WO2008068435A1

WO2008068435A1 - Device for fresh air supply in an supercharged-type internal combustion engine

Info

Publication number: WO2008068435A1
Application number: PCT/FR2007/052287
Authority: WO
Inventors: Alain Gabriel Lefebvre
Original assignee: Renault S.A.S
Priority date: 2006-12-06
Filing date: 2007-10-31
Publication date: 2008-06-12
Also published as: FR2909730A1; FR2909730B1

Abstract

A fresh air supply device for an supercharged-type internal combustion engine; this internal combustion engine supply system comprises at least one air supply pipe (12) on which are arranged compression means (18) for an air flow of said engine, and is characterized in that it also comprises, arranged on said air supply pipe, an absorption device (24) for the pressure wave generated by said engine in said air flow so as to regulate the pressure of the said air flow.

Description

Device for supplying fresh air to an internal combustion engine of the supercharged type

The invention relates to a device for supplying fresh air to an internal combustion engine, such as supercharged for example by turbocharger or centrifugal compressor. The invention is particularly intended to be implemented in a motor vehicle. A limitation encountered on engines of the supercharged type, whether gasoline, diesel or gas type (Liquefied Petroleum Gas Type (LPG), or Natural Gas Vehicles (CNG)), concerns the aerodynamic phenomenon called "pumping" Compression means including the compressor or turbocharger type. This pumping phenomenon results in rapid fluctuations in flow and pressure of the fresh air flow for the internal combustion engine. The pumping of the compression means thus causes unstable operation of the turbomachine and therefore of the engine. This pumping phenomenon is therefore detrimental to the proper functioning of the engine on the vehicle. This phenomenon is particularly penalizing to obtain high compression ratios and high performance at low engine speeds, that is to say, in the case of operation of the engine at low speed.

It is known to avoid the pumping phenomenon of the compression means by reducing the compression ratio of the compression means. This, however, has a negative effect on the level of engine performance. Furthermore, DE 102 17 760 discloses a device for distributing a flow of fresh air in an atmospheric internal combustion engine, especially a motor vehicle, comprising a fresh air distributor in fluid communication, on the inlet side , with a fresh air supply duct and, on the outlet side, with an internal combustion engine by means of several connecting ducts. Each connecting conduit is connected to a combustion chamber of the engine. The fresh air distributor is also in fluid communication with a Helmholtz resonator whose resonance frequency is adapted to improve the fresh air filling of the combustion chambers at a certain predetermined speed by means of an oscillation supercharger. admission, that is to say by means of a supercharging in which the fresh charge is slightly precompressed by a pressure oscillation resulting from a resonance in the Helmholtz resonator. Thus, the Helmholtz resonator is implemented in this application so as to amplify the pressure wave.

In addition, the volume of the Helmholtz resonator can be modified according to the engine speed to adapt its resonant frequency to the engine speed. The throat connecting the volume of the resonator to the air distributor can also be closed by means of a butterfly valve.

However, this document relates to an atmospheric engine, that is to say not supercharged, and therefore does not evoke the problem of pumping the compression means in a fresh air supply device of a supercharged engine. In addition, it can be noted that the compression of the fresh air supply of a supercharged type engine, generally carried out by means of a turbocharger or a centrifugal compressor, is significantly greater than the compression achieved here, the The purpose is only to provide sufficient filling of the combustion chamber so that the fuel is not in excess in the combustion chamber relative to the fresh air.

An object of the invention is to provide a device for supplying fresh air to an internal combustion engine of the supercharged type which does not have the above-mentioned defects and which makes it possible, in particular, to reduce or even to avoid the pumping phenomenon of the means compression without compromising the performance level of the engine, especially at low speed.

This object of the invention is achieved by means of a device for supplying fresh air to an internal combustion engine comprising at least one air supply duct on which means for compressing a flow of air are arranged. supply air of said engine, remarkable in that it further comprises, disposed on said air supply duct, a device for damping the pressure wave generated by said engine in said air flow of in order to regulate the pressure of said air flow.

Thus, as will become more apparent from the description that will be given of the invention, it is possible to damp the pressure waves due to engine vibrations, which appear upstream of the combustion chamber, by means of the damping device. The pumping phenomenon is reduced. Indeed, it has been found that the pumping phenomenon of the compression means can be accentuated by the pressure waves which are generated by the engine and possibly amplified by elements of the intake line, these pressure waves tending to amplify variations in instantaneous rates and compression ratios of the compression means.

