Engine cooling system

Abstract: An engine unit is equipped with a cylinder head and a crank case in which an oil feed pump and a scavenge pump are disposed. A cooling system for the engine unit is provided with a drysump type lubrication unit and comprises an oil tank (2) constituted by a hollow main tube (18), a hollow down tube (19), a hollow bridge tube (24) connecting the main tube (18) and the down tube (19) so as to communicate with each other through port means and frame members (25) covering a space defined by the respective tubes, a feed pipe (9) connecting the down tube to the feed pump, a scavenge pipe (7) connecting the oil tank to the scavenge pump, and a flowout pipe (4) directly or indirectly connecting the cylinder head to the oil tank. The port means are of the oil ports formed in the main tube, the down tube and the bridge tube and these ports are reduced opening sizes for effectively separating air from the engine oil during the circulation thereof.

Description: The present invention relates to a cooling system according to the pre-characterizing part of claim 1. In a conventional art, with respect to a four-cycle engine of a motorcycle, for example, an engine oil is circulated through an oil tank device as a cooling medium for cooling the engine as well as lubricating the same (US-A-3945463). The engine oil is forcibly supplied to the cam shaft and the crank shaft and is cooled on its return passage formed within the down tube of the motorcycle which is provided with cooling fins. Usually, in the conventional engine system described above, there is a fear of agitating the engine oil returned in the oil pan because of the arrangement of a number of rotating members such as gears and crank shaft and, hence, increasing the temperature of the engine oil, resulting in the degradation of the engine oil. Furthermore, in this connection, there is also a fear such that the rotating members agitate a voluminous amount of the engine oil in an oil pan, resulting in the mechanical loss of the rotating members. As stated above, in a conventional motorcycle, the system utilizing an oil tank device is composed by combining a hollow main tube, a hollow downtube, a hollow tension tube, and the like for circulating the engine oil, for example, as described in the Japanese Patent Publication Nos. 5130/1977 and 5131/1977. In another type of conventional motorcycle, there is provided a frame member having an inner hollow portion which is utilized as an oil tank. The object of the present invention is to provide an engine cooling system of a motorcycle capable of improving the engine cooling efficiency and preventing the engine oil from being degraded and improving mechanical loss of components arranged in a cylinder unit of the motorcycle. This object is achieved in accordance with the characterizing feature of claim 1. According to the cooling system of the characters described above, the engine oil after cooling the cylinder head is directly or indirectly returned in the oil tank through the scavenge pipe, whereby an amount of the engine oil to be dropped in the crank case is substantially reduced and, hence, the engine oil is not significantly agitated in the crank case, thus reducing the temperature increase of the engine oil in the crank case and preventing degradation of the engine oil as well as the mechanical loss of the engine components. The improved engine cooling function can also be attained. For a better understanding of the present invention and to show how the same may be carried out into effect, reference will now be made, by way of preferred embodiments, to the accompanying drawings, in which: Fig. 1 is a side view of a motorcycle to which the present invention is applicable; Fig. 2 is a perspective view of one embodiment of an engine cooling system utilizing an oil tank device of a motorcycle according to the present invention; Fig. 3 is a brief side view of an engine unit and the engine cooling system shown in Fig. 2; Fig. 4 is a sectional view taken along the line IV-IV of Fig. 3; and Fig. 5 is a side view similar to that shown in Fig. 3 showing a modification thereof according to the present invention. Fig. 1 is a side view of a motorcycle to which an engine cooling system mainly composed of an oil tank device according to the present invention is arranged. Referring to Fig. 1, a front wheel 200 is rotatably supported by a front fork 100 at a front portion of a motorcycle body and a rear wheel 500 is supported vertically swingably by a swing arm 300 at a rear portion of the motorcycle body. An engine unit 400 is arranged substantially the central portion of the motorcycle body below a fuel tank 600 disposed between a seat 700 for a rider and a head pipe 800. A main tube 901 extends obliquely rearwardly from the head pipe 800 and a down tube 902 also extends from the head pipe 800 downwardly. The main tube 901 and the down tube 902 are mutually connected through a bridge tube 903 and a space defined by the main tube 901, the down tube 902 and the bridge tube 903 constitutes an oil tank space by covering the space by a pair of side frame members. Fig. 2 is a detailed perspective view in an enlarged scale of the arrangement of the tube members shown in Fig. 1 constituting an engine cooling system according to the ppresent invention and Fig. 3 is a side view of the arrangement of Fig. 1 including a four-cycle engine unit. The lubrication for the engine unit 1 shown in Fig. 3 is carried out on the basis of a drysump lubrication system provided with an oil tank 2, which is arranged in association with a head pipe 4 of a body frame 3 of a motorcycle. The oil lubrication of the drysump lubrication system is carried out in the following manner. An engine oil stayed in an oil pan, not shown, in a crank case 5 is circulated in the oil tank 2 through a scavenge pipe 7 by means of a scavenge pump 6 and stored in the oil tank 2. The oil stored in the oil tank 2 is fed by means of a feed pump 8 to respective components of the engine unit such as piston and cam shaft through a feed pipe 9 to thereby lubricate them. According to this embodiment, as described above, the oil pump 8 acts to feed a part of the engine oil in the oil tank 2 as lubricating oil and to feed the reminder of the engine oil to a cylinder head 10 of the engine to positively cool the cylinder head 10. The engine oil for cooling the cylinder head 10 is fed into an oil passage 12 shown in Fig. 4 through a hole for inserting a stud bolt, not shown, for securing the cylinder head 10 to a cylinder block 11. The cylinder head 10 is provided with a combustion chamber 13, an exhaust port 14 and an intake port 15, both ports being communicated with the combustion chamber 13. The oil passage 12 is positioned below the exhaust port 14. The oil passage 12 is provided with an oil flowout port 16 on one side, left side as viewed in Fig. 3, of the cylinder block 11 (i.e. cylinder head 10). To the flowout port 16 is fitted a flowout pipe 17 at one end and the other end thereof is connected to the scavenge pipe 7. According to this structure, the engine oil passing the oil passage 12 and cooling the peripheral portions of the combustion chamber 13 and the exhaust port 14 flows into the scavenge pipe 7 through the flowout port 16 and the flowout pipe 17. Thereafter, the engine oil for cooling is combined with the engine oil passing the scavenge pipe 7 under pressure by means of the scavenge pump 6 and then fed into the oil tank 2. The structure of the engine cooling system utilizing an oil tank device and the flow of the engine oil will be described in detail with reference to Fig. 2. The body frame 3 includes a head pipe 4 having an upper portion to which a hollow main tube 18 is connected so as to extend downwardly and a lower portion to which a down tube 19 is connected so as to extend downwardly. The main tube 18 may have a structure acting as a tank rail for a fuel tank. A pair of body tubes 20 are connected to a lower portion of the main tube 18 so as to extend downwardly and a pair of lower tube 21 are connected to a lower portion of the down tube 19. The body tubes 20 are connected to the lower tubes 21, respectively, whereby a space is defined by the main tube 18, the down tube 19, the body tubes 20 and the lower tubes 21, the space being utilized for a space into which the engine unit 1 is arranged. A pair of seat rails 22 are connected to the upper portions of the body tubes 20 and a pair of side tubes 23 are also connected to the lower portions of the body tubes 20, both the tubes 22 and 23 extending rearwardly, leftwardly as viewed in Fig. 1, of the motorcycle body. A bridge tube 24 is stretched between intermediate portions of the main tube 18 and the down tube 19 so as to reinforce these members. Both bilaterial sides of the main tube 18, the down tube 19 and the bridge tube 24 in the assembled condition are covered by plate-like tank frame members 25 so as to define a space therebetween which constitutes an oil tank 2. The upper end of the scavenge pipe 7 extends upwardly into an inner space of the upper portion of the main tube 18. The inner hollow portion of the main tube 18 ends at a portion slightly below the connection to the bridge tube 24. According to the described construction, the engine oil in the scavenge pipe 7 first flows in