Steering Column Leadscrew Assembly With Uniform Bearing Preload
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Solution Overview
Problem
Current electrically powered rake and telescope leadscrew assembly designs are complex, requiring multiple components and torque operations for assembly, leading to variability in preload, potential bending of the lead screw, and non-uniform stiffness due to the use of a spring element and nut, which can result in increased audible noise and reduced steering column stability.
Innovation Solution
A simplified actuator leadscrew assembly using a longitudinally extending leadscrew shaft with two pressed ball bearings and a housing, assembled through press operations, eliminating the need for a nut and utilizing a retaining ring for crash load retention, with dynamic preload control via a piezo-electric load cell system to ensure consistent and uniform stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a nut and spring element are used to control bearing preload, then overload strength during crash events is provided, but manufacturing precision deteriorates due to variability in preload from torque and back-off process
Solution Approach 1:
The patent removes the nut and spring element from the assembly, replacing the complex preload control mechanism with a simplified bearing and housing structure. This extraction eliminates the torque and back-off processes that caused preload variability, while the housing and bearing arrangement maintains the necessary mechanical strength for crash events.
Solution Approach 2:
The invention changes the fundamental approach to preload control by eliminating adjustable mechanisms (nut and spring) and using a fixed geometric relationship between the housing and bearing. The preload is determined by the pressing operation that seats the bearing against the housing, providing consistent and repeatable results without requiring torque adjustment.
2Strength
If torque operations are used to assemble the nut, then overload strength is achieved, but device complexity increases due to multiple components and assembly steps
Solution Approach 1:
The patent extracts and removes the nut component entirely from the assembly. The housing directly supports the bearing without requiring a separate nut, and the spring element is eliminated in favor of a direct pressing operation. This reduces the component count and simplifies the assembly process while maintaining structural integrity.
Solution Approach 2:
The functions previously performed by separate components (nut for retention, spring for preload) are merged into an integrated housing structure. The housing simultaneously provides mechanical support, bearing retention, and preload application through its geometric relationship with the bearing, eliminating the need for multiple discrete parts.
3Reliability
If a nut is used for both adjustment and retention functions, then overload protection is provided, but ease of manufacture deteriorates due to complex assembly processes
Solution Approach 1:
The patent removes the multi-functional nut and replaces it with a simpler bearing and housing arrangement. The bearing is pressed directly into the housing, which provides both retention and preload functions without requiring adjustment operations. This simplifies the manufacturing process while maintaining reliability through the robust housing-bearing connection.
Solution Approach 2:
The housing and bearing arrangement is designed to be self-aligning and self-retaining through the pressing operation. The bearing is pressed into the housing until it seats against the housing face, automatically establishing the correct position and preload without requiring external adjustment or complex assembly procedures.
4Adaptability or versatility
If the spring element is used to provide preload, then compliance is achieved, but stiffness uniformity deteriorates in different loading directions
Solution Approach 1:
The patent removes the spring element from the assembly and replaces it with a rigid housing-bearing structure. The preload is provided directly by the geometric constraint of the bearing pressed against the housing, eliminating the compliance introduced by the spring. This results in uniform stiffness in all loading directions while maintaining the necessary mechanical strength.
Data Source
AI summary
An actuator leadscrew assembly is provided. The assembly includes a leadscrew shaft extending longitudinally. The assembly also includes a first bearing pressed over the leadscrew shaft. The assembly further includes a housing pressed over the leadscrew shaft and in abutment with the first bearing. The assembly yet further includes a second bearing pressed over the leadscrew shaft and in abutment with the housing. The assembly also includes a retaining ring disposed over the leadscrew shaft retaining the second bearing.