JP4659632B2 - SENSOR CONTROL DEVICE, GAS SENSOR SYSTEM, SENSOR CONTROL DEVICE CONTROL METHOD, AND CONCENTRATION INFORMATION FOR DETECTING CONCENTRATION GAS COMPONENT - Google Patents

Description

  The present invention relates to a sensor control device that outputs a concentration signal related to the concentration of a specific gas component by using a detection current corresponding to the concentration of the specific gas component (for example, oxygen) obtained by operating a gas sensor element. The present invention relates to a conventional gas sensor system, a control method for such a sensor control device, and a method for detecting concentration information relating to a specific gas component.

  As the exhaust gas regulations of automobiles become stricter year by year, precise air-fuel ratio control of internal combustion engines is required. For this reason, higher detection accuracy is required for the exhaust gas sensor and its control device. In general, an internal combustion engine using a three-way catalyst currently used in many gasoline automobiles has the highest catalyst efficiency when operated at a stoichiometric air-fuel ratio, and the purification efficiency of harmful exhaust gas is high. Therefore, how close to the stoichiometric air-fuel ratio can control the operation becomes important for making the exhaust gas low pollution.

  As an oxygen sensor used for such control, in general, a λ sensor that emits a binary sensing output corresponding to the oxygen concentration in the exhaust gas, and a sensing output that maintains linearity over a wide range of oxygen concentration All-region oxygen sensors that emit light are known. In particular, the full-range oxygen sensor can perform air-fuel ratio control with high accuracy. In addition to the stoichiometric combustion control in which the air-fuel ratio is feedback-controlled in the vicinity of the stoichiometric air-fuel ratio, the all-region oxygen sensor can accurately perform lean combustion control in which the air-fuel ratio is feedback-controlled in a predetermined lean region.

  In general, the entire region oxygen sensor uses a detection current corresponding to the oxygen concentration in the exhaust gas as a sensing output. For this reason, the sensor control device detects the current value of the detected current at the first stage. For example, Patent Documents 1 and 2 disclose specific means of the current detection unit. That is, in these conventional techniques, a detection current from the gas sensor element is passed through a detection resistor, and a voltage at both ends of the detection resistor is differentially amplified in a differential amplifier circuit to obtain a voltage output corresponding to the detection current. ing.

Japanese Patent Laid-Open No. 1-152356 JP 2004-205488 A

  However, in the differential amplifier circuit as described above, characteristic variations due to variations in characteristics of elements in the circuit and temperature characteristics thereof are unavoidable. Therefore, in order to perform engine control with higher accuracy, it is desirable to eliminate the influence of such factors.

  The present invention has been made in view of such a situation, and a sensor control device capable of acquiring concentration information related to a specific gas component with high accuracy from a concentration signal related to the concentration of the specific gas component such as oxygen, and the like. It is an object of the present invention to provide a sensor system using a sensor, a control method for a sensor control device, and a method for detecting concentration information regarding a specific gas component.

  The solution is a sensor control device that outputs a concentration signal related to the concentration of the specific gas component by using a detection current corresponding to the concentration of the specific gas component obtained by operating the gas sensor element. A differential amplifier that differentially amplifies the first input voltage input to the input terminal and the second input voltage input to the second input terminal, and a first detection voltage at one end of the detection resistor through which the detection current flows The first input voltage, the second detection voltage at the other end of the detection resistor as the second input voltage, the first reference voltage as the first input voltage, and the second reference voltage as the second input voltage. A sensor control device including a first switch for switching between input voltage and input voltage.

  In the sensor control device of the present invention, the first switch causes the first detection voltage at one end of the detection resistor to be the first input voltage and the second detection voltage at the other end of the detection resistor to be the second input voltage. Since the differential amplifier amplifies the voltage across the detection resistor, an output voltage corresponding to the detection current of the gas sensor element can be obtained from the differential amplifier. The sensor control device outputs the output voltage or a signal corresponding thereto as a concentration signal. By using this concentration signal, it is possible to detect the concentration information relating to the specific gas such as the concentration of the specific gas such as the oxygen concentration and the air-fuel ratio.

On the other hand, when the known first reference voltage is set as the first input voltage and the known second reference voltage is set as the second input voltage by the first switch, the differential amplifying unit uses the first and second reference voltages. Since the difference is amplified, the sensor control device outputs an output voltage obtained by amplifying the difference or a signal (reference amplification signal) corresponding to the output voltage. Therefore, by using this signal (reference amplification signal), it is possible to know the actual amplification factor of the differential amplifier at that time. Thus, by acquiring the actual amplification factor of the differential amplifier when the sensor control device is activated, more accurate concentration information on the specific gas is obtained from the concentration signal based on this amplification factor. It becomes possible.
Therefore, even when the amplification factor of the differential amplifier varies due to variations in circuit element characteristics, it is possible to detect concentration information regarding a specific gas with higher accuracy than in the past. In addition, even if there is a gain drift caused by a temperature change of the differential amplifier, a gain change due to deterioration over time, etc., the concentration information on the specific gas is accurately detected without being affected by these changes. Can be detected.

  In detecting concentration information related to a specific gas component, in addition to a method for calculating concentration information using the actual amplification factor itself obtained based on the reference amplification signal, an amplification factor (design value) to be originally obtained. It is also possible to take a method of obtaining concentration information reflecting the actual amplification factor by calculating the concentration information once using the amplification factor and correcting the obtained information using the actual amplification factor obtained. .

In addition, as a gas sensor element that outputs a detection current corresponding to the concentration of a specific gas component, a stacked gas sensor element of two or more cells including at least a pump cell and an electromotive force cell can be exemplified, and control is performed by a so-called limit current method. A one-cell type gas sensor element is also included.
Examples of the differential amplifying unit include a differential amplifying circuit composed of individual components such as a bipolar transistor, a MOS transistor, and a resistor. Further, a differential amplifier circuit configured with an operational amplifier and a resistor, a differential amplifier circuit configured with an operational amplifier circuit and a resistor configured in an ASIC, and the like can be given. A differential amplifier circuit using an operational amplifier is preferable because it allows easy setting of an amplification factor, setting of an offset voltage, and configuration of a negative feedback circuit.
Further, the amplification factor may be appropriately selected in consideration of the magnitude of the obtained first and second detection voltages. In addition to the case where it exceeds x1, the case where it is x1 or below x1 There is also a possibility.
In addition, an appropriate switch element such as a relay can be used as the first switch. However, in consideration of durability and the like, it is preferable to use a semiconductor switch using a semiconductor element such as an FET. The same applies to the second switch described later.

The sensor control device in the present specification only needs to include the above-described differential amplifying unit and the first switch, and does not need to include a detection resistor in the sensor control device. The same applies to components constituting a reference voltage power supply unit, which will be described later, and resistors and capacitors for determining control constants of the PID control circuit shown in the embodiment. Accordingly, when assuming that the sensor control device is configured on a single member, for example, an ASIC or hybrid IC formed on a single substrate (chip) and not including a detection resistor or the like is assumed. Can do.
On the other hand, a sensor control device can be formed as a whole by using parts such as a detection resistor and a reference voltage power supply unit as external parts such as the ASIC. Furthermore, as an example in which these are integrated members, a board in which an external component such as a differential amplifying unit, an ASIC including a first switch, and a component constituting a detection resistor and a reference voltage power supply unit are mounted on the same substrate. And hybrid ICs.

  Further, in the above sensor control device, the reference voltage power supply unit outputs the first reference voltage and the second reference voltage, and the second reference voltage is divided by a voltage dividing resistor. The sensor control device may be a reference voltage or a reference voltage power supply unit that divides a predetermined voltage with a voltage dividing resistor to obtain the first reference voltage and the second reference voltage.

  If such a reference voltage power supply unit is provided, two voltages (first and second reference voltages) as a reference can be easily obtained. In addition, when the reference voltage power supply unit outputs the first reference voltage and the second reference voltage obtained by dividing the first reference voltage by the voltage dividing resistor, even if the first reference voltage fluctuates, the fluctuation occurs. Accordingly, since the second reference voltage varies in the same direction, the influence of the variation can be reduced. Similarly, when the reference voltage power supply unit outputs the first and second reference voltages obtained by dividing the predetermined voltage by the voltage dividing resistors, even if the predetermined voltage fluctuates, Since the first and second reference voltages fluctuate in the same direction, the influence of the fluctuation of the predetermined voltage can be reduced in this case as well.

  Furthermore, in the above sensor control device, the accuracy of the resistance value of the voltage dividing resistor is higher than the accuracy of the resistance value of the resistor involved in determining the amplification factor of the differential amplifier. It may be a control device.

  As described above, when the accuracy of the resistance value of the voltage dividing resistor used for voltage division in the reference voltage power supply unit is increased, accurate voltage values of the first and second reference voltages are obtained. When the accurate first and second reference voltages are input to the differential amplifier and amplified as described above, an error in the amplification factor of the differential amplifier can be accurately detected from the output voltage.

  Furthermore, in the sensor control device according to any one of the above, the differential amplification unit differentially amplifies the first input voltage and the second input voltage different from each other, and the differential amplification unit It is preferable that the sensor control device includes a second switch for switching to a state in which only the offset voltage is output.

