JP4905726B2 - Air-fuel ratio detection device - Google Patents

Description

  The present invention relates to an air-fuel ratio detection device that detects an air-fuel ratio of an internal combustion engine with an air-fuel ratio sensor.

  Conventionally, limit current type air-fuel ratio sensors (so-called A / F sensors) that can linearly detect the air-fuel ratio (oxygen concentration) of exhaust gas discharged from an internal combustion engine have been put into practical use. This air-fuel ratio sensor has a sensor element made of a solid electrolyte body, and is configured such that an element current corresponding to the air-fuel ratio flows by applying a voltage to the sensor element. The element current flowing through the sensor element of the air-fuel ratio sensor is measured by the sensor control circuit, and an air-fuel ratio signal corresponding to the measured element current is output from the sensor control circuit. As described above, the air-fuel ratio is detected by the air-fuel ratio sensor, so that feedback control can be performed so that the air-fuel ratio becomes a desired air-fuel ratio.

In general, the sensor control circuit of the air-fuel ratio sensor has characteristic variations due to individual differences, and this may cause a problem that the detection accuracy of the air-fuel ratio decreases due to the characteristic variations. As a countermeasure, for example, in the technique disclosed in Patent Document 1, when it is determined that the air-fuel ratio sensor is in an inactive state that is not activated, the output value of the sensor control circuit and a preset output value are determined. An output error (circuit error) with respect to (reference output value) is detected, and the air-fuel ratio conversion map is calibrated based on the output error.
JP-A-8-201334

  However, the above-mentioned Patent Document 1 only discloses a technique for detecting an output error (circuit error) of the sensor control circuit in an inactive state where no current is generated in the air-fuel ratio sensor, which is caused by the temperature of the sensor control circuit. The detection error of the air-fuel ratio due to the output error of the sensor control circuit that occurs as a result is not taken into consideration.

  Therefore, in view of the above problems, the present invention provides an air-fuel ratio detection apparatus capable of compensating for an air-fuel ratio detection error caused by the temperature of a sensor control circuit and improving the air-fuel ratio detection accuracy. Objective.

Therefore, in the invention according to claim 1 of the present application, an air-fuel ratio sensor that detects the air-fuel ratio of gas, and a sensor that detects an electric current that flows when a voltage is applied to the air-fuel ratio sensor and generates an output corresponding to the detected current. Air-fuel ratio detection comprising: a control circuit; and conversion means for converting the output of the sensor control circuit into an air-fuel ratio using conversion data (such as a map or a mathematical expression) for converting the output of the sensor control circuit into an air-fuel ratio In the apparatus, the temperature detection means detects or estimates the temperature of the sensor control circuit, and in accordance with the temperature of the sensor control circuit, a conversion error due to the output error of the sensor control circuit caused by the temperature of the sensor control circuit is detected. is corrected by the correction means corrects the output of the sensor control circuit in accordance with the temperature of the sensor control circuit, the output of the corrected so converted to an air-fuel ratio by said conversion data Those were. In this way, by correcting the conversion error due to the output error of the sensor control circuit caused by the temperature of the sensor control circuit, the air-fuel ratio can be detected accurately even when the temperature of the sensor control circuit changes. It becomes possible.

Here, as a specific correction method of the conversion error, as in the invention according to claim 1 , the output of the sensor control circuit is corrected according to the temperature of the sensor control circuit by the correction means, and the output after correction is performed. Is converted into the air-fuel ratio by the conversion data, the air-fuel ratio can be detected with high accuracy.
According to a second aspect of the present invention, the apparatus includes: a cooling temperature detecting unit that detects a cooling temperature of the internal combustion engine; and an air temperature detecting unit that detects an intake air temperature supplied to the internal combustion engine. The temperature of the sensor control circuit may be estimated based on the parameter of the intake air temperature.
Further , as in the invention according to claim 3, the conversion data is corrected according to the temperature of the sensor control circuit, and the output of the sensor control circuit is converted into an air-fuel ratio using the corrected conversion data. Also good. Even if this correction method is used, the air-fuel ratio can be detected with high accuracy.

  In addition, in the invention according to claim 3, when the conversion data is created by a map (table), the map data may be corrected according to the temperature of the sensor control circuit, and the conversion data is formulated into a formula. In such a case, the coefficient of the mathematical formula may be corrected according to the temperature of the sensor control circuit.

