Power transmission box

Abstract

The invention relates to a power transmission box, the bearing (9) of which comprises a driving member (10) and a driven member (11) each having two rolling tracks (10a, 10b;11a, 11b) forming two paths (12, 13) in each of which a row (14, 15) of spherical rolling bodies (16) is arranged, the rows (14, 15) being arranged opposite an upstream portion (10a1, 10b1) – respectively downstream (11a2, 11b2) – of the driving tracks (10a, 10b) – respectively driven (11a, 11b) –, the driving member (10) comprising a driving ring (17) and the driven member (11) comprising two driven rings (18, 19) on each of which is formed a portion (11a4, 11a2) of the first track (11a), the oscillation rates of the upstream portion (10a1) and of the downstream portion (11a2) are each between 0.51 and 0.57, the sum of the oscillation rates of the upstream portion (10b1) and the downstream portion (11b2) being less than the sum of the oscillation rates of the upstream portion (10a1) and the downstream portion (11a2). Figure 3;

Description

Title of the invention: Power transmission box

[0001] The invention relates to a power transmission box comprising an assembly intended to be driven in rotation by a transmission pinion, said assembly comprising a rotor carrying in rotation a variable geometry unit.

[0002] It applies in particular to power transmission boxes for a rotorcraft rotor carrying variable pitch blades, such as a helicopter tail rotor.

[0003] In order to be able to adjust the pitch of the blades, the box comprises a control rod which is actuated in translation, said rod being connected to a control shaft by means of a rolling bearing to transform a translation of said rod into a modification of the pitch of the blades.

[0004] Given the high axial stresses to which the rolling bearing is subjected, document EP-3 587 845 describes the use of a bearing comprising two rows of angular contact balls which are mounted so that in the event of damage to one, the other remains operational in order to secure the blade pitch control function.

[0005] To limit the complexity of mounting the bearing according to this prior art, document EP-4 166 803 provides a bearing design comprising two rows of angular contact balls in a raceway respectively, in which a clearance is formed between the tracks of said races and said rows, said clearances being arranged so that the axial forces in one direction are transmitted exclusively through one of said races and that, in the event of deterioration of said raceway, the transmission of said axial forces is transferred to the other raceway.

[0006] The invention aims to improve the prior art by proposing in particular a transmission box comprising two rows of angular contact balls in a respective raceway, in which the design of said races is improved to secure the transfer of the axial load from one degraded raceway to the other raceway, and this in a bearing whose manufacture and assembly are facilitated.

[0007] To this end, the invention proposes a power transmission box comprising an assembly intended to be driven in rotation by a transmission pinion, said assembly comprising a rotor carrying in rotation a variable geometry unit, said box comprising a control rod of a mechanism for adjusting the geometry of said unit, said rod being actuated in translation and said mechanism comprising a control shaft connected to said rod by means of a rolling bearing, said mechanism being arranged to transform a translation of said rod into a modification of the geometry of the unit, said bearing comprising a driving member integral in rotation with the rod and a driven member integral in rotation with the control shaft, each of said members having two axially spaced rolling tracks forming with the tracks of the other member two rolling paths in each of which a row of spherical rolling bodies is arranged to guide the relative rotation of said members, the rows of spherical rolling bodies being arranged opposite an upstream - respectively downstream - portion of the driving - respectively driven - rolling tracks along a direct load line to transmit the translational force in a main direction extending from a first to a second of said rows, the driving member comprising a driving ring on which the first driving rolling track is formed and the driven member comprising two driven rings on each of which a portion of the first driven rolling track is formed, said driven rings being axially joined to form said first driven rolling track,the oscillation rates of the upstream portion of the first driving track and the downstream portion of the first driven track each being between 0.51 and 0.57, the sum of the oscillation rates of the upstream portion of the second driving track and the downstream portion of the second driven track being less than the sum of the oscillation rates of the upstream portion of the first driving track and the downstream portion of the first driven track.

[0008] Other objects and advantages of the invention will appear in the following description, given with reference to the appended figures, in which:

[0009] [Fig.l] schematically represents a longitudinal section of a transmission box according to an embodiment of the invention;

[0010] [Fig.2],

[0011] [Fig.3] and

[0012] [Fig.4] each represent in longitudinal section one side of a rolling bearing for a transmission box, respectively according to one embodiment of the invention.

