The Mechanical Efficiency Analysis and Industrial Applications of Involute Gear Transmission System

Autor: Hsiu-Chen Tang, 唐修晨
Rok vydání: 2014
Druh dokumentu: 學位論文 ; thesis
Popis: 103
Transmission efficiency is an indicator for the designing gear transmission, how to increase the transmission efficiency, has been the important subject. In this thesis, based on the principle of gear meshing and its characteristics, that meshing efficiency formula of internal and external gear pair (including helical gear pair) is derived. Based on the concept of “Stribeck Curve”, the empirical formula of friction coefficient by “Buckingham” must be modified. In this thesis, the modified empirical formula of friction coefficient is proposed for calculating the average friction coefficients. The average friction coefficients are obtained by considering surface roughness of gears, type of lubricants, meshing velocity, and meshing load. This thesis also analyzes the corresponding bearing loss and oil seal loss, and then the transmission efficiency of gear box is found. In this thesis, helical spur gear reducers with single gear pair (transmission system for electric scooter) and with two gear pairs (transmission system for electric vehicle) are the two examples for theoretical analysis and experimental verification. 1. For the helical spur gear reducer with single gear pair, the theoretical transmission efficiencies are between 98.6% ~99.1% (40N-m, 120~1200rpm) and the experimental transmission efficiencies are between 89.4%~91.1%. There are 6.8%~9.2% errors between theoretical and experimental values. 2. For the helical spur gear reducer with two gear pairs, the theoretical transmission efficiencies are between 98.6% ~99.1% (400N-m, 150~1500rpm) and the experimental transmission efficiencies are between 97.0% ~98.1%. There are 1.0%~1.7% errors between theoretical and experimental values. The second part of this thesis to analyze the meshing and transmission efficiencies of planetary gear reducer. Based on the latent power theorem, the meshing efficiency formula of planetary gear reducer is derived. Then, the meshing efficiencies of external and internal gear pairs are substituted into equation, the corresponding meshing efficiency of planetary gear reducer is obtained. And then, the bearing loss and oil seal loss are analyzed to calculate its corresponding theoretical transmission efficiencies. In this thesis, the servo planetary gear reducer (with reduction Rr=4), 4.3KW 2-stage planetary gear reducer of electric elevator (with reduction Rr=20), and 4.3KW compound planetary gear reducer of electric elevator (with reduction Rr=20) are the three examples for theoretical analysis and experimental verification. 1. For the servo planetary gear reducer (with reduction Rr=4), the theoretical transmission efficiencies are between 96.0% ~98.1% (80N-m, 200~1600rpm) and the experimental transmission efficiencies are between 93.8%~95.2%. There are 2.2%~3.0% errors between theoretical and experimental values. 2. For the 4.3KW 2-stage planetary gear reducer of electric elevator (with reduction Rr=20), the theoretical transmission efficiencies are between 97.5%~98% (400N-m, 300~1500rpm) and the experimental transmission efficiencies are between 95.1% ~96.1%. There are 2.0%~2.7% errors between theoretical and experimental values. 3. For the 4.3KW compound planetary gear reducer of electric elevator (with reduction Rr=20), the theoretical transmission efficiencies are between 96.3%~97.5% (400N-m, 300~1500rpm) and the experimental transmission efficiencies are between 92.1% ~94.5%. There are 2.8%~4.7% errors between theoretical and experimental values. In this thesis, five design cases are used to be the examples for theoretical analysis and experimental verification. The experimental values of transmission efficiencies of case II ~ case V are very close to theoretical values, showing the theorem in this thesis is trustworthy. However, experimental values of transmission efficiencies of case I (helical spur gear reducer with single gear pair) are lower 6.8%~9.2% than theoretical values. The reasons may be as follows: 1. The teeth number of pinion is too small (pinion NP=4 and gear NG=77). In order to increase the contact ratio of gear pair, the shift coefficient of pinion is increased and helical angle is also larger than traditional design. That makes larger contact friction losses. 2. The teeth number of pinion is too small (pinion NP=4), the strength of pinion is not enough that makes shaft of pinion deformed and result greater friction losses. 3. The transmission uses grease lubrication and grease fills the internal volume of gearbox about 35%~45%. When gearing, the grease is squeezed out and results large friction losses (low efficiency). Hence, this thesis also get conclusions: “Unless necessary, do not use the pinion with few teeth and do not use grease as the lubricant of gear transmission.”
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