1. Fuel supply system structure
The bulldozer is equipped with a Chongqing Cummins NT855 diesel engine, which uses a PT fuel supply system with gear pump low-pressure fuel supply and injector high-pressure injection. The gear pump feeds fuel into the fuel injector. When the diesel engine camshaft (shares a camshaft with the diesel engine intake and exhaust valves) rotates, the injector needle valve is driven by the ejector rod, the adjusting bolt and the rocker arm to inject the fuel Fuel is ejected from the device.
The amount of fuel supplied by the PT fuel supply system in each working cycle depends on the amount of fuel that enters the injector, and the amount of fuel that enters the injector depends on the pressure of the low-pressure fuel path to supply the fuel into the injector, and the amount of fuel that the injector enters. The opening and closing time of the metering hole of the oil port. The first letter P of the PT fuel supply system represents the injection pressure (Pressure), and the second letter T represents the injection time (Time). The PT fuel system uses the coordination of pressure and time to make the fuel injection timing and fuel supply volume. Meet the requirements of various working conditions of diesel engines.
The opening and closing of the fuel inlet metering hole of the fuel injector is controlled by its needle valve. Adjust the stroke of the needle valve of the fuel injector so that the opening and closing time of the metering hole meets the requirements of the maintenance manual to ensure the fuel supply of the diesel fuel supply system.
2. How to adjust the injector stroke
The PT fuel supply system injector stroke adjustment method includes two types: regular and simple, as described below.
(1) Routine adjustment method
The needle valve of the injector of the PT fuel supply system is pushed by the rocker arm. The end of the rocker arm is equipped with a stroke adjustment bolt. The rocker arm and the stroke adjustment bolt are located in the valve chamber of the diesel engine. Usually the injector and the valve clearance are adjusted at the same time, as shown in Figure 2a Shown. The drive belt wheel at the front end of the diesel engine is marked with A, B, and C, and the gear chamber cover is provided with arrows. The fuel injector should be adjusted cylinder by cylinder according to these marks. First turn the crankshaft of the diesel engine clockwise (viewed from the front of the diesel engine). When you see that the mark on the belt wheel is aligned with the arrow on the gear cover, you can adjust the injector and intake and exhaust valves. When the relevant marks are aligned, the injector stroke adjustment and valve adjustment sequence are shown in the attached table. Taking the alignment of point A as an example, the stroke of the injectors of the III and IV cylinders and the clearance of the intake and exhaust valves of the V and II cylinders can be adjusted.
The conventional adjustment method needs to be adjusted according to the injector model and the special dial indicator for Cummins NT855 diesel engine. The adjustment method is as follows: First, place the measuring point of the dial indicator on the rocker arm at the top of the injector. Secondly, turn the adjusting bolt to lower the injector needle valve to the lowest point until the injector rocker arm stroke reaches the specified value (5.79±0.01) mm, that is, the needle valve stroke is (5.79±0.01) mm, and then the stroke Tighten the adjusting bolt and lock nut, and the tightening torque is 40～45 Nam. Again, manually swing the rocker arm up and down 2 to 3 times to check whether the adjusted stroke value is correct. Then, turn the diesel engine to find the position of the injector stroke adjustment of the next cylinder, and adjust the injector stroke of this cylinder according to the above method. Then adjust the working stroke of all the injectors in a cycle. Finally, start the diesel engine, and after running for 20 minutes, move the accelerator lever to observe the operation of the diesel engine. If it runs normally, the adjustment can be ended. If the operation is not normal, readjust it according to the situation.
This adjustment method is more suitable when the dedicated dial indicator is complete or adjustment in the maintenance workshop. If there is no dedicated dial indicator, it cannot be adjusted. The maintenance conditions in the field are poor, and the sludge dirt is easier to fall into the diesel engine gas distribution during the adjustment process. Indoor, adjustment quality cannot be guaranteed.
(2) Simple adjustment method
We have summed up a simple adjustment method as follows in many years of practice. Rotate the diesel engine, align the A, B, and C marks on the drive belt wheel with the arrows on the gear chamber cover, identify and determine the injector stroke adjustment sequence. When it is determined that a certain cylinder can adjust the stroke, use a wrench to loosen the lock nut of the cylinder injector stroke adjustment bolt, and use a flat screwdriver to turn the stroke adjustment bolt down (clockwise) to make the injector rocker arm Press the injector needle valve to move downward.
When the cylinder adjusting bolt is screwed to the end (that is, the needle valve falls into the bottom of the needle valve seat), tighten the adjusting bolt to 20～30Nom. Make a mark on the outer edge of the end face of the adjusting bolt, and use a flat screwdriver to turn the adjusting bolt counterclockwise by 2 1/2 to 2 3/4 turns. Tighten the lock nut with a wrench to complete the adjustment of the injector stroke. After measurement, the injector stroke adjustment bolt is American fine thread (UNF). The pitch of the adjustment bolt is 20 threads per inch, which is converted into a metric system with a pitch of 1.27mm. If the adjustment bolt is rotated by 2 circles, its stroke size It is 3.175mm. The distance between the rocker arm shaft and the stroke adjustment bolt is 40.75mm, the distance between the rocker arm shaft and the injector is 74.25mm, and the stroke of the 2 de-turning adjustment bolt is converted to the injector needle valve stroke of 5.79mm. Use a flat screwdriver to rotate the adjusting bolt counterclockwise by 2 1/2 to 2 3/4 turns to ensure that the stroke of the needle valve reaches the specified value (5.79±0.01) mm.
Tighten the adjusting bolt to the end (the needle valve falls into the needle valve seat), and then tighten the adjusting bolt to 20～30 N·m. This is to squeeze the fuel in the cavity of the injector valve body to make the needle valve secure. Drop into the needle valve seat. The mark on the outer edge of the end face of the adjusting bolt is for reference when rotating the adjusting bolt in the reverse direction to prevent over-tightening or under-tightening of the stroke. It can be seen that this adjustment method can meet the needs of injector stroke adjustment, and the amount of adjustment meets the requirements of the maintenance manual.
The simple adjustment method can shorten the maintenance time, improve the maintenance quality, reduce the required tools and instruments, and is more suitable for field maintenance operations. The maintenance personnel can master the adjustment method after simple training. This method has been applied in maintenance operations of more than 30 Cummins NT855 diesel engines, and good results have been achieved.