CONTEMPORARY PLANETARY GEARBOXES AND THEIR CALCULATION

The increased demands for driver comfort and stringent pollution control measures have resulted in a revival of planetary gearboxes for road applications, due to their possibility to change the transmission ratio under load in synchronism with engine operation. Modern boxes provide as many transmission ratios as possible from the least possible number of simple component planetary gear trains (PGTs) by providing links between elements of multiple component PGTs. The application conditions decide to prioritize either the maximum number of transmission ratios, or ruggedness and reliability. Power circulation, hollow shafts, or complex planet carrier arrangements are avoided if possible. This paper deals with multispeed complex PGTs composed of at least two interconnected simple component PGTs controlled by brakes and clutches. Several variants of complex PGTs and the placement of brakes and clutches on external shafts of the gear trains are examined, and the transmission ratio functions derived. The kinematics of multi speed gear trains are obtained as combinations of two or more two-speed gear trains. An analysis of several contemporary gearbox layouts is provided together with the transmission ratio functions, together with an overview of the procedure for the calculation of creation of multi-speed gear trains is given.