JPH07269554A - Casting connecting rod - Google Patents

Abstract

PURPOSE:To improve the strength more than the I-section structure since the generated stress is dispersed, by making a connecting part in a hollow structure, and opening further partially the connecting part by a casting connecting rod which forms the smaller end and the larger end integrally. CONSTITUTION:The connecting part 8 of a connecting rod is made in a hollow structure, and the connecting part 8, the smaller end 1, and the larger end 11 are formed integrally by a casting. The outer surface of the connting part 8 can be made in a smooth curved surface by making in a hollow structure, the tip of the flange where a local stress concentration is liable to generate can be eliminated in the form, and a stress concentration at the foot of the connecting part, and the increase of the stress by the bad influence of an eccentric load can be relaxed. And by manufacturing in a casting, the connecting part 8, the smaller end 1, and the larger end 11 can be formed smooth integrally, so as to eliminate an uneven surface or the unevenness of quality generated at a welding part and the like. Consequently, the stress distribution can be smoothed, the fatigue strength is improved, and it can be used to an engine with a severe condition more than an I-section structure in the same section area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connecting rod connecting a piston and a crankshaft for converting the reciprocating motion of a piston in a reciprocating engine into a rotary motion of a crankshaft.

[0002]

2. Description of the Related Art In a reciprocating engine, the connecting portion of the connecting rod is repeatedly stressed as the engine rotates.
The forces that generate this stress are roughly classified into the following three. (1) In the explosive stroke, the explosive pressure in the cylinder is transmitted to the connecting rod via the piston, and a force for compressing the connecting portion is generated. In recent years, multi-valve and multi-point injection to increase engine output of automobiles,
Explosion pressure is increasing with the adoption of superchargers. (2) The reciprocating mass of the piston system mass and the connecting rod system mass generates an inertial force due to a reciprocating motion accompanied by a change in acceleration, and a tensile force and a compressive force are generated at the connecting portion.
In recent years, the maximum engine speed has become higher for higher output, and along with this, the inertial force is becoming larger. (3) The mass of the connecting portion of the connecting rod generates an inertial force in the swinging direction, that is, a force for whipping the connecting rod around the rotation axis of the crankshaft, for each reciprocating motion. Similar to (2) above, this force is also increasing due to the increase in maximum rotation speed. The repeated stress applied to the connecting portion of the connecting rod is a combination of the stresses generated by the above three forces.

The repetitive stress applied to the connecting portion of the connecting rod is analyzed in more detail in the above three items.
Repeated tensile / compression stress uniformly applied to the entire joint surface according to item (2), and stress with a linear gradient in the cross section of the joint part that reverses positive / negative in the swing direction according to item (3) ,
It can be seen that it is the total stress of "oscillation stress". For this reason, conventionally, the connecting portion of the connecting rod has a so-called I-shaped cross section having a flange in the whipping direction in order to reduce rocking stress as much as possible to improve fatigue strength and strength against buckling. Generally widely used. This is because it is believed that the I-shaped cross section can effectively increase the cross-sectional secondary moment in the whipping direction and maximize the strength with a small cross-sectional area. Further, if it has an I-shaped cross section, it can be easily formed by die forging, which is advantageous in terms of manufacturing cost.

On the other hand, connecting rods and the like which give the highest priority to weight reduction have a so-called H-shaped cross-section with a flange having an I-shaped cross section rotated by 90 degrees, or a combined I-type and H-shaped one (for example, JP-A-2-107816, JP-A-2-129305, and JP-A-63-168.
No. 317), a flange having an I-shaped cross section is reinforced to improve strength (for example, Japanese Utility Model Laid-Open No. 62-71415). Further, an assembly (for example, JP-A-62-24019, JP-A-62-242116) in which the connecting portion is a steel plate having a hollow structure and which is connected to the small end and the large end by welding or brazing is available. is there.

