Aluminum rod reduces shock load to crank

[digger]

You could make an aluminium rod that has exactly the same rigidity as a steel rod.It would weigh the same as a steel rod,or about 99.8% as much as a steel rod.In round figures,aluminium is 1/3 the density and its elastic modulus is 1/3.
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don't forget that flexibility also comes from the big and little end stiffness which is not under just axial load but subjected to bending moment aswell and therefore the aluminium is going to be more stiff (and stronger) in bending near the bearing area for the same weight

[Kevin Johnson]

You could make an aluminium rod that has exactly the same rigidity as a steel rod.It would weigh the same as a steel rod,or about 99.8% as much as a steel rod.In round figures,aluminium is 1/3 the density and its elastic modulus is 1/3.

All this means is a LIGHTER rod (if it's the same length) will stretch or compress more for a given force,REGARDLESS OF WHETHER IT IS ALUMINIUM OR STEEL.If your aluminium rods are 2/3 the weight of a steel rod,they have more cushion and will stretch/compress 50% more.If you made a steel rod the same weight,it would do exactly the same.

A rod that has more length will also stretch or compress more for a given applied force.

(Length divided by weight) would be in proportion to the amount the rod will stretch/compress for a given force.That's a fair indication of the "cushion" effect.It doesn't matter if it's aluminium or steel,unless the length/weight ratio changes.

In the patent, a key claim is that simply using a different aluminum alloy heretofore not used will result in a higher compressive yield strength and in this case will result in approximately a 25% increase over then-current state-of-the-art. The densities of the aluminum alloys are very similar to oneanother (as are the moduli of elasticity, as you point out).

... 2014-T6 aluminum alloy, which has a compressive yield strength of 58 ksi. More recently, 7075-T6 aluminum alloy has been used, which has a substantially higher compressive yield strength of 72 ksi.

... 7055-T77511, also referred to as HP007. This aluminum alloy has been available from Alcoa for some time, but never made into extruded bar stock for forging. By working with Alcoa, the inventors of the invention described herein obtained 7055-T77511 aluminum alloy from Aluminum Company of America “Alcoa” in extruded bar stock suitable for forging.

Under testing in drag racing engines generating in excess of 6,000 horsepower, the improved high performance aluminum connecting rod of the present invention has been found to have a compressive yield strength of 25 percent greater than 7075-T6.

... wherein said high performance aluminum connecting rod has a compressive yield strength of approximately 90 ksi.

[Kevin Johnson]

it is true that flexible components can absorb high frequency or extremely short duration load spikes (from poor combustion/knock etc) just like a suspension system. The crank, rod, piston is a spring mass system afterall

I am wondering if the significantly different speed of sound in aluminum versus steel is important to the selection of aluminum over steel. This would tend to create destructive interference when combined with a steel crankshaft and careful tuning could allow a crankshaft to survive longer at peak design loads. Jon posed a question of how to allow nitro cranks to survive longer. If you have an excess in compressive yield strength available as a safety factor then you can afford to vary the harmonics of individual connecting rods in positioning along the crankshaft as a secondary means of tuning the rotating assembly. Careful attention to mass distribution should allow the dynamic balancing to be otherwise equivalent.

http://wiki.answers.com/Q/How_does_the_ ... und_in_air

typical sound velocities (longitudinal waves) in different materials:
air 343 m/s
aluminium alloyed 6380 m/s
aluminium unalloyed 6320 m/s
aluminium oxide 9000-9850 m/s
steel (austenitic) 5650-5850 m/s
steel (ferritic) 5920 m/s
steel casting 5730 m/s

[nhrastocker]

Taking it one step more.....Suppose you have an engine that's breaking crankshafts with steel rods.Lets say this engine is not an alcohol or nitro fuel engine.. Would the crank last longer with aluminum rods? Yes,many variables,just a theory question.

