JP5338596B2 - Fuel supply control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel supply control device for an internal combustion engine capable of suppressing thermal deterioration due to overheating of an exhaust emission purifying catalyst by introducing such a system that the catalyst temperature does not exceed the overheat point even in case a catalyst temperature has risen owing to a reaction of a reducer in the exhaust emission purifying catalyst with the oxygen in the exhaust gas when a fuel cut is conducted after a fuel incremental control. <P>SOLUTION: A CPU of an electric controller prohibits the fuel cut when the catalyst temperature Tc sensed by a catalyst temperature sensor is at or over a threshold temperature Tcat1 calculated by a fuel cut prohibition judging Routine in case the fuel cut conditions are met. On the other hand, the CPU executes the fuel cut when the catalyst temperature is lower than the threshold in case the fuel cut conditions are met. The threshold temperature is decided on the basis of the fuel increasing rate Kotp used in the fuel incremental control immediately before transition of the engine to the deceleration state (amount of the reducer supplied to the exhaust emission purifying catalyst). <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a fuel supply control device for an internal combustion engine.

  2. Description of the Related Art Conventionally, there is known an internal combustion engine that performs a fuel increase operation that “operates by increasing the fuel injection amount relative to the normal fuel injection amount” for the purpose of increasing the output in a high load region. Further, as disclosed in Patent Document 1, when the vehicle is decelerated after the fuel increase operation is finished, “hydrogen sulfide (H 2 S) is generated from the exhaust purification catalyst disposed in the exhaust passage”. 2. Description of the Related Art A fuel supply control device for an internal combustion engine that performs a fuel cut to stop the supply of fuel in order to suppress the generation of a catalyst exhaust odor due to the above is known.

  The device described in Patent Document 1 performs the fuel cut for a certain period in order to suppress the generation of hydrogen sulfide when the vehicle is decelerated after the fuel increase operation is completed. However, as described above, since the fuel increase operation is performed for the purpose of increasing the output in a high load region, the temperature of the exhaust purification catalyst is high when the fuel increase operation is terminated. After that, when the fuel cut is performed, the exhaust gas containing excess oxygen flows into the exhaust purification catalyst and reacts with the reducing agent held in the exhaust purification catalyst. For this reason, if the fuel cut is performed after the fuel increase operation is ended, the exhaust purification catalyst may be deteriorated due to overheating. Therefore, in the control apparatus for an internal combustion engine described in Patent Document 1, when the vehicle is decelerated after the fuel increase operation is finished, as the deterioration suppression control that suppresses deterioration of the exhaust purification catalyst due to overheating, It is determined whether or not the fuel cut prohibition control for prohibiting the fuel cut is necessary.

  Here, whether or not the deterioration suppression control (fuel cut prohibition control) is necessary is determined when the vehicle is in a decelerating state and when the conditions for executing the fuel cut are satisfied, the temperature of the exhaust purification catalyst ( Hereinafter, it is determined simply based on the catalyst temperature. Specifically, the fuel cut is performed when the catalyst temperature at the time when the conditions for performing the fuel cut are satisfied does not exceed a predetermined reference temperature.

  However, during the fuel cut execution period, the catalyst temperature rises due to reaction heat generated when the reducing agent held in the exhaust purification catalyst reacts with oxygen in the exhaust. Therefore, even when the catalyst temperature does not exceed the reference temperature at the beginning of the fuel cut, the catalyst temperature may exceed the reference temperature with the passage of time from the start of the fuel cut. . The reference temperature is set to an upper limit temperature (overheating temperature) that does not cause deterioration due to overheating of the exhaust purification catalyst. Therefore, the catalyst temperature may exceed the overheating temperature during fuel cut, and the exhaust purification catalyst may be deteriorated due to overheating. On the other hand, if the reference temperature is set to a lower temperature, the possibility of catalyst deterioration is reduced, but the opportunity for fuel cut is reduced. There is a problem that the fuel consumption increases or the fuel consumption increases.

  The present invention has been made in view of the above-described problems, and one of its purposes is to perform fuel cut when the operating state of the internal combustion engine is in a deceleration state that satisfies a predetermined fuel cut condition. It is an object of the present invention to provide a fuel supply control device for an internal combustion engine that can be appropriately implemented within a range in which the exhaust purification catalyst does not deteriorate due to overheating.

JP 2005-163747 A

An internal combustion engine control apparatus according to the present invention includes:
An exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine and having an oxidizing ability;
Fuel increase control for supplying fuel to the engine so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes a rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio, and mixing supplied to the engine One of the normal air-fuel ratio control for supplying fuel to the engine so that the air-fuel ratio of the air becomes an air-fuel ratio other than the rich air-fuel ratio (selectively according to the operating state of the engine) is executed. Fuel supply means;
Fuel cut means for stopping the supply of fuel to the engine when the operating state of the engine is in a deceleration state satisfying a predetermined fuel cut condition;
A fuel supply control device for an internal combustion engine comprising:
When the operating state of the engine is in a deceleration state that satisfies the fuel cut condition,
The temperature of the exhaust purification catalyst is set to be lower as the amount of reducing agent supplied to the exhaust purification catalyst during the fuel increase control by the fuel supply means is larger, and the deceleration is performed immediately after the fuel increase control is terminated. The first threshold temperature is set higher as the period until the state becomes longer , and is higher than the first threshold temperature , and is supplied to the exhaust purification catalyst during the fuel increase control. The internal combustion engine is set lower as the amount of the reducing agent is lower and lower than the second threshold temperature set higher as the period from immediately after completion of the fuel increase control to the deceleration state becomes longer. If the speed of the vehicle on which the vehicle is mounted is equal to or higher than a predetermined reference vehicle speed, the fuel cut means is operated,
If the temperature of the exhaust purification catalyst is equal to or higher than the first threshold temperature, lower than the second threshold temperature, and the speed is lower than the reference vehicle speed, the operation of the fuel cut means is prohibited.
If the temperature of the exhaust purification catalyst is equal to or higher than the second threshold temperature, the operation of the fuel cut means is prohibited.
Fuel cut prohibition means,
It is provided with.

