JPH0640928Y2 - 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.

[Conventional technology]

A plunger driven by the engine, a fuel pressurizing chamber filled with fuel and pressurized by the plunger, and when the fuel pressure exceeds a predetermined pressure in response to the fuel pressure in the fuel pressurizing chamber. The needle that opens, 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 moves in the axial direction of the sliding hole to overflow. The present applicant has already proposed a unit injector that includes a piezoelectric element that controls the opening and closing of a flow valve, and that performs fuel injection when the overflow valve is closed (Japanese Patent Application No. 62-335259). (See the official gazette). 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 enlarged heads, and this pressurized fuel introducing chamber is connected to the fuel pressurizing chamber. An overflow valve back pressure chamber defined by an annular fitting portion is formed in the sliding hole, and a spring for urging the overflow valve in the valve opening direction is inserted into the overflow valve back pressure chamber. The back pressure chamber and the fuel overflow chamber are connected to each other via a fuel passage formed in the overflow valve, and the overflow valve is closed against the spring force of the spring inserted in the overflow valve back pressure chamber. By this, fuel injection is started, and when the expansion head is separated from the valve seat by the spring force of this spring, the pressurized fuel in the fuel pressurizing chamber overflows into the fuel overflow chamber via the pressurized fuel introducing chamber, As a result, fuel injection is stopped.

[Problems to be solved by the device]

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, the high pressure acts on the overflow valve in the valve closing direction. On the other hand, when the fuel pressure in the fuel overflow chamber becomes high, the high-pressure fuel flows into the overflow valve back pressure chamber through the fuel passage formed in the overflow valve. As a result, the fuel pressure in the overflow valve back pressure chamber becomes high, and the high pressure causes a force in the valve opening direction to act on the overflow valve. However, if a fuel passage that connects the overflow valve back pressure chamber and the fuel overflow chamber is formed in the overflow valve, the cross-sectional area of this fuel passage is limited because of the diameter of the overflow valve. This is not possible and therefore this fuel passage has a relatively high flow resistance. Therefore, when a high pressure is generated in the fuel overflow chamber, this high pressure is not immediately transmitted to the overflow valve back pressure chamber through the fuel passage, and the fuel pressure is lowered while flowing in the fuel passage. The fuel pressure generated in the back pressure chamber becomes low. Thus, the strong force in the valve opening direction does not act on the overflow valve, and the force in the valve closing direction that acts on the overflow valve is strong, so that the overflow valve opens again as soon as it opens. The valve will be closed. As a result, the fuel is not properly injected, and there is a problem that the fuel injection is particularly short.

[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 that includes an actuator that controls the overflow of fuel from the fuel pressurizing chamber, and that injects fuel when the overflow valve stops the overflow of fuel from the fuel pressurizing chamber. An annular valve seat is formed on the inner wall surface of the hole, an annular fitting portion is formed at one end of the overflow valve for sealingly contacting the inner peripheral surface of the slide hole, and an annular valve is formed on the outer peripheral surface of the overflow valve. Forming an annular valve portion that is spaced from the fitting portion and that can be seated on the valve seat; An annular pressurized fuel introducing chamber is formed around the outer peripheral surface of the overflow valve between the annular fitting portions to connect the pressurized fuel introducing chamber to the fuel pressurizing chamber, and at the side opposite to the pressurized fuel introducing chamber with respect to the valve seat. The fuel overflow chamber is formed, and the overflow valve back pressure chamber defined by the annular fitting portion is formed in the sliding hole on the side opposite to the pressurized fuel introduction chamber with respect to the annular fitting portion. A spring for urging the overflow valve toward the fuel overflow chamber is inserted into the chamber, so that the overflow valve back pressure chamber and the fuel overflow chamber are connected to the fuel passage formed in the overflow valve and the surroundings of the overflow valve. Communicate with each other through separate fuel passages formed in the housing, and pressurize the pressurized fuel in the fuel pressurizing chamber through the pressurized fuel introducing chamber when the annular valve portion of the overflow valve separates from the valve seat. I try to make it overflow into the overflow chamber.

[Action]

The cross-sectional area of the fuel passage can be increased by providing a plurality of fuel passages that communicate the overflow valve back pressure chamber and the fuel overflow chamber. As a result, when a high pressure is generated in the fuel overflow chamber, a high pressure is immediately generated in the overflow valve back pressure chamber, and a strong force in the valve opening direction acts on the overflow valve. As a result, once the overflow valve opens, it will continue to open.
Thus, the fuel injection is stopped immediately.

