JP4877291B2 - Heater deterioration detector - Google Patents

Description

  The present invention relates to a heater deterioration detection device that detects deterioration of a heater for a gas sensor.

  As this type of gas sensor, there are an O2 sensor and an A / F sensor for detecting the oxygen concentration, a NOx sensor for detecting the nitrogen oxide concentration, etc., and by controlling the fuel injection amount based on the detection signal of the gas sensor, Emissions are being improved. Further, this type of gas sensor is provided with a heater for heating the sensor element. When the sensor element is not activated, such as when the internal combustion engine is started, the sensor element is heated by the heater. As a result, the sensor element is activated at an early stage, and the deterioration of emissions at the time of starting the internal combustion engine or the like is suppressed. For this reason, if a disconnection or a short circuit occurs in a circuit that supplies power to the heater, the emission is deteriorated. On the other hand, it is known to detect the presence or absence of a short circuit or disconnection of the circuit based on a potential difference between both ends of the heater (for example, see Patent Document 1).

On the other hand, in recent years, it has been desired to detect the deterioration of emissions based on a stricter standard. On the other hand, it is known to detect aged deterioration of a heater (see, for example, Patent Document 2). As the heater deteriorates, the impedance of the heater increases, and consequently the heater current flowing through the heater decreases. Therefore, in the invention described in Patent Document 2, the deterioration of the heater is detected based on the heater current.
Japanese Patent Laid-Open No. 11-6812 JP 2001-241352 A

  However, the heater current is determined by the voltage between the terminals of the heater and the impedance of the heater. For this reason, the heater current also changes due to fluctuations in the input voltage to the heater. Moreover, the change in the heater current accompanying the deterioration of the heater is not particularly large. Therefore, in the invention described in Patent Document 2, in detection of heater deterioration, erroneous detection may occur due to fluctuations in the input voltage to the heater. In addition to the heater, various electric loads such as an electromagnetic valve are connected to the battery that supplies power to the heater, and it is considered that the detection of deterioration of the heater is also affected by the power consumption state of the electric load. .

  The present invention has been made in order to solve the above-described problems, and has as its main object to provide a heater deterioration detection device that accurately detects deterioration of a heater for a gas sensor.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The present invention relates to a heater for a gas sensor fed from a battery via a first feeding path, current measuring means for measuring a heater current flowing through the first feeding path, and a battery different from the first feeding path. Voltage measuring means connected through two power supply paths and measuring the voltage of the battery, and based on the heater current measured by the current measuring means and the battery voltage measured by the voltage measuring means, It is a heater deterioration detection device that detects deterioration.

  In such a configuration, depending on the power consumption state of the electrical load other than the heater that is fed through the first feeding path or the second feeding path, there is a difference between the voltage drop in the first feeding path and the voltage drop in the second feeding path. As a result, a difference occurs between the input voltage to the heater and the battery voltage measured by the voltage measuring means. When these voltages differ greatly, even if the battery voltage measured by the voltage measuring means is taken into account in detecting the deterioration of the heater as described above, fluctuations in the input voltage to the heater cannot be compensated by the battery voltage. . As a result, the accuracy of heater deterioration detection is reduced.

  Therefore, in the first aspect of the present invention, the power consumption state of the electric load fed through at least one of the first power feeding path and the second power feeding path is detected, and the heater is detected according to the detected power consumption state. Permits or prohibits deterioration detection. According to the first aspect of the present invention, detection of deterioration of the heater is prohibited when the difference between the input voltage to the heater and the battery voltage measured by the voltage measuring means is large according to the power consumption state of the electric load. It is possible. Thereby, the accuracy of heater deterioration detection can be increased.

  A system in which a plurality of electrical loads are provided, and the electrical loads are divided into a first electrical load group that is fed via the first feeding path and a second electrical load group that is fed via the second feeding path. Then, depending on the difference in power consumption state between the two electric load groups, the difference in power consumption by the two electric load groups changes, and as a result, the difference between the input voltage to the heater and the battery voltage measured by the voltage measuring means Change.

