NVH - PASS

By joining our community you will have the ability to post topics and access other forums reserved for members. Registration is quick, simple and absolutely free. Join our community today by clicking here.

Posted: Tue Jan 23, 2007 11:59 am

stands for - Noise - Vibration - harshness,

I'm on my level three masters test, this was handed to me 2 nights ago
before leavening work, I'm part way through the book and kinda stuck,
to let ya know, math was never my best subject during my school yrs,
so maybe some of ya mates can help me, "/ means divide" I have no
number pad for my LT.

The layout of the math is like this:
Crankshaft pulley dia. / Accessory Pulley Dia. = Pully Ratio
Even numbers are simple: 6 / 2 = 3

Engine RPM X Pulley Ratio = Accessory RPM
Even numbers are simple: 2400 x 3 = 7200

Accessory RPM / 60 = Accessory Frequency
Even numbers are simple: 7200 / 60 = 120Hz

Here what gets me is the odd numbers, about 15 questions of this:

Crankshaft pulley dia. / Accessory Pulley Dia. = Pully Ratio
Odd numbers 8 / 2.25 = 3.55555555555556
6 is greater than 5 so do I say 3.6 or stay with 3.5

Engine RPM X Pulley Ratio = Accessory RPM
Odd numbers 2800 x 3.6 = 10080 or 2800 x 3.5 = 9800

Accessory RPM / 60 = Accessory Frequency
10080 / 60 = 168 or 9800 / 60 = 163.3333333333
Confused

here is another - 8 / 4.75 = 1.6842105 - I think should be 1.7
am i correct? 8 is greater than 6 or 4

so 2800 x 1.7 = 4760 then divide by 60 - 4760 / 60 = 79.333333333

still Confused

, Their is no time limit on this test but would to finish this week,
this is home study course, once pass I summit and thin I go to school
for 3 days in Atlanta or George don't know which yet.

Thanks mates for any help, this is tough test, their more to it than just
that, 200 hundred page book.

Posted: Tue Jan 23, 2007 12:35 pm

Quote:

Crankshaft pulley dia. / Accessory Pulley Dia. = Pully Ratio
Odd numbers 8 / 2.25 = 3.55555555555556
6 is greater than 5 so do I say 3.6 or stay with 3.5

If you are rounding to 1 decimal place then it's 3.6.

Quote:

here is another - 8 / 4.75 = 1.6842105 - I think should be 1.7
am i correct?

Yes.

Posted: Tue Jan 23, 2007 12:40 pm

Wow crossfire! Shocked

I'm taking DC Circuits and elementary algebra at the same time... talk about confusion!!

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

The rule is:

Add 5 to the digit you want to lose, and then drop it.

1.474312 + 0.05 = 1.524312, so 1.5

Or, just remember that 5 or more rounds up, less than 5 rounds down.

The hard bit is remembering that
1.449999999999 is 1.4 or 1.45

I don't know what you've been told to do, but I would always quote to four significant figures:

1.6842105 becomes 1.684
79.333333333 becomes 79.33
163.33333333 becomes 136.3

because almost all physical measurements can only be measured to about three figures accurately without using laboratory techniques. The exceptions are time and frequency, which may of course have a bearing here, but even then you'd be struggling to get five significant figures.

Posted: Tue Jan 23, 2007 12:46 pm

In our DC Circuits lab, the professor told us to round to the nearest even number (2, 4, 6, etc) to get a 3 didget number... Like if you have 75.35845, you would just say 75.4 ... but that's electronics... Confused

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

^^^ That gives you 2 1/2 digits, which I suppose would be appropriate for field measurements. I can't think of any other reason for it.

Posted: Tue Jan 23, 2007 6:40 pm

Thanks so much,

DD, weasel, thud, you've been a lot help,

The + 0.05 is working great. Very Happy

I must score a 85% or better to pass this test.

weasel it seem your into or maybe circuit design and or repair,
thats great, i hope you succeed, thats something I wanted to do also

I'm out of that step now, Engine Accessory Formula,
next is Engine Firing Frequency here the formula for that:

Calculate engine firing frequency by the following,

Divide the engine rpm in which the vibration occurs by 60
Example, RPM 2,400 / 60 = 40
Multiply that number by the number of cylinders in engine
40 x 6 (six cylinder engine) = 240
Multiply that number by 0.5 for the engine firing freqency
240 x 0.5 = 120Hz

This is deep, 1st question: eight cylinder engine,
What would the engine firing frequency be at the following engine speed?
1,000 rpm _____________
1,500 rpm _____________
2,000 rpm _____________
2,800 rpm _____________
3,200 rpm _____________

anyway, thanks for the help... Very Happy

Posted: Tue Jan 23, 2007 7:32 pm

thud419 wrote:

Or, just remember that 5 or more rounds up, less than 5 rounds down.

