Worm Drive Pretensioning in Electric Power Steering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electromechanically assisted steering systems with worm drives require additional components to compensate for production tolerances and dimensional changes due to temperature, humidity, and wear, increasing complexity and cost.
Innovation Solution
An electromechanically assisted steering system using a worm drive with a spring element to provide axial pretensioning, eliminating the need for additional components by selecting a spring stiffness that maintains the pretensioning force within a predefined tolerance range, typically between 200 N to 300 N, using a coil spring or wave spring with reduced spring stiffness and optimized structural support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional components are used to compensate for production tolerances and dimensional changes in the worm drive, then the pretensioning force can be maintained within tolerance range, but the device complexity and production costs increase
Solution Approach 1:
The patent changes the spring stiffness parameter of the spring element to a lower value than conventional designs. This parameter change allows the spring to accommodate dimensional variations and production tolerances while maintaining the pretensioning force within the required tolerance range, eliminating the need for additional compensation components
Solution Approach 2:
The spring element is designed to perform multiple functions simultaneously: it provides the necessary pretensioning force to the worm shaft, compensates for production tolerances in the worm drive, and accommodates dimensional changes due to temperature, humidity, and wear - all without requiring additional components
2Reliability
If additional components are used to compensate for production tolerances, then the pretensioning force can be maintained, but production costs increase
Solution Approach 1:
By optimizing the spring stiffness parameter to a lower value, the patent enables a single spring element to handle tolerance compensation, reducing the bill of materials and simplifying manufacturing processes compared to designs requiring multiple components
Solution Approach 2:
The patent extracts and eliminates unnecessary additional compensation components from the design, relying solely on the optimized spring element to maintain pretensioning force stability, thereby reducing production costs
3Reliability
If high spring stiffness is used to maintain pretensioning force, then the force can be kept within tolerance, but the system becomes more sensitive to axial dimensional variations
Solution Approach 1:
The patent inverts the conventional approach by using low spring stiffness instead of high stiffness. This counterintuitive parameter change enables the spring to absorb axial dimensional variations through greater deflection, while still maintaining the pretensioning force within the required 200N to 300N range
Solution Approach 2:
The compliant spring element acts as a beforehand cushioning mechanism, absorbing axial dimensional variations and shocks before they can affect the pretensioning force stability, thereby protecting the worm drive from tolerance-related issues
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
This solution reduces production costs and simplifies assembly by relying solely on the spring element for tolerance compensation, making the system less sensitive to axial dimensional variations and allowing for reduced spring stiffness while maintaining effective pretensioning within specified limits.
Implementation Method 1
The spring element is connected to the first bearing portion or to the second bearing portion so as to transmit axial force in the axial direction, such that the spring element axially pretensions the worm shaft relative to the worm gear
Data Source
AI summary
An electromechanically assisted steering system is proposed, having a worm drive which comprises a worm shaft and a worm gear, an electric motor which has a drive shaft, and a spring element. At an end assigned to the electric motor, the worm shaft has a first bearing portion which is connected to the drive shaft in a torque-transmitting manner. The worm shaft has a second bearing portion which is arranged at an end of the worm shaft remote from the first bearing portion. The spring element is connected to the first bearing portion or to the second bearing portion so as to transmit axial force in the axial direction, such that the spring element axially pretensions the worm shaft relative to the worm gear. A tolerance compensation of the worm drive in the axial direction of the worm shaft is carried out exclusively via the spring element.