[0005]

However, due to the following reasons, the above I-shaped cross section is not actually the optimum shape in practice. (1) In the actual connecting rod, the stress is not uniform in the cross section of the connecting portion even by the tensile / compressive force. That is, as shown in FIG. 3, for example, when the small inertia 1 receives a tensile inertia force 6 of a piston system, the connecting portion 7 and the root 2 of the small end 1 are received.
In the vicinity, stress concentration is likely to occur, and particularly in the case of the I-shaped cross section 3, large stress is likely to be applied to the top portion 4 of the flange. (2) The I-shaped cross section is easily affected by the eccentric load, and since the top portion 4 of the flange is located away from both the neutral surface 5a in the whipping direction and the neutral surface 5b in the right angle direction, a slight eccentric load is generated. Therefore, similarly to the above (1), a large stress is likely to be generated at the top of the flange. (3) The I-shaped cross section is generally formed by forging black leather,
The fatigue strength of black leather is usually weaker than the true material strength, and defects such as defects and decarburized layers are likely to occur. When the extra stress due to the above (1) and (2) is applied to the top portion 4 of the flange formed by the black leather, the strength of the actual connecting rod is significantly reduced. (4) In order to minimize these adverse effects,
The overall I-shaped cross section is shot-peened or the top part 4 of the flange is coined to improve the strength, but the fatigue strength of the actual connecting rod is only 1/2 to 1/3 of the true fatigue strength of the material. I can't get it. At this time, the fracture starting point is almost in the vicinity of the top portion 4 of the flange, and this portion can be said to be the weakest portion of the I-shaped cross section. In the case of the H-shaped cross section, stress concentration similar to that of the I-shaped cross section occurs, and the strength problem cannot be solved.

For an assembly having a hollow cross section, the connecting portion and the connecting portion of the small end portion and the large end portion must be connected by welding or brazing. However, with these methods, the connecting portion is uniformly and smoothly. Difficult to connect. therefore,
Even if the strength of the connecting portion can be improved by making the cross section hollow, the strength of the actual connecting rod does not necessarily increase because the connecting portion is a weak point.

It is an object of the present invention to solve the above problems and further improve the strength of the actual connecting portion, which has a limit in the conventional connecting rod.

[0008]

The connecting rod of the present invention for solving the above-mentioned problems enables a hollow structure of the connecting portion, and allows the connecting portion, the small end portion and the large end portion to be integrally formed. It is characterized by being a cast connecting rod. In addition, a part of the hollow connecting portion is opened.

[0009]

[Function] By making the cross-sectional shape hollow, the outer surface of the connecting portion can be made into a gently curved surface, the top of the flange where local stress concentration is likely to occur can be geometrically eliminated, and stress concentration at the joint root and Reduces the increase in stress due to the adverse effect of eccentric load. Also, by manufacturing by casting, the connecting portion, the small end portion, and the large end portion can be smoothly integrally formed, and unevenness and unevenness of the material which are seen in the welded portion can be eliminated. This makes it possible to make the stress distribution smooth,
The fatigue strength of the actual connecting rod is improved, and if it has the same cross-sectional area, it can be used for an engine with severer conditions than the I-shaped cross section. Further, in order to obtain the same fatigue strength as the I-shaped cross section, the cross-section can be designed with a smaller cross-sectional area, and the connecting rod can be made lighter.

[0010]

EXAMPLES Examples of the present invention will be described in detail below. (Example 1) Fig. 1 shows a hollow connecting rod of the present invention manufactured by casting, (A) is a front view showing a connecting rod body, and (B) is a sectional view of aa portion of (A). . In order to make it hollow, the baseboards 9 and 10 of the core 8 are the small end 1 and the large end 11 of the connecting rod. The wall thickness of the hollow portion was 3 mm. The hollow connecting rod of the present invention and the I-shaped cross-section connecting rod of the conventional example were cast under the same conditions to prepare a test product. The material is F, which is a common cast material, spheroidal graphite cast iron.
It was set to CD700.

These connecting rods were subjected to a tensile / compression fatigue test between the small end and the large end to compare the fatigue strength. The results are shown in Table 1. Here, the numerical value indicated as the nominal tensile / compressive fatigue limit is a value obtained by dividing the tensile / compressive fatigue limit load by the cross-sectional area of the connecting portion.

