AU2010200039B2

AU2010200039B2 - Oil passage for cooling cylinder head of multi-cylinder engine

Info

Publication number: AU2010200039B2
Application number: AU2010200039A
Authority: AU
Inventors: Hiroyuki Sugiura; Shunji Yokokawa
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2009-02-25
Filing date: 2010-01-06
Publication date: 2015-02-19
Anticipated expiration: 2030-01-06
Also published as: BRPI1000363B1; BRPI1000363A2; AU2010200039A1

Abstract

OIL PASSAGE FOR COOLING CYLINDER HEAD OF MULTI-CYLINDER ENGINE Abstract 5 There is provided an oil passage for cooling a cylinder head of a multi-cylinder engine where a supply oil passage connected from a cylinder block to an ignition plug oil jacket in a cylinder head and a discharge oil passage are formed, the oil passage for cooling a cylinder head of a multi-cylinder engine comprising: a bypass oil passage that bypasses the ignition plug oil jacket and is provided to 10 the cylinder block. -- 26 35 A0 37 Al11A 28 33 53 34 A5 A14---

Description

S&F Ref: 927659 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Honda Motor Co., Ltd., of 1-1, Minami-Aoyama 2 of Applicant: chome, Minato-ku, Tokyo, 107-8556, Japan Actual Inventor(s): Hiroyuki Sugiura Shunji Yokokawa Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Oil passage for cooling cylinder head of multi-cylinder engine The following statement is a full description of this invention, including the best method of performing it known to me/us: RA~r9rs/A7Q33 1) 1 OIL PASSAGE FOR COOLING CYLINDER HEAD OF MULTI-CYLINDER ENGINE TECHNICAL FIELD The present invention relates to an oil passage for cooling a cylinder head of an air cooled multi-cylinder engine, particularly relates to a bypass oil passage provided to the oil passage. BACKGROUND OF THE INVENTION In the related art, an engine provided with a supply oil passage that conducts oil to an ignition plug oil jacket of a cylinder head and a discharge oil passage that discharges the oil so as to cool the cylinder head is disclosed (for example, refer to JP 2006-97611 (Figs. 5, 6)). In this art, as all oil for cooling is conducted to the oil jacket, cooling performance is high, however, there is considerable difference in temperature between oil before passing the oil jacket and the oil after passing it, in a cylinder block where a supply passage and a discharge passage respectively which the oil passes are arranged, difference in temperature is made between the supply side and the discharge side, and unevenness in cooling may occur in the cylinder block. Therefore, it is desired that difference in temperature between the supply side and the discharge side in the cylinder block is reduced, maintaining cooling performance in the oil jacket. Further, JP 2000-97611 shows an oil passage extended in an axial direction of the cylinder is bored in a circumference corresponding to the cylinder head of each cylinder and is connected to the oil passage of the cylinder head. As boring work is required by the number of oil passages extended in the axial direction of the cylinder, working man-hours, and cost, is increased. A reduction of the working man-hours is desired. OBJECT OF THE INVENTION It is the object of the present invention to address one or more of the foregoing needs.

2 SUMMARY A first aspect of the present invention provides an oil passage for cooling a cylinder head of a multi-cylinder engine where a supply oil passage is connected from a cylinder block to an ignition plug oil jacket in the cylinder head and the discharge oil passage is formed, the oil passage comprising a bypass oil passage that bypasses the ignition plug oil jacket is provided to the cylinder block. The bypass oil passage is preferably configured by a groove formed on a top face of the cylinder block and a bottom of the cylinder head that closes an upside of the groove. The engine is preferably an air-cooled engine provided with an air cooling fin in the cylinder block, the supply oil passage is arranged on the front side of a cylinder in a traveling direction of a vehicle and the discharge oil passage is arranged on the rear side of the cylinder. The engine is preferably a parallel multi-cylinder engine provided with cylinders on both sides with a driving member housing that houses a valve system driving member between both sides and the bypass oil passage is arranged in the cylinder block between the driving member housing and the cylinder adjacent to the driving member housing. The bypass oil passage is preferably arranged for only the cylinder on one side with the driving member housing between both sides, in the cylinder on the other side with the driving member housing between both sides, the cross section of the supply oil passage connected to a groove formed on the top face of the cylinder block and the cross section of the discharge oil passage are reduced, compared with each cross section of the supply oil passage and the discharge oil passage on one side. The bypass oil passage is preferably configured by forming the groove on the top face of the cylinder block and further, a branching oil passage that branches lubricating oil for lubricating a valve system is formed on the top face of the cylinder block on the reverse side to the bypass oil passage with the driving member housing between both sides in the shape of a groove.

2a Preferably, oil is distributed and is recovered by a connecting oil passage for connecting the supply oil passage that conducts oil to the ignition plug oil jacket for each cylinder to the cylinder head of the multi-cylinder engine and the discharge oil passage for discharging oil from each oil jacket to a rising oil passage and a lowering oil passage which are respectively not branched for each cylinder to the cylinder block, wherein the connecting oil passage is configured by a groove formed on a top face of the cylinder block and a bottom of the cylinder head that closes the upside of the groove of the cylinder block.

3 Preferably, a joint of a rising oil passage in the cylinder block or a lowering oil passage in the cylinder block connected to the groove on the top face of the cylinder block is located in a range formed by connecting joints of the plural supply oil passages in the cylinder head or the plural discharge oil passages in the cylinder head connected to the 5 groove. Preferably, a joint of a rising oil passage in the cylinder block or a lowering oil passage in the cylinder block connected to the groove on the top face of the cylinder block is located outside a range formed by connecting joints of the plural supply oil passages in the cylinder head or the plural discharge oil passages in the cylinder head io connected to the groove. The joint of the rising oil passage in the cylinder block and the joint of the lowering oil passage in the cylinder block respectively connected to the grooves on the top face of the cylinder block are preferably set off in a direction in which the cylinders are arranged. is Preferably, on the supply side where the joint of the rising oil passage in the cylinder block connected to the groove on the top face of the cylinder block is located outside the range formed by connecting the joints of the plural supply oil passages in the cylinder head connected to the groove, the width of the groove from a position of an opening at an upper end of the rising oil passage in the cylinder block to the joint on the 20 close side out of the joints of the plural supply oil passages in the cylinder head is widened and the width of the groove on the distant side from the joint on the close side is narrowed. The cylinder block is preferably provided with bolt insertion holes for inserting each bolt for fixing the cylinder block to a crankcase and the groove is formed with the 25 groove avoiding the bolt insertion hole on the top face of the cylinder block on the distant side from the center of the cylinder. The engine is preferably a parallel multi-cylinder engine provided with plural cylinders on both sides with a driving member housing that houses a valve system driving member between both sides, either of the rising oil passage or the lowering oil passage in 30 the cylinder block is arranged close to the driving member housing outside the range formed by connecting the joints of the plural supply oil passages or the plural discharge oil passages connected to the distributing groove or the recovering groove on the top face of the cylinder block in the cylinder head and the other of the rising oil passage or the lowering oil passage in the cylinder block is arranged in the range formed by connecting 4 the joints of the plural supply oil passages or the plural discharge oil passages connected to the above-mentioned groove in the cylinder head. The engine is preferably an engine mounted in a small-sized vehicle, the cylinders are arranged in a direction of vehicle width, a pair of right and left rising/lowering oil passages arranged close to the driving member housing in the cylinder block, the pair of right and left rising oil passages are formed at the front of the vehicle engine and each lower end of the right and left rising/lowering oil passages in the cylinder block is connected to an oil gallery extended in the direction in which the cylinders are arranged. The driving member housing is preferably overhanged at the front of the cylinder block in a higher position of an upper part of the cylinder block and the oil gallery provided to the front of the engine and extended in the direction in which the cylinders are arranged is arranged in the vicinity of a starting point of the overhang. The valve system driving member preferably uses a cam chain for a driving transmitting member, a cam chain tensioner fitting to which a tensioner that tensions the chain is attached is provided to an outside face of the driving member housing and the oil gallery connected to the lowering oil passage in the cylinder block and extended in the direction in which the cylinders are arranged is let to pass on the downside of the cam chain tensioner fitting. According to an embodiment of the present invention, oil that is not heated in the oil jacket can be merged into oil in the discharge oil passage passing the cylinder block by providing the bypass oil passage that bypasses the oil jacket to the cylinder block and directly conducting a part of taken oil from the supply oil passage to the discharge oil passage without passing the oil jacket, the temperature of the oil in the discharge oil passage passing the cylinder block can be lowered, the difference in temperature of the oil in the cylinder block can be decreased, and unevenness in cooling in the cylinder block can be inhibited. According to an embodiment of the present invention, the configuration of the bypass oil passage can be simplified, compared with a case that the bypass oil passage is formed in the cylinder block by piercing the cylinder block, the working can be simplified, and the working cost can be reduced.

4a According to an embodiment of the present invention, when the supply oil passage and the discharge oil passage are arranged on the front side and on the rear side of the cylinder in the air-cooled engine, unevenness in cooling is particularly apt to occur, however, the unevenness in cooling by oil can be possibly inhibited owing to the bypass oil passage.

5 According to an embodiment of the present invention, as the bypass oil passage is arranged between the cylinder and the driving member housing, the bypass oil passage is hardly influenced by heat from the cylinder, a part forming a side wall of the driving member housing is not influenced by the heat and the strength is not deteriorated even if s the bypass oil passage is arranged because the part has relatively high strength. According to an embodiment of the present invention, as the bypass oil passage is provided in only the cylinder block on one side of the driving member housing, the cross section of the oil passage in the cylinder head connected to the groove on the top face of the cylinder block on the other side is reduced and the quantity of oil in the oil 10 jackets on both sides can be balanced. According to an embodiment of the present invention, as the bypass oil passage and the lubricating oil branching oil passage are formed for the cylinders on both sides of the driving member housing in the shape of a groove, the plural oil passages can be worked on the same plane from the same direction in working the cylinder block, a man is hour is reduced, and the deterioration of the strength of the cylinder block can be inhibited because the oil passages are formed in the shape of a groove. According to an embodiment of the present invention, the supply oil passages and the discharge oil passages in an axial direction of the cylinder in the cylinder block can be reduced by forming the distributing oil passage by the groove formed on the top 20 face of the cylinder block, working in the axial direction of the cylinder can be reduced, and the working cost can be reduced by forming the distributing oil passage by the groove. According to an embodiment of the present invention, when the joint of the rising oil passage in the cylinder block or the lowering oil passage in the cylinder block 25 connected to the groove on the top face of the cylinder block is located in the range formed by connecting the joints in the groove of the plural supply oil passages or the plural discharge oil passages in the cylinder head, there is an advantage that the groove is not required to be particularly extended. According to an embodiment of the present invention, the oil passage can be 30 compacted utilizing vacant space by enhancing a degree of freedom in arrangement such as the joint of the rising oil passage in the cylinder block or the lowering oil passage in the cylinder block connected to the groove on the top face of the cylinder block can be arranged close to an end in the direction in which the cylinders are arranged of the cylinder block.

6 According to an embodiment of the present invention, the length of the oil passage on the top face of the cylinder block can be varied by setting the joint of the rising oil passage in the cylinder block and the joint of the lowering oil passage in the cylinder block respectively connected to the groove on the top face of the cylinder block 5 off in the direction in which the cylinders are arranged, and cooling performance can be optimized by setting a long oil passage on the supply side on which oil is required to be cooled by running wind via a fin for cooling of the cylinder block and setting a short oil passage on the discharge side on which oil is not required to be cooled. According to an embodiment of the present invention, the deterioration of oil 1o pressure caused because a flow rate decreases is inhibited by narrowing the width of the groove on the distant side from the joint of the supply oil passage in the cylinder head on the close side to the position of the opening at the upper end of the rising oil passage in the cylinder block and a flow of oil can be secured. According to an embodiment of the present invention, as the groove is arranged is in a direction distant from the cylinder when the groove is formed close to the outside of the cylinder in forming the groove avoiding the bolt insertion hole, the rise of the temperature of oil by combustion heat in the cylinder can be inhibited. According to an embodiment of the present invention, cooling performance can be enhanced by varying the length of the oil passage between the supply side and the 20 discharge side according to whether the cooling of oil is required or not. According to an embodiment of the present invention, as the oil passage connected to the oil gallery is located close to the driving member housing, a long oil galley is not required and the oil gallery is short. The oil gallery is hardly striking by arranging the shorter oil gallery at the front of the engine and the appearance quality of 25 the engine can be kept. According to an embodiment of the present invention, the oil passage is simply configured by arranging the oil gallery in a position upon which the overhang of the driving member housing has no effect and the molding such as working can be facilitated. According to an embodiment of the present invention, the oil gallery extended in 30 the direction in which the cylinders are arranged can be arranged without interfering with the tensioner fitting. The oil passage extended in the direction in which the cylinders are arranged is formed to be low by letting the oil gallery pass on the downside of the tensioner fitting and can be made hardly striking.

