FR2942003A1 - SUPERSIFIED DIESEL TYPE INTERNAL COMBUSTION ENGINE AND METHOD OF CONTROLLING AIR FLOW IN SUCH A MOTOR - Google Patents

Abstract

A supercharged diesel type internal combustion engine comprising: a particulate filter 12 and a controlled exhaust louver 14 mounted in the exhaust pipe; a partial recirculation loop of the low-pressure exhaust gas including a controlled recirculation valve 16, said loop connecting the exhaust pipe 11, downstream of the particulate filter with the air inlet pipe 4, in upstream of the supercharger 6; and an electronic control unit 21 capable of receiving engine operating parameter values and controlling different engine components; characterized in that the electronic control unit is capable of determining the pressure losses experienced by the flow of exhaust gases and by the air admitted into the engine, the electronic control unit comprising means for calculating position setpoint values of the recirculation valve 16 or the exhaust flap 14 from setpoints of the air flow rate admitted into the engine, as a function of said pressure drops.

Description

B07-3546EN - AxC / EVH

Société par Actions Simplifiée known as: RENAULT s.a.s. Internal combustion engine of the supercharged diesel type and method for controlling the air flow rate in such an engine Invention of: LEBERRUYER Nicolas NOTH Frédéric GUINOIS Arnaud LOMBARDIN Olivier Jacques BUIS Emmanuel

FIELD OF THE INVENTION The present invention relates to the control of an internal combustion engine, that is to say to the engine management technique. with all of its sensors and actuators. The supercharged diesel type internal combustion engines comprising a partial recirculation loop of the exhaust gases will mainly be considered. The set of control laws or software strategy and characterization parameters such as the different calibrations of the engine are contained in a computer or electronic control unit (ECU). Standards limiting the amount of pollutants produced in the exhaust of a vehicle, including nitrogen oxides (so-called NOx, where x varies depending on the oxide in question) and soot particles, are increasingly severe. In order to comply with these standards, it is known to provide on a diesel type engine, a partial exhaust gas recirculation loop (called EGR for, in English, Exhaust Gas Recirculation) part of the exhaust gas is then reintroduced to the engine. 'admission. Therefore, the mixture of gases admitted to the engine is composed of fresh air from the compressor, mixed with exhaust gases from the exhaust manifold. A controlled valve is generally inserted to regulate the flow of recycled exhaust gas (called EGR valve). The recycled exhaust gases being inert with respect to combustion have the effect of reducing the maximum combustion temperature and thus reducing the excess oxygen compared with the same engine without exhaust gas recirculation. . However, the formation of nitrogen oxides is favored during a combustion whose temperature and oxygen content are high while the formation of soot particles is favored by a low oxygen level. The partial recirculation of the exhaust gas therefore has the direct consequence of reducing the quantity of nitrogen oxides and of increasing the number of soot particles resulting from the combustion. In order to overcome this increase in soot particles, a particulate filter is installed in the exhaust line between the turbine of the turbocharger and the silencer, which may for example be composed of a set of microchannels in which the major part soot particles are trapped. Once the filter is saturated with particles, it should be emptied by burning the particles, during a phase called regeneration. This regeneration is triggered at a suitable time and is performed by a temperature rise produced by a heater or by specific engine settings that have the effect of increasing the temperature of the gases passing through the filter. In order to further reduce the amount of nitrogen oxides produced by the combustion, it has been imagined to cool the mixture of gases admitted to the engine by means of an air / water cooling device placed in the gas recirculation loop. exhaust. The reduction of the temperature of the gases admitted to the engine makes it possible to introduce a larger mass of exhaust gases since the filling of the engine increases with the decrease in the temperature of the admitted mixture. The quantity of nitrogen oxides emitted thus decreases both under the effect of the decrease in temperature and under the effect of the increase in the mass of the recycled exhaust gases.

