JP2019078208A - Combustion chamber structure for engine - Google Patents

Abstract

To provide a combustion chamber structure for an engine, capable of securing high ignitability of air-fuel mixture by making the air-fuel mixture exist on an ignition part of a spark plug and in its vicinity during ignition.SOLUTION: A crown surface 50 of a piston 5 is provided with a cavity 51 recessed in a cylinder axial direction. The cavity 51 is provided in a region including a lower area of the ignition part of the spark plug in plan view from the cylinder axial direction. In plan-viewing the cavity 51 from the cylinder axial direction, the peripheral edge of the cavity 51 is provided with a lateral erected surface part 512 further erected in the cylinder axial direction than a bottom surface part 511 inside of the peripheral part. The lateral erected surface part 512 is provided at a position where the ignition part of the spark plug is held in a X-direction when the piston 5 is at a compression top dead center, for functioning as a guide part to guide air-fuel mixture from a combustion chamber to the ignition part of the spark plug.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a combustion chamber structure of a spark ignition engine.

  In a spark ignition type engine in a vehicle such as an automobile, fuel is injected from an injector into a combustion chamber, and air or the like is introduced from an intake port to form an air-fuel mixture in which the fuel is atomized. A configuration of using and igniting is employed.

  Patent Document 1 discloses an engine that injects fuel near the compression top dead center and performs ignition (spark ignition) with an ignition plug. Moreover, in the engine of patent document 1, the cavity is provided in the crown face of the piston.

  As described above, in the spark ignition type engine, by providing the cavity on the crown surface of the piston, it becomes easy to secure the moving distance for atomizing the fuel injected from the injector, and fuel injection near the compression top dead center Even if it does, sufficient atomization is possible in a short time.

JP, 2017-61907, A

  By the way, in an engine such as a vehicle, a fuel injection period may be set during an intake stroke in order to secure a long mixing time of fuel and air. In such a case, in order to ensure homogeneous mixing of fuel and air in the mixture, the mixture is made to exist around the ignition part of the spark plug at the time of ignition while securing the cavity diameter in the piston as large as possible. It is desirable to ignite.

  The present invention has been made to solve the above problems, and by ensuring that the mixture is present at the time of ignition and in the vicinity of the ignition portion of the spark plug, it is possible to ensure high ignitability of the mixture. It is an object of the present invention to provide a combustion chamber structure of an engine capable of

  A combustion chamber structure of a spark ignition type engine according to one aspect of the present invention is mounted on a crown surface of a piston, a combustion chamber ceiling surface formed in a cylinder head, and the combustion chamber ceiling surface, An ignition plug having an ignition part arranged to face a chamber, wherein the crown surface of the piston is the cylinder in a region including the lower side of the ignition part of the ignition plug in plan view from the cylinder axial direction; The cavity has an axially recessed portion, and the peripheral edge of the cavity rises in the axial direction of the cylinder than the region inside the peripheral edge, and when the piston is at compression top dead center It has a guide part which interposes the said ignition part and guides the mixture in the said combustion chamber to the said ignition part.

  In the combustion chamber structure of the engine according to the above aspect, the guide portion is provided to sandwich the ignition portion of the spark plug when the piston is at the compression top dead center, so the piston rises with the piston during the compression stroke. When the in-cylinder flow in the combustion chamber is concentrated in the cavity, the air-fuel mixture is guided by the guide portion to the ignition portion of the spark plug and the periphery thereof.

  Therefore, in the combustion chamber structure of the engine according to the above aspect, by causing the air-fuel mixture to exist in the ignition portion of the ignition plug and the periphery thereof at the time of ignition, high ignitability of the air-fuel mixture can be secured.

  The combustion chamber structure of the engine according to another aspect of the present invention is the above aspect, and the cavity is formed in a bowl shape convex in a direction away from the combustion chamber ceiling surface in the cylinder axial direction.

  In the combustion chamber structure of the engine according to the above aspect, the cavity adopts a bowl shape that is convex (downwardly convex) in a direction away from the ceiling surface of the combustion chamber, in other words, a bowllike cavity without an upward convex obstacle in the bottom portion Therefore, flame propagation after ignition is smoothly performed throughout the combustion chamber.

  The combustion chamber structure of an engine according to another aspect of the present invention is the above aspect, further comprising two intake ports opened to the ceiling surface of the combustion chamber and arranged along the engine output shaft direction with each other, The ignition unit of the ignition plug is disposed between the two intake ports, and the guide unit is a both-side portion of the cavity in the direction of the engine output shaft in plan view from the cylinder axis direction. The guide portion and the inner region are both configured with a curved surface curved in the cylinder axis direction, and the radius of curvature of the guide portion is the radius of curvature of the inner region. Less than.

  In the combustion chamber structure of the engine according to the above aspect, the guide portion is configured by the curved surface, and the radius of curvature of the guide portion is smaller than the radius of curvature of the inner region, so the spark plug The flame formed by the ignition of the ignition unit can be smoothly spread in the combustion chamber in the engine output shaft direction.

  The combustion chamber structure of the engine according to another aspect of the present invention is the above aspect, and the curved surface is in contact with each other at the boundary portion between the guide portion and the inner region.