〔Example〕

1 to 7 show the case where the present invention is applied to a unit injector.

Referring to FIGS. 3 to 6, 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. 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. 5 and 6, 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. 6, 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. Overflow valve 31 on the second annular fitting portion 39 side
A concave groove extending to the vicinity of the fuel passage 46 at the center of the end face 48 of the
49 is formed. 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.

On the other hand, as shown in FIGS. 1, 3, and 4, the plunger hole slightly above the fuel supply port 20.
An annular groove 50 is formed on the inner peripheral surface of 11, and the circumferential groove 26 formed on the plunger 12 is formed at a position communicating with the annular groove 50 when the plunger 12 reaches the vicinity of the lowermost position. As shown in FIG. 1, the annular groove 50 is provided on the one hand with the fuel passage.
Connected to the fuel overflow chamber 42 via 51, on the other hand a fuel passage
The overflow valve back pressure chamber 44 is connected via 52, so that the overflow valve back pressure chamber 44 is connected to the fuel overflow chamber 42 via the fuel passages 51 and 52. Therefore, the overflow valve back pressure chamber 44 and the fuel overflow chamber 42 are connected to the fuel passages 46 and 47 formed in the overflow valve 31 and the overflow valve 31.
Fuel passages 51, 52 formed in the surrounding housing body 1
Will be able to communicate with each other.

As shown in FIG. 4, a fuel overflow passage 53 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 passage 53 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. 1, the lower portion of the fuel overflow chamber 42 is connected to a fuel outflow passage 54, and the fuel flowing out from this fuel outflow passage 54 is returned to, for example, a fuel tank (not shown).

Large-diameter hole of sliding hole 30 as shown in FIG. 5 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. A rod back pressure chamber 65 is formed between the inner end portion of the rod guide 61 and the large diameter portion 64 of the rod 60, which is brought into contact with the end surface 48 of the overflow valve 31. 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 opposite to the large diameter portion 64. An actuator 70 is arranged above the pressure control chamber 66. As shown in FIGS. 5 and 6, the rod 60 has a hollow cylindrical shape, so that the mass of the rod 60 is considerably small.

Actuator 70 as shown in FIGS. 5 and 7.
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, while when the electric charge charged in the piezoelectric element 77 is discharged, the piezoelectric element 77 is discharged. Contract axially, resulting in an increase in the volume of variable volume chamber 78.

As shown in FIG. 7, 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 downward, 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. 7, the lower end of the cooling chamber 80 is connected to, for example, a low pressure fuel pump (not shown) through 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. Further, as shown in FIGS. 5 and 6, the lower end of the cooling chamber 80 is connected to the rod back pressure chamber 65 through the fuel passage 95, so that the rod back pressure chamber 65 is ^{2 to 3} kg / cm ^2.
Filled with fuel.

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. 5 and 6 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 channel 53 and the pressurized fuel introducing chamber 41, and the fuel supplied to the fuel overflow chamber 42 is the fuel. It is discharged from the outflow passage 54. Therefore, at this time, the pressurized fuel introduction chamber 41 and the fuel overflow chamber 42
Also, the overflow valve back pressure chamber 44 is filled with low-pressure fuel of 2-3 kg / cm ² .

