Engine with auxiliary combustion chamber

Abstract

To provide a structure that securely generates sparks by using internal and external discharge gaps without sideways abnormal discharge in an auxiliary combustion chamber in an engine in which the internal and external discharge gaps are provided in the auxiliary combustion chamber.SOLUTION: An intermediate electrode 34 is held by a bottom plate 30 of an auxiliary combustion chamber 15 via a holder 37, and an internal discharge gap 35 and an external discharge gap 36 are opened on upper and lower sides of the intermediate electrode 34. Length d of the intermediate electrode 34 is about three times of each of clearance dimensions a, b of the internal and external discharge gaps. An interval c between the internal discharge gap 35 and a peripheral wall 29 is larger than the length d of the intermediate electrode 34. Since the length d of the intermediate electrode 34 is short and electric resistance is small, this can prevent a phenomenon of abnormal discharge from the internal discharge gap 35 to the peripheral wall so as to securely generate sparks 39, 40 in the internal and external discharge gaps 35, 36.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an engine having a sub-combustion chamber in a cylinder head. [Background technology]

[0002] It has been proposed to provide a pre-combustion chamber in the cylinder head of an engine such as a gasoline engine. The pre-combustion chamber is used in conjunction with a spark plug, and the flame generated in the pre-combustion chamber is ejected from the nozzle into the main combustion chamber to ignite the main fuel. The flame generated in the pre-combustion chamber has excellent fuel ignition properties, so it has the advantage of being able to reliably burn the fuel even if the fuel in the mixture is on the lean side. Therefore, it is attracting attention as a promising technology for improving fuel efficiency and promoting cleaner exhaust gases.

[0003] There are two methods for igniting the mixture in the pre-combustion chamber: a passive method in which the mixture ejected from the intake port is taken into the pre-combustion chamber and ignited by an ignition plug exposed inside the pre-combustion chamber, and an active method in which fuel is taken into the pre-combustion chamber through a dedicated path and ignited by an ignition plug.The former passive method has a simple structure and does not require a control device, making it superior in terms of cost and adaptability to actual equipment.

[0004] On the other hand, a problem with the passive system is that when the temperature of the air-fuel mixture is low, such as during a cold start, the ignition of the fuel becomes poor, which can lead to misfires.To address this issue, Patent Document 1 proposes a pre-combustion chamber structure in which a discharge gap is provided between the inside and outside of the pre-combustion chamber. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-44268 Summary of the Invention [Problem to be solved by the invention]

[0006] Now, in order to eject the combustion gas generated in the auxiliary combustion chamber as a flame from the nozzle into the main combustion chamber, the auxiliary combustion chamber needs to have a certain volume so that the required combustion gas is generated. However, in Patent Document 1, the distance from the center electrode and intermediate electrode to the inner peripheral surface is only about twice the distance of the inner and outer discharge gaps, and therefore it is questionable whether the required flame can be generated in the auxiliary combustion chamber.

[0007] Furthermore, in Patent Document 1, an insulating part made of ceramic or titanium is placed between the center electrode and the metal housing, and this insulating part forms a pre-combustion chamber, and the center electrode is fixed to the bottom of the insulating pre-combustion chamber, but it is unclear how a hollow pre-combustion chamber would be formed in the insulating part, and this is considered to be unlikely to be practical.

[0008] The present invention was made against this background and aims to disclose a highly practical structure for an engine having discharge gaps inside and outside the auxiliary combustion chamber, which structure also has excellent ignition performance. [Means for solving the problem]

[0009] The engine of the present invention comprises: "It has a main combustion chamber partially formed by a cylinder head, and an auxiliary combustion chamber provided in the cylinder head so that at least a portion of the auxiliary combustion chamber is exposed to the main combustion chamber, The auxiliary combustion chamber is formed with a nozzle hole that communicates with its interior and the main combustion chamber, and is concentrically arranged with a center electrode disposed inside the auxiliary combustion chamber, a ground electrode exposed to the main combustion chamber, and an intermediate electrode that has one end facing the center electrode across an internal discharge gap and the other end facing the ground electrode across an external discharge gap. In this basic configuration, The distance from the internal discharge gap to the inner peripheral surface of the auxiliary combustion chamber is at least three times the gap dimension of the internal discharge gap, and the length of the intermediate electrode is greater than the gap dimensions of the internal discharge gap and the external discharge gap. The structure is as follows.

