JPH07197834A - Euel feed control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the occurrence of temporary deterioration owing to inflow of high temperature air and to improve durability of a catalyst and exhaust gas purifying performance. CONSTITUTION:It is decided by a control unit 20 to command control and a function whether it is a deceleration time. When it is a deceleration time, a catalyst inlet temperature T by an exhaust temperature sensor 11 is read. The catalyst inlet temperature T is compared with a given temperature T0, and in a case T>=0, it is estimated that a catalyst temperature is high and rich control is executed regardless of establishment of a fuel cut condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel supply control device for an internal combustion engine, and more particularly to a technique for preventing deterioration of an exhaust purification catalyst due to lean air-fuel ratio during deceleration.

[0002]

2. Description of the Related Art Conventionally, as a fuel supply control device for an internal combustion engine, since output is not required during deceleration operation,
There is known a technique for improving fuel efficiency by cutting fuel (stopping fuel supply). However, when the fuel is cut during deceleration, the air that has flowed into the combustion chamber is discharged as it is, the amount of oxygen supplied to the exhaust purification catalyst increases, and the oxidation reaction is rapidly accelerated, which causes the catalyst temperature to rise excessively. There is a risk of deterioration of the catalyst and dissolution of the catalyst carrier.

For this reason, there has been proposed a technique for preventing an increase in the temperature of the catalyst while maintaining a good fuel consumption characteristic by making the air-fuel ratio lean at the time of deceleration (JP-A-2-
(See Japanese Patent Publication No. 91438).

[0004]

However, when the engine operating condition is such that the catalyst temperature becomes high at high speed and under high load, for example, fuel cut is performed during deceleration and the air-fuel ratio is reduced. When leaned, excess air flows into the catalytic converter in a high temperature state, hot oxygen in the air combines with rhodium (Rh) of the catalyst, and the purification capacity of the catalyst temporarily decreases (deterioration of the catalyst. ) Problem arises.

The present invention has been made in view of the above circumstances, and provides a fuel supply control device for an internal combustion engine capable of preventing temporary deterioration of the catalyst due to an excess air state of the exhaust purification catalyst at high temperature. With the goal.

[0006]

Therefore, the present invention is based on FIG.
As shown in FIG. 3, in an internal combustion engine having an exhaust purification catalyst in the exhaust passage of the internal combustion engine and fuel cut means for stopping the fuel supply by the fuel supply means at the time of deceleration, the catalyst temperature for estimating the temperature of the exhaust purification catalyst An estimating means, a comparing means for comparing the estimated value of the catalyst temperature estimating means with a predetermined temperature set in advance, and when the estimated catalyst temperature value from the comparison result of the comparing means is equal to or higher than the predetermined temperature, the fuel cut means is used. And a fuel cut prohibition means for prohibiting fuel cut.

Further, in addition to the configuration of FIG. 1, the engine operating state detecting means, and the determining means for determining whether the engine operating state detected by the engine operating state detecting means is in the fuel increase region or not.
An operating time measuring means for measuring an operating time in the fuel increase area when the determining means determines that the fuel is in the fuel increasing area when the estimated catalyst temperature is equal to or higher than a predetermined temperature based on the comparison result of the comparing means, and the operating time measuring means. And a fuel cut prohibition canceling means for canceling the prohibition of the fuel cut by the fuel cut prohibiting means when the measured time exceeds a preset predetermined time.

Further, the engine operating state detecting means, the determining means for determining whether the engine operating state detected by the engine operating state detecting means is in the fuel increase range or not, and the estimated catalyst temperature is determined by the comparison result of the comparing means. When the determination means determines that the temperature is equal to or higher than the temperature, the fuel increase value calculation means calculates the fuel increase value in the fuel increase area and the comparison result of the comparison means determines that the estimated catalyst temperature is equal to or higher than a predetermined temperature. At this time, the fuel reduction value calculation means for calculating the fuel reduction value based on the fuel cut by the fuel cut means, and the value obtained by subtracting the fuel reduction value from the calculated fuel increase value becomes a predetermined value or more, It may be configured to include fuel cut prohibition canceling means for canceling the prohibition of fuel cut by the fuel cut prohibiting means.

[0009]

In this structure, when the exhaust purification catalyst temperature is estimated to be high, the fuel is not cut even if the engine operating condition satisfies the fuel cut condition, and the fuel is supplied by the fuel supply means. As a result, it is possible to prevent the air-fuel ratio from becoming lean due to fuel cut when the exhaust purification catalyst is at a high temperature, the high temperature exhaust purification catalyst is not exposed to the lean atmosphere, and high temperature oxygen adheres to the catalyst surface. It becomes possible to prevent the temporary deterioration of the exhaust purification catalyst caused by the above.

Further, when the exhaust purification catalyst is estimated to be at a high temperature, the fuel cut is prohibited when the operating time in the fuel increase region becomes a predetermined time or more, or when the fuel is increased more than a predetermined value. By canceling it, it is possible to prevent temporary deterioration of the catalyst due to lean air-fuel ratio at high temperature of the catalyst, prevent misfire of the engine due to excessive fuel supply during deceleration, and prevent deterioration of deceleration feeling, It is possible to prevent deterioration of fuel efficiency.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 2 showing the configuration of the first embodiment of the present invention, an intake passage 2 and an exhaust passage 3 are connected to the engine body 1. The intake passage 2 is provided with an air cleaner 4, an air flow meter 5 for detecting the intake air flow rate Q, and a throttle valve 6 for controlling the intake air flow rate Q in conjunction with an accelerator pedal. The throttle valve 6 is provided with a throttle sensor 7 that serves as a throttle switch that detects the throttle opening TVO and also detects the fully closed position of the throttle. In addition, an electromagnetic fuel injection valve 8 is provided for each cylinder in the manifold portion of the intake passage 2. The fuel injection valve 8 is opened and driven by an injection pulse signal from a control unit 20 which will be described later, and injects fuel which is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator.

Further, the exhaust passage 3 is provided with an oxygen sensor 9 for detecting the oxygen concentration in the exhaust gas, and on the downstream side thereof, CO and HC in the exhaust gas are oxidized and NO _x is reduced in the exhaust gas for purification. A catalytic converter 10 including a three-way catalyst as an exhaust gas purification catalyst is installed. Furthermore, the catalytic converter 10
An exhaust temperature sensor 11 for detecting the exhaust temperature is provided on the inlet side of, and the temperature of the three-way catalyst is estimated by the exhaust temperature on the inlet side of the catalytic converter 10 detected by the exhaust temperature sensor 11.
Here, the exhaust temperature sensor 11 corresponds to the catalyst temperature estimating means.

Incidentally, the three-way catalyst may be any one such as a monolith catalyst having a honeycomb shape, a metal catalyst, a product made of stainless wool, a pellet type or the like. Further, in the present embodiment, NO _x and C that are high in stoichiometric air-fuel ratio are used.
A three-way catalyst that exhibits a purification rate of O and HC will be described, but of course, an oxidation catalyst or the like may be used. Furthermore, the engine body 1
Is provided with a water temperature sensor 12 that detects the cooling water temperature Tw in the cooling jacket and a crank angle sensor 13 that outputs a crank unit angle signal and a crank reference angle signal in synchronization with the rotation of the crankshaft. The crank rotation angle N from the crank angle sensor 13 is counted for a predetermined time, or the cycle of the crank reference angle signal is measured to determine the engine rotation speed N.
Is detected. Reference numeral 14 is a start switch that is provided on a key switch in the vehicle compartment and outputs a start signal.

The control unit 20 includes a CPU 21, R
OM22, RAM23 and input / output port (I / O port) 24
And a basic fuel injection amount Tp (= K · Q / N, based on the intake air flow rate Q signal from the air flow meter 5 and the engine rotation speed N signal from the crank angle sensor 13). K is a constant), and the air-fuel ratio is brought close to the target air-fuel ratio (theoretical air-fuel ratio) based on the oxygen concentration detected by the oxygen sensor 9.
The air-fuel ratio feedback correction coefficient α is calculated by proportional-plus-integral control. Then, the basic fuel injection amount Tp is set to the air-fuel ratio feedback correction coefficient α and various correction coefficients COE.
The fuel injection amount Ti (= Tp × α × COEF + Ts) is calculated by the correction by F, the voltage correction amount Ts, and the like, and the fuel injection valve 8 is drive-controlled according to the fuel injection amount Ti. Further, an ignition signal is generated at a predetermined time based on the crank unit angle signal from the crank angle sensor 13
Ignite 15 to burn the mixture.

The control unit 20 further includes
When a fully closed signal of the throttle valve 6 is generated from the throttle sensor 7 (during deceleration), it has a fuel cut function of stopping the fuel supply based on, for example, the engine speed N signal from the crank angle sensor 13, and the like. As shown in the flow chart of FIG. 3, the catalyst inlet temperature detected by the exhaust temperature sensor 11 is compared with a preset predetermined temperature, and when the catalyst inlet temperature is equal to or higher than the predetermined temperature, the catalyst is estimated to be high temperature. It also has a fuel cut prohibition function of prohibiting the fuel cut. Therefore, the control unit 20 corresponds to the fuel cut means, the fuel cut prohibition means, and the fuel supply means.

