JP4538006B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detection device for detecting automobile exhaust gas and malodorous gas contained in the atmosphere.

  Japanese Laid-Open Patent Publication No. 2001-281185 includes a damper that switches the air circulation path to the vehicle interior to either outside air introduction or inside air circulation, and automatically opens and closes the damper to control the interior of the vehicle interior. Disclosed is a gas detection device for use in an air quality control system that keeps air clean.

  This gas detection device detects whether or not exhaust gas is contained in the atmosphere, and the air quality control system automatically performs damper switching control based on the detection result. That is, the gas detection device compares the exhaust gas concentration in the atmosphere with a predetermined threshold level and outputs the result to the air quality control system. Then, the air quality control system switches the damper to the inside air side when the exhaust gas concentration exceeds the threshold level based on the detection signal from the gas detection device, and dirty outside air enters the vehicle interior. When the exhaust gas concentration falls below the threshold level, the damper is switched to the outside air side to introduce clean outside air into the vehicle interior.

  However, this gas detection device outputs the result of comparing the level of the exhaust gas concentration in the atmosphere and the threshold level to the air quality control system, and the air quality control system uses the detection result to set the damper. Since switching to the inside air side or the outside air side, the threshold level could not be set on the air quality control system side. Therefore, on the air quality control system side, it is not possible to set the exhaust gas concentration when switching the damper to the inside air side or the outside air side, and user convenience is poor. Therefore, in order to improve such inconvenience, it has been desired to output a contamination signal indicating the degree of contamination of the outside air from the gas detection device.

  In addition, when a dirt signal is output from the gas detection device, an air quality control system in which an activated carbon filter is installed in the middle of the duct connecting the damper and the passenger compartment, and the exhaust gas in the air is adsorbed by the activated carbon filter. In order to suppress the adsorption capacity of the activated carbon filter from being lowered or deteriorated in a short time, it is possible to adjust the opening / closing angle of the damper and the air volume of the fan according to the detection result of the gas detection device. . That is, when the exhaust gas concentration is high, the damper is almost closed and slightly ventilated, and when the exhaust gas concentration is low, the damper is slightly closed and the ventilation rate is increased. By controlling the opening / closing angle, it is possible to suppress the adsorption capacity of the activated carbon filter from decreasing or deteriorating in a short time, but in order to control such an opening / closing angle, the degree of contamination of the outside air from the gas detection device is controlled. It is necessary to output the dirt signal shown.

  As described above, when it is desired to output a contamination signal from the gas detection device to the air quality control system, it is conceivable to output the contamination signal as an analog signal (for example, a voltage signal). However, when the gas detector is installed in an automobile, it is difficult to match the signal ground level between the gas detector and the air quality control system in the automobile, and the digital signal is converted into an analog signal on the gas detector side. Since the D / A converter requires an A / D converter for converting an analog signal into a digital signal on the air quality control system side, there is a problem in that the cost increases.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a gas detection device that can output a contamination signal indicating the degree of contamination of outside air to the outside without incurring high costs. provide.

  The gas detection device according to the present invention is an air quality control system that controls the quality of air in the vehicle interior by changing the amount of outside air introduced into the vehicle interior and the amount of internal air circulating in the vehicle interior. A dirt signal indicating the degree of dirt in the outside air is output. This gas detection device includes a sensor, a gas detection means, and a signal output means. The sensor generates an output signal indicating the gas concentration of the detection target gas. The gas detection means outputs a dirt signal indicating the degree of dirt in the outside air based on the output signal of the sensor. The signal output means outputs the contamination signal input from the gas detection means as a digital quantity.

  As described above, the signal output means, which is a characteristic part of the present invention, outputs a dirt signal indicating the degree of dirt in the outside air in a digital quantity. Therefore, in the air quality control system, the signal output means is based on the dirt signal sent in a digital quantity. Detecting the degree of outside air contamination, and keeping the air inside the vehicle interior clean by changing the amount of outside air introduced into the vehicle interior and the amount of inside air circulating through the vehicle interior according to the degree of outside air contamination Can do. In addition, since the signal output means outputs the dirt signal in a digital quantity, a D / A converter is provided in the gas detector as in the case of outputting the degree of dirt in the outside air as an analog signal, or an air quality control system. There is no need to provide an A / D converter, and the cost of the gas detection device and the entire system can be reduced.

  Here, it is also preferable that the dirt signal input from the gas detection means is converted into a PWM signal whose duty ratio changes discretely according to the degree of dirt in the outside air, and the open collector output is 1 as the dirt signal. If it is, signal output means can be realized, and signal output means can be realized with a simple circuit.

  Further, as the sensor, an oxidizing gas sensor for detecting an oxidizing gas discharged from a diesel vehicle, and a reducing gas sensor for detecting a reducing gas including exhaust gas and bad odor gas from a gasoline vehicle. Are provided with the gas detection means corresponding to each of the oxidizing gas sensor and the reducing gas sensor, and both gas detection means are dirt indicating the degree of contamination of the outside air from the output signals of the corresponding sensors. It is preferable to output a signal, and the signal output means converts the dirt signal having a greater degree of dirt out of the dirt signals input from both gas detection means into the PWM signal and outputs the PWM signal. Thus, the two gas detection means respectively output a dirt signal indicating the degree of dirt of the outside air from the outputs of the oxidizing gas sensor and the reducing gas sensor, and the signal output means indicates the degree of dirt among these dirt signals. Since the larger one is converted into a PWM signal and output, the degree of contamination of the outside air is reliably detected and output to the air quality control system even in an environment where exhaust gas or odorous gas from diesel vehicles or gasoline vehicles exists. can do.

  Further, the sensor is composed of a gas sensitive body whose resistance value changes according to the gas concentration of the gas to be detected, and the gas detecting means sets the resistance value of the gas sensitive body in clean air as a reference value. The difference between the resistance value of the gas sensor in the detection target gas and the reference value is obtained, and the resistance ratio is calculated by dividing the difference by the reference value, and further, the resistance value variation of each gas sensor is calculated. It is also preferable to output a value obtained by multiplying the resistance ratio by a correction coefficient for correction as the dirt signal. The resistance value of the gas sensitive body may vary depending on temperature and humidity, but the gas detection means obtains the difference between the resistance value and the reference value, and divides this difference by the reference value to convert it into a resistance ratio. Therefore, the fluctuation of the value due to temperature and humidity can be reduced. In addition, since the gas detection means uses the value obtained by multiplying the calculation result of the resistance ratio by the correction coefficient as the contamination signal, it is possible to correct variations in sensitivity of individual gas sensitive bodies.

