A Mitsubishi automatic transmission, like any other automatic transmission, is a device connecting directly to the engine of the vehicle which is designed to translate the comparatively stable output of the engine from low speed/high torque settings when starting out, to high speed/low torque settings once the vehicle is already underway. Without such a device in place, driving a vehicle above 10 miles an hour would be next to impossible.
The Mitsubishi automatic transmission sits between the engine and the crankshaft, which in turn connects to the vehicle's drive axle. The inner workings of an automatic transmission are quite different from a manual transmission. The primary piece of a Mitsubishi automatic transmission is the planetary gearset. This is a series of hollow gears of different sizes and tooth numbers. The center gear is called the sun gear. Around that revolve multiple planet gears, and around that revolves a ring gear.
In between these gears are a set of bands and clutch plates to lock parts of the gear set at will, as well as a hydraulic pump system designed to engage or disengage parts of the gear set at will called a valve body. This series of gears is connected to the engine at one end and to the driveshaft at the other.
A Mitsubishi automatic transmission works by the planetary gear sets--there are often two sets working together rather than one--being engaged and disengaged by the valve body. The specific configuration of the planetary gear sets is what creates the slow change from high torque/low speed to low torque/high speed. This configuration is determined by the valve body. The valve body opens and closes different valves within the planetary gear set, which are connected to the clutches and brake bands. These hold some of the gears in place while allowing others to move, changing the gear ratio. The valve body governs which valves to open and close based on the engine's energy output.
