Patent Publication Number: US-2023160345-A1

Title: Arrangement for an aircraft turbine engine having improved lubrication, the arrangement comprising a shaft rotatably coupled to a following member by means of splines

Description:
TECHNICAL FIELD 
     The present invention relates to the field of aircraft turbine engines. It more particularly relates to an arrangement for being implemented in such turbine engines, this arrangement comprising a rotating shaft rotatably coupled to a following member via a splined connection. 
     The invention relates in particular to the management of the lubrication of the constituent members of such an arrangement. 
     The invention applies preferably to turbine engines comprising a fan driven by a reduction gear, as is known for example from document FR 2 987 402 A1. 
     STATE OF PRIOR ART 
     In aircraft turbine engines, arrangements are provided in which a rotating shaft is rotatably coupled to a following member, via a splined connection. For example, it is a drive shaft rotatably coupled to a gear wheel of a speed reduction gear driving a fan of the turbine engine. According to another example, this gear wheel may be a mechanical power take-off gear on the drive shaft to which it is rotatably coupled. 
     Typically, this type of arrangement is lubricated by being immersed in an oil bath with very little renewal. However, this conventional lubrication technique may not be sufficient if the torque to be transmitted within such arrangements increases. Indeed, such an increase generates higher contact pressures between splines, with a need to discharge energy dissipated at these contacts. 
     This lubrication problem is in addition to the problem of relative axial displacements between the drive shaft and the following member. Such displacements can be caused by differential thermal expansion effects between the component members of the arrangement, especially when the drive shaft has a long axial length. 
     DISCLOSURE OF THE INVENTION 
     In order to address at least partially the above-mentioned drawbacks, one object of the invention is first an arrangement for an aircraft turbine engine comprising a shaft rotating along an axis of rotation, as well as a following member centred on the axis of rotation and rotatably coupled to the shaft by a splined connection comprising first splines integral with the following member, as well as second splines integral with the rotating shaft and cooperating with said first splines. According to the invention, the arrangement additionally includes:
         on either side of the splined connection, respectively an upstream connection for radially centring the following member relative to the shaft, and a downstream connection for radially centring the following member relative to the shaft, the upstream and downstream radial centring connections being axially sliding;   means for spraying a lubricant into a lubricant collection cavity;   at least one lubricant intake passage made through the rotating shaft or the following member, the lubricant intake passage opening on the one hand into said lubricant collection cavity, and on the other hand into a spline lubrication cavity delimited in part by the upstream and downstream radial centring connections; and   at least one lubricant discharge passage made through the rotating shaft or the following member, the lubricant discharge passage opening on the one hand into said spline lubrication cavity, and on the other hand externally to the arrangement.       

     By means of the two radial centring connections, each of which is sliding in the axial direction, the arrangement according to the invention makes it possible to cope with relative axial displacements between the rotating shaft and the following member, for example as a result of differential thermal expansion. 
     In addition, since radial centring is no longer affected by the splines, large radial clearances can be provided at the end of these splines, promoting passage of a stream of lubricant capable of discharging the part of the power dissipated at the contacts between these splines. 
     Furthermore, the design provided for the arrangement according to the invention allows not only satisfactory lubrication of the splines, but also efficient lubrication of the two radial centring connections. 
     The invention moreover has at least one of the following optional characteristics, taken individually or in combination. 
     Preferably:
         the upstream radial centring connection is made by a first upstream centring portion provided on the following member, as well as a second upstream centring portion provided on the shaft and cooperating with the first upstream centring portion so as to define an upstream radial clearance within the upstream radial centring connection;   the downstream radial centring connection is formed by a first downstream centring portion provided on the following member, as well as a second downstream centring portion provided on the shaft and cooperating with the first downstream centring portion so as to define a downstream radial clearance within the downstream radial centring connection; and   each of the upstream and downstream radial clearances is strictly less than the radial clearances at the end of each of the first and second splines.       

     Preferably, the lubricant intake passage(s) is/are made through the first upstream centring portion provided on the following member, and/or the lubricant discharge passage(s) is/are made through the second downstream centring portion provided on the rotating shaft. Nevertheless, any other solution remains possible, without departing from the scope of the invention. 
     Preferably, the lubricant collection cavity is annular and centred on the axis of rotation, said collection cavity being radially inwardly open, and radially outwardly closed. 
     Preferably, the lubricant collection cavity is made within the following member. Alternatively, this cavity could be made of an insert to the following member. 
     Preferably, the following member is arranged around the rotating shaft. 
     Preferably, the following member is a gear wheel. 
     The invention also relates to an aircraft turbine engine comprising such an arrangement. 
     Preferably, the turbine engine includes a fan driven by a reduction gear equipped with at least one gear wheel forming the following member of the arrangement. 
     Finally, one object of the invention is a method for lubricating such an arrangement, implemented by spraying lubricant into the lubricant collection cavity, such that:
         the lubricant passes through said at least one lubricant intake passage to penetrate the spline lubrication cavity, from which the lubricant separates into a main lubrication stream of the first and second splines, and a first connection lubrication stream, passing through the upstream connection from inside to outside the spline lubrication cavity;   then, after passing through the splines, the main lubrication stream of the first and second splines separates into a leakage stream through said at least one lubricant discharge passage, and a second connection lubrication stream, passing through the downstream connection from inside to outside the spline lubrication cavity.       

     Further advantages and characteristics of the invention will become apparent from the non-limiting detailed description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This description will be made with regard to the attached drawings, among which: 
         FIG.  1    represents a schematic side view of a turbojet engine according to the invention; 
         FIG.  2    represents a schematic side view of a part of the turbojet engine shown in the previous figure; 
         FIG.  3    represents a partial cross-sectional view of an arrangement according to one preferred embodiment of the invention, implemented within the turbojet engine shown in  FIGS.  1  and  2   ; and 
         FIG.  4    represents a partial cross-sectional view taken along line IV-IV of  FIG.  3   . 
     
    
    
     DETAILED DISCLOSURE OF PREFERRED EMBODIMENTS 
     With reference to  FIG.  1   , a twin spool turbojet engine  1  is represented. The turbojet engine  1  conventionally includes a gas generator  2 , on either side of which a low-pressure compressor  4 , and a low-pressure turbine  12  are arranged. The gas generator  2  comprises a high-pressure compressor  6 , a combustion chamber  8  and a high-pressure turbine  10 . 
     Hereinafter, the terms “upstream” and “downstream” are considered along a main flow direction of the gases through the turbojet engine, this direction being shown by arrow  14 . The low-pressure compressor  4  and the low-pressure turbine  12  form a low-pressure spool, and are connected to each other by a low-pressure shaft  11  centred on a central longitudinal axis  3  of the turbojet engine. Similarly, the high-pressure compressor  6  and the high-pressure turbine  10  form a high-pressure spool, and are connected to each other by a high-pressure shaft  13  centred on the axis  3  and arranged around the low-pressure shaft  11 . The shafts are supported by roller bearings  19 , which are lubricated by being arranged in oil enclosures. The same applies to the hub of the fan  17 , which is also supported by roller bearings  19 . 
     The turbojet engine  1  moreover includes, at the front of the gas generator  2  and the low-pressure compressor  4 , a fan  15  which is here arranged directly behind an engine air inlet cone. The fan  15  is rotatable along the axis  3 , and surrounded by a fan casing  9 . The fan  15  is not driven directly by the low-pressure shaft  11 , but is driven indirectly by the low-pressure shaft  11  via a reduction gear  20 , which allows it to rotate at a slower speed. 
     Furthermore, conventionally, the turbojet engine  1  defines a primary duct  16  through which a primary stream is to pass, as well as a secondary duct  18  through which a secondary stream radially outwardly located with respect to the primary stream, is to pass. 
     With reference now to  FIG.  2   , a part  22  of the turbojet engine is represented schematically, comprising the reduction gear  20  and the low-pressure shaft  11 , as well as a lubrication system  24 . 
     More precisely, the lubrication system  24  first includes an oil enclosure  26  enclosing the reduction gear  20 , through which the low-pressure shaft  11  passes. It also includes a lubricant tank  28 , as well as a feed pump (not represented) which can be mechanically driven by the rotation of the high-pressure shaft  13  via a known transmission system. Alternatively, the feed pump may be decoupled from the shaft  13  and rotatably driven by an electric motor so that its lubricant flow rate may be adjusted by controlling the speed of rotation of the pump by controlling the speed of the electric motor. The tank  28  communicates with a lubricant intake duct  34 , one end of which communicates with means  36  for spraying a lubricant. These means  36  preferably take the form of one or more nozzles, or similar means. They are configured to spray lubricant onto all or part of the gearing of the reduction gear  20 . 
     The enclosure  26  has a bottom  38 , and a lubricant recovery duct  40  communicates with a low point  42  of the enclosure bottom  38 . It allows the lubricant that has been previously sprayed by means  36  onto the reduction gear to be collected by gravity and redirected to the tank  28 . 
     The reduction gear  20  is centred on the geometric axis  3  of the low-pressure shaft  11 , which is also the geometric axis of the hub of the fan  17 . Also, this axis  3  corresponds to the axis of rotation of the fan  17  and the low-pressure shaft  11 . The reduction gear  20  includes an epicyclic gear train, which in the configuration represented is conventionally equipped with a gear wheel  52  forming an internal sun gear, centred on the axis  3 . The internal sun gear  52  is rotatably coupled about an upstream end of the low-pressure shaft  11 , in a manner specific to the invention which will be detailed below. 
     The reduction gear moreover comprises an external sun gear, also called the external ring gear  54 , corresponding to the output member of the reduction gear which is rotatably integral with the hub of the fan  17 . Finally, it includes a fixed planet carrier  58 , supporting an annular row of planet gears  56  arranged between the sun gears  52 ,  54 . Other configurations are of course possible for the reduction gear, in particular with a rotating planet carrier corresponding to the output member of the reduction gear, a rotating internal sun gear and a fixed external ring gear. 