  Further, as in the invention according to claim 4, when the current is not flowing through the air-fuel ratio sensor (hereinafter referred to as “reference state”), the reference state obtained from the output of the sensor control circuit and the converted data is used. An error from the output of the sensor control circuit (hereinafter referred to as “reference output”) is learned, the converted data or the output of the sensor control circuit is corrected by the learning correction unit based on the error, and after the correction is completed, the sensor The conversion error due to the output error of the sensor control circuit may be corrected according to the temperature of the control circuit. Thereby, after learning the error between the output of the sensor control circuit and the reference output, it is possible to further correct the error due to the temperature of the sensor control circuit, so that the air-fuel ratio detection accuracy can be further improved. It becomes possible.

  According to a fifth aspect of the present invention, there is provided a state switching means for switching the sensor control circuit from a state in which current flows to the air-fuel ratio sensor to a state in which current does not flow, and current flows to the air-fuel ratio sensor by the state switching means. It is preferable to learn an error between the output of the sensor control circuit and the reference output after switching to the non-existing state. In this way, after switching from a state in which current flows to the air-fuel ratio sensor to a state in which current does not flow, learning conversion data or sensor control circuit output can be used to accurately detect errors caused by individual differences caused by circuit characteristic variations and the like. It becomes possible to correct well.

  Further, as in the invention according to claim 6, in the sensor control circuit, a switch is provided in the current circuit connected to the air-fuel ratio sensor, and the switch is opened, so that the current does not flow from the state in which the current flows to the air-fuel ratio sensor. It is good to switch.

  In this case, as in the invention according to claim 7, when the control based on the output of the air-fuel ratio sensor is not executed, the error between the output of the sensor control circuit and the reference output may be learned. Thereby, in order to learn the error, it is not necessary to stop the control based on the output of the air-fuel ratio sensor, and it is possible to avoid the deterioration of the emission caused by stopping the control based on the output of the air-fuel ratio sensor.

  Further, the error learning is related to the output of the air-fuel ratio sensor at the time of fuel cut when the fuel is not supplied to the internal combustion engine as in the invention according to claim 8, or as in the invention according to claim 9. Alternatively, the fuel injection control and / or the air amount control may be performed when the open loop control is executed. In these cases as well, the deterioration of the emission accompanying the learning of the error is avoided in the same manner as in the seventh aspect. be able to.

  Further, as in the invention according to claim 10, when the air-fuel ratio sensor is not activated, an error between the output of the sensor control circuit and the reference output may be learned. Even in this case, it is possible to accurately correct an error caused by an individual difference caused by circuit characteristic variation or the like.

As in the invention according to claim 11, the reference output is preferably the output of the sensor control circuit corresponding to the theoretical air-fuel ratio obtained from the conversion data .

[Embodiment (1)]
Hereinafter, embodiment (1) of this invention is described based on FIGS.
In the present embodiment (1), an air-fuel ratio detection device for detecting an air-fuel ratio (oxygen concentration) of exhaust gas (combustion gas) discharged from an in-vehicle engine is embodied, and the detection result of the air-fuel ratio is configured by an engine ECU or the like. Used in an air-fuel ratio control system. In the air-fuel ratio control system, stoichiometric combustion control in which the air-fuel ratio is feedback-controlled in the vicinity of the stoichiometry, lean combustion control in which the air-fuel ratio is feedback-controlled in a predetermined lean region, and the like can be realized. In the following description, the air-fuel ratio is described as “A / F” as necessary.

  First, the configuration of an A / F sensor capable of linearly detecting the air-fuel ratio of exhaust gas will be described with reference to FIG. The A / F sensor has a sensor element 10 having a laminated structure, and FIG. 2 shows a cross-sectional structure of the sensor element 10. Actually, the sensor element 10 has a long shape extending in a direction orthogonal to the plane of FIG. 2, and the entire element is accommodated in a housing or an element cover.

  The sensor element 10 is composed of a solid electrolyte 11. More specifically, the sensor element 10 includes a solid electrolyte 11, a diffusion resistance layer 12, a shielding layer 13, and an insulating layer 14, which are stacked on the top and bottom of FIG. 2. A protective layer (not shown) is provided around the sensor element 10. The rectangular plate-shaped solid electrolyte 11 (solid electrolyte body) is a sheet made of partially stabilized zirconia, and a pair of upper and lower electrodes 15 and 16 are disposed opposite to each other with the solid electrolyte 11 interposed therebetween. The electrodes 15 and 16 are made of platinum Pt or the like. The diffusion resistance layer 12 is made of a porous sheet for introducing exhaust gas into the electrode 15, and the shielding layer 13 is made of a dense layer for suppressing permeation of the exhaust gas. Each of these layers 12 and 13 is formed by molding a ceramic such as alumina or zirconia by a sheet forming method or the like, but has different gas permeability due to the difference in the average pore diameter and porosity of the porosity. .

