Planetary wheel drives offer an off-road edge

The demands to reduce size and weight, and yet achieve improved price/performance ratios, are familiar to designers of mobile equipment, worldwide. In their attempts to meet these demands, designers have focused on the area of drive systems, seeking simpler and more efficient alternatives to the conventional axle drive systems that are still used widely. Increasingly, engineers are finding the answers to their questions in this area with planetary wheel and track drives.

The reason for this lies with the planetary design.

Comprising several smaller planetary gears around an input pinion (instead of one larger gear running to one side), this arrangement offers a number of major advantages including: high efficiency - usually 97-98% per stage; reduced size - planetaries facilitate multiple reduction stages in a very compact space; and increased reliability - the result of a design that reduces radial loads.

In addition, because the torque being transmitted at any time in a planetary is shared between multiple sets of teeth on the primary drive pinion, torque capability is greatly increased.

Brevini has developed the planetary principle, proven in its range of industrial gearboxes, into highly compact wheel and track drives.

The wheel drives are used widely on such vehicles as agricultural machines, access platforms, fork lift trucks, sweepers and low speed wheeled vehicles; and the track drive units are specifically designed for use on tracked vehicles, such as excavators and earthmoving machines, weighing from 1.5 to 40t.

Both the wheel and track drive units permit a much neater and more compact design solution than axle drives and provide greater clearance for rough terrain vehicles.

The wheel drives offer the ability to accept directly mounted standard wheel rims and packaged hydraulic motors; and the track units are designed to mount inside the track sprockets of vehicles.

The wheel drive units employ the highly efficient combination of a planetary gear unit and high-speed hydraulic motor.

This combination is much more economical than using large slow-speed hydraulic motors on their own, and offers significant operating advantages.

In the event of hydraulic fluid contamination only the inexpensive package motor need be replaced, and this can be removed and refitted in minutes.

And the gearbox/ motor combination is capable of the very low speeds required when, for example, inching vehicles into position.

The wide range of ratios available with the wheel drive units makes it easy for designers of mobile plant to adapt the reduction unit to the most suitable hydraulic transmission.

In addition, further flexibility is provided by the ability of the wheel drives to accommodate the mounting of all types of orbit, geared and axial piston type hydraulic motors into their universal input.

Also included in the comprehensive design specification is a mechanical disconnect device.

This is manually operated from the hub end-plate and enables a vehicle to be towed in an emergency.