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From: jackh@zehntel.UUCP (jack hagerty)
Newsgroups: net.auto
Subject: Re: Camless valve operation
Message-ID: <1737@zehntel.UUCP>
Date: Thu, 10-Jan-85 17:53:53 EST
Article-I.D.: zehntel.1737
Posted: Thu Jan 10 17:53:53 1985
Date-Received: Sat, 12-Jan-85 02:58:53 EST
References: <6848@watdaisy.UUCP>
Distribution: net
Organization: Zehntel Automation Systems Inc, Walnut Creek CA
Lines: 53

> It has been suggested that the valves in an engine be operated
> electrically rather than by a cam.  There is no doubt that such
> operation could give more nearly optimal valve operation than
> a fixed cam.
> 
> The above scheme has been implemented for the purposes of engine
> testing (I can't remember the reference, it was either PM or C&D or
> R&T in the last 10 years).  The trouble is that the solenoids to
> operate the valves are tremendously inefficient and consume a
> significant fraction of the overall output from the engine.  
> 
> If someone could invent an efficient mechanism to control the valves
> like this, he would indeed have a better mousetrap.

This article, and the one suggesting the use of solenoids to operate
springless, desmodronic valves, miss the point. What you have to do
is separate the energy required to open the valves from the control
of that energy.

Assuming that we stay with valves opened by engine-driven cams and
closed by springs, how can we vary the lift and overlap of the valve
timing?

Well, as it turns out, the elements of a system to do that have already
been marketed although one beat a hasty retreat. For five years now,
Alfa Romeo has had dynamic valve timing on their 4 cylinder, twin cam
engines. The intake cam can rotate several degrees relative to its drive
sprocket. It is set to be fully retarded at low speed to give a smooth
idle and good low end torque. It advances to produce a good degree of
overlap at high speeds for top end power. Orignally the cam timing was
controlled by a govenor but now that they've gone to the new Bosch
FI, it's controlled by the same module that controls the spark timing.

Cadillac's ill fated "modulated displacement" 4-6-8 engine (marketing
wouldn't allow "variable displacement" because of the acronym) had
an ingeniously simple method of shutting off the unused cylinders.
A solenoid was positioned above the pivot of each rocker arm. If the
cylinder was to be "on", the solenoid was extended forcing the rocker
onto its pivot and the valve worked normally. If the cylider was to
be "off", then the solenoid retracted allowing the rocker arm to "float"
with the tip of the arm pivoting on the valve stem.

Of course, this represents the "bang-bang" approach to valve lift
control: full lift or no lift at all. It seems that a variation on
this idea could produce the infinitely variable lift desired.

I realize that this postulates a twin cam engine with rocker arms, a
rather odious thought to those of us that admire the simplicity of
the classic twin cam design. But at least that's much more in the realm
of accepted engine design than solenoid-actuated desmodronic valve trains!

                     Jack Hagerty, Zehntel Automation Systems
                      ...!ihnp4!zehntel!jackh