  The insulating layer 14 is made of a ceramic such as alumina or zirconia, and an air duct 17 is formed at a portion facing the electrode 16. In addition, a heater 18 made of platinum Pt or the like is embedded in the insulating layer 14. The heater 18 is a linear heating element that generates heat when energized by a battery power source, and heats the entire element by the generated heat. In the following description, the electrode 15 may be referred to as a diffusion layer side electrode and the electrode 16 may be referred to as an atmosphere side electrode. In the present embodiment (1), a terminal connected to the atmosphere side electrode 16 is a positive side terminal (+ terminal), and a terminal connected to the diffusion layer side electrode 15 is a negative side terminal (− terminal).

  In the sensor element 10, the surrounding exhaust gas is introduced from the side portion of the diffusion resistance layer 12 and reaches the diffusion layer side electrode 15. When the exhaust gas is lean, oxygen in the exhaust gas is decomposed by the diffusion layer side electrode 15 by applying a voltage between the electrodes 15, 16, is ionized, passes through the solid electrolyte 11, and is discharged from the atmosphere side electrode 16 to the atmosphere duct 17. Is done. At this time, a current (positive current) flows in the direction from the atmosphere side electrode 16 to the diffusion layer side electrode 15. On the contrary, when the exhaust gas is rich, oxygen in the atmospheric duct 17 is decomposed by the atmospheric side electrode 16, ionized, passes through the solid electrolyte 11, and then discharged from the diffusion layer side electrode 15. And it reacts with unburned components such as HC and CO in the exhaust gas. At this time, a current (negative current) flows from the diffusion layer side electrode 15 toward the atmosphere side electrode 16.

  FIG. 3 is a drawing showing basic voltage-current characteristics (VI characteristics) of the A / F sensor. In FIG. 3, a flat portion parallel to the voltage axis (horizontal axis) is a limit current region for specifying the element current Ip (limit current) of the sensor element 10, and the increase / decrease in the element current Ip is the increase / decrease in the air / fuel ratio (that is, , Lean and rich). That is, the element current Ip increases as the air-fuel ratio becomes leaner, and the element current Ip decreases as the air-fuel ratio becomes richer.

  In this VI characteristic, the lower voltage side than the limit current region is a resistance dominant region, and the slope of the primary straight line portion in the resistance dominant region is specified by the DC internal resistance Ri of the sensor element 10. The DC internal resistance Ri changes according to the element temperature, and when the element temperature decreases, the DC internal resistance Ri increases, and the slope of the primary linear portion of the resistance dominating region becomes small (the linear portion is in a sleeping state). Further, when the element temperature rises, the DC internal resistance Ri decreases, and the slope of the primary linear portion of the resistance dominating region increases (the slope of the linear portion increases).

  Next, the configuration of the sensor control system, which is the main part of the present invention, will be described with reference to FIG. The sensor control system includes a microcomputer (hereinafter abbreviated as “microcomputer”) 20 and a sensor control circuit 30, which detects air-fuel ratios and sensor elements based on the detection results of the A / F sensor (sensor element 10). Ten impedances (element impedance Zac) are detected.

  In FIG. 1, a microcomputer 20 is composed of a logic operation circuit including a CPU, various memories, an A / D converter, an I / O port, and the like, and a current signal (analogue) detected by a sensor control circuit 30 described later. Signal) through an A / D converter, and an A / F value and an element impedance Zac are appropriately calculated. The A / F value calculated by the microcomputer 20 is output to, for example, an engine ECU (not shown) and used for air-fuel ratio feedback control and the like.

  In the sensor control circuit 30, a reference power supply 33 is connected to a positive terminal connected to the atmosphere side electrode 16 of the sensor element 10 via an operational amplifier 31 and a current detection resistor 32, and the diffusion layer of the sensor element 10 is An applied voltage control circuit 36 is connected to the negative terminal connected to the side electrode 15 via an operational amplifier 34 and a switch 35. In this case, one end (point A in FIG. 1) of the current detection resistor 32 is held at the same voltage as the reference voltage Vf (for example, 2.2 V). The element current Ip flows through the current detection resistor 32, and the voltage at point B in FIG. 1 changes according to the element current Ip. If the exhaust gas is lean when the switch 35 is ON, the element current Ip flows from the positive terminal to the negative terminal in the sensor element 10, so that the point B voltage rises and conversely If it is rich, the element current Ip flows through the sensor element 10 from the negative terminal to the positive terminal, so that the voltage at the point B decreases.

  The applied voltage control circuit 36 monitors the B point voltage, determines a voltage to be applied to the sensor element 10 according to the voltage value, and controls the D point voltage via the operational amplifier 34 and the switch 35. However, when the air-fuel ratio detection is performed only near the stoichiometric range, the applied voltage can be fixed.