It can then increase the compression ratio of the engine, even at low speed, which improves the performance of the engine. Preferably, the device for supplying fresh air to an internal combustion engine of the supercharged type according to the invention has one or more of the following characteristics, taken alone or in combination:

said damping device is of the Helmholtz resonator type comprising a cavity capable of being placed in fluid communication with said air supply duct;

said cavity is connected in series with said air supply duct;

- Said Helmholtz resonator type damping device is connected in parallel with said supply duct, a groove opening on the one hand into said cavity and on the other hand into said air supply duct; it comprises selectively activatable means for blocking fluid communication between said cavity and said air supply duct;

- It further comprises means for modifying the section of said groove;

it comprises means for modifying the volume of said cavity; said means for modifying said volume of said cavity comprise means for moving, in leaktight manner, at least one wall of said cavity;

- Said means for moving a wall of said cavity comprises a worm integral with said wall and rotated by an actuator, a fixed nut relative to said cavity being mounted on said worm;

said damping means are disposed on said supply duct, downstream of said compression means; and

said damping means are disposed on said supply duct, upstream of said compression means. Other features and advantages of the invention will appear on reading the description of the invention which follows, given by way of illustrative example with reference to the figures in which FIGS. 1 to 4 show schematically a detail of a fresh air supply device of a supercharged type internal combustion engine according to different embodiments of the invention. In the figures, identical elements or identical function are identified by the same reference numeral.

Referring firstly to Figure 1 which shows schematically a detail of a fresh air supply device 10 of an internal combustion engine, the type supercharged for example by turbocharger or centrifugal compressor, in a motor vehicle, according to a first embodiment.

This device 10 comprises a supply duct 12 fresh air comprising in this case two branches 12a, 12b. The branches 12a, 12b of the supply duct are conventionally cylindrical. The supply duct 12 puts in fluid communication a fresh air inlet 14 which can be provided with an air filter device, at an outlet of the duct 16, in fluid communication with the combustion chambers of the combustion engine. internal combustion to be fed (not shown) for example by means of an intake distributor (not shown). The branches 12a, 12b are preferably made of plastic. The branches 12a, 12b may be manufactured in pieces to be assembled for example by welding, heat sealing or by any other means of assembly.

Fresh air compression means 18 are mounted between the two branches 12a, 12b of the supply duct 12. In the present case, these compression means 18 are of the compressor type, but other types of compression means can be envisaged as including a turbocharger. These compression means 18 make it possible to compress the flow of fresh air 20 at atmospheric pressure coming from the inlet of fresh air 14, so as to obtain a flow of compressed fresh air 22 intended to feed an internal combustion engine of the supercharged type.

Remarkably, the device 10 according to the invention comprises a damping device 24, in this case of the Helmholtz resonator type, arranged to be in fluid communication with the supply duct 12.

In a manner known per se by those skilled in the art, the Helmholtz resonator, which comprises a cavity in which a flow of air engages, makes it possible to smooth the variations of an air flow as a function of the frequency of the air. waves.

According to the first embodiment of the invention, the damping device 24, of the Helmholtz resonator type, is connected in parallel with the supply duct 12 and comprises a groove 26 of section S _gor and of length L _gor leading to part in the supply duct 12 and, secondly, in a cavity 28, in this case cylindrical, of volume V (shown in dotted line), delimited by an envelope 30.

The damping effect of the damping device 24 of the Helmholtz resonator type can be accentuated by implementing acoustic energy absorbing materials such as honeycombed materials or even rock wool type.

Preferably, the envelope 30 is made of plastic for reasons of weight and cost. However, the casing 30 can also be made of steel, aluminum or cast iron depending on the temperature and pressure constraints.

Preferably, the groove 26 opens, as shown in FIG. 1, into the feed duct 12 downstream of the compression means 18, and even more preferably in the immediate vicinity of the compression means 18. In this case, the high temperatures and pressures of the air stream 22 may require the use of stainless steel type materials.

