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Differential Protection System (DPS)

Differential Protection System (DPS)


On Saab 9-5s with automatic transmission, the Trionic T7 has a function that protects the differential in the transmission in the event of violent wheel spin. The function, known as the Differential Protection System (DPS), is only active at speeds below 80 km/h. The DPS should not be confused with TCS.

DPS reduces engine torque by reducing the air mass per combustion to reduce violent wheel spin. The principle is to reduce the quantity of air greatly in the event of very violent wheel spin and less so during less violent wheel spin.

“Wheel speed, front right” and the new bus message “Vehicle speed, output shaft speed” from the TCM are used as input signals.

If the difference between these is more than 15 km/h engine torque will be reduced after a brief delay. For example, if the difference in speed between "Wheel sensor, front right” and “Vehicle speed, output shaft speed” is 20 km/h, the maximum permitted torque is 150 Nm.

The delay is determined by the engine torque. If the torque is 300 Nm or more, the delay is 1.0 second. If the engine torque is 150 Nm during wheel spin the delay is 0.5 seconds. In other words, the higher the torque, the longer the delay.