According to the fuel supply control apparatus for an internal combustion engine according to the present invention, when the operating state of the engine is in a deceleration state that satisfies the fuel cut condition, the temperature of the exhaust purification catalyst is set to “fuel increase executed before then”. When the temperature is equal to or higher than a second threshold temperature determined based on the “amount of reducing agent (unburned fuel such as HC) supplied to the exhaust purification catalyst during the control”, the fuel cut by the fuel cut means is prohibited. .

The amount of increase in the catalyst temperature when the fuel cut is performed is the amount of the reducing agent remaining in the catalyst when the fuel cut is performed (thus, the amount of the reducing agent supplied to the catalyst during the fuel increase control). ) Will vary depending on. Therefore, according to the above configuration, the fuel cut is performed so that the catalyst temperature does not reach the “temperature at which the catalyst may be deteriorated due to overheating (overheating temperature)” by performing the fuel cut. The “ second threshold temperature” that determines whether or not can be appropriately determined.

  As a result, according to the present apparatus, it is possible to prevent the catalyst temperature from exceeding the overheating temperature while the fuel cut is being performed, and thus it is possible to suppress the exhaust purification catalyst from being deteriorated due to overheating. it can.

The fuel cut prohibiting means is
Wherein the second threshold temperature, said setting greater the amount of supplied to the exhaust purifying catalyst reducing agent lower on the fuel increase control in accordance with the fuel supply means.

The amount of increase in the catalyst temperature when the fuel cut is performed is the amount of reducing agent remaining in the catalyst when the fuel cut is performed (thus reducing the oxidizing component supplied to the catalyst during fuel increase control). The larger the amount of reducing agent (excess amount relative to the amount required), the larger the amount. Therefore, as the amount of the reducing agent increases, the “ second threshold temperature” that determines whether or not to perform the fuel cut is lowered so that the catalyst temperature does not exceed the overheating temperature during the fuel cut. can do.

Furthermore,
The fuel cut prohibiting means is
Wherein the second threshold temperature, the fuel increase control you set high immediately after the completion longer the period until the deceleration state satisfying the fuel cut-off condition by the fuel supply means.

When the engine is in the deceleration state when a predetermined period has elapsed since the fuel increase control of the engine has been executed, the normal air-fuel ratio control (for example, mixing supplied to the engine) is performed during the predetermined period. An operation in which the average air-fuel ratio of the air becomes an air-fuel ratio other than the rich air-fuel ratio such as the stoichiometric air-fuel ratio) is executed. When the normal air-fuel ratio control is performed, the exhaust gas containing oxygen flows into the exhaust purification catalyst. Therefore, the reducing agent that is supplied to and held by the exhaust purification catalyst during the fuel increase control is the same as the exhaust purification catalyst. Is consumed by reaction (combustion) with oxygen in the exhaust gas flowing into the exhaust gas. Therefore, the longer the period from when the fuel increase control is performed to when the vehicle is in the deceleration state (that is, the period during which the normal air-fuel ratio control is performed), the longer the amount of reducing agent held in the exhaust purification catalyst. Therefore, even if the fuel cut is performed thereafter, the temperature increase amount of the exhaust purification catalyst is small. Therefore, if the second threshold temperature is set as in the above configuration, it is possible to increase the chance of performing the fuel cut without causing deterioration of the exhaust purification catalyst. On the other hand, the temperature of the exhaust purification catalyst is lower than the second threshold temperature and “a temperature lower than the second threshold temperature, and the amount of reducing agent supplied to the exhaust purification catalyst during the fuel increase control is large. The internal combustion engine control device is mounted and is set to be lower as it is higher than the first threshold temperature that is set higher as the period from when the fuel increase control is completed to when the vehicle is in the deceleration state is longer. When the vehicle speed is equal to or higher than the predetermined vehicle speed (reference vehicle speed), the exhaust purification catalyst is efficiently cooled by the traveling wind, so the catalyst temperature does not reach the overheating temperature. In this case, fuel cut by the fuel cut means is performed. On the other hand, when the temperature of the exhaust purification catalyst is lower than the second threshold temperature and equal to or higher than the first threshold temperature, and the vehicle speed is lower than the predetermined vehicle speed, fuel cut is prohibited. Thereby, prohibition of useless fuel cut is avoided.

It is a schematic block diagram of the fuel supply control apparatus of the internal combustion engine which concerns on each embodiment of this invention. 2 is a flowchart showing a fuel injection control routine executed by a CPU of the electric control device shown in FIG. 1 in each embodiment of the present invention. 2 is a flowchart showing a fuel increase rate calculation routine executed by a CPU of the electric control device shown in FIG. 1 in each embodiment of the present invention. 2 is a flowchart showing a fuel cut condition determination routine executed by a CPU of the electric control device shown in FIG. 1 in each embodiment of the present invention. 3 is a flowchart showing a fuel cut prohibition determination routine executed by a CPU of the electric control device shown in FIG. 1 in each embodiment of the present invention. It is a time chart for demonstrating the action | operation of 2nd Embodiment of this invention. 6 is a flowchart showing a part of a fuel cut prohibition determination routine executed by a CPU of the electric control device shown in FIG. 1 in a second embodiment of the present invention.

  Embodiments according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a configuration of a fuel supply control apparatus for an internal combustion engine according to an embodiment of the present invention. The internal combustion engine 10 is a 4-cylinder spark ignition internal combustion engine using gasoline as fuel. The engine 10 is mounted on the vehicle as a vehicle drive source (not shown). The engine 10 includes an intake system 20, an engine body 30, an exhaust system 40, and a control system 50.

  The intake system 20 includes an intake pipe 21 and an intake manifold 22 connected to the intake pipe 21. An air cleaner 23 and a throttle valve 24 are arranged in the intake pipe 21 in order from the upstream side to the downstream side of the flow of air supplied to the engine 10. The throttle valve actuator 24a changes the opening degree of the throttle valve 24 in response to an instruction signal from an electric control device 51 described later.

