JPH0828253A - Secondary air feeding device for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a secondary air feeding device which is constituted to feed a proper amount according to an operation state and prevent the damage of purifying characteristics. CONSTITUTION:Secondary air for cooling exhaust gas is taken out from a place situated downstream from a supercharger 103 and fed in exhaust gas from a venturi 113 installed in an exhaust pipe 111 through an air control valve 119. A bypass pipe 114 bypassing the venturi is located in the exhaust pipe and an exhaust gas control valve 115 is installed in the bypass pipe 114. During high rotation high load running, the exhaust control valve is closed and since all exhaust gas passes an exhaust gas pipe, a secondary air amount is increased to cool exhaust gas. In this case, since exhaust gas is brought into air rich and purifying performance of nitrogen oxide of a three-dimensional catalyst 117 is lowered, an EGR valve 121 is opened and exhaust gas is returned in intake air. Further, Heat-exchange is practicable between secondary or and exhaust gas and the temperature of exhaust gas is lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary air supply device for an internal combustion engine, and more particularly to a secondary air supply device capable of controlling the amount of supplied air according to the operating condition.

[0002]

2. Description of the Related Art In order to reduce carbon monoxide (CO) and hydrocarbons (HC) contained in exhaust gas discharged from an internal combustion engine, the air-fuel ratio is maintained at a stoichiometric air-fuel ratio in almost all operating regions. Is normal. However, since the exhaust gas temperature rises in the high rotation and high load range,
The exhaust pipe or catalyst will be exposed to high temperatures.

In order to solve this problem, it has been proposed that the exhaust pipe or the catalyst has a double pipe structure, and the exhaust gas or the catalyst is cooled by introducing the atmosphere into the outer pipe. Particularly in a vehicle equipped with a turbocharger or a supercharger, the cooling effect can be enhanced by using cooling air as supercharged air downstream of the turbocharger or the supercharger.

Further, it has been proposed that a venturi portion is provided in the exhaust pipe, and secondary air is introduced into this venturi portion to directly reduce the temperature of the exhaust gas (Japanese Patent Laid-Open No. 6-242242).
2-118019).

[0005]

However, in the secondary ventilator for supplying the secondary air proposed in the above-mentioned prior art, the secondary air amount is controlled by the exhaust gas flow and the secondary air amount is positively controlled. The problem arises that you cannot do it. Furthermore, when secondary air is introduced, there is a problem that nitrogen oxides (NOx) are not purified in the catalyst.

The present invention has been made in view of the above problems, and an internal combustion engine capable of supplying an appropriate amount of secondary air according to the operating state and not impairing the purification characteristics of nitrogen oxides. It is an object of the present invention to provide a secondary air supply device.

[0007]

A secondary air supply device for an internal combustion engine according to a first aspect of the present invention includes a venturi portion provided in an exhaust pipe of the internal combustion engine, and a secondary air supply pipe opening to the venturi portion. A bypass exhaust pipe that bypasses the venturi portion and a flow rate control unit that is installed in the bypass exhaust pipe and controls the flow rate of exhaust gas flowing through the bypass exhaust pipe are provided.

A secondary air supply system for an internal combustion engine according to a second aspect of the present invention is installed downstream of a supercharger installed in an intake pipe, a confluence of an exhaust pipe having a venturi portion and a bypass exhaust pipe. A three-way catalyst, a secondary air supply pipe that branches from the intake pipe on the downstream side of the supercharger and supplies a secondary air supply to the venturi portion, an air control valve that controls opening and closing of the secondary air supply pipe, and a venturi portion. An exhaust gas recirculation pipe that branches from the upstream exhaust pipe and recirculates the exhaust gas to the intake pipe upstream of the supercharger, an EGR valve that controls the amount of exhaust gas flowing through the exhaust gas recirculation pipe, and an operation in which the exhaust gas temperature rises excessively In the state, the air control valve and the EGR valve are further provided with valve opening control means, and heat exchange between the exhaust gas and the secondary air between the EGR valve and the secondary air supply pipe is possible. It is characterized by being placed in.

[0009]

In the secondary air supply system for the internal combustion engine according to the first aspect of the present invention, the secondary air is supplied to the venturi installed in the exhaust pipe to reduce the temperature of the exhaust gas, and the bypass exhaust bypasses the venturi. The flow rate of exhaust gas flowing through the pipe is set and controlled by the flow rate control means.

In the secondary air supply system for the internal combustion engine according to the second aspect of the present invention, the secondary air is taken out from the downstream side of the supercharger to compensate for the deterioration of the nitrogen oxide purification capability of the three-way catalyst. The exhaust gas is recirculated upstream of the supercharger, and the EGR valve is cooled by the secondary air.

[0011]

1 is a block diagram of an embodiment of a secondary air supply system for an internal combustion engine according to the present invention, showing a case where a supercharger is used as a supercharger. That is, the intake air drawn from the air cleaner 101 is pressurized by the supercharger 103 after the flow rate is controlled by the throttle valve 102.

After that, the intake air is cooled by the interclave 104, and is taken into the cylinder 107 from the surge tank 105 through the intake valve 106. The intake pressure is the surge tank 105.
An injector 1 for injecting fuel to the upstream side of the intake valve 106, which is detected by an intake pressure sensor 108 installed in
09 is installed.

Exhaust gas generated in the cylinder 107 is exhaust gas 1
The gas is exhausted to the exhaust pipe 111 through the exhaust pipe 11
1 is an oxygen sensor 1 for detecting the air-fuel ratio of the exhaust gas.
12 are installed. Exhaust pipe 1 downstream of the oxygen sensor 112
A venturi 113 is installed at 11, and a bypass pipe 114 that bypasses the venturi 113 is installed.

Further, the bypass pipe 114 joins the exhaust pipe 111 downstream of the venturi 113, and an exhaust control valve 115 for controlling the flow rate of the exhaust gas flowing through the bypass pipe 114 is installed in the bypass pipe 114. The exhaust control valve 115 is driven by the exhaust control valve actuator 116. Further, the bypass pipe 114 of the exhaust pipe 111
A three-way catalyst 117 for purifying exhaust gas is installed on the downstream side of the confluence point with.

The secondary air supply pipe 118 branched from the downstream of the intercooler 104 and the upstream of the surge tank 105 is
Venturi 11 via air control valve 119 which is a solenoid valve
Open to 3. That is, by using the intake air pressurized by the turbocharger 103 as the secondary air, it is possible to omit the dedicated pump for supplying the secondary air.

Further, the exhaust gas temperature of the internal combustion engine becomes higher as the rotation speed and load increase, but the supercharging pressure also becomes higher as the rotation speed and load increase, so that sufficient cooling air can be secured. . The upstream of the branch point of the bypass pipe 114 of the exhaust pipe 111 and the upstream of the turbocharger 103 are connected by an exhaust gas recirculation pipe 120 that recirculates exhaust gas to intake air.

The amount of exhaust gas recirculated is the exhaust gas recirculation pipe 1.
It is controlled by an EGR valve 121 installed at 20.
The outside of the EGR valve 121 is covered with a secondary air supply pipe 118, and the EGR valve 121 exposed to high temperature by exhaust gas is cooled by the secondary air.

The supercharger 103 is directly connected to an electromagnetic clutch 123 driven by a crank pulley 122. The throttle valve 102 is driven by the throttle actuator 124. The secondary air supply device for an internal combustion engine according to the present invention is controlled by the control unit 130 including a microcomputer, but the intake pressure detected by the intake pressure sensor 108 and the exhaust gas detected by the oxygen sensor 112 The residual oxygen content of the control unit 1
Read in 30.

Further, the injector 109, the exhaust control valve actuator 116, the air control valve 119, and the EGR valve 12
1, the electromagnetic clutch 123 and the throttle actuator 124 are driven by the output of the control unit 130. FIG. 2 is a flowchart of the control routine executed by the control unit 130, which is executed at regular time intervals.

