JP2827752B2 - Heating control device for electrothermal catalytic converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating control device for an electrothermal catalytic converter, and more particularly to a catalytic converter provided with a lean air-fuel ratio catalyst having good NOx conversion efficiency even at a lean air-fuel ratio in addition to a three-way catalyst. The present invention relates to a heating control device suitable for

[0002]

2. Description of the Related Art Conventionally, as an electrothermal catalytic converter,
For example, there is one disclosed in JP-A-53-95417. This technology detects an engine temperature and a catalyst temperature, respectively, and operates a heating device to heat the catalyst when the engine temperature is equal to or lower than a predetermined value and the catalyst temperature is equal to or lower than a predetermined value, thereby quickly activating the catalyst. To reduce harmful components in the exhaust gas.

[0003]

However, the heating control method of the above-described conventional apparatus is intended for a catalytic converter provided with only a general three-way catalyst, and there is no problem in this case. A catalytic converter suitable for an internal combustion engine that switches between a stoichiometric air-fuel ratio and a lean air-fuel ratio in accordance with
In addition to a three-way catalyst in which the NOx conversion efficiency drops sharply when the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio, a catalyst capable of reducing NOx to some extent even when the exhaust gas contains a large amount of oxygen (even during lean combustion) When the present invention is applied to a catalytic converter which is also provided with a lean NOx catalyst so that the NOx emission can be reduced even during lean combustion, the following problems occur.

That is, between the three-way catalyst and the lean NOx catalyst, the activation temperature of the catalyst at which the catalyst can effectively exhibit the NOx conversion performance differs due to the difference in the supported components and the like.
The catalyst is higher. For this reason, in a conventional apparatus in which the target heating temperature is set irrespective of the engine operating conditions, if the target heating temperature is set in accordance with the activation temperature of the three-way catalyst, the lean NOx catalyst is not activated and the lean NOx catalyst is not activated. The NOx conversion under the fuel ratio operation condition becomes insufficient. Such problems are:
This can be solved by setting the target heating temperature in accordance with the activation temperature of the lean NOx catalyst, but in this case, the heating is continued even if the activation temperature of the three-way catalyst is exceeded under the stoichiometric air-fuel ratio operating condition, There is a problem that wasteful power is consumed.

[0005] The present invention has been made in view of the above problems, and has as its object to provide a heating control device for a catalytic converter capable of eliminating wasteful power consumption and saving fuel consumption.

[0006]

SUMMARY OF THE INVENTION For this reason, the present invention has been described with reference to FIG.
As shown in the figure, in a heating control device for an electrothermal catalytic converter in which a metal carrier carrying a catalyst is energized by heating and activating the catalyst, the metal carrier of the catalytic converter has a high NOx conversion efficiency at a stoichiometric air-fuel ratio. While carrying a three-way catalyst and a lean air-fuel ratio catalyst having a good NOx conversion efficiency even at a lean air-fuel ratio, the engine operating condition detecting means, the catalyst temperature detecting means, and the engine operating condition detecting means are used based on the detection results. Air-fuel ratio setting means for setting the air-fuel ratio by
Target temperature setting means for variably setting a heating target temperature of the catalytic converter in accordance with the air-fuel ratio set by the fuel ratio setting means , and comparing the set value of the target temperature setting means with the detection value of the catalyst temperature detecting means. Means, and energization control means for energizing the metal carrier when the detected value is equal to or lower than the target temperature based on the comparison result of the comparison means.

The target temperature setting means is configured to set the air-fuel ratio.
The air-fuel ratio set by the means is lean air-fuel ratio or stoichiometric air-fuel
According to the determination result of determination means for determining the ratio, the stoichiometric air-fuel
The configuration may be such that the target heating temperature of the catalytic converter is switched to the activation temperature of the three-way catalyst at the time of the ratio and to the activation temperature of the catalyst for the lean air-fuel ratio at the time of the lean air-fuel ratio.

Further, the target temperature setting means, the air-fuel ratio and the catalytic converter is set by the air-fuel ratio setting means
But it may also be configured to variably set the target temperature of the catalytic converter in accordance with the passing flow rate of the definitive exhaust.

