JP2013015054A - Cylinder injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in a cylinder injection type internal combustion engine that fuel consumption degrades because of insufficient use of energy due to fuel, flame, or the like contacting with a cavity, causing a heat loss.SOLUTION: The cylinder injection type internal combustion engine includes a piston, a cavity formed on a top face of the piston and formed with a bottom face and a sidewall face, a fuel injection means for injecting fuel toward the cavity, and an injection period control means for controlling an injection period of the fuel. The cavity includes a first cavity located on an outer circumferential side of the piston and a second cavity located on an inner circumferential side of the piston, and the second cavity is formed on a bottom face of the first cavity. The cylinder injection type internal combustion engine controls the fuel injection period by using the cavity located lower than a virtual extended bottom face which the bottom face of the first cavity is extended toward a central axis of the piston.

Description

  The present invention relates to an in-cylinder injection internal combustion engine, and more particularly to an in-cylinder injection internal combustion engine in which a cavity including a bottom surface and a side wall surface is provided on the top surface of a piston, and a fuel injection injector is provided at a position facing the top surface of the piston. It is about the institution.

  Some in-cylinder injection internal combustion engines are provided with a recess called a cavity on the top surface of a piston. For example, Patent Document 1 discloses a so-called toroidal cavity shape in which the bottom surface of the cavity becomes lower as it goes to the outer peripheral side of the piston.

Patent Document 2 discloses a cavity shape in which a protrusion is further added to the bottom surface of a toroidal cavity. The injection period of the fuel injected toward the cavity is controlled, and collides with the cavity side wall surface in the first half of the injection period, and collides with the protrusion on the bottom surface of the cavity in the second half of the injection period. As a result, the injected fuel can be diffused and sufficiently mixed with air over the entire injection period, and premixed combustion is realized.
JP 2003-83119 A JP-A-2005-315211

  However, in the above-described cylinder injection internal combustion engine, the thermal energy of the flame and the high-temperature combustion gas generated in the combustion chamber by burning the injected fuel cannot be sufficiently utilized.

  In Patent Document 1, a flame or high-temperature combustion gas flows while being in contact with the bottom surface and the side wall surface of the cavity. At this time, since the bottom surface and the side wall surface of the cavity are lower in temperature than the flame and the high-temperature combustion gas, the heat of the flame and the high-temperature combustion gas is taken away. That is, a flame or high-temperature combustion gas may come into contact with the bottom surface and the side wall surface of the cavity to cause heat loss, which may deteriorate fuel consumption.

  In Patent Document 2, there is a case where the fuel collides with the side wall surface and a case where the fuel collides with the projecting portion. In any case, the flame and the high-temperature combustion gas, the bottom surface of the cavity (including the projecting portion), and the side wall surface Since contact cannot be suppressed, heat loss may occur and fuel consumption may deteriorate.

  The present invention has been made in view of the above problems, and an object thereof is to reduce heat loss by suppressing contact between a flame or a high-temperature combustion gas and a cavity, thereby improving fuel consumption.

  In order to solve the above-mentioned problem, the invention described in claim 1 is a fuel provided in a piston, a cavity provided on a top surface of the piston, which is composed of a bottom surface and a side wall surface, and fuel injected into the cavity. An in-cylinder injection internal combustion engine comprising injection means and fuel injection period control means for controlling a fuel injection period, wherein the cavity is a first cavity located on the outer peripheral side of the piston, and an inner peripheral side of the piston The second cavity is provided on the bottom surface of the first cavity, and is below the virtual extended bottom surface extending from the bottom surface of the first cavity toward the central axis of the piston. The fuel injection period control means is configured such that the intersection of the center axis of the fuel injected by the fuel injection means and the cavity is the Located on the outer peripheral side than the inner edge of one cavity and so as not located in the second cavity, a cylinder injection type internal combustion engine and controlling the injection period of the fuel.

  The invention described in claim 2 is the direct injection internal combustion engine according to claim 1, wherein the fuel injection period control means calculates a base injection period corresponding to an engine operating region, and When the intersection of the central axis of the fuel injected by the fuel injection means and the cavity is located in the second cavity during the injection period, the base injection is performed so that the injection in the base injection period ends earlier in the compression stroke. The cylinder injection internal combustion engine is characterized in that the base injection period is corrected such that the period is corrected and the base injection period starts later in the expansion stroke.

