JP2005016396A - Catalyst warming-up system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst warming-up system of an internal combustion engine, in which even when atmospheric pressure surrounding the internal combustion engine is reduced, an exhaust-emission catalyst is properly warmed up to suppress discharge of exhaust gas to the outside without being properly purified by the catalyst. <P>SOLUTION: In the exhaust-emission control system of an internal combustion engine having an exhaust-emission control catalyst in a discharge gas passage, an intake-air flow controller for determining an intake-air flow to the engine on the basis of operation condition of the engine, an atmospheric pressure detector for detecting atmospheric pressure, and an intake-air flow correction means (S103-S106) are provided. In warming-up time of the catalyst, the intake-air flow correction means increase an intake-air flow determined by the intake-air controller in correspondence with decrease in the atmospheric pressure detected by the atmospheric-pressure detector. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst warm-up system for warming up an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine.
[0002]
[Prior art]
An NOx storage reduction catalyst that stores NOx and reduces the stored NOx in the presence of a reducing agent in order to purify NOx contained in exhaust gas discharged from an internal combustion engine, particularly an internal combustion engine that performs lean combustion (hereinafter referred to as NOx catalyst). An exhaust purification catalyst such as “NOx catalyst” is provided in the exhaust passage. However, in order for the exhaust purification catalyst to exhibit its purification ability efficiently, the temperature of the exhaust purification catalyst needs to be equal to or higher than a predetermined activation temperature. In particular, when the internal combustion engine is cold-started, the temperature of the exhaust purification catalyst is reduced to the same level as the air temperature. Therefore, if the temperature of the exhaust purification catalyst is not sufficiently raised to the activation temperature, the purification is sufficiently performed. Exhaust that has not been performed is discharged to the outside air.
[0003]
Therefore, a technique is known in which the temperature of the exhaust purification catalyst is set to the activation temperature by adjusting the fuel injection amount and ignition timing in the internal combustion engine to increase the exhaust temperature flowing into the exhaust purification catalyst.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2-102337
[Patent Document 2]
Japanese Patent Laid-Open No. 3-78544
[Patent Document 3]
JP-A-63-124865
[Patent Document 4]
JP-A-3-57879
[0005]
[Problems to be solved by the invention]
Here, when the atmospheric pressure decreases in an environment where the internal combustion engine is placed, for example, when a vehicle equipped with the internal combustion engine moves from a low altitude land to a high land, the air density decreases, The amount of air sucked into the engine decreases, and it becomes difficult to sufficiently warm up the exhaust purification catalyst. If the exhaust purification catalyst is not warmed up sufficiently, exhaust purification is not performed well.
[0006]
The present invention has been made in view of the above-described problems, and even when the atmospheric pressure at which the internal combustion engine is placed decreases, the exhaust purification catalyst is sufficiently warmed up and sufficiently purified by the exhaust purification catalyst. It is an object of the present invention to provide a catalyst warm-up system for an internal combustion engine that suppresses exhaust gas not being discharged to the outside air.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention focuses on fluctuations in atmospheric pressure at which an internal combustion engine is placed. When the atmospheric pressure at which the internal combustion engine is placed fluctuates, the density of the air sucked into the combustion chamber of the internal combustion engine fluctuates.For example, even if the intake throttle valve of the internal combustion engine opens at a predetermined opening for a predetermined time, Actually, the intake air amount to the internal combustion engine becomes an amount different from the original air amount, the combustion state in the combustion chamber does not become the originally assumed state, and the exhaust purification catalyst may not be sufficiently warmed up. Because there is.
[0008]
Therefore, in a catalyst warm-up system for an internal combustion engine that is provided in an exhaust passage of the internal combustion engine and warms up an exhaust purification catalyst that purifies exhaust gas, it is provided in the intake passage of the internal combustion engine and is based on the operating state of the internal combustion engine. The intake air amount control means for determining the intake air amount to the internal combustion engine, the atmospheric pressure detection means for detecting the atmospheric pressure, and the atmospheric pressure detection means when the exhaust purification catalyst is warmed up. Intake air amount correction means for performing correction to increase the intake air amount determined by the intake air amount control means as the air pressure decreases.
[0009]
In the internal combustion engine, fuel is combusted according to the amount of intake air. Therefore, as the amount of intake air increases, the amount of fuel used for combustion increases, the exhaust temperature rises, and an exhaust passage is provided. The temperature of the exhaust purification catalyst also gradually increases.
[0010]
Here, the intake air amount control means determines the intake air amount to the internal combustion engine based on the operating condition such as the warm-up condition of the exhaust purification catalyst and the engine output torque required for the internal combustion engine. That is, the intake air amount control means determines the intake air amount to the internal combustion engine based on the warm-up condition of the exhaust purification catalyst and the operating state of the internal combustion engine, and the fuel corresponding to the intake air amount is combusted in the internal combustion engine. By being provided, it becomes possible to set the exhaust temperature to a temperature necessary for warming up the exhaust purification catalyst or to exhibit the engine output torque required for the internal combustion engine.
