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Does anyone know what the camshaft angles actually mean ? (ie. Position of intake camshaft of right (or left) cylinder bank)
What are they measuring ? Opening? Centerline ? Closing point ?
Yes, I understand how Mercedes variable valve timing works and the mechanics of it (as well as how other manufactures accomplish it)
I was specifically looking to find out what icarsoft's measurement was actually measuring. LCA (lobe center angle ? opening event ? closing event ?. There is no mention either if the measurements are at BTDC, ATDC, BBDC, ABDC).
By the way, I have a M273 when has the intake cams driven via the timing chain and the exhaust cams driven via geared teeth on the intake cam sproket.
I have not touched my icarsoft MB 2.0 for a long time, it is too weak a scanner.
I can't remember what are the actual values it represent for cam angles or is it is accurate or not as there are by right two parameters, ECM demanded/specified angle and actual achieved angle.
What I can show you is how Xentry reads the valve timing and on my M276.820 3.0 Turbo
In Xentry, it represent advance and retard of camshaft angle in relation to TDC of the piston.
Remember the old days before VVT and when we make ourselves those adjustable camshaft sprocket but only 1 static value we can adjust.
Like this one , but a company made for retail and not DIY custom I had long time ago.
Yes, I would always worry that they would slip when I was driving the car. (hahaha)
LOL, memory lane indeed.
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I think we should start to think more like the ECM and can't be too mechanical-analog.
I am sure if say we can get the base timing chart like below but specific to our engine without VVT activation, it would be awesome
I too at one moment was puzzled by angle value, but for high pressure fuel injection pump (HPFP) my engine has..... being a direct injection engine.
You see the data shown on Xentry for the HPFP activation is not duty cycle, instead it is shown as actuation angle of the fuel quantity valve. Max as 90 degrees I seen.
The HPFP is a single piston design and it get its pumping power from intake camshaft FUEL PUMP lobes at Bank1.
At first my logic was to assume the angle of reference in question is of the camshaft rotation, but when I scoped the HPFP and many scratching head later,
I then realized the angle of reference is the crankshaft
Initially I was trying to figure out a what-if-scenario, how would a dynamic VVT system confuses the accuracy of the HPFP activation command ?
M276 3.0 turbo and M278 get a 4 lobes fuel lobe camshaft, M276 3.5L get a 3 lobes one.
Our HPFP is a normally open unit, so when fuel quantity valve not energize or failed it will not build up to the 200 BAR pressure but will allow 4-5 BAR fuel pressure from the electric
low pressure fuel pump at the fuel tank.
Basically the ECM must time the fuel quantity valve activation (close) based on camshaft angle to define where is the fuel lobe TDC and BDC are, because pressurization will only occur
at fuel lobe BDC to TDC spin. TDC to BDC is suction or normally open.
So a 66 degrees of HPFP total actuation angle of fuel quantity valve if based on camshaft revolution does not make sense, but when we use crankshaft revolution it started
to make sense as 1 crankshaft revolution is only 1/2 revolution of camshaft and 66 degrees or maximum 90 degrees of CRANKSHAFT is equal to 33 to 45 degrees of CAMSHAFT revolution.
Viola !! 45 degrees of CAMSHAFT is indeed the maximum fuel pressurization zone for a 4 lobes fuel lobe.
This is assuming in good faith the activation timing can be done with very good accuracy as 45 degrees at the wrong part of the lobe wont do any good.
Camshaft tone wheel is fix, but camshaft to crankshaft connection via VVT sprocket is dynamically variable.
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M278 get twin HPFP, M276 get single pump
Now imagine, intake camshaft VVT range is 40 degrees.
VVT response is not super fast or accurate during a fast full throttle RPM rise, ECM triggers the magnetic phasor, magnetic phasor push the oil control valve, oil valve send oil to VVT sprocket internal vane yada yada. Oil pressure variation because of variable RPM is also a factor. Electrically ECM processor speed is no issue, but electro-mechanical and hydraulic has lag.
As seen on the Xentry test I did, delay or inaccuracy or under/over shoot will happen in a fast engine RPM rise.
Here it gets me wondering in a 1st gear WOT pull scenario, ECM must probably do predictive calculation and activation at some point for HPFP actuation angle of fuel quantity valve.
There is not enough time or too much variable if ECM were to wait for camshaft angle vs crankshaft angle feedback.
In a 4 lobes fuel lobe camshaft, only 45 degrees of camshaft revolution out of per 90 degrees can do fuel pressurization, so a 40 degrees worth of VVT variable means some
degree of under/over shoot can happen.
In a 5,000 crankshaft RPM scenario with 4 fuel lobes camshaft, 10,000 times per minute is the HPFP pumping action.
166 times HPFP pumping per second.
1,000 / 166 = 6 milliseconds per 1 event of pumping
Only half of 6 ms or 3 ms should be activation of fuel quantity control valve, the pressurization section.
This is fuel injector accuracy territory...wow.
Last edited by S-Prihadi; Jan 2, 2023 at 01:18 AM.
I think we should start to think more like the ECM and can't be too mechanical-analog.
I am sure if say we can get the base timing chart like below but specific to our engine without VVT activation, it would be awesome
I looked around for this information years ago but couldn't find it. It would certainly be great to have.
The link below shows how the intake cam advances at wide open throttle up to redline increasing overlap as the rpms climb. The exhaust cams stay relatively stable retarded at -15 deg from their base setting. Oddly enough, back in the day, you wanted to close the intake valve as late as possible ABDC to make use of the surge from the high flowing column of air coming into the cylinder (for a cam designed for high rpm power). It would be interesting to see what Mercedes's line of thinking was when they set their advance/retard curves for the camshafts.
Also, the cam advance/retard settings (degrees) for both the intake/exhaust cams are almost identical at idle and at wot redline I noticed. (approx 5 deg difference).
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Yes, I would always worry that they would slip when I was driving the car. (hahaha)
