GB2404704A

GB2404704A - A method of manufacture of a gearbox.

Info

Publication number: GB2404704A
Application number: GB0318229A
Authority: GB
Inventors: Neil Walter Adcock
Original assignee: Adcock Technology Ltd
Current assignee: Adcock Technology Ltd
Priority date: 2003-08-04
Filing date: 2003-08-04
Publication date: 2005-02-09
Anticipated expiration: 2023-08-04
Also published as: GB2404704B; GB0318229D0; GB2404704A9

Abstract

A method of manufacture of a gearbox casting having a number of gearbox casing parts(2,5); bringing the casing parts (2,5) together to define a pair of aligned apertures, each aperture being defined by both casing parts (2,5); tapping a screwthread (21) in the aligned apertures; separating the cast casing parts (2,5) assembling the gearbox with the casing parts (2,5) encasing components comprising meshing gears (3,7); engaging an externally threaded adjuster collar (8) with the screwthread (21) in the aperture of the assembled gearbox; and rotating the adjuster collar (8) relative to the gearbox casing to adjust clearance between the encased components.

Description

2404704

- 1 -

A METHOD OF MANUFACTURE OF A GEARBOX

The present invention relates to method of manufacture of a gearbox and to a gearbox made by the 5 method.

Small robust low cost gearboxes are needed in many applications. For instance, such gearboxes are used often with electric motors. For example, 10 electric motors are often used in electrically operated seat sliding mechanisms for vehicle seats. In such mechanisms there is a need to convert the rotary motion of an electric motor into a linear motion.

15

The present invention in a first aspect provides a method of manufacture of a gearbox comprising casting a plurality of gearbox casing parts;

bringing the cast gearbox casing parts together to 20 define a pair of aligned apertures, each aperture being defined by surfaces of both casing parts;

tapping a screwthread in at least one of the aligned apertures; separating the cast casing components with the screwthread formed thereon; assembling the gearbox 25 with the casing parts encasing components comprising at least one pair of meshing gears; engaging an externally threaded adjuster collar with the screwthread in the aperture of the assembled gearbox; and rotating the adjuster collar relative to the 30 gearbox casing to adjust clearance between the encased components.

The present invention in a second aspect provides a gearbox comprising a pair of cast casing parts; 35 a worm gear journailed in apertures in the pair

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of cast casing parts and having a socket accessible to the exterior of the gearbox; a rotating nut which meshes with the worm gear and which is journalled in a pair of bearing inserts located inside the cast casing 5 parts, the rotating nut having an inner thread engageable with a lead screw when the lead screw is passed through the gearbox within the rotating nut and the bearing inserts; and an adjuster collar axially aligned with the rotating nut and the bearing inserts 10 through which the lead screw can also pass; wherein the adjuster collar has an external thread which meshes with an internal thread formed in an aperture defined by the pair of cast casing parts and the adjuster collar is accessible to the exterior of the 15 gearbox and rotatable relative to the gearbox casing and with rotation of the adjuster collar resulting in axial displacement thereof with the adjuster collar being able to displace axially relative to the gearbox casing one or all of the rotating nut and the bearing 20 inserts.

A preferred example of a method of the prevent invention will now be described with reference to the accompanying drawings in which:

25

Figure 1 is an exploded view of a gearbox made by a method according to the present invention;

Figure 2 is a perspective view of the Figure 1 gearbox when assembled;

30 Figure 3 is side view of the gearbox of Figures 1

and 2;

Figure 4 is an end elevation view of the gearbox of Figures 1 to 3;

Figure 5 is a bottom plan view of the gearbox of 35 Figures 1 to 4; and

Figure 6 is a cross-sectional view of the gearbox

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of Figures 1 to 5 taken along the line A-A of Figure 4.

Turning first to Figure 1 it can be seen that the 5 gearbox of the present invention comprises a first gearbox casing half 2, a second matching gearbox casing half 5 and two gearbox damping caps 1A and IB which all can be interlocked together to provide a gearbox casing as illustrated in Figure 2.

10

Each gearbox casing half 2,5 is formed as a die casting, preferably from an alloy of zinc The halves 2,5 are not identical, but instead are handed.

15 A drive worm gear 3 is journalled in aligned apertures, e.g 55, provided in the gearbox casting halves 2 and 5.

The drive worm gear 3 meshes with a rotating nut 20 7. The rotating nut 7 comprises a central splined portion 71 and then two end bearing portions 72 and 73. The bearing portions 72 and 73 are journalled in zinc alloy bearing inserts 4A and 4B. Sandwiched between the bearing insert 4B and the splined portion 25 71 of rotating nut 7 is a thrust washer 6B. Similarly sandwiched between the bearing insert 4A and the splined portion 71 of rotating nut 7 is a thrust washer 6A. The thrust washers 6A and 6B are typically made of a material which is both hard wearing and also 30 which has low friction characteristics.

