JP2003314259A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To promote activation of an exhaust gas purifying catalyst of an internal combustion engine, and to improve an exhaust gas purifying function. <P>SOLUTION: An activation parameter showing the degree of activation of the exhaust gas purifying catalyst on the basis of the elapsed time after starting of an engine and a starting time water temperature is calculated. When the catalyst is determined to be in an unactivated state on the basis of the activation parameter, evaporative fuel from a canister is purged to an exhaust passage on the upstream side of the catalyst. Here, target HC concentration of a supply gas to the catalyst containing the purge gas is calculated on the basis of the activation parameter, and driving of a purge pump is controlled so as to become the target HC. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification technique for an internal combustion engine, and more particularly to a technique for improving exhaust gas purification performance by using an evaporated fuel processing device.

[0002]

2. Description of the Related Art In an internal combustion engine for a vehicle, an air-fuel ratio of an air-fuel mixture supplied to an engine is made rich when an exhaust purification catalyst (hereinafter also simply referred to as a catalyst) arranged in an exhaust passage is inactive at a low temperature. To increase HC (unburned fuel) in the exhaust gas
There is one in which the catalyst is activated by oxidizing C with a catalyst to generate heat (JP-A-7-158).
430).

[0003]

However, in the above-mentioned prior art, the air-fuel ratio is forcibly made rich when the catalyst is inactive, resulting in deterioration of fuel consumption and deterioration of drivability. The present invention has been made in view of such conventional problems, and an object thereof is to activate a catalyst without deteriorating fuel efficiency and driving performance.

[0004]

According to the present invention, when the exhaust purification catalyst arranged in the exhaust passage is judged to be inactive, the evaporated fuel adsorbed in the canister is purged into the exhaust passage upstream of the catalyst. As a result, the evaporated fuel supplied to the catalyst undergoes an oxidation reaction and heat is generated at the catalyst, and the catalyst can be heated and activated, and the catalyst can be activated without degrading fuel efficiency and drivability. The throughput of fuel can be increased.

Further, the purge amount is increased as the degree of activation of the catalyst by purging the evaporated fuel is increased, so that the oxidation treatment capacity of the evaporated fuel is increased as the degree of activation of the catalyst is increased. Since the evaporated fuel is purged, the catalyst activation time can be shortened as much as possible while suppressing the discharge of untreated HC. Further, after the catalyst is activated, the purge amount is gradually decreased to suppress a sudden decrease in exhaust pressure due to a decrease in the purge amount in the exhaust passage, and to prevent a rapid increase in the cylinder intake air amount accordingly. It is possible to prevent deterioration of drivability due to leanness.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a system configuration diagram of a vehicle internal combustion engine including an exhaust emission control device according to the present invention. In FIG. 1, air is sucked into each cylinder of an internal combustion engine 1 mounted on a vehicle through an air cleaner 2, an intake pipe 3, and an electronically controlled throttle valve 4.

The electronically controlled throttle valve 4 is a system configured to open and close the valve body of the throttle valve by an actuator such as a motor. Further, an electromagnetic fuel injection valve 5 is provided so as to inject fuel (gasoline) into the intake port of each cylinder. The fuel injection valve 5 energizes a solenoid in response to an injection pulse signal output from the control unit 20 to open the valve, and injects fuel whose pressure is adjusted to a predetermined pressure. Then, the air-fuel mixture formed in the combustion chamber is ignited and burned by the spark plug 6 controlled based on the ignition signal from the control unit 20.

However, the engine may be constructed such that a fuel injection valve is provided in the combustion chamber and the fuel is directly injected. Exhaust gas from the engine 1 is discharged through an exhaust pipe 7, and an exhaust purification catalyst 8 is installed in the exhaust pipe 7. Also, the fuel tank 9
An evaporative fuel treatment device is provided to treat the evaporative fuel generated from the fuel vapor.

The canister 10 is an airtight container filled with an adsorbent 11 such as activated carbon, and an evaporated fuel introducing pipe 12 from a fuel tank 9 is connected to the canister 10. Therefore, institution 1
Evaporative fuel generated in the fuel tank 9 while the
It is guided to the canister 10 through the evaporated fuel introducing pipe 12 and is adsorbed and collected there. Further, the canister 10 has a fresh air introduction port 13 and the purge pipe 1
4 has been derived. A purge control valve 15 whose opening area is controlled by a control signal from the control unit 20 is interposed in the purge pipe 14.

