DRIVE SHAFT WITH INTEGRATED TRIPODE STAR

Description

[0001] The invention relates to a drive shaft for the drive train of a motor vehicle, according to the preamble of claim 1.

[0002] To transmit the drive torque of a vehicle's drive system to the vehicle wheels, constant velocity joints are used in the drive shafts. These joints must compensate not only for angular changes between the vehicle wheels and the drive system, but also for changes in length. Therefore, the wheel-side constant velocity joint is typically a fixed joint, while the transmission-side constant velocity joint usually allows for axial movement. On the drive side, the constant velocity joint is preferably designed as a tripod joint. This tripod joint comprises an outer joint part and an inner joint part that is accommodated by the outer part, with a central body to which three pins are integrally formed, thus creating a tripod star. A roller element is arranged on each pin and supported by a needle bearing. The central part is designed as a ring for mounting on a shaft.The connection between the central body and the shaft is achieved via a splined connection, which is implemented both on the shaft and in the central body. Such a tripod joint is described, for example, in DE 10 2020 212 991 A1, US 2021 / 0372485 A1, DE 11 2007 003 668 T5, DE 10 2011 052 474 A1, US 2017 / 122377 A1, and the generic JP 2017 141945 A.

[0003] Manufacturing a drive shaft equipped with a tripod joint proves to be very complex. First, the tripod joint is usually produced using a forming process and fitted with splined teeth, and the shaft itself must also be splined. Subsequently, the tripod joint must be fitted onto the shaft and axially secured during assembly.

[0004] This is where the present invention comes in. The invention is based on the objective of providing a drive shaft with a tripod joint for the drive train of a motor vehicle, which can be manufactured with minimal effort. According to the invention, this objective is achieved by a drive shaft with the features of claim 1.

[0005] The invention provides a drive shaft with a tripod coupling for the drivetrain of a motor vehicle, which can be manufactured with minimal effort. Because the tripod coupling is formed by a formed section of the shaft body, a one-piece drive shaft is achieved, eliminating the need for complex gear manufacturing and assembly of the tripod coupling onto the shaft. Furthermore, the one-piece design enables the transmission of higher torques compared to a positive-locking connection between the shaft and tripod coupling formed by gearing. Preferably, the tripod coupling is formed by upsetting the shaft. Particularly preferably, the drive shaft is designed as a forged part.

[0006] The shaft body has a tripod star at both ends, with the drive shaft being made of a steel alloy. .

[0007] In a further development of the invention, the shaft body is hollow, in particular tubular. This results in a reduction in the weight of the drive shaft.

[0008] In an embodiment of the invention, the shaft body has a thicker wall thickness in an end section located upstream of the tripod pin of the tripod star compared to a central, preferably cylindrical, section. This increases the torsional stiffness of the shaft in the region of the tripod star, thereby enabling the transmission of higher torques.

[0009] According to the invention, the drive shaft is made of a steel alloy. This allows for cost-effective manufacturing while maintaining high strength. Furthermore, this material enables area-specific hardening. Advantageously, the steel alloy is a high-performance steel, in particular 42 SiCrNbB 8-4, known under the trade name "CPDUR 2000".

[0010] In a further development of the invention, the tripod pins are cylindrical and preferably hardened. Preferably, the tripod star has three tripod pins regularly distributed around its circumference.

[0011] In a particularly preferred embodiment of the invention, the tripod pins are provided with an axial bore. This results in a further reduction in weight.

[0012] In a further development of the invention, the tripod pins each accommodate a roller unit comprising a plurality of roller bodies and preferably formed by a needle bearing.

[0013] The invention further aims to provide a method for the cost-effective production of a drive shaft with a tripod star for the drive train of a motor vehicle. According to the invention, this objective is achieved by a method with the features of claim 10. In this method, a tripod star is formed at both ends of a metal tube, in particular a steel tube, by forming, in particular by upsetting, and each tripod star has at least three circumferentially arranged tripod journals. The tripod star is then machined, with the tripod journals of the two opposing tripod stars being arranged offset from one another.

[0014] In a further development of the invention, the forming process is carried out at least partially by a forging process. This makes it possible to achieve a homogeneous material structure.

[0015] In an embodiment of the invention, the metal tube is formed in such a way that a thicker tube wall thickness is formed in the area of ​​the tripod star than in the middle area of ​​the tube.

[0016] In a further embodiment of the invention, the at least one tripod star is hardened, at least in the region of its tripod journals. Preferably, the hardening process is carried out by means of heat treatment with low-pressure carburizing followed by quenching. This improves the mechanical properties of the surface layer, such as wear resistance. Preferably, the quenching is carried out using a high-pressure gas. Such "dry quenching" eliminates the need to clean the drive shaft after heat treatment.

[0017] In a further development of the invention, the drive shaft is coated with a copper layer, at least in certain areas, before hardening. This achieves a covering of areas not to be hardened, thus preventing carbon absorption. Furthermore, reduced dimensional deviations result from the temperature-independent heat transfer during high-pressure gas quenching, as well as improved mechanical properties, particularly improved fatigue resistance, since no intergranular oxide layer is formed.

[0018] Other embodiments and configurations of the invention are specified in the remaining dependent claims. An exemplary embodiment of the invention is illustrated in the drawings and is described in detail below. The drawings show: Figure 1: Schematic representation of a drive shaft with: Figure 2: Representation of the drive shaft made of Figure 1in longitudinal section; Figure 3: the representation of the drive shaft from Figure 1 without roller body and Figure 4: the representation of the drive shaft from Figure 3 in longitudinal section.

[0019] The drive shaft 1 selected as an exemplary embodiment is made of a steel alloy and comprises a tubular shaft body 11 with a central cylindrical section 12, to which a tapered end section 13 is attached on each side. The two end sections 13 have a thicker wall than the cylindrical central section 12. At their ends, the two end sections 13 each transition seamlessly into a tripod joint 2.

[0020] The tripod star 2 comprises a tripod ring 21, to which three tripod pins 22 are integrally formed around its circumference, each offset from the others by 120 degrees. Each of the three tripod pins 22 is provided with an axial bore 23 in its center. In the exemplary embodiment, the tripod pins 22 are surface-hardened. The two tripod stars 2 located at the ends of the shaft body 11 are arranged with their tripod pins 22 offset from each other by 60 degrees.

[0021] Each tripod pin 22 has a roller unit 3 mounted on it, which is rotatably mounted on the tripod pin 22 via a needle bearing 31. The roller units 3 are axially secured by a retaining ring 32, which engages in a groove 34 provided for this purpose on the tripod pin.

[0022] The drive shaft 1, with the tripod stars 2 arranged on it, is manufactured in one piece from a cylindrical tube using a forming process. First, a forged part with tapered end sections 13 and upset tripod stars is produced. Subsequently, the contour of the tripod stars 2 is pre-milled, and the inner contour 25 of the tripod rings 21 is pre-turned to a precise fit with a tolerance. The entire component is then copper-plated using a dip process. Next, the tripod journals 22 are re-milled to remove the copper layer and subjected to a hardening process involving low-pressure carburizing. This results in a hard surface on the tripod journals 22 with a soft inner core. The tripod journals are then milled to their final contour. Optionally, the shaft body 11 can now be stripped of its copper layer.Subsequently, the roller units 3 with the needle bearings 21 are placed on the tripod pins 22 and axially secured with a retaining ring 32.

Claims

1. Drive shaft for the drive train of a motor vehicle, comprising a shaft body (11), provided with a tripod star (2) on at least one end, comprising at least three tripod pins (22) for taking up one roll unit (3) each, wherein the tripod star (2) is formed by a reshaped section of the shaft body (11), characterised in that the drive shaft (1) is made of a steel alloy, wherein the shaft body (11) has a tripod star (2) on its two ends.

2. Drive shaft in accordance with claim 1, characterised in that the shaft body (11) is formed hollow, in particular tubular.

3. Drive shaft in accordance with claim 2, characterised in that the shaft body (11) has a wall thickness that is thicker in an end section (13) that is in front of the tripod pins (22) of the tripod star (2) than a medium, preferably cylindrical, section (12).

4. Drive shaft in accordance with one of the preceding claims, characterised in that the tripod pins (22) are formed cylindrical.

5. Drive shaft in accordance with one of the preceding claims, characterised in that the tripod star (2) has three tripod pins (22) that are distributed at regular intervals across the circumference.

6. Drive shaft in accordance with one of the preceding claims, characterised in that the tripod pins (22) of the two opposite tripod stars (2) are arranged offset against each other.

7. Drive shaft in accordance with one of the preceding claims, characterised in that the tripod pins (22) each hold a rolling unit (3) that comprises a plurality of rolling bodies that is preferably formed by a needle bearing (31).

8. Drive shaft in accordance with one of the preceding claims, characterised in that the tripod pins (22) are formed hardened.

9. Drive shaft in accordance with one of the preceding claims, characterised in that the tripod pins (22) are provided with an axial bore (23).

10. Procedure for manufacturing a drive shaft in accordance with one of the preceding claims, wherein a tripod star (2) that has at least three circumferentially arranged tripod pins (22) is formed on a metal tube, particularly a steel tube, by reshaping on both ends, following which the tripod star (2) is machined in post-processing.

11. Method in accordance with claim 10, characterised in that the tripod pins (22) are provided with an axial bore (23).

12. Method in accordance with claim 10 or claim 11, characterised in that the at least one tripod star (2) is hardened at least in the area of the tripod pins (22).

13. Method in accordance with claim 12, characterised in that the drive shaft is provided with a copper layer at least in some areas before hardening.