JPH08296521A - Needle valve controller of injector - Google Patents

Abstract

PURPOSE: To obtain good initial injection characteristics even if time interval between injections is short and suppress initial injection rate without worsening spill characteristics. CONSTITUTION: A needle valve controller 50 of an injector is provided with a piston 56 which is pressed and moved from its original position in a control chamber 52 due to the supply of high fuel pressure to lower a needle valve and an orifice 59 which is formed in the piston 56 and discharges fuel in the control chamber 52 appropriately when the needle valve is lifted. It is further provided with a communicating passage 66 which passes fuel in the control chamber 52 into a rear surface side 65 of the piston 56 in a process in which the piston 56 returns to its original position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injector needle valve control device, and more particularly to a device for controlling a needle valve in an injector for injecting high-pressure fuel to a diesel engine or the like in order to optimize its initial injection. is there.

[0002]

2. Description of the Related Art Generally, a high pressure fuel is accumulated in a kind of surge tank called a common rail, and the high pressure fuel is injected and supplied to a diesel engine or the like.
Formula) injectors are known. This injector has an advantage that a high injection pressure is always obtained regardless of the engine speed, and a high injection pressure advantageous for forming a combustible mixture is obtained even in a low rotation range. Further, since the injection timing can be freely set, multi-stage injection is possible, which is extremely effective for improving output, exhaust gas characteristics, noise, odor, and the like. FIG. 9 schematically shows the multistage injection. According to this, the pilot injection is first performed, and the main injection is performed after a predetermined interval time. Also, as shown in (), after-injection may be performed after the main injection.

Usually, such injectors are provided with a device for controlling the lift or ascent rate of the needle valve or nozzle needle in order to optimize its initial injection, ie the spray immediately after the start of injection. .

FIG. 10 shows a conventional needle valve control device. As shown in the drawing, a damping orifice valve d, an orifice spring e, and a slide valve are provided in a control chamber c defined by an upper body a and a lower body b. Movable pistons or pilot orifice valves f are respectively installed. A solenoid valve (not shown) is provided above the control chamber c. By this switching, a high fuel pressure, that is, a high pressure due to the fuel during no injection, and a low pressure generated by leaking the fuel during injection are supplied or introduced through the pressure guiding port g. It is like this.

Explaining the specific operation, when no injection is performed, as shown in FIG. 11 (d), a high pressure is introduced into the control chamber c, and the command piston h is lowered by the high pressure, and a nozzle connected to this command piston h. The injection hole (not shown) is closed by a needle (not shown). When the injection is started, the solenoid valve is switched, and as shown in FIG. 11A, the pressure in the pressure guiding port g becomes low, and the orifice hole i from the control chamber c is changed.
As the fuel moves through the control chamber c, the pressure inside the control chamber c becomes low, and the command piston h and the nozzle needle are allowed to lift. In particular, this orifice hole i determines the flow rate of the fuel passing therethrough and controls the lift speed of the nozzle needle. Therefore, the hole diameter is determined so as to optimize the initial injection.

At the end of the injection, the high pressure from the pressure introducing port g lowers the pilot orifice valve f, thereby giving a high pressure to the command piston h and lowering the nozzle needle. Therefore, the injection hole is closed and the injection is completed. In this state, the pressure guide port g side chamber inside the control chamber c bordering the pilot orifice valve f, that is, the one end side chamber j
Since the pressure inside and the pressure inside the damping orifice valve d side chamber, that is, the inside of the other end side chamber k on the opposite side are substantially the same high pressure, due to the biasing force of the orifice spring e and the movement of the fuel through the orifice hole i, FIG. 11 (c),
Pilot orifice valve f in the order of (d)
Rises. Then, the state of FIG. 11 (d) becomes a standby state for the next injection.

[0007]

By the way, since such a one-cycle operation is performed for each injection, even in the case of multi-stage injection, pilot injection, main injection, and after injection are performed. Will be done.

However, in the case of the above apparatus, when the interval time between the pilot or after injection and the main injection becomes short, the state of FIG. 11 (b) shifts to the state of (d), that is, the next injection standby state. Return is not done promptly,
There is a problem that accurate injection cannot be performed.