  In the combustion chamber structure of the engine which concerns on the said aspect, since the curved surfaces of a guide part and the area | region of inner side contact at a boundary part, the said boundary part is comprised smoothly. Therefore, in the combustion chamber structure of the engine according to the above aspect, the flame formed by the ignition of the ignition part of the ignition plug can be spread more smoothly in the combustion chamber in the engine output shaft direction.

  The combustion chamber structure of an engine according to another aspect of the present invention is the above aspect, wherein the crown surface of the piston is closer to the intake side than the ignition portion of the spark plug in a side view from the engine output shaft direction. At a portion close to the cylinder wall surface, when the piston is at compression top dead center, a clearance is provided along a corresponding region in the cylinder axial direction upper side in the combustion chamber ceiling surface, and the ignition portion of the spark plug is It has an inclined surface portion formed to be directed, and the inclined surface portion and the corresponding region constitute a squish flow generation portion that generates a squish flow when the piston is raised, by a combination thereof.

  In the combustion chamber structure of the engine according to the above aspect, the sloped surface portion is provided on the crown surface of the piston, and the squish flow generation unit is configured by a combination with the corresponding region of the combustion chamber ceiling surface. And since the inclined surface portion is provided to point to the ignition portion of the spark plug when the piston is at compression top dead center, when the piston ascends during the compression stroke, it is directed to the ignition portion of the spark plug A squish flow can be generated. Therefore, in the combustion chamber structure of the engine according to the above aspect, it is possible to scavenge residual gas in the ignition portion of the spark plug and the periphery thereof by utilizing the squish flow generated when the piston ascends.

  The combustion chamber structure of an engine according to another aspect of the present invention is the above aspect, further including an injector provided on the ceiling surface of the combustion chamber, wherein the injector is directed to the cavity in the middle of an intake stroke. Fuel injection.

  In the combustion chamber structure of the engine according to the above aspect, fuel injection is performed from the injector in the middle of the intake stroke, so fuel is injected in a stage where the in-cylinder flow is relatively weak (middle of the intake stroke) It will be done. In the combustion chamber structure of the engine according to the above aspect, when adopting the timing of fuel injection as described above, it is possible to suppress the adhesion of fuel to the cylinder wall surface by concentrating the spray in the cavity.

  In the combustion chamber structure of the engine according to each of the above aspects, by causing the air-fuel mixture to exist in the ignition portion of the ignition plug and the periphery thereof at the time of ignition, high ignitability of the air-fuel mixture can be secured.

It is a schematic cross section which shows the combustion chamber structure of the engine which concerns on 1st Embodiment. It is a model perspective view showing composition of a piston in an engine. It is a model top view showing composition of a crown face of a piston. It is a figure which shows the IV-IV cross section of FIG. 3, Comprising: It is a schematic cross section which shows the structure of the crown face of a piston. It is a figure which shows the VV cross section of FIG. 3, Comprising: It is a schematic cross section which shows the structure of the crown face of a piston. It is a figure which shows the VI-VI cross section of FIG. 3, Comprising: It is a schematic cross section which shows the structure of the crown face of a piston. It is a model top view which shows the positional relationship of the cavity of a piston, the ignition part of a spark plug, and an injector. It is a schematic cross section which shows the relationship between the suction side plane part and suction side slope part in the crown face of a piston, and the suction side top face part in a cylinder head. It is a time chart which shows a fuel injection period and ignition timing. It is a model top view which shows the fuel injected into the combustion chamber, and the swirl flow which arises in a combustion chamber. (A) is a schematic cross section showing the combustion chamber when the piston is moving upward in the first half of the compression stroke, and (b) is a schematic cross section showing the combustion chamber when the piston is near compression top dead center It is. It is a schematic cross section which shows the squish flow which arises between the suction side plane part and the suction side slope part of a piston, and the suction side top face part of a cylinder head. It is a time chart which shows the fuel injection period and ignition timing concerning a 2nd embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The form described below is an aspect of the present invention, and the present invention is not limited to the following form except for the essential configuration.

  In the drawings used in the following description, the X direction is the engine output shaft direction of the engine, and the Z direction is the cylinder axis direction.

First Embodiment
1. Overall Configuration of Engine A combustion chamber structure of a spark ignition type engine according to the first embodiment will be described with reference to FIG.

  The engine according to the present embodiment is a multi-cylinder engine mounted on a vehicle including a cylinder and a piston as a power source for driving a vehicle such as an automobile. The engine includes the engine body 1 and auxiliary devices such as an intake / exhaust manifold and various pumps attached thereto (the illustration of auxiliary devices such as the intake / exhaust manifold and various pumps is omitted). The fuel supplied to the engine body 1 contains, for example, gasoline as a main component.

  As shown in FIG. 1, the engine body 1 includes a cylinder block 3, a cylinder head 4 and a piston 5. The cylinder block 3 has a plurality of cylinders aligned in the X direction (in FIG. 1, only one cylinder is shown). In the engine body 1 according to the present embodiment, the cylinder wall 2 is constituted by a cylinder liner 20 which is fitted inside.

  The cylinder head 4 is mounted on the cylinder block 3 and closes the upper opening of the cylinder. The piston 5 is accommodated in each cylinder so as to be capable of reciprocating and reciprocating, and is connected to the crankshaft via a connecting rod (in FIG. 1, illustration of the connecting rod and the crankshaft is omitted).

