JP2015161570A - gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor for detecting concentration of a plurality of gas components, by means of a single sensor, in a simple configuration.SOLUTION: A gas sensor 1 for detecting concentration of gas components included in a gas to be inspected includes: an oxygen supply section 10 for supplying oxygen; a first electrode 11 arranged on the side of the gas including the oxygen and disposed at one end of the oxygen supply section 10; a second electrode 12 arranged on the side of the gas to be inspected and disposed at the other end of the oxygen supply section 10; a power source 13 connected between the first electrode 11 and the second electrode 12; and temperature adjustment sections 15, 16, 21 for adjusting temperature of the oxygen supply section 10. The temperature of the oxygen supply section 10 is adjusted by the temperature adjustment sections 15, 16, 21 sequentially so as to facilitate reaction between oxygen and the gas components included in the gas to be inspected. The concentration of the gas components is detected at each of the adjusted temperatures.

Description

  The present invention relates to a gas sensor that detects the concentrations of a plurality of gas components contained in a test gas.

  In order to perform various controls such as engine control of automobiles with high accuracy, a gas sensor for detecting the concentration of a specific gas component contained in gas used as fuel or exhausted gas is required, and various gas sensors have been developed. Yes. For example, in Patent Document 1, a reference electrode exposed to the atmosphere is arranged on one end side of zirconia (solid electrolyte), and a high temperature side detection electrode and a low temperature side detection electrode exposed to a test gas are arranged on the other end side. It is disclosed that a gas component sensor detects the concentrations of two specific gas components from current data measured by two detection electrodes.

JP-A-9-189679

  Natural gas, which is clean energy that emits less carbon dioxide during combustion than oil or the like, is used as a fuel for automobile engines or thermal power generation. Natural gas contains various gas components (methane, ethane, propane, butane, etc.) composed of carbon and hydrogen. Natural gas containing these various gas components has different gas component configurations and concentration ratios depending on the production area. When performing engine control using natural gas as fuel, unless the composition and concentration ratio of gas components are known, optimal combustion cannot be performed, which affects exhaust gas and fuel consumption. Therefore, in order to efficiently burn natural gas, it is necessary to detect each concentration of the gas component of the natural gas used with high accuracy.

  However, the gas component sensor disclosed in Patent Document 1 can detect only the concentrations of two types of gas components, and cannot detect the concentrations of various gas components contained in natural gas. Moreover, most of the known conventional gas sensors are sensors that detect one kind of gas component. Therefore, in order to detect the concentrations of various gas components, a plurality of gas sensors are required, the sensor configuration is complicated, and the cost is high.

  Therefore, in this technical field, there is a demand for a gas sensor that can detect the concentrations of a plurality of gas components with a simple configuration using a single sensor.

  A gas sensor according to one aspect of the present invention is a gas sensor that detects the concentrations of a plurality of gas components contained in a test gas, and is provided on an oxygen supply unit that supplies oxygen and a gas side that contains oxygen. A first electrode provided on one end side of the supply unit, a second electrode disposed on the test gas side and provided on the other end side of the oxygen supply unit, and connected between the first electrode and the second electrode. A power supply and a temperature adjustment unit that adjusts the temperature of the oxygen supply unit are provided, and the temperature of the oxygen supply unit is sequentially adjusted to each temperature at which multiple gas components contained in the test gas and oxygen easily react with each other. The concentration of the gas component is detected at each adjusted temperature.

  In this gas sensor, electrodes are provided at both ends of the oxygen supply section, the first electrode side at one end thereof is exposed to a gas containing oxygen (for example, the atmosphere), and the second electrode side at the other end is covered. Exposed to gas detection. When a voltage is applied between the electrodes from the power source, the oxygen supply unit supplies oxygen (particularly, first electrode) from the first electrode (minus electrode) side exposed to the gas containing oxygen to the second electrode (plus electrode) side. The state in which electrons are received by one electrode to become oxygen ions) moves to supply oxygen to the second electrode side. On the second electrode side, the oxygen and a gas component contained in the test gas chemically react to generate heat. Each gas component has a temperature at which it easily reacts in this reaction with oxygen. By using each temperature at which each gas component easily reacts, it is possible to detect the concentration of each gas component from various amounts that change due to the reaction of each gas component with oxygen at each temperature. Therefore, in the gas sensor, the temperature adjusting unit sequentially adjusts the temperature of the oxygen supply unit to each temperature at which the gas component and oxygen easily react. In the gas sensor, the amount of gas consumed in the reaction (that is, the gas component) from the amount changed by the reaction (for example, the amount of oxygen supplied by the oxygen supply unit, the amount of heat generated by the reaction) at each temperature. ) Is detected. This detection is repeatedly performed for each temperature at which it easily reacts with oxygen of a plurality of gas components contained in the test gas. When the temperature is sequentially changed, the temperature may be changed from the highest temperature to the lowest temperature, or may be changed from the lowest temperature to the highest temperature. In this way, this gas sensor sequentially changes to each temperature that easily reacts with oxygen of a plurality of gas components contained in the test gas, and sequentially detects the concentration of each gas component from the chemical reaction at each temperature, Each concentration of a plurality of gas components can be detected with a simple configuration by a single sensor.

  The test gas is a gas containing a plurality of gas components (which may be gas components that become impurities), and is, for example, natural gas or exhaust gas. However, the gas component whose concentration can be detected by the gas sensor according to the present invention is a gas that generates heat by chemically reacting with oxygen and has a temperature at which the chemical reaction easily occurs. The oxygen supply unit can supply oxygen by applying a voltage to move oxygen (particularly oxygen ions), for example, a solid electrolyte (zirconia or the like).

