Cross-Joint Coupling Needle Roller Skew Suppression
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Solution Overview
Problem
The existing cross shaft joints in vehicle steering devices experience torque fluctuations due to skewing of needle rollers, which is exacerbated by reduced radial gaps, leading to poor steering feel and durability issues.
Innovation Solution
A cross shaft joint design featuring bearing cups with a projected part that contacts the needle roller within an axial range containing its center, maintaining a tight fit and reducing skew, with a height of the projected part set between 60% to 70% of the needle roller's length and a radial gap of -0.03mm ≤ s < 0, to equalize contact pressure and prevent peak pressure peaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the radial gap of the needle roller is reduced to maintain tight fit, then the torque transmission improves, but the needle roller skew increases causing torque fluctuation
Solution Approach 1:
The invention addresses the axial point contact issue by extending the curved part's action into the axial dimension. The curved part is designed with a height that spans a significant portion of the needle roller's axial length, transforming the contact from a zero-dimensional point to a one-dimensional line contact along the axial direction, thereby preventing skew while maintaining tight radial fit
Solution Approach 2:
The invention optimizes specific geometric parameters of the curved part, including its height (set to 60-70% of the needle roller length), radial curvature radius (0.5-2 times the needle roller radius), and axial positioning. These parameter changes ensure the curved part contacts the needle roller along its axial center region, preventing skew while maintaining appropriate tight fit
2Manufacturing precision
If the curved part of the bearing cup is designed to press the needle roller tightly, then the radial gap is reduced, but the contact area becomes too small causing stress concentration
Solution Approach 1:
The curved part is designed to extend in the axial dimension, transforming point contact into line contact. This dimensional extension distributes the pressing force along the axial direction, reducing stress concentration at any single point while maintaining the necessary radial tight fit
Solution Approach 2:
The height of the curved part is specifically set to 60-70% of the needle roller length, and its radial curvature radius is set to 0.5-2 times the needle roller radius. These parameter optimizations ensure adequate contact area along the axial direction, distributing stress evenly while maintaining appropriate radial compression
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 design effectively suppresses needle roller skew and torque fluctuations, enhancing durability and maintaining a stable steering feel even with reduced radial gaps, while minimizing abrasion and damage.
Implementation Method 1
a plurality of needle rollers rolling on outer peripheral faces of the shaft parts
Implementation Method 2
each of the cylindrical parts is provided with a projected part which is projected radially inward of the cylindrical part in a curved shape... the needle rollers are maintained in a tight fit state between the shaft parts and the bearing cups
Data Source
Figure 1
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AI summary
A cross shaft joint 10 includes a cross shaft 1 including: four shaft parts 3 which are arranged in a shape of a cross; a plurality of needle rollers 6 rolling on outer peripheral faces of the respective shaft parts 3; bearing cups 5 each having a cylindrical part 5a and a bottom part 5b for closing an opening at one end of the cylindrical part 5a, the bearing cups 5 externally fitted to the shaft parts 3 via the needle rollers 6; and yokes 21, 23 provided with bearing holes 22, 24 into which the bearing cups 5 are inserted. The needle rollers 6 are maintained in a tight fit state between the shaft parts 3 and the bearing cups 5. In the cross shaft joint 10, each of the cylindrical parts 5a is provided with a projected part 5d which is projected radially inward of the cylindrical part 5d in a curved shape, at an inner peripheral side thereof, and an apex of the projected part 5d is in contact with the needle roller 6 within a range in an axial direction of the needle roller 6, the range containing an axial center of the needle roller 6 in the axial direction.