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| Illustration 1 | g00576598 |
Lockup Clutch Selector Valve (1) Spool (2) Passage (3) Passage (4) Passage (5) Spring (6) Cover (7) Screw (8) Stop (9) Spool (10) Passage (11) Passage (12) Body (13) Cover | |
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| Illustration 2 | g00577426 |
(14) Lockup clutch selector valve | |
Lockup clutch selector valve (14) is fastened to the front of the transmission case above the input shaft.
Lockup clutch selector valve (14) controls the lockup clutch in the torque converter. Three different conditions control the lockup clutch.
- Elevator operation
- Transmission input shaft speed (rpm)
- Load piston in the selector and the pressure control valve
Transmission Input Shaft Speed
A pitot tube on the input shaft of the transmission monitors the input shaft speed. When the input shaft is rotating at 1480 rpm or above 1480 rpm, oil is forced into passage (3) from the pitot tube. The oil pressure from passage (3) goes through passage (2). The oil pressure then causes spool (9) to move to the right. As the spool moves to the right, the lockup clutch signals that the oil in passage (4) is blocked. The oil cannot flow to the drain through passage (10). The signal pressure for the lockup clutch will increase. The spool in the reducing valve will move due to this increase. This will engage the lockup clutch in the torque converter. The machine will now be in direct drive.
If the load increases and the transmission input shaft decreases to 1360 rpm or below 1360 rpm, the pressure of the oil in passage (3) will decrease. Spring (5) will move spool (9) to the left. When the spool is on the left, the lockup clutch signals that the oil pressure in passage (4) will flow to the drain. The oil pressure will flow through passages (10) and (11). Movement of the spool in the reducing valve will block the flow of oil to the lockup clutch. The lockup clutch will disengage and the machine will now be in converter drive. Screw (7) is used to adjust the rpm setting for the valve.
Load Piston
When the machine is in direct drive and the operator changes the position of the transmission control lever, the load piston will move to the right. This will open a passage to the drain. The lockup clutch signals that the oil pressure will decrease. The lockup clutch also signals that the spool in the reducing valve will move. This will then block the flow of oil to the lockup clutch. The pressure in the lockup clutch signals that the circuit pressure will increase as the load piston moves to the left.
Elevator Operation
When the elevator on the scraper is engaged in the forward position, pilot oil flows through the elevator pilot valve. A pressure switch reads the pilot oil after the oil flows through the elevator pilot valve. The pressure switch sends an electrical signal to the torque converter lockup clutch solenoid. The torque converter lockup clutch solenoid then sends air pressure into the cavity between cover (13) and spool (1). The air pressure will cause the spool to move to the right. As the spool moves to the right, the signal oil for the lockup clutch will flow to the drain through passages (10) and (11). The spool in the reducing valve will move. The movement of the spool in the reducing valve will block the flow of oil to the lockup clutch. The lockup clutch will disengage and the machine will now be in converter drive.