GB2042126A

GB2042126A - Transmission shaft with splined coupling

Info

Publication number: GB2042126A
Application number: GB7939515A
Authority: GB
Original assignee: Gelenkwellenbau GmbH
Current assignee: Gelenkwellenbau GmbH
Priority date: 1978-11-15
Filing date: 1979-11-15
Publication date: 1980-09-17
Also published as: GB2042126B; JPS5569323A; IT7905250A0; IT1207880B; SE7908613L; RO77140A; FR2441760A1; DD146990A5; FR2441760B1; IT7907086V0; PL219573A1; DE2849541A1; ES484067A1

Abstract

A pair of telescopically arranged shaft parts (6, 11), are each provided with longitudinally arranged splines (7) whereby torque may be transmitted from one shaft part to the other, the inner shaft part (6) being so dimensioned that its outer diameter (D) divided by its inner diameter (d) is less than or equal to 1.2. Such a shaft assembly may be incorporated in a cardan shaft of sufficient strength while considerably reducing the weight thereof, relatively to shafts of prior art. <IMAGE>

Description

SPECIFICATION A cardan shaft Description of invention The present invention relates to a cardan shaft of the type comprising a pair of telescopically arranged shaft parts each shaft part being provided with longitudinally arranged splines, the splines of one shaft part co-operating with the splines of the other, so that torque may be transmitted from one shaft part to the other. Such a cardan shaft will hereinafter be referred to as a cardan shaft of the type specified.

One or both of the cardan shaft parts may be connected to one part of a universal joint, for example a bifurcated yoke, forming part of a Hookes joint.

Cardan shafts of the type specified are disclosed in British Patent Specification No. 1,296,240. The cardan shaft described and illustrated in this Patent Specification has a first bifurcated yoke formed integrally with the shaft partshaving internally arranged splines, the yoke and shaft part being formed from solid material. The other yoke has a shoulder axially extending therefrom, the yoke and shoulder also being formed from solid material.

Such a design has the disadvantage of being heavy because of the amount of material in the construction and furthermore, because of the large amount of material, is expensive to construct.

In order to reduce the cost and weight, the diameter of the shoulder or shaft part could be reduced. However, in this case, the torque or stress which can be transmitted by the shaft is considerably reduced. Furthermore, the interengaging splines of the respective shaft parts will be displaced from the central axis of the shaft by a smaller distance and hence there will be higher contact pressure between the splines which cannot always be compensated for by increasing the axial length of the splines, since the length of the spline section is determined by the required relative axial displacement of the shaft parts to be accommodated.

Other cardan shafts are known, for example as disclosed in West German Patent Specification No.

821,449 in which a bore is formed both in a shaft part and also through a joint fork forming part of the universal joint so that a saving weight is achieved.

However, the bored shaft part and fork has the disadvantage that the bending stiffness is reduced leading to possible deformation. Deformation of the shaft/joint fork gives an adverse effect in the functioning of the shaft and in particular on the bearings associated therewith increasing the load on the bearings and thereby considerably reducing the life of the cardan shaft.

It is an object of the present invention to provide a cardan shaft that overcomes or reduces the abovementioned problems.

According to the present invention we provide a cardan shaft of the type specified wherein the inner shaft part is hollow, the dimensions of such inner shaft part being such that the outer diameter divided by the inner diameter is less than, or equal to, 1.2.

An advantage is gained with such an arrangement compared with the solid shaft part having the same weight but of considerably less diameter, in that the forces acting on the splined connection between the shaft parts are reduced since they decrease as the radial distance between the central axis of the shaft and the spline connection increases thus the life of the shaft will be favourably influenced.

Furthermore, by using a thin-walled tubular section for the inner shaft having relative dimensions of the inner and outer diameters as described above, a considerable weight saving is achieved.

