Motorized Power Steering Stick Slip Reduction
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Solution Overview
Problem
Electric power steering devices experience stick slip and vibrations due to increased load on rolling bearings, leading to discomfort and abnormal noise, as the output shaft distorts and tilts, causing repeated fixing and sliding between the outer and inner peripheral faces of the bearings.
Innovation Solution
Interposing a lubricant between the inner rings of the rolling bearings and the outer peripheral face of the rotation shaft, and optionally using an elastic material, to reduce friction and prevent stick slip, while maintaining a lubricated state over a long period, thereby supporting the rotation shaft with a single row deep groove-type ball bearing and a clearance fit on one side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the output shaft is supported by rolling bearings with a clearance fit, then the output shaft can be freely rotatable with respect to the housing, but stick slip and vibrations occur due to axial displacement and tilting under increased load
Solution Approach 1:
A lubricant is introduced as an intermediary substance between the inner peripheral face of the inner ring and the outer peripheral face of the output shaft. This lubricant film prevents direct metal-to-metal contact, reduces friction, and eliminates stick slip phenomenon while maintaining the clearance fit configuration that enables free rotatability.
Solution Approach 2:
The physical state and properties of the interface between bearing and shaft are changed by introducing lubricant. This changes the friction coefficient and contact characteristics, transforming the dry friction condition into a lubricated condition that prevents stick slip while preserving the mechanical clearance fit structure.
2Force
If the output shaft distorts under increased load, then the steering device can handle higher forces, but the central axis tilts causing repeated fixing and sliding between bearing faces
Solution Approach 1:
The lubricant acts as a mediator that decouples the harmful mechanical interaction between the distorted shaft and bearing inner ring. Even when the shaft tilts and displaces axially under load, the lubricant film maintains continuous contact without stick slip, preventing the generation of abnormal noise and vibrations.
Solution Approach 2:
The axial displacement and tilting of the output shaft under increased load, which previously caused harmful stick slip, is converted into a beneficial condition. The lubricant allows this displacement to occur smoothly without generating noise or vibrations, transforming a harmful phenomenon into an acceptable operational characteristic.
3Device complexity
If a single row deep groove-type ball bearing is used, then the device complexity is reduced, but the bearing may not adequately prevent stick slip under high load conditions
Solution Approach 1:
The lubricant serves as an intermediary that enhances the performance of the simple single row deep groove-type ball bearing. It enables this structurally simple bearing to effectively prevent stick slip under high load conditions by reducing friction and allowing smooth relative motion between the shaft and bearing inner ring.
Solution Approach 2:
The introduction of lubricant changes the friction parameter at the bearing interface, transforming a potentially high-friction dry contact into a low-friction lubricated contact. This parameter change allows the simple single row bearing design to reliably prevent stick slip without increasing structural complexity.
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 effectively reduces or prevents stick slip, eliminating vibrations and abnormal noise, ensuring a smooth and comfortable steering experience by maintaining a stable lubricated state and reducing the occurrence of axial displacement between the bearing faces.
Implementation Method 1
a lubricant is interposed between the inner peripheral face of at least one of the inner rings, or more preferably all of the inner rings, which constitute the rolling bearings, and the outer peripheral face of the output shaft
Data Source
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AI summary
An electric power steering device is provided with a construction that can suppress the generation of stick slip between the outer peripheral face of a rotation shaft (13), and the inner peripheral face of inner rings (20a, 20b) of rolling bearings (19a, 19b). Therefore, in the present invention a lubricant (24) or an elastomer (25) is interposed between the inner peripheral face of at least one of the inner rings of the inner rings (20a, 20b), and the outer peripheral face of the rotation shaft (13). Additionally in the case where a lubricant (24) is interposed at a part of the rotation shaft (13), there is provided a surface for retaining the lubricant in this part.