WO2007148007A1

WO2007148007A1 - Exhaust gas recirculation system for a combustion engine of the supercharged diesel type and method for controlling such an engine

Info

Publication number: WO2007148007A1
Application number: PCT/FR2007/051451
Authority: WO
Inventors: Emmanuel Buis
Original assignee: Renault S.A.S
Priority date: 2006-06-19
Filing date: 2007-06-18
Publication date: 2007-12-27
Also published as: FR2902466A1

Abstract

Exhaust gas recirculation system for a combustion engine of the supercharged diesel type and method for controlling such an engine. System for recirculating exhaust gases at low pressure for a motor vehicle combustion engine of the supercharged diesel engine type comprising a particulate filter device (7) and an exhaust valve (19) both mounted in its exhaust line, a recirculation loop looping back between the exhaust line downstream of the particulate filter and an air intake pipe, an exhaust gas recirculation valve (10) mounted in said loop, comprising means for controlling the position of the recirculation valve and of the exhaust valve and means for regulating an operating parameter of the engine, these means being designed to act on the means that control the position of the exhaust valve, characterized in that the means for controlling the position of the recirculation valve are designed to open or close said valve fully, independently of the regulating means.

Description

Exhaust gas recirculation system for a supercharged diesel type combustion engine and method for controlling such an engine

The present invention relates to a low-pressure exhaust gas recirculation system for a motor vehicle combustion engine, supercharged diesel type, comprising a particulate filter device. The invention also relates to a method for controlling such a combustion engine.

The present invention relates to the control of combustion engines, that is to say the management of the operation of the motors by means of a set of sensors and actuators responding to software control laws according to parameters of characterization and calibration of the engine, stored in a computer called "electronic control unit" (ECU).

Standards limiting the amount of pollutants in the exhaust gases of a motor vehicle engine, in particular nitrogen oxides (NOx) and soot particles, are becoming more severe. To meet these standards, it is necessary to change the engine design. In recent years, the combustion engines thus have a recirculation loop connecting the exhaust manifold to the plenum of the intake manifold. Through this recirculation loop, a part of the exhaust gas called "EGR" (for, in English: "Exhaust Gas

Recirculation ") are reintroduced upon admission. Therefore, the mixture admitted into the engine is composed of fresh air from the compressor, mixed with EGR exhaust gas from the exhaust manifold. A valve (called "EGR" valve) can be inserted into this recirculation loop to regulate the amount of exhaust gas recycled at the intake.

The exhaust gases thus recycled and readmitted into the engine, are inert with respect to combustion and have the effect of reduce the maximum combustion temperature and excess oxygen. The formation of NOx nitrogen oxides is favored by a high temperature and a high oxygen level in the combustion while the formation of the soot particles is favored by a low level of oxygen. As a direct consequence of this, the intake of recycled exhaust gas has the effect of reducing the quantity of nitrogen oxides NOx and of increasing the number of soot particles resulting from combustion. It is therefore necessary to manage the amount of exhaust gas recycled carefully so as to obtain an acceptable compromise between the amount of NOx nitrogen oxides and the amount of soot particles.

To reduce the emissions of soot particles, a particulate filter comprising, for example, a micro-compressor assembly, is generally installed between the turbine of the turbocharger which receives the engine exhaust gas and the silent device mounted in the exhaust line. channels in which a large part of the particles are trapped. When the filter is saturated with soot particles, it is necessary to empty it by burning the particles during a phase called "regeneration". The regeneration of the particulate filter may be achieved either by a specific heating means or by a control of the operation of the engine allowing oxidation of the soot particles by the exhaust gases.

To further improve the pollution performance of diesel engines, several modifications of the exhaust gas recirculation loop have been developed.

