JP2003120474A - Fuel injection nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of soot, and to reduce HC in the exhaust gas while suppressing the increase of NOx by increasing the initial injection ratio to the injection pressure. SOLUTION: In a fuel injection nozzle in which an inlet of a nozzle hole 3 provided on a tip of a nozzle body 1 is covered by a needle tip surface 5 on the downstream side of a valve seat 4, a recess 7 with the position immediately downstream of the valve seat 4 as an upstream end thereof and the position facing the inlet in a maximum lift state of a needle 2 as a downstream side thereof is formed in a tip end face 5. By increasing the depth of the recess 7 toward the downstream side, the reduction loss of a fuel passage from the valve seat 4 to the nozzle hole 3 is reduced even in the initial injection, the flow rate coefficient is increased, and the initial injection ratio to the fuel injection pressure is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection nozzle, and more particularly to a valve covered orifice type fuel injection nozzle in which an inlet of an injection hole provided in a nozzle body is covered with a needle tip surface downstream of a valve seat. It is a thing.

[0002]

2. Description of the Related Art In a fuel injection nozzle of a valve covered orifice type in which an inlet of an injection hole provided in a nozzle body is covered with a needle tip surface downstream of a valve seat, a volume of a nozzle sack which causes a drool is reduced. Therefore, there is an advantage that the HC concentration in the engine exhaust can be reduced.

However, in such a type of fuel injection nozzle, when the needle lift amount at the initial stage of opening the needle is small, the thickness of the fuel passage formed between the needle tip surface and the inner surface of the nozzle cone ( Since the width is narrow, the flow path resistance is large, and since the flow into the injection hole is poor, the initial injection rate becomes low with respect to the injection pressure.

Therefore, in the conventional valve-covered-orifice type fuel injection nozzle, ignition combustion is started in the vicinity of the nozzle at the beginning of injection with a small needle lift and at the time of operation in a light load region, and the subsequent fuel spray is generated. Since the fuel gas is entrained and burned, an increase in the local equivalence ratio cannot be avoided, and there is a concern that combustion leading to the generation of soot may occur.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and by improving the tip shape of a needle used for a fuel injection nozzle, the initial injection rate is increased with respect to the injection pressure. Therefore, it is an object to suppress the generation of soot while suppressing the increase of NOx, and further, to reduce the HC in the exhaust gas and suppress the generation of PM.

[0006]

In order to solve the above problems, the present invention provides a fuel injection nozzle in which an inlet of an injection hole provided at a tip of a nozzle body is covered with a needle tip surface downstream of a valve seat, A recess is formed in the front end surface with the position immediately downstream of the valve seat as the upstream end and the position facing the inlet in the maximum lift state of the needle as the downstream end, and the depth of the recess reaches the downstream side. It is characterized by making it deeper. It is desirable that the depth of the recess be smoothly reduced at the downstream end, or that the opening edge of the inlet of the injection hole be chamfered at least on the upstream side of the recess.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a cross-sectional view of an essential part showing an embodiment of a fuel injection nozzle according to the present invention, in which a needle valve 2 is housed in a nozzle body 1 so as to be able to move up and down, and a nozzle hole 3 provided at the tip of the nozzle body 1 is shown. To form a valve-covered orifice type fuel injection nozzle in which the inlet of the valve is covered with the needle tip surface 5 downstream of the valve seat 4.

In the fuel injection nozzle, when the needle 2 is lifted upward in the figure against the seating biasing force of the needle spring (not shown) in response to a signal from a control unit (not shown), the nozzle body 1 and The fuel in the fuel passage 6 formed between the needles 2 is transferred to the nozzle body 1
Of the common rail injection system, which flows into the injection hole 3 through the space between the inner surface of the cone and the tip surface 5 of the needle 2 and is injected into the combustion chamber (not shown). It may be a pressure-responsive fuel injection nozzle in which the needle 2 is automatically lifted against the urging force of the needle spring when the pressure rises.

Here, in the present embodiment, the position immediately downstream of the valve seat 4 is defined as the upstream end, and the position opposite to the inlet of the injection hole 3 in the maximum lift state of the needle 2 shown by the two-dot chain line in FIG. 1 is the downstream end. A recess 7 is provided on the tip surface 4. Then, by gradually increasing the depth of the recess 7 toward the downstream side, it is possible to prevent the cross-sectional area of the recess 7 from decreasing with a decrease in the projected area of the tip surface 5 of the needle 2 and to avoid an increase in the flow path resistance. is doing.

The bottom surface of the downstream end of the recess 7 and the tip surface 5
The general surface of the hollow is smoothly connected by an arcuate surface so that the depth of the hollow 7 is smoothly reduced at the downstream end, and the upstream side of the hollow 7 at the opening edge of the inlet of the injection hole 3 is chamfered with a circular arc surface.
By doing so, the fuel that has flowed through the recess 7 is allowed to smoothly flow into the injection hole 3 without being accompanied by a contraction flow due to a sudden direction change.

That is, in the fuel injection nozzle as described above, a flow path is formed by the recess 7 between the portion immediately downstream of the valve seat 4 of the needle 2 and the inlet of the injection hole 3 before the needle 2 is lifted. The cross-sectional area of this flow path increases as the lift amount of the needle 2 increases.

