JP2010180763A - Fuel injection nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection nozzle capable of suitably improving the properties of fuel spray injected under extremely low pressure at the time of pilot injection or initial injection when the fuel flow mode changes according to the amount of needle lift.
SOLUTION: A fuel injection nozzle 1 includes a nozzle body 2 provided with a hemispherical sack portion 26, an injection hole 27 communicating with the sack portion 26, and a needle slidably accommodated in the nozzle body 2. 3 is provided. A first chamfered portion R <b> 1 is formed in an upstream portion located upstream of the fuel flow among the inlets of the nozzle holes 27, and is located downstream of the fuel flow among the inlets of the nozzle holes 27. A second chamfered portion R2 having a smaller radius of curvature than the first chamfered portion R1 is formed in the downstream portion. The nozzle hole 27 is disposed such that the downstream portion is the upper end of the sack portion 26.
[Selection] Figure 3

Description

  The present invention relates to a fuel injection nozzle, and more particularly to a fuel injection nozzle whose fuel flow mode changes according to a needle lift amount (hereinafter referred to as a needle lift amount).

  2. Description of the Related Art Conventionally, there is known a fuel injection nozzle including a nozzle body provided with an injection hole and a needle that is slidably received in the nozzle body. In such a fuel injection nozzle, the fuel supply to the injection hole is shut off by the contact between the seat portion of the nozzle body and the contact portion of the needle, and the valve is closed. Further, when the seat portion of the nozzle body and the contact portion of the needle are separated from each other, fuel can be supplied to the nozzle hole and the valve is opened. With regard to the nozzle hole of such a fuel injection nozzle, for example, Patent Document 1 or 2 proposes a technique considered to be related to the present invention.

  Patent Document 1 discloses a fuel injection nozzle in which an upstream portion located upstream of a fuel flow in a nozzle hole inlet is chamfered with an arc surface. In this fuel injection nozzle, a depression facing the nozzle hole inlet is provided in the needle, and by providing the depression, an increase in the resistance of the fuel flow path is avoided and the initial fuel injection rate is increased. In this fuel injection nozzle, the upstream portion of the nozzle hole inlet is further chamfered with an arcuate surface so that the fuel flows smoothly into the nozzle hole to reduce the inflow loss and improve the initial injection rate. It contributes.

  Patent Document 2 discloses a fuel injection nozzle in which a chamfered portion having a large curved radius is formed in an upstream portion of a nozzle hole inlet and a chamfered portion having a small curved radius is formed in a downstream portion. In this fuel injection nozzle, by forming such a chamfered portion, bending loss from the upstream where the flow rate is relatively large is reduced, thereby increasing the flow rate of the injected fuel and promoting atomization of the fuel spray based thereon. I am trying. In addition, for example, Patent Document 3 proposes a technique that is considered to be related to the present invention in that the jet flow is changed according to the needle lift amount.

JP 2003-120474 A Japanese Patent Laid-Open No. 10-331747 JP 2007-51589 A

  By the way, in the fuel injection nozzle, since the fuel is injected under extremely low pressure at the time of pilot injection or initial injection with a small needle lift, the penetration force of the fuel spray is generally weak. For this reason, in such a fuel injection nozzle, a fuel spray with thick coarse droplets is formed by pilot injection or initial injection. As a result, the amount of smoke generated increases or the coarse droplets adhere to the combustion chamber wall surface. There was a risk that the discharge amount would increase. In this regard, in the fuel injection nozzle disclosed in Patent Document 1, although the initial injection rate is improved and the penetration force of the fuel spray injected at the initial stage is increased, the fuel pressure is instantaneously decreased at the initial stage of injection, so that a small amount. It is considered that there is a possibility that atomization of the fuel spray is not always sufficiently obtained in the pilot injection for injecting the fuel.

  In the fuel injection nozzle, the fuel distribution mode may change depending on whether the needle lift amount is small or large. For this reason, when the fuel flow mode changes according to the amount of needle lift in improving the fuel spray properties in contrast to the formation of a thick fuel spray as described above, the fuel flow mode is further improved. It is necessary to improve in consideration of changes. However, in the fuel injection nozzle disclosed in Patent Document 2, although the flow velocity of the fuel flowing into the nozzle hole from the upstream side is increased to promote atomization of the fuel spray, the change in the fuel circulation mode is particularly considered. Not. For this reason, the fuel injection nozzle disclosed in Patent Document 2 has a problem in that the properties of fuel spray at the time of pilot injection and initial injection with a small needle lift amount may not be improved sufficiently.

  Therefore, the present invention has been made in view of the above problems, and the characteristics of fuel spray injected under extremely low pressure at the time of pilot injection or initial injection when the flow mode of fuel changes according to the amount of needle lift. It aims at providing the fuel-injection nozzle which can improve suitably.

  The present invention for solving the above problems includes a nozzle body provided with a hemispherical sac portion, an injection hole communicating with the sac portion, a needle slidably accommodated in the nozzle body, A first chamfered portion is formed in an upstream portion located upstream of the fuel flow among the inlets of the nozzle holes, and a downstream located downstream of the fuel flow among the inlets of the nozzle holes The nozzle hole is formed such that a second chamfered portion having a curved surface radius smaller than that of the first chamfered portion is formed in the side portion or an edge portion is formed, and the downstream side portion is an upper end portion of the sack portion. Is a fuel injection nozzle.

  Moreover, it is preferable that this invention is the structure which made the curved-surface radius of the said 1st chamfer part 0.1 mm or more.

  In the present invention, when the edge portion is formed in the downstream portion, the angle formed by the wall surface of the upper end portion of the sack portion and the wall surface of the downstream portion on the nozzle hole side is 90 degrees or less. A configuration is preferred.

  ADVANTAGE OF THE INVENTION According to this invention, when the distribution | circulation mode of a fuel changes according to the amount of needle lifts, the characteristic of the fuel spray injected under the extremely low pressure at the time of pilot injection or the initial injection can be improved suitably.

It is a figure which shows typically the internal combustion engine 50 with each structure concerned. It is a figure which shows fuel injection nozzle 1 typically with a vertical section. It is a figure which expands the principal part of the fuel-injection nozzle 1 in the state where needle lift amount is small, and is typically shown with a vertical cross section. It is a figure which expands the principal part of the fuel-injection nozzle 1 in the state where the amount of needle lifts is large, and shows it typically in a vertical section. It is a figure which shows the relationship between each of the spray particle size, the spray length, and the amount of cavitation generation, and the needle lift amount. It is a figure which shows the relationship between the curved-surface radius of the chamfering part R provided in the entrance of the nozzle hole 27, and the amount of cavitation generation. FIG. 4 is a diagram showing the relationship between the radius of curvature of a chamfered portion R provided at the entrance of the nozzle hole 27 and the cavitation ratio in the nozzle hole 27. It is a figure which expands the principal part of fuel-injection nozzle 1 'which formed the edge part L, and shows it typically in a vertical cross section. The fuel injection nozzle 1 'is substantially the same as the fuel injection nozzle 1 except that an edge portion L is formed instead of the second chamfered portion R2. It is a figure which shows the relationship between the amount of cavitation generation | occurrence | production, and a spray particle diameter. It is a figure which shows the relationship between a spray particle diameter and the amount of smoke generation. In the figure which expands the principal part of the fuel-injection nozzle 1, and is typically shown with a vertical cross section, it is the figure which illustrated the spreading angle (beta). It is a figure which shows that the needle lift amount (gamma) from which the fuel distribution mode changes between the 1st and 2nd distribution modes changes according to the spreading angle (beta).

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for implementing the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically showing the internal combustion engine 50 together with related components. The internal combustion engine 50 is a diesel engine and includes a cylinder block 51, a cylinder head 52, a piston 53, and an injector 54. The cylinder block 51, the cylinder head 52 and the piston 53 form a combustion chamber 55. The injector 54 is disposed in a substantially central portion above the combustion chamber 55 in the cylinder head 52 and directly injects fuel into the combustion chamber 55. High pressure fuel is supplied to the injector 54 from the fuel injection pump 61 via the common rail 62. The injector 54 and the fuel injection pump 61 are electrically connected to an ECU (Electronic Control Unit) 70 that is a fuel injection control device as a control target. Various information such as the engine speed, the accelerator opening, and the coolant temperature is input to the ECU 70. The injector 54 includes the fuel injection nozzle 1 on the tip side.

  FIG. 2 is a view schematically showing the fuel injection nozzle 1 in a vertical section. The fuel injection nozzle 1 includes a nozzle body 2 and a needle 3. The nozzle body 2 is a bottomed cylindrical member, and includes a first hollow portion 21, a second hollow portion 22, a fuel pool forming portion 23, a fuel supply passage 24, a seat portion 25, and a sack. A portion 26 and a nozzle hole 27 are provided. The first hollow portion 21 has a cylindrical surface, opens at a substantially central upper end (rear end) of the nozzle body 2, and extends downward (front end side) along the axial direction. The lower end of the first hollow portion 21 is connected to the fuel pool forming portion 23. The fuel reservoir forming part 23 forms an annular fuel reservoir 40 together with the needle 3. A fuel supply passage 24 communicates with the fuel reservoir 40. A second hollow portion 22 is connected to the lower end of the fuel pool forming portion 23. The second hollow portion 22 has a cylindrical surface whose diameter is smaller than that of the first hollow portion 21. The second hollow portion 22 extends downward from the lower end of the fuel pool forming portion 23 along the axial direction.

  The lower end of the second hollow portion 22 is connected to the seat portion 25. The seat portion 25 has a truncated cone surface that gradually decreases in diameter toward the lower side. The lower end of the seat portion 25 is connected to a hemispherical sack portion 26. The sack portion 26 is provided in the tip portion of the nozzle body 2. The nozzle hole 27 is provided at the tip of the nozzle body 2 and communicates the sack portion 26 with the outside. A plurality of nozzle holes 27 are provided along the circumferential direction. The plurality of nozzle holes 27 can be provided, for example, at substantially equal intervals along the circumferential direction. A needle 3 is accommodated in the nozzle body 2 so as to be slidable along the axial direction of the nozzle body 2.

  The needle 3 includes a large diameter cylindrical portion 31, a small diameter cylindrical portion 32, a first reduced diameter portion 33, a second reduced diameter portion 34, a contact portion 35, and a tip portion 36. The large-diameter cylindrical portion 31 is loosely fitted with the first hollow portion 21. The small-diameter cylindrical portion 32 extends along the axial direction from the vicinity of the fuel reservoir 40 to the vicinity of the seat portion 25. The outer diameter of the small diameter cylindrical portion 32 is smaller than the inner diameter of the second hollow portion 22, and a fuel passage 41 is formed between the small diameter cylindrical portion 32 and the second hollow portion 22. The first and second reduced diameter portions 33 and 34 have a truncated cone surface. The lower end of the first reduced diameter portion 33 is connected to the upper end of the second reduced diameter portion 34. The first reduced diameter portion 33 is gradually reduced in diameter toward the lower side with a smaller degree than the second reduced diameter portion 34. The second reduced diameter portion 34 is gradually reduced in diameter toward the lower side with a greater degree than the first reduced diameter portion 33. A circular contact portion 35 is formed at a connection position of the first and second reduced diameter portions 33 and 34. The lower end of the second reduced diameter portion 34 is connected to a conical tip portion 36. The distal end portion 36 gradually decreases in diameter toward the lower side with a degree greater than that of the second reduced diameter portion 34, and a part of the distal end portion 36 is accommodated in the sack portion 26 in a closed state.

  The fuel is supplied to the nozzle hole 27 through the fuel supply passage 24, the fuel reservoir 40 and the fuel passage 41. On the other hand, when the contact portion 35 is in contact with the seat portion 25, the fuel supply is cut off and the valve is closed. On the other hand, when the needle 3 is lifted and the contact portion 35 is separated from the seat portion 25, fuel can be supplied and the valve is opened. The needle 3 is lifted when the force to push downward is smaller than the force to push the supplied fuel upward. In this respect, the injector 54 includes a control chamber (not shown) that applies a back pressure of a working fluid (for example, high-pressure fuel) to the needle 3 and an electric switching valve (not shown) that controls the flow of the working fluid into and out of the control chamber. The back pressure in the control chamber generates a force that pushes the needle 3 downward. The ECU 70 controls the needle lift amount by switching the back pressure applied to the needle 3 by controlling the electric switching valve.

  Next, the fuel distribution mode will be described with reference to FIGS. In the fuel injection nozzle 1, the fuel flow mode changes according to the needle lift amount. When the needle lift amount is small (when it is the first lift amount), the circulating fuel is throttled by the seat portion 25. In this case, the fuel distribution mode is the first distribution mode. As shown in FIG. 3, the first flow mode is a fuel flow mode in which the main flow is the flow that flows into the nozzle hole 27 from the downstream side of the nozzle hole 27 after the fuel flows into the sack portion 26. At this time, the fuel is injected from the nozzle hole 27 under extremely low pressure. On the other hand, when the needle lift amount is large (when the lift amount is a second lift amount larger than the first lift amount), the flowing fuel is throttled by the injection hole 27. In this case, the fuel distribution mode is the second distribution mode. As shown in FIG. 4, the second circulation mode is a fuel circulation mode in which the flow of fuel flowing into the nozzle hole 27 from the upstream side of the nozzle hole 27 is the main stream.

  In contrast to the change in the flow mode of the fuel, the inlet of the injection hole 27 is specifically formed in the fuel injection nozzle 1 as shown below. That is, the inlet of the nozzle hole 27 is formed with a first chamfered portion R1 having a large curved radius at the upstream portion located upstream of the fuel flow, and at the first downstream portion located downstream of the fuel flow. A second chamfered portion R2 having a smaller radius of curvature than the chamfered portion R1 is formed.

  As a result, during pilot injection or initial injection with a small needle lift amount, when the fuel flows into the injection hole 27 as shown in FIG. 3, the fuel flow is easily separated at the second chamfered portion R2. Cavitation can be generated in the nozzle hole 27. Further, in the fuel injection nozzle 1, since the sac portion 26 is formed in a hemispherical shape, the fuel smoothly turns in the sac portion 26 in the first flow mode. For this reason, attenuation of the fuel flow flowing into the nozzle hole 27 can be suppressed thereby, which can contribute to the separation of the fuel flow and the occurrence of cavitation. And after fuel is injected from the injection hole 27, since cavitation grows rapidly and collapses, this can promote atomization of fuel spray.

  On the other hand, at the time of main injection with a large needle lift amount, the fuel flows smoothly into the nozzle hole 27 along the first chamfered portion R1 as shown in FIG. For this reason, in this case, separation of the fuel flow can be prevented or suppressed, and as a result, the occurrence of cavitation can be prevented or suppressed. Further, since the flow rate coefficient is increased and the fuel flow velocity is increased, the penetration force of the fuel spray injected from the nozzle hole 27 can be strengthened, thereby promoting atomization of the spray by shear splitting with the atmosphere as in the prior art. . As a result, as in the prior art, a large amount of fuel can be injected in a short period of time, and high output can be handled.

  Further, in the fuel injection nozzle 1, the injection hole 27 is arranged so that the downstream side portion of the inlet of the injection hole 27 becomes the upper end portion of the sack portion 26 in the vertical section. As a result, the fuel can suitably reach the nozzle hole 27 with less attenuation of the fuel flow both when the fuel flows into the nozzle hole 27 from the upstream side and when it flows from the downstream side. In other words, this makes it possible to arrange the nozzle hole 27 at a well-balanced position for both the first and second flow modes. In addition, when the fuel flow mode changes according to the needle lift amount, the pilot can be improved in that the properties of the fuel spray can be improved while maintaining the atomization of the spray when the needle lift amount is large. It is possible to suitably improve the properties of fuel spray injected under extremely low pressure during injection or initial injection.

  Next, the relationship between the spray length, the cavitation generation amount, the spray particle size, and the needle lift amount will be described with reference to FIG. In FIG. 5C, the conventional case is also shown by a broken line for reference. In the fuel injection nozzle 1, the needle lift amount is controlled by the injector 54 under the control of the ECU 70. In controlling the injector 54, the ECU 70 specifically controls the injector 54 with an injection pattern capable of suppressing the fuel adhesion to the piston 53 and the combustion chamber 55 wall surface (cylinder wall surface) that causes HC emission. With this spray pattern, the spray length is as shown in FIG.

  At the time of pilot injection or initial injection, the needle lift amount is in the seat throttle region (the region where fuel is throttled by the seat portion 25). In this case, since the fuel is injected under extremely low pressure, the penetration force of the fuel is reduced. However, when the needle lift amount is in the seat restricting region, as described above, the fuel flow is separated at the chamfered portion R2. Therefore, in this case, cavitation occurs in the nozzle hole 27 as shown in FIG. 5 (b), and as a result, the discharge of HC is suppressed by the collapse of cavitation as shown in FIG. 5 (c). The fuel can be atomized.

  On the other hand, during main injection, the needle lift amount is in the injection hole throttle region. In this case, as described above, since the fuel smoothly flows into the nozzle hole 27 along the chamfered portion R1, the penetration force is increased. In this case, cavitation does not occur as shown in FIG. Therefore, in this case, as shown in FIG. 5C, the atomization of the fuel can be achieved while suppressing the discharge of HC by shear splitting with the atmosphere. That is, according to the fuel injection nozzle 1, atomization of fuel spray can always be achieved even in the injection pattern that can suppress the discharge of HC.

  Next, the preferable magnitude | size of the curved-surface radius of 1st and 2nd chamfer part R1, R2 is demonstrated using FIG. 6, FIG. As shown in FIG. 6, the amount of cavitation generation tends to decrease as the radius of the chamfered portion R provided at the entrance of the injection hole 27 increases, and finally to zero. In this regard, more specifically, as shown in FIG. 7, when the radius of curvature of the chamfered portion R is 0.1 mm or more, the cavitation ratio in the nozzle hole 27 is substantially zero, while the chamfered portion R It turns out that it will become large gradually when the magnitude | size of less than 0.1 mm. Therefore, the radius of curvature of the first chamfered portion R1 is preferably 0.1 mm or more from the viewpoint of preventing or suppressing the occurrence of cavitation.

  On the other hand, the radius of curvature of the second chamfer R2 from FIG. 7 is preferably less than 0.1 mm from the viewpoint of generating more cavitation. In this respect, more preferably, instead of forming the second chamfered portion R2 in the downstream portion of the inlet of the injection hole 27, it is desirable to form the edge portion L (see FIG. 8). Thereby, since more cavitation can be generated, atomization of fuel spray can be further promoted as shown in FIG. Further, since atomization of fuel spray can be further promoted, the amount of smoke generated can be further reduced as shown in FIG. When the edge portion L is formed, the angle formed by the edge portion L (the angle formed by the wall surface of the upper end portion of the sack portion 26 and the wall surface of the downstream portion on the nozzle hole 27 side in the vertical section) α is 90 degrees or less. It is preferable. As a result, the fuel flow can be more suitably separated, so that cavitation can be generated more reliably.

  Next, the setting of the spread angle β (see FIG. 11), which is the angle formed by the distal end portion 36 of the needle 3 and the upper end portion of the sack portion 26, will be described with reference to FIG. This divergence angle β is important in appropriately changing the fuel flow mode between the first and second flow modes according to the needle lift amount. As shown in FIG. 12, when the spread angle β is 15 degrees or more, it can be seen that the fuel flow mode becomes the first flow mode when the needle lift amount is small. It can be seen that as the spread angle β increases, the range of the needle lift amount in which the first flow mode is maintained is widened to the larger side.

  For this reason, in appropriately changing the fuel flow mode between the first and second flow modes according to the needle lift amount, the fuel flow mode changes between the first and second flow modes. It is preferable to set the spread angle β so that the needle lift amount γ at that time is equal to or greater than the maximum needle lift amount during pilot injection. In this respect, since the maximum needle lift amount at the time of pilot injection is 0.03 mm in the fuel injection nozzle 1, the spread angle β is required to be approximately 30 degrees or more in order to appropriately maintain the first flow mode at the time of pilot injection. It becomes. By managing the setting of the divergence angle β in this way, when the fuel flow mode changes according to the needle lift amount, the fuel flow mode is appropriately changed between the first and second flow modes. Therefore, the properties of fuel spray injected under extremely low pressure during pilot injection or initial injection can be further improved.

The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.
For example, in the above-described embodiment, since the management of the setting of the spread angle β is easy, the example in which the tip portion 36 is provided on the needle 3 separately from the second reduced diameter portion 34 has been described. However, the present invention is not necessarily limited to this. For example, the tip portion may be integrally provided at the same inclination angle as the second reduced diameter portion.

DESCRIPTION OF SYMBOLS 1 Fuel injection nozzle 2 Nozzle body 25 Seat part 26 Sack part 27 Injection hole 3 Needle 33 1st diameter reduction part 34 2nd diameter reduction part 35 Contact part 36 Tip part 40 Fuel reservoir 41 Fuel passage 50 Internal combustion engine 54 Injector 61 Fuel injection pump 62 Common rail 70 ECU

Claims (3)

A nozzle body provided with a hemispherical sac portion and an injection hole communicating with the sac portion;
A needle slidably accommodated in the nozzle body,
A first chamfered portion is formed in an upstream portion located upstream of the fuel flow among the inlets of the nozzle holes, and a downstream portion located downstream of the fuel flow among the inlets of the nozzle holes. Forming a second chamfer with a smaller radius of curvature than the first chamfer, or forming an edge,
A fuel injection nozzle in which the injection hole is disposed so that the downstream portion is an upper end portion of the sack portion. The fuel injection nozzle according to claim 1,
A fuel injection nozzle in which a radius of curvature of the first chamfered portion is 0.1 mm or more. The fuel injection nozzle according to claim 1 or 2,
A fuel injection nozzle in which, when the edge portion is formed in the downstream portion, an angle formed by a wall surface of the upper end portion of the sack portion and a wall surface of the downstream portion on the nozzle hole side is 90 degrees or less.

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