Title of Invention

CRANKSHAFT SUPPORTING STRUCTURE

Abstract

[Document Name] Abstract of the Disclosure [Abstract] [Problem] To simplify, in a crankshaft supporting structure wherein ball bearings through which crankshaft journals are inserted are supported by bearing sections provided in an aluminum-alloy crankcase, the structures of the bearing sections and effectively prevent, when the engine is heated, the generation of clearances between the bearing sections and the ball bearings. [Solution] Bushes 54 formed of an iron alloy are provided on radially inward sides of bearing sections 53, respectively, and a radial thickness "b" of bush supporting layers 55 which support the bushes 54 in the bearing section 53 from radially outside is one-third a radial thickness "a" of the bushes 54 or smaller. [Selected Drawing] Fig. 3

Full Text

[Document Name] Specification [Title of the Invention] CRANKSHAFT SUPPORTING STRUCTURE [Technical Field] [0001] The present invention relates to a crankshaft supporting structure in a reciprocating engine of, for example, a vehicle. [Background Art] [0002] Crankshaft supporting structures which have been used in reciprocating engines of, for example, vehicles include those in which outer circumferences of ball bearings, through which crankshaft journals are inserted, are supported by cast-iron bushes cast to be integral with an aluminum alloy crankcase and steel bushes press-fitted in the cast-iron bushes (see Patent Document 1, for example). Such crankshaft supporting structures are designed to prevent, when an aluminum-alloy crankcase thermally expands, the generation of clearances between the inner circumferences of bearing sections and the outer circumferences of iron-alloy ball bearings. [Patent Document 1] JP-A No. 2003-184648 [Disclosure of the Invention] [Problem to be Solved by the Invention] [0003] Even though the crankshaft supporting structure as described above can slightly lower the coefficient of thermal expansion of the bearing sections, it poses problems such as a complicated bearing section structure resulting from the adoption of a dual bush configuration and an additional manufacturing process required to press-fit the steel bushes. Furthermore, since a difference in the coefficient of thermal expansion remains between the bearing sections and the ball bearings, the possibility of clearance generation between them is not removed. An object of the present invention is to simplify, in a crankshaft supporting structure wherein ball bearings through which crankshaft journals are inserted are supported by bearing sections provided in an aluminum-alloy crankcase, the structures of the bearing sections and effectively prevent, when the engine is heated, the generation of clearances between the bearing sections and the ball bearings. [Means for Solving the Problem] [0004] To address the above problems, the invention according to Claim 1 provides a crankshaft supporting structure in which a ball bearing (for example, the ball bearing 52 of the following embodiment) through which a journal (for example, the journal 42 of the following embodiment) of a crankshaft (for example, the crankshaft 15 of the following embodiment) is inserted is supported by a bearing section (for example, the bearing section 53 of the following embodiment) provided in a crankcase (for example, the crankcase 16 of the following embodiment) formed of an aluminum alloy; wherein a bush (for example, the bush 54 of the following embodiment) formed of an iron alloy is provided on a radially inward side of the bearing section, and wherein a radial thickness (for example, the thickness "b" of the following embodiment) of a bush supporting layer (for example, the bush supporting layer 55 of the following embodiment) which supports the bush from radially outside is one-third a radial thickness (for example, the thickness "a" of the following embodiment) of the bush or smaller. [0005] The invention according to Claim 2 provides the crankshaft supporting structure wherein the radial thickness of the bush is larger than an axial thickness (for example, the thickness "c" of the following embodiment) of the bush. [Effect of the Invention] [0006] According to the invention according to Claim 1, increasing the portion of the bearing section accounted for by the bush formed of an iron alloy efficiently brings down the coefficient of thermal expansion of the bearing section close to that of the iron alloy. It is, therefore, possible to effectively prevent, when the engine is heated, the generation of a clearance between the inner circumference (bearing supporting surface) of the bush and the outer circumference (bearing surface to be supported) of the ball bearing, so that the generation of vibrations and noise attributable to such a clearance can be prevented. With no more bush than the single bush required for the bearing section 53, the bearing section can be configured simply and manufactured through a simple process. [0007] According to the invention according to Claim 2, the decrease in the bush supporting rigidity caused by the thinness of the bush supporting layer can be made up for by the rigidity of the bush itself. Also, by increasing the portion of the bearing section accounted for by the bush, the coefficient of thermal expansion of the bearing section can be efficiently brought down close to that of the iron alloy. [Best Mode for Carrying Out the Invention] [0008] An embodiment of the present invention will be described below with reference to drawings. Note that, unless otherwise specified, the directions left, right, front, and rear mentioned in the following description are as seen in the forward direction of the vehicle. In the drawings referred to in the following, the arrows marked "FR," "LH," and "UP" denote a forward direction, a leftward direction, and an upward direction of the vehicle, respectively. [0009] A scooter-type motorcycle 1 shown in Fig. 1 has a headpipe 3 which is located in a front end portion of a body frame 2 and which steerably supports a front fork 5 and a steering handlebar 6, the front fork 5 rotatably supporting a front wheel A. A rear portion of the body frame 2 supports an integrally structured swing-type power unit (hereinafter referred to as the "swing unit") 11 including, in a front portion thereof, an engine 7 which drives the motorcycle 1 and, in a rear portion thereof, a rear wheel 8 which is a drive wheel. [0010] t A lower front portion of the swing unit 11 is vertically swingably supported at a lower rear portion of the body frame 2 via a link member 12. A rear end portion of the swing unit 11 is supported at a rear end portion of the body frame 2 via a rear cushion 13 provided as a cushioning device. The swing unit 11 that can, pivotally turning about the link member 12, vertically swing together with the rear wheel 8 makes up a so-called swing-type rear suspension. [0011] The swing unit 11 integrally includes the engine 7 provided in a front portion thereof and a power transmission mechanism 14 provided in a rear left side portion thereof. The engine 7 is a water-cooled, four-stroke, OHC single-cylinder engine mounted such that the rotary axis (crank axis) CI of a crankshaft 15 extends laterally (in the vehicle width direction) and such that a cylinder 17 projects from a front end portion of a crankcase 16 approximately horizontally forwardly (to be more precise, slightly upwardly forwardly). In Fig. 1, reference code C2 denotes the axis (cylinder axis) of the cylinder 17. [0012] Referring to Fig. 2, the crankcase 16 includes a left half case 18 and a right half case 19 with a division plane between them lying perpendicularly to the lateral direction. A left case body 21 is formed integrally with the left half case 18 of the crankcase 16. It bulges leftward from a rear left side portion of the left half case 18 and, from the bulging portion, extends rearward. The left case body 21 and a left case cover 22 attached to the left side of the left case body 21 make up a transmission case 23 included in the power transmission mechanism 14. [0013] The transmission case 23 accommodates a belt-type continuously variable transmission 24 included in the power transmission mechanism 14. A drive pulley 25 of the belt-type continuously variable transmission 24 is coaxially supported on a left side portion of the crankshaft 15. A kick starter device 26 is disposed laterally outside the belt-type continuously variable transmission 24 accommodated in the transmission case 23. A fan 25a for introducing cooling air into the transmission case 23 is provided on the left side of the drive pulley 25. [0014] The right half case 19 of the crankcase 16 is, on its right side, attached with a right case cover 28 which supports a radiator 27. Inside the right case cover 28, a generator 29, which generates electric power for the motorcycle 1, is installed coaxially with the crankshaft 15. An outer rotor 29a located on the right of the generator 29 is supported on a right side portion of the crankshaft 15 to be rotatable integrally with the crankshaft 15. A fan 29b is provided on the right of the outer rotor 29a, the fan 29b being for supplying cooling air to the radiator 27 installed adjacently on its right. The outer rotor 29a is shaped like a cup positioned to be open rightwardly. Inside the outer rotor 29a, a stator coil 29c is disposed to be supported by the right half case 19. [0015] The cylinder 17 of the engine 7 includes a cylinder body 31 attached directly to a front end portion of the crankcase 16, a cylinder head 32 attached to a front end portion of the cylinder body 31, and a head cover 33 attached to a front end portion of the cylinder head 32. Inside the cylinder body 31: a piston 35 demarcating a