WO2013030887A1 - Method for adding fuel - Google Patents

Abstract

This method for adding fuel to an exhaust channel further upstream than an exhaust emission control device comprises: calculating a required addition amount of fuel to be added from a fuel addition valve on the basis of the state of the exhaust emission control device; reading out a unit addition amount (L_U) of fuel that corresponds to an energizing time (t_U) per cycle of the fuel addition valve; adding the unit addition amount of fuel to the exhaust channel using a drive period that corresponds to the requested addition amount; correcting the energizing time (t_UT) that corresponds to a target addition amount as a function of (L_U/g) and updating the target addition amount (L_UT) as the new unit addition amount (L_U) for the case in which E_DT - E_DU < E_A - (L_U - g), where E_A and E_DU are the maximum allowed error that corresponds to the unit addition amount and the maximum dispersion error of the fuel addition valve, g is the addition amount of fuel actually added to the exhaust channel in relation to the unit addition amount, L_UT is the target addition amount in which the addition amount is less than the unit addition amount by a fixed amount, and E_DT is the maximum dispersion error that corresponds to the target addition amount; and adding fuel to the exhaust channel from the fuel addition valve using the function (L_U/g) as the new energizing time (t_U).

Description

Fuel addition method

The present invention relates to a fuel addition method for efficiently performing activation processing and regeneration processing of an exhaust purification device in an internal combustion engine incorporating the exhaust purification device.

In recent years, in order to cope with strict exhaust regulations on internal combustion engines, activation of an oxidation catalyst constituting an exhaust purification device can be promoted at the start of the internal combustion engine, or its active state can be maintained during operation of the internal combustion engine. It is necessary. 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. This exhaust heating device generates a heated gas in the exhaust gas, and supplies the generated heated gas to the exhaust gas purification device on the downstream side, thereby activating the oxidation catalyst and maintaining its active state. It is. For this reason, the exhaust heating device generally includes a fuel addition valve that adds fuel to the exhaust passage, and an ignition device such as a glow plug that generates heated gas by heating and igniting the fuel.

JP 2010-059886 A

When controlling the fuel added to the exhaust passage from the fuel addition valve, the control is to minimize the change in exhaust temperature and the change in air-fuel ratio caused by the fuel added from the fuel addition valve to the exhaust passage. It can be said that it is preferable in avoiding hunting.

On the other hand, in the conventional exhaust heating apparatus proposed in Patent Document 1 and the like, the fuel addition valve for adding fuel to the exhaust passage has the same configuration as the fuel injection valve for injecting pressurized fuel at a predetermined drive cycle Basically has. Therefore, it is necessary to shorten the drive cycle for the fuel addition valve as much as possible, shorten the energization time per time as much as possible, and reduce the amount of fuel added to the exhaust passage as much as possible by this energization time per time. This is effective in avoiding control hunting.

However, it is known that the conventional fuel addition valve has a characteristic that the variation in the amount of fuel added to the exhaust passage rapidly increases as the energization time per time is shortened. This is due to the influence of the viscosity of the fuel itself in addition to the structure of the fuel addition valve itself, and that different amounts of fuel are added to the exhaust passage according to manufacturing tolerances for each individual fuel addition valve. means. Since such a technical background lies in the fuel addition valve, it is essentially impossible to set the energization time per time as short as a dark cloud. For this reason, the maximum variation error of the addition amount that is conventionally brought about according to the manufacturing tolerance of each fuel addition valve is the maximum allowable amount of fuel added to the exhaust passage with respect to the energization time per time for the fuel addition valve. The energization time per time is specified so as to be less than the error.

Therefore, the conventional exhaust heating apparatus has the following problems. That is, when the amount of fuel added to the exhaust passage is not so large, the drive period of the fuel addition valve becomes longer, and the ignitability of the fuel decreases. In addition, when the fuel is added and when the fuel is not added, changes in the exhaust temperature and the air-fuel ratio become large, and the control hunting phenomenon becomes obvious.

An object of the present invention is to provide a fuel addition method capable of making the energization time per one time to the fuel addition valve shorter than that of the conventional one.

The present invention is a method of adding fuel from a fuel addition valve to an exhaust passage upstream of an exhaust purification device, and the fuel to be added from the fuel addition valve to the exhaust passage based on the state of the exhaust purification device calculating the required addition amount, a step of reading the unit amount L _U of fuel added to the exhaust passage in response to the energization time t _U per one with respect to the fuel addition valve, the required addition amount a step of reading the steps of the fuel unit amount L _U from the fuel addition valve by the driving cycle corresponding intermittently added to the exhaust passage, the maximum permissible error E _a corresponding to the unit amount L _U in , the amount of the unit amount L reading out maximum variation error E _DU of the fuel addition valve corresponding to _U, the fuel that is actually added to the exhaust passage with respect to the unit amount L _U Calculating a, a step of amount than the unit amount L _U is set less target amount L _UT predetermined amount, the maximum variation error E of the fuel addition valve that corresponds to the target amount L _UT a step of reading the _{DT, E DT -E DU <E} a - determining whether _(L U -g) an either _{not, E DT -E DU <E a} - If it is _(L U -g) If determined, the step of correcting the energization time t _UT for the fuel addition valve corresponding to the target addition amount L _UT as a function of (L _U / g), and the target addition amount L _UT as a new unit addition amount L and updated as _U, the function of (L _U / g) the drives fuel addition valve as a new current time t _U, comprising the step of adding fuel to the exhaust passage.

In the fuel addition method according to the present invention, the step of reading the unit addition amount L _U of the fuel added to the exhaust passage corresponding to the energization time t _U per time for the fuel addition valve is the updated latest unit. it may be designed to read the amount L _U.

When the amount of fuel to be added from the fuel addition valve exceeds twice the unit addition amount at every drive cycle of the fuel addition valve corresponding to the required addition amount, ½ of the amount to be added is added You may do it.

Request status of the added amount exhaust gas purification device for calculating the Do temperature of the exhaust purification device, or if the air-fuel ratio of the exhaust gas flowing here, intermittently to the exhaust passage of fuel from the fuel addition valve at energization time t _U The execution of the step of adding may further comprise the step of determining whether the temperature of the exhaust gas purification device or the air-fuel ratio of the exhaust gas flowing therethrough has converged. Whether or not E _DT −E _DU <E _A − (L _U −g) is satisfied only when it is determined that the temperature of the exhaust gas purification device or the air-fuel ratio of the exhaust gas flowing therethrough has converged. The step of determining may be executed. Here, the step of determining whether the temperature of the exhaust gas purification device or the air-fuel ratio of the exhaust gas flowing therethrough has converged is whether at least one of the temperature of the exhaust gas purification device and the rate of change thereof falls within a predetermined range. Or a step of determining whether or not at least one of the air-fuel ratio of the exhaust gas flowing through the exhaust purification device and the rate of change thereof is within a predetermined range.

When the sum of the detection error of the air-fuel ratio and the detection error of the intake air amount is smaller than the maximum allowable error, the step of determining whether or not E _DT −E _DU <E _A − (L _U −g) is executed It may be done.

The method may further include a step of determining whether or not the amount of HC passing through the exhaust purification device is equal to or less than a predetermined value. Here, when it is determined that the amount of HC passing through the exhaust purification device is equal to or less than a predetermined value, the step of determining whether or not E _DT −E _DU <E _A − (L _U −g) is executed. It may be a thing.

