HOSE AS 4221998 - Caterpillar

Constant Horsepower Control
Illustration 4 g00860180
Main pump regulator in the STANDBY position (1) Pilot pump (2) Horsepower control (3) Load sensing control (4) Power shift pressure (5) Control valve (6) Main pump (7) Charge pump (8) Stop (minimum angle) (9) Servo piston (maximum angle) (10) Swashplate (11) Servo piston (minimum angle) (12) Stop (maximum angle)STANDBY Position
The pump controls work together in order to regulate the pump flow according to fluid demand and hydraulic horsepower requirements. Pump system pressure is always pushing on the maximum side of the servo piston in order to move the swashplate to the maximum angle. This action causes the pump to upstroke. Pilot pressure is always pushing on the minimum side of the servo piston in order to move the swashplate to the minimum angle. This action causes the pump to destroke. When the control valves are in the NEUTRAL position, no signal pressure is directed to the left side of the load sensing regulator. When there is no signal pressure on the left side of the load sensing regulator, standby pressure moves the load sensing spool to the left.When the implement controls and the travel controls are in the NEUTRAL position, the machine electronic control module energizes the solenoid valve for the neutral flow control valve. When the neutral flow control valve is energized, the neutral flow control valve is open and most of the pump oil flows through the neutral flow control valve to the hydraulic tank. The machine electronic control module also sets the power shift pressure to a level that is dependent on engine speed. The increased power shift pressure moves the horsepower control spool to the right until the center land on the horsepower control spool moves past the passage to the minimum angle piston. Delivery pressure from the main pumps is directed around the load sensing spool and around the horsepower control spool to the minimum side of the servo piston. The servo piston then moves the swashplate toward the minimum angle.Note: Throughout the description of the operation of the pump control, assume that the power shift pressure remains at a constant value. The pumps can upstroke or the pumps can destroke when the power shift pressure changes.UPSTROKE Position
Illustration 5 g00860201
Main pump regulator at the start of the UPSTROKE position (1) Pilot pump (2) Regulator adjustment screw (3) Load sensing regulator adjustment (4) Load signal pressure (5) Power shift pressure (6) Control valve (7) Main pump (8) Charge pump (9) Stop (minimum angle) (10) Servo piston (maximum side) (11) Swashplate (12) Servo piston (minimum side) (13) Stop (maximum angle)The following three conditions can cause an increase in flow from the main pumps:
An increase in the load signal pressure
An increase in power shift pressure
A decrease in pump outputIllustration 5 illustrates an increase in pump flow due to an increase in the load signal pressure. When the load signal pressure increases and when the implement pumps upstroke, the increase in pump flow results in an increase in system pressure. When one or more