Firstly, a heat exchanger was placed in the exhaust gas recirculation loop to cool the mixture to the intake and thus to increase the engine filling and the amount of recycled exhaust gas admitted. in the engine. According to another development, a new low-pressure exhaust gas recirculation loop has been used. Such a recirculation loop draws the exhaust gas downstream of the particulate filter between the latter and the silencer, in the exhaust line of the engine. Low exhaust The pressure thus collected is then reintroduced upstream of the compressor so that the entire mixture admitted into the engine passes through the heat exchanger acting as a cooler mounted between the compressor and the intake plenum. Since the efficiency of this cooler is high and the exhaust gases taken downstream of the particulate filter have much lower temperatures than at the engine outlet, such a low pressure recirculation loop makes it possible to obtain higher temperatures. low for the admitted mixture that in the case of a conventional recirculation loop even when it includes a cooling device. As a result, it is possible to further reduce the amount of NOx oxides produced in the exhaust by lowering the temperature. Moreover, according to this technology, the exhaust gases reintroduced into the engine contain very few soot particles since they first passed through the particulate filter contrary to what was the case in a gas recirculation loop. exhaust system of conventional type where the exhaust gas reintroduced at the intake was not filtered and fouled the recirculation loop and the intake plenum and the engine. The patent application US 2005/0006978 describes such a low-pressure exhaust gas recirculation loop in which the introduction of the recycled exhaust gas into the mixture at the intake is made by means of a venturi creating a vacuum capable of aspirating the gases to be recycled. The rate of the recycled exhaust gas in the admitted mixture is regulated by a position control of the recirculation valve mounted on the bypass branch of the recycled exhaust gas. The rate of the recycled exhaust gas is the ratio of the flow rate of these gases to the total flow rate of the mixture admitted to the engine. This rate is estimated from a measurement of three temperatures, namely the temperature of the mixture admitted downstream of the venturi, the temperature of the air upstream of the venturi and the temperature of the exhaust gas entering the venturi. In this embodiment, the pressure difference across the recirculation valve is related to the operating point of the engine. For a running point of the engine at low rotational speed, the vacuum created by the venturi is very low. As a result, the flow rate of the recycled exhaust gas is limited and related to the pressure difference across the recirculation valve.

US Patent Application 2005/0045407 and US Pat. No. 5,806,308 also disclose a low pressure recirculation loop. In these two documents, there is provided both an EGR recirculation valve in the recirculation loop and a variable orientation flap placed in the exhaust line. With such an embodiment that no longer uses a venturi as in the previous document, it is possible to create a pressure difference across the EGR recirculation valve which is independent of the operating point of the engine. However, no control law is provided in this document for proper control of the engine control.

The subject of the present invention is a system and a method for controlling a combustion engine of the supercharged diesel type with recirculation of low-pressure exhaust gases which makes it possible to take account, under the best conditions, for the regulation of the recirculation of the exhaust gases. exhaust, the instantaneous operating point of the motor while ensuring a minimum response time of the regulation. The object of the invention is also to improve the control dynamics of such an exhaust gas recirculation system.

In one embodiment, a low pressure exhaust gas recirculation system is associated with a supercharged diesel type motor vehicle combustion engine including a particulate filter device and an exhaust flap mounted in its line. exhaust. A recirculation loop is provided between the exhaust line downstream of the particulate filter and an air intake line, with a recirculation valve mounted in said loop. The system includes position control means of the recirculation valve and the exhaust flap and means for regulating an engine operating parameter, adapted to act on the control means of the position of the exhaust flap. The control means of the position of the recirculation valve are adapted to cause the opening or closing in all or nothing of said valve independently of the regulating means acting on the exhaust flap.

The regulation is done by acting only on the position of the exhaust flap, while the recirculation valve remains in the open position. The response time of the system is improved.

In a preferred embodiment, the system further comprises means for activating and deactivating the regulation means, capable of activating and deactivating the regulation means and also of acting on the means for controlling the position of the recirculation valve for causing said valve to open or close.

The activation and deactivation means may receive information concerning the operation of the engine, the condition of the control means or the environment of the vehicle and deduce from it the deactivation or activation of the exhaust gas recirculation and the regulation. In the event of deactivation, the recirculation valve remains in the closed position.

