Abstract
Hydrogen-based energy will replace fossil fuels in the future, but it will take long time. Needless to say, better fuel economy and reducing the generation of CO2 emissions is one of the most important goals in the automotive industry. Any improvement in the functional part of an automobile should be made with this goal in mind.
Hybrid systems that combine an internal-combustion engine and electric motor are one of the promising solutions to minimizing fuel consumption. The hybrid transmission should work as the key control element that manages two power sources and regenerative braking. There are two kinds of major hybrid systems in the market at this moment. The first one is called a series-parallel hybrid system that features two electric motors, and the second one is called a parallel hybrid system with only one electric motor. Both systems have their own characteristics. The electric motor of a parallel hybrid is smaller than that of a series-parallel hybrid due to the ratio coverage of the mechanical transmission. And, the concept of minimization of electric systems reveals the lower costs that help make hybrid vehicles more popular.
In this paper, a new concept of a hybrid system that combines an infinitely variable transmission (IVT) with an electric motor is discussed. The traction drive toroidal variator has been manufactured since 1999, and its performance in power transmission efficiency has been improved drastically. One of the features of a toroidal variator is its ability to provide adequate torque control. The control of transmitting torque is a key technology of an IVT. The authors have studied an IVT with a toroidal variator recently, and found that the IVT is suitable for the parallel hybrid transmission. The hybrid IVT can potentially improve fuel economy in comparison with a conventional parallel hybrid system.
The IVT has an extremely large torque ratio around zero speed. This characteristic helps with minimization of an electric motor design. Also, the speed range of regenerative braking is expanded due to its large speed ratio. These features of the IVT help automakers achieved both lower design costs and improve fuel economy. Design concept, performance, and some simulation results such as fuel economy of the hybrid toroidal IVT are described below.
Keywords: hybrid, toroidal, traction drive, IVT, fuel economy