WO2016083885A1

WO2016083885A1 - An aspiration system for internal combustion engines

Info

Publication number: WO2016083885A1
Application number: PCT/IB2015/002226
Authority: WO
Inventors: Giorgio Girondi
Original assignee: Ufi Filters S.P.A.
Priority date: 2014-11-24
Filing date: 2015-11-23
Publication date: 2016-06-02

Abstract

An aspiration system (200) for an internal combustion engine (100) comprising at least: an aspiration conduit (205); an air filter (210) located in the aspiration conduit (205), and a porous wall (705) located in the aspiration conduit (205) downstream of the air filter (210).

Description

AN ASPIRATION SYSTEM FOR INTERNAL COMBUSTION ENGINES

Prior Art

The present invention relates to an aspirating system of comburent air for an internal combustion engine, for example a Diesel or petrol engine. In particular, the invention relates to an aspirating system for an internal combustion engine, for example a motor vehicle, truck or another heavy vehicle.

Prior Art

As is known, internal combustion engines of vehicles include an aspirating system of the comburent air, which usually comprises an aspiration conduit able to convey the air coming from the external environment towards the engine cylinders, possibly passing through an aspiration manifold.

An air filter is commonly located along the aspiration conduit, which comprises one or more filter walls able to intercept the flow of air in aspiration, so as to retain the solid particles and the impurities possibly present therein, with the aim of preventing the particles and impurities from reaching the engine cylinders.

Downstream of the air filter, the aspiration conduit can be provided with a mass flow meter, i.e. a device for measuring an air flow rate aspirated internally of the internal combustion engine.

The functioning of the mass flow meter can be essentially based on the measurement of the electric current necessary for maintaining a certain target temperature (for example 120°C) a sensitive element made of a conductor material, for example a membrane (film) or a wire, which is immersed in the air flow in inlet. The sensitive element is in fact heated by the passage of electric current and cooled by the air flow which subtracts heat therefrom by convection. In this way, an increase in the electric current necessary for maintaining the element sensitive to the target temperature corresponds to an increase in the air flow in inlet to the engine.

Downstream of the air filter, the aspiration conduit can further be provided with a compressor able to increase the air pressure directed towards the cylinders, thus enabling a supercharging of the engine and therefore an increase in performance.

The compressor can for example be a rotary compressor activated by a turbine located along the exhaust conduit of the engine, thus realizing a supercharging system which is commonly known as a turbocompressor.

In the usual aspiration systems, the compressor receives an air flow which, possibly cleaned of solid and/or liquid particles retained by the main filter, freely flows upstream of the flow which reaches the compressor. In this way the distribution of the flow that reaches the compressor is affected by the conformation of the aspiration conduit, internally of which vortices and/or turbulent currents can form which reduce the efficiency of the compressor. Further, in order to reduce the pollutant emissions, in particular nitrogen oxides (NOx), modern internal combustion engines can be provided with a recycling system of the low-pressure exhaust gases (LP-EGR), which comprises a recycling conduit which branches from the exhaust conduit and opens into the aspiration conduit between the air filter and the compressor. A heat exchanger is generally located along the recycling conduit which reduces the temperature of the recycled exhaust gases before they reach the aspiration conduit.

A drawback of these aspiration systems consists in the fact that under certain conditions, during the passage through the recycling conduit and the relative heat exchanger, the moisture present in the exhaust gases tends to condensate, forming droplets.

The recycled exhaust gases can also contain droplets of oil leaking from the cylinders of the engine and which can be leaked from metal filters usually located in the recycling conduit.

When these droplets of water and/or oil reach the aspiration conduit, the air flow accelerates them and projects them at a high velocity towards the compressor, the impeller of which is therefore subjected to numerous and repeated micro-impacts which over time can lead to early wearing-out.

A further drawback of the known aspiration systems consists in the fact that during the replacement of the air filter, small but not insignificant quantities of solid particles and other impurities, previously trapped in the filter walls, might be released internally of the aspiration conduit due to the vibrations and/or the small amounts of jerking to which the filter walls are inevitably subjected during these operations.

On next start-up of the engine, these particles and impurities are also accelerated by the air flow in aspiration and disadvantageously conveyed towards the engine cylinders.

During the travel towards the engine, the particles and the impurities can further impact against the sensitive element of the mass flow meter and/or the impeller of the compressor, risking damage thereto.

