A recent thread in the Technical Forum has touched on the issue of crankshaft resonances and the limiting effect they have on engine RPM’s. Here are a couple of questions I have on this matter;
1. Do F1 cranks use dampers of any form? Presumably this would mitigate the effects of resonances unless they are so destructive that the only effective design approach is to stay below the peak resonance point.
2. Has any F1 design varied the effective masses of the piston/con rod assembly in inverse proportion to the distance from the power takeoff at the transmission end? This in effect would mean larger bore sizes at the power take off end of the crank. A smaller mass at the far end of the crank would increase the longitudinal the resonance frequency and the larger masses near the power take off point would be better coupled due to the shorter length of crank involved.
3. Has any modern F1 engine used a centralized power take off point to reduce resonance effects? It was not unusual in the days of long whippy straight eights cranks to use a centralized power takeoff point to reduce crank loadings.
4. Has any crank used a varying journal sizes or a hollowed crank to vary the crank's torsional strength (and weight) in proportion to the torque loadings, which are higher at the power takeoff end? This would also lower the mass of the crank at the far end and reduce resonance effects slightly.
The shortness of a V10 crank makes it a very stiff object and I wonder if the resonance effects are as severe as we are making it out to be. If crank resonances were indeed the principal RPM limiting factor in F1, I would be surprised if the brute force method of ‘stronger is better’ is the only approach used and wonder why. If this were a bridge or building, structural elements would be sized in proportion to the loadings whereas the crankshaft and it’s rotating masses are not as far as I know.
Any help on this topic?
F1 Crankshaft Resonances Limiting RPM's.
Started by
Yelnats
, Sep 26 2001 14:49
10 replies to this topic
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#2
leegle
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Posted 26 September 2001 - 23:08
IIRC the last engine to take the power from the centre of the crank was the Honda V12 of 1964/65. 
The later 3-litre Honda may have as well but I don't think so.
The later 3-litre Honda may have as well but I don't think so.
#3
Wellington
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Posted 04 October 2001 - 14:54
Hi, let me see if I am in it...
Each and every rotating beam (or whatever) has its own natural frequencies (nf). While rotating, a bending of the beam may be induced because of a poor balance or radial loads (like those from the pistons). This bending generates vibrations.
The vibrations are at their peak if the beam rotates at a speed close to one of its nf, and that is the resonnance. Rotating speeds causing resonnance are the bending critical rotation speeds (crs).
Consequences:
1-the beam may be destroyed if the amplitude of the vibrations is not (mechanicaly) restrained.
2-the bearings may suffer due to the break-up of the oil film.
Solutions:
1-using the beam at rotation speeds inferior to the first crs.
2-using the beam at rotation speeds far greater than the 1st crs and below the 2nd crs (which means one must brace while accelerating through the 1st one).
The 2nd solution allows the designer not to oversize the beam.
In the case of a crankshaft, we have a beam with lots of bearings, which limit the bending phenomenon. However, it still occurs because the bearings must be mounted with a little play. The induced whirling may prove fatal if the oil film breaks up and if there is metal-to-metal contact at the bearings.
Interestingly, the bending at high rotation speeds may cause a gyroscopic behavior of the elements attached to the beam. This tends to keep it in a balanced position and increases the 1st crs.
All in all, I would think that what limits the rpm is the nature of the contact at the bearings: material, interface, play. The loads and temperatures are great and may not be greater at that time. Speaking of damping the vibrations, the pendulum of Sarrazin was succesful for aircraft engines (Hispano-Suiza and Wright), but I cannot figure a device rotating freely around its axis, mounted on a flywheel. Dimensions are crucial...
Regards
Xavier
Each and every rotating beam (or whatever) has its own natural frequencies (nf). While rotating, a bending of the beam may be induced because of a poor balance or radial loads (like those from the pistons). This bending generates vibrations.
The vibrations are at their peak if the beam rotates at a speed close to one of its nf, and that is the resonnance. Rotating speeds causing resonnance are the bending critical rotation speeds (crs).
Consequences:
1-the beam may be destroyed if the amplitude of the vibrations is not (mechanicaly) restrained.
2-the bearings may suffer due to the break-up of the oil film.
Solutions:
1-using the beam at rotation speeds inferior to the first crs.
