JPH08158986A - Fuel injection pressure control device of fuel injection device - Google Patents

Abstract

PURPOSE: To automatically restrain excessive rise of fuel injection pressure by setting the pressure receiving area of a pressure receiving part giving energization force in the valve opening direction to a valve body closing the outlet side opening interposed in a fuel charge/discharge passage larger than the pressure receiving area of a pressure receiving part giving energization force in the valve closing direction to the valve body. CONSTITUTION: A plunger 7 is reciprocatably fitted in a plunger room 6 communicated to a nozzle 17 to be opened or closed by a usually closed type needle valve 20 through fuel passages 10A, 10B. A fuel chamber 21 is formed on the way of a fuel charge/ discharge passage 11 charging/discharging fuel against the plunger chamber 6, and an opening 21A on the outlet side integratedly formed on one end of the fuel chamber 21 is opened/closed by the valve body 27 driven by an electromagnetic actuator 28. The valve body 27 is formed with a first pressure receiving part 36 giving energization force in the valve closing direction and a second pressure receiving part 37 having the larger pressure receiving area than the first pressure receiving part 36 and giving energization force in the valve opening direction, and hence this device functions to automatically restrain excessive rise of fuel injection pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection pressure control device for a fuel injection device, and more particularly to a fuel injection pressure control device for a cam-driven unit injector.

[0002]

2. Description of the Related Art In a unit injector, which is one of fuel injection devices, a plunger chamber formed in a housing of a unit slidably supports a plunger reciprocated by a driving unit such as a cam, and the plunger chamber is provided in the plunger chamber. The injection hole communicated via the fuel passage is closed by a needle valve that is biased in the closing direction. Fuel is supplied to the plunger chamber through a fuel supply / discharge passage opened / closed by a solenoid valve.When the fuel injection timing is appropriate, the solenoid valve is closed by a signal from the control means, and the plunger chamber is reciprocated by the plunger chamber. The fuel is pressurized to lift the needle valve and open the injection port to inject the fuel. In the case of the unit injector in which the plunger is driven by the drive source such as the cam as described above, the injection pressure of the fuel pressurized by the plunger is determined by the engine speed. That is, as the engine speed increases, the drive speed of the drive unit and the sliding speed of the plunger increase, so the injection pressure also increases, but when the engine speed is low, the injection pressure becomes low.

[0003]

Therefore, it is possible to secure a high injection pressure even in the low engine speed region by changing the shape of the cam.
The injection pressure, that is, the fuel pressure, rises excessively in the high speed region, which may damage the device or increase the driving force. In practice, the injection pressure in the low speed range is sacrificed, and the ideal injection pressure is obtained in the high speed range. It caused the exhaust gas and fuel consumption to deteriorate.

[0004]

Therefore, in the invention according to claim 1, the injection hole facing the combustion chamber of the engine, the normally closed needle valve for opening and closing the injection hole, the injection hole and the fuel passage are provided. A plunger chamber that communicates with each other and accommodates fuel for injection, and one end of which faces the plunger chamber, and reciprocates in the plunger chamber in synchronization with the rotation of the engine to increase or decrease the volume of the plunger chamber. A fuel supply / discharge passage communicating with the plunger chamber for supplying / discharging fuel in / from the plunger chamber, a fuel chamber interposed in the fuel supply / discharge passage and provided with an outlet side opening at one end, and the outlet side. A valve body having an umbrella portion that opens and closes an opening and a stem portion that is connected to the umbrella portion and penetrates the fuel chamber and projects from the other end side of the fuel chamber to the outside of the fuel chamber; The pressure inside the fuel chamber Based on the pressure in the fuel chamber, the first pressure receiving portion for applying an urging force to the valve body in the valve closing direction and the stem portion or the umbrella portion are provided to the valve body in the valve opening direction. An electromagnetic type that applies a biasing force and that drives the valve body to close the outlet side opening in response to the reciprocating movement of the second pressure receiving portion having a pressure receiving area enlarged from the first pressure receiving portion and the plunger. An electromagnetic unit injector having an actuator, operating state detecting means for detecting the operating state of the engine, and outputting a control signal to the electromagnetic actuator according to the operating state of the engine detected by the operating state detecting means. And a control means. In the invention according to claim 2, the stem portion is
A first stem portion slidably fitted in the housing of the electromagnetic unit injector is connected to the first stem portion and the umbrella portion, and a cross-sectional area smaller than the cross-sectional area of the first stem portion is connected. The second chamber has a second stem part, and the fuel chamber is formed around the second stem part. In the invention according to claim 3, the fuel chamber is formed by expanding the inner peripheral wall having the same sectional area as the sectional area of the sliding hole into which the first stem portion is inserted and the inner peripheral wall near the outlet side opening. An expanded part is formed, a first pressure receiving part is formed in a step part between the first stem part and the second stem part, and a second pressure receiving part is formed in an umbrella part facing the expanded part. In the invention according to claim 4, an inner peripheral wall having a cross-sectional area larger than the cross-sectional area of the sliding hole into which the first stem portion is fitted is formed in the fuel chamber, and the first pressure receiving portion is provided with the first stem portion and the first stem portion. The second pressure receiving portion was formed on the step portion of the two stem portions, and the second pressure receiving portion was formed on the umbrella portion. In the invention according to claim 5, the pressure receiving area of the first pressure receiving portion is S1,
When the pressure receiving area of the pressure receiving portion is S2, the area ratio S2 / S1 between the pressure receiving area S1 and the pressure receiving area S2 is S2 / S1 = 1.
The range was set to 1 to 2.0. In the invention according to claim 6, the fuel supply / discharge passage has at least a fuel supply passage that communicates the plunger chamber and the low-pressure fuel supply source. In the invention according to claim 7, the fuel supply / discharge passage has a branch passage for carrying out the fuel, which is branched from the fuel supply passage, and the outlet side opening is provided in the branch passage. In the invention according to claim 8, the fuel supply / discharge passage has a fuel discharge passage which is provided independently of the fuel supply passage and communicates with the plunger chamber, and the fuel discharge passage is interposed in the outlet side opening. In the invention according to claim 9, in a rotation range exceeding the middle rotation range of the engine,
The plunger chamber and the plunger are arranged so that the biasing force of the second pressure receiving portion in the valve opening direction is larger than the biasing pressure of the electromagnetic actuator and the first pressure receiving portion in the valve closing direction. Formed.

[0005]

According to the first aspect of the invention, when the electromagnetic actuator is driven based on the control signal of the control means and the valve body closes the outlet side opening, the plunger moves due to the movement in the volume decreasing direction inside the plunger chamber. As the pressure of the fuel in the chamber rises, the needle valve closed and urged against the injection hole is lifted to inject fuel into the combustion chamber. Further, the urging force applied to the second pressure receiving portion of the valve body in the valve opening direction is
When the urging force of the valve body in the valve closing direction by the electromagnetic actuator and the first pressure receiving portion is exceeded, the valve body is automatically displaced in the valve opening direction and the outlet side opening is opened, so that the electromagnetic unit injector The rise in fuel injection pressure is suppressed. According to the invention of claim 2, the stem portion of the valve body is slidably inserted into the housing of the electromagnetic unit injector, and the first stem portion and the umbrella portion of the valve body are provided. The second stem portion has a cross-sectional area smaller than the cross-sectional area of the first stem portion to be connected, and the fuel chamber is formed around the second stem portion. Flow resistance is reduced. According to the invention of claim 3, the fuel chamber expands the inner peripheral wall having the same sectional area as the sectional area of the sliding hole into which the first stem portion is inserted and the inner peripheral wall near the outlet side opening of the combustion chamber. And an extension formed by
Since the pressure receiving portion is formed in the step portion between the first stem portion and the second stem portion, and the second pressure receiving portion is formed in the umbrella portion facing the expansion portion, the cross-sectional area of the inner peripheral wall with respect to the second pressure receiving portion. However, the sectional area of the inner peripheral wall with respect to the first pressure receiving portion also becomes large, and the fuel pressure applied to the second pressure receiving portion becomes larger than the fuel pressure applied to the first pressure receiving portion. According to the invention described in claim 4, the fuel chamber has an inner peripheral wall having a cross-sectional area larger than the cross-sectional area of the sliding hole into which the first stem portion is inserted, and the first pressure receiving portion is the first stem portion. Formed on the stepped portion of the second stem portion,
Since the second pressure receiving portion is formed on the umbrella portion, the cross-sectional area of the inner peripheral wall with respect to the second pressure receiving portion becomes larger than the cross-sectional area of the inner peripheral wall with respect to the first pressure receiving portion, and the fuel pressure applied to the second pressure receiving portion is increased. It becomes higher than the fuel pressure applied to the first pressure receiving portion. According to the invention of claim 5, the area ratio S2 / of the pressure receiving area S1 of the first pressure receiving portion and the pressure receiving area S2 of the second pressure receiving portion.
When S1 was set to S2 / S1 = 1.1 to 2.0, good results were obtained. According to the invention of claim 6,
Since the fuel supply / discharge passage has at least a fuel supply passage that communicates the plunger chamber and the low-pressure fuel supply source, fuel for injection is sent to the plunger chamber by the low-pressure fuel supply source through the fuel supply passage. According to the invention of claim 7,
The fuel supply / discharge passage has a branch passage for carrying out fuel, which is branched from the fuel supply passage that connects the plunger chamber and the low-pressure fuel supply source, and the outlet side opening of the fuel chamber is interposed in the branch passage. When the fuel pressure of the injection fuel sent from the fuel supply passage to the plunger chamber rises and the valve body of the outlet side opening opens, excess fuel is introduced into the branch passage through the fuel chamber. According to the invention of claim 8, the fuel supply / discharge passage has a fuel discharge passage which is provided independently of the fuel supply passage and communicates with the plunger chamber, and the outlet side opening of the fuel chamber is interposed in the fuel discharge passage. Therefore, when the fuel pressure of the injection fuel sent from the fuel supply passage to the plunger chamber rises and the valve body of the outlet side opening opens, excess fuel is introduced into the fuel discharge passage through the fuel chamber. . According to the invention described in claim 9, in the rotation range exceeding the middle rotation range of the engine, the valve by the second pressure receiving section is more than the biasing pressure in the valve closing direction to the valve body by the electromagnetic actuator and the first pressure receiving section. Since the plunger chamber and the above-mentioned plunger are formed so that the urging force to the body in the valve opening direction becomes large, as the engine speed increases, the sliding speed of the plunger in the plunger chamber increases and the fuel in the plunger chamber is pressurized. When the engine speed exceeds the middle speed range, the urging force that urges the valve body in the valve opening direction by the fuel pressure applied to the second pressure receiving portion is applied to the valve by the fuel pressure applied to the first pressure receiving surface and the electromagnetic force of the electromagnetic actuator. It becomes larger than the urging force that urges the body in the valve closing direction, and the valve body is automatically displaced in the valve opening direction.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a fuel injection pressure control device for an electromagnetic unit injector 2 which is a fuel injection device. The electromagnetic unit injector 2 injects fuel 38 for injection into the combustion chamber E1 of the engine E, and is attached to the cylinder head E2. The electromagnetic unit injector 2 includes an injection nozzle 3, an injection pump 4, and a fuel control unit 5 that controls the supply and discharge of the fuel 38 to the injection pump 4.

The injection pump 4 is formed in the housing 2A of the electromagnetic unit injector 2, has a plunger chamber 6 for containing the fuel 38, and a plunger for slidably supported in the plunger chamber 6 for increasing or decreasing the volume of the plunger chamber 6. 7,
The drive mechanism 9 is configured to press the plunger 7 against the elastic force of the return spring 8. The plunger chamber 6 has an inlet 1 for a high-pressure fuel passage 10A communicating with the injection nozzle 3.
0a and the outlet 22a of the fuel supply passage 22 forming the fuel supply / discharge passage 11 are open. Plunger 7
Of the tappet 12 is slidably supported above the plunger chamber 6 and is biased upward by a return spring 8.
Is locked to the lower end 12a of the. Top 1 of tappet 12
One end 14a of a rocker arm 14 pivotally attached to a support shaft 13 constituting the drive mechanism 9 is in contact with 2b. The other end 14b of the rocker arm 14 has a cam 15 that rotates at half the rotation speed of a crankshaft (not shown) of the engine E,
They are in contact with each other via a push rod 16 which is reciprocally slid by the cam. As shown by the solid line in FIG. 4, the cam 15 has a cam profile in which the maximum injection pressure from the injection hole 17 is sufficiently obtained from the low engine speed region.

The injection nozzle 3 is integrally fastened to a housing 2B located below the plunger chamber 6 by a nozzle holder 3A. The injection nozzle 3 has a nozzle chamber 18 formed at the tip thereof and connected to a plurality of injection holes 17 facing the combustion chamber E2, a needle valve 20 biased by a pressure spring 19 to close the injection holes 17,
Fuel passage 1 for communicating the fuel passage 10A with the nozzle chamber 18
And 0B. As shown in FIG. 2, the needle valve 20 has a pressure receiving portion 20A formed near the tip thereof arranged in the nozzle chamber 18, and the pressure in the nozzle chamber 18 (hereinafter referred to as “nozzle internal pressure”) is a pressure. When it becomes larger than the spring force of the spring 19, it slides upward to open the injection hole 17.

On the other hand, in the housing 2A located on the left side of the injection pump 4, a fuel chamber 21 which is interposed in the fuel supply / discharge passage 11 is formed. The fuel chamber 21 is formed with an outlet-side opening 21 </ b> A that is provided in a branch passage 26 that branches from a fuel supply passage 22 that is connected to a fuel tank 25 via a feed pump 23 and a one-way valve 24. One-way valve 24
Is configured to open in the direction in which the fuel 38 can be supplied to the plunger chamber 6 from the feed pump 23 side.

The fuel control section 5 includes a poppet valve 27 as a valve body for opening and closing the outlet side opening 21A, an electromagnetic actuator 28 for driving the poppet valve 27, and a controller 29 as a control means for controlling the electromagnetic actuator 28.
It is composed of a rotation sensor 30 and an accelerator opening sensor 31 as an operating state detecting means for detecting the engine rotational speed, which is the operating state of the engine, and engine load information.

The poppet valve 27 includes a stem portion 32 and an umbrella portion 3.
3 and 3. The stem portion 32 is provided in the fuel chamber 21.
The first stem portion 32a slidably fitted in the sliding hole 2C formed in the housing 2A above the housing and penetrating to the fuel chamber 21, and connecting the first stem portion 32A and the umbrella portion 33,
The second stem portion 32b has a smaller diameter than the first stem portion 32A. A step is formed between the first stem portion 32a and the second stem portion 32b, and this step serves as the first pressure receiving surface 36 that gives the poppet valve 27 a biasing force in the valve closing direction. The poppet valve 27 keeps the outlet side opening 21A open except for the fuel injection timing.
A coil spring 34 urges the valve seat 21B formed in the outlet side opening 21A and the umbrella portion 33 to separate from each other.

The controller 29 is composed of a microcomputer as its main part, and has a rotation speed sensor 30.
An accelerator opening sensor 31, and a temperature sensor (not shown) that outputs warm-up information of the engine and the like are connected. Based on the information from these sensors, the controller 29 calculates the optimum fuel injection timing at a suitable time, and when the fuel injection timing arrives, the electromagnetic actuator 28 is energized to generate an electromagnetic force to suck the poppet valve 27. The umbrella side 33 closes the outlet side opening 21A. The poppet valve 27, as shown in FIG. 4, has a limit pressure range A of the electromagnetic unit injector 2.
It is configured to open at a set pressure lower than the fuel pressure of. That is, when the rotation speed of the engine E increases and reaches the set pressure, the second pressure receiving portion 37 and the coil spring 3
The size of each part is set so that the total sum of the urging forces in the valve opening direction by 4 exceeds the total sum of the urging forces in the valve closing direction by the first pressure receiving portion 36 and the electromagnetic actuator 28.

The inner peripheral wall 21C of the outlet side opening 21A is shown in FIG.
As shown in FIG. 5, the sliding hole 2C is formed to have the same cross-sectional area, and the expansion portion 35 is formed near the valve seat 21B. The expanded portion 35 is formed so that its cross-sectional area is larger than the cross-sectional area of the inner peripheral wall 21C. The second pressure receiving portion 37 that applies a biasing force to the poppet valve 27 in the valve opening direction is an umbrella portion 33 located inside the expansion portion 35. That is, the pressure receiving area S2 for the second pressure receiving portion 37 is set to be larger than the pressure receiving area S1 for the first pressure receiving portion 36. In this embodiment, the area ratio S2 / S1 between the pressure receiving area S2 and the pressure receiving area S1.
Is set to S2 / S1 = 1.5.

According to the fuel injection pressure control system 1 for the electromagnetic unit injector 2 having such a structure, when the ignition switch (not shown) is turned on, the feed pump 23 shown in FIG. 38 is supplied from the fuel supply passage 22 to the plunger chamber 6 at a constant discharge pressure. When the engine E starts and the cam 15 rotates counterclockwise here, the push rod 16,
The plunger 7 slides downward through the rocker arm 14 to pressurize the fuel in the plunger chamber 6. This time,
If it is not the fuel injection timing, the outlet side opening 21A remains open, so the pressurized fuel 38 is released to the fuel tank 25 via the fuel supply passage 22 and the branch passage 26.

At the fuel injection timing, the controller 29 energizes the electromagnetic actuator 28 to lift the poppet valve 27, and the outlet side opening 21A opens the umbrella portion 33.
Is blocked by. When the outlet side opening 21A is closed, the pressurized fuel 38 is supplied to the nozzle chamber 18 through the fuel passages 10A and 10B, the nozzle internal pressure rises, and the biasing force in the valve opening direction due to the nozzle internal pressure increases the pressure spring 19.
When the valve closing biasing force applied to the needle valve 20 is exceeded, the needle valve 20 slides upward and fuel injection is performed.

Here, as shown in FIG. 3, the poppet valve 2
The force in the valve closing direction applied to 7 is W, and the electromagnetic actuator 2
If the electromagnetic force by 8 is F, the spring force of the coil spring 34 is fs, and the fuel injection pressure at the time of fuel injection is P, then W = F-fs + Pf (S1-S2). In this embodiment, the pressure receiving area S1 of the first pressure receiving portion 36 is
Since the pressure receiving surface S2 of the pressure receiving portion 37 is set large, the condition for opening the poppet valve 27, that is, W <0.
This is the case where F-fs + Pf (S1-S2) <0, that is, P> (F-fs) / (S2-S1).

FIG. 4 is a graph showing the relationship between the engine speed and the maximum fuel injection pressure. The horizontal axis represents the engine speed.
The vertical axis is the maximum injection pressure. The solid line shows the maximum injection pressure characteristic obtained by the cam profile of this embodiment, the broken line shows the maximum injection pressure characteristic obtained by the conventional cam profile, and the dashed-dotted line shows the ideal maximum injection pressure characteristic. The range indicated by symbol A indicates the limit pressure range of the electromagnetic unit injector 2. FIG. 5 shows the injection pressure fluctuation of the injection nozzle 3 when the engine speed is Ne1, where the vertical axis represents the injection pressure and the horizontal axis represents the time.

According to the profile of the cam 15 used in this embodiment, originally, the poppet valve 27 is in a state in which the outlet side opening 21A is closed by the electromagnetic actuator 28. At the time of several Ne1, the maximum injection pressure Pf reaches the limit pressure range A, but since the pressure receiving area S2 of the second pressure receiving portion 37 is larger than the pressure receiving area S1 of the first pressure receiving portion 36, the maximum injection pressure Pf Is larger than the set pressure (F-fs) / (S2-S1), the force W applied to the poppet valve 27 becomes negative. That is, since the urging force applied to the second pressure receiving portion 37 in the valve opening direction becomes large, the poppet valve 27 is pushed into the fuel chamber 21 and the umbrella portion 33 and the valve seat 2 as shown in FIG. 3.
A gap is generated between 1B and 1B.

Therefore, the pressurized fuel 38 in the injection nozzle 3 leaks from the branch passage 26 into the fuel chamber 21 through the outlet side opening 21A, and the original maximum injection pressure Pf shown by the solid line in FIG.
However, as shown by the broken line, the pressure is cut at the set pressure, and the rise in the nozzle internal pressure is suppressed. Therefore, the maximum injection pressure characteristic due to the cam profile that has reached the limit pressure region A shown in FIG. 4 does not rise above the set pressure as shown by the chain double-dashed line, and the durability of the electromagnetic unit injector 2 can be secured. . At the same time, a large amount of fuel does not have to be injected into the combustion chamber E1 at one time, and sufficient fuel injection can be performed from the low rotation speed range. Therefore, N which is a combustion exhaust
It is possible to reduce generation of Ox and the like, loss of driving force in a high rotation range, or deterioration of fuel efficiency due to unstable combustion due to insufficient fuel pressure. Further, with a simple configuration in which the pressure receiving areas S1 and S2 for the first pressure receiving portion 36 and the second pressure receiving portion 37 are made different, a limit valve function of automatically opening the poppet valve 27 even at the fuel injection timing is realized. be able to. In this embodiment, the pressure receiving area S2 /
The pressure receiving area S1 is set to 1.5, but the present invention is not limited to this. The pressure receiving area S2 / pressure receiving area S1 = 1.
It may be in the range of 1 to 2.0.

Next, a modification of the first embodiment shown in FIG. 6 will be described. Since this modification has the same configuration as the fuel injection pressure control device 1 of the electromagnetic unit injector 2 in the first embodiment except the fuel supply / discharge passage, the same components are used in the first embodiment. The same reference numerals are assigned and the description and action are omitted. Fuel supply / discharge passage 11 'in a modified example
Comprises a fuel supply passage 22 connected to the plunger chamber 6 and a fuel discharge passage 26 'which is independent of the fuel supply passage 22 and has one end directly connected to the plunger chamber 6 and the other end connected to the fuel tank 25. There is. Fuel discharge passage 26 '
A fuel chamber 21 having an outlet side opening 21 </ b> A opened and closed by a poppet valve 27 is interposed therein.

According to this structure, the fuel 3 pumped from the fuel tank 25 by the feed pump 23.
8 is supplied into the plunger chamber 6 through the fuel supply passage 22. At the fuel injection timing, the electromagnetic actuator 28 is driven to close the outlet side opening 21A by the poppet valve 27, and the fuel 38 is pressurized by the plunger 7 slid by the rocker arm 14, and the injection of the injection nozzle 3 is performed. It is injected from the hole 17 into the combustion chamber E1. When the pressure of the fuel 38 becomes equal to or higher than the set pressure, the urging force of the poppet valve 27 in the valve opening direction becomes larger than the urging force of the valve in the valve closing direction, and the outlet side opening 21A is slightly increased. The fuel 38 that is opened and pressurized is in the plunger chamber 6 and the fuel discharge passage 2
6 ′ flows into the fuel chamber 21 and is returned to the fuel tank 25. In this way, by providing the fuel discharge passage 26 ′ independently of the fuel supply passage 22, the fuel supply / discharge passage 11 ′ is provided.
It is possible to give flexibility to the piping configuration of.

In the above-described first embodiment and modification, the cross-sectional area of the inner peripheral surface 21C of the outlet side opening 21A is set to the poppet valve 27.
The cross-sectional area of the slide hole 2C into which the first stem portion 32a is inserted is the same as that of the slide hole 2C, but as shown in FIG. It may be formed in C. Also in this case, the second stem portion 32b is positioned in the outlet side opening 21A, and the first pressure receiving portion 36 and the second pressure receiving portion 37 are connected to the first stem portion 32a and the second pressure receiving portion 37.
The pressure receiving areas S1 and S of the pressure receiving portions are formed on the step portion of the stem portion 32b and the umbrella portion 33 located at the outlet side opening 21A, respectively.
By setting 2 to S2 / S1 = 1.1 to 2.0, the fuel pressure applied to the second pressure receiving portion 37 becomes higher than the fuel pressure applied to the first pressure receiving portion 36. Further, in the modification, one end of the fuel discharge passage 26 ′ is configured to be directly connected to the plunger chamber 6, but the present invention is not limited to this, and the fuel passage 10A that communicates the plunger chamber 6 and the nozzle chamber 18 with each other. Alternatively, it may of course be configured to connect to the fuel passage 10B.

[0023]

According to the first aspect of the invention, the pressure receiving area of the second pressure receiving portion for applying a biasing force in the valve opening direction to the valve body that closes the outlet side opening provided in the fuel supply / discharge passage, By making it larger than the pressure receiving area of the first pressure receiving portion that gives the valve body an urging force in the valve closing direction, the urging force due to the fuel pressure applied to the second pressure receiving portion becomes equal to the urging force due to the fuel pressure applied to the first pressure receiving portion. When it becomes larger than the sum of the urging forces of the electromagnetic actuator, the valve body automatically opens and the rise in fuel pressure is suppressed. Therefore, even if the fuel injection pressure is excessively increased in the high rotation region by using the cam having the cam profile capable of producing the high fuel injection pressure from the low rotation region, the urging force applied to the first pressure receiving portion in the closing direction of the device is increased. By setting the pressure lower than the limit pressure, the rise of the fuel injection pressure is suppressed, and while maintaining the durability of the fuel injection device, the fuel injection of the fuel injection device that can obtain the high fuel injection pressure from the low engine speed range with a simple configuration A pressure control device can be provided.

According to the second aspect of the present invention, the second stem portion for connecting the first stem portion and the umbrella portion of the valve body slidably fitted in the housing of the electromagnetic unit injector to the first stem portion is provided. The step area is smaller than the step area of the stem part, and the second
Since the fuel chamber is formed around the stem portion, the flow resistance between the fuel and the stem portion toward the fuel chamber can be reduced, the fuel injection pressure can be quickly reduced, and the durability of the fuel injection device can be improved. According to the third, fourth and fifth aspects of the invention, the pressure receiving area of the valve body with respect to the umbrella portion is made larger than the pressure receiving area of the valve body with respect to the stem portion. The pressure becomes higher than the fuel pressure applied to the stem portion, the valve body is opened, the pressurized fuel escapes to the fuel chamber, and it is possible to prevent the fuel injection pressure from rising excessively, and the durability can be improved.

According to the sixth aspect of the present invention, it is possible to prevent the fuel injection pressure from rising excessively, and the injection fuel supply / discharge passage has at least a fuel supply passage that connects the plunger chamber and the low pressure fuel supply source. Then, the injection fuel is sent to the plunger chamber through the fuel supply passage by the low-pressure fuel supply source, so that it is possible to stabilize the injection of fuel every time.

According to the seventh aspect of the invention, it is possible to prevent the fuel injection pressure from rising excessively, and to use the fuel discharge branch passage branching from the fuel supply passage that connects the plunger chamber and the low-pressure fuel supply source. By interposing it in the outlet side opening of the chamber, when the pressure of the injection fuel sent from the fuel supply passage to the plunger chamber rises and the valve body of the outlet side opening opens, the pressurized fuel passes through the fuel chamber. Since it is introduced into the branch passage, it is possible to prevent fuel from accumulating in the fuel chamber.

According to the present invention, the fuel discharge passage communicating with the plunger chamber independently of the fuel supply passage is provided, and the fuel discharge passage is provided with the outlet side opening of the fuel chamber. The degree of freedom in the exhaust passage piping configuration is increased.

According to the ninth aspect of the invention, when the engine speed exceeds the middle speed range, the urging force for urging the valve body in the opening direction by the fuel pressure applied to the second pressure receiving portion is applied to the first pressure receiving surface. The fuel pressure becomes larger than the urging force that urges the valve body in the closing direction due to the applied fuel pressure and the electromagnetic force of the electromagnetic actuator, and the valve body is automatically opened. Can be Therefore, it is possible to improve the durability of the fuel injection device, improve the combustion exhaust matter, and reduce the loss of the driving force in the high speed region.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a fuel injection pressure control device for a fuel injection device showing a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a tip of a fuel injection nozzle.

FIG. 3 is a cross-sectional view of an electromagnetic actuator, a valve body, and the vicinity thereof.

FIG. 4 is a diagram showing the relationship between engine speed and maximum injection pressure.

FIG. 5 is a characteristic diagram showing a change in injection pressure of a fuel injection nozzle.

FIG. 6 is a schematic configuration diagram showing a modified example of the first embodiment.

FIG. 7 is a side sectional view showing a modified example of the fuel chamber.

[Explanation of Codes] 1 Fuel injection pressure control device 2 Electromagnetic type unit injector 2A Housing 2C Sliding hole 6 Plunger chamber 7 Plunger 10A, 10B Fuel passage 11, 11 'Fuel supply / discharge passage 17 Injection hole 20 Needle valve 21 Fuel chamber 21A Outlet side opening 21C, 21'C Inner peripheral wall 22 Fuel supply passage 23 Low pressure fuel supply source 26 Branch passage 26 'Fuel discharge passage 27 Valve body 28 Electromagnetic actuator 29 Control means 30, 31 Operating state detection means 32 Stem portion 32a 1st Stem portion 32b Second stem portion 33 Umbrella portion 35 Expansion portion 36 First pressure receiving portion 37 Second pressure receiving portion 38 Fuel for injection E Engine E1 Combustion chamber S1 Pressure receiving area of first pressure receiving portion S2 Pressure receiving area of second pressure receiving portion

Claims (9)

[Claims] 1. A nozzle chamber facing the combustion chamber of an engine, a normally closed needle valve for opening and closing the nozzle hole, a plunger chamber communicating with the nozzle hole through a fuel passage and containing fuel for injection. A plunger that has one end facing the plunger chamber and reciprocates in the plunger chamber in synchronization with the rotation of the engine to increase or decrease the volume of the plunger chamber; and the plunger to supply and discharge the fuel in the plunger chamber. A fuel supply / exhaust passage communicating with the chamber, a fuel chamber interposed in the fuel supply / exhaust passage and provided with an outlet-side opening at one end, and an umbrella portion for opening / closing the outlet-side opening and the umbrella portion A valve body having a stem portion penetrating through the fuel chamber and protruding from the other end side of the fuel chamber to the outside of the fuel chamber; and a valve closing direction for the valve body formed on the stem portion based on the pressure in the fuel chamber. 1st receiver that gives urging force to A pressure portion and either the stem portion or the umbrella portion, which applies a biasing force in the valve opening direction to the valve body based on the pressure in the fuel chamber, and which is expanded by the first pressure receiving portion. An electromagnetic unit injector having a second pressure receiving portion having an area and an electromagnetic actuator that drives the valve body to close the outlet side opening in response to the reciprocating movement of the plunger, and an operating state of the engine. A fuel for a fuel injection device, comprising: an operating state detecting means for detecting; and a controlling means for outputting a control signal to the electromagnetic actuator according to the operating state of the engine detected by the operating state detecting means. Injection pressure control device. 2. The stem portion connects a first stem portion slidably fitted in a housing of the electromagnetic unit injector, the first stem portion and the umbrella portion, and
The fuel according to claim 1, comprising a second stem portion having a cross-sectional area smaller than that of the first stem portion, and the fuel chamber being formed around the second stem portion. Fuel injection pressure control device for injector. 3. The fuel chamber is formed by expanding an inner peripheral wall having the same sectional area as that of a sliding hole into which the first stem portion is fitted and an inner peripheral wall near the outlet side opening. An expansion part, the first pressure receiving part is formed in a step part of the first stem part and the second stem part, and the second pressure receiving part is formed in the umbrella part facing the expansion part. 3. The method according to claim 2,
A fuel injection pressure control device for the fuel injection device described. 4. The fuel chamber has an inner peripheral wall having a cross-sectional area larger than a cross-sectional area of a slide hole into which the first stem portion is fitted and inserted, and the first pressure receiving portion is the first stem portion and the first stem portion. The fuel injection pressure control device for a fuel injection device according to claim 2, wherein the second pressure receiving portion is formed on a stepped portion of the second stem portion, and the second pressure receiving portion is formed on the umbrella portion. 5. When the pressure receiving area of the first pressure receiving portion is S1 and the pressure receiving area of the second pressure receiving portion is S2, the area ratio S2 / S1 between the pressure receiving area S1 and the pressure receiving area S2 is S2 / S1 = The fuel injection pressure control device for a fuel injection device according to claim 1, 2, 3 or 4, wherein the range is set to 1.1 to 2.0. 6. The fuel according to claim 1, wherein the fuel supply / discharge passage has a fuel supply passage that communicates at least the plunger chamber and a low-pressure fuel supply source. Fuel injection pressure control device for injector. 7. The fuel supply / exhaust passage has a fuel discharge branch passage branched from the fuel supply passage, and the outlet side opening is interposed in the branch passage. Item 7. A fuel injection pressure control device for a fuel injection device according to item 6. 8. The fuel supply / discharge passage has a fuel discharge passage which is provided independently of the fuel supply passage and communicates with the plunger chamber, and the outlet side opening is interposed in the fuel discharge passage. The fuel injection pressure control device for a fuel injection device according to claim 6, wherein: 9. The internal pressure of the engine, wherein the urging force of the second pressure receiving portion in the valve opening direction of the valve body is greater than the urging pressure of the electromagnetic actuator and the first pressure receiving portion in the valve closing direction of the valve body. The plunger chamber and the plunger are formed so as to be large in a rotation range exceeding a rotation range.
9. A fuel injection pressure control device for a fuel injection device according to any one of claims 8 to 8.