TECHNICAL FIELD

The invention relates to a component for a splined connection, comprising a shaft piece which has longitudinal ridges and grooves mutually alternating in the circumferential direction and is intended at a first end to accommodate in axial movement a shaft piece with complementary ridges and grooves. The invention also relates to a method and a device for production of such a component.

BACKGROUND

Such splined components, which are subject to severe stresses in particularly heavy vehicles, are usually manufactured by machining from forged solid high-strength steel. The great strength requirements make these components heavy, difficult to machine and expensive, all of which runs counter to a general endeavour to keep down costs, and particularly weight, of vehicle parts with a view to reducing the fuel consumption of vehicles.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide components for splined connections which can be produced with lower weight and at smaller cost than previously without resulting in inferior strength characteristics.

This is achieved by the features indicated in the attached claims.

According to one version of the invention, the component with the ridges and grooves is produced by press hardening of a thin-walled piece of tube made of boron steel. Thin- walled components of very high-strength lightweight structure can thus be achieved without any machining at all, thereby making it possible to reduce the component's weight and manufacturing cost.

The press hardening comprises forming of the ridges and grooves by radial deformation of the piece of tube.

A second end of the component is connected to a shaft component by laser welding. By laser welding it is possible to avoid loss of hardening due to powerful heating.

The shaft component may be a coupling fork for a universal coupling which is likewise produced by hot forming and press hardening of a thin- walled piece of boron steel.

The coupling fork may be produced by connecting together, e.g. by adhesive bonding, two thin-walled fork pieces which fit into one another. It is thus possible to use thin- walled parts which are easy to form and can be joined together to provide great strength corresponding to that of an equivalent thick- walled fork piece.

Other features and advantages of the invention are indicated by the following detailed description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts part of a universal shaft made up of components according to the invention;

FIG. 2 depicts in exploded view components according to the invention;

FIG. 3 depicts in section and with parts cut away a splined connection according to the invention; and FIGS. 4 and 5 depict schematically in different working positions an arrangement for for the forming of a splined component according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIGS. 1 and 2 depict a propeller shaft denoted generally by ref. 10 and provided with components according to the present invention. The propeller shaft 10 comprises in a known manner a torque tube 12, one end of which has a splined coupling 20 to a universal coupling fork 40. Only the torque tube 12 itself is of conventional design, whereas the main components of the splined coupling 20 and the coupling fork 40 are configured according to the invention.

As may be seen in particular in FIG. 3, the splined coupling 20 comprises an inner splined component 22 and an outer splined component 32. In a conventional manner, the inner splined component 22 has external ridges 24 and external grooves 26, whereas the outer splined component 32 has corresponding internal ridges 34 and internal grooves 36, so that the inner splined component 22 can by telescopic movement be accommodated in the outer splined component 32 and that torque can at the same time be transmitted between the components 22, 32.

According to the invention,, each of the splined components 22 and 32 is produced by press hardening of a thin- walled piece of tube made of unhardened boron steel. It is known per se that a hardenable steel with a small addition of boron can be press- hardened to become an ultra high-strength steel with an elastic limit (yield point) of approximately 1100 MPa. Press hardening here means hot forming of a heated workpiece which is hardened by rapid cooling.

Each of the splined components 22, 32 may be formed by a forming arrangement 60 schematically depicted in FIGS. 4 and 5. A fixed inner forming element 62 has an outside contour matching the inside contour of the splined component 22, 32 which is to be produced. Radially movable outer forming elements 68 are evenly distributed round the inner forming element 62 and can be driven to and fro by linear actuators 72.

A splined component such as the component 22 is formed from a thin-walled piece of tube or tube blank 30 which has been furnace-preheated to, for example, 94O0C. The heated tube blank 30 is slipped over the inner forming element 62 as depicted in FIG. 4. Thereafter all the actuators 72 are activated so that each of the movable forming elements 68 presses the portion of the tube blank 30 which faces it radially into a relating recess 64 in the fixed forming element 62. The shape of the movable forming elements 68 may be such that in the applied position they precisely cover the whole circumference (not depicted) of the blank 30, i.e. they not only engage in the recesses 64 but also with the portion of the blank 30 which rest on the protrusions 66 between the recesses 64. On both sides of each of the movable forming elements 68 which enter the recesses 64, however, it is possible, as indicated in FIGS. 4 and 5, for there to be instead separate forming elements 70 which resiliently engage with the portions of the tube blank 30 which rest on the protrusions 66.

The respective outer ends 28 and 38 facing away from one another of the coupled- together splined components 22 and 32 are intended, as depicted in FIG. 1, to be connected respectively to the universal coupling fork 40 and the torque tube 12. The ends 28 and 38 therefore maintain a circular cylindrical shape. This is achieved in an undepicted manner by corresponding shape of the inner forming element 62 and the outer forming elements 68 so that the ridges 24, 34 and the grooves 26, 36 terminate in a rounded manner at a distance from the ends 28, 38. According to the invention, the torque tube 12 and the coupling fork 40 are connected to the splined components by laser welding. Using laser welding involves no risk of the hardened parts being heated to such an extent that the steel material loses hardness.

During or at the end of the forming process, the completed splined component 22 is rapidly cooled in a conventional manner, e.g. by water. To this end, the fixed and movable forming elements 62, 68, 70 may be provided with undepicted internal ducts in which the water can circulate. The universal coupling fork 40 is likewise manufactured by hot forming and press hardening of thin- walled unhardened boron steel. As may be seen in FIG. 2, the coupling fork 40 is made up of two parts, viz. an outer fork piece 42 and an inner fork piece 46. Like the splined components 22, 32, the outer fork piece 42 may be formed from an undepicted tube blank, while the inner fork piece 46, which has a bottom 50, may be formed by deep drawing from an undepicted flat sheet blank. Although the fork pieces 42 and 46 in FIGS. 1 and 2 are depicted with a circular cylindrical shape, it is preferable that they actually have a more cup-shaped outer periphery which widens from the region 28 of connection with the splined component 22. Each of the fork pieces 42, 46 further has in a conventional manner a pair of transverse spindle holes 44, 44 and 48, 48 respectively for an undepicted coupling cross. A pair of bearing bushes 52, 52 extend through the spindle holes as pivotable supports for the spindle ends of the undepicted coupling cross. Each bearing bush 52 may be laser- welded to the coupling fork 42. The outer contour of the fork piece 46 has a fine fit to the inner contour of the outer fork piece 42. The fork pieces 42, 46 may be connected together by adhesive bonding.