EPS Worm Shaft Preload Limiting to Prevent Gear Disengagement
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Solution Overview
Problem
Electric power steering systems with worm gears experience disengagement and noise issues due to pivoting movements caused by uneven road conditions and engagement forces, leading to unreliable power transmission and compromised steering feel.
Innovation Solution
An electric power steering system with a worm gear featuring a spring-loaded actuator and limiting device that sets a defined clearance to prevent disengagement, combined with a damping mechanism to reduce noise, and adjustable pre-tensioning and clearance settings based on ambient temperature and humidity profiles to optimize performance across different environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pre-tensioning device with spring-loaded actuator is used to maintain engagement between worm shaft and wheel, then reliability of power transmission is improved, but friction between worm shaft and wheel increases, degrading steering feel
Solution Approach 1:
The patent applies parameter changes by introducing a limiting device that dynamically controls the pre-tensioning force applied to the worm shaft. The limiting device adjusts the engagement parameters between worm shaft and wheel, maintaining sufficient pre-tensioning for reliable engagement while preventing excessive pre-tensioning that would cause harmful friction and noise. This resolves the contradiction by optimizing the engagement parameters to balance reliability and steering feel.
2Reliability
If higher pre-tensioning force is applied to prevent disengagement of worm shaft and wheel, then reliability is improved, but disturbing noises increase
Solution Approach 1:
The limiting device modifies the pre-tensioning force parameter by imposing a defined limit on the maximum force that can be applied to the worm shaft. This prevents the pre-tensioning force from exceeding optimal levels that would cause harmful noises and vibrations during steering operation, while still maintaining sufficient engagement reliability.
3Reliability
If clearance of worm shaft is reduced to prevent disengagement, then reliability is improved, but friction increases and steering feel deteriorates
Solution Approach 1:
The limiting device optimizes the clearance parameter of the worm shaft by preventing excessive pre-tensioning that would reduce clearance to harmful levels. It maintains an optimal clearance range that ensures reliable power transmission while preserving sufficient clearance to minimize friction and maintain good steering feel.
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
Ensures reliable power transmission, reduces noise, and improves steering feel by maintaining engagement between the worm shaft and wheel while adapting to environmental conditions, thus enhancing the overall performance and durability of the steering system.
Implementation Method 1
a pre-tensioning device comprising a spring-loaded actuator element extending through the passage opening of the guide bush and acting on the worm shaft in the direction of the worm wheel with a defined pre-tensioning force
Implementation Method 2
the pre-tensioning device comprises a limiting device which is adapted to limit a pivoting movement that displaces the worm wheel away from the worm shaft
Data Source
AI summary
An electric power steering system with a worm gear includes a worm shaft and a worm wheel, wherein an electric motor is associated with the worm shaft, which is connected to the worm shaft in a force-transmitting manner. A bearing element, arranged on the worm shaft at the end of the worm shaft facing away from the electric motor, is received in a guide bush, wherein the guide bush has, on its circumferential side, a passage opening. It is provided a pre-tensioning device comprising a spring-loaded actuator element extending through the passage opening of the guide bush and acting on the worm shaft in the direction of the worm wheel with a defined pre-tensioning force (K), wherein the pre-tensioning device comprises a limiting device which is adapted to limit a pivoting movement that displaces the worm wheel away from the worm shaft. Furthermore, it is proposed a method for the production of steering systems and a test system for performing the method.