Method for Producing a Leaf Spring, and Leaf Spring

Abstract

The present disclosure relates to a method for producing a leaf spring 1 for a vehicle axle suspension, wherein the at least one spring arm 5 bordering on a clamping portion 2 is formed from a rod-shaped preliminary material 7, 8 by a rolling process. By the rolling process for shaping the leaf spring a preliminary material rod 7, 8 having a rounded cross-sectional geometry is rolled out to produce a rectangular cross-sectional geometry in the clamping portion 2 and in the at least one spring arm 5, and thus the portion of the preliminary material rod 7, 8 provided for forming the clamping portion 2 in the finished leaf spring 1 is also reshaped by the rolling process and as a result a rolled structure is also formed therein.

Claims

1-17. (canceled)

18. A method for producing a leaf spring of a vehicle axle suspension comprising: at least one spring arm, which adjoins a clamping portion and is formed out of a bar-shaped base material by means of a rolling process, wherein, the rolling process for forming the leaf spring comprises a base material bar having a rounded cross-sectional geometry that is rolled out into a rectangular cross-sectional geometry in the clamping portion and in the at least one spring arm, wherein, the base material bar of the rolling process for forming the clamping portion in the leaf spring is reshaped and a rolled microstructure is also formed therein, a surface layer is mechanically removed from the base material bar before the base material bar for forming the leaf spring of the rolling process is rolled out, and the rolling out of the at least one spring arm is carried out in a direction from the clamping portion to its other end in such a way that the cross-sectional area is reduced in at least one portion of the spring arm.

19. The method of claim 18, wherein the rolling out of the clamping portion of the leaf spring is carried out with a reshaping rate of 15% or more.

20. The method of claim 18, wherein the cross-sectional geometry of the base material bar is circular.

21. The method of claim 18, wherein the base material bar for forming the clamping portion is reshaped by more than 25 to 30%.

22. The method of claim 18, wherein the circular cross-sectional geometry of the base material bar is created by removing the surface layer.

23. The method of claim 22, wherein the surface layer is carried out by mechanically working the base material bar with a defined cut.

24. The method of claim 18, wherein the rolling process is carried out several times.

25. The method of claim 18, wherein a leaf spring comprising two spring arms is produced.

26. The method of claim 18, wherein the base material bar is rolled out of spring steel and is heated to curing temperature after a surface layer has been removed and before the rolling process, and the rolling process is carried out at the same curing temperature and a formed leaf spring is subsequently cooled in order to freeze the rolled microstructure.

27. The method of claim 18, wherein the rolling out of the spring arm is carried out under an effect of a tensile load acting on the base material bar and an associated elongation.

28. A leaf spring of a vehicle axle suspension, comprising: a clamping portion formed by a first and a second contact surface and comprising at least one spring arm integrally formed thereon and formed by a rolling process, wherein the clamping portion comprises a rolled microstructure formed by the rolling process, and a reshaping rate and associated grain elongation reduces towards the short sides, the at least one spring arm being rolled out to form a parabolic spring.

29. The leaf spring of claim 28, wherein the clamping portion has a smaller width than the at least one spring arm integrally formed thereon.

30. The leaf spring of claim 18, wherein a fastening element is formed at the end of the at least one spring arm that is opposite the clamping portion.

31. The leaf spring of claim 18, wherein the leaf spring comprises two spring arms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 schematically shows a parabolic spring comprising a clamping portion and a spring arm integrally formed thereon,

[0019] FIG. 2 shows a parabolic spring according to a further embodiment comprising two spring arms integrally formed on its clamping portion,

[0020] FIG. 3a, 3b schematically shows the cross-sectional variation when producing the parabolic spring from FIG. 1 proceeding from a hot-rolled base material bar into various portions of the parabolic spring (FIG. 3a), and shows a plan view depicting the change in width (FIG. 3b),

[0021] FIG. 4: is a schematic representation of an image of a microstructure of a base material bar in a normalized state, and

[0022] FIG. 5: is a schematic representation of a microstructure from the clamping portion of the parabolic spring from FIG. 1 with a sectional plane in the longitudinal extension of the parabolic spring.

DETAILED DESCRIPTION

[0023] A parabolic spring 1 includes a clamping portion 2 comprising an upper contact surface 3 and a lower contact surface 4. The clamping portion 2 is used to connect the parabolic spring 1 to the axle of a vehicle. The connection to the axle takes place as is known for conventional parabolic springs, and therefore does not have to be described in more detail at this stage. A spring arm 5 is integrally formed on the clamping portion 2, the end of which arm is formed so as to provide a fastening means for connecting the parabolic spring 1 to the chassis of a vehicle at an eye 6. The parabolic spring 1 is formed by way of a rolling process, as will be explained in the following with respect to FIGS. 3a and 3b. The spring arm 5 is rolled out in the shape of a parabola and therefore has a cross-sectional area that reduces successively proceeding from its clamping portion 2 in the direction of the eye 6.

