JP2006002185A - Method for heat-treating hollow-power transmission shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for heat-treating a hollow-power transmission shaft with which a hardening-crack inspection on the surface part in the inner periphery can be simplified. <P>SOLUTION: A high frequency induction heating coil 10 is disposed at the outer peripheral surface 19 side of a hollow shaft base stock 1' and a high frequency induction-hardening is performed from the outer peripheral surface 1g side to the axial direction zone L. In this time, piping members 11 are connected to both end parts of the hollow shaft base stock 1', and cooling water is made to flow into the inner peripheral part of the hollow shaft base stock 1' through the piping members 11. When the high frequency induction-hardening is performed, a non-hardening layer S0 is formed in a prescribed depth range from the inner peripheral surface 1i by allowing the inner peripheral surface 1i of the hollow shaft base stock 1' to contact with the stream of the cooling water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat treatment method for a hollow power transmission shaft connected to a joint such as a constant velocity universal joint, and the hollow power transmission shaft includes, for example, a drive shaft (drive shaft) constituting a power transmission system of an automobile, It can be applied to a propeller shaft (propulsion shaft).

  For example, in a power transmission system of an automobile, a power transmission shaft that transmits power from a speed reducer (differential) to drive wheels may be called a drive shaft (drive shaft). In particular, a drive shaft used in an FF vehicle requires a large operating angle and constant velocity during front wheel steering, and also requires a function of absorbing axial displacement in relation to the suspension system. Is connected to the reducer side through a sliding type constant velocity universal joint such as a double offset type constant velocity universal joint or a tripod type constant velocity universal joint, and the other end is connected to a barfield type constant velocity universal joint (Zepper joint). In many cases, a mechanism that is connected to the drive wheel side via a fixed-side constant velocity universal joint is employed.

  As a drive shaft as described above, a solid shaft is often used in the past and now, but the weight of the car is improved, the function is improved by increasing the rigidity of the drive shaft, and the tuning of the bending primary natural frequency is optimized. Recently, there has been an increasing demand for a drive shaft to be a hollow shaft from the viewpoint of improving the quietness of the interior of the vehicle.

  As a hollow power transmission shaft applied to a drive shaft or the like, for example, those described in Patent Documents 1 to 3 below are known.

  In Patent Document 1, the inner peripheral surface of the hollow shaft is heat-cured over almost the entire region in the axial direction. This thermosetting treatment is performed on the entire depth region from the outer peripheral surface to the inner peripheral surface by, for example, induction hardening and tempering from the outer peripheral surface side of the hollow shaft (see paragraph number 0012 of the same document). ).

  In Patent Document 2, for example, thermosetting treatment is performed on the entire depth region from the outer peripheral surface to the inner peripheral surface over almost the entire axial direction of the hollow shaft by induction hardening and tempering (paragraph of the same document). No. 0012).

In Patent Document 3, in order to make the static strength and torsional fatigue strength of the hollow shaft equal to or higher than that of the solid shaft, the hollow shaft is surface quenched at a quenching rate of 0.7 to 0.9. Here, the quenching rate is defined as the ratio h / t between the quenching depth h from the outer peripheral surface quenched to a hardness of HV400 or more and the shaft wall thickness t (see paragraph 0014 of the same document). ).
JP 2002-349538 A JP 2002-356742 A JP 2003-90325 A

  Generally, in this type of hollow power transmission shaft, in order to increase static strength such as static torsion strength, it is effective to increase the depth from the outer peripheral surface of the heat-treated cured layer. In this regard, in Patent Documents 1 and 2, the entire depth region from the outer peripheral surface to the inner peripheral surface is heat-treated and cured (referred to as such thermosetting hereinafter) on both sides in the axial direction of the hollow shaft or almost the entire region in the axial direction. The process is called “fully cured”) to ensure the maximum static strength of the hollow shaft.

  By the way, this kind of hollow power transmission shaft often requires strict quality control against burning cracks during the thermosetting process, and usually the burning crack inspection is performed after the thermosetting process.