[0013] In relation to these figures, a power transmission box is described below comprising an assembly intended to be driven in rotation by a transmission pinion 1, said assembly comprising a rotor 2 carrying in rotation a unit 3 with variable geometry.

[0014] According to an envisaged application, the box allows power transmission to a rotorcraft rotor 2 carrying variable pitch blades 3a, such as a helicopter tail rotor 2.

[0015] [Fig.l] shows schematically a rotor 2 equipped with external teeth 4 for its rotational drive by the transmission pinion 1, said rotor being supported along an axis of rotation A by a set of bearings 5, the blades 3a being mounted according to a variable angular pitch on said rotor.

[0016] The box comprises a rod 6 for controlling a mechanism 7 for adjusting the geometry of the unit 3 with variable geometry, said rod being actuated in translation along the axis A to, in the envisaged application, control the pitch of the blades 3a of the rear rotor 2, in particular to a value adapted to provide a thrust which balances the reaction torque of the main rotor of the helicopter.

[0017] The adjustment mechanism 7 comprises a control shaft 8 which is connected to the rod 6 by means of a rolling bearing 9, said mechanism being arranged to transform a translation of said rod along the axis of rotation A into a modification of the geometry of the unit 3. [Fig.l] schematizes the bearing 9 and a connection 7a between the control shaft 8 and the blades 3a so that a translation of said shaft induces a rotation of said blades on the rotor 2.

[0018] The bearing 9 comprises a driving member 10 integral in rotation with the control rod 6 and a driven member 11 integral in rotation with the control shaft 8. In the figures, the driving member 10 is external, the driven member 11 being internal. However, depending on the structure of the transmission box, the reverse configuration can be envisaged.

[0019] Each of the members 10, 11 has two rolling tracks 10a, 10b; 11a, 11b spaced axially apart, forming with the tracks 11a, 11b; 10a, 10b of the other member 11, 10 two rolling paths 12, 13 in each of which a row 14, 15 of spherical rolling bodies 16 is arranged to guide the relative rotation of said members around the axis A.

[0020] In the description, the terms of positioning in space are taken in relation to the axis of rotation A of the bearing 9 which is coincident with the axis of translation of the rod 6 and control shaft 8. In particular, the terms “interior” and “exterior” are understood to mean a location respectively close to and far from the axis A.

[0021] The rows 14, 15 of spherical rolling bodies 16 are in oblique contact in the raceways 12, 13 by being arranged opposite an upstream portion 10a1, 10b1 - respectively downstream 11a2, 11b2 - of the driving raceways 10a, 10b - respectively driven 11a, 11b - following a direct load line La to transmit the translational force in a main direction SI extending from a first 14 to a second 15 of said rows.

[0022] In the description, the terms “upstream”; “downstream”; “first” and “second” are defined in relation to the main direction SI of application of a control force by the rod 6 on the shaft 8, namely from left to right in the figures.

[0023] The driving member 10 comprises a driving ring 17 on which the first driving rolling track 10a is formed, the driven member 11 comprising two driven rings 18, 19 on each of which an upstream portion 11a4 and the downstream portion 11a2 of the first driven rolling track 11a are formed.

[0024] The driven rings 18, 19 are axially joined to form the first track. 1 the driven rolling bearing, in particular by being held axially by means of a connecting ring.

[0025] Each of the portions 10a1, 10b1, 11a2, 11b2 of rolling tracks 10a, 10b, 11a, 11b has an oscillation rate which is the ratio of the radius of curvature of said portion to the diameter of the spherical rolling bodies 16. The oscillation rates of the upstream portion 10a1 of the first driving track 10a and of the downstream portion 11a2 of the first driven track 11a are each between 0.51 and 0.57.

[0026] In particular, these oscillation rates increased compared to a standard value of 0.50 make it possible to form a clearance B, C, in particular between 0.1 and 0.5 mm and more precisely between 0.2 and 0.3 mm, between the first row 14 of rolling bodies 16 and each of the portions 10a1, 11a2 of tracks 10a, 11a.

