A selected illustrative embodiment of the invention will now be described in some detail, with reference to the drawings. It should be understood that only structures considered necessary for clarifying the present invention are described herein. Other conventional structures, and those of ancillary and auxiliary components of the system, are assumed to be known and understood by those skilled in the art.
Referring now to
A crankshaft supporting part 10 is formed on joined faces of the upper crankcase 2A and the lower crankcase 2B, and a crankshaft 11 is rotatably supported in this part. A main gallery 12 and a lubricating oil passage 13 are provided under the crankshaft supporting part 10. A transmission shaft supporting structure 14 is provided to the rear of the crankcase 2, and a camshaft supporting part 15 for driving an intake/exhaust valve is provided on an upper part of the cylinder head 4. A water jacket 17 is provided within inner circumferences of the cylinder block 3 and the cylinder head 4 and the cylinder bulkhead 16.
An upper crank journal wall 20A and a lower crank journal wall 20B are provided on the upper and lower crankcases 2A, 2B, respectively, and are parts that correspond to a crank journal portion of the cylinder bulkhead 16. A journal bearing 21 is provided to the crankshaft supporting part 10 formed in the crank journal walls 20A, 20B. The upper crankcase 2A and the lower crankcase 2B are fastened together by plural fastening bolts. The front of the crankshaft supporting part 10 is fastened by a front fastening bolt 22, and the rear of the crankshaft supporting part is fastened by a rear fastening bolt 23, the respective fastening bolts 22, 23 being particularly long.
In this embodiment, a large opening 24 having an anomalous, or irregular, peripheral shape is provided in the crank journal wall 20A of the upper crankcase 2A. The opening communicates with spaces corresponding to adjacent cylinders. The opening is provided with the anomalous shape because it does not have a circular shape formed by normal machining but is formed in an arbitrary shape if necessary. A small circular opening 25, having a circular section and extending through the plural crank journal walls 20A, is located rearward of the large anomalous outline opening 24 of the crank journal wall 20A of the upper crankcase 2A, and extends in parallel with the crankshaft 11. The small circular opening 25 is formed by drilling or other means.
As described above, the small circular opening 25 is formed having a circular section, and is formed in the crank journal wall 20A of the upper crankcase 2A by drilling or other methods. The end of the rear bolt hole 31 is open to, and communicates with, the small circular opening 25. The end of the rear fastening bolt 23, when screwed into the rear bolt hole 31, protrudes into the small circular opening 25 as shown in
b) shows the an enlarged view of the upper end of a bolt hole 30′ in a conventional crankcase in which no protrusion is formed in a crank journal wall 20A′ at a location corresponding to a circumference of the end of the bolt hole 30′, and the end of a fastening bolt 22′ is present in the bolt hole 30′. As shown in
In contrast, as shown in
Further, since a tensile force F acts on the fastening bolt 22 resulting from the vibration of the crankshaft when the internal combustion engine is driven, a larger compressive stress is produced in the vicinity of the bolt hole in the crank journal wall 20A when the protrusion 32 is formed thereon, and the fatigue strength of the crank journal wall 20A is increased.
As described in detail above, since this embodiment has the above-mentioned configuration, the following effect is produced.
Generally, when the end of the fastening bolt remains within the bolt hole, the concentration of stress is generated in the crankcase wall at a location corresponding to the circumference of the bolt hole at a boundary between a part of the bolt hole in which the fastening bolt is fitted and a part of the bolt hole in which the fastening bolt is not fitted. In this embodiment, since the ends of the bolt holes 30, 31 are made to communicate with the openings 24, 25 formed the crank journal wall 20A, and the ends of the fastening bolts 22, 23 protrude into the respective openings, the concentration of stress in the circumferences of the bolt holes 30, 31 at the ends of the bolts is avoided. Therefore, since the stress is dispersed along the whole of the fastened parts of the bolt holes, the durability is enhanced and the crankcase can be reduced in weight.
Since the crank journal wall 20A, at a location corresponding to the circumference of the end of the bolt hole 30, protrudes into the large opening 24 in the crank journal wall 20A, stress applied to the end of the bolt hole 30 is relieved by the protrusion 32 and the rigidity of the crankcase is more enhanced. In addition, a sufficient fastened length of the bolt hole 30 is secured.
In the protrusion 32, since the enlarged diameter part 33, the inside diameter of which is longer than the diameter of the bolt hole, extends from the upper end of the bolt hole 30 to the inside thereof by the predetermined distance, and since no screw thread is formed within the enlarged diameter part, the protrusion of the bolt 22 into the opening 24 in the crank journal wall 20A can be inhibited. In addition, the exposure of the acute-angled edge of the termination of the bolt hole caused in working a screw can be prevented.
The large opening 24 in the crank journal wall 20A is not necessarily required to have a regular shape such as a round shape, but instead can be formed in an arbitrary anomalous or irregular shape. As a result, the shape can be varied in accordance with the necessity of securing the rigidity of the crankcase, and the opening in the crank journal wall can be maximally expanded. In addition, the V-shaped rib 34 is arranged along the peripheral edge of the opening, and the end of the bolt hole is located in the center of the rib 34. As a result, tensile stress applied to the opening from the fastened part can be dispersed in the whole crankcase, and weight-reduction and securing the rigidity of the crankcase is achieved.
Since the openings 24, 25 provided to the crank journal wall function for pressure relief between cylinders, pumping loss is reduced and friction is also reduced.
When the circular opening 25 is provided in the crank journal wall, tensile stress applied to the opening can be uniformly received in the circumference of the circular part. Moreover, since the inside diameter of the opening is set to the double or less the diameter of the corresponding bolt hole, the reduction of the rigidity of the crankcase is possibly inhibited, and the dispersion of the tensile stress is enabled.
Although the present invention has been described herein with respect to a number of specific illustrative embodiments, the foregoing description is intended to illustrate, rather than to limit the invention. Those skilled in the art will realize that many modifications of the preferred embodiment could be made which would be operable.
For example, in the above-mentioned embodiment, the opening is provided in the crank journal wall, however, a position of the opening is not limited to the crank journal wall. Al such modifications, which are within the scope of the claims, are intended to be within the scope and spirit of the present invention.
Number | Date | Country | Kind |
---|---|---|---|
2006-287091 | Oct 2006 | JP | national |