JP2011043208A - Crank shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the durability of a crank shaft by easing a stress concentration at round parts portions formed on the crank shaft. <P>SOLUTION: Butting stepped parts 41, 42, at which the end side surface of a connecting rod butts, are provided on the crank shaft 14. Butting round parts 43, 44 are provided between the butting stepped parts 41, 42 and the end of a pin 33. Inclined surfaces 45a, 46a are formed on the inside facing surfaces 45, 46 of respective crank arms 34, 35 and balance weights 36, 37, and inside round parts 47, 48, each having a radius of curvature larger than the butting round parts 43, 44, are provided between the inclined surfaces 45a, 46a and the butting round parts 43, 44. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a crankshaft of an internal combustion engine, and more particularly to an integrated crankshaft in which a crank arm and a crankpin are integrated.

  The internal combustion engine has a piston that is mounted on a cylinder block so as to be capable of linear reciprocation, and a crankshaft that is coupled to the piston via a connecting rod, and the crankshaft is rotationally driven by linear reciprocation of the piston. . The crankshaft has a journal rotatably supported by the crankcase, a pin to which the end of the piston rod is assembled, and an arm that extends radially from the journal toward the pin and is provided with a pin at the tip. The arm is provided with a balance weight projecting radially outward at the base end portion.

  As described in Patent Document 1, the crankshaft includes an integral crankshaft in which a pin and an arm are integrated, and as described in Patent Document 2, the pin is press-fitted or shrink-fitted into the tip of the arm. There is an assembly type crankshaft adapted to be assembled.

Japanese Utility Model Publication No. 47-21012 Japanese Patent Laid-Open No. 61-218823

  An integrated crankshaft is mainly used for a 4-cycle engine, and an assembly-type crankshaft is often used for a 2-cycle engine because a journal is mounted on a journal. When a single-cylinder engine is used as a drive source, such as an engine generator, either an integral type or an assembled type can be used, and the crankshaft of the single-cylinder engine is a connecting rod Two crank arms are provided in pairs between the pin to which the end of the arm is attached and the two journals supported by the crankcase, and a balance weight is provided at the base end of the crank arm. It has been.

  The integrated crankshaft is made by induction hardening in order to increase its wear resistance on the outer peripheral surface of the pin to which the connecting rod is mounted after forging a steel bar into a predetermined shape. Surface treatment is applied, and a hardened and hardened layer is formed on the outer peripheral surface of the pin by induction hardening. At the boundary between the pin and the crank arm, there is an abutment step where the end surface of the connecting rod attached to the pin is abutted. When the outer peripheral surface of the pin is induction hardened, the arc surface of the abutment step A hardened and hardened layer is also formed in the abutting R portion of the shape. The inner opposing surfaces of the two crank arms that form a pair in the conventional crankshaft are parallel to each other, and an arcuate inner R portion is formed between the inner opposing surface of the crank arm and the outer peripheral edge of the stepped portion. Is formed.

  A combustion pressure load is applied to the pin of the crankshaft through the piston and the connecting rod, and torsional vibration and bending vibration are applied to the crankshaft by the reciprocation of the piston. Even if these loads and vibrations are applied to the crankshaft, a hardened hardened layer is formed in the abutting R portion by induction hardening, so that the abutting R portion abuts against the stress caused by vibration. The strength of the part is ensured.

  On the other hand, even if the outer peripheral surface of the pin is subjected to induction hardening treatment, a hardened hardened layer is not formed on the inner R portion of the crank arm, but the pin portion is more hardened than a hardened layer formed by hardening to the pin portion. Thus, a softened layer having a low strength is exposed. This is a characteristic of the quenching boundary of induction hardening, and the softening layer is applied to the inner R part because the heat transfer diffuses due to the sudden expansion of the cross section of the crank arm part and the quenching temperature is rapidly lowered. Because there is. As described above, when the softened layer exists in the inner R portion, excessive stress concentration overlaps the inner R portion and cracks are generated due to the application of combustion pressure and torsional vibration or bending vibration to the crankshaft when the engine is driven. There is a risk that the durability of the crankshaft will be reduced. Therefore, a sufficient thickness of the crank arm is ensured so that the inner R portion has a strength that does not cause cracks due to stress concentration. In order to reduce the length of the crankshaft to reduce the size of the engine, it is necessary to reduce the thickness of the crank arm and the balance weight. The thickness dimension could not be reduced.

