WO2014064522A1

WO2014064522A1 - Connecting rod

Info

Publication number: WO2014064522A1
Application number: PCT/IB2013/002524
Authority: WO
Inventors: Takahiro Mochihara; Yann DROUVIN
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2012-10-22
Filing date: 2013-10-21
Publication date: 2014-05-01
Also published as: JP2014084916A

Abstract

A connecting rod (1) includes a connecting rod main body (11) that attaches to a crankshaft (4), a connecting rod cap (12), and a connecting bolt (13) that fastens the connecting rod cap (12) to the connecting rod main body (11). A bolt insertion portion (12a) into which the connecting bolt (13) is inserted is formed on the connecting rod cap (12), and a recessed portion (12c) is formed on a surface of the connecting rod cap (12) at a position on an opposite side of the bolt insertion portion (12a) from the crankshaft (4).

Description

CONNECTING ROD

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to ^~a ^"connecting rod. ^" More particularly, the invention relates to a connecting rod that includes a connecting rod main body, a connecting rod cap, and a connecting bolt that , fastens the connecting rod -cap to the connecting rod main body.

2. Description of Related Art

[0002] A connecting rod is used in an internal combustion engine to transmit reciprocating motion of a piston to a crankshaft, and thus convert the reciprocating motion into rotary motion (see Japanese Patent Application Publication No. 5-71525 (JP 5-71525 A), for example). This connecting rod is formed by an arm portion (a connecting rod main body), and a large end portion half body (a connecting rod cap that engages with the arm portion.

[0003] A small end portion that attaches to the piston is formed on one end portion of the arm portion, and an arm-side large end portion half body that attaches to the crankshaft is formed on the other end portion of the arm portion. Also, the arm-side large end portion half body and the large end portion half body are attached to the crankshaft by being fastened by a bolt (a connecting bolt).

[0004] Also, the connecting rod described in JP 5-71525 A is made of an aluminum alloy to reduce weight. An aluminum alloy connecting rod reduces an inertia load (dynamic load) on the crankshaft, so an increase in the engine speed of the internal combustion engine is expected. Also, aluminum alloy material is less strong (rigid) than steel, so nickel - phosphorous plating is applied to the surface to ensure strength.

SUMMARY OF THE INVENTION [0005] However, considering that the strength of the connecting rod is ensured in this way, if the rigidity is increased by surface treatment or the like, the rigidity of the portion on the -outside (i.e., the portion on the sid« opposite the side where the erankshaf is - ·^■ - arranged) of the bolt around the mating surfaces of the arm-side large end portion half body of the arm portion (i.e., the connecting rod main body) and the large end portion half body (i.e., the connecting rod cap) will increase. Therefore, a difference in rigidity between the portion on the inside (i.e., the portion on the side where the crankshaft is arranged) of the bolt around the mating surfaces of -the arm-side large end portion half body and the large end portion half body, and the portion to the outside of the bolt around the mating surfaces of the arm-side large end portion half body and the large end portion half body will increase. As a result, when the bolt is fastened, bending deformation may occur such that the area around the mating surface, and the bolt, may have a depressed shape toward the side (the crankshaft side) where he rigtdity is low (that is soft); -

[0006] As a result, when the engine is driven and a dynamic load is applied due to bending deformation when the bolt is fastened, stress amplitude in the bolt may deteriorate (i.e., increase). The stress amplitude is a value of half the difference between the maximum stress and the minimum stress that is applied to the bolt. If this value becomes comparatively large, the bolt itself may fracture (i.e., fail). Also, the portions on the inside of the arm-side large end portion half body and the large end portion half body is difficult to reinforce due to the fact that there are many restrictions, for example, the crankshaft is arranged there.

[0007] The invention thus provides a connecting rod capable of reducing the stress amplitude in a connecting bolt.

[0008] One aspect of the invention relates to a connecting rod that includes a connecting rod main body that attaches to a crankshaft, a connecting rod cap, and a connecting bolt that fastens the connecting rod cap to the connecting rod main body. A bolt insertion portion that the connecting bolt is inserted into is formed on the connecting rod cap; and a recessed portion is formed on a surface of the connecting rod cap at a position on an opposite side of the bolt insertion portion from the crankshaft. According to this aspect, the stress amplitude in the connecting bolt is able to be reduced. The effect of the stress amplitude in the connecting bolt being able to be reduced has been confirmed by analysis results obtained by the inventors, which will be described later.

[0009] That is, it is presumed that the connecting rod according to this aspect of the invention has structure that includes a connecting rod main body that attaches to a crankshaft, a connecting rod cap, and a connecting bolt that fastens the connecting rod cap to the connecting rod main body. Also, a bolt insertion portion that the connecting bolt is inserted into is formed on the connecting rod cap in this aspect, and a recessed portion is formed on a surface of the connecting rod cap at a position on the opposite side of the bolt insertion portion from the crankshaft.

[0010] According to this aspect, the rigidity of the portion of the connecting rod cap at a position on the opposite side of the bolt insertion portion from the crankshaft is - able to be reduced. Thus, the difference in rigidity between the portion on the crankshaft side, and the portion on the side opposite the crankshaft, of the bolt insertion portion of the connecting rod cap is able to be reduced (i.e., made smaller). As a result, bending deformation in the connecting rod main body, the connecting rod cap, and the connecting bolt when the connecting bolt is fastened is suppressed, so the stress amplitude in the connecting bolt when a dynamic load is applied is able to be reduced.

[0011] A plurality of specific structures of the invention will be described below.

[0012] In the connecting rod according to the aspect described above, the recessed portion of the connecting rod cap may have a semicircular shape when viewed from an axial direction of the crankshaft. According to this kind of structure, stress is able to be inhibited from concentrating at the recessed portion, so the stress amplitude in the connecting bolt is able to be reduced while inhibiting the connecting rod cap on which the recessed portion is formed from failing.

[0013] Also, in the connecting rod according to the aspect described above, the connecting rod cap may be formed following an outer shape of the crankshaft, the bolt insertion portion of the connecting rod cap may include a first bolt insertion portion formed on one end portion of the connecting rod cap, and a second bolt insertion portion formed on the other end portion of the connecting rod eap, and a first recessed portion, may be formed on a surface of the connecting rod cap at a position on an opposite side of the first ^' bolt insertion portion from the crankshaft arid a second recessed portion may be formed on a surface of the connecting rod cap at a position on an opposite side of the second bolt insertion portion from the crankshaft. According to this kind of structure, unlike in a case in which the recessed portion is formed on either one end portion or the other end portion of the connecting rod cap, a difference in rigidity between the portion on the crankshaft side and the portion on the side opposite the crankshaft, of the bolt insertion hole of the connecting rod cap is able to be reduced (made smaller) at both end portions of the connecting rod cap. As a result, the stress amplitude in the connecting bolt is able to be effectively reduced.

[0014] In this case, the first recessed portion and the second -recessed portion, of the connecting rod cap may be formed in positions that are line-symmetrical with respect to a direction in which the connecting rod main body extends, when viewed from the axial direction of the crankshaft. According to this kind of structure, the stress amplitude in the connecting bolt is able to be reduced, while maintaining the weight balance of the connectmg rod cap.

[0015] The connecting rod of the aspect described above enables the stress amplitude in the connecting bolt to be reduced.

.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a perspective view schematically showing an engine provided with a connecting rod according to one example embodiment of the invention;

FIG. 2 is a front view of the connecting rod, a piston, and a crankshaft and the like according to the example embodiment; FIG 3 is an enlarged view showing an assembled state of the connecting rod and a connecting rod cap according to the example embodiment;

FIG. 4 is an enlarged sectional view showing the assembled state of the connecting rod and the connecting rod cap according to the example embodiment;

FIG. 5 is a view of stress amplitude in a male screw portion of a connecting bolt according to the example- embodiment;

FIG. 6 is an enlarged view showing an assembled state of a connecting rod- and connecting rod cap according to Comparative example 1 ;

FIG 7 is a view of stress amplitude in a male screw portion of a connecting bolt according to Comparative example 1 ;

. FIG 8 is a view of stress amplitude in a male screw portion of a connecting bolt according to Comparative example 2; and

FIG 9 is a graph showing a stress safety factor of the connecting bolts according to the example embodiment, Comparative example 1,· Comparative example 2, Comparative example 3, and Comparative example 4.

DETAILED DESCRIPTION OF EMBODIMENTS

[0017] Hereinafter, an example embodiment of the invention will be described with reference to the accompanying drawings.

[0018] First, the structure of a connecting rod 1 according to the example embodiment, and an engine 2 provided with this connecting rod 1 will be described with reference to FIGS. 1 to 4.

[0019] As shown in FIG. 1, the engine 2 provided with the connecting rod 1 is configured such that a piston 3 and a crankshaft 4 are connected together by the connecting rod 1, and reciprocating motioii of the piston 3 is converted into rotary motion of the crankshaft 4 by the connecting rod 1. A fuel mixture (mixed gas) is ignited and combusted inside a combustion chamber 5 above the piston 3, and the piston 3 is moved in a reciprocating manner, such that the crankshaft 4 rotates, by the combustion energy of this gas. [0020] As shown in FIGS. 2 and 3, the connecting rod 1 includes a connecting rod main body 11 that extends linearly, a connecting rod cap 12 arranged below the connecting rod main body 11 , and two connecting bolts 13. Hereinafter, these connecting bolts 13 may be referred to in the singular for the sake of simplicity.

[0021] The piston 3 is connected by a piston pin 14 to a small end portion la formed on an upper end of the connecting rod 1. Also, a shaft hole I c to which a crank pin 4a of the crankshaft 4 is connected is formed in a large end portion lb formed on a lower end of the connecting rod 1. This shaft hole 1 c is formed by a semicircular portion 111 that is formed oh a lower end of the connecting rod main body 11, and a semicircular portion 121 of the connecting rod cap 12,

[0022] The connecting rod cap 12 is fastened to a portion on the semicircular portion 111 side (i.e., the side opposite the piston 3) of the connecting rod main body 11. The connecting rod cap 12 is generally C-shaped when viewed from an axial direction of the crankshaft 4.

r. ^■

[0023] Also, as shown in FIG 4, bolt insertion holes 12a into which the connecting- bolts 13 are inserted from below are formed one on each of two end portions of the large end portion lb of the connecting rod cap 12. These bolt insertion holes 12a in the connecting rod cap 12 are formed through the connecting rod ca 12. Also, bolt insertion holes 11a into which the connecting bolts 13 are inserted from below are formed one on each of two end portions of the large end portion lb of the connecting rod main body 11. Hereinafter, these bolt insertion holes 11a and 12a may be referred to in the singular for the sake of simplicity.

[0024] That is, the connecting rod cap 12 is fastened to the connecting rod main body 11 at two locations by the connecting bolts 13 being inserted through the bolt insertion holes 12a in the connecting rod cap 12 and^' the bolt insertion holes 1 la i the connecting rod main body 11. The bolt insertion holes 12a are one example of the "first bolt insertion portion" and the "second bolt insertion portion" of the invention.

[0025] The connecting bolt 13 has a male screw portion 132 on a tip end side of a middle position (i.e., with respect to mating surfaces 11c and 12b) of a shaft portion 131, and a male screw portion 133 on a head portion 134 side of the middle position (i.e., with respect to the mating surfaces 11 c and 12b) of the shaft portion 131. Also, a female screw ^' portion lib is formed in the bolt insertion hole ^"11a of the connecting rod main body 11¹. Also, a straight portion lid is formed along the mating surface 1 lc from the female screw portion lib, in. the bolt insertion hole 11a.

[0026] Here, in this example embodiment, a recessed portion 12c is formed on a surface on the outside of the bolt insertion hole 12a (i.e.; the surface on the side opposite the crankshaft 4), of an outer peripheral surface of the connecting rod cap 12, as shown in FIGS. 2 to 4. This recessed portion 12c is one example of the "first recessed portion" and the "second recessed portion" of the invention. As shown in FIG. 2, two recessed portions 12c are formed in positions below (i.e., on the side opposite the piston 3) a center portion of the crankshaft 4 (crank pin 4a). Also, the two recessed portions 12c are formed in positions that are line-symmetrical with respect to the direction in which the connecting rod main body 11 extends, when viewed from the axial direction of the crankshaft 4 (crank pin 4a). Hereinafter, these recessed portions 12c may be referred to in the singular for the sake of simplicity.

[0027] Also, as shown in FIGS. 3 and 4, the recessed portion 12c is formed in a semicircular shape that is recessed toward the crankshaft 4 (crank pin 4a) side when viewed from the axial direction of the crankshaft 4 (crank pin 4a). Also, as shown in FIG 4, the recessed portion 12c is formed recessed in a direction substantially orthogonal to -an axial direction of the connecting bolt 13. That is, a portion on the connecting bolt 13 side of the recessed portion 12c is shaped so as to be closer to the connecting bolt 13 side than the portion around the recessed portion 12c.

