JP3158971B2 - Cast crankshaft - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a crankshaft used for a piston engine or the like, and more particularly, to a cast crankshaft manufactured by casting.

[0002]

2. Description of the Related Art Crankshafts are generally made of steel from the viewpoint of strength and durability, but their weight is closely related to the size of a balance weight, the height of a cylinder block, and the like. The impact on the engine weight is significant. For this reason, attempts have been made to reduce the weight of the crankshaft. However, since it is difficult to reduce the weight of a steel material in terms of material characteristics, for example, Japanese Utility Model Laid-Open No. 2-4017 discloses that
As shown in FIG. 6, there has been proposed a cast iron crankshaft that has been cast out (synonymous with lightening) by casting. FIG.
Reference numeral 100 denotes a crankpin, and reference numerals 102, 1
Reference numeral 04 denotes a crank web, and reference numerals 106 and 108 denote crank journals, respectively. In the above-described conventional casting, a blanked portion 110 is formed which penetrates the crankpin 100 in the axial direction and opens to the crank webs 102 and 104 on both sides.
An opening is formed on the lower inner surface of the bottom 104, and the back portion is formed with cast-out portions 112 and 114 that enter the crank journals 106 and 108.

[0003]

By the way, when a steel material, which is a conventional material of a crankshaft, is compared with a high-strength cast iron (for example, FCD700-800), the steel material has a Young's modulus of 21,000 kg / mm ^2. The high-strength cast iron has a Young's modulus of about 17000 kg / mm ² , and a reduction in rigidity of about 20% is inevitable due to a difference in material properties. According to the experiment of the present inventor, when the crank pin is provided with a cast-out portion penetrating in the axial direction, FIG.
As shown in Fig. 5, it was confirmed that the bending stiffness of the crankshaft, the so-called bending rigidity, was reduced by about 20 to 30% in accordance with the length of the cast-out portion. Therefore, as in the above prior art,
In the case where a cast portion penetrating in the axial direction is provided on the crank pin, the bending rigidity is reduced by the provision of the cast portion, and the rigidity reduction in the above-described material properties is added. Will be greatly reduced to about half.

[0004] Further, it has been found by experiments that even if the cast-out portion formed on the crankpin is not long enough to penetrate, if there is some cast-out portion on the crankpin, the bending rigidity is significantly reduced. did. As described above, when the bending rigidity decreases, the impact force of the crank journal on the main bearing, that is, the so-called bearing impact force increases. This impact is transmitted to the engine body via the crankcase, resulting in an increase in engine vibration and noise. According to a further experiment by the inventor, the bending rigidity and the torsional rigidity of the entire crankshaft are greatly affected by the rigidity of the crankpin, and FIG.
As shown in the above, it was confirmed that the rigidity of the journal side crank web had almost no effect. The present invention provides a cast crankshaft that can achieve weight reduction with almost no reduction in bending stiffness and that can contribute to reduction in engine weight without increasing engine vibration and noise. With that purpose.

[0005]

SUMMARY OF THE INVENTION The present invention is based on the above-described experimental facts, and performs casting while avoiding a shaft structure portion such as a crankpin which is related to a decrease in bending stiffness, in a range away from the shaft structure portion. Has taken the idea of making a significant undercut. Based on this idea, in the invention according to claim 1, a solid crankpin, a crank web extending from a shaft end of the crankpin in a direction perpendicular to the axis,
A crank journal that is provided on the outer surface of the crank web and extends along the axis of the crank pin; only the crank web, within a range of the thickness of the crank web in the axial direction of the crank journal, A first cast-out portion whose opening area gradually increases from the outer surface side of the crank web to the inner surface side of the crank web, which is connected to the crank journal;
A second cast-out section which is continuously provided over a range from the position of the open end of the first cast-out section to the inner side surface and has an opening area larger than the open area of the open end of the first cast-out section; Is formed.

In the invention according to claim 2, the first cast-out portion has an opening shape that extends only in the lateral width direction of the crank web, and the shaft of the crank journal finally moves toward the crank journal. It is formed in a substantially circular shape with the center as the center, and the second cast-out portion is formed in a substantially heart shape in which the top is located below the crank web in the longitudinal width direction. I have. According to a third aspect of the present invention, in the configuration of the second aspect, a configuration is adopted in which a substantially circular radius of the first cast-out portion is equal to or smaller than の of a radius of the crank journal. According to the fourth aspect of the invention,
Alternatively, in the configuration described in 3, the configuration is adopted in which the entirety is formed of a cast steel material.

[0007]

According to the first, second or third aspect of the present invention, the first cast-out portion is formed within the range of the crank web, and the inside of the crank web separated from the crank journal as a shaft structure portion. Since the second cast-out portion having a larger opening area is formed closer to the side surface, the weight of the entire crankshaft is significantly reduced. In addition, since the crankpin is reduced in weight while maintaining a solid shape that does not reduce rigidity, the bending rigidity and torsional rigidity of the entire crankshaft are hardly impaired. Therefore, the bearing impact force does not increase, and the increase in vibration and noise of the engine is suppressed. Further, it is possible to contribute to a reduction in engine weight. According to the fourth aspect of the present invention, since the material is cast steel, the Young's modulus is close to that of a steel material, and rigidity equivalent to that of a steel material is obtained. Therefore, it is possible to significantly reduce the weight while maintaining the same strength as that of the steel material, and also achieve a reduction in cost in terms of material.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. As shown in FIGS. 1 and 2, the cast crankshaft (main part) 2 is provided with a solid crankpin 4, and both ends of the crankpin 4 have a direction perpendicular to the axis. The crank webs 6 and 8 are extended. On the outer surfaces 61, 81 of the respective crank webs 6, 8,
Crank journals 10 and 12 extending along the axis of the crank pin 4 are provided continuously. Crank web 6,
8 has first cast-out portions 14, 14 within the axial thickness range of the crank journals 10, 12, respectively.
16 and second cast-out portions 18 and 20 are formed.
In addition, the cast crankshaft 2 in this example is formed of a spheroidal graphite cast steel material.

