Active PTM
Active PTM
The active all-wheel-drive system (Porsche Traction Management or PTM) is standard in the Cayenne, Cayenne S and Cayenne Turbo and was designed to influence longitudinal and lateral dynamics. The system provides increased driving stability, traction and more agile handling, depending on the driving situation.
PTM comprises the following systems:
- Active all-wheel drive with electronically and map-controlled multiple-disc clutch
- Automatic Brake Differential (ABD)
- Anti-slip regulation (ASR)
The PTM on the Cayenne, Cayenne S and Cayenne Turbo is designed as an active all-wheel drive (hang-on all-wheel drive). The system is characterised by a compact overall design.
The multiple-disc clutch installed in the PTM transfer case is controlled by an electric motor and regulates the distribution of drive power between the full-time drive rear axle and the front axle in a way that is fully variable without a fixed basic distribution. The vehicle permanently monitors the driving state and can thus react to different driving situations and driver requests (e.g. accelerator pedal s position, steering wheel angle or PSM switch positions, Sport button, etc.). This allows the installation of additional software that is designed for the driving dynamics of the hang-on all-wheel drive and enables the vehicle to react to certain situations and even prevent undesired slip on an axle before it occurs. However, the software can only be installed if a hang-on all-wheel system is integrated in the other chassis systems. Sensors continuously monitor various parameters, including the speeds of all four wheels, axial and lateral acceleration of the vehicle and the steering angle. If the rear wheel spins during acceleration, for example, additional drive power (if necessary up to 100% more) is distributed forward through greater intervention of the multiple-disc clutch. The all-wheel drive is therefore fully variable.
The distribution of the drive torque across the front and rear axles depends on a number of factors such as speed, acceleration, the selection of Normal or Sport as well as the selected PSM mode, etc. In order to achieve good traction when driving off or accelerating, the front axle torques tend to be higher in these situations than when the vehicle travels constantly in a straight line. The vehicle reacts to a consistent driving style by reducing the drive torque on the front axis to minimize friction losses, for example.
PTM function
The control unit (4) calculates a standard torque split using different pieces of input information.
Depending on the nature of this information, the servo motor is activated and a worm drive (3) then turns the ball ramp (2), which pushes against the multiple-disc clutch (8).
The torque generated is transferred to the output shaft (5) via a chain (6) and passed on to the front axle.
One obvious advantage of the PTM system is that if wheel slip is anticipated (e.g. after accelerating sharply), the vehicle can react before the wheel actually slips. The transmission ratio of the two sprockets is 1.12.
Lubrication
Even though the PTM can generate extremely powerful forces and temperatures and some components require good lubrication and efficient cooling, the PTM can operate without requiring an additional pump.
The drive chain (6) turns when the front wheels turn. At the same time, oil is drawn from the sump and supplied to the chain enclosure (arrow). Oil guide devices integrated in the chain enclosure channel the oil into the multiple-disc clutch and create a flow of oil from the inside outwards.
Lubrication of the clutch without an additional oil pump helps minimize losses in efficiency and reduce fuel consumption.
Temperature measurement / Component protection.
A calculation model is used to calculate the temperature and the load on the multiple-disc clutch due to the variable nature of the input information. The advantage of this method over the measurement of temperatures with a sensor is that response times are considerably quicker.
In the event of overloading, immediate measures can therefore be implemented to protect the components. The process involves three different stages. In stage 1, the PSM is automatically activated if it was deactivated previously. In stage 2, the engine torque is reduced by modifying the timing angles. If this does not achieve the required effect, the multi-disc clutch is opened completely in stage 3.
Maintenance calculator
The all-wheel control unit is equipped with an internal maintenance calculator. Calculations are made using wear integrators:
- Chain load
- Multiple-disc clutch load
- Distance since last oil change
- Counter indicating how frequently the clutch was closed almost 100%
If the calculated value exceeds the diagnostic threshold of 145 kWh a corresponding entry is made in the fault memory.
This value must be read out during maintenance using the PIWIS Tester and the oil changed if necessary. The process is menu-guided in the PIWIS Tester.
Operation
Different driving programs can be selected using the rocker switch on the center console. Whenever the rocker switch is pushed forward, the vehicle becomes one step more suitable for off-road driving and whenever it is pulled back, the vehicle becomes one step more suitable for on-road driving.
The different settings are as follows depending on the equipment:
A Road driving program
B Off-road driving program
C Center differential lock is enabled 100 %
D Rear differential lock is enabled 100 %
Light-emitting diodes next to the rocker switch indicate the preset driving program.
In addition, when the selected driving program is activated, a corresponding indicator appears on the instrument cluster for a few seconds.
It is only possible to change from the on-road to the off-road program at speeds below 19 mph (30 km/h). Changing from the off-road to the on-road program is possible at any time.
Off-road mode 1
In Off-road mode 1 (display B), for example, all relevant systems such as the all wheel control system are switched to a traction-orientated off-road program. Porsche Hill Control is also activated (on gradients of at least 12 percent) and High Level I is also selected on vehicles with air suspension including PASM. The rocker switch for the air suspension also permits selection of High Level II in order to increase the approach/departure angle and fording depth.
Off-road mode 2
If the off-road rocker switch is pressed further forward, Off-road mode 2 (display C) is activated for the Cayenne, Cayenne S and Cayenne Turbo -- in this case the multiple- disc clutch is closed 100 % for better traction on difficult terrain.
Off-road mode 3
If the conditions require, it is possible to activate Off-road mode 3 (display D) with 100 % locking of the rear axle differential by pressing the off-road rocker switch once more.