How will teams handle V6 imbalance?

[Tommy Cookers]

I assume(d) that the OP and others were thinking of purpose-designed race V6s ie 3 crank throws, not road-related V6s
(that these days have a configuration that functions as 6 crank throws, however called)

In the 60s etc we had (in production by accident) both the Ferrari/Fiat 65 deg 3 throw engines (from front-engined F2/1 use), and 90 deg 3 throw engines from Buick, Honda and Renault/Peugeot/Volvo (all the 90 deg were cut-downs of intended V8s)
3 throw engines are compact and light, but still have a bit of vibration
(reciprocating elements/inertia forces leave uncancelled moments at engine frequency, (primary couple), producing some vibration at the mounts, silarly the usual much smaller (rod angularity) inertia effects at twice engine frequency (secondary couple)
the Renault and Honda via F2 (production block) led to the 90 deg or 80 deg V6 in F1
the (race) 60 deg is the best package but the worst crank (uneven inertia force intervals)
the (race) 120 deg is the worst package but has ideal even inertia force intervals for higher rpm (Ferrari won F1 1961 this way)
the (race) 80-90 deg is the best overall compromise today

in production by design, not accident, there were road 6 throw 60 deg V6s eg UK and German Ford designs
(inherently heavy and long, but less vibratory, having only the (much smaller) secondary couple )
the 60 deg angle was crucial to give even firing intervals, for a refined road car (despite the disadvantage to related V4s)

Buick, then all others, usefully went to 'split-throw' crankshaft designs that combine much of the compactness of the 3 throw with the benefits of the old 6 throw, and use mostly 70-90 deg angles) ...... thanks, Mr Buick !!

split-throw crankshaft designs are not suited/pointless in F1 though ? (even compared to the 3 throw 90 deg crank)
(although split-throw is best suited to very high bore:stroke ratios in current F1)
some other bastard designs are conceivable for 2014 (worse vibration, but gains including better exhaust pulses to turbo)
(although vibration is eased by the low rpm and small bore in 2014, minimum bearing friction is very important)

we normally act as if vibration forces come only from the piston, rod, and crankshaft group
however, Keith Duckworth pointed out that vibration forces from valve motion (in race engines) were greater than those from the vibration sources normally considered

[aussiegman]

For exactly the reasons you mention and that RPM's are now down to more "sane" numbers (a relative term), the desire for beneficial exhaust pulse separation and speed may in some way drive the crank design over exhaust packaging and length concerns. Again, with efficiency the primary driver and a basic clean slate within the set parameters perhaps engine designers may step away from the norm and do something box of the box.

[aussiegman]

we normally act as if vibration forces come only from the piston, rod, and crankshaft group
however, Keith Duckworth pointed out that vibration forces from valve motion (in race engines) were greater than those from the vibration sources normally considered

I hadn't heard that. I had been told it can cause harmonics from the springs and other mechanisms if they aren't matched to the expected operational speed of the engine, but as the camshaft(s) rotate at half crankshaft speed any vibrations would be 0.5 order engine speed.

Camshaft length can be a problem if the torsional vibration is close to or at or passes through the natural frequency of the camshaft billet. Cyclic resistance to rotation as well as vibrations and harmonics in the belt/drive chain can also be sources of torsional vibrations. However these harmonic frequencies are typically above the max engine RPM.

Do you have any links to any of Duckworth's commentary etc??

