Method and error simulator for checking the error detection of a control unit

Abstract

Method for checking the error detection of a control unit (14) of an internal combustion engine in the event of a malfunction of a connected broadband lambda probe (10), wherein the check is carried out using an error simulator (12) arranged between the broadband lambda probe (10) and the control unit (14), and wherein the error simulator (12) specifically modifies electrical signals exchanged between the broadband lambda probe (10) and the control unit (14) in order to simulate errors of the broadband lambda probe (10), characterized in that a Nernst voltage UN0 mess (11) of the broadband lambda probe (10) and a pump current IP MSG (16) of the control unit (14), that the fault simulator (12) of the broadband lambda probe (10) a pump current IP Sonde (15) and the control unit (14) a Nerst voltage UN0 stell(13) and that the fault simulator (12) for simulating faults of the broadband lambda probe (10) supplies the Nernst voltage UN0 supplied to the control unit (14) stell (13) compared to the Nernst voltage UN0 output by the broadband lambda sensor (10) mess (11) is changed, whereby the pump current IP output to the broadband lambda probe (10) Sonde (15) the pump current IP output by the motor control (14) MSG (16) or that the pump current IP output to the broadband lambda probe (10) Sonde (15) by the fault simulator (12) based on the Nernst voltage UN0 output by the broadband lambda probe (10) mess (11) is specified or that the pump current IP output to the broadband lambda probe (10) Sonde (15) by the fault simulator (12) depending on the pump current IP output by the control unit (14) MSG (16), wherein the pump current IP is dependent on the pump current MSG(16) pump current IP specified by the fault simulator (12) and output to the broadband lambda probe (10) Sonde (15) larger or smaller and / or delayed in time compared to the pump current IP MSG (16) is specified.

Description

Prior ArtThe invention relates to a method for checking the fault detection of a control unit of an internal combustion engine in the event of a malfunction of a connected broadband lambda probe, wherein the checking is carried out with a fault simulator arranged between the broadband lambda probe and the control unit, and wherein the fault simulator changes electrical signals exchanged between the broadband lambda probe and the control unit in a targeted manner in order to simulate faults of the broadband lambda probe.DE 10 2006 008 539 A1 discloses a method and a circuit arrangement ( 10) for simulating fault states in a control device and a computer program and a computer program product. Here, a multiplexer (12) and an error generation circuit (14) are used, wherein the multiplexer (12) is implemented in a relay technology and the error generation circuit (14) is implemented in a semiconductor technology.WO 01 / 90 734 A1 discloses a test and calibration device for an evaluation circuit of a linear oxygen probe (S) of an internal combustion engine has a probe equivalent circuit (SES)-having the same connections (Vs+, Vs- / Vp-, Vp+ and Rc) as the oxygen probe (S)-which substantially simulates the electrical and chemical behaviour of the oxygen probe (S) and can simulate probe errors and which is connected to the evaluation circuit at least during a test and calibration process instead of the oxygen probe (S) or in parallel therewith.The invention further relates to a fault simulator for checking the fault detection of a control device of an internal combustion engine in the event of a malfunction of a connected broadband lambda probe, wherein the fault simulator is arranged between the broadband lambda probe and the control device for simulating faults of the broadband lambda probe.DE 10 2008 027 895 A1 relates to a method and a circuit arrangement (L-FST) for the functional testing of motor control units (MSG). The circuit arrangement (L-FST) is in this case connected between a control unit (MSG) and a broadband lambda probe for function testing and has a controllable current source (S1), which manipulates the current through the pump cell of the broadband lambda probe.In order to optimize pollutant emission and exhaust gas after-treatment, lambda probes are used in modern internal combustion engines for determining the composition of the exhaust gas and for controlling the internal combustion engine. Lambda sensors determine the oxygen content of the exhaust gas, which is used to control the air-fuel mixture supplied to the internal combustion engine and thus the exhaust gas lambda upstream of a catalytic converter. In this case, the air and fuel supply of the internal combustion engine is regulated via a lambda control circuit in such a way that an optimum composition of the exhaust gas is achieved for the exhaust gas after-treatment by catalytic converters provided in the exhaust gas duct of the internal combustion engine. In spark ignition engines, the system is generally controlled to a lambda of 1, i.e. a stoichiometric ratio of air to fuel. The pollutant emission of the internal combustion engine can thus be minimized.Various forms of lambda sensors are used. Wide-band lambda sensors, also referred to as steady or linear lambda sensors, make it possible, in contrast to two-point lambda sensors, to measure the lambda value in the exhaust gas over a wide range around lambda=1. Thus, for example, an internal combustion engine can also be controlled for lean operation with excess air.The sensor element of a broadband lambda probe has an opening on the surface through which exhaust gas enters. The inlet opening is followed by a porous layer through which the exhaust gas diffuses into a cavity. This cavity is separated from the external exhaust gas by an oxygen ion-conducting electrolyte material. Both on the outside of the electrolyte and on the side of the cavity are electrodes which are connected to plug contacts via cables. The intermediate electrolyte is referred to as a pump cell. Furthermore, inside the sensor element, separated from the cavity by the same electrolyte material, is a reference gas having a certain constant oxygen concentration. In contact with the reference gas is another electrode which is also connected to a plug contact. The electrolyte between this and the cavity-side electrode is referred to as a measuring cell.According to the Nernst principle, an electrical voltage, referred to below as Nernst voltage UNO, is present across the measuring cell, which is determined by the concentration of oxidizing and reducing exhaust gas components in the cavity and in the reference gas. Since the concentration in the reference gas is known and invariable, the dependence on the concentration in the cavity is reduced.In order to operate the lambda probe, it must be connected via the plug to corresponding operating electronics, usually to an engine control unit. The Nernst voltage UNO is detected via the electrodes and transmitted to the motor control unit. In the motor control unit there is a control circuit which keeps the Nernst voltage across the measuring cell at a setpoint value by driving a so-called pump current IP through the pump cell. For this purpose, the control loop contains a pump current regulator, which is frequently also referred to as a Nernst voltage regulator according to its controlled variable. Since the current flow in the electrolyte is effected by oxygen ions, the oxygen concentration in the cavity is influenced. In order to keep the Nernst voltage UNO constant in the steady state, exactly as much oxygen must be pumped out of the cavity in the lean range (λ>1) as is rediffusing through the diffusion barrier. In the rich range (λ<1), on the other hand, sufficient oxygen must be pumped into the cavity to compensate for the postdiffusing reducing exhaust gas molecules. Taking into account the fact that the oxygen balance in the cavity is kept constant by the pump current regulator, the diffusion equation produces a linear relationship between the diffusion current, and thus the pump current, and the oxygen concentration in the exhaust gas. The pump current is now measured in the motor control unit or is predefined by the motor control unit as a function of the measured Nernst voltage. The pump current represents a linear signal for the oxygen balance in the exhaust gas.If a broadband lambda probe is faulty, this must be detected by the engine control unit. To check whether an engine control unit recognizes the relevant errors of a broadband lambda probe, error simulators are nowadays used which are arranged between the engine control unit and the broadband lambda probe during the check. In this case, the fault simulator behaves with respect to the engine control unit like a broadband lambda probe with the faults to be checked. The engine control unit must recognize the relevant fault cases without software or application changes.One of the fault cases to be simulated is a change in the lambda signal of the broadband lambda probe. In this case, a delayed or distorted signal of the broadband lambda probe is predefined for the engine control unit. In fault simulations known today, the pump current is changed to simulate this fault, in order thus to bring about changes in the broadband lambda probe and a corresponding reaction in the engine control unit. These changes must be detected and indicated by the diagnostic function in the engine control unit.The change in the pump current for simulating a fault of the broadband lambda probe may result in the fault simulation itself being too slow. This may result in the engine controller responding, for example, to real signal changes that are due to real changes in the composition of the exhaust gas, although the fault simulator should suppress these changes.In motor control devices in which a pump current that is set represents the measurement signal and no back measurement of the resulting pump current takes place, the pump current is the output and the Nernst voltage UNO is the input signal of the pump current regulator. A fault simulation by changing the pump current signal acts here first on the broadband lambda probe. As a result, the Nernst voltage UNO and thus the input signal of the pump current regulator change. The known method for fault simulation via a change in the pump current has the disadvantage here that the change in the pump current only arrives late in the signal detection in the engine control unit. Therefore, real reactions of the broadband lambda probe to signal changes generally cannot be completely suppressed.It is an object of the invention to provide a method for simulating faults in a broadband lambda probe which avoids disruptive influences, such as become visible in the engine control unit, for example, as a result of delayed reactions or signal transit times.It is a further object of the invention to provide a corresponding fault simulator.Disclosure of the InventionThe object of the invention relating to the method is achieved in that a Nernst voltage UN0 mess of the broadband lambda probe and a pump current IP MSG of the control unit are supplied to the fault simulator, in that the fault simulator supplies a pump current IP Sonde to the broadband lambda probe and a Nernst voltage UN0 stell to the control unit, and in that the fault simulator changes the Nernst voltage UN0 stell supplied to the control unit compared to the Nernst voltage UN0 mess output by the broadband lambda probe in order to simulate faults in the broadband lambda probe.According to a particularly preferred embodiment variant of the invention, it can be provided that the fault simulator for simulating a changed pump current IP MSG changes the Nernst voltage UN0 stell supplied to the control device with respect to the Nernst voltage UN0 mess output by the broadband lambda sensor.During regular operation of the internal combustion engine, the deviation of the Nernst voltage UNO from the Nernst voltage setpoint value is the input variable of the pump current regulator. The pump current IP is the output signal of the pump current regulator and at the same time the measured variable which is further processed in the control unit. By changing the Nernst voltage UN0 stell supplied to the control unit with respect to the Nernst voltage UNO mess output by the broadband lambda sensor, the error simulator can bring about a change in the pump current signal. Since this change takes place before the control itself, no undesired reactions to changes in the pump current signal due to changes in the real exhaust gas occur in the control unit. Furthermore, control units in which a set pump current represents the measurement signal and no back measurement of the resulting pump current takes place can be checked.Different errors of the broadband lambda probe, for example a response behavior delayed due to aging effects or a corrupted Nernst signal, can be simulated in that the error simulator outputs a predefined Nernst voltage UN0 stell or a Nernst voltage UN0 stell variable as a function of time to the control unit in order to simulate errors.In this case, it can be provided that the fault simulator specifies the predefined Nernst voltage UN0 stell or the Nernst voltage UN0 stell which varies as a function of time, independently of or as a function of the Nernst voltage UN0 mess output by the broadband lambda sensor. The output Nernst voltage UN 0 stell may be predefined by a μ controller provided in the fault simulator.According to a preferred embodiment variant of the invention, it can be provided that• the pump current IP Sonde output to the broadband lambda sensor corresponds to the pump current IP MSG output by the engine controller, or• the pump current IP Sonde output to the broadband lambda sensor is predefined by the fault simulator on the basis of the Nernst voltage UN0 mess output by the broadband lambda sensor, or• the pump current IP Sonde output to the broadband lambda sensor is predefined by the error simulator as a function of the pump current IP MSG output by the control device.The choice of the pump current IP Sonde output to the broadband lambda probe can be made in this case as a function of the fault to be simulated. If the pump current IP Sonde corresponds to the pump current IP MSG, output by the engine controller, the pump current can be looped through by the engine controller through the fault simulator to the broadband lambda probe. If the pump current IP Sonde is predefined by the fault simulator, the pump current IP MSG provided by the engine controller can be lowered in the fault simulator.If the pump current IP Sonde output to the broadband lambda sensor is predefined by the error simulator as a function of the pump current IP MSG output by the control device, it can be provided that the pump current IP Sonde predefined by the error simulator as a function of the pump current IP MSG and output to the broadband lambda sensor is predefined to be greater or smaller and / or delayed in time in comparison to the pump current IP MSG.To monitor the operational readiness of the broadband lambda probe, in particular to monitor its operating temperature, a regular determination of the internal resistance of the broadband lambda probe is provided during regular operation. Therefore, it can be provided that the fault simulator simulates a load and makes a corresponding voltage signal available with respect to the control device for an internal resistance measurement.Various errors of the broadband lambda probe can be simulated in that the changes of the Nernst voltage UN0 stell output by the error simulator to the control unit and of the pump current IP Sonde output to the broadband lambda probe with respect to the Nernst voltage UN0 mess output by the broadband lambda probe and the pump current IP MSG output by the control unit take place simultaneously or separately from one another.The object of the invention relating to the fault simulator is achieved in that a Nernst voltage UN0 mess of the broadband lambda probe and a pump current IP MSG of the control unit are supplied to the fault simulator, in that a pump current IP Sonde is supplied to the broadband lambda probe and a Nernst voltage UN0 stell is supplied to the control unit from the fault simulator, and in that the fault simulator is designed to change the Nernst voltage UN0 stell supplied to the control unit compared to the Nernst voltage UN0 mess output by the broadband lambda probe. The fault simulator thus enables the method described to be carried out.The invention is explained in more detail below with reference to an exemplary embodiment shown in the figure. It shows: FIG. 1 shows a fault simulator for checking the fault detection of a control device.FIG. 1 shows a fault simulator 12 for checking the fault detection of a control unit 14. the fault simulator 12 is connected between a broadband lambda probe 10 and a control unit 14. The error simulator 12 is supplied with a Nernst voltage UNO mess11 of the broadband lambda probe 10, and a pump current IP MSG16 of the control unit 14. The fault simulator 12 supplies a pump current IP Sonde15 to the broadband lambda probe 10 and a Nernst voltage UN0 stell13 to the control device 14. The signals are represented by corresponding arrows, the number of signal lines represented is limited to the number necessary for the representation of the invention.Fault simulators 12 are used to test specific fault scenarios in broadband lambda sensors 10. For this purpose, the fault simulator 12 is connected between the broadband lambda probe 10 and the associated control device 14. The fault simulator 12 behaves with respect to the control unit 14 like a broadband lambda probe 10 with the faults to be checked, while the broadband lambda probe 10 continues to be operated. The control device 14 must recognize the errors specified by the error simulator without software or application changes. A fault case to be simulated is a change in the lambda signal of the broadband lambda probe 10, so that a delayed or distorted lambda signal is simulated to the control unit 14. In known fault simulators 12, the pump current IP is changed for this purpose, in order thus to bring about changes in the broadband lambda probe 10. These changes must be recognized by the control unit 14 by a diagnostic function.The change in the pump current IP for simulating a fault of the broadband lambda probe 10 can result in the fault simulation itself being too slow. This may result in the control unit 14 responding, for example, to real signal changes with a corresponding real change in the exhaust gas composition, although the fault simulator 12 should suppress this change.According to the invention, it is therefore provided that the fault simulation is carried out by the fault simulator 12 on the basis of the Nernst voltage UNO. For this purpose, the fault simulator 12 also interrupts the supply of the Nernst voltage UN0 mess11 output by the broadband lambda sensor 10 to the control unit 14 and outputs a correspondingly changed Nernst voltage UN0 stell13 to the control unit 14. The fault simulator 12 can thus bring about a change in the pump current IP MSG16 by correspondingly changing the Nernst voltage UN0 stell13. Since this change takes place before the control itself, no undesired reactions to changes in the pump current signal due to a change in the real exhaust gas are visible in the control unit 14.The control device 14 can arbitrarily specify the Nernst voltage UN0 stell13 which is output and, in particular, a change over time in the Nernst voltage UN0 stell13. This can be done by a μ controller provided in the fault simulator 12, for example as a function of the measured Nernst voltage UN0 mess or else independently thereof.The pump current IP MSG16 then calculated and output by the control unit 14 can be forwarded directly by the fault simulator 12 to the broadband lambda probe 10. Alternatively, the pump current IP MSG16 in the fault simulator 12 can be lowered without affecting the broadband lambda probe 10. A third possibility is to manipulate the pump current IP Sonde15 as a function of the pump current IP MSG16 and to forward it to the broadband lambda probe 10. In this case, the pump current IP Sonde15 can be selected to be greater, smaller or delayed in time with respect to the pump current IP MSG16.

Claims

Method for checking the fault detection of a control unit (14) of an internal combustion engine in the event of a malfunction of a connected broadband lambda probe (10), wherein the checking is carried out with a fault simulator (12) arranged between the broadband lambda probe (10) and the control unit (14), and wherein the fault simulator (12) specifically changes electrical signals exchanged between the broadband lambda probe (10) and the control unit (14) for simulating faults of the broadband lambda probe (10), characterized in that a Nernst voltage UN0 mess(11) of the broadband lambda probe (10) and a pump current IP MSG(16) of the control unit (14) are fed to the fault simulator (12), the fault simulator (12) supplies a pump current IP Sonde(15) to the broadband lambda sensor (10) and a Nernst voltage UN0 stell(13) to the control device (14), and the fault simulator (12), for simulating faults in the broadband lambda sensor (10), changes the Nernst voltage UN0 stell(13) supplied to the control device (14) with respect to the Nernst voltage UN0 mess(11) output by the broadband lambda sensor (10), wherein the pump current IP Sonde(15) output to the broadband lambda sensor (10) corresponds to the pump current IP MSG(16) output by the engine controller (14), or that the pump current IP Sonde(15) output to the broadband lambda sensor (10) is predefined by the fault simulator (12) on the basis of the Nernst voltage UN0 mess(11) output by the broadband lambda sensor (10), or that the pump current IP Sonde(15) output to the broadband lambda sensor (10) is predefined by the fault simulator (12) on the basis of the pump current IP MSG(16) output by the control unit (14), wherein the pump current IP Sonde(15) which is predetermined by the error simulator (12) as a function of the pump current IP MSG(16) and is output to the broadband lambda probe (10) is predetermined to be greater or smaller and / or delayed in time in comparison with the pump current IP MSG(16).Method according to Claim 1, characterized in that, for simulating a changed pump current IP MSG(16) the fault simulator (12) changes the Nernst voltage UN0 stell(13) supplied to the control unit (14) with respect to the Nernst voltage UNO mess(11) output by the broadband lambda sensor (10).Method according to Claim 1 or 2, characterized in that the fault simulator (12) outputs a predefined Nernst voltage UNO stell(13) or a Nernst voltage UNO stell(13) which varies as a function of time, to the control unit (14).Method according to one of Claims 1 to 3, characterized in that the fault simulator specifies the predefined Nernst voltage UNO stell(13) or the Nernst voltage UNO stell(13) which varies as a function of time, independently or as a function of the Nernst voltage UNO mess(11) output by the broadband lambda sensor (10).Method according to one of Claims 1 to 4, characterized in that the fault simulator (12) simulates a load and makes a corresponding voltage signal available for measuring the internal resistance with respect to the control unit (14).Method according to one of Claims 1 to 5, characterized in that the changes of the Nernst voltage UN0 stell(13) output by the fault simulator (12) to the control unit (14) and of the pump current IP Sonde(15) output to the broadband lambda probe (10) with respect to the Nernst voltage UNO mess(11) output by the broadband lambda probe and the pump current IP MSG(16) output by the control unit (14) take place simultaneously or separately from one another.Fault simulator (12) for checking the fault detection of a control device (14) of an internal combustion engine in the event of a malfunction of a connected broadband lambda probe (10), wherein the fault simulator (12) is arranged between the broadband lambda probe (10) and the control device (14) for simulating faults of the broadband lambda probe (10), characterized in that a Nernst voltage UNO mess(11) the broadband lambda probe (10) and a pump current IP MSG(16) of the control device (14) are fed to the fault simulator (12), in that a pump current IP Sonde(15) is fed to the broadband lambda probe (10) and a Nernst voltage UN0 stell(13) is fed to the control device (14) from the fault simulator (12), and in that the fault simulator (12) is designed to be able to generate a voltage UN0 which is fed to it, changing the Nernst voltage UN0 stell(13) supplied to the control unit (14) with respect to the Nernst voltage UNO mess(11) output by the broadband lambda sensor (10), wherein the pump current IP Sonde(15) output to the broadband lambda sensor (10) corresponds to the pump current IP MSG(16) output by the engine controller (14), or that the pump current IP Sonde(15) output to the broadband lambda sensor (10) is predefined by the fault simulator (12) on the basis of the Nernst voltage UNO mess(11) output by the broadband lambda sensor (10), or that the pump current IP Sonde(15) output to the broadband lambda sensor (10) is predefined by the fault simulator (12) on the basis of the pump current IP MSG(16) output by the control unit (14), wherein the pump current IP Sonde(15) which is predetermined by the error simulator (12) as a function of the pump current IP MSG(16) and is output to the broadband lambda probe (10) is predetermined to be greater or smaller and / or delayed in time in comparison with the pump current IP MSG(16).

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