NVH - PASS

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Posted: Wed Jan 24, 2007 1:33 pm

Well Impresed!!

I not only find a scam baiting forum that gives me much gigglymode in the thermalloaders, I then find a thread discussing engineering/physics Shocked

truly a font of all knowledge

I am back at University later this year, I'll call on you guys an gals when my brain hurts Embarassed

.

Posted: Wed Jan 24, 2007 1:35 pm

My brain alread hurts and I'm only 2 weeks into my degree! Shocked

Posted: Wed Jan 24, 2007 1:39 pm

Charlie Muggins wrote:

....The last time I was a student America was killing it's young men in some futile war the other side of the globe, whilst announcing it's intentions to go to the moon....... No change there then!

^^^^

You might want to keep the politics out, the mods do bite when it comes to that. There are a lot of different views here on this board, so it is best to keep discussions like that elsewhere (not on this forum). Sorry for the backseat modding, I just don't want this thread locked.

Trust me, your brain will hurt quite a bit from the math!

Posted: Wed Jan 24, 2007 1:40 pm

jojobean wrote:

Sorry for the backseat modding

It's ok, I've been watching the thread. Cool

Posted: Wed Jan 24, 2007 1:48 pm

Point taken.......Trots off to shread CND tee shirt and delete comment

Posted: Wed Jan 24, 2007 9:01 pm

The vibration formula:

1. Divide vehicle speed kph by 8 (mph by 5)
The resulting number indicates the number of 8 kph (5 mph increments.
for example, If the corresponding speed of an NVH problem on a vehicle
is 72.4 kph (45 mph), the resulting 8 kph (5 mph) Is nine
8 kph (5 mph) increments = Vehicle speed mph/5

2. Obtain the corresponding tire size frequency at 8kph (5 mph) from the
Revolution Chart.(I have a chart in book with tire sizes and Rev/Sec @
5 mph)
Example 1: If the tire size on the vehicle is LT295/40R20, then the
revolution per second a 8 kph (5 mph) is 0.99
Example 2: If the tire size on the vehicle is P185/70R14, then the
Revolution per second at 8 kph (5 mph)is 1.19

3. Multiply the 8 kph (5 mph) increments by the revolutions per second
at 8 kph (5 mph)
In example 1, the results is 9 time 0.99 or 8.9 Hz. This means the
tire/wheel assembly has a frequency of 8.9 Hz or (9 Hz) at the vehicle
speed of 72.4 kph (45 mph)
In example 2, the results is 10.71 Hz or (11Hz), this means the tire
/wheel assembly has a frequency of 10.71 Hz or (11Hz) at the vehicle
speed of 72.4 kph (45 mph)
Tire/wheel frequency = 8 kph (5 mph) increments x tire revolutions

The calculated frequency of 9Hz is the first-order tire/wheel frequency

Determine revolutions per 8 kph (5 mph) using the following formula:
Rev at 8 kph (5 mph) = 20800/tire diameter/3600 x 5
Example using above tire size:
20800/tire diameter - 20800/25.76 = 80745
807.45 x 5 = 4037.25
4037.25/3600 = 1.2 revs at 8 kph (5 mph) Confused

Where are they coming up with 20800 and 3600?
My book does not tell me this... Confused

? What would the first and second order tire/wheel frequency be at the
following vehicle speeds
32 kph (20 mph) _________________
56 kph (35 mph) _________________
80.5 kph (50 mph) ________________
120.7 kph (75 mph) _______________

? Using a P265/75R15 tire, what is the tire diameter

30.64

If math is correct:
75x265=19875
19875/25440 = 7.82
7.82x2 = 15.64
15.64 + 15 = 30.64

Still don't know where their coming up with the 2540
Maybe ye mates can figure it out, this is tough... Confused

my brain hurts...

Posted: Wed Jan 24, 2007 9:07 pm

No worries people, Persephone rolled the dice....... the answer is 5 Cool

Posted: Thu Jan 25, 2007 11:26 am

Looks like jojo and I have similar interests, kind of. I was a self-taught electrical engineer and engineering technician. I went to work for 20 years loving my job. I love electronics, it is still magical to me. My favorite thing about electronics, specifically electrical current flow is that it is invisible.

As to Algebra and higher maths, embrace it ! You all have the ability to learn it, it is key to understanding life as well as making money doing something you love. At some point you will start to "see" equations in hallucinations as well as in real life....

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

Quote:

Rev at 8 kph (5 mph) = 20800/tire diameter/3600 x 5

From first principles:

distance per wheel revolution = pi d

if d is in inches, then so is the distance; divide by 63,360 to get miles.

miles/revolution = pi d / 63360

revolutions/mile = 63360 / (pi d)

multiply top and bottom by 1 hour

rev per hour / mile per hour = 63360 / (pi d)

seconds = hours x (seconds in minute) x (minutes in hour)
seconds = hours x 3600

rev per second = rev per hour / 3600

rev per second / mile per hour = 63360 / (pi d) / 3600

to convert from mph to 5mph units, divide by 5. eg. 20mph is 4 5mph units.

In this case, since mph is on the bottom, we multiply.

rev per second / 5mph = 63360 / (pi d) / 3600 x 5

The trouble is, I make 63360 / pi = 20168, ie 3% lower than the figure you have.

5mph = 8kph, accurate to 0.5%, so that isn't it.

Maybe it's a Finagle Factor. Or maybe it only works for small values of pi.

