JPH06146866A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce generation of aldehyde and keep electric consumption due to electric supply to an electric heat catalyst (EHC) minimum. CONSTITUTION:An objective catalyst temperature K C is set with which generation of aldehyde corresponding to a methanol density M is suppressed (S2). An actual catalyst temperature To is detected by means of a temperature sensor provided on a catalyst outlet (S3). The catalyst temperature To is compared with the target catalyst temperature K (S4). When the value To is not less than the value K, electric supply to an electric heat catalyst (EHC) is cut (S5), since generation of aldehyde is already suppressed. When To is less than K, electricity is supplied to the EHC (S6) since the generation of aldehyde is not suppressed. After the temperature of the catalyst is raised, steps from the S3 are repeated once, so that the objective catalyst temperature K is substantially kept.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to controlling the temperature of an exhaust gas purification catalyst located downstream of an exhaust passage of an engine in which a fuel containing alcohol such as methanol can be used. By doing so, the present invention relates to a technique for reducing the production of aldehyde which is an intermediate product.

[0002]

2. Description of the Related Art In an internal combustion engine for a vehicle, in order to purify exhaust gas, HC (unburned gas), CO
An exhaust gas purification catalyst for purifying NO _{X and the} like is provided.
Such an exhaust gas purification catalyst cannot exhibit a sufficient catalytic action unless it is heated up to a predetermined activation temperature. For example, immediately after a cold start of the engine, the exhaust gas purification performance is sufficient. Since it takes a certain amount of time to reach the level, there is a structure in which the catalyst carrier carrying the catalyst is heated by using an electric heater or the like (for example, Japanese Utility Model Laid-Open No. 63-67609). reference).

[0003]

By the way, particularly in an engine using a fuel containing alcohol such as methanol, when the temperature of the catalyst is low, the purification efficiency of the catalyst is extremely lowered and unburned methanol is completely removed in the catalyst. However, there is a problem that exhaust emission is deteriorated by being generated as an aldehyde which is an intermediate product without being oxidized.

Further, when the temperature of the catalyst is raised by energizing and heating an electric heater disposed downstream of the catalyst in order to suppress the production of such aldehyde, the relationship between the amount of aldehyde produced and the catalyst temperature shown in FIG. As shown in, the amount of aldehyde produced differs depending on the methanol content of the fuel. That is, in the figure, M ₀ (alcohol, for example, gasoline with a methanol content of 0%) produces almost no aldehyde regardless of the catalyst temperature, but M ₈₅ (gasoline with a methanol content of 85%) produces no aldehyde. The lower the temperature, the more aldehyde is produced. Therefore, when the methanol concentration increases and becomes high, the catalyst temperature must be raised, but when the methanol concentration is low, aldehydes are less likely to be generated, so the catalyst temperature can be kept low and the electric heater can be energized. It is not necessary to raise the catalyst temperature by heating.

In the conventional exhaust gas purifying apparatus for an internal combustion engine, the catalyst temperature is raised by energization heating of the electric heater regardless of the methanol concentration, because the catalyst temperature is raised for the purpose of activating the catalyst. After that, the energization is turned off and does not contribute to the reduction of aldehyde production. Also, even after the catalyst activation, to keep the catalyst temperature raised by continuing to energize the electric heater to reduce aldehyde production, power consumption becomes excessive and fuel consumption deteriorates, alternator capacity increases, and battery size increases. In addition, it will accelerate the deterioration of the catalyst, which is not preferable.

The present invention has been made in view of such conventional problems, and the temperature of the catalyst located downstream of the exhaust passage of the engine in which the fuel containing alcohol can be used is matched with the aldehyde production conditions. It is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine, which is capable of effectively reducing the amount of aldehyde produced with a minimum amount of power consumption by controlling energization of an electric heater so that the temperature becomes constant. .