7 Brief Description of Drawings A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Fig. I is a side view showing a motorcycle in which a four-cylinder engine 5 equivalent to one embodiment of the present invention is mounted; Fig. 2 is a longitudinal section showing the engine viewed from the right side; Fig. 3 is a longitudinal section showing a main part of the engine including a cam chain chamber of the engine and viewed from the right side; Fig. 4 is a front view showing an air-cooled oil cooler shown in Fig. 2; 10 Fig. 5 is a front view showing the center of a cylinder block; Fig. 6 is a sectional view viewed along a line VI-VI in Fig. 5; Fig. 7 is a top view showing the cylinder block; Fig. 8 is a bottom view showing a cylinder head; Fig. 9 is a top view showing the cylinder head; 15 Fig. 10 is a sectional view viewed along a line X-X in Fig. 9; Fig. 11 is a top view showing a cover for an oil jacket; Fig. 12 is a sectional view viewed along a line XII-XII in Fig. 11; Fig. 13 is a sectional view viewed along a line XIII-XIII in Fig. 11; Fig. 14 is a rear view showing the cylinder block; 20 Fig. 15 is a bottom view showing the cylinder block; Fig. 16 is a side view showing a circumference of an oil return pipe; and Fig. 17 is a top view showing a lower crankcase. Description of Embodiment 25 Fig. 1 is a side view showing a motorcycle 2 in which a four-cylinder engine I equivalent to one embodiment of the present invention is mounted. An arrow F denotes a forward direction. A body frame of the motorcycle 2 includes a head pipe 3, a main frame 4 extended diagonally backward from the head pipe 3, a center frame 5 extended downward from a rear end of the main frame 4, an auxiliary frame 6 that connects the 30 head pipe 3 and the main frame 4, a down frame 7 extended downward from the auxiliary frame 6, a seat stay 8 extended backward from the main frame 4 and a mid-frame 9 that connects the center of the center frame 5 and the center of the seat stay 8. A front fork 11 that supports a front wheel 10 is steerably supported by the head pipe 3. A steering handlebar 12 is coupled to the front fork 11. A rear fork 14 that supports a rear wheel 13 35 is vertically swingably supported by the rear of the center frame 5 and a cushion unit 15 is 8 provided between a joint of the seat stay 8 and the mid-frame 9 and the rear fork 14. The engine I is supported by the down frame 7, the main frame 4 and the center frame 5 and the power of the engine 1 is transmitted to the rear wheel 13 via a chain 16 for driving the rear wheel. A fuel tank 17 is provided to the main frame 4 on the upside of the engine 1 5 and a tandem seat 18 for a rider and a passenger is attached on the seat stay 8. An exhaust pipe 19 is extended from the engine 1, is bent downward, is further extended backward, and is connected to a muffler 20 in the rear. An air-cooled oil cooler 21 is provided to the down frame 7 in front of the engine 1. Fig. 2 shows a longitudinal section viewed from the right side of the engine 1. 10 The engine 1 is an air-cooled 4-cylinder DOHC wet sump engine and in Fig. 2, a cooling oil circuit is shown. A cylinder 24 shown in Fig. 2 is equivalent to a section viewed along a line II-Il shown in Fig. 7. An arrow F denotes a forward direction corresponding to the front of a vehicle when the engine is mounted in the vehicle. The engine is acquired by integrating an internal combustion engine 25 and a transmission 26. A cover of the is engine I is configured by a crankcase 27 formed by an upper crankcase 27A and a lower crankcase 27B, a cylinder block 28, a cylinder head 29, a cylinder head cover 30 and an oil pan 31. A crankshaft 32, a main shaft 33 of the transmission and a countershaft 34 are rotatably supported by a bearing on joined surfaces of the crankcase 27 vertically divided in two. 20 The cylinder block 28 includes four cylinders, a piston 35 is slidably housed in each cylinder 24, and the piston is connected to the crankshaft 32 via a connecting rod 36. A combustion chamber 37 is provided in a lower part opposite to a top face of each piston 35 of the cylinder head 29. An ignition plug 38 is inserted toward each combustion chamber 37 from the upside of the cylinder head 29 and its end is opposite to the inside of 25 the combustion chamber 37. An intake port 39 and an exhaust port 40 respectively connecting with each combustion chamber 37 are provided to the cylinder head 29 and respective inner ends are open to the combustion chamber 37. An intake valve 41 and an exhaust valve 42 that open or close respective openings are provided to the openings at the inner ends of the intake port 39 and the exhaust port 40. A valve train 45 including an 30 inlet camshaft 43 and an exhaust camshaft 44 is provided to joined surfaces of the cylinder head 29 and the cylinder head cover 30. The oil pan 31 provided with a shallow bottom part and a deep bottom part is connected to a lower part of the lower crankcase 27B. An oil suction pipe 47 provided with a strainer 46 is provided to the deep bottom part of the oil pan 31 and an oil pump 48 35 is connected to its upper part. The oil pump 48 is configured by an oil pump for cooling 9 and an oil pump for lubricating and the oil pumps are connected to the same oil pump shaft. A cooling oil circuit and a lubricating oil circuit are independently provided to the engine 1. Oil is separately supplied to the respective oil circuits from the oil pump for 5 cooling and the oil pump for lubricating. Fig. 2 shows the oil pump 48 for cooling and the cooling oil circuit, and the oil pump for lubricating and the lubricating oil circuit are omitted. As the present invention is limited to the description of a cooling system, the oil pump 48 for cooling and the cooling oil circuit are merely called the oil pump 48 and the oil circuit in the following description. 10 Though the details of the oil passage are described later, the whole configuration of the oil passage will be first described. In the oil passage shown in Fig. 2, a discharge pipe Al connected to the oil pump 48 is extended forward in the oil pan, is bent upward, and reaches an oil cooler coupler 49 in a lower part of the front of the lower crankcase 27B. A pipe A2 bound for the oil cooler is connected to the oil cooler coupler 49 and 15 connects with the air-cooled oil cooler 21 on the upside in front of the engine. Oil cooled in the oil cooler is carried to an oil inlet 50 in a lower part of the front of the cylinder block 28 via an oil cooler return pipe A3. The oil inlet 50 connects with an oil gallery A4 on the supply side. For members for driving a valve system, a cam chain and a timing belt can be 20 given, however, as in the engine I in this embodiment, a cam chain 51 (see Fig. 3) is used, a valve system driving member housing is called a cam chain chamber 52 in the following description. As the engine is a parallel 4-cylinder engine in which four cylinders 24 are laterally arranged when the engine is mounted in the vehicle (see Fig. 7) and the cam chain chamber 52 is provided in the center, two of the cylinders 24 are 25 laterally made a pair. The oil passage is laterally divided in the oil gallery A4 on the supply side and connects with a rising oil passage A5 in the cylinder block respectively toward the right and left sides of the cylinder block. An upper part of the rising oil passage A5 in the cylinder block connects with a distributing groove A6 on a top face of the cylinder block every the right side or the left side of the cylinder block. A lower end 30 of a supply oil passage A7 independently provided for each cylinder in the cylinder head is open at the bottom that covers an upper part of the distributing groove A6 of the cylinder head 29 with the lower end communicating with the distributing groove A6. An upper end of the supply oil passage A7 in the cylinder head communicates with an ignition plug oil jacket A8 and the circumference of the ignition plug 38 is cooled with 35 supplied oil.

10 The ignition plug oil jacket A8 connects with an oil discharge passage A9 provided for each cylinder in the cylinder head on the rear side of the cylinder 24. A lower end of the oil discharge passage A9 in the cylinder head is open to a recovering groove A10 on the top face of the cylinder block every the right side or the left side of the s cylinder block. The recovering groove Al 0 on the top face of the cylinder block connects with an oil gallery A12 on the discharge side provided to a lower part of the cylinder block 28 via one lowering oil passage Al I in the cylinder block per the right side and the left side of the cylinder block. As the oil gallery A12 on the discharge side is laid on both right and left sides of the cylinder block, the lowering oil passage Al l in the cylinder 1o block separately provided on the right side and on the left side of the cylinder block is united in the oil gallery and connects with a discharge oil passage A13 in the crankcase via a discharge joint 53. An oil return pipe A14 connects with a lower end of the discharge oil passage A13 in the crankcase and is open on the upside of the oil pan 31. Fig. 3 shows the longitudinal section viewed from the right side of the engine 1 IS including the cam chain chamber 52. The cam chain chamber 52 is provided to the substantial center in a lateral direction of the engine 1. The cam chain chamber 52 shown in Fig. 3 is equivalent to a section viewed along a line III-III in Fig. 7. As shown in Fig. 3, the intake camshaft 43 and the exhaust camshaft 44 are rotatably supported on the joined surfaces of the cylinder head 29 and the cylinder head cover 30 and a camshaft 20 driven sprocket 56 is provided to each camshaft. A camshaft driving sprocket 57 having a half diameter of the camshaft driven sprocket 56 is provided to the crankshaft 32 supported by the joined surfaces of the upper and lower crankcases 27A, 27B. The cam chain 51 is wound on these sprockets, and the intake camshaft 43 and the exhaust camshaft 44 are rotated according to the rotation of the crankshaft 32. 25 The crankshaft 32 is rotated in a direction shown by an arrow W. A cam chain guide is provided around the cam chain 51. In detail, a fixed upper cam chain guide 58 is provided on the upside between the two driven sprockets, a fixed front cam chain guide 59 is provided to the cam chain 51 on the front lead-in side of the cam chain chamber 52, and a swinging cam chain guide 60 is provided to the cam chain 51 on the rear feeding 30 side of the cam chain chamber 52. The swinging cam chain guide 60 is swung with a lower end bolt 61 in the center. A cam chain tensioner 63 is provided to a cam chain tensioner fitting 62 on a rear wall of the cylinder block 28, the swinging cam chain guide 60 is pressed by its protruded shaft 63a, and the cam chain 51 is prevented from being loosened.

