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Add: JinYi Industrial Park, NO.6 Lianyun Road, Luogang District, Guangzhou, Guangdong, China

Knowledge

Common Komatsu excavator maintenance knowledge Daquan

1. What is an OLSS system?

     The OLSS system is an open center load sensing system for the Komatsu excavator. It is an energy-saving system that reduces the fuel consumption by controlling the inclination of the swash plate type variable displacement piston pump. During operation, the hydraulic loss can be reduced due to the function of the system, so as to increase the fine adjustment control and properly control the output of the oil pump.

2.What is the impact of Pt pressure too high and too low on the variable system?

     Common faults have abnormal Pt pressure of the sensor, sometimes the pressure will reach 5Mpa or even higher, because the pressure relief valve has foreign matter stuck. Once the Pt pressure is too high, the flow rate of the plunger pump will become very small, and the excavator will have no work. If the Pt pressure is too low, the plunger pump flow will become very large. If the pressure drops to zero, the engine will stall when the excavator starts.

3.What is the construction and working principle of the TVC valve?

    The TVC valve is controlled by the balance spring force after the discharge pressures Pp1 and Pp2 of the main pump and the output pressure Pc2 of the TVC valve.

When the main pump load is small (when the transfer switch is turned on in the L state), the discharge pressures Pp1 and Pp2 of the main pump are low. Therefore, the spool 2 is pushed by the spring 1 to the lower end. As a result, the discharge pressure Pc of the control pump becomes the same as the output pressure Pt2 of the TVC valve. At this time, the TVC valve output pressure Pt2 becomes maximum, and the servo valve increases the inclination angle of the plunger pump and the flow rate is also maximum.

When the main pump load is large (when the transfer switch is turned on in the S state), since the main pump discharge pressures Pp1 and Pp2 increase, the piston is pushed outside, and the spool 2 moves upward due to the slit a and b holes on the spool. The oil is throttled, and the opening of the b hole and the c hole (discharge hole) becomes large. Therefore, at this time, the TVC valve output pressure Pt2 is lowered, and the servo valve makes the inclination angle of the plunger pump small, and the flow rate also becomes small.

When the changeover switch is turned on in the L state, the solenoid valve 7 is powered on, and the shaft 6 pushes the piston 5 upward to achieve the effect of increasing the spring 1.

When the solenoid valve line on the TVC valve fails, the machine will lose the fine-tuning function during operation, and there is no automatic function. When the solenoid valve line fails, the work of the excavator will be affected. 7. How does the electronically controlled OLSS automatic deceleration system work?

When the operating mechanism joystick is in the middle position, it can automatically reduce the engine speed. When the operating mechanism starts to work, that is, when the joystick is pulled to the working position, the engine speed of the throttle valve handle can be automatically accelerated to the working position of the crude oil door. Speed.

Turn the automatic deceleration switch to ON. When the operating mechanism and the connecting mechanism linkage are not in the middle position, the microcomputer from the control box sends a signal to start the solenoid valve, and the hydraulic cylinder is extended. The engine speed is reduced to 4 seconds. 1150r/min, the throttle handle position remains unchanged. If the working mechanism starts to work, the solenoid valve is immediately closed, the hydraulic rod and the governor lever are automatically reset to the original handle position, and the rotation speed is automatically restored to the original speed.

4.What is the difference between the TCC valve of the Komatsu PC200, PC300, PC400, PC600 excavator and the TVC valve?


     The function of the TVC valve is just more electronic control. If the electronic control part is broken, it is the same as the TCC valve. The TCC valve uses two 2-position 3-way valves to regulate the Pc oil pressure. They all function the same. Structurally speaking, the TCC valve is more complicated and has many faults. Because there are a lot of parts, be careful when disassembling. Many users don't know if they don't have a part drawing, they don't have one piece installed, or they are in the wrong direction.

5.What is the role of the CO valve and what is its structure and working principle?

     The CO valve is a sub-power regulator. When the oil discharge pressure of the main oil pump is less than the pressure regulator overload pressure, the spool valve 2 is pushed by the spring 1 to the bottom, so that the a hole and the b hole are connected to each other, so that T. V. The C valve output pressure Pt is equal to the CO valve output pressure Pc0. At this time, the output pressure Pc0 of the CO valve becomes maximum, and the servo valve maximizes the inclination angle of the main oil pump. Therefore, the pump flow is also the largest. When the main oil pump discharge pressure is close to the pressure regulator overload pressure, Pp2 pushes the piston 3, and the pressure of Pc0 pushes the piston 4. The thrust of both exceeds the spring force of the spring 1, and the spool 2 moves upward. Due to the slit action on the spool valve, the oil passage of the a hole to the b hole is narrowed, and the discharge hole of the b hole to the c hole is widened. Therefore, the output pressure of the CO valve is lowered, and the servo valve makes the inclination angle of the plunger pump small. The pump flow is also reduced. The CO valve is a sub-power regulating valve, which means that it can only regulate the flow of one of its own plunger pumps.

6.What is the relationship between the jet sensor and the NC valve?

    The NC valve operates on signals sent by the jet sensor. The working principle is that the pressure of the jet sensor reaches a maximum value (1.6 MPa) when the control valve is in the middle position. Thus, the output pressure Pt of the jet sensor is greater than the sum of the force of the spring and the other output pressure Pd of the jet sensor, so that the spool is pushed downward. At this time, the passage between the c hole and the b hole is narrowed, and the passage (discharge hole) between the b hole and the d hole is widened, so that the output pressure Pi of the NC valve becomes minimum. The servo valve makes the tilt angle of the plunger pump small. The pump flow is also reduced. When the lever is pulled, the pressure difference (Pt-Pd) of the jet sensor is reduced to a minimum value. Can achieve a pressure difference equal to zero. The spool is then reset upwards. The passage between the c-hole and the b-hole is widened, the output pressure of the NC valve is increased, the servo valve causes the inclination angle of the plunger pump to become large, and the pump flow rate is increased.

The Komatsu PC200-2, PC300-2 and PC400-2 excavator NC valves have different configurations, but the working principle is the same.

Because the structure of the NC valve is relatively simple, there are not many faults, and many small faults are artificial. For example, the assembly is not assembled, the cleaning is not cleaned, and even some oil pipes are connected incorrectly. Therefore, it is necessary to understand the two oil pipe joints of the NC valve, one is the Pt port and the other is the Pd port. Once the connection is reversed, the load of the excavator will be very heavy, and black smoke will be emitted when the boom is lifted.