JP2009156108A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of compatibly reducing an energization amount to a heater when an internal combustion engine is automatically stopped, and ensuring the responsiveness to the detection request of the air-fuel ratio after the internal combustion engine is re-started. <P>SOLUTION: A control device of an internal combustion engine includes: an exhaust emission purification catalyst provided in an exhaust passage of the internal combustion engine; an air-fuel ratio sensor provided in the exhaust passage, a heater for raising the temperature of the air-fuel ratio sensor, a temperature control means for controlling the temperature of the air-fuel ratio sensor to the target value by controlling the energization amount to the heater; an automatic control means which automatically stops the internal combustion engine when the automatic stopping condition of the internal combustion engine is established, and restarts the internal combustion engine when the automatic stopping condition is released; and a period estimation means for estimating the detection non-request period before the detection request of the air-fuel ratio is output firstly to the air-fuel ratio sensor after the internal combustion engine is restarted when the automatic control means automatically stops the internal combustion engine. The target temperature while the internal combustion engine is automatically stopped is set to the lower temperature side as the detection non-request period is longer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine.

  In general, the exhaust passage of the internal combustion engine is provided with an exhaust purification device that purifies harmful substances contained in the exhaust from the viewpoint of improving exhaust emissions. When this exhaust purification device includes an exhaust purification catalyst, the temperature of the exhaust purification catalyst is increased, the harmful substances (for example, NOx, PM, etc.) in the exhaust in the exhaust purification catalyst are purified, and the purification capability of the exhaust purification catalyst is restored. In some cases, a reducing agent is supplied to the catalyst to achieve the above.

  For example, when the exhaust purification device includes an NOx storage reduction catalyst, the purification capacity decreases as the storage amount of NOx or SOx stored in the catalyst increases. Therefore, by reducing the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst by supplying a reducing agent (for example, an unburned component of the fuel), recovery processing (for example, NOx reduction processing) for recovering the purification ability of the catalyst. , SOx poisoning recovery processing, etc.) are performed.

  Further, the exhaust purification device includes a catalyst having an oxidizing ability (hereinafter also referred to as “oxidation catalyst”) and a particulate filter (hereinafter referred to as “filter”) that collects particulate matter (PM) in the exhaust gas. In this case, a PM regeneration process is performed in which the temperature of the filter is raised by supplying the reducing agent to the catalyst, and the PM deposited on the filter is oxidized and removed.

  Here, when the reducing agent is supplied to the exhaust purification catalyst, the supply amount of the reducing agent may be feedback controlled based on the detection value of the air-fuel ratio sensor installed in the exhaust passage of the internal combustion engine. In order for this air-fuel ratio sensor to operate properly, the air-fuel ratio cannot be detected properly unless the temperature of the sensor is maintained at a high temperature (for example, about 650 to 750 ° C.) or higher. Therefore, the air-fuel ratio sensor is generally provided with a heater for raising the temperature of the sensor, and the temperature of the sensor is adjusted by adjusting the energization amount to the heater.

  By the way, when the vehicle on which the internal combustion engine is mounted is an eco-run vehicle having a so-called idling stop function or a hybrid vehicle, the internal combustion engine may be automatically stopped. For example, the internal combustion engine is automatically stopped when the vehicle stops temporarily, such as when waiting for a signal, and the internal combustion engine is automatically restarted when the stopped vehicle starts to improve the fuel efficiency of the internal combustion engine. You can plan.

In Patent Document 1, energization of the heater attached to the air-fuel ratio sensor is continued even while the internal combustion engine is automatically stopped, and the air-fuel ratio sensor is prevented from being inactivated during the automatic stop of the internal combustion engine. Technology to do is released. In this prior art, the air-fuel ratio of the exhaust can be detected immediately after the internal combustion engine is restarted when the vehicle re-starts.
JP-A-9-88688 JP-A-8-220059 JP 2004-101274 A

  However, in the above prior art, the air-fuel ratio sensor is maintained in an active state regardless of whether the internal combustion engine is operating or stopped, so that the amount of power consumed for energizing the heater becomes excessive.

  On the other hand, simply reducing the temperature of the air-fuel ratio sensor during the automatic stop of the internal combustion engine in order to reduce the energization amount of the heater will delay the activation timing of the air-fuel ratio sensor after the restart of the internal combustion engine. As a result, the time at which the detection of the air-fuel ratio can be started is delayed, and it becomes difficult to ensure responsiveness to the air-fuel ratio detection request.

  The present invention has been made in view of the above-described prior art. The object of the present invention is to reduce the amount of current supplied to the heater during the automatic stop of the internal combustion engine and to detect the air-fuel ratio after the internal combustion engine is restarted. It is to provide a technology that can ensure both responsiveness to requests.

In order to achieve the above object, a control apparatus for an internal combustion engine according to the present invention employs the following means.
That is, an exhaust purification catalyst provided in the exhaust passage of the internal combustion engine,
An air-fuel ratio sensor provided in the exhaust passage;
A heater for raising the temperature of the air-fuel ratio sensor;
Temperature control means for controlling the energization amount to the heater to control the temperature of the air-fuel ratio sensor to a target temperature;
Automatic control means for automatically stopping the internal combustion engine when the automatic stop condition for the internal combustion engine is satisfied and restarting the internal combustion engine when the automatic stop condition is canceled;
When the automatic control means automatically stops the internal combustion engine, period estimation means for estimating a detection non-request period from when the internal combustion engine is restarted until the first air-fuel ratio detection request is issued to the air-fuel ratio sensor When,
With
The target temperature during the automatic stop of the internal combustion engine is set to a lower temperature side as the detection non-request period is longer.

