Differential Protection System, DPS

On Saab 9-5 vehicles which are equipped with an automatic transmission, there is a Trionic T7 function which protects the transmission differential when there is excessive wheel spin. The function only operates at speeds below 80 km/h. The function is called DPS, (Differential Protection System). DPS should not be confused with TCS. The function is not present in diesel engined vehicles.

The differential protection system reduces the engine torque by limiting the air mass/combustion ratio of the engine during excessive wheel spin. The torque reduction is greater when the wheel spin is rapid and less when the spin is slower.

The function uses the following input signals: "Wheel speed right-hand front" and the bus message "Car speed, output speed" from the TCM.

If the difference between these two signals is greater than 15 km/h the engine torque will, after a certain delay, be reduced. For example, if the difference between "Wheel speed right-hand front" and "Car speed, output speed" is 20 km/h the maximum permissible engine torque is 150 Nm.

The delay time is dependent on the engine torque. When the engine torque is 300 Nm or more the delay is 1.0 s. If the engine torque during wheel spin is 150 Nm, then the delay is 0.5 s. The principle is that there is a greater delay when the engine torque is large and a lesser delay when the engine torque is smaller.