JPH0551773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine exhaust purification device.

(Prior art) An exhaust gas purification catalyst is often installed in the exhaust passage of an engine in order to reduce harmful components in the exhaust gas, but this purification catalyst is effective only at a certain high temperature. It has no effect on In other words, at low load times, such as when idling, when the exhaust gas flow rate is low and the absolute amount of harmful components is small, the purification catalyst remains relatively low temperature and its purification effect is hardly performed. When the load is high and the absolute amount of harmful components increases, the reaction is activated and the temperature reaches a high temperature, resulting in effective purification.

In this way, in order to use a purification catalyst whose purification ability changes depending on the temperature to quickly purify exhaust gas when the load is high, it is necessary to , it is necessary to promptly raise the temperature of the purification catalyst. For this reason, conventionally, when the engine load exceeds a set value, the purification catalyst is activated by enriching the air-fuel mixture supplied to the engine's intake system and supplying secondary air to the exhaust passage upstream of the purification catalyst. The reaction was activated to actively raise the temperature.

In this way, in systems that temporarily enrich the air-fuel mixture to raise the temperature of the purification catalyst, it is disadvantageous in terms of fuel efficiency, so it is desirable to shorten the time for enriching the air-fuel mixture as much as possible. be. For this reason, as shown in Japanese Unexamined Patent Publication No. 54-9319, a temperature sensor is provided to detect the temperature of the purification catalyst, and feedback control using this temperature sensor allows
A system has also been proposed in which the active temperature rise of the purification catalyst is stopped (the supply of the rich air-fuel mixture is stopped) once the temperature of the purification catalyst has risen to a temperature at which it can effectively function.

However, the device using the temperature sensor as described above is expensive and undesirable in terms of cost. In addition, recently, monolith types have been increasingly used as purification catalysts instead of pellet types. As a result, accurate detection is not possible, which reduces the significance of feedback control using this temperature sensor, and also causes a delay in response.

(Objective of the Invention) The present invention has been made in consideration of the above-mentioned circumstances, and it is possible to prevent the engine load from exceeding a set value by a type of prospective control without using a special sensor such as a temperature sensor. An object of the present invention is to provide an engine exhaust gas purification device that can quickly raise the temperature of a purification catalyst to a necessary and sufficient temperature when the temperature is low.

(Structure of the Invention) The present invention was made by focusing on the fact that the temperature of the purification catalyst increases faster as the amount of unburned components in the exhaust gas increases. After considering the predetermined amount of unburned components necessary for the catalyst to reach a specific temperature, set the time required to reach this predetermined amount of unburned components according to the engine load, and set this setting. This system temporarily enriches the air-fuel mixture and supplies secondary air for the specified amount of time.

Specifically, assuming an engine exhaust purification device in which an exhaust gas purification catalyst is disposed in the engine exhaust passage, as shown in Figure 1, the fuel that adjusts the amount of fuel supplied to the engine intake system will be explained. a supply device; a secondary air supply device for supplying secondary air to the exhaust passage upstream of the exhaust gas purification catalyst; a load detection means for detecting engine load; receiving an output from the load detection means; a catalyst temperature control device that enriches the air-fuel mixture and supplies secondary air to the exhaust passage for a predetermined period of time when the engine load exceeds a set value; It is equipped with a correction means for setting the length so that the length becomes shorter as the load increases;

With this configuration, the time (predetermined time) for supplying the rich mixture and secondary air is set according to the temperature rise gradient of the purification catalyst according to the engine load, that is, the amount of unburned components. , it is possible to quickly raise the temperature of the purification catalyst to a necessary and sufficient temperature while preventing unnecessary supply of a rich mixture to the purification catalyst.

(Example) Examples of the present invention will be described below based on the attached drawings.

In FIG. 2, reference numeral 1 denotes an engine body, and an air cleaner 3, an air flow meter 4, a throttle valve 5, and a fuel injection valve 6 are disposed in the intake passage 2 in this order from the upstream side. In addition, exhaust passage 7
An O ₂ sensor 8 as a secondary air-fuel ratio sensor and an exhaust gas purification catalyst (three-way catalyst in the embodiment) 9 are arranged in this order from the upstream side, that is, from the engine body 1 side.

