A diesel engine with a precombustion chamber

Abstract: A diesel engine comprising a Plurality of cylinders (1) each having a precombustion chamber (21) and a fuel injector (23). A first camshaft (4) for driving intake valves (2) and a second camshaft (5) for driving exhaust valves (3) are arranged on the cylinder head (10) and extended in parallel to the longitudinal axis of the engine body. Each precombustion chamber (21) and each fuel injector (23) is arranged centrally between the first camshaft (4) and the second camshaft (5).

Description: The present invention relates to a diesel engine according to the preamble of claim 1. The GB-A-674 713 discloses a know generic Diesel engine comprising plural cylinders, each having a pair of inlet and exhaust valves respectively arranged on opposite side of the engine which cylinders are provided with precombustion chambers. The precombustion chambers are arranged above the centre of each cylinder. This Diesel engine, however, has the disadvantage that under certain condition temperature problems will arise, since the cooling of the precombustion chamber and the cylinder is difficult. The US-A-444 0 125 shows a Diesel engine having only one inlet valve and one exhaust valve. The precombustion chamber is aranged beside the inlet valve and the exhaust valve. However this reference discloses only the arrangement of the precombustion chamber for one cylinder having one inlet and one exhaust valve per cylinder. According to the DE-A-3113 308 showing a Diesel engine having a plurality of inlet and exhaust valves per cylinder the precombustion chambers are located between the intake valves. However, with this Diesel engine also temperature problem can arise, since camshafts of the inlet and the exhaust valves are not warmed up regulary. In a known diesel engine equipped with a precombustion chamber, the precombustion chamber is normally arranged above and slightly offset from the end portion of the main combustion chamber, i.e., is positioned in a direction perpendicular to the longitudinal axis of the engine body (see, for example, Japanese Unexamined Utility Model Publication No. 62-152022). Where, however, a pair of camshafts are used for driving an intake valve and an exhaust valve, if the precombustion chamber is arranged above and slightly offset from the end of the main combustion chamber, in the direction perpendicular to the longitudinal axis of the engine body as mentioned above, one of the camshafts is positioned close to the precombustion chamber and the other camshaft is remote from the precombustion chamber. In this case, since the temperature of the precombustion chamber becomes very high, if one of the camshafts is arranged close to the precombustion chamber and the other camshaft is remote from the precombustion chamber, the temperature of the camshaft close to the precombustion chamber, and the temperature of the bearing for the camshaft close to the precombustion chamber, become high due to a transfer of heat from the precombustion chamber. Accordingly, when the temperature of the camshaft and the temperature of the bearing of the camshaft become high, as mentioned above, the cams of the camshaft are thermally expanded, and thus the cam phases of the cams will become different from the required cam phases. As a result, a problem arises in that the opening and closing timing relationship between the intake valve or the exhaust valve driven by the camshaft close to the precombustion chamber and having a high temperature, and the intake valve or the exhaust valve driven by the camshaft remote from the precombustion chamber and having a relatively low temperature, will not meet the required opening and closing timing relationship. Further, as mentioned above, if the temperature of only one of the camshafts and the temperature of the bearing of that camshaft become high, that camshaft and the bearing thereof are subjected to considerable changes in temperature when the engine is repeatedly operated and stopped, and as a result, a problem arises in that the operating life of the overheated camshaft and bearing thereof will be shorter than that of the remote camshaft and bearing thereof. Furthermore, in a direct injection type Diesel engine, the fuel injectors do not project from the cylinder head to a great extent, but in a Diesel engine equipped with a precombustion chamber, since the fuel injector is arranged above the precombustion chamber, the fuel injector is projected far from the cylinder head. In this case, where the precombustion chamber is arranged above and slightly offset from the end of the main combustion chamber, perpendicular to the longitudinal axis of the engine body as mentioned above, the fuel injector is laterally projected far from the cylinder head. If the fuel injector is laterally projected far from the cylinder head, there is a much greater chance that the fuel injector and the piping thereof will come into contact with other parts of the engine, and as