Then, when the plunger 12 descends, the fuel supply port 20 is closed by the plunger 12, but the fuel in the fuel pressurizing chamber 15 is closed because the overflow valve 31 is open, so that the fuel in the fuel pressurizing chamber 15 is overflowed by the fuel overflow passage 53 And flows into the fuel overflow chamber 42 through the pressurized fuel introduction chamber 41. Therefore, at this time as well, the fuel pressure in the fuel pressurizing chamber 15 is 2 to
The low pressure is about 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. 5 and 6, 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 53, 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, the masses of the rod 60 and the overflow valve 31 are small. Therefore, when the fuel pressure in the pressure control chamber 66 decreases, the rod 60 and the overflow valve 31 are immediately moved by the spring force of the compression spring 45, as shown in FIGS. In the figure, the annular valve portion 40 of the overflow valve 31 moves to the right and the valve seat 35
The overflow valve 31 opens immediately away from. 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 via the fuel overflow channel 53 and the pressurized fuel introducing chamber 41,
As a result, the fuel pressure in the fuel pressurizing chamber 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, since the second annular fitting portion 39 is formed between the end surface 48 of the large diameter portion 37 of the overflow valve 31 and the fuel overflow chamber 42, the high pressure generated in the fuel overflow chamber 42 overflows. It does not act on the end surface 48 of the large diameter portion 37 of the flow valve 31. As a result, the high pressure generated in the fuel overflow chamber 42 is only in the valve opening direction of the overflow valve 31 with respect to the area obtained by subtracting the sectional area of the small diameter hole 32 from the sectional area of the large diameter hole 33 of the sliding hole 30. Therefore, the overflow valve 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 supplied into the overflow valve back pressure chamber 44 through the fuel passages 46 and 47 in the overflow valve 31, and on the other hand. Then, the fuel is supplied into the overflow valve back pressure chamber 44 through the fuel passage 51, the annular groove 50 and the fuel passage 52 formed in the housing body 1. As described above, the high-pressure fuel in the fuel overflow chamber 42 is supplied into the overflow valve back pressure chamber 44 through the plurality of fuel passages, so that the flow passage area of the fuel passage is increased. The high-pressure fuel is immediately supplied to the overflow valve back pressure chamber 44 without a pressure drop. Therefore, the fuel overflow chamber 42
As soon as high pressure is generated in the overflow valve back pressure chamber 44, high pressure is generated in the overflow valve back pressure chamber 44, and as a result, the fuel pressure in the overflow valve back pressure chamber 44 causes the overflow valve 31 to open strongly. A biasing force in the direction acts. Further, when a high pressure is generated in the fuel overflow chamber 42, the fuel flowing in the fuel passages 46, 47 in the overflow valve 31 is ejected from the fuel passage 47 into the overflow valve back pressure chamber 44. 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. When the overflow valve 31 is opened in this way, the fuel overflow chamber 42
The internal valve portion of the overflow valve 31 because the urging force in the valve opening direction acts on the overflow valve 31 due to the pressure increase in the inside, the fuel injection action from the fuel passage 47, and the pressure increase in the overflow valve back pressure chamber 44. 40 is the seat
As soon as it leaves 35, the overflow valve 31 is opened rapidly, and once the overflow valve 31 is opened, it is kept in the open state. 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. On the other hand, in order to open the overflow valve 31, the piezoelectric element 77
When the fuel pressure in the variable volume chamber 78 is reduced and the fuel pressure in the variable volume chamber 78 is reduced,
If the fuel pressure becomes lower than the fuel pressure in FIG. 7, low-pressure fuel is replenished into the variable volume chamber 78 via the check valve 82.

Then, when the plunger 12 is further lowered, the circumferential groove 26 formed on the outer peripheral surface of the plunger 12 communicates with the inside of the annular groove 50.
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 thus the circumferential groove 26 Is an annular groove
When communicating with 50, the high-pressure fuel sent from the fuel escape hole 27 into the annular groove 50 through the circumferential groove 26 is, on the one hand, the fuel passage 51.
Is supplied to the fuel overflow chamber 42 via the
It is supplied to the overflow valve back pressure chamber 44 via 52. as a result,
A strong force in the valve opening direction acts on the overflow valve 31, and thus the overflow valve 31 is forcibly opened. Therefore, these circumferential groove 26 and annular groove 50 are overflow valves.
31 provides a fail-safe action to prevent the valve from being held closed.

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

8 to 10 show another embodiment of the unit injector. This embodiment has almost the same structure as the embodiment shown in FIGS. 1 to 10, so only the different parts of the structure will be explained.

In this embodiment, the annular groove 50 and the fuel passages 51 and 52 formed on the inner peripheral surface of the plunger hole 11 as shown in FIGS. 1, 3 and 4 are not provided, As shown in the figure, a fuel passage 100 that communicates the fuel overflow chamber 42 and the overflow valve back pressure chamber 44 is formed in the housing body 1 in place of the fuel passages 51 and 52. Also in this embodiment, the fuel overflow chamber
When high-pressure fuel is jetted into the inside 42, a part of this high-pressure fuel is supplied into the overflow valve back pressure chamber 44 through the fuel passages 46 and 47 in the overflow valve 31 on the one hand, and inside the housing body 1 on the other hand. It is supplied into the overflow valve back pressure chamber 44 through the fuel passage 100 formed in the. Therefore, as soon as a high pressure is generated in the fuel overflow chamber 42, a high pressure is generated in the overflow valve back pressure chamber 44, so that the overflow valve 31 is strongly driven by the fuel pressure in the overflow valve back pressure chamber 44. A biasing force in the valve opening direction will act.

