General Information
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| Illustration 1 | g01336135 |
(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) Solenoid valve for the secondary auxiliary function (6) Isolator compensator assembly for the auxiliary function (7) Isolator compensator assembly for the tilt cylinders (8) Isolator compensator assembly for the lift cylinders (9) Isolator compensator assembly for the secondary auxiliary function (10) Relief valve for the auxiliary function (11) Relief valve for the tilt cylinders (12) Relief valve for the secondary auxiliary function (13) Relief valve for the tilt cylinders (14) Solenoid valve for the secondary auxiliary function (15) Solenoid valve for the lift function (16) Solenoid valve for the tilt function (17) Solenoid valve for the auxiliary function | |
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| Illustration 2 | g01338310 |
(1) Control valve (work tool) (18) Auxiliary control spool (19) Tilt cylinder control spool (20) Lift cylinder control spool (21) Secondary auxiliary control spool | |
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| Illustration 3 | g01354582 |
Instruction decal for the right-hand joystick (22) Right-hand joystick | |
Note: All references to the joystick control are based on the standard Caterpillar Joystick Control Pattern. Refer to the machine 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".
The control valve (work tool) (1) is an electrohydraulic controlled, closed center valve. Any movement of the right-hand joystick (22) will send a Pulse Width Modulation Signal (PWM signal) 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 the right-hand joystick (22) is not moved, oil flows into the inlet and oil is blocked by the spools. The springs keep the spools centered because the pilot oil is not flowing to the spool. No movement of the implements occur.
The control valve (work tool) (1) contains four control valve spools. Valve spool (21) controls the secondary auxiliary function. The secondary auxiliary control spool (19) is controlled by solenoid valves (5) and (14). Valve spool (20) controls the lift cylinder functions. lift cylinder control spool (20) is controlled by solenoid valves (4) and (15). Valve spool (19) controls the tilt cylinder functions. The tilt cylinder control spool (19) is controlled by solenoid valves (3) and (16). Valve spool (18) controls the main auxiliary functions. The main auxiliary control spool (18) is controlled by solenoid valves (2) and (17).
The control valve (work tool) (1) uses isolator compensator assemblies in order to prevent working port pressure from increasing back pressure on the hydraulic pump. Refer to "Isolator Compensator Assembly Explanation" for the explanation of the isolator compensator assembly.
Secondary Auxiliary Section
HOLD Position
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| Illustration 4 | g01336105 |
Secondary auxiliary spool in HOLD position (21) Secondary auxiliary control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (25) Spring (26) "A" port for the secondary auxiliary valve (27) "B" port for the secondary auxiliary valve (28) Spring | |
The "AUX 3" switch and the "AUX 4" switch on the right-hand joystick (22) are momentary push-button switches.
When no push-button switch on the right-hand joystick (22) is pressed, the secondary auxiliary spool (21) is in the HOLD position. When no push-button switch on the right-hand joystick (22) is pressed, no PWM signal is sent to the machine ECM. Oil flows through the inlet to the secondary auxiliary spool (21) through the central supply passage (24). Refer to Illustration 1 and Illustration 3 under "General Information".
The spool blocks the oil from entering any of the passages. Oil cannot flow to port "A" (26) or port "B" (27). Spring (25) and spring (28) keeps the spool centered because the pilot oil is not flowing to the spool. No movement in the secondary auxiliary circuit occurs.
"AUX 4" Position
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| Illustration 5 | g01336156 |
Secondary auxiliary spool in "AUX 4" position (21) Secondary auxiliary control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (25) Spring (26) "A" port for the secondary auxiliary valve (27) "B" port for the secondary auxiliary valve (29) Passage to compensator spool and bridge (30) Cross drilled hole (31) Bridge passage for the secondary auxiliary (32) Pilot oil | |
When the "AUX 4" push-button switch on the right-hand joystick (22) is pressed, the joystick sends a signal to the machine ECM. The machine ECM will send an electrical current to the C+ solenoid (14) on the control valve (work tool) (1). The C+ solenoid (14) will direct pilot oil to the left end of the secondary auxiliary control spool (21). Refer to Illustration 1 and Illustration 3 under "General Information". Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for "AUX 4" position of the right-hand joystick.
