Resin Coupling Member for EPS Power Transmission
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Solution Overview
Problem
Conventional electric power steering apparatuses experience rattle noise and increased rotational resistance due to gear wear and road surface impacts, leading to an unpleasant steering experience.
Innovation Solution
A power transmission device with a motor driving shaft featuring an accommodation part and a coupling member with axial through-holes and ribs, which reduces backlash and rotational resistance by elastic deformation and damping, ensuring stable force transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the compression spring is used to rigidly engage the worm gear with the worm wheel gear, then the engagement rigidity is improved, but the rattle noise increases due to backlash from gear wearing-out and impact transmission
Solution Approach 1:
The patent changes the engagement parameter from rigid (compression spring) to elastic (resin material with controlled modulus). The resin material's elastic properties allow it to deform under impact loads, maintaining continuous contact between gear teeth while absorbing shock, thereby reducing rattle noise without sacrificing engagement rigidity
Solution Approach 2:
The patent uses a composite structure combining metal components (driving shaft, worm shaft) with a resin material (elastic body). This composite approach allows the resin to provide elastic cushioning against impacts and wear, reducing backlash and rattle noise, while the metal components maintain structural strength and precision
2Ease of operation
If the driving shaft and worm shaft are positioned coaxially, then the rotational resistance is reduced, but manufacturing errors and assembly errors cause misalignment
Solution Approach 1:
The resin material acts as an intermediary element between the driving shaft and worm shaft. It compensates for manufacturing and assembly errors in coaxial alignment by deforming elastically, allowing the shafts to maintain proper rotational relationship without requiring precise pre-alignment, thereby reducing rotational resistance
Solution Approach 2:
The resin material provides beforehand cushioning for potential misalignment issues. Its elastic properties anticipate and compensate for manufacturing tolerances and assembly variations, preventing binding and excessive rotational resistance before they occur during operation
3Stability of the object's composition
If the bearings are rigidly fixed to support the worm gear, then the support stability is improved, but the locking feeling occurs due to accumulated errors
Solution Approach 1:
The patent changes the bearing support from rigid to elastic by using resin material. This allows the bearing to have controlled compliance, absorbing accumulated errors from manufacturing and assembly without creating locking feelings, while maintaining sufficient support stability for proper gear engagement
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 solution effectively reduces rattle noise and rotational resistance, enhancing the driver's steering experience by maintaining coaxial alignment and damping road surface impacts.
Implementation Method 1
a resin material which is elastically compressively deformed
Implementation Method 2
damping road surface impacts
Implementation Method 3
the compression screw 255 moves to contract the compression spring 265, and consequently, the worm gear 245 can be rigidly engaged with the worm wheel gear 240 by the compression force of the compression spring 265
Data Source
AI summary
The present invention relates to a power transmission device of an electric power steering apparatus. The power transmission device includes: a driving shaft of a motor having an accommodation part formed at a rotation center thereof; a coupling member inserted into the accommodation part and having an axial through-hole formed therethrough; and a gear shaft including a coupling part formed on one side thereof to be coupled to the axial through-hole, and a gear part formed on the other side thereof. According to the present invention as described above, in a power transmission device of an electric power steering apparatus, it is possible to reduce rattle noise generated as backlash increases due to wearing-out of a gear or generated due to impact transmitted from a road surface through a vehicle wheel and a steering shaft while improving a driver's steering feeling by reducing a locking feeling and a rotational resistance between a driving shaft of a motor and a gear shaft.