Composite Worm Wheel Thermal Expansion Compensation
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Solution Overview
Problem
Worm gearboxes in electromechanical power steering systems face issues with backlash and stiffness due to thermal and humidity changes, leading to noise and reduced performance, as different materials expand at different rates, requiring complex and costly solutions to maintain consistent engagement between the worm shaft and worm wheel.
Innovation Solution
A device with a worm wheel made of a metal hub and a plastic sprocket, supported by a compensating element with similar thermal expansion properties, which ensures consistent engagement by accommodating diameter changes through suitable material selection and design, reducing the need for large metal hubs and complex spring-loaded systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a large metal hub and thin plastic sprocket are selected to match thermal expansion coefficients, then the thermal expansion matching is improved, but the component becomes expensive and heavy
Solution Approach 1:
The worm wheel is constructed as a composite component with a plastic sprocket mounted on a metal hub, allowing the overall thermal expansion coefficient to be tailored to match the housing material. This composite structure enables thermal compatibility without requiring excessive metal content, thus avoiding the weight and cost penalties of purely metal constructions.
Solution Approach 2:
The invention adjusts the proportions and material properties of the composite worm wheel to achieve a specific effective thermal expansion coefficient that matches the housing. By changing the parameters of the composite structure (material selection, geometry, distribution), the thermal behavior is optimized without requiring a large metal hub.
2Stability of the object's composition
If a complex spring-loaded system is used to compensate for thermal expansion, then the backlash compensation is improved, but the device complexity increases
Solution Approach 1:
The worm wheel's own thermal expansion, when properly designed with composite materials, automatically compensates for temperature-induced backlash changes. The system serves itself by using the natural physical property of the materials rather than requiring external compensating mechanisms like springs or adjustable devices.
Solution Approach 2:
The invention deliberately utilizes thermal expansion of the composite worm wheel to maintain proper clearance. By selecting materials and geometries where the effective expansion coefficient matches the housing, the system automatically adjusts for temperature changes without complex compensation mechanisms.
3Temperature
If the worm wheel diameter changes due to temperature or humidity, then thermal expansion occurs, but the engagement pressure becomes inconsistent
Solution Approach 1:
The composite worm wheel is designed with homogeneous thermal expansion behavior relative to the housing material. By matching the effective expansion coefficient, the worm wheel expands and contracts uniformly with the housing, maintaining consistent engagement pressure across temperature variations.
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 provides a simpler, cost-effective means to maintain consistent backlash and contact pressure between the worm shaft and worm wheel, reducing noise and improving stiffness across temperature and humidity variations, while minimizing weight and material costs.
Implementation Method 1
the compensating element is made of a material whose expansion change is similar to the expansion change of the radius of the worm wheel
Data Source
AI summary
A worm gearbox having a worm wheel is arranged, in a torsionally resistant manner, on a steering shaft and rotates around a steering axis. A worm shaft is supported to rotate around a rotational axis, with the worm shaft having an end on the engine side and an end away from the engine. Worm toothing engages the teeth of the worm wheel and when the worm shaft rotates around the rotational axis, the worm wheel and the steering shaft rotate around the steering axis. A gearbox housing supports the worm wheel and the worm shaft and allows them to rotate. A compensating element has a middle section, a rear end section connected to the gearbox housing and a front end section retaining the end away from the engine of the worm shaft or a holder accommodating the end away from the engine of the worm shaft.