Report and Opinion 2010;2(3) http://www.sciencepub.net/report reportopinion@gmail.com 1 Design and Simulation of a New Bevel Multi-Speed Gearbox for Automatic Gearboxes Majid Yaghoubi 1* , Seyed Saeid Mohtasebi 1 1. Department of Agricultural Machinery, Faculty of Engineering and Technology, University of Tehran, Karaj, Iran yaghoub@ut.ac.ir * , mohtaseb@ut.ac.ir Abstract: In this paper, a new mechanism was developed as a gearbox for power transmission between concentric shafts. With this approach, reduction ratios range from 10:1 to millions to one is possible for single-stage. This mechanism is very cheaper than planetary gears. The mechanism consists of one drive shaft and one driven shaft, conical gears which one of them is fixed and the others are driven. In this mechanism, with attention to the type of design, despite very small occupied space, by combination several ratios bevel gear can use as a gearbox. We first present the kinematic diagrams and then the equations of motion. Simulation results using Visual Nastran, Autodesk Inventor Dynamic, and COSMOS Motion software with three different input rotational speeds showed that this mechanism can have high reduction ratio. Finally, tension analysis of the mechanism using ANSYS workbench software showed that the highest tension occurred in the pinion gear No. 2. [Report and Opinion. 2010;2(3):1-7]. (ISSN: 1553-9873). Key words: Gears; Kinematic diagram; Power transmission; Reducer; Visual Nastran, In power transmission systems of the most farm and construction machineries, various types of mechanisms are used to reduce the input velocity to required value. Based on law of conservation of energy, by decreasing velocity, the transmission torque increases [Shirkhorshidian, 2004]. At present, the gears are mainly used in differential of automobiles (cramwheel), final drive of tractors and heavy machineries as reducer. Because they take up much space, they can not be used for high velocity reduction. Planetary gearboxes have lower occupied space and more reduction velocity than the others [Bennett, 1979; Hojjati, 2000; Makevet et al, 2001; Martin, 1969]. As we all know, in gears systems to have more torque ratio, gears radius must be chosen larger or the number of gears must be increased. Therefore, because it takes up too space and also because of using ring gears in planetary gearboxes, these mechanisms have much production cost (Figure 1) [Shirkhorshidian, 2004; Martin, 1969]. One of the other reducers is worm gear which has much more reduction velocity ratio. It is also used in power transmission of some helicopters. But because of its much depreciation, for increasing its efficiency, hydrostatic lubrication is commonly used (Figure 2) [Michael, 1987; Samuel, 1988; Samuel, 1975; Seth, 1986]. Another mechanism consists of a big sun gear and a ring gear which has high reduction ratio. But because of its sun gear off center, it produces slight pulsations in output [Oberto et al, 2000; Wright, 1993; Reimpel et al, 2002; Cantor, 2008]. Proposed mechanism consists of some conical gears that have smaller cost with respect to ring gears and it has high-ratio speed reduction in compact trains with concentric input and output shafts. Combining of some pinions with different ratios in the mechanism, it can be used as a multi-speed gear box. Figure 1. Steps of reducing velocity in a helicopter