More specifically, at the end of injection shown in FIG. 11 (b), a high pressure is sent from the pressure guiding port g into the one end side chamber j, and the pilot orifice valve f is moved downward from its original position at the upper end in response to this high pressure. Is pushed to. As a result, the inside of the other end side chamber k is compressed to a high pressure which is almost the same as the inside pressure of the one end side chamber j such that the command piston h can be lowered. Then, the orifice spring e gives a rising force to the pilot orifice valve f, and at the same time, the fuel in the one end side chamber j moves into the other end side chamber k through the orifice hole i, so that the pilot orifice valve f becomes as shown in FIG. It gradually rises and returns to its original position as shown in FIG. As can be seen, the return of the pilot orifice valve f is
Especially, since the diameter of the orifice hole i is relatively small, it is not performed immediately.

However, when the interval time becomes short, injection starts before the pilot orifice valve f returns (for example, the state shown in FIG. 11 (c)), and the one end side chamber j
Due to the reduced pressure inside, the pilot orifice valve f suddenly rises. In this case, the pressure in the other end side chamber k is rapidly reduced, and the command piston h and the nozzle needle are rapidly lifted.
Accurate control of lift speed becomes impossible.

As a result, the initial injection rate increases and N
Ox, combustion noise, and the like are increased, and drastic increase in fuel injection amount and poor control cause deterioration of drivability.

Therefore, the present invention was devised to solve the above problems, and an object thereof is to provide an injector needle capable of obtaining good initial injection characteristics even when the interval time between injections is short. It is to provide a valve control device.

[0013]

In order to achieve the above object, a needle valve control device for an injector according to the present invention comprises a piston that is pushed from its original position in a control chamber by the supply of high fuel pressure to lower the needle valve. An orifice formed in the piston for appropriately discharging the fuel in the control chamber when the needle valve is lifted, and a communication passage for passing the fuel in the control chamber to the back side of the piston in the process of returning the piston to the original position. It is equipped with. According to this, in the process in which the piston lowered when the injection is completed returns to the original position, the fuel in the control chamber is moved to the back side of the piston also through the communication passage different from the orifice. As a result, the return movement of the piston is quickly performed, and its responsiveness is improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 shows the entire injector to which the needle valve control device according to the present invention is applied. As illustrated, the injector 1 has a split injector body 4 mainly composed of a lower body 2 and an upper body 3. The lower body 2 and the upper body 3 have a valve nut 5
And the cap body 6 is put on them. A solenoid 7 is provided inside the cap body 6, and electric power is supplied to the solenoid 7 from an external terminal 8. A nozzle body 10 is joined to the tip end or the bottom end of the lower body 2 through a tip packing 9 using a retaining nut 11. The boss mounting portion 12 on the side of the lower body 2 has an inlet boss 13 for introducing high-pressure fuel from a common rail (not shown) and an outlet boss 14 for discharging low-pressure fuel due to a leak.
And are attached.

A nozzle hole 15 is provided at the tip of the nozzle body 10, and the nozzle hole 15 is a needle valve or nozzle needle 16.
It is opened and closed by moving up and down. The high-pressure fuel from the inlet boss 13 is led from the branch 17 to the nozzle-side high-pressure passage 18 and stored in the oil sump chamber 19. When the nozzle needle 16 moves up, the fuel is injected from the injection hole 15 through the gap on the outer circumference of the nozzle needle 16. A tapered surface 20 is formed on the nozzle needle 16 at the position of the oil sump 19, and the tapered surface 20 gives a rising force by the high pressure fuel to the nozzle needle 16, which will be described in detail later.

In the center hole 21 of the lower body 2, a command piston 22 formed in a shaft shape is slidably inserted in the sliding portion 23 of the center hole 21, the spacer 24 and the shim 25. A nozzle spring 27 is inserted in the spring accommodating portion 26 of the center hole 21.
The nozzle needle 16 through the pressure pin 28.
Is pressed or urged downward, that is, in the closing direction. The lower end surface of the command piston 22 is brought into contact with the center of the pressure pin 28.

The solenoid body 29, which substantially houses the solenoid 7, is coupled to the upper body 3 by the cap body 6 via the ring spacer 30. A sliding shaft 31 is fixed to the axial center of the solenoid body 29, and a solenoid valve element 32 and a spring 33 are fitted to the sliding shaft 31. The solenoid valve element 32 is slidable with respect to the outer peripheral surface of the sliding shaft 31 and the inner peripheral surface of the sliding hole 34 at the axial center of the upper body 3. Further, the solenoid valve element 32 is biased downward by the spring 33, and is moved upward when the solenoid 7 is energized to be in the injection state.

