• Preface
  • Hybrid forms
  • Micro hybrid
  • Mild Hybrid
  • Serial Hybrid Drive
  • Parallel Hybrid Drive
  • Plug-in hybrid
  • Energy recovery
  • System overview Toyota Prius
  • System overview Mitsubishi Outlander
  • Transmission of a hybrid vehicle

When fossil fuels are burned, carbon dioxide (CO2) is released. This CO2 accumulates in the atmosphere. When the sunlight falls on the earth, the heat radiation due to the CO2 accumulation can no longer escape, causing the 'greenhouse effect'. 120g CO2/km corresponds to:

  • 5,2 l petrol / 100 km
  • 4,5 l diesel / 100 km
  • 4,4 kg natural gas / 100 km
  • 1,0 kg hydrogen / 100 km
  • 20 kWh of electricity / 100 km

With the hybrid technology, the CO2 reduction (emissions) is reduced. Manufacturers are currently busy developing more and more techniques to realize an energy transition from CO2-neutral driving.

Hybrid forms:
Vehicles with hybrid drive use both the combustion engine and an electric motor. The main purpose of the hybridization is to reduce fuel consumption and exhaust emissions. Additional benefits thanks to the electric motor(s) are higher torque and more comfort.

With hybrid drives, a distinction is made between Micro-Hybrid, Mild-Hybrid and Full-Hybrid vehicles.

A vehicle with a fully electric drive does not fall under the "hybrid" category. We can classify a vehicle equipped with a range extender as a “series hybrid”.

The diagram below shows the different hybrid forms of a low to high form of electrical support or. drive.

Micro hybrid:
A micro-hybrid vehicle does not have an electric motor to support the combustion engine while driving, but is equipped with various fuel-saving technologies. So there is no such thing as a HV (High Voltage) system. The fuel saving is achieved through the start/stop system, which automatically shuts down the engine and starts it when the vehicle is stationary, and a battery regeneration system. This regeneration system allows the alternator to charge to maximum when the vehicle brakes. The energy that is normally lost in the brake pads is now partly used to charge the 12-volt battery. As a result, when driving at a constant speed, no additional fuel injection is required for the increased load on the alternator and fuel is saved.

Mild Hybrid:
On Mild-hybrid vehicles, the Internal combustion engine supported by one or two 48 volts electric motors that provide extra power under different operating conditions. The electric motor assists the combustion engine when accelerating. When driving at a constant speed, the electric motor is automatically switched off again. The vehicle cannot therefore drive fully electrically.

The electric motor is located near the flywheel, or there is a chain / toothed belt transmission between the electric motor and the end of the crankshaftThe relatively compact 48-volt battery is usually located in the trunk.

The illustration shows an electric motor in the flywheel housing of the combustion engine. This is also not an HV system. A technician without a NEN certificate may therefore also work on the electric powertrain.

Also, a micro-hybrid vehicle can be equipped with a 48-volt starter motor generator, which is actually a combination of an alternator and starter motor. Manufacturers give the following designations to this type of starter motor generator:

  • Dynastart;
  • starter generator;
  • Belt driven starter alternator;
  • Belt integrated starter generator (BSG).

With the aid of a mechanism, the multi-ribbed belt can be tightened on the correct side – depending on loading or starting.

The three images below show the three possible positions during (regenerative) charging of the battery, starting the combustion engine and the electric motor mode, where it supports the combustion engine. The support for turbo engines mainly takes place in the low rev range, in which the "boost" of the electric motor absorbs the so-called turbo lag.

Electric motor

A 48-volt starter alternator replaces the "normal" 12-volt alternator. In addition to the 48-volt battery, we also have the 12-volt battery for the on-board network that provides energy for the lighting, door locks and accessories in the car. A DC-DC converter / converter (transformer) convert 48 volts to 12 volts to charge the battery.

Serial Hybrid Drive:
A vehicle with a serial hybrid drive is only driven by the HV electric motor powered. There is no direct connection between the combustion engine and the wheels. The image below shows an example of a rear-wheel drive series hybrid car.
There is a coupling (1) between the combustion engine (3) and the generator (2). When the engine is running and the clutch is closed, the HV battery (7) by means of the generator (3) and the converter cq. inverter (6) charged. The inverter regulates the AC voltage supplied by the generator to a regulated DC voltage.

The electrical components in the powertrain of a serial hybrid operate at a high voltage (HV). This can be recognized by orange cables and plugs. Only certified technicians are allowed to work on the HV system.

Advantages of a serial hybrid system:

  • Simple construction because the combustion engine does not directly provide the drive.
  • Suitable for fully electric driving, if the battery is large enough.
  • No clutch required to drive away from a standstill; the electric motor takes care of this.
  • No reverse gear required because the electric motor can rotate in two directions.
  • Suitable for charging via the mains (plug-in).


  • The electric motor must provide the full driving power
  • Greater mass than a parallel drive vehicle.

Parallel Hybrid Drive:
In a vehicle with a parallel hybrid drive, there may be a direct connection between the combustion engine and the wheels. When the couplings (3 and 5) in the picture below are closed, the vehicle can run on the combustion engine. The electric motor (4) serves both to charge the battery and to drive the wheels.
A parallel hybrid can also only run on the electric motor. By opening clutch 3, the connection with the combustion engine is broken; this can be switched off, so that purely electric driving can be done. Clutch 5 is engaged when starting from a standstill.

Like the series, the parallel hybrid is equipped with a HV installation with orange cables and plugs.