  In the sensor control device of the present invention, the differential amplifier unit is configured to differentially amplify the first input voltage and the second input voltage different from each other by switching the second switch, that is, in a state where normal differential amplification is possible. In addition, a state in which only the offset voltage of the differential amplifier is output can be selected.

Therefore, a differential signal corresponding to the detected current of the gas sensor element can be obtained by differentially amplifying the first input voltage and the second input voltage by the differential amplifier.
On the other hand, by setting only the offset voltage of the differential amplifier to be output, the sensor control device outputs this offset voltage or a signal (offset signal) corresponding thereto. Therefore, if this signal (offset signal) is used, the actual offset voltage of the differential amplifier at that time can be known.
Thus, by acquiring the actual offset voltage of the differential amplifying unit when the sensor control device is activated, the concentration signal is obtained based on this offset voltage together with the gain obtained as described above. Thus, it is possible to obtain more accurate concentration information on the specific gas component.
In addition, even if the offset voltage drifts due to the temperature change of the differential amplifier, etc., or the offset voltage changes due to deterioration over time, etc., it can be accurately identified without being affected by this change. Concentration information regarding the gas component can be detected.

  In detecting the concentration information regarding the specific gas component, there is a method of calculating the concentration information using the actual offset voltage itself obtained. In addition, the density information is once calculated using the offset voltage (offset voltage as a design value) that should be obtained, and corrected by using the actual offset voltage thus obtained. It is also possible to take a technique for obtaining density information reflecting the offset voltage.

Further, in this specification, the offset voltage refers to a voltage value of an output signal that is output when an equal input is made to the first input terminal and the second input terminal of the differential amplifier.
Therefore, for example, when the first input terminal and the second input terminal of the differential amplifier are short-circuited with each other, only the offset voltage is output from the differential amplifier. The relationship between the first and second input voltages and the output voltage in the differential amplifier is a relationship of output voltage = (first input voltage−second input voltage) × amplification factor + offset voltage.
Further, in order for the differential amplifier to be in a state in which only its own offset voltage is output, a circuit that can forcibly equalize the first input voltage and the second input voltage that are substantially differentially amplified. May be provided. For example, in the case where an operational amplifier circuit and a passive component such as a resistor for determining the amplification factor are used in the differential amplifier, the input resistors connected to the inverting input terminal and the non-inverting input terminal of the operational amplifier circuit, respectively. Among them, there is a circuit configuration in which a short circuit that short-circuits the ends opposite to the operational amplifier is provided.

That is, in the sensor control device, the differential amplification unit includes an operational amplifier circuit, a first input resistor connected to an inverting input terminal of the operational amplifier circuit and transmitting the first input voltage, and the operational amplifier circuit. A second input resistor connected to a non-inverting input terminal and transmitting the second input voltage, wherein the second switch is opposite to the operational amplifier of the first input resistor and the second input resistor. It is preferable to use a sensor control device that opens and closes a short circuit that short-circuits the end portions on the side.
The sensor control device configured as described above has a simple configuration in which a short circuit and a second switch for opening and closing the short circuit are provided, and the second switch allows the differential amplifying unit to be connected to a first input voltage and a second input different from each other. It is possible to switch between a state in which the voltage is differentially amplified and a state in which only the offset voltage of the differential amplifier is output.

  Still another solution is a gas sensor system comprising the sensor control device according to any one of the above and the gas sensor element.

In the gas sensor system of the present invention, the sensor control device includes a first switch. Therefore, by switching the first switch, the differential amplifier obtains an output voltage corresponding to the first and second detection voltages, and accordingly corresponding to the detection current, and using this or a concentration signal corresponding to this, a specific gas is obtained. Concentration information about the component can be detected.
In addition, by switching the first switch, the first and second reference voltages are input to the differential amplifying unit, so that signals corresponding to the first and second reference voltages and the amplification factor of the differential amplifying unit (reference (Amplified signal) can be output. Since the first and second reference voltages are known, the amplification factor at that time of the differential amplifier can be known from this signal.
Therefore, even if there is a change in the amplification factor of the differential amplification unit due to drift of the amplification factor caused by temperature change of the differential amplification unit, deterioration over time, etc., the amplification factor obtained as described above should be used. Thus, it is possible to detect the concentration information regarding the specific gas component with high accuracy without being affected by the change in the amplification factor.

  Another solution is a sensor control device that outputs a concentration signal related to the concentration of the specific gas component using a detection current corresponding to the concentration of the specific gas component obtained by operating the gas sensor element. A differential amplifier for differentially amplifying the first input voltage input to the first input terminal and the second input voltage input to the second input terminal; and a first one of the detection resistors through which the detection current flows The detection voltage is the first input voltage, the second detection voltage at the other end of the detection resistor is the second input voltage, the first reference voltage is the first input voltage, and the second reference voltage is And a first switch for switching between the second input voltage and the second input voltage, wherein the first reference voltage is the first input voltage, and the second reference voltage is the first input voltage. 2 input voltage from above sensor control device A reference signal output step for outputting a reference amplification signal corresponding to the first reference voltage, the second reference voltage, and the amplification factor of the differential amplifier; the first detection voltage as the first input voltage; And a density signal output step of outputting the density signal from the sensor control apparatus using the two detection voltages as the second input voltage.

  According to the control method of the sensor control device of the present invention, in the reference signal output step, the first reference voltage is the first input voltage, the second reference voltage is the second input voltage, and the amplification factor of the differential amplifier is increased. A corresponding reference amplification signal is output. Thereby, the amplification factor of the differential amplifier at this time can be known. In the concentration signal output step, the concentration signal is output using the first detection voltage as the first input voltage and the second detection voltage as the second input voltage. Therefore, in detecting the concentration information regarding the specific gas component using this concentration signal, the concentration information regarding the specific gas component such as the oxygen concentration can be detected more accurately in consideration of the amplification factor of the differential amplifier. .

  Further, in the control method of the sensor control device described above, the reference signal output step may be a control method of the sensor control device that is performed at a stage before activation of the gas sensor element.

In the control method of the present invention, the reference signal output step is performed before the activation of the gas sensor element. As a result, since the amplification factor of the differential amplifier can be acquired in advance, the concentration information on the specific gas component can be accurately obtained using the concentration signal and the amplification factor by performing the concentration signal output step after the gas sensor element is activated. Can be acquired immediately.
As a method for detecting whether or not the gas sensor element is before activation, any known method that can appropriately detect whether or not the gas sensor element is before activation can be employed. For example, before activation, using the energization time and integrated power amount from the start of energization to the heater for heating the gas sensor element, the change in potential appearing at each terminal of the gas sensor element, the temperature of the cooling water for cooling the engine, etc. It can be determined whether or not. More specifically, for example, in a gas sensor element having a pump cell and an electromotive force cell, there is a method of detecting whether or not the internal impedance of any one of the cells is activated.

  Furthermore, it is preferable that the control method of the sensor control device according to any one of the above, wherein the reference signal output step is a control method of the sensor control device that is periodically performed after the gas sensor element is activated.

In general, the amplification factor of the differential amplifier is not always constant. For example, it varies with time, such as fluctuating depending on the ambient temperature.
On the other hand, in the control method of the sensor control apparatus of the present invention, the reference signal output step is periodically performed after the activation of the gas sensor element. For this reason, even if the amplification factor of the differential amplification unit changes, the concentration information regarding the specific gas component can always be detected with high accuracy by using the periodically obtained amplification factor and the concentration signal.
In addition, what is necessary is just to set suitably as an space | interval which performs a reference signal output step by the environment etc. which use a gas sensor element and a sensor control apparatus.

  Furthermore, in the control method for a sensor control device according to any one of the above, when the reference signal output step does not need to output the concentration signal from the sensor control device after activation of the gas sensor element. It is good to use the control method of the sensor control apparatus to perform.

  In the control method of the present invention, the reference signal output step is performed when it is not necessary to output a concentration signal from the sensor control device after activation of the gas sensor element. By doing in this way, even if the period is a period in which the concentration information related to the specific gas needs to be detected, the concentration signal cannot be output from the sensor control device by performing the reference signal output step. Can be eliminated. Thereby, the concentration information regarding the specific gas component can be detected at an appropriate time, and engine control or the like can be appropriately performed.

  In addition, when it is not necessary to output a concentration signal from the sensor control device, although it depends on the application and environment in which the gas sensor element and the sensor control device are used, for example, there is a period before the gas sensor element is activated. Further, for example, when a gas sensor element and a sensor control device are mounted on an automobile and the oxygen concentration and air-fuel ratio in exhaust gas are measured using these, when the driver releases the accelerator during driving (engine braking) Time). In this case, since fuel is not injected into the engine, it is not necessary to measure the oxygen concentration or the air-fuel ratio.

  Further, in the control method of the sensor control device according to any one of the above, the sensor control device may cause the differential amplifying unit to perform the first input voltage and the second input voltage having different values. And a second switch that switches between a state in which only the offset voltage of the differential amplifier is output, and an offset signal corresponding to the offset voltage of the differential amplifier from the sensor control device. A sensor control device control method including an offset signal output step to output is preferable.

According to the control method of the present invention, in the offset signal output step, the offset voltage is output from the differential amplifier, and the offset signal is output from the sensor control device. Since the offset voltage of the differential amplifying unit can be known from this offset signal, it is even higher if these values are used together with the above-described amplification factor when detecting concentration information regarding a specific gas component from the concentration signal. The concentration of the specific gas component can be obtained with accuracy.
The offset signal output step is preferably performed before or after the above-described reference signal output step. This is because it is preferable to obtain the amplification factor and the offset voltage of the differential amplifier at the same time.

  Further, in the control method of the sensor control device described above, the offset signal output step may be a control method of the sensor control device that is performed at a stage before the activation of the gas sensor element.

  In the control method of the present invention, the offset signal detection step is performed before the activation of the gas sensor element. As a result, the offset voltage of the differential amplification unit can be acquired in advance. Therefore, after the gas sensor element is activated, the offset signal output step is performed, so that the specific gas component is obtained using the concentration signal, the amplification factor, and the offset voltage. Concentration information on can be obtained accurately and immediately.

  Furthermore, in any of the above-described sensor control device control methods, it is preferable that the offset signal output step is a sensor control device control method that is periodically performed after the gas sensor element is activated.

In general, the offset voltage of the differential amplifying unit is not always constant. For example, it varies with time, such as fluctuating depending on the ambient temperature.
On the other hand, in the control method of the sensor control apparatus of the present invention, the offset signal output step is periodically performed after the gas sensor element is activated. For this reason, even if the offset voltage of the differential amplifying unit changes, the offset voltage acquired periodically, the amplification factor and the concentration signal described above are used, and the specific gas component is always highly accurate. Concentration information can be detected.
In addition, what is necessary is just to set suitably as the space | interval which performs an offset signal output step by the environment etc. which use a gas sensor element and a sensor control apparatus.

  Furthermore, in the control method of the sensor control device according to any one of the preceding two items, the offset signal output step does not need to output the concentration signal from the sensor control device after the gas sensor element is activated. It may be a sensor control device control method that is sometimes performed.

  In the control method of the present invention, the offset signal output step is performed when it is not necessary to output a concentration signal from the sensor control device after activation of the gas sensor element. By doing so, the concentration signal cannot be output from the sensor control device by performing the offset signal output step even though the period is a period in which the concentration information related to the specific gas needs to be detected. Can be eliminated. Thereby, the concentration information regarding the specific gas component can be detected at an appropriate time, and engine control or the like can be appropriately performed.

  Still another solution is a sensor control that outputs a concentration signal related to the concentration of the specific gas component using a gas sensor element and a detection current corresponding to the concentration of the specific gas component obtained by operating the gas sensor element. A differential amplifier for differentially amplifying a first input voltage input to a first input terminal and a second input voltage input to a second input terminal, and a detection resistor through which the detection current flows A first detection voltage at one end of the detection resistor as the first input voltage, a second detection voltage at the other end of the detection resistor as the second input voltage, and a first reference voltage as the first input voltage, A sensor control device having a first switch for switching between a case where a second reference voltage is the second input voltage, and a method for detecting concentration information regarding a specific gas component using the sensor control device, wherein the first reference voltage is First input voltage, before Using the second reference voltage as the second input voltage, the sensor control device outputs a reference amplification signal corresponding to the first reference voltage, the second reference voltage, and an amplification factor of the differential amplifier, and the differential An amplification factor detection step for detecting an amplification factor of the amplification unit, the first detection voltage as the first input voltage, the second detection voltage as the second input voltage, and the concentration signal output from the sensor control device And a concentration information detection step of detecting concentration information related to the specific gas component using the amplification factor.

According to the concentration information detection method relating to the specific gas component of the present invention, in the amplification factor detection step, the first reference voltage is set as the first input voltage, and the second reference voltage is set as the second input voltage. A reference amplification signal corresponding to the amplification factor of the dynamic amplification unit is output. Then, using this reference amplification signal, the amplification factor at that time of the differential amplifier is detected.
Further, in the concentration information detection step, a concentration signal is output from the sensor control device with the first detection voltage as the first input voltage and the second detection voltage as the second input voltage. And the density information regarding a specific gas component is detected using the amplification factor of the differential amplification part already obtained. Thereby, the concentration information regarding the specific gas component can be detected more accurately.

  In the density information detection step, a method of calculating density information using the actual amplification factor itself obtained in the amplification factor detection step can be used. In addition to this, by calculating the concentration information once using the amplification factor (amplification factor as a design value) that should be originally obtained, and correcting this using the actual amplification factor obtained, A technique for obtaining concentration information reflecting the amplification factor can also be taken.

  Furthermore, in the above-described concentration information detection method for the specific gas component, it is preferable that the amplification factor detection step be a concentration information detection method for the specific gas component that is performed before the activation of the gas sensor element.

  In the concentration information detection method of the present invention, the amplification factor detection step is performed before the activation of the gas sensor element. As a result, the amplification factor of the differential amplifying unit can be acquired in advance. Therefore, after the gas sensor element is activated, the concentration information detection step is performed, so that the concentration information regarding the specific gas component is accurately obtained using the concentration signal and the amplification factor. And can be obtained immediately.

  Further, in any one of the above-described detection methods for concentration information relating to the specific gas component, the amplification factor detection step may be performed periodically after the activation of the gas sensor element. It is preferable to do this.

  In the concentration information detection method of the present invention, the amplification factor detection step is periodically performed after activation of the gas sensor element. By doing in this way, the concentration information regarding a specific gas component can always be detected with high accuracy in the concentration information detection step using the periodically obtained amplification factor.

  Furthermore, in the method for detecting concentration information relating to the specific gas component according to any one of the above, the amplification factor detection step needs to output the concentration signal from the sensor control device after activation of the gas sensor element. It is preferable to use a method for detecting concentration information regarding a specific gas component that is performed when no gas is present.

  In the concentration information detection method of the present invention, the amplification factor detection step is performed when it is not necessary to output a concentration signal from the sensor control device after activation of the gas sensor element. By doing so, the concentration signal is not output from the sensor control device by performing the amplification factor detection step even though the period is a period in which the concentration information related to the specific gas needs to be detected. It is possible to eliminate the situation where the concentration information regarding the specific gas cannot be detected appropriately. Thereby, engine control etc. can be performed appropriately.

  Furthermore, in the method for detecting concentration information related to the specific gas component according to any one of the above, the sensor control device is configured to change the differential amplifier unit between the first input voltage and the second input voltage that are different from each other. A second switch for switching between a state of differentially amplifying the signal and a state in which only the offset voltage of the differential amplifier is output, and the sensor control device outputs an offset signal corresponding to the offset voltage of the differential amplifier And detecting the offset voltage of the differential amplifier, the concentration information detecting step is for detecting the concentration information on the specific gas component based on the amplification factor and the offset voltage. It is preferable to use a method for detecting concentration information regarding gas components.

According to the concentration information detection method of the present invention, in the offset detection step, the offset voltage is output from the differential amplifier and the offset signal is output from the sensor control device. Then, the offset voltage of the differential amplifier is detected using this offset signal.
Further, in the concentration information detection step, concentration information relating to the specific gas component is detected based on the amplification factor and the offset voltage.
Thereby, it is possible to detect the concentration information regarding the specific gas component with higher accuracy in consideration of not only the amplification factor of the differential amplifier but also the offset voltage.

  In the density information detection step, it is possible to take a method of calculating density information using the actual offset voltage itself obtained in the offset detection step. In addition, the density information is once calculated using the offset voltage (offset voltage as a design value) that should be obtained, and corrected by using the actual offset voltage thus obtained. It is also possible to take a technique for obtaining density information reflecting the offset voltage.

  Further, in the concentration information detection method regarding the specific gas component described above, it is preferable that the offset detection step is a concentration information detection method regarding the specific gas component performed at a stage before the activation of the gas sensor element.

  In the concentration information detection method of the present invention, the offset detection step is performed before the gas sensor element is activated. As a result, the offset voltage of the differential amplifying unit can be acquired in advance. After the gas sensor element is activated, the concentration information detection step is performed, and this offset voltage, the concentration signal, and the amplification factor described above are used to specify the offset voltage. Concentration information on gas components can be obtained accurately and immediately.

  The concentration information detection method for specific gas components according to any one of the preceding two items, wherein the offset detection step is periodically performed after the gas sensor element is activated. Is preferable.

The offset voltage of the differential amplifying unit also has a temperature characteristic as in the case of the amplification factor, and therefore changes with the temperature around the differential amplifying unit.
On the other hand, in the concentration information detection method of the present invention, the offset detection step is periodically performed after activation of the gas sensor element. By doing in this way, the density | concentration information regarding a specific gas component can always be detected with a high precision using the offset voltage of the differential amplification part acquired periodically, and the above-mentioned amplification factor.

  Furthermore, in the method for detecting concentration information on the specific gas component according to any one of the preceding three items, the offset detection step needs to output the concentration signal from the sensor control device after activation of the gas sensor element. It is preferable to use a method for detecting concentration information regarding a specific gas component that is performed when no gas is present.

  In the concentration information detection method of the present invention, the offset detection step is performed when it is not necessary to output a concentration signal from the sensor control device after activation of the gas sensor element. By doing so, the concentration signal cannot be output from the sensor control device by performing the offset detection step even though the period is a period in which the concentration information related to the specific gas needs to be detected. In addition, it is possible to eliminate the situation where the concentration information regarding the specific gas cannot be detected. Thereby, engine control etc. can be performed appropriately appropriately.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
An equivalent circuit diagram of the gas sensor system 10 according to the present embodiment is shown in FIG. The gas sensor system 10 includes a gas sensor element 160, a sensor control device 100, and an engine control device 150.
Among these, the gas sensor element 160 is an air-fuel ratio sensor that has a configuration that will be described later, is attached to an exhaust pipe of an engine (not shown), and flows a detection current Ip corresponding to the oxygen concentration (air-fuel ratio) in the exhaust gas.

In addition to the control circuit 110 configured as an ASIC, the sensor control apparatus 100 sets the control constants of the reference voltage power supply unit 140, the detection resistor Rd, the resistor R1, and the PID control circuit 123 that are externally attached thereto. Resistors R2 to R4 and capacitors C1 to C3 are provided, and these are mounted on one board. The sensor control device 100 (control circuit 110) controls the gas sensor element 160 based on an instruction from the engine control device 150, and directs the concentration signal SC or the like corresponding to the oxygen concentration (air-fuel ratio) to the engine control device 150. Output.
The engine control device 150 detects the oxygen concentration (air-fuel ratio) in the exhaust gas using the concentration signal SC output from the sensor control device 100 (control circuit 110), and controls a gasoline engine (not shown).

  In the present embodiment, although externally attached, the reference voltage power supply unit 140, the detection resistor Rd, the resistor R1, or any or all of the resistors R2 to R4 and the capacitors C1 to C3 are appropriately controlled. The circuit 110 and the circuit 110 may be housed in one substrate.

As shown in FIG. 1, the gas sensor element 160 and the control circuit 110 are electrically connected at terminals Vs +, COM, Ip + of the gas sensor element 160 and terminals VS +, Vcent, IP + of the control circuit 110, respectively. Yes.
Further, the control circuit 110 and the engine control device 150 can transmit signals between the terminals VIP and CI of the control circuit 110 and the terminals AD and CT of the engine control device 150, respectively. Further, the control circuit 110 and the engine control device 150 are electrically connected to the terminals CC5 and G-VIPAL of the control circuit 110 and the terminal VCCA of the engine control device 150 via the reference voltage power supply unit 140. .

  The gas sensor element 160 has a configuration in which a pump cell 163 and an electromotive force cell 165 are stacked via a spacer that forms a hollow measurement chamber into which exhaust gas can be introduced, and faces the measurement chamber of the electromotive force cell 165. It has a known structure in which an electrode located on the opposite side to the side is closed by a shielding layer. Each of the pump cell 163 and the electromotive force cell 165 has a plate-like solid electrolyte having oxygen ion conductivity as a base, and electrodes are formed of porous platinum on both surfaces thereof. One end (left end in the figure) of the electrode of the pump cell 163 and one end (right end in the figure) of the electromotive force cell 165 are electrically connected to each other and are connected to a terminal COM that is an output terminal of the gas sensor element 160. The other end (right end in the figure) of the electrode of the pump cell 163 is connected to the terminal Ip + which is an output terminal of the gas sensor element 160, and the other end (left end in the figure) of the electromotive force cell 165 is connected to the terminal of the gas sensor element 160. It is connected to the terminal Vs +.

  The sensor control apparatus 100 allows the pump cell current (flowing through the pump cell 163 so that the electromotive force cell voltage Vs generated at both ends of the electromotive force cell 165 is 450 mV while flowing the minute current Icp through the electromotive force cell 165 of the gas sensor element 160. (Detection current) Ip is controlled, and oxygen in the exhaust gas introduced into the measurement chamber is pumped and pumped out. Note that the current value and direction of the pump cell current Ip flowing through the pump cell 163 changes according to the air-fuel ratio (in other words, the oxygen concentration in the exhaust gas), and therefore the direction and magnitude of the pump cell current Ip are changed. By detecting, the air-fuel ratio (oxygen concentration in the exhaust gas) can be detected.

  The engine control device 150 includes an A / D converter 151 and a CPU 153. Among these, the A / D converter 151 takes in an output signal (density signal SC or the like) output from the terminal VIP of the control circuit 110 via the terminal AD which is an input terminal, converts it into a digital value, and converts it into a CPU 153. Output to. Based on the digitized output signal of the control circuit 110, the CPU 153 calculates an air-fuel ratio, an amplification factor, and an offset voltage as will be described later. Further, the engine control device 150 controls on / off of the switches SW1 to SW3 in the control circuit 110 through the terminal CT and the terminal CI of the control circuit 110. Further, the engine control device 150 can output a predetermined voltage to the reference voltage power supply unit 140 via a terminal VCCA that is an output terminal.

  In the sensor control apparatus 100, the control circuit 110 supplies a minute current Icp to the electromotive force cell 165 of the gas sensor element 160, and the control resistor 120 that controls the pump cell current Ip, and the detection resistor Rd when the pump cell current Ip flows. And an output processing unit 130 for sending this information to the engine control device 150 using the detected voltage Vd generated at both ends of the output.

  Among these, the control unit 120 includes a constant current source 121 for supplying a minute current Icp to the electromotive force cell 165, an input buffer 122, an output buffer 126, and a PID control circuit 123. The output buffer 126 keeps the potential of the terminal COM constant (3.6 V) and causes the pump cell current Ip to flow in the pump cell 163 through the terminal IP + through the positive and negative. The PID control circuit 123 causes the pump cell to flow through the pump cell 165 so that the potential difference between the terminal Vs + of the gas sensor element 160 connected via the input buffer 122 (terminal VS + of the control circuit 110) and the terminal Vcent is always 450 mV. PID control is performed to determine the magnitude of the current Ip. Capacitors C1 to C3 and resistors R2 to R4 for determining PID control constants are connected to terminals P1, P2, P3, and Pout that are connected to the PID control circuit 123, respectively.

  On the other hand, as shown in FIG. 1, the detection resistor Rd is arranged in a current path through which the pump cell current Ip flows. Therefore, a detection voltage Vd (V) corresponding to the magnitude of the pump cell current Ip is provided at both ends thereof. Will occur. In the present embodiment, since the resistance value of the detection resistor Rd is Rd = 300Ω, the pump cell current Ip (A) is obtained by the equation of Ip = Vd / 300. When the potential of one end Rd1 of the detection resistor Rd (the potential of the terminal Vcent) is the first detection voltage Vd1, and the potential of the other end of the detection resistor Rd (the potential of the terminal Pout) is the second detection voltage Vd2, The detection voltage Vd is given as a difference between the first detection voltage Vd1 and the second detection voltage Vd2 (Vd = Vd1−Vd2).

On the other hand, in the control circuit 110, the output processing unit 130 includes operational amplifiers OP1 and OP2 that operate as buffers, a differential amplification circuit (differential amplification unit) 131, and switches SW1 and SW2. The switches SW1 and SW2 are configured to operate in conjunction with each other, and by switching, the first detection voltage Vd1 and the second detection voltage Vd2 are respectively input to the non-inverting input terminals of the operational amplifiers OP1 and OP2. A state in which a first reference voltage Vb1 and a second reference voltage Vb2 to be described later are input can be selected.
A combination of the switch SW1 and the switch SW2 corresponds to the first switch of the present invention.

The differential amplifier circuit 131 differentially amplifies the first input voltage Vi1 input to the first input terminal 132 and the second input voltage Vi2 input to the second input terminal 133 with a predetermined amplification factor, An output signal is output toward the terminal VIP.
In the differential amplifier circuit 131, the operational amplifier OP3 and the resistors R5 to R10 form a basic form of the differential amplifier circuit, and the amplification factor G is determined by the resistors R5 to R10. The resistance values of the resistors are R5 = R7, R6 = R8, and R9 = R10.
A predetermined reference offset voltage Voff is applied to the non-inverting input terminal of the operational amplifier OP3 via the operational amplifier OP4 that operates as a buffer and the resistor R10. This reference offset voltage Voff determines the reference voltage of the output signal output from the differential amplifier circuit 131.
Thus, in the differential amplifier circuit 131, the first input voltage Vi1 and the reference offset voltage Voff are applied to the non-inverting input terminal (+ terminal) of the operational amplifier OP3 via the resistors R5 and R6. On the other hand, to the inverting input terminal (− terminal) of the operational amplifier OP3, the second input voltage Vi2 via the resistors R7 and R8 and the output of the operational amplifier OP3 itself via the feedback resistor R9 are negatively fed back.

By using the differential amplifier circuit 131 configured as described above, it is possible to effectively remove common mode noise included in common in the first and second input signals Vi1 and Vi2. For this reason, an appropriate output signal with less noise can be output to the terminal VIP.
The output signal output from the differential amplifier circuit 131 has a value having an offset voltage OFS (OFS≈Voff) substantially equal to the reference offset voltage Voff. However, the offset voltage OFS of the differential amplifier circuit 131 does not necessarily match the reference offset voltage Voff input to the non-inverting input terminal of the operational amplifier OP3. This is because when the operational amplifier OP3 itself has an offset voltage, this value is also added to the offset voltage OFS.

Specifically, the differential amplifier circuit 131 of this embodiment has an amplification factor G = 4.5 and a reference offset voltage Voff = 2.3 V≈OFS. Therefore, when the switches SW1 and SW2 are switched and the first and second detection voltages Vd1 and Vd2 are the first and second input signals Vi1 and Vi2, the resistance value of the detection resistor Rd is 300Ω as described above. Therefore, the relationship between the pump cell current Ip (A) and the concentration signal SC (V) that is the output signal is expressed by the following equation.
SC (V) = (Vd1−Vd2) × G + OFS (Formula 1)
= Ip × 300 × G + OFS (Formula 2)
= Ip × 300 × 4.5 + 2.3
Thus, the concentration signal SC output from the differential amplifier circuit 131 has a linear function relationship with the pump cell current Ip in accordance with the change in the pump cell current Ip.

  The concentration signal SC output from the differential amplifier circuit 131 is output from the terminal VIP of the control circuit 110 (sensor control device 100) and input to the terminal AD of the engine control device 150. In the engine control device 150, the concentration signal SC is converted into a digital value by the A / D converter 151, a predetermined process is performed by the CPU 153, the pump cell current Ip or a value corresponding thereto is obtained, and the oxygen concentration in the exhaust gas (Air-fuel ratio) is detected. Then, engine control such as fuel injection control is performed using the obtained oxygen concentration (air-fuel ratio).

Further, the differential amplifier circuit 131 includes a node 134A between resistors R5 and R6 connected in series to the non-inverting input terminal of the operational amplifier OP3, and a resistor connected in series to the inverting input terminal. A short circuit 134 that short-circuits the node 134B between R7 and R8 is provided, and the switch SW3 opens and closes the short circuit 134.
The switch SW3 is turned off when the concentration signal SC is output from the differential amplifier circuit 131 and when a reference amplification signal SG described later is output, that is, the short circuit 134 is opened.

Next, the case where the switch SW3 is turned on, that is, the short circuit 134 is closed and the node 134A and the node 134B are short-circuited (during offset calibration) will be described.
When the switch SW3 is turned on, the node 134A between the resistors R5 and R6 and the node 134B between the resistors R7 and R8 are short-circuited, that is, the first and second input terminals 132 and 133 are connected. Even if the first and second input voltages Vi1 and Vi2 have different values, the potentials of the node 134A and the node 134B are forcibly set to the same potential. Accordingly, when the switch SW3 is turned on, it is substantially the same as adding the same input to the first and second input voltages Vi1 and Vi2 of the first and second input terminals 132 and 133. Therefore, from the differential amplifier circuit 131, the output signal (offset detection signal) SO including only the offset voltage OFS of the differential amplifier circuit 131 is not related to the first and second input voltages Vi1 and Vi2, and is supplied to the terminal VIP. Is output toward.

In the differential amplifier circuit 131 of the present embodiment, resistors R5 and R7 are provided on the upstream side of the node 134A and the node 134B (left side in FIG. 1). For this reason, even if the first and second input voltages Vi1 and Vi2 having different values are output from the operational amplifiers OP1 and OP2 (buffers), the operational amplifiers OP1 and OP2 that flow through the resistor R5, the short circuit 134, and the resistor R7. Since the magnitude of the output current (short-circuit current) is limited by the resistors R5 and R7, there is no problem.
The switch SW3 corresponds to the second switch of the present invention.

  As described above, the offset detection signal SO is output from the differential amplifier circuit 131 by turning on the switch SW3. The offset detection signal voltage SO is input to the terminal AD of the engine control device 150 via the terminal VIP of the control circuit 110 (sensor control device 100), converted into a digital value by the A / D converter 151, and then by the CPU 153. It is processed. As described above, since the offset detection signal SO is an output signal including only the offset voltage OFS of the differential amplifier circuit 131, the offset of the differential amplifier circuit 131 at the time when the switch SW3 is turned on from the offset detection signal SO. The voltage OFS can be detected.

  In general, the offset voltage included in the output signal of the differential amplifier circuit is not necessarily constant and varies depending on each individual. Further, it changes due to temperature characteristics due to ambient temperature changes and deterioration with time. In the present embodiment, the temperature characteristics and changes with time of the power source that generates the reference offset voltage Voff, the characteristics and temperature characteristics of the operational amplifier OP3, changes with time, the resistance values of resistors R5 to R10, the temperature characteristics, and changes with time. Also, the offset voltage OFS of the differential amplifier circuit 131 has a different value. That is, the offset voltage OFS has a variation for each individual and changes with time.

On the other hand, in the gas sensor system 10 (sensor control device 100) of the present embodiment, as described above, by turning on the switch SW3, the offset of the differential amplifier circuit 131 at each time point from the offset detection signal SO. The voltage OFS can be detected.
Therefore, in the gas sensor system 10 (sensor control apparatus 100) of this embodiment, the offset voltage OFS of the differential amplifier circuit 131 at that time can be detected by turning on the switch SW3 at an appropriate time.
Then, the switches SW1 and SW2 are switched so that the first and second detection voltages Vd1 and Vd2 are the first and second input signals Vi1 and Vi2, and the concentration signal SC is output from the differential amplifier circuit 131. Therefore, by applying the calculated offset voltage OFS to the above-described equation 2: SC = Ip × 300 × G + OFS, the pump cell current Ip can be accurately obtained, and the oxygen concentration (air-fuel ratio) can be accurately detected. it can. Therefore, engine control such as fuel injection control can be performed more appropriately.

Next, reference voltage power supply unit 140 and detection of amplification factor G using the same will be described.
The reference voltage power supply unit 140 includes a regulator 143 and reference resistors R11 and R12 that divide the output. The regulator 143 is driven by being connected to the terminal VCCA of the engine control device 150, and outputs the first reference voltage Vb1 with high accuracy. In the present embodiment, the first reference voltage Vb1 is 5V. The first reference voltage Vb1 is input to the terminal CC5 of the control circuit 110 and further connected to the switch SW1.
The first reference voltage Vb1 is divided by directly connected reference resistors R11 and R12, and a 4.5V second reference voltage Vb2 is obtained from these voltage dividing points. The second reference voltage Vb2 is input to the terminal G-VIPAL of the control circuit 110 and further connected to the switch SW2.
In the reference voltage power supply unit 140, as described above, the first reference voltage Vb1 is divided by the reference resistors R11 and R12 to obtain the second reference voltage Vb2. In this case, even if the first reference voltage Vb1 output from the regulator 143 changes for some reason, the second reference voltage Vb2 also changes in the same direction along with the change. For the voltage, the fluctuation is suppressed.

Note that the resistance values of the reference resistors R11 and R12 included in the reference voltage power supply unit 140 are included in the differential amplifier circuit 131 and are more accurate than the resistors R5 to R10 involved in determining the amplification factor. A resistor is used. Specifically, the accuracy of the resistance values of the resistors R5 to R10 (the degree of variation with respect to the target resistance value) is about 2-3%, whereas the accuracy of the resistance values of the reference resistors R11 and R12 is 1. %. Therefore, the amplification of the differential amplifier 131 due to the variation of the resistance values of the resistors R5 to R10 rather than the accuracy of the voltage values of the first and second reference voltages Vb1 and Vb2 due to the variation of the resistance values of the reference resistors R11 and R12. The variation in rate G is greater.
However, in gain calibration, by using the first and second reference voltages Vb1 and Vb2 with high accuracy, the amplification factor G is measured with higher accuracy than the variation of the amplification factor G that the differential amplifier 131 originally has. Therefore, it is possible to detect the pump cell current Ip and the oxygen concentration (air-fuel ratio) with high accuracy from the concentration signal SC while using the resistors R5 to R10 having relatively large variations in resistance value.

As can be easily understood from FIG. 1, in the switch SW1, either the first detection voltage Vd1 or the first reference voltage Vb1 can be selected and set as the first input voltage Vi1 by switching. In the switch SW2, by switching, either the second detection voltage Vd2 or the second reference voltage Vb2 can be selected and set as the second input voltage Vi2.
Therefore, hereinafter, a case will be described in which the switches SW1 and SW2 are switched and the first and second reference voltages Vb1 and Vb2 are set to the first and second input voltages Vi1 and Vi2 (at the time of gain calibration). Note that the switch SW3 is turned off.

In this case, Vi1 = 5.0V is input to the differential amplifier circuit 131 as the first input voltage Vi1, and Vi2 = 4.5V is input as the second input signal Vi2. Then, the differential amplification circuit 131 outputs a reference amplification signal SG obtained by amplifying the difference (0.5 V) between the first and second reference voltages Vb1 and Vb2 by the differential amplification circuit 131 toward the terminal VIP. The
When the first and second reference voltages Vb1 and Vb2 are the first and second input signals Vi1 and Vi2, the relationship with the reference amplification signal SG (V) is expressed by the following equation.
SC (V) = (Vb1−Vb2) × G + OFS (Formula 3)
= 0.5 x G + OFS
The reference amplification signal SG is input to the terminal AD of the engine control device 150 via the terminal VIP of the control circuit 110 (sensor control device 100), converted into a digital value by the A / D converter 151, and processed by the CPU 153. Is done.
As described above, the offset voltage OFS can be obtained by turning on the switch SW3 as described above. Since the values of the first and second reference voltages Vb1 and Vb2 are known, the amplification factor G of the differential amplifier circuit 131 at that time can be detected from the reference amplification signal SG.

  In general, the amplification factor of the differential amplifier circuit is not necessarily constant and varies depending on each individual. Further, it changes due to temperature characteristics due to ambient temperature changes and deterioration with time. In the present embodiment, the temperature characteristics and changes with time of the power source that generates the reference offset voltage Voff, the characteristics and temperature characteristics of the operational amplifier OP3, changes with time, the resistance values of resistors R5 to R10, the temperature characteristics, and changes with time. Also, the amplification factor G of the differential amplifier circuit 131 has a different value. That is, the amplification factor G varies with time and varies with time.

On the other hand, in the gas sensor system 10 (sensor control device 100) of the present embodiment, as described above, by turning on the switch SW3, the offset of the differential amplifier circuit 131 at each time point from the offset detection signal SO. The voltage OFS can be detected. Further, the switches SW1 and SW2 are switched while the switch SW3 is off, and the first and second reference voltages Vb1 and Vb2 are input to the differential amplifier circuit 131. The amplification factor G of the differential amplifier circuit 131 can be detected.
Therefore, in the gas sensor system 10 (sensor control device 100) of the present embodiment, the gain G of the differential amplifier circuit 131 at that time can be detected by switching the switches SW1 and SW2 at an appropriate time.
Then, the switches SW1 and SW2 are switched so that the first and second detection voltages Vd1 and Vd2 are the first and second input signals Vi1 and Vi2, and the concentration signal SC is output from the differential amplifier circuit 131. Therefore, by applying the calculated offset voltage OFS and amplification factor G to the above-described equation 2: SC = Ip × 300 × G + OFS, the pump cell current Ip is obtained more accurately, and the oxygen concentration (air-fuel ratio) is more accurately obtained. Can be detected. Therefore, engine control such as fuel injection control can be performed more appropriately.

  In the present embodiment, the offset voltage OFS can be obtained by turning on the switch SW3 as described above. However, when the switch SW3 and the short circuit 134 are not provided, or when the offset voltage OFS is considered to be substantially equal to the reference offset voltage Voff, the reference offset voltage OFS is not obtained separately, and instead, the reference offset Using the voltage Voff, the amplification factor G can be obtained, or the pump cell current Ip and the oxygen concentration (air-fuel ratio) can be detected from the concentration signal SC.

  The switches SW1 to SW3 are switched from a terminal CT that is a communication output terminal of the engine control device 150 through a terminal CI that is a communication input terminal of the control circuit 110 in accordance with a control program executed by the CPU 153 of the engine control device 150. Switching is controlled according to the input instruction.

Next, specific control methods of the gas sensor system 10 and the sensor control device 100 will be described based on the flowcharts shown in FIGS.
When the car key is turned on, control of the gas sensor system 10 and the sensor control device 100 is started. First, in step S1, the engine control device 150 is initialized. Specifically, each flag and each numerical value are initialized, and the switches SW1 to SW3 are turned off. At this stage, the pump cell current (detection current) Ip is not yet flown through the pump cell 163 (Ip = 0). This is because the gas sensor element 160 is not yet sufficiently warmed (not activated).

Next, the process proceeds to a subroutine of step S2 (see FIG. 3), and offset calibration (offset detection step) before activation of the gas sensor element 160 is performed.
First, in step S21, the switch SW3 is turned on. Specifically, the switch SW3 in the differential amplifier circuit 131 of the sensor control device 100 is turned on from the engine control device 150 through the terminal CT, and the short circuit 134 is short-circuited. As a result, as described above, the offset detection signal SO is output from the differential amplifier circuit 131, and is acquired by the engine control device 150 using the A / D converter 151 (step S22). This step corresponds to an offset signal output step in the control method of the sensor control device.

  In step S23, the offset voltage OFS of the differential amplifier circuit 131 is calculated using the above-described equation 2 and the like, and stored (updated) in a predetermined location. Thereafter, in step S24, the switch SW3 in the differential amplifier circuit 131 of the sensor control apparatus 100 is turned off from the engine control apparatus 150 through the terminal CT, the short circuit 134 is opened, and the process returns to the main routine. In this manner, the offset voltage OFS of the differential amplifier circuit 131 is acquired and updated before the gas sensor element 160 is activated.

Next, the process proceeds to a subroutine of step S3 (see FIG. 4), and gain calibration (amplification factor detection step) before activation of the gas sensor element 160 is performed.
First, in step S31, the switch SW1 is switched to the terminal CC5 side of the control circuit 100, and the switch SW2 is switched to the terminal G-VIPAL side. That is, the first and second reference voltages Vb1 and Vb2 are set as the first and second input voltages Vi1 and Vi2. Specifically, the switches SW1 and SW2 in the differential amplifier circuit 131 of the sensor control device 100 are switched from the engine control device 150 through the terminal CT. Thus, as described above, the reference amplification signal SG is output from the differential amplifier circuit 131, and is acquired by the engine control device 150 using the A / D converter 151 (step S32). This step corresponds to a reference signal output step in the control method of the sensor control device.

  In step S33, the amplification factor G of the differential amplifier circuit 131 is calculated using the above-described equation 2 and the like, and stored (updated) in a predetermined location. Thereafter, in step S34, the switch SW1 is switched to the terminal Vcent side of the control circuit 100, and the switch SW2 is switched to the terminal Pout side. That is, the first and second detection voltages Vd1 and Vd2 are set as the first and second input voltages Vi1 and Vi2. Specifically, the switches SW1 and SW2 in the differential amplifier circuit 131 of the sensor control device 100 are switched from the engine control device 150 through the terminal CT. Thereafter, the process returns to the main routine. In this way, the gain G of the differential amplifier circuit 131 is acquired and updated in the stage before the activation of the gas sensor element 160.

Next, it progresses to step S4 and it is judged whether the gas sensor element 160 was activated. As a method for determining this, in the present embodiment, an impedance detection circuit (not shown) for detecting the internal impedance of the electromotive force cell 165 is separately provided, and it is determined whether or not the impedance is activated based on the size of the internal impedance. Since the technique for detecting the internal impedance of the electromotive force cell 165 is known in Japanese Patent No. 3645665, detailed description thereof is omitted here.
If NO in step S4, that is, if it is determined that the gas sensor element has not yet been activated, steps S2 to S4 are repeated until the gas sensor element 160 is activated (Yes). At the stage of activating the gas sensor element 160, the temperature of the gas sensor element 160 also rises greatly, but the temperature of the sensor control device 100 (control circuit 110) often changes greatly. Therefore, immediately after it is determined that the gas sensor element 160 is activated, these are updated so that the pump cell current Ip and the oxygen concentration (air-fuel ratio) can be appropriately measured using the appropriate offset voltage OFS and the amplification factor G. This is because it is preferable to update the value to.

On the other hand, if it is determined as YES (activated) in step S4, the process proceeds to step S5 and the timer is started.
Next, proceeding to step SB, it is determined whether 10 msec has elapsed. In this step SB, NO, that is, if 10 msec has not elapsed, this step SB is repeated until 10 msec elapses. On the other hand, if 10 msec elapses and the determination is YES, the process proceeds to the next step S6. The elapsed time determined here is not related to the measurement time of the timer.
In step S <b> 6, the first and second detection voltages Vd <b> 1 and Vd <b> 2 are input to the differential amplifier circuit 131, the concentration signal SC is output, and this is acquired by the engine control device 150 using the A / D converter 151. This step corresponds to the concentration signal output step in the control method of the sensor control device.

  Next, the process proceeds to step S7. In step S7, it is determined whether or not the timer has passed a predetermined time. The predetermined time is determined by how often the offset calibration (step S2) and the gain calibration (step S3) are periodically performed, and is set to 5 seconds in the present embodiment.

If NO is determined in step S7, the process proceeds to a subroutine of step S8 (see FIG. 5) to detect the oxygen concentration (air-fuel ratio) (concentration information detection step).
Specifically, first, in step S81, the pump cell current Ip is calculated using the above-described equation 2 and the like using the gain G and the offset voltage OFS of the differential amplifier circuit 131 that has already been acquired and stored. The pump cell current Ip is calculated using the gain G and the offset voltage OFS acquired recently, so that the gain G and the offset are compared with the case where the gain or offset voltage as a design value given in advance is used. Variations and changes in the voltage OFS can be reflected, and the pump cell current Ip can be calculated more accurately.
In step S82, the pump cell current Ip is used to detect the oxygen concentration (air-fuel ratio) in the exhaust gas. Again, since the accurate pump cell current Ip is used, the oxygen concentration (air-fuel ratio) in the exhaust gas can be detected more accurately. Thereafter, the process returns to the main routine.

Subsequently, in step S9, control such as engine fuel control (air-fuel ratio control) is performed using the obtained oxygen concentration (air-fuel ratio), and the process returns to step SB. Thus, the passage of 10 msec (step SB), acquisition of the concentration signal SC (step S6), detection of the oxygen concentration (air-fuel ratio) (step S8), engine fuel control (air-fuel ratio control, step S9), step S7 Repeat until it is judged as Yes. In this manner, more appropriate engine fuel control or the like can be performed based on an accurate oxygen concentration (air-fuel ratio).
In step S81, not the value of the pump cell current Ip itself but a value corresponding to the pump cell current Ip is calculated in relation to numerical processing, and in step S82, this is used to calculate the oxygen concentration (air-fuel ratio) in the exhaust gas. ) May be detected. In step S82, not the oxygen concentration (air-fuel ratio) in the exhaust gas itself but the value corresponding thereto is detected, and in step S9, this is used to perform engine fuel control (air-fuel ratio control). You can go.

  On the other hand, if it is determined as YES (predetermined time has elapsed) in step S7, the process proceeds to a subroutine of step S2 (see FIG. 3) to perform offset calibration (offset detection step) after activation of the gas sensor element 160. The offset voltage OFS of the differential amplifier circuit 131 at that time is acquired and updated. Since the contents of the offset calibration (offset detection step) in step S2 have already been described, description thereof will be omitted. Similarly, step S22 corresponds to an offset signal output step in the control method of the sensor control device.

  Further, the process proceeds to a subroutine of step S3 (see FIG. 4), performs gain calibration (amplification factor detection step) after activation of the gas sensor element 160, and acquires the amplification factor G of the differential amplifier circuit 131 at the time point, Update. Since the contents of the gain calibration (amplification factor detection step) in step S3 have already been described, description thereof will be omitted. Similarly, step S32 corresponds to a reference signal output step in the control method of the sensor control device.

  Next, the process proceeds to step SA and the timer is started again. Thereafter, the process returns to the above-described step SB, and 10 msec elapse (step SB), acquisition of the concentration signal SC (step S6), and detection of the oxygen concentration (air-fuel ratio) until it is determined Yes in step S7 (step SB). S8) and engine fuel control (air-fuel ratio control, step S9) are repeated.

  As described above, in the gas sensor system 10 (sensor control apparatus 100) and the control method thereof according to the present embodiment, even if the offset voltage OFS and the amplification factor G of the differential amplifier circuit 131 change, the switch SW1. , SW2 and SW3 can be used to obtain the offset voltage OFS and amplification factor G of the differential amplifier circuit 131 at each time point, and to obtain the pump cell current Ip and oxygen concentration (air-fuel ratio) with high accuracy.

In the gas sensor system 10 (sensor control device 100) and the control method (oxygen concentration measurement method) of the present embodiment, first, offset calibration (offset detection step) and gain calibration (amplification rate detection step) are performed. This is performed before the gas sensor element 160 is activated. In this way, when the gas sensor element 160 is activated, an accurate oxygen concentration (air-fuel ratio) can be immediately acquired based on the previously acquired offset voltage OFS and amplification factor G.
Furthermore, offset calibration and gain calibration are also performed periodically after the gas sensor element 160 is activated. In this way, even if the offset voltage OFS and the amplification factor G fluctuate, the oxygen concentration (air-fuel ratio) can be calculated based on the offset voltage OFS and the amplification factor G acquired each time. (Air-fuel ratio) can be acquired.

(Modification 1)
Next, a first modification of the above embodiment will be described with reference to FIG. In the control method (oxygen concentration measurement method) described in the first embodiment, a timer is started in steps S5 and SA, and whether or not a predetermined time has elapsed in step S7 is detected, and offset calibration ( S2) and gain calibration (S3) are performed.
On the other hand, in the control method (oxygen concentration measurement method) of the first modification, it is time when offset calibration (S2) and gain calibration (S3) may be performed, and when it is necessary to perform these. Control to do these.
Therefore, the description will focus on the parts different from the first embodiment, and the description of the same parts will be omitted or simplified.

First, Steps S1 to S4 are the same as in the embodiment.
The same applies to the subroutine for the offset calibration (offset detection step) in step S2 and the subroutine for the gain calibration (amplification factor detection step) in step S3. Similarly, step S22 corresponds to an offset signal output step in the sensor control device control method, and step S32 corresponds to a reference signal output step in the sensor control device control method.

If it is determined Yes in step S4, the process proceeds to step S41, and the calibration flag is reset. This flag will be described later.
Next, the process proceeds to step SB, and it is determined whether 10 msec has elapsed as in the above-described embodiment. After 10 msec has elapsed, the process proceeds to the next step S6.
In step S6, the first and second detection voltages Vd1 and Vd2 are input to the differential amplifier circuit 131 and the concentration signal SC is output to the differential amplifier circuit 131, as in the above-described embodiment. Obtained by the control device 150. This step corresponds to the concentration signal output step in the control method of the sensor control device.

  In step S42, it is determined whether the calibration flag is set. Here, when it is determined No (not set), the process proceeds to the same steps S8 and S9 as in the above-described embodiment, and the pump cell is obtained using the offset voltage OFS and the amplification factor G acquired in steps S2 and S3. The current Ip and the oxygen concentration (air-fuel ratio) in the exhaust gas are calculated.

Further, the process proceeds to step S44, and it is determined whether or not the present is a period in which calibration is possible. Specifically, the period during which the calibration is possible is that during the traveling, the driver releases the accelerator, the fuel is not injected into the engine, and the oxygen concentration (air-fuel ratio) of the exhaust gas is measured. There is no need to calculate the pump cell current Ip and the oxygen concentration (air-fuel ratio) in the exhaust gas, such as a period when it is not necessary (specifically at the time of fuel cut), and switch SW1, SW2 or SW3 is switched, Even if the offset voltage OFS or the amplification factor G is measured, a period without influence is mentioned.
If it is determined that the present time is a period during which calibration is possible (Yes), the process proceeds to step S45. On the other hand, if it is determined that the current calibration period is not possible (No), steps S45 and S46 are skipped and the process returns to step SB.

In step S45, it is further determined whether or not it is time for calibration. The time when calibration is necessary includes a case where a certain amount of time has passed since the previous calibration. In addition, there may be a case where a change in the amplification factor G of the differential amplifier circuit 131 or the offset voltage OFS is suspected for some reason.
If it is determined that calibration is necessary (Yes), the process proceeds to step S46. On the other hand, if it is determined that calibration is not necessary (No), step S46 is skipped and the process returns to step SB.

  In step S46, a calibration flag is set, and then the process returns to step SB. This calibration flag is a flag that is determined in step S42 described above as to whether or not it is set.

  On the other hand, if it is determined as Yes (set) in step S42, the process proceeds to the same subroutine (see FIG. 3) of step S2 as in the embodiment and before the activation of the gas sensor element. Here, offset calibration (offset detection step) after activation of the gas sensor element 160 is performed, and the offset voltage OFS of the differential amplifier circuit 131 at that time is acquired and updated. Note that the details of the offset calibration (offset detection step) in step S2 have already been described in the embodiment, and thus description thereof will be omitted. Similarly, step S22 corresponds to an offset signal output step in the control method of the sensor control device.

  Further, the process proceeds to a subroutine of step S3 (see FIG. 4), performs gain calibration (amplification factor detection step) after activation of the gas sensor element 160, and acquires the amplification factor G of the differential amplifier circuit 131 at the time point, Update. Since the contents of the gain calibration (amplification factor detection step) in step S3 have already been described in the embodiment, the description thereof will be omitted. Similarly, step S32 corresponds to a reference signal output step in the control method of the sensor control device.

  In step S43, the calibration flag is reset. Thereafter, the process returns to step SB described above. Therefore, again, 10 msec has elapsed (step SB), the concentration signal SC is acquired (step S6), and the oxygen concentration (air-fuel ratio) is detected (step S8) until the calibration flag is set in step S46. The engine fuel control (air-fuel ratio control, step S9) is repeated.

(Modification 2)
Next, a second modification of the embodiment will be described with reference to FIG.
In the above-described embodiment, the reference voltage power supply unit 140 obtains the first and second reference voltages Vb1 and Vb2 using the two reference resistors R11 and R12.
In contrast, in the second modification, the reference voltage power supply unit 240 uses the regulator 243 that generates the reference voltage Vb, and the reference voltage Vb is divided by three reference resistors R21, R22, and R23 connected in series. Pressed. Then, the node between the reference resistors R21 and R22 is connected to the terminal CC5, and the first reference voltage Vb1 is supplied. Further, the node between the reference resistors R22 and R23 is connected to the terminal G-VIPAL to supply the second reference voltage Vb2.
Even in the reference voltage power supply unit 240, as in the case of the reference voltage power supply unit 140 of the embodiment, even if the reference voltage Vb output from the regulator 243 fluctuates, the first and second reference voltages are accompanied by the fluctuation. Since Vb1 and Vb2 also fluctuate in the same direction, the first reference voltage Vb1, the second reference voltage Vb2, and the difference voltage are suppressed from changing, so that there is an advantage that the influence is less affected as the reference voltage Vb changes. is there.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment and the first and second modifications, and can be appropriately modified and applied without departing from the gist thereof. Needless to say, it can be done.
In the above-described embodiment, after the gas sensor element 160 is activated, offset calibration and gain calibration are performed every predetermined time (periodically, every 5 seconds in this embodiment) by a timer. However, it is considered that a change in the ambient temperature of the control circuit 110 including the differential amplifier circuit 131 becomes small if, for example, a certain amount of time elapses after the vehicle starts running. Accordingly, the calibration interval can be appropriately changed while performing offset calibration and gain calibration periodically, such as changing the set time of the timer according to the situation.

