fuel injection device

Abstract

Even if deposits caused by fuel form around the armature bolt, malfunctions of the armature bolt due to such deposits are suppressed. [Solution] A fuel injection device (10) that injects fuel into an internal combustion engine comprises a first member (50) that moves back and forth in the axial direction, and a second member (37) that has a sliding hole (37a) into which the first member (50) is inserted and slidably supports the first member (50). The first member (50) and the second member (37) are provided in the region through which the fuel flows, and the thermal expansion coefficient of the second member (37) is smaller than that of the first member (50).

Description

Technical Field

[0001] The present invention relates to a fuel injection device that injects fuel into a combustion chamber of an internal combustion engine.

Background Art

[0002] A fuel injection device (fuel injector) that injects fuel into a combustion chamber of an internal combustion engine such as a diesel engine includes a housing having a fuel injection hole formed at one end, and a nozzle needle provided inside the housing so as to be reciprocally movable and opening and closing the fuel injection hole. Further, the fuel injection device includes a pressure control chamber formed inside the housing so as to face an end portion of the nozzle needle on the side opposite to the fuel injection hole side, and a pressure control valve that opens and closes a discharge hole for discharging fuel from the pressure control chamber.

[0003] In the fuel injection device, when the pressure control valve opens the discharge hole, the fuel in the pressure control chamber is discharged, and the pressure of the fuel in the pressure control chamber decreases. As a result, the force that presses the nozzle needle toward the fuel injection hole side by the pressure of the fuel in the pressure control chamber decreases, the nozzle needle moves to the side opposite to the fuel injection hole, the fuel injection hole is opened, and fuel is injected from the fuel injection hole into the combustion chamber.

[0004] For example, Patent Document 1 discloses an armature bolt provided with a valve body for opening and closing an opening / closing orifice passage (discharge hole) connected to a pressure control chamber, an armature guide into which the armature bolt is inserted, and a spring that applies an urging force to the armature bolt, and a fuel injection device in which the outer periphery of the armature bolt is supported in a sliding hole provided in the armature guide.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] However, in the pressure control valve described in Patent Document 1, the gap between the armature bolt and the sliding hole of the armature guide is narrow, and deposits caused by fuel may be generated. In particular, in fuel injection systems that use biofuels such as FAME (Fatty Acid Methyl Ester), deposits are more likely to be generated in the aforementioned narrow gap compared to fuel injection systems that use conventional fuels. If the amount of deposit buildup becomes large, it can create sliding resistance in the armature bolt, which may prevent the fuel injection system from supplying the desired amount of fuel to the engine.

[0007] The present invention has been made in view of the above problems, and provides a fuel injection system that can suppress malfunction of an armature bolt due to deposits caused by fuel, even when such deposits occur around the armature bolt. [Means for solving the problem]

[0008] To solve the above problems, according to one aspect of the present invention, a fuel injection device for injecting fuel into an internal combustion engine is provided, comprising: a first member that moves back and forth in the axial direction; and a second member that has a sliding hole into which the first member is inserted and slidably supports the first member, wherein the first member and the second member are provided in a region through which fuel flows, and the thermal expansion coefficient of the second member is smaller than that of the first member. [Effects of the Invention]

[0009] As described above, according to the present invention, even if deposits caused by fuel are generated around the armature bolt, malfunctions of the armature bolt due to such deposits can be suppressed. [Brief explanation of the drawing]

[0010] [Figure 1]This is a schematic diagram showing an example of the basic configuration of a fuel injection system according to the present disclosure. [Figure 2] This is a partial cross-sectional view showing the configuration of the pressure control valve of the fuel injection system according to this embodiment. [Figure 3] This is an explanatory diagram showing the clearance between the armature bolt and the armature guide during operation of an internal combustion engine. [Figure 4] This is an explanatory diagram showing the gap between the armature bolt and the armature guide when an internal combustion engine is stopped, based on a reference example. [Figure 5] This is an explanatory diagram showing the gap between the armature bolt and the armature guide during the startup of an internal combustion engine, based on a reference example. [Figure 6] This is an explanatory diagram showing the gap between the armature bolt and the armature guide when the internal combustion engine is stopped according to this embodiment. [Figure 7] This is an explanatory diagram showing the gap between the armature bolt and the armature guide when starting the internal combustion engine according to this embodiment. [Modes for carrying out the invention]

[0011] Preferred embodiments of this disclosure will be described in detail below with reference to the attached drawings. The specific dimensions, materials, numerical values, etc., shown in the following embodiments are merely examples to facilitate understanding of the invention and do not limit this disclosure unless otherwise specified. In this specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals to avoid redundant explanations. In the following description, the directions up, down, left, and right refer to the directions shown in the illustrations.

