Worm Gear Bimetal Spring Compensation for Steering Backlash
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Solution Overview
Problem
Electromechanical power steering systems face issues with noise and component wear due to temperature-related expansion and contraction of worm gear components, leading to increased play and forces at low and high temperatures, which existing solutions like shape memory alloys fail to adequately address cost-effectively.
Innovation Solution
A worm gear design incorporating an eccentric lever and a bimetallic spring with a wedge element, supported by a stop pin, provides temperature compensation and noise reduction by adjusting the engagement between the worm wheel and worm shaft, with the bimetallic spring being helical and arranged to minimize space usage and costs.
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 cost increases and performance deteriorates with operating cycles
Solution Approach 1:
The patent replaces expensive shape memory alloy with a bimetallic spring that is more cost-effective. The bimetallic spring consists of two different metal layers bonded together, providing temperature compensation through differential thermal expansion without the high cost and performance degradation issues of shape memory alloys.
Solution Approach 2:
The bimetallic spring uses composite construction with two different metal layers bonded together. This composite structure enables temperature compensation functionality while being more economical and durable than single-material shape memory alloy solutions.
2Ease of manufacture
If bimetallic spring is used instead of shape memory alloy, then cost is reduced, but temperature compensation effectiveness may be compromised
Solution Approach 1:
The bimetallic spring compensates for temperature changes by utilizing differential thermal expansion parameters of two different metals. As temperature varies, the two metal layers expand or contract at different rates, causing the spring to deflect and adjust the preload force on the worm gear, thereby maintaining proper engagement across the operating temperature range from -40°C to +80°C.
Solution Approach 2:
The bimetallic spring directly exploits thermal expansion differences between two bonded metal layers. When temperature changes, the differential expansion causes the spring to change shape and exert varying forces on the worm gear, providing automatic temperature compensation without requiring complex control systems.
3Object-affected harmful factors
If worm wheel contracts at low temperatures, then backlash increases and noise increases, but component wear is not affected
Solution Approach 1:
The bimetallic spring performs preliminary action by pre-adjusting the preload force on the worm gear to account for anticipated temperature changes. At low temperatures, the spring maintains sufficient compression force to prevent excessive backlash and keep gear teeth in proper contact, thereby preventing noise before it occurs.
Solution Approach 2:
The bimetallic spring converts the harmful effect of thermal contraction into a beneficial force. As the worm wheel contracts at low temperatures, the bimetallic spring's differential expansion creates additional compressive force that compensates for the contraction, maintaining proper gear engagement and eliminating backlash-induced noise.
4Object-affected harmful factors
If worm wheel expands at high temperatures, then forces in gear teeth increase and component wear increases, but backlash is not affected
Solution Approach 1:
The bimetallic spring provides dynamic adjustment of preload force based on temperature conditions. At high temperatures, as the worm wheel expands, the bimetallic spring's differential contraction reduces the compression force on the worm gear, preventing excessive forces in the gear teeth and reducing component wear while maintaining appropriate engagement.
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 by compensating for temperature-related changes in the worm gear engagement, maintaining performance across a wide temperature range while being economically viable.
Implementation Method 1
an eccentric lever and a bimetallic spring operatively connected to the eccentric lever compensate for temperature-related play in the engagement between the worm wheel and the worm shaft
Implementation Method 2
a bimetallic spring operatively connected to the eccentric lever compensate for temperature-related play
Implementation Method 3
A wedge element is provided between the gearbox housing and the bimetallic spring, which is supported on a stop pin on the gearbox housing. The wedge element is arranged between the gearbox housing and the eccentric lever, so that the eccentric lever can be moved towards or away from the worm wheel by moving the wedge element
Implementation Method 4
The eccentric lever is part of a pivot bearing for adjusting the preload of the engagement between the worm shaft and the worm wheel
Implementation Method 5
an eccentric lever and a bimetallic spring operatively connected to the eccentric lever compensate for temperature-related play
Implementation Method 6
The eccentric lever preferably has an elastic damper on its outer circumferential surface in the area of the stop pin, thus reducing noise
Implementation Method 7
an elastic damper on its outer circumferential surface in the area of the stop pin, thus reducing noise
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
The invention relates to a worm gear of an electromechanical power steering system of a motor vehicle, comprising a worm shaft (2), which meshes with a worm wheel (4), wherein the worm wheel (4) and the worm shaft (2) are arranged in a common gear housing. An eccentric lever (7) and a bimetal spring (16) that is operatively connected to the eccentric lever (7) compensate for a temperature-related play in the engagement between the worm wheel (4) and the worm shaft (2).