  According to the present invention, the fuel is not directly injected into the second cavity, but is injected to the outer peripheral side from the inner edge of the first cavity. The fuel injected to the outer peripheral side from the inner edge of the first cavity collides with the side wall surface in the first cavity and flows along the bottom surface in the first cavity, and the bottom surface in the first cavity faces the central axis of the piston. It goes to the piston central axis along the extended virtual extension bottom.

  Or it collides with the bottom face in a 1st cavity, flows as it is along the bottom face in a 1st cavity, and goes to a piston central axis along the virtual extended bottom face which extended the bottom face in a 1st cavity toward the central axis of the said piston.

  At this time, since the second cavity is positioned below the virtual extension bottom surface, the contact between the fuel injected into the first cavity and the second cavity can be suppressed. That is, rectification is performed so as to suppress contact with the second cavity.

  The flame and high-temperature combustion gas generated by burning the fuel injected from the inner edge of the first cavity to the outer peripheral side also suppresses contact with the second cavity located below the virtual extension bottom surface as well as the fuel. Is rectified as follows. Therefore, the heat loss resulting from the contact between the flame or the high-temperature combustion gas and the second cavity is reduced, and the fuel consumption can be improved.

  Further, the fuel injection period control means controls the fuel injection period (including the injection start timing and the injection end timing), thereby preventing the fuel from being directly injected into the second cavity. Thereby, the effect of more reliable heat loss reduction and fuel consumption improvement can be acquired.

1 is a longitudinal sectional view showing a schematic configuration of a direct injection internal combustion engine according to an embodiment of the present invention. It is one of the principal part enlarged views of the cavity shape of a piston top surface. It is one of the principal part enlarged views of the cavity shape of a piston top surface. In the cavity of this invention, it is the figure which showed a mode that fuel spray, a flame, and high temperature combustion gas flowed. It is a flowchart of the fuel injection period control which ECU performs. In the flowchart of FIG. 5, it is the figure which showed the outline | summary about correction | amendment control of the fuel-injection period at the time of a piston raise. In FIG. 1, it is the figure which arranged the heat-shielding material in the 1st cavity. It is the figure which showed the mode of the fuel spray at the time of using gas fuel as fuel to inject and setting the injection angle to a wide angle. It is the figure which showed a mode that fuel spray, a flame, and high temperature combustion gas flow in the conventional cavity.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  In Example 1 which concerns on this invention, light oil is used as a fuel to inject. FIG. 1 shows a schematic configuration in the first embodiment, and is a longitudinal sectional view taken along a vertical plane including a central axis C of a piston 10. In FIG. 1, only one cylinder is shown, but multiple cylinders may be used.

  The piston 10 is formed in a substantially cylindrical shape, has an outer peripheral surface 11 and a top surface 12, and is connected to a crankshaft that is an output shaft of the internal combustion engine via a piston pin and a connecting rod (not shown).

  The outer peripheral surface 11 is a portion that slides facing the cylinder bore inner surface 13 at a predetermined interval. A plurality of ring grooves 14 are formed on the outer peripheral surface 11, and piston rings 15 are fitted into the ring grooves 14, respectively. A cavity 20 is formed in the top surface 12.

  The cavity 20 is a recess formed in the top surface 12 of the piston 10 and is formed of a bottom surface and a side wall surface. Here, the bottom surface is a surface facing an engine head (not shown), and the side wall surface is a surface extending from the edge of the bottom surface toward the top surface 12 of the piston 10.

  Although only the longitudinal cross-sectional shape of the piston 10 and the cavity 20 is shown in FIG. 1, the same shape is continuously formed around the central axis C, and viewed from the direction of the top surface 12. In plan view, the piston 10 and the cavity 20 are formed in a circular shape.

  In the present embodiment, as shown in FIG. 1, the combustion chamber shape using the circular piston 10 in which the same shape is continuously formed around the central axis C as a center is used. However, the present invention is not limited to this. Absent. For example, the central axis C and the injector 16 may be offset (offset), or may have a pent roof type combustion chamber shape.

  FIG. 2 shows one of the enlarged views of the main part of the cavity 20. The cavity 20 includes a first cavity 21 and a second cavity 22. The first cavity 21 is positioned on the outer peripheral side of the piston 10, and the second cavity 22 is positioned on the inner peripheral side of the piston 10, and is provided on the bottom surface 21 b in the first cavity.

