i seem to remember that these "wankel"(hope thats spelt right!)
engines first came out in the early sixties, but didn't seem to catch-on, for some reason. now, i've just seen a t.v ad, for some sporty-looking car with "the revolutionry new rotary engine".
questions:
why did they not catch-on?
do they produce more power than the equivalent piston engine?
with less individual moving parts, are they more reliable?
billy.
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Hi Billy,
Its the new Mazda RX-8 that has this engine.
I know very little of how it works, but I stole the following off a website i googled to:
"a wankel rotary engine it quite different in its set up. Instead of pistons going up and down, there are usually 2 or 3 triangular rotars ("pistons") going around and around. A good way to tell if a car has a wankel rotary engine is how the displacement is displayed. 654x2cc is a pretty good indication (654 cubic centimeters x 2 rotars) There is still the usual compression and ignition and the exhaust phases.
Wankel rotary engines have their weaknesses and strengths over tradition engines. There are less moving parts so they are more reliable, which makes them more expensive, however fuel economy is a little poorer with the wankel rotary. Wankel rotary engine is a fun phrase to say.
So that is the RX-8 and how a wankel rotary engine works in a very thin nutshell. I hope you enjoyed the past few paragraphs"
So there you go! :-)
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Midst the rust in the old brain box is a thought that the problem in the 60"s was it not that the ceramic tips of the rotary pistons kept burning out and losing compression?
DVD
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more or less correct DVD, situation made worse when the engine over revved, extremely easy with the smoothness of the engine.
We won't mention the Norton bikes with twin rotor engine which used to cut the spark to one rotor out at low power.
Trickling along in traffic on one rotor and then suddenly......shhhhiiiii.........!!!!
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DVD/FiF
Yes, the key snag with the rotor tip seals was and is that their load on the walls inceases with engine speed due to centrifugal effects, unlike a conventional piston engine. Makes material choice and lubrication very tricky, and a problem not easily solved.
Regards
John S
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thanks hawsey,
i was hoping i'd spelt it right! not much allowance for a typo! so i'll refer to them as "rotary" from now on.
haven't had time to google myself, but just been informed (by "old mate") that these engines were in fact used before the sixties, in some of the german ww2 planes!!
billy.
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It was invented by Felix Wankel (schoolboy humour misses the German pronunciation which makes it "Vankel") and to answer your questions in order:
1. They didn't catch on because of reliability issues during early production and fuel economy in the early 70s (and therefore modern emmisions)
2. They do produce more power than a piston engine but then it depends on how you calculate the swept volume! If you calculate all three chambers for each rotor instead of just one chamber then the power is similar.
3. An Engineer will tell you that fewer parts is always better, but there are several issues with spark plug fouling, the rotor seals (equivalent of of piston rings) and fueling which makes for a lot of development work. As Mazda are the only car manufacturer who uses the technology there isn't the same pool of knowledge and so it takes longer.
As an aside, NSU were the first to use the Wankel engine in a production car, the NSU Spyder where the car's low weight masked the engine's lack of torque at low revs. The sporty nature of the car also meant that the engines were usually thrashed which made them drive well. When a larger version was used in the NSU Ro80 they used a semi-automatic transmission to hide the lack of torque but the owners often lugged the engine at low revs, fouling the spark plugs. Some owners - amazed with the engine's smoothness compared to other 1967 cars reved them way past the red line with obvious consequences.
In the 1960s lots of manufacturers took out licences from NSU to develop this exciting technology in their own cars, but the Ro80 had development problems early on, not helped by dealers misunderstanding the tricks to fix them. Replacement engines were offered when not always needed and this, combined with the relatively poor fuel economy in the early 70s killed the engine off. As a result, NSU was sold to VW who used them for the NSU K70, turned into the VW K70 - their first watercooled car. Incidentally, the Ro80 was for Rotary engined, the K70 was Koblenz (German for piston) engined.
All a bit of a sad end, when you consider that in 1967 you could still buy an Austin Cambridge compared to the revolutionary Ro80.
Gareth
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thanks gareth,that comprehensively answers my questions nicely,
however, i hope mazda have got it right this time,and the engine takes off(no pun intended to the aeroplane ref in my other post) be rather nice i think, to have another choice, especially if it's as smooth as you suggest.
billy.
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Saw one of these for the first time in Leeds last week. The engine sounded peculiar to say the least. From such a sleek machine I expected a nice throaty roar, unfortunately it didn't have one!
