JP2010008121A - Sensor output processor and sensor output processing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor output processor capable of correcting the shift of the output value of an output circuit to a detection signal with high precision while keeping the detection signal outputted from a sensor in a normal state. <P>SOLUTION: The sensor output processor includes output circuits 431, 432 each of which has a shunt resistor Rs for converting the sensor cell current Is (detection signal) outputted from an NOx sensor 10 to a voltage change signal and outputs the voltage change signal, a standard current circuit 433 for adjusting the current flowing through the shunt resistor Rs to a definite standard current regardless of the change of the sensor cell current Is, and switch circuits SW1 and SW2 switching a sensor output processing mode for stopping the function of the adjustment by the standard current circuit 433 to change the current value flowing through the shunt resistor Rs corresponding to the change of the sensor cell current Is and a measuring mode for operating the function of the adjustment by the standard current circuit 433. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sensor output processing apparatus and a sensor output processing system applied to a current output type sensor that converts a physical quantity change to be sensed into a current change and outputs it as a detection signal.

Examples of this type of current output type sensor include a NOx sensor that detects the NOx concentration in the exhaust gas of an internal combustion engine, an A / F sensor that detects an excess air ratio, and the like. And the conventional sensor output processing apparatus which processes the detection signal output from such a sensor has the shunt resistance which converts the detection signal of an electric current change into the signal of a voltage change, and the voltage change converted by the shunt resistance The output signal is subjected to processing such as amplification and output (see Patent Document 1).
JP 2003-166773 A

  Here, the output value of the output circuit with respect to the detection signal is shifted due to the performance error of the circuit components such as the shunt resistor and the aging deterioration. Therefore, the present inventors have studied to provide the sensor output processing device 40x with a circuit 42x for allowing a constant reference current to flow through the shunt resistor Rs as shown in FIG. Specifically, the microcomputer 41x measures the output value (correction measurement value) of the output circuit when the reference current is passed through the shunt resistor Rs, and the difference between the output value with respect to the reference current and the theoretical value is corrected for the deviation. The microcomputer 41x calculates the value.

  When measuring the correction measurement value in this way, the switch 43x is turned on to input the reference current to the shunt resistor Rs. On the other hand, when the NOx concentration or the like is detected according to the detection value from the sensor, the switch 43x is turned off and the detection value is input to the shunt resistor Rs.

  However, in this device 40x, the current of the detection signal that varies according to the NOx concentration or the like flows into the shunt resistor Rs separately from the reference current. For this reason, since the measurement value for correction with respect to the reference current cannot be measured with high accuracy, the deviation cannot be corrected with high accuracy.

  To solve this problem, the present inventors provide a switch 44x between the shunt resistor Rs and the sensor 10, and turn off the switch 44x when measuring the correction measurement value, thereby detecting the detection signal to the shunt resistor Rs. The method of avoiding the inflow of water was examined. However, if the switch 44x is turned off to electrically disconnect the sensor 10 from the sensor output processing device 40x, depending on the type of the sensor 10, a normal detection signal may be output for a while after the next switch 44x is turned on. Output may not be possible.

  The present invention has been made to solve the above-described problems, and its object is to maintain the detection signal output from the sensor in a normal state and to accurately shift the output value of the output circuit with respect to the detection signal. An object of the present invention is to provide a sensor output processing device and a sensor output processing system that can be corrected.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

The invention according to claim 1 is applied to a current output type sensor that converts a physical quantity change to be sensed into a current change and outputs it as a detection signal.
An output circuit having a shunt resistor for converting the detection signal into a voltage change signal, and outputting a voltage change signal converted by the shunt resistor;
A reference current circuit for adjusting a current flowing through the shunt resistor to a constant reference current regardless of fluctuations in the detection signal;
A sensor output processing mode in which the adjustment function by the reference current circuit is stopped and the value of the current flowing through the shunt resistor is changed in accordance with a change in the detection signal, and a measurement in which the adjustment function by the reference current circuit is activated. A switching circuit for switching between modes,
It is characterized by providing.

  According to this, since the reference current circuit functions to make the current flowing through the shunt resistor a constant reference current regardless of the fluctuation of the detection signal in the state switched to the measurement mode by the switching circuit, the output circuit for the reference current Can be accurately measured as a correction measurement value. Therefore, if the measurement value for correction measured with high accuracy is used, the output value deviation of the output circuit with respect to the detection signal can be corrected with high accuracy.

  Moreover, since the sensor output processing mode and the measurement mode are switched without making the sensor electrically disconnected from the sensor output processing device, the detection signal output from the sensor is maintained in a normal state. Measurement values for correction can be measured with high accuracy.

  According to a second aspect of the present invention, the reference current circuit is a circuit configured to output an inversion current having a value corresponding to the fluctuation to the shunt resistor so as to cancel the fluctuation of the detection signal. To do.

  According to this, when the current value of the detection signal flowing into the shunt resistor fluctuates so as to increase, the inverted current reduced by the increase is output to the shunt resistor. On the other hand, when the current value of the detection signal fluctuates so as to decrease, an inverted current increased by the decrease is output to the shunt resistor. Therefore, the detection signal and the inversion current flow through the shunt resistor, but the current value obtained by adding the inversion current to the detection signal is constant regardless of the fluctuation of the detection signal. Therefore, it is possible to preferably realize that the current flowing through the shunt resistor is a constant reference current in the measurement mode.

  According to a third aspect of the present invention, an output terminal of an operational amplifier (see symbol OPa in FIG. 2) provided in the reference current circuit is connected to the sensor side of the shunt resistor. An input terminal of the operational amplifier is connected to the side opposite to the sensor, and the inverted current is output from the output terminal by performing a negative feedback operation of the operational amplifier.

