277C, 277C2, 287C, 287C2 and 297C Multi Terrain Loaders Machine Systems Caterpillar

General Information

Illustration 1	g01332600
(1) Control valve (work tool) (2) Solenoid valve for the auxiliary function (3) Solenoid valve for the tilt function (4) Solenoid valve for the lift function (5) Load check valve for the auxiliary control valve (6) Load check valve for the tilt control valve (7) Load check valve for the lift control valve (8) Outlet (9) Inlet (10) Relief valve for the head end of the lift cylinder (11) Relief valve for the head end of the tilt cylinder (12) Relief valve for the "B" port on the auxiliary valve (13) Relief valve for the rod end of the tilt cylinder (14) Solenoid valve for the lift function (15) Solenoid valve for the tilt function (16) Solenoid valve for the auxiliary function (53) Main relief valve for the work tool hydraulic system

Illustration 2	g01357011
Section view of the tilt cylinder control valve The auxiliary control valve works in the same way as the tilt control valve. (3) Solenoid valve for the tilt function (6) Load check valve for the tilt control valve (15) Solenoid valve for the tilt function (17) Central return passage to valve outlet (18) "B" port on the tilt control valve (19) Bridge passage for the tilt control valve (20) "A" port on the tilt control valve (21) Central supply passage (through passage) (22) tilt cylinder control spool

Illustration 3	g01356997
Instruction decal for the right-hand joystick (23) "A1" position (24) Right-hand joystick (25) "A2" position

Note: All references to the joystick control are based on the standard Caterpillar Joystick Control Pattern. Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls". Refer to the section on "Selectable Control Pattern and Dedicated Control Pattern".

Illustration 4	g01357129
(22) Tilt cylinder control spool (26) Lift control spool (27) Auxiliary control spool

The control valve (work tool) (1) is an electrohydraulic controlled, open center valve. Any movement of the right-hand joystick (24) will send a Pulse Width Modulation Signal signal (PWM) to the machine Electronic Control Module (ECM). The machine ECM will regulate electrical current to the corresponding solenoid in order to regulate pilot oil to the control valve spool.

If right-hand joystick (24) is not moved, oil flows into inlet (9), past each of the spools and out of outlet (8) to the tank. No movement of the implements occurs.

The control valve (work tool) (1) contains three control valve spools. Valve spool (26) controls the lift cylinder functions. Lift cylinder control spool (26) is controlled by solenoid valves (4) and (14). Valve spool (22) controls the tilt cylinder functions. The tilt cylinder control spool (22) is controlled by solenoid valves (3) and (15). Valve spool (27) controls the auxiliary functions. The auxiliary control spool (27) is controlled by solenoid valves (2) and (16) .

The control valve (work tool) (1) contains a main relief valve and four line relief valves. The main relief valve (53) limits the maximum system pressure in the work tool hydraulic system. The line relief valves limit the maximum hydraulic pressure in the individual lines.

Illustration 5	g01357869
Cutaway view of the lift control valve (7) Load check valve for the lift control valve (21) Central supply passage (29) "A" port for the lift control spool (30) "B" port for the lift control spool (31) Series passage to tilt spool and auxiliary spool (36) Series passage to tilt spool and auxiliary spool

The return oil from "A" port (29) and the "B" port (30) on the lift function is in series with the central supply passage (21). Return oil from the lift function is not directed to the tank passage. All return oil from the lift cylinders is directed back through a series passage. The series passage (31) connects the "A" port (29) to the central supply passage (21). The series passage (36) connects the "B" port (30) to the central supply passage (21). This return oil is now available to the tilt function and to the auxiliary function. When the tilt cylinder control spool is in the FLOAT position, both ends of the lift cylinder are connected to the tank passage. Refer to "Lift Control Section " for additional information.

Each function of the control valve contains a load check valve. The load check valve is used in order to prevent the work tool from drifting. When system pressure increases above the pressure in the work tool circuit, load check valve opens allowing system oil to flow to the work tool.

Lift Control Section

HOLD Position

Illustration 6	g01333520
(8) Outlet (9) Inlet (17) Central return passage (21) Central supply passage (through passage) (26) Lift control spool (28) Spring (29) "A" port for the lift control spool (30) "B" port for the lift control spool

When the right-hand joystick (24) is in the HOLD position, no PWM signal is sent to the machine ECM. Oil flows through the inlet (9) to the lift control spool (26) through the central supply passage (21). Refer to Illustration 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for lift control of the right-hand joystick.

