JP6974053B2 - Air-fuel ratio detector - Google Patents

Description

The present invention relates to an air-fuel ratio detector.

The air-fuel ratio detection device disclosed in Patent Document 1 includes an air-fuel ratio detection unit having electrodes on both sides of the first solid electrolyte layer. The electrodes on one surface of the first solid electrolyte layer are exposed to the exhaust, which is the gas to be measured. The electrodes on the other side of the first solid electrolyte layer are located in an atmospheric chamber partitioned by a partition wall. When a voltage is applied between these electrodes on both sides, an amount of current corresponding to the difference between the oxygen partial pressure in the exhaust gas and the oxygen partial pressure in the atmosphere chamber flows between the two electrodes. The oxygen partial pressure in the exhaust gas is calculated based on this current value.

Further, the air-fuel ratio detection device disclosed in Patent Document 1 includes an oxygen supply / discharge unit for adjusting the oxygen partial pressure in the atmospheric chamber to a constant partial pressure. The oxygen supply / discharge unit includes electrodes on both sides of the second solid electrolyte layer. The electrodes on one surface of the second solid electrolyte layer are arranged in the atmosphere chamber. A voltage is applied between the electrodes on both sides of the second solid electrolyte layer and a current flows. The current value at this time is controlled so as to match the current value flowing between the electrodes on both sides of the first solid electrolyte layer. As a result, the same amount of oxygen as the amount of oxygen passing through the first solid electrolyte layer passes through the second solid electrolyte layer, and the oxygen partial pressure in the air chamber is maintained substantially constant.

Japanese Unexamined Patent Publication No. 11-72473

Even if the current value flowing through the oxygen supply / discharge unit is controlled as in the air-fuel ratio detector disclosed in Patent Document 1, the amount of oxygen passing through the first solid electrolyte layer and the second solid electrolyte layer is strictly. May not match. If such a slight error accumulates over a long period of time, there is a risk that a non-negligible difference will occur between the oxygen partial pressure in the atmosphere chamber and the oxygen partial pressure in the actual atmosphere. As a result, the accuracy of calculating the oxygen partial pressure of the gas to be measured deteriorates, and the accuracy of calculating the air-fuel ratio deteriorates.

The air-fuel ratio detection device for solving the above problems includes a first solid electrolyte body, a gas detection electrode arranged on one surface of the first solid electrolyte body and exposed to the measured gas, and the first solid electrolyte body. A reference electrode that is arranged on the other surface of the solid electrolyte and is not exposed to the gas to be measured, a power supply unit that applies a current between the gas detection electrode and the reference electrode, and between the gas detection electrode and the reference electrode. It is equipped with an air-fuel ratio calculation unit that calculates the oxygen partial pressure of the measured gas according to the current flowing through the. Further, the air fuel ratio detection device includes a second solid electrolyte body arranged on the reference electrode side of the first solid electrolyte body, a pair of electrodes sandwiching the second solid electrolyte body, and the second solid electrolyte body. The electromotive force between the partition wall arranged on the opposite side of the body from the first solid electrolyte body and partitioning the reference air chamber in which one of the pair of electrodes is arranged and the pair of electrodes is measured. The electromotive force measuring unit is provided, and the air-fuel ratio calculation unit calculates the oxygen partial pressure of the measured gas in consideration of the electromotive force measured by the electromotive force measuring unit.

In the above configuration, the electromotive force between the pair of electrodes sandwiching the second solid electrolyte reflects the difference between the oxygen partial pressure near the reference electrode and the oxygen partial pressure in the reference atmosphere chamber. Therefore, even if there is a difference between the oxygen partial pressure near the reference electrode and the oxygen partial pressure in the atmosphere, if the oxygen partial pressure in the reference atmosphere chamber is kept at the oxygen partial pressure in the atmosphere, the subject caused by the difference will be covered. The oxygen partial pressure of the measured gas can be calculated after taking into account the deviation of the oxygen partial pressure of the measured gas. Therefore, deterioration of the calculation accuracy of the oxygen partial pressure of the gas to be measured can be suppressed, and as a result, the calculation accuracy of the air-fuel ratio is also improved.

Schematic diagram of an internal combustion engine to which an air-fuel ratio detector is applied. Sectional drawing of the air-fuel ratio detection device. The figure which showed the output characteristic of an air-fuel ratio sensor. A flowchart showing the processing procedure of the air-fuel ratio calculation process. The cross-sectional view which showed the modification example of the air-fuel ratio detection device.

Hereinafter, an embodiment of the air-fuel ratio detection device mounted on the internal combustion engine will be described with reference to the drawings. First, a schematic configuration of the internal combustion engine E will be described. As shown in FIG. 1, the internal combustion engine E includes an intake passage 11 for introducing intake air from the outside. A cylinder 10 for burning a mixture of fuel and intake air is connected to the intake passage 11. An exhaust passage 21 for exhausting exhaust gas to the outside is connected to the cylinder 10.

