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| Illustration 1 | g03413063 |
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Hydraulic schematic for BOOM RAISE (High Speed) (1) Boom cylinders (2) Line (3) Line (4) Pilot line (5) Main control valve (6) Boom I control valve (7) Port (8) Port (9) Port (10) Pilot line (11) Boom drift reduction valve (12) Port (13) Load check valve (14) Passage (15) Return passage (16) Boom up-limit valve (17) Boom regeneration PRV (18) Boom II control valve (19) Parallel feeder passage (20) Load check valve (21) Pilot line (22) Pressure reducing valve for boom priority (23) Pilot control valve (24) Pilot line (25) Drive pump (26) Pilot pump (27) Idler pump | |
A BOOM RAISE operation at high speed is accomplished when the oil delivery from both idler pump (27) and drive pump (25) is supplied to the head end of boom cylinders (1). Boom I control valve (6) and boom II control valve (18) operate during the high speed operation. A BOOM RAISE operation at low speed is accomplished when the oil delivery from only drive pump (25) is supplied to the head end of boom cylinders (1). During the low speed operation, boom I control valve (6) operates alone.
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| Illustration 2 | g03413183 |
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Main control valve (6) Boom I control valve (8) Port (12) Port (18) Boom II control valve | |
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| Illustration 3 | g03413184 |
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BOOM RAISE (7) Port (6) Boom I control valve (9) Port (11) Boom drift reduction valve (12) Port (13) Load check valve (14) Passage (15) Return passage (18) Boom II control valve (19) Parallel feeder passage (20) Load check valve (28) Spring (29) Spring (30) Spool (31) Passage (32) Passage (33) Passage (34) Passage (35) Passage (36) Passage (37) Passage (38) Passage (39) Spool (40) Spring (41) Spring | |
During a BOOM RAISE operation at high speed, the oil delivery from drive pump (25) flows through passage (14) in main control valve (5). The oil then flows through boom I control valve (6) and through boom drift reduction valve (11) to port (12). The oil delivery from idler pump (27) flows through boom II control valve (18), to parallel feeder passage (19), and into main control valve (5). The oil then flows through check valve (20) and to port (12). The combined pump flow from drive pump (25) and idler pump (27) is supplied to port (12).
When the joystick for the boom is moved to the full BOOM RAISE position, the pilot oil flows from pilot control valve (23) through pilot line (24) to boom up-limit valve (16). The pilot oil flows through line (4) and divides into three flow paths. Part of the pilot oil flows through pilot line (4) to port (7) of main control valve (5). The remainder of the pilot flow in pilot line (4) flows to pilot line (10) and port (9) which acts on boom II control valve (18). Part of the pilot oil also flows through pilot line (21).
The pilot oil in pilot line (21) flows to the pressure reducing valve for boom priority (24). During a combined operation of BOOM RAISE and STICK IN, pilot oil flows to the pressure reducing valve for boom priority (22). This action causes the boom circuit to receive oil flow priority and allows the boom to raise at a high speed.
The pilot oil flow from port (7) shifts spool (30) of boom I control valve (6) against the force of spring (28) and spring (29). The oil delivery from the drive pump in passage (14) flows through load check valve (13). From load check valve (13), the oil flows to passage (35) and to passage (34). The oil then flows to boom drift reduction valve (11) and shifts boom drift reduction valve (11) to the left. The oil delivery from the drive pump then flows through port (12) to the head end of boom cylinders (1).
The pilot oil flow in port (9) of boom II control valve (18) shifts spool (39) against the force of spring (40) and spring (41). The oil delivery from the idler pump in parallel feeder passage (19) now flows through passage (38) to check valve (20). The oil delivery from the idler pump shifts check valve (20) to the right. The oil delivery from the idler pump then combines with the oil delivery from the drive pump. The combined pump oil flows from port (12) through line (3) to the head end of boom cylinders (1).
Return oil from the rod end of boom cylinders (1) flows through line (2) to boom I control valve (6). The oil then flows through passage (37) , through return passage (15), and into the hydraulic tank.
