JPH01155261A - Detecting device of oxygen concentration - Google Patents

Abstract

PURPOSE:To keep a heater element at a target temperature, by constituting a bridge circuit of a correction resistor having a resistance value corresponding to a resistance value of the heater element at the target temperature and of the heater element, and by controlling the quantity of electricity fed to a heater by a potential balance retaining means. CONSTITUTION:When a resistance value RH of a heater element 20 lowers below a prescribed value with the lowering of the temperature of an oxygen concentration detecting element, a partial pressure V0 rises in relation to a partial pressure V1 and an output level of a comparator circuit 28 turns to be H. A transistor (Tr) 29 turns ON, a voltage VB is impressed on a series circuit of the element 20 and a reference resistor 27, a heater current flows through the element 20, and the temperature of the oxygen concentration detecting element rises. When the temperature of the element 20 rises with the rise in the temperature of the oxygen concentration detecting element and the resistance value RH thereof exceeds a prescribed value, on the other side, V0 lowers in relation to V1, the output level of the circuit 28 turns L, the feeding of electricity to the element 20 is broken by the Tr 29 turning OFF, and the temperatures of the element 20 and the oxygen concentration detecting element become low. By the repetition of this operation, a heater current is controlled so that the resistance value of the element 20 be a prescribed value.

Description

Detailed Description of the Invention Technical Field The present invention relates to an oxygen concentration detection device, and more particularly, the present invention relates to an oxygen concentration detection device, and more particularly, the temperature of an oxygen concentration detection section configured by providing an electrode pair on an oxygen ion-conducting solid electrolyte member can be determined by controlling the temperature of an oxygen concentration detection section by using a current that heats the detection section. The present invention relates to an oxygen concentration detection device that can maintain a predetermined temperature regardless of variations in temperature characteristics of a heating element.

Background Art As such an oxygen concentration detection device, Japanese Patent Application Laid-Open No. 57-2039
The device shown in Japanese Patent No. 40 is known.

In this oxygen concentration detection device, in order to improve the measurement accuracy of oxygen concentration, the resistance value of the current heating element (hereinafter simply referred to as the heater element) that heats the oxygen concentration detection section and the reference resistor that constitutes the bridge circuit is determined by the heater. By keeping the potential balance of the bridge circuit according to the temperature characteristics of the element, even if the temperature characteristics of the heater element are not unified, the temperature of the heater element and the temperature of the oxygen concentration detection part can be adjusted to a predetermined target temperature. The structure is such that it can be maintained.

However, in the above configuration, the temperature characteristics of the heater element and the resistance value of the reference resistor selected accordingly must be in a proportional relationship, and the temperature characteristics of the heater element that occur during manufacturing must be proportional to each other. Since the variation occurs within a relatively narrow range, there is an inconvenience that a custom-made component that is difficult to obtain must be used as a resistor having a resistance value that corresponds to the temperature characteristics of the heater element.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention provides an oxygen concentration detection device that can maintain a heater element at a predetermined target temperature regardless of variations in temperature characteristics of the heater element without using circuit components that are difficult to obtain. is intended to provide.

In the oxygen concentration detecting device according to the present invention, an oxygen concentration detecting section is configured by providing an electrode pair on an oxygen ion conductive solid electrolyte member and a gas diffusion restricted region, and the oxygen concentration detecting section is configured such that an oxygen concentration detecting section is provided with an electrode pair on an oxygen ion conductive solid electrolyte member. A correction resistor having a resistance value corresponding to the resistance value is provided, a bridge circuit is formed from a reference resistor and a heater element connected in parallel to the correction resistor, and the amount of power supplied to the heater element is controlled by a potential balance maintaining means. It is configured to control and maintain potential balance of the bridge circuit.

Example Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show an oxygen concentration detection device according to the present invention. In this device, the oxygen concentration detector 1 is disposed, for example, in an internal combustion engine exhaust pipe, and the input and output of the oxygen concentration detector 1 is connected to an ECU (Electrical Control Unit) via a connector 2.
onlc Control Unlt)3. Connector 2 is the connector 2a on the detector 1 side and the ECU
The connector 2a constitutes a detection unit U together with the detector 1. The connector 2a on the detector side is provided with a correction resistor 4, which will be described in detail later.

