JP2004212284A - Gas concentration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain an influence of a noise from a heater driving system to enhance detection precision for a gas concentration. <P>SOLUTION: A gas sensor 100 is provided with a pump cell 110, a monitor cell 120 and a sensor cell 130, and those cells 110-130 are held in activated states by heating of a heater 151. Currents flowing in the respective cells 110-130 are measured by a sensing circuit 200 when detecting the gas concentration. The heater 151 is intermittently electrified by a heater driving circuit 250. A grounding pattern for setting a reference potential in the sensing circuit 200 is provided separatedly from a grounding pattern for setting a reference potential in the heater driving circuit 250, using a grounding terminal part or its vicinity as a start point. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas concentration detection device that detects a gas concentration of a specific component in a gas to be detected.
[0002]
[Prior art]
As this type of gas concentration detecting device, there is a device which uses a limiting current type gas concentration sensor and detects, for example, NOx (nitrogen oxide) in exhaust gas discharged from a vehicle engine. The gas concentration sensor has a sensor element composed of, for example, a pump cell, a sensor cell, and a monitor cell. In the pump cell, oxygen in exhaust gas introduced into the chamber is discharged or pumped, and at the same time, oxygen concentration in the exhaust gas is detected. The sensor cell detects the NOx concentration (gas concentration of a specific component) from the gas after passing through the pump cell, and the monitor cell detects the residual oxygen concentration in the chamber after passing through the pump cell.
[0003]
In the above gas concentration sensor, the oxygen concentration and the NOx concentration are normally detected on the assumption that the sensor element is in a predetermined active state. Therefore, in general, a heater is provided near the sensor element, and the sensor element is heated by the heat generated by the heater to maintain the element active state. For example, the resistance value of a sensor element is detected, and the heater is intermittently energized so that the element resistance value becomes a target value corresponding to the activation temperature (for example, see Patent Document 1).
[0004]
More specifically, in a gas concentration sensor (a so-called NOx sensor), NOx in exhaust gas is decomposed at a NOx active electrode of a sensor cell, and oxygen ions generated at that time flow in the sensor cell. At this time, the NOx concentration is detected by measuring the current flowing in the sensor cell. The sensor cell current is a minute current of the order of nA (nano-ampere), and the minute current is measured through a high-resistance (for example, 1.5 MΩ) current detection resistor in the sensing circuit. On the other hand, the heater is energized intermittently by the heater drive circuit. At this time, the heater current on the order of A (ampere) is ON / OFF controlled.
[0005]
[Patent Document 1]
JP-A-2000-171435
[0006]
[Problems to be solved by the invention]
As described above, the sensor cell current for detecting the NOx concentration is on the order of nA, whereas the heater current is on the order of A, and the current level differs by a factor of 10 ＾ 9 when compared simply. Usually, the sensing circuit and the heater drive circuit are mounted on the same circuit board in a mixed state. Therefore, noise generated when the heater is turned on / off may be superimposed on the sensing circuit, and the necessary detection accuracy of the NOx concentration may not be secured.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas concentration detection device capable of suppressing the influence of noise from a heater drive system and improving the gas concentration detection accuracy. It is to be.
[0008]
[Means for Solving the Problems]
In the gas concentration detection device of the present invention, as a premise, a current flowing through the sensor element is measured by the sensing circuit at the time of gas concentration detection. Then, the gas concentration is detected based on the measured current value. On the other hand, the heater is intermittently energized by the heater drive circuit, and the sensor element is maintained in a predetermined active state. The sensing circuit and the heater drive circuit are mounted on the same circuit board, and each of these circuits receives a reference potential from outside through a ground terminal. In particular, in the invention of claim 1, a ground pattern for setting a reference potential in the sensing circuit and a ground pattern for setting a reference potential in the heater drive circuit are provided separately from the ground terminal portion or its vicinity as a starting point.
[0009]
In short, when heater energization by the heater drive circuit is intermittent (ON / OFF), noise is generated due to this. At this time, while the heater current is on the order of A (ampere), the current flowing at the time of detecting the gas concentration is a minute level of nA (nano ampere) to mA (milliampere). Is concerned. On the other hand, in the present invention, since the respective ground patterns are separately arranged with the ground terminal portion interposed therebetween as described above, it is possible to prevent the heater current from flowing into the sensing circuit. That is, the fluctuation of the reference potential in the sensing circuit can be prevented, and the reference potential is stabilized. Therefore, the influence of noise from the heater drive system can be suppressed, and the detection accuracy of the gas concentration is improved.
[0010]
However, the "ground terminal portion" is defined to include not only the ground terminal itself but also a portion corresponding to the ground terminal connected to the ground terminal and held at the same reference potential.
