Regeneration control device for a diesel particulate filter

FIELD OF THE INVENTION

0001This invention relates to regeneration control of a filter which traps particulate matter contained in the exhaust gas of a diesel engine.

BACKGROUND OF THE INVENTION

0002A well known measure to decrease black smoke discharged from a diesel engine of a vehicle is to use a diesel particulate filter (hereinafter referred to as DPF) which traps particulate matter contained in the exhaust gas of the diesel engine.

0003When the amount of trapped particulate matter reaches a certain level, the DPF performs regeneration by burning the trapped particulate matter, and thus becomes able to trap particulate matter again. In order to burn the particulate matter, the temperature of the exhaust gas is raised by fuel injection control, or the temperature of the DPF is raised using a heater.

SUMMARY OF THE INVENTION

0004However, the operating condition of a diesel engine for a vehicle varies constantly, and hence it is not always possible to remove all of the particulate matter trapped in the DPF in one regeneration operation. As a result, regeneration ends with a part of the particulate matter remaining in the DPF. Such a state will be referred to as partial regeneration in the following description.

0005If particulate matter trapping is resumed in a partially regenerated state, errors are likely to occur when estimating the amount of particulate matter trapped in the DPF in order to determine the next regeneration timing.

0006Tokkai Hei 5-106427, published by the Japan Patent Office in 1993, proposes a method in which, following partial DPF regeneration, the DPF is heated by a heater until an end face of the DPF reaches a set temperature, and the required heating time is measured. Meanwhile, a fixed amount of air is supplied to the DPF before and after partial regeneration, and a difference in the flow velocity thereof is measured. Thus the amount of particulate matter remaining in the DPF is precisely estimated on the basis of the required heating time and the difference in the flow velocities of air. The start timing of the next regeneration is determined in consideration of the amount of particulate matter remaining in the DPF.

0007This prior art turns on the heater which is installed in the DPF when regeneration of the DPF is determined to be necessary. In the course of regeneration, the particulate matter trapped in the DPF burns due to the high temperature produced by the heater, and heat produced by the combustion of the particulate matter further raises the temperature of DPF. As a result, the temperature of DPF may rise excessively, which promotes early deterioration of the catalyst or substrate supporting the catalyst in the DPF.

0008It is therefore an object of this invention to maintain the temperature of DPF during regeneration in a preferable range.

0009In order to achieve the above object, this invention provides a regeneration device for a diesel particulate filter which traps particulate matter contained in an exhaust gas of a diesel engine. The device comprises a mechanism which raises a temperature of the exhaust gas in order to burn the particulate matter trapped in the filter. The mechanism is configured to raise the temperature of the exhaust gas to a higher temperature as an amount of particulate matter trapped in the filter decreases.

0010Preferably, the device further comprises a sensor which detects an amount of particulate matter trapped in the filter, and a programmable controller programmed to set a target exhaust gas temperature such that the target exhaust gas temperature is increased as the amount of the particulate matter trapped in the filter decreases, and control the mechanism to raise the exhaust gas temperature to the target exhaust gas temperature.

0011This invention also provides a regeneration method for a diesel particulate filter which traps particulate matter contained in an exhaust gas of a diesel engine. The method comprises raising the temperature of the exhaust gas to a higher temperature as an amount of particulate matter trapped in the filter decreases.

0012The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

0013<figref idref="f0001">FIG. 1</figref> is a schematic diagram of an engine for use in a vehicle, comprising a DPF regeneration device according to this invention.

0014<figref idref="f0002">FIG. 2</figref> is a flowchart illustrating a DPF regeneration control routine executed by an engine controller according to this invention.

0015<figref idref="f0003">FIG. 3</figref> is a diagram showing the characteristic of a map of an amount of trapped particulate matter PMi, which is stored by the engine controller.

0016<figref idref="f0003">FIG. 4</figref> is a timing chart showing an example of temporal change in a DPF bed temperature <i>Tbed.</i>

0017<figref idref="f0004">FIG. 5</figref> is a diagram showing the characteristic of a map of an amount of burned particulate matter <i>PMr,</i> which is stored by the engine controller.

0018<figref idref="f0005">FIG. 6</figref> is a flowchart illustrating a subroutine for calculating an effective regeneration time <i>Te</i> executed by the engine controller.

