JP3979150B2 - NOx purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a NOx purification device for an internal combustion engine provided with a NOx catalyst having an exhaust gas NOx purification action in an oxygen-excess atmosphere.
[0002]
[Prior art]
There is known a NOx purifying apparatus that uses ammonia generated by hydrolysis by adding urea water to exhaust gas or ammonia by direct addition as a reducing agent for a selective reduction catalyst. When such a NOx purifying device is mounted on a vehicle equipped with an internal combustion engine such as an engine, a selective reduction catalyst that can purify NOx in an exhaust system of the internal combustion engine in an oxygen-excess atmosphere, a so-called urea SCR catalyst (hereinafter referred to as a urea SCR catalyst). (Referred to as “NOx catalyst”), and urea water or ammonia is added to the exhaust gas as a reducing agent from the upstream side of the catalyst and supplied to the NOx catalyst.
In particular, in a system in which urea water is added as a reducing agent, urea water is supplied from the reducing agent supply means via a supply passage communicating with the exhaust system upstream of the NOx catalyst, but can be quickly added to the exhaust gas flowing through the exhaust system. As described above, pressurized air is supplied from the air supply means to the supply passage upstream of the urea water supply portion supplied from the reducing agent supply means, and the pressurized air flowing through the supply passage and the urea water are mixed and added. It is sprayed with a nozzle and added to the exhaust gas.
[0003]
When urea water is added to the exhaust gas, it is hydrolyzed and thermally decomposed as shown in formula (1), so that ammonia (NH₃) Is generated.
(NH₂) 2CO + H₂O → 2NH₃+ CO₂(1)
Ammonia on NHx catalyst (NH₃) And nitrogen oxides (NOx) depending on the catalyst temperature, that is, the reaction of Formula (2) is mainly performed at high temperatures and the Formula (3) is mainly performed at low temperatures. It has been.
4NH₃+ 4NO + O₂→ 4N₂+ 6H₂O ... (2)
2NH₃+ NO + NO₂→ 2N₂+ 3H₂O ... (3)
Such a NOx catalyst using ammonia as a reducing agent has a higher NOx purification rate as the amount of ammonia adsorbed on the NOx catalyst increases as shown by the solid line in FIG. In order to obtain it, it is preferable to control the ammonia adsorption amount high. There is a limit to the ammonia adsorption amount that can be adsorbed to the NOx catalyst, and the adsorption limit value indicated by the solid line L1 in FIG. 11 depends on the catalyst temperature.
[0004]
[Problems to be solved by the invention]
In such a NOx purification device that adds urea water as a reducing agent, even if urea water is not added to prevent the urea component from adhering to the inside of the pipe due to evaporation of the water of urea water, the supply passage is blocked. Pressurized air is supplied by operating the air supply means. The air supply means may have a drive source alone, or may use an engine that transmits the rotation of the crankshaft of the engine using drive transmission means such as a belt and a pulley as the drive source. For this reason, suppressing the operating rate of the air supply means when urea water is not added is an effective method for reducing power consumption and improving fuel consumption due to operation of equipment mounted on the vehicle. . However, if the operating rate of the air supply means is suppressed more than necessary, it becomes difficult to prevent the supply passage from being clogged with urea components.
An object of the present invention is to provide a NOx purification device capable of reducing the power consumption of a vehicle and improving the fuel efficiency and improving the NOx purification rate.
An object of the present invention is to provide a NOx purification device capable of achieving both improvement of NOx purification rate, prevention of clogging of a supply passage due to urea components, reduction of vehicle power consumption and improvement of fuel consumption. And
[0005]
[Means for Solving the Problems]
An NOx purification device for an internal combustion engine according to the present invention is provided with an NOx catalyst provided in an exhaust system of an internal combustion engine for selectively reducing NOx in exhaust gas, and urea water via a supply passage communicating with an exhaust system upstream of the NOx catalyst. A reducing agent supplying means for supplying, an air supplying means for supplying pressurized air to a supply passage upstream from a supply site of urea water supplied from the reducing agent supplying means, and a catalyst temperature of the NOx catalyst or a parameter correlated with the catalyst temperature The urea water supply amount setting means for setting the urea water supply amount according to one of the above, and the stop / operation of the air supply means are controlled according to the urea water supply state set by the urea water supply amount setting means Control means. Therefore, the stop / operation of the air supply means is controlled by the control means in accordance with the urea water supply state set by the urea water supply amount setting means.
[0006]
As the control means, when the urea water supply amount set by the urea water supply amount setting means is zero, the pressurized air supplied from the air supply means after a predetermined period has elapsed after the supply amount is set to zero A mode in which the air supply means is controlled so as to stop the supply of air.
[0007]
As the air supply means, the supply path upstream of the supply site of urea water supplied from the reducing agent supply means is driven by an internal combustion engine to supply pressurized air, or the driving force is obtained from a single drive source. The aspect which is driven by this and supplies pressurized air is mentioned.
[0008]
Examples of the urea water supply amount setting means include a mode in which the urea water supply amount is set to zero when the temperature of the NOx catalyst becomes lower than a set value based on the catalyst temperature of the NOx catalyst or a parameter correlated with the catalyst temperature. .
As the urea water supply amount setting means, the actual adsorption amount of the reducing agent adsorbed on the NOx catalyst differs from the target adsorption amount set in advance based on the catalyst temperature of the NOx catalyst or a parameter correlated with the catalyst temperature by a predetermined amount or more. In some cases, the supply amount of urea water is set to zero.
As the urea water supply amount setting means, when the actual NOx purification rate by the NOx catalyst is different from the preset NOx purification rate based on the catalyst temperature of the NOx catalyst or a parameter correlated with the catalyst temperature by a predetermined amount or more, the urea water The aspect which sets the supply amount of this to zero is mentioned.