The detected temperature rise Yutakadai [Delta] T _C determining whether the division value E _{T /} [Delta] T _C is less than the maximum allowable error E _A in the exhaust purification apparatus per the error E _T unit time of the exhaust gas purifying device You can even have more. Here, if it is determined that the _{E T / ΔT C <E A} , E DT -E DU <E A - be those wherein determining whether _(L U -g) is performed It's okay. In this case, the method may further include a step of determining whether or not the amount of HC passing through the exhaust purification device is equal to or less than a predetermined value. Here, only when it is determined that the amount of HC passing through the exhaust purification device is equal to or less than a predetermined value, the step of determining whether or not E _T / ΔT _C <E _A may be executed. .

According to the fuel addition method of the present invention, it is possible to reduce the unit addition amount as compared with the conventional one without exceeding the maximum allowable error, thereby shortening the drive cycle of the fuel addition valve and the control hunting phenomenon. Can suppress more than

When reading the unit amount L _U of fuel added to the exhaust passage, by reading the updated latest unit amount L _U, it is possible to improve the initial accuracy of the time of addition amount decreasing.

When the amount of fuel to be added from the fuel addition valve exceeds twice the unit addition amount at every drive cycle of the fuel addition valve corresponding to the required addition amount, ½ of the amount to be added is added By this, the rapid change of the addition amount per time can be suppressed. Thereby, it is possible to further suppress the control hunting phenomenon accompanying the change in the amount of fuel added. Moreover, the main effect of this invention can be acquired continuously by continuing adding a fuel by unit addition amount as much as possible.

Only when it is determined that the temperature of the exhaust gas purification device or the air-fuel ratio of the exhaust gas flowing there has converged, it is determined whether E _DT -E _DU <E _A- (L _U -g) When performing the steps, control in a transient situation can be avoided. As a result, the control hunting phenomenon can be more reliably suppressed. In particular, it is determined whether at least one of the temperature of the exhaust purification device and its rate of change falls within a predetermined range, or whether at least one of the air-fuel ratio of the exhaust gas flowing through the exhaust purification device and its rate of change falls within a predetermined range. By doing so, it is possible to reliably avoid control in a transient situation.

When the sum of the detection error of the air-fuel ratio and the detection error of the intake air amount is smaller than the maximum allowable error, control is performed by determining whether or not E _DT −E _DU <E _A − (L _U −g). Can be reliably maintained.

When it is determined that the amount of HC passing through the exhaust purification device is equal to or less than a predetermined value, whether or not E _DT −E _DU <E _A − (L _U −g) is determined to ensure control reliability. Can be maintained.

If the detected temperature rise Yutakadai [Delta] T _C value E _{T /} [Delta] T _C divided by the exhaust purification apparatus per the error E _T unit time of the exhaust gas purification device is determined to be smaller than the maximum allowable error E _A, E _DT - By determining whether or not E _DU <E _A − (L _U −g), a similar effect can be obtained. In particular, only if the amount of HC passing through the exhaust purification device is equal to or less than a predetermined value, by determining whether the _{E T / ΔT C <E A} , maintain more reliable reliably controlled It is possible.

FIG. 1 is a conceptual diagram schematically showing an engine system of a vehicle in which an exhaust heating apparatus that is an object of the present invention is incorporated. FIG. 2 is a control block diagram of the main part in the embodiment shown in FIG. FIG. 3 is a graph schematically showing a change in the required addition amount corresponding to the drive cycle of the fuel addition valve in the embodiment shown in FIG. FIG. 4 is a graph schematically showing the relationship between the energization time of the fuel addition valve, its maximum allowable error, and the maximum variation error of each fuel addition valve. FIG. 5 is a graph schematically showing the characteristics of the air flow meter. FIG. 6 is a graph schematically showing the characteristics of the air-fuel ratio sensor. FIG. 7 is a graph schematically showing the relationship between the amount of HC in the exhaust gas and the lean deviation amount of the detected value of the air-fuel ratio sensor. FIG. 8 is a map schematically showing the relationship between the catalyst temperature, the reaction rate of the catalyst, the amount of HC in the exhaust gas, and the O ₂ concentration. FIG. 9 is a flowchart showing the setting procedure of the amount of fuel added per time from the fuel addition valve in the catalyst activation mode together with FIG. 10 in the embodiment shown in FIG. FIG. 10 is a flowchart showing the setting procedure of the fuel addition amount per one time from the fuel addition valve in the catalyst activation mode together with FIG. FIG. 11 is a flowchart showing the contents of a fuel addition subroutine in the flowchart shown in FIG. FIG. 12 is a flowchart showing a procedure for setting the amount of fuel added per time from the fuel addition valve in the catalyst regeneration mode together with FIG. 13 in the embodiment shown in FIG. FIG. 13 is a flowchart showing the setting procedure of the fuel addition amount per one time from the fuel addition valve in the catalyst regeneration mode together with FIG.

An embodiment in which the present invention is applied to a compression ignition 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, gasoline, alcohol or LNG: The present invention is also effective for an internal combustion engine spark ignition system for igniting this as (L iquefied N atural G as liquefied natural gas) fuel and by the ignition plug.

The main part of the engine system in this embodiment is schematically shown in FIG. 1, and the control block of the main part is shown in FIG. In FIG. 1, in addition to a valve mechanism, a throttle mechanism, and a silencer for intake and exhaust of the engine 10, a general EGR device as an auxiliary machine of the engine 10 is omitted. It should be noted that some of the various sensors required for smooth operation of the engine 10 and the above-described auxiliary machines are omitted for convenience.

The engine 10 in this embodiment is a compression ignition type multi-cylinder internal combustion engine that spontaneously ignites by directly injecting light oil as fuel into the combustion chamber 10a in a compressed state from the fuel injection valve 11. 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 from the fuel injection valve 11 is supplied to the combustion chamber 10a, due 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 crank angle sensor 18 that detects the rotational phase of the crankshaft 17c to which the piston 17a is connected via the connecting rod 17b, that is, the crank angle, and outputs it to the ECU 15 is attached to the cylinder block 17 in which the piston 17a reciprocates. It has been. Based on the information from the crank angle sensor 18, 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 17c and the engine rotational speed in real time.

The intake pipe 19 connected to the cylinder head 12 so as to communicate with the intake port 12a defines an intake passage 19a together with the intake port 12a. The exhaust pipe 20 connected to the cylinder head 12 so as to communicate with the exhaust port 12b defines an exhaust passage 20a together with the exhaust port 12b.

An exhaust turbine supercharger (hereinafter simply referred to as a supercharger) 21 is disposed so as to straddle the intake pipe 19 and the exhaust pipe 20. The supercharger 21 supercharges the combustion chamber 10a by using the kinetic energy of the exhaust gas flowing through the exhaust passage 20a, and increases the charging efficiency of the intake air. The supercharger 21 in the present embodiment is a turbocharger whose main part is composed of a compressor 21a and an exhaust turbine 21b that rotates integrally with the compressor 21a. The compressor 21a is incorporated in the middle of the intake pipe 19 located upstream from the surge tank 19b provided in the middle of the intake pipe 20. The exhaust turbine 21b is incorporated in the middle of the exhaust pipe 20 connected to the cylinder head 12 so as to communicate with the exhaust port 12b. An intercooler 21c is incorporated in order to reduce the intake air temperature heated via the compressor 21a by heat transfer from the exhaust turbine 21b exposed to high-temperature exhaust. This intercooler 21c is arranged in the middle of the intake passage 19a between the compressor 21a and the surge tank 19b formed in the middle of the intake pipe 19.

Further, in the intake pipe 19 upstream of the compressor 21a of the supercharger 21, a flow rate of intake air (hereinafter referred to as intake air amount) _VA flowing through the intake passage 19a is detected and this is detected by the ECU 15. An air flow meter 22 is provided for output.

In the middle of the exhaust pipe 20 between the exhaust turbine 21b of the supercharger 21 and a silencer (not shown), an exhaust purification device for detoxifying harmful substances generated by combustion of the air-fuel mixture in the combustion chamber 10a. 23 is attached. Exhaust purification apparatus 23 in this embodiment is generally in order from the upstream side to the well-known NO _X (Nitrogen Oxides: nitrogen oxides) and storage catalyst 23a, a DPF (D iesel P articulate F ilter ) 23b, an oxidation catalyst 23c Have.

An exhaust heating device 24 is incorporated in the middle of the exhaust passage 20 a between the exhaust port 12 b and the exhaust turbine 21 b of the supercharger 21. The exhaust heating device 24 heats the exhaust led from the engine 10 to the exhaust purification device 23, activates the oxidation catalyst 23c of the exhaust purification device 23 and maintains the active state, or performs regeneration processing or NO _{X of the} DPF 23b. This is for reducing the storage catalyst 23a. The exhaust heating device 24 in the present embodiment includes a fuel addition valve 24a and a glow plug 24b.

The amount of fuel supplied from the fuel addition valve 24a attached to the exhaust pipe 20 to the exhaust passage 20a is supplied to the fuel addition amount setting unit 15e of the ECU 15 based on a determination result in a fuel addition request determination unit 15d of the ECU 15 described later. Is set. The fuel addition valve drive unit 15f of the ECU 15 controls the operation of the fuel addition valve 24a so that the amount of fuel set by the fuel addition amount setting unit 15e is supplied from the fuel addition valve 24a to the exhaust passage 20a.

The glow plug 24b for igniting the fuel supplied from the fuel addition valve 24a to the exhaust passage 20a is exhausted so that the heat generating portion projects into the exhaust passage 20a and faces the injection region of the fuel injected from the fuel addition valve 24a. It is fixed to the tube 20. The glow plug 24b is connected to an in-vehicle power source (not shown) via a glow plug drive unit 15g of the ECU 15, and the glow plug drive unit 15g is connected to the glow plug 24b based on a determination result in the fuel addition request determination unit 15d of the ECU 15. Switch energization on / off.

The exhaust passage 20a upstream of the fuel addition valve 24a, and the first exhaust temperature sensor 25 is disposed, the first exhaust temperature sensor 25, it detects the exhaust gas temperature T _I flowing into DPF23b It outputs to ECU15.

The exhaust passage 20a between _the NO _X storage catalyst 23a and DPF23b, are arranged air-fuel ratio sensor 26, the air-fuel ratio sensor 26, it detects the air-fuel ratio _{R N} of the exhaust gas flowing here ECU15 Output to. Further, the catalyst temperature sensor 27 is incorporated to output this by detecting the temperature _{T C} of the oxidizing catalyst 23c in ECU15 between the DPF23b the oxidation catalyst 23c. Further, the exhaust passage 20a downstream of the oxidation catalyst 23c, the second exhaust temperature sensor 28 that outputs this by detecting the exhaust gas temperature T _O passing through the oxidation catalyst 23c in ECU15 is incorporated.

Fuel addition request determining section 15d of the ECU15 is based on the determination result of the operation state in the operation state determination unit 15a, NO _X reduction process in the reproducing process and _the NO _X storage catalyst 23a in need or DPF23b activation of the oxidation catalyst 23c Determine the need for If NO _X reduction process in the reproducing process and the NO _X storing catalyst 23a in the activation and DPF23b of the oxidation catalyst 23c in the fuel addition request determining unit 15d is determined to be necessary, the addition of fuel from the fuel addition valve 24a Is to be executed. The determination result in the fuel addition request determination unit 15d is output to the glow plug drive unit 15g, the fuel addition amount setting unit 15e, and a unit addition amount update unit 15h described later.

The fuel addition request determination unit 15d of the ECU 15 determines that there is a fuel addition request, that is, the exhaust heating device 24 needs to be operated, in any of the following cases a to d. That is,
a: If an oxidation catalyst 23c is either inactive, or is expected to be inactive b: If DPF23b is clogged by the deposition of HC c: NO _X occluding occluded saturation of the NO _X by the catalyst 23a D: When DPF 23b needs to be regenerated even when it is not clogged. In the case of a, the determination can be made based on the temperature information T _I , T _O and T _C from the first and second exhaust temperature sensors 25 and 28 and the catalyst temperature sensor 27. In the case of b, it can be estimated from the accumulated operation time of the engine 10 or the accumulated fuel injection amount from the fuel injection valve 11, but it can also be determined using an exhaust pressure sensor. Similarly, in the case of c, it can be estimated from the accumulated operation time of the engine 10, the accumulated fuel injection amount from the fuel injection valve 11, and the like.

The fuel addition amount setting unit 15e of the ECU 15 sets the amount of fuel to be added to the exhaust passage 20a (hereinafter referred to as a required addition amount) L _TA and L _TR in order to maintain the function of the exhaust purification device 23 normally. Set.

More specifically, the exhaust gas temperature T _I, and a suction amount V _A of air per predetermined time (for example, one second), the active request to be added to the exhaust passage 20a to maintain the active state of the oxidation catalyst 23c The addition amount _LTA is set based on the following formula (1). Exhaust gas temperature T _I is an exhaust gas temperature of the upstream side flows through the nearest of the exhaust passage 20a of the oxidation catalyst 23c than the oxidation catalyst 23c, hereinafter referred to as the catalyst upstream exhaust gas temperature. Further, an air intake amount per predetermined time (hereinafter referred to as an intake amount) _VA is acquired from the air flow meter 22.

L _TA = {(T _L −T _I ) V _A · C} / J (1)
However, TL is the lowest temperature at which the oxidation catalyst 23c is activated, and is stored in advance in the fuel addition amount setting unit 15e. C is the specific heat of the air, J is the heat value of the fuel added to the exhaust passage 20a, and these are also stored in the fuel addition amount setting unit 15e in advance. Incidentally, the catalyst upstream exhaust gas temperature T _I is obtained from the first exhaust temperature sensor 25 earlier.

Also, if the NO _X reduction process in the reproducing process and _the NO _X storage storage catalyst in DPF23b constituting the exhaust gas purification device 23 by the fuel addition request determining unit 15d is determined to be necessary, it is added to the exhaust passage 20a The required regeneration required addition amount _LTR is set based on the following equation (2).

L _TR = (V _A / R _T ) −q (2)
However, _RT is an air-fuel ratio (hereinafter, referred to as a target air-fuel ratio) of exhaust that flows through the exhaust passage 20a flowing into the exhaust purification device 23, which is stored in advance in the fuel addition amount setting unit 15e. Yes. Further, q is an injection amount of fuel injected from the fuel injection valve 11 into the combustion chamber 10a of the engine 10, and is obtained from the fuel injection valve drive unit 15c.

The fuel addition amount setting request amount set by unit 15e _{L TA,} L TR _(hereinafter sometimes referred to as these collectively convenience required addition amount L _T) information on the fuel addition ECU15 It is output to the valve drive unit 15f and the unit addition amount update unit 15h.

