JP2013072381A - Exhaust gas heating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve a quick rise of an exhaust gas temperature since it is difficult to always highly maintain the combustion ratio of fuel, in a conventional exhaust gas heating system.SOLUTION: This method heats exhaust gas guided to an exhaust emission control device 26 from an engine 10 by heating and igniting the fuel supplied to an exhaust passage 23a by supplying the fuel to the exhaust passage 23a on the upstream side of the exhaust emission control device 26, and includes a step S20 of supplying the fuel to the exhaust passage 23a at a first supply rate, a step S22 of determining an ignition state of the fuel supplied to the exhaust passage 23a, and a step S24 of supplying the fuel to the exhaust passage 23a at a second supply rate higher than the first supply rate based on a determining result in the step S22 of determining the ignition state of the fuel.

Description

  The present invention relates to an exhaust heating method for increasing the temperature of exhaust gas in order to activate and maintain the exhaust purification device in an internal combustion engine provided with the exhaust purification device.

  In recent years, in order to cope with strict exhaust regulations for an internal combustion engine, it is necessary to promote activation of an exhaust purification device at the start of the internal combustion engine or to maintain the active state during operation of the internal combustion engine. . For this reason, Patent Document 1 and the like propose an internal combustion engine in which an exhaust heating device is incorporated in an exhaust passage upstream of the exhaust purification device. The exhaust gas heating device generates a heating gas in the exhaust gas, and supplies the generated heating gas to the exhaust gas purification device on the downstream side, thereby promoting activation of the exhaust gas purification device or maintaining an active state. Is. For this reason, the exhaust heating device generally includes a fuel addition valve that supplies fuel to the exhaust passage, and an ignition device such as a glow plug that generates heated gas by heating and igniting the fuel. Further, in the conventional exhaust heating device disclosed in Patent Document 1, a collision plate for promoting diffusion and atomization of fuel supplied from the fuel addition valve to the exhaust passage is opposed to the fuel addition valve. It is arranged in the exhaust passage.

JP 2010-84710 A

  It is preferable that the exhaust heating device is capable of quickly raising the temperature of exhaust gas from the purpose of use. In this respect, the exhaust heating device described in Patent Document 1 has relatively good ignition performance of fuel supplied to the exhaust passage from the fuel addition valve and combustion stability of the fuel, but the use condition thereof is high oxygen. And it is limited to the case of a low exhaust flow rate. Further, it has been found that the combustion rate is remarkably lowered depending on the supply amount of the fuel supplied in a pulse form from the fuel addition valve and the supply cycle thereof. For example, when the amount of fuel supplied per time is large and the supply cycle is long, a delay in ignition of the fuel occurs and most of the fuel becomes unburned. More specifically, when the exhaust temperature is 100 ° C., a combustion rate of only about 20% may be obtained.

  An object of the present invention is to provide an exhaust heating method in which the combustion rate of the fuel added to the exhaust passage from the fuel addition valve can always be kept high.

  In the present invention, fuel is supplied to an exhaust passage upstream of the exhaust purification device, and the fuel supplied to the exhaust passage is heated and ignited to heat the exhaust led from the internal combustion engine to the exhaust purification device. A method comprising: a step of supplying fuel to the exhaust passage at a first supply rate; a step of determining an ignition state of the fuel supplied to the exhaust passage; and a determination in the step of determining the ignition state of the fuel And supplying the fuel to the exhaust passage at a second supply rate higher than the first supply rate based on the result.

  In the exhaust heating method according to the present invention, the step of supplying the fuel to the exhaust passage includes a step of obtaining at least one of an air-fuel ratio and an intake air amount, and based on at least one of the obtained air-fuel ratio and intake air amount, A supply ratio may be set.

  The step of determining the ignition state of the fuel includes a step of integrating the elapsed time from the start of the step of supplying the fuel to the exhaust passage at the first supply ratio, and the accumulated elapsed time exceeds a preset time. In this case, the step of supplying the fuel to the exhaust passage at the second supply rate may be executed.

  Alternatively, the step of determining the ignition state of the fuel includes a step of detecting an exhaust temperature flowing into the exhaust purification device, and when the exhaust temperature exceeds a preset temperature, the fuel is exhausted at the second supply rate. The step of supplying to the passage may be performed.