If a hollow shaft has an inner diameter equal to 0.3 to 0.4 of the outer diameter, the moment of resistance is reduced by only about 0.8 to 2.6% compared with a solid shaft. There is however a weight saving of 9% to 16% in relation to the whole shaft. Making use of this knowledge by providing a hollow thinwalled connecting part of a joint member to the inner shaft part, there only needs to be a reinforce mentofthis part of 8% to 10% in order to provide a torque capacity similar to that of a solid shaft.

However, in this case the saving is 60% to 70% compared with the weight of a solid shaft.

Preferably, the inner shaft part carries part of the universal joint such as the bifurcated yoke of a Hookes joint and, when it is required that the cardan shaft capable of transmitting a specific torque, it has been found advantageous that the relationship between the outer diameter of the inner shaft part, the outer diameter being the diameter of the externally splined part of the inner shaft part, and the diameter of rotation of the joint part is such that the diameter of rotation of the joint part divided by the outer diameter of the inner shaft part is less than or equal to 1.7.

The diameter of rotation of the joint part is the diameter of the circular locus of the radially outermost part of the joint part from the axis of revolution.

Each of the above parts forming the cardan shaft may carry part of a universal joint.

In view of the above arrangement, the outer diameter of the externally splined surface of the inner shaft part can be determined, after consideration of the rotational diameter of the yoke of the universal joint.

Thus, the outer diameter of the inner shaft part can be calculated after which the wall thickness of the inner shaft part may also be determined.

The externally splined inner shaft part may be manufactured integrally with a joint part, for example a joint yoke. With such an arrangement the hollow shaft part may be formed by forming a bore, preferably a blind bore, in the centre of the shaft.

Alternatively, it is possible for the externally splined inner shaft part to be formed as a pressed part and secured to a joint part by any suitable method such as welding. For example, the shaft section may be produced as a deep-drawn cup and subsequently welded to the yoke. The externally splined surface may be formed during the drawing or pressing operation during the forming of the shaft part or alternatively, may be formed as a separate operation. The pressed or drawn cup forming the shaft part may have a closed end which is subse quently pierced by a bore or alternatively may be formed with an open end.

The inner shaft part may comprise an externally splined hollow shaft part which in turn may be connected to one end of a connector part, the other end of which connector part is connected to the joint part, the connector part may also be tubular.

The invention will now be described in more detail by way of example only with reference to the accompanying drawings wherein: Figure 1 is a view partly in section of a cardan shaft according to the present invention connecting a pair of universal joints; Figure 2 is a part-sectional view of part of a cardan shaft of the present invention formed integrally with the bifurcated yoke; Figure 3 is a part-sectional view of part of a cardan shaft of the present invention including a bifurcated yoke the shaft part being assembled from two parts; and Figure 4 is a part-sectional view of another cardan shaft of the present invention interconnecting a pair of universal joints.

The cardan shaft shown in Figure 1 comprises two co-axial cardan shaft sections 1 and 2 which carry respective universal joints 3 and 4 at their outer ends.

The cardan shaft section 1 has an inner shaft part 5 provided with externally arranged splines 7. The splines 7 co-operate with internal splines provided on the inner surface of outer shaft part 11, thus allowing relative co-axial movement of the shaft part while preventing relative rotational movement between the shaft parts in order that torque may be transmitted from one to the other. Torque is thus transmitted from one universal joint 3 to the universal joint 4 through the splines 7. The inner shaft part 5 is of hollow tubular-like configuration and provided with an inner cavity 8.

The inner shaft 5 is shown in more detail in Figure 2 and in this case is shown as being constructed integrally with a bifurcated yoke 9. The inner surface of the yoke i.e. the surface extending transversely to the axial direction of the cardan shaft is closed forming a closed end for the cavity 8 formed within the inner shaft part 5. The external surface of the shaft part 5 being provided with longitudinally arranged splines 7 for transmission of torque to the other shaft part.

The outer diameter D of the splined surface of the shaft part 5 is so related to the inner diameter dof the inner shaft part 5 so that the outer diameter D divided by the inner diameter d is equal to or less than 1.2.

