JP3613673B2 - Exhaust passage switching device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust passage switching device for an internal combustion engine, and more particularly, to an exhaust passage upstream of a catalyst, a passage provided with an adsorbent that adsorbs unburned components in exhaust gas, and a passage that bypasses the adsorbent. The present invention relates to an exhaust passage switching device for an internal combustion engine that drives a switching valve to purge unburned components adsorbed on an adsorbent toward a catalyst when a predetermined condition is satisfied.
[0002]
[Prior art]
Conventionally, as disclosed in, for example, JP-A-6-58139, an apparatus for purifying exhaust gas discharged from an internal combustion engine is known. This device includes a switching valve that selectively switches the exhaust passage between a bypass passage provided with an adsorbent that adsorbs unburned components such as HC in the exhaust gas and a main passage that bypasses the adsorbent. Yes. Further, this apparatus includes a catalyst that is provided in an exhaust passage on the downstream side of the adsorbent and purifies the exhaust gas.
[0003]
When the internal combustion engine is cold, such as immediately after starting, the unburned components contained in the exhaust gas increase. Further, the catalyst cannot effectively purify unburned components in the exhaust gas when cold. Further, the adsorbent becomes difficult to adsorb unburned components as the temperature increases, and has a characteristic of starting to release adsorbed unburned components to the outside from, for example, a temperature exceeding 80 ° C. Hereinafter, the temperature at which the unburned component adsorbed by the adsorbent starts to be released is referred to as the adsorbent desorption temperature. Therefore, in the conventional apparatus, the switching valve switches the exhaust passage to the bypass passage when cold. In this case, as the exhaust gas flows through the bypass passage, the unburned components in the exhaust gas are adsorbed by the adsorbent. The switching valve switches the exhaust passage to the main passage when the temperature of the exhaust gas reaches the desorption temperature of the unburned components. In this case, the adsorbent is not exposed to the exhaust gas, and a large amount of unburned components are prevented from desorbing from the adsorbent. Therefore, according to the conventional apparatus, it is possible to avoid a large amount of unburned components in the exhaust gas being released into the atmosphere, and as a result, it is possible to prevent the exhaust emission from deteriorating.
[0004]
By the way, when an unburned component is adsorbed on the adsorbent, it is necessary to desorb the unburned component from the adsorbent and purify the unburned component with a catalyst in order to regenerate the adsorbent. . Hereinafter, desorption of unburned components from the adsorbent is referred to as “purging” of unburned components. Therefore, in the above conventional apparatus, when the temperature of the catalyst reaches an active temperature, the switching valve switches the exhaust passage from the main passage to the bypass passage, so that the unburned components adsorbed by the adsorbent are changed. The purge to the catalyst is started. When unburned components are purged from the adsorbent, the oxygen concentration in the exhaust gas is reduced by that amount, and the air-fuel ratio is changed to the rich side. When the amount of unburned component purged decreases, the amount of change of the air-fuel ratio to the rich side decreases. Therefore, the purge of unburned components into the catalyst is terminated when the switching valve switches the exhaust passage from the bypass passage to the main passage when the amount of change of the air-fuel ratio in the exhaust gas to the rich side decreases.
[0005]
[Problems to be solved by the invention]
As described above, when the temperature reaches the desorption temperature, the adsorbent starts releasing the unburned components to be adsorbed to the outside. When the temperature reaches, for example, around 250 ° C., the unburned components are hardly adsorbed. It becomes a state. When unburned components are not adsorbed on the adsorbent, it is not necessary to purge from the adsorbent. However, in the above-described conventional apparatus, even when the unburned component is not adsorbed by the adsorbent, the purge of the unburned component from the adsorbent is started each time the temperature of the catalyst reaches an active temperature.
[0006]
Further, the air-fuel ratio in the exhaust gas not only varies due to the desorption of unburned components from the adsorbent, but also varies depending on factors such as the operating state of the internal combustion engine. For this reason, in the conventional apparatus described above, the purge is ended even though a large amount of unburned components are adsorbed by the adsorbent, that is, the exhaust passage on the upstream side of the catalyst passes from the bypass passage to the main passage. A situation may occur in which the switching valve is driven so as to switch to. Thus, in the conventional apparatus, the unburned component adsorbed by the adsorbent has not been purged at an appropriate timing.
[0007]
The present invention has been made in view of the above points, and is an exhaust of an internal combustion engine that can purge unburned components in exhaust gas adsorbed by an adsorbent toward a catalyst at an appropriate timing. An object is to provide a passage switching device.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, the exhaust passage provided with the catalyst and the exhaust passage upstream of the catalyst are provided with an adsorbent that adsorbs unburned components in the exhaust gas. A switching valve that selectively switches between the second passage and the second passage that bypasses the adsorbent, and purges unburned components adsorbed on the adsorbent toward the catalyst when a predetermined condition is satisfied. Therefore, in the exhaust passage switching device for an internal combustion engine, comprising: switching valve control means for driving the switching valve so that the exhaust passage on the upstream side of the catalyst is switched to the first passage,
The switching valve is driven using a negative pressure generated in the intake passage downstream of the throttle valve as a drive source,
Of the adsorbenttemperatureA state quantity detecting means for detecting
The switching valve control means includesThe internal combustion engine is in an idle state where the opening of the throttle valve is a predetermined value or less, andWhen the temperature detected by the state quantity detection means becomes equal to or higher than a first predetermined value, an exhaust passage on the upstream side of the catalyst is configured to start purging of unburned components adsorbed on the adsorbent. This is achieved by an exhaust passage switching device for an internal combustion engine, wherein the switching valve is driven to switch to the first passage.
