The planetary gear laid is the device that produces dissimilar gear ratios through the same laid of gears. Any planetary gearset has 3 principal components:
· The sun gear
· The planet gears in addition to the planet gears' carrier
· The ring gear
Each of these 3 components tin hold upward the input, the output or tin hold upward held stationary. Choosing which slice plays which purpose determines the gear ratio for the gearset.
Compound Planetary gearset - The automatic transmission uses a laid of gears, called a compound planetary gearset that looks similar a unmarried planetary gearset but genuinely behaves similar ii planetary gearsets combined. It has 1 band gear that is e'er the output of the transmission, but it has ii Sun gears in addition to ii sets of planets.
The figure below shows a chemical compound planetary gearset:
First Gear- In outset gear, the smaller Sun gear is driven clockwise past times the turbine inwards the torque converter. The planet carrier tries to spin counterclockwise, but is held however past times the one-way clutch (which alone allows rotation inwards the clockwise direction) in addition to the band gear turns the output. The modest gear has thirty teeth in addition to the band gear has 72, in addition to then the gear ratio is:
Ratio = -R/S = - 72/30 = -2.4:1
So the rotation is negative 2.4:1, which agency that the output management would be opposite the input direction. But the output management is genuinely the same as the input management -- this is where the play tricks alongside the ii sets of planets comes in. The outset laid of planets engages the minute set, in addition to the minute laid turns the band gear; this combination reverses the direction. You tin run into that this would likewise crusade the bigger Sun gear to spin but because that clutch is released, the bigger Sun gear is gratis to spin inwards the opposite management of the turbine (counterclockwise).
Second Gear - The ii planetary gearsets connected to each other alongside a mutual planet carrier.
The outset phase of the planet carrier genuinely uses the larger Sun gear equally the band gear. So the outset phase consists of the Sun (the smaller Sun gear), the planet carrier, in addition to the band (the larger Sun gear).
The input is the modest Sun gear; the band gear (large Sun gear) is held stationary past times the band, in addition to the output is the planet carrier. For this stage, alongside the Sun equally input, planet carrier equally output, in addition to the band gear fixed, the formula is:
1 + R/S = 1 + 36/30 = 2.2:1
The planet carrier turns 2.2 times for each rotation of the modest Sun gear. At the minute stage, the planet carrier acts equally the input for the minute planetary gear set, the larger Sun gear (which is held stationary) acts equally the sun, in addition to the band gear acts equally the output, in addition to then the gear ratio is:
1 / (1 + S/R) = 1 / (1 + 36/72) = 0.67:1
To buy the farm the overall reduction for minute gear, nosotros multiply the outset phase past times the second, 2.2 x 0.67, to buy the farm a 1.47:1 reduction.
Third Gear- Most automatic transmissions accept a 1:1 ratio inwards tertiary gear. To accomplish a ratio of 1:1 engage the clutches that lock each of the Sun gears to the turbine. If both Sun gears plough inwards the same direction, the planet gears lockup because they tin alone spin inwards opposite directions. This locks the band gear to the planets in addition to causes everything to spin equally a unit, producing a 1:1 ratio.
Overdrive Gear- An overdrive has a faster output speed than input speed. When overdrive is engaged, a shaft that is attached to the housing of the torque converter (which is bolted to the flywheel of the engine) is connected past times clutch to the planet carrier. The modest Sun gear freewheels, in addition to the larger Sun gear is held past times the overdrive band. Nothing is connected to the turbine; the alone input comes from the converter housing. This fourth dimension alongside the planet carrier for input, the Sun gear fixed in addition to the band gear for output.
Ratio = 1 / (1 + S/R) = 1 / (1 + 36/72) = 0.67:1
So the output spins in 1 lawsuit for every two-thirds of a rotation of the engine. If the engine is turning at 2000 rotations per infinitesimal (RPM), the output speed is 3000 RPM. This allows cars to drive at motorway speed spell the engine speed stays overnice in addition to slow.
Reverse Gear- Reverse is real similar to outset gear, except that instead of the modest Sun gear existence driven past times the torque converter turbine, the bigger Sun gear is driven, in addition to the modest 1 freewheels inwards the opposite direction. The planet carrier is held past times the contrary band to the housing. So, according to our equations from the final page, nosotros have:
Ratio = -R/S = 72/36 = 2.0:1
So the ratio inwards contrary is a piddling less than outset gear inwards this transmission.Summary of Gear Ratios- Transmission having iv forrad gears in addition to 1 contrary gear.