JP2003090248A - Engine exhaust purification device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the durability of a catalyst by preventing the occurrence of heat shock on a catalyst carrier. SOLUTION: A means (11) for estimating the adhering amount of the purifying ability reducing substance to a catalyst (7) provided in an exhaust passage of an engine, and a purifying ability adhering to the catalyst based on the estimated adhering amount. Temperature raising means (1) for raising the catalyst temperature to the target temperature when it is time to release the substance
(1) an air-fuel ratio control means (11) for maintaining the exhaust air-fuel ratio of the catalyst in an air-fuel ratio state slightly richer than the stoichiometric air-fuel ratio when it is time to release the purifying ability reducing substance attached to the catalyst. In the exhaust gas purifying apparatus for an engine, the first temperature raising means (11) wherein the temperature raising means (11) retards the ignition timing of the ignition device (6).
And a second stage temperature raising means (11) for executing fuel supply in the expansion stroke following fuel supply in the compression stroke by the fuel supply device (5) with the ignition timing retarded thereafter. Become.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust gas purification device.

[0002]

2. Description of the Related Art As an engine exhaust gas purification device, NOx in exhaust gas is trapped (for example, absorbed) when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and when the oxygen concentration in the exhaust gas decreases There is a catalyst that desorbs NOx trapped until then when the fuel ratio is switched to stoichiometric or rich air-fuel ratio, and reduces the desorbed NOx under reducing components such as HC and CO in the exhaust gas. Kaihei 6
-336916).

By the way, in general, the fuel and lubricating oil of an engine contain a sulfur content (substance for reducing purification ability), and especially when the operation at a lean air-fuel ratio continues for a long time, the catalyst is exhausted. SOx (sulfur oxide) is easily absorbed and deposited, and so-called sulfur poisoning proceeds. When this sulfur poisoning progresses, the NOx trapping ability that should be originally trapped by the catalyst is reduced, and the exhaust composition is deteriorated accordingly. Therefore, a device that cancels this sulfur poisoning is disclosed in Japanese Patent Laid-Open No. 8-61052.
It is proposed by Japanese Patent No. 4 publication.

[0004]

In order to release sulfur poisoning of the above catalyst, generally <1> ensure a certain internal temperature of the catalyst (for example, 650 ° C or higher), <2> theoretical air-fuel ratio. It is necessary to maintain operation in a slightly richer air-fuel ratio state.

On the other hand, for the purpose of reducing the heat capacity of the catalyst carrier having a honeycomb structure (honeycomb structure) to accelerate the activation of the catalyst, a honeycomb structure having a thin wall thickness has been developed (SAE PAPER). 2000-01-
0890). When such a thin-wall type catalyst carrier is applied to the catalyst for the NOx trap, if the catalyst temperature is rapidly raised toward the target temperature of <1>, the catalyst carrier will be heat-shocked in order to release SOx. It has been experimentally found that excessive stress may occur in the.

This will be described in detail with reference to FIG. In the figure, when the sulfur poisoning release condition is satisfied at t1 during lean operation, the catalyst temperature rises with a first-order lag when the sulfur poisoning release flag is switched from 0 to 1 and the temperature rise of the catalyst is started. (See the uppermost row of FIG. 2) If the temperature rises sharply as indicated by the one-dot chain line, heat shock may occur and excessive stress may occur on the catalyst carrier having the honeycomb structure. Therefore, it is necessary to control the temperature rising rate so that the actual temperature rise of the catalyst does not become too rapid.

However, the conventional apparatus merely suggests a method of raising the temperature to the target temperature, and there is nothing to point out that it is necessary to suppress the rising rate of the catalyst temperature. JP 2000
In Japanese Patent Laid-Open No. 130223, if the NOx trapping ability of the catalyst is lowered by the accumulated SOx, one cylinder group is made rich on the premise of an engine in which the air-fuel ratio can be independently controlled for each of the two cylinder groups. By operating the air-fuel ratio and the other cylinder group at a lean air-fuel ratio, the reaction heat in the catalyst is increased to raise the temperature of the catalyst, and the ignition timing of all cylinders is retarded from the optimum ignition timing to reduce the exhaust temperature. The temperature of the catalyst is raised by raising the temperature. Here, the means for operating one cylinder group at the rich air-fuel ratio and the other cylinder group at the lean air-fuel ratio are the temperature raising means by the air-fuel ratio control, and the means for retarding the ignition timing is the increase by the ignition timing control. It is a warming means. That is, since the control range is limited only by the temperature raising means by the air-fuel ratio control, by adding the temperature raising means by the ignition timing control, the control range in which the temperature of the catalyst can be raised can be widened and the two temperature rises can be performed. It is intended to raise the temperature of the catalyst early by simultaneously operating the means. For this reason,
When this conventional device is applied to a catalyst provided with a thin-wall type catalyst carrier, the actual temperature rise of the catalyst may become too rapid as indicated by the dashed line at the top of FIG. Excessive stress is generated on the catalyst carrier.

In view of the above, the present invention provides a catalyst having a thin-wall type catalyst carrier by controlling the degree of temperature rise (temperature rising rate) by the temperature raising means so as not to give a heat shock to the catalyst carrier. Even when it is provided, it is intended to prevent the occurrence of heat shock to the catalyst carrier and enhance the durability of the catalyst.

