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Starting, Function - GF07.10-P-1001MRH

Engine 274.9 in model 205.047/053/054/147/247/253 

Engine 274.9 in model 253.353/953 

Engine 274.9 in model 253.354/954 

Starting function requirements, general points 

Starting, general points 

The start of the internal combustion Engine is initiated if the vehicle needs energy for the traction which cannot be delivered purely electrically or if changes in system conditions requires starting of the internal combustion Engine.

The start of the internal combustion Engine is initiated automatically, without action on the part of the driver. The automatic Engine start is dependent on various system conditions and from the current driving condition. It is requested by the ME-SFI [ME] control unit (N3/10). Starting takes place with the vehicle at a standstill, preferably via the electrical machine (A79/1) and in the electrical operation via the starter (M1).

The internal combustion Engine is also started over the starter in the vehicle standstill condition if the charge level of the high-voltage battery (A100g1) is not adequate.

The ME-SFI [ME] control unit reads in the following signals for starting:

The ME-SFI [ME] control unit actuates the following assembly parts or sends requests to the following control units to start the internal combustion Engine:

Function sequence for start 

The starter control in the ME-SFI [ME] control unit takes on actuation and switching off of the starter and a request for the electrical machine and the wet clutch.

The ME-SFI [ME] control unit coordinates the injection and firing order during starting based on the signals from the crankshaft Hall sensor and the camshaft Hall sensors.

The rest of the function sequence is subdivided into the following operation steps:

Function sequence for starting with the starter in a vehicle standstill condition 

When the ignition key (transmitter key A8/1) is turned into the start position, the ME-SFI [ME] control unit receives the driver's start request from the powertrain control unit via the drive train CAN, via the suspension FlexRay from the electronic ignition lock control unit.

Start begin

The ME-SFI [ME] control unit uses a ground signal to actuate the starter circuit 50 relay (K40/8kH) on both sides. The power contact on the starter relay closes and the starter solenoid switch is supplied at "circuit 50" with voltage from "circuit 30".

Ending start

When Engine cranking speed has reached 400 to 700 RPM, or after a starting time of 5 to 40 s (dependent on coolant temperature), the ME-SFI [ME] control unit interrupts the negative activation of the circuit 50 starter relay and thus terminates the starting procedure.

The starting procedure can only be aborted by switching off the ignition.

Function sequence for starting with the electrical machine in a vehicle standstill condition 

The required motor torque of the electrical machine is calculated by the ME-SFI [ME] control unit for starting the internal combustion Engine with the electrical machine in a vehicle standstill condition. In order to connect the internal combustion Engine to the transmission the ME-SFI [ME] control unit makes the request via the drive train CAN to the fully integrated transmission control unit to actuate the wet clutch.

After receiving the respective feedback over the closed wet clutch, the ME-SFI [ME] control unit requests actuation of the electrical machine via the hybrid CAN from the power electronics control unit in order to start the internal combustion Engine.

Recognition of the start end takes place over the motor speed or, over a differential torque analysis, between the motor torque generated by the electrical machine and the torque from the internal combustion Engine. When Engine cranking speed has reached 400 to 700 RPM, or after a starting time of 5 to 40 s (dependent on coolant temperature), the ME-SFI [ME] control unit interrupts the Start request to the power electronics control unit and thus ends the starting procedure.

Function sequence for starting with the starter and electrical machine in electrical operation 

During electrical operation with an opened wet clutch, starting always occurs first over the starter up to a certain rotational speed of the internal combustion Engine. This should prevent any risk of jerking caused by the moment of inertia of the internal combustion Engine.

The function sequence up to reaching the starting speed is identical with the function sequence for starting with the starter in a vehicle standstill condition 

If the required starting speed is achieved, the wet clutch is closed and the internal combustion Engine is brought up to the idle speed by the Engine drag torque of the drivetrain and starting over the starter is ended.

Starting is stopped after reaching the idle speed.

IMPORTANT A voltage dip limiter (R62) is installed at the positive battery terminal. Its task is to prevent a drop in the battery voltage below a defined voltage value during the starting procedure of the internal combustion Engine. This is performed through temporary limitation of the starter current. One should observe here that 12 V should only be applied to the starter PLUS line during the starting process. Before and after the start the starter-plus line must be free of tension otherwise the voltage dip limiter is defective.

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