JPH05163935A - Exhaust emission control device for diesel engine and catalyst converter - Google Patents

Abstract

PURPOSE:To enhance exhaust emission control by improving each efficiency of rapid heating and catalyst combustion of an exhaust emission purifying catalyst at low temperature operation of an engine. CONSTITUTION:A catalyst unit 6 comprising a catalyst 7 with a heater and a normal catalyst 8 is disposed on an exhaust pipe 5 of an engine 3. Secondary air is introduced upstream of the catalyst unit through an air introducing-in pipe 10 with a control valve 12 in operation at a low temperature. A microcomputer 13 estimates unburnt quantity of the secondary air on the basis of a fuel behavior model and engine condition detecting data, to calculate or data-retrieve a quantity of secondary air suitable for catalyst combustion on the basis of the unburnt quantity. The quantity of secondary air is controlled through the control valve 12. Otherwise, the quantity of secondary air is controlled to be increased or decreased per fine unit in such a manner as to maximize a deviation between a real secondary air-fuel ratio and a target secondary air-fuel ratio, both of which are detected by an air-fuel ratio sensor 11, and a temperature of the catalyst unit 6. Alternatively, the quantity of secondary air is controlled to be increased or decreased according to the opening or closing of the exhaust valve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust gas purification apparatus, and more particularly to a technology for purifying exhaust gas during low temperature operation such as cold start and warm-up operation.

[0002]

2. Description of the Related Art Conventionally, a catalytic converter is arranged in an exhaust pipe in order to purify engine exhaust gas. Since the catalyst has a low temperature and is not sufficiently activated during low temperature operation of the engine, unburned components in the exhaust gas are discharged without being purified unless some measures are taken.

Therefore, for example, JP-A-53-95417 is used.
In the exhaust gas purification device disclosed in Japanese Patent Publication No. 54-79319, the catalyst is heated by an electric heater to improve the purification efficiency when the engine is operating at low temperature. In the device disclosed in JP-A-54-79319, an electric heater is provided in addition to the main catalyst. To reduce the heating capacity of the heater, and to introduce the air in the exhaust pipe to the upstream side of the sub-catalyst (the secondary air is used to distinguish it from the air in the intake system) for catalytic combustion. Techniques have been proposed for promoting and enhancing exhaust purification efficiency.

In addition to this, Japanese Patent Laid-Open No. 59-96424
In the device disclosed in the publication, secondary air is introduced upstream of the three-way catalytic converter in the exhaust pipe, and this secondary air is periodically fluctuated at a constant frequency (1 Hz to 2 Hz) with respect to the stoichiometric air-fuel ratio. ing. The technology to perform this periodic fluctuation is
Three-way catalyst window (hazardous components HC and C in exhaust gas
When trying to reduce O and NOx at the same time by using a three-way catalyst, the air-fuel ratio region where the purification efficiency is 80% or more is called a window, and the range of the theoretical air-fuel ratio purification efficiency is the largest). It is intended to improve the purification efficiency, and is effective especially after the temperature of the three-way catalyst reaches the temperature required for activation.

That is, the three-way catalyst has an oxygen retaining function. Therefore, by introducing secondary air, the air-fuel ratio (the air-fuel ratio here has a slightly different meaning from the original air-fuel ratio, and the amount of fuel supplied to the total air amount of the engine (the sum of intake air and secondary air) Ratio, which is referred to as the secondary air-fuel ratio in the text to distinguish it from the original air-fuel ratio), is changed periodically, and when the secondary air-fuel ratio is leaner than the theoretical air-fuel ratio, the three-way catalyst is used. Takes NOx from NOx and NOx
And retains the deprived oxygen. When the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, the retained oxygen is released to oxidize CO and HC. By repeating this cyclically, even if the reference air-fuel ratio deviates from the stoichiometric air-fuel ratio, high purification efficiency is obtained, and the width of the window, which is originally narrow, is widened as much as possible.

[0006]

As described above, various exhaust gas purifying devices have been conventionally proposed. this house,
Especially at low temperature operation, it is considered effective to heat the auxiliary catalyst with an electric heater and introduce secondary air to promote catalytic combustion of unburned components. No consideration was given as to whether or not it should be introduced based on the judgment, and there was an unsolved problem to raise its effectiveness.

In particular, during low temperature operation, the original air-fuel ratio is also changed in accordance with the engine warm-up transition (in other words, the change in cooling water temperature). The amount of secondary air is not uniform,
It is desirable to control the amount of secondary air appropriately.

The present invention has been made in view of the above points, and its main purpose is to optimize the secondary air amount according to the operating condition while reducing the heating capacity of the catalyst during low temperature operation of the engine. Therefore, the catalytic combustion efficiency and thus the exhaust gas purification efficiency are further enhanced, and the time required for the temperature rise of the catalyst is shortened to save the energy of the catalyst heating source (electric heater).

[0009]

In order to achieve the above object, the present invention comprises, as a catalyst portion of this type, a normal catalyst and a catalyst with a heater arranged upstream thereof and electrically heated during low temperature operation of the engine. And 2 upstream of this catalytic part
Assuming that a means for introducing secondary air is provided, the following secondary air amount control system is provided.

First, the amount of unburned fuel discharged into the exhaust pipe during low temperature operation is estimated from the fuel behavior model and the detection data regarding low temperature operation to calculate or prestore a secondary air amount suitable for catalytic combustion. It has a means for searching from the data map described above, and is set to control the secondary air amount based on the result of this calculation or search (this is the first means for solving problems).

One is that the secondary air-fuel ratio in the exhaust pipe during low-temperature operation of the engine is detected by an air-fuel ratio sensor, and the deviation between the actual secondary air-fuel ratio and the target secondary air-fuel ratio makes it suitable for catalytic combustion. A means for calculating the secondary air amount is provided, and the secondary air amount is set based on the calculation result (this is set as the second
To solve the problem).

One is to detect the temperature of a catalyst with a heater or its vicinity during low temperature operation by a temperature sensor, and control the secondary air amount in small quantized units so as to maximize the temperature detection value. Means for doing so (this is a third means for solving problems).

One is to use a sensor for detecting the opening and closing of an exhaust valve when controlling the amount of secondary air to be supplied during low temperature operation to an amount suitable for catalytic combustion in accordance with engine operating conditions. A means for controlling the amount of air in accordance with the flow rate of exhaust gas which changes according to the opening / closing operation of the exhaust valve is provided (this is referred to as a fourth problem solving means).

[0014]

[Action]

Operation of the first problem solving means: A part of the fuel injected from the injection valve adheres to the intake pipe wall or collides with the intake valve to form a liquid film (liquid fuel), which flows into the combustion chamber, When the engine is cold, part of it is discharged as an unburned component during the exhaust stroke. The unburned fuel amount at low temperature can be estimated by associating this series of fuel behavior models with detection data (for example, cooling water temperature in the engine, rotation speed, load, etc.) relating to low temperature operation.

Then, with respect to the estimated unburned fuel amount, the secondary air amount that makes the catalytic combustion of the electrically heated catalyst (catalyst with a heater) optimum is calculated from the ratio, or a data map stored in advance is searched. Can be obtained by By controlling the amount of secondary air by this, the catalyst with the heater is also in the low temperature operation in which the air-fuel ratio changes according to the warm-up condition (the catalyst with the heater is heated by the electric heater in the low temperature operation). Enhances catalytic combustion efficiency. Therefore, the time required for the catalyst to reach a predetermined temperature is also shortened.

The operation of the second means for solving the problems ... As described above, if the amount of secondary air introduced into the exhaust pipe is optimum, efficient catalytic combustion is performed. Whether it is introduced or not is determined by using the air-fuel ratio sensor.
It can be known by detecting the next air-fuel ratio. Then, if the target secondary air-fuel ratio at which the catalytic combustion in the low temperature starting operation is optimum is set in association with the data regarding the engine operation (for example, the cooling water temperature, the rotation speed, the load, etc.), the engine operation detection data can be obtained. From the target secondary air-fuel ratio,
The deviation between this and the actual secondary air-fuel ratio is obtained.

The secondary air correction amount required for the target secondary air-fuel ratio can be calculated from this deviation, and the secondary air control is performed based on this to increase the catalytic combustion efficiency.

Operation of the third means for solving the problem: In the low temperature operation, if the secondary air-fuel ratio (in other words, the amount of secondary air) of the electrically heated catalyst is optimum for achieving catalytic combustion, then that time The temperature of the electrically heated catalyst or its vicinity (hereinafter referred to as the catalyst detection temperature) is maximum, but when it deviates from the optimum value, the temperature decreases.

