JP2600330B2 - Fuel injection device - Google Patents

Description

The present invention relates to a fuel injection device.

[Conventional technology]

A plunger driven by the engine, a fuel pressurized 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 pressurized chamber. A needle that opens the valve, a sliding hole and a pressure control chamber coaxially arranged with each other, and a sliding hole that is slidably inserted into the sliding hole and responsive to the working liquid pressure in the pressure control chamber. An overflow valve slidably controlled in the direction of a common axis of the pressure control chamber, a piezoelectric element whose axis is substantially perpendicular to the above-mentioned common axis, and a variable element which is filled with a working liquid and whose volume is controlled by the piezoelectric element. A volume chamber, and a working liquid passage communicating the variable volume chamber and a pressure control chamber disposed on the axis of the piezoelectric element. The overflow valve is closed by an increase in the working liquid pressure in the pressure control chamber. The fuel overflow from the fuel pressurization chamber stops. Unit injector fuel is injected has already been proposed by the present applicant (see Japanese Patent Application Sho 62-335259 discloses) when the. 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 the sliding hole. The overflow valve is located in the fuel overflow chamber and is located on the valve seat. It has an enlarged head that can be seated, and when the pressure of the working liquid in the pressure control chamber suddenly rises due to a sudden decrease in the volume of the variable volume chamber due to the extension action of the piezoelectric element, the enlarged head of the overflow valve rises. The overflow valve closes upon sitting on the valve seat, thereby stopping the overflow of the fuel from the fuel pressurizing chamber and starting the fuel injection.

[Problems to be solved by the invention]

However, the extension action of the piezoelectric element is extremely fast, so that the working liquid in the pressure control chamber rapidly increases in pressure. As a result, the sliding valve is rapidly urged in the valve closing direction by the pressure-raised working fluid, so that the enlarged head of the overflow valve collides with the valve seat at high speed. As described above, when the enlarged head collides with the valve seat at a high speed, the enlarged head rebounds at the valve seat, and thus, once the overflow valve is closed, it is opened again. When the enlarged head rebounds at the valve seat, the overflow valve is again urged in the valve closing direction by the working liquid pressure in the pressure control chamber, and again collides with the valve seat and rebounds. As described above, when the overflow valve is to be closed, the overflow valve repeats the opening and closing operation, so that the fuel pressure in the fuel pressurizing chamber rises while fluctuating sharply. However, if the fuel pressure in the fuel pressurized chamber fluctuates drastically, the fuel injection rate fluctuates drastically, making it impossible to form a good spray. Further, since the fuel injection pressure does not become sufficiently high, let's inject a certain amount of fuel In this case, there is a problem that the injection period becomes longer.

However, whether or not the overflow valve rebounds at the valve seat depends on the mass of the overflow valve. That is, the inertial force in the opening direction of the overflow valve when the overflow valve rebounds at the valve seat increases as the mass of the overflow valve increases. On the other hand, since the working liquid pressure generated in the pressure control chamber is substantially constant, the force in the valve closing direction acting on the overflow valve by the working liquid pressure is substantially constant. When the mass of the overflow valve is large, and thus the inertial force in the opening direction of the overflow valve is large, the inertial force overcomes the hydraulic fluid pressure, so that the overflow valve is once closed and then opened again. On the other hand, when the mass of the overflow valve is small, and thus the inertia force in the opening direction of the overflow valve is small, the working liquid pressure overcomes the inertial force, and thus, once the overflow valve is closed, the overflow valve is closed. Is held. Therefore, in order to prevent the overflow valve from rebounding at the valve seat, the mass of the overflow valve should be as small as possible.

[Means for solving the problem]

In order to solve the above problems, according to the present invention, a plunger driven by an engine, a fuel pressurized chamber filled with fuel and pressurized by the plunger, and a fuel pressurized chamber in response to fuel pressure in the fuel pressurized chamber are provided. A needle that opens when the fuel pressure exceeds a predetermined pressure, a sliding hole and a pressure control chamber coaxially arranged with each other, and a pressure control slidably inserted into the sliding hole and An overflow valve slidably controlled in a common axis direction of the sliding hole and the pressure control chamber in response to the working liquid pressure in the chamber, a piezoelectric element having an axis substantially perpendicular to the common axis, and a working liquid. A variable volume chamber filled with and having a volume controlled by a piezoelectric element, and a working liquid passage communicating the variable volume chamber and the pressure control chamber. The valve closes and fuel overflows from the fuel pressurization chamber. The fuel injection system of fuel injection is performed when it is allowed to stop, the pressure control chamber is arranged eccentrically to the sliding hole side with respect to the axis of the piezoelectric element.

