980M and 982M Wheel Loaders Power Train, Steering, Braking, Hydraulic, and Machine Systems Caterpillar

Illustration 1	g06212797

The transmission hydraulic system consists of the following primary components: sump (7), pump-gear (two-section) (1), filter-transmission (3), valve-relief (eMRV) (4J), modulating valves, torque converter group (5), valve-relief (torque converter inlet) (4L), and cooler group (transmission) (6).

The bottom of the output transfer gear case contains the oil sump from which the transmission oil pump pulls oil from. Transmission oil pump is a two-section positive displacement gear pump. The transmission oil pump has one inlet and two outlet ports. The two outlet ports are the controls flow (high pressure) and converter charging flow (low pressure). As the pump rotates, oil from the controls flow (high pressure) oil flows to the transmission oil filter. Oil from the transmission oil filter then flows to the modulating valves (control group). Oil from the converter charging flow (low pressure) flows to the, Valve-relief (eMRV) (4J), Valve-relief (torque converter inlet) (4L), and torque converter.

Modulating valves are mounted on the top of the transmission. There is one modulating valve for each of the six transmission clutches. In order to move the machine, a direction clutch solenoid, and a speed clutch solenoid must be energized. Clutch solenoid modulating valves are used to directly modulate the oil pressure that is sent to each individual clutch. The clutch oil leakage and the return oil flows to the bottom of the transmission to the sump. All oil from non-energized modulating valves flows to the bottom of the transmission to the sump. The oil sump is the bottom of the output transfer gear case.

Transmission hydraulic valve-relief (eMRV) controls the pressure for the modulating valves. Oil flows into transmission hydraulic control relief valve (4J) at a maximum pressure of 2896 ± 138 kPa (420 ± 20 psi) at high idle (2200 RPM) and with transmission in neutral. The oil pressure overcomes the spring force of transmission hydraulic control relief valve. The torque converter inlet oil flows to torque converter group (5) at a maximum pressure of 900 kPa (130 psi) at high idle (2200 RPM) and with transmission in neutral.

The oil from torque converter flows to relief valve. Relief valve maintains the outlet oil pressure that is inside torque converter at a minimum of 450 ± 50 kPa (65 ± 7 psi) at high idle (2200 RPM) and with transmission in neutral.

The oil cooler is located in the cooling package at the rear of the machine. After the oil has been cooled, the oil flows to the transmission. The oil provides lubrication and cooling for the transmission. The oil flows through internal passages in the transmission to the bearings, gears, and clutches. The oil then flows to the bottom of the transmission. The oil then flows to oil sump in the bottom of the case for the output transfer gears.