JPH0640930Y2 - Fuel injector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a fuel injection device for use in an internal combustion engine.

[Prior Art] A plunger driven by an engine, a fuel pressurizing chamber filled with fuel and pressurized by the plunger, and the fuel pressure in response to the fuel pressure in the fuel pressurizing chamber has a predetermined pressure. The needle that opens when the pressure exceeds the limit, the overflow valve that is slidably inserted into the sliding hole and that controls the fuel overflow in the fuel pressurizing chamber, and the overflow valve that is in the axial direction of the sliding hole. The present applicant has already proposed a unit injector that includes a piezoelectric element that controls the opening and closing of an overflow valve by moving the valve to a position where the fuel injection is performed when the overflow valve is closed. See Japanese Patent Application No. 62-335259). In this unit injector, the end of the sliding hole is opened into the large diameter fuel overflow chamber, and a valve seat is formed at the end of this sliding hole so that the overflow valve is located in the fuel overflow chamber and above the valve seat. Has an enlarged head that can be seated on, and an annular fitting portion that seals contact with the inner peripheral surface of the sliding hole is formed at the end of the overflow valve on the side opposite to the enlarged head. A pressurized fuel introducing chamber is formed around the outer peripheral surface of the overflow valve between the expansion heads, and this pressurized fuel introducing chamber is connected to the fuel pressurizing chamber, and the overflow valve is biased in the opening direction. The fuel injection chamber is started when the expansion head is separated from the valve seat by the spring force of this spring and the overflow valve is closed against the spring force of this spring. Of the pressurized fuel overflows into the fuel overflow chamber via the pressurized fuel introduction chamber, thereby stopping the fuel injection.

However, in this unit injector, when the overflow valve is opened to stop fuel injection, high-pressure fuel overflows into the fuel overflow chamber, and as a result, the fuel pressure in the fuel overflow chamber temporarily becomes high. Since the high pressure acts on the tip surface of the enlarged head of the overflow valve, a force in the valve closing direction acts on the overflow valve, and as a result, the overflow valve is closed again as soon as it is opened. become. Therefore, the fuel is not properly injected, and there is a problem that the fuel injection is particularly short.

In order to solve such a problem, a plunger driven by an engine, a fuel pressurizing chamber filled with fuel and pressurized by the plunger, and the fuel pressure in advance in response to the fuel pressure in the fuel pressurizing chamber Needle that opens when the specified pressure is exceeded, overflow valve slidably inserted in the slide hole, and fuel pressurization chamber by moving the overflow valve in the axial direction of the slide hole. And an actuator for controlling the overflow of fuel from the fuel cell, wherein the overflow valves are spaced from each other in the axial direction of the sliding hole and are in sealing contact with the inner peripheral surface of the sliding hole. And a second annular fitting portion, forming an annular valve seat on the inner wall surface of the sliding hole between the first annular fitting portion and the second annular fitting portion, and An annular valve portion that can be seated on this valve seat is formed on the outer peripheral surface of the overflow valve between the two annular fitting portions, and An annular pressurized fuel introduction chamber is formed around the outer peripheral surface of the overflow valve between the annular fitting portions, the pressurized fuel introduction chamber is connected to the fuel pressurization chamber, and between the annular valve portion and the second annular fitting portion. An annular fuel overflow chamber is formed around the outer peripheral surface of the overflow valve, and the back pressure chamber formed in the sliding hole on the side opposite to the fuel overflow chamber with respect to the second annular fitting portion is 2 to 3 kg / cm. The fuel with a feed pressure of ² is introduced to apply a feed pressure of ² to 3 kg / cm ² to the outer end surface of the second annular fitting portion, and the fuel is pressurized when the annular valve portion of the overflow valve separates from the valve seat. The present applicant has already proposed a fuel injection device in which the pressurized fuel in the chamber is made to overflow into the fuel overflow chamber through the pressurized fuel introduction chamber (Japanese Patent Application No. 63-2.
See 34822). In this fuel injection device, by providing the overflow valve with the second annular fitting portion, the high-pressure fuel overflowing into the fuel overflow chamber when the overflow valve is opened acts on the outer end surface of the second annular fitting portion. Therefore, since the valve closing force of the high pressure fuel does not act on the overflow valve, the overflow valve will continue to open once it opens.

