JPS638829Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a secondary air supply device for an internal combustion engine, and is particularly suitable for use in automobile engines equipped with exhaust gas purification measures using a three-way catalyst. Depending on the oxygen concentration in the exhaust gas,
The present invention relates to an improvement in a secondary air supply device for an internal combustion engine that supplies secondary air so that the oxygen concentration on the catalyst inlet side is close to the stoichiometric air-fuel ratio.

Harmful components emitted from internal combustion engines such as automobile engines include hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). There are various measures to reduce these emissions, among which one uses a three-way catalyst. This means that when the oxygen concentration in the exhaust gas on the catalyst entry side is the oxygen concentration when a mixture at the stoichiometric air-fuel ratio is combusted (hereinafter referred to as equivalent to the stoichiometric air-fuel ratio), the catalyst
It uses a single catalyst to purify harmful components in exhaust gas by combining the effects of oxidizing HC and CO and reducing NOx. There are various types of exhaust gas purification devices that use such three-way catalysts, but among them, the oxygen concentration at the entrance side of the catalyst is equivalent to near the stoichiometric air-fuel ratio, depending on the oxygen concentration in the exhaust gas detected in the exhaust system. Some devices are equipped with a secondary air supply device that supplies secondary air. this is,
For example, as shown in FIG. 1, an air cleaner 10, a carburetor 12 in which a throttle valve 12a is disposed, an intake manifold 14, an engine body 16 having an engine combustion chamber (not shown), an exhaust manifold 18, and a downstream side of the exhaust manifold 18. In an automobile engine having a three-way catalytic converter 20 arranged therein, an oxygen concentration sensor 22 which is arranged in the exhaust manifold 18 and detects the oxygen concentration in the exhaust gas on the catalyst inlet side is connected to the intake manifold 14. an intake-side secondary air supply pipe 24 that has been opened and closed, and an intake-side secondary air control valve 26 that has a valve body 26a and a valve seat 26b that controls the opening and closing of the intake-side secondary air supply pipe 24.
According to the output of the oxygen concentration sensor 22, the intake side 2 is adjusted so that the oxygen concentration in the exhaust gas on the inlet side of the three-way catalytic converter 20 is close to the stoichiometric air-fuel ratio.
Electronic control circuit 2 that controls opening and closing of the next air control valve 26
8. In the figure, 30 is an air filter.

According to such a secondary air supply device, the intake side is adjusted so that the oxygen concentration on the inlet side of the three-way catalytic converter 20 corresponds to the vicinity of the stoichiometric air-fuel ratio according to the oxygen concentration in the exhaust gas detected by the oxygen concentration sensor 22. Since the secondary air control valve 26 is controlled to open and close, the three-way catalytic converter 20 has the characteristic of being able to exhibit sufficient purification performance. Since secondary air was supplied only to the intake side through the passage 24, there was a problem during idling and deceleration when the throttle valve 12a is closed. That is, in order to maintain smooth engine rotation during idling, it is desirable that the air-fuel ratio of the air-fuel mixture supplied to the engine combustion chamber of the engine body 16 be slightly richer than near the stoichiometric air-fuel ratio; In the conventional example, since the intake side secondary air control valve 26 is controlled to open and close according to the output of the oxygen concentration sensor 22 even during idling, the air-fuel ratio is maintained near the stoichiometric air-fuel ratio, and the air-fuel ratio is leaner than the desired air-fuel ratio. As a result, idle rotation may become unstable. Furthermore, during deceleration, the throttle valve 12a is closed even though the engine itself is rotating at high speed, so fuel components adhering to the inner wall of the intake manifold 14, etc., rapidly evaporate, causing engine combustion in the engine body 16. Since the air-fuel mixture in the room becomes too rich and a large amount of combustion gas is discharged to the exhaust manifold 18, it is difficult to supply enough secondary air with the amount of secondary air supplied only from the intake side secondary air supply pipe 24. The three-way catalytic converter 2 was unable to be supplied with exhaust gas that had an oxygen concentration lower than that equivalent to the stoichiometric air-fuel ratio.
0 overheats. In order to solve the former problem, it is conceivable to supply secondary air to the exhaust manifold 18 instead of the intake manifold 14, but with the method of supplying secondary air only to the exhaust manifold 18, the secondary air during deceleration Not only is there a shortage of air supply, but the air-fuel ratio in the intake system must always be maintained on the richer side than the stoichiometric air-fuel ratio, resulting in a reduction in fuel efficiency.

The present invention was made to eliminate the above-mentioned conventional drawbacks, and provides a secondary air supply device for an internal combustion engine that can prevent both idling instability during idling and catalyst overheating during deceleration without deteriorating fuel efficiency. The purpose is to provide.