(Operation)

By arranging the pressure control chamber eccentrically on the sliding hole side with respect to the axis of the piezoelectric element, the axial length of the overflow valve becomes shorter,
Thus, the mass of the overflow valve is reduced.

〔Example〕

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

Referring to FIGS. 1 to 4, reference numeral 1 denotes a housing body, 2 denotes a nozzle having a nozzle port 3 formed at the tip thereof, 4
Denotes a spacer, 5 denotes a sleeve, and 6 denotes a nozzle holder for fastening the nozzle 2, the spacer 4, and the sleeve 5 to the housing body 1, respectively. Nozzle port 3 in nozzle 2
A needle 7 for controlling the opening and closing of the needle 7 is slidably inserted, and the top of the needle 7 is connected to a spring retainer 9 via a pressure pin 8. The spring retainer 9 is constantly pressed downward by the compression spring 10, and this pressing force is transmitted to the needle 7 via the pressing pin 8. Therefore, the needle 7 is normally urged by the compression spring 10 in the valve closing direction.

On the other hand, a plunger hole 11 is formed coaxially with the needle 7 in the housing body 1, 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 constantly urged upward by a compression spring 14. This tappet
13 is moved up and down by a cam (not shown) driven by the engine, whereby the plunger 12 is moved up and down in the plunger hole 11. On the other hand, a fuel pressurizing chamber 15 defined by a lower end surface 12a of the plunger 12 is formed in the plunger hole 11 below the plunger 12. This fuel pressurization chamber
Numeral 15 is connected to a needle pressurizing chamber 18 via a rod-shaped filter 16 and a fuel passage 17 (FIG. 4).
Is the nozzle port 3 through the annular fuel passage 19 around the needle 7
Linked to On the inner wall surface of the plunger hole 11, there is formed a fuel supply port 20 which opens into the fuel pressurizing chamber 15 when the plunger 12 is at the upper position, as shown in FIG. 2-3k in fuel pressurization chamber 15
Fuel at 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. As shown in FIG. 3, a fuel port 21 which is inevitably formed in the operation of drilling the fuel supply port 20 is formed on the side opposite to the fuel supply port 20 with respect to the plunger hole 11. The outer end of 21 is closed by blind plug 22. This fuel port 21 is a fuel supply port
It extends coaxially with 20 and opens into the plunger hole 11. A circumferential groove 23 extending from the fuel supply port 20 to the fuel port 21 is formed on the inner wall surface of the plunger hole 11. Therefore, the plunger 12 is lowered and the plunger 12 is moved to the fuel supply port 20.
And the fuel supply port 20 when the 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
The same feed pressure as in 20 is maintained. A compression spring housing chamber 24 for housing the compression spring 10 for pressing the needle 7 is connected to the fuel supply port 20 via a fuel return passage 25, and the fuel leaking into the compression spring housing chamber 24 is supplied to the fuel return passage 25. Returned to 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 face 12a of the plunger, and the circumferential groove 26 is The inside of the pressurizing chamber 15 is communicated.

