driveshaft conversion

Duk
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Re: driveshaft conversion

Post by Duk »

MD wrote:Hahaa. I can see myself going up another level soon if this keeps going.

I am going to make a torque tube ...

Anyone got a cheap Porsche for sale :mrgreen:
Gunna need a big lathe for that!

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Re: driveshaft conversion

Post by MR2 Zig »

Gunna need a big lathe for that!


Got one here! 21inch by 20 feet between centers!
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Duk
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Re: driveshaft conversion

Post by Duk »

Rather than looking toward the front engined Porsche's MD, how about looking at the rear TA Corvette's?

Lol, 'Rubber Biscuit' :P
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MD
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Re: driveshaft conversion

Post by MD »

Naah. That's just an Alfa shaft with a big French Letter over it. :mrgreen:

Make no mistake, the Porsche set up has problems of its own especially come service time..however this is an Alfa site and so Iam going to stop this sideways mental doodling.
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PietereQ
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Re: driveshaft conversion

Post by PietereQ »

After having driven the setup for a while I guess I'll chime in.
As MD said, there is a rather unpleasant hammering/rattling noise in around 1-1.2K rpm. Past this and it's totally gone. I would rather find it unacceptable in a street car, but on a racer is fine. Other than that, no balance issues or any unsettling noises so far :)

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MD
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Re: driveshaft conversion

Post by MD »

Vindication at last !!

Hey Zeefa. Took your advice and sent my triple CV shaft on a 3 500 Km round trip to the Benincas workshop for balancing. Finally it is good.

Hey Jes, you never did tell us how your CF shaft with the swanky front coupling went on the racer (or at least I must have missed the post).
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Re: driveshaft conversion

Post by kevin »

MD I see you have three CV's . From another discussion on on having a vibration damper on front pulleys what are you doing about the prop where you do experience "pulsation caused by each engine cylinder firing creates a pulsating torsional energy. This energy, which otherwise could destroy system components, is absorbed by the rubber section."
I also realise you don't vibrations from been out of phase etc with cv as well but it worth reading .
http://www.machineservice.com/products/ ... ve-shafts/

This is a quote a copied from a leading propshaft manufacturer who has numerous patents out . They are also motorsport orientated not only industrial .
I have noticed a bit a trend amongst prop designers in certain race cars to use torque resilient tubes here in UK . I did post a pic one a few months back on a GTV which had two uj and a cv .
Its an interesting read in the design when they take into consideration no of cyl , flywheel mass , hp , torque , rpm in order to get the correct " spring " or resilience from the rubber .

Here is article and also posted is another on types of prop vibration you can experience . I'm in the process of getting one of these props made here in uk due to issues I have on my project car .

ll rotating equipment have one or more frequencies. When the system rotational speed corresponds with one of the natural frequencies, a condition of resonance occurs. At resonant speeds, the amplitude of the system vibrations are greatly magnified. If the system is allowed to operate at resonance, the vibrations can quickly destroy bearings, bolted joints, instruments, mounts, or other associated equipment, as well as the drive shaft. Next to catastrophic overloads, operating at or near resonance are probably the fastest way to damage rotating equipment.



The spring constant of the tubular drive shaft is very efficiently reduced by using an ISO-TEC two-tube shaft, one with a larger diameter than the other. The smaller tube fits inside the larger one and they are joined together with a molded-in rubber element. The thickness, length and durometer of the rubber section determine the spring constant, and therefore the natural frequency of the drive system. The ISO-TEC shaft provides additional protection, isolating the drive and the driver. Even if the systems are not operating at their natural frequency, the pulsation caused by each engine cylinder firing creates a pulsating torsional energy. This energy, which otherwise could destroy system components, is absorbed by the rubber section.
There are five types of drive shaft induced vibrations that are associated with the installation parameters of a drive shaft. We’re going to explain all of them in the hope that you can “head-off” a problem before it occurs. They are:

Transverse vibrations
Torsional vibrations
Inertial excitation vibrations
Secondary couple vibrations, and…
Critical speed vibrations


Transverse Vibrations

Are caused by imbalance.

All drive shafts should be balanced at their application speeds.

Think about this…when was the last time you DID NOT have your tires balanced?
Drive shafts are heavy…much heavier than a tire
Drive shafts rotate much faster than a tire.
Common sense says that we should not hesitate to balance an object that is heavier and rotates faster than our tires…especially if there is a possibility that it can lead to a serious failure.

All drive shafts should be inspected for missing balance weights at every service interval.

A transverse vibration ALWAYS occurs at drive shaft speed, and occurs at once per revolution. If you experience a vibration that is speed sensitive, have your drive shaft balance checked at your closest Machine Service, Inc location.



Torsional vibrations

Are caused by two things:

The U-joint operating angle at the “drive” end of the drive shaft, and…
The orientation (phasing) of the yokes at each end of the drive shaft
A torsional vibration is a twice per revolution vibration.

A torsional vibration will cause the drive shaft, “downstream” of the front U-joint, to “speed up” and “slow down” twice per revolution.

That means that a power supply producing a constant speed of 3,000 RPM can actually be attached to a drive shaft that is changing speed 6,000 times per minute.