  In one embodiment of the gas sensor, the gas sensor includes a current detection unit that detects a current flowing between the first electrode and the second electrode, and the temperature of the oxygen supply unit is adjusted by the temperature adjustment unit to include a plurality of gas components and oxygen Are sequentially adjusted to each temperature at which they are likely to react, and the oxygen amount supplied by the oxygen supply unit is sequentially determined based on the current value detected by the current detection unit at the adjusted temperature, and the derived oxygen amount From this, the concentration of the gas component is detected.

  In this gas sensor, each time the temperature of the oxygen supply unit becomes a temperature at which the gas component and oxygen easily react, the current value flowing between the electrodes is detected by the current detection unit. Since the electrons corresponding to the current value are received and oxygen is converted into oxygen ions, the gas sensor derives the amount of oxygen supplied by the oxygen supply unit from the detected current value, and the gas consumed by the chemical reaction from the amount of oxygen. The amount (ie, the concentration of the gas component) is detected. Thus, the gas sensor can easily detect the amount of oxygen used in the chemical reaction (and hence the concentration of the gas component) by using the current value corresponding to the amount of oxygen supplied from the oxygen supply unit. . In particular, in the case of this detection method, since the amount of heat that is easily affected by the environment is not used in the process of detecting the concentration of the gas component, the detection accuracy is high.

  The gas sensor according to one aspect includes a calorific value detection unit that detects an amount of heat that increases due to a reaction between a gas component and oxygen, and the temperature of the oxygen supply unit is adjusted by the temperature adjustment unit so that a plurality of gas components and oxygen contained in the test gas It adjusts to each temperature which is easy to react, and detects the density | concentration of a gas component from the calorie | heat amount detected by the calorie | heat amount detection part at the said adjusted temperature.

  In this gas sensor, every time the temperature of the oxygen supply unit becomes a temperature at which the gas component and oxygen easily react, the calorific value detection unit detects the amount of heat that increases due to heat generated by the chemical reaction. The gas sensor detects the amount of gas consumed by the chemical reaction (that is, the concentration of the gas component) from the increased amount of heat. Thus, the gas sensor can easily detect the concentration of the gas component consumed by the chemical reaction by using the amount of heat increased by the chemical reaction. In particular, in the case of this detection method, since the temperature sensor used in the temperature adjustment unit can be shared as the heat quantity detection unit, a simpler configuration is possible.

  In one aspect of the gas sensor, the temperature of the oxygen supply unit is sequentially adjusted from the high temperature side to the low temperature side among the temperatures easily reacting with oxygen of a plurality of gas components contained in the test gas by the temperature adjustment unit. . As described above, this gas sensor changes the concentration of the gas component by changing the temperature from the high temperature side to the low temperature side in order to change the concentration of the gas component due to the heat generated by the reaction between the gas component and oxygen. It becomes difficult to receive the detection, and the detection accuracy is improved.

  In one embodiment of the gas sensor, the application of a voltage by the power source is started each time the temperature of the oxygen supply unit is adjusted to a temperature at which any gas component contained in the test gas and oxygen easily react with the temperature adjusting unit. Each time the detection of the concentration of the gas component is completed, the application of the voltage by the power supply is terminated. Thus, this gas sensor can reduce the power consumption by the gas sensor by adjusting the temperature at which each gas component easily reacts and starting / stopping the application of the voltage by the power source every time the concentration is detected.

  In one form of gas sensor, voltage is continuously applied by the power source during detection by the gas sensor. In this way, this gas sensor can detect the temperature range before and after the temperature at which each gas component easily reacts by continuously applying a voltage from the power source during detection, so the concentration in those temperature ranges is also taken into account. Thus, the concentration of each gas component can be detected with higher accuracy, and the detection accuracy is improved.

  According to the present invention, each concentration of a plurality of gas components can be detected with a simple configuration by a single sensor.

It is a figure which shows typically the structure of the gas sensor which concerns on 1st Embodiment. It is a figure which shows the temperature which is easy to react with oxygen of each gas component contained in natural gas. It is an example of a gas concentration-calorific value map. It is a flowchart which shows the flow of the gas concentration ratio detection by the gas sensor which concerns on 1st Embodiment. It is a figure which shows typically the structure of the gas sensor which concerns on 2nd, 3rd embodiment. It is an example of an oxygen amount-current value map. It is an example of a gas concentration-oxygen amount map. It is a flowchart which shows the flow of the gas concentration ratio detection by the gas sensor which concerns on 2nd Embodiment. It is a flowchart which shows the flow of the gas concentration ratio detection by the gas sensor which concerns on 3rd Embodiment.

  Hereinafter, an embodiment of a gas sensor according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the element which is the same or it corresponds in each figure, and the overlapping description is abbreviate | omitted.

  In the present embodiment, the gas sensor according to the present invention is applied to a gas sensor used in a natural gas vehicle using natural gas (particularly, compressed natural gas (CNG)) as fuel. The gas sensor according to the present embodiment detects the concentration of each gas component contained in natural gas used as fuel, and derives the concentration ratio of the gas component from these concentrations. The gas sensor according to the present embodiment may be a case where the gas used as fuel before being used in the engine is a test gas, or a case where the gas used as exhaust after being used in the engine is a test gas ( In the case of exhaust, the concentration of the unburned gas component remaining without being burned may be detected), or in either case. Therefore, the gas sensor according to the present embodiment is attached to a predetermined location in a fuel tank for storing natural gas (CNG), a pipe for supplying natural gas to the engine, an exhaust pipe, or the like.

In the present embodiment, four types of concentration detection of methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), and butane (C ₄ H ₁₀ ) are detected as gas components contained in natural gas. Assumed to be performed. However, it is also possible to detect the concentration of gas components other than the four types contained in natural gas, or only three or two of these four types may be detected. In the present embodiment, the timing for detecting the gas concentration ratio (the gas concentration of each gas component) may be performed only when the engine is started, or may be always performed while the engine is operating, or When the CNG is supplied to the tank, when CNG is stored in multiple tanks, the gas concentration ratio of the gas component contained in the natural gas may change, such as when the tank used for fuel is switched You may go at the time.

