JP2007309751A - Gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detector hard to cause an error in the supply quantity of power to a heater even if the output voltage of a power supply is varied after the start of the supply of a current to the heater and capable of suppressing the lowering of gas detecting precision. <P>SOLUTION: The gas detector 150 is constituted so that battery voltage VB is detected over a plurality of times in the current supply time band (voltage application executing time Ton) to the heater in one cycle of PWM control and the power quantity ΣWi supplied to the heater 4 is operated on the basis of the detected battery voltage VB. That is, this gas detector 150 can judge the quantity of the power actually supplied to the heater 4 even if the battery voltage VB is varied after the supply of a current to the heater 4 is started and the supply quantity of the power to the heater 4 can be allowed to precisely approach the target quantity of power. In this gas detector 150, the temperature control of a gas sensor element due to the heater 4 becomes well and the change in the activated state of the gas sensor element caused by the variation of temperature can be suppressed and the lowering of gas detecting precision can be suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gas sensor element whose sensor resistance value changes according to the concentration of a specific gas, a heater that generates heat by power supplied from a power supply device and heats the gas sensor element, and a specific gas in a measurement target gas based on the sensor resistance value. The present invention relates to a gas detection device having gas detection determination means for determining a gas concentration change.

  Conventionally, a gas sensor element whose sensor resistance value changes according to the concentration of the specific gas, a heater that generates heat by the power supplied from the power supply device and heats the gas sensor element, and a specific gas in the measurement target gas based on the sensor resistance value There is known a gas detection device having gas detection determination means for determining a concentration change of the gas.

  As such a gas detection device, for example, the voltage applied to the heater from the power supply device (battery) is subjected to PWM control (Pulse Width Modulation control), and the power supply amount to the heater is set to the target power amount. Thus, a gas detection device configured to heat the gas sensor element to a target temperature (activation temperature) has been proposed (Patent Document 1).

  In the gas detection device, PWM control is performed on the assumption that the power supply output voltage value output from the power supply device is a constant value, and the duty ratio is controlled so that the amount of power supplied to the heater becomes the target power amount. There is something to do. However, in the gas detection device having such a configuration, when the power supply output voltage fluctuates, an error occurs in the amount of power supplied to the heater, and the actual amount of power supplied to the heater is the target power amount. May have different values.

On the other hand, in the gas detection device described in Patent Document 1, when the power supply output voltage fluctuates by detecting the power supply output voltage and controlling the duty ratio in the PWM control according to the fluctuation of the power supply output voltage. Even so, it is configured to suppress an error in the amount of power supplied to the heater.
JP 2002-156350 A (Claim 8 etc.)

  However, in the above conventional gas detection device, although the duty ratio is controlled according to the fluctuation of the power supply output voltage, the detection time of the power supply output voltage is before the start of energization to the heater. If the power supply output voltage fluctuates after energization has started, there is a risk that an error will occur in the amount of power supplied to the heater.

  That is, the conventional gas detection device is configured to set the duty ratio of PWM control based on the power supply output voltage value detected before the start of energization to the heater, and to control the power supply amount to the heater to the target power amount ( Processing). When the power supply output voltage fluctuates after starting energization of the heater, the duty ratio is a value determined based on the power supply output voltage before the fluctuation, and is not a value determined based on the power supply output voltage after the fluctuation. For this reason, the amount of power supplied to the heater deviates from the target power amount, and an error occurs in the amount of power supplied to the heater.

  In the above conventional gas detection device, the power supply output voltage is detected every PWM cycle and before the heater energization is started. However, the power supply output voltage is detected by a plurality of PWM cycles (for example, It is possible to carry out the above processing simply by performing it every three cycles). However, in this case, the power supply output voltage is more likely to fluctuate, so that an error tends to occur in the amount of power supplied to the heater.

  When the amount of power supplied to the heater becomes a value different from the target power amount in this way, the temperature of the gas sensor element moves away from the target temperature (activation temperature), and the activation state of the gas sensor element changes. . As a result, the correlation between the concentration of the specific gas and the sensor resistance value also changes, causing a phenomenon that the sensor resistance value fluctuates even though the specific gas concentration is constant, and the gas detection There is a risk that the accuracy may decrease.

  Therefore, the present invention has been made in view of these problems, and even when the power supply output voltage fluctuates after the start of energization of the heater, an error is unlikely to occur in the amount of power supplied to the heater, and gas detection accuracy is improved. It aims at providing the gas detection apparatus which can suppress a fall.

  The invention according to claim 1, which has been made to achieve such an object, heats the gas sensor element that generates heat by supplying power from a power sensor and a gas sensor element that changes in sensor resistance value according to the concentration of the specific gas. A gas detection device having a heater and gas detection determination means for determining a change in concentration of a specific gas in a measurement target gas based on a change in sensor resistance value, wherein the heater from the power supply device is controlled by PWM control of the voltage applied to the heater. Supply power control means for controlling the amount of power supplied to the power supply, and power supply output voltage detection means for detecting the power supply output voltage output from the power supply device a plurality of times in the energization time zone of the heater in one cycle of PWM control The supplied power amount supplied to the heater after the start of energization to the heater is detected by the power supply output voltage detection means for each cycle of the PWM control. A supplied power calculating means for calculating based on the source output voltage, and the supplied power control means is configured to supply PWM with a target power amount for heating the gas sensor element to the activation temperature. After each start of energization of the heater, it is determined whether the supplied power amount calculated by the supplied power calculation means is equal to or greater than the target power amount, and the supplied power amount is equal to or greater than the target power amount. Then, the gas detection device is characterized in that energization of the heater is stopped.

  This gas detection device detects a power supply output voltage a plurality of times during the energization time period of the heater in one cycle of PWM control, and calculates a supplied power amount supplied to the heater based on the detected power supply output voltage. It has a configuration. For this reason, even if the power supply output voltage fluctuates during voltage application to the heater, this gas detection device accurately calculates the supplied power amount actually supplied to the heater based on the fluctuating power supply output voltage. Can do.

  The gas detection device can calculate the supplied power amount actually supplied to the heater as described above even when the power supply output voltage fluctuates after the energization of the heater is started. By stopping energization of the heater when the power exceeds the target power amount, the power supply amount to the heater can be accurately approximated to the target power amount, and the error in the power supply amount to the heater can be reduced. . As a result, the control accuracy in the temperature control of the gas sensor element by the heater is improved, the change in the activation state of the gas sensor element due to the temperature fluctuation can be suppressed, the sensor resistance value fluctuates despite the specific gas concentration being constant, etc. Therefore, it is possible to prevent the gas detection accuracy from being lowered.

  Therefore, according to the present invention, even when the power supply output voltage fluctuates after the start of energization to the heater, it is difficult to cause an error in the amount of power supplied to the heater, and the control accuracy in the temperature control of the gas sensor element by the heater can be improved. A decrease in gas detection accuracy can be suppressed.

  Note that the target power amount used by the supplied power control means is the power amount to be supplied to the heater in order to heat the gas detection element to the activation temperature. The target power amount may be a fixed value determined in advance based on the component conditions such as the activation temperature of the gas detection element and the electric resistance value of the heater, or may be based on the component conditions such as the outside air temperature. It is good also as a fluctuation value defined in consideration of fluctuation conditions.

  Next, in the above-described gas detection device, as described in claim 2, for each cycle of the PWM control, the target power of the cycle is determined from the supplied power amount from the energization start timing to the energization stop timing to the heater. An excess supply power amount calculation means for calculating an excess supply power amount obtained by subtracting the amount, and a corrected target power amount obtained by subtracting the excessive supply power amount of the previous cycle from a predetermined basic target power amount is calculated as a target power amount. A corrected target power amount calculating means, and the supplied power control means is calculated by the supplied power amount calculated by the supplied power calculating means and the corrected target power amount calculating means after energization of the heater is started. The corrected target power amount is compared, and when the supplied power amount is equal to or greater than the corrected target power amount, the heater can be configured to stop energization.

  In this gas detection device, the target power of the cycle of the supplied power amount actually supplied to the heater (the supplied power amount from the energization start timing to the energization stop timing) for each cycle of PWM control. The excess power supply amount obtained by subtracting the amount is calculated, and the corrected target power amount obtained by subtracting the excess supply power amount from the basic target power amount is calculated as a new target power amount.

  Then, the supply power control unit, after starting energization of the heater, when the supplied power amount calculated by the supplied power calculation unit is equal to or greater than the corrected target power amount calculated using the excessive supply power amount of the previous cycle. Stop energizing the heater. That is, the supplied power control unit uses the corrected target power amount calculated by the corrected target power amount calculating unit as the target power amount supplied to the heater in one cycle of PWM control.

  In other words, this gas detection device has a corrected target power amount (excess supply) in the next cycle even if the amount of power actually supplied to the heater exceeds the target power amount and an excess supply power amount occurs in a certain cycle. Heater control is performed using a power amount determined in consideration of the power amount.

  Thus, the gas detection device configured in this way can reduce the amount of power supplied to the heater in the current cycle by an amount corresponding to the amount of excess power supplied in the previous cycle, and the power supplied in the previous cycle and the current cycle. The average value of the amounts can be brought close to the basic target power amount, and the error in the amount of power supplied to the heater can be further reduced.

  Therefore, according to the present invention, even if the amount of power actually supplied to the heater exceeds the basic target power amount and an excessive amount of power is generated, an error in the amount of power supplied as an average value in a plurality of cycles. Can be further reduced, and the control accuracy in the temperature control of the gas sensor element can be further improved.

  Note that the basic target power amount is the amount of power to be supplied to the heater when the gas detection element is heated to the activation temperature, and is based on the component part conditions such as the activation temperature of the gas detection element and the electric resistance value of the heater. It can be determined in advance.

  Next, in the above-described gas detection device, as described in claim 3, the supplied power calculation means has a boundary between detection times of the power supply output voltage by the power supply output voltage detection means in the energization time zone to the heater. Is provided with unit supply power amount calculating means for calculating the unit time supply power amount supplied to the heater in the unit time period, and the supply power control means is provided with one cycle of PWM control. A supply power remaining amount variable initial setting means for setting a target power amount as an initial value of a supply power remaining amount variable representing the remaining amount of power to be supplied to the heater in the cycle before starting the energization of the heater; When the power supply output voltage is detected by the power supply output voltage detecting means after the energization of the heater is started, the unit time supply power amount in the unit time zone that ends the voltage detection time and the voltage detection time A variable determination unit that compares the determined supply power remaining amount variable and determines whether the unit time supply power amount is smaller than the supply power remaining amount variable, and when the variable determination unit makes an affirmative determination, Supply power remaining amount variable resetting means for resetting the value obtained by subtracting the unit time supply power amount from the supply power remaining amount variable to the supply power remaining amount variable, and the amount of supplied power when the variable determination means makes a negative determination. Is determined to be equal to or greater than the target power amount, and heater energization stopping means for stopping energization of the heater can be provided.

  This gas detection device calculates the unit-time supply power amount supplied to the heater for each unit time zone that is divided with the detection time of the power supply output voltage as a boundary in the energization time zone to the heater, and the power output When the voltage is detected, it is determined whether or not the unit time supply power amount in the unit time zone whose end is the detection time is smaller than the supply power remaining amount variable.

  When the variable determination unit makes an affirmative determination (when the unit time supply power amount is smaller than the supply power remaining amount variable), the supply power remaining amount variable resetting unit supplies the unit time supply from the supply power remaining amount variable. The value obtained by subtracting the electric energy is reset to the remaining power supply variable. In addition, when the variable determination unit makes a negative determination (when the unit time supply power amount is equal to or greater than the supply power remaining amount variable), the supplied power amount has reached the target power amount or more at the heater energization stop unit. And the power supply to the heater is stopped.

  Note that the supplied power remaining amount variable is set to an initial value by the supplied power remaining amount variable initial setting unit before the start of energization of the heater every PWM control cycle. This initial value is the target power amount, and is the power amount to be supplied to the heater in one cycle of PWM control when the gas detection element is heated to the activation temperature.

  That is, this gas detection device sets the amount of power to be supplied to the heater in one cycle of PWM control as the initial value of the supply power remaining variable, and from the supply power remaining variable to the unit every time the power output voltage is detected. The time supply power amount is subtracted, and the power supply to the heater is stopped when the unit time supply power amount becomes equal to or greater than the supply power remaining amount variable.

  In other words, this gas detection device is configured to stop energization of the heater when the integrated value of the unit time supply power amount becomes equal to or greater than the initial value of the remaining power supply variable after the start of energization of the heater. By controlling the amount of power supplied in this way, the amount of power necessary for heating the gas detection element to the activation temperature can be supplied to the heater.

  The unit time supply power amount is the amount of power actually supplied to the heater in the unit time zone divided from the detection time of the power supply output voltage in the energization time zone to the heater. Even when the power supply output voltage fluctuates after the start of energization, the value corresponds to the amount of power actually supplied to the heater.

  In other words, this gas detection device can determine the amount of power actually supplied to the heater even when the power supply output voltage fluctuates after the start of energization of the heater. The amount of power supplied to the heater can be reduced, and the control accuracy in the temperature control of the gas sensor element by the heater can be improved.

The supply power remaining amount variable can also be used as a variable representing the remaining amount of power to be supplied to the heater in the cycle.
Next, in the gas detection apparatus including the excess power supply amount calculation means and the corrected target power amount calculation means among the above, the supplied power calculation means includes the energization time zone for the heater as described in claim 4. Among these, a unit supply power amount calculation that calculates a unit time supply power amount supplied to the heater in the unit time zone for each unit time zone divided with the detection timing of the power output voltage by the power output voltage detection means as a boundary. The supply power control means is an initial stage of a supply power remaining amount variable that represents the remaining amount of power to be supplied to the heater in this cycle before the start of energization to the heater every PWM control cycle. When the power supply output voltage is detected by the power supply output voltage detection means after the start of energization of the heater, the supply power remaining amount variable initial setting means for setting the target power amount as a value is terminated. The unit time supply power amount in the unit time zone to be compared with the supply power remaining amount variable set at the voltage detection time, and whether or not the unit time supply power amount is smaller than the supply power remaining amount variable is determined. A variable determination unit that resets and a supply power remaining amount variable resetting unit that resets a value obtained by subtracting the unit time supply power amount from the supply power remaining amount variable to the supply power remaining amount variable when the variable determination unit makes an affirmative determination And a heater energization stop unit that determines that the supplied power amount is equal to or greater than the target power amount and stops energization of the heater when a negative determination is made by the variable determination unit. The means can be configured to calculate a value obtained by subtracting the value of the remaining power supply variable from the unit time supply power amount as the excess supply power amount when a negative determination is made by the variable determination means.

  In this gas detection device, when the amount of supplied power per unit time becomes equal to or greater than the supply power remaining amount variable that is successively reduced, a negative determination is made by the variable determination means, and the energization to the heater is stopped. At this time (when a negative determination is made by the variable determination means), the difference value between the unit time supply power amount and the supply power remaining amount variable is the target power amount (or the corrected target power among the power actually supplied to the heater). It corresponds to the amount of power exceeding the amount) (the amount of excess supply power).

  For this reason, when a negative determination is made in the variable determination means, the excess supply power amount calculation means calculates the value obtained by subtracting the value of the remaining power supply variable from the unit time supply power amount as the excess supply power amount, It is possible to obtain a power amount (excess supply power amount) that exceeds a target power amount (or corrected target power amount) among the power amounts actually supplied to the heater.

The supply power control means controls the power supply amount to the heater using the corrected target power amount as the new target power calculated using the excessive supply power amount of the previous cycle.
Thereby, this gas detection apparatus can make the average value of the power supply amount in the previous cycle and the current cycle approach the basic target power amount, and can further reduce the error of the power supply amount to the heater.

  Therefore, according to the present invention, even if the amount of power actually supplied to the heater exceeds the basic target power amount and an excessive amount of power is generated, an error in the amount of power supplied as an average value in a plurality of cycles. Can be further reduced, and the control accuracy in the temperature control of the gas sensor element can be further improved.

As an embodiment of the present invention, a vehicle outside air introduction control system including a gas detection device to which the present invention is applied will be described with reference to the drawings.
First, FIG. 1 shows a schematic configuration diagram of an integrated gas sensor element 10 provided in a gas detection device to which the present invention is applied. As shown in FIG. 1, the integrated gas sensor element 10 includes a reducing gas gas sensor element 2, an oxidizing gas gas sensor element 3, and a heater 4 formed on a single ceramic substrate 1.

Among these, the gas sensor element 2 for reducing gas (hereinafter also simply referred to as G element 2) is a resistor made of an oxide semiconductor containing SnO ₂ as a main component, and mainly reduces CO, HC (hydrocarbon) and the like. It has a property that its resistance value (hereinafter also referred to as G sensor resistance value Rg) changes in response to a reactive gas. The gas sensor element 3 for oxidizing gas (hereinafter also simply referred to as D element 3) is a resistor made of an oxide semiconductor mainly composed of WO ₃ and reacts mainly with an oxidizing gas such as NOx. The resistance value (hereinafter also referred to as D sensor resistance value Rd) varies.

  Note that the G element 2 and the D element 3 do not react with gas at room temperature, and have an activation state that reacts with a reducing gas or an oxidizing gas by reaching an activation temperature of 200 ° C. or higher, respectively. Become. Since the G element 2 in the activated state changes in a direction in which the G sensor resistance value Rg decreases as the concentration of the reducing gas increases, the reducing gas is changed based on the change in the G sensor resistance value Rg. Concentration change can be detected. Further, since the D element 3 in the activated state changes in the direction in which the D sensor resistance value Rd increases as the concentration of the oxidizing gas increases, the oxidizing gas is changed based on the change in the D sensor resistance value Rd. Concentration change can be detected.

  The heater 4 is composed of a resistance wiring formed on the ceramic substrate 1 and is configured to generate heat when a predetermined voltage is applied. The G element 2 and the D element 3 are brought to a target temperature that is equal to or higher than the activation temperature. It is provided for heating and maintaining to be in an activated state. The heater 4 is configured by selecting characteristics such as a resistance value so that at least the G element 2 and the D element 3 can be heated to the activation temperature or higher.

  In the integrated gas sensor element 10 shown in FIG. 1, the D element terminal 5 is connected to the second AD conversion input terminal 103 of the microcomputer 101 (see FIG. 2 described later), and the G element terminal 6 is connected to the micro sensor described later. Connected to the first AD conversion input terminal 102 of the computer 101 (see FIG. 2), the heater terminal 7 is connected to the positive electrode of the power supply device 191 (see FIG. 2) described later, and the reference terminal 8 is connected to the power supply device 191 (FIG. 2) described later. Connected to a ground having the same potential as the negative electrode of (see).

  Next, FIG. 2 is a configuration diagram showing the configuration of the vehicle outside air introduction control system 100 including the gas detection device 150 to which the present invention is applied. The vehicle outside air introduction control system 100 detects changes in the oxidizing gas concentration and the reducing gas concentration contained in the outside air by the gas detection device 150, and based on the detection result, the outside air introduction flap 174 (hereinafter referred to as the outside air introduction flap 174). Simply opening and closing the flap 174).

  The vehicle outside air introduction control system 100 includes a power supply device 191 (hereinafter also simply referred to as battery 191) that outputs a constant voltage (rated voltage 12 [V]; hereinafter also referred to as battery voltage VB), and a microcomputer 101 (referred to as battery 191). Hereinafter, it is also referred to as a microcomputer 101), a G element circuit 110 that outputs a voltage according to a change in the G sensor resistance value Rg in the G element 2, and a voltage according to a change in the D sensor resistance value Rd in the D element 3. D element circuit 120, heater 4 for heating and maintaining G element 2 and D element 3 at the activation temperature, heater circuit 131 for controlling energization of heater 4, and drive voltage Vcc (5 [V]) Regulator circuit 140 and an electronic control assembly 160 for controlling the flap 174.

  In the outside air introduction control system 100 for a vehicle, the power supply device 191, the G element circuit 110, the D element circuit 120, the heater 4, the heater circuit 131, and the microcomputer 101 constitute a gas detection device 150.

  The power supply device 191 includes a voltage output unit 192 that outputs a battery voltage VB, and a Zener diode 193 having an anode connected to the ground having the same potential as the negative electrode of the voltage output unit 192 and a cathode connected to the positive electrode of the voltage output unit 192. The maximum output voltage that can be output is limited to 40 [V]. That is, when a surge voltage exceeding 40 [V] is generated in the power supply path from the power supply device 191 to each part of the device, the Zener diode 193 breaks down and the voltage value of the power supply path is set to 40 [V]. Restricted to:

  The electronic control assembly 160 controls the outside air introduction flap 174. The outside air introduction flap 174 is provided to switch between the inside air intake duct 172 and the outside air intake duct 173 connected to the duct 171 connected to the interior of the automobile. In other words, the outside air introduction flap 174 is provided in the duct 171 connected to the vehicle interior in the air conditioning system provided in the automobile, and is provided to switch the circulation state of the air flow into the vehicle interior to outside air introduction or inside air circulation. Yes.

  The electronic control assembly 160 includes a flap control circuit 161 and an actuator 162. Among these, the flap control circuit 161 is connected to the output terminal 106 (OUT terminal 106) of the microcomputer 101, and drives the actuator 162 in accordance with the assembly control signal (flap opening / closing signal Sf) from the output terminal 106, and the flap 174. Is rotated to connect either the inside air intake duct 172 or the outside air intake duct 173 to the duct 171. Note that a fan 175 is provided inside the duct 171 to pressure-feed air toward the passenger compartment.

  For example, when the flap 174 is disposed at a position closing the outside air intake duct 173 as shown by a solid line in FIG. 2, the outside air is prevented from entering the room, and the duct 171 is connected to the inside air intake duct 172. It communicates and it will be in the inside air circulation state which circulates the air in a vehicle interior. On the other hand, when the flap 174 is disposed at a position that closes the inside air intake duct 172 as shown by a broken line in FIG. 2, the duct 171 communicates with the outside air intake duct 173 to allow the air outside the vehicle interior to pass through the vehicle interior. It will be in the outside air introduction state to take in.

  Next, although not shown in detail, the microcomputer 101 has a known configuration, a microprocessor that performs arithmetic operations, a RAM that temporarily stores programs and data, a ROM that stores programs and data, and an analog signal that is converted into a digital signal. An A / D conversion circuit is included. Note that the A / D conversion circuit converts analog signals input from the first AD conversion input terminal 102, the second AD conversion input terminal 103, and the third AD conversion input terminal 104 into digital signals that can be used by a microprocessor or the like. Further, the microcomputer 101 includes a PWM terminal 105 that outputs a pulse command signal Sh to the heater circuit 131.

  Furthermore, the regulator circuit 140 is configured to always output a constant drive voltage Vcc (5 [V]) by the regulator 141 regardless of the fluctuation of the battery voltage VB. The microcomputer 101, the G element circuit 110, D Power is supplied by outputting the drive voltage Vcc to the element circuit 120 or the like. The microcomputer 101 receives the drive voltage Vcc at the power receiving terminal 107 (Vcc terminal).

  The G element circuit 110 is a circuit that resistively divides the drive voltage Vcc between the G element 2 and the first resistor 111 having the resistance value Ra. The G element circuit 110 and the first resistor 111 are divided by the voltage dividing point (hereinafter referred to as operation). (Also referred to as point Pg) is connected to the first AD conversion input terminal 102 of the microcomputer 101. The potential at the operating point Pg (hereinafter also referred to as G element voltage Vg) changes according to the change in the G sensor resistance value Rg. Specifically, reducing gas (CO, HC, etc.) As the concentration of increases, the G element voltage Vg decreases.

