JPH0812175B2 - Gas sensor control device - Google Patents

Description

The present invention relates to an apparatus for controlling a gas sensor having a structure having a gas diffusion limiting chamber.

[Prior Art] Conventionally, as a gas sensor for detecting the exhaust composition of an internal combustion engine or various combustion equipment from the concentration of oxygen, incompletely burned gas, unburned gas, etc. in the exhaust gas, for example, on both surfaces of an oxygen ion conductive solid electrolyte. With two elements with porous electrodes,
It is known that one porous electrode of both elements is arranged so as to be in contact with a gas diffusion limiting chamber in which gas diffusion is limited.

This type of gas sensor is provided with a control device for controlling this gas sensor in order to detect the gas composition in the exhaust gas, and under the control of this control device, the surrounding oxygen concentration or incomplete combustion gas / unburned gas Is configured to detect the concentration of. The control device uses one element constituting the gas sensor as an oxygen concentration battery element and the other element as an oxygen pump element to operate at a predetermined temperature or higher so that the voltage generated at the electrodes across the oxygen concentration battery element becomes constant. It controls the current that flows through and outputs the value of this current (hereinafter referred to as pump current I _p ). At this time, the pump current I _p has a value corresponding to the oxygen concentration or the incompletely burned / unburned gas concentration of the gas around the gas sensor. Therefore, by using such a gas sensor and its control device, the air-fuel ratio of the air-fuel mixture of the internal combustion engine or the like can be detected based on the exhaust gas composition.

[Problems to be Solved by the Invention] However, in such a gas sensor and its control device, the absolute value of the pump current I _p becomes excessively large depending on the atmosphere around the gas sensor, the temperature of the gas sensor, etc. There was a problem that it could be electrochemically destroyed. For example, when the heater that heats the gas sensor to its activation temperature is deteriorated and cannot be sufficiently heated, an excessive pump current I _p is necessary to keep the output voltage of the oxygen concentration battery element constant, and this state Over a long period of time, the oxygen pump element is destroyed. Also,
If the atmosphere around the gas sensor is greatly deviated, for example, if the gas sensor is installed in the exhaust system of an internal combustion engine and the mixture becomes extremely rich, the oxygen partial pressure in the gas diffusion limiting chamber should be kept constant. Requires an excessive pump current I _p , which leads to a similar problem.

The present invention has been made for the purpose of solving the above-mentioned problems and sufficiently protecting a gas sensor that suitably detects a gas concentration.

Structure of the Invention A structure of the present invention for achieving the above object will be described below.

[Means for Solving the Problems] As shown in FIG. 1, a gas sensor control device according to the present invention has a gas diffusion limiting chamber in which the flow of the measured gas around is restricted.
A detection element M2 which is in contact with M1 and outputs a signal according to the oxygen concentration in the gas diffusion limiting chamber M1, and the gas diffusion limiting chamber
A gas sensor M4 equipped with an oxygen pump element M3 for moving oxygen ions between M1 and the gas to be measured, and controlling the current flowing through the oxygen pump element M3 based on the output signal of the detection element M2, In a gas sensor control device comprising a concentration detecting means M5 for detecting a gas concentration in a measurement gas, and a pump voltage applied to the oxygen pump element M3 or a pump current flowing in the oxygen pump element M3 is a predetermined value or more. When the pump voltage or pump current reaches a predetermined value or more for the first time, the first energization interruption is performed for a short period of time, and the pump voltage or pump current exceeds the predetermined value after the second time. In the case of, the interruption means M7 for interrupting the energization for a longer period than the first interruption of the energization is provided.

Here, the detection element M2 and the oxygen pump element M3 may be elements in which a pair of porous electrodes are provided on the front and back surfaces of the oxygen ion conductive solid electrolyte plate. Typical oxygen ion conductive solid electrolytes used in these devices are solid solutions of zirconia and yttria, or solid solutions of zirconia and calcia, and other solid solutions of cerium dioxide, thorium dioxide and hafnium dioxide. Perovskite type oxide solid solution, trivalent metal oxide solid solution, etc. can also be used. Further, as the porous electrodes provided on both surfaces of the solid electrolyte, platinum or rhodium having a catalytic action of an oxidation reaction can be used, and as a forming method thereof, a paste containing these metal powders as a main component is used,
A method of forming by printing after using a thick film technique and sintering, or a method of forming using a thin film technique such as flame spraying, chemical plating, vapor deposition or the like may be used. Further, it is preferable that the porous electrode exposed to the gas to be measured is further provided with a porous protective layer of alumina, spinel, zirconia, mullite or the like on the porous layer by using a thick film technique.

Further, as the detection element M2, an oxygen gas detection element whose main component is a transition metal oxide and whose resistance changes according to the surrounding oxygen gas partial pressure may be used. As the transition metal oxide, SnO ₂ , One or more substances selected from TiO ₂ , CoO, ZnO, Nb ₂ O ₅ and Cr ₂ O ₃ can be used.

The gas diffusion limiting chamber M1 may be formed, for example, as a gas chamber in which a gas diffusion limiting portion for limiting diffusion of gas is provided and a surrounding gas to be measured is introduced in a diffusion limited manner. In such a gas chamber, a spacer as a layered intermediate member made of Al ₂ O ₃ , spinel, forsterite, steatite, zirconia or the like is sandwiched between the detection element M2 and the oxygen pump element M3, so that the detection element M2 It can be formed as a flat closed space formed between the porous electrode and the porous electrode of the oxygen pump element M3. Further, the gas diffusion limiting portion may be a hole which is provided in a part of the spacer and which connects the surrounding measured gas atmosphere and the gas diffusion limiting chamber M1. The gas diffusion limiting portion is for allowing the surrounding measurement gas atmosphere and the gas chamber to communicate in a diffusion limiting manner and is not limited in shape. For example, a part or all of the spacer is replaced with a porous body. Or, a hole is provided in the spacer (including the thick film coat), and further, a spacer is provided only between the terminal side of the detection element M2 and the terminal side of the oxygen pump element M3 to detect the detection element M2 and the oxygen pump element M3. It is also possible to form an air gap between and and to provide this air gap as a gas diffusion limiting gap that is integral with the gas chamber. Further, a porous agent (which is preferably electrically insulating) may be arranged throughout the gas diffusion limiting chamber M1.

The gas sensor M4 including the gas diffusion limiting chamber M1, the detecting element M2, and the oxygen pumping element M3 is provided with a reference oxygen chamber in contact with the surface of the detecting element M2 that does not face the oxygen pumping element M3. It can be considered to be used as a reference when detecting the oxygen concentration with the detection element M2. The reference oxygen chamber may be a gas chamber formed so as to introduce the atmosphere from the outside, or a gas chamber formed so as to communicate with the gas diffusion limiting chamber M1 via the leakage resistance portion. It is also possible to use the communication hole itself of the porous electrode provided on the surface of the detection element M2 that does not face the oxygen pump element M3 as the reference oxygen chamber without providing such a gas chamber.

Concentration detection means M5 is a means for controlling the current flowing through the oxygen pump element M3 based on the output signal of the detection element M2, is a means for detecting the gas concentration in the measured gas, generally oxygen content of the gas diffusion limiting chamber M1. The oxygen concentration in the gas to be measured (concentration of incompletely burned gas / unburned gas in some cases) is detected from the pump current I _p required to control the pressure at a constant level. The concentration detecting means M5 is the pump state detecting means M6.
Although it can be easily realized as a discrete circuit together with the interruption means M7, the inter-electrode voltage of the detection element M2 is once converted into a digital value and read, and the oxygen pump element is formed by an arithmetic logic operation circuit using a well-known microprocessor. It may be configured to control the pump current (detection current) I _p of M3. In this case, the concentration detecting means M5 can be integrated with the pump state detecting means M6 and the interrupting means M7.

The pump state detecting means M6 can be simply configured by a comparator or the like, but when configured as an arithmetic logic operation circuit together with the concentration detecting means M5 and the like, the voltage or current applied to the oxygen pump element M3 is once converted into a digital signal. It is also possible to provide a converter for converting to and to detect by comparing the digital signal with a predetermined value. Further, when the pump state detecting means M6 detects that the voltage applied to the oxygen pump element M3 is equal to or higher than a predetermined value for more than 30 seconds, it interrupts the energization to the oxygen pump element M3 and generates an alarm signal. Providing a means is also effective in increasing the reliability of the entire system.