  There are three forms in the present embodiment. The first embodiment is a form in which the temperature is adjusted from the low temperature side to the high temperature side sequentially and the concentration is detected from the amount of heat. The third embodiment is a mode in which the temperature is sequentially adjusted from the low temperature side to the high temperature side and the concentration is detected from the current value, and the third embodiment sequentially adjusts from the high temperature side to each temperature on the low temperature side, and In this form, the concentration is detected from the current value.

  The concentration ratio of the gas component detected by the gas sensor is used for engine control (for example, setting of optimum combustion conditions (fuel injection amount, etc.), feedback control, engine failure diagnosis) of a natural gas vehicle. When the concentration ratio of the gas component of natural gas used as fuel changes, the combustion state in the cylinder changes, and the pressure in the cylinder changes. In addition, if the combustion state deteriorates, it will affect exhaust gas, fuel consumption, engine output, engine durability, etc. Therefore, it is important to know the concentration ratio of the gas components of natural gas used as fuel. Very important in control.

  With reference to FIGS. 1-3, the gas sensor 1 which concerns on 1st Embodiment is demonstrated. FIG. 1 is a diagram schematically showing the configuration of the gas sensor 1 according to the first embodiment. FIG. 2 is a diagram showing temperatures at which each gas component contained in natural gas easily reacts with oxygen. FIG. 3 is an example of a gas concentration-heat generation amount map.

  The gas sensor 1 uses a chemical reaction between a gas component and oxygen (oxygen ions) in order to detect the concentration of the gas component contained in natural gas. In particular, in order to sequentially detect the concentrations of the four gas components, the gas sensor 1 changes the temperature at which each gas component reacts with oxygen and easily oxidizes and burns from a low temperature to a high temperature in order. The amount of heat increased by reaction heat is derived, and the concentration of the gas component is detected from the increased amount of heat. For this purpose, the gas sensor 1 includes an oxygen pump 10, a reference electrode 11, an electrode 12, a power source 13, a switch 14, a heater 15, a temperature sensor 16, and a control unit 21.

  In the first embodiment, the oxygen pump 10 corresponds to the oxygen supply unit described in the claims, the reference electrode 11 corresponds to the first electrode described in the claims, and the electrode 12 corresponds to the patent. It corresponds to the second electrode described in the claims, the power source 13 corresponds to the power source described in the claims, and the processing in the heater 15, the temperature sensor 16 and the control unit 21 is the temperature described in the claims. It corresponds to the adjustment unit, and the processing in the temperature sensor 16 and the control unit 21 corresponds to the heat quantity detection unit in the claims.

  The oxygen pump 10 is a pump that receives oxygen and electrons on one side, moves oxygen ions from one side to the other side, and supplies oxygen ions to the other side. The oxygen pump 10 is made of solid electrolyte zirconia. Zirconia (solid electrolyte) is a solid that can move ions by an electric field applied from the outside, and a current flows by the movement of the ions. In particular, when a voltage is applied to zirconia and oxygen is present on one side of zirconia, oxygen is combined with electrons to form oxygen ions, oxygen ions move to the other side, and oxygen ions can be supplied to the other side. The oxygen pump 10 has, for example, a rectangular parallelepiped shape or a cubic shape.

The reference electrode 11 is an electrode provided on one end face of the oxygen pump 10 and serves as a negative electrode for receiving electrons. The reference electrode 11 is attached to the entire surface or a part of one end surface of the oxygen pump 10 and is preferably a porous material so that oxygen can pass through the entire surface. In some cases, the reference electrode 11 is a porous material. It does not have to be. As shown in FIG. 1, the reference electrode 11 side attached to one end face of the oxygen pump 10 is disposed in a gas containing oxygen so as to be exposed to a gas containing oxygen (O ₂ ) (for example, the atmosphere). Or a gas containing oxygen is introduced through a pipe.

The electrode 12 is an electrode provided on the other end face of the oxygen pump 10 and serves as a positive electrode that emits electrons. The electrode 12 is attached to the entire surface or a part of the other end surface of the oxygen pump 10 (the surface opposite to the one end surface to which the reference electrode 11 is attached). In the case of the entire surface, the electrode 12 is included in oxygen ions or natural gas. A porous material is preferable so that a gas component can pass through, and in some cases, the material may not be a porous material. As shown in FIG. 1, the electrode 12 side attached to the other end face of the oxygen pump 10 has four types of gas components (methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), It is arranged in a fuel tank in which natural gas is stored so as to be exposed to natural gas containing butane (C ₄ H ₁₀ )) or in a pipe through which natural gas (or exhaust gas) flows.

  The power source 13 is a power source that applies a DC voltage between the reference electrode 11 and the electrode 12 (and thus the oxygen pump 10). The power source 13 has a negative side connected to the reference electrode 11 and a positive side connected to the electrode 12 via the switch 14. The voltage value of the power source 13 is determined according to the characteristics of zirconia used in the oxygen pump 10.

  The switch 14 is a switch for applying / stopping voltage application by the power supply 13. The switch 14 is connected between the positive side of the power supply 13 and the electrode 12. The switch 14 is turned on / off by the control unit 21.

When the switch 14 is turned on and a voltage is applied from the power source 13 to the reference electrode 11 and the electrode 12 (oxygen pump 10), electrons (e- ¹ ) flow. On the reference electrode 11 side, as shown in the following formula (1), oxygen (O ₂ ) receives electrons (e ⁻¹ ) and becomes oxygen ions (O ²⁻ ). In the oxygen pump 10, the oxygen ions (O ²⁻ ) are moved to the electrode 12 side. The electrode 12 side, for example, as shown in the following formula (2) in the case of methane (CH _4), by methane (CH ₄₎ is oxidized and burnt by reacting with oxygen _{(O 2),} carbon dioxide While changing into (CO ₂ ) and water (H ₂ O), reaction heat is generated. This reaction heat raises the ambient temperature. At this time, on the electrode 12 side, as shown in the formula (1), oxygen ions (O ²⁻ ) become oxygen (O ₂ ) and electrons (e ⁻¹ ), and electrons (e ⁻¹ ) are emitted.