It has also been conceived to have a low-pressure exhaust gas recirculation loop which draws the exhaust gas at the outlet of the particulate filter downstream of the turbine of the turbocharger and reinjects it upstream of the compressor. Such a low pressure recirculation loop is more advantageous than a conventional high pressure recirculation loop which draws the exhaust directly into the exhaust manifold and feeds back into the intake plenum, downstream of the compressor. In a high pressure recirculation loop, in fact, the recycled exhaust gas is not filtered and may foul the recirculation loop, the recirculation valve and the intake plenum and the engine. In order to best determine the trade-off between the amount of nitrogen oxides and soot particles produced for a given operating point of the engine, it is important to be able to precisely regulate the rate of the exhaust gases recycled via the engine. the air flow introduced through the air filter and admitted into the engine. Such a regulation of the air flow is generally done by acting on two organs, namely on the one hand, the control valve of the recycled exhaust gas or EGR valve located in the low-pressure recirculation loop, and, on the other hand, an exhaust flap, mounted in the exhaust line downstream of the tapping of the recirculation loop, and upstream of the silencer installed in the exhaust line. Patent application US 2004/0006978 discloses the use of a low-pressure exhaust gas recirculation loop in which the stitching of the exhaust gases to be recycled is made between the particulate filter and the silencer , the return of the exhaust gas being made between the air filter and the compressor. A controlled recirculation valve or EGR valve, as well as a chiller device, are mounted in the low pressure recirculation loop. This also includes a venturi device creating a vacuum that sucks the recycled exhaust gas. US Patent 5,806,308 and US Patent Application 2005/0045407 propose to remove the venturi and replace it with an exhaust flap placed in the exhaust line. It is then possible to create a pressure difference across the EGR valve, independent of the operating point of the motor. The patent application WO 2007/066033 (RENAULT) proposes a method for controlling a supercharged engine with a low pressure recirculation loop with regulation of the intake air flow, by acting on the EGR valve disposed in the recirculation loop. and an exhaust flap mounted in the exhaust line. The difference between the set point and the measured value for the intake air flow is sent to an air regulator which translates this difference into a position setpoint. This setpoint is sent to a setpoint separator which provides two separate setpoints, one for the position of the EGR valve and the other for the position of the exhaust flap. Although the device proposed in this prior document is satisfactory, however, it is found that its calibration is complex and that the control law lacks robustness, the regulator must not only compensate for disturbances but also take into account the non-linearity of the system. regulate constituted by all of the EGR valve and the exhaust flap. The object of the present invention is to improve this regulation and to make the regulator more robust, better suited to systems to be controlled and simpler to calibrate. In one embodiment, a supercharged diesel type internal combustion engine comprises: a particulate filter and a controlled exhaust flap, mounted in the exhaust duct; and a partial recirculation loop of low pressure exhaust gas including a controlled recirculation valve, said loop connecting the exhaust pipe, downstream of the particulate filter with the air inlet pipe, upstream of the compressor of overeating. An electronic control unit is capable of receiving engine operating parameter values and controlling different engine components. The electronic control unit is able to determine the pressure losses experienced by the flow of exhaust gas and by the air admitted into the engine. The electronic control unit notably comprises means for calculating position setpoint values of the recirculation valve or the exhaust flap from set values of the air flow rate admitted into the engine, as a function of said losses of charge. The flow control value of the exhaust gas recirculated by the low pressure recirculation loop is separated into two position setpoints, one for the recirculation valve and the other for the exhaust flap. For optimum operation with minimum fuel consumption, only one of these devices is controlled, the other being kept in the open position. The choice of the organ to be controlled is made from the pressure losses experienced by the exhaust gases and by the air admitted into the engine. In an advantageous embodiment, the electronic control unit comprises means for comparing an estimated value of the pressure drop experienced by the flow of the exhaust gases in the recirculation loop when the recirculation valve or the shutter exhaust are in the fully open position, with the sum of the pressure drops experienced by the flow of air in the air supply pipe