[0010]
By the way, the amount of unburned components adsorbed on the adsorbent depends on the temperature of the adsorbent. That is, the adsorbent releases unburned components to the outside when the temperature rises, even if the exhaust passage upstream of the catalyst is not switched to the first passage, while all unburned components rise when the temperature rises further. Release.Further, since the switching valve is driven by using the negative pressure generated in the intake passage on the downstream side of the throttle valve as a drive source, it is necessary to maintain the negative pressure generated in the intake passage at a certain low level in order to drive the switching valve properly. There is. During operation of the internal combustion engine, if the opening of the throttle valve is less than or equal to a predetermined value, a certain level of negative pressure is generated in the intake passage. Therefore, the switching valve control means adsorbs the adsorbent when the internal combustion engine is in an idle state where the throttle valve opening is equal to or less than a predetermined value and the temperature of the adsorbent becomes equal to or higher than the first predetermined value. In order to start purging of the unburned components, the switching valve is driven so that the exhaust passage on the upstream side of the catalyst is switched to the first passage having the adsorbent. Therefore, according to the present invention, unburned components in the exhaust gas adsorbed by the adsorbent are purged toward the catalyst in a state where the exhaust passage can be properly switched by the switching valve and at an appropriate timing. be able to.
[0012]
still, Claims2As claimed in1In the internal combustion engine exhaust passage switching device,
The switching valve control means is a temperature detected by the state quantity detection means.BeforeWhen the second predetermined value that is higher than the first predetermined value is reached, the switching valve is arranged so that the exhaust passage on the upstream side of the catalyst is switched to the second passage in order to end the purge. May be driven.
[0015]
by the way,According to invention of Claim 1,When the opening degree of the throttle valve does not become a predetermined value or less, the switching valve is not driven. In such a case, when the temperature of the adsorbent exceeds the first predetermined value to start purging of the unburned components adsorbed on the adsorbent and reaches a third predetermined value, the unburned components are It can be judged that all desorbed without remaining in the adsorbent. In this case, it is not necessary to switch the exhaust passage to the first passage by the switching valve.
[0016]
Therefore, the claims3As claimed in1In the internal combustion engine exhaust passage switching device,
The switching valve control means has a third predetermined value in which the temperature detected by the state quantity detecting means is higher than the first predetermined value before the opening of the throttle valve becomes less than or equal to the predetermined value. When the value reaches the value, the driving of the switching valve may be prohibited.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration diagram of an exhaust passage switching device according to an embodiment of the present invention. Moreover, FIG. 2 shows the principal part enlarged view of the exhaust passage switching device of a present Example. The system of this embodiment includes an electronic control unit (hereinafter referred to as ECU) 10 for an internal combustion engine, and is controlled by the ECU 10.
[0018]
As shown in FIG. 1, the system of this embodiment includes an internal combustion engine 12. The internal combustion engine 12 includes an intake manifold 14 for sending intake air into the cylinder, and an exhaust manifold 16 for releasing exhaust gas generated in the cylinder to the atmosphere. A first exhaust pipe 18 is connected to the exhaust manifold 16. A start catalyst 20 made of a three-way catalyst is provided in the vicinity of the upstream end of the first exhaust pipe 18. A second exhaust pipe 22 is connected to the downstream side of the first exhaust pipe 18. A main catalyst 24 made of a three-way catalyst is provided in the vicinity of the upstream end of the second exhaust pipe 22. Both the main catalyst 24 and the start catalyst 20 are activated when the temperature is, for example, 350 ° C. or higher, and the exhaust gas can be purified. Hereinafter, the temperature at which the main catalyst 24 or the start catalyst 20 is activated is referred to as an activation temperature.
[0019]
As shown in FIGS. 1 and 2, an HC adsorbing device 28 is provided at a connection portion between the first exhaust pipe 18 and the second exhaust pipe 22. The HC adsorption device 28 includes a main passage 30 that communicates the first exhaust pipe 18 and the second exhaust pipe 22 with a large opening area at the center thereof, a bypass passage 32 that bypasses and communicates with the main passage 30, And a switching valve 34 for switching a communication path between the first exhaust pipe 8 and the second exhaust pipe 22 between the main passage 30 and the bypass passage 32.
[0020]
An HC adsorbent 36 is disposed in the bypass passage 32. The HC adsorbent 36 has a function of adsorbing hydrocarbon (HC) as an unburned component contained in the exhaust gas. Further, the HC adsorbent 36 becomes difficult to adsorb HC as the temperature is higher, and has a characteristic of starting to release adsorbed HC to the outside from, for example, a temperature exceeding 80 ° C. Hereinafter, the temperature at which the HC adsorbed by the HC adsorbent 36 starts to be released to the outside is referred to as a desorption temperature.