[0009]
The NOx purification device for an internal combustion engine according to the present invention includes vehicle speed detection means for detecting the vehicle speed of a vehicle on which the internal combustion engine is mounted, and the control means has a vehicle speed detected by the vehicle speed detection means when the vehicle speed is equal to or higher than a predetermined value. The air supply means is controlled to prohibit the supply stop of the pressurized air supplied from the air supply means. For this reason, when the vehicle speed is equal to or higher than a predetermined value, the supply of pressurized air is prohibited from being stopped, and the vehicle is ready for the restart of urea water supply.
[0010]
In the NOx purification device for an internal combustion engine according to the present invention, the urea water supply restart estimation means for estimating the urea water supply restart timing after the urea water supply amount set by the urea water supply amount setting means is set to zero. And the control means controls the air supply means so as to start the supply of pressurized air supplied from the air supply means before a predetermined period of the urea water resumption timing estimated by the urea water supply resumption estimation means. Features. For this reason, the pressurized air supply is restarted before a predetermined period of the supply restart timing of the urea water.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An internal combustion engine NOx purification device as a first embodiment of the present invention will be described. In FIG. 1, reference numeral 1 denotes a diesel engine (hereinafter referred to as “engine”) mounted on a vehicle (not shown). The output of the engine 1 is controlled by the engine control device 5. Here, the engine control device 5 is a signal indicating an engine operating state such as an intake air flow rate from a known air flow sensor arranged in the intake system, a fuel injection amount obtained from the fuel system, a fuel injection amount, an engine speed, and the like. Is output to the exhaust system control unit 3. The exhaust system control unit 3 and the engine control device 5 are configured by a known microcomputer, and are connected to each other via a control system communication line.
[0013]
The NOx purification device of this embodiment is provided in an exhaust pipe 28 connected to the exhaust manifold 25 of the engine 1 and constituting the exhaust system 2 to selectively reduce NOx in the exhaust gas 24, and an exhaust pipe upstream of the NOx catalyst 17. The reducing agent supply means 30 for supplying urea water via an injection pipe 31 serving as a supply passage communicating with 28, and pressurized air is supplied to the injection pipe 31A upstream from the supply site of urea water supplied from the reducing agent supply means 30. Air supply means 7 to be supplied, urea water supply quantity setting means 4 for setting the supply quantity of urea water according to the catalyst temperature Tg of the NOx catalyst 17, and the urea water supply state set by the urea water supply quantity setting means 4. Accordingly, control means 8 for controlling the stop / operation of the air supply means 7 is provided. The exhaust system control unit 3 includes urea water supply amount setting means 4 and control means 8.
[0014]
The NOx catalyst 17 is obtained by attaching a catalyst component to a catalyst carrier having a honeycomb structure, or by forming a honeycomb structure with a catalyst component, and is accommodated in a casing of a NOx catalytic converter 27 provided in the exhaust pipe 28. . Examples of the NOx catalyst 17 that is a selective reduction catalyst include vanadium, platinum, and zeolite. The NOx catalyst 17 is ammonia (NH₃) To selectively reduce NOx in the exhaust gas 24. In the ammonia adsorption state, the NOx in the exhaust gas 24 depends on the atmospheric temperature, that is, at the high temperature, the above-described formula (2), the low temperature Sometimes, the above-described reaction of the formula (3) is mainly performed to promote the denitration reaction between ammonia and nitrogen oxides.
[0015]
The NOx catalyst 17 is provided with a catalyst temperature sensor 22 that outputs a catalyst temperature Tg. The catalyst temperature sensor 22 constitutes catalyst temperature deriving means for deriving the catalyst temperature of the NOx catalyst 17. In addition, an estimated value of the catalyst temperature is calculated and used as the catalyst temperature Tg in consideration of the engine speed, the fuel injection amount, the operation time for each engine operation region, and the outside air temperature, which are parameters correlated with the catalyst temperature. Also good.
[0016]
The reducing agent supply means 30 includes an addition nozzle 18 for spraying and adding urea water toward the upstream opening side of the NOx catalytic converter 27, an injection pipe 31 connected to the addition nozzle 18, and urea connected to the injection pipe 31. A water supply pipe 34, a urea water tank 35 containing urea water for addition, a pump 36 that pumps urea water in the urea water tank 35 from the urea water supply pipe 34 to the injection pipe 31, and the injection pipe 31 And an electromagnetic flow rate adjusting valve 37 for adjusting the flow rate of the urea water. The addition nozzle 18 is attached to the exhaust pipe 28 between the front NOx sensor 19 and NOx catalyst 17 as NOx detection means attached to the exhaust pipe 28 immediately after the exhaust manifold 25. In this embodiment, a sensor 12 as urea water supply detection means for detecting the presence or absence of supply of urea water by detecting the presence or absence of operation of the flow rate adjustment valve 37 is mounted in the vicinity of the flow rate adjustment valve 37. The sensor 12, the pump 36, and the flow rate adjusting valve 37 are connected to the control means 8 through signal lines.
[0017]
The air supply means 7 includes an air tank 32 connected to the upstream end of the injection pipe 31A, an electromagnetic on-off valve 33 that controls the supply of pressurized air to the injection pipe 31, and a driving force from the engine 1 that generates a belt and pulley. An air compressor 38 that rotates by being transmitted through a well-known drive transmission system 39A, and an electromagnetic compressor clutch 39 that interrupts driving force from the engine 1 to the air compressor 38. ing. The air compressor 38 and the air tank 32 are communicated with each other through an air pipe 38A. The on-off valve 33 and the compressor clutch 39 are connected to the control means 8 by signal lines.
[0018]
The compressor clutch 39 functions to transmit driving force from the engine 1 to the air compressor 38 when turned on by the control means 8 and to cut off transmission of driving force from the engine 1 to the air compressor 38 when turned off. The air tank 32 is provided with a relief valve (not shown) that opens when the tank internal pressure exceeds a predetermined pressure, and a known pressure sensor. The pressure sensor detects the tank internal pressure and outputs the detected value to the control means 8.