On the other hand, a sliding hole 30 extending in the lateral direction is formed in the housing body 1 near the side in the plunger hole 11.
Accordingly, the sliding hole 30 is formed such that its axis is parallel to the straight line substantially perpendicular to the common axis of the plunger 12 and the needle 7 with a space therebetween. An overflow valve 31 is slidably inserted into the sliding hole 30. As shown in FIGS. 1 and 2, the sliding hole 30 is composed of a small-diameter hole 32 and a large-diameter hole 33 coaxially arranged with each other, and a small-diameter hole is provided between the small-diameter hole 32 and the large-diameter hole 33. A step 34 that is substantially perpendicular to the common axis of the hole 32 and the large diameter hole 33 is formed. The step 34 and the small-diameter hole 32
An annular valve seat 35 is formed at the connection portion with the valve seat 35. on the other hand,
The overflow valve 31 includes a small diameter portion 36 located in the small diameter hole 32 and a large diameter portion 37 located in the large diameter portion 33. At the outer end of the small diameter portion 36, a first annular fitting portion 38 which comes into sealing contact with the inner wall surface of the small hole diameter 32 is provided.
Is formed at the outer end of the large-diameter portion 37, and a second annular fitting portion 39 that is in sealing contact with the inner wall surface of the large-diameter hole 33 is formed. The overflow valve 31 between the first annular fitting portion 38 and the second annular fitting portion 39
An annular valve portion 40 which can be seated on the valve seat 35 is formed on the outer peripheral surface of the valve seat 35. 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 is formed between the annular valve portion 40 and the second annular fitting portion 39. An annular fuel overflow valve 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 defining the fuel overflow valve 42 is formed larger than the diameter of the small-diameter hole 32. Therefore, the volume of the fuel overflow chamber 42 is considerably small. Is formed. The outer end of the small diameter hole 32 is closed by a blind plug 43, and an overflow back pressure chamber 44 is formed between the blind plug 43 and the overflow valve 31. A compression spring 45 that urges the annular valve portion 40 of the overflow valve 31 away from the valve seat 35, that is, biases the overflow valve 31 in the valve opening direction, is inserted into the overflow valve back pressure chamber 44. . A fuel passage extending in the radial direction inside the large diameter portion 37 of the overflow valve 31 and opening into the fuel overflow chamber 42
A fuel passage 47 is formed in the small diameter portion 36 and extends in the axial direction and opens into the overflow valve back pressure chamber 44. These fuel passages 46 and 47 communicate with each other in the overflow valve 31. Therefore, the overflow valve back pressure chamber 44 communicates with the fuel overflow chamber 42 via the fuel passages 46 and 47. Overflow valve on the second annular fitting part 39 side
At the center of the end face 48 of the 31, a concave groove 49 extending to the vicinity of the fuel passage 46 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.

As shown in FIG. 4, a fuel overflow channel 50 extending upward from the fuel passage 17 and always opening into the pressurized fuel introduction chamber 41 is formed in the housing body 1. The fuel overflow channel 50 is always in communication with the fuel pressurizing chamber 15, and therefore the pressurized fuel introducing chamber
41 is always in communication with the fuel pressurization chamber 15. 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.
3 is connected to the fuel port 21 as shown in FIG. As shown in FIG. 7, the fuel overflow chamber 42 is connected to a fuel outflow passage 53, and the fuel flowing out of the fuel outflow passage 53 is returned to, for example, a fuel tank (not shown).

As shown in FIGS. 1 and 2, a rod guide for guiding and supporting the rod 60 is provided at the outer end of the large diameter hole 33 of the slide hole 30.
The rod guide 61 has a sliding hole inside.
A rod hole 62 coaxial with 30 is provided. The rod 60 is a hollow cylindrical small-diameter portion 63 slidably inserted into a rod hole 62.
The large diameter portion 64 is slidably inserted into the large diameter hole 33, and the end face of the large diameter portion 64 is brought into contact with the end face 48 of the overflow valve 31. A rod back pressure chamber 65 is formed between the inner end of the rod guide 61 and the large diameter portion 64 of the rod 60. At the end of the rod 60 opposite to the large diameter portion 64, a pressure control chamber 66 defined by an end surface 63a of the small diameter portion 63 is formed. The pressure control chamber 66 is arranged coaxially with the sliding hole 30, and an actuator 70 is arranged above the pressure control chamber 66. 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 reduced.

Actuator as shown in FIGS. 1 and 5
70 is an actuator housing 72 integrally formed with the housing body 1 and having a piston hole 71 formed therein;
A piston 73 slidably inserted into the piston hole 71,
An end plate 74 for covering the top of the actuator housing 72, an end plate holder 75 for fixing the end plate 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. A piezo-electric element 77 in which a number of piezoelectric element plates are stacked is inserted between the piston 73 and the end plate 74, and a variable volume chamber 78 defined by the lower end surface of the piston 73 is formed in a piston hole 71 below the piston 73. Is done.
The variable volume chamber 78 communicates with the pressure control chamber 66 via a 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 urges the piston 73 upward is inserted into the cooling chamber 80. When charge is applied to the piezoelectric element 77, the piezoelectric element 77 extends in the axial direction, and as a result, the variable volume chamber 78
Volume is reduced. 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. 1, the axis M of the piezoelectric element 77 is substantially perpendicular to the common axis of the sliding hole 30 and the pressure control chamber 66, so that the axis of the piezoelectric element 77 is
It is substantially parallel to the common axis of 12 and the needle 7. The pressure control chamber 66 is disposed on an axis N that is eccentric to the sliding hole 30 side by e with respect to the axis M of the piezoelectric element 77, and the fuel passage 79 extends along the axis N from the variable volume chamber 78 to the pressure control chamber 78. Extends to 66. When the pressure control chamber 66 is brought closer to the sliding hole 30 in this way, the axial lengths of the overflow valve 31 and the rod 60 are reduced, and thus the masses of the overflow valve 31 and the rod 60 are reduced.

