JP2583226Y2 - Engine secondary air supply device - 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 on which a three-way catalyst device is mounted, and more specifically, to shut off the supply of secondary air introduced at the time of cold start at an appropriate timing. Related to the device to perform.

[0002]

2. Description of the Related Art A three-way catalyst device for purifying exhaust gas of an engine controls a mixture ratio (air-fuel ratio) of an air-fuel mixture supplied to the engine to a stoichiometric air-fuel ratio, thereby obtaining three elements H in the exhaust gas.
C, CO and NOx can be efficiently removed.
The control of the stoichiometric air-fuel ratio is usually performed by feedback control using an oxygen sensor provided upstream of the catalyst. or,
At the time of cold start of the engine, the air-fuel mixture becomes rich (rich), so it is common to supply secondary air to the upstream of the catalyst by a secondary air supply device in order to reduce HC and CO and promote catalyst activation. It is being done. As a method of supplying the secondary air, there are a forced supply by an air pump and a natural supply by a reed valve (one-way valve) using exhaust pulsation (pulsation).

[0003] By the way, when the supply of the secondary air at the time of the cold start is continued forever, the catalyst becomes active and the oxygen becomes excessive.
Although CO can be oxidized and removed, NOx has a problem that it cannot be removed because it has a reducing effect.Therefore, in the conventional one, the catalyst becomes active when the engine water temperature reaches a certain water temperature after a cold start. It is deemed to be in a state, and after that, measures are taken to cut off the supply of the secondary air. (References, Japanese Patent Laid-Open No. 622-2)
Further, as another method, there is a method in which secondary air is supplied for a certain period of time after a cold start and then cut off.

Conventionally, the function of the three-way catalyst after the activation of the catalyst (after the start of the catalytic reaction) is ensured in this way.

[0005]

However, in the above-mentioned prior art, the activation state of the catalyst is determined based on the engine temperature or a fixed time, so that the secondary air is supplied even though the catalyst is not actually activated. There is a problem that the secondary air is continuously supplied even after cutting or activation, which causes a problem in exhaust gas cleaning. That is, HC and CO cannot be reduced in the former,
In the latter case, NOx cannot be reduced.

[0006] In addition, since the catalyst may deteriorate over time and the starting point of the activity may change, in such a case,
If an attempt is made to determine the activation state based on the temperature or the time, the catalyst will be different when the catalyst is new and when the catalyst is used, which again causes a problem in exhaust gas purification.

This invention solves the problem that the supply of secondary air is controlled in accordance with the actual activation state of the catalyst so that the secondary air is cut even though it has not been activated, or is supplied even after activation. To provide a secondary air supply device for an engine that efficiently purifies the exhaust by controlling the purifying action of the engine when it is new and when it is in use by controlling the change with time. It is intended to solve.

[0008]

In order to achieve the above object, the present invention provides a three-way catalyst device interposed in an exhaust pipe, and supplies secondary air to an exhaust pipe upstream of the three-way catalyst device. A secondary air supply device having an air pump or a reed valve; an oxygen sensor provided in an exhaust pipe downstream of the three-way catalyst device; and an activation state of the three-way catalyst device based on a detection signal of the oxygen sensor. And a determining means for determining
When it is determined that the three-way catalyst device is in an inactive state,
When secondary air is supplied and it is determined that
Control means for controlling the secondary air supply device so as to cut off the supply of the secondary air. The determining means determines that the three-way catalyst device is in an inactive state when the oxygen sensor detects an amplitude value exceeding a predetermined value, and determines that the three-way catalyst device is in an active state when detecting an amplitude value equal to or less than the predetermined value. Is to be determined.

