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| Illustration 1 | g06015185 |
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(1) Displacement change valve (left travel motor)
(2) Displacement change valve (right travel motor) (3) Swing brake (4) Passage (5) Swing control valve (6) Pilot line (pilot pressure to implement pressure switch) (7) Implement pressure switch (8) Travel pressure switch (9) Passage (10) Left travel control valve (11) Right travel control valve (12) Boom I control valve (13) Main control valve (14) Line (pilot oil to swing brake solenoid valve) (15) Boom Up-limit valve (16) PRV for boom regeneration (17) Travel pilot control valve (18) Swing priority valve (19) Idler pump pressure sensor (20) Passage (21) Straight travel control valve (22) Drive pump pressure sensor (23) Boom II control valve (24) Pilot line (pilot oil to the pressure reducing valve for boom priority) (25) Pressure reducing valve for boom priority (26) Pilot control valve for stick and swing (27) Pressure sensor (boom down control) (28) Pilot control valve for bucket and boom (29) Pilot line (BOOM RAISE) (30) Pilot line (pilot pressure to displacement change valves) (31) Pilot line (STICK IN) (32) Pilot line (BOOM LOWER) (33) Pilot line (pilot oil to pilot control valves) (34) Travel speed solenoid valve (35) Swing brake solenoid valve (36) Passage (37) Pilot manifold (38) Passage (39) Passage (40) Valve (hydraulic activation) (41) Hydraulic activation solenoid valve (42) Pilot line (pilot oil flow to pilot oil manifold) (43) Pilot relief valve (44) Pilot filter (45) Pilot line (pilot oil flow from pilot pump to pilot oil filter) (46) Idler pump (47) Drive pump (48) Pilot pump (49) Proportional reducing valve (power shift pressure) | |
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| Illustration 2 | g03411623 |
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Ports and solenoids at the pilot manifold (34) Travel speed solenoid valve (35) Swing brake solenoid valve (40) Valve (hydraulic activation) (41) Hydraulic activation solenoid valve | |
The pilot circuit pressure is limited by pilot relief valve (43).
The oil delivery from pilot pump (48) performs the following main functions:
- Create pilot oil pressure to control the output flows of the main pumps.
- Provide pilot oil pressure to the pilot control valves for implements, swing, and travel to perform machine operations.
- Create pilot oil pressure to automatically operate the control devices.
Note: Each pilot circuit performs one of the functions above.
The pilot circuit is classified into the following circuits:
- Power shift pressure system
- Pilot control valve circuit
- Pressure switch circuits
- Pressure sensors
- Straight travel valve circuit
- Swing parking brake
- Boom priority
- Swing priority
- Automatic travel speed change
- Boom regeneration
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| Illustration 3 | g03411627 |
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(13) Main control valve
(19) Idler pump pressure sensor (22) Drive pump pressure sensor (46) Idler pump (49) Proportional reducing valve (PS pressure) (47) Drive pump (48) Pilot pump (50) Engine ECM (51) Engine speed pickup (52) Machine ECM (53) Engine speed dial (54) Switch panel ECM (55) Monitor | |
During machine operation, machine ECM (52) receives input signals from the following components:
- Engine ECM (50)
- Switch panel ECM (54)
- Engine speed dial (53)
- Monitor in the cab (55)
- Drive pump pressure sensor (22)
- Idler pump pressure sensor (19)
Machine ECM (52) continually monitors all the input signals. The input signals are processed by the machine ECM and an output signal is sent to proportional reducing valve (49) at the drive pump regulator. The proportional reducing valve helps with controlling the output flow of drive pump (47) and idler pump (46).
The oil delivery from pilot pump (48) flows through pilot filter (44) to proportional reducing valve (49) at the drive pump regulator. The electrical signal that is sent from machine ECM (52) causes proportional reducing valve (49) to regulate the pilot pressure to a reduced pressure. This reduced pressure is called power shift pressure (PS). The proportional reducing valve sends the reduced pilot oil pressure through the drive pump regulator and through the idler pump regulator. The output flow of drive pump (47) and idler pump (46) is controlled in accordance with the power shift pressure. The power shift pressure is used to regulate the maximum allowable hydraulic pump output.
