METHOD AND DEVICE FOR DIAGNOSING A HEATING ELEMENT OF AN EXHAUST GAS SENSOR OF AN INTERNAL COMBUSTION ENGINE

Abstract

A method for diagnosing a heating element of an exhaust gas sensor of an internal combustion engine. The exhaust gas sensor includes a temperature measurement device. A modeled temperature at the point of the exhaust gas sensor is continuously ascertained with the aid of a temperature model. The temperature of the exhaust gas sensor is increased by a heating process. The diagnosis of the heating element of the exhaust gas sensor is provided as the result an enable condition. Upon enablement of the diagnosis, a temperature difference between the modeled temperature of the exhaust gas sensor and the measured temperature of the exhaust gas sensor are ascertained. The heating element of the exhaust gas sensor is recognized as defective when the ascertained temperature difference exceeds a predefinable temperature threshold value.

Claims

1. A method for diagnosing a heating element of an exhaust gas sensor of an internal combustion engine, the exhaust gas sensor including a temperature measurement element, the method comprising the following steps: continuously ascertaining a modeled temperature at a point of the exhaust gas sensor, using a temperature model; increasing the temperature of the exhaust gas sensor by a heating process; wherein the diagnosis of the heating element of the exhaust gas sensor is provided as a result of an enable condition; upon the enablement of the diagnosis, ascertaining a temperature difference between the modeled temperature of the exhaust gas sensor and the measured temperature of the exhaust gas sensor; recognizing the heating element of the exhaust gas sensor as defective when the ascertained temperature difference exceeds a predefinable temperature threshold value.

2. The method as recited in claim 1, wherein a start temperature is ascertained with a start of the heating process and the diagnosis is enabled upon exceedance of the start temperature by a predefinable temperature increase.

3. The method as recited in claim 2, wherein the start temperature is ascertained in a sensor-based or model-based manner.

4. The method as recited in claim 1, wherein the diagnosis is enabled as a function of a predefinable time period after a start of the heating process.

5. The method as recited in claim 1, wherein a heat quantity introduced into the exhaust gas system is ascertained as a function of the modeled temperature, the diagnosis being enabled when the ascertained heat quantity exceeds a predefinable heat quantity.

6. The method as recited in claim 1, wherein a heat quantity introduced into the exhaust gas system is ascertained as a function of the ascertained temperature, the diagnosis being enabled when the ascertained heat quantity exceeds a predefinable heat quantity.

7. The method as recited in claim 1, wherein a setpoint temperature for the heating process is predefined, the diagnosis being enabled when the modeled temperature reaches or exceeds the predefined setpoint temperature.

8. The method as recited in claim 1, wherein a setpoint temperature for the heating process is predefined, the diagnosis being enabled when an instantaneous temperature reaches the predefined setpoint temperature.

9. The method as recited in claim 1, wherein the temperature model of the exhaust gas sensor is configured in such a way that the temperature model models an aged exhaust gas sensor at a lower tolerance range.

10. The method as recited in claim 1, wherein the temperature model is ascertained as a function of a temperature of an intake air of the internal combustion engine, of a battery voltage of the internal combustion engine, of a pulse width-modulated activation ratio for the heater of the exhaust gas sensor, of a wall temperature at the point of the exhaust gas sensor, of an exhaust gas temperature, and of a coolant temperature at the output of internal combustion engine.

11. The method as recited in claim 1, wherein the heating of the exhaust gas sensor is carried out using a heating element integrated into the exhaust gas sensor.

12. A method for diagnosing a heating element of an exhaust gas sensor of an internal combustion engine, the exhaust gas sensor including a temperature measurement element, the method comprising: continuously ascertaining a modeled temperature at a point of the exhaust gas sensor using a temperature model; ascertaining a heating power as a function of a measured temperature; increasing a temperature of the exhaust gas sensor by a heating process; ascertaining a heater power and a modeled heater power as a function of the temperature model; wherein the diagnosis of the heating element of the exhaust gas sensor is provided as a result of an enable condition; upon enablement of the diagnosis, ascertaining a power quotient based on a measured heater power of the exhaust gas sensor and the modeled heater power of the exhaust gas sensor; and recognizing the heating element of the exhaust gas sensor as defective when the ascertained power quotient exceeds a predefinable power threshold value.

