JPS61135979A - Fuel injection valve for diesel engine - Google Patents

Abstract

PURPOSE:To obtain an appropriate injection quantity of fuel, by constituting a fuel injection valve in a double-needle valve structure having two coaxial needle valves which are closed at different pressures, in order to promote atomization of fuel at the time oif low-load opera tion of an engine by injecting fuel from a first nozzle hole having a small opening area and to inject fuel also from a second nozzle hole having a large opening area at the time of high-load operation of the engine. CONSTITUTION:When a fuel injection pump starts supply of fuel under pressure, pressure rise of fuel at first acts on the pressure receiving surface 14a of a first needle valve 14 via a first fuel passage and then acts on the prssur receiving surface 15a of a second needle valve 15 via a connecting port 25a at the top of the first needle valve 143 and a second fuel passage 25. Here, since the pressure at which the first needle valve 14 is opened by a spring 20 is set lower than the pressure at which the second needle valve 15 is opened by a spring 23, the first needle valve 14 is at first raised upward and a first nozzle hole 12 having a smaller diameter is opened for injecting fuel. At the time of low-load operation of an engine, fuel pressure is not raised sufficiently, so that the second needle valve 15 is kept closed. On the other hand, when fuel pressure is raised siffuciently at the time of high- load operation of the engine, the second needle valve 15 is also opened and fuel is injected also from a second nozzle hole 13 having a larger diameter.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a fuel injection valve for a diesel engine.

<Conventional technology> Conventional fuel injection valves for diesel engines include, for example,
There is something like the one shown in Figure 3 (SAEpaper 8
10479).

In the figure, a needle valve 2 is fitted into a nozzle body 1 so as to be freely slidable in the vertical direction, and as the needle valve 2 moves up and down, fuel is injected from a nozzle hole formed at the tip of the nozzle body 1. Ru. The needle valve 2 is biased in the valve closing direction by a spring 4 via a bushing rod 3, and a central plunger 5 is disposed on the top wall of the bushing rod 3 with a predetermined gap and can move freely up and down. In addition, a pressure chamber 6 formed above the central plunger 5 and a fuel reservoir (not shown) formed between the nozzle body 1° needle valve 2 are filled with fuel.
It is communicated by l path 7.

Fuel, which is pumped by the reciprocating motion of the plunger of the fuel injection pump (not shown), is introduced into this fuel reservoir, and the pressure of the fuel increases, causing the needle valve 2 to rise as shown in the figure, and the bushing rod 3 to hit the central plunger 5. Thereafter, the needle valve 2 rises while pushing the central plunger 5 up against the fuel pressure in the pressure chamber 6, so that the needle valve 2 is prevented from rising.

As a result, the expansion of the actual nozzle hole area is suppressed, and the injection pressure is increased in the low load range where the fuel pressure delivered from the fuel injection pump is relatively low, promoting atomization of the spray and reducing black smoke and It has the characteristic that the amount of HC generated is reduced.

<Problems to be Solved by the Invention> However, in such conventional fuel injection valves, in order to sufficiently suppress the opening operation of the needle valve 2 in order to improve characteristics in the low load range, Valve 2 and central plunger 5
If the ratio of the pressure receiving area and the pressure receiving area of the fuel and the fuel to the respective pressure receiving areas approaches 1:1, the fuel injection period in the high load range becomes too long, deteriorating combustibility, leading to frequent black smoke and deterioration of fuel efficiency.

In addition, in this type of injection valve, if the nozzle hole part is a bottle type or throttle valve type, the bottle provided at the tip of the needle valve 2 enters the nozzle hole at the beginning of injection and narrows the nozzle hole area, so the spray However, in the case of a hole type with multiple injection holes, the area of the injection holes is not narrowed down, so even if you try to increase the injection pressure by suppressing the opening speed of the needle valve 2, the atomization of the spray will not be achieved. The problem was that it was not carried out effectively.

The present invention was developed in view of these conventional problems, and uses a coaxial double needle valve mechanism with different valve opening pressures to achieve good combustion in all operating ranges, reduce HC and black smoke, and improve fuel efficiency. The purpose of the present invention is to provide a fuel injection valve for a diesel engine that can improve performance.