  The engine body 30 includes an intake port connected to the intake manifold 22, an intake valve that opens and closes the intake port, an exhaust port and an exhaust valve that opens and closes the exhaust port (both not shown), and a fuel injection valve 31. ing. A combustion chamber 32 is formed in the engine body 30 by a cylinder head lower surface, a cylinder wall surface, an upper surface of a piston, and the like. The fuel injection valve 31 is opened in response to an instruction signal (fuel injection signal) from an electric control device 51 described later, and fuel is injected and supplied into the combustion chamber 32 through an intake port.

  The exhaust system 40 includes an exhaust manifold 41 connected to an exhaust port (not shown) and an exhaust pipe 42 connected to the exhaust manifold 41. An exhaust purification catalyst 43 is disposed in the exhaust pipe 42.

  The exhaust purification catalyst 43 is a three-way catalyst having a well-known oxygen storage function. That is, the exhaust purification catalyst 43 can store and hold oxygen and a reducing agent (for example, hydrocarbon HC) and has an oxidizing ability and a reducing ability. When there are unburned components such as carbon monoxide CO and hydrocarbon HC in the exhaust gas, the exhaust purification catalyst 43 oxidizes and purifies the unburned components using the stored oxygen. On the other hand, when there is an oxidizing component such as NOx in the exhaust gas, the exhaust purification catalyst 43 purifies the exhausted component by reducing the oxidizing component using a held reducing agent. The exhaust purification catalyst 43 may be an oxidation catalyst that can store and retain the reducing agent. The exhaust pipe 42 may be provided with a downstream catalyst downstream of the exhaust purification catalyst 43.

  The control system 50 includes an electric control device 51 mainly composed of a microcomputer including a CPU, a ROM, a RAM, a backup RAM, and the like, and performs various controls related to the operation of the internal combustion engine 10.

  The electric control device 51 is connected to various sensors such as an air flow sensor 52, a throttle valve opening sensor 53, an engine speed sensor 54, an air-fuel ratio sensor 55, a catalyst temperature sensor 56, an oxygen concentration sensor 57, and an accelerator opening sensor 58. The acquired values detected by these sensors are input.

The air flow sensor 52 detects the amount of air taken into the combustion chamber 32 through the intake pipe 21, that is, the intake air amount Ga.
The throttle valve opening sensor 53 detects the opening degree TA of the throttle valve 24.
The engine rotation speed sensor 54 detects the rotation speed NE of the engine 10.
The air-fuel ratio sensor 55 detects the air-fuel ratio AF of the exhaust flowing into the exhaust purification catalyst 43.
The catalyst temperature sensor 56 detects the catalyst temperature Tc of the exhaust purification catalyst 43.
The oxygen concentration sensor 57 outputs a low voltage VL when the exhaust gas flowing out from the exhaust purification catalyst 43 contains oxygen, and outputs a high voltage VH when the exhaust gas does not contain oxygen.
The accelerator opening sensor 58 detects the opening AC of the accelerator pedal AP.

  The electric control device 51 performs control according to the operating state of the engine 10 by inputting detection values of various sensors. For example, the electric control device 51 outputs an instruction signal to the throttle valve actuator 24a so that the opening degree of the throttle valve 24 increases as the opening degree AC of the accelerator pedal AP detected by the accelerator opening degree sensor 58 increases.

  Next, the operation of the fuel supply control device for an internal combustion engine configured as described above will be described.

  The CPU (hereinafter simply referred to as “CPU”) included in the electric control device 51 of the first embodiment performs the fuel injection control routine shown in FIG. 2 for any cylinder while the internal combustion engine is operating. Each time the crank angle coincides with a predetermined crank angle before the intake top dead center (for example, 90 ° crank angle before the intake top dead center), the process is repeatedly executed. A cylinder whose crank angle coincides with a predetermined crank angle before the intake top dead center is hereinafter also referred to as a “fuel injection cylinder”.

  The CPU starts the execution of the fuel injection control routine from step S200 and proceeds to step S210, and the intake air amount Ga input from the air flow sensor 52 and the engine speed input from the engine speed sensor 54 at that time. Based on the speed NE, the cylinder intake air amount Mc is calculated. The cylinder intake air amount Mc is the amount of air taken into the fuel injection cylinder.

  Next, the CPU proceeds to step S220, and the basic fuel injection amount Fb that is injected into one cylinder per cycle by dividing the in-cylinder intake air amount Mc by the theoretical air-fuel ratio (for example, 14.7). Is calculated.

  After the basic fuel injection amount Fb is calculated, the CPU proceeds to step S230, and calculates the corrected fuel injection amount Fi by multiplying the basic fuel injection amount Fb by the fuel increase rate Kotp and the feedback correction coefficient KAF. . The fuel increase rate Kotp is calculated separately by a routine described later. The feedback correction coefficient KAF is the theoretical value of the air-fuel ratio of the air-fuel mixture supplied to the engine 10 when the fuel increase rate Kotp is 1.0 and the value of a fuel cut flag XFC described later is “0”. Based on the signals from the air-fuel ratio sensor 55 and the oxygen concentration sensor 57, it is calculated according to a known method so as to coincide with the air-fuel ratio. Further, the feedback correction coefficient KAF is set to 1.0 when the fuel increase rate Kotp is a value other than 1.0.

  Next, the CPU proceeds to step S240 to determine whether or not the value of the fuel cut flag XFC is “1”. The fuel cut flag XFC is a flag indicating whether or not to stop fuel injection (perform fuel cut). That is, when the value of the fuel cut flag XFC is set to “1”, fuel injection is stopped. On the other hand, when the value of the fuel cut flag XFC is set to “0”, fuel injection is executed. The value of the fuel cut flag XFC is set by a routine described later. The value of the fuel cut flag XFC is set to “0” in an initial routine executed when an ignition key (not shown) is changed from OFF to ON.

