Crankcase for multiple cylinder engine

Abstract: Problem : To ensure a sufficient opening area of breathing holes in a multiple cylinder engine. Means Of Solution : One journal wall (13) of an in-line four cylinder engine is provided with an oilway (42) and screw holes (45), being bolt fastening sections. A center (C1) of a breathing hole (24) punched in this journal wall (13) avoids the oilway (42) and screw holes (45) by being offset by an amount (Δc) with respect to a center (C2) of a breathing hole (25) formed in an adjacent journal wall. In this way, it is possible to make the diameter of the breathing hole (24) sufficiently large to alleviate friction loss without making the oilway (42) complicated or shortening the screw holes (45).

Description: Technical Field The present invention relates to a crankcase for a multiple cylinder engine, and more particularly to a structure for providing breathing holes having a sufficient hole diameter in journal walls of the crankcase. Related Art In a multiple cylinder engine, there are large variations in internal pressure of a crank chamber accompanying high speed rotation, caused by reciprocal movement of the pistons, and as a result friction loss becomes large. In order to solve this, breathing holes are formed opening into journal walls. These sort of breathing holes for each journal wall are formed at one time by machine processing in a direction parallel to a central axis of the crankshaft with respect to a cast cylinder block, and this results in each breathing hole being arranged coaxially (see, for example, Japanese patent laid-open No. Hei. 10-77905 or document DE 37 27 670 A). Problems To Be Solved By The Invention However, oilways and bolt fastening section are provided in the journal walls, and since these are integrally formed at the time of casting the cylinder block. In the case where breathing holes are formed after that using the above described machining method, the hole diameter must be made small in order to avoid the oilways and bolt fastening sections, which makes it difficult to make the hole diameters large enough to reduce friction loss. The object of the invention of this application is to solve this type of problem. Means Of Solving The Problems In order to solve the above described problem, a first invention relating to a crankcase of a multiple cylinder engine of the present application is a crankcase for a multiple cylinder engine having crank chambers for each cylinder of the multiple cylinder engine arranged along the axial direction of a crankshaft, and provided with breathing holes communicating between the crank chambers and respective journal walls supporting the crankshaft and constituting wall sections of each crank chamber, wherein the breathing holes are lined up along the crankshaft, and at least one of the breathing holes has a center different from centers of the other breathing holes. In this case, since breathing holes are provided for each journal wall, the number of breathing holes is the same as the number of journal walls, and it is sufficient if at least one of these breathing holes has a center different from the others. Accordingly, various combinations of breathing holes are included, from a combination where only the center position of one breathing hole is different, to a combination where the center positions of all the breathing holes are different. A second invention is basically the first invention, in which the journal wall in which the breathing hole having a different center is provided has an oilway, and is formed at a position avoiding this oilway. A third invention is basically the first or second invention in which the journal wall in which the breathing hole having a different center is provided has a bolt fastening section, and is formed at a position avoiding this bolt fastening section. Effects of the Invention According to the first invention, since at least one of a plurality of breathing holes that have been provided in each journal wall has a center different from all the others, it is possible to vary the position of the breathing holes according to the structure of the journal wall, with the result that the diameter of the breathing holes can be made sufficiently large and it is possible to ensure an opening area sufficient to reduce friction loss. According to the second invention, in the case where an oilway is provided in the journal wall, since the breathing hole is formed avoiding the oilway, it is possible to form the breathing hole having a sufficiently large diameter without complicating the oilway. According to the third invention, in the case where a bolt fastening section is provided in the journal wall, and the breathing hole is formed avoiding the bolt fastening sections, it is possible to form the breathing hole having a sufficiently large diameter without shortening the