JP5053657B2 - Oxygen sensor degradation signal generator - Google Patents

Description

  When the oxygen sensor capable of outputting a sensor output signal that changes according to the oxygen concentration in the exhaust gas of the internal combustion engine and suddenly changes the output value with the theoretical air-fuel ratio as a boundary deteriorates, the oxygen sensor The present invention relates to a degradation signal generation device that artificially generates an output sensor output signal as a degradation signal.

  Conventionally, an oxygen sensor is known which is attached to an exhaust passage of an internal combustion engine such as an automobile engine and detects whether the air-fuel ratio of the exhaust gas is on the rich side or the lean side based on the oxygen concentration in the exhaust gas. ing. The sensor element of this oxygen sensor has a cylindrical or plate-shaped solid electrolyte body mainly composed of zirconia, and a pair of electrodes opposed via the solid electrolyte body. Then, by exposing one electrode of the sensor element to the exhaust gas and exposing the other gas to the reference gas, the output voltage (sensor output signal) of the sensor element (oxygen sensor) depends on the concentration of oxygen in the exhaust gas. (In other words, with the theoretical air-fuel ratio as a boundary), it exhibits a behavior that changes in a binary manner. The sensor output signal output from the oxygen sensor is transmitted to an ECU (electronic control unit) that controls various types of engine control. The ECU adjusts the fuel injection amount in the engine based on the received sensor output signal. Feedback control is performed.

  Such an oxygen sensor may be deteriorated because the sensor element is exposed to an exhaust passage having a severe use environment and is used. Therefore, in the development of the ECU, the optimal air-fuel ratio feedback is also applied to the sensor output signal (deterioration signal) at the time of oxygen sensor deterioration so that the accuracy of the air-fuel ratio feedback control can be maintained even when the oxygen sensor is deteriorated to some extent. Designs have been made so that control parameters can be determined, and programs for detecting sensor deterioration have been designed. For example, oxygen sensors with different degrees of deterioration are prepared by accelerated endurance tests, and the signal state at the transient stage of the deterioration signal is predicted using the deterioration signals obtained from these oxygen sensors and the sensor output signal of a normal oxygen sensor. Parameter settings.

  By the way, when performing a test for confirming the exhaust gas purification state in an actual vehicle, in order to confirm whether or not the air-fuel ratio feedback control by the ECU is correctly performed even when the oxygen sensor is deteriorated, as described above. An oxygen sensor deteriorated by the accelerated durability test is attached to the actual vehicle. However, since it is used for such a test, it is difficult to create each oxygen sensor that reproduces several types of deterioration states as intended by an accelerated durability test. In addition, in the test, it takes time to replace the oxygen sensor having a different deterioration state every time the test is performed. Therefore, a deterioration signal generation device (deterioration simulator) that can generate a deterioration signal of the oxygen sensor in a pseudo manner has been developed (see, for example, Patent Document 1).

Such a degradation signal generation device is interposed between the normal oxygen sensor that is a reference attached to the actual vehicle (in other words, the oxygen sensor that is a reference for generating the degradation signal) and the ECU. The sensor output signal of the oxygen sensor is processed to generate a pseudo deterioration signal, and this deterioration signal is output to the ECU. Specifically, in the degradation signal generation device of Patent Document 1, the gain of the sensor output signal of the entire region air-fuel ratio sensor in which the sensor output signal changes linearly according to the oxygen concentration in the exhaust gas, or the sensor output A pseudo deterioration signal is generated by causing a delay in the response characteristic of the signal.
JP 2004-93957 A

  There are various forms of deterioration of the oxygen sensor. For example, a large amount of water (for example, condensed water) present in the exhaust pipe is applied to the sensor element, and microcracks over the front and back surfaces of the solid electrolyte body are caused by thermal shock at that time. There is a degradation state that occurs. When such deterioration occurs, gas flow through the microcracks occurs even slightly, so the atmosphere of the reference gas changes, and the value of the sensor output signal differs from the value of the sensor output signal of the normal oxygen sensor. Shift to the larger or smaller side. Therefore, when such a deterioration state occurs, in an oxygen sensor in which the value of the sensor output signal changes in a binary manner according to the oxygen concentration of the exhaust gas, the difference (range) in which the binary value can change changes. In this case, the binary value is changed up and down. On the other hand, in the full-range air-fuel ratio sensor as in Patent Document 1, the direction (positive / negative) of the current flowing through the solid electrolyte body is reversed between when the exhaust gas air-fuel ratio is rich and when it is lean. When a similar deterioration state occurs, the range of values that can be taken by the sensor output signal is shown. For this reason, even if the offset correction performed on the sensor output signal of the full-range air-fuel ratio sensor is directly applied to the oxygen sensor in which the value of the sensor output signal changes in a binary manner, the deterioration state of the oxygen sensor is correctly simulated. There was a problem that it was difficult.

  The present invention has been made in order to solve the above-described problems, and a sensor output signal output when an oxygen sensor whose sensor output signal changes suddenly at the boundary of the theoretical air-fuel ratio deteriorates is generated in a pseudo manner as a deterioration signal. An object of the present invention is to provide an oxygen sensor deterioration signal generation apparatus capable of performing offset correction.

In order to achieve the above object, the oxygen sensor deterioration signal generating apparatus according to the first aspect of the present invention changes in accordance with the oxygen concentration in the exhaust gas of the internal combustion engine and suddenly changes its output value at the stoichiometric air-fuel ratio. when the oxygen sensor is deteriorated, which outputs a sensor output signal, which is the oxygen sensor to a deterioration signal generation device, as a reference to artificially generate a sensor output signal in which the oxygen sensor output as a deterioration signal reference A reference signal acquisition means for acquiring the reference signal and connected to a reference oxygen sensor that outputs a sensor output signal that changes according to the oxygen concentration in the exhaust gas as a reference signal; and the reference signal And an offset value setting means for setting an offset value for changing the value indicated by And a deterioration signal generation means.
In the oxygen sensor deterioration signal generation apparatus according to the present invention, the offset value setting means may be able to set the offset value to different values separately for the rich side and the lean side.
In the oxygen sensor deterioration signal generation apparatus according to the present invention, the offset value setting means and the deterioration signal generation means may be constituted by a CPU of a microcomputer.

  According to the oxygen sensor deterioration signal generation device of the first aspect of the invention, an arbitrary offset value can be superimposed on the value indicated by the reference signal output from the reference oxygen sensor. Thus, a pseudo deterioration signal can be generated in a state where the range of possible values of the binary value of the sensor output signal that changes suddenly is arbitrarily raised or lowered. Therefore, by using the deterioration signal generation device of the present invention, when developing a system that realizes air-fuel ratio feedback control using an oxygen sensor in which the sensor output signal changes suddenly at the theoretical air-fuel ratio, the deterioration signal generator is actually deteriorated. It is not necessary to prepare an oxygen sensor, and the development period can be shortened.

  Hereinafter, an embodiment of a degraded signal generation apparatus embodying the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a schematic configuration of a sensor simulator 1 as an example of a deterioration signal generation device according to the present embodiment. The oxygen sensor connected to the degradation signal generation device of the present invention is an oxygen sensor that can output a sensor output signal that changes according to the oxygen concentration in the exhaust gas and whose output value suddenly changes with the theoretical air-fuel ratio as a boundary. In the following description, it is assumed that the reference sensor 2 is a normal (not deteriorated) oxygen sensor.

  Since a known oxygen sensor is used, a detailed description of its structure and the like will be omitted, but the following will briefly explain the principle of detecting the air-fuel ratio of the exhaust gas by the sensor element used for the oxygen sensor. Explained. This sensor element has a cylindrical or plate shape in which a solid electrolyte body made of zirconia having a property of showing oxygen ion conductivity at an activation temperature or higher is sandwiched between a pair of porous electrodes, and two solid electrolyte bodies are used. This utilizes the movement of oxygen ions in the solid electrolyte body when there is a difference in oxygen partial pressure between the two atmospheres. Specifically, when the solid electrolyte body separates an exhaust gas atmosphere and a reference gas atmosphere (an atmosphere having a reference oxygen concentration) and the oxygen partial pressure is balanced between the two atmospheres, Electrons are carried by the moving oxygen ions, so that an electromotive force (sensor output signal) is generated between the porous electrodes. The value (electromotive force) of the sensor output signal output from the oxygen sensor varies in a binary manner between the rich side and the lean side when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio. When the air-fuel ratio is on the rich side, the value of the sensor output signal output by the sensor element is about 0.9 V, and when it is on the lean side, it is about 0.05 V. As an example of such an oxygen sensor, in the present embodiment, an oxygen sensor disclosed in Japanese Patent Application Laid-Open No. 2004-138599, in which a heater is inserted into a cylindrical sensor element, and a tip portion of the sensor element is attached to the oxygen sensor. In the following description, it is assumed that an oxygen sensor having a configuration in which the sensor element is held inside the metal shell is used in a form arranged in a protector with a gas flow hole.

