EP2569458A1

EP2569458A1 - Steel side shaft produced by rotary swaging

Info

Publication number: EP2569458A1
Application number: EP11718347A
Authority: EP
Inventors: Markus Halfmann; Jens Wahnschaffe; Christian Felchner
Original assignee: Neapco Europe GmbH
Current assignee: Neapco Europe GmbH
Priority date: 2010-05-11
Filing date: 2011-05-02
Publication date: 2013-03-20
Also published as: WO2011141310A1; DE102010028898A1

Abstract

The invention relates to a side shaft for transmitting torque between an axle differential and a wheel of a motor vehicle, wherein the side shaft is produced at least partially from a steel material. The side shaft is preferably hollow and has a reduced diameter in end portions. The reduced diameter is produced preferably in a rotary swaging process, wherein the degree of deformation of the semifinished parts used for producing the side shaft is kept low. In this way, it is possible to use a steel material with a high carbon fraction. The steel material need not have expensive alloying elements added to it for the purpose of ensuring hardenability.

Description

Description: SIDE WAVE MADE OF STEEL MADE BY ROUND KNEES

The invention relates to a side shaft for transmitting torque between an axle differential and a wheel of a motor vehicle. Such waves are also called side waves. The generic side shaft is at least partially made of a steel material and designed as a tubular shaft. It has a longitudinal axis and a shaft portion, which in turn has a first diameter and a first wall thickness, two end portions, which are formed by forming portions of the shaft portion, so that in regions in the end portions, a second diameter and a second wall thickness is formed. Furthermore, the invention relates to a method for producing a side wave according to the preamble of claim 7.

Drive shafts are used in the vehicle for transmitting torque and are usually subjected to a heat treatment. A heat treatment of a drive shaft is known from DE 39 36 368 AI. However, this method relates to a hardening process for the drive shaft between a transmission and a differential, so a propeller shaft. Cardan shafts often have a much larger outer diameter than the side shafts between the differential and the drive wheels, which are also called side shafts.

In the end sections, generic side shafts usually have an area which is suitable for at least partial positive transmission. For this purpose, an external toothing, which in a korres- ponding internal toothing of a corresponding to be connected part of a constant velocity joint can intervene. The teeth are often referred to as spline area.

The side shafts are made of a semi-finished product, which may be a pipe section made of a steel material. The end portions have a different diameter than the shaft portion. The side shafts are provided by cold forming the end sections, which are to have a smaller diameter, by a rotary swaging method, as disclosed, for example, in DE 199 52 229 B4.

The degree of deformation is defined as the ratio of the dimensions before and after the deformation in a direction in which the maximum deformation takes place. Since generic side shafts are manufactured in a rotary swaging process and are not deliberately heated to significant temperatures, cracking and fractures can easily occur in the material.

The tendency for cracking can be reduced by reducing the carbon content. Generic side shafts have relatively low carbon contents, in particular less than about 0.30 wt% carbon. However, semi-finished products with low carbon content are less suitable for a hardening process. In order to make the steel materials nevertheless curable, the steel material in the prior art expensive alloying element such. As chromium, vanadium, nickel, molybdenum or titanium attached. Therefore, to be provided for the production of side shafts semi-finished products are relatively expensive.

The definition for terms used below, such as: As "unalloyed steel" and "low alloy steel" can be found in relevant literature, such as the DUBBEL, Paperback for Mechanical Engineering, 20th Edition. Information on the so-called austenitizing temperature, for example, ROOS, MAILE, material science for engineers, fundamentals, applications and testing, 3rd edition, are removed. Also for the definition of "bainite" and "martensite" refer to the latter literature. The object underlying the invention is to reduce the cost of providing semi-finished products for the production of side shafts while ensuring the hardenability.

The object is achieved by a side shaft according to claim 1 and a method for producing a side wave according to claim 7. Advantageous embodiments of the invention will become apparent from the respective dependent claims, which can be combined with each other in any technologically meaningful way and show other advantages of the invention. In addition, advantageous features of the invention in the description, in particular in the description of the figures are shown.

The drive shaft according to the invention serves to transmit a torque between an axle differential and a wheel of a motor vehicle. It is therefore a so-called side wave. The side shaft according to the invention is at least partially made of a steel material and designed as a tubular shaft. According to the invention, it has a longitudinal axis and a shaft portion having a first outer diameter Di and a first wall thickness Si. The drive or side shaft according to the invention is characterized in that at least one end portion, with a second diameter (D ₂ ) and a second wall thickness (S ₂ ) is made of a carbon steel.

A particularly preferred steel material, which is suitable for producing a side shaft according to the invention, is the steel C-45 according to DIN EN10083. This is available at low cost.

It has surprisingly been found by empirical experiments that with the steel grades used and skillful choice of the degree of deformation forming, for example by rotary swaging, is possible and at the same cracking is avoided and the ability to achieve sufficient strength by heat treatment is opened. For a given first outer diameter Di and a first wall thickness Si of the shaft section as well as an end section formed by the reshaping with a second diameter Sers D ₂ and second wall thickness S ₂ according to the invention the degree of deformation Phi = In [(Di-Si) / (D ₂ -S ₂ )] of the amount less than or equal to 0.3.

