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| Illustration 1 | g00637786 |
Hydraulic valve locations (A) Speed clutch "A" (B) Speed clutch "B" (C) Speed clutch "C" (1) Number one speed clutch (2) Number two speed clutch (3) Number three speed clutch (F1) First direction clutch F1 (F2) Second forward direction clutch F2 (REV) Reverse direction clutch F1 (MC1) Modulating solenoid (MC2) Modulating solenoid | |
The transmission hydraulic control valve is mounted externally on the right hand side of the center housing of the transmission. The transmission hydraulic control performs the actual application and the actual release of the speed clutches and the direction clutches.
The transmission hydraulic control contains twelve separate hydraulic valves. Eleven of the hydraulic valves are electronically controlled solenoid valves. Also, there is one regulating valve. Out of the eleven electronically controlled solenoid valves, there are nine solenoid valves that control the application of the six speed and three direction clutches. The remaining two solenoid valves are for modulating the engagement of the three direction clutches. Modulating solenoid (MC1) is for direction clutch (F1). Modulating solenoid (MC2) is for direction clutches (F2) and (R) .
The transmission hydraulic control and the modulating solenoids are energized and controlled by the Electronic Transmission Control. This system receives a signal that is from the transmission control lever linkage and the foot-operated inching clutch control.
A regulating valve that is located on the right side of the transmission hydraulic control is set at 1825 ± 70 kPa (265 ± 10 psi). The regulating valve maintains a constant oil pressure in the low pressure circuit of the machine. The low pressure circuits include the following circuits: transmission hydraulic control, lubrication of the transmission clutches, PTO control, service brake control and hydraulic oil cooler.
Operation of the Regulator Valve
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| Illustration 2 | g00459695 |
Regulator valve | |
Supply oil that is present in passage (A) of regulator valve (2) is also connected to the clutch circuits at passage (B). This oil cannot escape until spool (5) has moved to the right. Oil enters the hollow spool through an opening and orifice plate (1). The oil that is passing through orifice plate (1) is filling the passage in spool (5). The oil pressure that is acting on the left side of spool (5) forces the spool to the right. Spool (5) moves against the opposing force of two springs (3) and shims (4). Shims (4) are used in order to make adjustments to the low pressure circuit. When spool (5) moves, any surplus oil that is required for the operation of clutches and modulating solenoids passes through passage (C). This oil is used for the lubrication and cooling circuits.
Operation of the Clutch Valve
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| Illustration 3 | g00459706 |
Clutch valve | |
Each of the nine solenoid valves for the clutch circuits operate in an identical manner. However, the application of the direction clutches are modulated or proportionally controlled. These circuits allow the application and the release of the clutch circuits for the direction clutches to be cushioned. The solenoid valve spools for the six speed clutches have a throttling slot in order to help regulate the rate of the clutch engagement. The solenoid valve spools for the direction clutches do not have the throttling slot.
The nine solenoid valves for the clutch circuits are open or the solenoid valves are closed. Solenoid valve spool (6) prevents the regulated oil pressure in passage (A) from flowing to supply port (S). Coil spring (7) holds the solenoid valve spool in the closed position.
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| Illustration 4 | g00459752 |
When coil (8) is energized, the core of valve spool (9) is magnetically drawn into the surrounding tube (10). This allows the clutch circuit to open to the regulated oil supply.
The coil spring is positioned in the hollow end of the valve core. The coil spring acts as a shock absorber when the valve is energized. The coil spring is a return device when the electrical signal is removed in order to close the valve spool.
Any supply oil that leaks through the valve will exit to the outside of gallery (R) that is connected to the sump. When the valve closes, oil that is in the clutch pack returns through passage (S) to sump (R) .
Operation of the Modulation Valve
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| Illustration 5 | g00637608 |
Modulation valve (13) is controlled by the Electronic Transmission Control. Modulation valve (13) proportionally varies the pressure that is being sent to the direction clutches. The variation is determined by the extent of movement of modulating spool (21). The modulating spool is controlled by the strength of the electrical signal that is from the Electronic Transmission Control.
Regulated oil pressure from passage (A) flows around modulating spool (21) to passage (D). Passage (D) is connected to the clutch circuits for the direction clutches. Since solenoid coil (14) is not energized, oil that is passing into the center of the modulating spool cannot overcome the same oil pressure which is present in chamber (E) which is assisted by the force of spring (20) .
Solenoid coil (14) has now been energized and pilot valve spool (17) is drawn off seat (18) that is inside of solenoid housing (16). This allows oil to flow from chamber (E) over seat (18) to the sump through port (R). The magnitude of flow is controlled by the removable orifice (12) that is protected by filter screen (11). Also, the amount of draw for the pilot valve spool controls the flow.
The extent of movement of the pilot valve is dictated by the strength of the current that is supplied to solenoid coil (14). When the current is turned off, return spring (15) will reseat pilot valve spool (17) on seat (18). The seat is also protected by a filter screen (19) .
As the oil flows across the seat (18), the pressure in chamber (E) is reduced. This is dependent on the rate of flow. Also, the balance of modulating spool (21) is reduced. This causes the spool to move to the right. This allows the pressure at passage (D) to be regulated by the throttling effect of the spool which opens to the sump through passage (R) .
The strength of the electrical current to the modulating solenoids will determine the actual rate of application of the direction clutches. This also determines the actual rate of release of the direction clutches. All signals to the modulating solenoids are controlled by the Electronic Transmission Control.