The output signal that is sent from the machine ECM to proportional reducing valve (49) will change when the machine ECM detects a change in any of the input signals. The power shift pressure that is sent to the regulators at the drive pump and the idler pump will change to regulate the maximum allowable hydraulic pump output. The desired engine speed is maintained.
A decrease in engine speed increases the power shift pressure. An increase in power shift pressure causes a destroke condition of the drive pump and the idler pump. The maximum allowable hydraulic power output is decreased.
An increase in engine speed decreases the power shift pressure. A decrease in power shift pressure causes an upstroke condition of the drive pump and the idler pump. The maximum allowable hydraulic power output is increased.
Oil from pilot pump (48) flows through pilot line (45), through pilot filter (44), and into pilot line (42). Pilot oil then flows into pilot manifold (37). When the hydraulic activation control lever is shifted to the UNLOCKED position, the machine ECM energizes hydraulic activation solenoid valve (41). The pilot oil then flows through hydraulic activation solenoid valve (41) and shifts valve (40) downwards. The pilot oil now flows through valve (40) and into pilot line (33). The pilot oil then flows to pilot control valves (17), (26) and (28) for the implements, swing, and machine travel operations. When the joysticks and/or travel levers/pedals are moved from the NEUTRAL position, pilot oil flows to main control valve (13) to control the machine functions.
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| Illustration 4 | g03411629 |
When joystick (26) and/or joystick (28) is operated, the pilot control valves send pilot pump oil through the pilot lines to pilot ports at the main control valve to shift the spools in the main control valve. Refer to Illustration 4 and Table 1 for the location of the pilot lines and machine operations.
| Pilot line | Control Valve | Machine Operation |
| (56) | Bucket control valve | BUCKET CLOSE |
| (57) | Attachment control valve | WORK TOOL (if equipped) |
| (58) | Stick II control valve | STICK OUT |
| (59) | Boom II control valve | BOOM RAISE |
| (60) | Boom I control valve | BOOM RAISE |
| (61) | Right travel control valve | FORWARD RIGHT TRAVEL |
| (62) | Left travel control valve | FORWARD LEFT TRAVEL |
| (63) | Stick regeneration control valve | STICK IN |
| (64) | Swing control valve | SWING RIGHT |
| (65) | Stick I control valve | STICK OUT |
Pilot oil from the pilot control valves flows through pilot lines to the ports on the bottom of the main control valve to perform the opposite operation.
The following example is given for a BOOM LOWER operation and a BOOM RAISE operation. Machine operations for a stick operation, bucket operation, travel operation, and swing operation are accomplished in the same manner as the boom operation.
When the joystick for the boom is moved to the BOOM RAISE position, pilot oil from pilot control valve (28) flows through pilot line (29) and through boom up-limit valve (15). Pilot oil then flows to boom I control valve (12) and boom II control valve (23). The pilot pressure shifts the boom I control valve and the boom II control valve. The oil delivery from the hydraulic pumps flow to the head end of the boom cylinders to perform the BOOM RAISE operation.
When the joystick for the boom is moved to the BOOM LOWER position, pilot oil from pilot control valve (28) flows through pilot line (32) and to boom I control valve (12). The pilot pressure shifts the boom I control valve upwards. The BOOM LOWER operation is now performed.
For more information concerning the operation of the boom, refer to Systems Operation Manual, "Boom System".
When the travel controls are in the NEUTRAL position, the pilot pressure in passage (9) remains low and travel pressure switch (8) is OFF. The machine ECM recognizes the OFF condition of all the pressure switches. The AEC system is activated to lower the engine rpm. If either travel control is moved from the NEUTRAL position, the pilot oil pressure in passage (9) increases and travel pressure switch (8) is turned ON. The machine ECM activates the AEC system to increase the engine rpm.