  More specifically, the cavity 20 is formed by connecting the inner edge A of the bottom surface 21 b in the first cavity 21 and the upper end of the side wall surface 22 a in the second cavity 22.

  Further, in the cavity 20, the second cavity 22 is positioned below a virtual extended bottom surface 21 c obtained by extending the bottom surface 21 b of the first cavity 21 toward the central axis C of the piston 10. That is, when the cavity 20 is viewed from the top surface 12 of the piston 10, the second cavity 21 is positioned vertically below the virtual extended bottom surface 21c.

  In addition, the shape of the 1st cavity 21 and the 2nd cavity 22 will not be specifically limited if the above-mentioned positional relationship is maintained.

  For example, in FIG. 2, which is one of the enlarged views of the main part of the cavity 20, the bottom surface 22 b of the second cavity 22 is formed in a cone shape that gradually decreases from the central axis C of the piston 10 toward the outer peripheral side. . Further, the connection between the side wall surface 21a and the bottom surface 21b in the first cavity 21 is formed by a smoothly continuous curved surface.

  On the other hand, in FIG. 3, which is one of the enlarged views of the main part of the cavity 20, the bottom surface 22b of the second cavity is formed in a planar shape. Further, the connection between the side wall surface 22a and the bottom surface 22b in the first cavity 21 is constituted by a discontinuous straight surface. Also in FIG. 3 configured as described above, a positional relationship is established in which the second cavity 22 is positioned below the virtual extended bottom surface 21 c, and such a cavity 20 may be provided in the piston 10.

  FIG. 4 shows the flow of the fuel 30 injected by the injector 16 as fuel injection means and the flow of the flame generated by the ignition of the fuel 30 and the high-temperature combustion gas 31 in this embodiment.

  Here, the flow state of the fuel 30 and the flow state of the flame and the high-temperature combustion gas 31 will be described more specifically with reference to FIGS. 4 and 2 described above.

The injection angle at which the injector 16 injects fuel is such that the fuel 30 can be injected into the first cavity 21 without being directly injected into the second cavity 22, so that good fuel can be realized. A suitable angle θ ₁ (for example, θ ₁ = 155 °) is set.

  The period during which the injector 16 injects the fuel 30 is controlled by the ECU 17 which is a fuel injection period control means based on the flowchart of FIG. Thus, the injected fuel 30 is injected into the first cavity 21 without being directly injected into the second cavity 22 according to the operating state of the internal combustion engine and the position of the piston 10.

  The fuel 30 injected based on the control of the ECU 17 is not directly injected into the second cavity 22, but is injected into the first cavity 21, and after colliding, flows to the bottom surface 21b. After flowing along the bottom surface 21 b, the fluid flows along the virtual extended bottom surface 21 c extending from the bottom surface 21 b toward the central axis C of the piston 10, and is rectified so as to go toward the central axis C of the piston 10.

  At this time, the fuel 30 also passes in the vicinity of the second cavity 22, but the second cavity 22 is positioned vertically below the virtual extended bottom surface 21c, so that contact between the fuel 30 and the second cavity is suppressed.

  The flow of the flame and the high-temperature combustion gas 31 generated when the injected fuel 30 is ignited is rectified as described above, and the contact with the second cavity is suppressed.

  On the other hand, FIG. 9 shows the flow of the fuel 30, the flame, and the high-temperature combustion gas 31 when the conventional cavity 23 is used. The bottom surface 23b of the cavity 23 is formed of a uniformly continuous curved surface or plane.

  The fuel 30 injected toward the cavity 23 collides with the cavity 23 and then flows to the bottom surface 23b. And it goes to the central axis C of the piston 10 along the bottom face 23b.

  Since the flame and the high-temperature combustion gas 31 also flow in the same process as the fuel 30, the flame and the high-temperature combustion gas 31 travel toward the central axis C of the piston 10 along the bottom surface 23 b. That is, since the fluid flows while being in contact with the entire bottom surface 23b, heat loss caused by the contact with the bottom surface 23b cannot be suppressed.

  On the other hand, when the fuel is burned using the cavity 20 of the present embodiment, the contact between at least the second cavity 22 and the flame and the high-temperature combustion gas 31 can be suppressed. Can do.

  Here, the control of the fuel injection period executed by the ECU 17 as the fuel injection control means will be specifically described with reference to the flowchart of FIG.

