ITS NOISE THAT ANNOYS

NZ Truth, Issue 1240, 5 September 1929, Page 19

ITS NOISE THAT ANNOYS

Silence A Desirable Feature CAUSES OF NOISE ANE> RATTLE It is remarkable how public opinion changes. Ten years ago it was a very difficult matter to sell closed cars, while to-day their preponderating influence will readily be observed wherever automobiles foregather. ' *a;,,

JUST as one is- obliged to. endure a certain amount- of '; inconvenience .with folding: hoods • and adjusting .sidescreens on open touring cars,, the' fatigue of both drivers arid passengers of closed cars largely depends .upon the degree <of silence m running. "y From experience i the writer has come to -.the conclusion that, continuous noise is just, as irritating and tiring as cramped seating positions or stiff controls. A'V.A -A In niany closed cars -such, noises ■ as body drumming, -rear axle ;^"miban," clicking; -of -engine tappets,,? besides sundry, rattles and squeaks IhatA are produced whenever the road .; surface changes .from fair to .rough,' are calculated'to have a serious', effect upon theA-nervous system of .the occupants, especially the driver.,;.. ... . ■ ' v These.; so unpVy^^ ably'yfroriv |th¥rpjeasure:df ; handling a. se.dah,Aa.rid : ! 'Vnay^ be"" classed as dangero.uis/'if only^for? the "reason, that, they produce,; an "irritable '.frame of ; t mj.nd''^hWi i.s^anytHjng'but';. ' conduciy'eA^6.;.<alm actions ip em^r;g^npies*^:^i-y •Many of the noises: 'wijich make -their , presence.felt m a;clqs.e"p^;par''eome frqm the chassis or body rHVork^whlle '.others may be, called isefeprida.ty -npjsfes, m that they are set'^u^y^y^.syirip^tnletic-. vibra- " tion "• of y.s.dm.e >part,jAsubh- ; asya-' nietal panel which is Excited at certain speeds (varying accordilng : to'.its-.natu.rall'r;esoii^ anpe),.by, vjb'i*a.tf6ris coming ;§pnie part pf.y>ttie.':';.engine :- ■■; ; or,'ti : aiishvissibn sys'tem.-'Ai. L '■'".■ , ;■■.-.„>. ' .> .'Yyv, ; i;: ;■' -A^v „ !. -kCyy S^6ri(dary^;;Ga^Sesy . v y^&> ■ ' Synil^thptiC: ; a well-known :'pliehbHlenpri;:Vu*'goo'd example being\a/bo^vi; of; thin- 'glass on. a piano! which will respond to the striking of a' certain note; but .to no other, while if the Resonance is m exact accord with the pitch of the note tlie vibration may-eyen Jbe so- violent as to fracture 1 the glass. -„"... •'. In. order .to give .a. rough idea of :' some of. tho chief offenders m connection, with -primary and secondary noises ' m, a. car, we reproduce an illustration showing a sedan m section wherein: direct sources of noise arc numbered,' .while the secondary causes of ynoise, • i.e., those parts producing sounds- \vheri set into vibration are indicated by letters. ' -; ' ■'.•'-"'. „' A' ' In the former category there' is the engine, gearbox, exhaust system,- back axle; propellor -shaft, tyros and all

ferable to the fabric type from the view point of silent, running m closed cars;' because, unless the propellor shaft is kept running perfectly true without wobble or whip; -it -will;- set' up. vibrations which .are picked up. by the; bodywork and give rise to .drumming. A Another important i.factor is the silenc-r. ing system,' which/has' really been brought to : a remarkable • degree of efficiency, ' so that beyond a pleasant- rumble at full throttle, the driver has little to remind him that the car is propelled by a series of explosions. . Tyres and Body The exhaust note is, however, important;- on some cars it gives a,, pleasing sense of power arid, well-being, while on , others it resembles an irritating crackle. : A Another aspect affecting silent running is that the swish of tyres on the road differs m intensity : according t6 the tread designs, and may easily become irritallhgly strident., A ■ 7 Unfortunately,, it would seem that the only way of getting tyre silence is. to employ a tread with very poor non-skid properties, and, of course, everyone prefers safety to silence. ' ; Nevertheless, there should be room for research here, particularly for large. cars, m which the noise of the. tyres is , unusually obtrusive owing to the silence of every i other component. ; ' • .« There remains the bodywork m our list of- noise producers, which is only too apt to develop irritating squeaks and rattles from the joints and doors when a car has been driven hard without much regard'-'lo; the road surface" ';for a few thousand "miles. ' Here, of course,-- is one of the advantages of the Weymann construction m whicji- .-no.. -jt.wo .-.; wooden ifca'me .members touch ..one, janQpifir.. '„.',.'...- ; , :y,Other ways . in\which „b odies could be," improved are found. lij the mounts ing, "Which should give' greater immunity from strains due to chassis whip, and iri the method of- securing the doors, the rubber buffers on which should be adjustable for wear. Apart from the question of allowing for chassis whip, there seems no doubt that a body which is secured to the frame at a few points only — preferably' through the .medium •of rubber buffers — is- less liable to pick up vibrations and convert them into noise than a body which makes contact .with, the chassis side-members throughout the distance between the dash and the rear dumb-irons. Besonance and DrummingTurning to the parts which ! can be classed as. secondary noise producers, the chief offenders, are flat, unsupported sheet-metal surfaces, which- are very apt to vibrate and drum' m sympathy with any vibrations set ..-up by the engine or transmission. In most cars there is a period at some. speed; between 30 m-.p':h.

