HEAT EXCHANGER MODULE FOR A MOTOR VEHICLE

Description

[0001] The invention relates to a heat exchanger module for a motor vehicle.

[0002] The invention relates to the automotive field, and more particularly to the field of air circulation for cooling the engine and its equipment.

[0003] Motor vehicles, whether combustion or electric, need to evacuate the calories generated by their operation and are therefore equipped with heat exchangers. A motor vehicle heat exchanger generally comprises tubes, in which a heat transfer fluid is intended to circulate, in particular a liquid such as water, and heat exchange elements connected to these tubes, often referred to as "fins" or "spacers". The fins increase the exchange surface area between the tubes and the ambient air.

[0004] However, in order to further increase the heat exchange between the heat transfer fluid and the ambient air, it is common for a ventilation device to be used in addition, to generate or increase an air flow directed towards the tubes and fins.

[0005] Such a ventilation device most often comprises a propeller fan, which has several disadvantages. Such a ventilation device is described in document DE 10 2008 020310 A1.

[0006] Firstly, the assembly formed by the propeller fan and its motorization device occupies a significant volume.

[0007] In addition, the distribution of the air ventilated by the propeller, often placed in the center of the row of tubes, is not uniform over the entire surface of the heat exchanger. In particular, certain regions of the heat exchanger, such as the ends of the heat transfer tubes and the corners of the heat exchanger, are not or only slightly reached by the air flow ejected by the propeller.

[0008] Furthermore, when it is not necessary to start the ventilation device, in particular when the heat exchange with the ambient air is sufficient to cool the heat transfer fluid, the propeller blades partially obstruct or "mask" the flow of ambient air towards the tubes and fins. This limits the heat exchange between the ambient air, on the one hand, and the tubes and fins, on the other hand.

[0009] Furthermore, in this case, the engine friction is reduced less quickly, which increases the vehicle's fuel consumption and therefore carbon dioxide emissions. Document EP0233174A1 discloses a vehicle with a reciprocating fan, of the tangential type, which powers the cooling radiator.

[0010] An object of the invention is to provide a ventilation device for a heat exchanger which does not have at least some of the disadvantages of known ventilation devices for heat exchangers.

[0011] For this purpose, the invention relates to a heat exchanger module according to claim 1.

[0012] Thus, advantageously, the plurality of tubes from which air is ejected makes it possible to replace the conventional propeller arranged in front of the tubes for circulating a heat transfer fluid of the heat exchanger, without presenting the drawbacks mentioned above.

[0013] Indeed, with equal heat exchange capacities, the volume occupied by such a ventilation device is much smaller than that of a propeller ventilation device. In addition, the distribution of air ventilated by the tubes is easier to control and can be made more homogeneous.

[0014] Furthermore, thanks to the device according to the invention, the obstruction of the air flow towards the heat exchanger is limited. Indeed, the tubes of the ventilation device can advantageously be arranged opposite low heat exchange zones of the heat exchanger, called "dead zones", such as the front faces of the tubes crossed by the heat transfer fluid, which are not in contact with cooling fins. This is not achievable with a conventional propeller.

[0015] Furthermore, the invention makes it possible to relocate the air ejection means supplying air flow to the tubes of the ventilation device, away from the row of heat transfer fluid circulation tubes, which offers greater freedom in the design of the heat exchanger.

[0016] According to the invention, the device comprises at least one manifold for distributing air to the tubes, at least one turbomachine being arranged in said at least one manifold, said at least one turbomachine comprising a tangential fan, said at least one manifold forming a volute of the tangential fan.

[0017] According to the invention, the volute comprises an air inlet in the collector through which an air flow can be sucked in by the tangential fan, and an air outlet through which the sucked air flow can be distributed to the tubes, the tubes extending parallel to a longitudinal direction of the tubes, called the longitudinal direction, the tangential fan extending in a direction orthogonal to the longitudinal direction, called the suction direction, another direction, called the forward direction, orthogonal to the longitudinal direction and to the suction direction.

[0018] According to another characteristic of the invention, the air inlet comprises a first inlet wall making with said longitudinal direction an angle of between 40° and 75°, and preferably 58°.

[0019] According to another characteristic of the invention, one end of the first wall opposite the air inlet is curved in a plane containing the longitudinal direction and the direction of advancement, the length of which is between 1 mm and 8 mm and a minimum distance between said end and a disc delimited by the tangential fan in said plane is between 0.5 mm and 1.5 mm.

