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| Illustration 1 | g01394155 |
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Transmission Hydraulic Control Group (1) Number 1 clutch solenoid modulating valve (2) Number 2 clutch solenoid modulating valve (3) Number 3 clutch solenoid modulating valve (4) Number 4 clutch solenoid modulating valve (5) Number 5 clutch solenoid modulating valve (6) Number 6 clutch solenoid modulating valve | |
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| Illustration 2 | g01394338 |
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(7) Transmission Hydraulic Control Relief Valve
(8) Inlet chamber (9) Discharge chamber (10) Torque converter inlet relief valve (11) Transmission control passage (12) Main relief valve | |
The transmission hydraulic control group controls the oil pressure to the torque converter and to the transmission clutches. The transmission hydraulic control group is located on the top of the transmission planetary group. The transmission hydraulic control group consists of the following components: six clutch solenoid modulating valves, transmission hydraulic control relief valve (7) and torque converter inlet relief valve (10).
Pressurized oil for the operation of the transmission hydraulic control group flows from the transmission oil pump to the transmission oil filter. The oil flows through the transmission hydraulic control group in order to supply transmission hydraulic control relief valve (7) with oil. The oil also flows to the six clutch solenoid modulating valves and the modulating valve for the lockup clutch.
The six clutch solenoid modulating valves are mounted on the top of the transmission. Each transmission clutch has an individual clutch solenoid modulating valve. In order to move the machine, a direction clutch solenoid and a speed clutch solenoid must be energized. The clutch solenoid modulating valves are used to directly modulate the oil pressure that is sent to each individual clutch.
The following table provides the combination of the energized solenoids and engaged clutches for each forward speed and for each reverse speed.
| Speed Range and Direction | Energized Solenoids | Engaged Clutches |
| Sixth Speed Forward | 4 and 3 | 4 and 3 |
| Fifth Speed Forward | 4 and 2 | 4 and 2 |
| Fourth Speed Forward | 5 and 3 | 5 and 3 |
| Third Speed Forward | 5 and 2 | 5 and 2 |
| Second Speed Forward | 6 and 3 | 6 and 3 |
| First Speed Forward | 6 and 2 | 6 and 2 |
| Neutral | 4 | 4 |
| First Speed Reverse | 6 and 1 | 6 and 1 |
| Second Speed Reverse | 5 and 1 | 5 and 1 |
| Third Speed Reverse | 4 and 1 | 4 and 1 |
Transmission hydraulic control relief valve (7) controls the pressure of the oil that is supplied to the clutch solenoid modulating valves and the torque converter. The oil pressure must overcome the spring force of main relief valve (12). This will maintain a stable supply pressure to the clutch solenoid modulating valves.
The supply oil pressure to transmission hydraulic control relief valve (7) is maintained by main relief valve (12). Oil enters transmission hydraulic control relief valve (7) through inlet chamber (8). The oil flows past main relief valve (12) to transmission control passage (11) until the pressure setting of main relief valve (12) is exceeded. The main relief valve will move to the right. This will allow the excess oil to flow into passage (9) and to the torque converter. The maximum torque converter inlet pressure is controlled by torque converter inlet relief valve (10). When the torque converter inlet pressure reaches the maximum, the torque converter inlet relief valve will open and the excess oil will return to the oil sump.
The clutch solenoid modulating valves are outputs of the power train electronic control module (ECM). The clutch solenoid modulating valves are proportional solenoid valves. The clutch solenoid modulating valves are used by the power train ECM to directly modulate the oil pressure that is sent to each individual clutch. When the operator selects a direction or when the operator selects a speed the power train ECM sends a pulse width modulated signal (PWM) in order to vary the current to the clutch solenoid. The distance that is travelled by the solenoid plunger (valve) is proportional to the electrical current of the solenoid. The position of the solenoid plunger (valve) controls the oil pressure of the selected clutch. The amount of current that is sent to the clutch solenoid modulating valve regulates the amount of oil pressure that is supplied to the selected clutch. When the power train ECM sends the maximum current to the clutch solenoid modulating valve, the oil pressure in the clutch is at the maximum. The maximum oil pressure of clutch solenoid modulating valve is equal to the maximum oil pressure of the transmission hydraulic control relief valve. When no current is sent to the clutch solenoid modulating valve, the oil pressure in the clutch should be zero.
The power train ECM will activate the transmission clutch solenoid modulating valve that is selected by the operator. Clutch solenoid modulating valves (1), (2) and (3) supply oil to the direction clutches. Clutch solenoid modulating valves (4), (5) and (6) supply oil to the speed clutches. In order for the machine to move, one speed clutch solenoid and one direction clutch solenoid must be energized. When the transmission is shifted to neutral, clutch 4 is energized.