Ball Screw Sleeve for Thermal Expansion Compensation
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Solution Overview
Problem
Electromechanical power steering systems face challenges in compensating for thermal expansion between bearing shells and steering housing, leading to potential damage and inadequate heat compensation, especially with angular contact ball bearings and single-row bearing spring-loaded arrangements.
Innovation Solution
A double-row angular contact ball bearing with a sleeve made of material having greater thermal expansion than aluminum and steel, where the sleeve is designed to absorb thermal expansion between the housing and ball nut, and a corrugated spring is used to enhance tilting rigidity and damping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If angular contact ball bearings are used to support the ball nut, then high axial and tilting forces can be withstood, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The bearing system is divided into modular components: the ball nut with integrated inner ring, separate outer rings received in sleeves, and intermediate elements like wave springs. This segmentation allows standardized manufacturing of complex angular contact ball bearings while simplifying assembly and maintenance.
Solution Approach 2:
Sleeves are introduced as intermediary elements between the bearing outer rings and the housing. These sleeves simplify the bearing mounting and allow for thermal expansion compensation without increasing the complexity of the bearing itself.
2Reliability
If a single-row bearing spring-loaded arrangement is used, then thermal expansion can be compensated, but tilting stiffness and heat dissipation are insufficient
Solution Approach 1:
The patent combines multiple functions into the double-row angular contact ball bearing: both rows of balls provide simultaneous support for axial and tilting forces, while the rigid connection between outer rings and housing (via sleeves) provides thermal expansion compensation. This merging eliminates the need for separate spring-loaded mechanisms.
Solution Approach 2:
The bearing system uses composite construction with different materials optimized for specific functions: hardened steel for bearing rings and balls to withstand loads, and sleeves (potentially different material) for thermal expansion accommodation, creating a composite system that addresses multiple requirements simultaneously.
3Force
If two angular contact ball bearings with spring-loaded outer rings are used, then high axial forces can be transmitted, but sufficient heat dissipation cannot be achieved
Solution Approach 1:
The spring-loaded intermediate element (wave spring) is extracted from the bearing itself and placed in the sleeve, separating the force transmission function from the thermal management function. This allows the bearing to focus on force transmission while the sleeve and housing handle heat dissipation.
4Manufacturing precision
If the bearing is rigidly fixed in the housing, then positioning precision is improved, but thermal expansion causes gaps and component damage
Solution Approach 1:
The sleeve design allows controlled changes in dimensional parameters due to thermal expansion. The sleeve acts as a compliant element that absorbs dimensional changes caused by temperature variations, preventing stress concentration and component damage while maintaining bearing positioning.
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 compensates for thermal expansion, improves tilting rigidity, and enhances noise characteristics by transmitting high axial forces while maintaining structural integrity and reducing component damage.
Implementation Method 1
the sleeve is designed to compensate for thermal expansions between the housing and the ball nut, and the sleeve is made of a material that has a greater coefficient of thermal expansion than aluminum and steel
Implementation Method 2
a wave spring is arranged enclosed by the sleeve, which, lying between the sleeve and the outer bearing ring, dampens an axial movement of the component
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to an electromechanical servo-assisted power steering system (1), in particular for a motor vehicle, having a servo motor (9), which drives an axially displaceable component (6) via a ball nut (13), which is rotatably mounted in a bearing (15) in a housing (21), wherein the ball nut (13) engages with a threaded spindle (6') formed on the component (6), wherein the bearing (15) is a two-rowed angular ball bearing having at least one bearing inner ring (16) and at least one bearing outer ring (18), and wherein the at least one bearing outer ring (18) is accommodated in a sleeve (19), which is arranged in a bearing seat (20) of the housing (21).