FR2844009A1 - INTAKE AIR CIRCUIT FOR A HEAT ENGINE WITH A TURBOCHARGER - Google Patents

Abstract

The invention relates to an intake air circuit for a heat engine (10) comprising a main air duct (16) connecting a turbocharger (18) to the engine intake (12) and a main cooler (20 ) mounted on the main air duct to cool the charge air sent to the engine intake. The main charge air cooler (20) is installed on the engine (10), preferably in an air intake plenum (40) that the engine contains, while a secondary exchanger (36) for the The charge air is placed upstream of the main cooler (20) on the main air duct (16). Application to diesel engines of motor vehicles.

Description

Intake air circuit for thermal engine with a turbocharger

  The invention relates to the field of internal combustion engines

  turbocharger, in particular for motor vehicles.

  It relates more particularly to an intake air circuit 10 for a heat engine provided with a

  turbocharger, of the type comprising a main air duct connecting the turbocharger to the engine intake and a main cooler mounted on the main air duct for cooling the charge air supplied to the engine intake.

  Heat engines used on motor vehicles, and in particular diesel engines, are most often fitted with a turbocharger to improve engine performance.

  The turbocharger, driven by the engine exhaust, produces pressurized air, also called "charge air", which is sent to the engine intake. Thus, a turbocharger heat engine is supplied by pressurized air, unlike the conventional heat engine which is supplied by air at atmospheric pressure. However, since the air coming from the compressor is at a high temperature, it is necessary to cool it before sending it to the engine intake, so that the latter

  can operate under optimal conditions.

  This is the reason why a charge air cooler (abbreviated RAS) is used which is placed at the outlet of the turbocharger to lower the temperature of the charge air. It is known for this to use a main air / air type cooler which cools the charge air by heat exchange with an external air flow.

  It is also known to have, upstream of the main air / air type cooler, a secondary exchanger which is water cooled, which is also called "precooler" (term 10).

  We also know that diesel engines are usually equipped with a particle trap to limit the emission of harmful particles into the environment. It is known to reduce the noise due to combustion and to facilitate the regeneration of this particulate trap by heating the intake air with another exchanger, called "intake air heater" ("RAA"). for short), which is supplied by the engine cooling water. The presence of these different exchangers, in particular that of the main charge air cooler, and of their different connection conduits has the drawback of occupying a large volume under the engine hood. This goes against the requirements of current automobiles, in which the space allocated to equipment, in particular under

  the engine hood is more and more limited.

  One solution is to reduce the size of this main cooler 30, but this is of course to the detriment of the performance of the latter, and then requires the use of a

  larger secondary exchanger.

  The object of the invention is in particular to overcome this drawback. 35 It aims in particular to optimize the operation of the intake air circuit of turbocharged engines

  equipped with a charge air cooler.

  To this end, the invention provides an intake air circuit of the type defined in the introduction, in which the main charge air cooler is installed on the engine, while a secondary exchanger for charge air. is placed upstream of the main cooler on the duct

main air.

  Thus, the charge air is first precooled by the secondary exchanger and then cooled by the cooler.

  main which is installed on the engine.

  This allows greater freedom to install the main cooler on the engine, while benefiting from the

  precooling carried out by the secondary exchanger.

  The main cooler is therefore designed each time to adapt to the engine which receives it, while the exchanger

  secondary can be made up of standard elements.

  This also has the advantage of sending to the main cooler supercharged air already precooled by the action of the secondary exchanger.

  Preferably, the main charge air cooler is located in an air intake plenum (also called air intake chamber) that the engine comprises. This makes it possible to integrate the main air cooler into the plenum and to limit the size of the latter while simplifying the circulation circuit and limiting the

associated connections.

  According to another characteristic of the invention, the intake air circuit comprises a bypass duct directly connecting the engine intake to the main air duct, at a point located downstream of the secondary exchanger and upstream of the main cooler, as well as selection means mounted at the intersection of the main air duct and the bypass duct to send the charge air coming from the secondary exchanger, either to the cooler

  main either directly at the engine intake.

  Thus, thanks to this bypass duct, it is possible to send the charge air from the turbocharger and the exchanger directly to the engine intake.

  secondary, bypassing the main cooler.

  This has the advantage, in particular during an acceleration of the engine, of improving the response time of this engine.

  On the other hand, in normal operating mode, the selection means direct the supercharged air, already precooled, to the main cooler to produce a flow of cooled air which is sent to the intake of the engine.

  In the sense that it is used here, the term "admission"

  generally designates the intake manifold which receives the charge air and which directs it towards the cylinders of the engine.

  In engines of the aforementioned type, it is also known to recirculate part of the exhaust gases by sending them to the intake manifold in order to re-burn them in the engine cylinders and reduce the emission of harmful gases.

  According to another characteristic of the invention, the main air duct comprises an adjustment valve used to control the flow rate of charge air sent to the intake of the engine.

  In a preferred embodiment of the invention, the selection means comprise an upstream valve placed downstream of the secondary exchanger and upstream of the main cooler, for selectively directing the charge air 5 either towards the main cooler or to the bypass duct. The invention allows different implementations of the main charge air cooler on the engine. As already indicated, in a particularly advantageous embodiment, the main charge air cooler is located in the air intake plenum (air intake chamber) that the engine comprises. 15 This solution makes it possible to remove connecting conduits and,

  therefore, to limit the size.

  In this latter embodiment, a closure flap located in the plenum can be provided, downstream of the main charge air cooler, to prevent the charge air sent directly to the intake of the

  engine to flow back to the main cooler.

  Furthermore, because the main charge air cooler is supplied with precooled air, the main cooler can be formed in part from a material with lower thermal resistance than the secondary charge air exchanger. Thus in an advantageous embodiment, the main charge air cooler comprises a plastic casing, for example made of polyamide, while the secondary charge air exchanger 35 comprises a metal casing, for example made of an alloy

aluminum or stainless steel.

  According to yet another characteristic of the invention, the secondary charge air exchanger is located at

  distance from main cooler.

  Even if the performance of the main cooler is insufficient, for example due to an insufficient volume for its installation, the secondary exchanger makes it possible to achieve sufficient overall performance due to the precooling action that it performs. 10

  In the following description, made only as

  For example, reference is made to the appended drawings, in which: - Figure 1 shows an air intake circuit according to the invention in a first mode of operation where the precooled charge air is sent directly to the 'engine intake; - Figure 2 shows the intake air circuit of Figure 20 1 in a second mode of operation where the precooled charge air is sent to the main charge air cooler; - Figure 3 is an overall perspective view of an engine 25 and a circuit according to Figures 1 and 2, without the heat exchanger for cooling the recirculated exhaust gases; - Figure 4 and Figure 5 are respectively a top view and a side view corresponding to Figure 3; and - Figure 6 is a detail of Figure 5 showing the

  structure of the selection valve.

  Reference is first made to FIG. 1 which represents a heat engine 10, in particular a diesel engine, intended for a

  motor vehicle, in particular a passenger vehicle.

  The engine 10 includes an intake manifold 12 (hereinafter called "intake" for simplicity) and an exhaust manifold 14 (hereinafter called "exhaust" for simplicity). The engine 10 is supplied by an intake air circuit comprising a main air duct 16 connecting a turbocharger 18 to the intake 12 of the engine. The turbocharger 18 is driven by the exhaust gases from the engine and is supplied by outside air. It produces a pressurized air flow, called "charge air", which is sent to the engine inlet 12. The main air duct 16 supplies a main cooler 20 of charge air (called "RAS" for short) which is installed on the engine 10, as will be seen in detail below. This cooler has the function of cooling the charge air 20 by heat exchange with the liquid of a secondary cooling circuit (not shown). he

  it is therefore an air / water type heat exchanger.