  When the value of the fuel cut flag XFC is “1”, the CPU proceeds from step S240 to step S250, sets the corrected fuel injection amount Fi to 0, and then proceeds to step S260. On the other hand, when the value of the fuel cut flag XFC is “0”, the CPU proceeds directly from step S240 to step S260. In step S260, the CPU sends an instruction signal to the fuel injection valve 31 of the fuel injection cylinder so that the fuel of the corrected fuel injection amount Fi currently calculated is injected into the fuel injection cylinder.

  As described above, when the fuel cut flag XFC is “0”, the fuel of the corrected fuel injection amount Fi obtained in step S230 is supplied to the engine 10, and when the fuel cut flag XFC is “1”, the fuel is supplied. Is stopped. That is, the fuel cut is executed.

  Next, the fuel increase rate calculation routine for calculating the fuel increase rate Kotp used in step S230 of the above-described fuel injection control routine will be described with reference to FIG. The CPU executes this routine every predetermined time. The fuel increase rate Kotp is set to 1.0 by the above-described initial routine.

  Hereinafter, the description will be started assuming that the current time is immediately after the start of the engine 10.

  At a predetermined timing, the CPU starts execution of the fuel increase rate Kotp calculation routine from step S300 and proceeds to step S310, and determines whether or not the current value of the fuel increase rate Kotp is 1.0. judge. According to the above assumption, since the present time is immediately after the start of the engine 10, the value of the fuel increase rate Kotp is set to 1.0 by the initial routine. Therefore, the CPU makes a “Yes” determination at step S310 to proceed to step S320.

  In step S320, the CPU determines whether the catalyst temperature Tc of the exhaust purification catalyst 43 detected by the catalyst temperature sensor 56 is equal to or higher than the reference catalyst temperature T0th. The reference catalyst temperature T0th is set to a temperature at which the catalyst temperature needs to be lowered by performing fuel increase control when the catalyst temperature Tc is equal to or higher than the reference catalyst temperature T0th. That is, in step S320, the CPU determines whether it is necessary to perform fuel increase control for avoiding catalyst overheating.

  According to the above assumption, since the current time is immediately after the engine 10 is started, the catalyst temperature Tc has not reached the reference catalyst temperature T0th, so the CPU makes a “No” determination at step S320 to proceed to step S330. After the value of the fuel increase rate Kotp is set (maintained) to 1.0, this routine is once ended. As a result, the corrected fuel injection amount Fi calculated in step S230 in FIG. 2 is set to a value that maintains the air-fuel ratio of the air-fuel mixture supplied to the engine at the stoichiometric air-fuel ratio, so-called “normal air-fuel ratio control”. Is executed.

  Next, as a result of continuing high load operation after the engine 10 has started operation, the exhaust purification catalyst 43 is exposed to high-temperature exhaust discharged from the engine main body 30, so that the catalyst temperature Tc becomes the reference catalyst temperature T0th. The description will be made on the assumption that the above has been achieved.

  In this case, when the CPU starts the routine shown in FIG. 3 from step S300 and proceeds to step S310, the CPU determines “Yes” in step S310 and proceeds to step S320. It determines with "Yes" and progresses to step S340.

  In step S340, as shown in the block, the CPU calculates and sets the value of the fuel increase rate Kotp based on the deviation (Tc−T0th) between the catalyst temperature Tc and the reference catalyst temperature T0th. The value of the fuel increase rate Kotp is determined so as to gradually increase in the range of 1.0 or more as the deviation (Tc−T0th) increases. That is, when the deviation (Tc−T0th) is not “0”, the fuel increase rate Kotp> 1.0 is set. Thus, when the fuel increase rate Kotp is set to a value larger than 1.0, the corrected fuel injection amount Fi calculated in step S230 of FIG. 2 is the air-fuel ratio of the air-fuel mixture supplied to the engine. Is a value that controls the air-fuel ratio richer than the stoichiometric air-fuel ratio (rich air-fuel ratio). That is, fuel increase control is executed. Thereafter, the CPU once ends this routine. When the CPU sets the fuel increase rate Kotp to a predetermined value larger than 1.0, the CPU stores the value in the RAM until the next time the fuel increase rate Kotp is set to another predetermined value larger than 1.0. It is to be held (stored).

  After this point, when the CPU starts this routine again from step S300, the CPU proceeds to step S310. At this time, since the current value of the fuel increase rate Kotp is larger than 1.0, the CPU makes a “No” determination at step S310 to proceed to step S350.

  In step S350, the CPU determines whether or not a fixed time (fuel increase control execution time) has elapsed since the start of fuel increase control. Since the engine 10 is immediately after the start of the fuel increase control, the predetermined time has not elapsed since the start of the fuel increase control. Therefore, the CPU determines “No” in this step S350 and is currently set. This routine is terminated once while maintaining the value of the fuel increase rate Kotp. Accordingly, the CPU executes the fuel increase control using the currently set value of the fuel increase rate Kotp until a predetermined time has elapsed after the start of the fuel increase control.

  When the CPU executes this routine immediately after a predetermined time has elapsed since the start of the fuel increase control, the CPU makes a “Yes” determination at step S350 following step S310, proceeds to step S330, and sets the value of the fuel increase rate Kotp. Is set to 1.0, and then this routine is terminated. Accordingly, the execution of the fuel increase control is stopped.

  As described above, when the catalyst temperature Tc becomes higher than the reference catalyst temperature T0th, the fuel increase rate Kotp is set to a value larger than 1.0 for a certain time, and the fuel increase control is executed.

  Next, each routine for setting the value of the fuel cut flag XFC referred to in step S240 of the above-described fuel injection control routine of FIG. 2 will be described. The value of the fuel cut flag XFC is set by the CPU executing the fuel cut condition determination routine shown in FIG. 4 and the fuel cut prohibition determination routine shown in FIG. The fuel cut condition determination routine and the fuel cut prohibition determination routine are executed continuously, and are executed in order of the fuel cut condition determination routine and the fuel cut prohibition determination routine every predetermined time.

