JP4140397B2 - Activity determination device for engine oxidation catalyst - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to determining the activity of an oxidation catalyst for an engine disposed in an exhaust passage of an engine.EquipmentIt is related.
[0002]
[Prior art]
  In general, an oxidation catalyst having an oxidation function is disposed in the exhaust passage of the engine, and HC (hydrocarbon) and CO (carbon monoxide) in the exhaust gas are purified by a catalytic reaction.
[0003]
  Further, since the oxidation catalyst has a property of generating reaction heat by a catalytic reaction, the oxidation catalyst is also used for raising the exhaust gas temperature.
[0004]
  For example, a small oxidation catalyst is placed immediately downstream of the exhaust manifold of the engine, and a normal three-way catalyst is placed downstream of the exhaust manifold. When the engine is cold started, a large amount of unburned fuel is supplied to the oxidation catalyst. By doing so, the oxidation catalyst is activated early, and the downstream three-way catalyst is activated early by utilizing the reaction heat of the oxidation catalyst generated thereby.
[0005]
  Also, for example, by placing a ceramic particulate filter that captures particulates while passing exhaust gas in the exhaust passage of a diesel engine or direct injection gasoline engine that can perform lean burn, exhaust gas discharged from the engine The carbon particles contained therein are captured. In this case, by placing an oxidation catalyst upstream of the particulate filter and supplying unburned fuel from the upstream of the oxidation catalyst, the temperature of the particulate filter is raised using the reaction heat of the catalyst of the oxidation catalyst. Also, a technique for regenerating the capturing ability of the particulate filter by burning and removing the captured fine particles is also known.
[0006]
  As a method for supplying unburned fuel to such an oxidation catalyst, in a so-called direct injection engine in which a fuel injection valve is arranged so as to be directed into the combustion chamber of the engine and fuel is directly injected into the combustion chamber from the fuel injection valve. A method of supplying unburned fuel by controlling the fuel injection timing and the injection amount is also known.
[0007]
  By the way, it is known that an oxidation catalyst exhibits a catalytic reaction when the active state of the oxidation catalyst is high, but does not exhibit a catalytic reaction when the active state is low. Therefore, for example, in the technology using the reaction heat of the oxidation catalyst as described above, even if the unburned fuel is supplied when the active state is low, the catalytic reaction hardly occurs, so that the reaction heat of the catalyst is generated. Is not promoted, and the temperature rise effect of the exhaust gas is hardly obtained.
[0008]
  Therefore, it is necessary to determine the activity of the catalytic reaction and adjust the operation of the engine in accordance with the activity.
[0009]
  For example, as a method for determining the activity of a catalyst, the following Patent Document 1 describes the temperature of a catalyst carrier detected by a temperature sensor directly attached to the catalyst carrier and the degree of deterioration of the catalyst obtained from the temperature history of such catalyst temperature. Based on the above, there is disclosed a technique for determining the activity or determining the activity from the change in the HC concentration upstream and downstream of the catalyst.
[0010]
  Further, in this document, the temperature of the EGR gas (exhaust gas recirculation gas) is adjusted so that the temperature of the exhaust gas from the engine is raised when the activity is low by determining the activity of the catalyst by such a method. The technology to do is also disclosed.
[0011]
[Patent Document 1]
    JP 2001-280123 A
[0012]
[Problems to be solved by the invention]
  However, as a result of the studies by the inventors of the present invention, the activity of the oxidation catalyst depends on the catalyst temperature, the degree of deterioration of the catalyst, and the HC concentration change between the upstream and downstream of the oxidation catalyst, as described in Patent Document 1. It was impossible to judge with higher accuracy, and the activity of the oxidation catalyst was found to be greatly related to other factors.
[0013]
  The inventors have found that one such other factor is the exhaust gas flow rate passing through the catalyst. In this case, it may be necessary not to determine the catalyst activity based on the exhaust gas flow rate alone, but also to determine the catalyst temperature in consideration at the same time in order to perform the activity determination with higher accuracy. I found it.
[0014]
  In the so-called direct injection engine, it has also been found that the other factor is the injection amount and the injection timing of the fuel injected from the fuel injection valve for supplying unburned fuel. In a direct injection engine, fuel is supplied directly into the combustion chamber in order to supply unburned fuel to the oxidation catalyst, and the amount of unburned fuel and unburned fuel are controlled by controlling the injection amount and timing of fuel. It was found that the unburned fuel supplied to the oxidation catalyst greatly affects the activity of the oxidation catalyst.
[0015]
  However, conventionally, when determining the activity of the oxidation catalyst, the flow rate of the exhaust gas passing through the oxidation catalyst, or when the unburned fuel is supplied to the oxidation catalyst from the fuel injection valve of the direct injection engine as described above. The determination based on the fuel injection amount and the injection timing is not known at all, and it is impossible to determine the activity with high accuracy.
[0016]
  The present invention has been made in consideration of the above-described problems, and its purpose is the flow rate of exhaust gas passing through the oxidation catalyst.,Supply unburned fuel to oxidation catalystforBy determining the degree of activity of the oxidation catalyst based on the fuel injection amount and the injection timing injected from the fuel injection valve, such activity level determination is performed with high accuracy.
