Relieved Enveloping Worm Teeth for Full-Depth Gear Meshing
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Solution Overview
Problem
Conventional enveloping worm teeth in gear systems experience partial tooth engagement at the beginning of the mesh cycle, leading to undesirable wear and degradation of the mating gear due to the shape of the worm thread, which is throated and larger at the ends, causing uneven stress distribution.
Innovation Solution
The worm is machined using a rack-form tool with varying thicknesses to create a conjugate-thread length and relieved ends, ensuring full-depth engagement only when the worm teeth are fully meshed, preventing partial engagement and subsequent wear by widening the tooth gaps at the ends.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the worm thread is shaped as a conventional enveloping tooth form (throated, narrower at center, larger at ends), then the worm can engage multiple pitches of the mating gear, but partial tooth engagement occurs at the beginning of the mesh cycle causing wear and degradation of the mating gear
Solution Approach 1:
The patent applies local quality by modifying only the end sections of the worm thread while keeping the central threaded section unchanged. The end sections are machined with a larger rack-form thickness to create widened tooth gaps, while the central portion maintains the original enveloping tooth form. This localized modification prevents partial engagement at the ends without affecting the multi-pitch engagement capability of the central section.
Solution Approach 2:
The worm thread is segmented into three distinct zones: a central threaded section with standard rack-form thickness for multi-pitch engagement, and two end sections with enlarged rack-form thickness for gap relief. This segmentation allows each zone to perform its specific function - the central section provides versatility while the end sections prevent harmful partial engagement.
2Reliability
If the rack-form thickness is increased at the end sections of the worm, then tooth gaps are widened to prevent partial engagement, but the manufacturing process becomes more complex requiring multiple machining operations
Solution Approach 1:
The patent applies preliminary action by first machining the entire worm thread with a standard rack-form tool to create the base enveloping tooth form, then performing a second machining operation on only the end sections with a larger rack-form thickness. This sequential approach ensures the central section has the required engagement geometry while the ends are pre-prepared with gap relief, achieving reliable mesh engagement without excessive complexity.
Data Source
AI summary
A worm comprises enveloping worm teeth having relieved ends. The worm is machined in three steps comprising machining a threaded section, machining a first end section, and machining a second end section. The threaded section is machined utilizing a rack-form tool having a rack-form thickness. The first end section and the second end section are machined utilizing a larger rack-form thickness, thereby, providing relieved ends. The teeth of the worm having such relieved ends mesh with the teeth of a mating gear at full depth throughout preventing partial teeth engagement.