Hydraulic Schematic for the Pilot Circuit
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| Illustration 1 | g02175457 |
(1) Displacement change piston (left travel motor) (2) Passage (3) Displacement change valve (left travel motor) (4) Displacement change piston (right travel motor) (5) Passage (6) Displacement change valve (right travel motor) (7) Line (front swing motor parking brake) (8) Passage (front swing motor parking brake) (9) Swing parking brake (front swing motor) (10) Solenoid valve (swing parking brake) (11) Passage (rear swing motor parking brake) (12) Swing parking brake (rear swing motor) (13) Proportional solenoid valve for left swing (14) Passage (15) Swing control valve (16) Passage (17) Proportional solenoid valve for right swing (18) Line (pilot oil to swing control valve and swing parking brake solenoid valve) (19) Line (pilot oil to neutral flow control solenoid) (20) Neutral flow control valve (21) Passage (pilot oil to neutral flow control valve) (22) Solenoid valve (neutral flow control) (23) Proportional solenoid valve for attachment spool (24) Passage (25) Proportional solenoid valve for bucket cylinder rod end (BUCKET OPEN) (26) Passage (27) Proportional solenoid valve for boom cylinder rod end (BOOM DOWN) (28) Passage (29) Solenoid valve (boom drift reduction/regeneration valve) (30) Line (pilot oil to solenoid valve for boom drift reduction/regeneration valve) (31) Passage (32) Boom regeneration valve (33) Line (pilot oil to travel motor displacement change valves) (34) Solenoid valve (travel motor displacement change) (35) Line (PS pressure to main pump) (36) Proportional reducing valve (PS pressure) (37) Solenoid valve (hydraulic activation) (38) Accumulator (39) Pilot relief valve (40) Passage (pilot oil manifold main feeder) (41) Valve (hydraulic activation) (42) Passage (pilot oil to hydraulic activation valve) (43) Pilot manifold (44) Proportional solenoid valve for stick cylinder rod end (STICK OUT) (45) Passage (46) Proportional solenoid valve for left travel (forward) (47) Passage (48) Proportional solenoid valve for right travel (forward) (49) Passage (50) Attachment control valve (51) Bucket control valve (52) Boom control valve (53) Stick control valve (54) Left travel control valve (55) Right travel control valve (56) Passage (57) Proportional solenoid valve for attachment spool (58) Passage (59) Proportional solenoid valve for bucket cylinder head end (BUCKET CLOSE) (60) Passage (61) Proportional solenoid valve for boom cylinder head end (BOOM UP) (62) Line (pilot oil to boom, bucket, and attachment proportional solenoid valves) (63) Stick regeneration valve (64) Solenoid valve (stick drift reduction/regeneration valve) (65) Line (pilot oil to solenoid valve for stick drift reduction/regeneration valve) (66) Passage (67) Line (pilot oil to travel and stick proportional solenoid valves) (68) Proportional solenoid valve for stick cylinder head end (STICK IN) (69) Passage (70) Proportional solenoid valve for left travel (reverse) (71) Passage (72) Proportional solenoid valve for right travel (reverse) (73) Passage (74) Line (pilot oil to pilot manifold) (75) Pilot filter (76) Line (pilot oil to pilot filter) (77) Line (main pilot outlet) (78) Pilot pump (79) Line (supply oil to pilot pump) (80) Swing pump (81) Line (pilot oil to swing pump control) (82) Ball resolver (83) Line (pilot oil to main pump control) (84) Main hydraulic pump (front pump and rear pump) (85) Check valve (86) Check valve (87) Regulator (front pump) (88) Regulator (rear pump) | |
Pilot Oil Circuit
The oil delivery from pilot pump (78) performs the following main functions.
- Control the output flows of the main and swing pumps.
- Operate the main control valve spools.
- Control the regeneration valves for the boom and the stick.
