EXHAUST GAS PURIFICATION SYSTEM FOR INTERNAL COMBUSTION ENGINE, INTERNAL COMBUSTION ENGINE, AND EXHAUST GAS PURIFICATION METHOD FOR INTERNAL COMBUSTION ENGINE

Abstract

An exhaust gas purification system for an internal combustion engine includes an oxidation catalyst device on an upstream side in an exhaust passage of an internal combustion engine and a lean NOx trap catalyst device on a downstream side, a controller which controls the exhaust gas purification system is configured to, when a temperature-rising control of an exhaust gas in a regeneration control is performed to recover a purification ability of the exhaust gas purification system, perform a control that changes a measurement position of a control temperature which is a control amount of a feedback control in the temperature-rising control, according to an excess air ratio or an oxygen concentration of the exhaust gas passing through the exhaust passage.

Claims

1. An exhaust gas purification system for an internal combustion engine, which includes an oxidation catalyst device on an upstream side in an exhaust passage of an internal combustion engine and a lean NOx trap catalyst device on a downstream side, wherein a controller which controls the exhaust gas purification system is configured to, when a temperature-rising control of an exhaust gas in a regeneration control is performed to recover a purification ability of the exhaust gas purification system, perform a control that changes a measurement position of a control temperature which is a control amount of a feedback control in the temperature-rising control, according to an excess air ratio or an oxygen concentration of the exhaust gas passing through the exhaust passage.

2. The exhaust gas purification system for the internal combustion engine according to claim 1, the exhaust gas purification system comprising: a first temperature sensor which measures a first temperature relating to a temperature of the oxidation catalyst device; and a second temperature sensor which measures a second temperature relating to a temperature of the lean NOx trap catalyst device, wherein the controller is configured to, when the temperature-rising control of the exhaust gas in the regeneration control is performed to recover the purification ability of the exhaust gas purification system, perform a control such that the control temperature is set as the first temperature when the excess air ratio or the oxygen concentration of the exhaust gas passing through the exhaust passage is higher than an upper limit threshold set in advance, and the control temperature is set as the second temperature when the excess air ratio or the oxygen concentration of the exhaust gas passing through the exhaust passage is lower than a lower limit threshold set in advance.

3. The exhaust gas purification system for the internal combustion engine according to claim 2, wherein the controller is configured to, when the temperature-rising control of the exhaust gas in the regeneration control is performed to recover the purification ability of the exhaust gas purification system, perform a control such that a weight coefficient is set to be changed according to the excess air ratio or the oxygen concentration of the exhaust gas passing through the exhaust passage, and the control temperature is set to a weighted average value of the first temperature and the second temperature obtained using the weight coefficient, when the excess air ratio or the oxygen concentration of the exhaust gas passing through the exhaust passage is equal to or less than the upper limit threshold and equal to or more than the lower limit threshold.

4. An internal combustion engine comprising: the exhaust gas purification system for the internal combustion engine according to claim 1.

5. An exhaust gas purification method for an internal combustion engine having an exhaust gas purification system for the internal combustion engine, which includes an oxidation catalyst device on an upstream side and a lean NOx trap catalyst device on a downstream side in an exhaust passage of the internal combustion engine, the method comprising: changing, when a temperature-rising control of an exhaust gas in a regeneration control is performed to recover a purification ability of the exhaust gas purification system, a measurement position of a control temperature which is a control amount of a feedback control in the temperature-rising control, according to an excess air ratio or an oxygen concentration of the exhaust gas passing through the exhaust passage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a view schematically illustrating a configuration of an internal combustion engine which includes an exhaust gas purification system for an internal combustion engine of an embodiment according to the present invention.

[0023] FIG. 2 is a view schematically illustrating a relation between a weight coefficient which is a weight ratio of a first temperature to a second temperature and an excess air ratio of the exhaust gas.

DESCRIPTION OF EMBODIMENTS

[0024] Hereinafter, an exhaust gas purification system for an internal combustion engine, an internal combustion engine, and an exhaust gas purification method for the internal combustion engine in the embodiment according to the present invention will be described with reference to the drawings. Incidentally, the internal combustion engine of the embodiment according to the present invention includes an exhaust gas purification system for an internal combustion engine of the embodiment according to the present invention, so as to make the same operational effect as an operational effect made by the exhaust gas purification system for the internal combustion engine (to be described later).

