PARTIALLY LIQUID-COOLING TYPE FORCEDLY AIR-COOLING SYSTEM FOR INTERNAL COMBUSTION ENGINE

Abstract: In a partially liquid-cooling type forcedly air-cooling system for an internal combustion engine which includes an air-cooled cylinder (4) and a liquid-cooled cylinder head (5), a centrifugal cooling fan (11) is provided in front of a crankcase (3) so as to rotate about the fore and rear axis thereof, and a cooling air delivery opening (29) is provided at the back portion (28) of a draft chamber (27) within a fan casing (24) which encircles the cooling fan (11) so as to orientate at least to the cylinder (4). And a portion (26), which is arranged at the side of the cylinder head (5), of the encircling wall (25) of the fan casing (24) is provided with an opening (38). And the cylinder (4) is adapted to be cooled adequately by the cooling air flow delivered through the opening (29), as well as a radiator (36) is adapted to be cooled effectively by the cooling air flow passing through the opening (38) provided in the encircling wall (25) of the fan casing (24) so that at least a portion of the cylinder head (5) can be cooled intensively.

Description: The present invention relates to a partially liquid-cooling type forcedly air-cooling system for an internal combustion engine, wherein at least a high temperature portion of a cylinder head is adapted to be cooled by means of cooling liquid. Generally, in a cooling system for an internal combustion engine, there are three kinds of systems, namely of an air-cooling type, of a liquid-cooling type and of a combination type comprising these air-cooling and liquid-cooling systems. An air-cooled internal combustion engine has such an advantage as being constructed simply and compactly because a delivery pump for cooling liquid and a radiator therefor are unnecessary therein. But, in a different aspect, since a cylinder head thereof tends to be heated excessively due to its relatively high thermal load, an enhancement of output of such an engine is limited by contraries. On the other hand, a liquid-cooled internal combustion engine has such an advantage that an enhancement of output thereof becomes possible owing to its intensive cooling system. But, in a different aspect, since the engine requires a delivery pump for cooling liquid and a radiator for such an intensive cooling, it becomes complicated and large in construction inevitably ( for example, refer to GB-A-2,127,487 ). And a partially liquid-cooled internal combustion engine has such an advantage that a cooling system can be reduced in size totally due to a decreased load in a liquid-cooling apparatus and also due to the accomplishment of a small-scale radiator and a reduced quantity of circulating cooling liquid because a cylinder subjected to a relatively small thermal load is cooled by means of cooling air and at least a portion of a cylinder head subjected to a high thermal load is cooled by means of cooling liquid. As for such a conventional partially liquid-cooling type forcedly air-cooling system, have been known the following ones. (1) Conventional Embodiment-1 ( JP-U-1959-18309) This cooling system comprises a centrifugal cooling fan disposed at the front side of the engine body of the vertical internal combustion engine so as to rotate about a fore and rear longitudinal axis thereof, a rectangular prism-shaped fan casing arranged so as to cover the cooling fan and the front sides of a cylinder and a cylinder head, a radiator located at an upper corner of the interior within the fan casing, and a cooling air guide casing extended backward from the fan casing throughout the cylinder and the cylinder head. And the radiator is adapted to be cooled by the cooling air flow passing through the fan casing, and the cylinder and the cylinder head are adapted to be cooled by the cooling air flow passing through the guide casing. However, there is a following disadvantage associated with the conventional embodiment-1. (a) The radiator gets larger in size. Since the cooling air flow delivered from the cooling fan to the radiator is apt to impinge to the upper wall of the fan casing at right angles therewith, a stagnation is presented in the space for the location of the radiator. Further, since the cooling air flow passing through the space for the location of the radiator is hindered by the cylinder head disposed at the lower reaches thereof, an air flow resistance gets increased. In this way, as the space of the location of the radiator has such a stagnation of the cooling air flow and the flow resistance gets increased, the flow of cooling air supplied to the radiator gets decreased. As the result, the heat quantity per unit area radiated from the radiator can't help decreasing, and the radiator gets larger in size correspondingly. (2) Conventional Embodiment-2 ( JP-U-1979-32085 ) This cooling system comprises an axial flow fan ( a cooling fan ) arranged aside at the front position of an engine body of a vertical internal combustion engine, a cooling air guide casing extended in the fore and rear direction from the location of the axial flow fan toward a