Drivetrain Components in Heavy-duty Vehicle Segments will Change due to Upcoming Electrification

It is predicted that drivetrain technologies are expected to face significant alterations regarding dimensions, packaging and gearing as electrification trend continues to gain power in the automotive industry. As design engineers consider the use of electrified components in many heavy-duty vehicle segments more and more frequently, it also sets a lot of questions regarding the prospects of componentry such as those currently integrated in drivetrain units. How will it change the structure of axle solutions in the future? Will the gearing technologies be affected at a certain point?

The Dana’s Spicer e-Axle concept

John Bennett, a senior official at Meritor Inc., expressed his visions and ideas on the automotive engineering of the future during the last MPT exhibition. He noted that fast adoption of electrified technologies will likely lead to significant changes within drivetrain systems including gearing. It is expected that designs of heavy-duty will change in every aspect.

Freudenberg Sealing Technologies is one of the many companies to accept it as a given. Seals will still be needed in some respects, but there will be fewer of them and the types used will change. Thus, the company has started to expand the assortment of its products by pumping financial resources into development of innovative products, which will find application in e-power solutions.

According to Mr. Bennett, the approaching automotive electrification will be strongly felt by manufacturers of powertrain systems, including engines and conventional transmissions. This becomes quite visible, as many engine makers have already started working on product differentiation, investing in innovative technologies. He also pointed out that less obvious impacts will touch upon optimizations of EV designs. Some alterations can involve the front axle and front suspension, for example, introducing changes to their standard construction. If adding an e-motor to an axle, the design of the axle thus also undergoes changes. Thus, every element of the drivetrain is influenced.

Mr. Bennett also pointed out that there are 4 key differences between diesel engines and e-motors which will play a significant role in determining of the number of gears in battery-electric vehicles (BEV) will have. E-motors offer the following benefits when compared to diesel engines:

This implies that not all e-motors require a transmission unit, while diesels actually do. Thus, it will be possible to replace the main powertrain elements (engine+gearbox) with a single e-motor. And this is actually how most BEVs are currently designed. Designs of direct drive electric vehicles do not include transmission units, using just an e-motor. This technology is widely used in China and it is considered by many analysts to an efficient way of shifting to electrification.

Meritor’s eISAS electric independent suspension equipped with a helical gearbox

At the same time, however, some BEVs come with a gearbox; such designs are more and more popular in North America and Europe where customers attach great importance to the performance capacity. The use of gear shifting units can also provide some benefits, for instance, it allows engineers to reduce size of the motor. A smaller motor, in turn, helps to cut expenses and reduce weight, thereby ensuring enhanced operating characteristics.

Alexander Eisner, representative of the German company ZF, supports the assumption that gear shifting solutions for EVs will have fewer gears. For example, 3-speed units will be integrated in electric powered systems, while 4-speed transmissions are usually installed in diesel-powered vehicles. But it seems like automotive engineers will have to deal with some problem here. Problems may arise when it comes to dealing with higher input speeds of e-motors vs. those used in diesel-driven machines.

E-motors are being developed to operate at much higher RPM rates than hydraulic motors or IC-engines for getting increased power density. Therefore, other drivetrain elements such as the gearbox will need to be modified to function properly at higher speeds. Drivetrains for heavy-duty applications will certainly require packaging adjustments, as e-motors are commonly bigger than hydraulic motors. Batteries also occupy much space, demanding further packaging adjustments. The possibility of using several motors for propulsion instead of a single IC-engine offers a great chance for construction modification of the drivetrain and optimization of the vehicle packaging. All of these facts create a room for maneuvering for drivetrain suppliers.

Dana’s Spicer Electrified e-Gearbox

It is pointed out that pointed out that the range of operation is a key issue for current EVs. Potential Improvements in this direction is a critical mission for many automakers at the moment. Therefore, providers of automotive parts for heavy-duty vehicles have to implement reductions in friction loss and drag. Some amount of energy losses (approximately 10%) from an IC- engine is caused by friction losses in the powertrain. For BEVs almost 1/3 of the total energy losses stems from friction losses. Thus, makers of automotive parts have a lot to do in order to reduce drag and facilitate to enhancement of EV ranges.

With EVs there are several potential bottlenecks, which should be taken seriously by automotive hardware manufacturers. Automotive engineers should remember that bearings will be affected by current flows in ways they never have before if placed in EVs. It can lead to problems with the lubrication layer between the rolling element and the race. Electrical shocks may appear in the bearing, damaging the bearing itself and consequently the system in which it is installed. Mr. Hemphill claimed that Schaeffler has already designed advanced surface solutions that can bring bearing technologies to a new level of robustness. Such innovative solutions can be beneficial for high-speed systems, as the rolling components are lighter and thus can operate better at higher speeds.

Future design possibilities

Mr. Bennett assumes that the motor will be eventually repositioned to the axle. Attaching the motor to the axle frees much needed space between the frame rails, which can be used for the batteries or other elements.

Technical ability to place the batteries between the frame rails has a positive impact on the vehicle safety by preserving them from any external influences. It also plays a positive role in weight reduction, since the batteries should not be cantilever fitted as they would if installed outside the frame rails. This design approach (relocating motor to the axle) allows reconfiguring and optimizing the vehicle design. Actually, it gives the vehicle makers a huge room for maneuvering when it comes to design changes in future vehicles. Thus, in terms of design, heavy-duty vehicles of the future can differ significantly from what is seen today.

Dana’s MD Direct Drive System

New design solutions will undoubtedly be accompanied with new packaging and placement of parts. In commercial vehicles, for example, the e-motor may be positioned vertical to the axle shaft or parallel to it. Anyway, gearing will still be an important part of these innovative design solutions. However, it is pointed out that the quantity and type of gears may differ significantly from conventional solutions used today.

Mr. Bennett also pointed out that there are some systems available with e-motors powerful enough to make a vehicle moving. Nowadays, these complex technologies are quite costly and thus not widely adopted, but if the costs go down, the electrification concepts can quickly become more than words for the automotive industry.

Meritor’s electric axle

According to Bennett, the upcoming automotive electrification will certainly affect transmission manufacturers. He assumes that the number of gears will be reduced, but he doesn’t think that the types of gears will remain the same. The question of noise, however, will come into the picture of the gear construction. As EVs usually operate quieter due to the lack of engines, increasing the likelihood of hearing noise from parts such as gears (in conventional vehicles this noise is soothed by the engine).

Rob Kress from Dana Inc., in turn, believes that in the near future, transmissions and elements positioned close to motors will go through significant adjustments as manufacturers invest heavily in improvements in efficiency and NVH parameters, as well as accommodation of higher RPMs. When EVs become a common thing in specific off-highway applications in the long term, driveline designs may go through significant changes, resulting in absolutely new driveline solutions.

In summary, Mr. Bennett expressed an opinion that automakers should not be taken by surprise by the fact that E-mobility gains momentum. They should seriously consider how their businesses may be affected and start preparing themselves for the times when EVs become more dominant on the automotive market.