a result, a problem arises in that the fuel injector and the piping thereof will be damaged. An object of the present invention is to provide a Diesel engine equipped with a precombustion chamber and able to maintain a stable operation for a long time. According to the present invention, this object is achieved by the features of claim 1. Advantageous further developments are set out in the dependant Claims. According to the present invention, it is possible to maintain the timing relationship of the opening and closing of the intake valve and the exhaust valve at the required opening and closing timing relationship, and to prevent an earlier thermally deterioration of only one of the camshafts. In addition, it is possible to prevent the fuel injector from coming into contact with other parts of the engine, and thus being damaged. The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings. In the drawings: Fig. 1 is a plan view of a two stroke Diesel engine; Fig. 2 is a cross-sectional view of the engine, taken along the line II-II in Fig. 1; Fig. 3 is a bottom view of the inner wall of the cylinder head; Fig. 4 is a cross-sectional view of the engine, taken along the line IV-IV in Fig. 1; and Fig. 5 is a view illustrating the piston during the downward stroke thereof. Figures 1 through 3 illustrate the present invention when applied to a two stroke diesel engine. Figure 1 illustrates one block of a V-type six-cylinder two-stroke Diesel engine, and thus three cylinders 1 are provided in this block. Each cylinder 1 comprises a pair of intake valves 2 and a pair of exhaust valves 3. The intake valves 2 of the cylinders 1 are arranged in a plane extending in parallel to the longitudinal axis a-a of the engine body and are driven by a camshaft 4 extended along the longitudinal axis a-a of the engine body. The exhaust valves 3 of the cylinders 1 are also arranged in a plane extending in parallel to the longitudinal axis a-a of the engine body and are driven by another camshaft 5 extended along the longitudinal axis a-a of the engine body. The camshaft 4 and the camshaft 5 are interconnected via a pair of meshing gears 6 and 7 fixed to the ends of the camshafts 4 and 5, respectively, and the camshaft 4 is connected to the crankshaft (not shown) via a timing belt. Figure 2 illustrates a cross-sectional view of the engine, taken along the line II-II in Fig. 1. Referring to Fig. 2, reference numeral 8 designates a cylinder block, 9 a piston reciprocally movable in the cylinder block 8, 10 a cylinder head fixed to the cylinder block 8, and 11 a main combustion chamber formed between the top face of the piston 9 and the flat inner wall of the cylinder head 10; 12 designates an intake port, and 13 an exhaust port. The intake valve 2 is obliquely arranged relative to the axis b-b of the cylinder bore so that the upper portion of the intake valve 2 is farther from the axis b-b of the cylinder bore than the lower portion of the intake valve 2, and the intake valve 2 is driven by the camshaft 4, arranged on the axis of the intake valve 2, via a valve lifter 14 slidably inserted in the cylinder head 10. The exhaust valve 3 is arranged substantially in parallel to the axis b-b of the cylinder bore and driven by the camshaft 5 via a rocker arm 15. A depression 16 is formed on the inner wall of the cylinder head 10 around the intake valve 2, and a valve seat for the intake valve 17 is arranged deep in the interior of the depression 16. The intake valve 2 comprises a conical shaped valve seat portion which is seated on the valve seat 17, and a cylindrical portion 2b which extends from the lower peripheral portion of the valve seat portion 2a toward the piston 9. As illustrated in Figs. 2 and 3, the depression 16 comprises a cylindrical peripheral wall portion 16a slightly spaced from the cylindrical portion 2b of the intake valve 2 and extending along the cylindrical portion 2b of the intake valve 2, which is located on the adjacent exhaust valve side, and a conical peripheral wall portion 16b diverged conically downward from the valve seat 17 at a position opposite to the cylindrical peripheral wall portion 16a. Therefore, when the amount of lift of the intake valve 2 is small or, in some cases, during the entire opening period of the intake valve 2, at least part of the cylindrical portion 2a of the intake valve 2 faces at least part of the cylindrical peripheral wall portion 16a, and at this time, an inflow of air to the main combustion chamber 11 via the clearance between the cylindrical peripheral wall portion 16a and the cylindrical portion 2a of the intake valve 2 is prevented. Consequently, the cylindrical peripheral wall portion 16a forms a masking wall preventing the inflow of air from the opening of the intake valve 2, which is located on the adjacent exhaust valve side when the amount of lift of the intake valve 2 is small or, in some cases, during the entire opening period of the intake valve 2. As illustrated in Fig. 2, a recess 18 