446B Backhoe Loader Transmission (Autoshift) Transmission Hydraulic System Caterpillar


Transmission Hydraulic System
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1.1. Torque Converter, Transmission Pump, Screen and Filter
2.2. Power Train Oil Cooler
3.2. Transmission Lubrication System

Torque Converter, Transmission Pump, Screen and Filter

A gerotor pump provides the oil for the operation and the cooling of the transmission and torque converter. The pump also delivers oil for lubrication of the transmission and torque converter. The pump is located on the front of the engine and the pump is driven by the engine.

The oil reservoir for the transmission and for the torque converter is in the bottom of the transmission case. The oil flows from the reservoir to the screen. The oil then flows through a transmission case passage to the suction side of the positive displacement pump. The oil from the pump flows to the filter. Then, the oil flows from the pump to the transmission hydraulic controls. A restriction in the oil filter or high viscosity oil will open a relief valve. The flow of oil will travel back to the sump of the transmission.




Illustration 1g00808536

(1) Oil filter

If the pressure differential of the inlet oil pressure to the oil filter is 138 ± 14 kPa (20 ± 2 psi) higher than the outlet oil pressure, the oil filter bypass valve will open allowing unfiltered oil to flow to the transmission components.

Unfiltered oil can cause damage to other components in the transmission oil system. The unfiltered oil will continue to flow to the transmission until the filter is replaced in order to avoid damage to the transmission due to lack of oil.

Correct maintenance must be used in order to make sure that the element does not become plugged and the element does not stop the flow of clean oil to the transmission oil system. The filter is mounted to the left side of the transmission case.




Illustration 2g00808537

(2) Screen

The screen (2) is mounted inside the transmission case. The screen can be removed on the right side of the case.

Power Train Oil Cooler




Illustration 3g00808863

(1) Transmission

(2) Torque converter outlet

(3) Radiator

The transmission system oil flows from the torque converter outlet (2) to the transmission cooler that is located in the bottom of the radiator (3). As oil flows through the cooler, coolant flows around the core assembly. In this way, heat is removed from the oil. The cooled oil is returned to the transmission sump.

Transmission Lubrication System




Illustration 4g00830715

(9) Reverse input shaft

(10) Input shaft

(11) Countershaft

(12) Rear output shaft

(13) Front output shaft

After the oil has been cooled by the oil cooler, the oil will flow through the following internal passages: reverse input shaft (9), input shaft (10), countershaft (11), rear output shaft (12) and front output shaft (13). The cooled oil flows through the oil passages in the input shafts and the oil provides the cooling and lubrication for the bearings, plates, and discs.

Splash lubrication keeps the other gears and bearings oiled. The movement of the gears in the oil reservoir causes oil to be thrown on all components.

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