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| Illustration 1 | g00643756 |
Three-point hitch hydraulic system (1) Top cover with pressure regulating valve (2) Block which contains the hitch relief valve (3) Three-point hitch control valve (4) Passage to the top cover of the rear axle housing (5) Passage for the load sensing signal to the pressure and flow compensator valve (6) Inlet passage for supply oil from the implement hydraulic pump (7) Inlet manifold (8) Three-point hitch lift cylinders (9) Return oil passage (10) Implement control valve bank (11) Load check valve (12) Solenoid valve (AA) Supply oil (HH) Blocked oil (LL) Sump oil | |
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| Illustration 2 | g00480061 |
(1) Pressure regulating valve | |
Inlet manifold (7) contains inlet passage (6) for supply oil from the implement hydraulic pump. Also, inlet manifold (7) contains outlet passage (5) for the load sensing signal to the pressure and flow compensator valve. Supply oil (6) from inlet manifold (7) is directed through implement control valve bank (10) and to three-point hitch control valve (3) .
Pressure regulating valve (1) supplies the pilot oil to electrohydraulic solenoids (12). Solenoids (12) are used in order to shift the main control valve spool in three-point hitch control valve (3) .
The supply port to the head end of three-point hitch lift cylinders (8) contains a load check valve (11). Load check valve (11) helps maintain the position of the three-point hitch while the hitch is in the HOLD position.
Supply oil is routed to a block that contains hitch relief valve (2). Hitch relief valve (2) protects the system from shock loads. The block routes the supply oil to the three-point hitch lift cylinders and from the three-point hitch lift cylinders. The rod ends of hydraulic cylinders (8) are always open to the tank (9) through the block.
A drain line that is from the bottom of the block is routed to the top cover of rear axle housing (4) .
The top cover of implement control valve bank (10) contains a pressure regulating valve (1). Pressure regulating valve (1) supplies reduced pilot oil to solenoid valves (12) through internal passages in the top cover.
Pressure regulating valve (1) is used in order to regulate supply pressure from the implement hydraulic pump to 3450 kPa (500 psi). Pressure regulating valve (1) is not adjustable.
When a signal is sent for raising the three-point hitch or lowering the three-point hitch, the valve spool in the respective solenoid valve (12) will shift back and forth. This regulates the pressure of the pilot oil that is sent to the end of the main control valve spool of the three-point hitch control valve.
The main control valve spool moves to the right in order for the three-point hitch to raise. The pressure of the supply oil opens load check valve (11). The supply oil is then routed to the head end of the three-point hitch lift cylinders. This causes three-point hitch lift cylinders (8) to extend. The extension of the three-point hitch lift cylinder causes the three-point hitch linkage to raise.
When the three-point hitch lowers, oil is forced out of the three-point hitch lift cylinders by the weight of the three-point hitch and the implements. When the main control valve spool moves left, the pressure of the supply oil opens load check valve (11). This allows blocked oil from the head end of the three-point hitch lift cylinders to flow to the common sump.
Hitch relief valve (2) is connected to the head end of the three-point hitch lift cylinders. Hitch relief valve (2) is installed in the block that is mounted to the front of three-point hitch control valve (3). Internal passages that are in the block route oil to the three-point hitch lift cylinders and from the three-point hitch lift cylinders. Also, oil is routed to the common sump.
Hitch relief valve (2) protects the components of the three-point hitch from high shock loads. When hitch relief valve (2) opens, the excess pressure dumps into drain line (4) that is connected to the rear axle housing. Hitch relief valve (2) is set at 21375 ± 345 kPa (3100 ± 50 psi). Hitch relief valve (2) is not adjustable.
The rod ends of three-point hitch lift cylinders (8) are always open to the common sump. The passage to the common sump is provided through the block that is mounted on the front of three-point hitch control valve (3).
HOLD Position
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| Illustration 3 | g00480110 |
Three-point hitch control valve (HOLD position) (3) Three-point hitch control valve (11) Load check valve (12) Solenoid (13) Flow control spool (14) Passage for supply oil from the pressure regulating valve (15) Main control valve spool (16) Piston (17) Centering springs (18) Primary resolver (19) Secondary resolver (AA) Supply oil (BB) Reduced supply oil (CC) Pilot oil for the three-point hitch (HH) Blocked oil (LL) Sump oil | |
No electrical current is applied to either solenoid (12) while the three-point hitch control valve is in the HOLD position. When no electrical current is applied to the solenoids, the spools keep both ends of main control valve spool (15) open to the common sump. Main control valve spool (15) remains centered by springs (17) that are at both ends.
Flow control spool (13) operates similarly to the flow control spools in the implement control valves. However, three-point hitch control valve (3) does not have the metering sleeve for manual flow adjustment.
