Knock Limitation

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.


NOTE: Knock control on modern engines is not a safety function but a normal function. Consequently, it is considered normal when knock control reduces engine torque in certain cases. The engine knock control increases for e.g. high intake air temperatures or high coolant temperatures. Further influencing factors are driving at high altitudes and low octane fuel.

Certain engine variants require petrol with an octane rating of 98 RON in order to provide the specified engine torque/power.


Vehicle speed limitation

Vehicle Speed Limitation:

When the engine speed reaches the maximum allowed, the engine torque will be limited by limiting the maximum permissible air mass/combustion.

The highest permitted speed varies between engine alternatives. The highest permitted speed for alternative B235E is 240 km/h and for alternative B235R the equivalent value is 250 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 is dependent on 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.