JP2013068210A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine control device configured to allow an air-fuel ratio sensor provided in an intake passage of an engine to be precisely corrected in terms of a reference value, with simple structure.SOLUTION: The engine control device includes: recirculation passages 19, 22 for exhaust recirculation which connects an exhaust passage 16 and an intake passage 12 of the engine 1 mounted on a vehicle; a recirculation gas control means 31b for controlling the recirculation gas flowing in the recirculation passages 19, 22; and the air-fuel ratio sensors 25, 26 which are arranged in the intake passage 12 downstream from a connection portion where the intake passage 12 is connected to the recirculation passages 19, 22. The engine control device further includes: a determining means 31d for determining whether the engine 1 is stopped or not (a correction condition has been established or not) after an operation state for reducing the amount of the recirculation gas by the recirculation gas control means 31b; and a correction means 31e for correcting the reference value of the air-fuel ratio sensors 25, 26 when the determination means 31d determines that the correction condition has been established.

Description

  The present invention relates to an engine control device for correcting a reference value of an air-fuel ratio sensor provided in an intake passage of an engine.

  In general, an engine performs fuel injection control and exhaust purification control using an oxygen concentration and an air-fuel ratio detected by an oxygen sensor and an air-fuel ratio sensor provided in the intake passage and the exhaust passage. Some engines have an exhaust gas recirculation passage (EGR passage) that leads exhaust gas to the intake passage again. The exhaust gas is circulated through the EGR passage to control the exhaust temperature or Control is performed to reduce the amount of NOx produced.

  The amount of exhaust gas (EGR gas) flowing through the EGR passage is controlled by the opening degree of a control valve provided in the EGR passage. The opening degree of the control valve is controlled using the output value of an oxygen sensor or an air-fuel ratio sensor provided downstream of the inlet of the EGR gas to the intake passage (that is, the connection portion between the EGR passage and the intake passage). Is done. For example, the combustion state is estimated from the oxygen concentration of the intake air (mixture of fresh air and exhaust gas) detected by the oxygen sensor and the air-fuel ratio of the intake air detected by the air-fuel ratio sensor, and control is performed so that appropriate combustion is achieved. The opening degree of the valve is controlled, and the EGR gas amount is adjusted to increase or decrease.

  These oxygen sensors and air-fuel ratio sensors have errors in their output values due to changes over time and cannot detect accurate values. Therefore, it is necessary to periodically correct in order to eliminate this output value error. This correction is called so-called reference value correction, for example, correcting a deviation in the reference value of the sensor output to be detected in an outside air environment that does not include exhaust. By regularly performing the reference value correction, the measurement accuracy of the sensor can be kept high.

  For example, Patent Document 1 describes a technique relating to output correction of an oxygen sensor disposed downstream of a recirculation gas inlet of an intake pipe of an engine. In this technique, first, in order to obtain a state suitable for performing the correction calculation, the oxygen concentration in the intake pipe is set to a known value (oxygen concentration in the atmosphere≈21%) by closing the fuel cut or the EGR valve. . Then, the rate of change in pressure is calculated using the output value of the pressure sensor provided in the intake pipe, and the output of the oxygen sensor is corrected based on this rate of change in pressure. Thus, correction can be made in consideration of the pressure dependency of the oxygen sensor, and it is said that an accurate oxygen concentration can always be detected.

JP-A-10-176777

  The technique of the above-mentioned patent document 1 considers the pressure dependency of the oxygen sensor in the output correction (reference value correction) of the oxygen sensor, but the air-fuel ratio sensor is similarly affected by the surrounding pressure ( That is, the output depends on the pressure of the gas to be detected), and an error occurs in the output value due to the pressure. For this reason, it is required to consider the influence of pressure even when correcting the reference value of the air-fuel ratio sensor.

  However, in the technique of the above-mentioned Patent Document 1, a coefficient called a rate of change in pressure is calculated, and a value (sensor specific value) determined by the thickness of the diffusion-controlling layer of the oxygen sensor, the diameter of the pores, etc. in the operating state at that time Since the correction is performed while updating the value so as to be a value unique to the oxygen sensor, the calculation is complicated. Further, since the accuracy of correction of the oxygen sensor depends on the calculation accuracy of the coefficient of change rate against pressure, that is, the detection accuracy of the pressure sensor, it is difficult to improve the correction accuracy.

