JP2020076343A - Bearing structure - Google Patents

Abstract

To reduce engine noise by suppressing deformation of a bearing housing.SOLUTION: A bearing structure includes a first bearing (23) fitted to a crank shaft (2), a second bearing (31) fitted to a balancer shaft (30) canceling rotational vibration of the crank shaft, and an aluminum alloy crank case (10) formed by casting a bearing housing (5) made of cast iron and covering outer peripheries of the first bearing and the second bearing. The bearing housing is formed in a manner of being kept into contact with an outer peripheral surface of the first bearing, and formed at an interval with respect to an outer peripheral surface of the second bearing.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a bearing structure.

  Conventionally, in order to improve the strength of the bearing hole of the crankcase, a technique of casting an annular insert made of a hard material around the entire circumference of the bearing hole has been proposed (see, for example, Patent Document 1). In Patent Document 1, a bearing is press-fitted into the annular insert, and the crankshaft is supported by the crankcase via the bearing.

  Further, in an engine equipped with a balancer shaft, in order to improve the strength of the bearing hole and suppress fluctuations in the axial distance between the crankshaft and the balancer shaft, a biaxially integrated insert may be cast into the bearing hole.

Japanese Utility Model Publication No. 59-42314

  However, when the integral insert is used, a nonuniform wall thickness may occur such as a thick wall between the two shafts. For this reason, there is a possibility that thermal strain in the bearing press-fitting holes on the crankshaft side of the insert becomes non-uniform as the temperature of the crankcase rises. As described above, the uneven deformation of the bearing press-fitting holes causes the noise of the bearing.

  The present invention has been made in view of the above point, and an object of the present invention is to provide a bearing structure capable of suppressing deformation of the bearing housing and reducing engine noise.

  A bearing structure for an engine according to an aspect of the present invention includes a first bearing fitted to a crankshaft, a second bearing fitted to a balancer shaft that cancels rotational vibration of the crankshaft, the first bearing, and An aluminum alloy crankcase formed by casting a cast iron bearing housing that covers the outer periphery of the second bearing, the bearing housing being formed so as to contact the outer peripheral surface of the first bearing. It is characterized in that it is formed so as to leave a gap with respect to the outer peripheral surface of the second bearing.

  According to the present invention, it is possible to suppress deformation of the bearing housing and reduce engine noise.

FIG. 3 is a perspective view of the engine according to the present embodiment. FIG. 4 is a front view showing the right side portion of the crankcase according to the present embodiment. FIG. 3 is a view on arrow A in FIG. 2. It is a B arrow line view of FIG. It is sectional drawing cut | disconnected along CC line of FIG. It is a top view and a side view of a bearing housing concerning this embodiment. FIG. 3 is a cross-sectional view of the engine according to the present embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following, an example in which the present invention is applied to a motorcycle engine will be described, but the application target is not limited to this and can be changed. For example, the present invention may be applied to other types of vehicles, for example, saddle type vehicles such as buggy type tricycles and four-wheeled vehicles. Regarding the direction, arrow FR indicates the front of the vehicle, arrow RE indicates the rear of the vehicle, arrow L indicates the left side of the vehicle, and arrow R indicates the right side of the vehicle. In addition, in each of the following drawings, a part of the configuration is omitted for convenience of description.

  First, the schematic configuration of the engine according to the present embodiment will be described with reference to FIGS. 1 to 4 and 7. FIG. 1 is a perspective view of the engine according to the present embodiment. FIG. 2 is a front view showing the right side portion of the crankcase according to the present embodiment. FIG. 3 is a view on arrow A of FIG. FIG. 4 is a view on arrow B of FIG. FIG. 7 is a sectional view of the engine according to the present embodiment.

  As shown in FIGS. 1 and 7, the engine 1 according to the present embodiment is a single-cylinder engine, and includes a left and right crankcase 10. The crankcase 10 is made of, for example, an aluminum alloy. The crankcase 10 accommodates various shafts such as the crankshaft 2. A cylinder block, a cylinder head, and a cylinder head cover (not shown) are attached to the upper part of the crankcase 10 in order from the bottom.

  The crankcase 10 includes a left case 11 and a right case 12 that can be divided into left and right parts on the center axis of the cylinder. By fastening the left case 11 and the right case 12 with bolts or the like, a space for accommodating various shafts (hereinafter, referred to as a crank chamber S1) is formed inside. The left side of the left case 11 is opened, and the opened space constitutes a magneto chamber S2 for accommodating a magnet 24 described later. The opening of the left case 11 is closed by the magneto cover 13. Further, the right side of the light case 12 is also opened, and the opened space constitutes a clutch chamber S3 that accommodates a clutch (not shown). The opening of the light case 12 is closed by the clutch cover 14.

  The crank chamber S1 is formed by a plurality of partition walls. Specifically, the left case 11 is formed with a first partition wall 15 that partitions the crank chamber S1 and the magneto chamber S2. Further, the light case 12 is formed with a second partition wall 16 for partitioning the crank chamber S1 and the clutch chamber S3. Although details will be described later, the crankshaft 2 is disposed between the first partition wall 15 and the second partition wall 16, the left end portion of the crankshaft 2 is supported by the first partition wall 15, and the right end portion of the crankshaft 2 is located at the second end portion. It is supported by the partition wall 16.

  The crankshaft 2 has a central axis (rotating axis) extending in the vehicle width direction (left-right direction) on an extension line of the central axis of the cylinder. Specifically, the crankshaft 2 includes a crank pin 20, a pair of left and right crank webs 21a and 21b provided on both sides of the crank pin 20, and a position eccentric from the crank pin 20 to a side from each of the crank webs 21a and 21b. It has a pair of left and right main journals 22a and 22b that project. The crank webs 21a and 21b project radially opposite to the crank pins 20 with respect to the main journals 22a and 22b. The protruding portion constitutes a weight portion of the crankshaft 2.

  The left main journal 22a and the right main journal 22b are located on the same axis, and constitute the rotation axis of the crankshaft 2. That is, the crank pin 20 has an axial center at a position eccentric from the rotary shaft of the crank shaft 2. The left main journal 22a is supported by the first partition wall 15 of the left case 11 via a bearing 23 (first bearing). The left bearing 23 is press-fitted from the vehicle inner side (right side) into the press-fitting hole 15a (see the difference in FIG. 7) formed in the left case 11 (first partition wall 15). The right main journal 22b is supported by the second partition wall 16 of the light case 12 via a bearing 23. The right bearing 23 is press-fitted into the press-fitting hole 16a formed in the light case 12 (second partition 16) from the inside (left side) of the vehicle. The left and right bearings 23 are fitted to the crankshaft 2, respectively.

  A magnet 24 is provided at the end of the left main journal 22a. The magneto 24 is a so-called generator and includes a stator 25 fixedly arranged around the main journal 22 a and a cylindrical rotor 26 surrounding the stator 25. The rotor 26 is fixed to the main journal 22a and is configured to rotate integrally with the crankshaft 2. Electric power is generated as the rotor 26 rotates relative to the stator 25. The magneto 24 is covered by the magneto cover 13. A primary drive gear 27 is provided at the end of the right main journal 22b.

  A piston 29 (see FIG. 7) is connected to the crankshaft 2 via a connecting rod 28. Specifically, one end of the connecting rod 28 is connected to the crank pin 20 between the pair of crank webs 21a and 21b, and the other end of the connecting rod 28 is connected to the piston 29. The connecting rod 28 is located on the split surfaces of the left case 11 and the right case 12. The piston 29 has a cylindrical shape corresponding to a cylinder bore (not shown) formed in the cylinder block. The axis of the cylinder bore is slightly inclined forward with respect to the vertical direction, and the piston 29 is reciprocally housed along the axis.

  Further, on the right side of the cylinder bore, that is, on the right side of the connecting rod 28, a cam chain chamber S4 for housing a cam chain (not shown) is formed. The cam chain chamber S4 is formed to extend vertically so that the cylinder head cover and the crankcase 10 (light case 12) communicate with each other. That is, the cam chain chamber S4 communicates with the clutch chamber S3 below.

  Next, various axial arrangements will be described. As shown in FIG. 2 to FIG. 4, the crankshaft 2 is arranged slightly biased to the front side with respect to the center of the crankcase 10 in the front-rear direction in a side view. A balancer shaft 30 is arranged in front of the crankshaft 2.