  In general, the inspection of the outer peripheral surface portion is relatively easy, but the inspection of the inner surface portion is technically difficult, and the non-destructive inspection by ultrasonic flaw detection or the like is usually the mainstream. Therefore, the inspection requires a large amount of cost and man-hours.

  On the other hand, in Patent Document 3, the surface of the hollow shaft is quenched at the above-described quenching rate of 0.7 to 0.9, and the inner peripheral surface portion is hardened as compared with the case of full hardening as in Patent Documents 1 and 2. Since the hardness decreases, the possibility of occurrence of burning cracks on the inner peripheral surface portion is somewhat reduced. That is, in this document, heating is performed up to the vicinity of the inner peripheral surface at the time of quenching, but in the vicinity of the heated inner peripheral surface, the air layer inside the shaft is heated at the time of heating, and the inner peripheral surface is transferred to the air layer. The heat transfer coefficient is lower than the heat transfer efficiency inside the metal, so that it is not rapidly cooled (see paragraph 0014 of the same document). However, if the quenching rate is 0.7 or more, it is difficult to completely eliminate the heat influence in the vicinity of the heated inner peripheral surface by the air layer inside the shaft.

  The subject of this invention is providing the heat processing method of the hollow-shaped power transmission shaft which can simplify the inspection of a burning crack of an inner peripheral surface part.

  In order to solve the above-described problems, the present invention provides a heat treatment method for a hollow power transmission shaft in which an axially intermediate portion is formed in a large diameter portion, and both side portions in the axial direction are formed in smaller diameter portions than the large diameter portion. The pipe material is subjected to plastic working to form a hollow shaft material having a large diameter portion and a small diameter portion, and a coolant is circulated through the inner periphery of the hollow shaft material, while the hollow shaft material Provided is a configuration in which quenching is performed from the outer peripheral side.

  As the plastic processing, swaging processing, press processing, or the like is employed. The former swaging process includes rotary swaging and link type swaging, both of which can be employed. For example, in rotary swaging, a pair or a plurality of dies and a backer incorporated in a main shaft in the machine perform a rotational motion, and a vertical stroke of a fixed stroke is performed by a peripheral roller and a protrusion on the backer, and then inserted. This is a processing method in which a pipe material is blown to perform drawing. The press working is a working method in which a pipe material is pressed into a die in the axial direction to perform drawing.

  The material of the pipe material is, for example, carbon steel for mechanical structures such as STKM or STMA, alloy steel to which alloy elements are added for improving workability and hardenability based on them, or SCr, SCM. It is possible to use bare steel such as SNCM.

  As the above quenching treatment, various means such as induction quenching, carburizing quenching, carbonitriding and quenching can be adopted depending on the material of the pipe material and the characteristics required for the power transmission shaft. The range and depth can be freely selected, and induction hardening is preferably employed from the viewpoint of improving fatigue fatigue resistance due to generation of residual compressive stress on the surface. In the present specification, the “quenching process” includes both a process of tempering after quenching and a process of not tempering after quenching. From the viewpoint of simplifying the treatment process, it is preferable that only quenching is performed and tempering is not performed.

  The hollow shaft material formed into a predetermined shape is quenched from the outer periphery side, and at this time, the coolant is circulated through the inner periphery of the hollow shaft material. As the coolant, for example, cooling water can be used. The cooling water here includes quenching cooling water (aqueous solution or the like) used for induction hardening or the like. During the quenching process, the inner surface of the hollow shaft material comes into contact with the coolant flow, so that a predetermined depth region from the inner surface of the hollow shaft material is unheated or a temperature lower than the austenitizing temperature. It is heated in or annealed. Therefore, a hardened layer is formed by quenching treatment from the outer peripheral surface of the hollow shaft material to a predetermined depth region, and an uncured layer that is not hardened by quenching treatment from the inner peripheral surface to the inner peripheral surface portion of the predetermined depth region. Is formed. In general, baked cracks occur when the steel structure austenitized by heating passes through the Ms point and transforms into martensite, but is formed by heating at a temperature lower than the austenitizing temperature. Since the martensite transformation does not occur in the uncured layer, no cracking occurs. In this case, the hardness of the uncured layer is in a state where the hardness at the inner peripheral surface portion of the hollow shaft material before quenching is maintained at the same level. Moreover, in the uncured layer formed in the annealed state, softening occurs, and thus no cracking occurs. In this case, the hardness of the uncured layer may be smaller than the hardness of the inner peripheral surface portion of the hollow shaft material before the heat treatment.