The present invention has been devised in view of such problems, and it is an object of the present invention to provide an engine control device capable of accurately correcting a reference value of an air-fuel ratio sensor provided in an engine with a simple configuration. Objective.
The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

(1) An engine control device disclosed herein includes a recirculation passage for exhaust gas recirculation that communicates an exhaust passage and an intake passage of an engine mounted on a vehicle, and a recirculation gas that controls the amount of recirculation gas flowing through the recirculation passage. An engine control device comprising a gas amount control means and an air-fuel ratio sensor disposed in the intake passage downstream of a connection portion between the intake passage and the return passage, wherein the return gas amount control After the operation state in which the recirculation gas amount is suppressed by the means, the correction condition is that the engine is stopped, the determination means for determining whether or not the correction condition is satisfied, and the determination means And correction means for correcting the reference value of the air-fuel ratio sensor when it is determined that the correction condition is satisfied.
In other words, the correction means is characterized in that the reference value correction of the air-fuel ratio sensor is performed after the return gas is purged from the intake air in the vicinity of the air-fuel ratio sensor by the return gas amount control means.

  (2) A filter provided in the exhaust passage for collecting particulate matter contained in the exhaust, and a regeneration control means for forcibly burning the particulate matter collected by the filter to regenerate the filter. It is preferable that the determination unit sets the correction condition that the regeneration control of the filter is performed by the regeneration control unit.

(3) An intake pressure sensor for detecting the pressure of the intake passage is provided, and the determination unit sets the correction condition that the pressure of the intake passage detected by the intake pressure sensor is equal to the atmospheric pressure. Is preferred.
(4) It is preferable that the determination unit sets the correction condition that the distance traveled after the previous correction of the reference value of the air-fuel ratio sensor is equal to or more than a predetermined distance set in advance.

  According to the engine control apparatus of the present invention, since the engine is stopped after the operation state in which the recirculation gas amount control means suppresses the recirculation gas amount is used as the correction condition for the reference value correction, Both the air and pressure inside can be made equivalent to the atmospheric condition. When it is determined that this correction condition is satisfied, the reference value correction of the air-fuel ratio sensor is performed, so that the reference value correction of the air-fuel ratio sensor can be performed accurately with a simple configuration. In the present invention, the correction is performed when the engine is stopped and the pressure in the intake passage is actually equal to the atmospheric pressure. Therefore, the reference value correction of the air-fuel ratio sensor is performed by eliminating the influence of the pressure. Can be implemented.

It is a block diagram which illustrates the control apparatus of the engine which concerns on one Embodiment. It is a graph which shows the relationship of the sensor output with respect to an actual air fuel ratio. It is a flowchart which shows the control content when implementing the reference value correction | amendment of the air fuel ratio sensor by the engine control apparatus which concerns on one Embodiment.

Hereinafter, embodiments will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment.
[1. Device configuration]
The control device of the present embodiment is applied to a diesel engine (engine) 1 mounted on a vehicle. FIG. 1 shows one of a plurality of cylinders 2 provided in the engine 1, but the other cylinders 2 have the same configuration. A piston 3 that reciprocates vertically is provided in the cylinder 2 of the engine 1. The piston 3 is connected to the crankshaft via a connecting rod. The piston 3 is formed with a cavity 3a serving as a combustion chamber on the top surface.

  An injector 4 for fuel injection is provided on the cylinder head above the cylinder 2. The injector 4 has a tip projecting from the in-cylinder space of the cylinder 2 and directly injects fuel into the cylinder 2. The injection direction of the fuel injected from the injector 4 is set to a direction toward the cavity 3 a of the piston 3. A fuel pipe is connected to the base end of the injector 4, and pressurized fuel is supplied to the injector 4 from the fuel pipe.

  The cylinder head is provided with an intake port 5 and an exhaust port 6 communicating with the in-cylinder space of the cylinder 2, and an intake valve 7 and an exhaust valve 8 for opening and closing each of these ports 5 and 6 are provided. An intake manifold (hereinafter referred to as intake manifold) 9 is provided on the upstream side of the intake port 5. The intake manifold 9 is provided with a surge tank 10 for temporarily storing air flowing to the intake port 5 side. The intake manifold 9 on the downstream side of the surge tank 10 is formed to branch toward the plurality of cylinders 2, and the surge tank 10 is located at the branch point. The surge tank 10 functions to mitigate intake pulsation and intake interference generated in each cylinder 2.

  A throttle body (not shown) is connected to the upstream end of the intake manifold 9, and an electronically controlled throttle valve 11 is built inside the throttle body, and the amount of air flowing to the intake manifold 9 side opens the throttle valve 11. It is adjusted according to the degree (throttle opening). The throttle opening is electronically controlled by the engine ECU 31. An intake passage 12 is connected further upstream of the throttle body. An air filter 13 is interposed at the most upstream side of the intake passage 12, and fresh air filtered by the air filter 13 is introduced into the intake passage 12.

  On the other hand, an exhaust manifold (hereinafter referred to as an exhaust manifold) 15, an exhaust passage 16, and an exhaust purification device 17 are provided downstream of the exhaust port 6 in the exhaust flow. The exhaust manifold 15 is formed so as to merge from the plurality of cylinders 2 and is connected to the exhaust passage 16 on the downstream side thereof. Further, the exhaust purification device 17 interposed in the exhaust passage 16 includes a catalyst 17a and a filter 17b. The catalyst 17a has a function of purifying hydrocarbon (HC) components, carbon monoxide (CO), nitrogen oxides (NOx) and the like contained in the exhaust, and is, for example, an oxidation catalyst or a three-way catalyst.

  The filter 17b is a porous filter (for example, a ceramic filter) that collects particulate matter (Particulate Matter, hereinafter abbreviated as PM) contained in the exhaust gas. In addition, PM is a particulate material in which fuel, lubricant components, sulfur compounds, and the like that remain unburned around carbon black smoke (soot) are attached. The inside of the filter 17b is divided into a plurality along the flow direction of the exhaust gas by a porous wall. A large number of pores having a size commensurate with the particulates of PM are formed in the wall, and PM is collected on the wall and on the surface of the wall when exhaust passes near or inside the wall. In the filter 17b, after the collected PM is continuously oxidized, regeneration control is performed in which the regeneration controller 31c provided in the engine ECU 31 forcibly burns the PM to regenerate the filter 17b.

  The intake / exhaust system of the engine 1 is provided with a turbocharger (supercharger) 18 that supercharges intake air into the cylinder 2 using exhaust pressure. The turbocharger 18 is a supercharger interposed between both the intake passage 12 and the exhaust passage 16. The turbocharger 18 rotates the turbine with the exhaust pressure in the exhaust passage 16 and uses the rotational force to drive the compressor, thereby compressing the intake air on the intake passage 12 side and supercharging the engine 1. . An intercooler 14 is provided downstream of the compressor in the intake passage 12 in the intake air flow to cool the compressed air.

  The engine 1 according to the present embodiment is provided with two recirculation passages (also referred to as exhaust recirculation passages and EGR passages) that recirculate exhaust gas flowing through the exhaust passage 16 to the intake passage 12. A first recirculation passage (hereinafter referred to as a first recirculation passage) 19 includes an exhaust passage 16 downstream of the exhaust purification device 17 and an intake passage 12 upstream of the compressor of the turbocharger 18 (here, the air filter 13). A so-called low pressure EGR (Exhaust Gas Recirculation) passage. A connecting portion between the first recirculation passage 19 and the intake passage 12 incorporates a first control valve (reflux gas amount control means) 20, and the recirculation gas amount flowing through the first recirculation passage 19 (that is, to the intake passage 12). The amount of exhausted gas) is adjusted according to the opening degree of the first control valve 20. The recirculation gas amount increases as the opening degree of the first control valve 20 increases, and becomes zero when the opening degree is zero (valve closing). The opening degree of the first control valve 20 is controlled by an opening / closing control unit 31b provided in the engine ECU 31.

  A second recirculation passage (hereinafter referred to as a second recirculation passage) 22 communicates the exhaust passage 16 upstream of the turbine of the turbocharger 18 and the intake passage 12 downstream of the compressor, thereby providing a so-called high pressure EGR passage. Configure. A second control valve (recirculation gas amount control means) 23 is built in the connection portion between the second recirculation passage 22 and the intake passage 12, and the recirculation gas amount flowing through the second recirculation passage 22 is reduced by the second control valve 23. It is adjusted according to the opening. The recirculation gas amount increases as the opening degree of the second control valve 23 increases, and becomes zero when the opening degree is zero (valve closing). The opening degree of the second control valve 23 is controlled by an opening / closing control unit 31b provided in the engine ECU 31. The first reflux passage 19 and the second reflux passage 22 are provided with reflux gas coolers 21 and 24 for cooling the reflux gas, respectively.

  Therefore, the intake port 5 of the engine 1 is introduced with intake air (air mixture) in which fresh air and exhaust gas (reflux gas) flowing from the first recirculation passage 19 and the second recirculation passage 22 are mixed. In this way, the recirculation gas is mixed in the intake air, so that excessive exhaust temperature rise and NOx emission are suppressed.

  Two air-fuel ratio sensors for detecting the air-fuel ratio of the intake air are arranged in the intake passage 12. The first air-fuel ratio sensor 25 is connected to the intake passage 12 and the first air passage 12 on the downstream side of the compressor provided downstream of the connection portion (portion in which the first control valve 20 is built) between the intake passage 12 and the first recirculation passage 19. Arranged upstream of the connection with the second reflux passage 22. Further, the second air-fuel ratio sensor 26 is disposed on the downstream side of the connection portion (portion in which the second control valve 23 is built) between the intake passage 12 and the second recirculation passage 22. These air-fuel ratio sensors 25 and 26 are so-called linear air-fuel ratio sensors that detect the oxygen concentration of the intake air flowing through the intake passage 12 and output a value substantially proportional to the oxygen concentration. These air-fuel ratio sensors 25 and 26 have a characteristic that, as the air-fuel ratio (oxygen concentration) is larger, for example, as indicated by the solid line in FIG. An output signal corresponding to the oxygen concentration detected by the air-fuel ratio sensors 25 and 26 is transmitted to the engine ECU 31.