11 Fig. 4 shows the air-cooled oil cooler 21 shown in Fig. 2 and viewed from the front. The left and the right in Fig. 4 are shown by arrows L, R corresponding to the left side and the right side of the vehicle when the engine 1 is mounted in the vehicle. The other drawings in the following description are also similar. An upper end of the pipe A2 5 bound for the oil cooler is coupled to the right side of the oil cooler 21 and a flange 66 at a lower end of the pipe is connected to the oil cooler coupler 49 in the front of the lower crankcase (see Fig. 2). An upper end of the oil cooler return pipe A3 is coupled to the left side of the oil cooler 21 and a flange 67 at a lower end of the return pipe is connected to the oil inlet 50 in the front of the cylinder block 28 (see Fig. 2). 1o Fig. 5 is a front view showing the center of the cylinder block 28. In Fig. 5, the upside corresponding to the upside of the vehicle of the engine is shown by an arrow Up together with the left and the right L, R when the engine 1 is mounted in the vehicle. The other drawings in the following description are also similar. In Fig. 5, the oil inlet 50 is provided to a lower part of the front of the cylinder block 28. The flange 67 (shown in is Fig. 4) at the lower end of the oil cooler return pipe A3 is connected to the oil inlet. The oil inlet 50 communicates with the oil gallery A4 on the supply side. The rising oil passage A5 in the respective cylinder blocks respectively rises from both ends of the oil gallery A4 on the supply side. As the cam chain chamber 52 is provided to the center in a lateral direction of the cylinder block 28 and the two cylinders are laterally united, oil is 20 laterally distributed via the oil gallery A4 on the supply side so as to feed oil to the right side and the left side. An upper end of the rising oil passage A5 in the cylinder block connects with the distributing groove A6 on the top face of the cylinder block. Fig. 6 is a sectional view viewed along a line VI-VI in Fig. 5 and shows a longitudinal section of the cylinder block 28 including the rising oil passage A5 in the 25 cylinder block. A lower part of the rising oil passage A5 in the cylinder block communicates with the oil gallery A4 on the supply side and the upper part of the rising oil passage A5 in the cylinder block communicates with the distributing groove A6 on the top face of the cylinder block. In Fig. 6, the recovering groove A10 on the top face of the cylinder block and the oil gallery A 12 on the discharge side are also shown. 30 Fig. 7 is a top view showing the cylinder block 28. As the cam chain chamber 52 is open to the center in the lateral direction of the cylinder block 28, the cylinders 24 are laterally divided into two groups each of which includes the two cylinders. In the engine 1, the upper crankcase 27A and the cylinder block 28 are integrated by stud bolts. Fig. 6 shows plural stud bolt insertion holes 68. On the top face of the cylinder block 28, 35 the distributing groove A6 is provided on both sides of the cam chain chamber 52. The 12 recovering groove A10 is also provided on both sides of the cam chain chamber 52. These grooves are provided with them curved outside the stud bolt insertion hole avoiding the stud bolt insertion hole 68. The upper end of the rising oil passage A5 in the cylinder block is open to each position shown by codes ml, m2 near the cam chain chamber 52 of 5 the respective distributing grooves A6 in a lateral direction of the cam chain chamber 52. An upper end of the lowering oil passage A 1 in the cylinder block is open to each position shown by codes nI, n2 of the respective recovering grooves A10 in the lateral direction of the cam chain chamber 52. Fig. 8 is a bottom view showing the cylinder head 29. The cam chain chamber io 52 is open to the center in a lateral direction of the cylinder head. An ignition plug insertion hole 69, a pair of two inner ends 39a of the intake port 39 and a pair of two inner ends 40a of the exhaust port 40 are open to each combustion chamber 37 corresponding to each cylinder 24 shown in Fig. 7. The ignition plug 38, the intake valve 41 and the exhaust valve 42 respectively shown in Fig. 2 are provided to these openings. Flat parts is before and after the combustion chamber 37 cover respective top faces of the distributing groove A6 on the top face of the cylinder block and the recovering groove A10 on the top face of the cylinder block respectively shown in Fig. 7. Respective lower ends of the supply oil passage A7 in the cylinder head and the oil discharge passage A9 in the cylinder head respectively shown in Fig. 10 described 20 later are open to the flat parts before and after the combustion chamber 37. The lower end of the supply oil passage A7 in the cylinder head is open to positions shown by codes fl, f2, f3, f4 of the distributing groove A6 on the top face of the cylinder block as shown in Fig. 7. The lower end of the oil discharge passage A9 in the cylinder head is open to positions shown by codes gl, g2, g3, g4 of the recovering groove A10 on the top face of 25 the cylinder block as shown in Fig. 7. Oil is supplied from the distributing groove A6 on the top face of the cylinder block to the supply oil passage A7 in the cylinder head. The oil is discharged from the oil discharge passage A9 in the cylinder head to the recovering groove A10 on the top face of the cylinder block. Fig. 9 is a top view showing the cylinder head 29. The cam chain chamber 52 is 30 open to the center. A pair of the two ignition plug insertion holes 69 are provided to the right side and the left side of the cylinder head. A pair of two intake valve mounting holes 70 are provided on the rear side of each ignition plug insertion hole 69. A pair of two exhaust valve mounting holes 71 are provided on the front side of each ignition plug insertion hole 69. A bearing 84 of the intake camshaft 43 is provided between the pair of 13 intake valve mounting holes 70 and a bearing 85 of the exhaust camshaft 44 is provided between the pair of exhaust valve mounting holes 71. The ignition plug oil jacket A8 is provided around each ignition plug insertion hole 69. The supply oil passage A7 in the cylinder head and the oil discharge passage A9 5 in the cylinder head connect with the ignition plug oil jacket A8. An upper part of the ignition plug oil jacket A8 is covered with a cover 72 for the oil jacket shown in Figs. 11 to 13 described later. Fig. 10 is a sectional view viewed along a line X-X in Fig. 9 and shows a longitudinal section of the cylinder head 29 including the ignition plug insertion hole 69. 10 The oil jacket A8 is provided around the ignition plug insertion hole 69. The oil jacket A8 is an annular groove (see Fig. 9) and the circumference of the ignition plug 38 (see Fig. 2) is cooled by supplied oil. The upper end of the supply oil passage A7 in the cylinder head reaches the front side of the ignition plug oil jacket A8. The rear side of the ignition plug oil jacket A8 connects with the oil discharge passage A9 in the cylinder is head and oil that finishes the cooling of the circumference of the ignition plug 38 is discharged into the oil discharge passage A9 in the cylinder head. The upper part of the ignition plug oil jacket A8 is covered with the cover 72 for the oil jacket. Figs. 11 to 13 show the cover 72 for the oil jacket, Fig. 11 is a top view, Fig. 12 is a sectional view viewed along a line XII-XII in Fig. 11, and Fig. 13 is a sectional view 20 viewed along a line XIII-XIII in Fig. 11. In this engine 1, the valve train 45 is covered with the cylinder head cover 30 (see Figs. 2 and 3), however, as the upside of the ignition plug 38 is not covered with the cylinder head cover 30, the cover 72 for the oil jacket touches an air flow. A fin 73 for cooling the cover is provided to a top face of the cover 72 for the oil jacket and is useful for cooling the circumference of the ignition plug 38. 