DE102021200701A1 - Method and device for diagnosing a catalytic converter with an electric heater - Google Patents

Abstract

The invention relates to a method and a device for diagnosing a catalytic converter (1) with an electric heater for treating exhaust gases from an internal combustion engine. During operation of the internal combustion engine, the electrical heating of the catalytic converter is activated and a measured (Q ^Sensor ) and a modeled amount of heat (Q ^ModOk ) of the exhaust gas after the catalytic converter (1) are compared.

Description

State of the art

The invention is based on a method and a device for diagnosing a catalytic converter with an electric heater according to the species of the independent patent claims. From the DE 10 2016 216492 A1 a catalytic converter with an electric heater is already known. As devices of this type become more widespread, there is a need to prove the functionality of this device at all times.

Advantages of the Invention

The method according to the invention and the device according to the invention for diagnosing a catalytic converter with an electric heater have the advantage that a reliable diagnosis of the catalytic converter and in particular the function of the electric heater can be ensured. Therefore, the functionality of the emission control system can be verified at any time. The ability to make such a diagnosis is essential to ensure adequate cleaning of the exhaust gas at all times.

Further advantages and improvements result from the features of the dependent patent claims. The measured amount of heat is determined in a particularly simple manner by determining a heat flow by measuring the temperature of the exhaust gas downstream of the catalytic converter. To ensure that only the influence of the heater on the heat flow is measured, a difference is made with a modeled temperature without activated electrical heating. The quantity of heat can be modeled in a particularly simple manner by means of a heat flow, which occurs as a result of a difference in a modeled temperature of the exhaust gas downstream of the catalytic converter with activated and without activated electrical heating. Alternatively, the amount of heat can be modeled by a heat flow, which is formed from an electrical output of the heater and an efficiency of the heater. The respective measured and modeled amount of heat can then be determined from the heat flows determined in this way by integration in a time window. Alternatively, to determine the start of the time window, switching on the electric heater or a measured output of the electric heater or the difference in the modeled temperature of the exhaust gas exceeding a threshold value can be used. Alternatively, to determine the end of the time window, switching off the electric heater or a measured power of the electric heater or falling below the difference in the modeled temperature with and without activated electric heating or exceeding the modeled quantity of heat via a threshold value can be used. The functionality of the heater can be diagnosed particularly easily by forming a quotient from the measured and modeled amount of heat and comparing it with a threshold value. A threshold value close to 1 indicates a functioning heater, while a gross deviation of the threshold value from the value 1 suggests a malfunction.

character list

• 1 eine Brennkraftmaschine und einen Katalysator,
• 2 Temperaturverläufe und Wärmemengen aufgetragen gegenüber der Zeit für einen funktionstüchtigen Katalysator,
• 3 Temperaturverläufe und Wärmemengen aufgetragen gegenüber der Zeit für einen funktionsuntüchtigen Katalysator, und
• 4 ein Ablaufdiagramm des erfindungsgemäßen Verfahrens.

Embodiments of the invention are shown in the drawings and explained in more detail in the following description. Show it:

• 1 an internal combustion engine and a catalytic converter,
• 2 Temperature curves and amounts of heat plotted against time for a functional catalytic converter,
• 3 Temperature courses and amounts of heat plotted against time for a non-functional catalyst, and
• 4 a flowchart of the method according to the invention.

description

1 1 shows an internal combustion engine 10 which is connected to a catalytic converter 1 via an exhaust pipe 4 . The catalytic converter 1 has an electric heater (not shown) in order to ensure a sufficient temperature of the catalytic converter 1 at all times during operation. The exhaust gases flowing through the catalyst 1 are passed through an exhaust pipe 5 to other catalysts for treating the exhaust gas or passed on to the environment. A temperature sensor 3 for measuring the temperature of the exhaust gas in front of the catalytic converter 1 is arranged in the exhaust pipe 4 . A temperature sensor 2 for measuring the temperature of the exhaust gas downstream of the catalytic converter 1 is arranged in the exhaust pipe 5 . The measured values of these two temperature sensors can be processed by a computer 6 in order to carry out the necessary calculation steps of the method according to the invention.