Flow control spool (13) acts as a load check valve. Also, flow control spool (13) controls the flow and pressure to main control valve spool (15). Flow control spool (13) maintains a pressure that is equal to the spring force value at main control valve spool (15).
When main control valve spool (15) is in the HOLD position, there is no pressure behind piston (16) for load check valve (11 ). Load check valve (11) will remain closed. This blocks the oil from the head end of three-point hitch lift cylinders (8) which allows the three-point hitch to maintain a given position.
RAISE Position
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| Illustration 4 | g00480151 |
Three-point hitch control valve (RAISE position) (3) Three-point hitch control valve (11) Load check valve (12) Solenoid (13) Flow control spool (14) Passage for supply oil from the pressure regulating valve (15) Main control valve spool (16) Piston (17) Centering springs (18) Primary resolver (19) Secondary resolver (20) Flow control spring chamber (AA) Supply oil (BB) Reduced supply oil (CC) Pilot oil for the three-point hitch (DD) Pilot signal oil (LL) Sump oil | |
When the three-point hitch control lever is pulled back to the RAISE position, the Chassis Control Module sends a pulse width modulated signal that is DC current to left solenoid valve (12) .
The pulse width modulation causes the spool in solenoid (12) to move back and forth at a specific rate. Movement of the spool in solenoid (12) provides modulation for the pilot oil. The lower rate for the three-point hitch during the FLOAT position is controlled by the three-point hitch lower rate control. This allows main control valve spool (15) to be controlled in a precise manner.
Pilot oil from pressure regulating valve (1) is routed through passage (14). The pilot oil then flows through the cross-drilled holes that are in solenoid (12) in order to fill the spring chamber that is at the left end of main control valve spool (15). This causes the main control valve spool to shift a specific amount to the right.
The supply oil at the work port is initially blocked by load check valve (11) .
The pressure of the load sensing signal enters the primary resolver (18) .
. The "-" port is open to the common sump. The pressure of the load sensing signal is then directed to both secondary resolver (19) and to the spring chamber for flow control spool (13) .
When only three-point hitch control valve (3) is activated, the pressure of the load sensing signal is sensed by the pressure and flow compensator valve. This causes the implement hydraulic pump to slightly upstroke.
Pressure from the load sensing signal plus the spring force value in flow control spring chamber (20) move flow control spool (13) to the right. This allows a greater pressure into the passage to the work port. The higher pressure will be sensed at the implement hydraulic pump.
The pump output pressure and pressure at the work port continue to increase until the pressure at the bottom of piston (16) is great enough to unseat load check valve (11) .
If an implement control valve is operating downstream, the pressure of the load sensing signal in the spring chamber would continue to increase until load check valve (11) is unseated.
When load check valve (11) is unseated, the load pressure is felt in the supply passage to the work port. The load pressure is sensed in flow control spring chamber (20) for flow control spool (13) before entering the pump signal control network for the implement control valves.
Left solenoid valve (12) continues to modulate. This keeps main control valve spool (15) shifted until the position of the three-point hitch that is detected by the feedback potentiometer agrees with the three-point hitch control lever.
The Chassis Control Module then stops the signal to the solenoid. The solenoid spool returns to the de-energized position. This allows the oil at the left end of main control valve spool (15) to flow to the common sump.
The right centering spring (17) returns main control valve spool (15) to the HOLD position.
LOWER Position
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| Illustration 5 | g00480242 |
Three-point hitch control valve (LOWER position) (3) Three-point hitch control valve (11) Load check valve (12) Solenoid (13) Flow control spool (14) Passage for supply oil from the pressure regulating valve (15) Main control valve spool (16) Piston (17) Centering spring (18) Primary resolver (19) Secondary resolver (20) Flow control spring chamber (21) Slot (AA) Supply oil (BB) Reduced supply oil (CC) Pilot oil for the three-point hitch (DD) Pilot signal oil (LL) Sump oil | |
When the three-point hitch control lever is pushed forward to the LOWER position, the Chassis Control Module sends a pulse width modulated signal that is DC current to the right solenoid valve (12).
The pulse width modulation causes the spool in solenoid (12) to move back and forth at a specific rate. Movement of the spool in solenoid (12) provides modulation for the pilot oil. This allows main control valve spool (15) to be controlled in a precise manner.
Pilot oil from pressure regulating valve (1) is routed through passage (14). The pilot oil then flows through the cross-drilled holes that are in solenoid (12) in order to fill the spring chamber that is at the right end of main control valve spool (15). This causes the main control valve spool to shift a specific amount to the left .
