FOAM 3P4371 - Caterpillar

Modulation Reduction Valve (Clutch Released)
Illustration 25 g01086010
When the clutch needs to be released, the position of the rotary selector spool will cause the pilot pressure to drain. The springs will move the selector piston against the stop. The passage between the load piston and the selector piston will be open to drain. The springs will move the load piston against the stop.The modulation reduction valve will shift. Movement of the modulation reduction valve closes the passage from the pump to the clutch. This opens the passage from the clutch to the drain.A decay orifice is located in the drain passage in order to control the amount of time that is required for the pressure in the clutch to reach zero. These orifices are color coded. The clutch that is used for reverse does not have a decay orifice.Electronic Clutch Pressure Control (ECPC)
Illustration 26 g01086011
Another method of electronic clutch engagement is called Electronic Clutch Pressure Control (ECPC). With ECPC, the transmission shifting function is controlled by the Power Train Electronic Control Module. The Power Train ECM responds to the operator shifting requests by controlling the amount of electrical current that is sent to the proportional solenoids.The ECM selects the transmission clutches to be engaged and the clutch pressure is modulated electronically. The proportional solenoid valves control the modulation of the clutch pressure. The ECM uses the transmission speed, engine speed, and the power train oil temperature signals in order to control smooth engagement of the clutches.Electronic clutch modulation allows the ECM to control the time that is required to fill a clutch with oil and the rate of the clutch pressure modulation.
Illustration 27 g01086013
The ECPC transmission clutches are hydraulically engaged and the spring released. The transmission modulating valve solenoid is energized (Illustration 27) in order to send supply oil to the clutch. As current is applied to the solenoid, magnetic force moves the rod to the right which pushes the ball closer to the orifice. The ball begins to restrict the amount of oil to drain. As the pressure at the left end of the spool increases, the spool shifts to the right and directs supply oil in order to engage the clutch.When the solenoid is de-energized, no force is acting on the rod and supply oil flows through the spool and the orifice to drain. The spring that is located on the right end of the valve spool moves the spool to the left. The valve spool opens the passage between the clutch and the tank. The valve spool blocks the passage between the clutch and the supply oil. Oil flow to the clutch is blocked. Oil from the clutch flows to the drain and the clutch is released.
Illustration 28 g01086015
Illustration 28 shows the ECPC transmission modulation cycle. The vertical axis represents current and clutch pressure. The current that is represented is from the Power Train ECM to the modulating solenoid valve. The pressure that is represented is supplied to each individual clutch. When the clutch is filled and the piston