JP5313965B2 - NOx sensor degradation simulator - Google Patents

Description

  The present invention relates to a NOx sensor deterioration simulator that artificially generates a detection signal (deterioration signal) output in a state where a NOx sensor capable of detecting NOx concentration in a gas to be detected has deteriorated.

  Conventionally, an oxygen sensor that is attached to an exhaust passage of an internal combustion engine such as an automobile engine and detects an oxygen concentration in exhaust gas is known. The sensor element of the oxygen sensor has a configuration having at least one cell in which a pair of electrodes are formed on a solid electrolyte body, and based on a detection signal corresponding to the oxygen concentration output through the cell, oxygen in the exhaust gas The concentration is detected. A detection signal output from the oxygen sensor is transmitted to an ECU (electronic control unit). The ECU calculates the oxygen concentration of the exhaust gas and thus the air-fuel ratio based on the received detection signal, and adjusts the fuel injection amount in the engine. The air-fuel ratio feedback control is performed.

  In such an oxygen sensor, since the sensor element is exposed to the exhaust gas in the exhaust passage, deterioration with time occurs with long-term use. Therefore, in the development of the ECU, the optimum feedback control parameters for the detection 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 has deteriorated to some extent. Designs have been made to be able to determine. 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 signal obtained from these oxygen sensors and the detection signal of a normal oxygen sensor. Parameter settings. However, since it is difficult to reproduce the target deterioration state in the accelerated durability test, a deterioration simulator capable of artificially generating the deterioration state of the oxygen sensor was developed, and the ECU was designed using the deterioration simulator. (For example, refer to Patent Document 1).

  There is also known a NOx sensor which is attached to an exhaust passage of an internal combustion engine such as an automobile engine and detects the NOx concentration in the exhaust gas. The sensor element of the NOx sensor includes a first measurement chamber for introducing exhaust gas, a first oxygen pump cell in which one electrode is disposed in the first measurement chamber and the other electrode is disposed outside the first measurement chamber, The second measurement chamber communicated with the first measurement chamber, and a second oxygen pump cell in which one electrode is disposed in the second measurement chamber and the other electrode is disposed outside the second measurement chamber. ing. In this NOx sensor, oxygen is pumped out or pumped in using the first oxygen pump cell so that the oxygen concentration in the exhaust gas introduced into the first measurement chamber is substantially constant. In addition to the adjustment, a constant voltage is supplied between the pair of electrodes of the second oxygen pump cell to reduce or decompose NOx contained in the oxygen concentration-adjusted gas introduced into the second measurement chamber. The NOx concentration in the exhaust gas is detected based on the magnitude of the current flowing through the oxygen pump cell 2.

  Even in such a NOx sensor, deterioration with the lapse of time due to long-term use occurs, and for example, the detection signal (output in the second oxygen pump cell) may drop and the sensitivity may decrease. In such a case, a deterioration simulator is used to detect the output from the NOx sensor with reduced sensitivity by variably adjusting the magnitude of the current flowing through the sensor element to detect the NOx concentration by the resistance value or the like. It is possible to simulate a signal (see, for example, Patent Document 2).

JP 2004-93957 A JP 2004-93400 A

  However, the deterioration simulator suggested in Patent Document 2 adjusts the magnitude of the current itself flowing through the sensor element of the NOx sensor variably by the resistance value as described above. Strictly speaking, the NOx sensor This is not a simulation of the state of deterioration of the NOx sensor, but merely a simulation of the state of deterioration of the NOx sensor control circuit (a circuit for passing a current through the sensor element). In the first place, it is sufficient to be able to detect the NOx concentration from the viewpoint of the use of the NOx sensor. Therefore, as a function of the deterioration simulator, it was considered sufficient to change the gain and simulate the state in which the detection signal is lowered.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a NOx sensor deterioration simulator capable of simulating various forms of deterioration signals output when the NOx sensor is deteriorated. To do.

