DE102008014070B4 - Method and device for operating an internal combustion engine - Google Patents

Abstract

Method for operating an internal combustion engine having an exhaust gas tract (1) comprising an exhaust gas catalytic converter (21) and an exhaust gas probe (42), wherein a lambda controller is provided whose control difference (D_LAMB) depends on a measurement signal (MS1) of the exhaust gas probe (42) and a Forced excitation signal (LAMB_SP) is determined and whose regulator control signal (LAM_FAC_FB) influences a fuel mass to be metered, in which
A first characteristic value (KW_1) is determined as a function of a distance integral of at least one component of the controller control signal (LAM_FAC_FB) with respect to a controller reference signal characteristic (LAM_FAC_FB_REF) over a predetermined period of time (T_INT), wherein the distance integral defines an absolute area between the controller reference signal characteristic (LAM_FAC_FB_REF) and the Control signal (LAM_FAX_FB) represents,
- Depending on the first characteristic value (KW_1) a quality value (GW) is determined and
- is detected depending on the quality value (GW) on either the presence (ERR) or the absence (N_ERR) of an error of the exhaust gas sensor (42).

Description

The The invention relates to a method and an apparatus for operating an internal combustion engine with an exhaust tract, the exhaust catalyst and includes an exhaust gas probe. A lambda controller is provided, whose Control difference dependent from a measurement signal of the exhaust gas probe and a forced excitation signal is determined and the controller control signal to be metered fuel mass affected.

always stricter legal regulations regarding permissible pollutant emissions of motor vehicles in which internal combustion engines are arranged, make it necessary to reduce pollutant emissions during operation Keep the internal combustion engine as low as possible. This can on the one hand, in which the pollutant emissions are reduced, the while the combustion of the air / fuel mixture in the respective Cylinder of the internal combustion engine arise.

To the others are in internal combustion engines exhaust aftertreatment systems in use, the pollutant emissions during the combustion process of the air / fuel mixture in the respective cylinders be harmless Convert substances.

To For this purpose, for example, catalytic converters are used, the carbon monoxide, hydrocarbons and nitrogen oxides in harmless substances convert.

Either the targeted influencing of the generation of pollutant emissions while combustion as well as the conversion of pollutant components with a high efficiency set by a catalyst very precise adjusted air / fuel ratio in the respective cylinder ahead.

From the textbook "manual internal combustion engines", published by Richard van Basshuysen, Fred Schäfer, 2nd edition, Vieweg & Sohn Verlagsgesellschaft mbH, June 2002, pages 559 to 561, a linear lambda control is known with a linear lambda probe, which is arranged upstream of a catalytic converter , and a binary lambda probe disposed downstream of the catalytic converter. A lambda setpoint is filtered by means of a filter that takes into account gas runtimes and sensor behavior. The lambda setpoint value thus filtered is the controlled variable of a PII ² D lambda controller whose manipulated variable is an injection quantity correction.

in the Connection with the lambda control comes the or the lambda probes a special meaning too. Because of this, are getting stricter legal requirements implemented, which is a very strict monitoring require the respective lambda probe. Thus, under the legislation of the California State (Title 13, California Code Regulations, Section 1968.2, Chapter (e) (7)) in addition to an existing dynamic diagnosis one upstream an exhaust gas catalytic converter arranged lambda sensor for detection In addition, the recognition of a dynamic, symmetrical aging asymmetrically aged lambda probe required. In this context is a dynamic, symmetrical aging of the lambda probe so too Understand that their response after changing the air / fuel ratio from lean to rich and vice versa symmetrically delayed. at dynamic asymmetric aging shows only the response one of the two transitions one Slowing down the signal response. The slowing down of the signal reaction manifests itself regularly in one delay the step response as a result of the mixture change, in a reduced Ramp steepness or in a combination of both. A special The challenge in this context is the required service life and considering all operating conditions robust and field-suitable diagnostic results to obtain, in particular taking into account increased mileage demands up to 150,000 miles.

From the US 5 179 929 A It is known to use the correction signal at the output of a controller for the diagnosis of a defective lambda sensor and to average this signal over time and, depending on this averaged value, to detect a defective lambda sensor.

