Porsche steers a new course

Rarely has a mechanical change evoked such comment or pontification before the fact. The news that Porsche's 911 was to get electric assisted power-steering (EPAS) in its latest 991 iteration was the elephant in the room at the vehicle's launch in California last week.

The good news is the system works well... Very well, in fact... But how is this the case when most other electrical steering systems fail to make the grade, and performance operations like BMW's M division still vigourously oppose EPAS' use.?

We asked the man in charge of the development of the system, Porsche's Ulrich Morbitzer.

Morbitzer explained that he was not enamoured with the idea at first but that now he's a convert to the abilities and potential of EPAS. The system in the 911, developed jointly between Porsche and ZF not only delivers fuel economy savings but also onroad and track performance that has been signed off by Porsche's driving dynamics 'guru', ex-world rally champ, Walter Rohrl.

"At the beginning we didn’t consider it necessary to introduce an electric steering system because if you want to improve driving dynamics then it is not necessarily a component which you need in a car," Morbitzer told motoring.com.au with the help of a translator.

"And while reducing fuel consumption was important... The most important thing for me, was improving or increasing comfort [confidence].

"In the beginning I really was worried. But now, having seen the system in the car, all the worries, all the concerns, have disappeared."

Morbitzer says the Porsche/ZF steering system is very different from other systems. It took around three years to develop, but the lion's share of development time was not the 'hard parts'.

"The most important parts are not the components -- are not the gears; not the mechanical [items]. It’s more the software intelligence; the intelligence you find at the controls. In the beginning, in the early phase of the development process, this required us to completely change or revise our philosophy," Morbitzer explained.

Part of the development process called on racing – the system used in the new 991 Series 911 is very similar to that used in the 997 GT3 RSR racer. But mostly it was on the road, where Morbitzer says the Porsche engineers concentrated on finding a solution that would deliver feeling to the driver when it counted.

Porsche's system does not change current to the electric motor as a way of altering assistance, rather it controls the torque output of the unit.

"All [the EPAS] systems I know, at the moment are regulating not the steering torque but the current of the electrical motor. We are able, with the new regulation system, to regulate indeed the [torque the motor applies to the] steering column

"And that’s different, because you have effects from temperature, you have effects from friction [in normal use], so if you regulate the current, you get different steering torque [because of these variance]. If you regulate the torque you [always] get that torque you want to have."

Morbitzer explained also that the power of the motor used in the Porsche EPAS system is quite high – it therefore doesn't require additional gearing to deliver the assistance levels required.

"This strong motor allows us also... very good dynamic performance. We can do about 1000 degrees [of rotation] per second... This is very important for a sports car. Other electrical systems stop their support when [they go lock to lock quickly].

"These two points I think are the main difference between the known electrical [steering] system."

The resulting system allows the engineers to 'tune' in the frequencies of feedback a driver needs. There is a direct mechanical link between steering wheel and front wheels, but a virtual 'inertial' mass, created by the system's electrically-generated torque, is used to filter out feedback such as kickback and roadshock – most of which occurs in a low frequency range. The valuable 'messages' such as the sense of a front tyre losing grip is in a different frequency range and arrives at the driver's hands unadulterated.

"So we are lucky on the one hand to have more comfort in the 911 from today or older.

"If you want to go straight on and you are on a very rough road [Morbitzer acts out constant left-right steering effort] you are sitting like this inside. Some people say that’s 911 feeling, but I say that’s not good information for the driver. It’s not very stable.

"[With the new car on the same sort of road] It’s very easy and comfortable and very calm, not nervous. But I think you don’t lose the feeling of the contact of the friction between tyre and street because of these two points, I told you."

Morbitzer says the steering system also gives Porsche the ability to highlight appropriate communication to the driver.

"I think we have, with this system we have more possibilities to react on special situations. You see, the hydraulic system is always the same -- it depends on the rotations of the engine. [With the Porsche/ZF EPAS system] we can introduce [augment] feedback in order to reinforce this feeling the driver has when understeering starts, for example."

Morbitzer says purists have nothing to fear, however.

"It is important to remember or bear in mind that these are all just assisting or supporting systems. We never want to come up with something which is man-made or artificial," he said.

Read the latest news and reviews on your mobile, iPhone or PDA at carsales' mobile site…