Planetary Steering

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Forward and reverse hydraulic clutches operation

Construction Mechanic Basic Volume 2

Hydrostatic Drive Train

Planetary Steering
Some tracked equipment may be steered by a system that combines planetary steering and pivot brakes. The planetary steering system (fig. 6-10) differs from the one previously described in that the planetary pinion gears are two gears of different sizes, machined into one piece. Two sun gears are also included. One sun gear is splined to the sprocket pinion shaft, and the other is machined on the steering brake hub. The sun gear, machined to the steering brake hub, performs the same function as the ring gear in a conventional planetary system. Bushings are used to isolate the sprocket drive shafts and the steering brake hubs from the bevel gear carrier and the planetary carrier. Lubrication is provided from the oil sump located below the assembly.

When the tracked equipment travels straight ahead, its steering brakes are held in the applied position by heavy coil springs. Braking prevents the steering brake hub and sun gear from rotating and forces the large planetary pinion gears to "walk" around the sun gear. Then power is transmitted to the sun gear on the sprocket drive shaft from the smaller planetary pinion gears.

When a gradual turn is being made, the operator moves one of the steering levers back far enough to release the steering brake on one end of the planetary system. When the brake is released, the planetary pinion gears stop "walking" around the sun gear on the steering brake hub. This hub then rotates with the planetary carrier, and no power is transmitted to the sprocket drive shaft.

Figure 6-10.- Planetary steering systems.

Occasionally, an adjustment of the steering brake is required to prevent slippage when it is engaged. Consult the manufacturer's service manual for adjustment procedures.

Pivot Brakes
The pivot brakes on tracked equipment are of the multiple disc type. Pulling the steering brake levers fully to the rear operates them. The middle discs (splined to the sprocket drive shaft) have laminated linings. The intermediate discs (held in position by studs) are smooth steel discs. An actuating disc assembly is two steel plates with steel balls between them. The assembly is located in the center of the discs and is connected to the operating linkage.

Ramps are machined on the steel plate of the actuating disc assembly, so when the brakes are applied, the steel balls move up the ramps and force the plates apart. Movement of the plates causes the discs to be squeezed together and to stop rotation of the sprocket drive shaft. When these brakes are fully applied, the tracks will stop. The steering levers are linked to the brakes independently to actuate them for sharp turns.

Adjustment of the pivot brakes is required to provide adequate braking with the steering levers. An adjustment is required when the steering levers can be pulled against the seat with the engine running. Consult the manufacturer's service manual for proper adjustment procedures.