[0007]

Therefore, according to the present invention, as shown in FIG. 1, the engine can use a fuel containing alcohol, and an exhaust gas purification catalyst provided in an exhaust passage of the engine can be used. A heating means provided to raise the temperature of the exhaust purification catalyst, a catalyst temperature detection means for detecting an outlet temperature of the exhaust purification catalyst, an alcohol concentration detection means for detecting an alcohol concentration in the fuel, The catalyst temperature setting means for setting a target catalyst temperature of the exhaust purification catalyst in which the generation of aldehyde is suppressed based on the alcohol concentration value, and the catalyst temperature detected by the catalyst temperature detecting means are set by the catalyst temperature setting means. An energization control unit that energizes and controls the heat generating unit so as to maintain the target catalyst temperature value near the target catalyst temperature value.

Further, the catalyst temperature detecting means may be means for predicting the catalyst temperature from the calorific value of the alcohol fuel based on the three values of the alcohol concentration value, the engine speed value and the load value. Further, the catalyst temperature setting means may be means for correcting and setting the target catalyst temperature of the exhaust gas purification catalyst in which the generation of aldehyde is suppressed based on the degree of deterioration of the catalyst.

[0009]

With this configuration, the alcohol concentration in the fuel containing alcohol by the alcohol concentration detecting means,
For example, the methanol concentration is detected, and the catalyst temperature setting means sets the target catalyst temperature of the exhaust gas purification catalyst on which the generation of aldehyde is suppressed based on the methanol concentration value.

Then, the outlet temperature of the exhaust purification catalyst detected by the catalyst temperature detection means is compared with the target catalyst temperature, and the energization control means energizes the heat generation means to set the temperature of the exhaust purification catalyst to the target catalyst temperature. Control to raise up. In this way, if the electricity supply to the heat generating means is controlled by the methanol concentration, the generation of aldehyde is suppressed according to the methanol concentration value, and the electricity supply to the heat generating means can be suppressed to the necessary minimum, resulting in deterioration of fuel efficiency. The deterioration of the catalyst can be suppressed. Further, if the catalyst temperature is predicted by the calorific value of the alcohol fuel based on the three values of the alcohol concentration value, the engine rotation speed value and the load value, the catalyst temperature control can be performed without detecting the catalyst temperature. Therefore, the cost of the exhaust emission control device can be reduced.

Further, when the degree of deterioration of the catalyst is obtained and the target catalyst temperature of the exhaust gas purification catalyst in which the generation of aldehyde is suppressed is corrected and set according to the degree of deterioration, the target degree of deterioration of the catalyst is set. It is possible to accurately control the reduction of aldehyde generation.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. First, referring to FIG. 2, the overall configuration of the exhaust emission control device according to the present invention will be described. The engine 1 can use a fuel containing alcohol, for example, methanol.
An exhaust gas purification catalyst 3 is interposed in the exhaust gas passage 2, and an electrothermal catalyst (EHC) 4 as a heat generating means having an exhaust gas purification function is provided in the exhaust gas passage 2 upstream of the exhaust gas purification catalyst 3. When the electrothermal catalyst is energized, it generates heat to function as an electrothermal heater and raise the temperature of the catalyst.

A temperature sensor 5 as a catalyst temperature detecting means for detecting the outlet temperature is attached to the outlet on the downstream side of the exhaust gas purification catalyst 3. In addition, in the fuel tank 9,
Alcohol sensor 6 as alcohol concentration detecting means for detecting alcohol concentration, for example, methanol concentration
Is provided. The detection signal of the temperature sensor 5, the methanol concentration M signal detected by the alcohol sensor 6, and the engine rotation speed N detected by the rotation speed sensor 7.
A signal, a fuel injection amount Tp signal as an engine load, etc. are input to the control unit 8, and the control unit 8
Controls the energization of the EHC 4 based on these detection signals.

Here, the function as the catalyst temperature setting means and the energization control means is provided by the control unit 8 as software. Next, the operation of the first embodiment of the present invention will be described with reference to the flowchart shown in FIG. First,
In step 1 (hereinafter referred to as "S1"), the detection value from the alcohol sensor 6 is read to detect the methanol concentration M of the fuel.

