It is well known that Dr. Alfred J Buchi invented the turbocharger in c. 1905 while in charge of Research at Sulzer Engines in Winterthur, Switzerland.  Not as well known is that he developed a "telescopic valve" engine in the 1950's, and an example is shown here: -

<IMG SRC="Buchi Telescopic Valve GA/2.gif" WIDTH=250 HEIGHT=446>

A close-up of the valve gear is shown here: -

<IMG SRC="Buchi Telescopic Valve only.gif" WIDTH=250 HEIGHT=216>

Sorry for the very poor reproduction, but it is the best available to me.

This illustration is from the Proceedings of the 1957 CIMAC held in Zurich, where Dr Buchi, then aged 78, presented a paper "Four-Cycle Internal Combustion Engines with the Buchi Telescopic Valve System", a copy of which I would like to get..  By scaling from known dimensions, this engine appears to be approx. ?105 X 118 bore & stroke, ie. about 1 litre/cylinder, and with a con-rod length of 220 mm, it has a rod to stroke ratio of 1.86:1. 

The exhaust valve can be seen to be concentric and internal to the hollow tulip shaped intake valve/ball valves, which I think uses the conventional helical valve springs.  The exhaust valve uses a pair of hairsprings and a special rocker to operate it.  Note the unusual shape of the exhaust (?) cam.

When the exhaust valve opens, the gas passes from the inside of the inlet valve, through windows in the bell and into the exhaust port.  There is a close fitting sliding gland separating the inlet and exhaust ports, created between the port walls and the inlet valve OD.  Leakage here could give you internal EGR, which is a sought-after commodity in recent diesel engines.

As far as I can tell, the exhaust valve is ?55 mm, and the inlet is ?62.5 mm.  One of the interesting features is that the inlet port obviously generates significant swirl, and the valve is on the centerline of the cylinder.  Also, the valves can open into the piston bowl, and so are not costrained in overlap at TDC as are conventional engines which limits their valve timing options.

This engine appears to be naturally aspirated, but apparently, at the time of this paper, Mercedes were evaluating the concept in car sized engines, complete with Acraener (?) supercharger.

I think this is an interesting design which should not be forgotten since you never know when new technology could have a need for such an arrangement.  Yes, the mechanism is likely heavy, which would limit it's top speed to less than conventional systems, but it does have some merits.  With a flat top piston, and with the chamber in the head, a desirable fixed geometry chamber is attained.......

Does anyone else have more information on this valve concept?  It is not referenced in Philip H Smith's "Valve Mechanisms for High Speed Engines", which covers most other types.  Comments and info appreciated.

I now have a better graphic of one of Dr. Buchi's telescopic valve engines; the one mentioned above as being approx 1 litre / cylinder.  The second graphic is my 3D CAD rendition of the two valves together but without the "windows" extruded through the inlet valve dome. At last, my web space is back up, so I am able to host these pictures.??Also due to Aorangi, I have been able to read the associated CIMAC paper which brings out some other points.



Essentially, it is a combustion concept for pressure-charged diesel engines in which high swirl is utilized to efficiently scavenge the cylinder and combustion chamber, and because both valves can be open during the gas exchange overlap, this same scavenge air is able to cool the valves and piston crown.??The cylinder head is relatively easy to manufacture, with easy port coring and a single large?diameter on-center bore for the valves.??Breathing areas are better than a 2-valve, and probably close to a 4-valve head.??The concentric telescopic valve arrangement was the elegant way to achieve the desired swirl and scavenging objective, not just an attempt at being clever or different.

As one might expect, the truck-size engine results quoted in the paper show the smoke limited bmep to be better than comparable conventional engines, due it is claimed, to the improved scavenging enabled by the greater valve overlap.??Little information is provided on the valvetrain challenges presented by the unorthodox arrangement.??Normally, one works to minimize the dynamic mass on the valve side of the rocker fulcrum, but in this case it is particularly high.??Both valves move off their seats independently, but following the gas exchange overlap, the exhaust valve with it's mass and spring force seats on the inlet valve and stays with it for the remainder of the event duration.??It does not seem like a mechanism suitable for very high speed engines.

All in all, it is an interesting combustion system concept, and it may have merit in the future because it is one of the few diesel chamber geometries which can accomodate variable valve timing (VVT).??When diesels start to require exhaust aftertreatment (2007 and later), VVT is one of the technologies which can be used to raise the normally cool exhaust temperature to a point where the catalyst will work.

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