7 replies to this topic

[Gerald Ryan]

McGuire

You posted some photographs of the Ford Calliope Can-Am engine a while back. As you know, the Calliope engine had two camshafts in the cylinder block with one cam located directly above the other. One cam was used to operate the inlet valves and one was used to operate the exhaust valves. The major benefit appears to be that the pushrods could be placed in-line or at least closer together so that there was more room for unobstructed inlet ports. There were three valves per cylinder, two inlets and one exhaust.

More recently the idea of two-cam-in-block engine achitecture has had attention from General Motors. An experimental engine, the XV8, was developed which appears to have repeated some of the features of the Ford Calliope. Since then the idea has been actively developed for the LS small block. I have read that GM will be able to deploy the system in a production engine soon.

General Motors patented the technology. Here is the patent number: US 6505592. It is for a two cam-in-block, three valves per cylinder, pushrod engine. I am surprised they were able to patent this layout, as it is not novel and inventive. The Ford Calliope is prior art which invalidates GM claims. Nevertheless I'd be very interested to see the Calloipe/XV8 architecture in production, even for a two valve engine.

Comments?

Regards

Gerald

[Engineguy]

If you try to find some kind of complete rationale and full justification without any contradiction when examining patents approved or denied, you will probably be driven insane.

Patents are notoriously difficult to read and understand... and I'm not going to devote that much time to studying a pushrod engine patent, but here's my quick take:

My understanding is that the 1996 GM patent this piggybacks on did not patent the two-cam-vertically-stacked-in-block layout... it patented the combination of that layout with timing phasers(s). The new patent ties up loose ends by more specifically nailing down every combination of valve tilt direction, lash take-up location and method, etc. that they could think of.

The availabilty of the single or dual phaser actuated cam-in-cam (new Viper) from a third party supplier takes some wind out of the GM two-cam-in-block scheme... except for the potential ability to place the exhaust pushrod directly above the intake pushrod/rocker, more likely to be done in a 60° vee engine.
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[McGuire]

What Engineguy said.

I would only add that an invention need not be unique or original to patentable, simply inventive -- which is an interesting word in patent law. Also, getting a patent and protecting it are two different things.

Often the OEs will obtain a series of patents to stake out general areas, which is what this looks like. It wouldn't be worthwhile for an individual since patents are pretty expensive, but they have people on staff or retainer. The small block Chevy V8 was "patented."

[McGuire]

Originally posted by Engineguy
The availabilty of the single or dual phaser actuated cam-in-cam (new Viper) from a third party supplier takes some wind out of the GM two-cam-in-block scheme... except for the potential ability to place the exhaust pushrod directly above the intake pushrod/rocker, more likely to be done in a 60° vee engine.
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The Mahle/Ricardo/Chrysler setup (there is someone else involved there too but I forgot who all) is pretty clever, but kinda limited in its usefulness as it is expensive and not terribly stable or robust. It works on the Viper because it had a big emissions problem. They are using it mainly to splay the lobe centerlines at idle.

[Engineguy]

Originally posted by McGuire
The Mahle/Ricardo/Chrysler setup (there is someone else involved there too but I forgot who all)

Mechadyne... self-proclaimed "The Variable Valve Actuation Specialists"

Lots of VVT explanations, etc.

http://www.mechadyne-int.com/

[Gerald Ryan]

Engineguy

Ah. I see what you mean.

BTW why do you reckon the application is more likely to be seen in a 60-degree V engine?

Regards

Gerald

[Engineguy]

Originally posted by Gerald Ryan
BTW why do you reckon the application is more likely to be seen in a 60-degree V engine?

With the head tilted 15° further inboard the exhaust pushrod (from the upper cam) can entirely clear all the intake valvetrain bits. I don't think you could reasonably put the exhaust cam high enough to do that with a 90° vee. With two intake valves (/springs/rockers), space for pushrods is precious.

[Gerald Ryan]

Engineguy

That makes sense. Thanks for explaining it for me.

Regards

Gerald