Rack Guide Sliding Surface Curvature Design
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Solution Overview
Problem
In rack-and-pinion mechanisms, production variations in the curvature radius of the sliding surface of the rack guide sheet or the rear surface of the rack bar can lead to increased friction forces due to the wedge effect, affecting the sliding performance, especially when the contact area deviates towards the periphery.
Innovation Solution
A sliding surface with a concave design that includes pairs of first and second arc surfaces, where the first arc surfaces are positioned on the periphery and the second arc surfaces on the bottom, with larger gaps between the first arc surfaces and the rack bar at positions equidistant from the contact points, to maintain a smaller angle and reduce friction when deviations occur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the curvature radius of the sliding surface is made closer to the curvature radius of the rack bar rear surface to widen the contact area, then the load dispersion and sliding performance are improved, but production variations cause the contact area to deviate toward the periphery, increasing the wedge effect and friction force
Solution Approach 1:
The sliding surface is divided into different zones with different gap characteristics: the periphery portion has larger gaps to reduce the wedge effect when contact deviates, while the central portion maintains smaller gaps for stable contact. This local differentiation allows the surface to accommodate production variations without excessive friction increase.
Solution Approach 2:
The gap between the sliding surface and rack bar rear surface is intentionally varied across different locations. The gap is larger at the periphery and smaller at the center, creating a gradient structure that compensates for curvature radius variations and maintains optimal contact conditions.
2Strength
If the contact area is widened by adjusting the curvature radius, then the load is dispersed and abrasion is reduced, but the wedge effect increases when contact deviates toward the periphery
Solution Approach 1:
Different regions of the sliding surface are designed with different gap characteristics: the periphery region has larger gaps to minimize wedge effect, while the central region has smaller gaps for stable load bearing. This local quality differentiation resolves the conflict between load dispersion and friction reduction.
Solution Approach 2:
The sliding surface is designed with a curved profile that matches the rack bar rear surface curvature, but with intentional gap variations. The curvature is optimized to maintain contact while the gap gradient (larger at periphery, smaller at center) compensates for manufacturing tolerances and reduces wedge effect.
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 reduces the influence of production variations on friction forces while widening the contact area, thereby stabilizing the sliding performance by minimizing the increase in friction force when deviations occur, particularly towards the periphery.
Implementation Method 1
a rack guide body which is biased toward the rear surface of a rack bar by means of resilient force of a coil spring inserted between a cap of a rack case and the rack guide body
Implementation Method 2
This design reduces the influence of production variations on friction forces while widening the contact area, thereby stabilizing the sliding performance by minimizing the increase in friction force when deviations occur
Data Source
Figure 1
Figure 2(A)~2(E)
Figure 3
AI summary
The objective of the present invention is to reduce the impact of production variability in a radius of curvature of a rear surface of a rack bar, for example, while enlarging a region of contact with the rack bar. A concave surface (330) is used as a rack guide seat (32) sliding surface (33). In a YZ cross section perpendicular to an axial direction of a rack bar, the concave surface (330) includes: a pair of first arcuate surfaces (331A, 331B) which are disposed on a peripheral edge side (320) of the sliding surface (33), from two positions of contact TA, TB with a rack bar rear surface (22), the positions of contact TA, TB having line symmetry with respect to a straight line O3 joining a center O of a rack bar (20) with a bottom portion center C of the sliding surface (33), and which have line symmetry with respect to the straight line O3; and a pair of second arcuate surfaces (332A, 332B) which are disposed on a bottom portion side (321) of the sliding surface (33), from the positions of contact TA, TB, and which have line symmetry with respect to the straight line O3. With regard to gaps to the rack bar rear surface (22) in positions separated by the same distance from the positions of contact TA, TB, the gaps from the first arcuate surfaces (331A, 331B) are greater than the gaps from the second arcuate surfaces (332A, 332b).