  Alternatively, the step of determining the ignition state of the fuel includes a step of calculating an integrated supply amount of the fuel supplied to the exhaust passage at the first supply ratio, and the integrated supply amount exceeds a preset amount The step of supplying the fuel to the exhaust passage at the second supply rate may be executed.

  The method may further include a step of determining whether or not fuel is supplied to the combustion chamber of the internal combustion engine, and the step of supplying the fuel to the exhaust passage may be executed based on the determination result in this step.

  According to the exhaust heating method of the present invention, the fuel is supplied to the exhaust passage at the first supply rate, and the fuel is supplied to the exhaust passage at the second supply rate higher than the first supply rate based on the ignition state of the fuel. The combustion rate can be improved as compared with the conventional one. In addition, it is possible to raise the exhaust temperature more quickly than the conventional one.

  When the step of supplying the fuel to the exhaust passage includes the step of obtaining at least one of the air-fuel ratio and the intake air amount, the fuel supply ratio may be optimally set based on at least one of the obtained air-fuel ratio and intake air amount. it can.

  When the step of determining the ignition state of the fuel includes the step of integrating the elapsed time from the start of fuel supply to the exhaust passage at the first supply ratio, the fuel is detected when the accumulated elapsed time exceeds a preset time. Can be supplied to the exhaust passage at the second supply rate. Thereby, exhaust temperature can be raised more rapidly.

  When the step of determining the ignition state of the fuel includes the step of detecting the exhaust temperature flowing into the exhaust purification device, the fuel is supplied to the exhaust passage at the second supply rate when the exhaust temperature exceeds a preset temperature. Can be supplied. Thereby, it is possible to raise exhaust temperature more rapidly.

  When the step of determining the ignition state of the fuel includes a step of calculating an integrated supply amount of the fuel supplied to the exhaust passage at the first supply ratio, the fuel is detected when the integrated supply amount exceeds a preset amount. Can be supplied to the exhaust passage at the second supply rate. Thereby, it is possible to raise exhaust temperature more rapidly.

  A step of determining whether or not fuel is supplied to the combustion chamber of the internal combustion engine can be further provided, and the step of supplying fuel to the exhaust passage can be executed based on the determination result in this step.

1 is a conceptual diagram of an engine system in an embodiment in which the present invention is applied to a vehicle mounted on a compression ignition type multi-cylinder internal combustion engine. It is a control block diagram of the principal part in embodiment shown in FIG. 4 is a graph schematically showing the relationship between the intake air amount and the fuel addition amount. It is a graph which represents typically the relationship between an air fuel ratio and fuel addition amount. It is a graph which represents typically the relationship between a fuel addition period and the combustion rate of the fuel. 6 is a graph schematically showing the relationship between the time from the start of fuel addition until the initial flame is formed and the amount of fuel added. It is a flowchart showing the fuel addition procedure in this embodiment.

  An embodiment in which an exhaust heating method according to the present invention is applied to a compression ignition type multi-cylinder internal combustion engine will be described in detail with reference to FIGS. However, the present invention is not limited to such an embodiment, and the configuration can be freely changed according to required characteristics. For example, the present invention is also effective for a spark ignition type internal combustion engine in which gasoline, alcohol, LNG (liquefied natural gas) or the like is used as fuel and is ignited by a spark plug.

  A main part of the engine system in the present embodiment is schematically shown in FIG. 1, and a control block of the main part is schematically shown in FIG. In FIG. 1, in addition to a valve mechanism and a silencer for intake and exhaust of the engine 10, a general exhaust turbo supercharger, an EGR device, and the like are omitted as auxiliary equipment of the engine 10. It should be noted that some of the various sensors required for smooth operation of the engine 10 are omitted for convenience.

  The engine 10 according to the present embodiment is a compression ignition type multi-cylinder internal combustion engine that spontaneously ignites by directly injecting light oil, which is fuel, from a fuel injection valve 11 into a combustion chamber 10a in a compressed state. However, a single cylinder internal combustion engine may be used due to the characteristics of the present invention.

