FONZIE

What are the factors/equipment in the Renesis that limits its rpm to 9000-9500?

eccles

As revs increase, the loads on the stationary gears increase exponentially. I'm impressed that they even managed to lift the limit to nine grand in a production engine - the rotor lightening must have had a lot to do with it.

neit_jnf

The loads on the apex seals, bearings and eccentric shaft increase with rpm as well as heat. There's also the airflow limits. After 8500 rpm the power drops, maybe when porting gets figured out this can be changed.

wakeech

yup
it has to do with the limitations of both the stationary gear (the outer gear, which is actualy in the centre of the rotor and keeps it on its orbital path), and the eccentric shaft.

the rotors themselves spin at only 1/3 the speed of the e-shaft (which is equivalent to a crank shaft in a piston engine), but the e-shaft sees the full speed of the rotation.

because it's design doesn't lend itself easily to being spun fast (the e-lobes create pretty significant imbalances on the shaft, lightened racing style or not), not to mention it's completely without support through the middle of the block (there are only the two bearings in the end housing plates... the intermediate plate only has a hole...).

another problem to worry about is that classic problem of the wankel engine, sealing the apices effectively. the new seals go back to the old (more often reliable) 2 peice assembly, but have cut down in height (they seat higher up in the groove in the rotor, i believe) and made them of a different (harder, and lighter) material too. all this reduces the mass of the seals so they can more effecively seal at high rpm (moving in and out with the contours of the rotor housing).

...there are of course other normal things to deal with like how to get the engine to breathe well across a wider range of rpm, and ignition stuff at a higher compression, but that's the basic mechanical issues they've dealt with in this engine.

Doctorr

Don't forget the speed the alternator has to cope with....
I am surprised the a/c and alternator can handle the rotation, they have to be adequate at idle, yet not explode at 9k!
I assume that is one of the reasons the power steering is not belt driven, also.
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doc

wakeech

that's right ray... but isn't that why the air conditioning pump "turns off" or is disconnected somehow after 5k rpm or somethign??? who found that out...

...and darn neit jnf stealin' my thing while i was typing :p

neit_jnf

What? I don't get it...

FONZIE

I would think the eccentric shaft would be the easiest problem to solve. I just think of all the industrial engines, turbines, military applications (submarines prop shafts, helicopter rotor shafts), etc and the stresses on them. The tech to design a lighter, stronger eshaft must exist........

zoom44

edit: ooops

Reeko

I think the drive shaft is CF, not the Eshaft.

Psylence

Yeah, the eccentric shaft is plain old metal. Engine internals cannot be made out of carbon!

zoom44

oops typing and answering before thinking again. sorry if i caused any confusion.

rxphink

The biggest problem with rotaries is resonace at about 11,000 RPM.

I read somewhere in the past that at above 12,000 RPM's early rotaries were being shaken apart by resonance.

Even the old rotaries could rev past 9,000 without a problem. I had my FD rev limited at 9000 with mostly stock internals. I did use the competition bearings and oil injectors though.

With proper engine management a rotary can reach some pretty amazing RPM's.

Just think, there is no valve train to worry about.


Also I hope this post doesn't come across as being the only reason, the others mentioned above are valid as well. Most all are easily addressable, and so is the resonace issue.

Lighter rotating mass that is perfectly balanced and a few extra dowel pins should help.

DisneyDestroyer

I thought early testers said that they had run tests with the Renesis at 15k RPM, intimating that it would be a possible design for race engines...

rxphink

Yep they did, but this was after they figured out they needed to lighten the rotating mass and all that.

I'll have to find the book I read all this in.

wakeech

sure, stronger alloys and exotic means of manufacture exist (like lightened e-lobes from the factory, or in-shaft counterweights so the balance is uniform along its length), but the problem lies in the cost vs. performance ratio: in hte end, Mazda still has to make a profit on every part of the car, and costs have to be kept to a resonable minimum.

...and neit_jnf, i was talkin' about the sealing issue.

eccles

Somewhere around here I have a copy of "Rotary Engine" by Mr Rotary himself, Kenichi Yamamoto. Published by the SAE, it dates back to the early 80's, and is barely more than a collection of technical papers, but it contains some fascinating facts and figures. The one that always stuck in my mind was the aforementioned stationary gear loads - over about 12,000rpm, the graph went balistic!

Ripside

YES THEY CAN BE MADE OUT OF CARBON!!!! WOOOTTT HELLO NASA!!!!

Red Devil

I was wondering how this thread re-surfaced.

And look, even a new member that did a search. You must have seen the thread regarding searching that has been raging for a few days.

yiksing

I don't think its just a matter of the shaft or weight of the rotor but the engineers have to take into account of drivability convenience. I guess (just a guess), lightening the rotor too much would have the same effect of a lightened flywheel. It can spin faster but also slows down faster, the engine might have to idle at higher rpm otherwise it might stall.

arghx7

I read somewhere that the JDM Rx-8 redlines at 9500. Is this just a myth?

Red Devil

Yes, it doesn't redline at 9500, it is the same as USDM.

lefty63

I think the AC shuts off at 7500

DARKMAZ8

Whatever happened to Wakeech?????

His last post was last new years eve.......??????

zoom44

hes a busy busy man - too busy for the likes of us