According to the invention, the catalytic converter 1 is diagnosed with an electric heater by evaluating a measured and a modeled quantity of heat in the exhaust gas after the catalytic converter. By measuring the temperature of a flowing gas, the amount of heat transported by the flowing gas per unit of time, i.e. a heat flow transported by the exhaust gas, can be determined. By measuring the temperature of the exhaust gas in front of the catalytic converter 1 using the temperature sensor 3, the heat flow that is supplied to the catalytic converter 1 by the exhaust gas can be determined. By measuring the temperature of the exhaust gas after the catalytic converter 1, the heat flow that flows out of the catalytic converter 1 can be determined. A corresponding quantity of heat that flowed into and out of the catalytic converter 1 and also which quantity of heat was generated by the electric heater in the catalytic converter 1 can then be determined by integrating the respective heat flow over time.

mit:

• $\frac{d{Q}^{Sensor}}{dt}:$
  
  Wärmestrom (Wärmemenge Q pro Zeit) aufgrund Messung des Temperatursensors 2,
• $c_p^{Abgas}:$
  
  spezifische Wärmekapazität des Abgases
• $\frac{d{m}^{Abgas}}{dt}:$
  
  Abgasmassenstrom
• $T_{nKat}^{Sensor}:$
  
  Temperatur-Sensorwert nach Heizkatalysator
• $T_{nKat}^{Mod0}:$
  
  Temperatur-Modellwert nach Heizkatalysator (mit defekter/nicht aktiver Heizfunktion).

The heat flow generated by the electric heater in catalytic converter 1 (ie heat quantity per time) can be determined from a temperature measurement after the catalytic converter as follows: $$\frac{\mathrm{i.e}{Q}^{SensO\mathrm{right}}}{\mathrm{i.e}t}=c_p^{AbGas}\ast \frac{\mathrm{i.e}{m}^{AbGas}}{\mathrm{i.e}t}\ast \left(T_{nKat}^{SensO\mathrm{right}}-T_{nKat}^{MO\mathrm{i.e}0}\right)$$

With:

• $\frac{\mathrm{i.e}{Q}^{SensO\mathrm{right}}}{\mathrm{i.e}t}:$
  
  Heat flow (quantity of heat Q per time) based on measurement of temperature sensor 2,
• $c_p^{AbGas}:$
  
  specific heat capacity of the exhaust gas
• $\frac{\mathrm{i.e}{m}^{AbGas}}{\mathrm{i.e}t}:$
  
  exhaust mass flow
• $T_{nKat}^{SensO\mathrm{right}}:$
  
  Temperature sensor value after the heated catalytic converter
• $T_{nKat}^{MO\mathrm{i.e}0}:$
  
  Temperature model value after the heated catalytic converter (with defective/inactive heating function).

mit p_Heizer(t) ist die elektrischen Leistung des Heizers und η für den Wirkungsgrad des Heizers. Im Fall einer Stromrückmessung kann die tatsächlich abgerufene Leistung berechnet p_Heizer (t) zu jeden Zeitpunkt berechnet werden. In Fall das kein Strom gemessen werden kann, kann die theoretische oder Soll-Leistung des Katalysators verwendet werden. An expected or modeled heat flow results from the electrical parameters of the heater: $$\frac{\mathrm{i.e}{Q}^{MO\mathrm{i.e}elekt\mathrm{right}}}{\mathrm{i.e}t}=n\ast p_{Hei\mathrm{e.g}e\mathrm{right}}\left(t\right)$$

where p _heater (t) is the electrical power of the heater and η is the efficiency of the heater. In the case of a reverse current measurement, the power actually called up can be calculated p _heater (t) at any point in time. In the event that no current can be measured, the theoretical or target performance of the catalyst can be used.

For a time interval t1 to t2, the measured or modeled amount of heat occurring in the time interval can be calculated from the heat flow by integration: $$Q^{SensO\mathrm{right}}={\displaystyle {\int }_{t1}^{t2}\frac{\mathrm{i.e}{Q}^{SensO\mathrm{right}}}{\mathrm{i.e}t}}\mathrm{i.e}t\text{and}{Q}^{MO\mathrm{i.e}elekt\mathrm{right}}=n\ast {\displaystyle {\int }_{t1}^{t2}{p}_{Hei\mathrm{e.g}e\mathrm{right}}\left(t\right)\mathrm{i.e}t}$$

Bei einem ordnungsgemäß funktionieren Heizsystem sollte diese Heizkatalysator-Effizienz näherungsweise 1 betragen. Starke Abweichung deuten auf eine Störung hin.A division results in an actual heating catalyst efficiency: $${\mathrm{right}}_{Kat}=\begin{array}{c}{Q}^{SensO\mathrm{right}}\\ Q^{MO\mathrm{i.e}elekt\mathrm{right}}\end{array}$$