Then, in S2, the methanol concentration M is calculated from the ROM map which stores the relationship between the methanol concentration shown in FIG. 4 and the catalyst temperature K at which the formation of aldehyde is suppressed.
The target catalyst temperature K ° C corresponding to is searched and set. still,
Here, the setting of K ° C. may be set higher than the actual limit value with a margin. This is because it takes time for the catalyst temperature to rise after the EHC4 is turned on and the power is turned on immediately after the catalyst temperature becomes K ° C. or lower, and therefore it is necessary to suppress the generation of aldehyde even within the period. is there.

In S3, the actual catalyst temperature T _O is detected by the temperature sensor 5 provided at the catalyst outlet. And S
At 4, the catalyst temperature T _O is compared with the target catalyst temperature K to determine whether T _O is higher than K. And
If T _o ≧ K, the catalyst temperature at which the production of aldehyde is suppressed has already been reached.
If FF and T _O <K, the catalyst temperature at which the production of aldehyde is suppressed has not been reached.
After heating the catalyst by turning on the electricity to the target catalyst, the steps from S3 are repeated once more to obtain the target catalyst temperature K.
Keep near.

Here, S1 is alcohol concentration detecting means, S2 is catalyst temperature setting means, and S3 is
As the catalyst temperature detecting means, S4 to S6 function as the energization control means. In this way, the amount of electricity required to maintain the target catalyst temperature K at which the generation of aldehyde is suppressed is controlled according to the methanol concentration, so that the generation of aldehyde is suppressed and the fuel consumption is improved and the alternator is improved. It is possible to reduce the capacity and battery size.

Next, a second embodiment which is a modification of the first embodiment shown in FIG. 3 will be described with reference to the flow chart shown in FIG. Since S1 to S3 are the same as those in FIG. 3,
The same reference numerals are given and the description thereof is omitted, and only different steps from S4A onward will be described. In S4A, an average temperature gradient f ₁ is calculated based on the change in the catalyst temperature for tsec before the time when the catalyst temperature T _O becomes K ° C or less.

That is, as shown in FIG. 6, the catalyst temperature y is
It is represented by y = f ₁ T + b, and the average temperature gradient f ₁ is given as a slope gradient from point A to point B in the figure.
In S5A, the catalyst temperature T ₀ is compared with the target catalyst temperature K to determine whether T _O is higher than K or not. And
If T _O ≧ K, it is already at the catalyst temperature at which the formation of aldehyde is suppressed, and therefore the power supply to EHC4 is turned off in S6A.
And F, if T _O <K, the process proceeds to the following S7A. S7A
Then, it is determined whether or not the average temperature gradient f ₁ obtained in S4A is 0 or more, that is, whether or not the catalyst temperature T ₀ tends to increase. If f ₁ > 0, the catalyst temperature T ₀ tends to increase, so that the power supply to the EHC 4 is turned off in S8A, and the steps from S3 are repeated again to maintain the temperature near the target catalyst temperature K. Also, f ₁
If ≦ 0, the process proceeds to S9A.

[0020] In S9A, the absolute value of f ₁ | f ₁ | is whether the difference is less than a predetermined value c, that is, whether or not the rate of decrease of the catalyst temperature is small. Then, if | f ₁ | ≦ c, the rate of decrease in the catalyst temperature is small, that is, it can depend on the exhaust gas temperature discharged from the engine. Therefore, in order to reduce power consumption, the power is supplied to the EHC 4 in S10A. After turning on the power supply to turn on about 1/2 of the rated output, the steps from S3 are repeated once again to maintain the temperature around the target catalyst temperature K. Also, if | f ₁ |> c, the rate of decrease in catalyst temperature is large, so in S11A, EHC4
After the energization to the ON is turned on and the energization at the rated output is started, the steps from S3 are repeated once more to maintain the temperature around the target catalyst temperature K.

Here, S4A to S11A have a function as an energization control means. As described above, the change in the catalyst temperature is predicted by the average temperature gradient f ₁ of the catalyst temperature, and the energization control to the EHC 4 is performed based on this, so that the aldehyde production reduction performance is further improved by the accurate control of the catalyst temperature. Can be increased. Further, by changing the output value of the energization to the EHC 4 to the energization of about 1/2 of the rated output according to the average temperature gradient f ₁ value, the reduction of the power consumption can be further promoted.

Next, according to the flow chart shown in FIG.
The operation of the third embodiment of the present invention will be described. Incidentally, S1 to S3
Since the above is the same as FIG. 3, the same reference numerals are given and the description thereof is omitted, and only different steps from S4B onward will be described. In S4B, an average gradient f ₂ of N · T _P obtained by multiplying the engine rotation speed and the load torque for tsec before the time when the catalyst temperature becomes K ° C. or less is calculated.

That is, as shown in FIG. 8, N · T _P = y
Is represented by y = f ₂ T + b, and the average slope f ₂ is given as a slope slope from point C to point D in the figure.
In S5B, the actual catalyst temperature T ₀ detected in S3 is compared with the target catalyst temperature K to determine whether T ₀ is higher than K or not. If T ₀ ≧ K, the catalyst temperature at which the production of aldehyde has already been suppressed has been reached, so S6
When the power supply to the EHC 4 is turned off at B and T ₀ <K, the process proceeds to S7B and below.

In S7B, it is determined whether or not the average gradient f ₂ obtained in S4B is 0 or less, that is, whether or not the rotational speed / load N · T _P tends to decrease. And
If f ₂ ≦ 0, it is expected that the catalyst temperature also tends to decrease because N · T _P tends to decrease, so EH at S8B
After turning on the power to C, repeat the steps from S4B. Further, if f ₂ > 0, it is expected that the temperature of N · T _P tends to increase and the catalyst temperature tends to increase due to warming by the high temperature exhaust gas, so that the power supply to the EHC 4 is turned off in S6B.

Here, S4B to S8B have a function as an energization control means. As described above, the temperature sensor 5 controls the energization of the EHC 4 by further adding the average gradient f ₂ element based on the integrated value of the engine rotation speed N and the load T _P to the one shown in the first embodiment. The change state of the catalyst temperature can be predicted earlier than the detection of the catalyst temperature, and wasteful energization of the EHC 4 can be avoided, and reduction of power consumption can be further promoted.

Next, according to the flow chart shown in FIG.
The operation of the fourth embodiment of the present invention will be described. Incidentally, S1 to S2
Since the above is the same as FIG. 3, the same reference numerals are given and the description thereof is omitted, and only different steps from S3C onward will be described. In S3C, engine speed N, load Tp
And the calorific value Q _M according to the methanol concentration of the catalyst based on the methanol concentration _M is searched from the three-dimensional map.

Then, in S4C, the catalyst temperature T ₁ is predicted based on the following equation. That is, if the relational expression of Q _M1 + Q _E1 = A (T ₁ −T ₀ ) is established from the equilibrium equation of the amount of heat and the initial temperature T _{0 of the} catalyst is known, then T ₁
And the catalyst temperature at that time is predicted.

Here, Q _E is the amount of heat generated by the EHC4 electric power, which is obtained in advance from the rated power consumption and the energization time (execution cycle of this routine). A indicates the heat capacity of the catalyst. In general, the following relational expression holds between the catalyst temperatures T _{0 to} T _{n that} change with time shown in FIG.

Q _M1 + Q _E1 −0 = A (T ₁ −T ₀ ) (Q _M2 + Q _E2 ) − (Q _M1 + Q _E1 ) = A (T ₂ −T ₁ ) ・ ・ ・ ・ ・ ・ ・ (Q _Mn + Q _{En) - (Q Mn-1} + Q En-1) = a (T n -T n-1) Therefore, adding all these, relational expression _{(Q Mn + Q En) =} a (T n -T 0) Is guided.