The supply oil to the work port crosses through slot (21) in main control valve spool (15) and into the "-" work port. Supply oil also flows behind piston (16) for load check valve (11). When the "-" work port is plugged, the pressure increases in order to unseat load check valve (11) .
The pressure of the load sensing signal enters primary resolver (18). The "+" port is open to the common sump. The pressure of the load sensing signal is then directed to both secondary resolver (19) and to flow control spring chamber (20) .
The pressure of the load sensing signal is sensed by the pressure and flow compensator valve. This causes the implement hydraulic pump to slightly upstroke. The pump output pressure and work port pressure continue to increase until load check valve (11) is unseated.
Load check valve (11) is held open at a pressure of 17090 ± 620 kPa (2480 ± 90 psi).
When load check valve (11) is unseated, the work port is opened to the common sump. The oil that is between the head end of three-point hitch lift cylinders (8) and load check valve (11) is allowed to flow to the common sump. The weight of the three-point hitch aids in the moving of oil to the common sump. This results in the lowering of the three-point hitch.
Right solenoid valve (12) continues to modulate. This keeps main control valve spool (15) shifted until the position of the three-point hitch that is detected by the feedback potentiometer agrees with the three-point hitch control lever.
The Chassis Control Module then stops the signal to the solenoid. The solenoid spool returns to the de-energized position. This allows the oil at the right end of main control valve spool (15) to flow to the common sump.
Left centering spring (17) returns main control valve spool (15) to the HOLD position.
FLOAT Position (If Equipped)
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| Illustration 6 | g00637953 |
Three-point hitch control valve (FLOAT position) (3) Three-point hitch control valve (11) Load check valve (12) Solenoid (13) Flow control spool (14) Passage for supply oil from the pressure regulating valve (15) Main control valve spool (16) Piston (17) Centering spring (18) Primary resolver (19) Secondary resolver (20) Flow control spring chamber (21) Slot (AA) Supply oil (BB) Reduced supply oil (CC) Pilot oil for the three-point hitch (DD) Pilot signal oil (LL) Sump oil | |
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| Illustration 7 | g00637965 |
Three-point hitch raise/lower switch that is equipped with a FLOAT position | |
The three-point hitch may be lowered below the depth that is set by the three-point hitch control lever. Press and hold the front of switch (22) in order to allow the three-point hitch to float. The three-point hitch now has the ability to float past the lower limit on the feedback potentiometer. This will not disturb the depth that was selected by the three-point hitch control lever. When switch (22) is released, the three-point hitch will return to the depth that was set by the three-point hitch control lever.
When the front of switch (22) is held down, the Chassis Control Module sends a pulse width modulated signal that is DC current to the right solenoid valve (12) .
The pulse width modulation causes the spool in solenoid (12) to move back and forth at a specific rate. Movement of the spool in solenoid (12) provides modulation for the pilot oil. This allows main control valve spool (15) to be controlled in a precise manner.
Pilot oil from pressure regulating valve (1) is routed through passage (14). The pilot oil then flows through the cross-drilled holes that are in solenoid (12) in order to fill the spring chamber that is at the right end of main control valve spool (15). This causes the main control valve spool to shift a specific amount to the left.
The supply oil to the work port crosses through slot (21) in main control valve spool (15) and into the "-" work port. Supply oil also flows behind piston (16) for load check valve (11). When the "-" work port is plugged, the pressure increases in order to unseat load check valve (11) .
The pressure of the load sensing signal enters primary resolver (18). The "+" port is open to the common sump. The pressure of the load sensing signal is then directed to both secondary resolver (19) and to flow control spring chamber (20) .
The pressure of the load sensing signal is sensed by the pressure and flow compensator valve. This causes the implement hydraulic pump to slightly upstroke. The pump output pressure and work port pressure continue to increase until load check valve (11) is unseated.
Load check valve (11) is held open at a pressure of 17090 ± 620 kPa (2480 ± 90 psi).
When load check valve (11) is unseated, the work port is opened to the common sump. The oil that is between the head end of three-point hitch lift cylinders (8) and load check valve (11) is allowed to flow to the common sump. The weight of the three-point hitch aids in the moving of oil to the common sump. This results in the lowering of the three-point hitch. The three-point hitch lift cylinders are now free to float in the downward direction as well as the upward direction.
Solenoid valve (12) continues to modulate. This keeps main control valve spool (15) shifted until switch (22) is released.
Once switch (22) is released, the Chassis Control Module stops the signal to the solenoid. The solenoid spool returns to the de-energized position. This allows the oil at the right end of main control valve spool (15) to flow to the common sump.
The Chassis Control Module will then signal the appropriate solenoid valve (12). This will raise the three-point hitch or this will lower the three-point hitch. The three-point hitch will return to the original position that was selected by the three-point hitch control lever.