GF07.10-P-1016MAW Camshaft Adjustment, Function
GF07.10-P-1016MAW Camshaft Adjustment, Function
ENGINES 156.9 in MODEL 204.0 /2 /3, 212.0 /2
Function requirements for camshaft adjustment, general points
^ Circuit 87M (engine timing ON)
^ Engine running
Camshaft adjustment, general points
Camshaft adjustment allows all four camshafts to be adjusted continuously by up to 40° CKA (CranK Angle). This means the valve overlap in the event of a load change can be varied within This optimizes engine torque characteristics and improves the exhaust characteristics.
Valve overlap
The intake valves open before the exhaust valves close.
For camshaft adjustment, the ME-SFI [ME] (N3/10) control unit reads the following sensors:
- Oil temperature sensor (B1)
- LH and RH hot film MAF sensor (B2/6, B2/7), engine load
- LH and RH intake camshaft Hall sensor (B6/4, B6/5), intake camshaft positions
- LH and RH exhaust camshaft Hall sensor (B6/6, B6/7), exhaust camshaft positions
- Coolant temperature sensor (B11/4)
- Crankshaft Hall sensor (B70), engine speed
Function sequence for camshaft adjustment
The function sequence is described in the following Operation
^ Function sequence for release of the camshaft adjustment
^ Function sequence for adjustment
^ Function sequence for adjustment range
^ Function sequence for start position
^ Function sequence for valve overlap
^ Function sequence for camshaft positions monitoring
^ Function sequence for diagnosis
Function sequence for release of the camshaft adjustment
The ME-SFI control unit enables camshaft adjustment according to vehicle speed, engine speed and engine oil temperature.
Engine oil temperature is important, even when the oil is hot, to ensure that there is sufficient oil pressure (greater than 1.5 bar) for adjusting the camshafts.
If the oil pressure is inadequate, first of all adjustment of the exhaust camshafts is not guaranteed, as these must be adjusted when the engine speed is dropping (low oil pressure) opposite to the direction of rotation of the engine.
Release of the camshaft adjustment occurs dependent on:
- Vehicle speed greater than 10 km/hour
- Engine speed greater than 1000 rpm (except during catalytic converter heating)
- Engine oil temperature greater than-10°C
Function sequence for adjustment
The LH and RH intake camshaft solenoids (Y49/4, Y49/5) and the LH and RH exhaust camshaft solenoids (Y49/6, Y49/7) are actuated by the ME-SFI [ME] control unit by means of a PWM (pulse width modulated) signal.
The control plungers are adjusted via the characteristics map- dependent duty cycle. Depending on their positions, the oil quantities (pressure oil) are controlled for the swivel motor adjuster.
In the swivel motor adjusters, the rotors, fixed to the camshafts, are therefore displaced by the pressure oil.
Function sequence for adjustment range
Intake camshafts: 14° CKA before TDC (Top Dead Center) to 28° CKA after TDC
Exhaust camshafts: A 17° CKA before TDC to a 25° CKA after TDC
Function sequence for start position
Intake camshafts: A 28° CKA after TDC
Exhaust camshafts: A 17° CKA before TDC
The camshafts are locked in a fixed position for starting by catch bolts (locked). This start position is unlocked hydraulically at the first actuation of the intake and exhaust camshaft solenoids.
Shown with camshaft adjustment (left exhaust camshaft)
1 Left camshaft adjustment housing
1/1 Switching oil ducts to switching oil pilot bushing
1/2 Solenoid
1/3 Switching oil control valve
2 Switching oil pilot bushing
2/1 Pulse wheel of exhaust camshaft
3 Swivel motor adjuster
4 Exhaust camshaft
B6/6 Left exhaust camshaft Hall sensor
Y49/6 Left exhaust camshaft solenoid
Swivel motor adjuster illustration
3/1 Torx screws
3/2 Front cover
3/3 Catch bolt with spring and spring cup
3/4 Rotor
3/5 Stator
3/6 Dowel pin
3/7 Rear cover
3/8 Front gearwheel (main toothed wheel)
3/9 Front gearwheel (tensioning wheel)
3/10 Springs (gear backlash compensation)
3/11 Fixing screw M5 B8 (for disassembly and assembly of swivel motor adjuster)
3/12 Circlip (gear backlash compensation)
Function sequence for valve overlap
At low engine speed and load, the ME-SFI [ME] control unit sets a large valve overlap in order to produce internal exhaust gas recirculation. Less fresh air is admitted, as exhaust gases with low oxygen content are still present in the cylinders. This lowers the combustion temperature and reduces the formation of nitrogen oxides (NOx).
The intake air mass is reduced by the amount of exhaust gases present. The ME-SFI [ME] control unit shortens the injection time accordingly.
The smallest valve overlap for gas exchange occurs if the exhaust camshaft is adjusted to the maximum BTDC (advanced) and the intake camshaft to the maximum after TDC (retarded).
The resulting increased fresh air content produces more engine torque and engine power.
Function sequence for camshaft positions monitoring
The camshafts positions are detected by the intake camshaft Hall sensors and the exhaust camshaft Hall sensors, and communicated to the ME-SFI [ME] control unit. Detection of the positions takes place through detection of the positions of pulse wheels which are located at the front on the camshafts
Function sequence for diagnosis
During diagnosis of the camshaft adjustment, the ME-SFI [ME] control unit checks whether the camshafts are in start position at engine start and whether the required adjustment has been reached after the engine has been running for a short time. Output stage errors in the camshaft solenoids (integrated with the ME-SFI [ME] control unit) and faulty camshaft Hall sensors are also detected.