The regulating means advantageously comprise a regulator comprising an integral function. In this case, a threshold comparator is preferably provided for receiving the control signal from the position of the exhaust flap and suppressing the action of said integral function when the thresholds are exceeded.

Also preferably, the exhaust gas recirculation system comprises means for initializing said integral function during the activation of the regulation means.

It may be advantageous, to improve the dynamics of the regulation, to provide means for prepositioning the control signal of the position of the exhaust flap capable of determining a prepositioning value according to the operating point of the motor and adding this value to the output signal of the regulating means.

The quantity regulated by the regulating means may be the flow of air admitted into the engine or the recirculation gas rate or any other relevant parameter.

The set values of these quantities are preferably determined by means of mapping of set values as a function of the operating point of the engine, these maps being stored in the system.

Regulated quantities are further measured or estimated by appropriate means of determination.

Another aspect of the invention relates to a method for controlling a combustion engine of a supercharged diesel type motor vehicle with recirculation of low pressure exhaust gas, in which a regulation of an engine operating parameter is activated. by acting only on a flap mounted in the exhaust line of the engine, the controlled valve being in the open position, or the closing of the valve is commanded, the deactivation of the regulation and the flap is placed in the open position.

Preferably, the regulation is further activated and deactivated as a function of parameters related to the operation of the engine or regulation or of environmental parameters.

As previously, the regulated quantity may be, for example, the air flow rate or the rate of the exhaust gas admitted into the engine.

The invention will be better understood from the study of a particular embodiment taken by way of nonlimiting example illustrated by the appended figures in which: FIG. 1 illustrates the main components of a combustion engine and the buckle exhaust gas recirculation EGR; Figure 2 illustrates the general principle of the invention; and Figure 3 shows by way of example a more detailed embodiment of a system according to the invention.

As illustrated in FIG. 1, a combustion engine 1, which is here a diesel engine, comprises an intake manifold 2 and an exhaust manifold 3. A turbocharger 4 comprises a turbine 41 and a compressor 42. A cooler 2a is mounted between the compressor 42 and the intake manifold 2. The exhaust gases 6 which pass through the turbine 41 are conveyed to a particulate filter 7 from which a bypass line 8 recirculates a portion of the exhaust gases. Exhaust to the compressor 42. In the pipe 8 are arranged a cooler 9 and an EGR 10 recirculation valve so as to cool and control the flow of recycled exhaust gas. The pipe 8 opens into a pipe 1 1 in which air 13 can flow at a flow rate that can be measured by a flow meter 14. It will be noted that the air 13 comes from an air filter 15 connected to an inlet. 16. The assembly composed of the pipe 8, the particulate filter 7, the turbocharger 4 and the pipe 1 1 forms a low pressure recirculation loop schematized by the circle 17 in FIG.

At the outlet of the particulate filter 7, the exhaust gases that are not recycled are discharged into an exhaust pipe 18 in which are mounted an exhaust flap 19 and a silencer 20. The exhaust flap 19 is controlled via a connection 21 through which a control signal from an ECU electronic control unit 22 passes. The recirculation valve 10 is also controlled via a connection 23 which receives a signal. control signal from the electronic control unit 22. Said electronic control unit 22 receives various information from the motor by connections not shown as well as measuring the flow of air from the flowmeter 14, the signal being conveyed by the connection 24. With reference to FIG. 2, which illustrates in principle the system according to the present invention, it can be seen that this system comprises control means referenced 25 as a whole capable of emitting a control signal of the position of the shutter of FIG. exhaust 19 by the connection 21. At the input of the regulation means 25, the error signal ε comes from a comparison between a setpoint value C _ons of a regulation quantity and a measured or estimated value M _es of the same regulation quantity. The comparison is carried out by means of the adder 26 which receives the reference value on its positive input and the value measured on its negative input.