The empirically determined value of 0.3 also applies to flared end sections, not only for end sections narrowed in a rotary swaging method, as shown in FIG.

Surprisingly, it has been found that at a degree of deformation of less than or equal to 0.3, a semifinished product, for example a pipe section made of a steel material, with a relatively high carbon content of 0.35 to 0.8 wt .-%, in particular from 0.4 to 0.5 wt .-% during the forming is not prone to cracking.

To ensure the hardenability of a side wave according to the prior art, the steel materials alloying elements such. As vanadium, nickel, chromium, molybdenum and / or titanium added. By keeping the degree of deformation low, these relatively expensive alloying elements can be dispensed with. Due to the relatively high proportion of carbon, the side wave can also be subjected to a heat treatment, in particular a hardening process, after the forming.

For hardening the side shaft, a heat treatment is preferred, which comprises the following steps:

o inductive heating in a ring inductor or in a surface inductor, in particular at a surface temperature above an austenitizing temperature, for a period of less than 15 seconds, in particular less than 10 seconds,

o rapid cooling of the side wave in water or a

Water polymer emulsion either by immersion or a combination of dipping and barking, wherein a bainitic martensitic mixed structure is sought.

The success of the heat treatment can be checked in a micrograph of a cross section through a side wave. In the case of inductive heating in a ring inductor or a surface inductor, an alternating magnetic field heats the components. The effects of the ring inductor or the

Area Inductores on the side wave is preferably long enough that the austenitizing temperature, at which a conversion of the crystal structure of the steel material from cubic body centered to cubic face centered can be expected, is achieved.

The cooling of the side waves can be done by exposure to water or a water polymer emulsion. For this purpose, the side wave may be dipped or exposed to the water or the water polymer emulsion in a combination of dipping and buffing. The cooling must be designed so that a bainitic-martensitic steel structure is formed. Bainite forms only when the cooling rate is sufficiently high. If the cooling rate is too high, however, an excessive amount of martensite is formed. If the martensite content is too high, the side waves are too hard and prone to brittle fractures. The austenitizing temperature is between 800 and 1200 °, a preferred cooling rate is between 1 second and 100 seconds, in particular between 1 second and 50 seconds.

Preferably, the austenitizing temperature is only achieved in near-surface edge layers of the side shaft, so that adjusts a particularly high hardness during quenching near the surface. By using this hardening method, a side wave can be provided in which the hardness increases outward over the wall thickness. It can be achieved that outer, near-surface regions of the side shaft have a higher hardness than further inner regions. The hardness of the steel material decreases towards deeper layers. In this way, the hardness of the side shaft of the load is adjusted because the voltage in waves increases in torque loading with the distance from the longitudinal axis. The higher the hardness of the side shaft, the more torque it can transmit. Inventive side shafts are suitable for the transmission of torques of 1500 Nm to 5500 Nm, in particular 2800 Nm to 3800 Nos.

For example, a shaft produced by the process according to the invention has a hardness of between 40 and 60 Rockwell, in particular between 45 and 55 Rockwell, on its surface.

The cooling rate can be slowed down by interrupting the drowning or dipping of the side wave and the side wave in the air, which has a significantly lower heat transfer factor than water, or a water polymer emulsion, and therefore slower cooling, is maintained.

According to an advantageous embodiment of the method according to the invention for producing a side wave, the hardened side waves are tempered after the hardening process in an annealing process. Through diffusion processes in the steel structure, the material "relaxes" and any residual stresses in the side shaft can be reduced, which raises the load limit of side shafts, where failure is expected 300 ° C. Tempering is preferably carried out directly after the hardening process, whereby the cooling does not have to be interrupted, it only has to be slowed down at a temperature between 150 ° C. and 300 ° C. The side waves can directly during the cooling with the hardness be cooled only to 300 ° C and kept at this temperature.

Before the hardening process, a spline area or an external toothing for the positive transmission of a torque is provided on the side shafts in the end areas. The spline region can be provided by grooves in the end region, which run in the direction of the longitudinal axis, milled out, punched or cut out in a machining production step. Furthermore, the spline region can be provided by incorporating corresponding recesses during the deformation of the side wave.

Further advantages and features of the invention will become apparent from the following description of the drawing. In this shows:

Fig. 1: a side shaft according to the invention in a perspective view with a partially cut section.

In Fig. 1, a side shaft 10 for transmitting torque is shown. Such side shafts 10 are suitable for transmitting the torque between a differential and a wheel of a vehicle. Between the side shaft 10 and the differential or the wheel is usually a synchronous handle, arranged for example a tripod joint. However, other types of constant velocity joints are also suitable for this purpose. To transmit the torque between the side shaft 10 and the corresponding input portion of the constant velocity joint, a spline region 20 is formed on the side shaft 10. In order to clarify and illustrate the state which arises after a first forming step according to the invention, there is no at the end of the side shaft 10 pointing to the left in FIG

Spline area 20 emerged.