[Problems to be solved by the device]

However, in this fuel injection device, a feed pressure of 2-3 kg / cm ² is acting on the outer end surface of the second annular fitting portion of the overflow valve, but this feed pressure causes the overflow valve to close. Directional force is acting. Therefore, this feed pressure causes a problem that the opening area of the overflow valve becomes small when the overflow valve is opened, and the disconnection of the injection becomes worse especially at high speed operation. This problem becomes particularly serious when the feed pressure of the fuel is increased in order to eliminate the insufficient filling of the fuel into the fuel pressurizing chamber from the fuel supply port at the time of high engine speed.

[Means for Solving the Problems]

To solve the above problems, according to the present invention, a plunger driven by an engine, a fuel pressurizing chamber filled with fuel and pressurized by the plunger, and a fuel pressurizing chamber in response to fuel pressure in the fuel pressurizing chamber Needle that opens when the fuel pressure exceeds a predetermined pressure, overflow valve slidably inserted in the slide hole, and move the overflow valve in the axial direction of the slide hole. A fuel injection device, comprising: an actuator for controlling the overflow of fuel from the fuel pressurizing chamber, wherein fuel is injected when the overflow valve stops the overflow of fuel from the fuel pressurizing chamber. The valve includes a first annular fitting portion and a second annular fitting portion that are spaced apart from each other in the axial direction of the sliding hole and are in sealing contact with the inner peripheral surface of the sliding hole. Forming an annular valve seat on the inner wall surface of the sliding hole between the first portion and the second annular fitting portion, and The overflow valve between the annular fitting and the second annular fitting is formed with an annular valve that can be seated on the valve seat on the outer peripheral surface of the overflow valve, and the overflow valve between the annular fitting and the first annular fitting is formed. An annular pressurized fuel introducing chamber is formed around the outer peripheral surface to connect the pressurized fuel introducing chamber to the fuel pressurizing chamber, and an annular valve around the outer peripheral surface of the overflow valve between the annular valve portion and the second annular fitting portion. The fuel overflow chamber is formed, and the back pressure chamber formed in the sliding hole on the side opposite to the fuel overflow chamber with respect to the second annular fitting portion is opened to the atmosphere and is attached to the outer end surface of the second annular fitting portion. Atmospheric pressure is applied so that the pressurized fuel in the fuel pressurizing chamber can overflow into the fuel overflow chamber via the pressurized fuel introducing chamber when the annular valve portion of the overflow valve separates from the valve seat. .

[Action]

By applying atmospheric pressure to the outer end surface of the second annular fitting portion, the force in the valve closing direction based on the pressure in the back pressure chamber does not act on the overflow valve.

〔Example〕

1 to 8 show the case where the present invention is applied to a unit injector.

Referring to FIGS. 1 to 4, 1 is a housing body,
Reference numeral 2 denotes a nozzle having a nozzle opening 3 at its tip, 4 denotes a spacer, 5 denotes a sleeve, and 6 denotes a nozzle holder for fixing the nozzle 2, the spacer 4, and the sleeve 5 to the housing body 1. A needle 7 for controlling the opening / closing of the nozzle port 3 is slidably inserted into the nozzle 2, and the top of the needle 7 is attached to a spring retainer 9 via a pressure pin 8.
Connected to. This spring retainer 9 is a compression spring 10
Is always pressed downward, and this pressing force is transmitted to the needle 7 via the pressing pin 8. Therefore, the needle 7 is always urged by the compression spring 10 in the valve closing direction.