combustion chamber 34 is reciprocatably fitted; a small end portion of a connecting rod 36 is swingably linked to the piston 35 via a piston pin 35a; and a crankpin 37 of the crankshaft 15 is turnably linked to a large end portion of the connecting rod 36 via a roller bearing 38. In Fig. 2, reference numeral 39 denotes a spark plug exposed in the combustion chamber 34. [0016] The crankshaft 15 integrally includes left and right crank webs 41 supporting the crankpin 37, left and right journals 42 projecting from the left and right crank webs 41 leftwardly and rightwardly, respectively, and left and right support shafts 43 extending from the left and right journals.42 leftwardly and rightwardly, respectively. The crankshaft 15 is assembled of left and right split bodies coupled together with a crankpin 37, the left and right split bodies including the left and right crank webs 41, left and right journals 42, and left and right support shafts 43, respectively. [0017] A drive sprocket 45 for driving a camshaft 44 in the cylinder head 32 is coaxially mounted on the base end side of the right support shaft 43. The cam shaft 44 is disposed in the cylinder head 32 in parallel with the crankshaft 15 with left and right side portions thereof rotatably supported by the cylinder head 32. A driven sprocket 46 is coaxially mounted on a right end portion of the camshaft 44. A cam chain 47 is wound around the driven sprocket 46 and the drive sprocket 45. A cam chain chamber 47a to accommodate the cam chain 47 is provided on the right of the cylinder 17. When the camshaft 44 rotates in association with the rotation of the crankshaft 15, intake and exhaust valves supported in the cylinder head 32 are driven to open and close intake and exhaust ports (valves and ports are not shown). [0018] A water pump 48 to circulates cooling water through various parts of the engine is mounted to the right of the cylinder head 32 to be rotatable coaxially and integrally with the cam shaft 44. A cooling water inlet port (or outlet port) of the water pump 48 is connected to a cooling water outlet port (or inlet port) of a radiator 27 with a cooling water hose 48a. A water jacket 49 for circulating cooling water from the water pump 48 is appropriately formed inside the cylinder head 32 and an upper portion of the cylinder body 31. [0019] A drive gear 45a for driving an oil pump, not shown, is provided immediately on the right of the drive sprocket 45. The oil pump is disposed, for example, in a lower inside portion of the crankcase 16. The engine oil discharged from the oil pump is supplied to around the connecting rod 36 via the crankpin 37 as well as to around the camshaft 44 via the cylinder body 31 and the cylinder head 32. [0020] Left and right side walls 51 which are approximately perpendicular to the crank axis CI in the crankcase 16 (left and right half cases 18 and 19) are provided with left and right bearing sections 53 which support the left and right journals 42 of the crankshaft 15 via left and right ball bearings 52. The left and right bearing sections 53 include left and right axially thick portions (portions with a large width along the axial direction) formed, to support the left and right ball bearings 52, around left and right through-holes which are formed through the left and right side walls 51 and about the crank axis CI and left and right bushes 54 fitted inside the left and right axially thick portions. [0021] The crankcase 16 (including the left and right half cases 18 and 19) is formed, for example, by casting an aluminum alloy (conforming to JIS 5302, for example). The crankshaft 15 is formed, for example, by forging an iron alloy (conforming to JIS 4051, for example). The linear coefficient of thermal expansion of the crankcase 16 (of an aluminum alloy) is about 2.4 x 10"5/K. The linear coefficient of thermal expansion of the crankshaft 15 (of an iron alloy) is about 1.2 x 10"5/K. [0022] The left and right ball bearings 52 include outer races and inner races formed of an iron alloy (conforming to JIS 4805, for example) with a coefficient of thermal expansion equivalent to that of the crankshaft 15. The left and right bushes 54 are formed of an iron alloy (conforming to JIS 5502, for example) also with a coefficient of thermal expansion equivalent to that of the crankshaft 15. [0023] The left and right bushes 54 are formed annularly about the crank axis CI. They each have a cross-section which is perpendicular to their circumferential direction and which is approximately rectangular, having two sides approximately in parallel with the crank axis CI and other two sides perpendicular to the crank axis CI. The outer races of the left and right ball bearings 52 are press-fitted inside the left and right bushes 54, respectively. The left and right journals 42 are inserted through and supported in the inner circumferences of the left