JP2004340859A - Method of determining activation of oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a determination time for determining activation of an oxygen sensor, and to enhance determination precision. <P>SOLUTION: The activation of the oxygen sensor is determined (step S15), when an output voltage VO2 of the oxygen sensor decreases from an initial bias voltage value V1 of a pumping voltage Vp for supplying a flow-in current to a detecting element 20 (step S11), after starting heating for the oxygen sensor of a pseudo-reference electrode type, and when the voltage VO2 is brought into a determination value VR/L or less for determining rich/lean conditions of an oxygen concentration (step S12) and comes again to the determination value VR/L or more (step S14). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an activation determination method of an oxygen sensor suitable for detecting an air-fuel ratio (mixing ratio of fuel and intake air) of an automobile engine or the like as an oxygen concentration in exhaust gas.
[0002]
[Prior art]
Generally, in an internal combustion engine such as an automobile engine, for example, an oxygen sensor is provided in the middle of an exhaust pipe, and the concentration of oxygen remaining in exhaust gas is detected by the oxygen sensor.
[0003]
In an oxygen sensor of this type of the prior art, which is a pseudo reference electrode (having no reference atmospheric chamber), for example, as shown in the schematic configuration of FIG. 4, a detection element 40 for detecting the oxygen concentration in exhaust gas is measured. It generates an electromotive force E corresponding to the oxygen concentration of the gas (exhaust gas) and has an internal resistance Ri. When the pumping voltage Vp for the pseudo reference electrode is applied to the detecting element 40, and the pumping current Ip as a flowing current is supplied to the detecting element 40 via the receiving resistor R0, the output voltage VO2 of the oxygen sensor is expressed by the following equation. Is represented by
[0004]
(Equation 1)
VO2 = E + (Ri × Ip)
Assuming that the output voltage VO2 in a state where the air-fuel ratio (A / F) becomes the stoichiometric air-fuel ratio (A / F = 14.7) is a reference voltage (for example, 450 mV), this reference voltage is compared with the output voltage VO2, It has been determined whether the fuel ratio is rich (rich) or lean (lean) with respect to the stoichiometric air-fuel ratio. That is, when the output voltage VO2 is higher than the reference voltage, the air-fuel ratio is richer than the stoichiometric air-fuel ratio (for example, A / F <14.7) and the amount of oxygen in the exhaust gas is small. When the output voltage VO2 is lower than the reference voltage, it is determined that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio (for example, A / F> 14.7) and that a large amount of oxygen exists in the exhaust gas.
[0005]
In such an oxygen sensor, in order to detect the air-fuel ratio satisfactorily, it is necessary that the detection element 40 be at a predetermined temperature or higher and be activated. The internal resistance Ri of the oxygen sensor has a temperature dependency, and the internal resistance decreases as the temperature of the detection element 40 is increased by heating. Utilizing such characteristics, the value of the internal resistance Ri is detected, and when the detected internal resistance value becomes smaller than a predetermined value, the oxygen sensor becomes higher than a predetermined temperature and is activated. Was determined to be. As this type of technology, for example, those described in the following documents are known (see Patent Documents 1 and 2).
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. Sho 62-197759
[Patent Document 2]
JP-A-5-249077
[Problems to be solved by the invention]
As described above, in the conventional oxygen sensor that determines activation of the oxygen sensor based on the value of the internal resistance Ri, although there is a correlation between the internal resistance Ri and the element temperature of the detection element, The internal resistance Ri varied in temperature characteristics. For this reason, when the activation is determined based on the resistance value of the internal resistance Ri, the accuracy of the determination depends on the temperature, which causes a problem that the accuracy of the determination is poor.
[0009]
Therefore, in order to accurately determine activation based on the value of the internal resistance Ri, it is necessary to set a certain margin for the value of the internal resistance Ri for determining activation in consideration of the variation of the internal resistance Ri. there were.
[0010]
That is, as shown in FIG. 5 showing the relationship (temperature characteristic) between the internal resistance Ri and the element temperature of the detection element, the determination value of the internal resistance Ri for determining activation is determined when the internal resistance Ri is standard (FIG. 5). 5 (a), it is necessary to set the minimum value of the internal resistance Ri that varies in the temperature characteristic when the internal resistance Ri varies as shown in FIG. 5B. Therefore, as shown in FIG. 5, the activation is determined at a temperature higher than the element temperature at which the detection element is actually activated. As a result, the activation determination is delayed, and the activation determination time becomes longer.
[0011]
In a pseudo reference electrode type oxygen sensor, a heater is energized and heats the detection element simultaneously with the normal operation of the sensor, and at the same time, a flowing current for accumulating oxygen in the reference electrode flows. Therefore, as shown in FIG. 6B showing the relationship between the output voltage VO2 of the sensor and the time after energization of the heater, the output voltage VO2 of the inactive oxygen sensor is equal to or higher than the reference voltage. Therefore, in the oxygen sensor of the pseudo reference electrode type, activation cannot be accurately determined only by monitoring the output voltage VO2.
[0012]
On the other hand, in the case of an oxygen sensor having an atmosphere chamber, as shown in FIG. 6A, when the output voltage VO2 rises with heating and reaches a predetermined range, and then reaches an outside of a predetermined range. Activation was determined.
[0013]
Further, in the oxygen sensor of the pseudo reference electrode type, an AC voltage applying device 41 for applying an AC voltage to the internal resistance Ri is required as shown in FIG. 4 in order to measure the resistance value of the internal resistance Ri. Had become. For this reason, the configuration has been increased in size, leading to an increase in cost.
[0014]
Therefore, the present invention has been made in view of the above, and it is an object of the present invention to provide an oxygen sensor that has achieved both shortening of a determination time for determining activation of an oxygen sensor and improvement of determination accuracy. An object of the present invention is to provide an activation determination method.
[0015]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is a detection element for detecting the oxygen concentration in the gas to be measured after the heating of the oxygen sensor of the pseudo reference electrode type is started. From the initial voltage value of the pseudo reference electrode bias voltage for supplying the current to the battery, becomes equal to or less than the determination value for determining the rich / lean state of the oxygen concentration, and again determines the rich / lean state of the oxygen concentration. When the value becomes equal to or more than the value, it is determined that the oxygen sensor is activated.
[0016]
In the above feature, since the activation of the oxygen sensor is determined by monitoring the output voltage of the oxygen sensor, the activation determination time is reduced without depending on the temperature around the oxygen sensor, In addition, the accuracy of activation can be improved.
[0017]
Further, an AC voltage applying device for detecting the internal resistance of the detecting element is not required, and the configuration of the sensor can be reduced in size and simplified, and the manufacturing cost can be reduced.
[0018]
According to a second aspect of the present invention, in the first aspect of the present invention, the initial voltage value of the pseudo reference electrode bias voltage is larger than the determination value for determining the rich state / lean state of the oxygen concentration and is active. The value is set to a value smaller than the output voltage of the oxygen sensor indicating the rich state after the conversion.
[0019]
With the above feature, the activation timing of the oxygen sensor can be accurately determined in a shorter time than in the conventional case.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0021]
FIG. 1 is a flowchart showing a procedure of a method for determining activation of an oxygen sensor according to a first embodiment of the present invention, FIG. 2 is a diagram showing an electrical schematic configuration of the oxygen sensor, and FIG. FIG. 5 is a diagram showing a time change of the output voltage VO2 and the pumping voltage Vp.
[0022]
Before describing the procedure of the determination method of the first embodiment with reference to FIG. 1, the electrical configuration and operation of a pseudo reference electrode type oxygen sensor will be described with reference to FIG. In FIG. 2, a detection element 20, which is included in an oxygen sensor and detects, for example, the oxygen concentration in exhaust gas, generates an electromotive force E corresponding to the oxygen concentration of the gas to be measured (exhaust gas) and has an internal resistance Ri. have. A pumping voltage Vp, which is a bias voltage for a pseudo reference electrode, is applied to the detecting element 20, and a pumping current Ip as a flowing current is supplied to the detecting element 20 via a receiving resistor R0. When the pumping current Ip is supplied to the detecting element 20, the output voltage VO2 of the oxygen sensor is expressed by the above-described equation (1).
