JP4870922B2 - Connecting rod, engine, motor vehicle and manufacturing method of connecting rod - Google Patents

Description

  The present invention relates to a connecting rod for connecting a crankshaft and a piston and a method for manufacturing the connecting rod, and more particularly to an integral connecting rod and a method for manufacturing the same. The present invention also relates to an engine or a motor vehicle having such a connecting rod.

  In an engine used for an automobile or the like, a member called a connecting rod (or connecting rod) is used to connect a crankshaft and a piston. FIGS. 17A and 17B show a general connecting rod 401. The connecting rod 401 is made of steel, and includes a small end portion 410 connected to the piston, a large end portion 420 connected to the crankshaft, and a connecting portion 430 that connects the small end portion 410 and the large end portion 420. And have.

  The small end portion 410 has a through hole 412 through which the piston pin passes, and the large end portion 420 has a through hole 422 through which the crank pin passes. The connecting portion 430 has a rod-like shape, and the strength is improved by making the cross-sectional shape H-shaped or I-shaped.

  A connecting rod 401 shown in FIGS. 17A and 17B is a connecting rod of a type called an integral type. In addition, as a connecting rod, a split type connecting rod in which a large end portion is divided into two is known.

  When the integrated connecting rod 401 is assembled to the crankshaft, a rolling bearing such as a roller bearing is disposed in the through hole 422 of the large end 420. Since the inner peripheral surface 422a of the through hole 422 of the large end 420 is in contact with a rolling element of a rolling bearing (for example, a roller of a roller bearing), high pressure resistance is required. In order to increase the pressure resistance of the inner peripheral surface 422a, generally, the hardness of the inner peripheral surface 422a is increased by carburizing.

  FIG. 18 shows a general manufacturing process of the integrated connecting rod 401. First, a steel material is prepared, and this steel is formed into a connecting rod shape by forging. As a material, for example, SCM420 which is chrome molybdenum steel is used.

  Next, copper plating is applied to the surface of the molded body, and then a predetermined machining is performed to form the through hole 412 of the small end portion 410, the through hole 422 of the large end portion 420, and the like.

  Subsequently, carburization, quenching, and tempering are sequentially performed. At this time, a portion of the large end 420 not covered with the plating layer such as the inner peripheral surface 422a (a portion where the plating layer has been removed by cutting during machining) increases the amount of carbon in the vicinity of the surface due to carburization. So it hardens. Carburization is performed, for example, under conditions such that the effective hardening depth is 1.0 mm. “Effective curing depth is 1.0 mm” here means that the depth from the surface of a point of 550 HV is 1.0 mm. On the other hand, the portion covered with the plating layer such as the connecting portion 430 (that is, the portion subjected to the carburizing prevention treatment) hardly hardens because the amount of carbon hardly increases even by carburizing.

  Thereafter, finishing is performed to complete the connecting rod 401. FIG. 19 shows a hardness distribution of a connecting rod 401 manufactured by the above-described method (hereinafter referred to as a carbon-proof method) using SCM420 as a material. As shown in FIG. 19, according to the carbon prevention method, the hardness of the inner peripheral surface 422 a of the large end 420 can be increased while suppressing an increase in the hardness of the connecting portion 430. The pressure resistance strength of the inner peripheral surface 422a can be increased while ensuring toughness.

  However, since the connection part 430 is hardly hardened in the carbon-proof method, if the connection part 430 is formed thin in order to reduce the weight of the connecting rod 401, the bending strength of the connection part 430 may be insufficient.

  Thus, as disclosed in Patent Document 1, a method of performing carburization twice (hereinafter referred to as a double carburizing method) has been proposed. FIG. 20 shows a manufacturing process of the connecting rod 401 using the twice carburizing method.

  First, a steel material is prepared, and this steel is formed into a connecting rod shape by forging. Next, the surface of the molded body is subjected to carbon-proofing (application of a carbon-proofing agent), and then subjected to predetermined machining to form the through-hole 412 of the small end 410, the through-hole 422 of the large end 420, and the like. To do.

  Subsequently, the first carburization is performed. This carburization is performed shallower than the carburization in the carburizing method, for example, under the condition that the effective hardening depth is 0.5 mm.

  Next, the carburizing agent remaining on the surface of the connecting rod 401 is removed, and then the second carburizing, quenching, and tempering are sequentially performed. The second carburization is also shallower than the carburizing method, for example, the effective hardening depth of the portion exposed to the carburizing atmosphere for the first time such as the connecting portion 430 is 0.5 mm. Thereafter, a predetermined finishing process is performed to complete the connecting rod 401.

