FR2896545A1 - Internal combustion engine e.g. direct injection internal combustion engine for motor vehicle, has heat exchanger unit placed between exhaust circuit and intake circuit which has distributor with intake branches - Google Patents

Abstract

The engine has a heat exchanger unit placed between exhaust circuit (20) and intake circuit (10). The heat exchanger has a branch circuit (40) that includes a chamber connected to an upstream channel and down stream channel in the fluid flow direction. The intake circuit has an air conduit (11) and intake air distributor (13) which is provided with the intake branches. The exhaust circuit has exhaust branches connected to an end of a cylinder.

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention

  generally relates to internal combustion engines. The invention more particularly relates to an internal combustion engine with injection, direct or indirect, comprising an intake circuit and an exhaust circuit. It finds a particularly advantageous application for internal combustion engines spark ignition. BACKGROUND OF THE INVENTION 10 When direct or indirect injection direct-ignition internal combustion engines operate at partial load, that is, when the inlet pressure of the fresh gases in the combustion chamber is less than a bar, the fresh gas mixture mass present in the combustion chamber is low. To ensure the stability of the combustion, it is then desirable to reduce the density of the fresh gas mixture. Most often this decrease in the density of the fresh gas mixture is achieved by lowering the pressure of the fresh gas mixture. However, due to the low pressure of the mixture, a pumping phenomenon occurs at the beginning of the thermodynamic cycle of the engine. This pumping phenomenon, in part load, leads to overconsumption of fuel and an increase in polluting emissions. Several solutions exist to decrease the density of the fresh gas mixture while increasing the pressure of this mixture of fresh gas. The first solution is to dilute the fresh gas mixture with flue gas. However, the dilution of the fresh gas mixture by the flue gases must be limited so that the combustion of the fresh gas mixture remains stable. The second solution consists in reducing the effective displacement of the engine by using variable distribution means. According to this solution, the opening of the intake valve is delayed or the closure of this intake valve is anticipated. The volume of the gas mixture which is enclosed inside the cylinders is thus reduced, which increases the density and therefore also the pressure of the gas mixture since the temperature of the gas mixture is not affected. Such a solution is however complex and expensive to implement. OBJECT OF THE INVENTION The present invention proposes a new engine whose fuel consumption is reduced, especially when operating at partial load. For this purpose, it is proposed according to the invention an internal combustion engine injection, direct or indirect, comprising an intake circuit and an exhaust circuit, wherein there is provided means for heat exchange between the circuit exhaust and the intake circuit.

  The air present in the intake circuit recovers heat from the exhaust gas by heat transfer between the exhaust duct and the air intake circuit. Thanks to the invention, for partial load operation of the engine, the temperature of the air circulating in the intake circuit is increased before its introduction into the cylinder. The increase in the temperature of the air introduced into the cylinder makes it possible, after mixing with the injected fuel, to obtain a fresh gas mixture whose temperature is increased and therefore of lower density. The fresh gas mixture is not diluted and has a sufficient pressure, close to atmospheric pressure, to limit the work of pumping during admission. Increasing the temperature of the fresh gas mixture also promotes the propagation of combustion in the combustion chamber. This improvement in the propagation of combustion makes it possible to have a combustion of the fresh gas mixture in the combustion chamber faster and therefore more stable. The increase in fresh gas mixing temperature also makes it possible to increase the vaporization speed of the injected liquid fuel. Increasing the vaporization rate of the liquid fuel facilitates homogenization of the air mixture with the fuel constituting the fresh gas mixture. Since the thermodynamic conditions are favorable for the combustion of the fresh gas mixture, the engine according to the invention can therefore function normally in partial load with a fuel mixture of richness 1, while limiting the fuel consumption and the polluting emissions.

  In addition, the propagation of combustion being rapid, it is possible to proceed to the dilution of this mixture of fresh gas with flue gas, even for low torque and low speed operation phases, which further reduces the consumption of fuel and certain pollutant emissions such as nitrogen oxides (NOx). According to a first advantageous characteristic of the engine according to the invention, the heat exchange means comprise at least one bypass circuit coming from the intake circuit which envelopes at least a part of the exhaust circuit.

