Dual Actuator Vanos

[Herrubermensch]

A follow up question, Andrew, relating to my prior inquiry about resource assignment and polarity. In the tuning worksheet in the GPR package, there are maps for exhaust camshaft aim retard and inlet camshaft aim advance. Am I correct to assume that when the second actuator output for each cam is assigned and in use, the tuning maps for camshaft control automatically use the correct actuator output for retarding or advancing each cam? If so, how does the code know which actuator output is being used for retard and which for advance? The only way it would seem to work is if each actuator is hard-coded to a particular function. E.g., actuator output 1 for intake camshaft is advance and actuator output 2 for intake camshaft is retard. And if THAT is the case (which it seems it must be), then which actuator output serves which function for each camshaft? Help!

--Peter

[AndrewD]

The output signals are generated by the control strategy: if you assign a resource to both outputs the strategy assumes dual output Vanos operation.

When polarity is normal output will retard and output 2 will advance
When polarity is inverting output 2 will retard and output will advance

Or to answer in another way: you can't do any damage to a standard engine with cam control so just wire it up. If the cam goes the wrong way change the polarity.

[Herrubermensch]

Thanks, Andrew! That makes perfect sense, I just wanted to make sure, as the S62 is an interference engine, and getting the vanos operation backwards very well could lead to piston to valve contact, especially in my instance, where I run custom ground camshafts and solid lifters. Thanks again!

--Peter

[Herrubermensch]

Quick confirmation of another point. The allocation you described is the same for intake and exhaust cams, correct?

Specifically:

When polarity is normal output 1 will retard and output 2 will advance; and
When polarity is inverting, output 1 will advance and output 2 will retard;
regardless of whether we are talking about intake or exhaust cams, correct?

Please confirm, then I promise to cease and desist with the questions until I test! Thanks!

--Peter

[AndrewD]

Peter,

Any engine with camshaft phase control must be built to ensure that there is no chance of either piston to valve or valve to valve contact when the camshafts are move through the full control range. All OE cams are like this and any modifications should also guarantee the full movement range is safe.

Think about it this way, none of the following should not be able to destroy the engine:

1. A wiring fault
2. A stuck vanos solenoid
3. Typing the wrong number in the camshaft aim table

The camshaft control strategy is identical for inlet and exhaust. The difference is the way control is used:

• Inlet is minimum advance at idle. By convention this is 0deg advance and the cam will advance from this position.
• Exhaust is minimum retard at idle. By convention this is 0deg retard and the cam will retard from this position.

[Herrubermensch]

Andrew, I will only say that I have had one S62 blow up because of a vanos defect (something was stuck, preventing it from moving after the engine's warmup phase). I personally witnessed it and saw the results of the subsequent tear down. The same vanos we attempted to install on a second S62, but it stuck again. We determined this BEFORE starting the motor and so ultimately decided to delete the vanos altogether just to get that motor running. So all I can say is: I understand what you are saying, it is what I have always been told, but I can tell you from personal experience, it is not the case with an S62, at least, not with the cams I'm running, which are modest changes above the typical Schrick profiles available for my engine. Thus, I am uber-concerned with ensuring vanos does not do in yet another of my engines!

I appreciate the confirmation of the control strategy. The S62 technical manual uses a slightly different convention, using "advance" and "retard" with respect to both inlet and exhaust cams, but it is just a convention. That is, different symbols denoting the same concepts: at idle, the exhaust cams are "fully advanced" or "at zero retard" and the inlet cams are "fully retarded" or "at zero advance."

Apologies for the protracted explanation.

--Peter

[AndrewD]

... any modifications should also guarantee the full movement range is safe.

If the cam choice results in piston to valve contact anywhere in the vanos movement range then, respectfully, you are building a grenade. The engine builder must still guarantee appropriate clearances when camshaft control is used.

[Herrubermensch]

I hear you, but it is not the cams. The profile is modest. A stuck vanos did in that motor and would have done in a second one had we not changed it out. That vanos is in the trash bin now.

--Peter

[AndrewD]

What was the failure in the engine that resulted from the cam not moving?

[Herrubermensch]

What was the failure in the engine that resulted from the cam not moving?

First, I did not build the engine myself, which was mistake number one. Second, I had the vanos gears machined by Dr. Vanos here in the States to minimize vanos noise, which was mistake number two. I now build my own engines and refurbish my own vanos and do not care about vanos noise!

With that understanding, the bank 1 vanos seemed to allow the helical gear to go too deeply into the exhaust cam, allowing the cam gear to rotate beyond its factory rotation range, then stick and refuse to move. Piston to valve contact, resulting in smashed valve and cracked block and damaged pistons, all within 1:52 of startup.

On second engine, with the same vanos unit and same cams, the engine was cycled by hand enough to realize that exactly the same result would occur. Hence, the vanos was deleted. Engine ran fine, except then it became clear that the engine builder had used the incorrect piston material for the ductile iron sleeves in the block, such that the piston to wall clearance became too tight when the motor was hot. Engine was torn down and abandoned before catastrophic failure occurred. Only salvageable pieces were the cams, lifters and valvetrain.

It was a real mess. Live and learn.

--Peter