Method for heating an exhaust system, exhaust system and motor vehicle

Abstract

The invention relates to a method for heating an exhaust system (10) of a motor vehicle having a catalytic converter (12), wherein the exhaust system (10) comprises an electrically heatable heating disc (14) arranged in front of the catalytic converter (12) in the exhaust system (10) in the flow direction of a carrier mass flow (16), the method comprising the following steps: determining the value of one or more electrical properties at time intervals during the heating of the electrically heatable heating disc (14); determining whether there is a sufficiently large carrier mass flow (16) by evaluating the determined values of the one or more electrical properties of the electrically heatable heating disc (14). The invention also relates to an exhaust system and a vehicle having an exhaust system.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for heating an exhaust system of a motor vehicle, to an exhaust system of a motor vehicle and to a motor vehicle having such an exhaust system. BACKGROUND

[0002] To ensure low emissions, a heating disc can be used to pre-heat the exhaust system of a motor vehicle. To this end, a carrier mass flow, for example air, flows around or perfuses the electrically heatable heating disc, and a downstream catalytic converter is heated. If the carrier mass flow is not present or is insufficient, overheating or damage to the heating disc can occur.

[0003] US 5740675 A discloses a system and a method for estimating the temperature of an exhaust system having an electrically heatable catalytic converter, wherein the temperature of the exhaust system is estimated by means of an electrical property of the electrically heatable catalytic converter.

[0004] Here, it is disadvantageous that the absence or insufficiency of the carrier mass flow cannot be reliably detected, and the heating disc cannot be protected from damage due to overheating. SUMMARY

[0005] The problem addressed by the invention is to provide a method for heating an exhaust system of a motor vehicle, an exhaust system of a motor vehicle and a motor vehicle having such an exhaust system, in which the absence or insufficiency of the carrier mass flow can be reliably detected, and damage to the heating disc due to overheating can be prevented.

[0006] The problem is solved by a method for heating an exhaust system of a motor vehicle, an exhaust system of a motor vehicle and a motor vehicle according to the following embodiments.

[0007] Method for heating an exhaust system of a motor vehicle having a catalytic converter, in particular for heating or pre-heating the catalytic converter, wherein the exhaust system comprises an electrically heatable heating disc, which is arranged in front of the catalytic converter in the exhaust system in the flow direction of a carrier mass flow, for example air, the method comprising the following steps:

[0008] During heating of the electrically heatable heating disc, the (current) values, for example readings, of one or more electrical properties are determined at time intervals, in particular at regular intervals.

[0009] By evaluating the determined values of the one or more electrical properties of the electrically heatable heating disc, it is determined whether a sufficiently large carrier mass flow is present.

[0010] For example, a leak or clamping of a valve of a line leading to the heated disk and the carrier mass flow can result in an insufficient carrier mass flow. An insufficient carrier mass flow can be an absence of the carrier mass flow and / or an interrupted carrier mass flow in a time interval. An insufficient carrier mass flow can also be present when the carrier mass flow is (constantly) present but insufficient (i.e. not sufficient to dissipate the thermal energy from the heated heated disk such that it can overheat).

[0011] By evaluating the determined value of the one or more electrical properties, it can be reliably determined whether a carrier mass flow is present and whether the carrier mass flow is sufficient to dissipate the thermal energy from the heated heated disk. If it is determined that the carrier mass flow is insufficient, the heated disk can be closed, for example, so that overheating of the heated disk can be prevented.

[0012] Preferably, the carrier mass flow in the exhaust system can be provided by a secondary air pump or an electric turbocharger.

[0013] Preferably, the one or more electrical properties of the electrically heatable heated disk are the current intensity, the electrical resistance, the voltage and / or the electrical power of the electrically heatable heated disk.

[0014] The electrical power cannot be determined (measured) directly. However, the electrical power can be found (determined), for example, in a calculated manner, from the determined voltage and current intensity.

[0015] Preferably, the evaluation of the determined value of the one or more electrical properties can comprise:

[0016] Creating at least one time-based function from the determined value of the at least one electrical property. Preferably, a characteristic curve is created from the determined value of the property and the time interval in which the value has been determined. In other words, the determined values of the property are plotted over time in a graph, thus forming a characteristic curve.