cylinder and a cylinder head, and a radiator arranged within a space provided laterally outside of the cylinder head as well as in the cooling air guide casing in such a manner as extending in the fore and rear direction thereof. And the radiator is adapted to be cooled by means of cooling air flowing obliquely backward within the cooling air guide casing, as well as the cylinder and the cylinder head are adapted to be cooled by means of cooling air flow of which course is diverted transversely thereof. However, there is a number of following disadvantages associated with the conventional embodiment-2. (b) The external size of the internal combustion engine gets larger. Since the axial flow fan and the cooling air guide casing project laterally outside of the engine body, the external size of the internal combustion gets larger. (c) A transmission arrangement for driving the cooling fan is complicated. Since the axial flow fan as a cooling fan is disposed aside at the front side of the engine body, a complicated transmission arrangement is required for interlockingly connecting the input shaft of the axial flow fan to the crankshaft beared in the engine body. (d) The radiator gets larger in size. Since the cooling air flows obliquely backward relative to the radiator which is so arranged to extend in the fore and rear direction, the flow of cooling air supplied to the radiator gets uneven along its length inevitably. Further, the total quantity of cooling air passing by the radiator gets decreased because the cylinder head located at the lower reaches thereof serves to hinder the passing of cooling air flow as a large flow resistance. In this way, as the flow of cooling air is supplied to the radiator unevenly and in a small quantity, the heat exchanging efficiency of the radiator cant' help getting worse as a whole and as a result a large-sized radiator gets necessary owing to a small quantity of radiation heat per unit area. (e) The cylinder head and the cylinder are cooled under an unbalanced condition. Since the flow of cooling air supplied to the radiator is hindered by the radiator located at the upper reaches thereof and to the contrary a large quantity of cooling air is supplied to the cylinder due to a small flow resistance prevailing at the upper reaches thereof, the cylinder head is apt to be heated excessively by its large thermal load and the cylinder subjected to a comparatively small thermal load is apt to be cooled excessively. Either of the coolings is unbalanced. As a result, the cylinder head tends to cause a sticking trouble as well as to bring in a bad combustion performance. By the way, besides above-mentioned embodiments, the inventor of the present invention will mention another cooling system wherein there is provided a cooling air discharge hole in the cooling air guide casing projected laterally outside of the engine body and a radiator is disposed so as to cover the discharge hole, but which has a following disadvantage. (f) Since the radiator is located at a lateral outside of the cooling air guide casing projected laterally outside of the engine body, the external size of the internal combustion engine gets further larger. The present invention is directed to solving the problems noted above, and has for its object to provide a small-sized high power internal combustion engine in which the external size of the radiator for cooling liquid is reduced, the transmission arrangement for driving the cooling fan is simplified and the good cooling balance is maintained between the cylinder and the cylinder head. For accomplishing above-mentioned object, a partially liquid-cooling type forcedly air-cooling system of the present invention is constructed as follows. That is, the front side of a crankcase of an internal combustion engine of the type including an air-cooled cylinder and a liquid-cooled cylinder head is provided with a centrifugal cooling fan which rotates about the fore and rear longitudinal axis thereof. The back surface of a draft chamber within a fan casing which covers the cooling fan is provided with a cooling air distribution opening at least orientated to the cylinder, as well as the encircling wall of the fan casing is provided with an opening at the side of the cylinder head. And the cylinder is adapted to be cooled adequately by means of cooling air flow delivered through the distribution opening, as well as at least a portion of the cylinder head is adapted to be cooled intensively by cooling the radiator effectively with the cooling air delivered through the opening of the encircling wall of the the fan casing. Accordingly, the present invention attains the following advantages. (a) The radiator for the cooling liquid can be reduced in size. Since the opening for the cooling air delivery and the radiator are provided respectively at the external positions in the diametral direction of the centrifugal cooling fan, the radiator can be supplied with a sufficient quantity of cooling air evenly and powerfully. Further, since at the upper reaches as well as at the lower reaches of the radiator there are no obstacles