Assembly including an AGB and an oil tank

An assembly that includes an accessory gearbox (AGB) and a tank for a liquid lubricant for a turbojet engine. The AGB includes a gear connected to parallel shafts for mechanically driving accessories. The assembly includes a housing with two compartments and a partition perpendicular to the shafts for separating the compartments, a compartment defining the accessory gearbox and a compartment defining the liquid tank. The assembly can be compact and easily manufactured.

The invention relates to an assembly comprising an accessory gearbox and a reservoir of lubricant for a turbojet engine.

A turbojet engine comprises, from the upstream and downstream in the direction in which the gases flow, a fan, one or more compressor stages, for example a high-pressure compressor, a combustion chamber, one or more turbine stages, for example a high-pressure turbine and a low-pressure turbine and a jet pipe through which the gases are exhausted. Each compressor has a corresponding turbine, the two being connected by a shaft, thus, for example, forming a high-pressure spool and a low-pressure spool.

Some of the power generated by a turbojet engine is used to power various auxiliaries of the turbojet engine. This power is tapped mechanically off the shaft of the high-pressure (HP) spool of the turbojet engine by a power take-off shaft which drives an input shaft of an accessory gearbox.

The accessory gearbox is well known to those skilled in the art by its English abbreviation AGB (which stands for accessory gearbox or auxiliary gearbox). This is a box containing gearing (a mechanism) connected to a certain number of auxiliaries or accessories, such as an electric generator, a starter motor, an alternator, hydraulic, fuel or oil pumps, etc, for example. These various accessories are mechanically driven by the gearing of the AGB which, via the input shaft entering the AGB, transmits to them the power tapped from the HP shaft.

The AGB generally comprises a box which is produced as a casting; it thus comprises a cast wall defining a housing to accommodate the gearing that drives the accessories. Each gearwheel of the gearing is secured to a driveshaft connected to an accessory. The various accessories driven by the AGB are mounted directly on the cast box, the drive shafts of the accessories passing through the wall of this box in order to drive them.

The engine also comprises a lubricating circuit which supplies oil to the various engine components that need it. The lubricating circuit more specifically comprises an oil reservoir, a lubricating unit (which circulates the oil through the circuit), and oil lines that carry the oil to the components that require lubrication. The lubricating unit is generally mounted near the AGB because it is driven thereby.

In some engines, for reasons of compactness and to save on piping it is preferable for the oil reservoir to be mounted directly on the AGB. To do that, the oil reservoir can in fact be formed as an outgrowth on the casting that forms the housing part of the AGB. The problem with this type of casting is the difficulty in the designing and manufacturing thereof because casting is a technique that is difficult to master and the cost of such a component with an outgrowth, which is therefore complicated, is considerable.

In other engines, the oil reservoir is separated from the AGB, making it possible for the AGB to be formed directly by machining a metal slug. Such components that are produced directly by machining are commonly known to those skilled in the art as components that are “machined from solid”, for which the equivalent French terms are “usinées-masse” or “taillées-masse”. More specifically, in this case, the AGB can be formed using a technique known as “split-line” (an expression derived from the fact that there is a dividing line), in which two half-shells are used to form the AGB housing. The oil reservoir, formed as a casting, is therefore remote from the AGB and needs to be connected to it, this entailing the use of piping to connect the two together.

The invention aims to propose a simpler design of AGB and oil reservoir, that allows these items to be manufactured at lower cost.

Thus, the invention relates to an assembly comprising an accessory gearbox and a reservoir of lubricant for a turbojet engine, the accessory gearbox comprising gearing connected to mutually parallel shafts that mechanically drive the accessories, the assembly being characterized in that it comprises a box with two compartments and a partition, perpendicular to said shafts, that separates the compartments, one compartment forming the accessory gearbox and one compartment forming the lubricant reservoir.

Thanks to the invention, the assembly is an integral one and therefore compact, whereas its manufacture is simple because of the way the compartments are arranged in relation to the shafts connected to the gearing.

According to a preferred embodiment, the box for the whole assembly (and therefore the compartments) has generally a shape that is elongate and curved, designed to follow the shape of a cylindrical casing of the turbojet engine to which it is intended to be fixed.

It will be understood that, in this case, with the turbojet engine running generally along an axis, the gearing of the accessory gearbox is intended to be driven by a power take-off shaft substantially perpendicular to the axis of the turbojet engine.

According to one preferred embodiment, the compartments are manufactured by machining from a solid block of metal. The use of such a method of machining from a block of material means that the compartments are formed without a casting operation; in other words, this type of method allows the manufacture of components generally known by the expression “machined from solid” (for which the French equivalents are “usinées-masse” or “taillées-masse”). The use of such a method resolves the problems listed above in terms of the use of casting and is made possible by the abovedefined configuration of the compartments of the assembly.

According to one preferred embodiment, the compartments are formed of two half-shells fixed together.

According to one preferred embodiment, each half-shell comprises at least one opening delimited by an edge and the half-shells are fixed together along this edge, preferably with the partition.

According to one preferred embodiment, the opening of each half-shell has dimensions which are greater than or equal to those of the projection, onto a plane perpendicular to the drive shafts, of the gearing of the accessory gearbox.

According to one preferred embodiment, the half-shells are fixed together, preferably with the partition, removably, for example by screw-fastening. Thus, it is possible for them to be taken apart in order to gain access to the interior of the compartment that forms the box part of the AGB for servicing and maintenance purposes.

According to one preferred embodiment, the partition is secured nonremovably to the half-shell that forms the lubricant reservoir, for example is welded thereto.

According to one embodiment, the compartments are of a shape that is elongate in a general direction perpendicular to the accessory drive shafts.

According to a preferred embodiment, the compartment that forms the lubricant reservoir also acts as a support for at least some of the accessories driven by the accessory gearbox.

According to one form of embodiment which is preferred in this instance, with the drive shafts that drive said accessories extending at least partially into the compartment that forms the reservoir, protective tubes, along which said shafts extend, are mounted in the reservoir.

The invention is described with reference to a turbojet engine. The turbojet engine comprises a high-pressure spool and a low-pressure spool, each spool comprising a compressor and turbine, in the conventional way. Mounted on the high-pressure spool is a power take-off mechanism driving a power take-off shaft mechanically connected to an accessory gearbox1hereinafter known by its abbreviation AGB1. More specifically, the power take-off shaft transmits the movement from the rotary shaft of the high-pressure spool to an input (or drive) shaft of the AGB1. The input shaft of the AGB1is connected to the AGB1by a connecting piece11fixed to a wall of the AGB, in this instance to the upper wall inFIG. 1. The input shaft, supported by the connecting piece11, passes through the upper wall of the AGB1in the conventional way.

The turbojet engine also comprises a lubricating circuit comprising an oil reservoir2, a lubricating unit9a(not depicted inFIG. 1but visible inFIG. 2) and lines carrying the oil to the components that need lubricating, the lines not being depicted. Note, as shown inFIG. 3, that the lubricating lubricant unit9acomprises in this instance an oil feed pump feeding oil to a main line200from which the oil is guided so that it can be fed to all the oil supply lines201that supply the various engine components202with oil, these lines being connected directly or indirectly to the main oil line. The lubricating unit9afurther comprises a plurality of pumps—in this instance four pumps—which suck up the oil recovered (generally under gravity) from the turbojet engine components that have been lubricated; the oil thus recovered is reintroduced into the oil reservoir2from where it is pumped into the main line of the circuit. The lubricating circuit supplies lubricating oil to those engine components or auxiliaries that need it, for example to the engine shaft bearings or the gearing of the AGB1.

With reference toFIG. 1, the AGB1and the oil reservoir2are designed to form an integrated assembly E. This assembly E comprises a box4formed of two half-shells4a,4bdefining a first compartment5aand a second compartment5b, respectively, the two compartments5a,5bbeing separated by a partition6.

The first compartment5aforms the AGB1. For this purpose, it creates a housing for gearing7(or a mechanism7) mechanically connected to the input shaft of the AGB1, the gearing7being designed to transmit the movements of the input shaft from the AGB1to accessories9a,9b,9c,9d,9e,9fof the turbojet engine. The gearing7comprises a plurality of gearwheels7a,7b,7c,7d,7e,7fsecured to a plurality of shafts8a,8b,8c,8d,8e,8fdriving respective accessories9a,9b,9c,9d,9e,9f. It further comprises a gearwheel7g, in this instance a bevel gear7g, secured to one of the shafts8d, which meshes with a bevel gear secured to the input shaft of the AGB1to drive all the wheels7a-7fof the gearing7by the input shaft of the AGB1. Each drive shaft8a,8b,8c,8d,8e,8fextends along an axis8a′,8b′,8c′,8d′,8e′,8f′. The shafts8a-8fare arranged parallel to one another in a way that is conventional in an AGB1. In this particular instance, the accessories comprise the lubricating unit9a, a fuel pump9b, an air-driven starter9c, a low-power generator9dsuch as a permanent-magnet motor, a starter generator9eand a hydraulic pump9f; these accessories9a-9fare listed by way of example.

The second compartment5bacts as an oil reservoir for the lubricating circuit; or in other words, it forms the oil reservoir2for this circuit. It forms a closed space in which the oil lies.