  Hereinafter, the operation of the CPU by these routines will be described assuming that the current time is immediately after the start of the engine 10. Note that the value of the fuel cut flag XFC and the value of a fuel cut preparation flag XFCK, which will be described later, are set to “0” by the above-described initial routine.

  When starting the “fuel cut condition determination routine” from step S400 at a predetermined timing, the CPU proceeds to step S410 to determine whether or not the value of the fuel cut flag XFC is “0”. According to the assumption, since the current time is immediately after the engine 10 is started, the value of the fuel cut flag XFC is set to “0”. Therefore, the CPU makes a “Yes” determination at step S410 to proceed to step S420.

  In step S420, the CPU detects that the rotation speed NE of the engine 10 detected by the engine rotation speed sensor 54 exceeds a predetermined rotation speed (fuel cut start rotation speed) α and is detected by the throttle valve opening sensor 53. It is determined whether the throttle valve opening degree TA is equal to or less than a predetermined throttle valve opening degree β (for example, “0”, that is, the throttle valve fully closed opening degree). In other words, the CPU determines in step S420 whether or not the operating state of the engine 10 has become a deceleration state that satisfies the fuel cut condition. According to the above assumption, since the current time is immediately after the engine 10 is started, the rotational speed NE is not so high as to exceed the predetermined rotational speed α. The routine is temporarily terminated.

  Following the fuel cut condition determination routine, the CPU executes a fuel cut prohibition determination routine of FIG. The CPU starts the execution of this fuel cut prohibition determination routine from step S500, proceeds to step S510, and determines whether or not the value of the fuel cut preparation flag XFCK is “1”. According to the above assumption, since the value of the fuel cut preparation flag XFCK remains set to “0” by the initial routine, the CPU makes a “No” determination at step S510 to end the present routine tentatively. The above process is repeatedly executed until the determination in step S420 of FIG. 4 is “Yes”.

  Next, when the engine 10 is continuously operated, the catalyst temperature Tc becomes equal to or higher than the reference catalyst temperature T0th, and the fuel increase rate Kotp is set to a value larger than 1.0 (that is, the fuel increase control is executed). Thereafter, it is assumed that the throttle valve opening TA is changed to a predetermined throttle valve opening β or less in a state where the engine rotation speed NE exceeds the predetermined rotation speed α.

  In this case, when starting execution of the fuel cut condition determination routine from step S400, the CPU determines “Yes” in step S410 and proceeds to step S420.

  According to the above assumption, the engine rotational speed NE exceeds the predetermined rotational speed α, and the throttle valve opening TA is equal to or smaller than the predetermined throttle valve opening β. Therefore, the CPU makes a “Yes” determination at step S420 to proceed to step S430, sets the value of the fuel cut preparation flag XFCK to “1”, and then ends this routine once. The fuel cut preparation flag XFCK indicates that an initial determination condition (fuel cut start condition) for executing the fuel cut is satisfied when the value is “1”, and the value is “0”. It indicates that the initial judgment condition is not satisfied at a certain time.

  Next, when starting the fuel cut prohibition determination routine of FIG. 5 from step S500, the CPU determines “Yes” in step S510 because the value of the fuel cut preparation flag XFCK is “1” in step S510. Then, the process proceeds to step S520.

  In step S520, the CPU acquires the value of “immediate fuel increase rate Kotp”. “The previous fuel increase rate Kotp is the fuel increase rate Kotp during the fuel increase control executed at the timing closest to the present time. As described above, this value is held in the RAM. Hereinafter, the fuel increase control executed at the timing closest to the current time is also referred to as “previous fuel increase control”.

  Next, the CPU proceeds to step S530, acquires the elapsed time ta after the engine 10 has finished the previous fuel increase control (elapsed time after completion of increase), and then proceeds to step S540.

  After acquiring the catalyst temperature Tc detected by the catalyst temperature sensor 56 in step S540, the CPU proceeds to step S550.

  In step S550, the CPU calculates a reference threshold temperature Tcat1s. The reference threshold temperature Tcat1s is a map (a graph shown in a block adjacent to step S550 in FIG. 5) representing a “relationship between the reference threshold temperature Tcat1s and the fuel increase rate Kotp” stored in the ROM of the electric control device 51 in advance. ) Is calculated by applying the fuel increase rate Kotp acquired in step S520. According to this map, it is determined that the reference threshold temperature Tcat1s decreases as the fuel increase rate Kotp increases. The value A in the graph is a threshold temperature when the fuel increase rate Kotp is 1.0. In other words, the value A indicates that the normal air-fuel ratio control has been executed when the fuel increase control has not been executed once after the start of the engine 10 or when the normal air-fuel ratio control has been executed for a sufficiently long time from the previous fuel increase control. The threshold temperature in the case.

Next, the CPU proceeds to step S560, and calculates the threshold temperature Tcat1 by substituting the elapsed time ta acquired in step S530 and the reference threshold temperature Tcat1s acquired in step S550 into the following equation (1). To do. In this equation (1), “tb” is a value representing a predetermined time immediately after the end of the fuel increase control, which is determined in advance by experiments or the like, and is the reduction supplied to the exhaust purification catalyst 43 by the fuel increase control. This is the time until all of the agent is consumed by the normal air-fuel ratio control after the fuel increase control. The time ta is limited so as not to exceed the time tb.

  According to the equation (1), the threshold temperature Tcat1 gradually approaches the value A from the “reference threshold temperature Tcat1s obtained in step S550” as the elapsed time ta after the end of the increase becomes longer (closer to the time tb). (Increases gradually).

  After calculating the threshold temperature Tcat1 in step S560, the CPU proceeds to step S570 and determines whether or not the catalyst temperature Tc acquired in step S540 is lower than the calculated threshold temperature Tcat1.

  Here, when the catalyst temperature Tc is lower than the threshold temperature Tcat1, it can be determined that the catalyst temperature does not become excessively high even if the fuel cut is executed (the catalyst does not deteriorate). Therefore, when the catalyst temperature Tc is lower than the threshold temperature Tcat1, the CPU makes a “Yes” determination at step S560 to proceed to step S580, and sets the value of the fuel cut flag XFC to “1”. Thereafter, the CPU proceeds to step S590, sets the fuel cut preparation flag XFCK to “0”, and then ends this routine once. As a result, the CPU performs fuel cut (see step S240 and step S250 in FIG. 2).

