TM-9-2520-234-35 Technical Manual for M109 Transmission XTG-411-2A Download

PAR 28-30 OPERATION OF HYDRAULIC SYSTEMS CHAP 2, SEC IV Section IV. OPERATION OF HYDRAULIC SYSTEM 28. PRELIMINARY INSTRUCTIONS a. Hydraulic Schematics — (figs. 6 through 19, and fig. 372- fold-out 1) (1) The hydraulic system, because of its importance to the operation of the power train, should be carefully studied and under- stood. There are 14 partial hydraulic sche- matics in color (figs. 6 through 19) and a fold- out hydraulic schematic (fig. 372). The color- ed schematics show positions of valves and moving components, and the various hydraulic circuits as indicated by the captions. The fold-out schematic, in black and white, shows the entire hydraulic system. (2) Hydraulic schematic views (figs. 6 through 18) parallel the torque path schematic views (figs. 22 through 34) in Section III of this chapter. The hydraulic schematic views illustrate what happens hydraulically, while the torque path schematic views illustrate what happens mechanically. b. Explanations of Hydraulic System (1) In the schematic views, a particu- lar color or color variation in figs. 6 through 18, is continued in the system until it passes through a regulator or an orifice which changes the pressure of the oil. (2) To avoid needless repetition, refer- ences are made to initial explanations. To link the hydraulic action with the correspond- ing mechanical action, references are made to the paragraphs explaining the mechanical actions. 29. GENERAL INFORMATION a. Torque Converter and Lockup Drive. Regardless of gear or steer condition, drive from the vehicle engine to the range gearing is either hydraulic (torque converter) or me- chanical (lockup clutch engaged). b. Transmission Oil Levels (1) The hydraulic system is designed so that after the vehicle engine has been operat- ing a short time, two distinct oil levels are established in the transmission. The oil level in the transmission rear housing is compara- tively low (fig. 19). The other is in the trans- mission sump, which surrounds (but is sepa- rated from) the range gear section in the main transmission housing. The two levels guaran- tee a sufficient oil reserve, while maintaining the most efficient oil level in the operating sections of the transmission. (2) Two oil levels exist because air pumped by the scavenge pump is discharged into the transmission rear housing. This creates a constant air pressure on the oil in this housing. The air pressure forces the oil level down, pushing the oil into the reservoir, until air can escape into the reservoir. The upper areas of the input transfer housing and the main transmission housing are connected. A breather, located near the top of the input transfer housing, allows atmospheric pressure to be present in these housings. 30. HYDRAULIC SYSTEM FUNCTION – NEUTRAL RANGE (fig. 6) Note. Refer to par. 46 and fig. 22 for the torque path through the power train. a. In neutral range, main pressure is supplied only by the input pressure pump (pump not shown in fig. 6; see fig. 372, fold-out 1). This oil is directed to four points at all times. These points are: the main-pressure regulator valve, the lockup cutoff valve, the throttle and throttle regulator valves, and the steer pres- sure regulator valve. This part of the hydrau- lic circuit always is charged when the power train is operating. b. At the main-pressure regulator valve, oil enters the valve bore at two points. The upper connection directs the oil between two of the valve lands. It surrounds the valve stem and flows into holes drilled in the stem, which carry the oil through a spring-loaded ball check valve to the cavity above the large 25