FIG. 5 shows that the housing body 1 has a check valve
82 is inserted. The check valve 82 includes a ball 84 that controls opening and closing of the valve port 83, a rod 85 that regulates the lift of the ball 84, and a compression spring 86 that constantly presses the ball 84 and the rod 85 downward. Thus, valve port 83 is normally closed by ball 84. The valve port 83 of the check valve 82 is connected to, for example, a low-pressure fuel pump (not shown) via a fuel inflow passage 87, and low-pressure fuel of ^{2 to 3} kg / cm ² is supplied from the fuel inflow passage 87. The check valve 82 can only flow toward the inside of the variable volume chamber 78, so that when the fuel pressure in the variable volume chamber 78 drops below ² to 3 kg / cm ² , the fuel is It is replenished in the room 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 a low-pressure fuel pump (not shown) through a fuel inflow passage 88, for example.
Low-pressure fuel of ~ 3 kg / cm ² flows from the fuel inflow passage 88 to the cooling chamber 80.
Supplied within. The piezo element 77 is cooled by this fuel. As shown in FIG. 3, the lower end of the cooling chamber 80 is connected to the fuel supply port 20 via a fuel outflow passage 89. In the fuel supply port 20, the cooling chamber 80 extends from the cooling chamber 80 toward the fuel supply port 20. A check valve 90 that can only flow is arranged. This check valve 90 is a ball that controls opening and closing of the valve port 91.
The ball 92 includes a rod 93 that regulates the lift of the ball 92 and a compression spring 94 that constantly presses the ball 92 and the rod 93 upward. After the fuel in the cooling chamber 80 cools the piezoelectric element 77, the fuel is supplied to the fuel supply port 20 through the fuel outlet passage 89.
Supplied to As shown in FIGS. 1 and 2, 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 2-3 kg / cm ^2.
Filled with fuel.

As described above, the fuel flows into the cooling chamber through the fuel inflow passage 88.
The fuel is supplied into the fuel supply port 20 through the fuel outflow passage 89 and the check valve 90 after cooling the piezoelectric element 77. When the plunger 12 is in the upper position as shown in FIG.
The fuel is supplied into the fuel pressurizing chamber 15 from the fuel pressurizing chamber 15, so that the pressure in the fuel pressurizing chamber 15 is low at about ² to 3 kg / cm ^{2 at} this time. On the other hand, at this time, the piezoelectric element 77 is at the maximum contraction position, and at this time, the pressure of the working liquid in the variable volume chamber 78 and the pressure control chamber 66, for example, the fuel is a low pressure of about ² to 3 kg / cm ² . Accordingly, at this time, the overflow valve 31 is moved rightward in FIGS. 1 and 2 by the spring force of the compression spring 45, and the annular valve portion 40 is separated from the valve seat 35, that is, the overflow valve 31 is opened. doing. Therefore, the low-pressure fuel in the fuel pressurizing chamber 15 is supplied to the fuel overflow chamber 42 through the fuel overflow channel 50 and the pressurized fuel introduction chamber 41 on the one hand, and the fuel passages 52 and 51 and the overflow valve The fuel is supplied into the fuel overflow chamber 42 through 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 inside of the pressurized fuel introduction chamber 41, the fuel overflow chamber 42, and the overflow valve back pressure chamber 44 are also filled with low-pressure fuel of ^{2 to 3} kg / cm ² .

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 pressurization chamber 15 flows through the fuel overflow channel 50 and the overflow. It flows out into the fuel overflow chamber 42 via the pressurized fuel introduction chamber 41 of the flow valve 22. Therefore, also in this case, the fuel pressurization chamber
The fuel pressure in 15 is as low as about 2-3 kg / cm ² .

