HYDRAULIC SYSTEM

TM 9--2520--215--34 0005 00--2 THEORY OF OPERATION -- CONTINUED 0005 00 HYDRAULIC SYSTEM – Continued Action Of Hydraulic System in Neutral Converter Drive, No Steer NOTE Refer to Torque path in neutral -- converter drive, no steer schematic view for the torque path through the transmission. Normal oil flow lubricating the pump drive gear train accumulates in the lower cavities of the torque converter housing when the engine is running and the input scavenge pump and oil pressure are in operation. The two--section scavenge pump picks up the oil (along with air) and pumps it to the output reduction gear where it lubricates the brakes and gearing. The same oil and air then return to the transmission at the output gear compartment. Oil from the sump lubricates the brakes coolant pump, output--driven pressure pump, and the input--driven pressure pump. Only the input--driven pressure pump and scavenge pump are rotating while the vehicle is not mov- ing, so only the input--pressure pump is supplying pressure. Oil pumped by the input--driven pump flows through a pair of filters to the main pressure--regulator valve and to the range--selector valve. There is a relief valve parallel to the filters, which opens only if the filters are clogged. The main pressure--regulator valve moves down to a position in which oil pressure into the regulator balances the spring pressure pushing upwards on the valve. A passage connecting the range--selector valve at the top of the main pressure--regulator valve supplies additional main pressure to act upon the valve and push it downward. This result in a lower main pressure in neutral (and intermediate and high ranges). In neutral, main pressure is blocked at the range--selector valve except for the passage to the top of the main pressure--regulator valve mentioned above. Excess oil from the main pressure--regulator valves flow to the steer clutch pressure--regulator valve and to the steer valves. The steer clutch pressure--regulator valve moves to the right and permits oil flow to the torque con- verter and, when pump volume is sufficient, through bypass ports to the lubrication system. In the no--steer position, no oil passes through the steer valves. Oil to the torque converter branches off to the right and actuates the converter pressure--regulator valve. This valve regulates the oil flow to the converter at 80 psi. Any excess oil bypasses the converter and is directed by the converter pressure--regulator valve to the oil cooler. The remainder of the oil flows through the converter and then to the cooler circuit. A relief valve parallels the cooler circuit but opens only if the cooler is clogged or cannot handle the volume of flow directed to it. From the cooler, oil passes through a pair of filters and to the lubrication--regulator valve. A relief valve paral- lels this line but opens only if the filter is clogged. Excess oil beyond that required to maintain lubrication pressure returns to transmission reservoir. In addition to supply lubricating oil to the steer clutch lubrication valve and other points in the transmission, the lubrication circuit supplies the governor with oil. The pilot--type (or fluid velocity--type) governor produces a pressure which is proportional to the speed of a rotating, oil--filled ring. This pressure actuates the shift inhibitor and lockup-- relay valve. However, in neutral operation, these components have no function.