In the above structure, when the purge control valve 15 is controlled to be opened, the suction negative pressure of the engine 1 acts on the canister 10, and as a result, the air introduced from the fresh air introduction port 13 causes the adsorbent 11 of the canister 10 to enter. The adsorbed fuel vapor is purged, and purge air containing the purged fuel vapor is drawn into the intake pipe 3 downstream of the throttle valve 4 through the purge pipe 14, and thereafter in the combustion chamber of the engine 1. Burned.

In the structure of the basic evaporated fuel processing device,
The structure of the present invention for activating the inactive catalyst 8 by purging the fuel vapor to the catalyst 8 is added. That is, a second (exhaust side) purge pipe 31 that connects the evaporative fuel lead-out side of the canister 10 and the exhaust pipe 7 upstream of the catalyst 8 is provided,
An electric purge pump 3 for pumping the evaporated fuel in the canister 10 to the exhaust pipe 7 upstream of the catalyst 8 in the purge pipe 31.
Interpose 2.

The control unit 20 includes a CPU and R
A microcomputer including an OM, a RAM, an A / D converter, an input / output interface, and the like is provided, input signals from various sensors are received, arithmetic processing is performed based on the input signals, and the fuel injection valve 5 and the spark plug 6 are provided. In addition to controlling the operation of the purge control valve 15 and the like, the purge pump 32 is controlled to be driven when the catalyst 8 is inactive to control the amount of evaporated fuel purged to the catalyst 8.

As the various sensors, a crank angle sensor 21 for detecting the crank angle of the engine 1 is provided, and the engine rotation speed Ne is calculated based on the detection signal from the crank angle sensor 21. In addition, an air flow meter 22 that detects the intake air flow rate Qa upstream of the throttle valve 4 of the intake pipe 3, a throttle sensor 23 that detects the opening TVO of the throttle valve 4, a water temperature sensor 24 that detects the cooling water temperature Tw of the engine 1, An air-fuel ratio sensor 25 for detecting the exhaust air-fuel ratio based on the oxygen concentration in the exhaust gas is provided, and an HC concentration sensor 26 for detecting the HC concentration in the purge gas supplied to the catalyst 8 via the purge pipe 31. Is provided.

Next, the state of purge control of the evaporated fuel for activating the catalyst 8 by the control unit 20 will be described with reference to the flowcharts of FIGS. 2 and 3. The flow starts when the ignition switch is turned on. In step S1, various operating conditions for detecting an inactive state of the catalyst 8, specifically, a low temperature state are read. Specifically, as the first embodiment, the elapsed time after starting ts and the starting water temperature Tw are read.

At step S2, the elapsed time after the start t
Based on s and the starting water temperature Tw, an activity parameter indicating the degree of activity of the catalyst 8 is calculated by searching a map or the like. Specifically, since the temperature of the catalyst 8 increases as the post-start elapsed time ts increases and the start-time water temperature Tw increases, the value of the activation parameter (activity level) is calculated to increase.

In step S3, it is determined whether the catalyst 8 is activated (activity parameter is 100%) based on the value of the activity parameter. When it is determined in step S3 that the catalyst 8 is activated, step S3
4, the process determines whether or not the engine has just started after the start-up elapsed time ts. If it is determined in step S4 that the engine has just started, a so-called hot restart (warm restart) is performed.
Since there is no need to purge the activated catalyst 8 with the evaporated fuel, it is time to stop the purge pump 32 (OF
Maintaining F), this routine ends. If it is determined in step S4 that the engine has not just been started, the process proceeds to step S7 and subsequent steps to perform purge stop control. This will be described later.

When it is determined in step S3 that the catalyst 8 is inactive, the routine proceeds to step S5, where the target HC concentration of the purge gas supplied to the catalyst 8 is set in accordance with the value of the activation parameter calculated in step S2. , Calculated from a table or the like. Specifically, the larger the value of the activation parameter, that is, the higher the degree of activity, is, the more the oxidation treatment capacity of the evaporated fuel by the catalyst 8 increases. It is set to increase.

In step S6, based on the target HC concentration calculated in step S3 and the actual HC concentration in the purge gas for the catalyst 8 detected by the HC concentration sensor 33, the actual HC concentration is determined to be the target HC concentration. The drive amount of the purge pump 32 is controlled so that In this way
The vaporized fuel purged when the catalyst 8 is inactive oxidizes in the catalyst 8 and generates heat, which raises the temperature of the catalyst 8 and activates it.
By increasing the purge amount of the evaporated fuel as the degree of activity increases and the evaporated fuel oxidation treatment capacity of the catalyst 8 increases, it is possible to prevent HC from being discharged without being processed by the catalyst 8 and to the extent possible. In addition, the activation time of the catalyst 8 can be shortened.

When the activation of the catalyst 8 is completed by the above activation control, that is, in step S3, the catalyst 8 is activated.
When the activation of is completed and it is determined in step S4 that it is not immediately after the start, the process proceeds to step S7 and thereafter to perform the purge stop control. In step S7, the engine speed N
Based on e and the basic fuel injection amount Tp as a representative value of the engine load, the evaporative fuel purge reduction amount to the catalyst 8 is calculated by searching a map or the like. Specifically, since the exhaust pressure (exhaust flow rate) in the exhaust pipe 7 increases as the rotation speed increases and the load increases, the exhaust pressure change is small even if the purge reduction amount is increased, and the increase of the cylinder intake air amount can be suppressed. The purge reduction amount is set to a large value, and the exhaust pressure is smaller when the engine speed is low and the load is low. Therefore, the purge reduction amount is set to a small value to suppress an increase in the cylinder intake air amount.

In step S8, the drive current of the purge pump 32 is reduced in accordance with the evaporative fuel purge reduction amount calculated in step S7 to reduce the discharge amount (evaporated fuel purge amount). In step S9, it is determined whether or not the discharge amount of the purge pump 32 has reached 0, and until it reaches 0, step S7
Then, the reduction control is continued, and when it becomes 0, the process proceeds to step S10, and the drive of the purge pump 32 is stopped.
That is, the discharge amount is gradually reduced and the driving is stopped.

As a result, it is possible to suppress the change in the exhaust pressure when the purging of the exhaust pipe 7 is stopped and prevent the air-fuel ratio from becoming lean. In the above-described embodiment, the degree of activity of the catalyst 8 is calculated based on the elapsed time after start-up and the water temperature at start-up in step S2, but the degree of activity is estimated by estimating the catalyst temperature as follows. It may be configured. That is, FIG.
4, an outside air temperature sensor 41 for detecting the outside air temperature is provided (the intake air temperature sensor may detect the intake air temperature as the outside air temperature), and as shown in FIG.
At the outside temperature Ta, the water temperature Tw, the engine rotation speed Ne,
The temperature of the catalyst 8 is estimated based on the basic fuel injection amount Tp. Specifically, the amount of heat generated by combustion and supplied to the catalyst 8 via the exhaust gas is calculated based on these parameters, and the amount of heat released from the catalyst 8 to the outside air is calculated to obtain the transfer of the amount of heat. Then, when considering the steady state, when a heat amount that becomes a reference temperature for activation of the catalyst 8, for example, 450 ° C. or higher is transferred, the excess heat amount that is equal to or higher than the reference temperature is calculated as a plus, When the amount of heat that is less than the reference temperature is exchanged, the amount of insufficient heat that is less than the reference temperature is added as a negative value, and the catalyst temperature is estimated from this integrated value.

Then, the catalyst 8 estimated in step S3 '
It is determined whether or not the catalyst 8 is activated (catalyst temperature is equal to or higher than a predetermined value) based on the temperature of, and when the catalyst 8 is determined to be inactive in step S3 ′, the process proceeds to step S5 ′. The target HC concentration of the purge gas supplied to the catalyst 8 is calculated according to the catalyst temperature by searching a table or the like.

In the purge stop control, the reduction amount of the discharge amount of the purge pump is set based on the engine operating condition (rotational speed, load) in step S7, but as shown in FIG. 5, step S7 ' In step 3, the reduction amount of the purge pump discharge amount is set based on the HC concentration detected by the HC concentration sensor 26, that is, the HC concentration of the gas supplied to the catalyst 8 so that the HC concentration does not suddenly decrease. It may be configured to.

Further, technical ideas other than the claims which can be grasped from the above embodiment will be described below together with their effects. In the exhaust gas purification apparatus for an internal combustion engine according to claim 1, purging of the evaporated fuel adsorbed in the canister to the exhaust passage upstream of the catalyst is performed by connecting the canister and the exhaust passage upstream of the catalyst by a purge pipe. An exhaust emission control device for an internal combustion engine, characterized by being driven by driving an interposed electric purge pump.

According to this structure, when the catalyst is inactive, the purge pump is driven to control the discharge amount, so that the purge control to the exhaust passage upstream of the catalyst can be performed easily and accurately. The exhaust purification system for an internal combustion engine according to claim 1, wherein the determination of the degree of activity of the exhaust purification catalyst is performed based on the elapsed time after starting the engine and the water temperature during startup. .

According to this structure, the amount of heat supplied from the exhaust gas to the catalyst increases as the elapsed time after the engine starts increases,
Further, since the exhaust temperature is higher and the amount of heat supplied to the catalyst is increased as the starting water temperature is higher, it is possible to determine the catalyst temperature and thus the degree of activity of the catalyst based on these conditions. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the determination of the activity degree of the exhaust gas purification catalyst is performed by determining the outside air temperature, water temperature, engine rotation speed, engine load (for example, basic fuel injection amount).
And an exhaust gas purification device for an internal combustion engine.

According to this configuration, as already described in the embodiment, it is possible to estimate the catalyst temperature by estimating the transfer of the amount of heat with respect to the catalyst, and thus to judge the degree of activity of the catalyst. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the amount of decrease in the evaporated fuel purge amount after activation of the exhaust gas purification catalyst is set based on the engine speed and the engine load (for example, basic fuel injection amount). An exhaust gas purification device for an internal combustion engine, characterized in that

According to this structure, the exhaust pressure (exhaust flow rate) is determined by the engine speed and the load, so that the evaporative fuel purge amount is decreased so as to suppress the increase of the cylinder intake air amount due to the change of the exhaust pressure. By setting, it is possible to prevent the air-fuel ratio from becoming lean. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the HC concentration in the gas supplied to the exhaust gas purification catalyst is detected, and a decrease amount of the evaporated fuel purge amount after activation of the catalyst is supplied to the catalyst. The exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas purifying apparatus is set based on the HC concentration in the gas to be generated.

According to this configuration, the air-fuel ratio can be prevented from becoming lean as in the above case by setting the decrease amount of the purge pump discharge amount so that the HC concentration does not drop sharply.

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration of an internal combustion engine in an embodiment.

FIG. 2 is a flowchart showing a former stage of purge control in the embodiment.

FIG. 3 is a flowchart showing a latter stage of purge control in the embodiment.

FIG. 4 is a flowchart showing a part of purge control according to the second embodiment.

FIG. 5 is a flowchart showing a part of purge control in the third embodiment.

[Explanation of symbols]

1 ... Internal combustion engine 9 ... Fuel tank 10 ... Canister 20 ... Control unit 21 ... Crank angle sensor 26 ... HC concentration sensor 31 ... Second purge pipe 32 ... Purge pump 41 ... Outside temperature sensor

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Claims (3)

[Claims] 1. The degree of activity of an exhaust purification catalyst disposed in an exhaust passage is determined, and when the catalyst is inactive, the evaporated fuel adsorbed in a canister is purged into the exhaust passage upstream of the catalyst to remove the catalyst. An exhaust emission control device for an internal combustion engine, characterized in that it is activated. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the purge amount of the evaporated fuel is increased as the degree of activation of the exhaust gas purification catalyst is increased. 3. The internal combustion engine according to claim 1, wherein after the exhaust purification catalyst is activated, the purge amount of the evaporated fuel is gradually decreased to stop the purge. Exhaust purification device.