Ball Screw Support Shaft for Coaxial Electric Steering Gears
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Solution Overview
Problem
Conventional electric power steering gear assemblies experience premature failures due to radial and tangential forces causing the ball nut to tilt relative to the ball screw, leading to suboptimal force transmission and responsiveness.
Innovation Solution
A hollow ball screw mounted on an inner shaft that can deflect axially under radial loads, maintaining a coaxial relationship with the tilting ball nut, combined with a support bushing to limit tilt and a low friction coating, enhances force transmission and reduces stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional rigid ball screw is used, then structural stability is maintained, but the ball nut tilts relative to the ball screw under radial and tangential forces, leading to premature failures
Solution Approach 1:
The patent applies the dynamics principle by making the ball screw hollow instead of solid, allowing it to flex and deflect under external loads. This dynamic characteristic enables the ball screw to maintain coaxial alignment with the ball nut even when subjected to radial and tangential forces, preventing tilt and improving reliability
Solution Approach 2:
The patent changes the structural parameter of the ball screw from solid to hollow, which fundamentally alters its mechanical properties. The hollow construction provides flexibility while maintaining strength, allowing the ball screw to adapt its shape under load and preserve the coaxial relationship with the ball nut, thereby resolving the alignment stability issue
2Stability of the object's composition
If the ball nut is constrained to prevent tilting, then coaxial alignment is maintained, but the assembly complexity increases due to additional support structures
Solution Approach 1:
The patent extracts the need for complex external support structures by making the ball screw itself flexible through its hollow design. The ball screw's inherent flexibility replaces the need for additional constraints or support mechanisms, maintaining coaxial alignment without increasing assembly complexity
Solution Approach 2:
The hollow ball screw serves itself by using its own structural flexibility to maintain coaxial alignment with the ball nut. The design eliminates the need for separate alignment maintenance mechanisms, as the ball screw's flexible nature automatically compensates for external forces and preserves the coaxial relationship
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
Improves force transmission and reduces premature failures by allowing the hollow ball screw and ball nut to maintain a coaxial alignment, enhancing steering responsiveness and assembly durability.
Implementation Method 1
an inner shaft disposed in the cavity of the hollow ball screw and rigidly attached to the hollow ball screw at a first end, the inner shaft is configured to enable deflection of the hollow ball screw relative to the axial direction in response to external loads exerted by the ball nut
Implementation Method 2
a low friction coating, enhances force transmission and reduces stress
Data Source
AI summary
An electric powered steering assembly for a commercial vehicle includes a housing, a hollow ball screw, a ball nut, and an inner shaft. The housing includes a substantially cylindrical portion extending in an axial direction. The hollow ball screw is disposed in the housing, and defines a cavity extending in the axial direction. The ball nut is disposed in the housing circumferentially surrounding the hollow ball screw and configured to translate axially relative to the housing. The inner shaft is disposed in the cavity of the hollow ball screw and rigidly attached to the hollow ball screw at a first end. The inner shaft is configured to enable deflection of the hollow ball screw relative to the axial direction in response to external loads exerted by the ball nut.