HYBRID ELECTRIC VEHICLES

Hybrid drive is a name that means starting a vehicle using several different energy sources. The advantages of the hybrid drive are low noise, low exhaust emissions and a high degree of efficiency. The main disadvantages are: high price of the vehicle, higher weight of the vehicle compared to the same with classic drives and smaller luggage, ie cargo space. Hybrid electric vehicles (HEVs) are low-emission vehicles (LEVs). They are based on two energy sources - the energy conversion unit (SUS engine or fuel cell) and the energy storage unit (batteries or ultracapacitors). The complete drive system consists of: heat engine, electric generator, electric motor, energy converter and rechargeable batteries. The meaning of HEV lies in the fact that these vehicles do not have problems with the radius of movement because they use chemical fuel to drive the heat engine and at the same time are more environmentally friendly and efficient than conventional vehicles because they use the benefits of electric propulsion. Plug-in hybrid electric vehicles (PHEVs) use batteries that are charged by connecting the plug to an external power source (a normal wall-mounted electrical outlet). Other components are the same as for other electric drives. Today, PHEVs are mostly used as passenger cars, but there are also commercial vehicles and vans, utility trucks, buses, motorcycles, scooters and military vehicles. Figure 1 shows the distribution of characteristic aggregates in PHEV. The paper deals with hybrid electric vehicles with an emphasis on the propulsion composition of these vehicles and it can be: serial, parallel and serial-parallel. A vehicle with serial hybrid drive in city driving, or when driving at a constant speed, is powered by an electric motor, which is supplied with electricity from batteries. During this time, the SUS motor starts the generator, which supplies electricity to the electric motor, while the batteries are charged with excess electricity. Therefore, the traction torque of the drive wheels is obtained from the electric motor and in this variant the SUS motor is not active (its clutch is switched off). In parallel hybrid drive, torque is provided by either a SUS motor or an electric motor. The SUS engine will also run a generator that supplies electricity to the electric motor, and the batteries are charged with excess. In the event of a higher load or when driving a longer distance, the parallel hybrid drive means that the traction torque will be given by the SUS engine. Then the batteries are recharged via the generator, and also during braking, when the electricity is obtained from the inertial energy of the vehicle. The paper also presents the characteristics of HEV as well as the development of these vehicles at individual manufacturers