  In order to suppress engine vibration, the balance weight needs to secure a predetermined mass to ensure rotational balance.If the balance weight is made too thin, the rotational balance will decrease, resulting in increased vibration and reduced engine strength. Connected. Even if the crank arm is thin, if the radius of curvature of the inner R portion is increased, the stress concentration in the portion can be reduced. However, since the thickness of the base end portion of the crank arm is reduced, a predetermined balance weight is provided. In order to ensure the mass, it is necessary to increase only the thickness of the balance weight and provide a step between the crank arm base end portion. In this case, the stepped portion becomes a stress concentration portion, which lowers the durability of the crankshaft and may cause deterioration of castability due to the stepped portion.

  An object of the present invention is to alleviate the stress concentration in the inner R portion formed on the crankshaft, to improve the durability of the crankshaft and to secure an optimal rotation balance.

  The crankshaft according to the present invention is a crank arm in which two journals rotatably supported by a crankcase and a pin in which a base end portion is integrated with the journal and an end of a connecting rod is attached to a tip portion are integrated. And an integral crankshaft having a balance weight integrated with a base end portion of the crank arm, and an abutting step portion at the distal end portion of the crank arm against which an end side surface of the connecting rod is abutted The abutting R portion provided between the end portions of the pins, the crank arm and the balance weight are provided on the inner facing surfaces of the balance weight, and are opposed to the tip end portion of the balance weight from the base end portion of the crank arm. An inclined surface which is inclined in a direction approaching the other crank arm and the balance weight, and the inclined surface Wherein provided between the abutting R unit, characterized in that the abutment R of curvature than radii has a large inner R unit.

  The crankshaft of the present invention is characterized in that a softened layer inside an induction-hardened hardened layer formed on the outer peripheral surface of the pin is positioned in the inner R portion. The crankshaft of the present invention is characterized in that the radius of curvature of the inner R portion is at least three times the radius of curvature of the abutting R portion.

  According to the present invention, the crankshaft has two crank arms that are opposed to each other and a balance weight integrated with the crank arm, and the crank arm and the balance weight are opposed to each other. Since the surface is provided with an inclined surface, the radius of curvature of the inner R portion can be set larger than that of the abutting R portion without providing a step portion on the inner facing surface. Thereby, the stress applied to the portion can be relaxed without excessive stress concentrating on the inner R portion overlapping the induction hardening softened layer when the engine is driven. Thereby, durability of a crankshaft can be improved.

  By providing an inclined surface on the inner facing surface of the crank arm and the balance weight, it is possible to reduce the engine size by shortening the axial length of the crankshaft while ensuring a predetermined mass in the balance weight.

It is sectional drawing which shows the engine which has the crankshaft which is one embodiment of this invention. It is a front view which shows the crankshaft shown by FIG. 1 and the engine component attached to this. FIG. 3 is a perspective view showing a crankshaft shown in FIGS. 1 and 2. FIG. 4 is a front view of FIG. 3. It is an expanded sectional view which shows a part of FIG. 6 is a partially cutaway front view showing a crankshaft of Comparative Example 1. FIG. 10 is a front view showing a crankshaft of Comparative Example 2. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The engine shown in FIG. 1 is a four-cycle single-cylinder engine, and is a general-purpose engine used as a drive source for an engine generator, a rammer, or the like. As shown in FIG. 1, the engine 10 includes a crankcase 12 provided with a cylinder 11. A piston 13 is provided in the cylinder 11 so as to be capable of linear reciprocation. The piston 13 is connected to a crankshaft 14 rotatably attached to the crankcase 12 via a connecting rod 15. It is rotationally driven by the linear reciprocation of the piston 13. As shown in FIG. 2, the end of the crankshaft 14 is an output end 14a. When the engine 10 is used as a power source for a general-purpose engine such as a generator or a rammer, the output end 14a is not covered. The driven member is rotationally driven by being connected to the driving member.

  A cylinder head 16 is attached to the cylinder 11, and an intake port 18 for supplying a mixture of air and fuel to the combustion chamber 17 and an exhaust port 19 for discharging combustion gas are formed in the cylinder head 16. Yes. An intake valve 21 for opening and closing the intake port 18 and an exhaust valve 22 for opening and closing the exhaust port 19 are provided in the cylinder head 16, respectively. An intake-side rocker arm 24a that drives the intake valve 21 to open and close and an exhaust-side rocker arm 24b that opens and closes the exhaust valve 22 are swingably mounted on the rocker shaft 23 attached to the cylinder head 16. The valve shaft 21a of the intake valve 21 abuts on one end of the rocker arm 24a, and opens and closes the intake port 18 by swinging of the rocker arm 24a. A valve shaft portion (not shown) of the exhaust valve 22 abuts on one end portion of the rocker arm 24b, and opens and closes the exhaust port 19 by swinging of the rocker arm 24b. Reference numeral 20 denotes a spark plug.

  As shown in FIG. 2, a camshaft 25 is disposed in parallel to the crankshaft 14, and the camshaft 25 is rotatably mounted on the cylinder head 16. The other end portions of the respective rocker arms 24a and 24b are in contact with the valve operating cams 26 provided on the camshaft 25, and the respective rocker arms 24a and 24b are moved via the valve operating cams 26 by the rotation of the camshaft 25. It is swung. A timing belt 28 is stretched between a sprocket 27 attached to the camshaft 25 and a sprocket (not shown) attached to the crankshaft 14, and the camshaft 25 is driven to rotate by the crankshaft 14.

  As shown in FIG. 2, a governor 29 is disposed adjacent to the crankshaft 14, and the governor 29 is mounted on the crankcase 12 and adjusts the engine speed to a speed corresponding to the set accelerator opening. To do. The governor 29 has a driven gear 30 b that meshes with a driving gear 30 a attached to the crankshaft 14.

  As shown in FIGS. 3 and 4, the crankshaft 14 has two journals 31 and 32 that are rotatably supported by the crankcase 12, and the crankshaft 14 is the center of rotation of the journals 31 and 32. It is driven to rotate about the axis O. The crankshaft 14 has a pin 33 to which the end of the connecting rod 15 is attached. The center of the pin 33 is eccentric from the rotation center axis O of the journals 31 and 32. Both ends of the pin 33 are integrated with tip ends of crank arms 34 and 35 extending radially outward from the respective ends of the journals 31 and 32, and the pin 33 is connected to the journal 31 via the crank arms 34 and 35. , 32.

  Balance weights 36 and 37 projecting radially outward in the opposite direction to the crank arms 34 and 35 are integrally provided at the base end portions of the crank arms 34 and 35. Thus, the crankshaft 14 is an integral type in which the journals 31 and 32, the pin 33, the crank arms 34 and 35, and the balance weights 36 and 37 are integrated as a whole.

  One end portion of the connecting rod 15 is a small-diameter end portion, and the connecting rod 15 is connected to the piston 13 by a piston pin 38 penetrating therethrough. On the other hand, the other end of the connecting rod 15 is a large-diameter end, and the large-diameter end has a semicircular concave surface formed with a semicircular concave surface and a bolt 39 on the rod main body 15a. It is formed with the connection metal fitting 40 fastened by.

  The crankshaft 14 is provided with abutting step portions 41 and 42 against which the left and right side surfaces of the large-diameter end portion of the connecting rod 15 are abutted at the tip portions of the crank arms 34 and 35, respectively. Therefore, when the large-diameter end portion of the connecting rod 15 is attached to the pin 33, both side surfaces of the large-diameter end portion face the abutting step portions 41 and 42. The abutting step portions 41 and 42 are provided with abutting R portions 43 and 44 that are connected in an arc shape at the end of the pin 33, and the abutting R portions 43 and 44 are connected when the engine is driven. The first stress concentration portion where stress is concentrated by the thrust applied from the rod 15 to the crankshaft 14.