Next, when electric charge is charged in the piezoelectric element 77 to start fuel injection, the piezoelectric element 77 extends in the axial direction, and as a result, the piston 73 moves down, so that the variable volume chamber 78 is moved.
And the fuel pressure in the pressure control chamber 66 sharply increases. 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 Part 40 is valve seat 35
And the overflow valve 31 is closed. As described above, the pressure control chamber 66 is positioned with respect to the axis M of the piezoelectric element 77 by e.
The spill valve 31 is located only on the eccentric axis N.
And the mass of the rod 60 is small, so that the overflow valve 31 is
Since there is no rebound when colliding with 35, once the overflow valve 31 is closed, it is kept in the closed state. Furthermore, overflow valve 31
Since the fuel passages 46 and 47 and the concave groove 49 are formed therein, the mass of the overflow valve 31 is small, and since the rod 60 has a hollow cylindrical shape, the mass of the rod 60 is also small. Accordingly, the structures of the overflow valve 31 and the rod 60 also contribute to preventing the overflow valve 31 from rebounding from the valve seat 35.

When the overflow valve 31 is closed, the fuel pressure in the fuel pressurizing chamber 15 rises rapidly due to the downward movement of the plunger 12, and the fuel pressurizing chamber 15
When the fuel pressure in the chamber exceeds a predetermined pressure, for example, a constant pressure of 1500 kg / cm ² or more, the needle 7 opens and the nozzle port 3 opens.
The fuel is injected from. At this time, high pressure is also applied to the pressurized fuel introduction chamber 41 of the overflow valve 31 via the fuel overflow channel 50, but since the pressure receiving areas at both axial end surfaces of the pressurized fuel introduction chamber 41 are equal, the high pressure overflows. No driving force acts on the flow valve 31.

Next, when the electric charge charged in the piezoelectric element 77 is discharged to stop the fuel injection, the piezoelectric element 77 contracts. As a result, since the piston 73 is raised by the spring force of the compression spring 81, the fuel pressure in the variable volume chamber 78 and the pressure control chamber 66 decreases. As described above, the mass of the rod 60 and the overflow valve 31 is small, so that when the fuel pressure in the pressure control chamber 66 decreases, the rod 60 and the overflow valve 31
1 and 2 immediately due to the spring force of the compression spring 45.
It moves to the right in the figure, and the annular valve portion 40 of the overflow valve 31 is a valve seat.
The overflow valve 31 opens immediately away from 35. When the overflow valve 31 is opened, high-pressure fuel in the fuel pressurization chamber 15 is jetted into the fuel overflow chamber 42 via the fuel overflow channel 50 and the pressurized fuel introduction chamber 41, and as a result, the fuel pressurization chamber The fuel pressure in 15 drops rapidly. On the other hand, when the pressurized fuel is ejected 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 overflow valve 31
Since the second annular fitting portion 39 is formed between the end face 48 of the large diameter portion 37 and the fuel overflow chamber 42, the high pressure generated in the fuel overflow chamber 42 causes the large diameter portion 37 of the overflow valve 31 to flow. Does not act on the end face 48 of the As a result, the high pressure generated in the fuel overflow chamber 42
The cross-sectional area of the small-diameter hole 32 is subtracted from the cross-sectional area of the small-diameter hole 32 and acts only in the valve opening direction of 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 jetted into the fuel overflow chamber 42, part of the high-pressure fuel is jetted from the fuel passage 47 into the overflow valve back pressure chamber 44 through 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. Also, the high pressure fuel overflows the back pressure chamber 44
When the fuel flows into the overflow valve back pressure chamber 44, the fuel pressure in the overflow valve back pressure chamber 44 increases. As a result, a biasing force acts on the overflow valve 31 in the valve opening direction by the fuel pressure in the overflow valve back pressure chamber 44. When the overflow valve 31 is thus opened, the pressure in the fuel overflow chamber 42 increases, the fuel is ejected from the fuel passage 47, and the pressure in the overflow valve back pressure chamber 44 increases. Overflow valve due to the urging force of
As soon as the annular valve portion 31 of the 31 leaves the valve seat 35, the overflow valve 31 is rapidly opened, and once the overflow valve 31 is once opened, it is maintained 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 reduced. Therefore, when the overflow valve 31 is opened, the needle 7 is immediately lowered and the fuel injection is stopped. On the other hand, when the piezo 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 reduced by the fuel inflow passage 87 (fifth embodiment). When the fuel pressure becomes lower than the fuel pressure in the figure, low-pressure fuel is supplied into the variable volume chamber 78 via the check valve 82.