The partition6that separates the two compartments5a,5bfrom one another is fixed between the two half-shells4a,4bthat form the compartments5a,5band prevents any fluidic communication between the two so as to prevent oil from the reservoir2from flowing unwantedly into the compartment5aof the AGB1. The partition6runs perpendicular to the shafts8a,8b,8c,8d,8e,8f.

The assembly E comprising the AGB1and the oil reservoir2is, in this instance of a shape that is generally elongate. More specifically, the box4of the assembly E has generally a shape that is elongate and curved, in this instance designed to follow the shape of a (cylindrical) casing of the turbojet engine to which it is intended to be fixed. A person skilled in the art speaks often of a “banana” or “kidney bean” shape; this more specifically is a shape with faces (the front and rear faces inFIG. 1) that are perpendicular to the drive shafts8a-8fwhich are planar and mutually parallel, these (front and rear) faces being connected by faces (lower and upper faces inFIG. 1) each of which is in the shape of a portion of a cylinder; the ends of the box4are formed by the curved faces that continuously connect the cylindrical faces together. The major (mean) dimension of the assembly E is perpendicular to the shafts8a-8fthat drive the accessories9a-9f.

Each half-shell4a,4bhas an opening over the entirety of a face which is perpendicular to the drive shafts8a-8fthat drive the accessories9a-9f. The opening of each half-shell4a,4bis delimited by an edge10a,10b, here in the form of a respective flange10a,10b; thus, this flange10a,10bruns perpendicular to the drive shafts8a-8f. The half-shells4a,4bare fixed together along these flanges10a,10bin this instance by screw-fastening. The dividing partition6is also fixed to the assembly E by screw-fastening; in this particular instance, the same screws join the flanges10a,10btogether and to the periphery of the dividing partition6which is sandwiched between the flanges10a,10b.

Thanks to the configuration of the assembly E with a dividing partition6perpendicular to the shafts8a-8f, it is possible for the AGB1and the oil reservoir2to be manufactured simultaneously by a method of machining from a solid block of metal, for example a metal slug, made of aluminum, of titanium or of magnesium, for example. Such a machining method is far less expensive to implement than a method of manufacture involving casting. It is to some extent a method that makes it possible to obtain a box4constructed in “split-line” technology, with two compartments separated by a partition and performing distinct functions.

In as much as the dividing partition6is perpendicular to the drive shafts8a-8f, that means that the opening of the half-shells4a,4bthat form the AGB1and the oil reservoir2are sufficient in size to allow a machining method to be employed and, in particular to allow the machine tools, for example milling cutters, to pass. In particular, the openings here have dimensions corresponding to the projected image of the set of gearing7that the AGB1is to contain onto a plane perpendicular to the drive shafts7, for example onto a mean plane of the dividing partition8; this projected image or projection corresponds to the transverse space that needs to be allowed, with respect to the axes8a′-8f′of the drive shafts8a-8f, for the gearing7of the AGB1.

According to an alternative form of embodiment that has not been depicted, the dividing partition6is fixed securely and nonremovably to the half-shell4bthat forms the oil reservoir2; such an attachment may for example be achieved by welding. The advantage of such a solution is as follows: it may sometimes prove necessary to remove the assembly E comprising an AGB1and a reservoir2in order to carry out maintenance operations on the gearing7of the AGB1. Such operations are not, however, needed on the oil reservoir2. Consequently, it is possible for the partition6to be secured fixedly to the oil reservoir2but fixed (together with the oil reservoir2) removably to the half-shell4athat forms the AGB1.

With reference toFIG. 2(but not toFIG. 1where they have not been depicted), certain accessories9a,9c,9eare mounted directly on the half-shell4bthat forms the oil reservoir2. More specifically, the lubricating unit9ais mounted, in part, directly within the volume of the oil reservoir2(inside a protective sleeve12) and thus the pumps of the lubricating unit9asuck up the oil from or deliver oil to the reservoir2directly. The air-powered starter9cand the starter—generator9eare mounted on the wall of the half-shell4bthat faces the dividing partition6and therefore extends at right angles to their drive shafts8a-8f(it is the front wall inFIG. 1). These drive shafts8c,8etherefore pass through the volume of the compartment5bthat forms the oil reservoir2and in order for the fact that the shafts8c,8eextend through the compartment5bnot to be a problem, protective tubes8c″,8e″ are mounted in the compartment5b, between the dividing partition6and the opposite wall of the half-shell4b, to house the drive shafts8c,8ewhich therefore extend through these protective tubes8c″,8e″, the protective tubes preventing any direct contact between the drive shafts8c,8eand the oil contained in the reservoir2.