SWIRL CHAMBER TYPE COMBUSTION CHAMBER FOR DIESEL ENGINE

Abstract: A swirl chamber type combustion chamber for a diesel engine has an injection passage (2) to guide a stream of combustion gas gradually spreading right and left during injection from a swirl chamber (3) to the main combustion chamber (1), a top surface of a piston head (8) is provided with a concavity (7) formed in such a configuration as gradually spreading right and left as progressing from the inlet end (10) to the outlet end (12) thereof, for example like an unfolded-fan. The inlet end (10) of the concavity is located so as to face to the outlet of the injection passage (2). The stream of combustion gas injected from the injection passage is to be guided so as to be sufficiently diffused in the main combustion chamber by the concavity.

Description: The present invention relates to an improvement of a swirl chamber type combustion chamber for a diesel engine in which a stream of combustion gas is injected from a swirl chamber to a main combustion chamber so as to spread out right and left. A basic construction of a swirl chamber type combustion chamber for a diesel engine, which being concerned in the present invention, is as described hereinafter. Referring to Fig.3, at an offset position relative to a main combustion chamber 1 in a diesel engine, there is provided a swirl chamber 3 which is in communication with the main combustion chamber 1 through an injection passage 2, the axis 4 of which is directed in such an oblique direction as it gets near the center of the main combustion chamber as progressing from the swirl chamber 3 to the main combustion chamber 1. The injection passage 2 is formed in such a shape as it spreads the right and left portions of the stream of combustion gas expanded in the swirl chamber 3, at a spread angle towards the main combustion chamber. Generally, it is known in the art that an injection passage which is simply formed in a cylindrical shape can not enhance a specific air utilization in the swirl chamber type combustion chamber because the combustion gas stream doesn't spread so widely in the main combustion chamber 1 when it is injected thereinto through the passage 2 from the swirl chamber 3. Therefore, the applicant( the assignee ) of the present invention has disclosed in Japanese Patent Publication of No. 59410 of 1982 an improved injection passage that is formed in such a shape as it spreads gradually at the both sides thereof towards the main combustion chamber 1 like a diffuser in order to enhance the diffusion of the combustion gas stream and then the specific air utilization. That is, the injection passage 2 comprises a round through hole and a pair of swelled side channels connected thereto on both sides thereof. Accordingly, the injection passage 2 is adapted to produce a main stream of combustion gas along the axis 4 thereof as well as right and left sub-streams of combustion gas spread out to both sides of the main stream like an unfolded fan when the combustion gas stream is injected onto a flat top surface of a piston head ascended near the top dead center in order that the specific air utilization may be enhanced. On the other hand, in order to enhance the swirl mixing efficiency in the swirl chamber, since it is necessary that the volume of the swirl chamber 3 might be enlarged possibly and that of the main combustion chamber 1 might be reduced possibly, the top clearance above the piston is narrowed extremely at the top dead center of the piston. Thereupon in the above-mentioned prior art, the injection passage 2 is almost closed by the flat top surface of the piston while the piston passes by the top dead center thereof. Hence, it becomes impossible owing to the large resistance at the outlet of the injection passage 2 for the stream of combustion gas expanded in the swirl chamber 3 to flow smoothly, properly and forwardly into the main combustion chamber 1, and further the stream of combustion gas injected thereinto is apt to be disturbed by the excessive spread thereof to both right and left sides, for example over an angle of ab.120 degree in comparision with an ideal spread angle of 60 degree at the top dead center of the piston. Thus, since the stream of combustion gas can't mix uniformly with air which exists in a forward portion thereof, the operating characteristics of the engine, such as, for example, power and specific fuel consumption are made worse owing to the bad sepcific air utilization. Further, since the fuel-air mixture in the right and left portions of the combustion gas stream generated by the excessive spread thereof becomes too rich to ensure the complete combustion, much carbone deposit produced there is apt to cause piston-ring stickings or scuffings. Moreover, since the positions where the carbon deposit is produced are near the sliding surfaces of the piston and the cylinder, the deposit is apt to drop therebetween and to make the stick worse and worse. And since the stream of combustion gas is obstructed as described above and the portions adjacent to the injection passage are heated locally so as to cause uneven heating in the combustion