JP2014066232A - Internal combustion engine and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine and a method of controlling the same, effective in purifying NOx, and executing purification of NOx by calculating an effective reduction timing free from degradation of fuel economy.SOLUTION: In an engine 1, an ECU 18 includes: catalyst temperature raising means C5 for making an injector 15 inject in multistage at a temperature raising timing calculated on the basis of a timing estimation parameter including a temperature parameter detected by catalyst temperature detecting means C1, a NOx concentration parameter detected by NOx concentration detecting means C2, and an exhaust gas flow rate parameter detected by exhaust gas flow rate detecting means C3, to raise a temperature of an LNT catalyst 16; and reduction enhancing means C7 for enhancing reduction of NOx in the LNT catalyst 16 at a reduction timing calculated on the basis of the redetected timing estimation parameter after temperature raise of the LNT catalyst 16 by the catalyst temperature raising means C5.

Description

  The present invention relates to an internal combustion engine that purifies NOx without deteriorating fuel efficiency even at low load when purifying NOx (nitrogen oxide) using a deNOx catalyst (NOx purifying catalyst), and a control method thereof. .

  Conventionally, in order to purify NOx in exhaust gas discharged from an engine (internal combustion engine), an LNT catalyst (lean-NOx-trap catalyst; NOx occlusion reduction catalyst, etc.) or a urea SCR catalyst (urea selective catalytic reduction catalyst) DeNOx catalysts such as are used.

  In this deNOx catalyst, at a temperature lower than the temperature at which the catalyst is activated (hereinafter referred to as the activation temperature), the catalytic reaction is lowered and the NOx reduction efficiency is lowered. In particular, the NOx purification rate at low loads such as when the engine is started is low.

For example, an LNT catalyst that stores and reduces NOx can store NOx even in a lean state where the fuel ratio is lower than the stoichiometric air-fuel ratio even at a relatively low temperature. However, in order to release and reduce NOx in a rich state where the fuel ratio is higher than the stoichiometric air-fuel ratio, the LNT catalyst needs to be heated to a high temperature (hereinafter referred to as rich reduction). The purification rate decreases. On the other hand, in the urea SCR catalyst, the reduction efficiency of NH ₃ (ammonia) decreases at low temperatures, so the purification rate at low load also decreases.

  In exhaust gas evaluation modes such as traffic jams outside the exhaust gas evaluation mode and NEDC (New European Driving Cycle) mode that starts from a cold state with a low load, the deNOx catalyst does not function sufficiently for the above reasons and purifies NOx. I couldn't.

  Therefore, in response to this problem, when the catalyst temperature of the oxidation catalyst when NOx is to be released from the NOx storage reduction catalyst is lower than a predetermined temperature, an engine cycle for performing post injection is started and the post injection is performed. There is an apparatus in which the start time of the engine cycle is set earlier than the start time of exhaust system injection by a predetermined preceding time, and the preceding time is set longer as the temperature of the oxidation catalyst is lower (for example, see Patent Document 1). .

  In addition, it has a catalyst temperature detecting means for detecting the temperature of the catalyst, and an activation determining means for determining whether or not the catalyst is activated based on a detection value of the catalyst temperature detecting means. Control means for selecting and executing either an exhaust temperature raising mode that prioritizes raising the exhaust temperature as an engine operation mode or an exhaust component reduction mode that prioritizes reducing exhaust components based on the results; There is also an apparatus (for example, refer to Patent Document 2) including the above.

  These devices use multistage injection to raise the exhaust temperature in order to raise the temperature of the deNOx catalyst. However, since this multistage injection for raising the temperature is accompanied by deterioration of fuel consumption, it can always be performed. Can not. In order to solve the problem that the fuel efficiency deteriorates, Patent Document 1 discloses that multistage injection is performed when NOx should be released from the NOx storage reduction catalyst. Patent Document 2 discloses that it is determined whether or not the catalyst is activated based on the detection value of the catalyst temperature detecting means, and multistage injection is performed based on the determination result.

However, these devices use the temperature of the catalyst as a criterion for multistage injection, and can suppress the deterioration of fuel consumption compared to those that always perform multistage injection, but cannot suppress the deterioration of fuel consumption to a minimum. In addition, there is an appropriate timing for promoting the reduction after the deNOx catalyst is activated, and by promoting the reduction at that timing, it becomes possible to further suppress the deterioration of fuel consumption.

JP 2010-038116 A JP 2010-112192 A

  The present invention has been made in view of the above problems, and an object of the present invention is to calculate an effective timing at which the fuel consumption does not deteriorate even at a low load of the internal combustion engine, and to purify NOx. It is to provide an engine and its control method.

  An internal combustion engine of the present invention for solving the above-described object is an internal combustion engine comprising a fuel injection valve capable of multi-stage injection of fuel and a NOx purification catalyst provided in an exhaust passage. A control unit including a detection unit and an exhaust gas flow rate detection unit; the control unit detects a temperature parameter detected by the catalyst temperature detection unit; a NOx concentration parameter detected by the NOx concentration detection unit; and the exhaust gas flow rate detection Catalyst temperature raising means for raising the temperature of the NOx purification catalyst by performing multi-stage injection control of the fuel injection valve at a temperature raising timing calculated using a timing estimation parameter including an exhaust gas flow rate parameter detected by the means; After the NOx purification catalyst is heated by the catalyst heating means, the return calculated using the timing estimation parameter detected again. In timing, and provided with a reduction promoter means for facilitating the reduction of NOx in the NOx purifying catalyst.

