At the risk of sounding trite, Porsches might be some of the most usable, real world-friendly machines thanks in large part to their sophisticated all-wheel drive systems. With all four wheels intelligently propelling their cars up the road, astronomical amounts of power and torque can be harnessed by the least experienced drivers in the most treacherous conditions. As it turns out, this system was pioneered in one of Porsche’s first racing cars, taken rallying, and then later honed through decades of high-performance road cars.
Technology Borne from Motorsport
The complicated Cisitalia racer. Photo credit: LarryStevens/CC BY-SA 3.0
The 1947 Type 360/Cisitalia racing car employed an all-wheel drive system to harness the power of its supercharged twelve-cylinder engine, and while that made it usable on tighter corners, it also laid the foundation for the future of Porsche’s road cars. Fast forward thirty-four years, and a study of an all-wheel driven 911 Turbo hit the Geneva Auto Show; hinting at the promising future of all-wheel drive. This led to the Dakar-winning 953 and 959, which utilized a center-differential lock and rear differential locks like the current Porsche Traction Management (PTM) system does.
Introducing the First Carrera 4
Forty-one years after the Cisitalia began paving the way, Porsche’s road cars got to enjoy all-wheel drive. The 1988 Carrera 4 was the first production-series car which used “differential slip-controlled” drive. It adjusted for slippage with its ABS sensors and two electronically controlled multi-disc locks, which controlled the flow of forces to the front axle and between the wheels of the rear axle.
The ’88 Carrera 4 cutaway.
In the course of six years, a new model introduced a simpler, viscous-coupling system to reduce weight and improve traction in the form of the all-wheel driven 993s. Available now with the Turbo models, this system directly drove the rear axle and, in the event of speed differences between the front and rear axles, a passive viscous coupling transmitted some of the propulsion force to the front axle. Using the ABS system, these Porsches would also apply braking torque to individual spinning wheels with a system known as Automatic Brake Differential. This system would also provide a proportional amount of drive to the opposite wheel in such a situation, which improved wet-weather stability immensely.
Increased Complexity for Improved Control
With the introduction of the Cayenne, Porsche began using an electronically controlled multi-plate clutch operated by an electric motor as a variable center-differential lock. This made it possible to vary the distribution ratio according to the driving situation and to actively influence longitudinal and lateral dynamics. More complex than its predecessor, the Cayenne’s new system did more than respond to slippage; its sensors also detected vehicle speed, lateral acceleration, steering angle and accelerator control to calculate the correct amount of lock.
Sharpening the System for the 997 Turbo
To improve performance, the 997 Turbo’s PTM system featured an electronically controlled and electro-magnetically actuated multi-plate clutch, which further improved distribution of propulsion between the front and rear axles. A maximum response time of 100 milliseconds means the Porsche responds faster than the driver or the engine, and this makes for incredible usability over sodden backroads, debris, and real-world surface imperfections.
The 997’s updated PTM gave it a level of stability unrivaled by any contemporary sports cars.
Constant refinement of their stability management systems give the heavier machines in the Porsche stable—namely the Macan and the Panamera—the same sort of otherworldly, ultra-capable performance. For this reason, Porsche’s plusher people carriers have a level of real-world usability and speed that belies their heft; a trait which continues to set the marque apart from its rivals.