Noise dampener for dampening noise generated by a centrifugal pump

Description

[0001] The present invention relates to a noise attenuator, in particular of noise generated by a turbine of a centrifugal pump. It applies more particularly but not specifically to a device for recovering brake dust particles, in particular emitted during a braking action of a motor vehicle whose air is sucked in by means of such a centrifugal pump. The field of application of the invention relates more particularly but not exclusively to the recovery of brake dust generated during a braking action of a vehicle, whether road (for example: automobile, heavy goods vehicle, motorcycle) or rail (train, tram, metro).

[0002] Generally speaking, the braking of a railway or road vehicle, and in particular of a motor vehicle, is carried out by a friction braking system, as is the case for example with "disc brakes". The invention can be applied to other types of braking systems, such as drum brakes or any other type of friction brake. A disc brake comprises a disc rotating around an axis fixed to a hub of a wheel of the vehicle and brake pads provided with linings made of friction material and mounted on either side of the disc by means of a brake caliper.

[0003] During a braking action, the brake pads, which are movable relative to the caliper, come to bear on the discs rotating around the vehicle's wheels, in order to apply a braking torque and enable braking by converting kinetic energy into heat.

[0004] However, with each braking action, the friction of the brake pads produces, in addition to the release of heat, wear of the friction materials of the linings, as well as wear of the metal discs or drums. This wear by abrasion produces a significant emission of particles. Since the brakes of a motor vehicle are generally not completely closed, these brake dust particles are then directly dispersed into the ambient environment.

[0005] In addition to being dirty for the immediate environment of the wheels, especially the rims, these particles are especially harmful to health. Indeed, these particles can be nanoparticles or microparticles, the finest particles being recognized as being particularly harmful to the health of individuals in general, with in particular an increased risk of developing respiratory, allergic and cardiovascular diseases.

[0006] In order to reduce pollution by brake dust particles, it is known from the state of the art to place a particle filtration device near the braking system.

[0007] Such a filtration device comprises a housing delimiting a collection body and housing for example a filtration member such as a particle filter and / or a cyclonic structure, the housing comprising an inlet for dirty air flow and an outlet for purified air flow, the circulation of the air taking place between the inlet and the outlet through the filter and / or the cyclonic structure.

[0008] In order to cause air circulation inside the housing, it is known from the prior art to connect the outlet of the housing to a "turbine", which is the designation commonly used to designate a centrifugal pump.

[0009] Such a pump generally takes the form of a volute-shaped pump body housing a rotating propeller which draws in the pump axially, accelerates radially and finally discharges the purified air leaving the housing after filtration tangentially.

[0010] In this way, the dust generated by friction between the brake lining and the wheel during braking is captured and filtered in the filtration device. In fact, by means of the suction centrifugal pump, a flow of air carrying dust is sucked into the filtration housing. The air flow is purified through the filtration device(s) before reaching the centrifugal pump which will discharge it to the outside.

[0011] However, the filtration device with centrifugal pump has the disadvantage of being a source of significant noise pollution, over a range of potentially undesirable sound frequencies and which may be complained about by motor vehicle users.

[0012] Document US 3,144,913, for example, discloses such an acoustic attenuation device for an electromechanical device traversed by a gas flow capable of propagating acoustic waves.

[0013] The invention aims in particular to remedy this drawback by making it possible to reduce the noise resulting from the operation of the centrifugal pump with minimal bulk and a significant sound frequency damping range.

[0014] To this end, the invention relates to an acoustic attenuation device for an electromechanical device traversed by a gas flow capable of propagating acoustic waves, comprising inlet and outlet orifices for a gas flow, in particular for the purpose of evacuation into the atmosphere, characterized in that the device comprises a channel of generally curvilinear general shape around a main axis of the device defining a flow path of the gas flow substantially curvilinear between the inlet and outlet orifices, and comprises a plurality of acoustic attenuating elements tuned to an attenuation resonance frequency, arranged consecutively in series along said channel so as to interact with the gas flow flowing in the channel, the acoustic attenuating elements being formed by quarter-wave resonator cavities.

[0015] Thanks to this curvilinear arrangement around the main axis of the resonators in the acoustic attenuation channel, the acoustic attenuation device is space-saving because it can be easily installed inside a centrifugal pump body. In particular, thanks to the invention, it is possible to arrange a plurality of resonators in a reduced space while allowing attenuation of sound frequencies over a wider frequency range.

[0016] In a preferred embodiment, the channel has a generally annular general shape about the axis defining a quasi-circular flow path between the inlet and outlet ports.

[0017] In a preferred embodiment, the channel at least partially coils in an outwardly expanding spiral configuration between the inlet port and the outlet port.

[0018] In a preferred embodiment, the channel is provided with an internal geometric structure extending inside the channel in a substantially circumferential direction, configured to delimit the plurality of cavities and leave free passage a main passage for the flow of the gaseous flow inside which the cavities open.

[0019] In a preferred embodiment, the internal geometric structure comprises a plurality of radial partitions delimiting with walls of the channel a plurality of compartments forming the plurality of cavities.

[0020] According to the invention, a wall of the channel has a stepped profile defining an incremental depth which varies from one cavity to another in a circumferential direction of the channel.

[0021] In a preferred embodiment, the depth from one cavity to the next varies increasing or decreasingly over the series of resonators in the direction from the input to the output.

[0022] In a preferred embodiment, at least first and second resonators having first and second resonant frequencies respectively associated with first and second frequency bands of attenuation greater than twenty decibels, the circumferential distance between the two resonators is determined to produce a coupling phenomenon of the two resonators on a continuous frequency band of attenuation greater than twenty decibels.

[0023] Circumferential distance means the distance separating two elements along a circumferential median line of the canal.

[0024] In a preferred embodiment, an optimal pitch Popt(i) between two consecutive resonators Ai and Ai+1 being given by the following formula: Popt i = v 8 × 1 f 0 i + 1 f 0 i + 1 in which f0(i) is the resonant frequency of the resonator Ai, fo(i+1) is the resonant frequency of the resonator Ai+1 and v is the speed of sound, the pitch P(i) between two consecutive resonators Ai and Ai+1 is within a range of values ​​from 50% to 150% of the value of Popt(i).

