FR2810697A1 - Method of control of motor vehicle internal combustion engine has engine operated with homogenous or stratified charge operation with exhaust recycling - Google Patents

Abstract

The method of control of a motor vehicle internal combustion engine with exhaust gas recycling operates with a homogenous or stratified fuel-air mixture. During a recycling function of the engine, with stratified charge operation, exhaust recycling is interrupted after detection of engine stoppage. Functioning of the engine is maintained with a stratified mixture when the throttle valve is at least partially open.

Description

The invention relates to a method for controlling an internal combustion engine, provided with an exhaust gas recycling device, which operates selectively, as a function of operating parameters, with a homogeneous air-fuel mixture. or with a layered air-fuel mixture.

To further reduce the fuel consumption of motor vehicles with a spark-ignition engine, internal combustion engines are increasingly used which, selectively, except with a stoichiometric mixture (lambda = 1), operate also with a lean mixture. In this respect, a distinction is made between two basic types of operation.

In the lower load range, the internal combustion engine operates with a highly stratified cylinder load and a high excess of air (stratified load operation). This is obtained by means of a late injection in the compression time, shortly before the ignition time. The injected air-fuel mixture is distributed in a stratified manner in the combustion chamber. In the area of the spark plug, an easily flammable mixture is formed, while a very lean mixture is found at the peripheral locations in the combustion chamber. With such a stratified charge operation, it is possible, in addition to saving fuel, to also obtain a significant reduction in NOX emissions. The lambda air / fuel ratio can, in stratified load operation, take values between 2 and 4.5. The engine operates to a large extent without throttling.

In the upper load range, the engine operates with a uniform cylinder load. The injection takes place already before the admission time or during the admission time, in order to obtain a good intimate mixture of the fuel and the air. The mass air flow admitted is adjusted by means of a throttle valve in a manner corresponding to the torque requested by the driver. The injection flow required is for example calculated from the mass air flow and the speed of rotation and corrected, among other things, by means of lambda regulation.

The fuel is injected either in a conventional manner into the intake pipe, or, preferably, directly into the engine cylinder (s) (direct injection).

To further reduce the proportion of nitrogen oxides in engine exhaust gases, exhaust gas recycling devices are used. Through an exhaust gas recycling line, part of the exhaust gas is recycled in the intake path, more precisely in the manifold of the intake pipe. By means of signals from a control device, an exhaust gas recycling valve arranged in the recycling line is controlled and thus the mass of the recycled exhaust gases is adjusted. Since, in their essential constituents, the exhaust gases of the internal combustion engine constitute an inert gas, it is possible, by adding and mixing exhaust gases to the intake combustion air, to drop the temperature of peak combustion and thereby reduce nitrogen oxide emissions. The mass of recycled exhaust gases compared to the sum of the mass of fresh gases (intake air) and the mass of recycled exhaust gases is generally called the exhaust gas recycling rate.

For an exhaust gas recycling rate of 10%, nitrogen oxide emissions are already reduced by around 50%. The higher the proportion of recycled exhaust gases, the lower the emissions of nitrogen oxides. The efficiency of the engine increases with the mass of the recycled exhaust gases, since less heat is supplied to the cylinder walls and the pumping losses are reduced.

From a determined high rate of exhaust gas recycling, misfires multiply sharply, so that the HC emissions also exhibit an unacceptably large increase. A means of measuring the frequency of misfires and of only partial combustion of the air-fuel mixture in the cylinders is constituted by the irregularities in operation. The engine's HC and CO emissions cannot be reduced significantly by the exhaust gas recirculation device. The recycling rate should be set as precisely as possible, since otherwise the rate of HC and CO in the exhaust gas would increase with too high a recycling rate. .

The maximum exhaust gas recycling rate is limited by the combustion lambda, since, when recycling increases, the proportion of oxygen in the air-fuel mixture drops and therefore, for an intake charge remaining constant, less oxygen is available for combustion. Driving irregularity in the vehicle increases and this can lead to poor travel quality and, due to misfires, higher HC emissions. The value corresponding to the maximum exhaust gas recycling rate can be read from a characteristic table depending on the load point of the engine.

When the engine is stopped, the recycled exhaust gases present in the intake pipe manifold must be removed quickly, so that the next time the engine is started, the air-fuel mixture can be ignited. a safe way without further delay.

For this purpose, when the engine is stopped, it is possible to switch from stratified charge operation to homogeneous cylinder charge operation. On this occasion, the intake load must also be reduced, in order to allow operation under homogeneous cylinder load. As a result, the exhaust gases present in the intake pipe manifold are expelled slowly.

This is why the invention aims to provide a method of controlling an internal combustion engine, provided with an exhaust gas recycling device, which, when the engine is stopped, gives the assurance that the recycled exhaust gases present in the intake path are removed as quickly as possible.

To this end, the subject of the invention is a process, of the generic type defined in the introduction, characterized in that, during an operation of the internal combustion engine with recycling of the exhaust gases and with a layered air fuel mixture , the exhaust gas recycling is immediately interrupted after the discovery of a desire to shut down the engine, which, on the other hand, the operation of the internal combustion engine is maintained with an air-fuel mixture stratified when the throttle valve is at least partially open, and in that the fuel injection and the ignition of the air-fuel mixture of the internal combustion engine are maintained for each time a preset time.

