JP2005207269A - Cylinder block - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder block enabling an increase in the strength of a connection part. <P>SOLUTION: In this cylinder block 10, a crankshaft 13 is supported by a block body 11 and a bearing cap 12, and a fixing bolt 17 is threaded to a screw hole 15 formed in the block body 11 to fix the bearing cap 12 to the block body 11. A cutout part 23 projecting to the radial outer side is formed in the internal surface of the screw hole 15 circumferentially at a portion to which a stress occurred is concentrated by a load given from the crankshaft 13. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cylinder block of an engine, and more particularly to a cylinder block in which stress generated in a screw hole into which a fixing bolt for fastening a bearing cap to a block body is screwed is reduced to prevent generation of a crack or the like. It is.

  First, the outline of the cylinder block of the engine will be described with reference to FIG.

  As shown in the figure, the cylinder block 10 includes a block main body 11 in which a cylinder (not shown) is accommodated, and a bearing cap 12 connected to a lower portion of the block main body 11, and between the block main body 11 and the bearing cap 12. The crankshaft 13 is rotatably supported via a bearing (not shown).

  Bolt fastening is used to fix the block body 11 and the bearing cap 12. That is, a plurality of screw holes 15 are formed on the lower surface of the block main body 11 at positions on both sides of the crankshaft 13, and bolt insertion holes 16 are formed in the bearing cap 12 at positions corresponding to the screw holes 15. . The bearing cap 12 is fastened and fixed to the block body 11 by screwing the fixing bolt 17 through the insertion hole 16 of the bearing cap 12 and the screw hole 15 of the block body 11.

  By the way, the fastening portion between the block main body 11 and the bearing cap 12 receives a load from the crankshaft 13, but this load becomes higher (severe) with the recent increase in engine output. On the other hand, the cylinder block 10 (the block body 11, the bearing cap 12, etc.) is made of an aluminum alloy having a strength lower than that of the steel material for the purpose of reducing the engine weight. As a result, the screw hole 15 of the block body 11 cannot withstand the load (stress) received from the crankshaft 13, and a crack or the like may occur on the inner surface of the screw hole 15.

  For this reason, it is a problem to improve the strength of the fastening portion of the cylinder block 10 by measures other than the material surface and the size surface (that is, without increasing the weight).

  Here, Patent Document 1 describes that a part of the seating surface of the bolt head is inclined as a measure for improving the strength of the bolt fastening portion. According to this configuration, a gap (relief) is formed between the bolt head and the seating surface, so that deformation of the bolt can be allowed and stress generated in the bolt and screw hole can be reduced.

JP 2000-288957 A

  However, when this structure is applied to the fastening portion of the cylinder block 10, the gap between the block body 11 and the bearing cap 12 changes due to the deformation of the fixing bolt 17, which causes the following problem.

  1) Since the gap between the crankshaft 13 and the cylinder block 10 changes, the crankshaft 13 may be damaged.

  2) Since the gap between the crankshaft 13 and the bearing changes, there is a risk of bearing seizure (damage).

  3) There is a risk of noise and vibration.

  In other words, in the cylinder block 10, it is not a good idea to increase (allow) deformation of the fixing bolt 17 to reduce stress.

  Therefore, an object of the present invention is to provide a cylinder block that can improve the strength of the fastening portion without increasing the deformation of the fixing bolt.

  In order to achieve the above object, the present invention provides a cylinder block in which a crankshaft is supported by a block body and a bearing cap, and a fixing bolt is screwed into a screw hole formed in the block body to fix the bearing cap to the block body. In the circumferential direction of the inner surface of the screw hole, a notch portion that protrudes radially outward is formed at a portion where stress is concentrated by a load received from the crankshaft.

  Here, it is preferable that the notch is formed in a portion adjacent to the crankshaft in the circumferential direction of the screw hole.

  The notch may be formed in a portion where stress is concentrated by a load received from the crankshaft in the longitudinal direction of the screw hole.

  According to the present invention, since the maximum stress generated in the screw hole is reduced, the excellent effect that the strength of the fastening portion can be improved without increasing the deformation of the fixing bolt is exhibited.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The schematic structure of the cylinder block of this embodiment is the same as that shown in FIG.

  That is, the cylinder block 10 of the present embodiment includes a block main body 11 in which a cylinder (not shown) is accommodated, and a bearing cap 12 connected to a lower portion of the block main body 11. In the meantime, the crankshaft 13 is rotatably supported via a bearing (not shown).

  A plurality of screw holes 15 are formed on the lower surface of the block body 11 at positions on both sides of the crankshaft 13, and bolt insertion holes 16 are formed in the bearing cap 12 at positions corresponding to the screw holes 15. The bearing cap 12 is fastened and fixed to the block body 11 by screwing the fixing bolt 17 through the insertion hole 16 of the bearing cap 12 and the screw hole 15 of the block body 11.