is formed on the top face of the piston 9, so that the piston 9 and the intake valve 2 will not interfere with each other when the piston 9 reaches the top dead center. The exhaust valve 3 is arranged so that the front face of the valve head thereof is located at the same level as the inner wall of the cylinder head 10. As illustrated in Figure 4, a recess 19 is formed in the cylinder head 10 above the end portion of the main combustion chamber 11, and a chamber member 20 is inserted in the recess 19 from the inner wall side of the cylinder head 10. The chamber member 20 is stationarily held between the cylinder block 8 and the cylinder head 10, and a precombustion chamber 21, i.e., a swirl chamber in the embodiment illustrated in Fig. 4, is formed in the recess 19. The precombustion chamber 21 is in communication with the main combustion chamber 11 via an opening 22 formed in the chamber member 20, and a fuel injector 23 is arranged at the top of the precombustion chamber 21 to inject fuel toward the precombustion chamber 21. As illustrated in Fig. 2, a glow plug 24 is inserted in the cylinder head 3 from the lateral side thereof, and as illustrated in Fig. 4, the tip portion 24a of the glow plug 24 projects into the precombustion chamber 21. Fuel is injected by the fuel injector 23 toward the tip portion 24a of the glow plug 24. As illustrated in Fig. 4, a cooling water passage 25 is formed around the precombustion chamber 21 and the fuel injector 23 via a thin wall 10a, and thus the precombustion chamber 21 and the fuel injector 23 are sufficiently cooled by the cooling water. As illustrated in Figs. 1 and 3, the paired intake valves 2 of each cylinder 1 are arranged opposite to the paired exhaust valves 3 of each cylinder 1 with respect to the longitudinal axis a-a of the engine body, and the precombustion chamber 21, the opening 22, and the fuel injector 23 of each cylinder 1 are arranged on the longitudinal axis a-a of the engine body. As can be seen from Fig. 1, the precombustion chamber 21, the opening 22, and the fuel injector 23 are arranged at the end portion on the same side of each cylinder 1, and thus two of these precombustion chamber 21, two of the openings 22, and two of the fuel injectors 23 are arranged between the adjacent cylinders 1. Each opening 22 is directed to a point between the corresponding paired intake valves 2 and the corresponding paired exhaust valves 3 in Fig. 1, and thus the burning gas is injected from each opening 22 to a point between the corresponding paired intake valves 2 and the corresponding paired exhaust valves 3 in Fig. 1. As illustrated in Fig. 1, a pair of camshafts 4 and 5 are symmetrically arranged with respect to the longitudinal axis a-a of the engine body, and thus the precombustion chamber 21, the opening 22, and the fuel injector 23 for each cylinder 1 are arranged substantially centrally between the camshafts 4 and 5. As mentioned above, since the precombustion chambers 21 are arranged substantially centrally between the camshafts 4 and 5, heat generated in the precombustion chambers 21 is substantially equally transferred to the camshafts 4 and 5. As a result, since the amount of the thermal expansion of the camshaft 4 becomes substantially equal to that of the thermal expansion of the camshaft 5, the relationship between the opening and closing timing of the intake valves 2 and the opening and closing timing of the exhaust valves 3 is maintained at the required opening and closing relationship. Further, since the heat generated in the precombustion chambers 21 is substantially equally transferred to the camshafts 4 and 5, a shortening of the life of only one of the camshafts due to thermal deterioration is prevented, and a more rapid wear of only one of the camshafts is also prevented. Furthermore, the fuel injectors 23 are arranged between the camshafts 4 and 5, and thus the fuel injectors 23 are protected by the pair of the camshafts 4 and 5 so that the fuel injectors 23 cannot come into contact with other parts of the engine. Although not shown in the drawings, the cylinder head 10 is covered by a head cover, and thus the fuel injectors 23 and the pipings thereof are further protected by this head cover. In addition, as illustrated by the broken line in Fig. 1, head bolts 26 for fixing the cylinder head 10 to the cylinder block 8 are arranged symmetrically with respect to the longitudinal axis a-a of the engine body, on each side of the precombustion chamber 21 of each cylinder 1, and consequently, since the heat generated in the precombustion chambers 21 is equally transferred to the head bolts 26, almost no difference exists among the forces of the head bolts 26 fixing the cylinder head 10 to the cylinder block 8. Therefore, it is possible to completely prevent a leakage of burned gas from between the cylinder head 10 and the cylinder block 8. Furthermore, since almost no difference exists among the forces of the head bolts 26 fixing the cylinder head 10 to the cylinder