Method for estimating deterioration degree of o2 sensor, program and device

Abstract

To estimate the deterioration degree of an O2 sensor at an early stage when the O2 sensor provided in a heat treatment chamber deteriorates during carburizing heat treatment.SOLUTION: A method for estimating the deterioration degree of an O2 sensor 14 comprises: measuring O2 concentration in order to control a carbon potential when supplying enriched gas to an atmosphere in a heat treatment chamber 11 to be subjected to carburizing heat treatment; and previously acquiring characteristics that the carbon potential rises with time from the supply start of the enriched gas to refer to a carbon potential calculation value CPcal calculated on the basis of the output of the O2 sensor 14 to a reference carbon potential rise characteristic CPstnd used as a reference and estimate the deterioration degree of the O2 sensor 14 (S11-S13).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method, a program, and an apparatus for estimating the degree of deterioration of an O2 sensor used to calculate and control the carbon potential of the atmosphere in a heat treatment chamber where carburizing heat treatment is performed. [Background technology]

[0002] In carburizing heat treatment, the carbon potential of the atmosphere in the heat treatment chamber is controlled to a target value by supplying enriched gas into the heat treatment chamber. Patent Document 1 discloses that, in controlling the carbon potential of carburizing heat treatment, the carbon potential is calculated based on the oxygen concentration measured by a zirconia-type O2 sensor, and enriched gas is supplied so that the calculated value of the carbon potential reaches the target value.

[0003] O2 sensors deteriorate over long periods of use, causing the measured oxygen concentration to deviate from the actual oxygen concentration. When the measured oxygen concentration deviates from the actual oxygen concentration, the calculated carbon potential also deviates from the actual carbon potential. Patent Document 2 discloses a method for diagnosing the degree of deterioration of an O2 sensor based on a value obtained by integrating an area calculated by multiplying an opening instruction signal of a control valve provided in a system that supplies enriched gas into a heat treatment chamber by time over a predetermined period from the start of the supply of enriched gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-73798 [Patent Document 2] Japanese Patent Publication No. 2022-95446 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 2, the deterioration level of the O2 sensor is diagnosed based on the integrated value of the area calculated by multiplying the control valve opening instruction signal by time over a predetermined period from the start of the supply of enriched gas, making it difficult to diagnose the deterioration level early.In particular, it is not possible to diagnose the deterioration level of the O2 sensor early after the start of the supply of enriched gas when the control valve is at its maximum opening and enriched gas is being supplied.

[0006] An object of the present invention is to enable early estimation of the degree of deterioration of an O2 sensor provided in a heat treatment chamber. [Means for solving the problem]

[0007] (1) In order to solve the above problem, the present invention provides a method for estimating the degree of deterioration of an O2 sensor, which measures the O2 concentration in order to control the carbon potential when an enriched gas is supplied to the atmosphere in a heat treatment chamber and a carburizing heat treatment is performed. The method estimates the degree of deterioration of the O2 sensor by referring to a carbon potential calculated based on the output of the O2 sensor, relative to a reference carbon potential increase characteristic that is a pre-acquired reference characteristic of how the carbon potential increases over time from the start of the supply of the enriched gas.

[0008] (2) The reference carbon potential increase characteristic is a characteristic when the enriched gas is supplied at a constant flow rate.

[0009] (3) The estimation is based on the difference between the calculated carbon potential and the carbon potential read value on the reference carbon potential increase characteristic until the calculated carbon potential reaches the target value.

[0010] (4) In order to solve the above problem, the program of the present invention is a program for estimating the degree of deterioration of an O2 sensor that measures O2 concentration in order to control the carbon potential when an enriched gas is supplied to the atmosphere in a heat treatment chamber and a carburizing heat treatment is performed, and causes a computer to execute the following steps: estimating the degree of deterioration of the O2 sensor by referring to a carbon potential calculated value calculated based on the output of the O2 sensor, with respect to a reference carbon potential increase characteristic that is a reference and that is a characteristic of the carbon potential increasing over time from the start of the supply of the enriched gas that is previously acquired.

[0011] (5) In order to solve the above problems, the device of the present invention is a device for estimating the degree of deterioration of an O2 sensor that measures the O2 concentration in order to control the carbon potential when an enriched gas is supplied to the atmosphere in a heat treatment chamber and a carburizing heat treatment is performed, and the device estimates the degree of deterioration of the O2 sensor by referring to a carbon potential calculated value calculated based on the output of the O2 sensor, relative to a reference carbon potential increase characteristic that is obtained in advance and serves as a reference for the characteristic of the carbon potential increasing over time from the start of the supply of the enriched gas. [Effects of the Invention]

[0012] According to the present invention, the degree of deterioration of an O2 sensor provided in a heat treatment chamber can be estimated at an early stage. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a configuration diagram of a heat treatment system. [Figure 2] 1 is a flowchart of a carburizing heat treatment including estimation of a degree of deterioration. [Figure 3] This is a diagram showing the relationship between oxygen concentration and electromotive force in an O2 sensor. [Figure 4] FIG. 4(A) is a time chart of the carbon potential characteristics, and FIG. 4(B) is a time chart of the enrichment valve opening command value. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Heat treatment system configuration] 1 shows the overall configuration of a heat treatment system 1. The heat treatment system 1 is composed of a heat treatment chamber 10, a gas supply device 20, and a control device 30. The heat treatment chamber 10 is equipped with a fan 11, a heater 12, a temperature sensor 13, and an O2 sensor 14. The gas supply device 20 is equipped with a modified gas tank 21, piping 22, a valve 23, an enriched gas tank 24, piping 25, and a valve 26. The control device 30 is equipped with a carbon potential calculation unit 31 (hereinafter also referred to as the CP calculation unit 31), a data storage unit 32, a deterioration degree estimation unit 33, and a carbon potential control unit 34 (hereinafter also referred to as the CP control unit 34). The workpiece 100 is made of steel and is placed in a case, a support stand, or the like.

[0015] The fan 11 agitates the atmosphere in the heat treatment chamber 10 to ensure uniform temperature and component distribution. The fan 11 is driven by an electric motor and controlled by the control device 30. The heater 12 heats the atmosphere in the heat treatment chamber 10. The power supplied to the heater 12 is controlled by the control device 30 so that the treatment temperature corresponds to the carburization conditions of the workpiece 100. The temperature sensor 13 detects the temperature of the atmosphere in the heat treatment chamber 10. The temperature sensor 13 outputs the detected value to the control device 30. The O2 sensor 14 measures the oxygen concentration in the atmosphere in the heat treatment chamber 10. The O2 sensor 14 outputs an electromotive force E corresponding to the oxygen concentration to the control device 30.

[0016] The modified gas contains hydrogen (H), carbon monoxide (CO), and nitrogen (N), and constitutes the atmosphere in the heat treatment chamber 10. The enriched gas contains propane (C3H8), butane (C4H 10 These are hydrocarbon gases such as benzene (CH), methane (CH), and acetylene (C2H2), which increase the carbon potential (CP) of the atmosphere. Note that hereinafter, carbon potential will also be simply referred to as CP. Valves 23 and 26 are solenoid valves that adjust the flow rate of gas supplied into heat treatment chamber 10.

[0017] The CP calculation unit 31 calculates CP based on the output value of the temperature sensor 13 and the output value of the O2 sensor 14. The data storage unit 32 stores a reference carbon potential increase characteristic CP, which is a characteristic of CP increasing over time from the start of the supply of enriched gas and is previously acquired as a reference. stnd The deterioration degree estimation unit 33 stores the reference carbon potential increase characteristic CP stnd On the other hand, the CP calculation value CP calculated by the CP calculation unit 31 is cal The CP control unit 34 estimates the deterioration degree of the O2 sensor 14 by referring to the value of CP calculated by the CP calculation unit 31. cal and the deterioration degree of the O2 sensor 14 estimated by the deterioration degree estimation unit 33, the CP calculated value CP cal By correcting the above, the opening command value MV of the valve 26 is adjusted to appropriately control CP.

[0018] [Heat treatment process] In the heat treatment system 1, the control device 30 executes a program for controlling the entire process of the carburizing heat treatment of the workpiece 100. When the workpiece 100 is placed in the heat treatment chamber 10, modified gas is introduced into the heat treatment chamber 10 through the piping 22. The modified gas is supplied to the heat treatment chamber 10 at a predetermined flow rate throughout the carburizing heat treatment, and is exhausted to the outside through the exhaust pipe 15. When the heat treatment chamber 10 is filled with modified gas, the heater 12 raises the temperature until it reaches a treatment temperature corresponding to the carburizing conditions of the workpiece 100. When the treatment temperature is reached, the output of the heater 12 is controlled to maintain the treatment temperature. Furthermore, when the treatment temperature is reached, the control device 30 controls the valve 26 to start the supply of enriched gas. The control device 30 controls the CP of the atmosphere in the heat treatment chamber 10 to a target CP value CP corresponding to the carburizing conditions of the workpiece 100. SV The supply of enriched gas is controlled so that

[0019] During the carburizing heat treatment, the CP of the atmosphere is controlled by the process shown in the flowchart of Figure 2. When the supply of enriched gas to the heat treatment chamber 10 starts, in step S11, the CP calculation unit 31 calculates the CP of the atmosphere based on the output value of the temperature sensor 13 and the output value of the O2 sensor 14. A well-known formula is used to calculate CP.

[0020] In step S12, the CP calculated value CP cal (Calculated carbon potential) is the target value CP SV The reference carbon potential rise characteristic CP at the time td reached stnd The above value is the reference CP obtained value CP d (Carbon potential reading) is obtained. Reference carbon potential increase characteristic CP stnd is the calculated CP value CP calculated by the CP calculation unit 31 after the supply of enriched gas into the heat treatment chamber 10 is started during a period in which it is determined that the new O2 sensor 14 has not substantially deteriorated since its installation. cal The time-dependent change data of the reference carbon potential increase characteristic CP is acquired in advance and stored in the data storage unit 32. stnd When the value of CP is acquired, the valve 26 is set to the fully open state. SV A constant flow rate of enriched gas is supplied until the time ts is reached, and the reference carbon potential rise characteristic CP stnd is the CP increase characteristic when enriched gas is supplied at a constant flow rate. Therefore, the standard carbon potential increase characteristic CP stnd It is possible to obtain a stable standard carbon potential increase characteristic CP with little variation. stnd As long as the above can be obtained, the valve 26 does not have to be fully opened, and may be opened at a constant degree, for example, 80%.

[0021] In step S13, the reference CP acquisition value CP d and the calculated CP value at time td calThe difference ΔCP between the O2 sensor 14 and the O2 sensor 14 is calculated. That is, the calculated ΔCP is an estimated value of the deterioration degree of the O2 sensor 14.

[0022] In step S14, the target value CP of CP is calculated based on the estimated deterioration degree (ΔCP) of the O2 sensor 14. SV and CP calculation value CP cal The deviation from the difference ΔCP is corrected, and the opening command value MV of the valve 26 is changed accordingly to appropriately control CP. Note that no correction is made if ΔCP is zero or in a range that can be practically ignored. Also, the degree of deterioration is not measured as the difference ΔCP itself, but as the reference CP acquisition value CP of the difference ΔCP. d Or target value CP SV Ratio to (i.e., ΔCP / CP d , or ΔCP / CP SV Alternatively, the deterioration degree of the O2 sensor 14 may be calculated by multiplying the reference CP value CP d and target value CP SV The ratio of one to the other (i.e., CP d / CP SV , or CP SV / CP d ) may be calculated based on the deterioration degree of the O2 sensor 14. cal The atmospheric CP was controlled by correcting the target value CP SV The CP of the atmosphere may be controlled by correcting the setting of

[0023] Also, the CP calculation value CP cal is the target value of CP SV However, the degree of deterioration may be estimated at an earlier timing. For example, when the target value CP SV It is also possible to use a CP value obtained by multiplying the target value by a percentage such as 60%. In this case, an even earlier estimation is possible. On the other hand, to ensure the accuracy of the estimation, the target value CP SV The timing when it reaches

[0024] Also, CP is properly set to the target value CP SV The correction to control to the CP calculated value CP calThe correction is not limited to automatic correction of some parameter in the program, such as correction of CP, but may be performed by an operator of the heat treatment system 1. When some parameter in the program is automatically corrected, the deterioration degree calculated by the deterioration degree estimation unit 33 is set as a correction value, and the calculated CP value CP cal The degree of deterioration is corrected to the reference CP acquisition value CP d and the calculated CP value at time td cal When the difference ΔCP is calculated from the calculated CP value CP calculated at the time of correction, the CP control unit 34 calculates the calculated CP value CP cal By subtracting the difference ΔCP from cal In addition, for example, if the degree of deterioration is greater than the reference CP acquisition value CP d and the calculated CP value at time td cal When the CP is calculated as a ratio of the calculated CP value CP cal By multiplying this ratio, the CP calculation value is CP cal When the correction is performed by the operator, the deterioration degree estimation unit 33 displays the calculated deterioration degree on the monitor. The operator can grasp the deterioration degree of the O2 sensor 14 by looking at the display on the monitor, and input a correction value to the control device 30 based on the deterioration degree. When the correction value is input to the control device 30, the CP control unit 34 uses the input correction value to calculate the CP calculated value CP cal Correct the following.