to the supply of the cooling air toward the radiator, the flow resistance for the cooling air can be restrained within a small degree. Therefore, the whole of the radiator can be supplied with a sufficient quantity of cooling air so as to enhance the heat exchange efficiency thereof. Accordingly, the radiator can be constructed in a small size because of an increased radiation heat quantity per unit area thereof. (b) The external size of the internal combustion engine can be reduced. Since the centrifugal cooling fan is provided at the front location of the crankcase so as to rotate about the fore and rear axis, the fan casing to encircle the cooling fan can be reduced in its extent projecting laterally outside the engine body. Further, since the radiator is arranged at the side of the cylinder head outside the fan casing, it can be accommodated within the rectangular space of the internal combustion engine. As a result, the external size of the engine can be reduced. (c) Since the cooling fan is directly connected to a rotation shaft such as a crankshaft, the transmission means such as a transmission belt, transmission pulleies and so on can be omitted and the transmission arrangement for the cooling fan can be simplified resultantly. (d) A good cooling balance can be maintained between the cylinder and the cylinder head. Since the radiator is cooled sufficiently by the cooling air delivered through the opening while the cylinder is cooled adequately by the cooling air delivered through the distribution opening, the cylinder subjected to a comparatively small thermal load can be prevented from being cooled excessively and the cylinder head subjected to a large thermal load can be cooled intensively. Accordingly, the cylinder and the cylinder head can be cooled under a well-balanced cooling condition so that both the enhancement of the combustion performance and the prevention of the burnt sticking in the cylinder head can be attained simultaneously. By the above-mentioned advantageous features of the items from (a) to (d), the internal combustion engine according to the present invention can have a small-scale construction and a high output power. (e) Additionally, in case that a delivery opening for the cooling fan is provided so as to orientate to the cylinder and the cylinder head as well as the cylinder head is provided with a cooling air passage of which inlet is orientated to the delivery opening of the fan casing, further following advantages can be attained. That is, since the cylinder head is cooled by the cooling air delivered through the delivery opening, a capacity of the radiator can be lessened correspondingly thereto. Hence, a reduction of the radiator size as well as a decrease of the circulation quantity of the cooling liquid can be accomplished, and the size of the cooling system can be reduced as a whole. Figure 1 through Figure 7 show embodiments of the present invention; Figures 1 and 2 show the first embodiment; Figure 1 is a front view showing an internal combustion engine including a fan casing shown in a vertical sectional view; Figure 2 is a vertical sectional side view of the internal combustion engine; Figure 3 is a partial view showing a variant example of the above-mentioned first embodiment; Figures 4 through 6 show the second embodiment; Figure 4 is a view corresponding to Fig.1; Figure 5 is a view corresponding to Fig.2; Figure 6 is a vertical sectional back view of a principal part; and Figure 7 is a partial view showing a variant example of the above-mentioned second embodiment. Figures 1 and 2 show the first embodiment of the present invention. An internal combustion engine 1 is an overhead-valve type direct-injection Diesel engine constructed as follows. An engine body 2 comprises a crankcase 3, a cylinder 4 integrally formed at the upper side thereof, a cylinder head 5 and a rocker cover 6 each of which is arranged in order upwardly. The crankcase 3 is equipped with a crankshaft ( rotation shaft ) 8 supported rotatably at a middle level position thereof in such a state as extending in the fore and rear direction ( in the left and right direction in Fig. 2, the same as this definition hereinafter ). The crankshaft 8 projects outwardly from the front and back opposite walls 9, 10 of the crankcase 3. The back end portion thereof projected from the back wall ( the right side wall ) 10 is formed as an output portion, and the other end portion thereof projected from the front wall ( the left side wall ) 9 has a centrifugal cooling fan 11 fixedly secured thereto. And a piston 13 is fitted vertically sildably into the cylinder 4 and there is provided a combustion chamber 14 above the piston 13. And the cylinder head 5 is provided with an intake port 16 and an exhaust port 17 therein and further equipped with a fuel injector 18. The tip portion of the fuel injection nozzle of the injector 18 is present in the combustion chamber 14 so as to provide a direct-injection type one. And there is provided a valve actuation mechanism 20 within a rocker arm chamber 19 enshrouded by the rocker cover 6. The cooling fan 11 comprises a