  A combustion chamber 6 is formed above the crown surface 50 on the + Z side of the piston 5. An intake port 41 and an exhaust port (not shown) are opened in the combustion chamber ceiling surface 6U of the combustion chamber 6. In the engine body 1 according to the present embodiment, two intake ports 41 and two exhaust ports are opened.

  An intake port communicates with the intake port 41, and an exhaust port communicates with the exhaust port (the intake port and the exhaust port are not shown). The cylinder head 4 is assembled with an intake valve 11 for opening and closing the intake port 41 and an exhaust valve (not shown) for opening and closing the exhaust port.

  The combustion chamber ceiling surface 6U is a bottom surface (surface on the -Z side) of the cylinder head 4 and has a pent-roof shape (flat pent roof shape) slightly convex upward (in the direction of + Z).

  Here, in the present embodiment, the wall surface of the combustion chamber that divides the combustion chamber 6 includes the cylinder wall surface 2, the crown surface 50 of the piston 5, the combustion chamber ceiling surface 6U that is the bottom surface of the cylinder head 4, and the intake valve 11. It is comprised by the valve surface and the valve surface of an exhaust valve. That is, the cylinder block 3, the cylinder head 4, the piston 5, the intake valve 11, and the exhaust valve can be regarded as combustion chamber constituent members constituting the combustion chamber 6.

  An ignition plug 17 is attached to the cylinder head 4, and the ignition unit 170 of the ignition plug 17 is disposed to face the combustion chamber 6 from the combustion chamber ceiling surface 6U. The spark plug 17 discharges a spark from the ignition unit 170 in response to the power supply from the ignition circuit (not shown), and ignites the air-fuel mixture in the combustion chamber 6.

  Further, an injector (fuel injection valve) 18 is attached to the cylinder head 4 and the injection hole 181 of the injector 18 is disposed to face the combustion chamber 6 from the combustion chamber ceiling surface 6U. A fuel supply pipe connected to the high pressure fuel pump is connected to the injector 18 (the high pressure fuel pump and the fuel supply pipe are not shown). A common rail (not shown) for accumulating pressure common to all the cylinders of the engine body 1 is provided between the high pressure fuel pump and the fuel supply pipe. With these configurations, high-pressure fuel is injected from the injection holes 181 of the injector 18 into the combustion chamber 6.

2. Configuration of Piston 5 The configuration of the piston 5 will be described with reference to FIGS. 2 is a schematic perspective view showing the configuration of the piston 5, FIG. 3 is a schematic plan view showing the configuration of the crown surface 50 of the piston 5, and FIGS. 4 to 6 are views of the crown surface 50 of the piston 5. It is a schematic cross section which shows a structure.

  As shown in FIG. 2, the piston 5 includes a piston head 5 </ b> A and a piston skirt 5 </ b> S connected to the lower side (−Z side) thereof. The piston head portion 5A has a cylindrical shape and has a crown surface 50 forming a part (bottom) of the wall surface of the combustion chamber 6 on the upper surface (surface on the + Z side), and a side circumferential surface slidingly contacting the cylinder wall 2 Equipped with

  The piston skirt portion 5S is disposed on the + Y side and the −Y side of the piston head portion 5A, and is a portion that suppresses swinging and swinging when the piston 5 reciprocates.

  On the lower side (−Z side) of the piston head portion 5A, a piston boss portion 5B is provided which defines a pin hole extending in the X direction. The piston pin is inserted into the pin hole of the piston boss 5B.

  The crown surface 50 of the piston 5 is a surface opposed to the combustion chamber ceiling surface 6U in the Z direction, and includes a bowl-shaped cavity 51 in a substantially central portion in the radial direction (X direction and Y direction). The cavity 51 is a portion that is recessed toward the −Z side (a recessed portion), and is a portion that receives fuel injection from the injector 18.

  The upper convex portion 52, the intake side flat portion 53, the exhaust side flat portion 54, the intake side slope portion 55, and the exhaust side slope portion 56 are provided on the outer peripheral portion surrounding the cavity 51 in the crown surface 50 in plan view from the + Z side. Is provided. The upper convex portion 52 is provided on the outer peripheral portion on the −X side and the + X side with respect to the cavity 51, and is a portion that is provided in a frustum shape protruding toward the + Z side.

  The intake side flat portion 53 is provided on the outer peripheral portion on the + Y side with respect to the cavity 51, and the exhaust side flat portion 54 is provided on the outer peripheral portion on the −Y side with respect to the cavity 51. In the piston 5 according to the present embodiment, the intake side flat portion 53 is configured to have a larger area than the exhaust side flat portion 54.

  The intake side slope portion 55 is provided in a region between the cavity 51 and the intake side flat portion 53, and rises toward the + Z side as it goes from the + Y side to the -Y side. The exhaust-side slope portion 56 is provided in the region between the cavity 51 and the exhaust-side flat portion 54, and rises toward the + Z side as it goes from the -Y side to the + Y side.

  As shown in FIG. 3, the cavity 51 has a side elevation surface portion 512, an exhaust side elevation surface portion 513, an intake side elevation surface portion 514, and a bottom surface portion 511. Among these, the side elevation surface portion 512, the exhaust side elevation surface portion 513, and the intake side elevation surface portion 514 are disposed at the peripheral portion of the cavity 51 when the crown surface 50 of the piston 5 is viewed in plan. . On the other hand, the bottom surface portion 511 is disposed in the region inside the cavity 51.