[0009]

A first aspect of the present invention is directed to a fuel supply device for directly supplying fuel to a combustion chamber, an ignition device for performing spark ignition on a mixture in the combustion chamber, and an exhaust passage of an engine. And a means for estimating the amount of the purifying ability-decreasing substance attached to the catalyst, and the timing at which the purifying ability-decreasing substance attached to the catalyst should be released based on the estimated amount (eg, depending on SOx). A determination means for determining whether or not it is time to release the poisoning), and an increase in the catalyst temperature to the target temperature when the timing for releasing the substance with reduced purification ability adhering to the catalyst by this determination means is reached. The temperature control means and the air-fuel ratio control that keeps the exhaust air-fuel ratio of the catalyst slightly richer than the stoichiometric air-fuel ratio when it is time to release the substance with reduced purification capacity attached to the catalyst. In the exhaust gas purifying apparatus for an engine, the temperature raising means raises the ignition timing by the ignition device in a first stage and the fuel supply is performed after the ignition timing is retarded. The apparatus comprises a second stage temperature raising means for executing fuel supply in the expansion stroke subsequent to fuel supply in the compression stroke.

In a second invention, in the first invention, the temperature raising means in the first step retards the ignition timing by the ignition device at a predetermined speed, and the predetermined speed is relative to the catalyst carrier. Set so that heat shock is not given.

In a third aspect of the invention, in the first aspect, the temperature raising means in the second stage sets the fuel supply amount in the expansion stroke so as not to give a heat shock to the catalyst carrier. To do.

In a fourth aspect of the invention, in any one of the first to third aspects of the invention, the exhaust air-fuel ratio of the catalyst is slightly richer than the stoichiometric air-fuel ratio during the operation of the temperature raising means of the first stage. Change to the fuel ratio state.

In a fifth aspect of the present invention, a means for detecting the actual catalyst temperature according to any one of the first to fourth aspects is provided, and the temperature difference between the target temperature and the actual catalyst temperature is within the first set range. When settled, the temperature rise by the temperature raising means in the second stage is started.

In a sixth aspect of the invention, in any one of the first to fifth aspects of the invention, when the fuel supply amount in the expansion stroke is less than the minimum fuel supply amount of the fuel supply device, the fuel in the expansion stroke is Discontinue supply.

In a seventh invention, in any one of the first to sixth inventions, the actual catalyst temperature is higher than the target temperature, and the temperature difference between the actual catalyst temperature and the target temperature is the second setting range. When it exceeds, the fuel supply in the expansion stroke is stopped.

In an eighth aspect of the invention, in any one of the first to seventh aspects of the invention, the fuel supply in the expansion stroke is performed at the timing when the release of the purification ability lowering substance attached to the catalyst is completed. Stop and return to the value before retarding the ignition timing.

In a ninth aspect of the present invention, in the first aspect of the present invention, the temperature raising means in the first step retards the ignition timing retarded by the ignition device such that the temperature rise of the catalyst carrier is equal to or lower than a predetermined temperature rise rate. To be set.

In a tenth aspect of the present invention, in the first aspect of the present invention, the temperature raising means of the second stage controls the fuel supply amount in the expansion stroke such that the temperature rise of the catalyst carrier becomes a predetermined temperature rise rate or less. Set to.

In the eleventh invention, in the ninth or tenth invention, the predetermined temperature rising speed is a limit rising speed at which the catalyst carrier causes a heat shock.

[0020]

The first, second, third, fourth, fifth, sixth, and
According to the ninth, tenth, and eleventh inventions, since the catalyst temperature can be raised to the target temperature and the degree of increase in the catalyst temperature can be controlled within a range where heat shock does not occur in the catalyst carrier, a thin-wall type Even if a catalyst having a catalyst carrier is used, the catalyst carrier can be improved in durability without giving a heat shock to the catalyst carrier.

According to the seventh aspect of the present invention, it is possible to prevent the temperature of the catalyst carrier during the sulfur poisoning removal from rising excessively and maintain it at a temperature suitable for the sulfur poisoning removal.

According to the eighth aspect, it is possible to quickly return to the state before the start of the temperature raising control.

[0023]

FIG. 1 shows the configuration of an engine control system according to the first embodiment. In the figure, the air measured by the throttle valve 4 is sucked into the combustion chamber of the engine 1,
By mixing with the fuel injected from the fuel injection valve 5 (fuel supply device), a mixture having a predetermined air-fuel ratio is formed in the combustion chamber. The fuel injection valve 5 must inject fuel directly into the combustion chamber because it is necessary to inject fuel in the expansion stroke to raise the exhaust gas temperature as described later.

The air-fuel mixture is ignited and burned by spark ignition by the spark plug 6 (ignition device), and the combustion gas is discharged to the exhaust passage 3 as exhaust gas.

The target air-fuel ratio of the air-fuel mixture is predetermined by the operating region. For example, in the low load side operating range where a large engine output is not required, operation is performed with the lean side air-fuel ratio as the target value in order to improve fuel efficiency. The operation is performed with the stoichiometric air-fuel ratio as the target.