It is a block diagram of the air quality control system using the gas detection apparatus of one Embodiment of this invention. It is explanatory drawing of a reference value update same as the above. It is the front view which abbreviate | omitted a part of gas sensor used for the same as the above. It is a flowchart of the air quality determination operation | movement using an oxidizing gas sensor. It is a flowchart of the air quality determination operation | movement using a reducing gas sensor. It is a flowchart of the routine which updates the reference value with respect to the sensor resistance of an oxidizing gas sensor in a clean direction. It is a flowchart of the routine which updates the reference value with respect to the sensor resistance of a reducing gas sensor in a clean direction. It is a flowchart of the routine which updates the reference value with respect to the sensor resistance of an oxidizing gas sensor in the dirt direction. It is a flowchart of the routine which updates the reference value with respect to the sensor resistance of a reducing gas sensor in the dirt direction. It is a disassembled perspective view of a gas detection apparatus. It is an external appearance perspective view of a gas detection apparatus. It is an external appearance perspective view which fractures | ruptures partially which shows the other structure of the gas sensor used for the same as the above. It is an external appearance perspective view of the gas sensitive body used for the same as the above.

Hereinafter, the present invention will be described in detail based on preferred embodiments.
(First embodiment)
FIG. 1 shows a block diagram of a gas detection device A of the present embodiment. The gas detection device A includes an oxidizing gas sensor 1 having sensitivity to oxidizing gas such as NOx discharged from a diesel vehicle, hydrocarbon (HC) and carbon monoxide (CO) discharged from a gasoline vehicle, A gas concentration of diesel exhaust gas is detected based on the electric characteristic values of the reducing gas sensor 2 having sensitivity to a reducing gas such as malodorous gas, the A / D converters 31 and 32, and the oxidizing gas sensor 1. 1 gas detection unit 33, a second gas detection unit 34 that detects the gas concentration of a reducing gas such as gasoline exhaust gas or malodorous gas based on the electrical characteristic values of the reducing gas sensor 2, A PWM signal output unit 35 that outputs a dirt signal Vp composed of a PWM signal representing the degree of dirtiness of the outside air as a duty ratio based on the detection results of the two gas detectors 33 and 34; An updating unit 36, and a sensor driver 37 as main components. The A / D converters 31 and 32, the first and second gas detection units 33 and 34, the PWM signal output unit 35, the reference value update unit 36, and the sensor driving unit 37 include an A / D converter. It is configured using a microcomputer.

  This gas detection device A is used in an air quality control system for automobiles. The air quality control system includes an outside air introduction duct 52 that introduces air outside the vehicle (outside air) and an inside air introduction duct that circulates and guides the air inside the vehicle (inside air) upstream of a duct 51 that sends air into the vehicle interior. The duct 53 is connected. A damper 50 for switching the air inflow path to the duct 52 or the duct 53 is disposed at a connection portion between the ducts 52 and 53 and the duct 51. The damper 50 is controlled to be opened and closed by the damper driving unit 40. The In addition, a fan for blowing air (not shown) is arranged on the downstream side of the duct 51. When the fan is operated, air taken in from the duct 52 or 53 is guided to the vehicle interior through the duct 51.

  Here, the gas detection device A uses the oxidizing gas sensor 1 and the reducing gas sensor 2 to detect the gas concentrations of exhaust gas and malodorous gas discharged from diesel vehicles and gasoline vehicles, and expresses the gas concentration as a duty ratio. The dirt signal Vp consisting of the PWM signal is output. The air conditioning control microcomputer 41 outputs a control signal for controlling the opening / closing of the damper 50 based on the dirt signal from the gas detection device A, and the damper control unit 40 drives the damper 50 to open / close based on this control signal. For example, when the exhaust gas concentration or the malodorous gas concentration becomes high, the air conditioning control microcomputer 41 outputs a control signal for setting the inside air circulation mode for circulating the air in the vehicle interior to the damper driving unit 40, and the damper driving unit 40 ducts the damper 50. Switch to the 53 side (inside air side) to prevent the inflow of dirty air. On the other hand, when the exhaust gas concentration and the malodorous gas concentration become low, the air conditioning control microcomputer 41 outputs a control signal for setting the outside air introduction mode for introducing outside air into the vehicle interior to the damper driving unit 40, and the damper driving unit 40 causes the damper 50 to turn on the damper 50. By switching to the duct 52 side (outside air side), clean outside air is taken into the vehicle interior.

The oxidizing gas sensor 1 used in the gas detection apparatus A is a conventionally known semiconductor gas sensor, and as shown in FIG. 3, a gas-sensitive gas formed in a substantially spherical shape mainly composed of a metal oxide semiconductor such as tin oxide (SnO ₂ ). A body 11 is provided. The gas sensitive body 11 is formed of a material having sensitivity characteristics that selectively detect oxidizing gas such as NOx discharged from a diesel vehicle. When the gas concentration of the oxidizing gas increases, the gas sensitive body 11 Changes in the direction of increasing the electrical resistance. The gas sensing element 11 is embedded with a heater electrode 12 made of coiled platinum and a resistance detection electrode 13 made of a noble metal wire so as to penetrate the center of the coil of the heater electrode 12. . The lead wires 3 and 5 are formed from both ends of the heater / electrode 12 protruding from the gas sensitive body 11, and the lead wire 4 is formed from one end of the resistance detection electrode 13 protruding from the gas sensitive body 11. The oxidizing gas sensor 1 is attached to three terminals 6 to 8 penetrating a resin base 9 via lead wires 3 to 5.