  Similarly, the D element circuit 120 is a circuit that resistively divides the drive voltage Vcc between the D element 3 and the second resistor 121 having the resistance value Rb, and a voltage dividing point (hereinafter referred to as “D voltage”) between the D element 3 and the second resistor 121. The operation point Pd) is connected to the second AD conversion input terminal 103 of the microcomputer 101. The potential at the operating point Pd (hereinafter also referred to as the D element voltage Vd) changes according to the change in the D sensor resistance value Rd. Specifically, the concentration of the oxidizing gas (NOx, etc.) Increases, the D element voltage Vd increases.

  Then, the microcomputer 101 executes a gas detection determination process (S140), which will be described later, to change the G element voltage Vg and the D element voltage Vd input to the first AD conversion input terminal 102 and the second AD conversion input terminal 103. In response, the concentration change of the reducing gas or oxidizing gas is detected. Further, the microcomputer 101 outputs a flap opening / closing signal Sf to the electronic control assembly 160 based on the detection result of the concentration change of the reducing gas or the oxidizing gas, and controls the switching of the flap 174 provided in the duct 171. Process.

The heater circuit 131 includes a switching circuit 132 and a voltage detection circuit 180.
Among these, the voltage detection circuit 180 includes resistors 181 and 182 and a capacitor 183, and divides the applied voltage value from the battery 191 to the heater 4 (in other words, the battery voltage VB) and divides the divided voltage. The battery voltage VE is configured to be input to the third AD conversion input terminal 104 of the microcomputer 101. That is, the voltage detection circuit 180 is configured to convert the voltage applied to the heater 4 into a voltage level that can be input to the third AD conversion input terminal 104 of the microcomputer 101 and output the voltage to the microcomputer 101.

  The switching circuit 132 is configured to be able to switch the power supply path to the heater 4 between the energized state and the cut-off state based on the pulse command signal Sh from the microcomputer 101. That is, the switching circuit 132 is configured such that the pulse command signal Sh from the microcomputer 101 is input to the base of the transistor 135 through the resistor 134, and the transistor 135 is turned on (energized) in accordance with the state of the pulse command signal Sh. State) or off state (blocking state). The resistor 136 is a bias resistor. With such a change in the state of the transistor 135, the gate potential of the p-channel MOSFET 133 connected to the connection point between the resistor 137 and the resistor 138 changes, and the MOSFET 133 is turned on (energized) in accordance with the state of the pulse command signal Sh. Or it is set to an off state (blocking state).

  That is, the switching circuit 132 is configured to perform PWM control on the voltage applied to the heater 4 by switching between energization and interruption of the heater 4 in accordance with the pulse command signal Sh from the microcomputer 101.

Next, normal routine processing executed in the microcomputer 101 will be described with reference to the flowchart shown in FIG.
The normal routine process is continued until the outside air introduction control system 100 for the vehicle is started and the process is started, and continues until the outside air introduction control system 100 for the vehicle is stopped.

When normal routine processing is started, first, in S110 (S represents a step), initial setting processing including initialization of RAM operation and the like is performed.
The initial setting process in S110 includes a process for starting the gas detection standby time counter update process, a process for starting the heater control interrupt process, and the like. The gas detection standby time counter update process performs a process of updating the gas detection standby time counter used for the determination process in the next S120 to a value corresponding to the elapsed time. The processing content of the heater control interrupt processing will be described later.

  In the next S120, it is determined whether or not the gas detection standby time has elapsed. If an affirmative determination is made, the process proceeds to S130, and if a negative determination is made, the same step is repeatedly executed to perform a gas detection standby. Wait until time has passed.

  Although there are various methods for determining whether or not the gas detection standby time has elapsed, in this embodiment, the gas detection standby time counter is compared with the standby time reference value, and the gas detection standby time counter An affirmative determination is made when the standby time reference value is exceeded, and a negative determination is made when the gas detection standby time counter is less than the standby time reference value. The standby time reference value can be a predetermined constant. In this embodiment, “0.1 [sec]” is set as the standby time reference value.

In the next S130, processing for resetting the gas detection standby time counter is executed.
In continuing S140, a gas detection determination process is performed.
In the gas detection determination process, the gas detection process of the reducing gas detected by the G element 2 and the gas detection process of the oxidizing gas detected by the D element 3 are respectively executed, and the flap open / close signal corresponding to the detection result A process of outputting Sf is executed.

  The gas detection determination process can be performed using a known method (process), and thus detailed description thereof will be omitted. In the present embodiment, the present applicant discloses in Japanese Patent Laid-Open No. 2005-308451. The detected gas detection process was executed.

When the process of S140 ends, the process proceeds to S120 again.
That is, in the normal routine process, by performing the gas detection determination process (the process in S140) periodically (in other words, every time an affirmative determination is made in S120), the oxidizing gas concentration contained in the outside air and A process of detecting a change in the reducing gas concentration and outputting a flap opening / closing signal Sf for controlling opening / closing of the outside air introduction flap 174 based on the detection result is executed.

Next, the processing content of the heater control interrupt processing will be described. FIG. 4 is a flowchart showing the contents of the heater control interrupt process.
The heater control interrupt process is repeatedly executed at predetermined intervals (execution cycle TB). In the present embodiment, the execution cycle TB of the heater control interrupt process is set to “1/128 of one cycle in PWM control”. Note that one cycle (execution cycle TA) of PWM control in the present embodiment is set to 1/30 [sec].

  When the heater control interruption process is started, in S310, it is determined whether or not it is a timing to start voltage application to the heater. If an affirmative determination is made, the process proceeds to S320, and if a negative determination is made. Proceeds to S350.

  There are various methods for determining whether or not it is the voltage application start timing for the heater. In this embodiment, the heater voltage application start determination counter is compared with the application start determination reference value to apply the voltage to the heater. It is determined whether it is a start timing. Specifically, an affirmative determination is made when the heater voltage application start determination counter is greater than or equal to the application start determination reference value, and a negative determination is made when the heater voltage application start determination counter is less than the application start determination reference value.

  The application start determination reference value is determined in advance as a value corresponding to one cycle (execution cycle TA) of PWM control. In this embodiment, the application start determination reference value corresponds to “1/30 [sec]”. Value to be set ".

  The heater voltage application start determination counter is a counter used for determining the passage of time. In addition to being used for determining one cycle of PWM control, the heater voltage application start determining counter is also used for determining battery voltage detection timing. The heater voltage application start determination counter is initialized (cleared to zero) before the heater control interrupt process is started in S110 in the normal routine process, and is incremented by the process in S350 each time a unit time elapses. (Addition) is made, and when the determination in S310 is affirmative and the process proceeds to S340, it is cleared to zero.

  When an affirmative determination is made in S310 and the process proceeds to S320, in S320, a process of setting target power to be supplied to the heater in the current cycle in PWM control (in other words, the current heater voltage application period) is executed. Specifically, a value obtained by subtracting the excess supply power amount AW in the previous cycle from the basic target power amount W is set as the initial value SW (0) of the remaining supply power variable SW (n). The initial value SW (0) of the remaining power supply variable SW (n) set in this way is also referred to as “corrected target power amount SW (0)” in the following description.

  The basic target power amount W is the amount of power to be supplied to the heater 4 in order to heat the G element 2 and the D element 3 to the activation temperature, and the activation temperature of the G element 2 and the D element 3 and the heater 4 is a fixed value determined in advance based on various conditions such as an electric resistance value of 4. In the present embodiment, the basic target power amount W is stored in the storage unit (ROM, RAM, etc.) of the microcomputer 101. In S320, the basic target power amount W is read from the storage unit, and the remaining power supply variable SW ( This is used when setting the initial value SW (0) of n) (the corrected target power amount SW (0)).