Exhaust gas contains harmful three components of HC, CO, and NOx, and at the time of operation at the stoichiometric air-fuel ratio, these three components are simultaneously purified efficiently by the three-way catalyst 7 provided in the exhaust passage 3. , N when operating with lean air-fuel ratio
A large amount of Ox is generated, and this NOx cannot be efficiently purified by a three-way catalyst. Therefore, when the air-fuel ratio of the exhaust is lean, the NOx in the exhaust is trapped, and when the air-fuel ratio of the exhaust is the stoichiometric air-fuel ratio or the rich side, the trapped NOx is released and the released NOx is then released. The NOx trap catalyst for reducing CO and HC contained in the exhaust gas of NOx as a reducing agent is integrated with the three-way catalyst 7. A three-way catalyst 7 in which a NOx trap catalyst is integrated is called a NOx trap-type three-way catalyst, but will be abbreviated as catalyst 7 below.

An engine controller 11 is provided for controlling the fuel injection amount from the fuel injection valve 5, the fuel injection timing, and the timing of spark ignition by the spark plug 6 in accordance with operating conditions. As is well known, the engine controller 11 includes a microcomputer.

The engine controller 11 receives signals of the rotation speed from the crank angle sensor 12 and the intake air flow rate from the air flow meter 13, and outputs from the O ₂ sensor 14 installed upstream of the catalyst 7 and the catalyst 7. The output from the wide-range air-fuel ratio sensor 15 installed downstream is input, the fuel injection amount from the fuel injection valve 5 and the fuel injection timing are controlled based on these, and the timing of spark ignition by the spark plug 6 and further EGR. EGR valve 22 provided in passage 21
Control the opening of. For example, the target equivalence ratio Tfbya determines whether to operate at the lean air-fuel ratio or the stoichiometric air-fuel ratio, and the target equivalence ratio Tfbya is multiplied by the fuel injection amount Tp at which the stoichiometric air-fuel ratio is obtained. Determine the fuel injection amount. Further, when the stoichiometric air-fuel ratio is targeted, the air-fuel ratio feedback correction coefficient α is calculated based on the two outputs from the O ₂ sensors 14 and 15, and the basic fuel injection amount is corrected by this. In this way, the fuel injection valve 5 outputs the injection pulse signal including the fuel injection pulse width Ti given by the formula of Ti = Tp × Tfbya × α + Ts.

Signals from a water temperature sensor 16 for detecting the engine cooling water temperature, an accelerator position sensor 17 for detecting the accelerator depression amount, etc. are also input to the controller 11, and the opening of the throttle valve 4 is variably controlled based on these signals. is doing.

In the controller 11, especially when the NOx trapping ability is deteriorated by depositing and depositing sulfur oxides (SOx) in the exhaust gas on the catalyst 7 such as when the operation at the lean air-fuel ratio is continued, the sulfur poisoning of the catalyst 7 is deteriorated. Release control is performed. In order to release SOx adhering to the catalyst 7, generally,
<1> It is necessary to secure a certain degree of internal temperature of the catalyst (for example, 650 ° C. or higher), and <2> to maintain the operation in an air-fuel ratio state slightly richer than the theoretical air-fuel ratio.

Then, when the sulfur poisoning release condition is satisfied,
Due to <1>, the catalyst 7 is raised to the target temperature while controlling the degree of rise (rise rate) of the catalyst temperature by a two-stage operation of retarding the ignition timing and injecting twice per combustion cycle. This will be described in more detail with reference to FIG.
Shows a model of the idea of the temperature rise control of the present invention in a steady operation state. In the figure, when the sulfur poisoning cancellation condition is satisfied at t1 during lean operation, the sulfur poisoning cancellation flag is set to 0.
The temperature is switched from 1 to 1 and the temperature rise of the catalyst 7 is started.

In this case, first, the temperature raising control in the first stage is performed in which the ignition timing is retarded from the basic ignition timing IT0 during lean operation at a predetermined speed, here a constant speed. Since the exhaust temperature rises due to the retard of the ignition timing, the catalyst temperature rises with a primary delay (see the uppermost stage in FIG. 2). The degree of increase in the catalyst temperature at this time depends on the retardation speed of the ignition timing (the slope of the straight line between t1 and t2), and the catalyst temperature rises sharply as the retardation speed increases.

In this case, the thermal efficiency decreases with the retard of the ignition timing, and the intake air amount increases and the fuel amount increases in response to this, so that equal torque is obtained before and after the retard of the ignition timing. . This means that when the ignition timing is retarded as the temperature raising means in the first stage, the temperature raising control of the catalyst 7 can be performed while maintaining a constant torque (the accuracy of the catalyst temperature raising control improves). Means that.

On the other hand, the degree of increase in the catalyst temperature is related to the durability of the catalyst 7, and when the wall thickness of the catalyst carrier having a honeycomb structure is particularly thin, the catalyst shock is generated in the catalyst carrier due to the heat shock accompanying the rapid increase in the catalyst temperature. It has been confirmed by experiments that excessive stress may occur, which may lead to breakage of the catalyst carrier. Therefore, if the temperature is further increased more rapidly, the limit of the temperature rise rate at which heat shock occurs (see the broken line at the top of FIG. 2) is previously determined by experiments so that the actual temperature rise of the catalyst 7 does not exceed this limit. By setting the retarding speed of the ignition timing (that is, so as to change as indicated by the solid line at the top of FIG. 2), the temperature rising speed of the catalyst can be controlled.

