JPH1089051A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the purifying factor of NOx by always supplying the suitable amounts of hydrocarbon to a NOx catalyst to be used in various temperature distributions under various operating conditions. SOLUTION: A NOx discharging amount from a diesel engine 11 is calculated (step 102) on the basis of signals of an accelerator sensor 27 and an engine speed sensor 28, and the upstream side temperature TA, the center temperature TB and the downstream side temperature TC of a catalyst are detected (step 103). The hydrocarbon supplying amount HA equivalent to the catalyst upstream side temperature TA, the hydrocarbon supplying amount HB equivalent to the catalyst center temperature TB and the hydrocarbon supplying amount HC equivalent to the catalyst downstream side temperature TC are calculated (step 104) from a hydrocarbon supplying amount map in the reference NOx discharging amount. These hydrocarbon supplying amounts HA, HB, HC are multiplied by the coefficient of weight and summed, the summed value is multiplied by the ratio of the NOx discharging amount to the reference NOx discharging, and the final hydrocarbon supplying amount is found (step 105).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine which reduces nitrogen oxides contained in the exhaust gas of the internal combustion engine.

[0002]

2. Description of the Related Art In order to purify nitrogen oxides (NOx) emitted from an internal combustion engine in which fuel is burned under an excessive amount of oxygen such as a diesel engine, a catalyst is installed in an exhaust pipe to form a hydrocarbon (generally, a fuel). ) Is supplied to a catalyst as a reducing agent to purify nitrogen oxides. As shown in FIG. 2, the purification rate of the catalyst is such that the purification rate of hydrocarbons increases as the catalyst temperature increases, but the purification rate of nitrogen oxides falls within a predetermined activation temperature range (for example, 200 ° C. for a Pt catalyst). (300 ° C.) only. The purification rate of nitrogen oxides can be increased by supplying hydrocarbons (fuel) as a reducing agent to the catalyst. However, when the catalyst temperature is low, the supplied hydrocarbons are discharged without reacting. On the contrary, if the emission deteriorates, or if the catalyst temperature is high, on the contrary, the catalyst temperature rises beyond the activation temperature range due to the reaction heat of the hydrocarbons, and on the contrary, the purification rate of nitrogen oxides decreases. In some cases.

To solve this problem, Japanese Patent Application Laid-Open No. 5-26362 discloses
In Japanese Patent Application Publication No. 4 (JP-A) No. 4 (1998), a method for calculating a hydrocarbon supply amount from a hydrocarbon supply amount map experimentally adapted for each engine and an exhaust gas temperature at a catalyst inlet is proposed.

[0004]

However, in practice, since the internal combustion engine is operated under various conditions, the catalyst is used in various temperature distributions and active states, and the exhaust gas temperature at the catalyst inlet is reduced. Even in the same case, the temperature distribution and the active state of the catalyst change depending on the operating state. Therefore, as described in the above publication, if the hydrocarbon supply amount is calculated uniformly from the exhaust gas temperature at the catalyst inlet, the actual catalyst temperature distribution and active state are
A state in which the hydrocarbon supply amount is too large or too small is likely to occur, and a stable nitrogen oxide purification rate cannot be obtained. In addition, since the fuel supplied to the catalyst uses fuel, if the amount of supplied hydrocarbon is too large, the fuel efficiency will be deteriorated.

[0005] The present invention has been made in view of such circumstances, and therefore has an object to always provide a catalyst which is used under various operating conditions and under various temperature distributions and active conditions. An exhaust gas of an internal combustion engine that can supply a large amount of hydrocarbons, improve the purification rate of nitrogen oxides, and reduce the amount of unreacted hydrocarbons and improve fuel efficiency. It is to provide a purification device.

[0006]

To achieve the above object, an exhaust gas purifying apparatus for an internal combustion engine according to claim 1 of the present invention is provided.
A hydrocarbon supply means for supplying hydrocarbons as a reducing agent for nitrogen oxides to the catalyst is provided. The temperature of a plurality of positions of the catalyst is detected or estimated by the catalyst temperature determination means, and the operation state of the internal combustion engine is detected. Detect by means.
Then, the control means for controlling the hydrocarbon supply means estimates the reduction and purification capacity of the nitrogen oxides at the plurality of positions of the catalyst from the temperatures at the plurality of positions of the catalyst and the operating state of the internal combustion engine, and determines the nitrogen oxides at the upstream position. Weighting is performed so as to increase the contribution of the reduction and purification ability of the product, and the reduction and purification ability of nitrogen oxides of the entire catalyst is estimated, and the hydrocarbon supply amount to be supplied to the catalyst is obtained from the estimated value.

Here, the reason why weighting is performed so as to increase the contribution of the reduction and purification ability of nitrogen oxides at the upstream position is that the concentration of hydrocarbons inside the catalyst becomes higher toward the upstream side,
This is because the selective reduction of nitrogen oxides is increased. As in the present invention, if the weight of the reduction and purification ability of the nitrogen oxides at the upstream side is weighted so as to increase the contribution, the reduction and purification capacity of the nitrogen oxides of the entire catalyst is estimated. The reduction purification ability can be accurately estimated. Therefore, if the amount of hydrocarbon supply is determined from the estimated value, it is possible to always supply an appropriate amount of hydrocarbon to the catalyst used in various temperature distributions and active states under various operating conditions, The purification rate of nitrogen oxides can be improved, and hydrocarbons discharged without being reacted can be reduced to improve fuel efficiency.