and by the flow of gases in the exhaust pipe, these pressure losses being estimated from the set values of the air flow. The electronic control unit preferably comprises means for deriving from the comparison made, a set point value of the recirculation valve or the exhaust flap which is not in the open position. Advantageously, the electronic control unit comprises means for modeling the pressure drop in the form of memorized maps of the pressure drop coefficients as a function of the position of the recirculation valve and the exhaust flap. The regulation of the intake air flow is thus done using a modeling of the losses of loads experienced by the exhaust gases in the low-pressure recirculation loop and in the exhaust line as well as the pressure drops experienced by the air admitted into the engine. This results in a linearization of the system controlled by the air regulator, which improves the performance of the regulation. In another embodiment, the engine may further include a high pressure partial exhaust gas recirculation loop including a controlled high pressure recirculation valve. The electronic control unit then comprises means for calculating position reference values of the high pressure recirculation valve. In another aspect, there is provided a method of controlling the air flow rate in a supercharged diesel type internal combustion engine comprising: a particulate filter and a controlled exhaust flap, mounted in the exhaust duct; and a partial recirculation loop of low pressure exhaust gas including a controlled recirculation valve, said loop connecting the exhaust pipe, downstream of the particulate filter with the air inlet pipe, upstream of the compressor of overeating. According to this method, the pressure losses experienced by the flow of the exhaust gas and by the air admitted into the engine are determined and a parameter related to the admission of the gases into the engine is regulated by acting on the valve of the engine. recirculation or on the exhaust flap taking into account said pressure losses. Advantageously, the air flow admitted into the engine is regulated by acting solely on the exhaust flap, the recirculation valve being kept in the open position, the position of the exhaust flap being determined from the pressure drop which results. Alternatively, the flow rate of air admitted into the engine is regulated by acting solely on the recirculation valve, the exhaust flap being held in the open position, the position of the recirculation valve being determined from the pressure drop which in results. The invention will be better understood from the study of an embodiment described by way of non-limiting example, and illustrated by the accompanying drawings in which: - Figure 1 shows the main elements of an internal combustion engine of supercharged diesel type according to the invention; FIG. 2 illustrates the main components of an air flow control system; and FIG. 3 illustrates a practical embodiment of a set separation device according to the invention. As illustrated in FIG. 1, a combustion engine 1, for example a Diesel type engine, comprises four cylinders 2. The fresh air admitted into the engine 1 passes through an air filter 3 before being conveyed. by an air supply line 4 which comprises a flowmeter 5, at the inlet of a compressor 6, which is part of a turbocharger 7 comprising the compressor 6 and a turbine 8 mounted on the same mechanical shaft 9, the compressor 6 is thus rotated by the turbine 8. The exhaust gases from the combustion in the engine 1, taken up by the exhaust manifold 10, are fed through a pipe 10a to the inlet of the turbine 8 where they give up some of their energy in order to drive the compressor 6 in rotation. At the outlet of the turbine 8, the exhaust gases flowing in the exhaust pipe 11 pass firstly through a filter. particles 12, then a silent device 13, before being rejected to the atmo sphere. A controlled exhaust flap 14 is mounted in the exhaust pipe 11 upstream of the silencer 13. Of course it will be understood that other exhaust gas treatment devices could also be mounted in the exhaust line, for example an oxidation catalyst or the like. A partial recirculation loop of the low-pressure exhaust gas referenced 15 includes a controlled recirculation valve 16 called EGR valve and connects the exhaust pipe 11 to the air inlet pipe 4 upstream of the compressor 6. tapping of the recirculation loop 15 on the exhaust pipe 11 is disposed upstream of the exhaust flap 14. In this way, a portion of the exhaust gas having already passed through the expansion turbine 8 and the particulate filter 12 is taken up by the recirculation loop 15 to be mixed with the intake air in line 4, the mixture being compressed by the compressor 6. The compressed mixture whose temperature has been raised due to the compression is brought by the pipe 17 to a heat exchanger 18, which allows the cooling of the mixture before admission into the engine 1 through the intake pipe 19 and the intake manifold 19a. A controlled intake flap 20 is further mounted in the intake duct 19 downstream of the exchanger 18.