In the case of an exhaust gas purification device using a ceramic thin wall carrier having a honeycomb structure as the catalyst carrier,
The application of the present invention is particularly effective.

On the other hand, from t1, the fuel amount is gradually increased from the fuel injection amount Glean during lean operation, and the temperature difference ΔT between the actual catalyst temperature and the target temperature falls within the first set width due to the retard of the ignition timing t2. The fuel injection amount G0 at which the air-fuel ratio is slightly richer than the theoretical air-fuel ratio can be obtained at the timing of, and from the timing of t2, the ignition timing is maintained as it is at the retarded value ITrtd and until then. The second-stage temperature rise control is performed in which the fuel injection is performed only once in the compression stroke, but once in each combustion cycle, the fuel is injected once, and the expansion stroke injection is additionally performed.

In this case, in the temperature increase control of the second stage, the second injection amount G2 (fuel injection amount in the expansion stroke) contributes to the increase of the catalyst temperature. Therefore, the actual catalyst temperature and the target are set as the second injection amount G2. A value corresponding to the temperature difference ΔT from the temperature is given. Therefore, after t2, the value of G2 is the largest at the timing of t2 where the temperature difference ΔT is the largest, and then G2 becomes smaller as ΔT becomes smaller. Although the catalyst temperature further rises by the second injection in this expansion stroke, the second injection amount G2 is set so that the degree of catalyst temperature rise does not exceed the temperature increase rate limit at this time as well.

The catalyst temperature is further increased by the second injection in the expansion stroke, and the high temperature state near the target temperature is maintained from t3 when the actual catalyst temperature is equal to or higher than the target temperature.
Therefore, in the figure, the second injection is continued from t3 and the catalyst 7 is maintained near the target temperature (see the second stage from the bottom in FIG. 2).

However, when a value less than the minimum injection amount Gmin (the lower limit injection amount that can be injected by the fuel injection valve 5) is instructed to the fuel injection valve 5, no fuel is injected from the fuel injection valve 5, so the second injection is performed. When the amount G2 is less than Gmin, the second injection must be stopped. This 2
If the temperature of the catalyst 7 seems to drop due to the suspension of the second injection, it is necessary to take measures such as further retarding the ignition timing.

Next, the completion of the sulfur poisoning release process is managed by the elapsed time from t3, and when the first set time TM1 has elapsed from the timing of t3, it is judged that SOx is completely released from the catalyst 7, and the ignition timing is reached. , And control for returning both the fuel injection amounts to the state before the start of the sulfur poisoning cancellation processing. That is, at the timing of t4 when the first set time TM1 elapses, the second injection is ended and returned to the single injection of only the compression stroke,
At the same time, the fuel injection amount Glea during lean operation is set.
At the same time as starting the operation of gradually decreasing to n, advancing the ignition timing at a constant speed, the fuel injection amount and the ignition timing substantially return to the values before the start of the sulfur poisoning cancellation processing at the timing of t5. The poison release processing ends.

During the sulfur poisoning release process, the EGR valve 22
It is desirable to stop the operation of 1 and leave the EGR valve 22 in a fully closed state.

The details of this control performed by the engine controller 11 will be described in detail with reference to the following flow chart.

FIG. 3 is for setting the sulfur poisoning cancellation flag, and is executed at a fixed cycle (for example, at fixed time intervals).

In step 1, the sulfur poisoning release flag is checked. This sulfur poisoning release flag is initially set to zero when the engine is started. Therefore, at the beginning of start-up, the routine proceeds to step 2, where SO is determined based on the vehicle speed detected by the vehicle speed sensor 18.
x Estimate the adhered amount. The method for estimating the SOx adhesion amount is known. For example, the traveling distance of the vehicle is calculated for each unit time from the vehicle speed signal, the traveling distances are integrated to obtain a traveling distance integrated value, and the SOx adhesion amount is estimated based on the traveling distance integrated value.

The estimated SOx adhesion amount and the upper limit value are compared in step 3. When the SOx adhesion amount is less than or equal to the upper limit value, the routine proceeds to step 5, where the sulfur poisoning release flag is set to 0,
When the SOx adhesion amount exceeds the upper limit value, the routine proceeds to step 4, where the sulfur poisoning cancellation flag = 1 is set. Therefore, it is possible to determine whether or not the sulfur poisoning cancellation condition is satisfied by the sulfur poisoning cancellation flag.

FIG. 4 is for setting two flags used for ignition timing control (ignition timing retard flag and ignition timing return flag) and one flag used for fuel injection control (second injection flag). It is executed in a cycle (for example, every fixed time).

In step 9, the sulfur poisoning release flag is checked. When the sulfur poisoning cancellation flag = 0, the current processing is ended. When the sulfur poisoning release flag = 1, the routine proceeds to step 10, where the actual catalyst temperature Tcat detected by the temperature sensor 19 is read, and the actual catalyst temperature Tca is read.
Step 11 compares t with the target temperature.

Here, the target temperature is a temperature at which sulfur poisoning can be released (for example, a constant value of about 650 ° C.). The actual catalyst temperature may be estimated by a known method, instead of being detected by the temperature sensor 19 as in the embodiment. For example, the vehicle speed, the engine load, and the retard amount of the ignition timing can be considered as parameters used for temperature estimation.The higher the vehicle speed and the engine load, and the greater the retard amount of the ignition timing, the higher the catalyst temperature. Is created in advance as a map, and this map may be searched by a parameter.

If the actual catalyst temperature Tcat is less than the target temperature, the routine proceeds to step 13, where the target temperature and this actual catalyst temperature Tc
After the temperature difference ΔT with respect to at (= target temperature-Tcat) is calculated in step 13, the temperature difference ΔT and the first set width are compared in step 13. In the present embodiment, first, the exhaust gas whose temperature has been raised by the retard of the ignition timing is guided to the catalyst to raise the temperature of the catalyst 7 (first stage temperature raising means), and if the catalyst temperature rises to some extent by this operation, the ignition timing is kept Then, the injection is started twice, that is, the compression stroke injection and the expansion stroke injection, and the exhaust gas whose temperature has been raised by the expansion stroke injection, which is the second injection in this case, is guided to the catalyst 7 (or the catalyst 7).
Temperature of the catalyst 7 is controlled so as not to give a heat shock to the catalyst carrier by these two-stage temperature raising means. The first set width is a value for determining whether or not it is the switching timing from the first stage temperature raising means to the second stage temperature raising means. (Constant value). Therefore, the first set width satisfies the following two conditions 1 and 2.

Condition 1: The temperature difference is such that the temperature rise of the catalyst due to the second injection in the expansion stroke is the temperature rise that does not damage the catalyst carrier.

Condition 2: The second injection amount G2 in the expansion stroke is not less than the minimum injection amount Gmin.

When the temperature difference ΔT is larger than the first set width, first the ignition timing is retarded in step 14
Then, the ignition timing retard flag (initially set to zero at startup) is set to 1. When the temperature difference ΔT is equal to or less than the first set width, the ignition timing is maintained as it is and the injection is performed twice in the compression stroke and the expansion stroke. Therefore, the process proceeds to steps 15 and 16, and the ignition timing retard flag is set to zero and the second injection is performed. Set the flag (initially set to zero at startup) to 1.
As a result, the ignition timing retard flag becomes ignition timing retard flag = 1 only between t1 and t2 (see the third stage in FIG. 2).

When the actual catalyst temperature Tcat is equal to or higher than the target temperature, the routine proceeds from step 11 to step 17 to check the previous comparison result of the actual catalyst temperature Tcat and the target temperature. If the actual catalyst temperature Tcat is lower than the target temperature last time, it is judged that the temperature has reached the target temperature or higher for the first time, the process proceeds to step 18 and the timer is started, and then the processes of steps 15 and 16 are executed. Here, the timer is for measuring the elapsed time after the actual catalyst temperature Tcat reaches the target temperature.
An internal timer provided in the engine controller 11 may be used as the timer.

When the actual catalyst temperature Tcat was above the target temperature last time (when Tcat is above the target temperature continuously), the routine proceeds from step 17 to step 19, where the above timer value is compared with the second set time TM2. To do. Here, the second set time TM2 is a value (constant value) that determines the time at which the sulfur poisoning cancellation processing ends.

When the timer value is shorter than the second set time TM2, the routine proceeds to steps 20 and 21, where the temperature difference ΔT (= Tcat-target temperature) between the target temperature and the actual catalyst temperature Tcat is calculated, and this temperature difference ΔT is calculated. Compare with the second set width (see FIG. 2). The second set width is a value (constant value) for defining the upper limit of the allowable temperature range suitable for releasing sulfur poisoning centering on the target temperature. By maintaining the temperature difference ΔT within the second set width, SOx is released from the catalyst 7.

When the temperature difference ΔT is less than or equal to the second set width, the routine proceeds from step 21 to step 22, and the timer value is compared with the first set time TM1. The first set time TM1 is a value that defines the time for which the catalyst temperature is maintained at the target temperature or higher and within the allowable temperature range suitable for removing sulfur poisoning. SOx is released from the catalyst 7 by maintaining the catalyst temperature at a temperature higher than the target temperature and suitable for releasing sulfur poisoning. Therefore, the time (constant value) at which the release of all SOx ends is obtained in advance by experiments. Then, this time may be set as the first set time TM1.

When the timer value is shorter than the first set time TM1, the routine proceeds from step 22 to steps 15 and 16 to continue the processing of steps 15 and 16.

When the timer value is the first set time TM1 or more, the second
When the time is equal to or less than the set time TM2, the routine proceeds from step 22 to steps 23 and 24 to finish the second injection and to return the ignition timing to the basic ignition timing IT0. Sometimes set to zero). As a result, from t2 to t
The second injection flag is set to 1 only during 4 (see the bottom row of FIG. 2).

Even when the temperature difference ΔT exceeds the second set width, the routine proceeds from step 21 to steps 23 and 24, and the processing of steps 23 and 24 is executed. This is because the catalyst temperature rises excessively and exceeds the second setting range even between t3 and t4 in order to maintain the catalyst temperature in the temperature range (second setting range) suitable for removing sulfur poisoning. When the temperature is reached, with the sulfur poisoning release flag = 1, the second injection flag = 0,
This is because the catalyst timing is once lowered and the sulfur poisoning release is continued with the ignition timing return flag = 1.

When the timer value exceeds the second set time TM2, the routine proceeds from step 19 to steps 25 and 26, where the sulfur poisoning cancellation flag is set to zero in order to end the sulfur poisoning cancellation processing,
The ignition timing return flag is set to zero in preparation for the next sulfur poisoning cancellation processing. As a result, the sulfur poisoning release flag = 1 is set between t1 and t5 (see the second stage in FIG. 2), and the ignition timing return flag = 1 is set only between t4 and t5 (FIG. 2).
See the fourth row).

FIG. 5 is for calculating the ignition timing command value using the flags (sulfur poisoning release flag, ignition timing retard flag, ignition timing return flag) set by FIG. 3 and FIG. (Crank angle reference position signal)
Run in sync with.

In step 31, the basic ignition timing IT0 is calculated according to the operating conditions. The calculation of the basic ignition timing is known. For example, if the optimum ignition timing such as the ignition timing at which MBT is obtained is used as the basic ignition timing, the optimum ignition timing may be calculated by searching a predetermined map from the engine rotation speed and the engine load.

At steps 32, 33 and 34, three flags, that is, a sulfur poisoning release flag, an ignition timing retard flag and an ignition timing return flag are checked. This is t1 to t in FIG.
This is for determining which of the periods 2, t2 to t4, and t4 to t5 or the other periods (before t1 and after t5).

When the sulfur poisoning release flag = 1 and the ignition timing retard flag = 1 (time period from t1 to t2), the routine proceeds to step 35 to retard the ignition timing and advances to step 35 to set the ignition timing retard amount ΔIT1 [ [°] is calculated, and a value obtained by subtracting the retard amount ΔIT1 from the basic ignition timing IT0 [° BTDC] is calculated as an ignition timing command value IT in step 36. Since the ignition timing command value IT is, for example, the crank angle [° BTDC] measured from the compression top dead center to the advance side,
The reduction of the value of IT by subtracting ΔIT1 from IT0 means that the ignition timing shifts to the retard side.

The ignition timing retard amount ΔIT1 is as follows.
A subroutine (not shown) is used to calculate a value that increases by a predetermined value A each time the Ref signal is input or every predetermined time. This predetermined value A determines the retarded speed of the ignition timing. The calculation method of the predetermined value A itself is known, and for example, the vehicle speed and the load may be calculated as parameters. Here, since the exhaust temperature rises as the vehicle speed or engine load increases, the predetermined value A is set so that the retardation speed decreases as the vehicle speed or engine load increases. As described above, the predetermined value A is set so that the temperature rise rate limit (see the broken line at the top of FIG. 2) at which heat shock occurs when the temperature is further increased more rapidly than the actual temperature rise of the catalyst 7 does not exceed. Needless to say.

When the sulfur poisoning release flag = 1, the ignition timing retard flag = 0, and the ignition timing reset flag = 0 (t
During the period from 2 to t4), the routine proceeds from step 33, 34 to step 37, where the previous ignition timing command value IT _-1 is set as the current ignition timing command value IT, so that the ignition timing (IT in FIG. 2).
rtd)).

When the sulfur poisoning release flag = 1, the ignition timing retard flag = 0 and the ignition timing return flag = 1 (t
(From 4 to t5), the process proceeds from step 33, 34 to step 38, the positive ignition timing advance amount ΔIT2 is calculated, and the value obtained by adding this advance amount ΔIT2 to the basic ignition timing IT0 is determined in step 39. It is calculated as the ignition timing command value IT. Increasing the value of IT by adding ΔIT2 to IT0 means that the ignition timing is returned to the advance side.

As the ignition timing advance amount ΔIT2,
This is also calculated by a subroutine (not shown) with a value that increases by a predetermined value B each time the Ref signal is input or every predetermined time. This predetermined value B determines the return speed (advance speed) of the ignition timing. The predetermined value B may simply be the same as the above-mentioned predetermined value A.

When the sulfur poisoning release flag is 0 (before t1 or after t5), the routine proceeds from step 32 to step 40, where the basic ignition timing IT0 is used as it is as the ignition timing command value IT.

The ignition timing command value IT calculated in this way is transferred to the ignition register in step 41, and the crank angle before compression top dead center is I by the ignition control flow (not shown).
When it coincides with T, the primary current of the ignition coil is cut off.

FIG. 6 is for calculating the fuel injection amount using the flag (sulfur poisoning release flag, second injection flag) set by FIG. 3 and FIG. )Run.

At step 50, the sulfur poisoning release flag is checked. When the sulfur poisoning release flag = 1, the routine proceeds to step 51, where the fuel injection amount G0 is calculated to obtain an air-fuel ratio slightly richer than the theoretical air-fuel ratio. The method of calculating the fuel injection amount G0 is known. For example, G0 = basic fuel injection amount × Tfbya × α where, basic fuel injection amount: fuel injection amount per combustion cycle at which the theoretical air-fuel ratio is obtained, Tfbya: target equivalent ratio, α: air-fuel ratio feedback correction coefficient When the fuel injection amount G0 is calculated by
The target equivalence ratio Tfbya is set to a value slightly larger than 1.0 and the air-fuel ratio feedback correction coefficient α is clamped to 1.0, or the target equivalence ratio Tfbya is set to 1.0 and the average of α that changes by the proportional derivative operation is set. The value may be set to a value exceeding 1.0.

