HOUSING-FRONT 1541672 - Caterpillar

Upstroke
Illustration 4 g06031886
Upstroke condition
(1) Load sensing spool
(2) Horsepower control spool
(3) Hydraulic modulation solenoid
(4) Main control valve
(5) Unloading valve
(6) Signal limiting valve
(7) Main relief valve
(8) Signal drain valve
(9) Main pump group
(10) Maximum angle piston
(11) Power shift piston
(12) Lever
(13) Actuator piston
(14) Minimum angle piston
(15) Port - inletThe following are some of the conditions that cause the pump to upstroke:
An increase in the flow demand when the pump flow is being controlled only by load sensing spool (1) and is not on the horsepower curve.
An increase in power shift pressure when the pump flow is being controlled by the horsepower control.
A decrease in the system pressure when the pump flow is being controlled by the horsepower control.Illustration 4 shows the pump in the UPSTROKE position when flow increases due to a change in the position of load sensing spool (1).The pump is upstroked because of an imbalance in forces working on load sensing spool (1). This imbalance causes load sensing spool (1) to shift to the left. Minimum angle piston (14) is open to the tank through load sensing spool (1) and horsepower control spool (2).Supply pressure and the maximum angle piston spring move the swashplate toward the maximum angle to increase pump flow.When a hydraulic circuit is activated from the low-pressure standby condition, additional circuits are operated, or a single circuit is shifted requiring more flow, the force or forces working on the left end of load sensing spool (1) and the force working on the right end of load sensing spool (1) are no longer balanced.On the right end of load sensing spool (1), the margin spring and the load sensing signal pressure from main control valve group (4) work against the pump supply pressure on the left end of load sensing spool (1). When more flow is required, the forces on the right end of load sensing spool (1) are greater than on the left end causing load sensing spool (1) moves to the left.This action opens the minimum angle piston chamber to the tank around load sensing spool (1) and horsepower control spool (2). Pump supply pressure and spring force on maximum angle piston (10) move the swashplate toward maximum angle and pump flow increases. When the pump upstrokes due to an increase in flow requirements, unloading valve (5) will close.As the pump upstrokes, actuator piston (13) rides along the top of lever (12) and moves farther away from the pivot pin and the mechanical advantage increases. As long as the increased force is not able to overcome the power shift pressure, the change in flow demand will have no impact on the horsepower control.Constant Flow
Illustration 5 g06032003
Constant flow condition
(1) Load sensing spool
(2) Horsepower control spool
(3) Hydraulic modulation solenoid
(4) Main control valve
(5) Unloading valve
(6) Signal limiting valve
(7) Main relief valve
(8) Signal drain valve
(9) Main pump group
(10) Maximum angle piston
(11) Power shift piston
(12) Lever
(13) Actuator piston
(14) Minimum angle piston
(15) Port - inletAs the pump flow increases to meet the flow demand, the pump supply pressure will increase. When the pump