The interruption means M7 interrupts the energization of the oxygen pump element M3, and can be constituted by a monostable multivibrator or the like. Of course, it may be configured as a timer in the arithmetic logic operation circuit. Such interruption means M7
After releasing the interruption of energization, the time until the oxygen concentration in the gas diffusion limiting chamber M1 becomes substantially constant, it is also provided with a stop means for stopping the operation of the concentration detection means M5, oxygen in the measured gas. This is suitable for improving the detection accuracy of (or incompletely burned / unburned gas) concentration. If the pump voltage or the pump current is detected to be the predetermined value or more for the first time, the energization is interrupted for 0.5 to 2 seconds, and if it is detected that it is the predetermined value or more for the second time and thereafter, 4 to It is preferable to interrupt the power supply for 10 seconds.

[Operation] The gas sensor control device of the present invention configured as described above controls the current flowing through the oxygen pump element based on the output signal of the detection element of the gas sensor to detect the gas concentration in the gas to be measured. To work. Then, it is detected that the pump voltage or the pump current of the oxygen pump element has exceeded the predetermined value, and when the pump voltage or the pump current exceeds the predetermined value for the first time, the first energization is interrupted for a short period of time.
When the value becomes equal to or more than the predetermined value after the first time, the energization is interrupted for a longer period than the first interruption.

For example, when the vehicle is suddenly accelerated, the air-fuel ratio of the air-fuel mixture may temporarily become extremely rich and the pump voltage or pump current may exceed a predetermined value, but wait about 1 second. For example, the air-fuel ratio will recover normally. Therefore, in the present invention, when the pump voltage or the pump current exceeds the predetermined value for the first time, the first energization interruption for a short period of time is performed. Therefore, the interruption time of the energization to the oxygen pump element can be suppressed to the minimum with respect to such a temporary disturbance of the air-fuel ratio, so that the time for the performance deterioration of the gas sensor due to the interruption of the energization can be shortened.

Also, if the air-fuel ratio becomes extremely rich for a long period of time, or if the temperature of the sensor element drops due to deterioration of the heater of the sensor element, etc., it is not possible to obtain an excessive value by simply interrupting energization as described above. Since the pump current does not return to the original state, the pump voltage and the pump current again become the predetermined value or more. Therefore, in the present invention,
When the pump voltage or the pump current exceeds the predetermined value after the second time, the energization is interrupted for a longer period than the first interruption of the energization. As a result, damage to the gas sensor due to an excessive pump current can be prevented.

That is, in the present invention, in this way, it is possible to improve the performance of the gas sensor by avoiding the excessive influence of the interruption of energization due to the local concentration bias, and furthermore, the temperature of the gas sensor is insufficient or the atmosphere It is possible to reliably protect the gas sensor by restricting an excessive current flow caused by the case where the gas sensor is extremely rich.

[Embodiment] In order to further clarify the configuration of the gas sensor control device described above, a preferred embodiment of the present invention will be described. A gas sensor control device as an example has a function of controlling a gas sensor provided in an exhaust system of an internal combustion engine (not shown) to detect an air-fuel ratio A / F of an internal combustion engine mixture. FIG. 2 is a schematic configuration diagram of the control device for the gas sensor.

As shown in the figure, this gas sensor control device comprises a sensor element section 1, a pump current supply circuit 2 and a gas sensor control circuit 3.

The sensor element portion 1 includes an oxygen pump element 7 in which porous electrodes 5 and 6 made of platinum or the like are provided on both sides of an oxygen ion conductive solid electrolyte plate 4 made of stabilized zirconia or the like.
Similarly to the oxygen pump element 7, a porous electrode 9 made of platinum or the like is formed on both sides of the oxygen ion conductive solid electrolyte plate 8.
And an oxygen concentration battery element 11 provided with 10. The oxygen pump element 7 and the oxygen concentration cell element 11 form a gas diffusion limiting chamber 12 and are arranged so as to face each other, and their feet are fixed via a spacer 13.
The gas diffusion limiting chamber 12 thus formed is in communication with the surrounding gas atmosphere to be measured through the throttle communication hole 14 provided in the upper portion thereof.

