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| Illustration 1 | g00431858 |
Pilot control valve (travel) (1) Travel control lever (2) Pedal (3) Rod (4) Seat (5) Spring (6) Spring (7) Spool (8) Passage (9) Passage (10) Spring (11) Spool (12) Return port (13) Return chamber (14) Passage (15) Passage (16) Pilot port (17) Passage (18) Port (19) Passage (20) Passage (21) Passage (22) Port (23) Piston chamber (24) Orifice (25) Piston (26) Spring (27) Spring (28) Spring chamber (29) Ball (30) Rod (31) Spring (32) Spring (33) Spring chamber (34) Ball | |
Travel control lever (1) is moved to the FORWARD TRAVEL position. Pedal (2) moves rod (3) and seat (4) in a downward direction against the force of springs (5) and (6). Spool (7) moves downward and spool (7) opens passage (19) by compressing spring (6) .
As passage (19) is opened, the oil from pilot port (16) goes through passages (21), (19), (20) and (9). Oil flows through port (18) to the travel control valve. The pilot oil causes the stem of the travel control valve to shift. Main pump oil now goes through the main control valve to the travel motor for forward travel.
When travel control lever (1) is moved for fine travel, rod (3) moves seat (4) in a downward direction. Spring (6) moves spool (7) downward. The oil pressure increases in port (18). Spool (7) moves upward against the force of spring (6). Passage (8) opens to return chamber (13). The oil pressure at port (18) decreases. Spool (7) is balanced between the pressure at port (18) and the force of the spring. Spool (7) modulates the pressure.
Note: For more information, refer to Systems Operation, "Pilot Valve (Joystick)".
When lever (1) is moved to FULL STROKE position, rod (3) and seat (4) push spool (6) downward against the force of springs (5) and (7). When spool (6) moves down, passage (9) opens. Full pilot pressure of approximately 3450 kPa (500 psi) develops at port (16) .
Return pilot oil from the travel control valve enters the pilot control valve through port (22). Spool (11) is pushed upward by the force of spring (10). The return oil from port (22) flows through passage (17), passage (15), passage (14) and return chamber (13). The oil then returns to the hydraulic tank.
When the control lever is released, spring (5) forces seat (4) and rod (3) upward. The compression force of spring (6) is released and spool (7) moves upward. The oil in port (18) flows through passages (9), (20) and (8). The oil then flows through return camber (13) and back to the hydraulic tank.
When lever (1) is moved to the REVERSE TRAVEL position, the pilot control valve receives pilot oil through port (22). Return oil flows through port (18) in the same manner as the return oil flows for the FORWARD TRAVEL position.
The damper mechanism is built in this pilot control valve. This mechanism gives operation feeling of travel control lever (1). This mechanism prevents vibration when travel control lever (1) is released.
When travel control lever (1) is moved faster than normal, pedal (2) pushes rod (3) downward. Rod (3) pushes piston (25) downward and rod (3) pushes springs (26) and (27) downward. The hydraulic oil in spring chamber (28) is pressurized. Ball (29) closes the opening. The pressurized oil moves out of spring chamber (28) gradually into piston chamber (23) through orifice (24). Rod (30) is pushed up by springs (31) and (32). The oil pressure in spring chamber (33) pushes up ball (34) from chamber (13). As a result, rod (30) follows the movement of pedal (2).
When travel control lever (1) is partially moved for fine control, rod (3) is pushed down slowly. As a result, the oil pressure in spring chamber (28) and in piston chamber (23) becomes equal soon, so that the damper force is weak.