fuel injector

Abstract

Fuel injector, which has the following features: a nozzle body (1) having a valve seat (5) in a conical shape, formed within a blind chamber (6) to collect pressurized fuel that has passed through the interior of the valve seat (5), and an injection orifice (3) to inject pressurized fuel supplied to the blind chamber (6) to an outside; and a needle (2) having a seat section (8) for cutting off the supply of pressurized fuel to the blind chamber (6) when placed on the valve seat (5), and a conical section (9) having a conical shape with a boundary at the seat section (8), wherein the conical section (9) is inserted into the blind chamber (6), the needle (2) being driven in a linear direction within the nozzle body (1), wherein the needle (2) must move upwards in one direction when fuel injection is started, the needle (2) must move downwards in one direction when the fuel injection is stopped, an upward movement amount of the needle (2) is a lifting amount, a direction along which the needle (2) must move, an axial direction (h), an axial straight line which passes through the center of the bag chamber (6) is a bag centerline (L1), an opening area of ​​a throttle section (x) which is defined between an upper end of the sack chamber (6) and the conical section (9), is a throttle opening area S1, a straight line which is drawn by extending a central axis of the injection hole (3) into the blind chamber (6) is an extended injection hole line (L2), a place where the injection hole (3) opens into the blind chamber (6), is an injection hole inlet (3a), a straight line which passes through a lower end of the injection hole inlet (3a) and extends parallel to the injection hole (3) is an extended lower end line (L3), one half of an area which is surrounded by the throttle section (x), the needle (2), an inner wall of the blind chamber (6) and the extended lower end line (L3) in a cross-section of the blind chamber (6) recorded along the blind center line (L1), is an injection hole upstream surface S2, a passage surface of the injection hole (3) is an injection surface S3, a lift-off amount if the throttle opening area (S1) is equal to an area calculated by multiplying the injection hole area by the number of injection holes, a predetermined lift-off amount L is, a viscosity coefficient of fuel a coefficient is, an index value Sa is calculated in accordance with an equation as below, S a = ρ 2 ∫ h = 0 h = L ( S 1 S 2 − S 1 ) 2 ie and the index value of Sa satisfies an inequality of Sa ≥ 0.5.

Description

CROSS-REFERENCE TO A RELATED REGISTRATION

[0001] The present application is based on Japanese patent application No. 2015-126865, which was filed on June 24, 2015, the disclosure of which is incorporated herein by reference. TECHNICAL AREA

[0002] The present disclosure relates to a fuel injector nozzle for injecting fuel. STATE OF THE ART

[0003] A fuel injection nozzle of a conical insertion type, disclosed in, for example, patent literature 1, has a conical section provided at a tip end of a needle and a sac chamber axially overlapping in a nozzle body. PREVIOUS TECHNICAL LITERATURE PATENT LITERATURE

[0004] Patent Literature 1: JP-A-2010-174819

[0005] The following description assumes that a needle moves in an axial direction and ascends to initiate fuel injection. In a low-lift condition, where the needle lift is small immediately after injection is initiated, strong turbulence develops in the fuel flow within a blind chamber. Such turbulence can undesirably decrease the blind chamber flow rate coefficient, which is a measure of the rate at which fuel is introduced or delivered from the blind chamber into an injection orifice. When the blind chamber flow rate coefficient becomes small, the spray penetration force is weak.The term "spray penetration force," referred to herein, represents a force with which atomized fuel, injected from the injection orifice, is carried a considerable distance. If a spray penetration force becomes weak, atomized fuel cannot be carried far. As the lift-off magnitude increases, the flow of fuel passing through the blind chamber changes with a variance in the lift-off magnitude. More precisely, fuel that flowed along the conical section in the low-lift condition changes to flow along an inner wall of the blind chamber as the lift-off magnitude increases. For this reason, the flow of fuel in the blind chamber can become unstable.

[0006] DE 10 2006 043 460 A1 discloses a method for optimizing an injection nozzle for an internal combustion engine, comprising a nozzle body and a nozzle needle axially displaceable in a bore of the nozzle body against a closing force, wherein the nozzle needle has a valve sealing surface on its combustion chamber-side end face, with which it interacts with a valve seat surface of the nozzle body to control a flow cross-section to at least one injection port in the combustion chamber of the internal combustion engine, wherein a mathematical method in the form of Particle Swarm Optimization (PSO) is used for the geometric design of the injection nozzle when using an arbitrary selection of independent parameters, and the criteria determined as optimal are used in the design of the injection nozzle.