In step 201, the internal combustion engine speed Ne, the intake pressure PM and the air-fuel ratio λ in the exhaust gas are read. At step 202, it is judged if the air-fuel ratio λ is equal to the theoretical air-fuel ratio λr. If an affirmative decision is made in step 202, the routine proceeds to 203, where it is decided whether or not it is in the secondary air cooling region.

FIG. 3 is a graph for determining the secondary air cooling region, where the horizontal axis represents the internal combustion engine speed Ne and the vertical axis represents the intake pressure P.
Take M. When the coordinates determined by the current internal combustion engine speed Ne and the intake pressure PM are in the shaded area, that is, when the engine speed is high and the load is high, the exhaust control valve 115 is controlled to be closed. That is, the exhaust control valve 115 is controlled to open when the engine speed is high and the load is not high.

That is, when an affirmative decision is made in step 203,
That is, when it is determined that the engine speed is high and the load is high, the routine proceeds to step 204, where a full closing command is output to the exhaust control valve actuator 116 that drives the exhaust control valve 115. In step 205, the solenoid of the air control valve 119 is excited to open the air control valve, and the intake air pressurized by the supercharger 103 is supplied as secondary air from the venturi 113 to the exhaust pipe 111.

When the exhaust control valve 115 is controlled to be fully closed, all the exhaust gas passes through the venturi 113, so the so-called Venturi effect becomes large and the secondary air is sufficiently sucked. As a result, the mixed gas of secondary air and exhaust gas is supplied to the three-way catalyst 117, and the oxygen sensor 11
Even if the exhaust gas is detected to have the stoichiometric air-fuel ratio by No. 2, the mixed gas supplied to the three-way catalyst 117 is in an air rich state and the nitrogen oxides are not sufficiently purified.

Therefore, the routine proceeds to step 206, where the EGR valve 1
The solenoid 21 is excited to open the valve, and the exhaust gas is recirculated upstream to the supercharger 103 to reduce nitrogen oxides generated by combustion in the cylinder 107. Since the exhaust gas has a high temperature in an operating state of high rotation and high load, the EGR valve 121 is placed in a severe operating environment.

Therefore, the secondary air pipe 118 is connected to the EGR valve 1
By arranging so as to cover 21, the heat exchange between the secondary air and the exhaust gas is enabled and the temperature rise of the EGR valve 121 is suppressed. In step 207, a fuel injection amount correction coefficient for making the air-fuel ratio the stoichiometric air-fuel ratio is calculated, and this routine ends.

When the determinations at steps 202 and 203 are negative, at step 208 the exhaust control valve 115
Is fully opened, and almost the entire amount of exhaust gas is allowed to flow through the bypass pipe 114. The air control valve 119 is closed in step 209, the EGR valve 121 is closed in step 210, and this routine is ended. FIG. 4 is a first graph showing the opening degree of the exhaust control valve, in which the horizontal axis represents the rotation speed Ne and the vertical axis represents the opening degree.

That is, when the internal combustion engine speed Ne is B or less, the exhaust control valve 115 is fully opened, and almost all of the exhaust gas passes through the bypass pipe 114 and is not cooled by the secondary air. When the internal combustion engine speed Ne becomes B or more, the exhaust control valve 115 is fully closed, and the exhaust gas is venturi 11
It cools by secondary air through 3.

FIG. 5 is a second graph showing the opening degree of the exhaust control valve. When the rotation speed Ne becomes higher than B or higher, the exhaust control valve 115 is gradually opened and the exhaust pressure back pressure is increased. Suppress rising. FIG. 6 is a flowchart of the exhaust control process executed in place of step 204 of the control routine shown in FIG.

In order to perform this process, the back pressure sensors 131 and 2 are provided upstream of the branch point of the bypass pipe 114 of the exhaust pipe 111.
A secondary air flow rate sensor 132 is additionally installed. If an affirmative decision is made in step 203 of the control routine shown in FIG.
Proceeding to step 61, the exhaust pressure PE and the secondary air flow rate Q
Read s. In step 62, the secondary air flow rate Q
It is determined whether or not s has decreased by a predetermined value ε or more from the secondary air flow rate QB at the time of the previous processing.

