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Farewell to the six-cylinder?

The change in the combustion engine scene

“There is no substitute for displacement. Except ... through even more cubic capacity! ”Has been an often-quoted saying in the traditional car scene in recent years. And if you have observed the developments over the past decades, the manufacturers have so far adapted the displacements and the number of cylinders to the zeitgeist. The six-cylinder was the most common engine from the luxury class onwards, for example in the BMW 520 or Mercedes E 230 or E 280. The spirit of the times and the stricter emissions standards breathe new concepts under the bonnet of conventional engines. A look at the trends in the conventional combustion engine.

Downsizing as a global trend

The large-volume six, eight or twelve-cylinder engines are often only available in combination with the absolute top equipment variants. Here, customers dig deeper into their pockets for luxury and prestige. Those who want to swim in the spirit of the times now also have a significantly larger selection of economical and low-emission 4-cylinder variants.

“Downsizing” is the buzzword when it comes to more critical and environmentally conscious customers in the new car sector. Jeep, as a traditional advocate of large-volume and powerful engines, also likes to use the shallower “rightsizing”. Drive like this
the new models of the Compass, Renegade or Wranger exclusively with compact 3 or 4 cylinder motors. This makes it easier to comply with the stricter emissions standards according to the WLTP process.

Rainer Golloch, author of the VDI book “Downsizing in Combustion Engines” (Springer 2005) in the reports of the VDI Nachrichten points out that on the one hand the image of passenger cars plays a major role and that certain advantages of the larger engines cannot be ignored. “The silky engine running of a 6-, 8- or even 12-cylinder cannot be compared with a 4-cylinder.” However, according to Golloch, today's turbocharged engines have, in some cases, noticeably better elasticity than large-volume naturally aspirated engines. The torque as an engine parameter makes a significant contribution to a tangible driving experience and is classified as important by the drivers. "The characteristics of the power delivery are perceived as very pleasant in modern, supercharged engines."

But the trend is also in the upper class towards smaller, energy-saving motors. The legal requirements force manufacturers to significantly reduce fuel consumption and emissions. With the introduction of the CO2 tax in 2021, the lowering of consumption values ​​will play an increasingly important role in the future. Accordingly, the smaller-sized motors will be found more and more frequently in the luxury class. A decisive purchase factor are comprehensive measures to reduce noise and vibration so that customer acceptance is increased. In the niches, 8- and 12-cylinder engines will probably also find their own clientele.

The engineers in engine construction have already turned to the specific demands of small, supercharged engines. The use of wear-resistant materials, the new possibilities in manufacturing technology and the test runs in the development phase are increasing in quality. Technically, the new challenges have already been adapted to the new conditions in the past few decades.

In the language used by manufacturers, the term downsizing tends to be avoided. Here, terms like “rightsizing” or “technological upgrading” are more in the foreground. The manufacturers are adjusting to the demands of customers for more power and torque with less consumption.

Full hybrid cars

The range of full hybrid cars is increasing continuously. In addition to the pioneers from Toyota with the Lexus premium segment, many other global players have also entered the segment. Drivers who value a long range or tow a trailer usually opt for hybrid cars. The full hybrid cars are very much in vogue. It is probably due to the advantage of not needing any electrical charging options and using recuperation to cover short distances without a combustion engine. What should be considered when buying?

The all-electric range is interesting for many buyers. The built-in battery capacity and consumption in the electrical sector are decisive for the actual range in the short-haul area. The battery capacities vary depending on the type and installation within the vehicle. They are often installed below the center console, under the rear bench seat or in the trunk.

Energy recovery via recuperation

In all vehicles, the original recovery takes place primarily when the vehicle is braked. In vehicles with relatively small batteries, the energy recovery can often be seen very well in the displays even when braking hard, for example from high speed. Using the digital displays, the energy fed into the battery can be read directly from the scale or the energy monitor. Environmentally conscious driving can usually be experienced on the basis of the energy gained or saved.

The temperature range and the battery capacity are of decisive importance for the electrical range. In warm external conditions, a moderate driving style in the short distance range is 10 to 15 kWh per 100 km; in winter conditions also like twice the values ​​due to the switched on consumers. The battery capacity in full hybrid cars is usually tight in order to save weight and space. Common types are batteries that promise a good durability.
The shortest possible service life is important for battery operation. The battery can be damaged if it has not been used for more than a year. The constant use of the vehicle is also crucial for the longest possible service life of the battery. Normally, the battery is designed for the service life of the car, with the built-in batteries different guarantees are offered up to a defined mileage. It is worth taking a look at the manufacturers' exact warranty conditions.

Stable value

The discussion about the pollution of conventional drives has already brought measurable value stability to the first generations of Toyota hybrid models. The factors sustainability and low environmental impact will play an important role in the sale of used cars in the future. The recently passed diesel driving bans and the trend away from diesel support a high level of value retention in the sale of used hybrid cars. The manufacturers often offer an extended manufacturer's guarantee when buying a new car. This is definitely an argument when it comes to reselling the vehicle.

In contrast to its big brothers - the plug-in hybrid and the full hybrid - the mild hybrids are not able to drive routes purely electrically. The combustion engine is required for the drive in mild hybrids and is usually supported by a weak electric motor. The electric machine serves as a generator and e-machine and can also replace the alternator at the same time. While “real” hybrid vehicles or electric cars are equipped with a high-voltage network of at least 110 volts (400-volt systems are common), the opposite development is also being further developed with a 48-volt drive. The systems known as mild hybrids can help to drastically reduce fuel consumption in the future - but driving purely electrically is not (yet) possible.

