INTAKE PORT STRUCTURE FOR INTERNAL COMBUSTION ENGINE

Abstract: An intake port structure of an internal combustion engine wherein the tumble strength can be improved without lowering a maximum flow rate. An intake port (44) is constituted in such a fashion that its tumble flow side half portion (44a) is wider than its other half portion (44b) and an intake flow center of the intake port (44) is deviated towards the tumble flow side. In this way, the intake gas flow from the intake port (44) promotes a tumble flow.

Description: The invention relates to an internal combustion engine comprising a combustion chamber and intake ports, each connected with respective intake passages, said combustion chamber being defined by a cylinder bore, a piston fitted in said cylinder bore and a pentroof formed on a wall of a cylinder head adjacent to said combustion chamber, the pentroof being associated with said cylinder bore and having first and second inclined walls, said intake passages opening through the first inclined wall and each being formed as a linear, i.e. straight passage, whereby an intake air flow from said intake passage is guided by the second inclined wall and is allowed to flow along an inner wall of said cylinder bore, said inner wall extending in continuation with the second inclined wall, to generate a tumble flow within said combustion chamber. Such an internal combustion engine having such a conventional intake port is known from the EP-A-390589, which represents the closest state of the art. In order to enlarge the area of the intake port for each combustion chamber of the internal combustion engine two intake passages per combustion chamber are provided. An air-fuel mixture is caused to flow into each combustion chamber through two intake passages. For improving the combustion a vertical swirl, i.e. a so-called tumble flow (tumble swirl) F (Fa, Fm) is produced in the cylinder during the intake stroke as it is shown in FIGS. 29 and 30 which illustrate the conventional internal combustion engine of EP-A-390589. This internal combustion engine comprises a cylinder block 22, a cylinder bore 24, a piston 26, a cylinder head 28, and a combustion chamber 30. Also illustrated are a pentroof 34 formed in an upper wall of the combustion chamber 30, and two intake passages 40',42' provided with each cylinder. An intake port 44' of each of the intake passages 40',42' is provided with an intake valve 58. The pentroof 34 is provided with such an inclined wall that can guide an intake air flow, which has been introduced from each intake passage 40' or 42', downwardly along an inner wall of the cylinder bore 24. While also assisted owing to the guidance by the pentroof 34, the intake air flow from the intake passage 40' or 42' therefore advances in the direction of such a tumble flow as indicated by arrow Fa or Fm. In the illustrated example, only one of the intake passages, i.e., only the intake passage 42' is provided with an injector 12. A spark plug 10 is disposed in the vicinity of the intake port 44' of the intake passage 42' equipped with the injector 12. To promote the tumble flow, the shape of the intake passages 40', 42' is important. In general, it is devised to straighten the flow by forming the intake passages 40', 42' into a linear, i.e., straight passage as shown in FIGS. 29 and 30 or by constricting the intake passages 40', 42' as depicted in FIG. 33. In FIGS. 29 and 30, symbols 40F,42F indicate conventional intake ports which are not straight ports. Although the cross-section of such an intake port 44' is generally formed in a circular shape as shown in FIG. 31, it may also be formed in a substantially square shape in addition to such an elliptical or oval shape as depicted in FIG. 32. A tumble flow (tumble swirl) produced as described above is effective in increasing the flame propagation velocity and the combustion stability. Illustrative experimental data of heat release Q, cylinder pressure P and heat release rate dQ are presented in FIG. 34. Compared with the standard (the conventional construction in which no tumble flow is produced intentionally), it is understood that a tumble swirl (i.e., formation of a tumble flow) produces smaller cyclic variations in heat release Q, cylinder pressure P and heat release rate dQ and exhibits better combustion stability. In the drawings, numeral 47 indicates an exhaust port provided in communication with an exhaust passage 60 while numeral 59 designates an exhaust valve. Where the intake passages 40', 42' has a circular or elliptical, cross-sectional shape, formation of the intake passages 40', 42' as a straight passage to make the tumble flow stronger, however, results in the structure that the intake passages 40', 42' extends at an acute angle relative to a valve seat 62 and the cross-sectional area of the flow passage obviously becomes smaller. Further, constriction of the intake passages 40', 42' as depicted in FIG. 33 obviously results in a reduction in the cross-sectional area of the flow passage, leading to a reduction in the maximum flow rate. In other words, the strength of a tumble flow (the strength of tumbling) and the maximum flow rate (flow coefficient) are in such a contradictory relationship that the latter decreases as the former increases. Such a decrease in the maximum flow rate leads to a reduction in the full-open performance of the engine