BOLT 5342163 - Caterpillar

Introduction
Proportional reducing valves for negative flow control are used to control the amount of negative flow control (NFC) signal to the pump regulators. The machine ECU receives various input signals to control the flow limitation from the main hydraulic pumps. When the NFC valves are de-energized by the machine ECU, pilot oil pressure is directed to the main hydraulic pump regulators from pilot solenoid manifold (1). The NFC pilot oil pressure controls the swashplate angle which therefore controls the pump output flow.
Illustration 1 g03586157
Proportional reducing valve (negative flow control)
(1) Pilot solenoid manifold
(2) Negative flow control PRV (front pump)
(3) Negative flow control PRV (rear pump)
Illustration 2 g06303629
Negative flow control operation (control valves in the NEUTRAL position)
(1) Pilot solenoid manifold
(2) Negative flow control PRV (front pump)
(3) Negative flow control PRV (rear pump)
(4) Pilot pump
(5) Front pump
(6) Rear pump
(7) Swashplate angle sensor (front pump)
(8) Swashplate angle sensor (rear pump)
(9) Left travel pilot pressure sensor
(10) Right travel pilot pressure sensorDemanded pump flow is determined by the joysticks and/or travel levers/pedals. The joysticks send an X and Y position signal to the machine ECU with the requested flow from the operator. The travel levers/pedals requested flow is determined by travel pilot pressure sensors (9) and (10). The machine ECU receives the requested flow input from the joysticks or travel levers/pedals. The machine ECU then sends a PWM driver to negative flow control PRV (2) and negative flow control PRV (3). Pilot oil is supplied to the pump control manifold block from the pilot pump. The pilot oil flows through the NFC PRV's and to the pump regulators.The pump swashplate moves to meet the flow demand. Front pump (5) and rear pump (6) are each equipped with a swashplate angle sensor. The swashplate angle sensor sends a feedback control signal to the machine ECU. The NFC PWM driver from the machine ECU adjusts the current command to the NFC PRVs if the actual flow does not meet the requested flow.Note: A decrease in current causes an increase in NFC hydraulic pressure which is then sent to the pump regulators. This increase in NFC pressure to the pump regulators causes the main hydraulic pumps to destroke, decreasing the flow.Note: An increase in current to the negative flow control PRV causes a decrease in NFC hydraulic pressure to the pump regulators. This decrease of NFC pressure to the pump regulators causes the main hydraulic pumps to upstroke, increasing the flow.