GB2283074A

GB2283074A - Improvements in worm gears

Info

Publication number: GB2283074A
Application number: GB9421151A
Authority: GB
Inventors: Michael John Neale
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-10-22
Filing date: 1994-10-20
Publication date: 1995-04-26
Anticipated expiration: 2014-10-20
Also published as: GB9321887D0; GB9421151D0; GB2283074B

Abstract

A worm gear in which the working surfaces of the wheel teeth are each split into two or more separate pads 8, 9 and which may incorporate arrangements to feed lubricant between the pads, in addition to the conventional lubricant supply at the entry to the tooth contact. The pads 8, 9 are separated by a groove 10 in each tooth, or by a groove extending circumferentially around the wheel, the width of the groove in each case being at least one-twentieth of the total axial length of each tooth. Lubricant may be fed to the zone of contact between the worm and wheel by approximately radial holes 6 in the wheel which enter the gaps 7 between successive teeth. <IMAGE>

Description

IMPROVEMENTS IN WORM GEARS The invention relates to worm gears which are used to transmit a drive between two shafts at right angles, while providing a fixed speed ratio between the two.

In worm gears1 the worm has a form that is broadly similar to a screw thread and is usually made from a steel material having a hardened polished surface. The mating wheel which is usually made from a non ferrous metal has teeth cut on its periphery, which intermesh with the worm. A limitation on the performance of worm gears is that the teeth of the wheel suffer from pitting which can extend to substantial areas of the tooth surface from the trailing edge of its contact with the worm.

With known worm gears the wheel teeth generally have an axial length about 4 or 5 times as long as their radial depth. This is dictated by the general geometry and the need for an adequate tooth size to transmit the loading. However it is known from the principles of operation of relatively flat surfaces in sliding contact that improved lubricant films are obtained if the contact geometry for such load bearing surfaces have a length to width ratio of 2 or less.

According to the present invention there is provided a worm gear in which the geometry of the lubricated contact between the worm and wheel is improved by dividing the working surfaces of the wheel teeth into two or more separate pads with spaces between them which may also be used as lubricant feeds in addition to any lubricant feed at the outside of the wheel.

Some specific embodiments of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 Is a view looking along the axis of the wheel and in which a portion of the wheel at its contact region with the worm has been sectioned on its vertical centre line.

Figure 2 Is a view looking along the axis of the worm in which the lower side of the wheel has been sectioned on its vertical centre line.

Figure 3 Is a section through a worm wheel with a central supporting web and which includes a view of a wheel tooth gap when looking inwards toward the axis of the wheel.

Figure 4 Is a section through a worm wheel with an offset supporting web.

In the embodiment shown in Figure 1 and Figure 2 the outer circumference of the wheel (1) incorporates a circumferential slot or groove (2) extending inwards radially through the teeth in order to divide them into two separate load bearing pads. The depth of the slot may extend over either a part of the radial tooth depth, or to the full depth of the teeth or inwards beyond the teeth, to produce a continuous circumferential groove around the body of the wheel. This groove may be fed with lubricant under pressure from a jet (3) feeding the lubricant in a direction which is generally in the plane of the wheel so as to provide a lubricant feed to the centre of the tooth contact. It can be seen in Figure 2 that the groove divides the wheel tooth contact area into two separate contact areas (4) and (5) of a more optimum geometry, than that which would be obtained with an ungrooved wheel.

The arrangement shown in Figure 1 and 2 divides the wheel teeth into two separate contact areas but it will be appreciated that the principle can be extended to arrangements with two or more slots, subdividing each tooth into three or more separate contact areas. The optimum number of slots would depend on the particular worm and wheel geometry.

In an alternative arrangement shown in Figure 3, the working surfaces of each wheel tooth is divided into two separate pads (8) and (9) by an approximately radial groove (10), which may be fed with lubricant via the drillings (6) that are approximately radial and which enter the gaps (7) between the wheel teeth. The drillings may be fed by a lubricant feed groove (11) which may be fed by lubricant sprays. These sprays are positioned circumferentially to provide a feed of lubricant, around the sector of the wheel, where the teeth are in contact with the worm, or just ahead of this position.

It is also possible, if the drillings are radial as shown in Figure 4, to arrange for the diameter of the drillings, at least in the radial position where they pass through the tooth gap, to be sufficiently large to form the radial grooves in the tooth surfaces of the wheel.

Claims

1. A worm and wheel drive in which the surfaces of the wheel teeth in contact with the worm are divided axially into two or more contacting zones separated by radial slots or grooves with a width of at least one twentieth of the total axial length of the wheel teeth.

2. A worm and wheel drive as in claim 1 in which the radial slot or slots in the wheel teeth are formed from one or more circumferential grooves running around the periphery of the wheel, and cutting through the teeth.

3. A worm and wheel drive as in claim 1 in which the radial groove or grooves in the tooth surfaces are of a curved cross sectional profile.

4. A worm and wheel drive as in claim 3 in which the curved profile of the groove or grooves is part of a cylinder co-axial with an approximately radial drilling passing inwards into the body of the wheel rim in the gaps between the wheel teeth, and emerging into the space inside the rim of the wheel.

5. A worm and wheel drive as in claim 2 in which the circumferential groove running around the periphery of the wheel is fed with oil in order to lubricate the wheel teeth.

6. A worm and wheel drive as in claim 4 in which the radial drillings, connecting with the gaps between the wheel teeth, are fed with oil from their radially inward end at the inside of the wheel rim.

7. A worm and wheel drive as in claims 5 and 6 in which the oil is fed at a circumferential position on the wheel so that it feeds oil to the wheel teeth at or just before their contact with the worm.

8. Any worm and wheel drive which is substantially as illustrated in the accompanying drawings.