[0010] The present invention can be developed in various ways. For example, claim 2 states: The length of the intermediate electrode is smaller than the distance from the internal discharge gap to the inner circumferential surface of the auxiliary combustion chamber. The structure is as follows. [Effects of the Invention]

[0011] In the present invention, the distance from the internal discharge gap to the inner peripheral surface of the pre-combustion chamber is three or more times the gap dimension of the internal discharge gap, so that the volume necessary for flame generation can be secured in the pre-combustion chamber. Note that in Patent Document 1, the interior of the pre-combustion chamber is a nearly flat circular space with the injection holes opening in the bottom plate, but in an engine with a pent roof type combustion chamber, it is preferable that the injection holes open in the peripheral wall of the pre-combustion chamber, and for this purpose, it is preferable that the internal space of the pre-combustion chamber expands both above and below the internal discharge gap.

[0012] Now, it is practical to integrate the auxiliary combustion chamber into the metal housing in which the ground electrode is formed, or to manufacture it as a separate part from the housing and then fix it to the housing by welding. In this case, it is preferable to fix the intermediate electrode to the auxiliary combustion chamber via an insulating holder. However, if the length of the intermediate electrode is set to a dimension larger than the gap dimension of the internal and external discharge gaps, as in the present invention, there is an advantage that the intermediate electrode can be secured to a length that allows it to be firmly held by the holder.

[0013] In addition, the present invention forms a suitable space around the internal gap to ensure the volume required for flame generation, and also facilitates the placement of the intermediate electrode to improve feasibility. It also ensures sparks at the internal and external discharge gaps, preventing misfires and enabling starting and operation even in low-temperature environments.

[0014] The distance from the internal discharge gap to the inner peripheral surface of the auxiliary combustion chamber needs to be a certain size in order to ensure the necessary volume for the auxiliary combustion chamber. However, by adopting the configuration of claim 2, the length of the intermediate electrode can be made as short as possible to reduce the electrical resistance, thereby ensuring the correct volume for the auxiliary combustion chamber while ensuring reliable discharge in the internal and external discharge gaps and improving the function of preventing misfires in low-temperature environments. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a longitudinal sectional front view of an engine according to an embodiment. [Figure 2] (A) is an enlarged cross-sectional view of the main part, and (B) is a cross-sectional view taken along the line BB of (A). [Figure 3] FIG. 10 is a partial cross-sectional view of a comparative example.

[0016] (1) Basic structure of the engine Next, an embodiment of the present invention will be described with reference to the drawings. Hereinafter, the terms "front-rear" and "left-right" will be used to specify directions. The front-rear direction is the crankshaft axis direction, and the left-right direction is the direction perpendicular to the crankshaft axis direction and the cylinder bore axis direction. Regarding "front" and "rear," the side where the timing chain is located is referred to as the front, and the side where the transmission is located is referred to as the rear.

[0017] This embodiment is applied to an automobile engine. The basic structure of the engine is the same as that of a conventional engine, but will be explained with reference to Figure 1 for clarity. The engine has, as its basic elements, a cylinder block 1 and a cylinder head 3 fixed to its upper surface via a gasket 2. The cylinder block 1 has a plurality of cylinder bores 4 formed in a row in the front-to-rear direction.

[0018] On the other hand, a pent roof-shaped combustion chamber recess 5 is formed in the cylinder head 3 facing the cylinder bore 4, and a main combustion chamber is formed by the cylinder bore 4 of the cylinder block 1 and the combustion chamber recess 5 of the cylinder head 3 (or by the cylinder head 3 and the piston), but for convenience, the combustion chamber recess 5 will be referred to as the main combustion chamber below. The piston is not shown in the illustration.

[0019] The cylinder head 3 is formed with a pair of intake ports 6 and a pair of exhaust ports 7, distributed on both the left and right sides of the crank axis, corresponding to each combustion chamber recess 5. The intake outlet holes of the intake ports 6 are opened and closed by intake valves 8, and the exhaust inlet holes of the exhaust ports 7 are opened and closed by exhaust valves 9. The valves 8, 9 are biased in the closing direction by springs 10, 11.

[0020] The pair of intake ports 6 are independent over the entire length and each open to the intake side surface 3a of the cylinder head 3. An intake manifold 12 is fixed to the intake side surface 3a of the cylinder head 3. Fuel injectors 13 are attached to the intake manifold 12 (or to the cylinder head 3) corresponding to each intake port 6. Note that the fuel injectors 13 can also be attached to the cylinder head 3.

