DE19849256A1 - Method and appliance for diagnosing exhaust gas recirculation system of IC engine monitors effect of controlled change in rate of recirculation on emission levels - Google Patents

Abstract

The diagnosis involves changing the rate of recirculation and monitoring the change in Lambda number and/or air quantity ml. If their change is within a specific tolerance band this indicates that the system emission meets legal requirements. The prerequisites for the diagnosis are, that the engine is in a specific speed/load window, the system is active and in a defined state, the motor temperature is above a set threshold

Description

State of the art

The invention relates to a method for diagnosing a Exhaust gas recirculation (EGR) in a combustion process, especially in an internal combustion engine.

Exhaust gas recirculation, especially in internal combustion engines has grown in importance in recent years. The Exhaust gas recirculation not only has a positive effect on the Energy conversion and thus fuel consumption, but plays because of the positive influence on it Exhaust behavior plays an important key role for the Fulfillment and compliance with the current and in the near future required strict emissions standards. Especially at Internal combustion engines that operate with a high proportion of air be (BDE), whereby the proportion of nitrogen oxides (NOx) in the With this technology, exhaust gas increases enormously the nitrogen oxides reached up to 80%.

For this reason and because of the American regulation  for on-board diagnosis (OBD) of all exhaust-relevant components the diagnosis of exhaust gas recirculation is essential Measure.

In order to meet the exhaust gas limit values, the mixture must (Fresh air / fuel ratio) in the combustion chamber like this can be set so that the catalyst works optimally. To do this, the exhaust gas air ratio lambda must first be determined. Based on the exhaust air ratio lambda, which is advantageous is determined using a broadband lambda probe (LSU) and actually the difference in oxygen concentration between the ambient air and the exhaust gas flow indicates the Air ratio in the mixture can be closed. Then you can use the control unit of the internal combustion engine, for. B. by Change in the EGR rate or intervention in the electronic controlled throttle valve (EGAS) the fresh air / fuel Ratio can be changed so that the desired Exhaust gas composition is achieved.

The as yet unpublished patent application 197 19 278.5 describes a method for diagnosing a Exhaust gas recirculation, where a control factor is both switched on as well as when switched off Exhaust gas recirculation is recorded and stored and in which the Difference of the control factors when the on and off Exhaust gas recirculation formed with a predetermined value compared and in the event of a deviation an error signal is issued.

This procedure is quite time consuming because of the rule factor both when switched on and when switched off Exhaust gas recirculation is recorded and stored and the  Control factor can be averaged over a certain period of time got to. Furthermore, the operating conditions of the Change internal combustion engine during the diagnosis, whereby the diagnostic result can be falsified.

The present invention is based on the object Method for diagnosing exhaust gas recirculation Generic type to improve such that with given a reliable statement about the functionality of the exhaust gas recirculation can be.

Advantages of the invention

The object of the present invention is achieved with the Features of claim 1 solved.

The particularly great advantage of the present invention lies in that no additional technical means such. B. Pressure sensors or temperature sensors are required to the functionality of the exhaust gas recirculation diagnose. It is also a quantitative one Information about exhaust gas recirculation possible. If no Device for detecting lambda is available alternatively, the signal ml of an air mass meter Diagnosis can be used. Furthermore, the Use of both quantities Lambda and ml for EGR diagnosis increases the reliability of the diagnosis.

In an advantageous embodiment of the invention be provided that the exhaust gas recirculation changes, lambda and / or ml detected, fed to an evaluation device, in  the evaluation device is checked whether the change of Lambda and / or ml in a specified tolerance range lies and when leaving the tolerance range Error signal is output.

By changing the EGR rate with the help of a Adjustment of the EGR valve actively diagnoses the Exhaust gas recirculation carried out. Will when the EGR valve a change in lambda or ml can be found on a working EGR valve getting closed. If no change in lambda or ml is determined, then can not on a working valve to be closed.

In a further advantageous embodiment of the invention it can be provided that the exhaust gas recirculation changes, Lambda and / or ml detected, an evaluation device is supplied, it is checked in the evaluation device whether the value of lambda and / or ml reached after the change is within a specified tolerance range an error signal is output outside the tolerance range becomes.

