Meet Robert Carter, Principal Engineer for the Powertrain of the Volta Zero

By Duncan Forrester | 18 March 2021

Can you tell us what jobs you've done previously, and how you ended up leading the development work on the powertrain of the Volta Zero?

"I’ve been involved in EV powertrain development for over a decade, from designing high performance electric motors through to ultra-efficient range extender systems and complete powertrain development. I’ve had the opportunity to work with both small and large manufacturers, on everything from light-weight electric sports cars to range extended commercial vehicles. In 2018 I stepped back from engineering to undertake an MBA at Imperial College London, with the aim of better understanding the wider picture required to make and grow successful businesses. I returned to the automotive sector with a renewed sense that sustainability applied to more than just the vehicle, choosing then to focus on developing business strategies to support fledgling electric vehicle programmes. When the opportunity to join Volta Trucks came up in 2020, I jumped at the chance to be a part of helping grow an organisation focussed on both a pioneering vehicle and the customer orientated Truck as a Service concept.."

The process of specifying the powertrain on a full electric truck must be very different to that of a legacy internal combustion engine. How does the process differ and what are the most important factors?

"The Volta Zero is designed around the driver, but the whole concept really goes beyond this to consider the needs of the driver, the fleet operator and other road users. The powertrain specifications fit around, and help address, these needs, from the packaging constraints required to deliver the low cab position to the charging performance that enables fleet operators to effectively integrate an electric vehicle into their existing operations. Taking the time to carefully evaluate how each decision would impact the end-product, without needing to work around legacy design, was certainly the biggest difference compared to specifying a powertrain in a conventional vehicle. On the other hand, there were several fixed targets such as ensuring the Volta Zero has the driving performance expected from a 16-tonne vehicle and delivers maximum reliability throughout its life. There was also a lot of focus on specifying the energy consumption of various systems on the vehicle. Every component has a role to play in delivering the overall vehicle efficiency target and we must keep that in mind much more than on a conventional internal combustion engine vehicle."

What are the main opportunities and challenges you have in developing the powertrain for a 16-tonne full electric commercial vehicle?

"One key opportunity for improving overall efficiency arises from the need to electrify all vehicle systems that might conventionally have been driven from the internal combustion engine. The use of electric ancillaries such as fans, pumps and refrigeration systems is much more efficient and offers the flexibility to locate them around the vehicle. Some of the challenges faced relate to the sensitivity in balancing key electric vehicle performance targets. For example, there is a strong relationship between range, charge time and available payload capacity when sizing the battery. Here the vehicle performance is much more sensitive than it would be to the capacity of a fuel tank and there isn’t the flexibility to infinitely vary the battery capacity as with a liquid fuel. Fundamentally, good understanding of the customer use cases and required vehicle performance is the key to solving these challenges."

You recently announced Meritor as the supplier for the innovative eAxle, being an integrated motor, transmission, and axle unit. Why did you choose that solution, rather than a more conventional central motor and prop shaft set up?

"The eAxle solution quite quickly became an essential part of delivering the key targets set for the Volta Zero. The compact installation provided by an eAxle allows us to locate the entire high-voltage battery system between the chassis frame rails, maximising the protection and safety of the battery. The single motor and gearbox combination provides the Volta Zero with the performance required when fully laden and aligns vehicle usage to the most efficient operating range of the motor. At the same time, the eAxle configuration selected reduces the cost and complexity associated with multi- motor drives, ensuring the Volta Zero is a robust product both technically and commercially."

You've also announced Proterra as your battery provider. Clearly range is important, but that's a function of battery size. How do you decide the range of the vehicle, and what other considerations go into the choice of supplier and battery technology / chemistry?

"The Volta Zero battery was specifically chosen to meet the daily usage of a 16-tonne urban delivery vehicle, whilst also providing flexibility around different shift patterns and key use cases such as the fitting of a refrigerated load box. This influences capacity requirements, but also the lifetime cycle requirements and the allowable charge rate to ensure the vehicle can operate on fast turnaround shifts. The battery on an electric commercial vehicle is inevitably a sizable component and achieving a high specific energy was always a key target. Every kilogram of weight saved leaves more capacity for cargo. This is certainly one element of the cell chemistry choice along with factors such as cost, lifetime degradation and automotive maturity. The Proterra product selected provides the Volta Zero with the target combination of physical attributes and performance at both a cell and pack level. In addition, the use of the latest chemistry gives us opportunity for further improved performance ensuring the Volta Zero will remain a competitive vehicle long into the future."

This is clearly a very fast-moving arena. If you look ahead to five years’ time, how do you think the battery and motor technology will have evolved, and what should we expect to see?

"Electric trucks stand to benefit significantly from improvements in battery technology because the battery strongly influences factors such as payload capacity, lifetime cost and operating flexibility. I expect to see commercial vehicles taking advantage of cell and pack level improvements to deliver more range, reduced weight, faster charge times and improved battery life. All of which make the transition to electric vehicles more compelling for fleet operators. I also hope we will see a transition to technologies with improved lifecycle sustainability. The size of key powertrain components like the drive motors means there are significant gains to be made by switching to technologies that have simple end-of-life recycling methods. There are already maturing technologies that can deliver in this area and I think we will see those increasingly adopted in commercial vehicles. The electric vehicle technology for trucks is already moving fast and I expect to see this trend continuing. For example, today we see a lot of the high-voltage components available as discrete products, e.g. one unit is a charger and the other is an inverter. Although this lends itself to packaging flexibility, I think it’s inevitable that we will see more integrated products where one unit can serve multiple functions. We’ve already seen this transition in passenger vehicles where it reduces cost and weight, and our eAxle is a perfect example of the start of this transition in commercial vehicles."

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