  FIG. 1 shows the configuration of a circuit that controls energization to the heater electrode 12 of the oxidizing gas sensor 1 and detects a gas to be detected from a change in resistance value of the gas sensitive body 11. A constant voltage Vc is applied to the heater electrode 12 via the switch element Q1, and the heater electrode 12 is energized when the switch element Q1 is turned on. On the other hand, one end of the resistance detection electrode 13 is connected to one end of a series circuit of the switch element Q2 and the load resistor R12 and one end of the load resistor R11. When the switch element Q2 is on, the load resistors R11, R12 are connected. The constant voltage Vc is applied through the parallel circuit, and when the switch element Q2 is turned off, the constant voltage Vc is applied only through the load resistor R11. One end of the resistance detection electrode 13 is also connected to the input terminal of the A / D converter 31.

  The switch elements Q1 and Q2 are turned on / off by drive signals a and c input from the sensor drive unit 37, respectively. When the switch element Q1 is turned on by the drive signal a, the heater electrode 12 is energized, and the gas sensitive body 11 is heated by the heat generated by the heater electrode 12. Therefore, the sensor driving unit 37 performs duty control to energize the heater electrode 12 for a predetermined time (about 0.16 mS) every predetermined period (for example, about every 7.8 mS), so that the gas sensitive body 11 is heated to about 300 ° C. Heat to.

  During the period when the heater combined electrode 12 is not energized, the A / D converter 31 performs A / D conversion on the output voltage of the oxidizing gas sensor 1 every predetermined sampling period ts, and the sensor output converted into a digital value. Vd is output to the first gas detector 33. Here, when the switch element Q2 is turned on by the drive signal b, the load resistor R12 is connected in parallel with the load resistor R11, and the combined resistance value of the load resistor connected to the resistance detection electrode 13 is switched in two ways. That is, when the signal level input to the A / D converter 31 is reduced, the sensor driving unit 37 is input to the A / D converter 31 by turning on the switch element Q2 to reduce the load resistance value. The signal level is increased to prevent the detection accuracy of the sensor output from being lowered.

The reducing gas sensor 2 is also composed of a semiconductor gas sensor having the same structure as that of the oxidizing gas sensor 1, and includes a gas sensitive body 21 formed in a substantially spherical shape with a metal oxide semiconductor such as tin oxide (SnO ₂ ) as a main component. . The gas sensitive body 21 is formed of a material having a sensitivity characteristic that selectively detects reducing gas such as HC and CO or malodorous gas (for example, ammonia) contained in exhaust gas from a gasoline vehicle. As the gas concentration of the gas increases, the resistance value of the gas sensitive body 21 changes in the direction of decreasing. The gas sensitive body 21 is embedded with a heater electrode 22 made of coiled platinum and a resistance detection electrode 23 made of a noble metal wire so as to penetrate the center of the coil of the heater electrode 22. .

  A constant voltage Vc is applied to the heater combined electrode 22 of the reducing gas sensor 2 via the switch element Q3. One end of the resistance detection electrode 23 is connected to one end of the load resistor R21 and one end of a series circuit of the switch element Q4 and the load resistor R22. When the switch element Q4 is on, the load resistors R21, R22 are connected. The constant voltage Vc is applied through the parallel circuit, and when the switch element Q4 is turned off, the constant voltage Vc is applied only through the load resistor R21. One end of the resistance detection electrode 23 is connected to the input terminal of the A / D converter 32.

  The switch elements Q3 and Q4 are turned on / off by drive signals c and d input from the sensor drive unit 37, respectively. When the switch element Q3 is turned on by the drive signal c, the heater serving electrode 22 is energized and the gas sensitive body 21 is heated. Thus, the sensor driving unit 37 performs duty control to energize the heater electrode 22 for a predetermined time (about 0.19 mS) every predetermined period (for example, about every 7.8 mS), so that the gas sensitive body has a constant temperature. To be heated.

  Then, during the period when the heater electrode 22 is not energized, the A / D converter 32 A / D converts the output voltage of the reducing gas sensor 2 every predetermined sampling period ts, and the sensor output is converted into a digital value. Vg is output to the second gas detector 34. In the sensor driving unit 37, when the signal level input to the A / D converter 32 decreases, the signal input to the A / D converter 32 is turned on by turning on the switch element Q4 to lower the load resistance value. The level is increased to prevent the detection accuracy of the sensor output from being lowered. Further, in the sensor driving unit 37, the switching elements Q1 and Q3 are turned on half a cycle so that the heater heating period of the oxidizing gas sensor 1 and the heater heating period of the reducing gas sensor 2 do not overlap each other, thereby reducing current consumption. I am trying.

  Next, operation | movement of this gas detection apparatus A is demonstrated based on the flowchart of FIGS.

  FIG. 4 shows an operation in which the first gas detection unit 33 detects the oxidizing gas discharged from the diesel vehicle based on the output of the oxidizing gas sensor 1, and FIG. 5 shows the operation in which the second gas detection unit 34 has the reducing gas sensor 2. The operation of detecting reducing gas such as exhaust gas and odorous gas from gasoline cars based on the output of is shown. The first and second gas detection units 33 and 34 are configured to detect both sensors 1 and 2 based on the sensor outputs Vd and Vg input from the A / D converters 31 and 32 every time a predetermined sampling period elapses. Resistance values Rd and Rg are obtained (steps S1 and S11). Here, if 8-bit A / D converters are used for the A / D converters 31 and 32, the full scale (256) is Vc, and the resistance value of the load resistance is 256, both sensors 1 and 2 The resistance values Rd and Rg are expressed by the following formulas (1) and (2).

Rd = Vd × 256 / (256−Vd) (1)
Rg = Vg × 256 / (256−Vg) (2)
When the calculation of the resistance values Rd and Rg is completed, the reference value update unit 36 is set to the resistance value when the gas sensitive bodies 11 and 21 are placed in clean air, and dirt signals D and G described later are set. Update processing of the reference values Rdm and Rgm used for the determination is performed. First, the reference value update unit 36 determines whether or not an update period t for updating the reference values Rdm and Rgm in the clean direction has elapsed (steps S2 and S12).

  As a result of the determination in S2, if the update period t of the reference value Rdm used to calculate the contamination signal D indicating the degree of contamination by the oxidizing gas has elapsed, the reference value update unit 36 updates the reference value Rdm in the clean direction. After executing the processing routine (step S3), the process proceeds to a dirt calculation routine (step S6). As a result of the determination in S2, if the update period t has not elapsed since the previous update, the reference value update unit 36 determines whether or not the update period T for updating the reference value Rdm in the dirt direction has elapsed. (Step S4). Here, if the update cycle T has elapsed, the reference value updating unit 36 executes a routine for updating the reference value Rdm in the dirt direction (step S5), and then proceeds to the dirt calculation routine to send the dirt signal D. Calculate (step S6).

  Further, as a result of the determination in S12, if the update period t of the second reference value Rgm used for calculation of the dirt signal G indicating the degree of dirt due to the reducing gas has elapsed, the reference value update unit 36 determines that the resistance value Rg is It is determined whether or not the reference value Rgm0 is not less than the reference value Rgm0 at the previous update (step S13), and if the resistance value Rg is not less than the reference value Rgm0, a routine for updating the reference value Rgm in the clean direction is executed (step S14). If the update period t has not elapsed since the previous update in the determination in S12, or if the resistance value Rg is less than the reference value Rgm0 in the determination in S13, an update period T for updating the reference value Rgm in the dirt direction is set. It is determined whether or not it has elapsed (step S15). If the update period T has elapsed as a result of the determination in S15, the reference value update unit 36 executes a routine for updating the reference value Rgm in the dirt direction (step S16). Then, if the process of S14 or S16 is ended, or if the update period T has not elapsed since the previous update as a result of the determination of S15, the process shifts to a dirt calculation routine to calculate the dirt signal G (S17). ).

  Here, a routine for updating the reference value Rdm for the sensor resistance of the oxidizing gas in the clean direction will be described with reference to FIG. The reference value update unit 36 determines whether or not the reference value update in the clean direction is prohibited (S21). If the update process is not prohibited, the current sampled sensor resistance Rg and the previous reference value Rgm0 are determined. The contamination signal G obtained from the above is compared with a predetermined determination value G3 (S22). If the contamination signal G is greater than or equal to the determination value G3, updating of the reference value Rdm in the clean direction is prohibited (S25). Then, the update routine is terminated without updating the reference value. If the contamination signal G is smaller than the determination value G3 in the determination of S22, the reference value update unit 36 compares the resistance value Rd of the oxidizing gas sensor 1 sampled this time with the previous reference value Rdm0 (S23). ), If Rdm0 ≧ Rd, a value obtained by subtracting a value obtained by multiplying a reference value Rdm0 by subtracting the sensor resistance Rd from the reference value Rdm0 from the reference value Rdm0 at the previous update, The value Rdm is set (S24), and the update routine is terminated. Here, when the update ratio is 1 / Cd (Cd> 1), the reference value Rdm is expressed by the following equation.

Rdm = Rdm0− (Rdm0−Rd) / Cd (3)
If Rdm0 <Rd as a result of the determination in S23, the reference value update unit 36 ends the update routine without updating the reference value.

  As described above, the reference value update unit 36 prohibits the update of the reference value Rdm on the oxidizing gas sensor 1 side in the clean direction when the contamination signal G becomes equal to or higher than the determination value G3, but cancels the prohibition of the update process. The condition for this is that after the dirt signal G once falls below the judgment value G4 smaller than the judgment value G3, the state below the judgment value G3 continues for a predetermined number of times of sampling. That is, when the reference value update process is prohibited in S21, the reference value update unit 36 compares the size of the dirt signal G and the determination value G4 (S26), and if it is less than G4, sets 1 to the flag SSDRNW. Therefore, the process proceeds to step S29, and if it is equal to or greater than G4, the size of the dirt signal G and the determination value G3 are compared (S28). If the dirt signal G is greater than or equal to the determination value G3 in the determination of S28, the process proceeds to step S33, and if the dirt signal G is less than the determination value G3, it is determined whether or not the value of the flag SSDRNW is 1 (S29). Here, if the value of the flag SSDRNW is 0, the count value of the counter is reset to 0 (S33), and the processing routine is ended. On the other hand, when the value of the flag SSDRNW is 1, it is determined whether or not the counting of the predetermined number of samplings by the counter is finished (S30), and if the count is finished, prohibiting the update of the reference value in the cleaning direction is performed. After canceling (S31) and setting the value of the flag SSDRNW to 0 (S32), the process proceeds to step S23 to update the reference value. As a result of the determination in S30, if the count value has not reached the predetermined number of samplings, the processing routine is terminated.

  A routine for updating the reference value Rgm for the sensor resistance of the reducing gas in the clean direction will be described with reference to the flowchart of FIG. The routine for updating the reference value Rgm in the clean direction eliminates the process in S23 in the routine for updating the reference value Rdm in the clean direction by executing the process in S13 of FIG. 5 before proceeding to this update routine. Except for the points described above, the same processing as that of the update routine for the reference value Rdm is performed, and thus detailed description thereof is omitted. The processing of this update routine will be summarized and described. When the dirt signal D obtained from the previous reference value Rdm0 and the sensor resistance of the oxidizing gas sensor 1 becomes equal to or higher than a predetermined judgment value D3, the dirt signal D is once judged value D4. The process of updating the reference value Rgm in the clean direction is prohibited until the value less than (<D3) and then the state less than the determination value D3 reaches the predetermined number of samplings. When the update process of the reference value Rgm in the cleaning direction is not prohibited, the reference value update unit 36 multiplies the value obtained by subtracting the reference value Rgm0 at the previous update from the sensor resistance Rg. In addition, a value obtained by adding the reference value Rgm0 is set as a new reference value Rgm. Here, when the update ratio is 1 / Cg (Cg> 1), the reference value Rgm is expressed by the following equation.

Rgm = Rgm0 + (Rg−Rgm0) / Cg (4)
Next, a routine for updating the reference value Rdm for the sensor resistance of the oxidizing gas in the dirt direction will be described with reference to the flowchart of FIG. First, the reference value update unit 36 compares the sensor resistance Rd with the previous reference value Rdm0 (S46), and if Rd <Rdm0, sets the previous reference value Rdm0 as the new reference value Rdm and updates the update routine. If Rd ≧ Rdm0, the previous stain signal D is compared with the predetermined determination value D5 (S47). If the dirt signal D is less than the determination value D5 in the determination of S47, a value obtained by multiplying the value obtained by subtracting the reference value Rdm0 from the sensor resistance Rd by a predetermined update ratio (1 / Pd) is the update amount (= (Rd−Rdm0 ) / Pd) (S49), and if the dirt signal D is greater than or equal to the determination value D5, the dirt signal D is set to a constant Ld for adjusting the amount of update amount to a value obtained by subtracting the reference value Rdm0 from the sensor resistance Rd. A value obtained by multiplying the value divided by (Ld / D) is set as an update amount (= (Rd−Rdm0) × Ld / D) (S50). When the update amount is obtained in S49 or S50, the reference value update unit 36 determines whether or not the update amount is 1 or more (S51). If it is 1 or more, the update amount obtained in S49 or S50 to the previous reference value Rdm0. A value obtained by adding 1 is set as a new reference value Rdm (S52), and if it is less than 1, a value obtained by adding 1 to the previous reference value Rdm0 is set as a new reference value Rdm. That is, if the dirt signal D is less than the determination value D5, the reference value Rdm is expressed by the following equation (5), and if it is greater than or equal to the determination value D5, the reference value Rdm is expressed by the following equation (6). Note that Pd> 1 and Ld / D <1.

Rdm = Rdm0 + (Rd−Rdm0) / Pd (5)
Rdm = Rdm0 + (Rd−Rdm0) × Ld / D (6)
A routine for updating the reference value Rgm for the sensor resistance of the reducing gas sensor 2 in the dirt direction will be described with reference to the flowchart of FIG. In the routine for updating the reference value Rgm in the dirt direction, the same processing as the routine for updating the reference value Rdm in the dirt direction is performed, and thus detailed description thereof is omitted. The processing in this update routine will be described in summary. When the previous reference value Rgm0 is less than the sensor resistance Rg sampled this time, the previous reference value Rdm0 is set as a new reference value Rgm. On the other hand, if the previous reference value Rgm0 is greater than or equal to the sensor resistance Rg, and if the dirt signal G is less than the predetermined determination value G5, the new reference value Rgm is expressed by the following equation (7) and is greater than or equal to the determination value G5. For example, the new reference value Rgm is expressed by the following equation (8).

Rgm = Rgm0− (Rgm0−Rg) / Pg (7)
Rgm = Rgm0− (Rgm0−Rg) × Lg / G (8)
However, if Pg> 1, Lg / G <1, and (Rgm0−Rg) / Pg is less than 1 or (Rgm0−Rg) × Lg / G is less than 1, then Rgm = Rgm0-1.

  When the reference values Rdm and Rgm are determined as described above, the first and second gas detection units 33 and 34 perform the dirt signal calculation process using the sensor resistances Rd and Rg and the reference values Rdm and Rgm. Execute. That is, the gas detection units 33 and 34 subtract the reference values Rdm and Rgm determined in the above update routine from the resistance values Rd and Rg of the sensors 1 and 2 obtained by the equations (1) and (2). By dividing the value by the reference values Rdm and Rgm to obtain the resistance ratio, the sensitivity is normalized so that it does not depend on the sensor resistance value that varies with temperature and humidity, and the sensitivity between the sensors is multiplied by a correction coefficient. Are converted into a dirt signal D indicating the degree of air pollution caused by exhaust gas from the diesel vehicle, and a dirt signal G indicating the degree of air dirt caused by exhaust gas and bad odor gas from the gasoline car, respectively. Here, if Kd is a correction coefficient (Kd> 1) for correcting the variation among individuals of the oxidative gas sensor 1, and Kg is a correction coefficient (Kg> 1) for correcting the variation among individuals of the reducing gas sensor 2, contamination is caused. Signals D and G are expressed by the following equations.

D = (Rd−Rdm) × Kd / Rdm
G = (Rgm−Rg) × Kg / Rgm
The contamination signals D and G calculated by the first and second gas detection units 33 and 34 are input to the PWM signal output unit 35. The PWM signal output unit 35 sets the values of the contamination signals D and G as follows. The duty ratio is converted according to Table 1. Note that the duty ratio is 256 for one cycle of the PWM signal, and the ON period (period in which the signal level is H level) in one cycle is displayed as a fraction.

ＰＷＭ信号出力部３５は、上記の表１を用いて汚れ信号Ｄ，Ｇの値をデューティ比に変換すると、２つの信号から求めたデューティ比の内、デューティ比が大きい方を選択し、選択されたデューティ比のＰＷＭ信号からなる汚れ信号Ｖｐを上述の空調制御マイコン４１に出力する。すなわち、ＰＷＭ信号出力部３５では、汚れ信号Ｄ，Ｇの汚れ度合いに応じてデューティ比が離散的に変化するＰＷＭ信号を生成している。このように、ＰＷＭ信号出力部３５から空調制御マイコン４１へ汚れ信号をデジタル量（ＰＷＭ信号）で出力しているので、空調制御マイコン４１では、ＰＷＭ信号出力部３５からデジタル量で出力される汚れ信号、すなわちＰＷＭ信号のデューティ比をもとに、外気の汚れ度合いを検出することができ、汚れ度合いに応じてダンパ５０の開閉制御やファンの風量調整などの制御を行うことが可能になる。また、ダンパ５０と車室とを繋ぐダクト５１の途中に活性炭フィルタ（図示せず）を装着し、ダクト５１を通過する空気中の排出ガスを活性炭フィルタで吸着するようにした空質制御システムにおいて、活性炭フィルタの吸着能力が短時間で低下したり劣化するのを抑制するために、ＰＷＭ信号のデューティ比から求めた汚れ度合いに応じてダンパ５０の開閉角度を調整することも可能になる。さらに、ＰＷＭ信号出力部３５から汚れ信号をデジタル量で出力しているので、外気の汚れ度合いをアナログ信号で出力する場合のようにガス検出装置ＡにＤ／Ａ変換器を設けたり、空質制御システムにＡ／Ｄ変換器を設ける必要が無く、ガス検出装置Ａおよび空質制御システム全体のコストを低減することができる。しかも、ＰＷＭ信号出力部３５は、外気の汚れ度合いをデューティ比で示すＰＷＭ信号を出力しているので、オープンコレクタ出力が１点あればＰＷＭ信号出力部３５を実現できる。なお、本実施形態では汚れ信号をＰＷＭ信号で出力するＰＷＭ信号出力部３５を設けているが、ＰＷＭ信号以外のデジタル信号で汚れ信号を出力しても良く、ＬＩＮ−ＢＵＳなどのデータ・バスを介して汚れ信号を伝送する信号出力手段を用いても良いし、ＲＳ２３２ＣやＬＩＮ−ＢＵＳなどの通信規格で汚れ信号を伝送するようにしても良い。

The PWM signal output unit 35, when converting the values of the dirt signals D and G into the duty ratio using Table 1 above, selects the duty ratio obtained from the two signals and selects the larger one. The dirt signal Vp consisting of the PWM signal with the duty ratio is output to the air conditioning control microcomputer 41 described above. That is, the PWM signal output unit 35 generates a PWM signal in which the duty ratio changes discretely according to the degree of dirt of the dirt signals D and G. Thus, since the dirt signal is output from the PWM signal output unit 35 to the air conditioning control microcomputer 41 as a digital amount (PWM signal), the air conditioning control microcomputer 41 receives the dirt output from the PWM signal output unit 35 as a digital amount. The degree of contamination of the outside air can be detected based on the duty ratio of the signal, that is, the PWM signal, and control such as opening / closing control of the damper 50 and fan air volume adjustment can be performed according to the degree of contamination. In the air quality control system, an activated carbon filter (not shown) is installed in the middle of the duct 51 connecting the damper 50 and the passenger compartment, and the exhaust gas in the air passing through the duct 51 is adsorbed by the activated carbon filter. In order to prevent the adsorption capacity of the activated carbon filter from decreasing or deteriorating in a short time, the opening / closing angle of the damper 50 can be adjusted according to the degree of contamination obtained from the duty ratio of the PWM signal. Further, since the dirt signal is output in a digital amount from the PWM signal output unit 35, a D / A converter is provided in the gas detector A as in the case of outputting the degree of dirt in the outside air as an analog signal, There is no need to provide an A / D converter in the control system, and the cost of the gas detection device A and the entire air quality control system can be reduced. In addition, since the PWM signal output unit 35 outputs a PWM signal indicating the degree of contamination of the outside air as a duty ratio, the PWM signal output unit 35 can be realized if there is one open collector output. In this embodiment, the PWM signal output unit 35 that outputs the dirt signal as a PWM signal is provided. However, the dirt signal may be output as a digital signal other than the PWM signal, and a data bus such as LIN-BUS may be used. A signal output means for transmitting a dirt signal may be used, or the dirt signal may be transmitted according to a communication standard such as RS232C or LIN-BUS.

  By the way, in this embodiment, the reference value update unit 36 updates the reference values Rdm and Rgm for each sensor according to the update routine described above, and the car is located in the city center, factory, sewage treatment plant, waste treatment plant, ranch, etc. When moving to an area where the exhaust gas concentration or malodorous gas concentration is high and the surrounding average gas concentration gradually increases, the reference value Rdm increases and the reference value Rgm decreases accordingly. The damper 50 remains switched to the inside air side by air containing a small amount of exhaust gas, which may be referred to as fresh air, or by air containing a minute amount of malodorous gas that the nose is used to and feels no odor. Can be prevented. Also, if the car moves from the city center to the suburbs and the surrounding exhaust gas concentration and bad odor gas concentration decrease, the reference value Rdm decreases and the reference value Rgm increases accordingly, so it is included in clean air in the suburbs. A small amount of exhaust gas and odorous gas can be detected, the damper can be switched to the inside air side, a reference value of clean air is set according to changes in the surrounding environment, and human senses It is possible to perform damper control according to the above. In other words, even when the gas concentration when a person feels that the air is dirty due to a difference in location or the like, the presence or absence of exhaust gas or odorous gas can be reliably detected using the dirt signals D and G.

  In addition, the reference value update unit 36 sets the reference value in the clean direction by setting an update cycle T for updating the reference value in the dirt direction to a longer time than the update cycle t in the clean direction as shown in FIG. Since the update speed for updating in the dirt direction is slower than the update speed for updating to the dirt direction, the reference value can be changed slowly in the dirt direction when the gas concentration changes in the dirt direction. Can be switched to the inside air side. On the other hand, when the gas concentration changes in the clean direction, the reference value can be changed in the clean direction in a short time. Therefore, a small amount of exhaust gas or malodorous gas in clean air is detected, and the damper 50 is It can be switched to the inside air side. In this case, however, the update ratios 1 / Pd and 1 / Cd are set to substantially the same value, and the update ratios 1 / Pg and 1 / Cg are set to substantially the same value. In FIG. 2, X indicates the output Rd of the oxidizing gas sensor 1, and Y indicates the reference value Rdm.

  By the way, in this embodiment, the oxidizing gas sensor 1 which has selectivity with respect to the oxidizing gas discharged | emitted from a diesel vehicle, and the reduction | restoration which has selectivity with respect to reducing gases, such as the exhaust gas of a gasoline vehicle, and malodorous gas. However, the selectivity of both sensors 1 and 2 is not perfect, and the oxidative gas sensor 1 has some sensitivity to exhaust gas and odorous gas from gasoline cars. The reducing gas sensor 2 also has some sensitivity to diesel vehicle exhaust.