[0017]
[Means for Solving the Problems]
  To achieve this purpose, this bookinventionIn the engine exhaust passageAcidOxidation catalyst with catalytic functionAnd a fuel injection valve for directly injecting fuel into the combustion chamber of the engine, and the fuel injection valve based on the operating condition of the engine so that unburned fuel is supplied from the fuel injection valve to the oxidation catalyst. And an injection control means for controlling the injection amount and the injection timing of the fuel injected by the engineIn the engine oxidation catalyst activity determination device for determining the activity of the oxidation catalyst,
  Temperature detecting means for detecting a temperature related to the catalyst temperature upstream of the oxidation catalyst;
  Exhaust gas flow rate estimating means for estimating the exhaust gas flow rate of exhaust gas passing through the oxidation catalyst;
  The detected temperature and the estimated exhaust gas flow rateBased on the fuel injection amount injected in the engine expansion stroke and the fuel injection timing,Determination means for determining the activity of the oxidation catalyst,
The determination means determines that the higher the detected temperature, the higher the activity of the oxidation catalyst, and the greater the estimated exhaust gas flow rate, the greater the fuel injection amount injected in the expansion stroke. As the fuel injection timing in the expansion stroke is delayed, it is determined that the activity of the oxidation catalyst is low.It is characterized by that.
[0018]
  Usually, an oxidation catalyst contains a catalyst metal, and the exhaust material is oxidized by the catalyst metal and the exhaust material contained in the exhaust gas approaching or contacting each other. The inventors have found that the activity of the oxidation catalyst differs between when the exhaust gas flow rate is high and when the exhaust gas flow rate is low, even if the environment surrounding the other oxidation catalyst is the same.
[0019]
  The reason for this is that when the exhaust gas flow rate is high, the contact time and the approach time between the catalyst metal and the exhaust material are shortened, so that the oxidation action to exhaust materials such as HC and CO is suppressed. It is thought that the oxidation as a whole of the oxidation catalyst is suppressed and the activity is lowered. On the other hand, when the exhaust gas flow rate is slow, the contact time and the approach time between the catalytic metal and the exhaust material are relatively long, and the oxidation action to the exhaust material is promoted, and the activity is considered to be improved.
[0020]
  Therefore,The present inventionIn this case, the activity can be determined with high accuracy by determining the activity of the oxidation catalyst based on the flow rate of the exhaust gas passing through the catalyst. In addition, the determination can be made in consideration of the temperature related to the catalyst temperature upstream of the oxidation catalyst, and the activity can be determined more accurately.
[0021]
  Also,A fuel injection valve that directly injects fuel into the combustion chamber is provided, and the engine cylinderIs the expansion strokeWhen the fuel injection is performed so that unburned fuel is supplied from the fuel injection valve to the oxidation catalyst in the exhaust passage, the supply state such as the unburned fuel supply amount is controlled by controlling the fuel injection amount and the injection timing. It is adjusted.
[0022]
  In this case, the greater the amount of fuel injected for supplying unburned fuel, or the later the injection timing, the more the miscibility between the unburned fuel and the exhaust gas (vaporization, mixing) is suppressed. Under this influence, even when the environment surrounding the other oxidation catalyst is the same, when the injection amount is large and small, or when the injection timing is late (retarded side) and early (advanced side), The inventors have found that the activity of the oxidation catalyst as a whole is different.
[0023]
  The reason for this is that the greater the injection amount or the later the injection timing, the more the unburned fuel mixability is suppressed, and the oxidation reaction of the catalyst in the entire oxidation catalyst is not actively performed, and the reaction heat is suppressed. Thus, as a result of locally suppressing the temperature rise inside the oxidation catalyst, it is considered that the activity of the entire oxidation catalyst is gradually increased. On the other hand, the smaller the injection amount or the earlier the injection timing, the better the mixing of unburned fuel, the reaction with the oxidation catalyst is promoted, the temperature inside the oxidation catalyst is increased, and the oxidation catalyst as a whole. It is thought that the increase in the activity is performed quickly.
[0024]
  Therefore,In the present invention,In addition to the flow rate of exhaust gas passing through the oxidation catalyst and the temperature related to the catalyst temperature upstream of the oxidation catalyst, the activity of the catalyst is determined based on the above injection amount and injection timing. Yes. Therefore, even when unburned fuel is supplied from the fuel injection valve to the oxidation catalyst, it is possible to accurately determine the activity of the oxidation catalyst.
[0025]
  the aboveThe exhaust velocity estimation means isIt flows into the combustion chamber detected by the intake air amount detection means.The exhaust gas flow rate is estimated based on the intake air amount, the injection amount of the fuel injected by the injection control means, and the detected temperature.Can be.
[0026]
  With this configuration, the exhaust gas flow rate can be accurately estimated based on the intake air amount sucked into the combustion chamber, the fuel injection amount, and the temperature related to the detected catalyst temperature upstream of the oxidation catalyst. Even if a sensor for directly detecting the exhaust gas flow rate is not disposed in the exhaust passage, the activity of the oxidation catalyst can be determined accurately and inexpensively. Moreover, since the intake air amount is an actual measurement value detected by the intake air amount detection means, the exhaust gas flow rate can be estimated more accurately, and the accuracy of determination of the activity can be improved.
[0027]
  So, for example, abovePurifying unit that has an oxidation catalyst and purifies exhaust substances contained in exhaust gasIn the case where the exhaust passage is provided,Based on the determined activity of the oxidation catalyst, the amount of fuel injected by the fuel injection valve and the injection so as to supply unburned fuel to the purification unit and raise the temperature of the purification unit Control at least one of the timesTo dobe able to.
[0028]
  In addition,The exhaust material refers to gases such as HC and CO in the exhaust gas, carbon particles that are one kind of fine particles, and the like.
[0029]
ThisThus, it is possible to accurately determine the degree of activity of the oxidation catalyst, for example, by controlling at least one of the fuel injection amount and the injection timing in the subsequent supply of unburned fuel. Due to the inability to do so, the current active state of the oxidation catalyst may cause problems such as excessively unburned fuel being supplied and the temperature of the purification section becoming abnormally high, resulting in damage to the purification section, or unburned fuel Therefore, the temperature of the purification section can be appropriately raised without causing a problem that the temperature rise performance of the purification section is deteriorated due to too little. As a result, exhaust purification performance can be improved.
[0030]
UpThe purification unit includes an oxidation catalyst and a particulate filter disposed downstream of the oxidation catalyst and capable of capturing exhaust particulates in the exhaust gas.LikeThe injection control means supplies the unburned fuel to the oxidation catalyst so that the temperature of the particulate filter becomes a high temperature at which trapped exhaust particulates can be incinerated and removed. And at least one of the injection timings is controlledCan be.
[0031]
  In order to incinerate and remove exhaust particulates captured by the particulate filter when an oxidation catalyst is placed in the exhaust passage and a particulate filter is placed downstream of the exhaust passage to increase the temperature of the downstream particulate filter by raising the temperature of the oxidation catalyst. Requires a large amount of unburned fuel to be supplied to the oxidation catalyst. When supplying such a large amount of unburned fuel, if the amount of unburned fuel supplied is not accurately controlled based on an accurate determination of the activity of the oxidation catalyst, for example, excess unburned fuel is supplied. As a result, the problem that the temperature of the purification unit becomes abnormally high and damages the purification unit, or the problem that the temperature rise performance of the purification unit deteriorates due to too little unburned fuel is more likely to occur. .
[0032]
  On the contrary,The injection control means, when supplying unburned fuel to the oxidation catalyst, the injection amount and the injection timing, so that the temperature of the particulate filter is high enough to incinerate and remove the trapped exhaust particulates, Since at least one of them is controlled, it is possible to prevent the occurrence of the above-described problems and to accurately raise the temperature of the particulate filter, and to improve the incineration removal property of the exhaust particulates.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0034]
  (overall structure)
  FIG. 1 shows an example of an engine exhaust gas purification apparatus A according to an embodiment of the present invention. Reference numeral 1 denotes a diesel engine mounted on a vehicle. This engine 1 has a plurality of cylinders (cylinders) 2, 2,... (Only one is shown), and a piston 3 is inserted into each cylinder 2 so as to be reciprocally movable. A combustion chamber 4 is defined in 2. In addition, an injector 5 (fuel injection valve) is disposed on the ceiling of the combustion chamber 4, and high-pressure fuel is directly injected into the combustion chamber 4 from the nozzle at the tip.
[0035]
  On the other hand, the base end portion of the injector 5 for each cylinder 2 is connected to a common fuel distribution pipe 6 (common rail) by branch pipes 6a, 6a,... (Only one is shown). The common rail 6 is connected to a high-pressure supply pump 9 by a fuel supply pipe 8, and is in a high-pressure state so that fuel supplied from the high-pressure supply pump 9 can be supplied to the injectors 5, 5,. The fuel pressure sensor 7 for detecting the internal fuel pressure (common rail pressure) is disposed.
[0036]
  The high-pressure supply pump 9 is connected to a fuel supply system (not shown), and is drivingly connected to the crankshaft 10 by a toothed belt or the like, and pumps fuel to the common rail 6 and part of the fuel is an electromagnetic valve. The amount of fuel supplied to the common rail 6 is adjusted by returning to the fuel supply system via the. The opening of the electromagnetic valve is controlled by an ECU 40 (described later) in accordance with a value detected by the fuel pressure sensor 7 so that the fuel pressure is controlled to a predetermined value corresponding to the operating state of the engine 1.
[0037]
  Further, although not shown, a valve operating mechanism for opening and closing the intake valve and the exhaust valve is disposed at the upper part of the engine 1, while the rotation angle of the crankshaft 10 is detected at the lower part of the engine 1. A crank angle sensor 11 and an engine water temperature sensor 13 for detecting the temperature of the cooling water are provided. Although not shown in detail, the crank angle sensor 11 is composed of a plate to be detected provided at the end of the crankshaft and an electromagnetic pickup arranged so as to face the outer periphery of the plate, and the entire circumference of the outer periphery of the plate to be detected. A pulse signal is output every time projections formed at equal intervals pass through.
[0038]
  An intake passage 16 for supplying air (fresh air) filtered by an air cleaner 15 to the combustion chamber 4 of each cylinder 2 is connected to one side (right side in the figure) of the engine 1. A surge tank 17 is provided at the downstream end of the intake passage 16, and each passage branched from the surge tank 17 communicates with the combustion chamber 4 of each cylinder 2 through an intake port. An intake pressure sensor 18 for detecting the pressure state of the intake air is provided.
[0039]
  The intake passage 16 is driven by a hot film type air flow sensor 19 for detecting the flow rate of air sucked into the engine 1 from the outside in order from the upstream side to the downstream side, and a turbine 27 to be described later. , An intercooler 21 that cools the intake air compressed by the compressor 20, and an intake throttle valve 22 that is a butterfly valve. The intake throttle valve 22 is in an arbitrary state from the fully closed state to the fully opened state by rotating the valve shaft by the stepping motor 23. Even in the fully closed state, the intake throttle valve 22 and the intake passage 16 are connected to each other. A gap is formed between the peripheral wall and air to allow air to flow in.