0019<figref idref="f0006">FIGs. 7A-7C</figref> are timing charts showing temporal change in a DPF inlet temperature, the DPF bed temperature <i>Tbed,</i> and a remaining amount of particulate matter <i>PMx</i> as a result of the execution of the DPF regeneration control routine.

0020<figref idref="f0007">FIG. 8</figref> is a timing chart showing temporal change in the DPF bed temperature <i>Tbed</i> for describing a computational algorithm of an effective regeneration time <i>Te</i> according to a second embodiment of this invention.

0021<figref idref="f0004">FIG. 9</figref> is a diagram showing the characteristic of a map of an effective regeneration time temperature coefficient K, which is stored by an engine controller according to the second embodiment of this invention.

0022<figref idref="f0005">FIG. 10</figref> a flowchart illustrating a subroutine for calculating the effective regeneration time <i>Te</i> executed by the engine controller according to the second embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0023Referring to <figref idref="f0001">FIG. 1</figref> of the drawings, a diesel engine 20 for a vehicle comprises an intake passage 32 and an exhaust passage 30 connected to a combustion chamber 20A.

0024The diesel engine 20 burns a mixture of air that is aspirated into the combustion chamber 20A from the intake passage 32 and fuel that is injected into the combustion chamber 20A by a fuel injector 23 by means of compression ignition. The combustion gas is discharged from the exhaust passage 30 as exhaust gas.

0025An air cleaner 35, a compressor 29A of a turbocharger 29, an inter cooler 28, and an intake throttle 21 are provided on the intake passage 32. The intake air in the intake passage 32 is purified by the air cleaner 35, compressed by the compressor 29A, cooled by the inter cooler 28, and then aspirated into the combustion chamber 20A via the intake throttle 21.

0026A turbine 29B of the turbocharger 29 and a DPF 10 are provided on the exhaust passage 30. The exhaust gas that is discharged from the combustion chamber 20A into the exhaust passage 30 drives the turbine 29B to rotate. The exhaust gas is then discharged into the atmosphere after trapping particulate matter in the DPF 10.

0027A part of the exhaust gas in the exhaust passage 30 is recirculated into the intake air via an exhaust gas recirculation passage (EGR passage) 33. The EGR passage 33 connects the exhaust passage 30 upstream of the turbine 29B to the intake passage 32 downstream of the intake throttle 21. An exhaust gas recirculation valve (EGR valve) 22 for regulating the exhaust gas recirculation flow (EGR flow) is provided on the EGR passage 33.

0028The DPF 10 traps particulate matter contained in the exhaust gas in the exhaust passage 30, and regenerates by burning the trapped particulate matter at a predetermined regeneration temperature. A known ceramic porous filter may be used as the DPF 10.

0029Regeneration of the DPF 10 is performed by raising the exhaust gas temperature through control of the fuel injection amount and fuel injection timing of the fuel injector 23 in response to signals output from an engine controller 16. Fuel injection control to raise the exhaust gas temperature includes well-known methods such as post-injection and injection timing retardation.

0030The engine controller 16 is constituted by a microcomputer comprising a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), a clock, and an input/output interface (I/O interface). The controller may be constituted by a plurality of microcomputers.

0031To control regeneration of the DPF 10, detection data from an air flow meter 34 which detects the intake air amount, a differential pressure sensor 12 which detects the differential pressure between the inlet and outlet of the DPF 10, a temperature sensor 13 which detects the exhaust gas temperature upstream of the DPF 10, a temperature sensor 14 which detects the exhaust gas temperature downstream of the DPF 10, and an air/fuel ratio sensor (A/F sensor) 15 which detects from the oxygen concentration in the exhaust gas the air/fuel ratio of the air/fuel mixture supplied to the combustion chamber 20A are input respectively into the engine controller 16 as signals. A universal exhaust gas oxygen sensor or a less expensive oxygen sensor may be used as the A/F sensor 15.

0032Next, referring to <figref idref="f0002">FIG. 2</figref>, a control routine for regenerating the DPF 10, which is executed by the engine controller 16, will be described. The engine controller 16 starts the routine together with the beginning of an operation of the diesel engine 20. As soon as the routine ends, the next execution of the routine begins, and hence the routine is executed substantially constantly while the diesel engine 20 is operative.

0033First, in a step S101, the engine controller 16 estimates an amount of trapped particulate matter <i>PMi</i> in the DPF 10 on the basis of the differential pressure detected by the differential pressure sensor 12.

0034Next, in a step S102, the engine controller 16 determines whether or not the amount of trapped particulate matter <i>PMi</i> has reached a reference trapped amount <i>PMα</i> for regenerating the DPF 10. The reference trapped amount <i>PMα</i> for regenerating the DPF 10 is determined in advance through experiment.

0035If the amount of trapped particulate matter <i>PMi</i> has not reached the reference trapped amount <i>PM</i>α for regenerating the DPF 10, the engine controller 16 repeats the process from the step S101.

0036When the amount of trapped particulate matter <i>PMi</i> has reached the reference trapped amount <i>PMα</i> for regenerating the DPF 10, the engine controller 16 determines in a step S103 a target DPF inlet temperature <i>Td</i> from the amount of trapped particulate matter <i>PMi.</i>

0037This determination is performed by looking up a map previously stored in the ROM and having the characteristic shown in <figref idref="f0003">FIG. 3</figref>. According to this map, the target DPF inlet temperature <i>Td</i> decreases as the amount of trapped particulate matter <i>PMi</i> increases. If the amount of trapped particulate matter <i>PMi</i> is large, then the amount of particulate matter that is burned by a regeneration operation of the DPF 10 increases, and hence the temperature of the DPF 10 becomes likely to rise excessively as a result of the combustion heat.

0038By setting the target DPF inlet temperature <i>Td</i> to decrease as the amount of trapped particulate matter <i>PMi</i> increases, such excessive rises in temperature can be prevented.

0039The dotted line in the figure denotes the characteristic of the target DPF inlet temperature <i>Td</i> that gradually decreases according to increases in the amount of trapped particulate matter <i>PMi.</i> In practice, however, the target DPF inlet temperature <i>Td</i> may be set to vary in a step-wise fashion as shown by the solid line in the figure. It is preferable to set the number of steps to more than three. If the target DPF inlet temperature <i>Td is</i> set vary in a step-wise fashion, it takes only several values, e.g., <i>Td1, Td2</i> and <i>Td3</i> in the figure, thereby simplifying temperature control of the DPF 10.

0040Next, in a step S104, an operation to raise the temperature of the exhaust gas is begun in order to realize the target DPF inlet temperature <i>Td.</i> This operation is performed by means of fuel injection control such as retardation of the fuel injection timing, or post-injection whereby additional fuel is injected following normal fuel injection. In cases where the regeneration device comprises a heater, the exhaust gas temperature may be raised using the heater.

0041Next, in a step S105, the engine controller 16 estimates a bed temperature <i>Tbed</i> of the DPF 10 from an exhaust gas temperature <i>T1</i> upstream of the DPF 10, which is detected by the temperature sensor 13, and an exhaust gas temperature T2 downstream of the DPF 10, which is detected by the temperature sensor 14, in accordance with the following equation (1).<maths id="math0001" num="(1)"><math display="block"><mi mathvariant="italic">Tbed</mi><mo mathvariant="italic">=</mo><mi mathvariant="italic">b</mi><mo>⁢</mo><mn mathvariant="italic">1</mn><mo mathvariant="italic">⋅</mo><mi mathvariant="italic">T</mi><mo>⁢</mo><mn mathvariant="italic">1</mn><mo mathvariant="italic">+</mo><mi mathvariant="italic">b</mi><mo>⁢</mo><mn mathvariant="italic">2</mn><mo mathvariant="italic">⋅</mo><mi mathvariant="italic">T</mi><mo>⁢</mo><mn mathvariant="italic">2</mn></math><img file="EP1517028B1_D0001.tif" /></maths> where, <i>b1, b2</i> = experimentally determined constants.

0042Next, in a step S106, the engine controller 16 calculates an effective regeneration time <i>Te.</i>

0043This calculation is performed by the execution of a subroutine shown in <figref idref="f0005">FIG. 6</figref>.

