All you need to know about hybrid vehicles

Climate change, increasing emission levels: According to a study by the Intergovernmental Panel on Climate Change, traffic is responsible for 24% of all CO₂ emissions worldwide. That’s why mobility must become carbon neutral – not in the distant future, but as soon as possible. Reliance on gasoline and diesel engines needs to be reduced so that fossil fuels can be replaced. They are increasingly being replaced with electrified drive systems.

However, in many cases, pure electric cars are not able to keep up with conventional vehicles: They have a smaller driving range, batteries are expensive, which translates into higher vehicle prices, and, in many regions, the network of charging stations is inadequate. Hybrid vehicles offer a solution: They combine an electric drive system and an internal combustion engine. This means that the vehicles can drive further than pure electric cars, and they consume less gasoline or diesel than vehicles running solely with an internal combustion engine.

They may also be able to meet the increasingly more stringent limits for passenger cars as specified, for example, by the EU. From 2021, the EU fleet-wide average emission target for new cars will be 95 g CO₂ per kilometer. And by 2030, this target is to be reduced by a further 37.5%. Many other countries have also defined strict limits.

The word “hybrid” has Greek roots and means “from two origins”. Accordingly, a hybrid vehicle obtains its energy from two different sources and therefore has more than one drive system: generally, an electric motor and an internal combustion engine – usually with gasoline as fuel; diesel is less common. The aim of a hybrid drive is to combine the advantages of both drive systems and balance out their disadvantages:

• Currently, the main benefit of a car with a gasoline or diesel engine compared to an electric drive system is its range. This is not because of the motor itself, but due to the energy storage unit: the battery. As batteries become more efficient, the range will increase. Another advantage of vehicles with internal combustion engines is that they are still less expensive to purchase than electric cars. But on the negative side, they consume fuel, cause emissions, and are noisy. A considerable proportion of the energy from the fuel is wasted.
• A car with an electric motor does not produce local exhaust gases or noise, and it doesn’t use fossil fuels, provided the electricity comes from renewable sources. With electric motors, acceleration is also faster and more dynamic. However, because of the battery, electric cars have a shorter range than cars with internal combustion engines. And they need a large and hence more expensive battery.

The synthesis of both drive systems enables lower fuel consumption and emissions at acceptable additional purchase costs, dynamic drivability and a long range. The electric motor either supports or replaces the internal combustion engine – especially where it is inefficient – and, in certain situations, boosts performance.

For this reason – and due to various government promotion programs – sales figures for hybrid vehicles are increasing. While more than a million new hybrid vehicles were registered throughout the EU in 2019, this number already stood at more than 1.4 million by 2020, according to data service provider Jato Dynamic. This means a 47 percent increase compared to 2019.

The power for hybrid vehicles comes, on the one hand, from fossil fuel and, on the other, from electrical energy. Consequently, a hybrid vehicle has at least two energy storage systems – a fuel tank and a battery – and at least two energy converters, the electric motor and the IC (internal combustion) engine. Other important components of a hybrid drive system are an electronic control device that decides when to switch between the two drive systems, and an inverter that converts the direct current from the battery into alternating current and controls the electric motor.

The individual components of a hybrid drive

As well as many other components, the following parts play an important role in a hybrid vehicle:

• The electric motor forms the core. It has two functions: On the one hand, it drives the vehicle electrically in certain driving situations. As a generator, it converts the kinetic energy from braking into electric energy and feeds this energy back to the battery via the inverter. This is known as recuperation.
• The internal combustion engine is the conventional drive system that gets its energy mainly from gasoline or, occasionally, diesel. An internal combustion engine is especially efficient when it works at a constant speed at the optimum operating point.
• The electric control device connects the electric motor and the IC engine and automatically switches to the optimum drive, depending on which is the most efficient at that time. Electronic power flow management ensures that the vehicle runs efficiently.
• The inverter connects the battery with the electric motor. The power electronics convert the DC voltage of the battery into high-frequency AC voltage, which forms the electromagnetic field for power generation in the electric motor.
• The battery supplies electricity for the electric motor. In a hybrid vehicle, the lithium ion battery works with a battery management system. With the exception of mild hybrids (48V battery), high-voltage batteries are used.
• The fuel tank stores the fossil energy, in other words, gasoline or diesel. The range of the vehicle depends on the size of the tank.
  
