Roller bearing mounted shaft

Abstract

A roller-bearing mounted shaft may include a shaft tube having a shaft outer face with at least one rolling body running face. The shaft tube may have at least one functional element joined thermally thereto, wherein the shaft tube is formed as a welded and drawn tube and includes a carbon content of greater than 0.45 percent by mass.

Claims

1. A roller-bearing-mounted shaft, comprising: a shaft tube having a shaft outer face with at least one rolling body running face, the shaft tube having at least one receiving element joined thermally thereto; wherein the shaft tube includes a cold-drawn steel material having a high-frequency inductively welded seam extending along a longitudinal axis of the shaft tube, and wherein the cold-drawn steel material of the shaft tube includes a carbon content of greater than 0.45% by mass, a phosphorus content of less than 0.025% by mass and a sulphur content of less than 0.025% by mass; and wherein the at least one rolling body running face extends circumferentially about the shaft tube with respect to the longitudinal axis and transverse to the high-frequency inductively welded seam, and wherein the shaft outer face defining the at least one rolling body running face is case hardened via localized heat treatment.

2. The shaft according to claim 1, wherein the hardened rolling body running faces has a surface hardness of greater than 58 HRC.

3. The shaft according to claim 1, wherein the shaft tube includes a wall thickness between 2 mm and 4 mm.

4. The shaft according to claim 1, wherein the shaft tube is a camshaft.

5. The shaft according to claim 1, wherein the at least one receiving element is at least one of a cam, a bearing ring, a positioning aid, a gearwheel and a balancing weight.

6. The shaft according to claim 1, wherein the shaft tube is one of an outer shaft of an adjustable camshaft and a balance shaft.

7. The shaft according to claim 6, wherein the at least one rolling body running face has a surface hardness of greater than 58 HRC.

8. The shaft according to claim 1, wherein the at least one rolling body running face includes a wall thickness in a radial direction with respect to a longitudinal axis of the shaft tube, and wherein the at least one rolling body running face is case hardened in a radially outer portion of the wall thickness without heat modification to a radially inner portion of the wall thickness with respect to the longitudinal axis.

9. An internal combustion engine, comprising: a shaft having a longitudinal axis and at least one rolling body running face extending circumferentially to the longitudinal axis on a shaft outer face, wherein the shaft is mounted via at least one roller bearing, the at least one roller bearing having at least one rolling body which rolls directly on the at least one rolling body running face of the shaft; wherein the shaft is a high-frequency inductively welded tube of a cold-drawn steel material defining a longitudinally extending weld seam and a case-hardened outer surface extending along the at least one rolling body running face and transverse to the weld seam; and wherein the cold-drawn steel material of the high-frequency inductively welded tube includes a carbon content of greater than 0.45 percent by mass, a phosphorus content less than 0.025% by mass and a sulphur content of less than 0.025% by mass.

10. The engine according to claim 9, wherein the case-hardened outer surface of the at least one rolling body running face has a surface hardness of greater than 58 HRC.

11. The engine according to claim 10, wherein the at least one rolling body running face includes a wall thickness in a radial direction with respect to a longitudinal axis of the shaft, and wherein the case-hardened outer surface of the at least one rolling body running face is on a radially outer portion of the wall thickness without heat modification to a radially inner portion of the wall thickness with respect to the longitudinal axis.

12. A roller-bearing-mounted shaft, comprising: a high-frequency inductively welded shaft tube of a cold-drawn steel material having a longitudinal axis and an outer face defining at least one rolling body running face configured to mount at least one roller bearing; wherein the high-frequency inductively welded shaft tube defines a weld seam extending along the longitudinal axis and the cold-drawn steel material includes a carbon content of greater than 0.45% by mass, a phosphorous content of less than 0.025% by mass and a sulphur content of less than 0.025% by mass; and wherein the at least one rolling body running face extends circumferentially about the high-frequency inductively welded shaft tube with respect to the longitudinal axis and transverse to the weld seam, and wherein the outer face defining the at least one rolling body running face is case hardened to include a localized surface hardness of greater than 58 HRC.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) A preferred exemplary embodiment of the invention is shown in the drawing and is explained in the description below.

(2) The single FIG. 1 shows a sectional diagram through a roller-bearing-mounted shaft according to the invention, which is formed as a camshaft.

DETAILED DESCRIPTION

(3) According to FIG. 1, a roller-bearing-mounted shaft 1 according to the invention has a shaft tube 2 having a shaft outer face that is formed in some regions as a rolling body running face 3. In the present case, the shaft 1 is formed as a camshaft and has a plurality of cams 4 joined thermally thereto. Of course, other functional elements, such as bearings, positioning aids or gearwheels can also be joined thermally to the shaft tube 2 instead of the cams 4. For example, if the shaft 1 is formed as a balance shaft, functional elements formed as balancing weights are arranged thereon. According to the invention, the shaft tube 2 is then formed as a welded and then drawn tube and has a carbon content of >0.45% by mass. It is thereby possible to harden, in particular induction harden, the shaft tube 2 on its outer face, i.e. in the region of the rolling body running faces 3 and thereby allow direct, wear-free rolling of rolling bodies 5 on the rolling body running face 3 of the shaft tube 2 in the first place. For this use, a carbon content of >0.45% by mass is necessary, it being impossible to weld such tubes previously. However, it is now possible thanks to a novel manufacturing method to produce welded and drawn tubes having a carbon content of over 0.45% by mass and use them for example as camshafts. To this end, a high-frequency induction welding method is used.

(4) The shaft 1 according to the invention offers the great advantage of economical and thus cost-effective manufacture in comparison with conventional shafts having a seamlessly drawn shaft tube. Furthermore, better diameter tolerances can be formed both on the outer diameter and on the inner diameter of the shaft tube 2. Owing to the much reduced manufacturing tolerances, it is also possible to join a plug in the inner diameter of the shaft tube 2 without additional machining. Furthermore, better concentricity of the inner diameter to the outer diameter of the shaft tube 2 can also be produced, producing fewer runouts of the joined plug. Owing to the reduced tolerances and the reduced edge decarbonisation, an oversize for subsequent machining, in particular what is known as a grinding allowance, can also be reduced. Bevels on the inner diameter of the shaft tube 2 that are necessary for guiding can also be made smaller.

(5) In general, the shaft tube 2 has a phosphorus content and a sulphur content of <0.025% by mass. Such low phosphorus and sulphur contents increase the vibration fatigue strength and tolerable Hertzian stresses of the shaft tube.

(6) At least the regions of the rolling body running faces 3 are case-hardened, for example induction-hardened, as described above and have a surface hardness of >58 HRC. Owing to the hardening of the rolling body running faces 3, direct, wear-free rolling of the rolling bodies 5, roller bearings 6 on the shaft outer face is possible, as a result of which the roller bearing 6 per se can be kept simple. A wall thickness of the shaft tube 2 is between 2 and 4 mm.

(7) Of course, the shaft 1, in particular in if it is formed as a camshaft, can be joined in a module in a similar manner to a balance shaft, it of course also being conceivable for the camshaft to have fixed cams 4 and an inner shaft on the inside, which is connected to the cams mounted rotatably on the outer shaft, i.e. in the present case on the shaft tube 2.