[0007] DE 10 2014 118 062 A1 discloses a fuel injector in which a side surface and a seat surface are both smoothly connected in a cross-section with an axis of a nozzle body by an arc of a circle that encompasses both the side surface and the seat surface. A portion of a needle located adjacent to a tip end face of a seat section is a cone with a diameter that is reduced in the axial direction towards a tip end face of the cone. Therefore, the seat surface or the side surface has no corner or edge, and the seat surface and the side surface form a curved surface. Since cavitation generated in a blind chamber can be reduced, even when the injection quantity is very small, so that an injection orifice does not restrict the injection flow, the flow coefficient of the injection flow is improved, and injection penetration can be maintained.

[0008] DE 10 2015 111 079 A1 also discloses a fuel injector. This fuel injector has a connecting surface that joins an inner blind wall surface and a seat surface, and a conically tapered surface with a taper ratio greater than that of the seat surface. This connecting surface directs the fuel towards a radial center point after it has flowed along the seat surface and then into a blind chamber. Since the fuel has thus been directed towards the injection holes after flowing through a region near the radial center point in the blind chamber, the fuel is guided into the injection hole along an axis of a flow path of the injection hole.This prevents an interruption of fuel flow that occurs near an inlet opening of the injection hole and the formation of cavitation in the injection hole. SUMMARY OF THE INVENTION

[0009] It is an object of the present disclosure to manufacture a fuel injector of a conical insertion type which is able to increase a flow rate coefficient in a blind chamber and to stabilize a flow of fuel in the blind chamber.

[0010] The inventors of the present disclosure found that the flow of fuel in a blind chamber can be controlled by controlling a throttle opening area S1 and an injection hole upstream area S2. More precisely, the inventors of the present disclosure found that equation (1) as shown below, which uses the throttle opening area and the injection hole upstream area, is proportional to a flow rate coefficient in the blind chamber. Flow rate coefficient in the bag ∝ρ2∫h=0h=L(S1S2−S1)2dh

[0011] Setting an index value Sa, calculated in accordance with the above equation (1), to 0.5 or greater not only allows an increase in the flow rate coefficient in the bag chamber, but also allows a stabilization of the fuel flow in the bag chamber.

[0012] According to one aspect of the present disclosure, a fuel injector nozzle has a nozzle body 1 having a valve seat 5, which is in a conical shape and is formed within a blind chamber 6, which is formed to collect pressurized fuel that has passed through an interior of the valve seat and an injection orifice 3 to inject the pressurized fuel supplied to the blind chamber to an exterior. The fuel injector nozzle further has a needle 2 having a seat section 8, which is for cutting off the supply of pressurized fuel to the blind chamber when it is placed on the valve seat, and a conical section 9, which is in a conical shape with a boundary at the seat section, the conical section being inserted into the blind chamber, the needle being driven in a linear direction within the nozzle body.The needle must move upwards when fuel injection is started. The needle must move downwards when fuel injection is stopped. An upward movement of the needle is called a lift-off. A direction along which the needle must move is called an axial direction h. An axial straight line passing through the center of the blind chamber is called a blind centerline L1. An opening area of ​​a throttle section x, bounded between an upper end of the blind chamber and the conical section, is called a throttle opening area S1. A straight line drawn into the blind chamber by extending a central axis of the injection hole is called an extended injection hole line L2. A location where the injection hole opens into the blind chamber is called an injection hole inlet 3a.A straight line passing through the lower end of the injection port inlet and extending parallel to the injection port is an extended lower end line L3. Half of an area enclosed by the throttle section, the needle, an inner wall of the blind chamber, and the extended lower end line in a cross-section of the blind chamber taken along the blind centerline is an injection port upstream area S2. A passage area of ​​the injection port is an injection area S3. A lift-off amount, when the throttle port area is equal to an area calculated by multiplying the injection port area by the number of injection ports, is a predetermined lift-off amount L. A viscosity coefficient of fuel is a coefficient. An index value Sa is calculated according to an equation as shown below. The index value Sa satisfies an inequality Sa ≥ 0.5. Sa=ρ2∫h=0h=L(S1S2−S1)2dh BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other functions, features, and advantages of the present disclosure will become clearer from the following detailed description, which is prepared with reference to the accompanying drawings. In the drawings: The above and other tasks, configurations and advantages of the present disclosure will become clearer from the following detailed description, taken in conjunction with the accompanying drawings, in which: Fig. 1 is a sectional view of a main section of a fuel injector nozzle along a sac centerline; Fig. 2. One view is used to examine a main section of the fuel injector nozzle; Fig. 3A is a view which is used to describe a throttle opening area; Fig. 3B is a view which is used to describe an injection hole upstream surface, and Fig. 3C is a view which is used to describe an injection hole surface; Fig. 4A and Fig. 4B views are used to describe an operation when an index value Sa is less than 0.5; and Fig. 5A and Fig. 5B views are used to describe an operation in the case where the index value Sa is set to 0.5 or greater. DESCRIPTION OF EXECUTION FORMS