[0012] <Fuel injection device> First, an example of the configuration of a fuel injection system according to the embodiment of this disclosure will be described.

[0013] Figure 1 shows a cross-sectional view of the fuel injection device 10. The illustrated fuel injection device 10 is, for example, provided in a fuel injection system equipped with a common rail, and injects fuel, which is supplied under pressure from a fuel supply pump and distributed by a common rail that stores the pressure, into the cylinders of an internal combustion engine.

[0014] The fuel injection system 10 comprises an injector housing 11, a nozzle body 13, a nozzle nut 14, a nozzle needle 19, a piston 23, and a holder 25. The nozzle body 13 is attached to the front end of the injector housing 11 using the nozzle nut 14. The holder 25 is attached to the rear end of the injector housing 11 by press-fitting or screwing.

[0015] The injector housing 11 has a hole extending in the axial direction, and a piston 23 is slidably disposed within this hole. The nozzle body 13 has a hole extending in the axial direction, and a nozzle needle 19 is slidably disposed within this hole. A fuel injection hole 12 is formed at the tip (lower end) of the hole. The hole in the injector housing 11 and the hole in the nozzle body 13 are located coaxially. Between the piston 23 and the nozzle needle 19, an intermediate member 21 is positioned in contact with both the piston 23 and the nozzle needle 19, respectively. The intermediate member 21 is constantly biased toward the nozzle needle 19 by the biasing force of a spring 22, biasing the nozzle needle 19 toward the fuel injection hole 12 (valve closing direction).

[0016] The fuel injector 10 includes a first fuel passage 15 and a second fuel passage 16 through which high-pressure fuel distributed from a common rail via an inlet body (not shown) passes. The high-pressure fuel flowing through the first fuel passage 15 is introduced into a gallery provided midway through the hole in the nozzle body 13. The pressure of the high-pressure fuel introduced into the gallery biases the nozzle needle 19 toward the rear end (in the valve opening direction). The high-pressure fuel flowing through the second fuel passage 16 is introduced into a pressure control chamber 17 formed on the rear end side of the piston 23. The pressure of the high-pressure fuel introduced into the pressure control chamber 17 biases the piston 23 toward the front end (in the valve closing direction).

[0017] The fuel injection device 10 includes a pressure control valve 30 that discharges high-pressure fuel in the pressure control chamber 17. The fuel injection hole 12 is closed by the nozzle needle 19 when the sum of the pressure in the pressure control chamber 17 (fuel back pressure) and the biasing force of the spring 22 exceeds the pressure in a gallery (not shown). On the other hand, when high-pressure fuel is discharged from the pressure control chamber 17 and the pressure in the pressure control chamber 17 decreases, and the sum of the pressure in the pressure control chamber 17 and the biasing force of the spring 22 is lower than the pressure in a gallery (not shown), the nozzle needle 19 retreats and the fuel injection hole 12 is opened to perform fuel injection.

[0018] The drive of the fuel injection device 10 is controlled by a control device based on the rail pressure and the target injection amount. The control device controls fuel injection by discharging fuel from the pressure control chamber 17 by opening the pressure control valve 30. The discharged fuel is discharged to a return pipe through a connector (not shown) connected to the holder 25 and returns to a fuel tank (not shown).

[0019] <Pressure control valve> FIG. 2 is a partial cross-sectional view showing in detail a configuration example of the pressure control valve 30.

[0020] The pressure control valve 30 is a solenoid valve that opens and closes a discharge hole 34 communicating with the pressure control chamber 17. The pressure control valve 30 includes an electromagnet 31, an armature plate 36, an armature bolt 50, an armature guide 37, a first spring 39, and a second spring 38. The armature bolt 50 is inserted into the armature plate 36, the first spacer 42, and the armature guide 37. The armature bolt 50 has a large-diameter head portion 52 on the rear end side (holder 25 side), and the first spring 39 abuts against the rear end side surface of the head portion 52. Also, the armature plate 36 abuts against the front end side (pressure control chamber 17 side) surface of the head portion 52.

[0021] The first spring 39 is supported in a compressed state by the holder 25 and the armature bolt 50. The first spring 39 applies a biasing force to the armature bolt 50 toward the pressure control chamber 17. The second spring 38 is supported in a compressed state by the armature plate 36 and the armature guide 37 via the first spacer 42. The second spring 38 applies a biasing force to the armature plate 36 toward the electromagnet 31. The armature bolt 50 and the armature plate 36 are held together as a single unit by the first spring 39 and the second spring 38.

