Suspension: Description and Operation

45 Porsche Stability Management (PSM 8)

General

With the introduction of the new 911 Carrera and 911 Carrera S, the Porsche Stability Management has now been made standard equipment. The PSM comprises the already known functions; ABS (anti-lock braking system), ASR (anti-slip regulation), EDTC (engine drag torque control), ABD (automatic brake differential), EBD (electronic brake-force distribution) and DDC (driving dynamics control).

A special Sport mode is available for the first time in PSM as part of the optional Sport Chrono Package Plus. This Sport mode facilitates a sportier drive and increases driving pleasure by allowing the driver to switch characteristics or functions in PSM via the Sport button.

The following objectives were achieved in the development of the PSM 8 for the 911 Carrera S:
- Reduction of braking distance and thereby extension of Porsche's market-leading position in the field of brake technology.
- The driver is to be allowed more freedom before PSM intervenes than on the previous 911 Carrera (996). Especially when the PSM is switched off. To this end, the system, which is still activated by pressing the brake, is only to be activated in real emergency situations.
- At the same time, the control comfort was noticeably improved and the PSM system's weight was reduced.

Implementation of Set Goals

More Agile Setup

PSM in the 911 Carrera/S offers more individual freedom than before thanks to the further development of its function logic. PSM deliberately waits until the last moment to intervene, particularly at low speeds of up to around 45 mph (70 km/h), enabling more agile driving behavior in tight corners.

Reduction of Braking Distances

A reduction of braking distance has been achieved through the higher control quality of the PSM and the optimized ABS setup in combination with the new tires. The valves used in the previous PSM to regulate pressure in the ABS system were conventional switching valves which enabled regulation in defined, although not very precise, pressure stages. The linear solenoid valves used in the new version allow virtually infinite and thus more precise regulation of the brake pressure. This way the control quality is improved and a more accurate ABS control, closer to the brake pressure optimum, has become possible. The result is a signification reduction in braking distance.

Increase In Comfort

Control comfort has been noticeably improved. PSM interventions with the new system are noticeably smoother and more harmonious thanks to enhanced control algorithms. Brake pedal pulsation with ABS has been reduced through the use of the new linear solenoid valves. PSM control noises have also been significantly reduced in comparison with the previous PSM.

SAFETY:
Limits of PSM
While PSM is designed to maintain driving stability and offer a significant improvement in driving safety, it is by no means capable of changing the laws of physics: in other words, the driver alone is solely responsible for all manoeuvre, even when using PSM.

Three measures were implemented to reduce the control noise:
- Specific PSM software customization to control the PSM hydraulic pump as required. The full pump performance and thereby pump speed, which is the main source of the noise, is only requested when absolutely necessary for the driving situation or the PSM intervention.
- Use of hydraulic damping elements in vicinity of the PSM hydraulic pump. These ensure that pressure pulsations caused inside the brake system during the PSM interventions are reduced.
- Installation of new, softer brake line holdings to isolate the brake line from the body to reduce hydraulic noise.

These implemented measures result in a noticeable reduction of the control noises during PSM intervention when compared to the previous system.

Reduced Weight

The introduction of the PSM 8 has permitted a significant reduction of the system's weight. As a result, the hydraulic pre-charge pump including bracket and hydraulic connecting line is no longer required. The PSM 8.0 pump can now ensure the dynamics required for the entire system (brake pressure build-up for PSM interventions) on its own without pre-charging, which has allowed the PSM system weight to be reduced by 25% (3.0 kg).