Piston rings developments.

[saviour stivala]

Piston rings developments.
Piston rings half more than halved in thickness since the 1980’s.
The initial piston ring configuration as used in formula one was identical to that used in mass production vehicles up to 1989 NA 3.5-litre engine formula, an engine formula where V12, FALT-12, V10, V8 engines reaching an RPM of 13000-14000 was raced. With the difference of using only two rings instead of three. The rings were formed from top ring with a rectangular cross section and an oil ring with a spacer expander inserted between rails.
By 1995 NA 3.0-litre V10 engine formula, such engines that by the year 2000 were reaching the 18000RPM mark, of which was made possible by the development and use of an expanded piston rings of 0.9mm width and 1.4mm tick with a rear expander (behind the ring). In this twin-ring configuration the ring were both the same and identical. The use of these rings increased engine speed by more than 1000RPM before ring flutter sets in. and achieved an oil consumption efficiency of 100KM/L range.
By 2006, the steel expanded rings were replaced by titanium in order to increase fluttering toughness by achieving further weight saving. Because titanium aggressivity would damage the piston grove sides and the expander, a tungsten carbide coating (WCC) was applied to the rings and a DLC coating was applied to the expander. The effect of the reduction in weight achieved through the use of titanium was tremendous. Preventing the increase in pressure in the sump due to fluttering at all engine speeds. And helping to enable oil consumption to reach 150 KM/L.
One important function of the piston rings is to enable heat to escape from the piston to the cylinder. In formula one engines, by contrast, the pistons are cooled by powerful oil jests. In addition, the heat transferring surface area of the expanded rings was also extremely small. The contribution of the piston rings to cooling was therefore minimal, and no issue resulted as by the use of titanium, a material with a low rate of thermal conductivity.
Maintaining the benefits provided by the expanded rings necessitated strict control of the 'taper angle' to very fine limits. (the taper angle of the face of the ring in contact with cylinder wall). This taper compensates and presents a flat contact face to the cylinder when the ring tilts-up when the piston is on its way down.
These rings developments, down to a reputed 0.7mm thick enabled the NA 2.4-litre V8'S to reach 19600-20000 RPM with acceptable ring flutter, blow-dawn gasses and oil consumption.

[godlameroso]

Piston rings developments.
Piston rings half more than halved in thickness since the 1980’s.
The initial piston ring configuration as used in formula one was identical to that used in mass production vehicles up to 1989 NA 3.5-litre engine formula, an engine formula where V12, FALT-12, V10, V8 engines reaching an RPM of 13000-14000 was raced. With the difference of using only two rings instead of three. The rings were formed from top ring with a rectangular cross section and an oil ring with a spacer expander inserted between rails.
By 1995 NA 3.0-litre V10 engine formula, such engines that by the year 2000 were reaching the 18000RPM mark, of which was made possible by the development and use of an expanded piston rings of 0.9mm width and 1.4mm tick with a rear expander (behind the ring). In this twin-ring configuration the ring were both the same and identical. The use of these rings increased engine speed by more than 1000RPM before ring flutter sets in. and achieved an oil consumption efficiency of 100KM/L range.
By 2006, the steel expanded rings were replaced by titanium in order to increase fluttering toughness by achieving further weight saving. Because titanium aggressivity would damage the piston grove sides and the expander, a tungsten carbide coating (WCC) was applied to the rings and a DLC coating was applied to the expander. The effect of the reduction in weight achieved through the use of titanium was tremendous. Preventing the increase in pressure in the sump due to fluttering at all engine speeds. And helping to enable oil consumption to reach 150 KM/L.
One important function of the piston rings is to enable heat to escape from the piston to the cylinder. In formula one engines, by contrast, the pistons are cooled by powerful oil jests. In addition, the heat transferring surface area of the expanded rings was also extremely small. The contribution of the piston rings to cooling was therefore minimal, and no issue resulted as by the use of titanium, a material with a low rate of thermal conductivity.
Maintaining the benefits provided by the expanded rings necessitated strict control of the 'taper angle' to very fine limits. (the taper angle of the face of the ring in contact with cylinder wall). This taper compensates and presents a flat contact face to the cylinder when the ring tilts-up when the piston is on its way down.
These rings developments, down to a reputed 0.7mm thick enabled the NA 2.4-litre V8'S to reach 19600-20000 RPM with acceptable ring flutter, blow-dawn gasses and oil consumption.

