Many developments of hybrid vehicles aim to reduce power of their electric propulsion chain, obviously for economic reasons, but not only. We can also get a better efficiency by reducing the energy transformations and a better safety by decreasing the electric voltage.
As described in a previous contest session, refer to: http://contest.techbriefs.com/2013/entries/transportation-and-automotive/3519, a series-parallel architecture with a dual train (two planetary gear systems) has this purpose. To illustrate, figure 1 compares the vehicle accelerations with a 10 KW dual electric chain to a vehicle with a 20 KW single electric chain. We almost get the same results.
Hybrid vehicles are frequently designed to run also in pure electric mode, but it requires higher electric power than in hybrid mode. We might experience a power shortage if power has been too much lowered. In a previous contest session, http://contest.techbriefs.com/2015/entries/sustainable-technologies/5453, figure 3, the OH segment is the characteristic in electric mode with a high gear ratio. Characteristic with a low gear ratio is also shown.
In the present innovation, the Generator is also able to work as a motor for helping the main electric Motor to propel the vehicle. This configuration is possible at two conditions: hybrid architecture should have two electric Machines (a Generator and a Motor) and we should be able to stop the Engine shaft for permitting the Generator power to go through the planetary gear system.
Many means can stop the Engine shaft: a brake, an actuated lock and even an engine braking… Presently, we propose an unidirectional wheel installed between the shaft and the body. The diagram of this architecture, (refer to: http://contest.techbriefs.com/2015/entries/automotive-transportation/5116), has been completed with the unidirectional wheel (12) on the Figure 2.
Specifically with the low gear ratio, the Generator rotation speed (working as a motor) is much higher than those of the Motor which usually rotates below its basic speed in electric mode. Consequently, the Generator is much more efficient to create a wheel torque which is amplified by the planetary gear mechanism. Consequently the electric Motor does not need to be huge.