Engine assembly for an aircraft comprising a primary structure of a mounting pylon equipped with a box extension comprising two parts in the overall shape of an arch

1. An engine assembly for an aircraft comprising:

a turbofan turbine engine having a fan which is driven by a reduction gear, the turbine engine comprising a reducing-gear case surrounding the reduction gear;

a turbine engine mounting pylon, comprising a primary structure equipped with a central box; and

an attachment mechanism to attach the turbine engine to the primary structure of the mounting pylon,

wherein the primary structure of the mounting pylon also comprises a box extension connected to a front of the central box, the box extension comprising:

a first component produced as a single piece and arranged in a vertical and transverse plane of the engine assembly, the first component comprising a first part in the overall shape of an arch extending around the reducing-gear case, and a first connecting structure constituting a transverse stiffening rib of the central box, the first part in the overall shape of an arch having two first opposite ends; and

a second component produced as a single piece and comprising a second part in the overall shape of an arch extending at least partly around the reducing-gear case, and a second connecting structure constituting an interior transverse stiffening rib of the central box, the second part in the overall shape of an arch having two second opposite ends respectively mounted on the two first opposite ends, the second part in the overall shape of an arch extending rearward and toward the central box from its second opposite ends, and

wherein the attachment mechanism comprises two lateral front attachments and a central front attachment, each of the two lateral front attachments connecting the reducing-gear case to one of the two first ends of the first part in the overall shape of an arch and each reacting load in a longitudinal direction and in a vertical direction of the engine assembly, and the central front attachment connecting the reducing-gear case to a first central portion of the first part in the overall shape of an arch and reacting load in a transverse direction of the engine assembly.

2. The engine assembly as claimed in claim 1 , wherein the second component of the box extension extends in a plane inclined with respect to the vertical and longitudinal directions of the engine assembly.

3. The engine assembly as claimed in claim 1 , wherein the second component of the box extension extends in a plane inclined with respect to the vertical and longitudinal directions of the engine assembly, inclined by an angle comprised between 30 and 60° with respect to the longitudinal direction.

4. The engine assembly as claimed in claim 1 , wherein the two lateral front attachments are arranged symmetrically with respect to a vertical and longitudinal midplane of the engine assembly, the vertical and longitudinal midplane passing through the central front attachment.

5. The engine assembly as claimed in claim 1 , wherein the two lateral front attachments are arranged in angular positions, one of them between 2 o'clock and 3 o'clock and the other between 9 o'clock and 10 o'clock.

6. The engine assembly as claimed in claim 1 , wherein the attachment means form a statically determinate load-reacting system and are made up of the two lateral front attachments, the central front attachment, and a rear attachment reacting load in the vertical direction.

7. The engine assembly as claimed in claim 1 , wherein the box extension comprises at least one skin externally covering the first and second parts in the overall shape of an arch.

8. The engine assembly as claimed in claim 1 , wherein the second opposite ends are mounted on the two first opposite ends by two shear pins respectively.

9. The engine assembly as claimed in claim 8 , wherein the two shear pins are oriented in the transverse direction.

10. The engine assembly as claimed in claim 1 , wherein the turbine engine comprises, in succession, from the front toward the rear, a fan case, an intermediate case, the reducing-gear case, a central case and a turbine case.

11. An aircraft comprising:

at least one engine assembly comprising:

a turbofan turbine engine having a fan which is driven by a reduction gear, the turbine engine comprising a reducing-gear case surrounding the reduction gear;

a turbine engine mounting pylon, comprising a primary structure equipped with a central box; and

an attachment mechanism to attach the turbine engine to the primary structure of the mounting pylon,

wherein the primary structure of the mounting pylon also comprises a box extension connected to a front of the central box, the box extension comprising:

a first component produced as a single piece and arranged in a vertical and transverse plane of the engine assembly, the first component comprising a first part in the overall shape of an arch extending around the reducing-gear case, and a first connecting structure constituting a transverse stiffening rib of the central box, the first part in the overall shape of an arch having two first opposite ends; and

a second component produced as a single piece and comprising a second part in the overall shape of an arch extending at least partly around the reducing-gear case, and a second connecting structure constituting an interior transverse stiffening rib of the central box, the second part in the overall shape of an arch having two second opposite ends respectively mounted on the two first opposite ends, the second part in the overall shape of an arch extending rearward and toward the central box from its second opposite ends, and

wherein the attachment mechanism comprises two lateral front attachments and a central front attachment, each of the two lateral front attachments connecting the reducing-gear case to one of the two first ends of the first part in the overall shape of an arch and each reacting load in a longitudinal direction and in a vertical direction of the engine assembly, and the central front attachment connecting the reducing-gear case to a first central portion of the first part in the overall shape of an arch and reacting load in a transverse direction of the engine assembly, and

a wing on which the engine assembly is mounted.

12. The aircraft as claimed in claim 11 , wherein the engine assembly is suspended beneath the wing.