In this problem solving means, by utilizing this phenomenon, the secondary air amount is controlled by the quantized minute unit, and the secondary air amount (secondary air-fuel ratio) that maximizes the catalyst detection temperature is obtained. ) Trial search. For example, when the secondary air amount is increased by a minute unit and the catalyst detection temperature rises, the secondary air amount is further increased. Therefore, when the catalyst detection temperature is lowered, the secondary air amount is determined by a so-called hill climbing method in which it is determined that the preceding secondary air amount corresponds to the maximum catalyst detection temperature (optimal catalyst combustion).

Even in this way, the catalytic combustion efficiency at low temperatures is enhanced.

Operation of Fourth Problem Solving Means ... The amount of exhaust gas is not always discharged uniformly, but changes depending on whether the exhaust valve of each cylinder is opened or closed. If the amount of secondary air is supplied to the changing exhaust gas at a constant level, the secondary air-fuel ratio will change and cannot be controlled to a desired value.

Therefore, the means for solving the problem is to adjust the secondary air amount to the exhaust flow rate which changes according to the opening / closing operation of the exhaust valve.
Control to change the amount of secondary air. As a result, the secondary air-fuel ratio can always be controlled to the optimum target value for catalytic combustion, and exhaust purification efficiency can be improved.

[0023]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram according to the first embodiment of the present invention.

In FIG. 1, the air measured by the air flow meter 1 is sucked into the engine 3 through the throttle valve 2 of the intake pipe. The fuel is metered by the injection valve 4 and supplied to the engine 3.

The exhaust gas after combustion is discharged to the exhaust pipe 5,
An auxiliary catalytic converter 6 and an ordinary main catalytic converter 9 are arranged in the exhaust pipe 5. The auxiliary catalytic converter 6 is arranged upstream of the main catalytic converter 9 and has a catalyst 7 with an electric heater.
And a normal catalyst 8 located downstream thereof are incorporated in one converter case. For example, a three-way catalyst is used as these catalysts. Besides, it may be an oxidation catalyst, a reduction catalyst or the like. In the low temperature operation, the catalytic converter 7 is set to be electrically heated and activated early. The ordinary catalysts 8 and 9 have poor activity at low temperatures and function after the engine is warmed up. Electric heating of the catalyst 7 is one of the countermeasures.

In addition to the auxiliary catalytic converter 6 and the main catalytic converter 9, the exhaust gas purification device includes a secondary air introducing pipe 10 with a control valve 12, an air-fuel ratio sensor 11, a heater circuit 14,
It is configured by a secondary air amount control system such as the microcomputer 13.

The secondary air introducing pipe 10 guides air (secondary air) upstream of the auxiliary catalytic converter 6 in the exhaust pipe 5, and the air-fuel ratio sensor 11 detects the air-fuel ratio from the exhaust gas upstream of the auxiliary catalytic converter 6. It is arranged. Secondary air inlet pipe 1
The 0 air intake port 15 is located near the exhaust pipe 5 and is designed to introduce as warm air as possible.

The microcomputer 13 has a function of inputting data of various sensors related to the engine control system and performing calculations necessary for engine control, and also inputting data necessary for the exhaust gas purification system and calculations necessary for control thereof. I have been given.
The signals from the air flow meter 1 and the air-fuel ratio sensor 11 are input to the microcomputer 13. In addition, the injection valves 4, 2
The valve 12 for controlling the secondary air amount Qa ₂ and the heater circuit 14 of the catalyst 7 operate by the control signal of the microcomputer 13.

In this embodiment, in order to enhance the catalytic combustion efficiency of the auxiliary catalytic converter 6 (particularly the catalyst 7 with an electric heater) during low temperature operation, the microcomputer 13 sets the secondary air amount suitable for the condition during low temperature operation. This secondary air amount is calculated by estimating the unburned fuel amount during low temperature operation from the fuel behavior model and the cooling water temperature, rotation speed, load, etc. for low temperature operation, and based on this result, the secondary air amount To calculate.

FIG. 2 shows the concept of a fuel behavior model for estimating the amount of unburned fuel discharged into the exhaust gas. FIG. 2A shows
It is a fuel behavior model during an intake stroke. The amount of fuel injected from the injection valve 4 that adheres to the intake pipe wall is Lm, and the amount of fuel in flight is Sm. Lm flows into the combustion chamber 20 with a stroke delay. Moreover, a part of Sm is the intake valve 21.
To form a liquid film. The amount of fuel that has adhered to the intake valve 21 and has flowed into the combustion chamber 20 is Lc ₁ , and the amount of fuel that has collided with the intake valve 21 to form a liquid film is Lc ₂ . After the combustion process,
When the exhaust stroke is as shown in FIG. 2B, the liquid film amounts remaining in the combustion chamber are Lc ₁ ′ and Lc ₂ ′, respectively. In the exhaust stroke, part of this is discharged into the exhaust pipe. Let this amount be Le. Taking these parameters, the cooling water temperature, the number of revolutions, the load, etc. into consideration, Le is obtained by making a mathematical model as shown in, for example, Equation 1.

[0032]

## EQU1 ## Le = K.TW.Lc where K is a coefficient determined by the engine operating state,
Tw is the cooling water temperature, and Lc is the liquid fuel flowing into the engine combustion chamber.

FIG. 3 shows the flowchart (in the figure,
S1 to S7 are steps). As shown in (a) of FIG. 3, the liquid fuel amount Lc in the combustion chamber is calculated from the cooling water temperature, the rotation speed, the load, etc. (S1), and the residual amount Lc 'of the liquid fuel after combustion is calculated (S2). ). Next, the liquid fuel amount Le in the exhaust pipe is calculated (S3), and the secondary air amount is determined (S3).
4). This amount of secondary air is determined so that the secondary air-fuel ratio before the catalyst becomes an optimum value at which catalytic combustion occurs. In controlling the supply of this secondary air amount, it is necessary to consider the fuel flow delay in the exhaust pipe 5 from the engine to the catalyst section. FIG. 3B is a flowchart of the secondary air supply control in consideration of the flow delay Td.

That is, after calculating the discharge amount Le of the unburned fuel to the exhaust pipe in S5, the flow delay Td in the exhaust pipe is calculated from the operating state of the engine (S6), and after the time Td, 2
Change the amount of secondary air. By doing so, the secondary air-fuel ratio can be accurately controlled and the efficiency of the catalyst can be improved.

In the system shown in FIGS. 2 and 3, the amount of liquid fuel in the combustion chamber and the exhaust pipe is calculated from the fuel behavior model, but it is stored in the memory of the control device (microcomputer). It may be stored in association with the operating state. An example of the map is shown in FIG. In FIG. 4, the liquid fuel amount Lc in the combustion chamber is stored as a function of the fuel injection pulse Tp and the engine speed. Similarly, the liquid fuel amount Le discharged to the exhaust pipe is also stored in the memory. The Lc and Le are obtained in advance by experiments.

According to this embodiment, the optimum secondary air amount (secondary air-fuel ratio) for the catalytic combustion of the auxiliary catalytic converter is supplied in accordance with the operating condition even in the low temperature operation where the air-fuel ratio is not uniform. Thus, it is possible to immediately improve the exhaust gas purification efficiency even in the low temperature operation and to raise the catalyst temperature of the auxiliary catalytic converter and thus the main catalytic converter in a chained manner.

Further, since the optimum secondary air-fuel ratio is maintained by controlling the secondary air amount on the exhaust side, the responsiveness is fast and the exhaust gas can be purified without changing the original air-fuel ratio on the engine intake side. When the engine has warmed sufficiently and the auxiliary catalytic converter 6 and the main catalytic converter 9 have reached the temperatures required for activation, the electric signal of the electric heater of the auxiliary catalytic converter 6 is stopped and controlled by a command signal from the microcomputer 13. The valve 12 is closed and the supply of the secondary air amount is stopped. Then, thereafter, using the air-fuel ratio sensor 11, normal air-fuel ratio control capable of maintaining the window of the three-way catalyst is executed.

FIG. 5 is an explanatory view showing a second embodiment of the present invention, in which (a) is a block diagram of the secondary air amount control system of the exhaust gas purifying device and (b) is an air-fuel ratio sensor used therefor. And (c) shows the operating characteristics of the air-fuel ratio sensor. Although not shown in the present embodiment, the engine system as shown in FIG. 1, the auxiliary catalytic converter 6, the main catalytic converter 9, the secondary air introducing pipe 10 with the control valve 12, the heater circuit 1 are shown.
4 and the like, and has a microcomputer 13A that controls the secondary air amount (secondary air-fuel ratio) described below.

