GB2241769A

GB2241769A - Drive shaft

Info

Publication number: GB2241769A
Application number: GB9104846A
Authority: GB
Inventors: Rudolf Beier; Peter Amborn; Wolfgang Exner; Herbert Frielingsdorf; Klaus Greulich
Original assignee: Loehr and Bromkamp GmbH; GKN Automotive GmbH
Current assignee: GKN Driveline Deutschland GmbH; GKN Driveline International GmbH
Priority date: 1990-03-08
Filing date: 1991-03-07
Publication date: 1991-09-11
Anticipated expiration: 2011-03-07
Also published as: FR2659403B1; JPH05263819A; IT1252046B; ITMI910448A0; DE4007284A1; ITMI910448A1; GB9104846D0; DE9007617U1; FR2659403A1; GB2241769B

Abstract

A drive shaft for a motor vehicle is of tubular configuration and formed in one piece, comprising end portions (11, 12) and a central portion therebetween, the end portions having a bending stiffness at least 20 times greater than the bending stiffness of the central portion. The central portion over its length (Rm) may be of constant or variable wall thickness (D), and variable or constant inner diameter (Di) or outer diameter (Da), so that its distribution of cross-sectional area is optimised to meet strength requirements, whilst the natural resonant frequency of the shaft is reduced to a low value which is subject to minimum eternal excitation. <IMAGE>

Description

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Title: Drive shaft Description of Inventio

This invention relates to a tubular drive shaft formed in one piece and comprising a central portion disposed between, and having a larger outside diameter than, two end portions which have parts, e.g., toothed, for torque transmitting connection to-universal joints. Such a drive shaft, which is particularly, but not exclusively, usable in the drivelines of motor vehicles, will hereafter be referred to as a drive shaft of the kind specified.

DE-PS 3009277 discloses a drive shaft of the kind specified which is used as a half shaft in a motor vehicle driveline. The drive shaft is tubular, comprising two end portions of stepped diameter and provided with parts for torque transmitting connection to the universal joints. The entire central region of the tubular shaft is cylindrical. To attain a uniform mechanical strength along the entire length of the shaft, the wall thickness is reduced with increasing outside diameter. All design attention is focused on the mechanical strength of the shaft and the natural frequency of the shaft with respect to bending vibrations is only able to be varied to a limited extent. Generally, the natural frequency may be within the range of an excitation frequency of the engine/gearbox system, so that vibration and noise cannot be avoided.

It is the object of the present invention to provide a drive shaft whose vibration behaviour is improved by adjusting its natural frequency to a value in a range which is likely to be externally excited to a minimum extent.

According to the invention, a drive shaft of the Und specified is characterised in that the end portions have a bending stiffness at least 20 times greater than the bending stilfhess of the central portion.

As a result of such an extreme ratio between the bending stiffness values of the end portions and central portion of the tubular shaft, a characteristic value for the natural frequency of the shaft is obtained 3 1 2 which is very low, and by suitable selection of shaft dimensions may be moved into a range which is likely to be subject to minimum external excitation. By moving the natural resonant frequency of the shaft in this way, it is possible to avoid undesirable vibration and noise. Particularly long drive shafts may be designed according to the invention.

Ile wall thickness of the central portion of the shaft may be constant, while the outer diameter thereof is constant or varies along its length.

By providing the drive shaft with a constant wall thickness while it has a constant or varying outer diameter, it is possible to achieve a distribution of cross-sectional area along the length of the shaft which is optimised from a functional point of view and which meets the requirements for strength of the shaft, with the torsional stiffness being adjusted while the natural resonant frequencies for both bending and torsional vibrations are brought within the respective requirements. This means that while torsional stiffness and acoustic behaviour of the shaft are optimised, the load bearing capacity of the parts of the shaft may greatly exceed actual requirements.

In an alternative shaft configuration, to achieve the abovementioned ratio between the bending stiffnesses of the end portions and central portion of the shaft, the inner and/or the outer diameter of at least part of the central portion may vary continuously in a symmetrical manner about the centre of the shaft.

Once again, the drive shaft may thus be dimensioned in such a way that its natural frequency is within a range which is subject to minimum external excitation.

A stepped cross-section of the shaft is another way in which a change in bending stiffness towards the centre of the shaft may be achieved.

In all embodiments of the invention, the maximum outer diameter may be adjacent the end portions or at the centre of the shaft. The shaft may be of conical configuration between its minimum and maximum outer i 1 3 diameters, to achieve a progressive change in its cross-sectional area. If the maximum diameter is at the centre of the shaft, the form of the first natural mode of vibration of the shaft is copied, with the increasing crosssectional area resulting in an increase in the resistance of the shaft to deformation, towards its centre.

The invention will now be described by way of example with reference to the accompanying drawings, Wherein:- Figure 1 shows in plan view a motor vehicle and the drive shafts thereof, Figure 2 is a longitudinal section through a first embodiment of a drive shaft according to the invention; Figures 3 to 8 are respective longitudinal sections through further embodiments of drive shaft according to the invention.