[0028] Here, with a typical connecting rod, a portion of the connecting rod main body and the connecting rod cap that is on the outside (i.e., the side opposite the crankshaft) of the connecting bolt has a tendency to be more rigid than a portion of the connecting rod main body and the connecting rod" cap' that S on the^"msiU^"e-(i.e;.,-the ^" crankshaft side) of the connecting bolt. Therefore, when the connecting rod main body and the connecting rod cap are fastened by the connecting bolt, the fastening portions of these deform (bend) so as to be recessed toward the inside. That is, the connecting rod main body, the connecting rod cap, and the connecting bolt deform in such a way that they ¾end toward the less rigid side (i.e., the softer side).

[0029] On the other hand,^' in this example embodiment, as described above, by forming the recessed portion 12c on a portion of the connecting rod cap 12 that is to the outside of the connectmg bolt 13 (the bolt insertion hole 12a), the rigidity of the portion of the connecting rod cap 12 that is to the outside of the connecting bolt 13 (the bolt insertion hole 12a) is reduced, so the difference in rigidity between the portion of the connectmg rod cap 12 that is to the inside of the connecting bolt 13 and the portion of the connecting rod cap 12 that is to the outside of the connecting bolt 13 is reduced.

[0030] Therefore, in this example embodiment, the amount of deformation in the fastening portions of the connecting rod main body 11 and the connecting rod cap 12 when these are fastened together by the connecting bolt 13 is able to be suppressed compared to a typical connecting rod. As a result, the stress amplitude (i.e., the value of half of the difference between the maximum stress and the minimum stress) in the connecting bolt 13 when the engine 2 is driven is able to be reduced. Hereinafter, the effect in which the stress amplitude in the connecting bolt 13 is able to be reduced will be described based on analysis results obtained by the inventors.

[0031] First, the stress amplitude in me connectmg bolt 13 that is attached to the connecting rod 1 according to this example embodiment will be described with reference to FIG. 5.

[0032] FIG. 5 is a view of the stress amplitude in a engaging portion of the male screw portion 132 of the connecting bolt 13 and the female screw portion lib of the • connecting rod main body 11. In FIG. 5, the stress amplitude for the male screw portion 132 of the connecting bolt 13 is shown, but the stress amplitude for the female screw portion 11 b of the connecting rod main body 11 is not shown.

[0033] In this example embodiment, for the analysis method of the stress amplitude in the connecting bolt 13, analysis was performed using- a -Finite -Element Method (FEM) that calculates the stress amplitude by dividing the engaging portion of the male screw portion 132 of the connecting bolt 13 and the female screw portion l ib of the connecting rod main body 11 into a plurality of elements. Also, regions Al, A2, A3, A4, A5, A6, and A7 shown in FIG 5 represent the stress amplitude, with region Al representing the largest stress amplitude, region A2 to region A6 representing gradually decreasing stress amplitudes in this order, and region A7 representing the smallest stress amplitude.

[0034] From the analysis results shown in FIG 5, it is evident that the largest stress amplitude is in a region (region X) between one tooth of the male screw portion 132 and another tooth of the male screw portion 132. It is also evident that the stress amplitude decreases along the screw tooth of the male screw portion 132 from the region (region X) between one tooth of the male screw portion 132 and another tooth of the male screw portion 132.

[0035] Also, it is evident that the regions where the stress amplitude is large (i.e., regions Al to A3) are concentrated in the region X (i.e., the region between one screw tooth and another screw tooth of the male screw portion 132).

[0036] Next, the stress amplitude in the connecting bolt 13 that is attached to a connecting rod 101 according to Comparative example 1 will be described with reference to FIG 6.

[0037] As shown i FIG. 6, the connecting rod 101 according to Comparative example 1 differs from the connecting rod 1 of this example embodiment in that a recessed portion is not formed on a connecting rod cap 120. That is, in the connecting rod 101 according to Comparative example 1, the rigidity of a portion of the connecting rod cap

120 that is to the outside of the connecting bolt 13 (the belt insertion hole- l-2a) is- greater - than the rigidity of a portion of the connecting rod cap 120 that is- to the -inside of the - connecting bolt 13 (the bolt insertion hole 12a). That is, the difference in rigidity between the outside portion of the connecting rod cap 120 and the inside portion of the connecting rod cap 120 is greater than it is in the example embodiment.

[0038] Therefore, the amount of deformation of the connecting rod cap 120, the connecting rod main body 11, and the connecting bolt 13 when fastening the connecting rod cap 120 to the connecting rod main body 11 by the connecting bolt 13, is larger than it is in the example embodiment. Therefore, the stress amplitude with respect to the connecting bolt 13 when the engine 2 is driven increases.

[0039] Next, an increase in the stress amplitude in the connecting bolt 13 of the connecting rod 101 according to Comparative example 1 will be described with reference to FIG. 7 based on analysis results obtained by the inventors.

[0040] FIG. 7 is a view of the -stress amplitude in an engaging portion of the male screw portion 132 of the connecting bolt 13 and the female screw portion lib of the connecting rod main body 11 of the connecting rod 101 according to Comparative example 1.

[0041] Also, regions Bl, B2, B3, B4, B5, B6, B7, and B8 shown in FIG. 7 represent the stress amplitude, with region Bl representing the largest stress amplitude, region B2 to region B7 representing gradually decreasing stress amplitudes in this order, and region B8 representing the smallest stress amplitude.

[0042] Also, from the analysis results shown in FIG. 7, it is evident that the largest stress amplitude is in a region (region Y) between one tooth of the male screw portion 132 and another tooth of the male screw portion 132. It is also evident that the stress amplitude decreases along the screw tooth of the male screw portion 132 from the region (region Y) between one tooth of the male screw portion 132 and another tooth of the male screw portion 132.

[0043] Also, it is evident that the regions where the stress amplitude is large (i.e., regions Bl to B4) are concentrated in the region Y (i.e., the region between one screw tooth and another screw tooth of the male screw portion 132). That is, it is evident that the stress amplitude in the connecting bolt 13 of the connecting rod 101 according to Comparative example 1 is larger than the stress amplitude in the connecting bolt 13 of the connecting rod 1 according to the example embodiment.

[0044] Next, the stress amplitude in the connecting bolt 13 of the connecting rod 102 according to Comparative example 2 will be described with reference to FIG 8. .

[0045] An analysis of a case in which it is assumed that the connecting rod 102 according to Comparative example 2 has the same structure as the connecting rod 101 according to Comparative example 1, but the rigidity has been increased by further ^' reinforcing a portion of the connecting rod cap 120 that is to the_. outside (i.e., the side opposite the crankshaft 4) of the connecting bolt 13 with a atch or the like will be now -be- described.

[0046] In this case, compared to the connecting rod 101 according to Comparative example 1 , the rigidity of the portion on the outside of the connecting rod cap 120 is even greater than the rigidity of the portion on the inside (i.e., the-crankshafi: 4 side) of the connecting rod cap 120. That is, the difference in rigidity between the portion on the outside of the connecting rod cap 120 and the portion on the inside of the connecting rod cap 120 is even larger than it is in Comparative example 1.

[0047] Therefore, the amount of deformation in the connecting rod cap 120, the connecting rod main body 11 , and the connecting bolt 13 when the connecting rod cap 120 is fastened to the connecting rod main body 11 by the connecting bolt 13 is even larger than it is in Comparative example 1. Thus, the stress amplitude in the connecting bolt 13 when, the engine 2 is driven increases even more.

[0048] Next, an increase in the stress amplitude in the connecting bolt 13 of the connecting rod 102 according to Comparative example 2 will be described with reference to FIG. 8 based on analysis results obtained by the inventors:

[0049] FIG. 8 is a view of the stress amplitude in an engaging portion of the male screw portion 132 of the connecting bolt 13 and the female screw portion lib of the connecting rod main body 11, of the -connecting . rod 102 - according - to -Comparative example 2.

[0050] Also, regions CI, C2, C3, C4, C5, C6, C7, and C8 shown in FIG. 8 represent the stress amplitude, with region CI representing the largest stress amplitude, region C2 to region C7 representing gradually decreasing stress amplitudes in this order, and region C8 representing the smallest stress amplitude.

[0051] Also, from the analysis results shown in FIG 8, it is evident that the largest stress amplitude is in a region (region Z) between one tooth of the male screw portion 132 and another tooth of the male screw portion 132. It is also evident that the . stress amplitude decreases along the screw tooth of the male screw portion 132 from the ^' region (region Z) between one tooth of the male screw portion 132 and another tooth of the male screw portion 132.