  In the above configuration, the internal combustion engine is automatically stopped when the automatic stop condition is established, and the internal combustion engine is restarted when the automatic stop condition is canceled. The automatic stop condition in the present invention is a condition for automatically stopping the internal combustion engine, and is satisfied when the eco-run vehicle or the hybrid vehicle is temporarily stopped. The automatic stop condition is when the driving condition of the hybrid vehicle shifts from a state where the power source of the vehicle is shared only by the internal combustion engine or the internal combustion engine and the electric motor to a state where the power source is shared only by the electric motor. Also holds. Then, when the automatic stop condition of the internal combustion engine is no longer satisfied, such as when the vehicle that is temporarily stopped is restarted, the internal combustion engine is automatically restarted by releasing the automatic stop condition.

  Here, during the automatic stop of the internal combustion engine, the exhaust gas is not discharged from the internal combustion engine. Therefore, the air-fuel ratio sensor is not requested to detect the air-fuel ratio, and is issued at least after the internal combustion engine is restarted.

  In the present invention, when the internal combustion engine is automatically stopped, the detection non-request period from when the internal combustion engine is restarted until the first air-fuel ratio detection request is issued to the air-fuel ratio sensor is estimated. The target temperature during the automatic stop of the internal combustion engine is set to the lower temperature side as the detection non-request period is longer. According to this, since the target temperature of the air-fuel ratio sensor is set to the high temperature side when the estimated detection non-request period is short, the air-fuel ratio sensor can be activated within the range of the detection non-request period. Therefore, the responsiveness to the air-fuel ratio detection request for the air-fuel ratio sensor can be ensured.

Also, if the estimated non-request period is long, the air-fuel ratio sensor temperature during the automatic stop is unnecessarily high while ensuring good response to the air-fuel ratio detection request after restarting the internal combustion engine. Can be suppressed. That is, the energization amount to the heater during the automatic stop of the internal combustion engine can be suitably reduced.

  Note that the target temperature during the automatic stop of the internal combustion engine may be continuously changed to the low temperature side as the detection non-request period becomes longer, or may be changed in stages.

  As described above, according to the present invention, it is possible to suitably achieve both reduction of the energization amount to the heater during the automatic stop of the internal combustion engine and ensuring responsiveness to the detection request of the air-fuel ratio after the restart of the internal combustion engine. it can.

  Here, since the exhaust is not discharged during the automatic stop of the internal combustion engine, the catalyst bed temperature of the exhaust purification catalyst decreases with time. If the decrease in the catalyst bed temperature becomes significant due to the prolonged automatic stop period of the internal combustion engine, the activity of the exhaust purification catalyst may be lost. The air-fuel ratio detection request for the air-fuel ratio sensor of the present invention may be issued at least when the exhaust purification catalyst is active.

  For example, when detecting the air-fuel ratio of exhaust when supplying the reducing agent to the exhaust purification catalyst, the air-fuel ratio detection request is issued in a state where the exhaust purification catalyst is active. If the activity of the exhaust purification catalyst is lost during the automatic stop of the internal combustion engine, it may take some time for the catalyst to reactivate after the internal combustion engine is restarted.

  Here, the relationship between the catalyst bed temperature of the exhaust purification catalyst and the detection non-request period during the automatic stop of the internal combustion engine is that the lower the catalyst bed temperature, the later the timing at which the exhaust purification catalyst is activated after the internal combustion engine is restarted. The detection non-request period becomes longer.

  Therefore, if the air-fuel ratio detection request to the air-fuel ratio sensor is issued at least when the exhaust purification catalyst is active, the detection non-request period is the catalyst bed temperature of the exhaust purification catalyst during the automatic stop of the internal combustion engine. It is preferable that the lower period is estimated as a longer period.

  According to this, in view of the fact that the detection non-request period differs according to the catalyst bed temperature of the exhaust purification catalyst during the automatic stop of the internal combustion engine, the target temperature of the air-fuel ratio sensor during the automatic stop is set according to the catalyst bed temperature. Can be set. Therefore, it is possible to more accurately realize reduction of the energization amount to the heater during the automatic stop of the internal combustion engine and ensuring responsiveness to the air-fuel ratio detection request after the restart of the internal combustion engine. In other words, when the detection non-request period is shorter, the air-fuel ratio sensor is surely activated within the range of the detection non-request period, and when the detection non-request period is long, the energization amount to the heater is reduced as much as possible. You can plan.

  Further, the exhaust purification catalyst in the present invention may be configured to include an NOx storage reduction catalyst. In the detection non-request period, after the internal combustion engine is restarted from the state where it is automatically stopped, the NOx reduction process for reducing NOx stored in the NOx storage reduction catalyst is performed for the first time. It may be a period.