From the US 5 052 361 A It is known to determine integrals between an upper threshold value of a voltage and the voltage curve of a lambda sensor signal in regions of exceeding a reference voltage and to determine the integral between the lambda sensor signal and a lower voltage threshold value in regions of undershooting of the reference voltage by the lambda sensor signal. Depending on the integrals thus determined, a characteristic value is determined, depending on which a defective exhaust gas sensor is diagnosed.

The Problem underlying the invention is to provide a method and to provide an apparatus for operating an internal combustion engine, the one simple and reliable Operation of the internal combustion engine allows.

The object is solved by the features of the independent claims. Advantageous embodiments of the invention are in the Unteran marked.

The Invention is characterized by a method and a corresponding thereto Device for operating an internal combustion engine with an exhaust gas tract, comprising an exhaust gas catalyst and an exhaust gas probe. A lambda controller is provided whose control difference depends on a measurement signal of Exhaust probe and a forced excitation signal is determined. The forced stimulus signal For example, it can be filtered. The regulator control signal of the lambda controller influences a fuel mass to be metered. A first characteristic value becomes dependent from a distance integral of at least a portion of a servo control signal the lambda controller based on a controller reference signal waveform over a determined time duration determined. Depending on the first characteristic value becomes a quality value determined. Dependent of the quality value is either on the presence or the absence detected an error of the exhaust gas sensor. This way can be very precise a fault of the exhaust gas probe, which in particular be a lambda probe can be recognized. So can For example, probe aging in terms of dead time, a change their PT1 behavior, symmetrical and asymmetrical signs of aging are detected.

Prefers In this context, a comparison of the quality value takes place with a predetermined threshold and depending on this comparison Recognize the presence or absence of the Error of the exhaust gas sensor.

For example the proportion of the regulator control signal can be a P and / or I component represent, so especially correlate to it.

According to one advantageous embodiment, a second characteristic value is determined, dependent from a distance integral of a forced excitation signal of the lambda controller based on a forced excitation reference signal waveform over the predetermined time duration. In this way can be particularly reliable the Exhaust gas probe can only be detected as defective if downstream of Catalytic converter a predetermined increased emission of pollutants can be expected and thus an unnecessary for the overall system fault diagnosis be narrowed down very much.

Under The term "distance integral" is in particular to understand that an absolute area between the controller reference signal waveform and the regulator control signal of the lambda controller is determined. The same applies to referred to the distance integral of the forced excitation signal of the lambda controller on the forced excitation reference waveform.

Of the Controller reference signal waveform can also correlate, for example to an oxygen loading setpoint course. The distance integral can in principle also be related to a reference distance integral that determines is for a reference exhaust gas probe.

According to one In another advantageous embodiment, the quality value depends on an averaged one first and / or averaged second characteristic value. To this Way you can Scatters are very easily filtered out and thus a special one reliable Recognize the presence or absence of the Error of the exhaust gas sensor are detected.

According to one Further advantageous embodiment of the reference signal waveform determined by filtering the regulator control signal. This way you can particularly easily determines a suitable controller reference signal waveform become.

According to one Another advantageous embodiment of the controller reference signal waveform dependent determined by a moving averaging of the controller control signal. Also in this way is a particularly simple suitable determination the controller reference signal waveform possible.

According to one Another advantageous embodiment of the Zwangsanregungsreferenzsignalverlauf determined by filtering the forced excitation signal. Also on this Way is particularly easy a suitable determination of the forced excitation course possible.

In In this connection, it is advantageous if the forced excitation reference signal course depends on a moving averaging of the forced excitation signal determined becomes. This is especially easy to implement computationally.

According to one Another advantageous embodiment is dependent on a comparison of quality value with a given error threshold on either the presence or the absence of the error of the exhaust gas sensor detected. In this way, computationally very simple and reliable is the Presence or non-existence of the fault of the exhaust gas sensor possible.

According to a further advantageous refinement, the fault threshold value is determined as a function of at least one variable representing the load on the internal combustion engine. In this way, a particularly precise recognition of the present the absence or absence of the fault of the exhaust gas sensor is possible.

According to one Another advantageous embodiment is the error threshold dependent determined by a predetermined aging characteristic of the catalytic converter. In this way, a relevance of the state of the exhaust gas probe especially with regard to pollutant emissions downstream of the catalytic converter simple and precise considered become.

According to one Another advantageous embodiment is the predetermined period of time a period of compulsory stimulation. This is then computational particularly easy to implement.

embodiments The invention are explained in more detail below with reference to the schematic drawings. It demonstrate:

1 an internal combustion engine with a control device,

2 a block diagram of a part of the control device,

3 a flowchart of a first program and

4 a flowchart of a second program.

elements same construction or function are cross-figurative with the same Reference number marked.

An internal combustion engine ( 1 ) comprises an intake tract 1 , an engine block 2 , a cylinder head 3 and an exhaust tract 4 , The intake tract 1 preferably includes a throttle 5 and a collector 6 and a suction tube 7 leading to a cylinder Z1 via an inlet passage in the engine block 2 is guided. The engine block 2 further comprises a crankshaft 8th , which has a connecting rod 10 with the piston 11 of the cylinder Z1 is coupled.

The cylinder head 3 includes a valvetrain with a gas inlet valve 12 and a gas outlet valve 13 ,

The cylinder head 3 further comprises an injection valve 18 that also in the suction tube 7 can be arranged. It also includes a spark plug 19 ,

In the exhaust tract 4 is an exhaust gas catalyst 21 arranged, which may be formed, for example, as a three-way catalyst. A control device 25 is provided, the sensors are assigned, which detect different parameters and each determine the value of the measured variable. Operating variables also include variables derived from this in addition to the measured variables. The control device 25 is designed to determine dependent on at least one of the operating variables manipulated variables, which are then converted into one or more actuating signals for controlling the actuators by means of corresponding actuators. The control device 25 may also be referred to as a device for operating the internal combustion engine.

The sensors are a pedal position transmitter 26 , which is an accelerator pedal position of an accelerator pedal 27 detected, an air mass sensor 28 , which is an air mass flow upstream of the throttle 5 detected, a first temperature sensor 32 , which detects an intake air temperature, an intake manifold pressure sensor 34 , which is an intake manifold pressure in the collector 6 detected, a crankshaft angle sensor 36 , which detects a crankshaft angle, which is then assigned a speed.

Furthermore, a first exhaust gas probe 42 provided upstream of the catalytic converter 21 or in the catalytic converter 21 is arranged and which detects a residual oxygen content of the exhaust gas and whose measurement signal MS1 is characteristic of the air / fuel ratio in the combustion chamber of the cylinder Z1 and upstream of the first exhaust gas probe 42 before the oxidation of the fuel, hereinafter referred to as the air / fuel ratio in the cylinders Z1 to Z4. The first exhaust gas probe 42 can also be so in the catalytic converter 21 be arranged that a portion of the catalyst volume upstream of the first exhaust gas probe 42 located.

The first lambda probe 42 For example, it can be a linear lambda probe or even a binary lambda probe.

Furthermore, a second exhaust gas probe is preferred 44 downstream of the catalytic converter 21 arranged, which is used in particular in the context of a trim control and which is preferably designed as a simple binary lambda probe.

ever according to embodiment The invention may be any subset of said sensors be present or it can also additional Sensors be present.

The actuators are, for example, the throttle 5 , the gas inlet and outlet valves 12 . 13 , the injection valve 18 or the spark plug 19 ,

In addition to the cylinder Z1, further cylinders Z2 to Z4 are preferably also provided, which are then also assigned correspondingly to the actuators and optionally sensors. in principle Thus, the internal combustion engine can have any number of cylinders.

A block diagram of a part of the control device 25 is in the 2 shown. A predefined desired value LAMB_SP_RAW of the air / fuel ratio can be predefined in a particularly simple embodiment. However, it is preferably determined, for example, depending on the current operating mode of the internal combustion engine, such as a homogeneous or a stratified operation and / or depending on operating variables of the internal combustion engine. In particular, the desired value LAMB_SP_RAW of the air / fuel ratio may be set as approximately the stoichiometric air / fuel ratio.

