SWITCH AS-PRESSURE 4592599 - Caterpillar

Illustration 3 g01229295
Note: The colors on the cross sections and on hydraulic schematics throughout this presentation signify various conditions within the system. The legend is as follows:
Red (pump supply pressure, or pressure in the high pressure side of the loop)
Red and white stripe (reduced pump supply pressure, or oil in the low pressure side of the propel loop)
Red and white hatch (further reduced pump supply pressure oil)
Orange (charge or pilot pressure)
Orange and white stripe (reduced charge pressure)
Orange and white hatch (further reduced charge pressure)
Green (line is open to tank)
Blue (blocked oil)
Yellow (moving part, or active valve envelope)The pump input shaft turns the rotating group and the charge pump when the engine is running. The rotating group contains a piston assembly and a cylinder barrel. Charge oil flows through internal passages to the charge relief valve. External lines carry charge oil to the charge filter and back to the propel pump. Filtered charge oil re-enters the propel pump. The filtered oil then flows to the multifunction valves and flows to the EDC.EDC
The EDC electric coils are mounted in a permanent magnet frame. The armature is mounted on a pivot and suspended in the magnetic field.Note: A flapper, which is part of the armature, is centered between the nozzles when there is no current supplied to the coils. The electric coils, the magnet, and the armature assembly make up the pressure control pilot valve. This valve is also referred to as a "torque motor".When the machine ECM sends an output signal to the EDC, electric current flows through the coils. Then, the ends of the armature become magnetically biased as either north or south pole. This causes the armature flapper to move toward one of the nozzles, which causes a pressure increase at that nozzle. The increased nozzle pressure attempts to move the flapper back toward the center position. When the armature flapper force equals the nozzle pressure feedback force, the system reaches equilibrium.When the system is in equilibrium, a pressure differential exists at both ends of the metering spool. The pressure differential causes the spool to move, which meters charge oil to the appropriate servo cylinder. The angle of the swashplate in the pump then tilts in the amount proportional to the strength of the EDC input signal.Servo Piston and Swashplate
Metered charge oil from the EDC metering spool acts against one side of the servo piston. The opposite side of the servo piston is vented to the case drain. The pressure of the metered charge oil on the servo piston causes the piston to move. This movement tilts the swashplate, and the movement causes piston displacement in the rotating group. As the swashplate tilts, the rotation of the pump generates oil flow. Pump supply oil then flows through the propel motor. The oil which is flowing through the motor causes the output shaft to rotate.Feedback Linkage
As the swashplate moves, the feedback linkage moves the barrel feedback in the opposite direction of the EDC metering spool's original motion. Once the angle