Engine management, function

The engine management includes all processes which are essential in order to achieve economic and ecological engine operation. The necessary computations for the engine management take place in the engine management (MCM) control unit (A4). It ensures together with the engine management (MCM) control unit (A60) that the engine runs in a particularly economical, low pollutant and low-noise way under all operating conditions.

One basic function of the engine management is control of the (common rail) diesel injection system. To do this the engine management (MCM) control unit (A4) continuously determines the operating condition of the engine (engine rpm, engine temperature, actual torque, etc.) and compares these or the determined actual values with the specified values stored in the characteristics map.

While taking account of the torque specified by the drive control (CPC) control unit (A3) the engine management (MCM) control unit (A4) finally calculates the optimal injection begin point as well as the injection quantity required for combustion. Both values effect when and how long the engine management (MCM) control unit (A4) actuates the solenoid valves in the fuel injectors the respective cylinder. At the same time the rail pressure is adapted through appropriate actuation of the quantity control valve on the rail at the engine rpm.

Furthermore the engine management also takes over regulation of the EGR (AGR) and the boost pressure to regulate the injection system as well as controlling of the engine brake. Further controlling such as the fan rpm occurs according to the vehicle equipment.

Upon request from the exhaust aftertreatment (ACM) control unit (A60) the engine management (MCM) control unit (A4) takes over controlling of the coolant stream to the AdBlue® components as well as active regeneration of the diesel particulate filter (DPF).

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The operating condition of the engine is basically determined based on input values from the following sensors:

 Atmospheric pressure sensor (in engine management (MCM) control unit (A4))

 Crankshaft position sensor (B600)

 Camshaft position sensor (B601)

 Fuel temperature sensor (B602)

 Oil pressure switch (B604)

 Exhaust coolant temperature sensor (B606)

 Fresh air differential pressure sensor (B613)

 Charge air pressure and temperature sensor (B616)

 Charge air temperature sensor in charge air housing (B617)

 Rail pressure sensor (B622)

 Fan rpm sensor (Y616 b1)

The values of the oxygen sensor (B624) are only needed for control of the EGR (AGR). The position of the exhaust gas recirculation positioner (Y621) is taken into account for controlling the EGR (AGR) as well as for controlling the largest possible engine brake stage.

The air temperature which is detected at the outlet of the compressor of the high pressure stage of the 2-stage turbocharger with the aid of the charge air temperature sensor in the compressor housing (B614) just serves to protect the turbocharger of the high pressure stage from excessively high thermal loads. The charge air temperature sensor in the compressor housing (B614) is therefore only installed in engine 936.916 (with 2-stage charging).

The pressures in the diesel fuel metering device for active regeneration of the diesel particulate filter (DPF) are only determined for vehicles with code M5Z (Engine version Euro VI). This occurs with the aid of the following sensors:

 Fuel pressure sensor (outlet) (B625)

 Fuel pressure sensor (inlet) (B626)

The specified torque, which is calculated by the drive control (CPC) control unit (A3) from (among other things) the position of the accelerator pedal, is routed over the drive train CAN (CAN 4) to the engine management (MCM) control unit (A4), which in turn sends the current engine torque and the maximum torque possible to the drive control (CPC) control unit (A3). Information is also exchanged via the drive train CAN (CAN 4) with the transmission (TCM) control unit (A5), the retarder (RCM) control unit (A11), the Predictive Powertrain Control (PPC) control unit (A56) and the exhaust aftertreatment (ACM) control unit (A60). Over the drive control (CPC) control unit (A3) there is also the option to exchange information with other electronic systems or control units which are networked over the CAN and LIN data bus system.

Through actuation of the engine start and engine stop button (S600) a signal is sent to the engine management (MCM) control unit (A4) as to whether the engine should be started or stopped. If the button is pressed during the starting procedure the engine management (MCM) control unit (A4) automatically increases the engine rpm up to the maximum governed rpm.

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The engine management (MCM) control unit (A4) actuates the following actuators according to the operating condition of the engine and the torque specified by the drive control (CPC) control unit (A3) to control the injection system:

 Cylinder 1 fuel injector (Y608)

 Cylinder 2 fuel injector (Y609)

 Cylinder 3 fuel injector (Y610)

 Cylinder 4 fuel injector (Y611)

 Cylinder 5 fuel injector (Y612)

 Cylinder 6 fuel injector (Y613)

 Pressure regulating valve (Y634)

 Quantity control valve (Y643)

To control the EGR (AGR) and the boost pressure it takes on actuation of the following components:

 Exhaust gas recirculation positioner (Y621)

 Boost pressure positioner (Y636)

To activate the engine brake the engine management (MCM) control unit (A4) actuates the following solenoid valve:

 Engine brake solenoid valve (Y637)

In the largest engine brake stage the exhaust gas recirculation positioner (Y621) and the boost pressure positioner (Y636) area also actuated.

If the temperature of the AdBlue® in the AdBlue® container drops below 8°C and if the coolant temperature has reached 65°C, the engine management (MCM) control unit (A4) actuates the AdBlue® coolant heater solenoid valve (Y627) to heat the AdBlue®.

 For vehicles with code M5Z(Engine version Euro VI):

In the active phase of regeneration of the diesel particulate filter (DPF) the engine management (MCM) control unit (A4) actuates the following valves as required:

 Fuel metering valve (Y628)

 Fuel shutoff valve (Y629)

Controlling of the fan speed takes place over the fan clutch solenoid valve (Y616).

Diagnosis

If a fault occurs on the drive train CAN (CAN 4) or on a system component for the engine management, the engine management (MCM) control unit (A4) proceeds according to a clearly defined pattern depending on the severity of the fault. Thus it will fall back on replacement values for less severe faults such as the failure of a sensor while it will go into emergency mode for severe faults such as failure of the drive train CAN (CAN 4). The driver is able to at least drive to the nearest workshop if there is a fault in the system.

 The engine management (MCM) control unit (A4) is part of the DAS, to which also the electronic ignition lock (EIS) (S1) and the transmission control unit (TCM) (A5) belong. If one of these control units or the electronic ignition lock (EIS) (S1) is replaced, then it must undergo teach-in using the Star Diagnosis in the DAS.