Air mass limitation

Air mass limitation

Maximum engine torque

The engine torque curve is stored in the control module memory. It specifies the maximum engine torque at various engine speeds.

The torque is directly proportional to the air mass/combustion at a certain speed.

The unit in the engine torque curve, Nm, is converted to mg air/combustion.

The value taken from the curve is the maximum air mass/combustion value the engine variant allows.

Manual gearbox, engine torque limitation

The maximum engine torque must be limited at low gear ratios for reasons of strength.

The control module calculates the engaged gear by comparing engine speed with vehicle speed.

If the gear ratio corresponds with gear 1 or R, the control module reads bus information "Reverse gear selected" from DICE to distinguish between them.

Engine Torque (for B235R) is limited to 250 Nm (230 Nm for the convertible) when gear 1 is selected. Engine torque limitation when reverse R is selected is 230 Nm. For 2nd gear, the torque is limited to 330 Nm (315 Nm for the convertible). Other gears are limited to 350 Nm. The torque value is converted to mg air/combustion and represents the max. value for the air mass/combustion that the gearbox allows. For corresponding torque limitation levels for B205L and R, see the table below.

Engine torque limitation

Motor Gear	B235R	B205L,R
R	230 Nm	230 Nm
1	250/230(con) Nm	230 Nm
2	330/315(cab) Nm	Unlimited
3	350 Nm	Unlimited
4	350 Nm	Unlimited
5	350 Nm	Unlimited

Automatic gearbox, stall limitation

The maximum engine torque must be limited when the car is stationary and the brake pedal is depressed for reasons of strength.

Engine torque is limited to 200 Nm.

Engine torque is converted to mg air/combustion and constitutes the maximum air mass/combustion permitted by the automatic transmission.

Automatic transmission, limitation in reverse gear

An engine-dependent torque limitation takes place when selector lever position R is selected to reduce the load on the powertrain mountings.

Engine torque is converted to mg air/combustion and constitutes the maximum air mass/combustion permitted by the automatic transmission.

TCM, engine torque limitation

The maximum engine torque must be limited while changing gear for reasons of strength. TCM sends continuous bus information indicating the maximum engine torque.

Trionic T7 converts Nm to mg air/combustion. The value constitutes the maximum air mass/combustion permitted by the automatic transmission.

Braking

The maximum engine torque must be limited when the brake pedal is depressed for reasons of strength. The following three conditions must be fulfilled for this function to be activated:

•	B+ on the input from brake light switch, pin 63.

•	B+ on the input from brake and clutch pedal switches, pin 29.

Engine torque is limited to 200 Nm.

Engine torque is converted to mg air/combustion and constitutes the maximum air mass/combustion permitted by the automatic transmission.

Knock limitation

Knock control first retards the ignition timing for each cylinder. If the mean value for the ignition retardation for all the cylinder exceeds a certain value, fuel enrichment will take place.

If the mean value for ignition retardation increases further, the maximum permissible air mass/combustion will be reduced.

This reduction takes place continuously as the ignition retardation increases.

The value constitutes the maximum air mass/combustion value permitted by knock control.

Vehicle speed limitation

When the vehicle speed reaches the set max. value, see below, the engine torque is limited due to the fact that the maximum allowed air mass/combustion is limited.

For B235R the vehicle speed is limited to max. 250 km/h.

For B205L and R the vehicle speed is limited to max. 240 km/h.

Engine speed limitation

When the engine speed reaches 6000 rpm and the coolant temperature falls below 60°C, the engine torque is limited due to the fact that the maximum allowed air mass/combustion is limited. If the coolant temperature is above 80°C a further 100 rpm is allowed, i.e. the maximum allowed air mass/combustion in this case is limited at 6100 rpm.

Turbo speed limitation

The maximum permissible air mass/combustion is limited at low atmospheric pressures to protect the turbo from overrevving.

Limitations after system faults

The maximum permissible air mass per combustion is limited in the following cases:

•	Electrical fault in the charge air control valve.

•	Mechanical fault in the charge air control valve causing the current air mass to exceed that requested.