The intake passage 11 is provided with an air cleaner 12 that filters the air introduced into the intake passage 11. A throttle valve 13 having a variable passage area is provided on the downstream side of the air cleaner 12 in the intake passage 11. An air flow meter 14 for detecting the flow rate of the air introduced into the intake passage 11 is provided between the air cleaner 12 and the throttle valve 13 in the intake passage 11. The air flow meter 14 outputs the detected air flow rate value to the electronic control unit 30 (hereinafter, abbreviated as ECU 30) which is a control device of the internal combustion engine E. An injector 15 for injecting fuel is provided on the downstream side of the throttle valve 13 in the intake passage 11.

The exhaust passage 21 is provided with a catalyst 22 that purifies the components in the exhaust. An air-fuel ratio sensor 50 is provided on the upstream side of the catalyst 22 in the exhaust passage 21. The air-fuel ratio sensor 50 constitutes the air-fuel ratio detection device 100 together with the ECU 30. The air-fuel ratio sensor 50 detects a current value corresponding to the oxygen partial pressure in the portion upstream of the catalyst 22 in the exhaust passage 21, and outputs the current value to the ECU 30. The ECU 30 calculates the air-fuel ratio of the air-fuel mixture supplied to the cylinder 10 based on the current value input from the air-fuel ratio sensor 50.

The detection values of various sensors such as the air flow meter 14, the accelerator sensor for detecting the operation amount of the accelerator pedal, and the rotation speed sensor for detecting the engine rotation speed are input to the ECU 30. The ECU 30 controls the throttle valve 13, the injector 15, and the like to control the air-fuel ratio according to the state of the internal combustion engine E grasped from the detected values of various sensors.

Next, a specific configuration of the air-fuel ratio detection device 100 will be described.
As shown in FIG. 2, the air-fuel ratio sensor 50 includes a rectangular plate-shaped heater support plate 51. In this embodiment, the direction orthogonal to the surface direction of the heater support plate 51 will be described as the vertical direction.

Inside the heater support plate 51, a heater 52 that adjusts the temperature of the air-fuel ratio sensor 50 is embedded. The heater 52 is a heating wire, and generates heat by supplying power from the heater power supply. The heater 52 is heated and controlled so that the temperature of the air-fuel ratio sensor 50 is approximately 650 to 750 ° C.

A first partition wall 53 having a rectangular plate shape as a whole is fixed to the upper surface of the heater support plate 51. The first partition wall 53 is made of, for example, alumina. The material density of the first partition wall 53 is high, and gas cannot pass through the first partition wall 53. A rectangular through hole 53a penetrates the first partition wall 53 in the vertical direction. In the first partition wall 53, a part of the wall portion (the portion on the left side in FIG. 2) surrounding the through hole 53a is open to the outside of the air-fuel ratio sensor 50. A square columnar diffusion resistor 54 matching the opened portion is fitted in the opened portion. The dimensions of the diffusion resistor 54 in the vertical direction are the same as the thickness of the first partition wall 53. The diffusion resistor 54 is made of, for example, alumina. The diffusion resistor 54 has a lower material density than the first partition wall 53 and allows gas to pass through.

A rectangular plate-shaped first solid electrolyte body 61 is fixed to the upper surfaces of the first partition wall 53 and the diffusion resistor 54. The first solid electrolyte body 61 is an electrolyte body having oxygen ion conductivity. The oxygen ion conductivity of the first solid electrolyte body 61 increases as the temperature of the first solid electrolyte body 61 increases due to heating by the heater 52. The gas chamber 58 to be measured is partitioned by the lower surface of the first solid electrolyte body 61, the inner surface of the through hole 53a of the first partition wall 53, and the upper surface of the heater support plate 51. Exhaust gas, which is the gas to be measured, flows into the gas chamber 58 to be measured via the diffusion resistor 54. A part of the outer surface of the diffusion resistor 54 constitutes a part of the outer surface of the air-fuel ratio sensor 50, and the exhaust gas flows into the gas chamber 58 to be measured via the diffusion resistor 54. Then, when passing through the diffusion resistor 54, the flow velocity of the exhaust gas decreases. Therefore, even if the flow velocity of the exhaust gas passing through the exhaust passage 21 is pulsated, the inflow speed of the exhaust gas flowing into the gas chamber 58 to be measured is substantially constant.

A plate-shaped gas detection electrode 62 is fixed to the lower surface of the first solid electrolyte body 61. The gas detection electrode 62 is arranged in the gas chamber 58 to be measured and is exposed to the exhaust gas in the gas chamber 58 to be measured. A plate-shaped first reference electrode 63 is fixed to the upper surface of the first solid electrolyte body 61. The thickness and dimensions of the first reference electrode 63 match the thickness and dimensions of the gas detection electrode 62. When the air-fuel ratio sensor 50 is viewed from above in a plan view, the first reference electrode 63 overlaps with the gas detection electrode 62. The first solid electrolyte body 61, the gas detection electrode 62 sandwiching the first solid electrolyte body 61, and the first reference electrode 63 function as a sensor cell 60 for detecting the partial pressure of oxygen in the exhaust.

A second partition wall 55 having a rectangular plate shape as a whole is fixed on the upper surface of the first solid electrolyte body 61. The second partition wall 55 is made of the same material as the first partition wall 53. A rectangular through hole 55a penetrates the second partition wall 55 in the vertical direction.

