FR3087225A1 - AIR INTAKE SYSTEM PROVIDED WITH AIR FLOW LIMITATION MEANS - Google Patents

Abstract

Air intake system (6) comprising at least one air intake pipe (17), the at least one air intake pipe (17) being intended to be connected to a combustion chamber (5) of a combustion engine (2) with positive ignition and being intended to be closed by an intake valve (22), characterized in that it comprises a means for limiting (18) a flow d air passing through the at least one air intake pipe (17), and in that the at least one air intake pipe (17) comprises a useful volume (VU) delimited upstream by the limiting means (18) and downstream by an intake valve (22) in a closed position, the useful volume (VU) being strictly less than a volume of a combustion chamber (VC) to which the line d 'air intake (6) is intended to be connected, said volume of a combustion chamber (VC) being defined at bottom dead center.

Description

Air intake system equipped with a means of limiting the air flow

Technical field of the invention

The present invention relates to an air intake system for a positive-ignition combustion engine. The invention also relates to a powertrain comprising such an air intake system. The invention also relates to a vehicle comprising such an air intake system or such a powertrain.

State of the art

In a spark ignition combustion engine, the rattling phenomenon is caused by the uncontrolled combustion of a fuel mixture in the combustion chamber. It generates noise, vibrations and shock waves in the combustion chamber which can damage the engine. The sensitivity of an engine to knock depends on the quality of the combustion chamber and the characteristics of the fuel mixture introduced, in particular its temperature and pressure. The hotter the fuel mixture, the higher the pressure of the fuel mixture, the greater the risk of rattling. The risk is therefore increased when the engine compression ratio is high and with the use of a turbocharger.

In order to prevent rattling, solutions are known which aim to limit the temperature in the combustion chamber. A first solution may consist in the use of a charge air cooler. A second solution, used in particular in automobile competition, is based on acoustic phenomena in the air intake line to generate an expansion of the gases during the intake phase. There is also known a method of operating a combustion engine comprising an early closing of the intake valves during the combustion cycle. This commonly used solution increases the specific performance of motors by limiting rattling at high loads. However, low temperatures are only obtained at the cost of a significant anticipation of the closing of the intake valves which generates a degradation of the structure of the aerodynamic field in the combustion chamber and therefore a degradation of the preparation of the mixture. . The maximum anticipated closing of the valves acceptable by an engine is then limited both by the supercharging capacities, and at the same time by the capacity of the combustion chamber to operate with a weak aerodynamic field. All these solutions require an increase in the boost pressure, i.e. an increase in the power of the turbocharger.

Subject of the invention

The object of the invention is to provide an air intake system and a powertrain overcomes the above drawbacks and improving the air intake systems and powertrains known from the prior art. In particular, the invention makes it possible to produce an air intake system and a powertrain making it possible to limit the knock phenomenon, the efficiency of which is improved, which is simple to assemble, and which has a reduced bulk.

The invention relates to an air intake system comprising at least one air intake pipe, the at least one air intake pipe being intended to be connected to a combustion chamber of a combustion engine with spark ignition and being intended to be closed by an intake valve, the air intake system comprising means for limiting an air flow rate passing through the at least one intake pipe air, and the at least one air intake pipe comprising a useful volume delimited upstream by the limiting means and downstream by an intake valve in a closed position, the useful volume being strictly less to a volume of a combustion chamber to which the air intake pipe is intended to be connected, said volume of a combustion chamber being defined at bottom dead center.

The means of limitation may include:

a valve, and / or a butterfly valve, and / or a guillotine valve, and / or a ball valve, and / or a venturi tube, and / or a tube comprising a section restriction, and / or an assembly of two tubes, in particular coaxial, an inner tube comprising orifices limiting an air flow between an outer tube and the inner tube.

The limiting means may include a geometrically variable intake section.

The useful volume can be variable, in particular the position of the limiting means with respect to the intake valve can be variable.

The useful volume can be less than or equal to a third, or even less than or equal to a quarter of the volume of a combustion chamber.

The air intake duct may comprise an intake manifold and a plurality of branches connected to the intake manifold, each branch being intended to be connected to a combustion chamber of a spark-ignition combustion engine, and each branch being intended to be closed by an intake valve, each branch comprising means for limiting an air flow rate passing through said branch.

The air intake system may include a throttle flap upstream of said limiting means.

The invention also relates to an engine group, in particular a powertrain comprising a spark-ignition combustion engine and an air intake system as defined above.

The engine group, in particular the powertrain may include a combustion engine with positive ignition and an air intake system as defined above, each limitation means comprising a geometrically variable intake section, and the powertrain not comprising no throttle flap.

The engine group, in particular the powertrain may not include a device for cooling an intake air, in particular it may not include a heat exchanger capable of cooling an intake air.

The engine group, in particular the powertrain as defined above may include a turbocharger.

The invention also relates to a motor vehicle comprising an air intake system as defined above and / or an engine group, in particular a powertrain as defined above.

The invention also relates to a generator comprising an air intake system as defined above and / or an engine group as defined above.

Brief description of the drawings

These objects, characteristics and advantages of the present invention will be described in detail in the following description of a particular embodiment made without limitation in relation to the attached figures, among which:

Figure 1 is a schematic view of a vehicle equipped with a powertrain according to the prior art.

FIG. 2 is a schematic view of a vehicle equipped with a powertrain according to an embodiment of the invention.

FIG. 3 is a schematic view of an engine comprising three cylinders and of an air intake system equipped with a means for limiting an air flow according to a first embodiment of the invention.

FIG. 4 is a schematic view of an engine comprising three cylinders and of an air intake system equipped with a means for limiting an air flow according to a second variant embodiment of the invention.

Figure 5 is a schematic sectional view of an engine and the air intake system according to the second embodiment of the invention.

Figure 6 is a schematic view of the air intake system equipped with a first improvement.

Figure 7 is a schematic view of the air intake system equipped with a second improvement.

Figure 8 is a graphical representation of the air pressure upstream of the intake valves during a combustion cycle.

Figure 9 is a pressure-volume diagram.

FIG. 10 is a schematic view of a powertrain according to a first alternative embodiment of the invention.

Figure 11 is a schematic view of a powertrain according to a second embodiment of the invention.

Figure 12 is a schematic view of an air intake system according to an embodiment of the invention.

Figures 13 and 14 are schematic views of an air intake system equipped with a first improvement according to an embodiment of the invention.

Description of an embodiment

Throughout the description, upstream and downstream are defined by following the direction of air flow in an engine: the air flowing from upstream to downstream. The term “air” can just as well designate fresh air taken from outside the vehicle as a gas obtained by recirculation of the exhaust gases or a gas obtained by the mixture of air and a fuel or even any other gas useful for combustion in a combustion engine.

FIG. 1 schematically illustrates a powertrain T according to the state of the art, that is to say a powertrain 1 ’which is not in accordance with the invention. This powertrain 1 ’conventionally comprises a combustion engine 2’ equipped with a housing 3 ’and here four pistons 4’ capable of sliding in four combustion chambers 5 ‘arranged in the housing 3’. The T powertrain also includes a 6 ’air intake system and a 7’ turbocharger. By observing the air intake system 6 'from upstream to downstream, it comprises an external air intake 8', an air filter 9 ', a first intake duct 10' arranged between the air filter 9 'and a compressor 1T of the turbocharger, a second intake pipe 12' arranged between the compressor 11 'and a heat exchanger 13', and a third intake pipe 14 'arranged between the heat exchanger 13 'and a throttle flap 15'. Downstream of the throttle valve flap 15 ’, the air intake system 6’ comprises an intake manifold 16 ’from which extend four branches 17’ opening respectively into each of the four combustion chambers 5 ’. Two intake valves (not shown) allow the air inlet to each of the combustion chambers to be shut off or not following a four-stroke combustion cycle. The combustion cycle conventionally comprises an air intake phase, a compression phase, a combustion phase and an exhaust phase. Each of the 17 ’branches has a constant section, which may be a circular section. The powertrain also includes an 18 '' gas exhaust system including an 19 '' exhaust manifold extended by a 20 '' exhaust line. A turbine 21 ’of the turbocharger 7’ is capable of being driven in rotation by the exhaust gases.

