Camshaft Adjustment, Function - GF07.10-P-1016MRT

Engine 256.9 in model 213, 238, 257, 290 

up to model year 2021 

Engine 256.9 in model 222 

Function requirements, general 

• Engine runs

The ME-SFI [ME] control unit (N3/10) detects the engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

Camshaft adjustment, general points 

With the camshaft adjustment, the two camshafts can be continuously adjusted by up to 40° CKA (crank angle) to "advanced" and "retarded". This means the valve overlap in the event of a gas exchange 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.

The ME-SFI [ME] control unit evaluates the following signals to implement camshaft adjustment:

• Intake camshaft position

  Intake camshaft Hall sensor (B6/15)

• Exhaust camshaft position

  Exhaust camshaft Hall sensor (B6/16)

• Coolant temperature

  Coolant temperature sensor (B11/4)

• Engine load

  Pressure and temperature sensor downstream of turbocharger (B28/17)

• Engine speed

  Crankshaft Hall sensor

• Engine oil level

  Engine oil fill level sensor (B40/6)

• Oil pressure and oil temperature

  Engine oil pressure and temperature sensor (B149/1)

The function sequence is described in the following steps:

• Release of camshaft adjustment 
• Oil pressure 
• Adjustment 
• Adjustment range 
• Start position 
• Valve overlap 
• Monitoring the camshaft positions 
• Diagnosis 
• Intake camshaft valve lift adjustment 

Release of camshaft adjustment 

Camshaft adjustment is enabled by the ME-SFI control unit dependent on engine speed and engine oil temperature.

The ME-SFI [ME] control unit determines the engine oil temperature based on different operating data (e.g. coolant temperature, time, engine load) and a saved temperature model.

The 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.

Enable of adjustment of the exhaust camshaft does not occur until a higher rotational speed compared to the intake camshaft. 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. There is a return spring located for support in each camshaft positioner.

If both camshafts are adjusted, adjustment of the exhaust camshaft 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 load-dependent:

• For an 80°C engine oil temperature from about 600rpm
• For an 120°C engine oil temperature (intake side) from about 800rpm
• For an 120°C engine oil temperature (exhaust side) from about 1050rpm

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 necessary (a saving on fuel).

Adjustment 

The intake camshaft solenoid (Y49/1) and the exhaust camshaft solenoid (Y49/2) are actuated by ME-SFI [ME] control unit by means of a pulse width modulated signal. The control plungers are adjusted via the characteristics map-dependent duty cycle. The oil filling quantities (hydraulic fluid) for the camshaft positioners are controlled according to their position. The vane plungers which are firmly connected to the camshafts are thus turned by the hydraulic fluid in the camshaft positioners.

Adjustment range 

• Intake camshaft: a 4° CKA before TDC (Top Dead Center) up to a 36° CKA after TDC (intake open)
• Exhaust camshafts: 25° CKA before TDC to 15° CKA after TDC (exhaust closes)

Start position 

• Intake camshafts: 36°CKA after TDC (intake opens)
• Exhaust camshafts: 25° 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 camshaft and exhaust camshaft solenoids.

Shown is oil flows in the intake camshaft camshaft positioner 

Courtesy of MERCEDES-BENZ USA

Valve overlap 

At low engine speed and load, the ME-SFI 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 (NO_X ).

The intake air mass is reduced by the amount of exhaust gases present. The ME-SFI control unit shortens the injection period accordingly.

The smallest valve overlap during gas exchange arises if the exhaust camshaft is adjusted to the maximum BTDC (advanced) and the intake camshaft to the maximum ATDC (retarded). A higher engine torque and a higher engine output are achieved due to the higher fresh air content.

Monitoring the camshaft positions 

The camshaft positions are detected by the intake camshaft Hall sensor and the exhaust camshaft Hall sensor and communicated to the ME-SFI [ME] control unit. Acquisition of the positions takes place through detection of the positions of pulse wheels which are located at the front on the camshafts.

Shown is the intake camshaft adjustment 

Courtesy of MERCEDES-BENZ USA

Shown: intake camshaft camshaft positioner 

Courtesy of MERCEDES-BENZ USA

Diagnosis 

During camshaft adjustment diagnosis, the ME-SFI [ME] control unit checks whether the camshafts are in the start position at engine start and whether the requested adjustment is achieved 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 defective camshaft Hall sensors are also detected.

Intake camshaft valve lift adjustment 

With the valve lift switchover, a two-stage switchover of the cams on the intake camshaft occurs depending on the characteristics map.

The intake valves close earlier due to the switchover of the camshaft to a shorter stroke. This leads to an optimization of the gas exchange in partial-load range. The valve lift switchover to the smaller cam stroke is performed in an rpm range of 1000 to 4000 rpm.

The ME-SFI [ME] control unit actuates the following component parts with a pulse width modulated signal for valve lift switchover:

• Cylinder 1 and 2 intake CAMTRONIC actuator (Y49/19)
• Cylinder 3 and 4 intake CAMTRONIC actuator (Y49/20)
• Cylinder 5 and 6 intake CAMTRONIC actuator (Y49/21)

In this process, a coil in the corresponding actuator is energized, and a tappet moves into a corresponding curved track on the camshaft. With the turning of the camshaft and the forming of the curved track, the camshaft is moved axially and the smaller cam affects the intake valves.

A bump in the curved track has the effect of bringing the tappet back to the default position.

To reset the camshaft to a long stroke, a second tappet moves in a corresponding curved track and the reset occurs in the same manner. The tappet position is determined using a Hall sensor integrated in the respective actuator; for valve lift switchover, this transmits a signal to the ME-SFI [ME] control unit.

View of intake camshaft from left 

Courtesy of MERCEDES-BENZ USA

	Electrical function schematic for camshaft adjustment	Engine 256.9 in model 213, 238 up to model year 2021	PE07.10-P-2716-97DBA
		Engine 256.9 in model 222	PE07.10-P-2716-97SEM
		Engine 256.9 in model 257 up to model year 2021	PE07.10-P-2716-97XBB
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRT