FR3046816A1 - INTERNAL COMBUSTION ENGINE HAVING DEVICE FOR DISSIPATING A PRESSURE BETWEEN A COMPRESSOR AND A GAS BUTTERFLY - Google Patents

Abstract

This device (28) for dissipating an overpressure is intended to be incorporated between a compressor (14) and a butterfly (26) of the gases of an internal combustion engine of a motor vehicle. It comprises a passage duct (34) for the gases, connected to the throttle valve (26) of the internal combustion engine, and having at least one orifice (38) opening into a closed chamber (44), variable shutter means (30) all or part of said orifice and control means (40, 42) of the closure means (30). The closed enclosure (44) comprises a porous wall (46), the control means (40, 42) being provided for controlling the variable closure means (30) as a function of the opening angle (α) of the butterfly (26) of the gases.

Description

FIELD OF THE INVENTION The invention relates to the field of internal combustion engines equipped with a turbocharger, and to motor vehicles equipped with such an engine.

Conventionally, an internal combustion engine, for example intended to be incorporated in a motor vehicle, comprises a crankcase provided with at least one cylinder inside which the combustion takes place. Each cylinder is fed with a gas intake circuit which will then be burned inside said cylinder, the flue gases being discharged from said cylinder by an exhaust circuit.

Such engines are generally equipped with a turbocharger, consisting of a turbine mounted in the exhaust circuit, a compressor mounted in the intake circuit and a turbocharger shaft which rotates the turbine and the compressor. . In this way, the intake circuit is divided into a low pressure intake duct, upstream of the compressor, and a high pressure intake duct, between the compressor and the crankcase. Similarly, the exhaust system is divided into a high pressure exhaust duct, located between the crankcase and the turbine, and a low pressure exhaust duct, located downstream of the turbine.

In order to be able to control the flow of gas admitted into the cylinders, a throttle valve is conventionally incorporated into the high-pressure intake duct, comprising a flap that can be pivoted between an orientation parallel to the flow, and an orientation perpendicular to the flow. The orientation of the flap is controlled by an engine control device, the flow being maximum when the flap is open and minimal when the flap is closed.

During a sudden closure of the throttle flap, the flow of fluid exiting the high pressure intake duct to the cylinder may drop excessively with respect to the flow of fluid entering the compressor. There is then a pumping phenomenon causing premature wear of the compressor.

To overcome this drawback, it is possible to use a discharge device whose function is to prevent the overpressure generated downstream of the compressor. Such a discharge device may comprise a discharge duct connecting the high pressure intake duct to the low pressure intake duct. A discharge valve is incorporated in the discharge duct. Thus, when there is an overpressure downstream of the compressor following closure of the throttle flap, it is possible to open the discharge valve, so as to evacuate the overpressure from the high pressure intake duct to the intake duct at low pressure. This prevents the occurrence of the pumping phenomenon. However, this solution is not fully satisfactory, in particular because it is at the origin of a discharge noise resulting in inconvenience for the driver and passengers of the vehicle. This disadvantage is all the more important as the discharge noise is generally transmitted and radiated by the low pressure intake duct in practically the entire body of the vehicle.

To overcome this drawback, it is possible to set up a shock absorber of the discharge noise, for example an acoustic resonator, on the intake duct at low pressure. However, this solution generates a significant amount of space under the hood of the vehicle.

An alternative solution is to delay the closing of the butterfly flap or to synchronize with the anticipated opening of a discharge valve located between the crankcase and the turbine. However, this solution has the disadvantage of delaying the deceleration of the vehicle when the driver lifts his foot off the accelerator pedal, which also results, inter alia, inconvenience to the driver.

In view of the foregoing, the object of the invention is to provide a device capable of dissipating the overpressure generated downstream of the compressor, by overcoming the aforementioned drawbacks. For this purpose, it is proposed a device for dissipating an overpressure intended to be incorporated between a compressor and a throttle valve of an internal combustion engine of a motor vehicle, comprising a conduit for passing the gas from the compressor to the throttle valve. gases of the internal combustion engine, and having at least one opening opening into a closed chamber, means for variable closure of all or part of said orifice and a means for controlling the closure means.

According to a general characteristic of this device, the closed enclosure comprises a porous wall, the control means being provided for controlling the variable closure means as a function of the opening angle of the flap of the throttle valve.

Such a device, in particular thanks to the combined use of a closed enclosure comprising a porous wall and a control means controlled as a function of the opening angle, allows an optimal dissipation of the overpressure generated downstream of the compressor, to avoid the occurrence of the pumping phenomenon without generating the discharge noise.

According to one embodiment, said orifice, that is to say the orifice when there is only one and the orifices when there are several, is of circular shape.

According to another embodiment, the closure means comprise a hollow cylinder with a substantially circular cross-section, the hollow cylinder being cylindrical with a substantially circular cross-section and capable of sliding, in the axial direction, inside the passage duct, said hollow cylinder comprising at least one perforation adapted to be disposed opposite said at least one orifice of the passage duct.

Advantageously, said perforation is substantially identical in shape to that of said orifice.

Advantageously, the control means is configured so as to always maintain a passage section through said orifice, that is to say the orifice when there is only one and the orifices when there has several, greater than a minimum section of occurrence of a pumping phenomenon, the minimum section being determined by the equation:

S ^ denotes the minimum section of passage through said orifice,

denotes the mass flow rate relative to the maximum supercharging pressure level of the full load curve projected on the right relative to the pumping limit, P denotes the density of the gases downstream of the compressor in the passage duct, p "" χ denotes the maximum supercharging pressure of the full load curve, and p atm denotes the atmospheric pressure.

It is possible to envisage several variants to control the variable shutter means depending on the opening angle of the throttle valve.

According to one of these variants, the control means comprises a mechanical system coupled to the throttle valve of the engine, said mechanical system operating according to the rack-and-pinion principle.

According to another variant, the control means comprises an electronic control unit and an actuator controlled by the electronic control unit and adapted to cause the displacement of the closure means relative to the passage duct.

Advantageously, the electronic control unit is configured to control the closing of said orifice when the

pressure of the gases flowing in the passage duct is lower than the atmospheric pressure.

In another aspect, there is provided an internal combustion engine for a motor vehicle, comprising at least one cylinder connected to an intake circuit, a turbocharger comprising a compressor mounted in the intake circuit, a throttle valve being incorporated in the intake circuit between the compressor and the cylinder, said motor comprising a device for dissipating an overpressure as described above.

In yet another aspect, there is provided a method of closing the throttle valve of an internal combustion engine as described above, wherein: - when the opening angle of the throttle valve is less than one lower intermediate opening angle, it maintains a total closure of the orifices, - when the opening angle of the throttle valve is between the lower intermediate angle and an upper intermediate opening angle, it gradually decreases the closure of the orifices when the opening angle of the throttle valve increases, and - when the opening angle of the throttle valve is greater than the upper intermediate angle, completely disables the closure of the orifices. Other objects, features and advantages of the invention will become apparent on reading the following description, given solely by way of nonlimiting example, and with reference to the appended figures in which: FIG. 1 is a schematic diagram an internal combustion engine equipped with a device for dissipating an overpressure according to a first exemplary embodiment of the invention; FIG. 2 represents the dissipation device of the engine of FIG. 1; FIG. 3b and 3c schematically represent the dissipation device of FIG. 2, in three different operating configurations, and FIG. 4 is a graph showing passage sections through various elements of the engine intake duct of FIG. 1 as a function of the opening angle of the throttle valve, - Figure 5 illustrates a method of closing the throttle valve which can be implemented at the m Figure 6 shows a second embodiment of a dissipation device that can be incorporated in the motor of Figure 1.

Referring to Figure 1, the internal combustion engine 2 comprises a crankcase 4 having one or a plurality of cylinders (in this case four cylinders unreferenced). The cylinders of the block 4 are supplied with gas intended to be burned by an intake circuit 6, an exhaust circuit 8 allowing the evacuation of the burnt gases from the combustion.

The engine 2 further comprises a turbocharger 10, consisting of a turbine 12, a compressor 14 and a shaft of the turbocharger 16. The turbine 12 is mounted in the exhaust circuit 8. The compressor 14 is mounted in the intake circuit 6. The shaft 16 rotates the turbine 12 and the compressor 14. In this way, the turbine 12 divides the exhaust circuit 8 into a high pressure exhaust duct 18, situated between the block 4 and the turbine 12, and a low-pressure exhaust duct 20, located downstream of the turbine 12. In the same way, the compressor 14 divides the intake circuit into a low-pressure intake duct 22 , located upstream of the compressor 14, and a high-pressure inlet duct 24, situated between the compressor 14 and the crankcase 4.

A throttle valve 26 is incorporated in the high pressure intake pipe 24. Thus, the throttle valve 26 is located in the gas flow between the compressor 14 and the crankcase 4. The throttle valve 26 is thus able to control the throttle valve. flow of gas admitted into the cylinders of the crankcase 4 to undergo combustion. To do this, the butterfly 26 comprises a flap (not referenced) planar pivotable so as to be oriented between a first orientation parallel to the axial direction of the conduit 24 at the butterfly 26, and a second orientation perpendicular to the axial direction supra. Throughout the present application, the term "opening angle" means the angle, denoted a, between the axial direction defined above and the plane of the butterfly flap 26. Two opening states of the butterfly 26 are then defined: a open state corresponding to an opening angle of 0 ° and a closed state corresponding to an opening angle of 90 °.

The engine 2 comprises a dissipation device 28 according to a first example of embodiment, serving to dissipate a local overpressure of gases intended to be burned, said excess pressure forming locally inside the intake circuit 6 downstream of the compressor. When the throttle is closed rapidly, as shown diagrammatically in FIG. 1, the device 28 is incorporated between the compressor 14 and the high-pressure intake duct 24 equipped with the throttle valve. The device 28 is detailed later. , with reference to FIG.

In particular, FIG. 2 shows the compressor 14, the throttle valve 26 and the dissipation device 28. The device 28 comprises an outer passage passageway 34 of cylindrical shape with a circular section. Throughout the present description, unless otherwise indicated, the terms "axial direction", "axially", "radial direction" and "radially" with respect to the axis of cylindricity of the duct 34 are defined. gas for combustion from the compressor 14 to the butterfly 26. The duct 34 comprises at least one orifice 38, opening on either side of said duct 34. In the illustrated embodiment, the duct 34 has eight orifices 38 of substantially equal diameters. Among these orifices 38, four are aligned in the axial direction, the other four being axially aligned with each other opposite the first and located symmetrically with respect to the axial direction. However, it is not beyond the scope of the invention to provide a different number of orifices. By means of the orifices 38, gas contained in the dissipation device 28 between the compressor 14 and the throttle valve 26 can be discharged to the outside of the intake circuit 6.

The device 28 comprises variable closure means comprising a hollow cylinder 30 of substantially circular section. The inside diameter of the passage duct 34 is slightly greater than the outside diameter of the hollow cylinder 30. The hollow cylinder 30 is introduced by one of its ends into the inside of the passage duct 34, so that it is able to slide, in the axial direction, with respect to the passage duct 34. The other end of the hollow cylinder 30 is capped by a shoulder of the high-pressure admission duct 24.

The inside diameter of the hollow cylinder 30 is substantially equal to the inside diameter of the high pressure inlet duct 24.

The passage duct 34 comprises a first end portion 36, projecting radially inwards, and which is integral with the compressor 14. It may for example be attached to a compressor housing 14. The end portion 36 plays the role of axial abutment, for the axial displacement of the hollow cylinder 30 with respect to the passage duct 34.

Advantageously, means (not shown) are provided to guarantee the tightness of the high-pressure admission duct 24 with the hollow cylinder 30, whatever the relative axial position of the hollow cylinder 30 with respect to the passage duct. 34.

Such an arrangement makes it possible for the hollow cylinder 30 to slide inside the passage duct 34 without the position of the high-pressure admission duct 24 being modified. In other words, the high-pressure admission duct 24 is fixed with respect to the passage duct 34, and these two ducts remain constantly in alignment with one another thanks to the hollow cylinder 30 which , on the one hand, slides inside the passage duct 34, and on the other hand, is capped by the high-pressure admission duct 24.

The cylinder 30 comprises at least one perforation 32 opening on either side of said cylinder 30. The cylinder 30 preferably comprises as many perforations 32 as the duct 34 comprises orifices 38, and distributed substantially identically. The perforations 32 are all substantially circular and of the same diameter as the orifices 38. However, it is not beyond the scope of the invention to provide perforations of different shape, for example of oval shape, of rectangular shape, or of the shape of two semicircles connected to each other by a rectangle. In this embodiment, the cylinder 30 has eight perforations 32. The perforations 32 may, depending on the relative position of the cylinder 30 relative to the conduit 34, be alternately completely offset, partially offset or totally opposite to the In this way, by modifying the above-mentioned relative position, the variable closure means respectively make it possible to completely or partially close off or not to close off the orifices 38.

Thus, in the exemplary embodiment illustrated, the relative movement of the cylinder 30 relative to the duct 34 causes the closure or the opening, synchronously, of all the orifices 38 of the duct 34. However, it is possible to envisage, without out of the scope of the invention, the relative displacement of the cylinder 30 relative to the duct 34 causes the opening of some of the orifices 38, while maintaining the closure of the other orifices 38.

The dissipation device 28 comprises a control means able to actuate the relative displacement of the cylinder 30 with respect to the duct 34. The control means is designed so as to progressively reduce the closing of the orifices 38 until they are completely open, when The control means comprises an electronic control unit 40 and an actuator 42. The unit 40 is capable of determining the opening angle a. The unit 40 drives the actuator 42 according to the determined angle. The actuator 42 is capable of causing the cylinder 30 to move axially relative to the duct 34, for example by moving a rod 33 fixed to the hollow cylinder 30 through a lumen 35 of the high-pressure admission duct 24. The operation of the control means will be further detailed later, in particular with reference to Figures 3a, 3b, 3c and 4.

Still with reference to FIG. 2, the device 28 comprises a closed enclosure 44. The enclosure 44 is integral with the passage duct 34 and disposed around it, so that all the orifices 38 are located inside. The enclosure 44 has a cylindrical wall 46, defined axially by two end walls 48 and 50 planes. A first front wall (reference 48 in FIG. 2) is fixed on the first end portion 36 of the passage duct 34, the other (reference 50 in FIG. 2) being fixed on the high pressure intake duct. 24. Advantageously, the wall 46 is porous. The end walls 48 and 50 may also be rigid. In this way, the chamber 44 allows the passage of gas through its porous wall 46, from the inside to the outside. Gas discharged through the orifice 38 partially closed or open can then be dissipated to the atmosphere outside the engine 2. The porous wall 46 is preferably made of a deformable material and / or able to filter the noise directly and indirectly generated by the opening of the orifices 38. The wall 46 prevents the transmission of vibrations to the intake circuit 6, so as to further reduce these noises. The end walls 48 and 50 have an outside diameter large enough that the chamber 44 defines a volume of expansion to absorb the overpressure caused by the closure of the butterfly 26, and thus to prevent the occurrence of the pumping phenomenon.

The control of the displacement of the closure means with respect to the intake duct 30 will now be detailed, with reference to FIGS. 3a, 3b, 3c and 4.