[0040]
  On the other hand, an exhaust passage 26 is connected to the side surface on the opposite side (left side in the figure) of the engine 1 so as to discharge combustion gas (exhaust gas) from the combustion chamber 4 of each cylinder 2. The upstream end portion of the exhaust passage 26 is an exhaust manifold that branches into each cylinder 2 and communicates with the combustion chamber 4 through an exhaust port. The exhaust passage 26 downstream from the exhaust manifold is provided on the downstream side from the upstream side. In turn, a linear O2 sensor 29 that detects the oxygen concentration in the exhaust, a turbine 27 that is rotated by receiving an exhaust flow, and an oxidation catalyst 28a that can oxidize harmful components (HC, CO, etc.) in the exhaust. A filter 28b capable of capturing fine particles such as carbon discharged from the combustion chamber is disposed downstream thereof.
[0041]
  The oxidation catalyst 28a is a general catalyst in which a cell layer of a porous ceramic honeycomb carrier is coated with a catalyst layer supporting a noble metal such as Pt. The catalyst component is adjusted so that the oxidation performance is particularly excellent. Further, the filter 28b is made of porous ceramics, and among the adjacent cells of the honeycomb, one of the cells is sealed at the upstream end, and the other cell is sealed at the downstream end. The cell surface is coated with a catalyst layer supporting a noble metal such as Pt. The temperature rise performance is improved by the reaction heat of the catalyst metal.
[0042]
  The filter 28b may not carry a catalyst metal, and conversely, the catalyst layer may contain an alkali metal or an alkaline earth metal in addition to the noble metal in order to further combine the NOx absorption capacity. .
[0043]
  In addition, the oxidation catalyst 28a and the filter 28b are spaced apart and arranged upstream and downstream, respectively, and the distance between the oxidation catalyst 28a and the filter 28b passes through the exhaust gas through which the temperature generated mainly by the oxidation reaction flows in the oxidation catalyst 28a. To the extent that it can be transmitted to.
[0044]
  The turbocharger 30 comprising the turbine 27 and the compressor 20 in the intake passage 16 is a variable turbo (hereinafter referred to as VGT) in which the cross-sectional area of the exhaust passage to the turbine 27 is changed by movable flaps 31, 31,. The flaps 31, 31,... Are connected to a diaphragm 32 via a link mechanism (not shown), and the magnitude of the negative pressure acting on the diaphragm 32 is an electromagnetic valve for negative pressure control. .., So that the rotational positions of the flaps 31, 31,... Are adjusted.
[0045]
  The exhaust passage 26 has an upstream end of an exhaust recirculation passage (hereinafter referred to as an EGR passage) 34 for recirculating a part of the exhaust to the intake side so as to open to a portion upstream of the turbine 27 toward the exhaust upstream side. It is connected. The downstream end of the EGR passage 34 is connected to the intake passage 16 between the intake throttle valve 22 and the surge tank 17 so that a part of the exhaust gas taken out from the exhaust passage 26 is returned to the intake passage 16. Yes. In the middle of the EGR passage 34, an EGR cooler 37 for cooling the exhaust gas flowing through the EGR passage 34 and an exhaust gas recirculation amount adjustment valve (hereinafter referred to as an EGR valve) 35 whose opening degree can be adjusted are arranged. The EGR valve 35 is of a negative pressure responsive type, and the magnitude of the negative pressure to the diaphragm is adjusted by the electromagnetic valve 36 in the same manner as the flaps 31, 31,. The flow rate of the exhaust gas recirculated to the intake passage 16 is adjusted by linearly adjusting the cross-sectional area. The EGR cooler 37 may not be provided.
[0046]
  Each of the injectors 5, the high pressure supply pump 9, the intake throttle valve 22, the VGT 30, the EGR valve 35, etc. operates in response to a control signal from a control unit (Electronic Control Unit: hereinafter referred to as ECU) 40. On the other hand, the ECU 40 receives output signals from the fuel pressure sensor 7, the crank angle sensor 11, the engine water temperature sensor 13, the intake pressure sensor 18, the air flow sensor 19, the linear O2 sensor 29, and the like, and further, an accelerator (not shown). An output signal from an accelerator opening sensor 39 that detects a pedal operation amount (accelerator opening) is input.
[0047]
  An exhaust gas temperature sensor 41 for estimating the temperature of the oxidation catalyst 28a or the temperature of the filter 28b is disposed upstream of the oxidation catalyst 28a. On the other hand, a filter upstream pressure sensor 42 for detecting the upstream exhaust pressure of the filter 28b is disposed in the exhaust passage 26 upstream of the filter 28b, preferably between the filter 28b and the oxidation catalyst 28a. A filter downstream pressure sensor 43 is disposed in the downstream exhaust passage 26. The ECU 40 further receives an output signal from the exhaust gas temperature sensor 41, an output signal from the filter upstream pressure sensor 42, and an output signal from the filter downstream pressure sensor 43.
[0048]
  (Fuel injection control)
  Next, the fuel injection control of this embodiment will be described.
