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Senior Analyst – UK
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With a background in computational biology, Rueben Scriven joined Interact Analysis two years ago and leads the warehouse automation and on-highway commercial vehicle research areas. Rueben has spoken at some of the leading industry events and moderated several panel discussions on the topic of commercial vehicle electrification. He’s also appeared on CNBC to provide insight on the global electric bus market.

Zero-emission transportation technology is a high-stakes issue. The clean air we experienced in our cities during COVID-19 lockdowns showed what could be achieved if the world rejects the internal combustion engine in its battle with climate-change. The reality is that the internal combustion engine will most likely be on our roads for some time to come, but there is major progress in the transport sector where electrification is concerned. The electric city-bus powertrain is at the forefront.

Electric Powertrains Are Evolving Rapidly

A typical electric city-bus powertrain configuration consists of an energy source (a battery) a single traction motor with controller, and a final drive differential gearbox. The German giant Siemens has been a leader in electric traction development for city buses. Using their industrial motor and inverter technology, they developed the Electric Low Floor Axle (ELFA) drive system for hybrid and electric vehicle applications. The flexibility of the Siemens system allows OEMs to design their own specific powertrain configuration but, typically, motors are housed in the middle of the bus, under the floor, with a prop shaft connecting the motor to the rear axle. Articulated buses are driven by a motor in each cabin.

The hegemony of the traditional vehicle powertrain is now being challenged by new powertrain architectures designed by newcomers to the market – typically, automotive-specialists, rather than electric motor specialists. ZF have led the way with their AxTrax AVE drive axle. These axel-mounted motors are easily integrated into the existing bus chassis and use standard components. The high-driving torque of one single AxTrax AVE drive axle, with synchronised motors attached to each wheel, is powerful enough to propel an articulated bus. This new system offers significant break-throughs in city-bus design, given the space-saving nature of portal axles. There is no large motor in the centre of the bus, and no prop-shaft underneath. Buses can be lower, and the internal design can be more spacious for passengers – a significant factor in this new era of social-distancing. Meanwhile, floor mounted battery packages can be denser – with no need to make space for the prop shaft; and assigning one motor per wheel on the rear axle allows vector torqueing of wheels for better turning. Figure 1 shows the breakdown of the EMEA electric bus market by powertrain architecture.

Powertrains For Electric Buses – Who Are The Leading Electric Motor Suppliers?

In 2019, there were approximately 1,900 electric buses delivered in the Europe, the Middle East and Africa (EMEA), up from just over 650 in 2018, and many European cities plan heavy electrification of their bus fleets in the foreseeable future.

Many of the larger electric bus manufacturers such as BYD develop their own electric motors in-house. But regional or mid-sized bus manufacturers, such as Solaris, look to electric motor producers to power their vehicles. This is where the market opportunity lies for electric motor manufacturers such as Siemens and ZF, who have already taken the initiative in EMEA. In 2019, ZF was the leading electric motor supplier for EMEA, having delivered 520 out of a total of just under 1,900 units. Siemens came in second, with 491 units (see figure 2). In the much smaller US market for electric buses, Siemens has been a well-established player, but ZF is making significant inroads, having recently taken orders for their AxTrax AVE drive axle powertrains for 100 electric buses for the cities of Minneapolis, Seattle, Boston and Los Angeles. Interestingly, in what could be seen as a challenge to Siemens, ZF is varying its offer, developing central drive-line motors similar to Siemens’ original idea, that it will market alongside its Portal Axle units. This will potentially allow them to encroach yet further on Siemens’ electric bus powertrain market share.

For an in-depth market analysis of the electric bus sector, which shines a light on the significant opportunities opening up as zero-emission policies proliferate, get in touch with our lead analyst on the topic – Rueben Scriven.

Posted by Rueben Scriven

Graduating from Durham University with a first-class degree in Biochemistry, Rueben is leveraging his background in science and computer modelling by joining our growing analyst team.