  As shown in FIG. 1, the sensor simulator 1 is a device interposed between a reference sensor 2 as an oxygen sensor attached to an exhaust passage (not shown) of an automobile and an ECU 3 that performs electronic control of the automobile. As described above, the reference sensor 2 outputs a sensor output signal corresponding to the oxygen concentration in the exhaust gas flowing through the exhaust passage, and this sensor output signal is input to the sensor simulator 1 as a reference signal. The sensor simulator 1 processes the input reference signal by executing a later-described deterioration signal generation program to generate a deterioration signal, and outputs the deterioration signal to the ECU 3. The ECU 3 performs engine control (for example, adjustment of the amount and timing of injection of fuel injected from the injector, adjustment of ignition timing, etc.) based on the input deterioration signal. The ECU 3 also supplies a heater drive voltage to a heater circuit (not shown) of the reference sensor 2 to achieve early activation of the sensor element (not shown) and stabilization after activation.

  The sensor simulator 1 includes a CPU 11 that controls itself, a rewritable EEPROM 12 in which a deterioration signal generation program and the like to be described later are stored, and a RAM 13 that temporarily stores various data in a casing (not shown). A microcomputer 10 is provided. Note that the CPU 11, the EEPROM 12, and the RAM 13 of the microcomputer 10 have a known configuration. The configuration of the storage areas of the EEPROM 12 and the RAM 13 will be described later.

  The microcomputer 10 has an A / D converter 30 for A / D converting a reference signal input from the reference sensor 2 via the input interface 20, and an output buffer 40 for a deterioration signal generated by a deterioration signal generation program to be described later. A D / A converter 50 that performs D / A conversion for output to the ECU 3 is connected. Further, the microcomputer 10 has a display control of an input unit 60 for a user to input setting values used for the deterioration signal generation program and a display unit 80 for displaying the input setting values and the like so that they can be confirmed. The display control unit 70 is connected to the display control unit 70. As the input unit 60, for example, a push switch or a rotary switch is used, and as the display unit 80, for example, an LCD display or the like is used. Although not shown, the sensor simulator 1 also includes a power supply circuit and the like.

  Next, a schematic configuration of the storage area of the EEPROM 12 and the storage area of the RAM 13 will be described with reference to FIGS. FIG. 2 is a conceptual diagram showing the configuration of the storage area of the EEPROM 12. FIG. 3 is a conceptual diagram showing the configuration of the storage area of the RAM 13.

  As shown in FIG. 2, the EEPROM 12 is provided with a set value storage area 121, a program storage area 122, and an initial value storage area 123. The set value storage area 121 stores initial values of various variables (voltage values Vin and Vout) used when the deterioration signal generation program is executed. In addition, a variable (offset value Offset) input from the input unit 60 by the user in advance is also stored. The offset value Offset is stored in the EEPROM 12 so that it can be saved even when the power is turned off. The program storage area 122 stores a deterioration signal generation program. By using the EEPROM 12, it is configured to flexibly cope with version upgrades and the like. The initial value storage area 123 stores initial values of variables used in the deterioration signal generation program. Further, the EEPROM 12 is provided with various storage areas not shown.

  Next, as shown in FIG. 3, the RAM 13 is provided with a work area 131 and a variable storage area 132. The work area 131 is a storage area where the deterioration signal generation program is read and expanded, and is used for execution thereof. The variable storage area 132 temporarily stores values of variables (Vin, Vout, Offset) used when the deterioration signal generation program is executed. Further, the RAM 13 is provided with various storage areas not shown.

  Here, each variable used in the deterioration signal generation program will be described. “Vin” is a variable for storing a voltage value of a reference signal that is a sensor output signal acquired from the reference sensor 2, and 0 is set as an initial value. “Vout” is a variable for storing the voltage value of the deteriorated signal generated by performing offset correction on the voltage value Vin of the reference signal, and 0 is set as the initial value. “Offset” is a variable for storing an offset value (correction value) for performing offset correction on the voltage value Vin of the reference signal. As described above, since the voltage value of the reference signal changes between about 0.05 V and about 0.9 V, the voltage value output at the theoretical air-fuel ratio is set to 0.45 V. When the voltage value Vin of the reference signal is shifted so that the voltage value of the reference signal is changed to the rich side (the higher voltage value side), the offset voltage Offset has a positive value of the voltage value. Entered by value. On the other hand, when the voltage value Vin of the reference signal is shifted so that the voltage value of the reference signal is changed to the lean side (low voltage value side), the offset voltage Offset has a negative value of the voltage value. Entered by value. A value preset by the user is set as the initial value of the offset value Offset.