[0023]
When the output voltage VO2 in a state where the air-fuel ratio (A / F) becomes the stoichiometric air-fuel ratio (A / F = 14.7) is set as a reference voltage (for example, about 450 mV), the reference voltage is compared with the output voltage VO2. It is determined whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio. That is, when the output voltage VO2 is higher than the reference voltage, the air-fuel ratio is richer than the stoichiometric air-fuel ratio (for example, A / F <14.7) and the amount of oxygen in the exhaust gas is small. When the output voltage VO2 is lower than the reference voltage, it is determined that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio (for example, A / F> 14.7) and that a large amount of oxygen exists in the exhaust gas.
[0024]
Next, the procedure of the activation determination method of the first embodiment will be described with reference to the flowchart of FIG.
[0025]
First, when the operation of the oxygen sensor is started, energization of a heater (not shown) for heating the detection element 20 is started to heat the detection element 20, and at the same time, a pumping voltage Vp for flowing a pumping current Ip to the detection element 20 is generated. , The initial bias voltage V1. The initial bias voltage V1 is higher than the reference voltage (for example, about 450 mV) serving as the determination voltage VR / L for determining the lean state / rich state and less than the output voltage VO2R (for example, about 900 mV) in the rich state. It is set, for example, to about 500 to 550 mV. In this way, by setting the pumping voltage Vp to the initial bias voltage V1, the output voltage VO2 after the start of the operation of the sensor once becomes reliably equal to or lower than the determination voltage VR / L. Immediately after the start of energization of the heater, since the element temperature of the detection element 20 is in a low state, the internal resistance Ri has a high value. In this state, since the resistance value of the internal resistance Ri is set sufficiently higher than the resistance value of the receiving resistance R0, the output voltage VO2 becomes the initial bias voltage V1 of the pumping voltage Vp (Step S10).
[0026]
Next, when the element temperature of the detection element 20 increases due to the heating of the heater, the resistance value of the internal resistance Ri decreases. As a result, the output voltage VO2 gradually decreases from the initial bias voltage V1, as shown by the solid line in FIG. The output voltage VO2 gradually decreases because the difference in voltage between the receiving resistor R0 and the internal resistor Ri gradually decreases due to the flowing current. When the output voltage VO2 becomes 1/2 of the initial bias voltage V1, it is considered that the resistance value of the internal resistor Ri has become equal to the resistance value of the receiving resistor R0 (step S11).
[0027]
Next, it is determined whether or not the output voltage VO2 has fallen below the determination voltage VR / L (step S12). That is, it is determined whether or not the output voltage VO2 indicates a lean state. As a result of the determination, when the output voltage VO2 becomes equal to or lower than the determination voltage VR / L, it is determined that the output voltage VO2 indicates a lean state.
[0028]
Subsequently, when the element temperature of the detection element 20 increases due to the heating of the heater and the resistance value of the internal resistance Ri further decreases, the pumping current Ip flowing into the detection element 20 starts to increase, and the oxygen The amount of accumulation is also secured. As a result, the output voltage VO2 starts to rise from the lowered state, as shown in FIG. 3A (step S13).
[0029]
Next, it is determined whether or not the output voltage VO2 has exceeded the determination voltage VR / L (step S14). That is, it is determined whether or not the output voltage VO2 indicates a rich state. As a result of the determination, when the output voltage VO2 is equal to or higher than the determination voltage VR / L, it is determined that the output voltage VO2 indicates a rich state. The output voltage VO2 decreases from the initial bias voltage V1 of the pumping voltage Vp, becomes equal to or lower than the determination voltage VR / L, and becomes an output state indicating a lean state, and then increases to indicate a rich state which becomes equal to or higher than the determination voltage VR / L. Being in the output state means that the detection element 20 is in a state where it can determine the rich state / lean state. That is, at this point, the oxygen sensor has been activated, and it is determined that the oxygen sensor has been activated (step S15).
