Servo Steering Helical Gear Bearing With Asymmetric Pivot Preload
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Solution Overview
Problem
Conventional electromechanical power steering systems face challenges in minimizing backlash and friction in worm gears, leading to noise and rattling issues, which existing bearing arrangements fail to adequately address.
Innovation Solution
A helical gear with a bearing arrangement featuring a fixed bearing surrounded by bearing shells with asymmetrical spring elements, reducing axial and torsional rigidity, and allowing the shaft to pivot at the toothing plane, thereby minimizing torque and friction during engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed bearing is used to support the worm shaft, then the bearing arrangement becomes simpler and more stable, but the shaft cannot pivot to maintain constant mesh with the helical gear, leading to increased backlash and friction
Solution Approach 1:
The patent transforms the static fixed bearing into a dynamic system by introducing spring elements that allow the shaft to pivot. The spring elements provide controlled compliance, enabling the shaft to adjust its position dynamically to maintain optimal mesh with the helical gear while still providing sufficient support.
Solution Approach 2:
The patent changes the stiffness parameter of the bearing arrangement by using spring elements with specific elastic properties. This allows the system to have high stiffness in normal operation for stability while permitting controlled pivoting movements when needed to maintain mesh consistency.
2Strength
If the pivot axis is positioned away from the tooth plane, then the bearing can better support the shaft, but negative forces and reaction torque act on the bearing, increasing friction and wear
Solution Approach 1:
The patent positions the pivot axis asymmetrically within the tooth plane of the helical gear rather than at the conventional bearing center. This asymmetric positioning is calculated to minimize the moment arm for reaction forces, thereby reducing negative forces and reaction torque on the bearing while maintaining adequate support capability.
3Stability of the object's composition
If symmetric spring elements are used to preload the fixed bearing, then the bearing is evenly supported, but the pivot axis does not align with the tooth plane, resulting in increased friction during gear engagement
Solution Approach 1:
The patent employs asymmetric spring elements with different preloads on opposite sides of the bearing. This asymmetric configuration is specifically designed to shift the pivot axis onto the tooth plane of the helical gear, thereby minimizing friction during engagement while maintaining sufficient bearing stability through the combined preload effect.
Solution Approach 2:
The patent applies different spring characteristics locally on opposite sides of the bearing. By varying the spring stiffness and preload asymmetrically, the system achieves optimal local conditions for reducing friction at the gear interface while maintaining overall bearing stability.
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 backlash and friction, ensuring quiet operation and consistent engagement between the worm shaft and worm wheel, preventing reaction torque and asymmetric friction, thus enhancing the overall performance of the electromechanical power steering system.
Implementation Method 1
a spring element arranged on each end face of the fixed bearing between the fixed bearing and the corresponding bearing shell, and with the spring elements asymmetrically preloading the fixed bearing
Data Source
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Figure 3~5
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AI summary
The invention relates to a helical gear transmission for an electromechanical servo steering, comprising a shaft (4) which meshes with a helical gear (5). The shaft (4) is arranged in a transmission housing (7), wherein a first end of the shaft is mounted in a drive-side bearing assembly (8) in a rotatable manner about a rotational axis (100), and a second end is mounted in a bearing assembly (9) remote from the drive in the transmission housing (7). The drive-side bearing assembly (8) has a fixed bearing (11), and the fixed bearing (11) is enclosed by two bearing shells (17), wherein a respective spring element (16) is arranged at both end faces of the fixed bearing (15) between the fixed bearing (11) and the corresponding bearing shell (17), and the spring elements (16) asymmetrically pretension the fixed bearing (11) such that a pivot axis, about which the shaft (4) can be pivoted in the direction of the helical gear (5), is arranged in the region of the toothing plane between the shaft (4) and the helical gear (5).