JPH06346814A - Fuel injection device for diesel engine - Google Patents

Abstract

PURPOSE:To suppress generation of NOx by reducing an initial injection ratio while making high pressure injection with good fuel consumption. CONSTITUTION:In the fuel injection device for a diesel engine formed in such constitution that fuel discharged from a fuel supplying pump 3 is accumulated in common rails 5, 5 and then injection-supplied into a plurality of combustion chambers through injectors 2, 2, cams 11, 11 for driving plungers 10, 10 of the fuel supplying pump 3 opposing to the opening valves of respective injectors 2, 2 are composed of concave cams so as to reduce an initial injection ratio. Discharging pipes 4, 4 leading from the fuel supplying pump 3 to the common rails 5, 5 and injection pipes 6, 6 leading from the common rails 5, 5 to respective injectors 2, 2 are composed of a taper pipe whose cross section is reduced toward a downstream side, so that pressure is increased by the discharging pipes 4, 4 and the injection pipes 6, 6 so as to reduce the load of the fuel supplying pump 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for a diesel engine, and more specifically, it accumulates fuel discharged from a fuel supply pump in a common rail and supplies the fuel to a plurality of combustion chambers from the common rail through injectors. The present invention relates to a pressure-accumulation injection device for a diesel engine.

[0002]

2. Description of the Related Art In a pressure-accumulation injection device for a diesel engine in which fuel discharged from a fuel supply pump is accumulated in a common rail and is injected and supplied from the common rail to a plurality of combustion chambers via an injector, Since the high-pressure fuel being injected can be injected in synchronization with the valve opening of the injector, the injection pressure of the fuel can be increased. When high-pressure injection is performed in this manner, atomization of the fuel spray is promoted, vaporization and mixing with air are improved, so fuel consumption and the amount of unburned substances in the exhaust are improved.

However, in such a pressure-accumulation type injection device, high-pressure fuel is injected at once in response to opening of the injector, so that the initial injection rate becomes high, which raises the combustion temperature and NOx. There is a problem that the generation of is promoted. In order to avoid such a situation, it is effective to delay the injection timing, but in this case, there is a problem that fuel consumption deteriorates.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an injection device capable of suppressing the generation of NOx by lowering the initial injection rate while performing high-pressure injection excellent in fuel consumption. The task is to do.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention accumulates fuel discharged from a fuel supply pump in a common rail, and injects the fuel from the common rail to a plurality of combustion chambers through injectors. In the fuel injection device of the diesel engine, the cam that drives the plunger of the fuel supply pump at the valve opening timing of each injector is a concave cam, and the discharge pipe from the fuel supply pump to the common rail and from the common rail to each injector It is characterized in that the injection pipe is composed of a tapered pipe whose cross-sectional area decreases toward the downstream side.

[0006]

When the cam of the fuel supply pump is driven, the plunger is moved up and down to discharge the fuel. The fuel discharged from the fuel supply pump accumulates pressure on the common rail and is supplied from each injection pipe to the injector. Then, each time the injector opens, fuel is injected and supplied to each combustion chamber.

By the way, since the cam for driving the plunger corresponding to the valve opening timing of the injector is a concave cam, the pressure of the fuel discharged from the fuel pump rises slowly. Therefore, the pressure of the fuel supplied from the common rail to the injector also rises slowly, the initial injection rate can be reduced, and there is no need to delay the injection timing and suppress the generation of NOx, so that the exhaust gas is exhausted. Both the characteristics and the fuel consumption can be improved. .

On the other hand, since the discharge pipe extending from the fuel supply pump to the common rail and the injection pipe extending from the common rail to the injector are formed by taper pipes, the injection pressure can be further increased by the pressure increasing action of these taper pipes. it can. Therefore, it is possible to reduce the load on the fuel supply pump that accompanies the high-pressure injection, and it is possible to further improve the fuel efficiency of the engine in combination with the improvement of the combustion efficiency due to the high-pressure injection.

[0009]

1 is a schematic diagram showing an embodiment of a fuel injection device for a diesel engine according to the present invention, and FIG. 2 is a schematic side view showing a state in which the fuel injection device shown in FIG. 1 is applied to a vehicle engine. is there. In these figures, injectors 2 are attached to the combustion chambers of the engine 1, respectively.
Moreover, the common rails 5 and 5 connected to the injectors 2 and 2 and the fuel supply pump 3 via the discharge pipes 4 and 4 are connected via the injection pipes 6 and 6, respectively, so that the fuel is discharged from the fuel supply pump 3. The fuel is accumulated in the common rail 5, and the fuel is supplied to the injectors 2 and 2 from the common rails 5 and 5 through the injection pipes 6 and 6. When the injectors 2 and 2 are opened by receiving a signal from a controller (not shown), the common rail 5 and
The fuel supplied from 5 is injected and supplied to the combustion chamber, and the fuel supply pump 3 discharges in synchronization with the opening of the injectors 2 and 2.