FIG. 3 shows the details at this time,
(A) shows a non-injection state (current OFF), (b) shows an injection state (current ON). First, in the non-injection state, the solenoid valve body 32 is positioned below, and the inclined surface 36 formed on the lower end peripheral edge of the reduced diameter portion 35 has a pressure guiding port 37 formed on the axial center portion of the upper body 3. The movement of the solenoid valve element 32 is regulated by hitting the deposit face 38 of the. At this time, the lateral hole 39 formed in the solenoid valve body 32 coincides with the circumferential groove 41 as the outlet end of the control-side high-pressure passage 40, and the reduced diameter portion 42 of the sliding shaft 31 is provided inside the lateral hole 39. Positioned, the high-pressure fuel in the lateral hole 39 leaks to the port connection hole 43. A control-side low-pressure passage 44 for leaking high-pressure fuel is connected to the lower end of the sliding hole 34, but in this state, the solenoid valve body 32 closes and no leak occurs. After all, the high-pressure (common rail pressure) fuel from the high-pressure passage 40 maintains the pressure and the pressure guiding port 3
Sent to 7.

Next, in the injection state, as shown in FIG. 3B, the solenoid valve element 32 is moved upward and the lateral hole 3
9 is slightly displaced from the circumferential groove 41, and the reduced diameter portion 42 blocks the inlet of the port connection hole 43. That is, similarly to the above, the chamfered portions of the lower end peripheral portion of the reduced diameter portion 42 and the upper end peripheral portion of the port connection hole 43 come into contact with each other. As a result, the high pressure fuel from the high pressure passage 40 is blocked and does not flow into the port connection hole 43. At this time, the reduced diameter portion 3 of the solenoid valve body 32
5 opens the pressure guiding port 37 and connects the pressure guiding port 37 to the low pressure passage 44, which in turn causes the high pressure fuel to leak from the pressure guiding port 37. As a result, the pressure in the pressure guiding port 37 becomes low. The leaked fuel is discharged from the outlet boss 14 through the passage 44a shown in phantom in FIG.

As shown in FIG. 2, the control side low pressure passage 44
Is communicated with a nozzle-side low pressure passage 46 formed in the lower body 2 through a gap 45 between the lower body 2 and the upper body 3. Further, the gap 45 is provided through the low pressure communication passage 47 formed in the upper body 3 to the solenoid valve body 32.
Is connected to the transfer chamber 48. The nozzle-side low pressure passage 46 is connected to the enlarged diameter portion 49 of the center hole 21, so that the low pressure fuel reaches the pressure pin 28 through the gap between the command piston 22 and the enlarged diameter portion 49, and the spring accommodating portion 26. . There is no intrusion of high pressure fuel into them.

Here, the needle valve control device 5 according to the present invention is provided at a boundary portion or a connecting portion between the lower body 2 and the upper body 3.
0 is provided. As shown in FIG. 1, the needle valve control device 50
Has a control chamber 52 defined by the inner surface of a bottomed cylindrical hole 51 formed in the axial center of the lower body 2 and the lower surface of the upper body 3. One end of the control chamber 52, that is, the upper end surface 53 is a flat surface, and the outlet end of the pressure guiding port 37 is opened at the center thereof. The diameter of the pressure guide port 37 near the outlet end is enlarged. A damping orifice valve 54 is provided at the other end, that is, the lower end of the control chamber 52. The damping orifice valve 54 is formed in a cylindrical shape with a bottom, and a damping orifice hole 54 a that substantially forms the outlet of the control chamber 52 is provided at the center position of the bottom. Since the central hole 21 is provided so as to communicate with the hole 51, the orifice hole 54a supplies fuel to the command piston 22 or supplies high pressure and low pressure. An orifice spring 55, which is a coil spring, is installed in the inner cylinder of the damping orifice valve 54. A pilot orifice valve 56, which is a piston, is urged upward through the orifice spring 55.

