Pre-stressed Torque Converter Shell Residual Stress
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Solution Overview
Problem
Torque converters experience failures due to cyclic operating stress, primarily affecting the front cover and impeller shell, leading to hydraulic fluid leakage and failure, with existing solutions increasing mass and manufacturing costs by thickening these components.
Innovation Solution
Introducing residual compressive stresses in high-stress regions of the torque converter shell through plastic deformation, shot peening, or hydraulic pre-stressing during the manufacturing process to enhance durability without increasing mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the front cover and/or impeller shell is increased to increase durability, then the durability against operating stress is improved, but the mass of the torque converter shell increases, which increases manufacturing costs and operating costs
Solution Approach 1:
The patent applies preliminary action by introducing residual compressive stresses into the front cover and impeller shell during the manufacturing process, before the component is put into service. This is achieved through plastic deformation that creates a pre-compressed state, allowing the component to better withstand subsequent operating tensile stresses without requiring increased thickness or mass.
Solution Approach 2:
The patent changes the stress state parameter of the component by transforming the initial stress-free or tensile-stressed state into a compressively pre-stressed state. This parameter change allows the same material thickness to provide greater durability, effectively resolving the contradiction between durability and mass.
2Reliability
If the thickness of the front cover and/or impeller shell is increased to increase durability, then the durability against operating stress is improved, but the manufacturing costs increase
Solution Approach 1:
The manufacturing process incorporates a preliminary plastic deformation step that introduces residual compressive stresses. This preliminary action enhances durability during normal operation without requiring additional material or complex post-manufacturing modifications, thereby avoiding increased manufacturing costs.
Solution Approach 2:
By changing the stress state parameter through controlled plastic deformation during manufacturing, the patent achieves improved durability using the same amount of material. This parameter transformation avoids the need for thicker sections, thus maintaining manufacturing cost efficiency.
3Reliability
If the thickness of the front cover and/or impeller shell is increased to increase durability, then the durability against operating stress is improved, but the operating costs increase due to increased weight and mass moment of inertia
Solution Approach 1:
The patent applies preliminary compressive stress during manufacturing, which allows the component to resist operating stresses more effectively. This preliminary action improves durability without increasing mass, thereby avoiding the increased energy consumption and operating costs that would result from a heavier torque converter shell.
Solution Approach 2:
By transforming the stress state parameter to include residual compression, the patent achieves improved durability with the same mass. This prevents the increase in weight and mass moment of inertia that would otherwise lead to higher operating costs and energy consumption.
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 method improves durability by aligning residual stresses with operating stresses, extending the torque converter's lifespan and reducing material thickness, thus lowering manufacturing and operational costs.
Implementation Method 1
The front cover is plastically deformed past the first near net shape in a direction of an operating stress and creates a first residual compressive stress in the torque converter shell after formation of the front cover
Implementation Method 2
The front cover is shot peened, at least in a radially outer region, to create a first residual compressive stress in the torque converter shell after formation of the front cover
Implementation Method 3
A hydraulic pressure that is greater than an operating pressure is supplied to a cavity defined by the front cover and the impeller shell to over-stress the torque converter shell
Data Source
AI summary
A method for manufacturing a torque converter shell is provided to induce favorable residual stress in a direction of a loading condition to improve durability during cycle pressurization. The method includes inducing favorable residual stress on a front cover, an impeller shell, or both the front cover and the impeller shell to improve the durability of these components. The induced residual stresses reduce the stress experienced by these components during operation. The front cover and impeller shell are welded together to form the torque converter shell.