JPWO2013047761A1 - Method for manufacturing camshaft for internal combustion engine - Google Patents

Abstract

  An object of the present invention is to provide a method of manufacturing a camshaft that can stably improve the wear characteristics such as pitting resistance and scuffing resistance. To achieve this object, a heat treatment step of heating a cam shaft formed by assembling a sintered cam piece to a shaft body of a steel pipe to a sintering temperature by a heat treatment device, and a heat-treated cam shaft In the method for manufacturing a camshaft for an internal combustion engine provided with a cooling process step for cooling the engine by a cooling processing device, the camshaft is surrounded by a graphite plate provided around the inside of the cooling processing device. The cooling is performed in two stages: a first stage cooling process that performs gradual cooling, and a second stage cooling process that performs rapid cooling by circulating the cooling gas injected into the cooling apparatus using a fan. I decided to.

Description

  The present invention relates to a method for manufacturing a camshaft for an internal combustion engine, and more specifically, to a method for manufacturing a camshaft formed by diffusion bonding a cam lobe made of sintered alloy powder and a steel shaft.

  Conventionally, as a camshaft for an internal combustion engine, a cast iron camshaft integrally formed by casting, a sintered camshaft in which a cam lobe of a sintered material is joined to a steel shaft, or the like is used. Here, although the cast iron camshaft is relatively inexpensive, there are problems in manufacturing such as difficulty in weight reduction and difficulty in forming the cam portion with high accuracy. Furthermore, the cast iron camshaft can only use a castable material, and it is difficult to make the cam portion excellent in wear resistance. Therefore, in the case of a cast iron camshaft, wear characteristics such as pitting resistance and scuffing resistance are inferior, and it has been difficult to cope with high performance and light weight of an internal combustion engine. On the other hand, the sintered camshaft can select an alloy component according to the performance required for the cam, and can hollow the shaft. For this reason, sintered camshafts with sintered cam lobes joined to steel shafts have high wear resistance, and are lighter camshafts that can withstand high surface pressures and high loads. It can be suitably used for the required internal combustion engine.

For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2001-271909) discloses a shaft and assembly suitably used for an assembling camshaft formed by diffusion bonding a cam lobe made of sintered alloy powder and a shaft made of steel. A method of manufacturing a camshaft is disclosed. Specifically, the camshaft of Patent Document 1 is formed by compacting a shaft obtained by subjecting a high carbon chromium bearing steel material to spheroidizing and annealing, and then drawing to a predetermined size, and sintered alloy powder. A cam lobe formed on a compacted body of a predetermined size is manufactured, the cam lobe is assembled to the shaft, and they are manufactured by diffusion bonding. In Patent Document 1, in the manufacture of assembled camshaft, by going through the steps of cooling after passing through the sintering furnace, in particular 10 to 20 ° C. / min cooling rate in the vicinity of A ₁ transformation point, It is disclosed that it is a base structure mainly composed of pearlite containing fine precipitated carbides (see paragraph 0024).

JP 2001-271909 A

  However, Patent Document 1 does not disclose any method for cooling the entire circumference of the camshaft uniformly at the same speed in the camshaft cooling step. If the entire circumference of the camshaft is not uniformly cooled at the same speed, the mechanical characteristics of the portions of the camshaft vary and the quality is degraded. Incidentally, a sintering furnace used for manufacturing a camshaft generally includes a sintering device for sintering the camshaft and a cooling device for cooling the sintered camshaft. In these sintering devices and cooling devices, for processing efficiency, for example, the camshaft is horizontally transported in a state where it is mounted on a jig in a state where a plurality of mounting plates are stacked horizontally and stacked in a plurality of stages. Are processed. When the sintering camshaft is cooled from a temperature higher than the sintering temperature, forced cooling is often performed by circulating a cooling gas in the cooling processing chamber of the cooling device, but the circulation speed of the cooling gas is reduced. However, there is an individual difference in the cooling rate between the camshaft mounting position on the inner side and the outer side.

  From the above, the present invention does not cause individual differences in the cooling speed of the camshaft depending on the mounting position in the cooling device, and cools the entire circumference of the camshaft almost uniformly, thereby preventing pitting resistance and scuffing resistance. It is an object of the present invention to provide a method for manufacturing a camshaft for an internal combustion engine that can stably obtain the effect of improving wear characteristics such as the above.