  First, in step S1, an engine speed and an engine load are detected by an engine speed sensor and an engine load sensor (not shown). Then, the ECU 17 calculates a base injection start time eainjbmn, which is the start time of the base injection period, and a base injection end time eainjbmx, which is the end time of the base injection period, corresponding to the engine speed and the engine load. The period from the base injection start time eainjbmn to the base injection end time eainjbmx is the base injection period.

When the base injection period calculated in step 1 is set near the compression top dead center (hereinafter referred to as TDC), the fuel 30 may be directly injected into the second cavity 22 and may come into contact with the second cavity 22. This is because when the fuel 30 is injected with the piston 10 approaching the injector 16, the fuel injection angle θ ₁ of the injector 16 is fixed and the relative distance between the piston 10 and the injector 16 is approached. This is because the center axis of the fuel 30 reaches the second cavity 22.

  Therefore, in the compression stroke, the base injection period is corrected so that the injection of the fuel 30 is completed before the piston 10 reaches the vicinity of TDC. At this time, among the injection end times at which the fuel 30 is not directly injected into the second cavity 22, the time closest to the TDC is defined as the allowable injection end time eaincmx.

  Further, in the expansion stroke, the base injection period is corrected so that the injection of the fuel 30 starts after the piston 10 moves away from the vicinity of the TDC. At this time, among the injection start timings at which the fuel 30 is not directly injected into the second cavity 22, the timing closest to the TDC is defined as the allowable injection start timing eainjemn.

  In step 2, the injection pressure of the fuel 30 to be injected is detected by a fuel injection pressure sensor (not shown), and the allowable injection end timing eainjcmx and the allowable injection start timing eainjemn are calculated by the ECU 17 based on the fuel injection pressure and the engine speed.

  Further, the allowable injection end timing eaincmx is corrected by the engine load.

  More specifically, when the engine load is large (the amount of fuel 30 injected is large), the allowable injection end timing eainjcmx is set to the previous period. This is because the period from when the command for injecting the fuel 30 is completed to when the injection of the fuel 30 is completely completed is increased by an amount larger than usual.

  When the engine load is small (the amount of fuel 30 injected is small), the allowable injection end timing eainjcmx is set later. This is because the period from when the command for injecting the fuel 30 is completed until the injection of the fuel 30 is completely completed is shortened by an amount smaller than the normal amount of fuel 30 injection.

  The base injection period, the base injection start timing eainjbmn, the base injection end timing eainjbmx, the allowable injection end timing eainjcmx, and the allowable injection start timing eainjemn are two-dimensional according to the values of the engine speed, engine load, and fuel injection pressure. The map may be stored in a RAM, which is a nonvolatile memory, and calculated from the two-dimensional map.

  In step S3, it is determined whether the base injection period calculated in step 1 is earlier or later than TDC.

  If it is determined in step S3 that the base injection period is set earlier than TDC, that is, if it is determined that the base injection period is in the compression stroke and the piston 10 is moving upward, step S4 Proceed to

  Here, step S4, step S6, and step S7 will be described with reference to the flowchart of FIG. 5 and FIG. In step S4, when it is determined that the base injection end timing eainjbmx before correction is later than the allowable injection end timing eainjcmx (1 in FIG. 6), the process proceeds to step S6, where the base injection end timing eainjbmx sets the allowable injection end timing eainjcmx. The base injection period is corrected earlier so as not to exceed (2 in FIG. 6).

  That is, the final injection end timing eainjfmx, which is the final fuel injection end timing derived by the control of the fuel injection period executed by the ECU 17, becomes the allowable injection end timing eainjcmx.

  If it is determined in step S4 that the base injection end timing eainjbmx is earlier than the allowable injection end timing eainjcmx (3 in FIG. 6), the process proceeds to step S7, where the initial base injection end timing eainjbmx is the final injection end timing eainjfmx. It becomes.

  If it is determined in step S3 that the base injection period is set later than TDC, that is, if it is determined that the base injection period is in the expansion stroke and the piston 10 is moving downward, the process proceeds to step S5. .

  Here, step S5, step S8, and step S9 will be described with reference to the flowchart of FIG. 5 and FIG. If it is determined in step S5 that the base injection start timing eainjbmn is earlier than the allowable injection start timing eainjemn (4 in FIG. 6), the process proceeds to step S8, where the base injection start timing eainjbmn exceeds the allowable injection start timing eainjemn. The base injection period is corrected later so as not to occur (5 in FIG. 6).