FIG. 2 schematically illustrates a motor vehicle V equipped with a powertrain 1 according to an embodiment of the invention. Vehicle V can be of any kind. In particular, the vehicle V can be a racing vehicle or more simply a private vehicle. The powertrain 1, in other words the engine group, comprises a combustion engine 2 equipped with a casing 3 and four pistons 4 capable of sliding in four combustion chambers 5 arranged in the casing 3. The combustion engine 2 is an engine spark ignition, that is to say an engine comprising a means of initiating the combustion of an oxidant in a combustion chamber, such as for example spark plugs. The combustion engine 2 can be a petrol engine. The powertrain 1 further comprises an air intake system 6 and a turbocharger 7. By observing the air intake system 6 from upstream to downstream, it comprises an air intake exterior 8, an air filter 9, a first intake pipe 10 arranged between the air filter 9 and a compressor 11 of the turbocharger, a second intake pipe 12 arranged between the compressor 11 and a heat exchanger 13, and a third intake pipe 14 arranged between the heat exchanger 13 and a throttle valve flap 15. The air filter 9 is used to filter the air so that undesirable particles do not enter the combustion chambers of the engine. Downstream of the throttle valve flap 15, the air intake system 6 comprises an intake manifold 16 from which extend four branches 17 opening respectively into each of the four combustion chambers 5. The branches 17 form fourth intake pipes. The term "bypass" or "intake pipe" will be used interchangeably in the rest of the document. For an engine comprising three or six cylinders, the intake manifold may be of the "fork" type, that is to say that the intake manifold comprises a single node 16b from which the branches 17 depart, as appears on Figures 6 and 7. Two intake valves 22 (visible in Figure 5) allow to shut off or not the air intake in each of the combustion chambers according to a four-stroke thermodynamic cycle. The thermodynamic cycle conventionally comprises an air intake phase, a compression phase, a combustion phase and an exhaust phase. The powertrain also includes a gas exhaust system 18 comprising an exhaust manifold 19 extended by an exhaust pipe 20. A turbine 21 of the turbocharger 7 is adapted to be driven in rotation by the exhaust gases. Alternatively, the turbocharger 7 could be replaced by an electric turbo, that is to say a turbo electrically powered. Such an electric turbo would in particular make it possible to more effectively manage the phases of operation of the engine in transient regime which could be disturbed by significant air requirements. Each of the branches 17 comprises a means 18 for limiting an air flow rate passing through the branch. The limitation means 18 and the throttle flap 15 are separate elements. The throttle flap is positioned upstream of the limiting means 18. The volume of air inside the intake system between the throttle flap 15 and the intake valves 22 can be arbitrary. The throttle flap 15 is configured and controlled so as not to disturb the operation of the limiting means 18.

Figures 3 and 4 illustrate more precisely the casing 3, the combustion chambers 5, the branches 17 and the limiting means 18. Note, the engine here comprises three cylinders or combustion chambers. In general, the invention can be implemented for an engine comprising any number of combustion chambers.

FIG. 3 illustrates a first embodiment of a limiting means

18. The limiting means 18 are produced here each by an identical venturi tube 23. By observing the venturi tube 23 from upstream to downstream, it comprises a first portion 24 of cylindrical shape, a second converging portion 25 of generally frustoconical shape, a narrow portion 26 which could also be called a "Neck", a divergent portion 27 of generally frustoconical shape. The diameter D1 of the first portion 24 can be defined so as to limit the pressure losses upstream of the air intake system. The outlet diameter D2 of the venturi tube can be imposed by the section of the cylinder head conduits. The diameter D1 can be substantially equal to the diameter D2 and significantly greater than the diameter D3 of the narrow portion 26. The narrow portion 26 defines an intake section, that is to say the section of the narrower limiting means by which passes the air flow passing through the limiting means. The venturi tubes each open out via a secondary bypass 28 into two air intake ports 29 formed in the casing 3. The valves 22 are movable between an open position in which the air present in the intake system can enter a combustion chamber, and a closed position in which valve heads 30 close each of the intake ports. The venturi tubes 23 are capable of limiting the flow of air passing through each of the branches 17 during the intake phase of the combustion cycle, that is to say when the valves 22 are in the open position. Advantageously, the use of a venturi tube does not create unnecessary turbulence in the branches, in other words it does not disturb the internal aerodynamics of the air intake system.