  In the NOx reduction process, a reducing agent is supplied to the catalyst so as to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst. In that case, the supply amount of the reducing agent can be feedback controlled by detecting the exhaust gas flowing out from the NOx storage reduction catalyst and the air-fuel ratio of the exhaust gas flowing in by the air-fuel ratio sensor.

Here, the relationship between the NOx occlusion amount stored in the NOx storage reduction catalyst and the detection non-request period will be considered. Since the NOx reduction process is performed before the NOx storage capacity of the NOx storage reduction catalyst is saturated, the NOx reduction process is performed later when the NOx storage amount is small than when the NOx storage amount is large. Accordingly, it is preferable that the detection non-request period in the present invention is estimated as a longer period as the NOx occlusion amount occluded in the NOx storage reduction catalyst decreases.

  According to this, since the detection non-request period is estimated as a more appropriate period according to the NOx occlusion amount, the target temperature of the air-fuel ratio sensor during the automatic stop of the internal combustion engine can be set more finely and accurately. it can.

  Here, if the catalyst bed temperature decreases excessively during the automatic stop of the internal combustion engine, condensed water may be generated in the exhaust passage. When the internal combustion engine is restarted in a state where condensed water is generated in this way, the condensed water may be guided to the air-fuel ratio sensor by the flow of exhaust gas discharged from the internal combustion engine, and the air-fuel ratio sensor may be flooded. If the sensor temperature when the air-fuel ratio sensor is wet is high, so-called water cracking may occur due to thermal shock. In other words, even when the air-fuel ratio sensor is flooded, thermal shock can be mitigated and water cracking can be prevented if the temperature of the sensor when flooded is relatively low.

  According to the present invention, the target temperature of the air-fuel ratio sensor can be set to the low temperature side under conditions where condensate is likely to be generated such that the catalyst bed temperature of the exhaust purification catalyst becomes low during the automatic stop of the internal combustion engine. In addition, water cracking of the air-fuel ratio sensor can be suitably suppressed.

  Further, the present invention for more reliably suppressing the occurrence of water cracking is that the target temperature is a sensor crack when the catalyst bed temperature of the exhaust purification catalyst during the automatic stop of the internal combustion engine is equal to or lower than the condensed water generation temperature. It is preferable that the temperature is set to a temperature not higher than the suppression temperature.

  Here, the condensed water generation temperature is an upper limit temperature of the catalyst bed temperature at which it is determined that condensed water is generated in the exhaust passage. The sensor cracking suppression temperature is the upper limit temperature of the air-fuel ratio sensor that can suppress water cracking even if condensed water is generated in the exhaust passage during the automatic stop of the internal combustion engine. Note that the condensed water generation temperature and the sensor cracking suppression temperature can be obtained in advance based on experiments or the like.

  According to the present invention, even when the catalyst bed temperature of the exhaust purification catalyst during the automatic stop of the internal combustion engine becomes equal to or lower than the condensed water generation temperature and condensed water is generated, the generation of water cracking is ensured. Can be suppressed.

  In addition, when the catalyst bed temperature of the exhaust purification catalyst during the automatic stop of the internal combustion engine is equal to or lower than the condensed water generation temperature, the target temperature can be appropriately set within a range equal to or lower than the sensor crack suppression temperature. That is, the target temperature set below the sensor cracking suppression temperature may be set as a substantially constant temperature, or the target temperature may be set to a lower temperature side as the catalyst bed temperature is lower.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  The present invention provides a technique capable of satisfying both reduction of the energization amount to the heater during the automatic stop of the internal combustion engine and ensuring responsiveness to the detection request of the air-fuel ratio after the restart of the internal combustion engine. Can do.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its exhaust system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 is a four-cycle diesel engine. Further, the vehicle on which the internal combustion engine 1 is mounted in the present embodiment is an economy running (eco-run) vehicle.

  An exhaust passage 2 is connected to the internal combustion engine 1. An occlusion reduction type NOx catalyst (hereinafter referred to as “NOx catalyst”) 3 is provided in the middle of the exhaust passage 2. The NOx catalyst 3 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have. Note that the NOx catalyst 3 in this embodiment is carried by a particulate filter that collects particulate matter in the exhaust gas.

  Furthermore, in this embodiment, a fuel addition valve 4 is provided for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage 2 upstream of the NOx catalyst 3. Here, the fuel addition valve 4 is opened by a signal from the ECU 20 described later to inject fuel. The fuel injected from the fuel addition valve 4 into the exhaust passage 2 enriches the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 2 and reduces NOx stored in the NOx catalyst 3. .

  The NOx catalyst 3 is provided with a bed temperature detection sensor 5 for detecting the catalyst bed temperature THc of the NOx catalyst 3. An air-fuel ratio sensor 6 that outputs a signal corresponding to the air-fuel ratio of the exhaust gas flowing through the exhaust passage 3 is attached to the exhaust passage 2 downstream of the NOx catalyst 3. The air-fuel ratio sensor 6 is provided with a heater 7 for raising the temperature of the air-fuel ratio sensor 6.

  Further, the internal combustion engine 1 is provided with a fuel injection valve 8 for supplying fuel into the cylinder of the internal combustion engine 1. The bed temperature detection sensor 5 may be attached upstream or downstream of the NOx catalyst 3.

