Porsche on Wednesday provided the first details on a new electric powertrain it's developing.
The powertrain consists of four electric motors, with each motor capable of independently controlling a corresponding wheel, something referred to by the automaker as “variably distributable drive power.”
Porsche said this torque control system can enable a high level of control in critical situations, such as entering a sharp curve with too much speed or hitting a patch of slippery road.
For the example of entering a curve with too much speed, a vehicle will tend to understeer and perhaps even slide in a straight line without slowing. To counter this, Porsche's system would brake the inside wheel at the rear axle while accelerating the outside wheel.
This is the same way a speed-sensing limited-slip differential works, but with electric motors the adjustments can be made much quicker—we're talking within milliseconds. Another benefit is that there's no wear like you get with a mechanical differential.
When driving down a slippery road, the system detects when a wheel slips and immediately directs the torque to the wheels that are turning more slowly and still have grip within fractions of a second.
The torque control system is in constant operation, with software distributing the torque in such a way that the handling always feels neutral. How effective is it? According to Porsche, its test vehicle in the critical situations mentioned above could continue with a brisk speed of 50 mph like it were on rails.
The biggest challenge in developing the system is determining what actions to take based on a variety of factors that stretch well beyond just wheel slip. These include how forcefully the steering wheel is being turned, how much the driver is accelerating, and how much the vehicle is turning around its vertical axis. The latter is provided by a yaw sensor.
Where issues tend to arise is when determining the weight distribution of the vehicle and the speed. The latter is usually derived from the speed of the wheels but on snow and ice slipping wheels will indicate a faster speed than actual. In both these cases, the system has to rely on estimates. Porsche uses additional information about the longitudinal and lateral acceleration in order to estimate the speed, while for weight distribution it checks how much the shock absorbers are compressed.
Porsche is testing the system in an SUV with a view for production, but didn't say when we might see it. A possibility is a range-topping version of the electric Macan the automaker will launch early next decade. The system can also be tuned for other motor configurations and vehicle types.