  In the double carburizing method, carburizing is performed twice on the inner peripheral surface 422a of the large end portion 420, while shallow carburizing is performed once on the connecting portion 430. Therefore, the pressure resistance strength of the inner peripheral surface 422a is increased. While making it high enough, the bending strength of the connection part 430 can be made high to such an extent that a toughness is not impaired.

In the split type connecting rod, since a sliding bearing called a connecting rod metal made of a soft metal is disposed in the through hole at the large end, the inner peripheral surface of the large end has a very high pressure resistance. Not required. Therefore, as shown in FIG. 21, by performing shallow carburization (for example, effective hardening depth of 0.5 mm) once on the entire connecting rod (this method is hereinafter referred to as a total carburizing method), as shown in FIG. In addition, the connecting portion can be made hard with a good balance between toughness and bending strength (see, for example, Patent Documents 2 to 4).
JP 2000-310329 A JP 2004-3554 A JP 2004-52775 A JP 2004-211731 A

  However, in the double carburizing method, it is necessary to perform carburization twice and also to remove the carburizing agent. Therefore, the manufacturing process is long and complicated, and the manufacturing cost increases. In addition, since carburizing, which is a main cause of quality variations, is performed twice, the quality variations become large.

  Further, in the integral type connecting rod, since the high pressure strength is required on the inner peripheral surface of the large end portion, it is not possible to use the full carburizing method used for the split type connecting rod.

  The present invention has been made in view of the above-mentioned problems, and its main purpose is to reduce the quality variation of an integrated connecting rod in which the toughness and bending strength of the connecting portion are suitably set at a lower cost than before. It is providing the manufacturing method of the connecting rod which can be manufactured.

  The connecting rod manufacturing method according to the present invention includes a small end portion having a through hole, a large end portion having a through hole larger in diameter than the through hole of the small end portion, and the small end portion and the large end portion. A connecting rod having a connecting portion to be connected, wherein the connecting rod having the small end portion, the large end portion, and the connecting portion is made from 0.3% by mass to 0.5% by mass of carbon. A step (a) of forming from steel containing, a step (b) of performing a heat treatment including a carburizing step on the connecting rod, and at least of the small end portion and the connecting portion after the step (b). Including the step (c) of further tempering the connection part selectively, whereby the above object is achieved.

  In a preferred embodiment, the selective tempering in the step (c) is performed by high frequency induction heating.

  In a preferred embodiment, the selective tempering in the step (c) is performed only on the connecting portion.

  In a preferred embodiment, the selective tempering in the step (c) is also performed on the small end portion.

  In a preferred embodiment, the step (b) is performed so that the internal hardness of the connecting rod after the heat treatment exceeds 500 HV.

  In a preferred embodiment, in the step (c), the connecting portion after selective tempering is covered with a surface layer having a hardness exceeding 500 HV and the surface layer, and is 300 HV or more and 500 HV or less. And an inner layer having a hardness of.

  The engine according to the present invention has a connecting rod manufactured by the above-described method for manufacturing a connecting rod.

  A motor vehicle according to the present invention includes an engine having the above-described configuration.

  The connecting rod according to the present invention includes a small end portion having a through hole, a large end portion having a through hole larger in diameter than the through hole of the small end portion, and a connection for connecting the small end portion and the large end portion. The connecting portion has a surface layer having a hardness exceeding 500 HV and an inner layer covered with the surface layer and having a hardness of 300 HV or more and 500 HV or less. When the depth of the boundary between the surface layer and the inner layer from the surface of the connecting portion is d (mm), the hardness (HV) of the connecting portion is the depth d from the surface of the connecting portion. The value obtained by subtracting 500 · d from the value integrated to (mm) is more than 0 HV · mm and not more than 70 HV · mm, thereby achieving the above object.

  In a preferred embodiment, the inner peripheral surface of the through hole at the large end has a hardness of 550 HV or more from the surface to a depth of at least 0.7 mm.

  The engine according to the present invention has a connecting rod having the above-described configuration.

  A motor vehicle according to the present invention includes an engine having the above-described configuration.

  In the manufacturing method of the connecting rod according to the present invention, the connecting rod is subjected to a heat treatment including a carburizing step to increase the hardness of the entire connecting rod, and then selectively tempering a part of the connecting rod including the connecting portion to thereby connect the connecting rod. Selectively reduce the hardness of the part. Therefore, the connecting portion can be made hard with a good balance between toughness and bending strength with a relatively small number of steps. In addition, since it is necessary to perform carburization that is a main cause of quality variations only once, quality variations can be reduced. Furthermore, steel having a carbon content higher than that of steel used as a conventional material, specifically, steel containing 0.3% by mass or more and 0.5% by mass or less of carbon is used as a material. The internal hardness of the connecting rod can be sufficiently increased in advance by a heat treatment (a heat treatment including a carburizing step) performed in advance. Therefore, it becomes easy to set suitably the toughness and bending strength of a connection part by the further tempering.

  Therefore, according to the connecting rod manufacturing method of the present invention, an integrated connecting rod in which the toughness and bending strength of the connecting portion are suitably set can be manufactured at a lower cost and with less variation in quality.

  Hereinafter, the manufacturing method of the connecting rod in this embodiment is demonstrated, referring drawings. FIG. 1 is a flowchart showing a method for manufacturing a connecting rod in the present embodiment.

  First, a steel having a specific composition is prepared. From this steel, an integrated connecting rod 1 having a small end portion 10, a large end portion 20 and a connecting portion 30 as shown in FIGS. Form (steps S1 to S3). The small end portion 10 of the connecting rod 1 has a through hole 12 for passing a piston pin, and the large end portion 20 has a through hole 22 for passing a crank pin. The through hole 22 of the large end 20 has a larger diameter than the through hole 12 of the small end 10. The rod-shaped connecting portion 30 that connects the small end portion 10 and the large end portion 20 typically has an H-shaped or I-shaped cross-sectional shape as shown in FIG. As a result, the strength is improved.

  The above process will be described more specifically. First, steel containing carbon of 0.3 mass% or more and 0.5 mass% or less is prepared as a material for the connecting rod 1 (step S1). In this embodiment, SCM435 which is chromium molybdenum steel is prepared. Table 1 shows the composition of SCM420 that has been used as a material for conventional connecting rods and SCM435 used in this embodiment. The balance is inevitable impurities such as iron and copper, phosphorus and sulfur.

  As shown in Table 1, SCM420 contains about 0.20% by mass of carbon, whereas SCM435 contains about 0.35% by mass of carbon. That is, in the present embodiment, steel having a higher carbon content than the conventional connecting rod material is used.

  Next, the prepared steel is forged into a connecting rod shape (step S2), and then subjected to predetermined machining to form the through-hole 12 in the small end 10 and the through-hole 22 in the large end 20 and the like. By forming (process S3), the connecting rod 1 shown to Fig.2 (a)-(c) is obtained. In this embodiment, the forming is performed by forging, but the present invention is not limited to this, and the forming may be performed by casting or sintering.

  Subsequently, heat treatment including a carburizing step is performed on the entire connecting rod 1 (step S4). Here, carburizing, quenching, and tempering are sequentially performed. Carburizing can be performed by a known method such as gas carburizing, and known methods can be used as appropriate for quenching and tempering. Further, nitriding (so-called carbonitriding) may be performed simultaneously with carburizing.

  Next, further tempering is selectively performed on at least the connecting portion 30 of the small end portion 10 and the connecting portion 30 (step S5). In this embodiment, this tempering is performed by high frequency induction heating. Local tempering can be performed by heating other portions using high frequency while preventing a portion of the connecting rod 1 (including the large end portion 20) from being heated at high frequency.

  This local further tempering may be performed only on the connecting portion 30 as shown in FIG. 3 (a), or on the small end portion 10 as shown in FIG. May be performed on both the connecting part 30 and the small end part 10). Whether or not to further temper the small end portion 10 may be determined according to strength characteristics required for the small end portion 10. When connecting to the piston pin, the inner peripheral surface 12a of the through hole 12 of the small end portion 10 is in contact with the piston pin on the surface without using a bearing, so that the inner peripheral surface of the through hole 12 of the small end portion 10 is In many cases, the pressure resistance of the inner peripheral surface 22a of the large end portion 20 is not required for 12a.

  Thereafter, a predetermined finishing process is performed (step S6) to complete the connecting rod. As the finishing process, for example, grinding or honing of the inner peripheral surface is performed.

  In the manufacturing method in the present embodiment, the connecting rod 1 is subjected to a heat treatment including a carburizing step to increase the hardness of the entire connecting rod 1 and then selectively further tempered on a part of the connecting rod 1 including the connecting portion 30. Thus, the hardness of the connecting portion 30 is selectively reduced. Therefore, it is possible to make the connecting portion 30 hard with a good balance between toughness and bending strength with a smaller number of steps than in the double carburizing method.

  In addition, since it is necessary to perform carburization that is a main cause of quality variations only once, quality variations can be reduced. There are two main causes of variations in heat treatment quality (hardness, strain, etc.). One is a temperature difference and an atmospheric gas concentration difference due to different positions in the carburizing furnace. The other is a difference in temperature history that occurs randomly during cooling. If carburization is performed twice, the position in the furnace cannot be made the same in the first and second times (and in most cases, the furnace itself needs to be different between the first and second times). The variation becomes large. Moreover, since cooling is also performed twice, this also increases the variation. Table 2 shows the relative standard deviation of the surface hardness and effective hardening depth when carburizing is performed only once and when carburizing is performed twice.

  As shown in Table 2, when carburizing is performed twice, the relative standard deviation is about 1.5 times that when carburizing is performed only once for both the surface hardness and the effective hardening depth. On the other hand, in the manufacturing method in this embodiment, since carburization is performed only once, the dispersion | variation in quality can be made small and a yield can be improved.

  Furthermore, in the manufacturing method in the present embodiment, steel having a higher carbon content than steel that has been used as a conventional material, specifically, steel containing 0.3% by mass or more and 0.5% by mass or less of carbon. Use as a material. Therefore, it is easy to suitably set the toughness and bending strength of the connecting portion 30 by further tempering. Hereinafter, this reason will be described by taking SCM420, which is steel containing 0.20% by mass of carbon, and SCM435, which is steel containing 0.35% by mass of carbon, as examples.

  The inventor of the present application has conducted a detailed study on the preferable internal hardness of the connecting portion 30, and the internal hardness of the connecting portion 30 is preferably 500 HV or less from the viewpoint of securing sufficient toughness, and sufficient bending From the viewpoint of securing the strength, it was found that it is preferably 300 HV or more. Therefore, in order to make the toughness and bending strength of the connecting portion 30 suitable, it is preferable that the internal hardness of the connecting portion 30 after further tempering is 300 HV or more and 500 HV or less.

  However, if the SCM 420 is used as the material for the connecting rod 1, even if the connecting rod 1 is manufactured in the same process as the manufacturing process shown in FIG. 1 (the same except that the SCM 420 is prepared in the process S1), It is difficult to set the hardness to 300 HV or more and 500 HV or less.

  In FIG. 4, the hardness distribution of the connection part 30 at the time of using SCM420 is shown before and after tempering by a high frequency. When SCM420 is used, as shown in FIG. 4, the internal hardness after tempering by high frequency is less than 300 HV. Therefore, the bending strength of the connecting part 30 is insufficient.

  On the other hand, when the SCM 435 is used, as shown in FIGS. 5 and 6, the internal hardness of the connecting portion 30 after tempering by high-frequency heating is within the range of 300 HV to 500 HV. Both toughness and bending strength can be made suitable. This is because SCM435 has a higher carbon content than SCM420 and originally has a high carbon content, so that the internal hardness is sufficient in advance by heat treatment (heat treatment including carburization process) performed prior to tempering by high frequency heating. It is because it can be made high.

  The material of the connecting rod 1 is not limited to the illustrated SCM 435. FIG. 7 shows the relationship between the carbon content and the internal hardness before and after tempering by high frequency. As can be seen from FIG. 7, the internal hardness of the connecting portion 30 after further tempering can be set to 300 HV or more and 500 HV or less by using steel containing 0.3% by mass or more and 0.5% by mass or less of carbon. On the other hand, if the carbon content is less than 0.3% by mass, the internal hardness of the connecting portion 30 may be less than 300 HV, and the bending strength may be insufficient. On the other hand, if the carbon content exceeds 0.5 mass%, the internal hardness of the connecting portion 30 may exceed 500 HV and the toughness may be insufficient. As steel containing 0.3 mass% or more and 0.5 mass% or less of carbon, in addition to SCM435, for example, SCM440, which is also chromium molybdenum steel, SCr435, which is chromium steel, and SMn438, which is manganese steel, are used. it can.

  In addition, the inventor of the present application has also performed detailed studies on the preferable surface hardness of the connecting portion 30. As a result, in order to obtain a sufficiently high bending strength, it was found that the surface hardness of the connecting portion 30 is preferably over 500 HV.