In the exhaust passage 7 on the upstream side of the O ₂ sensor 8, there are 2
A secondary air supply port 10 is opened, and an air pump 12 is connected to this secondary air supply port 10 via a pipe 11. An electromagnetic three-way switching valve 13 is connected to the middle of the pipe 11, and a relief pipe 14 is connected to the switching valve 13. As a result, depending on the switching mode of the switching valve 13, the secondary air supply state in which the secondary air from the air pump 12 is supplied from the secondary air supply port 10 to the exhaust passage 7, and the secondary air supply state in which the secondary air is supplied to the exhaust passage 7 from the secondary air supply port 10, and A state in which the supply of secondary air flowing to the pipe 14 is stopped is possible, and such switching of the switching valve 13 is performed by a secondary air control circuit 15, which will be described later. Reference numeral 16 in FIG. 2 is a fuel control circuit, which cooperates with the fuel injection valve 6 to constitute a fuel supply device. In the embodiment, in the operating mode shown in region B in FIG. 3, the air-fuel mixture is supplied to the engine body 1 based on the secondary air-fuel ratio signal from the O ₂ sensor 8 so that the secondary air-fuel ratio becomes the stoichiometric air-fuel ratio. It is now possible to perform a feedback operation to supply the fuel. This fuel control circuit 16 includes an intake air amount signal S ₁ from the air flow meter 4 and a throttle valve 5.
an opening signal S ₂ from a throttle sensor 17 that detects the opening of the engine;
In addition to the secondary air-fuel ratio signal S ₄ from the S ₃ and O ₂ sensor 8, the sensors are not shown, but as shown in FIG. 3, an engine coolant temperature signal S ₅ and an intake pressure signal S ₆ are input. The fuel control circuit 16 outputs the fuel to the fuel injection valve 6.

To briefly explain the function of the fuel control circuit 16 with reference to FIG. 4, first, the basic fuel calculation circuit 21 calculates the basic fuel injection amount based on the intake air amount and the engine rotation speed, and this calculation result is sent to the fuel correction circuit 22. Output to. In addition, the operating condition determination circuit 2
3 determines the engine operating conditions based on the engine speed, throttle opening, intake pressure, cooling water temperature, etc., and based on this determination result, the fuel increase rate setting circuit 24 determines the fuel increase rate ( (including fuel reduction and fuel cut), this determined fuel increase rate is output to the fuel correction circuit 22. Further, based on the signal from the O ₂ sensor 8, a comparison circuit 25 compares and determines whether the secondary air-fuel ratio is lean or rich, and outputs the comparison result to the fuel correction circuit 22. be done. Then, a pulse corresponding to the fuel amount corrected by the fuel correction circuit 22 is outputted from the pulse generation circuit 26 to the fuel injection valve 6.

The fuel control circuit 16 as described above operates in the feedback operation region shown in region B in _FIG .
Based on the signal from the sensor 8, fuel is injected from the fuel injection valve 6 while the fuel correction circuit 22 corrects the amount of injected fuel so that the secondary air-fuel ratio becomes the stoichiometric air-fuel ratio. In addition, feedback control is performed in the idling operation area shown in area A in Figure 3, the deceleration operation area shown in area C in Figure 3, and the high load or high rotational operation area shown in area D in Figure 2. In the case of open control, the fuel injector 6 injects fuel that has been corrected by the fuel correction circuit 22 so that the air-fuel mixture has an air-fuel ratio suitable for these operating ranges. Incidentally, since such a fuel control circuit 16 itself is well known in the past, further detailed explanation will be omitted.

The secondary air control circuit 15 is constituted by a microcomputer and functions as a catalyst temperature control means and a correction means in the present invention, but in addition to this, it controls the secondary air during deceleration operation. It is also equipped with a function for supplying electricity. In the embodiment, the temperature of the purifying catalyst 9 is actively increased, particularly when transitioning from idling operation to feedback operation. Note that during feedback operation, if secondary air is supplied, the air-fuel mixture is automatically enriched by feedback from the O ₂ sensor 8, so it is necessary to actively raise the temperature of the purification catalyst 9. The supply of a rich mixture as an element is performed indirectly through the supply of secondary air. That is, in FIG. 2, if the secondary air supply device is controlled to supply secondary air to the exhaust passage 7, a rich mixture is created by the feedback correction of the fuel control circuit 16 as the secondary air is supplied. We are trying to take advantage of the fact that it is supplied.

On the premise of the above, the control contents of the secondary air control circuit 15 will be explained based on the flowchart shown in FIG. First, in step 31, the engine speed and throttle opening are read. Next, in step 32, it is determined whether or not it is in the idling operation region. If it is in the idling operation region, the flag FI is set to 1 in step 33, and if it is not in the idling operation region, the flag FI is set to 0 in step 34. After that, the process moves to step 35.

In step 35, it is determined whether or not the vehicle is in the deceleration operation region, and if it is in the deceleration operation region, step 36 is performed.
After setting the flag FD to 1 in step 37, or setting the flag FD to 0 in step 37 if it is not in the deceleration operation region, the process moves to step 38. In this step 38, it is determined whether or not the flag FI is 1. When the FI is not 1, that is, when the engine is not idling, the throttle opening is sequentially integrated in step 39 to calculate the integrated opening SUM/TVO. , and during idling, the above integration is performed in step 40.
SUM and TVO are set to 0, and the process then proceeds to step 41.