[0021] A spark plug hole (ignition hole) 14 opens in the top surface of each combustion chamber recess 5 in the cylinder head 3, in a region surrounded by the intake outlet hole and the exhaust inlet hole, and an ignition plug 16 having a sub-combustion chamber 15 at its lower end is screwed into the spark plug hole 14. In Figure 1, reference numeral 17 denotes a water jacket through which cooling water flows.

[0022] (2) Main parts of the first embodiment As shown in FIG. 1, the spark plug 16 has a housing (main body) 20 with external threads. The housing 20 is formed with a hexagonal head 21 for attachment and detachment and a flange 22 located below the hexagonal head 21. The flange 22 overlaps a step 24 of the spark plug hole 14 via a conductive washer 23.

[0023] As shown in Fig. 2, a rod-shaped internal electrode 26 is disposed inside the housing 20 via an insulator 25. The upper part of the insulator 25 is exposed above the hexagonal head 21, and a concave-convex portion 27 for holding a plug is formed on the exposed portion, with the upper end of the internal electrode 26 exposed above the concave-convex portion 27. A small-diameter, tapered center electrode 28 protrudes downward from the lower end of the internal electrode 26. The center electrode 28 can be formed integrally with the internal electrode 26, or it can be manufactured as a separate member from the internal electrode 26 and fixed thereto by laser welding or the like.

[0024] The auxiliary combustion chamber 15 is formed integrally with the lower end of the housing 20 and has a peripheral wall 29 and a bottom plate 30. The lower half of the peripheral wall 29 is gently curved and tapered, and multiple (e.g., 4 to 10) injection holes 31 are arranged in the circumferential direction at the tapered portion. The injection holes 31 open in roughly the same direction as the inclined surface of the combustion chamber recess 5. Therefore, the flame is ejected across the upper and lower intermediate portions of the air-fuel mixture.

[0025] An L-shaped external electrode 32 is fixed to the underside of the bottom plate 30 of the auxiliary combustion chamber 15 by welding or the like, and a ground electrode 33 is formed on the external electrode 32, positioned concentrically with the internal electrode 26. The ground electrode 33 protrudes slightly upward from the tip of the external electrode 32, and about half of the tip is thinned. Therefore, it is bent like a crank when viewed from the front. The external electrode 32 is made of an alloy with excellent heat resistance and conductivity.

[0026] A cylindrical intermediate electrode 34 is disposed concentrically with the internal electrode 26 between the center electrode 28 and the ground electrode 33, with an internal discharge gap 35 being formed between the upper end (one end) of the intermediate electrode 34 and the center electrode 28, and an external discharge gap 36 being formed between the lower end (the other end) of the intermediate electrode 34 and the ground electrode 33. The intermediate electrode 34 is fixed to the bottom plate 30 of the auxiliary combustion chamber 15 via a ring-shaped holder 37 made of an insulator such as ceramic (including metals with high electrical resistance). Therefore, a hole for attaching the holder 37 is formed in the bottom plate 30 of the auxiliary combustion chamber 15, and the holder 37 is welded to the bottom plate 30, and the intermediate electrode 34 is welded to the holder 37.

[0027] The holder 37 is formed with a flange 37a that overlaps the bottom plate 30 from above, and the upper surface of the flange 37a forms a downwardly inclined surface 37b. This allows the flame to be guided to the nozzle hole 31. Note that, as shown by the dashed dotted line in Figure 2, it is also possible to carve out a recess 37c that guides the flame to the nozzle hole 31. The internal space of the auxiliary combustion chamber 15 extends above and below both the internal discharge gap 35 and the center electrode 28.

[0028] In particular, a large upper space 38 extends above the lower end of the internal electrode 26 (or the upper bottom surface of the combustion chamber recess 5). This ensures that the auxiliary combustion chamber 15 has just the right amount of volume to generate a strong flame. Although an annular space that tapers upward is provided between the internal electrode 26 and the insulator 25, it is also possible to place the insulator 25 in close contact with the internal electrode 26 without any gaps.

[0029] The lower end of the intermediate electrode 34 is formed into a straight small-diameter portion 34b via a tapered portion 34a, and most of the intermediate electrode 34 is hidden inside the holder 37 (it is also possible to extend the tapered portion 34a to the lower end without forming the straight small-diameter portion 34b). This allows the external discharge gap 36 to be positioned as high as possible. Furthermore, the overall length d of the intermediate electrode 34 is slightly larger than the basic diameter e, which reduces electrical resistance. In particular, in this embodiment, the length of the basic diameter portion of the intermediate electrode 34 is smaller than the outer diameter e, which has the advantage of reducing the electrical resistance of the intermediate electrode 34 and improving its electrical conductivity.