Fuel addition valve drive unit 15f performs a process of multiplying the calculation cycle t _P (e.g. 20 ms) to the required addition amount L _T set by the fuel addition amount setting section 15e for each the calculation cycle t _P Accumulate. Thus, when the integrated value of the fuel obtained at each calculation cycle t _P reaches the unit addition amount L _U updated by the unit addition amount update unit 15h, the energization corresponding to the unit addition amount L _U is performed. give time _{t U} to the fuel addition valve 24a. At the same time, the integrated value of the fuel so far is corrected to (integrated value−unit addition amount L _U ), and the fuel addition process is repeated again to drive the fuel addition valve 24a intermittently. That is, the driving distance of about fuel addition valve 24a is often required amount L _T per predetermined time is reduced, the driving distance of about fuel addition valve 24a is less required addition amount L _T conversely tend to be longer. The drive information from the fuel addition valve drive unit 15f to the fuel addition valve 24a is output to the surplus error calculation unit 15i of the ECU 15.

In a transient operation state of the engine 10 such as rapid acceleration in which a large amount of fuel needs to be added in a short time, the drive cycle t _C of the fuel addition valve 24 a is synchronized with the fuel explosion interval in each cylinder of the engine 10. It is necessary to let As a result, even when supplying unit fuel amount L _U to the exhaust passage 20a for each driving cycle t _C which matches the firing interval of fuel in each cylinder of the engine 10, the addition rate of the fuel is insufficient to properly control You may not be able to do it. In the present embodiment, the required addition amount ΔL _T (= L _TA · t _C , L _TR · t _C ) to be added every drive cycle t _C of the fuel addition valve 24a exceeds twice the unit addition amount L _U. only added to the exhaust passage 20a of the half of multiplying the driving period _{t C} required addition amount _{L T} from the fuel addition valve 24a when the. FIG. 3 schematically shows a change in the required addition amount ΔL _T to be added every time t ₁ to t _{5 in} the shortest drive cycle t _C of the fuel addition valve 24a. In FIG. 3, the required addition amount ΔL _T has accumulated over the unit addition amount L _U from time t ₁ to time t ₃ , but the required addition amount ΔL _{T for} each driving cycle t _C is 2 of the unit addition amount L _U. At times t ₃ and t ₄ exceeding the double, not the unit addition amount L _U but the amount of fuel of ΔL _T / 2 is added. Therefore, the time _t at the ₅ or later converge to less than twice the driving period _t required addition amount of each _C [Delta] L _T is a unit amount _{L U,} time _t 1, when the _{t 2} as well as the unit amount _{L U} is Added. As a result, it is possible to suppress a rapid change in the amount of fuel added from the fuel addition valve 24a to the exhaust passage 20a as well as suppressing control delay.

The ECU 15 includes a convergence determination unit 15j in addition to the operation state determination unit 15a and the fuel addition valve drive unit 15f described above.

Convergence determination unit 15j, based on the determination result of the operation state of the operation state determination unit 15a, whether the oxidation catalyst 23c by the addition of fuel from the fuel addition valve 24a is in a stable state reach the target activation temperature T _T Determine. Further, the air-fuel ratio R _N is similarly determined whether the stable state reached the target air-fuel ratio R _T by the addition of fuel from the fuel addition valve 24a.

The determination by the convergence determination unit 15j that the temperature of the oxidation catalyst 23c has converged and stabilized in the vicinity of the target activation temperature T _T is a case where the following two conditions are satisfied. The first condition is that the temperature of the exhaust gas flowing through the exhaust passage 20a closest to the oxidation catalyst 23c on the downstream side of the oxidation catalyst 23c from the target activation temperature T _T (hereinafter referred to as catalyst downstream exhaust temperature) T _O the absolute value of the value obtained by subtracting the is that is smaller than the positive threshold T _R set in advance. The second condition is that the absolute value of the rate of change dT _O of the exhaust gas temperature T _O is smaller than a preset threshold value dT _R (generally a positive value close to 0). This makes it possible to reliably determine that the operating state of the engine 10 is not transient, but when only one of the conditions is satisfied, the temperature of the oxidation catalyst 23c converges in the vicinity of the target activation temperature T _T. It is also possible to make a determination.

Similarly, when the air-fuel ratio R _N of the exhaust gas flowing through the exhaust passage 20a is determined by the convergence determination unit 15j of the stable and converges to the vicinity of the target air-fuel ratio R _T is that the following two conditions It is. The first condition is that the absolute value of the value obtained by subtracting the air-fuel ratio R _N which is acquired by the air-fuel ratio sensor 26 from the target air-fuel ratio R _T is smaller than the positive threshold R _R set in advance. The second condition is _(generally near a positive value to zero) air-fuel ratio R _N threshold dR R absolute value of the rate of change dR _N is preset is smaller than. Thus, although the operation state of the engine 10 can be reliably determined when not transient, if you meet only one condition, the air-fuel ratio R _N is the target air-fuel ratio of the exhaust gas flowing through the exhaust passage 20a It is also possible to determine that it has converged in the vicinity of _RT .

It is possible to confirm that the engine 10 is not in a transient operation state by such determination processing in the convergence determination unit 15j, and thereby to perform smooth control of the exhaust heating device 24. The determination result here is output to the surplus error calculation unit 15i.

Here shows a relationship between unit amount of added L _U and the maximum permissible error E _A and the maximum variation error E _D schematically in FIG. 4, rather than the positive and negative values centered on 0, conveniently percent Note that it is expressed as the absolute value of. To the unit amount L _U set by the unit amount updating unit 15h, the control of interest, for example, the value of the deviation which can converge the air-fuel ratio control of the Atsushi Nobori control and the exhaust of the oxidation catalyst 23c, that is, the maximum permissible error E _a may be represented as follows what percent of the unit amount L _U. Therefore, the maximum permissible error E _A of the percentage basically regardless of the magnitude of the unit amount L _U, can be represented as a constant value. On the other hand, the maximum variation error E _D of the addition amount caused by the mechanical characteristics of the fuel addition valve 24a itself, the viscosity of the fuel itself, etc., as the unit addition amount L _U decreases as shown by the solid line in FIG. It has a tendency to increase rapidly. Therefore, the maximum permissible error E _A and the maximum variation error E _D and equals the unit amount (hereinafter, the unit amount described as reference unit amount L _UC a) If you try to reduce the unit amount L _U than , it is necessary to take into account the maximum variation error E _D. This means that only the difference between the maximum variation error E _D and the maximum allowable error E _A, if so the error of the maximum permissible error E _A further small estimated by the unit amount L _U falls within (E A _{-E D)} Don't be.

The surplus error calculator 15i stores a map as shown in FIG. 4 in advance. Then, from the integrated value ΣL _{U of} the unit addition amount L _U set by the unit addition amount update unit 15h, a fuel addition amount actually detected corresponding to the integrated value ΣL _U (hereinafter referred to as an actual fuel addition amount) calculating the amount error E _U subtracts describing) g. Moreover, to calculate the surplus acceptable error Delta] E _A is subtracted from the maximum permissible error E _A corresponding to the calculated amount error E _U a current unit amount stored in the map of FIG. 4 L _U. The integrated value ΣL _U is a command value of the amount of fuel that is driven by a command from the fuel addition valve drive unit 15f and added to the exhaust passage 20a from the fuel addition valve 24a during the intake amount _VA detection period. Therefore, the addition amount error E _U can be expressed by (.SIGMA.L U _-g), the actual fuel amount g is calculated by the following equation (3).

g = (ΔT _I · V _A · C) / J (3)
Here, ΔT _I is the difference between T _I detected by the first exhaust temperature sensor 25 and the exhaust temperature T _O detected by the second exhaust temperature sensor 28, and is expressed by ΔT _I = T _O −T _I. The Therefore, the surplus acceptable error Delta] E _A is as in the following equation (4).

