Telescopic Valve Engines? 4

[PJGD]

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=&quot;Buchi Telescopic Valve GA/2.gif&quot; WIDTH=250 HEIGHT=446>

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

<IMG SRC=&quot;Buchi Telescopic Valve only.gif&quot; 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 &quot;Four-Cycle Internal Combustion Engines with the Buchi Telescopic Valve System&quot;, 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 &quot;Valve Mechanisms for High Speed Engines&quot;, which covers most other types. Comments and info appreciated.

PJGD

 

[PJGD]

OK, so the pictures did not come out! And I thought I knew how to import gif's into HTML...

Can someone provide some direction? Thanks

PJGD

 

[GregLocock]

You've put the name of the file in, not its web address. I'd like to see the photos. Cheers

Greg Locock

 

[aorangi]

PJGD,

I don't have the answer to your last question. I couldn't get the pictures neither and a search on Google for &quot;Buchi telescopic valve&quot; produced no result.

But... if my memory is right, I think I had the proceedings of the 1957 CIMAC Congress in my hand about 20 years ago.
It must still be there at the library of the engineering school of my hometown and I'll be able to check that on Monday.

I'll let you know and if I find it I can scan some pages for you.

Cheers
Aorangi

 

[ProgressiveRacing]

Are you referring to the valves mentioned at this website:

http://www.geocities.com/texmexcoyote/evolution.html

With such a reduction of effective valve area, I can't see much for increases in performance. Then again, I like the simpler things in life however inefficient they may be.

-Allen

 

[PJGD]

No, the Buchi telescopic valve arrangement is quite different, although there may be some slight similarities; hard to tell from the &quot;texmex&quot; web site. Certainly, the Buchi approach is based on more conventional engineering, with less snake oil.

Regret I am still unable to post the pictures of the Buchi system just yet. The web space at my hosting ISP is down with problems at present. ETA for repair: perhaps 19 March.

PJGD

 

[aorangi]

PJGD, I got the 1957 CIMAC Congress proceedings. Before to scan pages 89-112 I want to make sure I can send it to you. My e-mail adress is dovatf@bluewin.ch

Cheers
Aorangi

 

[PJGD]

With many thanks to Aorangi, 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 &quot;windows&quot; extruded through the inlet valve dome. At last, my web space is back up, so I am able to host these pictures.ÊÊAlso 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.ÊÊThe cylinder head is relatively easy to manufacture, with easy port coring and a single largeÊdiameter on-center bore for the valves.ÊÊBreathing areas are better than a 2-valve, and probably close to a 4-valve head.ÊÊThe 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.ÊÊLittle information is provided on the valvetrain challenges presented by the unorthodox arrangement.ÊÊNormally, one works to minimize the dynamic mass on the valve side of the rocker fulcrum, but in this case it is particularly high.ÊÊBoth 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.ÊÊIt 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).ÊÊWhen 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.

PJGD

 

[chasart]

I have done extensive patent searches on this valve design.
They go back as far as 1919 and as recent as 1998. Have a look at the tread &quot;Intake and Exhaust flow relation&quot;. The ideas are still alive and well.

 

[chasart]

I am looking for some information on deciding what relation I need between inlet and exhaust for a coaxial valve design. I am building a cylinder head to fit on a small motor cycle engine to demonstrate the full use of cylinder head area to valve use. The inlet valve is placed coaxial to the bore and the exhaust is place around the inlet in the shape of a trumpet valve. The area around the exhaust is enough to allow gasses out and to have a small spark plug. The intension of the design is to allow for maximum flow rate and high RPM since the valves will be operated solid and with no valve springs. The great advantage to this design is that the parts count is that of a two valve cylinger with the performance of a four valve cylinder. Will the intended high RPM influence the relation of valve ratio one another? A little advice will be most helpful.

 

[PJGD]

chasart:
My initial guess is that the area ratio rules expounded above would hold for concentric valves too. The areas might be biased a little one way or the other depending on how good the entry and exit flow geometry is, but essentially the rationale will be the same.

The problem I think will be with the weight of the valves for high speed work. By &quot;solid&quot; valvegear, I assume you are planning a desmodromic arrangement? Perhaps others can comment on whether with desmo valvetrains, higher valve accelerations can be achieved than with conventional systems, since the closing cam will restrain the valve. That is the claimed advantage anyway, but I don't know if it is exploited in practice, but you will probably need a robust valvetrain to get even typical valve accelerations with your proposed arrangement. When the exhaust valve opens, even if it is a relatively small lift, it has to lift the combined mass of both valves, if your layout is similar to Buchi. If the exhaust valve is totally separate from the inlet valve and has it's own seat in the head, then again it sounds like a heavy valve because of the large diameter.

Are you ready to share more details of your concept?

PJGD

 

[tbuelna]

chasart:

here's a US patent that may be of interest to you (no. 6,546,902):

http://patft.uspto.gov/netacgi/nph-...,546,902.WKU.&OS=PN/6,546,902&RS=PN/6,546,902

regards,
Terry