     Under normal operating conditions of the turbojet engine, the high-pressure shaft  13  rotates at a sufficiently high speed to drive the feed pump of the system  24 . Lubricant then flows at a high flow rate and pressure through the lubricant intake duct  34 , before being sprayed by the means  36  onto the gearing of the reduction gear  20 . The lubricant then flows by gravity to the enclosure bottom  38 , to be collected by the recovery duct  40 , and then reinjected into the system. 
       FIG.  3    represents an arrangement  60  according to one preferred embodiment of the invention, this arrangement being integrated with the turbojet engine part  22  shown in  FIG.  2   . 
     The arrangement  60  includes a drive shaft formed by the low-pressure shaft  11 , a following member formed by the internal sun gear  52 , and finally the nozzle  36 . 
     The sun gear  52 , centred on the axis  3  and arranged around an upstream end of the low-pressure shaft  11 , is rotatably coupled to the latter via a splined connection  62 . More precisely, the connection  62  includes first splines  62   a  integral with the sun gear  52  and radially inwardly projecting, as well as second splines  62   b  integral with the shaft  11  and radially outwardly projecting. The first and second splines  62   a ,  62   b  cooperate together in a circumferential direction. On the other hand, at the end of each of the first and second splines  62   a ,  62   b , there is a fairly large radial clearance J 3 , defined respectively with an external surface  63  of the shaft  11 , and an internal surface  64  of the sun gear  52 . As is visible in  FIG.  3   , it is from these surfaces  64  and  63  that the splines  62   a ,  62   b  inwardly and outwardly protrude respectively. 
     The external surface  63  of the shaft  11  and the internal surface  64  of the sun gear  52  thus radially delimit an annular lubrication cavity  66  of the splines  62   a ,  62   b , centred on the axis  3 . Axially, this annular cavity  66  is wholly or partly delimited by two connections for radially centring the shaft  11  and the sun gear  52 , these two connections being arranged on either side of the splines  62   a ,  62   b.    
     Firstly, there is an upstream connection  68   a  for radially centring the sun gear  52  relative to the shaft  11 , and then a downstream connection  68   b , still for radially centring the sun gear  52  relative to the shaft  11 . These two connections  68   a ,  68   b  are made to slide axially, in particular to absorb differential thermal expansions between the sun gear  52  and the shaft  11  in the axial direction. Preferably, these connections  68   a ,  68   b  also have a small radial clearance, also to absorb the radial differential thermal expansions between the sun gear  52  and the shaft  11 . This small radial clearance also allows for lubrication of the connections  68   a ,  68   b , as will be described below. 
     More precisely, the upstream centring connection  68   a  is made by a first upstream centring portion  70   a , in the form of an annular wall or flange protruding radially inwardly from the internal surface  64  of the sun gear  52 . It is also made using a second upstream centring portion  70   b , corresponding to a part of the external surface  63  of the shaft  11 . Between these two upstream portions  70   a ,  70   b , the upstream radial clearance J 1  is defined, corresponding to the radial clearance of the upstream connection  68   a.    
     Similarly, the downstream centring connection  68   b  is made by a first downstream centring portion  72   a , corresponding to a part of the internal surface  64  of the sun gear  52 . It is also made by a second downstream centring portion  72   b , in the form of an annular wall or collar radially outwardly protruding from the external surface  63  of the shaft  11 . It is noted that the annular wall  72   b  extends from a portion  11   a  of the shaft  11 , which has a diameter greater than that of the upstream end of the shaft bearing the second splines  62   b . Thus, the annular wall  72   b  radially outwardly extends beyond the second splines  62   b , and it is at this same wall  72   b  that the break in diameter between the portion  11   a  of the shaft  11 , and its upstream end incorporating the second splines  62   b  is marked. 
     Between the two upstream portions  72   a ,  72   b  forming the downstream connection  68   b , the downstream radial clearance J 2  is also defined, corresponding to the radial clearance of this downstream connection  68   b.    
     With the purpose in particular of ensuring that the splines  62   a ,  62   b  do not contribute to the radial centring of the sun gear  52  relative to the shaft  11 , it is ensured that the upstream and downstream radial clearances J 1 , J 2  are strictly less than the radial clearances J 3  at the end of the splines. This feature also makes it possible to provide a main lubrication stream through the splines  62   a ,  62   b , as will be described below. 
     At the upstream end of the sun gear  52 , the latter delimits an annular cavity  74  for collecting the lubricant sprayed by the nozzle  36 . This annular cavity  74  is delimited axially upstream by an annular rim  76  projecting radially inwardly from the internal surface  64  of the sun gear  52 , and delimited downstream by the first upstream centring portion  70   a . The cavity  74  is closed radially inwardly by a bottom  78  akin to a portion of the internal surface  64  of the sun gear  52 , while it remains open radially. In fact, a radial annular opening  80  faces radially a spraying end of the nozzle  36 , so that the lubricant sprayed by the nozzle  36  easily penetrates the annular collection cavity  74  centred on the axis  3 . 
     Moreover, the first upstream centring portion  70   a  has one or more lubricant intake passages  86 , for example axially oriented, passing therethrough. Each passage  86  thus opens on the one hand upstream into the lubricant collection cavity  74 , preferably in the vicinity of the bottom  78 , and on the other hand downstream into the cavity  66  for lubricating the splines  62   a ,  62   b.    
     Furthermore, the second downstream centring portion  72   b  has one or more lubricant discharge passages  88  passing therethrough, for example axially oriented. Each passage  88  thus opens on the one hand upstream into the lubrication cavity  66  of the splines  62   a ,  62   b , and on the other hand downstream, externally to the arrangement  60 , preferably into the aforementioned oil enclosure  26 . 
     As is depicted in  FIG.  4   , each lubricant discharge passage  88  assumes an angular position, with respect to the axis  3 , which is different from the angular position of each lubricant intake passage  86 . An angular offset of 120° can be assumed between these passages  86 ,  88 , as represented in  FIG.  4   . Other angle values are of course possible, for example 90°. This angular offset ensures that the lubricant is maintained when the turbojet engine is stopped, whatever the angular position of the rotating assembly  11 ,  52 . This feature avoids the risk of the turbojet engine starting dry, by ensuring a minimum of lubricant in the splines  62   a ,  62   b.    
     Returning to  FIG.  3   , the operation of the arrangement  60  and the method for its lubrication will be described. 
     The lubricant, preferably oil, is first sprayed from the nozzle  36  into the collection cavity  74 . The rotation of the rotating assembly  11 ,  52  causes a centrifugal force to force the lubricant towards the bottom  78  of the collection cavity  74 . All of the lubricant collected in the cavity  74  then passes downstream, through the lubricant intake passages  86  to penetrate the lubrication cavity  66  of the splines  62   a ,  62   b.    
     After penetrating the cavity  66 , the lubricant separates into a main lubrication stream F of the first and second splines  62   a ,  62   b , and a first connection lubrication stream F 1 , passing through the upstream connection  68   a  from inside to outside the cavity  66 . The dimensioning of the members of the arrangement  60  is made such that the first stream F 1  through the upstream connection  68   a  remains quite small compared to the main stream F to lubricate the first and second splines  62   a ,  62   b . For example, the first stream F 1  through the upstream connection  68   a  represents about ⅕ of the total flow rate introduced into the cavity  66 , while the main stream F represents about ⅘ of this total flow rate. 
     After passing through the splines  62   a ,  62   b , the main lubrication stream F separates into a leakage stream F′ through the lubricant discharge passage  88 , and a second connection lubrication stream F 2 , passing through the downstream connection  68   b  from inside to outside the cavity  66 . The lubricant of the leakage stream F′ is thus extracted axially from the arrangement  60  through the discharge passage  88  and then falls back preferentially by gravity into the bottom of the aforementioned oil enclosure  26 . 
     Here again, the dimensioning of the members of the arrangement  60  is made such that the second stream F 2  through the downstream connection  68   b  remains quite small compared to the leakage stream F′ through the lubricant discharge passage  88 . For example, the second stream F 2  through the upstream connection  68   b  also represents about ⅕ of the total flow rate introduced into the cavity  66 , while the leakage stream F′ represents about ⅗ of the total flow rate. 
     In general, the dimensioning of the members of the arrangement  60  is also made such that that non-zero flow rates are observed for each of the lubrication streams F 1 , F 2  and F′, whatever the operating conditions of the turbojet engine. 
     Of course, various modifications may be made by the person skilled in the art to the invention just described, solely by way of non-limiting examples, the scope of which is delimited by the appended claims.