In step 41, it is determined whether FD is 1 or not. When FD=1, which means deceleration, the process moves to step 42 to supply secondary air. In other words, during deceleration, HC, a harmful component in exhaust gas,
Since a large amount of is contained, the purification catalyst 9 is made to function as an oxidation catalyst.

If it is determined in step 41 that the flag FD is not 1, the process proceeds to step 43, where it is determined whether or not the integrated opening degree SUM·TVO in step 39 is smaller than a predetermined value X. This cumulative opening
When SUM/TVO is greater than or equal to the predetermined value X, the process proceeds to step 44, where the supply of secondary air is cut off, and when the integrated opening degree SUM/TVO is less than the predetermined value X, the process proceeds to step 45. Then, it is determined whether or not it is in the feedback operation area. If it is in the feedback operation area, the process moves to step 42 and secondary air is supplied. If it is not the feedback operation area, the process moves to step 44 and the secondary air is supplied.
Next, cut the air.

Here, the route from steps 43 to 45 and 42 is when secondary air is supplied in the feedback operation area, and this secondary air supply time is until the cumulative opening degree SUM・TVO reaches the predetermined value X. The longer the time, the longer it will be. In other words, the larger the throttle opening, the shorter the time it takes for the integrated opening SUM/TVO to reach the predetermined value Supply time becomes longer.

The above points are schematically shown in Figure 6. To explain this, the cumulative opening SUM/TVO is shown as the area of the diagram with the throttle opening and time as parameters. The time it takes for the area to reach the predetermined value X becomes shorter as the throttle opening becomes larger. In other words, for the α line with a large throttle opening, the predetermined value X is reached after _{t 1 second} from the integration start point (the time when idling is stopped), whereas for the β line with a small throttle opening, , it takes t ₂ seconds to reach the predetermined value X (t ₂ >
_t1 ). Of course, the area shown in FIG. 6 (predetermined value It is carefully set up.

Note that secondary air may also be supplied when transitioning from a high load/high rotation area to a feedback operation area, but in this case, when transitioning to a feedback operation area, the integrated opening degree SUM/
Since TVO has reached the predetermined value X or is sufficiently close to the predetermined value
), even if secondary air is supplied, the time is much shorter than when the transition from the idle operation area to the feedback operation area occurs, and the purification catalyst 9 will be heated. Such situations can be definitely prevented.

In the above embodiments, an electronically controlled fuel injection system that performs feedback control using the O ₂ sensor 8 is used as the fuel supply device, but a carburetor may also be used as the fuel supply device. In this case, in order to obtain a rich mixture, the fuel system jets (including air jets) may be directly controlled by the secondary air control circuit 15. Further, the engine load may be detected by the magnitude of the intake pressure other than the throttle opening.

(Effects of the Invention) As is clear from the above, the present invention has the following advantages:
The purification catalyst can be quickly raised to a required temperature without using an expensive temperature sensor for detecting the temperature of the exhaust gas purification catalyst, which is extremely advantageous in terms of cost.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the present invention. FIG. 2 is an overall system diagram showing one embodiment of the present invention. FIG. 3 is a diagram showing an example of classification of engine operating ranges. FIG. 4 is a diagram showing an example of a fuel control circuit. FIG. 5 is a flowchart showing an example of control of the secondary air control circuit. FIG. 6 is a diagram showing the relationship between the throttle opening and the time until the cumulative opening reaches a predetermined value X. 1: Engine body, 2: Intake passage, 5: Throttle valve, 6: Fuel injection valve, 7: Exhaust passage, 1
0: Secondary air supply port, 12: Air pump, 11:
Piping (for secondary air), 13: switching valve, 15: secondary air control circuit, 16: fuel control circuit.

Claims (1)

[Scope of Claims] 1. An exhaust gas purification device for an engine in which an exhaust gas purification catalyst is disposed in an exhaust passage of the engine, comprising: a fuel supply device that adjusts the amount of fuel supplied to the intake system of the engine; and the exhaust gas purification device. To the exhaust passage on the upstream side of the catalyst 2
a secondary air supply device for supplying secondary air; a load detection means for detecting the engine load; and upon receiving the output from the load detection means, when the engine load exceeds a set value, the air-fuel mixture is heated for a predetermined period of time. a catalyst temperature control device that increases the concentration of secondary air and supplies secondary air to the exhaust passage; and a correction device that receives an output from the load detection device and sets the predetermined time to become shorter as the load increases. An engine exhaust purification device characterized by: