Tech InDepth: What are Hybrid Electric Vehicles (HEVs) and how do they work?

Electric vehicles have been increasingly getting popular in India over the past year. Other than the multiple consumer-oriented two wheelers and four wheelers that have launched lately, we have also seen many public transport vehicles like city buses go electric in cities like Mumbai and Delhi.
However, while the electric revolution continues, many issues that stop consumers from getting into electric vehicles or EVs continue to ex. One of these is the lack of a widespread charging infrastructure, which potentially handicaps EV users from taking longer trips to more remote areas. To deal with these issues, brands have been coming up with hybrid electric vehicles (HEVs) – cars that club the benefits of both petrol engines and electric motors, while aiming to negate the cons of both.
In today’s edition of Tech InDepth, we’ll be looking at how exactly these hybrid engines function, how they’re different from conventional electric vehicles as well as other details you should know about if you’re looking at purchasing one of these.
What are Hybrid vehicles?
To understand hybrid vehicles or HEVs, let’s have a quick recap of how petrol and electric vehicles work. Petrol vehicles work on petrol engines and use combustion to power the vehicle. Here, controlled burning of fuel inside the car releases energy in the form of both heat and motion, the latter of which is converted to the spinning of the wheels, via a complex mechanism of pons, shafts, gears and axles.
In an electric car on the other hand, there is no engine and there are no gears. The power comes from a rechargeable battery, and the vehicle moves with the help of an electric motor. All the energy involved here is electric, which also means there aren’t a lot of moving parts that require regular servicing. However, the battery itself does gradually lose its ability to retain the same amount of charge over time. Also, the range of most EVs available today in India is also limited.
In hybrid vehicles, there are multiple types of mechanisms that power cars. The two most common ones are series-hybrid and parallel hybrid.
Series Hybrid cars
As the name suggests, these cars use an electric motor, connected with a petrol engine in series. In such mechanisms, the combustion engine has no contact with the wheels of the vehicle, except via the electric motor. The working here relies on the petrol engine burning fuel and creating energy, but instead of creating kinetic and heat energy, a generator converts the energy from the petrol engine directly to electricity, which powers the electric motor, giving power to the car.

Most series hybrid vehicles, while they rely on an electric motor, cannot be charged externally like conventional electric cars. They must be fueled, as only the petrol engine can create the power to generate electricity for the electric motor.
These vehicles are great for regions like India, where the infrastructure of electric charging remains scarce. Users still rely on fuel, but end up getting much better efficiency as the converted electric energy is more efficient than the combustion powering the vehicle directly. Additionally, mechanisms are also in place to recharge the electric motor every time time you brake, resulting in further savings.
Parallel Hybrid cars
With parallel hybrid cars, there is a common transmission in the vehicle that can pull power from both the electric motor and the fuel engine, both of which are connected in parallel. Such cars can be completely automatic, manual, or even CVT (Continuous Variable Transmission) based on the make and the mode a user drives in.
In such a mechanism, the electric motor itself can only be recharged from regenerative braking, while the fuel you put in the car will power the engine. Since both the motor and the engine can power the wheels, users have more control for when they want to drive efficiently versus when they want more responsive, sporty driving at the cost of fuel efficiency. As a result, wheel power keeps switching between the engine and the motor based on driving conditions.
Parallel hybrid designs are used a number of brands like Toyota, Hyundai, Ford, Honda, etc. They are also more popular over series hybrid cars majorly for one reason – better performance.
Series Parallel Hybrid cars
While they may not be as common, cars that implement both a series and a parallel hybrid architecture in the same vehicle also ex. These cars, like the Toyota Prius, combine the benefits of a series connection and a hybrid connection.
HEVs like the Honda City eHEV combine the workings of both series and parallel hybrid architecture. (Image Source: Honda)
The wheels can now be powered both the electric motor and the fuel engine, but power delivery is now in the hands of the user who can choose to power the vehicle completely the electric motor (series) or the engine (parallel). This works via a power switch that can choose where the wheels get their power from.
Which Hybrid cars are available in India?
While there are not a lot of Hybrid vehicles to choose from in India, manufacturers like Toyota and Honda have already entered the segment with cars like the Toyota Urban Cruiser Hyryder and the Honda City eHEV. Meanwhile, you also have options from brands like Maruti Suzuki, MG Hector and more expensive options from brands like Lexus and Porsche.