FR2877054A1 - DIESEL INTERNAL COMBUSTION ENGINE OR GASOLINE WITH DIRECT INJECTION TO INCREASED BURNER GAS RATE - Google Patents

Abstract

In this diesel internal combustion engine or gasoline direct injection, a valve lift system controls the at least partial opening of an exhaust valve (E2) during at least a portion of the intake phase, and architecture of at least the exhaust duct (3) whose valve (E2) opens during the intake phase is transverse flow type intended to create a swirl exhaust.

Description

Diesel Internal Combustion Engine or Direct Rate Injection Petrol

increased flue gas

  The invention relates to a diesel internal combustion engine or gasoline direct injection, especially for a motor vehicle.

  The depollution of the engines is today a priority in the developments made by the manufacturers; it requires the reduction of NOx emissions at the engine output.

  Among the solutions currently chosen to achieve the objectives in depollution, one is to reintroduce the gases from the combustion towards the admission through a recirculation circuit for the partial loads - it is the so-called EGR circuit (of English exhaust gas recirculation) - the other consists in improving the gas exchange in the combustion chamber by creating appropriate movements of the gas masses, including so-called swirl vertical swirl movements.

  The burnt gases enclosed in the cylinder of the combustion chamber consist on the one hand of the residual burned gases (GBR) which could not be emptied at the end of the preceding engine cycle and the external burned gases (EGR) which are brought by an external circuit connecting the exhaust to the intake. To promote the clearance, it is desirable to provide a high rate of flue gas. Strategies to increase EGR rates have already been proposed. They consist, for example, in attaching to the turbine wheel, in addition to the air compressor wheel, a second compressor wheel specifically dedicated to the compression of the EGR recirculating gases. This is the case in WO-A-00/79117 and US-A5937650. But in any case, the increase in the EGR rate reaches the limits set by the capacity of the external EGR system. We can therefore try to increase the GBR rate. To this end, US-A-2003/0196646 has proposed the opening of an exhaust valve during the amission phase, which effectively generates GBR.

  On the majority of diesel engines for road transport, an air movement generally having the axis of the cylinder as the axis of rotation is generated during the intake phase of air; this swirling movement is commonly referred to as swirl. When the piston rises from the bottom dead center, approximately at the end of the intake of the fresh air, towards the top dead center, this movement is geometrically amplified by the piston bowl. Most recent inventions have tended to improve the amplification process and to optimize the mixture obtained between the fuel injected near the top dead center and the fresh air. To reach the targets in depollution, it is desirable to increase the rate of swirl partial load while keeping a swirl cylinder head low, suitable for operation under full load. The cylinder head swirl is a compromise between low-load need (high swirl) and full load (low swirl). Because of this compromise, the cylinder head swirl is too high for full load, resulting in a reduced cylinder head permeability, detrimental to air filling and fully loaded performance. The strong swirl, necessary partial load, is possibly provided by a variable swirl device, for example by partial or complete closure of a conduit or intake ducts to the cylinder head inlet. But such devices cause significant losses of permeability to increase the swirl. So the compromise swirl / permeability is degraded. To optimize the swirl, the document RU-A2 177 553 discloses an orientation of the exhaust ducts in a cylinder head with four valves per cylinder, to generate a swirl movement during the exhaust phase.

  Other improvements have been proposed, for example that taught in document US-A-2004/0060284 describing a method for regulating the temperature of the exhaust gases and the engine air flow rate by means of a control system. variable valve lift, says WA (English variable valve actuation), the objective being to promote the reduction of emissions by the post-processing system.

  The invention aims to further improve the depollution performance of a diesel internal combustion engine or gasoline direct injection, including such a motor already equipped with an external EGR system.

  The invention achieves its goal thanks to a diesel internal combustion engine or gasoline direct injection, the engine comprising at least one cylinder closed by a movable piston and a cylinder head into which at least one intake duct and at least one duct an exhaust valve, via an exhaust valve and an intake valve whose four-stage openings depending on the crankshaft angle of the engine are controlled by a valve lift system controlling the opening of at least one exhaust valve during an exhaust phase between the bottom dead center and the top dead center of the piston and the opening of at least one intake valve during an intake phase between the top dead center and the neutral position the bottom of the piston, said system being adjusted to allow at least partial opening of an exhaust valve during at least part of the intake phase, characterized in that the architecture of at least the duct of ed Exhaust valve which opens during the intake phase is of cross flow type to create a swirl exhaust. Thus, according to the invention, the valve lift system, such as a VVA system, is operated to modify the opening of the exhaust valves (phasing, and / or spreading, and / or lifting) until reopening. in the intake phase, on the one hand, to provide the burned gases necessary for the depollution (reduction of NOx) and, on the other hand, to create and / or increase the swirl. It is thus possible to have a variable swirl without the lapse of cylinder head permeability associated with systems based on the closure of at least one of the intake ducts. It is also possible to increase the swirl in partial load, while keeping a swirl cylinder head rather low, suitable for operation under full load.

  Advantageously, the engine comprises an external exhaust gas recirculation system. The invention then makes it possible to provide high levels of flue gases (EGR + GBR), beyond the capacity of the external EGR circuit. In addition, the possibility of replacing the EGR with the GBR increases the temperature of the gases enclosed in the cylinder, which is beneficial for reducing emissions of unburnt hydrocarbons (HC) and CO at the beginning of the clean-up cycle when the exhaust gases are relatively cold.

  According to a first embodiment of the invention, the cylinder head of the engine is two valves per cylinder.

  According to a second embodiment, the cylinder head is four valves per cylinder, two exhaust and two intake.