  Therefore, as a result of intensive studies, the present inventors have solved the above-mentioned problems by satisfying predetermined conditions for the cooling treatment after sintering of the camshaft. Hereinafter, the present invention will be described.

  A method of manufacturing a camshaft for an internal combustion engine according to the present invention includes a heat treatment step of heating a camshaft formed by assembling a sintered cam piece to a shaft body of a steel pipe to a sintering temperature by a heat treatment device; A method of manufacturing a camshaft for an internal combustion engine comprising a cooling processing step of cooling the heat-treated camshaft by a cooling processing device. In the cooling processing step, a graphite plate provided around the cooling processing device is used. A first stage cooling process for performing slow cooling after placing the camshaft in an enclosed state; and a second stage cooling process for performing rapid cooling by circulating the cooling gas injected into the cooling processing apparatus as much as possible. It is characterized by cooling in the two-stage process.

  In the method for manufacturing a camshaft for an internal combustion engine according to the present invention, the heat treatment step is preferably performed at a temperature controlled at a sintering temperature of 900 ° C. to 1200 ° C. when performing the sintering.

  In the method for manufacturing a camshaft for an internal combustion engine according to the present invention, the first stage cooling treatment step may be performed at a cooling rate between 700 ° C. and 900 ° C. at a cooling rate of 10 ° C./min to 30 ° C./min. preferable.

  In the method for manufacturing a camshaft for an internal combustion engine according to the present invention, the second stage cooling process step is performed at a cooling rate of 30 ° C./min to 300 ° C./300° C. from the temperature after completion of the first stage cooling process step. It is preferable to cool at a speed of minutes.

  In the internal combustion engine camshaft manufacturing method according to the present invention, in the cooling processing step, the internal combustion engine camshaft is subjected to a cooling process in a state of being loaded in a plurality of mounting jigs stacked in a plurality of stages. Is preferred.

  According to the method for manufacturing a camshaft for an internal combustion engine according to the present invention, the cooling treatment is performed in a state where the periphery of the sintered camshaft disposed in the cooling device is surrounded by the graphite plate. It is possible to provide a camshaft for an internal combustion engine in which the effect of improving wear characteristics such as scuffing is stably achieved.

It is the front view illustrated in order to demonstrate the continuous sintering furnace used with the manufacturing method of the cam shaft for internal combustion engines which concerns on this invention. It is A-A 'sectional drawing of FIG. It is explanatory drawing from the front cross section for demonstrating the cooling device of FIG.

  A preferred embodiment of a method for manufacturing a camshaft for an internal combustion engine according to the present invention will be described in detail below with reference to the drawings.

  Manufacturing method of camshaft for internal combustion engine according to the present invention: a heat treatment step of heating a camshaft formed by assembling a cam piece of a sintered material to a shaft body of a steel pipe to a sintering temperature by a heat treatment device; A method of manufacturing a camshaft for an internal combustion engine, comprising: a cooling processing step of cooling the heat-treated camshaft by a cooling processing device, wherein the cooling processing step is surrounded by a graphite plate provided around the cooling processing device. After the camshaft is disposed in the state, a first stage cooling process for performing slow cooling, and a second stage cooling process for performing rapid cooling by circulating the cooling gas injected into the cooling processing apparatus with a fan. It is characterized by cooling in a two-stage process.

  FIG. 1 is a front view for explaining a continuous sintering furnace used in the method for manufacturing a camshaft for an internal combustion engine according to the present invention. FIG. 2 is a cross-sectional view taken along the line A-A ′ of FIG. 1. FIG. 3 is a front sectional view for explaining the cooling device of FIG. As illustrated in FIG. 1, a continuous sintering furnace 1 used in a method for manufacturing a camshaft for an internal combustion engine according to the present invention includes a vacuum standby chamber 2, a preheating device 3 for dewaxing, and a sintering device for sintering. 4 and the cooling device 5. In the continuous sintering furnace 1 shown in FIG. 1, an inlet door 11 for carrying in the camshaft before processing and an outlet door 12 for carrying out the camshaft after processing are driven up and down by opening and closing devices 13 and 14, respectively. It has become. In addition, also about 15-20 in a figure, it shows an opening / closing apparatus, respectively, and performs the raising / lowering drive of each door (not shown) which divides each chamber. A conveying roller 21 for conveying the camshaft W is provided over the entire length of the continuous sintering furnace 1.