[0030] The gap dimensions a and b of the internal discharge gap 35 and the external discharge gap 36 are determined by the voltage and are almost the same. The length d of the intermediate electrode 34 is set to about three times a and b, and the width c of the annular space surrounding the internal discharge gap 35 (the distance from the internal discharge gap 35 to the peripheral wall 29 of the auxiliary combustion chamber 15) is set to about four times a and b. The basic outer diameter e of the intermediate electrode 34 is set to about twice a and b.

[0031] The sum of the gap dimension a of the internal discharge gap 35 and the length d of the intermediate electrode 34 is almost the same as the width dimension c of the annular space surrounding the internal discharge gap 35. Therefore, the sum of the gaps a, b of the internal and external discharge gaps 35, 36 and the length d of the intermediate electrode 34 is slightly larger than the width dimension c of the annular space surrounding the internal discharge gap 35. Note that the width dimension c can also be defined as the distance from the outer periphery of the base of the center electrode 28 or the outer periphery of the intermediate electrode 34 to the peripheral wall 29.

[0032] (3) Summary of the first embodiment The inventors of the present application have tried several prototypes to achieve sparks inside and outside the pre-combustion chamber 15 while maintaining the desired volume in the pre-combustion chamber 15. As one example, a comparative example shown in FIG. 3 was created. This comparative example has a configuration basically similar to that of the embodiment, but the intermediate electrode 34 has a basic outer diameter e and a length d that is approximately 4.5 times the lengths a and b, and is largely exposed above the holder 37. In this comparative example, an abnormal spark 41 was observed, which discharged between the intermediate electrode 34 and the inner circumferential wall 29 of the pre-combustion chamber 15.

[0033] In contrast, in this embodiment, the phenomenon of abnormal spark 41 does not occur, and the internal spark 39 at the internal discharge gap 35 and the external spark 40 at the external discharge gap 36 can be reliably generated. This can be said to contribute to improving startability in low-temperature environments.

[0034] Although the exact reason why abnormal spark 41 occurs in the comparative example has not been clarified, it is thought that this is due to increased electrical resistance caused by the long length of intermediate electrode 34, or the ease of discharge caused by the outer circumferential surface of intermediate electrode 34 being largely exposed inside pre-combustion chamber 15. Therefore, measures to prevent this abnormal spark 41 are thought to be increasing the voltage and current, increasing the inner diameter of pre-combustion chamber 15, or further increasing the outer diameter of intermediate electrode 34 to reduce electrical resistance.

[0035] However, measures to change the voltage and current have the problem of requiring changes to the ignition device or increasing current consumption, which would result in a deterioration in fuel efficiency, while measures to increase the inner diameter of the auxiliary combustion chamber 15 are difficult to adopt in the first place because the inner diameter (outer diameter) of the auxiliary combustion chamber 15 is determined by the spark plug hole 14.Furthermore, measures to increase the diameter of the intermediate electrode 34 may cause instability of the sparks 39, 40 due to diffusion of the discharge, making both measures difficult to adopt.

[0036] In contrast, in this embodiment, a simple structure that reduces the dimensions of the intermediate electrode 34 makes it possible to make the intermediate electrode 34 compact while ensuring reliable internal and external sparks 39, 40. That is, by ensuring an appropriate outer diameter e for the intermediate electrode 34 and setting the length d to be slightly longer than the outer diameter, the flow of electricity is improved, and by setting the width c of the annular space surrounding the internal discharge gap 35 to be three or more times (for example, about four times) the values ​​a and b, the volume necessary for flame generation can be secured without changing the design of the spark plug hole 14. Therefore, this embodiment has excellent adaptability to actual situations and is of great practical value.

[0037] Additionally, because air (air-fuel mixture) is an electrical non-conductor, if the resistance of the intermediate electrode 34 increases beyond a certain level, the current cannot maintain enough energy to pass through the external discharge gap 36, causing the current to flow through the internal space of the auxiliary combustion chamber 15 to the peripheral wall 29 (abnormal spark 41). However, if (a+d) and c have approximately the same dimensions as in the embodiment, the linearity of the current combined with the reduced resistance of the intermediate electrode 34 allows the current to flow from the intermediate electrode 34 through the external gap 36 to the ground electrode 33, and it can be said that the external spark 40 can be stably generated in the external discharge gap 36.