In this case, in the second aspect, when estimating the reduction and purification ability of nitrogen oxides of the entire catalyst, weighting is performed so as to increase the contribution of the reduction and purification ability of nitrogen oxides at the upstream position. The reduction and purification abilities of the nitrogen oxides at the plurality of positions are summed to determine the reduction and purification abilities of the nitrogen oxides of the entire catalyst. This makes it possible to accurately estimate the nitrogen oxide reduction / purification capacity of the entire catalyst by a simple process of summing the nitrogen oxide reduction / purification abilities at a plurality of positions.

According to a third aspect of the present invention, the capability of reducing and purifying nitrogen oxides is calculated by representing the amount of hydrocarbon supplied. This eliminates the need to convert the reduction / purification capacity to the amount of hydrocarbon supply in the middle of the arithmetic processing, thereby simplifying the arithmetic processing.

According to a fourth aspect of the present invention, the reduction and purification ability of nitrogen oxides is calculated and expressed by a catalyst temperature, and weighting is performed so as to increase the contribution of the catalyst temperature at the upstream position, so that the temperature representing the entire catalyst is calculated. (Hereinafter, referred to as “catalyst representative temperature”), and the supply amount of hydrocarbons to be supplied to the catalyst is obtained based on the catalyst representative temperature and the detection result of the operating state detecting means. In this case, the catalyst representative temperature estimated by weighting is not simply the average thermal energy temperature of the catalyst but a temperature representative of the nitrogen oxide purification characteristics of the entire catalyst. It is an indicator of ability.
Therefore, even when this catalyst representative temperature is used, the amount of hydrocarbon supply to the catalyst can be accurately obtained, as in the above case.

By the way, an exhaust gas recirculation device for recirculating a part of the exhaust gas to the intake system (hereinafter abbreviated as "EGR device").
As shown in FIG. 15, in the internal combustion engine provided with EGR, the EGR rate increases during steady operation, whereby the temperature at the time of combustion decreases and nitrogen oxides in exhaust gas are reduced. However, at the time of acceleration, the actual EGR rate becomes lower than the target EGR rate obtained from the steady operation state, and the actual nitrogen oxide emission concentration becomes higher than the target concentration. As described above, the causes of the actual EGR rate being lower than the target EGR rate at the time of acceleration include the mechanical operation response delay of the EGR device, the delay of the flow of the EGR gas passing through the EGR pipe, and the like.
This is considered to be due to a delay in control for maintaining EGR control stability.

Therefore, in claim 5, the control means for controlling the hydrocarbon supply means corrects the amount of supply of hydrocarbons to the catalyst when the internal combustion engine is accelerated. Thereby, even if the concentration of nitrogen oxides in the exhaust gas increases at the time of acceleration, the nitrogen oxide purification performance of the catalyst can be improved, and the emission amount of nitrogen oxides can be reduced.

Further, when increasing the amount of hydrocarbon supply to the catalyst during the acceleration operation, the increase ratio is increased at the start of acceleration, and the increase ratio is reduced as time elapses from the start of acceleration. To be corrected. That is, as the time elapses from the start of acceleration, the delay of the EGR control decreases, and the actual nitrogen oxide emission concentration decreases. Therefore, by correcting the increase rate of the hydrocarbon supply amount as the time elapses from the start of acceleration, the hydrocarbon supply amount is reduced in response to the decrease in the nitrogen oxide emission concentration due to the elapse of time after the acceleration start. The amount can be appropriately corrected, and the hydrocarbons discharged without being reacted can be reduced to improve fuel efficiency while improving the purification rate of nitrogen oxides.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIGS. A catalyst 13 (so-called NOx catalyst) for reducing and purifying nitrogen oxides (hereinafter referred to as “NOx”) in exhaust gas is provided in the exhaust pipe 12 (exhaust gas passage) of the diesel engine 11 which is an internal combustion engine. On the upstream side, center and downstream side of the catalyst 13,
Exhaust gas temperature sensors 14, 15, 16 are provided, respectively, and the temperatures at a plurality of positions of the catalyst 13 are determined from the exhaust gas temperatures detected by the exhaust gas temperature sensors 14, 15, 16 respectively.
Therefore, each of the exhaust gas temperature sensors 14, 15, 16 is used as a catalyst temperature determining means described in the claims.

A hydrocarbon supply device 17 (hydrocarbon supply means) for supplying hydrocarbons (fuel such as light oil) as a reducing agent to the catalyst 13 is provided upstream of the catalyst 13.
Fuel is supplied to the hydrocarbon supply device 17 from a fuel injection pump 18 via a medium-pressure fuel pipe 19. The fuel injection pump 18 uses the power of the diesel engine 11 as a drive source, increases the pressure of fuel sucked from a fuel tank (not shown), and supplies the fuel to a fuel injection nozzle 21 of each cylinder of the diesel engine 11 via a high-pressure fuel pipe 20. The fuel is supplied, and fuel is injected from each fuel injection nozzle 21 into each cylinder and burned.

The exhaust pipe 1 of the diesel engine 11
A part of the exhaust gas is transferred between the intake pipe 22 and the intake pipe 22.
An EGR pipe 23 is connected to the EGR pipe 23, and an EGR valve 24 is provided in the middle of the EGR pipe 23. The opening of the EGR valve 24 is varied by a control valve 25, and the amount of EGR gas passing through the EGR pipe 23 is controlled by adjusting the opening. The control valve 25 is controlled by a control circuit 26 in accordance with the operating state of the engine.
The EGR pipe (23), the EGR valve (24) and the control valve (25) constitute an EGR device (exhaust gas recirculation device) (30).

The control circuit 26 is mainly composed of a microcomputer. The control circuit 26 includes information on the engine operating state output from operating state detecting means such as an accelerator sensor 27, an engine speed sensor 28, a vehicle speed sensor 29, etc., and the exhaust gas temperature sensor 14, Information on the temperature (distribution) of the catalyst 13 output from the catalysts 15 and 16 is read, and based on the information, a hydrocarbon supply amount is calculated by a hydrocarbon supply amount calculation routine shown in FIG. 7 described later. Supply device 1
7 is driven to control the amount of hydrocarbon supply to the catalyst 13.

In this case, the method of calculating the hydrocarbon supply amount is as follows:
The catalyst 13 estimates the NOx reduction / purification capacity at a plurality of positions of the catalyst 13 from the temperatures at the plurality of positions of the catalyst 13 and the engine operating state, and weights the catalyst 13 to increase the contribution of the NOx reduction / purification ability at an upstream position. The entire NOx reduction and purification capacity is estimated, and the hydrocarbon supply amount to be supplied to the catalyst 13 is calculated from the estimated value. Hereinafter, this calculation method will be considered.

First, the relationship between the temperature distribution of the catalyst 13 and the NOx purification rate was examined in detail. Representative examples will be described with reference to FIGS. FIG. 3 is a graph showing three types of temperature distributions a, b, and c in which the NOx purification rate is evaluated. In each case, the highest temperature in the catalyst is such that the NOx purification rate is the highest.
It will be 50 ° C. In FIG. 3, a is a temperature distribution that is constant at 250 ° C. from the catalyst inlet to the catalyst outlet, b is a temperature distribution where the catalyst inlet is 200 ° C. and the catalyst outlet is 250 ° C.
c is the temperature distribution where the catalyst inlet is 250 ° C. and the catalyst outlet is 200 ° C. FIG. 4 shows the measurement results of the NOx purification rate when the hydrocarbon supply concentration was changed for these three types of temperature distributions a, b, and c. In FIG. 4, when the hydrocarbon supply concentration is 1000 ppmc, NOx is sequentially set in the order of b, a, and c.
The purification rate was high, and the hydrocarbon purification rates increased in the order of a, c, and b, all of which were 90% or more.

Next, when the hydrocarbon feed concentration is 1000 ppm
The reason why the NOx purification rate of the temperature distribution b in which the temperature at the catalyst outlet side is higher than the temperature at the catalyst inlet side at the time of c is high will be described. Since the reaction activation energy of hydrocarbons is larger than the reaction activation energy of NOx, the lower the temperature, the higher the selective reduction of NOx by hydrocarbons. Therefore, under a constant hydrocarbon reaction amount (the hydrocarbon purification rate is substantially constant at 90% or more), the lower the catalyst temperature, the higher the NOx purification rate. On the other hand, hydrocarbons supplied to the catalyst are consumed in the process of passing through the catalyst, so that the concentration distribution of hydrocarbons inside the catalyst is higher on the upstream side of the catalyst and lower on the downstream side. Since b has a low temperature on the upstream side of the catalyst and a high hydrocarbon concentration, the selective reduction of NOx on the upstream side of the catalyst is high. It is considered that c has a lower temperature on the downstream side of the catalyst, but also has a lower hydrocarbon concentration, so that the NOx purification rate is lower than b. From the above test results, the NOx purification characteristic on the upstream side of the catalyst is
It can be found that the contribution to x purification characteristics is large.

On the other hand, when the hydrocarbon feed concentration is 3000 ppm
At the time of c, the NOx purification rate is higher in the order of a, c, and b, and the hydrocarbon purification rate is lower at b than at a and c. The reason why the NOx purification rate of b is low is that the lower the temperature, the higher the selective reduction of NOx by hydrocarbons. However, the lower the hydrocarbon purification rate, the lower the hydrocarbon reaction rate, and the lower the NOx purification rate.
It is considered that the reaction amount was reduced. In the case of c, although the temperature on the downstream side of the catalyst is low, the temperature on the upstream side of the catalyst is high and the hydrocarbon concentration is high, so that the degree of contribution of the NOx purification characteristics on the upstream side of the catalyst to the NOx purification characteristics of the entire catalyst increases. , B, the NOx purification rate is considered to be higher.

The hydrocarbon feed concentration is 5000 ppm
At the time of c, the NOx purification rate is higher in the order of a, c, and b, and particularly, the b has a lower NOx purification rate. The hydrocarbon purification rate is a, c
Is lower than b. Here, the reason why the NOx purification rate b is low is that the so-called low-temperature poisoning of the catalyst occurs because the supplied hydrocarbon (light oil) covers the surface of the catalyst because the temperature on the upstream side of the catalyst is low. It is considered that NOx is inhibited and NOx cannot be reduced and purified. In the case of c, although the temperature is low on the downstream side of the catalyst, the temperature on the upstream side of the catalyst is high, and the exhaust gas whose temperature has increased due to the heat of reaction on the upstream side flows downstream of the catalyst. In any case, it is considered that the NOx purification characteristics on the upstream side of the catalyst greatly contribute to the NOx purification characteristics of the entire catalyst.