  This is preferable because an inversion current can be easily generated. The “negative feedback operation” is a known operation in which, when a negative feedback is applied, a non-inverting input terminal and an inverting input terminal have the same potential among the input terminals of the operational amplifier due to a virtual short circuit.

  According to a fourth aspect of the present invention, the reference current circuit is configured to be able to change the value of the reference current. According to this, the output value (correction measurement value) of the output circuit with respect to the reference current can be acquired for each of the plurality of reference current values. Therefore, in correcting the output value deviation with respect to the detection signal in the sensor output processing mode, the output value deviation amount for the entire region of the current value of the detection signal can be calculated based on a plurality of correction measurement values. Therefore, it is possible to improve the calculation accuracy of the output value deviation amount for the entire region of the detection signal.

  Further, as a configuration example of the reference current circuit for changing the value of the reference current, an example in which the resistance value of the reference resistor connected in series to the shunt resistor can be changed as described in claim 5, and As described, there is an example in which the voltage applied to the reference resistor connected in series with the shunt resistor can be changed.

  According to a seventh aspect of the present invention, the sensor adjusts the concentration of a specific component from the pump cell that adjusts the oxygen amount in the detection gas introduced into the gas chamber to a predetermined concentration level, and the gas after the oxygen amount adjustment in the pump cell. The sensor cell is configured to be detected, and the detection signal is a sensor cell current value output from the sensor cell in accordance with the concentration of the specific component.

  When this type of sensor is electrically disconnected from the sensor output processing device, a normal detection signal cannot be output for a while after the next connection. Therefore, if the sensor output processing device according to claims 1 to 6 is applied to this type of sensor, it is unnecessary to make the sensor electrically disconnected from the sensor output processing device. The above effects are suitably exhibited.

  According to an eighth aspect of the present invention, the learning means for learning the difference between the output value of the output circuit with respect to the reference current and the theoretical value with respect to the reference current, and the sensor output processing mode based on the learning value by the learning means. Correction means for correcting the output value of the output circuit. By learning in this way, it is possible to suitably correct an output value deviation caused by aging of circuit components such as a shunt resistor.

  The invention according to claim 9 is a sensor output processing system comprising the sensor output processing device and the sensor. According to this sensor output processing system, the above-described various effects can be similarly exhibited.

  Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A sensor to which the sensor output processing device of this embodiment is applied is a NOx sensor that is provided in an exhaust pipe of an in-vehicle engine and detects the NOx concentration in the exhaust. The on-board engine is, for example, a diesel engine. An NOx purification catalyst (such as a NOx storage reduction catalyst or an ammonia selective reduction catalyst) serving as an exhaust purification device provided in the exhaust pipe of the engine is abnormal based on the output of the NOx sensor. Diagnosis etc. are to be implemented. For example, a NOx sensor is provided downstream of the NOx purification catalyst, and the NOx purification catalyst is abnormal when the NOx concentration (NOx purification rate) calculated from the output of the NOx sensor exceeds a predetermined abnormality determination value. Diagnosed.

  First, the structure and operation of the NOx sensor 10 will be described with reference to FIG.

  The NOx sensor 10 has a so-called laminated structure, and its internal structure is shown in FIG. The left-right direction in the figure corresponds to the longitudinal direction of the NOx sensor 10. The right side of the figure is the element base end side (exhaust pipe attachment site side), and the left side of the figure is the element tip side. The NOx sensor 10 has a so-called two-cell structure composed of two electrochemical cells, that is, a pump cell 31 and a sensor cell 35, and each cell is laminated and configured.

  In the NOx sensor 10, the solid electrolyte bodies 11 and 12 made of an oxygen ion conductive material such as zirconia are formed in a sheet shape, and are stacked at predetermined intervals above and below in the figure via spacers 13 made of an insulating material such as alumina. ing. Among these, an exhaust inlet 11a is formed in the upper solid electrolyte body 11 in the figure, and exhaust around the sensor element is introduced into the first chamber 14 through the exhaust inlet 11a. The first chamber 14 communicates with the second chamber 16 via the throttle unit 15. On the upper surface of the solid electrolyte body 11 in the figure, a porous diffusion layer 17 for taking in and out the exhaust gas with a predetermined diffusion resistance is provided, and an insulating layer 19 for defining an air passage 18 is provided.

  Further, an insulating layer 21 made of alumina or the like is provided on the lower surface of the solid electrolyte body 12 in the figure, and an atmospheric passage 22 is formed by the insulating layer 21. A heater (heating element) 23 is embedded in the insulating layer 21 for heating the entire sensor. In this case, the pump cell 31 and the sensor cell 35 are heated by the heater 23, and the cells 31 and 35 are activated. The heater 23 generates thermal energy by power supply from a battery power source (not shown).

  The solid electrolyte body 12 on the lower side of the figure is provided with a pump cell 31 so as to face the first chamber 14. The pump cell 31 takes in and out oxygen in the exhaust gas introduced into the first chamber 14. The residual oxygen concentration in the chamber 14 is adjusted to a predetermined concentration. The pump cell 31 has a pair of upper and lower electrodes 32 and 33 provided with the solid electrolyte body 12 sandwiched therebetween, and in particular, the electrode 32 on the first chamber 14 side is a NOx inert electrode (an electrode that is difficult to decompose NOx). Yes. The pump cell 31 decomposes oxygen present in the first chamber 14 in a state where a voltage is applied between the electrodes 32 and 33 and discharges it from the electrode 33 to the atmosphere passage 22 side.