As shown in FIG. 4, in the cavity 51, the bottom surface portion 511 is configured with a curved surface with a radius of curvature R ₅₁₁ , and the side surface surface portion 512 with a curved surface with a radius of curvature R _512. Is configured. The centers of curvature of the bottom surface portion 511 and the side elevation surface portion 512 exist on the + Z side.

In the piston 5 according to the present embodiment, the radius of curvature R ₅₁₁ and the radius of curvature R ₅₁₂ satisfy the following relationship.

[Equation 1] R ₅₁₁ > R ₅₁₂
In other words, the lateral rising surface portion 512 is configured by a curved surface that rises in the Z direction relative to the bottom surface portion 511.

Incidentally, as shown in the enlarged portion of FIG. 4, the lateral erected surface portion 512 and the bottom portion 511, the curved surfaces are in contact with each other at a mutual boundary portions P _51.

  Further, when viewing FIG. 1 and FIG. 4 collectively, the two side vertical surface portions 512 are located between the ignition portions 170 of the spark plug 17 when the piston 5 is at the compression top dead center (TDC). It is in the state of sandwiching Thereby, as shown in FIG. 5, the side vertical surface portion 512 is mixed when the in-cylinder flow in the combustion chamber 6 is concentrated in the cavity 51 as the piston 5 rises during the compression stroke. It functions as a guiding unit for guiding the air flow Flow 1 toward the ignition unit 170 of the spark plug 17.

  As shown in FIG. 6, the exhaust side elevation portion 513 and the intake side elevation portion 514 are also configured with a curved surface that rises in the Z direction relative to the bottom surface portion 511, and the boundary portion with the bottom surface portion 511 I am in contact with

  As shown in FIG. 6, the exhaust side elevation portion 513 is continuous with the exhaust side slope portion 56 with the ridge line interposed, and the intake side elevation portion 514 is a ridge line with respect to the intake side slope portion 55. It is continuous across.

3. The positional relationship between the cavity 51 of the piston 5 and the ignition unit 170 of the spark plug 17 and the injector 18 The positional relationship between the cavity 51 of the piston 5 and the ignition unit 170 of the spark plug 17 and the injector 18 will be described with reference to FIG. FIG. 7 is a schematic plan view showing the positional relationship between the cavity 51 of the piston 5 and the ignition unit 170 of the spark plug 17 and the injector 18.

  As shown in FIG. 7, the cavity 51 in the crown surface 50 of the piston 5 is provided in a region including the lower side (the direction perpendicular to the paper surface) of the ignition part 170 in the ignition plug 17. Further, two intake ports 41 and two exhaust ports 42 are provided in the combustion chamber ceiling surface 6U (see FIG. 1). The intake port 41 and the exhaust port 42 partially overlap the cavity 51 in plan view from the Z direction.

  The two intake ports 41 are provided in a state in which they are spaced from each other in the X direction, and are arranged to sandwich the ignition portion 170 of the spark plug 17 therebetween.

Further, an imaginary line LN ₁ along the X direction passes through the end on the + Y side of the intake side elevation portion 514, and an imaginary line LN ₂ along the X direction through the end on the -Y side of the intake port 41; In the region between the virtual line LN ₁ and the virtual line LN ₂ , lateral elevations 512 are arranged on both sides (+ X side and −X side) of the ignition part 170 of the ignition plug 17 when There is.

  Here, as shown in a portion surrounded by a two-dot chain line in FIG. 7, the ignition portion 170 of the ignition plug 17 is configured of a center electrode 171 and a ground electrode 172. The center electrode 171 and the ground electrode 172 are disposed with a discharge gap G therebetween. The ground electrode 172 is a tip portion continuous with the facing portion 173, and when viewed from the side of the facing portion 173 and the ground electrode 172, has an L shape as a whole.

  The injector 18 is provided above a substantially central portion of the cavity 51 in the crown surface 50 of the piston 5 so that fuel injection is performed from the injection hole 181 (see FIG. 1) into the cavity 51. It has become.

  As shown in FIG. 7, in plan view from the Z direction, in the engine body 1, the ignition part 170 of the ignition plug 17 is disposed between the part where the injector 18 is provided and the intake side flat part 53. It is done. Further, the spark plug 17 is disposed in a state in which the facing portion 173 faces the injector 18.

4. The intake-side flat portion 53 and the intake-side slope 55 on the crown surface 50 of the piston 5 and the intake-side top surface 43 in the cylinder head 4
The relationship between the intake-side flat portion 53 and the intake-side slope portion 55 on the crown surface 50 of the piston 5 and the intake-side top surface portion 43 of the cylinder head 4 will be described with reference to FIG. FIG. 8 is a schematic cross-sectional view showing the relationship between the intake-side flat portion 53 and the intake-side slope 55 on the crown surface 50 of the piston 5 and the intake-side top surface 43 of the cylinder head 4.

  As shown in FIG. 8, the intake-side top surface portion 43 in the cylinder head 4 is configured to be along the intake-side flat portion 53 and the intake-side slope portion 55 on the crown surface 50 of the piston 5. Then, as shown in FIG. 8, when the piston 5 is in the vicinity of the compression top dead center (TDC), the intake side top surface portion 43 of the cylinder head 4 and the intake side flat portion 53 and the intake side of the crown surface 50 of the piston 5 The slope portion 55 is opposed to the slope portion 55 with a slight gap.

