to the transmission member (3) by an additional tightening which does not significantly increase the tightening pre-stress, said dowel (16) continuing to extend under the same tension strain by plastic deformation.