JP2995202B2 - Secondary air supply for engine exhaust - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for supplying secondary air to an exhaust system having a three-way catalyst by using an air pump in order to reduce harmful components contained in exhaust gas discharged from an engine. And is mainly used for purifying exhaust of an automobile engine.

[0002]

2. Description of the Related Art At present, exhaust purification of an automobile engine is mainly performed by a system in which a mixture having a stoichiometric air-fuel ratio is supplied to the engine by electronic control and exhaust gas is treated by a three-way catalyst. In a cold state, the exhaust gas temperature is low, and therefore, in a low temperature state where the three-way catalyst does not reach the reaction temperature, there is a disadvantage that hydrocarbons are released in large quantities without being reduced.

On the other hand, in the near future, there is a movement to strengthen the regulation of the emission of harmful components in the exhaust of automobiles, and the main object is hydrocarbons, which are about to be reduced by about 40% from the current regulation value. . In order to cope with such tightening of regulations, it is necessary to rapidly raise the temperature of the three-way catalyst so as to reach the reaction temperature in a short period of time. It is conceivable that by introducing the catalyst into the original catalyst, the combustion in the catalyst is activated and the temperature is rapidly increased.

[0004] As one of the exhaust treatment techniques using a three-way catalyst and secondary air as described above, a rich air-fuel mixture is supplied to an engine and the concentration of oxygen in the exhaust gas discharged from the three-way catalyst is detected. It has been proposed to burn harmful components in high-temperature exhaust gas discharged from an engine by controlling the secondary air supply amount (Japanese Patent Application Laid-Open No. 49-13515).
Reference).

That is, according to the exhaust treatment technology disclosed in Japanese Patent Application Laid-Open No. 49-15515, when exhaust gas discharged from an engine is at a low temperature, harmful components can be sufficiently burned only by adding secondary air. Although it is not possible to use a three-way catalyst, the supply of secondary air pressurized by an engine-driven air pump must be adjusted to the oxygen concentration in the exhaust gas in order to effectively burn harmful components with the three-way catalyst. The air-fuel ratio of the air-fuel mixture when the engine is cold, ie, the amount of engine intake air, and the air-fuel ratio of the exhaust gas, ie, the amount of secondary air supplied when the three-way catalyst is low, are controlled independently of each other. .

Accordingly, while supplying the air-fuel mixture having the required air-fuel ratio according to the operating state from the cold state of the engine to the completion of warm-up, the harmful components in the exhaust gas introduced into the low-temperature three-way catalyst are sufficiently reduced. It is very difficult to make the three-way catalyst reach the reaction temperature in a short time by burning. In addition, since the system supplies a rich mixture to the engine and consequently reduces harmful components in the exhaust gas emitted from the three-way catalyst, the mixture is supplied to the engine with a stoichiometric air-fuel ratio by electronic control. Cannot be applied to currently mainstream systems.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an air-fuel mixture having a stoichiometric air-fuel ratio to an engine by electronic control. There is no technology to effectively link the supply of gas to the engine and the emission of exhaust gas with sufficiently reduced harmful components from the three-way catalyst.
In particular, it is difficult to supply a rich mixture to an engine in a cold state and burn the exhaust gas with a three-way catalyst in a low-temperature state to reach a reaction temperature in a short time while reducing harmful components. .

[0008]

In order to solve the above-mentioned problems, the present invention provides an air flow meter and an intake pipe having a fuel supply means for supplying fuel at a flow rate set according to the air flow rate, and a three-way catalyst. An exhaust pipe, a secondary air passage branched from a flow meter downstream of the intake pipe and connected to the three-way catalyst upstream of the exhaust pipe, and a part of the air in the intake pipe provided in the secondary air passage and exhausting the exhaust pipe. And a pressure control valve provided on the outlet side of the air pump to make the secondary air supply pressure proportional to the exhaust pressure. This provides a rich mixture to a cold engine under a system that supplies a stoichiometric air-fuel mixture to the engine, causing the low-temperature three-way catalyst to reach the reaction temperature in a short time and cause harmful components in the exhaust gas. Can be sufficiently reduced.