  The excess power supply amount AW is set to an initial value (for example, 0 [W]) before the heater control interrupt process is started in S110, and this initial value is used when S320 is executed for the first time. In the second and subsequent executions of S320, the value updated in S420 described later is used.

In the next S330, a process of starting voltage application control to the heater is executed.
Specifically, by outputting a high-level pulse command signal Sh from the PWM terminal 105 to the heater circuit 131, processing for starting voltage application to the heater 4 by the heater circuit 131 is executed. In S330, the heater control flag Fh, which is one of internal flags used for various control processes of the microcomputer 101, is set to the set state. The heater control flag Fh is a state flag indicating whether or not voltage application control to the heater is being performed. When the heater voltage application control is being performed, the heater control flag Fh is set to a set state and is not being subjected to heater voltage application control. In some cases, the reset state is set.

  Here, regarding the heater control by the gas detection device 150 of the present embodiment, the execution cycle TA of the PWM control and the execution cycle TB of the battery voltage detection process (in other words, the heater control interrupt process) will be described.

FIG. 5 is an explanatory diagram showing the waveform of the voltage applied to the heater. In FIG. 5, a pulse waveform for three cycles is shown on the upper side, and an enlarged waveform at the time of voltage application in the first cycle is shown on the lower side.
As shown in the upper side of FIG. 5, the execution cycle TA of the PWM control related to the heater control is a time interval between adjacent start timings (for example, the start timing ts1 of the first cycle and the start timing ts2 of the second cycle). This execution period TA can be divided into a voltage application execution time Ton and a voltage application stop time Toff.

  Among the pulse waveforms, start times ts1, ts2, and ts3 are the start time of one cycle in PWM control and the start time of voltage application to the heater, and each correspond to the execution time of S330 in the heater control interrupt process. The time interval between adjacent start times (in other words, the PWM control execution period TA) is determined by the application start determination reference value used in S310.

  Further, as shown in the lower side of FIG. 5, the voltage application execution time Ton can be divided into a plurality of unit time zones with the battery voltage detection time tVn as a boundary, and the time interval between adjacent battery voltage detection times tVn. Corresponds to the execution period TB of the heater control interrupt process.

Returning to the flowchart of FIG. 4, in the next S340, the heater voltage application start determination counter is cleared (zero cleared).
If a negative determination is made in S310 and the process proceeds to S350, a process of incrementing (adding 1) the heater voltage application start determination counter is executed in S350.

  As described above, since this heater control interrupt process is executed at regular intervals (execution period TB), the increment of the heater voltage application start determination counter in S350 is repeated while the negative determination in S310 is repeated. The process is repeatedly executed at regular intervals (execution cycle TB). Then, at the start timing of one cycle in PWM control (in other words, heater voltage application start timing), an affirmative determination is made in S310, and the heater voltage application start determination counter is cleared (S340).

  Therefore, regarding the control cycle (execution cycle TA) in PWM control, the heater voltage application start determination counter is used based on the heater voltage application start determination counter during the period from the heater voltage application start timing of the current cycle to the heater voltage application start timing of the next cycle. The approximate elapsed time from the voltage application start time to the can be determined. Specifically, a value obtained by multiplying the execution period TB of the heater control interrupt process and the heater voltage application start determination counter corresponds to the approximate elapsed time from the voltage application start time to the heater.

  In next S360, it is determined whether or not the heater voltage application control is being performed. If the determination is affirmative, the process proceeds to S370, and if the determination is negative, the process proceeds to S310 again. In S360, based on the state (set state or reset state) of the heater control flag Fh, it is determined whether voltage application control to the heater 4 is being performed.

When an affirmative determination is made in S360 and the process proceeds to S370, a process of detecting the battery voltage VB output from the battery 191 is executed in S370.
Specifically, the A / D conversion value of the divided battery voltage VE inputted to the third AD conversion input terminal 104 is acquired, and the battery is based on the divided battery voltage VE and the resistance divided value of the voltage detection circuit 180. The battery voltage VB is detected by calculating the voltage VB. Then, the detected value of the battery voltage VB is assigned to the battery voltage variable V (n) and stored.

  Note that the argument n of the battery voltage variable V (n) is a value determined according to the number of times of detection of the battery voltage in the current cycle in PWM control. In this embodiment, the numerical value of the heater voltage application start determination counter is set. Is done. For example, since the heater voltage application start determination counter is 1 at the first battery voltage detection time, n = 1 is set for the argument n, and similarly at the second battery voltage detection time. , N = 2 is set in the argument n.

  Further, as described above, since this heater control interrupt process is executed at regular intervals, while the negative determination in S310 is repeated and the affirmative determination in S360 is repeated, the battery voltage in S370 is determined. The detection process is executed at regular intervals according to the execution period TB of the heater control interrupt process.

  In the next S380, the heater control interrupt process repeatedly executed in the execution cycle TB corresponds to the battery voltage VB (in other words, the battery voltage variable V (n)) detected this time (for example, the nth time). A process of calculating the amount of power supplied to the heater is executed. In other words, in S380, in the n-th unit time zone among a plurality of unit time zones divided with the detection timing of the battery voltage VB as a boundary in the energization time zone (voltage application time zone) to the heater 4. A process of calculating the unit time supply power W (n) supplied to the heater 4 is executed.

  In the explanatory diagram shown in the lower part of FIG. 5, times tV1, tV2,..., TVn correspond to battery voltage detection times, and the divided areas divided by these detection times as boundaries are unit time zones. It corresponds to.

  In the present embodiment, a process of calculating a unit time supply power amount W (n) corresponding to the battery voltage variable V (n) is executed using map data indicating the correlation between the battery voltage and the unit time supply power amount. To do. Map data indicating the correlation between the battery voltage VB and the amount of power supplied per unit time is predetermined based on a simulation value or an actual measurement value, and is stored in a storage unit (ROM or the like) of the microcomputer 101.

In the explanatory diagram shown at the bottom of FIG. 5, the area of each divided region divided at times tV1, tV2,..., TVn is a value proportional to the unit time supply power amount W (n).
In the next S390, the remaining supply power variable SW (n-1) at the previous detection of the battery voltage is compared with the unit time supply power W (n) at the current detection of the battery voltage. It is determined whether or not the quantity variable SW (n−1) is larger than the unit time supply power amount W (n). If the determination is affirmative, the process proceeds to S400, and if the determination is negative, the process proceeds to S410. To do.

  Note that the value of the remaining power supply variable SW (n−1) at the previous detection of the battery voltage is substituted in S400 in the previous heater control interrupt process. Further, the unit time supply power W (n) at the current detection of the battery voltage is the value calculated in S380 in the current heater control interrupt processing.

  When an affirmative determination is made in S390 and the process proceeds to S400, in S400, a value obtained by subtracting the unit time supply power amount W (n) at the current detection from the supply power remaining amount variable SW (n-1) at the previous detection is calculated. A process of substituting in the remaining power supply variable SW (n) at the time of detection is executed.

  In other words, in S400, the remaining amount of power to be supplied to the heater is further calculated, and the calculation result is substituted into the supplied power remaining amount variable SW (n) at the time of the current detection and stored. .

If a negative determination is made in S390 and the process proceeds to S410, a process of stopping voltage application control to the heater is executed in S410.
Specifically, by outputting a low-level pulse command signal Sh from the PWM terminal 105 to the heater circuit 131, processing for stopping the voltage application to the heater 4 by the heater circuit 131 is executed. In S410, the heater control flag Fh is set to the reset state.

  Here, times te1, te2, and te3 in the pulse waveform shown on the upper side of FIG. 5 are the timing of stopping the application of voltage to the heater, and correspond to the timing of execution of S410 in the heater control interrupt processing. The time difference between the voltage application start time ts1 and the voltage application stop time te1 is the voltage application execution time Ton, and the ratio of the voltage application execution time Ton in the execution cycle TA is the duty ratio of PWM control. .

  Further, the voltage application execution time Ton takes a value corresponding to the amount of power already supplied to the heater ΣWi (= W (1) + W (2) +... + W (n)). The supplied power amount ΣWi to the heater is the sum of the unit time supplied power amounts W (i) (i = 1 to n) from the first time to the nth time in the battery voltage detection time.

  As shown on the lower side of FIG. 5, the voltage application execution time Ton can be divided into a plurality of unit time zones with the battery voltage detection time tVn as a boundary, and the unit supplied to the heater in each unit time zone. The sum total of the time supply power amount W (i) (i = 1 to n) corresponds to the supply power amount (power amount already supplied to the heater ΣWi) supplied to the heater during the voltage application execution time Ton.

  As shown in FIG. 5, since the area of the pulse waveform has a size corresponding to the amount of power supplied, the unit time power supply amount W (n) in each unit time zone is the duration of the unit time zone (in other words, , Based on the execution cycle TB) and the voltage applied to the heater.

  Returning to the flowchart of FIG. 4, in the next step S420, the remaining power variable SW (n−1) at the previous detection of the battery voltage is subtracted from the unit time supply power W (n) at the current detection of the battery voltage. A process of substituting the value into the excessive power supply amount AW is executed.

  The supplied power remaining amount variable SW (n) is set to the initial value SW (0) (the corrected target power amount SW (0)) (S320), and each time the battery voltage VB is detected (S370). Then, the unit time supply electric energy W (n) calculated based on the detected battery voltage (battery voltage variable V (n)) is subtracted (S400). The subtraction process at S400 is performed until the remaining power supply variable SW (n−1) at the previous detection becomes equal to or less than the unit time supply power W (n) at the current detection (until a negative determination is made at S390). ) Repeatedly executed.

  Then, when the processes of S340, S400, and S420 are finished or a negative determination is made in S360, the heater control interrupt process is finished. Furthermore, as described above, the heater control interrupt process is repeatedly executed at regular intervals (execution cycles).

Here, the excessive power supply amount AW will be described.
FIG. 6 shows the correlation among the supplied power amount ΣWi, the corrected target power amount SW (0), the excess supplied power amount AW, and the basic target power amount W from the first cycle to the third cycle in PWM control. An explanatory diagram is shown.

  First, the first cycle is the first heater control, and an initial value (0 [W]) is set as the excessive supply power amount AW in the previous cycle (S110), so that the corrected target power amount SW ( As 0), a value equal to the basic target power amount W is set.

  Then, the supplied electric energy ΣWi (= W (1) + W (2) +... + W (n)) supplied to the heater in the first cycle is the battery voltage detection time (time tVn in FIG. 5). When the supplied power amount ΣWi becomes equal to or greater than the corrected target power amount SW (0), supply of power to be supplied to the heater is completed in the first cycle, and voltage application to the heater is performed. Stopped.

  That is, when the supplied power amount ΣWi is equal to or greater than the corrected target power amount SW (0), the remaining power supply variable SW (n−1) is equal to or less than the unit time supply power amount W (n), and a negative determination is made in S390. Then, the voltage application to the heater is stopped (S410).

  Here, “the amount of power already supplied to the heater ΣWi (= W (1) + W (2) +... + W (n)) from the first time to the nth time in the battery voltage detection time” is actually The value obtained by subtracting the corrected target power amount SW (0) from this value corresponds to the amount of power supplied to the heater exceeding the target value (excess supply power amount AW). To do. In FIG. 6, the excess supply power amount AW in the first cycle is “AW1”, the excess supply power amount AW in the second cycle is “AW2”, and the excess supply power amount AW in the third cycle is “ AW3 ".

  Further, as shown in the first cycle of FIG. 6, “amount of electric power already supplied to the heater ΣWi (= W (1) + W (2) in the battery voltage detection timing from the first time to the (n−1) th time”. The total value of “+... + W (n−1))” and “the remaining power supply variable SW (n−1) at the time of previous detection” is equal to “the corrected target power amount SW (0)”. .

  Further, as shown in FIG. 6, it is obtained by subtracting the remaining power supply variable SW (n−1) at the previous detection from the unit time supply power W (n) at the current detection in the battery voltage detection time. The value corresponds to the amount of power supplied to the heater beyond the corrected target power amount SW (0) (excess supply power amount AW).

  For these reasons, the value obtained by subtracting the remaining power supply variable SW (n−1) at the previous detection from the unit time supply power W (n) at the current detection in S420 is the current period of the PWM control. , The excess power supply amount AW obtained by subtracting the “supplied power amount ΣWi (i = 1 to n)” from the “initial value SW (0) of the remaining power supply variable SW (n)”.

  In addition to the above-described method, for example, “the amount of power already supplied to the heater ΣWi from the first to the n-th of the battery voltage detection time” may be used as the calculation method of the excessive supply power amount AW in S420. It is also possible to take a method of calculating and subtracting the corrected target power amount SW (0) from the supplied power amount ΣWi.

  By the way, the unit time power supply amount W (n) in each unit time zone can be calculated based on the duration of the unit time zone (in other words, the execution cycle TB) and the voltage applied to the heater. The duration of the time zone corresponds to the execution period TB of the heater control interrupt process and is a constant value, but the voltage applied to the heater may vary depending on factors such as noise.

  On the other hand, in the present embodiment, since the unit time supply power amount W (n) is calculated using the detected battery voltage VB in S380 of the heater control interruption process, the applied voltage to the heater (in other words, Even when the battery voltage VB) fluctuates, the amount of power supplied to the heater 4 in the unit time zone can be detected according to the fluctuating voltage value.

  Therefore, according to the gas detection device 150 of the present embodiment, even when the battery voltage VB fluctuates after the energization of the heater 4 is started, an error hardly occurs in the amount of power supplied to the heater 4, and the gas sensor element (G In the temperature control of the element 2 and the D element 3), the temperature of the gas sensor element can be suppressed from moving away from the target temperature. For this reason, since the gas detection apparatus 150 can improve the control precision in the temperature control of a gas sensor element, it can suppress the change of the activation state of a gas sensor element by a temperature fluctuation, and can suppress the fall of a gas detection precision.

Next, the correction of the target power amount in the next cycle in the PWM control when the excessive supply power amount AW occurs in the control cycle in the PWM control will be described.
First, when a negative determination is made in S390, if the supplied power amount ΣWi matches the corrected target power amount SW (0), the power supplied to the heater is controlled to a value equal to the target value. However, when the supplied power amount ΣWi is larger than the corrected target power amount SW (0), the power amount supplied to the heater is supplied in excess of the target value. In such a case, a value obtained by subtracting the corrected target power amount SW (0) from the supplied power amount ΣWi supplied to the heater is the excess supply power amount AW. As described above, in FIG. 6, the excess power supply amount in the first cycle is represented as AW1.

  When such excessive power supply occurs, the power supply amount to the heater deviates from the target value, but the target power amount in the next cycle is corrected using the excessive power supply amount AW in the previous cycle. By doing so, it is possible to suppress the amount of power supplied to the heater from deviating from the target value.

  For example, as shown in FIG. 6, regarding the correction of the target power amount in the second cycle, a value (= W−AW1) obtained by subtracting the excess supply power amount AW1 in the first cycle from the basic target power amount W is calculated. Then, the calculation result is set as the corrected target power amount SW (0) in the second cycle (S320). Similarly, regarding the correction of the target power amount in the third cycle, a value (= W−AW2) obtained by subtracting the excess supply power amount AW2 in the second cycle from the basic target power amount W is calculated, and the calculation result is calculated. The corrected target power amount SW (0) in the third cycle is set (S320).

  In the gas detection device according to the present embodiment, by correcting the target power amount in this way, the supplied power amount ΣWi exceeds the corrected target power amount SW (0) in a certain cycle, and the excess supply power amount AW is increased. Even if it occurs, the target power amount in the next cycle can be corrected using the excess supply power amount AW, so that the average value of the supplied power amount per cycle can be brought close to the basic target power amount W. Thereby, the gas detection apparatus of this embodiment can suppress that the electric energy supplied to a heater deviates from a target value.

