METHOD FOR DETERMINING A FUNCTIONALITY OF AN EXHAUST GAS SENSOR IN AN EXHAUST GAS SYSTEM OF AN INTERNAL COMBUSTION ENGINE

Abstract

Determining a functionality of an exhaust gas sensor in an exhaust gas system having a catalytic converter and a first exhaust gas sensor upstream of the catalytic converter and a second exhaust gas sensor downstream of the catalytic converter. The first and the second exhaust gas sensors are heated to a temperature above a minimum operating temperature.; A first sensor signal of the first exhaust gas sensor; and a second sensor signal of the second exhaust gas sensor are determined. The first and the second sensor signals are compared in an operating period in which a temperature of the at least one catalytic converter does not exceed a temperature threshold value; and an operating parameter of the first exhaust gas sensor (121) is determined on the basis the comparison

Claims

1. A method (200) for determining a functionality of an exhaust gas sensor (121) in an exhaust gas system (120) of an internal combustion engine (110) having at least one catalytic converter (122) and a first exhaust gas sensor (121) upstream of the at least one catalytic converter (122) and a second exhaust gas sensor (123) downstream of the at least one catalytic converter (122), comprising: heating the first and the second exhaust gas sensor (121, 123) to a temperature above a minimum operating temperature of the relevant exhaust gas sensor (121, 123), determining (210) a first sensor signal of the first exhaust gas sensor (121), determining (220) a second sensor signal of the second exhaust gas sensor (123), comparing (230) the first and the second sensor signal in an operating period in which a temperature of the at least one catalytic converter (122) does not exceed a temperature threshold value, and determining (250) an operating parameter of the first exhaust gas sensor (121) on the basis of a result of the comparison (230) of the first and the second sensor signal.

2. The method (200) according to claim 1, wherein a gas transit time in the exhaust gas system (120) between a position of the first exhaust gas sensor (121) and a position of the second exhaust gas sensor (123) is taken into account in the comparison (230) of the first and the second sensor signal.

3. The method (200) according to claim 1, wherein the comparison (230) of the first and the second sensor signal in an operating period comprises determining a difference between the first and the second sensor signal and adding or integrating the difference over time.

4. The method according to claim 1, wherein the temperature threshold value is selected such that a storage capacity of the at least one catalytic converter (122) for exhaust gas components is at most 20% of a nominal storage capacity of the at least one catalytic converter (122).

5. The method (200) according to claim 1, wherein the temperature threshold value is selected from a range of from 0 C to 250 C.

6. The method (200) according to claim 1, wherein the first exhaust gas sensor (121) comprises a broadband lambda sensor and/or a switching-type lambda sensor and/or an NO.sub.x sensor and/or an oxygen sensor, and/or wherein the second exhaust gas sensor (123) comprises a broadband lambda sensor and/or a switching-type lambda sensor and/or an NO.sub.x sensor and/or an oxygen sensor.

7. The method (200) according to claim 1, comprising performing a measure (260) on the basis of the operating parameter.

8. The method (200) according to claim 7, wherein the measure comprises one or more of the group consisting of outputting a warning message and determining a correction value.

9. The method according to claim 7, wherein the measure comprises determining a correction value and the determined correction value is offset against the first sensor signal in order to obtain a corrected sensor signal.

10. A computing unit (130) configured to determine a functionality of an exhaust gas sensor (121) in an exhaust gas system (120) of an internal combustion engine (110) having at least one catalytic converter (122) and a first exhaust gas sensor (121) upstream of the at least one catalytic converter (122) and a second exhaust gas sensor (123) downstream of the at least one catalytic converter (122), by: controlling heating of the first and the second exhaust gas sensor (121, 123) to a temperature above a minimum operating temperature of the relevant exhaust gas sensor (121, 123), determining (210) a first sensor signal of the first exhaust gas sensor (121), determining (220) a second sensor signal of the second exhaust gas sensor (123), comparing (230) the first and the second sensor signal in an operating period in which a temperature of the at least one catalytic converter (122) does not exceed a temperature threshold value, and determining (250) an operating parameter of the first exhaust gas sensor (121) on the basis of a result of the comparison (230) of the first and the second sensor signal.

