Rack Bush Engagement Structure for Stable Rack-and-Pinion Steering
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Solution Overview
Problem
The conventional rack and pinion steering gear unit experiences instability of the rack bush when the steering wheel reaches its limit, leading to potential axial load issues and noise due to the lack of support between two members.
Innovation Solution
The design incorporates a rack bush with an engaging convex section and concave section, where the convex section is inclined outward, allowing it to be supported within the rack housing without looseness, even when not held between two members, using a pressing mechanism to maintain the meshed state of pinion and rack teeth and prevent axial displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the rack bush is held between two members (end case and stopper) to prevent axial movement, then the rack bush is stable during normal operation, but the structure becomes complex and requires additional components
Solution Approach 1:
The patent removes the end case and stopper components from the conventional structure. Instead of holding the rack bush between two members, the rack bush is directly fitted into the rack housing with its engaging convex section fitting into the engaging concave section of the housing, eliminating unnecessary components while maintaining stability
Solution Approach 2:
The rack housing serves multiple functions: it houses the pinion shaft and rack shaft, provides the engaging concave section for the rack bush, and acts as the support structure itself. This eliminates the need for separate end case and stopper components, simplifying the overall structure
2Device complexity
If the rack bush is not held between two members to simplify structure, then the device complexity is reduced, but the rack bush becomes unstable under large axial loads at steering limits
Solution Approach 1:
The rack bush has an asymmetric structure with an engaging convex section that fits into an engaging concave section of the rack housing. This asymmetric engagement provides stable positioning and load-bearing capability without requiring symmetric support from two members, maintaining reliability while simplifying structure
Solution Approach 2:
Instead of constraining the rack bush axially between two members (one-dimensional constraint), the patent uses radial engagement between the convex and concave sections to provide axial stability. The engaging convex section of the rack bush fits into the engaging concave section of the rack housing, transferring axial loads through radial contact surfaces
3Object-affected harmful factors
If the engaging convex section is held between stopper and stepped surface to prevent axial displacement, then noise from collision is prevented, but the rack bush posture becomes unstable under large axial loads
Solution Approach 1:
The rack bush is pre-positioned and stabilized through the engaging convex-concave section fit before any operational loads are applied. This preliminary stable positioning prevents both noise from collision and posture instability under load, eliminating the need for separate stopper and stepped surface components
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 stabilizes the rack bush's posture, prevents noise, and ensures smooth axial displacement of the rack shaft, maintaining the engagement between pinion and rack teeth under varying loads.
Implementation Method 1
The outer peripheral surface of the rack shaft is slidably supported by the inner peripheral surface of the tubular body of the rack bush
Implementation Method 2
a pressing mechanism that presses a pressed section of the outer peripheral surface of the rack shaft located on the side radially opposite to the portion provided with the rack teeth toward the pinion shaft
Data Source
AI summary
The rack housing has an engaging concave section having a bottom surface configured by a bottom inclined surface that is inclined in a direction outward in the radial direction toward the opening side of the rack housing, and the rack bush comprises an engaging convex section having a top surface configured by a top inclined surface that is inclined in a direction outward in the radial direction toward the opening side of the rack housing. The top inclined surface is pressed against the bottom inclined surface toward outside in the radial direction, and the outside surface of the engaging convex section facing the opening side of the rack housing is pressed against the inner side surface of the engaging concave section facing the inner side of the rack housing.