JPH01155260A - Detecting device of concentration of oxygen - Google Patents

Abstract

PURPOSE:To keep a heater element at a target temperature irrespective of nonuniformity in the temperature characteristic of the heater element, by impressing a voltage on a circuit element having a circuit constant corresponding to the target temperature and by adjusting the quantity of electricity fed to the heater element in accordance with a current flowing through the circuit element. CONSTITUTION:A control circuit 32 reads a voltage and a current of heater elements 19 and 20 and calculates a resistance value RH. Next, a current value I4 flowing to a resistor 4 is read thereby as an information showing the temperature characteristic of the elements 19 and 20 and a correction coefficient K is set. Then, a new resistance value RH is determined by multiplying RH by K, and a duty cycle ratio DR is set in accordance with a difference between a target resistance value RHT corresponding to a target temperature of a reference heater element, and the value RH, and outputted to a heater feeding circuit 35. The circuit 35 subjects the quantity of electricity fed to the elements 19 and 20 to a duty control in accordance with DR, so as to keep the temperature of the elements 19 and 20 at a desired target temperature.

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 the specified target. The structure is such that the temperature 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 circuit element having a circuit constant corresponding to the resistance value is provided, a voltage is applied to the circuit element, and the amount of power supplied to the heater element is adjusted according to the current flowing through the circuit element to maintain the temperature of the heater element at a target value. It is characterized by being equipped with a power supply means.

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.
onic Control υn1t)3. Connector 2 is the connector 2a on the detector 1 side and ECUB
connector 2b on the side, and connector 2a is connected to the detector 1.
Together, they constitute a detection unit U. A resistor 4, which will be described in detail later, is provided on the detection side connector 2a.

As shown in FIG. 2, inside the protective case 5 of the oxygen concentration detector 1 is a substantially cubic oxygen ion conductive solid electrolyte member 6.
is provided. Oxygen ion conductive solid electrolyte member 6
A gas retention chamber 7 is formed therein as a gas diffusion restricted area. The gas retention chamber 7 communicates with an introduction hole 8 through which exhaust gas of the gas to be measured is introduced from the outside of the solid electrolyte member 6.
is located in the exhaust pipe (not shown) of the internal combustion engine so that exhaust gas can easily flow into the gas retention chamber 7. 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 . Electrode pairs 12a and 12b are provided on the wall between the gas retention chamber 7 and the reference gas chamber 9 and between the gas retention chamber 7 and the electrode protection hole 10.
.

11a and llb 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 19 and 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 19 and 20 are electrically connected in parallel to each other 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 differential amplifier circuit 22, current detection resistors 24 and 25, a reference voltage source 26, an A/D converter 31, a control circuit 32, a drive circuit 33, and a heater power supply circuit 35. Become. Outer electrode 11 of oxygen pump element 15
a is connected to the output end of the differential amplifier circuit 22 via a resistor 24, and the inner electrode 11b is grounded. The outer electrode 12a of the battery element 16 is connected to the inverting input terminal of the differential amplifier circuit 22, and the inner electrode 12b is grounded.

A reference voltage source 26 is connected to a non-inverting input terminal of the differential amplifier circuit 22. The output voltage of the reference voltage source 26 is a voltage corresponding to the stoichiometric air-fuel ratio (for example, 0.4 V), and the voltage across the resistor 24 serves as the output of the oxygen concentration sensor. The voltage across the resistor 24 is supplied to the control circuit 32 via the A/D converter 31, and the pump current value I flowing through the resistor 24 is
P is read into the control circuit 32. The control circuit 32 consists of a microcomputer. The control circuit 32 is connected to a plurality of operating parameter detection sensors (not shown) that detect engine speed, intake pipe absolute pressure, cooling water temperature, etc., and is also connected to a solenoid valve 34 via a drive circuit 33. ing. The solenoid valve 34 is provided in a secondary intake air supply passage (not shown) that communicates with the intake manifold downstream of the engine carburetor throttle valve.

On the other hand, current is supplied to the heater elements 19 and 20 from the heater power supply circuit 35, and the heater elements 19 and 20 generate heat to heat the oxygen pump element 15 and the battery element 16 to an appropriate temperature higher than the exhaust gas. The heater power supply circuit 35 duty-controls the current supplied to the heater elements 19 and 20 in accordance with the duty cycle ratio output from the control circuit 32 to maintain the temperature of the heater elements 19 and 20 at a target value. Control circuit 35
The voltage across the heater elements 19 and 20 is supplied via the A/D converter 31, and the current IH flowing through the heater elements 19 and 20 and the voltage across the heater elements (heater voltage) vH are read into the control circuit 32. It has become. Further, in this embodiment, as a circuit element having a circuit constant corresponding to the temperature characteristics of the heater element 19, 20, a resistor 4 having a resistance value according to the temperature characteristic is provided in the detector side connector 2a. There is. A constant voltage vcC is applied to the resistor 4, and the current 4 flowing through the resistor 4 is inputted to the control circuit 32 via the A/D converter 31 as information indicating the temperature characteristics of the heater element 19, 20. It has become.