The amount of that change in speed, called the magnitude, or size of the change, is proportional to the size of the angle at the drive end of the drive shaft, or the amount of misalignment between the yokes at the drive and driven end of your drive shaft.



Torsional vibrations are SERIOUS vibrations

Why? Because when you vary the speed of a drive shaft, you not only vary the torque on all of its components, but you vary the torque on all of the components that are connected to the drive shaft Torque is LOAD.

When you vary the load, at twice per revolution, you start to bend components.

You know what happens then……the same thing that happens when you bend a can lid back and forth. IT BREAKS.



Here’s another way to explain it

Picture a drive shaft running at a constant speed and driving a truck or a large roller in a mill.
The front end of the drive shaft is connected to the power source and the torque coming out of the power source is fairly constant.
The rear end of the drive shaft is connected to the truck’s axle or to the roller and it sees varying loads based on terrain or on how much work it is doing.
As the front end produces the load, the back end passes it on into the vehicle or stationary application and if all is well, that load is relatively constant and well within the torque carrying capabilities of your drive shaft
When something happens to alter the operating angle at the front U-joint of the drive shaft a twice per revolution change in speed is introduced into the application.
The front of the drive shaft keeps going constant, but the back end of the drive shaft starts to see the twice per revolution change in speed, and is always playing “catch-up” with the front.
This causes a twice per revolution “twist” in the drive shaft
A twice per revolution “bending” moment is introduced into the drive shaft welds, slip splines, U-joints and into all of the connected components in the application.
You, in effect, run a torsional fatigue test on the drive shaft and everything used to attach it to your application.
Drive shaft manufacturers run fatigue tests on the components and welds in their drive shafts by doing the same thing in their test labs. They hold one end of the drive shaft stationary and hook the other end to a rotary actuator. Then they twist it until it fails.
If you have a torsional vibration problem you will experience drive shaft tube welds that break, splines that wear prematurely and nuts and bolts that start loosening.
You will also start to experience vibrations.
If you see a failure that looks like this, you should suspect a torsional vibration problem.
When a drive shaft is assembled, its inner components usually consist of a slip yoke on one end and a tube yoke on the other end, and they are usually assembled in relation to each other. This is called PHASING.

Most drive shafts are assembled with their yokes in line, or “IN PHASE”.

Phasing affects torsional vibrations

A drive shaft that is “in phase” and has the correct operating angles at the drive end of the shaft does not create a torsional vibration.

Drive shafts that are NOT in phase will vibrate with the same twice per revolution vibration as a drive shaft with incorrect operating angles.

The easiest way to make sure your drive shaft is in its correct phase is to mark the tube and slip yoke every time you take it apart so you can put it back in its original orientation when you re-assemble it.Re-assembling a drive shaft out of phase is the #1 cause of torsional vibration that “all-of-a-sudden appears” in your application. If you suspect that your drive shaft is not in phase, take it to the closest Machine Service location for inspection.



How do you make sure your drive shaft application will not create a torsional vibration?

Make sure the operating angle at the front of your drive shaft and the operating angle at the rear of your drive shaft are less than three degrees and are equal within one degree. Make sure these angles are correct. Rotate the pinion if the problem is in a vehicle. Shim the driving end or the driven end if the application is a stationary application. Correcting torsional vibration problems is not rocket science. Fix the angles and you will fix the problem, it’s that simple.
To make sure the torsional vibration does not enter your drive system, make the angles at each end of the drive shaft equal with each other to cancel out the torsional vibration. However, the vibration will still be there if the angles are too large…so do whatever necessary to make the operation angles small.
Make sure your drive shaft is in phase… the same phase as it was in when it was manufactured. Do not disassemble your drive shaft slip assembly unless it is absolutely necessary.
If you have a multi piece drive shaft set-up, make sure the operating angle at the front of each of your coupling shaft(s) (the shaft(s) with the bearing(s) or pillow block(s) on it (them)) are less than one and one-half degrees. Also make sure the operating angles on the rear drive shaft (usually the drive shaft with slip in it) are less than three degrees and are equal within one degree.


Inertial excitation vibrations

Inertial vibrations are also caused by the operating angle at the drive end of your drive shaft.
Inertial vibrations are created when you start changing the speed of a HEAVY drive shaft.
Inertial vibrations also create bending on drive shaft attaching components.
There is only ONE WAY to control an inertial vibration… ALWAYS make sure the operating angle at the drive end of your drive shaft is less than THREE degrees.
A large angle even if it is an “equal” angle will still cause inertia problems.


Secondary couple vibrations

Secondary couple vibrations are also caused by the operating angle at the drive end of your drive shaft.
Every U-joint that operates at an angle creates a secondary couple load that traverses down the centerline of the drive shaft.


Critical speed vibrations

Critical speed occurs when a drive shaft rotates too fast for its length.
It is a function of its rotating speed and mass and it is the RPM where a drive shaft starts to bend off of its normal rotating centerline.
As a drive shaft bends, it does two things:

It gets shorter. If it gets short enough, it can pull out of its slip and drop to the floor or ground.
It starts to “whip” up and down or back and forth like a jump rope. If it whips far enough, it will fracture in the middle of the tube.
CAUTION: If you ever see a drive shaft with a bent, fractured tube, do not replace it with a new drive shaft of the same construction.