[0020] According to another characteristic of the invention, the air inlet comprises a second inlet wall comprising a rounded edge shaped so that its curvature in a plane containing the longitudinal direction and the direction of advance is an arc of a circle whose center is located on a concentric circle of a disc delimited by the tangential fan in said plane.

[0021] According to another characteristic of the invention, the device comprises a junction part of the air inlet of the volute and the air outlet of the volute, called the intermediate part, shaped to house the tangential fan.

[0022] According to another characteristic of the invention, said intermediate part comprises a wall, called intermediate wall, curved according to an arc of a circle in a plane containing the longitudinal direction and the direction of advancement, said arc of a circle having a center distinct from the center of a disc delimited by the tangential fan in said plane.

[0023] According to another characteristic of the invention, a distance between the center of the intermediate wall and the center of the disc is less than or equal to the value of the radius of the disc.

[0024] According to another characteristic of the invention, a section of the intermediate part at the level of an interface between the intermediate part and the air outlet forms an angle, preferably non-zero, with the longitudinal direction, preferably within the interval [0° 20], more preferably within the interval ]0°,20°].

[0025] According to another characteristic of the invention, the tangential fan is suitable for creating an air flow with a flow rate of between 0 and 750 m 3 < / h and a pressure of between 0 and 900 Pa. To do this, the tangential fan comprises a rotor whose rotation speed can be between 2000 rpm and 13,000 rpm, preferably between 2500 rpm and 9000 rpm.

[0026] To do this, one or more of the following characteristics may be provided, taken alone or in combination: the rotor is formed of several stages of blades separated by reinforcing discs; the rotor has a blade height, defined as the sum of the height of the different stages of blades, measured parallel to the axis of rotation of the rotor, of between 100 and 600 mm; each stage of blades has a height, measured parallel to the axis of rotation of the rotor, of between 16 and 33 mm; each reinforcing disc has a thickness, measured parallel to the axis of rotation of the rotor, of between 0.8 and 1.5 mm; each stage of blades comprises between 15 and 30 blades, preferably between 20 and 28 blades; the different blades of each stage of blades 51 are inscribed in a ring of internal diameter Dint and external diameter Dext; the internal diameter is between 0 and 84 mm, preferably between 60 and 84 mm; the external diameter is between 35 and 120 mm, preferably between 60 and 120 mm;each blade has a crescent-shaped cross-section, the blades preferably being substantially cylindrical; a pitch angle γ of each blade, defined as the angle between the chord of the blade and an axis connecting the axis of rotation of the rotor to the geometric center of the cross-section of the blade 53, is between 0 and 30°; a flow angle at the leading edge of each blade, defined as the angle between the streamline at the leading edge of the blade and the tangent to the outer diameter of the rotor, is between 0° and 40°, preferably between 10° and 20°; a flow angle at the trailing edge of each blade, defined as the angle between the streamline at the trailing edge of the blade, and the tangent to the inner diameter of the rotor, is between 60° and 90°, preferably between 70° and 80°;the maximum thickness of the cross-section of each blade is between 0.35 and 1.6 mm, preferably between 0.8 and 1.2 mm; the length of the chord of the cross-section of each blade, connecting the leading edge to the trailing edge of the cross-section of each blade, along a rectilinear segment, is between 6 and 8 mm; the rotor is formed of several portions, rolling bearings being interposed between each portion; and the rotor is formed of a number of portions less than 4. ;

[0027] Other characteristics and advantages of the invention will appear on reading the description which follows. This is purely illustrative and must be read in conjunction with the appended drawings in which: there figure 1 illustrates an exploded perspective view of a heat exchange module equipped with a ventilation device according to the present invention; figure 2illustrates a cross-sectional view of two tubes of the figure 1 ; THE figures 3 to 6 illustrates a cross-sectional view of a collector of the device of the figure 1 , particular elements being drawn on the sectional view; the figure 7 is a detail view of one of the figures 3 to 6 ; there figure 8 is a perspective view of a first example of a rotor of the tangential fan implemented in the collector illustrated in figures 3 to 6 ; there figure 9 is a view analogous to the figure 8 of a detail of the rotor of the figure 8 ; there figure 10 is a schematic cross-sectional view of the rotor of the figures 8 and 9 ; THE Figures 11 and 12 are schematic cross-sectional views of a rotor blade of the figures 8 and 9 ; and the figure 13 is a perspective view of a second example of a rotor that can be implemented in the tangential fan inside the collector shown in figures 3 to 6 . Heat exchange module

[0028] The subject of the invention is a heat exchange module 100, comprising the ventilation device 1 and a heat exchanger 101.

[0029] As visible on the figure 1 , the ventilation device 1 and the heat exchanger 101 are positioned relative to each other so that an air flow set in motion by the ventilation device 1 supplies air to the heat exchanger, preferably to cool the engine of the motor vehicle.

[0030] The ventilation device 1 is arranged upstream of the heat exchanger 101 on the figure 1 (relating to an airflow coming from outside the moving vehicle).

[0031] However, the ventilation device can also be arranged downstream of the heat exchanger 101. Ventilation device

[0032] As seen in the figures, the ventilation device 1 comprises a plurality of tubes 3.

[0033] The tubes 3 are substantially straight, parallel to each other and aligned so as to form a row of tubes.

[0034] When the exchange module is installed in the motor vehicle, the tubes 3 can be arranged horizontally, parallel to a longitudinal direction of the ventilation device, noted X. According to another possible embodiment of the exchange module (not illustrated in the figures), the tubes can be arranged vertically.

[0035] A vertical direction is denoted Z.

[0036] A direction orthogonal to the X and Z directions, coinciding with a direction of advancement of the vehicle, is noted Y.

[0037] The ventilation device 1 also comprises a device for supplying air with an air flow F.

[0038] This device supplies the ventilation tubes 3 via an air supply circuit 4.

[0039] The air supply circuit 4 comprises in particular two air intake manifolds 5-1, 5-2 to which the ventilation tubes 3 are connected via air supply inlets located at each of their ends 6, 7.

[0040] Advantageously, the supply circuit also comprises one or more turbomachines 26 for ejecting the air through the intake manifolds 5-1, 5-2, into the ventilation tubes 3.

[0041] Advantageously, each turbomachine is a tangential fan.

[0042] On the figure 1 , the tangential fan 26 is housed in the collector 5-1.

[0043] The 5-1 manifold includes a single opening 27 extending along the 5-1 manifold.

[0044] As visible on the figure 2 , each ventilation tube 3 comprises at least one opening 10 distinct from the ends 6, 7, for ejecting air from the tube 3.

[0045] Preferably, the openings 10 are intended to be arranged opposite the heat exchanger.

[0046] As visible on the figure 2 , each tube 3 comprises a longitudinal wall 19 of which a cross section comprises a free leading edge 11, a trailing edge 15 and a first and a second profile 12, 14, each extending between the leading edge 11 and the trailing edge 15.

[0047] The trailing edge 15 is preferably arranged opposite the heat exchanger.

[0048] The longitudinal wall 19 is delimited by an internal surface 16 and an external surface 18.

[0049] Each opening 10 is made in the longitudinal wall 19 of the tube 3, preferably in one or other of the profiles 12, 14. Alternatively, an opening 10 can be made in the longitudinal wall 19 of the tube, in both profiles 12, 14.

[0050] On the figure 2, each opening 10 is positioned near the leading edge 11.

[0051] As also visible on the figure 2 , the openings 10 of the pair of tubes 3 illustrated are made in the profiles 12 facing each other.

[0052] Thus, the ventilation tubes 3 and their openings 10 are configured so that the air flow F circulating in the ventilation tubes 3 is ejected through the opening 10 by flowing along each profile 12, substantially up to their trailing edges 52, by Coanda effect.

[0053] The air flow F ejected from the tubes 3 makes it possible to accelerate another flow F' in a flow direction towards the heat exchanger.

[0054] It is noted that the cross sections of the tubes 3 are such that the profiles 12 extend in a direction away from the tubes 3 from the leading edges 11 to the trailing edges 15. Turbomachines of the ventilation device

[0055] As indicated previously, a turbomachine 26 for ejecting air through the intake manifolds 5-1, 5-2, into the ventilation tubes 3, are advantageously received in each intake manifold 5-1, 5-2. Advantageously again, each of these turbomachines is a tangential fan 26 comprising a rotor 50.

