GB2227548A - Length-adjustable shaft for torque transmission - Google Patents

Description

1 GMD/88085GB1 LENGTH-ADJUSTABLE SHAFT FOR TORQUE TRANSMISSION This

invention relates to a length-adjustable shaft for torque transmission, comprising a hollow outer part provided in its interior with axially extending teeth, and an inner part received within the outer part and having exte.-nal teeth engaging the internal. teeth of tne outer part for torque transmission and relative axial sliding movement. The outer part of the shaft has an internal sleeve axially spaced from its internal teeth and engaging the inner part to guide the latter. The invention is particularly, but not exclusively, applicable to a shaft which is universally jointed, wherein resistance of the shaft to bending (i.e. to the axes of the inner and outer parts becoming misaligned with one another) is dependent solely upon the effectiveness of the guidance of the inner part relative to the outer part.

In universally jointed length adjustable shafts, the interengaging torque transmitting teeth of the outer and inner parts are designed to meet the requirements of torque transmission and prevention of such bending. From the point of view of torque transmission, a shorter axial length of teeth is required than is necessary for preventing misalignment of the two parts. For the latter purpose, an outer part having very long internal teeth would be suitable, but such a part is expensive and difficult to produce. The longer the teeth are required to be, the greater is the difficulty of producing them accurately. Further, when torque is being transmitted loads are concentrated at the ends of the teeth, leading to high contact pressures. The selected amount of ( 1 2 overlap between the inner and outer parts therefore has to be a compromise between the various requirements.

Avoidance of bending is particularly important in the case of long and heavy shafts. Any bending can lead to noisy running.

It is therefore the object of the present invention to provide a length adjustable shaft providing an improved resistance to bending and thus quieter running characteristics in service.

According to the invention, we provide a lengthadjustable shaft for torque transmission, comprising a hollow outer part having a portion provided with internal axially extending teeth; an inner part received within the outer part and having external teeth engaging the internal teeth of the outer part for torque transmission and relative axial sliding movement; and a guide sleeve fitting within the outer part and axially spaced from said toothed portion thereof, the guide sleeve having internal teeth which engage the teeth of the inner part to guide the latter, and being circumferentially adjustable relative to the outer part when torque is applied.

In a shaft according to the invention, it is possible to design the toothed portion of the outer part to meet the torque transmitting requirements of the shaft, whilst the guide sleeve fitting within the outer part, axially spaced from the toothed portion, leads to an improvement in the resistance of the shaft to bending. The guide sleeve, being circumferentially adjustable, does not participate in torque transmission.

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3 The guide sleeve may be connected to the outer part in a non-positive way (by which we mean that there is no form-fitting connection which would prevent the guide sleeve from adjusting circumferentially), thereby ensuring that it is able to adjust circumferentially, so that the shaft does not become jammed against length adjustment, despite the axial spacing between the guide sleeve and toothed portion.

The internally toothed portion of the outer part may comprise a separate sleeve, non-rotatingly connected to the rest of the outer part.

The guide sleeve may be connected to the outer part by shrink fitting, press fitting, or by use of an adhesive, such that under torque transmission it is able to adjust itself circumferentially. Thus, the shrink or press fit should not be so tight as to prevent the guide sleeve from circumferential adjustment, or the adhesive used should be of a yieldable nature to permit such adjustment.

Alternatively, the guide sleeve may be connected to the outer part by one or more radially or axially extending pins, which may be soft to permit the guide sleeve to adjust itself circumferentially.

Preferably the guide sleeve is of a material which has advantageous, low friction, bearing properties.

Preferably, as above referred to, the shaft is a universally jointed shaft, with the outer part being connected to a first universal joint at one end of the shaft and the inner part being connected to a second universal joint at the other end of the shaft.

4 The invention will now be described by way of example with reference to the accompanying drawings, of which:- Figure 1 is a partly sectioned elevation of a first embodiment of shaft according to the invention; Figure 2 is an enlarged view of part of Figure 1; Figure 3 is a section on the line A-A of Figure 2; Figure 4 is a view as Figure 2, showing a further embodiment of shaft according to the invention; Figures 5 to 8 are yet further views as Figure 2, showing further embodiments of shaft according to the invention.

Referring firstly to Figure 1 of the drawings, the shaft there illustrated is a universally jointed shaft comprising two Hookes universal joints 2, 3. Each joint comprises, as is well known, two yokes 4, 5 connected to one another by a cross member 6. The respective yokes 5 of the joints are provided with flanges for torque transmitting connection to other components.

The respective yokes 4 of the two universal joints are connected to one another by a length-adjustable shaft comprising a hollow outer part 9 connected to the yoke 4 of joint 2 and an inner part 8 connected to the yoke 4 of joint 3. A torque transmitting connection between the inner and outer shaft parts is provided by a portion of the outer part provided with internal circumferentially spaced axially extending teeth, engaging with ( 1 complementary teeth provided on the external surface of the inner shaft part 8.

Universally jointed shafts of the type illustrated can sometimes be very long, and have to permit a large range of length adjustment. These two features together result in a high shaft weight, and in view of the unsupported length between the two joints 2, 3 it is important that bending of the shaft due to the. axes of the shaft parts 8, 9 becoming misaligned is resisted.

The quality of guidance against such bending is important for the quiet running characteristics of the shaft.

Referring now to Figures 2 and 3, these show part of the connecting shaft 7 of Figure 1 on an enlarged scale. The outer shaft part 9 has in its hollow interior 17 a toothed portion 15 with teeth 10 which extend parallel to the axis (indicated at Y-Y) of the shaft. These teeth engage the complementary teath 12 provided on the external surface 16 of the inner shaft part 8. The teeth may be involute shape, for example, or of SAE profile.