In addition to the above-mentioned means, there is provided a secondary air control valve which connects the air pump outlet side of the secondary air passage and the intake pipe by a return passage and opens and closes according to the air-fuel ratio of the exhaust gas at the three-way catalyst inlet. I let it. Further, in addition to the above-mentioned means, a temperature opening / closing valve which opens when the engine is cold and closes when the engine is warmed up is provided, or in addition to this, a load opening / closing valve which opens when the engine is under heavy load. Thus, the object of effectively performing the air-fuel ratio control of the air-fuel mixture and the purification of the exhaust gas in accordance with various operating states of the engine in association with each other can be achieved.

[0010] In addition to the above means, it is preferable to install a closing valve on the air pump outlet side of the secondary air passage when the secondary air supply is stopped to prevent the exhaust gas from flowing back into the intake pipe.

[0011]

The fuel is supplied in accordance with the air flow rate detected by the air flow meter, whereby the air-fuel mixture having the stoichiometric air-fuel ratio is basically supplied to the engine. On the other hand, a part of the air measured by the air flow meter is pressurized by the air pump and then controlled by the pressure control valve to a pressure proportional to the exhaust pressure and supplied to the exhaust pipe. In other words, the metered air is divided into two parts while maintaining the flow rate in direct proportion to the intake air of the engine and the secondary air of the exhaust pipe, and a constant rich air-fuel mixture is supplied to the engine while the secondary air is supplied. By supplying the unburned components, the unburned components are contained in the exhaust gas, and the unburned components are burned by a three-way catalyst with secondary air supplementing a highly rich air-fuel mixture to rapidly raise the reaction temperature.

A secondary air return passage is provided, a secondary air control valve appropriately controls the supply amount of secondary air according to the air-fuel ratio of the exhaust gas, and a temperature switching valve according to the engine temperature. To improve the output and purify the exhaust gas by supplying a rich mixture at high load.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. An intake pipe 3 from an air cleaner (not shown) to an engine 1 has a movable vane type air flow meter 4, a throttle valve 5, and a fuel injection valve 6 in that order. An exhaust pipe 7 extending from the engine 1 to a silencer (not shown) includes an air-fuel ratio sensor 8, a three-way catalyst 9,
It has an oxygen sensor 10. Output signals of the air flow meter 4, the air-fuel ratio sensor 8, the oxygen sensor 10, and the temperature sensor 11 of the engine cooling water 2 are sent to an electronic control unit 12. Further, the system is basically based on a system that sends a drive signal to the fuel injection valve 6 in accordance with the air flow rate detected by the air flow meter 4 to supply a mixture having a stoichiometric air-fuel ratio to the engine 1.

A secondary air passage 13 is provided downstream of the air flow meter 4 of the intake pipe 3 and upstream of the throttle valve 5 and connected to the exhaust pipe 7 upstream of the air-fuel ratio sensor 8. I have. The secondary air passage 13 is provided with a positive displacement air pump 14 composed of a Roots-type compressor, which is driven by the engine 1 or an electric motor (not shown) at a rotation speed of a fixed ratio to the rotation speed of the engine 1. A part of the air 3 is fractionated in proportion to the amount of intake air of the engine 1 and supplied to the exhaust pipe 7 through the secondary air passage 13. That is, the volume flow rate of the secondary air supplied to the exhaust pipe 7 by the air pump 14 is proportional to the intake air supplied to the engine 1 after the secondary air has been fractionated.

The air pump 14 in the secondary air passage 13
A return passage 15 branched from the outlet side of the intake pipe 3 and connected to a portion between the air flow meter 4 and the throttle valve 5 of the intake pipe 3, and a return passage 15 branched from the outlet side of the air pump 14 and connected to the return passage 15. A control passage 16 is provided, and a pressure control valve 17 is provided in the control passage 16.