Here, Q _Mn is obtained from a three-dimensional map based on N, Tp, and M, and Q _En and A are known in advance. Therefore, if T ₀ is known, the catalyst when an arbitrary time has elapsed is obtained. The temperature T _n will be obtained. The initial temperature T _{0 of the} catalyst is
It is calculated from the temperature when the engine is stopped and the time until the engine is next started. Then, as shown in FIG. 11, the catalyst temperature T _n after engine stop, first from becomes the same as the water temperature Tw is eventually reduced until the T _n = Tw and T _n times as time The temperature T ₀ is corrected and obtained, and thereafter, calculation is performed with T ₀ = Tw. The Tw is detected by the water temperature sensor. In S5C, the catalyst temperature T ₁ predicted in S4C is compared with the target catalyst temperature K, and T ₁
Is smaller than K. And T ₁ <K
If so, it is predicted that the temperature is at the catalyst temperature at which aldehyde is generated, so that the electricity is supplied to the EHC 4 at S8C, and if T ₁ ≧ K, the process proceeds to S6C.

In S6C, the target catalyst temperature K is determined within the predetermined time based on the predicted catalyst temperature T ₁ obtained in S4C.
It is determined whether or not the following is true, that is, whether or not the predicted catalyst temperature T ₁ has a decreasing tendency. Then, if it is predicted that the target catalyst temperature K or less will be turned ON in S8C, if it is not predicted that the target catalyst temperature K or less, the process proceeds to S7C to turn OFF the EHC4.
As stop. Here, S3C and S4C function as catalyst temperature prediction means, and S5C to S8C function as energization control means.

Thus, by predicting the catalyst temperature from the heat value of the catalyst and controlling the energization to the EHC 4, the catalyst temperature at which the generation of aldehyde is suppressed without detecting the catalyst temperature by providing a temperature sensor is used. Therefore, the product cost can be reduced by simplifying the exhaust gas purification device. Next, the operation of the fifth and sixth embodiments will be described with reference to the flowcharts shown in FIGS.

In both of these, the target catalyst temperature is changed based on the deterioration coefficient of the catalyst which is determined in advance by an experimental value, and the control for avoiding the formation of aldehyde is carried out. S1A is added to the first and fourth embodiments shown. Therefore, the same steps as those in the flowcharts shown in FIGS. 3 and 9 are designated by the same reference numerals, and the description thereof will be omitted. Only different steps will be described.

In S1A, the degree of deterioration of the catalyst is determined.
That is, the deterioration P indicating the degree of deterioration of the catalyst is given by P = N · T _P · K · δ, and assuming that the total running time is t, the deterioration P _t at that time is P _t = (N · T _P・ K · δ) dt = P · dt

Here, N is the engine speed, T _P is the fuel injection amount as the engine load, K is the catalyst temperature, δ is the deterioration coefficient, and δ is obtained as an experimental value during development.
Next, in S2, the target catalyst temperature K at which the generation of aldehyde is suppressed with respect to the methanol concentration value is corrected and set based on the deterioration degree P _t . That is, when the deterioration is P _t, the catalyst temperature at which the production of aldehyde is suppressed is
The target catalyst temperature K is set based on the methanol concentration value obtained in S1.

In this way, by controlling the target catalyst temperature by changing it according to the degree of deterioration of the catalyst, it is possible to cope with the catalyst temperature at which the generation of aldehydes that differ depending on the degree of deterioration of the catalyst is suppressed, and to reduce the generation of aldehyde with high accuracy. Control can be performed.

[0037]

As described above, according to the present invention,
If the electricity to the heat generating means is controlled by the methanol concentration,
It is possible to suppress the generation of aldehyde according to the methanol concentration value, suppress the energization of the heat generating means to the necessary minimum, and suppress the deterioration of fuel consumption and the deterioration of the catalyst.