In FIGS. 3a, 3b and 3c, schematically shown in plan view, the duct 34 and the hollow cylinder 30 are arranged relative to one another in three different operating configurations. In addition to the duct 34 and the cylinder 30, the butterfly 26, the orifices 38 and the perforations 32 are shown in dotted lines in these three figures. As the hollow cylinder 30 is disposed inside the duct 34, the perforations 32 are shown. in dashed lines when hidden by line 34.

In FIG. 3a, the cylinder 30 has been displaced by the actuator 42 so as to be relatively arranged with respect to the duct 34 in a total closure operating configuration, implemented when the butterfly 26 is in the open state. that is, when the angle a is close to 0 °. More specifically, the duct 34 is disposed around the cylinder 30, so that the orifices 38 are not opposite the perforations 32. The orifices 38 are thus completely closed by the cylinder 30.

In FIG. 3b, the closure means are represented in a partially closed configuration, implemented during an intermediate opening state of the butterfly 26, during a transition from the open state to the closed state. . In other words, this configuration is implemented when the angle has reached an intermediate value while increasing. To implement this configuration, the actuator 42 axially moves the cylinder 30 relative to the passage conduit 34, so that its perforations 32 are arranged partially opposite the orifices 38. In this way, the orifices 38 are partially closed. Gas can then exit the device 28 and enter the chamber 44 before being subsequently dissipated to the outside atmosphere of the engine 2.

In FIG. 3c, the closure means are represented in a totally open configuration, implemented when the butterfly is in a closed state, that is to say when the opening angle of the butterfly reaches a value close to 90 °. The actuator 42 then moves the cylinder 30 relative to the cylindrical duct 34 so that its perforations 32 are exactly opposite the orifices 38. In this way, the orifices 38 are no longer blocked by the cylinder 30, and the flow rate gas leaving the device 28 takes a maximum value.

Referring now to Figure 4, it is shown, according to the opening angle of the throttle valve 26, the evolution of different sections of gas passage. The following sections are particularly defined in the present description: the throttle passage section Si corresponds to the throttle passage section at the throttle inlet 26, the leakage passage section S2 corresponds to the passage section. through the openings 38 which is not obstructed by the cylinder 30, the exit passage section S3 corresponds to the total passage cross-section through which the gases flow, that is to say S3 = Si + S2, and - The minimum flow before discharge section Smin corresponds to the minimum value of output passage section S3, below which the pumping phenomenon occurs within the compressor 14.

In view of the above, the section Si is dependent on the angle a, the section S2 being dependent on the relative position of the cylinder 34 with respect to the conduit 30. The section Smin can be determined by the following calculation:

In the above equation, the data are defined as follows: (in kg / s) means the relative mass flow rate at the maximum supercharging pressure level of the full load curve, projected to the right relative to the pumping limit, - P (in kg / m3) is the density of the air in the high pressure duct downstream of the compressor, p ™ ra / max (in Pa) corresponds to the maximum supercharging pressure of the full load curve, and p atm (in pa) corresponds to the atmospheric pressure.

To determine the value of

for example, the value of the flow rate to be projected can be determined using a flowmeter. The position of the pumping limit, necessary to project the flow value on the line relative to the pumping limit, is then given

by the turbocharger supplier, or can be measured on a test bench by applying back pressure downstream of the compressor, in order to increase the compression ratio, and regulating the air flow. p

The pressure s "may be determined by measurement on test bench in the duct 24, on a full load ramp up. The atm pressure is constant at 1.01325.105 Pa.

The density P is obtained by applying the following equation:

where P24 (in bar) refers to the pressure within the high pressure inlet pipe 24, which can be measured in the same way as wa /. T24 (in K) designates the temperature within the duct 24. T24 can alternatively be measured, for example using a thermocouple, or be calculated from the pressure and temperature of the gases upstream of the compressor 14 and the boost pressure (measured).

