How Did Cam Shafts Survive Computer Controls?

Do you propose to synchronize some sort of super-heavy-duty-high-current-solenoids with an encoder? No thank you!

Don Kansas City

Dear BretCahill:

If the timing chain doesn't jump a tooth, you don't have valves hitting the piston. Sometimes the club and bearskin are cheaper.

David A. Smith

Yup, why change a winning trick, (often driven by "market forces", alias "the customer is always right") there's a lot of BS designs in most industries pretending to be better 'caus they're "bleeding edge" Nuf buzwords, I'm starting to gag. Good example: check out the Geneva intermittent drive devices on high speed packaging machinery. A lot of manufacturers have tried servo motors, AC drives etc. but they eventually manage to put something where it shouldn't be, with expensive results.

Mark.

Honda's VTEC system achieves some measure of variable valve timing while preserving the benefits of mechanical valve train drive and synchronisation.

tim

On the down side the head would probably have to come off after the cops disabled the computer with the microwave.

It would be hard to auction for much money.

Bret Cahill

Don't formula 1 cars use electric solenoids for the valves, instead of cams? I know they don't have the budget constraints that production carmakers have; but lots of stuff has made if from the race track to the street, after a while. My wife's Camry has a variable valve timing system; but that's just a pully thingy that advances the camshaft w.r.t. the crank (kinda like the age-old mechanical advance device on a distributor).

KG

While we're on the subject...am I the only person who sees the new Chrysler "hemi" that they're currently shoving down our throats as a thirty-year jump

*back* in technology? It seems to me that it's designed to appeal to technically-challenged middle-aged men who remember the old "hemi" of their youth and want to be able to say, "Yeah, my truck's got a hemi!"

Don Kansas City

What's the difference between the old one and the new one? If you added injection and a good engine management system to an old hemi it'd be a huge improvement and possibly not too far from current offerings, if a bit overweight.

Mark.

"Don A. Gilmore" wrote in news: snipped-for-privacy@uni-berlin.de:

Actually, the hemispherical combustion chamber is said to be one of the most efficient designs. Tis why it made so much power. The challenge is in the valve arraingment-more precisely, valve actuation. I do not believe the new engine is a 100% 'true' hemi, but close enough for the marketing dept to take over.

There's been a lot of debate over the decades. And since I grew up in Detroit, I got to hear and see a lot of it. A true hemispherical combustion chamber is an efficient way to distribute and utilize the force of combustion; but other shapes (like the "swirl-top" piston design that some automakers have used and advertized) can be better at mixing air and fuel. That can lead to BETTER combustion, and a net increase in power, even if the energy isn't perfectly distributed and used when combustion occurs.

The advent of computer controlled injection has changed things a lot, of course. Better mixture is possible with better injectors, and with precise control of air-fuel ratios. So it may be that the advantages of non-hemi combustion chambers, designed specifically to improve the mixing of air and fuel - have diminished. It might actually be a good idea to go back to the hemi now, with new ways to help take advanatage of it.

Of course, ignition systems are a lot more sophisticated now than they were when the hemi first became popular. And fuel-air ratios, and even fuels themselves (remember leaded gas, or 104 octane?) have changed a lot. It may be that there are other shapes that are more efficient than the hemi, now that other variables are more thoroughly controlled.

Having heard and seen the debates so many times over the years, I'm inclined to believe that the differences are often a matter of personal preference, and can be mostly (or completely?) mitigated by other aspects of an engine's design. Cleanliness, fuel efficiency, weight considerations, engine reliability, longevity, and more, have a lot to do with how a good engine is defined. Max power per cubic inch isn't the main issue, like it once was.

And, as someone else has pointed out, automakers are at least as good at marketing as they are at making cars. You have to factor that into almost anything you see or hear.

KG

Sixteen, 24 or 32 performance solenoids might cost more than one or 2 cam shafts.

Complexity might be a problem at $2/gallon.

At 4 or 6 dollars a gallon other options become realistic.

Bret Cahill

Kirk Gord>

Dear BretCahill:

Like external combustion engines that don't require camshafts? Now that the Prius has the electric motor to take over during the boiler warmup period...

David A. Smith

Kirk Gordon wrote in news: snipped-for-privacy@gordon-eng2.com:

The primary influences in piston design nowadays are: a) NVH (noise, vibration, harshness) and b) Emissions. These are not listed in order of importance, as both are on equal footing. Although they always want more power, achieving more power is more heavily a burden in the design of other aspects of the engine. The piston must be able to take the power generated, while maintaining the strict emissions and NVH levels, along with cycle life. NVH used to be most important within the first 40-60k miles. Now this is stretched out to over 100k. With that change, comes many design issues. The crown of the piston can be about any shape the manufacturer desires, within manufacturing and cost constraints. NVH drives such design criteria as: piston shape, ovality, pinbore offset, material thicknesses, etc. Emissions drives such things as ring location (relative to the crown), ring size, groove flatness, ring gap, etc. There are side benefits to the emissions design criteria in that many of the same elements also lead to more power produced, or more efficient use of the power that is produced, though better cylinder sealing, reduced friction, etc.

I believe most F1 cars use pneumatic valve actuation. This permits complete control over valve timing for the entire engine operating range. But more importantly it allowed engine speeds to be increase from around 13,000 rpm up to about 18,000 rpm.

This is because they use pneumatic force not just to open the valve but also to close it. This avoids the need for crazy-stiff valve springs to prevent valve float at the high rpm these engines run. It also reduced stresses and wear associated with using a cam actuated configuration in a high rpm application.

I've read that there was some experimentation with using eletrical solenoids rather than pneumatic valves but from what I've read they did not perform as well.

The reason such technology is not used in productions cars is cost.

Dave Parker

snipped-for-privacy@excite.com (Dave Parker) wrote in news: snipped-for-privacy@posting.google.com:

I believe they use nitrogen. However, Siemens recently developed an electric actuator specifically for this application.

You beat me to it. Good call.

Bret- Look at current camshaft system...cheap and extremely reliable. Compared to other problems cars have, camshafts problems are probably really low on the "occurance" list. 1 burned out solenoid and you're in the shop driving a loaner.

Next, figure out the cost of incorporating solenoids or other electro-mechanical device as well as the controllers and electrical infrastructure into the engine.

Just because it's newer doesn't always make it better...besides, what's terribly wrong with the current camshaft design? That's not to say that one day electro-mechanical devices might one day replace the camshaft, once they get more reliable and ATLEAST as cheap.

Dave

Pneumatic or solenoid actuators might not have the volume discounts of electronic consumer items but the number of copies should have _some_ impact on production costs.

On the other hand the big advantage of hybrid engines is they only run at one speed, so maybe the extra sophistication required for variable rpm -- including camless valves -- really is prohibitive.

Bret Cahill

snipped-for-privacy@excite.com (Dave Parker) >

Newsflash: countries in the real world market already pays US$3/4 gallon, and still use camshafts in their engines. A controled variable stroke/timed actuator for valves is a good idea but take it a step further: why use poppet valves at all?

Mark.

Invent and Patent a viable alternative and dedicate the Patent to the public.