Therefore, when the engine is stopped, the recycled exhaust gases which were still in the intake path, i.e. in the intake pipe and in the manifold, are expelled from a safe and fast way. When the engine is started again, there is no more exhaust gas in the intake path and the engine can be started more easily.

The method according to the invention can also have one or more of the following peculiarities - after the observation of a wish to stop, a counter which adds the number of injections is started, the sum is compared with a first prefixed threshold value and, when the first threshold value is exceeded, the injection is cut off, - after the recognition of a wish to stop, a counter which adds the number of ignitions, is started, the sum is compared with a second prefixed threshold value and, when the second threshold value is exceeded, the ignition is switched off, - after the recognition of a wish to stop, the injection is switched off after the prefixed duration s' has elapsed, after the recognition of a wish to stop, the ignition is switched off after the preset time has elapsed, the threshold values are determined experimentally and are deposited in tables characteristic of a internal combustion engine control device memory device, - the durations are determined experimentally and are stored in tables characteristic of a memory device of an internal combustion engine control device, - the second threshold value is chosen equal to or greater than the first threshold value, - the duration provided for switching off the ignition is chosen equal to or greater than the duration envisaged for switching off the injection, - after the injection is switched off, a counter which adds the number of ignitions is switched on, the sum is compared with a preset threshold value and, when the threshold value is exceeded, the ignition is switched off, - after the injection has been switched off, the ignition is cut off after another preset time has elapsed, the wish to stop is noted by means of a voltage analysis present on a terminal of an ignition-start switch of the vehicle driven by the internal combustion engine.

An exemplary embodiment of the invention is set out below in detail with reference to the appended schematic drawings. FIG. 1 shows an internal combustion engine comprising an exhaust gas recycling device and a control device making it possible to implement the method according to the invention and, in FIG. 2, a flow diagram of the progress of the process. FIG. 1 represents, in the form of a very simplified block diagram, an internal combustion engine with spark ignition and direct injection in which the method according to the invention is used. Only the components which are necessary for understanding the invention are shown. In particular, the fuel circuit and the exhaust gas aftertreatment device are not shown.

An intake path 1 includes a manifold 2 and an intake pipe 3. Furthermore, a load sensor, in the form of a mass air flow meter 4, and a throttle valve 5 are arranged in the intake path 1. The intake pipe 3 connects the manifold 2 to an inlet of a cylinder 6. The cylinder 6 is connected to an exhaust gas path 7 by which the exhaust gases are evacuated. An exhaust gas recycling pipe 8 runs off the exhaust gas path 7 and opens into the intake path 1 downstream of the throttle valve 5. The direction of flow of the intake air is indicated by an arrow symbol. An exhaust gas recycling valve 9, which comprises an electromagnetic actuator not shown, is arranged in the exhaust gas recycling pipe 8.

An electronic control device 10 comprises a preliminary processing unit 11 which formats signals from sensors which detect operating quantities of the motor. A throttle valve position sensor 12 detects the opening angle of the throttle valve 5, a rotation speed sensor 13 detects the current rotation speed of the crankshaft 15, an opening degree sensor 14 detects the degree opening the exhaust gas recycling valve 9 and an exhaust gas sensor 16 detects the oxygen content in the engine exhaust gases. For example, an engine temperature sensor or a coolant temperature sensor and an exhaust gas temperature sensor (not shown) provide other signals necessary for engine control and regulation. The electronic control device 10 further comprises an electrical device 17 used to control the actuator of the exhaust gas recycling valve 9 and regulating the degree of opening of this recycling valve 9 as a function of one or more engine operating variables, for example the opening angle of the throttle valve 5 and the speed of rotation of the crankshaft 15. By means of the signal from the exhaust gas sensor 16, the air-fuel ratio is subject to regulation in a manner corresponding to the prescribed setpoints in the various engine operating areas (homogeneous or layered cylinder load). This function is taken over by a lambda regulating device 18, known per se, which is preferably integrated into the electronic control device 10. In a known manner, this control device 10 determines, as a function of the parameters of engine operation, in particular of the load and the speed of rotation, a basic value for a mass of fuel, which is corrected by means of several correction factors, inter alia on the basis of the signal from the gas probe d 'exhaust. The mass of fuel thus determined is injected by working cycle of the cylinder 6 by means of injectors 19.

Furthermore, the reference 20 designates a vehicle battery, the plus pole of which is connected to a terminal KL30 of an ignition-start switch 21, while the minus pole is connected to the vehicle body. The terminals KL15 and KL50 of the ignition-start switch 21 are connected, inter alia, to the control device 10 by lines not bearing any particular mark. Terminal KL15 (no longer switched downstream of the vehicle battery) allows voltage to pass only when the ignition is on, i.e. when the ignition-start switch 21 is in the position designated by I .