[0009]

In this configuration, when the engine operating condition detecting means detects the operating condition at that time and the air-fuel ratio is set by the air-fuel ratio setting means according to the detected operating condition , the target temperature setting means : The heating target temperature of the catalytic converter is set according to the set air-fuel ratio . As a method of setting the heating temperature, for example, when the set air-fuel ratio is the stoichiometric air-fuel ratio or the lean air-fuel ratio
Depending on whether the ratio is the stoichiometric air-fuel ratio is set to the activation temperature of the three-way catalyst, when the lean air-fuel ratio is set to the activation temperature of the lean NOx catalyst. Then, the detected value of the catalyst temperature detecting means is compared with the target value by the comparing means, and when the detected value is equal to or less than the target value, the electric current is supplied to the metal carrier by the power supply controlling means to heat the catalyst.

Thus , based on the detection result of the engine operating condition ,
If the target heating value of the catalyst is variably set in accordance with the air-fuel ratio set based on the above , NOx can be effectively purified in each operation region, and unnecessary power consumption can be eliminated.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2 showing the system configuration of the embodiment, air is sucked into each cylinder of the V-type internal combustion engine 1 through an air cleaner 2, a throttle valve 3, and an intake manifold 4.
Each of the branch portions of the intake manifold 4 is provided with an electromagnetic injector 5.

The exhaust gas from the engine 1 is supplied to an exhaust manifold 6.
After being collected for each bank by a and 6b, they are guided to the muffler 8 by exhaust pipes 7a and 7b, respectively. Electrothermal catalytic converters 9A and 9B are interposed in the exhaust pipes 7a and 7b, respectively. The catalytic converter 9
Specifically, A and 9B have the structure shown in FIGS.

That is, as shown in FIG.
Lean NOx in which zeolite 32b ion-exchanged with copper (Cu) or palladium (Pd) is mixed with a base material 32a.
The lean NOx catalyst 32 of the wash coat is placed on the surface side,
Wash-coated three-way catalyst 33 in which a precious metal 33b and a co-catalyst 33c that assists the function of the precious metal 33b are mixed with a base material 33a.
As shown in FIG. 4, a honeycomb catalyst 9a having the inner layer supported thereon is housed in a case 9b via an insulating material 9c. If a three-way catalyst is disposed on the surface layer, H
As HC is oxidized and the HC / NOx is higher, the conversion efficiency of NOx becomes better. The HC / NOx of the lean NOx catalyst becomes smaller, and the conversion efficiency is lowered.
An Ox catalyst is provided. Then, the honeycomb catalyst 9
a has a plus (+) electrode 9d and a minus (-) electrode 9e.
Is connected. The insulating material 9f insulates the electrodes 9d and 9e from the case 9b. Thus, in the stoichiometric air-fuel ratio region, the inner three-way catalyst 33 and the surface lean NOx
NOx is reduced by the catalyst 32, and in the lean air-fuel ratio region, NOx is reduced favorably by the lean NOx catalyst 32 on the surface layer.
In each operation region, NOx emissions can be effectively suppressed. Also, the activation temperature of the three-way catalyst 33 (about
350 ° C) and the activation temperature of the lean NOx catalyst 32 (about 450
° C), the catalytic converters 9A, 9C
As shown in FIG. 5, the NOx conversion efficiency of B has different temperature characteristics depending on the air-fuel ratio. The broken line indicates the temperature characteristics of the three-way catalyst 33, and the solid line indicates the temperature characteristics of the lean NOx catalyst 32.

The positive electrode 9d of each of the catalytic converters 9A and 9B
Are connected to the positive poles of the batteries 21 and 22, and each of the negative electrodes 9e is turned on / off by a control unit 10 described later.
The collectors of the power transistors 23 and 24 that are FF controlled are connected to each other. The control unit 10 incorporates a microcomputer, calculates a fuel injection amount Ti by the injector 5 based on detection signals from various sensors as described later, and controls the opening of the injector 5 based on the fuel injection amount Ti. Thus, the fuel supply to the engine 1 is electronically controlled, and the power transistors 23 and 24 are controlled.
Of the catalytic converters 9A and 9B by controlling ON / OFF of the control.

The various sensors include a throttle valve 3
An air flow meter 11 for detecting an intake air amount Qa of the engine 1 upstream of the engine 1, a crank angle sensor 12 for extracting a rotation signal from a camshaft, a cooling water temperature sensor 13 for detecting a cooling water temperature Tw of the engine 1, an exhaust manifold 6a, Oxygen sensors 14a and 14b which are provided in the collecting section 6b to continuously detect the oxygen concentration in the exhaust for each bank, and a potentiometer type throttle sensor which detects the opening of the throttle valve 3
15, catalyst temperature sensors 16a and 16b for detecting the outlet temperatures Tb of the respective catalytic converters 9A and 9B are provided.

Reference numeral 17 denotes a control valve for adjusting the amount of intake air at the time of idling. The control valve 17 bypasses the throttle valve 3 and is provided with a bypass passage 18.
Adjust the amount of air supplied to the. Specifically, the control unit 10 determines the basic fuel injection amount Tp based on the intake air amount Qa detected by the air flow meter 11 and the engine speed N calculated based on the output signal from the crank angle sensor 12. Is calculated, and the final fuel injection amount Ti is calculated by performing various corrections on the basic fuel injection amount Tp according to operating conditions such as the cooling water temperature Tw, and the injector is determined based on the calculation result. 5 is subjected to duty drive control to inject and supply a fuel amount according to the operating conditions.

In this embodiment, as shown in FIG. 6, the air-fuel ratio of the engine intake air-fuel mixture on the operating range divided by the engine load represented by the basic fuel injection amount Tp and the engine speed N. Stoichiometric air-fuel ratio (air-fuel ratio = 14.7) and a lean air-fuel ratio region that controls the air-fuel ratio to be significantly leaner than the stoichiometric air-fuel ratio (for example, air-fuel ratio = 21). Then, it is determined which region the current operating condition corresponds to, and the fuel injection amount Ti corresponding to the set air-fuel ratio of the corresponding region is calculated.

The NOx of the catalytic converters 9A and 9B
Since the conversion efficiency has different temperature characteristics depending on the air-fuel ratio, the target heating temperature of the catalytic converters 9A and 9B is set to the activation temperature of the three-way catalyst based on the determination result of the region, or Is determined to be higher than the activation temperature of the lean NOx catalyst, and the determined value is compared with the detected value from each of the catalyst temperature sensors 16a, 16b. When the detected value is lower than the target temperature, the power transistors 23, 24 are determined. Is turned on, and if the detected value exceeds the target temperature, the power transistor 2
By turning off 3, 24, the heating of the catalytic converters 9A, 9B is stopped.

Next, the operation of controlling the energization of the catalytic converter of the present embodiment will be described with reference to the flowchart of FIG. This program is executed every 10ms. First, in step 1 (referred to as S1 in the figure, the same applies hereinafter),
The intake air amount Qa is measured based on a signal from the air flow meter 11.

In step 2, the engine speed N is measured based on a signal from the crank angle sensor 12. In step 3, it computes the basic injection amount Tp and a measured intake air amount Q _a and the engine speed N (Tp = K · Qa / N, K: constant). In step 4, based on the calculated basic injection amount Tp and engine speed N, it is determined from FIG. 5 whether the current operating condition is a lean region or a stoichiometric air-fuel ratio region. Note that the fuel injection amount Ti is calculated by adding to the basic injection amount Tp a correction coefficient for obtaining an air-fuel ratio appropriate for each operation region, an air-fuel ratio feedback correction coefficient by the oxygen sensors 14a and 14b, and the like.

In step 5, it is determined whether or not the area is a lean area based on the determination in step 4. Here, if YES, the process proceeds to a step 6, and if NO, a step 11 described later is performed.
Proceed to. When the operating condition is determined to be in the lean region and the process proceeds to step 6, the target heating value _TbL at the set air-fuel ratio in the lean region is set. That is, the target heating temperature T _bL is set to the activation temperature (for example, 450 ° C.) of the lean NOx catalyst.

