JPS63198716A - Secondary air supply control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the occurrence of after-fire pertinently by opening the secondary air supply control valve for an exhaust passage when a throttle valve has been closed and it has been detected that the density of oxygen in the exhaust passage is lean. CONSTITUTION:The secondary air supply conduit 12 connected to an air cleaner 10 is connected to an exhaust manifold 5 via the secondary air supply control valve 14 and the like. And the diaphragm chamber 17 of the secondary air supply control valve 14 is connected to a surge tank 2 via an electromagnetic valve 18, thereby opening an open/close valve 16. In this case, a throttle valve 11 is connected with a throttle switch 19 turning ON when the valve 11 is open for engine idling. Also, an oxygen density detector 20 is fitted within an exhaust pipe 6. Furthermore, each signal from the switch 10 and the detector 20 is inputted to a control unit 30. And when the throttle valve 11 is closed and the density of oxygen is lean, the open/close valve 16 is so controlled as to open.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a secondary air supply control device for an internal combustion engine.

[Conventional technology]

When the throttle valve is closed to decelerate the vehicle, the liquid fuel adhering to the inner wall of the intake manifold vaporizes, supplying a rich air-fuel mixture into the engine cylinders, resulting in a large amount of unburned HC and CO. Exhausted into the engine exhaust passage. As described above, an internal combustion engine is known in which secondary air is supplied into the exhaust passage during deceleration operation in order to purify unburned HC and GO that are discharged in large quantities during deceleration operation (Japanese Patent Application Laid-Open No. 1983-1993-1).
(See Publication No. 129833).

However, if secondary air is supplied when a large amount of unburned 11C and CO are being exhausted, the unburned 11C and CO will be explosively combusted in the exhaust passage, resulting in so-called afterfire. During deceleration operation, a large amount of IIC and Co are discharged at the beginning of deceleration, and moreover, IIC and Co are generated at the beginning of deceleration.
, the amount of CO increases as the vehicle speed at the start of deceleration driving increases.
That is, the larger the load in the intake manifold at the beginning of deceleration, the greater the load. Therefore, in order to prevent afterfire, the supply of secondary air is stopped at the beginning of deceleration, and the more the load on the intake manifold at the beginning of deceleration is, the longer the time during which the supply of secondary air is stopped is known. (Tokuko Sho 56
(Refer to Publication No. 1449).

[Problem that the invention seeks to solve]

However, the amount of unburned 11C and CO generated at the beginning of deceleration not only depends on the load inside the intake manifold at the beginning of deceleration, but also depends on the warm-up state of the engine, atmospheric pressure, etc. The amount of unburned IC and CO generated increases as the engine temperature decreases.

That is, when the engine temperature is low, ′i
! -amounts of unburned 11C and CO are emitted and unburned 11
C.

CO emission time becomes longer. Therefore, as mentioned above, it is difficult to appropriately control the secondary air supply stop in all operating conditions by simply changing the secondary air supply stop time depending on the magnitude of the negative pressure in the intake manifold. 6 [Means for Solving the Problems] In order to solve the above problems, the present invention provides a secondary air supply control valve that controls the supply of secondary air into the engine exhaust passage. , an internal combustion engine equipped with an oxygen concentration detector disposed in an engine exhaust passage; 2 when the detector generates a lean signal
Next, the air supply control valve is opened.

〔Example〕

Referring to FIG. 1, 1 is the engine main body, 2 is a surge tank, 3 is an intake branch pipe, 4 is a fuel injection valve, 5 is an exhaust manifold, 6 is an exhaust pipe, and 7 is a three-way catalytic converter. Surge tank 2 is connected to intake duct 8 and air flow meter 9
is connected to the air cleaner 10 via the intake duct B.
A valve 11 is arranged inside. A secondary air supply conduit 12 is connected to the air cleaner 10.
The secondary air supply conduit 2 is connected to the exhaust manifold 5 via a reed valve type check valve 13 and a secondary air supply control valve 14. The secondary air supply control valve 14 is connected to the diaphragm 1
5 and a diaphragm negative pressure chamber 17.
The diaphragm negative pressure chamber 17 is connected to the surge tank 2 via an electromagnetic switching valve 18 that can communicate with the atmosphere. When the diaphragm negative pressure chamber 17 is connected to the surge tank 2 by the switching action of the electromagnetic switching valve 1, the on-off valve 16 opens. At this time, secondary air is supplied into the exhaust manifold 5 due to the negative pressure generated within the exhaust manifold 5 due to the exhaust pulsation. On the other hand, when the diaphragm negative pressure chamber 17 is opened to the atmosphere by the switching action of the electromagnetic switching valve 18, the on-off valve 16 is closed and the supply of secondary air is stopped. This electromagnetic switching valve 18 is controlled by an output signal from an electronic control unit 30.

The electronic control unit 30 consists of a digital computer with ROMs interconnected by a bidirectional bus 35.
(Read Only Memo January 31, RAM (Random Access Memory) 32, CPU (Microprocessor)
33 and an I10 boat (input/output boat) 34. The I10 boat 34 is connected to the electromagnetic switching valve 18 via a drive circuit 36. On the other hand, the throttle valve 11 is
a detector that detects whether the nottle valve 11 is closed;
That is, it is connected to a throttle switch 19 that is turned on when the throttle 11 is idling, and the output signal of this throttle switch 19 is manually input to the I10 boat 34. In addition, an oxygen concentration detector (hereinafter referred to as 02) is installed inside the exhaust pipe 6.
20 (referred to as a sensor) are arranged. This 02 sensor 20
is 0 when the exhaust gas is an oxidizing atmosphere. ] It generates an output voltage of about 0.0 volts when the exhaust gas is in a reducing atmosphere.
Generates an output voltage of about 9 volts. Therefore, by comparing the output voltage of this 02 sensor 20 with a reference voltage of about 0.45 volts, it is possible to know whether the exhaust gas is in an oxidizing atmosphere or a reducing atmosphere. Hereinafter, the output signal of the 02 sensor 20 of 0.45 volts or less will be referred to as a lean signal.
The output signal of the 0□ sensor 20 of 45 volts or more is called a rich signal. Therefore, the 0□ sensor 20 generates a lean signal indicating that the exhaust gas is in an oxidizing atmosphere, or a rich signal indicating that the exhaust gas is in a reducing atmosphere. The output signal of the 0□ sensor 20 is input to the I10 boat 34 via the AD converter 37.

Next, a secondary air supply control method according to the present invention will be explained with reference to FIG. Note that the routine shown in FIG. 2 is executed by interrupts at fixed time intervals.

Referring to FIG. 2, first, in step 40, it is determined whether or not the throttle switch 19 is on. If the throttle valve opening 19 is not on, that is, if the throttle valve 11 is open, the process proceeds to step 41 and the electromagnetic switching valve 18 is turned off. At this time, the diaphragm negative pressure chamber 17 is opened to the atmosphere, and therefore the supply of secondary air is stopped.

Next, in step 42, a flag indicating that the electromagnetic switching valve 18 is on is reset. On the other hand, when the throttle valve 11 is closed and deceleration operation is started, the process proceeds from step 40 to the steering knob 43, where it is determined whether or not the flag "is set. Immediately after deceleration, the flag r is reset. Since the output voltage of the O2 sensor 20 is lower than 0.45 volts and is 1, the control knob 44 determines whether the O2 sensor 20 is generating a lean signal. 0□Sensor 2
Ste knob 41 when 0 is generating a rich signal.
The secondary air supply continues to be stopped.

On the other hand, 0. When the sensor 20 generates a lean signal, the process proceeds to step 45 and the electromagnetic switching valve 18 is turned on. At this time, the diaphragm negative pressure chamber 17 is connected to the surge tank 2, and the supply of secondary air is thus started. Next, in step 46, a flag " is set. Once the flag f is set, the processing routine is completed through steps 7 and 43 until the throttle valve 11 is opened again.

FIG. 4 shows changes in the output voltage (2) of the 02 sensor 20 and the on/off operation of the electromagnetic switching valve 18. T in Figure 4
When deceleration operation is started, the oxygen sensor 20 continues to generate a rich signal because a rich air-fuel mixture is supplied into the engine cylinder.

After a while, the air-fuel mixture becomes thinner and then reaches zero.
2 When the sensor 20 generates a lean signal, the electromagnetic switching valve 18
is turned on and the supply of secondary air is started.

Afterfire is likely to occur when (i) the exhaust gas contains a large amount of unburned HC and Co, (ii) the exhaust gas salt is high, and (iii) there is sufficient salt to burn off the large amount of unburned HC and CO. This is when three conditions are met: a suitable secondary air is being supplied.

The amount of unburned HC and Co in the exhaust gas depends on the air-fuel ratio, and when the Ox sensor 20 generates a rich signal, the amount of unburned HC and Co is large, and if secondary air is supplied at this time, Afterfire is raw).

On the other hand, when the 02 sensor 20 is generating a lean signal, the amount of unburned HC' and CO is small, and at this time the 02 sensor 20 is generating a lean signal.
Supplying additional air no longer causes afterfire.

In the present invention, as described above, 0. Since the supply of secondary air is started when the sensor 20 generates a lean signal, it is possible to prevent afterfire from occurring. If secondary air is supplied when the 02 sensor 20 is generating a rich signal regardless of the engine temperature, atmospheric pressure, or deceleration operating state, afterfire is likely to occur.
By controlling the supply of secondary air based on the output signal of the second sensor 20, it is possible to prevent afterfire from occurring regardless of the engine temperature, atmospheric pressure, or deceleration operating state.

Note that after deceleration, the exhaust temperature gradually decreases, and if the exhaust temperature decreases to a certain extent, a large amount of unburned 11c and CO will be present in the exhaust gas.
Even if it is rare, the supply of secondary air will not cause afterfire. FIG. 3 shows the secondary air control routine in consideration of such a decrease in exhaust gas temperature. Referring to FIG. 3, compared to FIG. 2, only step 47 has been added, and the other steps 40 to
Step 46 is the same as in FIG. That is, if the 0□ sensor 20 is generating a rich signal in step 44 of FIG. 3, the process advances to step 47, and the 0. It is determined whether a certain period of time has elapsed since the sensor 20 generated the rich signal. If a certain period of time has elapsed, the process proceeds to step 41 and the supply of secondary air continues to be stopped, and if a certain period of time has elapsed, the process proceeds to step 45 and the 02 sensor 20
The supply of secondary air is started even if the engine is issuing a rich signal.

Figure 5 shows o when performing secondary air control according to Figure 3.
2 shows the relationship between the output voltage (2) of the sensor 20 and the on/off operation of the electromagnetic switching valve 18. In FIG. 5, T indicates the start of deceleration. O2 sensor 20 as shown in Figure 5
Even if a lynch signal is generated, when a certain period of time has elapsed from the start of deceleration T, the electromagnetic switching valve 18 is turned on and the supply of secondary air is started. At this time, the exhaust gas temperature has decreased, so even if the 0□ sensor 20 generates a lynch signal, no afterfire occurs.

〔Effect of the invention〕

Unburnt 11C, C serves as a barometer for afterfire occurrence.
0 representing the slip of o. Since the supply of secondary air is controlled based on the output signal of the sensor, the occurrence of afterfire can be appropriately prevented regardless of the engine temperature, atmospheric pressure, deceleration operating state, etc.

[Brief explanation of the drawing]

Fig. 1 is an overall diagram of the internal combustion engine, Fig. 2 is a flowchart for executing secondary air control, Fig. 3 is a flowchart showing another embodiment, and Fig. 4 is a flowchart for executing secondary air control in Fig. 2. FIG. 5 is a time chart for explaining the secondary air control shown in FIG. 3. 2...Surge tank, 5...Exhaust manifold,
8... Intake duct, 12... Secondary air supply conduit, 13... Check valve, 14... Secondary air supply control valve, 20... 0□ sensor.

Claims (1)

[Claims] In an internal combustion engine equipped with a secondary air supply control valve that controls the supply of secondary air into the engine exhaust passage and an oxygen concentration detector disposed in the engine exhaust passage, is the throttle valve closed? The secondary air supply control valve of an internal combustion engine is equipped with a detector that detects whether the throttle valve is closed and the oxygen concentration detector generates a lean signal, and the secondary air supply control valve is opened. Supply control device.