  As shown in FIG. 7, the balancer shaft 30 extends in the left-right direction in parallel with the axial direction of the crankshaft 2. The balancer shaft 30 is formed thinner than the main journals 22a and 22b. Both ends of the balancer shaft 30 are supported by the crankcase 10 via bearings 31 (second bearings). The outer diameter of the bearing 31 is smaller than the outer diameter of the bearing 23. The bearing 31 on the left side is press-fitted into the press-fitting hole 15b formed in the left case 11 (first partition wall 15) from the inside (right side) of the vehicle. The right bearing 31 is press-fitted into the press-fitting hole 16b formed in the light case 12 (second partition 16) from the vehicle inside (left side). The bearings 31 on both the left and right sides are fitted to the balancer shaft 30.

  The balancer shaft 30 is provided with a balancer weight 32 that projects radially outward. The balancer weight 32 is located between the pair of crank webs 21a and 21b. Further, the right end side of the balancer shaft 30 projects further to the right than the right bearing 31, and a balancer driven gear 33 is provided at the tip thereof. The balancer driven gear 33 meshes with the primary drive gear 27. The balancer shaft 30 is rotated by the rotation of the crankshaft 2. This makes it possible to cancel the rotational vibration of the crankshaft 2.

  Returning to FIG. 2 to FIG. 4, the counter shaft 34 is disposed above and behind the crankshaft 2. The counter shaft 34 extends in the left-right direction in parallel with the axial direction of the crankshaft 2. The counter shaft 34 is provided with a clutch and various gears for shifting (both not shown), and the clutch is provided at the right end of the counter shaft 34. The clutch is covered by a clutch cover 14 (see FIG. 7). A drive shaft 35 is provided below the counter shaft 34. The drive shaft 35 is provided with various gears (not shown) for shifting. By changing the combination of various gears of the counter shaft 34 and the drive shaft 35, gear shifting is possible.

  Here, the bearing structure of the crank shaft and the balancer shaft will be described. FIG. 5 is a cross-sectional view taken along the line CC of FIG. FIG. 6 is a plan view and a side view of the bearing housing according to the present embodiment.

  As described above, in the left and right split crankcases, for example, the following structures exist for supporting the crankshaft. (1) Bearing structure with a metal bearing in which half-split metal is press-fitted into the crankcase. (2) A bearing structure with a ball bearing in which the ball bearing is pressed into the crankcase. This embodiment corresponds to the structure of (2) above.

  In the bearing structure of (2), there is one in which a cast iron bearing housing is cast inside the aluminum of the crankcase. The bearing housing connects the bearing press-fitting hole for the crankshaft and the bearing press-fitting hole for the balancer shaft adjacent thereto. This is to suppress fluctuations in the distance between the crank shaft and the balancer shaft and prevent unpleasant noise. Factors that cause the axial distance to change include, for example, deformation due to centrifugal force generated by rotational imbalance of the crank shaft and balancer shaft, thermal expansion of components, and the like.

  In the conventional bearing structure adopting the structure of (2), since the bearing housing encloses the two bearing press-fitting holes with cast iron having an appropriate thickness, it often has an 8-shape. Further, depending on the distance between the shafts and the thickness of the cast iron, the ring shapes surrounding the outer circumference of the crankshaft and the outer circumference of the balancer shaft may be close to each other and overlap each other. In this case, the shape of the bearing housing is designed by connecting the overlapping portions of two adjacent ring shapes with an appropriate R shape. Since this bearing housing is exposed in the bearing press-fitting hole, the inner surface of the bearing housing and the outer surface of the bearing of each shaft come into direct contact with each other.

  In the conventional 8-shaped bearing housing, the thickness of the cast iron enclosing each bearing may be uneven. If the cast iron has a non-uniform thickness, when the temperature of the bearing housing rises due to engine operation or the like, thermal deformation may cause a decrease in circularity in the crankshaft and balancer shaft journals. This causes uneven deformation of the press-fitted bearing. As a result, the rotation of the bearing is affected, which may cause unpleasant engine noise.

  Therefore, the inventors of the present invention have noticed that the ratio of the torque applied to each of the crank shaft and the balancer shaft is larger in the crank shaft than in the balancer shaft, and have conceived the shape of the bearing housing according to the present invention.

