GB2377741A

GB2377741A - Gearbox

Info

Publication number: GB2377741A
Application number: GB0211674A
Authority: GB
Inventors: Robin Child; David Norris
Original assignee: Systematic Drill Head Co Ltd
Current assignee: Systematic Drill Head Co Ltd
Priority date: 2001-05-30
Filing date: 2002-05-22
Publication date: 2003-01-22
Also published as: GB0113069D0; GB0211674D0; WO2002097306A1

Abstract

A gearbox 12 comprises a gear 46 encased in a close fitting cavity 34 defined by part of the gearbox. Lubricant may be arranged in the cavity to cover the teeth of the gear. In a preferred embodiment the gearbox has at least two planes or levels of casings for gears 14a-c, wherein the casing is a single piece of material having a plurality of cavities 32-44 machined therein. The casings 14a-c are preferably formed from plastic or aluminium. The gearbox is preferably used on with a drill head. The casings 14a-c are preferably held together with through dowels, pins, rods or the like.

Description

- 237774 1

Gearbox Lubrication The present invention relates to a method of lubricating a gearbox, a method of making a gearbox and a gearbox itself. The invention is to be used particularly, but not 5 exclusively, on a ( multi spindle) drill head.

Multi-spindle drill heads have spindles at dedicated centres and speeds, and at particular sizes to suit a tool and feature required on an engine component. For automotive transfer lines they are required to run constantly and remain cool so that 10 thermal expansion does not effect the part feature position.

For some time smooth circular surfaces of spindle bearings have been lubricated with grease to achieve this condition. The gearbox has remained lubricated by oil because of the gear tooth to tooth mesh lubrication.

Due to the centrifugal force generated by the revolving gear the oil is thrown off and so a constant supply of oil has to be provided by pumped circulation.

The use of grease is known in an open gear casing structure but its openness allows 20 grease to escape so that generous amounts have had to be continually applied to maintain tooth surface coating and prevent eventual drying off of the teeth from centrifugal action. This excess of grease causes heat so that the head only stays cool enough at slow speeds. Modern cutting condition require higher speeds.

25 The applicant has done a lot of research, known greased heads have generally been limited to heads at slow speeds or heads with only a few spindles. For example a known gearbox filled with grease could only achieve 1500 rpm.

Problems with condensation have occurred and so reworked heads used lubricant again.

An aim of the invention is to lubricate a gearbox in a way which maintains lubrication and allows high speed without excessive heat generation. High speed means more than 1 500 rpm.

S According to a first aspect of the invention there is provided a gearbox, comprising a gear encased in a close fitting cavity defined by a part of the gearbox.

According to a second aspect of the invention there is provided a gearbox, comprising a gear encased in a close fitting cavity defined by a part of the gearbox and lubricant 10 being arranged in the cavity so as to cover gear teeth.

Preferably, the cavity is closed in the direction of movement of the lubricant under centrifugal forces. This stops lubricant escape so it does not need to be replaced.

15 Preferably, the lubricant is a grease, such as KLUBER NBU 15. Oil could be used in which case the cavity would have to be effectively sealed.

The gearbox in accordance with the invention can operate without excessive heat generation at speeds of up to 10000 rpm.

According to a third aspect of the invention there is provided a method of lubricating a gearbox, comprising encasing a gear of a gearbox in a close fitting cavity defined by a part of a gearbox, and arranging a lubricant in the cavity so as to cover teeth of gear.

25 According to a fourth aspect of the invention there is provided a method of making a gearbox, comprising providing a casing having a cavity only slightly larger than a corresponding gear.

Preferably, the cavity is in the order of 0.001-0.01 inch (0.0254mm to 0. 254mm) 30 measured radially from the gear centre.

A plurality of cavities are preferably provided, each having a corresponding gear, and the cavity being only slightly larger than the corresponding gear in each case.

The casing may be a single piece of material having a plurality of such cavities 5 machined therein.

In a preferred embodiment of the invention the method of construction is limited to two planes or levels for gears, and generally heads are provided with three levels to allow for those arrangements that require it. The only way to allow three levels would 10 be to leave the centre level open, which may then again fail due to insufficient grease retention. To enable a third or more levels of gears to be used within close fitting casings the head is preferably provided with one or more plates creating a sandwich construction.

IS The advantage of three plates over one is that a gear (or spacer) can be smaller than a neighbouring bearing - i.e. the void is avoided.

To maintain accuracy between front and rear casing these two are preferably held 20 together for example doweled together so the intermediate cavity plates are to be located within the main casings.

The plates have no significant load bearing, therefore they are preferably made of plastics material, to avoid weight and reduce manufacturing cost. Of course it could be 25 made of steel, iron or other suitable material such as aluminium.

