JPH0783040A - Secondary air supply device for engine - Google Patents

Abstract

PURPOSE:To stably obtain catalyst activation effect by providing a control means which increases a total amount of secondary air to be supplied when fuel is heavy, compared to the case that the fuel is light. CONSTITUTION:A secondary air supply device 4 is provided on an engine 1 for supplying secondary air to an exhaust system on an upstream side of an exhaust purification catalyst 3. Oxidation (burning) of combustible components included in exhaust is promoted in the catalyst 3 by supplying the secondary air, and activation of the catalyst is accelerated after cold starting. An air pump 5 and a three-directional solenoid valve 8 are electronically controlled by means of a control unit 9. Information such as an intake air rate QA and a cooling water temperature TW of the engine 1 is input to the control unit 9, while detection signals from a fuel property sensor 10 is inputted thereto. When the fuel is heavy, a total amount of the secondary air to be supplied is increased compared to the case that the fuel is light. Catalyst activation effect is stably obtained, accordingly.

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, and more particularly to a technique for optimizing the supply amount of secondary air according to the property of fuel supplied to the engine.

[0002]

2. Description of the Related Art As a secondary air supply device for an engine,
For example, there is one such as disclosed in SAE paper 910840. The secondary air supply device supplies secondary air to the upstream side of the exhaust purification catalyst interposed in the exhaust system, and promotes oxidation of unburned components in the exhaust gas by supplying the secondary air. The purpose is to accelerate the rise in catalyst temperature (catalyst activity).

[0003]

The fuel supplied to the engine has heavy and light differences, and the required secondary air amount differs due to the difference in fuel properties. There was a problem that the intended purpose could not be achieved. That is, conventionally, the secondary air amount is controlled according to the operating condition of the engine, but the secondary air amount is not controlled according to the fuel property, and for example, normal light fuel is used. If the supply control of secondary air is adapted to, when using heavy fuel with an increase in unburned components (see Fig. 5), the amount of secondary air will be insufficient and the desired catalytic activation effect can be obtained. There was a fear that the amount of unburned components discharged would increase (see Fig. 6).

The present invention has been made in view of the above problems, and it is possible to stably obtain the effect of accelerating the catalytic activity by enabling the optimum secondary air supply without being affected by the change in the fuel property. The purpose is to do so.

[0005]

Therefore, a secondary air supply device for an engine according to the present invention is a secondary air supply device for an engine that supplies air to an upstream side of an exhaust purification catalyst interposed in an exhaust system of the engine. And is configured as shown in FIG. In FIG. 1, the fuel property determination means determines whether the fuel supplied to the engine is heavy or light, and the fuel property determination means 2
The secondary air amount control means increases the total amount of secondary air to be supplied when the fuel property is heavy based on the heavy or light quality of the fuel determined by the fuel property determination means as compared to when the fuel property is light.

[0006]

According to this structure, the heavy or light of the fuel supplied to the engine is determined, and when the fuel used is heavy, the total supply amount of the secondary air is increased as compared with the case where the light fuel is used. When the fuel is heavy and the amount of unburned components in the exhaust increases, the amount of secondary air is increased to reliably oxidize the unburned components, and when the fuel used is light, excess secondary air Supply can be avoided.

[0007]

EXAMPLES Examples of the present invention will be described below. FIG. 2 is a diagram showing the system configuration of the first embodiment. In FIG. 2, exhaust gas from the gasoline engine 1 is exhausted to the outside via an exhaust manifold 2 and an exhaust purification catalyst 3.

Further, the engine 1 of this embodiment is provided with a secondary air supply device 4 for supplying secondary air to the exhaust system upstream of the exhaust purification catalyst 3. The secondary air supply device 4 supplies the air pumped from the air pump 5 to the secondary air supply device 2.
The secondary air is guided to the exhaust system on the upstream side of the catalyst 3 through the secondary air passage 6, and the supply of the secondary air promotes the oxidation (combustion) of unburned components contained in the exhaust in the catalyst 3,
Thus, the catalyst activity immediately after the cold start is accelerated.

The secondary air passage 6 branches into two branch passages 6a and 6b on the way, and an orifice 7 is provided in one of the branch passages 6a, and two branch passages 6a and 6b are provided downstream of the orifice 7. Join together. A three-way solenoid valve 8 is provided at the confluence of the branch passages 6a and 6b.
So that either the secondary air guided through the orifice 7 via the orifice 7 or the secondary air guided around the orifice 7 via the branch passage 6b can be selectively supplied to the exhaust system by the three-way solenoid valve 8. It has become.

Here, the branch passage 6a is formed by the three-way solenoid valve 8.
If the introduction of secondary air via the side is selected, the branch passage 6
Compared with the case where b is selected, the effective opening area is restricted by the orifice 7 and the flow rate is limited.
2 depending on the selection of the branch passages 6a and 6b by the one-way solenoid valve 8.
The secondary air flow rate can be adjusted. The air pump 5 and the three-way solenoid valve 8 are electronically controlled by a control unit 9 containing a microcomputer, and the control unit 9 stores information such as the intake air amount QA of the engine 1 and the cooling water temperature Tw. A fuel property sensor (fuel property determination means) 10 for detecting the properties (heavy and light) of the fuel supplied and supplied to the engine 1.
The detection signal of is input.

The fuel property sensor 10 is, for example, an optical fuel sensor, in which a probe serving as an optical waveguide is immersed in fuel and a light emitting element and a light receiving element are provided at each end of the probe, It utilizes the refractive index to detect heavy or light fuel from the amount of incident light input to the light receiving element (see Japanese Patent Laid-Open No. 1-257245, etc.). As the sensor for detecting the heavy and light of the fuel used, in addition to the above-mentioned optical sensor, a sensor for catching a change in capacitance due to the heavy and light of the fuel may be used, and various known fuel sensors may be used. Can be used.

Further, in FIG. 2, 11 is an air cleaner for secondary air. Here, the state of the secondary air supply control by the control unit 9 will be described with reference to the flowchart of FIG. In this embodiment, the function as the secondary air amount control means depending on the fuel property is as shown in FIG.
Control unit 9 as shown in the flow chart
Is equipped with software.

In the flow chart of FIG. 3, first, in step 1 (denoted as S1 in the figure. The same applies hereinafter),
It is determined whether the engine 1 has been started. Engine 1
If is not started, the routine proceeds to step 12, where the air pump 5 is stopped and the secondary air is not supplied.
On the other hand, when the engine 1 is started, the process proceeds to step 2,
The detection signal of the fuel property sensor 10 is read, and in the next step 3, it is determined whether the used fuel is heavy or light based on the read detection signal.

When it is determined in step 3 that the fuel used is heavy, the routine proceeds to step 4, where the cooling water temperature Tw at the time of starting is read, and in step 5, based on the read cooling water temperature Tw. The time t _ON for continuing the supply of secondary air from the start is set. The supply time t _ON
As shown in FIG. 4, the characteristics for heavy fuel and the characteristics for light fuel are individually set in advance. In any of the fuel properties, the cooling water temperature Tw is low and the fuel vaporization property is low. The secondary air is supplied longer as the unburned components in the exhaust gas increase and the unburned components in the exhaust gas increase, and when the heavy fuel is used compared to the light fuel, the same cooling water temperature is used. Even under the condition of Tw, the secondary air is supplied for a longer time.

That is, the unburned components in the exhaust gas are affected by the vaporization characteristics that change depending on the engine temperature, and even if the engine temperature is the same, if the fuel is heavy, the vaporization property deteriorates and the unburned component Since the component tends to increase (see FIG. 5), when heavy fuel is used, the time t _ON for supplying the secondary air is lengthened to increase the amount of unburned component discharged when heavy fuel is used. I am trying to oxidize enough.

In step 6, it is judged whether or not the supply time t _ON set corresponding to the usage state of the heavy fuel in step 5 has elapsed, and the process proceeds to step 7 until the time t _ON has elapsed. , The air pump 5 is driven, and the branch passage 6b that provides a larger flow rate is selected by the three-way solenoid valve 8 so that the secondary air is supplied through the branch passage 6b.

On the other hand, when it is determined in step 3 that the fuel used is light, the secondary air is supplied in the same manner based on the starting water temperature read in step 8 as compared to when heavy fuel is used. When the time t _ON 'is set in step 9 and it is determined in step 10 that the set supply time t _ON ' has not been reached, the process proceeds to step 11 and the air pump 5
The three-way solenoid valve 8 to drive the branch passage 6
Secondary air is supplied through the orifice 7 of a.

When it is determined in step 6 or step 10 that the supply times t _ON and t _ON 'has elapsed,
Go to step 12 to stop the operation of the air pump 5,
Stop the supply of secondary air. Here, when the light fuel is used, the secondary air is supplied through the branch passage 6a in which the orifice 7 is interposed, so the secondary air is supplied through the branch passage 6b in which the orifice is not provided. The amount of secondary air supplied is smaller than when heavy fuel is used. In other words, when using heavy fuel with an increase in unburned components,
When the supply amount of secondary air per unit time is increased and the supply time is made longer than when using light fuel, the total amount of secondary air is based on the supply amount per unit time and the supply time. Is increasing.

That is, when heavy fuel is used, the amount of unburned component (HC) emitted from the engine 1 increases as shown in FIG. 5, and as shown in FIG. 6, secondary air suitable for light fuel is used. Since the amount is insufficient and the desired catalytic activity cannot be achieved, the amount is increased from both aspects of the unit supply amount and the supply time to sufficiently promote the oxidation of unburned components, and the catalytic activity (catalyst temperature Ascending) can be accelerated (see FIG. 7).

In the above embodiment, the secondary air amount is increased when the heavy fuel is used, both in the supply amount per unit time and the supply time, but only one of them is used as the secondary air amount. The amount of air may be increased. Further, in the above-described embodiment, the heavy fuel and light fuel are discriminated in two stages, heavy fuel and light fuel. However, the fuel may be further discriminated more finely and the supply time may be set more finely. Further, instead of controlling the amount of secondary air per unit time by selection of the branch passages 6a and 6b by the three-way solenoid valve 8, the secondary air is controlled by controlling the opening degree of the electromagnetic valve interposed in the secondary air passage 6. The air amount may be adjusted, and in this case, the secondary air amount may be set with higher accuracy in consideration of the information of the intake air amount QA of the engine 1 and the like.