- Control the speed of the travel motors
Pilot pump (78) is a gear type pump that provides oil flow to control the main hydraulic circuits. Pilot pump (78) is driven by the driveshaft of the cooling fan pump. The driveshaft of the cooling fan pump is driven by the driveshaft of swing pump (80). An auxiliary driven gear from the engine crankshaft drives the swing pump (80), the cooling fan pump, and pilot pump (78) .
Hydraulic oil from the hydraulic tank is supplied through line (79) to pilot pump (78). Pilot pump (78) pumps pilot oil through line (77) to three main lines. The three pilot oil lines are: line (76), line (81) and line (83)
Line (83) supplies pilot oil to check valve (85) and is used to control regulator (87). Line (83) supplies pilot oil to check valve (85) and is used to control regulator (87) .
Line (81) supplies pilot oil to ball resolver (82) in order to control the swing pump (80) .
Line (76) supplies pilot oil to pilot filter (75). Pilot oil then flows through line (74) to pilot manifold (43). Pilot oil flows into passage (40) within pilot manifold (43). The pilot oil circuit pressure is limited by pilot relief valve (39) .
Note: When the hydraulic activation control lever is shifted to the LOCKED position, solenoid valve (37) is de-energized. Valve (41) is not shifted. Pilot oil is not supplied to the proportional solenoid valves. However, pilot oil flows to accumulator (38). Pilot pressure that fills accumulator (38) is used to safely lower implements in the event of a power failure.
The pilot circuit is classified into the following circuits and each circuit performs one of the above functions.
- Main pump and swing pump control
- Power shift pressure system
- Proportional solenoid valve operation at the main control valve and the swing control valve
- Boom regeneration solenoid valve
- Stick regeneration solenoid valve
- Neutral bypass solenoid valve
- Swing parking brake
- Automatic travel speed change valve
Main Pump and Swing Pump Control
Part of the oil delivery from pilot pump (78) flows directly into swing pump (80) and main pump (84) through line (81) and line (83). When the main pump and the swing pump are at low delivery pressure, pilot pressure controls the angle of the swashplates. The angle of the swashplate controls the output flow of the pumps.
Pilot oil flow in line (81) flows to swing pump (80) and to ball resolver (82). When the pilot oil pressure is higher than the swing pump output, pilot oil shifts ball resolver (82). Swing pump output is blocked from flowing to the swashplate servo pistons. Pilot oil flows to the swashplate servo pistons. Pilot oil pressure controls swing pump (80) output.
Pilot oil flow in line (83) flows to main pump (84). Pilot oil flows to check valves (85) and (86). When the pilot oil pressure is higher than the main pump output, pilot oil flows to the swashplate servo pistons.
Pilot oil flow in line (83) flows to main pump (84) and to check valves (85) and (86). When the pilot oil pressure is higher than the main pump output, pilot oil shifts check valves (85) and (86). Main pump output is blocked from flowing to the swashplate servo pistons. Pilot oil flows to the swashplate servo pistons. Pilot oil pressure controls main pump (84) output.
Power Shift Pressure System
During machine operation, the machine ECM receives input signals from the following components:
- Engine speed dial
- Work mode control on the keypad
- Engine speed sensor that is located on the flywheel housing
The machine ECM continually monitors all of the input signals. The input signals are processed by the machine ECM and an output signal is sent to proportional reducing valve (36) at pilot oil manifold (43). The proportional reducing valve assists in controlling the output flow of main pump (84) .
The oil delivery from pilot pump (78) flows through line (77), line (76), pilot filter (75), and line (74) to pilot manifold (43). Pilot oil enters pilot oil manifold (43) and flows into passage (40). Pilot oil pressure in passage (40) is supplied to proportional reducing valve (36) .
The electrical signal from the machine ECM controls proportional reducing valve (36). Proportional reducing valve (36) regulates the pilot pressure that is supplied to the main pump regulators. This regulated pressure is called power shift pressure (PS). The proportional reducing valve sends the regulated pilot oil pressure through lines (35) to pump regulators (87) and (88) at main pump (84). The output flow of the front pump and the rear pump 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 from the machine ECM to proportional reducing valve (36) will vary as inputs change. The power shift pressure that is sent to regulator (87) and regulator (88) changes. The powers shift pressure changes in order to regulate the maximum allowable hydraulic pump output at the given engine speed. The desired engine speed is maintained.
