D8T POWER TRAIN ELECTRONIC CONTROL SYSTEM

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Power Train Hydraulic System

The three-section fixed displacement power train oil pump is mounted to the right front of the main case and is driven by a drive shaft connected to the rear of the implement pump. The transmission charging (C) section of the power train oil pump provides high pressure oil to the transmission main relief valve, which maintains a common top pressure for operation of the transmission modulating valves and the brakes.

With the common top pressure power train strategy, transmission clutch engagement pressure calibrations and brake pressure adjustments no longer need to be performed. (Clutch fill time calibrations and brake touch-up calibrations are still required.) When the transmission main relief valve is properly adjusted, all of the pressures for the transmission clutches and for the brakes are also properly adjusted.

The torque converter charging (B) section of the power train oil pump supplies oil to the torque converter, through the priority valve. Oil from the transmission charging section that flows past the main relief valve mixes with the lube oil from the power train oil cooler and is used to lubricate and cool the transmission and the bevel gears.

The scavenge (A) section of the power train oil pump draws oil from the transmission and bevel gear case and from the torque divider housing and directs it to the sump in the main case.

Clutch 4

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The torque converter inlet relief valve and the lube distribution manifold are located at the left front of the main case. They are consolidated into one dual purpose housing (1).

The electronic brake control valve (2) is installed on top of the main case.

The transmission charging section and the torque converter charging section of the power train oil pump draw their oil through the screened main sump suction manifold (3).

The three-section power train oil pump (4) is located at the right front of the main case and it is driven by a shaft that connects to the rear of the implement pump (not pictured). This drive shaft is covered with a guard when the machine is completely assembled.

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The fixed displacement, three-section power train oil pump is mounted to the right, front of the main case.

The power train oil pump scavenge section (1) draws oil from the transmission and bevel gear case (inside the main case). The scavenge section also draws oil from the torque divider housing (and lube oil from the flywheel housing) through the hose (5) on the left side of the pump. The oil from these two sources is pumped into the sump in the main case. The flow rate for the scavenge section of the power train oil pump is approximately 118 L/min (31.2 gpm).

The torque converter charging section (2) and the transmission charging section (3) of the power train oil pump draw their oil from the main power train oil sump through the screened, main suction manifold (4). The screen in the suction manifold may be easily accessed by removing the square cover, on top of the manifold. The flow rate for the torque converter charging section of the power train oil pump is approximately 162 L/min (42.8 gpm). The flow rate for the

transmission charging section of the power train oil pump is approximately 58 L/min (15.3 gpm).

The pump drive hub (6) connects to a shaft that is driven by a similar hub at the rear of the implement hydraulic pump.

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6

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The two, 6-micron power train oil filters and the priority valve are now located inside the forward compartment on the right fender.

Shown in the illustration above is the torque converter charge filter (1) and the transmission charge filter (2). The priority valve (3) is integrated into the filter base/housing. The priority valve adjustment screw is located on the back side of the housing (not visible here), and opposite the priority valve solenoid (4).

Accessible through the front compartment on the right fender are the following service points:

5. test port for transmission charge filter outlet pressure

6. test port for priority valve pressure/torque converter charge filter outlet pressure

7. test port for power train oil sampling (S•O•S)/torque converter charge filter inlet pressure 8. power train oil temperature sensor (main sump temperature)

9. bypass switch for the torque converter charge filter (The bypass switch for the transmission charge filter is located on the opposite side of this housing/filter base.) The status of the priority valve solenoid, the transmission oil temperature sensor, and both of the power train oil filter bypass switches may be viewed through the Advisor panel (Power Train System Status screens) or through Cat ET.

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The illustration above shows the priority valve in the Normal, or low pressure mode. The priority valve ensures that supply oil to the brake control valve and the transmission control group gets priority over supply oil to the torque converter circuit. The priority valve only operates at low pressure during certain conditions.

In Normal Mode, oil from the torque converter charging section of the power train oil pump enters the slug chamber through a hole in the center passage of the spool and also enters the spool cavity through the solenoid valve and the connecting passage. The oil pressure on the left end of the spool causes the spool to shift to the right, against the spring. This allows the oil from the torque converter charging section to flow around the spool and out to the torque

converter inlet relief valve. The pressure of the torque converter oil is lower than the pressure of the oil in the passage from the transmission charging section of the power train oil pump (going to the brakes and transmission). As a result, the check valve remains closed and the oil from the torque converter charging section of the power train oil pump does not mix with the oil from the transmission charging section.

The coil of the solenoid valve is normally ENERGIZED when in the Normal Mode of operation.

This strategy ensures that if communication is lost to the priority valve solenoid, the priority valve will default to the Priority Mode.

Spool

TC Charge SectionFrom of PTO Pump

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The illustration above shows the priority valve operating in the Priority Mode. The priority valve operates in the Priority Mode under the following conditions:

- power train oil (main sump) temperature less than 40°C (104°F) - engine speed below 1300 rpm

- during transmission speed or directional changes

During operation in the Priority Mode, the solenoid coil of the priority valve is DE-ENERGIZED.

The solenoid valve then blocks torque converter charge oil from entering the spool cavity and allows the oil from the spool cavity to drain to tank. With only tank pressure at the left end of the spool, the spring shifts the spool back to the left. With the spool shifted to the left, only a small amount of torque converter charge oil can flow into the passage going to the torque converter inlet relief valve. With the passage to the torque converter mostly blocked, the pressure of the torque converter charge oil increases until it overcomes the combined force of the check valve spring and the pressure of the oil from the transmission charging section of the power train oil pump. As a result, the check valve opens and the flow of torque converter oil mixes with the transmission and brake oil. This ensures that there is enough oil to safely operate the transmission and brakes.

The priority valve will default to Normal Mode when the parking brake is activated.

FLOW

To Brake Valve and Transmission

TC Charge SectionFrom of PTO Pump