Internal combustion engine

Abstract

When an amount of a backward tumble flow is smaller than an amount of a forward tumble flow, the intake-side valve recess is used as a first valve recess and the exhaust-side valve recess is used as a second valve recess. When the amount of the backward tumble flow is larger than the amount of the forward tumble flow, the exhaust-side valve recess is used as a first valve recess and the intake-side valve recess is used as a second valve recess. An inclination angle of the first valve recess is larger than an inclination angle of the second valve recess when comparing the inclination angle such that a height of the recess decreases gradually toward an inner side of a cross-section.

Claims

1. An internal combustion engine comprising: a mechanism configured to generate a swirl in a combustion chamber; and a piston having an intake-side valve recess, which is a recessed surface formed to avoid interference with an intake valve and an exhaust-side valve recess, which is a recessed surface formed to avoid interference with an exhaust valve, wherein when an amount of a backward tumble flow, which is a tumble flow flowing along a lower surface in the combustion chamber from the intake port toward the exhaust port is smaller than an amount of a forward tumble flow, which is a tumble flow flowing along an upper surface in the combustion chamber from the intake port toward the exhaust port, the intake-side valve recess is used as a first valve recess and the exhaust-side valve recess is used as a second valve recess, when the amount of the backward tumble flow is larger than the amount of the forward tumble flow, the exhaust-side valve recess is used as a first valve recess and the intake-side valve recess is used as a second valve recess, and when the piston is cut along a cross-section parallel to a central axis of the piston passing through the first valve recess and the second valve recess adjacent thereto, an inclination angle of the first valve recess is larger than an inclination angle of the second valve recess when comparing the inclination angle such that a height of the recess decreases gradually toward an inner side of the cross-section.

2. The internal combustion engine according to claim 1, further comprising two intake ports, which are a tangential port and a helical port, wherein the tangential port and the helical port are shaped such that the amount of the backward tumble flow is smaller than the amount of the forward tumble flow, and a valve recess corresponding to the tangential port is inclined further toward the center of the cross-section than a valve recess corresponding to the helical port.

3. The internal combustion engine according to claim 1, wherein at least one of the valve recesses close to the intake port is provided in parallel to at least one of the valve recesses close to the exhaust port.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an entire structure of an internal combustion engine;

(2) FIG. 2 illustrates a specific structure of an intake port;

(3) FIG. 3 is a top view of a piston according to Embodiment 1;

(4) FIG. 4 is a cross-sectional view of the piston according to Embodiment 1;

(5) FIG. 5 illustrates a forward tumble flow and a backward tumble flow;

(6) FIG. 6 is a top view of a piston according to Embodiment 2; and

(7) FIG. 7 is a cross-sectional view of the piston according to Embodiment 2.

DESCRIPTION OF THE EMBODIMENTS

(8) Hereinafter, specific embodiments to which the present disclosure is applied will be described in detail with reference to the drawings. However, the present disclosure is not limited to the following embodiments. In order to clarify the explanation, the following description and the drawings are simplified as appropriate.

Embodiment 1

(9) FIG. 1 is a diagram schematically illustrating an entire structure of an internal combustion engine 10 according to Embodiment 1 of the present disclosure. The internal combustion engine 10 is a compression ignition-type engine (for example, a diesel engine) in which fuel is injected from a fuel injection valve 18 positioned in each cylinder near a compression top dead center and is burnt by compression ignition. An intake passage 14 and an exhaust passage 16 communicate with a combustion chamber 12 of each cylinder of the internal combustion engine 10.

(10) An actuator for controlling the internal combustion engine 10 such as the fuel injection valve 18 is electrically connected to an electronic control unit (ECU) 20 and is driven according to an instruction from the ECU 20.

(11) FIG. 2 is a perspective view for describing a specific structure of an intake port included in the intake passage 14 illustrated in FIG. 1. As illustrated in FIG. 2, the intake passage 14 includes a tangential port 22 and a helical port 24 as an intake port connected to the same combustion chamber 12.

(12) The tangential port 22 is formed so as to be able to guide intake air so that the intake air flows into the combustion chamber 12 in a direction along a cylinder inner circumferential surface 26. According to the tangential port 22 formed in this manner, the larger the amount of intake air supplied from the tangential port 22, the stronger becomes the swirl flow generated in the combustion chamber 12. Moreover, the tangential port 22 generates a tumble flow simultaneously with the swirl flow.

(13) The tangential port 22 is mainly responsible for generation of a swirl flow in the internal combustion engine 10, and the helical port 24 is configured to supply an intake air of a spiral form in the same rotation direction as the generated swirl flow into the combustion chamber 12.

(14) The exhaust passage 16 includes two exhaust ports connected to the same combustion chamber 12.

(15) Next, a structure of a top surface of the piston will be described with reference to FIGS. 3 and 4.

(16) FIG. 3 is a view when the piston is seen from an upper side in an axial direction of the cylinder. Two intake-side valve recesses 31 for avoiding interference with two intake valves and two exhaust-side valve recesses 32 for avoiding interference with two exhaust valves are formed in the top surface of the piston.

(17) FIG. 4 is a view when the piston is cut along a cross-section (A-A cross-section in FIG. 3) parallel to a central axis of the piston passing through the intake-side valve recess 31 and the exhaust-side valve recess 32 adjacent thereto. A cavity which is a recess is formed in the top surface of the piston of the present embodiment, and a squish is provided on an outer periphery thereof.

(18) Valve recesses of a piston of a conventional internal combustion engine are provided to be inclined toward the outer side of the piston so as to comply with the inclinations of respective intake valves or respective exhaust valves.

(19) On the other hand, the intake-side valve recess 31 of the present embodiment is provided to be inclined toward the center of the A-A cross-section. The exhaust-side valve recess 32 is provided to be inclined toward the outer side of the piston.

(20) FIG. 5 is a view of a tumble flow generated in the cylinder. When a piston moves down in an open state of the intake valve, intake air is taken into the cylinder from the tangential port and the helical port. Although a swirl flow is generated in the cylinder due to the taken-in intake air, since the respective intake ports take in the intake air from an upper part of the cylinder, a tumble flow is also generated. This tumble flow can be classified into a forward tumble flow which is a tumble flow flowing along an upper surface in the combustion chamber from the intake port toward the exhaust port and a backward tumble flow which is a tumble flow flowing along the lower surface in the combustion chamber from the intake port toward the exhaust port. The present embodiment is configured such that the amount of the forward tumble flow is larger than the backward tumble flow.

(21) Since the forward tumble flow and the backward tumble flow are vortex flows of the opposite directions, these tumble flows weaken each other. However, in the conventional technique, since there is a difference in the amounts of the forward tumble flow and the backward tumble flow, the tumble flows do not weaken each other sufficiently, and the process proceeds to a compression process in a state in which the forward tumble component remains strong. When the piston moves up in a state in which the tumble flow component remains strong, a fuel is injected in a state in which the swirl flow is inclined due to the effects of the forward tumble flow. In this case, fuel may not be distributed uniformly, and combustion may not occur satisfactorily. As a result, smoke may be generated.

(22) In the present embodiment, the intake-side valve recess 31 is provided to be inclined toward the center of the A-A cross-section. Due to this, the resistance that the backward tumble flow receives from the intake-side valve recess 31 can be decreased, and attenuation of the backward tumble flow can be suppressed. On the other hand, the exhaust-side valve recess 32 is provided to be inclined toward the outer side of the piston. Due to this, the resistance that the forward tumble flow receives from the exhaust-side valve recess 32 becomes larger than the resistance that the backward tumble flow receives from the intake-side valve recess 31. Therefore, the attenuation amount of the forward tumble flow can be made larger than the attenuation amount of the backward tumble flow.

(23) Since the forward tumble flow of which the amount was originally large is attenuated, and the attenuation of the backward tumble flow of which the amount was small can be suppressed, the amounts of the forward tumble flow and the backward tumble flow can be made uniform or a difference between them can be decreased. As a result, since the forward tumble flow and the backward tumble flow cancel each other, and the effects of the tumble flow on the swirl flow can be reduced, the fuel injected into the combustion chamber 12 is stirred further and combustion occurs satisfactorily.

(24) More preferably, the valve recess corresponding to the tangential port 22 among the intake-side valve recesses 31 is provided to be inclined toward the center of the A-A cross-section. Since the amount of a tumble flow generated by the tangential port among the intake ports is larger than the amount of a tumble flow generated by the helical port, by forming the valve recess corresponding to the tangential port 22 so as to be inclined toward the center of the A-A cross-section, attenuation of a backward tumble flow can be suppressed further. Therefore, the amounts of the forward tumble flow and the backward tumble flow can be made uniform or a difference between them can be decreased.

(25) More preferably, at least one of the intake-side valve recesses 31 and at least one of the exhaust-side valve recesses 32 are provided in parallel to each other.

(26) More preferably, the valve recess corresponding to the tangential port 22 and at least one of the exhaust-side valve recesses 32 are provided in parallel to each other. Since valve recesses having the same inclination can be manufactured easily since it is not necessary to adjust the individual inclinations of jigs or the like for cutting during manufacturing. Here, the number of exhaust-side valve recesses provided in parallel to the valve recess corresponding to the tangential port 22 may be one or plural.

Embodiment 2

(27) In the present embodiment, the description of the same portions as those of Embodiment 1 will be omitted.

(28) The present embodiment is configured such that the amount of a backward tumble flow is larger than the amount of a forward tumble flow.

(29) A structure of a top surface of the piston will be described with reference to FIGS. 6 and 7.

(30) FIG. 6 is a view when the piston is seen from an upper side in an axial direction of the cylinder. Two intake-side valve recesses for avoiding interference with two intake valves and two exhaust-side valve recesses for avoiding interference with two exhaust valves are formed in the top surface of the piston.

(31) FIG. 7 is a view when the piston is cut along a cross-section (B-B cross-section in FIG. 6) parallel to a central axis of the piston passing through the intake-side valve recess and the exhaust-side valve recess adjacent thereto. A cavity which is a recess is formed in the top surface of the piston of the present embodiment, and a squish is provided on an outer periphery thereof.

(32) In the present embodiment, the exhaust-side valve recess is provided to be-inclined toward the center of the B-B cross-section, and the intake-side valve recess is provided to be inclined toward the outer side of the piston. Due to this, the resistance that the forward tumble flow receives from the exhaust-side valve recess can be decreased, and attenuation of the forward tumble flow can be suppressed. On the other hand, the intake-side valve recess is provided to be inclined toward the outer side of the piston. Due to this, the resistance that the backward tumble flow receives from the intake-side valve recess increases, and the backward tumble flow can be attenuated.

(33) Since the backward tumble flow of which the amount was originally large is attenuated, and the attenuation of the forward tumble flow of which the amount was small can be suppressed, the amounts of the forward tumble flow and the backward tumble flow can be made uniform or a difference between them can be decreased. As a result, since the forward tumble flow and the backward tumble flow cancel each other, and the effects of the tumble flow on the swirl flow can be reduced, the fuel injected into the combustion chamber 12 is stirred further and combustion occurs satisfactorily.

(34) More preferably, a valve recess corresponding to the exhaust port adjacent to the tangential port 22 among the exhaust-side valve recesses is provided to be inclined toward the center of the B-B cross-section. Since the amount of a tumble flow generated by the tangential port among the intake ports is larger than the amount of a tumble flow generated by the helical port, by forming the valve recess corresponding to the exhaust port adjacent to the tangential port 22 so as to be inclined toward the center of the B-B cross-section, attenuation of a forward tumble flow can be suppressed further. Therefore, the amounts of the forward tumble flow and the backward tumble flow can be made uniform or a difference between them can be decreased.

(35) More preferably, the surface of the valve recess corresponding to the exhaust port adjacent to the tangential port 22 is provided to be parallel to the surface of the intake-side valve recess. Since valve recesses having the same inclination can be manufactured easily since it is not necessary to adjust the individual inclinations of jigs or the like for cutting during manufacturing. Here, the number of intake-side valve recesses provided in parallel may be one or plural.

(36) A mechanism that generates a swirl in the combustion chamber 12 may be a swirl control valve provided in an intake port as well as the tangential port 22.

(37) While a diesel engine has been described, the internal combustion engine is not limited thereto but may be a gasoline engine.

(38) The present disclosure is not limited to the above-described embodiments but can be changed appropriately without departing from the spirit thereof.