In a properly functioning heating system, this heating catalyst efficiency should be approximately 1. Strong deviations indicate a fault.

mit: $T_{nKat}^{ModOK}:$

Temperatur-Modellwert nach dem Heizkatalysator mit funktionierender Heizfunktion, $T_{nKat}^{Mod0}:$

Temperatur-Modellwert nach Heizkatalysator (mit defekter Heizfunktion).In an alternative method, the catalytic converter efficiency can be calculated by modeling the temperature of the exhaust gas downstream of the catalytic converter, once with a heater and once without a heater. The expected value for the modeled heat flow after the heated catalytic converter is calculated as: $$\frac{\mathrm{i.e}{Q}^{MO\mathrm{i.e}OK}}{\mathrm{i.e}t}-c_p^{AbGas}\ast \frac{\mathrm{i.e}{m}^{AbGas}}{\mathrm{i.e}t}\ast \left(T_{nKat}^{MO\mathrm{i.e}OK}-T_{nKat}^{MO\mathrm{i.e}0}\right)$$

With: $T_{nKat}^{MO\mathrm{i.e}OK}:$

Temperature model value after the heated catalyst with functioning heating function, $T_{nKat}^{MO\mathrm{i.e}0}:$

Temperature model value after heating catalyst (with defective heating function).

und entsprechend $$r_{Kat}=\frac{Q^{Sensor}}{Q^{ModOK}}$$

The expected amount of heat for the modeled amount of heat after the heated catalytic converter is calculated as: $$Q^{MO\mathrm{i.e}OK}={\displaystyle {\int }_{t1}^{t2}\frac{\mathrm{i.e}{Q}^{MO\mathrm{i.e}OK}}{\mathrm{i.e}t}}\mathrm{i.e}t$$

and accordingly $${\mathrm{right}}_{Kat}=\frac{Q^{SensO\mathrm{right}}}{Q^{MO\mathrm{i.e}OK}}$$

• t1: Integrations-Startzeitpunkt = Beginn Heizphase
• t2: Integrations-Endezeitpunkt = Ende Heizphase inkl. Abkühlung oder alternativ ausreichend Wärmemenge aus Heizphase erreicht.

For all calculations of the quantity of heat by integration, the following applies:

• t1: integration start time = start of heating phase
• t2: integration end time = end of heating phase incl. cooling or alternatively sufficient amount of heat from heating phase reached.

The integration start time t1 or the release of the integration can be determined, for example, by exceeding a minimum value for the expected temperature rise due to the operation of the heater: $$T_{nKat}^{MO\mathrm{i.e}OK}-T_{nKat}^{MO\mathrm{i.e}0}>\mathrm{\Delta }{T}^{Min}$$

Alternatively, the point in time t1 at which the integration is started can also be determined simply by a switch-on signal from the heater. Another alternative possibility is to determine a measured power of the electric heater. If the electric heating exceeds a threshold value, a temperature difference should be generated with the heating working.

The integration end time t2 can be recognized analogously by falling below the minimum value for the expected temperature rise: $$T_{nKat}^{MO\mathrm{i.e}OK}-T_{nKat}^{MO\mathrm{i.e}0}<\mathrm{\Delta }{T}^{Min}$$

Alternatively, switching off the electric heater can also be used to determine the end of the integration. Another alternative possibility is to determine a measured power of the electric heater. If the electric heater falls below a threshold value, no temperature difference should be detectable. Furthermore, the integration can be terminated when the modeled amount of heat, i.e. the value of the integral over the modeled heat flow, exceeds a threshold value. At the end of the integration, a value for the efficiency can be determined as a monitoring variable using the measured and modeled heat quantities.

(Kurve 21), die modellierte Temperatur bei einem nicht funktionstüchtigen Heizer $T_{nKat}^{Mod0}$

(Kurve 22)und die gemessene Temperatur $T_{nKat}^{Sensor}$

(Kurve 23) gezeigt. In dem Messfenster zwischen den Zeitpunkten t1 und t2 zeigt die gemessene Temperatur $T_{nKat}^{Sensor}$

(23) eine deutlich stärkere Übereinstimmung mit der modellierten Temperatur $T_{nKat}^{ModOK}$

(21) bei einem funktionstüchtigen Heizer als mit dem nicht funktionstüchtigen $T_{nKat}^{Mod0}$