  When SCM420 is used as the material, as shown in FIG. 4, the surface hardness of the connecting portion 30 after tempering by high frequency is significantly lower than 500 HV. On the other hand, when SCM435 is used as the material, the surface hardness of the connecting portion 30 after tempering by high frequency exceeds 500 HV, as shown in FIGS. Therefore, a sufficiently high bending strength can be obtained.

  As can be seen from the comparison between FIG. 4 and FIG. 5 and FIG. 6, when SCM420 is used, the hardness near the surface is significantly reduced by further tempering compared to when SCM435 is used. This is because the amount of carbon is originally small in the case of SCM420, and therefore there is a large difference in the amount of carbon between the surface and inside after carburizing, quenching and tempering. This is thought to be due to the remarkable diffusion of In contrast, since SCM435 originally has a large amount of carbon, the difference in carbon content between the surface and the inside after carburizing, quenching, and tempering is small, and the amount of carbon from the surface to the inside during tempering by high frequency is small. Difficult to occur. Therefore, a significant decrease in hardness near the surface can be suppressed. As described above, by using a steel having a higher carbon content than the conventional steel (specifically, containing 0.3 mass% or more of carbon), not only the internal hardness is kept high but also the surface hardness is remarkable. The decrease can be suppressed, and the bending strength can be effectively improved.

  FIG. 8 shows the bending strength (0.2% yield strength) of the connecting portion 30 of the connecting rod 1 manufactured by the manufacturing method of the present embodiment using SCM435 as a material. In the same figure, the bending strength of the connection part of the connecting rod manufactured by the carbon-proof method using SCM420 as a raw material is also shown for comparison. As can be seen from FIG. 8, in the connecting rod manufactured by the carbon-proof method, the bending strength of the connecting portion is 1500 MPa, whereas in the connecting rod 1 manufactured by the manufacturing method of the present embodiment, the bending strength of the connecting portion 30 is 2450 MPa. It is. Thus, the bending strength of the connecting portion 30 can be effectively improved by the manufacturing method of the present embodiment.

  Moreover, in the manufacturing method of this embodiment, since the steel whose carbon content rate is higher than before is used, the time required for carburizing can be shortened. FIG. 9A shows the time required for carburization when SCM420 is used, and FIG. 9B shows the time required for carburization when SCM435 is used. As can be seen from FIGS. 9A and 9B, when SCM435 is used, the time required for carburizing can be reduced to half or less. According to the manufacturing method of this embodiment, compared with the conventional carbon-proof method, the cost reduction of about 23% was realizable by the omission of the carbon-proof process and shortening of the carburizing process.

  As already described, the internal hardness of the connecting portion 30 is preferably 300 HV or more and 500 HV or less, and the surface hardness of the connecting portion 30 is preferably more than 500 HV. In other words, the selective tempering step (step S5 in FIG. 1) for the connecting portion 30 includes a surface layer in which the connecting portion 30 after the selective tempering has a hardness exceeding 500 HV, It is preferable that the treatment is performed so as to have an inner layer that is covered with the surface layer and has a hardness of 300 HV to 500 HV.

  In order to set the internal hardness of the connecting portion 30 after selective tempering to 300 HV or more and 500 HV or less, as shown in FIG. 5, the connecting rod after carburizing, quenching and tempering (after step S4 in FIG. 1). It is preferable that the internal hardness of 1 exceeds 500 HV.

  Further, in order to sufficiently secure the pressure resistance strength of the inner peripheral surface 22a of the through hole 22 of the large end portion 20, the hardness of the inner peripheral surface 22a from the surface to a depth of at least 0.7 mm is 550 HV or more. preferable.

  Furthermore, the inventor of the present application has a strong correlation with the toughness and bending strength of the connecting portion 30, in which the hardness of the surface layer (the portion having a hardness exceeding 500 HV in the connecting portion 30) is integrated in the depth direction. Focusing on the relationship, a suitable range of the integral value was found experimentally.

  First, the inventor of the present application, as shown in FIG. 10, in the graph showing the hardness distribution of the connecting portion 30, the area of the hatched portion, that is, the hardness-depth curve, and the 0 mm depth scale line, It was found that the area of the portion surrounded by the scale line of hardness 500 HV has a strong correlation with the toughness and bending strength of the connecting portion 30. The area is the hardness (HV) of the connecting portion 30 when the depth from the surface of the connecting portion 30 (that is, the thickness of the surface layer) is d (mm) at the boundary between the surface layer and the inner layer. Is a value (HV · mm) obtained by subtracting 500 · d from the value obtained by integrating the surface of the connecting portion 30 to the depth d (mm). For simplicity of description, this value will be referred to as the “hardness / depth integrated value” of the surface layer below.