  It is important for this type of hollow power transmission shaft to ensure a balance between static strength such as static torsional strength and dynamic strength such as torsional fatigue strength. From the standpoint of increasing static strength, it is preferable to increase the quenching depth as much as possible. However, if it is fully cured, it may cause cracking of the inner peripheral surface portion, and the toughness of the inner peripheral surface portion may be reduced. There is a tendency for the dynamic strength to decrease as it decreases. In the present invention, as described above, since the coolant is circulated through the inner peripheral portion of the hollow shaft material during the quenching treatment, the quenching rate α is, for example, 0.7 or more (α ≧ 0.7), 0 at the maximum. Even if it is as large as about .9, it is possible to form the uncured layer on the inner peripheral surface portion. Therefore, according to the present invention, the quenching rate α can be increased as much as possible while preventing the cracking of the inner peripheral surface portion, and the strength balance between the static strength and the dynamic strength of the power transmission shaft can be increased. . Here, the quenching rate α is a ratio (h / t) between the depth (h) and the thickness (t) from the outer peripheral surface of the hardened layer having a hardness of HRC 40 or higher.

  The type, temperature, and flow rate of the coolant circulated in the inner periphery of the hollow shaft material may be determined according to the quenching treatment conditions and the required quenching rate α, etc., but when using cooling water as the coolant, Experiments have confirmed that favorable results can be obtained when the flow rate of cooling water is 10 L / min or more.

  ADVANTAGE OF THE INVENTION According to this invention, the heat processing method of the hollow power transmission shaft which can simplify the inspection of a burning crack of an inner peripheral surface part can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a hollow power transmission shaft 1, a sliding type constant velocity universal joint 2 connected to one end of the power transmission shaft 1, and a fixed type constant speed connected to the other end of the power transmission shaft 1. The power transmission mechanism of the motor vehicle provided with the universal joint 3 is shown. In the power transmission mechanism of this embodiment, the sliding type constant velocity universal joint 2 is connected to a reduction gear (differential), and the fixed type constant velocity universal joint 3 is connected to the drive wheel side. One end of the power transmission shaft 1 is splined to a tripod member 2a of the sliding type constant velocity universal joint 2, and a boot 2c is provided on the outer periphery of the outer ring 2b of the sliding type constant velocity universal joint 2 and the outer periphery of the power transmission shaft 1. Are fixed respectively. The other end of the power transmission shaft 1 is splined to the inner ring 3 a of the fixed type constant velocity universal joint 3, and a boot 3 c is provided on the outer circumference of the outer ring 3 b of the fixed type constant velocity universal joint 3 and the outer circumference of the power transmission shaft 1. Are fixed respectively. In the drawing, a tripod type constant velocity universal joint is illustrated as the sliding type constant velocity universal joint 2, and a barfield type constant velocity universal joint is illustrated as the fixed type constant velocity universal joint 3. Some types of constant velocity universal joints may be used.

  FIG. 2 shows a power transmission shaft (drive shaft) 1. The power transmission shaft 1 is hollow over the entire region in the axial direction, and has a large-diameter portion 1a at an axial intermediate portion and small-diameter portions 1b at both axial sides of the large-diameter portion 1a. The large-diameter portion 1a and the small-diameter portion 1b are continuous via a tapered portion 1c that is gradually reduced in diameter toward the shaft end side. The small-diameter portion 1b includes an end-side connection portion 1d used for connection with the constant velocity universal joints (2, 3), and an axial intermediate portion-side boot fixing portion 1e to which the boots (2c, 3c) are fixed. And a minimum diameter portion 1f between the connecting portion 1d and the boot fixing portion 1e. A retaining ring groove for attaching a spline 1d1 splined to the constant velocity universal joints (2, 3) and a retaining ring for axially retaining the constant velocity universal joints (2, 3) to the coupling portion 1d. 1d2 is formed. The boot fixing portion 1e is formed with a fitting groove 1e1 for fitting the inner circumference of the small diameter end portion of the boot (2c, 3c). The minimum diameter portion 1f has an inner diameter and an outer diameter that are substantially constant in the axial direction, and has a substantially uniform shape in the axial direction.