  In a manner known per se, the exhaust 14 of the engine is connected to an exhaust duct 22 to which is connected a valve 24 which allows part of the gases to be recirculated to the engine

  exhaust through a duct 26.

  Downstream of the valve 24 is mounted a heat exchanger 30 30 also called "exhaust gas recirculation cooler" (English term) whose function is to cool the recirculated exhaust gases which are sent to the engine. The exhaust gases thus recirculated are burned again, together with the intake air, in the engine cylinders to improve combustion and reduce the emission of harmful gases into the environment. The intake air circuit further comprises a secondary exchanger 36 for the charge air, which is placed upstream of the main cooler 20. This secondary exchanger, also called a "precooler", has the function 5 of pre-cooling the charge air before it is cooled by the main cooler 20. Like the main cooler 20, the secondary exchanger 36 is an air / water type exchanger. It is usually traversed by the engine coolant. This exchanger can also perform the function of heating the intake air to reduce noise and facilitate regeneration of the trap.

particles (not shown).

  In the circuit of the invention, a bypass duct 32 15 directly connects the main air duct 16, at a point located downstream of the secondary exchanger 36 and upstream of the main cooler 20, at the inlet 12 of the engine. A selection valve 34 (also called an "upstream valve") is placed between the secondary exchanger 36 and the main cooler 20, at the intersection of the main air duct 16 and the bypass duct 32. The selection valve 34 is also placed at the intersection of a duct 33 leading to the main cooler 20. The function of this selection valve is to direct the charge air, which has been precooled by the secondary exchanger 36, ie towards the cooler main 20 via conduit 33, either directly

  at the engine inlet 12 via the bypass duct 32.

  The selection valve 34 is advantageously a three-way type valve 30 actuated by a micromotor and controlled by an appropriate control circuit which takes account of the parameters

  of the heat engine.

  The main cooler 20 is installed on the engine 10, and more particularly in the air intake plenum 40 (also called air intake chamber), which allows

  to offer greater freedom of installation to the main cooler 20. The secondary exchanger 36 is in turn placed at a distance from the main cooler 20. This makes it possible to offer maximum volume to the main cooler 5 and therefore to obtain optimal performance from it. However, if the volume available for the main cooler is insufficient to allow it to have the required performance, the latter will nevertheless be achieved thanks to the combined action of the secondary exchanger and the main cooler.

  Since the main cooler 20 receives already precooled charge air, it can be formed in part from a material with lower thermal resistance than the secondary exchanger 36. Thus, in an exemplary embodiment, the main cooler 20 comprises a plastic casing, such as polyamide (in particular PA6.6), while the secondary exchanger 36 comprises a metallic casing, advantageously made of aluminum alloy or, if the temperature conditions

require, stainless steel.

  A closing flap 42 is installed in the plenum 40, downstream of the main cooler 20, to prevent the charge air 25 sent to the intake 12 of the engine from flowing back to the main cooler. The shutter can be, for example of the register type, which makes it possible to limit its

  footprint. An actuator 44 is used to control the shutter.

  The device of the invention operates as follows.

  In the operating mode of FIG. 1, the selection valve 34 directs the precooled charge air, which comes from the secondary exchanger 36, bypassing the main cooler 20. This precooled charge air 35 is directed directly to the intake of the engine 12, together with a portion of the recirculated exhaust gases, through the adjustment valve 24 which thus makes it possible to control the recirculation flow rate of the exhaust gases. Through

elsewhere, the flap 42 is closed.

  In this operating mode, the volume of air between the turbocharger 18 and the inlet of the engine cylinders is reduced, which improves the response time of the engine.

  engine, especially during acceleration.

  In contrast, in the normal operating mode as shown in Figure 2, the selector valve 34 directs the pre-cooled charge air to the main cooler

implanted in plenum 40.

