GB2073061A - Journal cross for a Cardan cross coupling - Google Patents

Abstract

The invention relates to a journal cross for a Cardan cross coupling of the kind produced by forging, and which consists of a centre part and four journals with their axes lying substantially in one plane. The invention is characterised in that on the centre part of the journal, viewed in the direction of the axis of rotation, the external contour (10) at the transition between two adjacent journals is rounded out by material- removing machining to form a type of concave chamfer (8). Preferably, the concave chamfer surface is a cylindrical surface. <IMAGE>

Description

SPECIFICATION Journal cross for a cardan cross coupling The invention relates to a journal cross for a Cardan cross coupling of the kind produced by forging, and which consists of a centre part and four journals with their axes lying substantially in one plane. Such a journal cross is known, for example, from German Patent Specification No.

28 25 556.

The known journal cross consists of a centre part and four journals which as a rule lie in one plane and on intersecting axes in pairs. A journal cross like this is normally drop forged from steel and then machined mainly only at the ends of the journals to accommodate the roller or sliding bearing. The known journal cross also has a central bore perpendicular to the intersection plane of the journal cross.

The introduction of power to the journal cross is effected from one of the two coupling forks which form the cross coupling, and which transmits the torque to two journals in the form of a tangential force. The torque is transmitted further via the other two journals, to the second coupling fork. In the process the journals themselves are subjected substantially to bending stress in their circular cross-section. Due to the fact that the torque is not introduced from a hub-type centre part-as in a wheel-but is picked up and transmitted further by the journals, the stressing direction on the journals is pairwise in a clockwise direction and pairwise in a counter-clockwise direction. Each journal thus has an adjacent journal which is deformed away from it when torque is supplied.

The greatest local material stress occurs here in the transitional zone between the journal and the centre part of the journal cross. This stress is even greater when the centre part has a central axial bore.

One disadvantage of the known design of such a journal cross is that the stress at this point can be so high that the capacity of the journal cross for transmitting torque is less than that of the other participating components of the cross coupling.

The invention is based on the problem of designing a journal cross, particularly one provided with a central bore, in such a way that, for a given set of main dimensions, stressing of the material is less than has been the case hitherto.

According to this invention the journal cross is characterised in that on the centre part, viewed in the direction of the axis of rotation, the external contour at the transition between two adjacent journals is rounded out by material-removing machining to form a type of concave chamfer.

Thus, the invention is based on the realisation that the shaping of the transition from the circular cross-section of the journal to the solid centre part of the journal cross and on again to the adjacent journal has a special significance.

Particularly when there is a bore, the tensile stress in the transitional zone increases considerably. A central axial bore through the journal cross is necessary, for example, to allow an actuating element for a tilt-inhibiting device to pass through.

However, the dividing plane of the drop-forging die part extends right in the gusset between two journals. The required slope on the surface terminates in a narrow flash with a small crosssection. The stress lines extend through this flash, becoming very strongly concentrated from the journal towards the small cross-section. The zone of highest tensile stress therefore lies in the region with the smallest cross-section. This leads to an increased risk of local over-stressing, with plastic deformation and the formation of cracks.

According to the invention, at the said transition between two journals, the journal cross is provided with a concave chamfer which extends in the axial direction. This concave chamfer lies closer to the centre of the journal cross and cuts out a certain area of the solid centre part. Material is thus removed intentionallynln this way the transitional zone between two journals is extended. During loading there is a deliberate deflection of the stress lines into a wider area. The advantage of this resides in the fact that basically not only the edge zone of the journal facing the adjacent journal is involved in bearing, but zones lying deeper within the journal cross-section are also involved in the tensile stress and bending strain.At a greater distance from the external diameter of the journal there is more cross-section available so that a supporting effect and, viewed as a whole, increased resistance to bowing is afforded. The stress lines are displaced into zones lying deeper in the journal and the centre part.

In this way, a considerably increased capacity for torque loading and, in a journal cross with a central bore, complete compensation for the loss of strength has been successfully achieved, so that a journal cross constructed in this way is endowed with the same capacity for torque loading as a journal cross without a bore.

A concept of the invention which develops the idea further resides in constructing the concave chamfer between two journals not only as a single cylindrical surface but as a continuously arched toroidal external surface. It may also be formed as a rounded out area composed of a plurality of surfaces. A particularly advantageous method for production is to machine the concave chamfer with a toroidally curved external surface symmetrical to the plane which is formed by the journal axes, this surface being adjoined on either side by cylindrical casing-type surfaces at a specific angle to the longitudinal axis of the journal cross, again being symmetrical to the said plane of symmetry. The transition from the unmachined centre to the journals is thereby made more flowing and the introduction of force is correspondingly smooth and free of jerks.

Two embodiment examples of the invention will now be described with reference to the accompanying Drawings, in which: Figure 1 is a view of a journal cross, looking in the direction of the axis of rotation, of the first embodiment.

Figure 2 is a partial section along the line Il-Il in Figure 1.

