JP2006234742A - Heater controller of sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heater controller of a sensor, capable of simplifying the constitution for controlling the applied voltage to a heater for heating a sensor element. <P>SOLUTION: One end of each of resistors 31, 32, 33 and 34 of resistances 140, 140, 430 and 430 (Ω) is connected to each of output ports P1, P2, P3 and P4 of a one-chip microcomputer. The other end of each of the resistors 31 through 34 is connected to the other end of the heater 30 of resistance Rz, of which the one end is grounded. When signals of Hi level (5V) is outputted from all output ports P1-P4 for 30 seconds, after the driving a gas sensor, a voltage of 4.2 V, as the divided voltage of composite resistances of the resistors 31-34 and the resistance of the heater 30, is applied to the heater 30. Then, when the output ports P3 and P4 are switched to Lo level (GND), a voltage of 3.2 V as the divided voltage is applied to the heater 30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sensor heater control device including a heater for performing heating for cleaning and activation of a sensor element.

Conventionally, sensor elements using oxide semiconductors whose electrical characteristics (for example, resistance value) change according to the concentration of a specific gas in the air are known. For example, a sensor element for detecting a change in the concentration of an automobile exhaust gas using a metal oxide semiconductor such as SnO ₂ or WO ₃ is a reducing gas such as CO or HC contained in the exhaust gas or NOx. The resistance value changes based on a change in the concentration of a specific gas such as an oxidizing gas.

Such a metal oxide semiconductor does not react with a specific gas at room temperature, but is activated by heating to about 200 to 400 ° C. and reacts with a specific gas. In addition, the metal oxide semiconductor is easily affected by humidity, and when the hydroxyl group OH ⁻ as moisture in the measurement atmosphere is adsorbed on the surface of the metal oxide semiconductor, molecular adsorption of a specific gas on the surface of the metal oxide semiconductor is performed. By obstructing, the sensitivity of the sensor element decreases.

Therefore, a metal oxide semiconductor is activated by providing a heater in the vicinity of the sensor element and heating the sensor element by generating heat by energization. In addition, heat cleaning is performed in which OH ⁻ adsorbed on the surface of the metal oxide semiconductor portion is forcibly desorbed by heating to restore the sensor element characteristics to the initial state.

  Such energization of the heater is generally performed by supplying an applied voltage from an output port of a battery or a power supply IC. At that time, the voltage applied to the heater is controlled by turning on and off the switching components with a microcomputer and switching the resistance of the voltage dividing circuit, or the power corresponding to the applied voltage is controlled by PWM control. The method of generating is used (for example, refer patent document 1).

In addition, when activating the metal oxide semiconductor by heating the heater or performing heat cleaning, a voltage higher than the normal heater applied voltage is applied immediately after turning on the power, and then Energization control such as switching to a normal heater applied voltage is performed. As a result, it is possible to realize early activation of the metal oxide semiconductor and efficient heat cleaning while maintaining good durability of the heater.
JP 2002-156350 A

  However, in order to control the voltage applied to the heater as described above, a switching component is necessary, and it is difficult to reduce the product cost. There is also a problem that it is difficult to reduce the size because it is necessary to secure a space for mounting the switching parts.

  The present invention has been made to solve the above-described problems, and provides a sensor heater control device capable of simplifying a configuration for controlling a voltage applied to a heater for heating a sensor element. With the goal.

  In order to achieve the above object, a sensor heater control device according to a first aspect of the present invention is a sensor heater control device for controlling energization to a heater attached to a sensor element, and each of which can output a voltage. A voltage output unit having a plurality of ports; and a first voltage applying unit that drives at least two or more of the plurality of ports and applies a first voltage to the heater electrically connected to the plurality of ports. And after the first voltage is applied to the heater for a predetermined time, some of the plurality of ports being driven are grounded, and a second voltage lower than the first voltage is applied to the heater. Second voltage applying means for applying.

