Epicyclic speed reducer designed for fitment to the transmission between the gas turbine and air compressor of an aircraft engine

Thursday 12 September 2013

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Abstract

A speed reducer has a sun gear for connection to an engine turbine and a planet carrier supporting a number of planet gears meshing with the sun gear and the ring gear mounted on the motor mounting. According to the present invention, the planet carrier having a first annular element having pairs of seats for the bolts in each of which rotates one of the planetary gears. A second annular element for connection to a motor compressor has a number of axial arms mounted within the respective cavities of the first annular. An axial end of each arm is connected to a first annular portion which is substantially equidistant between the seats of each pair of seats.
Description 
BRIEF DESCRIPTION OF THE DRAWINGS 
The speed reducer according to the present invention is described by way of example, with reference to the accompanying drawings , in which:. FIGURE Figure 1 shows a schematic view of an aircraft turbine engine equipped with a speed reducer according to the present invention;. Figure 2 shows a longitudinal section of the reducer ;. Figure 3 shows a section of the gearbox along line III - III of Figure 2;. Figure 4 shows a side view of the reducer ;Figures . 5, 6 and 7 show enlarged details of Fig . 2 section .
DETAILED DESCRIPTION OF THE INVENTION

Epicyclic speed reducer according to the present invention is designed for use in an aircraft turbine engine of the type shown schematically in Fig . 1 and comprising a gas turbine 1 and an air compressor driven by the turbine 2 1. Compressor 2 is connected to the impeller 1 by a shaft 3 and the speed reducer, indicated overall by 4, is mounted between the shaft 3 and the compressor 2 .As shown in the figure. 2, 4 reducer substantially comprises a sun gear 5 connected to shaft 3, as described below , and a planet carrier 6 coaxial with the sun gear 5 and which supports a number of planetary gear 7 meshing with the sun gear 5, and with a gear ring 8 installed on motor assembly 9 as described below .According to the present invention, the planet carrier 6 comprises a first annular element 10 provided with pins 13 supported at the ends in the seats 11 formed in two sidewalls of support 6 . Planetary gears 7 to rotate on pins 13 and , as shown in Fig . 3 are accommodated within the respective cavities 14 formed in holder 6 . In the embodiment shown , there is provided five planetary gears 15 separated by a bridge defined by the material of the element 10 .First annular element 10 also comprises a series of recesses 16 , each formed in a respective bridge 15 and thereby interposed between two adjacent planetary gear 7 .Planet carrier 6 also comprises a second substantially annular member 17 connected to the compressor 2 as described below, and which has a number of axial arms 18 , each designed to fit within one of the cavities 16 in element 10 , as shown in the figure. Two .Planet carrier 6 also comprises connection means 19 for connecting the end of each arm 18 a portion of element 10 is indicated by 20 and substantially equidistant with respect to the seats 11 of the pins 13 . Planetary gear teeth 7 frontally defined by surfaces 21 and 22 , each located on one side of a respective seat