The pilot oil (32) forces the secondary auxiliary control spool (21) to move to the right against the force of the spring (25). Oil flows from the central passage (24) through the cross drilled hole (30) into passage (29) for the compensator spool.
When pump pressure exceeds working pressure, the compensator spool in isolator compensator assembly (9) shifts up allowing flow to the bridge passage (31). Oil flows from the bridge passage (31) around the spool to port "B" (27). Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
The return oil flows into port "A" (26) and through the return passage (23) to the hydraulic tank .
When the "AUX 4" push-button switch on the right-hand joystick (22) is released, spring (25) shifts the spool back to the HOLD position.
"AUX 3" Position
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| Illustration 6 | g01336167 |
Secondary auxiliary spool in "AUX 3" position (21) Secondary auxiliary control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (26) "A" port for the secondary auxiliary valve (27) "B" port for the secondary auxiliary valve (28) Spring (29) Passage to compensator spool and bridge (30) Cross drilled hole (31) Bridge passage for the secondary auxiliary (33) Pilot oil | |
When the "AUX 3" push-button switch on the right-hand joystick (22) is pressed, the joystick sends a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the C− solenoid (5) on the control valve (work tool) (1). The C− solenoid (5) will direct pilot oil to the right end of the secondary auxiliary control spool (21). Refer to Illustration 1 and Illustration 3 under "General Information". Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for "AUX 3" position of the right-hand joystick.
The pilot oil (33) forces the secondary auxiliary control spool (21) to move to the left against the force of the spring (28). Oil flows from the central passage (24) through the cross drilled hole (30) into passage (29) for the compensator spool.
When pump pressure exceeds working pressure, the compensator spool in isolator compensator assembly (9) shifts up allowing flow to the bridge passage (31). Oil flows from the bridge passage (31) around the spool to port "A" (26). Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
The return oil flows into port "B" (27) and through the return passage (23) to the hydraulic tank .
When the "AUX 3" push-button switch on the right-hand joystick (22) is released, spring (25) shifts the spool back to the HOLD position.
Lift Control Section
HOLD Position
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| Illustration 7 | g01336112 |
Lift spool in HOLD position (20) Lift cylinder control spool (24) Central supply passage from the hydraulic pump (34) "A" port for the lift cylinder control valve (35) Spring (36) "B" port for the lift cylinder control valve | |
When the right-hand joystick (22) is in the HOLD position, no PWM signal is sent to the machine ECM. Oil flows through the inlet to the lift control spool (20) through the central supply passage (24). Refer to Illustration 1 and Illustration 3 under "General Information". Refer to the machine 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" (34) or port "B" (36). The spring (35) keeps the spool centered because the pilot oil is not flowing to the spool. No movement in the lift cylinders occurs.
RAISE Position
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| Illustration 8 | g01337085 |
Lift spool in RAISE position (20) Lift cylinder control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (34) "A" port for the lift cylinder control valve (35) Spring (36) "B" port for the lift cylinder control valve (37) Passage for compensator spool and bridge (38) Bridge passage (39) Pilot oil | |
When the right-hand joystick (22) 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 (15) on the control valve (work tool) (1). The raise solenoid (15) will direct pilot oil to the left end of the lift cylinder control spool (20). The pilot oil (39) forces the spool (20) to move to the right against the force of the spring (35). Oil flows from the central passage (24) around the spool (20) into passage (37) to the compensator spool. Refer to Illustration 1 and Illustration 3 under "General Information". Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for RAISE position of the right-hand joystick.
When pump pressure exceeds working pressure, the compensator spool in isolator compensator assembly (8) shifts up allowing flow to the bridge passage (38). Oil flows from the bridge passage (38) around the spool to port "B" (36). From port "B" (36), oil flows to the head ends of the lift cylinders in order to raise the lift arms. Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
Return oil from the rod ends of lift cylinders flows into port "A" (34), and through the passage (23) to the hydraulic tank .
When the right-hand joystick (22) is released from the RAISE position, the spring (35) shifts the spool back to the HOLD position.
LOWER Position
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| Illustration 9 | g01337087 |
Lift spool in LOWER position (20) Lift cylinder control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (34) "A" port for the lift cylinder control valve (35) Spring (36) "B" port for the lift cylinder control valve (37) Passage for compensator spool and bridge (38) Bridge passage (40) Pilot oil (41) Drilled passage | |
When the right-hand joystick (22) 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 (20). The pilot oil (40) forces the spool to move to the left against the force of the spring (35). Oil flows from the central supply passage (24) around the spool (20) into passage (37) to the compensator spool. Refer to Illustration 1 and Illustration 3 under "General Information". Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for LOWER position of the right-hand joystick.
When pump pressure exceeds working pressure, the compensator spool in isolator compensator assembly (8) shifts up allowing flow to the bridge passage (38). Oil flows from the bridge passage (38) around the spool to port "A" (34). From port "A" (34), oil flows to the rod ends of the lift cylinders in order to lower the lift arms. Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
Return oil from the rod ends of lift cylinders flows into port "B" (36), and through the drilled passage (41) into the return passage (23). The oil then flows through the return passage (23) to the hydraulic tank.
When the right-hand joystick (22) is released from the LOWER position, the spring (35) shifts the spool back to the HOLD position.
FLOAT Position
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| Illustration 10 | g01337091 |
Lift spool in FLOAT position (20) Lift cylinder control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (34) "A" port for the lift cylinder control valve (35) Spring (36) "B" port for the lift cylinder control valve (37) Passage for compensator spool and bridge (38) Bridge passage (40) Pilot oil (41) Drilled passage (42) Spring | |
When the FLOAT function has been activated, the right-hand joystick (22) will send a PWM signal to the machine ECM. Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for FLOAT position of the right-hand joystick. 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 (20). The pilot oil (40) forces the spool to move to the left against the force of the springs (35) and (42). Refer to Illustration 1 and Illustration 3 under "General Information".
Oil from the central supply passage (24) is blocked by the spool (20). Oil that is in the rod ends of the lift cylinders can flow to the tank through port "A" (34). Oil that is in the head ends of the lift cylinders can flow through port "B" (36) and through the drilled passage (41). The oil then flows through the return passage (23) to the hydraulic tank. 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 (20) will remain in the FLOAT position until the operator moves the right-hand joystick (22). When the right-hand joystick (22) is released from the FLOAT position, the spring (35) shifts the spool back to the HOLD position.
Tilt Control Section
HOLD Position
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| Illustration 11 | g01336113 |
Tilt spool in HOLD position (24) Central supply passage from the hydraulic pump (43) "A" port for the Tilt cylinder control valve (44) Spring (45) "B" port for the tilt cylinder control valve (46) Tilt cylinder control spool (47) Spring | |
When the right-hand joystick (22) is in the HOLD position, no PWM signal is sent to the machine ECM. Oil flows through the inlet to the tilt control spool (46) through the central supply passage (24). Refer to Illustration 1 and Illustration 3 under "General Information". Refer to the machine 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 spool blocks the oil from entering any of the passages. Oil cannot flow to port "A" (43) or port "B" (45). The spring (44) and spring (47) keeps the spool centered because the pilot oil is not flowing to the spool. No movement in the lift cylinders occurs.
TILT FORWARD Position
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| Illustration 12 | g01337099 |
Tilt spool in TILT FORWARD position (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (43) "A" port for the tilt cylinder control valve (44) Spring (45) "B" port for the tilt cylinder control valve (46) Tilt cylinder control spool (48) Bridge passage for the tilt cylinder control spool (49) Passage to the compensator spool and bridge (50) Drilled passage (51) Pilot oil | |
When the right-hand joystick (22) 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 (16) on the control valve (work tool) (1). The tilt forward solenoid (16) will direct pilot oil to the left end of the tilt cylinder control spool (46). The pilot oil (51) forces the spool (46) to move to the right against the force of the spring (44). Oil flows from the central supply passage (24) around the spool (46) into passage (49) to the compensator spool. Refer to Illustration 1 and Illustration 3 under "General Information". Refer to the machine 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.
When pump pressure exceeds working pressure, the compensator spool in isolator compensator assembly (7) shifts up allowing flow to the bridge passage (48). Oil flows from the bridge passage (48) around the spool to port "B" (45). From port "B" (45), oil flows to the head ends of the tilt cylinders. Oil flow to the head end of the tilt cylinder causes the work tool to tilt forward. Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
Return oil from rod ends of tilt cylinders flows into port "A" (43), through drilled passage (50), and return passage (23) to the hydraulic tank .
When the right-hand joystick (22) is released from the TILT FORWARD position, the spring (44) shifts the spool back to the HOLD position.
TILT BACK Position
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| Illustration 13 | g01337101 |
Tilt spool in TILT BACK position (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (43) "A" port for the tilt cylinder control valve (45) "B" port for the tilt cylinder control valve (46) Tilt cylinder control spool (47) Spring (48) Bridge passage for the tilt cylinder control spool (49) Passage to the compensator spool and bridge (52) Pilot oil | |
When the right-hand joystick (22) 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 (46). The pilot oil (52) forces the spool (46) to move to the left against the force of the spring (47). Oil flows from the central supply passage (24) around the spool (46) into passage (49) to the compensator spool. Refer to Illustration 1 and Illustration 3 under "General Information". Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 277C2, and 297C Multi Terrain Loaders", "Operator Controls " for TILT BACK position of the right-hand joystick.
When pump pressure exceeds working pressure, the compensator spool in isolator compensator assembly (7) shifts up allowing flow to the bridge passage (48). Oil flows from the bridge passage (48) around the spool to port "A" (43). From port "A" (43), oil flows to the head ends of the tilt cylinders. Oil flow to the head ends of the tilt cylinders cause the work tool to tilt back. Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
Return oil from the rod ends of tilt cylinders flows into port "B" (45), and through the return passage (23) to the hydraulic tank .
When the right-hand joystick (22) is released from the TILT BACK position, the spring (47) shifts the spool back to the HOLD position.
Auxiliary Control Section
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| Illustration 14 | g01336114 |
Auxiliary spool in HOLD position (18) Auxiliary valve control spool (24) Central supply passage from the hydraulic pump (53) Spring (54) Spring (56) "B" port for the auxiliary control valve (59) "A" port for the auxiliary control valve | |
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| Illustration 15 | g01354580 |
Instruction decal for the right-hand joystick (22) Right-hand joystick (72) "A1" Position (73) "A2" Position | |
The auxiliary hydraulic control for the work tool requires a work tool wiring harness in order for the machine to provide high flow. Using a high flow work tool without a work tool wiring harness will operate as a standard flow work tool. The thumb wheel on the right-hand joystick (22) is a return to center thumb wheel control. Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for auxiliary hydraulic controls on the right-hand joystick.
The machine ECM will recognize the presence of the work tool wiring harness. When the thumb wheel on the right-hand joystick (22) is moved, the joystick sends a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the "A1" solenoid (2) or the "A2" solenoid (17). If a work tool wiring harness is detected, the auxiliary control spool (18) may work against the force of spring (53) and spring (54). When no work tool wiring harness is detected, the auxiliary control spool (18) may only work against the force of spring (54). Refer to Illustration 1 and Illustration 3 under "General Information".
HOLD Position
When the thumb wheel on the right-hand joystick (22) is in the HOLD position, no PWM signal is sent to the machine ECM. Oil flows through the inlet to the auxiliary spool (18) through the central supply passage (24). Refer to Illustration 14 and Illustration 15. Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for auxiliary hydraulic control of the right-hand joystick.
The spool blocks the oil from entering any of the passages. Oil cannot flow to port "A" (59) or port "B" (56). The spring (54) keeps the spool centered because the pilot oil is not flowing to the spool. No movement in the auxiliary circuit occurs.
"A2" Position
"A2" Position Without a Work Tool Wiring Harness
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| Illustration 16 | g01337102 |
Auxiliary spool in the "A2" position (18) Auxiliary valve control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (54) Spring (55) Pilot oil (56) "B" port for the auxiliary control valve (57) Bridge passage for the tilt cylinder control spool (58) Passage to the compensator spool and bridge (59) "A" port for the auxiliary control valve | |
When the thumb wheel on the right-hand joystick (22) is pushed in the "A2" direction, a PWM signal is sent to the machine ECM. Refer to Illustration 15. The machine ECM will regulate current to the A2 solenoid (17) on the control valve (work tool) (1). Refer to Illustration 1 and Illustration 3 under "General Information". The "A2" solenoid (17) will direct pilot oil to the left end of the auxiliary valve control spool (18). If no work tool wiring harness is detected, the ECM signal to the "A2" solenoid (17) will limit the movement of spool (18). Movement of spool (18) works against the force of spring (54). The pilot oil (55) forces the auxiliary valve control spool (18) to move to the right against the force of spring (54). Oil flows from the central passage (24) around spool (18) into passage (58) to the compensator spool. Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for "A2" control on the right-hand joystick.
When pump pressure exceeds working pressure, the compensator spool (6) shifts up allowing flow to the bridge passage (57). Refer to Illustration 1 and Illustration 3 under "General Information". Oil flows from the bridge passage (57) around the spool to port "B" (56) at a standard flow rate. Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
The return oil flows into port "A" (59) and through the passage (23) to the hydraulic tank .
When the thumb wheel on the right-hand joystick (22) is released from the "A2" direction, spring (54) shifts the spool back to the HOLD position. Refer to Illustration 15.
"A2" Position With a Work Tool Wiring Harness
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| Illustration 17 | g01337105 |
Auxiliary spool in the "A2" position (18) Auxiliary valve control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (54) Spring (55) Pilot oil (56) "B" port for the auxiliary control valve (57) Bridge passage for the tilt cylinder control spool (58) Passage to the compensator spool and bridge (59) "A" port for the auxiliary control valve | |
When the thumb wheel on the right-hand joystick (22) is pushed in the "A2" direction, a PWM signal is sent to the machine ECM. Refer to Illustration 15. The machine ECM will regulate current to the "A2" solenoid (17) on the control valve (work tool) (1). Refer to Illustration 1 and Illustration 3 under "General Information". The "A2" solenoid (17) will direct pilot oil to the left end of the auxiliary valve control spool (18). When a work tool wiring harness is detected, the ECM signal to the "A2" solenoid (17) allows the movement of spool (18). Movement of spool (18) works against the force of spring (53) and spring (54). The pilot oil (55) forces the auxiliary valve control spool (18) to move to the right against the force of spring (53) and spring (54). Oil flows from the central passage (24) around spool (18) into passage (58) to the compensator spool. Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for "A2" control on the right-hand joystick.
When pump pressure exceeds working pressure, the compensator spool (6) shifts up allowing flow to the bridge passage (57). Refer to Illustration 1 and Illustration 3 under "General Information". Oil flows from the bridge passage (57) around the spool to port "B" (56) at a high flow rate. Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
The return oil flows into port "A" (59) and through the passage (23) to the hydraulic tank .
When the thumb wheel on right-hand joystick (22) is released from the "A2" direction, spring (54) shifts the spool back to the HOLD position. Refer to Illustration 15.
