Due to its shorter block length a V6 casing is typically a more rigid element for a given weight than a V8 or V10 while the shorter crankshaft is also less susceptible to torsional vibrations and flex. As a stressed member of the chassis (this is important to remember), this is critical as there are fewer isolation options to prevent harmonic transfer and propagation into the various systems like suspension and chassis. All these things allow it to be either lighter in the first instance or able to cope with the imbalances better for a similar components construction.
Tim.Wright wrote:I'm not an engine man, but I imagine they will just live with it. Its the nature of the beast and the same for everyone. Ride comfort is not important and I don't think it saps any performance.
It can and does take power and if not accounted for will dramatically affect reliability. However as above a V6 is generally torsionally stronger and the further reduction of RPM’s, with Renault saying that 12,500rpm is likely to be the limit due to fuel flow restrictions, would certainly help promote longevity as the 2nd order harmonics from net component speed imbalances through each period of crankshaft rotation is substantially reduced.
It’s also a consideration that vibrations from the engine can prematurely fatigue other components attached to it so a decision based on weight, longevity, packaging and serviceability would need to be made, as well as the FIA requirements for part longevity. A high degree of vibration from the engine can very easily fatigue gearbox casings, gearsets, driveshaft components, engine ancillaries (think Renault alternators as an example) or carbon constructions (fatiguing the layups) leading to premature wear and failure. So do you increase sizing and weight of the drivetrain/chassis/components or fix the inherent issue at the source??
This is a major issue as the vibration is generated by the non-symmetrical movement of the piston/rod assemblies throughout each crankshaft rotational period of 720°. Descending rods are moving at differing speeds through their rotation in relation to ascending assemblies (particularly at angles either side and at TDC and BDC), causing a net vertical imbalance twice each crankshaft revolution. Increases in stroke will give rise to a greater difference in these speeds and accelerations because of increased distance traveled. Increases in bore “CAN” result in an increase in mass (of the piston and rod assembly) which increases inertial forces and hence increase the imbalance again.
The biggest reason these need to be carefully considered is the amplitude of these harmonics, which due to the non-symmetrical movement at twice RPM's increases quadratically (x4) as RPM increase, no matter how well balanced the completed bottom end assembly is. As it is an asymmetry (distance vs. speed through crankshaft period) and not weight imbalance that causes the issue, balancing won't negate the problem.
Tim.Wright wrote:Apart from making joints and bolted interfaces a bit more vibration resistent i don't think there is anything extra to do.
2nd order harmonics (vibration) due to the above will need to be considered and rather than resistant I think isolation and insulation from the harmonics may be the path taken for various reasons.
Tommy Cookers wrote:IMO the vibration is caused by the (out of balance components of) inertia forces
Do you mean weight out of balance or movement out of balance??
AFAIK, there are two primary types of vibrations or harmonics in an engine. Rotational torque oscillations which are caused due to imbalances in the firing order and 2nd order harmonics that occur due to velocity differentials of the various piston rod assemblies in motion. Component balance is typically a minor, very well understood issue and easily overcome during engine construction.
Tommy Cookers wrote:the 90 deg V6 has less uneveness of combustion forces than does eg the traditional 60 or 65 deg V6
Are you simply talking about the firing order per degrees of revolution due to spacing on the crank of the journals or something else??
I was always told that the 60° angle is the most efficient from a minimization of harmonics and vibrations due to torsional and rotational imbalances for a V6. Nissan had the VQ series which were all 60° V6’s as well as the new VR38DETT GTR engine which uses a 60° V6. Ford with their various designs up to the recent Duratec V6 were more often than not 60° (Essex and Cologne IIRC). Then there is the ubiquitous Alfa V6 which was a 60° design also.
Tommy Cookers wrote:this helps the crankshaft design (to be better than the 60deg), but is not the true even firing of the 120 deg V6
90° V6’s typically see “more” vibrations/harmonics than a 60° V6’s which (I thought) was generally considered the most efficient V6 angle. Most 60 deg V6’s have been able to do away with balance shafts by using 120 deg, 6 throw cranks phasing cylinder pairs together, however some use 3 throw cranks with smaller counterweights or “flying arms” (no idea why they are called this) and balance shafts.
There is also the use of 30° split pin cranks which Mercedes particularly is fond of and modern manufacturing and metallurgy could make this a viable alternative if allowed under the rules.
Tommy Cookers wrote:spacing of inertia forces is of course related to spacing of combustion forces and is more important at F1 rpm
but at the 2014 12000 rpm some uneveness is less important (than at current 18000 rpm)
Absolutely. The torsional oscillations of the crank due what I expect to be a 120 degree firing order and the 2nd order harmonics from net component speed imbalances of the rotational assemblies are both going be greatly reduced and less of an issue with RPM’s coming down from 18,000rpm to 12,000/12,500rpm expected. It’s another reason (other than restricted fuel flow) expectations of the 15,000rpm limit rarely if even being used.
piast9 wrote:How about a balancer shaft? The overall weight of the F1 engine forced by the rules is much higher than manufactures are able to achieve. So it should be easy possible to make the engine a bit lighter and add the balancer shaft to cancel vibrations.
Increasing rotating mass, complexity, serviceability and the parasitic drag mean that the engineers will likely look to other ways of reducing and negating the effects of imbalance harmonics.
Driving a counter rotating mass damper assembly can take a noticeable amount of torque from the engine which might end up in a Mercedes vs. Renault straight line power/speed difference, especially as fuel flow is limited they’ll be looking for max power out of the engine for the limited fuel flow allowed I would expect. Its all about efficiency gains for 2014.
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