[0011]
According to the second aspect of the present invention, a ground pattern for setting a reference potential in the sensing circuit and a ground pattern for setting a reference potential in the heater drive circuit are integrally provided on the circuit board, and each of these ground patterns is provided. The ground terminal section is provided at a branch point of the above. In this case, as in the first aspect, the influence of noise from the heater drive system can be suppressed, and the detection accuracy of the gas concentration is improved.
[0012]
Further, according to the third aspect of the present invention, a ground pattern for setting a reference potential in the sensing circuit and a ground pattern for setting a reference potential in the heater drive circuit are integrally provided on the circuit board. The ground terminal portion is provided at a position shifted to one of the ground patterns or the opposite side to the branch point. In this case, as in the first aspect, the influence of noise from the heater drive system can be suppressed, and the detection accuracy of the gas concentration is improved. In other words, as long as the branch point of each ground pattern and the ground terminal portion are displaced within a range where there is substantially no influence (within a range where the reference potential does not fluctuate), it is allowed.
[0013]
Actually, as described in claim 4, it is preferable that the ground pattern for the sensing circuit and the ground pattern for the heater drive circuit are developed and provided in two different directions on the circuit board.
[0014]
Alternatively, the ground pattern for the sensing circuit and the ground pattern for the heater drive circuit may be provided so as not to be parallel on the circuit board. According to the configuration of the fourth and fifth aspects, the influence of the electromagnetic wave noise due to the heater current can be eliminated.
[0015]
According to the invention described in claim 6, the ground pattern for the heater drive circuit is partially narrowed in the vicinity of the connection portion with the ground pattern for the sensing circuit. In this case, a part of the ground pattern that is thin has high resistance. Therefore, the influence of noise when the heater power is turned ON / OFF is less likely to be transmitted to the sensing circuit side, and the reference potential of the sensing circuit is further stabilized.
[0016]
According to the seventh and ninth aspects of the present invention, the installation area of the sensing circuit and the installation area of the heater drive circuit on the circuit board are provided at positions separated from each other. In this case, in the heater drive circuit, a magnetic flux is generated by the heater current flowing in the circuit, and the electromagnetic wave noise accompanying the magnetic flux may cause deterioration of measurement accuracy in the sensing circuit. According to the present invention, such inconvenience is solved. Therefore, further improvement in gas concentration detection accuracy can be expected.
[0017]
According to the invention of claims 8 and 10, there is provided an apparatus whose circuit configuration is embodied using a multilayer substrate, wherein a ground pattern and a power supply pattern for a heater drive circuit are vertically stacked with an insulating layer interposed therebetween. And the direction of the current flow in each pattern is opposite to each other. In this case, when a current flows in each of the above-described patterns, a magnetic flux is generated in accordance with the direction of the flow of the current.If the directions of the currents flowing in the respective patterns are opposite to each other, the magnetic flux is canceled by the respective patterns. You. Therefore, the effect of electromagnetic wave noise generated by the heater current can be reduced.
[0018]
In the invention of claim 8 or 10, as described in claim 11, the ground pattern and the power supply pattern for the heater drive circuit may be provided so as to overlap by 50% or more over and below the insulating layer. More preferably, the overlapping portion of each pattern is set to 80% or more.
[0019]
For example, a NOx sensor that detects NOx in automobile exhaust gas is a pump cell that regulates the flow of oxygen in and out of a chamber, and a sensor cell that decomposes NOx from gas after passing through the pump cell and detects the NOx concentration from the amount of oxygen ions that move at that time. And the current flowing through the sensor cell is a minute current on the order of nA. The present invention can be suitably applied to such a NOx sensor. In short, as described in claim 12, the sensor element has a first cell that discharges or pumps oxygen in the gas to be detected introduced into the chamber, and a gas that has passed through the first cell, and takes in the gas. A second cell for decomposing the specific component and detecting the gas concentration of the specific component from the amount of oxygen ions moving at that time, wherein the sensing circuit measures at least a minute current flowing through the second cell. good.
[0020]
Further, the present invention can be suitably applied to, for example, an A / F sensor that detects an oxygen concentration (that is, an air-fuel ratio) in exhaust gas or an oxygen concentration detecting unit (pump cell) of a gas concentration sensor. In short, as described in claim 13, the sensor element decomposes oxygen in the gas to be detected and detects the oxygen concentration from the amount of oxygen ions moving at that time. It is preferable to measure a minute current flowing during decomposition. In other words, the measured current (mA order) at the time of detecting the oxygen concentration has a higher current level than the measuring current at the time of detecting the NOx concentration, even though it is a very small current. In the case where the ground pattern for the heater drive circuit is disposed at a position relatively close to the heater drive circuit, the influence of noise accompanying the heater drive is also concerned. Even in such a case, the variation of the reference potential can be suppressed by applying the present invention, and highly accurate detection of the oxygen concentration (air-fuel ratio) can be realized.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings. The gas concentration detection device according to the present embodiment is applied to, for example, an automobile engine, and uses a limiting current type gas concentration sensor to determine the oxygen concentration in the exhaust gas to be detected or the gas concentration of a specific component. Is detected.