  According to this configuration, the NOx purification catalyst is heated at the temperature rise timing calculated using the timing estimation parameter, and then the NOx reduction at the NOx purification catalyst at the reduction timing calculated using the redetected timing estimation parameter. Therefore, even when the internal combustion engine is at a low load, NOx can be purified while minimizing deterioration in fuel consumption.

  The NOx purification catalyst referred to here means an LNT catalyst (lean-NOx-trap catalyst; NOx occlusion reduction catalyst or the like) or a urea SCR catalyst (urea selective catalyst reduction catalyst). Multi-stage injection refers to normal combustion (premixed combustion and diffusion combustion) with the main injection timing delayed from the top dead center, and after injection or post injection is continuously performed in the diffusion combustion engine. An injection that opens the exhaust port while keeping the temperature high.

  In the internal combustion engine, the control device uses the first condition that the catalyst temperature of the NOx purification catalyst detected by the catalyst temperature detecting means is lower than a predetermined activation temperature, and the timing estimation parameter. A second condition in which the calculated storage amount of the NOx purification catalyst is equal to or greater than a predetermined determination storage amount, or the NOx purification rate of the NOx purification catalyst calculated using the timing estimation parameter is equal to or less than a predetermined determination purification rate. And the estimated fuel consumption deterioration rate calculated from the fuel injection amount required to raise the catalyst temperature to the activation temperature is stable at or below a predetermined determination fuel consumption deterioration rate. And a temperature increase timing at which the temperature increase timing is when all of the first condition, the second condition, and the third condition are satisfied. The NOx purification catalyst using the fourth condition for the catalyst temperature detected by the catalyst temperature detecting means to reach the activation temperature and the re-detected timing estimation parameter after the catalyst estimation means and the catalyst temperature raising means. The fifth reduction condition for which the estimated reduction quantity per hour of NOx reduced in step is equal to or greater than a predetermined judgment reduction quantity is determined, and both the fourth condition and the fifth condition are satisfied A reduction timing estimation means for setting the reduction timing as the reduction timing, NOx is effectively calculated by constantly calculating the storage amount of the catalyst, the NOx purification rate, the estimated fuel consumption deterioration rate, and the estimated reduction amount. Reduction can reduce NOx even under low load conditions.

  In addition, in the internal combustion engine, the NOx purification catalyst is formed of an LNT catalyst, and the control device includes a rich reduction means for maintaining the air-fuel ratio rich as the reduction promotion means.

  In the internal combustion engine, the NOx purification catalyst is formed of a urea SCR catalyst, and the control device includes urea water injection means for injecting urea water to the NOx purification catalyst as the reduction promoting means. To do.

  According to said structure, since the structure of each apparatus may be a conventional structure, there is no additional addition and the effect mentioned above can be acquired, without generating additional cost.

  Furthermore, the control method of the internal combustion engine of the present invention for solving the above object is a control method of an internal combustion engine comprising a fuel injection valve capable of multi-stage injection of fuel and a NOx purification catalyst provided in an exhaust passage. The fuel injection valve is subjected to multistage injection control at a temperature rise timing calculated using a timing estimation parameter including a temperature parameter of the NOx purification catalyst, a NOx concentration parameter, and an exhaust gas flow rate parameter, and the temperature of the NOx purification catalyst is increased. The method is characterized in that the NOx reduction in the NOx purification catalyst is promoted at a reduction timing calculated using the timing estimation parameter detected again after the temperature rises and the NOx purification catalyst rises in temperature.

  Moreover, in the control method for an internal combustion engine, the temperature increase timing is calculated using the first condition in which the catalyst temperature of the NOx purification catalyst is lower than a predetermined activation temperature and the timing estimation parameter. A second condition in which the storage amount of the NOx purification catalyst is equal to or greater than a predetermined determination storage amount, or the NOx purification rate of the NOx purification catalyst calculated using the timing estimation parameter is equal to or less than a predetermined determination purification rate; A third condition in which an estimated fuel consumption deterioration rate obtained by estimating a fuel injection amount required to raise the catalyst temperature to the activation temperature using a timing estimation parameter is stable at a predetermined determination fuel consumption deterioration rate or less. When all the conditions are satisfied, the reduction timing is set to a fourth condition in which the catalyst temperature detected after the temperature of the NOx purification catalyst is raised reaches the activation temperature, Using the known timing estimation parameter, the estimated reduction amount that estimates the reduction amount per hour of NOx that is reduced by the NOx purification catalyst satisfies both the fifth condition that is equal to or greater than a predetermined determination reduction amount. Sometimes it is preferred.

  According to the present invention, even when the internal combustion engine is at a low load, NOx can be purified by calculating an effective timing at which the fuel consumption does not deteriorate. Moreover, since the configuration of the apparatus may be a conventional configuration, there is no additional addition, and the effect can be obtained without generating additional costs.

