Information and Energy

The hydraulic system is simultaneously the central nervous system and bloodstream of the automatic transmission. Like the nervous system, it carries information vital to the proper functioning of the transmission to its many parts. Like the bloodstream, it uses a pressurized system to carry that information via hydraulic fluid through an intricate circuit of valves.

But more than information, the hydraulic system also sends massive amounts of energy between the engine and the transmission. The functions of the hydraulic system are vital to the propulsion of the vehicle as well as keeping the gears turning smoothly and synchronously.

The Valve Body

At a first glance, the valve body looks like a random array of grooves and channels but it is anything but. A modern valve body is similar in appearance to a computer’s circuit board and its function is very similar. Both are responsible for conveying information to other parts of the system and this information determines the input and output functions of their respective systems.

The valve body makes up a complex system of pathways, all of which have the job of delivering pressurized fluid to every part of the transmission and torque converter. And, just like a circuit board, the valve body of most modern automatic transmissions is controlled by the vehicle’s onboard computer system.

The Gear Pump

The gear pump is a multitasking unit that fills several roles in the operation the transmission. It draws in fluid from the bottom of the transmission, supplying it to the hydraulic system, cooler and torque converter.

The gear pump is, in and of itself, a series of gears. The inner gear is connected to the housing of the torque converter and spins at the same number of revolutions per minute as the engine. The outer gear is turned by the inner gear and is responsible for delivering hydraulic fluid drawn up from a sump at the bottom of the transmission to the hydraulic system.

The Governor

The name sounds a bit foreboding. It might be better understood if it were called «the messenger» as this really is its function. The governor «tells» the transmission how fast the vehicle is moving. It also has a spinning mechanism which relays this information. The faster the vehicle goes, the faster the governor spins.

Like the rest of the hydraulic system, the governor also utilizes fluid to get its job done. As it spins, a small valve inside it dilates, much like a camera’s aperture. As the governor spins, the valve opens and as it spins faster, the valve opens further. Fluid from the pump is then fed into the governor through the transmission’s output shaft based on how far dilated the valve is.Automatic Transmission Valve Body