  Here, the conveyance roller 21 has a cylindrical shape, and is disposed in the furnace body through the entrance door 11 and the exit door 12 so that the axis of the conveyance roller 21 is horizontal and parallel to the front-rear direction. A plurality of such conveying rollers 21 are arranged at the same height and at an interval narrower than the length in the conveying direction of the jig J on which the camshaft W is loaded. Further, each of the transport rollers 21 is supported so as to be rotatable about the axis of the roller. For example, all the rollers can be rotated in the same direction and at the same rotational speed by a chain (not shown) using a motor (not shown) as a power source. The continuous sintering furnace 1 used in the present invention mounts the camshaft W on the conveying roller 21 and heats or cools the camshaft W while gradually moving the camshaft W forward by the rotation of the conveying roller 21. This is a method that applies

  Based on the above, the heat treatment process and the cooling process in the present invention will be specifically described below. First, the heat treatment process in the method for manufacturing a camshaft for an internal combustion engine according to the embodiment of the present invention will be described. In the heat treatment process of the present invention, first, the camshaft W is carried into the continuous sintering furnace 1 through the carry-in entrance with the entrance door 11 of the continuous sintering furnace 1. The carried camshaft W is carried into the preheating heating chamber 3 by the rotation of the conveying roller 21 as conveying means, and is heated to, for example, 500 to 700 ° C. to evaporate and remove the previously added wax. Then, the camshaft W that has been processed in the preheating device 3 is carried into the sintering device 4 and heated to a sintering temperature of 900 to 1200 ° C. and sintered. The camshaft W after the sintering process is finished is cooled in the cooling device 5 and carried out from the outlet door 12 of the continuous sintering furnace 1.

  In addition, the preheating device 3 and the sintering device 4 provided in the continuous sintering furnace 1 used in the heat treatment process of the present invention are provided with heat sources (not shown) on the upper, lower, left and right surfaces of the camshaft W. The continuous sintering furnace 1 used in the heat treatment process of the present invention employs a roller hearth type, whereby the heat of the heat source disposed on the bottom surface between adjacent rollers can be directly transmitted to the camshaft W. As a result, according to the continuous sintering furnace 1 used in the heat treatment process of the present invention, all the camshafts W loaded on the jig J can be uniformly heat-treated, and the sintering temperature is increased. On the other hand, temperature control can be performed within a range of ± 10 ° C. Therefore, the continuous sintering furnace 1 used in the heat treatment process of the present invention performs the same processing as a batch-type sintering furnace that employs a method in which, for example, a carriage carrying a plurality of camshafts is moved to sequentially perform heat treatment. Although it is possible, the sintering time can be shortened.

  Next, the cooling process step in the method for manufacturing a camshaft for an internal combustion engine according to the embodiment of the present invention will be described. As shown in FIGS. 2 and 3, the cooling device 5 used in the cooling treatment process of the present invention is continuously arranged on the camshaft W carry-out side of the heat treatment device in the continuous sintering furnace 1. The loading door 59 for loading W and the exit door 12 for unloading the camshaft W are opened and closed, and the cooling device 5 can be sealed by closing these doors. The cooling device 5 according to the present invention can uniformly cool all of the plurality of camshafts W loaded on the jig J by performing cooling in a state where the inside is pressurized. The cooling device 5 used in the present invention has a structure in which a graphite plate 51 is provided so as to surround all the camshafts W loaded on the jig J, and heat insulation by the graphite plate 51 during the cooling process, and Each camshaft can be cooled at a uniform speed without any individual difference without being affected by the mounting position of the camshaft W on the jig J by the heat radiation action.