  With the branch circuit according to the invention, wherein is circulated a certain volume of air from the intake circuit so that it is heated and then reintroduced into the intake circuit to be mixed with another volume of air. unheated air and admitted into the cylinder, it is possible to precisely control the temperature of the air introduced into the cylinder. It is indeed possible to have an extended range of temperature values for the air admitted into the cylinder, since it is possible to reach a minimum temperature, the temperature of the atmosphere, by closing the inlet of the circuit bypass, and a maximum temperature, depending on the technical specificities of the engine and the efficiency of the heat exchange, by fully opening the branch circuit.

  Other advantageous and non-limiting features of the motor according to the invention are the following: each branch circuit envelops an exhaust branch of the exhaust circuit; the intake circuit comprising an air duct and an air intake manifold provided with intake branches, each branch circuit is connected at one end to the air duct upstream of the distributor and to the other end on an intake branch of the air distributor; the heat exchange means comprise a plurality of branch circuits connected in parallel, each branch circuit being associated with a cylinder; the heat exchange means comprise a single bypass circuit on the one hand, on the air duct upstream of the air intake manifold and, on the other hand, at one end of the distribution manifold. opposite air intake to the air duct this unique branch circuit locally surrounding each exhaust branch of each cylinder; the air intake circuit comprises means for deflecting the air flow from the air duct to the bypass circuit; the air intake distributor and the bypass circuit each comprise means for regulating the air flow rate that they convey; the heat exchange means comprise at least one bypass circuit from the exhaust circuit which envelops at least a portion of the intake circuit; - the bypass circuit completely envelops the air intake manifold; the bypass circuit comprises means for regulating the flow of the exhaust gas. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description with reference to the accompanying drawings of several embodiments, given as non-limiting examples, will make it clear what the invention consists of and how it can be achieved. In the accompanying drawings: - Figure 1 is a schematic view of the engine according to the invention in low load according to a first embodiment; FIG. 2 is a schematic view of the engine of FIG. 1 in intermediate load; - Figure 3 is a schematic view of the engine of Figure 1 in heavy load; FIG. 4 is a schematic view of the engine according to the invention at low load according to a second embodiment; - Figure 5 is a schematic view of the engine of Figure 1 in heavy load; FIG. 6 is a schematic view of a first generalization of the engine according to the invention of FIG. 1 to a motor provided with several cylinders; FIG. 7 is a schematic view of a second generalization of the engine according to the invention of FIG. 1 to a motor provided with several cylinders; - Figure 8 is a schematic view of the engine according to the invention in intermediate load according to a third embodiment.