From 60 volts, the on-board network of a car is referred to as high-voltage technology. This implements special care when working on the vehicle, especially for workshops. The 48-volt system, on the other hand, is a low-voltage system for which significantly lower safety standards apply. 12-volt drives used in conventional petrol and diesel vehicles can generate a small part of the braking energy and thus charge the lead battery, which only benefits the on-board power supply. In contrast, the electrical energy generated by a 48-volt system can be buffered in a lithium-ion battery and then used not only for electrical users in the car, but also for the drive. On average, this braking energy recovery can save up to 18 percent fuel.

48-volt mild hybrid - Copyright Continental
48-volt mild hybrid - Copyright Continental

48-volt mild hybrid

The production of 48-volt hybrids, which is now emerging worldwide, is not surprising in view of the strict regulations and CO2 limit values ​​as well as the threat of diesel driving bans. In order to be able to meet the requirements from 2020 onwards, car manufacturers are striving to develop technologies that not only contribute to reducing CO2 emissions and improving fuel efficiency, but also have relatively low costs.

The 48 volt mild hybrid system is one such relatively inexpensive technology. The 48-volt starter generator, which serves as an electric motor, replaces both the alternator and the 12-volt starter. This has the advantage that the starting process of the engine is reduced to a few tenths of a second, while with a normal 12-volt electrical system it takes one to two seconds to start the engine, which is particularly advantageous with start-stop systems.

The 48-volt starter can also support the torque of the combustion engine to such an extent that the acceleration is improved (boosting). Sailing mode, in which the combustion engine is switched off while driving, is also possible with the 48-volt hybrid system.

The mild hybrid system is particularly beneficial when driving around town: the electric machine also supports the combustion engine when accelerating and starting off. During braking or overrun, the crankshaft can then drive the electric motor via belts, which serves as a generator to generate electricity, which is then stored in the 48-volt battery.

The 48-volt on-board network is either installed in the vehicle in addition to the 12-volt on-board network that is already in use, in order to ensure bidirectional power transmission, or as the sole on-board network.

In addition to the 48-volt battery (lithium-ion), a 48-volt starter generator and a DC / DC converter are essential components of the 48-volt system. The usual 12-volt alternator and the 12-V starter are replaced by the 48-volt starter generator, which not only starts the engine, but also acts as a kind of dynamo, converting the rotary energy of the internal combustion engine into electrical energy. When braking, kinetic energy causes the generator to rotate - it can generate an output of up to 15 kW, which is then stored in the 48-volt battery.

The technique of the mild hybrid

The bidirectional voltage converter is used to connect the existing 12-volt on-board network with the 48-volt on-board network. The 48-volt system delivers an output of up to 3,5 kW to the 12-volt system; in some cases, the 12-volt on-board network can also supply the 48-volt on-board network. The use of the 48-volt system not only ensures better acceleration, but also significantly improves the efficiency of the engine.

The first series vehicles equipped with the 48-volt hybrid drive come from the Continental plant in Nuremberg. The diesel variants of the new Renault SCENIC and the Grand SCENIC were electrified with the low-voltage system by the supplier Continental. Renault has given its form of the mild hybrid the name "Hybrid Assist". Other car manufacturers have already launched their first vehicles in the new mild hybrid segment or are planning a market launch. Mercedes announced at the end of 2016 that the newly developed M 256 six-cylinder petrol engine would be equipped with a 48-volt electrical system and consistently equipped for electrification. The performance of the six-cylinder engine should be in the range of the eight-cylinder, i.e. over 300 kW (408 hp) and more than 500 Nm. The CO2 emissions have been reduced by around 6 percent compared to the V15 predecessor. The S-Class will probably be the first model to be equipped with the 48-volt electrical system and the new M256 engine.

Suppliers Continental and Schaeffler have already presented a 48-volt mild hybrid drive that promises fuel savings of up to 25 percent compared to a comparable vehicle with a normal drive. The “Spar-Focus” developed in cooperation with the manufacturer Ford was also equipped with an electrically heated 48-volt catalytic converter, which helps to comply with the EURO 6c emissions standard.

The Japanese manufacturer Suzuki launched the Suzuki Ignis, a mild hybrid system, on the German market in 2017. The 48-volt system called SHVS (Smart Hybrid Vehicle by Maruti Suzuki) offers fuel savings of 0,3 liters / 100 km and CO2 savings of just under 7 g / km compared to a normal drive. The energy saved during recuperation should generate additional torque of up to 6 Nm during acceleration phases.

Audi announced back in 2015 that by 2025 all new models except the e-tron models would be offered with a 48-volt electrical system. At the beginning of June, the Ingolstadt-based company announced that the new mild hybrid drives would move into the model range from mid-2017. The new generation of the Audi A8 is to be equipped with a 48-volt network. There is now a wide range of vehicles that we present in the overview. B

In the future, more 48-volt drives will probably be developed and brought onto the market - soft electrification at relatively low costs has great potential for car manufacturers.


The trend in traditional internal combustion engines is towards small-volume engines that will consume significantly less and reduce emissions. This year, the range of 48-volt mild hybrid variants will increase. Toyota will continue to focus on full hybrid cars.


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N. Hawthorn
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