  Next, when a specific study was made on the relationship between the integrated value of hardness and depth and the toughness and bending strength of the connecting portion 30, the integrated value of hardness and depth of the surface layer was set to 70 HV · mm or less. It was found that sufficient toughness can be obtained. Further, as described above, in order to obtain a sufficient bending strength, the connecting portion 30 preferably has a surface layer having a hardness of 500 HV or more. Therefore, the integrated value of the hardness and depth of the surface layer is used. Is preferably over 0 HV · mm. Therefore, sufficient toughness can be obtained while improving the bending strength by setting the integrated value of hardness and depth of the surface layer to more than 0 HV · mm and not more than 70 HV · mm.

  For reference, FIG. 11 shows the hardness distribution of the connecting part of the connecting rod manufactured by the carbon-proof method using SCM420, and FIG. 12 is the same process as the manufacturing method of this embodiment except that SCM420 is used. The hardness distribution of the connection part of the manufactured connecting rod is shown. In addition, in FIG. 11, the hardness distribution of the part which has not been subjected to the carbon-proof treatment (copper plating) is shown together, and in FIG. 12, the hardness distribution before tempering by high frequency is also shown.

  From FIG. 11, when the carbon-proof method is used, there is no surface layer having a hardness of 500 HV or more, and the hardness / depth integrated value of the surface layer does not exceed 0 HV · mm, so that the bending strength is insufficient. I understand that. Moreover, since the hardness / depth integral value of the surface layer exceeds 70 HV · mm in the portion where the anti-carbon treatment is not performed, it can be seen that the toughness is not sufficient.

  Further, from FIG. 12, when further tempering is performed when SCM420 is used, there is no surface layer having a hardness of 500 HV or more, and the integrated value of hardness / depth of the surface layer does not exceed 0 HV · mm. It can be seen that the strength is insufficient. Moreover, in the state before further tempering, since the hardness / depth integrated value of the surface layer has exceeded 70 HV · mm, it can be seen that the toughness is not sufficient.

  In FIG. 13, the hardness distribution of the connection part of the split type connecting rod manufactured by the total carburizing method using SCM420 is shown. From FIG. 13, it can be seen that when the total carburization method is used, the integrated value of hardness and depth of the surface layer can be over 0 HV · mm and 70 HV · mm or less, and the toughness and bending strength of the connecting portion can be suitably set. However, as already described, the total carburization method cannot secure the pressure resistance of the inner peripheral surface of the large end portion, and therefore the total carburization method cannot be used for the production of an integral connecting rod.

  FIG. 14 shows the relationship between the hardness / depth integrated value of the surface layer and the carbon content. As can be seen from FIG. 14, when steel containing 0.3 mass% or more and 0.5 mass% or less of carbon is used as the material, the hardness / depth integral value of the surface layer after further tempering exceeds 0 HV · mm. It can be in the range of 70 HV · mm or less. Therefore, by using a steel containing carbon of 0.3 mass% or more and 0.5 mass% or less as the material of the connecting rod, the internal hardness of the connecting portion 30 after further tempering is set to 300 HV or more and 500 HV or less, and the surface layer It is possible to make the integrated value of the hardness and depth of the steel exceeds 0 HV · mm and 70 HV · mm or less.

  As described above, according to the manufacturing method of the present invention, an integrated connecting rod in which the toughness and bending strength of the connecting portion are suitably set can be manufactured at a lower cost and with less variation in quality.

  The connecting rod manufactured by the manufacturing method of the present invention is widely used in engines for various automobiles such as passenger cars, motorcycles, buses, trucks, tractors, airplanes, motor boats, and civil engineering vehicles. Moreover, it is used also for the engine for various machines, such as a mower and a generator, and a general purpose engine. According to the manufacturing method of the present invention, since the toughness and bending strength of the connecting portion of the connecting rod can be suitably set, it is possible to reduce the connecting rod by reducing the connecting portion, thereby reducing the weight of the engine and improving fuel efficiency. And high output can be realized.

  FIG. 15 shows an example of the engine 100 including the connecting rod 1 manufactured by the manufacturing method of the present embodiment. The engine 100 includes a crankcase 110, a cylinder block 120, and a cylinder head 130.