and right ball bearings 52 . [0024] Referring to Fig. 3(a), the left and right bushes 54 are inserted in position, when the crankcase 16 (including the left and right half cases 18 and 19) is formed by casting an aluminum alloy, so that they are held integrally with the crankcase 16 with their outer circumferences and their left and right outer sides supported by the crankcase 16. In the following, left and right portions (forming aluminum alloy layers) which are included in the left and right axially thick portions of the left and right bearing sections 53, respectively, and which support the left and right bushes 54 from the outer circumference sides will be referred to as bush supporting layers 55. Even though Fig. 3(a) shows only the left bearing section 53, the configuration shown in Fig. 3(a) also applies to the right bearing section 53 unless otherwise mentioned. [0025] Left and right outside portions which are included in the left and right axially thick portions of the left and right bearing sections 53, respectively, and which support the left and right bushes 54 from left and right outsides, respectively, will be referred to as left and right bush outside supporting sections 56, respectively. Left and right radially inward portions (end portions) of the left and right bush outside supporting sections 56, respectively, will be referred to as left and right bearing outside supporting sections 57. The left and right bearing outside supporting sections 57 support left and right outs-ide portions of the outer races of the left and right ball bearings 52, respectively. [0026] The left and right bearing sections 53 are formed laterally asymmetrically to each other for the convenience of forming oil paths for engine oil in the crankcase 16. In the right bearing section 53, for example, an oil path communicated with an oil path 59 (see Fig. 2) formed in the right side wall 51 is appropriately formed in the right bush 54 to allow the engine oil to be supplied to the crankpin 37 via the right bush 54. [0027] If the bush supporting layers 55 formed of an aluminum alloy are thicker than the bushes 54 formed of an iron alloy, the bushes 54 are affected by the thermal expansion of the bush supporting layers 55 to be caused to expand excessively. As a result, the coefficient of thermal expansion of the bearing sections 53 as a whole rises close to that of the aluminum alloy. This causes the inner circumferences of the bearing sections 53 (bushes 54) to radially expand more than the outer circumferences of the ball bearings 52 made of an iron alloy to possibly generate clearances between them. [0028] In the bearing supporting sections 53 of the present embodiment, a radial thickness "b" of the bush supporting layers 55 is, as shown in Fig. 3(a), smaller than the radial thickness "a" of the bushes 54 (to be more concrete, one-third the radial thickness "a" or smaller). In this configuration, the bushes 54 account for a large portion of the bearing supporting sections 53, so that the coefficient of thermal expansion of the bearing supporting sections 53 as a whole comes close to that of the iron alloy. The bush supporting layers 55 may be partly cut out. [0029] In Fig. 3(b), curve J represents the variation of the coefficient of linear expansion of the bearing supporting sections 53 as a whole relative to the ratio b/a obtained by dividing the radial thickness "b" of the bush supporting layers 55 by the radial thickness "a" of the bushes 54. The curve J has been obtained based on plural values of the coefficient of linear expansion measured with varied values of the ratio b/a. In Fig. 3(b), linear lines A and F represent the coefficient of linear expansion of an aluminum alloy and that of an iron alloy, respectively. [0030] From Fig. 3(b), it is known that, as the radial thickness "b" of the bush supporting layers 55 decreases and the radial thickness "a" of the bushes 54 increases (i.e. as the ratio b/a decreases), the coefficient of linear expansion of the bearing sections 53 as a whole decreases to come closer to that of the iron alloy. It is also known that, when the ratio b/a lowers to or below 1/3, the coefficient of linear expansion of the bearing sections 53 as a whole decreases at a larger rate. Hence, reducing the ratio b/a to or below 1/3 makes it possible to efficiently decrease the coefficient of linear expansion of the bearing sections 53 as a whole bringing it close to that of the iron alloy. [0031] Referring to Fig. 3(a), an axial thickness "c" of the bush 54 in the bearing section 53 is approximately equal to the radial thickness "a" (to be more precise, the radial thickness "a" is slightly larger than the axial thickness "c"). This makes the cross-section perpendicular to the circumferential direction of the bush 54 approximately square, so that the bush supporting rigidity reduced by the thinness of the bush supporting layer 55 is made up for by the rigidity of the bush 54 itself in a well-balanced manner. [0032] As described above, in the crankshaft supporting structure of the present embodiment, the ball bearings 52 through which the journals 42 of the crankshaft 15 are inserted are supported by the bearing sections 53 provided in the crankcase 16 formed of an aluminum alloy. In this crankshaft supporting structure, the bushes 54 formed of an iron alloy are provided on radially inward sides of the bearing sections 53. In the bearing sections 53, the radial thickness "b" of the bush supporting layers 55 that support the bushes 54 from radially outside is as small as one-third the radial thickness "a" of the bushes 54 or smaller. [0033] In the above configuration, increasing the portion of the bearing sections 53 accounted for by the bushes 54 formed of an iron alloy efficiently brings down the coefficient of thermal expansion of the bearing sections 53 close to that of the iron alloy. It is, therefore, possible to effectively prevent, when the engine is heated, the generation of clearances between the inner circumferences (bearing supporting surfaces) of the bushes 54 and the outer circumferences (bearing surfaces to be supported) of the ball bearings 52, so that the generation of vibrations and noise attributable to such clearances can be prevented. With no more bush than the single bush 54 required for each of the bearing sections 53, the bearing sections 53 can be configured simply and manufactured through a simple process. [0034] In the above crankshaft supporting structure, the radial thickness "a" of the bushes 54 is larger than their axial thickness "c", so that the bush supporting rigidity reduced by the thinness of the bush supporting layers 55 is made up for by the rigidity of the bushes 54 themselves. The crankshaft supporting structure also makes it possible to efficiently bring down, by increasing the portion of the bearing sections 53 accounted for by the bushes 54 formed of an iron alloy, the coefficient of thermal expansion of the bearing sections 53 close to that of the iron alloy. [0035] The application of the present invention is not limited to the above embodiment. The invention can be applied not only to a motorcycle but also to, for example, other types of vehicles such as a three-wheeled vehicle or a four-wheeled vehicle or to various types of transport machines such as an airplane or a ship. Furthermore, the invention can be applied to general reciprocating engines having a crankshaft. The configuration of the above embodiment represents only an example of the invention, and it can be modified in various ways, for example, as to the number or arrangement of engine cylinders, without departing from the scope of the invention. [Brief Description of the Drawings] [0036] [Fig. 1] Fig. 1 is a left side view of a motorcycle according to an embodiment of the invention. [Fig. 2] Fig. 2 is a cross-sectional view of the engine of the motorcycle, taken along the crankshaft axis. [Figs. 3] Fig. 3(a) is an expanded view of a bearing section shown in Fig. 2, and Fig. 3(b) is a graph showing a variation of the coefficient of linear expansion of the bearing section relative to dimensional changes of the bearing section. [Description of Reference Numerals] [0037] 15... Crankshaft 16... Crankcase 42... Journal 52... Ball bearing 53... Bearing section 54... Bush 55... Bush supporting layer a... Radial thickness of bush b... Radial thickness of bush supporting layer c... Axial thickness of bush 18 [Document Name] Scope of Claims [Claim 1] A crankshaft supporting structure in which a ball bearing, through which a journal of a crankshaft is inserted, is supported by a bearing section provided in a crankcase formed of an aluminum alloy: wherein a bush formed of an iron alloy is provided on a radially inward side of the bearing section and a radial thickness of a bush supporting layer which supports the bush from radially outside is one-third a radial thickness of the bush or smaller. [Claim 2] The crankshaft supporting structure according to Claim 1, wherein the radial thickness of the bush is larger than an axial thickness of the bush.

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2308-CHE-2008 CORRESPONDENCE OTHERS 19-08-2014.pdf

2308-CHE-2008 FORM-1 19-08-2014.pdf

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2308-che-2008 claims.pdf

2308-che-2008 correspondence-others.pdf

2308-che-2008 description (complete).pdf

2308-che-2008 drawings.pdf

2308-che-2008 form-1.pdf

2308-che-2008 form-18.pdf

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2308-CHE-2008-Petition for POR.pdf

2308-CHENP-2008 AMENDED CLAIMS 14-03-2014.pdf

2308-CHENP-2008 AMENDED PAGE OF SPECIFICATION 14-03-2014.pdf

2308-CHENP-2008 EXAMINATION REPORT REPLY RECEIVED 14-03-2014.pdf

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