Next, 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 When the fuel cell 26 communicates with the fuel supply port 20 and the fuel port 21, the high-pressure fuel in the fuel pressurizing chamber 15 is jetted into the fuel supply port 20 and the fuel port 21 via the fuel escape hole 27 and the circumferential groove 26. At this time, the high-pressure fuel ejected 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, and the high-pressure fuel passes through the fuel passages 51 and 52. It flows into the overflow valve back pressure chamber 44 and further flows into the fuel overflow chamber 42 via the fuel passages 46 and 47 in the overflow valve 31. As a result, the pressure in the overflow valve back pressure chambers 46, 47 and the fuel overflow chamber 42 becomes high, so that a strong force in the valve opening direction acts on the overflow valve 31.
31 is forcibly opened. Accordingly, the circumferential groove 26 serves as a fail-safe function for preventing the overflow valve 31 from being kept closed for some reason.

Next, the plunger 12 moves up, returns to the upper end position, and starts lowering again.

Thus, a strong downward driving force is applied to the plunger 12 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 has a plunger
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 to extend 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, since the length of the fuel overflow channel 50 can be shortened, the volume of the fuel pressurizing chamber 15 including the fuel overflow channel 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, when the overflow valve 31 opens, the fuel pressure in the fuel pressurizing chamber 15 immediately decreases, and the fuel injection stops immediately. Therefore, since fuel injection does not continue under low pressure after the overflow valve 31 is opened, the generation of smoke can be suppressed, and the engine output can be improved and the fuel consumption rate can be improved. Further, in response to the opening / closing operation of the overflow valve 31, the fuel injection amount rises immediately and the fuel injection stops immediately, so that good pilot injection can be performed.

Further, by forming the sliding hole 30 so as to extend in the lateral direction on the side of the plunger 12, the lateral width of the unit injector can be reduced.
77 is arranged so that its axis is substantially perpendicular to the common axis of the slide hole 30 and the rod 60, that is, substantially parallel to the common axis of the plunger 12 and the needle 7. The width can be further reduced. In the illustrated embodiment, a fuel passage 79 communicating the pressure control chamber 66 and the variable volume chamber 78 is formed on an axis N parallel to the axis M of the piezoelectric element 77. May be arranged so that the opening to the pressure control chamber 66 is located closer to the sliding hole 30 than the opening to the variable volume chamber 78.

〔The invention's effect〕

By disposing the pressure control chamber eccentrically on the sliding hole side with respect to the axis of the piezoelectric element, the axial length of the overflow valve can be shortened, and thus the mass of the overflow valve can be reduced. . As a result, once the overflow valve is closed, it can be maintained in the closed state, so that the fuel injection rate increases smoothly,
Thus, a good fuel injection action can be ensured.

[Brief description of the drawings]

FIG. 1 is a side sectional view of the unit injector taken along the line II of FIG. 4, FIG. 2 is an enlarged side sectional view of a part of FIG. 1, and FIG. 3 is a III-III of FIG. FIG. 4 is a side sectional view taken along the line IV-IV in FIG. 1, and FIG. 5 is a side sectional view taken along the line VV in FIGS. 1 and 7. FIG. 6 is a plan view of FIG. 1, and FIG. 7 is a plan sectional view taken along line VII-VII of 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, 40 ... annular valve part, 41 ... pressurized fuel introduction chamber, 42 ... fuel overflow chamber, 60 ... rod, 66 ... pressure control chamber, 77 ... piezo piezoelectric element, 78… Variable volume chamber.

Claims (1)

(57) [Claims] A plunger driven by an engine, a fuel pressurization chamber filled with fuel and pressurized by the plunger, and a fuel pressure which is responsive to a fuel pressure in the fuel pressurization chamber, is set to a predetermined pressure. A needle that opens when the pressure exceeds the pressure, a sliding hole and a pressure control chamber arranged coaxially with each other, and inserted into the sliding hole so as to be able to be impulsively actuated in response to the hydraulic fluid pressure in the pressure control chamber. An overflow valve, which is slidably controlled in the direction of the common axis of the sliding hole and the pressure control chamber, a piezoelectric element whose axis is substantially perpendicular to the common axis, and a volume filled with the working liquid and filled by the piezoelectric element. And a working liquid passage communicating the variable volume chamber and the pressure control chamber. The overflow valve is closed by an increase in the working liquid pressure in the pressure control chamber, and the fuel is closed. When the overflow of fuel from the pressurized chamber is stopped The fuel injection system of fuel injection is performed, fuel injection system the pressure control chamber is arranged eccentrically to the sliding hole side with respect to the axis of the piezoelectric element.