Gearbox Spring Rate Step Change for Steering Rattle
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Solution Overview
Problem
Power assisted steering systems with worm and wheel gear assemblies experience rattle due to incomplete meshing caused by manufacturing tolerances, thermal changes, and wear, leading to noise issues, especially on rough roads or under low load conditions.
Innovation Solution
A gearbox assembly with a spring assembly that applies a biasing force to ensure the worm and wheel gears are fully engaged, featuring a step change in spring rate to maintain engagement under wear and resist disengagement, using a leaf spring with a cantilever design and an adjustable abutment to enhance the spring rate for improved torque transmission and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a resilient biasing means is provided to keep the worm and wheel engaged, then the rattle and noise are reduced, but the device complexity increases
Solution Approach 1:
The patent modifies the spring rate parameter of the resilient biasing means to optimize its performance. By carefully selecting the spring rate, the system maintains adequate engagement force between worm and wheel teeth while minimizing excessive complexity. The spring rate is tuned to compensate for manufacturing tolerances and thermal changes without requiring overly complex adjustment mechanisms.
Solution Approach 2:
The resilient biasing means is designed to automatically compensate for wear and dimensional changes without requiring external intervention or complex control systems. The spring continuously applies biasing force to maintain engagement, adapting to wear over time through its elastic properties, thereby eliminating the need for complex adjustment or monitoring mechanisms.
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 maintains worm and wheel engagement, reducing noise and rattle by applying a consistent biasing force during wear and increasing the required torque for disengagement, thus enhancing the gear wheel torque and reducing audible tooth-impact noises from road-induced disturbances.
Implementation Method 1
a spring assembly which acts between the housing and the first bearing assembly, in which in a neutral position the worm and wheel are fully engaged and the spring assembly applies a biasing force onto the second bearing in a first direction away from the neutral position so as to ensure that the worm and wheel are fully engaged
Implementation Method 2
the spring assembly also providing a resisting force against movement of the second bearing in a second direction, opposed to the first direction, in the event that the worm and wheel try to disengage
Data Source
AI summary
A gearbox assembly for all electric power steering apparatus comprises an input shaft which carries a worm gear and is supported relative to the housing at one end by a first bearing assembly and at the other by a second bearing assembly, an output shaft which carries a wheel gear which is fixed relative to a housing and which meshes with a worm gear on the input shaft, and a spring assembly which acts between the housing and the first bearing assembly, and the spring assembly applying a biasing force onto the second bearing in a first direction away from the neutral position so as to ensure that the worm and wheel are fully engaged. The spring assembly has a spring rate which has a step change about the neutral position such that the rate of change in the force exerted by the spring assembly on the second bearing assembly as the spring moves in the first direction from its neutral position is lower than the rate of change in the force as the spring moves in the second direction away from the neutral position.