[0019]
The front NOx sensor 19 detects the NOx concentration Snoxf on the upstream side of the NOx catalyst 17. A rear NOx sensor 26 is disposed in the exhaust pipe 28 downstream of the NOx catalyst 17 as NOx detection means for detecting the NOx concentration Snoxr downstream of the NOx catalyst 17. The NOx concentrations Snoxf and Snoxr from the NOx sensors 19 and 26 are output to an actual NOx purification rate deriving means 44 described later.
[0020]
The urea water supply amount setting means 4 is a basic addition amount deriving means 42 for deriving a basic addition amount Durea of urea water by the reducing agent supply means 30 and a target NOx purification rate derivation for deriving a target NOx purification rate Mη based on the catalyst temperature Tg. Means 43 and an actual NOx purification rate deriving means 44 for deriving an actual NOx purification rate η by the NOx catalyst 17.
[0021]
The target NOx purification rate deriving unit 43 derives a target NOx purification rate Mη correlated with the catalyst temperature Tg from a map of the target NOx purification rate Mη determined by the catalyst temperature Tg as shown in FIG. The target NOx purification rate Mη is obtained corresponding to an ammonia adsorption amount that is lower than the adsorption limit value indicated by the solid line L1 in FIG. 11, for example, a value that is ½ of the adsorption limit value L1 indicated by the broken line L2 in FIG. It is set as the purification rate.
[0022]
The basic addition amount deriving means 42 is brought into the engine operating state in consideration of the relationship of the ammonia amount obtained from the urea water of the formula (1) so as to satisfy the ammonia adsorption amount at the NOx catalyst 17 indicated by the broken line L2 in FIG. Accordingly, a basic addition amount map of urea water set in advance is provided, and the basic addition amount D of urea water is appropriately set according to the catalyst temperature Tg._ureaSelect.
[0023]
The actual NOx purification rate deriving means 44 performs a difference process by converting the NOx concentrations Snoxf and Snoxr from the NOx NOx sensors 19 and 26 to Snoxf−Snoxr, and further divides the value by Snoxf to calculate the actual NOx purification rate η. It is an arithmetic circuit. The urea water supply amount setting means 4 calculates the urea water supply amount D from the information obtained from these components._ureaFind (n).
[0024]
The control means 8 is constituted by a computer, and when a urea water supply amount set by the urea water supply amount setting means 4 is zero, a predetermined period of time has elapsed since the supply amount was set to zero. The air supply means 7 is controlled to stop the supply of pressurized air supplied from the air supply means 7 later. In this embodiment, the compressor clutch 39 is turned off and the driving force from the engine 1 to the air compressor 38 is cut off. The control means 8 includes urea water supply restart estimation means 9 for estimating the urea water supply restart timing after the urea water supply amount set by the urea water supply amount setting means 4 is set to zero. The control means 8 turns on the compressor clutch 39 to start the supply of pressurized air supplied from the air supply means 7 before a predetermined period of the urea water restart timing estimated by the urea water supply restart estimation means 9. Control is performed so that the driving force is transmitted from the engine 1 to the air compressor 38. The control means 8 monitors the output value from a pressure sensor (not shown) so that the tank internal pressure of the air tank 32 becomes a predetermined pressure. When the tank internal pressure falls below the predetermined pressure, the control means 8 turns on the compressor clutch 39 to turn on the air compressor. 38 is driven to supply air to the air tank 32. In this embodiment, on / off control of the compressor clutch 39 is performed to control the supply of pressurized air, but the opening / closing control of the on-off valve 33 may be performed simultaneously.
[0025]
In this embodiment, the control unit 8 has a function of controlling the driving of the on-off valve 33, the pump 36, and the flow rate adjustment valve 37 in order to execute the addition of urea water by the reducing agent supply unit 30. In this embodiment, the opening amount of the on-off valve 33 and the rotation speed of the pump 36 are made constant, and the urea water supply amount D provided by the urea water supply amount setting means 4._ureaThe opening degree or the valve opening period of the flow rate adjusting valve 37 is adjusted and controlled according to (n). Instead of opening and closing the flow rate adjusting valve 37, the opening degree of the opening and closing valve 33, the rotation speed control of the pump 36, or a combination of these controls may be used. The urea water supply amount setting means 4 has a basic addition amount D_ureaA correction amount for addition / subtraction is stored in advance in a memory (not shown) as map information (not shown).
[0026]
Next, NOx purification control by the NOx purification device will be described along the NOx purification processing routine of FIG. 2, and air supply control will be described along the air supply control routine shown in FIG.
[0027]
When driving the engine 1 of a vehicle (not shown) equipped with a NOx purification device, the engine control device 5 confirms whether or not the self-check result of whether or not the sensors of various control systems related to engine driving are normal, In normal (OK), a control signal is sent to a well-known fuel injection system and fuel supply system in accordance with each input value of the related sensor described above, control is executed, and the sensor output obtained at that time is sent to an exhaust system control unit. 3 is also transmitted. The exhaust system control unit 3 repeats the NOx purification processing control by the NOx purification processing routine of FIG. 2 at every predetermined control cycle simultaneously with turning on of the engine key, and interrupts the air supply control routine shown in FIG.
[0028]
In the NOx purification processing routine of FIG. 2, it is confirmed from the ignition key ON information whether the engine is being started in step A1, and the catalyst temperature Tg, NOx concentration Snoxf, Snoxr, and other data are captured in step A2. In step A3, the catalyst temperature Tg is a predetermined temperature Tg.₀It is determined whether or not the catalyst temperature Tg is higher than the predetermined temperature Tg0. When the catalyst temperature Tg is equal to or higher than the predetermined temperature Tg0, the process proceeds to Step A4.
[0029]
In step A4, the pump 36 of the reducing agent supply means 30 is driven, the compressor clutch 39 of the air supply means 7 is turned on, and the on-off valve 33 of the air tank 32 is opened to proceed to step A5. In step A5, the NOx concentration Snoxf, Snoxr is used to determine the actual NOx purification rate η, and the basic amount D of urea water necessary for obtaining the amount of ammonia to be newly adsorbed on the NOx catalyst 17 based on the catalyst temperature Tg._ureaAre calculated from the map which is the target NOx purification rate deriving means 43 based on the catalyst temperature Tg, and the process proceeds to Step A6.
[0030]
In step A6, the target NOx purification rate Mη and the actual NOx purification rate η are differentially processed to calculate a purification rate difference Gη between them, and the process proceeds to step A7. In step 7, when the purification rate difference Gη does not exceed the predetermined amount Zη as compared with the predetermined amount Zη that is an allowable width of the purification rate preset in the control means 8 and the purification rate difference Gη, that is, If the NOx purification rate η does not differ from the target NOx purification rate Mη by a predetermined amount or more, the process proceeds to step A10 on the assumption that ammonia supply to the NOx catalyst 17, that is, urea water can be added, and the basic addition amount D of urea water D_ureaTo correct actual addition amount D_ureaDetermine (n) and proceed to Step A11. In step A11, the actual addition amount D corrected in accordance with the comparison result between the actual NOx purification rate η and the target NOx purification rate Mη._ureaThe control cycle is terminated by drivingly controlling the opening degree or the valve opening period of the flow rate adjusting valve 37 of the reducing agent supply means 30 so that the amount of urea water corresponding to (n) can be added.
[0031]
When the purification rate difference Gη exceeds the predetermined amount Zη, that is, when the actual NOx purification rate η differs from the target NOx purification rate Mη by a predetermined amount or more, the ammonia on the NOx catalyst 17 is compared. Assuming that the supply is excessive, the process proceeds to step A8. In step A8, the supply amount of urea water is set to zero, and the process proceeds to step A9. In step A9, the flow rate adjustment valve 37 of the reducing agent supply means 30 is driven and controlled to stop in order to stop the supply of urea water. To complete the control cycle.
[0032]
Thus, when the actual NOx purification rate η does not differ from the target NOx purification rate Mη by a predetermined amount or more, the basic addition amount D_ureaAnd the flow rate adjustment valve 37 is maintained at the corrected corresponding opening or is opened for a predetermined period, and the flow rate of the urea water being pumped from the urea water tank 35 to the urea water supply pipe 34 by the pump 36 is adjusted. Then, the urea water is mixed with the pressurized air in the injection pipe 31 and supplied from the addition nozzle 18 to the exhaust pipe 28. Therefore, an appropriate amount of urea water is supplied to the NOx catalyst 17 so that the ammonia adsorption amount necessary for reducing the NOx emission amount is reduced, and the ammonia produced by hydrolysis and thermal decomposition of the urea water is adsorbed to the NOx catalyst 17. Can be made. When the actual NOx purification rate η is different from the target NOx purification rate Mη by a predetermined amount or more, the addition amount is set to zero to stop the urea water supply to the NOx catalyst 17 and the addition of the urea water is stopped. Since the control is performed, the occurrence of ammonia slip can be effectively suppressed.
[0033]
In step B1, the air supply control routine of FIG. 3 determines the state of the urea water addition amount in step A8 of FIG. 2, and proceeds to step B2 only when the addition amount is set to zero. In step B2, the time after urea water addition stops is measured by the timer 11, and the process proceeds to step B3. In step B3, it is determined whether or not the time measured by the timer 11 has passed a predetermined time preset in the control means 8, and when the predetermined time has passed, the process proceeds to step B4. The predetermined time is set as a period during which the urea component adhering to the injection pipe 31 can be sufficiently removed and discharged.
[0034]
In step B4, the measurement of the timer 11 is ended (reset), the process proceeds to step B5, and the compressor clutch 39 is turned off. For this reason, since the transmission of the driving force from the engine 1 to the air compressor 38 is interrupted after a lapse of a predetermined time after the supply of urea water is stopped, the operating rate of the air compressor 38 when the urea water is not added is reduced. In the case of this embodiment, fuel efficiency is improved.
[0035]
In such a control mode, the initial purpose is achieved, but in the air supply control routine of the present mode, the process continues to the next step. In step B6, the supply restart estimation time is estimated by the urea water supply restart estimation means 9, and the process proceeds to step B7. In step B7, it is determined whether or not it is a predetermined period before the estimated supply resumption timing. When the predetermined period before the supply resumption timing is reached, the compressor clutch 39 is turned on to resume the supply of pressurized air to the injection pipe 31. End the lever control.
[0036]
In this way, when the predetermined period before the supply restart estimation time estimated by the urea water supply restart estimation means 9 is reached, the compressor clutch 39 is turned on and the supply of pressurized air to the injection pipe 31 is restarted. In some cases, pressurized air will flow in the injection pipe 31 in advance, and it is possible to promote the atomization of urea water while suppressing the adhesion of the inner wall surface of the urea water in the injection pipe 31, and good from the beginning of the restart. A NOx purification rate can be obtained.
[0037]
The urea water supply resumption estimation means 9 stores the predicted engine operation region in which the NOx emission amount is expected to increase in advance in the control means 8 as map data from the engine speed, the accelerator opening, the exhaust gas temperature, etc., and step B5 The actual operation region after the compressor clutch 39 is turned off is determined from the engine speed, the accelerator opening, the exhaust gas temperature, etc., and the time until the transition to the current operation region and the expected engine operation region is estimated and the timer The measurement is started at 11, and a predetermined ratio of time to the estimated time is set as a predetermined time, and when this time is reached, the compressor clutch 39 is turned on. For example, a change in accelerator opening from when the compressor clutch 39 is turned off is detected and stored by a known throttle opening sensor, and the rate of change of the current accelerator opening with respect to the previous accelerator opening changes by a predetermined percentage. In such a case, it is assumed that the vehicle is moving toward the predicted engine operation region, and the time required to shift to the predicted engine operation region is estimated based on the rate of change.