  The description below is made for a direct-injection direct-injection engine that is to say a motor that includes a fuel injector located in each cylinder. Of course, the engine according to the invention can also be a combustion engine. 5 indirect injection (or indirect multipoint) comprising an injector located in the intake duct of each cylinder. Direct or indirect injection spark ignition engines do not include a carburetor. FIG. 1 shows a part of an internal direct injection combustion engine with direct injection of a motor vehicle. This engine comprises an intake circuit 10 attached to a cylinder block provided with a plurality of cylinders 5, and an exhaust circuit 20. The intake circuit 10 comprises an air duct 11 which draws air into the cylinder. the atmosphere and which, in the direction of flow of air, opens into a distributor 13 of air intake. This intake manifold 13 is extended by intake branches 14 which open into the cylinders 5 of the cylinder block The air duct 11 comprises a butterfly flap 30 which, depending on a driver's instruction, allows an acceleration , ie a deceleration, of varying the flow of air flowing through the air duct 11 and thus into the cylinders 5. The exhaust circuit 20 comprises exhaust branches connected to one of their ends. at the corresponding cylinder 5 of the cylinder block and connected at their other end to an exhaust manifold (not shown) and then downstream of the exhaust manifold to an exhaust pipe (not shown) which exhausts the exhaust gas Advantageously, according to the invention, there is provided between the intake circuit 10 and the exhaust circuit 20 a heat exchanger device 30 between these two intake and exhaust circuits. 10, 20. According to a first embodiment shown in Figures 1 to 3, the heat exchange means 40 consist of a bypass circuit 40 which comprises a chamber 43 connected to an upstream pipe 41 and a pipe downstream 42, in the direction of flow of the fluid. The end of the upstream pipe 41 opposite the chamber 43 is stitched on the air duct 11 to a connection node N1 located upstream of the inlet distributor 13, here at the junction between the air duct 11 and the inlet distributor 13. The end of the downstream pipe 42 opposite the chamber 43 is stitched on the intake branch 14 to a connection node N2. The inlet chamber 43 envelops part of the exhaust circuit 20. Here, the chamber 43 envelops part of the exhaust branch 21. Advantageously, as explained below for the operation of the engine, the fresh air which circulates in the chamber 43 passes around a portion of the exhaust branch 14 enveloped by the chamber 43. Thus, the calories of the exhaust gases are transferred by the wall of the exhaust branch to the fresh air which circulates in this chamber 43. There is provided at the first connection node NI deflection means 31 of the air of the air duct 11 to the bypass circuit 40. These deflection means 31 are here constituted by a valve 31 whose angular position varies continuously between a first extreme position where it completely closes the inlet of the inlet distributor 13 and a second end position where it completely closes the input of the bypass circuit 40 (see Figures 1 and 3). As shown in FIG. 2, this flap 31 can vary between these two extreme positions to direct part of the fresh air directly into the intake distributor 13 and another part to the bypass circuit 40 to be heated and mixed with the fresh air from the inlet distributor 13. It is thus possible to control the temperature of the air admitted into the combustion chamber.

  As shown in FIG. 6, it is possible to generalize these heat exchange means with several cylinders 5, 5A, 5B. Here, for a three-cylinder engine 5, 5A, 5B, the heat exchange means 40 comprise, as previously described, the bypass circuit 40 associated with the cylinder 5 and two additional branch circuits 40A, 40B connected in parallel and associated with the two Other cylinders 5. The operation of the engine according to the invention is described below. As shown in FIG. 1, when the engine is operating at low load, that is to say for example when the accelerator pedal is released, the throttle flap 30 of the air duct 11 closes part of the section passage of this air duct 11 to limit the flow of air while the valve 31 closes the inlet of the inlet distributor 13. The air then passes entirely into the bypass circuit 40 through the upstream pipe 41 and then opens in the chamber 43 where it is heated by circulating around the wall of the exhaust branch 21 enveloped by the chamber 43. Then, this heated air is conveyed by the downstream branch 42 and directed towards the intake branch 14 of the corresponding cylinder 5. This heated air has a lower density and a sufficient pressure so that after mixing with the fuel and obtaining the fuel mixture, the combustion in the combustion chamber of the cylinder 5 is stable. When the engine is operating under heavy load, that is to say for example when the user depresses the accelerator pedal as much as possible, the butterfly flap 30 is in the open position so as to release the passage section of the fuel line. 11 to admit a large air flow, while the valve 31 is positioned so that it completely closes the input of the bypass circuit 40. Thus, the air from the air duct 11 is directed to the inlet distributor 13 and then in the corresponding intake branch 14 and this air has a minimum temperature. Its density is then increased, which for operation of the engine with high load can stabilize the combustion and thus reduce fuel consumption. For an intermediate load, as shown in Figure 2, the valve 31 can take a position in which it passes, on the one hand, a certain portion of the air flow from the air duct 11 in the tundish 13 and, on the other hand, the other part of this air flow in the bypass circuit 40, to be heated. Thus, the engine according to the invention makes it possible to control the temperature and the pressure of the air admitted into the cylinders, and thus also of the mixture of fresh gases, to ensure the stability of the combustion in the combustion chamber.