  Therefore, when the reference value update unit 36 makes a difference in the update speed of the reference value between the dirt direction and the clean direction so that the reference value is easily changed in the clean direction, the exhaust gas discharged from the gasoline vehicle Since the resistance value of the oxidizing gas sensor 1 changes in the direction of decreasing (cleaning direction) in an atmosphere having a high concentration or malodorous gas concentration, the reference value Rdm for the oxidizing gas sensor 1 goes too far in the cleaning direction, and then cleans. If the resistance value of the oxidizing gas sensor 1 increases (dirt direction) when exposed to fresh air, it may be determined that there is exhaust gas from the diesel vehicle, and the damper 50 may be switched to the inside air side. . Further, since the resistance value of the reducing gas sensor 2 changes in an increasing direction (cleaning direction) in an atmosphere where the exhaust gas concentration discharged from the diesel vehicle is high, the reference value Rgm for the reducing gas sensor 2 goes too far in the cleaning direction. Then, when the resistance value of the reducing gas sensor 2 changes in the direction of decreasing (dirt direction) after being exposed to clean air, it is determined that there is exhaust gas or malodorous gas from the gasoline car, and the damper 50 There is a possibility of switching to the side.

  Therefore, in this embodiment, as described in the update routine shown in FIGS. 6 and 7, the oxidizing gas sensor 1 detects even a slight amount of exhaust gas discharged from the diesel vehicle, and the dirt signal D is the first threshold value. When the level (judgment value D3) or higher, the reference value update unit 36 prohibits the update of the reference value in the clean direction of the reducing gas sensor 2, so that the exhaust gas discharged from the diesel vehicle exists in a high concentration. The increase in the output Vg of the reducing gas sensor 2 prevents the reference value on the second sensor side from going too far in the clean direction, and prevents the malfunction of the damper switching to the inside air when the surroundings return to a clean atmosphere. it can. Further, when the reducing gas sensor 2 detects even a slight amount of exhaust gas or malodorous gas discharged from the gasoline vehicle and the dirt signal G becomes equal to or higher than the second threshold level (determination value G3), the reference value update unit 36 Since the update of the reference value in the clean direction of the oxidizing gas sensor 1 is prohibited, the output Vd of the oxidizing gas sensor 1 decreases in an environment where exhaust gas or malodorous gas discharged from a gasoline vehicle exists at a high concentration. Thus, it is possible to prevent the reference value on the first sensor side from going too far in the clean direction and to prevent a malfunction in which the damper is switched to the inside air side when the surroundings return to a clean atmosphere. Since the first and second threshold levels are provided with hysteresis (D3> D4, G3> G4), the operation for prohibiting the update of the reference value can be stably performed.

In the present embodiment, when the reference values Rdm and Rgm are updated in the dirt direction, if the dirt signals D and G are equal to or greater than the determination values D5 and G5, the update ratio applied to the difference between the sensor resistance and the previous reference value. Is set to a value inversely proportional to the magnitudes of the dirt signals D and G. If the update ratio is constant at 1 / Pd and 1 / Pg regardless of the magnitudes of the dirt signals D and G, the exhaust gas concentration and bad odor The renewal amount increases in an atmosphere with a high gas concentration. Therefore, when exposed to an atmosphere having a high exhaust gas concentration or bad odor gas concentration for a long time, the reference values Rdm and Rgm greatly change in the direction of dirt, and even if the exhaust gas concentration or bad odor gas concentration is slightly reduced, the damper 50 may be switched to the outside air side, and dirty air may flow in.
On the other hand, in this embodiment, when the dirt signals D and G are sufficiently large, that is, when D ≧ D5 >> 1 and G ≧ G5 >> 1, the update ratio is a value inversely proportional to the magnitude of the dirt signals D and G ( Ld / D) and (Lg / G), so that the renewal amount of the reference values Rdm and Rgm can be made inversely proportional to the magnitudes of the dirt signals D and G, and the exhaust gas concentration and malodorous gas concentration become high The update amount of the reference values Rdm and Rgm can be reduced by reducing the update rate of the reference values Rdm and Rgm in the contamination direction (that is, when the stain signals D and G become large). Therefore, even if the exhaust gas concentration and the malodorous gas concentration are exposed to an atmosphere for a long time, it is possible to delay the change of the reference values Rdm and Rgm in the dirt direction, and the exhaust gas concentration and the malodorous gas concentration are slightly reduced. It is possible to prevent the damper 50 from being switched to the outside air simply.

  In this embodiment, the update rate t for updating the reference value in the cleaning direction is made shorter than the update cycle T for updating the reference value in the dirty direction, so that the update rate of the reference value in the cleaning direction is updated in the dirty direction. The update cycle T and the update cycle t are substantially the same cycle, and the reference value is set in the clean direction compared to the update ratios 1 / Pd and 1 / Pg when the reference value is updated in the dirt direction. By increasing the update ratios 1 / Cd and 1 / Cg in the case of updating (that is, Pd> Cd> 1, Pg> Cg> 1), the clean direction is compared with the case where the reference value is updated in the dirt direction. If the reference value is updated, the update speed may be increased, and the same effect as described above can be obtained.

  Further, in this embodiment, both the exhaust gas and the malodorous gas of the gasoline car are detected by one sensor. However, the sensor particularly sensitive to the exhaust gas from the gasoline car, and the output of the sensor detects the gasoline. A gas determination unit that detects exhaust gas from a car, a sensor that is particularly sensitive to malodorous gas, and a gas determination unit that detects malodorous gas from the output of this sensor are provided separately. You may make it update the reference value of each gas determination part.

  By the way, the above-described gas detection device A is disposed, for example, between a front grill of an automobile (not shown) and a radiator inside the front grill, and detects the exhaust gas concentration in the outside air introduced from the front grill. To do. As shown in FIGS. 10 and 11, the gas detection device A includes a substantially box-shaped upper case 71 having a substantially entire rear surface opened, and a lower case 72 that fits and closes the opening of the upper case 71. 1 and a printed wiring board 73 on which the circuit of FIG. 1 is formed is accommodated in the case 70. The oxidizing gas sensor 1 and the reducing gas sensor 2 mounted on the printed wiring board 73 are arranged in a sensor arrangement hole 75 formed in the outer surface 74 of the upper case 71, and the sensor is provided on the outer surface 74 via a filter 76. A cover 77 is attached. The filter 76 is made of a highly water-repellent membrane sheet formed porous using, for example, PTFE (polytetrafluoroethylene), and is adhered to the outer surface 74. The diameter of the pores of the membrane sheet is 1 to 5 μm so as to allow gas to pass but prevent passage of water and dust, but is particularly preferably 3 μm. Moreover, it is preferable to stick the polyester nonwoven fabric for reinforcement on the back side of the membrane sheet. Here, the high water-repellent membrane sheet is provided on the front side of the polyester nonwoven fabric (that is, the side exposed to the outside air). If the polyester nonwoven fabric is provided on the front side of the membrane sheet, This is because the adhering water may hinder aeration. The sensor cover 77 covering the filter 76 has a diameter of 2 mm in a predetermined area E2 that surrounds the area facing the sensor arrangement hole 75 (that is, the facing area E1 shown in FIGS. 10 and 11) in a substantially ring shape. A large number of air introduction holes 78 each having a circular shape are formed at substantially equal intervals, and an air introduction path from the outside of the sensor cover 77 through the air introduction holes 78 to the sensor arrangement hole 75 is formed. Also, three L-shaped connection terminals 79 are connected to the printed wiring board 73, and the horizontal bar portion of each connection terminal 79 is disposed in a connector connection portion 80 that opens to the side of the upper case 71. ing.