Next, three types of temperature distributions d and e shown in FIG. 5 are used in order to perform the same evaluation as described above with a temperature distribution where the maximum temperature in the catalyst becomes 275 ° C. at which the NOx purification rate decreases from the peak. , F. d is a constant temperature distribution at 275 ° C. from the catalyst inlet to the catalyst outlet.
25 ° C, the center of the catalyst has the highest NOx purification rate of 250
° C, the temperature distribution at the catalyst outlet is 275 ° C, and f is the temperature distribution at the catalyst inlet at 275 ° C, the center of the catalyst at 250 ° C at which the NOx purification rate is the highest, and the catalyst outlet at 225 ° C. FIG. 6 shows the NOx purification rates when the hydrocarbon supply concentration was changed for each of the temperature distributions d, e, and f.

In FIG. 6, the hydrocarbon feed concentration is 1
At 000 ppmc, the NOx purification rates were higher in the order of e, d, and f, and the hydrocarbon purification rates were all 90% or more. Here, the reason why the NOx purification rates of d and f are low is that the selective reduction of NOx is low because the upstream side of the catalyst is at a high temperature, and that f is high at the upstream side of the catalyst despite the low temperature of the downstream side of the catalyst. This is because the reaction of hydrocarbons is promoted and only a small amount of hydrocarbons is supplied to the downstream side of the catalyst.

On the other hand, when the hydrocarbon feed concentration is 3000 ppm
At the time of c, the NOx purification rate is higher in the order of e, d, and f. FIG.
In FIG. 6, b indicates that the hydrocarbon purification rate has decreased (the hydrocarbon reaction amount has decreased) and the NOx purification rate has decreased. However, in FIG. 6, since the catalyst temperature has increased as a whole, in FIG. This is because there is no significant decrease.

The hydrocarbon supply concentration is 5000 ppm
At the time of c, the NOx purification rate is higher in the order of d, e, and f. FIG.
In b, the supplied hydrocarbon (light oil) covers the surface of the catalyst, so-called low-temperature poisoning of the catalyst occurs, and the catalytic reaction is inhibited, so that NOx cannot be reduced and purified. However, in FIG. 6, since the catalyst temperature has risen as a whole, there is no decrease in the NOx purification rate. The reason why the purification rate of f became higher than d was that a large amount of hydrocarbons reacted on the upstream side of the high-temperature catalyst, and the exhaust gas whose temperature increased due to the reaction heat flowed downstream of the catalyst. Is low, so that the selective reduction of NOx is high.

In view of the above evaluation test, if the catalyst has a temperature distribution, the NOx purification performance of the entire catalyst is estimated using the temperature at one point in the catalyst as the representative temperature of the entire catalyst. Shortage occurs. Therefore, it is necessary to estimate the NOx purification performance of the entire catalyst from the temperatures at a plurality of positions of the catalyst. Furthermore, since the catalyst activation state on the upstream side of the catalyst, in particular, the NOx purification characteristic on the upstream side of the catalyst greatly contributes to the NOx purification characteristic of the entire catalyst, N
When calculating the amount of hydrocarbon supply from the purification capacity of Ox,
Weighting is performed so as to increase the contribution of the NOx purification ability at the upstream position of the catalyst, and the hydrocarbon supply amount is calculated from the NOx purification ability at a plurality of positions. It has been found that the amount of hydrocarbon feed can be accurately calculated for the distribution.

The calculation of the hydrocarbon supply amount is performed by the control circuit 26 in accordance with the hydrocarbon supply amount calculation routine shown in FIG. This routine is started every predetermined time or every predetermined crank angle. When this routine is started, first, in step 101, the exhaust gas temperature sensors 14, 1
5 and 16, the accelerator sensor 27, and the signal output from the engine speed sensor 28 are read. Then, in the next step 102, based on the output signals of the accelerator sensor 27 and the engine speed sensor 28, that is, the accelerator opening and the engine speed, the NOx emission amount from the diesel engine 11 is determined from a map (not shown) or the like. calculate.

Thereafter, in step 103, the upstream temperature TA, the center temperature TB, and the downstream temperature TC of the catalyst 13 are detected from the output signals of the exhaust gas temperature sensors 14, 15, and 16.
In the next step 104, the hydrocarbon supply amount H corresponding to the catalyst upstream side temperature TA is obtained from the hydrocarbon supply amount map at the time of the reference NOx emission amount (for example, 10 grams / hour) shown in FIG.
A, hydrocarbon supply amount HB corresponding to catalyst center temperature TB,
A hydrocarbon supply amount HC corresponding to the catalyst downstream temperature TC is calculated. The HA, HB, and HC obtained in this manner serve as indices indicating the NOx reduction and purification ability at each position of the catalyst 13. Here, the hydrocarbon supply amount map at the time of the reference NOx emission amount shown in FIG. 8 takes into consideration the NOx purification characteristics with respect to the catalyst temperature, and when the NOx purification ratio is high, the hydrocarbon supply amount is set to be large, and the NOx purification ratio is reduced. At low temperatures, the hydrocarbon feed rate is set small.

Then, in the next step 105, the final hydrocarbon supply amount HCTOTAL is calculated from the NOx emission amount obtained in step 102 and the hydrocarbon supply amounts HA, HB, HC obtained in step 104 as follows. . First, a hydrocarbon supply amount HA corresponding to the catalyst upstream is multiplied by a weight coefficient k1 to obtain a hydrocarbon supply amount HB corresponding to the center of the catalyst.
Is multiplied by a weighting factor k2, and the hydrocarbon supply amount HC corresponding to the downstream of the catalyst is multiplied by a weighting factor k3 to obtain a total (k1 × HA).
+ K2 x HB + k3 x HC). This total value is an index indicating the NOx reduction and purification ability of the entire catalyst 13. here,
For example, k1 = 0.5, k2 = 0.33, k3 = 0.1
7 (where k1 + k2 + k3 = 1), the larger the weight coefficient on the upstream side of the catalyst (k1>k2> k3).
The reason for this is that, as described above, NOx
This is because the contribution of the purification ability is large.