and, hence, is not preferred. To strengthen the tumble flow, incidentally, the flow rate (flow velocity) of a flow on a side of the tumble flow, said flow being an upper flow in the intake port relative to a central axis of the intake valve 58 as a boundary (see arrow a in FIGS. 29 and 33), is required to be greater than the flow rate (flow velocity) of a flow on an opposite side (see arrow b in FIGS. 29 and 33). If such an imbalance in flow rate (flow velocity) can be positively developed, the strength of a tumble flow (the strength of tumbling) can be increased without lowering the maximum flow rate (flow coefficient). With a view toward achieving reductions in both vibrations and gas mileage by operating an internal combustion engine on an air-fuel mixture leaner than the stoichiometric air/fuel ratio, internal combustion engines equipped with two intake ports and fed with an air-fuel mixture through both the intake ports have also been proposed in recent years. As a spark plug is positioned between the two intake ports in the above case, operation on a small amount of fuel is accompanied by the potential problem that the ignition may be impaired. This has posed the inconvenience that the engine is difficult to operate on a smaller amount of fuel. An object of this invention is to provide an internal combustion engine having an intake port, which makes it possible to increase the strength of a tumble flow (the strength of tumbling) without lowering the maximum flow rate (flow coefficient) and also to operate the internal combustion engine on an air-fuel mixture leaner than the stoichiometric air-fuel mixture without deterioration in ignition. This object is obtained by an internal combustion engine having intake ports according to claim 1. Advantageous embodiments of the invention are described in claims 2 to 7. As the intake passage of the internal combustion engine of the present invention is broader in the tumble-flow-side half thereof than in the other half, the intake air flow through the intake passage is off-centered toward the side of the tumble flow. Therefore, an intake air flow fraction from the tumble-flow-side half of the intake passage, said fraction being a flow fraction acting to form the tumble flow, becomes stronger while an intake air flow fraction from the other half of the intake passage, said latter fraction acting as a fraction to suppress the tumble flow, becomes weaker, whereby the strength of the tumble flow can be increased without reducing the cross-sectional area of the flow passage in the intake passage. As a consequence, advantages can be obtained, including improvements in motoring gas mileage and improvements in driving limits. By forming the intake passage broader in the tumble-flow-side half than in the other half to have a substantially triangular cross-section, a cross-section in the form of a baseball home plate, or a tongue-shaped cross-section, the shape of the intake port capable of bringing about the above-described advantages can be defined rather easily. By forming the intake passage broader in the tumble-flow-side half than in the other half so that the broadest part of the intake passage is disposed at the position biased outwardly of the cross-sectional center of the valve stem at the position where the valve stem is internally in contact with the intake passage and the intake passage becomes gradually narrower from the broadest part toward the end portion thereof on the side of the other half, the shape of the intake passage capable of bringing about the above-described advantages can be defined rather easily and, moreover, efficiently. The interior of at least one intake passage (all the intake passages or some of the intake passages) is divided into two sections, one being on the side of the ignition means and the other on the side opposite to the ignition means, whereby feeding of fuel on the side of the ignition means makes it possible to stratify the fuel. Accordingly, a gas-fuel mixture rich in the fuel can be fed to the ignition means so that a gas-fuel mixture containing fuel in a smallest amount per the entire combustion chamber can be fed without impairing the ignition. As a result, the simple structure can increase the strength of a tumble flow (the strength of tumbling) without lowering the maximum flow rate (flow coefficient) and, in addition, permits operation of an internal combustion engine on an air-fuel mixture leaner than a stoichiometric air-fuel mixture without impairing the ignition. Advantageous embodiments of the invention are further explained by means of drawings. FIGS. 1-7 illustrate an intake port of an internal combustion engine, in which FIG. 1 is a schematic vertical cross-sectional view of the structure, FIG. 2 is a schematic cross-sectional view taken along a plane perpendicular to the flowing direction of its intake air (i.e., a cross-sectional view taken in the direction of arrows A-A of FIG. 1), FIG. 3 is a schematic cross-sectional view of a conventional intake port (a drawing corresponding to the cross-sectional view taken in the direction of arrows A-A of FIG. 1) and is added for the sake of comparison with the cross-sectional shape of the intake port of FIG. 2, FIG. 4 is a diagram showing the cross-sectional shape of the intake port of FIG. 1 and 2 as plotted on a coordinate system, FIG. 5 is a diagram of a right-hand half