The outer diameter D of the inner shaft part 5 is also related to the diameter of rotation R of the joint yoke 9. The respective dimensions of the diameter of rotation R of the joint yoke and the outer diameter of the inner shaft part 5 are such that the rotational diameter of the yoke divided by the outer diameter D of shaft part 5 is equal to or less than 1.7.

Figure 3 illustrates another embodiment of the inner shaft part 5. In this embodiment, the inner shaft part is formed, as a deep drawn cup 10, separately from the joint yoke 9. The cup 10 and the yoke 9 are subsequently connected together by welding. The exterior surface of the cup 10 is provided with splines 7. The end of the cup 10 remote from the joint yoke 9 may be left closed as shown in Figure 3a or it may be provided with an opening or bore as shown in Figure 3b.

The ratio of the outer diameter D compared with the inner diameter d is as aforedescribed in relation to the embodiment shown in Figure 2. Furthermore, the ratio of the outer diameter D relative to the rotational diameter R of the joint yoke 9 is the same as described in relation to the embodiment shown in Figure 2. The joint yoke 9 is once again formed with a closed inner surface which assists in providing the desired stiffness of the assembly.

Referring now to Figure 4, another cardan shaft embodying the invention is illustrated, the principle of construction being similar to that as shown in Figure 1 although in this case the shaft section 1, secured to the yoke 9 of the universal joint 3 is provided with an adaptor part 11 which has an internal splined surface which engages with the externally splined surface 7 of an inner shaft partS.

The inner shaft part 6 is connected to a connector part 12 which in turn is connected to a bifurcated yoke of a universal joint.

Once again, the outer diameter D of the splined external surface of inner shaft part 6 is such that the outer diameter D divided by the inner diameter d of the inner shaft part 6 is less than or equal to 1.2 and the rotational diameter R of the connected yoke 9, divided by the outer diameter D, is less than or equal to 1.7.

Both the joint yokes illustrated in this embodiment are provided with closed inner surfaces transverse to the longitudinal axis of the cardan shaft and since both the adaptor part 11 and connector part 12 are thin-walled members, the resulting cardan shaft is of very light construction.

Claims

1. Acardan shaft of the type specified wherein the inner shaft part is hollow, the dimensions of said inner shaft part being such that the outer diameter divided by the inner diameter is less than or equal to 1.2.

2. A cardan shaft as claimed in Claim 1 wherein the inner shaft is connected to a universal joint yoke and wherein the rotational diameter of the joint yoke divided by the outer diameter of the inner shaft part is less than or equal to 1.7.

3. A cardan shaft as claimed in Claim 2 wherein said shaft part is formed integrally with said joint yoke.

4. A cardan shaft as claimed in Claim 2 wherein said shaft part is formed from a drawn or pressed part and is subsequently connected to said joint yoke.

5. A cardan shaft as claimed in Claim 2 wherein a surface of said yoke transverse to the longituduinal axis of said shaft part is imperforate.

6. A cardan shaft as claimed in any one of the preceding claims wherein said outer shaft part is connected to a universal joint yoke.

7. A cardan shaft as claimed in Claim 2 wherein the said inner shaft part is connected to said universal joint yoke by a hollow connector member.

8. A cardan shaft of the type specified substan tally as hereinbefore described.

9. A cardan shaft substantially as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings.

10. A cardan shaft of the type specified including an inner shaft part substantially as hereinbefore described with reference to and as illustrated in Figure 2 of the accompanying drawings.

11. A cardan shaft of the type specified including an inner shaft part substantially as hereinbefore described with reference to and as illustrated in Figure 3 of the accompanying drawings.

12. A cardan shaft substantially as hereinbefore described with reference to and as illustrated in Figure 4 of the accompanying drawings.

13. A cardan shaft of the type specified including any novel feature or combination of features as described herein and or illustrated in the accompanying drawings.