  In particular, the two branch circuits 40A, 40B associated with the cylinder 5A, 5B each have as for the bypass circuit 40 an upstream pipe 41, 41B which is stitched to a connection node N3 on the upstream pipe 41 of the first circuit of bypass 40 and which opens into a chamber 43A, 43B which locally envelops an exhaust branch 21A, 21B associated with the cylinder 5A, 5B corresponding. There is provided downstream of this chamber 43A, 43B a downstream pipe 42A, 42B which is stitched at its end opposite the chamber 43A, 43B on the intake branch 14A, 14B of the corresponding cylinder 5A, 5B.

  FIG. 7 shows a variant of the embodiment of FIG. 6 according to which the heat exchange means 40 comprise a single bypass circuit 40, on the one hand, on the air duct 11 upstream of the air intake manifold 13 and, on the other hand, at one end of the air intake manifold 13 opposite to the air duct 11, this single branch circuit 40 surrounding locally, by means of the chambers 43, 43A, 43B, each exhaust branch 14 of each cylinder 5. Thus, the air which passes into the branch circuit by means of the bypass valve 31 is heated during its passage through the three successive chambers and is injected directly into the intake manifold and then distributed in the intake branches 14, 14A, 14B. The temperature of the air admitted into the cylinders is therefore substantially the same for all the cylinders. Of course for a greater number of cylinders, it is necessary to add branched bypass circuits on the upstream pipe of the first branch circuit and on the exhaust branch of the corresponding cylinder.

  According to a second embodiment of the engine according to the invention shown in FIGS. 4 and 5, the heat exchange means 40 between the intake circuit 10 and the exhaust circuit 20 comprise a bypass circuit 26 which is at both ends, it is inserted on the exhaust branch 21 of the cylinder 5.

  In particular, this bypass circuit 26 comprises an upstream pipe 22, one end of which is connected to the exhaust branch 21 to a connection node M1 located near the cylinder 5. This upstream pipe 22 opens into a chamber 23 of the cooling circuit. bypass 26 which envelops a portion of the intake manifold 13 of the intake circuit 10. Downstream of this chamber 23 the bypass circuit 26 comprises a downstream pipe 24, the end opposite the chamber 23 is stitched on the branch d exhaust 21 to a connection node M2 located in the flow direction of the exhaust gas downstream of the connection node M1. There is provided in this bypass circuit 26 a butterfly flap 25 for controlling the flow rate of the exhaust gas in the branch circuit 26. The operation of the engine according to this second embodiment is described below.

  As shown in FIG. 4, when the engine is operating at low load, similarly to the first embodiment (FIG. 1), the butterfly shutter 30 closes part of the passage section of the air duct 11, which limits the flow rate. of air circulating through the distributor 13 and then by the intake branch 14. The butterfly flap 25 of the bypass circuit 26 of the exhaust circuit 20 is then fully open to have a large flow of exhaust gas in the exhaust circuit. bypass 40 so that the heat exchange between the high temperature exhaust gas passing through the chamber 23 and the fresh intake gas flowing through the distributor 13, enveloped by said chamber 43, are important.

  For operation of the engine under heavy load (Figure 5), similarly to the first embodiment (Figure 2), the butterfly flap 30 is in the open position to leave free the passage section of the air duct 11 so as to admit a large air flow in the intake manifold 13 and the intake branch 14 of the corresponding cylinder 5.