25 As described above, as the ignition plug 38 has structure exposed to outside air, water may enter the circumference of the ignition plug 38. Therefore, a water drain hole 74 is provided to the cover 72 for the oil jacket. A pair of attaching screw insertion holes 72a are provided to the cover 72 for the oil jacket. A bypass groove B I from a part adjacent to the position m2 in which the upper 30 end of the rising oil passage A5 in the cylinder block is open in the distributing groove A6 on the top face of the cylinder block and shown by a code s to the part shown by the code g3 in the recovering groove A10 on the top face of the cylinder block is formed on the top face of the cylinder block 28 on the right side of the cam chain chamber 52 shown in Fig. 7. The position m2 in which the upper end of the rising oil passage A5 in the cylinder 35 block is open and a starting point s of the bypass groove BI communicate via a bypass 14 groove B2 formed at the bottom of the cylinder head shown in Fig. 8. When the top face of the cylinder block 28 is covered with the bottom of the cylinder head 29, a bypass oil passage B that closely brings the distributing groove A6 on the top face of the cylinder block and the recovering groove A1O on the top face of the cylinder block is formed by 5 the bypass grooves B 1, B2 without passing the oil jacket A8. This oil passage is provided to reduce difference in temperature between the front side and the rear side of the cylinder block 28 by merging cooled oil that rises from the rising oil passage A5 in the cylinder block and high-temperature oil passing the oil jacket A8 in the recovering groove A10 on the top face of the cylinder block and to eliminate unevenness in cooling in the cylinder 10 block 28. A lubricating oil distributing groove 75 for distributing lubricating oil that lubricates each part of the valve train 45 is formed on the reverse side of the bypass oil passage with the cam chain chamber 52 in the center, that is, on the top face of the left side of the cylinder block 28. Fig. 14 is a rear view showing the cylinder block 28. The recovering grooves is A10 on the top faces of the right side and the left side of the cylinder block shown in Fig. 7 are also shown in Fig. 14. The lowering oil passage Al I in the cylinder block is extended downward from the vicinities of the centers of the respective recovering grooves A10 on the right side and on the left side. A pair of the lowering oil passages A II in the cylinder block reach the oil gallery A 12 on the discharge side in the lower part of the 20 cylinder block and are merged there. The discharge joint 53 is provided slightly on the left side from the center of the oil gallery A12 on the discharge side and the oil gallery A12 on the discharge side communicates with the discharge oil passage A13 in the crankcase via the discharge joint. In Fig. 14, the tensioner fitting 62 is provided in the center of the rear of the cylinder block 28. 25 Fig. 15 is a bottom view showing the cylinder block 28. The discharge joint 53 for connecting the oil passage to the discharge oil passage Al 3 in the crankcase is open slightly on the left side of the center of the oil gallery A12 on the discharge side on the rear side of the cylinder block 28. In Fig. 15, the oil gallery A4 on the supply side and the oil inlet 50 are also shown. 30 Fig. 16 is a side view showing a circumference of the oil return pipe A14. The discharge joint 53 communicates with an upper end of the discharge oil passage A13 in the crankcase provided to an upper part of the upper crankcase 27A. The discharge oil passage A13 in the crankcase is a short oil passage. An upper end of the oil return pipe A14 is inserted into the lower end of the discharge oil passage A13 in the crankcase via a 35 sealing member 82 and an intermediate part of the oil return pipe A14 is detachably fixed 15 to the oil pump 48 via a supporting member 80. A lower part of the oil return pipe A14 is extended to the vicinity of the bottom of the lower crankcase 27B, however, the lower part is not protruded downward from the bottom of the lower crankcase 27B. A lower end of the oil return pipe A 14 is open toward the oil pan 31. In Fig. 16, a locus 79a of the 5 maximum periphery of a crank web 78 (see Fig. 2) is shown. In a side view, the oil return pipe A14 is overlapped with the locus 79a of the crank web 78. Fig. 17 is a top view showing the lower crankcase 27B. A bottom plate 27Ba is provided to respective bottoms at right and left ends and at a front edge of the lower crankcase 27B, however, a lower opening 27Bb is made at the bottom of the center to io connect with the oil pan. In Fig. 17, a section of the crankshaft 32 supported by a bearing 83 is shown. The oil return pipe A14 is inserted in small space among a side wall of the cam chain chamber 52, the crank web 78 and the oil pump 48 and is supported by the oil pump 48 via the supporting member 80. In the above-mentioned oil passage, oil for cooling the cylinder head fed via the is oil pump 48 from the oil pan 31 is returned to the oil pan 31 through the discharge pipe Al, the pipe A2 bound for the oil cooler, the oil cooler return pipe A3, the oil gallery A4 on the supply side, the rising oil passage A5 in the cylinder block, the distributing groove A6 on the top face of the cylinder block, the supply oil passage A7 in the cylinder head, the ignition plug oil jacket A8, the discharge oil passage A9 in the cylinder head, the 20 recovering groove A10 on the top face of the cylinder block, the lowering oil passage Al I in the cylinder block, the oil gallery A12 on the discharge side, the discharge oil passage A13 in the crankcase and the oil return pipe A14, and the oil for cooling the cylinder head cools the cylinder head 29, circulating. In this circulating path, a part of the oil flows via the bypass grooves BI, B2 without passing the ignition plug oil jacket A8 25 and eliminates unevenness in cooling in the cylinder block 28. As shown in Figs. 7 and 8, a bypass oil passage B (configured by bypass grooves BI and B2) acquired by short-cutting the distributing groove A6 on the top face of the cylinder block and the recovering groove A10 on the top face of the cylinder block without passing the ignition plug oil jacket A8 is provided to the top face of the cylinder 30 block 28 and to the bottom of the cylinder head 29. Oil not heated in the oil jacket A8 is merged into high-temperature oil passing the oil jacket A8 by directly conducting a part of taken oil from the distributing groove A6 into the recovering groove A10 without passing the oil jacket A8, the temperature of oil in the discharge oil passage passing the cylinder block 28 is lowered, the difference in temperature of oil between the front side 16 and the rear side of the cylinder block 28 is reduced, and unevenness in cooling between the front and the rear of the cylinder block 28 is reduced. The bypass oil passage B shown in Figs. 7 and 8 is configured by the groove BI formed on the top face of the cylinder block 28, the bypass groove B2 for communication 5 formed at the bottom of the cylinder head 29 and the bottom that functions as a cover of the groove BI of the cylinder head 29. This reason is that the bypass oil passage B can be simply configured, compared with a case that the bypass oil passage B is formed by piercing the cylinder block, the working can be simplified and the working cost can be reduced. 10 The engine I equivalent to this embodiment is an air-cooled engine in which an air cooling fin is provided to the cylinder block 28, the rising oil passage A5 is arranged on the front side of the cylinder in a traveling direction of the vehicle (see Fig. 5), and the lowering oil passage All is arranged on the rear side of the cylinder (see Fig. 14). In such arrangement, as the front of the cylinder block is cooled by running wind and the is back of the cylinder block is heated by discharge oil through the cylinder head, unevenness is apt to occur in cooling the cylinder block, however, in this embodiment, unevenness in cooling by oil can be possibly inhibited owing to the bypass oil passage B. As shown in Fig. 7, the bypass groove BI is arranged on the top face of the cylinder block 28 between the cam chain chamber 52 and the cylinder 24 adjacent to the 20 cam chain chamber. As the bypass oil passage B I is arranged between the cylinder 24 and the cam chain chamber 52, the bypass groove is hardly influenced by heat from the cylinder, even if the bypass groove BI is arranged, a part forming a side wall of the cam chain chamber 52 is not influenced by heat and the strength is also not deteriorated because the part is relatively strong. 