[0014] Embodiments for carrying out the present disclosure according to the drawings are described below. It should be acknowledged that the embodiments described below are merely an example and that the present disclosure is not limited to the embodiments described below. (First embodiment)

[0015] A first embodiment is described with reference to Fig. 1 to Fig. 5B. A machine attached to an automobile has a fuel injection device. A fuel injection device of the present embodiment is used for a diesel engine and has a common fuel rail to accumulate fuel under high pressure. The fuel injection device includes direct-injection injectors for injecting fuel under high pressure, which are attached to the respective cylinders of the engine and inject fuel directly into the attached cylinders.

[0016] The injector has a fuel injection nozzle. The fuel injection nozzle has a nozzle body 1 and a needle 2. The nozzle body 1 is supplied with pressurized fuel from the common fuel line. The needle 2 is driven linearly within the nozzle body 1. Hereinafter, the magnitude of an upward movement of the needle 2 is referred to as a lift magnitude, and the direction of movement of the needle 2 is referred to as an axial direction h.

[0017] A drive system for needle 2 is not limited to any specific system. Examples of applicable drive systems for needle 2 include, but are not limited to, an electromagnetic valve injector, a piezo injector, and an electromagnetically driven injector. In the electromagnetic valve injector, needle 2 is driven by hydraulic pressure controlled by an electromagnetic valve. In the piezo injector, needle 2 is driven by hydraulic pressure controlled by a piezo actuator. In the electromagnetically driven injector, needle 2 is driven directly by an electromagnetic actuator.

[0018] The fuel injector will now be described in detail. A nozzle hole 4, a valve seat 5, and a collection chamber 6 are provided within the nozzle body 1. Fuel under high pressure is supplied to the nozzle hole 4. The valve seat 5 is conical in shape. The collection chamber 6 has a spherical surface in which pressurized fuel, which has passed through the interior of the valve seat 5, is collected. The valve seat 5 is formed at the lower end of the nozzle hole 4. The conical surface of the valve seat 5 decreases in diameter from top to bottom.

[0019] The sack chamber 6 is formed by a combination of a cylindrical surface 6a, which extends downwards from a lower end of the valve seat 5, and a hemispherical surface 6b, which is coupled to a lower end of the cylindrical surface 6a. More precisely, a hemispherical bulge or swelling section 7, which is exposed to a combustion chamber of the machine, is provided on an outer surface of the nozzle body 1 at a lower end, and the sack chamber 6 is provided in the interior of the bulge section 7.

[0020] The nozzle body 1 is provided with one or more injection holes 3, from which pressurized fuel, supplied to the blind chamber 6, is injected onto an outer surface of the nozzle body 1. The following describes a configuration in which multiple injection holes 3 are formed as a specific example.

[0021] Each injection hole 3 is designed to pass through the swell section 7 from the inside to the outside. More precisely, the injection hole 3 is a hole that passes diagonally from an inner wall surface of the bag chamber 6 to an outer wall surface of the swell section 7, and is drilled by cutting with a drill blade, by electric arc machining, laser beam machining, or the like. Fig. Figure 1 shows a configuration in which the injection holes 3 are circular holes, each of which, as an example, has a constant diameter. However, it should be acknowledged that the shape of the injection holes 3 is not limited to the shape shown in Figure 1. Fig. 1 is shown.

[0022] The needle 2 is in a shaft or wave shape, extending in a top-to-bottom direction. The needle 2 is supported to be driven in the top-to-bottom direction at the center of the nozzle hole 4. The needle 2 is provided with an annular seat section 8. The seat section 8 is positioned on the valve seat 5 to cut off the supply of pressurized fuel to this chamber 6.