On the other hand, a plunger hole 11 is formed in the housing body 1 coaxially with the needle 7, and a plunger 12 is slidably inserted into the plunger hole 11. The upper end of the plunger 12 is connected to a tappet 13, which is a compression spring.
It is always urged upward by 14. This tappet 13
Is moved up and down by a cam (not shown) driven by the engine, and thereby the plunger 12 is moved up and down in the plunger hole 11. On the other hand, in the plunger hole 11 below the plunger 12, a fuel pressurizing chamber 15 defined by the lower end surface 12a of the plunger 12 is formed. This fuel pressurization chamber
15 is connected to a needle pressurizing chamber 18 via a rod-shaped filter 16 and a fuel passage 17 (FIG. 4).
Through the annular fuel passage 19 around the needle 7
Connected to. Further, as shown in FIG. 3, a fuel supply port 20 that opens into the fuel pressurizing chamber 15 is formed on the inner wall surface of the plunger hole 11 when the plunger 12 is in the upper position. 2-3k in fuel pressurization chamber 15
Fuel with a feed pressure of about g / cm ² is supplied. The fuel supply port 20 is, for example, a fuel tank (not shown) via a fuel discharge passage 20a extending in a direction perpendicular to the fuel supply port 20 and a relief valve (not shown) having a valve opening pressure of about ² to 3 kg / cm ^2. Connected to. Further, as shown in FIG. 3, a fuel port 21 is formed on the side opposite to the fuel supply port 20 with respect to the plunger hole 11, which is inevitably formed when the fuel supply port 20 is drilled. The outer end of 21 is closed by a blind plug 22. This fuel port 21 is a fuel supply port
It extends coaxially with 20 and opens in the plunger hole 11. A circumferential groove 23 extending from the fuel supply port 20 toward the fuel port 21 is formed on the inner wall surface of the plunger hole 11. Therefore, the plunger 12 descends and the plunger 12 moves to the fuel supply port 20.
And fuel supply port 20 when fuel port 21 is closed
And the fuel port 21 are communicated with each other through a circumferential groove 23, so that the fuel pressure in the fuel port 21 is proportional to the fuel supply port.
Maintained at the same feed pressure as in 20. The compression spring accommodating chamber 24 accommodating the compression spring 10 for pressing the needle 7 is connected to the fuel supply port 20 via the fuel return passage 25, and the fuel leaked into the compression spring accommodating chamber 24 passes through the fuel return passage 25. It is returned to the inside of the fuel supply port 20 via. On the other hand, a circumferential groove 26 is formed on the outer peripheral surface of the plunger 12 slightly above the lower end surface 12a of the plunger, and the circumferential groove 26 is formed through the fuel escape hole 27 formed in the plunger 12 to allow the fuel It is made to communicate with the inside of the pressure chamber 15.

On the other hand, a sliding hole 30 extending laterally is formed in the housing body 1 in the vicinity of the lateral side in the plunger hole 11. Therefore, the sliding hole 30 is formed such that its axis is parallel to the straight line substantially orthogonal to the common axis of the plunger 12 and the needle 7 with a space therebetween. An overflow valve is installed in this sliding hole 30.
31 is slidably inserted. As shown in FIGS. 1 and 2, the sliding holes 30 are small-diameter holes arranged coaxially with each other.
32 and a large-diameter hole 33, a step portion 34 is formed between the small-diameter hole 32 and the large-diameter hole 33 and is substantially perpendicular to the common axis of the small-diameter hole 32 and the large-diameter hole 33. An annular valve seat 35 is formed at the connecting portion between the step portion 34 and the small diameter hole 32. On the other hand, the overflow valve 31 comprises a small diameter portion 36 located in the small diameter hole 32 and a large diameter portion 37 located in the large diameter hole 33. A first annular fitting portion 38 is formed at the outer end of the small diameter portion 36 for sealingly contacting the inner wall surface of the small diameter hole 32, and the inner wall surface of the large diameter hole 33 is formed at the outer end of the large diameter portion 37. A second annular mating portion 39 is formed that sealingly contacts the. On the outer peripheral surface of the overflow valve 31 between the first annular fitting portion 38 and the second annular fitting portion 39, an annular valve portion 40 that can be seated on the valve seat 35 is formed. An annular pressurized fuel introduction chamber 41 is formed around the outer peripheral surface of the overflow valve 31 between the annular valve portion 40 and the first annular fitting portion 38, and between the annular valve portion 40 and the second annular fitting portion 39. An annular fuel overflow chamber 42 is formed around the outer peripheral surface of the overflow valve 31. As shown in FIG. 2, the diameter of the outer peripheral surface of the large diameter portion 37 that defines the fuel overflow chamber 42 is formed to be larger than the diameter of the small diameter hole 32. Therefore, the volume of the fuel overflow chamber 42 is considerably small. Has been formed. Small diameter hole
The outer end of 32 is closed by a blind plug 43, and an overflow valve back pressure chamber 44 is formed between the blind plug 43 and the overflow valve 31. A compression spring 45 is inserted into the overflow valve back pressure chamber 44 in a direction to separate the annular valve portion 40 of the overflow valve 31 from the valve seat 35, that is, to bias the overflow valve 31 toward the valve opening direction. . In the large diameter portion 37 of the overflow valve 31, a fuel passage 46 that extends in the radial direction and opens into the fuel overflow chamber 42.
A fuel passage 47 that extends in the axial direction and opens into the overflow valve back pressure chamber 44 is formed in the small diameter portion 36. These fuel passages 46, 47 communicate with each other in the overflow valve 31, so that the overflow valve back pressure chamber 44 communicates with the fuel overflow chamber 42 via the fuel passages 46, 47. Outer end surface 48 of the second annular fitting portion 39
A concave groove 49 extending to the vicinity of the fuel passage 46 is formed in the central portion of the. As described above, since the concave groove 49 and the fuel passages 46 and 47 are formed in the overflow valve 31, the mass of the overflow valve 31 is considerably reduced.

