Worm Gear Bimetal Spring Compensation for Steering Gear Play
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Solution Overview
Problem
Electromechanical power steering systems face challenges with temperature-induced noise and wear due to gear play variations at low and high temperatures, and existing solutions like shape memory alloys are ineffective and costly.
Innovation Solution
A worm gear design incorporating a spiral-shaped bimetallic spring and eccentric lever that compensates for temperature-related play between the worm shaft and worm wheel, reducing noise and wear while being cost-effective, using a bimetallic spring with a wedge element and elastic damper to adjust preload and minimize noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shape memory alloy is used to compensate for temperature differences, then temperature compensation is achieved, but the solution becomes expensive and less effective with increasing work cycles
Solution Approach 1:
The patent changes the material parameter from shape memory alloy to bimetallic spring, which provides temperature compensation through differential thermal expansion coefficients rather than phase transformation. This maintains reliability across temperature ranges while improving manufacturability and durability.
Solution Approach 2:
The bimetallic spring is a cost-effective alternative to expensive shape memory alloys. While the patent doesn't explicitly describe it as disposable, the principle of using cheaper materials that maintain functionality is applied, replacing costly specialty materials with more economical bimetallic construction.
2Temperature
If worm wheel and worm shaft are allowed to contract at low temperatures, then thermal contraction is natural, but gear play increases causing noise
Solution Approach 1:
The bimetallic spring applies preliminary counteracting force to compensate for thermal contraction. At low temperatures, the spring's differential expansion characteristics generate force that pushes the worm shaft and worm wheel together, preemptively counteracting the gap that would otherwise form due to thermal contraction.
Solution Approach 2:
The bimetallic spring utilizes differential thermal expansion of two bonded metals with different expansion coefficients. This creates a self-compensating mechanism where the spring's dimensional change with temperature directly counteracts the thermal contraction of the gear components, eliminating noise without restricting natural contraction.
3Temperature
If worm wheel expands at high temperatures, then thermal expansion is natural, but high forces in gearing increase wear
Solution Approach 1:
The bimetallic spring applies preliminary counteracting force in the opposite direction at high temperatures. As the worm wheel expands thermally, the spring's differential expansion characteristics generate a separating force that reduces the engagement pressure, preemptively preventing excessive wear that would result from uncontrolled thermal expansion forces.
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 noise and wear across temperature ranges by adjusting the engagement between the worm shaft and worm wheel, maintaining system performance and reducing component stress, while being economically viable.
Implementation Method 1
a bimetallic spring (160) compensates for a temperature-related play between the worm shaft (2) and the worm wheel (4)
Implementation Method 2
an elastic damper minimizes noise generated during engagement
Data Source
AI summary
A worm gear for an electromechanical power steering system of a motor vehicle, includes a worm shaft that meshes with a worm wheel. The worm wheel and the worm shaft are arranged together in a gear housing. An eccentric lever and a bimetallic spring that is operatively connected to the eccentric lever are configured to compensate for a temperature-related play in the engagement between the worm wheel and the worm shaft.