The value (k1.times.HA + k2.times.HB + k3.times.HC) obtained by multiplying by the weight coefficient in this manner is multiplied by the ratio of the NOx emission amount obtained in step 102 to the reference NOx emission amount. This is because when the NOx emission amount is larger than the reference NOx emission amount, the final hydrocarbon supply amount is increased and corrected according to the ratio, and when the NOx emission amount is smaller than the reference NOx emission amount, the final hydrocarbon supply amount is adjusted according to the ratio. This is to correct the final hydrocarbon supply amount by weight reduction.

As described above, the control circuit 26 controls the hydrocarbon supply device 17 based on the final hydrocarbon supply amount HCTOTAL calculated in step 105, and supplies an appropriate amount of hydrocarbon to the catalyst 13. Thereby, it is possible to always supply an appropriate amount of hydrocarbon to the catalyst 13 used under various operating conditions and various temperature distributions.

Next, a control example in which the present control is applied during acceleration and deceleration of a vehicle in which a temperature distribution occurs in the catalyst 13 will be described with reference to a time chart of FIG. When the vehicle starts accelerating from idle operation (vehicle speed is zero), the catalyst upstream side temperature TA
Immediately rises, but the catalyst center temperature TB rises slowly due to the heat capacity of the catalyst 13 and the catalyst downstream temperature TC rises more slowly, so that the catalyst 13 has a higher temperature on the upstream side than on the downstream side. Become. The T at each time calculated using the hydrocarbon supply amount map at the time of the reference NOx emission amount shown in FIG.
A, TB, TC, the hydrocarbon supply amounts HA, HB,
As for HC, HA takes a peak value in the first half of acceleration, HB takes a peak value in the middle of acceleration, and HC takes a peak value in the latter half of acceleration. Since the final hydrocarbon supply amount is obtained by multiplying HA, HB, and HC by a larger weighting factor toward the upstream side of the catalyst, the final hydrocarbon supply amount becomes large in the first half of the acceleration at which HA takes a peak value. In the middle of the acceleration where HB has a peak value, the final hydrocarbon feed rate also decreases due to a slight decrease in HA. In the latter half of the acceleration where HC takes a peak value,
As the HA is further reduced, the final hydrocarbon feed is further reduced.

When the vehicle starts to decelerate from constant speed running, the catalyst upstream side temperature TA immediately drops, but the catalyst center temperature TB
The temperature of the catalyst 13 gradually decreases due to the heat capacity of the catalyst 13, and the temperature TC on the downstream side of the catalyst only lowers more slowly. Therefore, the catalyst 13 has a lower temperature on the upstream side than on the downstream side. Calculated from the hydrocarbon supply amount map at the time of the reference NOx emission amount shown in FIG. 8,
Hydrocarbon supply amount H corresponding to TA, TB, TC at each time
As for A, HB, and HC, HA takes a peak value in the first half of deceleration, HB takes a peak value in the middle of deceleration, and HC takes a peak value in the second half of deceleration. The final hydrocarbon feed is HA,
Since HB and HC are obtained by multiplying HB and HC by a larger weight coefficient toward the upstream side of the catalyst, in the first half of deceleration at which HA takes a peak value,
The final hydrocarbon feed rate has a large value. In the middle of the deceleration in which HB has a peak value, the final hydrocarbon supply amount also decreases because HA slightly decreases. In the latter half of the deceleration in which HC takes a peak value, the final hydrocarbon supply amount further decreases because HA is almost zero.

As described above, the temperature T at each position of the catalyst 13
A, TB, TC, the hydrocarbon supply amounts HA, HB,
By calculating the final hydrocarbon supply amount by multiplying the HC by a larger weighting factor on the upstream side of the catalyst, an appropriate amount is always obtained for the catalyst 13 used in various operating conditions and various temperature distributions under various operating conditions. Can be supplied, NO
The purification rate of x can be improved, and the hydrocarbons discharged unreacted can be reduced to improve fuel efficiency.

[Embodiment (2)] In the hydrocarbon supply amount calculation routine shown in FIG. 7, the reference N shown in FIG.
The hydrocarbon supply amounts HA, HB, and HC are obtained from the hydrocarbon supply amount map at the time of the Ox emission amount, and the final hydrocarbon supply amount is obtained by multiplying by a weighting coefficient in step 105 and adding them. In the illustrated embodiment (2), the catalyst upstream side is set in advance by multiplying the hydrocarbon supply amount by a weight coefficient,
From the hydrocarbon supply map at the center of the catalyst and downstream of the catalyst, H
A, HB, and HC are determined, and the final hydrocarbon supply amount is determined by the following equation. Final hydrocarbon supply amount = (HA + HB + HC) x (NOx
(Emission amount / reference NOx emission amount) Even in this case, the same effect as in the first embodiment can be obtained.