The hard bit is remembering that
1.449999999999 is 1.4 or 1.45

Depending on how much of an arse your teacher is, this may not be entirely true.

As a rule- greater than 6, round up. Less than 4, round down. The difference comes when you have a five at the end, followed by nothing but zeros. Take this example for instance:

9.1215000

If you want to round to the thousandths, the number would be 9.122.

Now, to throw you off, consider the next example:

9.1225000

If you want to round to the thousandths, the number would be 9.121.

Confusing? This is the most statistically correct way to do rounding. In the event that a number ends in a 5 (followed by an infinite number of zeros) and you want to round to the place PRECEEDING the 5, then you use this rule: if the number to left of the 5 is odd, then you round up. If the number to the left of the 5 is even, then round down. This way, theoretically, 50% of the time you are rounding up, 50% of the time you are rounding down. Did that make sense? I hope so.

Anyway, for the above problem that you mentioned with the various engine firing frequency questions� you can use this simple formula to figure it out:

(x/60) * 8 * .5, where x is the engine speed.

Example: for an engine speed of 1000 rpm, you would have

(1000/60) * 8 *.5 = 66.7

The answers to your questions are

66.7, 100, 133.3, 186.7, 213.3 (respectively)

I hope this helps. Very Happy

Posted: Tue Jan 23, 2007 8:27 pm

9.99999999999999999999999999999999999999..... to infinity = 10 Fact!

10x = 99.999 (to infinity)
x = 9.999 (to infinity)

10x-x= 9x therefore 99.99 (infinity) - 9.99 (infinity) =90
9x = 90
x = 10

QED

Now, does anyone want the proof that root 2 is irrational?

Posted: Tue Jan 23, 2007 8:50 pm

Crossfire - I dare you to work that equation into your next bait!!
Bruin

Posted: Tue Jan 23, 2007 8:53 pm

jojo, thanks a bunch, Including the others, I came up close to the same
as you,

66.8, 100, 133.3, 186.8, 213.2, I'm sure this will pass me,
with the help of weasel, thud, you, I can see now how to my numbers,
Y'all seem better than the teacher I had in school Very Happy

weasel, I've already been through my basic electrical, my next is
after this is advance electrical, tho, I only work in ohms law, voltage,
amps, so algebra is not required for me too know, tho, It would hurt
to know it, maybe I'll buy me some books.

Thanks,

DD, where did you get that figure at, a book Very Happy

Posted: Tue Jan 23, 2007 9:21 pm

^^^

If you guys need help with your electrical, I can probably help with that. I got my degree in electrical engineering, so I like to think I am somewhat proficient in that area.

By the way Dan- 90 * infinity is undefined and therefore cannot be computed as shown. Infinity is not a definied number per se. You cannot perform calculations with infinity as you would an integer. It is not a 'real' number, but a limit.

I know, I am quite a nerd in this area. I was only one class away from that minor in math, but I was too lazy to take it.

Posted: Tue Jan 23, 2007 9:35 pm

When it comes to electricals I have only one pearl of wisdom to pass on.

Never, ever, ever trust an electrician with no eyebrows. Laughing

Posted: Tue Jan 23, 2007 9:35 pm

BRUIN wrote:

Crossfire - I dare you to work that equation into your next bait!!

Hum, new sig material, whats the bet?

Posted: Tue Jan 23, 2007 9:43 pm

jojo - gotta disagree. A maths prof told me the proof many moons ago and I am happy to take his word for it. I think he still teaches imaginary numbers and things surreal at the same Uni.

Posted: Tue Jan 23, 2007 10:33 pm

crossfire wrote:

after this is advance electrical, tho, I only work in ohms law, voltage, amps, so algebra is not required for me too know, tho, It would hurt to know it, maybe I'll buy me some books.

Uh... I hate to break this to you, but we had lots of calculations and home exercises with our DC and AC courses. Do as many exercises as you can, and do some extra math problems on your own. Talk to your classmates and solve some problems together.

Good luck with the studies Thumbs up

DON'T FEED THE TROLLS!!! · Posted: Tue Jan 23, 2007 10:50 pm

This is one of those threads that just means absolutely nothing to me..

Right over my head.