[0023] Seat section 8 is formed at the boundary between two conical surfaces, each with a different spread or angle of spread. More precisely, the angle of spread of a conical surface above seat section 8 is smaller than the angle of spread of the valve seat 5, whereas the angle of spread of a conical surface below seat section 8 is larger than the angle of spread of the valve seat 5. In the following description, the conical section below seat section 8 is referred to as conical section 9. This means that the needle 2 is formed with conical section 9 in a conical shape, the diameter of which decreases from seat section 8 to the underside, and is positioned at the boundary with seat section 8.

[0024] The fuel injector nozzle is of a conical insertion type. More precisely, a portion of the conical section 9 is inserted into the blind chamber 6. The conical section overlaps the blind chamber 6 in the axial direction h. This means that a recessed section 10, which is provided at a lower end of the conical section 9, is positioned below a boundary line 11 between the valve seat 5 and the blind chamber 6. The shape of the recessed section 10 is not limited to any specific form. As shown in Fig. As shown in Figure 2, the recess section 10 can be formed in the form of a flat surface perpendicular to the axial surface h. This differs from the shape shown in Figure 2. Fig. As shown in Figure 2, the recessed section 10 can be formed in the form of a conical surface which has a larger spreading angle than that of the other conical section 9.

[0025] The following is a supplementary description of the conical injector type. In a conical injector type fuel injector, the recess section 10 is positioned below the boundary line 11 when the seat section 8 is seated on the valve seat 5, and the conical section 9 and the blind chamber 6 overlap in the axial direction h. The conical section 9 can overlap the blind chamber 6 in the axial direction h when the needle 2 is raised to its maximum position. Alternatively, the conical section 9 can protrude from the blind chamber 6 when the needle 2 is raised to its maximum position.

[0026] In a state where needle 2 moves upwards and seat section 8 is not seated on valve seat 5, one side of the pressurized fuel supply is connected to the injection holes 3, and fuel is injected from the injection holes 3. Conversely, in a state where needle 2 moves downwards and seat section 8 is seated on valve seat 5, the communication between the pressurized fuel supply and the injection hole 3 is blocked, and fuel injection is stopped.

[0027] The fuel injector of the present embodiment will now be described in more detail. The axial dimension of the cylindrical surface 6a is a pocket length 1. The diameter of the cylindrical surface 6a is a diameter dimension ϕds. An axial straight line passing through the center of the pocket chamber 6, i.e., an axial straight line passing through the center of a cylinder forming the cylindrical surface 6a, is a pocket centerline L1. A straight line drawn by extending the central axis of the injection hole 3 into the pocket chamber 6 is an extended injection hole line L2. A location where the injection hole 3 opens into the pocket chamber 6 is an injection hole inlet 3a. A straight line passing through a lower end of the injection hole 3a and parallel to the extended injection hole line L2 is an extended lower end line L3.

[0028] Additionally, the opening area of ​​a throttle section x, defined between the upper end of the bag chamber 6 and the conical end 9, is a throttle opening area S1. Half of an area encompassed by the throttle section x, the needle 2, the inner wall of the bag chamber 6, and the extended lower end line L3 in the cross-section of the bag chamber 6 along the bag centerline L1 (see Fig. 1) is surrounded by an upstream injection hole surface S2. The through-hole surface of injection hole 3 is an injection hole surface S3 (see Fig. 3A to Fig. 3C).

[0029] A needle lift-off amount L is a predetermined lift-off amount L when the throttle opening area S1 is equal to an area calculated by multiplying the injection hole area S3 by the number of injection holes 3. As described, the number of injection holes can be one. A viscosity coefficient of fuel is a coefficient

[0030] The throttle opening area S1 is an area that varies with the amount of lift-off. More precisely, as the amount of lift-off increases, the distance from the upper end of the bag chamber 6 to the conical section 9 becomes greater. Consequently, the throttle opening area S1 becomes larger.

[0031] The injection hole upstream surface S2 will now be described in detail. Fig. Figure 1 shows a cross-section of bag chamber 6, taken along the bag centerline L1. In the cross-section of the Fig. 1 the injection hole upstream surface S2 is present on both sides across the bag centerline. Fig. Figure 2 shows one half of the cross-section of the bag chamber 6, which is located in Fig. Figure 1 shows the cross-section divided into two along the centerline of the bag. In the cross-section shown in Fig. Figure 2 shows that the area enclosed by the throttle section x, the needle 2, the inner wall of the sack chamber 6 and the extended lower line L3 is the inlet hole upstream surface S2.

[0032] The fuel injector of the present embodiment is of a wide-angle injection type. In a wide-angle injection type fuel injector, the injection angle Θ1 is set within a range of 60° to 85°. The specific example, which is described in Fig. The configuration shown in Figure 1 will now be described. The following will describe in more detail a configuration in which two injection holes 3 are opposite each other, separated by the center line L1. This means that in a wide-angle injection type fuel injector, the angle formed between the extended injection hole line L2 of one injection hole 3 and the extended injection hole line L2 of the other injection hole 3 by the center line L1 is 120°–170°.

[0033] Additionally, as a specific example, injection hole 3 is formed in such a way that the injection extension line L2 becomes perpendicular to a line normal to the hemispherical surface 6b. However, it should be acknowledged that the configuration of injection hole 3 is not limited to the configuration shown above.

[0034] The flow of fuel in the blind chamber 6 can be controlled by adjusting the throttle opening area S1 and the injection orifice upstream flow area S2. A flow rate coefficient in the blind chamber 6 is proportional to equation (1) above. In the fuel injector of the present embodiment, an index value Sa, calculated in accordance with equation (3) as shown below, satisfies an inequality of Sa ≥ 0.5. Sa=ρ2∫h=0h=L(S1S2−S1)2dh

[0035] More precisely, the index value Sa is set to 0.5 or greater by increasing the diameter dimension ϕds and decreasing the sag length 1. A configuration for such a setting will now be described in more detail. The throttle opening area S1 is increased by increasing the diameter dimension ϕds. Furthermore, the injection hole upstream area S2 is decreased by decreasing the sag length 1. The index value Sa is therefore set to 0.5 or greater.

[0036] In the equation (3) above, h = 0 indicates an axial position of needle 2 when injection is stopped, and h = L indicates an axial position of needle 2 when the lift-off amount reaches the predetermined lift-off amount L.

[0037] By referring to the Fig. 4A and Fig. 4B and Fig. 5A and Fig. 5B will compare the following operations in the case where the index value Sa is set to be less than 0.5 and in the case where the index value Sa is set to 0.5 or greater.

[0038] Fig. Figure 4A shows an operation in a low-lift condition where the index value Sa is set to be less than 0.5. When the throttle opening area S1 is small, fuel flowing into the blind chamber 6 gains force. Consequently, strong turbulence develops in the fuel flow within the blind chamber 6, and the flow rate coefficient in the blind chamber 6 is reduced.

[0039] Fig. Figure 4B shows an operation in a high-lift state in a case where the index value Sa is set to be less than 0.5. If the injection hole upstream area S2 is large, the fuel flow b1 entering the blind chamber 6 changes to flow along the inner wall of the blind chamber 6. Therefore, the fuel flow in the blind chamber 6 becomes unstable.

[0040] Fig. Figure 5A shows an operation in a low-lift condition where the index value Sa is set to 0.5 or greater. If the throttle opening area S1 is large, the force of the fuel flowing into the blind chamber 6 can be reduced. Therefore, fuel turbulence in the blind chamber 6 can be limited, and the flow rate coefficient in the blind chamber 6 can be increased.

[0041] Fig.5B shows an operation in a high-lift state in the case where the index value Sa is set to 0.5 or greater.

[0042] If the injection hole upstream area S2 is small, the fuel flow b2 into the blind chamber 6 changes little. This means that the fuel flow into the blind chamber 6 becomes stable. (First effect of the first embodiment)

[0043] As described, by setting the index value Sa, which is calculated in accordance with equation (3) above, to 0.5 or greater, the flow rate coefficient in the bag chamber 6 can be increased. Furthermore, a fuel flow in the bag chamber 6 can be stabilized. Accordingly, the first embodiment can provide a fuel injection nozzle with a strong spray penetration force that remains constant even when the lift-off amount varies. (Second effect of the first embodiment)

[0044] By setting the index value Sa, which is calculated in accordance with equation (3) above, to 0.5 or greater, the bag volume can be reduced. The bag volume is the volume between the nozzle body 1 and the needle 2 in the bag chamber 5. Due to the ability to reduce the bag volume, the amount of fuel remaining in the bag chamber 6 after an injection has stopped can be reduced. Thus, the first embodiment can achieve a reduction in HC in an exhaust gas that is generated when fuel remaining in the bag chamber 6 leaks into the combustion chamber through the injection holes 3. (Other embodiments)

[0045] It should be acknowledged that the present disclosure is not limited to the embodiment described above and that embodiments such as the following may also be used.

