4.1 Matching the electric drive and ICE

One of the most common matching elements used in hybrid electric passenger vehicles is the epicyclic, or planetary, gear set. Continuously variable transmissions of the compression belt and toroidal variator variety are gaining popularity in compact vehicles and passenger vans because of seamless transitions in ratio. For larger CVTs the issues of torque rating and efficiency at high ratio continue to be developmental areas.

Figure 4.1 shows the epicyclic gear in schematic form. This is a three port mechanical component used as a speed summing device. Most designs rely on a dual input and single output where one input source is the ICE and the second input comes from an electric M/G. Epicyclic gear ports may be defined as input or output according to the convection illustrated in Table 4.1. The epicyclic basic ratio, k = R _ring/ R _sun where R _x is the radius of ring and sun gears (can also be defined in terms of number of gear teeth).

Figure 4.1: Schematic of epicyclic gear set