The length of the toothed portion 15 is designed so as to have the required torque transmitting capacity engaging the teeth on the inner shaft part. The required overlap has to ensure torque transmission, taking into account permissible tooth pressures in view of the fact that only the end regions of the engaging toothed portions participate in torque transmission.

According to the invention, torque transmission is provided by a relatively short toothed portion 15 which in itself is not sufficient to adequately guide the outer part and inner shaft part 8, 9 relative to one another to prevent bending of the shaft. Hitherto, a compromise has generally been made between the amount of toothed portion 6 overlap required for torque transmitting purposes and that needed to ensure adequate guidance against bending. According to the invention, guidance against bending is provided by a guide sleeve 13 disposed at an axial centre distance X from the toothed portion 15. The guide sleeve 13 has internal teeth 11 which engage the teeth 12 of the inner shaft part 8. The guide sleeve 13 is received in a counterbore 18 in the outer shaft part 9, in a non-positive way which permits the guide sleeve 13 to adjust itself circumferentially under torque transmission and align itself with the teeth 12 of the inner shaft part 8, thereby avoiding any possibility of the shaft parts becoming jammed relative to one another due to the great distance of the toothed portion 15 and sleeve 13 from one another axially. Preferably the guide sleeve 13 is of a material having low friction properties (e.g. a bronze material), so that it is not detrimental to free axial movement of the shaft parts relative to one another.

The non-positive connection between the guide sleeve 13 and shaft part 9 may be provided by a shrink or press fit, insufficiently tight to prevent the guide sleeve from adjusting circumferentially. Alternatively a yieldable adhesive could be used. Yet a further possibility is that an elastomeric supporting bush could be used to retain the guide sleeve while permitting it resiliently to adjust circumferentially.

Referring now to Figure 4 of the drawings, this shows an embodiment which is generally as that of Figure 2, and the same reference numerals have been accorded to corresponding parts. In this embodiment, however, the guide sleeve 13 is retained in counterbore 18 in the outer shaft part 9 by a radially extending pin 19 which ( 1 7 engages the sleeve and outer shaft part, the pin being dimensioned or of a nature such that it does not take part in transmission of torque.

Figure 5 shows an embodiment as Figure 4, with the difference that instead of pin 19 a bolt 119 is provided, screw-threaded into the outer shaft part 9 and engaging with its point a recess in the guide sleeve 13. Again, the bolt 119 does noL take part in torque tranmission.

Figure 6 shows an embodiment differing from those above described in that the guide sleeve, indicated at 113, has a frusto- conical outer surface 120 engaging a complementary frusto-conical surface 118 provided in the counterbored end of the outer shaft part 9. The sleeve is held to the outer shaft part by a ring 21 secured to the outer shaft part by a number of circumferentially spaced axially extending bolts one of which is indicated at 22. When torque is being transmitted, the guide sleeve 113 can adjust itself circumferentially to align with the teeth 10 in the toothed portion of the outer shaft part.

Figure 7 shows an embodiment which is generally similar to that of Figure 4, with the difference that an axially extending pin 219 is provided to give a circumferentially yieldable connection between the guide sleeve 13 and outer shaft part 9.

Figure 8 shows yet a further embodiment in which the arrangement of guide sleeve 13 is the same as in Figure 7. In this embodiment, however, a separate sleeve 14 is provided at the other end of the outer shaft part to constitute the internally toothed portion thereof. This further sleeve 14 is received in a counterbore 218 in the 8 outer shaft part, and is secured by an axially extending pin 19a which transmits torque between the further sleeve 14 and the rest of the outer shaft part. The smaller pin 219 provides the circumferentially yieldable connection with the guide sleeve 13.

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Claims (8)

1 1. A length-adjustable shaft for torque transmission, comprising a hollow outer part having a portion provided with internal axially extending teeth; an inner part received within the outer part and having external teeth engaging the internal teeth of the outer part for torque transmission and relative axial sliding movement; and a guide sleeve fitting within the outer part and axially spaced from said toothed portion thereof, the guide sleeve having internal teeth which engage the teeth of the inner part to guide the latter, and being circumferentially adjustable relative to the outer part when torque is applied.

2. A shaft according to Claim 1 wherein the guide sleeve is nonpositively connected to the outer part.

3. A shaft according to Claim 2 wherein the guide sleeve is connected to the outer part by shrink fitting, press fitting, or by use of an adhesive.

4. A shaft according to Claim 1 wherein the guide sleeve is connected to the outer part by at least one radially or axially extending pin providing for said circumferential adjustment.

5. A shaft according to any one of the preceding claims wherein the guide sleeve is of a material having low-friction bearing properties.

6. A shaft according to any one of the preceding claims wherein the internally toothed portion of the outer part comprises a separate sleeve non-rotatingly connected to the rest of the outer part.

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7. A shaft according to any one of the preceding claims wherein the outer shaft part is connected to a first universal joint at one end of the shaft, and the inner shaft part is connected to a second universal joint at the other end of the shaft.

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8. A shaft substantially as hereinbefore described with reference to Figures 1, 2 and 3, or any one of Figures 4 to 8, of the accompanying drawings.

Published 1990atTliePatentoffice, State House.88n]. Holborn, London WC1R 4TP. Purther copies maybe obtained from The Patent 0Ince. Sales Branch, St Mary Cray, OrpingLon, Kent BR5 3RD. Printed by Multiplex techniques itd, St Mary Cray. Kent. Con. 1,87