Porsche Stability Management (PSM) is an electronic control system that uses a range of functions – including anti-lock braking (ABS) – to help stabilise the vehicle (and trailer, if fitted) in hazardous road scenarios. Throughout each journey, sensors monitor the direction, speed, yaw velocity and lateral acceleration of the car. Using this information, it is possible to calculate the actual direction of travel at any given moment. If the car begins to oversteer or understeer, PSM applies selective braking on individual wheels to restore stability. If necessary, PSM can also intervene in the engine management system to temporarily modify the amount of drive transmitted to the wheels.
PSM has three additional functions that help reduce braking distances. If the throttle pedal is released suddenly, PSM automatically readies the braking system. The pressure in the brake lines is marginally increased, bringing each of the pads into light contact with the corresponding disc. If the driver goes on to apply the brakes, the calipers respond more quickly and the braking distance is reduced.
In an emergency stop – i. e. when the pressure on the brake pedal exceeds a certain threshold – the brake assist function uses the PSM hydraulics to apply maximum braking force at all four wheels.
For added safety, the system also readies the brakes whenever a decreasing distance to the vehicle in front is detected. The optional adaptive cruise control and PSM interact to prefill the brakes.
Even if adaptive cruise control is inactive, the system registers the speed of the vehicle in front and automatically readies the braking system. In addition, the system alerts the driver to the decreasing distance by briefly tugging on the brakes.
PSM also features a trailer stabilisation function – for a significant contribution to car and trailer safety. Within the laws of physics, it compensates for load transfer caused by throttle and brake inputs up to the maximum degree of lateral acceleration. It also enhances the car’s driving dynamics and directional stability when accelerating on inconsistent road surfaces.
Other features include a special control strategy in the ABS for braking on loose surfaces. By briefly locking the wheels, a wedge is formed ahead of each tyre which provides additional purchase to help slow the car, e.g. on gravel or snow.
For a more involving driving experience, PSM can also be disabled, but remains active in the background.
Standard on all Cayenne models.