  Now, since the cylinder block 10 of this embodiment is characterized by the screw holes 15 formed in the block body 11, the structure of the screw holes 15 will be described below with reference to FIGS.

  1 is a front view of the screw hole 15 as viewed from the lower surface 11a side of the block main body 11, FIG. 2 (a) is a sectional view taken along line IIa-IIa in FIG. 1, and FIG. 2 (b) is IIb-IIb in FIG. FIG. 2C is a sectional view taken along line IIc-IIc in FIG.

  In FIG. 1, 20 indicates a thread of the screw hole 15, and 21 indicates a thread valley.

  As is apparent from the drawing, the feature of the screw hole 15 of the cylinder block 10 of the present embodiment is that a notch 23 projecting radially outward is formed on a part of the inner surface of the screw hole 15 in the circumferential direction. is there. The notch 23 of the present embodiment protrudes in an arc shape radially outward from the crest 20 of the screw hole 15, and the maximum projecting point P <b> 1 is equal to the position of the valley 21 of the screw hole 15. In the present embodiment, the cutout portion 23 is formed over substantially the entire region in the longitudinal direction (depth direction) of the screw hole 15.

  More specifically, the shape of the notch 23 of the present embodiment will be described. As shown in FIG. 3, the notch 23 has half the diameter D of the valley 21 of the screw hole 15 (D / 2) as the diameter D ′. It is formed by being cut out along the outer periphery of the circle 25 to be cut. That is, the hatched portion in FIG. 3 is a portion that is cut out. The notch 23 can be formed relatively easily using a drill, a slotter, or the like.

  By forming the notch 23, the area of engagement (screwing) between the fixing bolt 17 and the screw hole 15 is reduced at this portion. In particular, the engagement between the fixing bolt 17 and the screw hole 15 is completely released and released at the maximum projecting point P1 of the notch 23 and the vicinity thereof. Accordingly, in this portion, the load transmission from the fixing bolt 17 to the screw hole 15 is interrupted, and even if a load acts on the fixing bolt 17 from the crankshaft 13, the stress generated at this portion becomes almost zero. . Then, the corresponding stress is distributed to other portions in the circumferential direction of the screw hole 15. Therefore, the maximum stress generated in the screw hole 15 can be reduced by providing the notch 23 at a portion (stress concentration portion) where the stress generated when receiving a load from the crankshaft 13 is the largest. As a result, the strength of the screw hole 15 is improved. In order to obtain this effect, the maximum projecting point P1 of the notch 23 needs to be positioned radially outward from at least the peak of the fixing bolt 17 screwed into the screw hole 15.

  In order to find the optimal formation position of the notch 23, the present applicant has analyzed the stress generated in a normal screw hole not having the notch 23. The analysis image is shown by a solid line A in FIG. The figure shows the stress generated in the screw hole 15 located on the right side of the crankshaft 13, and the more the line A moves away from the center of the screw hole 15 in the radial direction, the higher the stress generated in that portion. ing.

  As is apparent from the drawing, the stress generated at the left side of the screw hole 15, that is, at the site on the crankshaft 13 side, is higher than the stress generated at the site (right side) far from the crankshaft 13. The stress becomes maximum at the point P ′ where the distance from the crankshaft 13 is the shortest.

  The reason for this will be described with reference to FIG. 5. In the combustion stroke of the engine, a downward pressing force acts on the crankshaft 13 and the bearing cap 12 that supports the crankshaft 13 as the piston descends. At this time, since the fixing bolt 17 is in a so-called cantilever state in which only its upper end is fixed, a force is generated to open the lower portions of the block body 11 and the bearing cap 12 outward as indicated by broken lines in the figure. As a result, a large tensile stress is generated at the position of the screw hole 15 on the crankshaft 13 side. If this stress is larger than the proof stress of the screw hole 15, it will cause permanent deformation (such as a crack) in the screw hole 15. Further, since this tensile stress is repeatedly applied every time the engine explodes (combusts), it also causes a fatigue failure on the inner surface of the screw hole 15.

  Therefore, as shown in FIG. 1, if the notch 23 is formed in a portion (stress concentration portion) close to the crankshaft 13 in the circumferential direction of the inner surface of the screw hole 15, the stress generated in that portion is transferred to another portion. The maximum stress generated in the screw holes 15 can be reduced. In particular, the maximum stress generated in the screw hole 15 is most effectively reduced if the maximum protrusion point P1 of the notch 23 is located at a position closest to the crankshaft 13 (point P ′ in FIG. 4). it can.

  The present applicant analyzed the stress generated in the screw hole 15 in which the notch 23 is formed in order to confirm the effect of reducing the stress by the notch 23. The analysis image is shown by a solid line B in FIG. The dotted line A in the figure shows the stress generated in the conventional screw hole shown in FIG. 4 for comparison.

