318E Excavator Systems Caterpillar

Pilot Hydraulic Schematic

Illustration 1	g06010726
(1) Displacement change valve (left travel motor) (2) Displacement change valve (right travel motor) (3) Swing brake (4) Passage (5) Swing control valve (6) Travel pressure switch (7) Passage (8) Left travel control valve (9) Right travel control valve (10) Boom I control valve (11) Main control valve (12) Travel pilot control valve (13) Line (pilot oil to swing brake solenoid valve) (14) Pilot control valve for stick and swing (15) Pilot control valve for bucket and boom (16) Pilot line (pilot oil to pilot control valves) (17) Swing priority valve (18) Passage (19) Idler pump pressure sensor (20) Straight travel control valve (21) Drive pump pressure sensor (22) Boom II control valve (23) Pilot line (pilot oil to the pressure reducing valve for boom priority) (24) Pressure reducing valve for boom priority (25) Pressure sensor (boom down control) (26) Pilot line (pilot pressure to implement pressure switch) (27) Implement pressure switch (28) Pilot line (pilot pressure to the pressure sensor for swing control) (29) Pressure sensor (swing control) (30) Pilot line (STICK IN) (31) Pilot line (BOOM RAISE) (32) Pilot line (pilot pressure to displacement change valves) (33) Passage (34) Passage (35) Valve (hydraulic activation) (36) Hydraulic activation solenoid valve (37) Pilot line (pilot oil flow to pilot oil manifold) (38) Pilot relief valve (39) Pilot filter (40) Proportional reducing valve (power shift pressure) (41) Proportional reducing valve (negative flow control) (42) PRV for boom regeneration (43) Pilot line (BOOM LOWER) (44) Travel speed solenoid valve (45) Swing brake solenoid valve (46) Passage (47) Pilot manifold (48) Pilot line (pilot oil flow from pilot pump to pilot oil filter) (49) Drive pump (50) Idler pump (51) Pilot pump (68) High-pressure solenoid

Pilot Oil Circuit

Illustration 2	g06007151
Ports and solenoids at the pilot manifold (35) Valve (hydraulic activation) (36) Hydraulic activation solenoid valve (44) Travel speed solenoid valve (45) Swing brake solenoid valve

The pilot circuit pressure is limited by pilot relief valve (38).

The oil delivery from pilot pump (51) performs the following main functions:

• Create pilot oil pressure in order to control the output flows of the main pumps.

• Provide pilot oil pressure to the pilot control valves for implements, swing, and travel in order to perform machine operations.

• Create pilot oil pressure in order 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

• Negative flow control

• High-pressure change control

Power Shift Pressure System

Illustration 3	g02492697
(11) Main control valve (19) Idler pump pressure sensor (21) Drive pump pressure sensor (40) Proportional reducing valve (PS pressure) (49) Drive pump (50) Idler pump (51) Pilot pump (52) Engine ECM (53) Engine speed pickup (54) Machine ECM (55) Engine speed dial (56) Switch panel ECM (57) Monitor

During machine operation, machine ECM (54) receives input signals from the following components:

• Engine ECM (52)

• Switch panel ECM (56)

• Engine speed dial (55)

• Monitor in the cab (57)

• Drive pump pressure sensor (21)

• Idler pump pressure sensor (19)

The machine ECM (54) 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 (40) at the drive pump regulator. The proportional reducing valve assists in controlling the output flow of drive pump (49) and idler pump (50).

The oil delivery from pilot pump (51) flows through the pilot filter to proportional reducing valve (40) at the drive pump regulator. The electrical signal that is sent from machine ECM (54) causes proportional reducing valve (40) 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 (49) and idler pump (50) 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 the proportional reducing valve 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 in order 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 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.

Pilot Control Valve Circuits

Oil from pilot pump (51) flows through pilot line (48), pilot filter (39), and pilot line (37) to pilot manifold (47). When the hydraulic activation control lever is shifted to the UNLOCKED position, the machine ECM energizes the hydraulic activation solenoid valve (36). The pilot oil then shifts valve (35). The pilot oil now flows through valve (35) and pilot line (16). The pilot oil now flows to pilot control valves (12), (14) and (15) for implements, swing, and travel in order to perform machine operations. When the joysticks and/or travel levers/pedals are moved, the pilot oil flows to main control valve (11) in order to control the machine functions.

Illustration 4	g06007157

When joystick (14) and/or joystick (15) are operated, the pilot control valves send pilot pump oil through the pilot lines to pilot ports at the main control valve in order 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 oil from the pilot control valves flows through pilot lines to the ports on the bottom of the main control valve in order to perform the opposite operation.

The following example is given for the BOOM LOWER operation and the 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 (15) flows through pilot line (31) to boom I control valve (10) and boom II control valve (22). The pilot pressure shifts the boom I control valve and the boom II control valve. The oil delivery from the drive pump flows to the head end of the boom cylinders in order 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 (15) flows through pilot line (43) to boom I control valve (10). The pilot pressure shifts the boom I control valve. The BOOM LOWER operation is now performed.

For more information concerning the operation of the boom, refer to Systems Operation, "Boom System".

Pressure Switch Circuits

When the travel controls are in the NEUTRAL position, the pilot pressure in passage (7) remains low and travel pressure switch (6) is OFF. The machine ECM recognizes the OFF condition of all of the pressure switches. The AEC system is activated in order to lower the engine rpm. If either travel control is moved from the NEUTRAL position, the pilot oil pressure in passage (7) increases and travel pressure switch (6) is ON. The machine ECM activates the AEC system in order to increase the engine rpm.