The same drawback can occur also in the case in which the air filter is damaged and therefore unable to effectively retain all the impurities present in the air directed to the engine.

Lastly, a further significant drawback of the known aspiration systems consists in the fact that the air flow normally flowing in the aspiration conduit exhibits a rather turbulent regime with a very non-uniform advancing front.

Owing to this non-uniformity, the quantity of heat removed by the sensitive element of the mass flow meter is not always precisely indicative of the mean air flow of the air being aspirated, so that the instrument can provide a measurement which sometimes is different from the correct one, with consequent negative implications on the control of the engine.

Summary of the invention

In the light of the foregoing, an aim of the present invention is to disclose a solution enabling protection of the components of the aspiration system of the solid particles and from the other impurities which can be released into the aspiration conduit during the replacement of the air filter or in a case of malfunctioning thereof.

A further aim is to protect the components of the aspiration system from the water droplets which form by condensation in the recycling conduit of the exhaust gases.

A further aim of the present invention is to make the air flow in aspiration to the engine uniform, so as to improve both the efficiency of the engine and the flow rate measurement performed by the mass flow meter.

These and other aims are attained by the characteristics of the invention as set down in the claims, where the independent claim delineates the essential characteristics of the invention, while the dependent claims delineate preferred and/or particularly advantageous aspects.

In particular, an embodiment of the present invention relates to an aspiration system for an internal combustion engine, comprising at least:

- an aspiration conduit,

- an air filter located in the aspiration conduit, and

- a porous wall located in the aspiration conduit downstream of the air filter. With this solution, during the replacement of the air filter or in a case of malfunctioning thereof, any solid particles or other impurities passing internally of the aspiration conduit can be retained by the porous wall located downstream, so that the impurities do not get projected (or at least not all together) towards the cylinders, with consequent risks for the components located along the pathway thereof.

In an aspect of the invention the porous wall can be conformed as a concave body having a concavity thereof facing in a flow direction of the air along the aspiration conduit, i.e. in an opposite direction with respect to the air filter located upstream.

In other words, the porous sector can generally be conformed as any body having an axial development and being internally hollow, which has an open end and a closed opposite end, where the closed end is facing towards the filter wall.

With this concave shape facing forwards, the front of the air current downstream of the porous wall is much more uniform over all the transversal section of the aspiration conduit.

In a particular aspect of the invention, the porous wall can be conformed such as to exhibit a vertex facing in an opposite direction to the air flow direction along the aspiration conduit.

With this solution, the porous wall slows the air flow progressively, obtaining, downstream, a good level of uniformity of the advancing front of the air flow. In an aspect of this embodiment, the vertex of the porous wall can be aligned with the central axis of the aspiration conduit.

In this way, the porous wall slows down the air flow along the aspiration conduit, first in the central zone of the conduit, where normally the air velocity is greatest, and then in proximity of the lateral walls, where the air velocity is generally slower due to friction, obtaining downstream an excellent uniformity of the air flow.

By way of example, the porous wall can be cap-shaped, for example a spherical cap, but it is possible for it to have a more tapered shape, for example a conical, ogival, parabolic shape, or more in general any internally hollow body, or more in general any internally hollow shape that is tapered and has an open end and a closed opposite end.

In other embodiments, the porous wall might have an elongate shape which comprises, for example, a cylindrical portion, a conical portion or in any case a tubular portion with any section and possibly tapered, having an open end and an opposite closed end, where the closed end can in turn be cap- shaped, for example a spherical cap, or a more tapered form, such as a conical, ogival or parabolic shape.

These embodiments have the advantage of being efficient from a functional point of view or being realisable in a rather simple and relatively economical way.

In some cases, for example in a case in which the porous wall is installed in proximity of a curved or non axial-symmetric portion of the aspiration conduit, the closed end of the porous sector might be displaced into an offset position with respect to the central axis of the aspiration conduit, such as for example an oblique cone shape.

In an aspect of the invention, a support flange (for example a plastic flange) is fixed to the mouth (i.e. the open end) of the internal cavity of the porous wall.

This support flange can be advantageously interposed and fixed between two portions of aspiration conduit, possibly with the interposing of appropriate seals, so as to obtain an easy and safe mounting of the porous wall. In a further aspect of the invention, the porous wall can be realised (for example entirely realised) with a non-woven textile material made of polymer fibres.

In this way the manufacturing costs of the porous wall can be kept relatively modest.

By way of example, the porous wall can be realised with fibres made of polypropylene, polyester or, in some applications, polyphenylene sulphide (PPS).

In a further aspect of the invention, the porous wall can have a mean porosity that is greater than the mean porosity of the air filter.

With this solution the porous wall does not in fact perform any air-filtering action during the normal functioning of the engine and does not introduce significant load losses.

In an embodiment of the present invention, the porous wall is realised using conductive fibres able to function as a sensitive element for a mass flow meter.

With this coupling of the mass flow meter with the porous wall, the number of components between the air filter and the engine can be reduced and therefore also the load losses in the aspiration conduit.

In an embodiment of the present invention, the porous wall can be located upstream of a mass flow meter, which is located in the aspiration conduit downstream of the air filter.

In this way the porous wall can perform the double function of protecting the mass flow meter from any impurities that have leaked from the air filter during the replacement steps (or in a case of malfunctioning) or to make the air flow striking the mass flow meter uniform so that the measurement taken by the mass flow meter is more accurate.

In an embodiment, the mass flow meter can comprise a sensitive element (for example a wire or membrane) of electrically conductive material located in the aspiration conduit so as to be struck by the air flow directed to the engine.

This type of mass flow meter has the advantage of being rather efficient and reliable, while remaining economical in terms of costs.

In general, the sensitive element of the mass flow meter can be realized with any electrically conductive material, for example a metal material, conductive plastic material, thermoplastic material loaded with conductive particles, and many others besides.

In a preferred aspect of the invention, the sensitive element of the mass flow meter is a thread of electrically conductive material which exhibits at least a portion which develops in the aspiration conduit in an X-shape (or a cross- shape).

In this way the wire made of conductive material develops in a rather extended area of the transversal section of the supply conduit, improving the exposure thereof to the air flow and therefore the reliability of the measurement taken by the mass flow meter.

In a further aspect of the invention, the sensitive element of the mass flow meter can be located at the mouth of the cavity of the porous wall.

In this way, the proximity between the porous wall and the hot wire guarantees that the hot wire is sufficiently protected and struck by an air flow that is substantially uniform.

In particular, the sensitive element might be directly fixed to the support flange of the porous wall (when present), for example comoulded with the flange or fixed thereto by mechanical means (for example clips, screws etc.). With this solution a single compact device could be obtained which includes both the mass flow meter and the porous wall for protecting/making the flow uniform.

In particular, the sensitive element of the mass flow meter can be fixed on the surface of the support flange which is facing the opposite way with respect to the porous wall.

In this way, the sensitive element is contained in the portion of the aspiration conduit in which the air has already crossed the porous wall, and is protected therefrom.

In an aspect of the invention, the sensitive element can however comprise electric terminals which cross the support flange (for example which are incorporated or comoulded therewith) so as to extend into the aspiration conduit upstream of the porous wall.

With this solution, the electric terminals can be connected to the control system of the engine, passing through the openings which are fashioned in the aspiration conduit upstream of the porous wall, so that any solid and/or liquid contaminants entering into the aspiration conduit from the openings would however be located upstream of the porous wall and could not therefore reach the sensitive element, nor flow towards the engine.

In a further embodiment of the invention, the porous wall might be located upstream of a compressor, which is positioned in the aspiration conduit downstream of the air filter.

In this way the porous wall is able to protect the compressor (for example the impeller of a rotary compressor) from the solid particles and/or other impurities which are released in the aspiration conduit during the replacement operations of the air filter, or which are not effectively retained by the air filter in a case of breakage and/or possible damage.

The porous wall is further able to increase the uniformity of the air flow in inlet to the compressor, improving the efficiency of the whole supercharging system.

In particular, the porous wall can be located downstream of an inflow point of a recycling conduit for exhaust gases, which is located in the aspiration conduit upstream of the compressor.

In this way the porous wall is also able to protect the compressor (for example the impeller of a rotary compressor) from the drops of water that can form in the recycling conduit and/or from the drops of oil which are transported by the discharge gases and which have not been effectively retained by any metal filters located along the recycling conduit.

Further, the porous wall is advantageously able to improve the mixing of exhaust gases in the air current coming from the external environment, improving the efficiency of the engine in terms of reduction of pollution from nitrogen oxides.

In an aspect of the invention, the porous wall might be directly associated to an inlet mouth of a casing of the compressor.

With this solution it would be advantageously possible to provide a single integrated component which includes both the compressor and the porous protection wall.

Alternatively the porous wall can be directly associated to an outlet mouth of a casing of the air filter.

With this solution it would be advantageously possible to provide a single integrated component which includes both the air filter and the porous protection wall.

Brief Description of the Drawings

Further characteristics and advantages of the invention will more fully emerge from a reading of the following description provided by way of non- limiting example, with the aid of the figures illustrated in the appended tables of drawings.

Figure 1 schematically illustrates an internal combustion engine provided with an aspiration and exhaust system according to an embodiment of the present invention.

Figure 2 is a perspective view of a protection device according to an embodiment of the present invention, shown by a side of the support flange. Figure 3 is a perspective view of the protection device of figure 2, shown by the side of the porous wall.

Figure 4 is an enlarged-scale detail of the aspiration system of figure 1 .

Figure 5 is a variant of the aspiration system of figure 4.

Figure 6 illustrates a second variant of the aspiration system of figure 4.

Figure 7 is a perspective view of a variant of the protection device, shown by a side of the support flange.

Figure 8 is a perspective view of the protection device of figure 7, shown by the side of the porous wall.

Figure 9 schematically illustrates an internal combustion engine provided with an aspiration and exhaust system according to an alternative embodiment of the present invention.

Figure 10 illustrates a variant of the aspiration system of figure 9. Figure 1 1 illustrates a second variant of the aspiration system of figure 9. Detailed description

The figure 1 schematically illustrates an internal combustion engine 100, for example a Diesel or petrol engine, belonging to a vehicle (not shown), such 5 as a motor vehicle, a truck, a lorry or another heavy work vehicle for transport or mixed.

The engine 100 generally comprises an engine body in which one or more cylinders 105 are fashioned, each of which houses an alternating piston (not visible). A mixture of air and combustible fuel (diesel or petrol) is cyclically fed i o internally of the cylinders 105 and set alight, so as to produce hot gases in rapid expansion which cause the alternating motion of the pistons. Usual con rod-crank couplings are used and the alternating motion of the pistons is transformed into the rotary motion of a drive shaft, which is connected to the vehicle traction organs, for example the drive wheels, via a suitable

15 transmission system.

The comburent air is fed internally of the cylinders 105 by means of an aspiration system 200, which generally comprises an aspiration conduit 205 which can convey an ambient air flow from an air filter 210 to an aspiration manifold 215, from which the air is lastly distributed internally of the single

20 cylinders 105.

The air filter 210 generally comprises an external casing 220 provided with an inlet mouth 225 connected to an air intake (not illustrated) and an outlet mouth 230 connected with the aspiration conduit 205. The external casing 220 houses one or more filter walls (not visible), which are able to intercept

25 all the air flow which flows from the inlet mouth 225 towards the outlet mouth

230, so as to retain solid particles and/or other impurities that may be transported by the air, preventing them from reaching the motor 100.

The combustion gases produced by the motor 100 exit from the cylinders 105 and are collected internally of an exhaust manifold 300, which is in

3 0 communication with an exhaust conduit 305 able to convey the combustion gases towards the external environment.

The exhaust conduit 305 can be provided with one or more anti-pollution devices able to modify the composition of the exhaust gases, so as to reduce the pollutant emissions of the engine 100. These devices can comprise filters able to retain some types of pollutants and/or catalyzing apparatus able to facilitate transformation of other pollutant substances into innocuous substances, or at least less damaging substances. In the illustrated example, the exhaust conduit 305 can comprise for example an oxidation catalyst 310 for example a Diesel oxidation catalyst - DOC) combined with an anti- particulate filter 315 (for example a Diesel particulate filter - DPF).

The internal combustion engine 100 can further be equipped with a supercharging system, which comprises a compressor 400 positioned along the aspiration conduit 205 downstream of the air filter 210, so as to increase the pressure of the air directed towards the cylinders 105 and therefore the performance of the engine 100.

The compressor 400 can be a rotary compressor which comprises an external casing 405 and an impeller 410, which is located internally of the casing 405 and is able to compress the air flowing from an axial inlet mouth 415 towards a radial outlet mouth 420.

The impeller 410 of the rotary compressor 400 can be activated by a turbine 425 which is arranged along the exhaust conduit 305 upstream of the oxidation catalyst 310, thus realizing a supercharging system commonly known as a turbocompressor.

The turbine 425 also comprises an external casing 430 and an impeller 435, which is mechanically connected to the impeller 410 of the compressor 400 and is located internally of the casing 430, so as to be set in rotation by the exhaust gases flowing from a radial inlet mouth 440 towards an axial outlet mouth 445.

In order further to reduce the pollutant emissions, in particular the emissions of nitrogen oxides (NOx), the internal combustion engine 100 can be further equipped with a recycling system of the exhaust gases (EGR), in the example with a low-pressure EGR. This recycling system essentially comprises a recycling conduit 500, which branches from a portion of the exhaust conduit 305 located downstream of the anti-particulate filter 315 and opens in a portion of the aspiration conduit 205 comprised between the air filter 210 and the compressor 400. A heat exchanger 505 can be located along the recycling conduit 500 with the aim of cooling the recycled exhaust gases, before they mix with the flow of air in aspiration.

The recycling conduit 500 can be further provided with a series of other functional components (not illustrated), among which one or more valves able to regulate the recycled exhaust gas flow, a bypass conduit with relative valves for enabling the exhaust gases to bypass the heat exchanger 505 in some functioning conditions (for example on engine start-up), as well as one or more filters, generally made of metal, able to retain some substances, such as for example solid non-combusted particles and drops of oil, which might be present in the exhaust gas flow.

The internal combustion engine 100 further comprises a mass flow meter 600, which is located in the aspiration conduit 205 downstream of the air filter 210 and is able to measure the air flow which is aspirated internally of the cylinders 105. In particular, the mass flow meter 600 can be located in the portion of the aspiration conduit 205 comprised between the air filter 210 and the inflow point of the recycling conduit 500 upstream of the compressor 400. The mass flow meter 600 can be of any known type. The mass flow meter 600 is preferably of a type which comprises a sensitive element 605 made of an electrically conductive material. The sensitive element 605 can be for example a film or a wire and can be realized with any electrically conductive material, for example a metal material, a plastic conductive material, a thermoplastic resin loaded with conductive particles and others besides.

The sensitive element 605 is inserted internally of the aspirating conduit 205, so as to be struck by the air flow moving towards the engine 00, while it is connected with a control circuit 610 so as to be passed through by an electric current. In this way, the sensitive element 605 is constantly heated, generally by Joule effect, by the passage of electric current, and at the same time cooled, generally by convection of the air in aspiration. By exploiting this principle, the control circuit 610 is normally configured such as to measure the electric current necessary for measuring the electric current necessary for maintaining the sensitive element 605 at a predetermined target temperature (for example 120°C) and thus obtain an indirect measurement of the air flow. In fact, given a same external air temperature, an increase in the electric current necessary for maintaining the sensitive element 605 at the target temperature corresponds to an increase in the air flow in inlet to the engine 100.

The aspirating system 200 can be further provided with a protection device 700, which is located in the aspiration conduit 205 downstream of the air filter 210. In particular, the protection device 700 can be located in the portion of the aspiration conduit 205 comprised between the air filter 210 and the compressor 400.

The protection device 700 generally comprises a porous wall 705, i.e. a wall exhibiting full parts and empty parts able to make it permeable to air but, at the same time, able to retain particles having dimensions greater than a certain granulometry. For example, the porous wall 705 can be constituted by a fibrous material, in particular by a non-woven textile material of polymer fibres which can be obtained with a melt-blown process or other known processes.

As the porous wall 705 is positioned downstream of the air filter 210, its main function is not to filter the comburent air during normal functioning of the engine 100, so that the average porosity thereof can be greater than the average porosity of the air filter 210, i.e. all the filter walls contained in the external casing 220. In this way, the porous wall 705 also attains the advantage of not introducing a significant load loss along the aspiration conduit 205.

As illustrated in figures 2 and 3, the porous wall 705 can be a slim-walled membrane, i.e. having a small thickness with respect to the other dimensions thereof, and can be profiled as a concave body. In other words, the porous wall can generally be conformed as any axially-developing and internally- hollow body having an open end at the largest section and an opposite end closed at the narrower section. In the illustrated example, the porous wall 705 exhibits a cap shape, in the example a spherical cap, but it might also have a more tapered shape, for example a conical, ogival, parabolic or more generally an internally-hollow shape which narrows starting from an open end, i.e. from the mouth of the internal cavity thereof, towards an opposite closed end, i.e. towards the bottom of the internal cavity thereof.