0044The effective regeneration time <i>Te</i> is a cumulative value of the time during which the bed temperature <i>Tbed</i> of the DPF 10 exceeds a target bed temperature <i>Tx.</i> The target bed temperature <i>Tx</i> is set to a temperature at which regeneration of the DPF 10 is performed reliably, or in other words a temperature at which the particulate matter is burned reliably. The target bed temperature <i>Tx</i> varies according to the amount of trapped particulate matter <i>PMi.</i>

0045For example, when the amount of trapped particulate matter <i>PMi</i> is 4.0 gram/liter, the target bed temperature <i>Tx</i> is 580 degrees Centigrade. When the amount of trapped particulate matter <i>PMi</i> is 2.0 gram/liter, the target bed temperature <i>Tx</i> is 600 degrees Centigrade.

0046Referring to <figref idref="f0003">FIG. 4</figref>, the bed temperature <i>Tbed</i> of the DPF 10 exceeds the target bed temperature <i>Tx</i> in time slots corresponding to <i>tx1-tx4.</i>

0047In a step S201 of <figref idref="f0005">FIG. 6</figref>, the engine controller 16 measures a time elapsed since the bed temperature <i>Tbed</i> exceeded the target bed temperature <i>Tx</i> using the clock function of the microcomputer which constitutes the engine controller 16.

0048In a next step S202, the engine controller 16 calculates a cumulative value of the durations of time during which the bed temperature <i>Tbed</i> exceeded the target bed temperature <i>Tx</i> as the effective regeneration time <i>Te</i> by the following equation (2).<maths id="math0002" num="(2)"><math display="block"><mi mathvariant="italic">Te</mi><mo mathvariant="italic">=</mo><mi mathvariant="italic">tx</mi><mo>⁢</mo><mn mathvariant="italic">1</mn><mo mathvariant="italic">⋅</mo><mi mathvariant="italic">tx</mi><mo>⁢</mo><mn mathvariant="italic">2</mn><mo mathvariant="italic">+</mo><mi mathvariant="italic">tx</mi><mo>⁢</mo><mn mathvariant="italic">3</mn><mo>+</mo><mi mathvariant="italic">tx</mi><mo>⁢</mo><mn mathvariant="italic">4</mn><mo>+</mo><mo>…</mo></math><img file="EP1517028B1_D0002.tif" /></maths>

0049After the processing of the step S202, the engine controller terminates the subroutine, and also terminates the processing of the step S106.

0050Whenever the bed temperature <i>Tbed</i> of the DPF 10 is updated in the step S105, the engine controller 16 recalculates the effective regeneration time <i>Te</i> in this way.

0051Next, in a step S107, the engine controller 16 refers to a map having the characteristic shown in <figref idref="f0004">FIG. 5</figref> and stored in the ROM in advance to determine an amount of burned particulate matter <i>PMr</i> from the bed temperature <i>Tbed</i> of the DPF 10 and the effective regeneration time <i>Te.</i> As shown in the map, the amount of burned particulate matter <i>PMr</i> increases as the bed temperature <i>Tbed</i> of the DPF 10 rises and the effective regeneration time <i>Te</i> lengthens.

0052Next, in a step S108, the engine controller 16 calculates an amount of remaining particulate matter <i>PMx</i> in the DPF 10 from the amount of burned particulate matter <i>PMr</i> and the amount of trapped particulate matter <i>PMi</i>, which was calculated in the step S101, using the following equation (3).<maths id="math0003" num="(3)"><math display="block"><mi mathvariant="italic">PMx</mi><mo mathvariant="italic">=</mo><mi mathvariant="italic">PMi</mi><mo mathvariant="italic">-</mo><mi mathvariant="italic">PMr</mi></math><img file="EP1517028B1_D0003.tif" /></maths>

0053Next, in a step S109, the engine controller 16 compares the amount of burned particulate matter <i>PMr to</i> a predetermined target amount of burned particulate matter <i>ΔPM.</i> If the amount of burned particulate matter <i>PMr</i> has not reached the target amount of burned particulate matter Δ<i>PM</i>, the engine controller 16 repeats the process from the step S106 onward. It should be noted that during this repetition period, the particulate matter trapped in the DPF 10 continues to be burned.

0054When the amount of burned particulate matter <i>PMr</i> reaches the target amount of burned particulate matter <i>ΔPM</i> in the step S109, the engine controller 16 compares the amount of remaining particulate matter <i>PMx</i> in the DPF 10 to a target amount of remaining particulate matter <i>PMd</i> in a step S110. The target amount of remaining particulate matter <i>PMd</i> corresponds to an allowable amount of particulate matter remaining in the DPF 10 at the end of a regeneration operation. This value is set in advance through experiment in accordance with the traveling condition of the vehicle. When the traveling condition is suitable for regeneration of the DPF 10, the target amount of remaining particulate matter <i>PMd</i> is set to 0.0 gram /liter. In other words, the DPF 10 should be regenerated completely. Under conditions other than the above, providing that the reference trapped amount <i>PMα</i> is set to 4.0 gram /liter, the target amount of remaining particulate matter <i>PMd</i> may be set to 2.0 gram/liter, half the amount of the reference trapped amount <i>PMα.</i>

0055If the remaining amount of particulate matter <i>PMx</i> has not reached the target amount of remaining particulate matter <i>PMd,</i> the engine controller 16 repeats the process from the step S103 onward. In this case, the target DPF inlet temperature <i>Td</i> is reset in the step S103 on the basis of the amount of remaining particulate matter <i>PMx</i> instead of the amount of trapped particulate matter <i>PMi</i> in the DPF 10. The operation to raise the temperature of the exhaust gas is then executed in the step S104 on the basis of the newly set target DPF inlet temperature <i>Td.</i>

0056Estimation of the bed temperature <i>Tbed</i> of the DPF 10 is also executed anew in the step S105, whereupon the newly estimated bed temperature <i>Tbed</i> of the DPF 10 is used to repeat the processing of the steps S106-S109.

0057By means of this process, a regeneration operation of the DPF 10 is executed with a different target DPF inlet temperature <i>Td</i> every time the amount of burned particulate matter <i>PMr</i> trapped in the DPF 10 reaches the target amount of burned particulate matter <i>ΔPM,</i> and the regeneration operation is executed continuously until the amount of remaining particulate matter <i>PMx</i> reaches the target amount of remaining particulate matter <i>PMd.</i>

0058When the amount of remaining particulate matter PMx reaches the target amount of remaining particulate matter <i>PMd in</i> the step S110, regeneration of the DPF 10 is complete. In this case, in a step S111, the engine controller 16 ends the operation to raise the temperature of the exhaust gas that was begun in the step S104. Following the processing of the step S111, the engine controller 16 ends the routine.

0059It should be noted that, as described above, the engine controller 16 begins to execute the next routine immediately after ending the current routine.

0060By executing the routine in <figref idref="f0002">FIG. 2</figref> continuously while the diesel engine 20 is operative in the manner described above, a regeneration operation of the DPF 10 is performed whenever the amount of trapped particulate matter <i>PMi</i> in the DPF 10 reaches the reference trapped amount <i>PMα.</i>

0061According to this invention as described above, the time during which the DPF bed temperature <i>Tbed</i> exceeds the target bed temperature <i>Tx</i> is cumulatively calculated as the effective regeneration time <i>Te,</i> and the amount of burned particulate matter <i>PMr</i> is determined on the basis of the effective regeneration time <i>Te</i>. Hence the amount of burned particulate matter <i>PMr</i> that is burned by the operation to raise the exhaust gas temperature, and the amount of remaining particulate matter <i>PMx</i> in the DPF 10, can be learned accurately.

0062Referring to <figref idref="f0006">FIGs. 7A-7C</figref>, variation in the DPF inlet temperature, the DPF bed temperature <i>Tbed</i> and the amount of remaining particulate matter <i>PMx</i> according to the execution of this DPF regeneration control routine will be described

0063The solid line in each figure denotes variation when the above DPF regeneration control routine is executed, whereas the dotted line in each figure denotes a case where regeneration of the DPF is performed with the target DPF inlet temperature <i>Td</i> set to a fixed value.

0064At a time <i>t0,</i> when regeneration of the DPF is started, the target DPF inlet temperature <i>Td</i> is set to the first target value <i>Td1</i> in the step S103. As shown in <figref idref="f0006">FIG. 7A</figref>, the first target value <i>Td1</i> is the lowest among the three candidate target values <i>Td1, Td2</i> and <i>Td3.</i> The reason why the lowest target value <i>Td1</i> is applied is that the amount of trapped particulate matter PMi in the DPF 10 is large when regeneration of the DPF 10 is determined in the step S102.

0065As a result of fuel injection control to raise the temperature of the exhaust gas, at a time <i>t1,</i> the DPF inlet temperature reaches the first target value <i>Td1.</i> The controller 16 then controls the fuel injection to stop raising the temperature of the exhaust gas further, while burning of the trapped particulate matter is continued. Since the target DPF inlet temperature <i>Td</i> is set to the lowest target value <i>Td1,</i> although the DPF bed temperature <i>Tbed</i> may exceed the target bed temperature <i>Tx</i> and reach a temperature <i>Tbed1</i> that is slightly higher than the target bed temperature <i>Tx</i> due to the combustion heat of the trapped particulate matter in the DPF 10, it will not rise far above the target bed temperature <i>Tx.</i>

0066At a time <i>t2,</i> when the amount of burned particulate matter <i>PMr</i> has reached the target amount of burned particulate matter Δ<i>PM</i>, the engine controller 16 raises the target DPF inlet temperature <i>Td</i> to a second target value <i>Td2</i> that is higher than the previous value <i>Td1.</i> The controller 16 then controls the fuel injection so as to raise the temperature of the exhaust gas until the DPF inlet temperature reaches the second target value <i>Td2.</i> After the time <i>t2</i>, since the amount of remaining particulate matter PMx has decreased, the heat produced by burning of the remaining particulate matter is less than that produced in the time period <i>t1-t2,</i> and hence the DPF bed temperature <i>Tbed</i> is kept at the temperature <i>Tbed1</i> despite the higher target DPF inlet temperature <i>Td2.</i> After the target DPF inlet temperature <i>Td2 is</i> reached, the engine controller 16 controls the fuel injection to stop raising the temperature of the exhaust gas further.

0067At a time <i>t3</i>, when the amount of burned particulate matter <i>PMr</i> has again reached the target amount of burned particulate matter <i>ΔPM,</i> the engine controller 16 then raises the target DPF inlet temperature <i>Td</i> to a third target value <i>Td3</i> that is the highest among the three candidate target values <i>Td1, Td2</i> and <i>Td3.</i>

0068The controller 16 then controls the fuel injection so as to raise the temperature of the exhaust gas until the DPF inlet temperature reaches the new target DPF inlet temperature <i>Td3.</i> Since the amount of remaining particulate matter PMx decreases further from the time <i>t2,</i> although the highest target value <i>Td3</i> for the target DPF inlet temperature <i>Td</i> is applied, the DPF bed temperature <i>Tbed</i> stays in the vicinity of the target bed temperature <i>Tx</i>.

0069After the time <i>t3,</i> the remaining particulate matter is further burned, and when the amount of remaining particulate matter <i>PMx</i> finally becomes zero as shown in <figref idref="f0006">FIG. 7C</figref>, regeneration of the DPF 10 is complete.

0070If, unlike in this invention, the target DPF inlet temperature <i>Td</i> is maintained at a fixed value <i>Td2</i> throughout the regeneration period, the bed temperature of the DPF 10 rises sharply once the trapped particulate matter starts to burn. It continues rising even after it has reached the temperature <i>Tbed1</i> as shown in <figref idref="f0006">FIG. 7B</figref>, and finally reaches a bed temperature <i>Tbed2</i> which is much higher than the target bed temperature <i>Tx</i>. Such a high bed temperature risks early deterioration of the catalyst contained in the DPF 10.

0071After reaching the temperature <i>Tbed2,</i> the bed temperature of the DPF 10 falls as the amount of remaining particulate matter <i>PMx</i> decreases through combustion. After the time <i>t3,</i> the fixed value <i>Td2</i> of the target DPF inlet temperature <i>Td</i> becomes lower with respect to the target value <i>Td3</i> that is set according to this invention. Since the amount of the remaining particulate matter <i>PMx</i> has become small at this stage, the heat produced by burning the remaining particulate matter is also small. The fixed target DPF inlet temperature <i>Td2</i> applied at this stage makes the time required for the completion of the regeneration longer than in the case of this invention.

0072As can be understood from the above, by progressively increasing the target DPF inlet temperature <i>Td</i> as the amount of remaining particulate matter <i>PMx</i> decreases, the bed temperature of the DPF 10 is prevented from rising excessively while the regeneration period is shortened. As a result, the energy consumed for the regeneration operation is minimized by this invention.

0073Next, referring to <figref idref="f0004 f0005 f0007">FIGs. 8-10</figref>, a second embodiment of this invention will be described.

0074The hardware constitution of this embodiment is identical to that of the first embodiment. The engine controller 16 according to this embodiment also executes the routine in <figref idref="f0002">FIG. 2</figref>. In this embodiment, however, the processing content of the step S106 in <figref idref="f0002">FIG. 2</figref> differs from that of the first embodiment.

0075In the step S106 in the first embodiment, by executing the subroutine of <figref idref="f0005">FIG. 6</figref>, the effective regeneration time <i>Te</i> was calculated as a cumulative value of the time during which the bed temperature <i>Tbed</i> of the DPF 10 exceeds the target bed temperature Tx.

0076As noted above, the target bed temperature <i>Tx</i> is the temperature at which the particulate matter is burned reliably, but even when the bed temperature <i>Tbed</i> of the DPF 10 does not reach the target bed temperature <i>Tx,</i> a part of the particulate matter can be burned as long as the bed temperature <i>Tbed</i> exceeds a temperature allowing combustion of the particulate matter. Hence in this embodiment, the amount of remaining particulate matter is calculated in consideration of the amount of particulate matter that is burned in this temperature region.

0077Referring to <figref idref="f0007">FIG. 8</figref>, in the process of reaching the target bed temperature Tx, the bed temperature <i>Tbed</i> of the DPF 10 passes through successive temperatures <i>Ta, Tb, Tc, Td....</i> Here, the temperature <i>Ta</i> indicates a minimum temperature allowing combustion of the particulate matter in the DPF 10. In this temperature increase process, time is expressed in the following manner. That is, the increase period from the temperature <i>Ta</i> to <i>Tb</i> is expressed as <i>ta1</i>, the increase period from the temperature <i>Tb</i> to <i>Tc</i> is expressed as <i>tb1,</i> and the increase period from the temperature <i>Tc</i> to <i>Td is</i> expressed as <i>tc1.</i>

0078The areas where the bed temperature <i>Tbed</i> falls are also expressed by time periods such as <i>tc2, tb2,</i> and <i>ta2.</i> Thus variation in the bed temperature <i>Tbed</i> can be understood by the temperature region and the duration of the region, and the effective regeneration time <i>Te</i> is cumulatively calculated according to the following equation (4) in order to adopt as the effective regeneration time <i>Te</i> a value obtained by multiplying the duration of a temperature region by a weighting coefficient <i>K</i> shown in <figref idref="f0004">FIG. 9</figref> which corresponds to the temperature region.<maths id="math0004" num="(4)"><math display="block"><mi mathvariant="italic">Te</mi><mo mathvariant="italic">=</mo><mi mathvariant="italic">Ka</mi><mo mathvariant="italic">⋅</mo><mi mathvariant="italic">ta</mi><mo mathvariant="italic">+</mo><mi mathvariant="italic">Kb</mi><mo mathvariant="italic">⋅</mo><mi mathvariant="italic">tb</mi><mo mathvariant="italic">+</mo><mi mathvariant="italic">Kc</mi><mo mathvariant="italic">⋅</mo><mi mathvariant="italic">tc</mi><mo mathvariant="italic">+</mo><mi mathvariant="italic">Kd</mi><mo mathvariant="italic">⋅</mo><mi mathvariant="italic">td</mi><mo mathvariant="italic">+</mo><mn mathvariant="italic">.....</mn><mo mathvariant="italic">+</mo><mi mathvariant="italic">tx</mi></math><img file="EP1517028B1_D0004.tif" /></maths> where, <dl id="dl0001" compact="compact"><dt><i>ta</i> =</dt><dd><i><b>∑</b> tan,</i></dd><dt><i>tb</i> =</dt><dd><i>∑ tbn,</i></dd><dt><i>tc</i> =</dt><dd><i>∑ tcn,</i></dd><dt><i>td</i> =</dt><dd><i><b>∑</b> tdn,</i></dd><dt><i>tx</i> =</dt><dd><i>∑ txn,</i></dd><dt><i>Ka</i> =</dt><dd>the weighting coefficient K of the temperature region from the temperature <i>ta</i> to <i>tb,</i></dd><dt><i>Kb</i> =</dt><dd>the weighting coefficient <i>K</i> of the temperature region from the temperature <i>Tb</i> to <i>Tc</i>,</dd><dt><i>Kc</i> =</dt><dd>the weighting coefficient <i>K</i> of the temperature region from the temperature <i>Tc</i> to <i>Td,</i></dd><dt><i>Kd</i> =</dt><dd>the weighting coefficient <i>K</i> of the temperature region from the temperature <i>Td</i> to <i>Tx</i>, and</dd><dt><i>n</i> =</dt><dd>integers starting from 1.</dd></dl>