  As is clear from the figure, in the screw hole 15 in which the notch 23 is formed, the stress generated at the point where stress has been concentrated (the maximum protruding point P1 of the notch 23) is significantly reduced compared to the conventional case, The stress which generate | occur | produces in the other site | part, especially the circumferential direction both ends P2, P3 of the notch part 23 has increased a little. In other words, the formation of the notch 23 means that stress that has been concentrated at one point in the past has been distributed to other parts in the circumferential direction, in particular, two points P2 and P3 at both ends of the notch 23. ing. Therefore, the maximum stress generated in the screw hole 15 (stress Sb generated in both end portions P2 and P3 of the notch 23) is significantly lower than the maximum stress Sa generated in the conventional screw hole. As a result, the strength of the screw hole 15 is improved and the occurrence of cracks and the like can be prevented. In particular, if the shape, size, etc. of the notch 23 are set so that the maximum stress Sb generated in the screw hole 15 is smaller than the proof stress of the screw hole 15, the occurrence of cracks and the like can be prevented more reliably. Since the stress generated in the entire screw hole 15 is the same as the conventional one, the area in the solid line B and the area in the dotted line A in FIG.

  Thus, according to the cylinder block of the present embodiment, the strength of the fastening portion can be improved at a low cost without increasing the weight of the cylinder block.

  Further, according to the cylinder block of the present embodiment, the maximum stress generated in the screw hole 15 and the fixing bolt 17 is reduced, so that the deformation (elongation) amount of the fixing bolt 17 is reduced as compared with the conventional case. Accordingly, the change in the gap between the block main body 11 and the bearing cap 12 is smaller than that in the prior art, and there is no problem as described in the section “Problems to be solved by the invention”.

  The present invention is not limited to the above embodiment.

  For example, the shape of the notch 23 is not limited to an arc shape, but may be other shapes such as a triangular shape.

  Further, the notch amount (diameter protrusion amount, circumferential length, etc.) of the notch portion 23 is not limited to the above embodiment, and may be appropriately set in consideration of the load on the screw hole 15. However, as a matter of course, the size and shape of the notch 23 are within a range in which the fastening force between the block body 11 and the bearing cap 12 can be sufficiently secured. However, when it is desired to sufficiently obtain the stress reduction effect (strength improvement effect) of the screw hole 15, the size of the notch portion 23 is set large, and the fastening force and the strength are reduced accordingly. It is also possible to compensate by making 17 screws fine.

  Furthermore, in the above-described embodiment, it has been described that the notch portion 23 is formed over the entire longitudinal direction of the screw hole 15, but the present invention is not limited in this respect, and the notch portion 23 is formed in the screw hole as shown in FIG. You may form only in a part of 15 longitudinal direction (depth direction). That is, the stress generated in the screw hole 15 is not uniformly generated in the longitudinal direction of the screw hole 15, but it is considered that there is a part where the stress is concentrated. Therefore, the stress concentrated part in the longitudinal direction is obtained by simulation or the like. If the notch 23 is formed only in that portion, the strength of the screw hole 15 can be improved while minimizing the decrease in fastening force (strength).

It is a front view of the screw hole of the block main body of the cylinder block which concerns on one Embodiment of this invention. (A) is the IIa-IIa sectional view taken on the line of FIG. 1, (b) is the IIb-IIb sectional view taken on the line of FIG. 1, (c) is the IIc-IIc sectional view taken on the line of FIG. It is a figure for demonstrating the shape of a notch part. It is a figure which shows the stress which generate | occur | produces in the conventional screw hole which does not have a notch part. It is a figure for demonstrating the force which generate | occur | produces in a cylinder block by the load received from a crankshaft. It is a figure which shows the stress which generate | occur | produces in the screw hole which has a notch part, and the conventional screw hole which does not have a notch part. It is side surface sectional drawing which shows the screw hole which concerns on other embodiment of this invention. It is the schematic of a cylinder block.

Explanation of symbols

10 Cylinder Block 11 Block Body 12 Bearing Cap 13 Crankshaft 15 Screw Hole 17 Fixing Bolt 23 Notch

Claims (3)

A cylinder block that supports a crankshaft by a block body and a bearing cap, and fixes a bearing cap to the block body by screwing a fixing bolt into a screw hole formed in the block body,
A cylinder block characterized in that a notch projecting radially outward is formed at a portion where stress is concentrated by a load received from a crankshaft in a circumferential direction of the inner surface of the screw hole.   The cylinder block according to claim 1, wherein the notch is formed at a portion adjacent to the crankshaft in a circumferential direction of the screw hole. The cylinder block according to claim 1 or 2, wherein the notch is formed in a portion where stress is concentrated by a load received from a crankshaft in a longitudinal direction of the screw hole.

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