However, according to other embodiments of the invention, this groove 26 can also open into the supply duct 12 upstream of the compression means 18. Plastic materials can then be used to produce the envelope 30. due to the low pressure and temperature of the airstream 20 upstream of the compression means 18. The cost of the device 10 according to the invention is reduced by such a choice of material.

The device 10 can be manufactured in separate elements (branches 12a, 12b of the supply duct 12, compression means 18, groove 26, casing 30). The various elements can then be assembled by welding, heat sealing or any other means of assembly.

The operation of the device 10 according to a first embodiment of the invention follows directly from the description which has just been given.

The flow of fresh air 20 upstream of the compression means 18 is compressed by the compression means 18. However, rapid variations of pressure and air flow can appear in the supply duct 12, especially at low speed. of the supercharged internal combustion engine to be powered (not shown).

These rapid variations of pressure and air flow in the duct 12 are accentuated by the pressure waves generated by the vibrations of the engine. To attenuate or eliminate these pressure waves generated by the motor, the Helmholtz resonator type damping device 24 is designed to have a natural frequency substantially equal to the frequency of one of these pressure waves generated by the motor. This significantly reduces the pressure and air flow fluctuations in the supply duct 12. Indeed, such a resonator has maximum damping characteristics in the vicinity of its natural frequency.

The dimensions of the groove 26 and of the cavity 28 are fixed so as to obtain a natural frequency of the damping device 24 of the Helmholtz resonator type, that is to say the most damped frequency in the air flow. by the resonator, in the vicinity of the frequency of the pressure wave generated by the motor, knowing that the natural frequency of a Helmholtz resonator type damping device is related to the characteristic dimensions of this resonator by the equation:

or :

- c represents the speed of sound in the air;

Sgo _r represents the surface of the cross section of the groove 26,

- Lgo _r represents the length of the groove 26 of the resonator; and - V represents the volume of the cavity 28 of the resonator.

Thus, the section and the length of the groove and the volume of the cavity of the resonator are chosen so as to obtain an own frequency f ₀ of the resonator substantially equal to the excitation frequency of the motor which is equal to the frequency of the resonator. pressure wave generated by the engine. By attenuating the pressure wave fronts in the feed duct 12, the operating stability of the compression means 18 and thus of the supercharged engine is increased. It is then possible to increase the boost pressure and therefore the performance of the engine.

Referring now to Figure 2, which shows a detail of a fresh air supply device 32 of a supercharged type internal combustion engine according to a second embodiment of the invention.

This fresh air supply device 32 differs from that shown in FIG. 1, in that the damping device 24 of the resonator type of Helmholtz is connected in series in the feed duct 12, in this case in the branch 12b located downstream of the compression means 18. In this case, the second branch 12b comprises:

- A first portion 12bi which opens on the one hand at the output of the compression means 18 and, secondly, in the cavity 28 of the damping device 24; and

a second portion 12b ₂ which opens on the one hand into the cavity 28 of the damping device 24 and, on the other hand, at an outlet of the conduit 16, in fluid communication with the combustion chambers of the internal combustion engine to feed (not shown) for example by means of an intake manifold (not shown).

Thus, unlike the first embodiment presented with reference to FIG. 1, the damping device 24 does not have a groove opening into the supply duct 12. The operation of the device according to this second embodiment does not differ, however. of the operation of the first embodiment.

The natural frequency of the damping device 24 which must correspond substantially to the _natural frequency of the pressure wave generated by the motor in the compressed air flow 22 then depends on the length Lg _0r of the portion 12bi of the branch 12b the air supply duct 12 of the engine which extends between the outlet of the compression means 18 and the inlet orifice 34 of the cavity 28. Similarly, the useful section S _g0r , which is the function of the _natural frequency of the Helmholtz resonator type damping device 24 according to the equation E1, is the section of the first portion 12b of the branch 12bi of the air supply duct 12.

Referring now to Figure 3, which shows a detail of a fresh air supply device 34 of a supercharged type internal combustion engine according to a third embodiment of the invention.

This third embodiment is distinguished by the fact that it comprises means 36 for modifying the volume V of the cavity 28.