length of the bolts. Embodiments Of The Invention An embodiment applied to a motor cycle engine will now be described below based on the drawings. Brief Description Of The Drawings Fig. 1 is a cross sectional drawing of a cylinder section to which the embodiment relates. Fig. 2 is a drawing showing a cut through a crank chamber section of this engine. Fig. 3 is a drawing showing a method of manufacturing breathing holes. Fig. 1 is a cross sectional drawing of a cylinder section to which the embodiment relates, Fig. 2 is a drawing showing a section through a crank chamber section of this engine, and Fig. 3 is a drawing showing a method of manufacturing breathing holes. First of all, an outline of the overall structure will be described using Fig. 2. This engine is a water-cooled in-line 4-cylinder engine. In the drawing, reference numeral 1 is a cylinder head, 2 is a crankcase, 3 is a cylinder section, 4 is a lower case and 5 is a transmission. The crankcase 2 is divided into two parts, namely an upper case, that is formed integrally with the cylinder section 3, and a lower case 4. Four cylinders 6 - 9 are formed in the cylinder section 3 and lined up along the axial direction of a crankshaft 10. The crankshaft 10 is connected to pistons 11 sliding within each of the cylinders 6 - 9 via connecting rods 12, and is supported by journal walls 13 - 17. The journal walls 13 - 17 each define cylinders 6 - 9 inside the crankcase 2 and crank chambers 20 - 23 corresponding to these cylinders. Breathing holes 24 - 28 are also formed in each of the journal walls 13 - 17. The breathing holes 24 - 28 are respectively formed one each in the journal walls 13 - 17, with the same diameter, and are aligned along the axial direction of the crankshaft 10 communicating with each of the crank chambers 20 - 23. In the drawing, reference numeral 30 is an ACG cover, reference numeral 31 is a cam shaft drive sprocket, reference numeral 32 is a cam chain, reference numeral 33 is a cam chain chamber, and reference numerals 34 - 38 are journal walls for the crankshaft 10 at the lower case 4 side. Next, the detailed structure of the journal walls of the cylinder section 3 will be described. Fig. 1 shows a journal wall 14, and a semicircular cavity 41 for housing the crankshaft 10 via a metal bearing 19 is formed in a lower surface 40 of the journal wall 14.An oilway 42 is also formed in the circumference of this cavity 41. The oilway 42 extends upwards and leads to an attachment hole 43 for a pressure switch (omitted from the drawing) formed in a side of the journal wall 14, extends from there through a side hole to the journal wall 13 (Fig. 2), bends at a thickened part of the journal wall 13 and connects to a separate oilway 44 that extends upwards. A pair of bolt attachment screw holes 45 are formed leading upwards from the lower surface 40 on either side of the cavity 41. These bolt holes 45 correspond to the bolt fastening sections of the present application and bolts, not shown, for joining the lower case 4 side are screwed into the holes from the side shown at the bottom of the drawing. A breathing hole 25 is formed at a position leading away from the oilway 42 and the screw holes 45. The diameter of this breathing hole 25 is sufficiently large to avoid friction loss, and is offset from a center position of a breathing hole 24 formed in the adjacent journal wall 13. Specifically, the center C1 of the breathing hole 24 is offset by Δc from the center C2 of the breathing hole 25, and is eccentric by Δc from the oilway 42, if the center of the breathing hole 24 for the journal wall 13 in which the oilway 42 and screw holes 45 are provided is used as a reference. The center of the breathing hole 24 is also positioned a sufficient distance away from the tips of the screw holes 45. As shown in Fig. 3, these breathing holes 24 - 27 are formed by punching the cast cylinder section 3 from a direction parallel to the axial direction of the crankshaft 10, using a suitable fabrication system, such as an NC machine tool using a tool 50. At the time the cylinder section 3 is cast, the cavity 41, oilway 42 and screw holes 45 before being tapped, etc. are integrally formed. The tool 50 comprises a blade section 52 having an outer diameter D and provided at a tip, and a shaft section 53 having an outer diameter d smaller than the outer diameter D. The diameter D of the blade section 52 is approximately equal to the inner diameter of each of the breathing holes 24 - 27, while the diameter d of the shaft section 53 is determined from the maximum offset amount of the breathing holes. First of all, the breathing hole 24 is punched on the center C1 using the tool 50, the blade section 52 passes through the journal wall 13, the shaft section 53 moves from there to the center C2, and the breathing hole 25 is formed in the journal wall 14. The amount of movement