AU2014298123B2

AU2014298123B2 - Control device for internal combustion engine and method of controlling internal combustion engine

Info

Publication number: AU2014298123B2
Application number: AU2014298123A
Authority: AU
Inventors: Hirohiko Ota
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2013-08-02
Filing date: 2014-07-30
Publication date: 2016-08-04
Anticipated expiration: 2034-07-30
Also published as: WO2015015296A1; EP3027887A1; AU2014298123A1; JP2015031211A

Abstract

A control device is provided for an internal combustion engine having a filter adapted to trap soot in exhaust gas, an addition valve provided downstream of the filter in a direction of flow of the exhaust gas, and a catalyst that reduces NOx using aqueous urea injected from the addition valve. The control device includes an electronic control unit configured to inhibit execution of automatic stop control for the internal combustion engine when a filter regeneration treatment for burning and removing the soot trapped by the filter is executed.

Description

CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE AND METHOD OF CONTROLLING INTERNAL COMBUSTION ENGINE

BACKGROUND OF THE INVENTION Γ. Field of the Invention ioooi] The invention relates to a control device for an internal combustion engine. 2. Description of Related Art [0002] An emission control system for purifying exhaust gas is provided in an exhaust passage of an internal combustion engine. As one type of the emission control system, a selective catalytic reduction (SCR) type emission control system using aqueous urea (i.e., an aqueous solution of urea) as a reducing agent is known (see, for example, Japanese Patent Application Publication No. 2010-71270 (JP 2010-71270 A)). In the emission control system as disclosed in JP 2010-71270 A, an addition valve from which aqueous urea is added to exhaust gas is installed in an exhaust pipe, and an SCR catalyst is installed downstream of the addition valve in a direction of flow of exhaust gas in the exhaust pipe. If aqueous urea is injected from the addition valve into exhaust gas, the aqueous urea is hydrolyzed in the exhaust gas and converted into ammonia. Then, in the SCR catalyst, the ammonia undergoes reduction reaction with NOx in the exhaust gas. As a result, the NOx in the exhaust gas is broken down into water and nitrogen.

[0003] In the internal combustion engine as described above, a filter for trapping soot in exhaust gas may be provided in addition to the SCR catalyst. The filter is located in a portion of the exhaust pipe upstream of the SCR catalyst as viewed in the direction of flow of exhaust gas. In this type of internal combustion engine, when the amount of soot deposited on the filter becomes equal to or larger than a predetermined amount, a regeneration treatment for restoring the function of the filter by burning and removing the soot is performed.

[0004] During execution of the filter regeneration treatment, the temperature of the filter rises due to combustion of soot. Therefore, if the internal combustion engine is automatically stopped during execution of the regeneration treatment, the heat of the filter may not be taken or removed by exhaust gas flowing through the exhaust pipe, and the temperature of the filter may be excessively elevated. In this case, the heat of the filter may be transferred to the addition valve of aqueous urea via the exhaust pipe, and the addition valve may be overheated. When the internal combustion engine is re-started in this case, the temperature of exhaust gas may be elevated to a high level when it passes through the filter whose temperature is excessively increased, and the addition valve may be overheated due to the heat of the exhaust gas. If the addition valve is overheated in this manner, thermal deterioration, such as reduction of the durability of the addition valve, and deterioration of its operating characteristics, may occur to the addition valve.

OBJECT OF THE INVENTION

[0004a] It is an object of the present invention to at least substantially overcome or at least ameliorate one or more of the foregoing disadvantages.

SUMMARY OF THE INVENTION

[0005] The invention relates to a control device for an internal combustion engine, with which thermal deterioration of an addition valve can be curbed or prevented.

[0006] A first aspect of the invention provides a control device for an internal combustion engine connected to an exhaust pipe, the exhaust pipe being provided with a filter adapted to trap soot in exhaust gas emitted from the internal combustion engine, an addition valve provided downstream of the filter in a direction of flow of the exhaust gas, and a catalyst that reduces NOx using aqueous urea injected from the addition valve, the control device comprising: an electronic control unit configured to inhibit execution of automatic stop control for the internal combustion engine when a filter regeneration treatment for burning and removing the soot trapped by the filter is executed, wherein the electronic control unit is configured to inject the aqueous urea from the addition valve when an estimated temperature of the addition valve increases to be higher than a predetermined temperature during execution of the automatic stop control.