[0025] FIG. 3 shows an example of an electromotive force characteristic A1, which indicates the relationship between the oxygen concentration and electromotive force E when the O2 sensor 14 is not degraded, using a solid line. Also, an example of an electromotive force characteristic A2, which indicates the relationship between the oxygen concentration and electromotive force E when the O2 sensor 14 is degraded, using a dashed line. When the oxygen concentration of the atmosphere decreases, the difference in oxygen concentration with the air increases, and when the O2 sensor 14 is not degraded, an electromotive force E is generated in accordance with the difference in oxygen concentration, as shown by the electromotive force characteristic A1. However, when the O2 sensor 14 is degraded, the value of the electromotive force E changes, as shown by the electromotive force characteristic A2. When the O2 sensor 14 degrades, the O2 ion conductivity of the zirconia solid electrolyte changes, and the electromotive force E is outputted in a larger value. When the O2 sensor 14 degrades and the output of the electromotive force E increases, the calculated CP value CPcal will be larger than the actual CP.

[0026] 4(A) and 4(B) are time charts after the start of the supply of enriched gas to the heat treatment chamber 10, where FIG. 4(A) is a time chart showing the carbon potential of the atmosphere, and FIG. 4(B) is a time chart showing the opening command value MV of the valve 26. In FIG. 4(A), the reference carbon potential increase characteristic CP stnd is indicated by a dashed line, and the CP calculated value CP calculated by the CP calculation unit 31 when the O2 sensor 14 is deteriorated. cal When the present invention is not applied, the CP calculated value CP based on the electromotive force E of the deteriorated O2 sensor 14 is cal is calculated to be larger than the actual CP, so the actual CP is sv Although the pressure has not yet reached the desired value, the valve 26 is not controlled to provide an appropriate CP.

[0027] In FIG. 4B, the O2 sensor 14 is not deteriorated, and the calculated CP value CP cal However, the standard carbon potential increase characteristic CP stnd The opening command value MV1 of the valve 26 is set when the O2 sensor 14 is degraded, and the opening command value MV2 of the valve 26 is set when the O2 sensor 14 is degraded, and the ... cal is the standard carbon potential increase characteristic CP stnd At time ts, the target value CP SV The opening command value MV1 is 100% until it reaches the target value CP SV After reaching CP, the CP calculation value CP cal is the target value CP SV However, if the O2 sensor 14 is deteriorated, the opening command value MV1 is set so that the calculated CP value CP cal At time td, the target value CP SVUntil the time td is reached, the opening command value MV2 is set to 100%, and after time td, the CP calculated value CP cal is the target value CP SV In this case, the actual CP of the atmosphere is set to the target value CP sv The amount of enriched gas required to achieve this is not supplied, and the actual CP is lower than the target value CP SV will remain lower than

[0028] The O2 sensor 14 has deteriorated and the CP calculation value CP cal Even if the calculated value is larger than the actual CP, the actual CP of the atmosphere is calculated based on the reference carbon potential rise characteristic CP while the opening command value MV is set to 100%. stnd If the O2 sensor 14 is deteriorated, the carbon potential rise characteristic CP stnd The value of CP above is the target value CP SV Until the time ts is reached, the calculated CP value CP cal is the standard carbon potential increase characteristic CP stnd Therefore, the standard carbon potential increase characteristic CP stnd The value of CP above is the target value CP SV At any timing up to the time ts when the reference carbon potential increase characteristic CP stnd On the other hand, the CP calculation value CP calculated by the CP calculation unit 31 is cal The deterioration degree of the O2 sensor 14 is estimated by referring to the above.

[0029] As shown in the deterioration degree estimation region in the embodiment of the present invention, the reference carbon potential increase characteristic CP stnd The value of CP above is the target value CP SV The region until the time ts when the reference carbon potential increase characteristic CP is reached is the region where the deterioration degree can be estimated. However, in the conventional case, the deterioration degree of the O2 sensor 14 cannot be estimated in the region where the opening degree of the valve 26 is 100% after the supply of enriched gas is started. In this embodiment, the deterioration degree of the O2 sensor 14 is estimated in the region where the opening degree of the valve 26 is 100% after the supply of enriched gas is started. stnd The value of CP above is the target value CPSV The degree of deterioration of the O2 sensor 14 can be estimated at any timing up to the time ts at which the O2 sensor 14 reaches the predetermined value, and can be estimated at an early stage.

[0030] [program] The program is configured as a program that executes the processes of steps S11 to S14 shown in the flowchart of Fig. 2. The program may be transmitted via a computer-readable storage medium or a network. Furthermore, the various processes of the program do not have to be configured on a single computer or medium, but may be distributed across multiple servers or computers that can send and receive data via network communication.

[0031] [Device] In terms of device configuration, the program of the control device 30, which is a controller that estimates the degree of deterioration of the O2 sensor 14, is configured with a CP calculation unit 31, a data storage unit 32, a deterioration degree estimation unit 33, and a CP control unit 34, and includes the processing program for steps S11 to S14 of Figure 2.

[0032] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims.

[0033] According to the present invention, a reference carbon potential increase characteristic CP stnd On the other hand, the CP calculated value CP is calculated based on the electromotive force E, which is the output of the O2 sensor 14. cal The deterioration degree of the O2 sensor 14 is estimated by calculating the difference ΔCP between them. Therefore, when the O2 sensor 14 deteriorates, the deterioration degree can be estimated early. Then, based on the deterioration degree, the accurate CP of the atmosphere can be grasped early and the CP can be appropriately controlled. In addition, the reference carbon potential increase characteristic CP stndis a characteristic when the enriched gas is supplied to the heat treatment chamber 10 at a constant flow rate, it is possible to obtain a stable characteristic with little variation, and therefore it is possible to improve the control accuracy of the CP. [Industrial Applicability]

[0034] The present invention can be widely applied as a method, program, and device for estimating the degree of deterioration of an O2 sensor used to calculate and control the carbon potential of the atmosphere in a heat treatment chamber where carburizing heat treatment is performed. [Explanation of symbols]

[0035] Heat treatment system 1, heat treatment chamber 10, fan 11, heater 12, temperature sensor 13, O2 sensor 14, gas supply device 20, modified gas tank 21, piping 22, valve 23, enriched gas tank 24, piping 25, valve 26, control device 30, CP calculation unit 31, data storage unit 32, deterioration degree estimation unit 33, CP control unit 34, and workpiece 100

Claims

1. Enriched gas is supplied to the atmosphere in the heat treatment chamber to control the carbon potential when carburizing heat treatment is performed. ２ Measure the concentration of O ２ A method for estimating a deterioration degree of a sensor, comprising: The carbon potential increases with time from the start of supply of the enriched gas, and a reference carbon potential increase characteristic is obtained in advance. ２ The carbon potential calculated based on the output of the sensor is referred to. ２ Estimate the degree of deterioration of the sensor. ２ A method for estimating the degree of sensor deterioration.

2. 2. The method according to claim 1, wherein the reference carbon potential increase characteristic is a characteristic when the enriched gas is supplied at a constant flow rate. ２ A method for estimating the degree of sensor deterioration.

3. 2. The method according to claim 1, wherein the estimation is based on a difference between a carbon potential reading on the reference carbon potential increase characteristic until the calculated carbon potential value reaches a target value and the calculated carbon potential value. ２ A method for estimating the degree of sensor deterioration.

4. Enriched gas is supplied to the atmosphere in the heat treatment chamber to control the carbon potential when carburizing heat treatment is performed. ２ Measure the concentration of O ２ A program for estimating a degree of deterioration of a sensor, On the computer, The carbon potential increases with time from the start of supply of the enriched gas, and a reference carbon potential increase characteristic is obtained in advance. ２ The carbon potential calculated based on the output of the sensor is referred to. ２ A program that causes the computer to estimate the degree of deterioration of the sensor.

5. Enriched gas is supplied to the atmosphere in the heat treatment chamber to control the carbon potential when carburizing heat treatment is performed. ２ Measure the concentration of O ２ A device for estimating a degree of deterioration of a sensor, The carbon potential increases with time from the start of supply of the enriched gas, and a reference carbon potential increase characteristic is obtained in advance. ２ The carbon potential calculated based on the output of the sensor is referred to. ２ A device that estimates the degree of deterioration of a sensor.

Images