"A1" Position
"A1" Position Without a Work Tool Wiring Harness
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| Illustration 18 | g01342709 |
Auxiliary spool in the "A1" position (18) Auxiliary valve control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (54) Spring (56) "B" port for the auxiliary control valve (57) Bridge passage for the tilt cylinder control spool (58) Passage to the compensator spool and bridge (59) "A" port for the auxiliary control valve (60) Pilot oil | |
When the thumb wheel on the right-hand joystick (22) is pulled in the "A1" direction, a PWM signal is sent to the machine ECM. Refer to Illustration 15. The machine ECM will regulate current to the "A1" solenoid (2) on the control valve (work tool) (1). Refer to Illustration 1 and Illustration 3 under "General Information". The "A1" solenoid (2) will direct pilot oil to the right end of the auxiliary valve control spool (18). If no work tool wiring harness is detected, the ECM signal to the "A1" solenoid (2) will limit the movement of spool (18). Movement of spool (18) works against the force of spring (54). The pilot oil (60) forces the auxiliary valve control spool (18) to move to the left against the force of spring (54). Oil flows from the central passage (24) around spool (18) into passage (58) to the compensator spool. Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for "A1" control on the right-hand joystick.
When pump pressure exceeds working pressure, the compensator spool (6) shifts up allowing flow to the bridge passage (57). Refer to Illustration 1 and Illustration 3 under "General Information". Oil flows from the bridge passage (57) around the spool to port "A" (59) at a standard flow rate. Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
The return oil flows into port "B" (56) and through the passage (23) to the hydraulic tank .
When the thumb wheel on the right-hand joystick (22) is released from the "A1" direction, spring (54) shifts the spool back to the HOLD position. Refer to Illustration 15.
"A1" Position With a Work Tool Wiring Harness
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| Illustration 19 | g01342710 |
Auxiliary spool in the "A1" position (18) Auxiliary valve control spool (23) Return passage to valve outlet (24) Central supply passage from the hydraulic pump (53) Spring (54) Spring (56) "B" port for the auxiliary control valve (57) Bridge passage for the tilt cylinder control spool (58) Passage to the compensator spool and bridge (59) "A" port for the auxiliary control valve (60) Pilot oil | |
When the thumb wheel on the right-hand joystick (22) is pulled in the "A1" direction, a PWM signal is sent to the machine ECM. Refer to Illustration 15. The machine ECM will regulate current to the "A1" solenoid (2) on the control valve (work tool) (1). Refer to Illustration 1 and Illustration 3 under "General Information". The "A1" solenoid (2) will direct pilot oil to the right end of the auxiliary valve control spool (18). When a work tool wiring harness is detected, the ECM signal to the "A1" solenoid (2) will allow the movement of spool (18). Movement of spool (18) works against the force of spring (53) and spring (54). The pilot oil (60) forces the auxiliary valve control spool (18) to move to the left against the force of spring (53) and spring (54). Oil flows from the central passage (24) around spool (18) into passage (58) to the compensator spool. Refer to the machine Operation and Maintenance Manual, SEBU8020, "277C, 277C2, 287C, 287C2, and 297C Multi Terrain Loaders", "Operator Controls " for "A1" control on the right-hand joystick.
When pump pressure exceeds working pressure, the compensator spool (6) shifts up allowing flow to the bridge passage (57). Refer to Illustration 1 and Illustration 3 under "General Information". Oil flows from the bridge passage (57) around the spool to port "A" (59) at a high flow rate. Refer to "Isolator Compensator Explanation" for the explanation of the isolator compensator assembly.
The return oil flows into port "B" (56) and through the passage (23) to the hydraulic tank .
When the thumb wheel on right-hand joystick (22) is released from the "A2" direction, spring (54) shifts the spool back to the HOLD position. Refer to Illustration 15.
Isolator Compensator Explanation
Note: For this explanation of the isolator compensator assembly, the Tilt Cylinder Control Spool will be used. The isolator compensator assembly for the Lift Cylinder Control Spool and the isolator compensator assembly for the auxiliary control spool work in the same manner.