[0007] With the above arrangement, unlike the case where the internal combustion engine is automatically stopped during execution of the filter regeneration treatment, exhaust gas flowing through the exhaust pipe can take heat from the filter during the regeneration treatment, so that the temperature of the filter is less likely or unlikely to be excessively increased. Thus, the addition valve is prevented from being overheated due to heat transferred from the filter to the addition valve through the exhaust pipe when the internal combustion engine is automatically stopped, and the addition valve is prevented from being overheated due to heat of exhaust gas heated when passed through the filter after the engine is re-started. Consequently, thermal deterioration of the addition valve, which would be observed when the internal combustion engine is automatically stopped during the filter regeneration treatment, can be curbed or prevented.

[0008] If the amount of soot deposited on the filter becomes excessively large, combustion reaction of soot may take place even when no regeneration treatment is performed, and the temperature of the filter may be elevated. In this case, if the internal combustion engine is automatically stopped, the temperature of the filter is excessively elevated, and the addition valve will be overheated.

[0009] In this respect, with the above arrangement, aqueous urea is injected when the estimated temperature of the addition valve increases to be higher than the predetermined temperature during execution of the automatic stop control. Therefore, the addition valve can be cooled by the aqueous urea, and the addition valve is less likely or unlikely to be overheated and subjected to thermal deterioration when the internal combustion engine is automatically stopped.

[0010] In the control device for the internal combustion engine as described above, the electronic control unit may be configured to increase a total amount of the aqueous urea injected from the addition valve as the estimated temperature of the addition valve is higher. With this arrangement, the total amount of aqueous urea injected from the addition valve increases as the estimated temperature of the addition valve is higher. Therefore, thermal deterioration of the addition valve can be more favorably curbed or prevented.

[0011] In the control device for the internal combustion engine as described above, the electronic control unit may be configured to increase an injection period of the aqueous urea as the estimated temperature of the addition valve is higher. With this arrangement, the total amount of aqueous urea injected from the addition valve can be increased.

[0012] A second aspect of the invention provides a method of controlling an internal combustion engine connected to an exhaust pipe, the exhaust pipe being provided with a filter adapted to trap soot in exhaust gas emitted from the internal combustion engine, an addition valve provided downstream of the filter in a direction of flow of the exhaust gas, and a catalyst that reduces NOx using aqueous urea injected from the addition valve, the method comprising: inhibiting execution of automatic stop control of the internal combustion engine when a filter regeneration treatment for burning and removing soot trapped by the filter is executed, and injecting the aqueous urea from the addition valve when an estimated temperature of the addition valve increases to be higher than a predetermined temperature during execution of the automatic stop control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Features of exemplary embodiments of the invention will be described below, by way of examples only, with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: FIG. 1 is a block diagram showing the overall configuration of an internal combustion engine having a control device according to one embodiment of the invention; FIG. 2 is a flowchart illustrating one example of exhaust emission control performed by the control device according to the embodiment of FIG. 1; FIG. 3 is a flowchart illustrating one example of exhaust emission control performed by a control device according to a second embodiment of the invention; FIG. 4 is a table indicating one example of relationship between an estimated value of a distal end temperature of an addition valve and a correction value, according to the second embodiment; FIG. 5 is a table indicating one example of relationship between an outside air temperature and a correction value, according to the second embodiment; FIG. 6 is a table indicating one example of relationship between the estimated value of the distal end temperature of the addition value and a correction value, according to the second embodiment; and FIG 7 is a table indicating one example of relationship between the outside air temperature and a correction value, according to the second embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0014] A control device for an internal combustion engine according to a first embodiment of the invention will be described with reference to FIG 1 and FIG 2. .