A porous wall 705 having this type of shape can be realised, for example, in a non-woven textile of polymer fibres obtained by means of any known process, preferably a melt-blown process.

In a further embodiment, the porous wall 705 can be shaped as a flat disc, which can for example lie on a plane that is substantially perpendicular to the axis of the aspiration conduit 205.

The porous wall 705 is therefore located internally of the aspiration conduit 205, so as to be crossed by the whole flow of air passing towards the cylinders 105 of the engine 100.

In particular, the porous wall 705 is preferably inserted in the aspiration conduit 205 so that the concavity thereof is facing in the air flow direction, i.e. in the opposite direction with respect to the air filter 210, and that the vertex thereof, i.e. the narrowest and most closed section, is facing in the opposite direction to the air flow direction along the aspiration conduit 205, projecting towards the air filter 210.

In this way, the porous wall 705 has the ability to progressively slow the air current which flows along the aspiration conduit 205, starting from the air which encounters the vertex located more upstream and successively the air that encounters the gradually more peripheral portions of the porous wall 705, thus obtaining the effect of making the advancing front of the air flow passing downstream of the filter wall 705 more uniform.

In this respect it can therefore be preferable for the vertex of the porous wall 705 to be substantially aligned with the central axis of the aspiration conduit 205, so that the porous wall 705 is able to slow first the air flow passing in the central zone of the conduit, where normally the air velocity is greater, and then the air flow passing in proximity of the lateral walls, where the air velocity is generally lower due to friction.

However in some cases, for example in a case in which the porous wall 705 is installed in proximity of a curved or non axial-symmetric portion of the aspirating conduit 205, the vertex or the position of the closed end of the porous wall might be displaced into an offset position with respect to the central axis of the aspiration conduit. For example, the porous wall 705 might have an oblique cone-shape.

To enable fixing the porous wall 705 internally of the aspiration conduit 205, the protection device 700 can comprise a support flange 710 (see figures 2 and 3), which is fixed to the mouth of the porous wall 705, i.e. at the free end thereof, and can be blocked between two contiguous portions of the aspiration conduit 205, possibly with the interposing of suitable seal gaskets. The support flange 710 can be made of a plastic material, for example by injection moulding, and can be fixed to the porous wall 705 by means of any known system, for example by gluing, heat-welding or by mechanical means. In any case the width of the support flange 710 is preferably as small as possible, so as not to create a significant load loss internally of the aspiration conduit 205.

In an embodiment, the porous wall 705 can be coupled to a flow guide, i.e. to a substantially rigid body, i.e. to a substantially rigid body that develops for a certain portion internally of the aspiration conduit 205 and which comprises one or more deflectors able to longitudinally subdivide the aspiration conduit 205 into sectors of smaller dimensions.

With this device, generally located at points in which the aspiration conduit 205 has curves, it is possible to direct the air flow optimally and guarantee the homogeneity thereof.

This flow guide can be positioned upstream of the porous wall 705 and/or downstream thereof. In general terms, the porous wall 705 (especially when it is conformed as a flat disc) can be positioned in the aspiration conduit 205, both upstream and downstream of the sensitive element 605 of the mass flow meter 600 with respect to the flow direction.

It has been found that in both cases the disc shape of the porous wall 705 enables making the air flow that strikes the sensitive element 605 of the mass flow meter 600 uniform.

In a case where there is a flow guide present, the flow guide can be advantageously positioned upstream of the sensitive element 605 of the mass flow meter 600 while the porous wall 705 can be positioned downstream of the sensitive element 605 of the mass flow meter 600 along the flow direction.

With reference to the embodiment illustrated in figures 1 and 4, the protection device 700 can be usefully located in the portion of the aspiration conduit 205 comprised between the air filter 210 and the mass flow meter 600. In this position, the porous wall 705 is crossed only by air at ambient temperature in arrival from the external ambient, so that it can be made of polymer fibre, either polypropylene or polyester.

With this positioning, the porous wall 705 can perform a double function. The first function is to protect the mass flow meter 600 from any impurities which can pass through the air filter 210, either during normal functioning of the engine 100 due to possible damage and/or breakage of the air filter 210 (and/or relative filter walls), or during the replacement steps of the air filter 210 (and/or the relative filter walls) due to the inevitable jerking. The second function is to make the air flow striking the sensitive element 605 of the mass flow meter 600 uniform, so that the measurement performed by the mass flow meter 600 is more reliable.