  The heater 15 is a heater that heats the oxygen pump 10. The heater 15 may be provided inside the oxygen pump 10 or outside the oxygen pump 10. A conventionally well-known heater is used as the heater 15, and the temperature is increased to a temperature higher than the highest temperature among the gas components (methane, ethane, propane, butane) that easily react with oxygen. Apply a heater that can. The heater 15 is turned ON (power supply) / OFF by the control unit 21.

  The temperature sensor 16 is a heater that detects the temperature of the oxygen pump 10. The temperature sensor 16 is provided in the oxygen pump 10 (particularly, around the electrode 12). However, when there are two temperature sensors 16 for temperature adjustment and heat quantity detection, the temperature sensor for temperature adjustment is provided in the oxygen pump 10 and the temperature sensor for heat quantity detection is provided in the oxygen pump 10 near the electrode 12 or Provided outside the oxygen pump 10. As the temperature sensor 16, a conventional well-known sensor is applied, and it is possible to detect a temperature higher than the highest temperature among the temperatures easily reacting with oxygen among gas components (methane, ethane, propane, butane). Apply temperature sensor. The temperature sensor 16 outputs the detected temperature information to the control unit 21.

  Since oxygen ions are supplied from the electrode 12 and oxygen and each gas component (methane, ethane, propane, butane) chemically react on the electrode 12 side, the temperature around the electrode 12 is raised even in the oxygen pump 10. It is necessary to detect the temperature around the electrode 12 (and hence the amount of heat).

  The control unit 21 is a control unit of the gas sensor 1 and may be configured as one function in an engine ECU (Electronic Control Unit) or the like, or may be a control device dedicated to the gas sensor 1. The processing performed by the control unit 21 includes temperature adjustment processing, gas concentration derivation processing, and gas concentration ratio derivation processing.

  The temperature adjustment process will be described. The four gas components (methane, ethane, propane, and butane) have different temperatures (reaction temperatures) at which they easily react with oxygen. FIG. 2 shows peak temperatures at which the four gas components (methane, ethane, propane, and butane) easily react with oxygen. Butane peak temperature T1 <propane peak temperature T2 <ethane Peak temperature T3 <butane peak temperature T4. Each gas component is most likely to react with oxygen at the peak temperatures T1, T2, T3, and T4, and is less likely to react with the distance from the peak temperatures T1, T2, T3, and T4. The reaction temperature region has a peak at T4. Therefore, when the temperature of the oxygen pump 10 (especially around the electrode 12 where the reaction takes place) reaches the respective temperatures T1, T2, T3, and T4, butane, propane, ethane, and butane are most easily reacted with oxygen. The gas concentration can be detected by using it.

  The control unit 21 turns on the heater 15 (power supply) at the start of detection, and starts heating by the heater 15. The control unit 21 acquires temperature information in the oxygen pump 10 from the temperature sensor 16. Each time the temperature T is acquired, the control unit 21 sequentially determines whether or not the temperature T has reached each of the temperatures Tx (x = 1, 2, 3, 4), and sets the temperature in the oxygen pump 10 to each of the temperatures Tx. Adjust to temperature Tx. First, it is determined whether the lowest temperature T1 has been reached, and thereafter, the determination is made in the order of T2, T3, and T4. At this time, the control unit 21 continues heating by the heater 15 until the highest temperature T4 is reached, and when the detection is completed, the heater 15 is turned off (power supply is stopped). In addition, while the temperature in the oxygen pump 10 is adjusted to each temperature T1, T2, T3, T4 and the concentration of each gas component is detected at that time, the temperature rise due to heating of the heater 15 is temporarily suppressed. Therefore, when the heating by the heater 15 is temporarily stopped or the output of the heater 15 can be adjusted, the output may be suppressed.

  The gas concentration derivation process will be described. Since each gas component (methane, ethane, propane, butane) reacts with oxygen to generate heat, its calorific value changes according to the amount of gas consumed in the reaction (gas concentration). FIG. 3 shows a map showing the relationship between the gas concentration and the calorific value in the case of methane (depending on the calorific value of the gas concentration) (the air-fuel ratio of oxygen and natural gas is constant, and methane is oxygen ), The gas concentration and the calorific value are proportional to each other. Ethane other than methane, propane, and butane also have a proportional relationship between the gas concentration and the calorific value. Such a gas concentration-calorific value map is obtained in advance for each gas component (methane, ethane, propane, butane) through experiments or the like, and is stored in the control unit 21.

  Every time the temperature is adjusted to each temperature Tx (x = 1, 2, 3, 4), the control unit 21 uses the temperature information from the temperature sensor 16 before the temperature in the oxygen pump 10 reaches each temperature Tx ( The temperature TA around the electrode 12 before the reaction of each gas component is acquired, and the temperature TB in the vicinity of the electrode 12 after each temperature Tx (after the reaction of each gas component) is acquired. And the control part 21 calculates the temperature difference (TB-TA) before and behind reaction from temperature TA before reaction, and temperature TB after reaction. This temperature difference (TB-TA) is considered to correspond to the temperature increased by the heat generated by the reaction of the gas component with oxygen. In the control unit 21, the amount of heat increased before and after the reaction (the amount of heat generated by the reaction) is calculated from this temperature difference (TB-TA). Then, the control unit 21 derives the gas concentration [ppm] corresponding to the increased heat amount (heat generation amount) based on the gas concentration-heat generation amount map of the gas component corresponding to the temperature Tx. Note that when heating is performed by the heater 15, the temperature rises even by heating by the heater 15, so it is better to temporarily suppress the heating by the heater 15 as described above.