  On the other hand, if the catalyst temperature Tc is equal to or higher than the threshold temperature Tcat1 at the time of determination in step S570, the CPU makes a “No” determination in step S560 to directly proceed to step S590 to set the fuel cut preparation flag XFCK to “ After setting to “0”, this routine is temporarily terminated. As a result, even when the operating state of the engine 10 is a deceleration state including the fuel cut condition and the value of the fuel cut preparation flag XFCK is set to “1”, the value of the fuel cut flag XFC is “1”. It is not changed to. That is, execution of fuel cut is prohibited.

  By the way, when the fuel cut flag XFC is set to “1” in step S580 of FIG. 5, when the CPU starts the fuel cut condition determination routine of FIG. 4 again from step S400 after this time, the CPU proceeds to step S410. If “No” is determined, the process proceeds to step S440.

  In step S440, the CPU determines whether the rotational speed NE detected by the engine rotational speed sensor 54 is equal to or lower than the return rotational speed (α−α1) or the throttle valve opening degree detected by the throttle valve opening degree sensor 53. It is determined whether TA exceeds a predetermined throttle valve opening β. That is, in step S440, the CPU determines whether or not a fuel cut end condition is satisfied.

  If the CPU makes a “No” determination at step S440, the CPU ends the routine as it is. In this case, the value of the fuel cut flag XFC is maintained at “1”, and the fuel cut control is continued.

  While the fuel cut flag XFC is set to “1” (while fuel cut control is being executed), the CPU does not proceed to step S430. Accordingly, the fuel cut preparation flag XFCK remains set to “0”. Therefore, when the CPU executes the fuel cut prohibition determination routine of FIG. 5, the CPU determines “No” in step S510 and immediately ends the routine.

  On the other hand, if the CPU determines “Yes” in step S440 in FIG. 4, the CPU proceeds to step S450, sets the value of the fuel cut flag XFC to “0”, and then ends this routine. Accordingly, in this case, the fuel cut control ends. As a result, the CPU proceeds from step S410 in FIG. 4 to step S420, and again monitors whether or not the fuel cut start condition is satisfied in step S420.

  If it is determined “No” in step S570 of FIG. 5, the value of the fuel cut flag XFC is maintained at “0”, and the value of the fuel cut preparation flag XFCK is set to “0”. Thereby, the CPU executes the processes of step S410 and step S420 of FIG. Therefore, if the fuel cut start condition continues to be satisfied, the value of the fuel cut flag is set to “1” again in step S410, so that the processing from step S510 to step S570 in FIG. 5 is executed.

  In this way, in the fuel injection control routine described above, the CPU sets the fuel increase rate Kotp calculated by executing the fuel increase rate calculation routine, the fuel cut condition determination routine, and the fuel cut prohibition determination routine described above. The fuel injection control is performed by using the value of the fuel cut flag XFC. Specifically, when the value of the fuel cut flag XFC is set to “1”, the CPU performs fuel cut, while when the value of the fuel cut flag XFC is set to “0”, Without performing the fuel cut, the normal air-fuel ratio control or the fuel increase control is performed according to the value set in the fuel increase rate Kotp.

(Second Embodiment)
Hereinafter, a second embodiment of a fuel supply control apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings.

  In the first embodiment, when the fuel cut start condition is satisfied, if the catalyst temperature Tc is higher than the threshold temperature Tcat1, execution of fuel cut is prohibited. However, even when the fuel cut is executed when the fuel cut start condition is satisfied and the catalyst temperature Tc at that time is higher than the threshold temperature Tcat1, the operating state of the engine 10 and / or the vehicle on which the engine 10 is mounted. Depending on the case, the catalyst temperature may not reach the superheat temperature.

  More specifically, the catalyst temperature Tc may change as shown in the time chart of FIG. 6, for example. In the example shown in FIG. 6, when the fuel increase control is executed before time t1, and the fuel cut start condition (the condition shown in step S420 described above) is satisfied and the fuel cut is executed at time t1. The change of the catalyst temperature Tc is shown. A broken curve C1 indicates the catalyst temperature Tc when the speed (vehicle speed) of the vehicle on which the engine 10 is mounted is equal to or higher than a predetermined vehicle speed, and a solid curve C2 indicates the catalyst temperature Tc when the vehicle speed is lower than the predetermined vehicle speed.

  In this example, the catalyst temperature Tc at time t1 is higher than the threshold temperature Tcat1. Here, when the fuel cut is executed after time t1, the catalyst temperature Tc rises. However, as shown by the curve C1, when the vehicle speed is equal to or higher than the predetermined vehicle speed, the exhaust purification catalyst 43 is efficiently cooled by the traveling wind, so the catalyst temperature Tc does not reach the overheat temperature. On the other hand, as shown by the curve C2, when the vehicle speed is less than the predetermined vehicle speed, the exhaust purification catalyst 43 is not efficiently cooled by the traveling wind, so the catalyst temperature Tc reaches the superheated temperature.

  Therefore, the fuel supply control device according to the second embodiment determines whether or not to perform the fuel cut using the threshold temperature Tcat1 and another threshold temperature Tcat2 set higher than the threshold temperature Tcat1. . Thereby, prohibition of useless fuel cut is avoided. In the following, the threshold temperature Tcat1 is referred to as “first threshold temperature Tcat1”, and the threshold temperature Tcat2 is referred to as “second threshold temperature Tcat2”.

  In the second embodiment according to the present invention, instead of the fuel cut prohibition determination routine in the first embodiment shown in FIG. 5, the period between “A” and “B” in the flowchart of FIG. 5 is shown in FIG. This is different from the first embodiment only in that a routine replaced with each step is executed. Therefore, hereinafter, the CPU will be described as being the time when the processing up to step S560 is completed after the execution of the fuel cut prohibition determination routine is started.

  In step S570, the CPU determines whether the catalyst temperature Tc detected by the catalyst temperature sensor 56 is lower than the first threshold temperature Tcat1 calculated in step S560. When the catalyst temperature Tc is lower than the first threshold temperature Tcat1, the CPU makes a “Yes” determination at step S570 to proceed to step S580. Thereafter, in step S580, the CPU sets the value of the fuel cut flag XFC to “1”, proceeds to step S590, sets the value of the fuel cut preparation flag to “0”, and then ends this routine once. To do. Therefore, in this case, the fuel cut is executed.

  On the other hand, when the catalyst temperature Tc is equal to or higher than the first threshold temperature Tcat1, the CPU makes a “No” determination at step S570 to proceed to step S710 to calculate the second reference threshold temperature Tcat2s. The second reference threshold temperature Tcat2s is a map (represented in a block adjacent to step S710 in FIG. 7) representing a “relationship between the reference threshold temperature Tcat2s and the fuel increase rate Kotp” previously stored in the ROM of the electric control device 51. 5), the fuel increase rate Kotp obtained in step S520 of FIG. 5 is applied.

  The second reference threshold temperature Tcat2s is higher than the first reference threshold temperature Tcat1s. Further, if the catalyst temperature Tc is lower than the second reference threshold temperature Tcat2s, the second reference threshold temperature Tcat2s is determined to be the fuel temperature even if the fuel cut is performed depending on the operating state of the engine 10 and / or the vehicle. It is a temperature that may not exceed the overheating temperature during cutting. The second reference threshold temperature Tcat2s is set so as to show the same tendency as the first reference threshold temperature Tcat1s with respect to the fuel increase rate Kotp. The value B in the graph is the second threshold temperature when the fuel increase rate Kotp is 1.0. In other words, the value B indicates that the normal air-fuel ratio control has been executed when the fuel increase control has not been executed once after the start of the engine 10 or when the normal air-fuel ratio control has been executed for a sufficiently long time from the previous fuel increase control. The second threshold temperature.

Next, the CPU proceeds to step S720, and calculates the second threshold temperature Tcat2s from the following equation (2) similar to the above equation (1).

  Next, the CPU proceeds to step S730 and determines whether or not the catalyst temperature Tc is lower than the second threshold temperature Tcat2 acquired in step S710. When the catalyst temperature Tc is equal to or higher than the second threshold temperature Tcat2, the CPU makes a “No” determination at step S730 to proceed to step S590, and sets the value of the fuel cut preparation flag XFCK to “0”. This routine is terminated. Therefore, in this case, fuel cut is prohibited. On the other hand, when the catalyst temperature Tc is lower than the second threshold temperature Tcat2, the CPU makes a “Yes” determination at step S730 to proceed to step S740.

  In step S740, the CPU determines whether or not the vehicle speed is equal to or higher than a reference vehicle speed based on a signal from a “vehicle speed sensor that detects the speed of the vehicle on which the engine 10 is mounted” (not shown) (that is, high vehicle speed operation). Whether or not).

  If the vehicle is operated at a high vehicle speed, the exhaust purification catalyst 43 is efficiently cooled by the traveling wind. Therefore, if the vehicle speed is equal to or higher than the reference vehicle speed, the CPU makes a “Yes” determination at step S740 to proceed to step S580. Then, after setting the value of the fuel cut flag XFC to “1” in step S580, the CPU proceeds to step S590, sets the value of the fuel cut preparation flag XFCK to “0”, and ends this routine. On the other hand, if the CPU makes a “No” determination in step S740, it proceeds directly to step S590, sets the value of the fuel cut preparation flag XFCK to “0”, and ends this routine.

  As described above, in the second embodiment, when the catalyst temperature Tc is equal to or higher than the first threshold temperature Tcat1 and lower than the second threshold temperature Tcat2, the fuel cut is performed at high vehicle speed operation. Further, when the catalyst temperature Tc is equal to or higher than the first threshold temperature Tcat1 and lower than the second threshold temperature Tcat2, the fuel cut is not performed, and when the catalyst temperature Tc is equal to or higher than the second threshold temperature Tcat2. Is prohibited. Thereby, prohibition of useless fuel cut is avoided.

  The conditions used in step 740 are “other conditions for determining whether or not the exhaust purification catalyst 43 is in an efficiently cooled state (for example, the shift position of the transmission of the vehicle is in a high speed stage, etc. ) ".

As described above, the fuel supply control device for an internal combustion engine according to each embodiment of the present invention includes:
An exhaust purification catalyst (43) disposed in the exhaust passage (42) of the internal combustion engine and having oxidation ability;
Fuel increase control for supplying fuel to the engine so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes a rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio, and mixing supplied to the engine One of the normal air-fuel ratio control for supplying fuel to the engine so that the air-fuel ratio of the air becomes an air-fuel ratio other than the rich air-fuel ratio (selectively according to the operating state of the engine) is executed. Fuel supply means (routines of FIGS. 2 and 3);
Fuel cut means (routine in FIG. 4 and steps S240 and s250 in FIG. 2) for stopping the supply of fuel to the engine when the operating state of the engine is in a deceleration state that satisfies a predetermined fuel cut condition;
A fuel supply control device for an internal combustion engine comprising:
When the operating state of the engine is in a deceleration state that satisfies the fuel cut condition (when determined “Yes” in step S420 in FIG. 4), the temperature (Tc) of the exhaust purification catalyst is the fuel supply means. When the fuel cut means has a temperature equal to or higher than a threshold temperature (Tcat1) determined based on the amount of reducing agent supplied to the exhaust purification catalyst during the fuel increase control according to (for example, an amount proportional to the fuel increase rate Kotp). Fuel cut prohibiting means (routine of FIG. 5) for prohibiting the operation is provided.