In this regard, in the embodiment illustrated schematically in figure 5, the sensitive element 605 of the mass flow meter 600 can be located at the mouth of the concavity of the porous wall 705, so that the extreme proximity between the porous wall 705 and the sensitive element 605 guarantees that the sensitive element 605 is sufficiently protected as well as struck by an air flow that is sufficiently uniform.

A particular evolution of this concept is realised in the protection device illustrated in figures 7 and 8, in which the sensitive element 605 of the mass flow meter 600 is directly fixed to the support flange 710 of the porous wall 705, thus obtaining a single integrated device.

The sensitive element 605 can be comoulded with the support flange 710 or fixed thereto by means of any appropriate mechanical means (for example clips, screws, etc.).

In particular, the sensitive element 605 of the mass flow meter 600 can be fixed on the surface of the support flange 710 which is facing the opposite side with respect to the porous wall 705 and can also be provided with electrical terminals 615 which cross the support flange 710, so as to extend into the aspiration conduit upstream of the porous wall 705 (see figure 8). These electric terminals 615 can for example be directly incorporated or comoulded together with the support flange 710.

With this solution, the electric terminals 615 can be connected with the control circuit 610 of the mass flow meter 600 and, more in general, with the engine 100 control system, passing through the walls of the aspiration conduit 205 which are upstream of the porous wall 705 (see figure 5). In this way, any solid and/or liquid contaminants which were to enter the aspiration conduit 205 from the openings for the passages of the electric terminals 615 would in any case be upstream of the porous wall 705 and could not reach the sensitive element 605, nor flow towards the engine 100.

In these and other cases, the sensitive element 605 of the mass flow meter 600 can be realised by a wire made of an electrically conductive material, which exhibits at least a portion that develops in a transversal section of the aspiration conduit in an X shape (or a cross shape). This X-shaped portion exhibits, in particular, four coplanar branches having a radial extension (with respect to the central axis of the aspiration conduit 205), which are connected in series by three arched portions, of which two portions are located in the centre of the support flange 710, in proximity of the central axis of the aspiration conduit 205, while a third intermediate portion is located at the periphery of the support flange 710.

In this way, the sensitive element 605 extends in a quite large zone of the transversal section of the supply conduit 205, improving the exposure thereof to the air flowing towards the engine and therefore the reliability of the measurement carried out with the mass flow meter 600.

It is however possible that in other embodiments the same effect can be obtained with a sensitive element 605 which extends in a different pathway or shape, for example a sinuous, spiral or serpentine pathway.

In a further embodiment of the invention, the porous wall 705 of the protection device 700 (independently of whether it is flat or concave) can be constituted by conductive fibres, which can for example be polymeric and/or metallic.

With this solution it is possible to heat the conductive fibres by means of a potential difference with the aim of using the porous wall 705 as a sensitive element 605 of the mass flow meter 600, a factor which enables reducing the number of components between the air filter 210 and the engine 100 and therefore also the load losses in the aspiration conduit 205.

In this case too the porous wall 705 can be coupled to a flow guide of the type described in the foregoing, which can advantageously be positioned upstream of the porous wall 705 with respect to the flow direction.

In all the above-described cases, the protection device 700 (with or without the sensitive element 605) might be directly associated to the outlet mouth 230 of the external casing 220 of the air filter 210, as illustrated in figure 6. In particular, the support flange 710 might be blocked between the outlet mouth 230 of the air filter 210 and the immediately successive portion of the aspiration conduit 205, so that the porous sector 705 is inserted and extends internally of the outlet mouth 230. In this way, it is advantageously possible to obtain a single integrated component that includes both the air filter 2 0 and the porous wall 705 and even the sensitive element 605 of the mass flow meter 600.

With reference to the embodiment illustrated in figures 9 and 10, the protection device 700 might alternatively be located in the portion of the aspiration conduit 205 comprised between the inflow point of the recycling conduit 500 and the compressor 400. In this position, the porous wall 705 can also be struck by relatively hot gas in arrival from the recycling conduit 500, so that it could be advantageous to manufacture it from polymeric fibres of polyphenylene sulphide (PPS).

