Starting procedure, function

W07.16-1058-79

General

The engine starting procedure is introduced when a corresponding start request is available via the drive CAN (CAN 4). For example, when starting the engine via the electronic ignition lock (EIS) (S1) or via the parameterizable special module control unit (PSM) (A22) or by the corresponding actuation of the engine start and engine stop button (S600).

Preconditions

 Power supply (terminal 30 and terminal 15) on the engine management (MCM) control unit (A4) (ignition switched on)

 Electronic immobilizer deactivated by drive authorization system and start enable issued by electronic ignition lock (EIS) (S1), i.e. the inserted transmitter key is authorized.

 Starter lockout canceled, i.e.:

– The transmission is in neutral position (only for start request via engine start and engine stop button (S600))

– Power take-off, where present, switched off

– Engine stopped or engine speed is < 50 rpm

Function

In order to start the engine, all requirements must be met. The drive CAN (CAN 4) receives the command to issue a start request. For example, when the start/stop button on the electronic ignition lock (EIS) (S1) is pressed and held in start position (level 2) or the parameterizable special module control unit (PSM) (A22) transmits a corresponding message with the start request. The engine management control unit (MCM) (A4) then actuates the engaging relay of the starter (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 injectors for cylinders 1 and 6 (Y608 and Y613), taking into account the current operating status of the engine.

At the same time, the engine management control unit (MCM) (A4) determines the injection quantity required for combustion. It actuates the quantity control valve (Y642) and the fuel injectors for cylinders 1 and 6 (Y608 and Y613) accordingly, thereby ensuring that this injection quantity is injected into the combustion chambers of cylinders 1 and 6 at the right time.

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 signals, part of the double ignition is switched off in each case. This happens until ignition TDC is detected when the engine speed gets too low, which happens when one piston is not in 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 quantiy independently of the accelerator pedal position in order to achieve a secure engine start with the lowest possible pollutant emission.

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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 control unit (MCM) (A4) for determining the height. The sensor is used to determine the air pressure of the ambient air, which allows the current height of the vehicle or engine to be derived.

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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. It is then maintained until the actuation of the starter (M1) either interrupts itself or is interrupted by the engine management control unit (MCM) (A4) after a certain time. This protects the starter (M1) against mechanical or thermal overload (start time limitation).

If the engine starts while the start/stop button on the electronic ignition lock (EIS) (S1) or the engine start and engine stop button (S600) are still being pressed, and if it reaches a certain engine speed, the 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, quicker smooth engine operation, an improved throttle response, lower white smoke emission, lower pollutant emissions, and lower noise emissions.