13. The method as recited in claim 12, wherein a heat quantity introduced into the exhaust gas system is ascertained as a function of the measured temperature, the diagnosis being enabled when the ascertained heat quantity exceeds a predefinable heat quantity.

14. The method as recited in claim 12, wherein a heat quantity introduced into the exhaust gas system is ascertained as a function of the modeled temperature, the diagnosis being enabled when the ascertained heat quantity exceeds a predefinable heat quantity.

15. A non-transitory machine-readable memory medium on which is stored a computer program for diagnosing a heating element of an exhaust gas sensor of an internal combustion engine, the exhaust gas sensor including a temperature measurement element, the computer program, when executed by a computer, causing the computer to perform the following steps: continuously ascertaining a modeled temperature at a point of the exhaust gas sensor, using a temperature model; increasing the temperature of the exhaust gas sensor by a heating process; wherein the diagnosis of the heating element of the exhaust gas sensor is provided as a result of an enable condition; upon the enablement of the diagnosis, ascertaining a temperature difference between the modeled temperature of the exhaust gas sensor and the measured temperature of the exhaust gas sensor; recognizing the heating element of the exhaust gas sensor as defective when the ascertained temperature difference exceeds a predefinable temperature threshold value.

16. An electronic control unit configured to diagnose a heating element of an exhaust gas sensor of an internal combustion engine, the exhaust gas sensor including a temperature measurement element, the electronic control unit configured to: continuously ascertain a modeled temperature at a point of the exhaust gas sensor, using a temperature model; increase the temperature of the exhaust gas sensor by a heating process; wherein the diagnosis of the heating element of the exhaust gas sensor is provided as a result of an enable condition; upon the enablement of the diagnosis, ascertain a temperature difference between the modeled temperature of the exhaust gas sensor and the measured temperature of the exhaust gas sensor; recognize the heating element of the exhaust gas sensor as defective when the ascertained temperature difference exceeds a predefinable temperature threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 schematically shows a representation of a subject lambda sensor from the related art,

[0030] FIG. 2 shows a first exemplary embodiment of the method according to the present invention based on a flowchart.

[0031] FIG. 3 shows a second exemplary embodiment of the method according to the present invention based on a flowchart.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0032] FIG. 1 schematically shows by way of example of a gasoline engine the technical setting in which the method for diagnosing exhaust gas sensor 15 according to the present invention may be employed. An internal combustion engine 10 is fed air via an air inlet 11 and its mass is determined using an air-flow sensor 12. Air-flow sensor 12 may be designed as a hot film air-flow sensor. The exhaust gas of internal combustion engine 10 is discharged via an exhaust gas channel 18, an emission control system 16 being provided in the flow direction of the exhaust gas downstream from internal combustion engine 10. Emission control system 16 normally includes at least one catalytic converter.

[0033] For controlling internal combustion engine 10, a control unit 100 is provided, which carries out a fuel metering via injection valves 13 in a known manner. In addition, the signals of air-flow sensor 12 and of exhaust gas sensors 15, 17 situated in exhaust gas channel 18 are received and stored. Exhaust gas sensor 15 in the example shown determines a lambda actual value of an air-fuel mixture fed to internal combustion engine 10. It may be designed as a broadband lambda sensor or continuous lambda sensor. Exhaust gas sensor 17 determines the exhaust gas composition downstream from emission control system 16. Exhaust gas sensor 17 may be designed as a bistable sensor or a two-point lambda sensor.

[0034] Exhaust gas sensor 15 includes as the main component a measuring cell that includes an integrated heating element and a temperature sensor, which supplies an output signal as a function of the oxygen content in exhaust gas channel 18, which serves as an input signal of a lambda control. The measuring cell in this case may be designed as a Nernst cell. The lambda control is usually a component of a function in control unit 100.

