The fuel supply timing refers to the correct fuel supply time of the fuel injection pump, which is generally expressed by the fuel supply advance angle. The oil supply advance angle refers to the crankshaft or camshaft rotation angle from the top dead center of the cylinder piston to the top dead center of the compression end when the first cylinder plunger of the fuel injection pump starts to supply oil. The combustion of diesel in the cylinder has a lag period of ignition. In order to make the piston obtain the maximum explosion pressure near the top dead center at the end of compression, the fuel injector must start to inject fuel before the top dead center. When the oil pump supplies oil to the injector, due to the elastic deformation of the high-pressure oil pipe and the increase and transmission of the pressure, it takes a certain time, so the time to start the fuel supply is earlier than the time to start the fuel injection.
The size of the fuel supply advance angle has a great influence on the working process of the diesel engine. When the fuel supply advance angle is too large, the rapid combustion period in the cylinder occurs before the top dead center at the end of compression, that is, the peak value of the explosion pressure in the cylinder occurs before the piston reaches the top dead center, which will cause power drop, rough work, Increased fuel consumption, serious knocking sound of ignition, poor idling, weak acceleration and difficulty in starting. When the fuel supply advance angle is too small, the rapid combustion period in the cylinder occurs farther after the top dead center of compression, which reduces the peak value of the burst pressure, and also causes the power drop, fuel consumption increase, acceleration weakness, etc., and will cause the engine overheat.
Therefore, it is very important for the diesel engine to have an optimal fuel supply advance angle. The so-called optimal fuel supply advance angle refers to the fuel supply advance angle that can obtain the maximum power, the minimum fuel consumption rate and the best exhaust gas purification under the condition of constant speed and fuel supply. For a running diesel vehicle, the optimal fuel supply advance angle of the engine should change with the change of the speed and the fuel supply amount. When the speed is higher and the fuel supply is greater, the optimal fuel supply advance angle is also
should be larger. For this reason, the fuel injection pump of some diesel engines is equipped with an automatic fuel supply advance angle adjuster, which can automatically adjust with the speed change on the basis of the initial fuel supply advance angle; amount) to determine a fixed optimal fuel supply advance
angle, which no longer changes during use.
During the use of the diesel engine, if there is a problem with the fuel supply timing or when the fuel injection pump is removed for inspection and re-installed into the engine, it is necessary to check and correct the fuel supply timing. The methods are as follows:
1. Check and correct the timing of fuel supply by empirical method
(1) Rotate the crankshaft of the diesel engine with a hand crank, so that the first cylinder piston is in the compression stroke. When the fixed mark is aligned with the oil supply advance angle mark or the specified angle on the flywheel or crankshaft drive pulley, stop shaking.
(2) Check whether the marking on the driven disc of the fuel injection pump coupling is aligned with the marking on the front end of the pump casing, as shown in Figure 2-81. If the marks on the two engraved lines are exactly aligned, it means that the time when the plunger of the first cylinder of the fuel injection pump starts to supply oil is accurate; The first cylinder plunger starts to supply oil late; on the contrary, if the engraved mark on the driven disc of the coupling has crossed the engraved mark on the front end of the pump casing, it means that the first cylinder plunger starts to supply oil early. If the plunger of the first cylinder of the fuel injection pump starts to supply oil too early or too late, loosen the coupling fixing screw, and tighten it when the above--alignment marks are aligned.
(3) Conduct a road test. Choose a flat, hard straight road or a special runway. After the car is hot, drive at the highest speed and the lowest stable speed, and then slam the accelerator pedal to the bottom to make the car accelerate rapidly. At this time, if you can hear a slight knocking sound from the diesel engine, and it gradually increases as the vehicle speed increases
If it gradually disappears, the timing of the fuel supply is correct; if the percussion sound is strong, and it does not disappear for a long time after the vehicle speed is increased, it means that the fuel supply time is too early; if the percussion sound of fire is not heard, and the acceleration is weak, If the power is insufficient, the fuel supply time is too late. When the fuel supply time is too early or too late, just stop and release the coupling of the fuel injection pump, so that the camshaft of the fuel injection pump rotates a little in the opposite direction or in the same direction of rotation. Repeated debugging several times can make the fuel supply timing accurate. .