In the graph of FIG. 4, the evolution is represented as a function of the angle a: in fine lines of the section Si, in dotted lines, of the section S2, in solid lines, of the section S3, corresponding to the sum of sections S1 and S2, and - in zigzag, the minimum section before pumping Smin.

The control means of the device 28 strives to maintain a section S3 greater than the section Smin. To do this, the control means implements a control method which will now be detailed with reference to FIGS. 4 and 5.

The control method according to the invention comprises an initialization step T00, during which it is determined whether the butterfly 26 is in an open or quasi-open state. To do this, the unit 40 determines whether the angle a is smaller than the angle ao by absolute value. Advantageously, one can choose as a value for ao any angle between 0.5 ° and 2 °, and preferably an angle

substantially 1 °. As long as the answer at the end of this step is no, the process is not initiated. As soon as the answer is yes, the process starts with a first step E01 during which the actuator 42 arranges the cylinder 30 with respect to the duct 34, so that the orifices 38 are completely closed by said cylinder 30. way, the section S2 is almost zero, the section Si being substantially equal to the total section S3. As a result, the flow of gas leaving the orifices 38 is zero.

During a first test step TOI, it is determined whether a closure of the butterfly 26 is engaged. To do this, the unit 40 determines for example if the angle a is equal to the value ao and if the time derivative

is strictly greater than zero.

As long as the answer to the TOI step is no, we stay at the current step. When the answer is yes, a second step E02 is applied during which the relative position of the cylinder 30 with respect to the duct 34 is modified while maintaining the total closure of the orifices 38. More particularly, the actuator 42 is activated so that that it slides the cylinder 30 relative to the duct 34, in the axial direction, the perforations 32 remaining completely offset relative to the orifices 38. In this way, the flow of gas exiting through the orifices 38 remains virtually zero. Alternatively, the step E02 may consist in keeping the parts 30 and 34 immobile relative to each other, the orifices 38 being always closed. At the end of the step E02, a second test step T02 is applied consisting of determining whether the butterfly 26 is between the open state and a first intermediate state. More particularly, the unit 40 determines during the step T02 if the angle a is less than a lower intermediate angle ai. An advantageous value of ai is for example between 25 ° and 40 °, and preferably substantially equal to 30 °. If the answer at the end of step T02 is yes, step E01 is again applied.

When the response at step T02 becomes no, a step E03 is applied, during which the actuator 42 is controlled so as to partially deactivate the closing of the orifices 32. To do this, the actuator 42 slides the 30 around the duct 34, so that the perforations 32 are located partially opposite the orifices 38. More specifically, the actuator 42 modifies the relative position of the cylinder 30 relative to the passage duct 34, so that the perforations 32 and the orifices 38 are even more opposite than the value of the angle a increases. In this way, the more the butterfly 26 is close to the closed position, the greater the passage section S2 is important. It follows a slowing down of the decrease of the total section S3. In the exemplary embodiment illustrated, the actuator 42 is controlled so that the section S2 increases linearly as a function of the angle a. At the end of the step E03, a second test step T03 is applied in the course of which it is determined whether the butterfly 26 is between the first intermediate state and a second intermediate state of closure. In other words, the unit 40 determines whether the angle a is smaller than an upper intermediate angle θ. Advantageously, the angle θ 12 is between 65 ° and 80 °, and more particularly substantially equal to 75 °. . If the answer at the end of the test step T03 is yes, step E03 is continued.

It should be noted that the value of 012 and the linear evolution profile of S2 as a function of the angle α are judiciously chosen, so that at the moment when stopping the step E03 is stopped, c that is, at the moment when the response at step T03 changes from no to yes, the orifices 38 are substantially opposite the perforations 32. At this moment, the section S2 is maximum, as is the flow of gas being able to exit through the orifices 38.

When the answer at the end of the test step T03 becomes no, it goes directly to another test step T04. In this way, between the test steps T03 and T04, the actuator 42 maintains the relative position of the parts 34 and 30 unchanged, and thus keeps the section S2 at its maximum value.

