Gear-Shaft Assembly With Guide Fit for Coaxial Press-Fitting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric power steering devices face challenges in ensuring proper alignment and engagement between the worm tooth and wheel teeth due to potential misalignment of the pinion shaft and worm wheel, leading to increased resistance and noise, and require precise dimensional tolerances that increase costs.
Innovation Solution
The assembly of a gear and rotating shaft involves a serrated shaft portion with a guide shaft portion and a clearance fit, allowing for improved coaxiality through a serrated shaft portion press-fitted into the center hole and a guide shaft portion with a smaller diameter, facilitating alignment and connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the pinion shaft and worm wheel are connected by press-fitting a cylindrical shaft portion into the center hole, then the connection strength is ensured, but the coaxiality between the gear and rotating shaft deteriorates due to potential misalignment
Solution Approach 1:
The shaft is divided into two distinct portions: a cylindrical shaft portion for press-fitting that provides connection strength, and a guide shaft portion with a smaller diameter that protrudes to enable precise alignment. This segmentation allows each portion to fulfill its specific function without compromising the other.
Solution Approach 2:
The guide shaft portion acts as an intermediary alignment tool that protrudes from the gear during the press-fitting process. It mediates the alignment between the pinion shaft and worm wheel by providing a physical reference that guides the insertion, ensuring coaxiality before the press-fitting operation completes.
2Manufacturing precision
If precise dimensional tolerances are specified for the center hole and shaft portions, then the coaxiality and engagement quality are improved, but the manufacturing cost increases
Solution Approach 1:
Different portions of the shaft have different dimensional requirements. The guide shaft portion has less stringent tolerance requirements since its primary function is alignment rather than precision engagement. This local differentiation of quality requirements reduces overall manufacturing costs while maintaining the necessary coaxiality through the guide function.
3Strength
If the outer diameter of the shaft portion is made larger than the inner diameter of the center hole for press-fitting, then the connection strength is improved, but the alignment accuracy deteriorates due to difficulty in insertion
Solution Approach 1:
The shaft is segmented into a cylindrical portion for interference fit (strength) and a guide shaft portion with smaller diameter for easy insertion and alignment. The guide portion's smaller diameter allows it to be inserted first to establish alignment, followed by the press-fitting of the cylindrical portion to create the strong connection.
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 approach ensures good coaxiality between the gear and rotating shaft, reducing engagement resistance and noise, while minimizing the need for precise dimensional tolerances and lowering production costs.
Implementation Method 1
the guide shaft portion has an outer diameter capable of being internally fitted in the center hole with a clearance fit
Implementation Method 2
connecting the gear and the rotating shaft by press-fitting the serrated shaft portion into the center hole
Data Source
AI summary
An assembly of a gear and rotating shaft, comprising: a gear having teeth on an outer peripheral surface thereof, and a center hole penetrating in an axial direction through a center portion thereof; and a rotating shaft including a serrated shaft portion having a male serration portion on an outer peripheral surface thereof and press-fitted into the center hole, and a guide shaft portion provided adjacent to one side in the axial direction of the serrated shaft portion and having an outer diameter capable of being internally fitted in the center hole with a clearance fit.