Suspension System Fundamentals ch67 PDF

 

After studying this chapter, you will be able to:

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Keeps the tires in firm contact with the road, even after striking bumps or holes in the road.

Describe the basic function of each suspension system sys tem com compon ponent ent..

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Prevents excessive bo body dy squa squatt (body tilts down in rear ar)) when hen acc cceele lerrat atiing or heavil avily y loade oaded. d.

Explain the operation of the four common types of spri spring ngs. s.

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Prevents excessive bo body dy dive ive (body tilts down in fr fron ont) t) wh when en br brak akin ing. g.

Comp Compar aree the the va vari riou ouss type typess of susp suspen ensi sion on syst system ems. s.

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Allows the front wheels to turn from side to side

Identify the major parts of a suspension system.

for steeri steering. ng.

Ex Expl plai ain n au auto tom matic atic susp suspen ensi sion on le leve veli ling ng syst system ems. s. Corr Correc ectl tly y an answ swer er AS ASE E ce cert rtif ific icat atio ion n te test st qu ques esti tion onss re req quir uiring ing a knowl nowled edge ge of sus suspens pensiion syst ystem con on stru struct ctio ion n and and desi design gn.. The susp suspen ensi sion on sy syst stem em allows a vehicle s tires and wheels to move up and down over bumps and holes in the road. It makes the vehicle ride more smoothly over rough roads. ads. The susp suspeensio nsion n syst ystem consi onsissts of a ser eriies of arms, rms, rod ods, s, ball all join oints (swi (swiv vel join oints) ts), bu busshing hings, s, and and othe otherr pa part rtss. The suspension system works in unison with the tires, unibody or frame, wheels, wheel bearings, brake system, and steering system to provide a safe and com fo fort rtab able le mean meanss of tr tran ansp spor orta tati tion on.. Thi hiss chapt hapteer wil will su sum mmariz izee the most im impo port rtaant part arts of a basic suspension system and introduce the most common suspension system designs. It will also prepare you you to bet better ter under ndersstan tand info inforrmati tio on on the dia diagnos gnosiis an and d repair of suspension systems presented in Chapter 68. Study Stu dy caref carefull ully y

Functions of a Suspension System A su susp spen ensi sion on sy syst stem em has has seve severa rall im impo port rtan antt func functi tion ons: s: • •

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Supports the weight of the frame, body, engine, tr tran ansm smis issi sion on,, dr driv ivee trai train, n, and and pass passen enge gers rs.. Provides a smooth, comfortable ride by allowing the wheels and tires to move up and down with minimum movement of the vehicle body.

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W oeels rkls s w thect e tstal eeignm rinmen ng ent. syt.stem to help keep the wh whee inith co corr rrec alig

As you will learn, a suspension system uses springs, swivel joints, dampening devices, movable arms, and othe otherr co comp mpon onen ents ts to ac acco comp mpli lish sh thes thesee fu func ncti tion ons. s. Te Tech ch Ti Tip p Chassis Chass is stiffn stiffness ess is a pr priimar ary y fac acttor af afffect ctiing the the quietness and smoothness of a vehicle s ride the the st stif iffe ferr the the chas chassi sis, s, the the bett better er.. Chas Chassi siss hert hertzz is a measurement of the stiffness of a vehicle s

st strruct uctur uree. A highigh-h her erttz ch chas asssis (25 her hertz tz,, fo forr ex exaample ple) is stif ifffer and st strron onge gerr than han a low ow--her erttz chassis.

Bas asiic Sus uspe pens nsio ion n Sy Syst stem em Bef efo ore discus scusssing ing suspe uspen nsi sion on syst steem compone ponent ntss in detail, you should be able to visualize each major part and understand how it functions in relation to the other Figure re 67 1. parts. As each part is introduced, look at Figu

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Control arm mo movable

lever that fastens

the

steering knuckle to the vehicle s body or frame.

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St Steeerin ering g kn knuc uckkle pro provi vide dess a spindle or bearing support for the wheel hub, bearings, and wheel assembly.

Allows rapid cornering without extreme bo body dy ro roll ll

connection that allows the all joint-movable control arm to move up and down while allowing

(v (veehicl hiclee lea ean ns to one one side de)).

the steering knuckle to swivel from side to side.

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Chapter 67

Suspension System Fundamentals

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Ot Othe herr wh whee eell no nott af affe fect cted ed

 body Frame~ inner structure

Whee Wheell push pushed ed p by bump

A

 

Control arm Cont buntro srol hin Co l gar arm m /

Figure 67-1. Elementary parts of a suspension th the e bas asic ic mo moti tion on of th the e com ompo pone nen nts. ts.

B

system tem. Study

the weight of the vehicle; per mits the control arm and wheel to move up and down.

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Spri pring su supp ppor ortts

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Shock absorber or damper keeps the suspens suspension ion from contin inu uin ing g to bounce aft fteer sp spri rin ng com compre ress sion sion and and exte extens nsio ion. n.

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ontrol arm bushing sleeve that all llo ows th thee con con trol arm to swing up and down on the frame.