[0035] The method according to the present invention is explained below as exemplified by exhaust gas sensor 15 designed as a two-point lambda sensor. This may be applied analogously also to other exhaust gas sensors that include a temperature-dependent output signal, a heating element and a temperature sensor.

[0036] One particular feature of the present invention is further represented by a temperature model for exhaust gas sensor 15, which is able to model the temperature at the point of exhaust gas sensor 15 during a heating process as a function of multiple input variables. The temperature model in this case is ascertained with the aid of control unit 100.

[0037] The temperature model in this case takes into account the heat input through the heater of exhaust gas sensor 15, as well as the external influences, such as the heat input or the heat dissipation via the exhaust gas surrounding exhaust gas sensor 15, in which exhaust gas sensor 15 is embedded.

[0038] The sensor temperature model in this case takes the external influences into account, the assumed heating power being set according to the activated heater voltage (assuming the specified heater resistance R.sub.i) in relation to the heat input or the resultant sensor temperature.

[0039] Exhaust gas sensors 15, 17 each further include a means for temperature measurement (i.e., a temperature measurement element), the temperatures of exhaust gas sensors 15, 17 being received by control unit 100 where they are stored.

[0040] The sensor temperature model or temperature model is ascertained as a function of an intake air temperature, of a battery voltage, of a pulse width-modulated activation ratio of the heater of exhaust gas sensor 15, of a wall temperature at the point of exhaust gas sensor 15, of an exhaust gas temperature at the point of exhaust gas sensor 15 and of a coolant temperature T.sub.coolant at the output of internal combustion engine 10. The electrical heating power of exhaust gas sensor 15 results from the instantaneous battery voltage and from the pulse width-modulated activation ratio as a function of given heater resistance R.sub.i. This heater resistance R.sub.i is temperature-dependent and specified for a functional exhaust gas sensor 15. As a result of, for example, ageing processes of the heater element, heater resistance R.sub.i may obtain an additional component, as a result of which the resultant heating power of exhaust gas sensor 15 is reduced. By way of this additional component, it is possible using the evaluation logic presented to distinguish between a functional and a marginal or a defective exhaust gas sensor 15.

[0041] An exemplary sequence of the method according to the present invention for diagnosing a heating element of an exhaust gas sensor 15 of an internal combustion engine 10 is shown in FIG. 2. A temperature model is stored on control unit 100, which models a temperature T.sub.mod at the point of exhaust gas sensor 15.

[0042] Mass flows, volume flows, temperatures of internal combustion engine 10, or temperatures of the intake air and of the exhaust gas of internal combustion engine 10, preferably temperatures ascertained upstream from exhaust gas sensor 15, for example, may be used as input signals for the temperature model. In one particularly advantageous embodiment, the temperature model is ascertained as a function of a temperature of an intake air of the internal combustion engine, of a battery voltage of the internal combustion engine, of a pulse width-modulated activation ratio for the heater of exhaust gas sensor 15, of a wall temperature at the point of exhaust gas sensor 15, of an exhaust gas temperature, of a coolant temperature T.sub.coolant at the output of internal combustion engine 10.

[0043] In an initial step 200, an enable condition for the method is checked.

[0044] In one first embodiment, the method for diagnosing a heating element of an exhaust gas sensor 15 of an internal combustion engine 10 is enabled when a predefinable time period t.sub.wait starting from the activation of the heating element of exhaust gas sensor 15 has elapsed. Time t is started with the start of the heating process in control unit 100.

[0045] If time t exceeds predefinable time period t.sub.wait, the method is then enabled and the method is continued in step 210.

[0046] In one second embodiment, the method for diagnosing a heating element of an exhaust gas sensor 15 of an internal combustion engine 10 is enabled when a start temperature T.sub.start of exhaust gas sensor 15, which is ascertained at the point in time of the activation of the heater element of exhaust gas sensor 15, is exceeded by a predefinable temperature increase S.sub.Temp. In this case, start temperature T.sub.start is received and stored in control unit 100 and it is continuously checked whether start temperature T.sub.start exceeds predefinable temperature increase S.sub.Temp.

[0047] Temperature T.sub.start observed in this case is ascertained in the process preferably via the temperature model or in a sensor-based manner via the temperature sensor of exhaust gas sensor 15.

[0048] The method may then be continued in step 210.

[0049] In one third embodiment, the method for diagnosing a heating element of an exhaust gas sensor 15 of an internal combustion engine 10 is enabled when a predefinable heat quantity w.sub.specification is exceeded by an ascertained heat quantity w.sub.Trg, which is started with the activation of the heater element of exhaust gas sensor 15. Starting with the activation of the heating process, heat quantity w.sub.Trg is continuously ascertained as a function of modeled temperature T.sub.mod.

[0050] Heat quantity w.sub.Trg results in a known manner from modeled temperature difference ΔT.sub.mod, from specified heat capacity c.sub.p of exhaust gas sensor 15 and from mass M of exhaust gas sensor 15. The calculation and the enabling are carried out in this case by control unit 100.

[0051] Alternatively, heat quantity w.sub.Trg may be ascertained also based on continuously ascertained temperature T.sub.sens of the temperature sensor of exhaust gas sensor 15.

[0052] In one alternative embodiment, modeled heat quantity w.sub.Trg may be ascertained over a predefinable time period. Starting at the point in time of the activation of the heater process until, for example, a predefinable period of time has elapsed. In one alternative embodiment, the ascertainment of heat quantity w.sub.Trg may also be carried out via a heater power P.sub.sens;P.sub.mod. The heater power may be ascertained on the one hand via the temperature model or via sensor-based variables.

[0053] The method is then continued in step 210.

[0054] In one fourth embodiment, the method for diagnosing a heating element of an exhaust gas sensor 15 of an internal combustion engine 10 is enabled when an ascertained temperature T.sub.Sens of exhaust gas sensor 15 exceeds a predefinable operating temperature TH.sub.setpoint.

[0055] For this purpose, temperature T.sub.Sens of exhaust gas sensor 15 is ascertained preferably starting from the activation of the heater process for the heater element of exhaust gas sensor 15, and when ascertained temperature T.sub.Sens exceeds predefinable operating temperature TH.sub.setpoint, enablement is provided and the method is continued in step 210.

[0056] For evaluating, modeled temperature T.sub.mod may alternatively also be used for the enablement. If modeled temperature T.sub.mod exceeds predefinable operating temperature TH.sub.setpoint, enablement is provided and the method is continued in step 210.

[0057] An operating temperature for a lambda sensor is, for example, approximately 700° C.

[0058] In a step 210, a temperature difference Diff.sub.T between modeled temperature T.sub.mod and ascertained temperature T.sub.Sens is continually ascertained upon enablement of the method by control unit 100.

[0059] If ascertained temperature difference Diff.sub.T exceeds a predefinable temperature threshold value T.sub.max, the heating element of exhaust gas sensor 15 is recognized as defective and the method may be terminated or started again at the beginning in step 200.

[0060] Alternatively, the evaluation of temperature difference Diff.sub.T may be carried out filtered against predefinable temperature threshold value T.sub.max, so that an exceedance of predefinable temperature threshold value T.sub.max by ascertained temperature difference Diff.sub.T must be present for a particular period of time before the heating element of exhaust gas sensor 15 is recognized as defective.

[0061] A second exemplary sequence for the method for diagnosing a heating element of an exhaust gas sensor 15 of an internal combustion engine 10 is shown in FIG. 3. A temperature model, which models a temperature T.sub.mod at the point of exhaust gas sensor 15 as well as a modeled heater power P.sub.mod, is stored on control unit 100.

[0062] With the specification of an operating temperature for exhaust gas sensor 15, an activation of the heater element of exhaust gas sensor 15 is started in a first step 300. With the activation of the heater element, the temperature of the intake air of internal combustion engine 10, the battery voltage of internal combustion engine 10, the pulse width-modulated activation ratio for the heater of exhaust gas sensor 15, the wall temperature at the point of exhaust gas sensor 15, the exhaust gas temperature and the coolant temperature T.sub.coolant at the output of internal combustion engine 10 are also continuously received and stored by control unit 100. A heater power P.sub.sens is ascertained by control unit 100 as a function of ascertained temperature T.sub.Sens of the battery voltage and of the pulse width-modulated activation signal for the heater.

