Analysis of the cause of failure
The reason is that the fuel supply (fuel injection) is unstable. The source of the oil supply instability is the failure of the single pump, and there may be 2 parts of the fault. One is the fuel leakage in the plunger cavity, and the two is the leakage of the oil recovery valve controlled by the electromagnetic coil.
A single pump is mounted on the engine cylinder and the lower side of the plunger cavity is located above the cam. If the plunger is seriously worn, it will lead to the entry of diesel oil into the cylinder oil. Because the engine oil is not deteriorated and the oil level rises, the leakage failure of the piston chamber can be determined.
The return oil sealing valve of the single pump is controlled by the electromagnetic coil. When the engine runs, the oil recovery valve needs to be closed and open at high speed. The high speed and closed reciprocating movement of the return oil closed valve will produce frequent friction. If the diesel oil is not good, the oil sealing valve will be worn out. After the oil recovery valve is badly worn, the fuel oil will be leaked. 4 single pumps are removed by dismantling. The oil return closing valve has found that the inlet and outlet ports have been seriously worn out and can not play a sealing role. The leakage location of the oil return valve of the monomer pump is shown in Figure 3.
The internal leakage of the return oil closed valve of the single pump causes the engine to supply less fuel at low idle speed, that is, the speed is unstable. And the engine is stable at high idle speed or working speed, because the fuel supply is increased correspondingly when the engine speeds up, and the internal leakage of the return oil closed valve of the single pump is started. The effect of the operation of the machine is reduced.
Liebherr R944C EFI engine low idle speed unstable troubleshooting
First, check the air filter of the engine without blockage. The turbocharger runs normally and the intercooler is normal.
Secondly, using the Liebherr SCULI software to check the engine oil supply, it is found that the fuel supply is constantly changing during the engine's low idle speed, which determines that the engine oil supply system has trouble.
Finally, the engine speed sensor, the engine controller (ECU), the diesel filter, the oil pump, the injector and the oil supply pipeline were not found. But after the new single pump was replaced, the engine was stable at low idle speed, and the buzz and buzz disappeared. Thus it was determined that the fault was caused by the wear of the single pump.
The working principle of the oil supply system of the R944C electric jet engine
The Liebherr R944C excavator is equipped with an oil supply system consisting of a single pump, a high-pressure pipe and an injector. The engine camshaft drives the intake and exhaust valves to drive the single pump tappet movement. When the cam turns, the top moving single pump tappet moves up and moves on the cylinder plug of the single pump. Controller (ECU). According to the electrical signal conveyed by the engine speed sensor, the electromagnetism coil of the upper oil return valve in the upper part of the pump is controlled and the electricity is broken, then the sealing and closing of the oil return valve is controlled and the oil recovery is closed.
The fuel pressure is pressurized in the closed period of the valve. When the fuel pressure reaches the injection pressure, the fuel is injected into the combustion chamber by the injector to realize the engine operation. The engine oil supply system of this type of excavator is shown in Figure 1.
The return oil sealing valve is installed on the upper part of the single pump, and the duration of the electromagnetism coil determines the fuel supply of the single pump. When the electromagnetic coil is broken, the single pump return oil channel opens and the plunger in the single pump can not set up high pressure even if the pump oil has been started. The oil passes through the high-pressure oil pipe into the injector and injecting oil. When the electromagnetic coil is broken, the return oil channel is opened, the single pump is rapidly overflowing and the oil supply is stopped. The working cycle of the single pump is shown in Figure 2, and the four working strokes of the single pump are described as follows.
Suction stroke: when the cam rotates, the plunger is driven down, so that the oil pump comes to the oil through the oil closed valve and enters the plunger cavity.
Preloading stroke: the cam drives the plunger upward and pressurize the fuel in the plunger chamber. At this time, the oil return closing valve is not closed, and the fuel in the plunger chamber keeps low pressure.
Output stroke: the cam continues to drive the plunger upward, when the electromagnetic coil is electrified, the oil recovery valve closes and the fuel pressure of the plunger chamber increases. When the fuel reaches the injection pressure, the fuel injector is injected.
Pressure relief stroke: the cam continues to rotate to drive the plunger upward. At this point, the electromagnetic coil has been cut off, the fuel injection is finished, the oil return closing valve is opened, and the plunger cavity is discharging oil.
