Gearboxes generally contain two principal shafts on which the gears are arrayed : the main shaft; and, the layshaft.

Both the mainshaft and the layshaft are disposed within the gearbox casing with their axes parallel to each other and each are supported at least by bearings disposed adjacent the ends thereof. Most gearboxes also contain a reverse idler gear support shaft and an input shaft which usually provides bearing support for one end of the mainshaft.

In an actual vehicle installation the gearbox may be installed with the two shafts orientated either generally one above the other or in a generally side by side relationship. The gearbox casing has a generally oval shape in cross section (orthogonal to the shaft axes) and the mainshaft and layshaft are generally disposed within the casing with the axes thereof orthogonal to and spaced apart along the major axis of the oval.

Where the gearbox is installed in a vertical arrangement with the mainshaft and layshaft one above the other, there is frequently sufficient room within the top portion of the casing to provide features such as oil catching troughs and the like which may be used to duct or otherwise convey additional oil to parts of the

gearbox, such as bearings, for example, which may be only marginally lubricated in the absence of such additional oil conveying means. Furthermore, in vertically orientated gearboxes, the layshaft, which is generally the lower shaft, tends to be more deeply immersed in the oil in the gearbox sump and thus, tends to disperse more copious quantities of oil around the interior of the gearbox casing by the centrifugal action of the rotating gears.

Horizontally orientated gearboxes on the other hand, i. e. those where the mainshaft and layshaft are disposed in a generally side-by-side relationship, often do not have suitable space available within the casing for the provision of oil catching troughs and the like in appropriate positions. Furthermore, a horizontally orientated gearbox, whilst probably containing an equivalent quantity of lubricating oil as in a vertically arranged gearbox, tends to have a lower oil level in the sump thereof since it is spread over a wider area. Thus, the layshaft dips less deeply into the oil and the resulting quantity distributed around the gearbox by the centrifugal action of the rotating gears may be correspondingly less and the oil level falls even further as the oil is being thus distributed.

US-A-5 699 877 describes a gearbox where oil is ducted to main bearings by a trough like oil-catching arrangement as described above.

DE-A-199 12 328 describes an arrangement for additional lubrication of gear-pairs by providing an overhead oil conduit having oil dispensing apertures which are blocked off until a particular gear-pair are selected in loaded

engagement beneath an aperture which is then opened to provide a source of additional lubricating oil to the gear-pair under load.

According to a first aspect of the present invention an arrangement for providing specific lubrication of a selected site within a gearbox comprises a lubricant receiving reservoir adjacent a pair of gearwheels from which lubricant is extruded, in use, during operation of said gearbox and duct means to convey said lubricant to said selected site.

According to a second aspect of the present invention, a method of providing specific lubrication to a selected site within a gearbox comprises the steps of: providing lubricant receiving reservoir means adjacent a pair of gearwheels from which lubricant is extruded, in use, during operation of said gearbox ; and providing duct means to convey said lubricant from said reservoir to said selected site.

The normal mode of distribution of lubricant (hereinafter referred to as"oil") within a gearbox is by oil being thrown around the inside of the gearbox casing by the centrifugal effect due to rotation of the gears. However, some parts of the gearbox may not always receive adequate quantities of oil to prevent damage occurring to bearings or oil seals, for example, when a gearbox is under load.

This is especially the case with large, heavily loaded gearboxes such as may be found in automotive trucks powered by large diesel engines, for example.

In some gearboxes there may not be sufficient room to provide oil catching troughs or the like to collect oil

thrown in a radial direction from the rotating gears.

However, where two gears mesh there is frequently a directional component to the oil flow which is extruded or otherwise expelled (the term"extruded"is ìntended to cover oil expelled in any manner from between meshing gear teeth) from the high pressure region between the meshing gear teeth in the form of a diffuse jet having sufficient directionality for at least some of that oil to be collected. In the more centrally disposed gear- pairs which are distributed along the mainshaft and layshaft there is usually insufficient room to collect this extruded oil and generally it is flung off of the gear to become part of the oil generally distributed around the gearbox by the centrifugal and splash effect described above. However, at the ends of the shafts, the outermost gears tend to be directly adjacent end walls of a gearbox casing where an oil reservoir means may be able to be created to collect oil extruded in a generally axial direction relative to the gearbox shaft axes.

In one embodiment of the present invention, the selected site requiring additional oil supply to correct an otherwise marginal lubrication condition may be a gearbox shaft main bearing, for example, a mainshaft main bearing. Furthermore, in this embodiment the oil collecting reservoir may be formed by a bearing cover member or bearing retaining ring member of the adjacent layshaft bearing or by a power take-off, for example.

The duct means may be formed by a single duct or by a plurality of intersecting or interconnecting duct portions or chambers formed in or on the gearbox casing.

The duct portions may be constituted by holes formed by drilling after casting or by cored holes produced during

the casing casting process, for example, and which may be connected by chamber portions created between casing ribs, for example, by the provision of blanking plates to seal off an inter-rib portion to create a chamber.

The oil may be conveyed from the oil collecting reservoir means to the selected site by means of gravity.

Consequently, the point of entry of the oil to the selected site must be lower under normal operating conditions than the exit point from the oil collecting reservoir means.

According to a third aspect of the present invention there is provided a gearbox having the arrangement of the first aspect and/or made by the method of the second aspect of the present invention.

In order that the present invention may be more fully understood, an example will now be described by way of illustration only with reference to the accompanying drawings, of which: Figure 1 shows a sectional view in plan of part of a gearbox rear main bearing region incorporating an arrangement according to the present invention; Figure 2 shows a part of the rear layshaft bearing of Figure 1 in more detail; Figure 3 shows an end view of the gearbox casing of Figures 1 and 2 ;

Figure 4 shows a more detailed cross sectional plan view of the duct means provided in the embodiment of Figures 1 to 3 ; Figure 5 shows an end view of a section through the reverse idler/reverse gear and layshaft; and Figure 6 which shows a further clarifying partial end view of the gearbox showing the mainshaft and layshaft support bearing bores and other detail.

Referring now to the drawings and where the same features are denoted by common reference numerals.

Figures 1 to 6 show partial cross sections and views through part of the output end of a gearbox 10. The gearbox includes a mainshaft 12 having a reverse gear 14 ; a layshaft 16 having a reverse gear portion 18'to co- operate with the reverse gear 14 of the mainshaft ; and, a reverse gear idler 20. A casing 22 contains all of the shafts and gears. In the embodiment shown and best depicted in Figure 1 which is a plan view, the mainshaft 12 having an axis of rotation 26 and the layshaft 16 having an axis of rotation 28 are disposed in a generally side-by-side relationship with the axes of rotation 26, 28 being parallel to each other. The mainshaft 12 is supported at its output end by a rolling element bearing 30, in this case a taper roller bearing having a plurality of rollers 32 ; the mainshaft 12 also having a output flange 36 to transfer drive to an axle (not shown). Similarly, the layshaft 16 is supported at the output end by a rolling element bearing 40 again in this case a taper roller bearing having a plurality of rollers 42. The roller bearing 40 is mounted in the casing 22 in

a bore 44 by means of the race 46, the bore 44 and bearing 40 being sealed from the ambient atmosphere by a layshaft bearing cover 50. The layshaft bearing cover 50 closes and defines an internal volume 52 between the bearing 40 and the inner surface 54 of the bearing cover 50; this volume 52 constituting an oil receiving reservoir. Lubricating oil 60 denoted by the large arrow 62 is directed into the oil receiving reservoir 52 by being extruded between the teeth of the mainshaft reverse gear 14 and the reverse idler gear 20 and is in the form of a jet (depicted by the arrow 62) having a directional component towards the layshaft bearing 40. The layshaft bearing 40 has itself a pumping action which tends to pump oil in the reverse direction away from the cover member 50 and thus, the extruded oil produced by the squeezing action of the gear teeth is in the form of a jet and is sufficient to overcome the opposite pumping action of the layshaft bearing 40. The volume 52 in the layshaft bearing cover 50 fills with oil up to a minimum level indicated by the root end 68 of arrow 70 shown in Figure 3, however, this is a minimum level and the level may be above this minimum depending upon shaft speed and inclination of the transmission, for example. The oil in the oil receiving reservoir 52 is ducted to the space 74 which lies axially outwardly of the mainshaft bearing 30 and axially inwardly of a mainshaft oil seal 76 which seals against the rotating mainshaft by a lip 80. Whilst the layshaft 16 and bearing 40 may be sealed with the cover 50 since the shaft 16 does not exit the casing 22, the mainshaft 12 must be provided with sealing means since it must exit the casing 22 to drive the flange 36 (the phrases"exit the casing"and"does not exit the casing"mean that at least the end of the relevant shaft is or is not exposed outside the casing to drive a shaft

or a power take-off, for example). Whilst the oil seal 76 retains oil within the casing 22 the rubbing lip 80 also requires to be lubricated to prevent wear thereof and consequent failure. The entry point 84 (depicted by the head of the arrow 70) of oil to the space 74 is at a level lower than the exit point from the reservoir 52.

