Reciprocating piston engines have changed a lot over the last 100 years or so. Fuel injection, variable valve timing on overhead cams, and distributorless spark ignition are just a handful of technologies that have revolutionized the way engines work. Despite so much change, though, one thing has remained the same in all this time—pistons have stayed round.
Ferrari is eager to change that, however. As covered by AutoGuide, the Italian manufacturer has filed a new patent for a V12 engine with pistons of a very unique shape. You might call them oval, but more accurately, they’re a “stadium” shape—featuring rounded ends with straight sides.
The simple fact is that round pistons exist for a reason—they’re easy to manufacture and they do the job well. Regardless, Ferrari has its reasons for going off-book. In this case. It all comes down to packaging.
Ferrari loves V12s, but they have one major drawback—they’re quite long. The hope is that by switching to these straight-sided oval cylinders, it would become possible to pack them closer together without reducing total cylinder volume. This could help reduce the length of the engine, enabling a large-displacement V12 to fit in a smaller engine bay.
Funnily enough, one could argue that you can’t call them “cylinders” in an engine like this, since they don’t have a round cross-section. Geometrically speaking, they’d be… stadium prisms? Argue about the terminology in the comments.
The innovation doesn’t stop there, either. In tandem with the oval cylinders, Ferrari has designed the engine so that opposing pistons can share a single connecting rod. Normally, each cylinder would be a little offset (i.e. not directly across from) to the one in the opposing bank so that each piston’s connecting rod could mate with its own spot on the crankshaft journal (sharing a crank journal isn’t uncommon).
Ferrari was able to combine the connecting rods for two pistons by adding a pivot on one side. This allows pistons to mate with the crankshaft with a single bearing. This allows further reduction of the engine’s total length.
Overall, the idea isn’t entirely novel. Honda famously built an oval-piston engine in the late 1970s. It was employed in the company’s NR500 racing bikes, which competed in the World Motorcycle Grand Prix series.
Notably, Honda followed this route for different reasons. The oval pistons were selected to allow room for eight valves per cylinder, which Honda believed necessary for its four-stroke engine to produce more power than its two-stroke rivals. Primary challenges involved figuring out how to machine functional oval piston rings [Ed Note: This was my first thought: Oval piston rings?! -DT] and to build robust dual connecting rods for the unique engine. The engine notably also aligned the pistons with the long edge parallel with the crankshaft, so it didn’t feature the packaging benefits of the Ferrari design.
There are no major mentions of the valvetrain in Ferrari’s patent. Regardless, it could follow in Honda’s footsteps and leverage the oval piston shape to fit more valves into each cylinder.
It’s unclear at this stage whether Ferrari plans to put such an engine into production. If it wished to do so, it would have to solve the issues around sealing oval pistons in their bores, and master the construction of the complicated pivoting connecting rods. Even with due attention, it seems unlikely such a complex engine design would reach the same longevity as a conventional round-piston engine. Still, given the low mileage seen by so many Ferraris, it might not be a major concern.
Image credits: Ferrari, European Patent, Honda, Ux z CC BY-SA 3.0
I’m not buying the link in the con rods. It seems like a recipe for some serious piston slap to me. I obviously could be wrong.
Do we think, they’ve built a prototype already, or they’re just holding the IP? With the amount of time it takes to get a patent, at least in the US, this might be already be in stress testing.
FTFY: Why Ferrari Might Build This Weird V12 Engine With
OvalStadium Pistons😉If this engine comes to fruition, I highly recommend a CarShield protection plan. 😉
So many potential issues, but I like seeing different ideas. Another issue I don’t see mentioned yet is controlling the flame front. Emissions aren’t getting easier. A lot of compromises just for better packaging. Really, the best case for this would be in a low rpm setup, which I don’t seem them doing. If packaging is that much of a challenge (and I have little doubt it is), I think they’d be better off making a small displacement, small size traditional V12 and relying more on the EV side for power.
ya, flame front control will be a significant issue…double-plug… likely multiple spark plugs with non-simultaneous timing?
this is gonna get complicated.
Shape of the combustion chamber, valve size (shape?) and timing, too. And there’s so much established data and experience with round pistons to draw from that this won’t have. Seems like an odd move approaching the probable sunset of the ICE, but this could just very well be a post-brainstorming patent application with no real intent to pursue.