In a block B1, a Zwangsanregungsrohsignal ZWA is determined and in the first summation point SUM1 the setpoint LAMB_SP_RAW of the Air / fuel ratio modulated with the Zwangsanregungsrohsignal ZWA. The coercive raw signal ZWA is preferably a rectangular one Signal with an optionally variable amplitude. It However, it can take other forms and so for example triangular or trapezoidal Be signal. The output of the first Summing point SUM1 is then the forced excitation signal LAMB_SP. The Forced excitation signal LAMB_SP is supplied to a block B2, the includes a feedforward and a lambda control factor LAMB_FAC_PC depending on the forced excitation signal LAMB_SP generated.

In a second summation point SUM2, depending on the forced excitation signal LAMB_SP and the detected air / fuel ratio LAMB_AV, that of the measuring signal MS1 of the exhaust gas probe 42 is determined and is optionally corrected by a trim controller intervention, by forming a difference, a control difference D_LAMB determined, the input is in a block B4.

In the block B4, a linear lambda controller is formed, preferably as a PII ² D controller. The manipulated variable of the linear lambda controller of the block B4 is an actuating signal LAMB_FAC_FB and can thus be, for example, a percentage value. In particular, the regulator control signal LAM_FAC_FB can also be added to the lambda ahead control factor LAM_FAC, for example. Thus, for example, in one situation, the lambda bias control factor LAM_FAC_PC may have a value of 1.02, and the regulator control signal may have a value of 0.03, which corresponds to 2, and thus the sum of the two and in the block and then together as the input of the Be supplied to the multiplier M1.

Regarding one possibly existing trim regulation is on the textbook "Manual combustion engine", publisher Richard van Basshuysen, Fred Schäfer, 2nd edition, Vieweg & Sohn Verlagsgesellschaft mbH, June 2002, pages 559 to 561, its contents hereby in this regard is involved.

The forced excitation signal may also be subjected to a filtering, for example, the gas transit times or the behavior of the catalytic converter 21 or the exhaust gas probe 21 in the form of a model.

Furthermore, a block B6 is provided, in which a basic fuel mass MFF to be metered is determined as a function of a variable LORD, which represents a load of the internal combustion engine and which may be, for example, an air mass flow, and the forced excitation signal LAMB_SP. In the multiplier M1, a fuel mass MFF to be metered is determined by forming the product of the basic fuel mass MFF to be metered and the lambda advance control factor LAM_FAC_PC and the regulator control signal LAM_FAC_FB, wherein, as explained above, the sum of the controller control signal LAM_FAC_FB and the lambda control factor LAM_FAC_PC can also be used. The injection valve 18 is then controlled according to the metering of the fuel mass MFF_COR to be metered. In a block B10, a filter for filtering the servo control signal is formed and the output of the block B10 is then a controller reference signal waveform. For example, the filter of block B10 may be configured to provide some form of averaging of the input signal, with particularly simple implementation being possible by moving averaging. In a particularly simple embodiment, the filter in the block B10 may also be dispensed with and the controller reference signal waveform LAM_FAC_FB_REF may also be fixed.

A block B12 is designed to determine a first characteristic value KW_1 as a function of a distance integral of at least one component of the regulator control signal LAM_FAC_FB with respect to the controller reference signal profile LAM_FAC_FB_REF over a predetermined time period T_INT. In this case, the predetermined period of time, for example, predetermined so that it corresponds to the period of the Zwangsanregungsrohsignals ZWA. The determination of the first characteristic value KW_1 in the block B12 preferably takes place cyclically, for example, so that a new, updated first characteristic value KW_1 is output regularly at the output of the block B12. Moreover, when determining the first characteristic value KW_1 after determining the distance integral, it is also possible to take into account a conversion and, to that extent, to take into account an oxygen loading equivalent, in which case at least one further operating variable of the internal combustion engine, such as the quantity LORD representing the load, is taken into account.

The Determining the distance integral can thus be done by means of Regulating control signal LAM_FAC_FB or even only a portion of the control signal LAM_FAC_FB, such as a P and / or I component.

In a block B14 is likewise preferably a filter, by means of which the forced excitation signal LAMB_SP is filtered and wherein the at the output of the block B14 is a forced excitation reference waveform LAM_SP_REF is output. In particular, the filter is formed and by guiding a mean-oriented filtering and can be so for example be designed to perform a moving average.

In In a simple embodiment, the forced excitation reference signal waveform LAM_SP_REF However, for example, be fixed.

Further a block B16 is provided, which is adapted to a second Characteristic KW_2 dependent from a distance integral of the forcible excitation signal LAM_SP to the forced excitation reference waveform LAM_SP_REF via the Predetermined time T_INT to determine. This is also a block B16, the second characteristic KW_2 preferably determined cyclically. Further can also basically when determining the second characteristic value after determining the respective Distance Integrals a conversion and thus take into account an oxygen loading equivalent respectively.

A first program stored in a memory of the control device 25 is stored and processed during operation of the internal combustion engine, is below with reference to the flowchart of the 3 explained in more detail. If necessary, variables can be initialized in step S1.

In a step S2 becomes a quality value GW dependent of at least the first parameter KW_1 and preferably additionally dependent determined by the second characteristic KW_2. Determining the quality value may include, for example, a quotient of the first and second Characteristic value KW_1, KW_2 is determined.

In a step S4, an error threshold value THD_ERR is determined, preferably as a function of a variable LORD, which represents a load of the internal combustion engine and / or an aging characteristic value AGE for an aging state of the catalytic converter 21 which particularly represents its oxygen storage ability. The determination of the error threshold value THD_ERR can be effected, for example, as a function of a predefined map. However, the error threshold THD_ERR can basically also be fixed in a simple embodiment.

In a step S6, it is then checked whether the quality value GW is greater than the error threshold value THD_ERR. If this is the case, the presence ERR of an error is detected in a step S8. On the other hand, if the condition of the step S6 is not satisfied, then in a step S10, the absence of N_ERR of an exhaust gas sensor error 42 recognized. Following the processing of steps S8 and S10, the processing is ended in step S12. Preferably, the program according to the 3 carried out again at regular intervals during operation of the internal combustion engine.

Another program, also in the memory of the control device 25 stored and during its operation according to the program in accordance with the 4 is processed, is started in a step S14, in which variables can be initialized if necessary.

In In a step S16, an averaged first parameter KW_1_MW is transmitted Means of first determined at several different calculation cycles Characteristic values KW_1 determined. In this case, for example, an averaging the determined first characteristic KW_1 be performed, for a given Number of time periods T_INT were determined, such as 5 or 10 or even more. In this context, in principle, too a moving averaging can be used.

Corresponding In step S16, an averaged second parameter KW_2_MW is also determined dependent determined by corresponding second characteristics KW_2.

One Step S18 then corresponds to step S2 insofar as determining the quality value GW instead of the first parameter KW_1 and / or the second characteristic value KW_2 by the averaged first characteristic KW_1_MW respectively the averaged second characteristic value KW_2_MW.

The Steps S20 to S28 then correspond to steps S4 to S12.

By determining the error threshold value THD_ERR depending on the aging state AGE of the catalytic converter, it is possible to check the presence ERR of the error of the exhaust gas de 42 in the case of a new catalytic converter, due to the greater efficiency of the catalytic converter, it can only be achieved with more pronounced dynamic probe defects. In the case of an older catalytic converter with lower efficiency, the error threshold value ERR can then be lowered so that an ERR error already occurs at low load peaks.

From values in the context of error detection, the effect in the system is evaluated and this makes it possible that errors only have to be recognized, even if excessive loads on the exhaust gas probe 42 be recorded. Thus, essentially no provisions are necessary, which in contrast are required when a direct diagnostic criterion is used, such as, for example, a conclusion of the measurement signal MS1 directly on emissions. In addition, all types of probe aging can be detected, such as dead time, change in PT1 behavior, symmetric and asymmetric aging phenomena, especially if this leads to a swinging of the lambda controller and thus its control loop signal LAM_FAC_FB.