The cylinder head 12 formed with the intake port 12a and the exhaust port 12b facing the combustion chamber 10a has a valve operating mechanism (not shown) including an intake valve 13a for opening and closing the intake port 12a and an exhaust valve 13b for opening and closing the exhaust port 12b. It has been incorporated. The previous fuel injection valve 11 facing the center of the upper end of the combustion chamber 10a is also assembled to the cylinder head 12 so as to be sandwiched between the intake valve 13a and the exhaust valve 13b. The amount and injection timing of fuel supplied to the combustion chamber 10a from the fuel injection valve 11, the ECU (E lectronic C ontrol U nit ) 15 based on operating conditions of the vehicle including the depression amount of the accelerator pedal 14 by the driver Be controlled. The amount of depression of the accelerator pedal 14 is detected by the accelerator opening sensor 16, and the detection information is output to the ECU 15.

  The ECU 15 is based on information from the accelerator opening sensor 16 and various sensors to be described later, an operation state determination unit 15a for determining the operation state of the vehicle, a fuel injection setting unit 15b, and a fuel injection valve drive unit 15c. Have The fuel injection setting unit 15b sets the fuel injection amount and the injection timing from the fuel injection valve 11 based on the determination result in the operation state determination unit 15a. The fuel injection valve drive unit 15c controls the operation of the fuel injection valve 11 so that the amount of fuel set by the fuel injection setting unit 15b is injected from the fuel injection valve 11 at the set time.

  A surge tank 18 is formed in the middle of the intake pipe 17 connected to the cylinder head 12 so as to communicate with the intake port 12a and defining the intake passage 17a together with the intake port 12a. A throttle valve 20 for adjusting the opening degree of the intake passage 17 a is incorporated in the intake pipe 17 upstream of the surge tank 18 via a throttle actuator 19. An air flow meter 21 that detects the flow rate of the intake air flowing through the intake passage 17a and outputs it to the ECU 15 is attached to the intake pipe 17 upstream of the throttle valve 20. Instead of the air flow meter 21, an exhaust flow sensor having the same configuration may be attached to a portion of the exhaust pipe 23 located between an exhaust heating device 22 described later and the exhaust port 12b of the cylinder head 12.

  The previous ECU 15 further includes a throttle opening setting unit 15d and a throttle valve drive unit 15e. The throttle opening setting unit 15d sets the opening of the throttle valve 20 based on the determination result of the previous operation state determination unit 15a in addition to the depression amount of the accelerator pedal 14. The throttle valve drive unit 15e controls the operation of the throttle actuator 19 so that the throttle valve 20 has the opening set by the throttle opening setting unit 15d.

  A crank angle sensor 25 that detects the rotational phase of the crankshaft 24c to which the piston 24a is connected via the connecting rod 24b, that is, the crank angle, and outputs it to the ECU 15 is attached to the cylinder block 24 in which the piston 24a reciprocates. It has been. Based on the information from the crank angle sensor 25, the driving state determination unit 15a of the ECU 15 grasps the traveling speed of the vehicle in addition to the rotational phase of the crankshaft 24c and the engine speed in real time.

The exhaust pipe 23 connected to the cylinder head 12 so as to communicate with the exhaust port 12b defines an exhaust passage 23a together with the exhaust port 12b. An exhaust purification device 26 for detoxifying harmful substances generated by combustion of the air-fuel mixture in the combustion chamber 10a is provided in the middle of the exhaust pipe 23 upstream of the silencer (not shown) attached to the downstream end side. It is attached. Exhaust purification apparatus 26 of this embodiment includes at least the oxidation catalyst 26a, it is also possible to incorporate the like In addition to this DPF (D iesel P articulate F ilter ) and _the NO _X storage catalyst. The oxidation catalyst 26a is mainly for oxidizing unburned gas contained in the exhaust gas, that is, for burning. In the exhaust passage 23a on the outlet side of the oxidation catalyst 26a, there is a catalyst temperature sensor 27 that detects the temperature of exhaust gas that has exited the oxidation catalyst 26a (hereinafter referred to as catalyst temperature) TO and outputs it to the ECU 15. It has been incorporated. Based on the information from the catalyst temperature sensor 27, the operation state determination unit 15a of the ECU 15 also grasps whether or not the oxidation catalyst 26a is in an active state.