Independent and Nonindependent Susp Su spen ensi sion on Sys yste tems ms Suspension systems may be grouped into two broad categories: independent and nonindependent. Both can be found on today s cars and trucks.

Indep Indepen ende dent nt Su Susp spens ensio ion n In Inde depe pend nden entt

su susp spen ensi sion on allows one wheel to move

up and down with minimal effect on the other wheels. Look at Figure 67-2A. Since each wheel in an indepen dent ent suspensi ensio on system is att ttaach ched ed to it itss own suspensi sio on unit nit mov movem emen entt of one whe heel el do does es not caus causee di dire rect ct move move ment of the wheel on the other side of the vehicle.

Figure 67-2. Comp Compar aris ison on of inde indepe pend nden entt and and noni nonind ndep epen ende dent nt suspension systems. A-In Ind dependent suspension allows one wheel to roll over a bump with minimal effect on the other wheel. B-Nonindependent suspension causes the action of one wheel to tilt and affect the other wheel.

There are many types of ind independ endent suspen ensi sio on sys te tems ms many many of which hich wil illl be dis iscu cuss ssed ed late laterr in this this chap chapte ter. r. In Inde depe pend nden entt su susp spen ensi sion on is wi wide dely ly used used on mode modem m vehi vehicl cles es especi esp eciall ally y passe passeng nger er cars. cars.

Noni No nind ndepe epend nden entt Su Susp spens ension ion Nonin oninde depe pend nden entt susp suspen ensi sion on has both the right and left wheels attached to the same solid axle. When one tire

hits a bump in the road it its upward movement causes a sl slig ight ht upwar pward d tilt of the other wheel. Hence n neeither wheel is independent of the the other F Fiigure 67-2B.

Und Un dersteer

and Oversteer

Understeer means that the vehicle is slow to respond to st steeeri ering chan ang ges in a tur turn. The rea rear tires res ret retain ain trac racti tio on but the front tires may slip on the road surface due to lack of downforce rce or other fac acttors. Oversteer basically means that the rear tires try to skid around sideways in a sharp or hard turn. The front ti tirres retai tain trac racti tio on but the the rea earr ti tirres sk skiid.

Suspension systems are designed to balance over stee eerr and unders rstteer eer. The perf erfec ectt suspen ensi sio on sy sysstem tem will provide ne neut utra rall st stee eeri ring ng all all four wheels have equal tr trac acti tio on in turn turns. s.

 

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Section 11

Susp Suspen ensi sion on,, Stee Steeri ring ng,, an and d Brak Brakes es

Later La teral al Acc Accel elera eratio tion n La Late tera rall ac acce cele lera rati tion on is the amount of side force a vehicle can handle before its tires lose traction and skid

in a sharp turn. It is measured in units of gravity, or  gg-fo forc rcee us usua uall lly y on a skidpad (rou (round nd or circ circul ular ar driv drivin ing g course). The higher the g s the better. Passenger cars can attain a lateral acceleration of about 1.0 g, while race cars can produce more than 3.0 g s in turns. Independent suspension systems generally obtain high higher er later ateraal ac acce celler erat atiion tha han n no noni nind ndep epen ende den nt de desi sign gns. s. They are able to keep all four tires in full contact with the road ro ad su surf rfac acee be bett tter er th than an olde older, r, he heav avie ier, r, so soli lidd-ax axle le de desi sign gns. s.

made of fibe berg rgla lasss. Altho lthoug ugh h leaf sprin prings gs were were onc ncee us used ed on front suspension systems, they are now limited to the rear of some cars. An exploded view of a leaf spring assembly is given in Figure 67-5. A monoleaf spring is made of a single, thick leaf, wh whic ich h is usual suallly made of reinfo inforc rced ed fiber ibergl glas asss. Mult ultiple iple leaf springs have several thin steel leaves sandwiched together. Each end of the leaf spring has an eye (cylinder shaped hole), which holds a bushing. The front spring eye normally bolts directly to the frame structure. Two large U-bolts secure the axle or axle housing to the leaf sprin prings gs.. A shackle fastens the rear leaf spring eye to the

Suspension System Springs Suspe uspens nsio ion n sy syst stem em spr priings ngs must jounce (compress) and rebound (ex exttend) nd) as a veh ehic iclle trave ravells ove verr bu bum mps and holes in the road surface. They must support the weight of the vehicle while still allowing suspension travel (movement). The most common types of springs are the coil spring, leaf spring, air spring, and torsion bar. See Fi Figu gurre 677-3. 3.

t A

Front di disc sc brak brake e Fron Frontt su susp spen ensi sion on

Figure B-Leaf

67-3. Suspension system springs. A-Coil spring. C-Air spring. D- Torsion bar.

spring.

7 ~1

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Coil Co il Sp Spri ring ng A coil coil spri spring ng is a length of spring-steel rod wound into a spiral. It is the most common type of spring found in modern suspension systems. Coil springs may be used on both the front and rear of the vehicle. See Figure 67-4.

Leaf Spring A leaf sp spri ring ng is commonly made of flat plates or strips of spring steel that are bolted together. A few are