When the joystick for the boom is moved less than half of the travel distance for a BOOM RAISE operation, low pilot oil pressure is supplied to boom I control valve (6) and boom II control valve (18).
When the boom is raised at a low speed, boom I control valve (6) shifts and boom II control valve (18) does not shift. The force of spring (28) and spring (29) in boom I control valve (6) is less than the force of spring (40) and spring (41) in boom II control valve (18). Because of the low pilot oil pressure, boom I control valve (6) will open and boom II control valve (18) will remain closed.
The oil delivery from drive pump (25) now flows to the head end of boom cylinders (1). Without the oil delivery from idler pump (27), the cylinder rod movement slows down when the boom is raised. A low speed boom operation is performed.
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| Illustration 4 | g03413187 |
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(5) Main control valve
(16) Boom up-limit valve (17) Boom regeneration PRV (22) Boom priority valve | |
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| Illustration 5 | g03413193 |
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Hydraulic schematic for BOOM RAISE and STICK IN (6) Boom I control valve (16) Boom up-limit valve (17) Boom regeneration valve (18) Boom II control valve (22) Boom priority valve (23) Pilot control valve (42) Stick I control valve (43) Stick regeneration valve (44) Stick II control valve (45) Pilot control valve | |
During combined operations of BOOM RAISE and STICK IN, the pilot oil pressure from the pilot control valve for the boom (23) activates the pressure reducing valve for boom priority (22). The pressure reducing valve for boom priority (22) causes oil flow priority to the head end of the boom cylinders (1) during this combined hydraulic operation.
When the joystick for the stick is moved to the STICK IN position, a portion of the pilot oil from pilot control valve (45) for flows through boom priority valve (22) to stick II control valve (44). As the joystick for the boom is moved farther from the NEUTRAL position during a BOOM RAISE operation, pilot oil pressure from pilot control valve (23) increases. This gradual increase in pilot oil pressure causes boom priority valve (22) to shift.
A portion of the pilot oil that flows to stick II control valve (44) from pilot control valve (45) is routed to the hydraulic tank. The pilot oil pressure that acts on the stick II control valve decreases. The stick II control valve shifts toward the NEUTRAL position. The amount of oil flow from the hydraulic pumps to the stick hydraulic circuit decreases. This action causes a greater portion of the oil flow from the hydraulic pumps to flow to the head end of the boom cylinders.
Since the pilot oil pressure from the pilot control valve for the boom (23) directly corresponds to the amount of movement or position of the joystick, a gradual change to boom priority occurs. Thus, boom priority is controlled by the position of the joystick for the boom, and boom priority automatically activates when the joystick reaches a certain position during a BOOM RAISE operation.
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| Illustration 6 | g03413194 |
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Hydraulic schematic for BOOM LOWER with regeneration (1) Boom cylinders (2) Line (3) Line (6) Boom I control valve (8) Port (11) Boom drift reduction valve (12) Port (13) Load check valve (14) Passage (16) Boom up-limit valve (17) Proportional reducing valve (18) Boom II control valve (23) Pilot control valve (25) Drive pump (26) Pilot pump (27) Idler pump (33) Passage (37) Passage (46) Passage (47) Spool (48) Port (49) Port (50) Port (51) Port (52) Line (53) Boom down pressure sensor | |
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| Illustration 7 | g03413195 |
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Boom I control valve (BOOM LOWER with regeneration) (6) Boom I control valve (8) Port (11) Boom drift reduction valve (13) Load check valve (14) Passage (18) Boom II control valve (28) Spring (29) Spring (30) Spool (33) Passage (34) Passage (39) Spool (40) Spring (41) Spring (47) Spool (48) Port (49) Port (51) Drain port (53) Passage (54) Return Passage (55) Passage (56) Center bypass passage (57) Passage (58) Passage (59) Passage (60) Check valve (61) Passage (62) Passage | |
During a BOOM LOWER operation, the oil delivery from only drive pump (25) is supplied to boom cylinders (1). Boom I control valve (7) operates alone. Boom II control valve (19) has a regeneration circuit that functions during the BOOM LOWER operation. This function supplies return oil from the head end of boom cylinders (1) to the rod end of the boom cylinders.