[0012] (Table 1) connecting cross-sectional area pulling, pressing nominal tension and compression fatigue limit load fatigue limit Classification test article ^{(mm 2) (kN) (} N / mm 2) Inventive Example hollow Konrotto Bu 190 447 235 Supporting Typical example I type cross section 140 140 247 177

As shown in Table 1, the conventional I-shaped connecting rod has a nominal tensile / compression fatigue limit of 177 N / mm ² due to stress concentration. On the other hand, in the hollow connecting rod of the example of the present invention, the stress concentration was relieved, so the nominal tensile / compression fatigue limit was improved to 235 N / mm ² , and the strength of the connecting portion was improved by about 30% in terms of the nominal stress. Further, in the conventional I-shaped cross-section connecting rod, the starting point of fatigue fracture was mostly at the top of the flange, but in the hollow connecting rod of the present invention, the starting points of fatigue fracture were scattered in each part, and the effect of stress dispersion was observed. In the actual operating state of the engine, the rocking stress acts as described above, so that the improvement effect over the present embodiment can be expected.

(Embodiment 2) FIG. 2 is a view showing another hollow connecting rod of the present invention manufactured by casting. (A) is a front view showing a connecting rod body, (B) is a cross-sectional view of the bb portion of (A). The skirting board 13 of the core 12 for making it hollow is an opening portion on the side surface of the connecting rod. By using a sideboard as the baseboard, it is possible to eliminate the need to make openings in the inner diameters of the small end and the large end. The shape and the size of the opening of the connecting portion are set so that the I-shaped cross-section connecting rod shown in the first embodiment has the same cross-sectional area as the cross-section shown in FIG. is doing. The hollow connecting rod of the present invention and the I-shaped connecting rod of the conventional example were cast under the same conditions as in Example 1 to prepare a test product. This test product was subjected to a tensile / compression fatigue test in the same manner as in Example 1. The results are shown in Table 2.

[0015] (Table 2) connecting cross-sectional area connecting rod tension and compression body mass fatigue limit load Classification test article (mm ²⁾ (kg) (kN) Inventive Examples hollow Konrotto Bu 140 0.32 288 Supporting come Example I type Cross-section control 140 0.32 247

As shown in Table 2, the conventional I-shaped connecting rod has a tensile / compression fatigue limit load of 247 kN. On the other hand, in the hollow connecting rod of the present invention example, the tensile / compression fatigue limit load is improved to 288 kN, and even with the same mass, the strength of the connecting portion can be improved by about 20%.

[0017]

As described above in detail, in the cast connecting rod of the present invention, the connecting portion has a hollow structure and the connecting portion, the small end portion and the large end portion are integrally molded, so that the following effects can be obtained. . (1) Stress concentration is alleviated and the fatigue strength of the actual connecting rod is improved, and even if it is designed with the same cross-sectional area and the same mass, it can be used for an engine under conditions severer than the I-shaped cross section. (2) Also, in order to obtain the same fatigue strength as the I-shaped cross section, it is possible to design with a smaller cross-sectional area, and the weight of the connecting rod can be reduced. The connecting rod having the above strength can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 shows a hollow connecting rod of an example of the present invention, (A) is a front view, and (B) is a sectional view of aa section.

FIG. 2 shows another hollow connecting rod of the example of the present invention, (A)
Is a front view, and (B) is a cross-sectional view of a bb section.

FIG. 3 is a front view showing a connecting rod having a connecting portion with an I-shaped cross section in a conventional example.

[Explanation of symbols]

1: Small end, 2: Base of connecting part, 3: I-shaped cross section, 4: Top of flange, 5a, 5
b: neutral surface, 6: inertial force, 7: connecting part,
8, 12: Core, 9, 10, 13: Baseboard,
11: Large end.

Claims (2)

[Claims] 1. A connecting rod for an engine in which a piston and a crankshaft are connected to each other, wherein the connecting portion has a hollow structure, and the connecting portion, the small end portion and the large end portion are integrally molded. 2. The cast connecting rod according to claim 1, wherein a part of the hollow connecting portion is opened.