[0017] Determining and evaluating at least one derivative (or gradient) of the time-based function of the determined value of the at least one electrical property of the electrically heatable heated disk.

[0018] Here, the derivative refers to the first derivative. The derivative in particular corresponds to the mathematical derivative, i.e. the slope of the time-based function with respect to the determined (measured) value of the electrical property.

[0019] Preferably, the evaluation of the derivative can comprise:

[0020] Comparing the curve of the derivative (or gradient) with the curve of an ideal derivative determined from an ideal function created from an ideal predetermined ideal value. The ideal derivative is also a first derivative in the mathematical sense.

[0021] In other words, a comparison of the actual gradient (derivative function) with the (ideal) target gradient (ideal derivative function) can be performed. It is also conceivable that the evaluation of the values is performed by comparing a time-based function according to the determined values with the ideal function or by comparing the individual values with the ideal values.

[0022] The ideal function can be created (determined) from ideal values corresponding to a sufficiently large carrier mass flow (i.e. in good condition). If a deviation is found in the comparison, it can be concluded that the carrier mass flow is not present and / or insufficient.

[0023] Preferably, the evaluation of the derivative function can comprise:

[0024] a comparison of the starting value of the derivative function with the ideal starting value of the ideal derivative function.

[0025] In particular, the deviation of the values (i.e. the distance between the respective X values in the characteristic curve diagram) can be greatest here. Thus, for example, directly at the beginning of the heating phase of the heating disc, it can be concluded that the carrier mass flow is not present and appropriate measures can be taken, such as switching off the heating disc and / or outputting an alarm signal (acoustically and / or visually) to the user or driver of the motor vehicle.

[0026] Preferably, the evaluation of the derivative function can comprise:

[0027] determination of the time period required to reach a predetermined threshold value of the derivative function.

[0028] comparison of the determined time period with an ideal time period required to reach a predetermined threshold value of the ideal derivative function.

[0029] If a deviation between the determined time period and the ideal time period is found, it can be concluded that the carrier mass flow is not present and / or insufficient.

[0030] According to the application, a motor vehicle exhaust system is proposed, which comprises at least one catalytic converter and at least one electrically heatable heating disc, wherein the exhaust system is configured such that at least one value of an electrical property of the electrically heatable heating disc can be determined (measured).

[0031] The exhaust system can comprise a secondary air pump or an electrically driven exhaust turbocharger.

[0032] Preferably, the exhaust system can be configured to be heated by the method explained above. With regard to the advantages that can be achieved in this way, reference is made to the relevant explanations regarding the method. Measures described and / or discussed below in connection with the method can be used for the further design of the exhaust system.

[0033] In particular, with the method, the catalytic converter of the exhaust system can be heated.

[0034] According to the application, a motor vehicle having an exhaust system according to the above-mentioned embodiments is proposed. With regard to the advantages thereby achievable, reference is made to the relevant explanations regarding the exhaust system. Measures described and / or discussed below in connection with the exhaust system can be used for the further design of the motor vehicle.

[0035] The motor vehicle can comprise a secondary air pump or an electrically driven exhaust turbocharger. BRIEF DESCRIPTION OF DRAWINGS

[0036] Further advantages and embodiments of the application will emerge from the following description and the drawings. Herein:

[0037] Figure 1 An exhaust system of a motor vehicle is schematically shown;

[0038] Figures 2a to 2h The behavior of the exhaust system at constant voltage is shown, with a time-based function of the determined characteristic value Figure 2c , Figure 2e , Figure 2g and its derivative Figure 2d , Figure 2f , Figure 2h ;

[0039] Figure 3 An enlarged view of the schematic diagram according to Figure 2d is shown;

[0040] Figures 4a to 4h The behavior of the exhaust system at constant power is shown, with a time-based function of the determined characteristic value Figure 4c , Figure 4e , Figure 4g and its derivative Figure 4d , Figure 4f , Figure 4h ; and

[0041] Figure 5 An enlarged view of the schematic diagram according to Figure 4h is shown. DETAILED DESCRIPTION

[0042] Figure 1 An exhaust system 10 of a motor vehicle having a catalytic converter 12 is schematically shown. The exhaust system comprises an electrically heatable heating disc 14. In the present case, a carrier mass flow 16 is provided by a secondary air pump 18 or an electrically driven turbocharger 20. The carrier mass flow 16 flows around or is perfused through the heating disc 14 and subsequently enters the catalytic converter 12. In other words, the heating disc 14 is arranged in front of the catalytic converter 12 in the exhaust system 10 in the flow direction of the carrier mass flow 16.

