COMBUSTION CHAMBER STRUCTURE IN AN INTERNAL COMBUSTION ENGINE

Abstract: A combustion chamber structure in a direct injection internal combustion engine, in which the exhaust valve (28) is provided over the upper surface of the piston (12) and partially overlaps a cavity (14) in the upper surface of the piston (12) in order to provide a good air utilization factor in the combustion chamber, and a superior combustion effi­ ciency. The exhaust valve (28) also may be positioned so as to form an auxiliary combustion chamber (30). A recess (24) may be formed in an upper position of the piston (12) facing the exhaust valve (28).

Description: This invention relates to a combustion chamber structure in a direct injection type internal combustion engine according to the preamble of the main claim. In such an engine, a substantially spherical cavity is formed in an upper surface of each piston. The opening of the cavity is made smaller in area than the bottom qf the cavity, to increase the speed of a swirl stream therein, and to positively utilize a squishing action to improve combustion efficiency. In such a combustion chamber structure, in order to increase the degree of utilization of the air at the periphery of the cavity while using an injection valve, such as a pintle valve, outwardlv-osening valve or swirl valve, which sprays widely, it is preferable that the cavity opening be reduced in area, and that the injection position be as far from the cavity center as possible but not so far that the spray strikes the wall of the cavity. For this purpose, the cavity opening has a spray relief. If the engine is disassembled after a certain period of operation , then (as shown in Figure 9) high-temperature-gas strike marks can be observed on a shaded portion of the upper surface of the piston P, which is located downstream of the injection position in the direction of the swirl stream in the cylinder and on a lower part of the cylinder head (not shown) which faces this shaded portion, while accumulated soot can be observed on other parts. That is, the partly-burned gas leaks into the narrow piston top clearance relatively early during combustion, and is cooled so as to form a soot cloud. Combustion ceases in the space above the piston, and accordingly the air utilization factor in that space is low. Accordingly, in a direct injection type diesel engine, the space above the piston should be made small in order to maximize the cavity volume and the compression ratio; however, machining accuracy limits the amount that this space may be reduced. If, bcwever,in a direct injection type internal combustion engine, if this space is decreased in size, the exhaust valve and the piston may interfere with each other, so that valve stamping may occur during operation. Also in an engine of the type that fuel spray from a fuel injection nozzle is caused to strike against the wall of the combustion chamber thereby to form a fuel film on the wall, or in an engine in which the cavity opening is not reduced in area, the unburned or partly-burned gas leaks onto the upper surface of the piston and is cooled there, so that the combustion is stopped, thus forming soot and hydrocarbons. In general, in a swirl chamber type diesel engine, in order to accelerat combustion in the main combustion chamber a recess substantially in the form of a clover is formed in the piston upper surface immediately below the communication channel. In view of the foregoing, an object of this invention is to pro vide a combustion chamber structure in an internal combustion engine in which combustion of unburned or partially-burned gas which leaks out to the cavity in the upper surface of the piston is positively accelerated, thereby reducing the amount of soot and hydrocarbons in the exhaust gas, improving combustion efficiency, and providing high power. This object is solved by the combustion chamber structure according to the main claim. Further advantageous features of the combustion chamber structure are evident from the subclaims. The invention is especially useful for direct injection type internal combustion engines using single-hole type injection nozzles. According to the invention, a combustion chamber structure in an internal combustion engine is provided which comprises a cylinder block forming a cylinder chamber; a cylinder head mounted on the cylinder block; a piston which is reciprocated in the cylinder chamber and forms a combustion chamber between the upper surface of the piston and the cylinder head; a generally spherical cavity formed in an upper surface of the piston; an intake system provided in the cylinder head, for forming an intake air swirl stream in the combustion chamber; an exhaust system provided in the cylinder head, for discharging exhaust gas from the combustion chamber through an exhaust valve; and an injection nozzle mounted on the cylinder head so that the injection hole thereof confronts the opening of the cavity, to spray fuel along the swirl stream in the cavity, the hightemperature exhaust valve being positioned to overlap the cavity on the upper surface of the piston for promoting the burning of unburned gas which leaks out of the cavity. The provision of the exhaust valve in this manner enables the thermal retention of the unburned or partly-burned gas which leaks out of the cavity, thus improving the air utilization factor of the piston top clearance to allow the exhaust gas to burn completely. Thus, combustion efficiency is increased, and the amount of exhaust gas is decreased. In a preferred embodiment of the invention, there is further provided an auxiliary combustion chamber which is defined between said combustion chamber and a lower surface of said exhaust valve. In another preferred embodiment of the invention, a recess is formed in the upper surface of the piston so as to face the exhause valve. The invention will be described below in detail with reference to the accompanying drawings, in which: Fig. 1 is a diagram of a combustion chamber in an internal combustion engine, as viewed along an axis of the piston, according to a first embodiment of this invention; Fig. 2 is a perspective view, with parts cut away, showing the positional relationship between the upper surface of the piston and an exhaust valve; Fig. 3 is a perspective view of the exhaust valve is viewed from below; Figs. 4 and 5 are a sectional view and a bottom view, respectively, showing the exhaust valve and its relevant components according to a first embodiment of the invention; Fig. 6 is a plan view, as viewed along an axis of the piston, showing the relationship between the exhaust valve and the cavity of an engine; Figs. 7 and 8 are plan views, corresponding to that in Fig. 6, showing the relationships between the exhaust valves and the cavities of other engines; and Fig. 9 is a diagram, as viewed along an axis of the piston, showing soot stuck to a conventional engine. Figs. 1 and 2 show a first embodiment of this invention. A generally spherical cavity 14 is formed in the upper surface of a piston 12 which is moved up and down within a cylinder block 10. The cavity 14 has a spray relief 16 which partially increases the opening area of the cavity 14 as viewed along an axis of the piston 12, and is faced by a fuel injection valve 20 which is secured to a cylinder head 18. The fuel injection valve 20 is so designed that it can spray fuel 22 from its single injection hole through the spray relief 16 into the cavity 14 in such a manner that the fuel spray goes along the swirl stream in the cavity 14. In the upper surface of the piston 12, a recess 24 is formed adjacent to the cavity 14, thus providing an auxiliary combustion chamber. As shown in Fig. 4, an exhaust valve 28 for opening and closing an exhaust port 26 in an exhaust system is provided in the cylinder head 18, in such a manner that it is shifted in the direction of enlargement of the combustion chamber (upwardly in Fig. 4) rather than towards the lower surface of the cylinder head 18, thus forming an auxiliary combustion chamber 30 in a manner similar to the recess 24. The auxiliary combustion chamber 30 has a cut 32 which is wider towards the exhaust valve 28 from the cavity 14, and is used for guiding leaked gas. As shown in Figs. 3 and 5, a cut 34 is formed in the bottom surface of the exhaust valve 28 in such a manner that the cut 34 is aligned with the aforementioned cut 32 while its width and depth are gradually increased, from the side adjacent to the cut 32 towards its other end. As is apparent from Fig. 1, the exhaust valve 28 is disposed in such a manner that it partially overlaps the cavity 14 as viewed along an axis of the piston 12. The exhaust valve 28 also overlies the recess 24 forming the one auxiliary combustion chamber provided on one side of the cavity 14 such that on the opposite side of the recess 24 the exhaust valve is provided. The intake valve 38 is adapted to open and close the intake port 36 which is a part of the suction system and forms the swirling air stream in the combustion chamber. During engine operation, whenever the piston 12 is moved upwardly, the fuel injection valve 20 jets fuel 22 into the cavity 14. At the same time, the air is compressed and the gas temperature in the combustion chamber is increased, as a result of which the fuel 22 thus jetted is ignited, combusted, and exploded. When the piston 12 is moved downwardly during combustion, burned and unburned gas begins to leak onto the upper surface of the piston from the cavity 14. The exhaust valve 28 is located near the cavity 14, so that the gas streaming from the cavity 14 to the exhaust valve 28 is maintained hot by the high temperature exhaust valve 28 and its atmospheric temperature. Therefore, combustion is complete, and the unburned gas, having its combustion accelerated, is discharged through the exhaust port 26. Combustion is further accelerated by means of the recess 24 and the auxiliary chamber 30. When the unburned or partly-burned fuel which leaks from the cavity 14 onto the upper surface of the piston 12 relatively early during combustion in the combustion chamber comes near the exhaust valve 28 at high temperature, combustion is accelerated, in order to achieve complete combustion. In other words, the air on the upper surface of the piston 12 is fully utilized. This eliminates the need for the conventional means for improving the air utilization factor, and the conventional method for increasing the volume ratio of the cavity 14 and decreasing the space between the top surface of the piston 12 and the lower surface of the cylinder head 18. Therefore, the amounts of soot and hydrocarbons (HC) which are created and discharged when the leaked gas is cooled or unburned in the clearance of the piston are decreased, so that power and fuel economy are enhanced. Furthermore, combustion efficiency is improved, and valve stamping by the exhaust valve 28 or the piston 12 is prevented, so that the space may be provided with a lower accuracy. Therefore, assembly is easier, and the machining cost is relatively low. If the space is the same as in the conventional structure, then the volume ratio of the piston 12 can be large, the air utilization factor is increased, and the combustion in the top clearance is carried out mainly in the auxiliary combustion chamber 30 