  The crank arm 34 and the balance weight 36 integrated with it are paired with the other crank arm 35 and the balance weight 37 integrated therewith. The inner facing surface 45 of the crank arm 34 and the balance weight 36 faces the inner facing surface 46 of the other crank arm 35 and the balance weight 37, and these inner facing surfaces 45, 46 face each other. . The two inner facing surfaces 45 and 46 that face each other are inclined in a direction in which they approach each other as they move toward the tip ends of the respective balance weights 36 and 37. As shown in FIG. 4, the inner facing surfaces 45 and 46 are inclined surfaces 45 a and 46 a that are inclined at an inclination angle θ with respect to the radial line V perpendicular to the rotation center axis O. . This inclination angle θ is set to 8 to 15 degrees.

  Between the inclined surfaces 45a, 46a and the abutting R portions 43, 44 in the respective inner facing surfaces 45, 46, inner R portions 47, 48 are provided to connect them in an arc shape. Each of the inner R portions 47 and 48 has an arc shape having a radius of curvature larger than the radius of curvature of the abutting R portions 43 and 44, and each of the inner R portions 47 and 48 is a second stress concentration portion. It has become.

  As shown in FIGS. 3 and 4, the crankshaft 14 is processed into an integrated shape having abutting R portions 43, 44, inclined surfaces 45 a, 46 a and inner R portions 47, 48 by forging, and then a high frequency. A quenching process is performed on the outer peripheral surface of the pin 33 by quenching. As a result, as shown in FIG. 5, a hardened and hardened layer 51 is formed at a predetermined depth on the outer peripheral portion of the pin 33 and the abutting R portions 43 and 44. Since the hardened layer 51 is also formed on the abutting R portions 43 and 44 as the first stress concentration portion, even if a load is applied to the abutting R portions 43 and 44 by the connecting rod 15, the strength of the portion is increased. Is secured and cracks can be prevented from occurring.

  On the other hand, when the induction hardening process is performed on the outer peripheral surface of the pin 33, a softened layer 52 having a lower hardness than the hardened layer 51 is formed inside the pin 33 with respect to the hardened hardened layer 51. When induction hardening is performed on the outer peripheral surface of the pin 33, the hardened layer 51 is also formed on the tip portions of the crank arms 34 and 35 via the butting steps 41 and 42, and the inner side of the hardened layer 51. The softened layer 52 formed on the inner R portions 47 and 48 is exposed. As described above, the softened layer 52 is applied to the inner R portions 47 and 48 because the cross-sectional area of the crank arms 34 and 35 is more rapidly expanded than the cross-sectional area of the pin 33, so that heat transfer during the quenching process is performed. This is because the diffusion at the front ends of the crank arms 34 and 35 decreases the quenching temperature of the inner R portions 47 and 48.

  The softened layer 52 is exposed to the inner R portions 47 and 48, but the radius of curvature of each of the inner R portions 47 and 48 is set larger than the radius of curvature of the abutting R portions 43 and 44. Even when a combustion pressure load is applied to the crankshaft 14 via the connecting rod 15, the stress is reduced in the inner R portions 47 and 48 without excessive stress concentration. . As a result, the durability of the crankshaft 14 can be improved.

  Experiments have been made that when the radius of curvature of the inner R portions 47 and 48 is set to be not less than three times the radius of curvature of the R portions 43 and 44, stress is relaxed without excessive stress concentration occurring in the inner R portion. Was found out. In the illustrated case, it is set to about 5 times.

  Thus, even if the radius of curvature of the inner R portions 47 and 48 is set to be three times or more than the radius of curvature of the abutting R portions 43 and 44, the inclined surfaces 45a and 46a are formed on the inner facing surfaces 45 and 46, respectively. Since the formation of the step portion on the inner facing surfaces 45 and 46 is prevented, the stress concentration portion due to the step portion is prevented from being formed on the inner facing surfaces 45 and 46, The durability of the crankshaft 14 can be increased.