[0043] When the heating disc 14 is heated (indicated by means of the arrow), it becomes hot and heats the carrier mass flow 16 flowing around or perfusing the heating disc 14. The carrier mass flow 16 heated in this way in turn heats the catalytic converter 12. If the carrier mass flow is not present or is not present sufficiently, the thermal energy is not removed or only insufficiently removed from the heating disc 14, so that overheating of the heating disc 14 can occur. This can be prevented by determining and evaluating a characteristic value of at least one electrical property of the heating disc 14.

[0044] Figures 2a to 2h The behavior of the exhaust system 10 at a constant voltage (U) is shown. In other words, the voltage (U) remains constant over time (t) (see Figure 2a ). In the present case, Figure 2b The difference between the presence of a sufficiently high carrier mass flow 16 (mSL) (solid line) and the absence of a carrier mass flow 16 (mSL) (dashed line) over time (t) is shown.

[0045] In Figure 2c , Figure 2e , Figure 2g time-based functions 22 of the determined characteristic values over time (t) are shown. The values of the time-based functions 22 are determined in the absence of a carrier mass flow 16. These time-based functions 22 are shown by means of the respective dashed line. In addition, an ideal function 28 over time (t) is shown by means of the solid line. The ideal functions 28 each correspond to ideal values measured in the presence of a carrier mass flow 16. Thus, the deviation of the respective values of the respective properties is shown as a function of the presence or absence of a carrier mass flow 16, respectively.

[0046] In Figure 2c , the change in the current intensity (I) over time (t) is plotted as a characteristic curve. In Figure 2e , the change in the resistance (R) over time (t) is plotted as a characteristic curve. In Figure 2g , the change in the electrical power (P) over time (t) is plotted as a characteristic curve.

[0047] Figure 2d , Figure 2f , Figure 2h The derivative functions 24 of the time-based functions 22 and the ideal derivative functions 26 of the ideal functions 28 are shown, respectively. Thus, in Figure 2d , the derivative of the current intensity (I’) over time (t) is plotted. In Figure 2f , the derivative of the resistance (R’) over time (t) is plotted. In Figure 2h , the derivative of the electrical power (P’) over time (t) is plotted.

[0048] Figure 3 is shownFigure 2d The diagram is an enlarged view. It can be seen that the initial value 30 of the derivative function 24 deviates significantly from the ideal initial value 32 of the ideal derivative function 26. In the current case, the comparison of these two initial values ​​30 and 32 can indicate the presence or absence of the carrier mass flow 16. In the current case, the initial value 30 is less than the ideal initial value 32.

[0049] Furthermore, the time required to reach the predetermined threshold 36 can be determined from the corresponding derivative functions 24 and 26. Therefore, after time period 34, the threshold 36 is reached in derivative function 24. In the ideal derivative function 26, the threshold 36 is reached after the ideal time period 38. In the current case, a comparison of these two time periods 34 and 38 can indicate the presence or absence of the carrier mass flow 16. In the current case, time period 34 is shorter than the ideal time period 38.

[0050] Figures 4a to 4h The behavior of exhaust system 10 under constant electrical power (P) is shown. In other words, the electrical power (P) remains constant with time (t) (see [reference]). Figure 4a In the current situation, Figure 4b The difference in time (t) between the presence of carrier mass flow 16 (mSL) (solid line) and the absence of carrier mass flow 16 (mSL) (dashed line) is shown.

[0051] exist Figure 4c , Figure 4e , Figure 4g In the diagram, time-based functions 22 representing the changes of the determined characteristic values ​​with time (t) are shown. The values ​​of the time-based functions 22 are determined in the absence of the carrier mass flow 16. These time-based functions 22 are shown by corresponding dashed lines. Additionally, ideal functions 28 representing changes with time (t) are shown by solid lines. Each ideal function 28 corresponds to an ideal value measured in the presence of the carrier mass flow 16. Therefore, the deviations of the corresponding values ​​of the corresponding characteristics are shown as functions of the presence or absence of the carrier mass flow 16.

[0052] exist Figure 4c In the diagram, the change in current intensity (I) over time (t) is plotted as a characteristic curve. Figure 4e In the diagram, the change in resistance (R) over time (t) is plotted as a characteristic curve. Figure 4g In the diagram, the change of voltage (U) over time (t) is plotted as a characteristic curve.

[0053] Figure 4d , Figure 4f , Figure 4h The time-based derivative 24 of function 22 and the ideal derivative 26 of ideal function 28 are shown respectively. Therefore, in Figure 4d The derivative of the current intensity (I') with time (t) is plotted.Figure 4f In the diagram, the derivative of the resistance (R') over time (t) is plotted. In Figure 4h In the diagram, the derivative of the voltage (U') over time (t) is plotted.

[0054] Figure 5 An enlarged view of the illustration in Figure 4h can be seen that the starting value 30 of the derivative function 24 deviates significantly from the ideal starting value 32 of the ideal derivative function 26. In the present case, a comparison of the two starting values 30, 32 can indicate the presence or absence of the carrier mass flow 16. In the present case, the starting value 30 is greater than the ideal starting value 32.

[0055] In addition, the time required to reach a predetermined threshold value 36 can be determined from the respective derivative functions 24, 26. Thus, after a time period 34, the threshold value 36 is reached in the derivative function 24. In the ideal derivative function 26, the threshold value 36 is reached after an ideal time period 38. In the present case, a comparison of the two time periods 34, 38 can indicate the presence or absence of the carrier mass flow 16. In the present case, the time period 34 is longer than the ideal time period 38.

Claims

1. A method for heating an exhaust system (10) of a motor vehicle having a catalytic converter (12), wherein the exhaust system (10) includes an electrically heated heating plate (14) arranged in front of the catalytic converter (12) in the exhaust system (10) along the flow direction of a carrier mass flow (16), the method comprising the steps of: - During the heating of the electrically heatable heating plate (14), the values ​​of one or more electrical characteristics are determined at time intervals; - Determining whether a sufficiently large carrier mass flow (16) exists by evaluating determined values ​​of one or more electrical characteristics of the electrically heatable heating plate (14), wherein the evaluation of determined values ​​of the one or more electrical characteristics includes: - Create at least one time-based function (22) based on the determined value of the at least one electrical characteristic; - Determine and evaluate at least one derivative function (24) of the time-based function (22) of the determined value of at least one electrical characteristic of the electrically heatable heating plate (14).

2. The method according to claim 1, characterized in that, The carrier mass flow (16) in the exhaust system (10) is provided by a secondary air pump (18) or an electric exhaust turbocharger (20).

3. The method according to claim 1 or 2, characterized in that, The one or more electrical characteristics of the electrically heatable heating plate (14) are the current intensity, resistance, voltage and / or electrical power of the electrically heatable heating plate (14).

4. The method according to claim 1, characterized in that, The time interval is a regular interval.

5. The method according to claim 1, characterized in that, The evaluation of the derivative function (24) includes: - Compare the curve of the derivative function (24) with the curve of the ideal derivative function (26) determined by the ideal function (28) created from the ideal predetermined ideal value.

6. The method according to claim 5, characterized in that, The evaluation of the derivative function (24) includes: - Compare the initial value (30) of the derivative function (24) with the ideal initial value (32) of the ideal derivative function (26).

7. The method according to claim 5 or 6, characterized in that, The evaluation of the derivative function (24) includes: - Determine the time period (34) required to reach the predetermined threshold (36) of the derivative function (24); - Compare the determined time period (34) with the ideal time period (38) required to reach the predetermined threshold (36) of the ideal derivative function (26).

8. An exhaust system (10) for a motor vehicle, the exhaust system comprising at least one catalytic converter (12) and at least one electrically heatable heating plate (14), wherein the exhaust system (10) is configured such that at least one value of the electrical characteristics of the electrically heatable heating plate (14) can be determined, the exhaust system (10) being configured to be heated using the method according to any one of claims 1 to 7.

9. A motor vehicle comprising an exhaust system (10) according to claim 8.

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