DRIVE GP-FINAL 3445163 - Caterpillar

Flow Control Under No Load
Illustration 1 g00753234
Regulation of pump flow (no-load condition) (1) Spring (2) Spring (3) Blade pump (4) Piston (5) Piston (6) Piston (7) Piston (8) Piston (9) Swashplate (10) Pin (11) Piston (12) Pilot Line (13) Pilot line (14) Port (15) Port (16) Passage (17) Passage (18) Passage (19) Passage (20) Passage (21) Passage (22) Passage (23) Passage (24) Orifice (25) PistonWhen the joysticks and/or the travel levers/pedals are in the NEUTRAL position or when the joysticks and/or the travel levers/pedals are partially moved from the NEUTRAL position, orifices in the main control valve control the negative flow control pressure. Pilot oil enters ports (14) and (15) through pilot lines (12) and (13). Therefore, the pressure in the pump delivery lines increases.When all of the hydraulic controls are in the NEUTRAL position, the main pump destrokes in the following manner.Pilot pressure acts on both ends of piston (8) through passage (17) and passage (18). Piston (8) shifts by the higher pressure and the low pressure oil flows through orifice (24), passage (23), passage (16), and piston chambers (25). Also, the negative flow control pressure in pilot line (12) and pilot line (13) are equal. Both pressure oils travel through orifices (24), passage (23), and passage (16) and to the chambers of piston (25) .The pressures of the chambers for piston (25) act on the right end of pistons (4) and (5). Piston (4) and piston (5) shift to the left, which pushes piston (6) and piston (7) to the left. Because of the mechanical linkage with pin (10), swashplate (9) is rotated against spring pressure (1) and (2) the swashplate angle decreases. As a result, the main pump destrokes.Horsepower Control Characteristic (Period Before Decreased Pump Stroke)
When any of the hydraulic controls are activated, the pump flow control changes. A change occurs from a destroked position of the pump (no-load condition) to an upstroke position of the pump (load condition) in the following manner.
Pump flow that passes orifice (24) decreases, as negative flow control pressure decreases.
Pressure that acts on the right end of piston (4) and piston (5) decreases. Pistons (4) and (5) are applying no force through pin (10) against swashplate (9). The angle of swashplate (9) begins to increase by the forces of spring (1) and (2) for pump upstroke.The angle of swashplate (9) increases in proportion to the decrease in negative flow control pressure.Main pump delivery pressure is directed to passages (19) and (20). The main pump delivery pressure goes through the inner passage of piston (4) and piston (5). This pressure acts on the surface area of pistons (6) and (7) with the same area as piston (4) and piston (5). The main pump delivery pressure acts on pin (10) and attempts to decrease the angle of swashplate (9) against the force of springs (1) and (2). Rotating direction of swashplate (9) is determined by the relationship between the forces of springs (1) and (2) and the total main pump delivery pressures.