According to the aspect of the present invention, a first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body are provided, and one electrode of the pair of first electrodes is detected. A first oxygen pump cell which is disposed in a first detection chamber into which gas is introduced and adjusts an oxygen concentration contained in the detected gas introduced into the first detection chamber; a second solid electrolyte body; A pair of second electrodes formed on the solid electrolyte body, wherein one of the pair of second electrodes is disposed in a second detection chamber communicating with the first detection chamber; The detected gas is introduced between the pair of second electrodes by reducing or decomposing NOx contained in the detected gas having an adjusted oxygen concentration introduced from the first detection chamber into the second detection chamber. The NOx concentration current corresponding to the NOx concentration in the second flow A first deterioration signal corresponding to the NOx concentration current when the NOx sensor is deteriorated to the first deterioration state targeted by the NOx sensor based on the NOx concentration current. A NOx sensor deterioration simulator that is generated automatically, acquired by a first detection signal acquisition means for acquiring a first detection signal indicating the NOx concentration current flowing in the second oxygen pump cell, and the first detection signal acquisition means A first deterioration processing means for changing the generated first detection signal according to a first deterioration target, and a first deterioration current is generated according to the first detection signal changed by the first deterioration processing means. And first output processing means for outputting the first deterioration current as the first deterioration signal to an external circuit, wherein the first deterioration processing means corresponds to the first deterioration target. Offset correction for raising and lowering the value of the first detection signal, time characteristic correction for delaying the time when the first detection signal starts to change in response to NOx concentration change in the detection gas, and the detection gas NOx concentration change response characteristic varying the rate of change of the first detection signal corresponding to the correction in, the are running at least one, in addition to generating the first degradation signal in a pseudo manner, before a second detection signal obtaining means for obtaining a second detection signal indicative of the oxygen concentration current corresponding to the oxygen concentration flowing through the pair of first electrodes of the serial first oxygen pumping cell, obtained by the second detection signal obtaining means A second deterioration processing unit that changes the second detection signal according to a second deterioration target; and a second deterioration current that is generated according to the second detection signal changed by the second deterioration processing unit; The second And a second output processing means for outputting a second deterioration current to the external circuit as a second deterioration signal corresponding to the oxygen concentration current .

  In the aspect of the present invention, the first deterioration signal corresponding to the NOx concentration current when the NOx sensor is deteriorated can be artificially generated and output to an external circuit. Conventionally, various tests and developments that have been performed by actually degrading the NOx sensor by the accelerated durability test can be performed more easily. In general, it is difficult to set the NOx sensor to the target deterioration state in the accelerated endurance test. In particular, in the case of a malfunction that may occur due to the NOx sensor that has generated a deterioration state that occurs rarely, a reproduction test should be performed. Is difficult. If the deterioration simulator according to the aspect of the present invention is used, at least one of offset correction, time characteristic correction, and response characteristic correction can be executed, so that not only a general deterioration state of the NOx sensor but also rarely occurs. Even in a deteriorated state, it can be easily reproduced, and various tests and developments can be performed reliably and accurately. Furthermore, since it is only necessary to interpose a deterioration simulator between the NOx sensor and the external circuit without having to bother removing the NOx sensor already attached to the automobile or the test apparatus, various tests and developments can be performed smoothly.

  In the aspect of the present invention, the first deterioration processing means can execute gain correction for changing the gain of the first detection signal, and the offset correction and the time can be performed according to the first deterioration target. Two or more of the characteristic correction, the response characteristic correction, and the gain correction may be executed. By performing gain correction in addition to offset correction, time characteristic correction, and response characteristic correction, various deterioration states of the NOx sensor can be reproduced, and various tests and developments can be performed more reliably, more accurately, and more. It can be done smoothly.

2 is a diagram showing an electrical configuration of a NOx sensor 10, a sensor control device 50, and a deterioration simulator 70. FIG. It is a flowchart of a deterioration simulation process. It is a figure for demonstrating the outline | summary of a gain degradation process, an offset degradation process, a response delay process, and a dead time delay process.

  Hereinafter, an embodiment of a NOx sensor deterioration simulator embodying the present invention will be described with reference to the drawings. The drawings to be referred to are used to explain the technical features that can be adopted by the present invention, and the configuration of the described sensors and devices, the flowcharts of various processes, etc. are particularly specific descriptions. As long as there is no, it is not the meaning limited only to it but an example of description. A deterioration simulator 70 shown in FIG. 1 is a device interposed between a NOx sensor 10 attached to an exhaust passage (not shown) of an automobile and a sensor control device 50 that controls the NOx sensor 10. First, the configuration of the NOx sensor 10 will be described.

  The NOx sensor 10 shown in FIG. 1 holds a detection element 11 capable of detecting the oxygen concentration in the exhaust gas and the NOx concentration in a housing (not shown) for attaching to the exhaust pipe (not shown). It has a known structure. Further, a signal line for extracting a signal output from the detection element 11 and a conduction line for energizing the heater element 35 provided along with the detection element 11 are drawn out from the NOx sensor 10. When the NOx sensor 10 is normally used, the NOx sensor 10 and the sensor control device 50 are electrically connected through these signal lines and energization lines. The sensor control device 50 corresponds to the “external circuit” in the present invention.

  The detection element 11 of the NOx sensor 10 has a layered structure in which insulators 15 and 16 made of alumina or the like are sandwiched between three elongated and long plate-like solid electrolyte bodies 12, 13, and 14, respectively. Formed. In addition, a heater element in which sheet-like insulating layers 36 and 37 mainly composed of alumina are laminated on the outer layer (lower side in FIG. 1) of the solid electrolyte body 14, and a heater pattern 38 mainly composed of Pt is embedded therebetween. 35 is provided integrally with the detection element 11. The heater element 35 is provided for activating the solid electrolyte bodies 12 to 14.