  A crankshaft 111 is accommodated in the crankcase 110. The crankshaft 111 has a crankpin 112 and a crank web 113.

  A cylinder block 120 is provided on the crankcase 110. The cylinder block 120 is fitted with a cylindrical cylinder sleeve 121, and the piston 122 is provided so as to reciprocate within the cylinder sleeve 121.

  A cylinder head 130 is provided on the cylinder block 120. The cylinder head 130 forms a combustion chamber 131 together with the piston 122 and the cylinder sleeve 121 of the cylinder block 120. The cylinder head 130 has an intake port 132 and an exhaust port 133. An intake valve 134 for supplying air-fuel mixture into the combustion chamber 131 is provided in the intake port 132, and an exhaust valve 135 for exhausting the combustion chamber 131 is provided in the exhaust port. .

  Piston 122 and crankshaft 111 are connected by connecting rod 1. Specifically, the piston pin 123 of the piston 122 is inserted into the through hole of the small end portion 10 of the connecting rod 1, and the crank pin 112 of the crankshaft 111 is inserted into the through hole of the large end portion 20, As a result, the piston 122 and the crankshaft 111 are connected. A roller bearing (rolling bearing) 114 is provided between the inner peripheral surface of the through hole of the large end portion 20 and the crank pin 112.

  Since the engine 100 shown in FIG. 15 has the connecting rod 1 manufactured by the manufacturing method of the present embodiment, it is possible to achieve a reduction in weight, fuel consumption, and output.

  FIG. 16 shows a motorcycle including the engine 100 shown in FIG.

  In the motorcycle shown in FIG. 16, a head pipe 302 is provided at the front end of the main body frame 301. A front fork 303 is attached to the head pipe 302 so as to be able to swing in the left-right direction of the vehicle. A front wheel 304 is rotatably supported at the lower end of the front fork 303.

  A seat rail 306 is attached so as to extend rearward from the upper rear end of the main body frame 301. A fuel tank 307 is provided on the main body frame 301, and a main seat 308 a and a tandem seat 308 b are provided on the seat rail 306.

  A rear arm 309 extending rearward is attached to the rear end of the main body frame 301. A rear wheel 310 is rotatably supported at the rear end of the rear arm 309.

  The engine 100 shown in FIG. 15 is held at the center of the main body frame 301. The connecting rod 1 manufactured by the manufacturing method of this embodiment is used for the engine 100. A radiator 311 is provided in front of the engine 100. An exhaust pipe 312 is connected to the exhaust port of the engine 100, and a muffler 313 is attached to the rear end of the exhaust pipe 312.

  A transmission 315 is connected to the engine 1. A drive sprocket 317 is attached to the output shaft 316 of the transmission 315. The drive sprocket 317 is connected to the rear wheel sprocket 319 of the rear wheel 310 via a chain 318. Transmission 315 and chain 318 function as a transmission mechanism that transmits the power generated by engine 100 to the drive wheels.

  Since the motorcycle shown in FIG. 16 includes the engine 100 using the connecting rod 1 manufactured by the manufacturing method of the present embodiment, suitable performance can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the connecting rod which can manufacture the integrated connecting rod by which the toughness and bending strength of the connection part were set suitably at low cost compared with the former and small quality variation is provided.

  The connecting rod manufactured by the connecting rod manufacturing method according to the present invention is widely used in engines for various motor vehicles, engines for various machines, and general-purpose engines.

