2. Controls the shifting pattern ofthetransmission.
This is done by switching hydraulic pressure to
programmed combinations of clutches and
brake bands based on vehicle speed and engine
3. Circulates the transmission fluid through a
remote cooler to remove excess heat that is
generated in the transmission and torque
4. Provides a constant fresh supply of oil to all
critical wearing surfaces of the transmission.
The hydraulic system for an automatic trans-
mission typically consists of the following.
The typical hydraulic pump (fig. 4-36) is an
internal-external rotor or gear-type pump. Located in
the front of the transmission case, it is keyed to the
torque converter hub so that it is driven by the engine.
As the torque converter spins the oil pump,
transmission fluid is drawn into the pump from the
transmission pan. The pump compresses the oil and
forces it to the pressure regulator. The pump has
several basic functions:
Produces pressure to operate the clutches, the
bands, and the gearsets.
Lubricates the moving parts in the transmission.
Keeps the torque converter filled with trans-
mission fluid for proper operation.
Circulates transmission fluid through the trans-
mission and cooling tank (radiator) to transfer
Operates hydraulic valves in the transmission.
The pressure regulator limits the maximum
amount of oil pressure developed by the oil pump. It is
a spring-loaded valve that routes excess pump pressure
out of the hydraulic system, assuring proper
Figure 4-36.Typical transmission hydraulic pump.