  In parallel, the butterfly flap 25 of the bypass circuit 26 of the exhaust circuit 20 is closed so as to completely obstruct the passage of the exhaust gases in the bypass circuit so that the air admitted into the intake branch 14 has a low temperature. As for the first embodiment, for operation of the engine in intermediate load, the butterfly flap 25 can take an intermediate position that allows to circulate a portion of the exhaust gas in the bypass circuit 26 and thus to heat the air circulating in the inlet distributor 13 and the intake branches 14 so that this air reaches a certain temperature. The other part of the exhaust gas is directed to the exhaust manifold and the exhaust line to be released into the atmosphere. Such multi-cylinder heat exchange means can be generalized by using a bypass circuit as described above for each cylinder and by providing in particular for each branch circuit such a chamber enclosing the part of the distributor located in the neighborhood of the corresponding intake branch. It is also possible for a motor comprising several cylinders to use a single branch circuit stitched on one of the exhaust branches associated with one of the cylinders, as explained above, and to provide a chamber that envelops the entire intake distributor. Thus, the temperature of the air admitted is the same in all intake branches and therefore in the corresponding cylinders. Preferably, as shown in FIG. 8, it is possible to replace the valve 31, which makes it possible to guide part of the air of the air duct 11 towards the distributor 13 and another part towards the bypass circuit 40, as well as the butterfly flap 30 which makes it possible to vary the flow of air flowing through the air duct II, by two butterfly flaps 32, 33. The butterfly flap 32 is located in the bypass circuit 40 while the butterfly flap 33 is located in the distributor 13 of air intake. These butterfly flaps 32, 33 constitute airflow control means conveyed by the air intake distributor 13 and the bypass circuit 40. The angular position of each of these butterfly flaps 32, 33 can vary continuously, regardless of the position of the other flap, between a first extreme position of complete shutter and a second extreme position of complete opening. Thus, thanks to these two butterfly flaps 32, 33, the flow of air to be heated through the bypass circuit 40 is independent of the cold air flow through the distributor 13 of air intake. We can then control the flow of heated air and cold air flow by means of two butterfly flaps 32, 33, on the one hand, to obtain the desired temperature of the air admitted into the cylinders 5 and other part to have a pressure gradient along the bypass circuit 40 which ensures that the heated air is sucked well by the cylinders 5 and not discharged into the intake circuit 10. The preferred arrangement of butterfly flaps 32, 33 can be applied to all the embodiments described above and to their variants. The present invention is not limited to the embodiments described and shown, but the skilled person will be able to make any variant within his mind.

Claims (11)

  An internal combustion engine with direct or indirect injection, comprising an intake circuit (10) and an exhaust system (20), characterized in that heat exchange means (40) are provided. between the exhaust circuit (20) and the intake circuit (10).   2. Motor according to claim 1, characterized in that the heat exchange means (40) comprise at least one bypass circuit (40) from the intake circuit (10), which envelops at least a portion of the circuit exhaust (20).   3. Motor according to the preceding claim, characterized in that each branch circuit (40) surrounds an exhaust branch (21) of the exhaust circuit (20).   4. Engine according to one of the two preceding claims, characterized in that, the intake circuit (10) comprising an air duct (11) and an air intake manifold (13) provided with d intake (14), each bypass circuit (40) is connected at one end to the air line (10) upstream of the distributor (13) and at the other end to an intake branch (14) of the air distributor (13).   5. Motor according to one of the three preceding claims, characterized in that the heat exchange means (40, 40A, 40B) comprise a plurality of branch circuits (40, 40A, 40B) connected in parallel, each circuit bypass (40, 40A, 40B) being associated with a cylinder (5).   6. Engine according to claim 2, characterized in that the heat exchange means (40) comprise a single branch circuit (40) transcribed on the one hand, on the air duct (11) upstream of the air intake distributor (13) and, on the other hand, at one end of the air intake distributor (13) opposite to the air duct (11), this single branch circuit (40) locally surrounding each exhaust branch (14) of each cylinder (5).   7. Engine according to one of claims 2 to 6, characterized in that the air intake circuit (10) comprises deflection means (31) of the air flow of the air duct (11). to the branch circuit (40).   8. Motor according to one of claims 2 to 6, characterized in that the air intake distributor (13) and the bypass circuit (40) each comprise means for regulating (32, 33) the flow rate of air they convey.   9. Motor according to claim 1, characterized in that the heat exchange means (40) comprise at least one bypass circuit (40) from the exhaust circuit (20), which surrounds at least a part of the circuit admission (10).   10. Motor according to the preceding claim, characterized in that the bypass circuit (40) completely envelops the distributor (13) of air intake.   11. Motor according to one of claims 9 and 10, characterized in that the bypass circuit (40) comprises means (25) for regulating the flow of the exhaust gas.