Means for Solving the Problems> For this reason, the present invention provides at least one first nozzle hole having a relatively small opening area on a side relatively far from the central axis of the tip of the nozzle body and on a side relatively close to the central axis. , one or more second nozzle holes having a relatively large opening area, and a hollow shape that can freely open and close the first nozzle hole by being inserted into the nozzle body and moving in response to fuel pressure. a first needle valve; and a second needle valve that is fitted into a cavity of the first needle valve and can freely open and close the second nozzle hole by moving in response to fuel pressure;
and a first fuel passage formed to communicate with the first needle valve tip via a pressure receiving surface formed on the outer peripheral wall of the intermediate portion of the first needle valve, and a first needle valve tip of the first fuel passage. near the part and the second
A second fuel passage formed by connecting a pressure receiving surface formed on the outer peripheral wall of the intermediate portion of the needle valve, a first return spring that biases the first needle valve in the valve closing direction, and a second fuel passage that connects the second fuel passage to a pressure receiving surface formed on the outer circumferential wall of the intermediate portion of the needle valve; The valve is configured to include a second return spring that biases in the valve closing direction with a force greater than the valve closing bias force of the one-needle valve.

With this configuration, only the first needle valve opens when the load is low, promoting atomization of the fuel injected from the first nozzle hole with a small opening area, reducing the generation of black smoke and HC, and When the load is high, the fuel pressure increases and the second needle valve also opens, and fuel is injected from the nozzle hole with a large opening area, which suppresses the increase in fuel injection period and prevents the generation of black smoke and deterioration of fuel efficiency. It can be prevented.

In addition, since the fuel pressure is propagated to the pressure receiving surface of the second needle valve through the second fuel passage through the vicinity of the nozzle hole, the second needle valve is opened with the fuel pressure near the nozzle hole sufficiently increased. , second
The spray properties from the nozzle hole are also good, and the second needle valve is prevented from lifting by a minute amount and causing dripping in the medium load range.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 1 showing the first embodiment, a nozzle body 11
At the tip (lower end in the figure), a plurality of small-diameter first nozzle holes 12 for use at low loads are opened on the outer periphery side relatively far from the central axis, and also on the inner periphery side relatively close to the central axis. A plurality of large-diameter second nozzle holes 13 for use during high loads are opened.

A hollow first needle valve 14 that opens and closes the first nozzle hole 12 is fitted into the nozzle body 11 having such a nozzle hole, and a second nozzle hole 13 is inserted into the cavity of the first needle valve 14. A second needle valve 15 that opens and closes is inserted.

A hollow housing 17 is joined to the top wall of the nozzle body 11 via a contact piece 16.
A first return spring 20 that biases the first needle valve 14 in the valve closing direction is fitted through a pair of retainers 18 and 19, and a second return spring 20 that biases the first needle valve 14 in the valve closing direction is inserted through a pair of retainers 21 and 22.
A second return spring 23 is inserted to bias the needle valve 15 in the valve closing direction.

Here, the first needle valve 14 is opened at a relatively low fuel pressure at a low load, and the second needle valve 15 is opened at a high fuel pressure at a high load. The set load of the spring 23 is set.

In addition, the housing 17. Contact piece 16. A first fuel passage 24 is formed in the nozzle body 11 so as to communicate with the tip of the first needle valve 14 via a pressure receiving surface 14a formed on the outer peripheral wall of the intermediate portion of the first needle valve 14. A plurality of communication holes 25a are formed in the first fuel passage 24 from the vicinity of the tip of the first needle valve 14 to the vicinity of the tip of the first needle valve 14 by communicating the inner and outer peripheral walls, and the inner peripheral wall of the first needle valve 14. A second fuel passage 25 is formed which communicates with a pressure receiving surface 15a formed on the intermediate outer circumferential wall of the second needle valve 15 through a gap with the outer circumferential wall of the second needle valve 15.

Next, the operation of the first embodiment will be explained.

When pressure feeding of fuel is started from a fuel injection pump (not shown), the increase in fuel pressure acts on the pressure receiving surface 14a of the first needle valve 14 via the first fuel passage 24, and then from near the tip of the nozzle body 11. It acts on the pressure receiving surface 15a of the second needle valve 15 via the second fuel passage 25.

As described above, the opening pressure of the first needle valve 14 is equal to that of the second needle valve 1.
Since the valve opening pressure is set lower than the valve opening pressure of No. 5, first the first needle valve 14 rises in the figure. This opens the first nozzle hole 12 and starts injection.

When the injection amount is low and the load is low, the first fuel 1tli path 24
Since the fuel pressure near the lower end of the fuel injection hole 12, that is, the fuel pressure near the first injection hole 12, does not rise sufficiently, the second needle valve 15 is maintained in a closed state.

In this case, the injection pressure is relatively low, but since the first nozzle hole 12 has a small diameter and a small opening area, the spray speed increases and atomization of the fuel is promoted, thereby improving combustibility. The amount of graphite and HC produced can be effectively reduced.