The new generation power units have lower operating speed, however to my understanding, ring thickness remains between .7-.5mm

[saviour stivala]

I do not know and have no information as to what piston ring thickness the present power units are using. But knowing that the present power units have reached an efficiency percentages never seen before, and knowing that 50%/60% of engine friction is generated by the pistons and rings, and that 50% of the pistons friction is in turn contributed by the piston rings, I have no doubt that they are using the least thickness possible for the loadings they are running at their present maximum power speed.
The thicker the ring the more the amount of load pushing outwards (radial tension) needed to ensure an adequate seal, the more radial tension, the more friction produced.

[Jolle]

I believe that the current PU’s use three rings again. Which makes sense because of the durability needed. The stress of seven race weekends without opening the casings, is the equivalent of 100.000 miles on road use.

[saviour stivala]

I believe that the current PU’s use three rings again. Which makes sense because of the durability needed. The stress of seven race weekends without opening the casings, is the equivalent of 100.000 miles on road use.

As I said. I do not know/have no information as to what piston rings configuration is being used by the present power units. What I know is that they are running at a level of efficiency the likes that have never been seen before and that means that reducing friction must have been one of their main priorities. If as you believe they have reverted back to a piston ring configuration (three ring pack) they abandoned at least 35 years ago. It means that they have added a not so small amount of friction to the ICE and not reduce it.

[Tommy Cookers]

Piston rings half more than halved in thickness since the 1980’s.
The initial piston ring configuration as used in formula one was identical to that used in mass production vehicles up to 1989 NA 3.5-litre engine formula, an engine formula where V12, FALT-12, V10, V8 engines reaching an RPM of 13000-14000 was raced. With the difference of using only two rings instead of three. The rings were formed from top ring with a rectangular cross section and an oil ring with a spacer expander inserted between rails.
....use of an expanded piston rings of 0.9mm width and 1.4mm tick with a rear expander (behind the ring). In this twin-ring configuration the ring were both the same and identical. ..... down to a reputed 0.7mm thick enabled the NA 2.4-litre V8'S to reach 19600-20000 RPM with acceptable ring flutter, blow-dawn gasses and oil consumption.

race rings in the 1980s would of course have been much thinner (than in mass production vehicles) for lightness
ring flutter (radial vibration) triggered by the piston tending to out-accelerate the piston early on the power stroke
(the outwards gas load on the ring collapsing as the gas leaks under the ring)
lighter rings have greater acceleration under gas-load so tolerate greater piston acceleration ie more rpm
ie the ring are designed so that their flutter rpm exceeds max permissible engine rpm
flutter would probably break the ring from fatigue
later thin race rings have less gas load and more groove friction so have less vibrational amplitude

alternatively the rings have been designed so flutter rpm is below the rpm range used eg in racing
eg the 1990s ? F1 Peugeot V10 engine introduced such a ring with a 'must-avoid' rpm c.8000 rpm
but they didn't tell one driver (Mr Brundle) - so producing an infamous volcano-style eruption seconds before the start
(and crankshafts (especially driving propellors) have been similarly 'must-avoid rpm' designed - though I can't name one)


current F1 engines gain efficiency most from (for SI) unprecedentedly low heat loss
their loads responsible for producing friction are high because of the high in-cylinder work eg even during compression
higher even than in the 1980s unlimited turbo era
the rod ratio isn't particularly large ?