  In the sensor simulator 1 having such a configuration, in accordance with the execution of the deterioration signal generation program shown in the flowchart of FIG. 4, a reference signal is acquired from the reference sensor 2 every 1 ms, processed to generate a deterioration signal, Output is being performed. Although not shown, the sensor simulator 1 may generate a deteriorated signal that has been subjected to various processes such as gain change, response delay, and signal delay, for example, with respect to the reference signal. The degradation signal generation program according to the present embodiment is provided as one process in the process of performing various types of processing on the reference signal. Hereinafter, offset correction applied to the reference signal will be described. An explanation shall be given.

  Hereinafter, details of the deterioration signal generation program shown in FIG. 4 will be described with reference to the graphs of FIGS. FIG. 4 is a flowchart of the deterioration signal generation program. FIG. 5 is a graph showing an example of the reference signal obtained along the time axis when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is alternated between the rich side and the lean side. FIG. 6 is a graph showing an example of a deteriorated signal subjected to offset correction for shifting the reference signal shown in FIG. 5 to the rich side (voltage side). FIG. 7 is a graph showing an example of a deteriorated signal subjected to offset correction for shifting the reference signal shown in FIG. 5 to the lean side (voltage side). Each step in the flowchart is abbreviated as “S”.

  In the sensor simulator 1, an arbitrary set value is input by the user. Specifically, an offset value Offset for shifting the value (voltage value) indicated by the reference signal up and down is set. The offset value Offset is input by operating the input unit 60 and stored in the set value storage area 121 of the EEPROM 12, so that the sensor simulator 1 can be used again after the power is turned off. It is configured to save previously entered settings.

  Generation of the deterioration signal from the reference signal of the reference sensor 2 by the sensor simulator 1 is started when a deterioration signal generation program (see FIG. 4) is read from the program storage area 122 of the EEPROM 12 into the work area 131 of the RAM 13 and executed. The As shown in FIG. 4, when the deterioration signal generation program is executed, first, various variables used in the deterioration signal generation program are initialized (S10). In this initialization process, the initial values (described above) of the variables (Vin, Vout) stored in the initial value storage area 123 of the EEPROM 12 are read and stored in the corresponding storage areas of the variable storage area 132 of the RAM 13. Done in Further, the offset value (Offset) set in advance by the user is read from the set value storage area 121 of the EEPROM 12 and similarly stored in the storage area of the corresponding variable storage area 132. That is, in the processing after S10 of the deterioration signal generation program, reading and writing of the values of each variable are all performed on the storage area of each variable corresponding to each processing provided in the variable storage area 132. .

  Next, in S11, reception of a reset signal every 1 ms is waited. In the present embodiment, a timer program (not shown) is executed in parallel with the deterioration signal generation program, and a reset signal is output every 1 ms. In S11, the reception of the reset signal is waited (S11: NO), and the process proceeds to S12 when the reset signal is received (S11: YES). In the processes of S12 to S20, the reference signal (voltage value Vin) acquired from the reference sensor 2 is offset-corrected to generate a deterioration signal (voltage value Vout), which is output to the ECU 3. . After the process of S20, the process returns to S11 to wait for the next reset signal. That is, each process of S12-S20 which processes a reference signal and produces | generates a degradation signal is performed for every 1 ms. In S10, the CPU 11 that reads the offset value Offset that has been input from the input unit 60 by the user in advance and stored and stored in the EEPROM 12 for use in the deterioration signal generation program, and stores it in the variable storage area of the RAM 13, is provided in the present invention. This corresponds to “offset value setting means”.

  In the next processing of S12 to S20, processing for superimposing the offset value Offset on the voltage value Vin of the reference signal to generate a deterioration signal (voltage value Vout) is performed. As described above, the reference sensor 2 of the present embodiment is a λ-type oxygen sensor, and when the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio, the output voltage value of the oxygen sensor is about 0.9V. When it is on the lean side with respect to the theoretical air-fuel ratio, about 0.05 V is indicated. Therefore, when the target air-fuel ratio of the air-fuel mixture is alternated between the rich side and the lean side about every 1 second, the voltage value of the reference signal of the λ-type oxygen sensor, that is, the reference sensor 2 is as shown in FIG. A steep change (for example, section [AB] or section [CD]) is shown between about 0.05 V and about 0.9 V every about one second.