and collectively in the recess 24. Therefore, oxygen is supplied to the recess 24 and the auxiliary combustion chamber 30 with the aid of the swirl stream therein, and the air utilization factor is further increased. In this case, the compression ration is scarcely decreased, so that the starting characteristic is maintained substantially unchanged, and engine performance is scarcely lowered during warm-up. In Fig. 6, reference character A designates a point where the fuel 22 strikes the wall of the cavity 14; L1, a line connecting the center 0 of the cavity 14 and the point A as viewed along an axis of the piston 12; and L2, a line extending radially from the cavity center 0 in such a manner that the line Lz is downstream of the swirl stream and forms an angle of 1300 with the line L1. In an engine in which as shown in Fig. 6, the cavity 14 has no recess 16, and the fuel 22 from the fuel injection valve 20 strikes the wall of the cavity 14, it is preferable that, when the rated speed is abut 4,000 rpm, the exhaust valve be positioned in a range of about 1300 from the position where the exhaust valve contacts the line L1 from the downstream side of the swirl stream, which extends, as shown.in the Figure, to the position where the exhaust valve contacts the line L2 from the downstream side of the swirl stream. In an engine in which as shown in Fig. 7, the cavity 14 has no recess 16, and the fuel 22 from the fuel injection valve 20 does not strike the wall of the cavity 14, it is desirable that the exhaust valve 28 is positioned in a range of about 30 from the position where the exhaust valve contacts a line L3 from the downstream side of the swirl stream, which extends, as shown in the Figure, to the position where the exhaust valve contacts a line L4 from the downstream side of the swirl stream. The line connects the center 0 of the cavity 14 and the fuel injection hole of the fuel injection valve 20. The line L4 is extended from the center 0 of the cavity 14 and forms an angle of 30 with the line L3. In an engine such as in the first embodiment, in which, as shown in Fig. 8, the cavity 14 has a recess 16, and the fuel 22 from the fuel injection valve 20 does not strike the wall of the cavity 14, similarly as in the case of the above-described engine, it is desirable that the exhaust valve is positioned in a range of about 30 downstream of the fuel injection hole of the fuel injection valve 20.

Claims: Claims 1. A combustion chamber structure in a direct injection type internal combustion engine, comprising a cylinder block (10) having a cylinder chamber formed therein; a cylinder head (18) mounted on the cylinder block (10); a- piston (12) which reciprocates within said clyinder chamber and forms a combustion chamber between an upper surface of said piston (12) and a lower surface of said cylinder head (18); said upper surface of said piston (12) having a substantially spherical cavity (14) formed therein; intake means (36, 38) provided in said cylinder head, (18) for forming an intake air swirl stream in said combustion chamber; ; exhaust means (26, 28) provided in said cylinder head (18) and an injection nozzle (20) mounted on said cylinder head (18) to spray fuel along the swirl stream in said cavity (14), said structure c h a r a c t e r i z e d i n t h a t said exhaust means (26, 28) includes an exhaust valve (28) for discharging exhaust gas from said combustion chamber, said exhaust valve (28) being positioned to overlap partially said cavity (14) for promoting the burning of unburned gas which leaks out of said cavity (14). 2. A combustion chamber structure as claimed in claim 1, further comprising an auxiliary combustion chamber (30) which is defined between said combustion chamber and a lower surface of said exhaust valve (28). 3. A combustion chamber structure as claimed in claim 1 or 2, wherein a recess (24) is formed in said upper surface of said piston (12) adjacent to said cavity (14) so as to face said exhaust valve (28), said recess (24) forming an auxiliary combustion chamber. 4. A combustion chamber structure as claimed in claim 3, wherein a spray relief (16) is provided between said cavity (14) and said injection nozzle (20) and upstream of said recess (24) in the direction of the swirl stream therein. 5. A combustion chamber structure as claimed in claim 1, wherein said injection nozzle (20) is of a type which sprays fuel against a wall of said cavity. 6. A combustion chamber structure as claimed in claim 5, wherein said exhaust valve (28) is positioned within 1300 from a point (A) where the fuel strikes the wall of said cavity downstream of said injection nozzle (20) in the direction of said swirl stream. 7. A combustion chamber structure as claimed in claim 1, wherein said injection nozzle (20) is of a type which sprays fuel in a manner not to impinge on a wall of said cavity (Fig. 7). 8. A combustion chamber structure as claimed in claim 7, wherein said exhaust valve (28) is positioned within 300 from a hole of said injection nozzle (20) downstream thereof in the direction of said swirl stream. 9. A combustion chamber structure as claimed in claim 4, wherein said injection nozzle (20) is of a type which sprays fuel in a manner not to impinge on a wall of said cavity (Fig. 8). 10. A combustion chamber structure as claimed in claim 9, wherein said exhaust valve (28) is positioned within 30 from a hole ofsaid injection nozzle (20) downstream thereof in the direction of said swirl stream.

Inventors: AOYAMA, TARO, MIZUTA, JUNICHI, SUNAMI, KIYOKAZU
Applicants: KABUSHIKI KAISHA TOYOTA CHUO KENKYUSHO
Application year: 1985
Main classification: F02B23
IPC codes: F02B23, F02B3