Yoke Cover Design for Torque Detection Assembly
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Solution Overview
Problem
The existing yoke cover for torque detection devices in automotive electric power steering systems requires high accuracy and strong press fitting, which complicates assembly and increases production costs due to the need for precise cylindrical surfaces and additional processing steps like fine blanking or shaving to achieve smooth shear surfaces.
Innovation Solution
The yoke cover is designed with first and second cylindrical surfaces formed by press punching in different directions, reducing the circumferential length of fitted portions and eliminating the need for additional processing, allowing for easier assembly and lower production costs by using shear surfaces and corner radius portions formed during punching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high accuracy cylindrical surfaces are provided on the yoke cover for press fitting to electromagnetic yokes, then the retentive force and assembly reliability are improved, but the manufacturing complexity and production cost increase due to the need for additional processing steps like fine blanking or shaving
Solution Approach 1:
The patent applies preliminary action by forming the cylindrical surfaces and corner radius portions directly during the press punching process before final assembly. The corner radius portions are created as shear surfaces during punching, which preliminarily prepare the fitting surfaces to reduce stress concentration and improve press fitting quality without requiring subsequent machining operations.
Solution Approach 2:
The press punching process itself serves multiple functions: it creates the cylindrical surfaces, forms the corner radius portions, and generates the shear surfaces all in one operation. The process is self-sufficient, eliminating the need for separate fine blanking or shaving operations that would otherwise be required to achieve the necessary surface quality for press fitting.
2Manufacturing precision
If additional processing steps like fine blanking or shaving are applied to achieve smooth shear surfaces, then the manufacturing precision is improved, but the productivity decreases and production cost increases
Solution Approach 1:
The patent merges multiple manufacturing operations into a single press punching process. The cylindrical surface formation, corner radius portion creation, and shear surface generation are all combined into one step, eliminating the need for sequential fine blanking or shaving operations. This integration maintains surface accuracy while significantly improving productivity.
Solution Approach 2:
The patent changes the punching parameters and tooling design to directly produce the required surface quality during the punching process itself. By optimizing the punch geometry and punching conditions, the shear surfaces achieve the necessary smoothness and accuracy without requiring additional machining, thus maintaining manufacturing precision while eliminating time-consuming post-processing steps.
3Ease of operation
If the circumferential length of fitted portions is reduced on the yoke cover, then the assembly ease and work efficiency are improved, but the retentive force may be compromised
Solution Approach 1:
The patent applies local quality by providing corner radius portions at specific locations where the cylindrical surfaces meet. These localized features concentrate the stress distribution and enhance the press fitting quality at critical points, compensating for the reduced overall circumferential contact length. The corner radius portions create localized high-quality fitting zones that maintain retentive force despite shorter fitted portions.
Solution Approach 2:
The corner radius portions introduce curvature at the transitions between cylindrical surfaces, creating smooth rounded corners instead of sharp edges. This curvature improves stress distribution and enhances the press fitting characteristics, allowing for adequate retentive force with reduced circumferential contact length by optimizing the contact geometry at critical locations.
Data Source
Figure 1~2(b)
Figure 3(a)~3(b)
Figure 4(a)~4(b)
AI summary
[Problem] It is an object of the invention to achieve reduction in production cost for a single yoke cover that is fitted to inner circumferences of cylindrical portions of two electromagnetic yokes configuring a torque detection device and retains the two electromagnetic yokes. [Solution] A single yoke cover 1 is interposed between two electromagnetic yokes 11a and 11b axially facing each other and is fitted to inner circumferences of cylindrical portions 11d and 11d of the electromagnetic yokes 11a and 11b. The yoke cover 1 includes a first cylindrical surface 2a fitted to the electromagnetic yoke 11a and provided in each of a plurality of first circumferential portions in an outer circumferential surface, and a second cylindrical surface 2b fitted to the electromagnetic yoke 11b and provided in each of a plurality of second circumferential portions circumferentially displaced from the first circumferential portions in the outer circumferential surface. The first cylindrical surface 2a and the second cylindrical surface 2b are shear surfaces formed by press punching in punching directions different from each other.