Gearbox Axial Preload for Steering Rattle Reduction
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Solution Overview
Problem
Gearbox assemblies in electric power assisted steering systems experience noise and vibration due to incorrect meshing between worm and wheel gears, caused by manufacturing tolerances, thermal changes, and torsional loads, which existing technologies fail to adequately address.
Innovation Solution
A gearbox assembly with axial and radial biasing means, including a resilient biasing system that applies pre-load to the input shaft, preventing axial movement of bearing races and ensuring proper meshing of worm and wheel gears, thereby reducing rattle and noise. The system includes a housing, input and output shafts, and bearing assemblies that allow for articulation and tilt, utilizing components like leaf springs and elastomeric elements to maintain optimal gear engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If axial pre-load is applied to the input shaft to eliminate bearing clearance, then rattle noise is reduced, but the complexity of the gearbox assembly increases due to additional biasing means
Solution Approach 1:
The patent combines the axial pre-load function with the existing bearing support structure by integrating the resilient biasing means into the bearing assembly. The first resilient biasing means is positioned to act directly on the first bearing means, merging the noise reduction function with the existing support structure rather than adding a completely separate mechanism.
Solution Approach 2:
The resilient biasing means is designed to automatically apply the necessary axial pre-load to the input shaft based on operating conditions. The resilient nature of the biasing means allows it to self-adjust and maintain optimal bearing clearance without requiring external control systems or complex adjustment mechanisms.
2Manufacturing precision
If resilient biasing means is added to apply axial load to the input shaft, then gear meshing accuracy is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent employs resilient biasing means that can accommodate dimensional variations and thermal expansion through their elastic properties. The resilient nature of the biasing elements allows the system to maintain proper gear meshing accuracy despite manufacturing tolerances and thermal changes, without requiring extremely precise manufacturing of all components.
Solution Approach 2:
The resilient biasing means provides dynamic adjustment capability, allowing the axial pre-load to vary with operating conditions such as thermal expansion and torsional loads. This dynamic characteristic enables the system to maintain optimal gear meshing accuracy throughout the operating range without requiring complex manufacturing precision for all components.
3Adaptability or versatility
If the first bearing means is allowed to move relative to the housing, then adaptability to thermal and mechanical changes is improved, but the stability of the gearbox assembly decreases
Solution Approach 1:
The patent employs resilient biasing means that provide dynamic adjustment capability, allowing the axial pre-load to vary with operating conditions such as thermal expansion and torsional loads. This dynamic characteristic enables the system to maintain optimal gear meshing accuracy throughout the operating range without requiring complex manufacturing precision for all components.
Solution Approach 2:
The resilient biasing means provides dynamic adjustment capability, allowing the axial pre-load to vary with operating conditions such as thermal expansion and torsional loads. This resilient characteristic enables the system to maintain proper gear meshing accuracy despite manufacturing tolerances and thermal changes, without requiring extremely precise manufacturing of all components.
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 rattle and noise by maintaining consistent contact between worm and wheel gear teeth, improving the robustness and reliability of the gearbox assembly while minimizing misalignment and friction.
Implementation Method 1
a (first) resilient biasing means adapted to apply an axial load to the input shaft, the resilient biasing means acting upon a part of the first bearing means
Implementation Method 2
It may comprise a leaf spring which is connected to the housing at one end and acts upon the first bearing means
Implementation Method 3
The teeth of the worm and wheel intermesh to transfer the torque
Data Source
AI summary
In a gearbox for use in an electric power assisted steering system comprises a housing, an input shaft located at least partially within the housing which carries a worm gear and includes means for coupling to a motor rotor at one end, an output shaft located at least partially within the housing which carries a wheel gear, and a first bearing means which supports the input shaft at a side of the worm distal from the end of the shaft which connects to the motor rotor and second bearing means which supports the input shaft at the other side of the worm, the invention comprises further providing a first biasing means adapted to apply an axial load to the input shaft to bias the axial clearance in the second bearing, the second biasing means acting upon a part of the first bearing means; and a second biasing means adapted to apply a radial load to the input shaft to bias the worm into engagement with the wheel gear, the second biasing means also acting upon a part of the first bearing means.