Posted: Thu Jan 25, 2007 8:36 pm

thud419,
That is awesome, you came very close to breaking the code, Cool

No where in my book do they break that down like you did, so
those figures have to already be in the math system to figure
the frequency and revs/Sec, once i get in class, I'll ask the
teacher to break it down for me and I'll catch up with or PM you
the results, I'm done with my tire and wheel figure, tho, one last
question:
?. Does the tire size make a difference in frequency at the same speed.
Lets do the math and find out:
Using a P265/75R15 (45 mph)
75 x 265 = 19875
19875 / 2540 = 7.82
7.82 x 2 = 15.64
15.64 + 15 = 30.64

Revs at (5 mph)
20800 / 30.64 = 678.85
678.85 x 5 = 3394.25
3394 / 3600 = 0.94
0.94 revs at (5 mph)

45 (mph) / 5 = 9
9 x (revs from above) 0.94 = 8.46 0r 8 Hz

Using a P185/75R14 (45 mph)
75 x 185 = 13875
13875 / 2540 = 5.46
5.46 x 2 = 10.92
10.92 + 14 = 24.92

Revs at (5 mph)
20800 / 24.92 = 834.67
834.67 x 5 = 4173.35
4173.35 / 3600 = 1.16
1.16 revs at (5 mph)

45 (mph) / 5 = 9
9 x (revs from above) 1.16 = 10.44 or 10 Hz
So the answer would be yes.

Thud419, my next and last test is Propeller Shaft Frequency Formula,
quite a bit of pages on this subject, knowing the tire/wheel frequency
I should be able to calculate the propeller shaft frequency.

Thanks for all the help

Posted: Sat Jan 27, 2007 4:30 pm

Hey mates, I need a little more help if you
don't mind..

Porpeller Shaft Frequency

Knowing the tire/wheel frequency allows for easy
calculation of propeller shaftv frequency.
To determine propeller shaft frequency, multiply
tire/wheel frequency by the ratio of the rear axle.
Calculate propeller shaft frequency by these steps:

1. Obtain the rear axle ratio from the metal tag on
the diff. cover.

For example, inspection of the diff. cover on a vehicle
with an NVH problem at 72.4 kph (45 mph) reveals a rear
axle ratio of 3.9

2. Multiply the tire/wheel ffrequency of 9 Hz
(determined in last section) with the rear axle ratio
of 3.9

This results in a propeller shaft frequency of 35.1 Hz
or (35 Hz) at the vehicle speed of 72.4 kph (45 mph).
. propeller shaft frequency = tire/wheel frequency x
axle ratio

The calculated frequency of 35 Hz is the first-order
propeller shaft frequency. The second-order frequency
of the propeller shaft frequency is twice this number,
or 70 Hz.

thud419,
They make it sound so easy using the examples,
but what if the axle ratio is 3.08:1, ok, i can
configure the tires: 245/70R16 (diameter(29.50))
(revs)0.98

Vehicle speed/5 x tire Revs = tire/wheel frequency

Question:
4. what would the first and second order propeller
shaft frequency be at the given speeds?
56 kph (35 mph) 63, 126 (if my math is correct)
72.4 kph (45 mph) _____________________
80.5 kph (50 mph) _____________________
96.6 kph (60 mph) _____________________
120.7 kph (75 mph) ____________________

5. same thing again except using P195/60R15 with 3.08:1
axle

6. same thing again except using P225/75R15 with 4.11:1
axle.

With my course kit, it also came with a tool called
a Sirometer, cool tool how it works, here a url if
you've never seen one.

http://treysit.com/TREYSIT_Presserei_Schwalmstadt/Sirometer/sirometer.html

Once I get done with these axle propeller test, I'll
be done, the i can do my 50 question test.

I really do thank you all your help, especially thud419,
I mean it too..

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

Someone's got lost, either you or me.

Speed = 35mph
Speed/5mph = 7 5mph

Wheel Freq = 0.98 Hz/5mph

Wheel frequency = 0.98 x 7 = 6.85 Hz
Prop shaft freq = 6.85 x 3.08 = 21.11 Hz

One of us is a facter of 2.98 out.

Posted: Sat Jan 27, 2007 6:37 pm

My numbers are wrong, yep lost but 0.98 is revs, to figure
frequency/Hz:
Vehicle speed/5
35 /5 = 7
7 x 0.98 = 6.86 Hz/frequency

6.86 x 3.08 = 21.12

Hee hee, thud419 I'm glad you seen my mistake, I did the figure
wrong, but u just showed me another way of doing it. you only too
one step to figure frequency, by the book, I've been breaking down
the math and doing it in steps, but I do see how to do it now.
In other words 3.08 or 4.11 you just multiply it like you see it, I don't
have to round up or round down those number, that whats was Confused

ing.

thanks for your reply.

Posted: Thu Feb 01, 2007 9:49 am

Thanks mates, for all your help, thud149 I really thank you for
helping me through the math, I did pass with 90%, now I can
get in to my Teacher led course, which is two days in Atlanta
and any other coures...

Very Happy

cf

Posted: Thu Feb 01, 2007 3:20 pm

Congrats to you crossfire and to all the other 419Eater gearheads. A 90% does not sound like just a "pass" to me. I would rate that as an "A". We need to make a SAE badge.

Posted: Thu Feb 01, 2007 6:33 pm

CLG, that would be nice, a ASE badge,
we would have too prove we passed to receive the badge
which I can

Thanks too you all

cf

Posted: Fri Feb 02, 2007 2:48 am

Nevada Vehicile Highway Pass? Pick one up in Tonopah, 10$. And off you go. Ever seen the movie "Tremors"? Easy.