Assembly comprising an air intake duct and a protective grille

Abstract

Title: Assembly comprising an air intake duct and a protective grille. The invention relates to an assembly (1) comprising: a housing (3) forming a main air duct, an air intake duct (4) connected to the housing (3) and configured to conduct an airflow into the housing (3), a protective grille (2) placed in the housing (3) and configured to be traversed by the airflow conducted through the air intake duct (4), the protective grille comprising: a frame (7) forming a principal plane (14) of the protective grille (2), at least three fins (8) spaced apart and supported by the frame (7), at least three of these fins forming angles αa, αb, αc with the principal plane of the protective grille, with αa < αb < αc. Figure for the abstract: Fig. 4

Description

Title of the invention: Assembly comprising an air intake duct and a protective grille

[0001] The present invention relates to an assembly comprising an air intake duct, at least one heat exchanger, and a protective grille configured to protect this heat exchanger. The protective grille allows airflow through the heat exchanger while protecting it from potential debris.

[0002] Patent application EP3943865 discloses an assembly comprising a heat exchanger including heat transfer fluid circulation tubes and a protective grid configured to protect this heat exchanger. The protective grid thus protects at least a portion of the heat exchanger against impacts from stones.

[0003] However, the protective grid creates a disturbance in the airflow through the exchanger, which reduces the performance of this exchanger.

[0004] The invention aims to provide an optimization of the protective grid bringing a number of advantages as will be seen below.

[0005] The invention relates to an assembly comprising: - a housing forming a main air duct, - an air intake duct connected to the case, and configured to direct an airflow into the case, - a protective grille placed inside the housing and configured to allow passage of the airflow through the air intake duct, the protective grille comprising: • a frame forming a main plane of the protective grid, • at least three fins spaced apart and supported by the frame, at least three of these fins forming with the main plane of the corner protection grid aa, ab, ac, with aa < ab < ac.

[0006] A lower side and a upper side of the protective grid are defined, as well as a height axis between this upper side and this lower side of the protective grid. Each point on the principal plane of the protective grid can thus be associated with a height on the protective grid, this height being between 0 and the height Hg of the protective grid.

[0007] According to one aspect of the invention, the protective grid is flat in shape, and the principal plane of the protective grid is the median plane of the grid.

[0008] Alternatively, the protective grid can be of any other shape, including a curved shape.

[0009] According to one aspect of the invention, the protective grid is made of plastic.

[0010] Alternatively, the protective grille is metallic, in particular made of aluminium or aluminium alloy.

[0011] According to one aspect of the invention, the protective grid is made by injection.

[0012] According to one aspect of the invention, each fin of the protective grille is presented in the form of a longitudinal band.

[0013] According to one aspect of the invention, the protective grid includes at least one crossbar which connects the fins, being perpendicular to the fins.

[0014] According to one aspect of the invention, the protective grid comprises a plurality of crossbars which connect the fins, being perpendicular to the fins, and these crossbars are in particular regularly spaced along the fins.

[0015] According to one aspect of the invention, the crossbeams are in the form of strips of material.

[0016] According to one aspect of the invention, the protective grid, with the fins and the crossbars, is made in one piece.

[0017] According to one aspect of the invention, the frame has a substantially rectangular shape.

[0018] According to one aspect of the invention, the protective grid comprises at least 20 fins, in particular at least 30 fins, in particular at least 40 fins, for example 50 fins.

[0019] According to one aspect of the invention, each fin is elongated in shape, in particular with an aerodynamic profile.

[0020] According to one aspect of the invention, each fin is substantially flat in shape.

[0021] According to one aspect of the invention, all the fins are identical.

[0022] Alternatively, some fins may have different shapes, including different profiles.

[0023] According to one aspect of the invention, a principal plane of the fin is defined for each fin, and the angle ai is defined as the angle formed in the counterclockwise direction between the principal plane of the fin and the principal plane of the protective grid.

[0024] According to one aspect of the invention, the fins extend laterally along the entire length of the protective grid.

[0025] According to one aspect of the invention, each fin has a main axis included in the main plane of the protective grid, and parallel to the top and bottom sides of the protective grid.

[0026] According to one aspect of the invention, a height Hi of the fin on the protective grid is defined for each fin.

[0027] According to one aspect of the invention, the fins are separated by a gap allowing the passage of air.

[0028] According to one aspect of the invention, the fins are distributed regularly between the upper and lower sides of the protective grid frame, and the intervals between the fins are identical between each of the fins.

[0029] Alternatively, at least one gap between two fins of the protective grid is of a different length from the other gaps.

[0030] According to one aspect of the invention, the intervals between the fins have a length Li between 1mm and 10mm, in particular less than 8mm.

[0031] According to one aspect of the invention, airflow lines are defined representing the flow of air through the protective grid.

[0032] According to one aspect of the invention, the airflow lines of the airflow intersect the main plane of the protective grid at an angle dependent on the height of the main plane of the protective grid.

[0033] According to one aspect of the invention, the angle ai formed by each fin with the main plane of the protective grid is defined so as to control the impact of the fin on the passage of the airflow.

[0034] In particular, the angle ai formed by each fin with the main plane of the protective grid is defined so as to minimize the impact of the fin on the passage of the airflow.

[0035] According to one aspect of the invention, the angle ai formed by each fin with the main plane of the protective grid is equal to the angle formed at the intersection of the flow lines and the main plane of the protective grid at the height of the fin.

[0036] According to one aspect of the invention, the angles ai formed by the fins with the main plane of the protective grid evolve monotonically from the bottom to the top of the protective grid over at least a portion of the protective grid.

[0037] According to one aspect of the invention, the angles ai formed by the fins with the main plane of the protective grid evolve monotonically between the lower side and the upper side of the protective grid.

[0038] According to one aspect of the invention, the angles ai formed by the fins with the main plane of the protective grid evolve in an increasing manner from the bottom side to the top side of the protective grid.

[0039] Alternatively, the angles ai formed by the fins with the main plane of the protective grid evolve in a decreasing manner from the bottom side to the top side of the protective grid.

[0040] According to one aspect of the invention, the air intake duct comprises at least one air inlet and at least one air outlet, and is arranged to conduct the airflow from the air inlet of the air intake duct to the air outlet of the air intake duct.

[0041] According to one aspect of the invention, the air inlet of the air intake duct has, for example, a substantially rectangular perimeter.

[0042] According to one aspect of the invention, the air outlet of the air intake duct has, for example, a substantially rectangular perimeter.

[0043] According to one aspect of the invention, the area of ​​the air inlet of the air intake duct is for example smaller than the area of ​​the air outlet of the air intake duct, for example at least twice as small.

[0044] According to one aspect of the invention, the housing and the air intake duct are formed as a single unit.

[0045] Alternatively, the housing and the air intake duct are two separate parts.

[0046] According to one aspect of the invention, the air intake duct is connected to the housing.

[0047] In particular, the air outlets of the air intake duct are connected to the housing.

[0048] According to one aspect of the invention, the protective grille has a higher height larger than the air outlets of the air intake duct.

[0049] According to one aspect of the invention, the air outlets of the air intake duct are rectangular in shape.

[0050] According to one aspect of the invention, the air outlets of the air intake duct are rectangular and coplanar, and define a plane of the air outlets of the air intake duct.

[0051] According to one aspect of the invention, a principal axis of the air outlet is defined, normal to the plane of the air outlets, and passing through the center of an air outlet.

[0052] According to one aspect of the invention, the main axis of the air outlet is parallel to the airflow circulating in the air intake duct.

[0053] According to one aspect of the invention, the air intake duct has a single air outlet.

[0054] According to one aspect of the invention, the air outlet of the air intake duct is placed opposite the bottom of the protective grille.

[0055] According to one aspect of the invention, the angles of inclination ai of the fins are distributed asymmetrically with respect to a midline of the grid, in particular if the air outlet is positioned closer to one side of the protective grid than to the opposite side.

[0056] According to one aspect of the invention, the protective grid comprises a group of lower fins including the fins placed closest to the lower side of the protective grid, and the angles ai formed with the main plane of the protective grid by these lower fins are between 70° and 110°, in particular between 80° and 100°, in particular between 85° and 95°, in particular equal to 90°.

[0057] According to one aspect of the invention, the protective grid comprises a group of upper fins including the fins placed closest to the upper side of the protective grid, and the angles ai formed with the main plane of the protective grid by these upper fins are between 90° and 180°, in particular between 100° and 150°.

[0058] According to one aspect of the invention, the air intake duct comprises a plurality of air outlets.

[0059] According to one aspect of the invention, the height of the protective grille is divided into a series of N intervals { Il = [0, Ll[ ; 12 = [Ll, L2[ ; ... ; IN = [LN-1, Hg]}, with N the number of air outlets of the air intake duct.

[0060] According to one aspect of the invention, the height of the protective grille is thus divided into as many intervals as the air intake duct has air outlets.

[0061] According to one aspect of the invention, the angles ai formed with the main plane of the protective grid by the fins evolve monotonically over each of the intervals Ik, with 2 < k < N.

[0062] According to one aspect of the invention, the angles ai vary monotonically when the fins move away from at least one air outlet of the air intake duct.

[0063] According to one aspect of the invention, the angles ai increase when the fins move away from the air outlets.

[0064] Alternatively, the angles ai decrease when the fins move away from the air outlets.

[0065] According to one aspect of the invention, each interval Ik of the protective grille is placed opposite an air outlet of the air intake duct, and configured to be traversed by the airflow exiting from this air outlet.

[0066] According to one aspect of the invention, a flat fin, namely forming an angle ai substantially equal to 90°, is placed at heights L1, L2,.. ,,LN-1, namely at the junction between the intervals Ik corresponding to the different air outlets.

[0067] According to one aspect of the invention, the air intake duct has two air outlets.

[0068] According to one aspect of the invention, an air outlet of the air intake duct is placed opposite the top of the protective grille, and an air outlet from the air intake duct is placed opposite the bottom of the protective grille.

[0069] According to one aspect of the invention, an air outlet of the air intake duct is aligned with the upper side of the protective grille, and an air outlet of the air intake duct is aligned with the lower side of the protective grille.

[0070] According to one aspect of the invention, at least one air outlet is offset from the top and bottom sides of the protective grille, namely, it is not placed opposite either the top or the bottom side of the protective grille.

[0071] According to one aspect of the invention, the protective grid is divided in its height into two intervals II and 12. In particular, interval II represents substantially the lower half of the protective grid, and 12 the upper half of the protective grid.

[0072] According to one aspect of the invention, the angles ai formed with the principal plane of the protective grid by the fins placed in the interval II increase as the height Hi of fin placement increases, and the angles ai formed with the principal plane the protection grid by the fins placed in the interval 12 increases when the height Hi of fin placement increases.

[0073] According to one aspect of the invention, the increment step of the angle between two adjacent fins is for example between 0.1° and 5°.

[0074] Alternatively, the angles increase in steps, i.e., there are groups of fins that are parallel to each other. For example, fins placed in the same interval Ik are parallel to each other.

[0075] For example there are at least two groups, in particular at least three groups of parallel fins.

[0076] According to one aspect of the invention, the assembly comprises at least one heat exchanger placed behind the protective grille in the direction of airflow.

[0077] According to one aspect of the invention, the heat exchanger comprises heat transfer fluid circulation tubes.

[0078] According to one aspect of the invention, the heat transfer fluid circulation tubes of the heat exchanger are made of metallic material and spaced apart from each other so as to allow an airflow between the tubes.

[0079] According to one aspect of the invention, each heat transfer fluid circulation tube of the heat exchanger is positioned opposite one of the fins of the protective grid.

[0080] According to one aspect of the invention, the heat exchanger is rectangular in shape and has a principal plane parallel to the principal plane of the protective grille. The heat exchanger is, for example, a radiator for a thermal management loop in a motor vehicle.

[0081] Alternatively, the main plane of the protective grid and the main plane of the heat exchanger are intersecting.

[0082] According to one aspect of the invention, the assembly includes a motor-fan unit configured to generate the airflow through the air intake duct and the protective grille.

[0083] According to one aspect of the invention, the motor-fan unit is placed behind the protective grille and at least the heat exchanger in the direction of airflow.

[0084] According to one aspect of the invention, the protective grille is placed perpendicular to the airflow.

[0085] In particular, the main plane of the protective grille is normal to the main axis of the air outlet of the air intake duct.

[0086] Alternatively, the protective grille is inclined with respect to the airflow, and the main plane of the protective grille forms with the main axis of the air outlet an angle [3, in particular an angle [3 between 20° and 90°.

[0087] According to one aspect of the invention, the assembly is configured to be mounted on a vehicle, in particular a motor vehicle.

[0088] The heat exchanger is, for example, a radiator for cooling a vehicle engine by means of a coolant cooled by air circulating through the radiator. To obtain an airflow through the radiator, it is placed on the front of the vehicle, for example.

[0089] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0090] [Fig.1] Fig.1 is a perspective representation of an assembly according to the invention comprising an air intake duct and a protective grille;

[0091] [Fig.2] Fig.2 is a perspective representation of an assembly according to 1' invention comprising an air intake duct and a protective grille;

[0092] [Fig.3] Fig.3 is a perspective representation of a protective grid an assembly according to the invention.