Therefore, even in the initial stage of valve opening when the lift amount of the needle 2 is extremely small, the resistance of the flow path connecting the downstream side of the valve seat 4 and the injection hole 3 is small and the flow coefficient is high. For this reason, the initial injection rate of fuel becomes high, and the penetration force of the fuel spray injected at the beginning is high, so the air utilization rate is high, and ignition occurs at a position sufficiently distant from the nozzle. As a result, no increase in the local equivalence ratio due to excessive entrainment of burned gas due to the subsequent fuel spray is observed, and soot generation is suppressed.

Further, when the initial injection rate is increased as described above, in the common rail injection system, the fuel pressure instantaneously decreases near the inlet of the injection hole 3 at the initial injection stage. Then,
Since the injection rate does not increase until the fuel pressure is restored, the injection amount during the ignition delay period is suppressed and the premixed combustion ratio becomes low, preventing an abnormal increase in combustion temperature and reducing NO.
Generation of x is suppressed.

Incidentally, when comparing the amount of smoke generated with respect to the NOx emission amount in two fuel injection nozzles having the same hydraulic flow rate and different initial injection rates, the common rail pressure,
Although the injection timing and other operating conditions are almost the same, as shown in FIG. 2, the high injection rate nozzle having a high initial injection rate has a smoke generation amount of about 1/5 or less, and the same injection rate. Then, the effect of reducing the amount of NOx produced was obtained by delaying the injection timing. If the injection pressure (common rail pressure) is increased so that the nozzle with a low initial injection rate has a similar injection rate to that of a nozzle with a high initial injection rate, the premixed combustion ratio increases and the NOx generation amount increases significantly. The characteristics of the nozzle having a high injection rate are significantly different from those of the high injection rate nozzle.

That is, in the nozzle having a high initial injection rate, the generation of soot can be suppressed while suppressing the increase of NOx, and moreover, the inlet of the injection hole 3 is formed by the tip surface 5 of the needle. Since the fuel injection nozzle of the valve covered orifice type is covered to cover, the sack capacity that causes fuel lag behind which is concerned after the injection is reduced, and the HC concentration in the exhaust gas is also low.

As shown in the embodiment, the recess 7
When the bottom surface of the downstream end and the general surface of the tip surface 5 are connected by an arcuate surface to reduce the depth of the recess 7 smoothly at the downstream end, the fuel flowing through the recess 7 is rapidly changed in direction. Since the smooth flow can be made to flow into the injection hole 3 without accompanying contraction flow, the pressure loss due to contraction flow can be made as small as possible and the initial injection rate can be made higher. It is not necessary to form the downstream end with an arcuate surface, and the downstream end may be formed with an arcuate surface or an inclined surface for guiding the fuel toward the injection hole 3.

Further, as shown in the embodiment, when the upstream side of the recess 7 at the opening edge of the inlet of the injection hole 3 is chamfered with an arcuate surface, the fuel flowing through the recess 7 is smoothly transferred to the injection hole 3. Since the inflow is small, the inflow loss is small and contributes to the improvement of the initial injection rate. However, the inflow loss into the injection hole 3 can be made smaller by chamfering the entire circumference of the inlet of the injection hole 3 with an arc surface or the like. The chamfering 8 at the inlet of the injection hole 3 can be easily performed by processing such as fluid polishing.

[0018]

As is apparent from the above description, according to the present invention, the position directly downstream of the valve seat provided on the needle is the upstream end and the position of the needle facing the inlet of the injection hole in the maximum lift state is the downstream end. The depression is formed on the tip end surface of the needle that covers the injection hole, and the depth of the depression is made deeper toward the downstream side, so that the valve seat reaches the injection hole even at the initial stage of injection when the needle lift amount is extremely small. The flow rate coefficient is increased by reducing the throttling loss of the fuel passage between the above period and the initial injection rate can be increased with respect to the injection pressure of the fuel, and the increase of NOx can be suppressed. Can be suppressed.

Further, since the valve-covered orifice type fuel injection nozzle is constructed by covering the inlet of the injection hole with the tip end surface of the needle, the suck capacity which may cause the fuel drooling after the injection is finished. H in the exhaust that becomes smaller
The C concentration is also low.

Further, since the depth of the recess is gradually increased toward the downstream side, the cross-sectional area of the fuel passage formed by the recess and the gap between the tip of the needle and the nozzle body reaches the downstream side. The flow path resistance does not decrease as the flow rate increases and the downstream end of the recess is set to a position facing the inlet of the injection hole in the maximum lift state of the needle. The flow coefficient of the fuel passage extending from the seat to the injection hole is kept high.

[Brief description of drawings]

FIG. 1 is a sectional view of essential parts showing an embodiment of a fuel injection nozzle according to the present invention.

FIG. 2 is a characteristic diagram comparing a smoke generation amount with a NOx emission amount due to a difference in initial injection rate.

[Explanation of symbols]

1 nozzle body 2 needles 3 injection holes 4 valve seat 5 Tip surface 6 Fuel passage 7 dimples 8 chamfers

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Claims (3)

[Claims] 1. A fuel injection nozzle in which an inlet of an injection hole provided at a tip of a nozzle body is covered with a needle tip surface downstream of a valve seat, and a maximum lift of the needle is set with a position immediately downstream of the valve seat as an upstream end. A fuel injection nozzle characterized in that a recess having a downstream end at a position facing the inlet in the state is provided on the tip end surface, and the depth of the recess is made deeper toward the downstream side. 2. The fuel injection nozzle according to claim 1, wherein the depth of the depression is smoothly reduced at the downstream end. 3. The opening edge of the inlet of the injection hole is chamfered at least on the upstream side of the depression.
Or the fuel injection nozzle according to 2.