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| Illustration 1 | g00442134 |
Downshift in Forward: Eighth Speed (1) Transmission input shaft (2) Second speed clutch (3) Third speed clutch (4) First speed clutch (5) Speed clutch C (6) Speed clutch B (7) Speed clutch A (8) Transmission oil cooler (9) Lube passage for power take-off (10) Solenoid for speed clutch 2 (11) Solenoid for speed clutch 1 (12) Solenoid for speed clutch 3 (13) Solenoid for speed clutch B (14) Solenoid for speed clutch C (15) Solenoid for speed clutch A (16) Passage to brake valve (17) Passage to PTO valve (18) Transmission filter (19) Passage to the charge circuits for the implement and steering systems (20) Tandem charge pump (21) Suction screen (22) Common sump (23) Solenoid for modulating clutch 2 (24) Solenoid for reverse (25) Solenoid for modulating clutch 1 (26) Pressure regulating valve (27) Cooler bypass valve (28) Lube relief valve (29) Solenoid for forward 1 clutch (30) Solenoid for forward 2 clutch (31) Reverse direction clutch (32) Forward 2 direction clutch (33) Forward 1 direction clutch (AA) High pressure oil (CC) Second pressure oil (EE) Pilot oil (FF) Reduced pilot oil (HH) Trapped oil (KK) Sump oil | |
Illustration 1 shows the hydraulic oil flow of the transmission during a downshift in the forward direction. The machine was in a speed of at least F11. The transmission is downshifting from ninth speed to eighth speed. Hydraulic oil flows from common sump (22) through filter (21) to tandem charge pump (20). Oil flows through the smaller section of the tandem charge pump which is dedicated to the transmission circuit. Oil flows from the small section of the tandem charge pump through transmission filter (18) and to the transmission hydraulic control. After entering the transmission hydraulic control, the oil flows through pressure regulating valve (26). The pressure regulating valve maintains a constant pressure in the transmission circuit of 1825 ± 70 kPa (265 ± 10 psi).
The oil pressure is regulated as oil fills the passage in the transmission hydraulic control. When you have moved the transmission control lever into the F8 speed, the Electronic Transmission Control activates the solenoids for speed clutches 1 and A. The solenoids energize and the solenoids pull the related spool backward. This will allow the passage to open permitting the pressure regulated oil flow to flow to the respective speed clutch. The oil that is entering the respective speed clutch will force the piston forward. The forward moving piston will compress the belleville springs and this will lock up the friction disc and the plates for the transfer of power. If the solenoids are de-energized, then the spool blocks the oil pressure from going to the clutch. The oil pressure is released to the sump. The belleville springs push the piston backward and this will release the pressure on the friction disc and plates.
The Electronic Transmission Control activates the MC2 modulating solenoid and the solenoid for the F2 direction clutch at the same time when the speed clutch engages. The MC2 modulating solenoid uses pulse width modulation (PWM) to control the flow of oil to the F2 clutch pack. When the MC2 modulating solenoid is energized, the pilot valve spool is pulled off of the seat and the spool is drawn into the solenoid housing. The movement of the pilot valve spool allows the oil from the right side of the chamber in the modulation valve to overflow the seat of the pilot valve. The oil will then drain to the sump. The amount of movement of the pilot valve is dictated by the strength of the current that is supplied to the solenoid. When the oil flows across the seat of the pilot valve, the pressure in the right side of the chamber in the modulation valve is reduced in order to allow the modulating spool to move to the right. The spool also allows the pressure in the left side to be regulated by the throttle control of the spool. As the spool opens the right side of the chamber will drain to the sump. The open and the closed positions of the pilot valve are controlled by the Electronic Transmission Control. The Electronic Transmission Control will regulate the flow of oil over the modulating spool and for a smooth lockup of the F2 direction clutch.
See Systems Operation/Testing and Adjusting, "Transmission Systems Hydraulic Component Operation" for more information.