JP2007046462A - Sensor control device and sensor mounting passage structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly eliminate output slippage when warming-up an exhaust gas sensor. <P>SOLUTION: In a sensor control device, an exhaust gas sensor is provided with a sensor element having function pumping oxygen, and the exhaust gas sensor mounted on an exhaust gas passage of an internal combustion engine is controlled. The sensor control device is provided with an atmosphere creation means making atmosphere around the sensor element a lean atmosphere, and an atmosphere control means controlling atmosphere around the sensor element to the lean atmosphere in a warming-up process of the sensor element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sensor control device and a sensor mounting passage structure. More specifically, the present invention relates to a sensor control device for controlling an exhaust gas sensor mounted in an exhaust passage connected to an internal combustion engine, and an attachment passage structure for attaching the exhaust gas sensor.

  Conventionally, JP-A-10-282045 discloses an oxygen sensor used in air-fuel ratio control of an internal combustion engine. The oxygen sensor includes a sensor element and a cover that protects the sensor element. The sensor element includes a solid electrolyte membrane and electrodes disposed on both sides of the solid electrolyte membrane. One of the electrodes is in contact with the atmosphere as a reference gas, and the other electrode is in contact with the detection gas. An electromotive force is generated between both electrodes of the oxygen sensor according to the oxygen concentration difference between the atmosphere and the detection gas, and a current flows. This electromotive force or current can be detected, and the oxygen concentration of the detected gas can be known based on the detected value.

  By the way, in an internal combustion engine, in order to reduce NOx in exhaust gas, for example, a system that circulates exhaust gas discharged from the internal combustion engine, such as an EGR device (exhaust gas recirculation device), or a PCV device ( A system that circulates and uses exhaust gas, air-fuel mixture, or the like (blow-by gas) leaked into the crankcase may be used, such as a blow-by gas reduction device. In such a system, exhaust gas and blow-by gas are supplied together with the atmosphere from the intake passage into each cylinder of the internal combustion engine. However, exhaust gas and blow-by gas contain sulfuric acid mist and oil mist (hereinafter referred to as “mist”) indefinitely. Therefore, when the exhaust gas or blow-by gas is circulated and reused, the gas supplied from the intake side becomes richer and indefinite than the atmosphere. For this reason, in the above prior art, an oxygen sensor is mounted in an intake passage of an EGR device, a PCV device or the like, and is used to detect the concentration of the supply gas supplied from the intake passage.

  Unlike the exhaust gas in the exhaust passage, the supply gas passing through the intake passage has a low temperature. For this reason, the mist in the circulated exhaust gas or blow-by gas is cooled and becomes highly viscous. Therefore, mist may adhere to and accumulate on the oxygen sensor mounted in the intake passage. It is conceivable that the accumulated mist clogs, for example, the vent hole of the cover of the oxygen sensor or the porous layer on the surface of the sensor element. As a result, there may be a difference in the concentration of exhaust gas between the inside and outside of the cover, or intake and exhaust in the porous layer on the surface of the sensor element may be difficult, and accurate sensor output may not be obtained.

  For this reason, in the above-described prior art, the negative electrode insulated by an insulator is disposed through the wall portion of the intake passage to which the oxygen sensor is attached. In addition, a positive electrode is insulated from the opposite side of the negative electrode. The oxygen sensor penetrates the negative electrode, and the sensor element portion is disposed so as to protrude from the negative electrode into the intake passage. During operation of the internal combustion engine, a predetermined high voltage is applied between the negative electrode and the positive electrode. As a result, an electric field is generated between the positive electrode and the negative electrode in the intake passage. At this time, the periphery of the sensor element of the oxygen sensor becomes a cathode. On the other hand, the mist has a property of being attracted to the anode side by electrostatic force. Therefore, according to the above prior art, mist around the oxygen sensor arranged on the cathode side is eliminated on the anode side, and adhesion of the mist to the oxygen sensor is suppressed.

Japanese Patent Laid-Open No. 10-282045 JP 2003-278594 A

  In the above prior art, a voltage is applied between the negative electrode and the positive electrode during operation of the internal combustion engine, that is, during detection of the oxygen concentration by the oxygen sensor, and an electric field is constantly generated in the intake passage. When the oxygen sensor is arranged in the electric field in this way, it is considered that the sensor output is shifted due to the influence of the electric field. Such a deviation in sensor output is not preferable in terms of performing a more accurate air-fuel ratio.

  Further, the above prior art takes into consideration that the oxygen sensor is mounted in the intake passage of the internal combustion engine. On the other hand, even in an exhaust gas sensor mounted in the exhaust passage, it is conceivable that a deviation occurs in sensor output due to adsorption of components in the exhaust gas. Specifically, the exhaust gas sensor in the exhaust passage may adsorb components in the exhaust gas as the element temperature after the internal combustion engine stops. This adsorbed species adheres to the sensor element at a low temperature, but has a property of desorbing at a high temperature. Therefore, as the sensor element warms up after the internal combustion engine is started, the adsorbed species adsorbed on the sensor element are desorbed again. The adsorbed species desorbed here generates a rich gas around the exhaust side electrode of the sensor element, reacts with the pumped oxygen, neutralizes, and is discharged. Therefore, after the start of the internal combustion engine, until the adsorbed species are completely neutralized and released, it is considered that an output shift due to the adsorbed species occurs in the output of the oxygen sensor. This output deviation is usually considered to be resolved before the exhaust gas sensor reaches the activation temperature. However, when the amount of adsorbed species has increased for some reason, the neutralization of the adsorbed species continues even if the sensor element reaches the activation temperature, so that accurate air-fuel ratio control cannot be performed. Become. In this regard, the above-described conventional technique suppresses adhesion of mist and the like to the oxygen sensor disposed in the intake passage, but quickly and reliably neutralizes and releases the adsorbed species of the exhaust gas sensor when the internal combustion engine is started. It does not contribute to that.

  Therefore, in order to solve the above problem, the present invention is an improved sensor control that can quickly eliminate the output deviation at the time of warming up of the exhaust gas sensor due to the influence of the adsorbed species adhering to the exhaust gas sensor. An apparatus and a sensor mounting passage structure are provided.

In order to achieve the above object, a first invention is a control device for an exhaust gas sensor mounted in an exhaust passage of an internal combustion engine,
The exhaust gas sensor includes a sensor element having a function of pumping oxygen,
Atmosphere generating means for making the atmosphere around the sensor element a lean atmosphere;
In the warm-up process of the sensor element, atmosphere control means for controlling the periphery of the sensor element to a lean atmosphere;
It is characterized by providing.

The second invention is the first invention, wherein
Temperature detecting means for detecting the temperature of the sensor element;
Activity determination means for determining whether or not the temperature of the sensor element has reached an activation temperature,
The atmosphere control means controls the atmosphere around the sensor element to a lean atmosphere from the start of warming-up of the sensor element until it is determined that the temperature of the sensor element has reached the activation temperature. Features.

In a third aspect based on the first aspect or the second aspect, the atmosphere generating means is
A bypass pipe that is connected to the exhaust passage and is arranged so that the exhaust gas flows in, the exhaust gas sensor is installed, and a space in the exhaust passage and a space around the sensor element;
A valve that is disposed at an exhaust gas inlet of the bypass pipe and opens and closes the bypass pipe,
The atmosphere control means controls the atmosphere in the bypass pipe to a lean atmosphere by closing the valve during the warm-up process of the sensor element.

Moreover, 4th invention is 1st or 2nd invention,
Warm-up determination means for determining whether or not the warm-up of the internal combustion engine has been completed,
The atmosphere generating means includes
An HC adsorption catalyst installed in the exhaust passage;
A three-way catalyst disposed downstream of the HC adsorption catalyst;
Connected to the exhaust passage and arranged so that the exhaust gas flows in, the exhaust gas sensor is installed, the HC adsorption catalyst and a space around the sensor element are partitioned, and the ternary A bypass pipe connected to the catalyst;
A valve disposed at an inlet of the bypass pipe and opening and closing the bypass pipe,
The atmosphere control means controls the atmosphere in the bypass pipe to a lean atmosphere by closing the valve from the start of the internal combustion engine until the completion of warm-up of the internal combustion engine is determined. And

Further, the fifth invention achieves the above object,
An exhaust passage for exhaust gas discharged from the internal combustion engine;
A bypass pipe disposed in the exhaust passage, where an exhaust gas sensor is installed, and a space around a sensor element of the exhaust gas sensor, and a space in the exhaust passage;
A valve for opening and closing the exhaust gas inlet of the bypass pipe;
It is characterized by providing.

  According to the first aspect, in the warm-up process of the sensor element of the exhaust gas sensor, the periphery of the sensor element is controlled to a lean atmosphere. Therefore, in the process of warming up the sensor element, the rich gas generated by the adsorbed species desorbed from the sensor element can be quickly neutralized, and the output deviation of the exhaust gas sensor can be recovered early. Accordingly, accurate air-fuel ratio control can be performed quickly after the sensor element is activated.

  According to the second invention, the atmosphere around the sensor element is controlled to be a lean atmosphere from the start of warm-up of the sensor element until it is determined that the temperature of the sensor element has reached the activation temperature. Therefore, while passing through a temperature range where desorption of adsorbed species is likely to occur, the sensor element periphery can be reliably maintained in a lean atmosphere, and the rich gas generated by desorption of adsorbed species can be reliably neutralized. .

  According to the third aspect of the invention, the exhaust gas sensor is installed in the bypass pipe that partitions the space in the exhaust passage and the space around the sensor element, and the valve at the inlet of the bypass pipe is closed during the warm-up process of the sensor element. To control. Therefore, exhaust gas discharged from the internal combustion engine during the warm-up process of the sensor element can be prevented from flowing into the sensor element periphery, and the sensor element periphery can be maintained in a lean atmosphere.

  According to the fourth invention, the exhaust gas sensor is installed in the bypass pipe of the catalyst purification device having the HC adsorption catalyst arranged in the exhaust passage, and the valve at the inlet of the bypass pipe is set during the warm-up process of the internal combustion engine. Control to close. Thereby, the sensor element periphery can be maintained in a lean atmosphere in the sensor element warm-up process by the mounting passage structure using the catalyst purification device.

  According to the fifth aspect of the present invention, the sensor element is provided with a mounting passage structure having a bypass pipe partitioning a space around the sensor element and a space in the exhaust passage, and a valve for opening and closing an exhaust gas inlet of the bypass pipe. The surrounding atmosphere can be temporarily isolated from the exhaust gas in the exhaust passage and kept in an atmosphere different from the exhaust gas.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment 1 FIG.
[System configuration of the first embodiment]
FIG. 1 is a schematic diagram for explaining a system according to Embodiment 1 of the present invention. As shown in FIG. 1, the system of Embodiment 1 includes an internal combustion engine 2. Although the internal combustion engine 2 includes a plurality of cylinders, only a cross section of one cylinder is shown in FIG. An intake manifold 6 is connected to the intake port 4 of each cylinder of the internal combustion engine 2. The intake manifold 6 is provided with a fuel injection valve 8. An exhaust port 10 of each cylinder of the internal combustion engine 2 is connected to a branch pipe of the exhaust manifold 12. The branch pipes of the exhaust manifold 12 gather into one main pipe. The main pipe of the exhaust manifold 12 is connected to a catalytic converter 16 containing a three-way catalyst 14. The catalytic converter 16 is connected to the exhaust pipe 18. An air-fuel ratio sensor 20 is disposed in the main pipe of the exhaust manifold 12 on the upstream side of the three-way catalyst 14. The air-fuel ratio sensor 20 is a sensor that generates an output voltage corresponding to the air-fuel ratio over a wide air-fuel ratio region. Further, an oxygen sensor 22 is disposed in the exhaust pipe 18 downstream of the three-way catalyst 14. The oxygen sensor 22 is a sensor whose output value changes stepwise near the theoretical air-fuel ratio. The fuel injection valve 8, the air-fuel ratio sensor 20, and the oxygen sensor 22 are connected to the control device 24.

FIG. 2 is a schematic diagram for explaining the air-fuel ratio sensor 20 used in the system of the first embodiment. As shown in FIG. 2, the air-fuel ratio sensor 20 includes a sensor element 30. The sensor element 30 has a tubular structure with one end closed. The outer surface of the tubular structure is covered with a diffusion resistance layer 32. The diffusion resistance layer 32 is composed of a heat-resistant porous ceramic, for example, a spinel type compound (MgO.Al ₂ O ₃ ) using alumina, and has a function of trapping poisonous substances contained in the exhaust gas. Yes. An exhaust side electrode 34 is provided inside the diffusion resistance layer 32. The exhaust side electrode 34 is in contact with the exhaust gas that has passed through the diffusion resistance layer 32. A solid electrolyte layer 36 is provided inside the exhaust side electrode 34. An atmosphere side electrode 38 is provided on the inner side of the solid electrolyte layer 36, that is, on the surface of the solid electrolyte layer 36 opposite to the exhaust side electrode 34. The exhaust side electrode 34 and the atmosphere side electrode 38 are electrodes made of a metal having high catalytic action such as Pt. The exhaust side electrode 34 and the atmosphere side electrode 38 are electrically connected to the control device 24 via a control circuit (not shown), and a necessary voltage is applied by being controlled by the control circuit. The solid electrolyte layer 36 is a sintered body containing ZrO ₂ or the like, and has a characteristic of conducting oxygen ions.

  An air chamber 40 that is open to the atmosphere is formed inside the sensor element 30. The atmosphere side electrode 38 is in contact with the atmosphere introduced into the atmosphere chamber 40. A heater 42 is installed in the atmospheric chamber 40. The heater 42 is electrically connected to the control device 24 via a control circuit (not shown), and the sensor element 30 can be heated and maintained at an appropriate temperature by being controlled by the control circuit. The sensor element 30 exhibits stable output characteristics at an activation temperature of about 700 ° C. In addition, the air-fuel ratio sensor 20 has a cover 44. The sensor element 30 is protected by a cover 44 and installed in the exhaust manifold 12. The cover 44 is provided with a plurality of vent holes 46 for introducing exhaust gas therein.

  The control device 24 controls the magnitude of the voltage applied to the exhaust side electrode 34 and the atmosphere side electrode 38 of the sensor element 30. The sensor element 30 changes the sensor current almost proportionally to the applied voltage in a region where the applied voltage applied between both electrodes is sufficiently low, and exhausts the sensor current as the applied voltage increases. It has a characteristic of converging to a limit current value corresponding to the difference between the oxygen concentration of the gas and the oxygen concentration of the atmosphere. By utilizing this characteristic, the oxygen concentration of the exhaust gas can be obtained by applying a predetermined voltage to the sensor element 30 and detecting the limit current value.

[Attachment passage structure of air-fuel ratio sensor of embodiment 1]
3 and 4 are schematic views for explaining an attachment passage structure for attaching the air-fuel ratio sensor 20 in the first embodiment of the present invention to the exhaust manifold 12. 3A shows a cross section perpendicular to the gas flow direction in the exhaust manifold 12, and FIG. 3B is a cross section in the AA ′ direction of FIG. 3A, in which the valve is closed. Represents the state. FIG. 4 is the same cross section as FIG. 3B and shows a state in which the valve is opened. As shown in FIGS. 3 (a) and 3 (b), a bypass pipe 50 for attaching the air-fuel ratio sensor 20 is provided in a part of the main pipe in the exhaust manifold 12. The bypass pipe 50 is installed at the center of the exhaust manifold 12. The air-fuel ratio sensor 20 is assembled to the bypass pipe 50 so that a portion protected by the cover 44 of the sensor element 30 protrudes into the bypass pipe 50. A valve 52 is disposed at the exhaust gas inlet of the bypass pipe 50. The valve 52 is connected to the control device 24 and opens and closes the bypass pipe 50 in response to an open / close signal from the control device 24. On the other hand, the outlet on the downstream side of the bypass pipe 50 opens toward the exhaust manifold 12.

  As shown in FIG. 3B, when the valve 52 is closed, the exhaust gas does not flow into the bypass pipe 50 and passes through the exhaust manifold 12 outside the bypass pipe 50. On the other hand, as shown in FIG. 4, when the valve 52 is opened, the exhaust gas flows into the bypass pipe 50.

[Adsorption mechanism]
FIG. 5A is a diagram for explaining how the adsorbed species 54 are adsorbed to the sensor element 30 after the internal combustion engine 2 is stopped. FIG. 5B is a diagram for explaining the influence of the adsorbed species 54 on the output of the sensor element 30 after the internal combustion engine 2 is started. As described above, the sensor element 30 is used in a state where the exhaust-side electrode 34 is in contact with the exhaust gas. The exhaust gas contains various components such as water vapor (H ₂ O), carbon dioxide (CO ₂ ), and oxygen (O ₂ ). When the sensor element 30 is in an active high temperature, these components are not adsorbed on the exhaust side electrode 34. However, after the internal combustion engine 2 is stopped, chemical adsorption may occur between these components and the exhaust-side electrode 34 in the process in which the temperature of the sensor element 30 decreases.

  According to the knowledge of the present inventor, this adsorption reaction is likely to occur when the temperature of the sensor element 30 is lowered to some extent. After the internal combustion engine 2 is stopped, the energization of the heater 42 is stopped, so that the temperature of the sensor element 30 inevitably decreases to the adsorption temperature range where the adsorbed species 54 starts to adsorb. For this reason, it is considered that the adsorbed species 54 are inevitably adsorbed on the surface of the sensor element 30 as shown in FIG.

On the other hand, the adsorbed species 54 adsorbed on the sensor element 30 starts to desorb from the surface of the sensor element 30 when the sensor element 30 is heated to an extent that exceeds the lower limit of the adsorption temperature range. That is, when the internal combustion engine 2 is started and energization of the heater 42 is started, the temperature of the sensor element 30 gradually increases. Then, when the temperature of the sensor element 30 reaches the lower limit of the adsorption temperature range, the desorption of the adsorbed species 54 starts as shown in FIG. When the adsorbed species 54 begins to desorb, hydrogen (H ₂ ), which is a reducing substance, is generated near the surface of the exhaust-side electrode 34. The generated hydrogen makes the vicinity of the surface of the exhaust side electrode 34 rich, and blocks the reaction site (reaction point) of the exhaust side electrode 34 to prevent the reaction between the exhaust side electrode 34 and oxygen. As a result, the output of the sensor element 30 is temporarily shifted to the rich side in the process of raising the temperature of the sensor element 30 to the activation temperature. Thereafter, desorption of the adsorbed species 54 proceeds as the temperature of the sensor element 30 rises, and when neutralization of the adsorbed species 54 is completed, the rich shift of the air-fuel ratio sensor 20 is eliminated.

[Problems and Solution Principle of Embodiment 1]
As described above, even if the exhaust gas atmosphere immediately after the start of the internal combustion engine 2 is in a lean state, the output of the air-fuel ratio sensor 20 is detected to be shifted to the rich side due to the effect of the desorbed adsorbed species 54. There is a case. In order to start the accurate air-fuel ratio control immediately after the internal combustion engine 2 is started, it is preferable that the period during which the output deviation due to the adsorbed species 54 occurs is short. The principle used in the first embodiment to satisfy the above requirements will be described below. FIG. 6 is a timing chart showing the relationship between the opening / closing timing of the valve 52 and the output of the air-fuel ratio sensor 20.

  As described above, the air-fuel ratio sensor 20 is assembled to the bypass pipe 50. A valve 52 is attached to the inlet of the bypass pipe 50. As shown in FIG. 6, the valve 52 is opened except for the period from the start of the start of the internal combustion engine 2 until the sensor element reaches the activation temperature. In the open state of the valve 52, the exhaust gas flows into the bypass pipe 50 as in the exhaust manifold 12. In this state, since air-fuel ratio control is performed based on the sensor output, the air-fuel ratio sensor 20 detects the oxygen concentration of the exhaust gas as usual. When the internal combustion engine 2 stops with the valve 52 opened, exhaust gas is gradually discharged from the exhaust manifold 12 and the entire interior of the exhaust manifold 12 is replaced with air. At this time, since the valve 52 of the bypass pipe 50 is opened, the inside of the bypass pipe 50 is similarly replaced with air.

  On the other hand, the valve 52 is closed immediately after the internal combustion engine 2 is started until the sensor element 30 reaches the activation temperature. The inside of the bypass pipe 50 is replaced with air while the internal combustion engine 2 is stopped, and a lean atmosphere is obtained. Therefore, while the valve 52 is closed, the inside of the bypass pipe 50 is kept in a lean atmosphere. Here, in general, in the warm-up process after the start of the internal combustion engine 2, the air-fuel ratio is controlled to be rich. Therefore, the exhaust gas in the warm air process has a rich atmosphere. However, by closing the valve 52, the rich exhaust gas discharged from the internal combustion engine 2 does not flow into the bypass pipe 50, passes through the exhaust manifold 12 outside the bypass pipe 50, and is discharged to the catalytic converter 16. Thereby, the inside of the bypass pipe 50 is maintained in a lean state.

  When the temperature of the sensor element 30 reaches the lower limit of the adsorption temperature range in the warm-up process of the sensor element 30 immediately after the internal combustion engine 2 is started until the sensor element 30 is heated to the activation temperature, the adsorption adhering to the sensor element 30 Species 54 begins to desorb. When the adsorbed species 54 are desorbed, hydrogen, which is a rich gas, is generated on the surface of the exhaust-side electrode 34. The generated hydrogen is neutralized by the reaction with the lean gas around the sensor element 30. When the sensor element 30 is directly installed on the exhaust manifold, it comes into contact with the rich exhaust gas during the warm-up process, so that it takes a certain amount of time to neutralize the rich gas generated by the desorption of the adsorbed species 54. However, according to the first embodiment, the neutralization reaction with the desorbed adsorbed species 54 is promoted by keeping the inside of the bypass pipe 50 in a lean atmosphere close to the atmosphere. As a result, neutralization can be completed by reacting the adsorbed species 54 desorbed from the sensor element 30 and the lean gas in the bypass pipe 50 at an earlier stage until the sensor element 30 reaches the activation temperature.

  As shown in FIG. 6, the output of the air-fuel ratio sensor 20 is affected by the rich gas generated by the adsorbed species 54 desorbed from the sensor element 30 after the internal combustion engine 2 is started. It is shifted to the richer side than lean gas. This output shift to the rich side is gradually offset as the neutralization reaction between the rich gas and the lean gas in the bypass pipe 50 proceeds. Since the periphery of the sensor element 30 is maintained in a lean atmosphere, this neutralization reaction is promoted, and neutralization of the adsorbed species 54 that has been desorbed is completed before reaching the activation temperature. Accordingly, when the sensor element 30 reaches the activation temperature and the valve 52 is opened, an accurate sensor output corresponding to the exhaust gas passing through the bypass pipe 50 can be obtained.

  FIG. 7 is a flowchart for illustrating a routine of valve 52 opening / closing control executed by control device 24 in the first embodiment of the present invention. The routine shown in FIG. 7 is a routine that is executed every time the internal combustion engine 2 is started. In the routine of FIG. 7, it is first determined whether or not it is immediately after the start of the internal combustion engine 2 (step S102). When the internal combustion engine 2 has not been started or when a sufficient time has elapsed after the start, the processing by this routine ends.

  On the other hand, if it is recognized that it is immediately after the start of the internal combustion engine 2, the valve 52 is then closed (step S104). Thereby, the inlet of the bypass pipe 50 is closed. Immediately after the start of the internal combustion engine 2, control is performed so that the rich operation is performed. Therefore, the exhaust gas contains a lot of rich gas and has a rich atmosphere. Here, by closing the inlet of the bypass pipe 50, inflow of rich exhaust gas discharged from the internal combustion engine 2 into the bypass pipe 50 is suppressed, and the inside of the bypass pipe 50 is replaced when the internal combustion engine 2 is stopped. A lean atmosphere is maintained. Next, heating of the sensor element 30 is started (step S106). The heating of the sensor element 30 is performed by controlling the voltage applied to the heater 42 by the control device 24.

  Next, it is determined whether or not the sensor element 30 has reached the activation temperature (step S108). The temperature of the sensor element 30 has a correlation with the impedance of the sensor element 30, and the impedance of the sensor element 30 decreases as the temperature of the sensor element 30 increases. Utilizing this property, here, the impedance of the sensor element 30 is detected, and it is determined whether or not the impedance has decreased to a predetermined activity determination value, whereby the activity determination of the sensor element 30 is executed. . If the sensor element 30 has not reached the activation temperature, the sensor element 30 is continuously heated (step S106).

  On the other hand, when the activity of the sensor element 30 is recognized in step S108, the valve 52 is opened (step S110). Thereby, the inlet of the bypass pipe 50 is opened. As a result, the exhaust gas discharged from the internal combustion engine 2 begins to flow into the bypass pipe 50, and the actual exhaust gas is also supplied to the surface of the sensor element 30 of the air-fuel ratio sensor 20. Therefore, the actual air-fuel ratio of the exhaust gas is detected by the air-fuel ratio sensor 20, and the air-fuel ratio feedback control of the internal combustion engine 2 based on the output of the air-fuel ratio sensor 20 is started. This routine is then terminated.

  As described above, according to the first embodiment, heating of the sensor element 30 is started, the adsorption species 54 adsorbed on the surface of the sensor element 30 passes through the desorption temperature region, and until the activation temperature is reached, The periphery of the sensor element 30 can be kept in a lean atmosphere close to the atmosphere. By making the concentration of the lean gas around the sensor element 30 in this way, the rich gas generated by the adsorbed species 54 desorbed from the surface of the sensor element 30 can be neutralized earlier. Therefore, the influence of the adsorbed species 54 can be eliminated at an early stage after the internal combustion engine 2 is started, and air-fuel ratio control based on the output of the air-fuel ratio sensor 20 can be started quickly.

  Further, according to the first embodiment, the exhaust gas does not flow into the bypass pipe 50 from the start of the internal combustion engine 2 until the activation determination of the sensor element 30 is performed, and the surface of the sensor element 30 is exhaust gas. It is supposed not to touch. Accordingly, it is possible to prevent the surface of the sensor element 30 from getting wet when the internal combustion engine is started. In addition, when the sensor element 30 is in a state of being wetted by using the attachment passage structure of the bypass pipe 50 and the valve 52, the sensor element 30 is wetted by closing the valve 52. Can be prevented. In this case, when the water generation condition of the sensor element 30 is avoided, by opening the valve 52, the air-fuel ratio sensor 20 can be normally operated again to detect the oxygen concentration of the exhaust gas.

  In the first embodiment, the case where the bypass pipe 50 is installed at the center of the exhaust manifold 12 has been described. However, in the present invention, the atmosphere around the sensor element 30 is not limited to the bypass pipe 50 arranged in this way, and the atmosphere around the sensor element 30 is temporarily made leaner than the atmosphere outside the sensor element 30. Anything can be used.

  8 to 11 are schematic views for explaining examples of other attachment passage structures in the first embodiment. In the first example shown in FIG. 8, the exhaust manifold 12 has a branch pipe 150 branched from the exhaust manifold 12 at the attachment position of the air-fuel ratio sensor 20. A valve 152 is provided near the inlet of the branch pipe 150. The air-fuel ratio sensor 20 is assembled in the branch pipe 150 on the downstream side of the valve 152 installation position so that the sensor element 30 protected by the cover 44 is exposed in the branch pipe 150. Also in such a mounting passage structure, as shown in the time chart of FIG. 6, the valve 152 is controlled to be closed only during the activation determination of the sensor element 30 immediately after the start of the internal combustion engine 2 is started. As a result, the periphery of the sensor element 30 is kept in a lean atmosphere immediately after the start of the internal combustion engine 2 until the activation determination, that is, while the temperature of the sensor element 30 passes through the adsorption temperature range where the adsorbed species 54 is desorbed. Be drunk. Therefore, even with the structure as shown in FIG. 8, hydrogen generated from the adsorbed species 54 released until the sensor element 30 is activated can be reliably neutralized at an early stage.

  9 to 11 show a cross section perpendicular to the gas flow direction of another mounting structure in the first embodiment. In the second example shown in FIG. 9, a bypass pipe 250 separated from the exhaust manifold 12 is provided at a position where the air-fuel ratio sensor 20 is attached in the exhaust manifold 12. The bypass pipe 250 is formed in a vertically long oval shape in the cross section of FIG. 9, and is disposed so as to contact the inner wall of the exhaust manifold 12 at the upper and lower positions in FIG. 9. The air-fuel ratio sensor 20 is assembled so that the sensor element 30 protrudes into the bypass pipe 250 at this contact position. A valve 252 is provided at the inlet of the bypass pipe 250, and opening / closing is controlled as described in the first embodiment. Even with such a structure, it is possible to obtain the same effect as that of the attachment passage structure shown in FIGS. In addition, it is preferable that the upper part of the sensor element 30 of the air-fuel ratio sensor 20 is actually in the atmosphere. According to this structure, the upper part of the sensor element 30 can be arranged in the atmosphere. .

  In the third example shown in FIG. 10, a bypass pipe 350 separated from the exhaust manifold 12 is provided at the attachment position of the air-fuel ratio sensor 20 in the exhaust manifold 12. The bypass pipe 350 is formed in a vertically long circular shape in the cross section of FIG. 10, and is disposed so as to contact the inner wall of the exhaust manifold 12 at an upper position in FIG. 10. The air-fuel ratio sensor 20 is assembled at this contact position so that the inside of the sensor element 30 protrudes into the bypass pipe 350. A valve 352 is provided at the inlet of the bypass pipe 350, and opening / closing is controlled as described in the first embodiment. Even with such a structure, it is possible to obtain the same effect as that of the attachment passage structure shown in FIGS. In addition, it is preferable that the upper part of the sensor element 30 of the air-fuel ratio sensor 20 is actually in the atmosphere, and this part also allows the upper part of the sensor element 30 to be arranged in the atmosphere.

  In the fourth example shown in FIG. 11, the exhaust manifold 12 includes a branch pipe 450 branched at the air-fuel ratio sensor 20 mounting position in the air-fuel ratio sensor 20 mounting position in the exhaust manifold 12. The branch pipe 450 is a semicircular pipe branched by a branch wall surface provided at the center of the exhaust manifold 12. The air-fuel ratio sensor 20 is assembled to the branch pipe 450 so that the inside of the sensor element 30 protrudes into the branch pipe 450 and the upper part of the sensor element 30 protrudes. A valve 452 is provided at the inlet of the bypass pipe 450, and opening / closing is controlled as described in the first embodiment. Even with such a structure, it is possible to obtain the same effect as the mounting passage structure shown in FIGS. 3 and 8 and to prevent the upper portion of the sensor element 30 of the air-fuel ratio sensor 20 from being exposed in the pipe. Can do.

  Further, the attachment passage structure of the air-fuel ratio sensor 20 is not limited to that shown in FIG. 3 or FIGS. If the atmosphere around the sensor element 30 is isolated from at least the atmosphere around the sensor element 30 from the start of the start until the activation determination, the mounting passage structure can be separated from other attachments. A passage structure may be used. At this time, as shown in FIGS. 9 to 11, it is preferable that the upper portion of the sensor element 30 of the air-fuel ratio sensor 20 is not exposed to the exhaust gas. In addition, the present invention is not limited to the mounting passage structure that isolates the atmosphere around the sensor element 30 as described above. For example, if a lean atmosphere can be temporarily created around the sensor element 30, other methods are used. Also good.

  In the present invention, the case where the air-fuel ratio sensor 20 is used has been described. However, the present invention is not limited to this. For example, the attachment passage structure shown in FIG. 3 or FIGS. 8 to 11 is provided in the exhaust pipe 18 and applied to the oxygen sensor 22. It may be a thing.

  For example, in the first embodiment, the “atmosphere generating means” of the present invention is realized by the bypass pipe 50 and the valve 52. In the first embodiment, the “atmosphere control means” of the present invention is realized by executing step 104. Further, by executing step S108, the “temperature detection means” and the “activity determination means” of the present invention are realized. Further, for example, in the first embodiment, the exhaust manifold 12 corresponds to the “exhaust passage” of the present invention, and the air-fuel ratio sensor 20 and the sensor element 30 correspond to the “exhaust gas sensor” and “sensor element” of the present invention, respectively. The bypass pipe 50 and the valve 52 correspond to the “bypass pipe” and the “valve” of the present invention, respectively.

Embodiment 2. FIG.
FIG. 12 is a schematic diagram for explaining a sensor mounting passage structure according to Embodiment 2 of the present invention. FIG. 12 shows a structure in which the air-fuel ratio sensor 20 is attached using a catalyst purification device having an HC adsorption catalyst. The system in the second embodiment is the same as that shown in FIG. 1 except that the catalyst purification device 60 shown in FIG. 12 is connected in place of the catalytic converter 16 in the system of FIG. 1 and the air-fuel ratio sensor 20 is installed in the catalyst purification device 60. It is the same as the system 1.

  Specifically, as shown in FIG. 12, the catalyst purification device 60 is connected to one end of the exhaust manifold 12 instead of the catalytic converter 16. Cooling fins 62 are arranged on the upstream side in the catalyst purification device 60. An HC adsorption catalyst 64 is installed on the downstream side of the cooling fin 62. A three-way catalyst 66 is built in the downstream side of the HC adsorption catalyst 64. A bypass pipe 68 that passes through the cooling fin 62 and the HC adsorption catalyst 64 in the direction in which the exhaust gas flows and is connected to the three-way catalyst 66 is disposed. A valve 70 is provided at the upstream inlet of the bypass pipe 68. An air-fuel ratio sensor 20 is installed on the downstream side of the valve 70 in the bypass pipe 68. The air-fuel ratio sensor 20 and the valve 70 are connected to the control device 24.

  In the catalyst purification device 60, the HC adsorption catalyst 64 has a property of adsorbing HC at a low temperature and desorbing HC at a high temperature. Therefore, in order to reliably remove HC in the exhaust gas, it is necessary to adsorb HC at a low temperature and keep the temperature of the HC adsorption catalyst 64 below the HC desorption temperature so that the adsorbed HC does not desorb. . For this reason, cooling fins 62 are provided upstream of the HC adsorption catalyst 64 so that the exhaust gas supplied to the HC adsorption catalyst 64 is cooled. Further, HC is discharged in a large amount during the warm-up process of the internal combustion engine 2, but the amount of discharge after the warm-up of the internal combustion engine 2 is small. Accordingly, until the warm-up of the internal combustion engine 2 is completed, the valve 70 is closed so that all exhaust gas passes through the outside of the bypass pipe 68, that is, through the cooling fins 62 and the HC adsorption catalyst 64. Since the temperature of the exhaust gas is low to some extent during the warm-up of the internal combustion engine 2, the exhaust gas can be reliably cooled to the HC desorption temperature or less by passing through the cooling fins 62. Therefore, HC in the exhaust gas is removed at a high purification rate during the warm-up process.

  On the other hand, after the warm-up of the internal combustion engine 2 in which the HC emission is reduced, the valve 70 is opened. As a result, most of the exhaust gas is introduced into the bypass pipe 68 and directly led to the three-way catalyst 66. The three-way catalyst 66 can purify the exhaust gas at a high exhaust gas temperature after warming up. At this time, a small amount of exhaust gas also flows into the outside of the bypass pipe 68, that is, the HC adsorption catalyst 64. However, a small amount of exhaust gas can be sufficiently cooled by the cooling fins 62. Therefore, the temperature rise of the HC adsorption catalyst 64 due to the exhaust gas inflow can be suppressed, and the HC adsorbed on the HC adsorption catalyst 64 can be prevented from desorbing. Further, since the amount of exhaust gas is small, even if the exhaust gas having a low temperature after passing through the HC adsorption catalyst 64 flows into the three-way catalyst 66, the temperature drop of the three-way catalyst 66 can be suppressed to be small. Therefore, a high purification rate by the three-way catalyst 66 can be maintained.

  As described above, opening and closing of the valve 70 of the bypass pipe 68 of the catalyst purification device 60 is executed in conjunction with warming up of the internal combustion engine 2. Further, the completion of warm-up of the internal combustion engine 2 and the activation determination of the sensor element 30 are realized almost in synchronization. That is, the time period from the start of the internal combustion engine 2 until the warm-up is determined is approximately the same as the time period after the start of the engine until the activation of the sensor element 30 is determined. Therefore, in the second embodiment, the air-fuel ratio sensor 20 is assembled and used in the bypass pipe 68 of the catalyst purification device 60. At this time, in addition to the warm-up process of the internal combustion engine 2, the valve 70 is controlled to be closed from immediately after the start of the internal combustion engine 2 until the activation determination of the sensor element 30. By controlling the valve 70 in this way, the opening and closing control of the valve 70 for exhaust gas purification by the catalyst purification device 60 is executed, and the sensor element 30 and its surroundings are in a lean atmosphere when the warm-up process of the internal combustion engine 2 is necessary. Can be kept in. Accordingly, it is possible to realize a high purification rate by the catalyst purification device 60, to quickly recover the influence of the adsorbed species 54 of the air-fuel ratio sensor 20, and to execute accurate air-fuel ratio control quickly.

  FIG. 13 is a flowchart for illustrating a control routine executed by the control device in the second embodiment of the present invention. The routine of FIG. 13 is the same as the routine of FIG. 7 except that step S202 is executed after step S108 and before step S110. Specifically, after the sensor activity is determined in step S108, it is determined whether the internal combustion engine 2 has been warmed up (step S202). Whether or not the warm-up has been completed is determined, for example, based on whether or not the integrated intake air amount is equal to or greater than a predetermined value. If it is determined in step S202 that the warm-up has not been completed, the warm-up determination is continued, and the valve 70 is kept closed until the completion of the warm-up is confirmed. On the other hand, when the completion of warm-up is recognized, the valve 70 is opened (step S110). As a result, the inflow of exhaust gas into the bypass pipe 68 is started, and detection of the actual exhaust gas concentration is started by the air-fuel ratio sensor 20. Most of the exhaust gas passes through the bypass pipe 68 and is sent directly to the three-way catalyst 66. Therefore, the exhaust gas can be reliably purified in the three-way catalyst 66, and the HC adsorbed on the HC adsorption catalyst flows into the exhaust gas at a high temperature. Detachment can be prevented.

  Further, according to the second embodiment, the air-fuel ratio sensor 20 is installed using the bypass pipe 68 of the catalyst purification device 60. This makes it possible to easily eliminate the output deviation due to the adsorbed species 54 of the air-fuel ratio sensor 20 at an early stage without providing a separate attachment passage structure such as the bypass pipe 68, and to improve the purification rate by the catalyst purification device 60. Can be planned.

  In the routine of FIG. 13, the control for opening the valve 70 has been described only when both the warm-up completion of the internal combustion engine 2 and the activation determination of the sensor element 30 are established. However, the present invention is not limited to this. For example, when priority is given to purification by the HC adsorption catalyst 64 and the three-way catalyst 66, the valve 70 may be opened only by the completion of the warm-up completion condition. . On the other hand, when priority is given to the completion of the activation of the sensor element 30 and the early stabilization of the air-fuel ratio control, the valve 70 may be opened only by determining the activation of the sensor element 30.

  The arrangement positions of the HC adsorption catalyst 64 and the bypass pipe 68 are not limited to this. In the present invention, any other arrangement structure may be used as long as it has a bypass pipe that is closed by closing the valve 70 for a certain period immediately after starting the internal combustion engine 2.

  For example, the “warm-up determination unit” of the present invention is realized by executing step S202 in the second embodiment. Further, for example, the HC adsorption catalyst 64 and the three-way catalyst 66 correspond to the “HC adsorption catalyst” and the “three-way catalyst” of the present invention, respectively, and the bypass pipe 68 and the valve 70 are respectively the “bypass pipe” of the present invention. , Corresponds to "valve".

  In the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., unless otherwise specified or clearly specified in principle, the number referred to It is not limited. Further, the structures described in the embodiments, steps in the method, and the like are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

It is a schematic diagram for demonstrating the system configuration | structure in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the air fuel ratio sensor in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the attachment passage structure of the air fuel ratio sensor in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the attachment passage structure of the air fuel ratio sensor in Embodiment 1 of this invention. It is a figure for demonstrating the mechanism of adsorption | suction of the adsorption | suction species adsorb | sucked to a sensor element. It is a time chart for demonstrating valve opening / closing timing in Embodiment 1 of this invention. It is a flowchart for demonstrating the control routine which a control apparatus performs in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the other attachment channel | path structure of the air fuel ratio sensor in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the other attachment channel | path structure of the air fuel ratio sensor in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the other attachment channel | path structure of the air fuel ratio sensor in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the other attachment channel | path structure of the air fuel ratio sensor in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the structure of the catalyst purification apparatus in Embodiment 2 of this invention. It is a flowchart for demonstrating the control routine which a control apparatus performs in Embodiment 2 of this invention.

Explanation of symbols

2 Internal combustion engine 4 Intake port 6 Intake manifold 8 Fuel injection valve 10 Exhaust port 12 Exhaust manifold 14 Three-way catalyst 16 Catalytic converter 18 Exhaust pipe 20 Air-fuel ratio sensor 22 Oxygen sensor 24 Control device 30 Sensor element 32 Diffusion resistance layer 34 Exhaust side electrode 36 Solid Electrolyte Layer 38 Atmosphere Side Electrode 40 Atmosphere Chamber 42 Heater 44 Cover 46 Ventilation Hole 50, 250, 350 Bypass Pipe 150, 450 Branch Pipe 52, 152, 252, 352, 452 Valve 54 Adsorption Type 60 Catalyst Purifier 62 Cooling Fin 64 HC adsorption catalyst 66 Three-way catalyst 68 Bypass pipe 70 Valve

Claims (5)

An exhaust gas sensor control device mounted in an exhaust passage of an internal combustion engine,
The exhaust gas sensor includes a sensor element having a function of pumping oxygen,
Atmosphere generating means for making the atmosphere around the sensor element a lean atmosphere;
In the warm-up process of the sensor element, atmosphere control means for controlling the periphery of the sensor element to a lean atmosphere;
A sensor control device comprising: Temperature detecting means for detecting the temperature of the sensor element;
Activity determination means for determining whether or not the temperature of the sensor element has reached an activation temperature,
The atmosphere control means controls the atmosphere around the sensor element to a lean atmosphere from the start of warming-up of the sensor element until it is determined that the temperature of the sensor element has reached the activation temperature. The sensor control device according to claim 1, characterized in that: The atmosphere generating means includes
A bypass pipe that is connected to the exhaust passage and is arranged so that the exhaust gas flows in, the exhaust gas sensor is installed, and a space in the exhaust passage and a space around the sensor element;
A valve that is disposed at an exhaust gas inlet of the bypass pipe and opens and closes the bypass pipe,
The sensor control apparatus according to claim 1, wherein the atmosphere control unit controls the atmosphere in the bypass pipe to a lean atmosphere by closing the valve during a warm-up process of the sensor element. Warm-up determination means for determining whether or not the warm-up of the internal combustion engine has been completed,
The atmosphere generating means includes
An HC adsorption catalyst installed in the exhaust passage;
A three-way catalyst disposed downstream of the HC adsorption catalyst;
Connected to the exhaust passage and arranged so that the exhaust gas flows in, the exhaust gas sensor is installed, the HC adsorption catalyst and a space around the sensor element are partitioned, and the ternary A bypass pipe connected to the catalyst;
A valve disposed at an inlet of the bypass pipe and opening and closing the bypass pipe,
The atmosphere control means controls the atmosphere in the bypass pipe to a lean atmosphere by closing the valve from the start of the internal combustion engine until the completion of warm-up of the internal combustion engine is determined. The sensor control device according to claim 1 or 2. An exhaust passage for exhaust gas discharged from the internal combustion engine;
A bypass pipe disposed in the exhaust passage, where an exhaust gas sensor is installed, and a space around a sensor element of the exhaust gas sensor, and a space in the exhaust passage;
A valve for opening and closing the exhaust gas inlet of the bypass pipe;
A sensor mounting passage structure comprising:

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