  Further, an operational amplifier 37 is connected to the reference power source 33, and an output of the operational amplifier 37 and a point B voltage are input to an operational amplifier (differential amplifier) 38 having a predetermined amplification factor. The operational amplifier 38 amplifies the voltage difference between the reference voltage Vf and the point B voltage and outputs the result as an output voltage AFO. In this case, as a configuration for amplifying the voltage difference between the reference voltage Vf and the B point voltage in the operational amplifier 38, a configuration in which the A point voltage and the B point voltage are input to the operational amplifier 38 is conceivable. An electric current flows through the current detection resistor 32, and an error may occur in air-fuel ratio detection. In contrast, in this configuration, since the output of the operational amplifier 37 and the point B voltage are input to the operational amplifier 38, the operational amplifier 37 functions as a feedback current absorption element, and an adverse effect on air-fuel ratio detection can be eliminated.

  A switch 40 and a capacitor 41 are provided on the path from the point B terminal of the current detection resistor 32 to the operational amplifier 38. In this case, the switch 40 is turned off (off) at the time of impedance detection described later, and the B point voltage at the time of the switch OFF is stored and held in the capacitor 41. As a result, even when the voltage applied to the sensor element 10 is changed in an alternating manner during impedance detection, it is possible to avoid the inconvenience that the output of the operational amplifier 38 is inadvertently changed due to the influence, and adversely affects air-fuel ratio detection. . Even when impedance is detected, an appropriate air-fuel ratio (actually a current signal immediately before the switch is turned off) can be obtained.

  The microcomputer 20 takes in the output voltage AFO of the sensor control circuit 30 from the A / D port, and uses the converted data (a map or a mathematical expression) for converting the fetched output voltage AFO into an A / F value. AFO is converted into an A / F value (this function corresponds to a conversion means). This A / F value is appropriately used for air-fuel ratio feedback control or the like. Note that the conversion data (such as a map or a mathematical expression) is stored in a nonvolatile storage unit such as a ROM of the microcomputer 20.

  Further, the microcomputer 20 instructs to temporarily change the applied voltage to the sensor element 10 in an alternating manner, and detects the element impedance Zac based on the current change amount at that time. More specifically, when the impedance is detected, the applied voltage control circuit 36 receives a command from the microcomputer 20, and the applied voltage to the sensor element 10 (D point voltage in FIG. 1) is positive or negative with a predetermined width (for example, 0.2V). Change on both sides. At this time, the microcomputer 20 measures the change in the B point voltage accompanying the change in the applied voltage, and based on the applied voltage change amount ΔV and the current change amount ΔI obtained by dividing the B point voltage change amount by the resistance value of the current detection resistor 32. The element impedance Zac is calculated (Zac = ΔV / ΔI). In the impedance detection, the current flowing through the sensor element 10 may be changed in an alternating manner, and the element impedance Zac may be calculated from the amount of change in current or voltage at that time.

  Impedance detection is performed at a predetermined cycle (that is, every predetermined time), and the execution timing is commanded from the microcomputer 20 to the applied voltage control circuit 36. Further, the microcomputer 20 controls energization to the heater 18 so that the element impedance Zac is maintained at a predetermined target value. As a result, the sensor element 10 is held in a predetermined active state.

  By the way, the sensor control circuit 30 is comprised by various components, such as resistance and an operational amplifier, as mentioned above. In such a sensor control circuit 30, the resistance of the sensor control circuit 30 and the characteristics of the operational amplifier change according to the temperature of the sensor control circuit 30. FIG. 4 shows an example of the output characteristic of the output voltage AFO of the sensor control circuit 30 with respect to the air-fuel ratio. The reference output characteristic (reference output characteristic) set in advance is indicated by a solid line and the sensor control is performed with respect to the reference output characteristic. The output characteristics shifted by the temperature of the circuit 30 are indicated by a one-dot chain line. When the temperature of the sensor control circuit 30 is different, an output error (offset) occurs in the output characteristic of the sensor control circuit 30 with respect to a preset reference output characteristic. Thus, when an output error occurs, the output voltage AFO of the sensor control circuit 30 is shifted by the output error, and the air-fuel ratio detection accuracy deteriorates.

