Facts : 1 1 Hydraulic automatic transmissions 1.1 Torque converter 1.2 Planetary gears train 1.3 Hydraulic controls Hydraulic automatic transmissions The predominant form of automatic transmission is hydraulically operated; using a fluid coupling or torque converter, and a set of planetary gearsets to provide a range of gear ratios
Facts : 2 A cutaway of an 8-speed ZF 8HP showing the major stages of a hydraulic automatic transmission: the torque converter (left), the planetary gearsets and clutch plates (center), as well as hydraulic and electronic controls (bottom)
Facts : 3 Hydraulic automatic transmissions consist of three major components: Torque converter A type of fluid coupling, hydraulically connecting the engine to the transmission
Facts : 4 It transmits and decouples the engine power to the planetary gears, allowing the vehicle to come to stop with the engine still running without stalling
Facts : 5 A torque converter differs from a fluid coupling, in that it provides a variable amount of torque multiplication at low engine speeds, increasing breakaway acceleration
Facts : 6 A fluid coupling works well when both the impeller and turbine are rotating at similar speeds, but it is very inefficient at initial acceleration, where rotational speeds are very different
Facts : 7 This torque multiplication is accomplished with a third member in the coupling assembly known as the stator, which acts to modify the fluid flow depending on the relative rotational speeds of the impeller and turbine
Facts : 8 The stator itself does not rotate, but its vanes are so shaped that when the impeller (which is driven by the engine) is rotating at a high speed and the turbine (which receives the transmitted power) is spinning at a low speed, the fluid flow hits the vanes of the turbine in a way that multiplies the torque being applied
Facts : 9 This causes the turbine to begin spinning faster as the vehicle accelerates (ideally), and as the relative rotational speeds equalize, the torque multiplication diminishes
Facts : 10 Once the impeller and turbine are rotating within 10 %%% of each other s speed, the stator ceases to function and the torque converter acts as a simple fluid coupling
Facts : 11 Planetary gears train Consisting of planetary gear sets as well as clutches and bands
Facts : 12 These are the mechanical systems that provide the various gear ratios, altering the speed of rotation of the output shaft depending on which planetary gears are locked
Facts : 13