When the implement controls are in the NEUTRAL position, the pilot pressure in passage (6) remains low and implement pressure switch (7) is OFF. The machine ECM recognizes the OFF condition of all the pressure switches. The AEC system is activated to lower the engine rpm. If any of the implement controls are moved from the NEUTRAL position, the pilot oil pressure in passage (6) increases and implement pressure switch (7) is turned ON. The machine ECM activates the AEC system to increase the engine rpm.
Pressure sensor (27) is connected to pilot oil for boom down control. This pressure sensor sends an electrical signal to the machine ECM.
When a boom DOWN operation is performed, pressure sensor (27) sends an electrical signal to the machine ECM. The machine ECM uses the pressure sensor information and then sends a signal to the following components:
- PRV for boom regeneration (16) limits pilot oil to the boom II control valve to control boom regeneration.
- The AEC system is activated to lower the engine rpm.
Drive pump pressure sensor (22) and idler pump pressure sensor (19) are on main control valve (13).
When a swing operation and/or implement operation is performed during a travel operation, pilot pressure in passage (4) increases and pilot oil flows through passage (20) to straight travel control valve (21). Pilot pressure shifts straight travel control valve (21) downward. The straight travel control valve maintains straight travel even though there is a swing operation or an implement operation during travel. For more information concerning the operation of the straight travel control valve, refer to Systems Operation Manual, "Control Valve (Straight Travel)".
When the hydraulic activation control lever is placed in the UNLOCKED position, pilot oil in passage (36) flows through valve (40) and passage (39) to provide oil to swing brake solenoid valve (35). When any of the joysticks are moved from the NEUTRAL position, the increase of pilot pressure activates implement pressure switch (7). The pressure switch sends an electrical signal to the machine ECM. An electrical signal from the machine ECM energizes swing brake solenoid valve (35) once the pilot oil pressure exceeds
For more information concerning the operation of the swing brake, refer to Systems Operation Manual, "Pilot Valve (Swing Parking Brake)".
During combined operations of BOOM RAISE and STICK IN, the pilot oil pressure in pilot line (31) and pilot line (24) activates pressure reducing valve for boom priority (25). Pressure reducing valve for boom priority (5) allows priority flow to the head end of the boom cylinders during these combined hydraulic operations by disabling the stick II control valve.
For more information concerning the pressure reducing valve for boom priority, refer to Systems Operation Manual, "Boom System".
During a swing operation, pilot oil flows from pilot control valve (26) to swing control valve (5). Pilot oil also flows to swing priority valve (18). The swing priority valve shift and blocks part of the oil supply from the idler pump to the stick control valve. Most of the flow from the idler pump now goes to the swing motor. For more information concerning the swing priority valve, refer to Systems Operation Manual, "Swing System".
Automatic Travel Speed Change Valve
Pilot oil in passage (38) flows to travel speed solenoid valve (34). When the travel speed switch on the right console is set at the HIGH SPEED position, the travel speed solenoid valve energizes. This action allows pilot oil to flow through travel speed solenoid valve (34) and through line (30). The oil then flows to displacement change valve (1) and displacement change valve (2). As the displacement change valve operates, the travel speed is maintained at the HIGH SPEED position.
When the travel speed switch on the right console is set at the HIGH SPEED position, the pressure sensor for the drive pump or idler pump delivery pressure controls the travel speed in accordance with the travel load. For example, low speed during a high load condition and high speed during a low load condition.
For more information concerning the operation of the displacement change valves, refer to Systems Operation Manual, "Displacement Change Valve".
Proportional reducing valve for boom regeneration (16) is used to control the amount of regeneration oil in the boom circuit. During a boom DOWN operation, pilot oil flows through PRV (16) to boom II control valve (23). The pilot oil shifts boom II control valve (23) allowing regen oil to flow from the head end of the boom cylinder to the rod end.
PRV for boom regeneration (16) can also limit the amount of pilot oil supplied to the boom II control valve. The amount of regeneration oil supplied to the rod end of the boom cylinder depends on the engine speed dial.
For more information concerning the operation of the boom regeneration system, refer to Systems Operation Manual, "Boom System".
For more information concerning the ECM logic of the boom regeneration system, refer to Systems Operation Manual, "Electrical Output Components".