A Glance at Direct Drive Electric Motors for EVs
Electric motors come in amazing variety, and electric cars are no exception. Last week I met CEO Gorazd Lampic and Marketing Manager Tjaša Hribar of Elaphe, a Slovenian company that manufactures so-called wheel hub motors for electric cars. These are motors attached directly to the wheels that transfer kinetic energy to the wheels directly. This offers several advantages, such as the elimination of drive axles, energy efficiency, and lower weight.
Wheel hub motors are nothing new. In the Technical Museum in Vienna, for example, there is a Lohner Porsche Phaëton dating from 1899 with wheel hub motors on the two front wheels.
Lohner Porsche had built entire racing cars with a proud 1,800 kilogram battery weight, such as this one from 1902, which had four wheel hub motors with a respective output of 1.5 kW.
Wheel hub motors are frequently used in streetcars. This allows stepless boarding because there is no need to install electric motors with drive axles in the vehicle floor. This fact allows to build skateboards with a battery pack floor, which bring high degrees of freedom for superstructures. The superstructures are not hindered by drive axles, motors, gearboxes and gimbal tunnels.
Other advantages are the lower weight of the motors, which at Elaphe are between 20 and 45 kilograms. The direct drive on the wheels means there is no need for a gearbox or drive axles, which also saves weight and reduces complexity. At the same time, the system achieves an efficiency of over 95 percent. Torque is 100 Nm/kg, with a maximum torque of 3,000 Nm at up to 2,700 RPM. Rim sizes between 14 and 21 inches can be covered by Elaphe.
To date, Elaphe’s wheel hub motors have been used in Lordstown, Aptera and Lightyear vehicles.
The disadvantages mentioned are the increase in unsprung masses at the wheels, which can impair ride comfort. Since the wheel hub motors are mounted directly on the wheels, they are more exposed to environmental influences such as water and road salt, as well as to accelerations, unlike conventional electric motors.
Here are more specifications of Elaphe’s solutions:
This article was also published in German.