The pressure control valve 17 has a butterfly shape, and has a first diaphragm 18 on which the air pressure discharged from the air pump 14 acts.
In addition, the opening and closing operation is performed in conjunction with the second diaphragm 19 and the link 20, which have a larger effective area than that of the exhaust pipe 7 and the exhaust pressure taken out from the upstream side of the three-way catalyst 9 by the back pressure passage 21. That is, air having a flow rate proportional to the amount of intake air of the engine 1 is pressurized by the air pump 14 and acts on the first diaphragm 18, and the air discharged therefrom is proportional to the square of the intake air amount, that is, the square of the exhaust amount. The pressure is applied to the second diaphragm 19. When the exhaust pressure rises, the opening degree of the pressure control valve 17 decreases, and the amount of air discharged from the control passage 16 to the return passage 15 decreases, thereby reducing the discharge air. The pressure, ie the secondary air supply pressure, is increased. When the exhaust pressure decreases, the degree of opening of the pressure control valve 17 increases and the amount of released air increases, thereby lowering the secondary air supply pressure. Therefore, by appropriately setting the effective area ratio of the two diaphragms 18 and 19, the secondary air amount of the exhaust pipe 7 can be made proportional to the intake air amount of the engine 1. In this case, it goes without saying that the secondary air supply pressure is always higher than the exhaust pressure.

Thus, the air measured by the air flow meter 4 is divided into the intake air of the engine 1 and the secondary air of the exhaust pipe 7 while maintaining the mass flow rate in a directly proportional relationship, and the secondary air is supplied. In a certain operating state, the fuel corresponding to the air flow rate measured by the air flow meter 4 is supplied from the fuel injection valve 6, so that a constant rich mixture is supplied to the engine 1.

Since the fuel is supplied so as to have a stoichiometric air-fuel ratio with respect to the total amount of the secondary air and the intake air, the fuel in the exhaust gas discharged without being burned by the engine 1 due to the rich mixture. Unburned components are theoretically completely burned by the secondary air. Engine 1 with rich mixture in cold state
As is well known, the exhaust gas supplied with the secondary air is burned by the three-way catalyst 9 and rapidly rises to the reaction temperature.

The fact that the engine 1 has been warmed up is input by the water temperature sensor 11 to the electronic control unit 12, and the air pump 14 is stopped based on this signal. Further, an electromagnetically driven shut-off valve 22 is provided on the outlet side of the air pump 14 in the secondary air passage 13, and closes the secondary air passage 13 based on the signal. That is, these operations are performed when the engine 1 is warmed up and the high-concentration air-fuel mixture is no longer required, and thereafter, theoretically under the feedback control for correcting the fuel flow rate based on the electric signal from the oxygen sensor 10. The air-fuel mixture is supplied to the engine 1.

If the air pump 14 is stopped, the secondary air passage 13 is closed depending on its structure.
However, if the shut-off valve 22 is provided, the high-pressure exhaust gas can be completely prevented from flowing back to the intake pipe 3.
When the shut-off valve 22 is installed, it may be always operated depending on the type of the air pump 14.

Next, an electromagnetically driven secondary air control valve 23 that opens and closes at a predetermined duty ratio based on an electric signal sent from the air-fuel ratio sensor 8 to the electronic control unit 12 is provided in the return passage 15. I have.

The secondary air control valve 23 is opened at a large duty ratio or fixed at the valve opening position when the secondary air supplied to the exhaust pipe 7 is excessive with respect to unburned components, ie, harmful components, in the exhaust. The amount of the secondary air discharged from the pump 14 flowing back to the intake pipe 3 through the return passage 15 is increased. On the other hand, when it is insufficient, it is opened with a small duty ratio or fixed at the valve closing position, and the amount of recirculation to the intake pipe 3 through the return passage 15 is reduced. Can be supplied.

Further, a temperature opening / closing valve 24 is provided at a portion between the branch point of the control passage 16 of the secondary air passage 13 and a closing valve 22 downstream thereof, and this temperature opening / closing valve 24 is connected to the control valve 16. A load control valve 26 is installed in a branch passage 25 provided in the secondary air passage 13 by bypass.

The temperature opening / closing valve 22 performs an opening / closing operation at a predetermined duty ratio by electromagnetic drive based on an electric signal sent from the water temperature sensor 11 to the electronic control unit 12, and the valve opening position when the engine 1 is in a cold state. Fixed to
As the temperature rises, the duty ratio is gradually opened, and after the warm-up is completed, the valve is fixed at the valve closing position. As the temperature of the engine 1 rises, the exhaust gas is exhausted through the secondary air passage 13. The amount of secondary air supplied to the pipe 7 is reduced, and the air-fuel mixture supplied to the engine 1 can gradually approach the stoichiometric air-fuel ratio from high concentration.