  Further, an intake pressure sensor 28 for detecting the pressure of intake air is disposed in the intake passage 12 between the second control valve 23 and the throttle valve 11. Further, the vehicle is provided with a pressure sensor (atmospheric pressure sensor) 30 for detecting atmospheric pressure, and the atmospheric pressure sensor 30 detects the pressure where the vehicle is traveling.

  The engine 1 is provided with various sensors other than the air-fuel ratio sensors 25 and 26, the intake pressure sensor 28, and the atmospheric pressure sensor 30, and the state of the engine 1 is detected by these sensors. For example, the exhaust passage 16 is provided with a temperature sensor and a flow rate sensor (not shown) that detect the temperature and flow rate of the exhaust, and the crankshaft of the engine 1 has a crankshaft rotation angle (that is, the actual rotation speed of the engine 1). A crank angle sensor (not shown) for detection is provided. Information detected by these sensors is also transmitted to the engine ECU 31.

  The vehicle is provided with an engine ECU (Engine Electronic Control Unit) 31 as an electronic control device. The engine ECU 31 is configured as, for example, an LSI device or a built-in electronic device in which a microprocessor, ROM, RAM, and the like are integrated, and other electronic control devices and control valves 20 and 23 via a communication line of an in-vehicle network provided in the vehicle. , Connected to various sensors.

  The engine ECU 31 is an electronic control device that controls a wide range of systems such as an ignition system, a fuel system, and an intake / exhaust system related to the engine 1. Specific control objects of the engine ECU 31 include the opening amounts of the control valves 20 and 23 for controlling the fuel amount and the injection timing and the amount of recirculated gas injected from the injector 4 during normal time and idling, and the opening amount of the throttle valve 11. And regeneration control of the filter 17b. In the present embodiment, the reference value correction of the oxygen concentration of the air-fuel ratio sensors 25 and 26 provided in the intake passage 12 will be described in detail.

  The reference value correction is equivalent to, for example, a balance that weighs and is adjusted so that the balance indicates zero, which is the reference value, with nothing on it (generally called zero point correction). If the measuring device itself can be adjusted, it means adjusting the device itself. Also, if the device itself cannot be adjusted, the indication value (that is, deviation from the reference value, error) when it should be zero, which is originally the reference value, is stored. This means that the corrected value for subtracting the indicated value is the original value. The reference value correction here means the latter.

  That is, since the air-fuel ratio sensors 25 and 26 provided in the intake passage 12 cannot be adjusted, the sensor values (oxygen values) detected by the air-fuel ratio sensors 25 and 26 when the intake passage 12 is made equal to the atmospheric state. The output signal corresponding to the concentration (eg, voltage signal, current signal, etc.) is compared with the atmospheric condition (oxygen concentration≈21%). At this time, if there is a deviation (error) from the atmospheric oxygen concentration (reference value), the error is stored. From the next time onward, it is determined that a value obtained by adding or subtracting this error from the sensor values detected by the air-fuel ratio sensors 25 and 26 is an output signal corresponding to the actual oxygen concentration in the intake passage 12. Such correction calculation is referred to as correction of the oxygen concentration reference value of the air-fuel ratio sensors 25 and 26.

[2. Control configuration]
The engine ECU 31 is provided with an idle stop control unit 31a, an opening / closing control unit 31b, a regeneration control unit 31c, a determination unit 31d, and a correction unit 31e as functional elements for performing the reference value correction.

  The idle stop control unit 31a has a determination unit that determines whether or not a predetermined automatic stop condition (idle stop condition) is satisfied. When the determination unit determines that the automatic stop condition is satisfied, the engine 1 is automatically activated. To stop. The stop of the engine 1 here means stopping the combustion injection from the injector 4. That is, even if the crankshaft is slightly rotating due to inertia, the engine 1 is stopped if the fuel injection is stopped. In addition, the automatic stop condition is, for example, that the vehicle speed is zero and the brake operation is performed, the vehicle speed is zero and the accelerator operation is not performed, or the like. As the control configuration of the idle stop control unit 31a, various known techniques can be applied, and details thereof are omitted.

