The hydraulic system of PC200-5, pc300-5 and pc400-5 Komatsu excavators is an open center load sensing system (olss system), which is an energy-saving system to reduce fuel consumption by controlling the swashplate angle (output flow) of swashplate axial variable piston pump. During excavator operation, due to the function of the system, the hydraulic loss can be reduced to enhance the fine-tuning control and control the oil supply of the oil pump. The hydraulic schematic diagram of PC200-5 excavator is shown in Figure 2-2. 1. Characteristics of F-type central load sensing system
(1) Fixed moment control.
Maintain the hydraulic pump drive torque. If the hydraulic pump load (pump pressure) increases, the output flow of the hydraulic pump decreases; If the hydraulic pump load (pump pressure) decreases, the hydraulic pump output flow increases. This function is controlled by the torque control valve (TVC valve).
(2) Truncation control.
The purpose is to reduce the profit flow loss during operation. If the load increases gradually, the output pressure of the hydraulic pump also increases. When the pressure is close to the overflow pressure, the oil discharge of the hydraulic pump decreases. This function is controlled by the block valve (co valve).
(3) Oil volume control.
When the control gear is in the middle position, the output oil drum of the hydraulic pump is the least. During fine control, the hydraulic pump supplies the appropriate required oil according to the stroke of the control lever. This reduces the waste of power in neutral or fine-tuning control, so as to reduce power loss. This function is controlled by the reverse control valve (NC valve) and the jet sensor (in the control valve).
Composition of open central load sensing system
(1) The open center load sensing system is composed of hydraulic pump system, control valve, oil cylinder for working device, excavator walking, simultaneous conversion hydraulic motor and other actuator components. The open center load sensing system is shown in Figure 2-3.
(2) The hydraulic pump system consists of two swashplate axial variable piston pumps (front and rear), pilot pump, torsional control valve, block valve, reverse control valve, servo valve, etc. its structure is shown in Figure 2-4