Figure 2-81; The first cylinder of the fuel injection pump starts to supply fuel
1- drive shaft; 2- coupling drive plate; 3- first cylinder oil supply mark; 4- pump casing front face; 5- coupling driven plate
To check the time when the plunger of the first cylinder of the fuel injection pump starts to supply oil, the following method can also be used: Rotate the crankshaft so that the marking on the driven plate of the coupling is aligned with the marking on the front end of the pump casing (at this time 1 The cylinder plunger starts to supply oil), and then observe the oil supply advance angle mark on the flywheel or crankshaft drive pulley or the relative position of the specified angle and the fixed mark. If the oil supply advance angle mark or the specified angle is just aligned with the fixed mark, it means that the advance angle of the first cylinder plunger to start oil supply is correct; if the oil supply advance angle mark or the prescribed angle has not turned to the fixed mark, it means that the The advance angle of the first cylinder plunger to start oil supply is too large, causing the oil supply to be too early; on the contrary, if the oil supply advance angle mark or the specified angle has turned the fixed mark, it means that the first cylinder plunger starts to start.
The advance angle of oil supply is too small, resulting in too late oil supply.
When the oil pump is removed from the vehicle and re-installed after inspection and debugging, just shake the crankshaft to make the oil supply advance angle mark or the specified angle align with the fixed mark, and then align the coupling driven plate with the pump casing. The two engraved marks on the front end face are aligned. In this case, refit the coupling and tighten the fixing screws to ensure the timing of the first cylinder oil supply. If there is any difference, it can be debugged in the road test.
The above is the inspection and correction of the fuel supply advance angle of the first cylinder of the fuel injection pump. Whether the fuel supply timing of other cylinders is correct depends on whether the fuel supply interval between the cylinders is correct.
2. Use the flash method to detect the fuel supply timing The fuel supply timing meter made by the flash method is basically the same as the ignition timing meter in its composition, working principle and use method.
The common diesel engine fuel supply timing meter, its oil pressure sensor is connected in series between the first cylinder high-pressure oil pipe and the injector or is clamped on the high-pressure oil pipe, which can turn the oil pressure into an electrical signal and trigger the frequency flash (timing). light). Every time the timing light flashes once, it means that the first cylinder is supplied with oil once, so the flashing is the same as that of the first cylinder.
Synchronized fuel supply. When the timing light is used to align the top dead center mark of the compression end of the first cylinder of the diesel engine, and flashes according to the actual fuel supply time, it can be seen that the rotating part (flywheel or crankshaft drive pulley) of the running diesel engine is illuminated by the flash. The oil supply advance angle mark or the specified angle has not reached the fixed mark, that is, the first cylinder piston has not reached the top dead center. At this time, if the potentiometer on the timing light is adjusted so that the flash is gradually delayed until the fuel supply advance angle mark on the rotating part or the specified angle is aligned with the fixed mark, then the delay flash time is the fuel supply advance time. Change it to display it on the indicator device, and then the fuel supply advance angle to be measured can be read out.
The fuel supply advance angle of the diesel engine should comply with the original factory regulations. The fuel supply advance angle of the fuel injection pump of common models is shown in Table 2-11.
3. Use the cylinder pressure method to detect the fuel supply timing
When using the cylinder pressure method to detect the fuel supply timing of the diesel engine, the fuel injector of the cylinder under test must be removed, and a cylinder pressure sensor must be installed in its hole. The removed fuel injector should still be connected to the original high-pressure fuel pipe, and the fuel pressure sensor should be connected in series between the two. For some models of diesel engines, the cylinder pressure sensor can also be installed in the glow plug hole or the air start valve. During the detection, the cylinder pressure sensor can collect the compression pressure signal of the tested cylinder, and its maximum pressure point is the top dead center of the piston compression end; the oil pressure sensor can also collect the oil supply start signal, and the crankshaft angle between the two is Fuel supply advance angle.
