Week 2 Session 7
Answer :
The Hybrid Electric Vehicle (HEV) architecture can be classified into three types as :
- Series type
- Parallel type
- Series-Parallel (or) Power split type
Series type :
In series type, the power required to propel the vehicle is provided solely by the electric motor. Internal Combustion Engine (ICE) drives an electric generator that delivers power to the battery through inverter.
Advantages :
- The need for a complicated multi-speed transmission and clutch is eliminated in series hybrids since only the electric motor directly drives the transmission, which may have one gear.
- Gasoline engines in series hybrids tend to be smaller and more efficient since they do not directly power the vehicle and are not subject to the highly variable power demands of stop-and-go driving.
- These design features make series hybrids the ideal car for urban and suburban driving conditions.
- The smaller, more efficient engine and greater use of electric power helps reduce harmful gas emissions in series hybrids.
Drawbacks :
- The series hybrid requires a larger, more complicated battery and motor to meet its power needs.
- The larger battery and motor and the addition of a generator often makes the series hybrid more costly than a parallel hybrid.
- Series hybrids are also not as efficient as parallel hybrids for highway driving since the engine is not directly connected to the wheels.
Parallel type :
In parallel type, the Internal Combustion Engine (ICE) and Electric motor are configured in parallel with a mechanical coupling that blends the torque coming from two sources. It is more efficient than series type and hence it is used in commercial applications. Example : Honda Civic IMA
Advantages :
- Overall efficiency is high over long distances.
- Less expensive than series hybrid type.
Drawbacks :
- It has a complex design.
- IC Engine is not decoupled with the wheels and thus it cannot be charged at standstill.
- It doesn’t operate in a narrow range of RPM and so the efficiency is low at low rotation speed.
Power split type :
In series-parallel type, the power split device allocates the power from IC engine to front wheels through driveshaft and electric generator depending on driving condition. Here both the ICE and electric motor will be working in parallel mode. Example : Toyota Prius, Chevrolet Volt.
Advantages :
- Eliminates the need for a complicated multi-speed transmission and clutch by using fixed step gearbox
- The smaller, more efficient engine and greater use of electric power helps reduce harmful gas emissions.
- Better efficiency than series hybrid and parallel hybrid.
Drawbacks :
- More expensive than series hybrid and parallel hybrid.
- Complicated in design
Thus based on the requirement, the architecture can be determined.