[0015] As shown in FIG 1, an exhaust pipe 1 is connected to an internal combustion engine 30. The exhaust pipe 1 is provided with an oxidation catalyst 2, and a filter 3 located downstream of the oxidation catalyst 2 in the direction of flow of exhaust gas. The filter 3 serves to traps soot contained in exhaust gases. A fuel injection valve 4 that injects fuel into the exhaust pipe 1 is provided in a portion of the exhaust pipe 1 located upstream of the oxidation catalyst 2 in the direction of flow of exhaust gas.

[0016] The exhaust pipe is provided with an aqueous urea supply device 20. The aqueous urea supply device 20 has an aqueous urea tank 21 in which aqueous urea (i.e., an aqueous solution, of urea) is stored, an electrically-operated aqueous urea pump 22 provided on the aqueous urea tank 21, and an addition valve 24 connected to the aqueous urea pump 22 via a . supply passage 23. When the aqueous urea pump 22 is driven, aqueous urea stored in the aqueous urea tank 21 is discharged into the supply passage 23. The speed of rotation of the aqueous urea pump 22 may be changed so as to change the amount of discharge of aqueous urea, and thereby change the pressure in the supply passage 23. A check valve 25 and a pressure sensor 26 for detecting the pressure in the supply passage 23 are provided in the supply passage 23. The check valve 25 is arranged to open when the pressure in the supply passage; 23 becomes equal to or higher than a given pressure, so as to return aqueous urea in the supply passage 23 to the aqueous urea tank21.

[0017] In the exhaust pipe 1, the addition valve 24 is installed downstream of the filter 3 in the direction of flow of exhaust gas. In the exhaust pipe 1, an SCR catalyst 5 is installed downstream of the addition valve 24 in the direction of flow of exhaust gas. In operation, aqueous urea injected from the addition valve 24 into the exhaust pipe 1 is hydrolyzed in exhaust gas and converted into ammonia. In the SCR catalyst 5, the ammonia undergoes reduction reaction with NOx in exhaust gas, so that NOx is broken down into water and nitrogen.

[0018] The internal combustion engine 30 as described above is provided with an electronic control unit 6. The electronic control unit 6 receives detection signals from various sensors provided in the engine 30. The sensors include a bed temperature sensor 7 for detecting the bed temperature of the fiber 3, a differential pressure sensor 8, and a gas temperature sensor 9 for detecting the temperature of exhaust gas that has passed through the filter 3, in addition to the pressure sensor 26 as described above. The differential pressure sensor 8 series to detect a pressure difference (differential pressure) of exhaust gas between the pressure measured on the exhaust upstream side of the filter 3 and the pressure measured on the exhaust downstream side of the filter 3. In addition, an outside air temperature sensor 10 for . detecting the outside air temperature is provided as one of the above-indicated sensors. The electronic control unit 6 performs exhaust emission control, such as a regeneration treatment for the filter 3.

[0019] Next, the procedure of exhaust emission control will be described with reference to the flowchart of FIG 2. The exhaust emission control is repeatedly executed at given intervals when the internal combustion engine 30 is in operation. As shown in FIG 2, it is initially determined whether a condition for execution of the regeneration treatment for the filter 3 is satisfied (step SI). In step SI, an affirmative decision (YES) is made when the differential pressure detected by the differential pressure sensor 8 is equal to or larger than a predetermined pressure. If an affirmative decision (YES) is made in step SI (step SI: YES), namely, if the amount of soot deposited on the filter 3 is equal to or larger than a predetermined amount, the electronic control unit 6 then proceeds to step S2, and starts the regeneration treatment for the filter 3. In the regeneration treatment for the filter 3, fuel is injected from the fuel injection valve 4 into exhaust gas, and the fuel is burned in the oxidation catalyst 2 so as to raise the temperature of the exhaust gas. Then, the high-temperature exhaust gas passes through the filter 3, so that the soot deposited on the filter 3 is burned and removed. Once the regeneration treatment as described above is started in step S2, the electronic control unit 6 then proceeds to step > S3 to set an automatic stop control permission flag F for the internal combustion engine 30 to “0”, and finishes this cycle of the routine of FIG. 2. The automatic stop control permission flag F is set to “0” until the amount of soot deposited on the filter 3 is reduced, and the regeneration treatment is completed. The automatic stop control is different from an engine stop when an ignition switch is turned off by a driver (IG-OFF). The electronic control unit 6 is configured to stop the internal combustion engine 30 in response to turning off the ignition by the driver. In contrast, the electronic control unit 6 is configured to execute the automatic stop control and stop the internal combustion engine 30 upon the satisfaction of the automatic stop conditions, even when the ignition switch is not turned off by the driver. That is, the electronic control unit 6 is configured to execute the automatic stop control upon, satisfaction of the automatic stop conditions when the ignition switch is on.

[0020] If, on the other hand, a negative decision (NO) is made in step SI (step SI: NO), namely, if the amount of soot deposited on the filter 3 is smaller than the predetermined amount, the electronic control unit 6 goes to step S4 without performing the regeneration treatment. In step S4, the automatic stop control permission flag F is, set to “1”. When the automatic stop control permission flag F is set to “1”, automatic stop control for the internal combustion engine 30 is executed when all of automatic stop conditions are satisfied. The automatic step conditions may include, for example, a condition that the vehicle speed is equal to or lower than a predetermined speed, a condition that the amount of operation of the accelerator pedal is equal to or smaller than a predetermined amount, and a condition that the brake pedal is depressed. If, on the other hand, the automatic stop control permission flag F is set to “0”, the automatic stop control is inhibited. Namely, the internal combustion engine 30 is not automatically stopped even if the above-indicated automatic stop conditions are satisfied.

[0021] Next, the operation of the control device for the internal combustion engine 30 according to this embodiment will be described. In this embodiment, once the regeneration treatment is started, the automatic stop control permission flag is set to “0”, and automatic stop control for the internal combustion engine 30 is inhibited. Therefore, unlike the case where the internal combustion engine 30 is automatically stopped during execution of the regeneration treatment for the filter 3, the exhaust gas flowing through the exhaust pipe 1 can take heat from the filter 3 during execution of the regeneration treatment for the filter 3, and an excessive temperature rise does not occur to the filter 3.

[0022] According to the first embodiment as described above, the following effect is obtained. The addition valve 24 is prevented from being overheated due to heat transferred from the filter 3 to the addition valve 24 through the exhaust pipe 1 during the regeneration treatment for the filter 3, and the addition valve 24 is prevented from being overheated due to heat of exhaust gas passed through the filter 3. As a result, thermal deterioration of the addition valve 24, which would be observed when the internal combustion engine 30 is automatically stopped during the regeneration treatment for the filter 3, can be curbed or prevented.

[0023] Next, a control device for an internal combustion engine according to a second embodiment of the invention will be described with reference to FIG 3. This embodiment is different from the first embodiment in steps following step S4 iirthe control routine of exhaust emission control as shown in FIG. 2. The same step numbers as used in FIG; 2 are assigned to the remaining steps, which will not be described in detail.

[0024] As shown in FIG 3, after executing step S4, the electronic control unit 6 proceeds to step S5 to determine whether the automatic stop conditions for the internal combustion engine 30 are satisfied. If an affirmative decision (YES) is made in step S5 (step S5: YES), namely, if the automatic stop control permission flag F is “1”, and the automatic stop conditions are satisfied, the electronic control unit 6 executes automatic stop control, and proceeds to step S6.

[0025] In step S6, the temperature of the distal end of the addition valve 24 is estimated. An estimated value 9i of the distal end temperature may be obtained based on, for example, the filter bed temperature, and the outside air temperature. The estimated value θΐ of the distal end temperature increases as the filter bed temperature is higher, and the outside air temperature is higher. Then, the electronic control unit 6 proceeds to step S7 to determine whether the estimated value 0i exceeds a predetermined value a. In this embodiment, the predetermined value a is set to the upper limit of a temperature range in which thermal deterioration does not occur to the addition valve 24. If an affirmative decision (YES) is made in step S7 (step S7: YES), namely, if the addition valve 24 is overheated, and may suffer from thermal deterioration, step S8 through step SI0 are sequentially executed so that aqueous urea is injected from the addition valve 24. In this embodiment, the injection pressure Pi of aqueous urea to be injected is set in step S8 in the following manner.