  6 is a partially cutaway front view showing a crankshaft 14 as a comparative example 1. FIG. 7 is a front view showing the crankshaft 14 as a comparative example 2. FIG.

  As shown in FIG. 6, when the inner facing surfaces 45 and 46 are formed in a direction perpendicular to the rotation center axis O without providing inclined surfaces on the inner facing surfaces 45 and 46, the radii of curvature of the inner R portions 47 and 48 are formed. Cannot be set larger than the abutting R portions 43 and 44. For this reason, since the softening layer 52 is exposed to the inner R portions 47 and 48 by the quenching process of the pin 33, when a combustion pressure load is applied to the inner R portions 47 and 48 via the connecting rod 15, It was inevitable that the inner R portions 47 and 48 would be excessive stress concentration portions, and it was difficult to improve the durability of the crankshaft. In contrast, in the crankshaft 14 of the present invention, the radius of curvature of the inner R portions 47, 48 is set to be three times or more that of the abutting R portions 43, 44. As a result, the durability of the crankshaft 14 can be improved.

  As shown in FIG. 7, in order to make the radius of curvature of the inner R portions 47, 48 larger than the radius of curvature of the abutting R portions 43, 44, the thickness of the crank arms 34, 35 is reduced and the balance weights 36, In order to secure a balance factor of 37, an attempt was made to make the balance weights 36, 37 thicker than the crank arms 34, 35. However, if the crankshaft 14 is processed into such a shape, it becomes inevitable that the step portions 54 and 55 are formed between the crank arms 34 and 35 and the balance weights 36 and 37. For this reason, in the case shown in FIG. 7, not only the shape of the crankshaft 14 is complicated and the forgeability is deteriorated, but also the step portions 54 and 55 become stress concentration portions where excessive stress is concentrated. There was a risk of cracks occurring in the portion, and it was difficult to improve the durability of the crankshaft.

  On the other hand, in the crankshaft 14 of the present invention, by forming the inclined surfaces 45a and 46a on the inner facing surfaces 45 and 46, forging workability can be improved while ensuring balance of the balance weights 36 and 37. In addition, the crankshaft 14 having excellent durability was obtained without concentrating stress on the inner R portions 47 and 48. In addition, without increasing the thickness of the crank arms 34 and 35, it is possible to relieve stress by preventing the occurrence of excessive stress concentration in the R portion, and to obtain a lightweight crankshaft that can shorten the axial length. Became.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, the crankshaft of the present invention is not limited to a single-cylinder crankshaft, and can be applied to a multi-cylinder crankshaft as long as it is an integral type. Further, the present invention can be applied not only to a 4-cycle engine but also to a crankshaft of a 2-cycle engine.

11 Cylinder 12 Crankcase 13 Piston 14 Crankshaft 15 Connecting rods 31 and 32 Journal 33 Pins 34 and 35 Crank arms 36 and 37 Balance weights 41 and 42 Abutting step portions 43 and 44 Abutting R portions 45 and 46 Inner facing surface 45a 46a Inclined surfaces 47, 48 Inside R portion 51 Hardened layer 52 Softened layer

Claims (3)

A crank arm having two journals rotatably supported by the crankcase; a crank arm having a base end integrated with the journal and a pin attached to the end of the connecting rod at the tip; and a base of the crank arm An integral crankshaft having an integral balance weight at the end,
An abutting R portion provided between an abutting step portion of the crank arm tip portion against which an end side surface of the connecting rod is abutted, and an end portion of the pin;
Provided on the inner facing surface of the crank arm and the balance weight, and inclines in a direction approaching the balance weight with another crank arm that forms a pair from the base end of the crank arm toward the tip of the balance weight Inclined surface,
A crankshaft comprising an inner R portion which is provided between the inclined surface and the abutting R portion and has a larger radius of curvature than the abutting R portion.   2. The crankshaft according to claim 1, wherein a softened layer inside an induction-hardened hardened layer formed on the outer peripheral surface of the pin is positioned in the inner R portion.   3. The crankshaft according to claim 1, wherein a curvature radius of the inner R portion is three times or more than a curvature radius of the abutting R portion.

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