ΔE _A = E _A −ΣL _U + (ΔT _I · V _A · C / J) (4)
The excess calculated by the surplus error calculating unit 15i acceptable error Delta] E _A is outputted to the unit amount updating unit 15h.

Unit amount updating section 15h in the present embodiment, once the fuel addition amount per energization time t _U of added from the fuel adding valve 24a to the exhaust passage 20a, i.e. to update the unit amount L _U, updated units and it outputs the amount _{L U} to the fuel addition valve drive unit 15f. In the present embodiment has the initial value L _US unit amount L _U is stored in advance in a unit amount updating unit 15h, a unit amount L _U as the initial value L each addition amount target unit from _US L _UT Control is performed so that the amount is decreased step by step. Basically, as the addition interval of the unit amount L _U as possible with respect to the set required addition amount L _T by the fuel addition amount setting section 15e (driving period t _C of the fuel addition valve _24a) is shortened in, go to update the unit amount L _U to a smaller value. In this case, the initial value L _US of the unit addition amount is set to a value sufficiently larger than the reference unit addition amount L _UC . The target unit addition amount L _UT is set to a value smaller than the current unit addition amount L _U by a predetermined amount, and is reduced to a smaller value by the update process when possible.

More specifically, a target unit addition amount _{LUT in} which the fuel is smaller than the current unit addition amount L _U by a certain amount is set, and this target unit addition amount L _UT is smaller and smaller than the reference unit addition amount L _UC. Different processing is performed depending on the case. That is, when the target unit amount L _UT is larger than the reference unit amount L _UC is not necessary to consider the maximum variation error E _D. Therefore, when the addition amount error E _U calculated by the surplus error calculating unit 15i is smaller than the maximum permissible error E _A updates the target unit amount L _UT as a new unit amount L _U.

The target unit amount L _UT is smaller than the reference unit amount L _UC, the fuel than current units amount L _U sets a fixed amount only small target unit amount L _UT. Further, the maximum variation error E _DT in the target unit addition amount L _UT and the maximum variation error E _DU in the current unit addition amount L _U are read from the map of FIG. Next, a surplus variation error amount ΔE _D (= E _DT − obtained by subtracting the maximum variation error E _DU corresponding to the current unit addition amount L _U from the maximum variation error E _DT corresponding to the target unit addition amount L _UT. E _DU ) and the surplus allowable error amount ΔE _A given from the surplus error calculation unit 15 i are compared. When the surplus acceptable error Delta] E _A is determined to be smaller than the excess variation error amount Delta] E _D, to update the target unit amount L _UT as a new unit amount L _U.

In any case, the energization time t _U corresponding to the updated unit amount L _U is corrected by the following equation (5).

t _U = t _UT × (ΣL _U / g) (5)
Note that the energization time t _U corresponding to the updated unit addition amount L _U can be corrected using any appropriate functional expression having (ΣL _U / g) as a variable other than the expression (5). For example, it is also effective to adopt the following formula (6).

t _U = t _UT + (ΣL _U / g) (6)
Further, in order to suppress a sudden change in (ΣL _U / g) on the right side of the expressions (5) and (6), (ΣL _U / g) is multiplied by a correction coefficient larger than 0 and 1 or less. Is also effective. Such a correction coefficient (5), by incorporating into (6), errors and based on the resolution of the sensors, which are used to calculate the unit amount L _U and actual fuel amount g, transient vehicle it is possible to avoid an adverse effect due to the calculation of the energization time t _U in Do operating conditions. This correction coefficient can be set in advance according to the magnitude of the error based on the resolution of the sensors, the transient driving state of the vehicle, and the like.

In this way, the current unit addition amount L _U is corrected to the target unit addition amount L _U by correcting the energization time t _UT corresponding to the target unit addition amount L _UT based on the ratio of the actual fuel addition amount g to the unit addition amount L _U. the amount even reduced to L _UT, can be kept below the maximum permissible error E _a. Thus, since the surplus acceptable error Delta] E _A may exceed the surplus variation error amount Delta] E _D, the weight loss of the current unit amount L _U to the target unit amount L _UT, which exceeds the maximum permissible error E _A, updating unit amount L _U is not performed.

As described above, the smaller the unit amount L _U for the requested amount L _T, added period t _C of the fuel added from the fuel adding valve 24a to the exhaust passage 20a is shortened. As a result, the temporal variation width of fuel added to the exhaust passage 20a is reduced, it is possible in particular to reduce the variation width of the air-fuel ratio R _N in the exhaust.

Unit amount updating section 15h in this embodiment includes an update determination unit 151 for determining whether regarding update processing unit described above amount L _U and the energization time t _U. When it is determined that the following conditions (A), (C), (E), and (B) or (D) are satisfied, the update availability determination unit 151 performs unit addition by the unit addition amount update unit 15h. The quantity L _U and the energization time t _U can be updated. Conversely, when it is determined that the conditions (A), (C), (E) and (B) or (D) are not satisfied, the unit addition amount L _U and the energization time t _U are not updated. , the unit amount updating section 15h stores the current unit amount L _U and the energization time t _U as the addition amount latest units L _U and the energization time t _U.
(A) ΔE A> ΔE _D
(B) E _A > E _VA + E _RT
(C) ΔE _S > ω · g
(D) E _A > (E _T / ΔT _C )
(E) E _A > E _U
Relates (A), as described above, if the surplus acceptable error Delta] E _A exceeds the excess variation error amount Delta] E _D, the weight loss of the current unit amount L _U to the target unit amount L _UT, which is the maximum allowed since it exceeds the error E _AT, updating the unit amount L _U is not performed.

Regarding (B), as is well known, the air flow meter 22 and the air-fuel ratio sensor 26 are known to have specific measurement errors due to these detection systems. The relationship between the intake air amount by the air flow meter 22 and the measurement error shown in FIG. 5 shows the relationship between the air-fuel ratio R _N and the measurement error due to the air-fuel ratio sensor 26 in FIG. 6. If in the previous equation (2) so as to calculate the reproduction request amount L _TR, the air-fuel ratio R _N of the exhaust gas detected by the intake air amount V _A and the air-fuel ratio sensor 26 is detected by the air flow meter 22 , Measurement errors E _VA and E _RT as shown in FIGS. 5 and 6 are included. As a result, these errors _{E VA,} depending on the combination condition of _{E RT} could exceed the maximum permissible error _{E A} for regeneration required addition amount _{L TR.} Therefore, when controlling the air-fuel ratio R _N of the exhaust in the present embodiment, the measurement error E _VA airflow meter 22 and the air-fuel ratio sensor _26, the sum of E _RT (%) exceeds the maximum permissible error E _A If not update the previous target unit amount L _UT as a new unit amount L _U. Also, the calculation of the previous equation (5) is not performed.

