[Diy_efi] Continuous VVT system

[Adam Wade]

--- Alexei Pavlov <alexis.pavlov at st.com> wrote:

> I'm trying to modify the VVT system to get a
> continuous angular cam positionning on intake and
> exhaust camshafts (as all 4cyl AR engines this is a
> twin cam one).

> Has someone already done this kind of systems ?

I believe Bosch's "Valvetronic" system, as found on
newer BMW cars, operates in this fashion.

> The principle of the original system is as follows:
> An electric activator pushes a button which allows
> engine oil entering a chamber, in which oil pressure
> pushes another piece that shifts the cam timing.

Honda may have an "infinite" VVT system, although I
know they have had several binary systems.

Some other binary methods I have seen are a second cam
lobe with what amounts to a collapsed hydraulic lifter
under it.  A hydraulic pump fills it with oil,
allowing the second lobe to act on the valve(s), at a
given engine speed.  I believe there's also one where
a rocker arm is shifted in and out from under a second
lobe as well.

> Modern continuous VVT systems (like Toyota/Lexus
> ones) often use the same principle, but can control
> the cam position in a continuous way. A slight mod
> of the Alfa VVT should allow me doing the same.

If the Alfa system is a "crippled" version of the
infinitely-variable system, then sure.  But they may
be substantially different in mechanical terms, even
though they seem to operate in a similar fashion.

> An additional ECU that controls VVT will contain
> maps with cam shifts as function of load and RPM.

That would make good sense.  I suspect the controller
used will need modification, if not replacement.

> I'm planning to use electro-magnetic sensors to get
> the current angular position of camshafts collected
> on the cams.

You may find a Hall-effect sensor to be a more robust
sensor for that application.  A differential sensor
based on the Hall effect would give you more angular
rotational information, and they are becoming more
commonplace in the automotive world now.


An infintely-variable system doesn't seem trivial to
me at all.  I think you may be in for some real
mechanical engineering challenges.

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