An increase in engine speed increases the power shift pressure. An increase in power shift pressure causes an upstroke condition of the front pump and the rear pump. The maximum allowable hydraulic power output is increased.
A decrease in engine speed decreases the power shift pressure. A decrease in power shift pressure causes a destroke condition of the front pump and the rear pump. The maximum allowable hydraulic power output is decreased.
Note: For more information concerning the operation of the machine ECM, refer to Systems Operation/Troubleshooting/Testing and Adjusting, "Machine Electronic Control System". For more information concerning the operation of the pump regulators, refer to Systems Operation, "Pump Control (Main Hydraulic)".
Proportional Solenoid Valve Operation at the Main Control Valve and the Swing Control Valve
When the hydraulic activation control lever is shifted to the UNLOCKED position, the machine ECM energizes solenoid valve (37). Pilot oil is able to flow through passage (42) and shifts hydraulic activation valve (41). Pilot oil in passage (40) flows to lines (18), (65), (67), (30), and (62) .
Pilot oil flows to proportional solenoid valves (19), (21), (23), (40), (42), (44), (57), (59), (61), (69), (71), and (73) in the main control valve.
Pilot system oil is supplied to the following proportional solenoid valves in the main control valve: proportional solenoid valve (23) and (57) at each end of attachment spool (50), proportional solenoid valve (59) for the bucket cylinder head end, proportional solenoid valve (25) for the bucket cylinder rod end at the ends of bucket control valve (51), proportional solenoid valve (61) for the boom cylinder head end, proportional solenoid valve (27) for the boom cylinder rod end at the ends of boom control valve (52), proportional solenoid valve (68) for the stick cylinder head end, proportional solenoid valve (44) for the stick cylinder rod end at the ends of stick control valve (53), proportional solenoid valve (70) for left travel (reverse), proportional solenoid valve (46) for left travel (forward) at the ends of left travel control valve (54), proportional solenoid valve (72) for right travel (reverse) and proportional solenoid valve (48) for right travel (forward) at the ends of right travel control valve (55) .
Pilot system oil is also supplied to proportional solenoid valves (13) for left swing and (17) for right swing in the swing control valve. The proportional solenoid valves are used to control swing control valve (15) .
Full pilot pressure keeps each control valve spool centered when all joysticks and/or pedals are in the NEUTRAL position.
During machine operation, the joysticks and/or pedals send an electrical signal input to the machine ECM. The machine ECM detects the amount of joystick and/or pedal movement. The machine ECM sends an electrical signal that corresponds to the amount of lever movement to the respective proportional solenoid valve.
When the proportional solenoid valve is energized, the pilot oil supply passage into the spring chamber begins to close. A return passage to the hydraulic tank in the spring chamber begins to open. Pilot system oil pressure in the spring chamber begins to decrease.
Pilot system pressure on the opposite end of the control spool moves the control spool toward the energized proportional solenoid valve. When the control valve spool shifts, the oil delivery from the main pumps flows through the control valve in order to perform the machine operation.
Note: The following example is given for 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 right joystick is moved to the BOOM RAISE position, the joystick sends an electrical input signal to the machine ECM. The machine ECM detects the amount of movement of the joystick.
The machine ECM sends an electrical signal to proportional solenoid valve (40) that is proportional to the amount of movement of the joystick. Proportional solenoid valve (40) shifts. The pilot oil pressure in passage (41) is now able to drain to the return hydraulic circuit. The pilot oil pressure in passage (68) is higher than the pilot pressure in passage (41). Spool (53) shifts which will cause main hydraulic oil to flow to the head end of the boom cylinders. The oil in the rod end of the cylinders flows to the return hydraulic system. The boom raises.