[0022] Furthermore, the pressure control valve 30 includes a holder 25 in which a fuel return channel 28 is formed for returning fuel to a fuel tank (not shown). The holder 25 and the electromagnet 31 are integrated in an electromagnet housing 32 and fastened to the joint with the injector housing 11 by a nut 33. Part of the internal space of the electromagnet housing 32 forms an armature chamber 32a in which the armature plate 36 is arranged. When a drive current is supplied to the electromagnet 31 from a control circuit (not shown), it generates an electromagnetic force that attracts the armature plate 36.

[0023] The armature bolt 50 has a head portion 52 at its rear end that abuts against the armature plate 36. The armature bolt 50 also has a valve holder 40 at its tip end. The valve holder 40 holds a valve body 41 that opens and closes the discharge hole 34.

[0024] The armature guide 37 is a cylindrical body having an axially extending sliding hole 37a. The armature bolt 50 is inserted into the sliding hole 37a so as to be axially slidable. The armature guide 37 is pressed against and fixed to the injector housing 11 by the electromagnet housing 32 via a second spacer 43 by fastening a nut 33. The armature guide 37 has a plurality of holes 37b for directing fuel discharged from the discharge hole 34 into the fuel return passage 28. These armature bolt 50, armature plate 36, and armature guide 37 are provided in the region through which fuel flows.

[0025] When high-pressure fuel is supplied to the pressure control chamber 17 and the valve body 41 is closing the discharge port 34, the nozzle needle 19 closes the fuel injection port 12 due to the pressure in the pressure control chamber 17 received via the piston 23 and the biasing force of the spring 22 (see Figure 1).

[0026] Meanwhile, when the electromagnet 31 of the pressure control valve 30 is energized and the armature plate 36 is pulled towards the electromagnet 31, the armature bolt 50 is also pulled up. Consequently, the pressure in the pressure control chamber 17 lifts the valve body 41, opening the discharge port 34, and the high-pressure fuel in the pressure control chamber 17 flows to the pressure control valve 30 side through the discharge port 34. As a result, the pressure inside the pressure control chamber 17 decreases, the piston 23 and nozzle needle 19 move towards the rear end, the fuel injection port 12 opens, and fuel injection occurs.

[0027] Furthermore, when the energization of the electromagnet 31 of the pressure control valve 30 is stopped, the force with which the electromagnet 31 attracts the armature plate 36 decreases. As a result, the armature bolt 50 is returned to the discharge port 34 side by the first spring 39, and the valve body 41 closes the discharge port 34. When the discharge port 34 is closed, fuel pressure acts on the piston 23 in the pressure control chamber 17, causing the piston 23 and the nozzle needle 19 to move toward the tip. As a result, the fuel injection port 12 is closed, and fuel injection ends.

[0028] When the pressure control valve 30 operates, the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50 slide against each other, which can cause deposits to form on the sliding surface due to fuel. For example, at the tip of the armature bolt 50, low-pressure fuel enters the sliding surface through the gap between the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50. This fuel also functions as a lubricant between the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50. The gap between the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50 is a narrow gap, for example, designed to be about 5 μm, and is not designed to actively allow fuel to pass through it. Therefore, there is almost no pressure gradient in this gap, and fuel has difficulty entering or leaving the gap, which can cause fuel to accumulate in the gap.

[0029] If fuel that has entered the gap remains, deposits may form depending on the fuel's composition or temperature conditions. For example, in fuel injection systems using biofuels, deposits are more likely to form on the sliding surface compared to fuel injection systems using conventional fuels. The deposits that are formed can accumulate to a thickness of, for example, about 5 μm, which corresponds to the size of the gap between the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50. If the amount of deposit accumulation increases, it becomes a sliding resistance for the armature bolt 50, causing a response delay in the pressure control valve 30. If the response of the pressure control valve 30 is delayed, the operation of the nozzle needle 19 will also be delayed, and there is a risk that the fuel injection system 10 will not be able to inject the desired amount of fuel at the desired timing.

[0030] In contrast, in the fuel injection device 10 according to this embodiment, the thermal expansion coefficient of the armature guide 37 is smaller than that of the armature bolt 50. This allows the size of the gap between the inner circumferential surface of the sliding hole 37a of the armature guide 37 and the outer circumferential surface of the armature bolt 50 to change between when the internal combustion engine is running and when it is stopped, thereby discharging any deposits generated in the gap.