[Embodiment (3)] The embodiment (1),
In (2), the NOx reduction / purification capacity at each position of the catalyst 13 was calculated and represented by the hydrocarbon supply amount.
In the embodiment (3) shown in FIG. 2, NO at each position of the catalyst 13
The reduction purification capability of x is expressed by the catalyst temperatures TA, TB, and TC, and weighted so as to increase the contribution of the catalyst temperature at the upstream position, and the temperature representing the entire catalyst 13 (hereinafter referred to as “catalyst representative”). The temperature is referred to as “temperature,” and the final hydrocarbon supply amount is calculated based on the catalyst representative temperature and the engine operating state.

The calculation of the final hydrocarbon supply amount is as follows.
This is performed according to the hydrocarbon supply amount calculation routine of FIG. The processing from step 201 to step 203 of this routine is the same as that of the embodiment (1). With these processing, the NOx emission amount from the diesel engine 11 is calculated based on the accelerator opening and the engine speed. The upstream temperature TA, the center temperature TB, and the downstream temperature TC of the catalyst 13 are detected. Then, the next step 204
Then, the representative catalyst temperature is calculated from the temperatures TA, TB, TC at the respective positions of the catalyst 13 as follows.

First, the weight coefficient k1 is added to the catalyst upstream temperature TA.
, The catalyst center temperature TB is multiplied by a weight coefficient k2, the catalyst downstream temperature light oil supply amount TC is multiplied by a weight coefficient k3, and these are summed to calculate a catalyst representative temperature. Catalyst representative temperature = k1 × TA + k2 × TB + k3 × TC Here, for example, k1 = 0.5, k2 = 0.33, k3 =
The weighting factor is set to be larger for the catalyst upstream side such as 0.17 (however, k1 + k2 + k3 = 1). The representative catalyst temperature serves as an index indicating the NOx reduction and purification ability of the entire catalyst 13.

Then, in the next step 205, the hydrocarbon supply amount map at the time of the reference NOx emission amount shown in FIG.
A hydrocarbon supply amount HCo corresponding to the catalyst representative temperature is calculated. Thereafter, at step 206, the hydrocarbon supply amount HCo
Is multiplied by the ratio of the NOx emission amount obtained in step 202 to the reference NOx emission amount to calculate the final hydrocarbon supply amount HCTOTAL. HCTOTAL = HCo × (NOx emission amount / reference NOx
Emissions)

Next, an example of control when the control of this embodiment (3) is applied during acceleration and deceleration of a vehicle in which a temperature distribution occurs in the catalyst 13 will be described with reference to a time chart of FIG.
When the vehicle starts accelerating from idling (zero speed),
The catalyst upstream temperature TA immediately rises, but the catalyst center temperature TB rises slowly due to the heat capacity of the catalyst, and the catalyst downstream temperature TC rises only more slowly. It gets hotter. The catalyst representative temperature rises relatively quickly, and the final hydrocarbon feed rate also increases rapidly.

When the vehicle starts to decelerate from constant speed running, the catalyst upstream side temperature TA immediately drops, but the catalyst center temperature TB
The temperature of the catalyst 13 gradually decreases due to the heat capacity of the catalyst 13, and the temperature TC on the downstream side of the catalyst only lowers more slowly. Therefore, the catalyst 13 has a lower temperature on the upstream side than on the downstream side. Even if the catalyst upstream-side temperature TA becomes low, the catalyst center temperature TB and the catalyst downstream-side temperature TC are still high, so that the catalyst representative temperature drops more slowly than the catalyst upstream-side temperature TA, and the final hydrocarbon supply The amount also decreases slowly.

According to the embodiment (3) described above, the representative catalyst temperature is calculated by performing weighting so as to increase the contribution of the catalyst temperature at the upstream position. This allows
The temperature representative of the NOx purification characteristics of the entire catalyst 13 can be calculated, not simply the average catalyst temperature in terms of thermal energy. By determining the final hydrocarbon supply amount from the catalyst representative temperature and the engine operating state, Embodiment (1),
As in the case of (2), an appropriate amount of hydrocarbons can always be supplied to the catalyst 13 used under various operating conditions and various temperature distributions under various operating conditions, and the NOx purification rate can be improved. The fuel efficiency can be improved by reducing the hydrocarbons discharged without being reacted while improving the fuel efficiency.

[Embodiment (4)] Each of the above embodiments (1)
13 to 14 show the case where the hydrocarbon supply amount is optimized in accordance with the catalyst temperature distribution. The embodiment (4) shown in FIGS. 13 and 14 employs the EGR control (exhaust gas recirculation control) during acceleration. The amount of hydrocarbon supply is optimized in accordance with the increase in NOx emission due to the delay.

First, ECR control during transient engine operation will be described with reference to FIG. When the vehicle starts accelerating from idle operation (vehicle speed is zero), the actual EGR rate becomes lower than the target EGR rate obtained from the steady operation state, so that the NOx emission concentration is a value that is higher than the target concentration. become. As described above, the cause of the actual EGR rate being lower than the target EGR rate during acceleration is the EGR rate shown in FIG.
This is considered to be due to a delay in the operation response of the control valve 25 and the EGR valve 24 of the device 30, a delay in the flow of the EGR gas passing through the EGR pipe 23, and a delay in control for maintaining the stability of the EGR control. On the other hand, during deceleration, the actual EG
Although the R rate is slightly delayed, it is controlled to be almost the target EGR rate of zero. This is considered to be due to only a response delay for shutting off the ECR valve 24. Therefore, there is almost no increase in NOx emission due to delay in EGR control during deceleration, and there is a problem in that increase in NOx emission due to delay in EGR control during acceleration.