In the embodiment, an example is shown in which the oxygen concentration (air-fuel ratio) is detected by using the actual gain G and the offset voltage OFS itself obtained at calibration (steps S2 and S3). It was.
However, in addition to this, a temporary oxygen concentration (air-fuel ratio) is temporarily calculated using an amplification factor and an offset voltage that should be originally obtained (amplification factor and offset voltage as design values). Thereafter, the calculated temporary oxygen concentration (air-fuel ratio) is corrected by using the actual gain G and the offset voltage OFS at each time point obtained in the calibration (steps S2 and S3). A method of obtaining a more accurate oxygen concentration (air-fuel ratio) reflecting the amplification factor G and the offset voltage OFS can also be taken.

It is a circuit diagram for demonstrating the circuit structure of the sensor control apparatus and gas sensor system which concern on embodiment. It is a flowchart explaining control of the sensor control apparatus which concerns on embodiment, and control of a gas sensor system. It is a flowchart explaining the subroutine of offset calibration. It is a flowchart explaining the subroutine of gain calibration. It is a flowchart explaining the subroutine of oxygen concentration calculation (air-fuel ratio calculation). It is a flowchart explaining the control which concerns on the modification 1 about the sensor control apparatus and gas sensor system which concern on embodiment. FIG. 10 is a circuit diagram illustrating a circuit configuration of a reference voltage power supply unit according to modification 2.

Explanation of symbols

10, 20 Gas sensor system 100, 200 Sensor control device 110 Control circuit (sensor control device)
VIP, CI, CC5, G-VIPAL, IP +, Vcent, Pout, P1, P2, P3, Icp + (control circuit) terminal 131 Differential amplifier (differential amplifier)
132 First input terminal 133 (for differential amplifier circuit) Second input terminal 134 (for differential amplifier circuit) Short circuit 134A (short circuit between nodes 134A and 134B) Node (operational amplifier OP3 of first input resistor R6) The opposite end)
134B node (the end of the second input resistor R8 opposite to the operational amplifier OP3)
OP1, OP2, OP3, OP4 Operational amplifier R9 Feedback resistor (resistor involved in gain determination)
R5, R6, R7, R8 resistors (resistors involved in gain determination)
R6 resistor (first input resistor)
R8 resistor (second input resistor)
R5 resistor (third input resistor)
R7 resistor (4th input resistor)
G Amplification factor OFS (differential amplifier circuit) Offset output voltage (offset voltage) (differential amplifier circuit)
Vi1 first input voltage Vi2 second input voltage SW1, SW2 switch (first switch)
SW3 switch (second switch)
140, 240 Reference voltage power supply unit Vb1 First reference voltage Vb2 Second reference voltage SC Concentration signal SG Reference amplification signal SO Offset detection signal 150 Engine control device 160 Gas sensor element Ip Pump cell current (detection current)
Rd detection resistor Rd1 (detection resistor) one end Rd2 (detection resistor) other end Vd1 first detection voltage Vd2 second detection voltage

Claims (13)

A sensor control device that outputs a concentration signal related to the concentration of the specific gas component using a detection current corresponding to the concentration of the specific gas component obtained by operating a gas sensor element,
A differential amplifier that differentially amplifies the first input voltage input to the first input terminal and the second input voltage input to the second input terminal;
A first reference voltage when a first detection voltage at one end of the detection resistor through which the detection current flows is the first input voltage, and a second detection voltage at the other end of the detection resistor is the second input voltage; A first switch for switching between the case where the first input voltage is used and the second reference voltage is the second input voltage;
A sensor control device comprising: The sensor control device according to claim 1,
A reference voltage power supply unit that outputs the first reference voltage and the second reference voltage;
The first reference voltage is divided by a voltage dividing resistor to be the second reference voltage, or
A sensor control device including a reference voltage power supply unit that divides a predetermined voltage by a voltage dividing resistor to obtain the first reference voltage and the second reference voltage. The sensor control device according to claim 2,
A sensor control device in which the accuracy of the resistance value of the voltage dividing resistor is higher than the accuracy of the resistance value of the resistor involved in determining the amplification factor of the differential amplifier. The sensor control device according to any one of claims 1 to 3,
The differential amplifier is
Differentially amplifying the first input voltage and the second input voltage different from each other;
A sensor control device comprising: a second switch that switches between a state in which only the offset voltage of the differential amplifier section is output. The sensor control device according to any one of claims 1 to 4,
A gas sensor system comprising the gas sensor element. A sensor control device that outputs a concentration signal related to the concentration of the specific gas component using a detection current corresponding to the concentration of the specific gas component obtained by operating a gas sensor element,
A differential amplifier that differentially amplifies the first input voltage input to the first input terminal and the second input voltage input to the second input terminal;
A first reference voltage when a first detection voltage at one end of the detection resistor through which the detection current flows is the first input voltage, and a second detection voltage at the other end of the detection resistor is the second input voltage; A first switch that switches between a case where the first input voltage is used and the second reference voltage is the second input voltage, and a control method of a sensor control device comprising:
Using the first reference voltage as the first input voltage and the second reference voltage as the second input voltage, the first reference voltage, the second reference voltage, and the amplification of the differential amplifier from the sensor control device A reference signal output step for outputting a reference amplified signal corresponding to the rate;
A concentration signal output step for outputting the concentration signal from the sensor control device using the first detection voltage as the first input voltage and the second detection voltage as the second input voltage;
A control method for a sensor control device comprising: It is a control method of the sensor control device according to claim 6,
A control method of a sensor control device, wherein the reference signal output step is performed at a stage before activation of the gas sensor element. A control method for a sensor control device according to claim 6 or 7,
A control method for a sensor control device, wherein the reference signal output step is performed when it is not necessary to output the concentration signal from the sensor control device after activation of the gas sensor element. It is a control method of the sensor control device according to any one of claims 6 to 8,
The sensor control device outputs only a state in which the differential amplifying unit differentially amplifies the first input voltage and the second input voltage having different values, and an offset voltage of the differential amplifying unit. A second switch for switching to a state;
A control method of a sensor control device comprising an offset signal output step of outputting an offset signal corresponding to an offset voltage of the differential amplifier from the sensor control device. It is a control method of the sensor control device according to claim 9,
A control method of a sensor control device, wherein the offset signal output step is performed at a stage before activation of the gas sensor element. A method for controlling the sensor control device according to claim 9 or 10, wherein:
A control method for a sensor control device, wherein the offset signal output step is performed when it is not necessary to output the concentration signal from the sensor control device after activation of the gas sensor element. A gas sensor element;
A sensor control device that outputs a concentration signal related to the concentration of the specific gas component using a detection current corresponding to the concentration of the specific gas component obtained by operating the gas sensor element,
A differential amplifier that differentially amplifies the first input voltage input to the first input terminal and the second input voltage input to the second input terminal; and
A first reference voltage when a first detection voltage at one end of the detection resistor through which the detection current flows is the first input voltage, and a second detection voltage at the other end of the detection resistor is the second input voltage; A sensor control device including a first switch for switching between a case where the first input voltage is used as the first input voltage and a second reference voltage used as the second input voltage, and a method for detecting concentration information regarding a specific gas component ,
The first reference voltage is the first input voltage, the second reference voltage is the second input voltage, and the reference corresponds to the first reference voltage, the second reference voltage, and the amplification factor of the differential amplifier. An amplification signal is output from the sensor control device, and an amplification factor detection step of detecting the amplification factor of the differential amplification unit,
The first detection voltage is the first input voltage, the second detection voltage is the second input voltage, the concentration signal is output from the sensor control device, and the amplification factor is used to relate to the specific gas component A concentration information detection step for detecting concentration information, comprising: a concentration information detection step for detecting concentration information. A method for detecting concentration information related to a specific gas component according to claim 12,
The sensor control device includes a state in which the differential amplification unit differentially amplifies the first input voltage and the second input voltage different from each other, and a state in which only the offset voltage of the differential amplification unit is output. A second switch for switching to
An offset signal corresponding to the offset voltage of the differential amplifier is output from the sensor control device, and includes an offset detection step of detecting the offset voltage of the differential amplifier.
The concentration information detecting step is a method for detecting concentration information relating to a specific gas component, wherein concentration information relating to the specific gas component is detected based on the amplification factor and the offset voltage.

Images