Next, the fuel supply operation of the first embodiment apparatus will be described with reference to the flow chart of FIG. Step 1
(Indicated as S1 in the figure. The same applies hereinafter), each sensor signal is read. In step 2, it is determined based on the read signal from the throttle sensor 7 whether or not the throttle valve 6 is in the fully closed deceleration state. If the vehicle is decelerating (YES), the process proceeds to step 3. If not decelerating (NO), step 7
Then, the normal air-fuel ratio control is executed.

In step 3, the catalyst inlet temperature T is read from the exhaust temperature sensor 11. In step 4, the read catalyst inlet temperature T is compared with a preset predetermined temperature T ₀ , and T ≧
If T ₀ (YES), it is estimated that the temperature of the catalyst is high, and the routine proceeds to step 5, where regardless of whether the fuel cut condition is satisfied, rich control is performed to prohibit fuel cut and make the air-fuel ratio rich. Run.

On the other hand, when T <T ₀ (NO) in step 4, it is judged that the temperature of the catalyst is not high and the routine proceeds to step 6.
In step 6, it is judged whether or not the fuel cut condition is satisfied. If the fuel cut condition is satisfied, the fuel cut is executed. If not satisfied, the process proceeds to step 7 and the normal air-fuel ratio control is executed.

As described above, when the catalyst temperature is estimated to be high during deceleration, even if the fuel cut condition is satisfied, the fuel cut is prohibited and the air-fuel ratio is controlled to be rich. It can be prevented that the oxygen in the hot air adheres to the rhodium of the three-way catalyst to temporarily lower the conversion rate of the catalyst. Moreover, the conversion rate of the catalyst can be recovered by setting the rich atmosphere. FIG. 4 shows the relationship between the catalyst inlet temperature and the catalyst conversion rate when fuel is cut during deceleration (conventional example) and when fuel is not cut (present invention).

In the first embodiment described above, the exhaust temperature sensor 11 is used to directly detect the catalyst inlet temperature to estimate the catalyst temperature. However, as in the second embodiment shown in the flowchart of FIG. The catalyst temperature may be estimated using a map from the engine rotation speed N and the basic fuel injection amount Tp that is the engine load. The operation of the second embodiment will be described according to the flowchart of FIG. The second embodiment is the same as the first embodiment except that the method for estimating the catalyst temperature is different.

In FIG. 5, in step 11, each sensor signal is read, and in step 12, the basic fuel injection amount Tp is calculated from the engine speed N and the intake air flow rate Q detected by the air flow meter 5. Then, in step 13, it is determined whether or not the vehicle is in the deceleration state. If the vehicle is decelerating, the processing proceeds to step 14, and if the vehicle is not decelerating, the processing proceeds to step 18 to execute normal air-fuel ratio control. When it is determined that the vehicle is decelerating and the routine proceeds to step 14, the catalyst temperature T _CA is estimated from the map of FIG. 6 based on the basic fuel injection amount Tp calculated at step 12 and the engine rotation speed N, and at step 15, Predetermined temperature T
Compare with _CH . As shown in FIG. 6, the estimated catalyst temperature T _CA increases as the basic fuel injection amount Tp increases and the engine speed N increases.

If T _CA ≧ T _CH , it is presumed that the temperature of the catalyst is high, and the routine proceeds to step 16, where the rich control is executed as in the first embodiment. On the other hand, in step 15, T _CA <T _CH
If it is, it is judged that the catalyst is not at a high temperature and the process proceeds to step 17, and if the fuel cut condition is satisfied, the fuel cut is executed, otherwise the process proceeds to step 18 and the normal air-fuel ratio control is executed. To do. Here, in the second embodiment, step 14 corresponds to the function of the catalyst temperature estimation means.

In addition to the same effects as the first embodiment, the second embodiment has the effect that the exhaust temperature sensor 11 is unnecessary. Next, a third embodiment of the present invention will be described with reference to the flowcharts of FIGS. FIG. 7 shows a basic routine of fuel supply.

At step 21, the start switch 14 is turned off.
If it is YES, the engine body 1
When it is determined that the start of the timer has been started, the process proceeds to step 22, and the timer TIAF is reset. If NO, step
Jump to 24. Immediately after the start-up, the temperature of the exhaust system such as the exhaust passage 3 is lowered, and the temperature of the catalytic converter 10 including the three-way catalyst is also low. Therefore, in step 23, the warm-up time T ₁ of the three-way catalyst is searched. To do. Here, since the engine temperature can be represented by the cooling water temperature Tw in the cooling jacket of the engine body 1, the cooling water temperature Tw _INT immediately after the engine is started is detected by the water temperature sensor 12 and immediately after the engine is started. The warm-up time T ₁ is obtained from the map shown in FIG. 9 in accordance with the cooling water temperature Tw _INT . As shown in FIG. 9, the warm-up time T ₁ is the cooling water temperature Tw _INT immediately after the engine is started.
The higher is, the shorter is.

In step 24, the catalyst temperature T _CA of the catalytic converter 23 in the current operating state is calculated. Here, the catalyst temperature T _CA is obtained from the map of FIG. 6 based on the basic fuel injection amount Tp as the load and the engine rotation speed N, as in the second embodiment described above. In step 25, it is determined whether or not the count value (count time) TIAF of the timer, which is the elapsed time after the start switch 14 is turned ON, is longer than the warm-up time T ₁ of the three-way catalyst obtained in step 23. To judge. Further, in step 26, it is determined whether or not the cooling water temperature Tw in the cooling jacket of the engine body ₁ is higher than the engine warm-up temperature Tw ₁ .

Then, TIAF> T ₁ and Tw> Tw ₁
In the case of, it is determined that the warm-up is completed and the process proceeds to step 27. In step 27, the catalyst temperature of the three-way catalyst is estimated on the assumption that the operating condition is an operating state in which the three-way catalyst may have a high temperature. Here, when the operating condition changes, the catalyst temperature of the three-way catalyst also changes. However, since the change in the catalyst temperature may be delayed with respect to the change of the operating condition, the catalyst temperature calculated and stored up to the previous time is considered. A value obtained by weighting and averaging the value Tc and the catalyst temperature T _{CA found in} step 24 this time is used as the catalyst temperature Tc [= (n−1) / n × Tc + (1
/ N) × T _CA ].

In step 28, it is determined whether the estimated stored catalyst temperature Tc is _{equal to} or higher than a predetermined temperature T _{CH, and} it is determined whether the three-way catalyst is in a high temperature state. When it is determined that Tc ≧ T _CH, it is determined that the operating condition is in the three-way catalyst high temperature region, the process proceeds to step 29, and it is determined whether or not the operating condition is in the three-way catalyst high temperature region. Set the determination flag F1 to 0
Memorize as. When it is determined that Tc <T _CH, it is determined that the operating condition is not within the three-way catalyst high temperature region, and the routine proceeds to step 31, where the catalyst high temperature region determination flag F
1 is stored as 1 (that is, the flag F1 is set to F1
= 0 indicates that the exhaust purification catalyst has a high operating temperature range, and F1 = 1 indicates that the exhaust purification catalyst has a high operating temperature range).

On the other hand, in step 25, TIAF≤T
If it is judged to be ₁ , or in step 26, Tw ≦
If it is determined to be Tw _1, it is determined that the warm-up has not been completed yet, and the three-way catalyst is not at a high temperature, and the process proceeds to step 30, and the previously stored value is updated with the catalyst temperature T _CA estimated in step 24 to update the catalyst. Store as temperature T _C. And the above steps
Proceed to 31.

In steps 21 to 31 described above, it is determined whether or not the operating temperature range of the exhaust purification catalyst is high. Next, at step 32, in the catalyst temperature high temperature region,
When the fuel cut condition is satisfied, a fuel cut prohibition determination routine for determining whether to perform the fuel cut or prohibit the fuel cut is executed based on the fuel increase degree at that time. The fuel cut prohibition determination subroutine will be described later with reference to the flowchart of FIG.

In step 33, based on the determination result of step 32, the basic fuel injection amount Tp, the air-fuel ratio feedback correction coefficient α, various correction coefficients COEF, and the voltage correction amount Ts.
, Etc., correct α, or clamp α to 1,
Actual fuel injection amount Ti (= Tp × α × COEF + Ts)
Is calculated. In step 34, the fuel injection amount Ti calculated in step 33 is set in the output register. As a result, the calculated fuel injection amount T is obtained at a predetermined fuel injection timing in synchronization with the engine rotation except when the fuel is cut.
A drive pulse signal having a pulse width of i is given to the fuel injection valve 8 to perform fuel injection.

At step 35, the start switch 14 is turned off.
The count value T of the timer, which is the elapsed time since it became N
The IAF is incremented by DT (execution cycle of this routine) (TIAF = TIAF + DT). This allows
The basic routine for fuel supply of this embodiment is ended and the process returns. Next, the fuel cut prohibition determination subroutine in the above-mentioned step 32 shown in FIG. 7 will be described.

In step 41, it is determined whether the catalyst high temperature region determination flag F1 stored in the above-mentioned basic routine is F1 = 0. Then, if F1 = 0, it is determined that the operating region where the temperature of the three-way catalyst becomes high, and the routine proceeds to step 42. In step 42, the basic fuel injection amount Tp as a load
Based on the engine rotation speed N and the engine rotation speed N, it is determined whether the engine operating condition is within the fuel increase range for increasing the fuel. Then, when it is determined that the current engine operating state is in the fuel increase region, the process proceeds to step 43. Where the step
This corresponds to the function of the determination means for determining whether 42 is in the fuel increase region.

In step 43, it is determined whether or not the rich time count flag F5, which determines whether to count (add) the operating time in the fuel increase range, is F5 = 0.
Here, the flag F5 indicates that the operation time is counted when F5 = 0, and the operation time is not counted when F5 = 1. If the flag determination in step 43 is F5 = 0, it means that the previous determination in step 42 is in the fuel increase range and the fuel increase has already been executed. When F5 = 1, the step is
It is shown that the fuel increase range determination of 42 is the first time, immediately after entering the fuel increase range, and before the fuel increase range is executed.

Therefore, when it is judged at step 43 that the rich time count flag F5 = 0, the fuel amount has already been increased, and the routine proceeds to step 44, at which the time count value T
RO is added to the previous value by DT and stored (TRO = T
RO + DT). In step 45, the time count value TRO in the fuel increase region measured in step 44 is compared with a preset predetermined time TROM, and when TRO <TROM,
Assuming that the fuel has not been increased enough to recover the catalyst, the routine proceeds to step 46, where the fuel cut prohibition determination flag F4 = 0 (indicating prohibition of fuel cut) is set. On the other hand, when TRO ≧ TROM, it is determined that the fuel has been increased enough to recover the catalyst, and the routine proceeds to step 47, where the fuel cut prohibition determination flag F4 = 1 (indicating cancellation of fuel cut prohibition) is set.

If it is judged at step 43 that the rich time count flag F5 = 1, it means that the judgment of the fuel increase range is the first time, and the routine proceeds to step 48, where the fuel increase range is calculated from the next calculation. Since it is necessary to start the measurement of the operating time at, the rich time count flag F5 is set to F5 = 0.
And On the other hand, if it is determined in step 42 described above that the fuel amount is not in the fuel increase range, the process proceeds to step 49, in which the fuel supply is stopped based on, for example, the throttle valve opening TVO and the engine speed N. Determine whether or not.

When it is judged that the fuel cut condition is satisfied, the routine proceeds to step 50, where it is judged if the rich time count flag F5 = 0. Where F5
If = 0, it is assumed that the previous operation range is the fuel increase range, the fuel increase has already been executed, and the process proceeds to step 51, where the time count value TRO is added to the previous value by DT (T
(RO = TRO + DT) and memorize, and further step 52
Then, the flag F5 = 1 is set so as to stop the counting of the operating time due to the deviation from the fuel increase range, and the routine proceeds to step 53.
In step 50, the rich time count flag F5 =
If it is judged to be 1, then the steps 51 and 52 are skipped and the process proceeds to the step 53.

In step 53, it is determined whether or not the fuel cut inhibition determination flag F4 = 0. Here, flag F4 = 0
If so, the fuel cut is prohibited, the air-fuel ratio feedback correction coefficient α is clamped to α = 1 in step 63, and this flow is ended. Further, if the flag F4 = 1, it is determined that the operation time of the fuel increase region has been performed for a predetermined time or more, the catalyst is recovered by the sufficient fuel increase and the fuel cut prohibition is released, and the routine proceeds to step 54, where the fuel increase amount is increased. The time count value TRO indicating the operating time in the range is reset to 0.

On the other hand, if F1 = 1 in step 41, and if it is judged in step 49 that the fuel cut condition is not satisfied (NO), the routine proceeds to step 55, where rich time count flag F5 = 0. To determine. Here, if the flag F5 = 0, it is assumed that the previous operation region is the catalyst high temperature region and the fuel amount increase region, and the fuel amount increase has already been executed. Add only DT (TRO = TRO + D
T) is stored, and the flag F5 is set to 1 in step 57 as in step 52. Then, in step 58, the time count value TRO measured in step 56 is compared with the predetermined time TROM, and when TRO <TROM, it is determined that the fuel has not been increased enough to recover the catalyst, and step 59 is executed. Then, the fuel cut prohibition determination flag F4 = 0 is set, and when TRO ≧ TROM, it is determined that the fuel amount has been increased enough to recover the catalyst, and the routine proceeds to step 60, where the fuel cut prohibition determination flag F4 = 1 is set. Meanwhile, step
When the rich time count flag F5 = 1 in 55, the steps 56 to 60 are skipped and the process proceeds to step 61. here,
The steps 44, 51 and 56 correspond to the function of the operation time measuring means for measuring the operation time in the fuel increase region,
Reference numeral 58 corresponds to the function of the comparison means, and steps 47 and 60 correspond to the function of the fuel cut prohibition cancellation means.

Then, in step 61, it is judged whether or not the operating condition is such that the air-fuel ratio feedback control may be performed. If the operating condition is the air-fuel ratio feedback control operating condition, YES is judged and the operation proceeds to step 62, in which the oxygen sensor 9 is operated. After the air-fuel ratio feedback correction coefficient α is calculated by proportional-plus-integral control so that the air-fuel ratio approaches the target air-fuel ratio (theoretical air-fuel ratio) based on the detected oxygen concentration, this flow is ended.

On the other hand, in step 61, if the operating condition does not require the air-fuel ratio feedback control (N
If it is judged to be O), the routine proceeds to step 63, where after the air-fuel ratio feedback correction coefficient α is clamped to α = 1,
This flow ends. As described above, in the third embodiment, under the operating condition in which the temperature of the catalyst becomes high, if the operating time in the fuel increase range is the predetermined time or more, the prohibition of the fuel cut is released and the fuel cut condition is satisfied. The fuel cut is performed when the above conditions occur, and the fuel cut is prohibited when the time is less than the predetermined time and other operating conditions. Therefore, by prohibiting the fuel cut, deterioration of the catalyst can be prevented, and by canceling the prohibition of the fuel cut in anticipation of a sufficient recovery time of the catalyst, it is possible to prevent wasteful fuel supply and prevent deterioration of fuel efficiency performance.

Next, another embodiment of the fuel cut prohibition determination subroutine in step 32 shown in FIG. 7 will be described with reference to FIG.
11 and FIG. 11 will be described. In this embodiment, the criterion for canceling the fuel cut prohibition is replaced with the fuel increase amount in the fuel increase region in the embodiment of FIG. It is the actual amount of increase in fuel obtained by subtracting the value.

First, at step 71, it is judged whether or not the catalyst high temperature region determination flag F1 is F1 = 0. If F1 = 0, it is determined that the catalyst is in a high temperature operating region and the routine proceeds to step 72. Based on the basic fuel injection amount Tp and the engine rotation speed N, it is determined whether or not the engine operating condition is within the fuel increase range for increasing the fuel. Then, when it is determined that the fuel amount is in the fuel increase region, the process proceeds to step 73.

In step 73, it is determined whether or not the lean time count flag F6 = 0. Here, the flag F6
Indicates that when F6 = 0, the counting of the fuel reduction value associated with the fuel cut is executed, and when F6 = 1, the counting is not executed. When the flag determination in step 73 is F6 = 0, it indicates that the fuel cut was performed in the previous flow execution cycle, and F6 =
A value of 1 indicates that the fuel cut has not been performed in the previous flow execution cycle.

Therefore, when it is judged at step 73 that the lean time count flag F6 = 0, the fuel cut has already been executed, and the routine proceeds to step 74, where the previous value of the count value KLR indicating the fuel increase amount is A new count value KLR is obtained by subtracting the value (DT x KFC) obtained by multiplying the current fuel cut time DT by the fuel cut reduction rate KFC.
(KLR = KLR-DT × KFC), step
At 75, the flag F6 = 1 is set, and it is stored that the fuel cut was not performed this time. On the other hand, when the flag F6 = 1 in step 73, it is determined that the fuel cut was not performed in the previous execution flow, the fuel reduction value is not measured, and steps 74 and 75 are skipped to proceed to step 76.

In step 76, it is determined whether or not the rich time count flag F5, which determines whether or not to count (add) the increment value in the fuel increment region, is F5 = 0. Here, when it is determined that the rich time count flag F5 = 0, the fuel increase has been executed in the previous flow,
Proceeding to step 77, a new count value KL is obtained by adding the previous value of the fuel increase count value KLR to the current fuel increase time DT multiplied by the increase rate KMR (DT × KMR).
Store R (KLR = KLR + DT × KMR).

In step 78, the calculated count value KLR of the fuel increase value is compared with a preset predetermined value KLRM. When KLR <KLRM, the fuel is not yet sufficiently increased until the catalyst is recovered. As step 79
Then, the fuel cut inhibition determination flag F4 = 0 is set. On the other hand, when KLR ≧ KLRM, it is determined that the fuel has been increased enough to recover the catalyst, and the routine proceeds to step 80, where the fuel cut prohibition determination flag F4 = 1 is set.

