Ball Screw Drive Radial Support for Steering Systems
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Solution Overview
Problem
Conventional ball screw drives in motor vehicle steering systems face challenges in absorbing high lateral forces, leading to material stress, damage, and acoustic deterioration due to excessive radial loads on the ball circulation.
Innovation Solution
A plain bearing element, designed as a sleeve with a conically shaped section, is introduced between the threaded spindle and the ball screw, providing adjustable radial clearance to absorb lateral forces and limit tilting moments, thereby reducing material stress and allowing for smaller spindle and rack diameters without exceeding permissible strengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional ball screw drive is used without additional radial support, then the structure remains simple, but high lateral forces cause excessive radial loads on the ball circulation leading to material stress and damage
Solution Approach 1:
A sliding bearing element is introduced as an intermediary component between the threaded spindle and the ball screw drive housing. This sliding bearing radially supports the threaded spindle, absorbing lateral forces and reducing the radial load on the ball circulation, thereby improving reliability without significantly increasing overall system complexity
Solution Approach 2:
The support function is segmented into two distinct mechanisms: the fixed bearing provides primary radial support at the ball nut, while the sliding bearing provides additional radial support at the threaded spindle end. This segmentation allows each bearing to be optimized for its specific location and load conditions, improving overall system robustness
2Strength
If the threaded spindle and rack diameters are increased to withstand high lateral forces, then strength increases, but the construction becomes more expensive and complex
Solution Approach 1:
The sliding bearing acts as an intermediary load-bearing element that absorbs lateral forces before they reach the threaded spindle and rack. This allows the threaded spindle and rack to be designed with smaller diameters while maintaining sufficient strength, as the sliding bearing carries a portion of the lateral load
Solution Approach 2:
The sliding bearing changes the load distribution parameters in the system by providing an additional radial support path. This alters the stress distribution so that the threaded spindle and rack experience reduced radial loads, allowing for optimized (smaller) dimensions while maintaining strength requirements
3Duration of action of stationary object
If the ball screw drive is designed to absorb high lateral forces, then durability improves, but manufacturing costs increase due to larger components
Solution Approach 1:
The sliding bearing serves as a cost-effective intermediary component that extends the service life of the ball screw drive by absorbing lateral forces. Rather than designing the entire system with oversized components, the sliding bearing provides the necessary lateral force absorption at a lower manufacturing cost
Solution Approach 2:
The sliding bearing provides beforehand cushioning against lateral forces by being positioned to radially support the threaded spindle before excessive loads can damage the ball screw drive. This preventive measure extends service life by protecting critical components from high-stress conditions
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 material stress and increases robustness by absorbing lateral forces, allowing for a cost-effective construction with improved operating properties and reduced acoustic issues, while maintaining normal steering operation unaffected by lower lateral loads.
Implementation Method 1
a sliding bearing element (20) is arranged between the end (2e) of the threaded spindle (2a) connected to one of the tie rods (3) and the ball screw drive (10), which radially supports the threaded spindle (2a) against the housing (GH)
Implementation Method 2
the sleeve (20) has a conically shaped section (22) which is conically shaped on its outer circumference in the axial direction (x) and bears against an inner wall (23) which is conically shaped in the housing (GH)
Data Source
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AI summary
The invention relates to a ball screw drive (10) used in a steering system. The ball screw drive (10) includes a lead screw (2a) for converting an auxiliary torque produced by an electric motor (M) into an auxiliary translational force which acts on a steering rack (2b) in the steering system of a motor vehicle. One end of the lead screw (2a) and one end of the steering rack (2b) are each connected to a track rod (3, 3') via an axial link (G), and the ball screw drive (10) has a ball nut (5) mounted in a housing (GH) with a fixed bearing (4). In order to withstand strong lateral loads or lateral forces coming from the track rod or rods (3, 3') and acting in the radial direction (y) there is provided between the end of the lead screw (2a) connected to the track rod (3) and the ball screw drive (10) a plain bearing element (20) which supports the lead screw (2a) radially against the housing (GH). The support is provided by an adjustable radial clearance, and the plain bearing element is preferably in the form of a sleeve (20) which surrounds the lead screw (2a), the sleeve (20) having a conically shaped portion (22) which is conically shaped on its outer periphery in the axial direction (x) and lies against a conically formed inner wall (23) in the housing (GH).