The fuel supply pump 3 includes a cam shaft 9 meshed with a crank shaft (not shown) of the engine 1 via gears 7 and 8, a plunger 10 driven by the cam shaft 9 and a delivery valve (not shown). Is equipped with. Every time the cams 11, 11 provided on the camshaft 9 lift the plunger 10, the fuel supplied from the fuel tank (not shown) via the feed pump is discharged and supplied to the common rails 5 and 5 via the delivery valve. There is.

Here, in the present invention, the camshaft 9
The cams 11, 11 provided on the above are constituted by concave cams. Therefore, although the plungers 10 and 10 are initially lifted at a slow speed, they are lifted rapidly as the cam angle increases.

For this reason, the pressure of fuel supplied from the fuel supply pump 3 to the injectors 2, 2 via the common rails 5, 5, that is, the injection pressure of fuel, is such that the cam angle advances as shown by the solid line in FIG. Gradually increases. Therefore, the initial injection rate can be made lower than that of the conventional example shown by the broken line, and when the injection timing is the same as that of the conventional case, the combustion temperature can be made lower, so that the generation of NOx is suppressed.

The discharge pipes 4 and 4 and the injection pipes 6 and 6 are tapered pipes whose cross-sectional areas gradually decrease toward the downstream side. Therefore, the discharge pipe 4 is supplied from the fuel supply pump 3 to the common rails 5 and 5 via the discharge pipes 4 and 4 and while being supplied from the common rails 5 and 5 to the injectors 2 and 2 via the injection pipes 6 and 6. 4 and the injection pipes 6, 6 increase the pressure.

That is, since the pressure of the fuel discharged from the fuel supply pump 3 is a pulsation that rises every time the plungers 10 and 10 are lifted, the pressure on the inner surfaces of the discharge pipes 4 and 4 formed of tapered pipes is increased. The pressure-increasing action is performed by the generated pressure reflected waves. Further, since the internal pressures of the common rails 5, 5 to which the fuel thus boosted in pressure is supplied also periodically change, the pressure boosting action by the injection pipes 6, 6 is similarly performed.

Therefore, the pressure of the fuel supplied to the injectors 2, 2 can be made higher than the pressure of the fuel discharged from the fuel supply pump 3, and the high-pressure injection can be performed without increasing the addition of the fuel supply pump 3. Can be done. Even in such a high-pressure injection state, since the cams 11, 11 are made of concave cams as described above, the initial injection rate can be lowered, so that the generation of NOx is suppressed.

The taper pipes forming the discharge pipes 4 and 4 and the injection pipes 6 and 6 are not limited to the linear taper but may be a curved taper. Further, the degree of pressure increase by the discharge pipes 4 and 4 and the injection pipes 6 and 6 varies depending on the pipe length and the cross-sectional reduction rate (taper degree), but generally, the outlet pressure is set to 1.5 times the inlet pressure. The discharge pressure of the fuel supply pump 3 can be reduced by an amount corresponding to the pressure increase by the discharge pipes 4 and 4 and the injection pipes 6 and 6 which are tapered pipes.

[0017]

As is apparent from the above description, according to the present invention, the cam for driving the plunger of the fuel supply pump is a concave cam to enable high-pressure injection while lowering the initial injection rate. Since the injection pressure is made higher by the pressure increasing function of the discharge pipe and the injection pipe,
High-pressure injection is possible without increasing the load on the fuel supply pump, and there is no need to delay the injection timing to suppress NOx generation, so fuel consumption is also improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a fuel injection device for a diesel engine according to the present invention.

FIG. 2 is a schematic side view of a state in which the fuel injection device shown in FIG. 1 is applied to a vehicle engine.

FIG. 3 is an injection pressure characteristic diagram comparing the injection pressures of the example and the conventional example.

[Explanation of symbols]

 1 Engine 2 Injector 3 Fuel Supply Pump 4 Discharge Pipe 5 Common Rail 6 Injection Pipe 7, 8 Gear 9 Cam Shaft 10 Plunger 11 Cam

Claims (1)

[Claims] 1. A fuel injection device for a diesel engine in which fuel discharged from a fuel supply pump is accumulated in a common rail and is injected and supplied from the common rail to a plurality of combustion chambers through injectors. The cam that drives the plunger of the fuel supply pump at a certain time is composed of a concave cam, and the discharge pipe from the fuel supply pump to the common rail and the injection pipe from the common rail to each injector are tapered pipes whose cross-sectional area decreases toward the downstream. A fuel injection device for a diesel engine, which is configured.