  The solid electrolyte bodies 12, 13, and 14 are made of zirconia and have oxygen ion conductivity. Porous electrodes 17 and 18 are provided on both surfaces of the solid electrolyte body 12 in the stacking direction of the detection element 11 so as to sandwich the solid electrolyte body 12. The electrodes 17 and 18 are made of Pt, a Pt alloy, or cermet containing Pt and ceramics. Porous protective layers 19 and 20 made of ceramic are formed on the surfaces of the electrodes 17 and 18, respectively. The protective layers 19 and 20 protect the electrodes 17 and 18 from being deteriorated by being exposed to poisoning components contained in the exhaust gas.

  The solid electrolyte body 12 allows current to flow between the electrodes 17 and 18, thereby allowing the atmosphere in contact with the electrode 17 (atmosphere outside the detection element 11) and the atmosphere in contact with the electrode 18 (atmosphere in the first detection chamber 23 described later). ) Can be pumped out and pumped in (so-called oxygen pumping). In the present embodiment, the solid electrolyte body 12 and the electrodes 17 and 18 are referred to as “Ip1 cell” 2. The Ip1 cell 2 corresponds to the “first oxygen pump cell” of the present invention, and the solid electrolyte body 12 and the electrodes 17 and 18 respectively correspond to the “first solid electrolyte body” and the “pair of first electrodes” of the present invention. Is equivalent to.

  In the normal use in which the NOx sensor 10 and a sensor control device 50 described later are directly connected, the electrode 17 is connected to an Ip1 + port 51 of a control circuit unit 55 (described later) of the sensor control device 50. Similarly, the electrode 18 is connected to the COM port 52 of the control circuit unit 55. For convenience, an Ip1 + port 41 corresponding to the Ip1 + port 51 and a COM port 42 corresponding to the COM port 52 are also provided on the NOx sensor 10 side (specifically, a signal for connection with the sensor control device 50) This corresponds to an electrode pad (not shown) of the detection element 11 to which the line is connected.)

  Next, the solid electrolyte body 13 is disposed so as to face the solid electrolyte body 12 with the insulator 15 interposed therebetween. Porous electrodes 21 and 22 are provided on both surfaces of the solid electrolyte body 13 in the stacking direction of the detection element 11 so as to sandwich the solid electrolyte body 13, respectively. Similarly, Pt or Pt alloy or Pt and ceramics are used. It is formed from cermet containing. Among them, the electrode 21 is formed on the surface facing the solid electrolyte body 12.

  Further, a first detection chamber 23 as a small space is formed between the solid electrolyte body 12 and the solid electrolyte body 13, and the electrode 18 on the solid electrolyte body 12 side and the electrode 21 on the solid electrolyte body 13 side. Are arranged in the first detection chamber 23. The first detection chamber 23 is a small space into which the exhaust gas flowing through the exhaust passage is first introduced into the detection element 11. On the front end side of the detection element 11 of the first detection chamber 23, as a partition inside and outside the first detection chamber 23, a porous first that restricts the flow rate of exhaust gas per unit time into the first detection chamber 23. A diffusion resistance unit 24 is provided. Similarly, on the rear end side of the detection element 11 of the first detection chamber 23, the flow rate of exhaust gas per unit time as a partition between the opening 25 connected to the second detection chamber 30 and the first detection chamber 23 described later. A porous second diffusion resistance portion 26 that restricts the above is provided.

  The solid electrolyte body 13 and the electrodes 21 and 22 are mainly composed of an atmosphere separated by the solid electrolyte body 13 (an atmosphere in the first detection chamber 23 in contact with the electrode 21 and a reference oxygen chamber 29 (described later) in contact with the electrode 22). Electromotive force can be generated according to the oxygen partial pressure difference between the (atmosphere). In the present embodiment, the solid electrolyte body 13 and the electrodes 21 and 22 are referred to as “Vs cells” 3.

  Note that, during normal use in which the NOx sensor 10 and a sensor control device 50 described later are directly connected, the electrode 21 is connected to a COM port 52 of a control circuit unit 55 (described later). Similarly, the electrode 22 is connected to the Vs + port 53 of the control circuit unit 55. For the sake of convenience, the Vs + port 43 corresponding to the Vs + port 53 is also provided on the NOx sensor 10 side as in the above.

  Next, the solid electrolyte body 14 is disposed so as to face the solid electrolyte body 13 with the insulator 16 interposed therebetween. Similarly, porous electrodes 27 and 28 made of Pt or a Pt alloy or cermet containing Pt and ceramics are also provided on the surface of the solid electrolyte body 14 on the solid electrolyte body 13 side.

  The insulator 16 is not disposed at the position where the electrode 27 is formed, and a reference oxygen chamber 29 is formed as an independent small space. In the reference oxygen chamber 29, the electrode 22 of the Vs cell 3 is disposed. The reference oxygen chamber 29 is filled with a ceramic porous body. Further, the insulator 16 is not disposed at the position where the electrode 28 is formed, and the second detection chamber 30 as an independent small space is formed. The solid electrolyte body 13 is also provided with an opening 31 so that the second detection chamber 30 communicates with the first detection chamber 23 via the second diffusion resistance portion 26 and the opening 25 described above.

  The solid electrolyte body 14 and the electrodes 27, 28 are oxygenated between the atmospheres separated by the insulator 16 (the atmosphere in the reference oxygen chamber 29 in contact with the electrode 27 and the atmosphere in the second detection chamber 30 in contact with the electrode 28). Can be pumped out. In the present embodiment, the solid electrolyte body 14 and the electrodes 27 and 28 are referred to as “Ip2 cell” 4. The Ip2 cell 4 corresponds to the “second oxygen pump cell” of the present invention, and the solid electrolyte body 14 and the electrodes 27 and 28 are the “second solid electrolyte body” and “a pair of second electrodes” of the present invention, respectively. Is equivalent to.

  In the normal use in which the NOx sensor 10 and a sensor control device 50 described later are directly connected, the electrode 27 is connected to the Ip2 + port 54 of the control circuit unit 55 (described later). Similarly, the electrode 28 is connected to the COM port 52 of the control circuit unit 55. For the sake of convenience, it is the same as described above in that an Ip2 + port 44 corresponding to the Ip2 + port 54 is also provided on the NOx sensor 10 side.

  Next, the configuration of the sensor control device 50 will be described. The sensor control device 50 is a device that is directly connected to the NOx sensor 10 and controls the detection element 11 and the heater element 35 during normal use of the NOx sensor 10. The sensor control device 50 includes a control circuit unit 55 that controls the driving of the detection element 11, a heater control unit 57 that controls the driving of the heater element 35, and a microcomputer that controls the driving of the control circuit unit 55 and the heater control unit 57. 56 and a communication unit 58.

  The control circuit unit 55 corresponds to each of the ports 41 to 44 (Ip1 +, COM, Vs +, Ip2 +) of the detection element 11 and is connected via a signal line to an Ip1 + port 51, a COM port 52, a Vs + port 53, Ip2 + port 54 is provided. The control circuit unit 55 includes a known Ip1 / Vs control circuit and an Ip2 control circuit (not shown). The Ip1 / Vs control circuit controls the electrodes 17 and 18 of the Ip1 cell 2 so that the voltage between the electrodes 21 and 22 of the Vs cell 3 (in other words, the electromotive force generated in the Vs cell 3) becomes a constant value (for example, 425 mV). A current flowing between them (hereinafter also referred to as “Ip1 current”) is controlled. In other words, oxygen in the first detection chamber 23 is pumped or pumped in the Ip1 cell 2 by flowing an Ip1 current so that the electromotive force generated in the Vs cell 3 is constant. Performs feedback control to adjust the density to a constant level. Detection of the oxygen concentration in the exhaust gas is performed based on this Ip1 current.

  Further, the oxygen concentration in the exhaust gas introduced into the first detection chamber 23 by the Ip1 cell 2 is adjusted to a predetermined concentration and introduced into the second detection chamber 30. The Ip2 control circuit supplies a current (hereinafter also referred to as “Ip2 current”) that flows between the electrodes 27 and 28 so that a constant voltage (for example, 450 mV) is applied between the electrodes 27 and 28 of the Ip2 cell 4. Control. That is, a voltage is applied to the electrode 28 to decompose NOx in the exhaust gas introduced into the second detection chamber 30, and oxygen derived from NOx is transported in the Ip 2 cell 4. Based on the Ip2 current flowing at this time, the NOx concentration in the exhaust gas is detected.

  The microcomputer 56 is a computing device including a known CPU, ROM, RAM, etc., and outputs a control signal to the control circuit unit 55 in accordance with a program incorporated in advance, and the driving states of the Ip1 / Vs control circuit and the Ip2 control circuit To control. The microcomputer 56 also outputs a control signal to the heater control unit 57 to control energization to the heater element 35. The microcomputer 56 receives the detection result of the oxygen concentration in the exhaust gas by the Ip1 / Vs control circuit and the detection result of the NOx concentration by the Ip2 control circuit. The microcomputer 56 outputs the above detection result via the communication unit 58 to a known ECU (electronic control unit) 5 that controls various electronic components mounted on the automobile.

  Next, the configuration of the deterioration simulator 70 will be described. As described above, the deterioration simulator 70 is a device interposed between the NOx sensor 10 and the sensor control device 50. In order to connect to the respective ports 41 to 44 (Ip1 +, COM, Vs +, Ip2 +) of the NOx sensor 10, the respective ports 101 to 104 (Ip1 +, COM, Vs +, Ip2 +) are provided. Similarly, each port 105-108 (Ip1 +, COM, Vs +, Ip2 +) corresponding to each port 51-54 (Ip1 +, COM, Vs +, Ip2 +) of the sensor control device 50 is also provided. Further, the deterioration simulator 70 incorporates a sensor control device 60 (the latter in the present embodiment) that is the same as the sensor control device 50 described above or simplified by omitting the configuration of the heater control unit 57, the communication unit 58, and the like. Further, the deterioration simulator 70 includes a microcomputer 79, detection resistors R1, R2, and R3, differential amplifier circuits 85 and 86, A / D converters 81 and 82, D / A converters 91 and 92, and voltage / current conversion circuits 95 and 96. , An Ip-Vs conversion circuit 97, and an operation unit 100.

  The ports 101 to 104 (Ip1 +, COM, Vs +, Ip2 +) on the input side of the deterioration simulator 70 are connected to the corresponding ports 61 to 64 (Ip1 +, COM, Vs +, Ip2 +) of the sensor control device 60, respectively. Yes. Among them, the detection resistor R1 is provided between the Ip1 + port 101 and the Ip1 + port 61. Both ends of the detection resistor R1 are connected to the differential amplifier circuit 85, and the Ip1 current flowing between the electrodes 17 and 18 of the Ip1 cell 2 is voltage-converted and amplified. Further, it is digitally converted via the A / D converter 81 and input to the microcomputer 79 as an oxygen concentration detection signal (Ip1 signal) indicated by the Ip1 current flowing through the Ip1 cell 2. In the microcomputer 79, an Ip1 simulation signal simulating a detection signal of the oxygen concentration when the NOx sensor 10 deteriorates based on the Ip1 signal by a deterioration simulation process performed by an Ip1 deterioration simulation circuit unit 88 described later. Simulated. The Ip1 simulation signal is converted into an analog signal via the D / A converter 91, and further input to the voltage-current conversion circuit 95 to be converted into an Ip1 deterioration current (corresponding to an Ip1 current in which deterioration is simulated). As an simulated Ip1 signal) from the Ip1 + port 105 to the sensor control device 50. A detection resistor R3 is provided between the voltage-current conversion circuit 95 and the Ip1 + port 105.

  Similarly, a detection resistor R2 is provided between the Ip2 + port 104 and the Ip2 + port 64. The Ip2 current flowing between the electrodes 27 and 28 of the Ip2 cell 4 is voltage-converted and amplified by the differential amplifier circuit 86 connected to both ends of the detection resistor R2, and further, via the A / D converter 82, the Ip2 cell 4 Is input to the microcomputer 79 as a NOx concentration detection signal (Ip2 signal) indicated by the Ip2 current flowing through the. In the microcomputer 79, an Ip2 simulation signal simulating a detection signal of NOx concentration when the NOx sensor 10 is deteriorated based on the Ip2 signal by a deterioration simulation process performed in an Ip2 deterioration simulation circuit unit 89 described later. Simulated. The Ip2 simulation signal is converted into an analog voltage via the D / A converter 92, and further input to the voltage / current conversion circuit 96 to be converted into an Ip2 deterioration current. As an Ip2 deterioration signal, the Ip2 + port 108 sends the signal to the sensor control device 50. Is output. The detection resistor R2, the differential amplifier circuit 86, and the A / D converter 82 correspond to the “first detection signal acquisition unit” in the present invention, and the D / A converter 92 and the voltage / current conversion circuit 96 are in the present invention. Corresponds to “first output processing means”.

  The COM port 102 connected to the COM port 42 of the NOx sensor 10 is directly connected to the COM port 106 connected to the COM port 52 so that the COM port 52 and the COM port 42 of the control circuit unit 55 have the same potential. Has been. Further, the voltage of the Vs + port 103 is input to the Ip-Vs conversion circuit 97. Further, both ends of the detection resistor R3 are connected to the Ip-Vs conversion circuit 97, and the magnitude of the Ip1 degradation current (Ip1 current simulating degradation) flowing through the detection resistance R3 is converted into the magnitude of the voltage. Entered. The Ip-Vs conversion circuit 97 is configured using an amplifier circuit or the like, amplifies the voltage-converted Ip1 degradation current (for example, amplifies it by about 10,000 times), and superimposes it on the voltage of the Vs + port 103 (in other words, Vs + port). 103 is offset according to the magnitude of the Ip1 degradation current.), And is output from the Vs + port 107 to the sensor control device 50. The Ip-Vs conversion circuit 97 simulates the electromotive force of the Vs cell 3 according to the degree of current deterioration simulated by the Ip1 deterioration current. The operation unit 100 is provided with an operation panel and a monitor (not shown), and the user performs various settings of the deterioration simulator 70 (setting of a gain factor Gain, a voltage value Offset, a dead time T, which will be described later, etc.). be able to. A connection port with an external device such as a personal computer (not shown) may be provided so that various settings can be made from the external device.