  Therefore, in the present embodiment (1), correction for the output error is performed in order to solve the problem of deterioration in the air-fuel ratio detection accuracy due to the output error generated according to the temperature of the sensor control circuit 30. More specifically, a correction amount corresponding to the output error is calculated according to the detected temperature of the sensor control circuit 30, and the output voltage AFO of the sensor control circuit 30 is corrected by the correction amount, thereby causing the temperature. Correct the output error that occurs. FIG. 5 shows correction data (map) in which the correction amount for the output error caused by the temperature of the sensor control circuit 30 is stored for each temperature of the sensor control circuit 30, for example, OFF (0). Is stored with a correction amount corresponding to the output error with respect to the reference output characteristic when the temperature of the sensor control circuit 30 is 0 ° C., and the correction data corresponding to the temperature of the sensor control circuit 30 is corrected using this correction data. Calculate the amount.

  Hereinafter, a program for correcting an output error (offset) with respect to a preset reference output characteristic will be described with reference to FIG. This program is activated every predetermined time by the microcomputer 20 and serves as a correction means for correcting an output error of the sensor control circuit 30 caused by the temperature of the sensor control circuit 30 according to the temperature of the sensor control circuit 30. Fulfill.

  When the program of FIG. 6 is started, first, in step S101, the temperature of the sensor control circuit 30 is detected. Since the temperature of the sensor control circuit 30 has a correlation with the temperature of an engine ECU (not shown), the temperature of the engine ECU is detected as the temperature of the sensor control circuit 30. In this case, it is essential for the engine ECU to include a temperature sensor for detecting the temperature. The temperature of the engine control circuit 30 may be estimated. For example, the temperature of the engine cooling water may be detected by a sensor, and the temperature of the sensor control circuit 30 may be estimated based on the temperature of the engine cooling water. Further, when the engine is cold started, the temperature of the sensor control circuit 30 and the intake air temperature (outside air temperature or cooling water temperature) are substantially the same, so the temperature of the sensor control circuit 30 is estimated based on the intake air temperature or the like. Then, the temperature of the sensor control circuit 30 may be corrected as time elapses after starting.

  When the temperature of the sensor control circuit 30 is detected in step S101, the process proceeds to step S102, and the correction amount OFF (T) corresponding to the output error with respect to the reference output characteristic is calculated. In step S102, using the correction data (map) of FIG. 5, the correction amount OFF corresponding to the output error between the output characteristic of the sensor control circuit 30 corresponding to the detected temperature T of the sensor control circuit 30 and the reference output characteristic is OFF. (T) is calculated. Here, the correction data in FIG. 5 is obtained by applying a voltage to the sensor control circuit 30 in a state where no current flows through the A / F sensor, for example, in a bench test (when the reference output characteristic is detected by a reference vehicle). Output (output voltage) is detected for each temperature, and the correction amount for the output error is detected based on the output of the sensor control circuit 30 detected for each temperature. Thus, by detecting the output of the sensor control circuit 30 in a state where no current flows to the A / F sensor for each temperature, the output error of the sensor control circuit 30 due to the temperature of the sensor control circuit 30 can be calculated. The correction amount based on the output error can be calculated.

  Next, in step S103, the output voltage AFO of the sensor control circuit 30 is read. In the next step S104, the read output voltage AFO is corrected with a correction amount OFF (T) corresponding to the output error. Specifically, the output voltage AFO read in step S103 is subtracted by the correction amount OFF (T) for the output error calculated in step S102. The method for correcting the output of the sensor control circuit 30 is not limited to the above method. For example, the output of the sensor control circuit 30 may be multiplied by a correction amount (correction coefficient) corresponding to the output error. good. In this case, in FIG. 5, the output error correction amount OFF (T) can be corrected by multiplying the output of the sensor control circuit 30 by the output error correction amount (correction coefficient). A correct value will be set.

By executing the program described above, the following effects can be obtained.
As described above, since the output error caused by the temperature of the sensor control circuit 30 is corrected, the detection accuracy of the air-fuel ratio can be improved. In addition, the air-fuel ratio stoichiometric control accuracy is improved by improving the air-fuel ratio detection accuracy, and as a result, improvement of exhaust emission can be realized.

Hereinafter, the effect obtained by executing the above-described program of FIG. 6 will be described with reference to FIG.
Originally, if the air-fuel ratio is controlled by stoichiometry, the purification rate of the three components (HC, CO, NOx) in the exhaust gas can be increased. In particular, the NOx purification rate is greatly deteriorated. On the other hand, if the stoichiometric control can be performed reliably by the above correction, the output characteristic of the A / F sensor becomes B (after correction), and a high purification rate can be maintained for the three components (HC, CO, NOx) in the exhaust gas.

  In this embodiment (1), the output (output voltage) of the sensor control circuit 30 is corrected with the correction amount for the output error. However, even if the reference output characteristic is corrected with the correction amount for the output error. good. In this case, for example, if the output error at that temperature is corrected once when the temperature of the sensor control circuit 30 does not change, an accurate air-fuel ratio can be obtained without sequentially correcting the output of the sensor control circuit 30. It is possible to calculate and to reduce the calculation load of the program.

[Embodiment (2)]
By the way, in the A / F sensor and the sensor control circuit 30, there are individual differences caused by circuit characteristic variations and the like, and the sensor output accuracy decreases due to the individual differences. FIG. 8 shows an example of the output characteristic of the output voltage AFO of the sensor control circuit 30 with respect to the air-fuel ratio. In FIG. 8, the reference output characteristic set in advance is indicated by a solid line, the characteristic variation of the sensor itself, the circuit characteristic variation, etc. The output characteristic having an offset error with respect to the reference output characteristic is indicated by a one-dot chain line. In the case of FIG. 8, according to the reference output characteristics, AFO = 2.2V in the stoichiometric state (A / F = 14.7, where the current flowing through the A / F sensor is Ip = 0 mA). On the other hand, when an offset error occurs, the output voltage AFO of the sensor control circuit 30 shifts by the offset error.

  Therefore, in this embodiment (2), after the microcomputer 20 learns (corrects) the offset error with respect to the reference output characteristic caused by the individual difference of the sensor control circuit 30, the sensor control circuit of the above embodiment (1) is used. A program for correcting an output error (offset) caused by the temperature of 30 is executed.

Hereinafter, differences from the embodiment (1) will be described.
The program shown in FIG. 9 is executed by the microcomputer 20 at a predetermined cycle, and serves as correction means in the claims. When this program is started, first, in step S201, it is detected whether or not the correction of the offset error caused by the individual difference of the sensor control circuit 30 has been completed. If it is determined in step S201 that the correction of the offset error caused by the individual difference of the sensor control circuit 30 has not been completed, the process proceeds to step S202, and the correction of the offset error caused by the individual difference described later is performed. A program (A / F output voltage correction program) is executed.

  On the other hand, if it is determined in step S201 that the correction of the offset error has already been completed, or if the offset error is corrected in step S202, the process proceeds to step S203, which is described in the embodiment (1). 6 is executed to correct an output error (offset) caused by the temperature of the sensor control circuit 30. In this case, in FIG. 6, the correction amount OFF (T) for the output error caused by the temperature of the sensor control circuit 30 is the sensor control in a state where no current flows through the A / F sensor during the bench test. The output of the sensor control circuit 30 detected when a voltage is applied to the circuit 30 is stored as data (map) for each temperature, and the offset error caused by individual differences is corrected using the data. The difference (output error) between the output of the sensor control circuit 30 at the temperature of the sensor control circuit 30 detected at the time of detection and the output of the sensor control circuit 30 at the temperature of the sensor control circuit 30 detected at that time. It is preferable to calculate the correction amount for the output error caused by the temperature based on the difference.

  Next, a correction program (A / F output voltage correction program) for offset errors caused by individual differences in the sensor control circuit 30 will be described. This program is executed by the microcomputer 20 firstly after executing a program for calculating an offset error caused by the individual difference in FIG. 10, and then executing a program for correcting the offset error in FIG. These programs play a role corresponding to the learning correction means in the claims.

  First, in the program of FIG. 10, when A / F = 14.7 (Ip = 0 mA) which is the stoichiometric air-fuel ratio (stoichiometric state), the output voltage of the sensor control circuit 30 at that time is AFO = 2.2V. Then, the sensor control circuit 30 is forced to be in a stoichiometric detection state (a state in which no current flows through the A / F sensor), and an offset error is obtained under such a state. Specifically, during normal engine operation, the switch 35 provided on the output side of the operational amplifier 34 is temporarily turned OFF, and the output voltage AFO of the sensor control circuit 30 at that time is measured. Then, an offset error K1 is calculated from the measured output voltage AFO, and the offset error K1 is appropriately used as a “correction amount”. Note that the state in which the switch 35 is turned on corresponds to the normal state, and the state in which the switch 35 is turned off corresponds to a state in which the offset error of the sensor control circuit 30 is detected.

  In FIG. 10, first, in step S301, it is determined whether or not it is the learning timing of the offset error K1. This learning timing is a timing at which the sensor control circuit 30 is temporarily detected in the stoichiometric state to learn the offset error K1, for example, air-fuel ratio control (intake amount control, fuel injection control) based on the output of the A / F sensor. It is preferable to set a state (open loop control state) in which the control is not performed as the learning timing. Further, for example, the learning timing may be set before the A / F sensor is activated or during fuel cut. Here, the process of updating (correcting) data is referred to as “learning”. Further, the process of updating and storing data may be “learning”.

  If it is the learning timing, the process proceeds to step S302, a switching signal is output to the switch 35, and the switch 35 is turned off for a predetermined time (for example, about 5 msec). In step S303, the output voltage AFO of the sensor control circuit 30 at that time is captured.

Thereafter, the process proceeds to step S304, and the offset error K1 is calculated from the output voltage AFO read in step S303 and the preset output voltage Vst.
K1 = AFO-Vst

  The output voltage Vst is the reference output (reference output voltage) of the sensor control circuit 30 that should be output at the stoichiometric air-fuel ratio (stoichiometric state). In this embodiment (2), Vst = 2.2V. Thereafter, the process proceeds to step S305, and the offset error K1 is stored in the standby RAM. On the other hand, if it is determined in step S301 that the learning timing condition is not satisfied, this flowchart is terminated.

  Next, a program for correcting the offset error caused by the individual difference of the output voltage AFO of the sensor control circuit 30 will be described with reference to FIG.

  In FIG. 11, first, in step S401, it is determined whether or not an error (offset error K1) between the output voltage of the sensor control circuit 30 and a preset output voltage has been calculated (learned). If is not calculated, this flowchart is terminated.

If it is determined in step S401 that the calculation of the offset error has been completed, the process proceeds to step S402, and the output voltage AFO of the sensor control circuit 30 at this time is captured. In subsequent step S403, the output voltage AFO is corrected by the offset error K1.
AFO = AFO-K1
In this way, air-fuel ratio feedback control or the like is performed using the calculated corrected output voltage AFO. Note that the corrected output voltage AFO may be learned.

  Further, in the program of FIG. 11, the output voltage AFO of the sensor control circuit 30 is corrected with the offset error K1 with respect to the reference output characteristic when the sensor control circuit 30 is forced to be in the stoichiometric detection state. The characteristic output voltage may be corrected by the offset error K1. In this case, the offset error K1 is added to the output voltage of the reference output characteristic. That is, in FIG. 8, the reference output characteristic of the solid line is corrected to match the output characteristic of the sensor control circuit 30 of the one-dot chain line. Further, the sensor control circuit 30 is forcibly set in the stoichiometric detection state. However, even when the A / F sensor is not activated, no current flows through the A / F sensor (Ip = 0 mA), the above correction (switch 35 in FIG. 1) is not provided, and the above correction may be performed when the A / F sensor is not activated. Note that when the engine temperature is low, such as when the engine is cold started, the A / F sensor is not in an active state.

  In addition, the configuration in which the sensor control circuit 30 is forcibly set to the stoichiometric detection state in the embodiment (2) is not limited to that in FIG. 1, and the configuration is such that no current flows through the A / F sensor. I just need it.

  In the present embodiment (2) described above, the output generated due to the temperature of the sensor control circuit 30 after learning (correcting) the offset error caused by the individual difference caused by the circuit characteristic variation of the sensor control circuit 30 or the like. The error (offset) was corrected. As a result, both the output error (offset error) of the sensor control circuit 30 caused by the individual difference and the output error (output error) of the sensor control circuit 30 caused by the temperature of the sensor control circuit 30 are corrected. Therefore, it is possible to detect the air / fuel ratio with high accuracy.

  Further, in the present embodiment (2), the correction of the offset error caused by the individual difference of the sensor control circuit 30 is preferably performed when the engine is started. In this case, an error (offset error, output error) of the output of the sensor control circuit 30 caused by the individual difference and the temperature of the sensor control circuit 30 can be corrected at an early stage after the engine is started. It is possible to detect the air-fuel ratio with high accuracy. In addition, the air-fuel ratio stoichiometric control accuracy is improved by improving the air-fuel ratio detection accuracy from an early stage after the engine is started, and as a result, improvement of exhaust emission can be realized.

  The A / F sensor may detect not only the air-fuel ratio of the exhaust gas discharged from the engine but also the air-fuel ratio of the gas supplied to the engine.

It is a circuit diagram which shows the electrical constitution of the sensor control circuit in embodiment of this invention. It is sectional drawing which shows the structure of a sensor element. It is a figure which shows the output characteristic of an A / F sensor (air-fuel ratio sensor). It is a figure which shows the output characteristic of a sensor control circuit. It is a figure which shows the relationship between a sensor control circuit and the correction amount for an output error. It is a flowchart which shows the flow of a process of the program which correct | amends an output error in embodiment (1). It is a figure which shows the exhaust gas purification characteristic of a gasoline engine. It is a figure which shows the output characteristic of a sensor control circuit. It is a flowchart which shows the flow of the process of the program which correct | amends an output error in embodiment (2). It is a flowchart which shows the flow of a process of the program of an offset error calculation process in embodiment (2). It is a flowchart which shows the flow of a process of the program of an A / F output voltage correction process in embodiment (2).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Sensor element 11 ... Solid electrolyte 20 ... Microcomputer (Conversion means, correction means, learning correction means)
30 ... Sensor control circuit 32 ... Current detection resistor 34 ... Operational amplifier 35 ... Switch

