JP2007327792A - Method of measuring activation time for oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring an activation time for an oxygen sensor, capable of measuring accurately a time required until the oxygen sensor is activated. <P>SOLUTION: A sensor signal waveform using a detection value (voltage value) as an ordinate axis and using an abscissa axis as a lapse time is formed based on the detection values of oxygen concentrations in exhaust gas with air-fuel ratios switched alternately in a lean side and a rich side in every fixed period Tms. A point B with the voltage value getting to the maximum value is extracted in the every period of the sensor signal waveform time-divided by the period 2Tms respectively once in the lean side and the rich side, a maximal value connection line D connected by a straight line is prepared between the adjacent periods, and the latest point F is extracted out of intersections with a rich side threshold value to be specified as a rich side determination intersection. The rich side determination intersection is compared with a lean side determination intersection (point H) obtained by the same manner to determine the later one as a right-off time required until the oxygen sensor is activated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an activation time measurement method for measuring the time required for activation of an oxygen sensor exposed to a gas to be measured.

  Conventionally, in internal combustion engines such as automobiles, CO, HC and NOx contained in exhaust gas have been purified using a three-way catalyst. In order to perform purification efficiently, the oxygen concentration in the exhaust gas is detected by an oxygen sensor attached to the exhaust pipe, and the fuel injection amount is adjusted based on the detected value, thereby mixing the fuel and air. Control is performed to bring the (air-fuel ratio) closer to the theoretical value.

  A zirconia solid electrolyte body is used as a sensor element of an oxygen sensor used for controlling the air-fuel ratio. The zirconia solid electrolyte body exhibits insulating properties at room temperature, and has a property of being activated and transmitting oxygen ions when heated to a predetermined temperature or higher (for example, 300 ° C. or higher). Stabilize. Since the exhaust gas does not have a high temperature immediately after the start of the automobile, the air-fuel ratio must be sufficiently controlled based on the detection result of the oxygen concentration until the oxygen sensor is heated and activated by the exhaust gas temperature. The exhaust gas cannot be sufficiently purified by the three-way catalyst. In view of this, an oxygen sensor that incorporates a heater and heats the sensor element with the heater so that the sensor element is quickly activated is used.

  In recent years, exhaust gas regulations have been strengthened, and the time until the sensor element of such an oxygen sensor is activated, more specifically, from the start of engine operation, the oxygen concentration detection signal output from the sensor is stabilized. There is a demand for shortening the time taken to do so (hereinafter referred to as “light-off time”). Improvements have been made to sensor element materials, heater material combinations, sensor element manufacturing methods, and the like, and oxygen sensors that can further reduce the light-off time have been developed (see, for example, Patent Document 1).

  In the process of developing such an oxygen sensor, the light-off time of the oxygen sensor is measured using an engine bench (an apparatus for performing various performance tests of an internal combustion engine) or the like, and used for performance evaluation. . As a specific method for measuring the light-off time, first, the oxygen sensor was exposed to the exhaust gas with a rich air-fuel ratio, and it took until the detected value exceeded a threshold at which it could be determined that the sensor element was activated. Time (rich side activation time) is measured. Next, the oxygen sensor is exposed to the exhaust gas whose air-fuel ratio is set to the lean side, and the lean side activation time is similarly measured. The light off time is measured by setting the time when the sensor element is activated on both the rich side and the lean side, that is, the later of the rich side activation time or the lean side activation time as the light off time. (First measurement method).

However, in the first measurement method described above, since the measurement is performed twice in the exhaust gas with the air-fuel ratio made rich and the measurement in the exhaust gas made lean, the light off time is Measurement takes time and effort. In addition, since the measurement is performed twice, it cannot be said that the measured rich side activation time and lean side activation time are measured under exactly the same conditions. Therefore, it is assumed that the air-fuel ratio of the exhaust gas is alternated between the rich side and the lean side at a constant cycle, exceeds a threshold at which it can be determined that the sensor element is activated on the rich side, and the sensor element is also activated on the lean side. A second measurement method is used in which the light-off time is when a threshold value that can be determined is exceeded.
JP 2002-296232 A

  However, in the second measurement method, since the air-fuel ratio is periodically alternated between the rich side and the lean side, the detection value of the oxygen sensor repeatedly fluctuates in accordance with the cycle. For example, when it is determined that the detected value of the oxygen sensor exceeds the rich-side threshold and the rich-side output is activated, the lean-side activation state cannot be immediately determined. That is, since the air-fuel ratio is alternated at a constant cycle, the determination of the lean-side active state must wait until the detected value of the oxygen sensor is shifted to the lean side due to the alternating air-fuel ratio. In addition, when the detected value of the oxygen sensor approaches the rich side threshold in a certain cycle as long as the air-fuel ratio is fixed to the rich side as it is, the detected value may exceed the rich side threshold immediately after that. However, if the detected value fluctuates toward the lean side before reaching the threshold value due to the alternating air-fuel ratio, the timing at which the detected value exceeds the rich threshold value is carried over to the next cycle. In other words, even with the same oxygen sensor, there may be a difference in the light-off time measured depending on the alternating cycle of the air-fuel ratio. There was a fear.

  The present invention has been made to solve the above-described problems, and provides an oxygen sensor activation time measuring method capable of more accurately measuring the time taken for the oxygen sensor to be activated. Objective.

