Question about the cylinder angle.

[heming]

I have a question with cylinder angle about F1's v10 engine.

Why should it be 72 or 90?
According to my caculation, 72 and 108 can keep the crank's best balance and make the vibration minimal. However, lots of teams are using 90 engine. Even, Renault had previously used wide-angle engine, but the angle is 111, but 108.

Thanks for ur attention and response.

[DaveKillens]

The angle between the cylinder banks can be determined for specific requirements. For many applications, as you stated, they are designed to deal with the primary and secondary vibrations.
And stated simply, you widen the angle and you most likely lower the CG.
But in F1, packaging is also very important. So the engineers (as always) try to find a compromise between harmful vibration and packaging requirements. And one major influence on engine/ gearbox packaging are aerodynamic needs.
Of course, with the new regulations requiring increased reliability, the design of that angle to eliminate vibrations takes a much higher priority.

[Monstrobolaxa]

Well like heming said 72º degrees is actually considered the best angle for a V configuration, not only has heming said it by P. Martinelli has also stated it and a few other engine manufacturers. The thing is that you can increase the V angle to the amount that you want seeking a determined amount of advantages. Engine manufacturers usually weigh the advantages and disadvantages of using a diferent angle then the 72º....if the advantages out-weigh the disadvantages then a new V-angle is used!

[DaveKillens]

360 divided by 5 equals 72. But a 60 degree V-12 is much nicer on the ears.

[Guest]

Does anybody know any good websites about this angle configuration stuff? Like I want to know why which angle causes less vibration and which one is best for combustion, etc.

West

P.S. By the way, F1 racing, in an interview w/ an F1 engineer, says that increasing the angle will NOT lower the CoG of the engine, because the crank is actually being pushed up, but u guys say otherwise...

[DaveKillens]

I hope this may help.
http://encyclopedia.laborlawtalk.com/Balance_shaft

I think that when you had the discussion with the BMW engineer, he was thinking of just the engine, not the complete package. If you examine an engine, and one modified with an increased cylinder bank angle, the CG would appear to move down, closer to the crankshaft. So relatively, the crank is being moved (pushed up) closer to the CG with an increase of cylinder bank angle.
But the harsh reality of engineering states that the crankshaft is as low to the ground as possible. Period. I'm sure that in a current F1 car, the crankshaft is not more than one of two cm. from the ground, when under maximum downforce.

[riff_raff]

I agree with Dave Killens, a V10 engine configuration is optimum with 72 deg between cylinder banks.

All F1 engines must be V10's per the rules, and 72 degrees provides an even firing interval for a V10. To understand the importance of firing interval, you need to look at a graph of an engine's instantaneous torque output. An engine with an even firing interval (like a 72 deg V10) will have a more consistent peak-to-mean torque output than an engine with an uneven firing interval (like a 100 deg V10). An engine with high instantaneous torque spikes (caused by two cylinders firing closer together than necessary) can cause unwanted drivetrain stresses, vibrations and loss of traction. In a conventional crankshaft/conrod engine, peak (or instantaneous) torque can be 2 or 3 times mean torque output.

For the F1 guys though, packaging and a low C-of-G may be more important than torque characteristics. And there are also other design considerations, such as acoustic resonance within the intake airbox or the 5-into-1 exhaust header.

As far as dynamic balance, the typical F1 engine has an extremely short stroke, very lightweight reciprocating masses and a limited fatigue life requirement so any unbalance factors due to odd v-angles is likely not a big concern.

Regards,
Terry

[DaveKillens]

Here is a decent description of primary and secondary vibrations, and more.
http://www.fordscorpio.co.uk/tech2_3.htm

[West]

I'm guessing that with Primary balance, there is no net force on the crank? And with firing order (from that website), we want to equalize the moments at the end of the crank?

[bcsolutions]

If the rules didn't dictate the configuration of the cylinders do you think most of the teams would elect a V configurated engine or are there better solutions for a 3.0L 10 cylinder N/A engine?

[riff_raff]

west,

With a 72 deg V10, primary and secondary inertia forces can be balanced. However there is a couple, acting in the plane of the cylinders, that cannot be balanced. This unbalanced couple tends to pitch the front and rear of the reciprocating masses up and down.