[0030]
Next, in the output state in which the output voltage VO2 becomes equal to or higher than the determination voltage VR / L, and the pumping voltage Vp is the initial bias voltage V1 lower than the output voltage VO2R in the rich state, the output voltage in the rich state The pumping current Ip flowing into the detection element 20 in the direction that is canceled by VO2R is reduced. In order to avoid this, at the same time when it is determined that the oxygen sensor has been activated, as shown in FIG. 3B, the pumping voltage Vp is changed from the initial bias voltage V1 to the output voltage VO2R indicating a rich state after activation. It is switched to the normal bias voltage V2 which is larger than that and can supply the current to the detection element 20 (step S16). The normal bias voltage V2 is set to, for example, about 1.5 V or more.
[0031]
As described above, in the activation determination method according to the first embodiment, the activation is not determined based on the resistance value of the internal resistance Ri of the detection element as in the related art, but the output voltage of the oxygen sensor is changed. Since the activation of the oxygen sensor is determined by monitoring VO2, the activation timing can be accurately determined without depending on the variation of the internal resistance Ri due to the temperature. Thus, the activation determination time can be shortened and the activation accuracy can be improved without depending on the temperature around the oxygen sensor.
[0032]
Further, since the resistance value of the internal resistance Ri of the detection element is not detected, an AC voltage applying device for detecting the resistance value of the internal resistance Ri as in the related art becomes unnecessary. Thereby, the configuration of the sensor can be reduced in size and simplified, and the manufacturing cost can be reduced.
[0033]
Further, technical ideas other than the claims that can be grasped from the above embodiment will be described below together with the effects.
[0034]
2. The activation determination method for an oxygen sensor according to claim 1, wherein after the activation of the oxygen sensor is determined, the bias voltage for the pseudo reference electrode is set to a rich state after activation from an initial voltage value. A method for determining activation of an oxygen sensor, wherein the value is set to a value larger than the output voltage of the sensor.
[0035]
In the above feature, it is possible to avoid a decrease in the current flowing into the detection element and to reliably supply the current flowing into the detection element.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a procedure of an activation determination method for an oxygen sensor according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an electrical schematic configuration of an oxygen sensor.
FIG. 3 is a diagram showing an output voltage VO2 of the oxygen sensor and a temporal change of a pumping voltage.
FIG. 4 is a diagram showing an electrical schematic configuration of a conventional oxygen sensor.
FIG. 5 is a diagram showing variations in internal resistance with temperature.
FIG. 6 is a diagram showing a time change of an output voltage VO2 after energization of a heater.
[Explanation of symbols]
20, 40 detecting element 41 AC voltage applying device Ip pumping current R0 receiving resistor Ri internal resistance V1 initial bias voltage V2 normal bias voltage VR / L determination voltage Vp pumping voltage VO2 output voltage VO2R Rich output voltage

Claims (2)

After the heating of the pseudo reference electrode type oxygen sensor is started, the output voltage of the oxygen sensor is the initial voltage of the pseudo reference electrode bias voltage that supplies a current to the detection element that detects the oxygen concentration in the gas to be measured. The oxygen sensor is activated when the value falls below the determination value for determining the rich state / lean state of the oxygen concentration and becomes equal to or greater than the determination value for determining the rich state / lean state of the oxygen concentration again. And determining whether the oxygen sensor has been activated. The initial voltage value of the pseudo reference electrode bias voltage is:
2. The oxygen sensor according to claim 1, wherein the value is set to be larger than the determination value for determining the rich state / lean state of the oxygen concentration and smaller than the output voltage of the oxygen sensor indicating the rich state after activation. For determining activation of an oxygen sensor.

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