  As described above, the cooling device 5 used in the cooling processing step of the present invention is a system in which the cooling processing is performed in a state in which the graphite plate 51 is provided so as to surround all the camshafts W loaded on the jig J. Adopted. Here, the graphite refers to a lump of carbon that can be formed by high-temperature heat treatment called graphitization. The graphite material is porous, and the air existing inside absorbs heat and functions as a heat insulating material. Also, the graphite itself has a good thermal conductivity (high thermal conductivity), so it can be used for heat dissipation and cooling. It can also be suitably used for a floor board or the like. That is, the graphite plate 51 that surrounds the camshaft W in the cooling device 5 used in the cooling process of the present invention also acts as a heat storage body, can prevent partial overcooling of the camshaft W, and By suppressing the heat radiation from the camshaft W by increasing the temperature, the temperature difference due to the arrangement position of the camshaft W can be reduced. As a result, according to the cooling device 5 used in the cooling processing step of the present invention, cooling can be performed at a uniform speed with respect to all the camshafts W in the cooling chamber 52, and mechanical portions are partially formed on the camshafts W. There is no variation in the characteristics and no deterioration in product quality. Incidentally, since the graphite plate is porous and air permeable, it is considered that these effects can be obtained. In view of this point, a porous ceramic plate having excellent thermal conductivity can be used instead. I can do it.

  Further, as shown in FIG. 2, a fan 53 is provided inside the cooling device 5 used in the cooling processing step of the present invention and is rotated by a motor stored in the fan driving device M, so that it is not shown. The cooling gas introduced from the cooling gas inlet can be circulated in the cooling processing chamber 52. Further, in the cooling device 5 used in the cooling processing step of the present invention, a heat exchanger 55 that distributes the heat of the refrigerant introduced from the refrigerant introduction pipe 56 and exchanges the heat and leads the refrigerant through the refrigerant outlet pipe 57 is installed in the cooling processing chamber 52. You can also When the cooling device 5 used in the cooling processing step of the present invention has such a structure, it is cooled each time the cooling gas or air circulating in the cooling processing chamber 52 comes into contact with the heat exchanger 55 and performs a rapid cooling process. I can do it. Further, a rectifying plate 58 is provided in the cooling processing chamber 52 for efficiently convectively circulating the introduced cooling gas. The fan 53 can change the circulation speed when the cooling gas is circulated. For example, the fan 53 can be controlled between a state where the fan speed is 0 Hz, which is a state where the cooling gas is not circulated, and a state where the fan speed is 20 Hz to 60 Hz. In FIG. 2, the fan 53 is configured and arranged to send the cooling gas from the side, but is not limited to this position. Moreover, what pressurized nitrogen, argon, helium etc. can be used for the cooling gas used at the cooling treatment process of this invention, for example.

The cooling device 5 used in the cooling treatment process of the present invention can impart desired mechanical characteristics to the camshaft by adopting the above-described method. In addition, the method for manufacturing a camshaft for an internal combustion engine according to the present invention employs a two-stage cooling method in the cooling process, and has a pearlite-based base structure excellent in wear characteristics such as pitting resistance and scuffing resistance. upon that, so that changing the cooling speed of the camshaft before and after the temperature in the vicinity of a ₁ transformation point. For example, in the cooling process of the present invention, by a just before passing through the temperature near the A ₁ transformation point the fan speed gradually cooled by setting so that 20Hz～30Hz, uneven temperature distribution possible to shorten cycle time by suppressing the deformation of the camshaft, a after passing through the temperature around the a ₁ transformation point rotational speed of the fan and quenched set to be 30Hz~60Hz due to occur I can do it.

  In the method for manufacturing a camshaft for an internal combustion engine of the present invention, the heat treatment step is preferably performed at a temperature controlled at a sintering temperature of 900 ° C. to 1200 ° C. during the sintering.

  In the heat treatment process of the present invention, the sintering temperature applied to the sintered camshaft is usually in the temperature range between 900 ° C. and 1200 ° C., although it varies slightly depending on the component composition of the sintered alloy powder used. Therefore, the sintering apparatus 4 used in the heat treatment process of the present invention is in a vacuum state and energized each heat source provided in the apparatus, and the temperature in the furnace is set to a predetermined temperature between 900 ° C. and 1200 ° C. By holding, the camshaft W is sintered. Incidentally, when the sintering temperature is 900 ° C. or lower, it takes time for the diffusion bonding of the metal particles or the diffusion bonding becomes insufficient, so that the quality of the camshaft W cannot be stabilized. And in the manufacturing method of the camshaft for internal combustion engines which concerns on this invention, as mentioned above, the heat source used as a heat source on the four surfaces of the camshaft W in a heat processing process is employ | adopted by employ | adopting a roller hearth type continuous furnace. Therefore, the temperature can be controlled within a range of ± 10 ° C. with respect to the sintering temperature regardless of the mounting position of the camshaft W. Therefore, according to the method for manufacturing a camshaft for an internal combustion engine according to the present invention, diffusion bonding between the shaft constituting the camshaft and the cam lobe can be appropriately performed in the sintering process.

  In the method for manufacturing a camshaft for an internal combustion engine according to the present invention, the first stage cooling treatment step is to cool between 700 ° C. and 900 ° C. at a cooling rate of 10 ° C./min to 30 ° C./min. Is preferred. When the cooling rate is less than 10 ° C./min, the cooling becomes too slow, the crystal structure becomes pearlite, and the strength is lowered, which is not preferable. On the other hand, when the cooling rate exceeds 30 ° C./min, the amount of retained austenite in the crystal structure becomes excessive and the toughness tends to decrease, which is not preferable.

The method for manufacturing a camshaft for an internal combustion engine according to the present invention is such that, in the first stage cooling process step, cooling between 700 ° C. and 900 ° C. is performed at a cooling rate of 10 ° C./min to 30 ° C./min. Generation of deformation due to cooling of the camshaft can be suppressed. Therefore, according to the method for manufacturing a camshaft for an internal combustion engine according to the present invention, it is not necessary to perform machining or the like so that the camshaft W has a predetermined size after being cooled, and the manufacturing cost can be reduced. It will be. Incidentally, 700 ° C. to 900 ° C. includes temperature near the A ₁ transformation point as described above, the steel or iron-based sintered material of the austenitic state slow cooling (cooling rate: about 20 ° C. / min) and pearlite structure when the This is a changing temperature range. In addition, the cooling device 5 used in the cooling process of the present invention performs the cooling process with the graphite plate 51 provided so as to surround all the camshafts W loaded on the jig J as described above. Unlike the case where the atmosphere in the cooling device is allowed to cool in a state where natural convection hardly acts as in the conventional cooling process, the camshaft can be uniformly cooled in a short time. Therefore, according to the method for manufacturing a camshaft for an internal combustion engine according to the present invention, a camshaft excellent in wear characteristics such as pitting resistance and scuffing resistance can be obtained in a short time.

  Moreover, in the method for manufacturing a camshaft for an internal combustion engine according to the present invention, the second stage cooling process includes the following temperature range from the temperature after completion of the first stage cooling process to a cooling rate of 30 ° C./min to 300 ° C. / It is preferable to cool at a speed of minutes.

  The method for manufacturing a camshaft for an internal combustion engine according to the present invention has a cooling rate of 30 ° C./min to 300 ° C./min in a temperature range from 600 ° C. to the following temperature range where the risk of occurrence of cooling distortion is low in the second stage cooling treatment step. Cooling at a high speed can significantly reduce the cooling processing time. As described above, the cooling device 5 used in the cooling processing step of the present invention includes the heat exchanger 57 in the cooling processing chamber 52 and increases the rotation speed of the fan 52 to improve the cooling efficiency. It is possible to further improve the cooling efficiency by maximizing the circulation speed of the cooling gas in the chamber 52. Even in this case, the cooling device 5 used in the cooling processing step of the present invention employs a method of performing the cooling processing in a state where the graphite plate 51 is provided so as to surround all the camshafts W loaded on the jig J. By doing so, it becomes possible to cool all the camshafts at a uniform speed. In the case of an internal combustion engine camshaft, the following temperature range from 600 ° C. is cooled at a cooling rate of 30 ° C./min to 300 ° C./min until the temperature of the internal combustion engine camshaft reaches 200 ° C., After that, even if it is allowed to cool, there is no effect on the product quality, but rather the manufacturing cost is reduced.

  In the internal combustion engine camshaft manufacturing method according to the present invention, in the cooling processing step, the internal combustion engine camshaft is cooled in a state of being loaded in a plurality of mounting jigs stacked in multiple stages. Is preferred.

