New Porsche Taycan and Its Transmission Unit
Recently, Porsche has presented its 2020 Taycan e-car and finally revealed a secret that has been widely discussed in the auto world: the new Taycan model will be equipped with a 2-speed transmission at the rear axle.
2020 Porsche Taycan at
Frankfurt Motor Show 2019
So-called “rear axle module” structure of the car includes the following components: motor, transmission, and power inverter. The whole “module” weighs about 170 kg.
The new Taycan is the 1-st e-car that comes with a 2-speed transmission, which has several strengths when compared to the 1-speed variant installed in other EVs. According to Porsche, the gear shifting unit for this EV is an in-house product. A multiple-speed solution in the EV powertrain can provide the same advantages that it does in gasoline-driven cars: better low-speed at speed-ups and higher performance capacity at higher speeds by lowering the RPM rate. To put it simply, the ratio spread of this transmission unit will have a positive impact on the car’s distance on one charge and its speed characteristics.
The Porsche's gear shifting unit has a single
planetary gear-set and 2 clutches that are responsible for the ratio swap or
disconnect the rear motor completely, ensuring effective operation with the
help of the forward-axle power. The gear step is quite big, with the 2-gear
ratio approximately half of the 1-st and the gear change point occurring at 80
km/h.
The unit has a torque-carrying capacity of 550 Nm. It and the whole rear module were developed to be as space-saving as possible. It is designed in such a way that the motor is at the rear, and its output shaft gets into a gearbox, which is expanded to a differential unit whose output is in line with the back axle. Porsche engineers integrated just one actuator for all gears (1-st, 2-nd, N, R, and P). According to representatives of the automaker, the gear shifting unit cools down thanks to the cooling jacket around the e-motor.
It is said that the low gear is a crucial element in the Taycan’s structure when it comes to stability in accelerations from dead stop —only 2.6 seconds to 60 mph, which Porsche claims can be reproduced 10 or more times, while also ensuring easy and efficient high-speed cruising. It is also claimed that in cases with less than half-a-charge, the car’s operational capacity will remain stable.
It should be noted that Tesla has long been using the architecture with 2 motors in its Model S cars. The Tesla’s design entails different gearing of the motors to achieve higher performance capacity objectives. Initially, the Tesla Roadster was planned to come with a 2-speed solution, but a fixed reduction-gear configuration was replaced by another solution after the unit was found not good enough during testing. It was unable to deal with the e-motor’s immense torque output.