The system as illustrated in Figure 2 further comprises means 27 for activation and deactivation which act by the connection 28 on the control means 25 so as to enable or disable the regulation. In addition, the activation and deactivation means 27 act by the connection 29 on a conditional activation block 30 which causes, by the connection 23, the opening or closing of the EGR 10 recirculation valve. When the regulation is activated, the recirculation valve EGR referenced 10 in FIG. 1 is opened instantaneously. Simultaneously, due to the activation of the regulating means 25, the position of the exhaust flap 19 is controlled so as to regulate the desired quantity to be regulated.

The quantity to be regulated may be the air flow rate, the recycled exhaust gas ratio or, in general, any appropriate size.

FIG. 3 more specifically illustrates a practical embodiment in which the main elements illustrated in the preceding figures and bearing the same references are found. In this practical embodiment, the regulation means

25 include a derivative integral proportional type (PID) regulator. Other types of regulators could be envisaged, including a proportional integral type regulator. The gain of proportional and integral functions is chosen appropriately.

In the example illustrated in Figure 3, the measured quantity is the air flow. The setpoint value Qair-cons is determined according to the operating point of the engine from a map 31 stored in the system as a function of the speed of rotation of the motor N _word and the torque C.

The value of airflow actually admitted _Q _r i - _m are measured by the flow meter 14 (Figure 1). Alternatively, a value estimated by one of the estimation means could be used.

In order to improve the operating dynamics of the regulation and to ensure that this regulation is preferably done in a linear range, provision has been made in the embodiment described in FIG. 3 for prepositioning the position control signal. of the exhaust flap 19. For this purpose, a prepositioning value "Pre" is determined by a map 32 also stored in the system according to the speed of rotation of the motor N _word and the engine torque. The prepositioning value thus determined is brought by the connection 33 to the positive input of an adder 34 which also receives on its other positive input the signal produced by the regulator 25.

The activation and deactivation means referenced 27 act directly via the connection 29 on the control block 35 which is capable of controlling the opening or closing of the recirculation valve 10. The position of the recirculation valve 10 is either open, which is shown schematically by the block 36 noted 1 in Figure 3, or closed, which is shown schematically by the block 37 noted 0 in Figure 3. It is therefore an order "all or nothing" and not a positional control proportional to any signal.

The deactivation and activation means 27 also act as previously indicated by the connection 28 on the regulation of the position control of the exhaust flap via a control block 38 which allows the transfer of the control signal from the adder 34 to the connection 21 or on the contrary neutralizes the control signal control leaving the exhaust flap in the open position, which is symbolized by the block 39 referenced 0 in Figure 3 In the embodiment illustrated in FIG. 3, it has also been provided a means of suppressing the integral function of the regulator 25 in the event of saturation of the control. The saturation block 40 verifies that the control signal developed by the regulator remains between a maximum threshold and a minimum threshold. In case of saturation, that is to say when the signal exceeds the maximum threshold or is below the minimum threshold, a signal is emitted by the return connection 41 neutralizing the integral function of the regulator 25.

Furthermore, in view of the fact that the regulation can be deactivated by the activation and deactivation means 27, it is useful to provide initialization means 42 for the integral part of the regulator 25 at the moment of activation of the regulation. . The initialization block 42 thus receives a signal via the connection 43 during the activation of the regulation and is capable of transmitting an initialization signal which is transmitted by the connection 44 to the regulator 25.

The deactivation of the regulation by the means 27 may depend on various information received by these means

For example, the regulation is advantageously deactivated in the event of a demand for high acceleration, in the starting phase of the vehicle, when the rotational speed of the engine exceeds a maximum threshold or, on the contrary, is below a minimum threshold, when the cooling temperature of the vehicle motor exceeds a maximum threshold or when the atmospheric pressure is below a minimum threshold. Control will also be deactivated if the regulation malfunctions are detected. This will be the case, for example, if the distance ε is negative, or if the operation of the recirculation valve or the exhaust flap is defective. Finally, the regulation will also be deactivated in the event of detection of malfunctions of various sensors that are useful for regulation, such as sensors for atmospheric pressure, air pressure at compressor outlet, engine coolant temperature or engine air temperature

When the regulation is deactivated, the EGR 10 is instantly closed and the setpoint value of the position of the exhaust flap 19 goes to zero thanks to the control block 38 (position in broken lines in FIG. 3). , thus placing the flap 19 in the open position.