As shown in FIG. 4, a fuel overflow passage 50 extending upward from the fuel passage 17 and constantly opening into the pressurized fuel introduction chamber 41 is formed in the housing body 1. This fuel overflow channel 50 is always in communication with the fuel pressurizing chamber 15, and therefore the pressurized fuel introducing chamber 41
Always communicates with the fuel pressurizing chamber 15. Further, as shown in FIG. 7, the overflow valve back pressure chamber 44 is connected to a vertically extending fuel passage 52 through a fuel passage 51, and the lower end portion of the fuel passage 52 is as shown in FIG. It is connected to the fuel port 21. Further, as shown in FIG. 7, the fuel overflow chamber 42 is connected to the fuel outflow passage 53, and the fuel flowing out from the fuel outflow passage 53 is returned to, for example, a fuel tank (not shown).

Large-diameter hole of sliding hole 30 as shown in FIG. 1 and FIG.
A rod guide 61 for guiding and supporting the rod 60 is provided at the outer end of 33.
The rod guide 61 has a rod hole
Equipped with 62. The rod 60 includes a hollow cylindrical small diameter portion 63 slidably inserted in the rod hole 62 and a large diameter portion 64 slidably inserted in the large diameter hole 33. Is brought into contact with the outer end surface 48 of the second annular fitting portion 39. A back pressure chamber is provided between the inner end of the rod guide 61 and the large diameter portion 64 of the rod 60.
65 is formed, and a pressure control chamber 66 defined by the end surface 63a of the small diameter portion 63 is formed at the end of the rod 60 on the side opposite to the large diameter portion 64. Above the pressure control chamber 66 is an actuator.
70 are placed. As shown in FIGS. 1 and 2, the rod 60 has a hollow cylindrical shape, so that the mass of the rod 60 is considerably small.

As shown in FIGS. 1 to 3 and 8, the back pressure chamber 65 formed between the inner end of the rod guide 61 and the large diameter portion 64 of the rod 60 has an atmosphere extending upward from the back pressure chamber 65. The lower end of the communication hole 67a opens. The upper end portion of the atmosphere communication hole 67a is connected to the annular groove 68 formed on the inner peripheral wall surface of the plunger hole 11 via the atmosphere communication hole 67b extending in the lateral direction. This annular groove
Further, 68 is connected to, for example, a fuel tank (not shown) via an atmosphere communication hole 67c. That is, the atmosphere communication hole 67c is opened to the atmosphere. Therefore, the back pressure chamber 65 is connected to the atmosphere communication holes 67a, 67
b, it is opened to the atmosphere through the annular groove 68 and the atmosphere communication hole 67c. The annular groove 68 is formed in the plunger hole 11
Also plays a role in capturing the fuel leaked through between the plunger 12 and.

