BIT 5268012 - Caterpillar

Hydraulic Pump
Illustration 1 g00893228
The hydraulic pump for the asphalt emulsion spray system is a variable displacement piston pump. The pump output is electrically controlled through the electrical displacement control (EDC). The EDC maintains the position of the swashplate in proportion to the electrical input.When the engine is running, the following components are rotating: shaft (1), barrel assembly (4) and charge pump (10). There are nine pistons (6) in barrel assembly (4). Spring (7) keeps a force on barrel assembly (4) in order to make a high pressure seal between barrel assembly (4) and valve plate (8). When barrel assembly (4) is rotating, each piston (6) follows the angle of swashplate (2). If the angle of swashplate (2) is at zero, the pistons do not move in and out of barrel assembly (4) and there is no oil flow.Charge oil from charge pump (10) performs the following functions: maintaining the oil pressure in the hydraulic pump, lubricating the components of the pump and recovering the internal loss of oil due to leakage. The position of swashplate (2) is controlled by the EDC and by servo piston (3). When the EDC receives an electrical signal from the flow control box, the electrical signal causes a servo valve inside the EDC to move. The servo valve routes the charge oil in order to activate servo piston (3). The charge oil also adjusts servo piston (3). Servo piston (3) controls the direction of the angle of swashplate (2) and the grade of the angle of swashplate (2) .Oil flows from the pump to the asphalt emulsion hydraulic motor and back to the pump through main circuit ports (9). The position of swashplate (2) determines the direction of the flow and the rate of the flow.EDC
Illustration 2 g00893231
(3) Servo Piston (11) Electrical Displacement Control (12) Sensing Piston (13) Spring (14) EDC (Neutral Adjustment) (15) Servo Control (16) Feedback Linkage (17) Manual Override (EDC) (18) Pressure Control Pilot Valve (PCP Valve) (19) Displacement Control Spool (20) Control Oil PassagesElectrical displacement control (EDC) (11) is mounted on the hydraulic pump.The pump control consists of the following three sections: EDC (11), displacement control spool (19) and servo control piston (15). EDC (11) is a two-stage electrohydraulic control. EDC (11) uses feedback linkage (16) and control oil (20) from the charge pump in order to set up a closed control circuit for the swashplate. EDC (11) receives an electrical input from the flow analyzer at pressure control pilot valve (18) .EDC (14) uses an electrohydraulic pressure control pilot in order to control the pilot pressure (differential). PCP valve (18) converts an electrical input signal to a hydraulic input signal in order to operate sensing piston (12) that is spring centered. Sensing piston (12) is mechanically connected with displacement control spool (20) through feedback linkage (16). As sensing piston (12) moves, displacement control spool (19) is moved. This movement creates a path that allows control oil (20) to move servo control piston (15). Servo control piston (15) tilts the