(22). Entsprechend zeigt sich auch im unteren Teil der 2 eine sehr starke Übereinstimmung zwischen der gemessenen Wärmemenge Q^Sensor (Kurve 24) und der modellierten Wärmemenge Q^ModOk für einen funktionstüchtigen Heizer (Kurve 25).In the 2 the upper graph shows the temperature profile and the lower graph shows the amount of heat for a functioning heater in a catalytic converter according to the invention, each plotted against time. In each case, the modeled temperature with a functional heater is used $T_{nKat}^{MO\mathrm{i.e}OK}$

(curve 21), the modeled temperature with a non-functional heater $T_{nKat}^{MO\mathrm{i.e}0}$

(curve 22) and the measured temperature $T_{nKat}^{SensO\mathrm{right}}$

(Curve 23). In the measurement window between the points in time t1 and t2 shows the measured temperature $T_{nKat}^{SensO\mathrm{right}}$

(23) a significantly better agreement with the modeled temperature $T_{nKat}^{MO\mathrm{i.e}OK}$

(21) with a functional heater than with the non-functional one $T_{nKat}^{MO\mathrm{i.e}0}$

(22). The lower part of the 2 a very strong correspondence between the measured amount of heat Q ^sensor (curve 24) and the modeled amount of heat Q ^ModOk for a functional heater (curve 25).

(21), die modellierte Temperatur bei einem nicht funktionstüchtigen Heizer $T_{nKat}^{Mod0}$

(22) und die gemessene Temperatur $T_{nKat}^{Sensor}$

(23) gezeigt. In dem Messfenster zwischen den Zeitpunkten t1 und t2 zeigt die gemessene Temperatur $T_{nKat}^{Sensor}$

(23) eine deutlich stärkere Übereinstimmung mit der modellierten Temperatur $T_{nKat}^{Mod0}$

(22) bei einem nicht funktionstüchtigen Heizer als mit dem funktionstüchtigen Heizer $T_{nKat}^{ModOK}$

(21). Entsprechend zeigt sich auch im unteren Teil der 2 eine sehr starke Abweichung zwischen der gemessenen Wärmemenge Q^Sensor (24) und der modellierten Wärmemenge Q^ModOk (25) für einen funktionstüchtigen Heizer.In the 3 the upper graph shows the temperature profile and the lower graph shows the amount of heat for a non-functioning heater in a catalytic converter according to the invention, each plotted against time. In each case, the modeled temperature with a functional heater is used $T_{nKat}^{MO\mathrm{i.e}OK}$

(21), the modeled temperature for a non-functional heater $T_{nKat}^{MO\mathrm{i.e}0}$

(22) and the measured temperature $T_{nKat}^{SensO\mathrm{right}}$

(23) shown. In the measurement window between times t1 and t2 shows the measured temperature $T_{nKat}^{SensO\mathrm{right}}$

(23) a significantly better agreement with the modeled temperature $T_{nKat}^{MO\mathrm{i.e}0}$

(22) with a non-functional heater than with the functional heater $T_{nKat}^{MO\mathrm{i.e}OK}$

(21). The lower part of the 2 a very strong deviation between the measured amount of heat Q ^Sensor (24) and the modeled amount of heat Q ^ModOk (25) for a functional heater.

In the 4 method steps of the method according to the invention are shown as a flowchart. The method starts in a first step 41. In the subsequent step 42, it is checked whether general release conditions are met. Such general release conditions can consist, for example, in a determination of normal operation of the internal combustion engine, an operational readiness of the sensors used and an operational readiness of other components of the system. If the general release conditions are not met, step 42 follows step 52. If the release conditions are met, step 42 follows step 43. In step 43, it is checked whether the start of a heating phase is detected. Such a heating phase is detected, for example, by switching on the electric heater. Alternatively, a measured output of the electric heater or an exceeding of the difference in the modeled temperature of the exhaust gas with an activated electric heater and without an activated electric heater can also be detected. If the start of a heating phase is not detected, step 43 is followed by step 52. If the start of a heating phase has been detected, step 43 is followed by step 44. In step 44, the heat quantities are calculated by integrating the heat flows , as described in formulas 1-8. Step 44 is followed by step 45, in which it is checked whether a termination condition is present. Such a termination condition is present, for example, when the heater is no longer operated because this no longer makes sense due to the operating conditions of the internal combustion engine. If the termination condition is met, step 45 is followed by step 52. If the termination condition is not met, step 45 is followed by step 46. In step 46, a check is made as to whether the conditions for integration of the quantity of heat are still present. If this is the case, step 46 is followed by step 44 and the taking of the integrals of the heat flows continues. If this is not the case, step 46 is followed by step 47. In step 47, a check is made as to whether the modeled quantity of heat determined is above a threshold value. If this is not the case, step 47 is followed by step 52. If this is the case, step 47 is followed by step 48 in which the measured and the modeled heat quantity of the exhaust gas after the catalyst are compared. This is done by calculating an efficiency, for example by forming a quotient between the measured amount of heat and the modeled amount of heat. In the subsequent step 49, a check is made as to whether the measured efficiency is greater than a first threshold and less than a second threshold. The threshold values are selected in such a way that the efficiency should be in a window around the value 1. Permissible deviations are defined by the threshold values, for example between 0.8 and 1.2. If the efficiency determined is within the limits of the threshold values, step 49 is followed by step 50, with which the heating system is evaluated as functional. If the efficiency is outside the limits of the threshold values, then step 49 is followed by step 51, with which the heating system is evaluated as non-functional.

Method step 52 can implement different alternatives. In a first alternative, the diagnosis is reset to the effect that all the integrals formed up to now are reset to 0 and with step 41, which follows step 52, the method is started anew from scratch. In a second alternative, it is provided that the integrals, by means of which the quantities of heat are calculated, are added up over a number of individual heating phases. In the method according to the first alternative, a diagnosis can only be made if there is a sufficiently long heating phase that allows the generation of a sufficiently large amount of heat. After the second alternative, several short heating phases are combined in order to gain a sufficiently large amount of heat for a diagnosis.

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102016216492 A1 [0001]

Claims (10)

Method for diagnosing a catalytic converter (1) with an electric heater for treating exhaust gases from an internal combustion engine (10), characterized in that during operation of the internal combustion engine, electrical heating of the catalytic converter is activated and a measured (Q ^sensor ) and a modeled amount of heat ( Q ^ModOk ) of the exhaust gas after the catalytic converter (1) can be compared. procedure after claim 1 , characterized in that to determine the measured amount of heat, a heat flow by a temperature measurement $\left(T_{nKat}^{SensO\mathrm{right}}\right)$

of the exhaust gas is determined after the catalytic converter with activated electrical heating. procedure after claim 2 characterized in that to determine the heat flow a difference in temperature measurement $\left(T_{nKat}^{SensO\mathrm{right}}\right)$

of the exhaust gas after the catalyst and a modeled temperature $\left(T_{nKat}^{MO\mathrm{i.e}0}\right)$

is formed without activated electrical heating. procedure after claim 1 , characterized in that to determine the modeled amount of heat, a heat flow through a difference in a modeled temperature $\left(T_{nKat}^{MO\mathrm{i.e}OK}\right)$

of the exhaust gas after the catalyst with activated electrical heating and a modeled temperature $T_{nKat}^{MO\mathrm{i.e}0}$

is formed without activated electrical heating. procedure after claim 1 , characterized in that to determine the modeled amount of heat, a heat flow per time is determined by an electrical power (p) of the heater and an efficiency of the heater. Method according to any of the preceding claims 2 until 5 , characterized in that the measured and the modeled amount of heat of the exhaust gas after the catalytic converter by integrating the respective heat flow per time in a time window (t1, t2) of the operation of the internal combustion engine are determined. procedure after claim 6 , characterized in that the start of the time window (t1) is determined by switching on the electric heater or by a measured power of the electric heater or by exceeding the difference between the modeled temperature of the exhaust gas after the catalytic converter with activated electric heating and a modeled temperature of the exhaust gas after the catalytic converter without activated electrical heating above a threshold value. procedure after claim 6 , characterized in that the end of the time window (t2) is determined by switching off the electric heater or by a measured power of the electric heater or by falling below the difference between the modeled temperature of the exhaust gas after the catalytic converter with activated electric heating and a modeled Temperature after the catalytic converter without activated electrical heating below a threshold value or by exceeding the modeled amount of heat above a threshold value. Method according to one of the preceding claims, characterized in that a quotient of the measured and modeled quantity of heat is formed and compared with a threshold value. Device for diagnosing a catalytic converter (1) with an electric heater for treating exhaust gases from an internal combustion engine (2), characterized in that means are provided which activate electrical heating of the catalytic converter during operation of the internal combustion engine and a measured (Q sensor) and compare a modeled quantity of heat (Q ^ModOk ) of the exhaust gas after the catalyst.

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