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| Illustration 20 | g01341848 |
(6) Isolator compensator assembly for the auxiliary function (7) Isolator compensator assembly for the tilt cylinders (8) Isolator compensator assembly for the lift cylinders (9) Isolator compensator assembly for the secondary auxiliary function (21) Secondary auxiliary control spool (20) Lift cylinder control spool (19) Tilt cylinder control spool (18) Auxiliary control spool (48) Bridge passage for the tilt cylinder control spool (49) Passage to the bottom of the compensator spool (61) Load sensing passage (62) Auxiliary pump passage | |
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| Illustration 21 | g01342156 |
(63) Spring (64) Orifice in isolator spool (65) Spring (66) Cross drilled hole (67) Compensator spool (68) Isolator spool | |
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| Illustration 22 | g01342154 |
Section view that shows the tilt cylinder control spool (19) Tilt cylinder control spool (23) Central return passage (24) Central supply passage from the hydraulic pump (43) Working port "A" (45) Working port "B" (48) Bridge passage (49) Passage to the bottom of the compensator spool (61) Load sensing passage (62) Auxiliary pump passage | |
Single Function
Shifting the spool will connect work port "A" (43) or work port "B" (45) to the bridge (48). Shifting the spool will also connect the central pump supply passage (24) to passage (49). Passage (49) connects passage (24) to the bottom of the compensator spool (67) .
Working pressure is communicated through a small cross drilled hole (66) in the upper portion of the compensator spool (67). Working pressure acts on the top of the compensator spool (67) and on the bottom of the isolator spool (68). The pressure on the bottom of the isolator spool will lift the isolator spool. Shifting up the isolator spool meters oil from the auxiliary pump passage (62) into the load sensing passage (61). Oil in the load sensing passage creates a load sensing signal to the hydraulic pump controller.
If working pressure is greater than hydraulic pump pressure, the compensator spool (67) remains shut for the load check function of the compensator.
When the pump pressure exceeds the working pressure, pump pressure will shift up the compensator spool (67) against the isolator spool (68) .
The isolator compensator is designed to maintain a 24 bar (348 psi) margin between the hydraulic pump pressure and working pressure. Hydraulic pump pressure must be greater than working pressure.
Multifunction
Each command function will generate an independent load sensing signal. Refer to "Single Function ".
Load sensing pressure is communicated to the top of each isolator spool through an orifice (64) in the spool. The isolator spool with the highest pressure creates the load sensing signal. This load sensing signal is sent to the hydraulic pump controller. This load sensing signal is also sent to the top of each of the other isolator spools.
The isolator spools with working pressures that are less than load sensing pressure are pushed down. These isolator spools also push the compensator spools. Pushing down the compensator spools partially closes the metering holes in the compensator spools. Closing the metering holes increase the pressure drop on these functions. Closing the metering holes also maintains the designed pressure margin. Closing the metering holes also prevent low-pressure functions from diverting flow from the high-pressure functions.
If the demand for oil flow is greater than the pump output, pump pressure will fall. Falling pressure causes load sensing pressure to push down the isolator compensators proportionally. This condition will avoid an implement stall condition.
Dual Pressure Load Sensing Relief Valve
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| Illustration 23 | g01346127 |
(69) Solenoid for the dual pressure load sensing relief valve (70) Load sensing relief valve (71) Shuttle valve assembly | |
When no auxiliary work tool is attached, or when a standard flow work tool is attached, the implement system operates normal system pressure.
Attach a high flow work tool and connect the high flow electrical work tool harness. The command for auxiliary flow will energize the dual pressure relief solenoid (69) on the dual pressure load sensing relief valve (70). Energizing the solenoid (69) will compress the load sensing relief valve spring. Compressing the load sensing relief valve spring will increase the relief valve setting.
If the operator commands the lift function or the tilt function during the dual pressure operation, the dual pressure relief solenoid (69) will de-energize. De-energizing the dual pressure relief solenoid will reduce maximum system pressure to the normal system pressure.
Shuttle Valve
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| Illustration 24 | g01343920 |
(C) Connection to the hydraulic pump (D) Connection to the work tool control valve (71) Shuttle valve assembly (74) Shuttle | |
An implement system that is equipped with the dual pressure load sensing relief valve may tend to oscillate under certain conditions. A shuttle valve (71) is used in order to maximize the initial response of the pump. The shuttle valve will also dampen the oscillation of the load sensing signal. Refer to Illustration 23 under "Dual Pressure Load Sensing Relief Valve".