[0025] In a preferred embodiment, the pitch between two resonators varies increasing or decreasing along the series of resonators in the direction from the input to the output.

[0026] In a preferred embodiment, the pitch between two consecutive resonators Ai and Ai+1 is constant along the series of resonators and corresponds to the average value of the minimum and maximum values ​​of the optimal pitch Popt(i) on the series of resonators Ai with i ranging from 1 to N.

[0027] In a preferred embodiment, the resonators are all dimensionally different in pairs to ensure absorption at a different resonant frequency.

[0028] In a preferred embodiment, the cavity of each resonator has a substantially tubular shape configured to open into the interior of the channel and has a depth corresponding substantially to a quarter of the wavelength of the acoustic wave of predefined resonant frequency.

[0029] In a preferred embodiment, the cross-section of each resonator cavity has curvilinear edges following inner and outer curvatures of the channel.

[0030] In a preferred embodiment, the channel is delimited radially by annular outer and inner peripheral walls around the axis, and transversely by upper and lower walls.

[0031] In a preferred embodiment, the upper wall is configured to axially delimit the depth of the resonance cavities forming the resonators.

[0032] The invention also relates to a centrifugal pump, comprising a casing, a shaft extending along a main axis of the pump, an impeller mounted on the shaft, a motor for driving the impeller in rotation, defining a flow path for a gas flow inside the casing of the pump between an inlet orifice and a discharge orifice for the gas flow, characterized in that it comprises an acoustic attenuation device according to the invention, the acoustic attenuation channel being arranged in a curvilinear configuration around the main axis of the pump inside the casing so that the gas flow circulating in the pump flows through said attenuation channel before being discharged into the atmosphere via the discharge orifice of the downstream casing.

[0033] In another embodiment, the casing comprises an upstream casing configured to house the wheel and a downstream casing configured to house the motor, the downstream casing comprising a body in the general shape of a hood delimiting an outer peripheral wall and an inner peripheral wall extending around a central space for housing the motor, the channel of the attenuation device extending between the two outer and inner walls of the downstream casing.

[0034] The invention finally provides a depolluting device for recovering brake dust particles, in particular produced by one or more pads of a brake arrangement of a motor vehicle, the device comprising a housing with an inlet orifice for a flow of dirty air loaded with particles and an outlet orifice for discharging a flow of purified air, and at least one separation member, housed in the housing, for separating particles from the flow of dirty air, through which the air flow circulates between the inlet and outlet orifices, characterized in that the device comprises a suction member comprising a centrifugal pump according to the invention and in that the inlet orifice is configured to be connected to the outlet orifice of the housing.

[0035] Other characteristics and advantages of the invention will appear in the light of the following description, given with reference to the appended drawings in which: [ Fig 1 ] : there figure 1 illustrates a schematic view of a motor vehicle incorporating a brake particle depollution system; [ Fig 2 ] : there figure 2 illustrates a schematic view of the environment of a wheel of the motor vehicle of the figure 1 including the pollution control system of the figure 1 ; [ Fig 3 ] : there figure 3 illustrates a schematic view of the pollution control system comprising a pollution control device according to the invention; [ Fig 4 ] : there figure 4 represents a perspective view of the decontamination device corresponding to the decontamination device shown schematically on the figure 3 ; [ Fig 5 ] : there figure 5 represents a perspective and exploded view according to a first viewing angle of a centrifugal pump according to the invention which can be mounted on the pollution control device of the figure 4 ; [ Fig 6 ] : there figure 6 represents a perspective and exploded view from a second angle of view of the pump of the figure 5 ; [ Fig 7 ] : there figure 7 is a longitudinal sectional view of the pump of the figures 5 And 6 ; [ Fig 8 ] : there figure 8 is a bottom view of an attenuation device according to the invention, intended to be mounted in the suction member of the figures 5 And 6 . [ Fig 9 ] : there figure 9 is a top view of the attenuation device figure 8 ; [ Fig 10 ] : there figure 10 is a schematic view of an acoustic attenuation channel of the acoustic attenuation device of the figures 8 et 9 ; [ Fig 11 ] : there figure 11 is a graph of the evolution of the damping in decibels as a function of the frequency in Hertz of a quarter-wave resonator of the acoustic attenuation device of the invention; [ Fig 12 ] : there figure 12 is a graph of the evolution of the damping in decibels as a function of the frequency in Hertz of two quarter-wave resonators of the acoustic attenuation device spaced by a first distance (dotted line curve) and a second distance (solid line curve); [ Fig 13 ] there figure 13 illustrates a first graph of the evolution of the damping in decibels as a function of the frequency in Hertz of a centrifugal pump according to the invention comprising the acoustic attenuation device according to the invention comprising a plurality of resonators spaced apart by a single fixed pitch; [ Fig 14 ] there figure 14 illustrates a second graph of the evolution of the damping in decibels as a function of the frequency in Hertz of a centrifugal pump according to the invention, in which the resonators are spaced from each other by an optimal pitch which varies along the resonators.

[0036] In the following description, the terms upstream and downstream will be used depending on the direction of fluid flow. Thus, when it is specified in this description that in a system, device or member, a first element is upstream of a second element, it should be understood that the fluid current circulating in said system, device or member passes through the first element before the second element.

[0037] Furthermore, in the following description, the terms “upper”, “lower”, “above”, “below”, “vertical”, “horizontal” refer to the elements in the position in which they are shown on the figures 1 à 14 . Furthermore, in the present description, by circumferential direction, we mean a direction tangent to a quasi-circular trajectory centered on the main axis X.

[0038] It has been represented on the figure 1 a motor vehicle comprising a depollution system by suction and collection of brake dust particles. This system is designated by the general reference 100 and the motor vehicle is designated by the general reference 10. In the preferred embodiment of the invention, the vehicle 10 is a motor vehicle, in this case a light car. Of course, the invention can be applied to other vehicles, such as heavy goods vehicles, or railway vehicles or others.