  In this case, in a first variant, the valve lift system controls the opening of a first exhaust valve during the exhaust phase and a second exhaust valve during a part of the exhaust phase. admission. In a second variant, the valve lift system controls the opening of the two exhaust valves during the exhaust phase and only one of these two exhaust valves during part of the intake phase.

  Other features and advantages of the invention will appear on reading an embodiment of the invention, with reference to the accompanying drawings, in which: FIG. 1 is a schematic view of a cylinder head with two valves per cylinder; intended to produce a swirl according to the invention.

  Figure 2 is a schematic view of a four-valve cylinder head for producing a swirl according to the invention.

  - Figure 3 shows three exhaust valve lift laws (a), (b) and (c) according to three embodiments of the invention.

  FIG. 1 therefore presents an embodiment for a cylinder head (not shown in detail, except by the trace 1 of a cylinder cooperating with the cylinder head to form a combustion chamber) with two intake valves respectively A and exhaust E. The cylinder head ducts, respectively intake 2 (ADM) and exhaust 3 (ECH), are arranged in a so-called cross flow flow architecture (in English, cross-flow) which allows the generation a swirling movement SE by the exhaust duct 3 in the same direction of rotation as that SA generated by the intake duct 2.

  The law governing the lift of the intake and exhaust valves as a function of the crank angle is given in Figure 3 (a), in solid lines for the exhaust valve E and in dashed lines for the valve of the crankshaft. admission A. The characteristic shape of the opening law is recognized in turn by the valves for the four-stroke cycles, first the exhaust valve E between the bottom dead center (BDC) and the top dead center (PMH) (exhaust phase) then the inlet valve A between the PMH and the new PMB (intake phase). According to the invention, the exhaust valve E is reopened during the intake phase (part 10 of the curve): by reopening this exhaust valve, the rate of GBR and the swirl SA + SE are increased. The phasing and the duration of this opening are chosen to regulate the GBR rate and the swirl rate required at each operating point.

  FIG. 2 presents a possible embodiment for a cylinder head with four valves per cylinder, respectively intake A1 and A2 and exhaust El and E2, the intake ducts 2 and exhaust 3 are also arranged according to a cross-flow architecture allowing the creation of a swirl. This point can be referred to the aforementioned document RU-A-2177553.

  Figure 3 (b) shows a possibility of valve lift law, wherein the opening of the valve E2 is completely shifted into the intake phase (curve portion). This choice allows a fairly high GBR rate, because it does not completely drain the cylinder in the previous cycle (the valve E2 is indeed closed during the exhaust phase). FIG. 2 illustrates the SE2 swirl resulting from the open exhaust duct coexisting with the SA1 + SA2 swirl resulting from the open intake ducts.

  Fig. 3 (c) shows another possibility of valve lift law, in which the two exhaust valves E1 and E2 operate normally during the exhaust phase and re-open the valve E2 during the intake phase (part 10 of curve). This choice allows a good emptying during the exhaust phase, so no more pumping work of the engine and yet an increase in the rate of GBR and swirl.

  For cylinder heads with four valves per cylinder, the invention is better suited to a pattern at 00, like that shown in Figure 2. However, the proposed principle can be applied to other architectures of admissions / exhaust provided that the exhaust valves can be opened independently of the intake valves. Similarly, other combinations of conduits (tangential or helical) are possible. If swirl is not required for fully loaded combustion, an architecture can be adopted in which the intake ducts are designed to provide maximum permeability (such as gasoline cylinder ducts without tumble-type aerodynamic motion). or swirl) to promote full load filling. The swirl required for partial load operation will then be generated entirely by one of the exhaust ducts.

  On the other hand, other combinations of the intake (eg, staggered) or exhaust (eg, different maximum lift and / or opening) valve lift laws may be envisaged which will allow obtain different combinations of GBR rate and swirl rate for optimal results at each point of partial load operation.

  Finally, this invention can be used with any variable valve opening system, from the simplest VVT (variable valve timing) on one of the exhaust valves without variable lift system, to the most complex (VVT + VVL or WA). The valve activation system can be mechanical, hydraulic or electromagnetic. These systems are known in themselves and will not be further described.

  Finally, the external EGR system is not shown in the figures, but this is conventional and it is possible to refer, for example, to the documents mentioned at the top of this memo.

Claims (6)

  1) Diesel internal combustion engine or direct injection gasoline, the engine comprising at least one cylinder closed by a movable piston and a cylinder head into which at least one intake duct (2) and at least one exhaust duct ( 3), via an exhaust valve (E, E1, E2) and an intake valve (A, Al, A2), whose openings in four stages depending on the engine crankshaft angle are controlled by a system valve lift controlling the opening of at least one exhaust valve during an exhaust phase between the bottom dead center and the top dead center of the piston and the opening of at least one intake valve during a intake phase between the top dead center and the bottom dead center of the piston, said system being adjusted to allow at least partial opening of an exhaust valve (E, E2) during at least a part of the phase d admission, characterized in that the architecture of at least the conduit of exhaust (3) whose valve (E2) opens during the intake phase is of transverse flow type to create a swirl exhaust.   2) Engine according to claim 1, characterized in that it comprises an external exhaust gas recirculation system.   3) Engine according to any one of claims 1 or 2, characterized in that the cylinder head is two valves (A, E) per cylinder.   4) Engine according to any one of claims 1 or 2, characterized in that the cylinder head is four valves per cylinder, two exhaust (El, E2) and two intake (Al, A2).   5) Engine according to claim 4, characterized in that the valve lift system controls the opening of a first exhaust valve (El) during the exhaust phase and a second exhaust valve (E2 ) during the admission phase.   6) Engine according to claim 4, characterized in that the valve lift system controls the opening of the two exhaust valves (E1, E2) during the exhaust phase and a single (E2) of these two exhaust valves during the intake phase.