  

How the battery charges in a hybrid vehicle

Hybrid vehicles usually generate the electric energy to charge the battery themselves – while the vehicle is driving. As in a pure electric drive system, the electric motor in a hybrid car also acts as a generator. During braking or coasting, in other words, when the vehicle is moving without using power, it converts kinetic energy back into electricity – this is known as recuperation. If the vehicle is a series hybrid (see below), the internal combustion engine also acts as a generator to generate energy. Only plug-in hybrids can also be supplied with electricity from a charging station.

When the different drive systems are active in a hybrid vehicle

Most hybrid vehicles switch automatically between the two drive systems or allow them to run together. This depends on the actual driving situation. For example, the electronic control unit switches to IC mode when the vehicle moves at a constant high speed. This is when the internal combustion engine works particularly efficiently.

A combination of the two systems may, for instance, be practical on hills or when overtaking. In these situations, an energy booster is needed for a short time and the electric motor supplements the power of the IC engine.

In many hybrid vehicles, the electric motor can also move the vehicle on its own. In this case, no fuel is consumed. Since an electric motor has a high degree of efficiency even at low speeds, it is especially suitable for starting and for low speeds.

A typical driving situation in a car with parallel hybrid configuration (see below) is as follows: when the car starts, only the electric motor is active. As the car speeds up, the internal combustion engine switches on. The IC engine is generally in use on highways.  If the driver brakes or allows the vehicle to coast, the energy is captured and stored in the battery – and is then used later by the electric motor as required.

The two drive systems in a hybrid vehicle can work together in different ways and the drive types can be weighted differently.

Hybrids differ with regard to their levels of electrification. According to the German automobile association ADAC, fuel savings of 15 to 25% are possible compared to an ICE vehicle, and even more with a plug-in hybrid.

Micro hybrid
A micro hybrid uses an automatic start-stop system to recuperate braking energy and store it in a classic 12V starter battery. However, the vehicle is driven exclusively by the internal combustion engine, which explains why micro hybrids are not listed as a hybrid concept in many drive classifications. In other words, micro hybrids are cars with an ICE drive system and well-engineered drive electronics. The level of fuel saving is low.

Mild hybrid
As opposed to micro hybrids, mild hybrids (Mild Hybrid Electric Vehicle, MHEV) have an electric motor in the drive system – but it never works on its own and is used only to support an internal combustion engine. It boosts the engine during acceleration, for example. In addition to the usual 12V battery, mild hybrids also have a 48-volt battery. Because of the higher voltage, a mild hybrid can recuperate more braking energy than a micro hybrid. The automatic start-stop system is also more efficient as the motor can be stopped more frequently and for longer. Mild hybrid vehicles consume up to 15% less fuel than those with conventional internal combustion engines.

Full hybrid
In a full hybrid (Full Hybrid Electric Vehicle, FHEV), an electric motor and an IC engine work together intelligently and flexibly. Pure electric driving is also possible, but usually only on short trips of a few miles. As opposed to mild hybrids, full hybrids do not have an additional 48V battery but have a high-voltage traction battery with several hundred volts. The power of the electric motor is also higher than that of a mild hybrid. The German Federal Environment Agency says that fuel savings of more than 20% compared to a pure ICE vehicle are possible.

Plug-in hybrids (Plug-In Hybrid Electric Vehicle, PHEV) are a further development of full hybrids. What set them apart from all other hybrids is that in addition to recuperation the battery can also be charged at a charging station or a wall socket, which explains the name, “plug-in” hybrid.

Like full hybrids, plug-in hybrids have a high-voltage battery, although it is much larger and more efficient. For example, depending on the model, ranges of up to 100 kilometers (around 62 miles) and more are possible in pure electric mode. This allows, for example, many commuters to make the daily trip from home to work and back without producing any emissions. Standard fuel consumption of a plug-in hybrid is up to 35% less than that of a comparable ICE vehicle. However, whether this is achieved under real road conditions depends largely on the driver recharging the battery regularly and actually taking advantage of the fuel saving potential. Seasonal fluctuations also have to be taken into account, as low winter temperatures reduce the range of the battery.