  In order to achieve the above object, an oxygen sensor activation time measuring method according to a first aspect of the present invention comprises exposing an oxygen sensor to a gas to be measured in which an air-fuel ratio is alternated between a rich side and a lean side at a constant cycle. Is an activation time measurement method for measuring an activation time required from when the oxygen sensor is activated to detection value acquisition for acquiring a detection signal output from the oxygen sensor as a detection value every predetermined time A detection value storage step for storing a plurality of detection values acquired in the detection value acquisition step, and a plurality of detection values stored in the detection value storage step, alternating once each on the rich side and the lean side When the set time is defined as one cycle, the maximum value extraction step for extracting the maximum detection value in the cycle as the maximum value for each cycle is stored in the detection value storage step. Among a plurality of detection values, a minimum value extraction step for extracting a minimum detection value in the cycle for each cycle as a minimum value and a plurality of maximum values extracted in the maximum value extraction step are adjacent to each other. A local maximum side connecting line acquisition step of connecting local maximum values with a straight line to acquire a local maximum side connecting line and a plurality of local minimum values extracted in the local minimum value extracting step are adjacent straight lines to each other. Among the intersections where the local minimum side connecting line is acquired by connecting the local area and the local maximum side threshold and the local maximum side connecting line intersect, the slowest crossing after exposure to the gas to be measured A first determination intersection acquisition step of acquiring the intersection as a first determination intersection, and an intersection where the minimum value side threshold set smaller than the maximum value side threshold and the minimum value side connection line intersect, The measured The second determination intersection acquisition step of acquiring the intersection that is the latest intersection after being exposed to the test as the second determination intersection is compared with the first determination intersection and the second determination intersection, and based on the latest determination intersection And an activation time acquisition step of acquiring the activation time.

  In addition to the configuration of the invention according to claim 1, the oxygen sensor activation time measuring method according to claim 2 includes the maximum value side threshold and the maximum value side in the first determination intersection acquisition step. When the intersection with the connecting line cannot be acquired, the activation time acquisition step acquires the activation time based on the second determination intersection.

  According to a third aspect of the present invention, there is provided an oxygen sensor activation time measuring method in addition to the configuration of the first aspect of the invention, in the second determination intersection acquisition step, the minimum value side threshold and the minimum value side. When the intersection with the connecting line cannot be acquired, the activation time acquisition step acquires the activation time based on the first determination intersection.

  In the method for measuring the activation time of the oxygen sensor according to the first aspect of the present invention, the detected value of the gas to be measured in which the air-fuel ratio is alternated between the rich side and the lean side at a constant period is time-divided for each period, It is possible to acquire a local maximum side connecting line connecting local maximum values and a local minimum side connecting line connecting local minimum values of each period. The maximum value side connection line and the minimum value side connection line correspond to detection values of the gas to be measured when the air-fuel ratio is fixed to the rich side and the lean side, respectively. That is, with respect to the first determination intersection that is the intersection of the latest time side connection line and the maximum value side threshold value, the time when the first determination intersection occurs is the activation when the air-fuel ratio is fixed to the rich side. It can be said that it corresponds to time. As a result, the activation time on the rich side could not be specified only in the period in which the air-fuel ratio is on the rich side, whereas the activation on the rich side is not possible even in the period in which the air-fuel ratio is on the lean side. The activation time can be specified, and the activation time on the rich side can be specified more accurately. The same applies to the determination of the activation time on the lean side, and based on the later determination intersection of the first determination intersection and the second determination intersection, more accurate activity required until the oxygen sensor is activated Conversion time can be obtained.

  In addition, since the acquisition of the activation time on the rich side and the acquisition of the activation time on the lean side can be performed in parallel, the activation time of the oxygen sensor can be obtained by a single measurement, and the measurement takes time. It does not take much time and can be reduced. Furthermore, the acquisition of the activation time on the rich side and the acquisition of the activation time on the lean side are performed under the same measurement conditions, so the oxygen sensor is more accurate. It is possible to obtain the activation time required for the conversion.

  By the way, there are cases where the first judgment intersection cannot be acquired, for example, when the oxygen sensor exposed to the gas under measurement whose air-fuel ratio is rich outputs a detection value equivalent to the activated state from the beginning of measurement. In such a case, as in the invention according to claim 2, it is considered that the rich side is already activated and the activation time of the oxygen sensor is acquired based on the second determination intersection. Similarly, when the second determination intersection cannot be obtained, it is assumed that the lean side has already been activated as in the invention according to claim 3, and the activation time of the oxygen sensor is determined based on the first determination intersection. Good to get.

  Hereinafter, an embodiment of an oxygen sensor activation time measuring method embodying the present invention will be described with reference to the drawings. First, referring to FIG. 1 to FIG. 3, an engine to which an oxygen sensor 30 for measuring the time taken for activation by a light-off time measuring device 10 using an activation time measuring method according to the present invention is attached. A schematic configuration of the bench system 1 will be described. FIG. 1 is a block diagram showing a schematic configuration of the engine bench system 1. FIG. 2 is a schematic diagram showing the configuration of each storage area of the HDD 18. FIG. 3 is a schematic diagram showing the configuration of each storage area of the RAM 15.

  The engine bench system 1 shown in FIG. 1 is a system that drives the engine 50 by assembling various engines such as an intake / exhaust system, a fuel system, and an electronic control system to the engine 50 in order to perform various performance tests of engines such as automobiles. It is composed. The engine 50 according to the present embodiment is a six-cylinder engine having six cylinders 51, an intake passage 52 for sending an air-fuel mixture into each cylinder 51, and an air-fuel mixture in the cylinder 51. An exhaust passage 53 for discharging exhaust gas generated by combustion is connected.

