Output Pulley Geometry for Lower Stress in Power Steering
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Solution Overview
Problem
Conventional power steering apparatuses experience stress concentration on the output pulley due to a sharp change in axial cross-sectional area, leading to increased maximum stress generation.
Innovation Solution
The output pulley is designed with a fastening target portion located radially inward of the boundary between the hub and winding/hanging portions, where the minor angle between the pulley's inner surface and nut's rotational axis reduces to 45 degrees, shifting the stress concentration area radially outward and distributing the axial force effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output pulley has a conventional design with a sharp change in axial cross-sectional area at the boundary between hub portion and winding portion, then the structure is simple and easy to manufacture, but stress concentration occurs leading to increased maximum stress and reduced reliability
Solution Approach 1:
The invention applies local quality by creating a fastening target portion with specific geometric characteristics (minor angle ≤ 45 degrees) in a localized region of the output pulley. This localized structural modification concentrates the stress-resistant properties where needed (at the screw fastening location) without requiring complex changes throughout the entire pulley structure, thus improving reliability while maintaining overall structural simplicity
Solution Approach 2:
The invention employs curvature principles by defining the boundary portion with a specific angular gradient (minor angle gradually reducing to 45 degrees). This curved transitional geometry eliminates sharp corners and abrupt cross-sectional changes, distributing stress more evenly and preventing stress concentration points that would occur with conventional sharp-edged designs
2Ease of manufacture
If the fastening target portion is positioned at the boundary between hub and winding portions, then assembly is simplified, but stress concentration increases due to sharp cross-sectional area changes
Solution Approach 1:
The fastening target portion is positioned in a specific location (overlapping the screw head portion radially and located radially inward of the boundary) with distinct geometric properties (minor angle ≤ 45 degrees). This localized positioning ensures that the stress-distributing geometric features are present exactly where the screw fastening occurs, maintaining ease of assembly while eliminating stress concentration
Solution Approach 2:
The invention performs a preliminary structural preparation by pre-defining the fastening target portion with its specific geometric characteristics (minor angle gradient) before the screw fastening operation. This preliminary creation of the stress-resistant geometry ensures that when the screw is installed, the stress is already distributed favorably, preventing stress concentration from occurring in the first place
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 reduces the maximum stress on the output pulley, enhancing durability and preventing material failure by distributing stress and reducing surface pressure, while also improving assembly and manufacturing accuracy.
Implementation Method 1
a screw inserted in the screw insertion hole, including a head portion and a shaft portion where a screw groove of a male screw is formed, fastening the nut and the output pulley to each other
Data Source
AI summary
Provided is a power steering apparatus capable of reducing a maximumly generated stress on an output pulley. An output pulley of a power steering apparatus includes a fastening target portion around a screw insertion hole of a hub portion. When a boundary portion between the hub portion and a winding and hanging portion is defined to be a portion where a minor angle, among relative angles formed between a tangential line of an inner surface of the output pulley and a rotational axis of a nut in an axial cross section of the output pulley that passes through the rotational axis of the nut, gradually reduces from a nut-rotational-axis side toward a radially outer side to then reach 45 degrees, the fastening target portion is a region that is located on an inner side in a radial direction with respect to the boundary portion and overlaps a head portion of a screw in a radial direction of the screw.