Rack Bar Support Fixing to Prevent Thermal Expansion Preload Loss

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Solution Overview

Problem

The existing rotation-linear motion conversion apparatuses experience a reduction in preload between the rack gear and pinion gear due to thermal expansion of the housing, leading to abnormal noise and dead zones during steering.

Innovation Solution

A configuration where the support block is fixed to the opposed surface of the housing, allowing the rack bar to move longitudinally and maintain engagement with the pinion shaft, preventing displacement and maintaining preload even with thermal expansion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the housing is surrounded by the rack bar in the conventional configuration, then the structure is simple and easy to manufacture, but the thermal expansion of the housing causes displacement of the rack bar and pinion shaft, reducing the preload amount between the rack gear and pinion gear

Engineering Contradiction:

Improvestructural simplicityVSAvoidpreload amount maintenance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

Instead of fixing the support part to the housing (conventional approach), the invention inverts the relationship by fixing the support part to the rack bar. This inversion ensures that when the housing expands thermally, the rack bar and pinion shaft remain relatively positioned, maintaining the preload amount between the rack gear and pinion gear. The support part moves with the rack bar rather than being constrained by the expanding housing.

Inventive Principle:

Principle #13The other way round (Inversion)

2Stability of the object's composition

If the support part is fixed to the housing, then the structure is stable, but thermal expansion of the housing causes the rack bar and pinion shaft to separate, reducing preload and causing abnormal noise or dead zone

Engineering Contradiction:

Improvestructural stabilityVSAvoidthermal expansion effect

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The invention converts the harmful effect of thermal expansion into a beneficial outcome. By fixing the support part to the rack bar instead of the housing, the thermal expansion of the housing no longer causes separation between the rack bar and pinion shaft. The system effectively uses the relative stability of the rack bar-pinion shaft assembly against housing expansion to maintain preload, turning the thermal expansion issue from a harmful factor into a non-issue.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Manufacturing precision

If the rack bar is supported by the housing, then the positioning is precise, but thermal expansion causes displacement in the direction of separation from the pinion shaft, reducing engagement preload

Engineering Contradiction:

Improvepositioning precisionVSAvoidthermal expansion displacement

Core Design Contradiction:

Manufacturing precisionVSTemperature

Solution Approach 1:

The invention introduces the rack bar as an intermediary between the support part and the pinion shaft. By fixing the support part to the rack bar rather than directly to the housing, the system creates a stable reference frame that is not affected by housing thermal expansion. This intermediary relationship ensures that the positioning precision is maintained relative to the pinion shaft regardless of housing temperature changes.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 configuration effectively prevents the reduction of preload between the rack gear and pinion gear, reducing abnormal noise and ensuring smooth steering operations.

Implementation Method 1

A rack and pinion apparatus converts a rotation motion of the pinion shaft into a linear motion of the rack bar by the action between the pinion gear and the rack gear.

Methodology Applied

Scientific EffectGear engagement: Gear

Implementation Method 2

the housing is thermally expanded due to engine heat in an engine room, exhaust pipe heat, external ambient heat, or the like

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10053136B2Rotation-linear motion conversion apparatus and steering apparatus

Publication Date: 2018.08.21 THK CO LTD

AI summary

A rotation-linear motion conversion apparatus (10) includes: a rack bar (30) in which a rack gear (32) is formed; a housing (40) that surrounds the rack bar (30); a pinion shaft (20) including a pinion gear (22) that engages with the rack gear (32) and that is inserted inside the housing (40); and a support part (50) that is provided on an opposed surface (41s1), which is opposed to the rack gear (32), of the housing (40) and that supports the rack bar (30) movably in a longitudinal direction of the rack bar (30).