[0093] [Fig.4] The [Fig.4] a schematic cross-sectional view of an assembly according to the invention.

[0094] [Fig. 5] Fig. 5 is a schematic cross-sectional view of an assembly according to the invention. in which the protective grille is inclined relative to the airflow.

[0095] [Fig.6] Fig.6 is a schematic cross-sectional view of an assembly according to the invention, in which the air intake duct has two air outlets.

[0096] [Fig.7] Fig.7 is a schematic cross-sectional view of an assembly according to the invention in which the housing and the air intake duct are formed as a single unit.

[0097] The features, variants, and different embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0098] Figures 1 and 2 represent an assembly 1 according to the invention.

[0099] Assembly 1 comprises a housing 3 forming a main air duct in which a protective grille 2, shown in [Fig.3], is placed. The protective grille 2 is, for example, made of plastic, in particular by molding.

[0100] Assembly 1 includes an air intake duct 4 connected to the housing 3.

[0101] The air intake duct 4 has an air inlet 5, an air outlet 6 connected to the housing 3, and is configured to conduct an airflow from the air inlet 5 to the housing 3.

[0102] The protective grille 2 is configured to be traversed by the airflow conducted through the air intake duct 4. The air intake duct 4 thus forms a kind of envelope to channel the airflow.

[0103] The protective grille 2 has a greater height than the air outlet 6 of the air intake duct 4.

[0104] Assembly 1 includes a heat exchanger 15, not shown in Figures 1 and 2, which is placed behind the protective grille 2 in the direction of airflow.

[0105] The heat exchanger 15, for example a radiator for a thermal management loop of a motor vehicle, comprises heat transfer fluid circulation tubes, these tubes being made of metallic material and spaced from each other so as to allow an airflow between the tubes, and each tube being positioned opposite one of the fins of the protective grid 2. According to one embodiment, several heat exchangers 15 can be placed behind the protective grid.

[0106] Each heat transfer fluid circulation tube is positioned opposite one of the fins 8 of the protective grid 2.

[0107] The heat exchanger 15 is rectangular in shape, and has a main plane parallel to the main plane of the protective grid.

[0108] Assembly 1 includes a motor-fan unit 13, here of the electric type, configured to generate the airflow through the air intake duct 4 and the protective grille 2.

[0109] The motor-fan unit 13 is placed behind the protective grille 2 and the heat exchanger 15 in the direction of airflow.

[0110] A protective grid 2 according to the invention is shown in [Fig.3].

[0111] The protective grid 2 is flat in shape, and the main plane of the grid protection 14, not shown in this figure, is the median plane of the protection grid 2.

[0112] According to an embodiment not shown, the protective grid 2 can be of any other shape, in particular a curved shape.

[0113] The protective grid 2 comprises a rectangular frame 7 forming the main plane of the protective grid 14, and fins 8 spaced apart and supported by the frame 7 of the protective grid 2.

[0114] The fins 8 of the protective grid 2 are separated by a gap allowing the passage of air.

[0115] The protective grid has at least 30 fins 8, distributed regularly between the upper sides 9 and lower sides 10 of the frame 7 of the protective grid 2. The intervals are therefore identical between each of the fins 8.

[0116] The intervals between the fins 8 measure less than 8mm, for example 5mm.

[0117] A top side 9 and a bottom side 10 of the protective grid 2 are defined, as well as a height axis between these sides. Thus, each point on the principal plane of the protective grid 2 can be associated with a height on the grid, this height being between 0 and the height Hg of the protective grid.

[0118] We therefore define for each fin a height Hi of the fin 8 on the protective grid 2.

[0119] Each fin 8 of the protective grid 2 is in the form of a longitudinal strip, and is substantially flat in shape.

[0120] In an embodiment not shown, each fin 8 is elongated in shape, in particular with an aerodynamic profile.

[0121] The fins 8 extend laterally along the entire length of the protective grid 2, and have a main axis included in the main plane of the protective grid and parallel to the upper 9 and lower 10 sides of the protective grid 2.

[0122] The protective grid 2 comprises a plurality of cross members 11 which connect the fins, being perpendicular to the fins, and these cross members are in particular regularly spaced along the fins.

[0123] The crossbars 11 are in the form of strips of material.

[0124] The protective grid 2, with the fins 8 and the crossbars 11, is made in one piece.

[0125] Figure [Fig.4] shows a schematic cross-sectional view of an assembly according to the invention.

