JPH0640931Y2 - Fuel injector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a fuel injection device.

[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. A needle for opening, an overflow valve slidably inserted in the sliding hole and coaxially arranged with the sliding hole, and driven and controlled by the pressure in the pressure control chamber, are connected to the pressure control chamber. And a variable volume chamber whose volume is changed by an actuator, and when the volume of the variable volume chamber is reduced and the pressure in the pressure control chamber rises, the overflow valve closes and the A fuel injection device for stopping the overflow of fuel has already been proposed by the present applicant (see Japanese Patent Application No. 62-33529).

[Problems to be solved by the device]

However, in this fuel injection device, when the volume of the variable volume chamber is reduced to start the fuel injection and the pressure in the pressure control chamber rises, the overflow valve is moved at a high speed in the closing direction, and then the overflow valve is moved. The valve is pressed against the valve seat at high speed. As a result, the overflow valve closes once, but rebounds and opens again to move away from the valve seat, and the fuel in the fuel pressurization chamber overflows, so that the fuel injection pressure smoothly rises to a high pressure. There is a problem not to do.

[Means for Solving the Problems]

In order 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 are used. Driving control is performed by the needle that opens when the fuel pressure exceeds a predetermined pressure and the pressure in the pressure control chamber that is slidably inserted into the sliding hole and is coaxially arranged with the sliding hole. And a variable volume chamber that is connected to the pressure control chamber and whose volume is changed by an actuator, and overflows when the volume of the variable volume chamber is reduced and the pressure in the pressure control chamber rises. In a fuel injection device in which the flow valve is closed to stop the fuel overflow from the fuel pressurizing chamber, when the volume of the variable volume chamber decreases, the speed is lower than the pressure rising speed in the variable volume chamber. Pressure in pressure control chamber Between the variable volume chambers and a pressure control mechanism that reduces the pressure in the pressure control chambers at a rate approximately the same as the pressure decreasing rate in the variable volume chambers when the volume of the variable volume chambers is increased. There is.

[Action]

The overflow valve moves at a low speed in the closing direction because the pressure in the pressure control chamber rises at a low speed, and thus the overflow valve does not bounce at the valve seat but once abuts on the valve seat, and then closes the valve. Held in a state. On the other hand, since the pressure in the pressure control chamber drops rapidly, the overflow valve opens rapidly.

〔Example〕

1 to 7 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. Overflow valve 31 on the joint 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.

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 end surface 48 of the overflow valve 31. 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. 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. 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.

On the other hand, a pressure control mechanism 67 is arranged adjacent to the pressure control chamber 66. The pressure control mechanism 67 includes a valve chamber 67a formed coaxially with the pressure control chamber 66, an annular valve seat 67b formed at a connecting portion between the pressure control chamber 66 and the valve chamber 67a, and a compression spring 67c. And a valve body 67d that is seated on the valve seat 67b,
A throttle passage 67e that connects the pressure control chamber 66 and the valve chamber 67a is formed in the valve body 67d. An actuator 70 is arranged above the valve chamber 67a.

