A FORCEDLY AIR-COOLED ENGINE

Abstract: In a forcedly air-cooled engine (1) a local high temperature portion (16) is adapted to be cooled effectively so that thermal distortion and thermal breakage of a cylinder (24) and/or a cylinder head (3) caused by such a local high temperature can be avoided. As the means for preventing thermal distortion, there is provided a cylinder jacket (17) for cooling part of its cylinder (24), provided in a partition wall (16) between the cylinder and its push rod chamber (18). As the means for preventing thermal distortion of the cylinder head (3), there is provided a cooling air passage (37) in a cylinder head (3) and a head jacket (33) for oil cooling around a divided combustion chamber (28) so as to circulate oil through the head jacket (33). Local high temperature portions of the cylinder and/or the cylinder head can thereby be effectively cooled.

Description: The invention relates to air-cooled engines in which a main combustion chamber is formed by the engine cylinder and a separate combustion chamber in communication with the main combustion chamber formed in the cylinder head of the engine. JP-A-54 32085 discloses an air-cooled internal combustion engine having a main combustion chamber in the engine cylinder and a separate combustion chamber in the cylinder head in communication with the main combustion chamber. The cylinder head has a cooling air passage and a hot region of the cylinder head adjacent the combustion chamber is further cooled by oil flowing through an oil passageway in the cylinder head. DE-OS-1751407 also discloses an air-cooled internal combustion engine having a cooling air passage in the cylinder head and a hot region in the cylinder head adjacent the valve seats oil-cooled by means of an oil passage in the cylinder head. Considering an engine as defined by JP-A-5432085 as representing the closest prior art, the object of the present invention is to provide an arrangement which achieves efficient cooling of an engine having a main combustion chamber in the engine cylinder and a separate combustion chamber in the cylinder head whilst limiting the overall size of the engine. This invention provides an air-cooled engine having front and rear ends, a cylinder head secured on a cylinder block to provide a main combustion chamber in the engine cylinder and a separate combustion chamber in the cylinder head in communication with the main combustion chamber through a narrow passage, the cylinder head having valve controlled inlet and outlet ports spaced apart in the fore and aft direction of the engine, a coolant passage extending through the head past the separate combustion chamber, means to circulate oil through the coolant passage in the cylinder head and an oil cooler for cooling the oil, an air passage through the cylinder head and a cooling fan at the front end of the engine for circulating cooling air over the engine including through the air passage: wherein the separate combustion chamber is formed on one lateral side of the cylinder head with respect to the fore and aft direction of the engine and the valve controlled inlet and outlet ports are formed on the other lateral side of the cylinder head; in that the cylinder head is formed with a coolant jacket to which the coolant passage is connected, the jacket encircling the separate combustion chamber over a substantial proportion of the chamber to cool the chamber through the flow of coolant oil from the coolant passage through the jacket around the chamber; and in that the cooling air passage formed in the cylinder head extends in the fore and aft direction through said other lateral side of the cylinder head, the passage receiving air from the cooling fan at the front end of the engine to provide air cooling for the part of the cylinder head through which the air passage extends. Preferably the coolant passage is formed in a lower part of the cylinder head, and the cooling air passage is formed in an upper part thereof. Since the major part of the cylinder and/or the cylinder head is/are adapted to be cooled by a forced air-cooling system while a local high temperature portion of the cylinder head is cooled by the oil, it is possible to make the amount of oil relatively less as well as to accomplish the reduction of the size as well as of the weight of the engine. There now follows a description of specific embodiments of the invention, by way of example, with reference to and as illustrated in the accompanying drawings in which: Figure 1 is a vertical sectional back view showing a head block and a cylinder block of an overhead-valve and divided