  Further, as shown with hatching in the figure, the power transmission shaft 1 has a substantially entire region L in the axial direction except for a partial region from the vicinity of the retaining ring groove 1d2 to the shaft end. It has the hardened layer S by the quenching process. In the axial region L, the hardened layer S is formed in a region having a predetermined depth h0 from the outer peripheral surface 1g, and a region from the hardened layer S to the inner peripheral surface 1i becomes an uncured layer S0 that has not been hardened by the quenching process. ing. In addition, a part of the region from the vicinity of the retaining ring groove 1d2 to the shaft end is not subjected to the quenching process, and the entire region from the outer peripheral surface 1g to the inner peripheral surface 1i is left in the state before the quenching process. Yes.

  The power transmission shaft 1 having the above configuration can be manufactured, for example, in the following manner. First, a rotary swaging process is applied to a pipe material such as a carbon steel pipe for machine structure (STKM) over the entire axial direction, and a hollow having a large-diameter portion 1a at an axial middle portion and small-diameter portions 1b at both axial sides. Molded shaft material. In the hollow shaft material formed in this way, work hardening by rotary swaging and thickening due to reduced diameter are recognized over the entire axial direction. A spline 1d1 is formed on the end of the small diameter portion 1b of the hollow shaft material by rolling or the like to form a connecting portion 1d, and the retaining ring groove 1d2 is formed on the connecting portion 1d by rolling or cutting. Form. Further, a boot fixing groove 1e1 is formed by rolling or cutting at a portion to be the boot fixing portion 1e.

  Thereafter, as shown in FIG. 3, for example, a movable high-frequency induction heating coil 10 is disposed on the outer peripheral surface 1 g side of the hollow shaft material 1 ′, and the outer peripheral surface 1 g Induction hardening from the side. At that time, the piping member 11 is connected to both ends of the hollow shaft material 1 ′, and the cooling water is circulated through the piping member 11 to the inner peripheral portion of the hollow shaft material 1 ′. The induction hardening may be performed by a stationary hardening method.

  By the induction hardening described above, the hardened layer S is formed in a region having a predetermined depth h0 from the outer peripheral surface 1g of the hollow shaft material 1 '. Further, when the inner peripheral surface 1i of the hollow shaft material 1 ′ is in contact with the flow of the cooling water during the induction hardening, a predetermined depth region from the inner peripheral surface 1i is, for example, an unheated or austenitizing temperature. The uncured layer S0 is formed by heating at a temperature below. The hardness of the uncured layer S0 is maintained at the same level as the hardness of the inner peripheral surface portion of the hollow shaft material 1 'before induction hardening, for example. That is, the uncured layer S0 has a structure in which martensite that causes burning cracks is not generated.

  The power transmission shaft 1 manufactured in this manner has a hardened layer S by induction hardening in a predetermined depth region h0 from the outer peripheral surface 1g and is not hardened by induction hardening on the inner peripheral surface portion including the inner peripheral surface 1i. Since it has hardened layer S0, there is no burning crack of an inner peripheral surface part, and the inspection of the burning crack of an inner peripheral surface part can be simplified. In addition, the strength balance between static strength and dynamic strength is excellent.

  The pipe material made of carbon steel for mechanical structure (STKM) is subjected to rotary swaging and subsequent machining to produce a hollow pipe material having the same form as the hollow pipe material 1 ′ shown in FIG. The hollow pipe material was subjected to induction quenching (quenching rate α ≧ 0.7) to produce power transmission shafts of Examples and Comparative Examples. For the hollow pipe material according to the example, the cooling water whose temperature was controlled in the inner periphery during the induction hardening (temperature controlled to the same level as the outer cooling water) was circulated at a flow rate of 10 L / min or more. . The hollow pipe material according to the comparative example was subjected to normal induction hardening, and cooling water was not distributed to the inner peripheral portion. The conditions for induction hardening were the same for the examples and comparative examples.