If it is determined in step 76 that the rich time count flag F5 = 1, it indicates that the fuel increase amount is determined for the first time, and the process proceeds to step 81, and the fuel increase value is calculated in the next calculation. In order to add, the rich time count flag F5 is set to F5 = 0. On the other hand, the above steps
If it is determined in 72 that the fuel amount is not in the increased fuel amount range, the process proceeds to step 82, and it is determined whether or not the fuel cut condition is such that the fuel supply is stopped.

When it is judged that the fuel cut condition is satisfied, the routine proceeds to step 83, where it is judged if the rich time count flag F5 = 0. Where F5
If = 0, it is assumed that the previous operation area is the fuel increase area, and the fuel increase has already been executed, and the routine proceeds to step 84, where the count value KLR of the fuel increase value is updated (KLR = K
LR + DT × KMR), and in step 85,
Since the fuel quantity is out of the fuel quantity increase range, the flag F5 is set to 1 to stop counting the fuel quantity increase next time, and the routine proceeds to step 86. If it is determined in step 83 that the rich time count flag F5 = 1, then step 84,
Jump 85 and go to step 86.

In step 86, it is determined whether or not the fuel cut prohibition determination flag F4 = 1. Here, the flag F4 = 1
If so, it is determined that the prohibition of fuel cut is lifted, and the step
In step 87, it is determined whether or not the lean time count flag F6 = 0. Then, when the flag F6 = 0, it is determined that the previous fuel cut has occurred, and the subtraction of the fuel reduction amount (KLR = KLR-DT × KFC) is executed according to the previous fuel reduction rate, and the routine proceeds to step 101. The fuel ratio feedback correction coefficient α = 1 is clamped, and this flow ends. If the flag F6 = 1, the process proceeds to step 89 and the flag F6 = 0
Set to and memorize this fuel cut, step
Go to 101 and end this flow. Also, in step 86,
When the fuel cut prohibition determination flag F4 = 0, the fuel cut is prohibited, and the process proceeds to step 101 to end this flow.

If F1 = 1 in step 71 and if it is determined that the fuel cut condition is not satisfied in step 82 (NO), the process proceeds to step 90, and it is determined whether or not the rich time count flag F5 = 0. judge. here,
If the flag F5 = 0, it is assumed that the previous operating region is the catalyst high temperature region and the fuel amount increasing region, and the fuel amount increasing has already been executed, and the routine proceeds to step 91, where the count value KLR of the fuel amount increasing value is updated (KLR). = KLR + DT × KMR) is executed, the flag F5 is set to 1 in step 92, and the process proceeds to step 96.

When it is determined in step 90 that the flag F5 = 1, the process proceeds to step 93, and it is determined whether or not the lean time count flag F6 = 0. Here, if the flag F6 = 0, it is determined that the previous fuel cut has occurred, the routine proceeds to step 94, and the subtraction of the fuel reduction amount (KLR = KLR-DT × KFC) is executed according to the previous fuel reduction rate. In step 95, the flag F6 is set to 1 to store the fact that the fuel cut has not been performed this time, and the process proceeds to step 96.

At step 96, the count value KLR of the fuel increase value calculated at step 91 or step 94 is compared with a predetermined value KLRM. If KLR <KLRM, sufficient fuel increase until the catalyst is recovered is obtained. If not, the fuel cut prohibition determination flag F4 = 0 in step 97.
When KLR ≧ KLRM, it is determined that the fuel has been increased enough to recover the catalyst, and the routine proceeds to step 98, where the fuel cut prohibition determination flag F4 = 1 is set, and the routine proceeds to step 99, respectively.

On the other hand, when the lean time count flag F6 = 1 in step 93, the process directly proceeds to step 99.
Then, in steps 99 to 101, similarly to the embodiment of FIG. 8, when the air-fuel ratio feedback control condition is satisfied in step 99, the process proceeds to step 100 to bring the air-fuel ratio close to the target air-fuel ratio (theoretical air-fuel ratio). After the air-fuel ratio feedback correction coefficient α is calculated by the proportional-plus-integral control, this flow ends. If it is not the air-fuel ratio feedback control condition, the routine proceeds to step 101, where the air-fuel ratio feedback correction coefficient α is clamped to α = 1, and then this flow is ended.
Here, steps 74, 88 and 94 correspond to the function of the fuel amount decrease value calculating means, steps 77, 84 and 91 correspond to the function of the fuel amount increasing value calculating means, and steps 80 and 98 correspond to the fuel cut prohibition canceling means. It corresponds to the function.

As described above, in this embodiment, the fuel increase amount in the fuel increase region and the fuel decrease amount due to the fuel cut are calculated, and the fuel decrease amount is subtracted from the fuel increase amount to obtain the substantial fuel increase value. I'm estimating. In other words, the fuel increase amount is estimated from the rich degree during the rich control period and the lean degree during the lean control period.
Compared with the embodiment of FIG. 8 in which the degree of catalyst recovery is estimated only by the operating time in the fuel increase area, the accuracy of estimating the degree of catalyst recovery can be further improved, resulting in waste of fuel consumption, catalyst durability, and exhaust gas. The performance can be further improved.