In step 7, the catalyst temperature sensors 16a, 16
The catalyst outlet temperature Tb is measured based on the signal from b. In step 8, the target heating temperature _TbL is compared with the measured value Tb. If Tb> _TbL , the activity of the catalyst is determined to be sufficient, and the process proceeds to step 9 where the power transistors 23 and 24 are turned off to stop energizing the metal carrier. I do. On the other hand, if Tb ≦ T _bL , the process proceeds to step 10 and the power transistors 23 and 24 are turned on.
Then, the metal carrier is energized to activate the catalyst at an early stage.

On the other hand, if NO is determined in step 5, the target heating value T in the stoichiometric air-fuel ratio region is determined in step 11.
Set to _bR . That is, the activation temperature of the three-way catalyst (for example, 35
(0 ° C.) to set the heating target temperature T _bR . Thereafter, in the same manner as in steps 7 to 10, in step 12, the catalyst temperature sensor
The catalyst outlet temperature Tb is measured based on signals from 16a and 16b, and in step 13, the target heating temperature _TbR and the measured value _TbR are measured.
If Tb> T _bR , the catalyst activity is determined to be sufficient and the process proceeds to step 14 to turn off the power transistors 23 and 24 to stop energization. If Tb ≦ T _bR , the process proceeds to step 15 and the process proceeds to step 15. , 24 are turned on to carry out the energization to achieve early activation of the catalyst.

As described above, in the stoichiometric air-fuel ratio region, the target heating value is set to the activation temperature of the three-way catalyst, and in the lean air-fuel ratio region, the target heating value is set to a higher lean NO.
By setting the activation temperature of the x-catalyst, the catalytic converters 9A and 9B perform NOx
Can be satisfactorily reduced and NOx emission can be reduced. In addition, in the stoichiometric air-fuel ratio region, the catalyst is prevented from being unnecessarily heated, so that unnecessary power consumption can be prevented and fuel efficiency can be saved.

In the above embodiment, the heating target value is set in two steps of the lean region and the stoichiometric air-fuel ratio region. However, as shown in FIG. 8, the air-fuel ratio (A / A /
If the target heating value is continuously and variably set in an analog manner according to F), the effect of power saving can be further enhanced. Further, as shown in FIG. 9, the temperature characteristic of the NOx conversion efficiency in the catalytic converters 9A and 9B greatly changes depending on the space velocity S / V at that time even in the same air-fuel ratio state, and the space velocity S / V The slower the activation temperature, the lower the activation temperature.

Here, the space velocity S / V is a flow velocity of the exhaust gas passing through a predetermined surface area and volume, which corresponds to the intake air amount Qa at that time. The data of the quantity Qa can be represented. Therefore, as shown in the flowchart of FIG.
If the heating target temperature is set based on the space velocity S / V and the air-fuel ratio A / F, the control accuracy can be further improved.

Referring to the flowchart of FIG. 10, steps 21 to 25 are the same as those in FIG.
Proceed to 26. In step 26, the space velocity S / V is calculated based on the measured intake air amount Qa.

In step 27, the calculated space velocity S / V
The heating target temperature _TbL is set from the map shown in FIG. 11 based on the air-fuel ratio A / F. The following steps 28 to 31 are the same as those in the flowchart of FIG. 7. By comparing the target value _TbL with the measured value Tb, the power transistors 23 and 24 are controlled to be ON or OFF to control the catalytic converters 9A and 9B. Is controlled.

Similarly, if it is determined in step 25 that the region is not the lean region, a space velocity S / V is calculated in step 32, and in step 33, the space velocity S / V and the air-fuel ratio A / F are calculated from the calculated space velocity S / V. The heating target temperature T _bR is set according to the map shown in FIG. 11, and by comparing this target value T _bR with the measured value Tb, the power transistors 23 and 24 are controlled to be ON or OFF to energize the catalytic converters 9A and 9B. Control.