  The minimum diameter portion (1f) of the power transmission shafts of Examples and Comparative Examples produced as described above was cut, and the hardness distribution of the cut surfaces was measured. The result is shown in FIG. In the figure, the horizontal axis represents the ratio between the depth from the outer peripheral surface and the thickness t (hereinafter referred to as “depth ratio”. Depth ratio 0 is the outer peripheral surface, and depth ratio 1 is the inner peripheral surface). The vertical axis represents Vickers hardness (Hv). The quenching rate α is defined by the ratio (h / t) between the depth h and the wall thickness t of a hardened layer having a Rockwell hardness of HRC40 (Hv391) or higher, and α = 0 in the power transmission shaft of the embodiment. .81 (≧ 0.7), α = 0.87 (≧ 0.7) in the power transmission shaft of the comparative example. As shown in the figure, in the power transmission shaft of the comparative example, there was a tendency that the hardness gradually decreased at a substantially constant ratio in a predetermined depth ratio region. And in the position of the vicinity of the inner peripheral surface, the hardness was higher than that before quenching, and the influence of thermosetting by induction hardening was observed on the inner peripheral surface portion. On the other hand, in the power transmission shaft of the embodiment, the hardness decreases with a relatively large slope in the region of the predetermined depth ratio, and the hardness is a substantially constant low value from the position of the predetermined depth ratio to the inner peripheral surface. There was a tendency to change. The hardness in the vicinity of the inner peripheral surface was almost the same as that before quenching, and no influence of hardening by induction hardening was observed on the inner peripheral surface portion.

  The same hollow pipe material as in Example 1 was subjected to induction hardening while circulating cooling water through the inner periphery. Induction hardening was performed by setting the output of the induction hardening apparatus to a reference value, a reference value of −10 kW, a reference value of +10 kW, and a reference value of +20 kW, and the cooling water flow rate to various values. And the minimum diameter part (1f) of the power transmission shaft after induction hardening was cut | disconnected, the hardness distribution of this cut surface was measured, and hardening rate (alpha) was calculated | required. The result is shown in FIG. As shown in the figure, when the flow rate of the cooling water is less than 10 L / min, depending on the output value, the quenching rate α was found to be 1.0 (total curing), but when the flow rate was 10 L / min or more It was confirmed that the quenching rate α settled in the vicinity of 0.8 at any of the above output values.

It is a figure which shows the power transmission mechanism of a motor vehicle. It is a partial sectional view showing a power transmission shaft concerning an embodiment. It is a partial cross section figure which shows the power transmission shaft which concerns on other embodiment. It is a figure which shows hardness distribution. It is a figure which shows the relationship between the output at the time of induction hardening, the flow volume of cooling water, and the hardening rate (alpha).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power transmission shaft 1 'Hollow pipe raw material 1a Large diameter part 1b Small diameter part 1i Inner surface 1g Outer surface S Hardened layer S0 Uncured layer

Claims (5)

A heat treatment method for a hollow power transmission shaft in which an axially intermediate portion is formed in a large diameter portion, and both side portions in the axial direction are formed in small diameter portions from the large diameter portion, respectively.
Plastic processing is performed on the pipe material to form a hollow shaft material having the large diameter portion and the small diameter portion,
A heat treatment method for a hollow power transmission shaft, wherein a quenching treatment is performed from an outer peripheral side of the hollow shaft material while a coolant is circulated through an inner peripheral portion of the hollow shaft material.   The hollow power transmission shaft according to claim 1, wherein a hardened layer is formed in a predetermined depth region from the outer peripheral surface by the quenching treatment, and an uncured layer that is not hardened by the quenching treatment is formed on the inner peripheral surface portion. Heat treatment method.   The heat treatment method for a hollow power transmission shaft according to claim 1, wherein the quenching treatment is induction hardening.   The heat treatment method for a hollow power transmission shaft according to claim 1, wherein the coolant is cooling water.   The heat treatment method for a hollow power transmission shaft according to claim 4, wherein a flow rate of the cooling water is 10 L / min or more.

Images