Method and device for diagnosing a heater of an exhaust system of an internal combustion engine

Abstract

A method and a device for diagnosing a heater (1) of an exhaust system (8) of an internal combustion engine (2) are proposed, wherein air is supplied to a combustion chamber (3) of the heater by a secondary air pump (6) and fuel is supplied by an injection valve (16). An air-fuel mixture thus formed in the combustion chamber (3) is ignited by a glow plug (4). The fuel is injected by controlling the injection valve (16) for individual partial injections at predetermined times. The combustion of the individual partial injections triggers a sensor signal in a pressure sensor (21) in the air supply to the combustion chamber (3) or a connecting pipe (9) from the combustion chamber to the exhaust system (8).By evaluating the pressure signal of the pressure sensor (21) with a frequency characteristic of the times of the partial injection and by evaluating the signal of a further sensor (10, 22), a continuous injection of fuel through the injection valve (16) is determined.

Description

Prior ArtThe invention is based on a method and a device for diagnosing a heater of an exhaust system of an internal combustion engine according to the species of the independent claims. From their DE 195 08 013 C1 a method for operating a heater of an exhaust system is already known. A rapid heating of the exhaust system is thus achieved.Advantages of the InventionThe method according to the invention and the device according to the invention having the features of the independent patent claims have the advantage over the related art that a faulty continuous injection of fuel into the combustion chamber of the exhaust gas heater is reliably detected. The operational reliability of the method according to the invention or of the device according to the invention is thus improved. In particular, it can thus be ensured that, in the event of a fault, the introduction of fuel into the exhaust system is reliably prevented by rapid detection of the fault. In this way, cost-intensive damage to the exhaust system due to incorrectly introduced fuel is reliably avoided.Further advantages and improvements are obtained by the features of the dependent claims. The diagnosis is carried out particularly easily and reliably with the aid of the signal of the lambda sensor. Alternatively, the signal of a control circuit can also be used for the regulation of the fuel quantity, which uses the lambda sensor. A pressure sensor for the fuel in the fuel supply for the injection valve in the combustion chamber is also suitable as a further sensor. If a faulty continuous injection is detected, a fuel valve in the fuel supply is expediently closed. By evaluating the time profile of the pressure in the fuel supply, the fault situation can then additionally be checked again. By temporarily increasing the air supply, the introduction of excess fuel from the combustion chamber into the exhaust system can be prevented. This ensures improved protection of the exhaust system.DRAWINGSExemplary embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. The following are shown: FIG. 1 schematically shows an internal combustion engine with an exhaust system and a heater for the exhaust system, FIG. 2 shows control signals for the injection valve, and FIG. 3 also shows control signals for the injection valve.DESCRIPTION OF THE INVENTIONFIG. 1 schematically shows the exhaust gas heater 1 and an internal combustion engine 2. The exhaust gases of the internal combustion engine 2 are conducted through an exhaust pipe 7 to an exhaust system 8. A lambda probe 11 is arranged in the exhaust pipe 7, by means of which the oxygen content of the exhaust gas of the internal combustion engine 2 is measured. The exhaust system 8 serves for cleaning the exhaust gases and usually has one or two 3-way catalytic converters and / or a system for NOx reduction and optionally also a particle filter. The exact details of the construction of the exhaust system 8 are not important for understanding the invention. Such an exhaust system 8 only purifies the exhaust gases from a certain operating temperature, which is ensured during operation by the heating by the hot exhaust gases. When the internal combustion engine 2 is started, in particular when the ambient temperature is cold, the exhaust system 8 is not yet ready for operation and high emissions of exhaust gases thus arise.In order to achieve rapid heating of the exhaust system 8, a heater 1 is shown in FIG. 1. The heater 1 has a secondary air pump 6, a shut-off valve 5 arranged downstream, then a combustion chamber 3 and then a connecting pipe 9. The combustion chamber 3 is provided with an injection valve 16 for fuel and a glow plug 4 as an igniter. Ambient air is drawn in by the secondary air pump 6 through an air filter 13 and an air flow is thus generated, which flows through the opened shut-off valve 5 into the combustion chamber 3. Between the air filter 13 of the secondary air pump 6 there is also arranged an air mass sensor 12 by means of which the quantity of air pumped by the secondary air pump 6 into the combustion chamber 3 is measured. Fuel is injected into the combustion chamber 3 by the injection valve 16, and the air-fuel mixture in the combustion chamber 3 is ignited by the glow plug 4. For this purpose, the glow plug 4 is typically heated to a temperature of approximately 1300° C. The exhaust gases of the combustion chamber 3 are conducted through the connecting pipe 9 to the exhaust system 8 and ensure a rapid temperature increase of the exhaust system 8. In the connecting pipe 9, a lambda probe 10 is arranged, which measures the oxygen content of the exhaust gas of the combustion chamber 3. This ensures rapid attainment of the operating temperature of the exhaust system 8, in particular in a cold starting situation of the internal combustion engine 2. Furthermore, a control device 100 is shown, which is used for regulating the temperature of the glow plug 4, for controlling the shut-off valve 5, the secondary air pump 6 and the injection valve 16. For this purpose, control unit 100 reads in the values of all the sensors shown, sends control signals to all actuators such as injection valve 16, shut-off valve 5 and secondary air pump 6, and exchanges data with an engine control unit, not shown here.In Figure 1, the shut-off valve 5 is shown in an open state to ensure an unhindered flow of air from the secondary air pump 6 through the combustion chamber 3 into the exhaust system 8. This is illustrated in FIG. 1 by the closure element 17 arranged parallel to the flow direction. If the heating device is not operated, this closure element 17 is arranged transversely to the flow, whereby a flow of exhaust gases from the exhaust system 8 or the exhaust pipe 7 back into the secondary air pump 6 is prevented. This prevents the secondary air pump 6 from being contaminated by the exhaust gases of the internal combustion engine 2. In addition, exhaust gas is prevented from reaching the environment via the intake air system in an uncleaned / unfiltered manner.For the purpose of supplying fuel, the injection valve 16 is connected via a fuel line 24 to a fuel pump, not shown. A fuel valve 23 is arranged in the fuel line 24, and a pressure sensor 22 is arranged between the fuel valve 23 and the injection valve 16. By closing the fuel valve 23, the supply of fuel to the injection valve 16 can be interrupted.Furthermore, at least one pressure sensor 21 is provided, which is arranged either in the air supply or in the connecting pipe 9. The pressure sensor can