Claims (12)

Method for operating an internal combustion engine with an exhaust gas tract ( 1 ), which is an exhaust gas catalyst ( 21 ) and an exhaust gas probe ( 42 ), wherein a lambda controller is provided whose control difference (D_LAMB) depends on a measurement signal (MS1) of the exhaust gas probe ( 42 ) and a forced excitation signal (LAMB_SP) is determined and whose regulator control signal (LAM_FAC_FB) influences a fuel mass to be metered, in which a first characteristic value (KW_1) depends on a distance integral of at least a portion of the regulator control signal (LAM_FAC_FB) relative to a controller reference signal characteristic (LAM_FAC_FB_REF) predetermined time duration (T_INT) is determined, wherein the distance integral represents an absolute surface between the controller reference signal waveform (LAM_FAC_FB_REF) and the servo control signal (LAM_FAX_FB), - a quality value (GW) is determined as a function of the first characteristic value (KW_1) and - depending on the quality value (GW) to either the presence (ERR) or absence (N_ERR) of a fault of the exhaust gas sensor ( 42 ) is recognized. Method according to claim 1, where a second Characteristic value (KW_2) from a distance integral of a forced excitation signal (LAMB_SP) the lambda controller based on a forced excitation reference signal waveform (LAMB_SP_REF) over the predetermined time (T_INT) is determined and - the quality value (GW) dependent is determined by the first and the second characteristic value (KW_1, KW_2). Method according to one of the preceding claims, in the quality value (GW) from an averaged first and / or averaged second characteristic value (KW_1, KW_2) is determined. Method according to one of the preceding claims, in the controller reference signal waveform (LAM_FAC_FB_REF) by filtering of the controller control signal (LAM_FAC_FB) is determined. Method according to one of the preceding claims, in the controller reference signal waveform (LAM_FAC_FB_REF) depends on a moving averaging of the controller control signal (LAM_FAC_FB) is determined. Method according to one of the preceding claims, in the forced excitation reference waveform (LAMB_SP_REF) Filtering the forced excitation signal (LAMB_SP) is determined. Method according to one of the preceding claims, in the forced excitation reference signal waveform (LAMB_SP_REF) depends on a moving averaging of the forced excitation signal (LAMB_SP) is determined. Method according to one of the preceding claims, in which, depending on a comparison of the quality value (GW) with a predetermined error threshold (THD_ERR), either the presence (ERR) or the absence (N_ERR) of an error of the exhaust gas sensor ( 42 ) is recognized. The method of claim 8, wherein the error threshold (THD_ERR) at least one of the load on the internal combustion engine representing Size (LORD) is determined. Method according to one of Claims 8 or 9, in which the fault threshold value (THD_ERR) is dependent on a predetermined aging characteristic value (AGE) of the catalytic converter ( 21 ) is determined. Method according to one of the preceding claims, in the predetermined time duration (T_INT) of a period of the forced excitation equivalent. Device for operating an internal combustion engine with an exhaust gas tract ( 1 ), which is an exhaust gas catalyst ( 21 ) and an exhaust gas probe ( 42 ), wherein a lambda controller is provided whose control difference depends on a measurement signal (MS1) of the exhaust gas probe ( 42 ) and a forced excitation signal (LAMB_SP) is determined, the controller Stellstell signal (LAM_FAC_FB) influences a fuel quantity to be metered, the device being designed to: a first characteristic value (KW_1) dependent on a distance integral of at least a portion of the regulator control signal (LAM_FAC_FB) of the lambda controller with respect to a controller reference signal characteristic (LAM_FAC_FB_REF) over a predetermined period of time (T_INT ), where distance integral represents an absolute area between the controller reference signal waveform (LAM_FAC_FB_REF) and the servo control signal (LAM_FAC_FB), determining a quality value (GW) as a function of the first characteristic value (KW_1) and depending on the quality value (GW) either Presence (ERR) or absence (N_ERR) of an exhaust sensor fault ( 42 ) to recognize.

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