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 valve chamber 67a via the fuel passage 79. An annular cooling chamber 80 is formed between the piston 73 and the actuator housing 72.
A compression spring 81 is inserted which always biases 73 upward. 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 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 variable volume chamber 7
8. The valve chamber 67a and the pressure control chamber 66 are constantly filled with fuel. On the other hand, as shown in FIG.
The lower end portion of is connected to, for example, a low pressure fuel pump (not shown) via a fuel inflow passage 88, and low pressure fuel of ^{2 to 3} kg / cm ² is supplied from the fuel inflow passage 88 into the cooling chamber 80. This fuel cools the piezoelectric element 77. Also, the third
As shown in the figure, the lower end of the cooling chamber 80 has a fuel outflow passage 89.
A check valve 90, which is connected to the fuel supply port 20 via the, and can flow only from the cooling chamber 80 toward the fuel supply port 20, is arranged in the fuel supply port 20. The check valve 90 includes a ball 92 that controls opening / closing of the valve port 91, a rod 93 that regulates a lift amount of the ball 92, a ball 92, and a compression spring 94 that constantly pushes the rod 93 upward. Cooling room 80
The fuel inside cools the piezoelectric element 77 and is then supplied to the fuel supply port 20 through the fuel outflow passage 89. Further, as shown in FIGS. 1 and 2, the lower end portion 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 has a pressure of 2-3 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. 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 open. 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 valve chamber 67a rises rapidly. At this time, since the valve body 67d is seated on the valve seat 67b, the high-pressure fuel in the valve chamber 67a gradually flows into the pressure control chamber 66 via the throttle passage 67e. As a result, the fuel pressure in the pressure control chamber 66 rises at a lower speed than the fuel pressures in the variable volume chamber 78 and the valve chamber 67a. When the fuel pressure in the pressure control chamber 66 rises at a low speed, the rod 60 moves to the left at a low speed in FIGS. 1 and 2, so that the overflow valve 31 also moves to the left at a low speed. The annular valve portion 40 of the overflow valve 31 comes into contact with the valve seat 35 at a low speed to close the overflow valve 31. Since the overflow valve 31 abuts the valve seat 35 at a low speed in this way, the overflow valve 31 does not bounce at the valve seat 35, and therefore, once the overflow valve 31 is closed, it is maintained in the closed state. Will be. Also,
Since the rod 60 can also be moved at a low speed, it does not separate from the overflow valve 31 when the overflow valve 31 comes into contact with the valve seat 35.
Therefore, the fuel pressure in the pressure control chamber 66 is continuously applied to the overflow valve 31, so that the overflow valve 31 is held in the closed state.
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 valve chamber 67a is reduced. When the fuel pressure in the valve chamber 67a decreases, the fuel pressure in the pressure control chamber 66 becomes higher, so the valve body 67d immediately opens away from the valve seat 67b, and thus the pressure in the pressure control chamber 66 increases. Decreases rapidly at about the same rate as the pressure in the variable volume chamber 78 and the valve chamber 67a. As described above, the masses of the rod 60 and the overflow valve 31 are small, and 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. 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 50 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 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 jetted out into the fuel overflow chamber 42, a part of this high-pressure fuel is injected into the fuel passage 46 inside the overflow valve 31.
Through the fuel passage 47 into the overflow valve back pressure chamber 44 through the.
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. Further, when high-pressure fuel is ejected into the overflow valve back pressure chamber 44, the fuel pressure in the overflow valve back pressure chamber 44 rises, and as a result, the fuel pressure in the overflow valve back pressure chamber 44 causes the overflow valve 31 to reach the overflow valve 31. Is actuated by an urging force in the valve 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 opens, the fuel pressurizing chamber
Overflow valve 31 because the fuel pressure in 15 decreases continuously and rapidly
Immediately after the valve is opened, the needle 7 descends and the fuel injection is stopped. Further, when the engine speed or the engine load increases, the pressure of the pressurized fuel in the fuel pressurizing chamber 15 increases, and therefore the pressure increase in the fuel overflow chamber 42 when the overflow valve 21 opens increases. . Further, at this time, the fuel injection action from the fuel passage 47 becomes strong, and the pressure increase 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 Check valve if it becomes lower than the fuel pressure in
Low-pressure fuel is supplied to the variable volume chamber 78 via 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]

When fuel injection should be started, the pressure in the pressure control chamber rises at a low speed, so that the overflow valve moves at a low speed in the valve closing direction. Therefore, once the overflow valve does not bounce on the valve seat and once comes into contact with the valve seat, the overflow valve is maintained in the closed state thereafter, so that the overflow valve can be reliably closed. As a result, the fuel injection pressure smoothly rises to a high pressure, and good fuel injection can be performed. Further, when the fuel injection should be stopped, the pressure in the pressure control chamber is rapidly decreased, so that the overflow valve is opened rapidly, and thus good fuel injection interruption can be secured.

[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, and FIG. 7 is a plan sectional view taken along the 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, 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, 66 …… pressure control chamber, 67 …… pressure control mechanism, 67a …… valve chamber, 67b …… valve seat, 67c …… compression spring, 67d …… valve body, 67e …… throttle passage, 77: 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. A needle that opens when the pressure exceeds a pressure, an overflow valve that is slidably inserted into the sliding hole and that is driven and controlled by the pressure in a pressure control chamber that is coaxially arranged with the sliding hole; A variable volume chamber which is connected to the pressure control chamber and whose volume is changed by an actuator, and when the volume of the variable volume chamber is reduced and the pressure in the pressure control chamber rises, the overflow valve closes. In a fuel injection device configured to stop the overflow of fuel from the fuel pressurizing chamber, when the volume of the variable volume chamber decreases, the pressure in the pressure control chamber is reduced at a speed lower than the pressure rising speed in the variable volume chamber. Raised and variable volume chamber Approximately the same velocity fuel injection system having a pressure control mechanism for reducing the pressure in the pressure control chamber between the variable volume chamber and the pressure control chamber with a variable volume chamber of the pressure reduction rate when the volume is increased.