Mechanical system for transmitting motion and an aircraft fitted with a corresponding system

Abstract

A mechanical system for transmitting rotary motion between at least two shafts movable in rotation respectively about a first axis and a second axis, the first and second axes intersecting, the mechanical system including a bevel gear set made up of a first bevel gear having teeth and movable in rotation about the first axis and a bevel wheel having teeth and movable in rotation about the second axis, the teeth of the first bevel gear and of the bevel wheel respectively being suitable for co-operating in complementary manner with one another, the first bevel gear, referred to as a power gear, presenting a first defining pitch surface of conical shape, and the bevel wheel presenting a second defining pitch surface of conical shape.

Claims

1. A mechanical system for transmitting rotary motion between at least two shafts movable in rotation respectively about a first axis and a second axis, the first and second axes intersecting, the mechanical system including a bevel gear set made up of a first bevel gear having teeth and movable in rotation about the first axis and a bevel wheel having teeth and movable in rotation about the second axis, the teeth of the first bevel gear and of the bevel wheel respectively being suitable for co-operating in complementary manner with one another, the first bevel gear, referred to as a power gear, presenting a first defining pitch surface of conical shape, and the bevel wheel presenting a second defining pitch surface of conical shape, the intersecting first and second axes being relatively positioned so as to define, during meshing between the power gear and the bevel wheel, a first operating pitch surface of conical shape relating to the power gear and a second operating pitch surface of conical shape relating to the bevel wheel, the first and second operating pitch surfaces being defined respectively by a common vertex arranged at the intersection between the first and second axes and by a circle corresponding to one of the respective pitch circles of the power gear and of the bevel wheel, the pitch circles being formed respectively by tangential circles centered on the first and second axes, the first operating pitch surface being selected to be identical to the first defining pitch surface and the second operating pitch surface being selected to be identical to the second defining pitch surface, the mechanical system including another bevel gear, referred to as an accessory gear, having teeth meshing with the teeth of the bevel wheel to transmit rotary motion to a third shaft movable in rotation about a third axis, the accessory gear presenting a third defining pitch surface of conical shape; wherein the accessory gear presents a third operating pitch surface obtained by the second and third axes being relatively positioned so as to enable the accessory gear to mesh with the bevel wheel, the third operating pitch surface of the accessory gear being selected to be different from the third defining pitch surface of the accessory gear, the third operating pitch surface being defined firstly by a third vertex arranged at an intersection between the third axis and the second axis and secondly by a pitch circle of the accessory gear, the third vertex being separate from the common vertex.

2. The mechanical system according to claim 1; wherein the conical shape of the third defining pitch surface is defined by a fourth vertex and by a defining half-angle .sub.def at the fourth vertex, the third operating pitch surface presenting an operating half-angle .sub.fonc at the third vertex, the defining half-angle .sub.def being different from the operating half-angle .sub.fonc.

3. The mechanical system according to claim 2; wherein the defining half-angle .sub.def and the operating half-angle .sub.fonc present a difference having an absolute value lying in the range 1 to 60.

4. The mechanical system according to claim 3; wherein the absolute value of the difference between the defining half-angle .sub.def and the operating half-angle .sub.fonc preferably lies in the range 10 to 60.

5. The mechanical system according to claim 1; wherein each of the teeth of the accessory gear presents a plurality of cross sections of mutually different shapes, the plurality of cross sections being arranged in respective section planes oriented substantially perpendicularly to the third axis.

6. The mechanical system according to claim 5; wherein each of the teeth of the accessory gear has an outer top land, and at least in the outer top land each tooth presents top widths measured in respective section planes oriented substantially perpendicularly relative to the third axis, which top widths vary with varying distance between the section plane in question and the fourth vertex.

7. The mechanical system according to claim 1; wherein the first and second axes are orthogonal.

8. The mechanical system according to claim 1; wherein the second and third axes are orthogonal.

9. The mechanical system according to claim 1; wherein the first and third axes are parallel.

10. The mechanical system according to claim 1; wherein the first, second, and third axes are coplanar.

11. The mechanical system according to claim 1; wherein the first, second, and third axes are not coplanar.

12. An aircraft including at least one engine and at least one rotor for providing the aircraft with propulsion and/or lift; wherein the aircraft includes at least one mechanical system according to claim 1, the mechanical system enabling rotary motion to be transmitted between a drive shaft of the at least one engine and a driven shaft of the at least one rotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail in the context of the following description of embodiments given by way of illustration and with reference to the accompanying figures, in which:

(2) FIG. 1 is a perspective view of an aircraft fitted with a mechanical system in accordance with the invention;

(3) FIG. 2 is a theoretical perspective view showing the operation of a prior art mechanical system;

(4) FIGS. 3 to 5 are various theoretical perspective views showing the operation of a first embodiment of a mechanical system in accordance with the invention having axes that are coplanar;

(5) FIG. 6 is a perspective detail view showing the teeth of an accessory gear of a mechanical system in accordance with the invention; and

(6) FIG. 7 is a theoretical perspective view showing the operation of a second embodiment of a mechanical system in accordance invention having axes that are not coplanar.

(7) Elements that are present in more than one of the figures are given the same references in each of them.

DETAILED DESCRIPTION OF THE INVENTION

(8) As mentioned above, the invention relates to a mechanical system and to an aircraft fitted with such a mechanical system.

(9) As shown in FIG. 1, the aircraft 1 may be in the form of a rotorcraft and may have an engine 2 such as an internal combustion engine or indeed a turbojet. The engine 2 then serves to drive rotation of a drive shaft 5, and the mechanical system 4 serves to transmit rotary motion from the drive shaft 5 to a driven shaft 6 with a change to the angular orientations of the respective axes of rotation of the drive and driven shafts 5 and 6.

(10) Such a driven shaft 6 can then drive rotation of at least one rotor 3 having blades for providing the aircraft 1 with lift and/or propulsion. Advantageously, a mechanical system 4 can also serve to reduce the speed of rotation of the driven shaft 6 relative to the speed of rotation of the drive shaft 5.

(11) In the prior art, and as shown in FIG. 2, a mechanical system 104 may include a bevel gear set 107 comprising a first bevel gear 112 that is movable in rotation about a first axis 111, and a bevel wheel 122 that is movable in rotation about a second axis 121. Also, such a mechanical system 104 may also include a second bevel gear 132 driven in rotation by the bevel wheel 122, the second bevel gear 132 being movable in rotation about a third axis 131.

(12) Under such circumstances, the theory that makes it possible to cause the teeth of the second bevel gear 132 to co-operate in complementary manner with the teeth of the bevel wheel 122 requires designers of this type of mechanical system 104 to cause all three axes 111, 121, and 131 to coincide at the vertex S.

(13) Consequently, the respective defining pitch surfaces 114, 134, and 124 of the first and second bevel gears 112 and 132 and of the bevel wheel 122 then coincide with the respective operating pitch surfaces 115, 125, and 135 of the first and second bevel gears 112 and 132, and of the bevel wheel 122.

(14) As shown in FIGS. 3 to 5, in a first embodiment, the mechanical transmission system 4 enables rotary motion to be transmitted between a first shaft 10 and a second shaft 20. The shafts 10 and 20 are movable in rotation about respective first and second mutually intersecting axes 11 and 21.

(15) The mechanical system 4 has a bevel gear set 7 including a first bevel gear 12, referred to as the power gear, and that has teeth 13. Such a power gear 12 is then movable in rotation about a first axis 11. The bevel gear set 7 then also has a bevel wheel 22 that has teeth 23. The bevel wheel 22 is movable in rotation about a second axis 21.

(16) The respective teeth 13 and 23 of the first power gear 12 and of the bevel wheel 22 may be of straight shape or of helical shape, and they are suitable for co-operating in complementary manner with one another. Also, the power gear 12 presents a first defining pitch surface 14 of conical shape while the bevel wheel 12 presents a second defining pitch surface 24 of conical shape.

(17) A relative positioning of the intersecting first and second axes 11 and 21 then makes it possible during meshing between the power gear 12 and the bevel wheel 22 to define a first operating pitch surface 15 of conical shape relating to the power gear 12 and a second operating pitch surface 25 of conical shape relating to the bevel wheel 22.

(18) Such first and second operating pitch surfaces 15 and 25 are defined respectively by a common vertex S arranged at the intersection between the first and second axes 11 and 21, and by a circle corresponding to one of the respective pitch circles 16 and 26 of the power gear 12 and of the bevel wheel 22.

(19) Furthermore, the mechanical system 4 includes a second bevel gear 32, referred to as an accessory gear, having teeth 33 meshing with the teeth 23 of the bevel wheel 22 in order to transmit rotary motion to a third shaft 30 that is movable in rotation about a third axis 31. In this first embodiment of the mechanical system 4, such first, second, and third axes 11, 21, and 31 are arranged so as to be coplanar relative to one another.

(20) As shown in FIG. 3, such an accessory gear 32 then also has a third defining pitch surface 34 that is conical in shape. Such a third defining pitch surface 34 is more particularly a cone that is tangential to the second defining pitch surface 24 relating to the bevel wheel 22. Such a third defining pitch surface 34 then presents symmetry of revolution about the third axis 31.

(21) In addition, and as shown in FIG. 4, such an accessory gear 32 presents a third operating pitch surface 35 obtained by the second and third axes 21 and 31 being relatively positioned so as to enable the accessory gear 32 to mesh with the bevel wheel 22. The third axis 31 then no longer intersects simultaneously with the first and second axes 11 and 21 at the vertex S.

(22) Consequently, and unlike the prior art, this third operating pitch surface 35 of the accessory gear 32 is then selected to be different from the third defining pitch surface 34 of the accessory gear 32. This third operating pitch surface 35 is defined firstly by a third vertex S arranged at an intersection between the third axis 31 and the second axis 21, and secondly by a pitch circle 36 of the accessory gear 32.

(23) The third defining pitch surface 34 is also defined by a fourth vertex S and by a defining a half-angle .sub.def at the fourth vertex S. Furthermore, the third operating pitch surface 35 present an operating half-angle .sub.fonc at the third vertex S. The defining half-angle .sub.def is then different from the operating half-angle .sub.fonc The absolute value of the difference between the defining half-angle .sub.def and the operating half-angle .sub.fonc may then lie in the range 1 to 60, and preferably the range 10 to 60.

(24) As shown in FIG. 5, the relative positioning between the second and third axes 21 and 31 then makes it possible, while the bevel wheel 22 and the accessory gear 32 are meshing, to define a fourth operating pitch surface 25 of conical shape relating to the bevel wheel 22 and the third operating pitch surface 35 of conical shape relating to the accessory gear 32.

(25) This fourth operating pitch surface 25 is defined firstly by a third vertex S arranged at an intersection between the third axis 31 and the second axis 21, and secondly by a pitch circle 26 of the accessory gear 22.

(26) The second operating pitch surface 25 of the bevel wheel is then different from the fourth operating pitch surface 25.

(27) As a result, the third vertex S is separate from the common vertex S with a distance d then lying between the common vertex S and the third vertex S. Such a distance d is oriented along the second axis 21.

(28) As shown in FIG. 6, each of the teeth 33 of the accessory gear 32 presents a plurality of cross sections 37 and 38 of mutually different shapes. The cross sections 37 and 38 of this plurality are also arranged in respective section planes P, P that are oriented substantially perpendicularly relative to the third axis 31.

(29) Finally, at least at the level of an outer top land 39 of the various teeth 33 of the accessory gear 32, each tooth 33 presents a land width e.sub.1, e.sub.2 measured in a respective section plane P, P oriented substantially perpendicularly relative to the third axis 31. As shown, this land width e.sub.1, e.sub.2 may then decrease the closer the section plane P, P is to the fourth vertex S so as to make it possible to optimize the contact area between the teeth 33 of the accessory gear 32 and the teeth 23 of the bevel wheel 22.

(30) Naturally, in another variant that is not shown, this land width e.sub.1, e.sub.2 could alternatively increase the closer the section plane P, P is to the fourth vertex S.

(31) As shown in FIG. 7, a second embodiment of the mechanical transmission system 4 has a bevel gear set 7 including a power gear 12. Such a power gear 12 is then movable in rotation about a first axis 11. The bevel gear set 7 then also includes a bevel wheel 22. The bevel wheel 22 is movable in rotation about a second axis 21.

(32) Such a mechanical system 4 also includes an accessory gear 32 driven in rotation by the bevel wheel 22, such an accessory gear 32 being movable in rotation about a third axis 31.

(33) As shown, the first, second, and third axes 11, 21, and 31 are arranged in mutually non-coplanar manner and thus allow the angular orientation of the rotary motion transmitted by such a mechanical system 4 to be modified.

(34) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several embodiments are described, it should readily be understood that it is not conceivable to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.