Steering Gearbox Bush Layout for Rack Shaft Load Distribution

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Solution Overview

Problem

Steering gearboxes in vehicles with large tie rod angles face increased load and difficulty in restricting displacement of the rack shaft due to increased vertical component forces, leading to higher surface pressure and strength requirements for bushes.

Innovation Solution

A steering gearbox design featuring multiple metal bushes aligned axially to increase contact area and length, allowing earlier contact with the rack shaft and facilitating balanced support, with optional chamfered portions and varying bush lengths to reduce surface pressure and enhance durability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the tie rod angle increases, then the steering capability for rough terrain is improved, but the vertical component force increases causing higher load on the bush

Engineering Contradiction:

Improvesteering capability for rough terrainVSAvoidstrength required for the bush

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

The single bush is segmented into multiple bushes (first bush and second bush) arranged in the axial direction. This segmentation distributes the vertical component force across multiple contact points, reducing the load on each individual bush while maintaining the required strength for rough terrain operation.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If the tie rod angle increases, then the steering capability is improved, but the displacement of the rack shaft due to falling becomes harder to restrict

Engineering Contradiction:

Improvesteering capability for rough terrainVSAvoiddisplacement restriction of the rack shaft

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The solution transitions from a single-point support to a distributed multi-point support system along the axial dimension. By arranging multiple bushes in the axial direction, the system creates a longer support zone that effectively restricts rack shaft displacement through distributed contact rather than concentrated support.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Stress or pressure

If a single long bush is used to increase contact area, then the surface pressure is reduced, but the manufacturing complexity and cost increase

Engineering Contradiction:

Improvesurface pressure between bush and rack shaftVSAvoidmanufacturing complexity

Core Design Contradiction:

Stress or pressureVSEase of manufacture

Solution Approach 1:

Instead of manufacturing one long bush with complex geometry, the solution segments the support function into multiple standard-sized bushes. Each bush can be manufactured using conventional processes, and they are simply arranged axially to achieve the cumulative contact area needed to reduce surface pressure.

Inventive Principle:

Principle #1Segmentation

4Stress or pressure

If multiple bushes are provided side by side in the axial direction, then the contact area is increased reducing surface pressure, but the device complexity increases

Engineering Contradiction:

Improvesurface pressure between bush and rack shaftVSAvoidnumber of bushes

Core Design Contradiction:

Stress or pressureVSDevice complexity

Solution Approach 1:

Multiple identical or similar bushes perform the same support function simultaneously, creating a redundant yet simple system. Each bush is a standard component that can be easily replaced or serviced, and their collective arrangement achieves the required surface pressure reduction without requiring complex individual component designs.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11485402B2Steering gearbox

Publication Date: 2022.11.01 YAMADA MANUFACTURING CO LTD

AI summary

A steering gearbox is equipped with a casing, a rack shaft, and a plurality of bushes. The rack shaft is accommodated in a casing to be movable in an axial direction. The plurality of bushes support the rack shaft to be movable in the axial direction and are attached to the casing.