In addition to their level of electrification, a distinction between hybrid vehicles is also made according to how they are constructed. These days, the most common are parallel hybrids, which include the above-mentioned mild, full, and plug-in hybrids. Series hybrids are also available, and power split hybrids are a combination of both concepts.

Parallel hybrid
These vehicle types have two drive systems – an electric motor and an IC engine. Both can move the vehicle forwards and are connected with the driving axle. They are deployed as required: the vehicle can be driven purely electrically, with only the IC engine, or with a combination of both. With this type of drive system, the powers of the electric motor and the ICE are added together to form the total power.

Series hybrid
Series hybrids have an electric motor and an ICE, but just one drive system. The power sources are connected in series: generally, the electric motor moves the vehicle forwards while the IC engine generates electricity for the battery. The power sources are not mechanically connected.

Range extender concepts also fall into this category. To put it simply, the IC engine acts only as a generator to recharge the battery when it is empty until the vehicle reaches the next charging station.

Power split hybrids
Series and parallel hybrid drives can also be combined in one vehicle. With power split or series-parallel hybrids, as they are also known, the driver chooses one of the two drives.

Compared to vehicles with just an internal combustion engine, hybrid drive systems or pure electric motors have many advantages:

• Depending on the driving situation and type, a hybrid vehicle can use the optimum drive, such as in the city and on rural roads.
• Fuel consumption is 15 to 50% lower depending on the type of vehicle. This applies especially to driving in city traffic with a lot of stop and go.
• The lower consumption and, in some cases, pure electric mode result in fewer emissions.
• The vehicle drives more efficiently. Less energy is lost than with gasoline or diesel, because energy from braking and coasting is captured and used.
• It is also possible to go on longer trips as the range is better than with a pure electric car.
• Compared to a conventional drive system, acceleration is increased by 10 to 20%. An internal combustion engine needs higher speeds for more torque. With an electric motor this is high from the start.
• Apart from plug-in hybrids, the vehicles do not have to be charged with electricity – consequently, drivers do not have to search for a charging station.

Hybrid vehicles also have a few disadvantages compared to those with internal combustion engines or only electric motors:

• They are more expensive to purchase than ICE vehicles, because the design of the double drive technology is more complicated. However, this disadvantage is balanced out over time by lower fuel consumption.
• The vehicle is heavier due to the two power sources and the additional battery. With some models, fuel consumption can be higher in certain situations where only the IC engine is working.
• The additional battery takes up space. This can mean that the trunk is smaller than in a conventional car.
• With plug-in hybrids, the overall carbon footprint depends on the electricity that is used to charge the battery – the more green electricity, the better.
• As opposed to pure electric vehicles, hybrids are still dependent on fossil fuels, and they produce emissions.

As usual, where electricity is generated, stored, or converted, microelectronics also plays an important part in electric and hybrid vehicles. Sensors measure various parameters; microcontrollers make the decisions – such as when current should flow at a specific part in the system and when not. And power semiconductor devices implement these decisions. The degree to which the electronics work intelligently and efficiently has a major influence on the range, performance and costs and, with plug-in hybrids and fully electric vehicles, also on battery charging time.  

Infineon began developing semiconductors especially for electric and hybrid vehicles very early on. The company is now the leading provider of electromobility chips. Infineon expects to see further growth. “This century, we will reach the point where the majority of all new vehicles worldwide will be semi or fully electric,” says Stephan Zizala, Vice President and General Manager Automotive High Power at Infineon. Accordingly, Infineon is investing in more production capacities. Such as in Villach in Austria. Here, at a cost of 1.6 billion euros, a new factory is being built to produce power electronics for hybrid and electric vehicles as well as other applications.

Infineon is also working on technology innovations to make electronics even more powerful and efficient. An example of this is the use of new semiconductor materials such as silicon carbide. In certain applications, chips made from silicon carbide enable more power and higher energy efficiency than traditional silicon chips. For example, this reduces energy losses when charging a plug-in hybrid and increases the range of electric vehicles.

Last update: July 2021