The pilot orifice valve 56 is installed slidably along the inner wall of the control chamber 52, and has a disk-shaped portion 57 that forms a substantial sliding portion thereof, and a portion below the center of the disk-shaped portion 57. It is formed in a substantially T-shaped cross section from the taper shaft portion 58 extending to the. Pilot orifice valve 56
An orifice or orifice hole 59 is formed on the upper side and a diameter-expanded hole 60 is formed on the lower side along the center thereof. This expanded hole 60 is used for the damping orifice valve 5
4 has the same diameter as the expanded diameter hole 61, but the orifice hole 5
9 has a smaller diameter than the damping orifice hole 54a. The taper shaft portion 58 has an extension length that forms a gap with the inner bottom surface of the damping orifice valve 54 when the disk-shaped portion 57 contacts the upper end surface of the damping orifice valve 54. The taper shaft portion 58 also plays a role of a guide for preventing the bending of the orifice spring 55 when the orifice spring 55 expands and contracts, together with the inner wall of the damping orifice valve 54.

Particularly, in the pilot orifice valve 56, a hole portion 62 penetrating along the axial direction is formed in a portion of the disc-shaped portion 57 on the outer side in the radial direction. Two hole portions 62 are formed at opposing positions, the inner diameter thereof is formed larger than the inner diameter of the orifice hole 59, and the upper and lower ends thereof are chamfered. The hole portion 62 is located radially outward of the opening at the outlet end of the pressure guiding port 37, so that when the upper end surface 63 of the disk-shaped portion 57 contacts the upper end surface 53 of the control chamber 52, that is, the pilot orifice. When the valve 56 is in the original position, the pressure guiding port 37 and the hole portion 62 are separated from each other so as not to communicate with each other. At this time,
The surfaces 63 and 53 are completely in contact with each other, and the pressure guiding port 37
Is closed except for the orifice hole 59. Further, the hole portion 62 has its center substantially located at the radial position formed by the inner wall of the damping orifice valve 54.

In this way, in the control chamber 52, one end, that is, the upper end side chamber 64 and the other end, that is, the lower end side chamber 65, which are bordered by the pilot orifice valve 56, are formed, and
The pilot orifice valve 56 is provided with a communication passage 66 having one end opened to the inside of the upper end side chamber 64 and the other end opened to the inside of the lower end side chamber 65 by the hole 62. In other words, the upper end side chamber 64 includes the upper end surface 53 of the control chamber 52 and the pilot orifice valve 5
6 is a space between the upper end surface 63 and the lower end side chamber 65,
A space between the pilot orifice valve 56 and the damping orifice valve 54.

Next, the injector 1 having the above structure
The operation will be described. As shown in FIG. 2, at the time of no injection, the high pressure fuel introduced from the inlet boss 13 receives the branch 17,
The oil is stored in the oil sump chamber 19 through the nozzle-side high-pressure passage 18, and a rising force is applied to the nozzle needle 16 via the tapered surface 20. On the other hand, the high pressure fuel branched to the control side high pressure passage 40 is sent to the pressure introducing port 37 as described above, and the control chamber 52
And a downward force is applied to the command piston 22. After all, this command piston 22 and nozzle spring 27
The downward force exerted on the nozzle needle 16 overcomes the upward force and presses the nozzle needle 16 downward to push the injection hole 1
Block 5 And at this time, as shown in FIG.
The pilot orifice valve 56 is located in the home position.

Next, at the time of injection, it is the same that the high-pressure fuel in the oil sump 19 gives rise to the nozzle needle 16,
The high-pressure fuel in the pressure guiding port 37 leaks to the control-side low-pressure passage 44 to have a low pressure, and the high-pressure fuel in the control chamber 52 is also discharged to the pressure guiding port 37 to have a low pressure, so that the descending force to the command piston 22 is remarkable. Will be reduced. After all, the ascending force overcomes the sum of the descending force to the command piston 22, the descending force to the pressure pin 28 by the low pressure fuel from the control side low pressure passage 44, and the descending force by the nozzle spring 27, and the nozzle needle 16 is moved. The nozzle hole 15 is lifted to open and the injection is performed.