A flow diagram of the process for controlling the internal combustion engine is presented in FIG. 2. When the engine is started, the program is started by a first step of process S1.

At a process step S2, the question is asked whether or not terminal 15 is currentless, that is to say whether the ignition-start switch 21 is therefore or not in position 0. This question is repeated continuously until the result of the question is affirmative. If this is the case, at a process step S3, the exhaust gas recycling valve 9 is immediately closed completely by means of signals from the device 17. Then, at a process step S4, a counter Z1 provided for the number of injection pulses and a counter Z2 provided for the number of ignition pulses from the moment at which terminal 15 is without current are both switched on.

The operation of the engine under stratified load is also maintained after a finding of the state without current of the terminal 15 and the throttle valve 5 also remains to a large extent open (no process S5). The injection and ignition are still maintained. At a process step S6, it is checked whether the state of the counter Z1 provided for the number of injections has or has not exceeded a prefixed threshold value SW1. This question runs in a wait loop. If this threshold value SW1 is exceeded, the injection is cut off (no S7 process). In a manner analogous to process steps S6 and S7, it is checked, at process steps S8 and S9, whether or not the state of the counter Z2 provided for the number of ignitions has exceeded a threshold value SW2. If this threshold value SW2 is exceeded, the ignition is cut off.

The two threshold values SW1 and SW2 are determined experimentally and are deposited, inside a memory device 22 of the control device 10, in characteristic tables KF1, KF2, for example as a function of the gas recycling rate exhaust.

To ensure in all circumstances a complete combustion of the entire air-fuel mixture, it is advantageous to choose the threshold value SW2 provided for the number of ignitions equal to or greater than the threshold value SW1 provided for the number of injections after switching to terminal 15 without current.

Then, at a process step S10, the two counters Z1, Z2 are brought back to the value 0 and the process has come to an end.

Instead of the addition, by means of the counters Z1 Z2, of the number of injections and of the ignitions after the transition to the state without current of terminal 15, and of the following comparison with threshold values SW1, SW2, it it is also possible to cut off the injection and the ignition after preset times have elapsed. In this case, the duration until the ignition is cut off must be chosen equal to the duration until the injection cuts out or longer than this.

Furthermore, it is also possible to activate the counter provided for the number of ignitions or the time counter provided for ignition, not in parallel with the counter provided for number of injections or the time counter provided for injection. , but only after the injection is stopped.

The flowchart is preferably produced in the control device 10 as a program. Alternatively, however, it can also be realized as a hardware wired circuit arrangement.

Claims (2)

<U> CLAIMS </U> 1. Method for controlling an internal combustion engine, provided with an exhaust gas recycling device, which operates selectively, according to operating parameters, with a homogeneous air-fuel mixture or with a layered air-fuel mixture, characterized in that, during operation of the internal combustion engine with an exhaust gas recycling and with a layered air-fuel mixture, the recycling of exhaust gas is interrupted after finding a wish to shut down the engine, - in that the operation of the internal combustion engine is maintained with a layered air-fuel mixture when the throttle valve is at least partially open - and that the fuel injection and the air-fuel mixture ignition internal combustion engine are maintained for each time a preset time. 2. Method according to claim 1, characterized in - after the observation of a wish to stop, a counter (Z1) which adds the number of injections, is started, - the sum is compared with a first threshold value (SW1) prefixed and, - when the first threshold value (SW1) is exceeded, the injection is cut. 3. Method according to claim 1, characterized in that - after the observation of a wish to stop, a counter (Z2) which adds the number of ignitions, is started, -. The sum is compared with a second threshold value (SW2) prefixed and, - when the second threshold value (SW2) is exceeded, the ignition is switched off. 4. Method according to claim 1, characterized in that after the discovery of a wish to stop, the injection is cut off after a preset time has elapsed. 5. Method according to claim 1, characterized in that after the recognition of a wish to stop, the ignition is switched off after a preset time has elapsed. 6. Method according to claim 3 when it depends on claim 2, characterized in that the threshold values (SW1, SW2) are determined experimentally and are deposited in characteristic tables (KF1, KF2) of a memory device (22) a control device (10) of the internal combustion engine. 7. Method according to any one of claims 4 and 5, characterized in that the durations are determined experimentally and are deposited in characteristic tables (KF1, KF2) of a memory device (22) of a control device (10) of the internal combustion engine. Method according to claim 6, characterized in that the second threshold value (SW2) is chosen equal to or greater than the first threshold value (SW1). Method according to Claim 7, characterized in that the duration provided for switching off the ignition is chosen to be equal to or greater than the duration provided for switching off the injection. Method according to Claim 2, characterized in that after the injection has been cut off, a counter (Z2) which adds the number of ignitions is started, the sum is compared with the prefixed threshold value (SW2) and, when the threshold value (SW2) is exceeded, ignition is cut. 1. Method according to claim 4, characterized in that after the injection has been cut off, the ignition is cut off after another preset time has elapsed. 2. Method according to claim 1, characterized in that the wish to stop is noted by means of an analysis of the voltage occurring on a terminal (KL15) of an ignition-start switch (21) of the driven vehicle by the internal combustion engine.