[0009]

When the catalyst is not activated, the output of the oxygen sensor installed downstream of the catalyst is displayed as a change in the oxygen concentration according to the pulsation of the exhaust gas, that is, the voltage of the pulsation of the oxygen portion flowing without being consumed. Will do. After the activation of the catalyst, the voltage output of this pulsation is averaged by the storage capacity of the catalyst and becomes a low level. Therefore, when the output becomes low level, it can be determined that the catalyst activation starts. More specifically, the pulsation of the oxygen portion flowing without being consumed by the catalyst is displayed as the amplitude value of the voltage detected by the oxygen sensor. Therefore, when the amplitude value becomes equal to or less than a predetermined value, the catalyst activation starts. It can be judged as the time. Therefore, when the output of the oxygen sensor changes, the supply of the secondary air is cut by the secondary air supply device, so that the supply of the secondary air is performed correctly. Even if the degree of deterioration changes over time between the time of new use and the time of use, the secondary supply is controlled in response to the changed activation start time. Can be dealt with.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

First, the configuration will be described with reference to FIG. In FIG. 1, an engine 1 has an intake valve 2 and an exhaust valve 3, and the air-fuel mixture is drawn into the combustion chamber 5 from the intake valve 2 by lowering a piston 4, compressed by rising of the piston 4, and compressed by an ignition plug (not shown). The piston 4 is lowered by being ignited to obtain an output. Then, the exhaust gas from the combustion chamber 5 is discharged to the exhaust pipe 6 via the exhaust valve 3 in the upward stroke of the piston 4, and is cleaned by a three-way catalyst device (hereinafter, also simply referred to as a catalyst) 7 and exhausted (tail pipe) 8. From the atmosphere. Catalyst 7
A control oxygen sensor (O ₂ sensor) 9 for performing feedback control of the air-fuel mixture to the stoichiometric air-fuel ratio is provided in the exhaust pipe 6 upstream of
The output signal is input to the fuel control device 10, and the output is output to the injector 12 attached to the intake manifold 11 upstream of the intake valve 2. The injector 12 performs duty-like on / off control based on the input signal, and injects the pumped fuel of the pump 14 in the fuel tank 13 to the intake port 15. A throttle valve 16 for controlling the amount of intake air is provided upstream of the intake manifold 11, and an air flow meter 17 and an air cleaner 18 are provided upstream of the throttle valve 16 in that order. The output signal of the air flow meter 17 is input to the fuel control device 10 and, thereby, is output to the injector 12 so as to inject a fuel amount corresponding to the air amount. Note that a water temperature signal 25 and the like are input to the fuel control device 10, and a command is issued to the injector 12 to make the air-fuel mixture rich at the time of a cold start.

An air pump 19 for supplying secondary air in response to the mixture richness at the time of the cold start is provided. A pipe 21 is provided so that the end is connected to the exhaust pipe 6 upstream of the catalyst 7. A control valve 22 as an air cut valve for cutting secondary air is provided in the middle of the pipe 21. The control valve 22 and the air pump 19 constitute a secondary air supply device. A so-called detection oxygen sensor 23 for detecting the activation state of the catalyst 7 is provided in the exhaust pipe 8, that is, downstream of the catalyst 7. The output signal of the oxygen sensor 23 is input to the secondary air control device 24, and the output signal is input to the control valve 22 and the air pump 19 to stop the operation. In the present embodiment, the secondary air control device 24 determines the activation state of the catalyst 7 based on the detection signal of the oxygen sensor 23, and the air pump 1
9 and a control valve for controlling a secondary air supply device having a control valve 22. The oxygen sensor 23
As shown in FIG. 2, before the catalyst is activated, as shown in FIG. Beyond
After the activation of the catalyst, the variation in the mixture ratio is averaged by the oxygen storage capacity in the catalyst as shown in B, and the amplitude value becomes equal to or less than a predetermined value, and the output becomes low (lean output). Therefore, when the output of the oxygen sensor 23 becomes equal to or less than the constant voltage V0 and the amplitude value becomes equal to or less than the predetermined value, the secondary air control device 24 stops the operation of the air pump 19,
The control is performed so that the control valve 22 is closed.

Next, the operation of the above embodiment will be described. At the time of cold start, the water temperature signal 25 to the fuel control device 10
For example, the fuel control device 10 instructs the injector 12 to operate so as to obtain a rich mixture. At this time, since the control oxygen sensor 9 is rich in air-fuel mixture as in the case of a cold start, its control is held. Then, the air pump 19 operates to supply the secondary air to the exhaust pipe 6 from the downstream of the air cleaner 18 via the pipes 20 and 21. At this time, of course, the air cut valve (control valve) 22 is open. By introducing secondary air into the rich air-fuel mixture, the catalyst 7 purifies exhaust components that are in an oxygen excess state near the stoichiometric air-fuel ratio. , CO
And purify the exhaust. Therefore, the catalyst 7
The downstream oxygen sensor 23 captures, as a voltage, an output in which the excess oxygen not consumed by the catalyst 7 changes according to the pulsation of the exhaust gas. (FIG. 2A).