[0031] First, referring to Figures 3 to 5, a reference example will be described in which the armature guide 37 and the armature bolt 50 are made of the same material and the thermal expansion coefficients of the armature guide 37 and the armature bolt 50 are equivalent. For example, the armature guide 37 and the armature bolt 50 are formed using steel.

[0032] Figures 3 to 5 are explanatory diagrams showing the size of the gap between the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50 during operation of the internal combustion engine, when the internal combustion engine is stopped, and when the internal combustion engine is restarted, respectively. These are enlarged cross-sectional views of the area indicated by the dashed line in Figure 2.

[0033] During operation of the internal combustion engine, the armature guide 37 and the armature bolt 50 both expand (thermal expansion) due to the rise in fuel temperature and the rise in temperature of the fuel injection device 10. Let D1 be the size of the gap (hereinafter sometimes simply referred to as "gap") between the inner circumferential surface of the sliding hole 37a of the armature guide 37 and the outer circumferential surface of the armature bolt 50 when both the armature guide 37 and the armature bolt 50 are expanded (see Figure 3).

[0034] When the internal combustion engine stops and the temperature of the fuel injector 10 decreases, the temperature of the armature guide 37 and armature bolt 50 also decreases, causing the expanded armature guide 37 and armature bolt 50 to contract. At this time, assuming that the thermal expansion coefficients of the armature guide 37 and armature bolt 50 are the same, the size of the gap D2 when the armature guide 37 and armature bolt 50 are contracted will be equal to or slightly smaller than the size of the gap D1 when the armature guide 37 and armature bolt 50 are expanded (see Figure 4). Therefore, if deposit 60 has accumulated in this gap, the deposit 60 will remain attached to the armature guide 37 and armature bolt 50 while the internal combustion engine is stopped.

[0035] In this case, even if fuel enters the gap when the internal combustion engine is started again, it will not be easy to expel the deposit 60 by the flow of fuel (see Figure 5). Furthermore, since the size D2 of the gap is equivalent to the size D1 of the gap when the armature guide 37 and armature bolt 50 are expanded, fuel will not be able to pass through the gap more easily. Therefore, even if the armature guide 37 and armature bolt 50 expand again due to a rise in fuel temperature and a rise in the temperature of the fuel injector 10, the accumulated deposit 60 will remain and may hinder the operation of the armature bolt 50.

[0036] Next, with reference to Figures 3, 6, and 7, an example of a fuel injection device 10 according to this embodiment, in which the thermal expansion coefficient of the armature guide 37 is smaller than that of the armature bolt 50, will be described. For example, the armature guide 37 is formed using Invar material, and the armature bolt 50 is formed using steel material. Furthermore, the size of the gap is designed based on the state in which both the armature guide 37 and the armature bolt 50 have undergone thermal expansion.

[0037] Figures 6 and 7 are explanatory diagrams showing the size of the gap between the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50 when the internal combustion engine is stopped and when the internal combustion engine is restarted, respectively, and correspond to Figures 4 and 5.

[0038] During operation of the internal combustion engine, the armature guide 37 and armature bolt 50 both expand (thermal expansion) due to the rise in fuel temperature and the rise in temperature of the fuel injection device 10. Let D1 be the size of the gap between the inner circumferential surface of the sliding hole 37a of the armature guide 37 and the outer circumferential surface of the armature bolt 50 when both the armature guide 37 and the armature bolt 50 are expanded (see Figure 3).

[0039] When the internal combustion engine stops and the temperature of the fuel injection device 10 decreases, the temperatures of the armature guide 37 and armature bolt 50 also decrease, causing the expanded armature guide 37 and armature bolt 50 to contract. At this time, since the thermal expansion coefficient of the armature bolt 50 is greater than that of the armature guide 37, the reduction in the diameter of the armature bolt 50 becomes greater than the reduction in the diameter of the sliding hole 37a of the armature guide 37.

[0040] Therefore, the size D2 of the gap when the armature guide 37 and armature bolt 50 are contracted is larger than the size D1 of the gap when the armature guide 37 and armature bolt 50 are expanded (see Figure 6). Figure 6 shows an example in which the diameter of the sliding hole 37a of the armature guide 37 does not decrease, but even if the diameter of the sliding hole 37a of the armature guide 37 decreases, the rate of decrease will be smaller than the rate of decrease of the outer surface of the armature bolt 50.

