Week 2 Session 7

The HEV's architecture has been classified into five different categories, which are mild/micro, parallel, series, power split, combined series-parallel hybrids.

1.mild/micro

2.Series HEV

3.Parallel HEV

4.Series - parallel HEV

5.power split HEV

1 MILD/MICRO HEV

Advantages to a mild-hybrid car:

As familiar as any conventional internal combustion engine car

Typically offer improved efficiency and emissions over equivalent petrol/diesel cars

No need to worry about charging them

Disadvantages to a mild-hybrid car:

Cannot be driven on electricity alone

No grants available unlike EVs

Don’t offer vast improvements to efficiency in the way ‘full’ hybrids do

2.SERIES-HEV

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.

Disadvantages

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. Plug-in hybrid models are available in both series and parallel that allow for electric-only operation and zero tailpipe emissions on shorter distance trips. The plug-in feature, however, also adds to the cost

Series HEV

Series drivetrains are the simplest hybrid configuration. In a series hybrid, the electric motor is the only means of providing power to the wheels. The motor receives electric power from either the battery pack or from a generator run by a gasoline engine. A computer determines how much of the power comes from the battery or the engine/generator. Both the engine/generator and the use of regenerative braking recharge the battery pack.

Series hybrids perform at their best during stop-and-go traffic, where gasoline and diesel engines are inefficient. The vehicle’s computer can opt to power the motor with the battery pack only, saving the engine for situations where it’s more efficient.

The engine is typically smaller in a series drivetrain because it only has to meet certain power demands; the battery pack is generally more powerful than the one in parallel hybrids in order to provide the remaining power needs. This larger battery and motor, along with the generator, add to the vehicle’s cost, making series hybrids more expensive than parallel hybrids.

3.Parallel HEV

In vehicles with parallel hybrid drivetrains, the engine and electric motor work in tandem to generate the power that drives the wheels. Parallel hybrids tend to use a smaller battery pack than series drivetrains, relying on regenerative braking to keep it recharged. When power demands are low, parallel hybrids also utilize the motor as a generator for supplemental recharging, much like an alternator in conventional cars.

Since the engine is connected directly to the wheels in parallel drivetrains, the inefficiency of converting mechanical power to electricity and back is eliminated, increasing the efficiency of these hybrids on the highway. This reduces, but does not eliminate, the efficiency benefits of having an electric motor and battery in stop-and-go traffic.

Series/parallel HEV

Series/parallel drivetrains merge the advantages and complications of the parallel and series drivetrains. By combining the two designs, the engine can both drive the wheels directly (as in the parallel drivetrain), and be effectively disconnected, with only the electric motor providing power (as in the series drivetrain). The Toyota Prius helped make series/parallel drivetrains a popular design.

With gas-only and electric-only options, the engine operates at near optimum efficiency more often. At lower speeds it operates more as a series vehicle, while at high speeds, where the series drivetrain is less efficient, the engine takes over and energy loss is minimized.

This system incurs higher costs than a pure parallel hybrid since it requires a generator, a larger battery pack, and more computing power to control the dual system. Yet its efficiencies mean that the series/parallel drivetrain can perform better—and use less fuel—than either the series or parallel systems alone