Therefore, in the embodiment (4), the hydrocarbon supply amount is increased and corrected during acceleration by the hydrocarbon supply amount calculation routine shown in FIG. 13. In order to further improve the accuracy of the increase correction, At the start of acceleration, the increase rate is increased, and correction is made so that the increase rate decreases as time elapses from the start of acceleration. This takes into account that as the time elapses from the start of acceleration, the delay of the EGR control decreases, and the actual NOx emission concentration decreases.

The details of the hydrocarbon supply amount calculation routine of FIG. 13 for performing the increase correction will be described below. This routine is also started every predetermined time or every predetermined crank angle. When this routine is started, first, at step 300
Then, the routine of FIG. 7 or FIG. 11 is executed to estimate the NOx reduction / purification ability at a plurality of positions of the catalyst 13 and to weight the catalyst 13 so as to increase the contribution of the NOx reduction / purification ability at the upstream position. The NOx reduction / purification capacity of the entire 13 is estimated, and a hydrocarbon supply amount (final hydrocarbon supply amount HCTOTAL) to be supplied to the catalyst 13 is calculated from the estimated value. Note that the final hydrocarbon supply amount may be calculated by the method of the embodiment (2).

In the next step 301, the rotational speed increase rate W is calculated based on the change rate of the signal of the engine rotational speed sensor 28.
In the next step 302, the rotational speed increase rate W is compared with a predetermined rotational speed increase rate Wo in order to determine whether or not the vehicle is in an acceleration state. If W ≦ Wo, it is determined that the vehicle is not in an acceleration state. Then, this routine ends without performing the subsequent processing. If it is determined in step 302 that W> Wo, it is determined that the vehicle is accelerating, and the process proceeds to step 303. In step 302, it is determined whether a timer for measuring an increase correction time described later is operating. In step 305, if not in operation, W1 = W is set in step 304, and then the process proceeds to step 305.

In this step 305, after the start of the increase correction of the hydrocarbon supply amount due to the start of acceleration, the rotation speed increase rate W is set to W to determine whether or not a more rapid acceleration is being performed.
Compared to 1, if W ≦ W1, it is determined that no more rapid acceleration has been performed, and the process proceeds to step 306, where a timer for measuring the increase correction time is started, or if the timer has already been started, Continue the timing operation, and go to Step 3.
Go to 09. If W> W1 in step 305, it is determined that a more rapid acceleration is being performed. In step 307, W1 = W is set, and in step 308, the timer is reset and restarted. Step 30
Go to 9. Accordingly, when a more rapid acceleration is performed after the start of the increase correction, the increase correction time is measured from the time when the acceleration is started.

In step 309, in order to determine whether or not the time required for the increase correction during acceleration has elapsed, it is determined whether or not a timer for measuring the increase correction time has elapsed a predetermined time. If the time has elapsed, it is determined that the increase correction of the final hydrocarbon supply amount is unnecessary, and the routine proceeds to step 310, where the timer for measuring the increase correction time is stopped, and this routine ends.

On the other hand, if it is determined in step 309 that the timer for measuring the increase correction time has not elapsed the predetermined time (that is, if the timer is in operation), the process proceeds to step 311 and the final carbonization calculated in step 300 is determined. By multiplying the hydrogen supply amount HCTOTAL by the correction coefficient k5, the final hydrocarbon supply amount HCTOTAL is increased and corrected. Here, the increase correction coefficient k5 decreases as the increase correction time elapses, for example, as shown in FIG.
The characteristic is set to 0 (that is, no correction). The reason for this is that the delay of the EGR control is greatest immediately after the start of acceleration, and then decreases. Step 3 above
After the correction of the final hydrocarbon supply amount is performed in step 11, this routine ends.

According to the embodiment (4) described above, the amount of hydrocarbon supply to the catalyst 13 is corrected to the increasing side in the operating state in which the diesel engine 11 is accelerated from low rotation to high rotation. As a result, even if the NOx emission concentration from the diesel engine 11 increases due to a delay in the EGR control during engine acceleration, the NOx purification performance of the catalyst 13 can be improved, and the emitted NOx can be reduced. In addition, the amount of increase in the amount of hydrocarbon supply is corrected so as to decrease as the time elapses from the start of acceleration, so that the amount of hydrocarbon supply is adjusted appropriately in response to the decrease in NOx emission concentration due to the elapse of time after the start of acceleration. Thus, while improving the NOx purification rate, it is possible to reduce the hydrocarbons discharged without being reacted and improve the fuel efficiency.

In the control shown in FIG.
Then, the hydrocarbon supply amount according to the catalyst temperature distribution is calculated by any one of the calculation methods of the embodiments (1) to (3).
The hydrocarbon supply amount may be calculated based on any one of the catalyst temperatures. Even in this case, it is possible to effectively cope with the increase in the NOx emission concentration due to the delay of the EGR control that occurs during acceleration by increasing the amount of supply of hydrocarbons, and to reduce the NOx that is emitted during acceleration compared to the conventional case.

[Other Embodiments] In each of the above embodiments, the catalyst temperature is detected at three points on the upstream side, the center, and the downstream side of the catalyst 13. However, only two points on the upstream side and the downstream side are detected. May be used to detect the catalyst temperature at four or more locations. Further, in each of the above embodiments, the NOx emission from the diesel engine 11 is calculated based on the accelerator opening and the engine speed. The NOx emission amount may be calculated using engine operating state parameters such as pipe pressure and fuel injection amount. In each of the above embodiments, fuel (light oil) is used as the hydrocarbon supplied to the catalyst 13.
However, a liquid hydrocarbon such as kerosene or a gaseous hydrocarbon such as propane may be used.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an entire exhaust gas purification system showing an embodiment (1) of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a catalyst temperature and a hydrocarbon purification rate and a nitrogen oxide purification rate.

