Stepped Assembly Ring Fit for Motor-to-Housing Tolerance Control
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Solution Overview
Problem
The assembly of a steering assistance motor in a power steering device is challenging due to large dimensional manufacturing tolerances and differing thermal expansion coefficients between steel and aluminum alloy materials, leading to unpredictable tightening, potential damage, and increased costs in existing solutions.
Innovation Solution
An assembly process using a cylindrical assembly ring with axially stepped sections, where the ring's internal and external faces are forcibly engaged with the motor and casing to create separate clamping contacts, allowing for individual adaptation to each part's tolerances and thermal expansion, thereby ensuring a secure and reproducible fit without excessive stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hot-shrinking the motor directly into the aluminum alloy housing is used, then the dimensional variations are compensated and effective clamping is guaranteed, but high residual stresses are generated in the casing leading to stress fracture risk
Solution Approach 1:
A tolerance ring is introduced as an intermediary component between the motor casing and the aluminum alloy housing. This ring absorbs the dimensional variations and thermal expansion differences through its wavy profile, which allows radial elasticity and deformation. The tolerance ring takes up the play between parts and ensures a solid link by friction, preventing direct stress transmission to the aluminum housing that would cause fracture.
Solution Approach 2:
The tolerance ring's wavy profile with specific amplitude and wavelength is designed to change its physical state under thermal and mechanical loads. The radial elasticity of the wavy shapes allows the ring to deform and adapt to dimensional variations, compensating for manufacturing tolerances and thermal expansion while maintaining a secure connection without generating excessive stresses.
2Reliability
If tolerance rings with significant interference are used to ensure solid assembly, then assembly integrity is maintained, but abrasion of the housing and metal shavings are generated creating short circuit risk
Solution Approach 1:
The tolerance ring's wavy profile parameters (amplitude and wavelength) are specifically designed to provide radial elasticity while limiting interference. The optimized geometry allows the ring to deform elastically under load, maintaining assembly integrity through friction without generating excessive contact pressures that would cause abrasion and metal shavings.
3Reliability
If high pressures are exerted by corrugated shapes on the casing, then the assembly remains solid without loosening, but plastic deformation or cracking of the casing occurs
Solution Approach 1:
The wavy profile of the tolerance ring is designed with specific amplitude and wavelength that allow it to deform elastically under thermal and mechanical loads. This controlled deformation maintains assembly stability through friction while limiting contact pressures to levels that prevent plastic deformation or cracking of the aluminum alloy housing.
4Adaptability or versatility
If the assembly is exposed to wide temperature ranges, then operational flexibility is achieved, but differential expansion causes loosening or increased internal stresses
Solution Approach 1:
The tolerance ring is specifically designed to accommodate differential thermal expansion between the steel motor casing and aluminum alloy housing. The wavy profile allows the ring to expand and contract radially with temperature changes, maintaining a secure friction-based connection throughout the operational temperature range from -40°C to +120°C without causing loosening or excessive stresses.
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 method provides a secure, reproducible, and cost-effective assembly that reduces the risk of part damage, maintains assembly integrity across temperature ranges, and simplifies manufacturing by using a simple, inexpensive assembly ring design.
Implementation Method 1
The radially internal face of the assembly ring is forcibly engaged on the first part, so as to create between the first part and the ring a clamping contact which secures the first part and the ring
Implementation Method 2
the radially internal face of the first ring section, intended to receive the first part, has a substantially frustoconical shape which converges towards the central axis in the opposite direction to the second ring section
Data Source
Figure 1~3
Figure 4~7
AI summary
The invention relates to an assembly method in which an assembly ring (3) is force-fitted between a first part (1) and a second part (2) such as to create: a tightening contact between the first part (1) and the inner face (3I) of the ring (3), by means of plastic deformation of the ring (3), said tightening contact occupying a first interference zone (Z1); and a tightening contact between the second part (2) and the outer face (3E) of the ring (3), said tightening contact occupying a second interference zone (Z2). The assembly ring (3) comprises a first ring segment (T1) and a second ring segment (T2) which are stepped axially in relation to one another and which have different radial dimensions from one another, such as to confine the first interference zone (Z1) to the first ring segment (T1) and the second interference zone (Z2) to the second ring segment (T2), in order to prevent the first interference zone and the second interference zone from overlapping axially.