The 8at transmission is a hydraulic automatic transmission (AT for short) with 8 forward gears.
Hydraulic automatic transmission is a transmission device that is a combination of a hydraulic torque converter and a planetary gear transmission. HYDRAULIC CONVERTER is a hydraulic transmission device that can change the transmitted torque.
There are four common types of automatic transmissions, namely hydraulic automatic transmission (AT for short), mechanical continuously variable automatic transmission (CVT for short), and electronically controlled mechanical automatic transmission (AMT for short) ,DCT.
Extended information
In 2006, Lexus first launched the LS460L equipped with an 8at gearbox, and later installed it on the GS460. This 8at gearbox was independently developed by Toyota. BMW, Audi, and Rolls-Royce models only launched models equipped with 8at gearboxes this year, using products from the German ZF company.
Models that widely use 8at gearboxes include: BMW 5 Series Gran Turismo, BMW's new 5 Series (2010 model), Lexus LS460L, Lexus GS460, IS-F, Rolls-Royce Ghost, Audi Brand new A8 (2010 model), Hyundai Genesis Coolpad 3.8 (2013 model).
Reference: Baidu Encyclopedia-8-speed automatic transmission