[0049]
  The ECU 40 calculates the accelerator opening amount (engine load) from the input signal from the accelerator opening sensor 39, calculates the engine speed from the signal input from the crank angle sensor 11, and outputs these values to the injection control unit. The expansion stroke injection F1 as an additional injection for regeneration of the main injection M and the filter 28b is basically controlled based on the engine load and the engine speed.
[0050]
  When the filter 28b is regenerated, the EGR valve 35 is closed by the ECU 40 so that exhaust purification control by additional injection can be executed accurately.
[0051]
  As shown in S1 of FIG. 2, the main injection M is a fuel injection performed by the injector 5 in the vicinity of the top dead center of the compression stroke for each cylinder. Since the indoor pressure is injected under a very high pressure, the main combustion is performed by self-ignition. Further, the injection amount by the main injection M is set in advance based on the torque (requested torque) corresponding to this output so that the required output by the passenger or the like can be obtained. 2 is a timing chart showing an operating state of a needle valve (not shown) of the injector 5.
[0052]
  Specifically, the ECU 40 includes a main injection amount map (not shown) set so that the main injection amount increases as the engine speed increases and the accelerator opening amount increases. A main injection timing map (not shown) in which the execution timing of the main injection M is set based on the rotation speed and the accelerator opening amount is stored, and the main injection amount and the injection are determined based on the engine rotation speed and the accelerator opening amount. The time is set.
[0053]
  The form of the main injection M is not limited to such a single injection, but a combination of so-called pilot injection that is temporarily performed slightly before the compression stroke top dead center and main injection in the vicinity of the compression stroke top dead center. Alternatively, the main injection M itself executed near the top dead center of the compression stroke may be divided and injected in multiple stages with a minute pause interval (approximately 1 ms or less).
[0054]
  During the operation of the diesel engine, the exhaust gas contains particulates, so the filter 28b is arranged to capture this. By the way, in normal diesel combustion, the temperature is relatively low from 150 ° C. to 300 ° C. At such a low temperature, the trapped fine particles are difficult to burn and incinerate. In general, when removing soot by incineration, it is necessary to maintain a high temperature of 500 ° C. or higher for several minutes. ing. When the difference in the exhaust pressure between the upstream and downstream of the filter 28b is equal to or greater than a predetermined value, it is determined that the particulates trapped by the filter 28b increase, and that these particulates need to be forcibly incinerated and removed. Thus, additional injection different from the main injection is performed toward the oxidation catalyst 28a and the filter 28b to maintain the high temperature by supplying the fuel and to regenerate the filter 28b. In order to carry out the incineration and removal of fine particles, it is necessary to maintain a fairly high temperature continuously. Therefore, the additional injection amount is inevitably required in the low rotation, low load region, medium rotation, and medium load region. It is set to be about 1.5 to 4 times larger than the main injection amount.
[0055]
  In the present embodiment, as the additional injection, as shown in S1 of FIG. 2, the expansion stroke injection F1 is executed after the completion of the main injection M during the expansion stroke period.
[0056]
  The injection timing of the expansion stroke injection F1 is advanced to the injection timing side of the main injection M to set it to the initial timing of the expansion stroke, or the injection timing of the expansion stroke injection F1 is kept as it is and the injection timing of the main injection M is delayed. When the angle is changed (when the period between the injection timing of the main injection M and the injection timing of the expansion stroke injection F1 is shortened), most of the injected fuel is affected by the main combustion caused by the main injection M. The amount of unburned fuel supplied to the oxidation catalyst 28a is reduced. However, since the unburned fuel supplied at this time is caused by the fuel injected at a high temperature and pressure in the combustion chamber, it has a high miscibility with the exhaust gas. The activation rate of the catalyst can be improved. At this time, the temperature rise of the exhaust gas itself exhausted from the combustion chamber 4 and supplied to the oxidation catalyst 28a is also promoted.
[0057]
  Conversely, when the injection timing of the expansion stroke injection F1 is retarded and set near the middle of the expansion stroke (when the period between the injection timing of the main injection M and the injection timing of the expansion stroke injection F1 is lengthened), Since the injected fuel is hardly burned by the main combustion, the supply amount of unburned fuel to the oxidation catalyst 28a is increased. Further, since the unburned fuel supplied at this time is caused by the fuel injected at a low temperature or pressure in the combustion chamber, the mixing property is as high as when the expansion stroke injection F1 is injected at the initial stage of the expansion stroke. Not so, but relatively high.
[0058]
  At this time, the effect of increasing the temperature of the exhaust gas supplied to the oxidation catalyst 28a is suppressed. In this case, as will be described later, unburned fuel having a certain degree of mixing is used as the oxidation catalyst 28a. Therefore, the activation rate of the oxidation catalyst 28a can be improved. When the activation rate of the oxidation catalyst 28a becomes high, high reaction heat is generated by the unburned fuel adhering to the oxidation catalyst 28a, and the downstream filter 28b is positively heated.
[0059]
  Further, when the injection timing of the expansion stroke injection F1 is greatly retarded and set to the latter stage of the expansion stroke, a large amount of unburned fuel with extremely low mixing properties is supplied to the oxidation catalyst 28a, as will be described later. Even if a large amount of such unburned fuel adheres to the oxidation catalyst 28a, the activity of the oxidation catalyst 28a is improved, but not so much. At this time, the temperature of the exhaust gas can hardly be expected.
