JPS639097B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary air supply system for an engine, and more particularly to a secondary air supply system for an engine having a three-way catalytic converter in the engine exhaust system.

As one type of catalytic converter for exhaust gas purification, a three-way catalytic converter is known that can simultaneously convert three components, HC, CO, and NOx, into harmless components. In order to effectively operate the three-way catalytic converter to purify these three components, the air-fuel ratio of the exhaust gas must be controlled within a fairly narrow range around the stoichiometric air-fuel ratio.

Therefore, in an engine equipped with such a three-way catalytic converter, the air-fuel ratio (primary air-fuel ratio) of the air-fuel mixture supplied to the engine is usually set to be lower than the stoichiometric air-fuel ratio, that is, on the richer side than the stoichiometric air-fuel ratio. Supplying secondary air into the exhaust gas generated by this,
The concentration of oxygen in the resulting exhaust gas is detected by an oxygen detector such as an 02 sensor, and the supply amount of the secondary air is controlled, and the secondary air is supplied to the three-way catalytic converter. Control is performed to maintain the air-fuel ratio (secondary air-fuel ratio) of the introduced exhaust gas within a certain narrow range around the stoichiometric air-fuel ratio necessary for effective operation of the three-way catalytic converter.

However, when performing the above-mentioned control, it is necessary to constantly supply the engine with a rich mixture with an air-fuel ratio that is considerably lower than the stoichiometric air-fuel ratio, resulting in poor fuel efficiency and a large amount of unburned components in the exhaust gas. , a problem arises in that the catalytic converter is more likely to overheat.

In view of the above problems, some of the secondary air is supplied to the engine intake system to bring the primary air-fuel ratio closer to the stoichiometric air-fuel ratio, thereby improving fuel efficiency and reducing unburned components in exhaust gas. Ivy secondary air supply devices have been considered in the past.

In the secondary air supply device as described above, the amount of secondary air supplied is generally controlled by a control valve driven by a pulse signal, and the secondary air is intermittently supplied by repeatedly opening and closing the control valve. Therefore, if secondary air is supplied to the engine intake system even during idling operation, combustion fluctuations between engine cycles will increase, and the engine may not operate stably, causing surging. Furthermore, if secondary air is supplied to the engine intake system during idling, the exhaust gas temperature at that time may drop excessively, and the catalytic converter may no longer function effectively.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an improved secondary air supply device that cuts off the supply of secondary air to the engine intake system during idling.

According to the present invention, this purpose is achieved by providing a first passage means for guiding secondary air to the engine exhaust system, a second passage means for guiding secondary air to the engine intake system, and a second passage means for guiding the secondary air to the engine intake system. an exhaust sensor that detects the concentration of exhaust components and generates a signal corresponding to the concentration; an arithmetic device that determines a correction air amount necessary for correcting the air-fuel ratio of the engine based on the signal generated by the exhaust sensor; a control valve that controls the flow rate of air flowing through the first and second passage means, and a cutoff valve that is provided in the middle of the second passage means and shuts off the passage means during idling operation. This is achieved by a secondary air supply device for the engine, which is characterized by:

The invention will now be described in detail by way of example embodiments with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing one embodiment of a secondary air supply system for an engine according to the present invention. In the figure, 1 indicates the engine, and engine 1
includes a piston 3 in its cylinder bore 2, and defines a combustion chamber 4 above the piston 3 in the drawing. The engine 1 takes in a mixture of fuel and air through a carburetor 5 and an intake manifold 6 through an intake port 8 that is opened and closed by an intake valve 7, and exhausts it through an exhaust port 10 that is opened and closed by an exhaust valve 8. Exhaust gas is discharged through a manifold 11, an exhaust pipe (not shown), and a three-way catalytic converter provided in the middle.

Reference numeral 14 indicates a secondary air supply pipe that guides secondary air to the engine exhaust system. The secondary air supply pipe 14 is connected at one end to a secondary air injection port 15 provided in the exhaust manifold 11, and at the other end to a control valve 16. A check reed valve 17 is installed in the middle of the secondary air supply pipe 14.
The check reed valve 17 includes a reed element 18 and is configured to only allow fluid flow from the control valve 16 toward the secondary air injection port 15 .

21 indicates a secondary air supply pipe that guides secondary air to the engine intake system. This secondary air supply pipe 21
is connected at one end to an air injection port 22 provided in the intake manifold, and at the other end to the middle of the secondary air supply pipe 14 between the check reed valve 17 and the control valve 16. .

The control valve 16 includes a valve element 25 that opens and closes the port 24.
The valve element 25 is connected to a diaphragm 27 of a diaphragm device 26 and is driven thereby. When negative pressure is applied to the diaphragm chamber 28, the diaphragm 27 is displaced upward in the figure against the action of the compression coil spring 29, lifting the valve element 25 and opening the port 24 and the atmospheric intake port 30. On the other hand, when atmospheric pressure is applied to the diaphragm chamber 28, it is displaced downward by the spring force of the compression coil spring 29, pushing down the valve element 25 and connecting the port 24 and the atmospheric intake port 30. It's starting to cut off communication.

Diaphragm chamber 28 is connected via conduit 31 to port 33 of electromagnetic control valve 32 . The electromagnetic control valve 32 closes the negative pressure port 3 when the electromagnetic coil (not shown) is energized.
4 and port 33, and when the electromagnetic coil is not energized, atmosphere port 35 and port 33 are communicated. The negative pressure port 34 is connected to an intake pipe negative pressure outlet port 38 of the intake manifold 6 via a conduit 37 having a throttle element 36 in the middle.

Power supply control to the electromagnetic coil of the electromagnetic control valve 32 is performed by a pulse signal of a predetermined duty ratio generated by an arithmetic unit 39. The computing device 39 receives a signal from the oxygen sensor 40 attached to the exhaust manifold 11,
Based on this signal, the corrected air amount necessary for correcting the air-fuel ratio of the engine is determined, and a pulse signal with a duty ratio corresponding to the corrected air amount is determined.

In addition, a shutoff valve 5 is provided in the middle of the secondary air supply pipe 21.
0 is set. The shutoff valve 50 is connected to the valve port 51
It includes a valve element 52 for opening and closing, which valve element is connected to and driven by a diaphragm device 54.
The diaphragm device 54 includes a diaphragm 55 , and when negative pressure is introduced into the diaphragm chamber 56 , the valve element 52 is lifted against the action of a compression coil spring 57 to open the valve port 51 and open the secondary air supply pipe 21 . On the other hand, when negative pressure is not applied to the diaphragm chamber 56, the valve element 52 is pushed down by the action of the compression coil spring 57, the valve port 51 is closed, and the secondary air supply pipe 21 is closed.
It has become possible to cut off communication between the two. The diaphragm chamber 56 is connected to an intake pipe negative pressure outlet port 59 via a conduit 58. Intake pipe negative pressure outlet port 5
9 is located upstream of the throttle valve 60 provided in the carburetor 5 when the throttle valve 60 is at the idling opening position, and is located downstream of the throttle valve 60 when the throttle valve 60 is opened beyond a relatively small predetermined opening position. It is set up to be located at.

The apparatus constructed as described above operates as follows.

The arithmetic unit 39 outputs a pulse signal with a predetermined duty ratio to the electromagnetic control valve 32 based on the signal generated by the oxygen sensor 40 . The duty ratio of the pulse signal increases as there is less surplus oxygen in the exhaust gas flowing through the exhaust manifold 11, in other words, when the secondary air-fuel ratio is smaller than the stoichiometric air-fuel ratio.

Therefore, the electromagnetic control valve 32 repeatedly and alternately connects the port 33 to the negative pressure port 34 and the atmospheric pressure port 35 according to the duty ratio of the pulse signal, and alternately connects the atmospheric pressure and the negative pressure to each other according to the duty ratio of the pulse signal. is applied to the diaphragm chamber of the control valve 16 with a time ratio corresponding to . As a result, the port 24 of the control valve 16 is repeatedly opened and closed at the same frequency as the pulse signal and at a time ratio corresponding to the duty ratio of the pulse signal. When the port 24 is open, secondary air is drawn into the exhaust manifold 11 from the atmosphere intake port 30 via the secondary air supply pipe 14 and the check reed valve 17 due to exhaust pulsation. At this time, if the throttle valve 60 is opened beyond the intake pipe negative pressure outlet port 59, in other words, if the engine 1 is being operated at a predetermined load or higher, the intake pipe negative pressure outlet port 59 and the negative pressure is introduced into the diaphragm chamber 56, the valve element 52 opens the valve port 51, and the secondary air supply pipe 21
communication is established. Therefore, at this time, secondary air is sucked into the intake manifold 6 through the secondary air supply pipe 21 due to the intake pipe negative pressure and is sent to the engine 1. As a result, the primary air-fuel ratio approaches the stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust gas generated by combustion of the air-fuel mixture with this air-fuel ratio in the combustion chamber 4, that is, the secondary air-fuel ratio, is exhausted from the air injection port 15. It is mixed with secondary air supplied into the manifold 11 and corrected to an air-fuel ratio close to the stoichiometric air-fuel ratio.

When the throttle valve 60 is not opened beyond the intake pipe negative pressure outlet port 59, in other words, when the engine 1 is idling or operating at low load, atmospheric pressure is present in the intake pipe negative pressure outlet port 59. and the atmospheric pressure is introduced into the diaphragm chamber 56 so that the valve element 52 is connected to the valve port 5.
1 is opened, and communication with the secondary air supply pipe 21 is cut off. Therefore, at this time, no air flows through the secondary air supply pipe 21 to the intake manifold 6, and no secondary air is supplied to the engine intake system. In this state, the secondary air-fuel ratio is corrected to an air-fuel ratio close to the stoichiometric air-fuel ratio only by the secondary air supplied into the exhaust manifold 11 from the secondary air injection port 15.

As mentioned above, when the engine 1 is idling or operating at low load, secondary air is not supplied to the engine intake system, so fluctuations in combustion from cycle to engine cycle due to the supply of secondary air are avoided. , the occurrence of surging is avoided.

FIG. 2 is a schematic diagram showing another embodiment of the secondary air supply device according to the present invention. In FIG. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals as in FIG. In such an embodiment, the secondary air is supplied by an air pump 41 driven by the engine.
The control valve 16' has a valve element 43 that selectively opens and closes the ports 42a and 42b. When negative pressure is applied to the diaphragm chamber 44, the valve element 43 closes the port 42b and opens the port 42a. The air pump 41 provides air to be discharged, and when atmospheric pressure is applied to the diaphragm chamber 44, the port 42a is closed and the port 42b is opened.
Air discharged by the air pump 41 is guided to a relief port 45.

A cutoff valve 50 is provided in the middle of the secondary air supply pipe 21, similar to the embodiment described above. Further, a check valve 46 for preventing backflow of exhaust gas is provided in the middle of the secondary air supply pipe 14.

Therefore, even in this embodiment, only when the intake pipe negative pressure is applied to the intake pipe negative pressure outlet port 59,
In other words, the throttle valve 60 is connected to its port 5.
Secondary air is supplied to the engine intake system only when the opening exceeds 9, and when the engine 1 is idling or operating at low load, secondary air is supplied to the engine intake system. Not possible. Therefore, in this embodiment as well, the same effects as in the above-mentioned embodiment can be obtained.

FIG. 3 is a schematic diagram showing still another embodiment of the secondary air supply device according to the present invention. still,
In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals as in FIG. In such an embodiment, the valve element 25 is connected to a core 61 which cooperates with a solenoid 62 and which moves upward in the figure against the action of a helical compression spring 63 when the solenoid 62 is energized. When the solenoid 62 is not energized, it is displaced downward as shown in the figure by the action of the compression coil spring 63 to push the valve element 25 down and open the port 24. is starting to close. The solenoid 62 is supplied with a pulse signal of a predetermined duty ratio generated by the arithmetic unit 39, and is driven thereby.

