| Author |
Message |
Sojourner (Jjimage)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 01, 2006 - 8:50 am: | |
I have work in Noise & Vibration Lab at General Motor Proving Ground in late 70’s. Did noise study on (new) GMC Astro 95 DD cabover tractors. Reported 98dba from 8/92NDD oil pump.
Vibration comes from;
1) Engine pulsations…fewer cylinders the greater
2) Engine harmonic…higher RPM the greater
Noise comes from;
1) Transmitting engine’s pulsation & harmonic mechanical movement thorough via engine/generator & exhaust system & air cleaner assembly mounts on coach to produce unwanted sound.
2) Sound from air intake
3) Sound from exhaust outlet
4) Cooling fan
5) Any other mechanical connection such as heavy wire cable & choke cable in between engine/generator to coach
6) Generators (main & small gen) produce “rrrrr” sound from magnetic pulsation
Remedy the problem;
1) Use best isolator in every area that vibrates…such as airmount (min-air-bag) engine to frame. Durometer number of rubber mounts should be the softest (lowest number) without over-stretch or compression problem
2) Two OEM or one long exhaust muffler with long small dia outlet pipe
3) Lined compartment with lead sheeting plus heavy soundown foam
4) Glass-pack muffler for air-intake…longer the better
5) SS flex braided coupling for exhaust connection from manifold to muffler
6) Better still pick 1800 RPM engine & generator
7) Better still pick water-cooled diesel of 4 cylinder or more
Links;
Material;
Soundown
http://www.soundown.com/rv.htm
Stainless Steel flex (super flex) braided coupling available from auto salvage yard with front-wheel drive or;
http://www.flex-ing.com/industrial/flex_metal.html
http://www.dezod.com/pd_stainless.cfm
Airmount
http://www.firestoneindustrial.com/Industrial/index.htm
Rubber mount
http://www.lord.com/Default.aspx?tabid=1106
Engineering;
http://www.lord.com/Portals/_default/LordDocuments/root/other/terms_and_definitions_ip.pdf
http://www.karman.com/selectvibro.cfm
http://www.earsc.com/HOME/engineering/TechnicalWhitePapers/Vibration/index.asp?SID=61
http://personal.cityu.edu.hk/~bsapplec/control.htm
FWIW
Sojourn for Christ, Jerry |
TomNPat
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 01, 2006 - 2:59 pm: | |
Boy, Jerry,
This is a posting I will print out as well as save on the computer.
A wealth of information!
Thanks.
TomNPat |
JR
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 01, 2006 - 9:00 pm: | |
Dude! You may have just solved some of my sound problem...the air filter is solidly mounted (who'd a thunk about this?) and the air intake is very noisy...makes a lot of fuss when removed. This air filter cannister is definitely transmitting some noise into the coach.
Thanks for the excellent post! JR |