[0022]
First, the configuration of the gas concentration sensor will be described with reference to FIG. The gas concentration sensor of FIG. 2 has a three-cell structure including a pump cell as a “first cell”, a sensor cell as a “second cell”, and a monitor cell as a “third cell”. It is embodied as a so-called composite gas sensor that can simultaneously detect the concentration and the concentration (however, it can be embodied as a NOx sensor). In the present embodiment, a sensor element is constituted by the three cells. Note that the monitor cell may be referred to as a second pump cell because it has a function of discharging oxygen in gas, similarly to the pump cell. FIG. 2A is a cross-sectional view illustrating the structure of the distal end portion of the sensor element, and FIG. 2B is a cross-sectional view taken along line AA of FIG. 2A.
[0023]
In the gas concentration sensor 100, solid electrolytes (solid electrolyte elements) 141 and 142 made of an oxygen ion conductive material are formed in a sheet shape, and are spaced apart from each other at predetermined intervals above and below the figure via spacers 143 made of an insulating material such as alumina. It is laminated. Among them, a pinhole 141a is formed in the solid electrolyte 141 on the upper side of the figure, and exhaust gas around the sensor is introduced into the first chamber 144 via the pinhole 141a. The first chamber 144 communicates with the second chamber 146 via the throttle 145. Reference numeral 147 is a porous diffusion layer.
[0024]
A pump cell 110 is provided in the lower solid electrolyte 142 so as to face the first chamber 144, and the pump cell 110 discharges or pumps oxygen in exhaust gas introduced into the first chamber 144. It works and detects the oxygen concentration in the exhaust gas when discharging or pumping oxygen. Here, the pump cell 110 has a pair of upper and lower electrodes 111 and 112 with the solid electrolyte 142 interposed therebetween. Among them, the electrode 111 on the side of the first chamber 144 is a NOx inert electrode (an electrode that hardly decomposes NOx gas). . The pump cell 110 decomposes oxygen existing in the first chamber 144 and discharges the oxygen from the electrode 112 to the atmosphere passage 150 side.
[0025]
Further, a monitor cell 120 and a sensor cell 130 are provided on the solid electrolyte 141 on the upper side of the figure so as to face the second chamber 146. The monitor cell 120 generates an electromotive force according to the residual oxygen concentration in the second chamber 146, or generates a current output according to the application of a voltage. The sensor cell 130 detects the NOx concentration from the gas after passing through the pump cell 110.
[0026]
In particular, in the present embodiment, as shown in FIG. 2B, the monitor cell 120 and the sensor cell 130 are arranged in parallel so as to be at the same position with respect to the flow direction of the exhaust gas. The electrode on the side of the atmosphere passage 148 is the common electrode 122. That is, the monitor cell 120 is composed of the solid electrolyte 141 and the electrode 121 and the common electrode 122 disposed opposite each other with the solid electrolyte 141 interposed therebetween, and the sensor cell 130 is similarly configured with the solid electrolyte 141 and the electrode 131 disposed opposite thereto with the electrode 131 interposed therebetween. And an electrode 122. The electrode 121 (electrode on the second chamber 146 side) of the monitor cell 120 is made of a noble metal such as Au-Pt which is inert to NOx gas, whereas the electrode 131 (electrode on the second chamber 146 side) of the sensor cell 130 is It is made of a noble metal such as platinum Pt or rhodium Rh which is active in NOx gas.
[0027]
FIG. 3A is a plan sectional view of the electrode arrangement of the monitor cell 120 and the sensor cell 130 viewed from the second chamber 146 side, and FIG. 3B is a view of the electrode arrangement of each of these cells viewed from the atmosphere passage 148 side. FIG. According to this configuration, the exhaust gas introduction distance is the same in the monitor cell 120 and the sensor cell 130. As a result, the sensitivity of the monitor cell 120 and the sensor cell 130 to residual oxygen after passing through the pump cell 110 becomes equal, and highly accurate gas concentration detection becomes possible. However, the electrodes of the monitor cell 120 and the sensor cell 130 are arranged in parallel in the flow direction of the exhaust gas as shown in FIG. It is also possible. For example, the monitor cell 120 is arranged on the upstream side (left side in the figure), and the sensor cell 13 is arranged on the downstream side (right side in the figure). Further, it is not essential to use the common electrode 122 in each cell, and it is also possible to use an individual electrode for each cell.
[0028]
An insulating layer 149 made of alumina or the like is provided on the lower surface of the solid electrolyte 142 in the figure, and the insulating layer 149 forms an air passage 150. Further, a heater (heating element) 151 for heating the entire sensor is embedded in the insulating layer 149. The heater 151 generates heat energy by external power supply in order to activate the entire sensor including the pump cell 110, the monitor cell 120, and the sensor cell 130.
[0029]
In the gas concentration sensor 100 having the above configuration, the exhaust gas is introduced into the first chamber 144 through the porous diffusion layer 147 and the pinhole 141a. When this exhaust gas passes near the pump cell 110, a decomposition reaction occurs by applying a voltage Vp between the pump cell electrodes 111 and 112, and oxygen is passed through the pump cell 110 according to the oxygen concentration in the first chamber 144. Get in and out. At this time, since the electrode 111 on the first chamber 144 side is a NOx inactive electrode, NOx in the exhaust gas is not decomposed in the pump cell 110, and only oxygen is decomposed and discharged to the atmosphere passage 150. Then, the concentration of oxygen contained in the exhaust gas is detected based on the current flowing through the pump cell 110 (pump cell current Ip).
[0030]
The exhaust gas that has passed near the pump cell 110 flows into the second chamber 146, and the monitor cell 120 generates an output according to the residual oxygen concentration in the gas. The output of the monitor cell 120 is detected as a monitor cell current Im by applying a predetermined voltage Vm between the monitor cell electrodes 121 and 122. In addition, when a predetermined voltage Vs is applied between the sensor cell electrodes 131 and 122, NOx in the gas is reduced and decomposed, and oxygen generated at that time is discharged to the atmosphere passage 148. At this time, the concentration of NOx contained in the exhaust gas is detected based on the current flowing through the sensor cell 130 (sensor cell current Is).
[0031]
Incidentally, in the pump cell 110, the applied voltage Vp is variably controlled according to the oxygen concentration in the exhaust gas (that is, the pump cell current Ip) in each case. For example, based on the limit current characteristic of the pump cell 110, Using the created applied voltage map, the applied voltage Vp is controlled according to the pump cell current Ip in each case. Thereby, the applied voltage control is performed such that the applied voltage shifts to the higher voltage side as the oxygen concentration in the exhaust gas increases.
[0032]
Next, the electrical configuration of the gas concentration detection device will be described with reference to FIG. Although FIG. 1 shows a gas concentration detection device using the above-described gas concentration sensor 100, the electrode arrangement of the monitor cell 120 and the sensor cell 130 is shown side by side for convenience.
[0033]
In FIG. 1, a microcomputer (hereinafter abbreviated as a microcomputer) 300 includes a well-known logical operation circuit including a CPU, an A / D converter, a D / A converter, an I / O port, and the like. Applied voltages to the cells 110 to 130 are appropriately output from D / A converters (D / A0 to D / A2). Further, the microcomputer 300 converts the voltages of the terminals Vc, Ve, Vd, Vb, Vg, Vh in the sensing circuit 200 into an A / D converter (A / D converter) in order to capture the measurement result of the current flowing through each of the cells 110 to 130. D0 to A / D5). The microcomputer 300 detects the oxygen concentration (A / F) and the NOx concentration in the exhaust gas based on the current values measured by the pump cell 110 and the sensor cell 130, and converts the detection result into a D / A converter (D / A4, D / A4). / A3) and output to an external engine ECU or the like via a communication circuit.
[0034]
For details of the configuration of the sensing circuit 200, in the pump cell 110, a reference voltage Va is applied to one electrode 112 by a reference power supply 201 and an operational amplifier 202, and to the other electrode 111 via an operational amplifier 203 and a current detection resistor 204. The command voltage Vb of the microcomputer 300 is applied. When a current flows through the pump cell 110 according to the oxygen concentration in the exhaust gas when the command voltage Vb is applied, the current is detected by the current detection resistor 204. That is, both terminal voltages Vb and Vd of the current detection resistor 204 are taken into the microcomputer 300, and the pump cell current Ip is calculated from the voltages Vb and Vd.
[0035]
The reference voltage Vf is applied to the common electrode 122 of the monitor cell 120 and the sensor cell 130 by the reference power supply 205 and the operational amplifier 206, and the operational amplifier 207 and the current detection resistor 208 are applied to the sensor cell electrode 131 different from the common electrode 122. The command voltage Vg of the microcomputer 300 is applied via the microcomputer 300. When a current flows through the sensor cell 130 in accordance with the NOx concentration in the gas when the command voltage Vg is applied, the current is detected by the current detection resistor 208. That is, both terminal voltages Vg and Vh of the current detection resistor 208 are taken into the microcomputer 300, and the sensor cell current Is is calculated based on the voltages Vg and Vh.
[0036]
The command voltage Vc of the microcomputer 300 is applied to the monitor cell electrode 121 which is different from the common electrode 122 via an LPF (low pass filter) 209, an operational amplifier 210 and a current detection resistor 211. When a current flows through the monitor cell 120 according to the residual oxygen concentration in the gas when the command voltage Vc is applied, the current is detected by the current detection resistor 211. That is, both terminal voltages Vc and Ve of the current detection resistor 211 are taken into the microcomputer 300, and the monitor cell current Im is calculated based on the voltages Vc and Ve. Note that the LPF 209 is realized by, for example, a primary filter including a resistor and a capacitor.