Actuator 70 as shown in FIGS.
Is an actuator housing 72 formed integrally with the housing body 1 and having a piston hole 71 formed therein, a piston 73 slidably inserted in the piston hole 71, and an end plate 74 covering the top of the actuator housing 72. , End plates
An end plate holder 75 for fixing the 74 to the top of the actuator housing 72 and a synthetic resin cap 76 for covering the upper end of the end plate 74 are provided. Between the piston 73 and the end plate 74, a piezo piezoelectric element 77 in which a large number of piezoelectric element plates are laminated is inserted,
A variable volume chamber 78 defined by the lower end surface of the piston 73 is formed in the piston hole 71 below the piston 73. The variable volume chamber 78 communicates with the pressure control chamber 66 via the fuel passage 79. An annular cooling chamber 80 is formed between the piston 73 and the actuator housing 72, and a compression spring 81 that constantly biases the piston 73 upward is inserted in the cooling chamber 80. When the piezoelectric element 77 is charged with electric charge, the piezoelectric element 77 expands in the axial direction, and as a result, the volume of the variable volume chamber 78 decreases. On the other hand, when the electric charge charged in the piezoelectric element 77 is discharged, the piezoelectric element 77 contracts in the axial direction, and as a result, the volume of the variable volume chamber 78 increases.

As shown in FIG. 5, the check valve 82 is attached to the housing body 1.
Is inserted. This check valve 82 is a ball 84 that controls the opening and closing of the valve port 83, and a rod that controls the lift amount of the ball 84.
85 and a compression spring 86 that constantly pushes the ball 84 and the rod 85 upward, so that the valve port 83 is normally closed by the ball 84. The valve port 83 of the check valve 82 is connected to, for example, a low-pressure fuel pump (not shown) via the fuel inflow passage 87, and low-pressure fuel of 2-3 kg / cm ² is supplied from the fuel inflow passage 87. The check valve 82 can flow only to the inside of the variable volume chamber 78. Therefore, when the fuel pressure in the variable volume chamber 78 falls below 2-3 kg / cm ² , the fuel volume is changed through the check valve 82. Replenished in chamber 78. Therefore the variable volume chamber 78
The inside is always filled with fuel. On the other hand, as shown in FIG. 5, the lower end of the cooling chamber 80 is connected to, for example, a low pressure fuel pump (not shown) via a fuel inflow passage 88, and
Low-pressure fuel of ~ 3 kg / cm ² flows from the fuel inlet passage 88 to the cooling chamber 80.
Supplied within. This fuel cools the piezoelectric element 77. Further, as shown in FIG. 3, the lower end of the cooling chamber 80 is connected to the fuel supply port 20 through the fuel outflow passage 89, and the cooling chamber 80 extends from the cooling chamber 80 toward the fuel supply port 20. A non-return valve 90 is provided which is only flowable. This check valve 90 is a ball that controls the opening and closing of the valve port 91.
92, a rod 93 that regulates the lift amount of the ball 92, and a compression spring 94 that constantly presses the ball 92 and the rod 93 upward. The fuel in the cooling chamber 80 cools the piezoelectric element 77 and then passes through the fuel outflow passage 89 to the fuel supply port 20.
Is supplied to.

As described above, the fuel is supplied to the cooling chamber 80 through the fuel inflow passage 88.
Then, this fuel cools the piezoelectric element 77 and then is supplied into the fuel supply port 20 through the fuel outflow passage 89 and the check valve 90. As shown in FIG. 3, when the plunger 12 is at the upper position, the fuel is supplied from the fuel supply port 20 into the fuel pressurizing chamber 15, so that the fuel pressurizing chamber 15 has an amount of about ² to 3 kg / cm ^{2 at} this time. The pressure is low. On the other hand, at this time, the piezoelectric element 77 is in the maximum contraction position, and at this time, the fuel pressure in the variable volume chamber 78 and the pressure control chamber 66 is a low pressure of about ² to 3 kg / cm ² . Therefore, at this time, the overflow valve 31 is moved to the right in FIGS. 1 and 2 by the spring force of the compression spring 45 so that the annular valve portion 40 is separated from the valve seat 35, that is, the overflow valve 31 is opened. is doing. Therefore, the low-pressure fuel in the fuel pressurizing chamber 15 is supplied to the fuel overflow chamber 42 via the fuel overflow passage 50 and the pressurized fuel introducing chamber 41 on the one hand, and the fuel passages 52, 51 and the overflow valve on the other hand. The fuel is supplied into the fuel overflow chamber 42 via the back pressure chamber 44 and the fuel passages 47 and 46 in the overflow valve 31, and the fuel supplied into the fuel overflow chamber 42 is discharged from the fuel outflow passage 53. Therefore, at this time, the pressurized fuel introduction chamber 4
1, ^{2 to 3} kg / cm ² in the fuel overflow chamber 42 and the overflow valve back pressure chamber 44
Filled with low pressure fuel.