The spool blocks the oil from entering any of the passages. Oil cannot flow to port "A" (29) or port "B" (30). The spring (28) keeps the spool centered because the pilot oil is not flowing to the spool. No movement in the lift cylinders occurs.

Oil in passage (21) will flow into the central return passage (17). The oil then flows through the outlet (8) to the hydraulic tank.

RAISE Position

Illustration 7	g01333525
(8) Outlet (9) Inlet (17) Central return passage (21) Central supply passage (through passage) (26) Lift control spool (28) Spring (29) "A" port for the lift control spool (30) "B" port for the lift control spool (31) Series passage to tilt spool and auxiliary spool (32) Pilot oil (33) Bridge passage for the lift control spool

When the right-hand joystick (24) is moved to the RAISE position, the joystick sends a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the raise solenoid (14) on the control valve (work tool) (1). The raise solenoid (14) will direct pilot oil to the left end of the lift cylinder control spool (26). The pilot oil (32) forces the spool (26) to move to the right against the force of the spring (28) . Refer to Illustration 1 and Illustration 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for RAISE position of the right-hand joystick.

Oil is blocked from the inlet (9) by the spool. The oil opens the check valve (7) for the lift circuit and flows through the bridge passage (33) and around the spool to port "B" (30). From port "B" (30), oil flows to the head ends of the lift cylinders in order to raise the lift arms. Refer to Illustration 1 and Illustration 5 under "General Information".

Return oil from the rod ends of lift cylinders flows into port "A" (29), and through the passage (31) into the central supply passage (21) .

If the tilt control spool and auxiliary control spool are in the HOLD position, oil in passage (21) will flow into central return passage (17). The oil then flows through the outlet (8) to the hydraulic tank.

When the right-hand joystick (24) is released from the RAISE position, the spring (28) shifts the spool back to the HOLD position.

LOWER Position

Illustration 8	g01333526
(8) Outlet (9) Inlet (17) Central return passage (21) Central supply passage (through passage) (26) Lift control spool (28) Spring (29) "A" port for the lift control spool (30) "B" port for the lift control spool (32) Pilot oil (33) Bridge passage for the lift control spool (34) Pilot oil (35) Drilled passage (36) Series passage to tilt spool and auxiliary spool (37) Poppet valve

When the right-hand joystick (24) is moved to the LOWER position, the joystick sends a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the lower solenoid (4) on the control valve (work tool) (1). The lower solenoid (4) will direct pilot oil to the right end of the Lift Cylinder Control Spool (26). The pilot oil (34) forces the spool to move to the left against the force of the spring (35). Refer to Illustration 1 and Illustration 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for LOWER position of the right-hand joystick.

Oil is blocked from the inlet (9) by the spool. The oil opens the check valve (7) for the lift circuit and flows through the passage (33) and around the spool to port "A" (29). From port "A" (29), oil flows to the rod ends of the lift cylinders in order to lower the lift arms. Refer to Illustration 1 and Illustration 5 under "General Information".

Return oil from the head ends of the lift cylinders flows into port "B" (30). Then, the oil builds pressure in order to open the poppet valve (37). The oil flows through the passage (36) into the drilled passage (35). The oil then flows into the central passage (21).

If the tilt control spool and auxiliary control spool are in the HOLD position, oil in passage (21) will flow into central return passage (17). The oil then flows through the outlet (8) to the hydraulic tank.

When the right-hand joystick (24) is released from the LOWER position, the spring (28) shifts the spool back to the HOLD position.

FLOAT Position

Illustration 9	g01333527
(8) Outlet (9) Inlet (17) Central return passage (21) Central supply passage (through passage) (26) Lift control spool (28) Spring (29) "A" port for the lift control spool (30) "B" port for the lift control spool (32) Pilot oil (33) Bridge passage for the lift control spool (34) Pilot oil (35) Drilled passage (36) Series passage to tilt spool and auxiliary spool (37) Poppet valve

When the FLOAT function has been activated, the right-hand joystick (24) will send a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the lower solenoid (4) on the control valve (work tool) (1). The lower solenoid (4) will direct pilot oil to the right end of the Lift Cylinder Control Spool (26). The pilot oil (34) forces the spool to move to the left against the force of the springs (28) and (39). Refer to Illustration 1 and Illustration 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for FLOAT position of the right-hand joystick.

Oil continues to flow from the inlet (9) through the central passage (21). If the tilt control spool and auxiliary control spool are in HOLD position, oil in passage (21) will flow into the central return passage (17). The oil then flows through the outlet (8) to the hydraulic tank.