When a negative determination is made in step 62, that is, when the decrease amount is small, the routine proceeds to step 63, where it is determined whether or not the secondary air flow rate Qs has increased by a predetermined value ε or more from the secondary air flow rate QB in the previous processing. judge. When the affirmative judgment is made in step 63, that is, when the increase amount is large, step 6
4, the exhaust gas back pressure PE is a predetermined threshold pressure P.
It is determined whether or not t or more.

When a negative determination is made in step 64, the routine proceeds to step 65, where the exhaust control valve 115 is opened. When a positive determination is made, the routine proceeds to step 66, where the exhaust control valve 115 is closed and the routine proceeds to step 67. When the affirmative determination is made in step 62, the process directly proceeds to step 66. Step 63
When a negative decision is made in step 67, the process directly proceeds to step 67.

At step 67, the secondary air flow rate Qs is stored as the secondary air flow rate QB at the time of the previous processing, and this routine is ended. According to this control, it becomes easy for secondary air to enter, and it is possible to prevent the back pressure of the exhaust pipe from rising above a predetermined level. A pressure sensor 133 may be provided in the venturi portion 113, and the venturi portion pressure PB may be used instead of the secondary air flow rate Qs.

FIG. 7 is a flow chart of the second control routine. In order to perform this processing, the exhaust gas temperature sensor 134 is provided upstream of the branch point of the bypass pipe 114 of the exhaust pipe 111.
And the gas temperature sensor 135 entering the three-way catalyst 117 inlet
Is added. In step 701, the exhaust gas temperature TE, the incoming gas temperature TC, and the air-fuel ratio λ in the exhaust gas are read.

At step 702, it is judged if the air-fuel ratio λ is equal to the stoichiometric air-fuel ratio λr. Step 702
If the affirmative determination is made in step 703, the process proceeds to step 703, and it is determined whether the exhaust gas temperature TE is equal to or higher than the predetermined temperature TH, that is, whether it is in the secondary air cooling region. When an affirmative decision is made in step 703, the routine proceeds to step 704, where the solenoid of the air control valve 119 is excited to open the air control valve, and the routine proceeds to step 705, where the EGR valve 121 is excited to solenoid and the EGR valve 121. Is opened.

In step 706, it is determined whether the incoming gas temperature TE is below a predetermined temperature TL. Step 706
If an affirmative decision is made in step 7, the process proceeds to step 707, and the exhaust control valve 115 is opened. On the contrary, if a negative determination is made in step 706, the process proceeds to step 708, and the exhaust control valve 115 is closed.

When a negative determination is made in step 702 and step 703, in step 709 the exhaust control valve 115
Fully open. The air control valve 119 is closed in step 710, the EGR valve 121 is closed in step 711, and this routine is ended. According to this control method, since the exhaust gas temperature is directly detected to control the secondary air amount, it is possible to improve the control accuracy.

Further, by installing the exhaust valve 136 in the exhaust pipe 111 downstream of the branch point of the bypass pipe 114, controllability can be improved. FIG. 8 is a first graph showing the opening degrees of the exhaust control valve and the exhaust valve, in which the horizontal axis represents the rotation speed Ne and the vertical axis represents the opening degrees. That is, when the rotation speed Ne is B or less, both the exhaust control valve 115 and the exhaust valve 136 are fully opened.

When the rotation speed Ne becomes B or more, the exhaust control valve 1
15 is fully closed and the amount of secondary air is increased. After that, the opening degree of the exhaust control valve 115 is increased according to the increase of the rotation speed Ne to suppress the increase of the back pressure of the exhaust gas. When the rotation speed Ne further increases and becomes C or more, the exhaust valve 136 is closed to prevent the venturi 113 from being exposed to a high temperature.

FIG. 9 is a second graph showing the opening degrees of the exhaust control valve and the exhaust valve. When the rotation speed Ne is B or less, the exhaust valve 136 is fully closed and the three-way catalyst 117 is the secondary. Prevents transient cooling by air. The above embodiments have been described with respect to the application example to the internal combustion engine equipped with the supercharger as the supercharger, but the present invention can also be applied to the internal combustion engine equipped with the turbocharger as the supercharger. .

FIG. 10 is a block diagram when the present invention is applied to an internal combustion engine equipped with a turbocharger,
A compressor 141 is installed downstream of the air cleaner 101 and the throttle valve 102 to pressurize intake air. The compressor 141 is driven by an exhaust turbine 142 provided in the exhaust pipe 111.

In FIG. 10, the exhaust turbine 142 is installed on the upstream side of the venturi 113.
It can be installed downstream from the confluence of 13 and the bypass pipe 114. In this case, since the exhaust turbine 142 is driven by the mixed gas of the secondary air and the exhaust gas,
Excessive rise in the temperature of the exhaust turbine is suppressed.

[0042]

According to the secondary air supply system for an internal combustion engine according to the first aspect of the present invention, not only the secondary air supplied from the venturi can reduce the temperature of the exhaust gas, but also the venturi. It is also possible to control the flow rate of the exhaust gas flowing through the bypass exhaust pipe that bypasses the exhaust gas by the flow rate control means.

According to the secondary air supply system for the internal combustion engine of the second aspect of the present invention, the secondary air supply pump is omitted by taking out the secondary air from the downstream side of the supercharger, and in the three-way catalyst. Not only can it be possible to suppress a decrease in the ability to purify nitrogen oxides, but it is also possible to prevent the EGR valve from becoming excessively high in temperature.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is a flowchart of a control routine.

FIG. 3 is a secondary air cooling area determination graph.

FIG. 4 is a first graph showing an opening degree of an exhaust control valve.

FIG. 5 is a second graph showing the opening degree of the exhaust control valve.

FIG. 6 is a flowchart of a first exhaust control process.

FIG. 7 is a flowchart of a second exhaust control process.

FIG. 8 is a first graph showing the opening degrees of the exhaust control valve and the exhaust valve.

FIG. 9 is a second graph showing the opening degrees of the exhaust control valve and the exhaust valve.

FIG. 10 is a configuration diagram of an embodiment of a vehicle equipped with a turbocharger.

[Explanation of symbols]

 101 ... Air cleaner 102 ... Throttle valve 103 ... Supercharger 104 ... Intercooler 105 ... Surge tank 106 ... Intake valve 107 ... Cylinder 108 ... Intake pressure sensor 109 ... Injector 110 ... Exhaust valve 111 ... Exhaust pipe 112 ... Oxygen sensor 113 ... Venturi 114 Bypass pipe 115 Exhaust control valve 116 Exhaust control valve actuator 117 Three way catalyst 118 Secondary air supply pipe 119 Air control valve 120 Exhaust gas recirculation pipe 121 EGR valve 124 Throttle actuator

Claims (2)

[Claims] 1. A secondary air supply device for an internal combustion engine, comprising: a venturi part provided in an exhaust pipe of an internal combustion engine; and a secondary air supply pipe opening to the venturi part, wherein the venturi part is bypassed. A secondary air supply device for an internal combustion engine, further comprising: a bypass exhaust pipe; and a flow rate control unit installed in the bypass exhaust pipe and controlling a flow rate of exhaust gas flowing through the bypass exhaust pipe. 2. A supercharger installed in an intake pipe, a three-way catalyst installed downstream of a confluence of the exhaust pipe having the venturi portion and the bypass exhaust pipe, and a three-way catalyst downstream of the supercharger. A secondary air supply pipe that branches from an intake pipe and supplies a secondary air supply to the venturi portion; an air control valve that controls the opening and closing of the secondary air supply pipe; and an exhaust pipe that is upstream from the venturi portion, An exhaust gas recirculation pipe that recirculates exhaust gas to an intake pipe upstream of the supercharger, an EGR valve that controls the amount of exhaust gas flowing through the exhaust gas recirculation pipe, and an operating state in which the exhaust gas temperature rises excessively And a valve opening control means for opening the air control valve and the EGR valve, wherein the EGR valve and the secondary air supply pipe can exchange heat between exhaust gas and secondary air. It has been arranged in the. Secondary air supply device for an internal combustion engine.