  The open / close control unit (reflux gas amount control means) 31b controls the opening degree (open / close) of the first control valve 20 and the second control valve 23 that control the amount of the recirculation gas flowing through the recirculation passages 19 and 22. . The opening / closing control unit 31b controls the amount of the recirculated gas by adjusting the opening of the control valves 20 and 23 based on the output request to the engine 1, the exhaust temperature, and the like. In addition, when the regeneration control of the filter 17b is performed by the regeneration control unit 31c, the opening / closing control unit 31b reduces the opening degree of the control valves 20 and 23, and controls the control valves 20 and 23 so as to suppress the recirculation gas amount. To control. Here, in order to make the recirculation gas amount most suitable for regeneration control to be zero, the control valves 20 and 23 are completely closed and the recirculation gas is cut.

  The regeneration control unit (regeneration control means) 31c estimates the amount of PM accumulated on the filter 17b, determines whether or not the regeneration of the filter 17b is necessary, and when it is determined that regeneration is necessary. The optimum regeneration time is judged and the PM collected by the filter 17b is forcibly burned to regenerate the filter 17b. Such a series of controls is called reproduction control, and is performed by a known method. For example, the regeneration control unit 31c determines that regeneration of the filter 17b is necessary when the pressure in the exhaust passage 16 exceeds a predetermined value. Further, in order to regenerate the filter 17b, it is necessary for the exhaust gas to be so hot that PM can burn, so the regeneration control unit 31c can be used when the exhaust gas temperature is high. It is determined that the optimal regeneration time is when a large amount of heat of reaction is obtained in the catalyst 17a in the previous stage. If it is determined that the filter 17b needs to be regenerated, the regeneration control unit 31c instructs the open / close control unit 31b to close the control valves 20 and 23 and cut the reflux gas.

  The determination unit (determination means) 31d determines whether a condition (correction condition) for correcting the reference value of the oxygen concentration of the air-fuel ratio sensors 25 and 26 is satisfied. Here, in order to perform the reference value correction of the air-fuel ratio sensors 25 and 26 described above, it is necessary to make the oxygen concentration in the intake passage 12 equal to the atmospheric state. Further, here, the pressure in the intake passage 12 is also made equal to the atmospheric pressure, the influence of the pressure is eliminated, and the reference value correction of the air-fuel ratio sensors 25 and 26 is performed with higher accuracy. The correction conditions determined by the determination unit 31d will be described below.

  First, the first correction condition is a condition for determining whether or not the reference value correction of the air-fuel ratio sensors 25 and 26 is necessary. When the first correction condition is satisfied, the correction is necessary. Determined. The first correction condition is that the travel distance of the vehicle is greater than or equal to a predetermined distance set in advance. The travel distance here is the distance traveled after the previous correction of the reference values of the air-fuel ratio sensors 25 and 26. That is, the travel distance is accumulated after the reference value correction is completed, and when the reference value correction is performed, the travel distance accumulated so far is reset to zero and accumulated again. The predetermined distance, which is the determination threshold, is a distance until the air-fuel ratio sensors 25 and 26 start to produce an error in their output values due to changes over time, and is obtained in advance by experiments or the like. When determining that the first correction condition is satisfied, the determination unit 31d determines the next second correction condition.

  The second correction condition is that the regeneration control of the filter 17b is performed by the regeneration control unit 31c. The second correction condition substantially means that both the first control valve 20 and the second control valve 23 are closed by the opening / closing control unit 31b. That is, during the regeneration control of the filter 17b, both the first control valve 20 and the second control valve 23 are closed, the recirculation gas is cut (the recirculation gas amount is zero), and the exhaust gas does not flow through the intake passage 12. The recirculated gas is purged from the intake air in the vicinity of the air-fuel ratio sensors 25 and 26. As a result, only fresh air flows in the intake passage 12, and the oxygen concentration in the intake passage 12 is made equal to the oxygen concentration in the atmosphere. When determining that the second correction condition is satisfied, the determination unit 31d determines the next third correction condition.

  The third correction condition is that the engine 1 is stopped. For example, in the case where it is determined that the automatic stop condition is satisfied by the idle stop control unit 31a and the engine 1 is stopped upon receiving a command to stop the engine 1, or in a hybrid vehicle having an electric motor as a drive source other than the engine 1 When the vehicle is driven only by the electric motor in response to a command to stop the engine, it is determined that the third correction condition is satisfied. Since the intake is stopped by stopping the engine 1, the pressure in the intake passage 12 becomes equal to the atmospheric pressure. In the present embodiment, the turbocharger 18 is provided. However, since this operation is also stopped when the engine 1 is stopped, there is no pressure change due to supercharging. If the determination unit 31d determines that the third correction condition is satisfied, the determination unit 31d determines the next fourth correction condition.

  The fourth correction condition is that the pressure in the intake passage 12 detected by the intake pressure sensor 28 is equivalent to the atmospheric pressure detected by the atmospheric pressure sensor 30. When the above third correction condition is satisfied, the pressure in the intake passage 12 should be equal to the atmospheric pressure, but in order to increase the accuracy of correction, the pressure is actually detected and compared with the atmospheric pressure. To do. Therefore, the fourth correction condition is a condition accompanying the third correction condition, and can be omitted. If it is determined that the fourth correction condition is satisfied, the determination unit 31d determines that the reference value correction of the air-fuel ratio sensors 25 and 26 can be performed. In addition, the oxygen concentration and pressure in the intake passage 12 are “equivalent” to the atmospheric state, which means that they do not have to be completely coincident with each other. That is, an error of several percent is allowed.

  When the determination unit 31d determines that the reference value correction of the air-fuel ratio sensors 25 and 26 can be performed, the correction unit (correction unit) 31e performs the reference value correction of the oxygen concentration of the air-fuel ratio sensors 25 and 26. It is. In the engine ECU 31, the relationship (map as shown in FIG. 2) of outputs from the air-fuel ratio sensors 25 and 26 with respect to the oxygen concentration (air-fuel ratio) is stored in advance for each sensor. When the determination unit 31d determines that the correction can be performed, the correction unit 31e performs correction of this map.

The reference value correction of the air-fuel ratio sensors 25 and 26 performed by the correction unit 31e will be described with reference to FIG. Although the air-fuel ratio sensor 25 will be described here as an example, the same applies to the air-fuel ratio sensor 26. FIG. 2 is a graph showing the relationship between the sensor value (output) and the actual air-fuel ratio (oxygen concentration). When the air-fuel ratio sensor 25 is new, it has a relationship between the output and the air-fuel ratio such as a graph a shown by a solid line in FIG. 2, the sensor value at the point P _A on the graph a when the air-fuel ratio is A X _a is detected.

However, when the air-fuel ratio sensor 25 changes with time, an error occurs in the output. For example, as shown in FIG. 2, even if the actual air-fuel ratio is A, the output from the air-fuel ratio sensor 25 becomes X _B , and an error ΔX (= X _A −X _B ) occurs in the sensor value. In other words, when the output from the air-fuel ratio sensor 25 is X _B , the point P _A ′ is shown on the graph a, so that the air-fuel ratio at this time is determined to be A ′, but the actual air-fuel ratio is A. As a result, a deviation occurs in the air-fuel ratio. Therefore, in order to know how much this error exists, the actual air-fuel ratio is set to a known value, and the sensor value output from the air-fuel ratio sensor 25 at this time is an output signal (sensor) corresponding to this known air-fuel ratio. If not (value), the sensor value error corresponding to that is stored. Then, at the time of detection by the air-fuel ratio sensor 25 after the next time, the stored air-fuel ratio is added or subtracted to determine the actual air-fuel ratio.

For example, when the actual air-fuel ratio (here, oxygen concentration) is a known value of atmospheric oxygen concentration A (about 21%), the sensor value to be output by the air-fuel ratio sensor 25 must be X _A. It is assumed that the sensor value X _B is output though it is necessary. Since the sensor value error at this time is ΔX (= X _A −X _B ), this ΔX is stored in the engine ECU 31. From this time on, the actual oxygen concentration can be detected by always adding this error ΔX to the sensor value output by the air-fuel ratio sensor 25.

That is, the correction unit 31e, the sensor value X _B is output when the oxygen concentration A (i.e., a point P _B) As described above, the correction of shifting the graph a shown in FIG. 2 to the right, aging A new graph b showing the relationship of the output with respect to the air-fuel ratio in the air-fuel ratio sensor 25 is created. In the subsequent detection by the air-fuel ratio sensor 25, it is possible to detect an accurate air-fuel ratio in consideration of the time-dependent change of the air-fuel ratio sensor 25 by using this graph b.

[3. flowchart]
Next, an example of the procedure for correcting the reference values of the air-fuel ratio sensors 25 and 26 performed by the engine ECU 31 will be described with reference to FIG. This flowchart operates at a predetermined cycle. Each of the following steps is performed by each function (means) assigned to the hardware of the computer being operated by software (computer program).
When the vehicle ignition switch (IG_SW) is turned on by the driver, the following control flow starts.

  As shown in FIG. 3, first, in step S10, it is determined whether or not the flag F = 0. Here, the flag F is a variable for checking whether or not the first correction condition is satisfied in the determination unit 31d described above, and the flag F = 0 is set at the start of control. Therefore, at the start of control, the YES route is obtained in step S10, and the process proceeds to step S20. In step S20, it is determined whether or not the travel distance is greater than or equal to a predetermined distance. That is, step S20 is a determination step of the first correction condition by the determination unit 31d. If the travel distance is equal to or greater than the predetermined distance, the process proceeds from the YES route to step S30, the flag F is set to F = 1, and the process proceeds to step S40. On the other hand, if the travel distance is less than the predetermined distance, the process proceeds from the NO route to step S90.