[0056] The rotor 50 of the tangential fan 26 is advantageously shaped to create an air flow with a flow rate of between 0 and 750 m 3 < / h, and a corresponding air pressure of between 0 and 900 Pa. The corresponding rotation speed of the rotor 50 is, for example, between 2000 rpm and 13000 rpm, preferably between 2500 rpm and 9000 rpm. Thus, the rotation speed of the rotor 50 of the tangential fan 26 is optimized to ensure an air flow rate allowing efficient cooling of the heat exchange module.

[0057] A first example of rotor 50 of such a tangential fan 26 is illustrated by the figures 8 to 12 .

[0058] This first example of rotor 50 is formed of several stages 51 of blades (or vanes) separated by reinforcing discs 52. In this case, the rotor 50 comprises thirteen stages of blades 51. In total, the rotor 50 has a blade height H51, defined as the sum of the height of the different stages of blades 51, measured parallel to the axis A50 of rotation of the rotor 50, of between 100 and 600 mm. Each stage of blades 51 has a height h51, measured parallel to the axis A50 of rotation of the rotor 50, of between 16 and 33 mm. These dimensions are intended to ensure the creation of the desired air flow.

[0059] Each reinforcing disc 52 has, for example, a thickness, also measured parallel to the axis A50 of rotation of the rotor 50, of between 0.8 and 1.5 mm. These dimensions make it possible in particular to ensure the mechanical strength of the rotor 50.

[0060] As visible on the figure 10 , in particular, each stage of blades 51 may for example comprise between 15 and 30 blades 53 (or vanes), preferably between 20 and 28 blades. It should be noted here that the blades 53 make it possible to obtain a desired air flow, but also to stiffen the rotor 50.

[0061] The different blades 53 of each blade stage 51 are inscribed in a ring 54 of internal diameter Dint and external diameter Dext. The internal diameter Dint is for example between 0 and 84 mm, preferably between 60 and 84 mm. The external diameter Dext is for example between 35 and 120 mm, preferably between 60 and 120 mm.

[0062] Each blade 53 has a cross-section, in a plane (X, Y) in the shape of a crescent. The shape of a blade 53 is described more precisely below, with regard to the Figures 11 and 12which illustrates the cross-section of a blade 53 in a plane (X, Y), the blades being substantially cylindrical with an axis parallel to the Z direction, here vertical.

[0063] As can be seen on the figure 11 , we define a pitch angle γ of a blade 53, as being the angle between the chord c53 of the blade 53 and an axis Δ1 connecting in the plane (X, Y) of the figure 11 , the axis of rotation A50 of the rotor at the geometric center O 53 of the blade 53. This setting angle γ is for example between 0 and 30°.

[0064] Furthermore, a flow angle at the leading edge β1 is defined as being the angle between the streamline at the leading edge 54 and the tangent 55 to the outer diameter of the rotor 50. The flow angle at the leading edge β1 is for example between 0° and 40°, preferably between 10° and 20°.

[0065] A trailing edge flow angle β2 is also defined as the angle between the streamline at the trailing edge 56 and the tangent 57 to the inner diameter of the rotor 50 at the trailing edge. This trailing edge flow angle β2 is, for example, between 60° and 90°, preferably between 70° and 80°.

[0066] The maximum thickness t of the cross-section of each blade 53, measured in a plane (X, Y), is for example between 0.35 and 1.6 mm, preferably between 0.8 and 1.2 mm.

[0067] Finally, the length of the chord c53 of each blade 53, connecting the leading edge to the trailing edge of the blade 53 considered, along a rectilinear segment in a plane (X, Y), is between 6 and 8 mm.