.':■'■'- In the above illustration,, sources of noise are: numbered, and secondary noise producers are lettered: I,' engine; -2, transmission,; 3, exhaust sys- - tern; 4, back axle; 5, propeller shaft and .joints; 6>- tyres; 7, bodywork joints and doors; A, bonnet; B,> scuttle; G.- petrol tank; D, roof. ,y

joints- of the; body'.w.ork, including the doors, but disregarding minor bearings which: should, not produce; squeaks if regularly lubricated. ' Mechanical Noise Modern engines should not produce any great riidchanicar noise when'' new; but as 'wear occurs" '■: the timing gear, '. valve geaiy and ; pistons are apt .tq(become offenders. 1; : The most serious engine trouble m that direction is probably vibration, which is transmitted through . the chassis frame and excites ; other parts of the car so that-they pro- A. duce irritating -sounds. ■■•' y .. ■ .' Tlie gearbox has received a tremendous amount of i study during the past few years with a view to reducing the. noise emitted on an indirect drive; and nowadays it is . almost invariably the practice. to (grind- the. gear teeth ■ after hardening. 'so as to correct, the effects of th'ei'distortion occasioned by -heat- treat - . merit. - ■.-:.'.- : ' ;Ay •A A. '-.-.. „-,."• Coupled with this, the mounting of the shaft has been improved, so that although the ideal condition , has., by no means been reached, the gearbox is not nearly; so bad an offender as it used to be as'far as noise is concerned; v Interesting ■ developiherits -. m this connection'- are .represented by.-'the-use-of internally, cut gear rings m America, and constant-mesh, ' -"helical -toothed; wheels A m - 'for. the third' gear ratio of : aAfouryspeedAbox, m order to promote silent running. ;. a Final. Drive. Gear A There hasi'been.a corresponding im- ; prpvement m . drive „ gears, .and bevels 'do no;t ; now, . as a rule, become noisy until a- considerable mileage/has been, covered. A. .- ..; y- ,A; ; A - yLatterly -several; important- manu- ; , facturers have gone .oyer. toAthe ;y. worm drive principle, and, whileit "'is--;-inpppV r tyne.;'t;oy'eriter--..iri^'y' j a .'■', technical ;disc;ussibn of its. relative i merits,, it may;' be , rernarße'd. that a. A, , wprm-apdXwheel gear,; if properly A;' ' ' lubricated^ never; foses Aits initial A silence of , operation. "• - .'flic prnpe'.loi- shaft .may- be,com.e • a. •noise-: producer/ if : fitted ,with : metal-to-meUil-t'ype universal jQints, the. I.ubrica> tio^ of- which is-- neglected, -but; heverthe-,.' less, thisvkihd of joint is, considered, pre.. ■ ■-.- ; . ■.' ■.'.'... '- ■ --"., - . .'■■• .'-■■■'■ - . ,- -->-

and 40 m.p.h. Adhere this sympathetic resonance occurs ' in' tune with the powerunit. - -..;•. ' Of course, the use of a six-cylinder engine helps to, improve matters, likewise flexible. supports between .the engine and the frame, such as rubber buffers or stiff leaf springs. Resonance and. drumming f of. this character, is apt to come from the bonnet and scuttle, the petrol tank (if fitted 'under the scuttle), the roof and even the door panels. The frequency of the sound produced is usually low, so that it gives rise to a ,most thudding against the ear drums.', A ■ A. y • :y. A ' There are various ways m which , such surfaces can be ; "deadened," a ' term which really means stiffening , the surface until its .natural period of vibration is so high that it will not respond to the ordinary range of chassis vibrations. Thus, a. metal panel can be stiffened by ribs attached to it, or pressed into it, or can be provided- with a backing of wood or fibre, y A. •" • A curved surface is stiff er than one which is. fiat, so that . an oval-section petrol -tank is less liable to drum than one of • rectangular section.. Another aspect of, the-, - subject is the use of the bodywork to .insulate the oct cupants of tlie car- from the' noises, produced; m the mechanism'; anyone' interested can make a simple experiment by removing tho carpet and .floorboards at the. front and driving the car without them. Most people who : try this are surprised by the amount of noise coming up from the. engine and gearbox. .