0079Referring to <figref idref="f0004">FIG. 9</figref>, the weighting coefficient <i>K</i> expresses the amount of burned particulate matter per unit time in a certain temperature region, and has a maximum value of 1.0. The weighting coefficient <i>K</i> takes a higher value as the bed temperature <i>Tbed</i> rises and the amount of trapped particulate matter <i>PMi</i> increases. In the region where the bed temperature <i>Tbed</i> equals or exceeds the target bed temperature <i>Tx</i>, the weighting coefficient <i>K</i> reaches 1.0.

0080The map of the weighting coefficient <i>K</i> of the characteristic shown in <figref idref="f0004">FIG. 9</figref> is stored in the ROM of the engine controller 16 in advance for the purpose of this calculation.

0081In the step S106 in the routine of <figref idref="f0002">FIG. 2</figref>, the engine controller 16 executes a subroutine shown in <figref idref="f0005">FIG. 10</figref> instead of the subroutine in <figref idref="f0005">FIG. 6</figref> of the first embodiment.

0082First, in a step S301, the engine controller 16 determines the current temperature region and measures an elapsed time since the start of the current temperature region. In other words, the engine controller 16 measures the time periods, <i>ta1, tb1, tc1, ... , tx1</i> in <figref idref="f0007">FIG. 8</figref>.

0083In a next step S302, the engine controller 16 determines the weighting coefficient <i>K</i> that is suitable for the current temperature region by referring to the map corresponding to <figref idref="f0004">FIG. 9</figref> from the bed temperature <i>Tbed</i> of the DPF 10 and the amount of trapped particulate matter <i>PMi</i>. In other words, the engine controller 16 determines <i>Ka, Kb, Kc, Kd</i> .... in the equation (4).

0084In a next step S303, the engine controller 16 calculates the effective regeneration time <i>Te</i> by performing the calculation of the equation (4).

0085After the processing of the step S303, the engine controller 16 ends the subroutine and thus the processing of the step S106 in <figref idref="f0002">FIG. 2</figref>.

0086To summarize the above, this embodiment is different from the first embodiment in that the engine controller 16 calculates the effective regeneration time <i>Te</i> using the equation (4) above in place of the equation (2). In other words, even if the bed temperature <i>Tbed</i> of the DPF 10 is equal to or lower than the target bed temperature <i>Tx,</i> as long as the bed temperature <i>Tbed</i> exceeds the minimum temperature <i>Ta</i> allowing combustion of the particulate matter, the duration of the corresponding temperature region is used in the calculation of the effective regeneration time <i>Te</i> based on the weighting coefficient <i>K</i> corresponding to the temperature region.

0087By calculating the amount of burned particulate matter <i>PMi</i> in the temperature regions equal to or below the target bed temperature <i>Tx</i> on the basis of the effective regeneration time <i>Te</i> calculated in this manner, and then calculating the amount of remaining particulate matter PMx, variation in the amount of remaining particulate matter <i>PMx</i> during a regeneration operation of the DPF 10 can be learned with a greater degree of precision.

0088Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, within the scope of the claims.

0089The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: