JP3202288B2 - Engine secondary air supply - Google Patents

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 engine.

[0002]

2. Description of the Related Art In many engines, an exhaust gas purifying catalyst is provided in an exhaust passage of the engine for purifying exhaust gas, and a three-way catalyst is generally used as this catalyst. While this three-way catalyst has the advantage of being able to perform oxidation and reduction, it can perform good exhaust gas purification only near the stoichiometric air-fuel ratio.

On the other hand, the air-fuel ratio of the intake air supplied to the engine may be required to be richer than the stoichiometric air-fuel ratio at the time of, for example, high load or acceleration. The secondary air is supplied to the exhaust passage upstream of the catalyst in accordance with
-10024).

However, when the secondary air is supplied to the exhaust passage upstream of the catalyst in accordance with the operating state of the engine, good exhaust gas purification is performed at one time, while good exhaust gas purification is performed at another time. It has been found that there may be cases where it will not be possible.

In pursuit of the cause of such a situation, it was found that the cause was a change in the amount of oxygen adsorbed by the catalyst itself. That is, the catalyst adsorbs (stores) oxygen in an oxygen-excess atmosphere and releases adsorbed oxygen in an oxygen-deficient atmosphere. Therefore, it is assumed that a certain amount of secondary air is supplied in a certain engine operating state. Also, depending on the oxygen adsorption state of the catalyst before the predetermined engine operation state, the excess or deficiency of the secondary air occurs.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a secondary air supply device for an engine capable of always purifying exhaust gas satisfactorily in response to the oxygen adsorption state of a catalyst.

In order to achieve the above object, the present invention has the following configuration. That is, in an engine in which an exhaust gas purifying catalyst is disposed in an exhaust passage of an engine and secondary air is supplied to an exhaust passage upstream of the catalyst, based on an operating time of a predetermined operating state set in advance. Means for detecting the amount of oxygen adsorbed on the catalyst, means for adjusting the amount of secondary air supplied, and means for adjusting the amount of secondary air; and the amount of oxygen adsorbed on the catalyst detected by the amount of adsorbed catalyst is large. And control means for controlling the secondary air adjusting means so that the amount of secondary air supplied to the exhaust passage is smaller than when the amount is small.

The operating time in the predetermined operating state for detecting the oxygen adsorption amount of the catalyst includes, for example, the following. In other words, the fuel is often cut when the engine is decelerated. However, when the fuel is cut, the catalyst is in an oxygen excess state in which the catalyst adsorbs oxygen. Can be. Further, when the engine is idling, an oxygen deficiency state occurs, so this idle time can be used as a parameter indicating the amount of oxygen adsorbed by the catalyst.

[0009]

According to the present invention, since an appropriate amount of secondary air is supplied according to the amount of oxygen adsorbed on the catalyst, deterioration of the purification performance of the catalyst due to excess or deficiency of the secondary air is prevented. do it,
Exhaust gas can always be effectively purified. Also,
Since the oxygen adsorption amount is detected based on the operation time in the predetermined operation state, it is not necessary to separately use a dedicated sensor for detecting the oxygen adsorption amount.

[0010]

In FIG. 1, reference numeral 1 denotes an engine main body. The engine main body 1 is of an otto type having four reciprocating in-line cylinders, and each cylinder C has an intake port 2 and an exhaust port. -3.

An intake passage 4 for supplying intake air to each cylinder C is
A surge tank 5 is provided on the way, and the surge tank 5 and the intake port 2 of each cylinder C are independent intake passages 6 independent of each other.
Connected by Each of the independent intake passages 6 is provided with a fuel injection valve 7. The upstream intake passage 8 for supplying intake air to the surge tank 5 includes:
From the upstream side to the downstream side, the air cleaner 9 and the air flow
A meter 10 and a throttle valve 11 are provided.

The exhaust gas discharged from the exhaust port 3 of each cylinder C passes through the independent exhaust passage 21 and finally passes through one common exhaust passage 22 to the atmosphere. A three-way catalyst 23 as an exhaust gas purification catalyst is connected to the common exhaust passage 22.

The air cleaner 9 in the upstream intake passage 8
An air passage 31 for supplying secondary air is extended between the air flow meter 10 and the air flow meter 10. The downstream end of the air passage 31 is opened in the common exhaust passage 22 on the upstream side of the catalyst 23. The air passage 31 is connected to a secondary air amount adjusting valve 32 composed of an electromagnetic on-off valve.

U in FIG. 1 is a control unit configured using a microcomputer. The control unit U receives signals from switches or sensors 41 and 42, while the control unit U outputs the control valve 3.
2 is output. The switch 41 is an idle switch that is turned on when the throttle valve 11 is fully closed. The sensor 42 is a rotation speed sensor that detects the engine rotation speed.

The control unit U controls the amount of secondary air as well as the amount of fuel injected from the fuel injection valve 7. The control of the amount of secondary air will be described. First, in the embodiment, the time when the exhaust gas supplied to the catalyst 23 is in an oxygen excess state is the time of deceleration of the engine or the time of fuel cut for preventing the engine from over-rotating. The fuel cut time is counted by a timer, and the timer value serving as the count value is regarded as the amount of oxygen adsorbed on the catalyst 23. When the secondary air is supplied from the air passage 31 to the common exhaust passage 22, as shown in FIG. 2, the larger the timer value at the time of fuel cut, the larger the amount of oxygen adsorbed on the catalyst 23. If so, the secondary air supply is reduced. Whether or not the fuel is cut can be determined by checking the engine speed on the assumption that the idle switch 41 is ON.

In the embodiment, the time when the exhaust gas supplied to the catalyst 23 is in an oxygen-deficient state is defined as an engine idle time. This idle time is counted by a timer, and the timer value serving as the count value is regarded as the amount of oxygen released from the catalyst 23 (the amount of oxygen that the catalyst 23 itself adsorbs). When the secondary air is supplied from the air passage 31 to the common exhaust passage 22, as shown in FIG. 3, it is assumed that the larger the timer value during idling, the smaller the amount of oxygen adsorbed on the catalyst 23. The secondary air supply is increased.

Here, the duty of the regulating valve 32 is basically controlled so that a predetermined amount of secondary air is supplied according to the current operating state of the engine. The duty ratio may be corrected.
In other words, the secondary air amount shown in FIGS. 2 and 3 can be set as a correction amount for the basic value, for example, a correction coefficient for the basic secondary air amount. In this case, the timer value of FIG. The larger the value, the smaller the correction coefficient. In the case of FIG. 3, the larger the timer value, the larger the correction coefficient.
In addition, the secondary air amount control according to the timer value may be limited to a predetermined time period in consideration of a change in the amount of oxygen adsorbed on the catalyst 23. You can also increase the time.

The control of the secondary air amount by the control unit U will be described with reference to a flowchart shown in FIG. In the following description, S indicates a step. First, after data is input in S1, in S2,
It is determined whether or not the idle switch 41 is ON,
If the determination in S2 is NO, the control is returned as it is.

If the determination in S2 is YES, it is determined in S3 whether or not there is a load. The determination in S3 corresponds to checking whether or not the idle switch 41 is ON other than at the time of idling, that is, checking whether or not the fuel is cut. When the determination in S3 is YES, that is, when the fuel is cut during deceleration or the like, the time of the fuel cut is counted up by a timer in S4. Next, in S5, it is determined whether or not the idle switch 41 has been turned off. If the determination in S5 is NO, the fuel cut is being continued, and in this case, the process returns to S4 and the timer value continues to be counted.

When the determination at S5 is YES, the control goes to S8.
In, the regulating valve 32 is controlled based on the timer value counted in S4 as shown in FIG. 2 (reduction control of the secondary air amount).

If the determination in S3 is NO, the engine is idle. In this case, the idle time is counted in S6. Next, in S7, it is determined whether or not the idle switch 41 is OFF. If the determination in S7 is NO, the process returns to S6 and the timer value continues to be counted up. If the determination in S7 is YES, S
At 8, the control valve 32 is controlled based on the timer value counted at S6 as shown in FIG. 3 (control of increasing the secondary air amount).

Although the embodiment has been described above, the catalyst 23
The parameter indicating the oxygen adsorption state of the catalyst is appropriately selected in addition to the fuel cut time and the idle time, as long as it is a factor that changes the oxygen adsorption state of the catalyst, for example, an acceleration time, a fuel increase time in a cold state, and the like. Can be done. In addition to simply setting time as a parameter, factors such as the engine speed and the catalyst temperature that change the amount of oxygen adsorbed on the catalyst 23 even during the same time are also added as parameters. You can also do so.

[Brief description of the drawings]

FIG. 1 is an overall system diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing setting of a secondary air amount corresponding to a deceleration time.

FIG. 3 is a diagram showing a setting of a secondary air amount corresponding to an idle time.

FIG. 4 is a flowchart showing a control example of the present invention.

[Explanation of symbols]

 1: Engine main body 7: Fuel injection valve 8: Upstream intake passage 22: Common exhaust passage 23: Catalyst 31: Air passage 32: Regulating valve 41: Idle switch 42: Engine speed sensor U: Control unit

Continuation of the front page (56) References JP-A-60-243316 (JP, A) JP-A-1-203633 (JP, A) JP-A-4-269319 (JP, A) JP-A-58-167847 (JP) , A) JP-A-64-53046 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/34 301 F01N 3/22 321 F02D 43/00 301

Claims (3)

(57) [Claims] An engine in which an exhaust gas purifying catalyst is provided in an exhaust passage of an engine and secondary air is supplied to an exhaust passage upstream of the catalyst in a predetermined operating state set in advance. Based on time
There are, a suction amount detecting means for detecting the oxygen adsorption amount of the catalyst, and the secondary air amount adjusting means for adjusting the supply amount of the secondary air, oxygen adsorption amount of the detected at the adsorption amount detection means high catalyst Control means for controlling the secondary air adjusting means so that the amount of secondary air supplied to the exhaust passage is smaller than when the amount is small. Feeding device. 2. The method of claim 1, when satisfying the predetermined conditions set in advance, the fuel cut means is provided to cut the fuel supply to the engine, the operating time of the predetermined operating conditions, before Symbol A secondary air supply device for an engine, wherein a fuel cut time by a fuel cut means is set . 3. The method of claim 1, of an engine in which the operation time of the predetermined operating states are the idle operation time of the engine, and wherein the two
Next air supply device .