With this positioning, the porous wall 705 can have various functions. A first function is to protect the compressor 400, in particular the impeller 4 0, from the solid particles and/or other impurities which might be released into the aspiration conduit 205, both during normal functioning of the engine 100, due to possible damage or breakage of the air filter 210 (and/or relative filter walls), and during the replacement operations of the air filter 210 (and/or the relative filter walls), due to the inevitable jerking. A second function of the porous wall 705 is to increase the uniformity of the air flow in inlet to the compressor 400, improving the efficiency of the whole supercharging system of the engine 100. A third function is to improve the mixing between the air and the recycled exhaust gases, thus improving the efficiency of the engine in terms of reduction of the pollution from nitrogen oxides. Lastly, a fourth function of the porous wall 705 is to protect the compressor 400, in particular the impeller 410, from the drops of water than can form in the recycling conduit 500 and/or from the drops of oil which can be transported by the exhaust gas and which have been effectively retained by the metal filters located along the recycling conduit 500.

In an aspect of this embodiment, the protection device 700 can be directly associated to the inlet mouth 415 of the compressor 400, as illustrated in figure 1 1. In particular, the support flange 710 might be blocked between the inlet mouth 415 of the compressor 400 and the portion immediately preceding the aspiration conduit 205, so that the porous wall 705 is inserted in the aspiration conduit 205, projecting externally of the inlet mouth 415. In this way it is advantageously possible to obtain a single integrated component which includes both the compressor 400 and the porous wall 705.

Naturally an expert technician in the sector might make numerous modification of a practical-applicational nature to what is described in the foregoing, without forsaking the scope of the invention as claimed in the following.

Claims

1. An aspiration system (200) for an internal combustion engine (100) comprising at least:

- an aspiration conduit (205),

- an air filter (210) located in the aspiration conduit (205), and

- a porous wall (705) located in the aspiration conduit (205) downstream of the air filter (210).

2. The system (200) of claim 1 , wherein the porous wall (705) is conformed as a concave body having a concavity thereof facing in a flow direction of the air along the aspiration conduit (205).

3. The system (200) of claim 2, wherein the porous wall (705) is conformed such as to exhibit a vertex facing in an opposite direction to the air flow direction along the aspiration conduit (205).

4. The system (200) of claim 3, wherein the vertex of the porous wall (705) can be aligned with the central axis of the aspiration conduit (205).

5. The system (200) of any one of the preceding claims, wherein the porous walls (705) is cap-shaped, or has a conical shape or an ogival shape.

6. The system (200) of any one of claims from 2 to 5, wherein a support flange (710) is fixed to the mouth of the internal cavity of the porous wall (705).

7. The system (200) of any one of the preceding claims, wherein the porous wall (705) is realized using a non-woven textile material made of polymer fibres.

8. The system (200) of any one of the preceding claims, wherein the porous wall (705) has a mean porosity that is greater than a mean porosity of the air filter (210).

9. The system (200) of claim 1 , wherein the porous wall (705) is realised using conductive fibres able to function as a sensitive element (605) for a mass flow meter (600).

10. The system (200) of any one of the preceding claims, wherein the porous wall (705) is located upstream of a mass flow meter (600), which is located in the aspiration conduit (205) downstream of the air filter (210).

11. The system (200) of claim 9, wherein the mass flow meter (600) comprises a sensitive element (605) of electrically conductive material located in the aspiration conduit (205) in such a way as to be struck by the air flow directed to the engine (100).

12. The system (200) of claim 10, wherein the sensitive element (605) of the mass flow meter (600) is a thread of electrically conductive material which exhibits at least a portion developing in the aspiration conduit (205) in an X-shape.

13. The system (200) of any one of claims from 9 to 1 1 , wherein the sensitive element (605) of the mass flow meter is located at the mouth of the cavity of the porous wall (705).

14. The system (200) of claim 12, wherein the sensitive element (605) is directly fixed to the support flange (710) of the porous wall (705).

15. The system (200) of any one of claims from 1 to 8, wherein the porous wall (705) is located upstream of a compressor (400), which is positioned in the aspiration conduit (205) downstream of the air filter (210).

16. The system (200) of claim 14, wherein the porous wall (705) is located downstream of a point of inflow of a recycling conduit (500) for exhaust gases, which is located in the aspiration conduit (205) upstream of the compressor (400).

17. The system 200) of any one of claims 14 and 15, wherein the porous wall (705) is directly associated to an inlet mouth (415) of a casing (405) of the compressor (400).

18. The system of any one of claims from 1 to 13, wherein the porous wall (705) is directly associated to an outlet mouth (230) of a casing (220) of the air filter (210).