A rectangular plate-shaped second solid electrolyte body 71 is fixed to the upper surface of the second partition wall body 55. The thickness and vertical and horizontal dimensions of the second solid electrolyte body 71 are the same as the thickness and vertical and horizontal dimensions of the first solid electrolyte body 61. The second solid electrolyte body 71 is made of the same material as the first solid electrolyte body 61. The reference gas chamber 59 is partitioned by the lower surface of the second solid electrolyte body 71, the inner surface of the through hole 55a of the second partition wall body 55, and the upper surface of the first solid electrolyte body 61. The reference gas chamber 59 is hermetically sealed. Atmosphere is taken into the reference gas chamber 59 in advance. The gas in the reference gas chamber 59 serves as a reference gas for calculating the oxygen partial pressure in the gas chamber 58 to be measured. The first reference electrode 63 is arranged in the reference gas chamber 59 and is exposed to the reference gas in the reference gas chamber 59.

A plate-shaped second reference electrode 72 is fixed to the lower surface of the second solid electrolyte body 71. The thickness and dimensions of the second reference electrode 72 are the same as the thickness and dimensions of the first reference electrode 63. The second reference electrode 72 is arranged in the reference gas chamber 59 and is exposed to the reference gas in the reference gas chamber 59.

A plate-shaped oxygen electrode 73 is fixed to the upper surface of the second solid electrolyte body 71. The thickness and dimensions of the oxygen electrode 73 are consistent with the thickness and dimensions of the second reference electrode 72. When the air-fuel ratio sensor 50 is viewed from above in a plan view, the oxygen electrode 73 overlaps with the second reference electrode 72. Since the exhaust gas circulates outside the air-fuel ratio sensor 50, the oxygen electrode 73 is exposed to the exhaust gas. The second solid electrolyte body 71 and the second reference electrode 72 and the oxygen electrode 73 sandwiching the second solid electrolyte body 71 supply oxygen to the reference gas chamber 59 and discharge oxygen from the reference gas chamber 59. It functions as a supply / discharge cell 70.

On the upper surface of the second solid electrolyte body 71, a plate-shaped monitor electrode 91 is fixed at a position different from the place where the oxygen electrode 73 is fixed. The size of the monitor electrode 91 is smaller than the size of the oxygen electrode 73. The thickness of the monitor electrode 91 coincides with the thickness of the oxygen electrode 73. In the present embodiment, the monitor electrode 91 and the second reference electrode 72 are a pair of electrodes that sandwich the second solid electrolyte body 71.

A third partition wall 93 provided so as to cover the monitor electrode 91 is fixed on the upper surface of the second solid electrolyte 71. The third partition body 93 is made of the same material as the first partition body 53. The third partition wall 93 rises from the upper surface of the second solid electrolyte body 71, and has a vertical wall portion 93a provided so as to surround the periphery of the monitor electrode 91 and a flat plate-shaped horizontal surface fixed to the upper end surface of the vertical wall portion 93a. It is provided with a wall portion 93b. The reference air chamber 95 isolated from the exhaust passage 21 is partitioned by the inner surface of the vertical wall portion 93a, the lower surface of the horizontal wall portion 93b, and the upper surface of the second solid electrolyte body 71. Although not shown, the reference atmosphere chamber 95 communicates with the outside of the vehicle so that the outside atmosphere is taken into the reference atmosphere chamber 95. The monitor electrode 91 is arranged in the reference atmosphere chamber 95 and is exposed to the atmosphere of the reference atmosphere chamber 95.

A first power supply 81, which is a power supply unit for applying a constant voltage, is connected to the gas detection electrode 62 and the first reference electrode 63. The positive electrode of the first power supply 81 is connected to the first reference electrode 63 side, and the negative electrode of the first power supply 81 is connected to the gas detection electrode 62 side. That is, when a current flows from the first reference electrode 63 side to the gas detection electrode 62 side, the current value becomes positive. On the other hand, when a current flows from the gas detection electrode 62 side to the first reference electrode 63 side, the current value becomes negative. In FIG. 2, the direction in which the current value A1 flows coincides with the direction in which the positive current value flows. The first power supply 81 is controlled by the ECU 30.

A current measuring device 83 is connected between the first reference electrode 63 and the first power supply 81. The current measuring device 83 measures the current value flowing between the gas detection electrode 62 and the first reference electrode 63 when a voltage is applied between the gas detection electrode 62 and the first reference electrode 63 by the first power supply 81. It is a current measuring unit. The current value measured by the current measuring device 83 is input to the ECU 30.

A second power source 82 for applying a voltage is connected to the second reference electrode 72 and the oxygen electrode 73. The positive electrode of the second power source 82 is connected to the second reference electrode 72 side, and the negative electrode of the second power source 82 is connected to the oxygen electrode 73 side. That is, when a current flows from the second reference electrode 72 side to the oxygen electrode 73 side, the current value becomes positive. On the other hand, when a current flows from the oxygen electrode 73 side to the second reference electrode 72 side, the current value becomes negative. In FIG. 2, the direction in which the current value A2 flows coincides with the direction in which the positive current value flows. The second power supply 82 variably controls the voltage applied to the second reference electrode 72 and the oxygen electrode 73. The application of the voltage by the second power supply 82 and the magnitude of the voltage at that time are controlled by the ECU 30.

