Teamwork in the powertrain
© Bet_noire (iStock)
April 2024

Teamwork in the powertrain

By Carsten Paulun
An ideal energy mix or a cop-out? In an interview, Dr. Reinhard Kolke, Director of the ADAC Technology Center in Landsberg am Lech, discusses the pros and cons of hybrid powertrains, the technical challenges posed to the interaction of electric motors and internal combustion (IC) engines, and prospects for the future.

Dr. Kolke, in a nutshell: What are the advantages of a hybrid powertrain compared to an all-electric powertrain or one that uses only an IC engine?
Dr. Reinhard Kolke: It’s necessary to differentiate between plug-in and mild or full hybrids in that context. In the case of a plug-in hybrid, the combination of the IC engine and electric motor with an adequately dimensioned battery makes it possible to cover a large part of one’s daily driving needs – such as commuting to work – in fully electric mode. At the same time, the on-board gasoline or diesel engine allows the driver to travel longer distances without stopping to charge the battery. As a result, the plug-in powertrain is suitable for all people that in addition to shorter urban distances need to travel longer distances as well. On the other hand, it’s also ideally suited for people that would like to primarily drive in all-electric mode but aren’t ready yet to completely switch to electric mobility. By contrast, when it’s designed as a mild or full hybrid, the technology primarily helps reduce the fuel consumption of the IC engine without the driver having to adjust to change or to reach for a charging cable. In combination with hybrid technology, the gasoline powertrain in many cases has already outperformed the pure diesel engine as the IC powertrain delivering the best fuel economy.

Teamwork in the powertrain
Dr. Reinhard Kolke,
Director of the ADAC Technology Center

“Hybrid powertrains are going to benefit from the rapid battery development as well.”

Many people consider the all-electric powertrain to be the only viable means of getting a handle on emissions that are harmful to the climate. Does that mean that other forms of powertrains like hybrid drive are dead?
Powered by green electricity, the battery-electric vehicle has an emissions-related advantage over other forms of powertrains in which an IC engine is still involved that’s hard to catch up with. In addition, a growing percentage of renewable energies in the power mix keeps improving the CO₂ burden caused by an electric car without forcing me to buy a new one. However, not every customer already has the opportunity or the desire to switch to a fully electric vehicle – be it because they have no means of charging the battery, because they’re skeptical, or because the costs are prohibitive for them. That’s why we’re going to continue to see new gasoline and diesel powertrains on the market in the medium run. In that regard, hybridization can help raise the fuel economy of IC engines – that, today, are already extremely efficient – to even higher levels.

Distinguishing between plug-in hybrids, full hybrids, and vehicles with range extenders – in your view, which form has the biggest chances and why?
Each of these technologies has its advantages and disadvantages. Plug-in hybrids are justified and will continue to play a major role because they give many customers the opportunity to cover a large part of their daily driving needs in fully electric mode. Especially in combination with cheap electricity from photovoltaic systems, that’s an attractive solution. Full hybrids and range extender models basically pursue one and the same goal: The convenience of driving with gasoline or diesel fuel, in other words short refueling stops and long range, is supposed to be retained, while concurrently making use of efficiency benefits and further reducing the environmental burden. Here the actual customer needs and the product portfolios of original equipment manufacturers (OEMs) and suppliers will no doubt determine how to best use the electric motor. I wouldn’t be surprised to see the range extender technology be more frequently used again in the future because, thanks to all-electric propulsion, that combination can do without a complex transmission and the IC engine always runs in the optimal operating range.

Do hybrid powertrains make sense in all vehicle classes and markets?
Basically, mild or full hybridization can help improve the fuel economy of the IC engine in any vehicle, so making it cleaner as well. The highest savings effect is achieved when the vehicle accelerates with assistance from the electric motor and decelerates through recuperation as often as possible, that is primarily in urban traffic. In that regard, small vehicles and downsized engines come to many people’s mind but hybridization makes sense in all vehicle classes. The reason is that while in Europe full-size and luxury car classes are typically used for long-distance travel, the global picture in the big megacities is different. Just look at Beijing, Mumbai, or Lima and you’ll find many large, heavy cars in the streets that rarely leave the city limits. While, with a little luck, you can traverse Munich in 20 minutes you’re at best going to travel a couple of kilometers in Beijing during that time. So, the distances in urban traffic in other regions are clearly longer and in stop-and-go traffic the hybrid powertrain definitely displays its advantages even more significantly.

The global technology corporation Schaeffler has created a powertrain scenario. According to that scenario, in 2030, around 40 percent of all newly produced vehicles will exclusively be using one (or several) electric motors, another 40 percent a hybrid powertrain, and 20 percent only an IC engine. That shows that in the medium run the IC engine, from a global perspective, will continue to play a major role. Strictly looking at emissions – is that good or bad news?
That assessment is very much in line with the competitive environment. Of course, the local emissions of electric motors are zero. . And if the power charging the batteries is produced by renewable energy sources there are no CO2 emissions either. But modern gasoline and diesel engines with professionally applied emission control technology can impress in terms of local emissions as wellHowever, despite all progress: Emissions, including CO2, cannot be totally reduced to zero.So, especially from the global perspective, it makes sense to continue developing IC engines in terms of emissions and efficiency. Compared to the vehicles existing worldwide, a large part of which are cars with older gasoline and diesel engines with clearly worse emissions, every new vehicle with an IC engine is going to contribute to a significant reduction of harmful emissions. In addition, synthetic fuels and biofuels such as the diesel substitute HVO100 can help make existing vehicles with IC engines more climate-friendly. Other emissions such as tire and brake abrasion will continue to be of concern to us regardless of the type of powertrain.