[0021]
The system of this embodiment also includes a diaphragm mechanism 40. The diaphragm mechanism 40 is provided with a diaphragm 42. The diaphragm 42 divides the internal space of the diaphragm mechanism 40 into a variable pressure chamber 44 (left room in FIG. 1) and an atmospheric pressure chamber 46 (right room in FIG. 1). The above-described switching valve 34 is connected to the diaphragm 42 via an operating rod 48. When the diaphragm 42 is not deflected, the switching valve 34 is fully opened to make the main passage 30 conductive, and when the diaphragm 42 is maximally bent toward the variable pressure chamber 44, the switching valve 34 is fully closed. The passage 30 is blocked.
[0022]
The pressure in the atmospheric pressure chamber 46 is always maintained at atmospheric pressure. The variable pressure chamber 44 is connected to one end of a negative pressure supply pipe 50. The other end of the negative pressure supply pipe 50 is connected to a vacuum switching valve (hereinafter referred to as VSV) 52. The negative pressure supply pipe 50 is provided with a pressure sensor 54 that outputs a signal corresponding to the internal pressure, that is, the pressure supplied to the variable pressure chamber 44 (hereinafter referred to as supply pressure P). The output signal of the pressure sensor 54 is supplied to the ECU 10. The ECU 10 detects the supply pressure P based on the output signal of the pressure sensor 54. Note that the pressure sensor 54 may be provided in the variable pressure chamber 44.
[0023]
A negative pressure passage 56 communicating with the intake manifold 14 is connected to the VSV 52. The VSV 52 includes an air opening that is open to the atmosphere. The VSV 52 conducts the negative pressure supply pipe 50 to the atmosphere opening port in the off state. On the other hand, when the ON signal is supplied from the ECU 10, the VSV 52 blocks the negative pressure supply pipe 50 from the atmosphere opening port and conducts to the negative pressure passage 56. Let
[0024]
A check valve 58 is provided in the negative pressure passage 56. The check valve 58 is directed from the negative pressure supply pipe 50 side to the intake manifold 14 when the negative pressure (hereinafter referred to as intake pressure) of the intake manifold 14 is lower than the pressure on the negative pressure supply pipe 50 side. It is a one-way valve that allows gas flow.
[0025]
A throttle valve (not shown) that varies the effective area of the flow path is provided on the upstream side of the portion of the intake manifold 14 where the negative pressure passage 56 is connected. In the vicinity of the throttle valve, there is disposed a throttle position sensor 60 that outputs an electrical signal corresponding to the opening (hereinafter referred to as throttle opening) θ of the throttle valve. The output signal of the throttle position sensor 60 is supplied to the ECU 10. The ECU 10 detects the throttle opening θ based on the output signal of the throttle position sensor 60.
[0026]
The ECU 10 also includes an engine speed sensor 62 that outputs a signal corresponding to the speed of the internal combustion engine 12 (hereinafter referred to as the engine speed NE), and the weight of the intake air that flows through the intake manifold 14 (hereinafter referred to as the engine speed NE). An air flow meter 64 that outputs a signal corresponding to the intake air amount Ga) is connected. The ECU 10 detects the engine speed NE based on the output signal of the engine speed sensor 62 and detects the intake air amount Ga based on the output signal of the air flow meter 64.
[0027]
In the above configuration, when the VSV 52 is off, atmospheric pressure is introduced into the variable pressure chamber 44 of the diaphragm mechanism 40 via the negative pressure supply pipe 50. In this case, since the variable pressure chamber 44 and the atmospheric pressure 46 are equal in pressure, the diaphragm 42 is not bent. As described above, the switching valve 34 is fully opened when the diaphragm 42 is not bent. Accordingly, when the VSV 52 is maintained in the OFF state, the switching valve 34 is fully opened, so that most of the exhaust gas does not pass through the bypass passage 32 from the first exhaust pipe 18, that is, It flows into the second exhaust pipe 22 via the main passage 30 without passing through the HC adsorbent 36.
[0028]
On the other hand, when the VSV 52 is in the ON state, the intake pressure is supplied to the variable pressure chamber 44 of the diaphragm mechanism 40 through the negative pressure supply pipe 50. In this case, since the pressure in the variable pressure chamber 44 is smaller than the pressure in the atmospheric pressure chamber 46, the diaphragm 42 is bent toward the variable pressure chamber 44 side. As described above, the switching valve 34 is fully closed when the diaphragm 42 is bent to the maximum extent toward the variable pressure chamber 44 side. Therefore, when the VSV 52 is turned on, the switching valve 34 is fully closed, so that the exhaust gas passes from the first exhaust pipe 18 through the bypass passage 32, that is, through the HC adsorbent 36. It flows into the second exhaust pipe 22.
[0029]
As described above, the switching valve 34, the operating rod 48, the diaphragm mechanism 40, the negative pressure supply pipe 50, and the VSV 52 use the intake pressure to exhaust gas at the connection portion between the first exhaust pipe 18 and the second exhaust pipe 22. This mechanism switches the flow path between the main passage 30 and the bypass passage 32. Hereinafter, the switching valve 34, the operating rod 48, the diaphragm mechanism 40, the negative pressure supply pipe 50, and the VSV 52 are collectively referred to as a switching mechanism.
[0030]
When the internal combustion engine 12 is cold, HC contained in the exhaust gas increases. Further, when the internal combustion engine 12 is cold, the start catalyst 20 and the main catalyst 24 are not activated, and therefore the exhaust gas purification by the start catalyst 20 and the main catalyst 24 is not effectively performed. Therefore, when the internal combustion engine 12 is cold, if the exhaust gas flows from the first exhaust pipe 18 into the second exhaust pipe 22 without passing through the HC adsorbent 36, the exhaust gas containing a large amount of HC is released to the atmosphere. End up.
[0031]
Therefore, in the system of this embodiment, the ECU 10 supplies an ON signal to the VSV 52 when the internal combustion engine 12 is cold. In this case, as described above, the exhaust gas passes through the HC adsorbent 36, whereby HC contained in the exhaust gas is adsorbed by the HC adsorbent 36. Accordingly, it is possible to prevent the exhaust gas containing a large amount of HC from being released into the atmosphere during the cold time when the exhaust gas purification by the start catalyst 20 and the main catalyst 24 is not effectively performed.
[0032]
As described above, the start catalyst 20 for purifying the exhaust gas is provided in the vicinity of the upstream end portion of the first exhaust pipe 18. Since the start catalyst 20 is disposed in a portion of the exhaust pipe close to the combustion chamber of the internal combustion engine 12, it is easier to warm up and activate than the main catalyst 24. After the start catalyst 20 is activated, even if the exhaust gas discharged from the internal combustion engine 12 contains HC, a large amount of HC is not discharged downstream of the start catalyst 20. For this reason, after the start catalyst 20 is activated, it is not necessary to distribute the exhaust gas via the HC adsorbent 36. That is, there is no problem even if the exhaust gas flow passage is switched from the bypass passage 32 to the main passage 30.
[0033]
Therefore, in the system of the present embodiment, the ECU 10 stops supplying the ON signal to the VSV 52 when the temperature of the start catalyst 20 (hereinafter referred to as the S / C temperature) reaches the activation temperature. In this case, the exhaust gas is released to the atmosphere via the main passage 30 without passing through the HC adsorbent 36.
[0034]
3 shows the temperature of the HC adsorbent 36 (hereinafter referred to as HC temperature) and the amount of HC adsorbed on the HC adsorbent 36 (hereinafter referred to as HC adsorption amount) after the start of the internal combustion engine 12 is started. FIG. FIG. 3 shows a change with time when a vehicle equipped with the internal combustion engine 12 of this embodiment travels in a predetermined speed pattern.
[0035]
When the start of the internal combustion engine is completed at time t = 0, the exhaust gas flow passage is switched from the main passage 30 to the bypass passage 32 in order to adsorb the HC contained in the exhaust gas to the HC adsorbent 36. This state is maintained until the S / C temperature reaches the activation temperature (for the time indicated by hatching in FIG. 3B). At this time, a large amount of HC is adsorbed on the HC adsorbent 36. When the S / C temperature reaches the activation temperature, the exhaust gas flow passage is switched from the bypass passage 32 to the main passage 30. In this case, the exhaust gas is released to the atmosphere via the main passage 30 without passing through the HC adsorbent 36 as described above.
[0036]
Even if the high-temperature exhaust gas does not pass through the HC adsorbent 36, the temperature of the HC adsorbent 36 is raised by heat transfer of the exhaust gas flowing through the main passage 30. When the HC temperature reaches the desorption temperature, the HC adsorbent 36 releases the adsorbed HC to the outside. Therefore, after HC is adsorbed by the HC adsorbent 36, even if the exhaust gas flow passage is switched to the main passage 30, the HC has an HC temperature around time t = 200 sec as shown in FIG. Desorption begins when the temperature reaches around 80 ° C.
[0037]
FIG. 4 is a diagram showing the relationship between the number of carbon atoms in one molecule and the boiling point. As shown in FIG. 4, the boiling point tends to increase as the number of carbon atoms in one molecule increases. When the exhaust gas flows through the main passage 30 without passing through the HC adsorbent 36, that is, when the HC adsorbent 36 is heated by heat transfer of the exhaust gas flowing through the main passage 30, the maximum HC temperature is reached. The temperature is lower than when the exhaust gas passes through the HC adsorbent 36. For this reason, when the exhaust gas flows through the main passage 30 without passing through the HC adsorbent 36, there is a possibility that HC having a large number of carbon atoms will not be desorbed from the HC adsorbent 36 even if the elapsed time increases. is there.
[0038]
When such a situation occurs, the adsorption performance of the HC adsorbent 36 decreases, and thereafter, there may be a disadvantage that HC in the exhaust gas is not properly adsorbed by the HC adsorbent 36. Therefore, when HC is adsorbed on the HC adsorbent 36, the HC is reliably desorbed from the HC adsorbent 36 and purified by the main catalyst 24 in order to regenerate the HC adsorbent 36 thereafter. Is required.
[0039]
When the high-temperature exhaust gas flows through the bypass passage 32 provided with the HC adsorbent 36, the HC adsorbent 36 quickly reaches a high temperature state due to heat transfer from the exhaust gas. In this case, all the HC adsorbed on the HC adsorbent 36 is desorbed. Hereinafter, desorption of HC from the HC adsorbent 36 by circulating high-temperature exhaust gas through the bypass passage 32 is referred to as “forced purge” of HC. Note that when high-temperature exhaust gas passes through the HC adsorbent 36 in a state where a large amount of HC is adsorbed on the HC adsorbent 36, a large amount of HC is desorbed from the HC adsorbent 36 in a short time, and the main catalyst 24. There may be a situation where all the HC from which is desorbed cannot be effectively purified.
