[Diy_efi] Continuous VVT system

[Alexei Pavlov]

espresso_doppio at yahoo.com wrote:
> 
> --- Alexei Pavlov <alexis.pavlov at st.com> wrote:
> 
> >> That would make good sense.  I suspect the
> >> controller used will need modification, if not
> >> replacement.
> 
> > No except ignition, as it's a MAF/RPM system.
> 
> I meant the valve timing controller.  I doubt they
> used an infinitely-variable design architecture for
> what is a binary system.

Of course, I'll use an additional ECU to control VVT.
In fact the VVT systems were very rare at that time, so
a binary one was already an exception.

The original ECU does not check if the VVT is working.
So I can modify it. It's even possible to disconnect
the VVT activator and everything works well (with less HP).

> 
> > You may find a Hall-effect sensor to be a more
> > robust sensor for that application.
> 
> > The problem is to mount the magnet on the camshaft.
> 
> Is the car EFI already?  If so, it may well have a
> Hall effect sensor on the camshaft already, although
> in many cases, it's a simple engine phase indicator,
> rather than an angular indicator.

It's EFI but without cam sensor as it's 2s per cylinder.

> 
> If it isn't, you may find that epoxy and some magnets
> may give you the desired effect.
> 
> > I'm afraid if I do that steel pieces will stay on
> > cams and destroy the cam/tappet surfaces,
> 
> I doubt you'd be using magnets powerful enough to do
> that, even if ferrous particles were to make their way
> to the top end.  Hall-effect sensors have been used on
> cams to detect engine phase for several decades witout
> incident.

Yes, but they are not in direct contact with the camshaft.
I would have to fix magnets on the camshaft, as the front of 
the camshaft is 'unshifted' (the VVT device is here).

And I'm not sure the epoxy (120 degres tolerant) will stay for
a long time if the oil is at 110 degres.

Another point is that magnets loose their 'magnetism' when
heated. And mine will constantly be washed by the engine oil.

The better would be to put sensors on the back of the
camshaft, but the engine bay wall is too close. For the moment
I'm trying to do so, next when I'll remove the head to improve
it I'll probably modify the sensor location.


> >> An infintely-variable system doesn't seem trivial
> >> to me at all.  I think you may be in for some real
> >> mechanical engineering challenges.
> 
> > Mechanically it's not complexe, you just have to
> > control the oil pressure in the VVT device.
> 
> I was more meaning adapting the cams, cylinder head,
> and hardware on the vehicle now.  Unless it has
> infinitely-variable design cams already, that's a big
> one.  The Valvetronic system uses not only a different
> cam timing, but a different duration as well,
> necessitating very unusual-looking cam lobes that
> change shape as the cams move laterally.  It would
> probably be easier to have infinitely variable
> advance/retard.  I'd be interested to see how much
> difference that made in comparison to the Valvetronic
> design.  My own experience with cam timing tells me
> that there's not a tremendous amount of power to be
> gained from changing timing alone, in many cases.

The Alfa Romeo engine without VVT should deliver something
like 90HP from a 2L engine. The VVT brings the power
at the 150 hp level on a 2s/cyl engine at 6000RPM, not so bad !

The gain come form the overlap and IVC modifications.

Of course I would prefer to also have the variable lift.
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