METHOD FOR MANUFACTURING A PROPELLER REDUCTION GEAR

Abstract

A method for manufacturing a propeller reduction gear, which includes measuring manufacturing defects of the casing; calculating a first angular play induced at each intermediate gear by the measured manufacturing defects; estimating a second angular play induced at each intermediate gear by deformations of the casing when the reduction gear transmits a threshold torque; calculating a total angular play from the first angular play and the second angular play; and selecting two intermediate gears with a phase difference that compensates for the total angular play.

Claims

1. A method for manufacturing a propeller reduction gear including: a casing including at least two front bearing seatings and two rear bearing seatings; an input gear; at least two intermediate gears, each intermediate gear including a first stage meshing with the input gear and a second stage, each intermediate gear being attached to the casing via at least one front bearing and one rear bearing, each front bearing being supported by one of the at least two front bearing seatings, each rear bearing being supported by one of the at least two rear bearing seatings; an output gear wheel meshing with the second stage of each of the at least two intermediate gears; the method including: (a) measuring manufacturing defects of the casing; (b) calculating a first angular play induced at each intermediate gear from the measured manufacturing defects; (c) estimating a second angular play induced at each intermediate gear by deformations of the casing upon transmitting a threshold torque by the reduction gear; (d) calculating a total angular play from the first angular play and the second angular play; (e) selecting two intermediate gears having a phasing difference compensating for the total angular play.

2. The method according to claim 1, wherein step (a) of measuring defects includes a step of measuring a real position of each bearing seating.

3. The method according to claim 2, wherein step (b) of calculating the first angular play includes: for each bearing seating, calculating a difference between the real position of the bearing seating and a reference position so as to obtain a bearing seating offset; for each intermediate gear: calculating an offset of the intermediate gear from the bearing seating offsets supporting the bearings of the intermediate gear; calculating the first angular play from the offset of the intermediate gear.

4. The method according to claim 1, wherein step (c) of estimating the second angular play includes: estimating a displacement of each bearing seating upon transmitting a threshold torque by the reduction gear; for each intermediate gear: calculating a displacement of the first stage from the displacements of the bearing seatings supporting the bearings of this intermediate gear; and calculating a second angular play from the calculated displacements.

5. A propeller reduction gear manufactured by a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0040] Further characteristics and advantages of the invention will better appear upon reading the detailed description that follows, in reference to the appended figures, which illustrate:

[0041] FIG. 1, a perspective view of a propeller reduction gear to which the method according to the first aspect of the invention is applied;

[0042] FIG. 2, a front face of a propeller reduction gear manufactured according to a manufacturing method of prior art;

[0043] FIGS. 3a, 3b and 4, schematic representations of a propeller reduction gear of prior art provided with a spring load distribution system;

[0044] FIG. 5, a view of the face of a propeller reduction gear according to one embodiment of the invention;

[0045] FIG. 6, a top view of a part of a propeller reduction gear according to one embodiment of the invention;

[0046] FIG. 7, a front view of the casing of the propeller reduction gear of FIG. 6;

[0047] FIG. 8, an enlarged view of a part of the casing of FIG. 7;

[0048] FIG. 9, a schematic representation of a method enabling the meshing offset to be calculated;

[0049] FIGS. 10a to 10c, schematic representations of the teeth of an intermediate gear used within the scope of a method according to one embodiment of the invention;

[0050] FIG. 11, a displacement field of the bearing seatings of the casing of FIG. 7 in the case of a threshold torque loading;

[0051] FIG. 12, a displacement field of an intermediate gear of the propeller reduction gear of FIG. 5;

[0052] FIG. 13, a view of the first stage of the propeller reduction gear of FIG. 5;

[0053] FIG. 14, a view of the second stage of the propeller reduction gear of FIG. 5;

[0054] FIG. 15, a view of a tooth of an intermediate gear meshing with a tooth of the gear wheel of the propeller reduction gear of FIG. 5;

[0055] FIG. 16a, a schematic representation of the torque transmitted by each of the intermediate gears of a propeller reduction gear in the absence of use of a method according to the invention;

[0056] FIG. 16b, a schematic representation of the torque transmitted by each of the intermediate gears of a propeller reduction gear manufactured by a method according to one embodiment of the invention.

[0057] For the sake of clarity, identical or similar elements are referred to as by identical reference signs throughout the figures.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

[0058] The method aims at manufacturing a propeller reduction gear as represented in the figures. This propeller reduction gear includes a casing 12. The casing 12 includes two front bearing seatings 13 and two rear bearing seatings 14. The casing 12 surrounds a gear chain enabling a propeller to be rotatably driven at a speed being different from the rotational speed of a crankshaft. For this, the gear chain includes an input gear 1 intended to be attached to a crankshaft and an output gear wheel 5 intended to be integral with a propeller to be rotatably driven. The gear chain also includes at least two intermediate gears 2. Each intermediate gear 2 includes a first stage 3 which meshes with the input gear 1 and a second stage 4 which meshes with the output gear wheel 5. Each intermediate gear is attached to the casing via: [0059] a front bearing 15 supported by one of the front bearing seatings 13 of the casing and [0060] a rear bearing 16 supported by one of the rear bearing seatings 14 of the casing.