[0052] Also, it is evident mat the regions where me stress amplitude is large (i.e., regions d to C4) are concentrated in the region Z (i.e., the region between one screw tooth and another screw tooth of the male screw portion 132). That is, it is evident from the analysis results that the stress amplitude in the connecting bolt 13 of the connecting rod 102 according to Comparative example 2 is larger than both the stress amplitude in the connecting bolt 13 of the connecting rod 1 according to the example embodiment and the stress amplitude in the connecting bolt 13 of the connecting rod 101 according to Comparative example 1.

[0053] Next, the stress safety factor of the connecting bolt according to the example embodiment, Comparative example 1, Comparative example 2, Comparative example 3, and Comparative Example 4 will be described with reference to FIG 9.

[0054] In the graph shown in FIG. 9, the horizontal axis represents an average stress [MPa] in the connecting bolt 13, with the average stress being comparatively smaller on the left side in the graph, and the average stress being comparatively larger on the right side in the graph. Also, the vertical axis represents the stress amplitude [MPa] in the connecting bolt 13, with the stress amplitude being comparatively smaller on the lower side in the graph, and the stress amplitude being comparatively larger on the upper side in the graph. The straight line that is sloped with respect to the vertical axis and the horizontal axis in the graph represents a fatigue limit line that is a limit point of the stress amplitude determined by the material of the connecting bolt.

[0055] In FIG 9, the stress safety factors of the connecting bolts of the connecting rods according to the example embodiment and the comparative examples were calculated and compared. The fatigue limits (stress amplitudes) of the average stress [MPa] are calculated from the values of the average stress [MPa] and the stress amplitude [MPa] obtained from the analysis results, and the stress safety factors (= the fatigue limits (stress amplitudes) / the stress amplitudes obtained from the analysis results) are calculated from these results.

J0056] First, with the connecting bolt 13 of the connecting rod 1 according to the example embodiment, it is evident from the average stress [MPa] and the stress amplitude [MPa] obtained from the analysis results that the stress safety factor is approximately 1.10.

[0057] With the connecting bolt 13 of the connecting rod 101 according to Comparative example 1, it is evident from the average stress [MPa] and the stress - amplitude [MPa] obtained from the analysis results that the stress safety factor is approximately 1.03.

[0058] With the connecting bolt 13 of the connecting rod 102 according to

Comparative example 2, it is evident from the average stress [MPa] and the stress amplitude [MPa] obtained from the analysis results that the stress safety factor is approximately 0.99.

[0059] From the results above, it is evident that the stress safety factor of the connecting bolt 13 of the connecting rod 1 according to the example embodiment is higher than the stress safety factors of Comparative example 1 and Comparative example 2.

[0060] Next, the stress safety factors of connecting bolts of connecting rods according to Comparative example 3 and Comparative example 4, in addition to Comparative example 1 and Comparative example 2 described above, will be described. For Comparative example 3 and Comparative example 4, the analysis results are not shown as they are in FIG. 5 and FIG. 7, but an analysis was performed using a structure in which the rigidity of the portion on the outside of the connecting rod cap was increased more than the rigidity of the portion on the inside of the connecting rod cap, similar to Comparative example 1 and Comparative example 2 described above.

[0061] With the connecting bolt of the connecting rod according to Comparative example 3, it is evident from the average stress [MPa] and the stress amplitude [MPa] obtained from the analysis results that the stress safety factor is approximately 1.05.

[0062] With the connecting bolt of the connecting rod according to Comparative example 4, it is evident from the ^" average stress^■ [MPa] and:the- stress amplitude [MPa] obtained from the analysis results that the stress safety factor is approximately 1.03.

[0063] From the results above, it is evident that the stress safety factor of the connecting bolt 13 of the connecting rod 1 according to the example embodiment is higher than the stress safety factors of Comparative example 3 and Comparative example 4, in addition to being higher than the stress safety factors of Comparative example 1 and Comparative example 2.

[0064] As described above,

:Je am le...- embodi·ment is able to yield effects such as those listed below.

[0065] In this example embodiment, the recessed portion 12c is formed on the surface of the connecting rod cap 12 at a position on the opposite side of the bolt insertion hole 12a from the crankshaft 4, as described above. Accordingly, the rigidity of the portion, on the side opposite the crankshaft 4, of the bolt insertion hole 12a of the connecting rod cap 12 is able_to be reduced,—As a. result, -the.. difference., in rigidity- - between the portion on the crankshaft 4 side and the portion on the side opposite the crankshaft 4, of the bolt insertion hole 12a of the connecting rod cap 12 is able to be reduced (made smaller). Therefore, bending deformation of the connecting rod main body 11, the connecting rod cap 12, and the connecting bolt 13 when the connecting bolt 13 is fastened is suppressed, so the stress amplitude in the connecting bolt 13 when a dynamic load is applied is able to be reduced.

[0066] Also, in this example embodiment, the recessed portion 12c of the connecting rod cap 12 is formed in- a seirroircular- shape when- viewed from- the axial direction of the crankshaft 4, as described above. Therefore, stress is able to be inhibited from concentrating at the recessed portion 12c, so the stress amplitude in the connecting bolt 13 is able to be reduced while inhibiting the connecting rod cap 12 on which the recessed portion 12c is formed from failing.

[0067] Also, in this example embodiment, as described above, the recessed portion 12c is formed on the surface of the connecting rod cap 12 at a position on the opposite side of the bolt insertion hole 12a from the crankshaft 4. Therefore, unlike in a case in which the recessed portion 12c is formed on either one end portion or the other end portion of the connecting rod cap 12, a difference in rigidity between the portion on the crankshaft 4 side and the portion on the side opposite the crankshaft 4, of the bolt insertion hole 12a of the connecting rod cap 12 is able to be reduced (made smaller) at both end portions of the connecting rod cap 12. As a result, the stress amplitude in the connecting bolt 13 is able to be effectively reduced.

[0068] As, in this example embodiment, the two recessed portions 12c of the connecting rod cap 12 are formed in positions that are line-symmetrical with respect to the direction in which the connecting rod main body 11 extends, when viewed from the axial direction of the crankshaft 4. Therefore, the stress amplitude in the connecting bolt 13 is able to be reduced, while maintaining the weight balance of the connecting rod cap 12.

[0069] The example embodiment disclosed herein is in all respects merely an example and should in no way be construed as limiting. The scope of the invention is indicated not by the foregoing description of the example embodiment, but by the scope of the claims for patent, and is intended to include all modifications that are within the scope and meanings equivalent to the scope of the claims for patent.

[0070] For example, in the example embodiment described above, a semicircular recessed portion is formed on the connecting rod cap, but the invention is not limited to this. For example, the recessed portion may also have a shape other than semicircular, such as a rectangular shape or a V-shape.

[0071] Also, in the example embodiment described above, one recessed portion is formed on each of the two end portions of the connecting rod cap, but the invention is not limited to this. For example, only one recessed portion may be formed on one end portion or the other end portion of the connecting rod cap, or two or more recessed portions may be formed on one end portion or the other end portion of the connecting rod cap.

[0072] The invention may be used for a connecting rod. In particular, the invention may be used for a connecting rod that includes a connecting rod main body, a connecting rod cap, and a connecting bolt that fastens the connecting rod cap to the connecting rod main body.

Claims

CLAIMS:

1. A connecting rod comprising:

a connecting rod main body that attaches to a crankshaft;

a connecting rod cap; and

a connecting bolt that fastens the connecting rod cap to the connecting rod main body, wherein

a bolt insertion portion that the connecting bolt is inserted into is formed on the connecting rod cap; and a recessed portion is formed on a surface of the connecting rod cap at a position on an opposite side of the bolt insertion portion from the crankshaft.

2. The connecting rod according to claim 1, wherein the recessed portion of the connecting rod cap has a semicircular shape when viewed from- an axial direction of the crankshaft.

3. The connecting rod according to claim 1 or 2, wherein the connecting rod cap is formed following an outer shape of the crankshaft; the bolt insertion portion of the connecting rod cap includes a first bolt insertion portion formed on one end portion of the connecting rod cap, and a second bolt insertion portion formed on the other end portion of the connecting rod cap; and a first recessed portion is formed on a surface of the connecting rod cap at a position on an opposite side of the first bolt insertion portion from the crankshaft and a second recessed portion is formed on a surface of the -connecting rod cap at a position on an opposite side of the second bolt insertion portion from the crankshaft.

4. The connecting rod according to claim 3, wherein the first recessed portion and the second recessed portion of the connecting rod cap are formed in positions that are line-symmetrical with respect to a direction in which the connecting rod main body extends, when viewed from the axial direction of the crankshaft.