It lets you build a V12 with a pancake motor on the end for the same length as a traditional V12. Or a V12 the same length as a traditional V8
With hybrid stuff taking up a lot of room making your engine shorter has never been more relevant. You can fit a lot of batteries in the space you save from making a V12 effectively 2 pistons shorter.
I’m aware of the packaging, but it seems like a lot of compromises and serious risk for that benefit when they could downsize a traditional V12 with reams of existing knowledge and data and rely more on the E side for performance. It’s not like any of these things are hurting for power, though I guess it’s tough to potentially dial back peak power from previous models (not that 99.9% of the owners can or would use it).
That’s gonna have a really short stroke, they should just call this the Chode design instead.
What’s Italian for Chode?
Chodé
Radial engines have been using master and slave rods forever.
Wasn’t the Honda engine a result of wanting the advantages of a V8 but the rules limited the maximum number of cylinders to 4?
Came here to remark on this and the radial master/slave rods thing. Kevin Cameron has a great writeup on the NR500 here. (But then, everything he publishes is worth reading.)
Isn’t it just?
There was also a street version crazy expensive IIRC..
Kinda wondering why this hasn’t been explored more in the past. Round pistons in rectangular spaces leave a lot of metal in between – assuming you can maintain structural integrity, you’d think weight savings would be a think. Especially back when iron was still the go-to for engine blocks.
Saw a few comments on “piston slap” but I’m guessing that can be engineered away?
Also, as far as space efficiently: if it’s possible to make pistons and their rings with two straights and two 180 degree arcs, why not get as close to rectangular as possible, with four straights and four 90 degree arcs?
I wonder how the space efficiency would balance out the combustion inefficiency from having corners.
You mean like in the shape of the IMS “oval”, or literally like a rectangle?
Possibly like the IMS, or possibly sharper cornered. I’m wondering what the tradeoffs are.
Well the Wankel rotary engine has rectangular combustion chambers, at least in one plane, and that brings some problems. A lot of problems.
Most of the effort in combustion engine design has been to make the combustion chamber as spherical as possible, given that the primary goal is to make it change volume and get air in and out when necessary.
If I absolutely needed to combine 12 cylinders, short length, and large displacement, I’d consider a W12 way before this. Or an X12. An X12 would have some interesting packaging opportunities. And maybe sleeve valves while you are at it. Lubricants are so much better now.
As a mechanical engineer, I’d say that ease of manufacture and as David pointed out the difficulty of getting piston rings to seal.
It’s really easy to make high precision round things. Any machinist with a half decent lathe and some good gage blocks can turn the outside of a piston or bore a cylinder with great accuracy. Once you get into non-circular shapes though, you start needing some form of CNC or other tool guidance, tool wear compensation becomes much more complicated, and your cycle time (time to make one part) climbs rapidly.
Absolutely. When you trade X, Y and Z for R, theta and Z, and then throw out theta since you’re doing many full revolutions, it is much easier for lots of reasons. But, given the preexistence of production engines with two 180 deg semicircles and two straight sides, and rings to match, a piston with four 90 deg quarter circles and four straights might not be much more of a stretch. Twice as many tangential transitions, but the same elements involved.
I think they should commit to the bit, and use oval (slot, stadium, obround) valves.
Ovalves, if you will.
Ovalves, rings, ovalve-rings, ovaries?
“Primary challenges involved figuring out how to machine functional oval piston rings [Ed Note: This was my first thought: Oval piston rings?! -DT] “
My first thought was: with a single connecting rod, how do you prevent the piston from tilting (piston slap)?
Deep piston skirts?
I did the layout of a straight six version of this sort of “oval” piston engine. The longitudinal axis of the piston was the same as a typical bore for a four cylinder engine of the same capacity.
So as a general guide piston slap will be the same for this V12 as for a round piston V8 of the same swept volume.
Why wouldn’t it be more likely to piston slap? If it were the same volume per cylinder, the circus piston would have to be taller than the diameter of the equivalent round one.
For a given capacity, say 5.0 litres, the “oval” piston V12 will have more piston slap than a round piston V12, yes.