the main tube 18 and then into the oil tank 2 through a port 30 or into the bridge tube 24 through a port 31. The engine oil through the oil tank 2 flows into the down tube 19 through a port 33 formed in the bridge tube 24 or a port 34 formed in the down tube 19 and the engine oil through the bridge tube 24 also flows into the down tube 19 through a port 32. The engine oil passes a strainer 26 and is then fed into the feed pump 8 disposed in the crank case 5 through the feed pipe 9. Thereafter, the engine oil is fed into the cylinder head 10 by the actuation of the feed pump 8 to cool the same and the engine oil after cooling the cylinder head 10 flows into the scavenge pipe 7 through a flowout pipe 17. The engine oil for cooling is then mixed with the engine oil for lubrication and the mixed engine oil is again fed into the main tube 18. A cylinder head 10 is covered by a cylinder head cover 28 (Fig. 3) to which the engine oil is fed through an overflow pipe 27. As described above, the engine oil after cooing the cylinder head 10 can be fed into the oil tank 2 through the flowout pipe 17 and the scavenge pipe 7, so that an amount of the engine oil naturally dropping into the oil pan in the crank case 5 can be substantially reduced, thus reducing the agitation of the engine oil in the crank case 5 by the rotating members such as crank shaft arranged in the crank case 5 and, hence, preventing the temperature of the engine oil from undesiredly increasing and also preventing the engine oil from being degraded. The mechanical loss of the rotating members can be also reduced. Fig. 5 shows a side view similar to that of Fig. 3 and represents a modified embodiment of the engine cooling system according to the present invention, in which like reference numerals are added to members corresponding to those shown in Figs. 2 to 4. Referring to Fig. 5, a flowout pipe 29 is connected to the flowout port 16 of the cylinder head 10 and the flowout pipe 29 is directly connected to the main tube 18 constituting the oil tank 2. According to this embodiment, the engine oil after cooling the cylinder head 10 is directly guided into the oil tank 2 without passing the scavenge pipe 7. The functions and effects of this embodiment are substantially identical to those attained by the first embodiment described in conjunction with Figs. 2 to 4.

Claims: A cooling system for cooling an engine unit (1, 104) equipped with a cylinder head (10) and a crank case (5) in which an oil feed pump (8) and a scavenge pump (6) are disposed, said cooling system comprising: an oil tank (2); a drysump type oil lubrication unit in which a part of the engine oil in the oil tank (2) is fed by the oil feed pump (8) into components of the engine unit for lubricating the same and the engine oil after the lubrication and dropped in the crank case (5) is again fed in the oil tank (2) by means of said scavenge pump (6); characterized in that a part of the engine oil pumped up by the oil feed pump (8) is fed into a first passage (12) in the cylinder head (10) as cooling oil and in that a second passage (7, 17, 29) returns this engine cooling oil after the cooling of the cylinder head (10) from the cylinder head into the oil tank (2). A cooling system according to claim 1, wherein the oil tank (2) is constituted by a hollow main tube (18), a hollow down tube (19), a hollow bridge tube (24) connecting said main tube (18) and said down tube (19) so as to communicate with each other though port means (31, 32), and frame members (24) covering a space defined by said main tube (18), said down tube (19) and said bridge tube (24); a feed pipe (9) connecting said down tube (19) to said feed pump (8); a scavenge pipe (7) connecting said oil tank (2) to said scavenge pump (6); and a flowout pipe (7, 17, 29) connecting said cylinder head (10) to said oil tank (2). A cooling system according to claim 2, wherein said flowout pipe (17) is indirectly connected to said oil tank (2) through said scavenge pipe (7). A cooling system according to claim 2, wherein said flowout pipe (29) is directly connected to said oil tank (2). A cooling system according to claim 2, wherein said scavenge pipe (7) is connected in oil communication to said hollow main tube (18) of the oil tank (2). A cooling system according to any of claims 1 to 5, wherein said feeding means that feed cooling oil to the cylinder head (10) comprise an oil passage (12) positioned below an exhaust port (14).

Inventors: MORITAKE HIROSHI, TAKAGI MASAHIRO, MORITAKE, HIROSHI, TAKAGI, MASAHIRO
Applicants: SUZUKI CO LTD, SUZUKI KABUSHIKI KAISHA
Application year: 1990
Main classification: F01M1
IPC codes: F01M1, F01P9, F02F7