Analizarea Sistemelor de Suspensie - Directie Utilizate la Autoturismele de Tip Mercedes-Benz Clasa S

2) Noiuni teoretice

2.1.Unghiuri de poziie ale roii directoare i ale pivotului [4]

n scopul asigurrii unei bune inute de drum a automobilului, roile de direcie se stabilizeaz. Prin stabilizarea roilor de direcie se nelege capacitatea acestora de a-i menine direcia la mersul n linie dreapt i de a reveni n aceast poziie dup ce au fost bracate. n acest scop, roile de direcie i pivoii fuzetelor prezint anumite unghiuri n raport cu planul longitudinal i transversal ale automobilului.

La puntea din fa se deosebesc urmtoarele unghiuri:

- unghiul de nclinare longitudinal a pivotului (unghiul de fug) este (0.

- unghiul de nclinare transversal a pivotului (0.

- unghiul de cdere al roii (nclinare transversal a fuzetei) (0.

- unghiul de convergen al roii (nclinare longitudinal a fuzetei) (0.

Unghiul de cdere sau de carosaj al roii (fig. 2) reprezint nclinarea planului roii fa de planul longitudinal al automobilului. Fetul su, stabilizator se manifest prin mpiedicarea tendinei roilor de a oscila n limita jocului din rulmenii butucului.

Datorit unghiului de cdere, (0, componenta axial ZRsin(0 a reaciunii normale ZR tinde s mping butucul roii spre interior, ceea ce face s dispar jocul din rulmeni, i descarc piuliele din captul fuzetei.

Unghiul de convergen al roilor, (0. (fig. 3) este format n plan orizontal de planul roii cu planul longitudinal al automobilului. Mrimea convergenei se exprim, de obicei, prin diferena distanelor f i s dintre planele jantelor, n plan orizontal, msurate n faa f i spatele s ale punii. Convergena roilor se prevede n scopul micorrii tndinei de deschidere al acestora datorit unghiului de cdere (0.

O convergen prea mare provoac o uzur accentuat a pneurilor pe flancurile exterioare, astfel nct se impune ca n timpul mersului rectiliniu roile s aib tendina s ruleze paralel.

Unghiul de nclinare longitudinal a pivotului (0 (unghiul de fug, fig. 4), reprezint nclinarea fa de vertical a axei pivotului (msurat n plan longitudinal), n aa fel nct prelungirea axxei sale ntlnete calea de rulare n punctul B, situat naintea punctului A de contact roat-cale. Mrimea unghiului de fug poate fi exprimat i prin distana a=r tg(0 , care reprezint lungimea braului sub care acioneaz fora lateral.

1.2.Analizarea mecanismului de suspensie al autoturismului Mercedes-Benz Clasa S

McPherson strutSee Figure 8 McPherson strut front suspension differs considerably from unequal length A-arm suspension. McPherson strut suspension is found most frequently on compact and subcompact cars, both domestic and imported. With this type of suspension, the shock absorber, strut and spindle are a combined unit, which is supported by the coil spring at the upper end and the lower control arm (sometimes called track control arm or transverse link) at the bottom.Another type of front strut suspension is referred to as a modified McPherson strut suspension, which is the same as the regular McPherson strut unit except the coil spring is mounted separately from the strut, between the lower control arm and the frame.There is only one ball joint in this design, and it is attached to the lower part of the spindle. Generally, this ball joint is not a load carrying ball joint, but a follower ball joint, which means it is isolated from vehicle weight.The shock absorber is built into the strut outer casing and, except for the modified McPherson strut, a coil spring sits on a seat welded to this casing. The upper mount of the shock absorber bolts to the vehicle body. On some models, the strut cartridge may be replaced, while on others the entire strut must be replaced. Due to the design of this type of suspension, the only front-end alignment procedure possible is toe-in adjustment, since caster and camber are fixed.FRONT SUSPENSION COMPONENT LOCATIONS

1. Lower control arm2. Ball joint3. Tie rod end4. MacPherson strut5. Halfshaft 6. Inner CV joint7. Outer CV joint8. Stabilizer (sway) bar9. Power steering gear10.Crossmember

Rear suspensions

There are three basic types of rear suspension: independent, semi-independent and live axle. Each of these suspension systems has their own distinctive variations, but the general principles and component types are relatively similar to that of front suspension systems described earlier in this chapter.Independent rear suspension systems may be found on both rear, front, and 4-wheel drive vehicles. They utilize control arms which allow one wheel to move separately from the other wheel.Semi-independent rear suspension systems are often found on front wheel drive vehicles. These systems utilize a cross member, which connects to two trailing arms. Despite the fact that there is a solid connection with the cross member and the trailing arms, the cross member will twist with each up and down movement of the wheels. This twisting action provides not only semi-independent movement, but also a stabilizer effect.Live axle rear suspension systems are usually found on rear and four wheel drive vehicles. These systems consist of leaf or coil springs utilized in conjunction with the live axle, which is the differential axle, wheel bearings, and brakes operating as a unit.Rear suspensions, in general, can be much simpler than front suspensions since all they have to do is support the rear of the vehicle and provide some sort of suspension control. However, some rear suspensions, especially those found on sports cars, are quite complex.Figure 23 The semi-independent axle used on many of today's front-wheel-drive vehicles.

1. Rear shock absorber

2. Axle housing

4. Leaf springs

5. Spring U-boltsSistemul de directie

Power steering units are mechanical steering gear units incorporating a power assist.Power steering for the recirculating ball type steering system consists of a pump, fluid reservoir, pressure and return hoses and steering gear. The pump, which is driven by an accessory drive belt, consists of an impeller, pressure valve, and fluid reservoir. Pump pressure builds only when the engine is running. The pump impeller turns, picking up hydraulic fluid from the reservoir and feeding it to the steering gear under pressure through the pressure line. The fluid is then returned to the fluid reservoir through the non-pressurized return line.The power assisted rack and pinion steering system is very similar to that of the recirculating ball system in that its power cylinder and control valve are in the same housing. The power piston is part of the rack while the rack housing is the cylinder. The pinion housing contains the control valve. Rotating the steering wheel moves the control valve, directing pressure to both ends of the steering rack piston. The rack and pinion system uses a pressure hose from the power steering pump to the control valve housing, and a return line to the fluid reservoir. 1.3.Analizarea mecanismului de direcie al autoturismului Mercedes-Benz Clasa S

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