Scandinavians blazing a trail
The Scandinavian truck makers are blazing a trail when it comes to e-mobility in South Africa. Scania launched its first electric truck in South Africa back in August 2022, when it delivered one to the Shoprite Group to pilot. Zero-emission vehicle sales by the company globally amounted to 246 units last year (versus 262 in 2022).
On the other hand, Volvo Trucks – which sold 1,977 electric trucks during 2023 (an increase of 256% compared to the previous year) – launched electric versions of the Volvo FH, the Volvo FM, and the Volvo FMX in South Africa in June 2023. They are available in truck tractor or rigid configurations, from 4x2 to 8x4.
Eight components make e-magic
But how do these trucks work? According to Fredrik Sundén, an e-mobility developer at Scania Research & Development, there are eight components that work together to make e-magic happen. They are:
- Batteries
- Power inverter/converter
- Electric motor
- Gearbox
- Propeller shaft, differential and axles
- Regenerative braking
- Wheels
- Digital management and control
Let’s start with the battery pack, which stores electrical energy. In Scania’s battery-electric vehicle (BEV) trucks, these battery packs are made up of modules of lithium nickel manganese cobalt oxide cells. These batteries are also commonly used in portable electronics, and energy storage systems due to their high energy density and relatively good performance characteristics. “We always make sure the capacity of the battery packs is optimised for the vehicle’s typical transport tasks and routes,” says Sundén.
Energy is converted
Next up is the power inverter/converter. The direct current (DC) electricity stored in the battery needs to be converted into alternating current (AC) to power the electric motor. A power inverter or converter performs this conversion. “AC motors are commonly used in electric vehicles because of their efficiency, power density and easier control of the motor speed,” explains Sundén.
The converted AC electricity is supplied to the electric motor. In Scania’s BEV trucks, the electric motor is a permanent magnet synchronous machine (PMSM).
In a PMSM, the rotor contains permanent magnets, usually made of materials like neodymium or samarium-cobalt, which generate a magnetic field. This magnetic field interacts with the rotating magnetic field produced by the stator windings to generate motion.
“This machine converts electrical energy into mechanical energy through a magnetic field in the stator, induced by the AC, which in turn causes the permanently magnetised rotor to rotate. A combination of strong magnets and high voltage results in greater power and torque from the electric motor,” explains Sundén.
Transmission differs from those found in cars
The fourth element is the gearbox. Unlike electric cars, which often can operate efficiently with a single-speed transmission, heavy transport vehicles such as BEV trucks need gears to enable high torque across different speeds.
The power from the electric motor is sent to the wheels via the propeller shaft through a differential and a set of axles.
Regenerative braking is key
Next up is regenerative braking, a key feature of BEVs. During braking or coasting, the electric motor operates in reverse, acting as a generator. It converts kinetic energy back into electrical energy, which is then sent back to the battery, improving the overall energy efficiency.
“The energy savings from recuperation are dependent on the operation,” says Sundén. “The best scenarios are urban operations or hilly terrain where there is a lot of braking required. In these scenarios, the energy efficiency can be improved by 30% or more by recuperating the kinetic energy.”
The final mechanical process is the transfer of power to the wheels, which is required in order to propel the truck forward. Electric powertrains are far more efficient than internal combustion engines, notes Sundén. “All in all, the powertrain of a BEV typically transfers two to four times more energy to the wheels than a combustion engine. The efficiency level of a BEV is around 85 to 90%, while combustion engine vehicles often have a powertrain efficiency of around 35%.”
Finally, this entire process is managed and controlled by the vehicle’s electronic control unit (commonly known as an “ECU”) and the battery management system. “These systems monitor and optimise various parameters such as battery temperature, state of charge, and power distribution to ensure efficient and safe operation,” says Sundén.
So, there you have it: electric trucks sliced and diced into eight easy-to-digest steps!