FIG. 4 illustrates a second embodiment of a limiting means 18. The limiting means 18 are here made each by an identical butterfly valve 31. The butterfly valve comprises a flap 32 which can be circular in shape. The flap 32 is able to pivot around one of its diameters to vary an air intake section.

As a variant, any other means of producing a means of limiting an air flow rate passing through the bypass could be used. For example, the limiting means 18 could be produced by any type of valve such as, for example, a ball valve or a guillotine valve. The limiting means could also include any type of tube provided with a section restriction or a nesting of two tubes making it possible to limit an air flow passing through it.

FIG. 12 illustrates a third embodiment of a limiting means 18 according to the invention. The limiting means 18 comprises two tubular portions 34, 35 nested one inside the other: an outer tubular portion 34 is connected upstream to the intake pipe 14 and an inner tubular portion 35 is connected downstream to a chamber 5. Preferably, the tubular portions 34, 35 are coaxial or substantially coaxial. The inner tubular portion 35 includes orifices 36 allowing the passage of air from the outer tubular portion 34 to the combustion chambers. As shown in FIG. 12, the orifices 36 have a generally elongated shape in the direction of the tubular portions and are distributed around the periphery of the interior tubular portion 35. The dimensions of these orifices are defined so as to produce the limitation of desired air flow. As a variant, the shape of these orifices could be different. According to another variant, the inner tubular portion could be connected to the intake pipe 14 while the outer tubular portion would be connected to a combustion chamber 5. The connection between the outer tubular portion 34 and the inner tubular portion 35 is sealed so that air cannot escape from the air intake system to the outside.

With reference to FIG. 5, a useful volume VU of each branch 17 can be defined as the volume delimited upstream by the limiting means 18 and downstream by an intake valve 22 in the closed position, that is to say by the valve head 30. When the limiting means is a valve able to be completely closed, the useful volume VU can be defined upstream by considering the closed position of this valve. When the limiting means comprises a section restriction such as for example a venturi tube 23, the useful volume can be defined upstream for example by a plane perpendicular to the air flow passing through the limiting means and positioned at the midpoint of the section restriction. For example, in the case where the limiting means is a venturi tube, the useful volume can be defined upstream by a plane perpendicular to the air flow and dividing the narrow portion 26 into two equal parts. One can also define the volume of the combustion chamber VC as being the volume of the combustion chamber 5 when the piston 4 reaches the bottom dead center, that is to say the maximum volume that the combustion chamber can reach at during a combustion cycle. The useful volume VU is strictly less than the volume of the combustion chamber VC. More particularly, the useful volume VU can be less than or equal to a third, or even less than or equal to a quarter of the volume of the combustion chamber VC.

FIG. 6 illustrates a first possible improvement of the air intake system according to the invention: the intake section is variable, and not fixed. Such a system makes it possible to adjust the air flow according to a given operating point. In particular, it avoids injecting air that is too cold when the engine is running at low load, and it helps cool the air when the engine is running at heavy load. In order to achieve this first improvement, it is possible to use venturi tubes whose narrow portion 26 is variable. It is also possible to use vannespapillon whose orientation of the flaps 32 is variable.

Figures 13 and 14 illustrate a particular embodiment of an air intake system with variable intake section. In this embodiment, the air intake system comprises two tubular portions

34, 35 nested one inside the other as described above and illustrated in FIG. 12. In addition, the air intake system comprises a cylinder 37 movable in translation and enveloping the inner tubular portion 35. In a first position of the cylinder 37, illustrated in FIG. 13, the cylinder 37 does not close the orifices 36. In a second position of the cylinder 37, illustrated in FIG. 14, the cylinder 37 partially closes the orifices 36. Thus, in depending on the position of the cylinder 37 the air passage section from the outer tubular portion 34 to the inner tubular portion 35 can be adjusted.

