Telescopic Shaft Radial Rigidity Control for Backlash Reduction
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Solution Overview
Problem
Conventional telescopic shafts experience locally high surface pressures and backlash between male and female shafts due to high bending moments, which are not effectively addressed by existing solutions.
Innovation Solution
The telescopic shaft design incorporates a male shaft with a reduced radial rigidity in specific axial regions, either through holes or smaller diameters, to mitigate surface pressures and backlash by distributing forces more evenly, allowing for reduced sliding resistance and improved durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the male shaft is fitted into the female shaft with protruding teeth and tooth grooves to transmit rotational torque and allow axial sliding, then the telescopic function is achieved, but high bending moments at both end portions cause high surface pressures and backlash
Solution Approach 1:
The patent applies different rigidity characteristics to different portions of the shaft. Specifically, the intermediate portion of the male shaft or female shaft is designed with lower radial rigidity than the end portions. This local differentiation allows the intermediate portion to deform elastically under load, reducing peak surface pressures at the tooth engagement interfaces and preventing backlash, while the rigid end portions maintain overall structural integrity and torque transmission capability.
2Ease of operation
If a resin covering portion is applied to the outer circumference of the protruding teeth to reduce sliding resistance, then low sliding resistance is achieved, but the resin layer deteriorates under high surface pressures at both end portions
Solution Approach 1:
The patent strategically places the resin covering portion only on the intermediate portion of the protruding teeth, avoiding application at both end portions where high surface pressures occur. This local application strategy allows the resin to provide low sliding resistance where bending moments are lower, while preventing resin deterioration and detachment at the high-stress end portions through alternative surface treatments or direct metal-to-metal contact.
3Reliability
If the radial rigidity is reduced at the intermediate portion to suppress surface pressures and backlash, then durability is improved, but the overall structural strength may be compromised
Solution Approach 1:
The patent implements a localized rigidity reduction strategy where only the intermediate portion of the shaft has reduced radial rigidity, while the end portions maintain high rigidity. This is achieved through features such as hollow sections, reduced wall thickness, or material property modifications specifically at the intermediate portion. The rigid end portions continue to provide adequate structural strength for torque transmission, while the compliant intermediate portion suppresses surface pressures and prevents backlash.
Solution Approach 2:
The patent divides the shaft into distinct functional segments: rigid end portions for structural support and torque transmission, and a compliant intermediate portion for pressure distribution and backlash prevention. This segmentation allows each portion to be optimized for its specific function without compromising the overall performance of the telescopic shaft assembly.
Data Source
AI summary
A telescopic shaft includes a male shaft having an outer circumference formed with a plurality of protruding teeth, and a female shaft having an inner circumference formed with a plurality of tooth grooves and fitted onto the male shaft. The protruding teeth and the tooth grooves are engaged such that the male shaft and the female shaft are relatively axially slidable and a rotational torque is transmittable between the male shaft and the female shaft. At least one of the male shaft and the female shaft is configured such that the radial rigidity of a portion of the at least one of the male shaft and the female shaft in an axial range of a region where the protruding teeth and the tooth grooves are engaged is lower than the radial rigidity of another portion of the at least one of the male shaft and the female shaft.