By the way, in the first embodiment, the period for supplying the secondary air is determined by the times t _ON and t _ON 'set according to the cooling water temperature Tw. Since the catalyst temperature is raised to the activation temperature early, the supply period of the secondary air may be determined based on the information of the catalyst temperature. A second embodiment for controlling the supply period will be described.

In FIG. 8 showing the system configuration of the second embodiment, in addition to the configuration shown in FIG. 2, a temperature sensor 12 for detecting the exhaust temperature at the outlet of the catalyst 3 is provided. 8 is the same as FIG. 2 except for the temperature sensor 12, so detailed description will be omitted. Next, the secondary air control in the second embodiment will be described with reference to the flowchart of FIG.

In the flowchart of FIG. 9, first, at step 21, it is judged if the engine 1 has been started.
Then, when the engine 1 is started, the detection signal of the fuel property sensor 10 is input in step 22, and in the next step 23, it is determined whether the used fuel is heavy or light.

When it is determined that the fuel used is light, the routine proceeds to step 24, where the outlet temperature T of the catalyst 3 detected by the temperature sensor 12 is read. Next, at step 25, the read outlet temperature T and the catalyst activity determination temperature T which is set in advance in conformity with the use of the light fuel.
Compare with _CAT (eg 350 ° C).

When it is determined that the actual outlet temperature T is lower than the catalyst activity determination temperature T _CAT ,
Proceeding to step 26, the three-way solenoid valve 8 so that the secondary air is supplied through the branch passage 6a in which the orifice 7 is interposed.
To control. On the other hand, when the outlet temperature T higher than the catalyst activity determination temperature T _CAT is detected, the routine proceeds to step 30, where the supply of secondary air is stopped.

When it is determined in step 23 that the fuel used is heavy, the catalyst outlet temperature T is read in step 27, and in the next step 28, the activity determination temperature T
It is determined whether or not the temperature obtained by adding a predetermined temperature ΔT (for example, 10 to 50 ° C.) to _CAT exceeds the read outlet temperature T. That is, when using heavy fuel with a large amount of unburned components, more secondary air is supplied by continuing the supply of secondary air until the temperature becomes higher than when using light fuel. I am trying to do so.

When it is determined in step 28 that the outlet temperature T is lower than the activity determination temperature T _CAT + ΔT,
Proceeding to step 29, the three-way solenoid valve 8 is controlled so as to supply the secondary air through the branch passage 6b, and the light fuel supplied through the branch passage 6a in which the orifice 7 is inserted is used as compared with when using the light fuel. , More secondary air is supplied. In the second embodiment as well, the fuel lightness and lightness may be finely determined, and the activity determination temperature may be finely set based on the determination result. Furthermore, both the time and the catalyst temperature parameters may be monitored. However, it is also possible to adopt a configuration in which the supply of secondary air is controlled.

[0028]

As described above, according to the present invention, the heavy or light of the fuel used in the engine is determined, and when the heavy fuel is used, it is compared with when the light fuel is used.
Since the total supply amount of the secondary air is increased, the supply amount of the secondary air can be increased according to the increase of the unburned component due to the use of the heavy fuel, without being affected by the heavy or light fuel. There is an effect that the optimum secondary air can be supplied, so that the catalyst activation effect by the supply of the secondary air can be stably obtained and the exhaust property immediately after the start can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention.

FIG. 2 is a system schematic diagram of the first embodiment.

FIG. 3 is a flowchart showing secondary air control in the first embodiment.

FIG. 4 is a diagram showing a correlation between a water temperature at startup and a secondary air supply time.

FIG. 5 is a diagram showing a correlation between heavy and light fuel and HC emission amount from an engine.

FIG. 6 is a diagram showing a correlation between a secondary air amount and an HC discharge amount at a catalyst outlet.

FIG. 7 is a diagram showing a correlation between a control state of secondary air and a change in catalyst temperature.

FIG. 8 is a system schematic diagram of a second embodiment.

FIG. 9 is a flowchart showing secondary air control in the second embodiment.

[Explanation of symbols]

 1 Engine 2 Exhaust Manifold 3 Exhaust Purification Catalyst 4 Secondary Air Supply Device 5 Air Pump 6 Secondary Air Passage 6a, 6b Branch Passage 7 Orifice 8 3-Way Solenoid Valve 9 Control Unit 10 Fuel Property Sensor 12 Temperature Sensor

Claims (1)

[Claims] 1. A secondary air supply device for an engine, which supplies air to an upstream side of an exhaust purification catalyst interposed in an exhaust system of an engine, the fuel property for determining whether the fuel supplied to the engine is heavy or light. A secondary air amount based on the fuel property that increases the total amount of secondary air to be supplied when the fuel property is heavy, based on the determining means and the heavy or light fuel quality determined by the fuel property determining means. A secondary air supply device for an engine, comprising: a control means.