In this manner, the temperature control of the catalyst can be finely controlled, and the conversion efficiency of the catalyst can always be controlled to an optimum value while minimizing the power consumption.

[0031]

As described above, according to the present invention, the heating target value of the catalytic converter having the lean NOx catalyst and the three-way catalyst is set based on the operating conditions of the engine.
Since it is configured to be variably set according to the constant air-fuel ratio, it is possible to supply the minimum necessary electric power in accordance with the lean air-fuel ratio or the stoichiometric air-fuel ratio, thereby preventing waste of electric power. Thereby, fuel economy can be saved.

Further, if the heating target temperature of the catalytic converter is continuously set according to the air-fuel ratio, the effect can be further enhanced. If the heating target temperature is set based on the space velocity and the air-fuel ratio in consideration of the space velocity that affects the conversion efficiency, control accuracy can be further improved.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram illustrating a system configuration according to an embodiment of the present invention.

3A and 3B are diagrams showing a configuration of a honeycomb catalyst of the catalytic converter according to the embodiment, wherein FIG. 3A is a perspective view, FIG.
(C) is an organization chart

FIG. 4 is a diagram showing a configuration of the catalytic converter according to the first embodiment;
Is a side sectional view, and (B) is a front view.

FIG. 5 is a characteristic diagram showing a relationship between NOx conversion efficiency and temperature according to an air-fuel ratio.

FIG. 6 is a diagram showing a stoichiometric air-fuel ratio region and a lean air-fuel ratio region;

FIG. 7 is a flowchart showing a heating control operation of the first embodiment.

FIG. 8 is a diagram illustrating an example of a case where a heating target temperature is set according to an air-fuel ratio, and illustrating a relationship between an air-fuel ratio and a heating target temperature.

FIG. 9 is a characteristic diagram showing a relationship between NOx conversion efficiency and temperature according to space velocity.

FIG. 10 is a flowchart illustrating a heating control operation according to the second embodiment.

FIG. 11 is a characteristic diagram of a target heating temperature set based on the space velocity and the air-fuel ratio in the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Injector 9A, 9B Catalytic converter 10 Control unit 11 Air flow meter 12 Crank angle sensor 16a, 16b Catalyst temperature sensor 23, 24 Power transistor

Claims (3)

(57) [Claims] 1. A heating control device for an electrothermal catalytic converter in which a metal carrier carrying a catalyst is energized by heating and activating the catalyst, the metal carrier of the catalytic converter has a high NOx conversion efficiency at a stoichiometric air-fuel ratio. While carrying a three-way catalyst and a lean air-fuel ratio catalyst having a good NOx conversion efficiency even at a lean air-fuel ratio, the engine operating condition detecting means, the catalyst temperature detecting means, and the engine operating condition detecting means are used based on the detection results. Air-fuel ratio setting means for setting an air-fuel ratio by
Target temperature setting means for variably setting a heating target temperature of the catalytic converter in accordance with the air-fuel ratio set by the ratio setting means , and a comparison comparing a set value of the target temperature setting means with a detection value of the catalyst temperature detecting means. And a power supply control means for supplying power to the metal carrier when a detected value is equal to or lower than a target temperature based on a comparison result of the comparison means. 2. The method according to claim 1, wherein the target temperature setting means sets the air-fuel ratio.
The air-fuel ratio set by the means is lean air-fuel ratio or stoichiometric air-fuel
According to the determination result of determination means for determining the ratio, the stoichiometric air-fuel
The heating target temperature of the catalytic converter is switched to the activation temperature of the three-way catalyst at the time of the ratio and to the activation temperature of the catalyst for the lean air-fuel ratio at the time of the lean air-fuel ratio. Item 2. A heating control device for an electrothermal catalytic converter according to Item 1. 3. The catalytic converter according to claim 1, wherein said target temperature setting means is configured to determine an air-fuel ratio set by said air-fuel ratio setting means .
2. The structure according to claim 1, wherein the heating target temperature of the catalytic converter is variably set in accordance with the flow velocity of the exhaust gas.
A heating control device for an electrothermal catalytic converter according to the above.