block 8, as mentioned above, and the head bolts 26 are arranged on each side of the precombustion chamber 21, the chamber members 20 (Fig. 4) are firmly held between the cylinder head 10 and the cylinder block 8. During the operation of the engine, when the piston 9 moves upward and begins to compress air in the main combustion chamber 11, the air in the main combustion chamber 11 is forced into the precombustion chamber 21 via the opening 22, and the air forced into the precombustion chamber 21 is caused to swirl in the precombustion chamber 21. Thereafter, when the piston 9 reaches the vicinity of the top dead center, fuel is injected by the fuel injector 23, and this fuel is burned in the precombustion chamber 21. Then burning gas is spouted from the opening 22 into the main combustion chamber 11, together with an unburned air-fuel mixture, and this unburned air-fuel mixture is burned in the main combustion chamber 11. Then, when the piston 9 moves downward and the exhaust valves 3 are opened, the burned gas in the main combustion chamber 11 is quickly discharged into the exhaust ports 13. Since a pair of the exhaust valves 3 are provided for each cylinder 1, the total flow area of the openings of the exhaust valves 3 is large, and consequently, when the exhaust valves 3 are opened, the pressure in the main combustion chamber 11 instantaneously drops. As a result, burned gas in the precombustion chamber 21 flows out into the main combustion chamber 11, and the pressure in the precombustion chamber 21 also instantaneously drops. When the intake valves 2 are opened, air pressurized by the supercharger (not shown) is forced into the main combustion chamber 11 from the intake ports 12. As mentioned above, the openings of the intake valves 2, which are located on the adjacent exhaust valve side, are masked by the cylindrical peripheral wall portions, i.e., the masking walls 16a of the corresponding depressions 16, and therefore, when the intake valves 2 are opened, air passes through the openings of the intake valves 2, which are located on the adjacent exhaust valve side, and then flows into the main combustion chamber 11, as illustrated by the arrow F₁ in Fig. 5. Thereafter, as illustrated by the arrow F₂ in Fig. 5, the air flows downward along the inner wall of the cylinder beneath the intake valves 2, flows along the top face of the piston 9, and then flows upward along the inner wall of the cylinder beneath the exhaust valves 3. In this way, since the air flows within the main combustion chamber 11 in the form of a loop shape, the burned gas remaining in the main combustion chamber 11 is pushed out into the exhaust ports 13, and thus a good scavenging operation in the main combustion chamber 11 can be obtained. Note that, even if the masking walls 16a are formed, since a pair of intake valves 2 is provided for each cylinder 1, the total flow area of the openings of the intake valves 2 is sufficiently large, and thus a sufficient amount of air can be forced into the main combustion chamber 11. When the piston 9 begins to move upward, the exhaust valves 3 are closed and then the intake valves 2 are closed. At this time, air in the main combustion chamber 11 begins to flow into the precombustion chamber 21 via the opening 22. As mentioned above, when the intake valves 2 are opened, air flows into the main combustion chamber 11 via the openings of the intake valves 2, which are located on the adjacent exhaust valve side, i.e., via the clearance between the cylindrical portion 2b of the intake valve 2 and the conical peripheral wall portion 16b of the depression 16. In this case, if the intake valve 2 is extended in parallel with the axis b-b of the cylinder bore, the gap between the cylindrical portion 2b of the intake valve 2 and the inner wall of the cylinder is maintained at a constant small value, regardless of the amount of lift of the intake valve 2, and thus air is not able to flow easily along the inner wall of the cylinder beneath the intake valve 2, as illustrated by the arrows F₁ and F₂. Nevertheless, in the embodiment according to the present invention, as illustrated in Figs. 2 and 5, since the intake valve 2 is obliquely arranged with respect to the axis b-b of the cylinder bore, the gap between the cylindrical portion 2b of the intake valve 2 and the inner wall of the cylinder becomes gradually larger as the amount of lift of the intake valve 2 is increased. Consequently, since air can easily flow, as illustrated by the arrows F₁ and F₂, a strong loop scavenging operation can be obtained. In addition, even if the depression 16 is formed on the inner wall of the cylinder head 10, this depression 16 is occupied by the cylindrical portion 2b of the intake valve 2, and thus there is no danger of an increase of the volume of the main combustion chamber 11. As will be obvious to a person skilled in the art, the present invention can be also applied to a four-stroke Diesel engine equipped with a precombustion chamber.