Also, in this embodiment, the circumferential groove formed on the plunger 12 is
26 is formed at a position where it communicates with the fuel supply port 20 and the fuel port 21 when the plunger 12 reaches the vicinity of the lowermost position, and therefore the circumferential groove 26 shown in FIGS. 8 and 9 is formed.
Are formed below as compared with the embodiment shown in FIGS. 3 and 4. Further, as shown in FIGS. 9 and 10, the fuel port 21 is connected to the overflow valve back pressure chamber 44 via a pair of fuel passages 101 and 102. When the plunger 12 reaches the vicinity of the lowermost position and the circumferential groove 26 communicates with the fuel supply port 20 and the fuel port 21, the overflow valve 31 is normally open. However, at this time, 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 26 becomes the fuel supply port.
When communicating with 20 and the fuel port 21, high-pressure fuel flows into the fuel supply port 20 and the fuel port 21 through the fuel escape hole 27 and the circumferential groove 26. At this time, since the check valve 90 is provided, the high-pressure fuel that has flowed into the fuel supply port 20 and the fuel port 21 is fed into the overflow valve back pressure chamber 44 through the fuel passages 101 and 102, thus The overflow valve 31 is forcibly opened. Therefore, also in this case, the circumferential groove 26 has a fail-safe function for preventing the overflow valve 31 from being held in the closed state. In any of the above-mentioned embodiments, the plunger 12 is given a strong downward driving force so that the fuel pressure in the fuel pressurizing chamber 15 becomes a high pressure of 1500 kg / cm ² or more. However, the sliding hole 30
Since it is arranged on the side of 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 channel 53 can be shortened, so that the volume of the fuel pressurizing chamber 15 including the fuel overflow channel 53 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 pressure in the fuel pressurizing chamber 15 immediately decreases when the overflow valve 31 opens, and the fuel injection immediately stops. 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]

By connecting the fuel overflow chamber and the overflow valve back pressure chamber to each other through a plurality of fuel passages, a strong force in the valve opening direction is applied to the overflow valve when the fuel pressure in the fuel overflow chamber becomes high. Can be operated. As a result, when the overflow valve is opened to stop the fuel injection, the overflow valve can be reliably held in the open state.

[Brief description of drawings]

1 is a plan sectional view of the unit injector taken along line II of FIG. 5, FIG. 2 is a plan view of FIG. 1, and FIG. 3 is a side sectional view taken along line III-III of FIG. Fig. 4 is a side sectional view taken along the line IV-IV in Fig. 5, Fig. 5 is a side sectional view taken along the line VV in Fig. 4, and Fig. 6 is a part of Fig. 5. FIG. 7 is an enlarged side sectional view of FIG. 7, FIG. 7 is a side sectional view taken along the line VII-VII of FIGS. 1 and 5, and FIG. 8 is a side sectional view showing another embodiment of the unit injector. 8 is a side sectional view taken along the line IX-IX in FIG. 8, and FIG. 10 is a plan sectional view taken along the line XX in FIG. 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 , 44 …… Overflow valve back pressure chamber, 46, 47, 51, 52, 100, 101, 102 …… Fuel passage, 50 …… Annular groove, 60 …… Rod, 66 …… Pressure control chamber, 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. An actuator for controlling the overflow of fuel, wherein the fuel injection device performs fuel injection when the overflow valve stops the overflow of fuel from the fuel pressurizing chamber, the inner wall surface of the sliding hole An annular valve seat is formed on the upper surface of the overflow valve, an annular fitting portion is formed at one end of the overflow valve for sealingly contacting the inner peripheral surface of the slide hole, and the annular fitting is formed on the outer peripheral surface of the overflow valve. An annular valve portion which is arranged at a distance from the joining portion and which can be seated on the valve seat, and An annular pressurized fuel introducing chamber is formed around the outer peripheral surface of the overflow valve between the fitting parts, the pressurized fuel introducing chamber is connected to the fuel pressurizing chamber, and the valve seat is opposite to the pressurized fuel introducing chamber. Side, a fuel overflow chamber is formed on the side, and an overflow valve back pressure chamber defined by the annular fitting portion is formed in the sliding hole on the side opposite to the pressurized fuel introducing chamber with respect to the annular fitting portion. A spring for urging the overflow valve toward the fuel overflow chamber is inserted into the flow valve back pressure chamber so that the overflow valve back pressure chamber and the fuel overflow chamber are connected to the fuel passage and the overflow passage formed in the overflow valve. The pressurized fuel in the fuel pressurizing chamber is introduced when the annular valve portion of the overflow valve is communicated with each other through separate fuel passages formed in the housing around the flow valve, and the pressurized fuel is introduced. A fuel injection device that allows the fuel to overflow into the fuel overflow chamber through the chamber.