Advantages parallel hybrid system:

  • Suitable for fully electric driving, provided the battery is large enough and there is a coupling between the combustion engine and electric motor.
  • No reverse gear required because the electric motor can rotate in two directions.
  • Suitable for charging via the mains (plug-in).
  • Smaller combustion engine, because the electric motor assists with acceleration.
  • Smaller electric motor, because the combustion engine can assist with acceleration.
  • Lower mass than a serial drive vehicle.


  • Mechanically complicated.
  • Clutch required for electric drive away.
  • Gearbox needed.

Plug-in hybrid:
The battery of a hybrid vehicle normally charges through regenerative braking, or by letting the combustion engine drive the electric motor (which is then used as a generator). The latter is obviously not efficient.

With a plug-in hybrid, the battery pack can be charged by connecting the vehicle with a plug at home to a socket or a public charging station and charging it with the electricity grid. When leaving by car, the first kilometers can be covered electrically (ie emission-free). Ideal when driving from the city to the highway. As soon SOC (State Of Charge)In other words, the state of charge of the battery becomes low, the combustion engine will start up and provide the main drive. When braking, regenerative braking will partially recharge the battery.

An additional advantage is that the electric auxiliary heating and / or air conditioning can be programmed at a pre-set time, so that you can enter a pleasant indoor climate, without this being at the expense of battery capacity or fuel.

In most cases, a plug-in hybrid has a limited electric range of 40 to 60 km. Examples are:

  • BMW 225XXE Active Tourer (2021): 55km;
  • Hyundai Ioniq (2021): 52km;
  • Mitsubishi Outlander PHEV model year 2015: 43 km and model year 2021: 54 km;
  • Volkswagen Passat GTE Business plug-in hybrid (2021): 55 km.

Please note: these are the specifications of the manufacturer. In adverse conditions, such as low temperatures or an unfavorable driving style, the range can be reduced by up to 30%.

Energy recovery:
When accelerating, the battery supplies electrical energy to the electric motor. The moment that deceleration (braking) takes place, the electric motor will have a generating effect; the electric motor will thereby charge the battery. This is also known as “regenerative braking” or “recuperative braking”. More information about this can be found on the pages about the reverse and the electric motor find.

System overview Toyota Prius:
The battery of a Toyota Prius contains a DC voltage of approximately 200 volts. the boost converter converts the battery voltage of 201,6 into a higher direct voltage (DC) of 650 volts. The boost converter is a DC/DC converter; it remains DC voltage, only the voltage is increased. The 650 volts DC voltage ends up in the inverter. The reverse converts direct current (DC) to alternating voltage (AC) and vice versa. We therefore call this converter an AC/DC rectifier or DC/AC converter. In addition to the conversion from DC to AC, the inverter also controls the electric motors by means of IGBTs. The two electric motors (MG1 and MG2) operate with a three-phase AC voltage of approximately 600 volts.

The battery voltage not only goes to the boost converter and the air conditioning compressor, but also to the DC/DC converter for the on-board battery. The voltage of 201,6 volts is converted to 14 volts to lead-acid battery to be able to load. The electrical components of the interior and exterior are connected to this 14-volt battery, such as the radio, lighting, door locks, etc.

System overview Toyota Prius

System overview Mitsubishi Outlander:
The following overview shows the components of a Mitsubishi Outlander (model year 2019 >).
This (plugin) hybrid behaves, depending on the driving conditions, as an EV, series hybrid or parallel hybrid. The abbreviations are as follows:

  • PDU: Power Drive Unit
  • GCU: Generator Control Unit
  • FMCU: Front Engine Control Unit
  • RMCU: Rear Engine Control Unit
  • GCU: Generator Control Unit
  • OBC: On Board Charger

EV mode: In fully electric driving, the multiple wet-disc clutch is decoupled and the electric motors (each with a maximum power of 60 kW) provide the drive. The gasoline engine and generator are turned off.

System overview Mitsubishi Outlander

Series mode: at a battery charge of <30% and a power demand of >60%, the petrol engine and generator are started. The clutch remains disengaged. The petrol engine drives the generator, which provides the battery charge (and therefore not the drive for the wheels). The system now behaves as a series hybrid. The speed of the petrol engine is approximately 1700 rpm while driving. / min. When accelerating and braking, the speed drops to 1100 rpm.

Parallel mode: at the moment that you drive faster than 65 km/h, there is an increased power demand or the SOC of the battery is <30 %, the transmission is switched in such a way that the parallel mode is created. The combustion engine and the front electric motor drive the wheels. The combustion engine and front electric motor speeds are synchronized before the clutch is engaged. In parallel mode, the rear electric motor is controlled up to 5% to avoid magnetic field resistance at high speeds when running without load.

Transmission of a hybrid vehicle:
Most manufacturers (Ford, Honda, GM) fit in 2019 CVT (Continuously Variable Transmission) technology as a transmission in their hybrid models.
The CVT technology of the Toyota Prius (see picture) is not obtained by a push belt and diameter-adjustable pulleys, but by an electrically controlled combination of electric motor, generator and planetary gear system. The advantage of this type of transmission compared to the mechanical CVT is that it is not subject to wear and has a lot less weight.

The Prius powertrain pictured consists of:

  • internal combustion engine (petrol engine);
  • electric motor MG1 (acts as generator/dynamo with regenerative braking);
  • electric motor MG2 (the motor for the drive);
  • planetary gear train (Power Split Device) that can couple and uncouple the combustion engine and electric motor from the powertrain;
  • chain transmission on sprockets connected to the differential.
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