  As indicated by the arrow A, the intake-side inclined surface 55 is provided to point to the ignition portion 170 of the spark plug 17 when the piston 5 is at compression top dead center (TDC).

  In the engine body 1 according to the present embodiment, as described above, the combination of the intake-side top surface portion 43 of the cylinder head 4 and the intake-side flat portion 53 and the intake-side slope portion 55 of the crown surface 50 of the piston 5 is used. The squish flow generation unit is configured. This will be described later.

  Further, the exhaust side top surface portion 44 in the cylinder head 4 is also configured to be along the exhaust side flat portion 54 and the exhaust side slope portion 56 in the crown surface 50 of the piston 5. Similarly to the above, when the piston 5 is in the vicinity of compression top dead center (TDC), the exhaust side top surface portion 44 in the cylinder head 4 and the exhaust side flat portion 54 and the exhaust side slope portion 56 in the crown surface 50 of the piston 5 Also with a slight gap between them.

5. Relationship between Fuel Injection Period and Ignition Timing The fuel injection period and the ignition timing according to the present embodiment will be described with reference to FIG. FIG. 9 is a time chart showing a fuel injection period and an ignition timing.

  As shown in FIG. 9, in the engine according to the present embodiment, the operation is established at least with the fuel injection period and the ignition timing of mode I and mode II.

(1) Mode I
Mode I is a mode applied when the engine body 1 is in an operating state from the high load low rotation region to the high load medium rotation region.

  As shown in FIG. 9, in mode I, the pre-stage injection PF1 in the middle stage of the intake stroke and the post-stage injection PF2 immediately before the compression top dead center (TDC) are performed. The pre-stage injection PF1 is started, for example, at timing T1 in the first half of the intake stroke and is ended at timing T2 of the steel plate of the intake stroke. The timing T1 and the timing T2 are set at timings sandwiching a crank angle (for example, 70 ° CA after TDC) at which the piston 5 drops about half of the stroke from TDC in the exhaust stroke. As described above, by performing the pre-stage injection PF1 in the middle of the intake stroke, it is possible to sufficiently secure the formation time of the air-fuel mixture in the combustion chamber 6.

  The second-stage injection PF2, for example, is started at a timing T3 in the second half of the compression stroke and is ended at a timing T4 immediately before the compression top dead center (TDC). The timing T3 can be, for example, 10 ° CA before compression top dead center (TDC). As described above, knocking can be prevented by executing the post-injection PF2 before the compression top dead center (TDC).

  The ignition IG1 by the spark plug 17 is executed at timing T5 near the compression top dead center (TDC).

  In mode I, the gas flow (in-cylinder flow) in the combustion chamber 6 can be strengthened immediately before the ignition by executing the post-injection PF2. The fuel pressure is set to a high pressure of, for example, 30 MPa or more, whereby the fuel injection period and the mixture formation period (mixing period) can be shortened, and the gas in the combustion chamber 6 can be reduced. The flow can be made stronger. For the fuel pressure, for example, 120 MPa can be set as the upper limit value.

(2) Mode II
Mode II is a mode that is applied when the engine body 1 is in an operating state in a high rotation range, and performs SI combustion.

  As shown in FIG. 9, in mode II, the injection PF11 is started from timing T11 of the first half of the intake stroke, and is ended at timing T12 of the first half of the compression stroke. In mode II, the fuel injection PF11 is performed collectively in the period from the intake stroke to the compression stroke.

  Ignition IG11 by the spark plug 17 is executed at timing T15 before compression top dead center (TDC).

  As described above, since the fuel injection PF11 in mode II is performed collectively in the period from the intake stroke to the compression stroke, a homogeneous or substantially homogeneous mixture can be formed in the combustion chamber 6. Further, in the mode II, in the state where the number of revolutions of the engine body 1 is high, the vaporization time of the fuel can be secured as long as possible, and the unburned loss can also be reduced.

  As described above, in the engine main body 1 in which the operation of the high rotation range is executed in the mode II, the air fuel ratio of the mixture is made substantially to the theoretical air fuel ratio, and from the combustion chamber 6 using the three way catalyst Exhausted exhaust gas can be purified, and abnormal combustion can be avoided by executing SI combustion.

6. Swirl Flow Generated in the Combustion Chamber 6 The swirl flow generated in the combustion chamber 6 will be described with reference to FIG. FIG. 10 is a schematic plan view showing the fuel injected into the combustion chamber 6 and the swirl flow generated in the combustion chamber 6.

  As shown in FIG. 10, fuel is injected radially from the injector 18 disposed substantially at the center of the combustion chamber 6 in plan view from the Z-axis direction (direction perpendicular to the drawing) (injection fuel 18E). Specifically, fuel is injected from the injector 18 toward the inside of the cavity 51 provided on the crown surface 50 of the piston 5.

  In the engine body 1 according to the present embodiment, the fuel injection from the injector 18 is such that the directional axis does not turn to the ignition unit 170 of the ignition plug 17. That is, the directional axis of the injected fuel 18E from the injector 18 passes both sides of the ignition part 170 of the ignition plug 17. Thereby, the occurrence of plug covering can be suppressed.

  Further, in the engine main body 1 according to the present embodiment, as described above, the facing portion 173 of the spark plug 17 is directed to the −Y side, and the ignition portion 170 faces the injection hole 181 of the injector 18. It has become. Also by this, it is possible to suppress the occurrence of plug covering.

