The starting procedure function is described using engine 926.9 (6 cylinders) as an example.
G07.15-A037-79
0 | Ignition OFF | S10 | Engine start button | |
1 | Circuit 15R ON | S11 | Engine stop button | |
2 | Circuit 15 On | Y600 | Cylinder 1 single injection pump | |
3 | Circuit 50 | Y601 | Cylinder 2 single injection pump | |
A3 | Drive control (CPC) control unit | Y602 | Cylinder 3 single injection pump | |
A6 | Engine management (MR) control unit | Y603 | Cylinder 4 single injection pump | |
B15 | Crankshaft position sensor | Y604 | Cylinder 5 single injection pump | |
B16 | Camshaft position sensor | Y605 | Cylinder 6 single injection pump | |
CAN 4 | Drive train CAN | A | Input signals | |
M1 | Starter | B | Output signals | |
S1a | Ignition lock |
General
The engine can be started:
Via an appropriate start request over the drive train CAN
With the ignition lock
Using the engine start button
Preconditions
Power supply (circuit 30 and circuit 15) available at engine management (MR) control unit
Electronic immobilizer from DAS deactivated
Starter lockout canceled, i.e.:
Transmission in neutral position (only for start request via the engine start button)
Power take-off, where present, switched off
Engine off or engine speed below 50 rpm
Function
If all preconditions are met and the ignition lock or the engine start button is actuated or a corresponding message with the start request is received via the drive train CAN, the engine management (MR) control unit actuates the engaging relay of the starter via a front-end relay.
The starter sets the engine in motion. The engine management (MR) control unit checks whether the starter is turning the engine at a minimum speed of 50 rpm.
Based on the signals from the crankshaft position sensor and the camshaft position sensor, the engine management (MR) control unit identifies the compression stroke of cylinder 1 to enable the start of delivery (for regulating the start of injection) to be calculated.
At the same time, the engine management (MR) control unit determines the injection quantity required for combustion and actuates the solenoid valves in the single injection pumps for cylinders 1 to 6 accordingly.
If the engine starts while the ignition lock or the engine start button are still being actuated, and reaches an engine speed of approx. 450 rpm (with a warm engine) to approx. 650 rpm (with a cold engine), the actuation of the starter is interrupted (starter disengagement speed).
The pinion is withdrawn from the ring gear on the flywheel while a transition from the engine management (MR) control unit to the idle speed control is made. This changeover is also known as starter disengagement and results exclusively in a change of the calculation method of the engine management (MR) control unit.
At particularly low outside temperatures and therefore with poor starting characteristics, the starting time is limited to 90 s in order to prevent overloading of the starter. Actuation of the starter and the solenoid valves in the single injection pumps for cylinders 1 to 6 is interrupted. It is then only after a waiting time (at the earliest 1 s after switching off the starter) that a new start procedure can be begun from the beginning.
The starting time can, however, be made significantly shorter for vehicles/engines with a flame starting system.