  Therefore, in the invention according to claim 2, in the system provided with a plurality of electric loads as described above, the power consumption state of each electric load group is detected, the power consumption states of both electric load groups are compared, Based on the comparison result, detection of deterioration of the heater is permitted or prohibited. According to the invention described in claim 2, the plurality of electric loads are divided into a first load group fed through the first feeding path and a second load group fed through the second feeding path. When the difference between the input voltage to the heater and the battery voltage measured by the voltage measuring means is large, that is, the fluctuation of the input voltage to the heater cannot be compensated by the battery voltage measured by the voltage measuring means. It is possible to prohibit the detection of heater deterioration. Thereby, in a system provided with a plurality of electric loads as described above, it is possible to accurately detect the deterioration of the heater.

  Here, the amount of power consumed by the first electric load group is determined by the electric load in the operating state among the electric loads of the first electric load group, and the amount of power consumed by the second electric load group is the second electric load. It is determined by the electric load in the operating state among the electric loads of the group. Therefore, the difference in power consumption between the two electric load groups is the combination of the electric load in the operating state among the electric loads in the first electric load group and the electric load in the operating state among the electric loads in the second electric load group. It changes according to. For this reason, the following configuration can be adopted. That is, a combination pattern of an electric load in an operating state among electric loads in the first electric load group and an electric load in an operating state among electric loads in the second electric load group, and both electric load groups in each combination pattern Power consumption data indicating the relationship with the power consumption state is stored. Then, the power consumption state of each electrical load group is detected as the power consumption state of each of the electrical load groups, and based on the detected electrical load using the power consumption data. Then, the power consumption states of the two electric load groups are compared, and the heater deterioration detection is permitted or prohibited based on the comparison result (claim 3).

  In addition, the power consumption state of each electrical load group is detected as the power consumption state of each electrical load group, and the detected power consumption of each electrical load group is integrated to calculate the calculated both electrical loads. It is also conceivable to compare the integrated values of the power consumption amounts for the load groups and permit or prohibit the detection of heater deterioration based on the comparison result. In such a case, it is possible to appropriately permit or prohibit the detection of heater deterioration by accurately reflecting the difference in power consumption between the two electric load groups.

  Even when heater deterioration detection is permitted, there is a concern that the accuracy of heater deterioration detection may be reduced due to the difference between the input voltage to the heater and the battery voltage measured by the voltage measuring means. Therefore, in the invention described in claim 5, when the heater deterioration detection is permitted, the heater deterioration is detected based on the power consumption state of the electric load in addition to the heater current. According to the fifth aspect of the present invention, it is possible to detect the deterioration of the heater according to the difference between the input voltage to the heater and the battery voltage measured by the voltage measuring means. Thereby, it is possible to improve the accuracy of heater deterioration detection.

  In the present embodiment, a heater deterioration detection device for detecting deterioration of a heater for an O2 sensor is constructed. The O2 sensor is assumed to be provided in the exhaust pipe of an in-vehicle engine. FIG. 1 is a diagram schematically illustrating an ECU that functions as a heater deterioration detection device. FIG. 1 shows an O2 sensor, a battery, and the like in addition to the ECU.

  The O2 sensor 10 includes a sensor element 10a that detects an oxygen concentration and a heater 10b that heats the sensor element 10a.

  The sensor element 10a outputs a detection signal of, for example, 0.9V when the excess air ratio λ is less than 1.0, and outputs a detection signal of, for example, 0V when the excess air ratio λ exceeds 1.0. That is, it can be said that the sensor element 10a is an element that binaryly detects whether or not the excess air ratio λ exceeds 1. A detection signal of the sensor element 10a is input to the ECU 20. An impedance circuit (not shown) that detects the impedance of the sensor element 10a is connected to the sensor element 10a. The detection signal of the impedance circuit is also input to the ECU 20. The ECU 20 calculates the element temperature of the sensor element 10a based on the detection signal of the impedance circuit. The heater 10b is for heating and activating the sensor element 10a. In particular, the sensor element 10a can be activated early by being used at the time of engine start.

  In the present embodiment, it is assumed that the arrangement of the O2 sensor 10 and the ECU 20 is greatly different. Specifically, it is assumed that the O2 sensor 10 is disposed in the exhaust pipe of the engine as described above, and the ECU 20 is disposed in the vehicle compartment or the engine room. Therefore, the heater 10b and the ECU 20 are supplied with power from the battery 11 through different power supply paths. Specifically, the input terminal RI of the main relay 12 is connected to the battery 11, and the first wire harness 13 and the second wire harness 14 are connected to the output terminal RO of the main relay 12. The first wire harness 13 and the second wire harness 14 are connected to the input terminal HI of the heater 10b and the power supply terminal EI of the ECU 20, respectively. Hereinafter, the power feeding path formed by the first wire harness 13 is referred to as a first power feeding path L1, and the power feeding path formed by the second wire harness 14 is referred to as a second power feeding path L2.

  In addition to the heater 10b and the ECU 20, a plurality of electrical loads 19 are connected to the first power supply path L1 and the second power supply path L2. As the electrical load 19, for example, an A / F sensor heater, a NOx sensor heater, an oil control valve, a purge valve, or the like can be considered. These electric loads 19 are respectively connected to the first power supply path L1 or the second power supply path L2 depending on the arrangement in the vehicle. The energization of each electric load 19 can be controlled by the ECU 20. Hereinafter, the electrical load 19 fed through the first feeding path L1 is referred to as a first electrical load group 17, and the electrical load 19 fed through the second feeding path L2 is referred to as a second electrical load group 18.

  The ECU 20 is an electronic control unit composed mainly of a microcomputer 21 composed of a CPU, ROM, RAM, EEPROM, and the like. The microcomputer 21 executes various programs stored in the ROM, and performs various controls of the engine system according to the engine operating state each time. For example, the ECU 20 performs duty control on energization of the heater 10b so as to keep the sensor element 10a at a constant temperature. Thereby, the sensor element 10a is maintained in a predetermined active state.

  Next, the configuration related to the energization control of the heater 10b will be described in detail. In addition to the microcomputer 21, the ECU 20 includes a heater drive circuit 22 that drives the heater 10 b under the control of the microcomputer 21. In the present embodiment, the heater driving circuit 22 includes a switching element 23 provided between the output terminal HO of the heater 10b and the ground. The microcomputer 21 turns the switching element 23 on and off in order to adjust the element temperature calculated based on the detection signal of the impedance circuit to a predetermined target temperature (for example, 300 ° C.). Thereby, the energization amount to the heater 10b is controlled.

  FIG. 2 is a characteristic diagram showing the relationship between the temperature of the heater 10b and the impedance of the heater 10b. The impedance of the heater 10b increases as the heater temperature rises as shown by the solid line graph, but also rises when the heater 10b deteriorates as shown by the broken line graph. For this reason, when the impedance becomes high due to the deterioration of the heater 10b, it becomes difficult for current to flow through the heater 10b. This leads to a situation where the activation of the sensor element 10a is delayed and a situation where the activation temperature (for example, about 300 ° C.) cannot be maintained. As a result, emissions will deteriorate.

  Therefore, the deterioration of the heater 10b is detected. Hereinafter, a configuration related to detection of deterioration of the heater 10b will be described in detail.

  As shown in FIG. 1, the ECU 20 includes a heater current detection circuit 25 that detects a current (heater current) flowing through the heater 10b through the first power supply path L1, and a power source connected to the battery 11 through the second power supply path L2. And a battery voltage detection circuit 29 that detects the voltage at the terminal EI as the battery voltage VBe. In this embodiment, the heater current detection circuit 25 includes a shunt resistor 26 provided between the switching element 23 and the ground, and an operational amplifier 27 that amplifies the voltage across the shunt resistor 26. The heater current detection circuit 25 outputs a signal correlated with the heater current to the microcomputer 21. In addition, the battery voltage detection circuit 29 includes, for example, a voltage dividing circuit that divides the battery voltage at the power supply terminal EI. The battery voltage detection circuit 29 outputs a signal correlated with the battery voltage at the power supply terminal EI to the microcomputer 21. The current detection circuit 25 corresponds to “current measurement means”, and the battery voltage detection circuit 29 corresponds to “voltage measurement means”.