Next, when the plunger 12 descends, the fuel supply port 20 and the fuel port 21 are closed by the plunger 12, but the overflow valve 31 is opened, so that the fuel in the fuel pressurizing chamber 15 overflows the fuel overflow passage 50. It flows into the fuel overflow chamber 42 via the pressurized fuel introduction chamber 41 of the flow valve 22. Therefore, at this time as well, the fuel pressurizing chamber 15
The fuel pressure inside is as low as 2-3 kg / cm ² .

Next, when the piezoelectric element 77 is charged with electric charge to start fuel injection, the piezoelectric element 77 expands in the axial direction, and as a result, the piston 73 descends, so that the variable volume chamber 78 is lowered.
And the fuel pressure in the pressure control chamber 66 rises rapidly. When the fuel pressure in the pressure control chamber 66 rises, the rod 60 moves to the left in FIGS. 1 and 2, so that the overflow valve 31 also moves to the left, and the annular valve of the overflow valve 31 moves. Part 40 is valve seat 35
And the overflow valve 31 is closed. When the overflow valve 31 is closed, the fuel pressure in the fuel pressurizing chamber 15 rapidly rises due to the downward movement of the plunger 12, and the fuel pressure in the fuel pressurizing chamber 15 is a predetermined pressure, for example 1500 kg / cm ² When the above constant pressure is exceeded, the needle 7 is opened and fuel is injected from the nozzle port 3. At this time, high pressure is also applied to the pressurized fuel introducing chamber 41 of the overflow valve 31 via the fuel overflow passage 50, but since the pressure receiving areas of both axial end faces of the pressurized fuel introducing chamber 41 are equal, the high pressure causes overflow. The driving force does not act on the flow valve 31.

Next, when the charge charged in the piezoelectric element 77 is discharged to stop the fuel injection, the piezoelectric element 77 is discharged.
77 contracts. As a result, the piston 73 is raised by the spring force of the compression spring 81, and the fuel pressure in the variable volume chamber 78 and the pressure control chamber 66 is reduced. As described above, since the back pressure chamber 65 is open to the atmosphere, the pressure in the back pressure chamber 65 does not generate the force for urging the overflow valve 31 in the valve opening direction. Further, the masses of the rod 60 and the overflow valve 31 are small, so that when the fuel pressure in the pressure control chamber 66 decreases, the rod 60 and the overflow valve 31 immediately move to the right in FIGS. 1 and 2 due to the spring force of the compression spring 45. Moving toward the annular valve part of the overflow valve 31
40 separates from the valve seat 35 and the overflow valve 31 opens immediately. When the overflow valve 31 is opened, the high-pressure fuel in the fuel pressurizing chamber 15 is jetted into the fuel overflow chamber 42 through the fuel overflow channel 50 and the pressurized fuel introducing chamber 41, and as a result, the fuel pressurizing chamber The fuel pressure in 15 drops rapidly. On the other hand, when the pressurized fuel is jetted into the fuel overflow chamber 42 because the volume of the fuel overflow chamber 42 is small, the fuel pressure in the fuel overflow chamber 42 temporarily becomes considerably high. As described above, the second portion is provided between the outer end surface 48 of the large diameter portion 37 of the overflow valve 31 and the fuel overflow chamber 42.
Since the annular fitting portion 39 is formed, the high pressure generated in the fuel overflow chamber 42 does not act on the outer end surface 48 of the large diameter portion 37 of the overflow valve 31, and the outer end surface 48 is affected by atmospheric pressure. is doing. As a result, the high pressure generated in the fuel overflow chamber 42 is due to the large diameter hole of the sliding hole 30.
It acts only in the opening direction of the overflow valve 31 with respect to the area obtained by subtracting the cross-sectional area of the small diameter hole 32 from the cross-sectional area of 33.
31 is urged in the valve opening direction by the high pressure generated in the fuel overflow chamber 42. When high-pressure fuel is ejected into the fuel overflow chamber 42, a part of this high-pressure fuel is ejected from the fuel passage 47 into the overflow valve back pressure chamber 44 via the fuel passage 46 in the overflow valve 31. When high-pressure fuel is ejected from the fuel passage 47 in this way, a biasing force in the valve opening direction acts on the overflow valve 31 due to the reaction force of the ejection action. In addition, the high-pressure fuel is overflow valve back pressure chamber
When jetting out into the 44, the fuel pressure in the overflow valve back pressure chamber 44 rises,
As a result, the fuel pressure in the overflow valve back pressure chamber 44 acts on the overflow valve 31 in the opening direction. When the overflow valve 31 is opened in this way, the pressure in the fuel overflow chamber 42 rises, the fuel is ejected from the fuel passage 47, and the pressure in the overflow valve back pressure chamber 44 rises. As soon as the annular valve portion 40 of the overflow valve 31 leaves the valve seat 35 due to the urging force of the overflow valve 31, the overflow valve 31 is rapidly opened, and the overflow valve 31 is opened once it is opened. Held in. Therefore, when the overflow valve 31 is opened, the fuel pressure in the fuel pressurizing chamber 15 is continuously and rapidly decreased. Therefore, immediately after the overflow valve 31 is opened, the needle 7 is lowered and the fuel injection is stopped. Further, when the engine speed or the engine load becomes high, the pressure of the pressurized fuel in the fuel pressurizing chamber 15 becomes high, so that the fuel overflow chamber 42 when the overflow valve 31 opens.
The pressure rise inside becomes large. Further, at this time, the fuel passage 47
The fuel injection action from is strong, and the pressure rise in the overflow valve back pressure chamber 44 increases. Therefore, as the engine speed or engine load increases, the force for urging the overflow valve 31 in the valve opening direction increases accordingly. On the other hand, when the piezo-piezoelectric element 77 is contracted to open the overflow valve 31 and the fuel pressure in the variable volume chamber 78 is reduced, the fuel pressure in the variable volume chamber 78 is changed to the fuel inflow passage 87 (the fifth If it becomes lower than the fuel pressure in the figure, low-pressure fuel is replenished into the variable volume chamber 78 via the check valve 82.