EGR diagnosis can also be performed by using the EGR rate is changed and the erect after the change Value of lambda and ml is detected. This is one Information about the permeability of the EGR line possible. It can advantageously be provided that the EGR rate in certain steps changed and the course of lambda and / or ml depending on the EGR rate, one Evaluation device is supplied in the  Evaluation device with the course of lambda and / or ml a predetermined course of lambda and / or ml compared and an error signal is output in the event of a deviation.

This allows a more reliable statement about the condition exhaust gas recirculation.

A further advantageous embodiment of the invention can are that the pressure in the intake manifold Internal combustion engine is constant during the diagnosis.

At constant pressure in the intake manifold there is a simple one Relationship between lambda and the EGR rate and ml and the EGR rate. If you also assume a constant injected fuel mass, there is a linear Relationship between lambda and the EGR rate and ml and the EGR rate. If the EGR rate is increased, it decreases Lambda and ml, however, the EGR rate is reduced, so the values for lambda and ml become larger. The slope of the Straight line that describes this linear relationship negative.

It can advantageously be provided that the method in an operating mode is carried out in the fresh air reaches the internal combustion engine without throttling, as a result of which Pressure in the intake manifold is almost constant, especially at the Combustion process in a gasoline direct injection Internal combustion engine (BDE) or in a diesel Internal combustion engine.

With unthrottled operating modes of the internal combustion engine adjusts itself due to the open throttle valve  constant pressure in the intake manifold, which corresponds to the atmospheric Pressure corresponds. This is an easy way given to set a constant pressure in the intake manifold.

It can also be advantageously provided that the pressure in the Intake manifold using a throttle angle speed Model or a throttle valve air mass flow Model is set to a constant value.

This allows the throttled operation Internal combustion engine and without using a pressure sensor in the Suction pipe in a relatively simple way a constant pressure in the Suction pipe can be adjusted.

It is particularly useful if the exhaust gas number from the Output signal from a broadband lambda probe (LSU) obtained becomes.

The broadband lambda probe delivers a signal that is proportional to the exhaust gas air ratio lambda. This can Changes in the fresh air / fuel ratio above covers a large area with sufficient accuracy become.

It can also be advantageously provided that the method is applied according to claim 1 in a heating system.

Since the conditions in a heating system with the Conditions in an internal combustion engine largely match, the procedures for Exhaust gas recirculation diagnosis of an internal combustion engine also a heating system can be transferred.  

The object of the present invention is also achieved with the Features for a control device of claim 10 solved.

With the help of an electronic control device and implemented functions can be very different Requirements for the operation of the internal combustion engine recorded, centrally coordinated and available Control variables are implemented. This makes a simple, robust and clear implementation of the implementation of the method according to the invention enables.

drawing

Embodiments of the invention are in the drawing shown and in the following description explained.

Fig. 1 shows schematically an illustration of the internal combustion engine with exhaust gas recirculation.

The FIG. 2 describes the relationship between the oxygen and the EGR rate and ml and the EGR rate.

The Fig. 3 schematically shows the flow of a method according to the invention, in which at a predetermined EGR rate lambda and / or ml is detected and evaluated on their position relative to an allowable tolerance range.

FIG. 4 shows schematically the sequence of a method according to the invention, in which the EGR rate is actively changed and in which the resulting change in lambda and / or ml is detected and evaluated.

The Fig. 5 schematically shows the flow of a method according to the invention, in which the EGR rate is actively changed and lambda / or detected ml and after the change and evaluated.

Description of the embodiments

As shown in FIG. 1, in an internal combustion engine with direct injection, fresh air is supplied to a combustion chamber 2 by means of an intake manifold 1 via an inlet valve 7 . The amount of fresh air fed into the combustion chamber 2 can be controlled via a throttle valve 3 . An air flow meter 4 detects the fresh air flowing into the internal combustion engine. The throttle valve 3 and also the entire internal combustion engine are controlled by means of a control unit 5 . The control unit 5 has an evaluation unit 6 . An injection valve 19 is arranged in the walls of the combustion chamber 2 . The fuel is brought to a high pressure by means of a high-pressure pump 20 and injected into the combustion chamber 2 via a fuel line 25 and injection valves 19 . Furthermore, the combustion chamber 2 has an exhaust valve 13 for ejecting the exhaust gases generated during combustion. The exhaust gas air ratio lambda can be measured by means of a broadband lambda probe (LSU) 24 in the exhaust pipe 14 , as a result of which the fresh air / fuel ratio in the mixture can be determined. An EGR conduit 16 connects the exhaust tube 14 to the suction pipe 1, whereby due to the higher pressure in the exhaust pipe 14 exhaust gases from the exhaust pipe 14 into the intake tube 1 to be passed. With the help of the EGR valve 17 , the exhaust gas flow in the EGR line 16 can be controlled. A tank ventilation line 22 leads from a fuel tank 21 to the intake manifold 1 , whereby additional fuel can get into the intake manifold 1 and thus also into the combustion chamber 2 . The fuel flow in the tank ventilation line 22 can be controlled by means of a tank ventilation valve 23 . The various sensors and actuators are connected to the control unit 5 via signal and control lines 26 . A display device 27 is switched on by the evaluation system 6 if there is a fault in the exhaust gas recirculation.

As can be seen from FIG. 2, both the relationship between lambda and the EGR rate and the relationship between ml and the EGR rate with a constant intake manifold pressure ps and a constant fuel supply rk are linear. If the EGR rate is changed, the lambda and ml also change. The extent and direction of the change provide information about the state of the exhaust gas recirculation and depend on the control strategy of the internal combustion engine.

By changing the EGR rate in certain steps and Lambda and ml can be recorded, a course of lambda and / or ml depending on the EGR rate become. This course can with a predetermined course of lambda and / or ml from z. B. a model or a stored previous history can be compared. The Amount of the deviation from the measured course and the The modeled course can then have a threshold be compared and if the threshold is exceeded can conclude a fault in the exhaust gas recirculation  become.

As can be seen from FIG. 3, in a method for diagnosing an exhaust gas recirculation of an internal combustion engine, in which the fresh air / fuel ratio is detected with the aid of a broadband lambda probe 24 and is fed to a control unit 5 after the EGR diagnosis is started in step 310 , in a step 320 first checked whether the basic requirements for an EGR diagnosis are met. Here it is checked whether predetermined switch-on conditions are present at the same time. These switch-on conditions are:

• - The internal combustion engine must be in a certain Speed / load window.
• - The exhaust gas recirculation must be activated and in one defined state.
• - The engine temperature must have a certain predetermined threshold exceed.

So long as the basic requirements for an EGR diagnosis are not EGR diagnosis cannot be continued become.

If, on the other hand, they are fulfilled, lambda and / or ml are recorded in a step 330 and fed to an evaluation system 6 . In general, the acquisition of lambda and / or ml takes place continuously, so that a separate acquisition of the time profile of lambda and / or ml is not necessary. In the evaluation system 6 , it is checked in a step 340 whether the lambda and / or ml at the currently set EGR rate are within a certain tolerance range, which is formed around an expected value. The expected value of lambda and / or ml is formed, for example, assuming an open or closed EGR valve. When the exhaust gas recirculation is triggered to open, the expected value for lambda and / or ml that is formed for an open exhaust gas recirculation must be reached. If lambda and / or ml lie within the tolerance range, the assumption is made in step 350 that the exhaust gas recirculation is OK, otherwise it is made in step 360 that the exhaust gas recirculation is not OK. In the event that the exhaust gas recirculation is not in order, appropriate measures are initiated in the control of the internal combustion engine in a step 370 , e.g. B. display and / or storage of the diagnostic result, adaptation factor for the normal operation of the internal combustion engine outside of the diagnosis, the sizes of the injection time, ignition angle and fresh air mass being adapted as a function of the state of the EGR system.

It can e.g. B. be checked whether when switched on Exhaust gas recirculation takes place and in to what extent this takes place. This is done at When the exhaust gas recirculation is switched on, the EGR valve is adjusted. If the exhaust gas recirculation is OK, you can at Lambda and ml observed a change.

In a method as can be seen from FIG. 4, steps 410 to 430 are first carried out equivalent to steps 310 to 330 of the method described in FIG. 3. In step 440 , the EGR rate is changed. In the evaluation system 6 , lambda and / or ml after the change in the EGR rate is recorded in a step 450 . In step 460 , the difference between the detected lambda and / or ml is formed before the change in the EGR rate and after the change in the EGR rate, and it is checked whether the difference lies within a specific tolerance range. If the changes in lambda and ml are within the tolerance range, the assumption is made in step 470 that the exhaust gas recirculation is OK, otherwise in step 480 the assumption is made that the exhaust gas recirculation is not OK. In the event that the exhaust gas recirculation is not in order, appropriate measures are initiated in the control of the internal combustion engine in a step 490 , e.g. B. display and / or storage of the diagnostic result, adaptation factor for the normal operation of the internal combustion engine outside of the diagnosis, the sizes of injection time, ignition angle and fresh air mass being adapted depending on the state of the EGR system.

In a method as can be seen from FIG. 5, steps 510 to 520 are first carried out equivalent to steps 310 to 320 of the method described in FIG. 3. The EGR rate is changed in step 530 and lambda and / or ml is detected in step 540 . In the evaluation system 6 , it is checked in a step 550 whether lambda and / or ml at the currently set EGR rate are within a certain tolerance range. If lambda and / or ml lie within the tolerance range, the assumption is made in step 560 that the exhaust gas recirculation is OK, otherwise in step 570 the assumption is made that the exhaust gas recirculation is not OK. In the event that the exhaust gas recirculation is not in order, appropriate measures are initiated in the control of the internal combustion engine in a step 580 , e.g. B. display and / or storage of the diagnostic result, adaptation factor for the normal operation of the internal combustion engine outside of the diagnosis, the sizes of the injection time, ignition angle and fresh air mass being adapted as a function of the state of the EGR system.

Claims (10)

1. Procedure for diagnosis of exhaust gas recirculation (EGR) at a combustion process especially in one Internal combustion engine with different Air / fuel ratio is operable with a Device for recording an exhaust gas air ratio lambda and / or a device for detecting a supplied Fresh air mass ml and an evaluation system, in which the evaluation system is used to check whether a predetermined relationship between lambda and an EGR rate and / or between ml and an EGR rate is met and that then if this relationship is not met, an error in the exhaust gas recirculation is recognized. 2. The method according to claim 1, characterized in that changed the exhaust gas recirculation, recorded lambda and / or ml, an evaluation device supplied in the Evaluation device is checked whether the change in lambda and / or ml is within a predetermined tolerance range and an error signal when leaving the tolerance range  is issued. 3. The method according to claim 1 or 2, characterized in that the exhaust gas recirculation changes, lambda and / or ml detected, is fed to an evaluation device in which Evaluation device is checked whether the after the change reached value of lambda and / or ml in a given Tolerance lies and when leaving the An error signal is output within the tolerance range. 4. Procedure according to at least one of the above Claims, characterized in that the EGR rate in certain steps changed and the course of lambda and / or ml depending on the EGR rate, one Evaluation device is supplied in the Evaluation device with the course of lambda and / or ml a predetermined course of lambda and / or ml compared and an error signal is output in the event of a deviation. 5. Procedure according to at least one of the above Claims, characterized in that the pressure in the intake manifold the internal combustion engine is constant during the diagnosis. 6. The method according to claim 5, characterized in that the Procedure is carried out in an operating mode in which Fresh air enters the internal combustion engine without throttling, whereby the pressure in the intake manifold is almost constant, especially in the combustion process in one Gasoline direct injection internal combustion engine (BDE) or in one Diesel internal combustion engine. 7. The method according to claim 5, characterized in that  the pressure in the intake manifold using a throttle valve angle Speed model or a throttle valve angle Air mass flow model at a constant value is set. 8. The method according to any one of the preceding claims, characterized in that the exhaust gas number from the Output signal from a broadband lambda probe (LSU) obtained becomes. 9. The method according to claim 1, characterized by its Application in a heating system. 10. Electronic control device with an evaluation system in an internal combustion engine with exhaust gas recirculation, the Signals from various detection devices originate from states of the internal combustion engine, these signals using algorithms and functions processed and Signals for controlling and / or regulating the internal combustion engine generates and outputs, characterized in that the Control device absorbs lambda and / or ml, u. a. a EGR rate outputs, the evaluation system checks whether between the output EGR rate and the recorded lambda and / or ml signals a given relationship is satisfied and that the control means a failure of this relationship evaluates as an error of the exhaust gas recirculation.