FR2867517A1 - Exhaust gas recirculation process for four cylinder engine, involves recirculating exhaust gas from one cylinder having maximum pressure at exhaust pipe, towards inlet pipe of another cylinder having minimum pressure at inlet pipe - Google Patents

Abstract

The process involves recirculating exhaust gas from a cylinder (1), when it is at maximum pressure at its exhaust pipe, towards an inlet pipe of a cylinder (2) when it is at minimum pressure at the inlet pipe, during a pre-determined time. The direction of the circulation of the gas is reversed for realizing an air injection at the exhaust pipe of the cylinder (1). An independent claim is also included for a four cylinder engine implementing an exhaust gas recirculating process.

Description

1 2867517

  The present invention relates to internal combustion engines spark ignition or compression ignition, naturally aspirated or supercharged.

  Exhaust gas recirculation, commonly referred to as exhaust gas recirculation (EGR), on internal combustion engines is a technique used to reduce fuel consumption, reduce nitrogen oxide emissions or improve engine performance. supercharged spark ignition. Its feasibility is nevertheless dependent on the difference in pressure between the exhaust gases and the intake air. For some engines, including supercharged engines, there are operating points for which exhaust gas recirculation is impossible, due to the adverse pressure gradient that exists between the exhaust and the intake.

  Typically, an EGR circuit takes a portion of the exhaust flow of the engine to reintroduce it to the intake, and the maximum flow rate of recirculated gas depends on the relative overpressure of the exhaust gas with respect to the intake air. This maximum flow is zero (and therefore reintroduction is impossible) when the exhaust pressure is lower than the intake pressure. The RPM zone (effective average pressure) that is unfavorable to recirculation is minimized by optimizing the permeability of the EGR circuit, but this is not sufficient to achieve the optimum EGR rate targets for all operating points. engine: EGR is required for points where the exhaust pressure is naturally lower than the intake pressure, for example supercharged engines at low engine speeds, or very high levels of EGR are needed for operating points where the pressure difference between intake and exhaust is low.

  In existing EGR circuits, the sampling point is unique, located on the exhaust manifold, which implies that the exhaust pressure seen by the EGR circuit is the average of the pressure oscillations due to the puffs of the different cylinders. Likewise, the introduction point 2 2867517 is frequently unique, and the intake pressure thus also incorporates all the oscillations. Solutions exist with one introduction point per cylinder, but in this case, oscillations of the instantaneous pressure at the intake are not exploited in the design of the EGR circuit.

  Another solution consists, in supercharged engines, in moving the point of introduction upstream of the compressor. In addition to the clogging of the compressor, this solution has the disadvantage of significantly increasing the volume of the circuit, which is problematic for the development of transients. Other documents, such as US 6102014, US 6263672 or US 20020073978 have addressed the issue of pressure gradients in the pressure circuit and have proposed various measures that, once again, do not exploit oscillations of the instantaneous pressure. .

  The present invention aims to maximize the operating area of the EGR circuit, while maintaining a compact architecture.

  The invention achieves its goal by means of an exhaust gas recirculation method for an offset cycle multi-cylinder heat engine, the exhaust phase of at least one at least one first cylinder being concomitant with the admission phase. at least one second cylinder, an exhaust gas recirculation system being provided between the exhausts of at least some cylinders and the admissions of at least some cylinders, at least one control valve being interposed on the control system. recirculation, characterized in that the exhaust gas of the first cylinder is recirculated for a predetermined time when it is substantially at a maximum of exhaust pressure towards the inlet of the second cylinder when it is substantially at a minimum pressure on admission. In other words, the recirculation of the gases is synchronized and is arranged between the rolls so that it is always done, preferably directly, from a maximum pressure to the exhaust of a cylinder to a minimum of pressure at the same time. intake of another cylinder, which in practice is possible due to the phase shift of the cylinders between them.

  The invention also relates to a multi-cylinder thermal engine with an offset cycle, the exhaust phase of at least one at least one first cylinder being concomitant with the intake phase of at least one second cylinder, a recirculation system of exhaust gas being provided between the exhausts of at least some cylinders and the admissions of at least some cylinders, at least one control valve being interposed on the recirculation system, characterized in that the recirculation system comprises a branch connecting the exhaust of the first cylinder to the exhaust of the first cylinder, a valve being interposed in said branch to open the flow for a predetermined time.

  In other words, according to the invention, the exhaust pressure maxima are made to coincide with the pressure minima on admission. This can be achieved in the case of a four-cylinder engine, by associating the exhaust duct of each station with the intake duct of the station which is in advance of a quarter of a period (a half-turn engine) : in this way, when a cylinder is in exhaust phase (maximum pressure), it is likely to feed that of its neighbors who is in the admission phase (minimum pressure), which maximizes the pressure difference between intake and exhaust and therefore the potential flow of EGR.

  The piloting of each valve interposed in the recirculation legs of the EGR system by a fast actuator (that is to say capable of opening or closing in a time less than a quarter or preferably one eighth of an engine revolution ) makes it possible to synchronize the opening of the EGR circuit with the exhaust pressure puffs.

  According to the invention, it may be advantageous, punctually, to reverse the direction of circulation to achieve an air injection to the exhaust. For this, it restricts a given time the opening of the valve in the hollow of the exhaust pressure, which allows a flow in the opposite direction of the flow EGR and thus supplies fresh air exhaust ducts: this comes back to use the EGR circuit as IAE circuit (exhaust air injection).

  Advantageously, the recirculation circuit comprises several recirculation branches between the exhaust of a cylinder and the intake of another cylinder offset by a half-turn motor.

  Advantageously, the length of the recirculation legs is substantially equal and the branches can be integrated in the cylinder head. The invention advantageously applies to a four-cylinder engine with four recirculation branches. Although it can be implemented on any other multicylinder engine, it is in the case where the number of cylinders is a multiple of four that the invention has the most interest, to be able to redirect the puff of Escape from a given post to another post that is in the admission phase.

  Other features and advantages of the invention will emerge from the following description of an exemplary embodiment. Reference will be made to the accompanying drawings in which: FIGS. 1 to 4 schematically represent a four-cylinder engine equipped with a recirculation device according to the invention, respectively at each of the four stages of its offset ignition cycle.

  The engine shown is shown schematically by its four cylinders 1, 2, 3, and 4 whose ignition order is 1-3-4-2. Each cylinder, shown at the end, comprises an intake manifold A1 to A4, resulting in two intake valves 5, and an exhaust manifold E1 to E4, starting from the two exhaust valves 6. The recirculation of the exhaust gases exhaust is effected by means of four branches 12, 24, 31, 43 connecting by withdrawal the exhaust pipes El, E2, E3, E4 of each cylinder 1, 2, 3, 4 to the inlet A2, A4, Al , A3 of another cylinder 2, 4, 1, 3, chosen so as to put in communication cylinders out of phase by a quarter period, that is to say half a motor revolution. The length of the branches in the drawing is schematically represented. In fact, in space, the length of the four branches is chosen to be substantially equal, so that the transit time of the flushes of gas passing through them is the same for all the stations, which guarantees a good distribution of the EGR rate. cylinder cylinder.

  In each branch 12, 24, 31, 43 recirculation is interposed a fast actuator valve 7, able to open and close the EGR circuit in a very short time in front of the engine cycle (less than a quarter of a motor revolution, and preferably less than one eighth) and capable of modulating the pressure drop of this circuit. The four valve actuators 7 are connected by links not shown to a control module, also not shown. The actuators can operate in all or nothing, the flow of gas being then controlled by the opening time of the valve, which is all the easier to achieve that the opening and closing times are short compared to the duration of puffs.

  The operation of the device of the invention is as follows: In FIG. 1, the cylinder 1 is in the exhaust phase and the cylinder 2 is in the intake phase. The valve 7 placed on the recirculation link 12 opens for a period of time adapted to the target EGR rate (the valves 7 of the other links are closed). It is known that the escape time is broken down into two phases: the exhaust puff, which lasts about a quarter of a turn, during which the pressure in the cylinder equilibrates with the exhaust pressure, then the repression which also lasts a quarter turn. The maximum gas pressure during the exhaust flash is about 50% of the exhaust gas flow. It is this phase that is exploited to maximize the rate of EGR: the opening of the valve 7 considered is limited to the exhaust breeze if we aim for a maximum rate of EGR, and for a different time if we aim for an intermediate flow of EGR. Then the valve 7 of the branch 12 is closed.

  In Figure 2, a quarter turn later, it is the cylinder 3 which is in the exhaust phase while the cylinder 1 is in the intake phase. It is then the valve 7 of the branch 31 which opens at a given moment to let a puff of exhaust gas to the inlet of the cylinder 1.

  In FIG. 3, a quarter turn later, that is to say a half-turn after the start of the escape of the cylinder 1, it is the cylinder 4 which is in the exhaust phase whereas the cylinder 3 is in the admission phase. It is then the valve 7 of the branch 43 which opens a determined time to let a puff of exhaust gas to the inlet of the cylinder 3.

  Finally, in Figure 4, at the last time, the cylinder 2 is in the exhaust phase while the cylinder 4 is in the intake phase. It is then the valve 7 of the branch 24 which opens a determined time to let a puff of exhaust gas to the inlet of the cylinder 4.

Then the cycle starts again.

  It is possible to have in each branch a heat exchanger sized to cool the exhaust gas if necessary. The heat exchange function may optionally be incorporated into the cylinder head design, providing for specific cores for the circulation of the EGR.

Claims (2)

7 2867517 Claims   1) Exhaust gas recirculation method for a multi-cylinder thermal engine (1, 2, 3, 4) with an offset ignition cycle (1- 3-4-2), the exhaust phase of at least one first cylinder (1) being concomitant with the intake phase of at least one second cylinder (2), an exhaust gas recirculation system being provided between the exhausts of at least some cylinders and the admissions at least some cylinders, at least one control valve being interposed on the recirculation system, characterized in that the exhaust gas of the first cylinder (1) is recirculated for a predetermined time when it is substantially at a maximum exhaust pressure to the inlet of the second cylinder (2) when substantially at a minimum of inlet pressure.   2) Process according to claim 1, characterized in that one punctually reverses the direction of circulation to achieve an injection of air exhaust.   3) A multi-cylinder thermal engine (1, 2, 3, 4) with an offset ignition cycle (1-3-4-2), the exhaust phase of at least one at least one first cylinder (1) being concomitant with the intake phase of at least one second cylinder (2), an exhaust gas recirculation system being provided between the exhausts of at least some cylinders and the admissions of at least some cylinders, at least a control valve being interposed on the recirculation system, characterized in that the recirculation system comprises a branch (12) connecting the exhaust of the first cylinder (1) to the inlet of the second cylinder (2), a valve ( 7) being interposed in said branch (12) to open the flow for a given time. i0   2867517 8 4) Motor according to claim 3, characterized in that it comprises several branches (12, 24, 31, 43) for recirculation between the exhaust of a cylinder and the intake of another cylinder shifted by a half-turn motor.   5) Motor according to claim 4, characterized in that the length of the recirculation legs (12, 24, 31, 43) is substantially equal.   6) Motor according to any one of claims 3 to 5, characterized in that it is a four-cylinder engine (1, 2, 3, 4) with four recirculation legs (12, 24, 31). , 43).   7) Motor according to any one of claims 3 to 6, characterized in that the actuation time of each valve (7) is less than half a motor revolution, and preferably a quarter motor revolution.