  The gas concentration ratio derivation process will be described. When all the gas concentrations of the four types of gas components (methane, ethane, propane, butane) are derived, the control unit 21 calculates the gas concentration ratio from each gas concentration of methane, ethane, propane, and butane. This gas concentration ratio is used for engine control.

  Note that the control unit 21 performs ON / OFF of the switch 14 to start / stop application of voltage from the power source 13 to the reference electrode 11 and the electrode 12 (oxygen pump 10). The ON / OFF for the switch 14 may be always turned on while the gas concentration is being detected, and may be turned off when all the detections are completed. In this way, when the voltage is constantly applied (that is, when oxygen can be constantly supplied by the oxygen pump 10), the concentration of each gas component is detected even in the temperature range before and after the temperature at which each gas component easily reacts. Therefore, it is possible to derive the gas concentration of each gas component with higher accuracy in consideration of the gas concentration in those temperature regions, and the detection accuracy can be improved. Alternatively, the switch 14 may be turned on each time the temperature Tx (x = 1, 2, 3, 4) is adjusted, and the switch 14 may be turned off every time the detection of each gas concentration is completed. As described above, when the application of voltage is started / stopped by the power source 13 every time the temperature is adjusted to each temperature Tx at which each gas component easily reacts (that is, oxygen is adjusted only when the gas concentration is detected by adjusting to each temperature Tx). When the pump 10 can supply oxygen), the power consumption by the gas sensor 1 can be reduced.

  With reference to FIGS. 1-3, the operation | movement at the time of detecting the gas concentration ratio by the gas sensor 1 is demonstrated along the flowchart of FIG. FIG. 4 is a flowchart showing a flow of gas concentration ratio detection by the gas sensor 1.

  When the gas concentration ratio detection starts, first, the control unit 21 initializes a variable x to 1 (S10). The variable x is a variable corresponding to x of the peak temperature Tx (x = 1, 2, 3, 4) that easily reacts with oxygen of each gas component. In this example, the variable x is 1, 2, 3, 4 but varies depending on the number of gas components to be detected. Since x is detected from the lowest temperature T1 (butane), x is initialized to 1. At this time, the switch 14 is turned on by the control unit 21, and a voltage is applied from the power source 13 between the reference electrode 11 and the electrode 12 (oxygen pump 10). In the heater 15, the controller 21 is turned on (power is supplied) to heat the oxygen pump 10. The temperature sensor 16 detects the temperature of the oxygen pump 10 and outputs the temperature information to the control unit 21.

  In the control part 21, the temperature T of the oxygen pump 10 is acquired from the temperature sensor 16 every fixed time (for example, control period of the control part 21) (S11). Then, the control unit 21 determines whether or not the acquired temperature T has become a temperature Tx (x = 1, 2, 3, 4) that easily reacts with oxygen of each gas component (S12). In this determination, first, the lowest temperature T1 is determined. After the temperature T1, the next temperature T2 is determined. After the temperature T2, the next temperature T3 is determined and the temperature T3 is reached. Is determined for the next temperature T4. When the temperature T4 is reached, the temperature determination ends. If it is determined in S12 that the temperature T is not equal to the temperature Tx, heating by the heater 15 is continued (S13), and the temperature of the oxygen pump 10 is increased.

  If it determines with temperature T having become temperature Tx by determination of S12, the control part 21 will acquire temperature TB after reaction from the temperature sensor 16 (S14). Further, the control unit 21 has already acquired the temperature TA before the reaction from the temperature sensor 16 (S11). And in the control part 21, the temperature difference (TB-TA) before and behind reaction is calculated from temperature TA before reaction, and temperature TB after reaction, and calorie | heat amount (calorific value) is calculated from this temperature difference (TB-TA). (S15). Further, the control unit 21 derives the gas concentration corresponding to the heat generation amount from the gas concentration-heat generation amount map of the gas component corresponding to the temperature Tx at this time (S16).

  The control unit 21 determines whether or not the variable x is 4 (S17). If it is determined in S17 that the variable x is not 4, the control unit 21 adds 1 to the variable x (S18). Then, in order to detect the gas concentration of the gas component having the temperature Tx that is the next highest temperature at which reaction is likely to occur, the operations of S11 to S17 are repeated.

  When the variable x is determined to be 4 in the determination of S17, the control unit 21 calculates a gas concentration ratio from each gas concentration of methane, ethane, propane, and butane (S19). This completes the detection of the gas concentration ratio. At this time, the switch 14 is turned off by the control unit 21 and the voltage application from the power supply 13 is finished. The heater 15 is turned off by the control unit 21 and the heating ends.

  According to the gas sensor 1, the temperature of each gas component contained in natural gas is changed to each temperature that easily reacts with oxygen, and the concentration of each gas component is sequentially detected from the chemical reaction at each temperature. With this sensor, each gas concentration of the plurality of gas components (and consequently the gas concentration ratio of the plurality of gas components) can be detected with a simple configuration. By performing engine control using this gas concentration ratio, optimum engine control can be performed, the combustion state in the cylinder becomes good, and the exhaust gas, fuel consumption, engine output, engine durability, etc. are positively affected. Moreover, since the concentration of various gas components can be detected by the gas sensor 1 having a simple configuration, the cost can be reduced.

  Further, according to the gas sensor 1, the concentration of the gas component can be easily detected by using the amount of heat increased by the reaction with oxygen in order to derive the gas concentration. In particular, in the case of this detection method, since the temperature sensor 16 used for temperature adjustment to detect the increased heat quantity can be shared, a simpler configuration is possible.

  A gas sensor 2 according to a second embodiment will be described with reference to FIGS. FIG. 5 is a diagram schematically showing the configuration of the gas sensor 2 according to the second embodiment. FIG. 6 is an example of an oxygen amount-current value map. FIG. 7 is an example of a gas concentration-oxygen amount map.