Advantageously, each of the limiting means whose intake section is variable can be electrically connected to an electronic control unit 33. The electronic control unit 33 can be able to issue control orders making it possible to modify the section of admission. In particular, it can control the orientation of the flap 32 in the case of a butterfly valve or the position of the cylinder 37 in the case of an air intake system according to the embodiment. illustrated in Figures 13 and 14. Thus, the electronic control unit 33 can vary the air flow rate passing through the limiting means.

FIG. 7 illustrates a second possible improvement of the air intake system according to the invention. This improvement consists in making the useful volume VU variable. In this perspective, the position of the limiting means 18 relative to the intake valve 22 can be variable. In particular, the position of the narrow portion 26 can be made variable when the limiting means is a venturi tube 23. Likewise, the position of the flap 32 of a butterfly valve can also be made variable. This variability can be obtained for example by sliding the venturi tube or the butterfly valve inside the bypass. Advantageously, an actuator, capable of varying the position of the limiting means, is electrically connected to the electronic control unit 33. The electronic control unit 33 may be able to issue control orders making it possible to modify the position of the means limit and thus the useful volume VU.

The installation of a limiting means 18 with variable intake section or with variable position makes it possible to adapt the air intake system to all the engine operating points. One can in particular consider using the air intake system according to the invention only for well-defined operating points and returning to conventional air intake system for use cases where it would not be not suitable (for example in case of too low air temperature or limited supercharging capacity).

Figures 8 and 9 illustrate the operation of the air intake system according to the invention. FIG. 8 represents a graph of the evolution of the air pressure upstream of the intake valves 22, that is to say the air pressure at the level of the useful volume VU, during a cycle thermodynamic. The pressure is indicated on the ordinate and the time is indicated on the abscissa. The graph is divided into four phases P1, P2, P3, P4 corresponding to the four phases of the combustion cycle: the exhaust phase P1, then the intake phase P2 of air, then the compression phase P3, then the combustion phase P4. The air pressure upstream of the valves during the exhaust phases P1, compression P3, and combustion P4 does not directly influence the combustion cycle because the intake valves are then closed. The P2 admission phase can be broken down into three successive periods P21, P22, P23.

During the first period P21, the air pressure upstream of the intake valves is high. This pressure is imposed by the configuration and / or the design of the turbocharger 7. A high pressure allows on the one hand an easy filling of the combustion chamber 5. Advantageously, the pressure is high enough so that the engine does not undergo or little loss "by pumping", that is to say loss caused by a vacuum in the combustion chamber during the descent of a piston 4 towards bottom dead center and which opposes the displacement of the piston. Advantageously, the pressure is even high enough to promote the descent of the piston. Thus, the work of the engine can be positive during the admission phase. On the other hand, high air pressure upstream of the intake valves increases the expansion potential of the air when the intake valves are opened. A person skilled in the art can adapt the design and / or configuration of the turbocharger to achieve the highest possible pressure upstream of the intake valves during this first period. The pressure of supercharged air at the outlet of the compressor 11 of the turbocharger 7 may for example be of the order of four to five Bar.

During the second period P22, an expansion of the air trapped in the useful volume occurs. The air pressure upstream of the intake valves drops. As illustrated in FIG. 5, the air initially confined in the useful volume VU now occupies the combustion chamber. A relaxation rate can be approximated by the following formula:

seen + VC ^πτ ~ seen

Thanks to this expansion, the air initially contained in the useful volume VU cools by several tens of degrees in the combustion chamber. Colder air can reduce or even eliminate the rattling phenomenon, that is, the phenomenon of abnormal combustion of gases in the combustion chamber. If the useful volume was too large, especially if it was greater than or equal to the volume of the combustion chamber, no expansion would occur and the air would not be cooled. The air flow through the limiting means 18 is significantly lower than the air flow entering the combustion chamber. As expansion occurs, the speed of air flow through the combustion chamber slows down. The air speed being a paramount parameter in the generation of the structure of an aerodynamic field in the combustion chamber, it may be advisable to limit the expansion of the air to obtain an effective aerodynamic field, that is to say ie to obtain a good homogeneity of the air and fuel mixture in the combustion chamber 5. In addition, a too low temperature in the combustion chamber can lead to difficulties in vaporizing the fuel. A person skilled in the art can adjust the expansion rate to a value which makes it possible to obtain a good compromise between the reduction in knocking and the difficulty in vaporizing the fuel. Furthermore, the expansion of the air in the combustion chamber is favorable to the generation of turbulence of the "tumble" type in the combustion chamber, which further reduces the risk of rattling.

During the third period P23, the air pressure upstream of the valves remains at a low level. The limiting means 18 prevents, at least in part, the pressurized air contained in the intake system upstream of the limiting means from entering the combustion chamber. The air entering the combustion chamber is therefore almost exclusively composed of air previously located downstream of the limiting means 18. On the one hand, this low pressure makes it possible to maintain the air present in the combustion chamber at low temperature . On the other hand, the retention of air by the limiting means makes it possible to increase the air pressure upstream of the limiting means. This retention therefore makes it possible to obtain a high air pressure for the first period P21 of the intake phase P2 of the following combustion cycle.

At the end of the P2 intake phase, the intake valves close. The useful volume VU gradually fills with air and the air pressure in the useful volume gradually increases. After some fluctuations, the air pressure upstream of the valves reaches the same level as at the start of the intake phase P2. We note that it typically takes the duration of one of the four phases of the motor for the pressure to return to its original level. It is therefore understood that the intake system according to the invention is also compatible with an engine operating on a two-stroke cycle.

FIG. 9 illustrates a diagram of the pressure in the combustion chamber as a function of the volume of the combustion chamber during a four-stroke cycle. Such a diagram, also called "pressure-volume diagram" or "Clapeyron diagram", makes it possible to visualize the work provided by the engine during a combustion cycle by observing the area defined inside the curve. The pressure inside the combustion chamber is indicated on the ordinate and the volume of the combustion chamber is indicated on the abscissa. On the same graph, the dashed line T1 represents the cycle of an engine equipped with an intake system according to the prior art, and the solid line T2 shows the cycle of an engine equipped with a admission system according to the invention. The direction in which the diagram is traversed during the combustion cycle is indicated by four arrows F1. The diagram includes two loops: an upper loop called the high pressure loop corresponding to the compression phases P3 and combustion P4, and a lower loop called the low pressure loop, corresponding to the exhaust phases P1 and inlet P2. The work produced by the engine is positive when traversing the high pressure loop, but also when traversing the low pressure loop because the air pressure during the intake phase is higher than the gas pressure during the exhaust phase. Note that the area defined by the solid line T2 is larger than the area defined by the dotted line T1 in two areas of the graph Z1, Z2, which means that the work produced by an engine equipped with a system intake according to the invention is more important than the work produced by an engine equipped with an intake system according to the prior art. A first zone Z1 illustrates the reduction in pumping losses. A second zone Z2 illustrates the gains obtained by reducing the rattling phenomenon.

The invention changes the shape of the pressure-volume diagram of the same engine and makes it possible to envisage simplifications of the powertrain. According to a first alternative embodiment of the powertrain, illustrated in FIG. 10, the heat exchanger is eliminated.

13. This removal is made possible by the drop in temperature of the air produced during the relaxation period P22 of the intake phase. The second pipe 12 is also saved since the compressor of the turbocharger is directly connected to the throttle flap. The flow of air through the air intake system is simplified and pressure losses related to the length of the air intake system or related to the passage of air through a heat exchanger are avoided. The powertrain thus obtained is also simpler to assemble and more compact. Alternatively, the heat exchanger 13 could not be deleted but be undersized compared to the heat exchangers of the state of the art.