  The upper solid electrolyte body 11 in the drawing is provided with a sensor cell 35 so as to face the second chamber 16. The sensor cell 35 detects the NOx concentration from the gas in the second chamber 16 in a state where surplus oxygen is discharged by the pump cell 31. The sensor cell 35 includes a solid electrolyte body 11 and electrodes 37 and 38 disposed to face each other with the solid electrolyte body 11 interposed therebetween. The electrode 37 (electrode on the second chamber 16 side) of the sensor cell 35 is made of a noble metal such as platinum Pt or rhodium Rh active in NOx.

  In the NOx sensor 10 having the above configuration, the exhaust is introduced into the first chamber 14 through the porous diffusion layer 17 and the exhaust introduction port 11a. Then, when this exhaust gas passes through the vicinity of the pump cell 31, a decomposition reaction occurs by applying a pump cell applied voltage V 0p between the pump cell electrodes 32, 33, and through the pump cell 31 according to the oxygen concentration in the first chamber 14. Oxygen is taken in and out. At this time, since the electrode 32 on the first chamber 14 side is a NOx inert electrode, NOx in the exhaust gas is not decomposed in the pump cell 31, but only oxygen is decomposed and discharged from the electrode 33 to the atmospheric passage 22. By such a function of the pump cell 31, the inside of the first chamber 14 is adjusted to a predetermined low oxygen concentration state.

  The gas that has passed in the vicinity of the pump cell 31 (the gas after oxygen concentration adjustment) flows into the second chamber 16 through the throttle unit 15 and is applied to the sensor cell electrodes 37 and 38 by applying a predetermined sensor cell applied voltage V0s. NOx is reduced and decomposed. Oxygen generated at this time is discharged from the electrode 38 to the atmospheric passage 18. At this time, the NOx concentration in the exhaust gas is detected by the current (sensor cell current Is) flowing through the sensor cell 35.

  Next, the amplifier 40 (sensor output processing device) will be described with reference to FIG.

  The amplifier 40 includes a microcomputer 41 (microcomputer) having a CPU, a RAM, a ROM, and the like, and the microcomputer 41 is a main body for sensor control. The microcomputer 41 controls the pump cell voltage V0p (see FIG. 1) applied between the electrodes 32 and 33 of the pump cell 31 and the sensor cell voltage V0s (see FIG. 1) applied between the electrodes 37 and 38 of the sensor cell 35, respectively. The measured values of the pump cell current Ip and the sensor cell current Is are sequentially input to the microcomputer 41, and the microcomputer 41 calculates the oxygen concentration and NOx concentration in the exhaust based on these measured values.

  The calculated oxygen concentration and NOx concentration are output to the ECU 50 that controls the engine. The ECU 50 controls the rich gas injection timing to the NOx storage reduction catalyst and the urea to the ammonia selective reduction catalyst based on the oxygen concentration and NOx concentration. Control water injection timing. As a result, the engine control can be performed so that NOx contained in the exhaust gas of the in-vehicle engine is equal to or less than the target value.

  The amplifier 40 includes the above-described microcomputer 41 and an analog circuit, and the analog circuit includes a current-voltage conversion circuit 431, an amplifier circuit 432, a reference current circuit 433, and the like. The current-voltage conversion circuit 431 and the amplifier circuit 432 correspond to an “output circuit” described in the claims.

  The current-voltage conversion circuit 431 includes a shunt resistor Rs and an operational amplifier OP1. The shunt resistor Rs converts the sensor cell current Is (sensor output signal) output from the sensor cell electrode 37 into a voltage change signal. The operational amplifier OP1 functions to stabilize the potential of the shunt resistor Rs on the NOx sensor 10 side at a constant potential V1.

  The amplifier circuit 432 includes an operational amplifier OP2 that amplifies the sensor cell voltage Vs converted by the current-voltage conversion circuit 431. The amplification gain Gs by the operational amplifier OP2 is set by the resistors R1 and R2 and the resistors R3 and R4 so that the peak value of the voltage change of the sensor cell voltage Vs approaches 5V. As a result, the sensor cell voltage Vs is largely changed in a voltage range (0 to 5 V) that can be processed by the A / D conversion circuit of the microcomputer 41, and the NOx concentration detection accuracy by the amplifier 40 is improved. The reference voltage V1 adjusted by the operational amplifier OP1 is input to the non-inverting input terminal of the operational amplifier OP2 through the resistor R3 and grounded through the resistor R4.

  The sensor cell voltage amplified analog signal output from the operational amplifier OP2 (corresponding to the “output value of the output circuit”) is input to the A / D conversion port of the microcomputer 41 and subjected to A / D conversion processing. The microcomputer 41 calculates the NOx concentration based on the A / D converted digital signal (output voltage Vd), and outputs the calculated NOx concentration information to the ECU 50. The microcomputer 41 stores a concentration calculation map (or calculation formula) that specifies the relationship between the output voltage Vd and the NOx concentration, and calculates the NOx concentration from the output voltage Vd using the map.

  By the way, the output value of the output circuit with respect to the detection signal is deviated due to performance errors and aging deterioration of various circuit components constituting the current-voltage conversion circuit 431 and the amplifier circuit 432. For example, the performance error of the shunt resistor Rs, the amplification error in the operational amplifier OP1 due to the performance error of the negative feedback resistors R1 and R2, the variation of the offset value generated in the operational amplifier OP1, and the like are examples of causes of the output value deviation.

  Therefore, in this embodiment, a reference current is passed through the shunt resistor Rs by a reference current circuit 433 described later, and the output value at that time is measured as a correction measurement value. Then, the output value deviation is compensated by correcting (learning) the above-described density calculation map based on the difference between the theoretical value with respect to the reference current and the correction measurement value. The microcomputer 41 that operates to learn the difference between the theoretical value with respect to the reference current and the correction measurement value corresponds to a “learning unit” and operates to correct the concentration calculation map based on the learned difference. The microcomputer 41 corresponds to “correction means”. Note that these means may be made to function by the microcomputer 41, and at least one of the learning means and the correction means may be made to function by a custom IC (not shown).

  More specifically, using FIG. 3A and FIG. 3B, FIG. 3 shows the current input to the shunt resistor Rs (that is, the sensor cell current Is or the reference current Ia) and the output from the sensor cell operational amplifier OP2. It is a figure which shows the characteristic straight line of the amplifier 40 which shows the relationship with a value or the output value after A / D conversion processing in the microcomputer 41. The microcomputer 41 that executes the correction process first corrects the output value from the operational amplifier OP2 when the reference current Ia is passed through the shunt resistor Rs or the output value after the A / D conversion process is performed by the microcomputer 41. Is stored as measured value Va. Then, a difference ΔVa between the theoretical value for the reference current Ia and the correction measurement value Va is calculated. The difference ΔVa calculated in this way is used as a correction value for the density calculation map. That is, the offset correction is performed so that the characteristic line as the map data indicated by the solid line in FIGS. 3A and 3B is decreased by ΔVa in the reference current Ia portion. By this correction, the characteristic straight line indicated by the solid line is offset-corrected to become the characteristic straight line indicated by the one-dot chain line in FIG. 3B, and the corrected characteristic straight line approaches the straight line indicating the theoretical value. . Note that FIGS. 3C and 3D describe a second embodiment to be described later.

  Next, the configuration of the reference current circuit 433, which is a main part of the present embodiment, will be described with reference to FIG.

  The reference current circuit 433 includes an operational amplifier OPa and a reference resistor Ra. The output terminal of the operational amplifier OPa is connected to the NOx sensor 10 side of the shunt resistor Rs, and the inverting input terminal of the operational amplifier OPa is connected to the side opposite to the NOx sensor 10 of the shunt resistor Rs. The reference resistor Ra is connected in series with the shunt resistor Rs on the opposite side of the shunt resistor Rs from the NOx sensor 10.

  A switch SW2 is disposed between the output terminal of the operational amplifier OPa and the shunt resistor Rs, and a switch SW1 is disposed between the output terminal of the operational amplifier OP1 and the shunt resistor Rs. The on / off operation of these switches SW1 and SW2 (corresponding to the “switching circuit” described in the claims) is controlled by the microcomputer 41.

  When the switch SW1 is turned on and the switch SW2 is turned off, the operation of the amplifier 40 enters the “sensor output processing mode”. Then, the operational amplifier OP1 functions to stabilize the potential of the shunt resistor Rs on the side of the NOx sensor 10 at a constant potential V1, and the function of the reference current circuit 433 such as flowing the reference current to the shunt resistor Rs is stopped. Become. Therefore, the value of the current flowing through the shunt resistor Rs varies according to the variation of the sensor cell current Is (detection signal) according to the NOx concentration. Therefore, the NOx concentration can be calculated using the above-described concentration calculation map.

  On the other hand, when the switch SW1 is turned off and the switch SW2 is turned on, the operation of the amplifier 40 enters the “measurement mode”. Then, the function of the operational amplifier OP1 is stopped, and the reference current circuit 433 functions to adjust the current flowing through the shunt resistor Rs to the reference current. That is, the current flowing through the shunt resistor Rs is adjusted to be stable at a constant reference current regardless of the fluctuation of the sensor cell current Is (detection signal) according to the NOx concentration.

  Next, the operation of the reference current circuit 433 in the measurement mode will be described with reference to FIG.

  In the measurement mode, since all the current after flowing through the shunt resistor Rs flows into the reference resistor Ra, the current flowing through the shunt resistor Rs matches the current flowing through the reference resistor Ra. Therefore, if the current flowing through the reference resistor Ra regardless of the fluctuation of the sensor cell current Is can be made a constant reference current, the current flowing through the shunt resistor Rs can be adjusted to a constant reference current. The value of the current flowing through the reference resistor Ra is determined by the potential at the connection point P between the shunt resistor Rs and the reference resistor Ra and the resistance value of the reference resistor Ra. That is, it is only necessary to adjust the potential at the connection point P to be constant.

  The connection point P is also connected to the inverting input terminal of the operational amplifier OPa. The potential of the inverting input terminal is negatively fed back to the operational amplifier OPa, so that the potential Vc of the non-inverting input terminal regardless of the fluctuation of the sensor cell current Is. Matches. That is, the potential at the connection point P is adjusted so as to be equal to the potential Vc of the non-inverting input terminal. Therefore, the current flowing through the shunt resistor Rs can be adjusted to a constant reference current.

  This negative feedback operation will be described mainly with reference to current flow. Even if the sensor cell current Is fluctuates, an inverted current having a value corresponding to the fluctuation is output from the output terminal of the operational amplifier OPa so as to cancel the fluctuation. That is, when the sensor cell current Is is smaller than the reference current, the shortage of the sensor cell current Is with respect to the reference current is output from the output terminal of the operational amplifier OPa. On the other hand, when the sensor cell current Is is larger than the reference current, an excess of the sensor cell current Is with respect to the reference current flows into the output terminal of the operational amplifier OPa. Therefore, the current flowing through the shunt resistor Rs can be adjusted to a constant reference current.

  As described above, according to the present embodiment, in the state where the switches SW1 and SW2 are switched to the measurement mode, by applying negative feedback to the operational amplifier OPa, the current flowing through the reference resistor Ra regardless of the fluctuation of the sensor cell current Is, that is, the shunt The current flowing through the resistor Rs is adjusted to a constant reference current. Therefore, the microcomputer 41 can accurately measure the output value from the operational amplifier OP2 with respect to the reference current as the correction measurement value. Therefore, the output value deviation correction for the density calculation map can be performed with high accuracy.