of the cross-sectional shape when the intake port of FIG. 1 and 2 for the internal combustion engine is plotted on a coordinate system, and FIGS. 6 and 7 are diagrams illustrating advantages of the intake port of FIG. 1 and 2, respectively; FIGS. 8-10 depict another intake port of an internal combustion engine, in which FIG. 8 is its schematic vertical cross-sectional view, FIG. 9 is its schematic cross-section taken along a plane perpendicular to the flowing direction of its intake air (i.e., a cross-sectional view taken in the direction of arrows B-B of FIG. 8), and FIG. 10 is a diagram showing its advantage; FIGS. 11-15 are, all, cross-sectional views showing modifications of the intake ports of internal combustion engines of this invention (drawings corresponding to the cross-sectional view taken in the direction of arrows A-A of FIG. 1); FIGS. 16-22 show a further intake port of an internal combustion engine, in which FIG. 16 is its schematic plan view, FIG. 17 is its schematic fragmentary vertical cross-sectional view, FIG. 18 is its schematic cross-sectional view taken along a plane perpendicular to the flowing direction of intake air through the intake port, FIGS. 19-21 are schematic cross-sectional views illustrating, in correspondence to FIG. 18, various examples of cross-sectional shapes taken along planes perpendicular to the flowing directions of their respective intake air; and FIG. 22 is a schematic plan view showing its modification in correspondence to FIG. 16; FIGS. 23-28 illustrate a still further intake port of an internal combustion engine, in which FIG. 23 is its schematic plan view, FIG. 24 is its schematic cross-sectional view taken along a plane perpendicular to the flowing direction of its intake air, FIGS. 25-27 are schematic cross-sectional views showing, in correspondence to FIG. 24, various examples of cross-sectional shapes taken along planes perpendicular to their respective flowing directions, and FIG. 28 is a schematic plan view showing a still further modification in correspondence to FIG. 23; FIGS. 29-33 depict conventional intake ports of internal combustion engines, in which FIG. 29 is a schematic vertical cross-sectional view of one of the conventional intake port and certain elements disposed around its associated combustion chamber, FIG. 30 is its schematic perspective view also depicting the elements arranged around its associated combustion chamber, FIG. 31 is its schematic cross-sectional view taken along a plane perpendicular to the flowing direction of its intake air (i.e., the cross-section taken in the direction of arrows C-C of FIG. 29), FIG. 32 is a cross-sectional view shoving another conventional example of its schematic cross-sectional view taken along a plane perpendicular to the flowing direction of its intake air (i.e., a drawing corresponding to the cross-section taken in the direction of arrows C-C of FIG. 29), and FIG. 33 is a schematic vertical cross-sectional view showing the other conventional example; and FIG. 34 diagrammatically illustrates advantages available from a tumble flow. In FIG. 1 the overall structure of each cylinder of an internal combustion engine, said cylinder being equipped with intake ports 44, is constructed, for example, substantially as in the conventional example shown in FIGS. 29 and 30. For elements of structure not shown in FIG. 1, reference may be made to FIGS. 29 and 30. The spark plug 10 is arranged in the vicinity of the intake port 44 on the side of the injector 12. Namely, each cylinder of the internal combustion, said cylinder being associated with the intake port 44, has the combustion chamber 30 which is formed by the cylinder bore 24, the piston 26 and the cylinder bead 28. The cylinder bore is formed in the cylinder block 22. The intake passages 40, 42 of respective intake port 44 communicate to the combustion chamber 30 and are provided with intake valves 58, respectively. The pentroof 34 is formed in the upper wall of the combustion chamber 30. The pentroof 34 is provided with an inclined wall so that intake air flows from the respective intake passages 40,42 can be guided downwardly along the inner wall of the cylinder bore 24. Owing to the guidance by the pentroof 34, the occurrence of a tumble flow as shown by arrow F is also promoted. Each intake passage 40, 42 of the internal combustion engine is formed as a linear, i.e., straight passage as shown in FIG. 1. In the cross-sectional shape of the straight passage, the tumble-flow-side half 44a of the intake port 44 (namely, the upper half of the intake port 44, through which upper half a principal fraction flow acting to develop the tumble flow advances) is formed broader than the other half 44b (namely, the lower half of the intake port 44, through which lower half such a fraction flow as acting to suppress the tumble flow advances) as shown in FIG. 2 so that the intake air flow through the intake port 44 is off-centered toward the side of the tumble flow (namely, toward the upper half 44a of the intake port 44). As a result, the intake air flow from the intake port 44 can easily develop the tumble flow F in the combustion chamber 30. In FIG.2 the intake port 44 is formed to have a substantially inverted triangular cross-section. Incidentally, designated at symbol 58A in FIG. 2 is the valve stem. A side contour of a cross-section 45 of the intake port 44 having such a substantially inverted triangular shape can be plotted on a coordinate system, for example, as illustrated in FIG. 4. In FIG. 4, x indicates the distance from the upper end of the cross-section 45 of the intake port while y shows the distance (width) of the cross-section 45 of the intake port from a vertical center line. Incidentally, the broken line in FIG. 4 illustrates a side contour of a cross-section 45' of such a conventional intake port 44' of an oval cross-section as depicted in FIG. 3. It is envisaged that the cross-section 45 of the intake port 44 is formed broader at the tumble-flow-side half 44a on an upper side (i.e., on a left side as viewed in FIG. 4) and the flow therethrough is off-centered toward the tumble-flow-side half 44a. In FIG. 5, both end portions of the curve of FIG. 4 are smoothly extended to complete the shape of the entire cross-section of the intake port 44. The cross-section is shown together with the cross-section 45' of a conventional intake port 44' whose cross-section is circular. The intake port 44 shown in FIGS. 4 and 5 is, in the cross-section thereof, formed in a curved shape with corner portions chamfered off. Its broadest part (the part where y takes the largest value) Pm is disposed at a position biased further toward the side of the tumble flow (i.e., the side where x is 0) beyond a cross-sectional center (see letter C) of the valve stem 58A at a position where the valve stem is internally in contact with the intake port 44. Further, the width of the intake port 44 is determined in such a way that it becomes gradually smaller from the broadest part Pm toward an end portion of the other half (i.e., the end portion of the side where x becomes greater). A crossing point Pc between the cross-sectional shape 45' of the intake port 44, which has a flow passage cross-sectional area equal to the intake port 44 and also a conventional circular, elliptical or oval, cross-sectional shape, and the cross-sectional shape 45 of the intake port 44 is located on the side of the tumble flow (i.e., the side where x is 0) beyond the center of the port (i.e., the center in the direction x ). Since the intake port according to FIG. 1 and 2 is constructed as described above, the intake air flow fraction from the tumble-flow-side half 44a of the intake port 44 is substantially stronger than the intake air flow fraction from the other half 44b of the intake port 44. The intake air flow fraction from the tumble-flow-side half 44a of the intake port 44 is a flow fraction which acts to develop the tumble flow, whereas the intake air flow fraction from the other half 44b of the intake port 44 is a fraction which acts to suppress the tumble flow. Because of the above-described imbalance in flow rate, the strength of the tumble flow can be increased without reducing the overall cross-section of the flow pass of the intake port, in other words, while maintaining the flow rate (flow velocity) of the intake air flow through the whole intake port 44. It is to be noted particularly that the broadest part Pm of the intake port 44 is disposed on the side of the tumble flow (i.e., the side where x is 0) beyond the cross-sectional center (see letter C) of the valve stem 58A at the position where the valve stem is internally in contact with the intake port 44 end the crossing point Pc with the cross-section of the intake port having the conventional circular, elliptical or oval cross-section is located on the side of the tumble flow (i.e., the side where x is 0) beyond the center of the port (i.e., the center in the direction x ). Even when the intake air flow on the side of the tumble flow is prevented by the valve stem 58A, a sufficient intake air flow therefore occurs on the side of the tumble flow so that the advantage described above can be obtained easily and surely. Such an advantage can also be envisaged, for example, from an observation of FIG. 6 which shows flow coefficient as a function of the strength of tumbling. In FIG. 6, the dots present measurement values of an intake port which is a conventional straight port having a circular, elliptical, oval or substantially square cross-sectional shape. Line L1 indicates characteristics obtained from these measurement values. It is understood that there is a contradictory relationship (i.e., a trade-off relationship), namely, that the maximum flow rate (flow coefficient) drops as the strength of the tumble flow (the strength of tumbling) is increased. In contrast, point P1 shows data of the present intake port 44. It is understood that the maximum flow rate (flow coefficient) does not drop even when the strength of the tumble flow (the strength of tumbling) is increased. Regarding the data of constant-speed motoring fuel mileages at varied air/fuel ratios, FIG. 7 illustrates data (indicated by triangles) of the present intake port 44 in comparison with data (indicated by circles) of a conventional intake port having a usual circular, elliptical or oval cross-sectional shape. It is envisaged that the best gas mileage is improved from LV2 to LV1 and the driving limit at the maximum air-fuel ratio is improved from LM2 to LM1. With reference to FIG. 8 the overall structure of each cylinder of an internal combustion engine equipped with intake ports 44A is substantially as in FIG. 1 described above so that its description is omitted herein. As is illustrated in FIG. 8, each intake passage 40A, 42A is a straight passage, but its upper part (i.e., on the side of the tumble flow) is not made extremely straight and is formed with a slight bulge. Although the cross-section of the intake port 44A is substantially triangular as depicted in FIG. 9, significant chamfering is applied so that the cross-section is more circular than that of the intake port of FIG. 2. Since the intake port according to FIG. 8 is constructed as described above, it can bring about substantially the same advantages as the intake port of FIG. 1 and 2. With regard to flow coefficient as a function of the strength of tumbling, for example, it is understood that the strength of tumbling and the flow coefficient can be set at higher levels compared with the corresponding characteristics (see line L1) of a conventional intake passage which is a straight passage having a circular, elliptical, oval or substantially square, cross-sectional shape as depicted in FIG. 10. As the cross-sectional shape of the intake port 44, those shown in FIGS. 11-15 can also be contemplated. The cross-section of an intake port 44B shown in FIG. 11 is formed in a triangular shape chamfered only a little. The cross-section of another intake port 44C illustrated in FIG. 12 is formed in a convex triangular shape in which each side is formed of a curve whose radius is R and in which each corner is chamfered only a little. The cross-section of a further intake port 44D depicted in FIG. 13 is formed in a concave triangular shape in which the two sides, i.e., right-hand and left-hand sides (relative to the direction of the width) are each formed of a curve having a radius R and in which each corner is chamfered only a little. The cross-section of a still further intake port 44E illustrated in FIG. 14 is formed in such a shape that upper parts of two sides, i.e., right-hand and left-hand sides (relative to the direction of the width) extend in parallel with each other and lower parts of the two sides extend with the width there-between gradually decreasing in the downwardly direction, that is, in the shape of a baseball home plate. The cross-section of a further intake port 44F depicted in FIG. 15 is formed in a tongue shape with the other half 44b being rounded. The intake ports 44B, 44C, 44D, 44E and 44F of these various cross-sectional shapes can also bring about substantially the same advantages as described above. Incidentally, substantially the same advantages as described above can also be obtained when the cross-section of the intake port 44 is defined such that, relative to the center line CL (see FIG. 5) as a boundary, the percentage of the area S2 lower than the boundary (the right-hand part of the center line CL in FIG. 5) based the area S1 higher than the boundary (the left-hand part of the center line CL in FIG. 5) does not exceed a prescribed value (for example, 95 percent), for example, is defined to satisfy S2 ≦ S1 x 0.95. The present invention will be described next with reference to FIGS. 16-28. As illustrated in FIGS. 16 and 17, each cylinder of an internal combustion engine, has the combustion chamber 30 which is formed by the cylinder bore 24, the piston 26 and the cylinder head 28. The cylinder bore is formed in the cylinder block 22. Two intake ports are connected with respective intake passages 46A,46B which communicate to the combustion chamber 30 and are provided with the intake valves 58, respectively. Two exhaust ports 47A,47B also communicate to the combustion chamber 30 and are provided with exhaust valves, respectively. The respective intake passages 46A,46B merge together on an upstream side and are communicated and connected commonly to the intake conduit 43. On the other hand, the exhaust ports 47A,47B merge together on a downstream side and are communicated and connected commonly to the exhaust passage 60. At a central part of the cylinder 25, the spark plug 10 as an ignition means is disposed so that the spark plug is positioned between the intake passages 46A and 46B. The pentroof 34 is also formed in the upper wall portion of the combustion chamber 30. This pentroof 34 is provided with an inclined surface so that intake air flows from the respective intake passages 46A,46B can be guided downwardly along the inner wall of the cylinder bore 24, said inner wall lying on extensions of the axes of the individual intake passages 46A,46B. Owing to the guidance by the pentroof 34, occurrence of a tumble flow is also promoted. The intake passages 46A,46B of the internal combustion engine are both formed as linear, i.e., straight passages as shown in FIG. 17. In the cross-sections of the straight passages, tumble-flow-side halves 46A-1, 46B-1 of the intake passages 46A,46B (namely, the upper halves of the intake passages 46A,46B, through which upper halves principal fraction flows acting to develop the tumble flow advance) are formed broader than the other halves 46A-2,46B-2 (namely, the lower halves of the intake passages 46A,46B, through which lower halves such fraction flows as acting to suppress the tumble flow advance) as shown in FIG. 18 so that the intake air flows through the intake passages 46A,46B are off-centered toward the side of the tumble flow (namely, toward the upper halves 46A-1,46B-1 of the intake passages 46A,46B). As a consequence, the intake air flows from the intake passages 46A,46B