  Here, as described above, when the deterioration of the heater 10b progresses, the impedance of the heater 10b increases, and the heater current flowing through the heater 10b decreases. Therefore, it is possible to detect deterioration of the heater 10b based on the heater current. In the present embodiment, the deterioration of the heater 10b is detected based on whether or not the heater current detected by the heater current detection circuit 25 falls below a predetermined threshold value TH.

  However, the heater current also changes depending on the input voltage to the heater 10b, that is, the fluctuation of the battery voltage at the input terminal HI of the heater 10b. On the other hand, in this embodiment, the fluctuation of the input voltage to the heater 10b is compensated by the battery voltage VBe. Specifically, as the battery voltage VBe is lower, the threshold TH used for detecting the deterioration of the heater 10b is set smaller.

  However, depending on the power consumption state of the first electric load group 17 and the second electric load group 18, the voltage drop from the battery 11 to the input terminal HI of the heater 10b in the first power supply path L1 and the battery in the second power supply path L2 There is a large difference between the voltage drop from 11 to the power supply terminal EI of the ECU 20, and the input voltage VIh to the heater 10b and the battery voltage VBe may differ greatly. When the difference between the two voltages VIh and VBe is large, the fluctuation of the input voltage VIh to the heater 10b cannot be compensated by the battery voltage VBe. Therefore, in this embodiment, when the difference between the input voltage VIh to the heater 10b and the battery voltage VBe is large, detection of deterioration of the heater 10b is prohibited.

  Hereinafter, the deterioration detection process of the heater 10b will be described with reference to FIG. FIG. 3 is a flowchart showing the flow of the heater deterioration detection program. In the present embodiment, it is assumed that the deterioration detection process of the heater 10b is realized by the microcomputer 21 executing this program at a predetermined cycle (every predetermined crank angle or at a predetermined time cycle).

  In step S <b> 11 shown in FIG. 3, the microcomputer 21 detects the electric load 19 that is in an operating state among the electric loads 19 of the first electric load group 17 and the second electric load group 18.

  In step S <b> 12, the microcomputer 21 determines the electric load 19 that is in the operating state among the electric loads 19 in the first electric load group 17 and the electric load 19 that is in the operating state among the electric loads 19 in the second electric load group 18. Based on the comparison result, it is determined whether or not the difference between the input voltage VIh to the heater 10b and the battery voltage VBe is large.

  That is, the amount of power consumed by the first electric load group 17 is determined by the electric load in the operating state among the electric loads 19 of the first electric load group 17, and the amount of power consumed by the second electric load group 18 is It is determined by the electric load in the operating state among the electric loads 19 of the two electric load group 18. Therefore, the difference in power consumption between the two electric load groups 17, 18 is the operation of the electric load 19 in the first electric load group 17 and the electric load 19 in the second electric load group 18. It changes according to the combination with the electrical load in the state. Therefore, as described above, the electric load that is in the operating state among the electric loads 19 of the first electric load group 17 and the electric load that is in the operating state among the electric loads 19 of the second electric load group 18 are By comparison, it can be determined whether or not the difference between the input voltage VIh to the heater 10b and the battery voltage VBe is large.

  For example, in the memory (ROM of the ECU 20), the electric load in the operating state among the electric loads 19 in the first electric load group 17 and the electric load in the operating state among the electric loads 19 in the second electric load group 18 are stored. A map in which the combination pattern and the determination result as to whether or not the difference between the input voltage VIh to the heater 10b and the battery voltage VBe increases in each combination pattern is stored in advance (see FIG. 4). Such a map is (1) an experiment in which the electric loads 19 of the electric load groups 17 and 18 are actually activated or deactivated, the voltages VIh and VBe are measured, and the difference between the voltages VIh and VBe is calculated. Based on the results, (2) the rated power consumption of each electric load 19 and the power supply path (first power supply path L1 or second power supply path L2) between each electric load 19 and the battery 11 It can be obtained by estimating whether or not the difference between the two voltages VIh and VBe becomes large in consideration of the distance, the electric resistance of the power feeding path, and the like. Then, the microcomputer 21 refers to the map and obtains a determination result as to whether or not the difference between the voltages VIh and VBe is large from the electrical load 19 that is in the operating state detected in step S11.