The fuel amount Qf from the injection valve, the engine speed N, the cooling water temperature Tw, etc. are input to the microcomputer 13A. From the data on these engines, the secondary air amount Qa ₂ that achieves the target secondary air-fuel ratio (the target secondary air-fuel ratio is set to the optimum value for achieving catalytic combustion) during low temperature operation is calculated. It is output to the control valve 12.
The secondary air-fuel ratio in the exhaust pipe is detected by the air-fuel ratio sensor 11. The detected secondary air-fuel ratio (A / F) is compared with the target secondary air-fuel ratio, and the deviation is multiplied by an appropriate gain Kf to correct the secondary air amount Qa ₂ so as to obtain the target air-fuel ratio. To do.

Here, the air-fuel ratio sensor 1 used in this embodiment
An example of No. 1 will be described with reference to FIGS. Figure 5
As shown in (b), electrodes 32a and 32b are attached to both sides of the oxide zirconia element 31, and the exhaust side electrode 32a is attached.
A porous protective film 33 is provided on the outer side of the. On the other hand, a heater 34 for heating is arranged on the atmosphere side of the element 31.

At the time of starting, the element 31 is heated by this heater so that the air-fuel ratio can be measured. The sensor 11 may output a linear output with respect to the air-fuel ratio, or may output a stepwise output with respect to the air-fuel ratio. Figure 5
(C) is an output example of the air-fuel ratio sensor 11, (a) is a sensor signal that produces a linear output with respect to the air-fuel ratio,
(B) is a signal of a sensor that outputs a stepwise output with respect to the air-fuel ratio. Even if the signal shown in (b) is lean,
Since the signal that changes with respect to the air-fuel ratio is obtained in the rich region, the secondary air-fuel ratio can be detected by reading the output voltage.

Also in this embodiment, since the secondary air amount is guided to the upstream side of the catalytic converter in the exhaust pipe in accordance with the target secondary air-fuel ratio, the catalytic combustion of the auxiliary catalytic converter is promoted during the low temperature operation of the engine to improve the purification efficiency. In addition, it is possible to shorten the time required for the temperature rise of the auxiliary catalyst and the main catalyst.

FIG. 6 is an explanatory view showing a third embodiment of the present invention,
FIG. 7 shows the control flowchart. In the drawings, the same reference numerals as those in the above-mentioned respective embodiments indicate the same or common elements.

Also in this embodiment, the structure of the catalytic converter provided in the exhaust pipe 5 and the secondary air introducing pipe 10 with the control valve 12 are the same as those in the above-mentioned respective embodiments.

In the secondary air amount control system according to this embodiment, the microcomputer 13B operates in the low temperature mode when the engine is operating at a low temperature.
The next air amount Qa ₂ is controlled by the quantized minute unit,
Further, it has a function of taking in the catalyst temperature detection data from the temperature sensor 40 and controlling the secondary air-fuel ratio so that the temperature of the catalytic converter or the vicinity thereof becomes maximum. Figure 6 (a)
As shown in FIG.
And is arranged between the electrically heated catalyst 7 and the catalyst 8.

When the secondary air-fuel ratio (A / F) in in the vicinity of the inlet of the auxiliary catalytic converter 6 during low temperature operation is changed, the temperature of the electrically heated catalyst 7 becomes the highest when the catalytic combustion is active.
Therefore, if the temperature is detected by the temperature sensor 40 while performing the trial search by controlling the secondary air amount Qa ₂ by a minute unit, the maximum temperature can be detected by the auxiliary catalytic converter 6 and the main catalytic converter 9
The heat of combustion raises the temperature and is activated quickly. FIG. 6B shows the relationship between the catalyst inlet secondary air-fuel ratio (A / F) in and the catalyst temperature Tcat, and Tcat becomes the highest at the secondary air-fuel ratio in FIG. 6B. Control is performed so as to achieve this secondary air-fuel ratio.

A flow chart of this control is shown in FIG.
In the example of FIG. 7, the catalyst temperature Tcat is first measured (S
1). Next, the secondary air amount Qa ₂ is increased by a minute unit ΔQa ₂ (S2). Here, when Tcat increases, Qa ₂ is further increased to make the air-fuel ratio thin (large) (S
3). As a result, when Tcat decreases, change Qa ₂ to ΔQ
It is decreased by a ₂ minutes (S4). Then again, step S
At 5, it is determined whether Tcat is increased or decreased. When Tcat increases, Qa ₂ is decreased again. Here, when Tcat decreases, this routine ends. As described above, the secondary air-fuel ratio that maximizes the catalyst temperature is found by the so-called hill-climbing method, in which the quantized minute unit is controlled by adjusting the secondary air amount.