On the other hand, in a high load range, the injection pressure increases as the injection amount increases, and the pressure acting on the pressure receiving surface 15a of the second needle valve 15 via the second fuel passage 25 causes the second needle valve 15 to open. When the pressure is exceeded, the second needle valve 15 also rises and the second nozzle hole 13 is also opened.

When the load is high, the injection pressure is sufficiently increased, so fuel is injected from the second nozzle hole 13 with a large opening area in a short period of time while the pressure in the combustion chamber is high, thereby reducing the combustion pressure and temperature. As a result, high output can be obtained, the generation of black smoke can be effectively prevented, and fuel efficiency can be improved.

In the high load range, the injection pressure is sufficiently increased and the flame volume in the combustion chamber is large, so that the spray from the second nozzle hole 13 having a large opening area does not increase HC.

Furthermore, in the present invention, the entrance of the second fuel passage 25 is
Since it is provided near the lit hole 12, the pressure near the injection hole acts on the pressure receiving surface 15a of the second needle valve 15, and the opening of the second needle valve 15 is ensured until the actual injection pressure increases reliably. can be suppressed to

Therefore, for example, when the second fuel passage is provided through the wall of the first needle valve 14 so as to directly connect the pressure receiving surface 14a and the pressure receiving surface 15a, the fuel pressure acting on the pressure receiving surface 15a is
By setting the injection pressure higher than the injection pressure near the nozzle hole 12, it is possible to reliably prevent the second needle valve 15 from lifting slightly during medium load, and also prevent the generation of HC due to fuel dripping due to the slight lift.

FIG. 2 shows a second embodiment. The difference from the first embodiment is that the second fuel passage 26 is formed inside the first needle valve 14 in the axial direction. The other configurations are the same as in the first embodiment, and therefore the operations and effects are also the same.

However, processing of the second fuel passage is easier in the first embodiment.

<Effects of the Invention> As explained above, according to the present invention, the first needle valve is provided with a first needle valve that opens and closes a nozzle hole with a small opening area, and a second needle valve that opens and closes two large nozzle holes with a large opening area. The opening pressure of the first needle valve is set lower than the opening pressure of the second needle valve, and a fuel passage is provided so that the fuel pressure near the injection hole inlet acts on the pressure receiving surface of the second needle valve. Therefore, in the low load range with low injection pressure, only the first needle valve opens to reduce the amount of HC generated, and in the high load range with high injection pressure, the second needle valve opens to improve fuel efficiency and output. Prevents slight lift of the two-needle valve and prevents H due to fuel dripping.
The generation of C can be effectively prevented.

[Brief explanation of the drawing]

FIG. 1 (4) is a sectional view showing the first embodiment of the present invention, FIG. 0 is a bottom view, and FIG. 2 (2) is a sectional view showing the second embodiment of the present invention. [F] is a bottom view, and FIG. 3 is a sectional view showing an example of a conventional fuel injection valve for a diesel engine. 11... Nozzle body 12... First nozzle hole 1
3... Second nozzle hole 14... First needle valve 14a.
...Pressure receiving surface 15...Second needle valve 15a...Pressure receiving surface 20...First return spring 23...
Second return spring 24...first fuel passage 2
5.26...Second fuel passage patent applicant Nissan Motor Co., Ltd. agent Patent attorney Fujio Sasashima 11...Nozzle body 18゜1
2...First nozzle hole 13...Second nozzle hole 2o71
4...First needle valve 14a...Pressure receiving surface 20...No. 1 return spring 23...Second return spring 24...First fuel passage 24-25
...Second fuel passage

Claims (1)

[Claims] One or more first nozzle holes with a relatively small opening area and one or more second nozzle holes with a relatively large opening area on a side relatively far from and a side close to the central axis of the tip of the nozzle body, respectively. and a hollow first needle valve that is fitted into the nozzle body and can freely open and close the first nozzle hole by moving in response to fuel pressure; The second
a second needle valve that can freely open and close the nozzle hole; and a first fuel that is formed to communicate with the tip of the first needle valve via a pressure receiving surface formed on the outer circumferential wall of the intermediate portion of the first needle valve. passage and the first
A second fuel passage formed by connecting the vicinity of the tip of the first needle valve of the fuel passage and a pressure receiving surface formed on the outer circumferential wall of the intermediate portion of the second needle valve and the first needle valve are biased in the valve closing direction. and a second return spring that biases the second needle valve in the valve closing direction with a force greater than the valve closing bias force of the first needle valve. fuel injection valve.