Porsche Stability Management (PSM)
Porsche Stability Management (PSM)
The new Cayenne features enhanced Porsche Stability Management (PSM). This offers superior active driving safety even at the performance limits of extreme longitudinal and lateral acceleration without affecting the typical Porsche agility. The PSM setup was modified and adapted to use of the new Porsche Traction Management (PTM) or new optional Porsche Torque Vectoring Plus (PTV Plus). PSM improves active safety through the following functions/systems:
- ABS (anti-lock brake system)
- MSR (engine drag torque control)
- ASR (anti-slip regulation)
- ABD (automatic brake differential)
- Brake assist
- Improved braking readiness through prefilling of the brake system
- Earlier prefilling of the brake system and readying of brake assist (in conjunction with adaptive cruise control)
- Trailer Stability Management
- Standstill management: Auto-Hold function in conjunction with the electric parking brake
- Longitudinal deceleration control in conjunction with adaptive cruise control
Enhanced braking readiness
The enhanced braking readiness through prefilling of the brake system serves to shorten the stopping distance in emergencies. When the accelerator pedal is released quickly, PSM places the brake system in a state of enhanced braking readiness: The prefilling of the brake system builds up a slight pressure in the system. This causes the brake pads to apply light pressure to the brake discs. If the driver then actually presses the brake, maximum braking power can be achieved more quickly and this results in a shorter stopping distance.
Brake assist
On identifying full braking - i.e. when a defined force is exceeded on the brake pedal - brake assist supplies the required brake pressure for maximum deceleration via the PSM hydraulic unit. With adaptive cruise control, PSM initiates selective braking action to maintain the preselected distance from the vehicle in front. If the environment sensors in the adaptive cruise control system report that the driver is getting closer to a vehicle in front, the brake system is automatically switched to enhanced braking readiness mode. In addition, the brake hydraulic system also supports the driver here in the event of an impending full-braking operation so that the required brake pressure is provided. The driver is first warned visually by a message on the display as well as by an audible signal. If the distance from the vehicle in front continues to decrease, there is a braking jolt as an additional warning.
Standstill management (Auto-Hold functionality)
The standstill management function (Auto-Hold function) prevents the vehicle from rolling back in the opposite direction to the desired driving direction. This assist system is available in the Cayenne without an additional operating control. If the vehicle is braked to a stop on an uphill gradient, the Auto-Hold function is active and the required brake pressure is maintained via PSM. On vehicles with 8-speed Tiptronic S, the Auto-Hold function also holds the vehicle if the driver allows the vehicle to coast to a stop on a gradient. The Auto-Hold function is also activated in the event of automatic distance control by the adaptive cruise control. As soon as the vehicle comes to a stop without any intervention by the driver, the brake pressure is maintained via PSM until the vehicle moves off again. The hold function is transferred to the electric parking brake after 5 minutes or if the system detects that the driver intends to leave the vehicle.
Porsche Torque Vectoring Plus (PTV Plus)
PTV Plus is a new system to enhance driving dynamics and stability. It functions with variable torque distribution at the rear wheels and an electronically regulated rear differential lock. PTV Plus improves the steering behaviour and steering precision as a function of the steering angle and steering speed, accelerator pedal position as well as yaw rate and speed through selective braking interventions on the rear wheel on the inside of a bend. As a result, the rear wheel on the outside of the bend receives a higher drive force and permits additional angular momentum in the steering direction. The result is direct and dynamic steering into the bend. This reduces the need for PSM control intervention.
Porsche Hill Control (PHC)
A further new sub-function of PSM is Porsche Hill Control (PHC), which is standard for all new Cayenne models. PHC assists the driver when driving slowly downhill at speeds between approx. approx. 2 mph (3 km/h) and approx. 19 mph (30 km/h), e.g. on steep slopes or wintery mountain roads. The function is active both when driving forwards and when reversing. The system limits the vehicle speed by selective braking intervention on all four wheels. ABS remains active in order to prevent the wheels from locking. PHC is activated for all models by way of the separate switch on the center console. In the Cayenne, Cayenne S and Cayenne Turbo, it is also activated by selection of Off-road mode 1 with the central off-road rocker switch.
Preconditions:
- PHC is switched on.
- The vehicle speed must not exceed approx. 19 mph (30 km/h).
- The downhill gradient must be at least approx. 12 %.
- The driver does not press the accelerator or brake.
Changing speed
- Brake or accelerate (the new desired speed is stored after the brake pedal or accelerator is released)
- With the cruise control or adaptive cruise control stalk
PSM hydraulic unit
The hydraulic unit is installed on the right of the engine compartment for noise reasons. The dual-circuit brake system is divided up between the front and rear axles (black/white distribution). There are no longer any markings on the hydraulic connections. The connections have different thread diameters in order to prevent the lines from being mixed up.
PSM control unit
Brake light sensor
Instead of a conventional brake light switch, a brake light sensor transmits the position of the brake pedal. The brake light sensor has a Hall sensor and is mounted directly on the brake master cylinder. The brake piston contains a permanent magnet, which generates a certain field strength depending on its position. This is evaluated by the Hall sensor.
Vacuum sensor
A vacuum sensor is installed in the vacuum line between the vacuum pump and brake booster. The Start Stop function is deactivated if the vacuum in the brake booster is insufficient. The engine is switched off if the requirements for the Start Stop function are met by the vacuum present in the brake booster. The engine is started again if the driver then moves the brake pedal.
Interaction with other chassis control systems
Depending on which other chassis control systems are available, e.g. EPB, PDCC, PASM and air suspension, PSM uses the sensor information provided by these chassis systems to optimally match PSM control in all sub-functions with the behavior of the other control systems. For example, the "clutch pedal position" signal sent by the EPB control unit is used for the Drive-Off Assistant. In addition, the self-steering properties of the vehicle are determined based on PDCC activity and the PSM intervention thresholds are optimally adapted to suit these properties. PASM supplies information about road contact forces and any uneven road surfaces. This information is read in by PSM and is used for optimal, situation-based fine-tuning of the ABS system in order to optimize the braking distance in emergency braking situations, even with different road conditions.