[0038]
A predetermined time with respect to the estimated time is set in the control means 8 and measurement is started by the timer 11. When the measured value by the timer 11 reaches the predetermined time, the compressor clutch 39 is controlled to be on. The parameters for obtaining the actual engine operation region and the predicted engine operation region are not limited to the above elements, but include the catalyst temperature (exhaust gas temperature) Tg, the NOx concentration Snoxf detected by the front NOx sensor 19, and the exhaust gas flow rate. G may be sufficient. In this case, each operation region is obtained from the NOx concentration Snoxf and the exhaust gas flow rate G, and the supply resumption estimation timing is determined according to the catalyst temperature (exhaust gas temperature) Tg, the NOx concentration Snoxf and the change rate of the exhaust gas flow rate G. That's fine.
[0039]
The NOx purification device for an internal combustion engine as the second embodiment of the present invention will be described with reference to FIG. The NOx purification device in this embodiment has basically the same configuration except that the configuration of the exhaust system control unit 130 is different from the configuration of the exhaust system control unit 3 in the first embodiment. Therefore, the same functions as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
[0040]
The exhaust system control unit 130 includes control means 80 and urea water supply amount setting means 140. The urea water supply amount setting means 140 includes an actual NOx purification rate deriving means 144 for deriving an actual NOx purification rate η by the NOx catalyst 17, a target adsorption amount setting means 150 for setting a target adsorption amount MNH3 of ammonia for the NOx catalyst 17, and an engine NOx emission amount deriving means 151 for estimating NOx mass flow rate Unox as NOx emission amount discharged from No. 1, NOx mass flow rate Unox estimated by NOx emission amount deriving means 151 and actual NOx purification rate deriving means 44 Calculated from consumption amount deriving means 152 for deriving the consumption amount f (η, Unox) of ammonia adsorbed to the NOx catalyst 17 based on the NOx purification rate η, and the urea water addition amount Durea by the reducing agent supply means 30. Ammonia consumption and consumption of ammonia f derived by the consumption derivation means 152 f (η, Unox) Flip adsorption amount deriving means 153 for deriving the actual adsorption amount SNH3 (n) of adsorbed ammonia in the NOx catalyst 17, the basic addition amount D of the urea water by the reducing agent supply means 30_ureaThe basic addition amount deriving means 154 for deriving the above, and the control means 80 for controlling both the reducing agent supply means 30 and the air supply means 7 are provided.
[0041]
The NOx emission amount deriving means 151 includes the NOx concentration Snoxf upstream of the NOx catalyst 17 detected by the front NOx sensor 19 and the exhaust gas flow rate from the engine control device 5 corresponding to the exhaust gas emission amount discharged from the engine 1. Based on G, the NOx mass flow rate Unox is derived.
[0042]
The actual NOx purification rate deriving means 144 performs a difference process by converting the NOx concentrations Snoxf and Snoxr from the respective NOx sensors 19 and 26 to Snoxf−Snoxr, and further dividing the value by Snoxf to obtain the actual NOx purification rate (η). An arithmetic circuit for calculating, and outputs the calculated actual NOx purification rate (η) to the consumption deriving means 152. The consumption amount deriving unit 152 is an arithmetic unit that calculates the ammonia consumption amount f (η, Unox) from the NOx mass flow rate Unox and the actual NOx purification rate (η).
[0043]
The target adsorption amount setting means 150 is a target adsorption amount M of ammonia adsorbed on the NOx catalyst 17 in accordance with the catalyst temperature Tg detected or estimated by the catalyst temperature detection means (catalyst temperature sensor 22)._NH3It is a map to set. Target adsorption amount M_NH3As shown by a broken line L2 in FIG. 11, the value is lower than the adsorption limit value shown by the solid line L1, for example, a value half that of the adsorption limit value L1, and the value increases as the catalyst temperature Tg increases. Is set to reduce. Target adsorption amount M_NH3Is not limited to a value that is ½ of the adsorption limit value L1, and other values may be selected as long as the value is lower than the adsorption limit value L1.
[0044]
The basic addition amount deriving means 154 considers the relationship of the ammonia amount obtained from the urea water of the above formula (1) so as to satisfy the ammonia adsorption amount at the NOx catalyst 17 shown by the broken line L2 in FIG. A basic addition amount map of urea water set in advance according to the operating state, and a basic addition amount D of urea water appropriately according to the catalyst temperature Tg_ureaIs selected and output to the adsorption amount deriving means 153. The urea water supply amount setting means 140 has a basic addition amount D_ureaIs stored in advance in a memory (not shown) as map information (not shown).
[0045]
The adsorption amount deriving unit 153 is configured to obtain the actual adsorption amount S derived last time._NH3(n-1), basic addition amount D of urea water derived by the basic addition amount deriving means 154_urea, And the estimated actual adsorption amount S in the NOx catalyst 17 based on the ammonia consumption amount f (η, Unox) derived this time._NH3This is an arithmetic circuit that derives (n) by the following equation (4). In this case, the suction amount S before correction_NH3By setting (n-1) to equation (4), the actual adsorption amount S_NH3More accurate actual adsorption amount S by reducing the error factor for (n)_NH3The calculation of (n) is intended.