be arranged in the air feed line, for example, in the air mass sensor 12; in particular, the pressure sensor can be embodied together with the air mass sensor jointly on a sensor component. Another arrangement of such a pressure sensor 21 in the air supply to the combustion chamber 3 is, for example, between the secondary air pump 6 and the shut-off valve 5 or between the shut-off valve 5 and the combustion chamber 3.The pressure sensor 21 can be used to determine the beginning of a combustion in the combustion chamber 3. As a result of the start of a combustion in the combustion chamber 3, a pressure wave is generated, which propagates from the combustion chamber 3 in the direction of the air filter 13 and in the direction of the exhaust system 8. By evaluating the time profile of the pressure of the pressure sensor 21, the start of a combustion in the combustion chamber 3 can thus be determined. This is particularly relevant since the combustion in the combustion chamber 3 is normally not continuous, but is designed intermittently, i.e. is carried out by short partial combustions which take place one after the other. This is achieved in that the injection of fuel by the injection valve 16 is not effected by a continuous jet of fuel, but rather in each case defined small partial injections are effected. Between these defined partial injections, there is a reduction in the intensity of the combustion in the combustion chamber 3 and with each partial injection an increase in the intensity of the combustion. The different intensities of the combustion cause a different pressure in the combustion chamber 3, which has an effect in the exhaust gas heater 1 and the exhaust system. By evaluating the pressure signal of a pressure sensor 21, these individual short partial burns can be detected.FIG. 2 schematically illustrates the profile of the control signal of the injection valve 16. The current I for activating the injection valve is plotted against the time t. At the beginning of each injection, a sharp increase in the current takes place in order to achieve rapid opening of the injection valve 16. The current then falls to a first higher level and still a short period of time to a second lower level. To end the respective individual partial injections, the current falls back to zero. The quantity of injected fuel is defined by the time length of this activation, so that different quantities are injected by varying the activation duration. The time profile is chosen here by way of example such that a new injection is started every 5 ms (milliseconds), wherein the time periods of the activation do not overlap. The time interval of 5 ms between the start of the individual partial combustions results in 200 pressure fluctuations per second in the combustion chamber 3. By evaluating the signal of the pressure sensor 21 with a frequency which is characteristic of these 200 intensity fluctuations of the burns per second, it can thus be reliably detected whether the corresponding partial burns take place. This can be effected particularly easily by a Fourier transformation, in particular a discrete Fourier transformation, with a frequency of 200 Hz.If it is detected by evaluating the signal of the pressure sensor 21 that the desired partial combustion does not take place, this can have various causes. A simple matter may be that the fuel valve 23 is erroneously closed. Further, the shut-off valve 5 may be erroneously closed or the secondary air pump 6 is defective and does not provide a sufficient amount of air.A particularly critical fault is when the injection valve 16 incorrectly does not reliably close and fuel is thus continuously injected into the combustion chamber 3. An excess supply of fuel then occurs, which reaches the normal exhaust system 8 of the internal combustion engine 2 through the connecting pipe 9. There, a reaction of the fuel with the components of the exhaust system 8 can occur, which can lead to a destruction of the exhaust system 8. It is therefore desirable to reliably detect the faulty continuous injection of fuel by the injection valve 16 and take countermeasures promptly. For this purpose, in addition to the evaluation of the signal of the pressure sensor 21, further sensors should also be taken into account.One possibility for detecting an erroneous continuous injection of fuel by the injection valve 16 is to take into account the sensor signal of the lambda sensor 10. This can be done particularly easily by defining a threshold value for the lambda signal. If an excessive fuel excess is indicated by the lambda signal and no partial burns are detectable at the same time by evaluating the signals of the pressure transmitter 21, the fault situation of a continuous injection by the injection valve 16 is highly likely to occur.An alternative method based on the signal of the lambda sensor is explained in FIG. 3. FIG. 3 again shows the control signal of the injection valve 16 with respect to time. In FIG. 3, a new start of an injection takes place every 5 ms by a corresponding current signal for activating the injection valve 16 as well. In contrast to FIG. 2, however, the duration of the activation, i.e. the duration between the start of the injection and the end of the injection, is significantly shortened. This is the result of a control loop for the injection duration, which evaluates the lambda signal. If an excess of fuel is detected on the basis of the lambda signal, the injection duration is shortened in order to achieve the desired lambda signal. The output signal of this control loop, the injection duration, is thus a direct indicator of a deviation of the lambda signal. Accordingly, the injection duration may be compared to a threshold value for the injection duration. If this threshold value for the injection duration is exceeded at the same time and no partial combustion is detectable on the basis of the evaluation of the signals of the pressure transmitter 21, the fault situation is a continuous injection by the injection valve 16.As an alternative to the lambda signal, the pressure signal of the fuel pressure sensor 22 may also be used with the detection of a lack of partial combustion. Due to the regular opening and closing of the injection valve 16, corresponding pressure fluctuations occur in the fuel supply for the injection valve 16, which are detectable by evaluating the signal of the fuel pressure sensor 22. These signals can also be advantageously evaluated by means of a Fourier transformation. Furthermore, the signal of the fuel pressure sensor 22 can also be used for a further type of diagnosis. If the fault situation has detected a continuous injection of the injection valve 16, the fuel valve 23 is advantageously closed in order to prevent further injection of fuel into the combustion chamber 3. If the injection valve 16 does not close reliably, a continuous pressure drop occurs even after the fuel valve 23 has been closed, since fuel continues to pass from the injection valve 16 into the combustion chamber 3. A further pressure loss after the closing of the fuel valve 23 is thus a further indicator of a defective opening of the injection valve 16.If the fault situation in which a continuous injection of fuel by the injection valve 16 has been detected, then an excess of fuel is very probably already present in the combustion chamber 3. The additional quantity of air introduced briefly in this case must be adapted to the quantity of excess fuel. Thus, the introduction of unburned fuel into the exhaust system 8 is prevented.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 195 08 013 C1

