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| Illustration 1 | g06188112 |
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Location of the Modulating Valves (Transmission Clutch) (1) Number 1 clutch modulating valve (2) Number 2 clutch modulating valve (3) Number 5 clutch modulating valve (4) Number 4 clutch modulating valve (5) Number 3 clutch modulating valve (6) Number 6 clutch modulating valve | |
The transmission clutch solenoid modulating valves are mounted on the top of the planet gears in the transmission. There is one modulating valve for each of the six transmission clutches.
The modulating valves are outputs of the Transmission Electronic Control Module (ECM). The transmission clutch solenoid modulating valves are proportional solenoid valves. The modulating valves are controlled by the Transmission (ECM) and directly modulate the oil pressure sent to each individual clutch. When the operator selects a direction or a speed, the Transmission ECM sends a pulse width modulated (PWM) signal to specific clutch solenoids. Proportional to the duty cycle sent by the Transmission ECM is the distance that is traveled by each solenoid plunger (valve). The position of the solenoid plunger (valve) controls the oil pressure of the selected clutch. The percentage of the duty cycle that is sent to the solenoid on the modulating valve regulates the amount of oil pressure supplied to the selected clutch. When the Transmission ECM sends the maximum duty cycle to the solenoid for a modulating valve, the oil pressure in the clutch is at the maximum. When no PWM signal is sent, the oil pressure in the clutch is at the minimum.
Refer to System Operations, "Transmission Hydraulic Control" in this manual for the assignments for the transmission clutches.
The Transmission ECM activates the modulating valves selected by the operator. Modulating valves supply oil to the clutches. Modulating valves supply oil to the corresponding clutch. In order for the machine to move, two clutch solenoids must be energized. When the transmission is in neutral, no modulating valves are energized.
The modulating valves have 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 coils are not to be operated at 24 VDC directly. The Transmission ECM sends a 24 V PWM signal at a duty cycle which provides an average voltage of 12 V to the solenoid coils. Do not energize the solenoid coils with 24 VDC (+battery). The life of the solenoid coils will be drastically reduced if the solenoid coils are energized with 24 VDC (+battery). If the solenoid coils must be energized by a source other than the Transmission ECM, use 12 VDC to energize the solenoid coils.
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| Illustration 2 | g03316117 |
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(A) Passage to tank
(B) Passage to clutch (C) Passage from gear pump (1) Solenoid (2) Pin (3) Ball (4) Drain orifice (5) Orifice (6) Test port (7) Valve spool (8) Spring | |
With no PWM duty cycle supplied to the solenoid (1) the modulating valve is not energized. With no signal, the flow of oil to the transmission clutch is blocked.
Oil (C) from the gear pump 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 (B) to the clutch is blocked and the oil is returned through passage (A) to the tank.
Spring (8) keeps pressure on valve spool (7). The pressure keeps drain orifice (4) open.
Commanded Duty Cycle Below Maximum
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| Illustration 3 | g03316118 |
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(A) Passage to tank
(B) Passage to clutch (C) Passage from gear pump (1) Solenoid (2) Pin (3) Ball (4) Drain orifice (5) Orifice (6) Test port (7) Valve spool (8) Spring | |
With the Pulse Width Modulated (PWM) duty cycle below the maximum supplied to solenoid (1), clutch engagement begins and the modulating valve is energized. The percentage of duty cycle is proportional to the pressure applied to the clutch during each stage of the engagement and disengagement cycle.
The start of clutch engagement begins when the current signal to solenoid (1) creates a magnetic field around pin (2). The magnetic force moves pin (2) against ball (3) in proportion to the strength of the current signal from the Transmission ECM. Ball (3) against drain orifice (4) begins to block drain passage (A) of the oil flow from valve spool (7) back to the tank. The partial restriction also causes the pressure at the left end of valve spool (7) to increase. The increased pressure moves valve spool (7) to the right against spring (8) and opens passage (B) from the gear pump to the clutch.
In the initial clutch filling stage, the Transmission ECM commands a high current pulse to move valve spool (7) quickly to start filling the clutch. During this short period, the clutch piston moves to remove the clearances between the clutch discs and plates to minimize the amount of time required to fill the clutch. The ECM then reduces the current signal, which reduces the pressure setting of the solenoid (1). The change in current signal reduces the flow of oil to the clutch. The point where the clutch plates and discs start to touch is called "TOUCH-UP".
Once "TOUCH-UP" is obtained, the Transmission ECM begins a controlled increase of the current signal to start the modulation cycle. The increase in the current signal causes ball (3) and pin (2) to restrict more oil through drain orifice (5) to the tank. The additional restriction causes a controlled movement of spool (7) to the right. Valve spool (7) movement allows the pressure in the clutch to increase.
During the modulation cycle, valve spool (7) working with the variable commanded current signal from the Transmission ECM acts as a variable pressure reducing valve.
The sequence of partial engagement is called "desired slippage". The desired slippage is controlled by the application program stored in the Transmission ECM.
Commanded Duty Cycle at Maximum
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| Illustration 4 | g03316120 |
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(A) Passage to tank
(B) Passage to clutch (C) Passage from gear pump (1) Solenoid (2) Pin (3) Ball (4) Drain orifice (5) Orifice (6) Test port (7) Valve spool (8) Spring | |
With the PWM duty cycle to solenoid (1) at maximum, the transmission 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 (C) 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 current signal to solenoid (1) to maintain the desired clutch pressure.