[0060]
  Specifically, the start timing of the expansion stroke injection F1 is between 0 ° and 130 ° after the compression stroke top dead center (ATDC) from the end of the execution of the main injection M, more preferably about 10 ° to 100 ° ATDC. Is set at a specific time in a predetermined allowable range period (not shown) set in accordance with the operating state. The predetermined permissible range period is set in the advance side range when the engine speed is low and the engine load is low, and in the retard side range when the engine speed is high and high. .
[0061]
  (Oxidation catalyst activity judgment control)
  Next, the activity determination control of the oxidation catalyst of this embodiment will be described.
[0062]
  The ECU 40 calculates the intake air amount from the signal input from the air flow sensor 19, and calculates the temperature of the exhaust gas upstream (immediately before the inlet) of the oxidation catalyst 28 a from the signal input from the exhaust gas temperature sensor 41. When the particulate matter trapped by the filter 28b is large and the filter 28b is being regenerated, first, the exhaust gas flow rate is estimated as follows. This is performed based on the intake air amount and the exhaust gas temperature thus detected, and the injection amount of the expansion stroke injection F1, which is the above-described additional injection for supplying unburned fuel.
[0063]
  This is because the flow rate of the exhaust gas is determined by the amount of intake air supplied into the combustion chamber 4 and the fuel injection amount. If the injection amount of the main injection M is further taken into account as the fuel injection amount, the estimated accuracy becomes higher. Will improve.
[0064]
  Next, the activation rate (unit:%, unit:%) of the oxidation catalyst 28a based on the actually measured value To of the detected exhaust gas temperature upstream of the oxidation catalyst To and the exhaust gas flow rate obtained previously. The activation rate of 50% means that the amount of exhaust gas flowing out is halved with respect to the amount of exhaust gas flowing in).
[0065]
  The exhaust gas flow rate of the exhaust gas passing through the oxidation catalyst and the activation rate of the oxidation catalyst 28a are greatly related. Specifically, when the exhaust gas flow rate is high, the contact time and approach time between the catalyst metal supported on the oxidation catalyst 28a and the exhaust material (for example, a reducing agent such as HC and CO) are shortened. As a result, the oxidation of the entire oxidation catalyst is also suppressed, so that the activation rate is considered to decrease. On the other hand, when the exhaust gas flow rate is slow, the contact time and the approach time between the catalytic metal and the exhaust material are relatively long, and the oxidation action to the exhaust material is promoted, so that the activity is considered to be improved. In addition, it has also been found that the activity is improved when the exhaust gas temperature is high. Therefore, in this embodiment, the exhaust gas flow rate and the exhaust gas temperature upstream of the oxidation catalyst 28a, that is, the measured value To of the catalyst temperature, are two. An original control map is provided, and the activation rate of the oxidation catalyst 28a is determined from this map.
[0066]
  This map will be described with reference to FIG.
[0067]
  In the map, the activation rate is set on the horizontal axis, and the catalyst temperature To, which is an actual measurement value, is set on the vertical axis. If the exhaust gas flow rate is the same (for example, on the Ma line), the catalyst temperature To increases. The activation rate is set to be high.
[0068]
  Even at the same catalyst temperature, the activation rate is set so as to decrease as the exhaust gas flow rate increases. For example, when the catalyst temperature is Tox, the activation rate when the exhaust gas flow rate is small Ma is AC3. In the case of Mb that is high and the exhaust gas flow rate is medium at the same catalyst temperature, the activation rate is medium and AC2, and in the case of Mc that has the same catalyst temperature and a large exhaust gas flow rate, the activation rate is as small as AC1. become.
[0069]
  Ma, Mb, and Mc indicate reference lines on the map when the exhaust gas flow velocity is a specific value and the temperature correction amount described later is not corrected.
[0070]
  The map format is not limited to that shown in FIG.
[0071]
  Next, the temperature correction amount for the exhaust gas temperature described above will be described.
[0072]
  The temperature correction amount is determined based on the injection amount of the expansion stroke injection F1 for supplying unburned fuel and the injection timing.
[0073]
  This is because the greater the injection amount of the expansion stroke injection F1 that is injected for supplying unburned fuel, or the later the injection timing, the lower the miscibility of the unburned fuel with the exhaust gas (vaporization, mixing). This is because of this. As a result, even when the environment surrounding the other oxidation catalyst is the same, when the injection amount is large and small, or when the injection timing is late (retarded side) and early (advanced side), respectively. This results in different activities of the oxidation catalyst as a whole.
[0074]
  Specifically, the greater the injection amount of the expansion stroke injection F1 or the later the injection timing, the more the miscibility between the unburned fuel and the exhaust gas is suppressed, thereby causing the reaction between the oxidation catalyst and the unburned fuel. And the heat of reaction accompanying the oxidation reaction of the catalyst is suppressed. Thus, as a result of locally suppressing the temperature rise inside the oxidation catalyst, it is considered that the activity of the entire oxidation catalyst is gradually increased.
[0075]
  On the other hand, the smaller the injection amount of the expansion stroke injection F1 or the earlier the injection timing, the higher the mixing property between the unburned fuel and the exhaust gas, and the reaction between the oxidation catalyst and the unburned fuel is promoted. It is considered that the temperature inside the whole is increased and the activity of the entire oxidation catalyst is rapidly increased.
[0076]
  Therefore, in the present embodiment, a binary control map of the injection timing and the injection amount in the expansion stroke injection F1 is provided. Based on the temperature correction amount determined by this map, the reference line on the map of FIG. The activation rate is obtained as described above by correcting Ma, Mb, Mc and the like. As shown in FIG. 4, the horizontal axis indicates the injection timing and the vertical axis indicates the injection amount. The more the injection timing is set to the retard side or the larger the injection amount, the more the temperature correction amount Tc. Is set to be larger.
