10134 Inverted semielliptic spring centrally pivoted tandem axle bogie suspension

(Figs 10.94, 10.95 and 10.96) This type of tandem axle suspension has either one or two semi-elliptic springs mounted on central pivots which form part of the chassis side members. The single springs may be low (Fig. 10.94) or high (Fig. 10.95) mounted. To absorb driving and braking torque reaction, horizontally positioned torque arms are linked between the extended chassis side members and the axle casing. If progressive slipper spring ends are used (Fig. 10.95), double torque arms are inclined so that all driving and braking torque reactions are transmitted through these arms and only the vehicle's laden vertical load is carried by the springs themselves.

Articulation of the axles is achieved by the inverted springs tilting on their pivots so that one axle will be raised while the other one is lowered when negotiating a hump or dip in the road. As the axles move up and down relative to the central pivots, the torque arms will also pivot on their

(al Equal driving torque distribution

Fig. 10.93(a and b) Non-reaction bell crank lever and rod

Fig. 10.94 Low mounted single inverted semi-elliptic spring with upper torque rods
Fig. 10.95 High mounted single inverted semi-elliptic spring with lower torque rods

rubber end joints. Therefore the axle casing vertical arms will remain approximately upright at all times.

Any driving or braking reaction torque is transmitted through both the springs and torque arms to the central spring pivot and torque rod joint pins mounted on the reinforced and extended chassis side members. Very little interference is experienced with the load distribution between the two axles when the vehicle is being accelerated or retarded.

For heavy duty cross-country applications the double inverted semi-elliptic spring suspension is particularly suitable (Fig. 10.96). The double inverted spring suspension and the central spring pivots, enable the springs to swivel a large amount (up to a 500 mm height difference between opposite axles) about their pivots when both pairs of axle wheels roll continuously over very uneven ground. This arrangement tolerates a great deal more longitudinal axle articulation than the single inverted spring and torque arm suspension.

Large amounts of transverse (cross) articulation are made possible by attaching the upper and lower spring ends to a common gimbal bracket which is loosely mounted over the axle casing (Fig. 10.96). The gimbal brackets themselves are supported on horizontal pivot pins anchored rigidly to the casing. This allows the axle to tilt transversely relative to the bracket's springs and chassis without causing any spring twist or excessive stress concentrations between flexing components.

Do It Yourself Car Diagnosis

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