Outboard epicyclic spur gear double reduction axle

Description of construction (Fig. 7.22) A gear reduction between the half shaft and road wheel hub may be obtained through an epicyclic gear train. A typical step down gear ratio would be 4:1. The sun gear may be formed integrally with or it may be splined to the half shaft (Fig. 7.22). It is made to engage with three planet gears carried on pins fixed to and rotating with the hub, thus driving

hub Brake drum

Fig. 7.22 Outboard epicyclic spur double reduction axle hub Brake drum

Fig. 7.22 Outboard epicyclic spur double reduction axle the latter against the reaction of an outer annulus splined to the stationary axle tube. The sun wheel floats freely in a radial direction in mesh with the planet pinions so that driving forces are distributed equally on the three planet pinions and on their axes of rotation. A half shaft and sun gear end float is controlled and absorbed by a thrust pad mounted on the outside end cover which can be initially adjusted by altering the thickness of a shim pack.

Description of operation (Fig. 7.22) In operation, power flows from the differential and half shaft to the sun gear where its rotary motion is distributed between the three planet pinions. The forced rotation of these planet pinions compels them to roll around the inside of the reaction annulus ring gear (held stationary) so that their axes of rotation, and the planet pins, are forced to revolve about the sun gear axis. Since the planet pins are mounted on the axle hub, which is itself mounted via a fully floating taper bearing arrangement on the axle tube, the whole hub assembly will rotate at a much reduced speed relative to the half shaft's input speed.

Outboard epicyclic bevel gear single and two speed double reduction axle (Fig. 7.23) This type of outboard double reduction road wheel hub employs bevel epicyclic gearing to provide an axle hub reduction. To achieve this gear reduction there are two bevel sun (side) gears. One is splined to and mounted on the axle tube and is therefore fixed. The other one is splined via the sliding sleeve dog clutch to the half shaft and so is permitted to revolve (Fig. 7.23). Bridging both of these bevel sun gears are two planetary bevel gears which are supported on a cross-pin mounted on the axle hub.

The planetary bevel gear double reduction axle hub may be either two speed, as explained in the following text, or a single speed arrangement in which the half shaft is splined permanently and directly to the outer sun gear.

High ratio (Fig. 7.23) High ratio is selected and engaged by twisting the speed selector eccentric so that its offset peg pushes the sliding sleeve outwards (to the left) until the external teeth of the dog clutch move out of engagement from the sun gear and into engagement with the internal teeth formed inside the axle hub end plate. Power is transferred from the differential and half shaft via the sleeve dog clutch directly to the axle hub without producing any gear reduction.

Low ratio (Fig. 7.23) When low ratio is engaged, the sleeve dog clutch is pushed inwards (to the right) until the external teeth of the dog clutch are moved out of engagement from the internal teeth of the hub plate and into engagement with the internal teeth of the outer bevel sun gear. The input drive is now transmitted to the half shaft where it rotates the outer bevel sun gear so that the bevel planet gears are compelled to revolve on the cross-pin. In doing so they are forced to roll around the fixed inner bevel sun gear. Consequently, the cross-pin which is attached to the axle hub is made to revolve about the half shaft but at half its speed.

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