Offset Hirth Serration Geometry for Inner-Tooth Overload Relief
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Solution Overview
Problem
Conventional Hirth gearing in wheel hub swivel joint arrangements experiences selective overload in the radially inner area due to the dependence of engagement on the bracing strength, leading to a risk of tooth breakage and inadequate material thickness, which affects torque transmission and resilience.
Innovation Solution
The design features a spur gear with tooth tips and troughs where the intersection point of the contact edge and tooth trough lines is offset from the axis of rotation, allowing for a higher material thickness in the radially inner area and a more resilient engagement by curving the construction lines to better adapt to structural conditions, reducing the risk of overload and enhancing torque transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional Hirth gearing with intersection point on the axis of rotation is used, then the structure is simple and manufacturing is easier, but the material thickness in the radially inner area is insufficient leading to selective overload and tooth breakage risk
Solution Approach 1:
The patent applies asymmetry by offsetting the intersection point of the construction lines from the axis of rotation to a specific distance in the direction of engagement. This asymmetric positioning increases the material thickness in the radially inner area where it is most needed for strength, while maintaining reasonable tooth geometry elsewhere. The offset creates a more favorable stress distribution that prevents selective overload in the inner area.
Solution Approach 2:
The patent changes the geometric parameter of the gearing by specifying that the intersection point of contact edge line and tooth trough line should be offset from the axis of rotation by a specific distance (0.05-0.15 times the outer radius). This parameter change fundamentally alters the tooth profile geometry to achieve better material distribution and stress characteristics in the radially inner area, directly addressing the strength issue.
2Ease of operation
If the two points of intersection on the axis of rotation are offset from one another to lead gearing axially, then axial engagement is improved, but selective overload in the radially inner area cannot be avoided
Solution Approach 1:
Instead of offsetting both intersection points along the axis (symmetric offset), the patent uses a single asymmetric offset in the direction of engagement. This asymmetric approach maintains adequate axial engagement while distributing stresses more evenly, preventing the selective overload that occurs with symmetric axial offsetting.
Solution Approach 2:
The patent applies local quality by concentrating the offset in the direction of engagement rather than distributing it axially. This creates a localized geometric modification that specifically addresses the radially inner area stress concentration without compromising overall engagement quality. The offset is applied where it provides maximum benefit for preventing inner area overload.
3Reliability
If conventional Hirth gearing is used, then manufacturing is straightforward, but the engagement depends heavily on bracing strength leading to inadequate torque transmission reliability
Solution Approach 1:
The patent modifies the manufacturing parameters by specifying the offset distance as a proportion (0.05-0.15 times the outer radius) rather than a fixed value. This proportional parameter makes the gearing more robust to manufacturing variations and bracing strength differences, improving reliability while maintaining manufacturability. The geometric modification ensures more consistent engagement characteristics across different manufacturing conditions.
Data Source
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AI summary
A component that is to be mounted so as to be rotatable about an axis of rotation and transmits torque along with a rotating partner includes a first serration that extends about the axis of rotation and is to mesh with the rotating partner which has an adequate second serration mating with the first serration. The first serration has a plurality of teeth which have tooth tips extending substantially in the direction of the axis of rotation and tooth valleys located between the tooth tips. The tooth tips of the first serration each have a meshing edge forming a first line, while the tooth valleys located between the teeth each define a second line. At least two adjacent second lines intersect at an imaginary point lying between the axis of rotation and the maximum circumference of the first serration, in the semicircular surface beyond the axis of rotation.