  Moreover, since the sensor output processing mode and the measurement mode are switched by the switches SW1 and SW2 without the NOx sensor 10 being electrically disconnected from the amplifier 40, the sensor cell current Is output from the NOx sensor 10 is used. The measurement value for correction can be accurately measured while maintaining the normal state.

(Second Embodiment)
In the first embodiment, the reference current flowing through the shunt resistor Rs is a fixed value, whereas the amplifier 401 (sensor output processing device) of the present embodiment shown in FIG. 4 is configured to be able to change the value of the reference current. is doing. More specifically, the alternate long and short dash line portion in FIG. 4 is different from FIG. 2, and in this embodiment, a transistor TR1 as a switch means and a capacitor C1 as a smoothing means are provided at both ends of the reference resistor Ra. It is connected. Therefore, the path of the reference current flowing through the shunt resistor Rs includes the path I1 flowing through the reference resistor Ra and the transistor TR1 and the path I2 flowing through the capacitor C1.

  When the transistor TR1 is turned on, the capacitor C1 is charged, and when the transistor TR1 is turned off, the capacitor C1 is discharged. The switching operation of the transistor TR1 is controlled by the microcomputer 41 (for example, PWM control), and the amount of current flowing through the path I2 is controlled by the control. For example, as the duty ratio by PWM control (here, the off-duty ratio) increases, the current amount of the path I2 increases (exactly, the amount of current flowing per time of the path I2 does not change and the current flows through the path I2. Time will be longer). Thus, since the current flowing through the reference resistor Ra is smoothed by the capacitor C1, the value of the current flowing through the reference resistor Ra is controlled by the on / off operation of the transistor TR1. That is, the operation is performed in the same manner as when the resistance value of the reference resistor Ra is variably controlled, so that the value of the reference current can be changed.

  In short, the microcomputer 41 PWM-controls the transistor TR1 to variably set the value of the reference current flowing through the shunt resistor Rs. For example, in the case of FIGS. 3C and 3D, the correction measurement value Va when the reference current Ia is passed through the shunt resistor Rs and the reference current Ib having a value different from the reference current Ia are used as the shunt resistor Rs. The measurement value Vb for correction when it is passed through is stored. Then, differences ΔVa and ΔVb between the respective theoretical values for the reference currents Ia and Ib and the corrected measurement values Va and Vb are calculated. The differences ΔVa and ΔVb calculated in this way are used as correction values for the density calculation map. That is, the characteristic straight line as map data indicated by the solid line in FIGS. 3C and 3D is corrected so as to decrease by ΔVa in the reference current Ia portion and decrease by ΔVb in the reference current Ib portion. By this correction, the characteristic straight line indicated by the solid line is corrected to become the characteristic straight line indicated by the one-dot chain line in FIG. 3D, and the corrected characteristic straight line approaches the straight line indicating the theoretical value ( In the example of FIG. 3D, the corrected characteristic straight line matches the theoretical value).

  Here, in the first embodiment, the map data (characteristic line) is corrected as shown in FIGS. 3A and 3B on the basis of one correction measurement value Va, so that the slope of the characteristic line is changed. It cannot be corrected and only offset correction is performed. On the other hand, according to the present embodiment, the correction measurement value for the reference current can be acquired for each of the plurality of reference current values Ia and Ib. Therefore, since the characteristic line can be corrected based on the correction measured values Va and Vb at a plurality of points (two points in the examples of FIGS. 3C and 3D), the inclination can be corrected in addition to the offset of the characteristic line. The characteristic line can be brought close to the theoretical value with high accuracy.

  Therefore, in the correction according to FIG. 3B, the accuracy of concentration calculation is low for the sensor cell current Is in a region away from the reference current Ia, whereas according to the correction of the present embodiment shown in FIG. In correcting the output value deviation with respect to the sensor cell current Is in the sensor output processing mode, the output value deviation amount for the entire region of the sensor cell current Is (the entire region on the horizontal axis in FIG. 3) is measured with a plurality of correction measurement values. Can be calculated with high accuracy. Therefore, it is possible to improve the calculation accuracy of the output value deviation amount for the entire region of the sensor cell current Is.

(Third embodiment)
In the second embodiment, the value of the reference current passed through the shunt resistor Rs can be changed by performing control equivalent to variably controlling the resistance value of the reference resistor Ra. On the other hand, in the amplifier 402 (sensor output processing device) of this embodiment shown in FIG. 5, the voltage applied to the reference resistor Ra connected in series with the shunt resistor Rs (that is, the potential at the point indicated by the symbol P in FIG. 5). ) Can be changed, so that the value of the reference current can be changed.

  5 is the difference from FIG. 2. In this embodiment, a capacitor C2 is connected to the non-inverting input terminal of the operational amplifier OPa, and a transistor TR2 as a switch means is connected via a resistor R5. It is connected. A reference power source Vc is connected to a connection point between the resistor R5 and the transistor TR2 via a resistor R6.

  The switching operation of the transistor TR2 is controlled by the microcomputer 41 (for example, PWM control), and the amount of charge accumulated in the capacitor C2 is adjusted by the control. Specifically, when the transistor TR2 is turned on, the charge of the capacitor C2 and the charge of the reference power supply Vc flow to the ground side via the transistor TR2 (see symbols I3 and I4), and the capacitor C2 is discharged. On the other hand, when the transistor TR2 is turned off, a current flows from the reference power source Vc to the capacitor C2 (see symbol I5), and the capacitor C2 is charged. Therefore, for example, the larger the duty ratio by PWM control (here, the on-duty ratio), the smaller the charge amount of the capacitor C2, and the lower the potential of the non-inverting input terminal of the operational amplifier OPa.

  As described above, the potential of the non-inverting input terminal and the potential of the inverting input terminal of the operational amplifier OPa become the same potential by applying negative feedback. Therefore, by adjusting the charge amount of the capacitor C2, the potential at the connection point P between the shunt resistor Rs and the reference resistor Ra can be adjusted, and as a result, the value of the reference current can be changed.

  In short, the microcomputer 41 PWM-controls the transistor TR2, thereby variably setting the value of the reference current flowing through the shunt resistor Rs. Therefore, the same effect as that of the second embodiment can be obtained in this embodiment.

(Fourth embodiment)
In the first to third embodiments, the NOx sensor 10 having a two-cell structure configured by including the pump cell 31 and the sensor cell 35 is targeted. On the other hand, in this embodiment shown in FIGS. 6 to 8, the NOx sensor 101 having a three-cell structure including the monitor cell 34 in addition to the pump cell 31 and the sensor cell 35 is targeted.

  The monitor cell 34 is arranged side by side at a position close to the sensor cell 35, and is composed of the solid electrolyte body 11, an electrode 36 and a common electrode 38 arranged to face each other with the solid electrolyte body 11 therebetween. Then, after the surplus oxygen is discharged by the pump cell 31 described above, the monitor cell 34 generates a current output in accordance with the electromotive force or voltage application according to the residual oxygen concentration in the second chamber 16. The output of the monitor cell 34 is detected as a monitor cell current Im when a predetermined monitor cell application voltage V0m is applied between the monitor cell electrodes 36 and 38.

  Next, output characteristics of the NOx sensor 101 will be described with reference to FIG.

  FIG. 7 shows the output characteristics (VI characteristics) of the sensor cell 35. The horizontal axis represents the sensor cell applied voltage V0s, and the vertical axis represents the sensor cell current Is. A flat portion parallel to the voltage axis (horizontal axis) is a limit current region for specifying the sensor cell current Is, and an increase or decrease in the sensor cell current Is corresponds to the NOx concentration in the exhaust gas. That is, the sensor cell current Is increases as the NOx concentration in the exhaust gas increases, and the sensor cell current Is decreases as the NOx concentration in the exhaust gas decreases. The sensor cell applied voltage V0s is set at a predetermined value Vα that allows the sensor cell current Is corresponding to a predetermined NOx concentration to be detected in the limit current region (flat region). The slope portion on the lower voltage side than the limit current region is a resistance dominant region, and the slope becomes smaller as the element temperature is lower.

  As shown in FIG. 7, even if the NOx concentration is 0 ppm, the value of the sensor cell current Is does not become zero, but has an offset value (about 5 μA in the example of FIG. 7). This is because the sensor cell 35 detects the residual oxygen adjusted to a predetermined concentration by the pump cell 31 together with NOx, and the residual oxygen concentration corresponds to the offset value. Specifically, this is because the sensor cell 35 detects both oxygen ions generated by decomposing oxygen molecules of residual oxygen and oxygen ions generated by decomposing NOx molecules.

  Although the pump cell 31 adjusts the residual oxygen concentration to a predetermined concentration as described above, the adjustment accuracy is not sufficiently smaller than the NOx concentration detection accuracy by the sensor cell 35. Therefore, in the present embodiment, the monitor cell 34 detects the residual oxygen concentration (offset value). According to this, the microcomputer 41 calculates the NOx concentration with high accuracy by subtracting the monitor cell current Im which is the detection value of the monitor cell 34 from the sensor cell current Is (value of the vertical axis in FIG. 7) which is the detection value of the sensor cell 35. it can.

  Next, the amplifier (sensor output processing device) according to the present embodiment will be described with reference to FIG. In addition, in the figure, the same code | symbol is attached | subjected to the part which is the same as that of each said embodiment, or description is used.

  The sensor cell current Is output from the NOx sensor 101 is converted into a voltage change signal by the shunt resistor Rs and amplified by the operational amplifier OP2, as in the above embodiments. Also, the monitor cell current Im output from the NOx sensor 101 is similar to the circuit components Rsm, OP1m, OP2m, R1m, R2m, R3m, shunt resistor Rs, operational amplifiers OP1, OP2, negative feedback resistors R1, R2, etc. R4m is provided. Therefore, the monitor cell current Im is converted into a voltage change signal by the shunt resistor Rsm and amplified by the operational amplifier OP2m.

  A signal corresponding to the sensor cell current Is amplified by the operational amplifier OP2 is input to the inverting input terminal of the operational amplifier OP3, and a signal corresponding to the monitor cell current Im amplified by the operational amplifier OP2m is passed through the resistor R9. Input to the inverting input terminal. The non-inverting input terminal is grounded via a resistor R10. The difference between these two signals is amplified according to the amplification gain set by the negative feedback resistors R7 and R8, and is output from the output terminal of the operational amplifier OP5 as the “output value of the output circuit”. The output value from the operational amplifier OP5 is input to the A / D conversion port of the microcomputer 41 and subjected to A / D conversion processing. The microcomputer 41 calculates the NOx concentration using the concentration calculation map based on the A / D converted digital signal (output voltage Vd), and outputs the calculated NOx concentration information to the ECU 50 (see FIG. 2).

  Also for the pump cell current Ip output from the NOx sensor 101, circuit components Rsp, OP1p, OP2p, R1p, R2p, R3p, similar to the shunt resistor Rs, operational amplifiers OP1, OP2, negative feedback resistors R1, R2, etc. R4p is provided. Therefore, the pump cell current Ip is converted into a voltage change signal by the shunt resistor Rsp, amplified by the operational amplifier OP2p, and input to the A / D conversion port of the microcomputer 41.

  The microcomputer 41 calculates the oxygen concentration based on the signal from the operational amplifier OP2p corresponding to the pump cell current Ip. Then, the pump cell voltage V0p (see FIG. 1) applied between the electrodes 32 and 33 of the pump cell 31 is controlled according to the calculated oxygen concentration. That is, when the calculated oxygen concentration value is large and it is desired to discharge more oxygen in the exhaust gas introduced into the first chamber 14, the value of the reference voltage Vcc input to the non-inverting input terminal of the operational amplifier OP1p. By lowering, the amount of oxygen discharged by the pump cell 31 is increased. Specifically, the amount of charge accumulated in the capacitor C3 connected to the non-inverting input terminal of the operational amplifier OP1p is controlled by the microcomputer 41 (for example, PWM control) for the switching operation of the transistor TR3, so that the non-inverting of the operational amplifier OP1p. The potential of the input terminal is controlled, thereby controlling the pump cell voltage V0p.

  Incidentally, the operational amplifiers OP4 and OP5 in FIG. 8 are voltage followers for stabilizing the potential of the common electrode 38 of the sensor cell 35 and the monitor cell 34 and the potential of the electrode 32 of the pump cell 31, respectively.

  In the present embodiment, an operational amplifier OPa and a reference resistor Ra similar to the reference current circuit 433 shown in FIG. 2 are provided for the sensor cell current Is. Further, in the present embodiment, a similar operational amplifier OPam and reference resistor Ram are provided for the monitor cell current Im. The microcomputer 41 also switches the switches SW1m and SW2m provided for the monitor cell current Im in synchronization with the operation of the switches SW1 and SW2 when switching between the “sensor output processing mode” and the “measurement mode”.

  In the state switched to the measurement mode, negative feedback is applied to the operational amplifier OPa in the same manner as in the first embodiment, so that the current flowing through the reference resistor Ra regardless of the fluctuation of the sensor cell current Is, that is, the current flowing through the shunt resistor Rs is constant. Adjusted to current. Similarly, by applying negative feedback to the operational amplifier OPam, the current flowing through the reference resistor Ram, that is, the current flowing through the shunt resistor Rsm, regardless of the fluctuation of the monitor cell current Im, is adjusted to a constant reference current. Therefore, the microcomputer 41 can accurately measure the output value from the operational amplifier OP3 with respect to the reference current of both the shunt resistors Rs and Rsm as the correction measurement value. Therefore, the output value deviation correction for the density calculation map can be performed with high accuracy.

(Fifth embodiment)
In the first to fourth embodiments, the sensor output processing device according to the present invention is applied to the NOx sensors 10 and 101, whereas in the present embodiment shown in FIG. This is applied to the A / F sensor 102 for detecting the oxygen concentration (air-fuel ratio: A / F). The structures of the A / F sensor 102 and the amplifier 403 (sensor output processing device) of the present embodiment are basically the same as the NOx sensor 10 and the amplifier 40 of FIG. The differences will be mainly described.

  The detection result of the air-fuel ratio by the A / F sensor 102 is used in an air-fuel ratio control system (not shown) constituted by the engine ECU 50 (see FIG. 2) and the air-fuel ratio detected by the A / F sensor 102 is The air-fuel ratio control system is feedback controlled by the engine ECU 50 so as to achieve the target air-fuel ratio. Note that stoichiometric air-fuel ratio control in which the target air-fuel ratio is in the vicinity of stoichiometric, lean air-fuel ratio control in which the target air-fuel ratio is a predetermined lean region, and the like are appropriately realized. Therefore, in the present embodiment, the A / F sensor 102 that can detect the air-fuel ratio in a wide range from the rich region (for example, A / F11) to the atmospheric state is employed.

  The A / F sensor 102 according to this embodiment has a two-cell structure similar to the NOx sensor 10 of FIG. 1, and the sensor cell current Is and the pump cell current Ip are input from the A / F sensor 102 to the amplifier 403. The The sensor cell current Is input to the amplifier 403 is converted into a voltage change signal by the shunt resistor Rs of the current-voltage conversion circuit 431, amplified by the differential amplifier circuit 432, and input to the A / D conversion port of the microcomputer 41. The The microcomputer 41 calculates the air-fuel ratio based on the A / D converted digital signal (output voltage), and the calculated air-fuel ratio information is output to the ECU 50 (see FIG. 2).

  The amplifier 403 includes an electromotive force monitor circuit and a voltage application circuit 434. The electromotive force monitoring circuit is a circuit that monitors the electromotive force generated in the sensor cell, that is, the sensor voltage corresponding to the sensor cell current Is converted by the shunt resistor Rs, and the voltage application circuit is configured to monitor the electromotive force (sensor The pump cell voltage V0p applied between the electrodes 32 and 33 (see FIG. 1) of the pump cell 31 is controlled according to the voltage. However, if the A / F sensor 102 is applied to an air-fuel ratio control system that does not perform lean air-fuel ratio control, and only assumes that the stoichiometric air-fuel ratio control is performed, the control of the pump cell voltage V0p is abolished. The voltage V0p may be fixed.

  In the present embodiment, an operational amplifier OPa and a reference resistor Ra similar to the reference current circuit 433 shown in FIG. 2 are provided for the sensor cell current Is. The microcomputer 41 switches the operation of the amplifier 40 to the “sensor output processing mode” by turning on the switch SW1 and turning off the switch SW2, and turns on the switch SW2 and turning on the switch SW2. Switch.

