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| Illustration 1 | g03662322 |
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View of the top of the transmission (1) Modulating valve (torque converter lockup clutch) | |
The modulating valve for the torque converter lockup clutch (1) is mounted to the rear of the torque converter housing.
The modulating valve is an output of the transmission electronic control module (ECM). The modulating valve for the torque converter lockup clutch is a proportional solenoid valve. The modulating valve is used by the transmission ECM to directly modulate the oil pressure that is sent to the torque converter lockup clutch. When the machine achieves a certain speed and the lockup clutch is to be engaged, the transmission ECM sends a pulse width modulated (PWM) signal in order to vary the current to the clutch solenoid. The distance that is traveled 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 modulating valve regulates the amount of oil pressure that is supplied to the selected clutch. When the transmission ECM sends the maximum current to the modulating valve, the oil pressure in the clutch is at the maximum. When no current is sent to the modulating valve, the oil pressure in the clutch is at the minimum.
The modulating valve has a connector with two contacts. One contact is the driver, which receives a variable PWM signal from the transmission ECM. The other contact is a return wire to the transmission ECM. Several solenoids share a return wire.
Note: The solenoid coil is not designed to operate at 24 DCV directly. The transmission ECM sends a 24 V PWM signal at a duty cycle which provides an average voltage of about 12 V to the solenoid coil. Do not energize the solenoid coil with 24 DCV (+battery). The life of the solenoid coil will be drastically reduced if the solenoid coil is energized with 24 DCV (+battery). If the solenoid coil must be energized by a source that is different from the transmission ECM, use 12 DCV to energize the solenoid coil.
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| Illustration 2 | g03298237 |
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Torque converter drive | |
With no current supplied to solenoid (1) the modulating valve is not energized. With no PWM signal, the flow of oil to the lockup clutch is blocked.
Oil from passage (D) flows into the modulating valve body. The oil flows around valve spool (7) and into a passage inside valve spool (7). The oil then flows through orifice (5) to drain orifice (4). Passage (C) to the lockup clutch is blocked and the oil is returned through passage (A) and passage (B).
Spring (8) keeps pressure on valve spool (7). The pressure keeps drain orifice (4) open.
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| Illustration 3 | g03298256 |
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Direct drive | |
With the PWM signal to solenoid (1) at maximum duty cycle, the lockup clutch is fully engaged. The maximum duty cycle to solenoid (1) pushes pin (2) and ball (3) firmly against drain orifice (4). Pressurized oil from passage (D) from the gear pump goes through orifice (5) and is blocked by ball (3). The blockage creates increased pressure that pushes valve spool (7) against spring (6). The transmission ECM automatically adjusts the PWM signal to solenoid (1) to maintain the desired lockup clutch pressure.