| |
| Illustration 1 | g03412070 |
|
Hydraulic schematic (negative flow control) (1) Center bypass passage (2) Center bypass passage (3) Orifice (4) Passage (5) Relief valve (negative flow control) (6) Passage (7) Orifice (8) Relief valve (negative flow control) (9) Return passage (10) Idler pump pressure sensor (11) Drive pump pressure sensor (12) Power shift solenoid valve (13) Idler pump (14) Drive pump (15) Return line (16) Negative flow control line (17) Negative flow control line (18) Pressure sensor for the drive pump (negative flow control) (19) Pressure sensor for the idler pump (negative flow control) | |
| |
| Illustration 2 | g03310099 |
|
Negative flow control system (16) Negative flow control line (17) Negative flow control line | |
When cylinders or motors are not in operation, negative flow control pressure flows from center bypass passage (1) and center bypass passage (2). When fine control of the pilot control valves is needed, negative flow control oil flows from center bypass passage (1) and center bypass passage (2).
| |
| Illustration 3 | g02537076 |
|
Relief valve (negative flow control) (3) Orifice (4) Passage (5) Relief valve (negative flow control) (8) Relief valve (negative flow control) (9) Return passage (23) Plug (24) Spring (25) Valve | |
Oil flow from drive pump (14) flows to center bypass passage (2). The oil then flows through passage (4) and orifice (3) to return passage (9). Orifice (3) restricts the oil flow. The pressure in passage (4) increases. A negative flow control pressure now flows through negative flow control line (16) to the pump regulator. The negative flow control of the regulator causes the pump to destroke.
Relief valve (5) consists of plug (23), valve (25) and spring (24).
When the oil flow in a center bypass passage suddenly changes, there will be a sudden rise in the negative flow control pressure. Relief valve (5) allows part of the oil to flow by valve (25) and through return passage (9).
When all controls are in NEUTRAL position, all of the drive pump oil flows through center bypass passage (2). The oil then flows through orifice (3) and return passage (9). The oil then flows back to the hydraulic tank.
Maximum negative flow control pressure in passage (4) now flows to the drive pump. The pump cylinder rotates to the minimum angle. At the minimum angle, the drive pump destrokes. The minimum amount of oil flow is provided.
| |
| Illustration 4 | g03027696 |
|
Stick control valve (1) Center bypass passage (26) Parallel feeder passage (27) Port (28) Spool (29) Passage | |
When partial implement operation is started, pilot pressure shifts spool (28) slightly downward. Pilot pressure partially opens passage (29). Pilot pressure partially closes center bypass passage (1). Part of the idler pump oil from center bypass passage (1) flows to orifice (7). The remainder of the oil flows through parallel feeder passages (26) and passage (29) to port (27). The oil flow in center bypass passage (1) now decreases. The resistance to oil flow through orifice (7) decreases and the negative flow control pressure in passage (29) decreases. The swashplate rotates to a larger angle. The larger angle causes the idler pump to upstroke. The oil flow increases.
When the implement is moved to full operation, spool (28) moves to the down. Center bypass passage (1) closes. There is no oil flow through passage (29). When there is no oil flow through passage (29), there is no negative flow control pressure. The output of the idler pump is held maximum. Oil flow of the idler pump is controlled by the constant horsepower flow control.
Modulation of the exact pump output is done by inching the control levers. This action allows fine operation of implements for precision work.
Negative flow control operates in the same manner for drive pump (14).