  The gas sensor 2 differs from the gas sensor 1 according to the first embodiment in the method for deriving the concentration of the gas component. The gas sensor 2 derives the amount of oxygen supplied during the reaction from the current value by measuring the current value flowing during the reaction for each temperature at which the gas component 2 easily reacts with oxygen, and from the supplied oxygen amount. Detect the concentration of gas components. For this purpose, the gas sensor 2 includes an oxygen pump 10, a reference electrode 11, an electrode 12, a power source 13, a switch 14, a heater 15, a temperature sensor 16, a current sensor 17, and a control unit 22.

  Since the oxygen pump 10, the reference electrode 11, the electrode 12, the power supply 13, the switch 14, the heater 15, and the temperature sensor 16 have been described in the first embodiment, only the current sensor 17 and the control unit 22 will be described. In the second embodiment, the processing in the heater 15, the temperature sensor 16, and the control unit 22 corresponds to the temperature adjustment unit described in the claims, and the current sensor 17 corresponds to the current detection unit in the claims. To do.

  The current sensor 17 is a sensor that detects a current value flowing between the reference electrode 11 and the electrode 12. The current sensor 17 is connected between the switch 14 and the electrode 12. As the current sensor 17, a conventionally known one is applied. The current sensor 17 outputs information on the detected current value to the control unit 22.

  The control unit 22 is a control unit of the gas sensor 2 and may be configured as one function in an ECU or the like of the engine or may be a control device dedicated to the gas sensor 2. Processing performed by the control unit 22 includes temperature adjustment processing, gas concentration derivation processing, and gas concentration ratio derivation processing. Since the temperature adjustment process and the gas concentration ratio deriving process are the same as the processes in the control unit 21 according to the first embodiment, only the gas concentration deriving process will be described.

The gas concentration derivation process will be described. On the reference electrode 11 side, as shown in the above formula (1), oxygen (O ₂ ) is converted to oxygen ions (O ²⁻ ), so that electrons (e ⁻¹ ) are received. The amount of (e ⁻¹ ) corresponds to the current value. Gas in the electrode 12 side, that the electronic in accordance with the amount of oxygen ions ^{(O 2-)} which corresponds to ^{(e -1)} supplying oxygen _{(O 2),} in accordance with the amount of supplied oxygen _{(O 2)} The amount of gas component is reacting. Therefore, the amount of oxygen supplied according to the current value can be derived, and the amount of gas consumed in the reaction (that is, the concentration of the gas component) can be derived according to the amount of oxygen.

  FIG. 6 shows a map showing the relationship between the flowing current value and the supplied oxygen amount (current value dependency of the oxygen amount), and there is a proportional relationship between the current value and the oxygen amount. Such an oxygen amount-current value map is obtained in advance through experiments or the like and stored in the control unit 22. FIG. 7 shows a map showing the relationship between the gas concentration and the oxygen amount (the oxygen amount dependency of the gas concentration) in the case of methane (the air-fuel ratio of oxygen and natural gas is constant, and methane Is completely combusted by reaction with oxygen), there is a proportional relationship between gas concentration and oxygen content. Ethane, propane and butane other than methane also have a proportional relationship between the gas concentration and the oxygen content. Such a gas concentration-oxygen amount map is obtained in advance for each gas component (methane, ethane, propane, butane) through experiments or the like and stored in the control unit 22.

  Each time the temperature is adjusted to each temperature Tx (x = 1, 2, 3, 4), the control unit 22 acquires a current value from the current sensor 17. Then, the control unit 22 derives the oxygen amount supplied according to the current value based on the oxygen amount-current value map. Further, the control unit 22 derives the gas concentration [ppm] corresponding to the oxygen amount based on the gas concentration-oxygen amount map of the gas component corresponding to the temperature Tx.

  With reference to FIGS. 5 to 7, the operation when the gas concentration ratio is detected by the gas sensor 2 will be described with reference to the flowchart of FIG. 8. FIG. 8 is a flowchart showing a flow of gas concentration ratio detection by the gas sensor 2.

  When the gas concentration ratio detection starts, the gas sensor 2 according to the second embodiment performs the operations of S20 to S23 in the same manner as S10 to S13 described in the operation of the gas sensor 1 according to the first embodiment.

  If it determines with temperature T having become temperature Tx (x = 1, 2, 3, 4) by determination of S22, the control part 22 will acquire an electric current value from the current sensor 17 (S24). Then, the control unit 22 derives the supply oxygen amount corresponding to the current value from the oxygen amount-current value map (S25). Further, the control unit 22 derives a gas concentration corresponding to the supplied oxygen amount from the gas concentration-oxygen amount map of the gas component corresponding to the temperature Tx at this time (S26).

  Thereafter, in the gas sensor 2 according to the second embodiment, the operations of S27 to S29 are performed in the same manner as S17 to S19 described in the operation of the gas sensor 1 according to the first embodiment. At this time, if it is determined in S27 that the variable x is not 4, the operations in S21 to S27 are repeated.

  This gas sensor 2 has the same effects as the gas sensor 1 according to the first embodiment (excluding the effect of using the amount of heat to derive the gas concentration), and also has the following effects. According to the gas sensor 2, by using the current value corresponding to the amount of oxygen supplied from the oxygen pump 10, the amount of oxygen used in the chemical reaction (and consequently the concentration of the gas component) can be easily detected. In particular, in the case of this detection method, since the amount of heat that is easily affected by the environment is not used in the gas component concentration detection process, the detection accuracy is high.

  A gas sensor 3 according to a third embodiment will be described with reference to FIGS. FIG. 5 is a diagram schematically showing the configuration of the gas sensor 3 according to the third embodiment.

  The gas sensor 3 is different in temperature adjustment method from the gas sensor 2 according to the second embodiment. The gas sensor 3 raises each gas component from the highest temperature among the temperatures at which it easily reacts with oxygen, and changes the temperature from the highest temperature to the lowest temperature. For this purpose, the gas sensor 3 includes an oxygen pump 10, a reference electrode 11, an electrode 12, a power supply 13, a switch 14, a heater 15, a temperature sensor 16, a current sensor 17, and a control unit 23.

  Since the oxygen pump 10, the reference electrode 11, the electrode 12, the power source 13, the switch 14, the heater 15, the temperature sensor 16, and the current sensor 17 have been described in the first and second embodiments, only the control unit 23 is described. explain. In 3rd Embodiment, the process in the heater 15, the temperature sensor 16, and the control part 23 is equivalent to the temperature adjustment part described in a claim.

  The control unit 23 is a control unit of the gas sensor 3 and may be configured as one function in the engine ECU or the like, or may be a control device dedicated to the gas sensor 3. Processing performed by the control unit 23 includes temperature adjustment processing, gas concentration derivation processing, and gas concentration ratio derivation processing. Since the gas concentration derivation process and the gas concentration ratio derivation process are the same as the processes in the control unit 22 according to the second embodiment, only the temperature adjustment process will be described.

  The temperature adjustment process will be described. The control unit 23 turns on the heater 15 (power supply) at the start of detection, and starts heating by the heater 15. In the control unit 23, information on the temperature in the oxygen pump 10 is acquired from the temperature sensor 16. Each time the temperature T is acquired, the control unit 23 determines whether or not the temperature T is higher than the highest temperature T4 among the temperatures Tx (x = 1, 2, 3, 4). At this time, the control unit 22 continues heating by the heater 15 until the temperature becomes higher than the highest temperature T4, and when the temperature becomes higher than the temperature T4, the heater 15 is turned off (power supply is stopped). Thereafter, since the temperature naturally decreases, each time the temperature T is acquired, the control unit 23 sequentially determines whether or not the temperature T has become the temperature Tx (x = 1, 2, 3, 4). Then, the temperature in the oxygen pump 10 is adjusted to each temperature Tx. First, it is determined whether or not the highest temperature T4 has been reached, and thereafter, the determination is made in the order of T3, T2, and T1. As described above, the temperature is adjusted from the high temperature side to the low temperature side in the opposite direction to the gas sensors 1 and 2 according to the first and second embodiments.

  With reference to FIGS. 5 to 7, the operation when the gas concentration ratio is detected by the gas sensor 3 will be described with reference to the flowchart of FIG. 9. FIG. 9 is a flowchart showing a flow of gas concentration ratio detection by the gas sensor 3.

  When the gas concentration ratio detection starts, first, the control unit 23 initializes the variable x to 4 (S30). First, since the temperature is raised to a temperature higher than the highest temperature T4, x is initialized with 4. The switch 14 is turned on by the control unit 23, and a voltage is applied from the power source 13 between the reference electrode 11 and the electrode 12 (oxygen pump 10). The heater 15 is turned on (power is supplied) by the control unit 23 to heat the oxygen pump 10. The temperature sensor 16 detects the temperature of the oxygen pump 10 and outputs information on the temperature to the control unit 23.

  The controller 23 acquires the temperature T of the oxygen pump 10 from the temperature sensor 16 at regular time intervals (S31). Then, the control unit 23 determines whether or not the acquired temperature T is higher than the temperature T4 (S32).

  If it is determined in S32 that the temperature T is not higher than the temperature T4, heating by the heater 15 is continued (S33), and the temperature of the oxygen pump 10 is increased. If it is determined in S32 that the temperature T is higher than the temperature T4, the heater 15 is turned off (power supply is stopped) by the control unit 23 (S34). Thereafter, the temperature of the oxygen pump 10 naturally decreases.

  The controller 23 acquires the temperature T of the oxygen pump 10 from the temperature sensor 16 at regular time intervals (S35). Then, the control unit 23 determines whether or not the acquired temperature T has become the temperature Tx (x = 1, 2, 3, 4) (S36). In this determination, first, the temperature T4 is determined. After the temperature T4 is reached, the next temperature T3 is determined. After the temperature T3 is reached, the next temperature T2 is determined. When the temperature T1 is reached and the temperature T1 is reached, the temperature determination is finished. If it is determined in S36 that the temperature T is not equal to the temperature Tx, the process waits until the next determination.

  If it determines with temperature T having become temperature Tx by determination of S36, the control part 23 will acquire an electric current value from the current sensor 17 (S37). Then, the control unit 23 derives the supply oxygen amount corresponding to the current value from the oxygen amount-current value map (S38). Further, the control unit 23 derives the gas concentration corresponding to the supplied oxygen amount from the gas concentration-oxygen amount map of the gas component corresponding to the temperature Tx at this time (S39).

  The control unit 23 determines whether or not the variable x is 1 (S40). If it is determined in S40 that the variable x is not 1, the control unit 23 subtracts 1 from the variable x (S41). And in order to detect the gas density | concentration of the gas component of the temperature Tx with the low temperature which is easy to react next, operation | movement of said S35-S40 is repeated.

  When the variable x is determined to be 1 in the determination in S40, the control unit 23 calculates a gas concentration ratio from each gas concentration of methane, ethane, propane, and butane (S42). This completes the detection of the gas concentration ratio. At this time, the switch 14 is turned off by the control unit 23 and the voltage application from the power source 13 is completed.

  This gas sensor 3 has the same effect as the gas sensor 2 according to the second embodiment, and also has the following effects. According to the gas sensor 3, when the temperature is sequentially changed, the temperature is gradually changed from the high temperature side to the low temperature side, thereby receiving the influence of the temperature rise due to the heat generated by the reaction between the gas component and oxygen when detecting the gas concentration. It becomes difficult and detection accuracy improves. Incidentally, in the case of sequentially changing from the low temperature side to the high temperature side, if there is a gas component having a similar reaction temperature when detecting the gas concentration of a certain gas component, in addition to the heating by the heater 15, reaction heat (disturbance) When the temperature rises due to the above, gas components having a reaction temperature close to that react with oxygen, which may make detection with high accuracy difficult. However, when changing from the high temperature side to the low temperature side sequentially, even if there is a gas component with a close reaction temperature when detecting the gas concentration of a certain gas component, the gas of the gas component with the higher reaction temperature is present. Since the concentration has already been detected, it is difficult to be affected by heat of reaction (disturbance), and highly accurate detection is possible. In addition, it is possible to accurately detect the concentration of the gas component in consideration of the concentration of the gas component on the higher reaction temperature side that has already been detected.

