How does a planetary gear work? | Design and operating principle simply explained

Summary

This video explains the structure and operation of a planetary gearbox, comparing it to a stationary gearbox. It describes how gear ratios are determined by the number of teeth on input and output gears, and explores how planetary gears differ in operation. The video covers the arrangement and function of gears, including the use of intermediate gears and how their alignment affects the gearbox. It also explains different transmission ratios achievable in planetary gearboxes and their applications in shiftable transmissions like bicycles and vehicle gearboxes.

Takeaways

• 😀 A stationary gearbox involves gears with fixed axes of rotation, where the input and output gears interact to create a transmission ratio.
• 😀 The transmission ratio in a stationary gearbox is calculated by multiplying the individual gear ratios, which depend on the number of teeth of the gears.
• 😀 The number of teeth on the idler gear does not affect the overall transmission ratio in a stationary gearbox.
• 😀 A ring gear can replace the external gear without changing the transmission ratio but reverses the output's direction of rotation.
• 😀 The alignment of input and output shafts can be achieved by adjusting the number of teeth on the idler gear.
• 😀 When multiple idler gears are used symmetrically, bending stress on the shafts can be avoided, and the torque capacity is increased.
• 😀 A planetary gearbox is essentially a more advanced version of a stationary gearbox, where the idler gears (planet gears) are mounted on a carrier.
• 😀 The planetary gearbox can provide different transmission ratios depending on which component (sun gear, carrier, or ring gear) is used for input and output.
• 😀 The planetary gearbox is compact, with coaxial shafts, and is ideal for applications requiring large transmission ratios.
• 😀 The use of clutches in shiftable gearboxes allows the locking of individual components to select the desired transmission ratio.

Q & A

What is the main difference between a stationary gearbox and a planetary gearbox?

A stationary gearbox has gears with fixed axes of rotation, whereas a planetary gearbox uses a set of gears (planet gears) mounted on a rotating carrier around a stationary sun gear and ring gear. The planetary system offers more flexible gear ratios and a compact design.

How is the total transmission ratio calculated in a stationary gearbox?

The total transmission ratio in a stationary gearbox is calculated by multiplying the individual gear ratios of the stages. The gear ratio of each stage is determined by the ratio of the number of teeth on the respective gears.

What role do the idler gears (planet gears) play in a planetary gearbox?

In a planetary gearbox, the idler gears, also known as planet gears, rotate around the central sun gear and mesh with the ring gear. They allow the gearbox to achieve various transmission ratios by altering which component (sun gear, carrier, or ring gear) is locked or used as the input or output.

Why is the number of teeth of the idler gear not important for the overall transmission ratio in a stationary gearbox?

In a stationary gearbox, the number of teeth on the idler gear has no effect on the overall transmission ratio because the idler gear merely transfers motion between the input and output gears without affecting the ratio, which depends on the input and output gear teeth.

What is the advantage of using a planetary gearbox compared to a conventional stationary gearbox?

The planetary gearbox has a compact design, with all shafts arranged coaxially, making it more space-efficient. It can also achieve a broader range of gear ratios and handle higher torque transmission due to the symmetrical arrangement of planet gears, which distribute the load.

How can a planetary gearbox be used to create a reverse gear?

A reverse gear can be created by interchanging the input and output shafts, which results in a negative transmission ratio. This reverses the direction of rotation between the input and output shafts.

What is the significance of locking the ring gear in a planetary gearbox?

Locking the ring gear in a planetary gearbox allows for different transmission ratios. When the ring gear is locked, the carrier can be used as the output shaft, providing a specific gear ratio. Locking different components (sun gear, ring gear, or carrier) changes the transmission ratio.

How does the number of planet gears affect the performance of a planetary gearbox?

The number of planet gears affects the balance and load distribution in a planetary gearbox. Using multiple planet gears symmetrically helps reduce unbalance forces at high speeds and increases the maximum torque that can be transmitted.

Can a planetary gearbox have multiple gear ratios, and if so, how?

Yes, a planetary gearbox can have multiple gear ratios depending on which component (sun gear, carrier, or ring gear) is used as the input and output. By locking different components or reversing the input/output, various ratios can be achieved.

What is a direct drive in the context of a planetary gearbox?

A direct drive in a planetary gearbox occurs when all components (sun gear, planet gears, and ring gear) are locked together, resulting in a transmission ratio of 1. This configuration is typically used for a direct connection between input and output without any gear reduction.