[0055]

As described above, according to the present invention, the fuel cut is prohibited so that the air-fuel ratio does not become lean in the operating state where the catalyst is presumed to be at high temperature. Therefore, at high temperature and in the lean atmosphere. It is possible to prevent the catalyst from temporarily deteriorating due to exposure to, and improve the durability and exhaust purification performance of the catalyst.

Further, if the prohibition of the fuel cut is released when the operating time in the fuel increase range is a predetermined time or more, in addition to preventing the deterioration of the catalyst, wasteful fuel consumption can be prevented, It is possible to prevent deterioration of fuel efficiency. Further, if the lean degree during the rich control period due to the fuel increase and the lean degree during the lean control period due to the fuel cut are estimated and the difference is obtained to estimate the degree of the fuel increase, the waste of fuel consumption is further reduced. It is possible to improve the durability of the catalyst and the exhaust gas purification performance.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a first embodiment of the present invention.

FIG. 3 is a flowchart for explaining the operation of the first embodiment.

FIG. 4 is a diagram showing the relationship between catalyst inlet temperature and catalyst conversion rate with and without fuel cut.

FIG. 5 is a flowchart for explaining the operation of the second embodiment of the present invention.

FIG. 6 Same as above, estimation map of catalyst temperature used in the second embodiment

FIG. 7 is a flowchart showing a basic routine of a third embodiment of the present invention.

FIG. 8 is a flowchart showing a fuel cut prohibition determination subroutine showing an essential part of the third embodiment.

9 is a diagram showing the relationship between the cooling water temperature and the warm-up time used in the basic routine of FIG.

FIG. 10 is a flowchart showing a fuel cut prohibition determination subroutine showing an essential part of a fourth embodiment of the present invention.

FIG. 11 is a flowchart following FIG. 10.

[Explanation of symbols]

 1 Engine Main Body 2 Intake Passage 3 Exhaust Passage 5 Air Flow Meter 6 Throttle Valve 7 Throttle Sensor 8 Fuel Injection Valve 9 Oxygen Sensor 10 Catalytic Converter 11 Exhaust Temperature Sensor 13 Crank Angle Sensor 20 Control Unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Shibata 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Hideharu Ehara 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (3)

[Claims] 1. An internal combustion engine comprising an exhaust purification catalyst in an exhaust passage of an internal combustion engine and fuel cut means for stopping fuel supply by a fuel supply means during deceleration, wherein a catalyst temperature for estimating the temperature of the exhaust purification catalyst. Estimating means, comparing means for comparing the estimated value of the catalyst temperature estimating means with a predetermined temperature set in advance, and when the estimated catalyst temperature value from the comparison result of the comparing means is equal to or higher than the predetermined temperature, the fuel cut means A fuel supply control device for an internal combustion engine, comprising: a fuel cut prohibiting means for prohibiting fuel cut. 2. An engine operating state detecting means, a determining means for determining whether or not the engine operating state detected by the engine operating state detecting means is in a fuel amount increasing range, and an estimated catalyst temperature is determined by a comparison result of the comparing means. When the determination means determines that the fuel amount is in the fuel increase range when the temperature is equal to or higher than the temperature, the operation time measuring means for measuring the operation time in the fuel increase area, and the measurement time of the operation time measuring means is equal to or more than a predetermined time set in advance. 2. The fuel supply control device for an internal combustion engine according to claim 1, further comprising: a fuel cut prohibition canceling unit that cancels prohibition of fuel cut by the fuel cut prohibiting unit. 3. An engine operating state detecting means, a determining means for determining whether or not the engine operating state detected by the engine operating state detecting means is in a fuel amount increasing range, and an estimated catalyst temperature is determined by a comparison result of the comparing means. When the determination means determines that the temperature is equal to or higher than the fuel increase area, the fuel increase value calculation means calculates the fuel increase value in the fuel increase area, and the comparison result of the comparison means indicates that the estimated catalyst temperature is equal to or higher than a predetermined temperature. At this time, the fuel reduction value calculation means for calculating the fuel reduction value based on the fuel cut by the fuel cut means, and the value obtained by subtracting the fuel reduction value from the calculated fuel increase value becomes a predetermined value or more. 2. The fuel supply control device for an internal combustion engine according to claim 1, further comprising a fuel cut prohibition canceling means for canceling prohibition of fuel cut by the fuel cut prohibiting means.