[0126] Four fins 8 numbered from 1 to 4, spaced apart and supported by the frame 7 of the protective grid 2, have been shown.

[0127] Thus, for each fin 8, a principal plane of the fin is defined, and an angle ai formed between the principal plane of the fin and the principal plane 14 of the protective grid 2.

[0128] The four fins 8 form angles a1, a2, a3 and a4 with the principal plane 14 of the protective grid 2, these angles all being different. There are therefore 3 angles aa, ab, ac formed by 3 fins with the principal plane 1' of the protective grid 2, such that aa < ab < ac.

[0129] The flow lines of the airflow passing through assembly 1 and representing the flow of the airflow through the protective grid 2 have also been shown.

[0130] These flow lines intersect the main plane 14 of the protective grid 2 at an angle dependent on the height on the main plane 14 of the protective grid 2.

[0131] A principal axis of the air outlet 6 is defined, normal to the plane of the air outlet, and passing through the center of the air outlet 6.

[0132] The main axis of the air outlet 6 is parallel to the airflow circulating in the air intake duct 4.

[0133] The protective grille 2 is placed perpendicular to the airflow, i.e. the main plane 14 of the protective grille 2 is normal to the main axis of the air outlet 6 of the air intake duct 4.

[0134] The angle ai formed by each fin 8 with the main plane 14 of the protective grid 2 is defined so as to control, in particular so as to minimize the impact of the fin 8 on the passage of the airflow.

[0135] In particular, the angle ai formed by each fin 8 with the main plane 14 of the protective grid 2 is equal to the angle formed at the intersection of the flow lines and the main plane 14 of the protective grid 2 at the height Hi of the fin 8.

[0136] The air intake duct 4 has a single rectangular air outlet 6 positioned opposite the bottom of the protective grille 2.

[0137] The air outlet 6 of the air intake duct 4 is positioned closer to the lower side 10 of the protective grille 9 than to the upper side of the protective grille.

[0138] The angles of inclination ai of the fins 8 are distributed asymmetrically with respect to a midline of the protective grid 2.

[0139] In particular, the angles ai formed by the fins 8 with the main plane of the protective grid 2 evolve monotonically, here increasingly, over at least a portion of the protective grid 2, here from the bottom side 10 to the top side 9 of the protective grid.

[0140] The increment step of the angle between two adjacent fins is, for example, between 0.1° and 5°. This increment step is not visible on the schematic figures, where a limited number of fins are represented for readability reasons.

[0141] According to an embodiment not shown, the angles ai formed by the fins 8 with the main plane of the protective grid 2 evolve in an increasing manner from the lower side 10 to the upper side 9 of the protective grid 2.

[0142] Figure 5 shows an assembly 1 according to the invention, in which the protective grid 2 is inclined relative to the airflow.

[0143] The protective grille 2 is inclined with respect to the airflow, and the main plane 14 of the protective grille 2 forms with the main axis of the air outlet 6 of the air intake duct 4 an angle [3, in particular an angle [3 between 20° and 90°.

[0144] Figure 6 shows an assembly according to the invention in which the air intake duct 4 has two air outlets 6.

[0145] The two air outlets 6 of the air intake duct 4 are rectangular and coplanar.

[0146] The height of the protective grid 2 is divided into a series of N intervals { It = [ 0, Ll[ ; 12 = [Ll, L2[ ; ... ; IN = [LN-1, Hg]}, with N the number of air outlets 6 of the air intake duct 4, here II = [0, Ll[ ; 12 = [Ll, Hg ].

[0147] The height of the protective grille 2 is thus divided into as many intervals as the air intake duct 4 has air outlets 6.

[0148] In a representation not shown, the air intake duct 4 has N air outlets, with N > 2.

[0149] Here, the air intake duct 4 has two air outlets 6, and the protective grille is divided in its height into two intervals II and 12. In particular, interval II represents substantially the lower half of the protective grille 2, and 12 the upper half of the protective grille 2.

[0150] An air outlet 6 of the air intake duct 4 is placed opposite the top of the protective grille 2, and an air outlet 6 is placed opposite the top of the protective grille 2.

[0151] Each interval Ik of the protective grid 2, here intervals II and 12, is placed opposite an air outlet 6 of the air intake duct 4, and configured to be crossed by the airflow exiting from this air outlet 6.

[0152] The protective grid 2 comprises a group of lower fins including the fins placed closest to the lower side of the protective grid, here the fins in interval II, and a group of upper fins including the fins placed closest to the upper side of the protective grid, here the fins in interval 12.

[0153] The angles ai formed with the main plane of the protective grid by the lower fins are between 70° and 110°, in particular between 80° and 100°, in particular between 85° and 95°, in particular equal to 90°, and the angles ai formed with the main plane of the protective grid by these upper fins are between 90° and 180°, in particular between 100° and 150°.

[0154] The angles ai formed with the main plane 14 of the protective grid 2 by the fins evolve monotonically over each of the intervals.

[0155] The angles ai vary monotonically when the fins 8 move away from the air outlets 6 of the air intake duct 4.

[0156] Here, the angles ai formed with the main plane 14 of the protective grid 2 by the fins 8 placed in the interval II increase when the height Hi of placement of the fins increases, and the angles ai formed with the main plane 14 of the protective grid 2 by the fins placed in the interval 12 increase when the height Hi of placement of the fins 8 increases.

[0157] A flat fin 8, namely forming an angle approximately equal to 90°, is placed at heights L1, L2, ..., LN-1, namely at the junction between the intervals Ik corresponding to the different air outlets. Here, a flat fin 8 is placed at height L1, at the junction between intervals II and 12.

[0158] Alternatively, the angles increase in steps, i.e., there are groups of fins that are parallel to each other. For example, fins placed in the same interval Ik are parallel to each other.

[0159] For example there are at least two groups, in particular at least three groups of 8 parallel fins.

[0160] Figure 7 shows an assembly 1 according to the invention in which the housing 3 and the air intake duct 4 are formed as a single unit.

[0161] The air intake duct 4 has two rectangular and coplanar air outlets 6.

[0162] The height of the protective grid 2 is divided into two intervals { Il = [0, Ll[ ; 12 = [L1,L2]}

[0163] The air outlets 6 of the air intake duct 4 are offset from the upper sides 9 and lower sides 10 of the protective grille 2, namely they are not positioned opposite either the upper side 9 or the lower side 10 of the protective grille 2.

[0164] The protective grid 2 comprises a group of lower fins including the fins placed closest to the lower side of the protective grid, here the fins in interval II, and a group of upper fins including the fins placed closest to the upper side of the protective grid, here the fins in interval 12.

[0165] The angles ai formed with the main plane 14 of the protective grid 2 by the fins evolve monotonically over each of the intervals.

Claims

Demands

1. Assembly (1) comprising: - a housing (3) forming a main air duct, - a heat exchanger (15), - an air intake duct (4) connected to the housing (3), and configured to conduct an airflow into the housing (3), - a protective grille (2) placed in the housing (3) to protect the heat exchanger (15), and configured to be traversed by the airflow conducted through the air intake duct (4), the protective grille comprising: • a frame (7) forming a principal plane (14) of the protective grille (2), • at least three fins (8) spaced apart and supported by the frame (7), at least three of these fins forming angles aa, ab, ac with the principal plane of the protective grille,with aa < ab < ac and the angle ai formed by each fin (8) with the main plane (14) of the protective grid (2) is equal to the angle formed at the intersection of the flow lines and the main plane (14) of the protective grid (2) at the height of the fin (8).

2. Assembly (1) according to claim 1, wherein the fins (8) are distributed regularly between the upper sides (9) and lower sides (10) of the frame of the protective grid (2), and the intervals between the fins (8) are identical between each of the fins.

3. Assembly (1) according to claim 1 or 2, wherein the angles ai formed by the fins (8) with the principal plane (14) of the protective grid (2) evolve monotonically from the bottom to the top of the protective grid over at least a portion of the protective grid (2), in particular from the bottom side (10) to the top side (9) of the protective grid (2).

4. Assembly (1) according to any one of the preceding claims, wherein the air intake duct (4) has a single air outlet (6), and the air outlet (6) is positioned opposite the bottom of the protective grille (2).

5. Assembly (1) according to any one of claims 1 to 3, wherein the air intake duct (4) has two air outlets (6).

6. Assembly (1) according to claim 5, wherein an air outlet (6) is placed opposite the top of the protective grille (2), and an air outlet (6) is placed opposite the bottom of the protective grille (2).

7. Assembly (1) according to any one of the preceding claims, wherein the height of the protective grille (2) is divided into a series of N intervals { Il = [0, Ll[ ; 12 = ]L1, L2[ ; ...; IN = ]LN-1, Hg]} with N the number of air outlets (6) of the air intake duct (4), and the angles ai formed with the principal plane (14) of the protective grille (2) by the fins (8) evolve monotonically over each of the intervals Ik, with 2 < k < N.