The plates may be retained in position with through dowel pins, rods or the like, or located at their periphery by machined locations in the casing.

30 According to yet another aspect of the invention there is provided a drill head having a gearbox in accordance with the first aspect fitted thereto.

Another aspect provides a set of one or more gears and one or more plates wherein one or more plates comprise a close fitting cavity for each of the one or more gears.

A method of lubricating a gearbox, a method of making a gearbox, a gearbox and a drill 5 head having a gearbox fitted thereto, all in accordance with the invention will now be described by way of example with reference to the accompanying schematic drawings in which; Figure I is a side view, partly in section, illustrates two gearboxes, above line A being a 10 known oil lubricated gearbox, and below line A being a grease lubricated gearbox designed in accordance with the invention, Figure 2 is one perspective view of a drill head having the gearbox in accordance with the invention fitted thereto, Figure 3 is another perspective view of a drill head having the gearbox in accordance with the invention fitted thereto, Figure 4 is an exploded perspective view of the gearbox, Figure 5 is another exploded perspective view of the gearbox, Figure 6 is a side view, partly in section, of the drill head showing configuration of plates of the gearbox, Figure 7 shows a side view of the gearbox showing cavity configuration on a plate, Figure 8 is a view along line VIII in Figure 3 of the gearbox.

30 Referring to Figure 1, the upper half shows a known gearbox configuration. The lower half shows a typical configuration of one embodiment in accordance with the invention.

The small size of the grease cavity of the invention is immediately noticeable with respect to the known oil lubricated cavity.

Referring to Figures 2 and 3, a drill head system 10 according to the invention 5 comprises a gearbox 12.

to one preferred form shown in Figures 4 and 5, the gearbox comprises three plates 14a, 14b, 14c sandwiched between a first casing 16 and a second casing 18. The first casing 16 and the second casing 18 define recesses to accommodate the plate nearest thereto, 10 i.e. first casing accommodates plate 14a, second casing accommodates plate 14c. It can be seen that the plates 14 a, b, c are housed mainly in casing 18.

Referring to figures 1 and 6, in another preferred embodiment of the invention, the plates 14 are housed mainly in the cavity of casing 16.

The first casing 16 comprises four apertures 20. The second casing 18 comprises four apertures 22 (only one of which is shown in Figure 5).

Plate 14a comprises four apertures 24, plate 14b comprises four apertures 26, and plate 20 14c comprises four apertures 28 (only some of which are referenced due to them being hidden or for clarity).

Apertures 20, 22, 24, 26, 28 are in alignment.

25 Four dowel rods 30 are provided, which locate through the apertures 20, 22, 24, 26, 28 to hold the plates 14a, 14b, 14c in place.

Each plate 14a, 14b, 14c comprises a plurality of cavities. For example, plate 14c comprises gear cavities 32-44 defined therein ( say, by CNC machining). The gear 30 cavities 32-44 house gears (referenced collectively as 46 for purposes of clarity). Teeth are omitted from gears for further clarity. The main point of the invention is the small clearance therebetween (this is possibly best shown in Figure 7). It will be noted that

some of the cavities 32-44 are in communication with each other to allow meshing of teeth (not shown) on certain gears.

It should be noted that the plates 14 are preferably oriented vertically but the grease is 5 pushed centrifugally and the closure in that direction tends to retain grease is in said cavities. Different cavities (unreferenced for clarity) are provided on the plate 14a for further gears (also unreferenced).

Referring to Figure 6, the central plate 14b has cavities aligning with gear cavities so that shafts 48, 50, 52, 54 can pass therethrough. In use the drill holding adapter part is positioned in apertures 55.

15 Figure 7 shows the radial clearance between gears and the corresponding cavities in one particular plate 14. This clearance is between the tooth tip and the cavity bore.

The optimum for the distance D between the cavity and its associated gear tooth tip is 0.5 mm on diameter (for clearance) + 0.25 mm tolerance on the radius.

Operation of the gearbox will not be described in detail since it is in many ways the same as the known gearbox. However the following points should be noted about the present invention.

25 Continuous lubrication systems are eliminated along with all the ancillary equipment that is expected as part of the drill head operation.

The pump is no longer needed, nor the filler, the sight glass, drain plug, flow meter, relief valve, inlet strainer, outlet filter or spray nozzles. Cross Grillings & piping can 30 also be dispensed with, so the problems of broken pipes and loose connections are avoided as well as blocked nozzles. Not only is oil loss eliminated, but so too is coolant in the oil.