2-using the beam at rotation speeds far greater than the 1st crs and below the 2nd crs (which means one must brace while accelerating through the 1st one).
The 2nd solution allows the designer not to oversize the beam.
In the case of a crankshaft, we have a beam with lots of bearings, which limit the bending phenomenon. However, it still occurs because the bearings must be mounted with a little play. The induced whirling may prove fatal if the oil film breaks up and if there is metal-to-metal contact at the bearings.
Interestingly, the bending at high rotation speeds may cause a gyroscopic behavior of the elements attached to the beam. This tends to keep it in a balanced position and increases the 1st crs.
All in all, I would think that what limits the rpm is the nature of the contact at the bearings: material, interface, play. The loads and temperatures are great and may not be greater at that time. Speaking of damping the vibrations, the pendulum of Sarrazin was succesful for aircraft engines (Hispano-Suiza and Wright), but I cannot figure a device rotating freely around its axis, mounted on a flywheel. Dimensions are crucial...
Regards
Xavier
#4
desmo
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Posted 04 October 2001 - 18:18
Pendulum of Sarazin (one r)? Now we're getting obscure, I love it! I found one (and only one) reference on Google:
Here
This is a critical subject in F1. Teams have tried MANY differing schemes to limit crank TVs. Bearing surface speed considerations force the main and big-end journal bearing sizes down as the rpm limit rises, compromising the stiffness of the crank. Various balancing devices have been looked at and to the best of my knowledge rejected, differing firing orders have been investigated in fact.
It is my belief that the most promising means of addressing crank TVs are to reduce the reciprocating masses through novel materials (Al MMC pistons most likely), or to use a steel matrix MMC (arguably legal given the tech regs) to raise the Young's modulus of the crank.
Here
This is a critical subject in F1. Teams have tried MANY differing schemes to limit crank TVs. Bearing surface speed considerations force the main and big-end journal bearing sizes down as the rpm limit rises, compromising the stiffness of the crank. Various balancing devices have been looked at and to the best of my knowledge rejected, differing firing orders have been investigated in fact.
It is my belief that the most promising means of addressing crank TVs are to reduce the reciprocating masses through novel materials (Al MMC pistons most likely), or to use a steel matrix MMC (arguably legal given the tech regs) to raise the Young's modulus of the crank.
#5
Chui
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Posted 05 October 2001 - 05:59
Actually, Porsche tried a center power take off on it's ill-fated [and properly aborted] 3.5L V-12 for the Footwork-Arrows team back in the early 90's.
#6
marion5drsn
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Posted 05 October 2001 - 18:48
Any answer as to vibration dampers on F1 engines is purely a guess. I was surprised when Wellington mentioned Sarrazin as the inventor of the pendulum vibration dampener as this I believe is the Frenchman who Pratt and Whitney found had invented the Pendulum dampener before they applied it to the radial engine of their manufacture.
This happened in the late 20’s or early 30’s.
It’s my belief that these engines use both Lancaster and Sarrazin type of dampers.
V-12s of 60-degree bank angle should not under need any type of vibration dampener but late in WW-2 all aircraft had added both Lancaster and Pendulum type dampeners.
72-degree V-10s need a full 10-counterweighted crankshaft due to the non-symmetrical crank necessary to achieve the desirable position to eliminate the Primary Moment. In spite of all the counterweighing of the crank at the speeds that these cranks turn gas pressures are just bound to create 3,4,5 etc. order vibrations. Allison’s V-12s had vibration dampeners on the mechanical driven supercharger plus on the crankshaft it self. One can read about the various dampeners on this engine in the book,” Vee’s For Victory”, by Daniel D. Whitney, pages 351 to 358.
Then in addition to the gas pressures we must add the different bank angles that are used that are not 72 degrees. That is 90,95,111 degrees bank angles. Making the pistons arrive at inopportune moments adding to the Secondary Shake. Unless they use extra crank arms or split crankpins they are going to have Secondary shake. The Primary
Shake and Primary Moment are easy to be rid of due to the 10 counterweights. It is my opinion that they just let the engine absorb the out of balance condition and put a low life expectancy on the engine components. Altho they still use as much balancing techniques as possible. If these teams had to run the same engine as they qualify with, we would see much different engine/race strategies used.