It is a figure showing composition of an internal-combustion engine of a 1st embodiment concerning the present invention. It is a figure which shows the structure of the control apparatus of FIG. It is a flowchart which shows the control method of the internal combustion engine of 1st Embodiment which concerns on this invention. It is a flowchart which shows the reduction | restoration promotion process of FIG. It is a figure which shows the structure of the internal combustion engine of 2nd Embodiment which concerns on this invention. It is a figure which shows the structure of the control apparatus of FIG. It is a flowchart which shows the control method of the internal combustion engine of 2nd Embodiment which concerns on this invention.

  Hereinafter, an internal combustion engine according to an embodiment of the present invention and a control method thereof will be described with reference to the drawings. In the following embodiment, an in-line four-cylinder diesel engine will be described as an example, but the present invention is not limited to a diesel engine, but can be applied to a gasoline engine. The number of cylinders and the arrangement of cylinders are Not limited. Note that the dimensions of the drawings are changed so that the configuration can be easily understood, and the ratios of the thicknesses, widths, lengths, and the like of the respective members and parts do not necessarily match the ratios of actually manufactured parts.

  First, an internal combustion engine according to a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the engine 1 includes an engine body 2, an exhaust manifold 3, an inlet manifold 4, an EGR (exhaust gas recirculation) system 5, a turbocharger 6, an air cleaner 7, an intercooler 8, an intake throttle 9, and An exhaust gas aftertreatment device 10 is provided, and each device is connected by an exhaust pipe or a pipe called an intake pipe to form an exhaust passage Ex and an intake passage In.

  The engine body 2 includes a fuel tank 12, a fuel pump 13, a common rail 14, and an injector 15 capable of multistage injection as a fuel injection system 11. The post-treatment device 10 includes a deNOx catalyst (NOx purification catalyst). An LNT catalyst (Lean-NOx-trap catalyst; NOx occlusion reduction catalyst) 16 and a DPF (diesel particulate collection filter) 17 are provided.

  In addition, a first temperature sensor S1 and a second temperature sensor S2 disposed before and after the LNT catalyst 16, a first NOx concentration sensor S3 and a second NOx concentration sensor S4 disposed before and after the LNT catalyst 16, and an exhaust gas flow rate sensor S5, etc. And an ECU (control device) 18 that controls each device.

  The injector 15 is a fuel injection valve capable of multistage injection using a known technique. The multistage injection referred to here means that the main injection timing is delayed from the top dead center with respect to normal combustion (premixed combustion and diffusion combustion), and after-injection or post-injection is continued in the diffusion combustion engine. This is an injection that is performed and opens the exhaust port while keeping the combustion temperature high.

The LNT catalyst 16 is an LNT catalyst that occludes and reduces NOx of a known technique. In the LNT catalyst 16, NO in the exhaust gas is oxidized by the catalytic action of the catalytic metal into NO ₂ under a high oxygen concentration atmosphere in which the exhaust gas is lean (lean combustion), and diffuses into the catalyst in the form of NO ₃ ^−. and, absorbing selectively NO ₂ in NOx-absorbing material.

When the exhaust gas becomes rich and the oxygen concentration decreases, NO ₃ ⁻ is released from the NOx storage material in the form of NO ₂ . The released NO ₂ is reduced to N ₂ by being catalyzed by the catalytic metal by a reducing agent such as unburned HC (fuel, etc.) or CO or H ₂ contained in the exhaust gas. This reduction action can prevent NOx from being released into the atmosphere. This reduction action in the rich state is hereinafter referred to as rich reduction.

  The engine 1 of the present invention performs NOx purification by calculating an effective temperature rise timing and reduction timing at which the fuel consumption does not deteriorate at low loads. Therefore, as shown in FIG. 2, the ECU 18 has the catalyst temperature detection means C1, NOx concentration detection means C2, exhaust gas flow rate detection means C3, temperature rise timing estimation means C4, catalyst temperature rise means C5, reduction timing estimation means C6, reduction. It has a promotion means C7 and a reduction end timing calculation means C8.

The catalyst temperature detection means C1 is means for the first temperature sensor S1 and the second temperature sensor S2 to detect the pre-temperature Ta ([° C.]) and the post-temperature Tb ([° C.]) of the LNT catalyst 16 as temperature parameters. In this embodiment, the previous temperature Ta detected by the first temperature sensor S1 is used as the catalyst temperature T _LNT ([° C.]).

  The NOx concentration detection means C2 detects the front NOx concentration Ca ([ppm]) and the rear NOx concentration Cb ([ppm]) of the LNT catalyst 16 as the NOx concentration parameters by the first NOx concentration sensor S3 and the second NOx concentration sensor S4. The exhaust gas flow rate detection means C3 is a means for detecting the exhaust gas flow rate Qg ([Kg / s]) flowing through the exhaust passage Ex as the exhaust gas flow rate parameter by the exhaust gas flow rate sensor S5.

  In this embodiment, the timing estimation parameters including the temperature parameter, the NOx concentration parameter, and the exhaust gas flow rate parameter are detected using the sensors S1 to S5. However, the present invention is not limited to this configuration. Instead of the information detected by the sensors S1 to S5, information such as the operating state of the engine 1 (vehicle speed and rotation speed of the engine 1) may be acquired, and the timing estimation parameter may be estimated from the information.

  The temperature rise timing estimation means C4 is a means for setting the temperature of the LNT catalyst 16 to rise when all of the first condition, the second condition, and the third condition calculated using the timing estimation parameters are satisfied. is there.

The first condition is that the catalyst temperature T _LNT is lower than the predetermined activation temperature Tx ([° C.]). The activation temperature Tx can be set to any temperature, and is preferably a temperature at which the LNT catalyst 16 is activated and rich reduction is promoted, and is set to 200 ° C. to 300 ° C., for example.

The second condition is that the NOx occlusion amount V _NOx ([g]) of the LNT catalyst 16 is equal to or greater than a predetermined occlusion amount Vx ([g]), or the NOx purification rate R _NOx ([%] of the LNT catalyst 16. ]) Is equal to or less than a predetermined determination purification rate Rx ([%]). This NOx occlusion amount _VNOx is a value calculated from the pre-NOx concentration Ca and the post-NOx concentration Cb and the exhaust gas flow rate Qg, and is calculated from the following mathematical formula (1), for example. Here, it is assumed that the NOx concentration difference is ΔC (Ca−Cb), the molecular weight of NOx is m ([g]), and the volume of 1 mol of gas in a standard state is 22.4 ([L]).

The NOx purification rate R _NOx is a value calculated from the pre-NOx concentration Ca and the post-NOx concentration Cb, and is calculated from the following formula (2), for example.

The above-described determination occlusion amount Vx and determination purification rate Rx can be set to arbitrary values, and values that can indicate a state in which the stored NOx needs to be released when the LNT catalyst 16 is in the lean state. preferable.

Furthermore, the third condition is that the estimated fuel consumption deterioration rate R _FUEL ([%]) is stable at a predetermined determination fuel consumption deterioration rate Ry ([%]) or less. The estimated fuel consumption deterioration rate R _FUEL is a value estimated from the fuel injection amount L1 ([L]) necessary for _raising the catalyst temperature T _LNT to the activation temperature Tx, and is necessary for raising the temperature. The fuel injection amount L1 is calculated from the activation temperature Tx, which is the temperature at which rich reduction functions in the LNT catalyst 16, the post-temperature Tb of the LNT catalyst 16, and the exhaust gas flow rate Qg, by calculating the estimated temperature.

The estimated fuel consumption deterioration rate R _FUEL is calculated from the following mathematical formulas (3) to (5), for example. In order to raise the temperature of the catalyst, the heating value is J ([J / s]), the specific heat of the exhaust gas is P ([J / Kg · K]), the localized heating value of the fuel is 38.2 ([MJ / L]). Let L2 ([L]) be the fuel injection amount other than the fuel injection amount required for the above.

Here, the estimated fuel consumption deterioration rate R _FUEL is stable at or below the determined fuel consumption deterioration rate Ry. The estimated fuel consumption deterioration rate R _FUEL is substantially constant at a value as close as possible to or below the determined fuel consumption deterioration rate Ry (for example, 5%). Say that. Further, the judged fuel consumption deterioration rate Ry can be set to an arbitrary value, but is preferably set to the smallest possible value.

For example, when the temperature of the LNT catalyst 16 is raised from 100 ° C. to 200 ° C. or higher and when the temperature is raised from 150 ° C. to 200 ° C. or higher, the latter has a smaller fuel consumption deterioration rate. Therefore, in order to raise the temperature of the LNT catalyst 16 without deteriorating the fuel consumption, it is necessary to estimate the latter condition. Therefore, it is possible to suppress the deterioration of fuel consumption by determining that the estimated fuel consumption deterioration rate R _FUEL is stable at a value equal to or less than the determination fuel consumption deterioration rate Ry.

According to the temperature increase timing estimation means C4, the state of the LNT catalyst 16 is determined from the first condition and the second condition, and then the third condition is determined using the estimated fuel consumption deterioration rate R _FUEL, thereby _reducing the fuel consumption. It is possible to calculate the temperature rising timing that minimizes the deterioration of.

  The catalyst temperature raising means C5 is means for performing multi-stage injection control of the injector 15 at the timing calculated by the temperature raising timing estimating means C4, whereby the exhaust gas temperature rises and the LNT catalyst 16 can be raised in temperature. . Further, by injecting fuel in multiple stages with this catalyst temperature raising means C5, the temperature of the exhaust gas can be raised, and the reduction efficiency can be increased to reduce NOx.

  In addition, if the catalyst temperature raising means C5 is provided with exhaust injection means for directly injecting fuel into the exhaust passage Ex separately from the multistage injection of the fuel, for example, the outlet of the exhaust manifold 3 up to 200 ° C. by multistage injection. It is also possible to raise the temperature of the exhaust gas in the vicinity and further raise the temperature to 300 ° C. by adding exhaust injection.

  The reduction timing estimation means C6, after the catalyst temperature raising means C5, again detects when both the fourth condition and the fifth condition calculated using the timing estimation parameters detected by the sensors S1 to S5 are satisfied. This is means for promoting the NOx reduction at the catalyst 16.

The fourth condition is that the catalyst temperature _TLNT reaches a predetermined activation temperature Tx. The fifth condition is that the estimated reduction amount V _RE ([ppm]) estimated using the re-detected timing estimation parameter is equal to or greater than a predetermined determination reduction amount Vy ([ppm]). The estimated reducing amount _{V RE} is calculated from the temperature Tb and the exhaust gas flow rate Qg after LNT catalyst 16, which is a reduced amount of NOx per predetermined rich (lambda depth and time).

This estimated reduction amount V _RE is obtained by, for example, using a map obtained by testing (a map storing the estimated reduction amount V _RE based on the catalyst temperature T _LNT and the exhaust gas flow rate Qg), and the catalyst temperature every moment during actual traveling. It is obtained from _TLNT and exhaust gas flow rate Qg.

  The determination reduction amount Vy can be set to an arbitrary value, but is preferably a value that increases the reduction amount of NOx per rich so as to be an effective timing for NOx purification, and is obtained on a trial basis. Value is used.

  According to the reduction timing estimation means C6, it is possible to calculate the reduction timing effective for NOx purification by estimating the state of the LNT catalyst 16 from both the fourth condition and the fifth condition.

  The reduction promotion means C7 includes a rich reduction means C9 that performs rich reduction with the LNT catalyst 16 while maintaining the air-fuel ratio rich, and a rich timer C10 that measures the time during which the rich reduction means C9 is performed. The rich of the rich reduction means C9 does not necessarily mean that the rich combustion is performed in the cylinder bore, but includes the amount of air supplied to the exhaust gas flowing into the LNT catalyst 16 and the amount of fuel (including the amount burned in the cylinder bore). )) Is close to the stoichiometric air-fuel ratio or a rich state where the fuel amount is greater than the stoichiometric air-fuel ratio.

The reduction end timing calculation means C8 determines that the NOx occlusion amount V _NOx calculated using the timing estimation parameters detected by the sensors S1 to S5 again after the reduction promotion means C7 performs rich reduction is predetermined. This is means for setting the reduction end timing when the storage amount Vx or less is reached. According to this, by calculating the reduction end timing and ending the reduction promotion means C7, it is possible to prevent the injection of excess fuel, and thus it is possible to suppress the deterioration of fuel consumption.

  The engine 1 of this embodiment is only required to have the injector 15 capable of performing multi-stage injection and to include the LNT catalyst 16 as a deNOx catalyst, and a known engine configuration can be used.

For example, this embodiment includes a so-called high pressure EGR system in which the EGR cooler 5a and the EGR valve 5b of the EGR system 5 are arranged on the upstream side of the turbocharger 6, but the EGR cooler 5a and the EGR valve 5b are connected to the turbocharger 6 It can also be replaced with a so-called low pressure EGR system disposed downstream. Further, a DOC (diesel oxidation catalyst) may be arranged on the upstream side of the DPF 17 of the post-processing device 10.

  Next, the operation of the engine 1 will be described with reference to the flowcharts of FIGS. First, when the engine 1 is started, each of the sensors S1 to S5 performs step S10 for detecting a timing estimation parameter. The timing estimation parameters are parameters including the pre-temperature Ta and the post-temperature Tb of the LNT catalyst 16, the pre-NOx concentration Ca and the post-NOx concentration Cb of the LNT catalyst 16, and the exhaust gas flow rate Qg.

Next, the temperature increase timing estimation means C4 that calculates the timing for increasing the temperature of the LNT catalyst 16 using the timing estimation parameter starts estimation of the temperature increase timing. First, as a first condition, step S20 is performed to determine whether or not the catalyst temperature _TLNT is equal to or lower than a predetermined activation temperature Tx.

Next, as a second condition, step S30 is performed to determine whether or not the calculated NOx storage amount _VNOx is equal to or greater than a predetermined determination storage amount Vx. In this embodiment, the NOx occlusion amount _{V NOx} is determined whether the determination storage amount Vx or more in step S30, instead, whether the NOx purification rate _{R NOx} calculated from the timing estimation parameter determination purification ratio Rx or less not You may perform the step which judges whether.

Next, as a third condition, step S40 is performed in which it is determined whether or not the estimated estimated fuel consumption deterioration rate R _FUEL is stable below a predetermined determination fuel consumption deterioration rate Ry. Since the exhaust temperature also varies depending on the traveling conditions during actual traveling, it is preferable to proceed to the next step after determining that the exhaust gas temperature has reached a certain level stably. Further, not only the exhaust temperature is estimated fuel efficiency rate R _FUEL after heating, so also contributes exhaust gas flow rate Qg, estimates an estimated fuel economy rate R _FUEL from the two by heating, if it is determined the stability Good.

  The temperature rise timing estimation unit C4 sets the temperature rise timing when step S20 of the first condition, step S30 of the second condition, and step S40 of the third condition are satisfied. If any of the first condition, the second condition, and the third condition is not satisfied, the process returns to step S10 again to estimate the temperature rise timing.

  Next, the catalyst temperature raising means C5 performs step S50 (catalyst temperature raising step) for raising the temperature of the LNT catalyst 16 by performing multistage injection control of the injector 15 at the temperature raising timing. At this time, the EGR system 5 is controlled to continuously supply EGR gas to the inlet manifold 4. Further, in order to achieve higher reduction efficiency, post-injection or exhaust injection for raising the temperature of the LNT catalyst 16 may be performed, and further, early rise by multistage injection after injection or injection timing feedback control. The temperature may be increased.

Next, each sensor S1-S5 performs step S60 which detects a timing estimation parameter again. Next, the reduction timing estimation means C6 that calculates the timing for promoting the reduction at the LNT catalyst 16 using the timing estimation parameter starts the estimation of the reduction timing. First, as a fourth condition, step S70 for determining whether or not the catalyst temperature _TLNT has reached the activation temperature Tx is performed. Next, as a fifth condition, the calculated estimated amount of reduction V _RE performs step S80 of determining whether a predetermined decision reducing the amount Vy more.

  The reduction timing estimation means C6 sets the timing when both the above-described fourth condition step S70 and the fifth condition step S80 are satisfied. If any of the fourth condition and the fifth condition is not satisfied, the process returns to step S50 again, the temperature of the LNT catalyst 16 is raised, and the estimation is performed again.

When the catalyst temperature T _LNT of the LNT catalyst 16 reaches the activation temperature Tx and the estimated reduction amount V _RE becomes equal to or higher than the determination reduction amount Vy in step S70 and step S80, the reduction promotion means C7 then moves the LNT catalyst. Step S90 (reduction promotion step) for performing rich reduction at 16 is performed.

In the reduction promoting step of step S90, as shown in FIG. 4, first, step S91 for calculating the maximum elapsed time t_max ([s]) is performed. The maximum age t_max is a calculated time to suppress the maintenance of unnecessary rich state, for example, a NOx occlusion amount V _NOx, may be calculated based on the estimated amount of reduction V _RE.

  Next, step S92 for starting the rich timer C10 is performed. Moreover, step S93 which starts the rich reduction | restoration means C9 simultaneously with starting of the rich timer C10 is performed.

  Next, as time elapses, the elapsed time t_rich ([s]) of the rich timer C10 increases every moment. Next, step S94 is performed to determine whether the elapsed time t_rich of the rich timer C10 is longer than a predetermined maximum elapsed time t_max. The maximum elapsed time t_max can be set to an arbitrary time. However, if the maximum elapsed time t_max is set to be relatively short, the waste of fuel and reducing agent used for rich reduction that occurs when the control for maintaining the rich state is performed for a long time. Release can be suppressed.

  If the elapsed time t_rich of the rich timer C10 is longer than the maximum elapsed time t_max in step S94, the process proceeds to step S96, and step S96 for ending the rich timer C10 is performed. Further, step S97 is performed to end the rich reduction means C9 simultaneously with the end of the rich timer C10.

  If the elapsed time t_rich of the rich timer C10 is equal to or shorter than the maximum elapsed time t_max in step S94, the process proceeds to step S96 and step S97 after passing through step S95 where the elapsed time t_rich of the rich timer C10 becomes zero.

When the above step S90 is completed, as shown in FIG. 3, next, step S100 for detecting the timing estimation parameter again is performed. Then, the reduction end timing calculating means C8, performs step S110 that the NOx occlusion amount V _NOx calculated to determine whether less than or equal to the determination storage amount Vx using the timing estimation parameters. In step S110, the rich reduction means C9 of step S90 is performed until the _NOx occlusion amount VNOx becomes equal to or less than the determined occlusion amount Vx, and this control method ends.

  According to this control method, the temperature of the LNT catalyst 16 is increased at the temperature increase timing calculated using the timing estimation parameter, and then the NOx of the LNT catalyst 16 is reduced at the reduction timing calculated using the redetected timing estimation parameter. Reduction can be promoted. Therefore, NOx can be purified while minimizing deterioration of fuel consumption even under low load conditions.

  Further, it is possible to always detect the timing estimation parameter and calculate the temperature rise timing and the reduction timing calculated from the timing estimation parameter. Furthermore, since the conventional configuration of the engine 1 can be used, there is no additional addition, and the effect can be obtained without generating additional costs.

The NOx occlusion amount V _NOx , the NOx purification rate R _NOx , the estimated fuel consumption deterioration rate R _FUEL , and the estimated reduction amount V _RE may be calculated using the timing estimation parameter, and the method described above It is not limited to.

Next, an internal combustion engine according to a second embodiment of the present invention will be described with reference to FIGS. The engine 20 includes a post-treatment device 21 as shown in FIG. 5 instead of the post-treatment device 10 of the engine 1 of the first embodiment, and the post-treatment device 21 includes a DOC (diesel oxidation catalyst). 22, a DPF 23, a urea SCR catalyst 24, and a urea water injection valve 25. Moreover, it is connected with each sensor S1-S5, and ECU (control apparatus) 26 which controls each apparatus is provided.

  As shown in FIG. 6, the ECU 26 includes urea water injection amount calculation means C21 and urea water injection means C22 as the reduction promotion means C20, and has conditions different from the conditions of the first embodiment. Reduction end timing calculation means C23 is provided.

  In the first embodiment, the first temperature sensor S1 and the second temperature sensor S2 arranged before and after the LNT catalyst 16 are arranged before and after the urea SCR catalyst 24 in this embodiment, and the LNT catalyst 16 The first NOx concentration sensor S3 and the second NOx concentration sensor S4 disposed before and after the urea SCR catalyst 24 are also disposed before and after the urea SCR catalyst 24. The values detected by the sensors S1 to S4 are the same as those in the first embodiment.

The urea water injection amount calculating means C21 is a means for calculating the injection amount Q _NH3 ([mm ³ ]) of urea water injected from the urea water injection valve 25, and the urea water injection amount Q _NH3 is stored in the stored NH. ₃ NH ₃ emissions and NH ₃ injection quantity obtained from the conversion amount and the _(ammonia), namely the determination purification rate injection amount obtained by Rx is a NOx purification rate of the target, which are inserted in the new urea SCR catalyst 24 Is calculated by adding the insufficient replenishment amount.

The stored NH ₃ release amount, NH ₃ conversion amount, and replenishment amount used in the urea water injection amount calculation means C21 are map values obtained from the test results, and are timing estimation parameters (for example, catalyst temperature T _LNT ). The value varies depending on Further, the urea injection amount calculation parameter for calculating the injection amount Q _NH3 in the urea water these values.

Urea water injection means C22 is from the urea water injection valve 25 to the urea SCR catalyst 24, the injection amount Q _NH3 calculated in the urea solution injection amount calculating means C21, a means for injecting the urea water.

The reduction end timing calculation means C23 determines again that the NOx purification rate R _NOx calculated using the timing estimation parameters detected by the sensors S1 to S5 again after the reduction promotion means C20 injects urea water. This is means for continuing the injection amount Q _NH3 of urea water when the purification rate Rx is reached. According to this, by calculating the reduction end timing and setting the optimal urea water injection amount _QNH3 , it is possible to suppress the injection of excess urea water.

  Next, a control method of the engine 20 according to the second embodiment of the present invention will be described with reference to the flowchart shown in FIG. In addition, about the process similar to the flowchart shown in FIG. 3, the same code | symbol is used and the description is abbreviate | omitted.

The method of this embodiment, as shown in FIG. 7, step S10~ to step S80, as a second condition for heating timing estimation unit C4, or calculated NOx purification rate _{R NOx} determination purification rate Rx less Except for performing step S200 for determining whether or not, it is substantially the same as the flowchart of the first embodiment shown in FIG.

  Then, when the reduction timing estimation means C6 estimates the reduction timing in step S70 and step S80, next, as shown in FIG. 7, step S210 for detecting the urea water injection amount calculation parameter is performed.

Next, the urea water injection amount calculation means C21 performs step S220 of calculating the urea water injection amount _QNH3 based on the urea water injection amount calculation parameter. Next, the urea water injection means C22 performs step S230 (urea water injection process) of injecting the urea water of the injection amount _QNH3 calculated in step S220 to the urea SCR catalyst 24.

Next, again, step S100 for detecting the timing estimation parameter is performed. Next, the reduction end timing calculation means C23 performs step S240 for determining whether or not the calculated NOx purification rate _RNOx has reached the judgment purification rate Rx. When the NOx purification rate R _NOx does not become the judgment purification rate Rx in step S240, the process returns to step S210 again. When the NOx purification rate _RNOx becomes the judgment purification rate Rx, the state at that time is continued, This control method is complete.

According to this control method, in a system using the urea SCR catalyst 24 as the deNOx catalyst, deterioration of fuel consumption can be minimized and NOx can be effectively reduced even under low load conditions. In addition, the urea water injection amount calculation parameter (NH ₃ storage amount, release amount, NH ₃ conversion amount, etc.), NOx purification rate, and estimated reduction amount are constantly calculated to calculate an effective reduction timing and reduction amount. Can do. In addition, the hardware configuration is conventional and there is no addition, and no additional cost is incurred.

Note that the calculation method of the urea water injection amount Q _NH3 is not limited to the above calculation method as long as it can be calculated from the urea water injection amount calculation parameter. In this embodiment, the urea water injection amount calculation parameter is the map value obtained from the test result. However, a sensor for detecting each value may be provided separately. Further, the urea water injection amount calculation parameter, for example, the storage amount of NH _3, NH ₃ from the conversion amount, can be expressed by a value obtained by subtracting the discharge amount and the NOx reduction amount of NH ₃ that slip amount and storage of NH ₃ You may calculate using.

  Since the internal combustion engine of the present invention can purify NOx by calculating an effective timing that does not deteriorate the fuel efficiency even at low load, it can be used particularly for vehicles such as trucks equipped with diesel engines. .