[0063] A modeled heater power P.sub.mod is also ascertained via the temperature model based on ascertained temperature T.sub.Sens.

[0064] The method is then continued in step 310.

[0065] With the start of the activation of the heater element of exhaust gas sensor 15, an enablement of the diagnosis of the heating element of an exhaust gas sensor 15 is started in step 310. In one first embodiment, the method for diagnosing a heating element of an exhaust gas sensor 15 of an internal combustion engine 10 is enabled when a predefinable time period t.sub.wait starting from the activation of the heating element of exhaust gas sensor 15 has elapsed. Time t is started with the start of the heating process in control unit 100.

[0066] If time t exceeds predefinable time period t.sub.wait, then the method is enabled and the method is continued in step 320.

[0067] In one alternative embodiment, the method for diagnosing a heating element of an exhaust gas sensor 15 of an internal combustion engine 10 is enabled when a predefinable heat quantity W.sub.specification is exceeded by an ascertained heat quantity w.sub.Trg, which is started with the activation of the heater element of exhaust gas sensor 15. Starting with the activation of the heating process, heat quantity w.sub.Trg is continuously ascertained as a function of measured temperature T.sub.Sens and/or of modeled temperature T.sub.mod.

[0068] Heat quantity w.sub.Trg results in a known manner from temperature difference ΔT.sub.mod, from specific heat capacity c.sub.p of exhaust gas sensor 15 and from mass M of exhaust gas sensor 15.

[0069] The calculation and the enablement in this case are carried out by control unit 100.

[0070] Alternatively, heat quantity w.sub.Try may be ascertained also based on continuously ascertained temperature T.sub.Sens of the temperature sensor of exhaust gas sensor 15.

[0071] In one alternative embodiment, modeled heat quantity w.sub.Trg may be ascertained over a predefinable time period. Starting at the point in time of the activation of the heater process until, for example, a predefinable period of time has elapsed. In one alternative embodiment, the ascertainment of heat quantity w.sub.Trg may also be carried out via a heater power P.sub.sens;P.sub.mod. The heater power may be ascertained on the one hand via the temperature model or via sensor-based variables.

[0072] The method may then be continued in step 320.

[0073] In a step 320, a power quotient Q.sub.P between ascertained heater power P.sub.Sens and modeled heater power P.sub.mod is continuously ascertained by control unit 100 upon enablement of the method. If ascertained power quotient Q.sub.P exceeds a predefinable power threshold value S.sub.Q, the heating element of exhaust gas sensor 15 is recognized as defective and the method is terminated or started again at the beginning in step 300.

[0074] The monitoring of power quotient Q.sub.P is based on the idea that power quotient Q.sub.P in the case of a functional heater element of exhaust gas sensor 15 is close to the value one.

[0075] For a defective heating element of exhaust gas sensor 15, the actual required heater power P.sub.Sens would always be greater than heater power P.sub.mod modeled based on the temperature model for a functional heater element of exhaust gas sensor 15.

[0076] If the heating power of the heater element of exhaust gas sensor 15 is limited, for example, by a defect, then the heater element must provide more heater energy in contrast to a heater element of a functional exhaust gas sensor, in order, for example, to reach a predefinable operating temperature or in order to maintain this operating temperature.

[0077] As a result of the continuous comparison of heater power P.sub.Sens with modeled heater power P.sub.mod, it thus possible to carry out a diagnosis of the heater element of exhaust gas sensor 15 in a robust manner.

[0078] If values greater than one result for power quotient Q.sub.P, then it must be assumed that the heating element of exhaust gas sensor 15 is severely limited in its efficiency or is even defective.

[0079] Alternatively, the evaluation of power quotient Q.sub.P may be carried out filtered against predefinable power threshold value S.sub.Q, so that an exceedance of predefinable power threshold value S.sub.Q by ascertained power quotient Q.sub.P must be present for a particular period of time before the heating element of exhaust gas sensor 15 is recognized as defective. The method may then be terminated or started from the beginning in step 300.