FIG. 3 is a diagram showing a temperature distribution of catalysts a, b, and c used in the test.

FIG. 4 is a graph showing the relationship between the hydrocarbon supply concentration and the NOx purification rate for catalysts a, b, and c used in the test.

FIG. 5 is a diagram showing a temperature distribution of catalysts d, e, and f used in the test.

FIG. 6 is a graph showing the relationship between the hydrocarbon supply concentration and the NOx purification rate for catalysts d, e, and f used in the test.

FIG. 7 is a flowchart showing a processing flow of a hydrocarbon supply amount calculation routine according to the embodiment (1).

FIG. 8 is a conceptual diagram of a map that defines a relationship between a catalyst temperature and a hydrocarbon supply amount at the time of a reference NOx emission amount according to the embodiment (1).

FIG. 9 is a time chart showing a control example of the embodiment (1).

FIG. 10 is a conceptual diagram of a map defining a relationship between a catalyst temperature and a hydrocarbon supply amount at the time of a reference NOx emission amount according to the embodiment (2).

FIG. 11 is a flowchart showing a processing flow of a hydrocarbon supply amount calculation routine according to the embodiment (3).

FIG. 12 is a time chart showing a control example of the embodiment (3).

FIG. 13 is a flowchart showing the flow of a hydrocarbon supply amount calculation routine according to the embodiment (4).

FIG. 14 is a diagram showing a change over time of an increase correction coefficient k5.

FIG. 15 is a time chart showing the behavior of EGR control during engine transient operation.

[Explanation of symbols]

11 ... Diesel engine (internal combustion engine), 12 ... Exhaust pipe (exhaust gas passage), 13 ... Catalyst, 14, 15, 16 ... Exhaust gas temperature sensor (catalyst temperature judgment means), 17 ... Hydrocarbon supply device (hydrocarbon supply means) , 18 ... fuel injection pump,
21 ... fuel injection nozzle, 22 ... intake pipe, 23 ... EGR pipe, 24 ... EGR valve, 25 ... control valve, 26 ... control circuit (control means), 27 ... accelerator sensor (operating state detecting means), 28 ... engine rotation Number sensor (driving state detecting means), 29 ... vehicle speed sensor (driving state detecting means), 3
0: EGR device (exhaust gas recirculation device)

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI F02D 45/00 360 F02D 45/00 360C (72) Inventor Tsukasa Kuboshima 1-1-1 Showa-cho, Kariya-shi, Aichi Prefecture Nippon Denso Co., Ltd.

Claims (6)

[Claims] 1. A catalyst disposed in an exhaust gas passage of an internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, catalyst temperature determining means for detecting or estimating temperatures at a plurality of positions of the catalyst, Operating state detecting means for detecting an operating state; hydrocarbon supplying means for supplying a hydrocarbon as a reducing agent for nitrogen oxides to the catalyst; information obtained from the catalyst temperature determining means and the operating state detecting means Estimating the reduction and purification capacity of the nitrogen oxides at a plurality of positions of the catalyst based on the above, weighting so as to increase the contribution of the reduction and purification capacity of the nitrogen oxides at the upstream side position, And control means for controlling the hydrocarbon supply means by estimating the reduction purification ability, obtaining the supply amount of hydrocarbons to be supplied to the catalyst from the estimated value, and controlling the hydrocarbon supply means. It is purified apparatus. 2. The control means, when estimating the reduction and purification ability of nitrogen oxides of the entire catalyst, performs weighting so as to increase the contribution of the reduction and purification ability of nitrogen oxides at an upstream position. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the reducing and purifying ability of the nitrogen oxides at a plurality of positions is summed to obtain the reducing and purifying ability of the nitrogen oxides of the entire catalyst. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the control means calculates the reduction and purification capacity of the nitrogen oxides by representing the amount of hydrocarbon supply. 4. The control means calculates a reduction / purification ability of the nitrogen oxides by expressing the reduction / purification ability in terms of a catalyst temperature, and performs weighting so as to increase the contribution of the catalyst temperature at an upstream position to represent the entire catalyst. A catalyst supply temperature to be supplied to the catalyst based on the catalyst representative temperature and a detection result of the operating state detecting means. Item 2. An exhaust gas purifying apparatus for an internal combustion engine according to item 1. 5. An exhaust gas recirculation device for recirculating a part of exhaust gas from an internal combustion engine to an intake system, a catalyst disposed in an exhaust gas passage of the internal combustion engine, for reducing and purifying nitrogen oxides in the exhaust gas, A hydrocarbon supply unit for supplying hydrocarbons as a reducing agent for nitrogen oxides, and a control for controlling the hydrocarbon supply unit by increasing and correcting the hydrocarbon supply amount to the catalyst when the internal combustion engine is accelerated. And an exhaust gas purifying apparatus for an internal combustion engine. 6. The control means increases the rate of increase at the start of acceleration and decreases the rate of increase as time elapses from the start of acceleration when correcting the amount of hydrocarbon supply to the catalyst during the acceleration operation. The exhaust gas purifying apparatus for an internal combustion engine according to claim 5, wherein the correction is performed in the following manner.