JP2007009845A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To calculate an accurate sensor output by correcting the deviation of the output due to the leak of oxygen from the gas seal part of an exhaust gas sensor and perform an air-fuel ratio control based on a calculated value. <P>SOLUTION: In this air-fuel ratio controller of an internal combustion engine, the air-fuel ratio is controlled based on the output of the exhaust gas sensor installed in the exhaust route of an internal combustion engine and detecting the air-fuel ratio of exhaust gases. The air-fuel ratio controller estimates the temperature of the gas seal part of the exhaust gas sensor and, based on that temperature, predicts the deviation of the output of the sensor due to the leak of a reference gas occurring at the gas seal part. A correction value for correcting the deviation of the output of the sensor is obtained to reflect it on a control to control the air-fuel ratio of the internal combustion engine. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine. More specifically, the present invention relates to an air-fuel ratio control device for an internal combustion engine that is suitable as a device for controlling the air-fuel ratio of the internal combustion engine based on the output of an exhaust gas sensor that is disposed in the exhaust path of the internal combustion engine and detects the air-fuel ratio of the exhaust gas. .

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 62-203050, an air-fuel ratio sensor is disposed in the exhaust path of the internal combustion engine, and the fuel injection amount is feedback controlled based on the output of the air-fuel ratio sensor. A system for controlling an air-fuel ratio of an internal combustion engine is known. The air-fuel ratio sensor has two electrodes, an exhaust gas side electrode exposed to the exhaust gas side and an atmosphere side electrode exposed to the atmosphere side, and both electrodes are arranged with a solid electrolyte layer interposed therebetween. When detecting the air-fuel ratio, a current corresponding to the difference in oxygen concentration between the exhaust gas and the atmosphere flows between the electrodes. The air-fuel ratio sensor detects the air-fuel ratio by detecting this current.

JP-A-62-203050

  In the above prior art system, in order to correctly detect the sensor current, it is necessary to reliably shut off the exhaust gas supplied to each electrode and the atmosphere to prevent leakage between the two gases. Also in the above-described conventional sensor, the atmosphere chamber that supplies the atmosphere to the atmosphere side electrode and the exhaust pipe in which the exhaust gas side electrode is disposed are sealed and blocked by the gas seal portion.

  However, the air-fuel ratio sensor is used in a wide temperature range of 200 ° C to 950 ° C. Moreover, the gas seal part is comprised by components with different thermal expansion coefficients, such as a metal component and a talc material. Specifically, the metal part has a larger coefficient of thermal expansion than the talc material. For this reason, when the air-fuel ratio sensor is heated to a high temperature, the metal portion is greatly expanded in comparison with other components, and as a result, the sealing performance of the gas seal portion may be lowered. Further, as the operating temperature of the air-fuel ratio sensor increases, the oxygen diffusion rate increases. For this reason, when the air-fuel ratio sensor is heated, oxygen tends to leak even from a slight gap, and the amount of leakage tends to increase. That is, it is considered that the gas sealing performance of the gas seal portion of the air-fuel ratio sensor is lowered by the thermal expansion of the metal and the increase of the oxygen diffusion rate accompanying the heating of the air-fuel ratio sensor.

  When the sealing performance of the gas seal portion is lowered, the atmosphere leaks near the exhaust gas side electrode. As a result, the oxygen concentration in the exhaust gas increases, the difference in oxygen concentration between the exhaust gas and the atmosphere decreases, and the output of the air-fuel ratio sensor shifts to the rich side. When the output deviation of the air-fuel ratio sensor occurs in this way, it is considered that the air-fuel ratio control may not be highly accurate.

  Therefore, in order to solve the above-mentioned problems, the present invention corrects an output shift accompanying a change in gas sealing performance of an exhaust gas sensor and improves an air-fuel ratio control apparatus for an internal combustion engine so as to obtain an accurate sensor output. Is to provide.

In order to achieve the above object, a first aspect of the present invention provides an air-fuel ratio control apparatus for an internal combustion engine that controls the air-fuel ratio based on the output of an exhaust gas sensor that is installed in the exhaust path of the internal combustion engine and detects the air-fuel ratio of the exhaust gas. The exhaust gas sensor is
A reference gas chamber into which a reference gas is introduced; a reference gas side electrode disposed in the reference gas so as to be exposed to the reference gas;
An exhaust gas side electrode disposed in the exhaust path so as to be exposed to the exhaust gas;
A gas seal portion that shuts off the reference gas chamber and the exhaust path,
The air-fuel ratio control device includes:
Temperature estimating means for estimating the temperature of the gas seal part;
Correction value calculating means for calculating a correction value for correcting an output deviation of the exhaust gas sensor based on the temperature of the gas seal portion;
Control means for reflecting the correction value in the control of the air-fuel ratio;
It is characterized by providing.

The second invention is the first invention, further comprising a cooling water temperature detecting means for detecting a cooling water temperature of the internal combustion engine,
The temperature estimating means includes
The temperature of the gas seal portion is estimated according to the cooling water temperature.

The third invention is the second invention, further comprising an annealing value calculation means for calculating an annealing value of the cooling water temperature,
The temperature estimation means estimates the temperature of the gas seal portion using the annealing value as the cooling water temperature.

Moreover, 4th invention is 2nd or 3rd invention,
The correction value for correcting the output deviation is shown as a function of the first correction value function as a function of the cooling water temperature before warming up the internal combustion engine and a function of the cooling water temperature after warming up the internal combustion engine. Correction value function storage means for storing a second correction value function;
Warm-up determination means for determining whether or not the internal combustion engine has reached a warm-up state,
The correction value calculating means includes
When it is determined that the internal combustion engine has reached a warm-up state, the correction value is calculated based on the second correction value function,
When it is determined that the internal combustion engine has not reached the warm-up state, the correction value is calculated based on the first correction value function.

The fifth invention is the fourth invention, wherein
A warm-up cumulative air amount function storage means for storing the cumulative intake air amount necessary to reach the warm-up state as a warm-up cumulative intake air amount function with respect to the starting coolant temperature;
Integrated air amount detection means for detecting the integrated intake air amount of the internal combustion engine;
A starting water temperature detecting means for detecting a cooling water temperature when starting the internal combustion engine;
A warm-up time cumulative intake air amount setting means for setting the warm-up time cumulative intake air amount according to the start-up water temperature detection means based on the warm-up time cumulative intake air amount function;
The warm-up determination means determines that the warm-up state has been reached when the cumulative intake air amount is equal to or greater than the warm-up cumulative intake air amount.

According to a sixth invention, in any one of the first to fifth inventions, an output to be generated from the exhaust gas sensor when the exhaust gas side electrode is exposed to a target air-fuel ratio is set as a base target value. Base target value storage means for storing,
The control means includes base target value correction means for correcting the base target value based on the correction value.

In a seventh aspect based on the sixth aspect, the base target value storage means stores the base target value as a base target value function with respect to the temperature of the sensor element,
Element temperature estimating means for estimating the temperature of the sensor element of the exhaust gas sensor;
Setting means for setting the base target value according to the temperature of the sensor element based on the base target value function;
It is characterized by providing.

In an eighth aspect based on the sixth or seventh aspect, the exhaust gas sensor is disposed downstream of the three-way catalyst and corrects the output of the upstream air-fuel ratio sensor disposed upstream of the three-way catalyst. A downstream oxygen sensor,
Deviation calculating means for calculating a deviation between the control target value corrected by the base target value correcting means and the output of the oxygen sensor;
Sensor correction amount calculating means for calculating a sensor correction amount for the output of the upstream air-fuel ratio sensor according to the deviation;
Upstream sensor correction means for correcting the output of the upstream air-fuel ratio sensor according to the sensor correction amount;
It is characterized by providing.

Further, a ninth invention comprises any one of the first to fifth inventions, comprising sensor output detection means for detecting a sensor output of the exhaust gas sensor,
The control device includes a sensor output correction unit that corrects the sensor output based on the correction value.

In a tenth aspect based on the ninth aspect, the exhaust gas sensor is disposed downstream of the three-way catalyst, and downstream oxygen for correcting the output of the upstream air-fuel ratio sensor disposed upstream of the three-way catalyst. A sensor,
Oxygen sensor output target value storage means for storing, as an oxygen sensor output target value, an output target value of the oxygen sensor for controlling the air-fuel ratio of the internal combustion engine to a target air-fuel ratio;
Deviation calculating means for calculating a deviation between the sensor output corrected by the sensor output correcting means and the oxygen sensor output target value;
Upstream sensor output correction value calculating means for calculating an upstream sensor output correction value for the output of the upstream air-fuel ratio sensor according to the deviation;
Upstream air-fuel ratio sensor correction means for correcting the output of the upstream air-fuel ratio sensor according to the upstream sensor output correction value;
It is characterized by providing.

  According to the first invention, the correction value is calculated according to the temperature of the gas seal portion of the exhaust gas sensor, and this correction value is reflected in the control. Therefore, it is possible to correct the output deviation of the exhaust gas sensor due to gas leakage in the gas seal portion that occurs according to the temperature of the gas seal portion. Therefore, the air-fuel ratio can be accurately controlled even when the sealing performance of the gas seal portion changes depending on the usage environment of the exhaust gas sensor.

  Further, according to the second and third inventions, the control device estimates the temperature of the gas seal portion according to the cooling water temperature. Therefore, the temperature of the gas seal portion can be easily estimated without requiring a complicated system.

  According to the fourth and fifth inventions, the control device stores the function of the correction value according to the coolant temperature as a different function before and after the internal combustion engine reaches the warm-up state. Therefore, it is possible to cope with a case where the coolant temperature and the gas leak amount have different correlations before and after warming up the internal combustion engine, and accurate air-fuel ratio control can be performed.

  According to the sixth aspect, the base target value can be corrected based on the calculated correction value. Therefore, the air-fuel ratio can be accurately controlled even when the sealing performance of the gas seal portion changes depending on the usage environment of the exhaust gas sensor.

  According to the seventh aspect, the base target value is stored as a function corresponding to the sensor element temperature, and is set according to the sensor element temperature. Therefore, the air-fuel ratio can be accurately controlled in response to a change in the output characteristics of the sensor due to a change in the sensor element temperature.

  According to the eighth invention, the exhaust gas sensor is disposed downstream of the three-way catalyst, and is used as a downstream oxygen sensor that corrects the output of the upstream air-fuel ratio sensor disposed on the upstream side of the three-way catalyst. Accordingly, since more accurate control is required, an accurate detection result can be obtained and accurate air-fuel ratio control can be performed in the downstream oxygen sensor that needs to eliminate the influence of leak gas.

  Also. According to the ninth aspect, the sensor output can be corrected based on the calculated correction value. Therefore, even when the sealing performance of the gas seal portion changes depending on the usage environment of the exhaust gas sensor, an accurate output result can be obtained and the air-fuel ratio can be accurately controlled.

  According to the tenth aspect of the invention, the exhaust gas sensor is used as a downstream oxygen sensor that is arranged downstream of the three-way catalyst and corrects the output of the upstream air-fuel ratio sensor arranged on the upstream side of the three-way catalyst. Accordingly, since more accurate control is required, an accurate detection result can be obtained and accurate air-fuel ratio control can be performed in the downstream oxygen sensor that needs to eliminate the influence of leak 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.
[Hardware Configuration of 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. An intake branch pipe 6 is connected to the intake port 4 of each cylinder of the internal combustion engine 2. The intake branch pipe 6 is provided with a fuel injection valve 8. The exhaust port 12 of each cylinder of the internal combustion engine 2 is connected to a common exhaust manifold 14. The exhaust manifold 14 is connected to a catalytic converter 18 that contains a three-way catalyst 16. The catalytic converter 18 is connected to a muffler (not shown) via the exhaust pipe 20. An air-fuel ratio sensor 22 is disposed in the exhaust manifold 14 on the upstream side of the three-way catalyst 16. The air-fuel ratio sensor 22 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 24 is disposed in the exhaust pipe 20 downstream of the three-way catalyst 16. The oxygen sensor 24 is a sensor whose output value changes stepwise in the vicinity of the theoretical air-fuel ratio. The fuel injection valve 8, the air-fuel ratio sensor 22 and the oxygen sensor 24 are connected to the control device 30.

2 and 3 are schematic diagrams for explaining the oxygen sensor 24 used in the system of the first embodiment. As shown in FIG. 2, the oxygen sensor 24 includes a sensor element 40. The sensor element 40 has a tubular structure with one end closed. The outer surface of the tubular structure is covered with a porous protective layer 42. The porous protective layer 42 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. ing. An exhaust gas side electrode 44 is provided inside the porous protective layer 42. The exhaust gas side electrode 44 is exposed to the exhaust gas that has passed through the porous protective layer 42. A solid electrolyte layer 46 is provided inside the exhaust gas side electrode 44. An atmosphere side electrode 48 is provided on the inner side of the solid electrolyte layer 46, that is, on the surface of the solid electrolyte layer 46 opposite to the exhaust gas side electrode 44. The exhaust gas side electrode 44 and the atmosphere side electrode 48 are electrodes made of a metal having high catalytic action such as Pt. An atmosphere chamber 50 is formed inside the sensor element 40. The atmosphere chamber 50 has a structure in which the atmosphere is guided. Therefore, the atmosphere side electrode 48 is exposed to the atmosphere. A heater 52 is installed in the atmospheric chamber 50.

  FIG. 3 is a schematic diagram for explaining an installation state of the oxygen sensor 24 to the exhaust pipe 20. As shown in FIG. 3, the sensor element 40 configured as described above is covered with a cover 54 in the exhaust pipe 20. The cover 54 is provided with a plurality of vent holes (not shown) for introducing exhaust gas therein. The cover 54 is fixed in the exhaust pipe 20 by a housing 56. More specifically, the housing 56 is engaged with the cover 54 at a portion disposed on the exhaust pipe 20 side, and is held in the exhaust pipe 20 with the upper edge portion of the cover 54 being caulked.

  The sensor element 40 and the heater 52 are installed in the cover 54 and the housing 56. On the outer peripheral surface of the solid electrolyte layer 46 of the sensor element 40, a solid electrolyte layer convex portion 58 protruding outward is provided. On the other hand, a housing convex portion 60 is provided on the inner peripheral surface of the housing 56 so as to protrude further inward of the inner peripheral circle. As shown in FIG. 3, the lower portion of the solid electrolyte layer convex portion 58 is supported by the upper portion of the housing convex portion 60, whereby the sensor element 40 is fixed and supported within the housing 56 and the cover 54.

  The solid electrolyte layer convex portion 58 and the housing convex portion 60 are sealed with a gas seal portion 62. Specifically, the gas seal portion 62 has a metal packing 64. A filling portion 66 is disposed on the solid electrolyte layer convex portion 58. The filling portion 66 is configured by filling a gap between the upper portion of the solid electrolyte layer convex portion 58 and the housing 56 with a talc material. An insulating glass 68 is disposed on the filling portion 66. A caulking metal ring 70 is disposed on the insulating glass 68. With this structure, the gas seal portion 62 including the metal packing 64, the filling portion 66, the insulating glass 68, and the metal ring 70 is caulked and fixed between the solid electrolyte layer 46 in the housing 56 and the housing 56. . That is, due to the structure of the gas seal portion 62 and the housing 56, the atmosphere chamber 50 and the exhaust pipe 20 are blocked, and leakage between the atmosphere in the atmosphere chamber 50 and the exhaust gas in the cover 54 is prevented. . In addition, a heater holding portion 72 is disposed inside the solid electrolyte layer 46, whereby the heater 52 is held in the atmospheric chamber 50.

  FIG. 4 is a block diagram showing an electrical connection relationship between the oxygen sensor 24 and the control device 30. As shown in FIG. 4, the sensor element 40 can be equivalently expressed using a resistance component and an electromotive force component. The heater 52 can be expressed equivalently using a resistance component. The control device 30 has a sensor element drive circuit 74. A sensor element drive circuit 74 is connected to the sensor element 40. The sensor element driving circuit 74 detects a bias control circuit for applying a desired bias voltage to the sensor element 40, a sensor current flowing through the sensor element 40, and a voltage generated between the electrodes of the sensor element 40. And a detection circuit.

  A microcomputer (hereinafter referred to as “microcomputer”) 80 is connected to a bias control circuit included in the sensor element driving circuit 74 via a low-pass filter (LPF) 76 and a D / A converter 78. The microcomputer 80 can instruct a voltage to be applied to the sensor element 40 to the bias control circuit via these elements. A microcomputer 80 is connected to the detection circuit via a D / A converter 82. The microcomputer 80 can read the detection result of the detection circuit via the D / A converter 82. During the air-fuel ratio measurement, a sensor current corresponding to the oxygen concentrations of the exhaust gas and the atmosphere flows through the sensor element 40. At this time, the microcomputer 80 can detect the air-fuel ratio by reading the voltage generated between the exhaust gas side electrode 44 and the atmosphere side electrode 48 via the detection circuit.

  The bias control circuit can apply an impedance detection voltage to the sensor element 40 in accordance with a command from the microcomputer 80. When an impedance detection voltage is applied to the sensor element 40, a change occurs in the sensor current corresponding to the change in the applied voltage. At this time, the ratio between the change amount of the applied voltage and the change amount of the sensor current becomes a value corresponding to the element impedance of the sensor element 40. Using this, the microcomputer 80 can calculate the element impedance of the sensor element 40 based on the sensor current generated under the condition where the impedance detection voltage is applied.

  A heater control circuit 84 is connected to the heater 52. A microcomputer 80 is connected to the heater control circuit 84. The heater control circuit 84 can receive a command supplied from the microcomputer 80, supply a drive signal corresponding to the command to the heater 52, and cause the heater 52 to generate a desired amount of heat.

[Basic control of air-fuel ratio by system of Embodiment 1]
The system of Embodiment 1 controls the air-fuel ratio. More specifically, the output voltage of the upstream air-fuel ratio sensor 22 is corrected in accordance with the output of the downstream oxygen sensor 24 to obtain the air-fuel ratio control parameters. The correction value calculated from the output of the oxygen sensor 24 is set by PID control so that the air-fuel ratio obtained from the output of the air-fuel ratio sensor 22 matches the target air-fuel ratio.

  FIG. 5 is a flowchart for illustrating a control routine executed by the control device according to the first embodiment of the present invention. In this routine, first, a sensor correction value calculation routine for the upstream air-fuel ratio sensor is executed according to the processing described later (step S100). By this routine, the sensor correction value ΔV for the upstream air-fuel ratio sensor is calculated.

Next, the output V22 of the upstream air-fuel ratio sensor ₂₂ is read (step S110). Controller 30, a voltage between the electrodes of the air-fuel ratio sensor 22 detected by the detection circuit, read as the output V ₂₂ of the air-fuel ratio sensor. Thereafter, the corrected output _{* V 22} obtained by correcting the output _{V 22} of the air-fuel ratio sensor 22 is calculated (step S112). Corrected output _{* V 22} includes an output _{V 22} of the air-fuel ratio sensor 22, the ΔV calculated in step S100, is calculated by the following equation (1).
* V ₂₂ = V ₂₂ + ΔV (1)
The correction output * V ₂₂ is a value that takes into account the correction value ΔV calculated from the output of the downstream oxygen sensor 24. In other words, the obtained corrected output * V ₂₂ is a value in which the deterioration with time and the output variation of the upstream air-fuel ratio sensor 22 are corrected.

Next, the fuel injection amount is calculated (step S114). Fuel injection amount is calculated using a correction output * V _22. The system of the first embodiment stores, for example, a fuel injection amount calculation method performed using modern control, and the fuel injection amount is calculated based on this method.

  Next, fuel injection is controlled based on the set fuel injection amount (step S116). More specifically, the control device 30 controls the fuel injection valve 8 to control the fuel injection amount to be injected. Thereby, the air-fuel ratio is controlled to be the target air-fuel ratio.

[Characteristic control of the first embodiment]
FIG. 6 is a graph showing the relationship between the element temperature of the oxygen sensor 24 and the impedance. In FIG. 6, the horizontal axis represents the element temperature (° C.), and the vertical axis represents the impedance (Ω). As shown in FIG. 6, the impedance of the sensor element 40 and the element temperature have a correlation, and the element temperature increases as the impedance decreases. The control device 30 stores the relationship between the element temperature and impedance of the sensor element 40 shown in FIG. The control device 30 can calculate the element temperature of the sensor element 40 from the stored relationship between the element temperature and the impedance.

  FIG. 7 is a graph showing the base target value Vbs of the oxygen sensor 24 with respect to the element temperature. In FIG. 7, the horizontal axis represents the element temperature, and the vertical axis represents the base target value. The base target value Vbs represents a sensor output corresponding to the element temperature when the air-fuel ratio of the internal combustion engine 2 is the target air-fuel ratio. However, this sensor output is an output when there is no leak in the gas seal portion 62. In the air-fuel ratio control by the control device 30 of the first embodiment, the air-fuel ratio is controlled to the target air-fuel ratio by controlling the output of the oxygen sensor 24 to match the base target value Vbs shown in FIG. . As shown in FIG. 7, the output characteristic of the sensor element 40 changes according to the element temperature. More specifically, the output characteristics of the sensor output change around an element temperature of 550 ° C. Therefore, the base target value Vbs is changed according to the element temperature in accordance with the change in the output characteristics. The control device 30 stores the relationship between the element temperature and the base target value Vbs as shown in FIG. 7 as a base target value Vbs map. Further, the base target value Vbs can be read according to the element temperature obtained from the impedance.

  Incidentally, as described above, in the oxygen sensor 24, the atmosphere chamber 50 of the sensor element 40 and the exhaust gas in the cover 54 are blocked by the gas seal portion 62. However, the sealing performance of the gas seal portion 62 changes due to the temperature change of the gas seal portion 62. More specifically, since there is a difference in the coefficient of thermal expansion between the metal part of the gas seal portion 62 and the talc material or the like, a difference occurs in the amount of thermal expansion accompanying the temperature rise of the oxygen sensor 24, and the gas seal portion 62. The sealing performance of the is reduced. Further, as the temperature rises, the oxygen diffusion rate increases. Therefore, the difference in the expansion amount of each component of the gas seal portion 62 and the increase in the oxygen diffusion rate are combined, and the leak amount increases as the temperature of the gas seal portion 62 increases. When the amount of leak to the exhaust gas side of the atmosphere increases, the oxygen concentration in the exhaust gas changes, and the output of the oxygen sensor 24 shifts to the lean side.

  The oxygen sensor 24 is installed in the exhaust pipe 20 downstream of the three-way catalyst 16. Therefore, the exhaust gas to be detected is the gas near the stoichiometric gas purified by the three-way catalyst 16. The output of the oxygen sensor 24 changes suddenly near the stoichiometric range. For this reason, even if a small amount of oxygen leaks from the gas seal portion 62 to the exhaust gas side, the effect of the leaked oxygen on the output of the oxygen sensor 24 is significant. Therefore, this system predicts the oxygen leak amount in the oxygen sensor 24 and sets a value obtained by correcting the base target value Vbs as the final control target value Vtg.

  FIG. 8 is a graph for explaining the temperature relationship between the oxygen leak amount and the gas seal portion 62. As shown in FIG. 8, the gas seal part 62 and the oxygen leak amount have a correlation. More specifically, the oxygen leak amount increases as the temperature of the gas seal portion 62 increases.

  FIG. 9 is a graph showing the temperature of the gas seal portion 62 and the temperature of the cooling water temperature of the internal combustion engine 2. In FIG. 9, the horizontal axis represents time (seconds), the left vertical axis represents the cooling water temperature (° C.), and the right vertical axis represents the temperature (° C.) of the gas seal portion 62. As shown in FIG. 9, the temperature of the gas seal portion 62 and the cooling water temperature of the internal combustion engine 2 have a correlation. Specifically, the temperature change with respect to the coolant temperature and the elapsed time of the gas seal portion 62 is relatively abrupt between the start of the internal combustion engine 2 and the complete warm-up. On the other hand, after the complete warm-up, the cooling water temperature and the temperature change of the gas seal portion 62 become very gradual as compared with the complete warm-up. Thus, the temperature of the gas seal portion 62 and the coolant temperature of the internal combustion engine 2 change in conjunction with each other. Therefore, the temperature of the gas seal portion 62 can be predicted from the relationship between the elapsed time and the cooling water temperature or the temperature of the gas seal portion 62 based on the cooling water temperature.

  The temperature change rate with respect to the elapsed time is different between the cooling water temperature and the temperature of the gas seal portion 62 in any case before the complete warm-up and after the complete warm-up. Further, the ratio of the change rate of the cooling water temperature with respect to the elapsed time and the change rate of the temperature of the gas seal portion 62 with respect to the elapsed time is also different between before the complete warm-up and after the complete warm-up. Therefore, the temperature change rate of the gas seal portion 62 with respect to the coolant temperature differs between before and after complete warm-up.

  FIG. 10 is a graph showing the relationship between the correction value Vrev considering the oxygen leak and the cooling water temperature. In FIG. 10, the horizontal axis represents the cooling water temperature, and the vertical axis represents the correction value Vrev. Here, the correction value Vrev is a value that should be subtracted from the base target value Vbs of the oxygen sensor 24, and is a value that corrects an output shift generated in the oxygen sensor 24 due to an oxygen leak amount. Therefore, the correction value Vrev is a value that changes in proportion to the temperature of the gas seal portion 62, similarly to the oxygen leak amount. As described above, the rate of change of the temperature of the gas seal portion 62 with respect to the cooling water temperature differs before and after complete warm-up. For this reason, when the correction value Vrev that changes in proportion to the temperature of the gas seal portion 62 is expressed as the correction value Vrev according to the coolant temperature, the rate of change of the correction value Vrev is different before and after complete warm-up. Become.

  More specifically, when the relationship between the coolant temperature and the correction value Vrev is calculated from the relationship between the coolant temperature and the temperature of the gas seal portion 62 before complete warm-up, the map of the correction value Vrev before complete warm-up is a correction value map. It can be represented by F1. On the other hand, the map of the correction value Vrev after complete warm-up can be represented by a correction value map F2 having a slope different from that of the correction value map F1, from the relationship of the coolant temperature to the temperature of the gas seal portion 62 after complete warm-up. In addition, since the correlation between the coolant temperature and the gas seal portion 62 is switched during complete warm-up, the intersection of the correction value maps F1 and F2 is during complete warm-up. The control device 30 stores the correction value maps F1 and F2. In calculating the correction value Vrev, it is determined whether it is before or after complete warm-up. The correction value map F1 is used before complete warm-up, and the correction value map F2 is used after complete warm-up.

FIG. 11 is a graph showing the relationship between the starting coolant temperature TW ₀ and the cumulative intake air amount until complete warm-up. In FIG. 11, the horizontal axis represents the starting coolant temperature TW ₀ and the vertical axis represents the cumulative intake air amount. In FIG. 11, the cumulative intake air amount represents a warm-up cumulative intake air amount (hereinafter referred to as “warm-up ΣGa ₀ ”) required until the internal combustion engine 2 is completely warmed up. As shown in FIG. 11, the warm-up ΣGa ₀ has a correlation with the starting coolant temperature TW ₀ . The control device 30 stores the relationship between the starting coolant temperature TW ₀ and the warm-up ΣGa ₀ shown in FIG. Further, control device 30 measures the accumulated intake air amount (hereinafter referred to as “integrated Ga”) of internal combustion engine 2 and compares accumulated Ga with warm-up ΣGa ₀ to determine whether the fully warmed-up state has been reached. It can be determined whether or not.

[Setting of control target value by control device of embodiment 1]
FIG. 12 shows a flowchart of the startup coolant temperature storage routine. In order to set the control target value, the start-time coolant temperature TW ₀ is required, so the routine shown in FIG. 12 is first executed. In this routine, first, it is determined whether or not 50 msec has elapsed after the ignition switch IG of the internal combustion engine 2 is turned on (step S122). As a result, if the establishment of the conditions is recognized, a determination is made at the start of the internal combustion engine 2, the cooling water temperature of the current of the internal combustion engine 2 is stored as the starting time coolant temperature TW ₀ (step S124). On the other hand, if the above condition is not satisfied, the current processing cycle is terminated without any processing.

  FIG. 13 is a flowchart for explaining a sensor correction value calculation routine executed as the process of step S100 of FIG. In this routine, first, the impedance is calculated (step S130). The impedance is calculated by supplying an impedance detection voltage to the sensor element 40 and measuring the sensor current flowing in response thereto. Next, the element temperature is calculated according to the calculated impedance (step S132). The element temperature is calculated based on a map of the relationship between the impedance and the element temperature stored in the control device 30 (see FIG. 6). Next, the base target value Vbs is calculated (step S134). More specifically, the base target value Vbs corresponding to the calculated element temperature is set based on a map (see FIG. 7) representing the relationship between the element temperature and the base target value Vbs stored in the control device 30. Is done.

Next, the cooling water temperature is measured (step S136). Next, an annealing value TW ₁ is calculated from the cooling water temperature (step S138). The annealing value TW ₁ is calculated by obtaining the average of the previous cooling water temperature annealing value TW ₂ stored when the routine of FIG. 13 was executed last time and the cooling water temperature measured this time. Next, the annealing value TW ₁ calculated in step S138 is stored in the control device 30 as the previous cooling water temperature annealing value TW ₂ (step S140). Stored moderation value TW ₂ is used to calculate a smoothed value when this routine is executed next time.

Next, the starting coolant temperature TW ₀ is read (step S142). Next, the integrated Ga is measured (step S144). The integrated Ga is obtained as an integrated amount of air taken into the internal combustion engine 2 from the start of the internal combustion engine 2. Next, the warm-up ΣGa ₀ is read (step S146). Specifically, it stored in the control unit 30, the map of the relationship between the startup cooling water temperature TW ₀ and warmed up ΣGa ₀ (see FIG. 11), the startup cooling water temperature TW ₀ read in step S142 The corresponding value is read as warm-up ΣGa ₀ . Next, it is determined whether or not the integrated Ga measured in step S146 is equal to or less than warm-up ΣGa ₀ (step S148). Thereby, it is determined whether it is before complete warm-up.

If it is determined in step S148 that the integrated Ga ≦ warm-up ΣGa ₀ is established, it is determined that the warm-up is not yet performed, and the correction value Vrev is calculated according to the correction value map F1 (see FIG. 10) (step S148). S150). More specifically, according to the control device 30 to the stored correction value map F1 (see FIG. 10), the correction value Vrev according to the smoothed value TW ₁ of the cooling water temperature is calculated. On the other hand, if establishment of accumulated Ga ≦ warm-up ΣGa ₀ is not recognized in step S150, it is determined that the warm-up has occurred, and the correction value Vrev is set according to the correction value map F2 (see FIG. 10) ( Step S152). More specifically, according to the control apparatus 30 stored correction value map in F2 (see FIG. 10), the correction value Vrev according to the smoothed value TW ₁ of the cooling water temperature is calculated.

Next, the control target value Vtg is calculated from the base target value Vbs calculated in step S134 and the correction value Vrev set in step S150 or S152 (step S154). Specifically, the control target value Vtg is calculated by subtracting the correction value Vrev from the base target value Vbs based on the following equation (2).
Vtg = Vbs-rev (2)

Then, the output _{V 24} of the oxygen sensor 24 is detected (step S156). More specifically, the control device 30 reads the voltage between the electrodes of the oxygen sensor 24 detected by the detection circuit as the output V ₂₄ of the oxygen sensor.

Next, a correction value ΔV ₂₄ for the output of the upstream air-fuel ratio sensor 22 is calculated (step S158). Specifically, a deviation ΔV ₂₄ (that is, ΔV ₂₄ = Vtg−V ₂₄ ) between the control target value Vtg calculated in step S154 and the oxygen sensor output V ₂₄ is calculated, and the air-fuel ratio sensor 22 is calculated from ΔV ₂₄ . A correction value ΔV for the output is calculated based on the following equation (3).
ΔV = KPΔV ₂₄ + KI (ΣΔV ₂₄ ) + KD (dΔV ₂₄ ) (3)
In Equation (1), KPΔV ₂₄ represents a proportional term, KI (ΣΔV ₂₄ ) represents an integral term, and KD (dΔV ₂₄ ) represents a differential term. KP, KI, and KD are gain coefficients for each term. In this correction value, the differential term and the proportional term are values that correct transient fluctuations, and the integral term is a value that corrects steady deviation.

  As described above, in the first embodiment, the base target value Vbs corresponding to the element temperature of the oxygen sensor 24 is corrected in consideration of the oxygen leak amount due to the temperature rise of the gas seal portion 62. Therefore, in particular, the oxygen sensor 24 on the downstream side of the three-way catalyst 16, which has a lean exhaust gas to be detected and is easily affected by oxygen leakage, can obtain a more accurate output.

In the first embodiment, the temperature of the gas seal portion 62 is estimated using the correlation between the cooling water temperature and the temperature of the gas seal portion 62, and correction is made based on the oxygen leak amount predicted from the temperature. Calculate the value. Therefore, it is possible to easily estimate the temperature of the gas seal part 62 without providing a temperature measuring means for the gas seal part 62 in particular. However, the temperature estimation means for the gas seal portion 62 in the present invention is not limited to this, and the temperature of the gas seal portion 62 may be estimated by other means. In the first embodiment, the case where the cooling water temperature annealing value TW ₁ is used has been described. However, the present invention is not limited to this. For example, the measured cooling water temperature may be directly used for calculating the correction value Vrev.

  Further, the relationship between the coolant temperature and the temperature of the gas seal portion 62 changes before and after the internal combustion engine 2 is completely warmed up. For this reason, in Embodiment 1, the case where the correction value map was switched before and after complete warm-up was described. Thereby, the output of the oxygen sensor 24 can be accurately corrected. However, the present invention may not switch maps. For example, if an average correction amount map that can be used before and after complete warm-up is used without switching maps, the base target value Vbs may be corrected with some oxygen leak amount. it can. Further, the control can be simplified by not switching the map.

Moreover, the case where the map of the relationship between the starting cooling water temperature TW ₀ and the warm-up ΣGa ₀ was used as a prediction method at the time of complete warm-up when switching the maps has been described. However, the prediction method at the time of complete warm-up is not limited to this, and another method may be used.

  Further, as described above, since the downstream oxygen sensor 24 uses the lean exhaust gas purified by the three-way catalyst 16 as a measurement object, even a slight oxygen leak tends to cause an output shift. For this reason, the correction of the output deviation due to the oxygen leak as described in the first embodiment can effectively control the air-fuel ratio, particularly when applied to the downstream oxygen sensor (sub O2 sensor). However, the control in the present invention is not limited to the downstream oxygen sensor 24, but to the air-fuel ratio sensor or oxygen sensor upstream of the three-way catalyst 16, or an air-fuel ratio sensor or oxygen sensor installed at another position. You may apply. As a result, more precise control of the air-fuel ratio can be performed.

  Further, the gas seal portion 62 of the oxygen sensor 24 is not limited to the structure shown in FIG. The atmosphere chamber 50 and the exhaust gas side may be blocked by a gas seal portion having another structure. Further, although the case where the atmosphere is used as the reference gas has been described, the present invention is not limited to this. For example, instead of the atmosphere, a gas whose oxygen concentration has been clarified in advance is used as the reference gas. There may be. Further, in the above embodiment, when the number of each element, number, quantity, range, etc. is mentioned, it is mentioned unless otherwise specified or clearly specified in principle. The number 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.

  For example, in the first embodiment, the atmosphere chamber 50 and the atmosphere side electrode 48 correspond to the “reference gas chamber” and the “reference gas side electrode” of the present invention, respectively. For example, in the first embodiment, the control device 30 stores the map shown in FIG. 7, thereby realizing the “base target value storage unit”. Further, for example, in the first embodiment, the “temperature estimation means” of the present invention is realized by executing steps S136 and S138, and the “correction value calculation means” is realized by executing steps S150 and S152. By executing step S154, “control means” and “base target value correction means” are realized.

  Further, for example, in the first embodiment, the “element temperature estimating means” of the present invention is realized by executing steps S130 and S132, and the “setting means” is realized by executing step S134. Further, for example, in the first embodiment, by executing step S136, the “cooling temperature detecting means” of the present invention is realized, and by executing step S138, the “annealing value calculating means” is realized. Further, for example, in the first embodiment, the “correction value function storage means” of the present invention is realized by storing the map shown in FIG. Further, for example, in the first embodiment, the “warm-up determination unit” of the present invention is realized by executing step S148. Further, for example, in the first embodiment, by storing the map shown in FIG. 11, the “warm-up time integrated air amount function storage means” of the present invention is realized. Further, for example, in the first embodiment, by executing step S144, the “integrated air amount detecting means” of the present invention is realized, and by executing step S142, the “starting cooling water temperature detecting means” is realized. By executing step S146, the “warm-up time integrated air amount setting means” is realized. Further, for example, in the first embodiment, by executing step S158, the “deviation calculating means” and the “sensor correction amount calculating means” of the present invention are realized, and by executing step S112, “upstream sensor correcting means” Is realized.

Embodiment 2.
The hardware configuration of the second embodiment is the same as the hardware configuration of the first embodiment. The control device of the second embodiment performs the same control as that of the first embodiment except that the output deviation due to oxygen leak is corrected by correcting the value of the sensor output.

  The correction value Vrev shown in FIG. 10 is a value for setting the control target value Vtg by subtracting the output shortage of the oxygen sensor 24 caused by oxygen leak from the base target value Vbs. That is, it is a value for correcting the output deviation of the oxygen sensor on the control target value side. However, the correction value Vrev can also be regarded as an output shortage of the oxygen sensor 24 caused by oxygen leak. In the second embodiment, the correction value Vrev is regarded as a value for correcting the output shortage, and the correction value Vrev is directly added to the output of the oxygen sensor 24, thereby correcting the output of the oxygen sensor 24.

  FIG. 14 is a flowchart for illustrating a sensor correction value calculation routine executed by control device 30 in the second embodiment of the present invention. The routine of FIG. 14 is a routine that is executed in step S100 of FIG. 5 instead of the routine of FIG. The routine of FIG. 14 is the same as the routine of FIG. 13 except that steps S154 and S158 are not executed, and steps S202 and S204 are executed after step S156.

Specifically, in step S202, the sensor output _{V 24} detected in step S156 is corrected. More specifically, the sensor output _{* V 24} after correction, the sensor output _{V 24,} is calculated by adding the Vrev calculated in step S150 or S152. The corrected sensor output * V ₂₄ is expressed by the following equation (4).
* V ₂₄ = V ₂₄ + Vrev (4)

Next, a correction value ΔV for the output of the upstream air-fuel ratio sensor 22 is calculated (step S204). Specifically, a deviation ΔV ₂₄ (ΔV ₂₄ = Vbs− * V ₂₄ ) between the base target value Vbs calculated in step S134 and the corrected oxygen sensor output * V ₂₄ is calculated, and the air-fuel ratio is calculated from ΔV _24. A correction value ΔV for the output of the sensor 22 is calculated. Similar to step S158 of the first embodiment, the calculation formula uses formula (3).

The deviation ΔV ₂₄ calculated here is obtained by subtracting the corrected oxygen sensor output * V ₂₄ from the base target value Vbs. Also, as shown in the equation (4), * V ₂₄ = V ₂₄ + Vrev. From the equation (2), Vtg = Vbs−Vrev. Therefore, the deviation [Delta] V ₂₄ calculated, the relationship of Equation (5) below holds.
ΔV ₂₄ = Vbs− * V ₂₄ = Vbs− (V ₂₄ + Vrev) = Vtg−V ₂₄ (5)
That is, even when the corrected control target value is used as in the first embodiment or when the sensor output V ₂₄ is corrected as in the second embodiment, the same air-fuel ratio sensor is used. The correction value ΔV can be obtained.

  For example, in the second embodiment, the “correction value calculating means” of the present invention is realized by executing steps S150 and S152, and the “sensor output detecting means” of the present invention is realized by executing step S156. By realizing step S202, the “control means” and the “sensor output correction means” are realized. Further, for example, by storing the map shown in FIG. 10 in the second embodiment, the “correction value function storage means” of the present invention is realized. Further, for example, in the second embodiment, the control device 30 stores the map of FIG. 7, thereby realizing the “oxygen sensor output target value storage means” of the present invention. Further, for example, in the second embodiment, by executing step S204, “deviation calculation means” and “upstream sensor output correction value calculation means” are realized.

It is a schematic diagram for demonstrating the air fuel ratio control apparatus in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the oxygen sensor in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the oxygen sensor in Embodiment 1 of this invention. It is a block diagram for demonstrating the electrical connection of the oxygen sensor and control apparatus in Embodiment 1 of this invention. 4 is a flowchart for illustrating a routine of air-fuel ratio control executed by the control device in Embodiment 1 of the present invention. It is a graph for demonstrating the relationship between sensor element temperature and the impedance of a sensor element. It is a graph for demonstrating the relationship between element temperature and the base target value of air fuel ratio control. It is a graph for demonstrating the relationship between the temperature of a gas seal part, and the amount of oxygen leaks. It is a graph for demonstrating the relationship between a cooling water temperature and the temperature of a gas seal part. It is a graph for demonstrating the correction value with respect to the cooling water temperature in Embodiment 1 of this invention. It is a graph for demonstrating the relationship between the cooling water temperature at the time of starting, and the intake air amount at the time of complete warming up. It is a flowchart for demonstrating the starting cooling water temperature memory | storage routine which a control apparatus performs in Embodiment 1 of this invention. It is a flowchart for demonstrating the sensor correction value calculation routine which the control apparatus performs in Embodiment 1 of this invention. It is a flowchart for demonstrating the sensor correction value calculation routine which the control apparatus performs in Embodiment 2 of this invention.

Explanation of symbols

2 Internal combustion engine 4 Intake port 6 Intake branch pipe 8 Fuel injection valve 12 Exhaust port 14 Exhaust manifold 16 Three-way catalyst 18 Catalytic converter 20 Exhaust pipe 22 Air-fuel ratio sensor 24 Oxygen sensor 30 Controller 40 Sensor element 42 Porous protective layer 44 Exhaust Gas side electrode 46 Solid electrolyte layer 48 Atmosphere side electrode 50 Atmosphere chamber 52 Heater 54 Cover 56 Housing 58 Solid electrolyte layer convex part 60 Housing convex part 62 Gas seal part 64 Metal packing 66 Filling part 68 Insulating glass 70 Metal ring 72 Heater holding part 74 Sensor element drive circuit 76 Low pass filter 78 D / A converter 80 Microcomputer 82 D / A converter 84 Heater control circuit Vtg Control target value Vbs Base target value Vrev Correction value TW ₀ Cooling water temperature at start TW ₁ Cooling water temperature annealing value TW ₂ Last cooling water temperature Better value

Claims (10)

An air-fuel ratio control apparatus for an internal combustion engine that controls an air-fuel ratio based on an output of an exhaust gas sensor that is installed in an exhaust path of the internal combustion engine and detects an air-fuel ratio of exhaust gas,
The exhaust gas sensor
A reference gas chamber into which a reference gas is introduced; a reference gas side electrode disposed in the reference gas so as to be exposed to the reference gas;
An exhaust gas side electrode disposed in the exhaust path so as to be exposed to the exhaust gas;
A gas seal portion that shuts off the reference gas chamber and the exhaust path,
The air-fuel ratio control device includes:
Temperature estimating means for estimating the temperature of the gas seal part;
Correction value calculating means for calculating a correction value for correcting an output deviation of the exhaust gas sensor based on the temperature of the gas seal portion;
Control means for reflecting the correction value in the control of the air-fuel ratio;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: A cooling water temperature detecting means for detecting a cooling water temperature of the internal combustion engine;
The temperature estimating means includes
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the temperature of the gas seal portion is estimated according to the cooling water temperature. An annealing value calculating means for calculating an annealing value of the cooling water temperature;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the temperature estimation means estimates the temperature of the gas seal portion using the smoothed value as the cooling water temperature. The correction value for correcting the output deviation is shown as a first correction value function as a function of the cooling water temperature before the internal combustion engine is warmed up and as a function of the cooling water temperature after the internal combustion engine is warmed up. Correction value function storage means for storing a second correction value function;
Warm-up determination means for determining whether or not the internal combustion engine has reached a warm-up state,
The correction value calculating means includes
When it is determined that the internal combustion engine has reached a warm-up state, the correction value is calculated based on the second correction value function,
4. The internal combustion engine according to claim 2, wherein when it is determined that the internal combustion engine has not reached a warm-up state, the correction value is calculated based on the first correction value function. 5. Air-fuel ratio control device. A warm-up cumulative air amount function storage means for storing the cumulative intake air amount required to reach the warm-up state as a warm-up cumulative intake air amount function with respect to the starting coolant temperature;
Integrated air amount detection means for detecting the integrated intake air amount of the internal combustion engine;
A starting water temperature detecting means for detecting a cooling water temperature when starting the internal combustion engine;
A warm-up time cumulative intake air amount setting means for setting the warm-up time cumulative intake air amount according to the start-up water temperature detection means based on the warm-up time cumulative intake air amount function;
The warm-up determination unit determines that the warm-up state has been reached when the cumulative intake air amount is equal to or greater than the warm-up cumulative intake air amount. An air-fuel ratio control apparatus for an internal combustion engine. Base target value storage means for storing, as a base target value, an output to be emitted from the exhaust gas sensor when the exhaust gas side electrode is exposed to a target air-fuel ratio;
6. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the control means includes base target value correction means for correcting the base target value based on the correction value. The base target value storage means stores the base target value as a base target value function with respect to the temperature of the sensor element,
Element temperature estimating means for estimating the temperature of the sensor element of the exhaust gas sensor;
Setting means for setting the base target value according to the temperature of the sensor element based on the base target value function;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 6, comprising: The exhaust gas sensor is a downstream oxygen sensor that is arranged downstream of the three-way catalyst and corrects the output of the upstream air-fuel ratio sensor arranged on the upstream side of the three-way catalyst,
Deviation calculating means for calculating a deviation between the control target value corrected by the base target value correcting means and the output of the oxygen sensor;
Sensor correction amount calculating means for calculating a sensor correction amount for the output of the upstream air-fuel ratio sensor according to the deviation;
Upstream sensor correction means for correcting the output of the upstream air-fuel ratio sensor according to the sensor correction amount;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 6 or 7, further comprising: Comprising sensor output detecting means for detecting a sensor output of the exhaust gas sensor;
6. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the control apparatus includes a sensor output correction unit that corrects the sensor output based on the correction value. The exhaust gas sensor is a downstream oxygen sensor that is arranged downstream of the three-way catalyst and corrects the output of the upstream air-fuel ratio sensor arranged on the upstream side of the three-way catalyst,
Oxygen sensor output target value storage means for storing, as an oxygen sensor output target value, an output target value of the oxygen sensor for controlling the air-fuel ratio of the internal combustion engine to a target air-fuel ratio;
Deviation calculating means for calculating a deviation between the sensor output corrected by the sensor output correcting means and the oxygen sensor output target value;
Upstream sensor output correction value calculating means for calculating an upstream sensor output correction value for the output of the upstream air-fuel ratio sensor according to the deviation;
Upstream air-fuel ratio sensor correction means for correcting the output of the upstream air-fuel ratio sensor according to the upstream sensor output correction value;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 9, comprising:

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