Oil that is in the rod ends of the lift cylinders can flow to the tank through port "A" (29). Oil in the head ends of the lift cylinders can flow through port "B" (30) and through the orifice (38) to the tank passage (17). The work tool will lower to the ground and the work tool will follow along the contour of the ground.

The Lift Cylinder Control Spool (26) will remain in the FLOAT position until the operator moves the right-hand joystick (24). When the right-hand joystick (24) is released from the FLOAT position, the spring (28) shifts the spool back to the HOLD position.

Tilt Control Section

HOLD Position

Illustration 10	g01333529
(8) Outlet (9) Inlet (17) Central return passage (18) Port "B" for the tilt control valve (20) Port "A" for the tilt control valve (21) Central supply passage (22) Tilt control spool (26) Lift control spool (27) Auxiliary circuit spool (40) Spring (41) Spring

When the right-hand joystick (24) is in the HOLD position, no PWM signal is sent to the machine ECM. Oil flows through the inlet (9), around the lift control spool (26), and to the tilt control spool (22) through the central supply passage (21). From the tilt control spool, the oil flows around the auxiliary circuit spool (27) into the central return passage (17). The oil then flows through the outlet (8) to the hydraulic tank. Refer to Illustration 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for tilt control of the right-hand joystick.

The spools block the oil from entering any of the passages. Oil cannot flow to port "A" (20) or port "B" (18). The spring (40) and spring (41) keep the spool centered because the pilot oil is not flowing to the spool. No movement in the tilt cylinders occurs.

TILT FORWARD Position

Illustration 11	g01333532
(8) Outlet (9) Inlet (17) Central return passage (18) Port "B" for the tilt control valve (19) Bridge passage for the tilt control valve (20) Port "A" for the tilt control valve (21) Central supply passage (22) Tilt control spool (40) Spring (42) Orifice (43) Internal passage (44) Pilot oil

When the right-hand joystick (24) is moved to the TILT FORWARD position, the joystick sends a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the tilt forward solenoid (15) on the control valve (work tool) (1). The tilt forward solenoid (15) will direct pilot oil to the left end of the tilt cylinder control spool (22). The pilot oil (44) forces the spool (22) to move to the right against the force of the spring (40). Refer to Illustration 1 and 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for TILT FORWARD position of the right-hand joystick.

Oil flows from the inlet (9) to the tilt control spool (22) through the central supply passage (21). Oil is blocked from the inlet (9) by the spool (22). The oil opens the check valve (6) for the tilt circuit and flows through the bridge passage (19) and around the spool to port "B" (18). From port "B" (18), oil flows to the head ends of the tilt cylinders in order to tilt the work tool forward. Refer to Illustration 1 and 2 under "General Information".

Oil that is returning from the rod ends of tilt cylinders flows into port "A" (20) and through the orifice (42). Then, the oil flows through the internal passage (43) into the central return passage (17). Oil in the central return passage (17) flows through the outlet (8) and to the hydraulic tank.

When the right-hand joystick (24) is released from the TILT FORWARD position, the spring (40) shifts the spool back to the HOLD position.

TILT BACK Position

Illustration 12	g01333534
(8) Outlet (9) Inlet (17) Central return passage (18) Port "B" for the tilt control valve (19) Bridge passage for the tilt control valve (20) Port "A" for the tilt control valve (21) Central supply passage (22) Tilt control spool (41) Spring (45) Pilot oil

When the right-hand joystick (24) is moved to the TILT BACK position, the joystick sends a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the tilt back solenoid (3) on the control valve (work tool) (1). The tilt back solenoid (3) will direct pilot oil to the right end of the tilt cylinder control spool (22). The pilot oil (45) forces the spool (22) to move to the left against the force of the spring (41). Refer to Illustration 1 and 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for TILT BACK position of the right-hand joystick.

Oil flows from the inlet (9) to the tilt control spool (22) through the central supply passage (21).

Oil is blocked from the inlet (9) by the tilt control spool (22) . The oil opens the check valve (6) for the tilt circuit and flows through the bridge passage (19) and around the spool to port "A" (20). From port "A" (20), oil flows to the rod ends of the tilt cylinders. Oil to the rod ends of the tilt cylinder causes the work tool to tilt back. Refer to Illustration 1 and 2 under "General Information".

Oil returning from the head ends of tilt cylinders flows into port "B" (18) and around the spool to the central return passage (17). Oil in the central return passage (17) flows through the outlet (8) and to the hydraulic tank.

When the right-hand joystick (22) is released from the TILT BACK position, the spring (41) shifts the spool back to the HOLD position.

