JPH02546B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection pump, and more particularly to a fuel injection pump characterized in that an initial injection rate is reduced by providing a small diameter portion at the tip of a plunger.

In order to achieve exhaust purification in diesel engines, it is necessary to (i) reduce the amount of NO generated by lowering the oxygen concentration and combustion temperature in the combustion chamber, and (ii) reduce smoke in the exhaust. There are two conditions that are necessary: not to cause this, and various methods are being explored to satisfy these conditions. One of the simplest and already implemented methods for satisfying condition (i) in direct injection engines is to delay the fuel injection timing, but if the fuel injection timing is delayed, incomplete combustion will occur. As a result, there is a drawback that the amount of smoke generated increases significantly. Fortunately, research by Kahn et al. revealed that this drawback can be corrected by performing high-pressure injection even if the injection timing is delayed. However, while high-pressure injection can suppress smoke generation, Due to various problems such as the following, a combination of delaying the injection timing and high-pressure injection alone is not a complete solution to purifying the exhaust gas of a direct-injection diesel engine.

The problems caused by high pressure injection are as follows.

(a) If the injection timing is delayed and high-pressure injection is performed all at once, abnormal combustion vibrations are likely to occur, and as a result, combustion noise may increase significantly.

(b) In general fuel injection devices other than unit injectors, the injection valve and injection pump are connected through the injection pipe, so after the injection valve closes, a pulsating wave is generated in the injection pipe due to tube end reflection. When high-pressure injection is performed, the tube end reflection also becomes larger, so the residual pulsating wave inside the tube also becomes larger, and as a result,
This will adversely affect the next injection. In addition, excessive force is applied to the injection pipe and its connecting parts at both ends due to water hammer, reducing the safety of these parts.

(c) During the suction process after the end of injection, the pressure inside the injection pipe is rapidly reduced, which may cause bubbles to form inside the injection pipe. However, in the case of high-pressure injection, these bubbles are crushed by an even greater force, resulting in the injection The vicinity of the valve inlet, injection pump outlet, etc. is likely to be eroded by cavitation, and these parts are likely to deteriorate or break down.

As described above, various problems arise with high-pressure injection, and therefore exhaust gas purification of direct injection engines cannot be achieved only by a combination of injection timing delay and high-pressure injection.

Therefore, recently it has been proposed to perform pilot injection in addition to delayed injection timing and high-pressure injection, or to perform pseudo two-stage injection with a lower initial injection rate. The purpose of this method is to suppress the amount of NO generated by lowering the oxygen concentration in the combustion chamber before main injection through pilot injection or initial injection, and as a result, solve the above problem (a). At the same time, the aim is to improve the problems in (b) and (c) above.

An object of the present invention is to provide a fuel injection pump for performing pseudo two-stage injection with a reduced initial injection rate. According to the fuel injection pump of the present invention, a low-pressure initial injection is performed prior to a high-pressure main injection, so that the injection rate of the main injection is relatively reduced and the problems (a) to (c) above are solved. As a result, it is possible to provide a fuel injection pump that can purify the exhaust gas of a direct injection diesel engine.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows plunger 1 of a conventional fuel injection pump.
and a schematic diagram of the vicinity of the delivery valve. As shown in the figure, in the conventional fuel injection pump, the tip of the plunger 1 is formed into a cylindrical shape having a uniform outer diameter as a whole. Therefore, when the top end surface of the plunger 1 rises above the fuel supply port 3 provided in the barrel 2 during the discharge stroke, pressure is suddenly applied to the fuel above the top end surface of the plunger 1, and the fuel becomes high pressure, and delivery valve 5
is pushed up into the injection tube (not shown). In this case, the pressure is zero until the top end surface of the plunger 1 passes through the fuel supply port 3, and increases rapidly immediately after the top end surface of the plunger 1 passes through the fuel supply port 3. Therefore, a large amount of fuel is injected into the combustion chamber of the engine at once, resulting in the
Problems such as (a) to (c) will arise. In contrast, in the fuel injection pump of the present invention, as shown in FIG. 2, a small diameter portion 41 is provided at the tip of the plunger 4, and when this small diameter portion 41 passes through the fuel supply port 3, low pressure initial injection is performed. It's becoming like that. The small diameter portion 41 has a truncated conical shape whose diameter gradually decreases toward the tip. The tip diameter d of the small diameter portion 41 can be, for example, about 0.85D to 0.975D, where D is the maximum outer diameter of the plunger 4, but it depends on the initial injection rate. . Further, the axial length L of the small diameter portion 41 is determined based on the same consideration, but is approximately 0.01D to 0.1D.
It can be determined within the range of In short, if the structure is such that the plunger 4 has a small diameter portion 41 in the shape of a truncated cone of equal height, the diameter gradually decreases toward the tip, and the diameter of the tip is large enough to pump a small amount of fuel. It is sufficient.

In a fuel injection pump having a plunger having such a shape, the initial injection is performed in the state shown in FIG. 3, and the subsequent main injection is performed in the state shown in FIG. 4. For initial injection, the small diameter portion 41 is the fuel supply port 3
Since the injection is carried out in a slightly tight state, the fuel escapes to the fuel supply port 3 through a slight gap between the inner circumferential surface of the barrel and the outer circumferential surface of the small diameter portion, and therefore the injection pressure is low. However, during the main injection, plunger 4
Since the fuel supply port 3 is closed by the large diameter part of the fuel supply port 3, injection is performed at high pressure, but since the stroke of the plunger 4 during the main injection is shorter than that of a conventional injection pump, the injection rate during the main injection is It is relatively lower than that in the case of single-stage injection.

Figure 5 shows a heat release rate diagram A and an injection pipe pressure waveform diagram B when a combination of injection timing delay and high-pressure injection is applied to a direct injection diesel engine. The solid curve a shows the results obtained using the conventional fuel injection pump, and the dotted curve b shows the results obtained using the fuel injection pump of the present invention.

Referring to each figure A to B of FIG. 5, when the fuel injection pump of the present invention is used, the heat release rate diagram and the pressure waveform diagram inside the injection pipe are compared with the case where the conventional fuel injection pump is used. It can be seen that improvements have been made. In other words, the timing of the heat release rate is slightly delayed compared to the conventional method, which contributes to reducing combustion noise. Furthermore, since the magnitude of the injection rate is proportional to the amount of NO generated, the fuel injection pump of the present invention improves thermal efficiency and suppresses the amount of NO generated at the same time. On the other hand, looking at the pressure waveform diagram inside the injection pipe,
It can be seen that when the fuel injection pump of the present invention is used, residual pulsation disappears because the tube end reflection is reduced.

As described above, according to the present invention, a fuel injection pump that can realize exhaust purification of a direct injection diesel engine is provided.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of a part of a conventional fuel injection pump, FIG. 2 is a diagram showing the tip of the plunger of the fuel injection pump of the present invention, and FIGS. 3 and 4 are the fuel injection pump of the present invention. FIG. 5 is a diagram showing the state of the engine when a conventional fuel injection pump and the fuel injection pump of the present invention are used. 1: Plunger, 2: Barrel, 3: Fuel supply port, 4: Plunger, 41: Small diameter section, 5: Delivery valve.

Claims (1)

[Claims] 1. In a fuel injection pump having a plunger, there is a small diameter portion at the tip of the plunger in the shape of a truncated cone with equal heights, the diameter of which gradually decreases toward the tip, and the diameter of the tip is large enough to pump a small amount of fuel. A fuel injection pump characterized by being provided with.