  The valve 34 directs the precooled charge air to the main cooler 20 located in the plenum 40. On leaving the main cooler 20, the charge air passes through the flap 42 which is open, to gain

engine intake 12.

  The shutter 42 can possibly take intermediate positions between the closed position of FIG. 1 and

  the open position of Figure 2.

  The intake air circuit of the invention thus makes it possible to offer numerous installation possibilities for the main cooler, due to its installation on the engine. In addition, in all operating modes, the charge air is cooled beforehand, which improves the performance of the engine. It also offers the advantage of being able to send the precooled charge air either directly to the engine intake or via the main cooler. The first operating mode makes it possible to limit the volume of air contained in the exchangers 35 and the air ducts, and to improve the response time of the

  engine, especially when accelerating.

  In the various embodiments of the invention, the control elements, in particular the selection means and the shutter controls, are controlled by an appropriate control circuit (not shown). This circuit takes account of the operating parameters of the heat engine, in particular the injection parameters, the engine load and the flow rate.

recirculated gases.

  Figures 3 to 5 are different views of an engine and a circuit according to Figures 1 and 2, the heat exchanger 30 for cooling the recirculated exhaust gases is not shown. The elements common with Figures 1 and 2 are designated by the same reference numerals. These figures show in particular the layout of the elements of the circuit 15 with respect to the motor 10. FIG. 6 shows how the selection valve 34 makes it possible to direct the charge air either towards the duct 32 or towards the duct 33. The invention finds application in vehicle engines

  automobiles, including passenger vehicles.

Claims (9)

claims   1. Intake air circuit for a heat engine provided with a turbocharger, comprising a main air duct 5 (16) connecting the turbocharger (18) to the intake (12) of the engine (10) and a main cooler (20) mounted on the main air duct for cooling the charge air supplied to the engine intake, characterized in that the main charge air cooler (20) is installed on the engine (10 ), and in that a secondary exchanger (36) for the charge air is placed upstream of the main cooler (20) on the duct main air (16).   2. Intake air circuit according to claim 1, characterized in that the main cooler (20) of charge air is located in an air intake plenum (40) that includes the engine.   3. Intake air circuit according to one of claims 1 and 2, characterized in that it comprises a bypass duct (32) directly connecting the intake (12) of the engine to the main air duct ( 16), at a point downstream of the secondary exchanger (36) and upstream of the cooler   main (20) of the charge air, as well as selection means (34) mounted at the intersection of the main air duct (16) and the bypass duct (32) to send the charge air coming from from the secondary exchanger 30 (36), either to the main cooler (20),   either directly at the engine intake (12).   4. Intake air circuit according to claim 3, characterized in that the main air duct (16) comprises an adjustment valve (28) serving to control the air flow of   boost sent to engine intake.   5. Intake air circuit according to one of claims 3 and 4, characterized in that the selection means comprise an upstream valve (34), placed downstream of the secondary exchanger (36) and upstream of the main cooler (20), 5 to selectively direct the charge air to either   the main cooler (20), either towards the bypass (32).   6. Intake air circuit according to one of claims 10 2 to 5, characterized in that it comprises a closing flap   (42) located in the plenum (40), downstream of the main cooler (20) of charge air, to prevent the charge air sent directly to the intake (12) of the engine from flowing back to the main cooler. 15   7. Intake air circuit according to one of claims 1 to 6, characterized in that the main cooler (20) of charge air is partly formed from a material with lower thermal resistance than the exchanger. secondary 20 (36) of charge air.   8. Intake air circuit according to claim 7, characterized in that the main cooler (20) of charge air comprises a plastic casing, for example polyamide, while the secondary exchanger (36 ) charge air comprises a metal casing, for example of a metal alloy or of stainless steel.   9. Intake air circuit according to one of claims   1 to 8, characterized in that the secondary exchanger (36) of charge air is located at a distance from the cooler main (20).