Figure 6 shows clearly the drive worm gear 3 meshed with the rotating nut 7. Also in this figure it can be seen that the rotating nut 7 has a threaded 35 interior surface 74.

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In use of the gearbox the drive worm gear 3 will receive from an external motor a rotating drive force. Typically an electric motor will be connected to the drive worm gear 3 by a flexible drive shaft one end of 5 which will engage a socket 31 defined in the end of the drive worm gear 3, this socket being accessible to the exterior of the finished gearbox as can be most clearly seen in Figure 3.

10 An externally threaded lead screw will pass through the rotating nut 7 and engage with the inner thread 74. The gearbox will be fixed in position and rotation of the rotating nut 7 will lead to linear motion of the lead screw (not shown) with respect to 15 the gearbox.

It is necessary to allow for some degree of motion of the rotating nut 7 in an axial direction. This is achieved using the adjuster collar 8 shown for 20 instance in Figure 1, as will be described later.

It is a problem to provide a thread on the two diecast gearbox halves 2 and 5. For a start, such a thread cannot be formed during diecasting because of 25 the inherent tolerance limitations of the diecasting process. Also, ensuring alignment between the thread on the internal surface of one diecast half 2 and the thread on the internal surface of the other diecast half 5 is very difficult to achieve.

30

To overcome the above-noted problem, prior to final assembly of the gearbox, the gearbox casing halves 2 and 5 are brought together on a mandrel. The prongs 22, 23, 24 and 25 of gearbox casing half 2 will 35 extend through apertures 51, 52, 53, 54 of gearbox

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casing half 5 to fix in alignment the two halves 2, 5. A sleeve is overlaid over the central parts of the casing halves 2, 5 to hold them together. Arcuate surfaces (e.g. 21) on the halves 2,5 together define 5 two circular apertures in the gearbox casing. In at least one of the two circular apertures a thread is tapped whilst the gearbox casing halves 2 and 5 are held together. Preferably a tap as described in the applicant's co-pending application No is used.

10

Once a screw thread has been formed in at least one circular aperture on a pair of arcuate surfaces, e.g. 21, of the gearbox casing halves 2 and 5, then the gearbox casing halves 2 and 5 will be separated 15 and all of the components assembled between them before they are then brought together and fixed together. The prongs 22, 23, 24, and 25 of the gearbox casing half 2 will again extend through apertures 51, 52, 53, 54 of the gearbox casing half 5 20 and will be rivetted to ensure that the two gearbox casing halves 2 and 5 remain together. The gearbox damping caps 1A and IB are inserted over opposite ends of the gearbox casing halves 2 and 5. The externally threaded adjuster collar 8 is screwed into 25 the threaded aperture in the gearbox casing.

Initially the assembly of bearing inserts 4A,4B rotating nut 7 and thrust washers 6A, 6B is a loose assembly of components. The slack in the assembly is 30 taken up by rotating the adjuster collar 8 in one direction until all slack is removed and then rotating the adjuster collar a specified number of turns in the other direction to introduce a chosen degree of slack in the assembly. The thread on the adjuster nut is 35 chosen so that the nut is self-locking, but if extra

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certainty is desired then the end cap IB could be crimped on to the adjuster collar 8.

The bearing inserts 4A and 4B are preferably 5 keyed so that they can engage slots formed in the interior surface of one or both of the gearbox casing halves 2, 5. Thus rotation of the bearing inserts relative to the casing is avoided.

10 It is preferred that the end caps 1A and IB are made out of EPDM with a Shore hardness of 60. The worm gear 3 can be moulded in polyamide, which has good strength, mouldability and bearing characteristiscs. Two thrust washers of the same material could be 15 electro-welded to the worm gear 3. Polyphenylene sulfide, e.g. sold under the name Fortron™ could also be used.

In use the drive worm 3 will be rotated by a 20 flexible drive shaft which engages socket 31 and the drive worm 3 by meshing with the rotating nut 7 will rotate the nut. The rotating nut 7 will have passing therethrough a lead screw which will mesh with the internal thread of the rotating nut 7. The gearbox 25 will be held firmly in place and thus the rotation of the rotating nut 7 will cause linear displacement of the lead screw passing through the gearbox. The lead screw in turn will be fixed for instance to a slider of a sliding seat mechanism.

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Claims

CLAIMS:-

1. A method of manufacture of a gearbox comprising: casting a plurality of gearbox casing parts;

5 bringing the cast gearbox casing parts together to define a pair of aligned apertures, each aperture being defined by surfaces of both casing parts;

tapping a screwthread in at least one of the aligned apertures;

10 separating the cast casing components with the screwthread formed thereon;

assembling the gearbox with the casing parts encasing components comprising at least one pair of meshing gears;

15 engaging an externally threaded adjuster collar with the screwthread in the aperture of the assembled gearbox; and rotating the adjuster collar relative to the gearbox casing to adjust clearance between the encased 20 components.