A reference oxygen chamber 16 is formed by the oxygen concentration battery element 11 and the concave shield 15 on the side of the oxygen concentration battery element 11 that is not in contact with the gas diffusion limiting chamber 12.
Are communicated with the gas diffusion limiting chamber 12 through through holes 17 provided in the oxygen ion conductive solid electrolyte plate 8. The material of the spacer 13 and the concave shield 15 is zirconia.

The pump current supply circuit 2 for supplying the pump current I _p to the sensor element unit 1 having the above-described configuration is composed of the operational amplifier 1
The pump current I _p is mainly composed of 8, 19 and 20 and controls the pump current I _p to the oxygen pump element 7 based on the output voltage of the oxygen concentration battery element 11.

Between the porous electrodes 9 and 10 of the oxygen concentration battery element 11, the reference voltage V1 of the reference power source E1 (10 [V] in this embodiment) is a resistor.
It is applied via R1 and R2. Therefore, a minute current I _cp flows through the oxygen concentration battery element 11, oxygen is supplied from the gas diffusion limiting chamber 12 to the reference oxygen chamber 16, and the oxygen partial pressure of the reference oxygen chamber 16 is kept constant. On the other hand, the voltage between both electrodes of the oxygen concentration battery element 11 depending on the oxygen concentration difference between the gas diffusion limiting chamber 12 and the reference oxygen chamber 16 is amplified by the operational amplifier 19, and the amplified voltage V _S and the reference power source E2 are further amplified. Reference voltage V _C (eg 450
[MV]) is operational amplifier 20, resistors R3, R4, capacitor C
The integrated circuit consisting of 1 compares and integrates and outputs as a detection voltage Vλ.

This voltage Vλ is input to one input terminal of the operational amplifier 18 via the resistor R5. The other input terminal of the operational amplifier 18 has an offset voltage V3 (5V in this embodiment).
A reference power source E3 for supplying [V]) is connected. Therefore, the output current from the operational amplifier 18, that is, the pump current I
_p is bidirectionally controlled based on the deviation between the voltages Vλ and V3.

Depending on the sign of the pump current I _p , oxygen is pumped out from the gas diffusion limiting chamber 12 to the surroundings of the sensor element unit 1 or from the surroundings to the gas diffusion limiting chamber 12, and the oxygen concentration in the gas diffusion limiting chamber 12 is It is always kept constant. That is, the pump current supply circuit 2 supplies the pump current I _p to the oxygen pump element 7 so that the oxygen concentration difference between the gas diffusion limiting chamber 12 and the reference oxygen chamber 16 is kept constant.

Therefore, the pump current supply circuit 2 as a whole supplies oxygen from the gas diffusion limiting chamber 12 to the reference oxygen chamber 16 by supplying a constant small current I _cp to the oxygen concentration battery element 11 to supply oxygen to the oxygen in the reference oxygen chamber 16. While keeping the partial pressure constant, the pump current I _p flowing through the oxygen pump element 7 is bidirectionally controlled so that the oxygen partial pressure in the gas diffusion limiting chamber 12 becomes constant, and the voltage Vλ corresponding to the current value is set. Output as a gas concentration detection signal.

Next, the configuration and function of the gas sensor control circuit 3 will be described. The gas sensor control circuit 3 is a circuit that calculates and outputs the air-fuel ratio λ based on the detection voltage Vλ and controls the pump current supply circuit 2, and the well-known CPU 31, ROM3.
It is configured as an arithmetic and logic operation circuit centering on 2, RAM 33 and the like. The gas sensor control circuit 3 includes a timer 35 and an input port 3 which are interconnected with these elements by a bus 34.
6. Along with the output port 37, the detection voltage Vλ from the pump current control circuit 2 is converted into a digital signal, and the digital signal output from the A / D converter 41 and the output port 37 which is input into the input port 36 is converted into an analog signal. A D / A converter 43 that outputs an air-fuel ratio signal is provided.
The output port 37 has several open collector output terminals, one of which is connected to the output of the operational amplifiers 20 and 18 via the diodes D1 and D2 of the pump current supply circuit 2 and the other of which is Each is connected to an alarm lamp 50.

The processing executed by the gas sensor control circuit 3 having the above configuration will be described based on the flowchart shown in FIG. The gas sensor control routine shown in the figure is always executed during the operation of the gas sensor control circuit 3 after it is determined that the sensor element unit 1 is activated.

When this routine is started, first, the pump current I _p (actually, the detected voltage Vλ corresponding to I _p ) is read as the output of the sensor element unit 1 via the A / D converter 41 (step 100). Then, it is determined whether or not the absolute value of the detected voltage Vλ is less than a predetermined allowable value Vr (step 110). If the detected voltage Vλ is less than or equal to the predetermined value Vr, then the air-fuel ratio is calculated (step 120).

The process for calculating the air-fuel ratio is performed based on the fact that the air-fuel ratio A / F of the air-fuel mixture sucked into the internal combustion engine (not shown) and the pump current I _p have the correlation shown in FIG. That is, the correlation shown in FIG. 4 is stored in the ROM 32 in advance, and the air-fuel ratio A / F is obtained according to the pump current I _p converted from the detection voltage Vλ read in step 100. After the process of calculating the air-fuel ratio, it is determined that the sensor element unit 1 is normal, and the variable N is set to the value 0 (step 130), and the process returns to step 100. Therefore, when the sensor element unit 1 is operating normally, the above-described processing, steps 100 to 130 are repeated.

On the other hand, the air-fuel ratio of the internal combustion engine becomes extremely rich due to the fuel injection amount control, and the sensor element unit 1
When a heater (not shown) deteriorates and a sufficient activation temperature cannot be obtained, for example, the pump current of the sensor element unit 1
_Ip becomes an abnormal value, the detected voltage Vλ becomes equal to or higher than the predetermined value Vr (step 110), and the process proceeds to step 140 or lower.

In this case, first, a low active reset signal is output to the pump current control circuit 2 via the output port 37. As a result, the outputs of the operational amplifiers 20 and 18 both fall to the ground level, and the pump current I _p becomes zero. Step 14
Following the processing of 0, the value of the variable N is incremented by 1 (step 150), and it is determined whether or not the value of the variable N is 1 (step 160). The detection voltage Vλ is
Immediately after the value exceeds the allowable value Vr for the first time, the value of the variable N is 1
Therefore, the processing shifts to step 170 and thereafter.

In this case, the timer 35 is accessed to start the internal timer T1 (step 170), wait for about 1 second (step 180), and then the reset signal is turned off (step 190). As a result, for the first time, the detected voltage Vλ becomes the allowable value V.
Immediately after reaching r or more, the energization of the oxygen pump element 7 of the sensor element unit 1 is interrupted for about 1 second. Then, after waiting for about 200 msec, the process returns to step 100 described above, and the process is executed again from the reading of the detection voltage Vλ. When the vehicle is suddenly accelerated, the air-fuel ratio of the air-fuel mixture may temporarily become extremely rich, but after waiting about 1 second, the air-fuel ratio returns to normal. Therefore, by the above-described processing of steps 140 to 200, the interruption time of energization to the oxygen pump element 7 can be minimized (about 1 second) against such a temporary disturbance of the air-fuel ratio.

On the other hand, if the air-fuel ratio becomes extremely rich over a long period of time, or the temperature of the sensor element unit 1 drops due to deterioration of the heater of the sensor element unit 1, etc. Pump current I _p never returns to its original state. Therefore, in step 110, which is executed again,
Again, it is judged that the detected voltage Vλ is equal to or higher than the allowable value Vr, and the output of the reset signal (step 140), the increment of the variable N (step 150) and the judgment regarding the variable N (step 160) are executed.

In this case, since the value of the variable N is larger than 1, the process proceeds to step 210 and below, and first, the timer T
Judge whether the value of 1 exceeds 30 seconds. If the operating state of the internal combustion engine and the heater of the sensor element unit 1 are normal,
It is considered that the detection voltage Vλ exceeds the allowable value Vr within 30 seconds. Therefore, it waits for 5 seconds until 30 seconds have elapsed (step 220), and then the above-mentioned processing, that is, the processing for turning off the reset signal (step 190) and 200 msec.
The waiting process (step 200) is executed. afterwards,
Returning to step 100 again, the detection voltage V of the sensor element unit 1
The process of measuring λ is repeated.