  A starter motor 9 for starting the internal combustion engine 1 is attached to the internal combustion engine 1. The starter motor 9 is driven by electric power supplied from a battery (not shown). A pinion gear (not shown) is attached to the drive shaft of the starter motor 9, and a ring gear (not shown) attached to one end of a crankshaft (not shown) of the internal combustion engine 1 is driven by this pinion gear. As a result, the internal combustion engine 1 is cranked, whereby the internal combustion engine 1 is started.

  The internal combustion engine 1 configured as described above is provided with an ECU 20 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 20 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the above sensors, the ECU 20 includes an accelerator opening sensor 11 that outputs an electric signal corresponding to the depression amount of the accelerator pedal, a brake opening sensor 12 that outputs an electric signal corresponding to the depression amount of the brake pedal, and an engine. A crank position sensor 13 for detecting the number of revolutions, a vehicle speed sensor 14 for outputting an electric signal corresponding to the speed (vehicle speed) of the vehicle, and a shift position sensor 15 for detecting the position of the shift lever are connected via electric wiring. The sensor output signal is input to the ECU 20.

On the other hand, the fuel injection valve 8, the fuel addition valve 4, the heater 7, and the starter motor 9 are connected to the ECU 20 through electrical wiring, and these are controlled by the ECU 20. That is, the ECU 20 can control the opening / closing timing, the valve opening period, and the like of the fuel injection valve 8 and the fuel addition valve 4.

  Further, the ECU 20 can heat the heater 7 by energizing the heater 7 from a power source (not shown), and can raise the temperature of the air-fuel ratio sensor 6 by the heat. Further, the ECU 20 can control the energization amount to the heater 7, thereby controlling the temperature of the air-fuel ratio sensor 6. Further, the ECU 20 can start the internal combustion engine 1 by driving the drive shaft of the starter motor 9.

  In this embodiment, when the NOx reduction process for reducing the NOx stored in the NOx catalyst 3 is performed, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 3 (hereinafter referred to as “inflowing exhaust air-fuel ratio”) is the target air-fuel ratio. In so doing, so-called rich spike control is executed to make the spike rich (short time) in a relatively short cycle.

  For example, the NOx reduction process is performed when the ECU 20 estimates the NOx occlusion amount occluded in the NOx catalyst 3 from the operation history of the internal combustion engine 1 and the estimated NOx occlusion amount is equal to or greater than a preset threshold value. Here, the threshold value is a value obtained by subtracting a predetermined margin from the amount of NOx that can be stored by the NOx catalyst 3, and it can be determined that the NOx reduction process should be executed when the NOx storage amount becomes equal to or greater than this value. Value.

  In addition to the NOx reduction process, the rich spike control performs an SOx poisoning recovery process for recovering the sulfur poisoning (SOx poisoning) of the NOx catalyst 3, or raises the temperature of the particulate filter. This is also performed when PM regeneration processing is performed to oxidize and remove PM deposited on the filter.

  Next, the control concerning the automatic stop and restart of the internal combustion engine 1 in the present embodiment will be described. The vehicle on which the internal combustion engine 1 is mounted in the present embodiment is an eco-run vehicle, and when the vehicle temporarily stops like waiting for a signal at an intersection, the internal combustion engine 1 is automatically stopped and the vehicle restarts. In this case, idling stop control for automatically restarting the internal combustion engine 1 is performed.

  Here, the idling stop control is a control executed by the ECU 20. The idling stop condition, which is an execution condition of the idling stop control, is that the ignition speed is ON, for example, the vehicle speed detection signal from the vehicle speed sensor 14 detects that the vehicle speed is “0”, and the brake opening degree sensor 12 This is established when it is detected that the brake pedal is depressed by a brake pedal depression signal. When the idling stop condition is satisfied, the ECU 20 issues a command to the fuel injection valve 8 and stops the internal combustion engine 1 by stopping the fuel injection (fuel cut). In this embodiment, the idling stop condition corresponds to the automatic stop condition in the present invention.

  On the other hand, the ECU 20 restarts the internal combustion engine 1 when the idling stop cancellation condition is satisfied while the internal combustion engine 1 is automatically stopped. The idling stop release condition is established by detecting that the brake pedal depression release operation is performed by a brake pedal depression release signal from the brake opening sensor 12 after the idling stop condition is established. The satisfaction of the idling stop cancellation condition means that, after the idling stop condition is satisfied, the state shifts to a state where the condition is not satisfied.

  When the idling stop cancellation condition is satisfied (corresponding to the cancellation of the automatic stop condition), the ECU 20 performs control for starting the fuel injection operation of the fuel injection valve 8 and operates the starter motor 9 to perform cranking. Restart. In the present embodiment, the ECU 20 that executes the idling stop control corresponds to the automatic control means in the present invention.

  Here, FIG. 2 is a time chart illustrating the time transition of the catalyst bed temperature THc of the NOx catalyst during the idling stop and after the internal combustion engine 1 is restarted. The time TMiss shown on the horizontal axis represents the time when the idling stop condition is satisfied, and the time TMise represents the time when the idling stop cancellation condition is satisfied. The vertical axis represents the catalyst bed temperature THc, and the symbol THca represents the activation temperature of the NOx catalyst 3 (hereinafter referred to as “catalyst activation temperature”). Note that idling stop means that the internal combustion engine 1 is being automatically stopped.