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Mazda have sold many thousands of the Rotary engined cars around the world,just not many in the UK.
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Mazda's forst rotary engine was the in the 1967 Cosmos
www.rx7-gallery.co.uk/binhist/p1history60/cosmo_67...g for those who don't know what I'm prattling on about!
Gareth
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Oops, that should be Cosmo!
Gareth
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The RX7 was/is? quite expensive. They burn a bit of oil but otherwise seem fairly reliable. I think there is a twin turbo version. Materials and manufacturing have improved no end since they were used in the 60's and 70's. One advantage to the engine is its small size and I understand that they will run on hydrogen fuel with only minor plumbing changes when this is available more widely and cheaply.
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Excellent commentary, Gareth.
The Wankel engines in the RO80 rarely lasted more than 20,000 miles and I now wonder if some of this was down to dealership ignorance, i.e. "Replacement engines were offered when not always needed".
Many RO80s had their Wankel engines replaced with Ford V4 engines, a terrible shame. Mazda have done very well to overcome (most of) the problems and to have kept the Wankel in production for such a long time. I'm not generally a Mazda fan but would enjoy having an RX-8 as a second car.
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Mazda won the 1991 Le Mans 24 hours with a Wankel engine powered car (the 787b). Johhny Herbert was one of the drivers - more details at
www.ebroadcast.com.au/ecars/Mazda/Cars/Le-Mans.html
If you want to see how an Wankel engine works there's a nice animated graphic and explanation at www.keveney.com/Wankel.html (NB the link is case sensitive)
They've also got a 'proper' rotary engine at www.keveney.com/gnome.html
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"Incidentally, the Ro80 was for Rotary engined, the K70 was Koblenz (German for piston) engined."
lol!
Koblenz is a town on the Rhine, in western Germany. The German word for pistons is 'Kolben'.
The Ro80 suffered from bad problems with tip seal wear. Many engines were replaced under warranty and that is what eventually bankrupted the company. Their assests were taken by Audi and the Ro80 ended up as the forerunner of the Audi 100.
Mazda improved upon the rotary engine and the 12A and 12B series of the early 1970's (in the RX2, Rx3 and RX4) were pretty good engines. I actually rebuilt some of these at the time. The tip seals rarely gave problems (Mazda made them from sintered iron), but the side seals, corner seals and rotor oil seals did wear quite badly. An oil feed system continuously pumps a small amount of sump oil into the combustion chanber to lubricate the seals. Although they say there are not many moving parts, when you add up all the seals there are actually quite a lot. Each rotor has 25 seperate sprung metal seals - on a twin rotor engine that's 50 seals to wear!
Rotory engines are poor on emissions. The combustion chanber is very long and shallow, meaning that the flame is swiftly quenched and thermal efficieny is relative poor (the rotor is internally cooled by oil and all rotary engines feature a large oil cooler). The large crevice gaps (the gaps around the seals that harbour unburnt fuel and hence give rise to high HC emissions) are also a major problem.
I rebuilt several 12A-series rotary engines in the mid-1970's and came to the conclusion that although an elegant engine (with very good power-to-weight ratio) the RE is not really suitable for 'general purpose' motoring - its good for application where a high power-to-rate ratio is necessary.
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Always fascinated by the Wankel - saw a cut-away model once, intrigueing and hypnotic to watch it rotating.
Didn't Suzuki have a go at a rotary engined bike once? or am I mistaken? Could have been late seventies ... I seem to remember reliability problems ...
oh, the mists of time - liked the Norton idea, shame I never rode one.
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Oops, Aprilia spots my error in technical / geographical German. Mazda must have done lots of development to get acceptable emissions recently, but as stated the RX-8 looks like an interesting car.
The Ro80s fitted with Ford V4s in the 70s must have been a terrible shame, replacing one of the smoothest engines with one of the roughest!
Gareth
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Between them, Gareth and Aprilia seem to have written the book on the Wankel and the problems with this engine in the Ro80. A good read!
I'll just add that the restrictions on combustion chamber shaping, as pointed out by Aprilia, mean that the Wankel concept can *never* be applied to diesel engines.
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My first car in 1977 was a 2 year old Mazda RX3 Coupe.Cost £400,seemed like the space age in comparison to mates Marina coupes and MK3 Cortina GTs.Ran on 2 star,120+MPH and very squeally Bridgestones,5 speed g/box,frameless doors,totally black 'sports' interior,Japanese Teak steering wheel(plastic)and well under 20MPG.Wish i could buy one now.
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