  In the middle of the exhaust pipe 23 upstream of the exhaust purification device 26, a heated gas is generated and supplied to the exhaust purification device 26 disposed downstream, so that its activation and active state are maintained. Exhaust heating device 22 is arranged. The exhaust heating device 22 in the present embodiment includes a fuel addition valve 28, a glow plug 29, and an oxidation catalyst (hereinafter referred to as an auxiliary oxidation catalyst for convenience in order to distinguish it from the oxidation catalyst 26 a of the exhaust purification device 26) 30. And has. In addition, it is also effective to arrange a collision plate as disclosed in Patent Document 1 for receiving the fuel supplied from the fuel supply valve 26 and promoting the atomization and scattering to the glow plug 29 side. .

  The fuel addition valve 28 has the same basic configuration as that of the normal fuel injection valve 11, and supplies an arbitrary amount of fuel to the exhaust passage 23a in a pulsed manner at arbitrary time intervals by controlling the energization time. Can be done.

The amount of fuel per one time supplied from the fuel addition valve 28 to the exhaust passage 23a is based on the operating state of the vehicle including the intake air amount and air-fuel ratio detected by the air flow meter 21, and the fuel addition setting unit of the ECU 15 It is set by 15f. For this reason, maps as shown in FIGS. 3 and 4 are stored in the fuel addition setting unit 15f, and the fuel addition amount per time is set based on these maps. Fuel addition setting unit 15f also on the basis of the difference between the current catalyst temperature T _O is detected by the catalyst temperature T _L and the catalyst temperature sensor 27 to be a target, even together to calculate the fuel amount F _T. The target catalyst temperature T _L is generally selected to be the lowest temperature at which the oxidation catalyst 26a becomes active (hereinafter referred to as the lowest catalyst activity temperature).

  In this embodiment, the air-fuel ratio is calculated by the operation state determination unit 15a of the ECU 15 based on the intake air amount and the amount of fuel added from the fuel addition valve 28. However, an air-fuel ratio sensor may be incorporated in the exhaust passage 23a and read from a detection signal from the air-fuel ratio sensor.

The fuel addition valve drive unit 15g of the ECU 15 controls the operation of the fuel addition valve 28 so that the amount of fuel set by the fuel addition setting unit 15f is injected from the fuel addition valve 28 at a set cycle. In this case, operation of the fuel addition valve 28, until the fuel amount F _N that is accumulated from the start of the fuel addition reaches a fuel amount F _T set by the fuel addition setting unit 15f, basically row Is called.

  Immediately after the start of fuel addition, the temperature of the exhaust gas flowing through the exhaust passage 23a is lowered, so that the addition amount per time, that is, the average value of the fuel addition amount per unit time is reduced, and the glow plug 29 ensures that Preferably, the fuel can be ignited. However, if the amount of fuel added per time is kept small, the rapid temperature rise of the exhaust gas is impaired. On the other hand, if the ignition of the fuel is stabilized and the exhaust temperature rises, even if the amount of fuel added per time is increased, the ignitability of the fuel is not impaired, and the exhaust temperature can be raised quickly. . Therefore, immediately after the start of fuel addition, the average value of the fuel addition amount per unit time is set to a small value to ensure that the fuel is ignited, and when the fuel ignition is stable and the exhaust temperature rises to some extent, It is effective to increase the average value of the amount of fuel added per hour.

  Here, the change in the combustion rate of the added fuel when the fuel addition cycle is changed while the average value of the fuel addition amount per unit time from the fuel addition valve 28 to the exhaust passage 23a is kept constant is schematically shown. As shown in FIG. As is apparent from FIG. 5, the combustion rate decreases as the fuel addition period is increased. In FIG. 5, when the addition period is 60 milliseconds or more, the combustion rate becomes constant at approximately 25%. Conversely, when the fuel addition period is shorter than 50 milliseconds, the combustion rate tends to increase rapidly as the addition period becomes shorter. Therefore, it will be understood that it is preferable to shorten the fuel addition period in order to improve the combustion rate of the fuel supplied from the fuel addition valve 28 to the exhaust passage 23a. However, in order to ensure a stable operation of the oxidation catalyst 26a in the exhaust purification device 26, it is necessary to keep the air-fuel ratio of the exhaust gas flowing through the exhaust passage 23a substantially constant. Therefore, when the fuel addition cycle is shortened, the amount of fuel added per time must be reduced. That is, it is necessary to appropriately set the fuel addition period based on the amount of fuel added per time while taking into account the air-fuel ratio of the exhaust gas flowing through the exhaust passage 23a.

  On the other hand, FIG. 6 shows the relationship between the time from the start of fuel addition until the initial flame is formed and the amount of fuel added, and the alternate long and short dash line in FIG. As is apparent from FIG. 6, the amount of fuel added and the formation time of the initial flame are proportional to each other, and the initial flame is formed approximately a certain time after the addition of the fuel is completed. It can be said that it is preferable to add fuel.

  Based on such a viewpoint, the fuel addition setting unit 15f in the present embodiment obtains the fuel addition amount per time from FIGS. 3 and 4 as described above, and the initial flame formation time shown in FIG. 6 corresponding thereto. From the above, the addition period taking into account the air-fuel ratio as described above is calculated. The second supply ratio tends to be larger than the first supply ratio.

In the present embodiment, the initial fuel addition amount from the fuel addition valve 28, which is the first supply ratio, is set to an equivalent ratio of the ignition space between the fuel addition valve 28 and the auxiliary oxidation catalyst 30. The main purpose is the formation of an initial flame. In the present embodiment, the second fuel addition, which is the second supply ratio, is executed when an initial flame is formed by the initial fuel addition and spreads. This can be set in advance by experiments or the like. As an example, when the exhaust pipe 23 has an inner diameter of 60 mm and the exhaust temperature is 100 ° C. and the exhaust flow velocity is about 3 m / sec, the initial fuel addition amount is 15 mm ³ and the start of the second fuel addition is completed. It is preferable to set about 25 milliseconds later.

  The second and subsequent fuel injections are controlled with priority given to the addition cycle, and the fuel supply ratio during fuel addition is adjusted by changing the fuel addition amount per time. In this case, attention is paid to the exhaust pulsation in the exhaust system, and the time is set such that the flame retention due to the previous fuel addition is within the spray range of the fuel addition valve 28. As an example, when the exhaust pipe 23 has an inner diameter of 60 mm and the exhaust temperature is 100 ° C. and the exhaust flow rate is about 3 m / sec, the addition period is preferably set to 30 milliseconds or less.

  In this way, the fuel adhering to the inner wall of the exhaust pipe 23 due to the initial fuel addition is minimized, and the ignition of the second and subsequent fuels is stabilized, and the exhaust upstream of the auxiliary oxidation catalyst 30 is upstream. It is effective to increase the combustion rate of fuel in the passage 23a. Thereby, the extinction of the fuel by the auxiliary oxidation catalyst 30 can be prevented. Further, the combustion of fuel in the exhaust passage 23a downstream of the auxiliary oxidation catalyst 30 is also stabilized, and the active state of the oxidation catalyst 26a in the exhaust purification device 26 can be stably maintained. It should be noted that the first supply rate is not limited to the first one, and it is possible to set the first supply rate to the first supply rate after the second shot until the ignition state is stabilized.

  The timing at which the fuel supply at the first supply ratio is switched to the second supply ratio is performed based on the initial ignition timing shown in FIG. 6, that is, the initial flame formation timing. In the present embodiment, the elapsed time since the fuel is supplied to the exhaust passage 23a at the first supply rate is integrated, and the fuel is supplied to the second supply rate when the integrated elapsed time exceeds a preset time. Is supplied to the exhaust passage 23a.

  However, the exhaust temperature flowing into the exhaust purification device 26 may be detected, and fuel may be supplied to the exhaust passage 23a at the second supply rate when the exhaust temperature exceeds a preset temperature. Alternatively, the integrated supply amount of the fuel supplied to the exhaust passage 23a is calculated at the first supply rate, and when the integrated supply amount exceeds a preset amount, the fuel is supplied to the exhaust passage at the second supply rate. It is also possible to supply to 23a.

  The glow plug 29 as the ignition means in the present invention is connected to an on-vehicle power supply (not shown) via a glow plug drive unit 15h of the ECU 15 as an on / off switch. Therefore, switching between energization and non-energization for the glow plug 29 is controlled by the glow plug drive unit 15h of the ECU 15 in accordance with a preset program.

