GF07.10-P-1016MMI Camshaft Adjustment, Function
GF07.10-P-1016MMI Camshaft Adjustment, Function
ENGINES 152.9 in MODEL 172.4
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 wide limits.
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:
- LH and RH intake camshaft Hall sensors (B6/4, B6/5), intake camshaft positions
- LH and RH exhaust camshaft Hall sensors (B6/6, B6/7), exhaust camshaft positions
- Coolant temperature sensor (B11/4)
- Pressure sensor downstream of throttle valve (B28/7), engine load
- Oil sensor (oil level, temperature and quality) (B40)
- Crankshaft Hall sensor (B70), engine speed
Function sequence for camshaft adjustment
The function sequence is described in the following Operation steps:
^ Function sequence for release of the camshaft adjustment
^ Function sequence for engine oil pressure
^ 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
Camshaft adjustment is enabled by the ME-SFI [ME] control unit depending on engine speed and engine oil temperature.
The engine oil temperature is determined by the oil sensor (oil level, temperature and quality).
The 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.
Release of adjustment of the exhaust camshafts takes place by means of a comparison to the intake camshafts, at first at a high rotational speed. In this way for exhaust, also at a low oil pressure level, reaching the locking position against the "retard" operating reaction torques of the camshaft are secured.
A return spring is located in each exhaust-side vane-Model adjuster for support.
If all four camshafts are adjusted, adjustment of the exhaust camshafts takes place after a delay (later). Oil supply problems are prevented and secure functioning of the locking mechanism achieved.
Release of the camshaft adjustment occurs dependent on load:
- For an 80°C engine oil temperature from about 600 rpm
- For a 120°C engine oil temperature (inlet side) from about 800 rpm
- For a 120°C engine oil temperature (exhaust side) from about 1050 rpm
Function sequence for engine oil pressure
The engine oil pressure is regulated via the engine oil pump valve (Y130) in order to ensure an adequate oil supply and to lower the oil pressure if required (a saving on fuel).
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 performance map-dependent duty cycle. The oil quantities (pressure oil) for the vane-cell adjusters are controlled according to their position. The vane plungers in the vane-cell adjusters which are firmly connected to the camshafts are turned by the pressure oil.
Function sequence for adjustment range
Intake camshaft: 4° CKA before TDC (Top Dead Center) to a 36°CKA after top dead center (inlet opens)
Exhaust camshaft: 30°CKA before TDC to a 10° CKA after top dead center (exhaust closes)
Function sequence for start position
Intake camshaft: 36°CKA after top dead center (inlet opens)
Exhaust camshaft: 30°CKA before TDC (exhaust closes)
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 is oil flows in the intake camshaft vane-cell adjuster
1/2 Control plunger
A Oil galleries for retarding the ignition timing
B Oil galleries for timing advance
C Pressure oil from the intake camshaft
D Rotation direction
The upper half of the illustration shows:
Filling oil galleries (A), oil galleries (B) open.
The lower half the illustration shows:
Filling oil galleries (B), oil galleries (A) open.
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.
Shown on intake camshaft adjustment
1 Control valve
1/1 Valve body
1/2 Control plunger
1/3 Return spring
2 Vane-Model adjuster
3 Intake camshaft
Y49/4 Left intake camshaft solenoid
Y49/5 Right intake camshaft solenoid
Shown is the intake camshaft vane-cell adjuster
2/1 Catch bolt
2/2 Apex seals with leaf springs
2/3 Compression spring
2/4 Vane-Model piston
2/5 Drive gear
2/6 Cover