25 The bypass oil passage B is arranged in only the cylinder block on one side (on the right side) with the cam chain chamber 52 between both sides. As no bypass oil passage is arranged in the cylinder block on the other side (on the left side) with the cam chain chamber 52 between both sides though a large quantity of oil is required to be supplied on the side on which the bypass oil passage B exists, a flow rate of oil there is 30 not much. Therefore, the cross section of the rising oil passage A5 in the cylinder block connected to the distributing groove A6 on the top face of the cylinder block on one side (on the right side) with the cam chain chamber 52 between both sides and the cross section of the lowering oil passage Al I in the cylinder block connected to the recovering groove A10 on the top face of the cylinder block are enlarged, the cross section of the 35 rising oil passage A5 in the cylinder block connected to the distributing groove A6 on the 17 top face of the cylinder block on the other side (on the left side) with the cam chain chamber 52 between both sides and the cross section of the lowering oil passage A II in the cylinder block connected to the recovering groove A 10 on the top face of the cylinder block are reduced, and the quantity of oil in the cylinder block on both sides is balanced 5 (not shown). Hereby, the quantity of oil supplied to the oil jacket A8 around the ignition plug can be equalized. As shown in Fig. 7, the bypass oil passage is configured by forming the groove BI on the top face of the cylinder block and further, a lubricating oil distributing groove 75 for branching lubricating oil for lubricating a valve system is formed on the top face of io the cylinder block on the reverse side to the bypass groove Bl with the cam chain chamber 52 between both sides. As the bypass groove B I and the lubricating oil distributing groove 75 are formed in the cylinder block on both sides of the cam chain chamber 52, the plural passages can be worked on the same plane from the same direction in working the cylinder block, a man-hour is reduced, and as the passages are grooves, the is deterioration of the strength of the cylinder block can be inhibited. As shown in Fig. 7, the distribution of oil toward the cylinder head and the recovery of oil discharged from the cylinder head are performed via the distributing groove A6 on the top face of the cylinder block, the recovering groove A10 on the top face of the cylinder block and the bottom that closes the upside of the groove of the 20 cylinder head 29. Supply and discharge oil passages in an axial direction of the cylinder in the cylinder block 28 are reduced by forming oil passages utilizing the distributing groove A6 on the top face of the cylinder block or the recovering groove A10 on the top face of the cylinder block, working in the axial direction of the cylinder is reduced, and the working cost can be reduced by forming supply and discharge oil passages in the type 25 of the grooves. As shown in Fig. 7, there is an advantage that as the joints n1, n2 of the lowering oil passages A II in the cylinder block connected to the recovering groove A10 on the top face of the cylinder block are located in a range g1 -g2 and in a range g3-g4 respectively formed by connecting the joints of the plural discharge oil passages A9 in the cylinder 30 head connected to the groove A10, the groove is not required to be particularly extended. As shown in Fig. 7, as the joints ml, m2 of the rising oil passages A5 in the cylinder block connected to the distributing groove A6 on the top face of the cylinder block are located outside a range fl -f2 and outside a range f3-f4 respectively formed by connecting the joints of the plural supply oil passages A7 in the cylinder head connected 35 to the groove, a degree of freedom in arrangement such as the joints ml, m2 are arranged 18 close to an end of each groove in a direction in which the cylinders 24 are arranged in the cylinder block 28 is enhanced and the oil passages can be compactly arranged utilizing vacant space. As shown in Fig. 7, the joints ml, m2 of the rising oil passage A5 in the cylinder 5 block to the distributing groove A6 on the top face of the cylinder block and the joints n 1, n2 of the lowering oil passage All in the cylinder block to the recovering groove A10 on the top face of the cylinder block are set off in the direction in which the cylinders are arranged. This reason is that cooling performance can be optimized by changing the length of the oil passage in the groove on the top face of the cylinder block 28 such as 10 setting the long oil passage on the supply side on which oil is required to be cooled by running wind via a fin 81 for cooling the cylinder block (see Figs. 6 and 7) and setting the short oil passage on the discharge side on which the cooling of the discharged oil is not required. As shown in Fig. 7, on the supply side, each joint ml, m2 of each rising oil is passage A5 in the cylinder block joined to each distributing groove A6 on the top face of the cylinder block is located outside each range fl-f2, f3-f4 formed by connecting joints of the plural supply oil passages A7 in the cylinder head joined to each distributing groove A6 on the top face of the cylinder block. The width of the groove between ml and f2 and the width of the groove between m2 and f3 from each position ml, m2 in 20 which the upper end of each rising oil passage A5 in the cylinder block is open to each joint f2, f3 on each nearer side of the plural supply oil passages A7 in the cylinder head are widened, and the width of the groove between f2 and fl on the farther side than the joint f2 and the width of the groove between f3 and f4 on the farther side than the joint £3 are narrowed. On the far side, the decrease of oil pressure by the decrease of a flow rate 25 is inhibited and a flow of oil can be secured. As shown in Fig. 7, the cylinder block 28 is provided with plural stud bolt insertion holes 68 for inserting the bolt for fixing the cylinder block to the crankcase 27. The distributing groove A6 on the top face of the cylinder block and the recovering groove A10 on the top face of the cylinder block are formed, avoiding the stud bolt 30 insertion hole 68 on the side apart from the center of the cylinder. Hereby, as the groove is arranged in a direction apart from the cylinder, the rise of oil temperature by combustion heat in the cylinder can be inhibited. As shown in Fig. 7, each position ml, m2 in which the upper end of each rising oil passage A5 in the cylinder block is open is arranged outside each range fl-f2, f3-f4 35 formed by connecting joints of the plural supply oil passages A7 in the cylinder head in 19 the distributing groove A6 on the top face of the cylinder block and close to the cam chain chamber 52, and each position nI, n2 in which the upper end of each lowering oil passage All in the cylinder block is open is arranged inside each range gl -g2, g3-g4 formed by connecting joints of the plural discharge oil passages A9 in the cylinder head in the s recovering groove A10 on the top face of the cylinder block. Cooling performance can be enhanced by varying the length of the oil passage in the groove on the supply side and on the discharge side according to whether cooling by oil is required or not. The pair of right and left rising oil passages A5 in the cylinder block arranged close to the cam chain chamber 52 as shown in Fig. 7 are formed on the front side of the 10 engine 1, that is, toward the front of the vehicle (see Fig. 5). Each lower end of the right and left rising oil passages A5 in the cylinder block is connected to the oil gallery A4 on the supply side extended in the direction in which the cylinders are arranged (see Fig. 5). The oil gallery A4 on the supply side extended in the direction in which the cylinders are arranged across the cam chain chamber 52 is shorter, compared with the oil gallery A12 is on the discharge side similarly extended in the direction in which the cylinders are arranged across the cam chain chamber 52 (see Figs. 14, 15). As the shorter oil gallery A4 on the supply side is arranged on the front of the engine (see Fig. 3), the oil gallery A4 on the supply side is made less striking and the appearance quality of the engine I is kept. As shown in Fig. 3, the cam chain chamber 52 is overhanged toward the front of 20 the cylinder on the upside of the cylinder 24. The oil gallery A4 on the supply side provided to the front of the engine and extended in the direction in which the cylinders are arranged is arranged in a position before the overhang is started. Molding such as working is facilitated by arranging the oil gallery A4 on the supply side in the position on which the overhang of the cam chain chamber 52 has no effect. 25 As shown in Fig. 3, the tensioner fitting 62 to which the cam chain tensioner 63 for drawing the cam chain 51 is attached is provided to an outside face of the rear of the cam chain chamber 52 of the cylinder block 28, and the oil gallery A12 on the discharge side extended in the direction in which the cylinders 24 are arranged is let to pass on the downside of the tensioner fitting 62. Hereby, the oil gallery A12 on the discharge side is 30 arranged without interfering with the tensioner fitting 62, is arranged on the downside of the tensioner fitting 62, and is made less striking.

