Interference-Fit Crankshaft Assembly to Prevent Compressor Rattling
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Solution Overview
Problem
The existing crankshafts in 3-cylinder rotary compressors face challenges in securing the fixation strength of the crank piece to the shaft portion, leading to rattling issues that affect compression performance, noise, and vibration due to gaps caused by key inaccuracies in divided type crankshafts.
Innovation Solution
A crankshaft design where the crank piece is formed as a separate element with a fitting hole and slit-like slot, allowing for easy assembly and secure fixation through interference fitting, with a bolt expanding the slot width to ensure precise alignment and secure attachment, preventing rattling and facilitating removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a divided type crankshaft with key fixation is used, then the number of processing steps is reduced and manufacturing cost decreases, but gaps are created between the key and shaft portion or key and crank piece due to accuracy limitations, reducing fixation strength
Solution Approach 1:
The invention changes the fixation method from key-based mechanical coupling to interference fitting. The crank piece is designed with a fitting hole that has a slightly smaller diameter than the shaft portion, creating an interference fit that eliminates gaps and ensures full fixation strength while maintaining ease of assembly through the elastic deformation capability of the crank piece material.
Solution Approach 2:
The invention removes the key component entirely from the fixation system. By extracting the key and replacing it with a direct interference fit between the shaft portion and crank piece, the design eliminates the source of gaps and fixation weakness while simplifying the overall structure and improving reliability.
2Manufacturing precision
If an integrated one-body crankshaft is used, then fixation strength is fully secured, but the number of operation steps increases and manufacturing cost increases due to repeated position shifting during grinding process
Solution Approach 1:
The invention divides the crankshaft into two separate components: the shaft portion and the crank piece. This segmentation allows each component to be manufactured independently with standard processes, avoiding the complex one-body manufacturing and repeated position shifting. The crank piece is then attached to the shaft portion through interference fitting, achieving full fixation strength while reducing manufacturing complexity and cost.
3Ease of operation
If a divided type crankshaft with key fixation is used, then assembly is simplified, but rattling occurs during operation due to gaps between key and shaft portion or key and crank piece, affecting compression performance and increasing noise and vibration
Solution Approach 1:
The invention changes the fixation mechanism from key-based to interference fit-based, where the crank piece material's elastic deformation capability enables gapless contact with the shaft portion. This eliminates rattling during operation while maintaining simple assembly procedures, thereby improving both operation stability and compression performance.
Solution Approach 2:
The invention utilizes the elastic deformation capability of the crank piece material as a beneficial feature. The slight elasticity allows the crank piece to deform during assembly to accommodate the interference fit, then maintains constant contact pressure during operation to eliminate gaps and prevent rattling, converting what could be a source of instability into a mechanism for ensuring reliable fixation.
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 design enhances the workability of assembling the crankshaft, secures the fixation strength of the crank piece, and prevents rattling during operation, ensuring improved performance and reliability of the rotary compressor.
Implementation Method 1
The slot is opened in both end surfaces of the crank piece. The fitting hole is deformed so as to expand a diameter of the fitting hole when expanding a width of the slot.
Data Source
AI summary
According to one embodiment, a crank portion is formed from a crank piece, an element separate from a shaft portion. The crank piece includes a fitting hole in which the shaft portion is fit by predetermined “interference” and a slit-like slot with one end opened in an inner circumferential surface of the fitting hole, and an other end closed inside the crank piece. The fitting hole is deformed so as to expand its diameter when expanding a width of the slot. The shaft portion is fit in the fitting hole of the crank piece by the predetermined “interference” when inserted in the deformed fitting hole and the fitting hole restores an original form while the shaft portion is in the fitting hole.