  In the combustion chamber 6, as indicated by the arrow, a swirl flow Flow2 occurs so as to go around the periphery of the cavity 51. Thus, the air and the fuel are sufficiently mixed by the swirl flow Flow 2 generated at the peripheral portion of the cavity 51, and are led to the ignition portion 170 of the spark plug 17 and the vicinity thereof.

  As described with reference to FIG. 5, the side elevation surface portion (guide portion) 512 provided on the peripheral edge portion of the cavity 51 allows the swirl flow Flow 2 to circulate while the ignition portion 170 of the ignition plug 17 and its vicinity The air-fuel mixture is lifted to the + Z side (the front side of the drawing) toward the end.

  Further, as described above, the air-fuel mixture can be guided to the ignition part 170 of the spark plug 17 and the vicinity thereof, so that the residual gas in the vicinity of the ignition part 170 can be flushed away.

7. The squish flow generated in the combustion chamber 6 The squish flow generated in the combustion chamber 6 will be described with reference to FIGS. 11 and 12. FIG. 11A is a schematic cross-sectional view showing the state of the combustion chamber 6 when the piston 5 is moving up in the first half of the compression stroke, and FIG. 11B is a vicinity of compression top dead center (TDC) of the piston 5. It is a schematic cross section which shows the state of the combustion chamber 6 in the case of being. FIG. 12 is a schematic cross-sectional view showing the squish flow generated between the intake-side flat portion 53 and the intake-side slope portion 55 of the piston 5 and the intake-side top surface portion 43 of the cylinder head 4.

  As shown in FIG. 11A, when the piston 5 is rising to the + Z side in the compression stroke, the distance between the intake-side flat portion 53 and the intake-side slope 55 of the piston 5 and the combustion chamber ceiling surface 6U narrows. In accordance with, the mixture present in the portion indicated by the arrow B is compressed.

  As shown in FIG. 11B, in a state where the piston 5 has reached near the compression top dead center (TDC), as indicated by an arrow C, the intake side flat portion 53 and the intake side slope portion 55 of the piston 5 and the combustion The room ceiling surface 6U is opposed with a slight gap left.

  As shown in FIG. 12, in the engine body 1 according to the present embodiment, the intake-side flat portion 53 and the intake-side slope 55 in the piston 5 and the intake-side top surface 43 in the cylinder head 4 are formed along the other It is done. Then, in the Y direction, the intake side slope portion 55 is provided in a region (region on the + Y side) from the cylinder wall surface 2 (not shown in FIG. 12) of the ignition portion 170 of the spark plug 17.

  The suction side slope portion 55 of the piston 5 is provided such that the directional axis DR faces the ignition portion 170 of the spark plug 17 in a state where the piston 5 is positioned at TDC.

  As described above, since the intake side flat portion 53 and the intake side slope portion 55 of the piston 5 are provided, the air-fuel mixture compressed with the intake side top surface portion 43 of the cylinder head 4 is the intake side slope portion 55. The gas is jetted out as a squish flow Flow 3 directed to the ignition part 170 of the spark plug 17 from the gap between the air intake side ceiling surface 43 and the air intake side ceiling surface 43. That is, the combination of the suction side slope portion 55 of the piston 5 and the suction side top surface portion 43 of the cylinder head 4 functions as a squish flow generation portion when the piston 5 is raised.

  Therefore, in the engine main body 1 according to the present embodiment, residual gas in the ignition part 170 of the ignition plug 17 and the periphery thereof can be scavenged using the squish flow Flow 3 generated when the piston 5 is raised.

  As shown in FIG. 11A, the piston 5 includes the exhaust side flat portion 54 and the exhaust side slope portion 56 and the exhaust side top surface portion 44 (see FIG. 8) of the cylinder head 4. Also in the state where the piston 5 is located at TDC, it faces with a slight gap left. Therefore, as the piston 5 moves up, a flow of air-fuel mixture along the combustion chamber ceiling 6U is also generated from the region on the exhaust side in the combustion chamber 6. As a result, the injection holes 181 of the injectors 18 in the combustion chamber 6 and the remaining side around the injection holes can be scavenged.

8. In the combustion chamber 6 of the engine body 1 according to the present embodiment, the side surface portion (guide portion) is disposed so as to sandwich the ignition portion 170 of the spark plug 17 when the piston 5 is at compression top dead center (TDC) Since the 512) is provided, when the in-cylinder flow in the combustion chamber 6 is concentrated in the cavity 51 with the rise of the piston 5 during the compression stroke, the air-fuel mixture is made by the side surface 512 It is led to the ignition part 170 of the spark plug 17 and its periphery.

  Therefore, in the engine body 1 according to the present embodiment, by causing the air-fuel mixture to exist in the ignition portion 170 of the ignition plug 17 and the periphery thereof at the time of ignition, high ignitability of the air-fuel mixture can be secured.

  Further, in the combustion chamber 6 of the engine body 1 according to the present embodiment, the cavity 51 has a convex (lower convex) hook shape in a direction away from the combustion chamber ceiling surface 6U. By employing the non-existing wedging cavity 51, flame propagation after ignition is smoothly performed throughout the combustion chamber 6.