[0039] In a general but non-limiting manner, this vehicle 10 comprises four wheels 12 and a braking system 20 which has the function of slowing the vehicle and keeping it stationary, in particular for relatively short periods. The braking system 20 is configured to apply a braking torque to at least two of the wheels 12 of the vehicle 10 and preferably to all four wheels 12 of the vehicle. Conventionally, the wheels 12 are capable of being driven in rotation by a powertrain, for example a thermal engine or an electric motor (not shown) or any other type of propulsion.

[0040] For this purpose, this braking system 20 preferably comprises four brake arrangements 30 associated with each of the wheels 12 and a unit for managing these brake arrangements (only two brake arrangements 30 are shown in the figure 1 ). Thus, a user of the vehicle 10 can control the braking system 20 via a control unit 40 of the vehicle 10 which controls the brake arrangements 30 of the braking system 20.

[0041] Such a brake arrangement 30 is illustrated as an example in the figure 2 . Preferably, this arrangement 30 is of the disc brake type. The figure 2 illustrates the brake arrangement 30 mounted on one of the wheels 12 of vehicle 10, this wheel 12 being partially represented with its suspension means 14.

[0042] Each brake arrangement 30 comprises, in a non-limiting manner, a rotor disc 32 rotating around an axis and integral in rotation with the wheel 12 with which it is associated. This axis is generally intended to be fixed on a hub 16 of a wheel 12 of the vehicle 10.

[0043] Furthermore, the brake arrangement 30 comprises a caliper support 34 arranged astride an outer edge of the disc 32 and rotationally secured to a fixed part of a chassis (not shown) of the vehicle 10. The brake arrangement 30 further comprises two brake pads 36 provided with linings made of friction material (not directly visible in the figures) and mounted on either side of the disc 32 via the caliper support 34.

[0044] These brake pads 36 are mounted to move, for example under the effect of a hydraulic cylinder (not shown), and are intended to clamp the rotor disc 32 to brake it until the latter stops by transforming the kinetic energy into thermal energy. The pad linings are generally made of friction material and release particles resulting from abrasion by rubbing against the disc 32. During braking, the friction between the brake lining and the disc 32 generates dust which possibly contains fine particles which are dangerous to health.

[0045] In order to recover the brake dust particles, the recovery and collection system 100 is intended to suck up and collect dust particles produced during a braking action of the motor vehicle 10, friction braking of the brake arrangements 30 of the vehicle 10 as described above.

[0046] The system 100 comprises at least one pollution control device 110 according to the invention and preferably comprises as many pollution control devices 110 as brake arrangements 30. For example, the system 100 comprises at least two pollution control devices 110 to equip the four brake arrangements 30 of the vehicle 10. In the remainder of the description, only one pollution control device 110 will be described in detail, which will be commonly designated by the general reference 110.

[0047] The device 110 has the function of recovering and collecting dust and braking particles, for example coming from one of the braking arrangements 30 of the motor vehicle and is illustrated schematically and functionally in the figures 3 And 4 .

[0048] As illustrated in detail in these figures, the device 110 comprises a housing body 112. This housing 112 has a generally tubular shape, for example cylindrical around a main axis X. This housing 112 is for example in two parts 114 and 115 assembled together by various releasable or non-releasable assembly methods which will not be detailed further.

[0049] Furthermore, this housing body 112 comprises an inlet orifice 116 for a flow of dirty air loaded with particles and taken from the immediate environment of the brake pads 30.

[0050] For this purpose, the device 110 also comprises a connector end piece 118 intended to be connected to the inlet orifice 116 and to be connected to two flexible pipes 124 opening near the brake pads 30 and shown schematically in figure 2 . This end piece 118 is divided along its main axis into a first part 120 intended to be connected to the inlet orifice 116 and into a second part 122 separated into two branches 122A and 122B. In the example illustrated, each of the branches 122A and 122B of the connector end piece 122 has an end for connection to a flexible pipe 124, preferably by fitting, which is provided for example with an external relief in the form of a fir tree. For example, the inlet orifice 116 is in the form of a cannula 126 and the connector end piece 122 is preferably connected by screwing onto the connection cannula 126 of the orifice 116.

[0051] Furthermore, the housing body 112 further comprises an outlet 130 for discharging a flow of purified air. In the example illustrated and preferably, the inlet orifice 116 and the outlet orifice 130 are provided respectively on end walls 132 and 134 of the tubular housing body 112, the housing body 112 having, for example, a substantially cylindrical peripheral wall 136 and the end walls 132 and 134, for example, having a generally circular shape.

[0052] Furthermore, the device 110 comprises at least one separation member 140, housed in the housing 112, for separating particles from the dirty air flow, through which the air flow circulates between the inlet 116 and the outlet 130.

[0053] Such a separation member 140 may comprise a filter cartridge 144 or even a cyclonic chamber 142, or even a multi-cyclonic chamber or even a combination of the two, as is shown very schematically in the figure 3 Such separation members 140 are well known in the prior art and are described in detail for example in patent application CN1864619A with their associated operations and will not be detailed further below.

[0054] Furthermore, preferably, the housing 112 is sized to be housed in a space surrounding a wheel 12 of a motor vehicle 10, for example around a leg of a suspension shock absorber 14 as illustrated in the figure 2 . For this purpose, in the example illustrated, the device 110 also comprises a circumferential flange 146 provided with two diametrically opposed radial extension tabs 148, each of the tabs being for example pierced to retain a fixing ring (not shown).

[0055] Furthermore, the housing 112 is connected, via the suction duct 124, to one of the disc brake arrangements 30. Preferably, the suction duct 124 comprises one of its ends located in the immediate vicinity of the area where this brake dust is likely to be generated. The other of its ends preferably opens into the interior of the collection body of the device 110 via the inlet orifice 116 of the housing 112 and the connector end piece 118.

[0056] The collection device 110 also comprises, for example, a collection reservoir 148 housed inside the housing 14 illustrated schematically by the figure 3 . For example, the reservoir 148 is associated with the first separation member 142 to form a chamber of the cyclonic separator 142. This cyclonic separator 142 is intended to capture particles having a diameter, for example, greater than 10 microns. In the example illustrated, the device 110 further comprises a second separation member 144, formed by the filter cartridge 144 responsible for treating particles having a diameter less than 10 microns.

