An automatic transmission employs multiple bands which are typically made of metal (steel) which are wrapped around or linked to a planetary gearset or clutch hub for the purpose of holding or resisting the rotation of the gears and hubs so that the input, output, and reaction components of the transmission act together to alter and ultimately direct the transmission of engine torque to the driveline's driveshaft.
Description:
Within an automatic transmission, there are a few important components that work together to facilitate smooth and efficient gear changes. Among them are automatic transmission bands. These bands play a crucial role in controlling the engagement and disengagement of different gear sets within the transmission.
How do automatic transmission bands work?
Inside the transmission housing, there are several rotating elements, such as planetary gear sets and sun gears. Each gear set is designed with a specific gear ratio, allowing the transmission to change gears as the vehicle accelerates or decelerates.
- Planetary gear set: A planetary gear set comprises three components - a sun gear, planet gears, and a ring gear. The sun gear is at the center, the planet gears revolve around the sun gear, and the ring gear encircles the planet gears.
- Sun gears: The sun gear connects to the transmission input shaft, which receives rotational power from the engine.
- Planet gears: These gears are situated between the sun gear and the ring gear, and they rotate around the sun gear.
- Ring gear: The ring gear connects to the transmission output shaft, which ultimately sends rotational power to the driveshaft and then to the wheels.
Now, let's delve into how the automatic transmission bands function:
Holding band: The holding band is primarily responsible for holding the ring gear in place to provide the appropriate gear ratio, preventing it from rotating. By holding the ring gear stationary, the planet gears can rotate freely around the sun gear. As a result, the appropriate gear ratio is achieved, altering the transmission's input and output speed.
Driven/reaction band: The driven band, also known as the reaction band, serves a different purpose. Instead of holding the ring gear stationary, it works to restrain the planet carrier - the structure that holds and rotates the planet gears - preventing it from rotating. In doing so, it creates a reaction against the planet gears, enabling them to drive the ring gear.
Lockup band: Some modern automatic transmissions may feature an additional component known as the lockup band. This band is typically used in the highest gear to directly connect the transmission input and output shafts, creating a direct mechanical connection similar to a manual transmission's engagement. This locks the torque converter and minimizes power loss, increasing fuel efficiency and providing a smoother driving experience at higher speeds.
Importance of automatic transmission bands
Automatic transmission bands play a critical role by allowing the transmission to change gears smoothly and efficiently. They provide precise control over the engagement and disengagement of gear sets, ensuring optimal gear ratios for different vehicle speeds and driving conditions. Without these bands, the transmission would not be able to function effectively, leading to erratic gear changes, reduced performance, and potential damage to other transmission components.
Additional notes
- Automatic transmission bands are typically made of high-strength materials like steel to ensure durability and withstand the immense rotational forces and heat generated within the transmission.
- The engagement and disengagement of these bands are often controlled by hydraulic pressure, which is generated by the transmission's hydraulic pump and regulated by various valves and sensors.
- Over time, automatic transmission bands can experience wear and tear due to friction and heat, which may necessitate their replacement or adjustment as part of regular transmission maintenance.
