this post was submitted on 29 Aug 2024
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Rotary Valves Make Normal Valves Look Silly - Why Aren't We Using Them? - YouTube (youtu.be)
submitted 3 months ago by BallShapedMan to c/cars
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I had no idea this type of valve was a thing. Interesting to learn a little about. Maybe something like this would make electrically controlled variable timing more viable and thus improve the efficiency of ICEs?

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[–] Delta_V 10 points 3 months ago (1 children)

Seems like an interesting option for naturally aspirated race cars. They let you hit high RPM without worrying about valve float and without using overly powerful and lossy springs.

The difficulty of keeping them sealed suggests they're less than optimal for high boost turbo applications, or high compression, fuel efficient commuter engines. Narrow tolerances may also increase manufacturing costs and decrease longevity, which is less of a problem for a race engine compared to something designed for mass production.

[–] BallShapedMan 3 points 3 months ago

That's a great point! And maybe part of the reason they're not widely used. Not long after these came around forced induction took off in motorsport and now it seems everything is a small engine with a turbo or two.

I wonder if optimized electronic timing could rival a small engine with a turbo for commuter cars?

[–] givesomefucks -2 points 3 months ago (2 children)

Known a few people with rotary engines

They are better, but I know they cost more upfront, and I'm fairly certain maintenance becomes pretty expensive.

But if you want a rotary engine, there's a couple options.

Mazada RX8 is the most common I think in America, just good luck finding a non dealer that will work on one.

[–] [email protected] 15 points 3 months ago (3 children)

That's not what the post is about, it's about rotary valves. I'd never heard of them before watching the video, but it sounds like they don't exist in any production cars.

[–] [email protected] 4 points 3 months ago* (last edited 3 months ago) (1 children)

I'd say a rotary engine exposes the difficulty/challenge of rotary valves, as it's essentially one big rotary valve.

Sealing has always been a bitch, especially as the seals wipe across the intake/exhaust openings. With a rotary valve on a piston engine, I wonder how the compression forces would impact valve sealing and rotation, where conventional valves are forced closed by compression.

I imagine the bigger issue would be airflow dynamics because of how such valves open.

I'm sure these have been considered, and not used for specific reasons.

[–] [email protected] 1 points 3 months ago (1 children)

I had the same thought, these seals aren't containing oil like a camshaft seal, they're actually dealing with compression forces. Maybe not directly, but still there's a pressure differential.

I didn't think of airflow dynamics, but yeah this thing is basically the lever valve thing in your garden hose adapter spinning at a few thousand rpm regulating combustion gasses. I could see it doing weird stuff when the valve is only partially open, especially when it starts to close.

[–] [email protected] 1 points 3 months ago

Exactly.

I hadn't really visualized it at speed either - I can only imagine the turbulence then.

[–] officermike 3 points 3 months ago* (last edited 3 months ago)

Rotary valves are more present in the musical instrument world, where they are used on French horns, some trombones, and some tubas.

On the topic of unconventional valves in automotive engines, I'd recommend taking a look at Koenigsegg's Freevalve technology.

https://carbuzz.com/what-happened-koenigsegg-camless-freevalve-technology/

[–] olympicyes 2 points 3 months ago (1 children)

Most people are familiar with rotary valves and the downsides if they think about it. It’s similar to the rotary “pick a setting” garden hose nozzles that tend to leak after a minimal amount of wear!

[–] [email protected] 2 points 3 months ago

That's funny, I just left another comment under this post comparing this to the lever valve on a garden hose splitter, just you know, really hot, fast, and constant

[–] [email protected] 3 points 3 months ago (1 children)

Had an RX8 for a tad. Rotary was fun, but reliability wasn't there. Apex seals are a routine thing. Miss that car, but don't miss the repairs.

These rotary valves are totally different, but I can imagine the additional distance and air pathway from the valve to combustion chamber would significantly decrease compression ratio. Turbo/supercharged would probably be mandatory to compensate. Perhaps this tech would probably find it's way on large displacement industrial engines first.

[–] [email protected] 1 points 3 months ago

Yep, this valve would have similar challenges to a rotary engine, since they're effectively one big rotary valving system.