The present invention is applied to a secondary air supply device for an internal combustion engine that supplies secondary air so that the oxygen concentration at the entrance side of the catalyst corresponds to the vicinity of the stoichiometric air-fuel ratio according to the oxygen concentration in the exhaust gas detected in the exhaust system. , an intake system secondary air supply means for supplying secondary air to the intake system, and an exhaust system secondary air supply means for supplying secondary air to the exhaust system, and when idling, the exhaust system secondary air supply means Supplying secondary air only to the exhaust system,
The above object is achieved by supplying secondary air to both the intake system and the exhaust system by the intake system secondary air supply means and the exhaust system secondary air supply means during deceleration.

Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 2, in this embodiment, the secondary air supply of an internal combustion engine is provided with an oxygen concentration sensor 22, an intake side secondary air supply pipe 24, and an intake side secondary air control valve 26, as in the conventional case. The air supply device further controls the opening and closing of an exhaust side secondary air supply pipe 40 connected to the exhaust manifold 18 and having a reed valve 42 disposed therebetween, and the exhaust side secondary air supply pipe 40. , valve body 44a, valve seat 44b, said valve body 44
a, a compression spring 44e that always urges the diaphragm 44d to the right, and a diaphragm chamber 44f; The intake negative pressure supplied from the negative pressure port 14a of the intake manifold 14 to the diaphragm chamber 44f of the exhaust side secondary air control valve 44 is opened/closed, and the exhaust side secondary air control valve 44 is opened before the end of engine warm-up. a temperature sensing valve 46 that prevents
A throttle valve opening switch 48 detects whether the throttle valve 12a is in idling or deceleration state from a fully closed state, a negative pressure switch 50 which detects deceleration state when the intake manifold 14 has a high intake negative pressure, and the oxygen concentration Depending on the outputs of the sensor 22, the throttle valve opening switch 48, the negative pressure switch 50, etc., when the engine is in a normal operating state other than idling or decelerating, the temperature sensing valve 46 is closed to control the temperature on the exhaust side. By closing the secondary air control valve 44 and controlling the opening and closing of only the intake side secondary air control valve 26 according to the output of the oxygen concentration sensor 22, the exhaust gas on the inlet side of the three-way catalytic converter 20 is By supplying secondary air only to the intake system so that the oxygen concentration in the engine is close to the stoichiometric air-fuel ratio, and at the time of idling, the intake side secondary air control valve 26 is closed and the temperature sensing valve 46 is opened. The exhaust side secondary air control valve 44 is opened to supply secondary air only to the exhaust manifold 18 via the exhaust side secondary air supply pipe 40 and the reed valve 42. On the other hand, during deceleration, the oxygen concentration sensor 22 The opening and closing of the intake side secondary air control valve 26 is controlled according to the output of the temperature sensing valve 46 after the engine has been warmed up.
By opening the exhaust side secondary air control valve 4
4 is also opened, and the intake side secondary air supply pipe 24 is opened.
and an electronic control circuit 52 that supplies secondary air to both the intake manifold 14 and the exhaust manifold 18 via the exhaust side secondary air supply pipe 40. In the figure, 54 is an air filter.

The action will be explained below. First, in a normal operating state in which the throttle valve opening switch 48, which detects the fully closed state of the throttle valve 12a, is off, the electronic control circuit 5
2 controls the opening and closing of only the intake side secondary air control valve 26 in accordance with the output of the oxygen concentration sensor 22, as in the conventional case. At this time, in the exhaust side secondary air control valve 44, since the temperature sensing valve 46 remains closed, the valve body 44a is moved to the valve seat 44b by the action of the compression spring 44e.
is kept closed. Therefore, all of the secondary air is supplied to the intake manifold 14, and feedback control is performed in the same manner as in the conventional art so that the oxygen acidity in the exhaust gas on the inlet side of the three-way catalytic converter 20 is close to the stoichiometric air-fuel ratio. At this time, the air-fuel ratio of the air-fuel mixture actually supplied to the engine combustion chamber of the engine body 16 is maintained near the stoichiometric air-fuel ratio, so that efficient combustion occurs in the engine combustion chamber and fuel efficiency is not degraded. It never happens.