  As shown in FIGS. 5 and 7, bearing housings 4 and 5 made of cast iron are cast in the crankcase 10. Specifically, the left bearing housing 4 is cast in the first partition wall 15 of the left case 11. The bearing housing 4 is formed in a ring shape so as to cover the outer periphery of the bearing 23. Further, the bearing 23 is press-fitted into the inner peripheral portion of the bearing housing 4, and the inner peripheral surface of the bearing housing 4 is in contact with the outer peripheral surface of the bearing 23. That is, the inner peripheral portion of the bearing housing 4 constitutes the press-fitting hole 15 a for the bearing 23. By covering the periphery of the bearing 23 with the bearing housing 4 made of cast iron which is harder than aluminum alloy, it is possible to firmly support the main journal 22a.

  As shown in FIGS. 5 to 7, the right bearing housing 5 is cast in the second partition wall 16 of the light case 12. The bearing housing 5 is formed in a ring shape that is long in the front-rear direction so as to cover the outer circumferences of the bearings 23 and 31. Specifically, as shown in FIGS. 6A and 6B, the bearing housing 5 includes an annular portion 50 that is long in the front-rear direction so as to cover the outer circumferences of the bearings 23 and 31, and the annular portion 50 on the bearing 31 side and the bearing 23 side. And an intermediate portion 51 for partitioning the front and rear. The bearing housing 5 has a vertically symmetrical shape with respect to a straight line L connecting the center C1 of the bearing 31 and the center C2 of the bearing 23.

  As shown in FIG. 6A, the annular portion 50 and the intermediate portion 51 have a uniform left-right width in the front-rear direction. Further, the thickness (horizontal width) of the bearings 23 and 31 on the right side is larger than the lateral width of the annular portion 50 and the intermediate portion 51. The right bearing 31 slightly protrudes to the left of the annular portion 50 and the intermediate portion 51. The right bearing 23 projects further to the left than the bearing 31. That is, the horizontal width of the bearing 23 is larger than that of the bearing 31.

  As shown in FIG. 6B, a part (second half) of the annular portion 50 and the intermediate portion 51 form an annular portion 52 that covers the entire circumference of the bearing 23. The annular portion 52 in the side view of FIG. 6B has a uniform thickness. When the bearing 23 is press-fitted into the inner peripheral portion of the annular portion 52, the bearing 23 is fitted into the annular portion 52, and the inner peripheral surface of the annular portion 52 is in contact with the outer peripheral surface of the bearing 23. That is, the inner peripheral portion of the annular portion 52 constitutes the press-fitting hole 16 a for the bearing 23. Therefore, when the bearing 23 is not press-fitted, the inner peripheral surface of the bearing 23 can be confirmed from the outside.

  The annular portion 50 is formed such that the vertical width thereof becomes smaller from the rear side toward the front side according to the shape of the bearings 23 and 31. In the front half of the annular portion 50, the annular portion 52 in the side view of FIG. 6B has a uniform thickness. Further, the upper and lower ends of the intermediate portion 51 forming a part of the annular portion 52 are smoothly connected to the annular portion 50. That is, the intermediate portion 51 forms a circular press-fitting hole 16a on the bearing 23 side at the connection portion with the annular portion 50. Further, the intermediate portion 51 forms an R-shaped fillet 53 that smoothly connects to the inner peripheral surface of the annular portion 50 on the bearing 31 side at the connection portion with the annular portion 50.

  Further, in the front half of the annular portion 50, a gap is formed between the outer peripheral surface of the bearing 23 and the inner peripheral surface of the annular portion 50 and the front surface of the intermediate portion 51. For example, the gap G2 between the inner peripheral surface of the annular portion 50 and the outer peripheral surface of the bearing 23 is smaller than the gap G1 between the front surface of the intermediate portion 51 and the outer peripheral surface of the bearing 23. The gap between the bearing 23 and the annular portion 50 and the intermediate portion 51 is filled with an aluminum alloy which is a main material of the light case 12.

  Further, the pair of upper and lower linear portions 54 forming the linear portion of the annular portion 50 are each formed with a protrusion 55 protruding toward the inner peripheral side. The protrusion 55 functions as a support location for the support pin 6 (see the phantom line in FIG. 6) that supports the bearing housing 5 at a predetermined position of the molding die when the bearing housing 5 is cast into the light case 12 for molding. To do. In addition to the above two points, the support location of the support pin 6 is also provided on the rear end side surface of the annular portion 52. The light case 12 is formed with holes 16c (see FIG. 3) for the support pins 6 at positions corresponding to these three support pins 6.

  In addition, a protrusion 56 that protrudes forward on the straight line L is formed at the foremost end of the annular portion 50. As shown in FIG. 6A, the protrusion 56 has a lateral width smaller than that of the annular portion 50 and is provided at the center of the annular portion 50 in the left-right direction. A through hole 57 is formed in the protrusion 56 so as to penetrate left and right. The center of the through hole 57 is located on the straight line L. The through hole 57 functions as a positioning hole for positioning the bearing housing 5. The positioning of the bearing housing 5 when the bearing housing 5 is cast is performed by the through hole 57 and the inner peripheral surface (press-fitting hole 16a) of the annular portion 52. Although not shown in the drawing, the light case 12 is provided with a recess at a position corresponding to the through hole 57.

  According to the bearing housing 5 configured as described above, both the outer circumferences of the two bearings 23 and 31 can be made to have a strong structure with the cast iron bearing housing 5 alone which is harder than an aluminum alloy. Therefore, it is possible to suppress the variation in the axial distance between the crankshaft 2 and the balancer shaft 30. Particularly, on the crankshaft 2 side where relatively large torque is applied, the inner peripheral surface of the annular portion 52 and the outer peripheral surface of the bearing 23 are in direct contact with each other. Therefore, the bearing 23 side can be effectively made to have a strong structure.

  On the other hand, on the balancer shaft 30 side, an annular portion 50 is formed with a gap from the outer peripheral surface of the bearing 31. On the balancer shaft 30 side, although the torque applied is smaller than that of the crankshaft 2, since the periphery of the bearing 31 is covered with the cast iron annular portion 50 and the intermediate portion 51 via the aluminum alloy, only the aluminum alloy is used. The structure can be stronger than when the light case 12 is molded. In this case, since the press-fitting hole 16b can be formed by machining the aluminum alloy portion of the second partition wall 16, the workability of the press-fitting hole 16b can be improved. Further, since the volume of the bearing housing 5 itself can be reduced, it is possible to reduce the weight of the light case 12 and further the engine 1 as a whole.

  Further, by making the thickness of the bearing housing 5 uniform, the heat distortion of the press-fitting holes 16a, 16b can be made uniform. As a result, it is possible to prevent the roundness of the press-fitting holes 16a and 16b from being reduced, and it is possible to suppress the generation of noise due to the deformation of the bearings 23 and 31. Further, it is possible to prevent casting defects such as sink marks when casting the bearing housing 5. Also, when the bearing housing 5 is cast into the light case 12, it is possible to prevent die casting defects. As described above, according to the present embodiment, it is possible to suppress deformation of the bearing housing 5 and reduce engine noise.

  Further, a gap G1 between the annular portion 50 on the opposite side of the annular portion 52 with the bearing 31 interposed and the outer peripheral surface of the bearing 31 is smaller than the gap G2 between the intermediate portion 51 and the outer peripheral surface of the bearing 31. When the bearing housing 5 is molded, the space between the two bearings 23 and 31 tends to be the thickest. Furthermore, if the connecting portion between the intermediate portion 51 and the annular portion 50 is connected by the fillet 53, the thickness becomes even thicker. Therefore, the thickness of the entire bearing housing 5 can be made uniform by intentionally making the gap G2 larger than the gap G1. In addition, since the width of the bearing housing 5 in the axial direction (horizontal direction) is uniform, the wall thickness of the entire bearing housing 5 can be made uniform. Further, by providing the R-shaped fillet 53 at the connecting portion between the intermediate portion 51 and the annular portion 50, it is possible to reinforce the connecting portion with a minimum increase in wall thickness.

