JP2024066675A - Abnormality detection device for electrically heated catalytic converter - Google Patents

Abstract

[Problem] To provide an abnormality detection device for an electrically heated catalyst device that can accurately determine heating abnormalities in an electrically heated catalyst. [Solution] In an abnormality detection device for an electrically heated catalyst device, a catalyst that purifies exhaust gas from an internal combustion engine is housed in a conductive housing in a state insulated from the housing, and electricity is passed through the catalyst to raise the temperature of the catalyst, the abnormality detection device stores in advance a reference resistance value when electricity is passed through the catalyst to raise its temperature (step S2), determines an actual resistance value when electricity is passed through the catalyst to heat it in a use state in which the catalyst is housed in the housing (step S6), determines an insulation resistance value based on the actual resistance value and the reference resistance value (step S7), and determines an abnormality in the electrically heated catalyst device based on the insulation resistance value and a predetermined determination threshold value (step S8). [Selected Figure] Figure 2

Description

This invention relates to an abnormality detection device for an electrically heated catalyst device equipped with an electrically heated catalyst that uses electricity to heat and increase the temperature of a catalyst installed in an exhaust passage.

Patent document 1 describes a vehicle control device that is provided with an insulation resistance detection device to detect leakage current in an electrically heated catalyst (EHC), and when the insulation resistance value detected by the insulation resistance detection device is less than a predetermined value, determines that there is a leakage current and turns off a relay switch to cut off the flow of current to the electrically heated catalyst.

According to the vehicle control device described in Patent Document 1, the insulation resistance value between the EHC carrier and a case (exhaust pipe) made of a metal material is monitored, and it is said that this insulation resistance value can be used to detect a decrease in insulation of the electrically insulating retaining mat (insulating coating) provided between the EHC carrier and the case.

JP 2012-072665 A

In an electrically heated catalyst, the catalyst and its case should be insulated from each other, but as described in Patent Document 1, the catalyst and its case may become electrically conductive due to the accumulation of conductive materials such as carbon. When two or more conductive points occur between the catalyst and the case, the case forms a parallel circuit with the catalyst, so current flows to the case, and abnormal heating of the catalyst occurs. The device described in Patent Document 1 detects the conduction between the two by passing a current through the insulation resistance detection device and measuring the electrical resistance between the catalyst and the case. When a current is passed through the EHC for heating/temperature increase, even if the catalyst and the case are conductive at only one point due to the accumulation of conductive materials such as carbon, a parallel circuit is not formed, so the current for heating does not leak, and the catalyst can be heated normally. However, when there is a conductive point, if a current is passed through the insulation resistance detection device, a current flows through the insulation resistance detection device because a circuit is formed between the case, catalyst, insulation resistance detection device, and the conductive part. In this case, the detected insulation resistance value may drop even though no heating abnormality is occurring, leading to a possibility of an abnormality being determined, and there is an issue that the accuracy of the determination is not necessarily high.

This invention was made with a focus on the above technical problems, and aims to provide an abnormality detection device for an electrically heated catalyst device that can accurately determine heating abnormalities in an electrically heated catalyst.

To achieve the above object, the present invention provides an abnormality detection device for an electrically heated catalyst device in which a catalyst for purifying exhaust gas from an internal combustion engine is housed in a conductive housing in a state insulated from the housing, and current is passed through the catalyst to raise the temperature of the catalyst, the abnormality detection device prestores a reference resistance value of the catalyst when current is passed through the catalyst to raise its temperature, calculates an actual resistance value when current is passed through the catalyst to heat it in a state in which the catalyst is housed in the housing, calculates an insulation resistance value based on the actual resistance value and the reference resistance value, and judges an abnormality in the electrically heated catalyst device based on the insulation resistance value and a predetermined judgment threshold value.

In addition, in this invention, the reference resistance value may be estimated from a predetermined relationship according to the detection value of any one of the exhaust pipe flow rate sensor, the air-fuel ratio sensor of the exhaust passing through the exhaust pipe, and the exhaust temperature sensor.

In addition, in this invention, the reference resistance value may be determined based on the detection value of a sensor attached to the catalyst.

The present invention also includes a current sensor that detects the value of the current flowing through the circuit when electricity is applied to heat the catalyst, and a voltage sensor that detects the voltage value of the circuit, and the actual resistance value may be determined by the current value and the voltage value.

The abnormality detection device for an electrically heated catalyst device of this invention stores in advance a reference resistance value when electricity is passed through the catalyst to heat it, calculates the actual resistance value when electricity is passed through the catalyst to heat it when it is housed in a housing and in use, calculates an insulation resistance value based on the actual resistance value and the previously stored reference resistance value, and judges an abnormality in the electrically heated catalyst device based on the insulation resistance value and a predetermined judgment threshold value, thereby accurately judging a heating abnormality in the electrically heated catalyst.

Specifically, the insulation resistance value is calculated based on a previously stored reference resistance value of the catalyst and the actual resistance value of the entire circuit of the electrically heated catalyst device. This insulation resistance value is the insulation resistance of the electrically heated catalyst device, and if a decrease in insulation is detected by the judgment threshold value, it is found that current is leaking somewhere other than the catalyst, and it can be determined that a heating abnormality has occurred in the electrically heated catalyst device.

In addition, with the electrically heated catalyst device anomaly detection device of this invention, the reference resistance value can be estimated from the detection values of the exhaust pipe flow sensor, the exhaust air-fuel ratio sensor of the exhaust passing through the exhaust pipe, and the exhaust temperature sensor. Therefore, by estimating the deterioration of the catalyst resistance over time and then calculating the insulation resistance value based on the resistance value of the deteriorated catalyst and the actual resistance value of the entire circuit of the electrically heated catalyst device, it is possible to determine the insulation deterioration due to deterioration over time and therefore determine that an abnormality has occurred in the electrically heated catalyst device.

In addition, according to the anomaly detection device for an electrically heated catalytic converter of this invention, the reference resistance value can be determined by detection by a sensor attached to the catalyst. Therefore, by calculating the insulation resistance value based on the actual measured resistance value of the catalyst and the actual resistance value of the entire circuit of the electrically heated catalytic converter, it is possible to determine the deterioration of insulation due to aging, and therefore to determine that an anomaly has occurred in the electrically heated catalytic converter.

In addition, according to the abnormality detection device for an electrically heated catalyst device of this invention, the actual resistance value is determined by the current value and voltage value detected by a current sensor that detects the current value flowing through the circuit when electricity is applied to heat the catalyst, and a voltage sensor that detects the voltage value of the circuit. This allows the resistance value of the entire circuit of the electrically heated catalyst device to be obtained as an actual measurement value, making it possible to more accurately determine abnormalities in the electrically heated catalyst device.

FIG. 1A is a schematic diagram for explaining the configuration of an embodiment of the invention, and FIG. 4 is a flowchart illustrating an example of a control executed in the embodiment of the present invention.

The abnormality detection device for an electrically heated catalytic converter in an embodiment of the present invention will be specifically described with reference to the drawings. Note that the embodiment described below is merely one example of how the present invention can be implemented, and is not intended to limit the present invention.

The configuration of an embodiment of the present invention will be described with reference to the schematic diagram in Figure 1 (A). An internal combustion engine (hereinafter referred to as engine) 1 is, as an example, a gasoline engine having multiple cylinders 2, which outputs power by burning a mixture of gasoline and air.

In each cylinder 2 of the engine 1, a mixture containing intake air introduced from an intake manifold 4 connected via an intake pipe 3 and fuel injected from an injector (not shown) is burned by spark discharge from an ignition device (not shown). Exhaust gas generated in each cylinder 2 by the combustion of the mixture is discharged to an exhaust pipe 6 connected via an exhaust manifold 5. At least a catalyst 7 is provided in the exhaust pipe 6.

The catalyst 7 is an exhaust purification catalyst that has been conventionally used in vehicles, such as an oxidation catalyst that oxidizes environmental pollutants such as hydrocarbons and carbon monoxide, or an occlusion-reduction catalyst that captures nitrogen oxides as nitrate nitrogen and then reduces them to render them harmless. It is housed in a conductive housing 8 while covered with an insulating material (not shown) such as glass. The front and rear ends of the housing 8 are connected to the exhaust pipe 6.

Because it takes time for the catalyst 7 to become active after the engine 1 is started, an electrically heated catalyst device (hereinafter sometimes referred to as EHC) 9 is provided to quickly activate the catalyst 7, and the temperature of the catalyst 7 is raised by electrically heating it, activating it.

Next, the electrically heated catalytic device 9 will be described with reference to FIG. 1. The electrically heated catalytic device 9 includes at least one electrode 10, the other electrode 11, a power converter 12, and a battery 13. The one electrode 10 functions as an electrode for applying a positive voltage, with an end fixed to the outer periphery of the catalyst 7, and the other electrode 11 functions as an electrode for applying a negative voltage, with an end fixed to the outer periphery of the catalyst 7. In addition, the one electrode 10 and the other electrode 11 are each covered with an insulator (not shown) made of an insulating material such as glass, and an insulating state is maintained between each of the electrodes 10, 11 and the housing 8.

The power converter 12 is a power supply circuit unit for converting the power of the battery 13, and the power of the battery 13 is converted to a predetermined voltage by an insulating transformer 14 inside the power converter 12. It is also equipped with a current sensor 15 and a voltage sensor 16 that detect the current I and voltage V applied to the catalyst. Therefore, by passing the power converted by the power converter 12 between the electrodes 10 and 11, the catalyst 7 is heated and its temperature is increased by Joule heat.

The resistance of the catalyst 7 itself is indicated as the EHC resistance REHC, and the resistance of the entire circuit determined from the detection values of the current sensor 15 and voltage sensor 16 is indicated as the real resistance R. If the vehicle is still in a new condition before initial operation, the electrically heated catalyst device 9 and the housing 8 should be guaranteed to be insulated, so the insulation resistance Rleak between the two is an infinitely high value. In other words, the real resistance R represents the EHC resistance REHC.

It has been known that the insulation resistance Rleak gradually decreases as the engine 1 is repeatedly operated. Examples of the causes of this include insulation deterioration due to initial manufacturing defects and insulation deterioration due to carbon deposition. In particular, when carbon contained in exhaust gas accumulates at multiple points on the edge of the catalyst 7, a conductive path is created between the part where the carbon is deposited between the catalyst 7 and the housing 8 (resistances Rα and Rβ) and the housing 8 (exhaust pipe 6) (resistance Rγ) connecting the part where the carbon is deposited, and the insulation resistance Rleak (in the above example, Rleak = Rα + Rβ + Rγ) of the electrically heated catalyst device 9 decreases, which means that sufficient current cannot reach the catalyst 7, causing heating abnormalities. The control for determining abnormalities in the electrically heated catalyst device 9 is executed by the electronic control unit (hereinafter referred to as ECU) 17 in the embodiment of this invention.

The ECU 17 is a device that controls at least the engine 1, and is mainly composed of a microcomputer consisting of arithmetic elements and memory, and is configured to perform calculations using input data and pre-stored data, and to output the results of the calculations as a control command signal.

The ECU 17 shown in FIG. 1A has a functional configuration that includes at least the functions of controlling an initial start determination means 18, an initial EHC resistance value calculation unit 19, an initial EHC abnormality determination means 20, an EHC resistance detection unit 21, an insulation resistance calculation unit 22, and an insulation degradation determination means 23.

The initial start determination means 18 has a function of determining whether or not the electrically heated catalytic device 9 including the catalyst 7 is in a new car state before initial operation. One specific example of the means is to connect an external tool to the ECU 17 when a new car is assembled at a factory, and send information indicating that the car is being started for the first time from the external tool to the ECU 17. The initial start determination means 18 determines whether or not the ECU has received such information indicating that the car is being started for the first time. Note that the "initial start" in the initial start determination means 18 does not necessarily have to be a new car, and may also be applied to a case where the electrically heated catalytic device 9 including the catalyst 7 has been replaced with a new one for repairs or other reasons.

The initial EHC resistance value calculation unit 19 has a function of calculating the value of the initial EHC resistance REHC_ini at the time of manufacture when the initial start determination means 18 affirmatively determines that this is an initial start. The initial EHC resistance REHC_ini at the time of manufacture can be calculated according to Ohm's law using values detected by the current sensor 15 and the voltage sensor 16 inside the power conversion device 12, for example.
REHC_ini=V/I (1)

In addition, since the value of the initial EHC resistance REHC_ini at the time of manufacture has initial variation at the time of manufacture, the initial EHC resistance value calculation unit 19 has a function of storing the value of the initial EHC resistance REHC_ini at the time of manufacture in the ECU 17 in order to grasp the degree of insulation deterioration due to aging, etc., which will be described later.

The initial EHC abnormality determination means 20 has a function of determining whether the value of the initial EHC resistance REHC_ini at the time of manufacture calculated by the initial EHC resistance value calculation unit 19 is within a predetermined range calculated assuming that no insulation failure occurs, or whether the deviation from the resistance value in a normal state without insulation failure or the like is within a predetermined range. If it is within the predetermined range, the electrically heated catalytic device 9 is determined to be normal, and if it is outside the predetermined range, the electrically heated catalytic device 9 is determined to be abnormal. Note that this predetermined range may be, as an example, a value read from an initial EHC resistance value map stored in advance in the ECU 17.

The EHC resistance detection unit 21 has a function of detecting and acquiring the EHC resistance REHC (corresponding to the reference resistance value in the embodiment of this invention) at times other than the initial start. As an example, a means for detecting the value of the EHC resistance REHC may be a conventionally known appropriate resistance meter. Alternatively, the deterioration of the resistance of the catalyst 7 over time may be obtained in advance by experiment or simulation and stored, for example, as a map, and the deterioration of the resistance of the catalyst 7 over time may be estimated from the map. Specifically, the EHC resistance REHC' after deterioration over time is estimated from an EHC resistance value map that has a predetermined relationship with the detection values of the flow rate sensor of the exhaust pipe 6, the air-fuel ratio sensor of the exhaust passing through the exhaust pipe 6, and the exhaust temperature sensor as parameters, or with any of the detection values as parameters, and the value obtained by adding the estimated deterioration EHC resistance REHC' to the value of the initial EHC resistance REHC_ini at the time of manufacture calculated and stored by the initial EHC resistance value calculation unit 19 can be set as the value of the EHC resistance REHC.

The insulation resistance calculation unit 22 has a function of calculating the insulation resistance Rleak of the circuit of the electrically heated catalytic device 9 based on the data (EHC resistance REHC) obtained by the EHC resistance detection unit 21. The insulation resistance Rleak can be calculated using the EHC resistance REHC and an actual resistance value R=V/I, which is the combined resistance of the entire circuit obtained from the detection values of the current sensor 15 and the voltage sensor 16. Specifically,
Rleak = REHC · (V / I) / {REHC - (V / I)} ... (2)
It should be noted that the equivalent circuit of the electrically heated catalytic converter 9 may be considered to be a series circuit in which the catalyst 7 acts as a resistor when the vehicle is initially in a new state, whereas if electrical conduction occurs between the catalyst 7 and the housing 8 for some reason, a parallel circuit is formed in which the housing 8 and foreign matter such as carbon that causes the conduction are connected in parallel to the catalyst 7. This is shown as an equivalent circuit in FIG. 1B. Therefore, as is known from the above formula (2), the insulation resistance Rleak can be calculated from the relationship between the voltage, current (i.e., the actual resistance) and the resistance value of the catalyst 7 itself.

The insulation degradation determination means 23 has a function of determining whether or not the value of the insulation resistance Rleak calculated by the insulation resistance calculation unit 22 exceeds a predetermined threshold value. If it exceeds the predetermined threshold value, the electrically heated catalytic device 9 is determined to be normal, and conversely, if it is equal to or less than the predetermined threshold value, the electrically heated catalytic device 9 is determined to be abnormal. Note that this predetermined threshold value may be, for example, a value that is predetermined as an insulation degradation map that is pre-stored in the ECU 17.

2 is a flowchart for explaining an example of control in the above-mentioned configuration, and is executed by the above-mentioned ECU 17. The control shown in the flowchart in FIG. 2 is repeatedly executed by the above-mentioned ECU 17 when the engine 1 is operating. In the control example shown in FIG. 2, first, it is determined whether or not it is the first start (step S1). It is determined whether or not the electrically heated catalyst device 9 including the catalyst 7 is in a new car state before initial operation, and this is determined by the first start determination means 18. If the determination in step S1 is affirmative, that is, if it is determined in step S1 that it is the first start, the value of the initial EHC resistance REHC_ini at the time of manufacture is calculated and stored (step S2). The initial EHC resistance value calculation unit 19 calculates the value of the initial EHC resistance REHC_ini at the time of manufacture using values detected by the current sensor 15 and the voltage sensor 16 inside the power conversion device 12, and stores it in the ECU 17.

Next, it is determined whether the value of the initial EHC resistance REHC_ini at the time of manufacture is within a predetermined range (step S3). This is performed by the initial EHC abnormality determination means 20 to determine whether the value of the initial EHC resistance REHC_ini at the time of manufacture calculated in step 2 is within a predetermined range that is determined in advance by design. If the determination in step S3 is affirmative, that is, if the value of the initial EHC resistance REHC_ini at the time of manufacture is determined to be within the predetermined range in step S3, the electrically heated catalytic device 9 is determined to be normal (step S4), and the routine shown in this flowchart is terminated once after the determination is completed. On the other hand, if the determination in step S3 is negative, that is, if the value of the initial EHC resistance REHC_ini at the time of manufacture is determined to be outside the predetermined range in step S3, the electrically heated catalytic device 9 is determined to be abnormal (step S5), and the routine shown in this flowchart is terminated once after the determination is completed. Therefore, in this case, some kind of warning or abnormality signal is output, and the device is replaced or repaired.

On the other hand, if the answer is negative in step S1, that is, if it is determined in step S1 that the engine is not being started for the first time, the EHC resistance REHC is detected (step S6). Here, the EHC resistance REHC can be determined from an appropriate sensor or an estimated value based on deterioration over time from the value of the initial EHC resistance REHC_ini at the time of manufacture stored in step S2, and is detected by the EHC resistance detection unit 21.

Next, the insulation resistance Rleak is calculated (step S7). Because the current and voltage are constantly detected by the above-mentioned sensors 15, 16, the overall resistance of the circuit, i.e., the actual resistance R (= V/I), is known, and the insulation resistance Rleak of the circuit of the electrically heated catalytic device 9 can be calculated based on this value and the EHC resistance REHC detected in step S6. That is, the insulation resistance Rleak is calculated by the insulation resistance calculation unit 22 using the above-mentioned formula (2).

Next, it is determined whether the insulation resistance Rleak exceeds a predetermined threshold value (step S8). Here, it is determined whether the value of the insulation resistance Rleak obtained in step S7 exceeds a predetermined threshold value, and this is performed by the insulation degradation determination means 23. If the determination in step S8 is affirmative, that is, if the value of the insulation resistance Rleak is determined to be higher than the predetermined threshold value in step S8, the electrically heated catalytic device 9 is determined to be normal (step S9), and after the determination is completed, the routine shown in this flowchart is temporarily terminated. On the other hand, if the determination in step S8 is negative, that is, if the value of the insulation resistance Rleak is determined to be equal to or lower than the predetermined threshold value in step S8, the electrically heated catalytic device 9 is determined to be abnormal (step S10), and after the determination is completed, the routine shown in this flowchart is temporarily terminated. In this case, as described above, some kind of warning or abnormality signal is output, and the device is replaced or repaired.

In the abnormality detection device for the electrically heated catalyst device 9 in this embodiment of the invention, in step S1, it is determined whether the electrically heated catalyst device 9 including the catalyst 7 is in a new car state before initial operation, and in step S2, the value of the EHC resistance in the new car state, i.e., the value of the initial EHC resistance REHC_ini at the time of manufacture, is stored in the ECU and held in advance. In addition, in step S3, it is determined whether the value of the initial EHC resistance REHC_ini at the time of manufacture is within a predetermined range, thereby detecting an abnormality due to an initial defect in the electrically heated catalyst device 9.

Furthermore, in step S6, the EHC resistance REHC is detected at times other than the initial start. When detecting the EHC resistance REHC, it may be obtained as an actual measurement value using an appropriate sensor, or the EHC resistance REHC' due to deterioration over time may be estimated and then combined with the value of the initial EHC resistance REHC_ini at the time of manufacture to obtain a more actual degree of deterioration of the EHC resistance REHC. Normally, the value of the initial EHC resistance REHC_ini at the time of manufacture is likely to vary, so there is a possibility that the accuracy of the deterioration estimation may be poor if the degree of deterioration of the EHC resistance REHC is estimated by considering only the change over time. In other words, by estimating the degree of deterioration of the EHC resistance REHC while taking into account the initial variation at the time of manufacture, the accuracy of the estimation of the deterioration of the EHC resistance REHC can be improved.

Then, in the next step S7, the value of the insulation resistance Rleak is calculated based on the value of the EHC resistance REHC detected in step S6. In this way, the value of the insulation resistance Rleak between the catalyst 7 and the housing 8 can be calculated based on the value of the resistance R of the entire circuit of the electrically heated catalytic device 9 and the value of the EHC resistance REHC, without directly measuring the value of the insulation resistance Rleak between the catalyst 7 and the housing 8. In the case of directly measuring the value of the insulation resistance Rleak between the catalyst 7 and the housing 8 as in the conventional case, even if there is only one carbon deposit, a voltage is intentionally applied between the catalyst 7 and the housing 8 to cause a current to flow, which may lower the value of the insulation resistance Rleak and erroneously determine that there is an insulation failure. In contrast, in this invention, the value of the insulation resistance Rleak is calculated based on the value of the resistance R of the entire circuit of the electrically heated catalytic device 9 and the value of the EHC resistance REHC, so that an abnormality in the electrically heated catalytic device 9 can be more accurately determined.

The present invention is not limited to the above-mentioned embodiments, and may be modified as appropriate within the scope of the invention.

REFERENCE SIGNS LIST 1 engine 2 cylinder 3 intake pipe 4 intake manifold 5 exhaust manifold 6 exhaust pipe 7 catalyst 8 housing 9 electrically heated catalyst device 10 one electrode 11 other electrode 12 power conversion device 13 battery 14 insulating transformer 15 current sensor 16 voltage sensor 17 ECU
18 Initial start determination means 19 Initial EHC resistance value calculation section 20 Initial EHC abnormality determination means 21 EHC resistance detection section 22 Insulation resistance calculation section 23 Insulation degradation determination means

Claims (4)

An abnormality detection device for an electrically heated catalyst device in which a catalyst for purifying exhaust gas from an internal combustion engine is housed in a conductive housing in a state insulated from the housing, and an electric current is passed through the catalyst to raise the temperature of the catalyst,
A reference resistance value of the catalyst when current is applied to raise the temperature of the catalyst is stored in advance,
determining an actual resistance value when current is applied to heat the catalyst in a state in which the catalyst is housed in the housing and in use;
determining an insulation resistance value based on the actual resistance value and the reference resistance value;
An abnormality detection device for an electrically heated catalyst device, comprising: a detecting unit for detecting an abnormality in the electrically heated catalyst device based on the insulation resistance value and a predetermined judgment threshold value. 2. The abnormality detection device for an electrically heated catalytic converter according to claim 1,
An abnormality detection device for an electrically heated catalytic converter, characterized in that the reference resistance value is estimated from a predetermined relationship based on the detection values of a flow sensor in the exhaust pipe, an air-fuel ratio sensor of the exhaust passing through the exhaust pipe, and a temperature sensor of the exhaust. 2. The abnormality detection device for an electrically heated catalytic converter according to claim 1,
13. An abnormality detection device for an electrically heated catalytic converter, comprising: a first resistance value detecting means for detecting an abnormality in an electrically heated catalytic converter; 4. An abnormality detection device for an electrically heated catalytic converter according to claim 1,
a current sensor that detects a value of a current flowing through a circuit when a current is applied to heat the catalyst, and a voltage sensor that detects a voltage value of the circuit;
2. An abnormality detection device for an electrically heated catalytic converter, comprising: a first electrode connected to a first terminal of the catalytic converter;

Images