[0061] A method for manufacturing such a reduction gear will now be described. It first includes a step (a) of measuring manufacturing defects of the casing. More precisely, during this step, the real position of each bearing seating is measured.

[0062] The method then includes a step of comparing the real position of each bearing seating and a reference position. Thus, in reference to FIGS. 7 and 8, the method includes a step of measuring the difference between a reference position 17 specified by the plans and the real position 18 of each bearing seating. Thus, a bearing seating offset (ΔYav, ΔZav) for each front bearing seating and (ΔYar, ΔZar) for each rear bearing seating is obtained.

[0063] The method then includes a step (b) of calculating a first angular play induced at each intermediate gear from the measured manufacturing defects. This step includes a step of calculating an offset of the first stage of each intermediate gear from the calculated bearing seatings. Thus, the intermediate gear 2b for example is attached to the casing through the front bearing seating 13 and through the rear bearing seating 14. In reference to FIG. 13, insofar as the front bearing seating offset 13 (ΔYav, ΔZav), the rear bearing seating offset 14 (ΔYar, ΔZar), the total length of the intermediate gear L, and the distance between the intermediate gear and one of the bearing seatings L1 are known, the offset (ΔY, ΔZ) of the first stage of the intermediate gear 2b is calculated:

[00001]$\Delta .Math..Math.Y=\frac{\Delta .Math..Math.\mathrm{Yar}*\left(L-L.Math..Math.1\right)+L.Math..Math.1*\Delta .Math..Math.\mathrm{Yav}}{L}$$\Delta .Math..Math.Z=\frac{\Delta .Math..Math.\mathrm{Zar}*\left(L-L.Math..Math.1\right)+L.Math..Math.1*\Delta .Math..Math.\mathrm{Zav}}{L}.$

[0064] The method then includes a step of calculating the first angular play from the offset (ΔY, ΔZ) of the first stage of the intermediate gear 2b. This first angular play is given by the following equations:

δ1=ΔZ/r+ΔY*tan(α)/r

[0065] where r is the primitive radius of the intermediate gear in mm.

[0066] The first angular play δ2 is calculated in the same way for the other intermediate gear 2a.

[0067] The method then includes a step of calculating the first total angular play δmanufacturing=δ1+δ2.

[0068] The method also includes a step of estimating a second angular play induced at each intermediate gear by deformations of the casing upon transmitting a threshold torque by the reduction gear. For this, in reference to FIGS. 11 and 12, a finite element calculation can for example be performed to know the displacement of each bearing seating due to the casing deformations upon transmitting a threshold torque by the reduction gear. This threshold torque is preferably the maximum torque for which the reduction gear has been dimensioned. Thus, the displacements (ΔY′av, ΔZ′av) of the rear bearing seatings are obtained.

[0069] The method then includes a step of calculating the displacement (ΔY′, ΔZ′) of the first stage of the intermediate gear 2b in the case of transmission of the threshold torque:

[00002]$\Delta .Math..Math.Y^{\prime }=\frac{\Delta .Math..Math.Y^{\prime }.Math.\mathrm{ar}*\left(L-L.Math..Math.1\right)+L.Math..Math.1*\Delta .Math..Math.Y^{\prime }.Math.\mathrm{av}}{L}$$\Delta .Math..Math.Z^{\prime }=\frac{\Delta .Math..Math.Z^{\prime }.Math.\mathrm{ar}*\left(L-L.Math..Math.1\right)+L.Math..Math.1*\Delta .Math..Math.Z^{\prime }.Math.\mathrm{av}}{L}.$

[0070] The method then includes a step of calculating the second angular play from the offset (ΔY′, ΔZ′) of the first stage of the intermediate gear 2b. This second angular play is given by the following equations:

Δ1′=ΔZ′/r+ΔY′*tan(α)/r

[0071] where r is the primitive radius of the intermediate gear in mm.

[0072] The second angular play δ2′ is calculated in the same way for the other intermediate gear 2a.

[0073] The method then includes a step of calculating the second total angular play δdeformation=δ1′+δ2′.

[0074] The method then includes a step of calculating a total angular play:

δtotal=δmanufacturing+δdeformation.

[0075] The method then includes a step of selecting a couple of intermediate gears causing a phase shift equal to −δtotal as represented in FIG. 15.

[0076] The method described thus enables the manufacturing and deformation defects to be compensated for by selecting a suitable couple of intermediate gears. Thus, it enables a balanced load distribution to be achieved between both intermediate gears. Thus, FIG. 16a represents the evolution of the torque transmitted by each of the intermediate gears 2a and 2b as a function of the torque Ce at the input of the reduction gear when the reduction gear is not manufactured by a method according to the invention. As can be seen in this figure, both intermediate gears transmit very different torques. FIG. 16b represents the evolution of the torque transmitted by each of the intermediate gears 2a and 2b as a function of the torque Ce at the input of the reduction gear when the reduction gear has been manufactured by a method according to one embodiment of the invention. As can be seen in this figure, the torque transmitted is thereby fairly distributed between both intermediate gears.

[0077] Of course, the invention is not limited to the embodiments described in reference to the figures and alternatives could be contemplated without departing from the scope of the invention. In particular, the method for manufacturing propeller reduction gears including more than two intermediate gears could be applied.