Exactly how does the M272 camshaft timing adjustment work? - Mercedes Benz SLK Forum

SLK R171 General Discussion SLK 200, SLK 280, SLK 300, SLK 350, SLK 55 AMG

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#1 Old 06-19-2012
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Exactly how does the M272 camshaft timing adjustment work?

There's copious posts (here and on other sites) about M272 engine timing, camshaft adjustment, balance shaft wear, hall sensors, and magnets. But I can't find anything about how the variable camshaft timing actually works. Obviously: 1) the camshaft timing adjustments are under the control of the Motronic ECU, and 2) each camshaft has it's own actuator and sensor. But the specifics of how the actuator, sensor, and ECU work and interact with one another aren't so obvious.

The training slides mention that the adjuster is "vane-type, oil pressure controlled". I wonder what that means really? Engine oil?

There appears to be a magnet involved -- I assume it's an electromagnet. Does its magnetic field control the camshaft timing? Is it also used for sensing?

What are the possible MB codes that can be posted related to the camshaft timing?

I'll post back any further information I find; if you have some, please share!
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#2 Old 06-19-2012
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these training slides, right?

http://www.billsden.org/fileadmin/me...ngine_m272.pdf
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#3 Old 06-19-2012
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Correct, Sgt!
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#4 Old 06-19-2012
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Well it appears to be a little complicated. The oil is engine oil. Here is what the shop manual says:

"The intake and exhaust camshafts can be adjusted continuously by 40 degrees. The infinitely variable adjustment of the camshafts is carried out by patented, electrohydraulically operated vane adjusters mounted on the front end of the camshafts, with integrated control valves.

Solenoids are located in the front of the respective camshaft. The solenoids actuated the control plunger on the vane-cell adjuster according to the performance map related duty cycle. Depending on their position, more or less pressure oil flows from the hollow camshaft to the oil galleries of the vane-type adjuster.

The solenoids for camshaft adjustment are designed as proportional magnets, i.e. the direction of the armature and thus the position of the control plunder in the vane-type adjuster are dependent on the intensity of the current in the coil.

The solenoids before the camshafts are actuated by the ME control unit at the ground end by means of a PWM signal (150 Hz). The voltage supply for the solenoid takes place from circuit 87. The vane-cell adjusters are actuated according to the performance map related to duty cycle. The maximum current (duty cycle 100%) is emitted for a short time (about 0.5 sec) for rapid adjusting of the anchor. A hold-in winding voltage with a small duty cycle is then set afterword’s.

Fill the oil Gallery:

Pressure oil flows out of the hollow camshafts into the van-cell adjuster. The camshafts adjust themselves to the respective direction of rotation. The inlet camshafts adjust to “advance”. The exhaust camshafts adjust themselves due to their reversed direction of rotation to “retarded”.

Depending on their position, the oil volume in the vane –type adjusters is controlled. This takes place through differently arranged holes in the control plunger as well as through oil ducts in the vane-cell adjusters. The adjusting range is limited by the forming of the vane-cell adjuster mechanically. If the solenoids are no longer actuated then resetting takes place against the direction of rotation.

Oil gallery closed:

Each camshaft position is detected by a camshaft Hall sensor. Once the requested adjustment has been achieved then the respective solenoid will be actuated in such a way that oil galleries in the vane-cell adjusters are close."

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#5 Old 06-19-2012
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Dictionary.com shows the definition of "vane" to be: any of a number of blades or plates attached radially to a rotating drum or cylinder, as in a turbine or pump, that move or are moved by a fluid, as steam, water, hot gases, or air.
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#6 Old 06-20-2012
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As above. The oil pressure which is present all the time after start-up moves the respective camshafts to their desired position.Based on many inputs from the around the engine. Such as road speed - throttle position – engine RPM-temperature and so on. Advancing the inlet cam and simultaneously retarding the exhaust with has such effects as to dial out overlap, increase manifold vacuum and clean up emissions low down and at idle. Swinging the opposite direction with the valve timing will increase top end engine performance
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#7 Old 06-30-2012
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Here's a picture of the inside of the camshaft adjustment magnet. The center circle (about 3MM in diameter) is actually the end of a small shaft that moves in and out of the magnet -- I presume under the control of the magnet.
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Here are some pictures of the harness connector for the camshaft hall sensor. Mine was broken, so I ordered a new one ($2.50) and replaced it.

There are three different "latches" involved in these connectors:
  1. The "outer" or main latch that secures the connector to the sensor. This is the latch you have to release to replace the sensor.
  2. Three plastic latches that are part of the connector. These serve to retain each of the three pins in the connector.
  3. A metal latch on each of the pins.

Larger images here
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#9 Old 07-24-2012
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Here is a great illustration of the camshaft adjuster. It shows the parts, but it doesn't show how they're fastened together. And it sure doesn't show the vanes anywhere. Methinks there is more to the picture.

2/5 is shown as "right handed threads" but I don't see any threads on the part. Any ideas where the threads are?
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Originally Posted by jbanks15 View Post
Wow, good training aid, have you got anything similar for the M111 Engine?

Cheers,

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#11 Old 01-30-2014
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