It is a flowchart which shows the manufacturing method of the connecting rod by this invention. (A)-(c) is a figure which shows typically the integral type connecting rod manufactured by the manufacturing method of the connecting rod by this invention, (a) is a front view, (b) is 2B in (a). FIG. 2C is a cross-sectional view taken along line 2C-2C ′ in FIG. (A) And (b) is a figure for demonstrating the part which performs further tempering. It is a graph which shows the hardness distribution of the connection part at the time of using SCM420 as a raw material before and after tempering by a high frequency. It is a graph which shows the hardness distribution of the connection part at the time of using SCM435 as a raw material before and after tempering by a high frequency. It is a graph which shows the hardness distribution of the connection part at the time of using SCM420 as a raw material and using SCM435 before and after tempering by a high frequency. It is a graph which shows the relationship between the content rate of carbon, and the internal hardness before and behind tempering by a high frequency. It is a graph which shows the bending strength (0.2% yield strength) of the connection part of the connecting rod manufactured by the manufacturing method of this invention using SCM435 as a raw material. (A) is a figure which shows the relationship between the temperature and time in the carburizing process at the time of using SCM420 as a raw material, (b) is the relationship between the temperature and time in the carburizing process at the time of using SCM435 as a raw material. FIG. It is a graph which shows the hardness distribution of the connection part of the connecting rod manufactured by the manufacturing method of this invention using SCM435 as a raw material. It is a graph which shows the hardness distribution of the connection part of the connecting rod manufactured by the carbon-proof method using SCM420 as a raw material. It is a graph which shows the hardness distribution of the connection part of the connecting rod manufactured using SCM420 as a raw material. It is a graph which shows the hardness distribution of the connection part of the connecting rod manufactured by the total carburizing method using SCM420 as a raw material. It is a graph which shows the relationship between the hardness and depth integral value of a surface layer, and carbon content. It is sectional drawing which shows typically the engine which has a connecting rod manufactured by the manufacturing method of this invention. Fig. 16 is a side view schematically showing a motorcycle including the engine shown in Fig. 15. (A) And (b) is a figure which shows a common integrated connecting rod typically, (a) is a front view, (b) is sectional drawing along the 17B-17B 'line in (a). It is. It is a flowchart which shows the manufacturing method of the connecting rod using a carbon-proof method. It is a graph which shows the hardness distribution of the connecting rod manufactured using the carbon-proof method. It is a flowchart which shows the manufacturing method of the connecting rod using a 2 times carburizing method. It is a flowchart which shows the manufacturing method of the connecting rod using a total carburizing method. It is a graph which shows the hardness distribution of the connection part of the connecting rod manufactured using the total carburizing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Connecting rod 10 Small end part 12 Through-hole 12a Inner peripheral surface 20 Large end part 22 Through-hole 22a Inner peripheral surface 30 Connection part

Claims (10)

Integrated type having a small end portion having a through hole, a large end portion having a through hole larger in diameter than the through hole of the small end portion, and a connecting portion for connecting the small end portion and the large end portion. A connecting rod manufacturing method of
Forming the connecting rod having the small end portion, the large end portion and the connecting portion from steel containing 0.3% by mass or more and 0.5% by mass or less carbon (a);
(B) performing a heat treatment including a carburizing step on the connecting rod;
After the step (b), including a step (c) of selectively further tempering at least the entire connecting portion of the small end portion and the connecting portion;
The heat treatment performed in the step (b) includes a tempering step for the entire connecting rod,
A method for manufacturing a connecting rod, wherein the large end portion is not tempered in the step (c).   The method for manufacturing a connecting rod according to claim 1, wherein the selective tempering in the step (c) is performed by high frequency induction heating.   The method for manufacturing a connecting rod according to claim 1 or 2, wherein the selective tempering in the step (c) is performed only on the connecting portion.   The method for manufacturing a connecting rod according to claim 1 or 2, wherein the selective tempering in the step (c) is also performed on the small end portion.   The said process (b) is a manufacturing method of the connecting rod in any one of Claim 1 to 4 performed so that the internal hardness of the said connecting rod after performing the said heat processing may exceed 500HV.   In the step (c), the connecting portion after selective tempering is a surface layer having a hardness exceeding 500 HV, and an inner layer having a hardness of 300 HV or more and 500 HV or less, which is covered with the surface layer. The manufacturing method of the connecting rod in any one of Claim 1 to 5 performed so that it may have. A small end portion formed of steel containing carbon of 0.3 mass% or more and 0.5 mass% or less and having a through hole; and a large end portion having a through hole larger in diameter than the through hole of the small end portion; , wherein the small end have a connecting portion for connecting the large end portion, an integral-type connecting rod which heat treatment is performed including carburization step and tempering process for the entire connecting rod,
The connecting portion includes a surface layer having a hardness of greater than 500 HV, covered by the surface layer, selective further tempered to have a an internal layer within the entire connecting portion having the following hardness above 300 HV 500 HV A connecting part made for
When the depth of the boundary between the surface layer and the inner layer from the surface of the connecting portion is d (mm), the hardness (HV) of the connecting portion is set to the depth d ( A connecting rod in which the value obtained by subtracting 500 · d from the value integrated up to mm) is more than 0 HV · mm and not more than 70 HV · mm. 8. The connecting rod according to claim 7 , wherein a hardness of the inner peripheral surface of the through hole at the large end portion is at least 550 HV from the surface to a depth of at least 0.7 mm. An engine having the connecting rod according to claim 7 or 8 . A motor vehicle comprising the engine according to claim 9 .

Images