HOUSING 9M3721 - Caterpillar

Illustration 1 g03420259
Transmission Hydraulic Control Group
(1) Six clutch solenoid modulating valves
(2) Torque converter inlet relief valve
(3) Transmission hydraulic control relief valve The transmission hydraulic control group controls the oil pressure to the torque converter and to the transmission clutches. The transmission hydraulic control group is installed on the top of the transmission planetary group. The transmission hydraulic control group consists of the following components: six clutch solenoid modulating valves (1), torque converter inlet relief valve (2) and transmission hydraulic control relief valve (3).Pressurized oil for the operation of the transmission hydraulic control group flows from the transmission oil pump to the transmission oil filter. The oil flows through a hose to the oil inlet in the transmission. The oil flows through internal passages in the transmission in order to supply transmission hydraulic control relief valve (3) with oil. The oil also flows to six clutch solenoid modulating valves (1).The six clutch solenoid modulating valves (1) are mounted on the top of the transmission. Each transmission clutch has an individual clutch solenoid modulating valve (1). In order to move the machine, a direction clutch solenoid and a speed clutch solenoid must be energized. The clutch solenoid modulating valves (1) are used to directly modulate the oil pressure that is sent to each individual clutch.The following table provides the combination of the energized solenoids and engaged clutches for each forward speed and for each reverse speed.
Table 1
Speed Range and Direction Energized Solenoids and Engaged Clutches
Fourth Speed Forward 3 and 2
Third Speed Forward 4 and 2
Second Speed Forward 5 and 2
First Speed Forward 6 and 2
Neutral 3
First Speed Reverse 6 and 1
Second Speed Reverse 5 and 1
Third Speed Reverse 4 and 1
Fourth Speed Reverse 3 and 1
Illustration 2 g01112314
(3) Transmission Hydraulic Control Relief Valve
(2) Torque converter inlet relief valve
(4) Main relief valve
(5) Transmission control passage
(6) Discharge chamber
(7) Inlet chamber Transmission hydraulic control relief valve (3) controls the pressure of the oil that is supplied to clutch solenoid modulating valves (1) and the torque converter. The oil pressure must overcome the spring force of main relief valve (4). The main relief valve will maintain a stable supply pressure to clutch solenoid modulating valves (1). The supply oil pressure to transmission hydraulic control relief valve (3) is maintained by main relief valve (4) which is set at a minimum pressure of 2340 735 kPa (339.9 5 psi). Oil enters transmission hydraulic control relief valve (3) through inlet chamber (7). The oil flows past main relief valve (4) to transmission control passage (5) until the pressure setting of main relief valve (4) is exceeded. The main relief valve will move to the right. The main relief valve will allow the excess oil to flow into passage (6) and to the torque converter. The maximum torque converter inlet pressure is controlled by torque converter inlet relief valve (2) which is set at 900 175 kPa (130 25 psi). When the torque converter inlet pressure reaches the maximum, the torque converter inlet relief valve