When the catalyst 7 is activated (reaction disclosed), exhaust purification by the catalyst 7 is performed entirely, but NOx purification is not performed because oxygen is excessive. However, in this embodiment, the pulsation of A is averaged because the catalyst 7 has a storage capacity due to the activation of the catalyst 7, and a substantially straight lean output is obtained.
The oxygen sensor 23 detects (FIG. 2B), and the output of the oxygen sensor 23 is input to the secondary air control device 24, so that the control valve 22 performs an air cut operation and the operation of the air pump 19 is also stopped. . Thus, since the secondary air is not supplied after the activation of the catalyst 7, the catalyst 7 can also purify NOx.

FIG. 3 shows a control flow chart of the air cut. To explain this, in step 1, when the engine starts, the air cut valve 22 opens. In step 2, it is determined whether the rear oxygen sensor 23 is activated (initialized). If it is determined that the oxygen sensor 23 is activated, the process proceeds to step 3. This part corresponds to the determination means for determining the activation state of the catalyst. In step 3, the output (amplitude ΔV) of the rear oxygen sensor 23 is monitored to determine whether the state is A or B in FIG. In step 4, when the output △ V <V0 (YES), the process proceeds to step 5, and the air cut valve 22 is closed. Thus, the secondary air is cut. This portion corresponds to control means for controlling the secondary air supply device so as to supply or shut off the secondary air according to the activation state of the catalyst.

At this point, since the warm-up is progressing, it goes without saying that the feedback control by the control oxygen sensor 9 is being performed. In this manner, the apparatus according to the present embodiment can appropriately purify the exhaust gas in response to the rich air-fuel mixture at the time of the cold start, and perform the following two operations during the normal operation.
Appropriate ternary exhaust gas purification by secondary air cut can be achieved.

In the above embodiment, the secondary air is introduced by the air pump. However, the present invention can be applied to a system using a reed valve utilizing exhaust pulsation instead. In addition, the control of the secondary air by the control valve 22 includes reduction to a small amount in addition to the above-described air cut.

[0018]

[Effects of the Invention] This invention has the above-described structure in the secondary air supply device of the engine equipped with the three-way catalyst device.
HC and CO by secondary air introduction at cold start
Of the three-way catalytic function after activation of the catalyst and the effect of promoting the activation of the catalyst can be achieved at the same time, and the effect of achieving the optimal control in accordance with the time-series deterioration of the catalyst can be obtained. be able to.

[Brief description of the drawings]

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

FIG. 2 shows the output V of the oxygen sensor downstream of the catalyst with respect to time t.
In the figure, A shows before catalytic activity and B shows after catalytic activity.

FIG. 3 is a control flowchart of air cut in FIG. 1;

[Explanation of symbols]

 Reference Signs List 6 exhaust pipe 7 three-way catalyst device (catalyst) 8 exhaust pipe (tail pipe) 9 control oxygen sensor 10 fuel control device 11 intake manifold 12 injector 19 air pump (secondary air supply device) 22 control valve (air cut valve, 2) Secondary air supply device) 23 oxygen sensor for detection 24 secondary air control device (judgment means, control means)

Claims (2)

(57) [Scope of request for utility model registration] 1. A three-way catalyst device interposed in an exhaust pipe, a secondary air supply device having an air pump or a reed valve for supplying secondary air to an exhaust pipe upstream of the three-way catalyst device, An oxygen sensor provided in an exhaust pipe downstream of the main catalyst device,
Determining means for determining the activation state of the three-way catalytic device based on the detection signal of the oxygen sensor; and supplying the secondary air when the determining means determines that the three-way catalytic device is in the inactive state. And control means for controlling the secondary air supply device so as to shut off the supply of the secondary air when it is determined that the engine is in the active state.
Next air supply device. 2. The determining means determines that the three-way catalytic converter is in an inactive state when the oxygen sensor detects an amplitude value exceeding a predetermined value, and determines an amplitude value equal to or less than the predetermined value.
The secondary air supply device for an engine according to claim 1, wherein the secondary air supply device determines that the engine is in an active state.