But about the same slap as a 5.0 V8 because those pistons are bigger.
All my CAD was on 2.0 I4 vs 2.0 I6, but it scales. The longest axis of the “oval” piston can easily be the same as the bore of a normal existing engine, albeit one with fewer pistons.
So the plural is “stadia”? Even better as stadia is a unit of distance measure!
Honda NR750 looks on disapprovingly.
As I understood it at the time, the point of the oval piston Honda was that rules limited the GP bikes to four cylinders. Someone at Honda thought a V8 configuration would yield certain advantages, so they built a four-cylinder “V8” with four commonly firing “pairs” of pistons.
Yep. The old bravado Soichiro Honda had based on his company’s technical prowess. “Fine. We’ll make (squ)oval pistons with two con rods. What else?”
I’m assuming the patents are expired?
Got me. It’s been decades, so likely?
“Decades” impossible, I can’t be that old..
They’ll only let people who have purchased 5 or 6 previous Ferraris buy one. And these cars will be stored in hermetically sealed bubbles. Durability is zero concern.
Just thinking they make these hybrid now so when you need to move it onto the pedestal in your shrine, you don’t have to worry about the exhaust fumes.
Seriously, at this point they could build one, test it at the ‘Ring, then sell the rest with salvage yard Iron Dukes, who would know?
My CAD program describes that shape as a “slot”. it does not differentiate between a slot-shaped hole or a slot-shaped solid. I suppose the bore in this case becomes the “piston slot”, which is kind of gross if you think about it too much.
Okay, no one – no one on earth – calls it “stadium shape”. That is not a thing.
It’s called “obround”.
Look it up.
To be fair, I’ve never heard anyone on Earth call it an obround, either. Until now.
Perhaps, but that’s actually what that shape is called. It’s not made up.
I believe you. I even looked it up as suggested!
I’ve seen it called a “racetrack” shape. If you buy a glass tabletop, that’s what they call it.
Furniture retailers also call a 1-person bed a twin.
Because they were traditionally sold in pairs.
Of course, people used to be a lot smaller, too.
That’s true. You can fit a lot of toddlers in a twin bed. It’s when they get bigger you start having problems.
Depends on how you cut them up.
Man, that got dark fast!
But you heard it all the time when you lived on Mars, right? RIGHT?
OK
A capsule (from Latin capsula, “small box or chest”), or stadium of revolution, is a basic three-dimensional geometric shape consisting of a cylinder with hemispherical ends. Another name for this shape is spherocylinder.
Ha! I just burned up a million kW making Google do that.
Technically, yes, obround. (technically correct, the best kind of correct)
No one on earth? Not according to Google trends:
(except Wisconsin apparently)
https://trends.google.com/trends/explore?date=all&geo=US&q=obround,stadium%20shape&hl=en
2018 was a very good year for the stadium shape.
As the “straight” edges are actually slight convex curves (in order to make the rings seal a la Honda) this shape is technically not an obround.
Christ knows what it is, I’ve been trying to find the right name for months.
Wow, TIL.
Either way, once the Italians are involved, the whole thing is going to end up a circus.
Dammit, glad I looked to see if someone else made a Circus Maximus/circus comment first!
It’s funy that in french it’s called “oblong” !
It’s ok, even the blue oval isn’t an oval LOL
You’re confusing oblong with oval.
“Stadium Pistons”.
If Ferrarri’s willing to slum it a little, it could be worth if for the marketing dollars alone:
“The Ferrari Stadium Pistons Stadium, home of the Detroit Pistons”
“The Piston Cup, hosted at Ferrari’s Stadium Piston Raceway, sponsored by Ferrari, the only manufacturer of NASCAR-track-shaped pistons”
If peak 80’s/90’s Honda couldn’t make this concept work, I doubt Ferrari in 2025 can make it work. Honda’s engineering was unmatched, *and* they didn’t have any emissions regulations / aftertreatment concerns to speak of on those motorcycles, while today’s cars need to have effectively undetectable levels of emissions to be sold. This thing will pass oil, which will poison the 3 way cats and plug the particulate filters (effectively mandatory in EU due to particle number regulation, even on gasoline cars).