[0057] According to the invention, in order to produce an efficient circulation of air inside the recovery housing 112 between the inlet 116 and the outlet 130 of this housing 112, the device 110 also comprises a member 150 for sucking up the purified air flow, shown schematically in figure 3 and in detail on the figures 5 à 7 .

[0058] According to the invention, the air flow suction member 150 comprises a centrifugal pump for suctioning the purified air flow, shown schematically in the figures 5 à 7 This pump 150 is mounted at the outlet of the housing 112, for example by sealed fluid connection, directly on the outlet orifice 130 of the collection device 110.

[0059] On the figure 7 , the arrow F represents the normal direction of circulation of a fluid in the centrifugal pump 150. Subsequently, the terms “upstream” and “downstream” are defined in relation to the normal direction of circulation of the fluid in the centrifugal pump 150.

[0060] In the embodiment of the invention, the centrifugal pump 150 comprises a shaft 152, defining a main axis X of the pump 150, an impeller 154 mounted on the shaft 152 and a motor 156, preferably electric, for driving the impeller 154 in rotation. The centrifugal pump 150 further comprises a casing 170 for housing the aforementioned elements. In this example, this casing 170 mainly comprises an upstream casing 172, housing the impeller 154 and the shaft 152, and a downstream casing 174 housing the motor 156.

[0061] For example, the wheel 154 also includes a central hub 158 on which the shaft 152 is mounted. In the example described, the wheel 154 is formed in one piece with the shaft 152.

[0062] Furthermore, preferably, the impeller 154 has a profile adapted to the centrifugal flow of a gas flow inside the pump chamber 182. In this example, the impeller 154 has a general shape of a truncated cone whose opening angle at the apex gradually narrows, for example according to a hyperboloid profile. The impeller 154 preferably carries on its external surface a plurality of guide vanes 155, each extending substantially transversely inside the upstream casing 172, as can be seen in the figure 7 .

[0063] Furthermore, the shaft 152 which extends along the main axis of the pump 150 is held axially by two guide bearings (not shown) positioned substantially at its ends.

[0064] Furthermore, the casing 170 of the centrifugal pump 150 comprises an inlet orifice 176 for admitting an incoming air flow and an outlet orifice 178 for discharging this air flow after circulation inside the casing 170.

[0065] As illustrated in the figures 5 à 7 , the upstream casing 172 comprises in the preferred embodiment of the invention, a lower body 173 and an upper body 180, which are assembled together to define a volume inside which the shaft 152 and the wheel 154 are placed.

[0066] In the example illustrated on the figures 5 à 7 , the lower body 173 of the upstream casing 172 has a generally hollow shape. The lower body 173 is preferably shaped to substantially envelop the wheel 154. For this purpose, the lower body 173 has a narrow upstream annular portion delimiting at its free upstream end the inlet orifice 176 and connected at its other downstream end to a conical cylindrical downstream portion which gradually widens upstream.

[0067] In the preferred embodiment of the invention, the lower body 173 also has a peripheral rim 184 delimiting an interior space for receiving the upper body 180.

[0068] Preferably, the upper body 180 has a general cup shape having, for example, a substantially flat central bottom connected to an annular peripheral wall forming an annular peripheral rim 186. Preferably, in the substantially flat bottom of the upper body 180, a central housing space 192 is provided for the end of the shaft 152, ensuring its retention along the main axis X.

[0069] Thus, in this embodiment, the assembly of the lower body 173 and upper body 180 is carried out in a sealed manner, the upper body 180 cooperating with the lower body by embedding, for example by complementarity of shape of the peripheral rim 186 of the upper body 180 and the peripheral rim 184 of the lower body 173.

[0070] Furthermore, in this example and in a manner known per se, the lower body 173 and the upper body 180 are configured to constitute, once assembled, an internal volume characteristic of a centrifugal pump 150, as will be detailed below.

[0071] In this example, the lower 173 and upper 180 bodies together delimit in the assembled state a toric compression chamber 190 for the flow of the gas flow of substantially circular shape around the main axis X of the pump 150. The lower 173 and upper 180 bodies each have, for example, at the periphery, a curved relief respectively 190A and 190B of substantially semi-cylindrical shape in a circumferential direction which, when assembled, delimits the toric compression chamber 190 ( figure 7 ). This toroidal compression chamber 190 is shaped to allow centrifugal circulation of the gas flow.

[0072] In this preferred embodiment, the upper body 180 comprises an outlet orifice 181 for the gas flow from the downstream casing 172, after circulation in the toroidal compression chamber 190, opening axially inside the upstream casing 174.

[0073] To this end, in this example, the compression chamber 190 terminates at its downstream end in a conduit 191 for discharging the gas flow, connected upstream to the outlet orifice 181 and configured to operate a deviation of the flow direction of the gas flow from its mainly tangential flow direction at the outlet of the toric compression chamber 190 to its axial flow direction in the outlet orifice 181 of the upstream casing 172.

[0074] Preferably, this conduit 191 has a curvilinear profile and is curved in a regular manner in order to reduce any resistance to the flow of the gas stream to reach the outlet orifice 181.

[0075] As illustrated in these figures, the downstream casing 174 comprises a cover of almost cylindrical general shape delimiting an outer peripheral wall 194 and an inner peripheral wall 196 extending around a central space 198 for housing the motor 156. Furthermore, in this example, the downstream casing 174 comprises a cover wall 199, for example attached by clipping onto the outer peripheral wall 194.

[0076] It will be noted that, in the illustrated example, the outer peripheral wall of the downstream casing 174 does not have a perfectly circular cross-section but is slightly elongated and in the shape of a “water drop”, that is to say having a rounded side and, on the opposite side, an end slightly tapered to a point. The same applies, in the illustrated example, to the geometry of the upper body 180 and the lower body 173. In this example, this tapered geometry makes it possible to adapt to the geometry of the conduit 191 for diverting the gas flow at the outlet of the toric compression chamber 190.

[0077] Furthermore, it will be noted that the casing 170 has means for fixing various functions which will not be detailed later. Furthermore, in this example in the figures, an electronic card 197 has been shown which may or may not be embedded and which includes means for electronic control of the engine 156.

[0078] In operation, the centrifugal pump 150 is configured to axially suck air through the inlet orifice 176, to accelerate radially inside the compression chamber 190, and to discharge the air through the intermediate orifice 181 of the compression chamber 190. It will be noted that the discharge of the gas flow out of the compression chamber 190 is done axially through the intermediate orifice 181, towards and inside the downstream casing 174 as will be explained in detail below.

[0079] The centrifugal pump 150 further comprises an acoustic attenuation device according to the invention, designated by the general reference 200. This attenuation device 200 is configured to be mounted on the flow path of the fluid inside the casing 170 of the pump 150, upstream of the discharge orifice 178 of the centrifugal pump 150 into the atmosphere.

[0080] In accordance with the invention, the acoustic attenuation device 200, hereinafter referred to as the attenuator device 200, is generally intended to be mounted on an electromechanical device traversed by a gas flow capable of propagating acoustic waves, and in the present case, in the centrifugal pump 150. With reference to figures 8 et 9 , the attenuator 200 comprises an inlet orifice 202 for the gas flow after circulation inside the casing 170 of the centrifugal pump 150, and in this example after circulation inside the compression chamber 190, and an outlet orifice 204 for the gas flow, in particular with a view to its discharge into the atmosphere.

[0081] In the preferred embodiment of the invention, the outlet orifice 204 of the gas flow corresponds to the discharge orifice 178 of the centrifugal pump 150, as will be described in more detail below. In this example, the inlet orifice 202 is in fluid communication with the outlet orifice 181 of the compression chamber 190.

[0082] As illustrated in the figure 8 , the attenuating device 200 is in the form of a channel 206 of generally curvilinear shape defining a flow path of the gas flow that is substantially curvilinear around a main axis between the inlet orifices 202 and outlet orifices 204. In the example described, the main axis of the channel 206 coincides with the main axis X of the pump 150.

[0083] In the example illustrated in the figures, the channel 206 has a generally annular general shape around the main axis X. For example, the inlet orifice 202 and the orifice 204 are arranged adjacent to each other. For example, the channel 206 closes on itself to form a ring by bringing the inlet 202 and the outlet 204 closer to each other. In this case, the flow path follows a quasi-circular route between the inlet orifice 202 and the outlet orifice 204.

[0084] However, in a variant not shown, the channel 206 may wrap at least partially around the X axis in a spiral configuration, preferably expanding outwardly between the inlet port 202 and the outlet port 204.

[0085] In particular, the device 200 comprises a plurality of acoustic attenuating elements 210 tuned to an attenuation resonance frequency f0 with an associated attenuation frequency band. The resonators 210 are distributed in series circularly along said channel 206 so as to interact with the gas flow flowing in the channel 206. According to the invention, the acoustic attenuating elements 210 are formed by cavities 212 of quarter-wave resonators.

[0086] It is recalled that the action frequency f of a quarter-wave resonator is defined, as a first approximation, by the following formula: f = 2 n + 1 4 v L

[0087] With v denoting the speed of sound, n denotes an integer (n=0, 1, 2...) corresponding to a resonant mode and L denotes the effective length of the quarter wave, that is to say the sum of the geometric length of a tube forming the quarter wave resonator and a fraction of the air volume of the main flow vein of the fluid in communication with it. To simplify the calculations in the rest of the description, we will neglect the fraction of the air volume of the main vein and we will define the length L of the resonator as being equal to the depth of the resonant tube.

[0088] It has been represented on the figures 8 à 10 , a plurality of resonators 210 arranged in series. In the remainder of the description, the resonators will be noted according to a series Ai for i ranging from 1 to N, A1 being the first resonator 210 of the series, located after the input 202 and AN being the last resonator 210, located after the output 204. On the figures 8 And 10, N has the value eleven because there are eleven 210 resonators arranged in series.

[0089] In the preferred embodiment of the invention, the attenuating device 200 comprises a body 220 provided with annular outer 220E and inner 220I peripheral walls so as to radially delimit the channel 206 around the axis X. The body of the channel 206 further comprises an upper transverse wall 222 and a lower transverse wall 224 axially delimiting the channel 206. The channel 206 is thus illustrated very schematically on the figure 10 .

[0090] In the preferred embodiment of the invention, the channel 206 of the attenuation device 200 extends in an annular space defined between the two outer 194 and inner 196 peripheral walls of the cover 174 of the pump 150, these two peripheral walls 194 and 196 forming the radial delimiting walls 220E and 220I of the channel 206.

[0091] Furthermore, it will be noted that in this preferred embodiment, the lower wall 224 is formed by an annular wall ( figure 8 ) extending around a central hole 228 housing the motor 156 which closes the channel 206 transversely (as can be seen in the figure 7 ). Furthermore, the lower wall 224 comprises an orifice defining the inlet 202 of the channel 206, configured to be positioned above the outlet orifice 181 of the downstream casing 172.

[0092] The acoustic attenuation channel 206 will now be described in more detail. In the embodiment of the invention, the channel 206 comprises an internal geometric structure 207, visible for example on the figure 8 , extending along a wall of the channel 206, configured to delimit an interior main flow passage of the free-path gas flow (generally free of any obstacle to the flow of the gas flow) and a plurality of cavities 212 opening into the passage.

[0093] Channel 206 is modeled geometrically and very schematically in figure 10 . On this figure 10 , the channel 206 comprises a generally annular shape in the form of a stepped crown, a first level corresponding to the main flow passage and a second level being compartmentalized or segmented to form the plurality of cavities 212 of the resonators 210.

[0094] For example, the internal geometric structure 207 comprises a plurality of radial separation partitions 214 delimiting with the outer 220E and inner 220I walls compartments forming the resonance cavities 212, the partitions 214 being sized to leave free a main flow passage of the gas flow inside the channel 206.

[0095] A wall of the channel 206 has, in a circumferential direction, a stepped profile configured to delimit the cavities 212 with an incremental height varying from one cavity 212 to another. According to the invention, the wall of the channel 206 having this incremental stepped profile is formed by the upper wall 222 of the channel 206 and extends transversely, for example inside the downstream casing 174.