Claims (11)

An air-fuel ratio sensor for detecting the air-fuel ratio of the gas;
A sensor control circuit for detecting a current flowing when a voltage is applied to the air-fuel ratio sensor and generating an output corresponding to the detected current;
In an air-fuel ratio detection apparatus comprising: conversion means for converting the output of the sensor control circuit into an air-fuel ratio using conversion data for converting the output of the sensor control circuit into an air-fuel ratio;
Temperature detecting means for detecting or estimating the temperature of the sensor control circuit;
The conversion means corrects a conversion error due to an output error of the sensor control circuit caused by the temperature of the sensor control circuit according to the temperature of the sensor control circuit detected or estimated by the temperature detection means. means seen including, the correction corrects the output of the sensor control circuit according to the temperature of the sensor control circuit by means corrected output the converted data by the air-fuel ratio, characterized in that in terms of the air-fuel ratio detection apparatus. An air-fuel ratio sensor for detecting the air-fuel ratio of the gas;
A sensor control circuit for detecting a current flowing when a voltage is applied to the air-fuel ratio sensor and generating an output corresponding to the detected current;
In an air-fuel ratio detection apparatus comprising: conversion means for converting the output of the sensor control circuit into an air-fuel ratio using conversion data for converting the output of the sensor control circuit into an air-fuel ratio;
Temperature detecting means for detecting or estimating the temperature of the sensor control circuit;
Cooling temperature detecting means for detecting the cooling temperature of the internal combustion engine;
Air temperature detecting means for detecting the intake air temperature supplied to the internal combustion engine,
The temperature detection means estimates the temperature of the sensor control circuit based on the cooling temperature of the internal combustion engine and / or the intake air temperature ,
The conversion means includes correction means for correcting a conversion error due to an output error of the sensor control circuit caused by the temperature of the sensor control circuit in accordance with the temperature of the sensor control circuit estimated by the temperature detection means. An air-fuel ratio detection apparatus comprising: The conversion means corrects the conversion data according to the temperature of the sensor control circuit by the correction means, and converts the output of the sensor control circuit into an air-fuel ratio using the corrected conversion data. The air-fuel ratio detection apparatus according to claim 2 . When no current flows through the air-fuel ratio sensor (hereinafter referred to as “reference state”), the output of the sensor control circuit in the reference state obtained from the output of the sensor control circuit and the converted data (hereinafter referred to as “the reference state”). Learning correction means for learning an error from the reference output) and correcting the converted data or the output of the sensor control circuit based on the error,
The correction means corrects the conversion data or the output of the sensor control circuit by the learning correction means, and then adjusts the sensor control circuit according to the temperature of the sensor control circuit detected or estimated by the temperature detection means. 4. The air-fuel ratio detection apparatus according to claim 1, wherein a conversion error due to an output error is corrected. A state switching means for switching the sensor control circuit from a state where current flows to the air-fuel ratio sensor to a state where current does not flow;
5. The learning correction unit learns an error between the output of the sensor control circuit and the reference output after the state switching unit switches to a state in which no current flows to the air-fuel ratio sensor. The air-fuel ratio detection device according to 1. In the sensor control circuit, a switch is provided in a current circuit connected to the air-fuel ratio sensor,
The air-fuel ratio detection apparatus according to claim 5, wherein the state switching means switches from a state in which current flows to the air-fuel ratio sensor to a state in which current does not flow by opening the switch.   The learning correction means learns an error between the output of the sensor control circuit and the reference output when control based on the output of the air-fuel ratio sensor is not executed. The air-fuel ratio detection apparatus according to one.   8. The air-fuel ratio detection apparatus according to claim 7, wherein the time when the control based on the output of the air-fuel ratio sensor is not executed is a fuel cut time during which fuel is not supplied to the internal combustion engine.   The time when the control based on the output of the air-fuel ratio sensor is not executed is when the open loop control is executed in which the fuel injection control and / or the air amount control is executed regardless of the output of the air-fuel ratio sensor. The air-fuel ratio detection apparatus according to claim 7.   The learning correction means learns an error between the output of the sensor control circuit and the reference output when the air-fuel ratio sensor is not active. The air-fuel ratio detection apparatus described.   The air-fuel ratio detection apparatus according to any one of claims 4 to 10, wherein the reference output is an output of the sensor control circuit corresponding to a theoretical air-fuel ratio obtained from the converted data.

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