Some ifo on CF props
http://www.machineservice.com/products/ ... ve-shafts/
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MD
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Re: driveshaft conversion

Post by MD »

Haahaaa Kevin, on page 16 of this topic set on the 28.02.2010 I was desperately trying to tell you guys EXACTLY about this:
Mats,
Enjoyed your last post. Very constuctive. While I was reading it, and idea came to mind that could see our respective approaches actually come together in a very slick way.

Using your version of CV's will give good results in terms of toughness etc which is what we all want.
The only modification I would suggest is one to keep the noise out and that could be done like one of the Ford upmarket cars do it. (Don't remember model)

What they do is use a splined shaft with one part inside the other at the front. The two splined parts are separated internally along part of the length of the shaft by a rubber bonding. The two parts do not slide or move and you could be forgiven if you beleived it was just a single shaft. This effectively puts a rubber "coupling" between the engine and the propshaft by separating the two splined parts.

I have searched high and low for an illustration but no luck. It must be called a specific name that I don't know what it is. Someone out there possibly does.

FInally to stop any other ringing noises in the shafts, they could have inserted inside them rubber dampening rings which are bonded to prevent movement and affect the balance. This is like putting your hand on a drum skin that stops the sound.

Perhaps you know the name of these "rubber splined joints" ?? "
"...an ISO-TEC two-tube shaft, one with a larger diameter than the other. The smaller tube fits inside the larger one and they are joined together with a molded-in rubber element."
So now we have a name for it :D

Top info Kevin. You get the Guru guernsey this week. :D
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Re: driveshaft conversion

Post by kevin »

I'm just slowly catching up to you . Its only when you start making custom props like I'm doing in my front mount car that you realise you got to do right . Its all about the input and output angles . Don't underestimate the role of the rubber surrounding the centre carrier bearing .

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Re: driveshaft conversion

Post by Mats »

There are a lot more variables than just angles and other installation stuff.
Regarding yoke angle phasing it's not at all as simple as described above, maybe in light trucks/pickups but almost never are the prop/drive shaft a straight line when viewed from above in a passenger car. So it's really a 3D installation.
Also Engine Fire motor torque pulsation and transmission error (gear engagement force) plays a major role in prop/driveshaft vibration problems.
It's really guessworks and black magic unless you have a very competent NVH-department backing you up and all the relevant CAD files and load cases...

So build what you feel is right and test it, if it doesn't work, change something. 8)
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Re: driveshaft conversion

Post by 75evo »

See, been telling' ya all this time. :lol:

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Re: driveshaft conversion

Post by Mats »

Well, there are some Best Practices of course. Like keeping joint angles low but not zero (no less than 1 deg.)
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Re: driveshaft conversion

Post by kevin »

MD , I get my prop back this week . Even though its a short prop of 855mm long it will be nearly identical to the rear section as in the transaxle pic above . I will find out how they balance it and get all the specs on type of GKN joints . As mentioned they us this on the lemans Aston Martins which is a much thicker torque resilient tube to handle 1000hp . These TRT's come in different sizes and differ in number of rubber strips inside them . Its also a design used on the Westfield cars as well .
Pic attached of my old bad design prop next to an Aston Martin prop .
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Re: driveshaft conversion

Post by BotswanaAlfa »

:idea: hi guys, forgive me if the idea sounds silly :lol: , but i was reading your replies and was thinking the problem in the drive shaft is pulse and initial pull off, am i right? with both exerting very large degrees of force on the drive shaft, so i was thinking of an idea which seems a bit contrary to any of those before this. my idea is perhaps to form some kind of clutch plate type thing, where the output from the engine connects to a large plate, with a secon plate mounted just behind it (as a sealed unit) with springs bridging the gap (perhaps via a tooth from the driveshaft end into a slot in the engine side where the spring can be sealed in a sort of chamber), thus on initial take off and during these pulses the springs absorb the force rather than the guibos in the middle and end. i hope that makes sense :P if not say so and ill do a quick drawing.
im not sure i explained right and have no software to draw my idea with (i havent even graduated high school yet). basically the tensile strength of the springs would have to be high to absorb the 150 hp + but once the car has pulled off the springs will only be compressing at a minimal amount as there will be little overall change in the forces before and after the clutch plate type mechanism.
i know there are som issues but you all seem quite clever. im just putting it out there as i dont have the tools, knowledge or manpower to attempt it myself.

Not to mention my alfa isnt drivable yet :oops:
Let me know what you guys think :P
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Re: driveshaft conversion

Post by Mats »

You just described a dual mass flywheel, standard on all new manual transmission cars with a few exceptions. Totally useless on a racecar because the weight is just enormous and they seen to fail prematurely if you are driving hard (dumping clutch at 7000 rpm starts and so on). Also a total PITA to tune correctly, the one in my daily driver is driving me nuts because the clutch judder is magnified by a factor of around 50 or so. :(
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