[Q026] Initially, a corrected injection pressure Pf is calculated by multiplying a predetermined basic injection pressure Pb by a correction value kpl calculated based on the estimated value θΐ of the distal end temperature, and a correction value kp2 calculated based on the outside air temperature. Then, the rotational speed of the aqueous urea pump 22 is adjusted so as to make the injection pressure Pi equal to the corrected injection pressure Pf.

[0027] As shown in FIG 4, the correction value kpl becomes larger as the ., •r estimated value θί of the above-indicated distal end temperature increases. As shown in V. FIG 5, the correction value kp2 becomes larger as the outside air temperature increases. ' Accordingly, as the estimated value θΐ of the distal end temperature and the outside air .. temperature become higher, the injection pressure Pi increases, and the amount of aqueous urea injected per unit time from the addition valve 24 increases. The relationship between the correction value kpl and the estimated value θΐ of the distal end temperature, and the relationship between the correction value kp2 and the outside air temperature, are stored as maps for use in computation, in the electronic control unit 6. After the injection pressure Pi is set in this manner in step S8, the electronic control unit 6 then proceeds to step S9 to set the injection period Ti in the following manner.

[0028] In step S9, a predetermined basic injection period Tb is multiplied by a correction value ktl calculated based on the estimated value θΐ of the distal end temperature, and a correction value kt2 calculated based on the outside air temperature, and the result of multiplication is set as the injection period Ti.

[0029] As shown in FIG. 6, the correction value ktl becomes larger as the estimated value 0i of the above-described distal end temperature increases. As shown in FIG. 7, the correction value kt2 becomes larger as the outside air temperature increases. Accordingly, the injection period Ti becomes longer as the estimated value 0i of the distal end temperature and the outside air temperature are higher. The relationship between the correction value ktl and the estimated value 0i of the distal end temperature, and the relationship between the correction value kt2 and the outside temperature, are stored as maps for use in computation, in the electronic control unit 6.

[0030] After the injection period Ti is set in step S9 in the above manner, the electronic control unit 6 proceeds to step S10 to inject aqueous urea from the addition valve 24 at the above-described injection pressure Pi, for the injection period Ti, and finish this cycle of the control routine. If a negative decision (NO) is made in step S5 (step S5: NO), or a negative decision (NO) is made in step S7 (step S7: NO), the current cycle of the routine ends.

[0031] The operation of the control device for the internal combustion engine according to this embodiment will be described. If the amount of soot deposited on the filter 3 becomes excessively large, combustion reaction of the soot may occur even when no regeneration treatment is performed, and the temperature of the filter 3 may rise. In this case, if the internal combustion engine 30 is automatically stopped, the temperature of the filter 3 may rise excessively, and the addition valve 24 may be overheated due to the heat of the filter 3.

[0032] In this embodiment, when the automatic stop control is being executed, the distal end temperature of the addition valve 24 is estimated, and aqueous urea is injected if the estimated value 0i exceeds the predetermined temperature a, so that the addition valve 24 is cooled by aqueous urea.

[0033] In this embodiment, as the estimated value 0i is higher, the injection pressure Pi is increased so as to increase the amount of aqueous urea injected per unit time, and the injection period Ti is increased. As a result, the total amount of aqueous urea injected from the addition valve 24 increases as the temperature of the addition valve 24 is higher, and the cooling efficiency of the addition valve 24 is enhanced. Thus, the addition valve 24 is more favorably cooled depending on the overheated condition of the addition valve 24.

[0034] According to the second embodiment as described above, the following effects are obtained. Even when the temperature of the.filter 3 rises due to combustion reaction of soot during execution of automatic stop control, the addition valve 24 is less likely or unlikely to be overheated and suffer from thermal deterioration due to the heat of the filter 3.

[0035] According to the above-described embodiment, the addition valve 24 can be more favorably cooled depending on the overheated condition of the addition valve 24. Each of the illustrated embodiments may be changed as follows and implemented.

[0036] In the second embodiment, the distal end temperature of the addition valve 24 is estimated based on the filter bed temperature, and the outside air temperature. However, the distal end temperature may be estimated based on the temperature of exhaust gas that has passed through the filter 3, which temperature is detected by the gas temperature sensor 9, as well as the filter bed temperature and the outside air temperature. The distal end temperature may be estimated using one or two: of the parameters^ such as the filter bed temperature, outside air temperature, and the exhaust gas temperature, or may be estimated based on another parameter or parameters correlated with the distal end temperature, or based on the parameter(s) in addition to the above-indicated parameters.

[0037] In the second embodiment, it is determined whether the addition valve 24 is overheated, using the estimated value 0i of the distal end temperature of the addition valve 24. However, the temperature of a portion of the addition valve 24 other than the distal end may be estimated, and it may be determined whether the addition valve 24 is overheated based on the temperature of this portion.

[0038] In the second embodiment, the outside air temperature, as well as the estimated value 0i of the distal end temperature of the addition valve 24, is used as a parameter for setting the injection period Ti. However, the method of setting the injection period Ti may be changed as appropriate; for example, the injection period Ti may be set using only the estimated value 0i of the distal end temperature.

[0039] In die second embodiment, the outside air temperature, as well as the estimated value 0i of the distal end temperature of the addition valve 24, is used as a parameter for setting the injection pressure Pi. However, the method of setting the injection pressure Pi may be changed as appropriate; for example, the injection pressure Pi may be set using only the estimated value 0i of the distal end temperature.

[0040] While both of the injection pressure Pi and the injection period Ti are set Variably according to the estimated value 0i of the distal end temperature of the addition valve 24 in the second embodiment, one of the injection pressure Pi and the injection period Ti may be set to a constant value. Also, both of the injection pressure Pi and the injection period Ti may be set to constant values. With this arrangement, too, some of the effects of the embodiments as described above can be obtained.

[0041] In the second embodiment, the injection period Ti is set in advance, and aqueous urea is injected from the addition valve 24 only for the injection period Ti. However, the distal end temperature of the addition valve 24 may be estimated at given intervals, and injection of aqueous urea may be terminated when the estimated temperature becomes equal to or lower than a predetermined temperature β that is sufficiently lower than the predetermined temperature a. * ‘ - - [0042] In the first and second embodiments, the automatic stop control is inhibited when the regeneration treatment is performed, and the inhibition is cancelled when the regeneration treatment is finished. However, the automatic stop control may continue to be inhibited until a given period of time elapses from the time when the regeneration treatment is finished. With this arrangement, the inhibition of the automatic stop control is cancelled, only after the temperature of the filter 3, which was elevated by the regeneration treatment, is reduced; therefore, the addition valve 24 is even more favorably prevented from being overheated during automatic stop control.

Claims

1. A control device for an internal combustion engine connected to an exhaust pipe, the exhaust pipe being provided with a filter adapted to trap soot in exhaust gas emitted from the internal combustion engine, an addition valve provided downstream of the filter in a direction of flow of the exhaust gas, and a catalyst that reduces NOx using aqueous urea injected from the addition valve, the control device comprising: an electronic control unit configured to inhibit execution of automatic stop control for the internal combustion engine when a filter regeneration treatment for burning and removing the soot trapped by the filter is executed, wherein the electronic control unit is configured to inject the aqueous urea from the addition valve when an estimated temperature of the addition valve increases to be higher than a predetermined temperature during execution of the automatic stop control.

2. The control device according to claim 1, wherein the electronic control unit is configured to increase a total amount of the aqueous urea injected from the addition valve as the estimated temperature of the addition valve is higher.

3. The control device according to claim 2, wherein the electronic control unit is configured to increase an injection period of the aqueous urea as the estimated temperature of the addition valve is higher.

4. A method of controlling an internal combustion engine connected to an exhaust pipe, the exhaust pipe being provided with a filter adapted to trap soot in exhaust gas emitted from the internal combustion engine, an addition valve provided downstream of the filter in a direction of flow of the exhaust gas, and a catalyst that reduces NOx using aqueous urea injected from the addition valve, the method comprising: inhibiting execution of automatic stop control of the internal combustion engine when a filter regeneration treatment for burning and removing soot trapped by the filter is executed, and injecting the aqueous urea from the addition valve when an estimated temperature of the addition valve increases to be higher than a predetermined temperature during execution of the automatic stop control.