Ball Nut Flange Positioning for Compact EPS Rack Drive
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Solution Overview
Problem
Existing electric power steering assemblies face challenges in terms of size, cost, packaging, and operating characteristics, particularly with the pulley and ball nut assemblies, which are not optimal.
Innovation Solution
A rack drive assembly with a ball nut assembly that includes a flange spaced remotely from the end of the ball nut, allowing for a reduced axial dimension and radial runout of the pulley, and utilizing spanner nuts to secure the bearing assembly, which reduces the overall size and weight of the ball nut assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional pulley assembly is used with the ball nut, then the steering function is achieved, but the axial dimension and radial runout of the pulley increase, leading to larger overall size and weight
Solution Approach 1:
The flange is positioned at an intermediate location on the ball nut rather than at the end, changing the spatial arrangement from axial to radial positioning. This dimensional shift allows the pulley to be mounted with reduced axial dimension while maintaining proper belt alignment and function.
Solution Approach 2:
The belt is pre-tensioned against the pulley flange before operation, establishing proper tension and alignment. This preliminary action ensures that the pulley operates with minimal radial runout and maintains optimal belt engagement without requiring excessive axial dimension.
2Volume of moving object
If a conventional pulley assembly is used with the ball nut, then the steering function is achieved, but the overall weight of the ball nut assembly increases
Solution Approach 1:
By repositioning the flange to an intermediate location on the ball nut, the design eliminates the need for a large axial dimension, which directly reduces the volume and consequently the weight of the ball nut assembly while maintaining functional requirements.
3Ease of manufacture
If the flange is positioned at the end of the ball nut, then assembly is simplified, but the radial runout of the pulley increases, affecting operating characteristics
Solution Approach 1:
The belt is pre-tensioned against the pulley flange mounted at the intermediate location, which compensates for any minor manufacturing variations and ensures minimal radial runout during operation. This preliminary tensioning action maintains precision without requiring the flange to be at the extreme end.
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 reduces the axial dimension and radial runout of the pulley, leading to a more compact and lightweight ball nut assembly, improving the packaging and cost-effectiveness of the electric power steering system.
Implementation Method 1
A belt transfers a torque from a driving pulley to a driven pulley attached to the ball nut assembly
Implementation Method 2
The rotational force of the ball nut is transmitted to the rack member by balls to drive the rack member axially
Implementation Method 3
a bearing assembly configured to be disposed in the rack housing and carried by the ball nut assembly for rotatably supporting the ball nut assembly relative to the steering member
Data Source
Figure 1
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AI summary
A rack drive assembly adapted for use in a vehicle electric power steering assembly includes a ball nut assembly having at least a first end portion and an opposite second end portion, a bearing assembly carried by the ball nut assembly for rotatably supporting the ball nut assembly, a pulley assembly configured to be carried by the ball nut assembly, and at least a first spanner nut configured to be carried by the first end portion of the ball nut for securing the bearing assembly on the ball nut assembly. The ball nut includes a flange provided on an outer portion thereof configured to connect the ball nut to a pulley of a pulley assembly for rotation therewith. The flange is spaced remote from an end of the second end portion of the ball nut.