Auxiliary Control Section

HOLD Position

Illustration 13	g01333535
(8) Outlet (9) Inlet (17) Central return passage (21) Central supply passage (22) Tilt control spool (26) Lift control spool (27) Auxiliary control spool (46) Spring (47) Port "B" for the auxiliary control spool (48) Port "A" for the auxiliary control spool (49) Spring

The "AUX 1" switch (25) and the "AUX 2" switch (23) on the right-hand joystick (24) are momentary push-button switches. Refer to Illustration 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for the auxiliary control on the right-hand joystick.

When no push-button switch on the right-hand joystick (24) is pressed, the auxiliary control spool (27) is in the HOLD position. When no push-button switch on the right-hand joystick (24) is pressed, no PWM signal is sent to the machine ECM. Oil flows through inlet (9), around lift control spool (26), tilt control spool (22), and to auxiliary control spool (27) through central supply passage (21). The oil then flows from the central supply passage (21) into the central return passage (17). From the central return passage (17), the oil flows through the outlet (8) to the hydraulic tank.

The control spools block the oil from entering any of the passages. Oil cannot flow to port "A" (48) or port "B" (47). Spring (46) and spring (49) keeps the spool centered because the pilot oil is not flowing to the spool. No movement in the secondary auxiliary circuit occurs.

Auxiliary Hydraulic Control "A1"

Illustration 14	g01333536
(8) Outlet (9) Inlet (17) Central return passage (21) Central supply passage (22) Tilt control spool (26) Lift control spool (27) Auxiliary control spool (46) Spring (47) Port "B" for the auxiliary control spool (48) Port "A" for the auxiliary control spool (50) Bridge passage for the auxiliary control spool (51) Pilot oil

When the "A1" push-button switch (25) on the right-hand joystick (24) is pressed, the joystick sends a signal to the machine ECM. The machine ECM will send an electrical current to the A1 solenoid (2) on the control valve (work tool) (1). The A1 solenoid (2) will direct pilot oil to the right end of the auxiliary control spool (27). Refer to Illustration 1 and 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for the "A1" control button of the right-hand joystick.

The pilot oil (51) forces the auxiliary control spool (27) to move to the left against the force of the spring (46). Oil flows through inlet (9), around lift control spool (26), tilt control spool (22), and to auxiliary control spool (27) through central supply passage (21).

Oil is blocked from the inlet (9) by the spool. The oil opens the check valve (5) in Illustration 1 for the auxiliary circuit and flows through the bridge passage (50) and around the spool to port "A" (48). From port "A" (48), oil flows to the lower auxiliary connection. Refer to Illustration 1 and 2 under "General Information".

Oil that is returning from the upper auxiliary connection flows into port "B" (47), and around the spool to the central return passage (17). From the central return passage (23), oil flows through the outlet (8) to the hydraulic tank .

When the "A1" push-button switch on the right-hand joystick (24) is released, spring (46) shifts the spool back to the HOLD position.

Auxiliary Hydraulic Control "A2"

Illustration 15	g01333537
(8) Outlet (9) Inlet (17) Central return passage (21) Central supply passage (22) Tilt control spool (26) Lift control spool (27) Auxiliary control spool (47) Port "B" for the auxiliary control spool (48) Port "A" for the auxiliary control spool (49) Spring (50) Bridge passage for the auxiliary control spool (52) Pilot oil

When the "A2" push-button switch on the right-hand joystick (24) is pressed, the joystick sends a signal to the machine ECM. The machine ECM will send an electrical current to the A2 solenoid (16) on the control valve (work tool) (1). The A2 solenoid (16) will direct pilot oil to the left end of the auxiliary control spool (27). Refer to Illustration 1 and 3 under "General Information". Refer to Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for the "A2" control button of the right-hand joystick.

The pilot oil (52) forces the auxiliary control spool (27) to move to the right against the force of the spring (49). Oil flows through inlet (9), lift control spool (26), around tilt control spool (22), and to auxiliary control spool (27) through central supply passage (21).

Oil is blocked from the inlet (9) by the spool. The oil opens the check valve (5) in Illustration 1 for the auxiliary circuit. The oil then flows through the bridge passage (50) and around the spool to port "B" (47). From port "B" (47), oil flows to the upper auxiliary connection. Refer to Illustration 1 and 2 under "General Information".

Oil that is returning from the lower auxiliary connection flows into port "A" (48), and around the spool to the central return passage (17). From the central return passage (23), oil flows through the outlet (8) to the hydraulic tank.

When the "A2" push-button switch on the right-hand joystick (24) is released, spring (49) shifts the spool back to the HOLD position.