FR2914698A3 - Exhaust gas recirculation device for e.g. oil engine, has by-pass duct with valve arranged downstream of heat exchanger, relative to circulation directions of exhaust gases in duct, that includes another valve arranged upstream of exchanger - Google Patents

Abstract

The invention relates to a device and a method for recycling the exhaust gases of an internal combustion engine, the device comprising a bypass duct (2) for the exhaust gases between the exhaust pipe (3) and the intake duct (4) of the engine, which bypass duct (2) comprises a heat exchanger (21) and a first valve (22) disposed downstream of the exchanger (21) relative to the direction of flow of the exhaust gas in the bypass duct (2), characterized in that the bypass duct (2) comprises a second valve (23) disposed upstream of the exchanger (21).

Description

The invention relates to a device for recycling the exhaust gases of a

  internal combustion engine. The invention also relates to an internal combustion engine provided with such a device.

  The invention can be applied equally to a turbocharged or non-turbocharged engine, diesel or gasoline type. On internal combustion engines, the presence of an exhaust gas recirculation device (also called EGR circuit) has become widespread for questions of pollution of the engine.

  However, the presence of such a circuit modifies the air filling of the engine (intake), in particular in areas of operation of the engine at full load. The engine performance levels are therefore affected by the presence of such a circuit, for the different operating speeds of the engine. It is known that the volume of the EGR circuit and the position of the valve of said circuit, arranged in the recirculation duct of the EGR circuit, are the main factors which affect the full load filling of the engine.

  An object of the invention is to provide a device for recycling the exhaust gas of an internal combustion engine to overcome these disadvantages. Another objective is also to propose a method of controlling such a device.

  Another object of the invention is to provide an internal combustion engine provided with the device according to the invention. In order to achieve at least one of these objectives, provision is made within the scope of the invention for a device for recycling the exhaust gases of an internal combustion engine comprising an exhaust gas bypass duct between the duct exhaust and the engine intake duct, which bypass duct comprises a heat exchanger and a first valve, disposed downstream of the exchanger, relative to the direction of flow of the exhaust gas in the bypass duct, characterized in that the bypass duct comprises a second valve disposed upstream of the exchanger. The device according to the invention may also have at least one of the following characteristics: for an internal combustion engine supercharged by a turbocharger, characterized in that the bypass duct connects the exhaust duct to the intake duct between a portion of said exhaust duct situated upstream of the turbine of the turbocharger, relative to the direction of flow of the exhaust gases, and a portion of said intake duct situated downstream of the compressor, relative to the direction of flow of the gases admitted into the engine; the valves are respectively disposed at one or the other of the ends of the bypass duct. In order to achieve at least one of these objectives, a method for controlling the exhaust gas recirculation device of an internal combustion engine according to one of the preceding claims is also provided within the scope of the invention. characterized in that: o if the engine is operating at low speed, the two valves of the bypass duct are closed or kept closed; o if the engine is running at half speed, the second valve is opened or kept open on the one hand and the first valve is closed or kept closed; o if the engine is running at high speed, it opens or keeps open the first valve on the one hand and closes or keeps closed the second valve on the other hand. Other features, objects and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the appended drawings, given as non-limiting examples and in which: FIG. 1 is a diagrammatic view an internal combustion engine equipped with an exhaust gas recirculation device according to the invention; FIG. 2 represents the evolution of the corrected volumetric efficiency of the engine ricoR as a function of the engine speed N, for various states of opening / closing of the valves of the device according to the invention. The device according to the invention comprises a bypass duct 2 of the exhaust gases between the exhaust duct 3 and the inlet 4 of the engine 1. The bypass duct 2 comprises a heat exchanger 21, a first valve 22 , located downstream of the exchanger, relative to the direction of flow of the exhaust gas in the bypass duct 2. The bypass duct 2 also comprises a second valve 23, disposed upstream of the heat exchanger 21 of the EGR circuit, always relative to the direction of flow 5 of the exhaust gas in the engine 1. The valves 22, 23 may be disposed at one or other of the ends of the bypass duct 2, respectively. The engine illustrated in FIG. 1 also comprises a turbocharger consisting of a turbine 6 and a compressor 7, but this configuration has nothing to limit the invention since it can be applied to an engine without a turbocharger . The device according to the invention makes it possible, in the operating ranges of the engine where the exhaust gases do not flow from the exhaust duct 3 to the intake 4, to modulate the resonance frequencies of the exhaust duct 3. and the intake duct 4 to facilitate the filling and emptying of the cylinder or cylinders of the engine 1. The control strategies for the opening / closing of one or the two or both valves 22, 23 are thus managed as a function of the natural frequencies of the intake ducts 4 and exhaust ducts 3.

  It is thus understood that these control strategies will depend on the engine speed, this regime providing the excitation frequency of the exhaust ducts 3 and intake 4. It is illustrated in Figure 2, the evolution of the corrected volumetric efficiency of the engine flCOR as a function of the evolution of the engine speed N (rpm), and for various configurations of the open / closed state of the valves 22, 23. The curve 10 (triangle) shows the evolution of the volumetric efficiency corrected of the engine according to the engine speed, when the two valves 22, 23 are closed. Under these conditions, no exhaust gas is recirculated to the inlet of the engine 1, and the bypass duct 2 is completely closed. Neither the resonant frequency of the exhaust duct 3 nor that of the intake duct 4 is modified by that of the bypass duct 2. In fact, it has been shown that the engine's efficiency iicoR is particularly high when the engine runs at low speed, for example below 2500rpm (Figure 2).

  Curve 20 (square) shows the evolution of the corrected volumetric efficiency of the engine according to the engine speed, when the second valve 23 (upstream valve) is closed and the first valve 22 (downstream valve) is open. Under these conditions, no exhaust gas is recirculated to the inlet of the engine 1, and the bypass duct 2 is open only on the engine intake side. The resonant frequency of the intake duct 4 is therefore modified by the volume of the bypass duct 2. In fact, it has been shown that the efficiency of the engine is then particularly high when the engine is operating at high speed, for example above 4000 rpm (Figure 2). Curve 30 (diamond) shows the evolution of the corrected volumetric efficiency of the engine according to the engine speed, when the second valve 23 (upstream valve) is open and the first valve 22 (downstream valve) is closed. Under these conditions, no exhaust gas is recirculated to the intake of the engine 1, and the bypass duct 2 is open only 5 on the engine exhaust side. The resonant frequency of the exhaust duct 3 is thus modified by the volume of the bypass duct 2. In fact, it has been possible to show that the efficiency riCOR of the engine is particularly high when the engine is running at half speed, for example between 2500 and 4000 rpm (Figure 2). The control method of the exhaust gas recirculation device of an internal combustion engine can therefore be summarized as follows: if the engine is operating at low speed, the two valves 22, 23 of the duct are closed or kept closed bypass 2; if the engine is running at half speed, the second valve 23 is opened or kept open on the one hand and the first valve 22 is closed or kept closed, on the other hand; if the engine is operating at high speed, the first valve 22 is opened or kept open on the one hand and the second valve 22 is closed or kept closed.

Providing two valves within the exhaust gas recirculation device, namely a valve on either side of the heat exchanger 21 of the bypass duct 2, associated with a control strategy of these two valves. two valves 22, 23 is therefore very advantageous.

The opening / closing control of the valves, and more precisely of the first valve 22, is conventionally performed by a computer (not shown), as a function of different motor parameters under open loop conditions, and as a function of closed loop valve positioning information; the engine speed being meanwhile information to manage the operation of the second valve 23. The calculator therefore has ultimately only one parameter (actuation of the second valve) in addition to manage, compared to a classic device. 10

Claims (5)

  An exhaust gas recirculation device of an internal combustion engine comprising an exhaust gas bypass duct (2) between the exhaust duct (3) and the engine intake duct (4). , which bypass duct (2) comprises a heat exchanger (21) and a first valve (22) disposed downstream of the exchanger (21) relative to the direction of flow of the exhaust gas in the bypass duct (2), characterized in that the bypass duct (2) comprises a second valve (23) disposed upstream of the exchanger (21).   2. Device according to the preceding claim, for an internal combustion engine supercharged by a turbocharger (6, 7), characterized in that the bypass duct (2) connects the exhaust duct (3) to the intake duct ( 4) between a portion of said exhaust duct located upstream of the turbine (6) of the turbocharger, relative to the direction of flow of the exhaust gas, and a portion of said intake duct (4) located downstream of the compressor (7), relative to the flow direction of the gases admitted to the engine.   3. Device according to one of the preceding claims, characterized in that the valves (22, 23) are respectively disposed at one or the other end of the bypass duct (2).   4. A method of controlling the exhaust gas recirculation device of an internal combustion engine according to one of the preceding claims, characterized in that: - if the engine operating at low speed, is closed or kept closed two valves (22, 23) of the bypass duct (2); if the engine is running at half speed, the second valve (23) is opened or kept open on the one hand and the first valve (22) is closed or kept closed; if the engine is operating at high speed, the first valve (22) is opened or held open on the one hand and the second valve (22) is closed or kept closed.   5. Internal combustion engine (1), characterized in that it comprises an exhaust gas recirculation device according to one of claims 1 to 3.