  As the idling stop control is performed at time TMiss, when the internal combustion engine 1 is automatically stopped and high-temperature exhaust gas is not discharged, the catalyst bed temperature THc gradually decreases as shown in the figure. When the idling stop is continued for a long period of time, such as when the vehicle stop time is prolonged, the catalyst bed temperature THc decreases to a temperature lower than the catalyst activation temperature THca, and the NOx catalyst 3 shifts from the active state to the inactive state. .

  When the idling stop is canceled and the internal combustion engine 1 is restarted at the time TMise, the exhaust temperature of the exhaust gas starts from the internal combustion engine 1 and thus the catalyst bed temperature THc rises. Then, the NOx catalyst 3 shifts from the inactive state to the active state during a time TMca in which the catalyst bed temperature THc rises above the catalyst active temperature THca (hereinafter referred to as “catalyst activation start time”).

  With reference to FIG. 2, the time when rich spike control is performed will be considered. Here, the rich spike control related to the NOx reduction process for the NOx catalyst 3 will be described as an example. In the rich spike control, an oxidation-reduction reaction is caused between the added fuel as the reducing agent added from the fuel addition valve 4 and the NOx occluded in the NOx catalyst 3. Therefore, the rich spike control has at least the catalyst bed temperature THc. It is necessary to carry out in a state where the catalyst activation temperature is THca or higher.

  Therefore, when the catalyst bed temperature THc is lower than the catalyst activation temperature THca at the time TMise as shown in the drawing, the rich spike control is performed at least after the catalyst activation start time TMca in which the NOx catalyst 3 is activated.

  In this embodiment, the air-fuel ratio of the exhaust is detected by the air-fuel ratio sensor 6 when rich spike control is performed. Based on the detection value of the air-fuel ratio sensor 6, the fuel addition amount feedback control by the fuel addition valve 4 is performed so that the inflow exhaust air-fuel ratio becomes the target air-fuel ratio. Therefore, it can be said that the air-fuel ratio detection by the air-fuel ratio sensor 6 in the present embodiment is performed at least in a state where the NOx catalyst 3 is active.

  By the way, the air-fuel ratio sensor 6 becomes inactive when the sensor element becomes low temperature, and it becomes difficult to operate normally. Therefore, in order to detect the air-fuel ratio of the exhaust gas during the execution of rich spike control, the temperature of the air-fuel ratio sensor 6 (hereinafter referred to as “air-fuel ratio sensor temperature”) THse is set to an activation temperature (hereinafter referred to as 650 to 750 ° C.), for example. It is necessary to maintain THsea (referred to as “sensor activation temperature”).

  On the other hand, it is considered that the air-fuel ratio sensor temperature THse may be maintained at the sensor activation temperature THsea even after the internal combustion engine 1 is automatically stopped. However, in this case, there is a contradiction that the energization amount to the heater 7 becomes excessive. Arise.

Therefore, in the present embodiment, the ECU 20 sets the target value (hereinafter referred to as “target sensor temperature”) THset of the air-fuel ratio sensor temperature during idling stop, after reducing the energization amount to the heater 7 and restarting the internal combustion engine 1. Is set so as to be compatible with ensuring the responsiveness to the air-fuel ratio detection request. Hereinafter, target sensor temperature THs during idling stop
et will be described in detail. In this embodiment, the target sensor temperature THset corresponds to the target temperature in the present invention.

  Here, a period from the time TMise when the internal combustion engine 1 is restarted to the time when the air-fuel ratio sensor 6 is first requested to detect the air-fuel ratio is referred to as a detection non-request period ΔTM. In the present embodiment, when the idling stop condition is satisfied and the internal combustion engine 1 is automatically stopped, the ECU 20 estimates the detection non-request period ΔTM. Then, the target sensor temperature THset during idling stop of the internal combustion engine 1 is set based on the detection non-request period. In this embodiment, the ECU 20 that estimates the detection non-request period ΔTM corresponds to the period estimation means in the present invention.

  Next, the relationship between the catalyst bed temperature THc during idling stop, the detection non-request period ΔTM, and the target sensor temperature THset will be described. Here, the detection non-request period ΔTM when the catalyst bed temperature THc is high and low at the same time (for example, time TMise) is compared. First, when the catalyst bed temperature THc is low, it takes time until the catalyst bed temperature THc rises to the catalyst activation temperature THca (that is, the period from the time TMise to the catalyst activation start time TMca becomes longer). Here, since the air-fuel ratio detection request to the air-fuel ratio sensor 6 is issued at least after the catalyst activation start time TMca, when the catalyst bed temperature THc during idling stop is low, detection is not required as compared with the high case. The period ΔTM becomes longer.

  Here, FIG. 3 is a map illustrating the relationship among the catalyst bed temperature THc, the detection non-request period ΔTM, and the target sensor temperature THset during idling stop. In the figure, the detection non-request period ΔTM is indicated by a broken line, and the target sensor temperature THset is indicated by a solid line. In the present embodiment, as shown in the figure, the detection non-request period ΔTM is estimated as a longer period as the catalyst bed temperature THc during idling stop is lower.