As described above, by controlling the supply amount of the secondary air by using one or both of the secondary air control valve 23 and the temperature on-off valve 24, the harmful components in the exhaust gas can be reduced sufficiently. The air is appropriately distributed to the engine 1 and the exhaust pipe 7 in accordance with the operating state of the engine 1 so that the air-fuel ratio control of the air-fuel mixture and the exhaust gas purification can be effectively performed.

The load on-off valve 26 is needle-shaped, and
7 is attached to the diaphragm 28 on which the negative pressure of the intake pipe taken out acts. When the intake pipe negative pressure is high, that is, when the load is medium or low, the intake pipe is closed. When the intake pipe negative pressure is low, that is, when the load is high, the branch pipe 25 is opened regardless of the open / close state of the temperature on-off valve 24. The amount of secondary air supplied to the exhaust pipe 7 is increased, and the amount of air supplied to the engine 1 is reduced, thereby enriching the air-fuel mixture and improving the output.

In the illustrated embodiment, the secondary air control valve 2
3. Although all of the temperature on-off valve 24 and the load on-off valve 26 are installed, a configuration in which one or both of the secondary air control valve 23 and the temperature on-off valve 24 are installed and the load on-off valve 26 is not used may be adopted. .

[0028]

According to the present invention, a portion of the air measured by the air flow meter is pressurized by the air pump and controlled to a pressure proportional to the exhaust pressure and supplied to the exhaust pipe. Under the system that supplies fuel according to the stoichiometric air-fuel ratio according to the engine and supplies the rich air-fuel mixture to the cold engine and supplies the secondary air to the exhaust while maintaining the rotation of the engine The low-temperature three-way catalyst can be sufficiently burned to effectively reduce harmful components and rapidly raise the reaction temperature. Also, a secondary air control valve,
When the temperature on-off valve and the load on-off valve are appropriately provided, the air-fuel ratio control of the air-fuel mixture, the exhaust purification, and the output improvement can be effectively performed in association with each other according to various operating states of the engine.

[Brief description of the drawings]

FIG. 1 is a layout diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 3 Intake pipe 4 Air flow meter 6 Fuel injection valve 7 Exhaust pipe 9 Three-way catalyst 12 Electronic control unit 13 Secondary air passage 14 Air pump 15 Return passage 17 Pressure control valve 22 Closing valve 23 Secondary air control valve 24 Temperature on-off valve 26 Load on-off valve

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01N 3/22 321 F01N 3/20 F01N 3/32 301

Claims (5)

(57) [Claims] An intake pipe having an air flow meter and a fuel supply means for supplying fuel at a flow rate set according to the air flow rate; an exhaust pipe having a three-way catalyst; A secondary air passage branched and connected to the three-way catalyst upstream side of the exhaust pipe, an air pump provided in the secondary air passage and feeding a part of the air of the intake pipe to the exhaust pipe, A secondary air supply device for engine exhaust, comprising: a pressure control valve provided on an outlet side of an air pump to make secondary air supply pressure proportional to exhaust pressure. 2. A return passage connecting an air pump outlet side of a secondary air passage and an intake pipe, and an exhaust space at a three-way catalyst inlet provided in the return passage. A secondary air supply device for engine exhaust, comprising: a secondary air control valve that opens and closes according to a fuel ratio. 3. In addition to the configuration according to claim 1, further comprising a temperature opening / closing valve on the air pump outlet side of the secondary air passage which opens when the engine is cold and closes when the engine is warm. Secondary air supply for engine exhaust. 4. A branch passage provided in a secondary air passage bypassing a temperature switch valve, and a load switch valve provided in the branch passage and opened when the engine is under a high load, in addition to the configuration according to claim 3. And a secondary air supply device for engine exhaust. 5. In addition to the configuration according to any one of claims 1, 2, 3, and 4, a closing valve is provided on the air pump outlet side of the secondary air passage when the secondary air supply is stopped. Secondary air supply for engine exhaust.