The duct path (schematically represented by the shaft of arrow 70 in Figures 3 and 6) of oil from reservoir 52 to space 74 is explained most clearly by reference to Figure 4 which shows a more detailed plan view of part of the area spanning the end of the layshaft 16 and cover 50 to the selected site of space 74 between the mainshaft bearing 30, to which it is desired to supply additional oil and the oil seal lip 80 which it is also desired to adequately lubricate. It must be remembered that whilst a small quantity of oil may be sufficient to lubricate, a greater quantity is required to provide adequate cooling.

Owing to the geometrical form of the casing 22 and the relative dispositions of the oil receiving reservoir 52 and the space 74 it is not possible to provide a single straight drilling, for example, from one to the other.

Therefore, a series of interconnected ducts and chambers are created to form the required duct path 70 (denoted in Figure 4 by three arrows 90,92, 94). Firstly, a hole 100 is drilled from the oil receiving reservoir 52 (i. e. the cavity inside the layshaft bearing cover 50) at a height of approximately one third to one half of the diameter of the layshaft support bearing bore 44 from the bottom of the bore to an enclosure 102 on the inside of the gearbox casing casting 22 (see also Figures 3 and 6). The direction of oil flow through the hole 100 is indicated by arrow 90. A second hole 104 is drilled from the cavity 102 to break into a third cross-hole 106 drilled from the outside of the casing 22; the direction of oil flow in

these latter two holes being indicated by arrows 92,94, respectively. Third hole 106 breaks into the cavity 74 between the rear mainshaft taper roller bearing 30 and the oil seal 76 just above the bottom of the mainshaft bearing bore 110. A blanking plate member 112 is fixed across the face of cavity 102 to thereby seal it and similarly, a blanking plug 114 is also provided to seal the end of hole 106 so as to provide a closed oil path 70 (see Fig. 3) from the oil receiving reservoir 52 to the cavity 74 and also to prevent an oil leak to the exterior of casing 22. The three cross drillings 100,104, 106 together constitute the oil path 70 and provide a fall in height from the oil receiving reservoir 52 to the cavity 74 so as to promote oil flow. The cavity 102 is formed between two stiffening ribs 120,122 of the casing casting 22 and the lands 124,126 surrounding the bearing receiving bores 44 and 110 (see Fig. 6). It is not necessary for the blanking plate 112 to provide a complete seal to the cavity 102 as any oil leakage will be internally into the gearbox casing.

Desirably, the fall in height from the layshaft bearing bore drilling 100 to the exit end of the drilling 106 is sufficient to allow for changes in normal driving attitude of the gearbox installed in a truck, for example, so that oil supply to the cavity 74 is continuous.

The above embodiment is merely one example of putting the present invention into effect and is thus not limiting.

Many changes may be made to the detailed implementation of the invention without departing from the spirit and scope thereof. For example, the blanking plate member 112 could be replaced in alternative designs of gearbox by a

conventional so-called core plug to blank off a hole produced by a removable core during the gearbox case casting process. Similarly, whilst the embodiment described above depicts a layshaft which does not exit the casing, gearbox designs exist where a power take-off shaft driven by the end of the layshaft which does exit the casing. Thus, the layshaft bearing cover 50 of the above embodiment may be replaced with a known power take- off assembly where a cover and seal arrangement or some other alternative arrangement is substituted, the arrangement being provided with a space acting as the oil receiving reservoir 52; for example, much in the manner of the space 74 described above. The oil path 70 is formed in the above described embodiment by three conduits 90,92, 94 and a chamber 102, the conduits being in non-linear relationship to each other. The arrangement described is a consequence of the particular gearbox casing design, but however, other gearbox casing designs may permit a straight conduit from the oil receiving reservoir to the selected site requiring additional lubrication. Alternatively, a non-linear conduit from one to the other may be created but nevertheless a single conduit in the sense that it is formed in a single operation, for example, as a removable core during the case casting process.