plurality of vanes 23 which are protruded on the front surface of a flywheel 22 fixed to the front end portion of the crankshaft 8. A fan casing 24 is attached to the engine body 2 in such a manner as encircling the cooling fan 11. The encircling wall 25 of the fan casing 24 has a portion 26 arranged at the side of the cylinder head 5, which is located at the same height as that of the upper end surface of cylinder 4 at the side of the cylinder head 5. In the back wall ( the right side wall in Fig.2 ) 28 of the draft chamber 27 formed within the fan casing 24, there is provided a delivery opening 29 orientated to the cylinder 4. That is, the front end wall of the crankcase 3 is extended transversely outwardly so as to form the back wall 30 of the draft chamber 27, and the back wall 30 is provided with the delivery opening 29 formed by cutting out the upper portion thereof 30. And the cooling air flow delivered through the opening 29 is adapted to come into contact with cooling fins 32 formed on the peripheral wall of the cylinder 4 in order to cool the cylinder 4 adequately. On the one hand, the cylinder head 5 has a liquid-cooling jacket 34 formed substantially throughout therein. The liquid-cooling jacket 34 is adapted to be supplied with a portion of the lubricating oil which is delivered to the cylinder head 5 under pressure by a lubricating oil delivery pump ( omitted in drawings ) from an oil pan 35 in order to lubricate the valve actuation mechanism 20 within the rocker arm chamber 19. The liquid-cooling jacket 34 is connected in communication to a radiator ( an oil-cooler ) 36 arranged above the fan casing 24 so that the lubricating oil passing through the jacket 34 can be cooled by means of the radiator 36 and then returned to the oil pan 35. Further, in the upper wall portion 26 of the encircling wall 25 of the fan casing 24 at the side of the cylinder head 5, there is provided a distribution opening 38 elongated laterally ( in the left and right direction in Fig.1 ). The radiator 36 is arranged so as to cover the outlet of the flow passage 39 of cooling air delivered through the opening 38. And the cooling air flowing along the flow passage 39 is adapted to come into contact with the radiator 36 and cool the radiator 36 sufficiently. In this case, since the radiator 36 also functions as an air flow resistance, the flow of cooling air delivered from the opening 29 to the cylinder 4 is prevented from decreasing extremely. By the way, instead of the cylinder head 5 in which the liquid-cooling jacket 34 is formed substantially throughout therein in this embodiment, may be adopted another cylinder head in which the liquid-cooling jacket 34 is formed only around the injection nozzle of the fuel injector 18 so as to carry out an intensive cooling of a portion subjected to a especially large thermal load. And the delivery opening 29 formed by the cutout at the upper portion of the back wall 30 of the draft chamber 27 may be replaced with another opening of the type comprising the fan casing 24 formed by an air guide plate configured in an annular shape viewing from a back side and the draft chamber 27 opened backward. Figure 3 is a view showing a variant example attained by modifying a portion of the first embodiment as follows. That is, the portion 26 of the encircling wall 2 of the fan casing 24 at the side of cylinder head 5 is formed in an upwardly swelled out state. The radiator 36 is arranged across a cooling air passage directed from the draft chamber 27 to the opening 38 within the swelled out portion 41. Figures 4 through 6 show the second embodiment. Now constructions different from the first embodiment will be explained hereinafter. In this second embodiment, the component parts having the same function as ones in the first embodiment are indicated by the same symbols. In this embodiment, an internal combustion engine 1 is a divided-combustion chamber type Diesel engine. And an upper portion 26 of an encircling wall 25 of a fan casing 24 at the side of cylinder head 5 is located substantially at the same height as that of an upper end surface of a cylinder head 5 at the side of a rocker arm chamber 19. And the back wall ( the right side wall in Fig. 5 ) 28 of a draft chamber 27 formed within the fan casing 24 is provided with a cooling air delivery opening 29 which is orientated to the cylinder 4 and the cylinder head 5. That is, the same as the above-mentioned first embodiment the back wall 30 of the draft chamber 27 is formed by the outward extensions of the front end wall of the crankcase 3, and a cooling air delivery opening 43 for the cylinder 4 is formed by cutting out the upper half of the back wall 30. Further, a cooling air delivery opening 44 for the cylinder head 5 is formed by opening backward the upper portion of the draft chamber 27 within the fan casing 24. These delivery openings 44, 43 for the cylinder and the cylinder head form the delivery opening 29 in combination. Further, as shown in Figures 4 and 6, the cylinder head 5 is provided with a cooling air passage 45 formed at the middle level thereof in such a way as extending