A voltage measuring device 97 is connected to the second reference electrode 72 and the monitor electrode 91. The voltage measuring device 97 is an electromotive force measuring unit that measures an electromotive force (voltage) generated between the second reference electrode 72 and the monitor electrode 91. The electromotive force measured by the voltage measuring device 97 is input to the ECU 30.

The ECU 30 functions as an air-fuel ratio calculation unit that calculates the oxygen partial pressure in the exhaust gas of the gas chamber 58 to be measured and calculates the air-fuel ratio of the air-fuel mixture supplied to the cylinder 10 based on the oxygen partial pressure. Here, the principle of calculating the oxygen partial pressure in the exhaust gas will be described.

The ECU 30 is exhausting based on the current value A1 flowing between the gas detection electrode 62 and the first reference electrode 63 when a voltage is applied between the gas detection electrode 62 and the first reference electrode 63 by the first power supply 81. Calculate the oxygen partial pressure. For example, when the air-fuel ratio of the air-fuel mixture supplied to the cylinder 10 is leaner than the theoretical air-fuel ratio, oxygen is taken into the reference gas chamber 59 from the exhaust gas of the gas chamber 58 to be measured through the first solid electrolyte 61. At this time, oxygen ions move from the gas detection electrode 62 side, which is the negative electrode side of the first power supply 81, to the first reference electrode 63 side, which is the positive electrode side of the first power supply 81. Then, a current flows from the first reference electrode 63 side, which is the positive electrode side of the first power supply 81, to the gas detection electrode 62 side, which is the negative electrode side of the first power supply 81. That is, the current value A1 measured by the current measuring device 83 is positive.

On the other hand, when the air-fuel ratio of the air-fuel mixture supplied to the cylinder 10 is richer than the theoretical air-fuel ratio, oxygen is taken out from the reference gas chamber 59 into the exhaust of the gas chamber 58 to be measured through the first solid electrolyte 61. .. At this time, oxygen ions move from the first reference electrode 63 side, which is the positive electrode side of the first power supply 81, to the gas detection electrode 62 side, which is the negative electrode side of the first power supply 81. Then, a current flows from the gas detection electrode 62 side, which is the negative electrode side of the first power supply 81, to the first reference electrode 63 side, which is the positive electrode side of the first power supply 81. That is, the current value A1 measured by the current measuring device 83 becomes negative.

The solid line in FIG. 3 shows the voltage-current characteristics for each air-fuel ratio in a state where the oxygen partial pressure of the reference gas chamber 59 is the oxygen partial pressure of the atmosphere (hereinafter referred to as a reference state). At each air-fuel ratio, the voltage-current characteristic has a critical current region in which the current value does not change even when the voltage is increased. The limit current value, which is the current value in this limit current region, increases with the oxygen partial pressure (air-fuel ratio of the air-fuel mixture) in the exhaust gas. That is, there is a one-to-one relationship between the limit current value and the oxygen partial pressure in the exhaust gas. Therefore, by measuring the limit current value, the oxygen partial pressure in the exhaust can be calculated based on the limit current value. When calculating the oxygen partial pressure in the exhaust gas, the voltage actually applied by the first power supply 81 between the gas detection electrode 62 and the first reference electrode 63 is a constant applied voltage Vp. This applied voltage Vp is a voltage in a region where the critical current regions at each air-fuel ratio overlap each other. By applying this applied voltage Vp, the critical current can be energized regardless of the air-fuel ratio of the air-fuel mixture.

Here, with the use of the air-fuel ratio sensor 50, the oxygen partial pressure of the reference gas chamber 59 may be different from the oxygen partial pressure of the atmosphere. In this case, the voltage-current characteristics for each air-fuel ratio are different from those in the case where the oxygen partial pressure of the reference gas chamber 59 is the oxygen partial pressure of the atmosphere. The two-dot chain line in FIG. 3 shows an example of voltage-current characteristics when the air-fuel ratio of the air-fuel mixture is 17, for example, when the oxygen partial pressure of the reference gas chamber 59 is different from the oxygen partial pressure of the atmosphere. ing. When the voltage-current characteristic changes due to the difference in the oxygen partial pressure of the reference gas chamber 59 from the oxygen partial pressure of the atmosphere, a predetermined applied voltage Vp is applied between the gas detection electrode 62 and the first reference electrode 63. When applied, a current value Ip2 different from the limit current value Ip1 that should be detected in the reference state is detected. Therefore, although the oxygen partial pressure of the reference gas chamber 59 is different from the oxygen partial pressure of the atmosphere, the calculation is based on the assumption that the oxygen partial pressure of the reference gas chamber 59 is the oxygen partial pressure of the atmosphere. If this is done, the calculation accuracy of the oxygen partial pressure in the exhaust deteriorates. Therefore, the ECU 30 of the present embodiment takes into account the difference between the oxygen partial pressure of the reference gas chamber 59 and the oxygen partial pressure of the atmosphere (hereinafter referred to as the oxygen partial pressure difference in the reference gas chamber 59), and the oxygen partial pressure in the exhaust gas. Is calculated.