The side shaft 10 is designed as a tube shaft. Semifinished products for producing side shafts 10 according to the invention are pipe sections which may be sections of pipes from mass production. Preference is given to using pipe sections made of the steel material C-45. The semi-finished products have a first outer diameter Di and a first wall thickness Si. During the forming, a second outer diameter D ₂ and a second wall thickness S _{2 are} set in the end sections 12. The shaft portion 16 substantially corresponds in size to the semi-finished product, which may be a pipe section from mass production. Therefore, the ratio of the dimensions (Di, Si) of the end portions 12 to the dimensions (D ₂ , S ₂ ) of the shaft portions 16 can also be measured on a manufactured side shaft 10 and the degree of deformation Phi can be determined. During the forming step in the rotary swaging process, the tube is compressed. The wall thickness Si changes and the value S _{2 is established} . Si can be between 0.5mm and 5mm. Di can be between 10 mm and 50 mm, preferably between 25 mm and 40 mm. After forming with a degree of deformation Phi of less than 0.3, the side shaft 10 can be tapered at assumed initial values Di = 30mm and Si = 5 mm in the end regions 12 to D ₂ = 25 mm, in which a wall thickness of about S ₂ = 6 mm is expected.

The end portions 14 are formed by a rotary swaging according to DE 199 52 229 B4 transforming from a semi-finished product, which has a uniform diameter Di over the entire length.

To enable a high degree of deformation Phi, the semi-finished product must have sufficient ductility, since the forming usually does not take place at high temperatures. The amount of carbon, which is the steel material for Ensuring sufficient hardenability must be added is therefore limited in the prior art. One is forced to more expensive alloying elements, such. As chromium, vanadium, titanium, molybdenum and / or nickel. This significantly increases the purchase price of the semi-finished products. To overcome this disadvantage and to be able to use a low-cost material with a relatively high carbon content, the present invention restricts the degree of deformation to a value of less than 0.3, preferably less than 0.28, more preferably less than 0.27. At these, relatively low degrees of deformation of the side shaft 10, there is no cracking during forming.

Claims

claims

1. side shaft (10) for transmitting torque between an axle differential and a wheel of a motor vehicle, wherein the side shaft is at least partially made of a steel material, designed as a tubular shaft, and comprising:

a longitudinal axis (L),

a shaft portion (16) having a first outer diameter (Di) and a first wall thickness (Si),

characterized in that

at least one end portion (12) of the side shaft (10) having a second diameter (D ₂ ) and a second wall thickness (S ₂ ) is made of a low alloy carbon steel, most preferably a C-45 steel.

2. side shaft according to one of the preceding claims, characterized in that the end portion is produced by at least partial forming, preferably rotary swaging, of the shaft portion (16).

3. side wave according to the preceding claim, characterized in that the degree of deformation Phi = In [(Di-Si) / (D ₂ -S ₂ )] of the amount is less than or equal to 0.3.

4. side shaft according to one of the preceding claims, characterized in that the outer diameter (Di) of the shaft portion (16) is greater than the diameter (D ₂ ) of the end portion (12).

5. side wave according to one of the preceding claims, characterized in that the steel, from which at least the end portion is made, a carbon content of more than 0.35 wt .-%; in particular more than 0.40 wt .-% and less than 1 wt .-%, preferably less than 0.8 wt .-%, particularly preferably less than 0.6 wt .-%.

Side wave according to one of the preceding claims, characterized in that the steel from which at least the end portion is made comprises less than 0.0008% by weight of boron, less than 0.3% by weight of chromium, less than 0, 3 wt% nickel, less than 0.08 wt% molybdenum, less than 1.65 wt% manganese, less than 0.4 wt% copper, less than 0.10 wt% vanadium and less than 1.0% by weight of alloying constituents.

7. A method for producing a side wave, comprising the steps of:

Providing a tubular section having a longitudinal axis having a first outer diameter (Di) and a first wall thickness (Si), the tubular section at least partially made of one of a low alloy, preferably unalloyed, steel, more preferably carbon steel, most preferably a C-45 Steel is made and forming the tube section so that it has a second outer diameter to the dimension (D ₂ ) and a second wall thickness to the dimension (S ₂ ), characterized

the degree of deformation Phi = In [(Di-Si) / (D ₂ -S ₂ )] is less than or equal to 0.3.

8. The method according to claim 7, characterized in that the degree of deformation is less than 0.27.

The method of any one of claims 7 or 8, further comprising the step of providing a spline area (20) by working out depressions in at least one end region of the side shaft (10), for example by machining.

10. The method according to any one of claims 7 to 9, further comprising the steps

- Heating at least the outer, near-surface edge regions of the side shaft (10) to the Austenitisierungstemperatur, and

- Rapid cooling of the side shaft (10) so that forms a bainitic-martensitic structure, at least in the edge regions.

11. A method for producing a side wave (10) according to any one of claims 7 to 10, characterized in that the steel has a carbon content of more than 0.35 wt .-%; in particular more than 0.40 wt .-% and less than 1 wt .-%, preferably less than 0.8 wt .-%, particularly preferably less than 0.6 wt .-%.

12. A method for producing a side shaft (10) one of claims 7 to 11, characterized in that the side shaft of the transmission of torque between an axle differential and a wheel of a motor vehicle is used.