JP2016151236A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine capable of reducing smoke and unburnt fuel.SOLUTION: A diesel engine includes a cylinder 3, a piston 23 arranged to freely reciprocate vertically in the cylinder 3, a cylinder head 24 arranged above the piston 23 and forming a combustion chamber 4 in cooperation with the cylinder 3 and the piston 23, and an injector 5 attached to the cylinder head 24 and injecting fuel to the combustion chamber 4. A stepped portion 26 heightened toward an outer side of the piston 23 is provided on an upper end edge of the piston 23, a recessed cavity 27 constituting at least a part of the combustion chamber 4 is provided in an inner side of the stepped portion 26 in the piston 23, and a protrusion 30 having a shape in correspondence with a shape of the stepped portion 26 is provided in a lower portion of the cylinder head 24.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an internal combustion engine.

  As a conventional internal combustion engine, for example, a diesel engine as described in Patent Document 1 is known. A diesel engine described in Patent Document 1 includes a cylinder, a piston that is disposed in the cylinder, a piston having a cavity formed at the center of the top surface, a cylinder head that is disposed at the top of the cylinder, and the cylinder. And an injector that is disposed on the head and injects fuel toward the outer periphery of the cavity. On the lip portion of the cavity portion, a stepped portion is formed over the entire circumference in the cylinder circumferential direction.

JP2012-189041A

  However, the following problems exist in the prior art. That is, when the fuel is injected from the injector when the piston reaches the vicinity of the compression top dead center, the air in the squish area is not sufficiently utilized, which causes smoke. In addition, the fuel reaches the low temperature area near the bore wall of the cylinder, a quench phenomenon occurs where the fuel does not burn, and as a result, the amount of unburned fuel increases.

  An object of the present invention is to provide an internal combustion engine capable of reducing smoke and unburned fuel.

  In one embodiment of the present invention, in an internal combustion engine that generates power by burning fuel, a cylinder, a piston disposed in a reciprocating manner in the cylinder, a piston disposed above the piston, and cooperating with the cylinder and the piston. A cylinder head that forms a combustion chamber, and a fuel injection valve that is attached to the cylinder head and injects fuel into the combustion chamber, and the upper end edge of the piston is stepped so as to rise toward the outside of the piston. A concave cavity portion that constitutes at least a part of the combustion chamber is provided on the inner side of the stepped portion of the piston, and the shape of the stepped portion is formed at the lower portion of the cylinder head. A convex portion having a corresponding shape is provided.

  In such an internal combustion engine, a stepped portion is provided at the upper edge of the piston so as to increase toward the outside of the piston, and a convex portion having a shape corresponding to the shape of the stepped portion is provided at the lower portion of the cylinder head. By providing, the squish area of the combustion chamber is reduced by the convex portion. For this reason, when the piston reaches the compression top dead center or near the compression top dead center, most of the air existing in the combustion chamber enters the cavity portion. Therefore, the air used for the combustion of the fuel injected from the fuel injection valve increases. Thereby, smoke can be reduced. Further, since the fuel that reaches the low temperature area near the bore wall of the cylinder is reduced when the fuel is injected, a quench phenomenon in which the fuel does not burn is less likely to occur. Thereby, the unburned fuel can be reduced.

  The tip surface of the convex portion may have a flat shape. In this case, the fuel can be flowed while ensuring the penetration force of the fuel injection.

  In addition, when the position detection unit for detecting the lift position of the piston and the position detection unit detect that the piston has reached the compression top dead center or near the compression top dead center, the main injection of fuel is performed. You may further provide the control part which controls a fuel injection valve. In this case, when the main injection of fuel is performed, smoke and unburned fuel can be reduced.

  According to the present invention, an internal combustion engine capable of reducing smoke and unburned fuel is provided.

It is a schematic structure figure showing a diesel engine as an internal-combustion engine of one embodiment. It is sectional drawing which shows the structure and operation | movement of an engine main body shown by FIG. It is a flowchart which shows the process sequence of the injector control performed by ECU shown by FIG. It is a graph which shows the fuel injection pattern by the injector shown by FIG. 1, and a heat release rate waveform. It is sectional drawing which shows one structure and operation | movement of the conventional engine main body as a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic configuration diagram illustrating a diesel engine as an internal combustion engine according to an embodiment. In FIG. 1, a diesel engine (hereinafter simply referred to as an engine) 1 according to the present embodiment is a direct injection type four-cylinder in-line diesel engine that generates power by burning fuel.

  The engine 1 includes an engine body 2. The engine body 2 includes four cylinders 3 and four injectors (fuel injection valves) 5 that inject fuel into combustion chambers 4 (described later) provided corresponding to the cylinders 3. The engine body 2 will be described in detail later.

  The engine 1 further includes a common rail 6 connected to each injector 5. The common rail 6 stores high-pressure fuel and supplies the high-pressure fuel to each injector 5.

  The engine 1 is connected to the engine body 2 via an intake manifold 7, connected to the combustion chamber 4 via an intake passage 8 for sucking air, and connected to the engine body 2 via an exhaust manifold 9. And an exhaust passage 10 for exhausting the exhaust gas after being discharged.

  An air cleaner 11, a compressor 13 of the turbocharger 12, an intercooler 14, and a throttle valve 15 are disposed in the intake passage 8 from the upstream side toward the downstream side. A turbine 16 and a DPF 17 with a catalyst of the turbocharger 12 are disposed in the exhaust passage 10 from the upstream side toward the downstream side.

  The engine 1 further includes an exhaust gas recirculation (EGR) unit 18 that recirculates a part of the exhaust gas after combustion to the combustion chamber 4 as exhaust gas recirculation gas (EGR gas). The EGR unit 18 has an EGR passage 19 that connects the intake passage 8 and the exhaust manifold 9. An EGR cooler 20 and an EGR valve 21 are disposed in the EGR passage 19 from the exhaust manifold 9 side toward the intake passage 8 side. A bypass passage 22 is connected to the EGR passage 19 so as to bypass the EGR cooler 20.

  FIG. 2 is a cross-sectional view showing the structure and operation of the engine body 2 shown in FIG. In FIG. 2, the engine main body 2 includes the above-described cylinder 3, a piston 23 that is reciprocated in the cylinder 3, a piston 23, and a piston 23 that is disposed above the piston 23. The cylinder head 24 that forms the combustion chamber 4 and the injector 5 that is attached to the cylinder head 24 and injects fuel into the combustion chamber 4.

  The combustion chamber 4 is a space surrounded by the bore wall 3 a of the cylinder 3, the cylinder head 24, and the piston 23. The piston 23 is connected to a crankshaft (not shown) via a connecting rod 25.

  An annular stepped portion 26 is provided on the upper end edge of the piston 23 so as to increase toward the radially outer side of the piston 23 over the entire circumference of the piston 23. The stepped portion 26 has a curved cross-sectional shape. Specifically, the stepped portion 26 includes a top surface 26a that constitutes the upper step surface, a bottom surface 26b that is disposed on the radially inner side (center side) of the piston 23 relative to the top surface 26a, and that constitutes the lower step surface, An inner peripheral surface 26c having a curved cross-sectional shape is disposed between the top surface 26a and the bottom surface 26b.

  A concave cavity portion 27 constituting at least a part of the combustion chamber 4 is provided on the radially inner side of the stepped portion 26 in the piston 23. The cavity portion 27 has an annular groove portion 28 having a substantially semicircular cross section. The annular groove portion 28 is disposed in the region outside the cavity portion 27 (on the stepped portion 26 side). The cavity portion 27 has a volume such that a predetermined compression ratio can be obtained in the compression stroke. A boundary portion between the stepped portion 26 and the cavity portion 27 constitutes a lip portion 29.

  A convex portion 30 having a shape corresponding to the shape of the stepped portion 26 is provided at the lower portion of the cylinder head 24. The convex portion 30 protrudes downward (on the piston 23 side) from the base surface 24 a of the cylinder head 24. The convex portion 30 has a circular shape in a bottom view.

  The front end surface 30a of the convex portion 30 (the lower end surface of the cylinder head 24) has a planar shape. The plane referred to here is a plane in appearance, and includes a plane having minute irregularities that cannot be seen with the naked eye. The outer peripheral surface 30 b of the convex portion 30 has a cross-sectional curved shape corresponding to the shape of the inner peripheral surface 26 c of the stepped portion 26.

  The injector 5 is attached to the central portion of the convex portion 30 of the cylinder head 24. The injector 5 injects the fuel radially toward the combustion chamber 4 at a predetermined injection angle (see a one-dot chain line in FIG. 2).

  Returning to FIG. 1, the engine 1 further includes a crank angle sensor 31 and an ECU (Electronic Control Unit) 32. The crank angle sensor 31 is a position detection unit that detects a lift position of the piston 23 relative to the cylinder 3 by detecting a crank angle that is a rotation angle of a crank shaft (not shown) connected to the piston 23.

  The ECU 32 controls the throttle valve 15 so that air is sucked into the combustion chamber 4 for each cycle of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke, and injects fuel from each injector 5 into the combustion chamber 4. Thus, each injector 5 is controlled. The ECU 32 is a control unit that controls each injector 5 based on the detected value of the crank angle sensor 31.

  FIG. 3 is a flowchart showing a procedure of injector control executed by the ECU 32.

  In FIG. 3, the ECU 32 first determines whether or not the piston 23 has reached a predetermined position on the way to the compression top dead center based on the detected value of the crank angle sensor 31 (step S101). The ECU 32 controls the injector 5 to perform the pilot injection A of the fuel as shown in FIG. 4 when the piston 23 reaches a predetermined position on the way to the compression top dead center (step S102). ). As a result, as shown in FIG. 4, the fuel is burned by the pilot injection A, and the temperature of the combustion chamber 4 rises.

  Thereafter, the ECU 32 determines whether or not the piston 23 has reached compression top dead center based on the detection value of the crank angle sensor 31 (step S103). When the piston 23 reaches the compression top dead center, the ECU 32 controls the injector 5 to perform the main injection B of fuel as shown in FIG. 4 (step S104). Thereby, as shown in FIG. 4, the combustion of the fuel by the main injection B is started at the compression top dead center.

  At this time, as shown in FIG. 2A, the fuel is injected from the injector 5 toward the annular groove portion 28 of the cavity portion 27. A convex portion 30 having a shape corresponding to the shape of the stepped portion 26 is provided at the lower portion of the cylinder head 24. For this reason, most of the air existing above the cavity 27 in the combustion chamber 4 is pushed into the annular groove 28 by the protrusion 30. Accordingly, the amount of air used for fuel combustion by main injection increases. Further, the fuel spray reaching the vicinity of the bore wall 3a of the cylinder 3 is reduced.

  Thereafter, the ECU 32 determines whether or not the piston 23 has reached a predetermined position in the middle of lowering from the compression top dead center based on the detection value of the crank angle sensor 31 (step S105). When the piston 23 reaches a predetermined position in the middle of lowering from the compression top dead center, the ECU 32 controls the injector 5 to perform the fuel after-injection C as shown in FIG. 4 (step S106). Thereby, as shown in FIG. 4, the fuel is burned by the after injection C, and the unburned fuel by the main injection B is burned.

  At this time, as shown in FIG. 2B, fuel is injected from the injector 5 toward the stepped portion 26 of the piston 23. Then, the fuel spray flows upward along the inner peripheral surface 26 c of the stepped portion 26, mixes with the air existing above the piston 23, and burns.

  FIG. 5 is a cross-sectional view showing one structure and operation of a conventional engine body as a comparative example. In FIG. 5, the engine main body 50 includes a cylinder 3, a piston 23, and a cylinder head 51. The convex part is not provided in the lower part of the cylinder head 51. An injector 5 is attached to the center of the cylinder head 51. Note that the volume of the annular groove 28 of the piston 23 in the engine body 50 is the volume of the annular groove 28 of the piston 23 in the engine body 2 so that the compression ratio when the piston 23 reaches the compression top dead center becomes equal. Is smaller than

  In such an engine main body 50, a stepped portion 26 is provided at the upper end edge of the piston 23. For this reason, as shown in FIG. 5B, when fuel is injected after the fuel is injected toward the stepped portion 26 of the piston 23, the fuel spray is applied to the stepped portion 26. The flow of the fuel spray is promoted.

  However, as shown in FIG. 5A, when the fuel is injected toward the annular groove 28 of the piston 23 by performing the main injection of the fuel, it exists in the squish area S of the combustion chamber 4. Since air is not fully utilized for fuel combustion, it becomes a factor in the generation of smoke. Further, since the fuel easily reaches a low temperature area near the bore wall 3a of the cylinder 3, a quench phenomenon that the fuel does not burn occurs, and the unburned fuel increases.

  On the other hand, in the present embodiment, a convex portion 30 having a shape corresponding to the shape of the stepped portion 26 of the piston 23 is provided in the lower portion of the cylinder head 24. For this reason, the squish area S (see FIG. 5A) of the combustion chamber 4 is reduced by the convex portion 30. Accordingly, in the state where the piston 23 reaches the compression top dead center, most of the air present in the combustion chamber 4 enters the cavity portion 27, so that the air used for the combustion of the fuel injected from the injector 5 increases. The air utilization rate of the combustion chamber 4 is increased. Thereby, smoke can be reduced. Further, since the fuel that reaches the low temperature area near the bore wall 3a of the cylinder 3 is reduced when the fuel is injected, the quench phenomenon is less likely to occur. Thereby, the unburned fuel can be reduced. As a result, the exhaust performance of the engine 1 can be improved, and consequently the output performance of the engine 1 can be improved.

  Moreover, since the front end surface 30a of the convex portion 30 of the cylinder head 24 has a flat shape, the fuel can flow while ensuring the penetration force of fuel injection.

  Further, when the piston 23 reaches the compression top dead center, the injector 5 is controlled so that the main injection of fuel is performed. Therefore, when the main injection of fuel is performed, the smoke and unburned fuel are removed. Can be reduced. For this reason, it becomes possible to reduce the fuel injection quantity at the time of implementing fuel after-injection.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the main injection of fuel is performed when the piston 23 reaches the compression top dead center. For example, when the piston 23 reaches the vicinity of the compression top dead center, specifically, immediately before the piston 23 reaches the compression top dead center or immediately after the piston 23 reaches the compression top dead center, the main injection of fuel is performed. May be. Also in this case, when the main injection of fuel is performed, smoke and unburned fuel can be reduced.

  Further, in the above embodiment, the tip surface 30a of the convex portion 30 of the cylinder head 24 has a flat shape, but the shape of the tip surface 30a of the convex portion 30 is not particularly limited, and is, for example, uneven. May be.

  In the above embodiment, the base surface 24a of the cylinder head 24 is disposed in the cylinder 3. However, the configuration is not particularly limited, and the base surface 24a of the cylinder head 24 is flush with the upper end surface of the cylinder 3. You may be comprised so that it may become.

  Moreover, in the said embodiment, although the step part 26 of piston 23 has the internal peripheral surface 26c of a cross-sectional curve shape, as a shape of the internal peripheral surface 26c of the step part 26, it is not restricted to it in particular, For example, the cross section may be linear. In this case, the outer peripheral surface 30 b of the convex portion 30 of the cylinder head 24 has a linear cross section corresponding to the inner peripheral surface 26 c of the stepped portion 26.

  Further, in the above-described embodiment, the pilot injection of the fuel is performed before the main injection of the fuel and the after-injection of the fuel is performed after the main injection of the fuel. At least one of pilot injection and after injection may not be performed.

  Moreover, although the said embodiment is a direct injection type diesel engine, the internal combustion engine of this invention is applicable also to a direct injection type gasoline engine etc.

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine (internal combustion engine), 3 ... Cylinder, 4 ... Combustion chamber, 5 ... Injector (fuel injection valve), 23 ... Piston, 24 ... Cylinder head, 26 ... Stepped part, 27 ... Cavity part, 30 ... Convex Part, 30a ... tip surface, 31 ... crank angle sensor (position detection part), 32 ... ECU (control part).

Claims (3)

In an internal combustion engine that generates power by burning fuel,
A cylinder,
A piston disposed in the cylinder so as to be capable of reciprocating up and down;
A cylinder head disposed above the piston and forming a combustion chamber in cooperation with the cylinder and the piston;
A fuel injection valve attached to the cylinder head and injecting the fuel into the combustion chamber;
The upper end edge of the piston is provided with a stepped portion that becomes higher toward the outside of the piston,
A concave cavity portion that constitutes at least a part of the combustion chamber is provided inside the stepped portion of the piston,
An internal combustion engine characterized in that a convex portion having a shape corresponding to the shape of the stepped portion is provided at a lower portion of the cylinder head.   The internal combustion engine according to claim 1, wherein a tip surface of the convex portion has a flat shape. A position detection unit for detecting the lift position of the piston;
A control unit that controls the fuel injection valve to perform main injection of the fuel when the position detection unit detects that the piston has reached compression top dead center or near compression top dead center; The internal combustion engine according to claim 1, further comprising:

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