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| Illustration 1 | g00820816 |
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| Illustration 2 | g00561237 |
Main Control Valve Compartment (Typical Example) (2) Manual valve lock of parking brake valve (3) Manual valve operation of transmission shift | |
The transmission shift/parking brake control valve is a solenoid operated valve. The parking brake solenoid activates the drive line parking brake in the transmission. The transmission shift solenoid controls the shifting of the transmission gears. Both valves are energized by toggle switches on the instrument panel.
The valve block includes the parking brake control valve and the transmission shift control valve. Both solenoid valves are two-way valves with spools and springs. The parking brake spool and the transmission shift spool are closed off at the top by the solenoid valves, and at the bottom by the sealing plugs. The left section of the valve block is made up of the parking brake and the right section is made up of the transmission shift.
The relief valve and a hydraulic accumulator are also used for controlling the parking brake. The relief valve that is installed in the valve block consists of a ball and a spring. The relief valve pressure setting is 1200 to 1400 kPa (175 to 200 psi).
Low transmission clutch pressure switch is installed at port "DS". When the transmission clutch pressure is less than 2500 kPa (360 psi), the low transmission clutch pressure switch is closed. The switch makes contact in order to light the low clutch pressure indicator. This also deactivates the travel activation solenoid.
Applied Parking Brake
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| Illustration 3 | g00561314 |
Transmission Shift/Parking Brake Control Valve (1) Parking brake solenoid (2) Manual valve lock of parking brake valve (3) Manual valve operation of transmission shift (4) Transmission shift solenoid (5) Spool (6) Port "P" (7) Passage (8) Passage (9) Passage (10) Port "T" (11) Port "A" (12) Passage (13) Port "DS" (14) Port "S" (15) Passage (16) Spring (17) Sealing plug (18) Relief valve (19) Passage (20) Passage (21) Spring (22) Sealing plug (23) Spool (24) Valve block (25) Passage (26) Ball (27) Nut (28) Adjustment screw (29) Cap (30) Spring | |
When the parking brake switch on the right console is in the ON position or the left console is in the RAISED position, the parking brake solenoid is de-energized. When the parking brake solenoid is de-energized, the clutch pressure at ports "A" and "B" is returned to the tank. The clutch spring forces the clutch piston against the clutch discs. Now, the clutch discs cannot rotate and the parking brake is applied. When the parking brake is activated, the travel activation solenoid is de-energized in order to block the pilot pressure to the travel pilot control valve. This prevents any activation of the travel circuit while the parking brake is applied.
When the parking brake switch is in the ON, the parking brake de-energizes the solenoid of the parking brake control valve. This allows control spool (5) to move upward and control spool (5) will stop the flow of oil between passages (7) and (8). Since passages (8) and (9) are connected, the pressure oil in passage (20) goes to relief valve (18). This unseats ball (26) against the force of spring (30). This allows a continuous relief of pressure from passage (9) through passage (25) to passage (19) and port "T" (10) to tank. The relief operation is supported by the discharging of the accumulator.
Released Parking Brake
Parking brake control solenoid valve is energized in order to release the parking brake. When the parking brake switch on the right console is in the OFF position and the left console is in the LOWERED position the parking brake solenoid is energized. When the parking brake solenoid valve is energized, pilot pressure is supplied to the following areas: parking brake accumulator and first gear piston or second gear piston. The pilot pressure forces the clutch piston against the clutch spring. Now, the clutch discs are free to rotate and the parking brake is released.
When the parking brake switch is in the OFF position and the left console is in the LOWERED position, the parking brake solenoid is energized and spool (5) is shifted against the force of spring (16). This opens the connection between passages (7) and (8), and oil pressure can go from port "P" (6) to passage (20). The solenoid of the gear shift control valve is not energized at this time so that the oil in passage (20) can go through passage (15) to passage (12) and through port "A" (11) to port "P1" of the transmission. The clutch discs for first gear are released and second gear is selected.
When the parking brake is released, oil pressure goes through port "S" (14) to the accumulator and to the low clutch pressure switch at port "DS".
Shifting to First Gear
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| Illustration 4 | g00561454 |
(3) Manual valve operation of transmission shift (4) Transmission shift solenoid | |
When the parking brake switch is in the OFF position, spool (23) is moved downward against the force of the spring (21). This opens the connection between passages (12) and (31). The line to the transmission from port "P1" is connected to port "A" and passages (12) and (31) to chamber (32) in spool (23) and through passage (19) to port "T" (10) .
The pressure oil flows from passage (15) through passage (33) to port "B". The pressure oil continues to flow through the connecting line to port "P2" of the transmission. The transmission shifts into first gear.
Shifting to Second Gear
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| Illustration 5 | g00561393 |
Transmission Shift and Parking Brake Control Valve (2) Manual valve lock of parking brake valve (3) Manual valve operation of transmission shift (4) Transmission shift solenoid (5) Spool (9) Passage (10) Port "T" (13) Port "DS" (14) Port "S" (15) Passage (16) Spring (17) Sealing plug (18) Relief valve (25) Passage (29) Cap (30) Spring (31) Passage (32) Chamber (33) Passage (34) Port "B" | |
When the parking brake control valve is in the OFF position, selecting second gear with the transmission gear switch on the instrument panel will de-energize the solenoid of the transmission shift control valve. The gear is indicated by the transmission gear indicator.
When the transmission gear switch is operated, spool (23) is pushed upward by the force of spring (21). This opens the connection between passage (12) to passage (15) and passage (8) to passage (19). The pressure oil flows from passage (20) through passage (15) and (12) to port "A" (11) through the connecting line to port "P1". The line to port "P2" of the transmission is connected through port "B" (34), passage (33) and passage (19) to port "T" (10). The transmission is shifted into second gear.
Manual Valve Operation
In the case of a failure, the transmission parking brake control valve can be operated manually. This procedure is necessary if the machine is towed. Turning manual valve lock (2) of the parking brake valve will move spool (5) against the force of spring (10). This also provides transmission clutch accumulator pressure in order to release the parking brake.
| NOTICE |
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For towing the vehicle, the disconnected clutch between the power take-off and transmission must be disengaged or possible machine damage may occur. Refer to Systems Operation, "Transmission". |