1.07 MM

battery-electric passenger cars, light commercial vehicles, and plug-in-hybrid electric vehicles (PHEVs) were registered in January 2024. That’s an increase of 63 % versus the same month of the previous year and equates to a 16-percent market share of new registrations. The PHEV segment is recording particularly strong growth (+91%). The driver of that growth is the Far East, especially China, where many PHEV models with ranges of 200 kilometers (124 miles) are already on the market.

Source: autovista24

Are you seeing any developments or actions that might cause a significant shift in the predicted distribution?
Legislation no doubt has a major impact on ramping up electric mobility. Currently, we’re assuming that from 2035 on no new vehicles with IC engines for fossil fuels will be approved in the EU anymore. However, from a global point of view, there are hardly any other countries pursuing a similarly strict approach, and especially in the two largest markets, China and the United States, we need to carefully observe the political development. A change in course by the respective governments can put a big damper on electric mobility in those markets. We need to be honest enough to admit that a lack of planning certainty for new powertrains also poses risks to the industry.

Technologically, has the hybrid powertrain already reached the end of its development or do you expect any significant improvements?
Hybrid electric vehicles are some of the most complicated automobiles to have been developed. Especially the full hybrid and the plug-in hybrid basically combine two complete powertrains in one automobile. Those powertrains not only have to work smoothly in isolation but their interaction must be impeccable too. By now, the technology has become rather sophisticated but, as in the case of pure IC engines, further optimizations can no doubt still be made. Moreover, hybrid powertrains are going to benefit from the rapid battery development.

All hybrids are not created equal

In automotive engineering, the term hybrid powertrain refers to a combination of IC engine and electric motor. There are different versions of hybrid electric vehicles.

In a mild hybrid a small electric motor assists the IC engine. However, this electric motor cannot propel the vehicle on its own. Instead, it eases the load acting on the gasoline or diesel engine during acceleration events, so reducing fuel consumption. During braking events, the electric motor turns into a generator recuperating energy that’s stored in the battery as electric power.

Unlike a mild hybrid, a full hybrid can travel in fully electric mode, albeit only for short distances and at limited speed. The electric motor is more powerful and the battery is larger. Full hybrids have better fuel economy than mild hybrids.

A plug-in hybrid electric vehicle uses an even more powerful electric motor and an even larger battery that’s charged via an external power source. Plug-in hybrids can travel longer distances in fully electric mode.

In the case of a range extender the IC engine does not power the wheels directly but drives a generator to produce electric power. Because the IC engine at constant engine speeds always operates with optimum efficiency emissions are supposed to be reduced. Depending on the concept, range extender vehicles use larger batteries, which, like those of plug-in hybrids, are charged from a power outlet or smaller ones like those of mild or full hybrids.

Read more on the subject:
Technologies from Schaeffler for hybrid and fully electric powertrain systems

Teamwork in the powertrain

What conspicuous design-related strengths and weaknesses do hybrid vehicles display at the ADAC Test Center?
The electrical part in the hybrid has advantages: The immediately available torque of the electric motor assists the IC engine exactly in the ranges that in terms of load tend to be unfavorable for diesel and gasoline units, for instance when starting. That can noticeably reduce consumption. The electric technology per se is largely inconspicuous in testing: We haven’t noticed any issues with hybrids neither with the motors nor the power electronics nor the batteries. However, the vehicle weight in some cases clearly increases compared to a pure IC powertrain, depending on the hybrid system. Especially in the case of plug-in hybrids with relatively large batteries, that may well amount to a couple hundred kilograms. To prevent that additional weight turning into a consumption disadvantage, it’s important to frequently charge a plug-in hybrid and to use it sensibly. People that cannot make use of the savings potential of a heavy plug-in should perhaps prefer a full or mild hybrid – or fully electric vehicle – that can do a better job of compensating for its equally high weight in everyday use.


bigger than in 2023: That’s what the worldwide market for hybrid electric vehicles (plug-in, mild, and full hybrids) could be in 2032, according to a forecast by market research institute Precedence Research. Accordingly, sales would grow from 513 billion to 5 trillion U.S. dollars.

Due to the teamwork of the electric motor and IC engine, are hybrid vehicles more trouble-prone than vehicles using only one type of propulsion?
Basically, for starters, let’s say that a vehicle with a larger number of components has a higher probability of one of them failing. In that regard, as previously mentioned, it’s an advantage that the electric technology is relatively robust and rarely causes problems. If trouble does occur, at least in the case of plug-in hybrids, specially trained personnel with high-voltage skills must respond – just like in the case of all-electric vehicles. By the way, that’s one reason why we train all our roadside assistance drivers in handling electrified vehicles. We cannot conceal the fact that in our breakdown statistics the 12V starter battery has been the cause of the breakdown in 64 % of all cases. Here the OEMs still need assistance.