  The auxiliary oxidation catalyst 30 is disposed in the exhaust passage 23 a downstream from the fuel supply position by the fuel supply valve 25 and upstream from the exhaust purification device 26. The auxiliary oxidation catalyst 30 has a cross-sectional area smaller than the cross-sectional area of the exhaust passage 23 a, and thus allows a part of the exhaust gas to pass without passing through the auxiliary oxidation catalyst 30. That is, the flow rate of the exhaust gas that passes through the auxiliary oxidation catalyst 30 is lower than the flow rate of the exhaust gas that does not pass through the auxiliary oxidation catalyst 30, and the exhaust gas that passes through the auxiliary oxidation catalyst 30 can be further heated. When the auxiliary oxidation catalyst 30 is sufficiently hot, that is, in an activated state, the energization of the glow plug 29 can be cut off and the air-fuel mixture can be directly combusted in the auxiliary oxidation catalyst 30. However, when the auxiliary oxidation catalyst 30 is not activated, such as when the engine 10 is cold-started, it is necessary to energize the glow plug 29. When the auxiliary oxidation catalyst 30 reaches a high temperature, hydrocarbons having a large number of carbon atoms in the unburned mixture are decomposed and reformed into hydrocarbons having a low carbon number and high reactivity. In other words, the auxiliary oxidation catalyst 30 functions on the one hand as a rapid heating element that rapidly generates heat, and on the other hand also functions as a fuel reforming catalyst that generates reformed fuel.

  In the present embodiment, when the engine 10 is in a motoring state, that is, when the opening degree of the accelerator pedal 14 becomes 0 and the fuel is not injected from the fuel injection valve 11 while the engine 10 is operating, The fuel addition process from the addition valve 28 is executed.

  Accordingly, the intake air supplied from the intake passage 17a into the combustion chamber 10a forms a mixture with the fuel injected from the fuel injection valve 11 into the combustion chamber 10a. Then, the piston 24a spontaneously ignites and burns in the vicinity of the compression top dead center of the piston 24a, and the exhaust generated thereby is discharged from the exhaust pipe 23 into the atmosphere through the exhaust purification device 26. When the engine 10 is in a fuel cut state, fuel is supplied from the fuel addition valve 28 to the exhaust passage 23a, thereby increasing the temperature of the exhaust gas flowing through the exhaust passage 23a and maintaining the active state of the oxidation catalyst 26a of the exhaust purification device 26. To do.

The fuel addition procedure in this embodiment will be described with reference to FIG. That is, first, in step S11, it is determined whether or not the fuel pedal is in a fuel cut state in which the opening of the accelerator pedal 14 becomes 0 during operation of the engine 10 and fuel is not injected from the fuel injection valve 11. If it is determined that there is a fuel cut state, that is, there is a possibility that the temperature of the exhaust purification device 26 is lowered and the oxidation catalyst 26a becomes inactive, the process proceeds to step S12. Then, it is determined whether or not the catalyst temperature T _O that has passed through the oxidation catalyst 26a is lower than the minimum catalyst activity temperature T _L. When it is determined in step S12 that the catalyst temperature T _O is lower than the minimum catalyst activation temperature T _L , that is, it is necessary to activate the oxidation catalyst 26a by adding fuel from the fuel addition valve 28 to the exhaust passage 23a. In step S13, the fuel addition amount FT is calculated. Next, in step S14, it is determined whether or not the first flag is set. However, since the first flag is not initially set, the process proceeds to step S15 and energization to the glow plug 29 is started. Next, in step S16, the timer starts counting up. In step S17, the first flag is set. Then, the process proceeds to step S18, and the timer count value _CN is set in advance. determines whether the threshold value C _a or more. Initially, the count value C _N of the timer returns without doing anything is smaller than the first threshold value CA, repeats the steps after S11.

After energization of the glow plug 29 is started in the previous step S15, the first flag is set. Therefore, if the steps S11 to S14 are continued, the process proceeds from the step S14 to the step S19. To determine whether or not the second flag is set. At first, since the second flag is not set, the process proceeds to step S18. Thus, at S18 in steps until the timer count value C _N is the first threshold value C _A above, usually repeated steps S11 to S19.

If it is determined in step S18 that the timer count value C _N is equal to or greater than the first threshold value C _A , that is, it is possible to ignite the fuel by the glow plug 29, the process proceeds to step S20 and the fuel addition valve 28 is moved. To start addition of fuel to the exhaust passage 23a in the first period. Next, it is determined at S21 in step after setting the second flag, whether the second threshold value C _B over which the process proceeds to S22 in step count C _N of timer preset. At this time, the timer count value C _N is smaller than the second threshold value C _B , so nothing is returned, and the steps after S11 are repeated.

