What’s a Planetary Gear, and How Does It Work?


Where Are Planetary Gears Used?

Planetary gears are used in applications where space is limited, as they are typically smaller than other types of gearboxes. They also form the basis of the most common type of automatic transmission, known as the hydraulic planetary automatic transmission. Most modern automatic transmissions in the automotive industry use planetary gears.

Elsewhere, planetary gears are used in equipment such as augers and wind turbines, and in-vehicle drive systems for helicopters and aircraft engines. Planetary gear sets are popular for industrial machinery too, where guided robots, laser cutting machines, and even hospital operating tables use them. There’s also a great chance that the sandwich meat in your refrigerator was cut on a slicer that used planetary gears.

Passenger vehicles with automatic transmissions use planetary gears, so your grandma’s Buick uses them, just like your neighbor’s annoying 1995 Ford Mustang V6.

Do Continuously Variable Transmissions Have Planetary Gears?

Where traditional automatic and manual transmissions feature gear ratios that are fixed, a continuously variable transmission (CVT) works with two cone-shaped pulleys connected with a belt. They are used to improve fuel economy, as CVTs are typically designed to keep the engine in its most efficient and ideal power delivery range. 

There are, however, versions of CVTs that use planetary gears. Called epicyclic CVTs, or planetary CVTs, these transmissions use planet gears to transfer torque. Toyota used one in the Prius back in the late 1990s.

How Does a Planetary Gear Relate to Portal Axles?

Portal axles are used to improve ground clearance and allow for gearing that reduces stress on the differential. Vehicles such as the Mercedes-AMG G63 6×6 truck and the Mercedes-Benz Unimog use portal axles. In these applications, an epicyclic (planetary) hub gearbox is used, which allows the half shafts to turn faster than the wheels. 

This reduces the amount of torque needed to generate the same level of power. In the case of vehicles like the Unimog and G63, the large wheels and tires already provide most of the necessary ground clearance, so the portal axles play a slightly different role.

FAQs About Planetary Gears 

You’ve got questions, The Drive has answers!

Q: How do I know if my car has planetary gears?

A: If you drive a modern car with an automatic transmission, there’s a solid chance that it has planetary gears. If you’re dedicated to finding out, check your vehicle’s maintenance manual for information on the gearbox, contact your dealer’s service department, or try that all-knowing search bar we’re all so dependent on.

Q: Are planetary gears more expensive than other types?

A: In general, yes. They are more expensive because they are more complex and are composed of more parts than other types of transmissions.

Q: Do planetary gears need lubrication?

A: Yes. Just like any other gear or mechanical component in your vehicle, planetary gears need lubrication to operate smoothly and to prevent damage or wear. Transmissions, like all other parts of your vehicle, need regular attention and servicing, which can include minor work such as fluid changes. Over time, the gears inside a transmission can wear, leading to slipping or odd noises, so it’s important to keep up with lubrication and regular maintenance to get on top of problems as quickly as possible.

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