Posted: Tue Jan 23, 2007 10:52 pm

^^^^

Is that why you can't you can't tune your avatar to the right frequency? Laughing

Posted: Tue Jan 23, 2007 11:22 pm

crossfire wrote:

weasel it seem your into or maybe circuit design and or repair, thats great, i hope you succeed, thats something I wanted to do also

Close.. I want to repair the machines that make the products that circuit designers design Smile

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

jojobean wrote:

9.1215000

If you want to round to the thousandths, the number would be 9.122.

Now, to throw you off, consider the next example:

9.1225000

If you want to round to the thousandths, the number would be 9.121.

I think you mean 9.122, ie round down to the nearest thousandth. 9.121 is 1.5 thousandths out. Whereas as far as I can see the options are 9.122 (round down) and 9.123 (round up).

It is true that 5 may have a statistical effect, but it is minor - most of the figures you come across are not 5 followed by all zeros. They are 5 followed by something, or 4 followed by something large.

@Dan Druff, If you prove root 2 is irrational, I'll prove one horse has an infinite number of legs.

@crossfire, no problem, glad we could help.

Since irrational numbers have been mantioned; around here we measure engine speed in radians per second: rads/s = Hz * 2 *pi. Which of course means that all your engine speeds are irrational, but engine speed * gearing * wheel diameter(in metres) = vehicle speed in m/s. Of course that proves that at all times either the speed of the engine, the speed of the vehicle, or the diameter of the tyres is irrational.

Posted: Wed Jan 24, 2007 12:43 am

419weasel wrote:

Close.. I want to repair the machines that make the products that circuit designers design Smile

Thats awesome weasel, never thought of that, good luck Thumbs up

Posted: Wed Jan 24, 2007 1:40 am

@thud419,

Your correct, but what about the unknown "Tire Revolution Per Second"
Wouldn't we start by verifying tire size on vehicle.
Tire size formula,
Tire diameter = 2(Aspect Ratio x Tire Width)/2540 +Wheel Diameter
Tire P195/70R15
70 x 195 = 13650
13650 / 2540 = 5.38
5.38 x 2 = 10.76
10.76 + 15 = 25.76 inches

Revs at 5mph = (Tire Diameter) - 20800/25.76 = 807.45
807.45 x 5 = 4037.25
4037.25/3600 = 1.12 revs @ 5mph

If my math is correct, once this is obtained I can use the vibration formula.. Yea my next step is tires and wheels, this is Confused

I got the
math down how to do the other, thanks for the help, I'm half through
the book. Very Happy

Posted: Wed Jan 24, 2007 1:47 am

Tricia wrote:

Talk to your classmates and solve some
problems together, Good luck with the studies Thumbs up

Well, I don't have class mates as of now, do have 2 calculators,
standard and scientific, Thanks

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

Wheel revs is just engine revs x gearing, where the gearing is the total (product) of gearbox, differential and anything else.

Unless you're testing the entire vehicle on a rolling road, that's probably a moot point for you. You'll probably be testing wheels on a separate rig to engines.

Posted: Wed Jan 24, 2007 1:25 pm

Dan Druff wrote:

jojo - gotta disagree. A maths prof told me the proof many moons ago and I am happy to take his word for it. I think he still teaches imaginary numbers and things surreal at the same Uni.

I see your point there Dan... I didn't realize that when you said 'to infinity' you meant and infinite number of nines. Embarassed

I thought you were multiplying 90 * infinity, which cannot be done. I can see that equation is quite interesting. I have never seen that proof before.

thud419 wrote:

I think you mean 9.122, ie round down to the nearest thousandth. 9.121 is 1.5 thousandths out. Whereas as far as I can see the options are 9.122 (round down) and 9.123 (round up).

You are correct sir! It is definitely 9.122 on that last one. I was trying to show that 9.1215 and 9.1225 would be rounded to the same number, 9.122. I'll edit that in my original one.

crossfire wrote:

after this is advance electrical, tho, I only work in ohms law, voltage, amps, so algebra is not required for me too know, tho, It would hurt to know it, maybe I'll buy me some books.

You will definitely need to sharpen up your algebra skills for circuit theory. There is a lot of algebra involved in that. Depending on how deep you get into circuit theory, a need for a basic understanding of differential equations and some calculus might be involved. If you are interested in some books that might be of help, I can definitely point you in the direction of a couple.

It is cool to see other people interested in electrical stuff, as nerdy as that sounds! I do power engineering, so I just deal mostly with high voltage, extra high and OCCASIONALLY ultra high voltage stuff (mostly 69,000-500,000V). I also do some basic protection programming as well.

I do like circuit design. A few years ago I got into designing tube guitar amplifiers. It was really fun, though quite expensive. It was pretty cool designing something like that and building it from scratch.