  In the “sensor output processing mode”, the operational amplifier OP1 functions to stabilize the potential of the shunt resistor Rs on the A / F sensor 102 side at a constant potential, and also causes the reference current circuit 433 to flow the reference current to the shunt resistor Rs. The function will be stopped. Therefore, the value of the current flowing through the shunt resistor Rs varies according to the variation of the sensor cell current Is (detection signal) according to the air-fuel ratio. Therefore, the air-fuel ratio can be calculated according to the detected sensor cell current Is.

  In the “measurement mode”, the above-described function of the operational amplifier OP1 is stopped, and the reference current circuit 433 functions to adjust the current flowing through the shunt resistor Rs to the reference current. That is, the current flowing through the shunt resistor Rs is adjusted to be stable at a constant reference current regardless of the fluctuation of the sensor cell current Is (detection signal) according to the air-fuel ratio. As described above, also in the present embodiment, the same effects as in the first embodiment are exhibited.

(Other embodiments)
The above embodiments may be implemented with the following modifications. Further, the present invention is not limited to the description of the above embodiment, and the characteristic configurations of the respective embodiments may be arbitrarily combined. For example, as in the second and third embodiments, the configuration that allows the value of the reference current to flow through the shunt resistor Rs to be changed can be applied to the fourth embodiment.

  -Although the A / F sensor 102 concerning the said 5th Embodiment is a 2 cell type provided with a pump cell and a sensor cell, the 1 cell type which abolished the pump cell and comprised with the sensor cell may be sufficient.

  In each of the above embodiments, the NOx sensors 10 and 101 and the A / F sensor 102 are applied to the sensor according to the present invention. However, a current that is converted into a current change and is output as a detection signal by converting a physical quantity change to be sensed If it is an output type sensor, the sensor of this invention is not restricted to these sensors.

  In each of the above embodiments, the concentration calculation map is corrected (learned) based on the difference between the theoretical value with respect to the reference current and the correction measurement value, and the NOx concentration is calculated from the output voltage Vd using the map. However, the ECU 50 may perform map correction and density calculation based on the output voltage Vd.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows the outline of a NOx sensor to which the amplifier (sensor output processing apparatus) concerning 1st Embodiment of this invention is applied. The figure which shows the structure of the amplifier shown by FIG. (A) and (b) are diagrams for explaining density calculation according to the first embodiment, and (c) and (d) are figures for explaining density calculation according to the first embodiment. The figure which shows the structure of the amplifier concerning 2nd Embodiment of this invention. The figure which shows the structure of the amplifier concerning 3rd Embodiment of this invention. The lineblock diagram showing the outline of the NOx sensor to which the amplifier concerning a 4th embodiment of the present invention is applied. The figure which shows the output characteristic of the NOx sensor shown by FIG. The figure which shows the structure of the amplifier shown by FIG. The figure which shows the structure of the amplifier concerning 5th Embodiment of this invention. The figure which shows the structure of the sensor output processing apparatus compared with this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,101 ... NOx sensor, 102 ... A / F sensor, 40 ... Amplifier (sensor output processing device), 41 ... Microcomputer, 431 ... Current-voltage conversion circuit (output circuit), 432 ... Amplifier circuit (output circuit), 433: Reference current circuit, Rs: Shunt resistor, SW1, SW2: Switch (switching circuit).

Claims (9)

It is applied to a current output type sensor that converts a physical quantity change to be sensed into a current change and outputs it as a detection signal.
An output circuit having a shunt resistor for converting the detection signal into a voltage change signal, and outputting a voltage change signal converted by the shunt resistor;
A reference current circuit for adjusting a current flowing through the shunt resistor to a constant reference current regardless of fluctuations in the detection signal;
A sensor output processing mode in which the adjustment function by the reference current circuit is stopped and the value of the current flowing through the shunt resistor is changed in accordance with a change in the detection signal, and a measurement in which the adjustment function by the reference current circuit is activated. A switching circuit for switching between modes,
A sensor output processing apparatus comprising:   2. The sensor according to claim 1, wherein the reference current circuit is a circuit configured to output an inversion current having a value corresponding to the fluctuation to the shunt resistor so as to cancel the fluctuation of the detection signal. Output processing device. An output terminal of an operational amplifier provided in the reference current circuit is connected to the sensor side of the shunt resistor,
The input terminal of the operational amplifier is connected to the anti-sensor side of the shunt resistor,
The sensor output processing apparatus according to claim 2, wherein the inverted current is output from the output terminal by performing a negative feedback operation of the operational amplifier.   The sensor output processing device according to claim 1, wherein the reference current circuit is configured to be able to change a value of the reference current.   5. The sensor output process according to claim 4, wherein the reference current circuit is configured to change a value of the reference current by changing a resistance value of a reference resistor connected in series to the shunt resistor. apparatus.   The sensor according to claim 4 or 5, wherein the reference current circuit changes a value of the reference current by changing a voltage applied to a reference resistor connected in series to the shunt resistor. Output processing device. The sensor includes a pump cell that adjusts the amount of oxygen in the gas to be detected introduced into the gas chamber to a predetermined concentration level, and a sensor cell that detects the concentration of a specific component from the gas after adjusting the amount of oxygen in the pump cell. Has been
The sensor output processing device according to claim 1, wherein the detection signal is a sensor cell current value output from the sensor cell in accordance with a concentration of the specific component. Learning means for learning a difference between an output value of the output circuit with respect to the reference current and a theoretical value with respect to the reference current;
Correction means for correcting the output value of the output circuit in the sensor output processing mode based on the learning value by the learning means;
The sensor output processing apparatus according to claim 1, wherein the sensor output processing apparatus includes:   A sensor output processing system comprising the sensor output processing device according to claim 1 and the sensor.

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