Direct fuel injection-type spark-ignition internal combustion engine

Abstract: A direct fuel injection-type spark-ignition internal combustion engine is disclosed. The engine comprises a spark plug, a fuel injection valve and a cavity formed on the top surface of the piston. The cavity has a bottom wall, a spark plug side wall and a fuel injection valve side wall. The fuel injection valve injects fuel toward the bottom wall of the cavity in stratified charge combustion. The fuel mainly proceeds toward the spark plug side wall of the cavity along the bottom wall, is deflected by the spark plug side wall and is led to the vicinity of the spark plug. In the engine, at least at a position where the fuel comes into collision, the bottom wall of the cavity is so inclined as to be deeper on the side of the fuel injection valve side wall than on the side of the spark plug side wall. An extended plane of the central portion of the fuel injection valve side wall intersects the upper wall of the cylinder at an obtuse angle on the side of said spark plug.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct fuel injection-type spark-ignition internal combustion engine. 2. Description of the Related Art There has heretofore been known a stratified charge combustion produced by directly injecting fuel into a cylinder to form a mixture (hereinafter referred to as combustible mixture) that can be favorably ignited only in the vicinity of a spark plug, at the ignition timing, to burn a lean mixture in the cylinder as a whole. To carry out the stratified charge combustion, in general, the fuel injection valve injects fuel in the latter half of the compression stroke. It is intended that the thus injected fuel proceeds into a concave combustion chamber formed in the top surface of the piston, is vaporized by robbing heat from the wall surfaces of the combustion chamber, is deflected by the shape of the combustion chamber toward the spark plug, and forms a combustible mixture near the spark plug. In the direct fuel injection-type spark-ignition internal combustion engine for performing the stratified charge combustion, in general, the spark plug is arranged nearly at the center in the upper part of the cylinder, the fuel injection valve is arranged in the periphery in the upper part of the cylinder, and the combustion chamber extends from nearly the central portion of the top surface of the piston toward the periphery of the top surface of the piston on the side of the fuel injection valve, and includes a bottom wall, a spark plug side wall, and a fuel injection valve side wall. Fuel injected into the combustion chamber collides with the bottom wall of the combustion chamber, thereafter proceeds toward the spark plug side wall along the bottom wall, and thereafter is deflected toward the spark plug by the spark plug side wall. In order to favorably vaporize the fuel utilizing heat of the wall surface of the combustion chamber, the distance for moving fuel along the wall surface of the combustion chamber must be lengthened so that the injected fuel stays in contact with the wall surface of the combustion chamber for an extended period. In order to realize this without changing the shape of the combustion chamber, it has been proposed to inject fuel at a relatively large acute angle with respect to the horizontal plane. This makes it possible to move the position where fuel collides with the bottom wall away from the spark plug side wall of the combustion chamber, while maintaining the same position of injection hole of the fuel injection valve, as compared with when the fuel is injected at a relatively small acute angle with respect to the horizontal plane, and, hence, to extend the distance the fuel moves on the bottom wall of the combustion chamber. When the fuel is injected at a relatively large acute angle with respect to the horizontal plane, however, fuel collided with the bottom surface is diverted and all of fuel does not proceed toward the spark plug side wall along the bottom surface; i.e., fuel only partly proceeds toward the fuel injection valve side wall along the bottom surface. Accordingly, an amount of the combustible mixture formed near the spark plug via the spark plug side wall of the combustion chamber is decreased, and the engine output is not produced as intended. Besides, the mixture formed by fuel proceeding toward the fuel injection valve side wall of the combustion chamber cannot be favorably burned, and unburned fuel may be emitted in increased amounts. A direct fuel injection-type spark-ignition internal combustion engine comprising the features summarized in the pre-characterizing portion of the only claim is known from document JP-A-10 33 9140. SUMMARY OF THE INVENTION It is an object of the present invention to further develop the direct fuel injection-type spark-ignition internal combustion engine comprising the features according to the preamble of the claim such that even when the fuel that has collided with the wall surface of the cavity is diverted toward the spark plug side wall of the cavity and toward the fuel injection valve side wall, all of fuel injected into the cavity is burned as the combustible mixture to produce the engine output as intended. According to the present invention, this object is achieved by the direct fuel injection-type spark-ignition internal combustion engine defined in the only claim. The present invention will be more fully understood from the description of a preferred embodiment of the invention set forth below, together with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Fig. 1 is a vertical sectional view schematically illustrating a main part of a direct fuel injection-type spark-ignition internal combustion engine according to an embodiment of the present invention. Fig. 2 is a plan view of a piston of Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 is a vertical sectional view schematically illustrating a main part of a direct fuel injection-type spark-ignition internal combustion engine according to an embodiment of the present invention, and Fig. 2 is a plan view of a piston shown in Fig. 1. In these drawings, reference numeral 1 denotes an intake port and 2 denotes an exhaust port. The intake port 1 is communicated with the cylinder via an intake valve 3, and the exhaust port 2 is communicated with the cylinder via an exhaust valve 4. Reference numeral 5 denotes a piston having a cavity 80 formed in the top surface thereof, and 6 denotes a spark plug arranged in nearly the central upper part of the cylinder. A fuel injection valve 7 is arranged in the upper periphery of the cylinder in the intake port side and injects fuel in a flat fan shape having a relatively small thickness. The cavity 80 formed in the top surface of the piston extends from nearly the central portion in the top surface of the piston toward the periphery in the top surface of the piston on the fuel injection valve side, and includes the bottom wall 80a, the spark plug side wall 80b and the fuel injection valve side wall 80c. The spark plug 6 is positioned on the center line of the contained angle of the fan of the fan-shaped fuel injected from the fuel injection valve 7, and faces the inside of the spark plug side wall 80b of the cavity 80. For example, in a uniform charge combustion region where a high engine output is required, the fuel injection valve 7 injects a required amount of fuel in the intake stroke thereby to form a uniform charge mixture in the cylinder at the ignition timing. On the other hand, in a stratified charge combustion region, a required amount of fuel is injected into the cavity 80 in the latter half of the compression stroke. Fuel injected into the cavity 80 collides with the bottom wall 80a of the cavity 80 so as to proceed toward the spark plug side wall 80b along the bottom wall 80a. Fuel proceeding on the bottom wall 80a radially spreads within the contained angle of the fan of fuel, and is gradually vaporized by favorably absorbing heat from a large area of the wall surface of the cavity. In addition to being smoothly connected to the bottom wall 80a, the spark plug side wall 80b of the cavity 80 has an arcuate shape in a plan view. Further, the distance from the center of the contained angle of the fan of fuel proceeding on the bottom wall 80a of the cavity to the spark plug side wall, is longer than the radius of the arcuate shape. Therefore, each part of fuel in the width direction arriving at the spark plug side wall 80b does not lose much speed, and proceeds along the spark plug side wall 80b. Here, in the central part of fuel in the direction of width, a velocity vector along the bottom wall 80a is converted into an upward velocity vector, and in both side parts of the fuel, due to collision with the spark plug side wall 80b at an acute angle in a plan view, a velocity vector along the bottom wall 80a is converted into a resultant of an upward velocity vector and a velocity vector in the direction of the center line of the contained angle of the fan of fuel. Further, the spark plug side wall 8b is provided with a deflecting portion 80d. Therefore, each part of the fuel proceeding along the spark plug side wall 80b is finally deflected toward the inside of the cavity 80. Thus, if all of the injected fuel proceeds toward the spark plug side wall 80b on the bottom wall 80a of the cavity 80 and is finally completely vaporized on the spark plug side wall 80b, a combustible mixture is formed near the spark plug at the ignition timing, and thus a favorable stratified charge combustion can be realized. In order to realize the favorable stratified charge combustion, first, it is important that the injected fuel is all completely vaporized at the ignition timing. If fuel partly exists in the form of a liquid, it does not favorably burn and is discharged as unburned fuel. In this embodiment, the distance for moving fuel along the wall surface of the cavity is lengthened and the injected fuel is permitted to stay contacted with the wall surface of the cavity for an extended period in order to favorably vaporize the fuel by utilizing the heat of the wall surface of the cavity. Concretely speaking, the fuel injection valve 7 injects fuel at a relatively large acute angle with respect to the horizontal plane, whereby the position where fuel collides the bottom wall 80a is moved away from the spark plug side wall 80b of the cavity 80, making it possible to lengthen the distance for moving fuel along the bottom wall 80a of the cavity 80. However, when the fuel 10 is injected at a relatively large acute angle with respect to the horizontal plane, as shown in Figs. 1 and 2, the fuel that has come into collision with the bottom wall 80a may be diverted into a fuel 100a proceeding toward the spark plug side wall 80b along the bottom wall 80a and a fuel 100b proceeding toward the fuel injection valve side wall 80c along the bottom wall 80a. The fuel 100b that flows after being thus diverted forms a mixture 100b' on the side of the fuel injection valve 7 in an upper part of the cylinder as shown in Fig. 1. From the standpoint of quantity, the amount of fuel 100a which proceeds toward the spark plug side wall 80b is the largest and the amount of fuel 100b which proceeds toward the fuel injection valve side wall 80c is the smallest. In the stratified charge combustion, however, only a minimum required amount of fuel is injected in the present engine operating condition. Therefore, if a part of the injected fuel does not exist as a mixture near the spark plug 6, the engine output is not produced as intended. Besides, if the mixture 100b' on the side of the fuel injection valve 7 in the upper part of the cylinder is separated from a combustible mixture 100a' near the spark plug, flame does not propagate well thereto and it can be emitted as unburned fuel. In the embodiment, the deflecting portion 80d on the spark plug side wall 80b of the cavity 80 is formed to be nearly uniform, so that the fuel 100a proceeding toward the spark plug side wall 80b is all led to the vicinity of the spark plug 6. At least at a position where fuel collides, further, the bottom wall 80a of the cavity 80 is so inclined as to be deeper on the side of the fuel injection valve side wall 80c than on the side of the spark plug side wall 80b. Further, the central extended plane 80c' of the fuel injection valve side wall 80c intersects the upper wall of the cylinder at an obtuse angle (TH) on the side of the spark plug 6. Therefore, the fuel injected from the fuel injection valve 7 comes into collision with the bottom wall 80a of the cavity 80 at a larger acute angle than that of when the bottom wall of the cavity is flat, whereby the amount of fuel 100b which proceeds toward the fuel injection valve side wall 80c increases and the inertial force thereof for proceeding toward the fuel injection valve side wall 80c increases. The position where fuel collides with the bottom wall 80a of the cavity 80 is relatively close to the fuel injection valve side wall 80c. Therefore, the fuel 100b arrives at the fuel injection valve side wall 80c without spreading much in the direction of width, and rises along the central portion of the fuel injection valve side wall 80c. The fuel 100b vaporizes upon absorbing heat from the bottom wall 80a of the cavity 80 and from the fuel injection valve side wall 80c, and the thus formed mixture further rises along the extended plane of the central portion of the fuel injection valve side wall 80c. The inertial force of the mixture is dependent upon the inertial force of fuel toward the fuel injection valve side wall 80c, and thus it is relatively great. Next, the mixture collides with the upper wall of the cylinder at the obtuse angle (TH) and easily moves toward the spark plug 6 along the upper wall of the cylinder due to the relatively large inertial force. Therefore, the mixture 100b' merges with the combustible mixture 100a' formed near the spark plug 6. Thus, all of the fuel injected into the cavity 80 can be reliably burned, making it possible to realize a favorable stratified charge combustion to produce the engine output as intended. In the embodiment, the amount of fuel 100b which proceeds toward the fuel injection valve side wall 80c of the cavity 80 is increased. However, the mixture formed by this fuel 100b can be reliably merged with the combustible mixture formed near the spark plug 6 due to the relatively large inertial force, without causing any problem. On the other hand, the amount of fuel 100a which proceeds toward the spark plug side wall 80b of the cavity 80 is decreased and, hence, an inertial force thereof for proceeding toward the spark plug side wall 80b decreases. Accordingly, this fuel 100a proceeds at a decreased speed along the bottom wall 80a of the cavity 80 and along the spark plug side wall 80b and, hence, stays in contact with the wall surfaces of the cavity 80 for a correspondingly extended period. Thus, this fuel 100a is easily vaporized. This makes it possible to inject an increased amount of fuel in the latter half of the compression stroke, and to expand the region of stratified charge combustion to realize a low fuel consumption toward the high engine load side. In this case, an amount of fuel 100b which proceeds toward the fuel injection valve side wall 80c of the cavity 80 increases. However, the amount is small in terms of an absolute value. Hence, the fuel 100b can be reliably vaporized by the bottom wall 80a of the cavity 80 and by the fuel injection valve side wall 80c, without causing any problem in the stratified charge combustion. By the way, in the uniform charge combustion in which fuel is injected during the intake stroke, the amount of fuel injected is larger than that in the stratified charge combustion since the engine load is high. In order to inject this large amount of fuel during the intake stroke, the fuel injection must be started from the initial stage of the intake stroke. In the uniform charge combustion, the injected fuel is diverted in the collision with the bottom wall of the cavity so as to be widely dispersed in the cylinder to form a favorable uniform mixture at the ignition timing. If a large amount of fuel proceeds only toward the spark plug side wall of the cavity, fuel tends to stay in a liquid form near the boundary between the bottom wall and the spark plug side wall of the cavity. The liquid fuel may not have been sufficiently vaporized at the ignition timing and may be emitted as unburned fuel. Fuel is diverted so as to proceed toward the fuel injection valve side wall of the cavity, whereby an amount of fuel which proceeds toward the spark plug side wall decreases, and thus this problem can be solved. In the embodiment as described above, the problem caused by the diversion of fuel in stratified charge combustion is solved, whereby the diversion of fuel can be positively utilized for uniform charge combustion. In the above embodiment, the fuel injection valve 7 injects fuel in a fan shape having a relatively small thickness, however, this is not to limit the invention. The above-mentioned effects can be obtained even when fuel is injected in a conical shape or in a cylindrical shape and fuel is diverted due to the collision with the bottom wall of the cavity. In the above embodiments, the cavity in the top surface of the piston has a shape in which the bottom wall, with which fuel comes into collision, the spark plug side wall for leading fuel proceeding on the bottom wall to the vicinity of the spark plug, and the fuel injection valve side wall can be distinguished. This, however, is not to limit the invention. For example, when the cavity has nearly a semispherical shape and the bottom wall, the spark plug side wall and the fuel injection valve side wall cannot be distinguished in shape, a portion where fuel comes into collision can be intended as the bottom wall of the cavity, a portion for leading fuel proceeding on the bottom wall toward the vicinity of the spark plug can be intended as the spark plug side wall of the cavity, and a portion facing the spark plug side wall can be intended as the fuel injection valve side wall of the cavity. Although the invention has been described with reference to specific embodiments thereof, it should be apparent that numerous modifications can be made thereto by these skilled in the art, without departing from the basic concept and scope of the invention.

Claims: A direct fuel injection-kind spark-ignition internal combustion engine comprising a cylinder, a piston, a spark plug (6), a fuel injection valve (7) and a cavity (80) formed on the top surface of the piston (5), said cavity (80) having a bottom wall (80a), a spark plug side wall (80b) and a fuel injection valve side wall (80c), said fuel injection valve (7) injecting fuel toward said bottom wall (80a) of said cavity (80) in stratified charge combustion, said fuel mainly proceeding toward said spark plug side wall (80b) of said cavity (80) along said bottom wall (80a), being deflected by said spark plug side wall (80b) and being led to the vicinity of said spark plug (6), wherein at least at a position where said fuel comes into collision with said bottom wall (80a) of said cavity (80), said bottom wall (80a) is so inclined as to be deeper on the side of said fuel injection valve side wall (80c) than on the side of said spark plug side wall (80a), characterized in that an extended plane (80c') of the central portion of said fuel injection valve side wall (80c) intersects the upper wall of the cylinder at an obtuse angle (TH) on the side of said spark plug (6), and in that said fuel is injected at a relatively large acute angle with respect to the horizontal plane, so that after the collision with said bottom wall (80a) a part of said fuel proceeds toward said fuel injection valve side wall (80c) along said bottom wall (80a), rises along said central portion of said fuel injection valve side wall (80c), and vaporizes to form a mixture which rises along said extended plane (80c') of said central portion of said fuel injection valve side wall (80c) and thereafter moves toward said spark plug (6) along said upper wall of said cylinder.

Inventors: HATTORI FUMIAKI, KANDA MUTSUMI, KASHIWAGURA TOSHIMI, SHIMIZU RIO, HATTORI, FUMIAKI, KANDA, MUTSUMI, KASHIWAGURA, TOSHIMI, SHIMIZU, RIO
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 2000
Main classification: F02B23
IPC codes: F02F3, F02B17, F02B75, F02F1, F02B23