An electronic control unit (ECU) referenced 21 in Figure 1, receives various information on the operation of the engine and associated bodies and allows the calculation of different signals for actuators necessary for the control of the engine.

The regulation of the air flow admitted into the engine 1 is done by acting on both the position of the EGR valve 16 and on the position of the exhaust flap 14. For this purpose, the electronic control unit 21 comprises a regulator 26 or air regulator which receives on its input the difference between an air flow setpoint value Qair_cons and the airflow value Qair as measured by the flowmeter 5 and fed to the electronic unit The output signal of the air regulator 26 represents the flow rate QEGR LP of the exhaust gases in the low-pressure recirculation loop 15. It will be noted that the regulation can also be made on the flow rate. recycled exhaust gas Qegr or the recycled exhaust gas rate (Tegr), these different quantities being connected to each other by the relations: = Qegr Qegr Qair Qair Qair Qair Qair qqqqq Qair is the flow of gases admitted da ns the engine 1.

The electronic control unit 21 also comprises a setpoint separation block 28 which receives the output signal QBP from the air regulator 26 and which is capable of determining position setpoints, respectively for the EGR valve 16 and for the exhaust flap 14. The set point for the EGR valve 16 is transmitted to the valve 16 via the connection 29. The set value for the exhaust flap 14 is transmitted to the flap 14 via the connection 30. a connection 20a is also illustrated in FIG. 1 which enables the electronic control unit 21 to transmit a position reference value to the admission flap 20.

Figure 2 illustrates more precisely one embodiment of the air regulator 26. In the example shown, the regulator 26 is a proportional integral type regulator. The input signal which corresponds to the difference between the measured airflow Qair and the setpoint Qaircop is brought to the input of the proportional block 29 which has a gain Kp and to the input of integral block 30 which has a gain K. It is also possible, as shown in the example of Figure 2, to provide a pre-positioning of the reference signal so as to accelerate the response of the control. For this purpose, the setpoint value Qair cops is fed to a pre-positioning block 31, which also receives an estimate of the flow Qmot of the gases admitted into the engine and which is capable of emitting a pre-positioning signal brought by the connection 32 on an adder 33 which also receives the respective output signals of the proportional branch and the integral branch of the regulator 26. The output signal QEGR BP is fed, as has been said previously, to the setpoint separation device 28. The setpoint separation is made from the calculation of pressure losses in the partial recirculation circuit of the low pressure exhaust gas, as illustrated in Figure 3 by way of example. If we consider the whole of the recirculation loop 15, we note that the atmospheric pressure is both upstream of the air filter 3 and downstream of the silencer 13. We can therefore write the equation: (Patmo Pamont flap) + (Pamont flap to Paval FaA) + (Paval FaA to Patmo o (1)

where Patmo is the atmospheric pressure, measured by a sensor not shown in the figures, Pavai FaA is the pressure downstream of the air filter 3, and Pamont flap is the pressure upstream of the exhaust flap 14. The pressure losses incurred by the exhaust gas during the passage of the exhaust flap 14 and the silencer 13, depend on the set air flow rate and the fuel flow injected into the engine. The value of these pressure drops is:

In the same manner, it is possible to define the pressure drop experienced by the exhaust gases in the recirculation loop 15, which depends on the flow rate QEGR BP of the exhaust gases in the said recirculation loop. low pressure. This loss of load is:

dPBP Paval FaA ùPamont component

Finally, the pressure drops experienced by the air passing through the air filter, which depend on the set air flow, can be written as:

dPFaA = Pavai FaA ùPatmo

We can therefore write taking into account equation (1),

dP olet ù dPBP + dPFaA = 0 (2) 30 which indicates that at each moment, we have:

dP olet + dPFaA = dPBP (3) To determine which actuator to use for regulation, i.e. either the EGR valve 16 or the exhaust flap 14, the reference separation block 28 takes into account the value of the estimated pressure drop in the low-pressure recirculation loop, when the EGR valve 16 is open, and for a recycled exhaust gas flow QEGR BP equal to the set-point value of the exhaust gas flow rate recycled (called EGR). This estimated value of pressure loss is noted open dPBp. As can be seen in the embodiment of the separation block 28, illustrated by way of example in FIG. 3, a comparison block 34 receives on one of its inputs the value of this estimated pressure drop dPBp open. and on its other input, the sum of the pressure losses of the air filter dPFaA and the open exhaust flap, this sum being calculated in an adder 34a which receives the measurements made respectively by the sensors 23 and 25. The loss of open pore charge is the pressure drop caused by the exhaust flap 14 in the open position. The output signal of the comparator 34 is brought to a decision block 35 which can then transmit an activation signal to one of the control blocks 36a or 36b. When the control block 36a is activated, the position setpoint of the EGR valve 16 emitted on the output connection 37a keeps the EGR valve in the open position. The output connection 38a transmits a signal which triggers a calculation in the block 39, for the determination of the position reference value of the exhaust flap 14. This position reference value can be obtained for example by modeling the loss of charge undergone by the flow of gas through the exhaust flap 14, that is to say by means of a map stored in the electronic control unit 21, the value of the pressure drop coefficient in function of the position of the exhaust flap 14. There is indeed the relation:

dvvolet kvolet Y.volet cons (4) where:

Qvoiet cons = Qmot_cons ùQEGR BP + Qin) where Qvoiet cons is the setpoint value of the flow through the exhaust flap, Qtnj is the fuel flow injected into the engine and Qmot cons is the setpoint of the flow of the gases admitted into the exhaust flap engine. Indeed, the flow rate through the exhaust flap 14 is equal to the flow rate of the gases from the engine less the flow rate of the recycled gases in the partial recirculation loop 15. The pressure drop coefficient kvoiet is a function of the position of the flap d 'exhaust. It is therefore possible, unlike to define a function giving the position of the exhaust flap as a function of the pressure drop coefficient.

Taking into account the previous equation, one can calculate the coefficient of loss of load kvoiet by the equation:

kvoiet = dPvoiet / Qvoiet cons is: kvoiet dvvoiet I (Qmotcons + Qinj ùQEGRBP) When the block 36b is activated instead, a position set signal for the exhaust flap 14 is given by the connection 38b, in order to maintain the flap 14 in the open position. On the output connection 37b, on the contrary, a signal triggers a calculation in the calculation block 40 to determine the position reference value for the EGR valve 16. The calculation is done in the same way as previously in the calculation block. , based on a modeling of the pressure drop across the recirculation valve 16. In fact: dPBP kvanne QEGR BP As previously, the coefficient of pressure drop across the recirculation valve EGR 16, denoted kvanne, depends on the position of the valve, so that by reversing the function, it is possible to determine the position of the valve corresponding to a determined coefficient of pressure loss. A map memorized in the electronic control unit makes it possible to provide the values of the pressure drop coefficient as a function of the position of the valve. Depending on the result of the comparison made by the comparator 34, two situations are then possible. In a first situation, the estimated pressure drop of the low-pressure recirculation loop 15 when the EGR valve is open is greater than the sum of the pressure losses experienced through, respectively, the air filter and the shutter. exhaust in the open state. So we have :

In this situation, the decision block 35 emits a signal so as to activate the calculation block 39. The EGR valve 16 is kept wide open and the position of the position of the exhaust flap 14 is determined in FIG. function of the pressure drop: 20 dl open flap = dPBP open ù dPFaA In a second situation on the contrary, the estimated pressure drop in the EGR recirculation loop for an open position of the EGR valve is less than the sum of the losses of load undergone 25 through the air filter and the open exhaust flap, we have:

dPBP open <dPF + open gun The decision block 35 activates the calculation block 40, so that the exhaust flap 14 is kept in the wide open position and the position of the EGR valve 16 is determined according to the loss of charge in the low-pressure recirculation loop according to the formula: dPBP = dPFaA + dPVole open where dPVolet open is the estimated pressure drop of the assembly formed by the exhaust flap 14 and the silencer 13 when the exhaust flap is maintained in the open position, for a flow rate through the exhaust flap equal to the set air flow rate increased fuel flow injected into the engine. All of the pressure losses mentioned above are estimated from the recycled flow rate reference values QEGR BP and the flow rate of gases admitted into the engine Qmot cons. Thanks to this control architecture using physical modeling by estimating the pressure losses in the partial recirculation loop of the low-pressure exhaust gas, it is possible to linearize the system controlled by the air regulator, which improves the performance of regulation. It should be noted that the same control structure can be used in the case where two exhaust gas recirculation circuits are provided. In this case, the low pressure recirculation loop mentioned above is associated with a second partial exhaust gas recirculation loop, this time at high pressure, connecting the exhaust manifold directly to the intake pipe. In this case, it will be possible to modify the pre-positioning value of the regulation as illustrated in FIG. 2, taking also into account the estimation of the flow rate of the recycled exhaust gases at high pressure according to the relation:

Qmot = Qair + QEGR BP + QEGR HP where QEGR BP is the flow of the exhaust gases recycled at low pressure in the loop 15, and where QEGR HP is the flow rate of the exhaust gases recycled at high pressure.