The ECU 30 grasps the oxygen partial pressure difference in the reference gas chamber 59 from the electromotive force measured by the voltage measuring device 97. Here, the electromotive force measured by the voltage measuring device 97 reflects the difference in oxygen partial pressure between the reference gas chamber 59 and the reference atmosphere chamber 95, as described below. For example, when there is a difference in oxygen partial pressure between the reference gas chamber 59 and the reference atmosphere chamber 95, the second reference electrode 72 arranged in the reference gas chamber 59 and the monitor electrode 91 arranged in the reference atmosphere chamber 95 Of these, at the electrode arranged on the side where the oxygen partial pressure is high, oxygen molecules receive electrons and become oxygen ions. On the other hand, at the electrode arranged on the side where the oxygen partial pressure is low, oxygen ions dissociate electrons and return to oxygen molecules. As a result of the potential difference between the two electrodes, an electromotive force is generated between the second reference electrode 72 and the monitor electrode 91. This electromotive force is measured by the voltage measuring device 97.

Next, the control of the second power supply 82 performed by the ECU 30 will be described. Here, according to the method of the air-fuel ratio detecting device disclosed in Patent Document 1, the second power supply 82 is controlled so that the oxygen partial pressure of the reference gas chamber 59 is maintained constant. On the other hand, in the present embodiment, the second power supply 82 is controlled so that a constant amount of oxygen is always taken into the reference gas chamber 59. Specifically, in the ECU 30, the sum of the current value A1 flowing between the gas detection electrode 62 and the first reference electrode 63 and the current value A2 flowing between the second reference electrode 72 and the oxygen electrode 73 is preset. The second power supply 82 is controlled so that the value becomes a constant positive value. By controlling the second power source 82 in this way, a constant amount of oxygen is always taken into the reference gas chamber 59.

For example, when the current value A1 is a large positive value, that is, when the amount of oxygen taken into the reference gas chamber 59 from the exhaust of the gas chamber 58 to be measured through the first solid electrolyte body 61 is large, the ECU 30 has a current value. The second power supply 82 is controlled so that A2 has a small positive value. In this case, a small amount of current flows from the second reference electrode 72 side to the oxygen electrode 73 side. Then, a relatively small amount of oxygen is taken into the reference gas chamber 59 from the exhaust gas outside the air-fuel ratio sensor 50 through the second solid electrolyte body 71.

On the other hand, when the current value A1 is a small positive value, that is, when the amount of oxygen taken into the reference gas chamber 59 from the exhaust of the gas chamber 58 to be measured through the first solid electrolyte body 61 is small, the ECU 30 causes the current. The second power supply 82 is controlled so that the value A2 becomes a large positive value. In this case, a large amount of current flows from the second reference electrode 72 side to the oxygen electrode 73 side. Then, a large amount of oxygen is taken into the reference gas chamber 59 from the exhaust gas outside the air-fuel ratio sensor 50 through the second solid electrolyte body 71. Further, when the current value A1 is a negative value, that is, when oxygen is taken out from the reference gas chamber into the exhaust of the gas chamber 58 to be measured through the first solid electrolyte body 61, the ECU 30 has a large positive current value A2. The second power supply 82 is controlled so as to have the value of. In this case, a large amount of current flows from the second reference electrode 72 side to the oxygen electrode 73 side. Then, a large amount of oxygen is taken into the reference gas chamber 59 from the exhaust gas outside the air-fuel ratio sensor 50 through the second solid electrolyte body 71.

Next, the air-fuel ratio calculation process executed by the ECU 30 will be described with reference to FIG. When the ignition switch is turned on, the ECU 30 executes the air-fuel ratio calculation process at predetermined intervals. When the ignition switch is turned on, the ECU 30 applies a predetermined applied voltage Vp between the gas detection electrode 62 and the first reference electrode 63 through the first power supply 81. Further, the ECU 30 controls the second power supply 82 as described above when the ignition switch is turned on.

As shown in FIG. 4, the ECU 30 proceeds to step S20 when the air-fuel ratio calculation process is started. In step S20, the ECU 30 acquires the current value A1 measured by the current measuring device 83. Then, the ECU 30 acquires the electromotive force V measured by the voltage measuring device 97 in step S30. After that, the ECU 30 proceeds to the process in step S40.

In step S40, the ECU 30 refers to the electromotive force map stored in advance in itself. The electromotive force map defines the relationship between the electromotive force generated between the second reference electrode 72 and the monitor electrode 91 and the oxygen partial pressure difference in the reference gas chamber 59. There is a one-to-one relationship between the electromotive force and the oxygen partial pressure difference in the reference gas chamber 59. When the electromotive force is 0, the oxygen partial pressure difference in the reference gas chamber 59 is 0. The larger the electromotive force, the larger the oxygen partial pressure difference in the reference gas chamber 59. The ECU 30 reads the oxygen partial pressure difference C in the reference gas chamber 59 corresponding to the electromotive force V measured by the voltage measuring device 97 from the electromotive force map. Then, the ECU 30 proceeds to the process in step S50.