There are too many variables. Moreover, merely stating "variables" tends to imply that higher order combinations of variables (and variables themselves) can be directly equated. Look at how Transcendental numbers differ fundamentally from numbers that are algebraic http://en.wikipedia.org/wiki/Transcendental_number

You need to guard against the fallacy of equivocation.

[Kevin Johnson]

Taking it one step more.....Suppose you have an engine that's breaking crankshafts with steel rods.Lets say this engine is not an alcohol or nitro fuel engine.. Would the crank last longer with aluminum rods? Yes,many variables,just a theory question.

There are too many variables. Moreover, merely stating "variables" tends to imply that higher order combinations of variables (and variables themselves) can be directly equated. Look at how Transcendental numbers differ fundamentally from numbers that are algebraic http://en.wikipedia.org/wiki/Transcendental_number

You need to guard against the fallacy of equivocation.

Time to brush up on your set theory, eh?

http://en.wikipedia.org/wiki/Russell's_paradox

Yes, that shit.



It is not a good sign that engineers need to be reminded of basic issues in logic more than a century after they were identified formally.

[140Air]

I am wondering if the significantly different speed of sound in aluminum versus steel is important to the selection of aluminum over steel. This would tend to create destructive interference when combined with a steel crankshaft and careful tuning could allow a crankshaft to survive longer at peak design loads. Jon posed a question of how to allow nitro cranks to survive longer. If you have an excess in compressive yield strength available as a safety factor then you can afford to vary the harmonics of individual connecting rods in positioning along the crankshaft as a secondary means of tuning the rotating assembly. Careful attention to mass distribution should allow the dynamic balancing to be otherwise equivalent.
s

If you look at the speed of sound in the rod compared to burn duration times, you should think there is no effect. Same for crank flex timings and harmonics. These phenomena are way much slower than speeds of sound. The coupling coefficient should be virtually nil. Finally, a difference in the speed of sound in the rods only changes the phase of impulses arriving at the crank compared to minute differences in the crank angle, not the time intervals between pulses.
However, if we are talking about detonation events, this becomes more interesting. Al might dampen shock wave propagation compared to steel. But, detonation is not usually a cause of crank failure when the pistons and rods themselves are not damaged, ...as far as I know... Is this correct?

[SchmidtMotorWorks]

Even if you could make a steel rod that had the same properties in regards to weight and stiffness, there will still be reasons to run aluminum rods relating to the damage that a broken rod does to the block.
There are only a few teams that can afford not to repair and reuse blocks that have been windowed.
I make and sell replacement bearing saddle inserts for those engines.

Parts are not always chosen for one or two particular technical reasons, there are often supplier relationship issues that have higher priority.

[SchmidtMotorWorks]

Jon posed a question of how to allow nitro cranks to survive longer. If you have an excess in compressive yield strength available as a safety factor then you can afford to vary the harmonics of individual connecting rods in positioning along the crankshaft as a secondary means of tuning the rotating assembly. Careful attention to mass distribution should allow the dynamic balancing to be otherwise equivalent.

Kevin, please I'm begging you, go find a nitro team in your area (even a nostalgia team will do) volunteer and get a feel for the priorities and decision making process involved in running a nitro car. Force yourself to be quiet and not suggest any solution to any problem for 6 months, just try to learn the what they do and why.

[SchmidtMotorWorks]

It is not a good sign that engineers need to be reminded of basic issues in logic more than a century after they were identified formally.

It is a worse thing to waste peoples time with distractions and not show any constructive process that results in improvement.

I'm curious can you think of a single crew chief that would be interested in Transcendental Number?
Do you really think that going down that rabbit hole is the best thing they can do with their time and energy to achieve the only goal that matters,,,getting their sponsors advertising in the winners circle?

[SchmidtMotorWorks]

But, detonation is not usually a cause of crank failure when the pistons and rods themselves are not damaged, ...as far as I know... Is this correct?

It can be, depending on the index of rotation when it occurs.

[Kevin Johnson]

It is not a good sign that engineers need to be reminded of basic issues in logic more than a century after they were identified formally.

It is a worse thing to waste peoples time with distractions and not show any constructive process that results in improvement.

You mean like reading through a patent and pointing out an alternate mode of manufacturing? A pretty obvious one at that.

I'm curious can you think of a single crew chief that would be interested in Transcendental Number?

You mean like using Pi in a calculation? Yes, I know it has been reduced to a button on a calculator like e.

Do you really think that going down that rabbit hole is the best thing they can do with their time and energy to achieve the only goal that matters,,,getting their sponsors advertising in the winners circle?

I think I am being rather patient with someone that apparently does not see the irony of extolling higher orders of smoothness in juxtaposition with this exchange.

[Kevin Johnson]

I am wondering if the significantly different speed of sound in aluminum versus steel is important to the selection of aluminum over steel. This would tend to create destructive interference when combined with a steel crankshaft and careful tuning could allow a crankshaft to survive longer at peak design loads. Jon posed a question of how to allow nitro cranks to survive longer. If you have an excess in compressive yield strength available as a safety factor then you can afford to vary the harmonics of individual connecting rods in positioning along the crankshaft as a secondary means of tuning the rotating assembly. Careful attention to mass distribution should allow the dynamic balancing to be otherwise equivalent.
s

If you look at the speed of sound in the rod compared to burn duration times, you should think there is no effect. Same for crank flex timings and harmonics. These phenomena are way much slower than speeds of sound. The coupling coefficient should be virtually nil. Finally, a difference in the speed of sound in the rods only changes the phase of impulses arriving at the crank compared to minute differences in the crank angle, not the time intervals between pulses.
However, if we are talking about detonation events, this becomes more interesting. Al might dampen shock wave propagation compared to steel. But, detonation is not usually a cause of crank failure when the pistons and rods themselves are not damaged, ...as far as I know... Is this correct?

My sense is that vibration from the combustion in this type of engine is related to that of rocket motors and a higher order than that normally seen in an IC engine. This vibration would be transmitted through the piston to the rod through the power and exhaust stroke.

[SchmidtMotorWorks]

You mean like reading through a patent and pointing out an alternate mode of manufacturing? A pretty obvious one at that.

In the context of the reality of the industry your suggestion is useless.

You mean like using Pi in a calculation? Yes, I know it has been reduced to a button on a calculator like e.

So you are saying that a crew chief should spend his time learning about how calculators work?

Do you really think that going down that rabbit hole is the best thing they can do with their time and energy to achieve the only goal that matters,,,getting their sponsors advertising in the winners circle?

I think I am being rather patient with someone that apparently does not see the irony of extolling higher orders of smoothness in juxtaposition with this exchange.

Next time you have less than 1 second to spare you can tell me everything you know about design of valve motion. Maybe you can link some antique from Taylor.

[Kevin Johnson]

You mean like reading through a patent and pointing out an alternate mode of manufacturing? A pretty obvious one at that.

In the context of the reality of the industry your suggestion is useless.

Given that my suggestion stemmed from another patent on rod manufacturing by a major manufacturer of rods I suggest you do a tad more research; this is a continuing theme however.

You mean like using Pi in a calculation? Yes, I know it has been reduced to a button on a calculator like e.

So you are saying that a crew chief should spend his time learning about how calculators work?

I am not sure how to tactfully respond to this.

Do you really think that going down that rabbit hole is the best thing they can do with their time and energy to achieve the only goal that matters,,,getting their sponsors advertising in the winners circle?

I think I am being rather patient with someone that apparently does not see the irony of extolling higher orders of smoothness in juxtaposition with this exchange.

Next time you have less than 1 second to spare you can tell me everything you know about design of valve motion. Maybe you can link some antique from Taylor.

As I said, the irony is lost.

[SchmidtMotorWorks]

Kevin can you demonstrate with specific examples how your wiki link is useful to anyone that makes decisions for a professional motorsports engine development program?