  A sensor heater control device according to a second aspect of the present invention is a sensor heater control device for controlling energization to a heater attached to a sensor element, and includes a plurality of ports each capable of outputting a constant voltage. A plurality of resistors installed in respective energization paths connecting the voltage output unit, each of the plurality of ports, and one end of the heater; and driving at least two or more of the plurality of ports; And a first voltage applying means for applying a first voltage to the heater, and after the first voltage is applied to the heater for a predetermined time, a part of the plurality of ports being driven is grounded, And a second voltage applying means for applying a second voltage lower than 1 to the heater.

  In the heater control apparatus for a sensor according to the first aspect of the present invention, at least two or more of the plurality of ports of the voltage output unit are driven to apply a voltage to the heater, and after a predetermined time, one of the driven ports. The voltage applied to the heater can be reduced by grounding the port of the part. That is, the voltage applied to the heater can be switched only by switching the port of the voltage output unit. For this reason, electronic parts such as switching elements are not required, and a space for attaching these electronic parts is also unnecessary, so that the product cost can be reduced and the sensor can be downsized. Furthermore, the control of the voltage applied to the heater can be simplified. Further, by applying voltage from a plurality of ports of the voltage output unit, it is possible to obtain a current necessary for driving a heater having a large load.

  In the sensor heater control apparatus according to the second aspect of the present invention, a resistor is installed in each of the energization paths connecting the plurality of ports of the voltage output unit and the heater, and the heater is driven by driving at least two or more ports. By applying a voltage to the resistor, a partial pressure of the voltage applied from the port can be applied to the heater by the combined resistance value of the resistor and the resistance value of the heater. Then, after a predetermined time, by grounding some of the driven ports, the voltage division ratio of the voltage applied to the heater can be switched and the applied voltage can be reduced. That is, the voltage applied to the heater can be switched only by switching the port of the voltage output unit. Furthermore, if the resistance value of each resistor and the resistance value of the heater are adjusted in advance, the partial pressure applied to the heater can be easily adjusted. By adopting such a configuration, electronic components such as switching elements can be dispensed with, and a space for mounting these electronic components is also dispensed with, thereby reducing product costs and reducing the size of the sensor. Can be achieved. Furthermore, the control of the voltage applied to the heater can be simplified. Further, by applying voltage from a plurality of ports of the voltage output unit, it is possible to obtain a current necessary for driving a heater having a large load.

  Hereinafter, an embodiment of a sensor heater control device embodying the present invention will be described with reference to the drawings. First, with reference to FIG. 1, the outline of the structure of the gas sensor 100 as an example of the sensor provided with the heater control apparatus is demonstrated. FIG. 1 is a diagram showing an outline of the configuration of the gas sensor 100.

  A gas sensor 100 shown in FIG. 1 includes a gas sensor element 10, a gas sensor element 20, a heater 30, and a one-chip microcomputer 50. The gas sensor elements 10 and 20 are integrally formed with the heater 30 as a pattern on an insulating ceramic substrate having a single rectangular plate shape.

The gas sensor element 10 is an oxide semiconductor containing SnO ₂ as a main component, and reacts mainly with a reducing gas such as CO and HC, and the resistance value Rg changes according to the concentration thereof. Further, the gas sensor element 20 is an oxide semiconductor mainly composed of WO ₃ and reacts mainly with an oxidizing gas such as NOx, and the resistance value Rd changes according to the concentration thereof. One end of each of the resistors 11 and 21 having specific resistance values Ra and Rb is connected in series to one end of each of the gas sensor elements 10 and 20 to form a voltage dividing circuit. Each other end is grounded. A voltage Vcc (5 V in the example of the present embodiment) is applied to each other end of the resistors 11 and 21.

  The voltage dividing points Pg and Pd of the gas sensor elements 10 and 20 and the resistors 11 and 21 are connected to AD conversion input terminals 53 and 54 (AD1 and AD2) of the one-chip microcomputer 50, respectively. Output potentials Vg and Vd that change based on the magnitudes of the resistance values Rg and Rd of 10 and 20 are input as signals, respectively. Since the resistance values Ra and Rb of the resistors 11 and 21 are constant, if the resistance values Rg and Rd of the gas sensor elements 10 and 20 change with the concentration change of the reducing gas or the oxidizing gas, they are changed to AD1 and AD2. The input output potentials Vg and Vd are configured to change.

