Rack-Assist Steering Ball Nut Support for Backlash and Noise Reduction
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Solution Overview
Problem
Conventional rack assist electric power steering apparatuses experience backlash and noise due to misalignment of the ball nut and rack bar centers, leading to increased ball nut length and friction, which are not effectively addressed by existing designs.
Innovation Solution
The apparatus incorporates a rotary support member with first and second inner rings coupled to the ball nut, a nut pulley, and an outer ring, along with rolling members and elastic members to absorb shock and reduce friction, aligning the rotary support member with the ball nut and rack bar coupling center, thereby minimizing the ball nut length and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the ball nut length is increased to align centers, then the alignment between ball nut and rack bar is improved, but the device complexity and friction are increased
Solution Approach 1:
A rotary support member is introduced as an intermediary component between the ball nut and the housing. This rotary support member includes a bearing that supports the ball nut, allowing the ball nut to rotate smoothly while maintaining proper alignment with the rack bar. The rotary support member acts as a mediator that enables center alignment without requiring an increased ball nut length, thus reducing device complexity while maintaining manufacturing precision.
2Ease of manufacture
If the ball is elastically deformed to be inserted between inner ring and outer ring, then the ball can be fitted in the bearing, but backlash occurs in the bearing generating noise
Solution Approach 1:
The ball is pre-heated before insertion into the bearing. This preliminary heating action causes thermal expansion of the ball, allowing it to be easily inserted between the inner ring and outer ring of the bearing without elastic deformation. After insertion, the ball cools and contracts, creating a tight fit that eliminates backlash and prevents noise generation. This preliminary thermal action resolves the contradiction between ease of manufacture and prevention of harmful backlash.
3Device complexity
If the center of ball nut coupling is not aligned with bearing center, then the structure is simpler, but the ball nut movement cannot be effectively prevented generating noise
Solution Approach 1:
The rotary support member serves as an intermediary that provides a bearing to support the ball nut. This bearing ensures that the ball nut rotates smoothly around its center, which is aligned with the rack bar coupling center. The bearing in the rotary support member prevents unwanted ball nut movement while maintaining structural simplicity, thus eliminating noise without requiring complex alignment 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
This configuration effectively reduces backlash and friction, aligns the rotary support member with the ball nut and rack bar coupling center, and minimizes the ball nut length, resulting in reduced noise and improved operational stability.
Implementation Method 1
a first rolling member disposed between the first inner ring and the outer ring, and a second rolling member disposed between the second inner ring and the outer ring
Implementation Method 2
shock between a rotary support member and a housing is absorbed
Data Source
AI summary
A rack assist electric power steering apparatus. Shock between a rotary support member and a housing is absorbed. Backlash and friction in the rotary support member are reduced. The length of a ball nut is minimized, and the rotary support member is supported by a portion in which the ball nut and a rack bar are coupled, so that noise is reduced.