[0077]
  When the temperature correction amount Tc is determined in this way, the temperature correction amount Tc is uniformly added to the reference line in FIG. 3 to obtain a correction line (for example, Mbm), and the correction line in FIG. The activation rate is determined based on the map.
[0078]
  Specifically, when the estimated exhaust gas flow rate is a predetermined value and the reference line Mb on the map is selected according to FIG. 3, the injection timing is on the advance side and the injection amount is small. When “0” is set as the temperature correction amount Tc, the reference line Mb is not changed. Therefore, if the measured value of the exhaust gas temperature is Tox at this time, the activation rate is AC2. However, when the injection timing is retarded and the injection amount is large, and the relatively large value “Tcx” is set as the temperature correction amount Tc based on FIG. 4, the reference line Mb on the map of FIG. The temperature is raised uniformly by Tcx (° C.), and the correction line Mbm is set. If the actual value To of the exhaust gas temperature at this time is Tox based on the correction line Mbm, the activation rate is AC2m (<AC2).
[0079]
  Thus, the activation rate is set to be lower as the injection timing of the expansion stroke injection F1 is retarded or the injection amount is larger, even if the measured value of the exhaust gas temperature flowing into the oxidation catalyst is the same.
[0080]
  Next, a control flowchart for determining the activation of the oxidation catalyst 28a in the present embodiment will be described with reference to FIG.
[0081]
  In FIG. 5, for example, after starting every predetermined time, in step SA1 and step SA2, the intake air amount is detected by the air flow sensor 19 and the exhaust gas temperature is detected by the exhaust gas temperature sensor 41, respectively. Next, in step SA3, the injection amount and the injection timing of the expansion stroke injection F1, which are injected immediately before the current time or a predetermined time slightly before the current time and affect the activity of the oxidation catalyst 28a at the current time, are stored. Read from the storage unit. Next, in step SA4, the exhaust gas flow rate is estimated based on the detected intake air amount, the detected exhaust gas temperature, and the injection amount of the expansion stroke injection F1. At this time, the exhaust gas flow velocity may be estimated based on the main injection amount. Next, in step SA5, the temperature correction amount Tc is calculated from the injection amount and the injection timing of the expansion stroke injection F1 using the map of FIG. 4 described above, and the process proceeds to step SA6. In step SA6, a reference line on the map of FIG. 3 is selected based on the estimated exhaust gas flow velocity, and the reference line is corrected as described above based on the temperature correction amount Tc, and a correction line is set. Next, at step SA7, the catalyst activation rate is determined from the measured value of the exhaust gas temperature based on the correction line on the map of FIG.
[0082]
  Next, a control flowchart of the injection control of the expansion stroke injection F1 will be described with reference to FIG.
[0083]
  In the control flowchart of FIG. 6, for example, after starting every predetermined crank angle, the engine speed and the engine load are detected in step SB1, and the process proceeds to step SB2. In step SB2, the exhaust gas temperature sensor 41 detects the oxidation catalyst 28a. Detect upstream exhaust gas temperature. Thereafter, in step SB3, the amount of fine particles trapped in the filter 28b is estimated from the pressure difference detected by the upstream pressure sensor 42 and the downstream pressure sensor 43. This is to estimate that the larger the differential pressure, the larger the trapped amount of particulates. In the next step SB4, when the estimated trapped amount of particulates is greater than or equal to a predetermined value, the captured particulates are incinerated to filter 28b. Is determined to be reproduced, and the process proceeds to step SB5. On the other hand, when the trapping amount is less than or equal to the predetermined value in step SB4, it is determined that the particulates are not accumulated enough to regenerate the filter 28b, and the process returns to step SB1. In step SB5, the injection timing and the injection amount are set based on the injection timing map (not shown) and the injection amount map (not shown) of the expansion stroke injection F1, and the process proceeds to step SB6.
[0084]
  The injection timing map and the injection amount map set the injection timing and the injection amount according to the engine speed, the engine load, and the activation rate of the oxidation catalyst 28a obtained in FIG. Specifically, the higher the rotation speed, the higher the load, and the higher the degree of activation of the oxidation catalyst 28a, the more retarded the injection timing is set. The reason for this is that in such a state, the exhaust gas temperature is already high only by the combustion of the main injection, and therefore the filter 28b is increased by increasing the amount of unburned fuel rather than raising the temperature of the exhaust gas flowing into the oxidation catalyst 28a. This is because the temperature can be increased.
[0085]
  Further, the injection amount is set to decrease as the rotation speed increases, the load increases, and the activation rate of the oxidation catalyst 28a increases. This is because the exhaust gas temperature is already high in this state, and if the injection amount is increased more than necessary, the fuel consumption deteriorates, or the filter 28b becomes abnormally hot due to a large amount of unburned fuel, resulting in melting or damage. This is to prevent a problem that the amount is excessive and a part of the fuel passes through the filter 28b and is discharged into the atmosphere without being purified to deteriorate the emission.
[0086]
  On the other hand, the lower the rotation speed, the lower the load, and the lower the activation degree of the oxidation catalyst 28a, the more advanced the injection timing is set. This is because in such a state, the exhaust gas temperature is low only by the combustion of the main injection, and the exhaust gas temperature is used to activate the oxidation catalyst 28a more than to supply the unburned combustion and raise the temperature of the filter 28b. This is for the purpose of efficiently performing additional injection without additional injection of excess fuel.
[0087]
  Further, the lower the rotation speed, the lower the load, and the lower the activation degree of the oxidation catalyst 28a, the higher the injection amount. The purpose of this is also to increase the exhaust gas temperature accurately by performing additional injection efficiently.
[0088]
  In step SB6, the expansion stroke injection F1 set in step SB5 in this way is executed when the detected crank angle reaches the set injection timing, and the process returns to step SB1.
[0089]
  According to such an embodiment, the activation rate of the oxidation catalyst 28a can be estimated with high accuracy, and the injection amount and the injection timing of the expansion stroke injection F1 are set based on such an accurate activation rate. Since the injection is executed, it is possible to appropriately and efficiently increase the temperature of the filter 28b by preventing excessive supply or supply shortage of unburned fuel to the oxidation catalyst 28a, and thereby the particulates trapped in the filter 28b can be increased. The incineration removal performance is improved, and as a result, the regeneration performance of the filter 28b can be improved.
[0090]
  (Other embodiments)
  In the embodiment of the present invention, at the time of regeneration of the filter 28b, the activation rate of the oxidation catalyst 28b is estimated as described above, and the control of the additional injection based on this is performed. It is not limited to 28b, but may be a normal catalyst device such as a three-way catalyst, an HC trap catalyst, or a NOx trap catalyst, or may be additionally injected for the purpose of raising the temperature thereof. .
[0091]
  In this case, since these normal catalyst devices have an oxidation catalyst function by themselves, there is no need for an oxidation catalyst upstream of these catalyst devices.
[0092]
  In the embodiment of the present invention, the main injection M is executed in the vicinity of the compression stroke top dead center. However, the main injection M is not limited to this, and the main injection M is in the vicinity of the compression stroke top dead center and the intake stroke on the advance side. The fuel may be injected several times over the compression stroke, or it may not be injected near the top dead center of the compression stroke, and it may be injected over the compression stroke from the intake stroke on the more advanced side. May be.
[0093]
  Further, in the embodiment of the present invention, after determining the activation rate of the oxidation catalyst 28a, the injection amount and the injection timing of the expansion stroke injection F1 are controlled based on this, but only one of them is controlled. Also good.
[0094]
  Further, in the embodiment of the present invention, the additional injection is performed only once for the expansion stroke injection F1, but the injection may be performed once or a plurality of times from the expansion stroke to the exhaust stroke. .
[0095]
  Further, in the present embodiment, the exhaust gas temperature upstream of the oxidation catalyst 28a is detected. However, the present invention is not limited to this, and the oxidation catalyst temperature is detected by a temperature sensor arranged directly upstream of the oxidation catalyst 28a. Also good.
[0096]
  The engine 1 may be a direct injection gasoline engine.
[0097]
【The invention's effect】
  As described above, in the present invention, the oxidation catalystIt is determined that the higher the detected temperature related to the upstream catalyst temperature is, the higher the activity of the oxidation catalyst is.Passes through the oxidation catalystIt is determined that the greater the estimated exhaust gas flow rate, the greater the fuel injection amount injected in the expansion stroke, and the lower the fuel injection timing in the expansion stroke, the lower the activity of the oxidation catalyst. Therefore, the determination accuracy becomes high.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an exhaust purification device for an engine according to an embodiment of the present invention.
FIG. 2 is an explanatory view schematically showing a state of an injection operation by an injector 5;
FIG. 3 is an explanatory diagram showing a map for obtaining an activation rate.
FIG. 4 is an explanatory diagram showing a map for obtaining a temperature correction amount.
FIG. 5 is a flowchart showing a control procedure for determining the activity of an oxidation catalyst.
FIG. 6 is a flowchart showing a control procedure of additional injection control.
[Explanation of symbols]
2: Cylinder
4: Combustion chamber
5: Injector (fuel injection valve)
19: Air flow sensor (intake air amount detection means)
28a: oxidation catalyst (purification section)
28b: Filter (purification unit)
41: Exhaust gas temperature sensor (temperature detection means)
F1: Expansion stroke injection

Claims (1)

Arranged oxidation catalyst having an oxidation function in an exhaust passage of the engine, and to supply the fuel injection valve for injecting fuel directly into a combustion chamber of the engine, unburned fuel to said oxidation catalyst from the fuel injection valve to, based on engine operating conditions, the fuel of the fuel injected by the injector injection amount and injection timing of and an injection control means for controlling the engine above the oxidation catalytic activity engine oxidation catalyst determines In the activity determination device,
Temperature detecting means for detecting a temperature related to the catalyst temperature upstream of the oxidation catalyst;
Exhaust gas flow rate estimating means for estimating the exhaust gas flow rate of exhaust gas passing through the oxidation catalyst;
Determination means for determining the activity of the oxidation catalyst based on the detected temperature, the estimated exhaust gas flow rate, the fuel injection amount injected in the engine expansion stroke, and the fuel injection timing ;
The determination means determines that the higher the detected temperature, the higher the activity of the oxidation catalyst, and the greater the estimated exhaust gas flow rate, the greater the fuel injection amount injected in the expansion stroke. Further, it is determined that the degree of activity of the oxidation catalyst is lower as the fuel injection timing in the expansion stroke is retarded .

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