  The output ports 61, 62, 63, and 64 (P1, P2, P3, and P4) of the one-chip microcomputer 50 have resistors 31, 32, 33, and 34 having specific resistance values Rx, Rx, Ry, and Ry, respectively. One end of each is connected. The heater 30 has a resistance value Rz, one end of which is grounded, and the other end of each of the resistors 31, 32, 33, and 34 is connected to the other end. The heater 30 raises the temperature of the gas sensor elements 10 and 20 when the gas sensor 100 is used, thereby performing heat cleaning for dissociating and evaporating other gas molecules and moisture adsorbed and adhered to the gas sensor elements 10 and 20, as well as the gas sensor. Used to activate the elements 10,20. In this embodiment, the specific resistance value Rx of the resistors 31 and 32 is set to 140Ω, the specific resistance value Ry of the resistors 33 and 34 is set to 430Ω, and the resistance value Rz of the heater 30 is set to 280Ω. The one-chip microcomputer 50, the resistors 31 to 34, and the heater 30 correspond to the “heater control device” in the present invention. The one-chip microcomputer 50 having P1 to P4 corresponds to the “voltage output unit” in the present invention.

  The one-chip microcomputer 50 includes a CPU 55, a ROM 56, and a RAM 57, and in a predetermined storage area of the ROM 56, a heater control program described later, initial values of variables used in the heater control program, and the like are stored. In a predetermined storage area of the RAM 57, various variables and counters used when a heater control program described later is executed are temporarily stored, and the heater control program is also read and executed in the predetermined storage area. A signal output terminal 51 (out) of the one-chip microcomputer 50 is connected to an electronic control assembly (not shown), and various controls based on the output of the gas sensor 100 are performed. The one-chip microcomputer 50 is supplied with a drive voltage Vcc through a Vcc terminal 52 (Vcc).

  The gas sensor 100 having such a configuration is used, for example, in an auto ventilation system that switches between introduction of outside air and circulation of inside air in an automobile. When the drive voltage Vcc is supplied to the gas sensor 100 at the time of starting, a heater control program (see FIG. 2) is executed, and the heater 30 is energized. By the way, it usually takes several tens of seconds to several hundred seconds until the gas sensor elements 10 and 20 are activated and their outputs are stabilized. In order to perform heat cleaning and early activation of the gas sensor elements 10 and 20, in the heater control program, a larger voltage is applied at the beginning of heating of the heater 30 than during normal operation.

  Hereinafter, the operation of the heater control program will be described with reference to FIGS. FIG. 2 is a flowchart of the heater control program. 3 to 5 are circuit diagrams for explaining the voltage applied to the heater 30. Each step in the flowchart is abbreviated as “S”.

  The heater control program is read from the ROM 56 and executed when the gas sensor 100 is driven. As shown in FIG. 2, when the heater control program is executed, a timer is first activated (S1). “0” is stored in the predetermined storage area of the RAM 57 as the initial value of the timer variable. The timer variable is numerically added in proportion to the elapsed time by a timer count program (not shown).

  Next, Hi level output signals are output from the output ports 61 to 64 (P1, P2, P3, P4), and a voltage of 5 V is applied to the resistors 31 to 34 (S2). At this time, as shown in FIG. 3, the voltage applied to the heater 30, that is, the potential Vz at the voltage dividing point Pz, is the combined resistance value of the resistance values Rx and Ry of the resistors 31 to 34 and the resistance value of the heater 30. Rz is a potential obtained by dividing the voltage of the output ports 61 to 64. Here, when the combined resistance value of the resistors 31 to 34 is obtained, it is 52.8Ω. Accordingly, when the potential Vz at the voltage dividing point Pz is obtained, it becomes 4.2 V, and a voltage of 4.2 V is applied to the heater 30.

  Next, as shown in FIG. 2, it is confirmed whether 30 seconds have elapsed after the timer is started (S3). If it is not determined that 30 seconds have elapsed based on the value of the timer variable, the process waits (S3: NO).