Claims: A Diesel engine comprising a plurality of cylinders (1) arranged in series along a longitudinal axis of the engine, each of said cylinders (1) being provided with a main combustion chamber (11), a pair of intake valves (2) being arranged in a cylinder head (10) on one side of the longitudinal axis of the engine and a pair of exhaust valves (3) being arranged in said cylinder head (10) opposite to said intake valves (2) with respect to the longitudinal axis of the engine, a first camshaft (4) for operating said intake valves (2), which is arranged on said cylinder head (10) on one side of, and extending substantially in parallel to the longitudinal axis of the engine, a second camshaft (5) for operating said exhaust valves (3), which is arranged on said cylinder head (10) opposite to said first camshaft (4) with respect to, and extending substantially in parallel to the longitudinal axis of the engine, and precombustion chambers (21) provided for each of said cylinders (1), being connected to the respective main combustion chambers (11) and arranged in said cylinder head (10) between said first camshaft (4) and said second camshaft (5) characterized in that the projection of said precombustion chamber (21) on a plane perpendicular to a longitudinal axis of said cylinder (1) is located partially outside of the projection of the corresponding cylinder (1) on said plane wherein the projection of the longitudinal axis of the engine on said plane intersects said projection of the precombustion chamber (21), each precombustion chamber (21) being located on the same side of said cylinders (1). A Diesel engine according to claim 1, characterized in that said precombustion chambers (21) are connected to said corresponding main combustion chambers (11) via corresponding openings (22) for spouting burning gas, said openings (22) being arranged substantially centrally between said first camshaft (4) and said second camshaft (5). A Diesel engine according to claim 2, characterized in that said openings (22) are formed to direct the burning gas spouted out therefrom between said pair of intake valves (2) and said pair of exhaust valves (3). A Diesel engine according to any of the preceding claims, characterized in that each of said exhaust valves (3) extends substantially in parallel to the axis of the corresponding cylinder (1) and each of said intake valves (2) is inclined relative to the axis of the corresponding cylinder (1) so that an upper portion of said intake valve (2) is tipped away from the axis of the cylinder (1). A Diesel engine according to claim 4, characterized in that said first camshaft (4) is arranged above said intake valve (2) so as to intersect an axis of said intake valve (2), wherein said intake valve (2) is driven via a valve lifter (14) slidably inserted into said cylinder head (10) and said second camshaft (5) is arranged above said exhaust valve (3) beside an axis of said exhaust valve (3), wherein said exhaust valve (3) is driven via a rocker arm (15). A Diesel engine according to one of the preceding claims, characterized in that fuel injectors (23) are provided for each of said precombustion chambers (21) and arranged between said first camshaft (4) and said second camshaft (5). A Diesel engine according to claim 6, characterized in that each of said precombustion chambers (21) and fuel injectors (23) is surrounded by a cooling water passage (25). A Diesel engine according to any of the preceding claims, characterized in that said cylinder head (10) is fixed to a cylinder block (8) by a plurality of head bolts (26) and a pair of said head bolts (26) is arranged symmetrically with respect to the longitudinal axis of the engine on each side of each precombustion chamber (21). A Diesel engine according to any of the preceding claims, characterized in that said first camshaft (4) has a gear (6) fixed thereto and said second camshaft (5) has a gear (7) fixed thereto and in mesh with the gear (6) of said first camshaft (4).

Inventors: NAGAOSA HIDEO, NAKAMURA NORIHIKO, UENO MAKOTO, NAGAOSA, HIDEO, NAKAMURA, NORIHIKO, UENO, MAKOTO
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1990
Main classification: F02B19
IPC codes: F01L1, H04M1, F02B3, F02B19, F02M61, F02F1, F01L3, F02B25