Claims

1. An oil passage for cooling a cylinder head of a multi-cylinder engine where a supply oil passage is connected from a cylinder block to an ignition plug oil jacket in the cylinder head and a discharge oil passage is formed, the oil passage comprising: a bypass oil passage that bypasses the ignition plug oil jacket and is provided to the cylinder block.

2. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 1, wherein the bypass oil passage is configured by a groove formed on a top face of the cylinder block and a bottom of the cylinder head that closes an upside of the groove.

3. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 1 or 2, wherein: the engine is an air-cooled engine where an air cooling fin is provided to the cylinder block; the supply oil passage is arranged on the front side of the cylinder in a traveling direction of a vehicle; and the discharge oil passage is arranged on the rear side of the cylinder.

4. The oil passage for cooling the cylinder head of the multi-cylinder engine according to any one of Claims 1 to 3, wherein: the engine is a parallel multi-cylinder engine provided with cylinders on both sides with a driving member housing for housing a valve system driving member between both sides; and the bypass oil passage is arranged in the cylinder block between the driving member housing and the cylinder adjacent to the driving member housing.

5. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 4, wherein: the bypass oil passage is arranged for only the cylinder on one side with the driving member housing between both sides; and for the cylinder on the other side with the driving member housing between both sides, each cross section of the supply oil passage and the discharge oil passage connected to each groove formed on the top face of the cylinder block is reduced, compared with each cross section of the supply oil passage and the discharge oil passage on one side. 21

6. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 4 or 5, wherein: the bypass oil passage is configured by forming the groove on the top face of the cylinder block; and further, a branching oil passage for branching lubricating oil for lubricating a valve system is formed on the top face of the cylinder block on the reverse side to the bypass oil passage with the driving member housing between both sides in the shape of a groove.

7. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 1, where oil is distributed and is recovered by a connecting oil passage for connecting the supply oil passage that conducts oil to the ignition plug oil jacket for each cylinder to the cylinder head of the multi-cylinder engine and the discharge oil passage for discharging oil from each oil jacket to a rising oil passage and a lowering oil passage which are respectively not branched for each cylinder to the cylinder block, wherein the connecting oil passage is configured by a groove formed on a top face of the cylinder block and a bottom of the cylinder head that closes an upside of the groove.

8. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 7, wherein a joint of the rising oil passage in the cylinder block or the lowering oil passage in the cylinder block connected to the groove on the top face of the cylinder block is located in a range formed by connecting joints of a plurality of supply oil passages in the cylinder head or a plurality of discharge oil passages in the cylinder head connected to the groove.

9. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 7, wherein a joint of the rising oil passage in the cylinder block or the lowering oil passage in the cylinder block connected to the groove on the top face of the cylinder block is located outside a range formed by connecting joints of the plurality of supply oil passages in the cylinder head or the plurality of discharge oil passages in the cylinder head connected to the groove.

10. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 8 or 9, wherein the joints of the rising oil passage in the cylinder block and the lowering oil passage in the cylinder block respectively connected to the groove on the top face of the cylinder block are set off in a direction in which the cylinders are arranged. 22

11. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 9, wherein on the supply side where the joint of the rising oil passage in the cylinder block connected to the groove on the top face of the cylinder block is located outside the range formed by connecting the joints of the plurality of supply oil passages in the cylinder head connected to the groove, the width of the groove from a position of an opening at an upper end of the rising oil passage in the cylinder block to the joint on the close side out of the joints of the plurality of supply oil passages in the cylinder head is widened and the width of the groove on the distant side from the joint is narrowed.

12. The oil passage for cooling the cylinder head of the multi-cylinder engine according to any one of Claims 7 to 11, wherein: the cylinder block is provided with a bolt insertion hole for inserting a bolt for fixing the cylinder block to a crankcase; and the groove is formed on the distant side from the center of the cylinder on the top face of the cylinder block, avoiding the bolt insertion hole.

13. The oil passage for cooling the cylinder head of the multi-cylinder engine according to any one of Claims 8 to 12, wherein: the engine is a parallel multi-cylinder engine provided with a plurality of cylinders on both sides with a driving member housing that houses a valve system driving member between both sides; either of the rising oil passage or the lowering oil passage in the cylinder block is located close to the driving member housing outside the range formed by connecting the joints of the plurality of supply oil passages or the plurality of the discharge oil passages in the cylinder head connected to a distributing groove or a recovering groove on the top face of the cylinder block; and the other of the rising oil passage or the lowering oil passage in the cylinder block is arranged in the range formed by connecting the joints of the plurality of supply oil passages or the plurality of discharge oil passages in the cylinder head connected to the groove. 23

14. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 13, wherein: the engine is an engine mounted in a small-sized vehicle; the cylinders are arranged in a direction of vehicle width; a pair of right and left rising/lowering oil passages arranged close to the driving member housing in the cylinder block, the pair of right and left rising oil passages are formed at the front of the vehicle engine; and each lower end of the right and left rising oil passages or the right and left lowering oil passages in the cylinder block is connected to an oil gallery extended in the direction in which the cylinders are arranged.

15. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 14, wherein: the driving member housing is overhanged at the front of the cylinder block in a higher position of an upper part of the cylinder block; and the oil gallery provided to the front of the engine and extended in the direction in which the cylinders are arranged is arranged in the vicinity of a starting point of the overhang.

16. The oil passage for cooling the cylinder head of the multi-cylinder engine according to Claim 14, wherein: the valve system driving member uses a cam chain for a driving transmitting member; a cam chain tensioner fitting to which a tensioner for tensioning the chain is attached is provided to an outside face of the driving member housing; and the oil gallery connected to the lowering oil passage in the cylinder block and extended in the direction in which the cylinders are arranged is let to pass on the downside of the cam chain tensioner fitting.

17. An oil passage for cooling a cylinder head of a multi-cylinder engine, the oil passage substantially as shown in the accompanying drawings. Honda Motor Co., Ltd. Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON