Module 1 - Planetary Gear Sets Operation (Page 3 of 5)
Lets start investigating how we can obtain these gears from one single planetary gear set.
In any planetary gear set, one component must be HELD, another must be the OUTPUT, and the remaining gear component is the INPUT. What does this mean? Lets investigate.
Quite simply, the OUTPUT componet of the planetary gear set is connected to the wheels through the transmission output shaft. The output device is driven by the input device.
The INPUT component of the planetary gear set is driven by the engine. Torque is transferred to the transmission through the torque converter. The torque converter is connected to the transmission input shaft.
The HELD component of the planetary gear set is held by a holding device inside the automatic transmisison. There are three different devices for achieving this task. More on this in the next module.
Drive 1 - maximum reduction (very high torque, very low speed)
Drive 1 gear is the first gear we use when accelerating our car from a standstill. This gear provides us with maximum torque but little speed. We need increased torque to get the vehicle moving from a standstill. Speed is sactificed.
Sun gear – INPUT from the engine through the torque converter and input shaft
Ring gear – HELD by the transmission
Carrier – OUTPUT to the transmission output shaft then to the rear wheels
RULE: Because the sun gear is considered the smallest gear, anytime it is the input device, the resulting gear will ALWAYS be reduction.
Drive 2 - moderate reduction (high torque, low speed)
Drive 2 gear is the second gear we use when after the vehicle has left a standstill and started moving. The transmission automatically shifts into this gear at the appropriate speed of approximately 15 to 25 kph. This gear sactifices some of the torque of first gear to give us additional speed. Maximum torque is no longer needed once the vehicle has started to move.
Sun gear – HELD by a transmission component
Ring gear – INPUT from the torque converter which is tranferring power from engine
Carrier – OUTPUT to the transmission output shaft which is connected to rear wheels
RULE: Because the planet carrier is considered the largest gear, the resulting gear is ALWAYS reduction when the planet carrier is the output gear.
Direct Drive - no reduction, 1:1 drive ratio
Direct drive is the next gear following Drive 2. The transmission shifts to direct drive, or third gear when the vehicle is moving at about 40 - 55kph. There is no gear reduction or overdrive in direct drive gear. Direct drive is achieved when any two planetary gear components are held to each other.
Sun gear – HELD to ring gear
Ring gear – HELD to sun gear
Carrier – OUTPUT to the rear wheels
RULE: Whenever any two components of a planetary gear set are held together, the resulting gear is always direct drive.
Module 1 (Page 3 of 5)