The flow rate of the recycled exhaust gases at high pressure can be estimated using the Barré Saint Venant formula, according to the formula: / ~ Pavt LEGRHP Seff .BSV JR.T vt Where Seff is the passage section of the control valve EGR of the high pressure recirculation loop, Pavt is the pressure upstream of the turbine 8, which is also the pressure at the inlet of the high pressure EGR valve. Tavt is the temperature upstream of the turbine which is also the temperature at the inlet of the high pressure EGR valve, Peol is the pressure in the intake manifold connected to the intake pipe.

The BSV function, which groups together several terms of the Barré Saint Venant formula, is a function that varies according to the pressure ratio downstream and upstream of the high pressure EGR valve.

Claims (8)

REVENDICATIONS1. A supercharged diesel type internal combustion engine comprising: a particulate filter (12) and a controlled exhaust flap (14) mounted in the exhaust duct; a low pressure partial exhaust gas recirculation loop (15) including a controlled recirculation valve (16), said loop connecting the exhaust pipe (11), downstream of the particulate filter with the inlet pipe air (4) upstream of the supercharger (6); and an electronic control unit (21) capable of receiving engine operating parameter values and controlling different engine components; characterized in that the electronic control unit is capable of determining the pressure losses experienced by the flow of exhaust gases and by the air admitted into the engine, the electronic control unit comprising means for calculating setpoint values of the position of the recirculation valve (16) or the exhaust flap (14) from setpoints of the air flow rate admitted to the engine, as a function of said pressure drops. 2. Motor according to claim 1 wherein the electronic control unit comprises means (34) for comparing an estimated value of the pressure drop experienced by the flow of exhaust gas in the recirculation loop when the valve of recirculation or the exhaust flap are in the fully open position, with the sum of the pressure drops experienced by the air flow in the air supply line and by the flow of gases in the exhaust pipe these pressure losses being estimated from the air flow setpoint values. 3. Motor according to claim 2 wherein the electronic control unit comprises means (35, 39, 40) for deriving from the comparison performed, a set position value of the recirculation valve or the exhaust flap which is not in the open position. 4. Motor according to claim 3 wherein the electronic control unit comprises means for modeling the pressure drop in the form of stored maps of the pressure drop coefficients as a function of the position of the recirculation valve and the flap. exhaust. 5. Motor according to one of the preceding claims further comprising a partial recirculation loop of the high pressure exhaust gas including a controlled high pressure recirculation valve, the electronic control unit comprising means for calculating setpoint values. position of the high pressure recirculation valve. A method of controlling air flow in a supercharged diesel type internal combustion engine comprising: a particulate filter (12) and a controlled exhaust flap (14) mounted in the exhaust duct; a low pressure partial exhaust gas recirculation loop (15) including a controlled recirculation valve (16), said loop connecting the exhaust pipe, downstream of the particulate filter with the air supply line upstream of the supercharger; characterized by the fact that the pressure losses experienced by the exhaust gas flow and by the air admitted into the engine are determined and a parameter related to the admission of the gases into the engine is regulated by acting on the recirculation valve or on the exhaust flap taking into account said pressure drops. 7. The method of claim 6 wherein regulates the flow of air admitted into the engine by acting solely on the exhaust flap, the recirculation valve being held in the open position, the position of the exhaust flap being determined to from the resulting loss of load. 8. The method of claim 6 wherein regulates the flow of air admitted into the engine by acting only on the recirculation valve, the exhaust flap being held in the open position the position of the recirculation valve being determined from the resulting pressure drop.