Inside the protective case 5 of the oxygen concentration detector 1, an oxygen ion conductive solid electrolyte member 6 is provided, as shown in FIG. A gas retention chamber 7 is formed within the oxygen ion conductive solid electrolyte member 6 as a gas diffusion restricted area. The gas retention chamber 7 communicates with an introduction hole 8 through which the exhaust gas of the gas to be measured is introduced from the outside of the solid electrolyte member 6. It is positioned so that it can easily flow into the interior. Further, a reference gas chamber 9 into which outside air or the like is introduced is formed in the oxygen ion conductive solid electrolyte member 1 so as to be separated from the gas retention chamber 7 by a wall.

An electrode protection hole 10 is formed in the wall of the gas retention chamber 7 on the side opposite to the reference gas chamber 9 . Wall between gas retention chamber 7 and reference gas chamber 9 and gas retention chamber 7 and electrode protection hole 10
On the wall between the electrode pairs 12a, 12b, lla, ll
b are formed respectively. The solid electrolyte member 6 and the electrode pair 11a, llb act as the oxygen pump element 15, and the solid electrolyte member 1 and the electrode pair 12a, 12b act as the battery element 16, respectively. Furthermore, heater elements 20 are provided on the outer wall surface of the reference gas chamber 9 and the outer wall surface of the electrode protection hole 10, respectively. The heater elements 20 are electrically connected to each other in series to uniformly heat the oxygen pump element 15 and battery element 16 and to improve heat retention within the solid electrolyte member 6.

As the oxygen ion conductive solid electrolyte member 1, ZrO2
(zirconium dioxide) is used, and pt (platinum) is used as the electrodes 11a to 12b.

As shown in FIG. 2, the ECU 3 includes a temperature control circuit 3a that maintains the temperature of an oxygen concentration detection section consisting of an oxygen pump element 15 and a battery element 16 at a predetermined temperature by controlling the amount of power supplied to the heater element 20, and an oxygen The oxygen concentration detection circuit 3b measures the output of the concentration detection section. The oxygen concentration detection circuit 3b supplies a signal representing the oxygen concentration in the exhaust gas obtained from the oxygen concentration detection section to the electromagnetic valve 21 provided in the intake secondary air supply path. In response to this signal, the solenoid valve 21 adjusts the supply amount of secondary air and adjusts the air-fuel ratio. The temperature control circuit 3a includes three reference resistors 25, 26, 27 forming a bridge circuit together with the heater element 20.
It consists of a comparator 28 and a transistor 29 as a power amplifier, and a reference resistor 27 is connected in series to the heater element 20. Reference resistor 27 and heater element 2
A series circuit consisting of reference resistors 25 and 26 is connected in parallel to the series circuit with reference resistors 25 and 26. In addition, the reference resistor 27
A series circuit consisting of a heater element 20 and a reference resistor 2
A predetermined voltage v8 is applied to the series circuit consisting of 5.26 through the collector and emitter of a transistor 29, which is a switching element. The divided voltage Vo generated by the heater element 20 and the reference resistor 27 and the divided voltage v1 generated by the reference resistor 25.26 are respectively supplied to the input terminal of the comparator circuit 28, and as a result of the comparison of the divided voltages VO+V+, ``The output signal of the comparison circuit 28 is supplied to the base of the transistor 29. By the way, in this embodiment, a correction resistor 4 having a resistance value depending on the temperature characteristics of the heater element 20 is provided in the connector 2a, and the correction resistor 4 is connected in parallel to the reference resistor 25. . Therefore, the divided voltage v
1 becomes a voltage divided by the reference resistors 25 and 26 and the correction resistor 4.

In this configuration, when the temperature of the heater element 20 decreases as the temperature of the oxygen concentration detection section decreases and the resistance value R of the heater element 20 falls below a predetermined value, the divided voltage Vo becomes smaller than the divided voltage v1. The output level of the comparator circuit 28 becomes high, and the transistor 29 is turned on. When the transistor 29 is turned on, a voltage v8 is applied to the series circuit of the heater element 20 and the reference resistor 27, a heater current flows through the heater element 20, and the temperature of the oxygen concentration detection section rises due to the heat generated by the heater element 20. On the other hand, when the temperature of the heater element 20 rises with the temperature rise of the oxygen concentration detection section and the resistance value RH of the heater element 20 exceeds a predetermined value, the divided voltage vo
decreases with respect to the divided voltage v1, the output level of the comparison circuit 28 becomes a low level, and the transistor 29 is turned off.