On the other hand, when the detected voltage Vλ exceeds the allowable value for 30 seconds or more (step 220), it is determined that the internal combustion engine is operating abnormally or the heater is out of order, and the step 23 is performed.
After shifting to the process of 0 and executing the alarm process, the process goes to "END" and the present routine is ended. The alarm processing includes, for example, turning on the alarm lamp 50 via the output port 37 to notify the driver that the sensor element unit 1 is not in a normal working state.

When the pump current I _p flowing through the oxygen pump element 7 of the sensor element unit 1 becomes excessive, the gas sensor control apparatus of the present embodiment configured as described above outputs this to the output of the pump current supply circuit 2. Detecting with the detection voltage Vλ, when the pump current I _p is abnormal for the first time, the energization to the oxygen pump element 7 is interrupted for about 1 second, and when it continues for about 5 seconds. Therefore, the problem that the pump current I _p becomes excessively large due to a temporary deviation of the air-fuel ratio and the oxygen pump element 7 is electrochemically destroyed can be solved sufficiently. As a result, the durability of the sensor element unit 1 is improved.

Further, when the state in which the pump current I _p exceeds the allowable value occurs for a long period of time, it is possible to stop the energization and give an alarm because it is considered that the heater or the like of the sensor element unit 1 has failed. It is also possible to solve the problem that the vehicle control such as the air-fuel ratio control is continued based on the erroneous detection of the exhaust gas composition by the sensor element unit 1 and the emission is deteriorated.

Although one embodiment of the present invention has been described in detail above,
The present invention is not limited to such an embodiment. For example, a configuration in which the magnitude of the detection voltage Vλ is discriminated by a window comparator and the output of the comparator is used as a reset signal is within the scope not departing from the gist of the present invention. Of course, it can be implemented in various modes.

Effects of the Invention As described above, according to the gas sensor control device of the present invention, when the pump voltage or the pump current becomes equal to or higher than the predetermined value for the first time, the first energization is interrupted for a short period of time, so that the temporary emptying is performed. With respect to the disturbance of the fuel ratio, it is possible to minimize the interruption time of the energization to the oxygen pump element, and thus it is possible to shorten the time for the performance deterioration of the gas sensor due to the interruption of the energization. Moreover, when the pump voltage or the pump current becomes equal to or higher than the predetermined value after the second time, the energization is interrupted for a longer period than the first interruption of the energization, so that the gas sensor can be prevented from being damaged by the excessive pump current. As a result, it is possible to extend the service life of the gas sensor and improve its reliability.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the basic configuration of the present invention, FIG. 2 is a schematic configuration diagram of a gas sensor control device as an embodiment of the present invention, and FIG. 3 is a gas sensor control routine executed in the embodiment. FIG. 4 is a graph showing the relationship between the pump current and the air-fuel ratio by experimental data. 1 ... Sensor element part 2 ... Pump current supply circuit 3 ... Gas sensor control circuit 7 ... Oxygen pump element 11 ... Oxygen concentration cell element 12 ... Gas diffusion limiting chamber

Claims (3)

[Claims] 1. A detection element which is in contact with a gas diffusion limiting chamber in which the flow of a gas to be measured is limited and which outputs a signal according to an oxygen concentration in the gas diffusion limiting chamber, and the gas diffusion limiting chamber and the above A gas sensor equipped with an oxygen pump element that moves oxygen ions between the gas to be measured and the current flowing through the oxygen pump element based on the output signal of the detection element is controlled to determine the oxygen concentration in the gas to be measured. A gas sensor control device comprising: a concentration detecting means for detecting; and a pump state detecting means for detecting that a pump voltage applied to the oxygen pump element or a pump current flowing through the oxygen pump element is a predetermined value or more. When the above-mentioned pump voltage or pump current exceeds a predetermined value for the first time, the first energization interruption is performed for a short period, and the pump voltage or pump current is the second or later. A control device for a gas sensor, comprising: an interrupting means for interrupting energization for a longer period of time than the first energization interruption when the value falls below a predetermined value. 2. The gas sensor according to claim 1, wherein the interruption time of the energization time by the interruption means is 0.5 seconds to 2 seconds at the first detection, and 4 seconds to 10 seconds at the second and subsequent detections. Control device. 3. An abnormality detecting means for interrupting energization to the oxygen pump element and generating an alarm signal when it is detected that the pump voltage or the pump current is a predetermined value or more for more than 30 seconds. 2. A control device for a gas sensor according to claim 1 or 2.