[Tommy Cookers]

just thinking out loud ...... IMO the losses that we associate with vibration are largely unrelated to vibration as we perceive it

vibration as we perceive it is due to the resultant of the force and moment summation inherent in the engine structure(s)
(ie what's transmitted to the vehicle structure via solid or elastic/fluid mounts)
this could be zero with some engine configurations, but there won't be a reduction in losses

major amounts of strain energy are flowing in and out of any crankshaft eg in bending and torsion as it rotates
(there is typically a steady bleeding of torsional strain energy by the crankshaft damper)
inertia forces are (typically) cancelled within the crankshaft by opposing reaction moments, but strain energy flow is unchanged
there is some internal energy loss (larger with a production crankshaft eg 'iron' casting or powder metallurgy type)

but the inertia forces are transmitted through the big-end bearings (this is much more lossy)
and some of their cancellation is done by the crankcase via the (also v lossy) main bearing (unless the crankshaft is infinitely stiff)
the bearing losses are vastly greater than these internal losses (hysteresis) eg in the crankshaft and crankcase

typically engines cancel within their crankshafts primaries (most of the inertia forces) and leave the secondaries uncancelled
cancellation of the secondaries by counterbalance shafts demands extra bearings, with consequent losses
(road motorcycles of this type remove these shafts for racing, and save about 2% of engine power)
complicated engines (eg horizontally-opposed or inline 6s) have full cancellation internally, but are bulky and need more bearings/bearing area for crankshaft stifness/strength (unless clever 180 deg Vs eg Ferrari 312, having only 4 main bearings)

[olefud]

we normally act as if vibration forces come only from the piston, rod, and crankshaft group
however, Keith Duckworth pointed out that vibration forces from valve motion (in race engines) were greater than those from the vibration sources normally considered

Could he be saying this because the DFV with the 180º crank was blurring drivers’ vision?

[Smokes]

aren't 4 strokes harmonicaly balanced with orders of 3 cylinders? as they cancel the second order of vibration?

[Tommy Cookers]

inline 3 cylinder engines (if they have equal intervals between the crankpins) have inertia forces balanced in magnitude but not in position, so there are residual moments equivalent to some quite small vibrating forces at the mounting points

this applies to first and second order inertia forces (unless I am wrong !)

[Greg Locock]

Well, you are sort of right. The rocking couple an I3 creates is an absolute bear to work with (as one piston goes down, the one at the other end goes up). The first car whose engine mounts I ever worked on was an I4 rear wheel drive, so having sorted that out I thought I knew all about it. Then the chief engineer for the advanced vehicles group rocks up with their pet 3 cylinder FWD car and asks me to make it quiet.

[Tommy Cookers]

@ Greg Locock
is the 4 (having only 2nd order residual forces) better isolatable with elastomer mounts because of the higher frequencies (compared to the 3's 1st order residual moments) ?
having said that, my impression is that 3s with (1st order only ?) counterbalance shafts are the standard, but have worse isolation than alternative 4s
surely the 3 throw V6s (without counterbalance shafts) were clearly less rough than any similar-sized inline 4 ?(without counterbalance shafts)
surely a 2014 12000rpm 1600 cc V6 must vibrate a lot less than the current 18000 rpm F1 engines ?

[DaveKillens]

There's a little bit of history to also consider. Back when Renault was formed from the remains of the Benetton team, one configuration they pursued was the 111 degree V-10. Because the cylinder banks were so splayed out, it offered lower center of gravity, and this was the engine that gave Alonso and the Renault team it's first win, at Hungary, a circuit demanding good handling.

But once the engine reliability regulations were instituted, that engine went the way of the dinosaur, because, as I assume, the inherent vibrations were a nightmare for reliability.

So although we're dealing with a lot less cylinders and smaller displacement, reliability cannot be ignored. There are many options and paramenters to be compared against reliability, such as whether to use balancing shafts, make the components stronger and thus heavier, limit RPM, and whether the emerging technologies of KERS and HERS can somehow be utilized to overcome any handicaps imposed by going in any certain design direction. Make the engine heavier, but with HERS and KERS it can be overcome in acceleration?

I'd love to be one of the engine design offices, and have access to data that will drive the final decisions on engine design.

[Greg Locock]

@ Greg Locock
1 is the 4 (having only 2nd order residual forces) better isolatable with elastomer mounts because of the higher frequencies (compared to the 3's 1st order residual moments) ?
2 having said that, my impression is that 3s with (1st order only ?) counterbalance shafts are the standard, but have worse isolation than alternative 4s
3 surely the 3 throw V6s (without counterbalance shafts) were clearly less rough than any similar-sized inline 4 ?(without counterbalance shafts)
4 surely a 2014 12000rpm 1600 cc V6 must vibrate a lot less than the current 18000 rpm F1 engines ?