[0011]
However, the density of air sucked into the internal combustion engine varies depending on the atmospheric pressure at which the internal combustion engine is placed. That is, the air density decreases as the atmospheric pressure decreases, and conversely, the air density increases as the atmospheric pressure increases. For example, the density of air taken into the internal combustion engine differs between when the vehicle equipped with the internal combustion engine is in a low altitude and when the vehicle is in a high altitude. The density of air taken into the internal combustion engine varies depending on the climate in which the internal combustion engine is placed. Therefore, even the intake air amount determined by the intake air amount control means based on the warm-up condition of the exhaust purification catalyst and the operating state of the internal combustion engine is originally required depending on the atmospheric pressure at which the internal combustion engine is placed. There is a possibility that it differs from the intake air amount. In particular, when the atmospheric pressure at which the internal combustion engine is placed decreases, the actual intake air amount to the internal combustion engine decreases, so the exhaust temperature decreases, and the exhaust purification catalyst is sufficiently warmed when the exhaust purification catalyst is warmed up. It becomes difficult to work.
[0012]
Therefore, when the exhaust purification catalyst is warmed up, the intake air amount correction means corrects the intake air amount to the internal combustion engine based on the atmospheric pressure at which the internal combustion engine is placed, so that the exhaust purification catalyst originally warms up. The amount of intake air used to create the exhaust temperature necessary for the machine. That is, the intake air amount correcting means performs a correction to increase the intake air amount determined by the intake air amount control means as the atmospheric pressure at which the internal combustion engine is placed decreases, and as the atmospheric pressure at which the internal combustion engine is placed increases. By performing the correction for reducing the intake air amount determined by the intake air amount control means, the influence of the fluctuation of the atmospheric pressure where the internal combustion engine is placed on the warm-up of the exhaust purification catalyst is suppressed.
[0013]
As a result, even when the atmospheric pressure at which the internal combustion engine is placed decreases, the exhaust purification catalyst is sufficiently warmed up and the exhaust gas that has not been sufficiently purified by the exhaust purification catalyst is prevented from being released to the outside air. It becomes possible to do.
[0014]
Further, when warming up the exhaust purification catalyst, it is preferable to correct the amount of intake air to the internal combustion engine based on the temperature of the exhaust purification catalyst. When the temperature of the exhaust purification catalyst is relatively low, it is preferable that the temperature of the exhaust gas flowing into the exhaust purification catalyst is high. However, the temperature of the exhaust purification catalyst is also high just before the warm-up of the exhaust purification catalyst proceeds and the warm-up is completed. When the exhaust gas flows in, the temperature of the exhaust purification catalyst rises excessively, and the exhaust purification catalyst may be thermally deteriorated.
[0015]
Therefore, the catalyst warm-up system for the internal combustion engine described above further includes catalyst temperature estimation means for estimating the temperature of the exhaust purification catalyst. The intake air amount correcting means detects the atmospheric pressure detected by the atmospheric pressure detecting means as the temperature of the exhaust purifying catalyst estimated by the catalyst temperature estimating means rises when the exhaust purifying catalyst is warmed up. Correction is performed to reduce the amount of intake air corrected according to the atmospheric pressure.
[0016]
As a result, the amount of intake air to the internal combustion engine is corrected based on the temperature of the exhaust purification catalyst in addition to the atmospheric pressure at which the internal combustion engine is placed. Is sucked into the internal combustion engine, and the exhaust purification catalyst is sufficiently warmed up. Further, an excessive temperature rise of the exhaust purification catalyst is avoided.
[0017]
Here, as the intake air amount correction means in the catalyst warm-up system of the internal combustion engine up to the foregoing, the internal combustion engine is increased by increasing the flow rate of the intake air flowing through the intake passage of the internal combustion engine when the exhaust purification catalyst is warmed up. Means for increasing the amount of intake air into the air. That is, by increasing the flow rate of intake air flowing through the intake passage, the intake air amount into the combustion chamber of the internal combustion engine per unit time is increased, and the actual intake air that is finally sucked into the combustion chamber of the internal combustion engine By setting the amount to be the amount of intake air that should be originally, a decrease in air density due to a decrease in atmospheric pressure in which the internal combustion engine is placed is compensated.