I also don’t believe that we have to worry about gyroscopic forces and the pendulum dampers are put in the arms of the crank. At the speeds that these engines turn external balancing just will not work. Some engines even used a pendulum mounted in the counter weight. M.L. Anderson
This happened in the late 20’s or early 30’s.
It’s my belief that these engines use both Lancaster and Sarrazin type of dampers.
V-12s of 60-degree bank angle should not under need any type of vibration dampener but late in WW-2 all aircraft had added both Lancaster and Pendulum type dampeners.
72-degree V-10s need a full 10-counterweighted crankshaft due to the non-symmetrical crank necessary to achieve the desirable position to eliminate the Primary Moment. In spite of all the counterweighing of the crank at the speeds that these cranks turn gas pressures are just bound to create 3,4,5 etc. order vibrations. Allison’s V-12s had vibration dampeners on the mechanical driven supercharger plus on the crankshaft it self. One can read about the various dampeners on this engine in the book,” Vee’s For Victory”, by Daniel D. Whitney, pages 351 to 358.
Then in addition to the gas pressures we must add the different bank angles that are used that are not 72 degrees. That is 90,95,111 degrees bank angles. Making the pistons arrive at inopportune moments adding to the Secondary Shake. Unless they use extra crank arms or split crankpins they are going to have Secondary shake. The Primary
Shake and Primary Moment are easy to be rid of due to the 10 counterweights. It is my opinion that they just let the engine absorb the out of balance condition and put a low life expectancy on the engine components. Altho they still use as much balancing techniques as possible. If these teams had to run the same engine as they qualify with, we would see much different engine/race strategies used.
I also don’t believe that we have to worry about gyroscopic forces and the pendulum dampers are put in the arms of the crank. At the speeds that these engines turn external balancing just will not work. Some engines even used a pendulum mounted in the counter weight. M.L. Anderson
#7
Yelnats
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Posted 09 October 2001 - 14:29
Desmo, Interesting to hear that a limit is imposed on journal diameters by bearing speed limitations. Certainly this would limit the possibility of using larger diameter journals at the power take of end to stiffen the crank.
marion5drsn, As you have mentioned, the torsional vibrations that limit engine RPMs in F1 are quite different to external engine vibrations related to differing engine configurations. Torsional Vibrations are caused by the piston/con rod masses resonanting with the fixed (driven) end of the crank which acts as a torsional spring between these masses. These cannot be resolved by the use of external rotating masses as is often done with external vibration dampers but would require decoupled masses directly affixed to the crank or a damping compliance interposed between the drive take-off. A very difficult solution indeed which I have not seen used on road engines.
I am not familiar with dampers you have described and would be interested to see how they function.Could you direct me to any sites that feature diagrams of these devices? I will try to find them independantly but you could save some time if you could help. Thanks.
marion5drsn, As you have mentioned, the torsional vibrations that limit engine RPMs in F1 are quite different to external engine vibrations related to differing engine configurations. Torsional Vibrations are caused by the piston/con rod masses resonanting with the fixed (driven) end of the crank which acts as a torsional spring between these masses. These cannot be resolved by the use of external rotating masses as is often done with external vibration dampers but would require decoupled masses directly affixed to the crank or a damping compliance interposed between the drive take-off. A very difficult solution indeed which I have not seen used on road engines.
I am not familiar with dampers you have described and would be interested to see how they function.Could you direct me to any sites that feature diagrams of these devices? I will try to find them independantly but you could save some time if you could help. Thanks.
#8
Ali_G
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Posted 10 October 2001 - 14:42
One question.
Has a wavy shaped crank ever been tried in an F1 engine. As it is the crank shaft are shaped with 90 degree bends in them.
But I was thinking of gradual bends to connect to the con rods.
This would make the crank shorter and of course lighter. But would this play havoc with vibration.
Niall
Has a wavy shaped crank ever been tried in an F1 engine. As it is the crank shaft are shaped with 90 degree bends in them.
But I was thinking of gradual bends to connect to the con rods.
This would make the crank shorter and of course lighter. But would this play havoc with vibration.
Niall
#9
marion5drsn
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Posted 10 October 2001 - 16:25
Yelnats, The external balancing I referred to is the vibration dampener on the front of the crankshaft and the flywheel (If any).