Further, in the combustion chamber 6 of the engine body 1 according to the present embodiment, as described with reference to FIG. 4, the side elevation surface portion 512 is configured with a curved surface, and the side elevation surface portion since the radius of curvature _{R 512} 512 is smaller than the radius of curvature _{R 511} of the bottom portion 511, the flame formed by the ignition in the ignition portion 170 of the spark plug 17, X-direction (engine output in combustion chamber 6 Can be spread smoothly in the axial direction).

Further, in the combustion chamber 6 of the engine body 1 according to the present embodiment, since the curved surfaces of the lateral erected surface portion (guide portion) 512 and the bottom portion 511 of the piston 5 is in contact with the boundary portion P _51, the and side erected surface portion 512 and the bottom portion 511 is configured to contact with the smooth boundary P _51. Therefore, in the combustion chamber 6 of the engine main body 1 according to the present embodiment, the flame formed by the ignition by the ignition unit 170 of the ignition plug 17 is made smoother in the X direction (engine output shaft direction) in the combustion chamber 6 It can be spread.

  Further, in the combustion chamber 6 of the engine body 1 according to the present embodiment, since the intake side slope portion 55 is provided on the crown surface 50 of the piston 5, the combination with the intake side top surface portion 43 of the cylinder head 4 is used. The squish flow generation unit is configured. Therefore, when the piston 5 ascends during the compression stroke, the squish flow Flow3 directed to the ignition unit 170 of the ignition plug 17 can be generated. Therefore, in the combustion chamber 6 of the engine body 1 according to the present embodiment, scavenging of residual gas in the ignition portion 170 of the spark plug 17 and the periphery thereof using squish flow Flow 3 generated when the piston 5 moves upward. it can.

  Further, in the combustion chamber 6 of the engine body 1 according to the present embodiment, fuel injection from the injector 18 is performed in the middle of the intake stroke, so that the flow in the cylinder is relatively weak (at the intake stroke In the middle stage, fuel will be injected. In the combustion chamber 6 of the engine main body 1 according to the present embodiment, when adopting the timing of fuel injection as described above, the adhesion of fuel to the cylinder wall surface 2 can be suppressed by concentrating the spray in the cavity 51. it can.

  Therefore, in the combustion chamber 6 of the engine body 1 according to the present embodiment, by causing the air-fuel mixture to exist in the ignition portion 170 of the ignition plug 17 and the periphery thereof at the time of ignition, high ignitability of the air-fuel mixture can be secured.

Second Embodiment
A spark ignition engine according to the second embodiment will be described with reference to FIG. FIG. 13 is a time chart showing a fuel injection period and an ignition timing according to the present embodiment.

  The engine according to the present embodiment adopts the same configuration as that of the first embodiment except that the fuel injection period is partially different, so only the fuel injection period and the ignition timing will be described.

  As shown in FIG. 13, also in the engine according to the present embodiment, the operation is established at least with the fuel injection period and the ignition timing of mode I and mode II. Among these, the mode II is the same as that of the first embodiment, and therefore only the mode I will be described below.

  In the mode I according to the present embodiment, the fuel injection PF21 from the middle stage of the intake stroke to the first half of the compression stroke is performed, but unlike the first embodiment, the fuel injection immediately before the compression top dead center (TDC) is not performed. That is, in the mode I according to this embodiment, the fuel injection PF21 starts fuel injection at timing T21 in the middle of the intake stroke and ends at timing T22 in the first half of the compression stroke.

  Here, the start timing T21 of the fuel injection PF21 can be, for example, 280 ° CA before the compression top dead center (TDC).

  The ignition IG 21 by the spark plug 17 is executed at timing T 25 near the compression top dead center (TDC), as in the mode I of the first embodiment.

  In mode I according to the present embodiment, by setting the period of the fuel injection PF 21 as shown in FIG. 13, it is possible to form an air-fuel mixture for CI (Compression Ignition) combustion in the outer peripheral portion of the combustion chamber 6 At the same time, in the central portion of the combustion chamber 6, an air-fuel mixture for SI (spark ignition) combustion can be formed.

  The air-fuel ratio λ in the central portion of the combustion chamber 6 is preferably 1 or less, and the air-fuel ratio in the outer peripheral portion is 1 or less (preferably less than 1). The air-fuel ratio (A / F) of the air-fuel mixture in the central portion of the combustion chamber 6 can be, for example, 13 or more and the theoretical air-fuel ratio (14.7) or less.

  The air-fuel ratio of the air-fuel mixture in the outer peripheral portion of the combustion chamber 6 may be, for example, 11 or more, the theoretical air-fuel ratio (14.7) or less, 11 or more, or 12.5 or more, 13 or less. .

  That is, in the present embodiment, since the time for the fuel injected by the fuel injection PF 21 to react becomes short when the engine main body 1 has a high rotational speed, the second-stage injection for suppressing the reaction of the air-fuel mixture (the first The second injection PF2) of the embodiment can be omitted.

  In the present embodiment, since the same configuration as the combustion chamber 6 of the engine body 1 according to the first embodiment is employed, the air-fuel mixture is ignited by the ignition portion 170 of the ignition plug 17 at the time of ignition as in the first embodiment. And by being present in the vicinity thereof, high ignitability of the mixture can be secured.