[0025] First, an internal combustion engine (hereinafter, engine) 10 and an exhaust gas purification system 20 of the internal combustion engine of the embodiment according to the present invention will be described with reference to FIG. 1. The engine 10 are provided with a fuel injection device 11, an intake valve 12, and an exhaust valve 13 facing a cylinder 10a, and further with an intake passage 14 communicating with the intake valve 12, an exhaust passage 15 communicating with the exhaust valve 13, and an EGR passage 16.

[0026] The intake passage 14 is provided with an air cleaner 17, a compressor 18b of a turbocharger (turbo type supercharger) 18, an intercooler 19a, and an intake throttle valve 19b in order from the upstream side. Further, the exhaust passage 15 is provided with a turbine 18a of the turbocharger 18 and an exhaust gas purification device 21 in order from the upstream side. In addition, the EGR passage 16 is provided by connecting the intake passage 14 on the downstream from the compressor 18b with the exhaust passage 15 on the upstream from the turbine 18a. The EGR passage 16 is provided with an EGR cooler 16a, an EGR valve 16b in order from the upstream side.

[0027] As needed, new air A guided from the atmosphere is fed to the cylinder (cylinder) 10a through the intake valve 12 in association with the exhaust gas (EGR gas) Ge flowing in the intake passage 14 from the EGR passage 16. In addition, the exhaust gas G generated in the cylinder 10a flows out to the exhaust passage 15 through the exhaust valve 13. Some of the exhaust gas G flows to the EGR passage 16 as the EGR gas Ge. The remaining exhaust gas Ga (=GGe) flows in the exhaust gas purification device 21 through the turbine 18a, and after being purified, is released as the purified exhaust gas Gc into the atmosphere through a muffler (not illustrated) and a tail pipe (not illustrated).

[0028] In the configuration of FIG. 1, the exhaust gas purification device 21 of the exhaust gas purification system 20 includes catalyst devices such as an oxidation catalyst (DOC) device 22, a particulate collection device (CSF) 23, a lean NOx trap catalyst device (LNT) 24, and a subsequent-stage oxidation catalyst (DOC) device 25. Incidentally, the catalyst devices may be provided in the exhaust gas purification device 20 in the reverse order to the arrangement order of the particulate collection device 23 and the lean NOx trap catalyst device 24, that is, in order of the oxidation catalyst device 22, the lean NOx trap catalyst device 24, the particulate collection device 23, and the subsequent-stage oxidation catalyst device 25.

[0029] The fuel injection device 26 which injects the unburned fuel into the exhaust passage 15 is arranged in the exhaust passage 15 on the upstream side of the oxidation catalyst device 22. The unburned fuel is injected into the exhaust passage 15 at the time of the temperature-rising control of the exhaust gas such as a NOx regeneration control on the lean NOx trap catalyst device 24, a sulfur purge control on the oxidation catalyst device 22 and the lean NOx trap catalyst device 24, and a PM regeneration control on the particulate collection device 23. By the injection, the hydrocarbon which is an unburned fuel is oxidized by the oxidation catalyst device 22 and the like, and by oxidation heat, the temperature of the exhaust gas Ga is increased. When the temperature of the exhaust gas Ga is increased or the temperature of the hydrocarbon is increased by the combustion in the catalyst devices 22, 23, and 24, the temperature of the lean NOx trap catalyst device 24 is increased to a temperature range of the release and the reduction of the occlusion NOx, the temperature of the particulate collection device 23 is increased such a temperature range that can realize the PM combustion, or the temperatures of the oxidation catalyst device 22 and the lean NOx trap catalyst device 24 are increased to such a temperature range that can realize desulfurization. In this manner, the exhaust gas purification ability of the catalyst devices 22, 23, and 24 are recovered.

[0030] The first temperature sensor 31 which detects the temperature TDOC of the exhaust gas Ga flowing in the oxidation catalyst device 22 is arranged in the exhaust passage 15 on the upstream side (inlet side) of the oxidation catalyst device 22. In addition, the second temperature sensor 32 which detects a temperature TLNT of the exhaust gas Ga flowing in the lean NOx trap catalyst device 24 is arranged in the exhaust passage 15 on the upstream side of the lean NOx trap catalyst device 24. In addition, the third temperature sensor 33 which detects the temperature TCSF of the exhaust gas Ga flowing out from the oxidation catalyst device 22 to flow in the particulate collection device 23 is arranged in the exhaust passage IS between the oxidation catalyst device 22 and the particulate collection device 23.