[e36jon]

Greetings all

I thought the Honda F1 info that was shared a few years ago might be relevant to this discussion (Saviour, please advise if you would like me to delete this.):





I have not seen any other F1 ring info in my web travels...

[saviour stivala]

Piston rings half more than halved in thickness since the 1980’s.
The initial piston ring configuration as used in formula one was identical to that used in mass production vehicles up to 1989 NA 3.5-litre engine formula, an engine formula where V12, FALT-12, V10, V8 engines reaching an RPM of 13000-14000 was raced. With the difference of using only two rings instead of three. The rings were formed from top ring with a rectangular cross section and an oil ring with a spacer expander inserted between rails.
....use of an expanded piston rings of 0.9mm width and 1.4mm tick with a rear expander (behind the ring). In this twin-ring configuration the ring were both the same and identical. ..... down to a reputed 0.7mm thick enabled the NA 2.4-litre V8'S to reach 19600-20000 RPM with acceptable ring flutter, blow-dawn gasses and oil consumption.

race rings in the 1980s would of course have been much thinner (than in mass production vehicles) for lightness
ring flutter (radial vibration) triggered by the piston tending to out-accelerate the piston early on the power stroke
(the outwards gas load on the ring collapsing as the gas leaks under the ring)
lighter rings have greater acceleration under gas-load so tolerate greater piston acceleration ie more rpm
ie the ring are designed so that their flutter rpm exceeds max permissible engine rpm
flutter would probably break the ring from fatigue
later thin race rings have less gas load and more groove friction so have less vibrational amplitude

alternatively the rings have been designed so flutter rpm is below the rpm range used eg in racing
eg the 1990s ? F1 Peugeot V10 engine introduced such a ring with a 'must-avoid' rpm c.8000 rpm
but they didn't tell one driver (Mr Brundle) - so producing an infamous volcano-style eruption seconds before the start
(and crankshafts (especially driving propellors) have been similarly 'must-avoid rpm' designed - though I can't name one)


current F1 engines gain efficiency most from (for SI) unprecedentedly low heat loss
their loads responsible for producing friction are high because of the high in-cylinder work eg even during compression
higher even than in the 1980s unlimited turbo era
the rod ratio isn't particularly large ?

Racing rings are not only much thinner than in mass production vehicles for lightness alone, they are thinner because they adapt better to a distorted bore and still seal better, they need much less pressure behind them to produce the same or much more radial tension against the bore face. The higher the RPM the more chance of ring flutter. I didn’t know/never heard about the F1 V10 Peugeot rings (must-avoid RPM c 8000), what I know about that engine is, it was the only F1 V10 at the time running with a roller bearing crankshaft. Before your editing of the post, as to when ‘propellors’ are involved, (sea propellors) are a main source of destructive ‘must avoid’ RPM band in the RPM range, I know of a very big engine that rotates at a maximum of 100 RPM which have a strict ‘no hold’ at RPM range.
As to ‘todays engines and the 1980’s unlimited turbo era’ friction comparison. Leaving aside any developments improved advancements made in the design, material and coatings used since that time, what counts is:- number of pistons used, size of pistons/bore size, number and thickness of rings used, stroke size, maximum power RPM used.

[saviour stivala]

Greetings all

I thought the Honda F1 info that was shared a few years ago might be relevant to this discussion (Saviour, please advise if you would like me to delete this.):

https://imageshack.com/i/pn1ilQxmj

https://imageshack.com/i/pmQjReG6j

I have not seen any other F1 ring info in my web travels...

“saviour. Please advice if you would like me to delete this”. Of course not, not only don’t but please except my honest/sincere thanks for managing to do what I did not manage to do (transferring that Honda paper information onto here) of which goes to prove all I quoted from it. Also re “I have not seen any F1 ring information in my web travels”. Although not F1 engine manufacturers official there was and still is reliable source of technical ring information around. As to the use of a ring thickness of 0.7mm I quoted, that was attributed to (claimed by a reliable source) to the Cosworth 20000 RPM 2.4-litre V8. As regards the ring thickness, the use of only 2-rings and the 2-rings being of the same configuration. At least the Cosworth TJ piston acquired by ‘mudflap’ from Brain G and his picture and drawings he posted on here shows that the TJ 2-ring configuration were not the same, top ring was thinner and its piston groove depth is deeper than the bottom ring. May be mudflap could post the measurements.