FIG. 8 is an explanatory diagram according to the fourth embodiment of the present invention. Also in this embodiment, the structure of the catalytic converter provided in the exhaust pipe 5 and the secondary air introducing pipe 10 with the control valve 12 are the same as those in the above-mentioned respective embodiments.

The microcomputer 13C, which is the center of the secondary air amount control system, changes the amount of secondary air supplied upstream of the auxiliary catalytic converter 6 during low temperature operation to the electrically heated catalyst 7.
In order to achieve the optimum catalytic combustion, the control is performed optimally (this secondary air amount control may adopt, for example, those described in the first to third embodiments), in addition to the following. Adopt control.

That is, as shown in FIG. 8A, the signal of the crank angle sensor 41 is the microcomputer 13 signal.
Input to C. The microcomputer 13C detects the opening / closing of the exhaust valve in each cylinder of the engine from the crank angle sensor 41, operates the control valve 12 in response to the change in the exhaust flow rate due to the operation of the exhaust valve, and operates the secondary air amount Q.
It has a function of controlling (changing) a ₂ .

The concept is shown in FIGS. 8B and 9.

In FIG. 8 (b), (a) shows the change in the exhaust amount. 2 for this changing displacement
If the secondary air amount Qa ₂ is supplied at a constant value as shown in (b) of FIG. 8 (b), the air-fuel ratio in front of the catalyst section 6 changes as shown in (c) and the secondary air amount The fuel ratio cannot be controlled accurately. Therefore, in the present embodiment, the secondary air amount Qa ₂ is controlled by the microcomputer 13C in accordance with the change in the exhaust amount as shown in FIG. 9 to accurately control the secondary air-fuel ratio. did. 9A shows a change in the exhaust amount, and FIG. 9B shows a change in the secondary air amount Qa ₂ in synchronism with the change in the above exhaust amount, which are changed as shown by solid lines and dotted lines, respectively. With respect to the secondary air-fuel ratio before the catalyst, a desired constant secondary air-fuel ratio can be always secured as shown by the dotted and solid lines in (c). When it is desired to control the secondary air-fuel ratio itself, the level of the secondary air amount may be increased or decreased as indicated by the dotted line and solid line.

FIG. 10 shows the secondary air amount Qa used in this embodiment.
An actuator for changing ₂ is shown. The solenoid 61 is a solenoid valve whose valve 61 moves up and down to change the secondary air amount Qa ₂ . A drive signal corresponding to the operation of the exhaust valve is given to the solenoid 60 from the microcomputer 13C.

FIG. 11 shows another method for changing the secondary air amount Qa ₂ . A method of operating the diaphragm pump 63 in response to the rotation of the crank shaft 62 of the engine 3 is adopted. The rotation of the crankshaft 62 is controlled by the diaphragm pump 6
3 is transmitted to the cam 64. Corresponding to this rotation operation,
The diaphragm 65 moves, and the secondary air amount Qa ₂ changes. As a result, the secondary intake air amount Q
a ₂ can be the acceleration control.

Next, another specific example of the auxiliary catalytic converter 6 used in each of the above embodiments will be described.

FIG. 12A shows a plurality of catalysts 7 each having an electric heater (electrically heated catalyst) 7 and a normal catalyst 7.
The sub-catalyst converter 6 is configured by subdividing into a, 7b, 7c and 8a, 8b, 8c and alternately arranging them in one converter case. In this way, FIG.
As in (b), it is possible to heat the entire catalyst more efficiently than heating the normal catalyst 8 with only one electrically heated catalyst 7. The effect is shown in FIG. That is, FIG. 12 (a)
In this arrangement, the temperature distribution of the entire auxiliary catalytic converter is shown in FIG.
It becomes like (a) of (c), and in the arrangement of FIG. 12 (b),
The temperature distribution shown in (b) of FIG. 12C is obtained, and the temperature of the entire catalyst becomes higher when the electrically heated catalysts are alternately arranged.
This is because the volume of the normal catalyst arranged downstream of the electrically heated catalyst is small, so that it easily rises due to the catalyst combustion heat of the electrically heated catalyst.