[0031] A -sensor 34 which measures the excess air ratio of the exhaust gas Ga or an oxygen concentration Co or an oxygen concentration sensor (not illustrated) is arranged on the downstream side of the exhaust gas purification device 20. The -sensor or the oxygen concentration sensor may be arranged on the upstream side of the exhaust gas purification device 20, or may be arranged in an exhaust manifold.

[0032] Herein, the temperature TDOC detected by the first temperature sensor 31 is set as a first temperature T1 relating to the oxidation catalyst device 22. The temperature TLNT detected by the second temperature sensor 32 is set as a second temperature T2 relating to the lean NOx trap catalyst device 24. The temperature TCSF detected by the third temperature sensor 33 is set as a third temperature T3 relating to the particulate collection device 23.

[0033] Incidentally, the average value of the temperatures detected by the temperature sensors before and after the oxidation catalyst device 22 may be set as the first temperature T1. The average value of the temperatures detected by the temperature sensors before and after the lean NOx trap catalyst device 24 may be set as the second temperature T2. In addition, the average value of the temperatures detected by the temperature sensors before and after the particulate collection device 23 may be set as the third temperature. Further, instead of the exhaust gas temperatures on the upstream side of the catalyst devices 22, 23, and 24, the exhaust gas temperatures on the respective downstream sides may be used.

[0034] A controller 40 is provided which controls the exhaust gas purification system 20 of the internal combustion engine of the present invention. Normally, the controller 40 is configured to be embedded in an engine control unit (ECU) which controls the whole operating condition of the engine 10, but may be configured separately.

[0035] In the exhaust gas purification system 20 of the internal combustion engine of the embodiment according to the present invention, when the temperature-rising control of the exhaust gas Ga in the regeneration control is performed for recovering the purification ability of the exhaust gas purification system 20, the controller 40 which controls the exhaust gas purification system 20 performs a control to change the measurement position of the control temperature Tc which is the control amount of the feedback control in the temperature-rising control, according to the excess air ratio or the oxygen concentration Co of the exhaust gas G passing through the exhaust passage 15.

[0036] With the configuration, at the time of the temperature-rising control of the exhaust gas Ga for the regeneration processing to recover the purification ability of the catalyst devices 22 to 25 included in the exhaust gas purification device 20, the amount of the unburned fuel (hydrocarbon) injected by the fuel injection device 26 is adjusted such that the control temperature Tc becomes a target temperature Tm set according to each regeneration processing. The measurement position of the control temperature Tc is changed according to the excess air ratio or the oxygen concentration Co of the exhaust gas Ga. More specifically, the measurement position is changed to the measurement temperature which reflects best the temperature (any one of T1, T2, and T3) of the catalyst device (any one of 22, 23, and 24) in which the heat generation amount is largest at that time in the exhaust passage and the temperature is increased most.

[0037] That is, when the temperature-rising control of the exhaust gas Ga in the regeneration control is performed for recovering the purification ability of the exhaust gas purification system 20, the controller 40 performs a control such that the control temperature Tc is set as the first temperature T1 when the excess air ratio or the oxygen concentration Co of the exhaust gas Ga passing through the exhaust passage 15 is higher than an upper limit threshold A1 set in advance, and the control temperature Tc is set as the second temperature T2 when the excess air ratio or the oxygen concentration Co is lower than a lower limit threshold A2 set in advance. Incidentally, the upper limit threshold A1 and the lower limit threshold A2 are set in advance by the experiments and the like, and are stored in the controller 40. In addition, when the control is simplified, the upper limit threshold A1 and the lower limit threshold A2 may be set the same as each other, and in this case, the first temperature T1 and the second temperature T2 preferably become the substantially same value.

[0038] In this manner, when the heat generation amount of the oxidation catalyst device 22 is larger than that of the lean NOx trap catalyst device 24, the excess air ratio and the oxygen concentration Co of the exhaust gas Ga is larger than the upper limit threshold A1. Thus, the first temperature T1 relating to the oxidation catalyst device 22 is set as the control temperature Tc, and the temperature-rising control can be performed at the first temperature T1 of the oxidation catalyst device 22. In addition, when the heat generation amount of the lean NOx trap catalyst device 24 is larger than that of the oxidation catalyst device 22, the excess air ratio and the oxygen concentration Co of the exhaust gas Ga is lower than the lower limit threshold A2 set in advance. Thus, the second temperature T2 relating to the lean NOx trap catalyst device 24 is set as the control temperature Tc, and the temperature-rising control can be performed at the second temperature T2 of the lean NOx trap catalyst device 24. Therefore, the temperature-rising control of the exhaust gas Ga can be optimized with the relatively simple control.

[0039] When the temperature-rising control of the exhaust gas Ga in the regeneration control is performed to recover the purification ability of the exhaust gas purification system 20, when the excess air ratio or the oxygen concentration Co of the exhaust gas Ga passing through the exhaust passage 15 is equal to or less than the upper limit threshold A1 and equal to or more than the lower limit threshold A2, the controller 40 performs a control to set a weight coefficient to be changed according to the excess air ratio or the oxygen concentration Co, and to set the control temperature Tc to a weighted average value T12 of the first temperature T1 and the second temperature T2 using the weight coefficient . In this manner, the temperature-rising control can be performed while a drastic change due to the switch of the control temperature Tc with respect to the change of the excess air ratio or the oxygen concentration Co is avoided.

[0040] The weight coefficient can be determined such that, for example, T12=T1+T2(1), or T12=(T1+T2)/(1+). The weight coefficient is set in advance by the experiments and the like with respect to the excess air ratio , and is stored in the controller 40. In FIG. 2, the weight coefficient is set to be increased as the excess air ratio is smaller, and to be decreased as the excess air ratio is larger. Incidentally, in FIG. 2, a correlation between the excess air ratio and the weight coefficient is a linear relation falling downward to the right. However, the linear relation of FIG. 2 is illustrated as an example, and a curvilinear relation convex to a lower left side or a curvilinear relation convex to an upper right side may be adopted.

[0041] Incidentally, on the basis of the oxygen concentration of the exhaust gas Ga, in a case where the number of the temperatures of the catalyst device as a maximum heat generation amount is three or more, for example, in the case of TDOC, TLNT, and TCSF, the number of the weight coefficient is increased, and a temperature as the control temperature Tc is obtained as a weighted average. For example, the weight coefficients and are set in advance with respect to the oxygen concentration of the exhaust gas Ga, and the control temperature Tc is set such that Tc=TDOC+TLNT+TCSF(1).

[0042] Next, the exhaust gas purification method for the internal combustion engine of the embodiment according to the present invention will be described. This method is an exhaust gas purification method for the internal combustion engine in the above-described exhaust gas purification system 20 of the internal combustion engine. In the method, when the temperature-rising control of the exhaust gas Ga in the regeneration control is performed to recover the purification ability of the exhaust gas purification system 20, the measurement position of the control temperature Tc which is the control amount of the feedback control in the temperature-rising control is changed according to the excess air ratio or the oxygen concentration Co of the exhaust gas Ga passing through the exhaust passage 15.

[0043] According to the exhaust gas purification system 20 of the internal combustion engine, the internal combustion engine 10, and the exhaust gas purification method for the internal combustion engine which are described above, at time of the temperature-rising control of the exhaust gas Ga for performing the regeneration processing on the catalyst devices 22, 23, and 24 included in the exhaust gas purification device 21, the measurement position of the control temperature Tc which is the control amount of the feedback control in the temperature-rising control, that is, the control temperature Tc to be the target temperature Tm is changed and set in consideration of the excess air ratio or the oxygen concentration Co of the exhaust gas Ga. and more specifically, the control temperature Tc is set to the temperatures T1, T2, and T3 relating to the catalyst devices 22, 23, and 24 in which the heat generation amount is largest at that time in the exhaust gas purification system 20 and the temperature is increased most, thereby optimizing the temperature-rising control of the exhaust gas Ga. Therefore, it is possible to avoid a lack of temperature increment of each of the catalyst devices 22, 23, and 24, an overshooting at the time of increasing a temperature, heat degradation of the catalyst, and erosion of the catalyst, and it is possible to perform the regeneration processing reliably.

REFERENCE SIGNS LIST

[0044] 10 engine (internal combustion engine) [0045] 11 fuel injection device [0046] 15 exhaust passage [0047] 20 exhaust gas purification system [0048] 21 exhaust gas purification device [0049] 22 oxidation catalyst (DOC) device [0050] 23 particulate collection device [0051] 24 selective reduction catalyst (SCR) device [0052] 25 subsequent-stage oxidation catalyst (DOC) device [0053] 26 fuel injection device [0054] 31 first temperature sensor [0055] 32 second temperature sensor [0056] 33 third temperature sensor [0057] 34 -sensor [0058] 40 controller [0059] A new air [0060] G generated exhaust gas [0061] Ga exhaust gas passing through exhaust gas purification device [0062] Gc purified exhaust gas [0063] Ge EGR gas