Trailing arms with central longitudinal wishbone and antiroll tube nondrive axle rear suspension

(Fig. 10.47) A rectangular hollow sectioned axle beam spans the two wheels and on either side are mounted a pair of coil springs. A left and right hand trailing arm links the axle beam to the body structure via rubber bushed pivot pins located at both ends of the arms at axle level (Fig. 10.47). To locate the axle beam laterally and to prevent it rotating when braking, an upper longitudinal wishbone arm ('A' arm) is mounted centrally between the axle and body structure. The 'A' arm maintains the axle beam spring mounting upright as the spring deflects in either bump or rebound, thus preventing the helical coil springs bowing. It also keeps the axle beam aligned laterally when the body is subjected to any side forces caused by sloping roads, crosswinds and centrifugal force.

Situated just forward of the axle beam is a transverse anti-roll tube welded to the inside of each trailing arm. When body roll occurs while the car is cornering, the inner and outer trailing arms will tend to lift and dip respectively. This results in both trailing arms twisting along their length. Therefore the anti-roll tube, which is at right angles to the arms, will be subjected to a torque which will be resisted by the tube's torsional stiffness. This tor-sional resistance thus contributes to the coil spring

Plan view

Fig. 10.46 Five link coil spring leading and trailing arm Watt linkage and Panhard rod dead axle rear suspension

Plan view

Fig. 10.46 Five link coil spring leading and trailing arm Watt linkage and Panhard rod dead axle rear suspension

Plan view

Fig. 10.47 Trailing arm coil spring with central longitudinal wishbone and anti-roll tube dead axle suspension

Plan view

Fig. 10.47 Trailing arm coil spring with central longitudinal wishbone and anti-roll tube dead axle suspension roll stiffness and increases in proportion to the angle of roll. With this type of suspension the unsprung weight is minimized and the wheels remain perpendicular to the ground under both laden weight and body roll changes.

Trailing arm and torsion bar spring with non-drive axle rear suspension (Fig. 10.48) The coil springs normally intrude into the space which would be available for passengers or luggage, therefore torsion bar springs transversely installed in line with the pivots of the two trailing arms provide a much more compact form of suspension springing (Fig. 10.48). During roll of the body, and also when the wheels on each side are deflected unequally, the axle beam is designed to be loaded torsionally, to increase the torsional flexibility and to reduce the stress in the material. The axle tube which forms the beam is split underneath along its full length. This acts as an anti-roll bar or stabilizer when the springs are unevenly deflected. The pivot for each trailing arm is comprised of a pair of rubber bushes pressed into each end of a transverse tube which forms a cross-member between the two longitudinal members of the floor structure of the body. The inner surface of the rubber bush is bonded to a hexagonal steel sleeve which is mounted on a boss welded to the outside of the trailing arm. In the centre of the trailing arm boss is a hexagonal hole which receives the similar shaped end of the torsion bar. To prevent relative movement between the male and female joint made between the boss and torsion bar, a bolt locked by a nut in a tapped radial hole in the boss presses against one of the flats on the torsion bar.

One torsion bar spring serves both suspension arms so that a hexagon is forged mid-way between the ends of the bar. It registers in a hexagonal hole formed in the steel collar inserted in and spot

Fig. 10.48 Trailing arm and torsion bar spring with dead axle rear suspension

welded to the transverse tube that houses the torsion bar spring. Again the torsion bar and collar are secured by a radial bolt locked by a nut.

In the static laden position a typical total angular deflection of the spring would be 20° and at full bump about 35°. To give lateral support for the very flexible trailing arms a Panhard rod is diagonally positioned between the trailing arms so that it is anchored at one end to the axle beam and at the other end to the torsion bar tubular casing. All braking torque reaction is absorbed by both trailing arms.

Trailing arm and coil spring twist axle beam nondrive axle rear suspension (Fig. 10.49(a, b and c)) The pivoting trailing arms are joined together at their free ends by an axle beam comprised of a tubular torsion bar enclosed by a inverted 'U' channel steel section, the ends of the beam being rU' ctisnnel bearTt rU' ctisnnel bearTt



<t>) Single wheel lift causes tube anci u* channel to twist

Fig. 10.49(a-c) Trailing arm twist axle beam rear suspension

butt welded to the insides of the both trailing arms (Fig. 10.49(a, b and c)).

When both wheels are deflected an equal amount, caused by increased laden weight only, the coil springs are compressed (Fig. 10.49(a)). If one wheel should be raised more than the other, its corresponding trailing arm rotates about its pivot causing the axle beam to distort to accommodate the difference in angular rotation of both arms (Fig. 10.49(b)). Consequently the twisted axle beam tube and outer case section will transfer the torsional load from the deflected trailing arm to the opposite arm. This will also cause the undeflected arm to rotate to some degree, with the result that the total body sway is reduced.

During cornering when the body rolls, the side of the body nearest the turn will lift and the opposite side will dip nearer to the ground (Fig. 10.49(c)). Thus the inner trailing arm will be compelled to rotate clockwise, whereas the outer trailing arm rotates in the opposite direction anticlockwise. As a result of this torsional wind-up of the axle beam, the outer wheel and trailing arm will tend to prevent the inner trailing arm from rotating and lifting the body nearest the turn. Hence the body roll tendency will be stabilized to some extent when cornering.

With this axle arrangement much softer coil springs can be used to oppose equal spring deflection when driving in the straight ahead direction than could otherwise be employed if there were no transverse interconnecting beam.

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