  That is, the final injection start timing eainjfmn, which is the final fuel injection start timing derived by the control of the fuel injection period executed by the ECU 17, becomes the allowable injection start timing eainjemn.

  If it is determined in step S5 that the base injection start timing eainjbmn is later than the allowable injection start timing eainjemn (6 in FIG. 6), the process proceeds to step S9, where the initial base injection start timing eainjmn is the final injection start timing eainjfmn. It becomes.

  As described above, in the internal combustion engine having the piston 10 in which the cavity 20 is formed, the control of the fuel injection period based on the flowchart of FIG. It is possible to prevent 31 from being directly injected into the second cavity 22. In addition, since contact between the fuel 30 and the flame or the high-temperature combustion gas 31 and the second cavity 22 is suppressed, heat loss is reduced and fuel efficiency is improved.

  In Example 2, as shown in FIG. 7, the heat shield 19 is disposed in the first cavity 21. The heat shield 19 is made of a material having a lower thermal conductivity than the material used for the piston 10, for example, ceramic.

  Thereby, even if the fuel 30 or flame injected from the injector 16 and the high-temperature combustion gas 31 come into contact with the first cavity 21, it is difficult for heat to be taken away.

  Therefore, according to the present embodiment, not only the heat loss generated in the second cavity 22 but also the heat loss generated in the first cavity 21 can be reduced, and the fuel efficiency can be further improved compared to the first embodiment.

In the third embodiment, as shown in FIG. 8, gas fuel, for example, hydrogen gas 32 is used as fuel injected from the injector 16, and a spark plug 19 is used as ignition means for the hydrogen gas 32. In addition, the injection angle θ ₂ of the hydrogen gas 32 is set to a sufficiently wide angle (for example, 170 °).

In this embodiment, since the injection angle theta ₂ sufficiently wide set, even when the injected hydrogen gas 32 in the vicinity of the top dead center, hydrogen gas 32 without impinging directly to the second cavity 22, The first cavity 21 can be made to collide. That is, it is not necessary to calculate the allowable injection start timing and the allowable injection end timing as in Embodiment 2 and prohibit the fuel injection near the top dead center.

If fuel injected is a liquid fuel, when injected at a wide angle, such as injection angle theta ₂ becomes difficult mixing with air, there is a possibility that emission degradation. But the fuel injected in this embodiment because the fuel gas (hydrogen gas 32) is easily mixed with even air is injected at a wide angle, such as injection angle theta _2, it is less fear that exacerbate emission performance.

  Therefore, fuel injection near the compression top dead center can be performed without deteriorating engine performance, so that injection based on the base injection period is always possible.

DESCRIPTION OF SYMBOLS 10 ... Piston, 11 ... Outer peripheral surface, 12 ... Top surface, 13 ... Cylinder bore inner surface, 14 ... Ring groove, 15 ... Piston ring, 16 ... Injector, 17 ... ECU, 18 ... Heat shield, 19 ... Spark plug, 20 ... Cavity, 21 ... first cavity, 22 ... second cavity, 23 ... conventional cavity, 30 ... fuel, 31 ... flame and high-temperature combustion gas, 32 ... hydrogen gas, A ... inner edge of bottom surface 21a of the first cavity, C ... Center axis

Claims (2)

A piston, a cavity provided on a top surface of the piston, and having a bottom surface and a side wall surface; fuel injection means for injecting fuel toward the cavity; and fuel injection period control means for controlling a fuel injection period. In the cylinder injection internal combustion engine provided,
The cavity consists of a first cavity located on the outer peripheral side of the piston and a second cavity located on the inner peripheral side of the piston,
The second cavity is a cavity that is provided on the bottom surface of the first cavity and is located below a virtual extended bottom surface that extends the bottom surface of the first cavity toward the central axis of the piston,
The fuel injection period control means is such that the intersection of the center axis of the fuel injected by the fuel injection means and the cavity is located on the outer peripheral side of the inner edge of the first cavity and not located in the second cavity. An in-cylinder internal combustion engine characterized by controlling a fuel injection period.
The fuel injection period control unit calculates a base injection period corresponding to an engine operating region, and an intersection of a center axis of fuel injected by the fuel injection unit and the cavity during the base injection period is located in the second cavity. If so, the base injection period is corrected so that the injection in the base injection period ends earlier in the compression stroke, and the base injection period is corrected so that the base injection period starts later in the expansion stroke. The in-cylinder injection internal combustion engine according to claim 1.

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