[0068] There figure 13illustrates a second example of rotor 50' for the tangential fan 26. This second example of rotor 50' differs from the first 50 which has just been described essentially in that it is formed of several portions 58, 59, 60. These portions 58, 59, 60 are here identical. The portions 58, 59, 60 are here three in number. The second example of rotor 50' may however comprise fewer portions 58, 59, 60, for example only two distinct portions, or more portions. Each portion 58, 59, 60 forms one or more stages of blades 51. Above all, here, each portion 58, 59, 60 has at its two longitudinal ends a lug 61 intended to be received in a rolling bearing (not shown). A rolling bearing is conventionally produced by means of a rolling bearing, in particular a ball bearing or roller bearing, for example.The rolling bearings make it possible in particular to break the natural frequencies and, thus, to limit the resonance phenomena which are the source of significant noise. At high rotational speed of the rotor 50, 50', it is advantageous to have a greater number of rolling bearings. Here, with a rotor 50' formed of three portions 58, 59, 60, four bearings can be implemented, which are placed at the points indicated P62. Advantageously, within the scope of the invention, the number of bearings implemented with the rotor 50, 50' is less than 4. It is also conceivable to provide no rolling bearing, in particular in the case where the rotor 50 has a low height, in particular less than 100 mm. In this case, the bearing of the drive rotor, driving the rotor 50, 50' in rotation about its axis of rotation A50, may be sufficient to keep the rotor 50, 50' stable. Volute

[0069] As it appears from the figures 3 to 7, the collector 5-1 delimits a volute 30 of the tangential fan 26.

[0070] The volute 30 comprises an air inlet 31, an air outlet 32 ​​and a junction portion between the air inlet 31 and the air outlet 32, called the intermediate portion 33.

[0071] The air inlet 31 comprises the opening 27 through which an air flow F is sucked in by the tangential fan 26.

[0072] The opening 27 is provided with a protective grille 28.

[0073] The air outlet 32 ​​is connected to each of the tubes 3 to distribute the air flow F there.

[0074] The intermediate part 33 forms a housing for the tangential fan 26.

[0075] The intermediate part constitutes a boundary between a suction zone A at the inlet 31 and a discharge zone B at the outlet 32.

[0076] As is evident from the figures 3 to 6, the section of the air inlet 31 is convergent from the opening 27, which makes it possible to accelerate the air flow and to avoid any stalling of the air flow behind parts with significant variations in angle.

[0077] Similarly, the intermediate section and the exit section have only gentle variations in orientation, as will be detailed.

[0078] THE figures 3 to 7 are sectional views in the plane (X, Y), noted plane P.

[0079] As illustrated on the figures 3 to 6 , the air inlet 31 comprises a first inlet wall 34, called the suction side wall, and a second inlet 35 opposite the first air inlet 34.

[0080] As visible on the figure 3 , the suction side wall 34 makes an angle α of between 40° and 75°, and preferably 58°, with the longitudinal direction X.

[0081] These angle values ​​ensure turbulence-free flow in the inlet 31 to the fan 26.

[0082] The suction side wall 34 extends from the opening 27 to a curved end 36 close to the blades p of the fan 26, called the anti-recirculation nozzle.

[0083] As particularly visible on the figure 7 , the end 36 is arranged between the suction and the discharge, and its curved shape, the dimensions of which are indicated below, prevents any recirculation of air in the volute.

[0084] End 36 is called the anti-recirculation nozzle.

[0085] Preferably, a length L of the nozzle 36 is between 1 mm and 8 mm and a minimum distance m between the nozzle and a disc D delimited by the tangential fan in the plane P is between 0.5 mm and 1.5 mm.

[0086] As already indicated, these dimensions of the nozzle 36 make it possible to avoid any recirculation of air in the volute 30 despite the high pressure reached in the discharge zone B.

[0087] As visible on the figure 4 , the second wall 35 of the air inlet 31 comprises a rounded edge 37 of the opening 27.

[0088] On the figure 4 , the curvature of the edge 37 is formed by an arc of a circle c whose center i is located on a circle C concentric with the disk D whose center is noted I.

[0089] On the figure 4 , we have illustrated another circle c' whose center i' is located on the circle C.

[0090] As visible on the Figure 5 , the intermediate part 33 comprises a wall, called intermediate wall 38, curved according to an arc of a circle a.

[0091] The circle CC including the arc of a circle a has a center II distinct from the center I of the disk D, that is to say that the circle CC is not concentric with the disk D.

[0092] As is also evident from the Figure 5 , a diameter dd of the intermediate part 33 is greater than a diameter d of the disc D.

[0093] Thus, the intermediate part 33 has a section which gradually increases in a direction of air flow between the air inlet 31 and the air outlet 32.

[0094] This increase makes it possible to significantly reduce air recirculation in the volute 30.

[0095] Advantageously, a distance between the center II of the intermediate wall 38 and the center I of the disc D is less than or equal to the value of the radius of the disc D.