It relates (C), the detection value R _N of the air-fuel ratio sensor 26 is shifted to the lean side in proportion to the amount of HC contained in the exhaust, are known to cause a so-called well-known lean side. Therefore, it is necessary to keep the error of the detected value R _N of the air-fuel ratio sensor 26 by the lean shift amount Delta] E _S to the maximum permissible error E _A of the unit amount L _U, when lean shift amount Delta] E _S is too large It does not update the previous target unit amount L _UT as a new unit amount L _U. Similarly, it is necessary not to perform the calculation of the above equation (5). In the present embodiment, when the value omega · g to the actual fuel amount g in purification rate omega obtained by integrating the HC by the exhaust gas purification device 23 is smaller than the lean shift amounts Delta] E _S, new ahead of the target unit amount L _UT performing the calculation of the previous equation (5) and updates as a unit amount L _U. Conversely, the exhaust gas purification device when the value omega · g obtained by integrating the actual fuel amount g in purification rate omega of HC is not less than the lean shift amounts Delta] E _S by 23, ahead of the target unit amount L _UT new units added not updated as the amount L _U, not performed operations of the previous equation (5).

The relationship between the lean shift amounts Delta] E _S of HC amount and the air-fuel ratio sensor 26 that the air-fuel ratio sensor 26 is included in the exhaust gas passing through the exhaust passage 20a disposed schematically shown in FIG. The operating state determination unit 15a of the ECU 15 stores a map as shown in FIG. 7 in advance, and the HC amount contained in the exhaust is determined by the intake air amount _VA , the fuel injection amount from the fuel injection valve 11, and the fuel addition valve 24a. Based on the amount of fuel added from the above, it is calculated by the update possibility determination unit 151. Further, the HC purification rate ω by the exhaust purification device 23 can be calculated by dividing the HC reaction speed v in the exhaust purification device 23 by the exhaust flow rate, here the intake air amount _VA . The reaction rate v of HC in the exhaust purification device 23 can be obtained from the relationship between the amount of HC and O ₂ concentration in the exhaust gas and the catalyst temperature. FIG. 8 shows the relationship between the HC reaction rate v, the HC amount and O ₂ concentration in the exhaust gas, and the catalyst temperature. Update determination unit 151 stores a such map in FIG. 8, reads the catalyst temperature T _C and the reaction rate v and a HC amount and O ₂ concentration in the exhaust gas. Next, the HC purification rate ω is calculated by dividing by the intake air amount _VA information by the air flow meter 22, and then the actual fuel addition amount g calculated from the above equation (3) is added to this to obtain the previous lean deviation compared to the amount ΔE _S. Only when ΔE _S > (v / V _A ) · g, the unit addition amount update unit 15h updates the unit addition amount L _U and its energization time t _U.

Regarding (D), when the control is performed based on the requested activity addition amount _LTA , it is necessary to avoid the influence of the detection error of the catalyst temperature sensor 27. Therefore, the error of the detected temperature of the exhaust purification device 23, that is the catalyst temperature T detected error temperature Yutakadai [Delta] T _C in a division value of the exhaust gas purification device 23 per the E _T unit time _C detected by the catalyst temperature sensor 27 (E _{T /} ΔT _C) determines whether less than the maximum allowable error E _a. When it is determined that E _A > (E _T / ΔT _C ), the unit addition amount L _U and its energization time t _U are updated.

Relates (E), in greater state than the target unit amount L _UT is the reference unit amount L _UC, as described above, when the additive amount error E _U is greater than the maximum allowable error E _A, the amount of added target unit L _UT Cannot be updated as a new unit addition amount L _U.

FIGS. 9 to 11 show the flow of fuel addition control according to the present embodiment in the catalyst activation mode in which the oxidation catalyst 23c is maintained in the active state. First, in step S11, it is determined whether or not there is a fuel addition request. Here, when it is determined that there is a fuel addition request, that is, it is necessary to activate the oxidation catalyst 23c in the exhaust purification device 23, the process proceeds to step S12 to calculate the activation request addition amount _LTA . Then, after obtaining the unit amount _{L U} from the unit amount updating section 15h of the ECU15 in S13 step, start addition of fuel to the exhaust passage 20a by driving the fuel addition valve 24a at step S14 subsequent thereto To do.

This fuel addition subroutine is shown in FIG. That is, it is determined in step S141 whether or not the required addition amount ΔL _TA per unit time is less than twice the unit addition amount L _U. Here, the required addition amount per unit time [Delta] L _TA is less than twice the unit amount L _U, that is, especially when determined that there is no problem even if continuing the addition of fuel units amount L _U is performs addition of fuel at transition to a unit amount L _U to S142 steps. Next, in step S143, it is determined whether the fuel addition flag is set. Initially, since the fuel addition flag is not set, the process proceeds to step S144 to set the fuel addition flag, and then it is determined whether or not there is a fuel addition request in step S145. Here, if it is determined that there is a fuel addition request, that is, the necessity of activation of the oxidation catalyst 23c in the exhaust purification device 23 is still continuing, the process returns to the main flow of FIG. Perform steps. If it is determined in step S145 that there is no fuel addition request, that is, it is not necessary to activate the oxidation catalyst 23c in the exhaust purification device 23, the process returns to the main flow in FIG. Execute.

On the other hand, if the required addition amount ΔL _TA per unit time exceeds twice the unit addition amount L _{U in} the previous step S141, that is, if the addition of the fuel of the unit addition amount L _U is continued, the addition of fuel Is determined to be insufficient, the process proceeds to step S146. Then, after adding the fuel of 1/2 of the required addition amount ΔL _TA per unit time from the fuel addition valve 24a to the exhaust passage 20a, the steps after S143 are executed.

In step S15, it is determined whether the target unit amount L _UT that is newly set for the current unit amount L _U is smaller than the reference unit amount L _UC. Initially, the newly set target unit amount L _UT is a reference unit amount L _UC or more, the amount error E _U proceeds to S16 in step is calculated by the excess error calculating unit 15i. Then, the processing proceeds to step S17 to determine whether this amount error E _U is less than the maximum allowable error E _A, added amount error E _U is less than the maximum allowable error E _A, i.e. a unit amount If the updating of L _U is determined to be possible, the process proceeds to S18 in step. Then, steps after the correction, again S11 as the energization time t _U for the corresponding fuel addition valve 24a (5) formula updates the target unit amount L _UT which is set as a new unit amount L _U Return to. The amount error E _U in step S17 is the maximum permissible error E _A above, that is, when it is determined that can not be updated in a unit amount L _U, the unit amount of current L _U and energization time t _U is maintained as it is, and the process returns to step S11 again.

Target unit amount newly set for the current unit amount L _U in step S15 of the previous L _UT is smaller than the reference unit amount L _UC, i.e. it is necessary to consider the maximum variation error E _D If it is determined, the process proceeds to step S19. Then, it is determined whether the absolute value of the value obtained by subtracting the current catalyst downstream exhaust gas temperature T _O of the target activation temperature T _T of the oxidation catalyst 23c is smaller than the threshold T _R. Here, when it is determined that the absolute value of the value obtained by subtracting the current catalyst downstream exhaust temperature T _O from the target activation temperature T _T is smaller than the threshold value T _R , that is, the oxidation catalyst 23c has reached the activation temperature, The process proceeds to step S20. And, now it determines whether the rate of change dT _O catalyst downstream exhaust gas temperature is less than the threshold value dT _R. Here, less than the exhaust gas temperature change rate dT _CO threshold dT _R, that is, when the temperature of the oxidation catalyst 23c is determined to be stable and converges to the activation temperature, the process proceeds to S21 in step. Calculating the amount error E _U Here, calculates a surplus acceptable error Delta] E _A at S22 in step calculates the excess variation error Delta] E _D at S23 in step.

The absolute value of the current catalyst downstream exhaust gas temperature T _O of the subtracted value from the previous S19: target activation temperature T _T in step is the threshold value T _R or more, that determines that the oxidation catalyst 23c is not converged to the activation temperature If so, the process returns to step S11. Note that in this case, the current unit addition amount L _U and energization time t _U are maintained. Similarly, the rate of change dT _CO of the exhaust temperature at step step S20 is a threshold dT _R or more, that even if the oxidation catalyst 23c is determined not to converge to the activation temperature, the unit amount of current L _U and current while maintaining the time _{t U} returns to step S11.

Following S23 in step determines whether excess tolerance Delta] E _A is greater than the excess variation error Delta] E _D at S24 in step. Here, excess tolerance ΔL is greater than the excess variation error Delta] E _D, that is, when it is determined that it is possible to lose weight by updating the unit amount L _U, the process proceeds to step S29. Then, the temperature Yutakadai [Delta] T _C by the value obtained by dividing the catalyst temperature T _C of the detection error E _T exhaust purification apparatus per unit time 23 (E _{T /} ΔT _C) are whether less than the maximum allowable error E _A judge. Here, (E _{T /} ΔT _C) is less than the maximum allowable error E _A, that is, when it is determined that it is possible to lose weight by updating the unit amount L _U, the process proceeds to S18 in step. Conversely, (E _{T /} ΔT _C) is the maximum permissible error E _A above, that is, when it is determined that can not be reduced by updating the unit amount L _U, the unit amount of current L _U and and it maintains the energization time _{t U} returns to step S11. Similarly, if it is determined in step S24 that the surplus allowable error ΔE _A is equal to or less than the surplus variation error ΔE _D , that is, if the unit addition amount L _U is updated, the current unit is deviated from the maximum permissible error E _A. The addition amount L _U and the energization time t _U are maintained, and the process returns to the step S11.

On the other hand, if it is determined in step S11 that there is no fuel addition request, that is, it is not necessary to activate the oxidation catalyst 23c in the exhaust purification device 23, the process proceeds to step S30 and the fuel addition flag is set. It is determined whether it is set. If it is determined that the fuel addition flag is set, that is, fuel addition from the fuel addition valve 24a to the exhaust passage 20a continues, the process proceeds to step S31 and the fuel addition process is stopped. . Next, in step S32, the fuel addition flag is reset, and the series of controls is terminated. If it is determined in the previous step S30 that the fuel addition flag has not been set, that is, the fuel addition process from the fuel addition valve 24a to the exhaust passage 20a has not been performed, the process is terminated without doing anything. .

Thus, when excess tolerance Delta] E is less than the excess variation error Delta] E _D, results the unit amount L _U is updated to a smaller target unit amount L _UT, temperature oscillations of the oxidation catalyst 23c is reduced, Fuel waste can be reduced and fuel consumption can be improved. Moreover, it is possible to fit the always maximum permissible error be allowed to lose weight unit amount L _U, desired control accuracy can be reliably maintained.

In the above-described embodiment, the temperature of the oxidation catalyst 23c is controlled. However, a similar control mode can be adopted when controlling the air-fuel ratio of the exhaust gas.

The flow of such an exhaust purification device fuel addition control according to this embodiment of the catalyst regeneration mode for performing reduction processing of the playback process and _the NO _X storage catalyst 23a of DPF23b constituting 23 are shown in FIGS. Regarding the steps S41 to S48, S51 to S54, and S60 to S62 in the present embodiment, the contents and basics of the steps S11 to S18, S21 to S24, and S30 to S32 in the flowcharts shown in FIGS. Are the same. However, the reproduction request amount L _TR in step S42 is calculated by the equation (2), the subroutine of added fuel at S44 takes the same procedure as in the previous embodiment shown in FIG. 11.

Now, it is necessary to consider the maximum variation error E _D when the target unit addition amount L _UT newly set with respect to the current unit addition amount L _U in step S45 is smaller than the reference unit addition amount L _UC. If it is determined, the process proceeds to step S49. Then, it is determined whether the absolute value of the value obtained by subtracting the value R _N of the current air-fuel ratio from the value R _T of the target air-fuel ratio is smaller than the positive threshold R _R set in advance. Here, the absolute value of the value obtained by subtracting the value R _N of the current air-fuel ratio from the value R _T of the target air-fuel ratio is smaller than the threshold value R _R, i.e. substantially reaching the air-fuel ratio R _N of current state to the target air-fuel ratio R _T If it is determined that it is, the process proceeds to step S50. And, now it determines whether the absolute value of the rate of change dR _N of the air-fuel ratio detected by the air-fuel ratio sensor 26 is smaller than the threshold value dR _R set in advance. Here, the absolute value of the rate of change dR _N of the air-fuel ratio R _N is smaller than the threshold value dR _R, i.e. when the air-fuel ratio R _N of the exhaust gas flowing through the exhaust passage 20a is stable and converges to the target air-fuel ratio R _T when it is determined calculates a surplus acceptable error Delta] E _a proceeds to S51 in step.

The absolute value of the target air-fuel ratio R _T value obtained by subtracting the current air-fuel ratio R _N from is equal to or larger than the threshold R _R, i.e. the current air-fuel ratio R _N converges to the target air-fuel ratio R _T at S49 in step If it is determined that it is not, the process returns to step S41. Note that in this case, the current unit addition amount L _U and energization time t _U are maintained. The absolute value of the rate of change dR _N of the air-fuel ratio is the threshold value dR _R or at S50 in step, i.e. the air-fuel ratio R _N of the exhaust gas flowing through the exhaust passage 20a is not converged to the target air-fuel ratio R _T, Even when it is determined that the state is unstable, the process returns to step S41. Also in this case, the current unit addition amount L _U and energization time t _U are similarly maintained.

Following S53 in step determines whether excess tolerance Delta] E _A is greater than the excess variation error Delta] E _D at S54 in step. Here, excess tolerance ΔL is greater than the excess variation error Delta] E _D, that is, when it is determined that it is possible to lose weight by updating the unit amount L _U, the process proceeds to step S55. Then, it is determined whether the measurement error _E VA airflow meter 22 and the air-fuel ratio sensor _26, the sum of _{E RT} less than the maximum allowable error _{E A.} Here, the measurement error E _VA, if the sum of E _RT determines that can be reduced by updating small, that a unit amount L _U than the maximum allowable error E _A, the process proceeds to S56 in step . Then, to calculate the amount of HC in the exhaust gas, calculates the lean shift amounts Delta] E _S of the air-fuel ratio sensor 26 in S57 in step, to calculate the catalyst purification rate ω at S58 in step. Moreover, the measurement error E _VA at S55 in _step, the sum of E _RT is maximum permissible error E _A above, that is, when it is determined that can not be reduced by updating the unit amount L _U has the current while maintaining the unit amount _{L U} and the energization time _{t U} returns to S41 in step.

Following S58 in step determines whether less or not than the value to which the lean shift amounts Delta] E _S is obtained by integrating the actual fuel amount g in HC purification rate ω in S59 step. Here, when lean shift amount Delta] E _S is determined to be smaller than a value obtained by integrating the actual fuel amount g in HC purification rate ω, the process proceeds to S48 in step. Conversely, when the lean amount of deviation Delta] E _S is determined to the HC purification rate ω is the actual fuel amount g cumulative value or more, i.e., it can not be reduced by updating the unit amount L _U is currently Back unit amount L _U and the energization time t _U of the maintained to S41 in step.

Thus, excess tolerance Delta] E in the present embodiment be less than the excess variation error Delta] E _D, the unit amount L _U is updated to a smaller target unit amount L _UT. As a result, the temperature amplitude of the oxidation catalyst 23c is reduced, the waste of fuel addition is reduced, and the fuel consumption can be improved. Moreover, it is possible to fit the always maximum permissible error be allowed to lose weight unit amount L _U, desired control accuracy can be reliably maintained.

It should be noted that the present invention should be construed only from the matters described in the scope of claims, and in the above-described embodiment, all the changes and modifications included in the concept of the present invention are possible other than the items described. It is. 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.

dT _O exhaust rate of change of the temperature change rate dT _R threshold dR _N air dR _R threshold Delta] E _A surplus acceptable error Delta] E _D surplus variation error amount Delta] E _S air sensor for each drive cycle of the lean shift amount [Delta] L _T fuel adding valve to be added to the required addition amount [Delta] T _C maximum permissible error E _D unit amount of Noboru Yutakadai E _a unit amount per unit time of the exhaust gas purifying apparatus for the maximum variation error E _U amount error E _RT air sensor measurement error g actual fuel amount L _TA activity required addition amount L _TR playback request amount L _T required addition amount L _U unit amount L _UC reference unit addition of measurement error E _T catalyst temperature sensor detection error E _VA air flow meter the amount L air-fuel ratio of the _US unit amount of the initial value L _UT target unit amount R _N exhaust R _T target air-fuel ratio R _R threshold t _C driving period t ₁ of the fuel addition valve ~ _{t 5} the time T _C Catalyst temperature T _O catalyst downstream exhaust gas temperature T _T target activation temperature T _R threshold v exhaust purification device in the HC by reaction velocity V _A intake air quantity ω exhaust purification system of the HC purification rate 10 engine 10a combustion chamber 11 the fuel injection valve 12 Cylinder head 12a Intake port 12b Exhaust port 13a Intake valve 13b Exhaust valve 14 Accelerator pedal 15 ECU
15a Operating state determination unit 15b Fuel injection setting unit 15c Fuel injection valve drive unit 15d Fuel addition request determination unit 15e Fuel addition amount setting unit 15f Fuel addition valve drive unit 15g Glow plug drive unit 15h Unit addition amount update unit 15i Surplus error calculation unit 15j Convergence determining unit 151 Update up / down determining unit 16 Accelerator opening sensor 17 Cylinder block 17a Piston 17b Connecting rod 17c Crankshaft 18 Crank angle sensor 19 Intake pipe 19a Intake passage 19b Surge tank 20 Exhaust pipe 20a Exhaust passage 21 Supercharger (exhaust Turbine supercharger)
21a Compressor 21b Exhaust turbine 21c Intercooler 22 Air flow meter 23 Exhaust purification device 23a NO _X storage catalyst 23b DPF
23c Oxidation catalyst 24 Exhaust heating device 24a Fuel addition valve 24b Glow plug 25 First exhaust temperature sensor 26 Air-fuel ratio sensor 27 Catalyst temperature sensor 28 Second exhaust temperature sensor

Claims (9)

A method of adding fuel from a fuel addition valve to an exhaust passage upstream of an exhaust purification device,
Calculating a required addition amount of fuel to be added from the fuel addition valve to the exhaust passage based on the state of the exhaust purification device;
Reading a unit addition amount L _U of the fuel added to the exhaust passage in correspondence with the energization time t _U per time for the fuel addition valve;
A step of intermittently added to the exhaust passage of the fuel of the unit amount L _U from the fuel addition valve by the driving period corresponding to the required addition amount,
A step of reading the maximum permissible error E _A corresponding to the unit amount L _U,
A step of reading the maximum variation error E _DU of the fuel addition valves corresponding to the unit amount L _U,
Calculating the amount g of fuel actually added to the exhaust passage with respect to the unit amount L _U,
A step of amount than the unit amount L _U is set less target amount L _UT predetermined amount,
Reading a maximum variation error E _DT of the fuel addition valve corresponding to the target addition amount _LUT ;
Determining whether E _DT −E _DU <E _A − (L _U −g);
When it is determined that E _DT −E _DU <E _A − (L _U −g), the energization time t _UT for the fuel addition valve corresponding to the target addition amount L _UT is a function of (L _U / g). A correction step;
Wherein the target amount L _UT updated as new unit amount L _U, drives the (L _U / g) the fuel addition valve as a new current time t _U function, adding fuel to the exhaust passage A fuel addition method comprising the steps of: Said step of reading the unit amount L _U of fuel added to the exhaust passage in response to the energization time t _U per one with respect to the fuel addition valve is updated latest of the unit amount L _U is read The fuel addition method according to claim 1, wherein: When the amount of fuel to be added from the fuel addition valve exceeds twice the unit addition amount for each drive cycle of the fuel addition valve corresponding to the required addition amount, the amount to be added is 1 The fuel addition method according to claim 1 or 2, wherein / 2 is added. The state of the exhaust purification device for calculating the required addition amount is the temperature of the exhaust purification device or the air-fuel ratio of the exhaust gas flowing therethrough,
By execution of said step of intermittently adding fuel from the fuel addition valve in the energization time t _U to the exhaust passage, or temperature of the exhaust gas purifier, or the air-fuel ratio of the exhaust gas flowing through here has converged A step of determining whether or not the temperature of the exhaust gas purification device or the air-fuel ratio of the exhaust gas flowing therethrough has converged, E _DT −E _DU <E _A − ( The fuel addition method according to any one of claims 1 to 3, wherein the step of determining whether or not L _U -g) is executed. The step of determining whether the temperature of the exhaust gas purification device or the air-fuel ratio of the exhaust gas flowing therethrough has converged is whether or not at least one of the temperature of the exhaust gas purification device and the rate of change thereof falls within a predetermined range. 5. The fuel addition method according to claim 4, further comprising a step of determining whether at least one of an air-fuel ratio of exhaust flowing through the exhaust purification device and a rate of change thereof is within a predetermined range. When the sum of the detection error of the air-fuel ratio and the detection error of the intake air amount is smaller than the maximum allowable error, the step of determining whether or not E _DT −E _DU <E _A − (L _U −g) 6. The fuel addition method according to claim 1, wherein the fuel addition method is executed. Further comprising the step of determining whether or not the amount of HC passing through the exhaust gas purification device is below a predetermined value,
If it is determined that the amount of HC passing through the exhaust purification device is equal to or less than a predetermined value, the step of determining whether or not E _DT −E _DU <E _A − (L _U −g) is executed. The fuel addition method according to any one of claims 1 to 6, characterized in that: Determining whether the exhaust gas purifier temperature Yutakadai [Delta] T _C value E _{T /} [Delta] T _C divided by the exhaust gas purifying device per the error E _T unit time of the detected temperature is smaller than the maximum permissible error E _A Further comprising the step of
If it is determined that E _T / ΔT _C <E _A , the step of determining whether or not E _DT −E _DU <E _A − (L _U −g) is performed. The fuel addition method according to any one of claims 1 to 6. The method further includes the step of determining whether or not the amount of HC passing through the exhaust purification device is less than or equal to a predetermined value, and only when it is determined that the amount of HC passing through the exhaust purification device is less than or equal to a predetermined value. fuel addition process according to claim 8, characterized in _{that T /} [Delta] T C _<the step of determining whether it is E _a is executed.

Images