[0096] Thus, in this embodiment, the upper wall 222 is configured to axially delimit the depth of the resonance cavities 212 forming the resonators 210. Of course, in a variant not illustrated, another wall of the channel 206 than the upper wall 222 can fulfill this function of delimiting the depth of the resonance cavities 212 210, for example the outer peripheral wall 220E.

[0097] Preferably, the height of a cavity 210 adjacent to the other varies increasing or decreasing in the direction from the inlet 202 to the outlet 204 and preferably incrementally.

[0098] On this figure 10 , the plurality of resonators 210 is delimited in the axial direction by steps of regularly decreasing height formed above the main free-path flow passage from the inlet 202 to the outlet 204. Thus, preferably, as clearly appears in this figure 10 , the channel 206 has a staircase structure rotating around a central cage formed in this example by the housing space 198 of the motor 156.

[0099] For example, the channel 206 having a generally substantially annular shape, the resonators 210 are circumferentially separated by partitions 214 positioned radially along the flow path of the gas flow in the channel 206 while leaving a main flow passage of the gas flow inside the channel 206, of free path (i.e. preferably not partitioned or generally free of obstacle to the flow of the gas flow).

[0100] Preferably, the cavity 212 of each resonator 210 has a substantially tubular shape configured to open inside the channel 206, and in this example the free flow passage and has a depth corresponding to a predefined resonant frequency.

[0101] As illustrated in the figure 8 , the cross-section of each cavity 212 of resonator 210 has curvilinear edges in the shape of an arc of a circle following the internal and external contour of the channel 206 which is of generally annular shape. Indeed, in the preferred embodiment of the invention, the general shape of the cavities 212 is delimited internally and externally by the respectively internal and external curvature of the channel 206. Of course, the general shape of the cavities 212 is not limited to the shape previously described.

[0102] Preferably, the resonators 210 are all dimensionally different two by two in order to ensure absorption of each resonator 210 at a different attenuation resonance frequency f0. The integration of a plurality of resonators A1 to AN all different two by two by their dimensional parameters makes it possible to ensure absorption of each resonator Ai at a different resonance frequency.

[0103] It is desirable that these different resonance frequencies f0 be sufficiently close to each other in order to obtain a sufficiently large partial overlap of the frequency bands each associated with a resonance frequency of a resonator Ai. This makes it possible to obtain a widened and continuous band of attenuation frequencies. This is achieved by choosing the dimensions and spacings of the resonators 210 appropriately, as will be explained below.

[0104] In this specific application of noise pollution linked to the operation of the centrifugal pump, the frequency band to be treated is between 2000 Hz and 8000 Hz and the requirement is to obtain an attenuation ("Transmission Loss") having a minimum value of 20 dB on the aforementioned frequency band.

[0105] It has been represented on the figure 11 a graph comprising a curve of the damping in decibels along the ordinate axis as a function of the frequency in Hertz along the abscissa axis of a resonator 210 having a resonance frequency f0 located around 3000 Hertz.

[0106] On the graph, we observe two frequency peaks of approximately 3000 Hertz, corresponding to the main resonant mode (n=0), and 8500 Hertz (n=1), corresponding to a harmonic mode, and each associated with an attenuation bandwidth of twenty decibels of approximately 160 Hertz and 80 Hertz respectively. Consequently, we note that with a single resonator 210 the attenuation is done discretely and not over a continuous range of frequencies. We will subsequently designate by "associated frequency band", the frequency band associated with a resonant frequency of a resonator within which the attenuation is greater than twenty decibels,

[0107] Thus, preferably, in the preferred embodiment of the invention, at least two resonators 210 have resonant frequencies f0 sufficiently close to have a partial overlap of their associated frequency bands. On will choose the circumferential distance separating at least two resonators 210 of the series such that a coupling phenomenon occurs between the two resonators 210 by continuous spectral overlap of their attenuation frequency bands greater than twenty decibels. This makes it possible to produce a broadened continuous frequency band of attenuation greater than twenty decibels.

[0108] For the purposes of the present invention, the circumferential distance is defined from center to center for each resonator 210 along a circular centerline of the channel 206, as schematically illustrated in the figure 10 The pitch P is defined as the circumferential distance separating two consecutive resonators in the series.

[0109] It has thus been noted that, for certain pitch values ​​P, the portion of the channel 206 extending between two adjacent resonators 210 behaves like a so-called "open-open" resonant tube which can be the origin of a so-called "anti-resonance" phenomenon. The portion of the channel 206 separating the two resonators 210 behaves like an open-open resonant tube which will amplify the acoustic waves close to the resonance frequency of the two adjacent resonators 210 by constructive interference of the acoustic waves. This constructive interference will be reflected on the spectral curve by an anti-resonance phenomenon of the attenuation in decibels forming an inverted peak.

[0110] In order to avoid the phenomenon of anti-resonance between the two adjacent resonators 210 which could reduce the overall effectiveness of the acoustic attenuation device, it is desirable to select the circumferential distance P in a predefined manner.

[0111] Indeed, it has been surprisingly observed that to produce this coupling phenomenon without anti-resonance between two adjacent resonators Ai and Ai+1 of the series, the optimal circumferential distance, designated by Popt(i) between two adjacent resonators Ai and Ai+1 must verify the following formula for determining the optimal pitch: Popt i = L i + L i + 1 2 L i = λ i 4 = v 4 f 0 i

[0112] Otherwise expressed: Popt i = v 8 × 1 f 0 i + 1 f 0 i + 1 with v: speed of sound in air (which is approximately 344 meters per second at 20°C and sea level). L(i): depth of the resonant cavity Ai f0(i): resonant frequency of the resonator Ai f0(i+1): resonant frequency of the resonator Ai+1.