During the test step T04, it is determined whether the butterfly 26 is in a closed or quasi-closed state. In other words, the unit 40 determines whether the angle a is smaller than a closing angle 013. Advantageously, it is possible to choose a value of the angle as between 88 ° and 90 °, and preferably an angle substantially equal to 89 °. As soon as the response at the end of the test step T04 is no, a step E04 is applied, during which the unit 40 drives the actuator 42 so that the latter maintains the relative position between the parts 30 and 34 for a predetermined time then moves the cylinder 30 relative to the conduit 34 so as to return to the initial state. Preferably, this predetermined time lasts long enough to allow a large part of the overpressure contained in the duct 34 to be evacuated and caused by the closure of the butterfly 26. For example, a suitable predetermined instant may last for a second. At the end of step E04, the control method is completed.

By implementing this method, it is ensured that the total section S3 is always greater than the minimum section Smin, below which the pumping phenomenon appears. More precisely, the opening profile of the orifices 38 as a function of the angle α is particularly advantageous, in that the orifices open in three stages: - a first stage, during which the overpressure is not yet present and during which the orifices 38 remain closed, - a second time, during which the overpressure appears, and during which the orifices 38 open gradually, and - a third time, during which the overpressure is maximum, and during which the orifices 38 are completely open.

Thus, the growth of the section S2 increases gradually, so that a leakage flow rate can be generated through the device 28 without, however, significantly penalizing the supercharging pressure of the engine 2.

In addition, thanks to the precise calculation of the minimum section Smin, it is possible to control the flow of gas leaving the device 28 so as to be just at the limit of the pumping phenomenon.

Advantageously, it is conceivable, without departing from the scope of the invention, to modify the method of FIG. 5 so that it returns to the initial state as soon as the time derivative becomes negative. This makes it possible to interrupt the process when the closure of the butterfly 26 is interrupted.

Thus such a method, implemented by means of a device according to the embodiment example above, effectively dissipates the overpressure caused by the sudden closure of the throttle valve 26. In particular, the use of variable closure means capable of progressively actuating the closing of the orifices 38, in combination with the use of a closed enclosure comprising a porous cylindrical wall, is advantageous in that it makes it possible to avoid the phenomenon of pumping while minimizing discharge noise. The use of a control means consisting of the electronic control unit 40 and the controlled actuator 42 is interesting in particular because it is possible to avoid the suction of the porous cylindrical wall 46 through the orifice 38. Indeed, the suction of the deformable wall 46 through the orifices 38 may be caused by the occurrence of a pressure inside the device 28 below the atmospheric pressure. In such a case, the unit 40 may advantageously be designed so as to command the actuator 42 to close the orifices 38.

Referring now to Figure 6, there is shown a device 52 for dissipating an overpressure according to a second embodiment of the invention, which can be incorporated in a motor such as that of Figure 1. The identical elements carry the same references.

This example differs from the first embodiment given with reference to FIGS. 1 to 5, in that the control means

comprises a mechanical system 54 of the rack-and-pinion type. The mechanical system 54 is controlled by the rotation of the throttle valve 26 about its axis and is capable of driving the relative displacement of the cylinder 30 with respect to the passage duct 34. For example, the mechanical system 54 may comprise a toothed wheel (no shown) can be rotated by the pivoting of the butterfly 26 about its axis. The toothed wheel cooperates with a rack (visible in FIG. 6) directed in the axial and integral direction of the cylinder 30. In this way, the rotation of the toothed wheel causes the displacement in translation along the axial direction of the rack, and therefore the displacement according to the same translation of the cylinder 30 with respect to the duct 34.

Such an embodiment is particularly advantageous in that it saves space, a less expensive and more reliable design of the overpressure dissipation device.