  Next, the relationship between the detection non-request period ΔTM and the target sensor temperature THset will be described. Since the air-fuel ratio sensor 6 is not requested to detect the air-fuel ratio during the detection non-request period ΔTM, the time when the air-fuel ratio sensor 6 is activated by raising the air-fuel ratio sensor temperature THse to the sensor activation temperature THsea is not required to be detected. It can be delayed as the period ΔTM becomes longer. Therefore, the target sensor temperature THset during idling stop is set to a lower temperature as the detection non-request period ΔTM is longer.

  Therefore, in this embodiment, the lower the catalyst bed temperature THc during idling stop, the longer the detection non-request period ΔTM is estimated, and the target sensor temperature THset is set to the lower temperature side. The energization amount to the heater 7 is controlled so that the air-fuel ratio sensor temperature THse becomes the target sensor temperature THset set by the ECU 20.

  According to this, the higher the catalyst bed temperature THc during idling stop, the higher the target sensor temperature THset is set to the higher temperature side. Therefore, even when the detection non-request period ΔTM becomes shorter, the air-fuel ratio sensor 6 becomes empty. The sensor 6 can be reliably activated before the request for detecting the fuel ratio is issued. That is, it is possible to suitably ensure the responsiveness to the air-fuel ratio detection request.

  Further, since the target sensor temperature THset is set to a lower temperature as the catalyst bed temperature THc is lower, the energization amount to the heater 7 can be reduced while ensuring the response to the air-fuel ratio detection request. Although the relationship between the catalyst bed temperature THc, the detection non-request period ΔTM, and the target sensor temperature THset shown in FIG. 3 is linearly expressed, it may be expressed in a curved line. It can ask for.

  Further, as the catalyst bed temperature THc during idling stop decreases, the estimated value of the detection non-request period ΔTM may be changed stepwise or may be changed continuously. Accordingly, as the catalyst bed temperature THc during idling stop decreases, the setting of the target sensor temperature THset may be changed stepwise or may be changed continuously.

  Next, a routine related to control of the air-fuel ratio sensor temperature THse while the ECU 20 is idling stopped will be described. FIG. 4 is a flowchart showing a control routine in the present embodiment. In this embodiment, the ECU 20 that executes this routine corresponds to the period estimation means and the temperature control means in the present invention.

  When this routine is executed, it is first determined in step S101 whether or not idling is stopped. Since the idling stop control execution condition, release condition, and the like have already been described, description thereof will be omitted. When an affirmative determination is made in this step (when it is determined that idling is stopped), the process proceeds to step S102, and when a negative determination is made, this routine is once ended.

  In step S102, the catalyst bed temperature THc is detected based on the output value of the bed temperature detection sensor 5. In the subsequent step S103, the detection non-request period ΔTM is estimated based on the catalyst bed temperature THc with reference to the map described in FIG. 3, and the target sensor temperature THset is calculated based on the estimated value of the detection non-request period ΔTM. . The target sensor temperature THset may be obtained directly based on the catalyst bed temperature THc.

  In step S104, the energization amount to the heater 7 is controlled so that the air-fuel ratio sensor temperature THse becomes the target sensor temperature THset. When the processing of this step is completed, this routine is once ended.

  According to this control, it is possible to achieve both reduction of the energization amount to the heater 7 during idling stop and ensuring of responsiveness to the air-fuel ratio detection request after the internal combustion engine 1 is restarted. Further, since this routine is repeatedly executed every predetermined period, the longer the idling stop duration period, the lower the target sensor temperature THset obtained in the process of step S103 shifts to the low temperature side with time. This is because the set value of the target sensor temperature THset is updated to a lower temperature side as the catalyst bed temperature THc decreases with time during idling stop. Accordingly, the effect of reducing the energization amount to the heater 7 by performing this control becomes more prominent as the idling stop duration is longer.

  In this embodiment, the case where the NOx storage reduction catalyst as the exhaust purification catalyst is disposed in the exhaust passage 2 is described as an example, but the present invention is not limited to this. For example, the application of the present invention is not hindered even if the types of catalysts such as an oxidation catalyst and a selective reduction type NOx catalyst are different.

  Next, Example 2 in the present embodiment will be described. Note that the internal combustion engine 1 and its exhaust system according to the present embodiment are the same as those of the first embodiment, and a description thereof will be omitted. Hereinafter, the relationship between the catalyst bed temperature THc and the target sensor temperature THset during idling stop of the present embodiment will be described with reference to FIG.

  FIG. 5 is a second map illustrating the relationship between the catalyst bed temperature THc, the detection non-request period ΔTM, and the target sensor temperature THset during idling stop. In the figure, similarly to FIG. 3, the detection non-request period ΔTM is indicated by a broken line, and the target sensor temperature THset is indicated by a solid line.

  First, the first difference between the second map shown in FIG. 5 and the map shown in FIG. 3 will be described. The symbol THcb shown on the horizontal axis in the figure represents the reference temperature THcb. The reference temperature THcb is a catalyst temperature at which the detection non-request period ΔTM is determined to be excessively short when the catalyst bed temperature THc during idling stop is equal to or higher than this temperature. That is, in this case, it means that there is a high possibility that an air-fuel ratio detection request is issued immediately after the internal combustion engine 1 is restarted.

  In this embodiment, the catalyst activation temperature THca is adopted as the reference temperature THcb. This is because if the catalyst bed temperature THc during idling stop is the catalyst activation temperature THca, rich spike control can be executed immediately after the internal combustion engine 1 is restarted. Further, when the catalyst bed temperature THc during idling stop is equal to or higher than the catalyst activation temperature THca, the detection non-request period ΔTM is estimated as zero. When the estimated value of the detection non-request period ΔTM in this embodiment is zero, the target sensor temperature THset is set as a temperature equal to or higher than the sensor activation temperature THsea.

  According to this, when the catalyst bed temperature THc is equal to or higher than the reference temperature THcb (for example, the catalyst activation temperature THca), the estimated value of the detection non-request period ΔTM becomes zero, and the target sensor temperature THset is equal to or higher than the sensor activation temperature THsea. Set to the temperature of. As a result, since the air-fuel ratio sensor temperature THse is maintained at the sensor activation temperature THsea or higher even when the idling stop cancellation condition is satisfied, it is possible to respond to the air-fuel ratio detection request immediately after the internal combustion engine 1 is restarted. Can do.

  Further, as a second difference between the second map shown in FIG. 5 and the map shown in FIG. 3, when the catalyst bed temperature THc is equal to or lower than the condensed water generation temperature THcu, the target sensor temperature THset is sensor cracking. The temperature is set to be equal to or lower than the suppression temperature THseu.

  When the catalyst bed temperature THc during idling stop becomes excessively low, condensed water is easily generated in the exhaust passage 2. When the internal combustion engine 1 is restarted in a state where condensed water is generated in the exhaust passage 2, the air-fuel ratio sensor 6 is flooded by the flow of exhaust from the internal combustion engine 1. If the air-fuel ratio sensor 6 gets wet with the air-fuel ratio sensor temperature THse being high, the air-fuel ratio sensor 6 is damaged (water cracking) due to thermal shock.

  On the other hand, even when the air-fuel ratio sensor 6 is flooded with condensed water, if the air-fuel ratio sensor temperature THse at that time is sufficiently low, the aforementioned water cracking is unlikely to occur. Therefore, in this embodiment, when the catalyst bed temperature THc is equal to or lower than the condensed water generation temperature THcu, the target sensor temperature THset is set as a temperature equal to or lower than the sensor cracking suppression temperature THseu.

  The condensed water generation temperature THcu is an upper limit temperature of the catalyst bed temperature THc at which it is determined that condensed water is generated in the exhaust passage 2. The sensor cracking suppression temperature THseu is the upper limit temperature of the air-fuel ratio sensor temperature THse at which it can be determined that the air-fuel ratio sensor 6 will not cause water cracking even if condensed water is generated in the exhaust passage 2 during idling stop. The relationship between the condensed water generation temperature THcu and the sensor cracking suppression temperature THseu can be obtained in advance based on experiments or the like.

  According to this, even when condensed water is generated in the exhaust passage 2 by continuing idling stop, the target sensor temperature THset is set within a range equal to or lower than the sensor cracking suppression temperature THseu. Water cracking of the sensor 6 can be suppressed.

In the second map, in the range where the catalyst bed temperature THc is equal to or lower than the condensed water generation temperature THcu, an example is shown in which the target sensor temperature THset is set as a substantially constant temperature within the range equal to or lower than the sensor cracking suppression temperature THseu. However, it is not limited to this. For example, as shown by a chain line, even when the target sensor temperature THset is set as a temperature equal to or lower than the sensor cracking suppression temperature THseu, the lower the catalyst bed temperature THc, the lower the target sensor temperature THset is set. You can also.

  Next, Example 3 in the present embodiment will be described. Note that the internal combustion engine 1 and its exhaust system according to the present embodiment are the same as those of the first embodiment, and a description thereof will be omitted. In this embodiment, the detection non-request period ΔTM and the setting of the target sensor temperature THset during idling stop are performed more finely according to the NOx occlusion amount occluded in the NOx catalyst 3.

  FIG. 6 is a third map illustrating the relationship between the NOx occlusion amount occluded in the NOx catalyst 3, the detection non-request period ΔTM, and the target sensor temperature THset. In the figure, the detection non-request period ΔTM is indicated by a broken line, and the target sensor temperature THset is indicated by a solid line. Since the NOx reduction process for the NOx catalyst 3 is performed when the NOx occlusion amount becomes equal to or greater than the threshold value, the smaller the NOx occlusion amount, the later the execution timing of the NOx reduction process. Therefore, as shown in the figure, in this embodiment, the detection non-request period ΔTM is estimated as a longer period as the NOx occlusion amount decreases. Therefore, the smaller the NOx occlusion amount, the lower the target sensor temperature THset during idling stop.

  FIG. 7 is a diagram illustrating a setting example of the target sensor temperature THset during idling stop. In the figure, the case where the NOx occlusion amount is large (broken line) and the case where it is small (solid line) are compared. Moreover, what is synonymous with the code | symbol used in FIG. 5 attaches | subjects the same code | symbol, and abbreviate | omits description.

  As shown in the figure, even when the catalyst bed temperature THc during idling stop is the same, the lower the NOx occlusion amount, the lower the target sensor temperature THset is set. In the present embodiment, since the target sensor temperature THset can be set more finely according to the NOx occlusion amount, the effect of reducing the energization amount to the heater 7 during idling stop can be more remarkably exhibited.

  In this embodiment, the method for setting the target sensor temperature THset according to the NOx occlusion amount of the NOx catalyst 3 has been described. However, the target sensor temperature THset can also be set from other viewpoints. The rich spike control is also executed when SOx poisoning recovery control for the NOx catalyst 3 and PM regeneration processing for the particulate filter are performed.

  Here, the smaller the SOx occlusion amount, the later the execution timing of the SOx poisoning recovery process after the internal combustion engine 1 is restarted. The smaller the PM accumulation amount, the more the execution timing of the PM regeneration process after the internal combustion engine 1 is restarted. Become slow. Therefore, it is preferable to estimate the detection non-request period ΔTM as a longer period as the SOx occlusion amount stored in the NOx catalyst 3 is smaller, and set the target sensor temperature THset during idling stop to a lower temperature side. Similarly, the smaller the amount of PM deposited on the particulate filter carrying the NOx catalyst 3, the longer the detection non-request period ΔTM is estimated, and the target sensor temperature THset is set to a lower temperature side. Also good.

  According to these, the target sensor temperature THset during idling stop can be set more finely according to the SOx occlusion amount and the PM accumulation amount. Thereby, the energization amount to the heater 7 during idling stop can be suitably reduced while ensuring responsiveness to the air-fuel ratio detection request after the internal combustion engine 1 is restarted.

  In addition, although the embodiments of the present invention have been described in the first to third embodiments, various changes and additions can be added without departing from the spirit of the present invention. For example, although the internal combustion engine 1 according to the present embodiment is mounted on an eco-run vehicle, it is needless to say that the internal combustion engine 1 may be mounted on a hybrid vehicle. Also, in the case of a hybrid vehicle, when the power source of the vehicle is shifted from the operating condition in which only the internal combustion engine 1 is used or the combined use of the internal combustion engine 1 and the electric motor to the operating condition in which only the electric motor is used as the power source. The internal combustion engine 1 is automatically stopped. Therefore, when the internal combustion engine 1 is automatically stopped even while the vehicle is traveling, the present invention can be applied to suitably perform control related to the temperature of the air-fuel ratio sensor 6 during the automatic stop.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an exhaust system thereof according to Embodiment 1. FIG. 6 is a time chart illustrating the time transition of the catalyst bed temperature THc of the NOx catalyst during idling stop and after restart of the internal combustion engine. 6 is a map illustrating a relationship among a catalyst bed temperature THc, a detection non-request period ΔTM, and a target sensor temperature THset during idling stop. 3 is a flowchart illustrating a control routine in the first embodiment. It is the 2nd map which illustrated the relationship of catalyst bed temperature THc in idling stop, detection non-request | requirement period (DELTA) TM, and target sensor temperature THset. It is the 3rd map which illustrated the relationship between NOx occlusion amount occluded by the NOx catalyst, detection non-request period ΔTM, and target sensor temperature THset. It is the figure which showed the example of a setting of the target sensor temperature THset during idling stop.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... NOx storage reduction catalyst 4 ... Fuel addition valve 5 ... Bed temperature detection sensor 6 ... Air-fuel ratio sensor 7 ... Heater 20・ ECU

Claims (4)

An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
An air-fuel ratio sensor provided in the exhaust passage;
A heater for raising the temperature of the air-fuel ratio sensor;
Temperature control means for controlling the energization amount to the heater to control the temperature of the air-fuel ratio sensor to a target temperature;
Automatic control means for automatically stopping the internal combustion engine when the automatic stop condition for the internal combustion engine is satisfied and restarting the internal combustion engine when the automatic stop condition is canceled;
When the automatic control means automatically stops the internal combustion engine, period estimation means for estimating a detection non-request period from when the internal combustion engine is restarted until the first air-fuel ratio detection request is issued to the air-fuel ratio sensor When,
With
The control apparatus for an internal combustion engine, wherein the target temperature during the automatic stop of the internal combustion engine is set to a lower temperature side as the detection non-request period is longer. The air-fuel ratio detection request is issued at least when the exhaust purification catalyst is active,
The control apparatus for an internal combustion engine according to claim 1, wherein the detection non-request period is estimated as a longer period as the catalyst bed temperature of the exhaust purification catalyst during the automatic stop of the internal combustion engine is lower. The exhaust purification catalyst includes an NOx storage reduction catalyst,
The control device for an internal combustion engine according to claim 1 or 2, wherein the detection non-request period is estimated as a longer period as the NOx occlusion amount stored in the NOx storage reduction catalyst decreases.   The target temperature is set as a temperature not higher than a sensor cracking suppression temperature when a catalyst bed temperature of the exhaust purification catalyst during automatic stop of the internal combustion engine is not higher than a condensed water generation temperature. The control device for an internal combustion engine according to any one of 1 to 3.

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