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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.

The engine torque (for the B235R) is limited to 250 Nm (230 Nm for the convertible) when 1st gear is engaged. Torque limitation in reverse gear R is 230 Nm. In 2nd gear, the torque is limited to 330 Nm (315 Nm for the convertible). Other gears are limited to 350 Nm. The torque is converted to mg air/combustion and constitutes the maximum value for the air mass/combustion allowed by the gearbox. Refer to the table below for corresponding torque limitation values for the B205E, L and R.

Engine torque limitation

Motor Gear B235R B205E,L,R
R

230 Nm

230 Nm

1

250/230(con) Nm

230 Nm

2

330/315(cab) Nm

Unlimited

3

350 Nm

350 Nm

4

350 Nm

350 Nm

5

350 Nm

350 Nm



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.

Traction Control, engine torque limitation


Cars with certain engine variants can be equipped with Traction Control. The Traction Control function is in the TC/ABS control module. The TCS function in the TC/ABS control module operates by employing both engine torque reduction (request from Trionic) and braking of the driving wheels. The rear wheel speed is used as a reference for comparing the speed of both driving wheels separately. Wheelspin is when one of the driving wheels rotates faster than the rear wheels.

TC/ABS receives 2 bus messages from Trionic T7:


• Engine Torque

The value of the bus message "Engine torque” can vary between -100 Nm to 400 Nm.

TC/ABS uses the engine torque value to calculate the current driving wheel torque.

• Pedal Position

TC/ABS uses this value to determine the amount of wheelspin to allow.


TC/ABS uses the above values together with vehicle speed and engine speed to calculate the current gear ratio. TC/ABS can calculate the driving wheel torque using the engine torque and current gear ratio.

TC/ABS sends one bus message to Trionic T7:



• Max permissible torque

The value of this requested torque is used for Traction Control.

Trionic T7 converts Nm to mg air/combustion. The value constitutes the max value of air mass/combustion allowed by TC/ABS.


For further information on Traction Control and TC/ABS, refer to System overview .

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.

Vehicle speed for B205E,L,R is limited to 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.

The function depends on the atmospheric pressure and engine speed.

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.