chamber type forcedly air-cooled vertical diesel engine applied to by one embodiment of the present invention; Figure 2 is a back view of said engine; Figure 3 is a horizontal sectional view on line A-A in Fig. 1; Figure 4 is a plan view showing the cylinder block of said engine; Figure 5 is a vertical sectional side view of said engine; Figure 6 is a vertical sectional view showing the principal part of an overhead-valve and divided chamber type forcedly air-cooled vertical diesel engine applied to by the first variant of the present invention; Figure 7 is a horizontal sectional plan view showing the cylinder head of said engine; As shown in Figs. 1 through 5, an overhead-valve and divided chamber type forcedly air-cooled vertical engine includes a crankcase 1 integratedly formed by means of casting of aluminium alloy and a cylinder block 2, on which a cylinder head 3 made of aluminum alloy is secured. Within the crankcase, a crank shaft 4, a balancer shaft 5 and a valve actuating cam shaft 6 are rotatably supported. The crank shaft 4 has the front end portion 4a projected forwardly out of the crankcase 1. A cooling fan 7 is fixedly secured to the front end portion 4a of the crank shaft 4. The cooling fan 7 and the front end surface are covered with an air guide case 8. Ambient air is sucked by the cooling fan 7 through the suction opening 9 provided at the front portion of the case 8, and sucked air is guided by the case 8 and supplied as cooling air to the cylinder block 2 and a cylinder head 3. A forced lubrication system 50 comprises an oil pump 10, an oil strainer 13, a lubricating oil supply line 14 and so on. In the back wall 1a of the crankcase 1 there is provided the oil pump 10 of a trocoid type. The oil pump 10 is adapted to be driven by the crank shaft 4 through gear means 11 so as to suck the crank shaft oil through the oil strainer 13 from the oil pan 12 provided in the bottom portion of the crankcase 1 and supply the lubricating oil to every portion required for lubrication in the engine through the supply line 14 formed within the crank shaft 4 and so on. From the lubricating oil supply line 14, a cooling oil service passage 15 is branched off so as to lead to a lower portion of one side of the cylinder block 2 through within the back wall 1a of the crankcase 1. Within the back side wall of the cylinder block 2, there is provided a push rod chamber 18 arranged vertically in parallel with the cylinder 24. In the partition wall 16 between the push rod chamber 18 and the cylinder 24, there is provided a cylinder jacket 17 for cooling part of the cylinder, which cylinder jacket 17 is vertically extended so as to have an opening at the upper end surface of the cylinder block 2. The inlet 17a of the cylinder jacket 17 is in communication with the cooling oil service passage 15 which leads to the delivery port 51 of the oil pump 10 through a relief valve 19. In this case, as shown in Fig. 4, the arcuate length of the cylinder jacket 17 in the circumferential direction of the cylinder 24 is defined a little shorter than that of the push rod chamber 18. In the push rod chamber 18, there are provided upper portions of a couple of tappets 21 which are reciprocated vertically by the cams 20 secured on the valve actuating cam shaft 6, and push rods 22 which are held in contact with the upper ends of the tappets respectively so as to reciprocate therewith. The push rod chamber 18 has an oil return port 23 formed at the bottom wall thereof which is in communication with the crank chamber 39. Further, in the front portion of the cylinder block 2, there is provided an oil return passage 27 which also serves as a breather passage and connects a rocker-arm chamber 26 within a head cover 25 to a crank chamber 39 within the crankcase 1. In the cylinder head 3 secured on the cylinder block 2, there are provided a divided chamber 28, an intake valve seat 29, an exhaust valve seat 30, an intake port 31 and an exhaust port 32. The divided chamber 28 is disposed eccentrically to the right side (but, to the left side in Fig. 1 and to the lower side in Fig. 3) as well as a little to the back side (but, to the left side in Fig. 3) relative to the center of the cylinder 24 as viewed from the front side of the engine. The intake valve seat 29 and the exhaust valve seat 30 are disposed respectively at the front side and at the back side on the center line defined in relation to the left and the right of the cylinder head 3. The intake port 31 extends from the intake valve seat 29 to the right side surface of the cylinder head 3 across the front of the divided chamber 28, and