[0024] FIG. 2 shows a further parabolic spring 1.1, on the clamping portion 2.1 of which two spring arms 5.1, 5.2 are integrally formed. The two springs arms 5.1, 5.2 have an eye 6.1, 6.2 at their ends. In the parabolic spring 1.1, the clamping portion 2.1 is eccentric. This is due to the specific design of the parabolic spring 1.1.

[0025] The production method for producing the leaf spring 1 is described in more detail in the following. The leaf spring 1.1 is produced in the same manner.

[0026] The starting product for producing the parabolic spring 1 is a base material bar 7 having a rounded cross-sectional geometry. The base material bar is a hot-rolled bar, such as are known, made of spring steel.

[0027] In a first step, the surface layer is removed from the base material bar 7 by mechanical working, and in particular by a paring process known per se for the described embodiment. In the embodiment shown, a surface layer of approximately 0.8 mm is removed from the base material bar 7. The thickness of the surface layer to be removed is indicated by dashed lines on the base material bar in FIG. 3a. The base material bar 7 that has been freed of its surface layer is denoted in FIG. 3a by reference sign 8. Removing the surface layer means that surface defects are removed, for example a decarburization layer, scale, surface imperfections and the like. The cylindrical lateral surface of the base material bar 8 then has a significantly improved surface for the subsequent rolling process. In any case, hitherto existing surface inadequacies are not rolled into the leaf spring and do not remain part thereof.

[0028] In a subsequent step, the base material bar 8 is heated to its curing temperature. In the embodiment shown, the base material bar 8 is heated to its austenitization temperature. The base material bar 8, at its curing temperature, is subsequently rolled once or several times, in particular in order to form its clamping portion 2 and to form its spring arm 5. FIG. 3a shows the cross-sectional geometries of the parabolic spring 1 from the region of the clamping portion 2, the spring arm 5 and the roll-out end, which is also part of the spring arm 5. The position of the cross sections with respect to the parabolic spring 1 are shown with reference to FIG. 3b. The parabolic spring in FIG. 3 is shown to be reduced in length. The roll-out end is rolled so as to have a constant thickness. The eye 6 is formed therefrom in a subsequent step.

[0029] In order to avoid the rolling part cooling too much, it can be intermediately heated once or several times, in particular in those portions which have not yet been rolled out.

[0030] The rolling process is thus carried out at the same heat and subsequently tempered after the parabolic spring 1 has been formed. This means that the rolled microstructure formed during rolling is frozen, but recrystallization is prevented. The roll-out of the spring arm is carried out under the effect of a tensile load such that the roll-out is associated with an elongation of the base material bar 8. If specific short sides or edge formations are desired, it can be useful to set these by vertically rolling the short sides.

[0031] The plan view of the parabolic spring in FIG. 3b highlights the particular narrowing of the clamping portion 2 compared with the spring arm 5. It should be noted that this already justifies a weight reduction. On account of the narrowing in the region of the clamping portion 2 compared with the spring arm 5, only a narrower design of U-bolt plates and fifth-wheel plates is required to connect the parabolic spring 1 to a vehicle axle. This also leads to a weight reduction. Installation spaced is also saved. As such, parabolic springs of this kind, when arranged beside one another horizontally, are positioned closer to one another. The narrowing offers sufficient space in order to arrange a fifth-wheel plate and U-bolt screws therein.

[0032] FIG. 4 is schematic representation of an image of the microstructure of the base material bar 8 with a sectional plane in the longitudinal extension thereof. The microstructure does not have a clear orientation. The grains have a largely symmetrical contour.

[0033] FIG. 5 is a schematic representation, by comparison, of an image of the microstructure from the clamping portion 2 of the parabolic spring 1, also with a sectional plane in the longitudinal extension of the parabolic spring 1. As a result of rolling out the clamping portion 2, as described above, the rolled microstructure shown in FIG. 5 has been formed. The microstructure is stretched, which results from a grain elongation. This microstructure is responsible for the above-described positive mechanical properties of the subsequent tempered microstructure.

[0034] A parabolic spring comprising integrally formed eyes is shown by way of example in the drawings. The advantages of the present disclosure also result in the same way in the case of spring leaves which do not comprise fastening means, such as eyes. Therefore, in the case of a spring assembly, each layer can be produced using the concept according to this present disclosure.

[0035] The present disclosure has been described on the basis of embodiments. Without departing from the scope of the current claims, there are numerous other embodiments for a person skilled in the art to be able to implement the present disclosure without further details regarding these embodiments having to be provided.

LIST OF REFERENCE SIGNS

[0036] 1, 1.1 Parabolic spring [0037] 2, 2.1 Clamping portion [0038] 3 Upper contact surface [0039] 4 Lower contact surface [0040] 5, 5.1, 5.2 Spring arm [0041] 6, 6.1, 6.2 Eye [0042] 7 Base material bar [0043] 8 Pared base material bar