It is also interesting to note, that there is no breather (which in the past allowed coolant ingress in the casing). Although there is air inside the cavity is considerably less an amount than in conventional gear cases and as such is a smaller volume to expand. This 5 expansion can take place through the spindle drive shaft bores, which now do not require seals. This is particularly advantageous for angles down heads where special lip seals have been necessary and rear lubrication pipes are generally employed. Remote tanks, & casings having extra features to create large enough oil reservoirs are also eliminated. The height from the saddle to the lowest spindle in order to allow for an oil 10 reservoir is no longer an installation constraint permitting more design flexibility.

In summary, much complexity has been eliminated, and with the addition of only these

relatively simple cavity plates and support pins, the applicant now offers a "substantially maintenance free" gearbox for a drill head.

Claims

1. A gearbox, comprising a gear encased in a close fitting cavity defined by a casing of the gearbox.

5

2. A gearbox according to Claim 1, wherein lubricant is arranged in the cavity so as to cover gear teeth.

3. A gearbox according to claim 2, wherein the cavity is closed in the direction of movement of the lubricant under centrifugal forces.

4. A gearbox according to claim 2 or 3, wherein the lubricant is a grease, such as KLUBER NBU 15.

5. A gearbox according to any preceding claim, wherein the cavity is in the order 1S of 0.001-0.01 inch (0.0254mm-0.254mm) measured radially from the gear centre.

6. A gearbox according to any preceding claim, wherein the gearbox casing defines a plurality of cavities, each having a corresponding gear, and the cavity being only slightly larger than the corresponding gear in each case.

7. A gearbox according to claim 6, wherein the casing is of a single piece of material, e.g. a plate, having a plurality of cavities machined therein.

8. A gearbox according to any preceding claim, wherein the gearbox is limited to 25 two planes or levels of casings for gears.

9. A gearbox according to any of claims 1-7, wherein the gearbox comprises three planes or levels of casings for gears.

30

10. A gearbox according to claim 9, wherein, to enable a third or more level of gears to be used within close fitting casings, the gearbox has one or more plates creating a sandwich construction.

11. A gearbox according to any of claims 8 to 10, wherein the gearbox comprises, to maintain accuracy between front and rear casing, holding the two planes or levels of casings together, for example with dowels, so that an intermediate cavity plate is located within the front and rear casings.

12. A gearbox according to any preceding claim wherein the gearbox comprises a plate of plastics material or aluminium.

13. A gearbox according to any of claims 8-11, wherein the gearbox comprises 10 retaining the planes or levels of casings in position with through dowel pins, rods or the like.

14. A method of lubricating a gearbox, comprising encasing a gear of a gearbox in a close fitting cavity defined by a casing of a gearbox, and arranging a lubricant in the 15 cavity so as to cover teeth of the gear.

15. A method of making a gearbox according to claim 14, comprising providing a casing having a cavity only slightly larger than a corresponding gear.

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16. A method of making a gearbox according to claim 15, the step of providing a cavity comprising providing a cavity in the order of 0.001-0. 01 inch (0.00254 mm to 0.0254 mm) measured radially from the gear centre.

17. A method of making a gearbox according to any of claims 14 to 16, and further 25 comprising providing a plurality of cavities, each having a corresponding gear, and the cavity being only slightly larger than the corresponding gear in each case.

18. A method of making a gearbox according to any of claims 14 to 17, and further comprising providing a casing of a single piece of material having a plurality of such 30 cavities machined therein.

19. A method of making a gearbox according to any of claims 14 to 18, wherein the method of construction is limited to two planes or levels for gears.

20. A method of making a gearbox according to any of claims 14 to 18, wherein the 5 method of construction comprises providing three planes or levels for gears.

21. A method of making a gearbox according to claim 20, wherein, to enable a third or more levels of gears to be used within close fitting casings, the gearbox is provided with one or more plates creating a sandwich construction.

22. A method of making a gearbox according to any of claims 14 to 21, wherein the method of construction comprises, to maintain accuracy between front and rear casing, holding the two planes or levels of casings together, for example with dowels, so that an intermediate cavity plate is located within the front and rear casings.

23. A method of making a gearbox according to any of claims 15 to 22, wherein the method of construction comprises providing plates of plastics material or aluminium

24. A method of making a gearbox according to any of claims 19 to 22, wherein the 20 method of construction comprises retaining the plates in position with through dowel pins, rods or the like.

25. A drill head having a gearbox in accordance with any of claims 1 to 13 fitted thereto.

26. A set of one or more gears and one or more plates, wherein the or each plate comprises a close fitting cavity for a respective gear.

27. A gearbox substantially as described herein with reference to one or more of the 30 appropriate accompanying drawings.

28. A method of making a gearbox substantially as described herein with reference to one or more of the appropriate accompanying drawings