chamber, thermal strains are apt to be generated in the piston. This invention provides a swirl chamber type combustion chamber for a Diesel engine having a swirl chamber connected to a main combustion chamber through an injection passage provided at an offset position with respect to the main combustion chamber axis, said injection passage being directed obliquely in such a way that the axis thereof is angled towards the axis of the main combustion chamber in the direction leading towards the main combustion chamber, said injection passage being formed with and increasing lateral spread along its length so as to spread gradually the stream of combustion gas expanded in the swirl chamber and at an angle gradually extending towards the main combustion chamber, and a piston having a head in the main combustion chamber; wherein the head of the piston is provided with a tapered channel for guiding the gas between the injection passage and combustion chamber, the channel having one end disposed opposite the injection passage and having straight side walls extending from said end which diverge from one another towards the other end of the channel, the channel having a bottom face which converges with the piston surface at said other end of the channel to guide gas flow between the injection passage and combustion chamber and vice versa. GB-A-2l60262 shows a piston crown having an elongate trench section into which flame from a swirl chamber is injected and having relatively shallow flame dispersing recesses on either side of the trench. The arrangement of the invention improves the diffusion of the stream of combustion gas in a main combustion chamber while a piston passing by the top dead center thereof and to enhance a specific air utilization therein. The invention also assists in avoiding lack of air locally in a main combustion chamber and preventing the generation of carbon deposit and piston-ring sticking. It also alleviates thermal strains produced in the piston. In one embodiment of the invention valve recesses may be provided in the piston head positioned to overlap partially with the tapered channel adjacent said other end thereof in order to avoid the interferences between the piston head and intake and exhaust valves. In one arrangement according to the invention said one end of the channel may be formed by a concave surface as seen in a longitudinal section through the piston. In a further construction said one end of the channel may be formed by a flat back wall inclined outwards as seen in a longitudinal section through the piston. In yet a further arrangement said one end of the channel may be formed by a back wall which is vertically straight as seen in a longitudinal vertical section through the piston. In any of the above arrangements the edge between the back wall of the said one end and the piston top surface may be rounded smoothly. Also in any of the above arrangements the bottom face of the channel between said one end and said other end of the channel may be formed as a flat ramp ascending towards the piston surface said other end of the channel. In a further arrangement the channel may have a uniform depth between said one end and a midway position along the channel. In the latter arrangement between the midway position along the channel and said other end, the bottom face of channel may be formed in the shape of a concavity as seen in the longitudinal vertical section of the piston. In a still further arrangement between the midway position along the channel and said other end, the bottom face of the channel may be formed as a flat ramp ascending towards the piston surface at said other end of the channel. In yet another arrangement the bottom face of the channel may be formed so as to progressively descend from said one end to the midway position and progressively ascend from the midway portion to said other end. In any of the above arrangements the channel may be formed in the shape of an unfolded fan, a triangle or a leaf of a ginkgo in plan view. The following is a detailed description of some specific embodiments of the invention reference being made to the accompanying drawings, wherein: Figure 1 is a plan view of a piston head showing the first embodiment of the present invention; Figure 2 is a vertical sectional right side view showing the principal parts of a main combustion chamber and a swirl chamber for a vertical diesel engine according to the present invention; Figure 3 is a vertical sectional right side view showing the principal part including a cylinder block and a cylinder head for the vertical diesel engine; Figure 4 is an explanatory view of an injection passage formed in a mouthpiece in Figure 3; Figure 5 is a vertical sectional right side view of a piston head showing the second embodiment of the present invention; Figure 6 is a view showing the third embodiment in correspondence with Figure 5. Figure 7 is a view showing the fourth embodiment in correspondence with Figure 1; Figure 8 is a view showing the fourth embodiment in correspondence with Fig.5; Figure 9 is a view showing the fifth embodiment in correspondence with Fig.5; Figure 10 is a view showing the sixth embodiment in correspondence with Fig.5; Figure 11 is a view showing the seventh embodiment including a piston head provided with vale recesses, in correspondence with Fig.1; Figure 12 is a view showing the seventh embodiment in correspondence with Fig.2; Figure 13 is a view showing a relative positional relation among a cocavity, valve recesses and other portions in correspondence with Fig.11; Figures 14 through 17 are views showing respectively other embodiments of the concavity in the case of the piston head provided with valve recesses; Figure 14 is a vertical sectional view of the piston head in accordance with the second embodiment; Figure 15 is a view in accordance with the third embodiment and in correspondence with Fig.13; Figure 16 is a view in accordance with the fourth embodiment and in correspondence with Fig.13; Figure 17 is a view in accordance with the fifth embodiment and in correspondence with Fig.13; Figures 18 through 20 are views showing respectively embodiments of relative relations between the spreading directions of combustion gas injected from the injection passage and the concavity; Figure 18 is a plan view of the concavity showing the state wherein both directions are in accord each other; Figure 19 is a plan view of the concavity showing the state wherein both directions are shifted longitudinally to each other; Figure 20 is a plan view of the concavity showing the state wherein the spreading angle of the concavity is larger than that of the combustion gas stream; Figures 21 through 24 are views showing other embodiments of injection passage; Figure 21 is a view of the injection passage comprising a main passage of an elliptic cylinder and side channels connected therewith, in correspondence with Fig.4; Figure 22 ia a view showing the injection passage having a small elongate hole at the upper end and a large elongate hole at the lower end, whose longitudinal directions are coincied each other, in correspondence with Fig.4; Figure 23 is a view showing the injection passage having an elongate hole at the upper end and a circular hole at the lower end, in correspondence with Fig.4; and Figure 24 is a view of the passage having a small elongate hole at the upper end and a large elongate hole at the lower end, whose longitudinal directions are crossed each other, in correspondence with Fig.4. As shown in Fig.s 1 through 4, in the preferred embodiment of the present invention, a diesel engine E has a cylider block 14 provided with a cylinder 15 around the center thereof, which guides a piston 6 slidably reciprocatingly therein. On the upside of the cylinder block 14, there is mounted a cylinder head 16, which has a cavity carved in the backward wall facing to a main combustion chamber 1 and a mouthpiece 20 fitted in the aperture formed in the lower portion of the cavity 19. A swirl chamber 3 is formed by the upper hemispherical portion of the cavity 19 and the lower hemispherical portion caved in the mouthpiece 20. The cylinder head 16 has a fuel injection nozzle 22 mounted in a bore 21 which is bored through from the upper end of the backward wall to the cavity 19 therein with the injection tip 23 being projected in the swirl chamber 3. In the mouthpiece 20, there is provided an injection passage 2 inclined backward, that is directed obliquely in such a way that the axis 4 of the injection passage 2 gets near the center of the main combustion chamber 1 as progressing to the main combustion chamber 1 from the swirl chamber 3. As shown in Fig. 4, the injection passage 2 comprises a central round through hole 24 as for a main injection channel and side channels 25 in the shape of swelled ridge connected thereto at somewhat forward positions from the transverse axis of the hole 24. The side channels 25 are formed in such configuration that the opposite side walls thereof spread right and left symmetrically relative to the axis of the round through hole 24 as progressing to the main combustion chamber 1 from the swirl chamber 3 as indicated at 35 in Figure 1 and so that the combusion gas is guided to spread to both sides thereof when it is injected from the swirl chamber 3 to the main combustion chamber 1. With reference to Figures 1 and 2, on the top surface of the piston head 8, there is provided a concavity 7 in a shape of a fan unfolded to an angle of ab.60 degree so as to face to the outlet of the injection passage 2 at the inlet end 10 corresponding with the pivot portion of the fan with straight divergent sides 36 terminating in a curved end face at the outlet end of the concavity. The concavity 7 is formed deepest at the inlet end 10 thereof and so as to get shallower as it progresses to the outlet end 12. Further, since the cavity 7 is positioned around at the central portion of the piston top surface so that the inlet end 10 faces the outlet of the injection passage 2 in the main combustion chamber 1, the stream of combustion gas injected from the passage 2 is guided to spread smoothly and properly throughout the concavity 7 from the inlet end 10 to the outlet end 12 thereof. The longitudinal sectional configuration of the concavity 7 comprises a spherical portion formed at the inlet end 10 and a single-curved surface (having no curvature longitudinally but having curvature transversely) formed like a ramp ascending from the inlet end 10 to the outlet end 12 and smoothly connected thereto. The function of the above-mentioned embodiment is now to be described hereinafter. Since the injection passage 2 is directed towards the inlet end 10 of the concavity 7 formed on the piston head 8 even while the piston 6 passing by the top dead centre thereof, the stream of combustion gas injected into the main combustion chamber 1 through the passage 2 pushes away the air in the concavity 7 towards the outlet end 12 smoothly without any resistances and also it is prevented that the stream of combustion gas is spreaded excessively by the approach of the piston top surface to the outlet of the passage 2. Thereupon, the stream of combustion gas can be diffused properly without causing turbulences in the main combustion chamber 1 in order to mix with the air effectively throughout the main combustion chamber 1. Accordingly, the present invention can obtain the following advantages. (1) Since the stream of combustion gas injected from the swirl chamber 3 is diffused properly without causing turbulences in the main combustion chamber 1 so as to facilitate the mixing with the air effectively throughout the chamber 1, a specific air utilization can be enhanced. (2) Since a local shortage of the air in the main combustion chamber 1 can be solved by the improvement of the diffusion of the combustion gas stream, carbon is scarcely produced therein. Thus, the sticking of the piston-rings can be prevented effectively between the sliding surfaces of the cylinder 15 and the piston 6. (3) Since the stream of combustion gas is smoothly injected forwardly in the main combustion chamber 1 even while the piston passing by the top dead center thereof, the local overheating for the piston head 18 by the combustion gas maldistributed near the outlet of the passage 2 can be prevented so as for the thermal strains in the piston 6 to be removed. In addition, modified embodiments are now to be described hereinafter. That is, since it is required as a necessary condition that the concavity 7 is to be formed in such a configuration as spreading right and left as progressing from the inlet end 10 to the outlet end 12, the longitudinal sectional configuration thereof is not limitted exclusively to the above-mentioned embodiment but may be modified as follows. In the second embodiment of the concavity 7 provided in the piston head 8 as shown in Fig.5, the concavity 7 comprises an oblique flat surface 30 inclinded backwards at the inlet end 10 , a holizontal flat surface 31 formed in a same depth from the inlet end 10 to the midway portion thereof and a single-curved concave 32( having a curvature longitudinally ) ascending from the midway portion to the outlet end 12 and connected smoothly to the flat surface 31. In this embodiment, since the concavity 7 has a larger capacity due to the formation of the concave 32 in comparison with that of the first embodiment, an excessive spreading of the stream of combustion gas can be prevented effectively. In the third embodiment of the concavity 7 shown in Fig.6, the edge between the the flat surface 30 and the piston top surface at the inlet end 10 as shown in the first embodiment is smoothly rounded so as to continuosly smoothly connect the cavity 7 to the top surface of the piston head 8. Therefore, the generation of cracks and/or a heat point can be prevented owing to the removal of the sharp edge at the inlet end 10. In the fourth embodiment of the concavity 7 shown in Figs 7 and 8, the area from the midway portin to the outlet end 12 of the concavity 7 in the third embodiment is formed in an oblique single-curved concave 34 having a curvature transversely and ascending forwardly, and the central flat surface 31 and the concave 34 are connected to each other like a folded line. In the fifth embodiment of the concavity 7 shown in Fig.9, the inlet end 10 shown in the first embodiment is modified so as to be formed by a vertical flat surface. In the sixth embodiment of the concavity 7 shown in Fig.10, the midway portion 40 between the inlet end 10 and the outlet end 12 is formed deepest. Thereupon, the concavity 7 is formed so as to progressively descend from the inlet end 10 to the midway portion 40 and ascend from the midway portion 40 to the outlet end 12. The flow resistance for the stream of combustion gas injected from the injection passage 2 can be reduced effectively because the depth of the concavity 7 gets gradually increased as progressing from the inlet end 10 to the midway portion 40. In the seventh embodiment shown in Fig.s 11 and 12, the piston head 8 is provided with valve recesses 100 in order to avoid the interferences between the piston head 8 and an intake and an exhaust valves. The intake valve recess 100a of large aperture and the exhaust valve recess 100b of small aperture are respectively formed in a proper depth at the left side and at the right side of a center line C on the piston head 8. In this case, the intake valve recess 100a is overlapped partially with the right half around the outlet end 12 ( overlapped part being indicated by 101 ), and the exhaust valve recess 100b is overlapped partially with the left half around the outlet end 12 ( overlapped part being indicated by 102 ). The longitudinal sectional configuration of the concavity 7 comprises a spherical inlet end 10 and an oblique flat surface ascending from the inlet end 10 to the outlet end 12 and connected smoothly thereto. Generally, as the compression ratio and the volume ratio of the swirl chamber being constant, the volume of the main combustion chamber 1 is also defined to be constant. And the volume of the main combustion chamber 1 consists of respective volumes of a disk-like clearance between the underside of the cylinder head 16 and the top surface of the piston head 8, the valve recesses 100 and the concavity 7. Further, as the volume of the cylidrical clearance and the volume of the valve recesss are respectively defined to be constant by the clearance at the top dead center of the piston 6 for the former and by the strokes of the intake and exhaust valves for the latter, the residual volume of the concavity 7 is to be defined constant uncoditionally. In this embodiment, since the volume of the concavity 7 is reduced by the overlapped portions thereof, the concavity 7 is to be deepened as compensation for the overlapped portions in order to maintain the constant volume of the concavity 7. Thereupon, the resistance for the combustion gas stream is reduced remarkably in the concavity 7. Accordingly, the excessive spreading of the combustion gas stream can be prevented more effectively than in the foregoing embodiments owing to the space enlarged at the outlet of the injection passage 2. On the other hands, in the Fig.7 showing another embodiment about a relative arrangement between the concavity 7 and the valve recesses 100, with differing from the seventh embodiment, the inlet end 10 of the concavity 7 is located on the center line C of the piston head 8, and the intake valve recess 100a and the exhaust valve recess 100b are respectively provided with the edge portions 103, 104 cut out at the peripheral edge 8a of the piston head 8. Hence, this embodiment solves the problem that the edge portions 103, 104 are apprehended to generate heat points owing to their sharp edges formed in the seventh embodiment. Fig.s 14 through 17 show the other embodiments having the valve recesses. Fig. 14 corresponds to the second embodiment, Fig.15 to the third Fig. 16 to the fourth and Fig. 17 to the fifth embodiment respectively. On the other hand, the relative positional relation between the injection passage 2 and the concavity 7 is not limited to one embodiment but may vary extensively. Fig. 18 shows another embodiment of the concavity 7, wherein the inlet end 10 thereof is aligned with the outlet of the injection passage 2 and the spread angle thereof is in accord with that of the stream of combustion gas injected from the passage. In Fig. 19 there is shown another embodiment having the concavity 7 whose spread angle is settled under the same condition as in Fig.18, the outlet of the injection passage 2 is positioned a little forwards with respect to the inlet end 10 of the concavity 7. Since the stream of combustion gas injected from the passage 2 is to flow through with its oposite side edges 35 being spaced a little inwards from the opposite side edges 36 of the concavity 7, vacuum pressure is to be produced adjacently along the outside of the side edges 35. Accordingly, air 37 is to be sucked into the concavity 7 through the side edges 36 so as to facilitate more effectively the mixing with the stream of combustion gas in the main combustion chamber 1. Fig.20 shows such an unfolded-fan shaped concavity 7 as having a spread angle settled a little larger than that of the combustion gas stream. As for the configuration of the concavity 7 which gradually spreads forwardly on both sides thereof, not only the shape of an folded-fan but also, for example the shape of a triangle, a crescent or leaf of ginkgo, etc. can be applied thereto. Further, the injection passage 2 may have only such a basic configuration as it guides the stream of combustion gas so as to gradually spread right and left, that is, such an injection passage is enough as to gradually spread the stream of combustion gas right and left as progressing to the main conbustion chamber. Accordingly, besides the first embodiment, the following variations can be applied to the injection passage 2, for example which comprising a main passage of an elliptical cylinder and side channels connected to said main passage at the laterals thereof as shown in Fig.21, having elongate holes of which longitudinal directions coincid to each other respectively at the upper and the lower ends as shown in Fig.22, having respectively an elongate hole at the upper end and a circular hole at the lower end as shown in Fig.23, and having a transversely elongate hole and a longitudinal elongate hole of which longitudinal directions are crossed each other, respectively at the upper and the lower ends as shown in Fig.24.

Claims: A swirl chamber type combustion chamber for a Diesel engine having a swirl chamber (3) connected to a main combustion chamber (1) through an injection passage provided at an offset position with respect to the main combustion chamber axis, said injection passage being directed obliquely in such a way that the axis (4) thereof is angled towards the axis of the main combustion chamber in the direction leading towards the main combustion chamber, said injection passage being formed with an increasing lateral spread along its length so as to spread gradually the stream of combustion gas expanded in the swirl chamber and at an angle gradually extending towards the main combustion chamber, and a piston (6) having a head (8) in the main combustion chamber; characterized in that the head of (8) of the piston is provided with a tapered channel (7) for guiding the gas between the injection passage and combustion chamber, the channel having one end disposed opposite the injection passage and having straight side walls extending from said end which diverge from one another towards the other end of the channel, the channel having a bottom face which converges with the piston surface at said other end of the channel to guide gas flow between the injection passage and combustion chamber and vice versa. A swirl chamber type combustion chamber defined in Claim 1, characterised in that valve recesses (100) are provided in the piston head (8) positioned to overlap partially with the tapered channel (7) adjacent said other end thereof in order to avoid the interferences between the piston head (8) and intake and exhaust valves. A swirl chamber type combustion chamber defined in Claim 1 or Claim 2, characterised in that said one end (10) of the channel (7) is formed by a concave surface as seen in a longitudinal section through the piston. A swirl chamber type combustion chamber defined in Claim 1 or Claim 2, characterised in that said one end (10) of the channel (7) is formed by a flat back wall inclined outwards as seen in a longitudinal section through the piston. A swirl chamber type combustion chamber defined in Claim 1 or Claim 2, characterised in that said one end (10) of the channel (7) is formed by a back wall which is vertically straight as seen in a longitudinal vertical section through the piston. A swirl chamber type combustion chamber defined in any of Claims 1 to 5, characterised in that the edge between the back wall of the said one end (10) and the piston top surface is rounded smoothly. A swirl chamber type combustion chamber defined in any of Claims 1 to 6, characterised in that the bottom face of the channel between said one end (10) and said other end (12) of the channel (7) is formed as a flat ramp ascending towards the piston surface at said other end of the channel. A swirl chamber type combustion chamber as defined in any of Claims 1 to 6, characterised in that the channel has a uniform depth between said one end (10) and a midway position (40) along the channel (7). A swirl chamber type combustion chamber defined in Claim 8, characterised in that between the midway position (40) along the channel and said other end (12), the bottom face of channel (7) is formed in the shape of a concavity as seen in the longitudinal vertical section of the piston. A swirl chamber type combustion chamber defined in Claim 8, characterised in that between the midway position (40) along the channel and said other end (12), the bottom face of the channel is formed as a flat ramp ascending towards the piston surface at said other end of the channel. A swirl chamber type combustion chamber defined in any of Claims 1 to 6, characterised in that the bottom face of the channel (7) is formed so as to progressively descend from said one end (10) to the midway position (40) and progressively ascends from the midway portion (40) to said other end (12). A swirl chamber type combustion chamber defined in any of Claims 1 to 11, characterised in that the channel (7) is formed in the shape of an unfolded fan in a plan view. A swirl chamber type combustion chamber defined in any of Claims 1 to 11, characterised in that the channel (7) is formed in the shape of a triangle in a plan view.

Inventors: HATAURA, KIYOSHI, NAGAHAMA, MASAHIRO
Applicants: KUBOTA LIMITED
Application year: 1987
Main classification: F02B19
IPC codes: F02B23, F02B3, F02B19