When the plunger 12 is further lowered, the circumferential groove 26 formed on the outer peripheral surface of the plunger 12 communicates with the fuel supply port 20 and the fuel port 21. At this time, the overflow valve 31 is normally open, but if the overflow valve 31 is closed for some reason, the fuel pressure in the fuel pressurizing chamber 15 is still high, and therefore the circumferential groove is closed. When 26 communicates with the fuel supply port 20 and the fuel port 21, the high-pressure fuel in the fuel pressurizing chamber 15 passes through the fuel escape hole 27 and the circumferential groove 26 and the fuel supply port 20.
And jets into the fuel port 21. At this time, the high-pressure fuel injected into the fuel supply port 20 and the fuel port 21 does not flow into the cooling chamber 80 because the check valve 90 is provided,
This high-pressure fuel is passed through the fuel passages 51 and 52 to the overflow valve back pressure chamber 44.
Into the fuel overflow chamber 42 via the fuel passages 46 and 47 in the overflow valve 31. As a result, the overflow valve back pressure chamber 4
6,47 and the fuel overflow chamber 42 becomes high pressure, so that the overflow valve 31
A strong force in the valve opening direction acts on the valve, and thus the overflow valve 31 is forcibly opened. Therefore, the circumferential groove 26 is
Plays a role as a fail-safe that prevents the valve from being held closed for some reason.

Next, the plunger 12 rises and returns to the upper end position, and starts descending again.

In this way, the fuel in the fuel pressurizing chamber 15 is
A strong downward driving force is applied to achieve a high pressure of 00 kg / cm ² or more. However, since the sliding hole 30 is arranged on the side of the plunger 12, the sliding hole 30 is not distorted, and thus the smooth sliding action of the overflow valve 31 can be ensured. Further, since the sliding hole 30 is arranged laterally on the side of the plunger 12, the sliding hole 30 can be arranged close to the fuel pressurizing chamber 15. As a result, the length of the fuel overflow passage 50 can be shortened, so that the volume of the fuel pressurizing chamber 15 including the fuel overflow passage 50 can be reduced. Therefore, the fuel pressure in the fuel pressurizing chamber 15 can be easily increased, and good atomization of the injected fuel can be ensured. Further, since the volume of the fuel pressurizing chamber 15 can be reduced, the fuel pressurizing chamber 15 can be opened when the overflow valve 31 is opened.
The fuel pressure in 15 drops immediately and the fuel injection stops immediately. Therefore, since the fuel injection does not continue under a low pressure after the overflow valve 31 is opened, it is possible to suppress the generation of smoke and to improve the engine output and the fuel consumption rate. Further, the fuel injection amount immediately rises in response to the opening / closing operation of the overflow valve 31, and the fuel injection immediately stops, so that good pilot injection can be performed.