  Further, since the bearing housing 5 has a symmetrical shape with respect to the straight line L, when the bearing housing 5 is cast, there is no effect even if the front and back are arranged reversely. Therefore, it is possible to arrange the bearing housing 5 at a predetermined position of the mold without considering the orientation of the bearing housing 5, and it is possible to improve the work efficiency during manufacturing. Further, by providing the through hole 57 as the positioning hole, it is possible to maintain the positioning accuracy of the bearing housing 5 at the two positions of the through hole 57 and the press fitting hole 16a.

  Further, the bearing housing 5 is provided on the right side where the balancer driven gear 33 is arranged in the axial direction. By providing the bearing housing 5 on the side of the balancer driven gear 33 to which more force is applied, of the left and right, it is possible to more effectively suppress fluctuations in the axial distance between the crankshaft 2 and the balancer shaft 30.

  In the above embodiment, the single-cylinder engine 1 is described as an example, but the configuration is not limited to this. For example, the engine 1 may be composed of a multi-cylinder engine having two or more cylinders, and the arrangement of each cylinder can be changed as appropriate.

  Further, in the above embodiment, the bearing housing 5 of the present invention is provided only in the light case 12, but the present invention is not limited to this configuration. The same bearing housing 5 may be provided in the left case 11.

  Further, in the above embodiment, the annular portion 50 and the bearing 31 are arranged with a gap therebetween, but the structure is not limited to this. The annular portion 50 and the bearing 31 may be in direct contact with each other.

  Moreover, although a plurality of embodiments and modifications have been described, other embodiments of the present invention may be a combination of the above-described embodiments and modifications in whole or in part.

  Further, the embodiment of the present invention is not limited to the above-mentioned embodiment, and may be variously changed, replaced, or modified without departing from the spirit of the technical idea of the present invention. Further, if the technical idea of the present invention can be realized in another way by the advancement of the technology or another derivative technology, the method may be implemented. Therefore, the claims cover all embodiments that may be included in the scope of the technical idea of the present invention.

  As described above, the present invention has the effect of suppressing deformation of the bearing housing and reducing engine noise, and is particularly useful for a bearing structure of an engine of a motorcycle.

1: Engine 2: Crankshaft 4: Bearing housing 5: Bearing housing 6: Support pin 10: Crankcase 11: Left case 12: Right case 16: Second partition wall 16a: Press-fit hole 16b: Press-fit hole 16c: Hole 22a: Main Journal 22b: Main journal 23: Bearing (first bearing)
30: balancer shaft 31: bearing (second bearing)
33: balancer driven gear 50: annular part 51: intermediate part 52: annular part 53: fillet (connecting part)
54: Straight part 55: Protrusion part 56: Protrusion part 57: Through hole C1: Center C2: Center FR: Arrow G1: Gap G2: Gap

Claims (8)

A first bearing fitted to the crankshaft,
A second bearing fitted to the balancer shaft for canceling the rotational vibration of the crankshaft;
An aluminum alloy crankcase formed by casting a cast iron bearing housing that covers the outer periphery of the first bearing and the second bearing,
The bearing structure is formed so as to be in contact with the outer peripheral surface of the first bearing, and is formed to have a gap with the outer peripheral surface of the second bearing. The bearing housing is
An annular portion covering the outer circumferences of the first bearing and the second bearing,
An intermediate portion that partitions the annular portion by the first bearing side and the second bearing side,
The bearing structure according to claim 1, wherein an annular portion into which the first bearing is fitted is formed by a part of the annular portion and the intermediate portion.   A gap between the annular portion and the outer peripheral surface of the second bearing opposite to the annular portion with the second bearing interposed is smaller than a gap between the intermediate portion and the outer peripheral surface of the second bearing. The bearing structure according to claim 2, which is characterized.   The bearing structure according to claim 3, wherein a connecting portion between the annular portion and the intermediate portion has an R shape.   The bearing structure according to claim 1, wherein a width of the bearing housing in the axial direction is uniform.   The bearing structure according to any one of claims 1 to 5, wherein the bearing housing has a symmetrical shape with respect to a straight line connecting the center of the first bearing and the center of the second bearing.   The bearing structure according to claim 6, wherein the bearing housing has a positioning hole on the straight line.   The bearing structure according to any one of claims 1 to 7, wherein the bearing housing is provided on the side where the balancer driven gear is arranged in the axial direction.

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