[0046] In the embodiment described above, the bag chamber 6 is formed by combining the cylindrical surface 6a and the hemispherical surface 6b. It should be noted that the shape of the bag chamber 6 is not limited to the shape described above. More precisely, the cylindrical surface 6a can be of a different shape, or the hemispherical surface 6b can be of a different shape, while the cylindrical surface 6a remains unchanged.

[0047] The above embodiment describes the wide-angle injection type with an injection angle Θ1 set to 60° to 85° as an example. However, it should be acknowledged that the injection angle Θ1 is not limited to the range specified above. The injection angle Θ1 can be set to less than 60° or greater than 85°.

[0048] The above embodiment describes a case in which the present disclosure is applied to a fuel injector used for a diesel engine. A diesel engine is a compression-ignition engine with internal combustion. The fuel injected by the fuel injector is not limited to light oil. Fuel injected by the fuel injector can be other types of fuel suitable for compression ignition, such as dimethyl ether.

[0049] The above embodiment described a case in which the present disclosure is applied to a fuel injector used for a diesel engine. It is noted that the present disclosure can be applied to a fuel injector used for a gasoline engine.

[0050] The fuel injector can be of a circumferential injection type, configured to inject fuel all around the nozzle. Alternatively, the fuel injector can be of a double-sided injection type, configured to inject fuel on both sides of the nozzle. Furthermore, the fuel injector can be of a single-sided injection type, configured to inject fuel on only one side of the nozzle.

[0051] While the above has described the present disclosure according to the embodiments, it should be understood that the present disclosure is not limited to the embodiments and structures described above. The present disclosure includes various modifications and alterations within the equivalent scope. Additionally, various combinations and embodiments, as well as other combinations and embodiments that further include one element alone and more or less than one element, are likewise within the scope and concept of the present disclosure.

Claims

[1] Fuel injector comprising the following: a nozzle body (1) having a valve seat (5) in a conical shape, formed within a blind chamber (6) to collect pressurized fuel that has passed through the interior of the valve seat (5), and an injection orifice (3) to inject pressurized fuel supplied to the blind chamber (6) to an outside; and a needle (2) having a seat section (8) for cutting off the supply of pressurized fuel to the blind chamber (6) when placed on the valve seat (5), and a conical section (9) having a conical shape with a boundary at the seat section (8), wherein the conical section (9) is inserted into the blind chamber (6), the needle (2) being driven in a linear direction within the nozzle body (1), wherein the needle (2) must move upwards in one direction when fuel injection is started, the needle (2) must move downwards in one direction when the fuel injection is stopped, an upward movement amount of the needle (2) is a lifting amount, a direction along which the needle (2) must move, an axial direction (h), an axial straight line which passes through the center of the bag chamber (6) is a bag centerline (L1), an opening area of ​​a throttle section (x) which is defined between an upper end of the sack chamber (6) and the conical section (9), is a throttle opening area S1, a straight line which is drawn by extending a central axis of the injection hole (3) into the blind chamber (6) is an extended injection hole line (L2), a place where the injection hole (3) opens into the blind chamber (6), is an injection hole inlet (3a), a straight line which passes through a lower end of the injection hole inlet (3a) and extends parallel to the injection hole (3) is an extended lower end line (L3), one half of an area which is surrounded by the throttle section (x), the needle (2), an inner wall of the blind chamber (6) and the extended lower end line (L3) in a cross-section of the blind chamber (6) recorded along the blind center line (L1), is an injection hole upstream surface S2, a passage surface of the injection hole (3) is an injection surface S3, a lift-off amount if the throttle opening area (S1) is equal to an area calculated by multiplying the injection hole area by the number of injection holes, a predetermined lift-off amount L is, a viscosity coefficient of fuel a coefficient is, an index value Sa is calculated in accordance with an equation as below, Sa=ρ2∫h=0h=L(S1S2−S1)2dh and the index value of Sa satisfies an inequality of Sa ≥ 0.

5. [2] Fuel injector according to claim 1, wherein the sack chamber (6) has a cylindrical surface (6a) which extends downwards from a lower end of the valve seat (5) and a hemispherical surface (6b) which is formed at a lower end of the cylindrical surface (6a). [3] Fuel injector nozzle according to claim 1 or 2, wherein an angle (Θ1) formed between a lower end side of the bag centerline (L1) and the extended injection hole line (L2) is set in a range of 60° to 85°.

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