An air flow sensor 57 and an air valve 56 are provided in the intake passage 52, and the flow rate of the intake air is adjusted by the control of the ECU 60 described later. The intake passage 52 is branched toward each cylinder 51, and an injector 40 is provided at each branch destination. The sucked air is mixed with the fuel injected from the injector 40 and supplied into each cylinder 51 as an air-fuel mixture. Further, the exhaust passage 53 is configured as a passage that combines exhaust gases discharged from the cylinders 51 after combustion of the air-fuel mixture, passes through the purifying device 54 made of a three-way catalyst, and discharges it to the outside. The three-way catalyst is a catalyst that uses platinum or the like to oxidize or reduce HC, CO, and NOx to H ₂ O, CO ₂ and N ₂ , and is efficiently oxidized or reduced by complete combustion of the air-fuel mixture. .

  Driving of the injector 40 (fuel injection timing and injection amount) is controlled by an electronic control unit (ECU) 60. The ECU 60 performs comprehensive control for driving the engine 50 including ignition timing of an ignition plug (not shown), and detection signals from various sensors 55 attached to the engine 50 are input for feedback control. Has been. Further, as will be described later, in the present embodiment, the oxygen concentration in the exhaust gas discharged from the engine 50 is lean at a constant cycle (the ratio of fuel in the air-fuel mixture is small, and a large amount of oxygen remains in the exhaust gas after combustion. The fuel is injected from the injector 40 so that it is alternated between the exhaust gas side) and the rich side (a state in which the proportion of fuel in the air-fuel mixture is large and most oxygen is used for combustion and the oxygen concentration in the exhaust gas is low). Adjustment of the fuel injection amount is performed, and an engine control computer 70 for control related to the adjustment is connected to the ECU 60.

  In the exhaust passage 53, the oxygen concentration in the exhaust gas as the gas to be measured is measured upstream of the purification device 54 by the full-range air-fuel ratio sensor 35 and the light off time measuring device 10 described later. And an oxygen sensor 30 for detecting The full-range air-fuel ratio sensor 35 is a sensor that detects the concentration of oxygen or unburned gas in the exhaust gas, and the detected value is input to the λ meter 36. The λ meter 36 obtains the air-fuel ratio of the air-fuel mixture burned by the engine 50 from the detection value of the full-range air-fuel ratio sensor 35, and calculates and outputs a λ value obtained by dividing the air-fuel ratio by the stoichiometric air-fuel ratio. In the light-off time measuring apparatus 10 of the present embodiment, recording of the λ value based on the detection value of the full-range air-fuel ratio sensor 35 is performed by executing a program different from the measurement program described later.

  The oxygen sensor 30 includes an oxygen concentration detection unit 31 that detects an oxygen concentration, and a heater unit 32 that heats the oxygen concentration detection unit 31 to achieve early activation and stabilization of an activated state. A detection value (voltage value) corresponding to the oxygen concentration in the exhaust gas is obtained from the oxygen concentration detection unit 31 of the oxygen sensor 30 and output via the A / D converter 11. The exhaust passage 53 is provided with a thermocouple or a temperature sensor (not shown), and is used for feedback control for keeping the temperature of the exhaust gas constant.

  Next, the light off time measuring apparatus 10 will be described. The light-off time measuring apparatus 10 performs A / D conversion on a detection value (voltage value corresponding to the oxygen concentration) of the measurement computer 12 which is a personal computer having a known configuration and the oxygen concentration detection unit 31 of the oxygen sensor 30. The A / D converter 11 and a heater drive circuit unit 26 that applies a drive voltage to the heater unit 32 of the oxygen sensor 30 are configured.

  The measurement computer 12 is provided with a CPU 13 for controlling itself. Connected to the CPU 13 are a ROM 14 storing BIOS and the like, a RAM 15 for temporarily storing data, various variables, flags, and the like when the CPU 13 processes data, and an I / O bus 16 for mediating data transfer. ing. The I / O bus 16 is connected to a mouse 24 and a keyboard 25 on which a measurer inputs an operation, and a display 23 that displays an operation screen when executing a measurement program, which will be described later. And a communication interface 20 for performing data communication with the engine control computer 70 is connected. A CD-ROM 21 in which a measurement program is recorded is inserted into the I / O bus 16 to read data, and a hard disk drive (hereinafter referred to as “HDD”) that is a data storage device. ) 18 is connected. The measurement program read from the CD-ROM 21 by the CD-ROM drive 19 is stored in a program storage area 181 (see FIG. 2) of the HDD 18 described later. An input / output port 17 is further connected to the I / O bus 16. The input / output port 17 is provided in the form of an expansion board connected to the I / O bus 16 via a PCI bus (not shown), and the A / D converter 11 connected to the oxygen concentration detector 31 of the oxygen sensor 30. The λ meter 36 connected to the full-range air-fuel ratio sensor 35 and the heater drive circuit unit 26 connected to the heater unit 32 of the oxygen sensor 30 are connected to perform input / output of each device.

  Next, the storage area of the HDD 18 will be described. As shown in FIG. 2, the HDD 18 is provided with a program storage area 181, an initial setting storage area 182, a measurement data storage area 183, and a write-off time storage area 184. The program storage area 181 stores various programs including a measurement program described later when installed. The initial setting storage area 182 stores initial setting values used when the measurement program is executed. In the measurement data storage area 183, the detection value (voltage value) of the oxygen sensor 30 acquired according to the execution of the measurement program is associated with the count value of the timer counter storage area 155 at the timing when the detection value is acquired. Remembered. In the light-off time storage area 184, a light-off time as an activation time taken from the time when the oxygen sensor 30 is attached to the exhaust passage 53 to the activation is obtained and stored by execution of the measurement program. The The HDD 18 is also provided with various storage areas not shown.

  Next, the storage area of the RAM 15 will be described. As shown in FIG. 2, the RAM 15 includes a work area 151, a sampling count storage area 152, a rich side activation time storage area 153, a lean side activation time storage area 154, and a timer counter storage area 155. Is provided. The work area 151 temporarily stores various variables, flags, count values, and the like used when the measurement program is executed. Also, the measurement program itself is read from the HDD 18 at the time of execution and expanded. In the sampling number storage area 152, the number of times of repetition (sampling number) of the detection (sampling) of the oxygen concentration in the exhaust gas by the oxygen sensor 30 is stored and subtracted along with the execution of the measurement program to determine the end of sampling. Used. In the rich-side activation time storage area 153, the time when the oxygen sensor 30 is considered to be activated when the air-fuel ratio is on the rich side is obtained and stored by executing the measurement program. Similarly, in the lean side activation time storage area 154, the time when the oxygen sensor 30 is considered to be activated when the air-fuel ratio is on the lean side is obtained and stored by executing the measurement program. The timer counter storage area 155 stores a count value that is incremented by 1 every predetermined time by a timer program (not shown). In the measurement program, the count value at that time is acquired as it is executed, and converted into time for use. The RAM 15 is also provided with various storage areas not shown, and the measurement program is read into a predetermined storage area and executed.

  Next, the principle by which the oxygen concentration is detected by the oxygen sensor 30 will be briefly described. The oxygen concentration detector 31 of the oxygen sensor 30 has a structure in which a zirconia solid electrolyte body that exhibits insulation properties at room temperature is sandwiched between platinum electrodes, one electrode is exposed to the atmosphere, and the other electrode is used as a gas to be measured. It is configured to be exposed to the exhaust gas. The zirconia solid electrolyte body is activated by heating to become conductive, and oxygen ions can move through the zirconia solid electrolyte body. When combustion is performed in a lean state with a low proportion of fuel in the air-fuel mixture supplied to the engine 50, the oxygen concentration (partial pressure) in the exhaust gas and the oxygen concentration (partial pressure) in the atmosphere are almost balanced. Therefore, oxygen ions do not move through the zirconia solid electrolyte body. On the other hand, when the air-fuel mixture is burned in a rich state, most of the oxygen in the air-fuel mixture is used for combustion, so the oxygen concentration in the exhaust gas (partial pressure) and the oxygen concentration in the atmospheric atmosphere (partial pressure) Are in a non-equilibrium state. For this reason, oxygen ions on the air atmosphere side move to the exhaust gas atmosphere side through the zirconia solid electrolyte body, and the electromotive force generated thereby is detected as a voltage value corresponding to the oxygen concentration. That is, a large change occurs in the detected value at the boundary between the rich state and the lean state, that is, when combustion is performed at the stoichiometric air-fuel ratio (when the λ value is 1). Become.

  As described above, since an output cannot be obtained from the oxygen sensor 30 unless the zirconia solid electrolyte body is activated, the oxygen sensor aimed at shortening the time until activation, that is, the light-off time described above. 30 is developed, and the light-off-time measuring device 10 of the present embodiment is used for the evaluation.

  Here, when the air-fuel ratio is fixed to the rich side, the output (detected value) of the oxygen sensor 30 increases as the temperature of the zirconia solid electrolyte body increases, and is stable when the zirconia solid electrolyte body is sufficiently activated. To do. Similarly, when the air-fuel ratio is fixed to the lean side, it is not stable unless the temperature of the zirconia solid electrolyte is sufficiently increased, and is stabilized when the zirconia solid electrolyte is sufficiently activated. Since it can be considered that the oxygen sensor 30 (zirconia solid electrolyte body) is activated only when the output of the oxygen sensor 30 is stabilized on both the rich side and the lean side, the activation time on the rich side is used for measuring the light-off time. And measurement of the lean side activation time are required.

  Therefore, in the present embodiment, the oxygen concentration of the exhaust gas in which the air-fuel ratio is alternated between the rich side and the lean side is detected, the activation time on the rich side, and the activation time on the lean side are measured. Is performed at the same time in one measurement, reducing the labor of measurement. Specifically, the oxygen sensor 30 is exposed to exhaust gas in which the air-fuel ratio is alternated between the rich side and the lean side, and the detection value (voltage value) obtained as a result is plotted on the vertical axis and the elapsed time is plotted on the horizontal axis. Draw the sensor signal waveform. As an example, FIG. 4 shows a graph in which a change (sensor signal waveform) of a detection value (voltage value) of the oxygen sensor 30 with respect to time is recorded. As shown in the graph of FIG. 4, the detection value (voltage value) obtained from the oxygen sensor 30 fluctuates in accordance with the alternating cycle between the rich state and the lean state, and the maximum for each cycle with time. The value and the minimum value become constant values and are stabilized. From this, a line graph in which the maximum values for each period are connected by a straight line is created, and this is used for measuring the activation time on the rich side. Similarly, on the lean side, the activation time is measured using a line graph in which the minimum values for each period are connected by a straight line. From both, the time when the oxygen sensor 30 is activated on both the rich side and the lean side is determined as the light off time, so that the light off time is measured more accurately.

