Gearbox Parallelogram Linkage for Steering Noise Reduction
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Solution Overview
Problem
Worm and wheel gearboxes in electric power assisted steering systems face issues with noise and vibration due to incorrect meshing between the worm and wheel gears, resulting in rattle at low torques or high friction at high torques, which existing solutions struggle to address effectively.
Innovation Solution
A gearbox design incorporating a parallelogram linkage with leaf springs to control the movement of the worm shaft, allowing relative freedom in one direction while restraining movement in orthogonal directions, and adjustment rings for fine angular adjustments to optimize the alignment and reduce friction and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed centre distance between the worm and gear wheel is used, then the gearbox structure is simple, but rattle occurs at low torque due to excessive clearance between gear teeth
Solution Approach 1:
The patent makes the centre distance between the worm and gear wheel variable rather than fixed. The bearing carrier is designed to move dynamically along the worm shaft axis, allowing the centre distance to adjust automatically based on operating conditions. This dynamic adjustment eliminates excessive clearance at low torque while maintaining simple structure.
2Object-generated harmful factors
If forced meshing between worm and wheel is used to eliminate clearance, then rattle is prevented, but high friction occurs at high torque
Solution Approach 1:
The patent changes the parameter of centre distance dynamically. By allowing the bearing carrier to move along the worm shaft axis, the centre distance adjusts automatically - increasing slightly at low torque to eliminate clearance and prevent rattle, then maintaining optimal spacing at high torque to reduce friction while still preventing gear tooth separation.
3Stability of the object's composition
If the tail bearing outer race is guided to move only in the gear wheel plane, then lateral stability is improved, but friction increases due to restriction of natural movement
Solution Approach 1:
The patent segments the constraint functions by providing separate guidance mechanisms: the bearing carrier guides lateral movement in the gear wheel plane for stability, while simultaneously allowing axial movement along the worm shaft to accommodate natural gear meshing variations. This segmentation reduces friction while maintaining lateral stability.
4Adaptability or versatility
If excessive clearance exists between gear teeth, then the gearbox can accommodate misalignment, but rattle occurs at zero or low torque
Solution Approach 1:
The patent uses dynamic adjustment of the bearing carrier position along the worm shaft axis. At low torque conditions, the carrier moves to reduce clearance between gear teeth, eliminating rattle. At higher torque or with misalignment, the system maintains sufficient clearance to accommodate variations while preventing excessive contact 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 vibration by ensuring proper alignment and contact between the worm and wheel gears, enhancing the stability and performance of the gearbox across varying torque levels.
Implementation Method 1
the carrier comprising a bearing carrier part which is fixed to the bearing assembly and a reaction part which is fixed to the gearbox housing, the bearing carrier part being connected to the reaction part by at least two connecting elements, the two elements being spaced apart so that they act, in effect, with the bearing carrier part and the reaction part to form a parallelogram linkage that enables the bearing carrier to be relatively free to move relative to the reaction part in one direction whilst being relatively restrained from movement in the two directions orthogonal to that direction
Data Source
AI summary
A gearbox for use in an electric power assisted steering system of the kind in which a motor is connected to a portion of a steering mechanism through the gearbox, comprises a housing, a worm gear carried by a worm shaft and a gear wheel carried by an output shaft, the worm shaft being supported relative to the housing by a tail bearing assembly, in which the bearing assembly is located relative to the gearbox housing by a bearing carrier, the carrier comprising a bearing carrier part which is fixed to the bearing assembly and a reaction part which is fixed to the gearbox housing, the bearing carrier part being connected to the reaction part by at least two connecting elements, the two elements being spaced apart so that they act, in effect, with the bearing carrier part and the reaction part to form a parallelogram linkage that enables the bearing carrier to be relatively free to move relative to the reaction part in one direction whilst being relatively restrained from movement in the two directions orthogonal to that direction.