Further, by forming the sliding hole 30 so as to extend laterally on the side of the plunger 12, the width of the unit injector can be narrowed, and further, the piezoelectric element 77.
Is arranged so that its axis is substantially perpendicular to the common axis of the sliding hole 30 and the rod 60, that is, substantially parallel to the common axis of the plunger 12 and the needle 7, the side of the unit injector is The width can be further narrowed.

[Effect of device]

Since the back pressure chamber is open to the atmosphere, when the overflow valve opens, the opening area of the overflow valve becomes sufficiently large. As a result, the fuel pressure in the fuel pressurizing chamber is rapidly reduced, so that good fuel injection can be ensured.

[Brief description of drawings]

1 is a side sectional view of the unit injector taken along the line II in FIG. 4, FIG. 2 is an enlarged side sectional view of a portion of FIG. 1, and FIG. 3 is a sectional view taken along the line III-III in FIG. FIG. 4 is a side sectional view taken along line IV-IV in FIG. 1, FIG. 5 is a side sectional view taken along line VV in FIGS. 1 and 7, and FIG. 6 is a plan view of FIG. 1, FIG. 7 is a plan sectional view taken along line VII-VII of FIG. 1, and FIG. 8 is a plan sectional view taken along line VIII-VIII of FIG. is there. 3 ... Nozzle port, 7 ... Needle, 11 ... Plunger hole, 12 ... Plunger, 15 ... Fuel pressurizing chamber, 20 ... Fuel supply port, 30 ... Sliding hole, 31 ... Overflow valve , 35 ... Valve seat, 38 ... First annular fitting part, 39 ... Second annular fitting part, 40 ... Annular valve part, 41 ... Pressurized fuel introducing chamber, 42 ... Fuel overflow chamber , 60 ... Rod, 65 ... Back pressure chamber, 66 ... Pressure control chamber, 67a, 67b, 67c ... Atmosphere communication hole, 77 ... Piezo-piezoelectric element, 78 ... Variable volume chamber.

Claims (1)

[Scope of utility model registration request] 1. A plunger driven by an engine, a fuel pressurizing chamber which is filled with fuel and pressurized by the plunger, and a pressure which is predetermined in response to fuel pressure in the fuel pressurizing chamber. The needle that opens when the temperature exceeds the limit, the overflow valve that is slidably inserted into the sliding hole, and the overflow valve that moves the overflow valve in the axial direction of the sliding hole to remove the overflow valve from the fuel pressurizing chamber. A fuel injection device, comprising: an actuator for controlling the overflow of fuel, wherein the fuel injection is performed when the overflow valve stops the overflow of fuel from the fuel pressurizing chamber. A first annular fitting portion and a second annular fitting portion which are spaced apart from each other in the axial direction of the moving hole and are in sealing contact with the inner peripheral surface of the sliding hole; The annular valve seat is formed on the inner wall surface of the sliding hole between the second annular fitting portions, and the first annular fitting portion and the first annular fitting portion are formed. An annular valve portion which can be seated on the valve seat is formed on the outer peripheral surface of the overflow valve between the annular fitting portions, and an annular valve portion is provided around the outer peripheral surface of the overflow valve between the annular valve portion and the first annular fitting portion. A pressurized fuel introducing chamber is formed, the pressurized fuel introducing chamber is connected to the fuel pressurizing chamber, and an annular fuel overflow is formed around the overflow valve outer peripheral surface between the annular valve portion and the second annular fitting portion. A chamber, and the back pressure chamber formed in the sliding hole on the side opposite to the fuel overflow chamber with respect to the second annular fitting portion is opened to the atmosphere to form a large space on the outer end surface of the second annular fitting portion. Fuel which is made to cause the pressurized fuel in the fuel pressurizing chamber to overflow into the fuel overflow chamber via the pressurized fuel introducing chamber when the annular valve portion of the overflow valve is separated from the valve seat by applying atmospheric pressure. Injection device.