The valve element 52 is also connected to a core 64 which cooperates with a solenoid 65.
When energized, the compression coil spring 6
The valve element 5 is displaced upwardly in the figure against the action of the valve element 5.
2 to open the valve port 51 and open the solenoid 6.
When the valve element 5 is not energized, the valve element 52 is displaced downward in the figure by the action of a compression coil spring 66 to push down the valve element 52 and close the valve port 51. Power supply control to the solenoid 65 is performed by the arithmetic unit 39. The arithmetic unit 39 is given a signal generated by the throttle switch 67, and the throttle switch 67
7, an ON signal is output to the solenoid 65 only when a signal indicating that the throttle valve 60 is below the idling opening or a relatively small predetermined opening is given.

Therefore, even in this embodiment, the solenoid 65 is not energized during idling or low-load operation, and the valve port 51 is closed by the valve element 52, so that communication with the secondary air supply pipe 21 is cut off. secondary air is not supplied to the engine intake system.

FIG. 4 is a schematic diagram showing still another embodiment of the secondary air supply device according to the present invention. still,
In FIG. 4, parts corresponding to those in FIG. 1 are designated by the same reference numerals as in FIG. In such embodiments, diaphragm chamber 56 is connected to conduit 68.
It is connected to the vent lily negative pressure outlet port 69 of the carburetor 5 by a.

In this embodiment, when the engine speed is low and the amount of intake air is accordingly low, such as during idling, sufficient negative pressure is not introduced into the diaphragm chamber 56, and as a result, the valve is closed in such operating ranges. Port 51 is closed by valve element 52 and communication with secondary air supply pipe 21 is interrupted. Therefore,
Even in this embodiment, when the engine speed is low, such as during idling, secondary air is not supplied to the engine intake system.

Although the present invention has been described in detail with respect to specific embodiments above, it will be appreciated by those skilled in the art that the present invention is not limited to these embodiments and that various embodiments can be made within the scope of the present invention. It should be obvious.

[Brief explanation of the drawing]

1 to 4 are schematic configuration diagrams showing embodiments of a secondary air supply device for an engine according to the present invention. 1...Engine, 2...Cylinder bore, 3...
Piston, 4... Combustion chamber, 5... Carburetor, 6...
Intake manifold, 7...Intake valve, 8...Intake port, 9...Exhaust valve, 10...Exhaust port, 11
...Exhaust manifold, 14...Secondary air supply pipe, 15...Secondary air injection port, 16...Control valve, 17...Check reed valve, 18...Reed element, 21...Secondary air supply Pipe, 22... Air injection port, 24... Port, 25... Valve element, 26
...Diaphragm device, 27...Diaphragm,
28...Diaphragm chamber, 29...Compression coil spring, 30...Atmospheric intake port, 31...Conduit, 3
2... Solenoid control valve, 33... Port, 34... Negative pressure port, 35... Atmospheric pressure port, 36... Throttle element, 37... Conduit, 38... Intake pipe negative pressure extraction port, 39... Arithmetic device, 40...Oxygen sensor,
41...Air pump, 42a, 42b...Port, 43...Valve element, 44...Diaphragm chamber,
45... Relief port, 46... Check valve, 50
... Shutoff valve, 51 ... Valve port, 52 ... Valve element, 54 ... Diaphragm device, 55 ... Diaphragm, 56 ... Diaphragm chamber, 57 ... Compression coil spring, 58 ... Conduit, 59 ... Intake Pipe negative pressure outlet port, 60... Throttle valve, 61...
... Core, 62 ... Solenoid, 63 ... Compression coil spring, 64 ... Core, 65 ... Solenoid, 6
6... Compression coil spring, 67... Throttle switch, 68... Conduit, 69... Bench lily negative pressure extraction port.

Claims (1)

[Claims] 1 A first passage means for guiding secondary air to the engine exhaust system, a second passage means for guiding secondary air to the engine intake system, detecting the concentration of exhaust components of exhaust gas discharged from the engine, and responding accordingly. an exhaust sensor that generates a signal generated by the exhaust sensor; an arithmetic device that determines a correction air amount necessary for correcting the air-fuel ratio of the engine based on the signal generated by the exhaust sensor; An engine characterized in that it has a control valve that controls the flow rate of air flowing through the second passage means, and a cutoff valve that is provided in the middle of the second passage means and shuts off the idling operation time passage means. secondary air supply device.