A "Sportronic" transmission is a marketing name for a special type of automatic transmission. With these types of transmissions, there is a planetary gearset, a set of bands that act to lock parts of a gearset, three wet-plate clutches to lock other parts of the gearset, a hydraulic system that controls the series of clutches and bands, and a large gear pump to move transmission fluid through the system.
The driving component behind any automatic transmission is the planetary gearset. This is essentially a set of gears, called "planet gears," which revolve around a center gear called a "sun gear." The planet gears are held in place by a carrier, which may also revolve around the "sun gear" itself.
The design of a planetary gear system allows the transmission to be compact and also allows for the changing of gear ratios without having to physically engage or disengage any of the gears in the system. Automatic Sportronic transmissions use a compound planetary gearset which behaves like two planetary geatsets put together. From this, we can have 4, 5, or 6 forward gears and a reverse gear.
These gears help to determine how fast the car will go according to the gear ratio selected.
A gear pump pumps transmission fluid through the transmission to keep all of the gears lubricated and to keep them from overheating. To do this, it draws fluid up from a sump in the bottom of the transmission and feeds it through the hydraulic system, which is permanently molded into the metal body of the transmission (as opposed to using a complex system of hoses).
The governor is a valve attached to the transmission, the purpose of which is to monitor how fast the car is moving. As the car picks up speed, the governor spins faster. Inside the governor is a spring-loaded valve that opens proportionally to the rate at which the governor spins to allow fluid to the governor.
As the car moves faster and faster, the governor valve opens wider, and the fluid pressure increases.
At certain intervals, gear ratios must be changed in order for the transmission to do its job. Without the governor, this would be impossible.
The entire system is controlled electronically through solenoids. In a normal automatic transmission, the car's computer can monitor the speed and shift through gears as needed to reach and maintain your desired speed.
With a Sportronic transmission, this process is "semi-automatic" in that the driver can allow the computer to choose when to shift into the appropriate gear, or he can manually shift the transmission into the appropriate gear.
All of this is done with an electronically controlled assist, so there is no need for a clutch pedal. To engage the "sportronic" option, the driver need only move the car's shifter into a special "gate" that is set off to the side of the "D" option in the gear selection box.
A "+" and "-" sign indicate to the driver a higher or lower gear selection. The driver need only push the shifter forward (+) to move up to a higher gear, and pull the shifter back (-) to shift to a lower gear.
If the RPMs reach the engine's red line, or if they drop below a certain point and the driver does not shift into the next appropriate gear, the car's computer will automatically shift the transmission to avoid damaging the engine from over-revving or to prevent the car from stalling because of the RPMs dropping too low.