[0001]

Claims

Method for diagnosing a heater (1) of an exhaust system (8) of an internal combustion engine (2), wherein air is supplied to a combustion chamber (3) of the heater by a secondary air pump (6) and fuel is supplied by an injection valve (16), wherein an air-fuel mixture formed in this way in the combustion chamber is ignited by a glow plug (4), wherein injection of the fuel takes place by actuating the injection valve (16) at individual partial injections at predefined points in time, wherein the combustion of the individual partial injections triggers a sensor signal in a pressure sensor (21) in the air supply to the combustion chamber (3) or a connecting pipe (9) from the combustion chamber (3) to the exhaust system (8), characterized in that by evaluating the pressure signal of the pressure sensor (21) at a frequency which characterizes the points in time of the partial injection and by evaluating the signal of a further sensor (10, 22) a continuous injection of fuel by the injection valve (16) is detected.Method according to Claim 1, characterized in that a lambda sensor (10) in the connecting pipe (9) from the combustion chamber (3) to the exhaust system (8) is used as a further sensor.Method according to Claim 2, characterized in that the signal of the lambda sensor (10) is used for a control circuit for a fuel quantity of the partial injections, and in that a continuous injection is detected if a fuel quantity of the individual partial injections predefined by the control circuit falls below a predefined threshold value.Method according to Claim 2, characterized in that continuous injection is determined if the lambda signal exceeds a predefined threshold value.Method according to Claim 1, characterized in that a pressure sensor (22) for the fuel in a fuel supply (24) for the injection valve is used as a further sensor.Method according to one of the preceding claims, characterized in that, in the event of a detected continuous injection of fuel, a fuel valve (23) in a fuel supply for the injection valve (16) is closed.Method according to Claim 6, characterized in that, after the closing of the fuel valve, the time profile of the pressure in the fuel supply (24) is evaluated.Method according to one of the preceding claims, characterized in that, in the case of a detected continuous injection of fuel, the supply of air to the heater (1) is increased.Device for diagnosing a heater (1) of an exhaust system (8) of an internal combustion engine (2), wherein air is supplied to a combustion chamber (3) of the heater by a secondary air pump (6) and fuel is supplied by an injection valve (16), wherein an air-fuel mixture formed in this way in the combustion chamber (3) is ignited by a glow plug (4), wherein injection of the fuel takes place by actuating the injection valve (16) at individual partial injections at predetermined times, wherein the combustion of the individual partial injections triggers a sensor signal in a pressure sensor (21) in the air supply to the combustion chamber (3) or a connecting pipe (9) from the combustion chamber to the exhaust system (8), characterized in that, means are provided for detecting continuous injection of fuel by the injection valve by evaluating the pressure signal of the pressure sensor (21) at a frequency characterizing the times of the partial injection and by evaluating the signal of a further sensor (10, 22).

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