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The reason for the excavator maintenance EFI diesel engine is unstable at low idle speed

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One. Excavator maintenance is the use of a bucket to dig materials above or below the bearing surface and load them into a transport vehicle or earthmoving machinery to a dump. The three most important parameters for maintenance excavator excavator: operating weight (mass), engine power and bucket capacity. Excavator maintenance fuel supply system r944c excavator works with a fuel supply system (referred to as PLD fuel supply system) consisting of a single pump, high pressure pipe and injector. The camshaft of the diesel engine drives the intake and exhaust valves to move, and at the same time drives the single pump lifter action. When the cam rotates, the lifter of the unit pump lifts up, and the lifter pushes the plunger of the unit pump up. The ECU controls the energization and de-energization of the solenoid coil of the oil return shut-off valve on the upper part of the unit pump according to the electrical signal sent by the diesel engine speed sensor, thereby controlling the opening and closing of the oil return shut-off valve. When the fuel pressure reaches the injection pressure, the fuel will be injected into the combustion chamber through the injector, thereby realizing the work of the diesel engine. The fuel supply system of the excavator diesel engine is shown in Figure 1. The oil return shut-off valve is installed on the upper part of the single pump, and the solenoid valve power-on time determines the fuel supply of the single pump. When the solenoid valve is cut off, the oil return channel of the unit pump is opened, and even if the plunger in the unit pump has started to pump oil, high pressure cannot be established. Only when the solenoid valve is energized and the oil return passage is closed can the oil pressure rise rapidly, and high-pressure fuel enters the injector through the high-pressure fuel pipe to inject fuel. When the electromagnetic coil is disconnected, the oil return channel is opened, the unit pump quickly overflows and decompresses, and the oil supply stops. Single pump working cycle as shown

2. The work of four single-pump strokes is as follows. When the plunger of the driving cam rotates downward, the fuel pump that returns to the oil through the oil enters the piston chamber and closes the valve: the intake stroke. Depression: After the cam moves the plunger, the column plugs the fuel plenum. At this time, the oil return valve is not closed, and the state of the fuel pressure of the plunger chamber is maintained. Output stroke: The piston drives the cam to continue upward. When the solenoid is energized, the fuel pressure in the piston chamber is closed when the oil return valve is closed. When the fuel reaches injection pressure, the injector is injected. Embossed stroke: The cam continues to rotate, driving the plunger, and the solenoid is de-energized. At this time, when the fuel injection ends, when the oil return shut-off valve opens, the piston chamber drains.

2. Excavator repair troubleshooting First, check the air filter without blocking the diesel engine. The turbocharger is operating normally and cold. Secondly, using special software to check the SCULI diesel, it was found that the diesel engine changed during the low idle fuel supply, thereby determining the existence of a fault in the diesel engine fuel supply system. When inspecting the engine speed sensor, problems with the engine controller (ECU), fuel filter, fuel pump, fuel injector and supply pipe were not discovered afterwards. However, after replacing the unit pump, the diesel engine remained stable at low idle speeds, and the "hum, hum" noise disappeared. In order to determine whether the fault is due to wear of a single pump.

three. The analysis of the reasons for the maintenance of the excavator shows that the low idling speed of the diesel engine is unstable due to the unstable fuel supply (injection). However, the root cause of the oil supply instability is the failure of the single pump, which may occur in two places: one is the leakage from the plunger cavity, and the other is the leakage from the closed oil return valve controlled by the solenoid. The single pump is installed on the cylinder block of the diesel engine, and the lower side of the plunger cavity is above the cam.

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