Fredrick William Lancaster invented the torsional vibration dampener
about 1909 in answer to the problems at that time in six cylinder inline engines. A picture of this is on page 83 of the book, “The Lanchester Legacy”. This along with many others of his inventions. This dampener has been undated to the present viscous type, which is nothing more than that of the original multidisc type. This is the dampener that millions of engines have on the front of the crankshaft.
The pendulum vibration dampener is just that a dual pendulum hung in any appropriate place on the crank, usually on the webs or on the counterweights. You may find an explanation of this on page 45 of, “Aircraft Powerplants” by Bent McKinley.
The types of vibrations you speak of are the Primary and Secondary Shake. I believe that a lot of misunderstandings of vibrations is the over use of the word Torsionals and or Harmonics. These words are used to shotgun every type of vibration and have reached the point of no meaning.
I have never found any place on the web that explains these dampeners altho they do mention that they exist.
The Plymouth Floating Power is shown in page 293 of C.F. Taylors book and is a torsionally decoupled mount for a four-cylinder engine. Auto.Ind.65, July 4, 12 (1931). This does not lower the vibration inside the engine it only reduces the effect on the mounting/frame.
Yours M. L. Anderson
Fredrick William Lancaster invented the torsional vibration dampener
about 1909 in answer to the problems at that time in six cylinder inline engines. A picture of this is on page 83 of the book, “The Lanchester Legacy”. This along with many others of his inventions. This dampener has been undated to the present viscous type, which is nothing more than that of the original multidisc type. This is the dampener that millions of engines have on the front of the crankshaft.
The pendulum vibration dampener is just that a dual pendulum hung in any appropriate place on the crank, usually on the webs or on the counterweights. You may find an explanation of this on page 45 of, “Aircraft Powerplants” by Bent McKinley.
The types of vibrations you speak of are the Primary and Secondary Shake. I believe that a lot of misunderstandings of vibrations is the over use of the word Torsionals and or Harmonics. These words are used to shotgun every type of vibration and have reached the point of no meaning.
I have never found any place on the web that explains these dampeners altho they do mention that they exist.
The Plymouth Floating Power is shown in page 293 of C.F. Taylors book and is a torsionally decoupled mount for a four-cylinder engine. Auto.Ind.65, July 4, 12 (1931). This does not lower the vibration inside the engine it only reduces the effect on the mounting/frame.
Yours M. L. Anderson
#10
Wellington
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Posted 11 October 2001 - 16:53
Hi
Just re-thinking about it... Could it be that rpm are limited by other moving elements? like the valves...
Operated by springs, there is another problem dealing with resonnance due to the imposed motion.
Operated by a pneumatic device, I think there may be a problem when the period of the motion interferes with the inertia of such a system (it always has to compensate for the lack of potential energy -is that the correct expression?- accumulated in stressed springs).
Or maybe increasing the travelling speed of the piston in its cylinder may compromise the quality of the joints.
Any idea?
Regards
Just re-thinking about it... Could it be that rpm are limited by other moving elements? like the valves...
Operated by springs, there is another problem dealing with resonnance due to the imposed motion.
Operated by a pneumatic device, I think there may be a problem when the period of the motion interferes with the inertia of such a system (it always has to compensate for the lack of potential energy -is that the correct expression?- accumulated in stressed springs).
Or maybe increasing the travelling speed of the piston in its cylinder may compromise the quality of the joints.
Any idea?
Regards
#11
Pioneer
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Posted 11 October 2001 - 17:34
Originally posted by Wellington
Hi
Just re-thinking about it... Could it be that rpm are limited by other moving elements? like the valves...
Operated by springs, there is another problem dealing with resonnance due to the imposed motion.
Operated by a pneumatic device, I think there may be a problem when the period of the motion interferes with the inertia of such a system (it always has to compensate for the lack of potential energy -is that the correct expression?- accumulated in stressed springs).
Or maybe increasing the travelling speed of the piston in its cylinder may compromise the quality of the joints.
Any idea?
Regards
The pneumatic devices currently being used to not lack accumulated potential energy... they are basically pneumatic springs. The valves are still operated by a camshaft, just that instead of there being a spring, work is done to compress gas in a piston/cylinder arrangement... then the gas uncompresses when the camshaft lifts away and the valve closes itself just like spring action.
Make sense?