S_NH3(N) = S_NH3(N-1) + D_urea-F (η × Unox) (4)
The control unit 80 is configured by a computer, and when the supply amount of urea water set by the urea water supply amount setting unit 140 is zero, a predetermined period of time has elapsed since the supply amount was set to zero. The air supply means 7 is controlled to stop the supply of pressurized air supplied from the air supply means 7 later. In this embodiment, the compressor clutch 39 is turned off and the driving force from the engine 1 to the air compressor 38 is cut off. The control means 80 is configured such that after the urea water supply amount set by the urea water supply amount setting means 140 is set to zero, the vehicle speed V detected by the vehicle speed sensor 10 is equal to or higher than a predetermined vehicle speed V1 as a predetermined value. In addition, in order to prohibit the supply of the pressurized air supplied from the air supply means 7, the compressor clutch 39 is turned on and control is performed so that the driving force is transmitted from the engine 1 to the air compressor 38.
[0046]
The control means 80 monitors the output value from a pressure sensor (not shown) so that the tank internal pressure of the air tank 32 becomes a predetermined pressure. When the tank internal pressure falls below the predetermined pressure, the control means 80 turns on the compressor clutch 39 to turn on the air compressor. 38 is driven to supply air to the air tank 32. In this embodiment, on / off control of the compressor clutch 39 is performed to control the supply of pressurized air, but the opening / closing control of the on-off valve 33 may be performed simultaneously. The predetermined speed V1 is stored in advance in the control means 80. The predetermined speed V1 is a speed at which there is a high possibility of shifting to the operation state of the catalyst temperature Tg or the high exhaust gas temperature, in which urea water needs to be resupplied immediately after the speed.
[0047]
The control unit 80 has a function of controlling the driving of the on-off valve 33, the pump 36, and the flow rate adjustment valve 37 in order to execute the addition of urea water by the reducing agent supply unit 30. In this embodiment, the opening amount of the on-off valve 33 and the rotation speed of the pump 36 are made constant, and the urea water supply amount D provided by the urea water supply amount setting means 4._ureaThe opening degree or the valve opening period of the flow rate adjusting valve 37 is adjusted and controlled according to (n). Instead of opening and closing the flow rate adjusting valve 37, the opening degree of the opening and closing valve 33, the rotation speed control of the pump 36, or a combination of these controls may be used.
[0048]
Next, NOx control processing by the NOx purification device will be described along the NOx purification processing routine of FIG. 6, and air supply control will be described along the air supply control routine shown in FIG.
[0049]
When the engine 1 of the vehicle (not shown) equipped with the NOx purification device is driven, the engine control device 5 has normal related devices and sensors that are appropriately executed in a plurality of control systems, for example, a fuel injection system and a fuel supply system. Whether or not the self-check result of whether or not is normal is confirmed, and if normal (OK), control is performed by sending a control signal to the fuel injection system and the fuel supply system according to each input value of each sensor described above. The sensor output obtained at that time is transmitted to the exhaust system control device 130 as well.
[0050]
The exhaust system control unit 130 repeats the NOx purification process control of the NOx purification process routine of FIG. 6 for each predetermined control cycle simultaneously with turning on of the engine key. In step C1, whether the engine is starting is confirmed by the ignition key ON information. In step C2, the catalyst temperature Tg, the exhaust gas flow rate G, the NOx concentrations Snoxf, Snoxr, and the previous adsorption amount S are checked._NH3(N-1), taking in other data. In step C3, the catalyst temperature Tg is a predetermined temperature Tg.₀It is determined whether or not the catalyst temperature Tg is a predetermined temperature Tg.₀At this time, the process proceeds to step C4, where the predetermined temperature Tg₀If less, the process proceeds to Step C9 described later.
[0051]
In step C4, the pump 36 of the reducing agent supply means 30 is driven, the compressor clutch 39 of the air supply means 7 is turned on, and the on-off valve 33 of the air tank 32 is opened, and the process proceeds to step C5. In step C5, the NOx mass flow rate Unox is determined using the exhaust gas flow rate G and the NOx concentration Snoxf, the actual NOx purification rate η is determined using the NOx concentrations Snoxf, Snoxr, and the NOx catalyst 17 is determined based on the catalyst temperature Tg. Basic ammonia addition amount D of urea water necessary to obtain a new ammonia amount to be adsorbed_ureaIs calculated from the map of the basic addition amount deriving means 154, and the target adsorption amount M corresponding to the catalyst temperature Tg is calculated._NH3Is calculated from the map which is the target adsorption amount setting means 150, and the process proceeds to Step C6.
[0052]
In step C6, the ammonia consumption f (η, Unox) is derived based on the NOx mass flow rate Unox and the actual NOx purification rate η, and the process proceeds to step C7. In step C7, the actual amount of ammonia is calculated using equation (4). Adsorption amount S_NH3(N) is calculated and derived, and the process proceeds to Step C8.
[0053]
In Step C8, the target adsorption amount M_NH3And actual adsorption amount S_NH3(N) is subjected to differential processing, and the adsorption difference G between the two_NH3Is calculated and the process proceeds to Step C9. In step C9, a predetermined amount Z that is an allowable width of the adsorption rate set in advance in the control means 80._NH3And adsorption difference G_NH3Compared to adsorption difference G_NH3Is the predetermined amount Z_NH3That is, the actual adsorption amount S_NH3(N) is the target adsorption amount M_NH3If there is no difference from the predetermined amount, the process proceeds to Step C12 assuming that ammonia can be supplied to the NOx catalyst 17, that is, urea water can be added._ureaTo correct actual addition amount D_ureaDetermine (n) and proceed to Step C13. In step C13, the actual adsorption amount S_NH3(N) and target adsorption amount M_NH3Actual addition amount D corrected according to the comparison result with_urea(n) The control cycle is terminated by drivingly controlling the opening degree or the valve opening period of the flow rate adjusting valve 37 of the reducing agent supply means 30 so that the amount of urea water corresponding to the amount can be added.
[0054]
Comparison result in step C9, adsorption difference G_NH3Is larger than the predetermined amount predetermined amount ZNH3, that is, the actual adsorption amount S_NH3When (n) is different from the target adsorption amount MNH3 by a predetermined amount or more, it is considered that the ammonia supply on the NOx catalyst 17 is excessive, and the process proceeds to Step C10. In step C10, the supply amount of urea water is set to zero, and the process proceeds to step C11. In step C11, the flow rate adjustment valve 37 of the reducing agent supply means 30 is driven and controlled to be closed in order to stop the supply of urea water. End the cycle.
[0055]
Thus, the actual adsorption amount S_NH3(N) is the target adsorption amount M_NH3If there is no more difference than the predetermined amount, the basic addition amount D_ureaAnd the flow rate adjustment valve 37 is maintained at the corrected corresponding opening or is opened for a predetermined period, and the flow rate of the urea water being pumped from the urea water tank 35 to the urea water supply pipe 34 by the pump 36 is adjusted. Then, the urea water is mixed with the pressurized air in the injection pipe 31 and supplied from the addition nozzle 18 to the exhaust pipe 28. Therefore, an appropriate amount of urea water is supplied to the NOx catalyst 17 so that the ammonia adsorption amount necessary for reducing the NOx emission amount is reduced, and the ammonia produced by hydrolysis and thermal decomposition of the urea water is adsorbed to the NOx catalyst 17. Can be made.
[0056]
Actual adsorption amount S_NH3(N) is the target adsorption amount M_NH3If the difference is more than a predetermined amount, the amount of addition is set to zero in order to stop the urea water supply to the NOx catalyst 17, and the flow rate adjustment valve 37 is closed to stop the addition of the urea water. Can be suppressed. Even when urea water is not added, the compressor clutch 39 is turned on and the on-off valve 32 is opened, so that pressurized air is supplied to the injection pipe 31 from the air tank 32, and the urea component Clogging of the injection pipe 31 due to adhesion can be prevented.
[0057]
In step D1, the air supply control routine of FIG. 7 determines the state of the urea water addition amount in step C10 of FIG. 6, and proceeds to step D2 only when the addition amount is set to zero. In step D2, the time after the urea water addition stops is measured by the timer 11, and the process proceeds to step D3. In step D3, it is determined whether or not a predetermined time preset in the control means 80 has elapsed in the measurement time of the timer 11, and when the predetermined time elapses, the process proceeds to step D4.
[0058]
In step D4, the measurement of the timer 11 is ended (reset), the process proceeds to step D5, and the compressor clutch 39 is turned off. For this reason, since the transmission of the driving force from the engine 1 to the air compressor 38 is interrupted after a lapse of a predetermined time after the supply of urea water is stopped, the operating rate of the air compressor 38 when the urea water is not added is reduced. In the case of this embodiment, fuel efficiency is improved.
[0059]
In such a control mode, the initial purpose is achieved, but in the air supply control routine of the present mode, the process continues to the next step. In step D6, the vehicle speed V from the vehicle speed sensor 10 is taken, and in step D7, it is determined whether or not the vehicle speed V is equal to or higher than a predetermined speed V1 at which the predetermined value is reached. As a result of the determination, when the vehicle speed V becomes equal to or higher than the predetermined speed V1, the compressor clutch 39 is turned on, the supply of pressurized air to the injection pipe 31 is resumed, and this control is finished.
[0060]
Thus, when the vehicle speed V becomes equal to or higher than the predetermined speed V1, which is a speed that is likely to shift to an operation state that requires resupply of urea water, the compressor clutch 39 is turned on and the pressurized air to the injection pipe 31 is turned on. Therefore, when the urea water is added to the operation state where the urea water needs to be resupplied, the pressurized air is already supplied into the injection pipe 31, and the reducing agent While suppressing adhesion of urea water supplied from the supply means 30 to the inner wall surface of the injection pipe 31, atomization of urea water can be promoted, and a good NOx purification rate can be obtained from the initial stage of restart.
[0061]
FIG. 8 shows another form of the NOx purification processing routine for performing NOx control processing by the NOx purification device. In this NOx control process, when the supply amount of urea water is set to zero, only the catalyst temperature Tg of the NOx catalyst 17 is used as a parameter.
[0062]
The NOx purification processing routine shown in FIG. 8 repeats the NOx purification processing control every predetermined control cycle simultaneously with turning on of the engine key. In FIG. 8, whether or not the engine is being started is confirmed by the ignition key ON information in step E1, and the catalyst temperature Tg and NOx concentrations Snoxf and Snoxr are fetched in step E2, and the process proceeds to step E3.
[0063]
In step E3, the pump 36 of the reducing agent supply means 30 is driven, the compressor clutch 39 of the air supply means 7 is turned on, and the on-off valve 33 of the air tank 32 is opened to proceed to step E4. In step E4, the basic addition amount D necessary for obtaining a new ammonia amount to be adsorbed on the NOx catalyst 17 based on the catalyst temperature Tg._ureaIs calculated from the map of the basic addition amount deriving means 42 or the basic addition amount deriving means 154, and the process proceeds to Step E5.
[0064]
In step E5, the predetermined temperature MTg, which is a predetermined value stored in the control means 8 or 80 in advance, is compared with the catalyst temperature Tg. If the catalyst temperature Tg is lower than the predetermined temperature, the temperature of the NOx catalyst 17 is increased. Although it is a temperature at which ammonia can be sufficiently adsorbed (see FIG. 11), the NOx purification rate is low (see FIG. 4), and the amount of ammonia consumption is small. In step E6, the supply amount of urea water is set to zero and the process proceeds to step E7. In step E7, the flow rate adjustment valve 37 of the reducing agent supply means 30 is driven and controlled to be closed in order to stop the supply of urea water. End the cycle.
[0065]
When the catalyst temperature Tg exceeds the predetermined temperature, it is assumed that the NOx purification rate is high, the amount of ammonia consumed is large, and the amount of ammonia adsorbed on the NOx catalyst 17 is reduced. Proceeding to step E8 assuming that urea water can be added, the basic addition amount Durea of urea water is corrected, and the actual addition amount D_ureaDetermine (n) and proceed to Step E9. In step E9, the actual addition amount D_ureaThe control cycle is terminated by drivingly controlling the opening degree or the valve opening period of the flow rate adjusting valve 37 of the reducing agent supply means 30 so that the amount of urea water corresponding to (n) can be added.
