Planetary gear hydraulics: all about the operation and applications

Planetary gear units are all about enabling efficient transmission of power within working machines. These gearboxes can be connected both directly and indirectly to an electric motor or hydraulic motor. Their use is widespread in many industries, including mechanical engineering, chemical and plastics processing, food production, construction, mining, agriculture and forestry, transportation and lifting equipment, shipbuilding, and wind turbines.

What is a hydrostatic transmission?

A hydrostatic transmission is the combination of a hydraulic pump and a hydraulic motor. Both components are connected to each other via pipes or hoses. In a hydrostatic transmission, a distinction is made between the open and closed hydraulic circuits.

Types of hydraulic gearboxes

Only transmission designs that are combined with a hydraulic pump or a hydraulic motor are considered here. A distinction is made between reduction and transmission gears in hydraulics:

Planetary gear

These hydraulic transmissions are reduction gears with very high torques and low speeds. Planetary gearboxes can be assembled in several stages. This makes very large transmission ratios and torques of up to 2,400,000 newton meters possible!

The areas of application for planetary gear units are extremely diverse. In conjunction with hydraulic motors, they can be found, for example, in pipe bending machines, wind turbines, tunnel boring machines, asphalt finishers, cable winches, the paper industry, shipbuilding, agricultural machinery and many more.

A special design of planetary gear units are wheel hub gear units. These are used on both tracked vehicles and vehicles with tires. Thus, wheel hub gears are often found as traction drives in agricultural and construction machinery.

Planetary gear manufacturer – selection

Bevel helical gearbox

The bevel gear consists of a bevel gear and a bevel pinion. The axes of these two components are typically offset by 90°, but other angles are also possible. Bevel gearboxes are used in applications where high reduction ratios, torques and movements are required. Bevel helical gear units are mainly found in agricultural engineering (e.g. in manure spreaders, scraper floor drives for loader wagons). As a rule, the bevel pinion is used as the drive, which allows both left-hand and right-hand rotation.

Torques from 450 Nm to 10000 Nm and transmission ratios from 1.9:1 to 43.6:1 are possible for bevel helical gear units. In many applications, these gear units are used in conjunction with oil motors (gerotor motors).

Bevel helical gear unit manufacturer – selection

Spur gear

Spur gears are mainly found as transmission gears for hydraulic pumps, but also as pump distribution ge ars or attachment gears. These gearboxes often consist of an aluminum housing and a simple strinwheel stage. These gearboxes are usually a cost-effective solution and are used in simple applications. This includes many areas in agricultural engineering (e.g. power take-off gearboxes for log splitters). But the gearboxes are also used in construction machinery.

Spur gear manufacturer – selection

Worm gear

Worm gearboxes are very often found in slewing drives. Other applications include conveyor belts, hose reels, box tippers and industrial applications.

Worm gear units are ideal for applications with limited space, as they allow a high gear ratio in a small space. These gear units are characterized by their high precision, performance and ability to reliably compensate for axis misalignments. Worm gearboxes are quiet and insensitive to interference.

Self-locking of worm gears

For a gear unit to be self-locking, the worm must have a low pitch and thus have an efficiency of 0.5 or less. Self-locking gear units are generally not economical at higher powers and longer operating times. A worm gear is considered self-locking at standstill if it is not possible to bring the driving worm wheel from standstill to start. For wheelsets and gearboxes, this is the case if the lead angle is less than 5°.

Worm gearbox manufacturer – selection

Which oil should be used for transmission and hydraulics?

Basically:

Special gear oil should always be used for gearboxes. Gear oils are very efficient even under extreme pressures and heavy loads. They are designed to protect the gearing from abrasion, which can cause significant damage. Ordinary hydraulic oils do not have these properties, so do not provide the appropriate protection.

Hydraulic oil is used in hydraulic systems to build up pressure and transmit energy. It usually has a lower viscosity and is specially designed for use in hydraulic systems. Hydraulic oil usually also has high heat resistance and is able to tolerate higher temperatures that occur during the operation of the hydraulic system.

The common viscosity ranges for hydraulic oil areISO VG 32, ISO VG 46 and ISO VG 68. Gear manufacturers (e.g. Reggiana Riduttori) specify a minimum viscosity of ISO VG 150 in their data sheets. This corresponds to a gear oil SAE 90.

In some modern applications it is possible to use special oils for hydraulic applications as well as in gearboxes. In any case, the manufacturer’s instructions must be observed!

All contributions to hydraulic gearboxes