FIG. 13 shows another mode of the auxiliary catalytic converter 6. In the catalytic converter shown in FIG. 13 (a), the electrically heated catalyst 7 provided in the preceding stage of the ordinary converter 8 is gradually adjusted from the inlet side to the outlet side according to the diameter of the exhaust pipe 5 and the diameter of the ordinary catalyst 8. It has a frustoconical shape that expands. this is,
Since the catalytic converter 6 is normally thicker than the exhaust pipe 5, if the entire electrically heated catalyst 7 is made smaller in diameter than the catalyst 8, the exhaust gas passing through the electrically heated catalyst 7 cannot reach every corner of the catalyst 8. So that's what we deal with. By allowing the electrically heated catalyst 7 to spread in this manner, the exhaust gas flow passing through the electrically heated catalyst 7 is evenly guided to the catalyst 8 located downstream of the electrically heated catalyst 7 to promote the temperature rise of the catalyst.

In FIG. 13B, the electric heating catalyst 7 and the ordinary catalyst 8 have the same diameter, and the exhaust flow guide 50 spreading in a truncated cone shape is arranged upstream of the electric heating catalyst 7 of the converter 6. Even in this way, the exhaust gas can be guided to all corners of the catalyst.

FIG. 14 shows another mode of the catalytic converter 6. In this example, a cover 52 that forms an exhaust bypass 51 is arranged around the case of the catalytic converter 6, and the exhaust gas is introduced into the catalytic converter 6 via the exhaust bypass 51. In this case, the catalyst is heated by exhaust heat in addition to electric heating and catalytic combustion, so that it has an effect of accelerating the temperature rise.

[0060]

As described above, according to the present invention, even when the engine is operated at a low temperature, the heating capacity of the electrically heated catalyst is reduced, and the secondary air amount suitable for the operating condition is optimally controlled. It is possible to further improve the combustion efficiency and thus the exhaust gas purification efficiency, and shorten the time required for the temperature rise of the catalyst to save the energy of the catalyst heating source (electric heater).

[Brief description of drawings]

FIG. 1 is a configuration diagram of a system according to a first embodiment of the present invention.

FIG. 2 is a model diagram of fuel behavior.

FIG. 3 is a flowchart showing the operation of the secondary air amount control system of the first embodiment.

FIG. 4 is a map that estimates the amount of fuel injected from the injection valve when a liquid film adheres to various parts of the engine.

FIG. 5 is an explanatory diagram according to the second embodiment of the present invention.

FIG. 6 is an explanatory diagram according to a third embodiment of the present invention.

FIG. 7 is a flowchart showing the operation of the secondary air amount control system of the third embodiment.

FIG. 8 is an explanatory diagram according to a fourth embodiment of the present invention.

FIG. 9 is an explanatory view showing the operation of the secondary air flow rate control system of the fourth embodiment.

FIG. 10 is a sectional view showing an example of a secondary air amount control valve used in the embodiment of the present invention.

FIG. 11 is a sectional view showing an example of a secondary air amount control valve used in the embodiment of the present invention.

FIG. 12 is an explanatory diagram showing an example of a catalytic converter used in each of the above embodiments.

FIG. 13 is an explanatory diagram showing an example of a catalytic converter used in each of the above embodiments.

FIG. 14 is an explanatory diagram showing an example of a catalytic converter used in each of the above embodiments.

[Explanation of symbols]

3 ... Engine, 5 ... Exhaust pipe, 6 ... Sub catalytic converter (catalyst part), 7 ... Catalyst with heater, 8 ... Catalyst, 9 ... Main catalytic converter, 10 ... Secondary air introduction pipe, 11 ... Air-fuel ratio sensor, 12 ... Secondary air amount control valve, 13, 13A, 13B,
13C ... Microcomputer, 14 ... Heater circuit, 4
0 ... Temperature sensor.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location F01N 3/24 C 9150-3G L 9150-3G N 9150-3G 3/32 G 9150-3G 301 B 9150-3G (72) Inventor Toshiharu Nogi 4026 Kujimachi, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd.

