Rack Guide Composite Structure for Steering Friction and Strength
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Solution Overview
Problem
Rack guides in rack-and-pinion type steering apparatuses face issues with mechanical strength and sliding friction, particularly when made of synthetic resin, as they experience stress relaxation due to temperature changes, leading to reduced securing force and smooth sliding support of the rack bar.
Innovation Solution
A synthetic resin-made rack guide with an arcuate concave surface and a curved sliding plate piece featuring a tubular projection and bulged portion, where the bulged portion is press-contacted with the rack guide base body around the circular through hole, maintaining the securing force even after stress relaxation, and a three-layered structure with a porous sintered metal layer and self-lubricating resin for improved wear resistance and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a synthetic resin rack guide is used, then sliding frictional resistance is reduced, but mechanical strength against impact load deteriorates
Solution Approach 1:
The rack guide is constructed as a composite structure combining a synthetic resin base body with a metal plate piece having arcuate concave surfaces. The metal plate provides high mechanical strength and wear resistance, while the synthetic resin provides self-lubrication properties and reduces sliding friction. This composite structure resolves the contradiction by integrating materials with complementary properties.
2Force
If a synthetic resin rack guide is used, then sliding friction is reduced, but dimensional accuracy deteriorates due to thermal expansion and shrinkage
Solution Approach 1:
The metal plate piece is embedded within the synthetic resin base body, creating a composite structure where the metal component maintains dimensional stability against thermal expansion while the resin matrix provides low friction sliding surfaces. This resolves the dimensional accuracy issue by using materials with different thermal properties in a composite configuration.
3Force
If the tubular projection is press-fitted into the through hole, then securing force is improved, but stress relaxation due to temperature rise reduces the securing force over time
Solution Approach 1:
Ribs are provided on the inner peripheral surface of the through hole that engage with corresponding features on the metal plate piece. This preliminary structural arrangement prevents relative movement and maintains securing force even when stress relaxation occurs due to thermal cycling, addressing the long-term durability issue.
Solution Approach 2:
The combination of metal plate piece and synthetic resin base body creates a composite structure where the metal component maintains dimensional stability under thermal stress, preserving the press-fitting securing force over extended periods despite temperature variations.
4Strength
If an iron-based sintered metal rack guide is used, then mechanical strength against impact load is improved, but sliding frictional resistance increases
Solution Approach 1:
Instead of using iron-based sintered metal alone, the invention combines a metal plate piece (providing strength) with a synthetic resin base body (providing self-lubrication). This composite approach achieves both high mechanical strength and low sliding friction, resolving the contradiction between strength and friction.
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 ensures the curved sliding plate piece remains firmly secured to the rack guide base body, maintaining smooth sliding support of the rack bar over extended periods, reducing sliding friction, and enhancing wear resistance and fracture strength.
Implementation Method 1
a three-layered structure with a porous sintered metal layer and self-lubricating resin for improved wear resistance and thermal conductivity
Implementation Method 2
a three-layered structure with a porous sintered metal layer and self-lubricating resin for improved wear resistance and thermal conductivity
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A rack-and-pinion type steering apparatus 1 includes a gear case 3, a steering shaft 6 supported rotatably in a hollow portion 2 of the gear case 3, a pinion 7 which is provided integrally on a shaft end of the steering shaft 6, a rack bar 10 which has rack teeth 8 meshing with the pinion 7, a rack guide 11 which guides and supports the rack bar 10 movably, and a coil spring 12 serving as a resilient means which resiliently presses the rack teeth 8 toward the pinion 7 by means of the rack guide 11.