Abstract
In traditional gear design, the design theory is based on a rigid hypothesis and is popularly adopted in the preparation of metal gear. Plastic gear designing lacks a mature design theory. Hence, scholars still follow the traditional gear design theory. There is a marked difference in the rigidity and stiffness between the conventional gear design and plastic gear features. In traditional design theory, the deformation is 0.2% (Note: To assess the material yield, conditional yield strength is calculated). Designing deformation can exceed 2% for plastic gears, and the difference can sometimes be more than tenfold. The traditional design theory cannot match the gear strength and precision in the design of plastic gear. In the case of plastic gear, due to numerous meshing teeth, the 2% deformation seen cannot be neglected and should be taken into account in the presence and absence of loading to improve the meshing condition. Improvement in the gear loading ability and reduction in the meshing noise can thus be achieved. Herein, we propose an unequal pitch design theory. The results of Finite Element Analysis (FEA) and experimental verification showed that the strength could be increased by 24% for unequal pitch design theory.
Highlights
The tooth thickness and the tooth addendum height of the cutter are small and different from the meshing worm owing to the tip clearance and backlash requirement [10]. In some appliances such as window lift, steel worm, and plastic helical gear train is widely used owing to its low cost, low noise, self-locking ability, and compact volume
The right side plastic helical gear is secured by two fixed plates and is attached to the base together
The results show that the meshing of gears with unequal pitch can improve the root strength of gears, and can improve the service life of gears under the same working conditions, which can provide a reference for the subsequent coordination of worm and plastic helical gears
Summary
Worm and Worm gear train is widely used in cross shaft transmission. It has many advantages, such as small volume, big speed ratio, low noise, simple structure, etc. [8]. The tooth thickness and the tooth addendum height of the cutter are small and different from the meshing worm owing to the tip clearance and backlash requirement [10] In some appliances such as window lift, steel worm, and plastic helical gear train is widely used owing to its low cost, low noise, self-locking ability, and compact volume. Appliances like window lift gears for cars, use a steel worm, and a plastic helical gear (=worm gear), where the tooth thickness of the steel worm has been reduced in favor of the tooth thickness of the plastic gear In this case, the gear strength may be limited by the shear strength of the loaded teeth, as given by the following equation [12], Fmax = n· f ·t·τ where n = number of teeth in (full) contact; f = tooth width (mm); t = tooth thickness (mm), τ = shear strength = σy /(1.7 × S) (MPa) where σy = yield strength at design temperature (MPa).
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