the exhaust port 32 extends backwards from the exhaust valve seat 30. A head jacket 33 for cooling part of the cylinder head 3 is formed over the range from the beginning end of the exhaust port 32 to the peripheral wall of the intake port 31 and around the divided chamber 28 of the cylinder head 3. An oil passage 34 is formed so as to run from the upper section 53 of the cylinder jacket 17 to the head jacket 33 through the wall 52 between the intake port 31 and the exhaust port 32. That is, the outlet 17b is connected in communication with the head jacket 33. In this case, it is important that the head jacket 33 for cooling part of the cylinder head is provided in a hot portion heated to a high temperature in the cylinder head 3. As the hot portions of the head block, may be mentioned, for example an exhaust valve seat, a peripheral wall of the exhaust port, a peripheral wall of a divided chamber and so on as described above, which are apt to be exposed and heated to a high temperature. Further, said hot portions thereof include ones such as the wall between the intake port and the exhaust port, to which cooling air can hardly get due to the obstruction of other portions and other parts, as well as ones such as a back side of a cylinder and so on, to which fresh cooling air can hardly be supplied and hence which is apt to be heated. To sum up, all the portions which can't be effectively cooled only by a forced air-cooling system and reach a higher temperature than any other ones are included in said hot portions. At the undersurface of the cylinder head 3, there is provided a cooling oil outlet passage 36 caved so as to be in communication with the push rod chamber 18. In oil cooler 35 is disposed at the upper section of the air guide case 8 so as to block it there and has an inlet 35a connected to the outlet 33a of said head jacket 33 and an outlet 35b connected to the inlet 36a of the cooling oil outlet passage 36. The oil cooler 35 is adapted to be cooled by a portion of cooling air supplied by the cooling fan 7 and guided by the air guide case 8. In case that the head jacket 33 is sufficiently supplied with much oil to restrict the temperature rise thereof to a relatively small extent, or the total amount of lubricating oil is much enough to cool down the heated lubricating oil soon after mixing with other portion thereof, the oil cooler 35 may be omitted because the thermal deterioration of said lubricating oil can be prevented effectively for long time. On the other hand, at the other portions except the head jacket 33 in the cylinder head 3, there is provided a cooling air passage 37 for passing the cooling air therethrough. The cooling air passage 37 is so provided between the push rod chamber 18 and both peripheral walls of the intake port 31 and the exhaust port 32 that the cooling air is supplied thereto under the guidance of the air guide case 8 so as to come in contact with said both peripheral walls during its flowing backwards therethrough. Further, as shown in Fig. 1 the cooling air passage 37 is formed so as to run lengthwise and also parallel with the oil passage 34 at the upper side of the cylinder head 3, which oil passage 34 runs transversely at the lower side of the cylinder head 3. Fins 150 are provided around the cylinder 24 so as to receive cooling air flows from the fan 7, thereby enhancing the cooling of cylinder 24. Now the functions of the overhead valve type forcedly air-cooled engine will be described hereinafter. (1) Though the cylinder head 3 and the cylinder block 2 are adapted to be forcedly cooled by the cooling air supplied by the cooling fan 7 and guided by the air guide case 8, the thick partition wall 16 between the push rod chamber 18 and the cylinder 24 are apt to suffer heat accumulation because it is remote from the inner surface of the cylinder 24 as well as from the outer surface of the cylinder block 2. Further, since the partition wall 16 is spaced from the cooling air passage 37 by the push rod chamber 18, it cannot be cooled by the cooling air. Therefore, since the partition wall 16 makes hot portion substantially under such cooling system comprising only the forced air-cooling system, the temperature distribution in the circumferential direction of the cylinder 24 becomes uneven. However, the temperature rising in the partition wall 16 can be prevented by cooling it with the lubricating oil. That is, the lubricating oil in the oil pan 12 is delivered by the lubricating pump 10, after being filtered by the strainer 13, to every portion required for lubrication in the engine through the lubricating oil supply line 