  If the microcomputer 21 determines that the difference between the input voltage VIh to the heater 10b and the battery voltage VBe is not large, the microcomputer 21 proceeds to the process of step S13. On the other hand, when the microcomputer 21 determines that the difference between the two voltages VIh and VBe is large, the microcomputer 21 ends the execution of the current program.

  In step S <b> 13, the microcomputer 21 causes the heater drive circuit 22 to start energization of the heater 10 b and then causes the heater current detection circuit 25 to detect the heater current. In subsequent step S <b> 14, the microcomputer 21 causes the battery voltage detection circuit 29 to detect the battery voltage VBe.

  In step S15, the microcomputer 21 compensates for fluctuations in the input voltage VIh to the heater 10b with the battery voltage VBe. Specifically, the microcomputer 21 variably sets the threshold value TH based on the battery voltage VBe. That is, the microcomputer 21 sets the threshold value TH used for detecting the deterioration of the heater 10b to be smaller as the battery voltage VBe is lower. For example, a map in which the battery voltage VBe and the threshold value TH are associated with each other is stored in advance in the ROM of the ECU 20. In this map, the threshold value TH decreases as the battery voltage VBe decreases. Then, ECU 20 refers to the map and sets a threshold value TH corresponding to battery voltage VBe detected in step S14.

  In step S16, the microcomputer 21 determines whether or not the heater current is smaller than the threshold value TH.

  If it is determined in step S16 that the heater current is smaller than the threshold value TH, the microcomputer 21 counts up the deterioration detection counter (see step S17), and the counter value of the deterioration detection counter is equal to or greater than a predetermined value. Whether or not (see step S18). Here, the deterioration detection counter is a counter indicating how many times the situation that the heater current is smaller than the threshold value TH is continuously detected. If the microcomputer 21 determines that the deterioration detection counter is greater than or equal to a predetermined value, the microcomputer 21 executes a predetermined fail process in step S19, and then ends the execution of the current program. As fail processing, it is conceivable to turn on a failure warning lamp (MIL) or store failure diagnosis data (diag data) in a backup memory (EEPROM or the like). On the other hand, when it is determined that the deterioration detection counter is smaller than the predetermined value, the microcomputer 21 ends the execution of the current program without executing the fail process.

  If it is determined in step S16 that the heater current is equal to or greater than the threshold value TH, the microcomputer 21 clears the deterioration detection counter (see step S20) and ends the execution of the current program.

  According to the deterioration detection process of the heater 10b described above, when the difference between the input voltage VIh to the heater 10b and the battery voltage VBe is large, that is, the fluctuation of the input voltage VIh to the heater 10b cannot be compensated by the battery voltage VBe. In this case, detection of deterioration of the heater 10b is prohibited. Thereby, it is possible to improve the accuracy of detecting the deterioration of the heater 10b.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  The power consumption of each electric load 19 of both electric load groups 17 and 18 is calculated, the calculated power consumption of the electric load 19 of each electric load group 17 and 18 is integrated, and the calculated both electric load groups The deterioration detection of the heater 10b may be permitted or prohibited based on the difference between the integrated values of the power consumption amounts 17 and 18. For example, when the amount of power supplied to the electrical load 19 is controlled by the ECU 20 as in the case of the heater 10b, the power consumption amount of each of the electrical loads 19 in the both electrical load groups 17 and 18 is a duty command value ( (Duty ratio). Thereby, the difference between the input voltage VIh to the heater 10b and the battery voltage VBe can be accurately reflected, and the detection of deterioration of the heater 10b can be preferably permitted or prohibited.

  Whether or not the heater 10b has deteriorated is determined regardless of whether or not the two voltages VIh and VBe are significantly different. When the difference between the two voltages VIh and VBe is large, the heater 10b The result of deterioration determination may not be adopted. For example, in FIG. 3, when the difference between both voltages VIh and VBe is not large by moving step S11 and step S12 between step S18 and step S19, the process proceeds to step S19, where both voltages VIh, If the difference in VBe is large, the execution of the program may be terminated. Even in this case, the same excellent effects as those of the above embodiment can be obtained.