[0037]
In the present embodiment, a so-called sweep method is used to detect the element impedance as the “element resistance value” for the monitor cell 120, for example. That is, when the impedance of the monitor cell 120 is detected, the microcomputer 300 instantaneously switches the monitor cell applied voltage (command voltage Vc) to at least one of the positive side and the negative side (for example, in a time of about several tens to 100 μsec). This applied voltage is applied to both electrodes of the monitor cell 120 while being sinusoidally smoothed by the LPF 209. The frequency of the AC voltage is preferably 10 kHz or more, and the time constant of the LPF 209 is set at about 5 μsec. Then, the element impedance of the monitor cell 120 is calculated from the voltage change amount and the current change amount at that time (impedance = voltage change amount / current change amount). Note that, instead of the element impedance, the element admittance, which is the reciprocal of the element impedance, may be detected as the element resistance value.
[0038]
Incidentally, in the monitor cell 120 and the sensor cell 130, one of the electrodes is used as the common electrode 122, so that the drive circuit on the reference voltage side can be reduced, and the number of lead wires from the gas concentration sensor 100 can be reduced. Can be In addition, since the monitor cell 120 and the sensor cell 130 are formed adjacent to each other with the same solid electrolyte 141, a current flows to the adjacent electrode during the sweep, and the detection accuracy of the element impedance may be deteriorated. Is provided, one electrode has the same potential, and this effect can be reduced.
[0039]
In the monitor cell 120, only a current of about several μA flows when detecting the residual oxygen concentration, whereas a current of about several mA flows when sweeping for impedance detection. If currents of different orders are detected by the same detection resistor, over-range may occur or detection accuracy may deteriorate. Therefore, in the present embodiment, the current detection resistor is switched between when the residual oxygen is detected by the monitor cell 120 and when the impedance is detected. Specifically, another current detection resistor 212 and a switch circuit 213 (for example, a semiconductor switch) are provided in parallel with the current detection resistor 211. The switch circuit 213 is configured to be turned ON / OFF by an output from an I / O port of the microcomputer 300. In this case, at the time of normal gas concentration detection, the switch circuit 213 is turned off (open), and the monitor cell current Im is detected by a resistance of about several hundred kΩ by the current detection resistor 211. On the other hand, at the time of impedance detection, the switch circuit 213 is turned on (closed), and the monitor cell current Im is detected by a resistance of about several hundred Ω by the current detection resistors 211 and 212.
[0040]
The heater 151 of the gas concentration sensor 100 is intermittently energized by the heater drive circuit 250. That is, the heater drive circuit 250 includes the MOSFET 251 as a switching element for driving the heater, the MOSFET 252 for backflow prevention connected to the MOSFET 251 in the opposite direction, and the driver 253 for driving the MOSFET. The CPU in the microcomputer 300 outputs the control command value Duty from the I / O port to drive the MOSFET driver 253. At this time, the power supplied from the power supply 254 (for example, battery power supply: VB = 12 V) to the heater 151 is PWM-controlled by the MOSFET 251, whereby the heater 151 is intermittently energized.
[0041]
The sensing circuit 200, the heater driving circuit 250, the microcomputer 300 described above, and the like are mounted on the same circuit board. Then, electrical connection to the gas concentration sensor 100, the engine ECU, and the like is made through a connector portion provided on the circuit board. In this case, the circuit board is configured by a multilayer board in which a plurality of (for example, six) insulating layers are stacked. That is, a conductor pattern made of copper foil or the like is provided for each insulating layer, a through hole is formed in the insulating layer, and conduction between the insulating layers is made through a conductor member filled in the through hole. Conventionally, various techniques have been proposed and put into practical use with respect to the multilayer substrate structure. Since the multilayer substrate structure may employ any technique, detailed illustration and description thereof will be omitted. The main configuration of the present embodiment will be described with reference to FIGS.
[0042]
First, a row of terminals provided on a circuit board will be described with reference to FIG. As shown in FIG. 4, a plurality of terminals (T1 to T9 and the like) are arranged in a line at a side edge of the circuit board, and each cell 110 to 110 of the gas concentration sensor 100 is arranged through these terminals. In addition to the electrical operation of the heater 130 and the heater 151, communication with another device is performed. To briefly explain the main components, the pump cell 110 is connected between the terminals T8 and T9, the monitor cell 120 is connected between the terminals T1 and T3, and the sensor cell 130 is connected between the terminals T2 and T3. The terminal T3 is a common terminal of the monitor cell and the sensor cell. The heater 151 is connected between the terminals T5 and T7. The terminal T4 is a ground terminal (ground terminal portion), and a reference potential (0 V in this embodiment) is taken in from the outside through the terminal T4. The terminal T6 is a battery terminal, and a battery voltage is taken in through the terminal T6.
[0043]
FIG. 5 shows a main part of two insulating layers Z1 and Z2 among a plurality of insulating layers. Each of the insulating layers Z1 and Z2 has the terminal row described in FIG. It is provided similarly. The power supply pattern P1 for the heater drive circuit 250 is provided on the insulating layer Z1 shown in FIG. The heater current ih flows through the power supply pattern P1 in the direction of the arrow in the figure.
[0044]
Further, a ground pattern P2 connected to the ground terminal T4 is provided on the insulating layer Z2 shown in FIG. The ground pattern P2 integrally has a ground pattern P3 for a sensing circuit and a ground pattern P4 for a heater drive circuit. These ground patterns P3 and P4 are separated from the ground terminal T4 as a starting point. Is provided. In other words, it can be said that the ground terminal T4 is provided at the branch point B1 of each of the ground patterns P3 and P4. In this case, in particular, the ground patterns P3 and P4 are provided in two different directions on the circuit board (that is, in a state where they are opened by about 180 degrees). The heater current ih flows through the ground pattern P4 for the heater drive circuit in the direction of the arrow in the figure.
[0045]
According to the ground pattern configuration shown in FIG. 5B, since the ground patterns P3 and P4 are separately arranged with the ground terminal T4 interposed therebetween, it is possible to prevent the heater current ih from sneaking into the sensing circuit 200, and , The stabilization of the reference potential can be realized. That is, while the heater current is on the order of A (Amperes), the sensor cell current is on the minute level of nA (NanoAmps), so that the sensing circuit 200 may be adversely affected by noise generated in the heater drive system. However, these problems are solved.
[0046]
5A and 5B, the installation region R1 of the sensing circuit 200 and the installation region R2 of the heater driving circuit 250 are indicated by dotted frames, and these regions R1 and R2 are separated from each other. It can be seen that they are provided at the positions shown. In this case, in the heater driving circuit 250, a magnetic flux is generated by the heater current ih flowing in the circuit 250, and the electromagnetic wave noise accompanying the magnetic flux may also cause the deterioration of the detection accuracy of the NOx concentration. However, according to the present configuration, such a disadvantage is solved. You.
[0047]
On the heater drive circuit 250 side, the ground pattern P4 and the power supply pattern P1 are provided on the different insulating layers Z1 and Z2 so as to overlap each other, and the directions of the heater currents ih of these patterns are opposite to each other. It has become. FIG. 6 is a plan view showing that the power-source-side and ground-side patterns P1 and P4 are arranged in an overlapping state. In this case, a magnetic flux is generated when the heater current ih flows through the patterns P1 and P4 on the power supply side and the ground side. However, since the directions of the heater currents ih flowing through the respective patterns are opposite to each other, the magnetic fluxes of the respective patterns are mutually different. Be countered. Therefore, the influence of the electromagnetic wave noise generated by the heater current ih can be reduced.
[0048]
By the way, comparing the case where the respective patterns on the power supply side and the ground side are provided side by side on the same insulating layer and the case where the respective patterns are provided on top of each other on different insulating layers, the former case shows the While the gap can be at least about 1 to 2 mm, in the latter case, the gap between the patterns (upper and lower intervals) is about 0.4 mm, which is the thickness of the insulating layer. Therefore, the effect of canceling out the magnetic flux can be enhanced by overlapping the patterns vertically.
[0049]
The patterns P1 and P4 are preferably provided so as to be overlapped with each other in an area of 50% or more with the insulating layer interposed therebetween. More preferably, the overlapping portion of each pattern is set to 80% or more. As the overlapping area of each pattern becomes larger, the effect of reducing electromagnetic wave noise is enhanced.
[0050]
Further, looking at the ground pattern P4 for the heater drive circuit, a part thereof becomes thinner in the vicinity of the connection with the ground pattern P3 for the sensing circuit (branch point B1) (part A in the figure). In this case, a part of the ground pattern P4 having a small thickness has high resistance. Therefore, the influence of noise when the heater power is turned ON / OFF is less likely to be transmitted to the sensing circuit 200 side, and the reference potential of the sensing circuit 200 is further stabilized.
[0051]
According to the present embodiment described in detail above,
(1) The ground pattern P3 for the sensing circuit and the ground pattern P4 for the heater drive circuit are separately arranged with the ground terminal T4 interposed therebetween.
(2) The installation area of the sensing circuit 200 and the installation area of the heater drive circuit 250 are provided at positions separated from each other;
(3) The ground pattern P4 and the power supply pattern P1 for the heater drive circuit are provided with the insulating layer interposed therebetween, and the directions of the current flows are reversed.
Thereby, the influence of noise from the heater drive system can be suppressed, and the detection accuracy of the NOx concentration is improved. In addition to this, the same effect is obtained in the detection of oxygen concentration by the pump cell 110, and the detection accuracy of oxygen concentration is improved.
[0052]
The present invention is not limited to the description in the above embodiment, and may be implemented, for example, as follows.
[0053]
In the above-described embodiment, the ground terminal is provided at a branch point between the ground pattern for the sensing circuit and the ground pattern for the heater drive circuit. A ground terminal may be provided at a position shifted to the ground pattern side or the opposite side. For example, the ground pattern P11 shown in FIG. 7 integrally includes a ground pattern P12 for a sensing circuit and a ground pattern P13 for a heater drive circuit. Each of the ground patterns P11 and P12 branches at a branch point B2. I have. In this case, unlike FIG. 5B, although the branch point B2 and the ground terminal T4 do not coincide with each other, the influence of noise from the heater drive system can be suppressed in such a case as in the above-described embodiment. Gas concentration detection accuracy is improved. In other words, as long as the difference between the branch point of each ground pattern and the ground terminal is within a range where there is substantially no influence (within a range where the reference potential does not fluctuate), it is allowed.
[0054]
In the above embodiment, the ground pattern for the sensing circuit and the ground pattern for the heater drive circuit are provided in two different directions on the circuit board (that is, in a state where they are opened by approximately 180 degrees). May be changed, and each ground pattern may be developed in an L shape or may be developed at an acute angle. However, it is preferable that the ground patterns do not intersect and are arranged so as not to be parallel.
[0055]
Instead of the configuration in which the ground terminal is provided directly on the ground pattern, a configuration corresponding to the ground terminal connected to the ground terminal and held at the same reference potential may be provided on the ground pattern. Specifically, as shown in FIG. 8, the ground pattern P2 and the ground terminal T4 are provided separately. Then, the terminal connection portion 11 (corresponding to the ground terminal portion) of the ground pattern P2 and the ground terminal T4 are electrically connected by the wiring 12. In this case, the terminal connection portion 11 may be provided at or near the branch point of the ground patterns P3 and P4, and even with such a configuration, the excellent effect described above is still obtained.
[0056]
In the gas concentration detection device of the above embodiment,
(1) a structure in which a ground pattern for a sensing circuit and a ground pattern for a heater drive circuit are separately arranged with a ground terminal interposed therebetween;
(2) a configuration in which the installation area of the sensing circuit and the installation area of the heater drive circuit are provided at positions separated from each other;
(3) a configuration in which a ground pattern and a power supply pattern for a heater drive circuit are provided with an insulating layer interposed therebetween, and the directions of current flow are reversed from each other;
Are adopted, but even if one or two of them are adopted, an effect which has not been achieved in the past can be obtained. Therefore, it is also possible to implement by selectively using the configurations (1) to (3).
[0057]
The configuration may be such that the plus side and the minus side of the electric wire for electrically connecting the circuit board and the heater are twisted. In this case, even if a magnetic flux is generated around the electric wire, the magnetic fluxes cancel each other, and the generation of noise is suppressed.
[0058]
In addition to the gas concentration sensor capable of detecting the NOx concentration, the present invention can be applied to a gas concentration sensor capable of detecting the HC concentration and the CO concentration as the gas concentrations of the specific components. In this case, the pump cell (first cell) exhausts excess oxygen in the gas to be detected, and the sensor cell (second cell) decomposes HC and CO from the gas after exhausting excess oxygen to reduce the HC and CO concentrations. To detect.
[0059]
The present invention is also applicable to an A / F sensor. For example, when the ground pattern for the sensing circuit and the ground pattern for the heater driving circuit are arranged at relatively close positions due to restrictions on the circuit arrangement, the influence of noise due to heater driving is also concerned. Even in such a case, the variation of the reference potential can be suppressed by applying the present invention, and highly accurate detection of the oxygen concentration (air-fuel ratio) can be realized.
[0060]
Furthermore, it is also possible to use the gas concentration detecting device other than those for automobiles, and to use gas other than exhaust gas as the gas to be detected.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an outline of a gas concentration detection device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration of a gas concentration sensor.
FIG. 3 is a plan sectional view showing electrode arrangement of a monitor cell and a sensor cell.
FIG. 4 is a plan view for explaining a terminal row of a circuit board.
FIG. 5 is a plan view showing a power supply pattern and a ground pattern.
FIG. 6 is a plan view showing a power supply pattern and a ground pattern.
FIG. 7 is a plan view showing another configuration example of the ground pattern.
FIG. 8 is a plan view showing another configuration example of the ground pattern.
[Explanation of symbols]
100 ... gas concentration sensor,
110 ... pump cell,
120 monitor cell,
130 ... sensor cell,
141, 142 ... solid electrolyte,
144 ... first chamber,
146 ... second chamber,
151 ... heater,
200… Sensing circuit,
250: heater drive circuit,
P1 ... power supply pattern,
P3, P12: Ground pattern for sensing circuit
P4, P13: Ground pattern for heater drive circuit,
T4: Ground terminal.

Claims (13)

The present invention is applied to a gas concentration sensor including a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected, and a heater for heating the sensor element to a predetermined active state. And a heater drive circuit for intermittently energizing the heater. Each of these circuits is mounted on the same circuit board, and each circuit has an external reference potential through a ground terminal. In a gas concentration detection device configured to take in
Gas concentration detection, wherein a ground pattern for setting a reference potential in the sensing circuit and a ground pattern for setting a reference potential in the heater drive circuit are provided separately from the ground terminal portion or its vicinity as a starting point. apparatus. The present invention is applied to a gas concentration sensor including a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected, and a heater for heating the sensor element to a predetermined active state. And a heater drive circuit for intermittently energizing the heater. Each of these circuits is mounted on the same circuit board, and each circuit has an external reference potential through a ground terminal. In a gas concentration detection device configured to take in
A ground pattern for setting a reference potential in the sensing circuit and a ground pattern for setting a reference potential in the heater drive circuit are integrally provided on the circuit board, and the ground terminal portion is provided at a branch point of each of the ground patterns. A gas concentration detection device, comprising: The present invention is applied to a gas concentration sensor including a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected, and a heater for heating the sensor element to a predetermined active state. And a heater drive circuit for intermittently energizing the heater. Each of these circuits is mounted on the same circuit board, and each circuit has an external reference potential through a ground terminal. In a gas concentration detection device configured to take in
A ground pattern for setting a reference potential in the sensing circuit and a ground pattern for setting a reference potential in the heater drive circuit are integrally provided on the circuit board, and any one of the branch points of these ground patterns is provided. A gas concentration detection device, wherein the ground terminal portion is provided at a position shifted to a ground pattern side or a reverse side thereof. 4. The gas concentration detection device according to claim 1, wherein a ground pattern for a sensing circuit and a ground pattern for a heater drive circuit are provided in two different directions on the circuit board. 4. The gas concentration detection device according to claim 1, wherein a ground pattern for the sensing circuit and a ground pattern for the heater drive circuit are provided so as not to be parallel on the circuit board. 6. The gas concentration detection device according to claim 1, wherein a ground pattern for the heater drive circuit is partially narrowed near a connection portion with the ground pattern for the sensing circuit. The gas concentration detection device according to claim 1, wherein an installation area of the sensing circuit and an installation area of the heater drive circuit on a circuit board are provided at positions separated from each other. The circuit board is a multilayer board in which a plurality of insulating layers are stacked, and a ground pattern and a power supply pattern for a heater drive circuit are provided one above the other with the insulating layer interposed therebetween, and the direction of current flow in each of the patterns is provided. The gas concentration detecting device according to any one of claims 1 to 7, wherein the gas concentration detecting devices are configured to be reversed. The present invention is applied to a gas concentration sensor including a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected, and a heater for heating the sensor element to a predetermined active state. And a heater drive circuit for intermittently energizing the heater. Each of these circuits is mounted on the same circuit board, and each circuit has an external reference potential through a ground terminal. In a gas concentration detection device configured to take in
A gas concentration detection device, wherein an installation area of the sensing circuit and an installation area of the heater drive circuit on a circuit board are provided at positions separated from each other. The present invention is applied to a gas concentration sensor including a sensor element having a solid electrolyte and detecting a gas concentration of a specific component in a gas to be detected, and a heater for heating the sensor element to a predetermined active state. And a heater drive circuit for intermittently energizing the heater. Each of these circuits is mounted on the same circuit board, and each circuit has an external reference potential through a ground terminal. In a gas concentration detection device configured to take in
The circuit board is a multilayer board in which a plurality of insulating layers are stacked, and a ground pattern and a power supply pattern for a heater drive circuit are provided one above the other with the insulating layer interposed therebetween, and the direction of current flow in each of the patterns is provided. Are configured to be opposite to each other. 11. The gas concentration detection device according to claim 8, wherein a ground pattern and a power supply pattern for the heater drive circuit are provided so as to be overlapped with each other in an area of 50% or more with an insulating layer interposed therebetween. The sensor element includes a first cell that discharges or pumps oxygen in the gas to be detected introduced into the chamber, and oxygen ions that take in the gas after passing through the first cell to decompose specific components in the gas and move at that time. The gas concentration according to any one of claims 1 to 11, further comprising: a second cell configured to detect a gas concentration of a specific component from the amount, wherein the sensing circuit measures at least a minute current flowing through the second cell. Detection device. The sensor element decomposes oxygen in the gas to be detected and detects the oxygen concentration from the amount of oxygen ions moving at that time, and the sensing circuit measures a minute current flowing at the time of decomposing oxygen. Item 12. The gas concentration detection device according to any one of Items 1 to 11.

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