As shown in FIG. 2, the fuel injection amount is not changed stepwise from lean fuel injection amount Glean to G0 at the timing of t1 when the sulfur poisoning release flag is changed from 0 to 1. , Must be slowly changed to G0 at the timing of t2 at which the temperature raising control of the first stage is finished, but details of this point are omitted. Therefore, G0 calculated in step 51 of FIG.
Also includes the fuel injection amount during the change to G0 (between t1 and t2 in FIG. 2).

In step 52 of FIG. 6, the second injection flag is checked. When the second injection flag = 0, only the injection in the compression stroke is performed, so the routine proceeds to step 55, where the above-mentioned fuel injection quantity G is added to the first injection quantity G1 which is the injection quantity in the compression stroke.
0 is entered, and zero is entered in the second injection amount, which is the injection amount in the expansion stroke.

When the second injection flag = 1, step 5
3, the actual catalyst temperature Tcat is compared with the target temperature, and the temperature difference ΔT is compared with the first setting width and the second setting width.

Here, the actual catalyst temperature Tcat is lower than the target temperature, and the temperature difference ΔT at that time (= target temperature-Tca)
temperature range in which t) is equal to or less than the first set width, and the actual catalyst temperature Tc
At is equal to or higher than the target temperature and the temperature difference ΔT (= T
The temperature range in which (cat-target temperature) is less than or equal to the second set width is the temperature range suitable for the two-time injection for releasing sulfur poisoning. Therefore, when the temperature range is not suitable for the double injection, the routine proceeds from step 53 or 54 to step 55 and step 55.
The process of is executed.

When the temperature range is suitable for double injection,
The process proceeds from steps 53 and 54 to steps 56 and 57, and the second injection amount G2 is calculated by searching the table having the contents of FIG. 7 from the temperature difference ΔT (the result of step 12 or step 20 of FIG. 4 is diverted). G as shown in FIG.
2 is a value that increases as the temperature difference ΔT from the target temperature increases.

In step 58, the second injection amount G2 is compared with the minimum injection amount Gmin. Here, the minimum injection amount Gm
in is a lower limit injection amount that can be injected by the fuel injection valve 5. That is, when the fuel injection valve 5 is commanded to have a value less than the lower limit injection amount, no fuel is injected from the fuel injection valve 5. Therefore, when the second injection amount G2 is less than the minimum injection amount Gmin, the second injection cannot be performed, so the routine proceeds to step 55. That is, when the second injection amount G2 is less than the minimum injection amount Gmin, all G0 is injected in the compression stroke.

However, in FIG. 2, the second injection amount G2 becomes less than the minimum injection amount Gmin during the period from t2 to t4, and 2
If the temperature of the catalyst 7 is likely to drop when the second injection must be stopped, it is necessary to take a method such as further retarding the ignition timing.

When the second injection amount G2 is equal to or larger than the minimum injection amount Gmin, the second injection can be executed. Therefore, the routine proceeds from step 58 to step 59, where the value obtained by subtracting the second injection amount G2 from G0 is the first injection amount G1. Calculate as

The first and second injection amounts G1 and G2 [kg / cycle] calculated in this way are calculated in step 6
When the conversion constant is 0, the fuel injection pulse width T1,
After being converted into T2 [ms / cycle], these fuel injection pulse widths T1 and T2 are stored in the injection register in step 61.

The fuel injection pulse widths T1 and T2 stored in this way are such that, in a fuel injection flow (not shown), when the crank angle reaches a predetermined crank angle in the compression stroke, the fuel injection amount of G1 changes in the next expansion stroke. The fuel injection valve 5 is opened twice in one combustion cycle so that the G2 fuel injection amount is supplied when the predetermined crank angle is reached.

Here, the operation of this embodiment will be described.

According to the present embodiment, the temperature raising means is the first stage temperature raising means for retarding the ignition timing of the spark plug 6 (ignition device) at a constant speed, and then the ignition timing is retarded. The ignition timing retardation speed of the ignition timing is constituted by the second stage temperature raising means for executing the fuel supply in the compression stroke and the fuel supply in the expansion stroke by the fuel injection valve 5 (fuel supply device) with the above value kept unchanged. Also, since the fuel supply amount in the expansion stroke is set so as not to give a heat shock to the carrier of the catalyst 7, it is possible to control the degree of increase in catalyst temperature (rate of increase). As a result, the catalyst temperature can be raised to the target temperature and the extent of the catalyst temperature rise can be controlled within a range in which a large stress caused by a rapid temperature change does not occur in the catalyst carrier. Even if it is used, the durability of the catalyst can be improved without giving a heat shock, which is a large stress caused by a rapid change in temperature, to the catalyst carrier.

In the embodiment, the means for performing the fuel supply in the expansion stroke subsequent to the fuel supply in the compression stroke by the fuel injection valve 5 as the temperature raising means in the second stage has been described, but the fuel supply in the expansion stroke is described. Instead of the above, fuel supply in the exhaust stroke is executed, or the air-fuel ratio can be controlled independently for each of the two cylinder groups, and one cylinder group is used as the second stage temperature raising means, and one cylinder group has a rich air-fuel ratio and the other has a rich air-fuel ratio. A means for raising the temperature of the catalyst by increasing the reaction heat in the catalyst by operating the cylinder group at a lean air-fuel ratio may be used.

In the embodiment, the case where the purification ability lowering substance is SOx has been described, but the substance is not limited to this.

In the embodiment, the catalyst is the NOx trap type three-way catalyst (or the NOx trap catalyst) in which the exhaust purification performance due to SOx is remarkably reduced. However, the catalyst may be the three-way catalyst or the SOx catalyst. I don't care.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of a first embodiment.

FIG. 2 is a waveform diagram showing a temperature increase control model of the present invention.

FIG. 3 is a flowchart for explaining setting of a sulfur poisoning cancellation request flag.

FIG. 4 is a flowchart for explaining setting of two flags used for ignition timing control and one flag used for fuel injection control.

FIG. 5 is a flowchart for explaining calculation of an ignition timing command value.

FIG. 6 is a flowchart for explaining calculation of a fuel injection amount.

FIG. 7 is a characteristic diagram of the second injection amount.

[Explanation of symbols]

5 Spark plug (ignition device) 6 Fuel injection valve (fuel supply device) 7 catalyst 11 engine controller 19 Temperature sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/24 F01N 3/24 L 3/28 301 3/28 301C F02D 43/00 301 F02D 43/00 301B 301C 45/00 312 45/00 312Z 314 314Z F02P 5/15 F02P 5/15 BF Term (reference) 3G022 DA02 EA01 GA01 GA05 GA06 GA09 GA19 3G084 BA09 BA13 BA15 BA17 BA24 DA10 FA04 FA05 FA07 FA20 FA29 FA33 FA38 309 AB11 BA11 BA14 BA33 CA01 CB02 CB03 CB05 DA02 DA07 EA01 EA05 EA18 EA19 EA30 EA38 EA39 FC01 GA06 3G301 HA01 HA13 JA21 LA01 LB02 MA01 MA11 MA19 MA23 MA25 MA26 ND12 ND15 NE01 NE12 NE13 NE18 NE23 PAZ PE03Z PE04 PE03Z

Claims (11)

[Claims] 1. A fuel supply device for directly supplying fuel to a combustion chamber, an ignition device for performing spark ignition on an air-fuel mixture in the combustion chamber, a catalyst provided in an exhaust passage of an engine, and a catalyst for the catalyst. Means for estimating the adhered amount of the purifying ability-lowering substance, and a judging means for judging whether or not it is time to release the purifying ability-lowering substance adhering to the catalyst based on the estimated adhering amount; When the timing to release the substance with reduced purification capacity attached to the catalyst is reached by the temperature raising means for raising the catalyst temperature to the target temperature, and when it is time to release the substance with reduced purification ability attached to the catalyst An engine exhaust gas purification apparatus comprising: an air-fuel ratio control means for maintaining an exhaust air-fuel ratio of a catalyst in an air-fuel ratio state slightly richer than a stoichiometric air-fuel ratio. First stage temperature raising means for delaying the ignition timing by the ignition device, and thereafter, with the ignition timing retarded, the fuel supply device executes the fuel supply in the expansion stroke subsequent to the fuel supply in the compression stroke. An exhaust gas purifying apparatus for an engine, comprising: 2. The first-stage temperature raising means retards the ignition timing of the ignition device at a predetermined speed so that the predetermined speed does not give a heat shock to the catalyst carrier. The exhaust gas purification device for an engine according to claim 1, wherein 3. The temperature raising means in the second stage sets a fuel supply amount in the expansion stroke so as not to give a heat shock to the carrier of the catalyst. Exhaust gas purification device for engine according to. 4. The method according to claim 1, wherein the exhaust air-fuel ratio of the catalyst is changed to an air-fuel ratio state slightly richer than the stoichiometric air-fuel ratio during the operation of the temperature raising means in the first stage. The exhaust emission control device for an engine according to any one of the above. 5. A means for detecting an actual catalyst temperature is provided, and when the temperature difference between the target temperature and the actual catalyst temperature falls within a first set range, the temperature raising means of the second stage starts the temperature rise. The exhaust gas purification device for an engine according to any one of claims 1 to 4, wherein 6. The fuel supply in the expansion stroke is stopped when the fuel supply quantity in the expansion stroke is less than the minimum fuel supply quantity of the fuel supply device. The exhaust gas purification device for an engine according to any one of the above. 7. When the actual catalyst temperature becomes higher than the target temperature and the temperature difference between the actual catalyst temperature and the target temperature exceeds a second set width, the fuel supply in the expansion stroke is stopped. The exhaust emission control device for an engine according to any one of claims 1 to 6, characterized in that 8. The fuel supply in the expansion stroke is stopped and the ignition timing is returned to the value before the ignition timing is retarded at the timing when the release of the purification ability lowering substance attached to the catalyst is completed. The exhaust emission control device for an engine according to any one of claims 1 to 7. 9. The temperature raising means in the first stage sets a speed for retarding an ignition timing by the ignition device so that a temperature increase of a carrier of the catalyst becomes a predetermined temperature increase speed or less. The exhaust emission control device for an engine according to claim 1. 10. The temperature raising means in the second stage sets the fuel supply amount in the expansion stroke so that the temperature rise of the catalyst carrier is below a predetermined temperature rise rate. Item 1. An engine exhaust emission control device according to item 1. 11. The engine exhaust gas purification apparatus according to claim 9, wherein the predetermined temperature increase rate is a limit increase rate at which the catalyst carrier causes a heat shock.