  Next, the deterioration simulation process performed in the microcomputer 79 of the deterioration simulator 70 will be described. The microcomputer 79 is a computing device including a known CPU, ROM, RAM, and the like, and performs a deterioration simulation process according to a program stored in advance in the ROM. In this embodiment, for the sake of convenience, the configuration of the microcomputer 79 in FIG. 1 is shown as a functional block diagram. The microcomputer 79 performs deterioration simulation processing on the input signal based on the Ip1 current (Ip1 signal obtained by converting the voltage of the Ip1 current and then converting it into a digital signal), and outputs an output signal (Ip1 simulation) that simulates the deteriorated state of the signal. Ip1 deterioration simulation circuit unit 88 is provided as a functional block for generating a signal. Similarly, a deterioration simulation process is performed on an input signal based on the Ip2 current (Ip2 signal obtained by converting the voltage of the Ip2 current and then converting it into a digital signal), and an output signal (Ip2 simulation signal) simulating the deteriorated state of the signal. Ip2 deterioration simulation circuit unit 89 is provided as a functional block for generating. The Ip2 deterioration simulation circuit unit 89 corresponds to the “first deterioration processing unit” in the present invention.

  The Ip1 deterioration simulation circuit unit 88 includes a gain deterioration block 71, an offset deterioration block 72, a response delay block 73, and a dead time delay block 74 as functional blocks. In each functional block, an Ip1 simulation signal is generated by sequentially performing gain deterioration processing, offset deterioration processing, response delay processing, and dead time delay processing on the Ip1 signal. Similarly, the Ip2 deterioration simulation circuit unit 89 includes a gain deterioration block 75, an offset deterioration block 76, a response delay block 77, and a dead time delay block 78 as functional blocks. In each functional block, an Ip2 simulation signal is generated by sequentially performing gain deterioration processing, offset deterioration processing, response delay processing, and dead time delay processing on the Ip2 signal. Note that the deterioration simulation process performed in each functional block of the Ip1 deterioration simulation circuit unit 88 is the same process as the deterioration simulation process performed in each functional block of the Ip2 deterioration simulation circuit unit 89. Therefore, hereinafter, the deterioration simulation process will be described by taking each process performed in each functional block of the Ip2 deterioration simulation circuit unit 89 as an example. Further, specific processing methods of gain deterioration processing, offset deterioration processing, response delay processing, and dead time delay processing are known, and a brief description will be given below. For details of the gain deterioration process, the response delay process, and the dead time delay process, see, for example, Japanese Patent Application Laid-Open No. 2007-315210. For details of the offset deterioration process, refer to, for example, Japanese Patent Application Laid-Open No. 2008-203152. The gain deterioration process, the offset deterioration process, the response delay process, and the dead time delay process correspond to “gain correction”, “offset correction”, “response characteristic correction”, and “time characteristic correction” in the present invention, respectively.

  The deterioration simulation process in the Ip2 deterioration simulation circuit unit 89 is performed according to a program executed by the microcomputer 79 as shown in the flowchart of FIG. An Ip2 signal based on the Ip2 current is input to the microcomputer 79 as needed. The Ip2 deterioration simulation circuit unit 89 acquires an Ip2 signal at every predetermined time (for example, 25 msec), performs deterioration simulation processing, generates an Ip2 simulation signal, and outputs it.

  As shown in FIG. 2, first, an Ip2 signal based on the Ip2 current is read and stored in a RAM (not shown) as a variable Vip2 (S11). A gain deterioration process (Vip2 ← Vip2 × Gain) is performed by multiplying the variable Vip2 by a preset gain factor Gain and overwriting the calculation result on the variable Vip2 (S13). The gain deterioration process is a process of generating an output signal that is amplified or attenuated by multiplying the voltage value of the input signal by the gain factor Gain. For example, as illustrated in FIG. 3, if gain deterioration processing (in this case, attenuation) is performed on the input signal shown in (A), the voltage value increases according to the gain factor Gain as shown in (B). Alternatively, a reduced (here reduced) output signal can be generated.

  Next, an offset deterioration process (Vip2 ← Vip2 + Offset) is performed to superimpose a preset voltage value Offset on the variable Vip2 and overwrite the calculation result on the variable Vip2 (S15). The offset deterioration process is a process for generating an output signal in which the voltage value of the input signal is shifted by a predetermined voltage value Offset. For example, as illustrated in FIG. 3, if the input signal shown in (A) is subjected to an offset deterioration process (in this case, a positive voltage value Offset is superimposed), the voltage value is increased or decreased as shown in (C). It is possible to generate an output signal shifted to (in this case, shifted upward).