When the implement controls are in the NEUTRAL position, the pilot pressure in passage (26) remains low and implement pressure switch (27) is OFF. The machine ECM recognizes the OFF condition of all of the pressure switches. The AEC system is activated in order to lower the engine rpm. If any of the implement controls are moved from the NEUTRAL position, the pilot oil pressure in passage (26) increases and implement pressure switch (27) is ON. The machine ECM activates the AEC system in order to increase the engine rpm.

Pressure Sensors

Pressure sensor (25) is connected to pilot oil for boom down control. Pressure sensor (29) is connected to pilot oil for a swing RIGHT operation and swing LEFT operation. These two pressure sensors send an electrical signal to the machine ECM.

When a boom DOWN function is performed, pressure sensor (25) sends an electrical signal to the machine ECM. The machine ECM then sends a signal to the following components:

• PRV for boom regeneration (42) limits pilot oil to the boom II control valve in order to control boom regeneration.

• The AEC system is activated in order to lower the engine rpm.

• Swing brake solenoid valve (45) is activated in order to release the swing parking brake.

• Negative flow control valve (41) regulates the pressure that will be supplied to the pump regulators. The negative flow control pressure forces the swashplate in the pump to the correct angle to limit the flow and pressure from the main pumps.

When a swing operation is performed, pressure sensor (29) sends an electrical signal to the machine ECM. The machine ECM then sends a signal to the following components:

• Swing brake solenoid valve (45) is activated in order to release the swing parking brake.

• Negative flow control valve (41) regulates the pressure that will be supplied to the pump regulators. The negative flow control pressure forces the swashplate in the pump to the correct angle to limit the flow and pressure from the main pumps.

Drive pump pressure sensor (21) and idler pump pressure sensor (19) are located on main control valve (11).

Straight Travel Valve Circuit

When a swing operation and/or implement operation is performed during a travel operation, the increase of pilot pressure in passage (4) and pilot oil flows through passage (18) to straight travel control valve (20). Pilot pressure shifts straight travel control valve (20) 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, "Control Valve (Straight Travel)".

Swing Parking Brake

When the hydraulic activation control lever is placed in the UNLOCKED position, pilot oil in passage (46) flows through valve (35) and passage (34) in order to provide oil to the swing brake solenoid valve (45). When any of the joysticks are moved from the NEUTRAL position, the increase of pilot pressure activates one of the following pressure sensors or pressure switches: implement pressure switch (27), pressure sensor (25) for boom down control and pressure sensor (29) for swing control. The pressure switch and/or the pressure sensor sends an electrical signal to the machine ECM. An electrical signal from the machine ECM energizes the swing brake solenoid valve (45) once the pilot oil pressure exceeds 500 kPa (73 psi). Pilot oil in line (13) flows to swing brake (3). This oil releases the swing brake.

For more information concerning the operation of the swing brake, refer to Systems Operation, "Pilot Valve (Swing Parking Brake)".

Boom Priority

During combined operations of BOOM RAISE and STICK IN, the pilot oil pressure in pilot line (30) and pilot line (23) activates the pressure reducing valve for boom priority (24). The pressure reducing valve for boom priority (24) 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, "Boom System".

Swing Priority

During a swing operation, pilot oil flows from pilot control valve (14) to swing control valve (5). Pressure sensor (29) for swing control sends an electrical signal to the machine ECM. The machine ECM sends an electrical signal to PRV for negative flow control (41) in order to limit swing relief loss during a swing operation.

Pilot oil also flows to swing priority valve (17). 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, "Swing System".

Automatic Travel Speed Change Valve

Pilot oil in passage (33) flows to travel speed solenoid valve (44). When the travel speed switch on the right console is set at the HIGH SPEED position, the travel speed solenoid valve opens. This action allows pilot oil to flow through travel speed solenoid valve (44) and through line (32). The oil then flows to the displacement change valve for the left travel motor (1) and the displacement change valve for the right travel motor (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 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, "Displacement Change Valve".

Boom Regeneration

Proportional reducing valve for boom regeneration (42) is used in order to control the amount of regeneration oil in the boom circuit. During a boom DOWN function, pilot oil flows through PRV (42) to the boom II control valve. The pilot oil shifts the boom II control valve allowing regen oil to flow from the head end of the boom cylinder to the rod end.

PRV for boom regeneration (42) can also limit the amount of pilot oil supplied to the boom II control valve. The machine ECM receives various input signals and determines how much regeneration oil is supplied to the rod end of the boom cylinder.

For more information concerning the operation of the boom regeneration system, refer to Systems Operation, "Boom System".

For more information concerning the ECM logic of the boom regeneration system, refer to Systems Operation, "Electrical Output Components".

Negative Flow Control

Proportional reducing valves for negative flow control (41) are used in order to control the amount of NFC signal to the pump regulators. The machine ECM receives various input signals in order to control the flow limitation from the main hydraulic pumps. When the NFC valves are energized by the machine ECM, pilot oil pressure is directed to the main hydraulic pump regulators from the pilot manifold. The pilot oil pressure causes the hydraulic pumps to destroke which reduces hydraulic oil flow.

For more information concerning the negative flow control system, refer to Systems Operation, "Negative Flow Control System".

High Pressure Change Control

Machines that are equipped with a high-pressure change solenoid have a high-pressure setting and a low pressure setting for the main relief valve. The machine ECM activates a solenoid valve during a boom UP when the head end cylinder pressure is high. The machine ECM also activates the solenoid during a travel operation. The solenoid valve directs pilot oil pressure to the pilot oil port on the main relief valve. The pilot oil pressure is ported through the valve in order to move a piston that creates a higher spring force on the main relief valve. The increase of spring force on the main relief valve causes the relief pressure in the main hydraulic system to rise.

For more information concerning the operation of the high-pressure change control system, refer to Systems Operation, "Relief Valve (Main)".