Batteries Not the Only Route to EV Efficiency

Allison CTO stresses efficiency and safety of propulsion units also are critical to reducing cost, improving performance and ultimately winning over customers.

Allison Transmission’s eGen Flex electric hybrid propulsion system can provide up to 10 miles of full electric drive capability, and can automatically geofence for zero-emission zones and passenger depots. (Allison Transmission)

Much of the talk around the switchover to electric power in commercial electric vehicles (EV) focuses on batteries, whether it be their range, weight, energy and power density, or expected life. Allison Transmission supplies hybrid propulsion products for transit buses and is bringing to market e-axles for battery-electric vehicles (BEV). For each of those applications, a different battery chemistry will win out as OEMs and operators factor the cost, performance, duty cycle and lifespan of the batteries into the vehicle’s total cost of ownership (TCO).

Since acquiring the e-axle IP from AxleTech in 2019, Allison engineers have put the product through extensive development and validation. (Allison Transmission)

Battery cost is falling but remains a high-value proportion of the TCO. For BEV applications, which might only require one daily discharge cycle and an overnight charge, nickel-manganese-cobalt (NMC) batteries seem to offer the best balance today. Other chemistries have a higher cycle life and power capability, but also come at a significantly higher cost. For hybrids, lithium-titanate-oxide (LTO) and other chemistries have much higher specific power and lifespan. With the constant movement of energy level in a hybrid battery, a higher cycle capability is required.

While batteries are essential, they are not the only key component in spurring the rollout of commercial EVs. The propulsion unit – which could be either a direct or central drive, or an e-axle – converts the electrical energy from the batteries into kinetic energy at the wheels. With all the traction power passing through this unit, the efficiency and safety of the propulsion unit is also critical to reducing cost, improving performance and ultimately winning over customers going forward.

The route Allison is taking for its propulsion systems, whether e-axle or central drive, is agnostic to the energy source, which could be a battery pack of a certain cell chemistry, or a hydrogen fuel cell as a range extender for the battery pack. Allison is aware that particular chemistries have the right amount of power and specific energy available for different lifecycles but, in supporting OEMs, try to remain agnostic to competing battery chemistries and suppliers.

Integration and development

Feedback from OEMs suggests that many like the e-axle location. Allison’s eGen Power 100D for vehicles with a 10-ton axle rating will be in production later in 2021. (Allison Transmission)
The Allison Hybrid 40/50 Electric Propulsion (H 40/50 EP) system, paired with the Cummins B6.7 and L9 diesel-electric hybrid engines, has received 2021 California Air Resources Board certification. (Allison Transmission)
Michael Foster, Chief Technology Officer for Allison Transmission. (Allison Transmission)

It is important to integrate electric propulsion with the entire system. That integration could be anything from the onboard energy management – integrating energy management across the accessories, the battery and propulsion components – down to the physical packaging.

One of the reasons Allison is producing e-axles, beginning later in 2021 with the eGen Power 100D product for vehicles with a 10-ton axle rating, is this location optimizes battery integration onboard the vehicle. For heavy vehicles requiring a lot of energy on board, having the drive system packaged between the wheels frees up space for the battery between the frame rails. It’s also important to understand how much energy capacity (kWh), and associated packaging volume, is required for a given vehicle on a given duty cycle.

Work on integrating electric powertrains has led to investment in updated development laboratories. As Allison continues to expand into a broader portfolio of EV propulsion, including e-axles, additional high-voltage battery emulator capacity is being installed alongside traditional, diesel-fired engines in test cells. That applies not only to dynamometer cells but also the new Vehicle Environmental Test (VET) Center in Indianapolis.

OEMs will decide whether direct, central or e-axle drive solutions best fit their applications, but their choices will be based, as always, upon packaging efficiency, durability and the TCO for the system. Since acquiring the e-axle IP from AxleTech in 2019, Allison engineers have put the product through extensive development and validation, both internally and with potential customers.

Trials in OEM vehicles continued throughout most of 2020 and are ongoing in 2021. Feedback received from OEMs thus far suggests that many like the e-axle location. There are, however, certain applications where a central drive to replace the engine and transmission is preferred. A port truck, for example, can have very high axle rating – in that case, a central drive can be installed and the existing attributes of the vehicle utilized.

Role of fleets and legislators

It’s not just OEMs that are stating their position on adopting new technologies and making commercial-vehicle operations more sustainable – fleets are as well. For them, as always, cost is key. Wherever barriers to adoption can be lowered or removed, including by increasing the efficiency of the electric powertrain, there will be a motivation to accelerate the changeover process.

Many of the big fleets have shared how they want their fleet to look 10 or 20 years from now. That’s a huge influence on how the market will develop, especially given the size of some of the larger fleets. They will motivate the OEMs, which in turn will look to Tier 1s to bring these products forward. We are already seeing developments in small-package and last-mile delivery fleets. With a boom in e-commerce, new OEMs and new types of vehicles are emerging.

The speed at which commercial EVs will switch over to electric power will differ from segment to segment, and from region to region. Some segments, notably transit, are moving faster than others. In North America, developments in medium-duty pickup and delivery will start to gather speed. The school bus sector is starting to move early, as are many port truck applications. All these sectors are looking to clean up areas where a high percentage of vehicles operate in a very a confined space.

The switchover also is happening in areas where subsidies and legislation are acting as a motivator for adoption. In Europe, for example, there has been movement towards hydrogen in some of the over-the-road tractors, which differs from North America currently. The trends will continue to evolve as infrastructure, subsidies and funding get put in place – anything that reduces the cost of adoption – so we need to be mindful of where those motivators are as we assess market opportunities.

Hydrogen and hybrids

When it comes to widespread use of hydrogen fuel cells, the progress of infrastructure will influence the long-term cost of fuel cells versus BEVs. As it stands today, the larger over-the-road applications seem to be a better fit for a fuel cell, as adding battery weight to extend range eats into the payload. For long-distance runs, the shorter refueling time also works in the fuel cell’s favor.

In the meantime, we shouldn’t ignore the role that hybridized ICEs could play. Where they thrive will be driven by emissions regulations for NOx and other greenhouse gases. BEV or ZEV zones will require emissions-free running, but emissions must also be reduced on the operational side. There’s definitely a place for the hybridization of conventional products to meet some of those regulations in the near to even the long term.

Diesel is going to be around for a very long time, so how do we continue to improve it and allow it to play its part from an emissions perspective, while BEVs or fuel-cell electrics have a slow ramp up? The hybridization of conventional propulsion systems is an opportunity to meet some of the regulatory items without a significant overhaul of the vehicle.

Michael Foster, Chief Technology Officer for Allison Transmission, wrote this article for SAE Media as part of the annual Executive Viewpoints series.