When the joystick for the boom is moved to the BOOM LOWER position, pilot oil from pilot control valve (18) flows to pilot line (52). The pilot oil flow then divides into three flow paths. Part of the pilot oil flows through port (47) to boom I control valve (7). Part of the pilot oil flows to boom regeneration PRV (53), and depending on the position of the boom will allow pilot oil flow to port (48) of boom II control valve (19). The remainder of the pilot oil flows through port (49) to spool (46).
The pilot oil flow from port (47) shifts spool (28) in boom I control valve (7) against the force of spring (26) and spring (27). The oil delivery from the drive pump in passage (14) flows through load check valve (13), passage (35) and port (9). The oil delivery from the drive pump then flows through line (2) to the rod end of boom cylinders (1).
The return oil from the head end of boom cylinders (1) flows through line (3), to port (12), and then to boom drift reduction valve (11). Since spool (46) is shifted by the pilot pressure from port (49), passage (31) is open to drain port (51). The oil pressure that is acting on boom drift reduction valve (11) becomes lower than the pressure in line (3). Valve (11) shifts to the left and the oil in line (3) flows to passage (32). Then, the oil flows through passage (55) and return passage (55) to the hydraulic tank. Since the return oil is restricted at passage (55), the movement of the boom cylinders is slowed and the boom can lower at an appropriate speed in accordance to the flow rate of the drive pump oil.
The boom regeneration function supplies return oil from the head end of boom cylinders (1) to the rod end of the boom cylinders.
Boom DOWN pressure sensor (53) measures the pilot oil hydraulic pressure for a boom DOWN operation. The pressure sensor sends a pulse width modulated signal (PWM) input to the machine ECM. The pressure information is used for boom regeneration control.
When boom down pressure sensor (53) detects pilot pressure, boom regeneration PRV (53) remains de-activated. Pilot oil is then directed through boom regeneration PRV (17) and to boom II control valve (18) allowing regeneration.
When pressure sensor for boom down control (53) detects pilot pressure, boom regeneration PRV (17) begins to receive a PMW signal from the machine ECM. The machine ECM begins to increase current flow which decreases the amount of pilot oil supplied to the boom II control valve. The boom regeneration circuit is then disabled.
Note: The amount of PMW signal to boom regeneration PRV (17) varies, depending on the position of the engine speed dial.
Boom regeneration PRV (17) is used in order to control the amount of regeneration oil in the boom circuit. The machine ECM receives an input signal from boom down pressure sensor (53).
When pressure in pilot line (52) increases, boom down pressure sensor (53) measures the pilot oil pressure during a boom LOWER operation. The pressure sensor for boom down control sends a pulse width modulated signal (PWM) input to the machine ECM. The machine ECM uses the pressure information to reduce engine speed and pump flow during a boom down operation. The machine ECM controls the signal to boom regeneration PRV (17) in order to regulate the amount of pilot oil flow through port (49) of boom II control valve. The pilot oil forces spool (39) against spring (40) and spring (41). Now, part of the return oil from the head end of the boom cylinders enters boom II control valve (18) and the oil flows through passage (61) to check valve (60). The check valve opens and the oil flows through passage (58) . The oil then flows through port (8) to the rod end of the boom cylinders.
When the joystick for the boom is moved to the BOOM LOWER position, spool (30) and spool (39) are shifted upward. Passage (57) and passage (59) are opened and passage (56) is restricted. Oil in the center bypass passage flows through opened passage (57) to passage (59). When passage (57) is opened enough, an optimum amount of oil flows through passage (56). Spool (30) regulates the amount of negative flow control pressure in order to destroke the drive pump since less oil flow is required for a boom lower.
Note: For more information on the negative flow control operation, refer to Systems Operation, "Negative Flow Control System".