  In step S40, it is determined whether the regeneration control of the filter 17b is performed by the regeneration control unit 31c. That is, step S40 is a determination step of the second correction condition by the determination unit 31d. If the regeneration control of the filter 17b is being performed, the control valves 20 and 23 are closed, so the process proceeds from the YES route to step S45, and during the regeneration control of the filter 17b, for example, the stop command for the engine 1 is issued by the idle stop control unit 31a. It is determined whether or not it is emitted. If the engine 1 stop command has been issued, the process proceeds from the YES route to step S50, and it is determined whether or not the engine 1 has been stopped during the regeneration control. That is, step S50 is a determination step of the third correction condition by the determination unit 31d.

  If it is determined in step S50 that the engine has been stopped during the regeneration control, the process proceeds from the YES route to step S60, and the pressure in the intake passage 12 (intake pressure) detected by the intake pressure sensor 28 is detected by the atmospheric pressure sensor 30. It is determined whether or not the atmospheric pressure is equivalent (substantially equal). That is, step S60 is a determination step of the fourth correction condition by the determination unit 31d. When the intake pressure is equal to the atmospheric pressure, the process proceeds from the YES route to step S70, and the reference value correction of the air-fuel ratio sensors 25 and 26 is performed by the correction unit 31e. In step S80, the flag F is reset to F = 0, the travel distance is also reset, and the process proceeds to step S90.

  On the other hand, if none of the determinations in step S40, step S45, step S50, and step S60 are satisfied, the process proceeds from the NO route to step S90. In step S90, it is determined whether or not the ignition switch has been turned off. If it has not been turned off, the process returns and proceeds to flag determination in step S10 again. At this time, if the flag F is set to F = 1 in step S30, the process proceeds from step S10 to step S40, and determinations in steps S40 to S60 are performed.

  That is, once it is determined in step S20 that the travel distance is equal to or greater than the predetermined distance, the reference value correction of the air-fuel ratio sensors 25 and 26 is necessary, so that the steps S40 to S40 are performed until the second to fourth correction conditions are satisfied. When the determination in S60 is repeatedly performed and all the conditions are satisfied, the reference value correction is performed in step S70. Note that when the ignition switch is turned off in step S90, the control flow is ended.

[4. effect]
Therefore, according to the present control device, the correction condition for the reference value correction is that the engine 1 is stopped after the operation state in which the amount of recirculated gas is suppressed by the first control valve 20 and the second control valve 23. Therefore, both the oxygen concentration and pressure of the air in the intake passage 12 can be made equal to the atmospheric state (atmospheric oxygen concentration and atmospheric pressure). If it is determined that the correction condition is satisfied, the reference value correction of the oxygen concentration of the air-fuel ratio sensors 25, 26 is performed. Therefore, the reference value correction of the air-fuel ratio sensors 25, 26 can be performed accurately with a simple configuration. . Further, in the present control device, correction is performed when the engine 1 is stopped and the pressure in the intake passage 12 is actually equal to the atmospheric pressure. Therefore, the air-fuel ratio sensor 25, Twenty-six reference value corrections can be performed.
In the above embodiment, since the first control valve 20 and the second control valve 23 are completely closed and the recirculation gas is cut, the intake passage 12 can be in a state of only fresh air. The reference value correction of the air-fuel ratio sensors 25 and 26 can be performed well.

  Here, the recirculation gas cut by the first control valve 20 and the second control valve 23 is performed during the regeneration control of the filter 17b by the regeneration control unit 31c (that is, the regeneration control is being performed). Correction conditions). During this regeneration control, the exhaust temperature is high, and even if the engine 1 is stopped to correct the reference values of the air-fuel ratio sensors 25 and 26, the exhaust temperature does not immediately decrease. Therefore, it is possible to prevent a situation in which the vapor in the exhaust is condensed (that is, water droplets are formed) due to the low exhaust temperature. That is, if the reference value correction of the air-fuel ratio sensors 25 and 26 is performed during the regeneration control, the water droplets condensed by the exhaust gas temperature drop are applied to the air-fuel ratio sensor, the temperature sensor, etc. (both not shown) provided in the exhaust passage. It is possible to prevent such a situation that it adheres and adversely affects the sensor.

Further, after actually detecting the intake pressure by the intake pressure sensor 28 and confirming that the pressure in the intake passage 12 is equal to the atmospheric pressure as compared with the atmospheric pressure detected by the atmospheric pressure sensor 30. Since the reference value correction is performed, the reference value correction can be performed more accurately.
Further, by making the correction condition that the travel distance is equal to or greater than the predetermined distance, the reference value correction of the air-fuel ratio sensor can be performed at an appropriate timing.

[5. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
In the above embodiment, the first to fourth correction conditions are determined, respectively, and the reference value correction is performed when all are satisfied. However, as described above, the fourth correction condition is omitted. Alternatively, the first correction condition may be omitted. That is, regardless of the travel distance, it may be configured to always perform correction when a condition for performing correction is satisfied, and in this case, an accurate value can always be obtained by the air-fuel ratio sensor.

  Further, the second correction condition may be immediately after the end of the regeneration control of the filter 17b, instead of during the regeneration control of the filter 17b. Even in this case, the oxygen concentration in the intake passage 12 can be made equal to the oxygen concentration in the atmosphere. Further, both the first control valve 20 and the second control valve 23 may be closed (that is, the reflux gas is cut). By setting the correction condition in this way, the reference value correction can be performed independently of the regeneration control of the filter 17b. Further, the present invention is not limited to the case where the recirculation gas is completely cut, and the recirculation gas is slightly introduced into the intake passage 12 as long as the oxygen concentration in the intake passage 12 can be made equal to the oxygen concentration in the atmosphere. It goes without saying that it may be done.

  Further, the stop of the engine 1, which is the third correction condition, is not limited to the case of idling stop. For example, the engine 1 is stopped immediately after turning off the ignition switch or when the reflux gas is cut off. It may be the case. The stop of the engine 1 may be such that the actual rotational speed of the engine 1 becomes zero. That is, it may be in a state where air is not flowing through either the intake passage 12 or the exhaust passage 16. In this case, the engine 1 needs to be stopped after a predetermined time has elapsed from when the recirculated gas is cut until the intake air containing the recirculated gas is scavenged.

  Further, the air-fuel ratio sensor that is subject to reference value correction by the present control device may not be a linear air-fuel ratio sensor that detects an output proportional to the oxygen concentration as described above. Further, the air-fuel ratio sensor does not have to detect the oxygen concentration. Any sensor that can measure at least the amount of a gaseous substance related to the combustion reaction may be used. For example, a sensor that detects the air-fuel ratio by detecting the carbon dioxide concentration may be used. That is, the air-fuel ratio sensor is not limited to the one that detects the oxygen concentration, and the reference value correction is not limited to the oxygen concentration reference value correction.

Further, the configuration of the engine 1 is not limited to that shown in FIG. 1. For example, the reflux path may be either the first reflux path 19 or the second reflux path 22. In this case, only one air-fuel ratio sensor needs to be provided. Further, the turbocharger 18 may not be provided.
Further, the present control device is not limited to a vehicle equipped with a diesel engine, but can be applied to a vehicle equipped with a gasoline engine, and may be applied to a hybrid vehicle equipped with an engine and an electric motor.

1 Diesel engine (engine)
12 Intake passage 16 Exhaust passage 17b Filter 19 First return passage (return passage)
20 First control valve (reflux gas amount control means)
22 Second reflux passage (reflux passage)
23 Second control valve (reflux gas amount control means)
25, 26 Air-fuel ratio sensor 28 Intake pressure sensor 30 Atmospheric pressure sensor 31 Engine ECU
31a Idle stop control unit 31b Open / close control unit (reflux gas amount control means)
31c Reproduction control unit (reproduction control means)
31d determination part (determination means)
31e Correction part (correction means)

Claims (4)

A recirculation passage for exhaust gas recirculation that connects an exhaust passage and an intake passage of an engine mounted on a vehicle, a recirculation gas amount control means that controls a recirculation gas amount flowing through the recirculation passage, the intake passage, and the recirculation passage An air-fuel ratio sensor disposed in the intake passage on the downstream side of the connection with the engine,
A determination means for determining whether or not the correction condition is satisfied, with the correction condition that the engine is stopped after an operation state in which the recirculation gas amount is controlled by the recirculation gas amount control means;
An engine control device comprising: a correction unit that performs correction of a reference value of the air-fuel ratio sensor when the determination unit determines that the correction condition is satisfied. A filter provided in the exhaust passage for collecting particulate matter contained in the exhaust;
Regeneration control means for forcibly burning particulate matter collected by the filter and regenerating the filter,
2. The engine control apparatus according to claim 1, wherein the determination unit sets the correction condition that the regeneration control of the filter is performed by the regeneration control unit. An intake pressure sensor for detecting the pressure in the intake passage;
The engine control apparatus according to claim 1 or 2, wherein the determination unit sets the correction condition that the pressure in the intake passage detected by the intake pressure sensor is equal to an atmospheric pressure. 4. The correction condition according to claim 1, wherein the determination means uses the correction condition that a distance traveled after the previous correction of the reference value of the air-fuel ratio sensor is equal to or more than a predetermined distance set in advance. The engine control device according to any one of the above.

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