[63l8qrrfy6]

I did not take accurate measurements but I remember sticking a 0.5mm feeler gauge in the top ring groove and there wasn't much left..

Too bad I don't have any rings, would be curious to know if Cosworth went for the torsion type rings too.

[saviour stivala]

I did not take accurate measurements but I remember sticking a 0.5mm feeler gauge in the top ring groove and there wasn't much left..

Too bad I don't have any rings, would be curious to know if Cosworth went for the torsion type rings too.

May be mudflap could please post the piston rings (top and bottom piston rings groove) depth and width measurements.

[PlatinumZealot]

Piston ring must not be too thin. You need it to have good boundary layer effect so it doesnt scrape the oil away.

[saviour stivala]

The effort required to push the ring against the cylinder wall is generated by the ring radial tension. A given load is required to create sufficient sealing against the cylinder wall. The larger the ring face area (thickness) touching the cylinder wall, the more radial tension is required to achieve the desired load. This greater outward tension greats more friction. The ess friction generated the more the ‘free HP’ gained.

[63l8qrrfy6]

Piston ring must not be too thin. You need it to have good boundary layer effect so it doesnt scrape the oil away.

True for the compression ring, partially true for the 2nd ring and false for the oil ring )

Compression rings have barreled faces and sometimes positive twist (as the Honda ring shown above) to create a hydrodynamic wedge which can compensate for the reduced face area. The lower the ring thickness the smaller the tension for the same width and the lower the radial force from gas loads - this is why it is possible to get away with very thin compression rings that don't scrape.

2nd rings (either taper type or napier) can only have negative twist (or no twist at all) so that they are somewhat hydrodynamic during up strokes but break through the film on the down strokes to scrape the oil into the crankcase.

Oil control rings are always breaking through the oil film.

[saviour stivala]

“True for the compression ring, partially true for the 2nd and false for the oil-ring”. That is a three ring pack you talking about, something which was abandoned by F1 engine makers in general since at least the start of the NA 3.0-litre V10 era in 1995 in preference of a two ring-pack. Not only that but with the exception of Cosworth’s TJ V-10 up to 2005, as was the case with their preferred type of Roots scavenge pump all other engine manufacturers preferred the use of both rings being of the same configuration (top and bottom rings being of same dimension). Of course in this two-ring type configuration it is still perfectly right to call the top ring a ‘compression’ ring and the bottom ring an ‘oil’ ring. When a three-pack ring as well as a two ring pack is used with an old style of a thicker oil ring, as seems to be the case with the TJ pistons. The oil ring produces by far the most friction of the lot. (Are you going to/willing to contribute to this thread by measuring and posting your TJ piston grooves width and thickness dimensions so as the rings used could be calculated?). Re the development of the face taper of the rings as per the Honda paper. This developed ring face taper (the top edge of the ring outer diameter being bigger than the lower edge of the ring outer diameter, when the piston/rings are in static condition there results a gap between the ring lower edge and the cylinder wall), will result in the rings presenting a flat face to the cylinder wall and total seal when the piston is going dawn and the rings tilt-up. If the rings does not present a flat-face and total seal to the cylinder wall, the high combustion pressure will get in between the gap created by the top edge of the ring tilting away from the cylinder wall and will push the ring into its groove and away from the cylinder wall with the resultant blow-by gasses into the crankcase. On the other hand when the piston is going up and the ring will tilt down the build-in gap at the bottom edge of the ring will increase and helps the top edge sealing onto the cylinder wall scrape the oil.