[Modification]
In the first embodiment and the second embodiment, the cavity 51 of the piston 5 has one bottom surface portion 511 and two side rising surface portions 512 in the IV-IV cross section (the cross section shown in FIG. 4) of FIG. In the present invention, the present invention is not limited thereto. For example, a cross-sectional configuration in which a curved surface or a flat surface is interposed between the bottom surface portion 511 and the side surface surface portion 512 can also be adopted.

In the first embodiment and the second embodiment, the bottom surface portion 511 and the side surface surface portion 512 are in contact with each other at the boundary portion P ₅₁ , but the present invention is not limited to this. Absent. It is also possible to cross at a minute angle. Also by this, it can be considered that there is almost no influence on the air flow in the cylinder.

  Further, in the first embodiment and the second embodiment, the intake-side flat portion 53, the exhaust-side flat portion 54, the intake-side slope portion 55, and the exhaust-side slope portion 56 in the piston 5 are respectively formed in planes. However, the present invention is not limited thereto. For example, it is also possible to comprise by a concave curve or a convex curve.

  In the first embodiment and the second embodiment, the intake side flat portion 53 of the piston 5 has a larger area than the exhaust side flat portion 54. However, the present invention is limited to this. It is not a thing. For example, an intake side flat portion and an exhaust side flat portion having the same area may be employed.

  However, in the case where the flow of the squish flow Flow3 from the intake side is made stronger than the flow of the air flow from the exhaust side, the function of scavenging residual gas in the ignition part 170 of the spark plug 17 and its periphery is considered. It is desirable to adopt the same configuration as the first embodiment and the second embodiment.

  In the first embodiment and the second embodiment, the combustion chamber ceiling surface 6U is formed in a flat pent roof shape, but the present invention is not limited to this. It is also possible to adopt a higher ratio pent roof shape. Such a high ratio pent-roof-shaped combustion chamber ceiling surface is advantageous in generating a strong tumble flow.

  Moreover, although the said 1st Embodiment and the said 2nd Embodiment did not make reference in particular with respect to the suction port etc. which are connected with the suction port 41, in this invention, a various variation structure can be employ | adopted. For example, one of the intake ports leading to the two intake ports may be provided with a swirl control valve. In the case of adopting such a configuration, it is possible to more positively generate the swirl flow Flow 2 in the combustion chamber 6 by the opening and closing control of the swirl control valve.

  Specifically, by closing the swirl control valve, it is possible to easily generate a swirl flow which is a vortex around the cylinder axis.

DESCRIPTION OF SYMBOLS 1 engine body 2 cylinder wall surface 3 cylinder block 4 cylinder head 5 piston 6 combustion chamber 17 ignition plug 18 injector 41 intake port 43 intake side top surface 50 crown surface 51 cavity 53 intake side flat portion 54 exhaust side flat portion 55 intake side slope portion (Sloped surface)
170 Ignition part 511 Bottom part 512 Side elevation part (guide part)

Claims (6)

In the combustion chamber structure of a spark ignition engine,
The crown face of the piston,
The combustion chamber ceiling surface formed on the cylinder head,
An ignition plug mounted on a ceiling surface of the combustion chamber and having an ignition part disposed to face the combustion chamber;
Equipped with
The crown surface of the piston has a cavity which is recessed in the axial direction of the cylinder in a region including the lower side of the ignition portion of the spark plug in plan view in the axial direction of the cylinder.
The peripheral portion of the cavity rises in the axial direction of the cylinder than the region inside the peripheral portion, and sandwiches the ignition portion when the piston is at compression top dead center, and mixing in the combustion chamber A guide unit for guiding air to the ignition unit;
Engine combustion chamber structure. A combustion chamber structure of an engine according to claim 1, wherein
The cavity is formed in a bowl shape convex in a direction away from the ceiling surface of the combustion chamber in the axial direction of the cylinder.
Engine combustion chamber structure. A combustion chamber structure of an engine according to claim 1 or 2, wherein
The combustion chamber further includes two intake ports opened on the ceiling surface of the combustion chamber and arranged along the engine output shaft direction with each other,
The ignition unit of the ignition plug is disposed between the two intake ports,
The guide portion is formed on both sides of the cavity in the direction of the engine output shaft in a plan view of the cavity in the axial direction of the cylinder.
The guide portion and the inner region are both configured by a curved surface curved in the cylinder axis direction,
The radius of curvature at the guiding portion is smaller than the radius of curvature of the inner region,
Engine combustion chamber structure. A combustion chamber structure of an engine according to claim 3, wherein
The curved surfaces are in contact with each other at boundary portions between the guide portion and the inner region.
Engine combustion chamber structure. A combustion chamber structure of an engine according to claim 3 or claim 4, wherein
The crown surface of the piston is the compression top dead center in a portion near the cylinder wall surface on the intake side of the ignition portion of the spark plug in a side view from the engine output shaft direction. It has an inclined surface portion which is formed to be directed to the ignition portion of the spark plug, along with a gap between the corresponding region in the cylinder axial direction upper side in the combustion chamber ceiling surface,
The inclined surface portion and the corresponding region constitute a squish flow generation unit that generates a squish flow when the piston is raised, by a combination thereof.
Engine combustion chamber structure. The combustion chamber structure of an engine according to any one of claims 1 to 5, wherein
The injector further comprises an injector provided on the ceiling surface of the combustion chamber,
The injector performs fuel injection toward the cavity in the middle of the intake stroke.
Engine combustion chamber structure.

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