Since the second flag is set after the fuel addition is started in step S20, if the processing in steps S11 to S14 and S19 is continued, the process proceeds from step S19 to step S23. It is determined whether or not the 3 flag is set. Since the third flag is not set at first, the process proceeds to step S22. Thus, at S22 in steps until the timer count value C _N is the second threshold value C _B above, usually repeated steps S11～S23.

Step by timer count value C _N of S22 is at the second threshold value C _B above, that is, when it is determined that can be scaled addition of fuel from the fuel addition valve 28 shifts to step S24, the second Fuel is added to the exhaust passage 23a at a cycle. Then, after setting the third flag at step S25, whether the fuel addition integrated quantity proceeds to step S26 F _N has reached the fuel amount F _T calculated in S13 in step judge. First, because the fuel addition integrated amount FN has not reached the fuel addition amount F _T is generally returned without any repeats S11 and subsequent steps.

Note that the timer count value C _N at S22 in step is less than the second threshold value C when it is determined that the _B or more and the oxygen concentration an air-fuel ratio is equal to or greater than the predetermined value of the exhaust gas flowing into the oxidation catalyst 26a exceeds a predetermined value Only in this case, it is more preferable to execute the steps after S24. That is, when the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 26a of the exhaust purification device 26 is less than a predetermined value, the air-fuel ratio becomes rich at the moment when the fuel is added in the second period, and the temperature rise performance of the exhaust gas is reduced. In addition to the reduction, the exhaust properties such as smoke increase. Further, when the oxygen concentration of the exhaust gas flowing into the oxidation catalyst 26a of the exhaust purification device 26 is equal to or higher than a predetermined value, if the fuel is added in the second period, the combustion proceeds vigorously and the exhaust temperature rises excessively. there is a possibility. Therefore, when the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 26a of the exhaust purification device 26 is less than the predetermined value and the oxygen concentration is higher than the predetermined value, the process goes from step S22 to step S26 without going through steps S24 and S25. It is preferable to shift and continue the fuel addition in the first period. The oxygen concentration can be calculated by the operating state determination unit 15a of the ECU 15 based on the amount of intake air and the amount of fuel added from the fuel addition valve 28, but by incorporating an O ₂ sensor into the exhaust pipe 23, More accurate detection is possible.

After the addition of fuel in the second cycle is started in step S24, the third flag is set. Therefore, if the processes in steps S11 to S14, S19, and S23 are continued, steps S23 to S26 are performed. Migrate to Then, until the fuel addition integrated amount F _N reaches the fuel addition amount F _T, usually repeated steps S11～S26.

Thus, when it is determined in step S26 that the fuel addition integrated amount F _N is equal to or greater than the fuel addition amount F _T , that is, the oxidation catalyst 26a is in the active state, the process proceeds to step S27. Then, stop the energization of the glow plug 29, and resets the count value C _N of the timer to 0, resets the first to third flag with further stops the addition of fuel from the fuel addition valve 28 to the exhaust passage 23a The process returns to step S11 again.

On the other hand, if it is determined in step S11 that the engine 10 is not in the fuel cut state, that is, the oxidation catalyst 26a is maintained in the active state by the high temperature exhaust from the combustion chamber 10a of the engine 10, the process proceeds to step S28. Transition. In step S28, it is determined whether or not the second flag is set. Similarly, if it is determined in step S12 that the catalyst temperature T _O is equal to or higher than the catalyst activation minimum temperature T _L , that is, it is not necessary to add fuel from the fuel addition valve 28 to the exhaust passage 23a, the process proceeds to step S28. Transition. If it is determined in step S28 that the second flag is not set, the process proceeds to step S29 to determine whether or not the first flag is set. If it is determined that the first flag is not set, the process returns without doing anything and the steps after S11 are repeated.

At step S29 if the first flag is determined to be set, stops energization to the glow plug 29 proceeds to step S30, further resets the count value C _N of the timer to zero. Thereafter, the process proceeds to step S31, the first flag is reset, and the process returns to step S11.

When the second flag is determined to have been set at S28 in step deenergized for the glow plug 29 proceeds to step S32, it resets the count value C _N of the timer to zero. Further, after stopping the addition of fuel from the fuel addition valve 28 to the exhaust passage 23a, the routine proceeds to step S33, where it is determined whether or not the third flag is set. If it is determined that the third flag is not set, the process proceeds to step S34 to reset the first flag and the second flag, and then returns to step S11. Conversely, if it is determined in step S33 that the third flag is set, the process proceeds to step S35 to reset the first to third flags, and then returns to step S11.

Thus, even during the addition of fuel by the fuel addition valve 28, or the fuel cut state is released in step S11, the catalyst temperature T _O is catalytically active minimum temperature for some reason T _L at step S12 When the above is reached, the addition of fuel from the fuel addition valve 28 is stopped. Thereby, the useless addition process of fuel can be prevented reliably.

  It should be noted that the present invention should be construed only from the matters described in the claims, and in the above-described embodiment, all the changes and modifications included in the concept of the present invention are other than those described. Is possible. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get.

DESCRIPTION OF SYMBOLS 10 Engine 10a Combustion chamber 11 Fuel injection valve 12 Cylinder head 12a Intake port 12b Exhaust port 13a Intake valve 13b Exhaust valve 14 Accelerator pedal 15 ECU
15a Operation state determination unit 15b Fuel injection setting unit 15c Fuel injection valve driving unit 15d Throttle opening setting unit 15e Throttle valve driving unit 15f Fuel addition setting unit 15g Fuel addition valve driving unit 15h Glow plug driving unit 16 Accelerator opening sensor 17 Intake Pipe 17a Intake passage 18 Surge tank 19 Throttle actuator 20 Throttle valve 21 Air flow meter 22 Exhaust heating device 23 Exhaust pipe 23a Exhaust passage 24 Cylinder block 24a Piston 24b Connecting rod 24c Crankshaft 25 Crank angle sensor 26 Exhaust purification device 26a Oxidation catalyst 27 Catalyst temperature sensor 28 Fuel addition valve 29 Glow plug 30 Auxiliary oxidation catalyst T _O catalyst temperature T _L Minimum catalyst activation temperature _FT Fuel addition amount F _N Accumulated fuel addition amount

Claims (6)

A method of heating exhaust gas guided from an internal combustion engine to an exhaust purification device by supplying fuel to an exhaust passage upstream of the exhaust purification device and heating and igniting the fuel supplied to the exhaust passage. ,
Supplying fuel to the exhaust passage at a first supply rate;
Determining the ignition state of the fuel supplied to the exhaust passage;
Supplying the fuel to the exhaust passage at a second supply rate higher than the first supply rate based on the determination result in the step of determining the ignition state of the fuel. Method.   The step of supplying fuel to the exhaust passage includes a step of obtaining at least one of an air-fuel ratio and an intake air amount, and a fuel supply ratio is set based on at least one of the obtained air-fuel ratio and intake air amount. The exhaust heating method according to claim 1, wherein:   The step of determining the ignition state of the fuel includes a step of integrating the elapsed time from the start of the step of supplying the fuel to the exhaust passage at the first supply ratio, and the accumulated elapsed time is set to a preset time. The exhaust heating method according to claim 1 or 2, wherein the step of supplying the fuel to the exhaust passage at a second supply rate is executed when exceeding.   The step of determining the ignition state of the fuel includes a step of detecting an exhaust temperature flowing into the exhaust purification device, and when the exhaust temperature exceeds a preset temperature, the fuel is supplied to the exhaust passage at a second supply rate. The exhaust heating method according to claim 1, wherein the step of supplying to the exhaust gas is performed.   The step of determining the ignition state of the fuel includes a step of calculating an integrated supply amount of the fuel supplied to the exhaust passage at the first supply ratio, and when the integrated supply amount exceeds a preset amount. The exhaust heating method according to claim 1 or 2, wherein the step of supplying fuel to the exhaust passage at a second supply rate is executed.   2. The method according to claim 1, further comprising a step of determining whether or not fuel is supplied to the combustion chamber of the internal combustion engine, and the step of supplying fuel to the exhaust passage is executed based on a determination result in this step. The exhaust gas heating method according to claim 5.

Images