[0027] Furthermore, the sum of the oscillation rates of the upstream portion 10b of the second driving track 10b and of the downstream portion 11b2 of the second driven track 11b is less than the sum of the oscillation rates of the upstream portion 10a of the first driving track 10a and of the downstream portion 11a2 of the first driven track 11a.

[0028] Thus, the control force in the main direction SI is applied to the driving ring 17 to be transmitted to the driven member 11 only by the second row 15 of spherical rolling bodies 16, to the extent that a clearance B, C is formed between the rolling bodies 16 and each of the tracks 10a, 11a of the first rolling path 12.

[0029] Furthermore, in the event of deterioration of the second rolling path 13, in particular over a clearance greater than the sum of the clearances B, C of the first rolling path 12, the rolling bodies 16 come into contact on said first path to transmit the force in the main direction SI through the first row 14 of rolling bodies 16.

[0030] According to one embodiment, the oscillation rate of the downstream portion 1 lb2 of the second driven track 11b and / or the oscillation rate of the upstream portion 10b 1 of the second driving track 10b are less than 0.51, in particular each being of the order of 0.50 which corresponds to a standard oscillation rate for an angular contact ball bearing.

[0031] Advantageously, at least one of the oscillation rate of the upstream portion 10a1 of the first driving track 10a and the oscillation rate of the downstream portion 11a2 of the first driven track 11a is between 0.53 and 0.54. In particular, the oscillation rate of the upstream portion 10a1 of the first driving track 10a is substantially equal to the oscillation rate of the downstream portion 11a2 of the first driven track 11a, for example being 0.538 to each form a clearance B, C of the order of 0.3 mm for each of said tracks.

[0032] In relation to [Fig.2], the driving member 10 comprises a single ring 17 on which the first 10a and second 10b driving raceways are formed.

[0033] Advantageously with respect to the assembly of the bearing 9, the second track leading 10b extends between two edges respectively front 20 and rear 21 in the main direction SI, said rear edge being inscribed in a diameter which is greater than the diameter in which said front edge is inscribed.

[0034] In particular, the second driving track 10b has a maximum diameter Dmax, the rear edge 21 being inscribed in a diameter which is greater than 90% of said maximum diameter.

[0035] Similarly, the driven member 11 according to [Fig.2] comprises a third driven ring 22 on which the second driven raceway 11b is formed, said second driven raceway extending between two edges, respectively front 23 and rear 24, in the main direction SI, said front edge being inscribed in a diameter which is less than the diameter in which said rear edge is inscribed.

[0036] In particular, the second driven track 11b has a minimum diameter Dmin, the front edge 23 being inscribed in a diameter which is less than 110% of said minimum diameter.

[0037] In relation to figures 3 and 4, the rolling bearing 9 allows the transmission of a translation force in an opposite direction S2 extending from the second 15 towards the first 14 row of rolling bodies 16. Thus, depending on the direction S1, S2 of translation of the rod 6, the adjustment mechanism 7 can adjust the pitch in one direction respectively.

[0038] In particular, the driving member 10 shown in these figures 3 and 4 comprises two rings 25, 26 on which respectively the first 10a and the second 10b driving raceways are formed, said rings being axially joined to form the driving member 10.

[0039] Furthermore, the driven member 11 comprises two driven rings 27, 28 on each of which is formed an upstream portion 1 lb4 and the downstream portion 1 lb2 of the second driven raceway 11b, said driven rings being axially joined to form said second driven raceway.

[0040] More precisely, the driven member 11 according to [Fig. 3] comprises two lateral rings 18, 28 axially joined on either side of a central ring 27, 19, said lateral rings respectively carrying the upstream portion 11a4 of the first driven raceway 11a and the downstream portion 11b2 of the second driven raceway 11b, the downstream portions 11a2 of said first raceway and upstream portions 11b4 of said second raceway being formed on either side of the central ring 27, 19.

[0041] In [Fig. 4], the driven member 11 comprises two central rings 19, 27 axially joined, the downstream portions 11a2 of the first driven track 11a and upstream 11b4 of the second driven track 11b being formed on either side on respectively one of said central rings, the driven member 11 further comprising two lateral rings 18, 28 axially joined respectively on either side of one of said rings central, said lateral rings respectively carrying the upstream portion 1 la4 of the first driven raceway 1 la and the downstream portion 1 lb2 of the second driven raceway 11b.