Next, for example, a calculation applying a first-order lag transfer function is performed on the variable Vip2, and a response delay process (Vip2 ← Vip2 × 1 / (1 + τs)) is performed to overwrite the calculation result on the variable Vip2 (S17). ). The response delay process is a process of slowing and changing the degree of change in the voltage value of the input signal. The first-order lag transfer function G (s) is expressed by the following equation.
G (s) = k / (1 + τs), where τ is a time constant and k is a gain (here, k = 1).
For example, as illustrated in FIG. 3, when response delay processing is performed on the input signal shown in (A), the voltage value is compared with an input signal that shows a sharp change in voltage value, as shown in (D). The change becomes slow, and an output signal representing a change that follows the input signal with a delay can be generated.

  Further, dead time delay processing is performed on the variable Vip2. The dead time delay process is a process for outputting an input signal after a time T set in advance as a dead time. For example, as illustrated in FIG. 3, if dead time delay processing is performed on the input signal shown in (A), an output signal whose timing is delayed from the input signal is generated as shown in (E). Can do.

  In the dead time delay process, after adding the elapsed time information (the first elapsed time is 0) to the current variable Vip2 that has been subjected to the gain deterioration process, the offset deterioration process, and the response delay process as described above ( S19), temporarily stored in the RAM (S21). Next, the elapsed time of all stored variables Vip2 is advanced by the unit time, respectively (S23). Then, the Ip2 simulation signal whose signal value is the variable Vip2 whose elapsed time held as the elapsed time information has reached the dead time T is deteriorated through the D / A converter 91 and the voltage-current conversion circuit 95 as described above. It is converted into current and sequentially output to the sensor control device 50 as an Ip2 deterioration signal (S25). On the other hand, the variable Vip2 based on the Ip2 signal acquired this time is held in the RAM until the dead time T elapses.

  After the deterioration simulation process of S11 to S25 is performed on the Ip2 signal, the process waits for a predetermined time (for example, 25 msec) (S27: NO), and returns to S11 (S27: YES) to obtain a new one. The deterioration simulation process is also performed for the Ip2 signal.

  As described above, the deterioration simulator 70 according to the present embodiment can artificially generate an Ip2 deterioration signal corresponding to the Ip2 current when the NOx sensor 10 deteriorates and output it to the sensor control device 50. In addition, various tests and developments that have been conventionally performed by actually degrading the NOx sensor by the accelerated durability test, such as the development of the ECU 5 and the performance test of the automobile, can be performed more easily. In general, it is difficult to set the NOx sensor to the target deterioration state in the accelerated endurance test. In particular, in the case of a malfunction that may occur due to the NOx sensor that has generated a deterioration state that occurs rarely, a reproduction test should be performed. Is difficult. If the deterioration simulator 70 of the present embodiment is used, at least one of the offset deterioration process, the dead time delay process, and the response delay process can be executed, so that not only the general deterioration state of the NOx sensor 10 but also the rare deterioration state is rare. Even in a deteriorated state that occurs only in the field, it can be easily reproduced, and various tests and developments can be performed reliably and accurately. Furthermore, since it is only necessary to interpose the deterioration simulator 70 between the NOx sensor 10 and the sensor control device 50 without having to bother to remove the NOx sensor 10 already attached to the automobile or the test apparatus, various tests and developments can be performed smoothly. It can also be done. If the gain deterioration process is executed in addition to the above, various deterioration states of the NOx sensor 10 can be reproduced, and various tests and developments can be performed more reliably, more accurately, and more smoothly. Further, in the deterioration simulator 70, an Ip1 deterioration signal corresponding to the Ip1 current when the NOx sensor 10 deteriorates can be generated in a pseudo manner and output to an external circuit, so that the Ip2 current depends on the deterioration state. The comprehensive deterioration state of the NOx sensor 10 including not only the case where it changes but also the case where the Ip1 current changes can be easily reproduced. Therefore, ECU development and automobile performance tests assuming various deterioration states of the NOx sensor 10 can be performed more reliably, more accurately, and more smoothly.

  Moreover, the deterioration simulator 70 can control the NOx sensor 10 with an existing circuit by incorporating the sensor control device 60 having substantially the same configuration as the sensor control device 50. Therefore, there is no contradiction in signals exchanged in the control of the NOx sensor 10. In addition, deterioration signals (Ip1 deterioration signal and Ip2 deterioration signal) obtained by processing the detection signals (Ip1 signal and Ip2 signal) obtained from the NOx sensor 10 can be output to the sensor control device 50.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the deterioration simulation process, the gain deterioration process, the offset deterioration process, the response delay process, and the dead time delay process can be executed independently of each other. The above processing may be executed.

