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 (with engine version Euro VI Standard only) | 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 engine starting procedure is introduced when a corresponding start request is available via the drive CAN (CAN 4). E.g. when starting the engine by accordingly actuating the external engine start/stop (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 off or engine speed < 50 rpm
Function
If all prerequisites are met and external engine start/stop (S600) is actuated or a corresponding message with the start request is received via the drive CAN (CAN 4), the engine management control unit (MCM) (A4) actuates the starter engaging relay (M1) via a front-end relay.
The starter (M1) sets the engine in motion and the engine management (MCM) control unit (A4)checks whether the starter (M1) is turning the engine at the 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 be calculated for the fuel injector for cylinders 1 and 6 (Y608 and Y613) under consideration of the current engine operating status.
At the same time, the engine management control unit (MCM) (A4) determines the injection quantity required for burning and causes it to be injected into the combustion chambers of cylinders 1 and 6 at the right point in time by accordingly actuating the quantity control valve (Y642) and the 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) does not deliver any pulses, part of the double firing is ceased in each case until ignition TDC is detected through the engine speed drop that occurs when a piston is not at ignition TDC. 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 starting injection quantity, the injection quantity is continuously increased until the engine starts or the limit value for the maximum starting 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 external engine start/stop (S600) are still actuated and reaches a specific engine speed, 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.