  That is, according to the present fuel supply control device, when the engine operating state is in a deceleration state that satisfies the fuel cut condition (that is, when the value of the fuel cut flag preparation XFCK is set to “1”), The catalyst temperature Tc of the exhaust purification catalyst is “supplied based on the amount of reducing agent (unburned fuel such as HC) supplied to the exhaust purification catalyst during fuel increase control executed before that (fuel increase rate Kotp). When the temperature is equal to or higher than a threshold temperature (Tcat1) determined on the basis of the amount of excess reducing agent), the fuel cut by the fuel cut means is prohibited.

  As a result, according to the present apparatus, it is possible to prevent the catalyst temperature from exceeding the overheating temperature while the fuel cut is being performed, and thus it is possible to suppress the exhaust purification catalyst from being deteriorated due to overheating. it can. Further, according to the present apparatus, when the catalyst temperature does not exceed the overheating temperature by performing the fuel cut, the fuel cut is performed, so that the fuel consumption can be reduced.

  In each of the embodiments according to the present invention, the catalyst temperature Tc is detected by the catalyst temperature sensor 54. However, by providing an exhaust temperature sensor in the exhaust pipe 42 upstream or downstream of the exhaust purification catalyst 43, exhaust purification is achieved. The catalyst temperature Tc may be estimated by detecting the temperature of the exhaust gas flowing into the catalyst 43 or flowing out from the exhaust gas purification catalyst 43.

  Further, in each of the above embodiments, the fuel increase control is performed for a certain period of time based on the fuel increase rate Kotp calculated when the catalyst temperature Tc is equal to or higher than the reference catalyst temperature T0th. Therefore, in this case, since the “amount of reducing agent supplied to the exhaust purification catalyst 43” changes only in accordance with the fuel increase rate Kotp, as shown in the above embodiments, it is based on the fuel increase rate Kotp. The reference threshold temperature Tcat1s may be determined.

  In addition, the fuel increase control may be executed by changing at least one of the fuel increase rate Kotp and the fuel increase control period. In this case, even if the fuel increase rate Kotp is a value that is changed based on, for example, the load of the engine 10 and the engine rotation speed (a value that increases as the load increases and increases as the rotation speed increases). Good.

  In such a case, the “amount of reducing agent supplied to the exhaust purification catalyst 43 during the period in which the fuel increase control is being performed” can be calculated from the fuel increase rate Kotp and the fuel increase control period. For example, the amount of reducing agent supplied to the exhaust purification catalyst 43 during the period in which this fuel increase control is being performed is the amount of fuel increase per unit time based on the fuel increase rate Kotp at each time point during the fuel increase period. Can be calculated by integrating this over the fuel increase period.

  On the other hand, in a mode in which the fuel increase control is executed so that the fuel increase rate Kotp is constant and the period during which the fuel increase control is performed is variable, “a value indicating the period during which the fuel increase control is performed (fuel increase control "Integrated time of period)" multiplied by the value of "Fuel increase rate Kotp during the fuel increase control" and "the integration of the reducing agent supplied to the exhaust purification catalyst 43 during the period when the fuel increase control is executed" The amount ”may be calculated, and the reference threshold temperature Tcat1s and the like may be determined based on the calculated integrated amount.

  In addition, it is assumed that the fuel increase control and the normal air-fuel ratio control are repeated a plurality of times within a relatively short period of time until the operating state of the engine 10 shifts to the deceleration state after the fuel increase control. In this case, the integration of the reducing agent (reducing agent remaining in the exhaust purification catalyst 43 as a result of supply and consumption) supplied to the exhaust purification catalyst 43 during the period when each “fuel increase control and normal air-fuel ratio control” is executed. The amount may be calculated, and the reference threshold temperature Tcat1s or the like may be determined based on the calculated integrated amount. When the calculated cumulative amount of reducing agent supplied to the exhaust purification catalyst 43 exceeds the amount of reducing agent that can be held by the exhaust purification catalyst 43 (limit holding amount), the exhaust purification catalyst 43 May determine that the amount of reducing agent corresponding to the limit holding amount is held, and determine the reference threshold temperature Tcat1s based on the limit holding amount.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 21 ... Intake pipe, 24 ... Throttle valve, 33 ... Fuel injection valve, 42 ... Exhaust pipe, 43 ... Exhaust purification catalyst, 51 ... Electric controller, 53 ... Throttle valve opening sensor, 54 ... Engine rotation Speed sensor 56 ... Catalyst temperature sensor.

Claims (1)

An exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine and having an oxidizing ability;
Fuel increase control for supplying fuel to the engine so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes a rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio, and mixing supplied to the engine Fuel supply means for performing any one of normal air-fuel ratio control for supplying fuel to the engine so that the air-fuel ratio of the air becomes an air-fuel ratio other than the rich air-fuel ratio;
Fuel cut means for stopping the supply of fuel to the engine when the operating state of the engine is in a deceleration state satisfying a predetermined fuel cut condition;
A fuel supply control device for an internal combustion engine comprising:
When the operating state of the engine is in a deceleration state that satisfies the fuel cut condition,
The temperature of the exhaust purification catalyst is set to be lower as the amount of reducing agent supplied to the exhaust purification catalyst during the fuel increase control by the fuel supply means is larger, and the deceleration is performed immediately after the fuel increase control is terminated. The first threshold temperature is set higher as the period until the state becomes longer , and is higher than the first threshold temperature , and is supplied to the exhaust purification catalyst during the fuel increase control. The internal combustion engine is set lower as the amount of the reducing agent is lower and lower than the second threshold temperature set higher as the period from immediately after completion of the fuel increase control to the deceleration state becomes longer. If the speed of the vehicle on which the vehicle is mounted is equal to or higher than a predetermined reference vehicle speed, the fuel cut means is operated,
If the temperature of the exhaust purification catalyst is equal to or higher than the first threshold temperature, lower than the second threshold temperature, and the speed is lower than the reference vehicle speed, the operation of the fuel cut means is prohibited.
If the temperature of the exhaust purification catalyst is equal to or higher than the second threshold temperature, the operation of the fuel cut means is prohibited.
Fuel cut prohibition means,
A fuel supply control device comprising:

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