SMCS Code:5050-NE; 5455
Introduction
The idler pump and the drive pump receive signal oil pressure from the center bypass passages of the main control valve. This signal oil pressure that is created in the center bypass passages of the main control valve is called negative flow control pressure. Negative flow control pressure flows to the regulators at the idler pump and the drive pump in order to control the output flow of the pumps. Negative flow control pressure is created during the following machine operating conditions.
•
All of the joysticks and travel levers/pedals are in the NEUTRAL position.•
Any of the joysticks and/or travel levers/pedals are partially moved from the NEUTRAL position in order to perform a fine control operation.•
A boom lower operation is performed alone.g00819938
Illustration 58
Main control valve (top view)
(12) Negative flow control line to drive pump (13) Negative flow control line to idler pump
The right body of the control valve receives supply oil from the idler pump. Negative flow control pressure from the right body of the main control valve flows through negative flow control line (13) to the idler pump. The left body of the control valve receives supply oil from the drive pump. Negative flow control pressure from the left body of the main control valve flows through negative flow control line (12) to the drive pump. The negative flow control operation of the idler pump and the drive pump is identical.
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Negative flow control operation (control valves in the NEUTRAL position)
(1) Center bypass passage (2) Return line
(3) Center bypass passage (4) Passage
(5) Relief valve (negative flow control) (6) Relief valve (negative flow control) (7) Negative flow control orifice (8) Port
(9) Negative flow control orifice (10) Passage
(11) Return passage (12) Negative flow control line (13) Negative flow control line (14) Drive pump
(15) Idler pump (16) Pilot pump
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Illustration 60
Bucket control valve (NEUTRAL position) (3) Center bypass passage
Illustration 59 shows the negative flow control operation at the main control valve when all of the control valves are in the NEUTRAL position. When all of the joysticks and the travel levers/pedals are in the NEUTRAL position, the spools of the individual control valves are in the NEUTRAL position. Oil flow to the cylinders and motors is blocked. Center bypass passages (1) and (3) are open.
All of the oil delivery from idler pump (15) flows through center bypass passage (3), passage (4) and negative flow control orifice (9) to return line (2). Negative flow control orifice (9) restricts the oil flow. The pressure in passage (4) increases. Increased negative flow control pressure now flows through passage (10) and negative flow control line (13) to the pump regulator. The negative flow control operation of the idler pump regulator causes the swashplate of the idler pump to move to the minimum angle position. The output flow of the idler pump is decreased due to the increased negative flow control pressure that is created in center bypass passage (3).
Since center bypass passage (1) is also open, the negative flow control operation of the drive pump regulator is identical to the negative flow control operation of the idler pump regulator.
Reference:For more information concerning the negative flow control operation of the main pump regulators, refer to Systems Operation, “Pump Control (Main Hydraulic)”.
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Negative flow control operation (bucket control valve in the BUCKET CLOSE position)
(1) Center bypass passage (2) Return line
(3) Center bypass passage (4) Passage
(5) relief valve (negative flow control) (6) relief valve (negative flow control) (7) Negative flow control orifice (8) Port
(9) Negative flow control orifice (10) Passage
(11) Return passage (12) Negative flow control line (13) Negative flow control line (14) Drive pump
(15) Idler pump (16) Pilot pump
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Illustration 62
Bucket control valve (BUCKET CLOSE position) (3) Center bypass passage
Illustration 61 shows the negative flow control operation at the main control valve when only the bucket control valve is in the BUCKET CLOSE position.
All of the control valves in the left body of the main control valve are in the NEUTRAL position. Center bypass passage (1) is open. All of the oil delivery from the drive pump flows through center bypass passage (1) to negative flow control orifice (7). Since all of the oil delivery from drive pump (14) is restricted by negative flow control orifice (7), negative flow control pressure (PN) in center bypass passage (1) is at maximum pressure. The negative flow control pressure flows through negative flow control line (12) to the drive pump regulator. The negative flow control operation of the drive pump regulator causes the swashplate of the drive pump to move to the minimum angle position. The output flow of the drive pump is decreased due to the increased negative flow control pressure that is created in center bypass passage (1).
The joystick for the bucket has been moved fully to the BUCKET CLOSE position. Pilot oil has fully shifted the bucket control valve. The oil delivery from idler pump (15) flows into the right body of the main control valve. The oil delivery flows through center bypass passage (3) to the bucket control valve. Since the spool in the bucket control valve is fully shifted, center bypass passage (3) is blocked. All of the oil delivery from the idler pump flows to the head end of the bucket cylinder. No oil flows to negative flow control orifice (9) and no negative flow control pressure is created in center bypass passage (3). Since no negative flow control pressure is sent to the idler pump regulator, the idler pump regulator moves the swashplate of the idler pump toward the maximum angle position. The output flow of the idler pump is increased since no negative flow control pressure is created in center bypass passage (3).