Camshaft adjustment, function - GF07.10-P-1016MI
ENGINE 272.9 (except 272.98) in MODEL 204.0 /2 as of model year 2009 /YoM 08
ENGINE 272.9 (except 272.98) in MODEL 204.9, 207.3 /4, 212.0 /2
ENGINE 273.9 in MODEL 207.3 /4, 212.0 /2
Function requirements for camshaft adjustment, general points
- Circuit 87M ON (engine control ON)
- Engine running
Camshaft adjustment, general points
Camshaft adjustment allows all four camshafts to be adjusted continuously by up to 40° CKA (C ran K A ngle). 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 (N3/10) control unit reads the following sensors:
- Hot film MAF sensor (B2/5), engine load
- 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)
- Crankshaft Hall sensor (B70), engine speed
Function sequence for camshaft adjustment
The function sequence is described in the following steps:
- 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
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 ME-SFI [ME] control unit using various operating data (e.g. coolant temperature, time, engine load) and a stored temperature model determined.
Engine oil temperature is important, even when the oil is hot, to ensure that there is sufficient oil pressure (>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.
A return spring is located in each exhaust-side vane-type 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 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.
Adjustment range function sequence
Intake camshafts: 4° CKA before TDC (T op D ead Center) to 36° CKA after TDC
Exhaust camshafts:20° CKA before TDC to 20° CKA after TDC
Start position function sequence
Intake camshafts: A 36° CKA after TDC
Exhaust camshafts:20° 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 is oil flows in the intake camshaft vane-cell adjuster
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.
Valve overlap function sequence
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.
Camshaft positions monitoring function sequence
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.
Diagnosis function sequence
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: the intake camshaft adjustment
Shown is the intake camshaft vane-cell adjuster
| Component description for ME-SFI [ME] control unit | N3/10 Engine 272 |
GF07.61-P-6000MI |