[0038] To elaborate further, if the width c of the annular space surrounding the internal discharge gap 35 is three times or more the width a, there will basically be no discharge (current flow) from the center electrode 28 to the peripheral wall 29. However, if the electrical resistance to the passage of the intermediate electrode 34 becomes excessively large, the current will flow from the center electrode 28 toward the peripheral wall 29, which may cause an abnormal spark 41. However, in this embodiment, the electrical resistance of the intermediate electrode 34 is small, so the current passes through the intermediate electrode 34 and heads toward the ground electrode 33. Therefore, the current flows to the ground electrode 33 via the discharge in the external discharge gap 36 without increasing the outer diameter e of the intermediate electrode 34, and it can be said that no abnormal spark 41 will occur inside the auxiliary combustion chamber 15.

[0039] As in the embodiment, by forming an upper space 38 in the auxiliary combustion chamber 15 that extends above the upper bottom surface of the combustion chamber recess 5, it is possible to ensure a sufficient volume for the auxiliary combustion chamber 15 while suppressing the amount of downward protrusion of the auxiliary combustion chamber 15, thereby suppressing changes in the compression ratio. In addition, since the upper space 38 is close to the water jacket 17, there is also the advantage that the cooling performance of the auxiliary combustion chamber 15 can be improved.

[0040] In addition, in this embodiment, the intermediate electrode 34 is attached to a holder 37 having a flange 37a at its upper end, and therefore a gap larger than the gaps a and b between the discharge gaps 35 and 36 is formed between the internal discharge gap 35 and the bottom plate 30 of the auxiliary combustion chamber 15, and therefore the auxiliary combustion chamber 15 also extends below the internal discharge gap 35. Therefore, the injection hole 31 can be positioned at a height lower than the internal discharge gap 35, and the flame can be diffused to the middle portion of the main combustion chamber, vertically.

[0041] Although the embodiments of the present invention have been described above, the present invention can be embodied in various other ways. For example, while the holder 37 in the embodiment has a flange 37a at its upper end and is inserted into the bottom plate 30 from above, it is also possible to provide a flange 37a at the lower end of the holder 37 and fit the holder 37 into the bottom plate 30 from below. The intermediate electrode 34 can also be cast into the holder 37 (fired integrally).

[0042] As a means for holding the intermediate electrode 34, a burred cylindrical portion may be provided on the bottom plate 30 of the auxiliary combustion chamber 15, and the intermediate electrode 34 may be arranged and fixed inside the cylindrical portion via a non-conductive film. [Industrial Applicability]

[0043] The present invention can be embodied in an engine equipped with a pre-combustion chamber, and is therefore industrially applicable. [Explanation of symbols]

[0044] 1 Cylinder block 3. Cylinder head 4 cylinder bore 5. Combustion chamber recess constituting the main combustion chamber 14 Plug Hole 15 Pre-combustion chamber 16 Spark plug 20. Housing 25 Insulators 26 Internal electrode 28 Center electrode 29 Peripheral wall 30 Bottom plate 31 Spiracle 32 External electrode 33 Ground electrode 34 Intermediate electrode 35 Internal discharge gap 36 External discharge gap 37 Holder 39 Internal Spark 40 External Spark a) Internal discharge gap b External discharge gap c) Width of the annular space surrounding the internal discharge gap (distance from the internal discharge gap to the peripheral wall) d Total length of intermediate electrode e Basic outer diameter of intermediate electrode

Claims

1. The combustion chamber has a main combustion chamber partially formed by a cylinder head, and an auxiliary combustion chamber provided in the cylinder head so that at least a portion of the auxiliary combustion chamber is exposed to the main combustion chamber, an engine with a pre-combustion chamber, wherein the pre-combustion chamber has a nozzle hole formed therein that communicates with the interior of the pre-combustion chamber and the main combustion chamber, and wherein a center electrode disposed inside the pre-combustion chamber, a ground electrode exposed to the main combustion chamber, and an intermediate electrode having one end facing the center electrode across an internal discharge gap and the other end facing the ground electrode across an external discharge gap are concentrically arranged, a distance from the internal discharge gap to an inner peripheral surface of the auxiliary combustion chamber is three times or more the gap dimension of the internal discharge gap, and a length of the intermediate electrode is greater than the gap dimensions of the internal discharge gap and the external discharge gap. Pre-combustion chamber engine.

2. The length of the intermediate electrode is smaller than the distance from the internal discharge gap to the inner circumferential surface of the auxiliary combustion chamber.

2. An engine with a pre-combustion chamber according to claim 1.

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