[0113] It should be noted that although an optimal coupling phenomenon is observed for a step value substantially equal to Popt(i), a sufficient result is obtained in a step value range P(i) defined as follows, with a tolerance which can thus go up to 50% of the optimal value of the step Popt(i) for a resonator Ai: P i ∈ 0.5 × Popt i ; 1.5 × Popt i

[0114] On the figure 12 , the attenuation curves, expressed in decibels along the ordinate axis, are represented as a function of the frequency (expressed in Hertz) along the abscissa axis, for two consecutive resonators 210 with resonance frequencies equal to 3000 Hertz and 3500 Hertz, with a separation of a circumferential distance of 56 millimeters (dotted lines) and with a separation of a circumferential distance of 27 millimeters (solid line).

[0115] According to the above formula, the pitch P between these two resonators 210 must be in the range of values ​​in millimeters of [13.3; 39.9] with an optimal coupling around the Popt value of 27 millimeters.

[0116] The first curve is shown in dotted line and illustrates the attenuation obtained with two 210 resonators separated by a circumferential distance equal to 56 millimeters, therefore located outside the recommended range as defined and obtained above. An anti-resonance peak is observed around the frequency of 3320 Hz.

[0117] The second curve shown in solid line illustrates the attenuation in decibels obtained by the two consecutive resonators separated this time by a circumferential distance equal to 27 millimeters. In the portion of channel 206 separating the two resonators 210, a phenomenon of destructive interference of the acoustic waves of frequencies close to the resonance frequency will occur. This destructive interference will be reflected on the spectral curve by a phenomenon of coupling of the attenuation resonance frequencies of the two adjacent resonators, as clearly appears on the curve in solid line.

[0118] As is clear from this second curve, the coupling phenomenon of the two consecutive resonators 210 has the effect of producing a continuous band of attenuation of the frequencies above twenty decibels between the two resonance frequencies associated with the two resonators 210.

[0119] In the preferred embodiment of the invention, the pitch between two adjacent resonators 210 varies in an increasing or decreasing manner along the series of resonators Ai and the pitch P(i) defined between the resonator Ai and the resonator Ai+1 is between the pitch P(i-1) defined between the resonator Ai-1 and the resonator Ai and the pitch P(i+1) of the resonator Ai+1 and the resonator Ai+2.

[0120] For example, looking for an attenuation of at least twenty decibels in the frequency range 2000 Hertz to 5500 Hertz, with resonance frequencies every 500 Hertz, the optimal pitch Popt(i) between an Ai resonator and an Ai+1 resonator varies in the frequency range from 16 millimeters to 39 millimeters.

[0121] In the illustrated embodiment of the invention, the pitch P can be chosen to be constant between two resonators 210 on the series of resonators 210, taking for example as the pitch value the average of the minimum optimal pitch Popt min and the optimal pitch Popt max of all the optimal pitches Popt(i) defined for the series of resonators Ai, otherwise expressed by the formula for determining the average average pitch P below: P moyen = Popt min + Popt max 2 Popt min = Minimum Popt i ∀ i et Popt max = Maximum Popt i ∀ i

[0122] It has been represented on the figure 13 , a first graph illustrating the curve representing the attenuation in decibels as a function of the frequency in Hertz for the attenuation device of the invention and in which the pitch corresponds to a constant pitch on the series of resonators 210 and chosen in accordance with the formula described above for defining an average pitch P average.

[0123] The resonance frequencies f0 of resonators A1 to AN are chosen between 2500 Hertz and 6000 Hertz, in increments of 500 Hertz.

[0124] We note that with this constant step, the curve presents a wide range of attenuated frequencies of at least 20 decibels, notably between 2500 Hertz and 6000 Hertz.

[0125] It has been represented on the figure 14 , a second graph illustrating the curve representing the attenuation in decibels versus the frequency in Hertz for the attenuation device of the invention and in which the pitch between two adjacent resonators Ai and Ai+1 varies over the series of resonators 210 and is chosen in accordance with the formula for determining the optimal pitch Popt(i).

[0126] An attenuation ("Transmission Loss") with a minimum value of 20 dB is obtained over the frequency band between approximately 2000Hz and 6300Hz, with a maximum attenuation for frequencies between 5000Hz and 6300Hz.

[0127] The main aspects of the operation of the braking particle recovery system according to the invention will now be described.

[0128] During a first step, the user of the vehicle 10 actuates the brake of his vehicle 10. During this braking action, brake dust particles linked to the abrasion of the brake linings are released. When the brake is actuated, the braking system simultaneously controls the activation of the centrifugal pumps 150 associated with each brake arrangement 30.

[0129] In the member 150, starting the rotating wheel 154 will produce a suction effect which will drive the flow of purified air through the member 150. Thus, the flow of dirty air is driven by suction by the pipe and enters the housing 112. It discharges part of its dust particles through the separation member(s) 140 which it passes through during its journey in the housing 112 of the device 110. The flow of dirty air thus purified leaves through the outlet orifice 130 of the housing 112 and enters the member 150.

[0130] For this purpose, the gas flow is sucked into the casing 170 of the pump 150 through the inlet orifice 174. The impeller 154 housed in the downstream casing 172 is rotated by the motor 156 to axially suck, radially accelerate and tangentially discharge the gas flow which is axially deflected through the conduit 191 to the orifice 181 at the outlet of the compression chamber 190. The gas flow enters axially into the channel 206 through the inlet orifice 202 and is then discharged through the outlet orifice of the channel 206, also the discharge orifice 178 of the pump 150. Along the acoustic attenuation channel 206, the sound waves are attenuated by at least 20 decibels in the frequency band between 2500 Hertz and 6000 Hertz, thanks to the series of 210 resonators arranged along the 206 channel.

[0131] In the example illustrated on the graph of the figure 13 or of the figure 14, we see in particular that in a range of frequencies chosen between 2500 hertz and 6000 hertz, the acoustic attenuation channel 206 makes it possible to significantly reduce the noise generated by the pump 150 in this range.

[0132] The invention has the advantage of being compact, allowing for example its integration into the motor casing of a centrifugal pump while being particularly efficient in the desired frequency range.

[0133] The invention is not limited to the embodiments previously described. Other embodiments within the reach of those skilled in the art may also be envisaged without departing from the scope of the invention defined by the claims below. Thus, in particular, one would not depart from the scope of the invention by modifying the detailed shapes of the pump and the channel.