[0041] Therefore, if deposit 60 accumulates in this gap, the shear stress F acting on the deposit 60 attached to the armature guide 37 and armature bolt 50 will increase. Also, since the size of the gap D2 is larger than when the internal combustion engine is running, fuel can pass through the gap more easily.

[0042] In this case, when the internal combustion engine is started again, the flow of fuel entering the gap will break up or detach the deposit 60, allowing it to be discharged from the gap (see Figure 7). Therefore, even if the size of the gap returns to the state shown in Figure 3 (gap size D1) due to the rise in fuel temperature and the temperature of the fuel injector 10, the risk of the deposit hindering the operation of the armature bolt 50 is reduced.

[0043] The following describes an example of the specific configuration of the armature guide 37 and armature bolt 50.

[0044] The armature guide 37 is formed from Invar material, for example, 32Ni-5Co-Fe. The armature bolt 50 is formed from steel, for example, SUJ2. In this case, the coefficients of thermal expansion of the armature guide 37 and the armature bolt 50 are 12.5 × 10⁻¹⁰, respectively. -6 , 1.3 × 10 -6 That is the case.

[0045] In the case of a fuel injection device 10 used in the fuel supply system of a diesel engine, the temperature near the pressure control valve 30 is around 120°C while the diesel engine is running, and the temperature near the pressure control valve 30 is ambient temperature when the diesel engine is stopped. For example, let's assume that the temperature of the fuel injection device 10 is 120°C while the diesel engine is running, and that the temperature of the fuel injection device 10 is 20°C when the diesel engine is stopped.

[0046] Assume that when the diesel engine is running and the fuel injection system 10 is at a temperature of 120°C, the diameter of the sliding hole 37a of the armature guide 37 is 3.0075 mm, the diameter of the armature bolt 50 is 2.9975 mm, and the size D1 of the gap between the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50 is 5.0 μm. In this case, when the diesel engine is stopped and the temperature of the fuel injection system 10 drops to 20°C, and the armature guide 37 and armature bolt 50 contract, the diameter of the sliding hole 37a of the armature guide 37 becomes 3.0074 mm, the diameter of the armature bolt 50 becomes 2.9963 mm, and the size D2 of the gap between the inner surface of the sliding hole 37a of the armature guide 37 and the outer surface of the armature bolt 50 becomes 5.6 μm, which is larger than when the diesel engine is running.

[0047] Therefore, even if deposits accumulate in the gap while the diesel engine is running, the shear stress F acting on the deposits increases when the diesel engine is stopped. When the diesel engine is started, the fuel flow passing through the enlarged gap breaks or separates the deposits, allowing them to be discharged from the gap. This allows the fuel injector to supply the desired amount of fuel to the diesel engine.

[0048] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to such examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0049] For example, the constituent materials of the armature guide 37 and armature bolt 50 described above are merely examples; similar effects can be obtained if the thermal expansion coefficient of the armature guide 37 is smaller than that of the armature bolt 50.

[0050] Furthermore, although the above embodiment describes an example in which the first and second members are the armature bolt 50 and armature guide 37 of the pressure control valve 30, respectively, the present disclosure is not limited to such an example. For example, the first and second members may be the piston 23 and the injector housing 11, or the nozzle needle 19 and the nozzle body 13, respectively. [Explanation of Symbols]

[0051] 10:Fuel injection device 30: Pressure control valve 31: Electromagnet 33: Nut 34: Discharge hole 37: Armature Guide 37a:Sliding hole 50: Armored Bolt 60: Deposit

Claims

1. A fuel injection device (10) that injects fuel into an internal combustion engine, It comprises a first member (50) that moves back and forth in the axial direction, and a second member (37) that has a sliding hole (37a) into which the first member (50) is inserted and slidably supports the first member (50), A fuel injection device in which the first member (50) and the second member (37) are provided in a region through which fuel flows, and the thermal expansion coefficient of the second member (37) is smaller than that of the first member (50).

2. The fuel injection device (10) includes a pressure control valve (30) that releases the fuel back pressure from a pressure control chamber (17) that generates fuel back pressure that pushes a nozzle needle (19) that opens and closes the fuel injection hole (12) toward the fuel injection hole (12). The first member (50) is an armature bolt (50) engaged with an armature plate (36) which is attracted to the side of the electromagnet (31) by the electromagnetic force generated by the electromagnet (31), The fuel injection device according to claim 1, wherein the second member (37) is an armature guide (37) that slidably supports the armature bolt (50).

3. The fuel injection device according to claim 1, wherein the first member (50) is made of steel and the second member (37) is made of Invar material.

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