Connecting means 19 substantially comprise a hinge , the axis of which is positioned radially in relation to the gearbox shaft and is equidistant in relation to seats 11.Each arm 18 of the element 17 has a substantially rectangular section (Figure 3) , and hinge connecting means 19 comprises a radial pin 25 (Figure 6) which is inserted inside respective radial holes in the element 17 and the arm 18 . Between the pin and said radial holes 25 , there are inserted bushes 26 , one between the pin 25 and the hole in the arm 18 , and two between the pin 25 and the hole in the element 17 . Bushings 26 advantageously has a collar shoulder 27. Pin 25 has an annular projection 28 designed to rest on one of the bushes 26 , and a screw 29 , the head 30 of which rests on the shoulder of one of the bushes 26 , is screwed into a threaded hole in the pin 25 in order to lock the pin assembly comprising the three caps 25 and 26 in the element 17.The planet carrier member 10 6 has a sleeve 33 (Figure 2) connected by a flange 34 to the air compressor 2 which , as shown in Fig . 2 projecting axially from the element 10 on the opposite side to that from which the arms 18 project .Each of the pins 13 on the planet gears revolve 7 has a central cylindrical portion 35 (Figure 5) constitutes a support seat for a respective planetary gear 7 and two cylindrical end portions 36 of lesser diameter than the central portion 35 and each force fitted inside a seat 11 formed in a respective cover 38, 39 equipped with the member 10 . The cover 38 is housed in a seat 40 in the element 10 , and has a radial projection 41 and a radial projection 42 resting on the shoulder 43 of the portions 36 of the pin 13 and is locked thereto by a nut threaded ring 44 . Cover 39 , also housed in a seat 45 in the element 10 , has a radial projection 46 resting on the shoulder 47 of the portions 36 and locked thereto by a ring nut 48 . The assembly comprising the pin 13 and covers 38 and 39 is prevented from moving axially to the right projection 41, and moves axially to the left by a ring 49 mounted by screws 39 to cover .According to the present invention, the cylindrical central portion 35 of each pin 13 has two annular grooves 50 , each open at the side facing the corresponding cylindrical portion 36, and each defined by a surface 51 of the outer surface mixture part 36 . The axial depth of each slot 50 desirably equals at least a fifth of the axial length of the central portion 35 of the pin 13.Between each pin 13 and respective planet gears 7 is inserted force cap 52 fitted inside the planetary gear 7 and the element 10 inside the cover 38 and each pin 13 is formed a conduit 53 ( Figure 5 ) to feed oil pressure in a cavity 54 in the surface of the central cylindrical portion 35, and which is conveniently fitted with a filter 56 locked by a cap 57 .Gears which are part of the epicyclic gear train conveniently presented two sets of helical teeth , as shown in Fig . Two . Therefore, ring gear 8 also has two sets of internal helical teeth 58, and comprises two rings 59 , each supporting , inside one of the above sets of teeth, and , externally , a set of external teeth 60 which mesh with corresponding teeth in a sleeve 61 having an annular rib to which are mounted two rings of shoulder 63 62 . Each ring 63 provides to axially lock one of the rings 59 on the sleeve 61 by bolts 64 .The gearbox also comprises an annular housing 65 mounted in any suitable way to mount the motor 9 and the cover rings 59, the sleeve 61 and the rings of shoulders 63 . Each ring of the shoulder 63 has a series of radial projections 66 outwards ( Figures 2 and 3 ) and the annular housing 65 two sets of radial projections 67 inwards. Between each projection 66 at one of the ring shoulder 63 and a corresponding shoulder 67 on the box 65 is inserted at least one flexible blade 68 . Each blade 68 is screwed to said protrusions as shown in Fig . 2 and , instead of a single sheet 68, the sheet packages can be used , or these can be replaced by rings (or rings packs ) connected as described above with projections 66 and 67. Blades ( or rings) 68 and provided to elastically connect the housing rings 59 and 65 and thus allows axial and radial displacement of the rings 59 relative to the housing 65 , as well as variations in the angular position of the rings and the box.Sun gear 5 has a hollow shaft 69 ( Figure 2 ) housed substantially within the sleeve 33 of element 17 and having internal teeth 70 which meshes with convex teeth formed on the convex outer surface of the shaft 3 of the turbine 1 so to form a hinge which also allows for variations in the angular position of the hollow shaft 69 and the shaft 3.

The gearbox according to the present invention operates as follows.Shaft 3, driven by the turbine 1 rotates the sun gear 5, which in turn rotates the planetary gears 7 . These mesh with the ring gear 8 which is fixed relative to the engine mount , so as to rotate the planetary carrier 6 and thus drive the air compressor 2 .During reducer operation , despite considerable pressure that is exchanged between the planetary gears respective pins 7 and 13, it was found that the pin 13 to undergo substantially no deformation to bending under design conditions and moderation of the pins. In fact , we have found the presence of grooves 50 formed in the central portion 35 of each pin 13 to contribute substantially to the reduction of the bending deformation of the pin, is also reduced by the presence of end portions smaller-diameter 36 and the manner in which portions 36 are restricted ( fitted ) inside the seats 11 formed in the covers 38, 39 integral with the element 10 .During reducer operation , extremely high torque is transmitted through the planetary gear 7 to first planet carrier element 10 6, and the element 10 through connecting means 19 to the arms 18 of the second element 17. Consequently, first annular each pin 10 is subjected to shear forces 13 on the seats 11 in which are fitted the end portions 36 of the pin 13 and the arms 18 are held by means of radial pins 25 of the attachment means 19 to other shear forces in a plane located substantially perpendicular to the gearbox shaft and equidistant in relation to the planes tangential forces exchanged between end portions 36 of pins 13 and seats 11. Element 10 is therefore subjected to a perfectly symmetrical forces resulting in substantially no deformation of the element 10 which may possibly affect the pressure distribution between the teeth of the planet gears 7, the sun gear 5 and the ring gear 8 . During operation, therefore, the pressure distribution between the gear teeth is substantially unaffected , and no dangerous buildup of pressure produced.Finally, the resilient connection between the ring 59 and the housing 25 allows a small amount of displacement of the rings 59 relative to the housing 25 , to compensate for errors in the assembly and any movement (axial , transverse and angular ) which produced during operation of the gearbox. As such, the pressure distribution between the teeth of the planetary gears ring gear 7 and 8 also is not affected during the operation.To those skilled in the art it will be clear that changes may be made to the speed reducer as described and illustrated herein without , however , departing from the scope of the present invention . 
Background of the Invention
 The present invention relates to an epicyclic speed reducer designed to be installed in the transmission between the gas turbine and air compressor of an aircraft turbine engine .In engines of the type mentioned above, the air compressor is driven by the turbine via a shaft. To achieve a high efficiency of the turbine and the compressor , however , the rotation speed of the compressor must be less than the turbine , for which the transmission between the turbine and the compressor normally has a speed reducer substantially comprises a planetary gear connected to the turbine , a planet carrier coaxial with the sun gear and supporting a number of planet gears meshing therewith, and a gear ring mounted on the assembly and with which the gears mesh planetary . Motor planetary carrier , which constitutes the gear unit output element is connected to the compressor through the rigid link means complex design .Planetary gear units of the above type have several drawbacks .The most important of which is the deformation in service , sometimes severe , which planet carrier is subjected and that can affect the geometry of the company and therefore , uniform distribution of the pressure between the teeth of reduction gears . This is because the connection means above that provided for transmitting torque between the planet carrier and the air compressor , exerting severe strain on the connecting portions of the carrier and their own connection means . As said connecting portions are in a side surface of the planet carrier , while the resultant of the forces transmitted between the gear teeth are substantially in the plane of the carrier , a distribution pattern of the tension very complex resulting in severe deformation originated within the carrier .Moreover, during operation of the gearbox , the flexural deformation is too severe to pins that support the planetary gears , that the deformation also has an adverse effect on the distribution of pressure between the teeth of the reduction gear .Finally, the uniform distribution of the pressure between the teeth of the reduction gear is also affected by the connection of the ring gear in the gearbox to the engine mounting , the connection is normally made using rigid connecting means allowing substantially any displacement of the ring gear in response to deformation in the other components of the gearbox.
 SUMMARY OF THE INVENTION 
It is an object of the present invention is to provide an epicyclic speed reducer of the type described above, designed to overcome the aforementioned drawbacks .

According to the present invention there is provided an epicyclic speed reducer designed to be installed in the transmission between the gas turbine and the air compressor of a turbine engine aircraft , said reducer comprises a planetary gear connected to said turbine , a planet carrier coaxial with said sun gear and which supports a number of planetary gears meshing with said sun gear , and a ring gear mounted to the motor assembly and with which said planet gears mesh , said planet carrier is connected to said compressor , characterized by the fact that the planet carrier comprising :a first substantially annular member having a number of pairs of seats for the pins in each of which rotates one of said planet gears , and a number of cavities, each interposed between two adjacent planetary gears ;a second compressor connected to said annular and has a number of axial arms , each designed to fit within said cavity in said first element ;connecting means for connecting the end of each said arm to a portion of said first element , which portion is substantially equidistant in relation to the seats in each of said pairs of seats of said pins .