Particularly, immediately after the start of injection, referring to FIG. 1, the pressure guiding port 37 becomes low in pressure, so that the high-pressure fuel in the lower end side chamber 65 moves to the pressure guiding port 37 through the orifice hole 59. At this time, the speed at which the moving flow rate changes from high pressure to low pressure is determined, and the initial lift speed or the initial injection characteristic of the nozzle needle 16 is determined. At this time, since the communication passage 66 is closed by the upper end surface 53 of the control chamber 52, the fuel does not move through the communication passage 66. Eventually, the pressure inside the lower end side chamber 65 stabilizes at a predetermined low pressure (leak pressure). The above state is the state of FIG.

When high-pressure fuel is sent into the pressure guiding port 37 again at the end of injection, the high-pressure fuel acts on the upper end surface 63 of the pilot orifice valve 56 and resists the urging force of the orifice spring 55 to cause the pilot orifice valve to move. Push 56 downwards. Then, the valve 56 comes into contact with the damping orifice valve 54 in a relatively short time, and the inside of the lower end side chamber 65 has a high pressure (approximately the same pressure as the common rail pressure). The damping orifice hole 54a determines the discharge flow rate of this high-pressure fuel, but the flow rate value is relatively large. In this way, a downward force is applied to the command piston 22, the nozzle needle 16 descends at a relatively high speed, and the injection is stopped. The above state is the state shown in FIG.

However, the greatest feature of this embodiment is that the subsequent return of the pilot orifice valve 56 as shown in FIGS. 11B to 11D is immediately performed. That is, when the pilot orifice valve 56 is moved to the lower end position, the communication passage 66 is opened and the upper end side chamber 64 is opened.
The inside is communicated with the inside of the lower end side chamber 65. Conventionally, only the orifice hole 59 communicated with these, but in the present embodiment, since the communication passage 66 different from this is formed, the passage area can be substantially expanded (changed). Therefore, the moving flow rate of the high-pressure fuel can be increased, and when the pilot orifice valve 56 tries to return to the original position by the biasing force of the orifice spring 55, the fuel in the upper end side chamber 64 is passed through the communication passage 66 to the rear side of the pilot orifice valve 56. It is possible to immediately move the pilot orifice valve 56 into the lower end side chamber 65 and increase the moving speed of the pilot orifice valve 56. As a result, the responsiveness of the pilot orifice valve 56 is remarkably improved, and good initial injection characteristics can be obtained even when the interval time is short especially in multi-stage injection. In addition, the problems such as the increase in NOx that accompanies this can be solved.

4A and 4B are graphs showing injection characteristics in multi-stage injection. FIG. 4A shows a state of an input signal for controlling injection / non-injection, and FIG. 4B shows an actual injection state.
In (b), the solid line represents the present embodiment, and the broken line represents the conventional case. From this, it can be seen that as the interval time becomes shorter, the initial injection characteristics are improved. Further, in the present embodiment, the communication passage 66 has a simple structure with the hole portion 62, and in particular, the upper end surface 53 of the control chamber 52 is connected to the communication passage 6
Since it is used for opening and closing 6, the cost can be reduced.

Next, a modified example will be described.

FIG. 5 shows a pilot orifice valve 56.
6 has one hole 62, and FIG. 6 has three holes 62.
The example which changed each passage area of the communicating passage 66 is shown. Although each of the hole portions 62 is a round hole, it can be formed in any shape such as a square hole.

In FIG. 7, a groove portion 67 extending along the axial direction is formed on the side surface of the disk-shaped portion 57, and a space defined by the groove portion 67 and the side wall of the control chamber 52 (not shown) is formed as a communication passage 66. Here is an example. Three groove portions 67 are formed at intervals of 120 ° in the circumferential direction and have a substantially semicircular cross section. Of course, the groove portion 67 can be arbitrarily changed.

In the example shown in FIG. 8, not the pilot orifice valve 56 but the groove 68 extending in the axial direction is formed in the side wall of the control chamber 52. The groove portion 68 and the side surface of the disk-shaped portion 57 form the communication passage 66.
To form a section. Here, the groove 68 extends from the upper end position of the control chamber 52 to at least the damping orifice valve 54.
Of the pilot orifice valve 56 so that the high-pressure fuel can move in the entire stroke region. It should be noted that three groove portions 68 are also formed at equal intervals in the circumferential direction and have a substantially semicircular cross section. Modifications are possible as described above.

Although not shown, for example, one end and the other end of the communication passage 66 may be opened in the side wall of the control chamber 52 to partition the communication passage 66 inside the lower body 2.

The above-mentioned embodiment is intended to improve the initial injection characteristics, but according to the modified examples described below,
The characteristics at the end of injection (spill characteristics) can also be improved.

As shown in FIG. 12, in this modification, the damping orifice valve 5 having the configuration shown in FIG. 1 is used.
4 is omitted. An orifice spring 55, which is a coil spring having a relatively large diameter, is provided in the control chamber 52, and a pilot orifice valve 56 having a different shape is slidably provided above the orifice spring 55. The lower end of the orifice spring 55 is in contact with the inner bottom surface of the hole 51, and the upper end of the orifice spring 55 is fitted into the circumferential groove 70 formed in the peripheral portion of the lower end of the pilot orifice valve 56.

The pilot orifice valve 56 has an upper end surface 71 formed in a dome shape or an arc shape in cross section, and a taper hole 72 is formed in the upper side and an orifice hole 73 is formed in the lower side through the center thereof. To be done. The lower end surface 74 of the pilot orifice valve 56 is formed flat except for the peripheral groove 70. An axially penetrating hole portion 62 that defines the communication passage 66 is formed at a radially outer portion of the pilot orifice valve 56. Similar to the above, two hole portions 62 are formed at opposing positions, and the inner diameter thereof is made larger than the inner diameter of the orifice hole 73.

In particular, this pilot orifice valve 56
, The side surface portion 7 forming a sliding surface with the inner wall of the hole 51
5 is formed to have a shorter length (axial length) than in the case of the above-mentioned embodiment, whereby frictional resistance at the time of sliding can be reduced and smooth and responsive operation can be realized. Further, since the lower end surface 74 is a flat surface, it is possible to improve the responsiveness by reducing the weight. The outer diameter of the side surface portion 75 is finished with high precision by precision processing to form a sliding surface.
Since the length is short, the processing length is reduced, and there is an advantage that the processing cost can be reduced. The same applies to the case of the above-described embodiment, but since the pilot orifice valve 56 slides along the inner wall of the hole 51 and there is no fuel movement between them, the flow rate of fuel movement between the upper end side chamber 64 and the lower end side chamber 65. Can be determined only by the sum of the flow passage areas of the orifice hole 73 and the hole portion 62, whereby the setting or change of the injection characteristics can be completely determined only by changing the hole diameter, the number of holes, and the like.

In addition, a valve seat 76 for restricting upward movement of the pilot orifice valve 56 is provided at the upper end of the control chamber 52. The valve seat 76 is fixed by press fitting into the hole 51, screwing to the upper end surface 53 of the control chamber 52, that is, the upper body 3, and the like, and the fixing method is arbitrary. Alternatively, it may be integrally formed with the upper body 3. The valve seat 76 has a pressure guide port 77 formed at the center thereof with the same diameter as the pressure guide port 37. The diameter of the upper end of the tapered hole 72 of the pilot orifice valve 56 is larger than that of the pressure guide port 77. When the upper end peripheral portion of the tapered hole 72 abuts on the valve seat 76, the upward movement of the pilot orifice valve 56 is restricted, and at this time, the lower end outlet of the pressure guide port 77 does not come directly from the upper end side chamber 64. Since the pressure guiding port 77 is blocked, the pressure guiding port 77 directly communicates only with the tapered hole 72.

Since the damping orifice valve 54 is omitted as described above, the central hole 21 of the lower body 2 is directly communicated with the control chamber 52. Since the fuel pressure acts on the control chamber 52, the command piston 22 does not enter the control chamber 52.

To explain the operation of the above structure, first, at the time of injection, the pilot orifice valve 56 is in contact with the valve seat 76, and the high pressure fuel in the lower end side chamber 65 is passed only through the orifice hole 73, the tapered hole 72 and the pressure introducing port 77. It is discharged to the pressure guiding port 37.

