PIN AS 2357638 - Caterpillar

To describe the operation of this system, there are four different segments of oil that need to be defined. Each segment of oil has a change in pressure when the machine goes from torque converter drive to direct drive. These pressures (AA), (BB), (CC), (DD), (EE), and (FF) are shown in Illustration 1 and Illustration 2.
Oil from the transmission charging pumpOil from the transmission charging pump flows through passage (14). This segment of oil flows to priority reducing valve (19), lockup solenoid (7), downshift solenoid (8), and upshift solenoid (9) .
Pilot oilThe segment of pilot oil is the oil that flows from priority reducing valve (19) through neutralizer valve (15) to rotary selector spool (16). Rotary selector spool (16) directs the pilot oil to the various clutch stations on pressure control valve (11) .
Oil in the clutch supply railOil in the passages from priority reduction valve (19) to clutch supply rail (22) is another segment of oil. This segment of oil is supply oil for all of the modulation reduction valves in each station on pressure control valve (11) .
Clutch oilAnother segment is the oil that flows past the modulation reduction valves in all seven stations in the pressure control valve. This oil in Stations "A", "B", "C", "E", "F", and "G" flows to the transmission clutches. In Station "D", this segment of oil flows under dual stage relief valve (20).
Table 1
Operation of Components in the Transmission Hydraulic Control    
Component     Operation (Function)    
Lockup solenoid (7)     This solenoid sends signal oil in order to activate the torque converter lockup clutch. This solenoid also activates Station "D" in direct drive in order to lower the pressure in clutch supply rail (22).    
Downshift solenoid (8)     This solenoid controls the movement of rotary actuator (10) during downshifts.    
Upshift solenoid (9)     This solenoid controls the movement of rotary actuator (10) during upshifts.    
Rotary actuator (10)     This actuator controls movement of the rotary selector spool (16) in selector and pressure control valve (24).    
Priority reduction valve (19)     In torque converter drive, priority reducing valve (19) controls the segment for pilot oil. In direct drive, the priority reducing valve controls the segments of oil for the transmission charging pump section and for the pilot oil. Priority reducing valve (19) is shimmed in order to set the pressure of the oil in the segments for the transmission charging pump and pilot oil in direct drive. The priority reducing valve is not shimmed in order to set the pilot oil pressure in torque converter drive. Pilot oil pressure in torque converter drive is a result of the setting of the pressure of the transmission charging pump section in direct drive.    
Dual stage relief valve (20)     In torque converter drive, the dual stage relief valve controls the segments of oil for the transmission charging pump section and for clutch supply rail (22). In direct drive, the dual stage relief valve controls the segment