By turning off the transistor 29, the power supply to the heater element 20 is cut off, and the temperature of the heater element 20 and the oxygen concentration detection section decreases. By repeating this operation, the heater current is controlled so that the resistance value of the heater element 20 becomes equal to a predetermined value. As is clear from the above, comparison circuit 2
8 and the transistor 29 act as potential holding means for maintaining potential balance of the bridge circuit by controlling the amount of power supplied to the heater element 20.

By the way, the resistance value R according to the temperature characteristics of the heater element 20
The correction resistor 4 with L is selected as follows. First of all,
The resistance value RH of the heater element 20 at a predetermined temperature is measured for each oxygen concentration detector 1 manufactured individually, and the reference value RH is used when determining the resistance value of the reference resistor 25, 26, 27 that constitutes the bridge circuit. It is selected according to the difference (RHs - RH) from the resistance value RHS of the reference heater element at the predetermined temperature. Here, in the present invention,
Since the correction resistor 4 is connected in parallel to the reference resistor 25, changing the resistance value of the correction resistor 4 through the above selection will change the combined resistance value of the parallel connection with the reference resistor 25, and Since the resistance value of the reference resistor is determined so that the potential balance of the bridge circuit is established at the target temperature (target resistance value) of the reference heater element targeted by the above temperature control, the potential balance of the bridge circuit is maintained. By doing so, it is possible to supply less power than the reference heater element to a heater element that exhibits a higher resistance value than the reference heater element at the same temperature, and conversely, to a heater element that exhibits a lower resistance value at the same temperature. In contrast, more power can be supplied than the amount of power supplied to the reference heater element, and the temperature of the heater element 20 can always be maintained at the target temperature.

Furthermore, in the gas sensor disclosed in Japanese Patent Application Laid-Open No. 57-203940, which is shown as a conventional example, a resistor having a resistance value proportional to the temperature characteristics of the heater element must be selected as the reference resistor itself constituting the bridge circuit. However, in the case of the present invention, by changing the correction resistor 4, the combined resistance value in parallel with the reference resistor 25 is changed, so the resistor to be prepared as the correction resistor 4 is changed. The step width of the resistance value is the difference in temperature characteristics of the heater element (R
HS-RH), and can be provided with easily available resistors specified by the JIS standard.

As described in detail of the invention, in the oxygen concentration detection device according to the present invention, an oxygen concentration detection section is configured by providing an electrode pair on an oxygen ion conductive solid electrolyte member and providing a gas diffusion restricted region. A correction resistor having a resistance value corresponding to the resistance value at the target temperature of the heater element for heating is provided in the detection unit, and a bridge circuit is configured from a reference resistor and the heater element connected in parallel to the correction resistor. Since the structure is such that the potential balance of the bridge circuit is maintained by controlling the amount of power supplied to the heater element using the potential balance maintaining means, it is possible to maintain the potential balance of the bridge circuit, regardless of variations in the temperature characteristics of the heater element. It is possible to maintain the heater element at a target temperature and provide an oxygen concentration detector with high measurement accuracy. Furthermore, since the correction resistor is provided in the detection unit, compatibility between individually manufactured detection units can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an oxygen concentration detection device according to the present invention;
FIG. 2 is a circuit diagram of an oxygen concentration detection device according to the present invention. Explanation of symbols of main parts 1...Oxygen concentration detector 2...Connector 3...ECU
4...Corrected resistance value 6...Oxygen ion conductive solid electrolyte member 15.
...Oxygen pump element 16...Battery element 20...Heater element 25.26.27...Reference resistor 28.
...Comparator 29.Old...Transistor U
...Detection unit applicant Honda Motor Co., Ltd.

Claims (1)

[Claims] A gas diffusion restricted region into which a gas to be measured is introduced is formed by an oxygen ion conductive solid electrolyte member, and a pump current is supplied between a pair of electrodes sandwiching the solid electrolyte member to transfer oxygen ions to the solid electrolyte member. an oxygen concentration detection unit that detects the oxygen concentration in the gas to be measured based on the pump current value while adjusting the oxygen concentration in the gas diffusion restricted region by conduction through the electrolyte member; and heating the solid electrolyte member. a detection unit comprising a current heating element and a correction resistor having a resistance value corresponding to a resistance value of the current heating element at a target temperature; and a bridge circuit connected in parallel to the correction resistor and together with the current heating element. An oxygen concentration detection device comprising: a reference resistor constituting the current heating element; and potential balance maintaining means for controlling the amount of power supplied to the current heating element to maintain potential balance of the bridge circuit.