At the end of injection, high-pressure fuel is sent from the pressure guiding port 37. The high-pressure fuel passes through the pressure guiding port 77 and then presses the inner wall of the tapered hole 72 of the pilot orifice valve 56. In this case, the pilot orifice valve 56 moves slightly downward, and at this moment, the above-mentioned shutoff from the upper end side chamber 64 disappears, the high pressure fuel flows into the upper end side chamber 64, and the pilot orifice valve 56 is moved from the upper end surface 71 thereof. Press. Further, the high-pressure fuel also passes through the tapered hole 72 and the orifice hole 73, but mainly flows into the lower end side chamber 65 through the large-diameter hole portion 62 and directly presses the command piston 22 in the central hole 21 downward. To do. As a result, the injection hole 15 is closed and the injection ends.

In particular, in the case of the above-mentioned form,
The high-pressure fuel was moved to the central hole 21 through the damping orifice hole 54a of the damping orifice valve 54. This is because the descending speed of the command piston 22, that is, the nozzle needle 16 is limited by passing the damping orifice hole 54a having a relatively small diameter in consideration of durability and the like. From the viewpoint of injection characteristics, it is preferable to increase the descending speed and immediately close the injection hole 15. This embodiment realizes this, that is, according to this embodiment, the nozzle needle 1
The falling speed of 6 can be increased to shorten the injection end time, suppress the generation of HC by making the fuel “cut” at the end of injection good, and greatly improve the characteristics at the end of injection. It should be noted that in FIG. 13, the injection characteristics are compared between the present embodiment and the above embodiment, and from this point onward, the injection end time is shortened as compared to the case where the present embodiment (solid line) is the above embodiment (broken line). I understand.

Further, in this embodiment, if the hole diameter and the number of the holes 62 are appropriately set and the sum of the passage areas of the communicating passages 66 is appropriately set, the descending speed of the nozzle needle 16 can be optimally determined. Then, as the moving flow rate to the central hole 21 increases, the descending stroke amount of the damping orifice valve 54 can be shortened, and the returning time of the damping orifice valve 54 can be shortened, so that the responsiveness is further enhanced. At the same time, simplification of the structure and cost reduction can be achieved by omitting the damping orifice valve 54. Of course, this embodiment also has the same advantage as the above-mentioned improvement of the initial injection characteristic. Further, since the pilot orifice valve 56 of this embodiment has a dome-shaped upper end surface 71,
There is also an advantage that the high pressure fuel in the upper end side chamber 64 can be smoothly guided to the hole 62.

As described above, the present invention is not limited to the above-mentioned modes, and various modes are possible.

[0048]

The present invention exhibits the following excellent effects.

(1) The interval time between injections can be set short.

(2) Good initial injection characteristics can be obtained even when the interval time between injections is short.

(3) Even if the initial injection rate is reduced, the characteristics at the end of injection (spill characteristics) are not deteriorated.

(4) NOx, combustion noise, etc. can be reduced and drivability can be improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view showing an embodiment of a needle valve control device according to the present invention.

FIG. 2 is a vertical sectional front view showing an injector in which the needle valve control device of FIG. 1 is adopted.

3A and 3B show a state of operation of a solenoid valve body, FIG. 3A shows a non-injection state, and FIG. 3B shows an injection state.

FIG. 4 is a graph showing injection characteristics in multi-stage injection,
(A) shows an input signal, (b) shows an injection state.

FIG. 5 is a perspective view showing a modified example.

FIG. 6 is a perspective view showing a modified example.

FIG. 7 is a perspective view showing a modified example.

FIG. 8 is a perspective view showing a modified example.

FIG. 9 is a diagram for explaining multi-stage injection.

FIG. 10 is a vertical sectional front view showing a conventional needle valve control device.

11 is a vertical cross-sectional front view showing the operation of the needle valve control device of FIG.

FIG. 12 is a vertical sectional front view showing a modified example.

FIG. 13 is a graph showing injection characteristics according to the modified example of FIG.

[Explanation of symbols]

 1 Injector 50 Needle valve control device 52 Control chamber 16 Nozzle needle (needle valve) 56 Pilot orifice valve (piston) 59 Orifice hole (orifice) 65 Lower end side chamber (rear side of piston) 66 Communication passage

Claims (1)

[Claims] 1. A piston that is pushed from its original position in a control chamber by supplying a high fuel pressure to lower a needle valve, and an orifice formed in the piston for appropriately discharging fuel in the control chamber when the needle valve is lifted. A needle valve control device for an injector, comprising: a communication passage that allows the fuel in the control chamber to pass to the back side of the piston when the piston returns to the original position.