11. A non-transitory, computer-readable medium containing instructions that when executed by a computer cause the computer to determine a functionality of an exhaust gas sensor (121) in an exhaust gas system (120) of an internal combustion engine (110) having at least one catalytic converter (122) and a first exhaust gas sensor (121) upstream of the at least one catalytic converter (122) and a second exhaust gas sensor (123) downstream of the at least one catalytic converter (122), by: controlling heating of the first and the second exhaust gas sensor (121, 123) to a temperature above a minimum operating temperature of the relevant exhaust gas sensor (121, 123), determining (210) a first sensor signal of the first exhaust gas sensor (121), determining (220) a second sensor signal of the second exhaust gas sensor (123), comparing (230) the first and the second sensor signal in an operating period in which a temperature of the at least one catalytic converter (122) does not exceed a temperature threshold value, and determining (250) an operating parameter of the first exhaust gas sensor (121) on the basis of a result of the comparison (230) of the first and the second sensor signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 schematically shows a vehicle having an internal combustion engine and a catalytic converter as can be used within the scope of the present invention.

[0023] FIG. 2 shows an advantageous embodiment of the invention in the form of a greatly simplified flow chart.

DETAILED DESCRIPTION

[0024] In FIG. 1, a vehicle as can be used within the framework of the invention is shown schematically and designated overall with the number 100. The vehicle 100 comprises an internal combustion engine 110, here for example having six indicated cylinders, an exhaust gas system 120 which has a first catalytic converter 122 and a second catalytic converter 124, and a computing unit 130 which is configured to control the internal combustion engine 110 and the exhaust gas system 120 and is connected to said system in a data-conducting manner. Furthermore, in the example shown, the computing unit 130 is connected to sensors 121, 123, 127 in a data-conducting manner, which sensors detect operating parameters of the internal combustion engine 110 and/or of the exhaust gas system 120. In the example shown, for example, a broadband lambda sensor 121 can be provided upstream and a switching-type lambda sensor 123 downstream of a three-way catalyst 122. It should be understood that further sensors which are not shown may be present. The exhaust gas system 120 may optionally also have further cleaning components, such as, for example, particle filters and/or further catalytic converters, which, however, are not shown here for the sake of simplicity.

[0025] For the sake of simplicity, only one individual three-way catalyst (TWC) 122 is considered below. However, the invention can also be applied analogously to further catalytic converters and/or other types of catalytic converter in the exhaust gas system 120 if a lambda probe or another exhaust gas sensor which in particular provides a lambda signal is present in front of and behind the relevant catalytic converter. The invention can in principle be used with any internal combustion engine which is operated stoichiometrically (for example gasoline, alcohol, gas, or hydrogen if applicable), in which in particular the use of a catalytic converter with oxygen storage capacity is appropriate. However, the invention is not limited to exhaust gas systems in which catalytic converters with oxygen storage capacity are installed.

[0026] In the example shown here, the computing unit 130 comprises a data memory 132 in which, for example, computation rules and/or parameters (e.g. threshold values, characteristic variables of the internal combustion engine 110 and/or the exhaust gas system 120, or the like) can be stored.

[0027] The internal combustion engine 110 drives wheels 140 and can also be driven by the wheels in certain operating phases (e.g. so-called overrun mode).

[0028] In FIG. 2, an advantageous embodiment of a method according to the invention is shown schematically in the form of a flow chart and denoted overall by the number 200.

[0029] References to components of a vehicle or to a part of a vehicle used in the description of the method 200 relate in particular to the vehicle 100 shown in FIG. 1.

[0030] The method 200 is shown step-by-step below in order to enable a better understanding of the invention. However, this should not be understood to mean that the invention is limited to a step-by-step implementation of the method 200. Rather, individual steps can also be carried out simultaneously or in another order, for example in reverse order, unless expressly stated otherwise. A substantially continuous execution of some of the steps described may also be advantageous where appropriate.

[0031] It should again be emphasized here that the method 200 is carried out in a state of the exhaust gas system 120 in which the catalytic converter 122 has a temperature which does not exceed a temperature threshold value. For example, the temperature threshold value may be 150° C. At a temperature below this temperature threshold value, a storage capacity and a catalysis capacity of the catalytic converter 122 are so low that a composition of the exhaust gas flowing through the catalytic converter 122 is not significantly changed.

[0032] In the context of a step 210 of the method 200, a first sensor signal of the lambda probe 121 is detected upstream of the catalytic converter 122. In a step 220, a second sensor signal of the lambda probe 123 is detected downstream of the catalytic converter 122.

[0033] In one example, the exhaust gas is regulated to lambda=1 in front of the catalytic converter on the basis of the signal of the first lambda probe 121 (broadband probe). A second control loop with the setpoint value lambda=1 is established on the basis of the second lambda 123 probe behind the catalytic converter. The control deviations of this second control loop are integrated and, for example, interpreted as a measurement deviation between the first lambda probe 121 (in front of the catalytic converter) and the second lambda probe 123 (behind the catalytic converter). In practice, the error thresholds are approximately 3% (fuel trim error) or 6% (offset error of the first sensor). The detected deviations are adapted.

[0034] In another example, the detected first and second sensor signal are compared with one another in a step 230. In this case, a gas transit time, which requires the exhaust gas to pass the section of the exhaust gas system 120 located between the position of the lambda probe 121 and the position of the lambda probe 123, is taken into account, so that signals relating to an identical exhaust gas are compared with one another.

[0035] The gas transit time can be calculated, for example, from a known distance or a known exhaust gas system volume between the two sensor positions in combination with a measured exhaust gas mass flow or a flow rate determined from a (differential) pressure measurement. For example, a lambda difference can be calculated during the comparison. The lambda difference determined in this way is preferably integrated or added over time, so that, in the event of a longer deviation between the two sensor signals in the same direction, an increasing comparison result is given, while in the case of a deviation with an alternating sign, the comparison result fluctuates around zero.

[0036] In a step 240, on the basis of the result of the comparison from step 230, for example on the lambda difference which is added or integrated over time, the rest of the method 200 is determined. For this purpose, the integrated lambda difference can be compared with one or more differential threshold values, for example. If the integrated lambda difference is below a first, low threshold value, which can be Δλ=0.03, for example, the method returns to steps 210 and 220.

[0037] However, if the lambda difference is above a second, high threshold value, which can be 0.06, for example, then the method continues with a step 260 in which a malfunction of the lambda probe 121 upstream of the catalytic converter 122 is determined and a corresponding measure, for example output of a warning message, in particular in the form of actuation of a malfunction indicator light, is carried out.

[0038] If the lambda difference is between the first and the second threshold value, the method can continue with a step 250 in which a correction value, for example in the form of a correction factor or an additive lambda offset, is determined, which value is stored in the data memory 132 of the computing unit 130 and is used for future evaluation of the first sensor signal. In particular, a cause of a particular deviation can also be determined on the basis of the determined deviation. For example, in the case of a relatively low deviation, a so-called fuel trim error can be assumed, which can be corrected or compensated for by an adjustment of the quantity of fuel supplied to the internal combustion engine, whereas, in particular in the case of higher deviations, the cause may be an offset between the lambda probe 121 and the lambda probe 123, which can be corrected computationally in the signal evaluation.

[0039] The specific first and second threshold values can of course be selected so as to be different from the examples given here. If, for example, the first, low threshold value is equal to zero, the determined deviation is always corrected continuously. The upper threshold value can also be omitted entirely, for example.