JPH06117228A - Fuel injection pump for diesel engine - Google Patents

Abstract

PURPOSE:To effectively make use of an NOx catalyst by providing a second stage cam to inject a small amount of fuel after injected fuel has been burned on a camshaft of a fuel injection pump for a diesel engine with an exhaust emission pipe in which an NOx reducing catalyst is located, in addition to a normal cam. CONSTITUTION:In a diesel engine which is provided with an exhaust gas pipe in which an NOx reducing catalyst is located to reduce NOx, a second stage cam 3 to inject a small amount of fuel after injected fuel has been burned is installed on a camshaft 1 of a fuel injection pump installed to inject fuel into a cylinder in addition to a normal cam 2 to inject fuel into the cylinder at the piston top dead center in the cylinder. Accordingly, when the piston is at the top dead center, correct burning is made by the activation of the normal cam 2 and, after the burning has been completed, a small amount of fuel is injected by the activation of the second stage cam 3. Then this small amount of fuel is vaporized without burning to produce HC gas, and HC is present in exhaust emission to effectively make use of the NOx reducing catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection pump for a diesel engine, which mainly supplies a shortage of hydrocarbons to a NOx reduction catalyst provided in an exhaust pipe as a measure for reducing NOx in exhaust gas of a diesel engine. It is a thing.

[0002]

2. Description of the Related Art As a measure for reducing NOx in the exhaust gas of an internal combustion engine, a system using a catalyst has been conventionally adopted, and this system is currently the mainstream in a gasoline combustion engine. However, a diesel engine has a problem that a catalyst for a gasoline engine cannot be used because the exhaust gas contains a large amount of oxygen. Therefore, in the catalytic reduction method which is being developed in recent years for diesel engines, hydrocarbons equal to or more than NOx (abbreviated as HC in the following description) are required as reducing agents.

[0003]

In the conventional diesel engine, as shown by the solid line in the characteristic diagram of HC and NOx in the exhaust gas and the load of the engine shown in FIG.
However, there is a problem that the catalyst does not function sufficiently because the emission amount of is small and the emission characteristics with respect to the load are different. That is, in order to make the above catalyst work effectively, NOx
It is necessary to supply the same amount or more of HC into the exhaust gas, and it is desirable that the HC be completely vaporized.

On the other hand, in the middle of the fuel supply passage connecting the fuel injection pump and each fuel injection nozzle, there are a fuel supply passage to a cylinder during a fuel injection period and a fuel supply passage to a cylinder in an exhaust stroke at the same time. Is provided in the fuel supply passage to the cylinder in the fuel injection period when the pressure in the fuel supply passage to the cylinder in the fuel injection period exceeds a certain value. Japanese Patent Laid-Open No. 3-68516 discloses an exhaust purification system for a diesel engine in which a relief valve is provided to relieve a fuel supply passage to a cylinder in the exhaust stroke and a catalyst is provided in the exhaust system.

However, this system has the problems that pressure fluctuations occur in the main fuel injection during the combustion stroke and the piping system becomes complicated. Further, in a denitration device that selectively denitrates NOx in exhaust gas with a catalyst layer,
A signal from a crank angle sensor installed in an internal combustion engine and a small amount fuel supply valve which is arranged in a cylinder or in an exhaust pipe upstream of the catalyst layer and injects a small amount of fuel for reducing NOx into exhaust gas is provided. A denitration device for an internal combustion engine having a valve opening controller that inputs and controls the small amount fuel supply valve to open according to a predetermined program is disclosed in Japanese Patent Application Laid-Open No. Hei 3 (1998)
-253713].

However, in this denitration device, the HC supply path for reduction is branched from the fuel tank, the HC supply pressure becomes low and the HC is difficult to vaporize, and the HC supply amount is controlled according to the NOx emission amount. is necessary. Further, in a diesel engine exhaust gas purification device including a catalytic converter provided in the middle of an exhaust pipe that discharges exhaust gas of a diesel engine, a fuel injection pump that supplies fuel to the engine and an upstream side of the exhaust pipe catalytic converter. An exhaust gas purifying device for a diesel engine, which is provided between the fuel injection pump and a part of fuel injected from a fuel injection pump, is introduced into an exhaust pipe as a reducing agent of a catalytic converter.
No. 41917].

However, in this purification device, for example, 4
A cylinder engine requires five plungers, and the characteristics of the added plungers are different, so a commonly used pump cannot be used, resulting in high cost and fuel vaporization at low temperature due to exhaust pipe injection. It has the drawback of being difficult to do. Although there are various technical problems in the above-mentioned known technology, it is desirable that the HC to be supplied in order to effectively operate the NOx reduction catalyst is vaporized, and that in the case where fuel is injected through the exhaust pipe, it is vaporized. Since it is difficult to inject the fuel in the high temperature cylinder, it is most effective in vaporizing the HC, and the present invention aims to provide a device that can realize this condition.

[0008]

A fuel injection pump of a diesel engine according to the present invention for achieving the above object is a fuel injection pump for injecting fuel into a cylinder of a diesel engine having an NOx reduction catalyst in an exhaust pipe. In addition to the normal cam for injecting fuel into the cylinder during the top dead center period of the piston in the cylinder, a second-stage cam for injecting a small amount of fuel after the combustion of the injected fuel is provided on the camshaft Has been done.