[0042] In relation to figures 3 and 4, the rows 14, 15 of spherical rolling bodies 16 are arranged opposite a downstream portion 10a3, 10b3 - respectively upstream 11a4, 11b4 - of the driving rolling tracks 10a, 10b - respectively driven 11a, 11b - following an indirect load line Lb to transmit the translation force in the opposite direction S2.

[0043] The oscillation rates of the downstream portion 10b3 of the second driving track 10b and of the upstream portion 1 lb4 of the second driven track 1 lb are each between 0.51 and 0.57, the sum of the oscillation rates of the downstream portion 10a3 of the first driving track 10a and of the upstream portion 1 la4 of the first driven track 11a being less than the sum of the oscillation rates of the downstream portion 10b3 of the second driving track 10b and of the upstream portion 1 lb4 of the second driven track 1 lb.

[0044] Thus, symmetrically to the forward direction SI, the control force in the reverse direction S2 is applied to the driving member 10 to be transmitted to the driven member 11 only by the first row 14 of spherical rolling bodies 16, to the extent that a clearance B', C' is formed between the rolling bodies 16 and each of the tracks 10b, 11b of the second rolling path 13.

[0045] And, in the event of deterioration of the first rolling path 12, in particular over a clearance greater than the sum of the clearances B', C' of the second rolling path 13, the rolling bodies 16 come into contact on said second path to transmit the force in the opposite direction S2 through the second row 15 of rolling bodies 16.

[0046] Advantageously, the downstream portion 1 la2 of the first driven track 1 la and the upstream portion 1 lb4 of the second driven track 1 lb have the same oscillation rate. Similarly, the upstream portion 1 la4 of the first driven track 1 la and the downstream portion 1 lb2 of the second driven track 1 lb have the same oscillation rate.

[0047] Similarly, symmetry can be provided between the first 12 and second 13 raceways with first 10a and second 10b driving tracks having the same oscillation rate.

Claims

Claims

1. Power transmission box comprising an assembly intended to be driven in rotation by a transmission pinion (1), said assembly comprising a rotor (2) carrying in rotation a unit (3) with variable geometry, said box comprising a rod (6) for controlling a mechanism (7) for adjusting the geometry of said unit, said rod being actuated in translation and said mechanism comprising a control shaft (8) connected to said rod by means of a rolling bearing (9), said mechanism being arranged to transform a translation of said rod into a modification of the geometry of the unit (3), said bearing comprising a driving member (10) integral in rotation with the rod (6) and a driven member (11) integral in rotation with the control shaft (8), each of said members having two rolling tracks (10a, 10b; 11a, 11b) spaced axially apart forming with the tracks (11a, 11b; 10a, 10b) of the other member (11, 10) two paths (12,13) of rolling in each of which a row (14, 15) of spherical rolling bodies (16) is arranged to guide the relative rotation of said members, the rows (14, 15) of spherical rolling bodies (16) being arranged opposite an upstream portion (10al, 10bl) - respectively downstream (1 la2, 1 lb2) - of the driving raceways (10a, 10b) - respectively driven (1 la, 11b) - following a direct load line (La) to transmit the translational force in a main direction (SI) extending from a first (14) to a second (15) of said rows, the driving member (10) comprising a driving ring (17) on which the first driving raceway (10a) is formed and the driven member (11) comprising two driven rings (18, 19) on each of which is formed a portion (1 la4, 1 la2) of the first driven raceway (1 la), said driven rings being axially joined to form said first driven raceway,said transmission box being characterized in that the oscillation rates of the upstream portion (10a1) of the first driving track (10a) and of the downstream portion (11a2) of the first driven track (11a) are each between 0.51 and 0.57, the sum of the oscillation rates of the upstream portion (10b1) of the second driving track (10b) and of the downstream portion (11b2) of the second driven track (11b) being less than the sum of the oscillation rates of the upstream portion (10a1) of the first driving track (10a) and of the downstream portion (11a2) of, the first track led (lia).

