How do the engines of electric and hybrid cars work?

How do engines of electric and hybrid cars work? Learn more about the engine of electric cars and the difference between full hybrid and plug-in hybrid drive technology.
18. June 2020

Advancement in its purest form – the electric car

Whether it is an internal combustion engine, an electric motor, or a combination of the two as a hybrid engine, the goal is to generate mechanical work that is transferred to the drive shaft to set the wheels in motion. In an internal combustion engine, chemical energy (the fuel) is converted into mechanical work using combustion, while in an electric car, the chemical energy stored in the battery is converted into mechanical work.

Hybrid vehicles with an internal combustion engine and an electric motor can have both engines acting simultaneously on the drive axle and thereby add up the kinetic energy generated. Alternatively, the combustion engine and electric motor are wired in series so that only the electric motor acts on the drive axle. The common types of drives for electric and hybrid vehicles will be explained in the following.

No harmful exhaust gases, no particulate matter, no engine noise, and no waste of fossil energy; the electric car will even make an environmentalist’s heart beat faster. If the necessary electricity is produced in a climate-neutral way, it will solve one of the major problems of recent history and allow mobility with virtually no harm to the environment.

But how exactly can a battery move a car?
The battery stores the energy required for movement, which is supplied externally via charging stations, such as a hesotec eSat series charging station.

The battery supplies the electric motor with electricity depending on the power currently required, and this is regulated by the power electronics. If an electric car moves at walking pace, it requires less energy than on the highway.

The electric motor is equipped with a stationary stator, which generates a constant magnetic field using the direct current from the battery. The counterpart to the stator is the rotatable rotor with its rotor poles, which rotates the stator like a windmill when it is supplied with alternating voltage.

A rotor pole is alternately a positive pole at one moment and a negative pole at the next, and is alternately repelled and attracted by the constant magnetic field of the stator. Thus, a rotor pole is alternately a positive pole, and at the next moment, a negative pole and wants to alternately repel and tighten from the constant magnetic field of the stator. This generates the kinetic energy that is transferred to the drive shaft of the electric car and sets it in motion.

The combination of combustion engine and electric motor – the hybrid car

The word “hybrid” is a synonym for “composed of different elements” or “of two different origins.” In the case of the hybrid car, these are the combustion engine and the electric motor, which are entirely different from a technical point of view but are combined to form one drive component. Both engine types have their strengths and weaknesses. The aim of this combination is to use the best of both to achieve higher efficiency in order to increase the range of the hybrid car and conserve fossil energy.

The combustion engine and electric motor can be combined in different ways, and there are hybrid cars with different hybrid concepts available on the market.

The full hybrid – internal combustion engine and electric motor without an external charging option

The key feature of the full hybrid car is that the battery does not have to be charged externally via a charging station but is automatically recharged while driving by excess energy, e.g., from braking or via a generator.

Depending on the traffic situation, it is possible to drive with an internal combustion engine, an electric motor, or both at the same time. The car is powered by the electric motor alone at low speeds, and when the vehicle is accelerating, the electric motor assists the internal combustion engine so that it consumes less fuel. The most energy-efficient operating mode is automatically determined and activated by the on-board electronics in order to drive as economically as possible at all times.

Full hybrid cars house a relatively small battery, and the range in pure electric drive is limited to a few kilometers.

The plug-in hybrid – more range due to larger battery and external charging options

The battery of the plug-in hybrid car is larger than that of the full hybrid, and the range in pure electric mode is increased to around 50 km. The battery can also be charged via a charging station.

The serial hybrid – with range extender for a greater range

Here, the combustion engine serves only as an auxiliary power unit for the electric motor, which is also referred to as a range extender. The drive is always provided by the electric motor, but it receives its energy from the battery, the generator, or both. The combustion engine transmits the energy to the electric motor via a generator.

Combustion engines are relatively small in size and are operated at the most ideal speed possible in order to fully exploit the savings potential. For example, if a lot of power is required during acceleration, the speed of the combustion engine increases, and additional energy is supplied from the battery.

One disadvantage of the serial hybrid is the multiple conversion from one form of energy to another. Chemical energy in the combustion engine is converted into thermal energy and then into mechanical energy to power the generator. Its energy is supplied to the electric motor to ultimately generate the kinetic energy to move the vehicle. Some thermal and mechanical energy is always lost with each of these energy transformations.

The parallel hybrid – smaller engines in combined operation

Contrary to the serial hybrid—in which only the electric motor acts on the drive and the combustion engine solely serves as a generator—the electric motor and the combustion engine are connected to the drive axle in the parallel hybrid. Both motors can serve as the drive either individually or together. Since the power of both engines is combined, the engines can be sized smaller to save fuel.

The parallel hybrid is further divided into the following drive types:

  • Micro hybrid
  • Mild hybrid
  • Full hybrid

Technically speaking, the micro hybrid is not a true hybrid because it only uses electrical energy to start the hybrid car. Compared to the micro hybrid, the mild hybrid has a larger battery. However, it cannot be used for pure electric driving either, and the mild hybrid is only used for support.


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