  In this embodiment, the Ip1 simulation signal and the Ip2 simulation signal are generated from the Ip1 signal and the Ip2 signal by software by executing the deterioration simulation processing program. However, a logic circuit is configured for some processes. An analog or digital hardware circuit may be produced, and an Ip1 simulation signal or an Ip2 simulation signal may be generated. For example, in the case of gain deterioration processing, when the Ip1 signal and Ip2 signal obtained by voltage-converting the Ip1 current and Ip2 current using the detection resistors R1 and R2 are amplified by the differential amplifier circuits 85 and 86, the amplification factor is arbitrarily set using a trimmer resistor. It can be changed to In the offset deterioration process, a reference voltage (for example, 5 V) is divided by a resistor, and the divided voltage (offset voltage) may be superimposed on the voltage values of the Ip1 signal and the Ip2 signal. At this time, the offset voltage may be arbitrarily changed by using a trimmer resistor for one of the voltage dividing resistors. The offset voltage may be the reference voltage of the differential amplifier circuits 85 and 86. In the case of response delay processing, the Ip1 signal and the Ip2 signal may be passed through, for example, a first-order low-pass filter, and the signal may be smoothed and output. Although the low-pass filter is composed of a capacitor and a resistor, the time constant τ representing the response can be calculated by C × R. Therefore, if the value of C or R is adjusted (for example, R is adjusted using a trimmer resistor). ), Responsiveness can be adjusted. The low-pass filter may be provided after the differential amplifier circuits 85 and 86.

2 Ip1 cell 4 Ip2 cell 10 NOx sensor 12, 14 Solid electrolyte body 17, 18, 27, 28 Electrode 23 First detection chamber 30 Second detection chamber 50 Sensor controller 70 Degradation simulator 75 Gain degradation block 76 Offset degradation block 77 Response Delay block 78 Dead time delay block 79 Microcomputer 81, 82 A / D converter 85, 86 Differential amplification circuit 88, 89 Degradation simulation circuit 91, 92 D / A converter 95, 96 Voltage-current conversion circuit 97 Ip-Vs conversion Circuit R1, R2 detection resistor

Claims (2)

A first detection having a first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body, wherein one of the pair of first electrodes introduces a gas to be detected. A first oxygen pump cell that is arranged in a room and adjusts the oxygen concentration contained in the detected gas introduced into the first detection chamber;
A second solid electrolyte body and a pair of second electrodes formed on the second solid electrolyte body, wherein one electrode of the pair of second electrodes communicates with the first detection chamber; 2 is disposed in the detection chamber and introduced into the second detection chamber from the first detection chamber to reduce or decompose NOx contained in the detected gas with the adjusted oxygen concentration, thereby A second oxygen pump cell in which a NOx concentration current corresponding to the NOx concentration in the detected gas flows between the second electrodes;
And a pseudo first generation signal corresponding to the NOx concentration current when the NOx sensor is deteriorated to the target first deterioration state based on the NOx concentration current. NOx sensor deterioration simulator,
First detection signal acquisition means for acquiring a first detection signal indicating the NOx concentration current flowing through the second oxygen pump cell;
First deterioration processing means for changing the first detection signal acquired by the first detection signal acquisition means in accordance with a first deterioration target;
First output processing means for generating a first deterioration current in response to the first detection signal changed by the first deterioration processing means and outputting the first deterioration current to the external circuit as the first deterioration signal;
With
In accordance with the first deterioration target, the first deterioration processing means performs offset correction for raising and lowering the value of the first detection signal, and the first detection signal corresponds to the NOx concentration change in the detected gas. Performing at least one of a time characteristic correction for delaying a time to start changing and a response characteristic correction for changing a change speed of the first detection signal corresponding to a NOx concentration change in the detected gas;
In addition to artificially generating the first deteriorated signal ,
A second detection signal obtaining means for obtaining a second detection signal indicative of the oxygen concentration current corresponding to the oxygen concentration flowing through the pair of first electrode before Symbol first oxygen pumping cell,
Second deterioration processing means for changing the second detection signal acquired by the second detection signal acquisition means in accordance with a second deterioration target;
A second deterioration current is generated according to the second detection signal changed by the second deterioration processing means, and the second deterioration current is output to the external circuit as a second deterioration signal corresponding to the oxygen concentration current. Second output processing means for
NOx sensor degradation simulator , further comprising: The first deterioration processing means includes
Gain correction for changing the gain of the first detection signal can be executed,
2. The NOx sensor according to claim 1, wherein two or more of the offset correction, the time characteristic correction, the response characteristic correction, and the gain correction are performed according to the first deterioration target. Deterioration simulator.

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