Thus, each of the two examples of devices which have been exposed makes it possible to dissipate the overpressure caused by the closure of the throttle valve, just enough to avoid the appearance of the pumping phenomenon at the origin of the premature deterioration of the compressor. In addition, the combined use of variable closure means controlled by a control means taking into account the opening angle of the butterfly and a closed chamber comprising a porous wall, optimally attenuates the noise. caused by the dissipation of the overpressure. Moreover, the implementation of a method of opening the orifice in three stages and gradually, allows to evacuate the overpressure while avoiding to penalize the boost pressure of the engine. The efficiency of the engine 2 is improved.

Claims (10)

1. A device (28, 52) for dissipating an overpressure intended to be incorporated between a compressor (14) and a throttle (26) of the gases of an internal combustion engine (2) of a motor vehicle, comprising a passage (34) connected to the throttle valve (26) of the internal combustion engine (2) and having at least one orifice (38) opening into a closed chamber (44), variable closing means (30) all or part of said orifice (38) and control means (40, 42, 54) of the closure means (30), characterized in that the closed chamber (44) comprises a porous wall (46), the means control means (40, 42, 54) being provided for controlling the variable shutter means (30) as a function of the opening angle (a) of the throttle valve (26). 2. Device (28, 52) according to claim 1, wherein the orifice (38) is circular in shape. 3. Device (28, 52) according to claim 1 or 2, wherein the closure means (30) comprise a hollow cylinder (30) with a substantially circular section, the passage duct (34) being cylindrical with a substantially circular section. the hollow cylinder (30) being slidable in the axial direction inside the passage duct (34), said hollow cylinder (30) comprising at least one perforation (32) adapted to be disposed opposite said at least one orifice (38) of the passage duct (34). 4. Device (28, 52) according to claim 3, wherein said perforation (32) is of substantially identical shape to that of said orifice (38). 5. Device (28, 52) according to any preceding claim, wherein the control means (40, 42, 54) are configured so as to always maintain a passage section (S2) through said orifice (38). ) greater than a minimum section of appearance (S min) of a pumping phenomenon, the minimum section (Smin) being determined by the equation: means the minimum cross-section through said orifice, means the relative mass flow rate at the maximum supercharging pressure level of the full load curve projected to the line relative to the pumping limit, P is the density of the gases downstream of the compressor (14) in the passage duct (30), suraimzs. denotes the maximum supercharging pressure of the full load curve, and p atm is the atmospheric pressure. 6. Device (52) according to any one of the preceding claims, wherein the control means comprise a mechanical system (54) coupled to the throttle valve (26) of the engine gases (2), said mechanical system (54) operating according to the principle of rack and pinion. 7. Device (28) according to any one of claims 1 to 5, wherein the control means comprise an electronic control unit (40) and an actuator (42) controlled by the electronic control unit (40) and adapted to cause the closing means (30) to move relative to the passage duct (34). Device (28) according to claim 7, wherein the electronic control unit (40) is configured to control the closing of said orifice (38) when the pressure of the gases flowing in the passage duct (34) is less than at atmospheric pressure. 9. Internal combustion engine (2) for a motor vehicle, comprising at least one cylinder connected to an intake circuit (6), a turbocharger (10) having a compressor (14) mounted in the intake circuit (6) , a throttle valve (26) being incorporated in the intake circuit (6) between the compressor (14) and the cylinder, said engine (2) comprising a device (28, 52) for dissipating an overpressure according to any one of claims 1 to 8. A method of closing the throttle (26) of the gases of an internal combustion engine (2) according to claim 9, wherein: - when the opening angle (a) of the throttle valve is less than an angle lower intermediate opening (ai), it maintains a total closure of the orifices (38), - when the opening angle (a) of the throttle (26) of the gas is between the lower intermediate angle (ai) and a upper intermediate opening angle (a2), the closing of the orifices (38) is progressively reduced when the opening angle (a) of the throttle valve increases, and - when the opening angle (a) of the butterfly (26) of the gas is greater than the upper intermediate angle (a2), it completely disables the closure of the orifices (38).