PLUG-ORIFICE 3T4968 - Caterpillar

Illustration 1 g01316808
(1) Modulating valvesNine modulating valves (1) are located on the left side of the transmission and on the front of the transmission.Each modulating valve has a designated letter, as shown. The letters have been cast into the transmission case. The designated letters are used to correlate the modulating valve to the corresponding transmission clutch.ReferenceSee Systems Operation/Testing and Adjusting, "Transmission Power Flow" for additional information.The modulating valve provides the following control functions:
Proportional control of pressure
Controls oil flow to clutch
Illustration 2 g00886268
Schematic for Modulating Valve (Transmission) (1) Modulating valve (transmission) (2) Test port (3) Transmission clutch (4) Spring (5) Line to sump (6) Spool orifice (7) Charge pressure oil (8) SolenoidModulating valve (1) is controlled by the transmission electronic control module (ECM). The modulating valve is used by the transmission ECM to directly modulate the oil pressure that is sent to each of the nine individual transmission clutches.When the operator selects a direction or when the operator selects a speed, the transmission ECM sends a pulse width modulated signal in order to vary the current to solenoid (8) .The distance that is travelled by the solenoid plunger is proportional to the electrical current that is sent to the solenoid. The position of the solenoid plunger controls the oil pressure that is sent to transmission clutch (3) .When the transmission ECM sends the maximum programmed current to the modulating valve, the oil pressure in the transmission clutch will be at the maximum desired pressure. When no current is sent to the modulating valve, the oil pressure in the transmission clutch will be zero.Valve Ports
Illustration 3 g01336456
Bottom View of Modulating Valve (Transmission) (5) To sump (7) Charge pressure oil (8) To transmission clutchIllustration 3 shows the bottom view of the modulating valve (transmission). The bottom view shows the porting for the inlet and outlet flow of hydraulic oil.Valve Operation
There are three basic stages of the controlled operation of the modulating valve:
No signal current
Partial signal current
Maximum signal currentThe operation of the modulating valve is not a simple on/off cycle. The transmission ECM varies the strength of the signal current through a programmed cycle in order to control the movement of the proportional solenoid valve spool.No Signal Current (Clutch Disengaged)
Illustration 4 g00774321
Modulating Valve (Transmission) (1) Modulating valve (transmission) (2) Test port (4) Spring (5) Line to sump (6) Spool orifice (7) Charge pressure oil (8) To transmission clutch (9) Solenoid (10) Ball (11) Valve spool (12) Drain orifice (13) PinThe transmission ECM controls the rate of oil flow through modulating valve (1) by changing the strength of the signal current to solenoid (9). When signal current is not being sent to the solenoid, the solenoid will be de-energized.Oil Flow in a De-energized Valve
Spring (4) holds the valve spool to the left in the valve body.The valve spool opens the passage between transmission clutch (3) and the sump.The valve spool blocks the passage between the transmission clutch and the charge pressure oil. Consequently, pressurized oil flow is blocked to the transmission clutch.Charge pressure oil (7) flows from