On the other hand, when it is detected that the throttle valve opening switch 48 is turned on and the throttle valve 12a is closed, it is determined whether the throttle valve is idling or decelerating depending on the output state of the negative pressure switch 50. be done. That is, since the engine speed is low, the intake negative pressure is also low, at about 500 mmHg, and when the output of the negative pressure switch 50 is off, it is determined that the engine is idling.On the other hand, because the engine speed is high, the intake negative pressure is low.
When the output of the negative pressure switch 50 is on at a high level of 600 mmHg or more, it is determined that deceleration is occurring. During idling when the negative pressure switch 50 is off, the intake side secondary air control valve 26 is closed, and after the engine has warmed up, the temperature sensing valve 46 is opened.
Diaphragm chamber 44 of exhaust side secondary air control valve 44
Intake negative pressure within the intake manifold 14 is transmitted to f. Therefore, the diaphragm 44d is sucked to the left in the figure against the compression spring 44e, and the valve body 44a is separated from the valve seat 44b, and the exhaust manifold 18 is moved through the reed valve 42 and the exhaust side secondary air supply pipe 40. Secondary air is supplied only to the At this time, since secondary air is not supplied to the intake manifold 14, an air-fuel mixture richer than the stoichiometric air-fuel ratio is supplied to the engine combustion chamber of the engine body 16, and idling is maintained stably.

On the other hand, during deceleration when the outputs of the throttle valve opening switch 48 and the negative pressure switch 50 are both turned on, the electronic control circuit 52 controls the opening and closing of the intake side secondary air control valve 26 according to the output of the oxygen concentration sensor 22. At the same time, secondary air is also supplied to the exhaust manifold 18 via the reed valve 42 and the exhaust side secondary air supply pipe 40 by the exhaust side secondary air control valve 44 which is opened together with the temperature detection valve 46 . Therefore, at this time, a large amount of secondary air is introduced into both the intake manifold 14 and the exhaust manifold 18, and it is ensured that the secondary air necessary for the reaction is sufficiently supplied and that the large amount of secondary air The cooling action prevents overheating of the catalyst and purifies the exhaust gas. Furthermore, after-burn is also prevented.

FIG. 3 shows the relationship between the intake pipe negative pressure and the total amount of secondary air supplied to the intake manifold 14 and the exhaust manifold 18 in this embodiment. As is clear from the figure, a larger amount of secondary air is supplied to the intake manifold and exhaust manifold during deceleration than during idling.

In the above embodiment, the throttle valve opening switch 48 and the negative pressure switch 50 were used to detect idling and deceleration, but the means for detecting idling and deceleration is limited to this. For example, it is of course possible to provide a shift position detection switch in the transmission and detect idling based on the shift position of the transmission.

In the embodiment described above, during normal operation, the intake system air-fuel ratio supplied to the intake manifold 14 is controlled by controlling the opening and closing of the intake side secondary air control valve 26 according to the output of the oxygen concentration sensor 22. However, the scope of application of the present invention is not limited to this, and during normal operation, the exhaust side secondary air control valve is controlled to open and close according to the output of the oxygen concentration sensor, thereby controlling the oxygen in the exhaust gas on the catalyst inlet side. It is obvious that the present invention can be similarly applied to a method in which the concentration is made to be close to the stoichiometric air-fuel ratio.

As explained above, the present invention has the excellent effect of preventing both unstable idling and catalyst overheating during deceleration without impairing fuel efficiency.

[Brief explanation of the drawing]

Fig. 1 is a block diagram including a partial sectional view showing an example of a conventional secondary air supply device for an internal combustion engine, and Fig. 2 shows an embodiment of the secondary air supply device for an internal combustion engine according to the present invention. FIG. 3 is a diagram showing the relationship between the intake pipe negative pressure and the total amount of secondary air in the embodiment. 12... Carburetor, 14... Intake manifold, 1
6...Engine body, 18...Exhaust manifold,
20... Three-way catalytic converter, 22... Oxygen concentration sensor, 24... Intake side secondary air supply pipe, 26
...Intake side secondary air control valve, 40...Exhaust side secondary air supply pipe, 42...Reed valve, 44...Exhaust side secondary air control valve, 46...Temperature sensing valve, 48...
... Throttle valve opening switch, 50... Negative pressure switch,
52...Electronic control circuit.

Claims (1)

[Scope of utility model registration request] The secondary air supply system of an internal combustion engine supplies secondary air to the intake system so that the oxygen concentration at the entrance side of the catalyst is equivalent to near the stoichiometric air-fuel ratio according to the oxygen concentration in the exhaust gas detected in the exhaust system. An intake system secondary air supply means for supplying secondary air, and an exhaust system secondary air supply means for supplying secondary air to the exhaust system, and when idling, the exhaust system secondary air supply means supplies only the exhaust system. An internal combustion engine characterized in that secondary air is supplied to both the intake system and the exhaust system by the intake system secondary air supply means and the exhaust system secondary air supply means during deceleration. secondary air supply device.