  If it is determined that 30 seconds have elapsed after the timer is started (S3: YES), the output signals of the output ports 63 and 64 (P3 and P4) are switched from the Hi level to the Lo level (S4). As shown in FIG. 4, the potentials of P1 and P2 are maintained at 5V, and the potentials of P3 and P4 are 0V (ground potential). That is, as shown in FIG. 5, the resistors 33 and 34 are similar to the state in which the resistors 33 and 34 are connected to the voltage dividing point Pz in parallel with the heater 30. The potential Vz at the voltage dividing point Pz is an output port 61, 62 based on the combined resistance value of the resistance values Rx of the resistors 31, 32 and the combined resistance value of the resistance value Rz of the heater 30 and the resistance value Ry of the resistors 33, 34. This is a potential obtained by dividing the voltage applied to. Here, the combined resistance value of the resistors 31 and 32 is 70Ω. Further, when the combined resistance value of the heater 30 and the resistors 33 and 34 is obtained, it is 121.6Ω. Therefore, when the potential Vz at the voltage dividing point Pz is obtained, it becomes 3.2 V, and a voltage of 3.2 V is applied to the heater 30.

  Then, as shown in FIG. 2, the heater control program is terminated while the potentials (output signals) of P1 to P4 are maintained. In other words, in the gas sensor 100, a voltage of 4.2 V is applied to the heater 30 for 30 seconds from the start of driving, and thereafter, a voltage of 3.2 V is applied and maintained.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the present embodiment, the output output of the output port is switched using two output ports, P1 and P2, and P3 and P4, as a set. It may be the above.

  Further, the resistance values Rx and Ry of the resistors 31 to 34 of the present embodiment and the resistance value Rz of the heater 30 are merely examples, and a divided applied voltage at which the heat generation temperature of the heater 30 becomes a desired temperature is obtained. It may be set arbitrarily as described.

  In S3 of the heater control program, the waiting time as a period for applying the initial voltage (4.2 V) to the heater 30 is set to 30 seconds. However, the waiting time is not limited to this, and an arbitrary waiting time may be set.

  In this embodiment, the gas sensor element for detecting a specific gas is described as an example of the sensor element heated by the heater that is energized and controlled by the heater control device. However, for example, the sensor element is used for a flow sensor. Alternatively, it may be a sensor element used for a humidity sensor. Further, the gas sensor elements 10 and 20 and the heater 30 are not limited to those formed on a rectangular plate-shaped insulating ceramic substrate, but a gas sensor element is formed on an insulating ceramic substrate having a diaphragm structure, and the heater is embedded in the substrate. You may apply this invention to what was formed.

  The present invention can be applied to a sensor heater control device including a sensor element that requires heating by a heater, such as a gas sensor, a flow rate sensor, and a humidity sensor.

It is a figure which shows the outline of a gas sensor 100 structure. It is a flowchart of a heater control program. 3 is a circuit diagram for explaining a voltage applied to a heater 30. FIG. 3 is a circuit diagram for explaining a voltage applied to a heater 30. FIG. 3 is a circuit diagram for explaining a voltage applied to a heater 30. FIG.

Explanation of symbols

10, 20 Gas sensor element 30 Heater 31-34 Resistor 50 One-chip microcomputer 61-64 Output port (P1, P2, P3, P4)
100 Gas sensor

Claims (2)

A sensor heater control device for controlling energization to a heater attached to a sensor element,
A voltage output unit having a plurality of ports each capable of outputting a voltage;
First voltage applying means for driving at least two or more of the plurality of ports and applying a first voltage to the heater electrically connected to the plurality of ports;
After the first voltage is applied to the heater for a predetermined time, a part of the plurality of driving ports is grounded, and a second voltage smaller than the first voltage is applied to the heater. A sensor heater control device comprising: a second voltage applying unit. A sensor heater control device for controlling energization to a heater attached to a sensor element,
A voltage output unit having a plurality of ports each capable of outputting a constant voltage;
A plurality of resistors installed in each energization path connecting each of the plurality of ports and one end of the heater;
First voltage applying means for driving at least two or more of the plurality of ports and applying a first voltage to the heater;
After the first voltage is applied to the heater for a predetermined time, a part of the plurality of driving ports is grounded, and a second voltage smaller than the first voltage is applied to the heater. A sensor heater control device comprising: a second voltage applying unit.

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