As for firing order, it is usually selected with regards to acoustic resonance in the intake and exhaust system. And of course, firing order can affect torsional vibration characteristics within the crankshaft.

Regards,
Terry

[Reca]

The 90° has actually some pretty valid advantages in term of vibrations compared with the 72°, isn’t just an angle chosen for packaging reasons although undoubtedly important.
The 90° V has an inherent property that doesn’t depend by the number of cylinders, it allows to balance independently each pair of cylinders sharing the same crank pin and this allows more freedom in the choice of the firing order. It’s a fundamental property because the real issue for F1 crankshafts are exactly the torsional vibrations, possibly the most important rpm limiting factor, and the “right” firing order helps a lot to reduce them, firing order choice is indeed mainly related to that.
The 72° V has, as already pointed out a severe imbalance in the first order couple (Honda used a balancing shaft to eliminate it) and to minimize it you are basically forced to use a certain disposition of the throws having consequently a limitation in the available choices for the firing order.
The evenly spaced ignitions, if could be useful in a slow revving engine with few cylinders is of basically no relevance on a high revving V10, or in any high revving engine for that matter. On the contrary, a common opinion is that the uneven firing interval could even be beneficial because doesn’t excite the natural frequencies of the crankshaft.
About acoustic tuning what is beneficial is to have evenly spaced the ignitions of the pistons from the same bank, the ones sharing the same exhaust and also in the 90° you have that. The Renault wide V10 had some problems related with acoustic mainly due to the shape of the airbox, pretty wide, a 90° doesn’t have such problems.

If the rules didn't dictate the configuration of the cylinders do you think most of the teams would elect a V configurated engine or are there better solutions for a 3.0L 10 cylinder N/A engine?

Remove the limitation on number of cylinders and make the car have a flat bottom instead of the current stepped one and, maybe, someone could be crazy enough to try, again, a W12 (3 banks with 4 cylinders), it could have a few theoretical advantages (to be verified in practice if they are more relevant than the disadvantages obviously) and I would definitively sympathize with them (not that that makes it a better choice...). But for a 10 or 8 cylinders, in the current cars, the V is basically the only choice.

[bcsolutions]

maybe, someone could be crazy enough to try, again, a W12

In a similar vein to the VW group W8 and W12 engines perhaps? I've often wondered of the benefits of this configuration?

[Reca]

This week I read an interview with Rory Byrne and there’s a question related with the v angle :

Q : The fact that they have a 72° engine can be an advantage for Renault given the current rules ?

RB : Yes, there are undoubtedly positive aspects about the installation on the car. Years ago, in 1994 (at Benetton), we used too a 72° engine. If we had to start the design today, from scratch, we could actually decide to use a narrower V. But obviously we don’t start from zero, we had to care about every detail to guarantee reliability. So, overall, it was better to keep the engine we were already using.

Actually, according to several sources the Ford V8 used till ’94 by Benetton was a 75° and the Renault V10 used in ’95 was a 67°, maybe he made a memory mistake (or maybe the mistake is of the translator/journalist), anyway the slightly different figure doesn’t change the essence of the answer.

In a similar vein to the VW group W8 and W12 engines perhaps? I've often wondered of the benefits of this configuration?

The VW group W engines are formed by two banks with an angle of 72° IIRC, and then inside each bank, the axes of the cylinders aren’t aligned but there’s a small angle, 15° I think, between odd and even cylinders; visually it looks like a standard V with two huge (wide) banks. The benefit is that you can reduce the distance between the cylinder centers to less than a cylinder diameter and this obviously makes a shorter crank and a shorter engine.

The configuration I was referring to on the contrary is the one used, and it’s better if we forget the results... by Life in 1989, with 3 separated banks of 4 cylinders, having a V of 60° between each bank. It would be a little nightmare to put it in a car, especially because of position of exhausts and intakes and it’s also pretty wide... actually I’m pretty sure a chief aerodynamicist would probably kill the engine designer proposing that solution, but I don’t know why I always liked it... maybe exactly because it would be a challenge to fit it in the car... or maybe for the same irrational reasons explaining why one of my preferred F1 cars is the F92A...

[bcsolutions]

So lets say that the engine designer drugged the aerodynamicist and managed to get his engine built. I can see how the total engine size (not length) would be an issue but what benefits do you think the engine might have over a regular V configurated engine?