Driving operation, function

W07.16-1143-79

If the drive control (CPC) control unit (A3) does not demand any idle or working speed control then this means normal driving mode. In driving mode the injection quantity is primarily adjusted according to requests from the driver. This means that the torque specification of the engine is primarily dependent on the position of the accelerator pedal. It is only in certain situations that it can happen that the engine speed is adapted independently of the accelerator pedal position or of the specified torque request, for example for downshifting for rotational speed comparison between the main shaft and the countershaft. In this case, the fuel pressure is additionally lowered to approx. 600 bar.

During operating status, the engine management control unit (MCM) (A4) initially compares the specified engine torque incoming from the drive control (CPC) control unit (A3), which is derived, for example, from the position of the accelerator pedal and provided via the drive train CAN (CAN 4), with the current actual engine torque, which represents the engine's actual operating conditions. If the required engine torque is less than the current actual engine torque, the engine management (MCM) control unit (A4) reduces the injection quantity, and if the required engine torque is greater than the current actual engine torque then it increases the injection quantity. At the same time the engine management (MCM) control unit (A4) increases the fuel pressure through corresponding actuation of the pressure regulating valve (Y634), according to the load, up to 1,800 to 2,400 bar.

If the specified engine torque is negative, e.g. in deceleration mode, and if the engine speed lies above 950 rpm, the engine management (MCM) control unit (A4) interrupts actuation of the fuel injectors for cylinders 1 to 6 ( Y608 to Y613) and lowers the fuel pressure in the rail via the pressure regulating valve (Y634). In this way the braking effect of the engine is used and the fuel consumption lowered. The engine brake can be activated to reinforce the braking effect. The driver can select between 3 brake stages.

If the engine speed drops below 950 rpm, the engine management (MCM) control unit (A4) increases the fuel pressure in the rail over the pressure regulating valve (Y634) and actuates the fuel injectors for cylinders 1 to 6 (Y608 to Y613).

 The engine management (MCM) control unit (A4) can limit the specified engine torque transmitted by the drive control (CPC) control unit (A3) for engine protection reasons, e.g. if the coolant temperature exceeds a specific value or the engine reaches its final or maximum governed rpm, to comply with the maximum permissible speed or due to a control intervention function of the anti-lock braking system (ABS) or the anti-slip control (ASR).
Limitation of the required engine torque always leads to limitation of the injection quantity.

The following input factors also have an influence on computation of the injection quantity required for normal driving:

 Engine speed

 Air mass

 Coolant temperature

 Fuel temperature

The altitude correction and smoke emission limitation can also influence the injection quantity (actuation period) as well as the start of actuation of the fuel injectors during normal driving.

Altitude correction

The altitude correction is designed primarily so that the established limits for the air/fuel ratio λ (Lambda) are not exceeded or undershot. To do this, the exhaust gas recirculation rate (EGR rate), the actuation begin as well as the actuation period (injection quantity) for fuel injectors for cylinder 1 to 6 (Y608 to Y613) are adapted.

Smoke limit

The fuel quantity is limited via the smoke limitation characteristics so that virtually no output of smoke occurs.

Exhaust gas recirculation (EGR)

The exhaust gas recirculation (EGR) is active throughout the whole driving mode to reduce the nitrous oxide emissions.

In the case of the exhaust gas recirculation (EGR), the suctioned out or supercharged fresh air is mixed with exhaust gas. This leads to the situation where the oxygen content of the suctioned out or supercharged air drops and its specific heat increases. One can therefore achieve a lower combustion temperature and thus reduced output of nitrogen oxides (NOx), whose proportion increases with increasing combustion temperatures. The amount of exhaust gases produced is also reduced.

Fan control

The fan speed is also regulated during driving dependent on the coolant temperature. The fan speed is determined based on input signals (A) from the fan rpm sensor (Y616 b1). Control takes place through appropriate actuation of the fan clutch solenoid valve (Y616).

Exhaust aftertreatment

The EATS is active immediately after the engine start during the whole engine operation. It ensures that the emitted emissions in the exhaust are reduced to meet the limits established for the respective emissions standard. Different measures are instigated according to the emissions standard. For engine version Euro VI Standard, the exhaust gas aftertreatment takes place, e.g. through:

 Selective Catalytic Reduction (SCR) with an ammonia locking CAT

 Diesel oxidation catalytic converter (DOC)

 Diesel particulate filter (DPF)

Camshaft adjustment

During operating status, the camshaft adjustment is generally not used. If the camshaft positioner is not actuated then the camshaft is the basic position "retarded".