  Next, an experimental result in which the influence on the heater control accuracy (in other words, the temperature control accuracy of the gas sensor element) when the battery voltage fluctuates using the gas detection device 150 of the present embodiment will be described. .

  The experiment was evaluated by determining whether the resistance value of the gas sensor element changes when the battery voltage VB is changed under the condition that the specific gas concentration in the measurement target gas is kept constant. .

  In the experiment, the battery voltage VB was forcibly varied by setting the output voltage (battery voltage VB) of the power supply device 191 (rated output 12 [V]) to a square wave (pulse wave). The square wave at this time is generated by alternately switching the voltage value between a low level voltage (10.5 [V]) and a high level voltage (13.5 [V]). It is a waveform generated by changing the period between 1 [Hz] and 100 [Hz]. A square wave was generated over 300 seconds.

  In addition, as a comparative example, an experiment was performed using a gas detection device having a conventional configuration. In the conventional configuration, the detection timing of the battery voltage in the heater control is set to a ratio of once every three PWM control cycles. Has been. In addition, the output voltage (battery voltage VB) of the power supply device (rated output 12 [V]) in the comparative example was forcibly varied under the same conditions as the gas detection device 150 of the present embodiment.

FIG. 7 shows the experimental results in the conventional gas detector, and FIG. 8 shows the experimental results in the gas detector 150 of the present embodiment.
7 and 8, signals corresponding to the resistance value of the G element 2 (G element signal) and the resistance value of the D element 3 (D element signal) are represented as sensor signals in the microcomputer.

In addition, the gas detection determination process in the gas detectors of both configurations is executed by the process disclosed in Japanese Patent Application Laid-Open No. 2005-308451 as described above.
As shown in FIG. 7, in the gas detector of the conventional configuration, the G element signal and the D element signal both fluctuate despite the specific gas concentration in the measurement target gas being constant. It can be seen that the determination value of the specific gas concentration determined based on the D element signal (described as the output level in FIG. 7) fluctuates.

  In other words, in the conventional gas detection device, when the battery voltage VB repeatedly fluctuates for a short time, the heater control becomes unstable, the temperature of the gas sensor element fluctuates, and the specific gas concentration changes. In spite of the absence, the sensor detection signal (in this embodiment, a signal corresponding to the resistance value of the sensor element) fluctuates, and the determination accuracy of the specific gas concentration is lowered.

  On the other hand, as shown in FIG. 8, the gas detection device 150 of the present embodiment has both the G element signal and the D element signal even when the battery voltage VB undergoes a short-term repeated fluctuation. It shows an almost constant value. For this reason, in the gas detection device 150, even when the battery voltage VB varies, the determination result of the specific gas concentration determined based on the G element signal and the D element signal is not changed (not shown).

  As described above, the gas detection device 150 of the present embodiment detects and detects the battery voltage VB a plurality of times in the energization time zone (voltage application execution time Ton) of the heater in one cycle of PWM control. The supplied power amount ΣWi supplied to the heater 4 is calculated based on the battery voltage VB. For this reason, even when the battery voltage VB fluctuates during voltage application to the heater 4, the gas detection device 150 can determine the supplied power amount ΣWi actually supplied to the heater 4 based on the fluctuating battery voltage VB. It is configured.

  That is, the gas detection device 150 can determine the amount of power actually supplied to the heater 4 even when the battery voltage VB fluctuates after the energization of the heater 4 is started. It can approach the target power amount well. For this reason, since the gas detection device 150 can reduce the error in the amount of power supplied to the heater 4, it can improve the control accuracy in the temperature control of the gas sensor elements (G element 2 and D element 3) by the heater 4. Good temperature control.

  From this, the gas detection device 150 can suppress the change in the activation state of the gas sensor element due to the temperature fluctuation, and the phenomenon that the sensor resistance value fluctuates even though the specific gas concentration is constant. Can be prevented.

  Therefore, the gas detection device 150 is less likely to cause an error in the amount of power supplied to the heater 4 even when the battery voltage VB fluctuates after the energization of the heater 4 is started, and improves the control accuracy in the temperature control of the gas sensor element by the heater 4. Since it can do, the change of the activation state of the gas sensor element by a temperature change can be suppressed, and the fall of gas detection accuracy can be suppressed.

  The gas detection device 150 is supplied to the heater 4 for each unit time zone divided by the detection time of the battery voltage VB in the energization time zone to the heater 4 by executing the heater control interruption process. The unit time supply power amount W (n) is calculated (S380).

  Further, in the heater control interrupt process, when the battery voltage VB is detected (S370), the unit time supply power amount W (n) in the unit time zone that ends the detection time is changed to the supply power remaining amount variable SW (n− It is determined whether it is smaller than 1) (S390).

  If an affirmative determination is made in S390 (when the unit time supply power amount W (n) is smaller than the supply power remaining amount variable SW (n−1)), in S400, the supply power remaining amount variable SW (n The value obtained by subtracting the unit time supply power amount W (n) from -1) is reset in the supply power remaining amount variable SW (n). Further, when a negative determination is made in S390 (when the unit time supply power amount W (n) is equal to or greater than the supply power remaining amount variable SW (n-1)), the supplied power amount reaches the target power amount or more. In step S410, energization of the heater is stopped.

  The supplied power remaining amount variable SW (n) is set to the initial value SW (0) by the process in S320 before the energization of the heater 4 is started for each cycle of the PWM control. This initial value SW (0) is the target power amount, and is the power amount to be supplied to the heater 4 in one cycle of PWM control when the gas detection element is heated to the activation temperature.

  That is, the gas detection device 150 sets the amount of power to be supplied to the heater in one cycle of PWM control as the initial value SW (0) of the remaining power supply variable SW (n), and each time the battery voltage VB is detected. Is subtracted from the power supply remaining amount variable SW (n−1), and the unit time supply power amount W (n) is equal to or greater than the power supply remaining amount variable SW (n−1). Then, the power supply to the heater 4 is stopped.

  The unit time power supply W (n) is actually applied to the heater in the unit time zone divided by the detection time of the battery voltage VB in the energization time zone (voltage application execution time Ton) to the heater 4. Since the electric power is supplied, even when the battery voltage VB fluctuates after the energization of the heater 4 is started, the electric power is a value corresponding to the electric power actually supplied to the heater 4.

  Further, when the unit time supply power amount W (n) becomes equal to or greater than the supply power remaining amount variable SW (n−1), the gas detection device 150 makes a negative determination in S390 and stops energizing the heater. The difference between the unit time supply power amount W (n) and the remaining power supply variable SW (n−1) is the corrected target power amount SW (of the supplied power amount ΣWi actually supplied to the heater 4. This corresponds to the excessive power supply amount AW exceeding 0).

  For this reason, when a negative determination is made in S390, a value obtained by subtracting the value of the remaining power supply variable SW (n−1) from the unit time supply power W (n) is calculated as the excess supply power AW in S420. By doing this, it is possible to obtain an excessive supply electric energy AW that exceeds the corrected target electric energy SW (0) in the supplied electric energy ΣWi that is actually supplied to the heater 4.

In the heater control interruption process, the power supply amount to the heater 4 is controlled using the corrected target power amount SW (0) calculated using the excessive supply power amount AW of the previous cycle.
Thereby, the gas detection device 150 can bring the average value of the power supply amount in the previous cycle and the current cycle closer to the basic target power amount W, and can further reduce the error of the power supply amount to the heater 4. it can.

  Therefore, according to the gas detection device 150, even when the amount of power actually supplied to the heater 4 exceeds the target power amount and the excessive supply power amount AW occurs, the supply power as an average value in a plurality of cycles The amount error can be further reduced, and the control accuracy in the temperature control of the gas sensor element can be further improved.

  In the present embodiment, the G element 2 and the D element 3 correspond to the gas sensor elements described in the claims, and the microcomputer 101 that executes S140 corresponds to the gas detection determination unit.

  Further, the microcomputer 101 that executes the heater control interrupt process corresponds to the supply power control means, the battery voltage VB corresponds to the power supply output voltage, and the microcomputer 101 that executes S370 and the voltage detection circuit 180 correspond to the power supply output voltage detection means. The microcomputer 101 that executes S380 and S400 corresponds to the supplied power calculation means.

  Further, the microcomputer 101 that executes S420 corresponds to the excessive power supply amount calculating means, the microcomputer 101 that executes S320 corresponds to the corrected target power amount calculating means, and the microcomputer 101 that executes S380 is the unit supplied power amount calculating means. It corresponds to.

  Further, the microcomputer 101 executing S320 corresponds to a supplied power remaining amount variable initial setting unit, the microcomputer 101 executing S390 corresponds to a variable determining unit, and the microcomputer 101 executing S400 corresponds to a supplied power remaining amount variable resetting unit. The microcomputer 101 that executes S410 corresponds to heater energization stopping means.

As mentioned above, although the Example of this invention was described, this invention is not limited to the said Example, A various aspect can be taken.
For example, in the above embodiment, the execution cycle TB of the heater control interrupt process is set to “1/128 of one cycle in PWM control”, but the execution cycle TB is not limited to the above numerical value. Even when the battery voltage fluctuates, the power supply amount to the heater may be set within a range that can be appropriately controlled to the target value. For example, by setting the execution cycle TB to “1/100 of one cycle in PWM control” or less, it is possible to appropriately detect battery voltage fluctuations, and to appropriately supply the amount of power supplied to the heater according to battery voltage fluctuations. Can be controlled.

  In addition, the amount of power supplied to the heater, the applied voltage to the heater, the rated output voltage of the power supply device, etc. are not limited to the values in the above embodiment, and other values can be set according to the application. It is.

Furthermore, the amount of power supplied to the heater (basic target power amount W) is not limited to a constant value, and may be a variable value set in accordance with changes in external conditions (such as ambient temperature).
Further, the use of the gas detection device is not limited to the vehicle outside air introduction control system, and can be used for other uses (for example, exhaust gas control, air-fuel ratio control, etc.).

It is a schematic block diagram of the integrated gas sensor element with which a gas detection apparatus is equipped. It is a block diagram showing the structure of the external air introduction control system for vehicles provided with a gas detection apparatus. It is a flowchart showing the processing content of normal routine processing. It is a flowchart showing the processing content of a heater control interruption process. It is explanatory drawing showing the voltage waveform applied to a heater, Comprising: The upper side is a pulse waveform for 3 periods, and the lower side is an enlarged waveform at the time of the voltage application in a 1st period. Explanatory drawing showing the correlation of supplied electric energy ΣWi, corrected target electric energy SW (0), excess supplied electric energy AW, and basic target electric energy W from the first period to the third period in PWM control. It is. It is an experimental result in the gas detection apparatus of a conventional structure. It is an experimental result in the gas detection apparatus of this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ceramic substrate, 2 ... Gas sensor element for reducing gas (G element), 3 ... Gas sensor element for oxidizing gas (D element), 4 ... Heater, 10 ... Integrated gas sensor element, 100 ... Outside air introduction control system for vehicles DESCRIPTION OF SYMBOLS 101 ... Microcomputer (microcomputer), 110 ... G element circuit, 120 ... D element circuit, 131 ... Heater circuit, 132 ... Switching circuit, 140 ... Regulator circuit, 150 ... Gas detector, 160 ... Electronic control assembly, 174 ... External air introduction flap, 180 ... voltage detection circuit, 191 ... power supply device (battery).

Claims (4)

A gas sensor element whose sensor resistance value changes according to the concentration of the specific gas;
A heater that heats the gas sensor element by generating heat by power supply from a power supply device;
Gas detection determination means for determining a change in concentration of the specific gas in the measurement target gas based on a change in the sensor resistance value;
A gas detection device comprising:
Supply power control means for controlling the amount of power supplied from the power supply device to the heater by PWM control of the voltage applied to the heater;
Power supply output voltage detection means for detecting the power supply output voltage output from the power supply device a plurality of times in the energization time zone of the heater in one cycle of the PWM control;
Supplyed power for calculating the supplied power amount supplied to the heater after the start of energization to the heater based on the power supply output voltage detected by the power supply output voltage detection means for each cycle of the PWM control. Computing means;
With
In supplying the target power amount for heating the gas sensor element to the activation temperature to the heater, the supply power control means, after the start of energization to the heater, for each cycle of the PWM control, It is determined whether the supplied power amount calculated by the supplied power calculation means is equal to or greater than the target power amount. When the supplied power amount is equal to or greater than the target power amount, energization of the heater is stopped. To do,
A gas detection device characterized by the above. Excess supply power amount calculation means for calculating an excess supply power amount obtained by subtracting the target power amount of the cycle from the supplied power amount from the start time of power supply to the heater to the stop time of power supply for each cycle of the PWM control. When,
A corrected target power amount calculating means for calculating, as the target power amount, a corrected target power amount obtained by subtracting the excess supply power amount of the previous cycle from a predetermined basic target power amount;
With
The supply power control means includes the supplied power amount calculated by the supplied power calculation means after the start of energization to the heater, and the corrected target power amount calculated by the corrected target power amount calculation means. And when the supplied power amount is equal to or greater than the corrected target power amount, stopping energization of the heater,
The gas detection device according to claim 1. The supplied power calculating means is, for each unit time zone divided with the detection time of the power supply output voltage by the power supply output voltage detection means as a boundary in the energization time zone to the heater, in the unit time zone. A unit supply power amount calculating means for calculating a unit time supply power amount supplied to the heater;
The supply power control means includes
For each cycle of the PWM control, before starting energization to the heater, the target power amount is set as an initial value of a supply power remaining amount variable indicating the remaining amount of power to be supplied to the heater in the cycle. Supply power remaining variable initial setting means;
When the power supply output voltage is detected by the power supply output voltage detection means after the start of energization of the heater, the unit time supply power amount in the unit time zone that ends the voltage detection time, and the voltage detection time Variable determination means for comparing the supply power remaining amount variable set to the above and determining whether the unit time supply power amount is smaller than the supply power remaining amount variable;
A supply power remaining amount variable resetting unit that resets a value obtained by subtracting the unit time supply power amount from the supply power remaining amount variable to the supply power remaining amount variable when an affirmative determination is made in the variable determination unit;
A heater energization stopping unit that determines that the supplied power amount is equal to or greater than the target power amount when the variable determination unit makes a negative determination, and stops energization of the heater;
Providing
The gas detection device according to claim 1, wherein: The supplied power calculating means is, for each unit time zone divided with the detection time of the power supply output voltage by the power supply output voltage detection means as a boundary in the energization time zone to the heater, in the unit time zone. A unit supply power amount calculating means for calculating a unit time supply power amount supplied to the heater;
The supply power control means includes
For each cycle of the PWM control, before starting energization to the heater, the target power amount is set as an initial value of a supply power remaining amount variable indicating the remaining amount of power to be supplied to the heater in the cycle. Supply power remaining variable initial setting means;
When the power supply output voltage is detected by the power supply output voltage detection means after the start of energization of the heater, the unit time supply power amount in the unit time zone that ends the voltage detection time, and the voltage detection time Variable determination means for comparing the supply power remaining amount variable set to the above and determining whether the unit time supply power amount is smaller than the supply power remaining amount variable;
A supply power remaining amount variable resetting unit that resets a value obtained by subtracting the unit time supply power amount from the supply power remaining amount variable to the supply power remaining amount variable when an affirmative determination is made in the variable determination unit;
A heater energization stopping unit that determines that the supplied power amount is equal to or greater than the target power amount when the variable determination unit makes a negative determination, and stops energization of the heater;
With
The excess supply power amount calculation means calculates, as the excess supply power amount, a value obtained by subtracting the value of the remaining power supply variable from the unit time supply power amount when a negative determination is made by the variable determination means. ,
The gas detection device according to claim 2.