Boom Regeneration Solenoid Valve
Boom regeneration valve (63) is used to route oil flow from the head end of the boom cylinders to the rod end. The mass of the boom, stick, and bucket causes back pressure in the head end of the boom cylinders. The boom regeneration valve controls the flow of the back pressure oil to the rod end of the boom cylinders. Diverting the back pressure oil to the rod end of the boom cylinders does not require the main pumps to upstroke.
Solenoid valve (66) controls boom regeneration valve (63) .
Oil from pilot oil manifold (39) flows through line (65) to solenoid valve (66) (boom regeneration). When the right joystick is operated during BOOM DOWN, the electrical signal from the joystick enters the machine ECM. The machine ECM sends an electrical signal to solenoid valve (66). Solenoid valve (66) shifts. Pilot oil flows through solenoid valve (66) to passage (64) and then to boom regeneration valve (63). Boom regeneration valve (63) shifts. Main hydraulic oil from the head end of the boom cylinders flows past the boom drift reduction valve and back to the rod end.
Stick Regeneration Solenoid Valve
Stick regeneration valve (28) routes oil flow from the rod end of the stick cylinder to the head end during a STICK IN operation. The volume of the head end of the stick cylinder is much larger than the rod end. The speed of a STICK IN movement is slower than a STICK OUT movement. By using the regeneration valve, the speeds for STICK IN and STICK OUT are more equal.
Solenoid valve (25) controls stick regeneration valve (28) .
Oil from pilot oil manifold (39) flows through line (27) to solenoid valve (25) (stick regeneration). When the left joystick is operated during STICK IN, the electrical signal from the joystick enters the machine ECM. The machine ECM sends an electrical signal to solenoid valve (25). Solenoid valve (25) shifts. Pilot oil flows through solenoid valve (25) to passage (26) and then to stick regeneration valve (28). Stick regeneration valve (28) shifts. Main hydraulic oil from the rod end of the stick cylinder flows past the boom stick reduction valve and back to the head end.
Neutral Bypass Solenoid Valve
Neutral bypass solenoid valve (47) is used to control neutral flow control valve (49). When no implement or travel function is performed, solenoid valve (47) is energized by the machine ECM. Pilot oil from line (46) flows through passage (48) and shifts neutral flow control valve (49). Main hydraulic oil pressure in the main control valve flows to the hydraulic tank through the return hydraulic system. The inside of the main control valve is maintained at a low pressure.
Swing Parking Brake
Oil from pilot oil manifold (39) flows through line (18) to solenoid valve (10) (swing parking brake). When the swing joystick is operated, the electrical signal from the joystick enters the machine ECM. An electrical signal from the machine ECM energizes solenoid valve (10) (swing parking brake). Pilot oil in line (18) flows to line (7), and passage (8), and passage (11). Pilot pressure enters swing parking brake (9) and swing parking brake (12). The pilot oil pressure releases the swing parking brakes.
Automatic Travel Speed Change Valve
Note: When the hydraulic activation lever is in the LOCKED position, pilot oil is supplied to the travel speed solenoid valve (34). However, the travel motors will be inoperable while the hydraulic activation lever is in the LOCKED position.
Pilot oil in passage (40) flows to travel speed solenoid valve (34). When the key for travel speed on the keypad is set at the HIGH SPEED position, solenoid valve (34) is energized by the machine ECM. When travel speed solenoid valve (34) is energized, pilot oil flows through travel speed solenoid valve (34) and through line (33). The oil then flows to displacement change valve (3) for the left travel motor and displacement change valve (6) for the right travel motor. Pilot oil flow shifts displacement change valves (3) and (6) .
When the displacement change valve shifts, the main hydraulic oil flow to the travel motor is able to flow into passage (2) and passage (5). Main hydraulic oil then flows into piston (1) and piston (4). Piston (1) and piston (4) move the swashplate within the travel motors so that the motor displaces less volume. Reducing the volume of the travel motor increases the speed of the travel motor. As the displacement change valves operate, the travel speed is maintained at the HIGH SPEED position.
In the HIGH SPEED position, the pressure sensor for 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.