HEV (Hybrid Electric Vehicle)
A hybrid electric vehicle (HEV) is a car that can independently run on fossil fuels and electric power. HEV vehicles are typically equipped with only a smaller traction battery and a less powerful electric motor. However, the electric motor’s performance is sufficient for the vehicle to run solely on electric power.
The abbreviation HEV (Hybrid Electric Vehicle) refers to a hybrid electric vehicle that is equipped with both a combustion engine and an electric motor. It thus meets the definition of a hybrid vehicle, as it uses two types of energy for propulsion. An HEV vehicle has a very similar technical foundation to the better-known plug-in hybrid electric vehicle, or PHEV. Simply put, both HEV and PHEV vehicles allow driving with the combustion engine alone, with the electric motor alone, or a combination of both. The main difference between an HEV and a PHEV lies in the capacity of the traction battery and the possibilities of recharging it.
Generally speaking, both HEV and PHEV hybrid-electric cars combine driving with a combustion engine and an electric motor to achieve the most efficient operation possible. What characterizes HEV vehicles is that although they use a combination of a combustion engine and an electric motor, they are not capable of recharging the traction battery directly from the electrical grid. An HEV must produce all its own electric energy. This is what distinguishes an HEV from the technically very similar PHEV, which can be charged from an outlet.
HEV vehicles recharge their batteries mainly through regenerative braking. During this process, kinetic energy is converted into electrical energy, which is then stored in the traction battery. The energy obtained this way is usually not very large, so an HEV requires only a smaller traction battery with lower capacity. Lower capacity, however, also means a shorter range in purely electric mode, usually up to 10 km. On the other hand, this smaller battery is cheaper and lighter.
Series HEVAllow me a small digression for completeness. Some HEV vehicles can recharge the traction battery using the combustion engine, usually in situations where the combustion engine is needed, but its full power is not being utilized. An extreme case of battery recharging using the engine is the so-called series hybrid. A Series HEV is a type of hybrid vehicle where the combustion engine does not directly drive the wheels but instead generates electrical energy, which powers the electric motor, and the electric motor then directly drives the wheels. |
Principle of HEV function:
From an energy source perspective, an HEV represents a transitional state between a vehicle with a conventional internal combustion engine (ICEV) and a battery electric vehicle (BEV). HEV contains both types of powertrains. HEV-type hybrid vehicles use an electric motor with a traction battery to increase efficiency. Higher efficiency leads to lower fuel consumption, which in turn reduces exhaust gas emissions.
During low-demand urban driving, the electric motor can advantageously provide zero-emission movement of the vehicle, while the combustion engine can demonstrate its benefits at higher travel speeds or on longer trips. The hybrid powertrain thus utilizes the advantages of both.
The vast majority of hybrid electric vehicles use a gasoline engine + electric motor combination. In HEV vehicles, the primary energy source is the fuel tank, and the secondary source is the battery.
The typical combustion engine of an HEV hybrid electric vehicle is a gasoline engine because it runs more smoothly with fewer vibrations, warms up faster, and produces fewer nitrogen oxides (NOx). The combustion engine in an HEV typically uses a combination of different combustion cycles (usually Atkinson or Miller) to achieve the lowest possible fuel consumption. The drawbacks of the Atkinson cycle (lower power and reduced torque) are compensated by the electric portion of the powertrain.
The typical traction battery of an HEV hybrid vehicle operates at a lower voltage than a typical PHEV battery, usually in the range of 200–300 V. The traction battery of an HEV is also smaller with a lower capacity, around 5–7 Ah. The battery of HEV passenger vehicles is much lighter, weighing around 35–45 kg. Due to these characteristics of the traction battery, the shorter electric-only range is typically just a few kilometers.
HEV and PHEV comparison
Advantages of HEV vehicles:
- lower fuel consumption and the related reduction in CO2 emissions compared to similarly sized and powerful vehicles equipped only with a combustion engine
- the possibility of regenerative braking, which not only reduces consumption but also saves the brakes
- better efficiency and more eco-friendly operation in the city
- wider use of electric drivetrain technology compared to MHEV vehicles
- cheaper than PHEV vehicles because they have smaller batteries
Disadvantages of HEV vehicles:
- shorter electric-only range than a structurally very similar PHEV
- limited ability to recharge the battery, as it cannot be recharged directly from the electric grid
- higher purchase price compared to conventional combustion engine vehicles
