992G Wheel Loader and 854G Wheel Dozer Power Train Transmission Hydraulic System Caterpillar


Transmission Hydraulic System
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Illustration 1g00670956

Hydraulic System Schematic

(1) Priority valve. (2) Lockup clutch solenoid valve (if equipped). (3) Impeller clutch solenoid valve. (4) Transmission hydraulic controls. (5) Oil filter. (6) Oil filter. (7) Torque converter. (8) Lockup clutch (if equipped). (9) Impeller clutch. (10) Oil pump. (11) Torque converter outlet relief valve. (12) Flow control orifice. (13) Magnetic screen. (14) Oil cooler. (15) Reservoir in output transfer gear case. (16) Outlet line from oil cooler to planetary lubrication. (A) Oil pump output pressure tap P1. (B) Pressure tap for oil pump. (C) Pressure tap for lockup clutch (if equipped). (D) Torque converter inlet pressure tap P3. (E) Pressure tap for oil pump. (F) Pressure tap for impeller clutch. (G) Lubrication pressure tap. (H) Torque converter outlet pressure tap.

The transmission hydraulic system contains a common reservoir. The reservoir is at the bottom of output transfer gear case (15). The reservoir supplies oil for the operation of the torque converter and for the operation of the transmission. The reservoir also provides lubrication oil for the different components in the system.

Oil is pulled from the reservoir through magnetic screen (13) by transmission oil pump (10). The transmission oil pump is fastened to the rear of the torque converter cover below the steering pump. Transmission oil pump (10) sends pressure oil to transmission oil filter (5) and transmission oil filter (6). The oil flows through the transmission oil filters. If there are any restrictions in the oil filters, a bypass valve in the filter housings allows the oil to flow around the filters.

The oil flows from the rear transmission oil filter to priority valve (1). The priority valve maintains a constant oil pressure to the solenoid valve for the torque converter lockup clutch (2) (if equipped) and the solenoid valve for the torque converter impeller clutch (3). The lockup clutch solenoid valve (2) supplies oil to lockup clutch (8) (if equipped). Impeller clutch solenoid valve (3) supplies oil to impeller clutch (9). The impeller clutch pressure drops during a directional shift and increases to full pressure after the transmission clutches engage.

The remaining oil from the priority valve and the oil that flows from the front transmission oil filter flows to transmission hydraulic control (4). The transmission hydraulic control regulates the oil pressure and the oil flow for the engagement of the transmission clutches. The transmission hydraulic control also provides the inlet oil to the torque converter.

Inlet oil for the operation of the torque converter flows through a hose to the torque converter. The converter inlet ratio valve limits the oil pressure to the torque converter. Oil leakage inside the torque converter lubricates the inside components. After the components are lubricated, the oil flows to the bottom of the torque converter housing. The oil then flows from the bottom of the torque converter housing to the reservoir in output transfer gear case (15) .

Oil from the torque converter flows to torque converter outlet relief valve (11). Torque converter outlet relief valve (11) maintains the pressure inside the torque converter at a specific rate. The oil flows from the torque converter outlet relief valve to power train oil cooler (14) .

After flowing through the power train oil cooler, the oil is at a lower temperature. This oil flows to the input transfer gears. The oil then flows to the transmission planetary group. This oil is for the lubrication of the inside components of the transmission and for the lubrication of the input transfer gears and the output transfer gears.

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