14 and to the partition wall 16 through the cooling oil service passage 15 and the relief valve 19 as a spilled out portion of the lubricating oil therefrom. The lubricating oil which flows into the cylinder jacket 17 provided in the partition wall 16 for cooling part of the cylinder serves to absorb the heat accumulated around the partition wall 16 as part of the cylinder 24 so as to effect the cooling for it. Thus, the temperature rising in the partition wall 16 is prevented and then the temperature distribution in the cylinder 24 is kept even substantially in the circumferential direction thereof by the absorption of the heat accumulated in the partition wall 16 as described above. Further the generation of thermal distortion in the cylinder block 2 as well as the decreases of engine power and engine durability by such thermal distortion are prevented. Although the lubricating oil spilled out of the relief valve 19 at a predetermined pressure is adapted to flow into the cylinder jacket 17 in this embodiment, the relief valve 19 may be omitted so that the lubricating oil can flow thereinto directly from the cooling oil supply line 15. (2) The lubricating oil supplied from the cylinder jacket 17 to the head jacket 33 through the oil passage 34 serves to absorb the heat around the peripheral wall of the divided chamber 28 and the thick wall between the intake port 31 and the exhaust port 32 during passing through the oil passage 34 and the head jacket 33 so as to prevent the temperature rising in these portions as parts of the cylinder head 3 and also to cool intake air through the perihperal wall of the intake port 31. Therefore, the thermal distribution in the cylinder head 3 is evened up so that the generation of thermal distortion in the cylinder head 3 and the decreases of engine power and engine durability by such thermal distortion can be prevented effectively and also the charging efficiency for intake air can be enhanced. (3) Further, in the divided chamber type forcedly air-cooled engine, by the circulation of the oil through the head jacket 33 which is formed only around the divided chamber 28, the peripheral portion around the divided chamber 28, which is apt to be heated to a high temperature, is cooled effectively. Since the peripheral portion of the divided combustion chamber is cooled by oil even though the other sections of the cylinder head 3 are subjected to air cooling, the overcooling of the peripheral portion is prevented. Accordingly, since the overcooling of the peripheral portion of the divided combustion chamber is avoided, at the cold start of the engine in a cold season, the warming-up time can be shortened. In the conventional embodiment wherein the whole of the cylinder head 3 is to be oil-cooled, the cooling oil cannot cool the intake support 31 sufficiently during the normal operation. In the present invention only the peripheral portion of the divided chamber 28 in the cylinder head 3 is oil-cooled and the intake port 31 is cooled intensively by the cooling air flow generated by the cooling fan 7 as a separate cooling means independent of the oil cooling system so that the charging efficiency for intake air is more improved and the engine output power is increased. (4) Moreover, in the case of using lubricating oil as the cooling oil, since the lubricating oil is adapted to be fed to the oil cooler 35 soon after being heated in the head jacket 33 and returned to the oil pan 12 after being cooled well in the oil cooler 35, the temperature of the lubricating oil in the oil pan is kept low enough to prevent its deterioration for a long time. (5) Since the cylinder jacket 17 for cooling part of the cylinder is formed in the partition wall 16 and the head jacket 33 for cooling part of the cylinder head is formed only around the periphery of the divided chamber 28, the necessary amount of the oil for cooling can be lessened so that the reduction of the engine dimension is facilitated by making the capacity of the oil pan 12 smaller. Further, since the lubricating oil serves to cool only parts of the cylinder block 2 and the cylinder head 3 respectively, the heat quantity absorbed during such cooling gets less in this cooling system than in the cooling system wherein the wholes thereof are oil-cooled, so that the reduction of the oil cooler dimension is facilitated by reducing the capacity of the oil cooler 35. (6) It is possible to provide a cooling oil system which might include the oil pump 10, the cylinder jacket 17, the head jacket 33 and the oil cooler 35 independently of the forced lubrication system 50 for the engine, whereas