ThinKing October 2019: Petite power pack - 80 percent lighter compact electric motor



Benefit from a greater payload or drive further on the same amount of energy.

The engineering firm Rainer & Oliver PULS GmbH has developed an electric drive for commercial vehicles which, by integrating functions, has only around one fifth of the weight of a conventional motor. This means that it can pack a bigger payload or drive further on the same amount of energy. It all comes down to the motor's much faster rotational speed. What is more, two motors and the transmission are located in a single load-bearing housing unit where they replace components such as the rear axle transmission, differential and limited slip differential. This not only saves material but also ensures much smaller dimensions of the drive unit.

The Development Agency for Lightweighting Baden-Württemberg presents this innovation in the October 2019 edition of the ThinKing. Leichtbau BW GmbH uses this label to showcase excellent lightweight technology products or services from Baden-Württemberg every month.

At a glance:
- Approximately 80 percent lighter than motors with a similar output: bigger payloads are possible with lower consumption
- The electric motor is smaller → more space for battery packs → longer ranges
- Two separate controllable motors and planetary gearheads are fitted in a housing as a load-bearing unit → fewer built-in components
- More design freedom, e.g. optimised positioning of battery packs in the vehicle floor

The engineering firm Rainer & Oliver PULS GmbH produces its own e-drive for commercial vehicles. The team relies entirely on the principle of lightweight functional integration: “Motor and planetary gearheads are integrated in a housing which is designed as a stable component and which can therefore absorb forces acting on the wheels and axle from the road”, explains managing director Rainer Puls. The motor and transmission unit, for example, can be integrated in a tubular dead axle as a force, bending and torque transmitting component; they do not need any additional parts for attachment to the chassis.
“This special design not only enables us to reduce the number of components built in, such as seals, bearings, couplings, flanges and fastening elements, it also enables us to achieve much greater efficiency”, explains Puls. This also reduces the spatial dimensions of the motor which can then be integrated directly in the motor. “This in turn saves further components as no additional brackets are needed on the chassis and no propeller shaft is required either”, according to Puls. “The high loss rear axle transmission, differential and limited slip differential are not required as each wheel of the axle is driven by its own motor, making an electronic differential and torque vectoring possible. The traction and braking forces for each wheel can be controlled and regulated separately”, continues Puls.

80 percent lighter than comparable conventional commercial vehicle motors
But can the “small” motor actually do as much as a bigger one? “Yes, because power is the product of speed and torque. The smaller torque reduces the installation space and is compensated simply by a higher speed. Our motor runs at speeds of up to 22,000 and 27,000 revolutions per minute and delivers the same driving performance as a comparable vehicle engine”, says Puls. The motor/gear unit itself and its two motors only weigh around 100 kilograms – a normal engine with the same output for a 7.5t to 12t vehicle with gearboxes would weigh around 500 kilograms, calculates Puls and adds: “Lighter drive components mean a much bigger payload.”

“Lightweighting saves money”
“Lighter vehicles also consume less fuel. The low weight of electric drives increases a vehicle’s range. However, when range implies more batteries, it becomes much heavier and more expensive. In other words, lightweight technology saves money”, explains Dr. Wolfgang Seeliger, Managing Director of the Development Agency for Lightweighting Baden-Wuerttemberg (Leichtbau BW GmbH). What is more, the motor will also make completely new vehicle ideas feasible. “The electric motor built by Puls is a fantastic example of a lightweighting concept. It's a completely new way of thinking about and designing a vehicle”, says Seeliger. And Puls adds: “The drive unit’s more compact dimensions enables more ground clearance, for example, and the battery pack to be positioned better in the body floor to enhance crash safety. Our two-motor solution also improves vehicle agility and turning radius including the associated option of torque vectoring”, says Rainer Puls.

About Rainer & Oliver PULS GmbH
The Karlsruhe-based company operates in the design, development and production of special gearboxes, complete drive systems with controls and test benches for all areas of industry.