  In order to perform offset correction for this reference signal, first, in the process of S12 in FIG. 4, first, the output voltage of the reference sensor 2 input via the A / D converter 30 (see FIG. 1) is acquired, The voltage value is stored as a variable Vin (S12). The A / D converter 30 and the CPU 11 that acquire the reference signal of the reference sensor 2 and store it as Vin in S12 correspond to the “reference signal acquisition means” in the present invention.

  Then, a process of superimposing the offset value on the reference signal is performed by adding the offset value Offset set in advance by the user to the voltage value Vin of the acquired reference signal (S14). As described above, the offset value Offset is a value for shifting the voltage value Vin up and down depending on its direction (positive / negative) and magnitude, and is obtained as a result of adding the voltage value Vin and the offset value Offset. The obtained voltage value is stored in the storage area of the variable storage area 132 as Vout. The CPU 11 that generates the deterioration signal (voltage value Vout) by superimposing the offset value Offset on the reference signal (voltage value Vin) of the reference sensor 2 in S14 corresponds to the “deterioration signal generation means” in the present invention.

  Here, FIG. 6 shows an example in which the value indicated by the reference signal is shifted to the rich side. FIG. 6 shows a waveform of a deteriorated signal when +0.5 is set as Offset. The graph of the degradation signal (voltage value Vout) indicated by the one-dot chain line shows a value that is 0.5 V higher than the graph of the reference signal (voltage value Vin) indicated by the dotted line at any timing. The voltage value of the deterioration signal shows a steep change between about 0.55 V and about 1.4 V every about 1 second.

  As described above, after the voltage value Vout of the deteriorated signal is obtained in S14, the process proceeds to S15, and when the voltage value Vout is outside the range of 0 V or more and less than 5 V due to offset correction, Correction is performed so as to be within the range of values. Specifically, if Vout is 5V or more (S15: YES), 4.99V is stored in Vout (S16). On the other hand, if Vout is less than 0V (S15: NO, S18: YES), 0V is stored in Vout (S19). If Vout is 0 V or more and less than 5 V (S15: NO, S18: NO), it is determined that Vout is an appropriate value, and no correction is performed.

  Here, FIG. 7 shows an example in which the value indicated by the reference signal is shifted to the lean side. FIG. 7 shows the waveform of the deterioration signal when −0.15 is set as Offset. The graph of the degradation signal (voltage value Vout) indicated by the one-dot chain line is the graph of the reference signal (voltage value Vin) indicated by the dotted line at the timing when the voltage value Vin of the original reference signal is greater than 0.15V. On the other hand, the voltage value is 0.15V lower. The degradation signal generated at the timing when the voltage value Vin is 0.15 V or less has its voltage value Vout corrected to 0V. The voltage value Vout of the generated degradation signal shows a steep change between 0 V and about 0.75 V every about 1 second.

  The deterioration signal (voltage value Vout) corrected to an appropriate value is output to the D / A converter 50 (S20), and the process returns to S11 to generate a deterioration signal at the next timing. Each process of S12 to S20 is executed again upon receipt of the next reset signal, and the voltage value Vout of the deteriorated signal is periodically updated. In the D / A converter 50, the voltage value Vout of the input degradation signal is D / A converted into an analog voltage value and output to the output buffer 40. The output buffer 40 outputs the deterioration signal converted into the analog voltage value to the ECU 3, but the voltage value is maintained until the next deterioration signal (voltage value Vout) is generated and output.

  As described above, in the sensor simulator 1 of the present embodiment, the preset offset value Offset is superimposed on the voltage value Vin of the reference signal, so that the voltage value is set to the rich side or the amount set arbitrarily. A deterioration signal (voltage value Vout) shifted to the lean side can be generated. In other words, according to the sensor simulator 1 of the present embodiment, the range of possible values (voltage values) of the binary value of the sensor output signal (reference signal of the reference sensor) that changes suddenly with the theoretical air-fuel ratio as a boundary is arbitrarily set. It is possible to generate a deteriorated signal (voltage value Vout) that is moved up and down.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, an input / output interface such as USB or RS232C may be provided, connected to a personal computer using a corresponding cable, and a setting value or the like may be input or displayed. Further, the reference signal of the reference sensor 2 or the generated deterioration signal may be output to a personal computer via its input / output interface, and an output waveform may be generated and monitored on the personal computer. The output waveform may be displayed on the unit 80.

