G07.16-3139-79
Shown on engine 471.9 |
A4 | Engine management control unit (MCM) | CAN 4 | Drive train CAN | |
B600 | Crankshaft position sensor | M1 | Starter | |
B601 | Camshaft position sensor | S600 | Engine start and engine stop button | |
B602 | Fuel temperature sensor | Y608 | Cylinder 1 fuel injector | |
B606 | Exhaust coolant temperature sensor | Y609 | Cylinder 2 fuel injector | |
B608 | Charge air pressure and temperature sensor in charge air pipe | Y610 | Cylinder 3 fuel injector | |
B611 | Temperature sensor downstream of air filter (only for engine version Euro VI Standard) | Y611 | Cylinder 4 fuel injector | |
B617 | Charge air temperature sensor in charge air distributor | Y612 | Cylinder 5 fuel injector | |
B621 | Exhaust gas recirculation (AGR) differential pressure sensor | Y613 | Cylinder 6 fuel injector | |
B622 | Rail pressure sensor | Y642 | Quantity control valve | |
B638 | Fuel filter module pressure sensor |
General
The starting procedure of the engine is introduced when a corresponding start request is submitted via the drive CAN (CAN 4). E. g. when the engine is started by pressing the engine start and engine stop button (S600) or via the ignition lock.
Preconditions
Power supply (terminal 30 and terminal 15) on the engine management (MCM) control unit (A4) (ignition switched on)
Electronic immobilizer from DAS deactivated
Starter lockout canceled, i.e.:
Transmission in neutral (only for start request using engine start and engine stop button (S600))
Power take-off, where present, switched off
Engine stopped or engine speed is < 50 rpm
Function
If all requirements are fulfilled and the engine start and engine stop button (S600) is pressed or a corresponding message with a start request is received via the drive CAN (CAN 4), the engine management (MCM) control unit (A4) actuates the engaging relay of the starter (M1) via a front-end relay.
The starter (M1) activates the engine. The engine management (MCM) control unit (A4) checks whether the starter (M1) is turning the engine at a specified minimum speed.
It also waits until it can recognize from crankshaft position sensor signals (B600) when cylinders 1 and 6 are at top dead center (TDC).
Only then can the start of actuation for the fuel injector of cylinders 1 and 6 (Y608 and Y613) be calculated taking into account the current operating status of the engine.
At the same time, the engine management (MCM) control unit (A4) calculates the required injection quantity for combustion and initiates the injection of this at the correct point in time into the combustion chambers of cylinders 1 and 6 through appropriate actuation of the quantity control valves (Y642) and fuel injectors for cylinders 1 and 6 (Y608 and Y613).
This so-called double ignition serves to accelerate the starting procedure. It is continued (afterwards follow cylinders 5 and 2, 3 and 4, then further with 1 and 6, etc.), until the ignition TDC of cylinder 1 is recognized with the aid of the camshaft position sensor (B601).
If the camshaft position sensor (B601) fails to return any pulses, then in each case a portion of the double firing is cutoff, until the dip in engine speed, which then occurs, when a piston is not in ignition TDC, enables ignition TDC to be recognized. Once ignition TDC is recognized, the engine continues to run in unchanged state. Nevertheless, the maximum torque of the engine will be limited to protect the engine from damage. The engine management (MCM) control unit (A4) can also regulate the limp-home speed.
Determining the injection quantity:
Determination of the injection volume independently of the accelerator pedal position in order to achieve a secure engine start with the lowest possible pollutant emission.
The injection quantity selected for the starting procedure is primarily geared to the coolant temperature, which is determined by the engine management (MCM) control unit (A4) via the exhaust coolant temperature sensor (B606).
Further variables for the injection quantity during the starting procedure are the current engine speed as well as the geographical altitude at which the vehicle or engine is located.
There is an atmospheric pressure sensor in the engine management (MCM) control unit (A4) over which the air pressure of the ambient air is determined for determination of the altitude and the current altitude of the vehicle or engine can be deduced.
The engine starts with this initial, primarily temperature-dependent, start injection quantity.
If the engine does not start with the start injection amount, then the injection quantity will be continuously increased until the engine starts or the limit value for the max. start injection quantity is reached. This is then maintained until the starter (M1) actuation is interrupted either by itself or after a specific time by the engine management (MCM) control unit (A4), to protect the starter (M1) against mechanical or thermal overload (start time limit).
If the engine starts while the ignition lock or the engine start and engine stop button (S600) is still actuated, and it reaches a specific engine speed, then actuation of the starter (M1) is interrupted (starter dump speed).
The pinion is withdrawn out of the ring gear on flywheel while the injection quantities in the idle speed control are provided by the start control. This changeover is known as starter disengagement which exclusively results in a change of the calculation method. Because the cold start ability of diesel engines at low outside temperatures is restricted by the engine's increasing resistance to rotation, lower combustion chamber temperatures and unfavorable fuel atomization conditions, under certain conditions a pilot injection is conducted.
This contributes significantly to shorter starting times, to quicker smooth engine operation, to an improved throttle response, to lower white smoke emission, to a lower pollutant emission and to a lower noise emission.