JP2008261235A - Fastening structure of cylinder block - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the fastening structure of a cylinder block wherein strength of a fastening part is improved when fastening a crank cap to the barrier plate of the cylinder block by a threaded fastener. <P>SOLUTION: A small diameter part 16 is inserted in a through hole 17 with a small diameter male threaded part 16b threadedly engaged with a small diameter female threaded part 17a, and thereby a cap part 15 made of aluminum is mounted to the tip part of the male threaded part 14 of a bolt 6. The tip 16a of the small diameter part 16 and a part of the small diameter male threaded part 16b protrudes upward from the tip face 15a of the cap part 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fastening structure of a cylinder block in an internal combustion engine, and more particularly to a fastening structure when a crank cap is fastened to a partition wall of a cylinder block with a screw part.

  Patent Document 1 describes a cylinder block in which a crank cap is fastened with a bolt to a lower portion of a partition wall that partitions cylinders. A cross section of such a cylinder block is shown in FIG. A partition wall through hole 36 is formed through the partition wall 30 so as to communicate between the cylinders, and a screw hole 31 is formed so as to communicate with the partition wall through hole 36 from the lower part of the partition wall 30. . The crank cap 38 is fastened to the lower portion of the partition wall 30 by inserting the bolt 33 penetrating the crank cap 38 into the screw hole 31. In such a cylinder block, FIG. 6 shows an enlarged cross-sectional view of a state in which the bolt 33 is inserted into the screw hole 31. A female screw portion 32 is formed on the inner peripheral surface of the screw hole 31 formed in the partition wall 30, and the bolt 33 is inserted into the screw hole 31 so that the male screw portion 35 of the bolt 33 is screwed into the female screw portion 32. ing. The front end surface 33 a of the bolt 33 does not protrude into the partition wall through hole 36, and the first male screw portion 35 a connected to the front end surface 33 a is screwed into the female screw portion 32.

JP-A-10-122202

  In such a cylinder block, stress in the longitudinal direction of the bolt 33 is generated in the vicinity of the fastening portion of the bolt 33 due to an explosion load caused by combustion of the engine. It is transmitted through the bolt 33 and the cylinder block, respectively, but generally, the bolt 33 and the cylinder block are made of different materials, and the bolt 33 is made of a high strength and high rigidity material such as an iron alloy. The stress tends to concentrate at the end of the connection, that is, the vicinity 37 (FIG. 5) of the end of the bolt 33. Further, the stress state at the bottom of the female screw valley is mainly the tensile stress in the axial direction of the bolt 33 (arrow X in FIG. 6) in the vicinity 37 of the screwing end. There has been a problem that fatigue failure is likely to occur from the female screw valley bottom 32a due to the tensile stress of the female screw valley bottom 32a near the end of threading 37, which is repeatedly generated by this explosion load. In particular, in recent engines, a cylinder block made of aluminum die casting may be used for the purpose of increasing output, reducing weight, improving productivity, and reducing costs. In this case, since the difference in rigidity between the bolt and the cylinder block is greater than when a cast iron cylinder block is used, fatigue failure from the internal thread valley bottom portion 32a is more likely to occur.

  The present invention has been made to solve such problems, and provides a cylinder block fastening structure in which the strength of a fastening portion when a crank cap is fastened to a partition wall of the cylinder block with a screw part is improved. Objective.

In a cylinder block fastening structure in which a crank cap is fastened with a screw part to a lower part of a partition wall that partitions cylinder blocks, a cap part made of a material having rigidity lower than that of iron is provided at a tip part of a male screw part of the screw part. It is characterized by being. By providing a cap made of a material that is less rigid than iron at the tip of the male screw part of the screw part to reduce the rigidity of the tip part of the male screw part, the gap between the tip part of the male screw part and the partition wall of the cylinder block is reduced. Since the difference in rigidity is small, stress concentration near the end of screwing is less likely to occur.
The distal end portion of the male screw portion is provided with a small-diameter portion having a smaller diameter and a small-diameter male screw portion than the male screw portion, and the cap portion has a through-hole that penetrates in the axial direction and is formed with the small-diameter female screw portion. The small diameter portion is inserted into the through hole so that the small diameter male screw portion and the small diameter female screw portion are screwed together, so that the cap portion is attached to the tip portion of the male screw portion, and the tip of the small diameter portion is connected to the cap portion. You may protrude from the front end surface.

  According to the present invention, the tip portion of the male screw portion and the cylinder block are provided by providing the cap portion made of a material having lower rigidity than iron at the tip portion of the male screw portion of the screw component to reduce the rigidity of the tip portion of the male screw portion. Since the difference in rigidity with the partition wall is small, stress concentration near the end of screwing is less likely to occur. Thereby, the intensity | strength of the fastening part at the time of fastening a crank cap to the partition of a cylinder block with a screw component can be improved.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows a cross-sectional view of a cylinder block according to this embodiment. A cylinder block 1 of an internal combustion engine includes a cylinder part 2 and a crankcase part 3 provided integrally with a lower part of the cylinder part 2. A cylinder bore 7 serving as a cylinder is formed inside the cylinder portion 2. A partition wall 4 is provided inside the crankcase portion 3, and the partition wall 4 partitions between the cylinder bore 7 and another cylinder bore (not shown) adjacent to the cylinder bore 7. A crank cap 5 is fastened to the lower portion of the partition wall 4 with two bolts 6, and a support portion 8 that supports a crankshaft (not shown) is formed between the two bolts 6 by the partition wall 4 and the crank cap 5. Has been. Here, the bolt 6 constitutes a screw part.

  In FIG. 2, the expanded sectional view of the fastening part of the crank cap 5 and the partition 4 is shown. The crank cap 5 is formed with a bolt insertion hole 11 penetrating the crank cap 5 from the lower part to the upper part, and the shaft part 6 b of the bolt 6 is inserted into the bolt insertion hole 11. The partition wall 4 is formed with a screw hole 13 extending upward from the lower part. A female screw portion 12 is formed in the screw hole 13. The shaft portion 6 b of the bolt 6 inserted into the bolt insertion hole 11 is further inserted into the screw hole 13 so that the male screw portion 14 formed on the shaft portion 6 b is screwed into the female screw portion 12. Thereby, the crank cap 5 is fastened to the lower part of the partition wall 4.

  In FIG. 3, the expanded sectional view of the front-end | tip part of the volt | bolt 6 is shown. An aluminum cap portion 15 is attached to the tip end portion of the male screw portion 14 of the bolt 6 made of a high strength and high rigidity iron-based alloy. The length of the cap portion 15 is preferably a length corresponding to about 10 to 15% of the total length of the male screw portion 14 of the bolt 6. The cap portion 15 has a cylindrical shape having the same outer diameter as that of the shaft portion 6 b, and a male screw portion 14 a is formed on the outer peripheral surface of the cap portion 15. A small diameter female screw portion 17 a is formed on the inner peripheral surface of the through hole 17 formed in the axial direction of the cap portion 15. On the other hand, a small diameter portion 16 having a diameter smaller than that of the shaft portion 6b is provided at the tip portion of the bolt 6 so as to extend in the longitudinal direction of the shaft portion 6b. A small-diameter male screw portion 16 b is formed on the outer peripheral surface of the small-diameter portion 16. The cap portion 15 is attached to the distal end portion of the male screw portion 14 by inserting the small diameter portion 16 into the through hole 17 so that the small diameter male screw portion 16b is screwed into the small diameter female screw portion 17a. Note that immediately before the small diameter portion 16 is inserted into the through hole 17, an adhesive is applied to the outer peripheral surface of the small diameter portion 16 to prevent the cap portion 15 from being detached. The tip 16a of the small diameter portion 16 and a part of the small diameter male screw portion 16b protrude upward from the tip surface 15a of the cap portion 15. The male screw portion 14b formed on the outer peripheral surface of the cap portion 15 and the male screw portion 14a formed on the outer peripheral surface of the shaft portion 6b are continuously threaded, and the male screw portion of the bolt 6 is formed by the male screw portions 14a and 14b. 14 is configured.

Next, in the cylinder block according to this embodiment, a stress generated by an explosion load caused by engine combustion will be described.
When combustion occurs in the cylinder, stress is generated by an explosion load in the longitudinal direction (arrow E) of the bolt 6 as shown in FIG. This stress is concentrated in the vicinity of the threaded end of the bolt 6, that is, in the vicinity of the female screw valley bottom 12 a to which the male screw portion 14 b 1 at the tip of the cap portion 15 is applied. This is because a downward force (arrow A) is applied to the female screw portion 12 by the male screw portion 14b1, and the stress is concentrated in the vicinity of the female screw valley bottom portion 12a when the screw groove of the female screw portion 12 is opened. However, in this embodiment, since the cap part 15 is made of aluminum having a rigidity lower than that of iron, the cap part 15 is compared with the case where the cap part 15 is not attached to the tip part of the male screw part 14 of the bolt 6. And the rigidity difference between the partition walls 4 is reduced. As a result, the downward force (arrow A) applied to the female screw portion 12 by the male screw portion 14b1 is reduced, so that the force concentrated on the female screw valley bottom portion 12a at the end of the bolt 6 is relaxed.

  Further, since the small-diameter male screw portion 16b and the small-diameter female screw portion 17a are screwed together, stress concentration is also generated in the female screw valley bottom portion 17a1 closest to the tip surface 15a of the cap portion 15 by the same principle. However, since the tip 16a of the small-diameter portion 16 and a part of the small-diameter male screw portion 16b protrude upward from the tip surface 15a, the bottom of the female screw valley at the end of the small-diameter male screw portion 16b does not exist, so stress concentration is reduced. Is done. Supplementally, in this embodiment, a downward force (arrow B) is applied from the small-diameter male screw portion 16b1 applied to the distal end surface 15a. As a result, also in the female thread valley bottom portion 17a1, like the other female screw valley bottom portions, a part of the force indicated by the arrow D is offset by the load indicated by the arrow C, and the extreme stress in the vicinity of the female screw valley bottom portion 17a1 is obtained. Concentration is eliminated.

Thus, by providing the aluminum cap portion 15 at the tip of the male screw portion 14, the difference in rigidity between the cap portion 15 and the partition wall 4 is reduced. The concentrated stress is relieved. Thereby, the durability of the fastening portion when the crank cap 5 is fastened to the partition wall 4 of the cylinder block 1 with the bolt 6 can be improved. Moreover, since the cap part 15 is provided in the front-end | tip part of the external thread part 14, compared with the case where the rigidity of the whole surface of a volt | bolt is reduced, a fastening strength is not reduced, and the internal thread of the bolt 6 end of a hook is carried out. Only stress concentrated on the valley bottom 12a can be relaxed. Furthermore, even in the case of an aluminum die-cast cylinder block, the durability of the fastening portion of the bolt 6 can be improved, so that high output and light weight can be realized.
Further, the small diameter portion 16 is inserted into the through hole 17 so that the small diameter male screw portion 16b and the small diameter female screw portion 17a are screwed together, so that the cap portion 15 is attached to the distal end portion of the male screw portion 14, and the small diameter portion 16 Since the tip 16a and a part of the small-diameter male screw portion 16b protrude from the tip surface 15a of the cap portion 15, the bottom end of the female screw valley of the small-diameter male screw portion 16b does not exist, and therefore concentrates on the female screw valley bottom portion 17a1. Stress can be relaxed.

In this embodiment, in the structure in which the small-diameter portion 16 is inserted into the through-hole 17 so that the small-diameter male screw portion 16b of the small-diameter portion 16 and the small-diameter female screw portion 17a of the cap portion 15 are screwed together, it is retained by an adhesive. However, retaining is not limited to this. Since the cap portion 15 may be fixed to the tip portion of the male screw portion 14 of the bolt 6, it may be prevented from coming off by welding or the like.
Further, the cap portion may be fixed by using a structure that is fitted by press-fitting without using screwing. Specifically, the inner diameter of the through hole of the cap part is formed slightly smaller than the outer diameter of the small diameter part of the bolt in a state before the cap part is fixed. In this state, the cap portion is fixed to the bolt by press-fitting the small diameter portion into the through hole. In this case, it is not necessary to form a thread on the inner peripheral surface of the through hole and the outer peripheral surface of the small diameter portion. In addition, since the cap portion is made of a material having a relatively low rigidity, an excessive force is not required for press-fitting, and a large load is not applied to the bolt. Since the cap part is slightly deformed by press-fitting, the male thread part of the bolt is formed on the surface of the bolt shaft part and the cap part after the cap is press-fitted.

  In this embodiment, the cap portion 15 is made of aluminum, but is not limited to aluminum. Any material may be used as long as it has a lower rigidity than iron. Examples of other materials include magnesium alloys.

It is sectional drawing of the cylinder block which concerns on embodiment of this invention. It is an expanded sectional view of the fastening part of a crank cap and a partition in a cylinder block concerning an embodiment. It is an expanded sectional view of the front-end | tip part of the volt | bolt used for the fastening structure of the cylinder block which concerns on embodiment. It is explanatory drawing which shows the principle in which stress is reduced in the cylinder block which concerns on embodiment. It is sectional drawing of the screw fastening part in the conventional cylinder block. It is an expanded sectional view of the screw fastening part in the conventional cylinder block.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Cylinder block, 4 Bulkhead, 5 Crank cap, 6 Bolt (screw part), 7 Cylinder bore (cylinder), 14 Male thread part, 15 Cap part, 15a (Cap part) tip surface, 16 Small diameter part, 16a (Small diameter part) ) Tip, 16b Small-diameter male thread, 17 Through hole, 17a Small-diameter female thread.

Claims (2)

In the cylinder block fastening structure in which the crank cap is fastened with screw parts to the lower part of the partition wall that partitions the cylinders of the cylinder block,
A fastening structure for a cylinder block, wherein a cap portion made of a material having rigidity lower than that of iron is provided at a tip portion of a male screw portion of the screw part. The distal end portion of the male screw portion is provided with a small-diameter portion having a smaller diameter than the male screw portion and a small-diameter male screw portion formed,
The cap portion is provided with a through hole that penetrates in the axial direction and is formed with a small-diameter female screw portion.
By inserting the small diameter portion into the through hole so that the small diameter male screw portion and the small diameter female screw portion are screwed together, the cap portion is attached to the tip portion of the male screw portion, and the tip of the small diameter portion is The cylinder block fastening structure according to claim 1, wherein the fastening structure projects from a front end surface of the cap portion.

Images