  The variable (Offset) that can be set by the user is copied from the set value storage area 121 of the EEPROM 12 to the variable storage area 132 of the RAM 13 in the initialization process of S10, and the stored value of the variable storage area 132 is stored in the subsequent processes. Although referred to, the stored value in the set value storage area 121 may be directly referred to without performing this process. In this way, when the user changes the set value during the execution of the deterioration signal generation program, the change result can be immediately reflected in the generated deterioration signal. Further, a general ROM instead of the EEPROM 12 may be used so that the user can input the set values of the three variables at the start of execution of the deterioration signal generation program.

  In the present embodiment, the deterioration signal is generated from the reference signal by software by executing the deterioration signal generation program. However, the analog or digital hardware circuit constituting the logic circuit is produced and the deterioration signal is generated. You may go.

  Further, in the present embodiment, an example is shown in which the offset value Offset is individually set to +0.5 and −0.15 by the user. However, the offset value is not limited to the above values, and other values can be arbitrarily set. Needless to say, it can be set individually.

  In addition, the sensor simulator 1 of the present embodiment can generate a degradation signal obtained by offset-correcting the reference signal, but can also generate a degradation signal in which the gain, response characteristics, and delay time of the reference signal are changed. You may be able to do it. Here, the gain means a state where the voltage value of the reference signal is amplified or attenuated. The response characteristic means that the sensor output signal output from the oxygen sensor starts changing when the target air-fuel ratio is changed from the rich side to the lean side or from the lean side to the rich side with a predetermined value as a boundary. The time required to reach a preset value. The delay time is the delay time until the sensor output signal output from the oxygen sensor starts to change when the target air-fuel ratio is changed from the rich side to the lean side or from the lean side to the rich side. Say. When the gain, response characteristic, and delay time of the reference signal are changed as described above, the target air-fuel ratio is set to the rich side for the gain rate for changing the gain, the transition rate for changing the response characteristic, and the delay time. By making it possible to set each separately when changing from lean to lean and when changing from lean to rich, it is possible to develop a system that can realize precise air-fuel ratio feedback control at a higher level. From the viewpoint of smoothness, it is even better.

  The present invention can be applied to a deterioration signal generating apparatus that can generate a deterioration signal in a pseudo manner in a state where an oxygen sensor whose sensor output signal changes suddenly with a theoretical air-fuel ratio as a boundary is deteriorated.

It is a block diagram which shows the schematic structure of the sensor simulator 1 as an example of the degradation signal production | generation apparatus of this Embodiment. 2 is a conceptual diagram showing a configuration of a storage area of an EEPROM 12. FIG. 3 is a conceptual diagram showing a configuration of a storage area of a RAM 13. FIG. It is a flowchart of a degradation signal generation program. It is a graph which shows the example which showed the reference signal obtained when the air-fuel ratio of the air-fuel mixture supplied to a combustion chamber alternates between the rich side and the lean side along the time axis. 6 is a graph showing an example of a deteriorated signal subjected to offset correction for shifting the reference signal shown in FIG. 5 to the rich side (the higher voltage side). 6 is a graph showing an example of a deteriorated signal subjected to offset correction for shifting the reference signal shown in FIG. 5 to the lean side (voltage side).

1 Sensor simulator 2 Reference sensor 11 CPU
12 EEPROM
13 RAM
60 Input section 121 Set value storage area 132 Variable storage area Vin Reference signal Vout Deterioration signal Offset Offset value

Claims (3)

Sensor output signal output by the oxygen sensor when the oxygen sensor that outputs a sensor output signal that changes according to the oxygen concentration in the exhaust gas of the internal combustion engine and outputs a sudden change at the stoichiometric air-fuel ratio is deteriorated Is a degradation signal generation device that artificially generates a degradation signal as a degradation signal,
A reference oxygen sensor, which is the reference oxygen sensor, is connected to a reference oxygen sensor that outputs, as a reference signal, a sensor output signal that changes according to the oxygen concentration in the exhaust gas, and acquires the reference signal A reference signal acquisition means;
An offset value setting means for setting an offset value for changing the value indicated by the reference signal up and down;
A deterioration signal generation device for an oxygen sensor, comprising: deterioration signal generation means for generating the deterioration signal by superimposing the offset value on the reference signal.   The oxygen sensor deterioration signal generation device according to claim 1, wherein the offset value setting means can set the offset value to different values for the rich side and the lean side individually.   The oxygen sensor deterioration signal generation apparatus according to claim 1 or 2, wherein the offset value setting means and the deterioration signal generation means are constituted by a CPU of a microcomputer.

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