2. A method as claimed in claim 1 wherein:

the plurality of gearbox casing parts are cast in a plurality of handed pairs;

25 each handed pair of casing parts is brought together to define a pair of apertures;

screwthreads are tapped in apertures of the handed pairs, each handed pair having a screwthread tapped in the at least one aperture thereof; 30 each handed pair of casing parts are assembled encasing components comprising at least one pair of meshing gears;

externally threaded adjuster collars are engaged one each with the screwthreads in the apertures of the 35 handed pairs;

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each threaded adjuster collar is rotated relative to the surrounding casing to adjust clearance between the encased components.

5

3. A method as claimed in claim 1 or 2 in which: in each assembled gearbox, one of the meshing gears is a rotating nut with a threaded aperture therethrough;

in the method each rotating nut is journalled in 10 each gearbox casing using a pair of bearing insert collars which sandwich the rotating nut; and in the method each adjuster collar is axially aligned with a respective rotating nut and the bearing insert collars therefor and is used to adjust 15 clearances there- between.

4. A method as claimed in claim 3 wherein at least one thrust washer is included between each of the bearing inserts and the rotating nut during assembly

20 of the gearbox.

5. A method as claimed in claim 3 or claim 4, wherein:

an externally threaded lead screw is engaged in

25 the threaded aperture of each rotating nut.

6. A method as claimed in any one of claims 3 to 5 wherein the rotating nut is meshed with a worm gear having an axis perpendicular to the axis of the

30 rotating nut, the worm gear being mounted in a second pair of aligned apertures in the assembled gearbox, each formed in a separate casing part.

7. A method as claimed any one of the preceding 35 claims wherein each adjuster collar is rotated

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relative to each gearbox casing in order to displace both of the meshed gears of the gearbox.

8. A method as claimed in any one of the preceding 5 claims, wherein:

end caps are pushed over opposed ends of the assembled gearbox, the opposed ends being the ends in which the aligned apertures are defined.

10

9. A method as claimed in any one of the preceding claims wherein after the adjuster collar has been rotated to set the clearance between the encased components then the adjuster collar is fixed in place relative to the surrounding gearbox casing by crimping 15 the gearbox casing.

10. A method as claimed in any one of the preceding claims wherein in each pair of gearbox casing parts one casing part has a plurality of prongs and the

20 other casing part has a matching plurality of apertures and the prongs are inserted into the apertures both when the casing parts are initially brought together to enable formation of the screwthread and also later when the casing parts are 25 brought together to encase the components which include the gears, the interaction of the prongs and the apertures ensuring alignment of the casing parts.

11. A method as claimed in claim 10 wherein ends of 30 the prongs are peened over to secure the casing parts togther.

12. A gearbox comprising:

a pair of cast casing parts;

35 a worm gear journalled in apertures in the pair

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of cast casing parts and having a socket accessible to the exterior of the gearbox;

a rotating nut which meshes with the worm gear and which is journalled in a pair of bearing inserts 5 located inside the cast casing parts, the rotating nut having an inner thread engageable with a lead screw when the lead screw is passed through the gearbox within the rotating nut and the bearing inserts; and an adjuster collar axially aligned with the 10 rotating nut and the bearing inserts through which the lead screw can also pass;

wherein the adjuster collar has an external thread which meshes with an internal thread formed in an aperture defined by the pair of cast casing parts 15 and the adjuster collar is accessible to the exterior of the gearbox and rotatable relative to the gearbox casing with rotation of the adjuster collar resulting in axial displacement thereof and with the adjuster collar being able to displace axially relative to the 20 gearbox casing one or all of the rotating nut and the bearing inserts.

13. A gearbox as claimed in claim 12 wherein the internal thread in the aperture of the gearbox casing

25 is a thread formed by bringing the pair of casing parts together prior to assembly of the gearbox and tapping the internal thread in the aperture and then separating the threaded casing parts prior to final assembly of the gearbox.

30

14. A gearbox as claimed in claim 12 or claim 13 wherein:

a pair of thrust washers are included in the gearbox sandwiching the rotating nut and being 35 interposed between the rotating nut and the bearing

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journal inserts.

15. A gearbox as claimed in any one of claims 12 to

14 wherein the axis of the worm gear is perpendicular 5 to the axis of the rotating nut.

16. A gearbox as claimed in any one of claims 12 to

15 wherein the worm gear is made of a plastics material.

10

17. A gearbox as claimed in claim 16 wherein the worm gear is made of polyamide.

18. A gearbox as claimed in claim 16 wherein the 15 gearbox is made of polyphenyline sulfide.

19. A gearbox as claimed in any one of the claims 12 to 18 comprising a pair of end caps which are secured one each surrounding opposed ends of the gearbox

20 casing.

20. A gearbox as claimed in any one of claims 12 to 19, wherein one gearbox casing part has a plurality of prongs extending therefrom which extend within

25 matching apertures in the other gearbox casing part to align the two gearbox casing parts.

21. A gearbox substantially as hereinbefore described with reference to and as shown in the accompanying

30 drawings.