What do I have to expect if I choose a hybrid car? (Parallel hybrid)


Photo by Leonid Mamchenkov

After the posts about the CNG and LPG engines, let’s focus on the hybrid cars and their advantages.

Hybrid vehicles use multiple traction energy generation systems (they normally combine a thermal and an electric power unit), combined with a system to recover energy during slowing down and braking.

Hybrid cars can be classified into three types:

    Thermal engine and electric motor both contribute to the traction.
    The electric motor is the only one connected to the wheels while the heat engine has the function of charging.
    The car can operate separately in both parallel and in series mode.


The parallel hybrid consists of a thermal engine (usually petrol or diesel) and an electric one.

The electric one acts in the starting phase and in low speed operations (parking, garage movement, etc.); after the start, the electric engine helps the thermal one during the acceleration to reduce consumption and emissions.

In fact, the electric motor has high torque (performance) at low revs, so it works when the efficiency of the thermal engine is low and recovers energy by recharging the batteries in slowing down and braking phases.

For optimal energy distribution between the thermal and electric propeller, the vehicle must be equipped with an automatic or robotised transmission.

This strategy helps to improve consumptions and emissions, this is due to the electric engine which helps the thermic one during the worst performances and recovers energy during the acceleration, recharging the batteries.


Photo by vernieman

A typical operating profile of a hybrid car is:

  1. always starting in electric;
  2. connection for the traction of the thermal engine starting from about 20km/h;
  3. from the connection of the thermal engine, the electric motor provides torque in acceleration and acts as a slowing brake.

Of course, more sophisticated operating strategies are possible, implemented by control systems, which, for each operating condition, split the effort between the two motors according to an optimization criterion.

At this point it is necessary to remember that the architectures of a parallel hybrid can be configured, mainly, in two options:

  1. thermal and electric motor acting on a single axis, normally the front one. (Pict. 1)
  2. thermal engine that acts on the front axle, while electric one acts on the rear axle. (Pict. 2)

Ibrido Parallelo Figura 1

Pict. 1

(ndr: Click on the picture to enlarge it)

Ibrido Figura 2

Pict. 2

(ndr: Click on the picture to enlarge it)

(In both layouts, arrows represent hybrid energy flows).

As can shown in the diagrams, parallel hybrid traction requires many additional components compared to a traditional car. Mainly they are:

  1. Traction batteries
  2. Inverter
  3. DC/DC (if not integrated in the inverter)
  4. Electronics for power and signal
  5. Power and signal wiring
  6. Electric depressor for power brakes
  7. Electric power steering pump (if required)
  8. Dialogue box with the thermal traction part
  9. Electric motor cooling and traction electronics system
  10. Instrument indicating the charge status of the traction batteries
  11. Electric/hybrid selector
  12. Mains battery charging socket
  13. Compressor of the electric conditioner
  14. Electric interior heater in the Plug-in solution


Given that the car always starts in electric, the thermal engine is turned on when the 15-18 km / h is reached; at about 22-25km / h, that engine connects to the traction.

The operating modes of a parallel hybrid car depend on the amount of energy of the traction batteries:

  1. Parallel hybrid
    The energy of the traction batteries is around 1 kWh, so normal electric-only circulation is not possible and the car always runs hybrid (Toyota Prius).
  2. Hybrid Plug-in
    The energy of the batteries makes it possible to carry out long journeys in pure electric (VW Tiguan GTE Hybrid, Audi Q7, Hyundai Ioniq, BMW 225xe and Mini Countryman E all4)
    The autonomy will depend on the energy that traction batteries can provide.

Photo by mariordo59

Hybrid Pulg-in

Recharging batteries in the Plug-in hybrid can be done:

  1. directly from the electricity grid, both domestic and public;
  2. using the heat engine which, under certain conditions, recharges them.

In simple words, the difference between hybrid cars and plug-in hybrid cars is that the second one, to recharge, can ALSO use a power outlet.

When the energy stored in the traction batteries exceeds 5 kWh two modes of operation are possible: pure electric and hybrid, the choice of which can be made through the selector.

By selecting the electric mode the car will only work in electric.
Indicatively with 5 kWh, a small car, in a purely urban circulation reaches 30 km of autonomy.


Photo by mariordo59


The Plug-in hybrid cars, reaching 50 km of autonomy in electric mode, will have the advantages of image because the new legislation, on emissions and consumption tests, benefits them a lot.

In fact, the NEDC homologation cycle is divided into two steps with this method:

  1. The first cycle can be run entirely in pure electric (CO2 = 0 g / km);
  2. The second one is performed in hybrid operation but with an important electric intervention (CO2 lower than 100g / km);
  3. Battery charging cannot be performed between the two cycles.

Since the CO2 approval value is the sum of the one produced in the two cycles, these Plug-in hybrids will SURELY deliver less than 50g / km of CO2.

All the plug-in hybrid cars in the market showing less than 50g / km of CO2 are so approved; consequently these cars will declare a consumption of about 1.8l /100km.

In this way, the average emissions of cars, sold by single auto maker, will certainly be in line with the new regulations of 2020, much more restrictive in terms of CO2 emissions.


Photo by Mike Weston


  1. In the city traffic consumption and emissions are drastically reduced
  2. The heat engine of the car is off during stops at traffic lights or proceeding to queue at speeds below 15km/h
  3. In the event of a fault, to any component of the electric traction, the car will work only with the heat engine, but with reduced performance, to allow the driver to reach the authorized service centre.


  1. The weight of the car increases considerably (typically 150/200 kg)
  2. On highway (or extra-urban high-speed) consumption and emissions are higher than a similar non-hybrid vehicle
  3. It is difficult to establish in advance the real savings, because it heavily depends on the conditions of use and the engine control strategy implemented by the manufacturers
  4. The life of traction batteries is limited
  5. The cost of the car is higher than the same model with a thermal engine


My personal opinion is that to have tangible benefits, the parallel hybrid should be predominantly used for urban routes or at most urban extra ones; the cars that most benefit from this engine are those of segments A and B.

Therefore, the most performing and heavy cars, in hybrid version, have overall consumption and emissions worse than the thermal only version of the same car.

Their development, and the subsequent commercialization of hybrid cars, is determined by the fact that this solution facilitates the approval with the most restrictive parameters that will come into force in the coming years.


  1. What do I have to expect if I choose a CNG car?
  2. What do I have to expect if I choose a LPG car?
  3. What do I have to expect if I choose a hybrid car? (Parallel hybrid)
  4. What do I have to expect if I choose a hybrid car? (Hybrid series)
  5. What do I have to expect if I choose a hybrid car? (Parallel/series)
  6. What do I have to expect if I choose an electric car?
  7. What do I have to expect if I choose a hydrogen-powered car?

Translated by Federica Izzo

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