1,20 engine (internal combustion engine)
2 Engine body 3 Exhaust manifold 4 Inlet manifold 5 EGR system 6 Turbocharger 7 Air cleaner 8 Intercooler 9 Intake cooler 10, 21 Aftertreatment device 11 Fuel injection system 12 Fuel tank 13 Fuel pump 14 Common rail 15 Injector (fuel injection valve)
16 LNT catalyst (lean-NOx-trap catalyst, NOx occlusion reduction catalyst)
17, 23 DPF (Diesel particulate filter)
18 ECU (control device)
22 DOC (diesel oxidation catalyst)
24 Urea SCR catalyst (urea selective catalytic reduction catalyst)
25 Urea water injection valve (urea water injection valve)
C1 catalyst temperature detection means C2 NOx concentration detection means C3 exhaust gas flow rate detection means C4 temperature rise timing estimation means C5 catalyst temperature rise means C6 reduction timing estimation means C7, C20 reduction promotion means C8, C23 reduction end timing calculation means

Claims (6)

In an internal combustion engine comprising a fuel injection valve capable of multistage injection of fuel and a NOx purification catalyst provided in an exhaust passage,
A control device including a catalyst temperature detection means, a NOx concentration detection means, and an exhaust gas flow rate detection means,
The control device is
At the temperature rise timing calculated using the temperature estimation parameter including the temperature parameter detected by the catalyst temperature detection means, the NOx concentration parameter detected by the NOx concentration detection means, and the exhaust gas flow rate parameter detected by the exhaust gas flow rate detection means, Catalyst temperature raising means for raising the temperature of the NOx purification catalyst by performing multi-stage injection control on the fuel injection valve;
Reduction promotion means for promoting reduction of NOx by the NOx purification catalyst at a reduction timing calculated using the timing estimation parameter redetected after the temperature rise of the NOx purification catalyst by the catalyst temperature raising means. An internal combustion engine characterized by that. The control device is
A first condition in which the catalyst temperature of the NOx purification catalyst detected by the catalyst temperature detection means is lower than a predetermined activation temperature;
The NOx purification catalyst storage amount calculated using the timing estimation parameter is equal to or greater than a predetermined determination storage amount, or the NOx purification rate of the NOx purification catalyst calculated using the timing estimation parameter is a predetermined determination purification. A second condition that falls below the rate,
The estimated fuel consumption deterioration rate calculated from the timing estimation parameter and estimated from the fuel injection amount required to raise the catalyst temperature to the activation temperature is stabilized below a predetermined determination fuel consumption deterioration rate. Judging three conditions,
A temperature rise timing estimating means for setting the temperature rise timing when all of the first condition, the second condition, and the third condition are satisfied;
A fourth condition for the catalyst temperature detected by the catalyst temperature detecting means to reach the activation temperature after the catalyst temperature raising means;
Using the re-detected timing estimation parameter, a fifth condition is determined in which an estimated reduction amount estimated from the NOx reduction amount reduced by the NOx purification catalyst per time is equal to or greater than a predetermined determination reduction amount. And
2. The internal combustion engine according to claim 1, further comprising reduction timing estimation means for setting the reduction timing when both the fourth condition and the fifth condition are satisfied. Forming the NOx purification catalyst with an LNT catalyst;
The internal combustion engine according to claim 1 or 2, wherein the control device includes rich reduction means for maintaining the air-fuel ratio rich as the reduction promotion means. Forming the NOx purification catalyst with a urea SCR catalyst;
The internal combustion engine according to claim 1 or 2, wherein the control device includes urea water injection means for injecting urea water to the NOx purification catalyst as the reduction promoting means. In a control method for an internal combustion engine comprising a fuel injection valve capable of multistage injection of fuel and a NOx purification catalyst provided in an exhaust passage,
The temperature of the NOx purification catalyst is increased by performing multi-stage injection control of the fuel injection valve at a temperature rise timing calculated using a timing estimation parameter including a temperature parameter of the NOx purification catalyst, a NOx concentration parameter, and an exhaust gas flow rate parameter. Warm,
An internal combustion engine control method, comprising: promoting NOx reduction at the NOx purification catalyst at a reduction timing calculated using the timing estimation parameter detected again after the temperature of the NOx purification catalyst is increased. The temperature rise timing is
A first condition in which the catalyst temperature of the NOx purification catalyst is lower than a predetermined activation temperature;
The NOx purification catalyst storage amount calculated using the timing estimation parameter is equal to or greater than a predetermined determination storage amount, or the NOx purification rate of the NOx purification catalyst calculated using the timing estimation parameter is a predetermined determination purification. A second condition that falls below the rate,
A third condition in which an estimated fuel consumption deterioration rate obtained by estimating the fuel injection amount required to raise the catalyst temperature to the activation temperature using the timing estimation parameter is stabilized at a predetermined fuel consumption deterioration rate or less. When all of the above are satisfied,
The reduction timing is
A fourth condition in which the catalyst temperature detected after raising the temperature of the NOx purification catalyst reaches the activation temperature;
Using the re-detected timing estimation parameter, the estimated reduction amount obtained by estimating the reduction amount per hour of NOx reduced by the NOx purification catalyst satisfies both of the fifth condition that is equal to or greater than a predetermined determination reduction amount. The method for controlling an internal combustion engine according to claim 5, wherein