[0018]
For example, when the flow rate of the intake passage is adjusted by adjusting the opening of the intake throttle valve provided in the intake passage, the intake throttle valve corresponding to the intake air amount determined by the intake air amount control means is adjusted. By increasing the opening degree further than the opening degree, the flow rate of the intake air flowing through the intake passage is increased. In addition, when an idle speed control device (hereinafter referred to as “ISC”) is provided in parallel with the intake throttle valve, the opening of the ISC valve in the ISC is further increased from the opening that should be intended. As a result, the flow rate of the intake air flowing through the intake passage is increased.
[0019]
Further, the intake air amount correcting means includes means for increasing the intake air amount to the internal combustion engine by increasing the engine speed of the internal combustion engine when the exhaust purification catalyst is warmed up. That is, by increasing the engine rotation speed of the internal combustion engine, the amount of intake air into the combustion chamber of the internal combustion engine per unit time is increased, and the actual intake air amount finally sucked into the combustion chamber of the internal combustion engine is reduced. By taking the intake air amount that should be originally intended, a decrease in air density due to a decrease in atmospheric pressure in which the internal combustion engine is placed is compensated. For example, when the ISC is provided, the idle rotation speed is increased in the ISC.
[0020]
Here, when warming up the exhaust purification catalyst, it is possible to sufficiently warm up the exhaust purification catalyst by raising the exhaust temperature. However, when the correction for increasing the intake air amount is performed by the intake air amount correction means, the flow rate of the intake air flowing through the intake passage and the engine rotational speed of the internal combustion engine may increase, and noise may be generated accordingly. Therefore, when the correction by the intake air amount correction means is performed, the ignition timing in the internal combustion engine when the exhaust purification catalyst is warmed up is delayed based on at least the atmospheric pressure detected by the atmospheric pressure detection means. Move to the corner.
[0021]
By shifting the ignition timing of the internal combustion engine to the retard side, the combustion energy of the fuel provided to the engine output of the internal combustion engine is reduced, so that the exhaust temperature rises. Therefore, since the temperature of the exhaust purification catalyst rises by shifting the ignition timing to the retarded angle side, correction is performed to increase the intake air amount by the intake air amount correction means, and an increase in the flow rate of intake air flowing through the intake passage or internal combustion The increase amount of the engine rotation speed of the engine can be suppressed, and noise can be suppressed. In addition, the amount of shift of the ignition timing to the retarded angle side is based on the atmospheric pressure at which the internal combustion engine is placed, so that it is more appropriate for the change in atmospheric pressure while taking into account the effect on the operating state of the internal combustion engine. It becomes possible to make it into quantity. Furthermore, the shift amount of the ignition timing to the retard side may be determined based on the temperature increase of the exhaust purification catalyst when the exhaust purification catalyst is warmed up. As a result, the ignition timing is more suitable for warming up the exhaust purification catalyst, and the exhaust purification catalyst is sufficiently warmed up.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
Here, an embodiment of a catalyst warm-up system for an internal combustion engine according to the present invention will be described based on the drawings. FIG. 1 is a block diagram showing a schematic configuration of a catalyst warm-up system to which the present invention is applied, an internal combustion engine 1 including the catalyst warm-up system, and a control system thereof.
[0023]
The internal combustion engine 1 has four cylinders 2 and includes a fuel injection valve 11 that injects fuel into the intake port 1a of each cylinder 2. The fuel injection valve 11 is connected to a pressure accumulation chamber 10 that accumulates fuel at a predetermined pressure. The cylinder 2 is provided with a spark plug 3 for igniting the air-fuel mixture.
[0024]
Next, an intake branch pipe 4 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 4 communicates with a combustion chamber of the cylinder 2 via an intake port 1a. Further, the intake branch pipe 4 is connected to an intake pipe 5, and an intake throttle valve 6 for adjusting the flow rate of intake air flowing through the intake pipe 5 is provided in the middle of the intake pipe 5. The intake throttle valve 6 is driven by an actuator 7 to adjust its opening.
[0025]
Further, in parallel with the intake throttle valve 6, an ISC 9 that adjusts the engine speed during idling of the internal combustion engine 1 is provided. The ISC 9 includes an ISC passage 9a that connects the intake pipe 5 on the upstream side of the intake throttle valve 6 and the intake pipe 5 on the downstream side, and an ISC valve 9b that adjusts the flow rate of intake air flowing through the ISC passage 9a. Further, an air flow meter 8 for detecting the amount of intake air flowing through the intake pipe 5 is provided in the intake pipe 5 upstream of the connection portion between the ISC passage 9 a and the intake pipe 5.
[0026]
On the other hand, an exhaust branch pipe 12 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 12 communicates with the combustion chamber of the cylinder 2 via the exhaust port 1b. Further, the exhaust branch pipe 12 is connected to an exhaust pipe 13, and this exhaust pipe 13 is connected to a muffler (not shown) downstream. In the middle of the exhaust pipe 13, there is provided a NOx catalyst 14 that stores and reduces NOx in the exhaust discharged from the internal combustion engine 1 to purify NOx in the exhaust.
[0027]
Here, the fuel injection valve 11, the actuator 7 that drives the intake throttle valve 6, and the ISC valve 9 are opened and closed by a control signal from an electronic control unit (hereinafter referred to as “ECU”) 20. Further, the ECU 20 is electrically connected to the air flow meter 8, the crank position sensor 21, the coolant temperature sensor 22, and the accelerator opening sensor 23, respectively, and the intake air amount, the rotation angle of the crankshaft of the internal combustion engine 1, the internal combustion engine The cooling water temperature and the accelerator opening of the engine 1 are detected.
[0028]
An exhaust temperature sensor 24 is provided in the exhaust pipe 13 upstream of the NOx catalyst 14. The exhaust gas temperature sensor 24 is electrically connected to the ECU 20 and detects the temperature of the exhaust gas flowing into the NOx catalyst 14. Further, the ECU 20 is electrically connected to the atmospheric pressure sensor 25 and detects the atmospheric pressure at which the internal combustion engine 1 is placed.
[0029]
Here, in order for NOx in the exhaust gas to be purified by the NOx catalyst 14, the temperature of the NOx catalyst 14 needs to rise to the activation temperature. Then, it is preferable to sufficiently warm up the catalyst that raises the temperature of the NOx catalyst 14 to the activation temperature. This is because if the NOx catalyst 14 is not sufficiently warmed up, the purification ability of the NOx catalyst 14 is reduced, so that the NOx purification by the NOx catalyst 14 is not performed efficiently, and the emission deteriorates.
[0030]
The NOx catalyst 14 is warmed up by allowing high-temperature exhaust to flow into the NOx catalyst 14. However, as the atmospheric pressure at which the internal combustion engine 1 is placed decreases, the density of the intake air drawn into the combustion chamber of the internal combustion engine 1 through the intake pipe 5 and the intake branch pipe 4 decreases. As a result, the amount of fuel injected from the fuel injection valve 10 decreases, so that the exhaust temperature decreases as compared to the case where the atmospheric pressure in which the internal combustion engine 1 is placed is relatively high. As a result, the NOx catalyst 14 is not sufficiently warmed up, and the emission may be deteriorated.
[0031]
Therefore, control for sufficiently warming up the NOx catalyst 14 (hereinafter referred to as “catalyst warm-up control”) regardless of fluctuations in the atmospheric pressure at which the internal combustion engine 1 is placed will be described with reference to FIG. FIG. 2 is a flowchart showing catalyst warm-up control. The catalyst warm-up control is executed by the ECU 20. In the present embodiment, the NOx catalyst 14 is warmed up by correcting the flow rate of air flowing through the ISC passage 9a (hereinafter referred to as “ISC flow rate”) in the internal combustion engine 1 that is in an idle operation state when the catalyst is warmed up. Plan. Details will be described below.
[0032]
First, in S101, the atmospheric pressure at which the internal combustion engine 1 is placed is detected by the atmospheric pressure sensor 25. When the process of S101 ends, the process proceeds to S102.
[0033]
In S102, the temperature of the NOx catalyst 14 is detected based on the temperature of the exhaust gas flowing into the NOx catalyst 14 detected by the exhaust temperature sensor 24. For example, a map of the temperature of the NOx catalyst 14 using the exhaust gas temperature detected by the exhaust gas temperature sensor 24 as a parameter is stored in the ROM in the ECU 20, and the temperature of the NOx catalyst 14 is detected by accessing the map. The When the process of S102 ends, the process proceeds to S103.
[0034]
In S103, an atmospheric pressure correction coefficient for ISC flow rate (hereinafter referred to as “kqcal”) is calculated based on the atmospheric pressure detected in S101. Specifically, kqcal is calculated based on the graph shown in FIG. FIG. 3 is a graph showing the relationship between the variation rate of the atmospheric pressure in which the internal combustion engine 1 is placed with respect to the reference atmospheric pressure, and kqcal.
[0035]
The horizontal axis of FIG. 3 is the atmospheric pressure fluctuation rate, and represents the fluctuation rate of the atmospheric pressure detected by the atmospheric pressure sensor 25 that is the atmospheric pressure where the internal combustion engine 1 is placed with respect to the reference atmospheric pressure. In the present embodiment, the reference atmospheric pressure is an atmospheric pressure at 0 m above sea level. Therefore, when the atmospheric pressure fluctuation rate is 1, the altitude at which the internal combustion engine 1 is placed is 0 m above sea level, and as the value becomes smaller than 1, the altitude at which the internal combustion engine 1 is placed increases. Moreover, the vertical axis | shaft of FIG. 3 represents kqcal. As shown in FIG. 3, the value of kqcal increases as the atmospheric pressure at which the internal combustion engine 1 is placed decreases, that is, as the altitude at which the internal combustion engine 1 is placed increases. When the atmospheric fluctuation rate is 1, that is, when the atmospheric pressure in which the internal combustion engine 1 is placed is the reference atmospheric pressure, the value of kqcal is 0. When the process of S103 ends, the process proceeds to S104.
[0036]
In S104, an ISC flow rate catalyst temperature correction coefficient (hereinafter referred to as “kcattemp”) is calculated based on the temperature of the NOx catalyst 14 detected in S102. Specifically, kcattemp is calculated based on the graph shown in FIG. FIG. 4 is a graph showing the relationship between the temperature of the NOx catalyst 14 and kcattemp.
[0037]
The horizontal axis of FIG. 4 represents the temperature of the NOx catalyst 14, and the vertical axis represents kcattemp. Here, when the temperature of the NOx catalyst 14 is equal to or lower than T1, the value of kcattemp is 1 at the upper limit. However, when the temperature of the NOx catalyst 14 falls within the range from T1 to T2, the temperature of the NOx catalyst 14 is As the value increases, the value of kcattemp decreases. When the temperature of the NOx catalyst 14 becomes equal to or higher than T2, the value of kcattemp becomes zero. Here, the temperature T2 is the minimum temperature of the NOx 14 for determining that the warming up of the NOx catalyst 14 has been completed. Further, the temperature T1 is a value lower than the temperature T2, and is a temperature at which the temperature of the NOx catalyst 14 is judged to rise excessively if high temperature exhaust gas continues to flow into the NOx catalyst 14. When the process of S104 ends, the process proceeds to S105.
[0038]
In S105, a basic ISC flow rate (hereinafter referred to as “qadd”) is calculated. For example, qadd is calculated based on correction amounts of a plurality of control parameters in the internal combustion engine 1 at the time when this control is performed. That is, the flow rate of the intake air flowing through the ISC passage 9a necessary for stably maintaining the engine speed of the internal combustion engine 1 in the idle operation state when the NOx catalyst 14 is warmed up is calculated. When the process of S105 ends, the process proceeds to S106.
[0039]
In S106, based on the kqcal calculated in S103 and the kcattemp calculated in S104, the qadd value calculated in S105 is corrected to calculate the final ISC flow rate qcal. Specifically, it is calculated based on the following formula 1.
[0040]
qcal = qadd * (1 + kqcal * kcattemp) (Equation 1)
[0041]
In Equation 1, as the value of kqcal and the value of kcattemp increase, the value of qcal, which is the final ISC flow rate, increases. That is, as the atmospheric pressure at which the internal combustion engine 1 is placed decreases, or the temperature of the NOx catalyst 14 decreases, the value of qcal increases. As a result, the amount of intake air to the internal combustion engine 1 increases and the exhaust temperature rises, so that the NOx catalyst 14 is sufficiently warmed up.
[0042]
Here, when the warming-up of the NOx catalyst 14 progresses and the temperature of the NOx catalyst 14 belongs to the range from the temperature T1 to the temperature T2, the value of qcal gradually decreases, and when the temperature reaches the temperature T2, The value of qcal is the same as the value of qadd. As a result, it is possible to avoid the NOx catalyst 14 from being excessively heated during the warm-up and the NOx catalyst 14 being thermally deteriorated.
[0043]
As described above, this control makes it possible to sufficiently warm up the NOx catalyst 14 even when the atmospheric pressure at which the internal combustion engine 1 is placed decreases, and thus the NOx catalyst 14 is sufficiently purified. It is possible to suppress the release of no exhaust to the outside air.
[0044]
In the present embodiment, the ISC flow rate flowing through the ISC passage 9a is corrected based on the atmospheric pressure in which the internal combustion engine 1 is placed or the temperature of the NOx catalyst 14, but similarly the atmospheric pressure in which the internal combustion engine 1 is placed or The flow rate of the intake air flowing through the intake pipe 5 may be controlled by adjusting the opening of the intake throttle valve 6 based on the temperature of the NOx catalyst 14. That is, as the atmospheric pressure at which the internal combustion engine 1 is placed becomes lower or the temperature of the NOx catalyst 14 is lower, the opening of the intake throttle valve 6 is increased and the flow rate of intake air flowing through the intake pipe 5 is increased. To do.
[0045]
<Second Embodiment>
Another embodiment of the catalyst warm-up control will be described with reference to FIG. FIG. 5 is a flowchart showing catalyst warm-up control. The catalyst warm-up control is executed by the ECU 20. In the present embodiment, the NOx catalyst 14 is warmed up by correcting the engine speed of the internal combustion engine 1 that is in an idling state when the catalyst is warmed up (hereinafter referred to as “idle speed”). Details will be described below.
[0046]
In S201 and S202, the atmospheric pressure at which the internal combustion engine 1 is placed and the temperature of the NOx catalyst 14 are detected in the same manner as in S101 and S102 described above. After the process of S202 is completed, the process proceeds to S203. In S203, the coolant temperature sensor 22 detects the coolant temperature of the internal combustion engine 1. When the process of S203 ends, the process proceeds to S204.
[0047]
In S204, an atmospheric pressure correction coefficient for final idle rotation speed (hereinafter referred to as “kntcal”) is calculated based on the atmospheric pressure detected in S201. Specifically, kntcal is calculated based on the relationship between kntcal and the variation rate of the atmospheric pressure in which the internal combustion engine 1 is placed with respect to the reference atmospheric pressure, which is expressed similarly to the graph shown in FIG. 3 described above. When the process of S204 ends, the process proceeds to S205.
[0048]
In S205, based on the temperature of the NOx catalyst 14 detected in S202, a final idle rotational speed catalyst temperature correction coefficient (hereinafter referred to as “kcattemp2”) is calculated. Specifically, kcattemp2 is calculated based on the relationship between the temperature of the NOx catalyst 14 and kcattemp2, which is expressed in the same manner as the graph shown in FIG. When the processing of S205 ends, the process proceeds to S206.
[0049]
In S206, an idle rotation speed correction amount (hereinafter referred to as “dlnt”) is calculated based on the coolant temperature detected in S203. Specifically, dlnt is calculated based on the graph shown in FIG. FIG. 6 is a graph showing the relationship between the cooling water temperature and dlnt. The horizontal axis in FIG. 6 represents the coolant temperature of the internal combustion engine 1, and the vertical axis represents dlnt. Here, when the cooling water temperature becomes 80 ° C. or higher, it is considered that the NOx catalyst 14 has been warmed up, and the value of dlnt becomes zero. When the process of S206 ends, the process proceeds to S207.
[0050]
In S207, based on kntcal calculated in S204 and kcattemp2 calculated in S205, the value of dlnt calculated in S206 is corrected and calculated as the final idle rotation speed (hereinafter referred to as “ntcal”). Specifically, it is calculated based on the following formula 2.
[0051]
ntcal = ntb + dlnt * (1 + kntcal * kcattemp2) (Expression 2)
[0052]
In Expression 2, ntb represents a basic idle rotation speed, and is a basic idle rotation speed determined by, for example, a shift position of a vehicle including the internal combustion engine 1. Therefore, the idle rotation speed of the internal combustion engine 1 when the internal combustion engine 1 is in the idle operation state is a rotation speed represented by the sum of the basic idle rotation speed ntb and the corrected rotation speed dlnt calculated from the coolant temperature. is there. That is, warming up of the internal combustion engine 1 is promoted by increasing the idle rotation speed as the cooling water temperature is lower.
[0053]
Further, in the idling operation state of the internal combustion engine 1 when the NOx catalyst 14 is warmed up, the corrected rotational speed dlnt is corrected based on kntcal and kcattemp2. That is, as the value of kntcal and the value of kcattemp2 increase, the value of the final idle rotation speed ntcal increases. That is, as the atmospheric pressure at which the internal combustion engine 1 is placed decreases or as the temperature of the NOx catalyst 14 decreases, the value of ntcal increases. As a result, the amount of intake air to the internal combustion engine 1 increases and the exhaust gas temperature rises, so that the temperature of the NOx catalyst 14 is sufficiently increased.
[0054]
As described above, this control makes it possible to sufficiently warm up the NOx catalyst 14 even when the atmospheric pressure at which the internal combustion engine 1 is placed decreases, and thus the NOx catalyst 14 is sufficiently purified. It is possible to suppress the release of no exhaust to the outside air.
[0055]
<Third Embodiment>
Another embodiment of the catalyst warm-up control will be described with reference to FIG. FIG. 7 is a flowchart showing catalyst warm-up control. The catalyst warm-up control is executed by the ECU 20. In the flowchart of the catalyst warm-up control shown in FIG. 7, the same processes as those in the flowchart of the catalyst warm-up control shown in FIG. 5 are denoted by the same reference numerals as those in FIG. Or simplify. In the present embodiment, the NOx catalyst 14 is warmed up by correcting the idle rotation speed of the internal combustion engine 1 and correcting the ignition timing in the internal combustion engine 1 when the catalyst is warmed up. Details will be described below.
[0056]
When the process of S203 ends, the process proceeds to S301. In S301, the load factor of the internal combustion engine 1 is detected. Here, the load factor of the internal combustion engine 1 refers to the ratio of the current intake air amount detected by the air flow meter 8 to the maximum intake air amount flowing through the intake pipe 5. When the process of S301 ends, the process proceeds to S302.
[0057]
In S302, an ignition timing atmospheric pressure correction coefficient (hereinafter referred to as “kacat”) is calculated based on the atmospheric pressure detected in S201. Specifically, kacat is calculated based on the relationship between the variation rate of the atmospheric pressure in which the internal combustion engine 1 is placed with respect to the reference atmospheric pressure and kacat, which is expressed in the same manner as the graph shown in FIG. 3 described above. When the process of S302 ends, the process proceeds to S303.
[0058]
In S303, an ignition timing catalyst temperature correction coefficient (hereinafter referred to as “kcattemp3”) is calculated based on the temperature of the NOx catalyst 14 detected in S202. Specifically, kcattemp3 is calculated based on the relationship between the temperature of the NOx catalyst 14 and kcattemp3 expressed in the same manner as the graph shown in FIG. 4 described above. When the process of S303 ends, the process proceeds to S304.
[0059]
In S304, based on the coolant temperature detected in S203 and the load factor of the internal combustion engine 1 detected in S301, a basic retard amount (hereinafter referred to as “acatb”) of the ignition timing in the internal combustion engine 1 is calculated. . Specifically, acatb is calculated based on the graph shown in FIG. FIG. 8 is a graph showing the relationship between the cooling water temperature of the internal combustion engine 1 and acatb. The horizontal axis of FIG. 8 represents the coolant temperature of the internal combustion engine 1, and the vertical axis represents acatb. Further, lines L1, L2, and L3 in FIG. 8 represent changes in acatb with respect to the cooling water temperature when the load factor of the internal combustion engine is 20%, 40%, and 60%, respectively. Therefore, when the load factor is 20%, the value of acatb is 0, and the ignition timing is not shifted to the retard side. Further, the amount of retardation increases as the load factor increases. When the process of S304 ends, the process proceeds to S305.
[0060]
In S305, based on kcat calculated in S302 and kcattemp3 calculated in S303, the value of acatb calculated in S304 is corrected and calculated as a final retardation amount (hereinafter referred to as “acat”). Specifically, it is calculated based on the following Equation 3.
[0061]
acat = acatb * (1 + kacat * kcattemp3) (Formula 3)
[0062]
In Equation 3, the value of the final retardation amount acat increases as the value of kcat and the value of kcattemp3 increase. That is, as the atmospheric pressure at which the internal combustion engine 1 is placed becomes lower or the temperature of the NOx catalyst 14 is lower, the ignition timing in the internal combustion engine 1 shifts to the retard side. As a result, the exhaust temperature rises, and thus the temperature of the NOx catalyst 14 rises. When the process of S305 is completed, the processes of S204 and S205 are sequentially performed. When the processing of S205 ends, the process proceeds to S306.
[0063]
In S306, an idle rotation speed correction amount is calculated in substantially the same manner as S206. However, in the calculation, an increase in exhaust temperature due to the shift of the ignition timing calculated in S305 to the retard side is taken into account. That is, since the temperature of the exhaust gas flowing into the NOx catalyst 14 rises by shifting the ignition timing to the retarded side, the final idle rotation speed increases much compared to the case where the ignition timing does not shift to the retarded side. There is no need to let them. Therefore, a value obtained by subtracting the rotational speed corresponding to the retard amount acat of the ignition timing from dlnt obtained from the relationship with the coolant temperature shown in FIG. 6 is calculated as the idle rotational speed correction amount dlnt2. When the process of S306 ends, the process proceeds to S307.
[0064]
In S307, as in S207, the value of dlnt2 calculated in S306 is corrected and calculated as the final idle rotation speed (hereinafter referred to as “ntcal2”). Specifically, it is calculated based on the following formula 4.
[0065]
ntcal2 = ntb + dlnt2 * (1 + kntcal * kcattemp2) (Expression 4)
[0066]
Thereby, as the atmospheric pressure at which the internal combustion engine 1 is placed becomes lower or the temperature of the NOx catalyst 14 is lower, the amount of intake air to the internal combustion engine 1 increases and the exhaust gas temperature rises. Therefore, the NOx catalyst 14 The temperature is sufficiently performed.
[0067]
As described above, even when the atmospheric pressure at which the internal combustion engine 1 is placed is reduced by this control, the idle rotation speed is increased according to the decrease in the atmospheric pressure, so that the NOx catalyst 14 is sufficiently warmed up. Therefore, it is possible to suppress the exhaust gas that has not been sufficiently purified by the NOx catalyst 14 from being released to the outside air. Furthermore, since the temperature of the NOx catalyst 14 can be raised to some extent by shifting the ignition timing in the internal combustion engine 1 to the retard side, the amount of increase in the idle rotation speed required for warming up the NOx catalyst 14 is reduced. It can be reduced. As a result, it is possible to reduce noise associated with an increase in idle rotation speed.
[0068]
In the present embodiment, the ignition timing in the internal combustion engine 1 is shifted to the retard side before determining the idle rotation speed when the catalyst is warmed up. Before the ISC flow rate is corrected in the catalyst warm-up control shown in FIG. 2, similarly, the ignition timing in the internal combustion engine 1 is shifted to the retard side, so that the increase in the ISC flow rate can be suppressed. This makes it possible to reduce noise due to an increase in the ISC flow rate.
[0069]
【The invention's effect】
The present invention relates to a catalyst warm-up system for an internal combustion engine that warms up an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine, taking into account the atmospheric pressure at which the internal combustion engine is placed, and reducing the amount of intake air to the internal combustion engine. to correct. As a result, even when the atmospheric pressure at which the internal combustion engine is placed decreases, the exhaust purification catalyst is sufficiently warmed up and the exhaust gas that has not been sufficiently purified by the exhaust purification catalyst is prevented from being released to the outside air. It becomes possible to do.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a catalyst warm-up system according to an embodiment of the present invention, an internal combustion engine including the catalyst warm-up system, and a control system thereof.
FIG. 2 is a flowchart showing control for warming up the catalyst in the catalyst warming-up system according to the embodiment of the present invention.
FIG. 3 is a graph showing a relationship between a variation rate of an atmospheric pressure in which an internal combustion engine is placed with respect to a reference atmospheric pressure and an ISC flow rate atmospheric pressure correction coefficient in the catalyst warm-up system according to the embodiment of the present invention.
FIG. 4 is a graph showing the relationship between the catalyst temperature and the ISC flow rate catalyst temperature correction coefficient in the catalyst warm-up system according to the embodiment of the present invention.
FIG. 5 is a second flowchart showing control for warming up the catalyst in the catalyst warming-up system according to the embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the cooling water temperature of the internal combustion engine and the idle rotation speed correction amount in the catalyst warm-up system according to the embodiment of the present invention.
FIG. 7 is a third flowchart showing control for warming up the catalyst in the catalyst warming-up system according to the embodiment of the present invention.
FIG. 8 is a graph showing the relationship between the coolant temperature of the internal combustion engine and the basic retard amount of the ignition timing in the internal combustion engine in the catalyst warm-up system according to the embodiment of the present invention.
[Explanation of symbols]
1 ... Internal combustion engine
3 ... Ignition plug
4 ... Intake branch pipe
5 .... Intake pipe
6 .... Inlet throttle valve
8. Air flow meter
9 .... Idle speed controller (ISC)
12 .... Exhaust branch pipe
13. Exhaust pipe
14 ... NOx catalyst
20 .... ECU
22 .... Cooling water temperature sensor
24 ... Exhaust temperature sensor
25 .... Atmospheric pressure sensor

Claims (5)

An exhaust purification catalyst that is provided in an exhaust passage of the internal combustion engine and purifies exhaust;
An intake air amount control means which is provided in an intake passage of the internal combustion engine and determines an intake air amount to the internal combustion engine based on an operating state of the internal combustion engine;
Atmospheric pressure detection means for detecting atmospheric pressure;
An intake air amount correction means for performing correction to increase the intake air amount determined by the intake air amount control means as the atmospheric pressure detected by the atmospheric pressure detection means decreases when the exhaust purification catalyst is warmed up; And a catalyst warm-up system for an internal combustion engine. A catalyst temperature estimating means for estimating the temperature of the exhaust purification catalyst;
The intake air amount correction means follows the atmospheric pressure detected by the atmospheric pressure detection means as the temperature of the exhaust purification catalyst estimated by the catalyst temperature estimation means rises when the exhaust purification catalyst warms up. The catalyst warm-up system for an internal combustion engine according to claim 1, wherein correction is performed to reduce the corrected intake air amount. The intake air amount correction means increases the intake air amount to the internal combustion engine by increasing the flow rate of the intake air flowing through the intake passage of the internal combustion engine when the exhaust purification catalyst is warmed up. The catalyst warm-up system for an internal combustion engine according to claim 1 or 2. 2. The intake air amount correction means increases the intake air amount to the internal combustion engine by increasing the engine speed of the internal combustion engine when the exhaust purification catalyst is warmed up. Item 3. A catalyst warm-up system for an internal combustion engine according to Item 2. When the correction by the intake air amount correction means is performed, the ignition timing in the internal combustion engine when the exhaust purification catalyst is warmed up is retarded based on at least the atmospheric pressure detected by the atmospheric pressure detection means The catalyst warm-up system for an internal combustion engine according to claim 3 or 4, wherein

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