2. Transmission box according to claim 1, characterized in that the oscillation rate of the downstream portion (1 lb2) of the second driven track (11b) and / or the oscillation rate of the upstream portion (10b) of the second driving track (10b) are less than 0.

51.

3. Transmission box according to one of claims 1 or 2, characterized in that at least one of the oscillation rate of the upstream portion (10a1) of the first driving track (10a) and the oscillation rate of the downstream portion (11a2) of the first driven track (11a) is between 0.53 and 0.

54.

4. Transmission box according to any one of claims 1 to 3, characterized in that the oscillation rate of the upstream portion (10a1) of the first driving track (10a) is substantially equal to the oscillation rate of the downstream portion (11a2) of the first driven track (11a).

5. Transmission box according to any one of claims 1 to 4, characterized in that the driving member (10) comprises a single ring (17) on which the first (10a) and second (10b) driving raceways are formed, said second driving raceway extending between two edges, respectively front (20) and rear (21) in the main direction (SI), said rear edge being inscribed in a diameter which is greater than the diameter in which said front edge is inscribed.

6. Transmission box according to any one of claims 1 to 4, characterized in that the driving member (10) comprises two rings (25, 26) on which respectively the first (10a) and the second (10b) driving raceways are formed, said rings being axially joined to form the driving member (10).

7. Transmission box according to any one of claims 1 to 6, characterized in that the driven member (11) comprises a third driven ring (22) on which the second driven raceway (11b) is formed, said second driven raceway extending between two edges, respectively front (23) and rear (24) in the main direction (SI), said front edge being inscribed in a diameter which is less than the diameter in which said rear edge is inscribed.

8. Transmission box according to any one of claims 1 to 6, characterized in that the driven member (11) comprises two driven rings (27, 28) on each of which is formed a portion respectively upstream (1 lb4) and downstream (1 lb2) of the second driven raceway. (11b), said driven rings being axially joined to form said second driven raceway.

9. Transmission box according to claim 8, characterized in that the driven member (11) comprises two lateral rings (18, 28) axially joined on either side of a central ring (27), said lateral rings respectively carrying the upstream portion (11a4) of the first driven raceway (11a) and the downstream portion (11b2) of the second driven raceway (11b), the downstream portions (11a2) of said first raceway and upstream portions (11b4) of said second raceway being formed on either side of the central ring (27).

10. Transmission box according to claim 8, characterized in that the driven member (11) comprises two central rings (19, 27) axially joined, the downstream portions (1 la2) of the first driven track (1 la) and upstream portions (1 lb4) of the second driven track (11b) being formed on either side on respectively one of said central rings, the driven member (11) further comprising two lateral rings (18, 28) axially joined respectively on either side of one of said central rings, said lateral rings respectively carrying the upstream portion (1 la4) of the first driven raceway (1 la) and the downstream portion (1 lb2) of the second driven raceway (11b).

11. Transmission box according to any one of claims 1 to 10, characterized in that the rows (14, 15) of spherical rolling bodies (16) are arranged opposite a downstream portion (10a3, 10b3) - respectively upstream (11a4, 11b4) - of the driving raceways (10a, 10b) - respectively driven (11a, 11b) - along an indirect load line (Lb) to transmit the translational force in an opposite direction (S2) extending from the second (15) to the first (14) of said rows, the oscillation rates of the downstream portion (10b3) of the second driving raceway (10b) and of the upstream portion (11b4) of the second driven raceway (11b) are each between 0.51 and 0.57,the sum of the oscillation rates of the downstream portion (10a3) of the first driving track (10a) and of the upstream portion (11a4) of the first driven track (11a) being less than the sum of the oscillation rates of the downstream portion (10b3) of the second driving track (10b) and of the upstream portion (11b4) of the second driven track (11b).,

12. Transmission box according to claim 11, characterized in that the downstream portion (1 la2) of the first driven track (1 la) and the upstream portion (1 lb4) of the second driven track (11b) have the same rate of oscillation.

13. Transmission box according to one of claims 11 or 12, characterized in that the upstream portion (1 la4) of the first driven track (1 la) and the downstream portion (1 lb2) of the second driven track have the same oscillation rate.

14. Transmission box according to any one of claims 11 to 13, characterized in that the first (10a) and second (10b) driving tracks have the same oscillation rate.

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