Referring firstly to Figure 1 of the drawings, the four-wheel drive vehicle indicated generally at 1 has a front engine 2, gearbox 3, and front axle differential 4 from which the front wheels 5 are driven by respective drive shafts 6. For driving the rear wheels 7, torque is transmitted from the front axle differential 4 to a rear axle differential 9 by a propeller shaft 8. Tle rear wheels 7 are driven from the rear differential 9 by respective rear drive shafts 10. The front and rear drive shafts 6, 10 are designed in accordance with the present invention.

Referring to Figure 2 of the drawings, one of the drive shafts 6 or 10 comprises respective end portions 11, 12 and a central portion therebetween. Ile end portions 11, 12 have toothed (splined) portions at their free ends, for torque transmitting connection with universal joints. The central portion of the shaft, after short transition portions leading to the end portions 11, 12, is of cylindrical form with constant wall thielmess D, inner diameter Di, and outer diameter Da, over its length Rm.

In the shaft shown in Figure 3 of the drawings, the central portion whose length is indicated at Rm has its maximum outside diameter Dmax at its opposite ends adjacent the end portions 11, 12. The central f 4 portion is of constant wall thickness D, and tapers conically from each of its ends to a minimum outside diameter at the centre M of the shaft.

In the shaft shown in Figure 4, the central portion of the shaft is of constant outer diameter Da and of a wall thickness which is at a maximum at each end of the central portion adjacent the end portions and a minimum at the centre of the shaft. The inner diameter of the central portion tapers conically from a minimum at each end of the central portion adjacent the end portions, to give the aforesaid maximum wall thickness, to a maximum at the centre M of the shaft to give the aforesaid minimum wall thickness.

In the shaft shown in Figure 5, both the inner and outer diameter of the central portion of the shaft taper conically towards the centre M of the shaft to give a maximum wall thickness at the centre. The maximum outer diameter Dmax is immediately adjacent the end portions 11, 12 of the shaft.

In the shaft shown in Figure 6 of the drawings, the central portion of the shaft has a maximum diameter Dmax at its centre M, and tapers in opposite directions towards the end portions of the shaft. Thus the shaft has, as it were, the shape of the first basic mode of its vibration.

The shaft shown in Figure 7 of the drawings has a central portion whose maximum outside diameter Dmax is adjacent the end portions of the shaft. The inner diameter Di of the central portion of the shaft is constant, while the outer diameter and hence the wall thickness both taper symmetrically from the ends of a central portion to the centre M thereof.

Figure 8 shows a shaft which is of stepped configuration, with the major part of the central porti6n of the shaft being cylindrical and of maximum outer diameter Dmax. The wall thickness D increases in steps to each of the end portions 11, 12 of the shaft.

All the above described embodiments of shaft have the above referred to relationship between the bending stiffnesses of the end portions and central portion, namely a ratio greater than or equal to 20:1 of the 1 end portion bending stiffness to the central portion bending stiffness. All the embodiments of shaft are axially and rotationally symmetrical.

Ile features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

1 6 CL-AIMS 1. A tubular drive shaft formed in one piece and comprising a central portion disposed betweeA and of larger outside diameter than, two end portions having parts for torque transmitting connection to universal joints, and wherein said end portions have a bending stiffness at least 20 times greater than the bending stiffness of the central portion.

Claims

2. A drive shaft according to Claim 1 wherein the central portion is

rotationally and axially symmetrical.

3. A drive shaft according to Claim 1 or Claim 2 wherein the central portion has a constant outer diameter and wall thickness.

4. A drive shaft according to Claim 1 or Claim 2 wherein the central portion has a constant wall thickness and varying outer diameter.

5. A drive shaft according to Claim 1 or Claim 2 wherein the inner diameter and/or the outer diameter of at least part of the central portion varies continuously and symmetrically about the shaft centre.

6. A drive shaft according to Claim 1 or Claim 2 wherein the central portion has a stepped diameter and has transition regions of conically tapering inner and/or outer diameter.

7. A drive shaft according to any one of the preceding claims wherein the central portion has a maximum outer diameter adjacent each of the two end portions.

8. A drive shaft according to any one of Claims 1 to 6 wherein the central portion has a maximum outer diameter at the centre of the shaft.

7 9. A drive shaft according to any one of Claims 1 to 5 wherein the central portion tapers conically between the end portions and the centre of the shafL 10. A drive shaft according to any one of Figures 2 to 8 of the accompanying drawings.

11. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.

Published 1991 at The Patent Office. Concept House. Cardiff d. Newport. Gwent NP9 1 RH. Further coptes nMY be Obudned frOrn Sales Branch. Unit 6. Nine Mile Point. CAmifehnfach. Cross Keys. Newport. NP l 7Hz. printed by Multiplex techniques lid. St Mary Cray. Kent.