  As mentioned above, although embodiment which concerns on this invention was described, this invention is implemented in various forms, without being limited to the said embodiment.

  For example, in this embodiment, natural gas is applied as the test gas. However, the present invention is applicable to a test gas that includes a plurality of gas components each having a temperature that easily generates a chemical reaction due to a chemical reaction with oxygen. Yes, it can also be applied to a test gas containing a gas component that becomes an impurity.

  Moreover, although applied to the gas sensor used with a natural gas vehicle in this Embodiment, it is applicable by each use using natural gas other than vehicles, such as thermal power generation.

  In this embodiment, zirconia is applied as an oxygen pump (oxygen supply unit). However, when a voltage is applied, oxygen ions move between the electrodes, and other substances (other than zirconia) can be used as long as they can supply oxygen ions. A solid electrolyte or the like may be applied.

  In the present embodiment, the concentration is derived from the concentration of each gas component to the concentration ratio. However, a configuration that does not derive the concentration ratio may be used. When the concentration of a certain gas component is 0, the gas component is not included in the natural gas. Therefore, the gas component configuration included in the natural gas can be derived depending on whether the concentration of each gas component is 0 or not. Is possible.

  In this embodiment, when the peak temperature Tx (x = 1, 2, 3, 4) of each gas component is adjusted, only the gas component that easily reacts with oxygen at the temperature Tx is considered. Although the gas concentration is derived from the current value, there is a possibility that other gas components having a reaction temperature close to the temperature Tx may also react with oxygen even at the temperature Tx (there are a plurality of temperature regions that react with oxygen). Since gas components may overlap each other), the concentration of each gas component may be derived in consideration of other gas components having a close reaction temperature. Therefore, at the peak temperature Tx of each gas component (or including the surrounding temperature region), the ratio of all gas components reacting with oxygen is obtained in advance through experiments, etc. It is advisable to derive the gas concentration in consideration of the above. This further improves the detection accuracy.

  In the first embodiment, each gas component is configured to detect the concentration of the gas component from the amount of heat at each temperature by changing the temperature from the low temperature side to the high temperature side at which the gas component easily reacts with oxygen. It is good also as a structure which detects the density | concentration of a gas component from the calorie | heat amount in each temperature by changing temperature from the high temperature side to the low temperature side like 3rd Embodiment. Also in this case, the influence of temperature rise due to reaction heat can be suppressed, so that the detection accuracy is improved.

  In the third embodiment, the temperature is first raised to a temperature higher than the highest temperature among the temperatures easily reacting with oxygen of each gas component, and is adjusted to each temperature after waiting for the temperature to drop naturally. However, the temperature may be lowered using a cooling means such as water cooling or air cooling.

  DESCRIPTION OF SYMBOLS 1, 2, 3 ... Gas sensor, 10 ... Oxygen pump, 11 ... Reference electrode, 12 ... Electrode, 13 ... Power supply, 14 ... Switch, 15 ... Heater, 16 ... Temperature sensor, 17 ... Current sensor 21, 22, 23 ... Control unit.

Claims (6)

A gas sensor for detecting each concentration of a plurality of gas components contained in a test gas,
An oxygen supply section for supplying oxygen;
A first electrode disposed on a gas side containing oxygen and provided on one end side of the oxygen supply unit;
A second electrode disposed on the test gas side and provided on the other end side of the oxygen supply unit;
A power source connected between the first electrode and the second electrode;
A temperature adjusting unit for adjusting the temperature of the oxygen supply unit;
With
The temperature of the oxygen supply unit is sequentially adjusted to each temperature at which the plurality of gas components contained in the test gas and oxygen easily react by the temperature adjusting unit, and the concentration of the gas component is adjusted at each adjusted temperature. Gas sensor to detect. A current detection unit for detecting a current flowing between the first electrode and the second electrode;
The temperature adjusting unit sequentially adjusts the temperature of the oxygen supply unit to each temperature at which a plurality of gas components contained in the test gas and oxygen easily react with each other, and is detected by the current detection unit at the adjusted temperature. 2. The gas sensor according to claim 1, wherein an oxygen amount supplied by the oxygen supply unit is derived based on the obtained current value, and a concentration of a gas component is detected from the derived oxygen amount. With a calorific value detection unit that detects the amount of heat that increases due to the reaction between the gas component and oxygen,
The temperature adjustment unit sequentially adjusts the temperature of the oxygen supply unit to each temperature at which a plurality of gas components contained in the test gas and oxygen easily react, and the calorific value detection unit detects the adjusted temperature. The gas sensor according to claim 1, wherein the concentration of the gas component is detected from the amount of heat generated.   The temperature of the oxygen supply unit is sequentially adjusted by the temperature adjusting unit from a high temperature side to a low temperature side among temperatures easily reacting with oxygen of a plurality of gas components contained in a test gas. The gas sensor according to any one of claims 3 to 4.   Every time the temperature of the oxygen supply unit is adjusted to a temperature at which any gas component contained in the test gas and oxygen can easily react with the temperature adjusting unit, voltage application by the power source is started, and the arbitrary gas component The gas sensor according to any one of claims 1 to 4, wherein the application of the voltage by the power source is terminated each time detection of the concentration of is terminated.   The gas sensor according to claim 1, wherein a voltage is continuously applied by the power source during detection by the gas sensor.

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