The SUMO powertrain systems family: A direct drive to success

September 22 2017

TM4 introduced its first SUMO powertrain system in the market during the summer of 2012, which means that this family of products is now entering its fifth year of deployment in dozens of vehicles applications. With more than 75 million kilometers of real road driving and no design-related failures, the technical and commercial success of this product family is evident. More importantly, it helped TM4 establish itself as a global supplier of electrified commercial vehicle drivetrains, both by expanding its direct sales and support network capabilities but also by forging alliances with major industry players, such as Cummins, for the development of PHEV bus range extender system.

Establishing our presence in the commercial vehicle space, step by step.

TM4 had its first experience in the commercial vehicle space more than 10 years ago, being contracted by Volvo to develop its I-SAM parallel-hybrid system and supply them for the initial prototypes runs. TM4 only had a prototyping workshop in 2007 and could not bid on the volume production project; hence Volvo went to other suppliers for volume production. That being said, the fact that this system is still used today by Volvo shows that the concept and the design made by TM4 were right for the application.

This proved to be a great introduction to the needs of these vehicles and helped TM4 to make more rational design choices when starting the development of powertrains for all-electric trucks and buses a few years later. Coming mostly from an automotive background, we first envisioned the development of a more powerful, high-RPM electric motor similar to what is found in our MOTIVE systems. Such a motor would need to be coupled to a multi-speed transmission in order to achieve the torque needed to operate the EV buses and trucks according to the same duty cycles that ICE buses are used to. However, looking at what was available on the market, there was no products available in production to couple with a performance machine. Everything was custom made, very expensive and produced in low volume. This is when we decided to go with a direct motor. While bigger, it still was less expensive than a motor + gearbox combination and also reduced the mechanical losses of the drivetrain, maximising the use of the on-board battery, which is the most expensive component. Moreover, the OEM can retain its standard axle and the installation of a direct-drive system is as simple as it gets and easily replicable in many vehicle platforms.

One important driver of its success was the set-up of our joint-venture with Prestolite Electric Beijing, PEPS, to serve the Chinese market with domestic production. This not only helped us develop a reliable low-cost/high volume supply chain there, but also allowed us to produce our systems in significant volumes in order to take advantage of the huge boom in electric bus sales of the 2010’s. A lot of in-field data generated in what are sometimes difficult conditions allowed us to quickly learn about ways to optimize our systems and make them even more rugged. Achieving  TS 16949 certification was also a big step for us as a company, enabling us to supply high-volume OEM programs.

Motor assembled at PEPS


Current market situation

Fast forward 5 years later and here we are, with thousands of buses and trucks equipped with our powertrain systems. The SUMO line has evolved as a family of powertrain systems offering more than 10 versions, each optimized to offer the best driveline efficiencies to different vehicle platforms according to selected duty cycles. Still, as we speak, there are no competitive multi-speed transmissions in mass production offered on the market for medium- and heavy-duty pure electric buses and trucks. There are certainly several initiatives that have been presented, but they are still either at a low maturity level or developed exclusively for/by select OEMs. Some have also adapted conventional transmissions to electric motors, but raises concerns about long-term reliability and efficiency optimization. Because of that, direct-drive is to this day the only powertrain electrification solution for buses and trucks that ticks all of the following boxes:

☑ affordable
☑ reliable
☑ proven
☑ efficient
☑ available in mass production.


What the future holds

This is not to say that we believe direct-drive is necessarily the best configuration for all types of vehicle platforms. Several electrified axles have started to make their way in the market and while they are generally more expensive and complex to integrate in the vehicle (reducing the amount of “standard” parts), they represent interesting alternatives for vehicles where space constraints are high. Their deployment is also part of a movement towards more integrated electric drivetrain systems. TM4 is not missing out on the trend, also working with axle manufacturers to offer optimized electric axle products, both for the on- and off-highway markets. One of such projects is with Axletech, and the focus is on the development of different types of electrified axles to tailor to the needs of medium- and heavy-duty bus and truck applications, as well as off-highway vehicles.

As we strive to maintain a leadership position in the electric powertrain field, we need to stay at the forefront of technologies, and regardless of whether or not direct-drive remains the most cost-effective solution to electrify the powertrains of commercial vehicles in the long run, this type of motor technology has shaped TM4’s as a company and helped us achieved global commercial success.

For the next 5 years, we already have a busy schedule of new products and innovation to introduce to the market, so be sure to follow us to stay informed of our latest projects!

Olivier Bernatchez
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