Claims

1. Acoustic attenuation device (200) for an electromechanical device (150) through which passes a gas stream capable of propagating acoustic waves, comprising inlet (202) and outlet (204) ports for a gas stream, in particular for the purpose of release into the atmosphere, characterized in that the device (200) comprises a channel (206) of an overall shape that is generally curvilinear around a main axis (X) of the device (200), defining a substantially curvilinear flow path for the gas stream between the inlet (202) and outlet (204) ports, and comprises a plurality of acoustic attenuator elements (210) tuned to an attenuation resonance frequency (f0), arranged consecutively in series along said channel (206) so as to interact with the gas stream flowing in the channel (206), the acoustic attenuator elements (210) being formed by cavities (212) of quarter-wave resonators and being referred to as resonators, a wall of the channel (206) having a stepped profile defining an incremental depth which varies from one cavity (212) to another along a circumferential direction of the channel (206).

2. Device (200) according to the preceding claim, wherein the channel (206) has an overall shape that is generally annular around the axis (X), defining a near-circular flow path between the inlet (202) and outlet (204) ports, or the channel (206) at least partially winds in an outwardly expanding spiral configuration between the inlet port (202) and the outlet port (204).

3. Device (200) according to any one of the preceding claims, wherein the channel (206) is provided with an internal geometric structure (207) extending inside the channel (206) in a substantially circumferential direction, configured to define the plurality of cavities (212) and to leave free of obstructions to the flow of the gas stream a main passage which the cavities (212) are open to.

4. Device (200) according to any one of the preceding claims, wherein the internal geometric structure (207) comprises a plurality of radial separation partitions (214) which define, with the walls of the channel (207), a plurality of compartments forming the plurality of cavities (212).

5. Device (200) according to any one of the preceding claims, wherein the depth from one cavity (212) to another (212) varies increasingly or decreasingly over the series of resonators (210), in the direction going from the inlet (202) to the outlet (204).

6. Device (200) according to any one of the preceding claims, wherein at least first and second resonators (210) having first and second resonance frequencies respectively associated with first and second frequency bands of attenuation greater than twenty decibels, the circumferential distance between the two resonators (210) is determined so as to produce a coupling phenomenon between the two resonators (210) over a continuous frequency band of attenuation greater than twenty decibels.

7. Device (200) according to any one of the preceding claims, wherein an optimal spacing Popt(i) between two consecutive resonators (210) Ai and Ai+1 being given by the following formula: Popt i = v 8 × 1 f 0 i + 1 f 0 i + 1 where f0(i) is the resonance frequency of resonator Ai, f0(i+1) is the resonance frequency of resonator Ai+1, and v is the speed of sound, the spacing P(i) between two consecutive resonators (210) Ai and Ai+1 is within a range of values extending from 50% to 150% of the value of Popt(i).

8. Device (200) according to any one of the preceding claims, wherein the spacing (P) between two resonators (210) varies increasingly or decreasingly along the series of resonators (210), in the direction going from the inlet (202) to the outlet (204).

9. Device (200) according to claim 7, wherein the spacing (P) between two consecutive resonators Ai and Ai+1 is constant along the series of a number N of resonators (210) and corresponds to the mean value of the minimum and maximum values of the optimal spacing Popt(i) over the series of resonators Ai, with i from 1 to N.

10. Device (200) according to any one of the preceding claims, wherein the resonators (210) are all dimensionally different when compared pairwise, so as to ensure an absorption at a different resonance frequency.

11. Device (200) according to any one of the preceding claims, wherein the cavity (212) of each resonator (210) has a substantially tubular shape configured to be open to the channel (206) and has a depth corresponding substantially to a quarter of the wavelength of the acoustic wave of predefined resonance frequency (f0).

12. Device (200) according to the preceding claim, wherein the cross-section of each resonator (210) cavity (212) has curvilinear edges which follow interior and exterior curvatures of the channel (206).

13. Device (200) according to any one of the preceding claims, wherein the channel (206) is defined radially by outer (220E) and inner (220I) peripheral walls which are annular around the axis (X), and transversely by upper (222) and lower (224) walls.

14. Device (200) according to the preceding claim, wherein the upper wall (222) is configured to axially define the depth of the resonance cavities (212) forming the resonators (210).

15. Centrifugal pump (150), comprising a casing (170), a shaft (152) extending along a main axis (X) of the pump, an impeller (154) mounted on the shaft (152), a motor (156) for rotating the impeller (154), defining a flow path for a gas stream inside the casing (170) of the pump (150) between an intake port (176) and a discharge port (178) for the gas stream, characterized in that it comprises an acoustic attenuation device (200) according to any one of the preceding claims, the acoustic attenuation channel (206) being arranged in a curvilinear configuration around the main axis (X) of the pump (150) inside the casing (170) so that the gas stream circulating in the pump (150) flows through said attenuation channel (206) before it is discharged into the atmosphere through the discharge port (178) of the downstream casing (174).

16. Centrifugal pump (150) according to the preceding claim, wherein the casing (170) comprises an upstream casing (172) configured to house the impeller (154) and a downstream casing (174) configured to house the motor (156), the downstream casing (174) comprising a body in the general shape of a cowling defining an outer peripheral wall (194) and an inner peripheral wall (196) extending around a central space (198) for housing the motor (156), the channel (206) of the attenuation device (200) extending between the two outer (194) and inner (196) walls of the downstream casing (174).

17. Pollution-removing device (110) for recovering brake dust particles, in particular those produced by one or more pads of a brake arrangement (30) of a motor vehicle (10), the device (110) comprising a housing (112) with an inlet port (116) for a flow of dirty air laden with particles and an outlet port (130) for the discharging a flow of purified air, and at least one separation member (140; 142, 144), housed in the housing (112), through which the air flow circulates between the inlet (116) and outlet (130) ports in order to separate particles from the flow of dirty air, characterized in that the device (110) comprises a suction member (150) comprising a centrifugal pump according to any one of claims 15 and 16 and in that the intake port (172) of the pump (150) is configured to be connected to the outlet port (130) of the housing (112).