can easily develop the tumble flow in the combustion chamber 30. In FIG. 18 the intake passages 46A,46B are each formed to have a substantially inverted triangular cross-section. According to this invention, the intake passages 46A, 46B are internally provided with partitions 21, respectively, so that each of the intake passages 46A,46B is axially divided into two halves. By each partition 21, the interior of the intake passage 46A or 46B in divided into two halves along the flowing direction of an air-fuel mixture, one being on a side of the spark plug (a center side half) and the other on a side opposite to the spark plug (on an outer side half). In the proximity of the junction of the intake passages 46A,46B, the injector 12 is disposed as fuel feeding means. This injector 12 feeds fuel to the center side halves of the intake passages 46A,46B, which halves are defined by the partitions 21, respectively (see FIGS. 16 and 18). The valve stem of each intake valve 58 axially extends through the associated partition 21. As the cross-sectional shapes of the intake passages 46A,46B provided with the partitions 21 that make the tumble-flow-side halves 46A-1,46B-1 broader than the other halves 46A-2,46B-2, various cross-sectional shapes can be contemplated in addition to that illustrated in FIG. 18, including a cross-sectional shape formed like a baseball home plate as depicted in FIG. 19, a cross-sectional shape rounded at the other halves 46A-2,46B-2 to present a tongue-like shape as illustrated in FIG. 20, and a cross-sectional shape in which the individual intake passage parts divided by the partitions 21 is in the form of a baseball home plate as shown in FIG. 21. Owing to the construction as described above, intake air is mixed with fuel injected through the injector 12 and flows into the combustion chamber 30 through the respective intake passages 46A,46B. After the air-fuel mixture is compressed and is then caused to expand (explode) within the combustion chamber 30, the resultant exhaust is discharged into the exhaust passage 60 through the respective exhaust ports 47A,47B. upon intake, the outer side halves of the intake passages 46A,46B, said outer side halves being defined by the corresponding partitions 21, are fed only with air, and the fuel is fed only to the center side halves of the intake passages 46A,46B, said center side halves being also defined by the corresponding partitions 21. The fuel and air are therefore stratified so that the air-fuel mixture in a fuel-rich layer is fed to the spark plug 10. Accordingly, a lean air-fuel mixture is fed to the entire combustion chamber 30 and the spark plug 10 is fed with the fuel in an amount sufficient to cause ignition. It is therefore possible to provide a fuel-rich region near the spark plug 10. This allows to operate the engine on an air-fuel mixture leaner than the stoichiometric air-fuel ratio without impairing the ignition. Further, the intake air flow fractions from the tumble-flow-side halves 46A-1,46B-1 of the respective intake passages 46A,46B become substantially stronger than the intake air flow fractions from the other halves 46A-2,46B-2. Namely, the intake air flow fractions from the tumble-flow-side halves 46A-1,46B-1 of the intake passages 46A,46B are flow fractions that develop the tumble flow, whereas the intake air flow fractions from the other halves 46A-2,46B-2 of the intake passages 46A,46B are fractions that suppress the tumble flow. Owing to the above-described imbalance in flow rate, the tumble flow can be increased in strength without reducing the cross-sectional area of the overall flow passage of the intake passage, in other words, while maintaining the flow rate (flow velocity) of the intake air flow through the whole intake passage. This embodiment can also be applied likewise to a 3-valve internal combustion engine equipped with two intake passages 46A,46B and one exhaust port 47 as depicted in FIG. 22. With reference to FIGS. 23-28, in an internal combustion engine according to another embodiment of the present invention, the partition 21 is not attached to each of the intake passages 46A,46B unlike the embodiment of FIGS. 16-22 but, as is illustrated in FIGS. 23 and 24, only one of the intake passages, i.e., only the intake passage 46A is divided into two halves, one being on a center side and the other on an outer side, by the partition 21 and the injector 12 is attached to the intake passage 46A alone. The remaining structure is similar to that described above in connection with the FIGS. 16-22. Namely, the two intake passages 46A,46B are arranged in communication with the combustion chamber 30 and are provided with the intake valves 58, respectively. The two exhaust ports 47A,47B are also arranged in communication with the combustion chamber 30 and are provided with exhaust valves, respectively. Further, the respective intake passages 46A,46B merge together on an upstream side and are communicated and connected commonly to the intake conduit 43. The respective exhaust ports 47A,47B merge together on a downstream side and are communicated and connected commonly to the exhaust passage 60. At a central part of the cylinder 25, the spark plug 10 as an ignition means is disposed so that the spark plug is positioned between the intake passages 46A and 46B. The pentroof 34 is formed in the upper wall portion of the combustion