  In the heat treatment process and the cooling process of the present invention, as shown in FIG. 3, for example, a plurality of camshafts W are horizontally placed so that the heat treatment and cooling of the sintered camshaft can be improved. It is preferable to process at a time in a state where a plurality of mounting plates are stacked. However, when a plurality of camshafts W are processed at the same time, a temperature difference is likely to occur depending on the position where they are placed. In particular, in order to obtain a desired mechanical property, the entire circumference of the camshaft W is as uniform as possible in the cooling process. Cooling is required. However, as described above, according to the cooling device 5 used in the cooling process of the present invention, since the graphite plate can be arranged on the bottom side even during the cooling process by adopting the roller hearth type, all the camshafts W It becomes possible to control the cooling rate of each of them without individual differences.

  From the above, according to the method for manufacturing a camshaft for an internal combustion engine according to the present invention, a large number of camshafts W having excellent wear characteristics such as pitting resistance and scuffing resistance can be manufactured in a single process. The manufacturing cost can be reduced.

  As mentioned above, according to the manufacturing method of the camshaft for internal combustion engines which concerns on this invention, the camshaft provided with especially high mechanical strength can be provided stably. As a result, the camshaft produced by the manufacturing method of the present invention can reduce the diameter of the shaft or reduce the thickness of the hollow type shaft while maintaining excellent durability. , Can achieve its weight reduction. Further, according to the method for manufacturing a camshaft according to the present invention, the cooling process, which takes a relatively long time compared to the heat treatment, can be shortened, so that each process can proceed efficiently. In other words, the continuous sintering furnace 1 uses the method for manufacturing a camshaft for an internal combustion engine according to the present invention to move the camshaft W by the transport roller 21 so as to sequentially move the processing devices 2 to 5. The camshaft W can be moved efficiently in the direction of the arrow shown in FIG. As a result, according to the method for manufacturing a camshaft for an internal combustion engine according to the present invention, the manufacturing cost can be reduced, so that high quality and high mechanical strength are required. It can be suitably employed for the sliding element.

DESCRIPTION OF SYMBOLS 1 Continuous sintering furnace 2 Standby chamber 3 Preheating apparatus 4 Sintering apparatus 5 Cooling apparatus 21 Conveying roller 11 Inlet door 12 Outlet door 51 Graphite plate 52 Cooling processing chamber 53 Fan 54 Wind collection induction duct 55 Heat exchanger 56 Refrigerant introduction Pipe 57 Refrigerant outlet pipe 58 Rectifier plate 59 Carry-in door J Jig M Fan drive motor device W Camshaft

Claims (5)

A heat treatment step of heating a camshaft formed by assembling a cam piece of a sintered material to a shaft body of a steel pipe to a sintering temperature by a heat treatment device;
A method of manufacturing a camshaft for an internal combustion engine, comprising: a cooling treatment step of cooling the heat-treated camshaft by a cooling treatment device;
In the cooling processing step, a first stage cooling processing step of performing slow cooling after arranging the camshaft in a state surrounded by a graphite plate provided around the inside of the cooling processing device,
A method of manufacturing a camshaft for an internal combustion engine, wherein the cooling gas injected into the cooling processing apparatus is cooled in a two-stage process including a second-stage cooling process process in which the cooling gas is circulated by a fan and rapidly cooled. .   2. The method for manufacturing a camshaft for an internal combustion engine according to claim 1, wherein in the heat treatment step, the sintering is performed at a temperature controlled at a sintering temperature of 900 ° C. to 1200 ° C. when sintering is performed.   3. The camshaft for an internal combustion engine according to claim 1, wherein the first stage cooling treatment step cools between 700 ° C. and 900 ° C. at a cooling rate of 10 ° C./min to 30 ° C./min. Production method.   The said 2nd step cooling process process cools the following temperature ranges from the temperature after completion | finish of the said 1st step cooling process step at the cooling rate of 30 to 300 degree-C / min. A method for manufacturing a camshaft for an internal combustion engine according to any one of the above.   5. The internal combustion engine according to claim 1, wherein in the cooling process step, the internal combustion engine is subjected to a cooling process in a state where a plurality of the camshafts for the internal combustion engine are stacked on a plurality of mounting jigs. Method for manufacturing a camshaft.

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