sure they are, sometimes. Although in some cases they’re referred to as “cam followers.” They’re especially useful in SOHC, 4 valve/cylinder heads.
OHC engines have used any manner of cam followers (rockers) while others use Direct-Acting Mechanical Bucket (DAMB) tappets.
I didn’t say that, Kevbo did.
Quite right. Here are some of the attempts to make rotary valves work:
http://www.douglas-self.com/MUSEUM/POWER/unusualICeng/RotaryValveIC/RotaryValveIC.htm
Roland Cross got nearest to success. A great engineer.
Oops. :o
Good catch. I was thinking & writing about DOHC, not SOHC. And realized my goof too late to fix.
Sorry about the mistaken attribution. :smack:
As a further nit I also should have mentioned that camshaft drive failure is guaranteed to leave at least one valve open only in multi-cylinder engines. In a 4-cycle single cylinder you’ll have all valves closed for 300-ish of the 720 degree operating cycle or 40ish% of the time.
As a practical matter the effect is the same following a cam drive failure since even in a single cylinder engine there will be a few revs of the crank and of the cam / valve system while both are spinning down at different rates. It’s pretty much a statistical certainty you’re going to have adverse overlap somewhere in there.
Pure hydraulic action is too slow for automotive engines but is used for some very large engines like in ships. (500 RPM max?) Or, the aerospace actuator pressures that might make this possible - 10,000-30,000 PSI - have their own set of cost and complication problems.
This is interesting: The new Fiat 500 Abarth (and Dodge Dart) has a hydraulically coupled lifter systemthat uses a solenoid valve to bleed off some of the valve lift or reduce the open/close timing from the mechanical camshaft.
As implied previously, electric solenoids don’t have the energy density to control high speed valves at typical valve openings - or they would burn out trying.
If you haven’t seen it, this is a decent explanation of the current state of non-traditional means of ICE valve actuation: Camless piston engine - Wikipedia
If it’s to be believed, electric solenoid actuation is still out of reach, but not by much. I don’t think it’s quite like fusion power: 10 years in the future and always will be.
Frank Aspin was the person who you are probably thinking of. A different thing to sleeve valves. Bristol were good at those.
The “heron” head is one in which the combustion chamber is in the piston.
the thing a lot of people don’t grasp is that it’s one thing to come up with a novel engine design which works in the lab. The other (harder) part is getting that design to the point where you can sell millions of them every year to people who expect them to run for 200,000 miles with no maintenance.
Good point. While new and better things are continually being sought, and do come along to a fair degree, there’s a reason why much of automotive technology remains the old tried and true.
Yep!
Another nice technology is pneumatic valve springs. Possibly fewer parts and springs that aren’t there can’t break. Works great in Formula 1 and was once looked at in NASCAR but was it too progressive - imagine that. :rolleyes: The problem is that these systems require a cannister of compressed gas to keep them working.
Slight highjack:
Does anyone know if the new turbo era F1 engines are still using the pneumatic valves? They don’t rev as high as v10’s or v8’s of old and I seem to remember reading the pneumatic system was only a benefit when revving above like 15k…
Another rotary system I remember was Coates. They built a 5 L Ford engine head that upped the rev limit to 14K and more than doubled the output. I’d love to see something like this in production.
Ok, so belts *originated *in European makers, but that only reemphasizes my point. The foreign car manufacturers (and car buyers) were all in shambles after WWII. They had to innovate cost-saving measures. The US makers went gangbusters from the 40s until the early 80s (when imports finally caught up). Until then the US auto industry had little to no use for cost-saving ideas because the market had no demand for them. Once they were in trouble cheaper designs like timing belts instead of gears or chains made financial sense (for the manufacturers anyway).
But again, they are always a disadvantage. They are the single weakest link in any engine design that uses them. Outside of high-performance muscle car engines I have never seen nor even heard of a timing chain failing.
Well here ya go, ignorance fought.
Lots more out there if you can be bothered to look.
Looks really cool, and expensive. Don’t rotary valves have problems with wear and seals?
Pushrod engines are derided as being low tech-but they seem to be quite reliable, and the shorter, stronger timing chain seems less prone to failure. As long as an engine runds under 5000 RPM, is a pushrod engine just as good?
at least as far as street engines go, the only people who deride OHV engines as “low tech” are Internet dummies who think horsepower per liter is a useful metric. Vs. an OHC setup, pushrod engines are more compact, can be lighter, and make equivalent power and economy.
check it. On the left is a 4.6 liter, DOHC 32 valve V8. On the right is a 5.0 liter OHV engine. Which one do you think would be easier to package under the hood of any given vehicle?
And since those V8’s are torquey, and make power down low, a car like the Corvette can get MPG that other performance cars can only dream of.
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I suspect that’s why they didn’t pursue it, which is a shame. Based on Coates site they have had success with power gen equipment.
That’s not why timing belts were invented.
Golly. I wonder why Pontiac had a timing belt engine in the mid 60’s?
I have. I’ve seen them stretch and jump teeth, and I’ve seen them break. I’ve also seen their sprockets shed teeth and their guides and tensioners wear out and fail. But I can see you love to hate timing belts. Don’t let mere facts get in the way.
I’m not so opinionated as either of you guys on this topic, but I would argue - and purely based on my exposure to diesel engines - that timing chains are more inherently reliable than timing belts. I’ve never seen a catastrophic timing chain failure. I acknowledge you have. However I have seen multiple timing belt failures, and heard through peers and so on, direct evidence of many more.
Maybe timing belts are cost effective and are making materials and design improvements, but in recent history I’d still say chains are more reliable than belts and I care not for minor noise or vibration improvements yielded by use of a belt.
anyway if they want to spend so much time, effort, R+D and special materials/design on timing belts to make them superior to chains (I see various manufacturers are promoting such efforts) the cost benefit may just disappear.