There has to be at least a dozen other options for increasing (volumetric) power density of an engine before you get to ‘what about making the pistons bigger in one direction than the other?’ on the brainstorming list.
Pushrods, again and always, FTW
I think a Ferrari engineer would rather commit hara-kiri than propose using pushrods to get the overhead space to increase the stroke on one of their engines! I love the thought of some old-boy American sauntering in and drawling “why don’t you move those Got-Damned cams into the block and save you some space?” to a room of shocked and dismayed Italians…
Their loss, lol
Yep! Because this has been demonstrated to be the correct solution by Mercedes in 1994. (2 valves per cylinder, even!)
That was only the “correct solution” within the context of the rules. At the time a pushrod engine was allowed 10 more psi of boost.
Yes, and more displacement – 3.4 vs 2.65 liters. BUT, it was both lighter and externally smaller than the DOHC engine it replaced, and made more power, which is (presumably) what this oval piston monstrosity is attempting to achieve – more displacement in the same packaging envelope.
Ferrari wouldn’t have to drop down to 2 valves/cylinder due to racing rules like Penske/Illmor/Mercedes did, which would at least partially offset the boost difference.
(It’s all silliness anyway, just an opportunity to trot out one of my favorite racing rulebook exploits ever).
It was extremely clever, that’s for sure.
Ladies and gentlemen, the Ford GT40 program in a nutshell:
“This thing will pass oil, which will poison the 3 way cats and plug the particulate filters (effectively mandatory in EU due to particle number regulation, even on gasoline cars).”
That’s okay… Ferrari will will just make replacing the cats as part of the standard 1 year/12,000 mile routine service.
Silly me, of course! This is the same company that had ‘SLOW DOWN’ warning lights on their cars in the early 80’s for when the cats overheated.
This does feel a little like someone is trying to bring back the ‘BB’ branding. And a shorter crankcase leaves room for the PHEV that they need to have to avoid usage restrictions their customers do not want.
(Hard to sell a Ferrari you can’t even drive into Milan!)
I would think pistons of this shape, oriented this way, would be highly prone to piston slap.
It’s the same degree of piston slap as a traditional V8 of the same capacity.
You could get 2 really big valves above those pistons.
Now I wonder what would be better… A Crap load of smaller valves you can tune individually? or 2 gimunginourmous ones?
The small valves could be opened and closed faster, I would think. The gigantic ones would be harder to keep under control.
Or rotary valves, and get rid of the cam entirely.
Has anyone solved the sealing issues with those? It would be awesome if someone could get those to work. They could possibly even be controlled with stepper motors instead of run off the crank.
My first question is how are they going to lubricate the rod pivot’s bearings? Oil flows through the crankshaft as normal, through the crankshaft bearings where a little gets bled off into the rod, through the pivot bearing, and finally get to the pivot “shaft”?
most car wrist pins are splash lubricated from the crankcase. Many modern turbocharged engines have a piston cooling jet shooting oil at the underside of each piston to keep it cool, which has the added benefit of delivering a *lot* of oil to the wrist pin, more than the general splashing would manage. Worst case you can rifle drill the rod to pressure lubricate the wrist pin via the crank as you describe, but that’s an unusual step – I know semi truck engines that don’t do that, and they’re much more heavily loaded joints *and* have million-mile durability targets.
If by ‘pivot bearing’ you mean the one down near the crank, not the one up at the piston, that one is even easier to lubricate. All WW2 radial engines used such a ‘master/slave’ rod arrangement; one cylinder would have its piston on the master rod, all the other cylinders would be hung off a slave rod – a 1-row radial only has one rod journal on the crank so that the engine is flat, and not a spiral of cylinders.
Of all the nonsense in this patent application, that particular joint would be the least of my worries! 🙂
Radial engines ran at much lower rpm and weren’t expected to last long in or between service. I agree, though, that pivot is not the top challenge.
Low RPM, but high load factor. And even fairly early engines like the P&W R1830’s used in DC3’s had ~1500 hour TBO’s. Not too shabby for the 30’s!
I think it’s a case of “oval” vs “elliptical,” myself.
I think “Stadium” pistons is fitting. I wonder how the extra pivot on the pistons will affect reliability. (Like anyone rich enough for a V12 Ferrari will care…)