  Hereinafter, the operation of the light-off-time measuring apparatus 10 accompanying the execution of the measurement program will be described with reference to FIGS. 1 to 3 and 8 according to the flowcharts of FIGS. 5 to 7 are flowcharts of the measurement program. FIG. 8 is a graph for explaining a method of measuring the light-off time by enlarging a portion surrounded by a dotted line from the graph showing an example of the sensor signal waveform of the oxygen sensor shown in FIG. Each step of the flowchart is abbreviated as “S”.

  As described above, for example, the measurement program provided via the CD-ROM 21 is installed in the measurement computer 12 of the write-off time measurement device 10 and stored in the program storage area 181 of the HDD 18. When the measurement program shown in FIG. 5 is executed by the measurement computer 12, first, an instruction is transmitted to the engine control computer 70, and the air-fuel ratio is set to the rich side and the lean side to the exhaust passage 53 at regular intervals. The supply of the exhaust gas alternated with is started (S11). Specifically, the engine control computer 70 that has received an instruction from the measurement computer 12 issues an instruction to the ECU 60 to start driving the engine 50. Further, the engine control computer 70 instructs the ECU 60 to alternate the air-fuel ratio between the rich side and the lean side at regular intervals (for example, T (ms)). The ECU 60 adjusts the amount of fuel injected from the injector 40 and the amount of air sucked into the intake passage 52 by adjusting the degree of opening of the air valve 56 to change the air-fuel ratio between the rich side and the lean side every Tms. Let the police take you.

  Next, in the sampling number storage area 152 of the RAM 15, an initial value of the sampling number stored in the initial setting storage area 182 of the HDD 18, for example, 2000 (when sampling every 10 ms for 20 seconds) is stored. The number of times of sampling is a number of times set in advance so that a sufficient time for the oxygen sensor 30 to be activated is obtained in advance through experiments or the like, and sampling is performed at least during that time. Further, 0 is stored in the rich side activation time storage area 153 and the lean side activation time storage area 154 of the RAM 15, and resetting is performed. Further, the count value in the timer counter storage area 155 is also reset, and the count is started from 0 (S12).

  Next, the oxygen sensor 30 to be measured for the light-off time is attached to the exhaust passage 53 (S13). The oxygen sensor 30 to be attached is a measurement object in which at least the temperature of the zirconia solid electrolyte body is normal and inactive. The oxygen sensor 30 is preliminarily wired to the A / D converter 11 and the input / output port 17, and a mounting tool (not shown) that can be easily attached to the exhaust passage 53 is assembled to the oxygen sensor 30. ing. During this process, an input dialog is displayed on the display 23 of the measurement computer 12 to confirm whether or not the attachment has been completed. The measurer attaches the oxygen sensor 30 to the exhaust passage 53 and simultaneously operates the mouse 24 or the keyboard 25 to inform the CPU 13 that the attachment is completed. In response to this, a drive start signal is transmitted to the heater drive circuit unit 26, and energization to the heater unit 32 of the oxygen sensor 30 is started (S15).

  And acquisition of a sensor signal is performed (S16). As described above, the detected value of the oxygen concentration in the exhaust gas by the oxygen sensor 30 is A / D converted by the A / D converter 11 and input to the input / output port 17, and the detected value at this timing is acquired. The Further, the count value in the timer counter storage area 155 of the RAM 15 is referred to, and the count value at that time is stored in the work area 151 of the RAM 15. Further, the count value and the detection value (voltage value) acquired in S16 are associated with each other and stored in the measurement data storage area 183 of the HDD 18 (S19). The process of storing the detection value of the oxygen sensor 30 in S19 in the measurement data storage area 183 corresponds to the “detection value storage process” in the present invention.

  Next, the value in the sampling count storage area 152 of the RAM 15 is referred to, and if it is 1 or more, sampling is continued (S20: NO). Since sampling is performed every 10 ms, the count value in the timer counter storage area 155 is referred to, and becomes a value corresponding to 10 ms after the count value (count value at the time of sensor signal acquisition) stored in the work area 151 in S19. Until the sampling wait time (S21: NO).

  If the count value of the timer counter storage area 155 that is repeatedly referred to becomes equal to or greater than a value that is 10 ms after the count value at the time of sensor signal acquisition, it is determined that the sampling waiting time has elapsed (S21: YES), The value in the sampling number storage area 152 is decremented by 1 (S23). Then, the process returns to S16, and sensor signals are acquired and stored (S16, S19) after 10 ms have elapsed since the previous sampling. Note that the processing of S16 in which the sensor signal is acquired every predetermined time by waiting for the sampling waiting time in S21 corresponds to the “detected value acquisition step” in the present invention.

  By repeating the processing of S16 to S23 until the number of times of sampling becomes 0 in this way, the detection value (voltage value) based on the oxygen concentration in the exhaust gas detected by the oxygen concentration detection unit 31 of the oxygen sensor 30 is 10 ms. Each time it is acquired and stored in the measurement data storage area 183, data is accumulated. Then, when the number of times of sampling reaches 0, it is determined that the sampling is finished (S20: YES), a drive end signal is transmitted to the heater drive circuit unit 26, and energization of the oxygen sensor 30 to the heater unit 32 is stopped ( S24).

  Next, as shown in FIG. 6, a sensor signal waveform is created from the sampling data of 2000 sensor signals stored in the measurement data storage area 183 of the HDD 18 (S31). The sensor signal waveform shows the sensor signal, that is, the voltage value obtained according to the oxygen concentration in the exhaust gas detected by the oxygen sensor 30 on the vertical axis, after the oxygen sensor 30 is attached to the exhaust passage 53 in S13 (more Specifically, the time is plotted with the elapsed time (from the timing when the first sensor signal is acquired in S16) (time conversion may be performed or the count value may be maintained) as the horizontal axis. As an example, FIG. 4 shows a graph of sensor signal waveforms. This sensor signal waveform is created by plotting the virtual graph drawing area formed in the work area 151 of the RAM 15. In the present embodiment, the sensor signal waveform is a set of points obtained by sampling. However, a curve connecting these points or a curve calculated from these points using a least square method or the like is drawn. May be.

  Then, as shown in FIG. 6, the engine control computer 70 is inquired about the timing for switching the air-fuel ratio from the lean side to the rich side (S32). The engine control computer 70 transmits a switching signal to the measurement computer 12 every time the air-fuel ratio is switched from the lean side to the rich side. The measurement computer 12 receives the switching signal twice, the count value in the timer counter storage area 155 is referred to at each reception timing, and the alternating cycle of the air-fuel ratio, that is, 2T (ms) is calculated from the count value. Calculated. Then, by reverse calculation from the reception timing of the switching signal, the sensor signal waveform formed in the work area 151 is divided for each period, that is, by the magnitude of the count value corresponding to 2T (ms), and time division is performed (S33). . As an example, a state in which the sensor signal waveform shown in FIG. 8 is time-divided with a time division line indicated by a two-dot chain line A every period 2T (ms) is shown.

  Next, as shown in FIG. 6, for each period of the time-divided sensor signal waveform, extraction of the point (sampled voltage value and count value at that time) at which the voltage value becomes maximum is performed ( S35). By the way, the air-fuel mixture is combusted and discharged as exhaust gas from the engine 50, and a time lag occurs until it reaches the oxygen sensor 30 through the exhaust passage 53. For this reason, the sensor signal waveform in each cycle starts to rise after reaching a minimum value slightly later than the timing when the air-fuel ratio is switched from the lean side to the rich side, and the air-fuel ratio is switched from the rich side to the lean side. A waveform is drawn in which the voltage value starts to fall after reaching the local maximum with a slight delay. For this reason, the maximum value of each period is usually obtained as a maximum value. As an example, the maximum value (maximum value) of the voltage value for each period obtained by time-division of the sensor signal waveform is shown in FIG. In S35, the process of extracting the point at which the voltage value becomes the maximum for each period of the time-divided sensor signal waveform corresponds to the “maximum value extracting step” in the present invention.

  Next, as shown in FIG. 6, a local maximum side connection line is created by connecting and connecting the maximum values extracted from the sensor signal waveform for each period with straight lines between adjacent periods (S36). As an example, in FIG. 8, a maximum value side connection line D in which maximum values (points B) of respective periods obtained by time-division of sensor signal waveforms are connected by a straight line is indicated by a dotted line. In S36, the process of creating a local maximum side connecting line in which the maximum values for each period are connected by a straight line corresponds to the “maximum value side connecting line acquisition step” in the present invention.

  Then, as shown in FIG. 6, the intersection of the maximum value side connecting line and the rich side threshold value is extracted (S37). As described above, since the zirconia solid electrolyte body of the oxygen sensor 30 is activated by being heated and a large amount of oxygen ions can move, the electromotive force is small in the inactive state. Therefore, the determination of activation can be made based on whether or not a voltage value higher than a predetermined voltage value is obtained as a sensor signal when the air-fuel ratio is on the rich side. Usually, the threshold value of the voltage value (rich side threshold value) that is a criterion for activation when the air-fuel ratio is on the rich side is set to 0.55V. Therefore, a point where the voltage value is 0.55 V on the maximum value side connecting line is extracted and stored in the work area 151 together with the count value obtained from the coordinates of the point. As an example, in FIG. 8, an intersection point between the local maximum side connecting line and the rich side threshold is indicated by a point F.

  Here, there may be a plurality of intersections between the extracted maximal value side connecting line and the rich side threshold value. In the present embodiment, the intersection at the latest timing on the time axis is defined as the rich side determination intersection. If the time is later than the time at this intersection (that is, if the count value is large), it is definitely assumed that the zirconia solid electrolyte body is activated when the air-fuel ratio is on the rich side. Therefore, as shown in FIG. 6, the intersection at the latest timing among the intersections between the maximum value side connecting line extracted in S37 and the rich side threshold is specified as the rich side determination intersection (S39). Then, the time at the specified rich side determination intersection is obtained from the graph, and the count value is acquired as the rich side activation time (S40). The rich side activation time is stored in the rich side activation time storage area 153 of the RAM 15. In S39, the intersection at the latest timing among the intersections between the maximal value side connecting line and the rich side threshold value corresponding to the “maximum value side threshold value” of the present invention corresponds to the “first determination intersection point” of the present invention. The process specified as the rich side determination intersection to be performed corresponds to the “first determination intersection acquisition step” in the present invention.

