A vehicle with two or more drive systems for propulsion is called a hybrid vehicle. The drive systems can drive the vehicle either together or independently. Typically, a Hybrid Electric Vehicle (HEV) has both electric motor and Internal Combustion Engine (ICE) for propulsion. Gasoline is used for ICE and battery power to supply the electric motor. The battery can be charged from ICE and during regenerative braking. In Hybrid Electric Vehicle , there is no provision to charge the battery from external supply.
A Plug-in Hybrid Electric Vehicle (PHEV) like a hybrid electric vehicle have both electric motor and an internal combustion engine. However, they differ from HEV by having larger battery and allowing the batteries to be charged by plugging in to the grid. This enables to run as an all-electric vehicle when battery power is available and as HEV when battery is low.
Hybrid drive train
In a hybrid vehicle, the drivetrain transmits the necessary power to the wheels. The drivetrain configuration determines the role of electric motor and the Internal combustion engine in the vehicle. Depending upon the configuration, the vehicle’s mechanical components work in conjunction with the electrical motor to operate the vehicle efficiently. The drivetrain affects the vehicle’s mechanical efficiency, fuel consumption, battery capacity, engine capacity, maintenance cost and cost of the vehicle.
There are different ways to combine the power from the electric motor and the engine. The two main configurations of PHEVs are
- Parallel configuration
- Series configuration
Both the internal combustion engine and the electric motor are connected to the wheels through mechanical coupling and both can drive the wheels directly.
Advantages:
- Smaller battery than the series configuration which can be recharged during regenerative braking.
- Best suited for highway driving
Disadvantages:
- Complex structure.
Vehicle with parallel hybrid structure :
- Chevrolet Malibu Hybrid, Honda Accord Hybrid
Only the electric motor is used to drive the wheels and internal combustion engine does not drive the wheels directly. The internal combustion engine drives an electric generator which is used to generate electricity for the motor. When the battery is fully charged, battery power is used to run the motor so that inefficient operation of engine is avoided. When the battery is depleted, IC engine is switched on to generate the power for the electric motor. The engine is typically smaller and the battery pack is more than the parallel configuration. Series hybrids are also referred to as extended-range electric vehicles (EREVs) or range-extended electric vehicles (REEVs).
Advantages:
- Simple configuration
- Suitable for city driving which has more start and stops.
- IC engines are smaller than the parallel configuration.
- Tailpipe emissions are lower than the conventional vehicles.
- Better fuel economy as ICE engine operates at its maximum efficiency and is independent of the load on the vehicle.
Disadvantages:
- Double conversion of power leads to reduced efficiency.
- Larger battery pack
- Expensive than parallel configuration.
Vehicle with series hybrid configuration
Chevrolet Volt, Honda Insight, Hyundai Ioniq
The IC engine and electric motor can provide power independently or in conjunction with one another. These vehicles incorporate power-split devices to decouple the power from one source to another. The vehicle can be operated in IC engine mode, electric mode, or combined mode in which both ICE and electric motor work together. Power distribution between the Internal Combustion Engine and motor is designed such that the engine can operate in its optimum operating range as much as possible. At lower speeds, it operates as a series hybrid so that efficiency is high.
Advantages
- Depending upon the requirement, vehicle can be operated in any of the three modes.
- Higher efficiency compared to series and parallel hybrid systems.
- Less fuel requirement compared to series and parallel hybrid systems.
Disadvantages
- Complex control.
- Higher cost compared to series and parallel hybrid systems.
Vehicle with series parallel hybrid structure
- Toyota Prius
- For short trips PHEV works as an all-electric vehicle and emits no tailpipe emissions.
- PHEVs use 30 to 60 % less fuel than the gasoline cars.
- The range limitation of all electric vehicle can be easily solved by a PHEV. When the battery runs out of power, internal combustion engine is used to drive the wheels. In the process of slowing down and braking, battery can be charged using regenerative power.
- As the size of the batteries in PHEV is smaller compared to an all-electric vehicle, the charging time of the battery is reduced.
- As most of the time PHEV runs as an all-electric car, the wear and tear on the engine is less resulting in lower maintenance cost than the conventional gasoline car.
Read more about electric vehicle basics
References
- www. afdc.energy.gov
Read Electric Vehicle 