[0040]
Therefore, in the system of this embodiment, the ECU 10 forcibly purges the remaining HC toward the main catalyst 24 when the HC temperature reaches a temperature at which it can be determined that the amount of HC remaining in the HC adsorbent 36 decreases to some extent. Therefore, an ON signal is supplied to the VSV 52. Then, the ECU 10 stops the supply of the ON signal to the VSV 52 when the HC temperature reaches a temperature at which it can be determined that all the HC adsorbed on the HC adsorbent 36 is desorbed. The system of the present embodiment is characterized in that the HC adsorbed on the HC adsorbent 36 is forcibly purged at the timing described above.
[0041]
The HC adsorbent 36 is heated by heat transfer of the exhaust gas discharged from the internal combustion engine 12 after the internal combustion engine 12 is started. The HC adsorbent 36 is more likely to be heated as the amount of exhaust gas per unit time is larger, that is, as the amount of intake air is larger, while the amount of exhaust gas per unit time is smaller, that is, the amount of intake air is smaller. It becomes difficult to raise the temperature. Therefore, in this embodiment, an HC adsorbent temperature counter that adds and subtracts according to the intake air amount every unit time is provided, and the temperature (HC temperature) of the HC adsorbent 36 is estimated based on the count value. . When the ignition timing of the internal combustion engine 12 is retarded, the temperature of the exhaust gas rises. Therefore, the count value of the HC adsorbent temperature counter may be corrected according to the retard amount of the ignition timing.
[0042]
The switching valve 34 opens and closes using a negative pressure (intake pressure) generated in the intake manifold 14 as a drive source. That is, the switching valve 34 cannot be opened / closed unless a certain amount of negative pressure is generated in the intake manifold 14. The intake pressure varies according to the throttle opening θ of the throttle valve provided in the intake manifold 14. When the throttle opening θ is large, the intake pressure is unlikely to be in a low pressure state, and when the throttle opening θ is small, the intake pressure is likely to be in a low pressure state. Therefore, the ECU 10 supplies the ON signal to the VSV 52 for forcibly purging the HC remaining in the HC adsorbent 36 when the throttle opening θ is small. Hereinafter, the characteristic part of a present Example is demonstrated.
[0043]
FIG. 5 shows a time chart realized after the internal combustion engine 12 is started in the system of the present embodiment. 5A shows the time change of the ignition switch of the internal combustion engine 12, and FIG. 5B shows the time change of the flag indicating whether or not negative pressure is generated in the intake manifold 14. As shown in FIG. C) shows the time change of the on / off state of the idle switch indicating whether or not the internal combustion engine 12 is in the idle state, FIG. 5D shows the time change of the HC temperature, and FIG. The time change of the ON signal to the VSV 52 is shown in FIG. 5F, and the time change of opening and closing of the switching valve 34 is shown.
[0044]
As shown in FIG.₀When the ignition switch is turned on at, the internal combustion engine 12 starts to start. Then time t₁When the engine speed NE of the internal combustion engine 12 is, for example, 400 rpm or more, a negative pressure is generated in the intake manifold 14 so that the switching valve 34 can operate properly between the fully open state and the fully closed state. Supply of the ON signal is started. And time t₂When the temperature of the start catalyst 20 (S / C temperature) reaches the activation temperature, the supply of the ON signal to the VSV 52 is stopped. In this case, a large amount of HC is adsorbed on the HC adsorbent 36.
[0045]
The estimated HC temperature is a temperature at which it can be determined that HC adsorbed on the HC adsorbent 36 is desorbed and HC remaining in the HC adsorbent 36 is reduced (for example, 180 ° C .; hereinafter, this temperature is referred to as a purge start temperature). ) (Time t in FIG. 5)₃), And the internal combustion engine 12 enters an idle state in which the throttle opening θ is equal to or less than a predetermined value (time t in FIG. 5).₄) And supply of the ON signal to the VSV 52 is started. In this case, the high-temperature exhaust gas passes through the HC adsorbent 36, so that the HC adsorbent 36 is brought into a higher temperature state. As a result, all the HC adsorbed on the HC adsorbent 36 is desorbed.
[0046]
And time t₅When the estimated HC temperature reaches a temperature at which it can be determined that all the HC adsorbed on the HC adsorbent 36 is desorbed (eg, 300 ° C .; hereinafter, this temperature is referred to as a purge end temperature), the VSV 52 is turned on. The signal supply is stopped. In this case, the exhaust gas flow passage is switched from the bypass passage 32 to the main passage 30 with no HC remaining in the HC adsorbent 36. Therefore, according to the present embodiment, the HC adsorbed on the HC adsorbent 36 can be forcibly purged toward the main catalyst 24 at an appropriate timing.
[0047]
The contents of processing for realizing the above functions in the system of this embodiment will be described below.
[0048]
FIG. 6 shows a flowchart of an example of a control routine executed by the ECU 10 in this embodiment in order to realize the above function. The routine shown in FIG. 6 is started every time the process is completed. When the routine shown in FIG. 6 is started, first, the process of step 100 is executed.
[0049]
In step 100, it is determined whether or not a condition for permitting the switching operation of the exhaust passage by the switching valve 34 (hereinafter referred to as a permit condition) is satisfied. Specifically, this permission condition is satisfied when the cooling water temperature or the outside air temperature of the internal combustion engine 12 is equal to or higher than a predetermined value (for example, −30 ° C.). As a result, if it is determined that the permission condition is not satisfied, the current routine is terminated without any further processing. On the other hand, if it is determined that the permission condition is satisfied, the process of step 102 is executed next.
[0050]
In step 102, it is determined whether or not the process of adsorbing the HC contained in the exhaust gas to the HC adsorbent 36 in the cold state is completed. As a result, when a negative determination is made, the current routine is terminated. On the other hand, if an affirmative determination is made, the process of step 104 is executed next.
[0051]
In step 104, the HC temperature estimated using the HC adsorbent temperature counter is the purge start temperature TH.₁It is determined whether or not it has been reached. HC temperature is purge start temperature TH₁If not, it can be determined that a large amount of HC still remains in the HC adsorbent 36. When high-temperature exhaust gas passes through the HC adsorbent 36 in such a state, a large amount of HC is desorbed from the HC adsorbent 36 within a short time, and all the HC from which the main catalyst 24 is desorbed cannot be effectively purified. Can occur. Therefore, the HC temperature is the purge start temperature TH.₁If it has not reached, it is not appropriate to perform a forced purge of HC from the HC adsorbent 36. Therefore, if such a determination is made, the process of step 106 is executed next.
[0052]
In step 106, processing for stopping the supply of the ON signal to the VSV 52 is executed in order to stop the forced purge of HC from the HC adsorbent 36. When the process of step 106 is executed, the switching valve 34 is maintained in the fully open state, or the exhaust gas flow passage becomes the main passage 30 by changing from the fully closed state to the fully open state. When the processing of step 106 is completed, the current routine is terminated.
[0053]
On the other hand, in step 104, the HC temperature is changed to the purge start temperature TH.₁In the case where the HC adsorbs to HC, it can be determined that the amount of HC adsorbed on the HC adsorbent 36 is low. In this case, even if the HC is forcibly purged from the HC adsorbent 36, a large amount of HC is not desorbed, and the main catalyst 24 can be effectively purified. Therefore, if such a determination is made, the process of step 108 is executed next. In step 108, it is determined whether or not the internal combustion engine 12 is in an idle state. When the internal combustion engine 12 is in the idle state, the opening of the throttle valve (throttle opening θ) provided in the intake manifold 14 is considerably reduced, so that the intake pressure becomes a low pressure state. When the intake pressure is maintained in a low pressure state, a large negative pressure is generated in the intake manifold, and the switching mechanism for opening and closing the switching valve 34 can be operated appropriately. Therefore, if it is determined in step 108 that the internal combustion engine 12 is in an idle state, the process of step 110 is executed next.
[0054]
In step 110, it is determined whether or not the HC forced purge from the HC adsorbent 36 has already been performed, that is, whether or not the switching valve 34 has been fully closed for the forced purge. As a result, if an affirmative determination is made, the process of step 112 is then executed. On the other hand, if a negative determination is made, the process of step 114 is executed next.
[0055]
In step 112, a process for supplying an ON signal to the VSV 52 is executed in order to forcibly purge HC from the HC adsorbent 36. When the processing of step 112 is executed, the switching valve 34 is fully closed, so that the exhaust gas flow passage becomes the bypass passage 32. When the processing of step 112 is finished, the current routine is finished.
[0056]
In step 114, the HC temperature estimated using the HC adsorbent temperature counter is the purge end temperature TH.₂(> TH₁) Is determined. HC temperature is purge end temperature TH₂If not, it can be determined that HC remains in the HC adsorbent 36, and it is appropriate to continue the forced purge of HC. Therefore, the HC temperature is equal to the purge end temperature TH.₂If it is determined that the value has not been reached, the process of step 112 is executed next. On the other hand, the HC temperature is the purge end temperature TH.₂Is reached, it can be determined that no HC remains in the HC adsorbent 36, and it is appropriate to stop the forced purge of HC. Therefore, the HC temperature is equal to the purge end temperature TH.₂If it is determined that the value has been reached, the process of step 106 is executed next. On the other hand, if it is determined in step 108 that the internal combustion engine 12 is not in the idle state, it can be determined that the throttle opening θ is large and the intake pressure is high. When the intake pressure is in a high pressure state, a large negative pressure is not generated in the intake manifold 14, so that it is impossible to properly operate the switching mechanism for opening and closing the switching valve 34. It is not appropriate to perform a forced purge of HC in such a state. Therefore, if it is determined in step 108 that the internal combustion engine 12 is not in an idle state, the process of step 116 is executed next.
[0057]
In step 116, it is determined whether or not the HC forced purge from the HC adsorbent 36 has already been performed, similar to the processing content of step 110. As a result, if an affirmative determination is made, the process of step 118 is then executed. On the other hand, if a negative determination is made, the process of step 120 is executed next.
[0058]
In step 118, the HC temperature is changed to the purge end temperature TH in the same manner as in step 114.₂It is determined whether or not it has been reached. As a result, when an affirmative determination is made, the process of step 106 is performed next. On the other hand, if a negative determination is made, the current routine is terminated.
[0059]
In step 120, the temperature TH estimated using the HC adsorbent temperature counter is a temperature TH at which it can be determined that all the HC adsorbed on the HC adsorbent 36 is desorbed.₃(= TH₂) Is determined. As a result, if a negative determination is made, the current routine is terminated. On the other hand, if an affirmative determination is made, it can be determined that all the HC adsorbed on the HC adsorbent 36 has been desorbed without performing a forced purge of HC. In this case, it is not necessary to perform a forced purge of HC thereafter. In the following, the above temperature TH₃Purge prohibition temperature TH₃Called. Therefore, if an affirmative determination is made, the process of step 106 is executed next.
[0060]
According to the above processing, when the HC temperature reaches a temperature at which it can be determined that the amount of HC remaining in the HC adsorbent 36 decreases, the forced purge of HC from the HC adsorbent 36 can be started. When the amount of HC remaining in the HC adsorbent 36 is small, a large amount of HC is not desorbed downstream of the HC adsorbent 36 even if the HC is forcibly purged. Further, when the HC temperature reaches a temperature at which it can be determined that all the HC adsorbed on the HC adsorbent 36 is desorbed, the forced purge of HC can be terminated. When HC is not adsorbed on the HC adsorbent 36, it is not necessary to perform a forced purge of HC. Therefore, according to the present embodiment, the HC adsorbed on the HC adsorbent 36 can be forcibly purged toward the main catalyst 24 at an appropriate timing. The forcibly purged HC is purified by the main catalyst 24. For this reason, deterioration of exhaust emission due to forced purge is avoided.
[0061]
Further, according to the above processing, the HC temperature is changed to the purge start temperature TH.₁And the forced purge of HC from the HC adsorbent 36 can be performed when the internal combustion engine 12 is in an idle state. When the internal combustion engine 12 is in the idle state, it can be determined that the throttle valve is closed to the vicinity of the fully closed state, and a large negative pressure is generated in the intake passage on the downstream side. In this case, the switching mechanism that opens and closes the switching valve 34 can be appropriately operated using the negative pressure as a driving source. Therefore, according to the present embodiment, the forced purge of HC adsorbed on the HC adsorbent 36 is performed in a state where the switching operation of the exhaust passage by the switching valve 34 can be performed properly, so that the adsorbed on the HC adsorbent 36. It is possible to reliably desorb HC. Further, according to the above processing, the internal combustion engine 12 is in the idle state, and the HC temperature is equal to the purge start temperature TH.₁Before the condition that the temperature has reached₃In this case, forced purge of HC from the HC adsorbent 36 can be prohibited. That is, the switching operation of the exhaust gas flow passage by the switching valve 34 from the main passage 30 to the bypass passage 32 for forcibly purging HC can be prohibited. HC temperature is the purge prohibition temperature TH₃If the HC adsorbent 36 is reached, it can be determined that all the HC adsorbed on the HC adsorbent 36 is desorbed and no HC remains in the HC adsorbent 36. In this case, there is no need to perform the switching operation of the exhaust passage by the switching valve 34. Therefore, according to the present embodiment, it is possible to avoid unnecessary operation of switching the exhaust passage by the switching valve 34.
[0062]
If the cooling water temperature or the outside air temperature of the internal combustion engine 12 is extremely low, for example, below −30 ° C., the switching mechanism 70 does not operate normally due to freezing or the like, and there is a risk that it will be damaged if operated forcibly. Therefore, in this embodiment, when the cooling water temperature or the outside air temperature is extremely low, the switching operation of the exhaust passage by the switching valve 34 is prohibited. That is, even if it is attempted to adsorb HC in the exhaust gas to the HC adsorbent 36 in the cold state, the switching of the exhaust passage by the switching valve 34 may not be performed. For this reason, if the forced purge is not performed, there may occur a situation in which the switching of the exhaust passage is not performed once during the period from the start of the internal combustion engine 12 to the end thereof. When such a situation occurs, the period during which the switching valve 34 is maintained in the fully closed state becomes long, and the switching valve 34 is likely to stick.
[0063]
However, in this embodiment, even when the switching operation of the exhaust passage by the switching valve 34 is not performed in the cold state, the internal combustion engine 12 is in an idle state and the HC temperature is equal to the purge start temperature TH.₁A forced purge is performed when the value is reached. That is, the switching operation of the exhaust passage by the switching valve 34 is performed. Therefore, according to this embodiment, the exhaust passage is switched at least once during the period from the start to the end of the internal combustion engine 12, so that the switching valve 34 can be reliably prevented from sticking. It has become.
[0064]
In this embodiment, the forced purge of HC from the HC adsorbent 36, that is, the opening / closing drive of the switching valve 34 for the forced purge depends on the intake air amount Ga detected using the existing air flow meter 64. This is performed based on the count value of the HC adsorbent temperature counter to be added or subtracted. For this reason, according to the present embodiment, it is not necessary to attach a temperature sensor for detecting the temperature to the HC adsorbent 36. Therefore, according to the system of the present embodiment, a mechanism for forcibly purging HC from the HC adsorbent 36 can be realized at low cost.
[0065]
In the above embodiment, the main catalyst 24 is the “catalyst” recited in the claims, and the communication path between the first exhaust pipe 18 and the second exhaust pipe 22 is the “catalyst” recited in the claims. The HC adsorbent 36 is in the “adsorbent” described in the claims, the bypass passage 32 is in the “first passage” in the claims, and the main passage 30 is in the “upstream exhaust passage”. In the "second passage" described in the claims, the purge start temperature TH₁The purge end temperature TH is added to the “first predetermined value” described in the claims.₂The purge prohibition temperature TH is added to the “second predetermined value” described in the claims.₃Corresponds to the “third predetermined value” recited in the claims.
[0066]
In the above embodiment, the ECU 10 calculates the HC adsorbent temperature (HC temperature) based on the count value of the HC adsorbent temperature counter that is added or subtracted according to the intake air amount detected using the air flow meter 64. By detecting the “state quantity detecting means” described in the claims, the “switching valve control means” described in the claims is realized by executing the processing of steps 104 to 120. Yes.
[0067]
By the way, in the above embodiment, the temperature of the HC adsorbent 36 is estimated based on the count value of the HC adsorbent temperature counter that is added or subtracted according to the intake air amount Ga detected using the air flow meter 64. The temperature sensor may be directly attached to the HC adsorbent 36 and its temperature may be detected.
[0068]
Further, in the above embodiment, the forced purge of HC from the HC adsorbent 36 is executed based on the temperature of the HC adsorbent 36, but the amount of HC adsorbed on the HC adsorbent 36 is determined. It is good also as detecting and performing a forced purge based on the adsorption amount.
[0069]
Furthermore, in the above embodiment, forced purge is always performed every time the process of adsorbing HC in the exhaust gas to the HC adsorbent 36 is completed in the cold state, but every time the process is completed a predetermined number of times. That is, when the number of times that HC is adsorbed to the HC adsorbent 36 in the cold state after the previous forced purge is performed (hereinafter referred to as the number of adsorption operations) reaches a predetermined number, the forced purge is performed. It is good also as performing. Note that this predetermined number of times is the number of times of an adsorption operation in which it can be determined that HC having a large number of carbon atoms in the exhaust gas is adsorbed to the HC adsorbent 36 by a certain amount. If the number of adsorption operations has not reached the predetermined number, it can be determined that a large amount of HC having a large number of carbon atoms has not been adsorbed to the HC adsorbent 36, and there is no need to perform forced purge. Therefore, if the forced purge is performed when the number of adsorption operations reaches a predetermined number, unnecessary switching operation of the exhaust passage by the switching valve 34 is avoided.
[0070]
【The invention's effect】
As described above, claim 1And 2According to the described invention,The exhaust passage can be switched properly by the switching valve.At an appropriate timing, unburned components in the exhaust gas adsorbed by the adsorbent can be purged toward the catalyst.
[0072]
Claims3According to the described invention, it is possible to avoid unnecessary switching operation of the exhaust passage by the switching valve.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an exhaust passage switching device according to an embodiment of the present invention.
FIG. 2 is an enlarged view of a main part of the exhaust passage switching device of the present embodiment.
FIG. 3 is a graph showing the relationship between the temperature of the HC adsorbent and the amount of HC adsorbed on the HC adsorbent after the start of the internal combustion engine is started.
FIG. 4 is a graph showing the relationship between the number of carbon atoms in one molecule and the boiling point.
FIG. 5 is a diagram showing a time chart realized after the start of the internal combustion engine is started in the system of the present embodiment.
FIG. 6 is a flowchart of an example of a control routine executed by the ECU in the present embodiment.
[Explanation of symbols]
10 Electronic control unit (ECU) for internal combustion engine
12 Internal combustion engine
24 Main catalyst
30 Main passage
32 Bypass passage
34 Switching valve
36 HC adsorbent
64 Air flow meter

Claims (3)

An exhaust passage provided with a catalyst, an exhaust passage upstream of the catalyst, a first passage provided with an adsorbent for adsorbing unburned components in the exhaust gas, and a second passage bypassing the adsorbent A switching valve that selectively switches between and an exhaust passage on the upstream side of the catalyst to purge unburned components adsorbed on the adsorbent toward the catalyst when a predetermined condition is satisfied. An exhaust passage switching device for an internal combustion engine, comprising: switching valve control means for driving the switching valve so as to switch to one passage;
The switching valve is driven using a negative pressure generated in the intake passage downstream of the throttle valve as a drive source,
Comprising state quantity detection means for detecting the temperature of the adsorbent;
The switching valve control means is when the internal combustion engine is in an idle state where the opening of the throttle valve is less than or equal to a predetermined value, and the temperature detected by the state quantity detection means is greater than or equal to a first predetermined value. And the switching valve is driven so that an exhaust passage upstream of the catalyst is switched to the first passage in order to start purging of unburned components adsorbed on the adsorbent. Engine exhaust passage switching device. The exhaust passage switching device for an internal combustion engine according to claim 1 ,
The switching valve control means, when the temperature detected by the state quantity detecting means reaches a second predetermined value higher than the previous SL first predetermined value, so as to terminate the purge of the catalyst An exhaust passage switching device for an internal combustion engine, wherein the switching valve is driven so that an upstream exhaust passage is switched to the second passage. The exhaust passage switching device for an internal combustion engine according to claim 1 ,
The switching valve control means has a third predetermined value in which the temperature detected by the state quantity detecting means is higher than the first predetermined value before the opening of the throttle valve becomes less than or equal to the predetermined value. When it reaches, the driving of the switching valve is prohibited, and the exhaust passage switching device of the internal combustion engine is characterized by.

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