chamber 30. This pentroof 34 is provided with an inclined surface so that intake air flows from the respective intake passages 46A,46B can be guided downwardly along the inner wall of the cylinder bore 24, said inner wall lying on extensions of the axes of the individual intake passages 46A,46B. The intake passages 46A,46B of the internal combustion engine are both formed as linear, i.e., straight passages as shown. In the cross-sections of the straight passages, the tumble-flow-side halves 46A-1,46B-1 of the intake passages 46A,46B (namely, the upper halves of the intake passages 46A,46B, through which upper halves principal fraction flows acting to develop the tumble flow advance) are formed broader than the other halves 46A-2, 46B-2 (namely, the lower halves of the intake passages 46A,46B, through which lower halves such fraction flows as acting to suppress the tumble flow advance) as shown in FIG. 24 so that the intake air flows through the intake passages 46A,46B are off-centered toward the side of the tumble flow (namely, toward the upper halves 46A-1,46B-1 of the intake passages 46A,46B). As a consequence, the intake air flows from the intake passages 46A,46B can easily develop the tumble flow in the combustion chamber 30. In this embodiment, the intake passages 46A,46B are also formed to have a substantially inverted triangular cross-section. The partition 21 is arranged inside one of the intake passages, i.e., in the intake passage 46A so that the interior of the intake passage 46A is axially divided into two halves. By the partition 21, the interior of the intake passage 46A is divided into the two halves along the flowing direction of the air-fuel mixture, one being on a side of the spark plug (a center side half) and the other on a side opposite to the spark plug (on an outer side half). Further, said one intake passage 46A is provided with the injector 12 as a fuel feeding means. The injector 12 serves to feed fuel to the center side half of the intake passage 46A, which center side half is defined by the partition 21 (see FIGS. 23 and 24). As the cross-sectional shapes of the intake passage 46A provided with the partition 21 and of the intake passage 46B not provided with the partition 21 that make the tumble-flow-side halves 46A-1,46B-1 broader than the other halves 46A-2,46B-2 as in the above-described third embodiment, various cross-sectional shapes can be contemplated in addition to that illustrated in FIG. 24, including a cross-sectional shape formed like a baseball home plate as depicted in FIG. 25, a cross-sectional shape rounded at the other halves 46A-2,46B-2 to present a tongue-like shape as illustrated in FIG. 26, and a cross-sectional shape in which, as shown in FIG. 27, the individual parts of the intake passage 46A divided by the partition 21 are each in the form of a baseball home plate and the intake passage 46B not provided with the partition 21 is in the form of a baseball home plate. Owing to the construction as described above, upon intake, only air is fed to the outer side half of the intake passage 46A, said outer side half being defined by the partition 21, and to the intake passage 46B and the fuel is fed only to the center side half of the intake passage 46A, said center side half being defined by the partition 21. Like the embodiment described in connection with the FIGS. 16-22, the fuel and air are stratified so that the air-fuel mixture in a fuel-rich layer is fed to the spark plug 10. Accordingly, a lean air-fuel mixture is fed to the entire combustion chamber 30 and the spark plug 10 is fed with the fuel in an amount sufficient to cause ignition. It is therefore possible to provide a fuel-rich region near the spark plug 10. This allows to operate the engine on an air-fuel mixture leaner than the stoichiometric air-fuel ratio without impairing the ignition. Further, the intake air flow fractions from the tumble-flow-side halves 46A-1, 46B-1 of the respective intake passages 46A, 46B become substantially stronger than the intake air flow fractions from the other halves 46A-2,46B-2. Namely, the intake air flow fractions from the tumble-flow-side halves 46A-1, 46B-1 of the intake passages 46A,46B are flow fractions that develop the tumble flow, whereas the intake air flow fractions from the other halves 46A-2,46B-2 of the intake passages 46A,46B are fractions that suppress the tumble flow. Owing to the above-described imbalance in flow rate, the tumble flow can be increased in strength without reducing the cross-sectional area of the overall flow passage of the intake passage, in other words, while maintaining the flow rate (flow velocity) of the intake air flow through the whole intake passage. This embodiment can also be applied likewise to a 3-valve internal combustion engine equipped with two intake passages 46A,46B and one exhaust port 47 as depicted in FIG. 28. With the internal combustion engine according to the invention, comprising the intake port as described above, the strength of a tumble flow can be increased without reducing the maximum flow rate (flow coefficient) and, in addition, the internal combustion engine can be operated on an air-fuel mixture leaner than the stoichiometric air-fuel ratio without impairing the ignition. Accordingly, is suited the internal combustion engine having such an intake port can especially be mounted on an automotive vehicle.

Claims: An internal combustion engine comprising a combustion chamber (30) and intake ports, each connected with respective intake passages (46A, 46B), said combustion chamber (30) being defined by a cylinder bore (24), a piston (26) fitted in said cylinder bore (24) and a pentroof (34) formed on a wall of a cylinder head (28) adjacent to said combustion chamber (30), the pentroof being associated with said cylinder bore (24) and having first and second inclined walls, said intake passages (46A, 46B) opening through the first inclined wall and each being formed as a linear, i.e. straight passage, whereby an intake air flow from said intake passages (46A, 46B) is guided by the second inclined wall and is allowed to flow along an inner wall of said cylinder bore (24), said inner wall extending in continuation with the second inclined wall, to generate a tumble flow within said combustion chamber (30), characterized in that the cross-section of said intake passages (46A, 46B) taken along a plane perpendicular to the flowing direction is broader in a tumble-flow side half (46A-1, 46B-1) thereof than in the other half (46B-2, 46B-2), the intake air flow through said intake passages (46A, 46B) is off-centered towards the side of the tumble flow, whereby the intake air flow from said intake passages (46A, 46B) can promote the tumble flow, said intake passages (46A, 46B) are provided with a partition (21) to divide the interior of at least one of said intake passages (46A, 46B) along the direction of a flow of a fluid therethrough into two sections, one being on a side of ignition means (10) in said combustion chamber (30) and the other on a side opposite to said ignition means (10), and fuel feed means (12) is arranged for feeding fuel to one of said two sections of said one intake passage, said one section being on the side of said ignition means (10). The internal combustion engine of claim 1, wherein each intake passage (46A, 46B) is provided with said partition (21). The internal combustion engine of claim 1, wherein some (46A) of said intake passages (46A, 46B) are provided with said partition (21). The internal combustion engine of any one of claims 1 to 3, wherein said intake passages (46A, 46B) are formed broader in said tumble-flow side half (46A-1, 46B-1) than in the other half (46A-2, 46B-2) to have a substantially triangular cross-section. The internal combustion engine of any one of claims 1 to 4, wherein said intake passages (46A, 46B) are formed broader in said tumble-flow-side half (46A-1, 46B-1) than in the other half (46A-2, 46B-2) to have a cross-section in the form of a baseball home plate. The internal combustion engine of any one of claims 1 to 4, wherein said intake passages 46A, 46B) are formed broader in said tumble-flow side half (46A-1, 46B-1) than in the other half (46A-2, 46B-2) to have a tongue-shaped cross-section. The internal combustion engine of any one of claims 1 to 4, wherein each intake passage (46A, 46B) is formed broader in said tumble-flow side half (46A-1, 46B-1) than in the other half (46A-2, 46B-2) so that a broadest part of said intake passage (46A, 46B) is disposed at a position biased outwardly of a cross-sectional center of a valve stem at a position where said valve stem is internally in contact with said intake passage (46A, 46B) and said intake passage (46A, 46B) becomes gradually narrower from said broadest part toward an end portion thereof on a side of said other half (46A-2, 46B-2).

Inventors: AKISHINO KATSUO, ANDO HIROMITSU, FURUKAWA KEIZO, HIRAKO OSAMU, IWACHIDO KINICHI, MATSUO SYUNSUKE, MOTOMOCHI MASAYUKI, MURAKAMI NOBUAKI, AKISHINO, KATSUO,, ANDO, HIROMITSU,, FURUKAWA, KEIZO,, HIRAKO, OSAMU,, IWACHIDO, KINICHI,, MATSUO, SYUNSUKE,, MOTOMOCHI, MASAYUKI,, MURAKAMI, NOBUAKI,, AKISHINO, KATSUO, 68, TAISYOGUN-ICHIJO-CHO, ANDO, HIROMITSU, 15, AZA-ACHIKA HASHIME-CHO, FURUKAWA, KEIZO 628-18, FUKAKUSA-TORIIZAKI-CHO, HIRAKO, O., 11-1, OOE-NISHISHINBAYASHI-CHO 1-CH., IWACHIDO, KINICHI, 4-B, DAINISUMIYOSHI-HAITSU, MATSUO, S., 309, SUN-CITY-KATSURAZAKASANBANKAN, MOTOMOCHI, MASAYUKI, 16-22, ITSUTSUGAOKA 2-CHOME, MURAKAMI, NOBUAKI, 51, OOYAKE-FURUKAIDO-CHO
Applicants: MITSUBISHI MOTORS CORP, MITSUBISHI JIDOSHA KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: F02M69
IPC codes: F02M35, F02B31, F02M69