[0009]

[Operation] With the fuel injection pump configured as described above, the fuel is normally burned at the top dead center of the piston by the normal cam, and a small amount of fuel injected by the second cam after the combustion is completed. Of the fuel is vaporized without burning and HC
The gas is made to stay in the cylinder, and HC equal to or more than NOx is present in the exhaust gas, so that the NOx reduction catalyst is effectively used.

[0010]

EXAMPLES Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view showing a cam profile of a fuel injection pump of a diesel engine according to an example of the present invention. FIG. 3 is a diagram showing the position of a piston in a cylinder during a fuel injection period by the cam profile of FIG. 1.

First, fuel is injected into a cylinder of a diesel engine not shown on the camshaft 1 of the fuel injection pump shown in FIG. 1 at the time of top dead center of the piston shown in FIG. A normal cam 2 is provided, and a second-stage cam 3 is provided for injecting a small amount of fuel during a period indicated by an arrow B after the combustion of the injected fuel is completed. Therefore, during the period indicated by arrow A, the fuel necessary for generating the output of the diesel engine is injected to perform normal combustion, and during the period indicated by arrow B, that is, during the period when combustion is not performed in the cylinder, a small amount of fuel is supplied. This fuel is injected to vaporize this fuel in a high temperature cylinder to generate HC gas.

Further, by mounting the fuel injection pump having the camshaft 1 having the cam profile described above, during the operation of the diesel engine, normal combustion is performed in the injection period indicated by the arrow A as in the conventional case. The small amount of fuel injected by the second-stage cam 3 added in the present invention is vaporized without burning because it is after normal combustion, and is discharged as HC gas.

In the diesel engine equipped with the fuel injection pump of the present invention, as shown by the broken line curve in FIG. 3, HC equal to or more than NOx can be generated, and the NOx reduction catalyst functions sufficiently. Can be made. In the embodiment described above, the cam shaft 1 of the fuel injection pump is provided with a two-stage cam consisting of cams 2 and 3 to generate HC. However, the normal NOx generation amount is NOx at a maximum rotation speed of about 2000 RPM. In order to generate HC that is substantially equal to or more than the generated amount, the additional fuel injection amount by the second-stage cam 3 is a small amount of about 4% of the total fuel injection amount. Further, a normal diesel engine has multiple cylinders of 4 to 12 cylinders, and therefore it is difficult to accurately perform additional fuel injection for each cylinder.

Therefore, in order to improve the accuracy of the injection amount, another embodiment is shown in FIG. . That is, like the camshaft 1 shown in FIG. 1, only the fuel injection pump 6 shown by arrow C that supplies fuel to one cylinder shown by arrow C among the plurality of cylinders of the diesel engine 5 shown in FIG. Two-stage cams 2 and 3 are provided to supply fuel to the cylinder indicated by arrow C twice.

Incidentally, in the case of the 6-cylinder diesel engine 5 of FIG. 4, the injection by the second-stage cam 3 for generating HC is one in comparison with the case of additionally injecting the charge into all-cylinder injection. Since the fuel is additionally injected into only the cylinder, the injection amount is increased by 6 times, so that the accuracy of the injection amount of the fuel for the reduction catalyst is improved by 6 times.

[0016]

The fuel injection pump for a diesel engine according to the present invention has a cam shaft of a fuel injection pump for injecting fuel into a cylinder of a diesel engine having an exhaust pipe provided with a NOx reduction catalyst, and a piston top dead center in the cylinder. In addition to the normal cam that injects fuel into the cylinder during the point period, a second-stage cam that injects a small amount of fuel after combustion of the injected fuel is provided is provided.

Therefore, since a small amount of fuel can be injected in the exhaust stroke from the cylinder to cause HC to be present in the exhaust gas in an amount equal to or greater than NOx, the NOx reduction catalyst can be effectively functioned, and the exhaust It is extremely effective as a measure to reduce NOx in gas. In particular, in the present invention, since a small amount of fuel is injected in the high temperature cylinder after the end of combustion, this small amount of fuel is not burned but is converted to vaporized HC gas and NOx reduction is performed together with the exhaust gas from the cylinder. It has the advantage of being fed to the catalyst.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a cam profile of a fuel injection pump of a diesel engine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a position of a piston in a cylinder during a fuel injection period by the cam profile of FIG.

FIG. 3 is a diagram showing a relationship between a load and HC, NOx in a diesel engine equipped with the fuel injection pump of the present invention shown in FIG. 1 and a conventional diesel engine.

FIG. 4 is a schematic view of another embodiment in which the fuel injection pump of the present invention is applied to a 6-cylinder diesel engine.

[Explanation of symbols]

 1 Cam shaft 2 Normal cam 3 Second stage cam 5 Diesel engine 6 Fuel injection pump

Claims (1)

[Claims] 1. A fuel injection pump for injecting fuel into a cylinder of a diesel engine having an NOx reduction catalyst provided in an exhaust pipe, has a camshaft for injecting fuel into the cylinder during a piston top dead center period of the cylinder. A fuel injection pump for a diesel engine, which is provided with a second-stage cam for injecting a small amount of fuel in a discharge stroke after completion of combustion of the injected fuel, in addition to the cam.