a of the centers at this time is equivalent to an offset amount between the breathing hole 24 and the breathing hole 25 in a vertical direction in the drawing. After punching the breathing hole 25, the shaft section 53 is again moved by only a distance b, and then the breathing hole 26 for the journal wall 15 is punched. In this way, the breathing hole 26 is formed having the center C3 offset by only the offset amount b in a vertical direction from the center C1 of the breathing hole 24. Continuing on from this, the breathing hole 27 and subsequent holes are punched in the same way. The offset amounts a and b in Fig. 3 are offset amounts in the vertical direction of the drawings. The breathing holes are also appropriately offset in the lateral direction of Fig. 1 equal to the above described Δc. This offset amount is appropriately determined taking into consideration avoidance of the oilway 42 and the screw holes 45, etc. and the structure of each of the journal walls 13 - 17. The outer diameter d of the shaft section 53 is determined with one of the breathing holes, for example the above described breathing hole 24, as a reference, so that a difference between the outer diameter D of the blade section 52 and the outer diameter d of the shaft section 53 is approximately at least double an offset amount by which some breathing hole is most offset from the reference breathing hole, i.e. a maximum offset amount. Next, the operation of this embodiment will be described. The oilway 42 and the screw holes 45 are provided in the journal wall 14. The breathing hole 25 is offset with respect to a breathing hole of another journal wall, for example the breathing hole 24 of the adjacent journal wall 13, so that the breathing hole 25 is formed away from the oilway 42 and the screw holes 45. As a result, it is possible to make the diameter of the breathing hole 25 sufficiently larger, similarly to the diameter of other breathing holes, and it is possible to ensure a sufficient opening area to alleviate friction loss. Furthermore, it is possible to avoid the oilway becoming complicated, and to avoid the situation where the bolts are shortened as a result of the screw holes being short. The breathing holes 24, and 26 - 28 for the other journal walls 13 and 15 - 17 are also the same and can be formed at the most convenient positions, and at this time if it is necessary for the oilway and screw holes to avoid other parts, they can be formed escaping with the same diameter. In summary, it is a problem to ensure a sufficient opening area of breathing holes in a multiple cylinder engine. According to the invention, this problem can be solved: One journal wall 13 of an in-line four cylinder engine is provided with an oilway 42 and screw holes 45, being bolt fastening sections. A center C1 of a breathing hole 24 punched in this journal wall 13 avoids the oilway 42 and screw holes 45 by being offset by an amount Δc with respect to a center C2 of a breathing hole 25 formed in an adjacent journal wall. In this way, it is possible to make the diameter of the breathing hole 24 sufficiently large to alleviate friction loss without making the oilway 42 complicated or shortening the screw holes 45.

Claims: A crankcase (2) for a multiple cylinder engine having crank chambers (20-23) for each cylinder (6-9) of the multiple cylinder engine arranged along the axial direction of a crankshaft (10), and provided with a plurality of breathing holes (24-28) communicating between the crank chambers (20-23) and respective journal walls (13-17) supporting the crankshaft (10) and constituting wall sections of each crank chamber (20-23), wherein the breathing holes (24-28) are lined up along the axial direction of the crankshaft (10), characterized in that at least one of the breathing holes (24-28) has a center offset from centers of the other breathing holes (24-28) in a direction orthogonal to the axial direction of the crankshaft (10), in order to avoid essential parts (42, 45) of the crankcase (2). The crankcase (2) for a multiple cylinder engine as disclosed in claim 1, wherein the journal wall (14) in which the breathing hole (25) having the different center (C2) is provided has an oilway (42), and the breathing hole (25) having the offset center (C2) is formed at a position avoiding this oilway (42). The crankcase (2) for a multiple cylinder engine as disclosed in claim 1 or 2, wherein the journal wall (14) in which the breathing hole (25) having the offset center (C2) is provided has a bolt fastening section (45), and is formed at a position avoiding this bolt fastening section (45).

Inventors: TAKAHASHI KATSUNORI, TANAKA YOICHI, TAKAHASHI, KATSUNORI, TANAKA, YOICHI, Tanaka, Yoichi c/o Honda Giken Kogyo K. K.
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1999
Main classification: F02F7
IPC codes: F02F7, F01M13, F16C3, F01M11, F02B75