  In the next processing of S41 to S47, the same processing as the series of processing in which the rich side activation time is acquired in S35 to S40 is performed on the lean side, and the lean side activation time is acquired. That is, a point (point C shown in FIG. 8 as an example) at which the voltage value is minimum is extracted for each period of the time-divided sensor signal waveform (S41), and for each period extracted from the sensor signal waveform. A minimum value side connecting line (minimum value side connecting line E shown by a dotted line in FIG. 8 as an example) is created (S43). Next, an intersection point between the minimum value side connecting line and the lean side threshold value (as an example, point G and point H shown in FIG. 8) is extracted (S44), and an intersection point (as an example in FIG. The point H) shown in FIG. 5 is specified as a lean side determination intersection (S45). Then, the time at the specified lean side determination intersection is obtained from the graph, the count value is acquired as the lean side activation time, and stored in the lean side activation time storage area 154 of the RAM 15 (S47). In S41, the process of extracting the point at which the voltage value becomes the minimum value for each period of the time-divided sensor signal waveform corresponds to the “minimum value extracting step” in the present invention. In S43, the process of creating the minimum value side connection line connecting the minimum values for each period with a straight line corresponds to the “minimum value side connection line obtaining step” in the present invention. In S45, the intersection at the latest timing among the intersections between the minimum value side connecting line and the lean side threshold value corresponding to the “minimum value side threshold value” of the present invention corresponds to the “second determination intersection point” of the present invention. The processing specified as the lean side determination intersection to be performed corresponds to the “second determination intersection acquisition step” in the present invention.

  Next, the rich side activation time (count value) obtained as described above is compared with the lean side activation time (count value) (S51). If the rich side activation time is later than the lean side activation time, that is, if the count value is large (S51: YES), the rich side activation time is regarded as the write-off time, and the time is converted, and the HDD 18 write-off is performed. It is stored (accumulated as data) in the time storage area 184 (S52). On the other hand, if the lean side activation time is the same time as the rich side activation time or a time later than that, that is, if the count value is large (S51: NO), the lean side activation time is the light-off time. And converted into time and stored in the write-off time storage area 184 of the HDD 18 (S53). In S51, the rich side activation time is compared with the lean side activation time, and the later one is acquired as the light-off time corresponding to the “activation time” of the present invention. This corresponds to the “activation time acquisition step”.

  By the way, in the process of S37 or S44 (see FIG. 6), there may be a case where the intersection between the maximum value side connection line and the rich side threshold value or the intersection point between the minimum value side connection line and the lean side threshold value cannot be obtained. For example, this is a case where the oxygen sensor 30 can output a voltage value equivalent to the activated state from the beginning of the measurement at the rich side or lean side air-fuel ratio. In such a case, the rich side determination intersection or the lean side determination intersection cannot be obtained by the process of S39 or S45, and the rich side activation time or the lean side activation time cannot be acquired by the process of S40 or S47 (FIG. 6). reference). However, in the present embodiment, in the process of S12 (see FIG. 5), 0 is stored in the rich side activation time storage area 153 and the lean side activation time storage area 154 of the RAM 15 to perform resetting. As a result, in the determination process of S51, the activation time on the side that can be acquired of the rich side activation time or the lean side activation time is compared with 0, and the activation time on the side that can be acquired is directly the write-off time. Is stored in the write-off time storage area 184. The stored light-off time can be used in other programs. Alternatively, the time may be converted and displayed on the display 23.

  Then, an input dialog is displayed on the display 23 of the measurement computer 12 to confirm whether or not the light-off time measurement is performed again (S56). When measuring the light-off time of another oxygen sensor 30 again (S56: YES), the measurer operates the mouse 24 or the keyboard 25 to inform the CPU 13 of that fact. Then, an instruction to remove the oxygen sensor 30 is displayed on the display 23, and the measurer removes the oxygen sensor 30 from the exhaust passage 53 according to this instruction (S60). Also at this time, an input dialog for confirming the completion of the removal is displayed on the display 23, and the measurer operates the mouse 24 or the keyboard 25 to report the completion of the removal of the oxygen sensor 30 to the CPU 13. And it returns to S12 of FIG. 5, and the measurement of the light-off time of the oxygen sensor 30 is performed again by repeating S12-S53.

  On the other hand, when the measurement of the light-off time of the oxygen sensor 30 is finished (S56: NO), the measurer operates the mouse 24 or the keyboard 25 on the dialog displayed on the display 23 and reports the fact to the CPU 13. Make it. Then, an instruction to stop driving the engine is transmitted to the engine control computer 70, and the ECU 60 stops driving the engine 50 in response to the instruction from the engine control computer 70, whereby the exhaust to the oxygen sensor 30 is performed. The gas supply is stopped (S57).

  Then, an instruction to remove the oxygen sensor 30 is displayed on the display 23, and the measurer removes the oxygen sensor 30 from the exhaust passage 53 according to this instruction (S59). Also at this time, an input dialog for confirming the completion of the removal is displayed on the display 23, and the measurer operates the mouse 24 or the keyboard 25 to inform the CPU 13 of the completion of the removal of the oxygen sensor 30. In response, the CPU 13 ends the execution of the measurement program.

  Needless to say, the present invention can be modified in various ways. For example, the sampling performed in S16 to S23 is started in response to the operation of a dialog that attaches the oxygen sensor 30 to the exhaust passage 53 in S13 and informs the CPU 13 of this, but the sensor signal is monitored after the operation of the dialog, Sampling may be started from the timing when the voltage value becomes higher than a predetermined value (for example, 0.1 V). Alternatively, after the operation of the dialog, a switching signal for switching the air-fuel ratio from the lean side to the rich side may be received from the engine control computer 70, and sampling may be started in response to the reception. In this case, if the count value of the timer counter storage area 155 is reset at the first sampling, the sensor signal waveform is divided at intervals of 0T (ms) to 2T (ms), and the time division of the sensor signal waveform performed in S33 is performed. It can be carried out.

  In this embodiment, the sensor signal waveform is drawn by plotting using the virtual graph drawing area in order to create the maximum value side connection line and the minimum value side connection line, but the waveform drawing is not necessarily performed. There is no need to do it. For example, data obtained by sampling is grouped by time division, and the maximum value (maximum value) of voltage values in each group is obtained. Then, when the maximum values are compared between adjacent groups, and there is a rich threshold value between the two maximum values, the voltage difference between the maximum values and the difference between the maximum value on the earlier side and the rich threshold value are calculated. Find the ratio of both. Furthermore, the time when both maximum values are obtained is obtained, and the difference is obtained. Thereby, the time when the rich side threshold value is reached can be calculated from the previously obtained ratio, and the rich side activation time can be obtained. The same applies to the lean side activation time.

  Also, an envelope of the sensor signal waveform is created, and this envelope is used as a substitute for the maximum value side connection line and the minimum value side connection line, and the same processing as in this embodiment is performed to measure the light-off time. May be.

  In the present embodiment, the passage of time is managed based on the count value, and the light-off time is obtained by converting the time in S52 or S53. However, the count value acquired together with the sensor signal is converted in time in S16 and managed. You may go.

  In addition to the oxygen sensor, it can also be applied to a method of measuring the activation time of the full-range air-fuel ratio sensor.

1 is a block diagram showing a schematic configuration of an engine bench system 1. FIG. 3 is a schematic diagram showing a configuration of each storage area of the HDD 18. FIG. 3 is a schematic diagram showing a configuration of each storage area of a RAM 15. FIG. It is a graph which shows an example of the sensor signal waveform of an oxygen sensor. It is a flowchart of a measurement program. It is a flowchart of a measurement program. It is a flowchart of a measurement program. 5 is a graph for explaining a method of measuring a light off time by enlarging a portion surrounded by a dotted line from a graph showing an example of a sensor signal waveform of the oxygen sensor shown in FIG. 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine bench system 10 Light off time measuring device 12 Measuring computer 13 CPU
15 RAM
18 HDD
30 Oxygen sensor 31 Oxygen concentration detector 32 Heater 50 Engine 53 Exhaust passage 151 Work area 152 Sampling count storage area 153 Rich side activation time storage area 154 Lean side activation time storage area 155 Timer counter storage area 181 Program storage area 182 Initial setting storage area 183 Measurement data storage area 184 Light-off time storage area

Claims (3)

An activation time measuring method for measuring an activation time required to activate an oxygen sensor after exposing the oxygen sensor to a gas to be measured whose air-fuel ratio is alternated between a rich side and a lean side at a constant cycle Because
A detection value acquisition step of acquiring a detection signal output from the oxygen sensor as a detection value every predetermined time;
A detection value storage step for storing a plurality of detection values acquired in the detection value acquisition step;
Of the plurality of detection values stored in the detection value storage step, when the time of alternating one time on the rich side and one on the lean side is defined as one cycle, the maximum detection value within that cycle for each cycle A maximum value extraction process for extracting the value as a maximum value;
Of a plurality of detection values stored in the detection value storage step, a minimum value extraction step of extracting a minimum detection value in the cycle as a minimum value for each cycle;
Among the plurality of maximum values extracted in the maximum value extraction step, adjacent maximum values are connected by a straight line to acquire a maximum value side connection line, respectively,
Among the plurality of minimum values extracted in the minimum value extraction step, a minimum value side connection line acquisition step of acquiring a minimum value side connection line by connecting adjacent minimum values with a straight line, and
A first determination intersection acquisition step of acquiring, as a first determination intersection, an intersection that is the latest intersection among the intersections at which the maximum value side threshold and the maximum value connection line intersect with each other;
Of the intersections where the minimum value side threshold value set smaller than the maximum value side threshold value and the minimum value side connecting line intersect, the intersection point that intersects the latest after being exposed to the measured gas is the second determination intersection point A second determination intersection acquisition step acquired as:
An activation time measurement for an oxygen sensor, comprising: an activation time acquisition step of comparing the first determination intersection with the second determination intersection and acquiring an activation time based on a late determination intersection Method.   In the first determination intersection acquisition step, when the intersection between the maximum value side threshold and the maximum value side connection line cannot be acquired, the activation time acquisition step determines the activation time based on the second determination intersection. The method for measuring an activation time of an oxygen sensor according to claim 1, wherein: In the second determination intersection acquisition step, when the intersection between the minimum value side threshold and the minimum value side connection line cannot be acquired, the activation time acquisition step determines the activation time based on the first determination intersection. The method for measuring an activation time of an oxygen sensor according to claim 1, wherein:

Images