Involute Ram Lug Profile for Impact Wrench Drive Assembly
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Solution Overview
Problem
Existing impact wrench drive assemblies experience inefficiencies and increased wear due to uneven contact between the ram and anvil, caused by imperfections in the flat driven surfaces, leading to high contact stresses and reduced mechanical efficiency.
Innovation Solution
The implementation of involute profiles on the drive and driven surfaces of the ram and anvil lugs, which facilitates a uniform distribution of load and reduces localized contact stresses, enhancing the mechanical efficiency and extending the lifespan of the components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat driven surface with a small rounded corner radius is used on the anvil, then the structure is simple and easy to manufacture, but uneven contact between the ram and anvil occurs due to imperfections in form, size, and symmetry, leading to high contact stresses and accelerated wear
Solution Approach 1:
The patent applies curvature by replacing the flat driven surface with a cylindrical surface having a radius of curvature between 0.060 inches and 0.125 inches. This curved surface allows the ram and anvil to maintain uniform contact along an extended area rather than at a single corner point, distributing contact stresses evenly and eliminating the uneven contact problems associated with flat surfaces and small rounded corners.
2Productivity
If a flat driven surface is used on the anvil, then the manufacturing process is simple, but imperfections in the form, size, and symmetry of the anvil yield uneven contact between the ram and anvil, potentially reducing efficiency and accelerating wear
Solution Approach 1:
The cylindrical surface with radius of curvature 0.060 inches to 0.125 inches compensates for manufacturing imperfections in the anvil's form, size, and symmetry. The curved geometry provides a tolerance buffer that maintains uniform contact between the ram and anvil even when dimensional variations exist, thereby preserving mechanical efficiency without requiring extremely tight manufacturing tolerances.
Solution Approach 2:
The patent changes the geometric parameter of the driven surface from flat (zero curvature) to cylindrical (positive curvature with radius 0.060-0.125 inches). This parameter change fundamentally alters the contact mechanics, transforming point or line contact into area contact, which distributes loads more uniformly and reduces the impact of manufacturing variations on contact uniformity.
3Force
If a relatively large amount of torque is transferred through the drive assembly, then the impact wrench can effectively loosen stuck fasteners, but relatively high contact stresses occur at the outer corner of the driven surface, accelerating wear
Solution Approach 1:
The cylindrical driven surface with radius of curvature 0.060 inches to 0.125 inches distributes the high contact stresses generated during torque transfer across a larger contact area. Instead of concentrating stresses at the outer corner of a flat surface, the curved geometry spreads the load along the cylindrical interface, allowing effective torque transfer while reducing peak contact stresses and preventing accelerated wear.
Data Source
AI summary
A drive assembly for an impact wrench includes a tool element for working on a workpiece. The drive assembly also includes a ram rotatable about a central axis. The ram includes a ram lug spaced from the central axis. The ram lug has at least one drive surface. The drive assembly further includes an anvil having an anvil lug with at least one driven surface engageable with the drive surface of the ram lug to drive the anvil. The anvil is connectable to the tool element to rotatably drive the tool element. At least one of the drive surface and the driven surface includes an involute profile.