Figure 3 is a view onto a journal cross, looking in the direction of the axis of rotation, of the second embodiment, and, Figure 4 is a partial section along the line IV--IV in Figure 3.

Figures 3 and 4 show the same reference symbols as Figures 1 and 2 wherever the relevant component parts correspond.

Figure 1 shows the journal cross 1 with a centre part 2, four journals 3, 4, 5, 6, and a central bore 7. The invention may also be applied to a journal cross without a bore. As shown, a particularly deeply incised concave chamfer 8 is provided between the journals. The arrows 9 show one possible loading direction into the journal, from which it will be appreciated that, for example, in the concave chamfer 8 between the journals 4 and 5 and also between the journals 3 and 6, particularly high prolonged alternating stresses arise. With loading in the direction of the arrows 9a, the highest stresses occur between the journals 3 and 4 and the journals 5 and 6.

Figure 2 shows a section through the centre part 2 in the vicinity of a concave chamfer 8, the dotted lines 10 (see also Figure 1) showing the contour appertaining to the transitional zone between two adjacent journals which would have been present without the measures taken in accordance with the invention. The zone which would have been most highly stressed lies within this cross-section enclosed by the contour 10.

Instead, due to the concave chamfer with a radius R which is, for example, cylindrically shaped, zones with a greater cross-section in the centre part 2 are involved in the tensile stress loading.

Referring to Figure 3 of the second embodiment of journal cross 20 incorporates features set out in Claims 4-6. This embodiment is basically the same as the first embodiment with extended machining in the vicinity of the concave chamfer 18, looking in the direction of the axis of rotation. Thus, comparing Figure 3 with Figure 1, it can be seen that the rounding out of the concave chamfer 1 8 with a radius R' extends into that region of the gusset between two adjacent journals which is visible on the end face of the journal cross.

Figure 4, is a section similar to Figure 2 and shows the machining of the concave chamfer 1 8, the central part of which, in the zone 12, is a torus surface with the centre 14, which centre, simultaneously, can also be the centre of the entire journal cross 20. Tangentially adjoining either side of this central part there are cylindrical surfaces in the areas 11 and 13, which extend symmetrically to the plane of the centre line of the journal. The cylindrical surfaces are each created preferably by material-removing machining using a tool, e.g. a milling machine, which has cutting edges with the radius R'. The journal cross is brought up to the toolor vice versa-in such a way that firstly the cylindrical surface, e.g. in the zone 11, is made by removing material. The tool or the journal cross is then pivoted around the centre 14, simultaneously continuing the machining so that with rotation through the angle 2a the torus surface is formed in the zone 12. As the tool is moved on in a straight line into the zone 13, the symmetrically arranged second cylindrical surface is produced.

By means of continuous uninterrupted machining a smooth transition, i.e. without any breaks or kinks, is produced between the surfaces of the zones 11 and 12 and 12 and 13, so that the desired constant distribution of the tensile stress over a wide cross-section is achieved.

Claims (8)

1. A journal cross for a Cardan shaft cross coupling of the kind produced by forging, and which consists of a centre part and four journals with their axes lying substantially in one plane, characterised in that on the centre part, viewed in the direction of the axis of rotation, the external contour at the transition between two adjacent journals is rounded out by material-removing machining to form a type of concave chamfer.

2. A journal cross according to Claim 1, characterised in that the concave chamfer section is a cylindrical surface.

3. A journal cross according to Claim 1 or 2, characterised in that the journal cross has a bore extending along its axis of rotation.

4. A journal cross according to Claim 1 or 3, characterised in that the concave chamfer between two adjacent journals is rounded in the form of an arched toroidal external surface.

5. A journal cross according to Claim 1 or 3, characterised in that the concave chamfer, viewed in a longitudinal section extending at 45 degrees between two adjacent journals is composed of a central section which is part of a torus surface, and two sections smoothly adjoining this on either side, which are sections of a cylindrical surface.

6. A Journal cross according to Claim 5, characterised in that the axes of the cylinder surfaces which are part of the concave chamfer are inclined at approximately 1 5 degrees relative to the longitudinal axis of the journal cross.

7. A process for producing a journal cross according to Claim 5, characterised in that the concave chamfer consisting of a plurality of sections between two adjacent journals is produced by material-removing machining using a tool which has cutting edges with a radius R', the following machining steps being carried out: a) the tool is moved in a straight line along an axis inclined at the angle a relative to the longitudinal axis of the journal cross, b) the tool is pivoted relative to the journal cross during the machining process, through the pivot angle 2a, around an axis of rotation parallel to the longitudinal axis of the journal cross, c) the tool is moved in a straight line along an axis inclined at the angle a relative to the longitudinal axis of the journal cross.

8. A journal cross bearing for a Cardan shaft cross coupling constructed, arranged and adapted for use substantially as hereinbefore described with reference to Figures 1 and 2, or 3 and 4 on the accompanying drawings.