1 yes, for instance if you have a 900 rpm idle then a 4 has 2nd order at 30 Hz, which is obviously about one octave or 6 dB more attenuation than the 1 order from a 3 cylinder

2 maybe they do now, 30 years ago in the chase for fuel economy a balancer shaft on a 1.2 litre engine would have been laughed out of court. This engine never made it into production, it was an early proposal for what became Rover's K series. It had more whacky ideas in it than a loony bin.

3 yes, a V6 is better than an i3, agreed

4 i expect so

[Smokes]

Greg
What I ment was 60° v6 and 60° v12 or flat 6 of flat 12 are better ballanced than a 90°v8 or 72°v10 or 90°v4, due to the firing order being divisible by 3 and the bank angle. Not sure how the flat plane crak affect things.

[Tommy Cookers]

Greg
What I ment was 60° v6 and 60° v12 or flat 6 of flat 12 are better ballanced than a 90°v8 or 72°v10 or 90°v4, due to the firing order being divisible by 3 and the bank angle. Not sure how the flat plane crak affect things.

every race-designed V6 has 3 throws and 4 main bearings, and the balance is nothing special
such race flat 6s as were had good balance and bad internal losses, because they had 6 throws and 7 main bearings
(such engines still have residual moments because the 'opposite' cylinders are far from truly opposite)
(the Porsche flat 8 F1 was similarly useless, with 9 main bearings it had more power at the pistons and less at the crankshaft than the 2 makes of British V8s that won everything with their 5 main bearings)
a 5 main flat 8 is possible (but the Porsche's air cooling, by spacing the cylinders far apart, forced them to have 9 mains)
a (British) Mr Anderson made a F2 flat 8 with 2 mains in the early 50s
the Porsche flat 12 had 13 main bearings (a V12 has 7)
Ferrari pseudo-flat 12s had 4 main bearings and won WDCs and WCCs

there is no law requiring a V6 to have equal interval crank throws, the Laverda 3 had for years a flat (single-plane) crank
the 90 deg V8 has only small moment residuals (with the usual cross-plane crank), so is very smooth
the flat crank (F1 V8s taken that way by the 2 British engines in 1962) is lighter and has better V8 exhaust layout, but vibrates as much as an inline 4 (while winning thousands of races)
inline 4s 'always' have flat cranks, but for race use the cross-plane crank 4 is now appearing (having well-spaced inertial torques)
(the flat crank 4 has badly-spaced inertial torques but well-spaced power load torques, good for road use)

they just don't design F1 engines to give low vibration, unless that happens for other reasons
eg the 1954 MB had an inline 8 (with central power takeoff intended for 4wd), the 1964 Honda had a transverse V12 with central power takeoff

[Greg Locock]

Greg
What I ment was 60° v6 and 60° v12 or flat 6 of flat 12 are better ballanced than a 90°v8 or 72°v10 or 90°v4,.

V12 of whatever angle is inherently balanced for L/r and inertial effects, which is what we're talking about.So that covers the flat 12. Flat 6 can be balanced depending on crank configuration - if it has 6 throws it will be, if it only has 3 then it is an I3 in disguise.

72 v10 is not balanced, 90 v8 i can't remember.

due to the firing order being divisible by 3 and the bank angle. Not sure how the flat plane crak affect things.

I think you are confusing balance, L/r inertial, equal firing intervals and perhaps some other things. I am talking about L/r and inertial only.

[coaster]

They will probably use a rattle style of harmonic balancer like the Buick V6 guys use in usa and maybe a beefed up bedplate, unlike todays paper thin ones.


The vibes are only gonna shorten the engines lifespan give the driver an itchy nose, lets not hope it's vice versa.