Worm Gear Preload Assembly for Quiet Electric Power Steering
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Solution Overview
Problem
Electric-motor assisted steering systems face challenges in maintaining reliable engagement between the worm shaft and worm wheel due to high component tolerances and wear, requiring complex and costly adjustment of preloading forces to prevent chattering noises and excessive stiffness.
Innovation Solution
A gear assembly with an elastic element and adjustment element that automatically adjusts and limits axial force, ensuring reliable engagement by expanding when necessary and limiting expansion to prevent excessive force, thereby simplifying the adjustment process and maintaining optimal preloading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a preloading device is provided to apply preloading force to the worm shaft, then reliable engagement between worm shaft and worm wheel is ensured, but the adjustment of preloading force becomes very expensive and complicated
Solution Approach 1:
The elastic element automatically adjusts the axial preloading force on the worm shaft based on the tolerance range, eliminating the need for expensive and complicated manual adjustment mechanisms. The system self-regulates the preloading force within the required range through the elastic properties of the element.
Solution Approach 2:
The invention changes the physical state of the preloading mechanism by using an elastic element that can deform axially, allowing the preloading force to vary dynamically within a tolerance range rather than requiring fixed, precise adjustment mechanisms.
2Reliability
If preloading force is increased to ensure reliable engagement, then engagement reliability improves, but the gearbox becomes stiff
Solution Approach 1:
The elastic element provides a dynamic preloading force that can adapt to operating conditions, maintaining sufficient engagement reliability while allowing the system to remain compliant and easy to operate. The elasticity enables the preloading force to decrease when needed, preventing excessive stiffness.
3Ease of operation
If preloading force is decreased to improve ease of operation, then steering operation becomes easier, but chattering noises occur
Solution Approach 1:
The elastic element acts as a cushioning element that maintains sufficient preloading force to prevent chattering noises and bearing contact loss, while its elastic properties prevent the force from becoming excessive. This beforehand cushioning ensures smooth operation without harmful vibrations.
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 ensures reliable engagement between the worm shaft and worm wheel, reduces chattering noises, and prevents excessive stiffness by automatically adjusting and limiting axial force within a predefined threshold, eliminating the need for complex preloading adjustments.
Implementation Method 1
in which recess there is arranged an elastic element which applies an axial force to the worm shaft
Implementation Method 2
the adjustment element, which is formed in such a way that it permits expansion of the elastic element in the axial direction when the axial force on the worm shaft exceeds a defined threshold value, and limits expansion of the elastic element when the axial force on the worm shaft lies below the defined threshold value
Data Source
AI summary
The disclosure specifies a gear assembly for an electric-motor assisted steering system, comprising an electric motor, a worm shaft which can be driven by the electric motor and which meshes with a worm wheel. The worm shaft has a recess on an end face which faces the electric motor, in which recess there is arranged an elastic element which applies an axial force to the worm shaft in the direction away from the electric motor. In the axial direction, the elastic element is supported by one end on an adjustment element, which is formed in such a way that it permits expansion of the elastic element in the axial direction when the axial force on the worm shaft exceeds a defined threshold value, and limits expansion of the elastic element when the axial force on the worm shaft lies below the defined threshold value.