[0096] As illustrated in the figure 6, a section 39 of the intermediate part 33 at an interface 40 between the intermediate part 33 and the outlet 32 ​​forms an angle α, preferably non-zero, with the direction X, advantageously included in the interval [0°, 20°], more advantageously in the interval ]0°, 20°], and more preferably of the order of 15°.

[0097] This angle makes it possible to homogenize the speed of the air at the outlet of the fan 26 because it increases the length of the air path closer to an outlet wall 40 (compared to a zero angle).

[0098] The outlet 32 ​​has the shape of a diverging cone from the intermediate part 33 towards the tubes 3, which also contributes to the homogenization of the speed in the tubes and ensures distribution of the air over the entire inlet surface of each tube 3.

Claims

1. Heat exchange module (100) comprising a heat exchanger (101) comprising tubes for circulating a heat transfer fluid and a ventilation device (1) for a motor vehicle comprising at least one manifold (5-1, 5-2) for distributing air to tubes (3) of the ventilation device (1), at least one turbomachine (26) being arranged in said at least one manifold (5-1, 5-2), said at least one turbomachine (26) comprising a tangential fan (26), said at least one manifold (5-1, 5-2) forming a volute (30) of the tangential fan (26), said volute (30) comprising an air inlet (31) in the manifold (5-1, 5-2) through which an air flow can be sucked in by the tangential fan (26), and an air outlet (33) through which the sucked air flow can be distributed to the tubes (3), the tubes (3) extending parallel to a longitudinal direction (X) of the tubes (3), called the longitudinal direction, the tangential fan (26) extending in a direction orthogonal (Z) to the longitudinal direction, called the suction direction, another direction (Y), called the forward direction, orthogonal to the longitudinal direction and to the suction direction, said ventilation device (1) and the heat exchanger (101) being positioned relative to each other so that the air flow set in motion by the ventilation device (1) supplies air to the heat exchanger (101)2. Heat exchange module (100) according to claim 1, wherein the air inlet (31) comprises a first inlet wall (34) making an angle of between 40° and 75°, and preferably 58°, with said longitudinal direction (X).

3. Heat exchange module (100) according to the preceding claim, wherein one end (36) of the first wall (34) opposite the air inlet (31) is curved in a plane (P) containing the longitudinal direction (X) and the direction of advance (Y), a length (L) of which is between 1 mm and 8 mm and a minimum distance (d) between said end (36) and a disc (D) delimited by the tangential fan in said plane (P) is between 0.5 mm and 1.5 mm.

4. Heat exchange module (100) according to one of claims 2 or 3, wherein the air inlet (31) comprises a second inlet wall (35), said second wall (35) comprising a rounded edge (37) shaped so that its curvature in a plane (P) containing the longitudinal direction (X) and the direction of advance (Y) is an arc of a circle whose center is located on a concentric circle of a disk (D) delimited by the tangential fan in said plane (P).

5. Heat exchange module (100) according to one of the preceding claims, comprising a junction portion of the air inlet (31) of the volute (30) and the air outlet (32) of the volute, called the intermediate portion (33), shaped to house the tangential fan (26).

6. Heat exchange module (100) according to the preceding claim, wherein said intermediate portion (33) comprises a wall, called intermediate wall (38), curved along an arc of a circle in a plane (P) containing the longitudinal direction (X) and the direction of advance (Y), said arc of a circle having a center distinct from the center of a disk (D) delimited by the tangential fan in said plane (P).

7. Heat exchange module (100) according to the preceding claim, wherein a distance between the center of the intermediate wall (38) and the center of the disk (D) is less than or equal to the value of the radius of the disk.

8. Heat exchange module (100) according to one of claims 5 to 7, wherein a section of the intermediate part (33) at an interface between the intermediate part (33) and the air outlet (32) forms an angle (α), preferably non-zero, with the longitudinal direction (X), preferably within the range [0°, 20°], more preferably within the range ├]0°,20°].

9. Heat exchange module (100) according to any one of the preceding claims, in which the tangential fan (26) is adapted to create an air flow with a flow rate of between 0 and 750 m3 / h and a pressure of between 0 and 900 Pa, the tangential fan comprising a rotor (50) whose rotation speed is preferably between 2000 rpm and 13,000 rpm, preferably between 2500 rpm and 9000 rpm.