[0066]
As in this NOx purification processing routine, paying attention to the relationship between the ammonia adsorption amount in the NOx catalyst 17 and the catalyst temperature Tg, control is performed to add or not add urea water according to the ammonia adsorption amount predicted from the catalyst temperature Tg. May be.
[0067]
FIG. 9 shows another form of an air supply control routine for performing air supply control by the NOx purification device. In step F1 of FIG. 9, it is determined whether or not the supply of urea water has been detected. For example, during the execution of the NOx purification processing routine shown in FIGS. 2, 6, and 8, whether or not the flow rate adjustment valve 37 is operating is determined based on whether or not there is an output from the detection sensor 12, and there is an output from the sensor 12. Suppose that there is a urea water supply, the compressor clutch 39 is turned on, and if there is no output from the sensor 12, the compressor clutch 39 is turned off because there is no urea water supply. Thus, if the compressor clutch 39 is controlled according to the presence or absence of the operation of the flow rate adjustment valve 37, the driving force loss can be reduced with a simple configuration.
[0068]
The air supply control routine shown in FIG. 3 used in the first embodiment and the air supply control routine shown in FIG. 7 used in the second embodiment may be used interchangeably.
[0069]
【The invention's effect】
  According to the present invention, since the stop / operation of the air supply means is controlled by the control means in accordance with the urea water supply state set by the urea water supply amount setting means, unnecessary pressurized air when the urea water supply is stopped By stopping the supply of power, the driving force loss can be reduced, and the power consumption of the vehicle can be reduced, and the fuel efficiency and the NOx purification rate can be improved.
  According to the present invention, when the vehicle speed is equal to or higher than the predetermined value, the supply stop of the pressurized air is prohibited, and the urea water supply is resumed, so that the vehicle again has the catalyst temperature of the urea water supply or the high exhaust temperature. Even when the operation state is shifted to, the urea water can be re-added quickly, and the power consumption of the vehicle can be reduced and the fuel consumption and the NOx purification rate can be improved.
  According to the present invention, since the pressurized air supply is resumed before a predetermined period of the urea water supply resumption timing, the NOx purification is promoted by pursuing the atomization of the urea water and the urea is blocked in the supply passage. Can be prevented.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a NOx purification device showing a first embodiment of the present invention.
2 is a flowchart showing a NOx purification process routine executed by the NOx purification apparatus of FIG. 1; FIG.
FIG. 3 is a flowchart showing a routine of air supply control executed in the first embodiment.
FIG. 4 is a characteristic diagram showing the relationship between the target NOx purification rate and the catalyst temperature.
FIG. 5 is an overall configuration diagram of a NOx purification device showing a second embodiment of the present invention.
6 is a flowchart showing a routine of NOx purification processing executed by the NOx purification device of FIG. 5. FIG.
FIG. 7 is a flowchart showing a routine of air supply control executed in the second embodiment.
FIG. 8 is a flowchart showing another routine of NOx purification processing.
FIG. 9 is a flowchart showing another routine of air supply control.
FIG. 10 is a characteristic diagram showing the relationship between the ammonia adsorption amount of the NOx catalyst and the NOx purification rate.
FIG. 11 is a characteristic diagram showing the relationship between the catalyst temperature of the NOx catalyst and the ammonia adsorption amount.
[Explanation of symbols]
1 Internal combustion engine
2 Exhaust system
4 Urea water supply amount setting means
7 Air supply means
8,80 Control means
9,90 Urea water supply resumption estimation means
10 Vehicle speed detection means
12 Urea water supply detection means
17 NOx catalyst
30 Reducing agent supply means
31 Supply passage
31A Upstream supply passage

Claims (2)

A NOx catalyst provided in an exhaust system of the internal combustion engine for selectively reducing NOx in the exhaust gas;
Reducing agent supply means for supplying urea water via a supply passage communicating with the exhaust system upstream of the NOx catalyst;
An air supply means for supplying pressurized air to the supply passage upstream from a supply site of urea water supplied from the reducing agent supply means;
Urea water supply amount setting means for setting the supply amount of urea water in accordance with one of the catalyst temperature of the NOx catalyst or a parameter correlated with the catalyst temperature;
Vehicle speed detection means for detecting the vehicle speed of the vehicle on which the internal combustion engine is mounted ;
Both by controlling the stop / operation of the air supply means in accordance with the supply state of urea water set by the urea water supply quantity setting means, when the vehicle speed detected by the vehicle speed detecting means is a predetermined value or more, the air supply And a control means for controlling the air supply means so as to prohibit the supply stop of the pressurized air supplied from the means . A NOx catalyst provided in an exhaust system of the internal combustion engine for selectively reducing NOx in the exhaust gas;
Reducing agent supply means for supplying urea water via a supply passage communicating with the exhaust system upstream of the NOx catalyst;
An air supply means for supplying pressurized air to the supply passage upstream from a supply site of urea water supplied from the reducing agent supply means;
Urea water supply amount setting means for setting the supply amount of urea water in accordance with one of the catalyst temperature of the NOx catalyst or a parameter correlated with the catalyst temperature;
Urea water supply restart estimation means for estimating the urea water supply restart timing after the urea water supply amount set by the urea water supply amount setting means is set to zero;
The stop / operation of the air supply means is controlled in accordance with the urea water supply state set by the urea water supply amount setting means, and a predetermined period of the urea water resumption timing estimated by the urea water supply restart estimation means A NOx purification device for an internal combustion engine , wherein the air supply means is controlled so as to start supply of pressurized air supplied from the air supply means before .

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