Referring to one of the crank webs 6, as shown in FIG. 2 and FIG.
The open end 141 on the inner surface 62 side of the crank web 6 has a substantially eyebrow shape that expands only in the lateral width direction of the crank web 6, and the start end 142 finally moves toward the crank journal 10 side. Shaft center 101
Is formed in a shape converging into a circle centered at. Here, the radius r ₁ of the starting end 142 is the crank journal 1
The radius is set to be equal to or less than １ ／ of the radius r ₂ of 0. this is,
For example, when a shaft hole with a diameter greater than the radius is formed in a round bar material,
This takes into account the experimental fact that the bending stiffness sharply decreases.

The upper side 141a of the open end 141 of the first cast-out portion 14 is centered on the axis of the crank pin 4 from the viewpoint of efficient casting and uniform load distribution. As an arc (in other words, R of the crank web 6)
(Along the line), and the bottom portion 141b is also shaped substantially along this. Further, from the viewpoint of maintaining the same strength, the shoulders 141 c and 141 d on both sides of the opening end 141 are also set corresponding to the outer shape of the crank web 6.

On the other hand, the second cast-out portion 18 is formed in a substantially heart shape over a range starting from the opening end 141 of the first cast-out portion 14 and opening to the inner side surface 62. Also,
The top portion 181 of the second blanked portion 18 is located far below the bottom portion 141b of the opening end 141, and has an opening area larger than that of the substantially eye-opening end 141. The upper side portion 182 of the second cast-out portion 18 has the same shape as the upper side portion 141 a of the open end 141 of the first cast-out portion 14.

As shown in FIG. 1, a cast-out range w ₁ of the first cast-out portion 14 in the thickness direction of the crank web 6.
And the relationship between the cast-out range w _{2 of} the second cast-out portion 18 is
As shown in FIG. 1, it is set so that w ₁ > w ₂ . This is based on the idea of the present invention that the casting is suppressed as much as possible in the vicinity of the crank journal 10 as the shaft structure portion related to the reduction of the bending rigidity, and the casting is performed boldly in the distant portion. As is clear from FIG. 1, the side surfaces (broken lines) of the first cast-out portion 14 and the second cast-out portion 18 have an inclined shape that decreases toward the inner side surface 62 side. It is based on the fact that the open end of the cutout 18 must be as far as possible from the danger section D. Further, the first cast-out portion 14 and the second cast-out portion 1
All the corner portions existing in 8 are formed in a curved shape in order to avoid stress concentration. Note that the above-described configurations are the same for the other crank web 8.

As described above, while the crankpin is made solid, the volume gradually increases in the direction away from the shaft structure portion (crank journal) side related to the decrease in bending rigidity within the range of the crank web. By casting in a shape and performing casting with a large opening area from a position distant from the crank journal to some extent, it is possible to achieve a significant reduction in weight without a decrease in bending rigidity. In the present embodiment, since the whole is formed of cast steel as a low carbon material, it is possible to achieve a significant reduction in weight while achieving the same strength and rigidity as steel, and further from the viewpoint of material Cost reduction can also be achieved. In the above embodiment, the shape of the main part of the cast crankshaft is specified, and the shapes of the first and second cast parts are specified and shown. However, the present invention is not limited to this. The design can be appropriately changed within a range in which the weight can be reduced without lowering the bending rigidity described above.

[Brief description of the drawings]

FIG. 1 is a main part side view showing one embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a perspective view of a cast-out portion.

FIG. 4 is a graph showing a relationship with bending rigidity when a cast portion is formed in a crank pin.

FIG. 5 is a graph showing a relationship with a bending rigidity when a cast portion is formed on a crank web.

FIG. 6 is a side view of a conventional example.

[Explanation of symbols]

4 crank pin 6 and 8 crank webs 10 and 12 crank journals 14 and 16 first cast punched portion 18, 20 second cast vent portion 141 first cast radius of the opening end r ₂ crank journal of the punching unit

Continuation of the front page (72) Inventor Taro Tatsumi 5-33-8 Shiba, Minato-ku, Tokyo, inside Mitsubishi Motors Corporation (56) References JP-A-57-73218 (JP, A) -4017 (JP, U) Hikaru 1-119913 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16C 3/08

Claims (4)

(57) [Claims] 1. A solid crankpin, a crank web extending from a shaft end of the crankpin in a direction perpendicular to the axis, and a crank web connected to an outer surface of the crank web and connected to an axis of the crank pin. provided a crank journal extending along is only in the crank web, within the scope of the crank web in the thickness in the axial direction of the crank journal, the clan provided continuously to said crank journal
A first cast-out portion whose opening area gradually increases from the outer surface side of the web to the inner surface side of the crank web; and from the position of the open end of the first cast-out portion to the inner side surface. And a second cast-out portion having an opening area larger than the opening area of the opening end of the first cast-out portion. 2. The method according to claim 1, wherein the first cast portion has an opening shape extending only in a lateral width direction of the crank web.
The second cast-out portion is formed such that the top portion is located vertically below the crank web in the longitudinal width direction, and is formed into a substantially circular shape centered on the axis of the crank journal toward the crank journal side. The cast crankshaft according to claim 1, wherein the cast crankshaft is formed in a substantially heart shape. 3. The cast crankshaft according to claim 2, wherein the radius of the substantially circular shape of said first cast portion is not more than 1/2 of the radius of said crank journal. 4. The cast crankshaft according to claim 1, wherein the cast crankshaft is formed of a cast steel material.