What is a hybrid car? How does it work?

what is a hybrid car

Electric cars are those vehicles use electricity as the energy source to propel the vehicle. A conventional car uses energy from the combustion of gasoline to move from one place to another. What is a hybrid car?

A hybrid car use more than one source of energy to propel. For example, a combination of an IC engine and electric motor. A hybrid electric car uses one or more other energy sources along with electricity to propel the vehicle.

Would you like to read a quick guide on how an electric vehicle (battery-electric car, hybrid electric car, and plug-in hybrid electric car) work?

What is a hybrid car?

Hybrid electric vehicle as we mentioned in the above section, operates using more than one energy sources. The common configuration of a hybrid car is electric motor and internal combustion engine. Since one of the sources of energy is electricity, these hybrids are also called hybrid electric cars.

Types of Hybrid Cars and How do they work?

First of all, let’s classify HEV based on their power train configuration. Hybrid electric vehicles are classified into three

#1 Parallel Hybrid Electric Car

In a parallel hybrid electric car, both the IC engine and Electric motor can run the vehicle simultaneously. They are connected to the wheels of the vehicle through a mechanical coupling. Torque from both ICE and electric machine get added and drives the vehicle.

Parallel Hybrid Electric Vehicle
Block diagram of Parallel Hybrid Electric Vehicle

If the car runs in torque-assist mode, electric machine supplements ICE whenever torque demand increases. The electric motor runs the vehicle at staring and slow speed since ICE efficiency is low at low speeds.

VCU calculates and finds the optimal operation and how the torque should be split between ICE and electric motor. During braking, the electric machine generates electricity and stores in battery – regenerative braking.

Regenerative braking is one of the methods to get the battery of HEV charged. VCU decides if the IC engine run the vehicle and generate electricity from electric machine simultaneously to charge the battery analyzing the state of charge of the battery, efficiency at operating points of ICE, etc.

Point to note: Hybrid Electric Cars can not be plugged into a power socket to charge the battery. They can charge the battery either from regenerative braking or the energy generated from electric machine prime moved by ICE.

A hybrid electric vehicle capable of getting charged from power socket is called plug-in hybrid electric vehicle.

If a single clutch is used in a hybrid car, both ICE and EM have to run together even if one of them doesn’t supply energy to the wheels.

When the car driver presses actuator pedal to accelerate the car (in effect torque is requested), Vehicle Control Unit (VCU) calculates how the requested torque should split between IC engine and electric motor.

Sometimes ICE drives the electric machine to generate electricity and charge the battery.

#2 Series Hybrid Electric Car

A series hybrid electric car works on an electric machine. And the ICE generates electricity by driving a generator coupled to it. Finally, only electric machine drives the vehicle. ICE does not have a direct connection to the wheel of the vehicle.

Series Hybrid Electric Vehicle
Block diagram of Series Hybrid Electric Vehicle

Since series hybrid electric vehicle does not have a connection between ICE and wheels, ICE can be run at a speed of maximum efficiency.

The motor that drives electric vehicle should be capable of solely driving the vehicle. It’s an assisted mode of the power train.

#3 Power-split or Series/Parallel Hybrid Electric Car

A series/parallel hybrid has advantages of both series and parallel hybrid electric vehicles. The power train of power-split hybrid incorporates the options to run the vehicle either by electric machine or ICE.

In oppose to series hybrid where only electric machine drives the wheel, the engine can drive the wheels if necessary in power-split hybrids.

What is a hybrid car
Block diagram of Series/Parallel Hybrid Electric Vehicle

Hybrid Electric vehicles are classified based on degree of hybridization

#1 Micro Hybrid car

Micro hybrids are strictly not a hybrid electric vehicle. They don’t have electric power train. Fuel economy of micro hybrids is a little bit high due to the techniques such as regenerative braking, and start-stop feature.

#2 Mild Hybrid Car

A Hybrid Electric Vehicle in which the motor and battery alone is not capable of drive the vehicle. Electric motor supports the internal combustion engine in the vehicle

#3 Strong Hybrid Car

A full hybrid or strong hybrid electric vehicle can run on just the engine, the batteries of a combination. A large high capacity battery provides battery-only operation for strong hybrid (reference)

Advantages and disadvantages of hybrid vehicles

Advantages specific to each category of hybrid cars are described in the above section. Now let’s consolidate the advantages and disadvantages of hybrid cars in a generic way.

Advantages of hybrid cars

Extended range of operation (fuel-efficient)

Hybrid cars travel more kilometers than conventional vehicle per unit fuel. Toyota says that its hybrid car travels 100km using 3 liters of petrol.

Environmental friendly

Emission from hybrid electric vehicles is less compared to conventional vehicles. HEVs travel more distance than ICE vehicles.

So the emission per kilometer is less. Internal combustion engine runs at maximum efficiency region most of the time in a hybrid electric vehicle to reduce the overall fuel consumption. Are Electric Vehicles really environmental friendly?

Economical benefits

The government provides tax benefits for hybrid car owners and other incentives to promote low emission vehicle. If it is a battery-electric vehicle then the initial cost is also subsidized. Then the important benefit comes – it’s the improved fuel economy.

Disadvantages of hybrid cars

Hybrid electric cars have a few disadvantages also.

High initial cost

The initial cost of hybrid cars is a little higher than conventional ICE vehicles. High voltage battery pack, electric motor, controller, etc. add additional cost to the vehicle.

Maintenance is more

A conventional vehicle has only an internal combustion engine and related accessories in the power train. But a hybrid car has electric motor, battery, and controllers in addition to the ICE. As a result, the total maintenance cost of HEV increases. Battery replacement is also a disadvantage of hybrid cars.

Risk of high voltage battery

Security has to be provided in a hybrid car to prevent fire hazard due to the high voltage battery. Are electric vehicles really safe in accidents?


We have seen what a hybrid car is. Classification of hybrid cars, their working principle, etc. are briefly discussed in the article. Did you enjoy reading? Have you ever driven a hybrid car? Feel free to comment 🙂

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