According to a second alternative embodiment of the powertrain, illustrated in FIG. 11, the throttle valve flap is also eliminated. Preferably, this deletion is accompanied by the use of limitation means 18, the admission section of which is variable, in accordance with the first improvement described above. So you can individually adjust the amount of air admitted to each of the combustion chambers. The powertrain thus obtained is even simpler to assemble and even more compact. In addition, individual control of the quantity of air admitted into each of the combustion chambers makes it possible to envisage more precise management of the air intake.

Thanks to the invention, it is therefore possible to design powertrains reducing or eliminating the rattling phenomenon and whose architecture is simplified. In addition, the limiting means acoustically isolates the engine from the air intake system. The vibrations of the air upstream of the air intake system are therefore not reflected downstream of the air intake system. Consequently, the design constraints of the air intake line upstream of the limiting means imposed by the operation of the engine are overcome. Advantageously, the power unit according to the invention can also equip a battery recharging device for a hybrid vehicle, or even machines different from a motor vehicle, such as for example a generator.

Claims (13)

Claims 1. Air intake system (6) comprising at least one air intake pipe (17), the at least one air intake pipe (17) being intended to be connected to a chamber of combustion (5) of a combustion engine (2) with positive ignition and being intended to be closed by an intake valve (22), characterized in that it comprises a means of limitation (18) of a air flow through the at least one air intake pipe (17), and in that the at least one air intake pipe (17) comprises a useful volume (VU) delimited upstream by the limiting means (18) and downstream by an intake valve (22) in a closed position, the useful volume (VU) being strictly less than a volume of a combustion chamber (VC) at which the air intake pipe (6) is intended to be connected, said volume of a combustion chamber (VC) being defined at bottom dead center. 2. Air intake system (6) according to the preceding claim, characterized in that the limiting means (18) comprises: - a valve, and / or - a butterfly valve (31), and / or - a guillotine valve, and / or - a ball valve, and / or - a venturi tube (23), and / or - a tube comprising a section restriction, and / or - an assembly of two coaxial tubes (34, 35) an inner tube (35) comprising orifices (36) limiting an air flow between an outer tube (34) and the inner tube (35). 3. Air intake system (6) according to one of the preceding claims, characterized in that the limiting means (18) comprises a geometrically variable intake section. 4. Air intake system (6) according to one of the preceding claims, characterized in that the useful volume (VU) is variable, in particular in that the position of the limiting means (18) relative to the inlet valve (22) is variable. 5. Air intake system (6) according to one of the preceding claims, characterized in that the useful volume (VU) is less than or equal to a third, or even less than or equal to a quarter of the volume of a combustion chamber (VC). 6. Air intake system (6) according to one of the preceding claims, characterized in that the air intake pipe (17) comprises an intake manifold (16) and a plurality of branches ( 17) connected to the intake manifold (16), each branch (17) being intended to be connected to a combustion chamber (5) of a combustion engine (2) with positive ignition, and each branch (17) being intended to be closed by an intake valve (22), each branch (17) comprising means for limiting (18) an air flow rate passing through said branch (17). 7. Air intake system (6) according to one of the preceding claims, characterized in that it comprises a throttle flap (15) upstream of said limiting means (18). 8. Engine group, in particular powertrain (1), characterized in that it comprises a combustion engine (2) with positive ignition and an air intake system (6) according to one of the preceding claims. 9. Engine group, in particular powertrain (1), characterized in that it comprises a combustion engine (2) with spark ignition and an air intake system (6) according to claim 6, each limiting means (18) comprising a geometrically variable intake section, and in that the engine unit does not include a throttle valve flap (18). 10. Engine group, in particular powertrain (1), according to one of claims 8 to 9, characterized in that it does not include a device for cooling an intake air, in particular in that it does not does not include a heat exchanger capable of cooling an intake air. 11. Engine group, in particular powertrain (1), according to one of claims 8 to 10, characterized in that it comprises a turbocharger (7). 12. Motor vehicle (V), characterized in that it comprises an air intake system (6) according to one of claims 1 to 7 and / or an engine group, in particular a powertrain (1) according to one of claims 8 to 11. 13. Generating set, characterized in that it includes a system 5 air intake (6) according to one of claims 1 to 7 and / or a power unit according to one of claims 8 to 11.