JPH0444841Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel injection valve for an internal combustion engine, and particularly to a structure of a fuel injection valve that is optimal for use in a diesel engine.

[Prior Art] In a diesel engine, a fuel injection valve having a structure as shown in FIG. 4 is generally used. Fuel pressure-fed from an injection pump (not shown) passes through the fuel feed hole 2 of the nozzle body 1 and reaches the oil reservoir 3, where hydraulic pressure is applied to the pressure stage 5 of the needle 4 and pushes the needle 4 up. There is a force that tries to do this. On the other hand, needle 4
is pressed against the valve seat of the nozzle body by a pressure spring 7 via a pressure pin 6. Therefore, the needle 4 is
If the force Po trying to push up becomes greater than the force Ps of the pressure spring 7, the needle 4
moves away from the valve seat, so fuel is injected. When the pressure feeding of fuel from the injection pump is finished and the oil pressure decreases, the needle 4 is moved to the pressure spring 7.
Since it is returned by the force of and touches the valve seat, the fuel injection ends.

In such a fuel injection valve, as shown in FIG. 5, a characteristic is obtained in which the flow rate of the injected fuel increases approximately linearly as the needle lift amount increases.

Looking at the characteristics of fuel injection valves from the perspective of engine performance,
It is desirable to have the following characteristics. In the low-speed, light-load range (exhaust gas regulation range), it is desirable to lengthen the injection period and set the injection rate to a low rate to allow sufficient combustion to reduce _NOx and to perform gradual combustion to reduce noise. In high-speed, high-load ranges, on the other hand, it is desirable to shorten the injection period and set a high injection rate to achieve quick combustion at the most efficient time to improve the output performance of the engine.

From this point of view, a structure is known in which a pressure accumulation chamber or a throttle passage is provided in the fuel injection valve, and the valve opening pressure of the needle is kept low when the lift amount is small, and increased when the lift amount is large. (Japanese Patent Application Laid-Open No. 1983-19967).

[Problems to be solved by the invention] In the conventional fuel injection valve as shown in Fig. 4, the relationship between the fuel pressure and the lift amount of the needle 4 exhibits a linear characteristic as shown in Fig. 6. Therefore, it is difficult to reduce the injected fuel flow rate even lower than the current level in the low-speed, light-load range with low fuel pressure.
Therefore, it is difficult to make the injection period longer than the current one. Furthermore, since the lift speed of the needle 4 also has a characteristic that is approximately proportional to the fuel pressure, it is difficult to lower the injection rate by suppressing the needle lift speed lower than the current situation.

On the other hand, in the high-speed, high-load range, the needle lift amount increases due to high fuel pressure, but the injection flow rate is increased by increasing the lift amount even more than the current one.
It is difficult to improve output. Further, although the needle lift speed can be increased as the fuel pressure increases, it is difficult to increase the needle lift speed higher than the current speed to achieve a high injection rate.

In addition, as mentioned above, in the low speed light load range, the fourth
The fuel injection valve shown in Japanese Patent Application Laid-open No. 19967-1983 is known as a structure that can suppress the injection flow rate to a smaller value than the fuel injection valve shown in the figure and increase the injection flow rate in high-speed, high-load ranges. However, the fuel injection valve according to this proposal has the disadvantage that the structure is significantly more complicated than that shown in FIG. 4, and the manufacturing cost is high.

The present invention focuses on the desirable characteristics required of a fuel injection valve as described above and the problems with the conventional proposed technology, and aims to provide a fuel injection structure that can obtain desirable injection period characteristics and injection rate characteristics according to the load over a certain period without significantly complicating the structure compared to a general fuel injection valve.

[Means for solving the problem] The fuel injection valve of the present invention to achieve this object lifts a needle provided in a nozzle body by applying fuel pressure to a pressure receiving surface of the needle, In the fuel injection valve that opens the nozzle hole at the tip by the lift and injects fuel from the fuel passage, the pressure receiving surface of the needle is connected to the first pressure receiving surface facing the oil reservoir that is always in communication with the fuel passage, and and a second pressure-receiving surface facing the shear chamber, and only when the fuel pressure in the oil reservoir acts on the first pressure-receiving surface and the lift amount of the needle exceeds a certain amount. The fuel passage is provided with a port that communicates with the pressure chamber.

[Operation] In such a fuel injection valve, in a low speed light load range, the fuel pressure is low, so the needle lift amount is small, and the fuel pressure is introduced only to the first pressure receiving surface. In the high-speed, high-load range, the fuel pressure increases and the needle lift amount increases, but when it increases beyond a certain amount, the nozzle body port opens.
Fuel pressure is introduced into the second pressure receiving surface, and the pressure receiving area increases rapidly. Therefore, the amount of lift also increases rapidly. Therefore, by appropriately setting the areas of the first pressure receiving surface and the second pressure receiving surface, the needle lift amount can be reduced in the low speed and light load range compared to the conventional general fuel injection valve as shown in Fig. 4. to a smaller value,
It is possible to increase it even more in the high-speed, high-load range. In addition, since the area of the first pressure receiving surface is suppressed to be smaller than that of the conventional pressure receiving surface, the lift speed of the needle is lower than that of the conventional pressure receiving surface, and the sum of the areas of the first pressure receiving surface and the second pressure receiving surface is lower than that of the conventional pressure receiving surface. is larger than the conventional pressure-receiving surface area, so that the lift speed is higher than the conventional one. As a result, in the low speed and light load range, the injected fuel flow rate is kept small, the injection period is lengthened, and the injection rate is kept low, achieving sufficient combustion and gradual combustion, reducing _NOx and noise. be done. In high-speed, high-load ranges, the injected fuel flow rate is higher than before, the injection period is shortened, and the injection rate is high, which allows combustion to occur quickly at the most efficient time and improve the engine's output performance. .

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a fuel injection valve according to a first embodiment of the present invention. In the figure, reference numeral 11 indicates a nozzle body of a fuel injection valve, and a nozzle hole 12 is provided at the tip of the nozzle body. A needle 13 is provided inside the nozzle body 11 so as to be movable in the vertical direction in the figure.
Fuel is injected from the nozzle hole 12 when the vehicle leaves the seating surface 14 inside, and fuel injection is stopped when the vehicle is seated on the seating surface 14. This needle 13 is urged toward the nozzle hole 12 by a pressure spring 16 via a pressure pin 15.

An oil reservoir 17 is formed above the nozzle hole 12 in the nozzle body 11, and fuel fed under pressure from an injection pump (not shown) is guided to the oil reservoir 17 through a high-pressure fuel passage 18.

The needle 13 is lifted by introducing fuel pressure from the high-pressure fuel passage 18 into the pressure receiving surface, and in this embodiment, this pressure receiving surface is configured as a two-stage pressure receiving surface. That is, the needle 13 has 2
A first pressure receiving surface 19 is formed with two stepped portions, faces the oil reservoir 17 that is always in communication with the fuel passage 18, and can be applied with fuel pressure regardless of the lift amount of the needle 13. A second pressure receiving surface 20 facing a pressure chamber 22 that communicates with the fuel passage 18 only when the amount exceeds a certain level.
is provided. Pressure chamber 22 is
It is formed between the second pressure receiving surface 20 and a surface 21 formed on the nozzle body 11 side opposite thereto.
A high-pressure port 23 is branched from the high-pressure fuel passage 18 toward the side surface of the needle 13, and only when the needle 13 is lifted by a predetermined amount or more, the fuel passage 18 and the pressure chamber 22 are connected through the high-pressure port 23. The fuel pressure can be introduced into the pressure chamber 22 and the fuel pressure of the second pressure receiving surface 20 can be applied.

One end of a fuel leak passage 24 formed in the needle 13 is open to the second pressure receiving surface 20, and the other end of the fuel leak passage 24 is open to the second pressure receiving surface 20.
It is open on the side. A fuel leak passage 26 is also formed on the nozzle body 11 side, and one end communicates with the low pressure chamber 25 (spring chamber in this embodiment), and the other end of the fuel leak passage 26 communicates with the needle 1.
It opens towards the side of 3. The fuel leak passage 2 at the side surface of the needle 13
The positional relationship between the openings 4 and 26 is determined such that when the lift amount of the needle 13 is below a certain amount, the passages 24 and 26 communicate with each other, and when the lift amount exceeds a certain amount, the communication is cut off.

The operation of such an embodiment device will be explained. First, in the low speed and light load range, the fuel pressure is low, so the lift amount of the needle 13 is also small. Therefore, the needle 13 is in the state shown in FIG. 1, for example, and the fuel pressure transmitted via the high-pressure fuel passage 18 and the oil reservoir 17 acts only on the first pressure receiving surface 19. Therefore, by setting the area of the first pressure receiving surface 19 appropriately small, the needle lift amount can be easily suppressed to a small value compared to the conventional fuel injection valve shown in FIG. . At this time, the high pressure port 23 and the pressure chamber 22 do not communicate with each other because the needle lift amount is small. The pressure chamber 22 also includes a fuel leak passage 2.
Since relatively low pressure fuel enters from the low pressure chamber 25 through 4 and 26, the pressure chamber 2
2 is not in a so-called vacuum state.

As a result of the needle lift amount being suppressed to a small value relative to the fuel pressure, as shown in Fig. 2, compared to the characteristic A of the conventional fuel injector, the present invention can obtain characteristics such as _B1 . , the fuel flow rate injected from the injection hole 12 where the lift amount is small is suppressed to a small amount. If the fuel flow rate is kept small, the injection period can be made longer than before. Furthermore, since the area of the first pressure receiving surface 19 is smaller than the area of the pressure receiving surface of a conventional fuel injection valve, the lift force acting on the needle 13 at low speed and light load is correspondingly reduced, and the lift speed is lowered. As a result, the injection rate is also lowered.

On the other hand, at high speed and high load, the fuel pressure becomes high, so the lift amount of the needle 13 becomes large.
When the lift amount exceeds a certain amount, the high pressure port 23
The pressure chamber 22 is in communication with the pressure chamber 22, and high pressure fuel pressure is also introduced into the second pressure receiving surface 20. Therefore, the fuel pressure receiving area of the needle 13 is the sum of the areas of the first pressure receiving surface 19 and the second pressure receiving surface 20,
Since the pressure receiving area increases rapidly, both the lift amount and lift speed increase dramatically. As a result, a characteristic like _B2 in FIG. 2 is obtained, which has a larger lift amount than the conventional characteristic A. When the lift amount is increased, the injected fuel flow rate is increased compared to the conventional one, and it becomes possible to correspondingly shorten the injection period at high speed and high load. Further, since the sum of the areas of the first pressure receiving surface 19 and the second pressure receiving surface 20 is larger than the pressure receiving surface area of a conventional fuel injection valve, the needle 13
The lift force acting on the engine also increases, increasing the lift speed and achieving a high injection rate.

When fuel injection is performed, the fuel pressure decreases as a result of the fuel injection, so the needle 13 descends, and the high pressure port 23 is eventually closed and the fuel leak passage 2
4 and 26 are connected. Due to this communication, the fuel pressure in the pressure chamber 22 is released to the low pressure chamber 25, so the residual pressure in the pressure chamber 22 is removed and the needle 13 is seated.

Next, FIG. 3 shows a second embodiment of the present invention.

In this embodiment, a fuel leak passage 32 is provided in the needle 31, and the fuel leak passage 32
is formed in an overflow passage 34 formed in the nozzle body 33 so as to be able to communicate or interrupt communication depending on the lift amount of the needle 31. Since the other configurations are similar to the first embodiment, the same reference numerals are given to the parts corresponding to those of the apparatus shown in FIG. 1, and the explanation thereof will be omitted. In this way, the overflow passage 34
The same function as that of the first embodiment can also be obtained.

In each of the above-described embodiments, the first pressure receiving surface and the second pressure receiving surface are simply configured in two stages, but the second pressure receiving surface may be configured in more stages. For example, if the needle is provided with three stepped portions and the stepped portions on the second and third surfaces are constructed in the same structure as the second pressure receiving surface shown in FIG. 1, the structure shown in FIG. The characteristics shown can be divided into three regions, for example, a low speed light load region, a medium speed medium load region, and a high speed high load region, and the characteristics in each region can be obtained as different nonlinear characteristics.

[Effect of the invention] According to the fuel injection valve of the invention, in addition to the first pressure receiving surface facing the oil reservoir that is always in communication with the fuel passage, the fuel injection valve is connected to the fuel passage only when the needle lift amount exceeds a predetermined amount. A second pressure-receiving surface facing the communicating pressure chamber is provided to suppress the needle lift amount and lift speed to be smaller than conventional fuel injection valves in the low speed and light load range, and to reduce the lift amount compared to conventional fuel injection valves in the high speed and high load range. , the lift speed was increased, so
In the low speed and light load range, it is possible to keep the injection flow rate low, lengthen the injection period, and use a low injection rate, allowing sufficient combustion to occur and reducing _NOx , while also allowing gradual combustion. At the same time, vibration and noise can be reduced, and in high-speed, high-load ranges, the injection flow rate can be increased to shorten the injection period and achieve a high injection rate, allowing for quick combustion at the most efficient time. As a result, the output of the engine can be improved. In the present invention, in addition to the first pressure receiving surface, the second pressure receiving surface
Since it is only necessary to add a pressure-receiving surface and provide an associated port, the structure does not become significantly more complicated than that of conventional general fuel injection valves as shown in Fig. 4, and it can be easily and inexpensively installed. Able to implement ideas.

[Brief explanation of the drawing]

Fig. 1 is a partial longitudinal cross-sectional view of a fuel injection valve according to the first embodiment of the present invention, Fig. 2 is a relationship between fuel pressure and needle lift amount of the device of Fig. 1, and Fig. 3 is a diagram of the relationship between the fuel pressure and the needle lift amount of the device of Fig. A partial vertical cross-sectional view of a fuel injection valve according to a second embodiment, FIG. 4 is a partial vertical cross-sectional view of a conventional fuel injection valve,
5 is a diagram showing the relationship between the needle lift amount and the injection flow rate for the device shown in FIG. 4, and FIG. 6 is a diagram showing the relationship between the fuel pressure and the needle lift amount for the device shown in FIG. 4. 11, 33...fuel injection valve, 12...nozzle hole, 1
3,31...Needle, 17...Oil pool, 18...
...High pressure fuel passage, 19...First pressure receiving surface, 20...
... second pressure receiving surface, 22 ... pressure chamber,
23... High pressure port, 24, 26, 32... Fuel leak passage, 25... Low pressure chamber, 34... Overflow passage.

Claims (1)

[Scope of utility model registration request] In the fuel injection valve, the needle provided in the nozzle body is lifted by applying fuel pressure to the pressure receiving surface of the needle, and the lift opens the nozzle hole at the tip and injects the fuel from the fuel passage. a first pressure receiving surface that faces an oil reservoir that constantly communicates with the fuel passage, the pressure receiving surface of the needle;
a second pressure-receiving surface facing the pressure chamber, and only when the fuel pressure in the oil reservoir acts on the first pressure-receiving surface and the lift amount of the needle exceeds a certain amount. A fuel injection valve characterized in that a port is provided that communicates the fuel passage with the pressure chamber.