Telescopic Valve Engines?
Telescopic Valve Engines?
<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. Ø105 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, 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 Ø55 mm, and the inlet is Ø62.5 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.