Indeed, according to this third embodiment of the invention, a movable wall 38, inserted inside the envelope 30, is able to slide in a sealed manner inside the envelope 30. The movements of this movable wall 38 are controlled by an actuator 40 which rotates a worm 42 mounted inside a nut 44 fixed relative to the casing 30 of the cavity 28, so that the rotational movement generated by the actuator 40 is transformed by the worm system + nut into a translational movement of the wall 38.

With such a system it is possible to vary the natural frequency f ₀ of the damping device 24 of the Helmholtz resonator type, in particular in order to adapt it to the engine speed. Indeed, the engine speed varying, the excitation frequency of the motor and therefore the frequency of the disturbing wave generated by the motor in the supply air flow varies. It is then advantageous to vary the natural frequency of the damping device 24 so as to obtain a maximum damping of the damping device 24 in the vicinity of and preferably at the instantaneous excitation frequency of the motor.

Preferably, the actuator 40 for moving the wall 38 is controlled by the engine computer.

Referring now to Figure 4, which shows a detail of a fresh air supply device 46 of a supercharged type internal combustion engine according to a fourth embodiment of the invention.

This device according to the fourth embodiment of the invention differs from the device of Figure 3 in that a shutter 48 for example of the butterfly valve type, is mounted in the groove 26 of the damping device so as to selectively closing the groove 26. Preferably, the shutter 48 is mounted in the vicinity of the orifice 50 through which the groove 26 opens into the conduit 12.

With the aid of this shutter 48, it is possible to control the closing of the orifice 50 of the groove 26 and thus to deactivate the damping device 24, for example in the event of a high engine speed. Indeed, the pumping phenomenon is lower in case of high engine speed, it may be that the implementation of the damping device 24 is not necessary.

This shutter 48 can also be implemented to vary the section S _gor of the groove 26 at the orifice 50 and to modify, thus, the natural frequency of the damping device 24 of the Helmholtz resonator type. In this case, the shutter 48 is preferably controlled by the engine control unit so as to slave the natural frequency of the Helmholtz resonator type damping device to the engine speed so that the maximum damping frequency of the device damping 24 corresponds to the excitation frequency of the motor, that is to say the natural frequency of the disturbing wave generated by the motor in the supply air flow. Of course, the invention is not limited to the embodiments described above and many modifications are possible without departing from the scope of the invention.

Thus, in particular, it is possible to envisage an air supply device according to the first embodiment which furthermore comprises a shutter of the orifice through which the groove opens into the supply duct so as to control the frequency the helmholtz resonator as a function of the engine speed, as explained with reference to FIG. 4.

Claims

1. Air supply device for an internal combustion engine comprising at least one air supply duct (12) on which are arranged means for compressing (18) a supply air flow of said engine, comprising a device (24) for damping the pressure wave generated by said motor in said air flow so as to regulate the pressure of said air flow disposed on said air supply duct, of the resonator type; Helmholtz (24) having a cavity (28) adapted to be placed in fluid communication with said air supply duct (12), characterized in that it comprises means (36) for modifying the volume of said cavity (28). ). .

2. An air supply device according to claim 1, characterized in that said cavity (28) is connected in series in said air supply duct (12).

3. An air supply device according to claim 1, characterized in that said Helmholtz resonator type damping device (24) is connected in parallel with said supply duct (12), a groove (26) opening out of partly in said cavity (28) and secondly in said air supply duct (12).

4. An air supply device according to claim 3, characterized in that it comprises means (48) selectively activatable blocking the fluid communication between said cavity (28) and said air supply duct (12). ).

5. An air supply device according to one of claims 3 and 4, characterized in that it further comprises means (48) for modifying the section of said groove (26).

6. An air supply device according to one of the preceding claims, characterized in that said means (36) for modifying said volume of said cavity comprise means (40, 42, 44) for moving, in a sealed manner, to the at least one wall (38) of said cavity (28).

7. An air supply device according to claim 6, characterized in that said means (40, 42, 44) for moving a wall (38) of said cavity (28) comprise a worm (42) integral with said wall (38) and driven in rotation by an actuator (40), a nut (44) fixed relative to said cavity (28) being mounted on said worm (42).

8. An air supply device according to any one of the preceding claims, characterized in that said damping means (24) are arranged on said supply duct (12), downstream of said compression means (18) .

9. An air supply device according to any one of the preceding claims, characterized in that said damping means (24) are arranged on said supply duct (12), upstream of said compression means (18). .