In step S50, the ECU 30 calculates the amount AZ in which the current value A1 measured by the current measuring device 83 deviates from the current value to be detected in the reference state according to the oxygen partial pressure difference in the reference gas chamber 59. .. AZ is calculated by the following equation (1).

AZ = A1 × C / Atmospheric oxygen partial pressure ・ ・ ・ Equation (1)
After that, in step S60, the ECU 30 corrects the current value A1 measured by the current measuring device 83 by the following equation (2).

A1m = A1 + AZ ・ ・ ・ Equation (2)
Here, A1m is the corrected current value. After that, the ECU 30 proceeds to the process in step S70.

In step S70, the ECU 30 refers to the current map stored in advance in itself. The current map defines the relationship between the current value flowing between the gas detection electrode 62 and the first reference electrode 63 when a predetermined applied voltage Vp is applied in the reference state, and the oxygen partial pressure in the exhaust gas. There is. There is a one-to-one relationship between the current value and the oxygen partial pressure in the exhaust. The ECU 30 reads the oxygen partial pressure in the exhaust gas corresponding to the corrected current value A1 m from the current map. After that, the ECU 30 proceeds to the process in step S80.

In step S80, the ECU 30 calculates the air-fuel ratio of the air-fuel mixture supplied to the cylinder 10 based on the oxygen partial pressure in the exhaust gas. In this way, the ECU 30 ends a series of processes.
Next, the effect of the air-fuel ratio detection device of the present embodiment will be described.

(1) When the oxygen partial pressure in the reference gas chamber 59 is different from the oxygen partial pressure in the atmosphere, the current value flowing between the gas detection electrode 62 and the first reference electrode 63 is the oxygen partial pressure in the reference gas chamber 59. Will be different from the current value that should be detected if is the partial pressure of oxygen in the atmosphere. If the oxygen partial pressure in the exhaust gas is calculated using such a current value, an inappropriate oxygen partial pressure is naturally calculated.

On the other hand, in the present embodiment, the reference atmosphere chamber 95 is provided on the side opposite to the reference gas chamber 59 with the second solid electrolyte body 71 interposed therebetween. Then, the second reference electrode 72 is arranged in the reference gas chamber 59, and the monitor electrode 91 is arranged in the reference atmosphere chamber 95, and the electromotive force between the second reference electrode 72 and the monitor electrode 91 is measured. .. By measuring the electromotive force generated between the second reference electrode 72 and the monitor electrode 91 in this way, it becomes possible to grasp the oxygen partial pressure difference in the reference gas chamber 59. The ECU 30 corrects the current value A1 flowing between the gas detection electrode 62 and the first reference electrode 63 based on this oxygen partial pressure difference, and calculates the oxygen partial pressure in the exhaust gas from the corrected current value A1m. Therefore, even if the oxygen partial pressure in the reference gas chamber 59 is different from the oxygen partial pressure in the atmosphere, the oxygen partial pressure in the exhaust can be adjusted in consideration of the deviation of the current value due to the oxygen partial pressure difference in the reference gas chamber 59. Can be calculated. Therefore, deterioration of the calculation accuracy of the oxygen partial pressure can be suppressed, and as a result, the calculation accuracy of the air-fuel ratio of the mixing ratio supplied to the cylinder 10 is improved.

(2) In the present embodiment, the sum of the current value A1 flowing between the gas detection electrode 62 and the first reference electrode 63 and the current value A2 flowing between the second reference electrode 72 and the oxygen electrode 73 is preset. The second power supply 82 is controlled so that the value becomes a constant positive value. By controlling the second power source 82 in this way, a constant amount of oxygen is always taken into the reference gas chamber 59. In this case, it is unlikely that the oxygen in the reference gas chamber 59 will be insufficient.

On the other hand, depending on the control method of the second power source 82, the oxygen partial pressure of the reference gas chamber 59 may become zero. When the oxygen partial pressure of the reference gas chamber 59 becomes 0, oxygen cannot be taken out from the reference gas chamber 59 to the gas chamber 58 to be measured. Therefore, if the air-fuel ratio of the air-fuel mixture supplied to the cylinder 10 is richer than the theoretical air-fuel ratio, even if a voltage is applied between the gas detection electrode 62 and the first reference electrode 63 by the first power supply 81, it is a reference. The transfer of oxygen from the gas chamber 59 to the gas chamber 58 to be measured becomes impossible. In this case, no current flows between the gas detection electrode 62 and the first reference electrode 63. Here, when the second power supply 82 is controlled according to, for example, the method of the air fuel ratio detection device disclosed in Patent Document 1 in a state where the oxygen partial pressure of the reference gas chamber 59 is 0, the gas detection electrode 62 If the current value A1 flowing between the first reference electrode 63 and the first reference electrode 63 is 0, the current value A2 flowing between the second reference electrode 72 and the oxygen electrode 73 is also 0. If the current value A2 is 0, oxygen is not taken into the reference gas chamber 59 from the exhaust gas outside the air fuel ratio sensor 50 through the second solid electrolyte body 71, so that the oxygen partial pressure of the reference gas chamber 59 is 0. The state of is maintained. As a result, the current value A1 is also maintained at 0, and the oxygen partial pressure in the exhaust gas cannot be calculated appropriately.

On the other hand, according to the present embodiment, since a constant amount of oxygen is always taken into the reference gas chamber 59, it is possible to avoid a situation where the oxygen partial pressure of the reference gas chamber 59 becomes zero. Therefore, the oxygen partial pressure in the exhaust gas can be appropriately calculated, and the accuracy of calculating the air-fuel ratio of the air-fuel mixture supplied to the cylinder 10 is improved.

(3) When the second power supply 82 is controlled so that a constant amount of oxygen is always taken into the reference gas chamber 59 as described in (2) above, the oxygen partial pressure of the reference gas chamber 59 becomes 0. Even if it can be avoided, there is a risk of causing an oxygen excess situation in which the oxygen partial pressure of the reference gas chamber 59 becomes higher than the oxygen partial pressure of the atmosphere. However, in the present embodiment, the current value A1 flowing between the gas detection electrode 62 and the first reference electrode 63 is corrected based on the oxygen partial pressure difference in the reference gas chamber 59, and the current value A1m after correction is used for exhaust. The oxygen partial pressure inside is calculated. Therefore, even if the oxygen partial pressure in the reference gas chamber 59 becomes excessive, it is possible to prevent the accuracy of calculating the oxygen partial pressure in the exhaust gas from deteriorating. That is, in the present embodiment, the reference gas chamber 59 does not become oxygen deficient and the calculation accuracy of the oxygen partial pressure in the exhaust does not deteriorate, and the reference gas chamber 59 becomes excessive oxygen and is in the exhaust. The calculation accuracy of the oxygen partial pressure does not deteriorate. As a result, the accuracy of calculating the air-fuel ratio of the air-fuel mixture supplied to the cylinder 10 is improved.

Although the reference gas chamber 59 is hermetically sealed, for example, gas can enter through a slight gap between the first solid electrolyte body 61 and the second partition wall body 55. Therefore, when the air-fuel ratio detection device 100 is not operating as in the case where the internal combustion engine E is stopped, gas is exchanged little by little with the atmosphere in the reference gas chamber 59, and the oxygen partial pressure in the reference gas chamber 59 becomes the atmosphere. It approaches the oxygen partial pressure of.

The above embodiment can also be modified and implemented as follows.
The shapes and arrangements of the various members constituting the air-fuel ratio sensor 50 can be appropriately changed provided that the air-fuel ratio sensor functions in the same manner as in the above embodiment. For example, the shape, size, and horizontal position of the gas detection electrode 62 and the first reference electrode 63 may be different from each other. The same applies to the second reference electrode 72 and the oxygen electrode 73. The first solid electrolyte body 61, the second solid electrolyte body 71, the heater support plate 51, the first partition wall body 53, and the second partition wall body 55 may have a shape other than a rectangle such as a square. The reference gas chamber 59 may be isolated from the gas chamber 58 to be measured and the exhaust passage 21, and may be communicated with the outside atmosphere without having a closed structure. The third partition body 93 may be a reference air chamber 95 communicating with the atmosphere and having a shape capable of partitioning the reference gas chamber 59, the gas chamber 58 to be measured, and the reference air chamber 95 isolated from the exhaust passage 21. Any shape may be used.

-The reference gas chamber 59 may be abolished. FIG. 5 shows an example of an air-fuel ratio detection device when the reference gas chamber 59 is abolished. In the air-fuel ratio sensor 50a of the air-fuel ratio detection device 100a, the reference gas chamber is abolished and the first reference electrode and the second reference electrode are shared. That is, the common reference electrode 163 is fixed to the upper surface of the first solid electrolyte body 61. Further, the second solid electrolyte body 171 is fixed on the upper surface of the first solid electrolyte body 61. A recess 171a recessed upward is formed on the lower surface of the second solid electrolyte body 171. A common reference electrode 163 is arranged in the recess 171a. A first power supply 81 is connected to the common reference electrode 163 and the gas detection electrode 62. Further, a current measuring device 83 is connected between the common reference electrode 163 and the first power supply 81. Further, a second power source 82 is connected to the common reference electrode 163 and the oxygen electrode 73. Further, a voltage measuring device 97 is connected to the common reference electrode 163 and the monitor electrode 91. In the air-fuel ratio detection device 100a, the common reference electrode 163 and the monitor electrode 91 form a pair of electrodes that sandwich the second solid electrolyte body 71. Further, in the air-fuel ratio detection device 100a, the first solid electrolyte body 61, the gas detection electrode 62, and the common reference electrode 163 form a sensor cell, and the second solid electrolyte body 71, the common reference electrode 163, and the oxygen electrode 73 form a sensor cell. It constitutes an oxygen supply / discharge cell.

The gas chamber 58 to be measured may be abolished and the gas detection electrode 62 may be covered with the diffusion resistor 54. In this case, the exhaust gas that has passed through the diffusion resistor 54 is directly supplied to the gas detection electrode 62.
The method for correcting the current value A1 flowing between the gas detection electrode 62 and the first reference electrode 63 is not limited to the electromotive force map and the correction method using the above equations (1) and (2). Any method may be used as long as the current value A1 can be appropriately corrected according to the electromotive force V measured by the voltage measuring device 97.

-In the above embodiment, the current value A1 is corrected, and the oxygen partial pressure is calculated based on the corrected current value A1m. However, the oxygen partial pressure may be calculated first based on the current value A1, and then the oxygen partial pressure may be corrected based on the electromotive force V.

The connection structure of the first power supply 81 to the gas detection electrode 62 and the first reference electrode 63 may be inverted from the connection structure of the above embodiment. That is, the positive electrode of the first power supply 81 is connected to the gas detection electrode 62 side, and the negative electrode of the first power supply 81 is connected to the first reference electrode 63 side. In this case, the connection structure of the second power supply 82 to the second reference electrode 72 and the oxygen electrode 73 is inverted from the connection structure of the above embodiment, that is, the positive electrode of the second power supply 82 is connected to the oxygen electrode 73 side, and the second power supply 82 is connected. Connect the negative electrode of the power supply 82 to the second reference electrode 72 side, and control the second power supply 82 so that the sum of the current value A1 and the current value A2 becomes a constant value of a preset negative value. For example, as in the above embodiment, a constant amount of oxygen can always be taken into the reference gas chamber 59.

Regarding the control of the second power supply 82, the sum of the current value A1 flowing between the gas detection electrode 62 and the first reference electrode 63 and the current value A2 flowing between the second reference electrode 72 and the oxygen electrode 73 is 0. The second power supply 82 may be controlled so as to be.

-Regarding the control of the second power supply 82, a constant voltage may always be applied between the second reference electrode 72 and the oxygen electrode 73, or a constant current may always be applied between the second reference electrode 72 and the oxygen electrode 73. You may shed it. In this case, sufficient voltage and current may be set so that the oxygen partial pressure in the reference gas chamber 59 does not excessively decrease in the operating region of the general internal combustion engine E.

30 ... ECU (air fuel ratio calculation unit), 61 ... first solid electrolyte body, 62 ... gas detection electrode, 63 ... first reference electrode, 81 ... first power supply (power supply unit), 71 ... second solid electrolyte body, 72 ... 2nd reference electrode, 91 ... monitor electrode, 93 ... 3rd partition body (partition partition), 95 ... reference atmosphere chamber, 97 ... voltage measuring device (electromotive force measuring unit), 100, 100a ... air fuel ratio detecting device, 163 ... Common reference electrode, 171 ... Second solid electrolyte.

Claims (2)

A first solid electrolyte, a gas detection electrode arranged on one surface of the first solid electrolyte and exposed to the gas to be measured, and a gas detection electrode arranged on the other surface of the first solid electrolyte. a first reference electrode that is not exposed to the measurement gas, and a power supply unit for applying a voltage between the gas sensing electrode and the first reference electrode, the depending on the current flowing between the gas sensing electrode and the first reference electrode It is an air fuel ratio detection device equipped with an air fuel ratio calculation unit that calculates the oxygen partial pressure of the measurement gas.
A second solid electrolyte that partitions the reference gas chamber in which the first reference electrode is arranged together with the first solid electrolyte.
A second reference electrode arranged on the surface of the second solid electrolyte body on the reference gas chamber side, and
A monitor electrode arranged on the surface of the second solid electrolyte body opposite to the first solid electrolyte body,
A partition wall arranged on the side opposite to the first solid electrolyte body with respect to the second solid electrolyte body and partitioning a reference air chamber in which the monitor electrode is arranged,
It is provided with an electromotive force measuring unit for measuring an electromotive force between the second reference electrode and the monitor electrode.
The air-fuel ratio calculation unit is an air-fuel ratio detection device that calculates the oxygen partial pressure of the gas to be measured by adding the electromotive force measured by the electromotive force measurement unit. A first solid electrolyte, a gas detection electrode arranged on one surface of the first solid electrolyte and exposed to the gas to be measured, and a gas detection electrode arranged on the other surface of the first solid electrolyte. A reference electrode that is not exposed to the measured gas, a power supply unit that applies a voltage between the gas detection electrode and the reference electrode, and the oxygen partial pressure of the measured gas according to the current flowing between the gas detection electrode and the reference electrode. It is an air-fuel ratio detection device equipped with an air-fuel ratio calculation unit that calculates
A second solid electrolyte body in which the reference electrode is arranged on the reference electrode side of the first solid electrolyte body and the reference electrode is arranged on the surface on the first solid electrolyte body side .
A monitor electrode arranged on the surface of the second solid electrolyte body opposite to the first solid electrolyte body,
A partition wall arranged on the side opposite to the first solid electrolyte body with respect to the second solid electrolyte body and partitioning a reference air chamber in which the monitor electrode is arranged,
It is provided with an electromotive force measuring unit for measuring an electromotive force between the reference electrode and the monitor electrode.
The air-fuel ratio calculation unit is an air-fuel ratio detection device that calculates the oxygen partial pressure of the gas to be measured by adding the electromotive force measured by the electromotive force measurement unit.

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