in this embodiment the oil pump 10 in the forced lubrication system 50 is adapted to serve as an oil pump for a cooling oil system in order to make use of the engine lubricating oil for cooling parts of the cylinder block 2 and the cylinder head 3. Therefore, the whole structure of the engine 1 can be simplified in this case. (7) Since the oil passage 34 is formed at the lower side of the cylinder head 3 and the cooling air passage 37 is provided at the upper side thereof, the cross section of the cooling air passage can be enlarged to maintain good cooling performance. (8) Since the core for forming the head jacket 33 is required to be located only around the divided chamber 28, the core supporting and the removal of sands after the completion of casting are carried out readily. Consequently the head jacket 33 is formed readily by casting. Fig. 6 and Fig. 7 show the first variant embodiment of the present invention. In the above-mentioned embodiment, the upper end portion of the partition wall 16 between the cylinder 24 and the push rod chamber 18 is cut out so that the lubricating oil can partially overflow from the cylinder jacket 17 to the push rod chamber 18 thereover, whereas in this embodiment there is not provided such cut out portion in the partition wall 16 so that all the lubricating oil supplied to the cylinder jacket 17 is adapted to flow into the oil passage 34. And the head jacket 33 for cooling part of the cylinder head 3 has an inlet 33a connected with the oil passage 34 at the lower side thereof and an outlet 33b opened at the upper portion thereof. In this construction, since the flowing direction of the lubricating oil within the head jacket 33 is the same as that of the natural convection therewithin, the flow resistance of the lubricating oil in the head jacket 33 is reduced so that the load for the oil pump 10 can be reduced. Further, since the lubricating oil is adapted to move up to the upper side in the head jacket 33 and flow out smoothly therefrom through the outlet 33b due to its temperature rising, the hot lubricating oil does not remain within the head jacket 33. Accordingly, the cooling effect of the lubricating oil for the head jacket 33 is not adversely affected by remaining of the hot lucricating oil and consequently more effective cooling for the divided chamber 28 is carried out. Cooling fins 150 are provided around the cylinder 24 to enhance the air-cooling of cylinder 24.

Claims: An air-cooled engine having front and rear ends, a cylinder head (3) secured on a cylinder block (2) to provide a main combustion chamber in the engine cylinder and a separate combustion chamber (28) in the cylinder head in communication with the main combustion chamber through a narrow passage, the cylinder head having valve controlled inlet and outlet ports (29, 30) spaced apart in the fore and aft direction of the engine, a coolant passage (34) extending through the head past the separate combustion chamber, means to circulate oil through the coolant passage in the cylinder head and an oil cooler (35) for cooling the oil, an air passage (37) through the cylinder head and a cooling fan (7) at the front end of the engine for circulating cooling air over the engine including through the air passage: characterised in that the separate combustion chamber (28) is formed on one lateral side of the cylinder head (3) with respect to the fore and aft direction of the engine and the valve controlled inlet and outlet ports (29, 30) are formed on the other lateral side of the cylinder head; in that the cylinder head is formed with a coolant jacket (33) to which the coolant passage is connected, the jacket encircling the separate combustion chamber over a substantial proportion of the chamber to cool the chamber through the flow of coolant oil from the coolant passage through the jacket around the chamber; and in that the cooling air passage (37) formed in the cylinder head extends in the fore and aft direction through said other lateral side of the cylinder head, the passage receiving air from the cooling fan at the front end of the engine to provide air cooling for the part of the cylinder head through which the air passage extends. An engine as claimed in Claim 1, characterised in that the coolant passage (34) is formed in a lower part of the cylinder head (3), and the cooling air passage (37) is formed in an upper part thereof.

Inventors: NISHIDA, TSUYOSHI, YAMADA, KIICHIRO, NISHIDA, TSUYOSHI, C/O KUBOTA LIMITED, YAMADA, KIICHIRO, C/O KUBOTA LIMITED
Applicants: KUBOTA LTD.
Application year: 1987
Main classification: F01P1
IPC codes: F01P3, F01P1, F01P9