When the regulation is again activated, the EGR 10 is instantly opened and the set point of the position of the exhaust flap 19 is equal to the sum of the prepositioning value "Pre" and the output signal of the regulator 25. At the time of reactivation of the regulation, the integral part of the PID regulator 25 is initialized. In the exemplary embodiment illustrated, the regulated quantity is the air flow rate. If the regulated quantity is the recycled exhaust gas (EGR) rate, the structure of the system is not changed. The measured or estimated value of the airflow is simply replaced by an estimated value of the recycled exhaust gas (EGR) rate. The patent application US 2004/0006978 already cited in the preamble of the present description gives an example of an estimate of such a rate from the measurement of three temperatures to which reference can be made.

Another way to make such an estimate is to use a conservation mass equation in the engine intake manifold. For this purpose, the temperature and pressure of the mixture of air and exhaust gas must be measured in the intake plenum. The intake airflow must also be measured or estimated. It is then possible to calculate the rate Q _word of the gases admitted to the engine according to the formula:

- "RT 120 or

T is the temperature in the plenum, P is the pressure in the plenum, R is the constant of perfect gases, η _vo i is the volumetric efficiency of the engine, N is the rotational speed of the engine, V _cy i is the total cubic capacity of the motor.

It is possible to deduce the rate t _egr of the recycled exhaust gases according to the formula:

and where Qair is the intake airflow as measured or estimated.

Claims

A low pressure exhaust gas recirculation system for a supercharged diesel type motor vehicle combustion engine, comprising a particulate filter device (7) and an exhaust flap (19) mounted in its diesel line. exhaust, a recirculation loop between the exhaust line downstream of the particulate filter and an air intake pipe, an exhaust gas recirculation valve (10) mounted in said loop, comprising control of the position of the recirculation valve and the exhaust flap and means (25) for regulating an operating parameter of the engine, adapted to act on the control means of the position of the exhaust flap, characterized in that the means for controlling the position of the recirculation valve (10) are adapted to cause the on-off opening or closing of said valve independently of the regulating means acting on the exhaust flap (19).

2. System according to claim 1 further comprising means (27) for activating and deactivating the regulating means, capable of activating and deactivating the regulating means (25) and also acting on the control means of the control means. the position of the recirculation valve to cause the opening or closing of said valve.

3. System according to claims 1 or 2 wherein the regulating means comprise a regulator having an integral function.

4. System according to claim 3 comprising a threshold comparator (40) receiving the control signal of the position of the exhaust flap and adapted to suppress the action of said integral function when the thresholds are exceeded.

5. System according to claims 3 or 4 comprising means (42) for initializing said integral function during activation of the control means.

6. System according to one of the preceding claims comprising means (32) for prepositioning the control signal of the position of the exhaust flap capable of determining a prepositioning value as a function of the operating point of the engine and adding this value at the output signal of the regulating means.

7. System according to one of the preceding claims, comprising a map (3 1) of set values of the flow rate of air admitted into the engine as a function of the operating point of the engine and a means for determining the flow rate of air admitted into the engine. the motor, said setpoint being brought to the input of the regulating means.

8. System according to one of claims 1 to 6 comprising a mapping of the nominal values of the recirculation gas rate admitted into the engine according to the operating point of the engine and a means for determining the recirculation gas content, said set point being fed to the input of the regulating means.

9. A method for controlling a supercharged diesel type motor vehicle combustion engine with recirculation of low pressure exhaust gas via a pipe provided with a controlled valve characterized by the fact that a regulation of a motor operating parameter by acting only on a flap mounted in the exhaust line of the engine, the controlled valve being in the open position, or the closing of the valve is commanded, the deactivation of the regulation and the flap is placed in open position.

10. The method of claim 9 wherein the control is activated and deactivated according to parameters related to the operation of the engine or regulation or environment parameters.