Ball Screw Bearing Support for Quiet Vehicle Steering
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Solution Overview
Problem
Vehicle steering devices with ball screws experience vibration and operating noise due to misalignment and non-uniform loads, leading to bearing displacement and hitting noise when encountering shock loads, necessitating enhanced noise reduction and retaining ability.
Innovation Solution
A vehicle steering device featuring an annular elastic member with two distinct load characteristics: a first elastic portion with a gently increasing spring rate and a second elastic portion with a keenly increasing spring rate, supporting the bearing across its entire circumference, formed from an elastic material to reduce vibration and noise, and attenuate shock loads, while maintaining the bearing's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single elastic member with constant spring rate is used to support the bearing, then the device complexity is reduced, but the ability to simultaneously reduce vibration during normal operation and retain bearing position under shock loads is insufficient
Solution Approach 1:
The elastic member is divided into two distinct elastic portions: a first elastic portion with a first spring rate for normal operation, and a second elastic portion with a second spring rate for shock load conditions. This segmentation allows each portion to be optimized for its specific function, reducing vibration during normal operation while providing strong retention under shock loads.
Solution Approach 2:
Different portions of the elastic member are given different local properties - the first elastic portion has a gentler spring rate characteristic suited for vibration reduction during normal operation, while the second elastic portion has a steeper spring rate characteristic for retaining bearing position under excessive shock loads. This local differentiation resolves the contradiction between simplicity and dual-function performance.
2Object-affected harmful factors
If the elastic member is made softer to reduce vibration during normal operation, then the vibration and noise are reduced, but the retaining ability under excessive shock load decreases
Solution Approach 1:
The elastic member transitions from a static, constant spring rate design to a dynamic, variable spring rate design. The spring rate changes based on the compression amount - using a lower first spring rate for small deformations during normal operation to reduce vibration, and switching to a higher second spring rate for large deformations under shock loads to maintain retaining ability.
Solution Approach 2:
The spring rate parameter of the elastic member is changed based on the operating conditions. The first elastic portion operates with a first spring rate parameter during normal vibration conditions, while the second elastic portion engages with a second spring rate parameter when excessive shock loads cause larger compression amounts, thus adapting the stiffness to match the operational requirements.
3Reliability
If the elastic member is made stiffer to retain bearing position under shock load, then the retaining ability is improved, but the vibration and operating noise during normal operation increase
Solution Approach 1:
Rather than using a constantly stiff elastic member, the design employs a dynamic spring rate that adapts to loading conditions. During normal operation with small vibrations, the first elastic portion provides a softer response that reduces noise. When shock loads occur, the second elastic portion engages to provide the necessary stiffness for retention, thus avoiding the constant vibration and noise that would result from an always-stiff design.
Solution Approach 2:
The spring rate parameter is varied based on compression amount - using a lower first spring rate for normal operation to minimize vibration and noise, and switching to a higher second spring rate under shock loads to ensure bearing position retention. This parameter change resolves the contradiction by matching stiffness to operational needs.
4Object-affected harmful factors
If a dual-stage spring rate elastic member is used to achieve both vibration reduction and retaining ability, then the noise reduction and retaining ability are improved, but the device complexity increases
Solution Approach 1:
The first elastic portion and second elastic portion are merged into a single integrated elastic member structure. This combination allows the dual-stage spring rate functionality to be achieved within one component rather than requiring separate elements, thus reducing overall device complexity while maintaining the benefits of both soft and stiff characteristics.
Solution Approach 2:
The elastic member is designed to perform multiple functions through its two elastic portions: vibration reduction during normal operation and bearing position retention under shock loads. This multi-functionality is achieved within a single component structure, avoiding the need for additional separate mechanisms and thereby limiting the increase in device 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 dual-stage spring rate effectively reduces vibration and operating noise during normal operation and retains the bearing's position under excessive shock loads, preventing hitting noise and protecting the ball screw and bearing from shock loads.
Implementation Method 1
an annular elastic member which includes: a first elastic portion that has a first load characteristic that gently increases a ratio of compression load per a unit compression amount deforming in the axial direction of the turning shaft
Implementation Method 2
The damping component includes a collar and an elastic member formed of rubber. The vibration and operating noise are attenuated by the damping component.
Data Source
AI summary
A vehicle steering device includes a turning shaft held in a housing so as to be movable in the axial direction, a ball screw transmitting drive force produced by an electric motor to the turning shaft, a bearing supporting a nut, which is a component of the ball screw, so as to be rotatable relative to the housing, and annular elastic members that support side faces of the bearing in the axial direction of the turning shaft across the entire circumference, and are formed of an elastic material. The elastic members include respective first elastic portions having a first load characteristic that gently increases the ratio of compression load per a unit compression amount deforming in the axial direction of the turning shaft, and respective second elastic portions having a second load characteristic that keenly increases the ratio in comparison with the first load characteristic.