  In this embodiment, a bead-shaped member as shown in FIG. 3 is used as the gas-sensitive member 11, but the gas-sensitive member 11 is not limited to the bead-shaped member. For example, FIG. A substrate-shaped gas sensitive body 11 ′ as shown in FIG. 13 may be used. This gas sensitive body 11 ′ is provided with two gold electrodes 15A, 15B for heaters and gold electrodes 16A ′, 16B ′ for gas sensitive parts at the four corners on the back surface of the alumina substrate 14 which is an insulating substrate. Are provided with gold electrodes 16A and 16B. The gold electrodes 16A and 16B are formed substantially on the back side of the gold electrodes 16A ′ and 16B ′, respectively, and the gold electrodes 16A and 16A ′ are electrically connected to each other through the through holes. Connected. A heater 18 made of ruthenium oxide is formed on the back surface of the alumina substrate 14 so as to extend between the gold electrodes 15A and 15B, and a gas sensitive material is provided on the surface of the alumina substrate 14 so as to extend between the gold electrodes 16A and 16B. A gas sensitive portion 17 is formed, and the gas sensitive portion 17 is formed so as to be positioned substantially on the back side of the heater 18.

  As shown in FIG. 12, the gas sensitive body 11 ′ has coil electrodes 15 A and 15 B electrically connected to the upper portions of the left and right terminals 6 and 8 via lead wires 19, respectively. The electrode 16B ′ is electrically connected to the upper portion of the terminal 6 via the lead wire 19, and the electrode 16 A ′ is electrically connected to the upper portion of the left terminal 6 via the lead wire 19. The lead wire 19 is a thin metal wire made of an alloy of gold (Au), palladium (Pd), and molybdenum (Mo). However, the lead wire 19 is not limited to the above alloy. Alternatively, a fine metal wire such as an aluminum wire may be used. The base 9 is attached with a bottomed cylindrical cap 60 opened at one end in the axial direction so as to cover the gas sensitive body 11 ′, and the ceiling portion of the cap 60 communicates the inside with the outside. An inflow port 60a is formed. For example, a stainless 100 mesh wire mesh 61 made of stainless steel is doubly fixed to the gas inlet 60a for explosion prevention, and gas is introduced into the gas sensitive body 11 'from the outside through the wire mesh 61.

  Since it is apparent that a wide variety of different embodiments can be constructed without departing from the spirit and scope of the present invention as described above, the invention is not limited to the specific embodiments except as defined in the appended claims. It is not restricted.

Claims (3)

By changing the amount of outside air introduced into the passenger compartment and the amount of inside air circulating in the passenger compartment, a contamination signal indicating the degree of contamination of the outside air is sent to an air quality control system that controls the air quality in the passenger compartment. An output gas detection device comprising the following configuration:
An oxidizing gas sensor, the oxidizing gas sensor comprising a gas sensitive body whose resistance value changes according to the gas concentration of the oxidizing gas discharged from the diesel vehicle;
A reducing gas sensor, the reducing gas sensor comprising a gas sensitive body whose resistance value changes in accordance with the gas concentration of the reducing gas including exhaust gas and malodorous gas of a gasoline vehicle;
The first gas detection means and the first gas detection means set the resistance value of the oxidizing gas sensor in clean air as a reference value for the oxidizing gas, and the oxidizing gas sensor in the detection target gas. A resistance value obtained by dividing the difference by the reference value and outputting a resistance ratio indicating the degree of contamination of the outside air;
The second gas detection means and the second gas detection means set the resistance value of the reducing gas sensor in clean air as a reference value for the reducing gas, and the reducing gas sensor in the detection target gas. A difference between the resistance value of the gas and the reference value for the reducing gas is obtained, and the resistance ratio obtained by dividing the difference by the reference value is output as a dirt signal indicating the degree of dirt in the outside air;
The reference value update unit and the reference value update unit each update an amount smaller than 1 by subtracting the reference value at the previous update from the current output of each gas sensor every time an update cycle longer than the sampling cycle of each gas sensor elapses. A value obtained by adding the reference value at the previous update to the value obtained by multiplying the ratio is set as a new reference value, and the contamination signal output from the first gas detection means is equal to or higher than the first threshold level. The reference value for the reducing gas is prohibited from being updated in the cleaning direction, and the reference value for the oxidizing gas is cleaned when the contamination signal output from the second gas detection means exceeds the second threshold level. Prohibit updates in direction;
The signal output means, and this signal output means outputs the dirt signal having the greater degree of dirt among the dirt signals input from the first and second gas detecting means as a digital quantity.   2. The gas detection apparatus according to claim 1, wherein the signal output means converts the dirt signal input from the gas detection means into a PWM signal whose duty ratio changes discretely according to the degree of dirt in the outside air and outputs the PWM signal. .   3. The gas detection device according to claim 1, wherein the first gas detection means is a correction obtained by multiplying the contamination signal by a correction coefficient for correcting a variation in resistance value of the oxidizing gas sensor. The value is output as a contamination signal, and the second gas detection means outputs a correction value obtained by multiplying the contamination signal by a correction coefficient for correcting variation in the resistance value of the reducing gas sensor as the contamination signal. .

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