JP2005048958A - Power transmitting shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power transmitting shaft which can secure its stable torsional fatigue strength. <P>SOLUTION: The power transmitting shaft 1 is an integrated hollow shaft, in which an intermediate pipe 1a having a maximum diameter and shafts 1b having connecting portions, such as a spline, etc. formed on the outer surfaces of the ends of the power transmitting shaft 1 are integrally formed from the same pipe material. The power transmitting shaft 1 contains 0.30-0.45 wt.% C, 0.05-0.35 wt.% Si, 1.0-2.0 wt.% Mn, and further, contains at most 0.05 wt.% Al, and at most 0.01 wt.% S. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power transmission shaft, for example, a power transmission shaft used for a drive shaft (drive shaft) and a propeller shaft (propulsion shaft) constituting a part of a power transmission system of an automobile.

  Shafts that make up the power transmission system of automobiles include drive shafts that connect the engine and wheel bearing devices, and propeller shafts that transmit power from the transmission to the reduction gear device, both of which are connecting elements such as splines at the shaft end. Is provided. The power transmission shafts are roughly classified into basic structures, and are divided into solid shafts machined from solid bars and hollow shafts machined from steel pipes.

  In the past, solid shafts were used. However, due to the recent demand for higher-performance automobiles and quieter interiors, power transmission shafts are not only strong and durable, but also lighter and more compact. Various functions such as improvement of NVH characteristics have become necessary. In addition, it is necessary to improve torsional rigidity in order to obtain a maneuverability and direct feeling when the vehicle is started. In order to improve the torsional rigidity, it is conceivable to increase the shaft diameter, but this results in an increase in weight and an increase in the amount of shaving of the connecting portion, resulting in an increase in cost. Further, when the vehicle is running, the engine vibration and the shaft resonate to cause noise in the vehicle. Therefore, tuning of the natural frequency is necessary to avoid the noise. In order to tune the natural frequency, it may be possible to attach a damper or the like to the power transmission shaft. However, this increases the cost due to an increase in the number of parts and an increase in assembly man-hours.

Because of these functional requirements, there is a tendency to use a hollow shaft in place of a solid shaft. This type of hollow shaft is roughly divided into an integral hollow shaft and a joined hollow shaft. The integral hollow shaft has a structure in which a central pipe portion having an outermost diameter portion and a shaft portion having a spline or other connecting portion formed on the outer peripheral surface of the end portion are integrally molded from the same raw tube (for example, Patent Documents 1 to 3). On the other hand, the joining type hollow shaft has a structure in which a pipe portion and a shaft portion (stub) are separately formed and joined by friction welding or welding (for example, Patent Document 4 below).
Japanese Patent Laid-Open No. 11-101259 Japanese Patent Publication No. 7-88876 JP 2001-32818 A Japanese Patent Laid-Open No. 10-267027

  By the way, the integral type and the joined type hollow shaft have a smaller section modulus than the solid shaft, and the maximum shear stress acting on the hollow shaft is large, so that the shear strength may be lowered. In addition, there is a case where an electric resistance welded tube having high wall thickness accuracy and stable strength is used for the hollow shaft for power transmission. However, the ERW pipe has a structure in which a steel material with good dimensional accuracy and finishing accuracy is formed into a pipe shape and butt-welded by electric resistance welding. Therefore, the ERW pipe is a welded portion extending along its axial direction. It is easily damaged and causes a reduction in strength of the power transmission shaft.

  Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to provide a power transmission shaft that can ensure a stable torsional fatigue strength.

  In order to achieve the above object, the present invention provides a power transmission shaft provided with connecting elements at both ends of a pipe made of steel, and the content of C is 0.30 wt% or more and 0.45 wt% or less, and the Si content is Provided is a configuration in which 0.05 wt% or more and 0.35 wt% or less, Mn content is 1.0 wt% or more and 2.0 wt% or less, and a hardening process is performed by induction hardening. By regulating the contents of C, Si, and Mn within the above range, it is possible to improve the induction hardenability and obtain the required hardness while preventing the workability from decreasing. Thereby, stable torsional fatigue strength can be ensured. Preferably, Al is contained at 0.05 wt% or less and S is contained at 0.01 wt% or less.

  According to the present invention, a stable torsional fatigue strength can be ensured, and a long-life and highly reliable power transmission shaft can be provided.

  A power transmission shaft 1 according to the embodiment shown in FIG. 1 is formed by integrally forming a central pipe portion 1a having an outermost diameter portion and a shaft portion 1b in which a connecting portion such as a spline is formed on an outer peripheral surface of an end portion from the same raw tube. It is an integrated hollow shaft made of a pipe. Note that, as in the power transmission shaft 2 of the embodiment shown in FIG. 2, a joined hollow shaft made of a pipe in which the pipe portion 2a and the shaft portion 2b are separately molded and joined by friction welding or welding or the like. Good. 3 is a cross-sectional view of the pipe portion 1a of the power transmission shaft 1 shown in FIG. 1 or the pipe portion 2a of the power transmission shaft 2 shown in FIG. Since the description is common to the embodiment of FIG. 1 and FIG. 2, it will be described in detail below based on the embodiment of FIG.

  The power transmission shaft 1 is an electric sewing tube with good wall thickness accuracy. In this ERW pipe, a plate material with good dimensional accuracy and finishing accuracy is formed into a pipe shape and butt-welded by electric resistance welding. Therefore, the ERW 3 is a welded portion formed along the axial direction. (See FIG. 3).

  The power transmission shaft 1 contains C in an amount of 0.30 wt% or more and 0.45 wt% or less, Si in an amount of 0.05 wt% or more and 0.35 wt% or less, and Mn in an amount of 1.0 wt% or more and 2.0 wt% or less. Furthermore, Al is contained at 0.05 wt% or less and S is contained at 0.01 wt% or less. The balance is Fe and inevitable impurities. The electric stitching portion 3 and the vicinity thereof are hardened to a Rockwell hardness of HRC45 or higher. Here, “the vicinity of the electric sewing portion” means a range of 5 mm from the central portion in the circumferential direction of the electric sewing portion to both sides in the circumferential direction.

  This hardening process is realized by subjecting the power transmission shaft 1 to induction hardening and tempering. The hatched portions in FIG. 1 and FIG. 2 show a state of being burned out in the region that has been induction hardened and tempered. By forming the power transmission shaft 1 with a steel material containing the above components, the electric stitching portion 3 and its vicinity can be hardened to a Rockwell hardness of HRC45 or more. Thereby, the strength of the pipe itself can be improved and a stable torsional fatigue strength can be ensured.

  Here, it is generally known that the hardness is a major factor for the torsional fatigue strength of the power transmission shaft 1, and the hardness greatly depends on the components of the steel material. That is, the element that determines the hardness after quenching is C, but in order to determine the hardness after quenching in the depth direction, these components are effective in that other elements (for example, Si, Mn, etc.) act effectively. Need to be adjusted.

C is an element necessary for ensuring the torsional fatigue strength of the power transmission shaft 1 and is required to be 0.30 wt% or more in order to obtain hardness after a predetermined heat treatment. Moreover, when exceeding 0.45 wt%, this is made into an upper limit at the point which the hardness of steel materials increases too much and workability is reduced. Si is an element necessary for securing a high-frequency hardenability of the steel material as well as a slight amount as a deoxidizer for the steel material, and this effect is small when the content is less than 0.05 wt%. On the other hand, if it exceeds 0.35 wt%, the workability is remarkably lowered, so this is the upper limit. Mn needs to be added in an amount of 1.0 wt% or more in order to ensure high induction hardenability of the steel material. However, if it exceeds 2.0 wt%, the workability is remarkably reduced, so this is the upper limit. Al is added as a deoxidizer for steel, and is desirably reduced so as not to impair the cleanliness of the steel, and the upper limit is 0.05 wt%. S lowers the deformability at the time of cold working, and when it exceeds 0.01 wt%, the deformability is significantly reduced, so 0.01 wt% is the upper limit.

  In order to supplement the induction hardenability of the steel material, Cr may be contained in an amount of 0.1 wt% to 0.35 wt% and B may be contained in an amount of 0.0005 wt% to 0.005 wt%. Both Cr and B may contain at least one of them. If the Cr content is less than 0.1 wt%, the effect of supplementing the induction hardenability of the steel material is small, and if added over 0.35 wt%, the cost of the steel material increases. Further, if the content of B is less than 0.0005 wt%, the effect of supplementing the induction hardenability of the steel material is small, and even if added over 0.005 wt%, the effect of the induction hardenability does not change. .

  Moreover, you may perform a shot peening process to the perimeter of the power transmission shaft 1 after an induction hardening and tempering process. By increasing the residual compressive stress on the surface portion of the power transmission shaft 1, the torsional fatigue strength can be further improved. Here, the shot peening treatment is to make the surface stress uniform by generally hitting a small steel grain against a metal surface with compressed air or centrifugal force.

  The applicant performs induction hardening and tempering treatment with the same inner diameter and outer diameter, and varies the content of C, Si, Mn, S, Al, Cr and B components and the Rockwell hardness HRC near the ERW. In addition, torsional fatigue strength tests were performed on eight power transmission shafts (samples Nos. 1 to 8). The test results are shown in FIG.

  The portions other than the electro-sewn portion were quenched and tempered so that the surface hardness at the outer diameter portion had a hardness distribution of Rockwell hardness HRC50 or higher. The hardness in the vicinity of the electro-sewn portion is the result of converting Vickers hardness measured at a position of 2 mm from the inner diameter side into Rockwell hardness. In this test, one end was fixed in a state where both ends of the power transmission shaft 1 were supported, and load torque was applied from the other end. Regarding the determination, the strength lower limit level of the solid shaft having the same shaft portion diameter was used as a determination criterion, and 400,000 times or more was regarded as acceptable.

  As is clear from the test results shown in FIG. 4, the power transmission shaft 1 has a C of 0.30 wt% or more and 0.45 wt% or less, an Si of 0.05 wt% or more and 0.35 wt% or less, and an Mn of 1. It is formed of a steel material containing 0 wt% or more and 2.0 wt% or less, Al 0.05 wt% or less and S 0.01 wt% or less, and the ERW 3 and the vicinity thereof have Rockwell hardness HRC 45 or more. Only the cured samples (Sample Nos. 4-8) passed in terms of torsional fatigue strength.

In the embodiment of the power transmission shaft according to the present invention, it is a front view including a partial cross-sectional portion showing an integrated hollow shaft. It is other embodiment of the power transmission shaft which concerns on this invention, and is a front view containing the partial cross-section part which shows a joining type | mold hollow shaft. It is sectional drawing which shows the electric sewing part of a pipe (electric sewing pipe). It is a table | surface which shows the result of a torsional fatigue strength test.

Explanation of symbols

  1,2 power transmission shaft

Claims (2)

  In a power transmission shaft provided with connecting elements at both ends of a pipe made of steel, the C content is 0.30 wt% or more and 0.45 wt% or less, and the Si content is 0.05 wt% or more and 0.35 wt% or less. A power transmission shaft, wherein the Mn content is 1.0 wt% or more and 2.0 wt% or less, and is subjected to hardening treatment by induction hardening. The power transmission shaft according to claim 1, further comprising Al in an amount of 0.05 wt% or less and S in an amount of 0.01 wt% or less.