Volkswagen’s modular electric drive matrix (MEB) platform is to be the key element in its future models as electrification increases. The platform, to be used by Volkswagen Group brands such as Audi, SEAT, Skoda and Volkswagen, has many sophisticated components optimized for electric drive systems.
One of these is the APP310 e-drive unit that will used for the Volkswagen ID.3 due in showrooms from mid-2020. The powerful unit transmits power to the driven wheels using an extremely compact gearbox with a single gear. The mechanism used has only a small number of cogs. It is manufactured by a Volkswagen subsidiary.
Is one gear enough?
But why is a single gear enough for the drive motor? The traction, ie the force that allows movement, and speed of a motor vehicle depend on the rotational speed of its drive system. As the speed of the drive system increases, the force transmitted to the wheels – the torque – can vary.
With a vehicle with a combustion engine, the torque increases along with the engine speed and then falls again. With an electric drive system, however, the maximum torque is available immediately and remains constant over a wide range of speeds. The use of a multi-speed gearbox to achieve the desired speed or the necessary torque along the speed curve is therefore not absolutely necessary.
One gear for every situation
That is why a 2-stage 1-speed gearbox is practical for the Volkswagen ID.3. When reversing the car, the direction of the electric drive system is simply reversed. In addition to various other components, power electronics are responsible for this and for the power characteristics of the drive system.
In order to generate the maximum output of 150 kW, the 90-kg electric drive unit must rotate at high speeds. For a high level of torque, a 10x transmission ratio is used. To save space, the gearbox has a two-stage design with two smaller cogs instead of one big one. As a result, the electric drive motor in the ID.3 provides maximum torque of 310 Nm constantly over a wide range of speeds. The maximum speed of 160 km/h is reached at a maximum of 16,000 rpm.
Precision manufacturing
Because an electric drive system is very quiet, the level of noise in an EV is very important. Even the tiniest sources of noise can be heard. The parts for the 1-speed gearbox must therefore be manufactured with great precision to ensure that they do not cause any additional noise. At the end of the production line, not only the power characteristics of the electric drive system checked but so are the relevant noise levels.