Further, when the catalyst temperature is predicted by the calorific value of the alcohol fuel based on the three values of the alcohol concentration value, the engine speed value and the load value, the catalyst temperature should be detected by the catalyst temperature detecting means. Since the catalyst temperature can be controlled without using the catalyst, the product cost of the exhaust emission control device can be reduced. Further, when the target catalyst temperature of the exhaust purification catalyst, in which the generation of aldehyde is suppressed based on the degree of deterioration of the catalyst, is corrected and set, it is possible to reduce the generation of aldehyde with high accuracy according to the degree of deterioration of the catalyst. Control can be performed.

[Brief description of drawings]

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

FIG. 2 is a system diagram showing the overall configuration of the present invention.

FIG. 3 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a relationship between a methanol concentration M and a catalyst temperature K at which aldehyde production is suppressed.

FIG. 5 is a flowchart showing the operation of another embodiment of the present invention.

FIG. 6 is an explanatory diagram for explaining an average temperature gradient f ₁ of the catalyst temperature.

FIG. 7 is a flowchart showing the operation of another embodiment of the present invention.

FIG. 8 shows N · multiplied by the engine speed and the load torque.
Explanatory view for explaining an average slope f ₂ of T _P.

FIG. 9 is a flowchart showing the operation of another embodiment of the present invention.

FIG. 10 is an explanatory diagram for explaining a relationship between catalyst temperatures T _{0 to} T _{n that} changes with time.

FIG. 11 is an explanatory diagram for explaining a state in which the catalyst temperature T _n decreases with time.

FIG. 12 is a flowchart showing the operation of another embodiment of the present invention.

FIG. 13 is a flowchart showing the operation of another embodiment of the present invention.

FIG. 14 is an explanatory diagram showing the relationship between the methanol concentration M and the catalyst temperature K at which the production of aldehyde is suppressed, which varies depending on the degree of deterioration of the catalyst.

FIG. 15 is an explanatory diagram for explaining the relationship between the production amount of aldehyde and the catalyst temperature.

[Explanation of symbols]

 1 Engine 2 Exhaust Passage 3 Exhaust Purification Catalyst 4 Electrothermal Catalyst (EHC) 5 Temperature Sensor 6 Alcohol Sensor 7 Rotational Speed Sensor 8 Control Unit 9 Fuel Tank

Continuation of the front page (51) Int.Cl. ⁵ Identification code Reference number in the agency FI Technical display location F02D 41/02 301 K 8011-3G 310 A 8011-3G 45/00 ZAB 7536-3G 364 K 7536-3G

Claims (3)

[Claims] 1. An engine can use a fuel containing alcohol, an exhaust gas purification catalyst provided in an exhaust passage of the engine, and a heat generating means provided to raise the temperature of the exhaust gas purification catalyst, A catalyst temperature detecting means for detecting an outlet temperature of the exhaust gas purifying catalyst; an alcohol concentration detecting means for detecting an alcohol concentration in the fuel; and an exhaust gas purifying catalyst for suppressing generation of aldehyde based on the alcohol concentration value. A catalyst temperature setting means for setting a target catalyst temperature and a catalyst temperature detected by the catalyst temperature detecting means are energized to the heat generating means so as to maintain the catalyst temperature near the target catalyst temperature value set by the catalyst temperature setting means. An exhaust emission control device for an internal combustion engine, comprising: an energization control unit that controls the exhaust gas. 2. The internal combustion engine according to claim 1, wherein the catalyst temperature detecting means is a means for predicting the catalyst temperature based on a calorific value of alcohol fuel based on three values of an alcohol concentration value, an engine speed value and a load value. Exhaust purification device. 3. The catalyst temperature setting means is a means for correcting and setting a target catalyst temperature of an exhaust gas purification catalyst in which aldehyde production is suppressed based on the degree of deterioration of the catalyst. Exhaust gas purification device for internal combustion engine.