Claims (11)

[Claims] 1. An exhaust gas purification device comprising a catalyst portion for purifying exhaust gas in an exhaust pipe of an engine, wherein the catalyst portion is provided with an ordinary catalyst and an upstream thereof and is electrically heated during low temperature operation of the engine. And a secondary air introducing means for introducing air (hereinafter, referred to as secondary air in order to distinguish it from the air of the engine intake system) upstream of the catalyst portion in the exhaust pipe. This secondary air amount control system is suitable for catalytic combustion by estimating the amount of unburned fuel discharged into the exhaust pipe during low temperature operation from the fuel behavior model and detection data regarding low temperature operation. An exhaust emission control device for an engine, comprising means for calculating or retrieving a secondary air amount from a previously stored data map, and setting the secondary air amount based on the result of the computation or search. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the detection data regarding the low temperature operation is a detection value regarding a cooling water temperature, a rotation speed, and a load of the engine. 3. An exhaust gas purification device comprising a catalyst portion for purifying exhaust gas in an exhaust pipe of an engine, wherein the catalyst portion is a normal catalyst and a heater arranged upstream thereof and electrically heated during low temperature operation of the engine. And a secondary air amount control system for introducing secondary air upstream of the catalyst section in the exhaust pipe.
This secondary air amount control system is a secondary air-fuel ratio in the exhaust pipe during low temperature operation of the engine [where the secondary air-fuel ratio is the total air amount upstream of the catalyst (the sum of the intake air amount and the secondary air amount. ) And the supplied fuel amount] is detected by the air-fuel ratio sensor, and a secondary air amount suitable for catalytic combustion is calculated from the deviation between the actual secondary air-fuel ratio and the target secondary air-fuel ratio. The engine exhaust gas purification device is characterized in that the secondary air amount is set based on the calculation result. 4. An exhaust gas purification device comprising a catalyst portion for purifying exhaust gas in an exhaust pipe of an engine, wherein the catalyst portion is provided with an ordinary catalyst and an upstream thereof, and is electrically heated during low temperature operation of the engine. And a secondary air amount control system for introducing secondary air upstream of the catalyst portion in the exhaust pipe.
This secondary air amount control system detects the temperature of the catalyst portion or its vicinity during low temperature operation by a temperature sensor, and the secondary air amount is quantized in minute units so that the detected temperature value becomes maximum. An exhaust emission control device for an engine, comprising an adjusting control unit. 5. An exhaust gas purification device comprising a catalyst portion for purifying exhaust gas in an exhaust pipe of an engine, wherein the catalyst portion is a normal catalyst and a heater arranged upstream thereof and electrically heated during low temperature operation of the engine. And a secondary air amount control system for introducing secondary air upstream of the catalyst portion in the exhaust pipe.
This secondary air amount control system uses a sensor that detects the opening / closing of an exhaust valve when controlling the amount of secondary air to be supplied during low temperature operation to an amount suitable for catalytic combustion according to engine operating conditions. An exhaust emission control device for an engine, comprising means for controlling the amount of secondary air in accordance with the flow rate of exhaust gas that changes depending on the opening / closing operation of an exhaust valve. 6. The exhaust gas purifying apparatus for an engine as claimed in claim 1, wherein the catalyst portion includes the catalyst with the heater and an ordinary catalyst incorporated in one converter case. .. 7. A catalytic converter for purifying exhaust gas arranged in an exhaust pipe of an engine, wherein a plurality of catalysts with a heater and a plurality of normal catalysts (catalysts without a heater) are used respectively, The catalyst converter is characterized in that the catalyst and the catalyst are alternately arranged in one converter case. 8. In a catalytic converter for purifying exhaust gas arranged in an exhaust pipe of an engine, a catalyst with a heater and a normal catalyst arranged downstream thereof are incorporated in one converter case, and the heater is equipped with the heater. The catalyst converter is characterized in that its inlet side is formed in a diameter of the exhaust pipe, while its outlet side is formed in a divergent shape that matches the diameter of the ordinary catalytic converter whose diameter is larger than that of the exhaust pipe. .. 9. A catalytic converter for purifying exhaust gas arranged in an exhaust pipe of an engine, wherein a catalyst with a heater and an ordinary catalyst arranged downstream thereof are incorporated in one converter case, and the heater is equipped with the heater. 2. A catalytic converter characterized in that a guide member for guiding the exhaust gas to the end of the catalyst with a heater is arranged in front of the catalyst. 10. A catalytic converter for purifying exhaust gas arranged in an exhaust pipe of an engine, wherein a catalyst with a heater and an ordinary catalyst arranged downstream thereof are incorporated into one converter case, and the converter case is provided. A catalytic converter characterized in that a bypass for the exhaust gas is provided around the exhaust gas. 11. The method according to any one of claims 1 to 5.
In claim 1, the catalyst portion is defined by any one of claims 7 to 1.
An exhaust gas purifying apparatus for an engine, characterized by using the catalytic converter described in any one of 0.