  Even when the detection of deterioration of the heater 10b is permitted, a difference may occur between the input voltage VIh to the heater 10b and the battery voltage VBe. Therefore, when the detection of the deterioration of the heater 10b is permitted, it is preferable to consider the power consumption state of both the electric load groups 17 and 18 when setting the threshold value TH of the heater current. For example, in step S15 of the heater deterioration detection program, the electric load that is in the operating state among the electric loads 19 in the first electric load group 17 and the electric load 19 in the second electric load group 18 are in the operating state. The threshold value TH is calculated based on the combination with the electric load. Thereby, since the threshold value TH is set according to the difference between the input voltage VIh to the heater 10b and the battery voltage VBe, it is possible to improve the accuracy of detecting the deterioration of the heater 10b.

  In the said embodiment, the 1st wire harness 13 and the 2nd wire harness 14 which branch from the main relay 12 were made into the 1st electric power feeding path L1 and the 2nd electric power feeding path L2, respectively. However, the present invention is not limited to this, and both wire harnesses 13 and 14 may be individually connected to the battery 11. For example, two relays may be connected to the battery 11 in parallel, and the first wire harness 13 and the second wire harness 14 may be connected to both relays, respectively.

  The present invention can also be applied to the case where an electrical load group is provided only in one of the first power supply path L1 and the second power supply path L2. The present invention can also be applied to heaters for gas sensors other than the O2 sensor 10, such as A / F sensors and NOx sensors.

The figure which shows the outline of the deterioration detection apparatus of the heater for O2 sensors. The characteristic view which shows the relationship between the temperature of O2 heater, and its impedance. The flowchart figure which shows the flow of the deterioration detection program of a heater.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... O2 sensor (gas sensor), 10b ... Heater, 11 ... Battery, 17 ... 1st electric load group, 18 ... 2nd electric load group, 19 ... Electric load, 20 ... ECU (heater deterioration detection apparatus), 21 ... Microcomputer (Detection means, permission means), 25 ... heater current detection circuit (current measurement means), 29 ... battery voltage detection circuit (voltage measurement means), L1 ... first power supply path, L2 ... second power supply path.

Claims (5)

A heater for a gas sensor fed from a battery via a first feeding path, a current measuring means for measuring a heater current flowing to the heater through the first feeding path, and a first different from the first feeding path for the battery. Voltage measuring means connected through two power supply paths and measuring the voltage of the battery, based on the heater current measured by the current measuring means and the battery voltage measured by the voltage measuring means In the heater deterioration detection device of the gas sensor for detecting deterioration of the heater,
Detecting means for detecting a power consumption state of an electric load fed through at least one of the first feeding path and the second feeding path;
Permission means for permitting or prohibiting deterioration detection of the heater according to the power consumption state detected by the detection means;
A heater deterioration detection device comprising: A plurality of the electrical loads are provided, and the electrical loads are divided into a first electrical load group that is fed via the first feeding path and a second electrical load group that is fed via the second feeding path. Applied to the system divided and
The detection means detects the power consumption state of each electric load group,
2. The heater deterioration detection device according to claim 1, wherein the permission unit compares the power consumption states of the two electric load groups, and permits or prohibits detection of deterioration of the heater based on the comparison result. Of the electric loads of the first electric load group, a combination pattern of an electric load that is in an operating state and an electric load that is in an operating state of the electric loads of the second electric load group; and Comprising storage means for storing power consumption data indicating the relationship with the power consumption state;
The detection means detects the operation or non-operation state of each electric load of the both electric load groups as the power consumption state of each electric load group,
The permission means uses the power consumption data stored in the storage means, and compares the power consumption states of the two electric load groups based on the electric load detected by the detection means as being in an operating state. Item 3. The heater deterioration detection device according to Item 2. The detecting means integrates the detected power consumption amount of the electric load of each electric load group and the means for detecting the electric power consumption amount of each electric load group as the power consumption state of each electric load group, respectively. And means for
The heater deterioration detection device according to claim 2, wherein the permission unit compares the integrated values of the power consumption amounts for both electric load groups calculated by the detection unit.   The deterioration of the heater is detected based on the power consumption state of the electric load in addition to the heater current when detection of deterioration of the heater is permitted by the permission unit. The heater deterioration detection device described.

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