in the fore and rear direction so that the inlet of the passage 45 is orientated to the delivery opening 29. And as shown in Fig. 6, the cylinder head 5 is provided with a liquid-cooling jacket 34 formed around the divided-combustion chamber 47. The lubricating oil delivered from a pump omitted in the drawings is adapted to be supplied to the liquid-cooling jacket 34 via a delivery port 48 provided at a lateral portion of the cylinder 4. The lubricating oil gets hot by a heat absorption in the jacket 34. Then it is adapted to be sent to a radiator 36 through its inlet pipe 49 in order to carry out a heat radiation therein and returned to an oil pan 35. And the cooling air flow delivered through the opening 29 is adapted to come into contact with cooling fins 32 formed on the peripheral wall of the cylinder 4 to cool the cylinder 4 adequately as well as to come into contact with the external periphery of the cylinder head 5 and the internal periphery of the cooling air passage 45 to cool the cylinder head 5. In this way, since the cylinder head 5 is cooled effectively by air, the capacity of the radiator 36 can be reduced correspondingly and as a result the radiator can be reduced in size. Figure 7 shows a variant example obtained by modifying a portion of the above-mentioned second embodiment as follows. That is, the portion 26 of the encircling wall 25 of the fan casing 24 at the side of the cylinder head 5 is swelled out upwardly. The radiator 36 is arranged within the swelled out portion 52 across the cooling air passage directed from the draft chamber 27 to the opening 38. By the way, the lubricating oil used as the cooling liquid for the cylinder head 5 in the above-mentioned respective embodiments may be replaced with water or other kinds of liquid. Further, instead of the vertical engine, a horizontal engine may be adopted as for the internal combustion engine.

Claims: A partially liquid-cooling type forcedly air-cooling system in an internal combustion engine, comprising a rotation shaft (8) projecting forwardly from a front wall (9) of a crankcase (3) of said internal combustion engine (1), said rotation shaft (8) having a centrifugal cooling fan (11) fixedly secured thereto in front of the crankcase (3), and said cooling fan (11) being encircled by a fan casing (24), a back portion (28) of a draft chamber (27) formed within said fan casing (24) being provided with a cooling air delivery opening (29) orientated at least to a cylinder (4), a liquid-cooling jacket (34) being formed at least in a portion of a cylinder head (5) so as to be connected in communication to a radiator (36) for a cooling liquid, characterized in that a portion (26), which is arranged at the side of said cylinder head (5) of an encircling wall (25) of said fan casing (24) is provided with an opening (38), and that said radiator (36) is arranged in a cooling air passage (39) passing through said opening (38). The system as claimed in Claim 1, characterized in that said portion (26), which is arranged at the side of the cylinder head (5) of the encircling wall (25) of the fan casing (24) is located substantially at the same height as that of the end surface, which is arranged at the side of the cylinder head (5) of the cylinder (4), and the delivery opening (29) for the cooling fan (11) is provided so as to orientate ot the cylinder (4). The system as claimed in Claim 1, characterized in that said portion (26), which is arranged at the side of the cylinder head (5) of the encircling wall (25) of the fan casing (24) is located substantially at the same height as that of the end surface, which is arranged at the side of a rocker arm chamber (19) of the cylinder head (5), that said delivery opening (29) for the cooling fan (11) is provided so as to orientate to the cylinder (4) and the cylinder head (5), and that said cylinder head (5) is provided with a cooling air passsage (45) therein, of which inlet is orientated to the delivery opening (29). The system as claimed in Claim 2 or 3, characterized in that said radiator (36) is arranged so as to cover the outlet side of the passage (39) for the cooling air delivered through the distribution opening (38) of the encircling wall (25) of the fan casing (24). The system as claimed in Claim 2 or 3, characterized in that said internal combustion engine (1) is a direct-injection Diesel engine. The system as claimed in Claim 2 or 3, characterized in that said internal combustion engine (1) is a divided-combustion chamber type Diesel engine. The system as claimed in Claim 5, characterized in that said liquid-cooling jacket (34) is provided only around an injection nozzle of a fuel injector (18). The system as claimed in Claim 6, characterized in that said liquid-cooling jacket (34) is provided only around the divided-combustion chamber (47). The system as claimed in Claim 5 or 6, charaterized in that said liquid-cooling jacket (34) is provided substantially throughout in the cylinder head (5).

Inventors: YAMADA, KIICHIRO
Applicants: KUBOTA LIMITED
Application year: 1988
Main classification: F01P9
IPC codes: F01P3, F02F7, F01P1, F01P9