Electronic differential
The main purpose of the electronic differential is to substitute the mechanical differential in multi-drive systems providing the demanded torque for each driving wheel and allowing different wheel speeds. When cornering, the inner and outer wheels rotate at different speeds. This happens because the former describes a smaller turning radius. The electronic differential uses the steering wheel command signal to control each wheel speed in order to smoothly perform the turning.
Functional description
The classical automobile drive train is composed by a single motor providing torque to one or more driving wheels. The most common solution is to use a mechanical device to distribute torque to the wheels. This device, called mechanical differential, is responsible to allow different wheel speed when cornering. With the emerging of electric vehicles new drive train configurations are possible. Multi drive systems become easy to implement due to the large power density of electric motors. These driving schemes with one motor per driving wheel need an additional top level controller which is responsible to perform the same task as the mechanical differential. Named electronic differential, it is capable of substituting its mechanical counterpart with significant advantages.
The ED scheme substitutes the mechanical differential with several advantages:
- simplicity, it avoids additional mechanical parts like gearboxes or clutch;
- independent torque for each wheel allows auxiliary functionalities (e.g., traction control, stability control);
- reconfigurable, it is reprogrammable in order to include new features or tuned according to the driver’s preferences;
- allows distributed regenerative braking;
- does not have the mechanical differential limitation where the torque limited by the lesser traction wheel.
Moreover, a multi-drive traction system with distributed electric motors have advantages over the traditional solutions[1]:
- faster response times;
- accurate knowledge of traction torque per wheel.
Applications
Several applications of this technology proved to be successful and have increased the vehicle performance. The application range is wide and includes the huge T 282B [2] from Liebherr which is considered the world largest truck. This earth-hauling truck is driven by an electric propulsion system composed by two independent electric motors. These motors providing a maximum power of 2700kW are controlled in order to adjust their speeds when cornering thus increasing traction and reducing tire wear. The Eliica is also equipped with electronic differential; this 8 wheeled electric vehicle is capable to drive till 370km/h maintaining perfect torque control on each wheel. Smaller vehicles for traction purposes and System on Chip controllers for generic vehicular applications are also available from WeMoveU company. [3] [4]