The control circuit 32 operates as shown in the flowchart shown in FIG. As shown in the figure, first, the control circuit 32 reads the heater element vH and the heater current IH (step S1).
, the resistance value RH of the heater element 19, 20 is calculated (step S2). Next, the current value I4 flowing through the resistor 4 is read as information indicating the temperature characteristics of the heater elements 19 and 20 (step S3), and a correction coefficient is set according to the current value I4, that is, according to the temperature characteristics of the heater elements 19 and 20. K is set by performing a map search or the like (step S4). A new resistance value RH is obtained by multiplying the resistance value RH obtained in step S2 by the correction coefficient K (step S5), and a target of a reference heater element having temperature characteristics that serves as a reference for temperature control of the heater element by the control circuit 32. The duty cycle ratio DR is set according to the difference between the target resistance value RHT corresponding to the temperature and the resistance value RH obtained in step S5 (step S6), and the duty cycle ratio DR is output to the heater power supply circuit 35 (step S6). Step 37).

Note that the resistor 4 having a resistance value RL depending on the temperature characteristics of the heater elements 19 and 20 is selected as follows. First, the resistance value R)4 of the heater element 19.20 at a predetermined temperature is measured for each individually manufactured oxygen concentration detector 1, and the resistance value RH9 of the reference heater element at the same temperature and the above-mentioned resistance value R)4 are measured. The difference (RH9-RH) between the
A resistor having a resistance value RL corresponding to RH6RH is selected based on a map prepared in advance by associating N and N correction coefficients Kl-KN. In this way, the resistance value RL can be selected based on the map, so the map can be
By making the resistor according to the resistance value of an easily available resistor specified by the S standard, there is no need to use a resistor that is difficult to obtain.

The heater power supply circuit 35 duty-controls the amount of power supplied to the heater element 19.20 according to this duty cycle ratio to maintain the temperature of the heater element 19.20 at a desired target temperature. In other words, for a heater element that exhibits a higher resistance value at the same temperature than the temperature characteristics of the reference heater element, less power is supplied than the amount of power supplied to the reference heater element,
Conversely, for a heater element that exhibits a low resistance value at the same temperature, the temperature of the heater element 19, 20 is always maintained at the target temperature by supplying more power than the reference heater element.

In addition, in the flowchart in Figure 3, the actual EC
Although the resistance value RH of the heater element 19,20 connected to U3 is determined and this resistance value RH is corrected, the target resistance value R)4T of the reference heater element may be corrected by the correction coefficient K. Also, without finding the resistance value RH, the duty cycle ratio DR can be calculated in the same way from the current value IH of the heater element 19.20 and the target current value IHT of the reference heater element.
It is also possible to obtain

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 detection unit is provided with a circuit element having a circuit constant corresponding to the resistance value at a target temperature of the heater element that heats the heater element, and a voltage is applied to the circuit element to adjust the amount of power supplied to the heater element according to the current flowing through the circuit element. Since the configuration is equipped with a power supply means that adjusts and maintains the temperature of the heater element at the target value, it is possible to maintain the heater element at the target temperature using easily available circuit components, regardless of variations in the temperature characteristics of the heater element. It is possible to provide an oxygen concentration detection device that can be maintained and has good measurement accuracy. Furthermore, since the circuit element 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 block diagram showing the oxygen concentration detection device according to the present invention, and FIG. 3 is a flow chart showing the operation of the control circuit. Explanation of symbols of main parts 1...Oxygen concentration detector 2...Connector 3...ECU
4...Resistor 6...Oxygen ion conductive solid electrolyte member 15.
... Oxygen pump element 16 ... Battery element 19.20 ... Heater element 32 ... Control circuit 35 ... Heater power supply circuit U ... ...Detection unit Fig. 1 Fig. 3

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 circuit element having a circuit constant corresponding to a resistance value of the current heating element at a target temperature; and a detection unit that applies a voltage to the circuit element and detects the An oxygen concentration detection device comprising a power supply means for adjusting the amount of power supplied to the current heating element and maintaining the temperature of the current heating element at a target value.