JP2015135070A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine control device for suppressing an increase in the concentration of NOx in exhaust gas during restoration from a fuel-cut state to actualize early recovery of the purifying performance of a catalyst, while suppressing an increase in the concentration of CO and HC in the exhaust gas.SOLUTION: An engine control device 140 includes air amount acquiring means 142 for acquiring the amount of intake air into an engine 100, and injection control means 144 for setting an injection pulse width not to fall below a first lower limit guard value on the basis of the acquired amount of intake air. The injection control means sets the injection pulse width to be a second lower limit guard value greater than the first lower limit guard value for a predetermined period from starting of the supply of fuel into the engine after fuel-cut.

Description

  The present invention relates to an engine control apparatus that performs fuel cut control.

  Conventionally, in order to improve the fuel consumption of a vehicle, so-called fuel cut is performed in which the fuel supply to the cylinder of the engine is stopped when the accelerator is turned off while the engine is at a certain rotational speed or higher. In the fuel cut state, combustion is not performed in the cylinder, and the intake air to the engine is directly discharged from the exhaust passage.

  A catalyst such as a three-way catalyst that purifies substances to be purified such as NOx, CO, and HC (hydrocarbon) in the exhaust gas is arranged in the exhaust passage, and fuel cut is performed to suck in from the exhaust passage. If the air is discharged as it is and the oxygen concentration in the exhaust flow path increases, oxygen is excessively stored in the catalyst, and the NOx purification performance of the catalyst decreases. In view of this, a configuration has been proposed in which an amount of fuel sufficient to make the air-fuel ratio (air mass / fuel mass) rich when returning from the fuel cut state (during recovery) is proposed (for example, Patent Document 1). When the fuel becomes rich, the oxygen stored in the catalyst is released, and the purification performance of the catalyst is restored.

  Also, a control process for determining the time during which the air-fuel ratio is maintained in a rich state and the control amount to the rich side of the air-fuel ratio based on the intake air amount to the engine after returning from the fuel cut state is disclosed. (For example, Patent Documents 2 and 3).

JP 2008-19729 A JP 2006-118433 A Japanese Patent Laid-Open No. 2005-69188

  As described above, during the recovery, the NOx purification performance of the catalyst in the exhaust passage can be recovered by temporarily increasing the fuel supply amount based on the intake air amount to the engine. However, for example, when the accelerator is turned on to return from the fuel cut state, if the throttle opening increases and the amount of intake air into the engine increases rapidly, the amount of intake air is increased due to structural factors of the air amount sensor. This causes a delay in response. Therefore, when the ECU derives the intake air amount based on the detection value of the air amount sensor, it may be estimated to be lower than the actual intake air amount. As a result, an increase in fuel is suppressed, and recovery of the NOx purification performance of the catalyst is delayed.

  In addition, when a response delay of the intake air amount occurs, after the NOx purification performance of the catalyst recovers, the fuel injection amount increases with a delay, and the CO and HC purification by the catalyst cannot catch up, and the CO in the exhaust gas, There is a risk that the concentration of HC will increase.

  In view of such a problem, the present invention suppresses an increase in the NOx concentration in the exhaust gas by early recovery of the purification performance of the catalyst when returning from the fuel cut state, and at the same time, CO and HC in the exhaust gas An object of the present invention is to provide an engine control device capable of suppressing an increase in the concentration of the gas.

  In order to solve the above problems, an engine control device of the present invention includes a catalyst for purifying exhaust gas provided in an exhaust system of an engine, an air amount acquisition means for acquiring an intake air amount of air sucked into the engine, During steady operation of the engine, an injection control means for setting the injection pulse width of the fuel injection valve based on the intake air amount so as not to fall below the first lower limit guard value, and temporary fuel injection at the time of engine fuel cut recovery A fuel increase correction means for increasing the amount and reducing the oxygen storage amount of the catalyst, and the injection control means sets a lower limit value of the injection pulse width for a predetermined period from the start of fuel increase by the fuel increase correction means. The second lower limit guard value is set to be larger than the first lower limit guard value.

  The second lower limit guard value may be updated according to the fuel pressure.

  The predetermined period may be a period until the injection pulse width before the correction by the second lower limit guard value is equal to or greater than the second lower limit guard value.

  The second lower limit guard value may converge to the first lower limit guard value by predetermined attenuation control after the elapse of a predetermined period.

  According to the present invention, when returning from the fuel cut state, the purification performance of the catalyst is recovered at an early stage to suppress an increase in the concentration of NOx in the exhaust gas, and an increase in the concentration of CO and HC in the exhaust gas is suppressed. It becomes possible.

It is a figure which shows the schematic structure of the intake / exhaust system of an engine. It is a flowchart explaining the flow of the determination process of the injection pulse width. It is explanatory drawing for demonstrating the increase process of the fuel injection quantity in a comparative example. It is the flowchart explaining the flow of the determination process of a guard value. It is explanatory drawing for demonstrating the increase process of the fuel injection quantity in this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a diagram showing a schematic configuration of an intake / exhaust system of engine 100. As shown in FIG. 1, in the engine 100, a cylinder head 106 is positioned on the top dead center side of the piston 104 in the cylinder 102, and fuel is generated in a combustion chamber 108 formed between the cylinder head 106 and the piston 104. As a result of combustion, the piston 104 reciprocates in the cylinder 102.

  An intake port 110 is formed in the cylinder head 106, and an intake manifold 112 communicates with the intake port 110. The engine 100 is composed of multiple cylinders, and an intake manifold 112 that communicates with each cylinder 102 is coupled to communicate with an air chamber 114.

  An intake pipe 116 communicates with the air chamber 114, and the intake air flowing into the intake pipe 116 is guided to the combustion chamber 108 via the air chamber 114 and the intake manifold 112. The intake valve 118 is configured to be able to open and close the intake port 110, and the intake amount (intake air amount) and intake timing of the intake air into the combustion chamber 108 are controlled by the opening and closing timing of the intake valve 118.

  The intake manifold 112 is provided with an injector 120 (fuel injection valve) for injecting fuel, and the cylinder head 106 is provided with a spark plug 122 having a tip directed toward the combustion chamber 108 side. The fuel is combusted in the combustion chamber 108 by controlling the injector 120 and the spark plug 122 by an engine control device 140 described later.

  The air amount sensor 124 is constituted by a thermal air amount meter, for example, and is provided in an air cleaner (not shown) disposed in the intake pipe 116, detects the amount of intake air flowing into the cylinder 102 of the engine 100, and takes in the intake air. A signal indicating the quantity is output to the engine control device 140.

  An exhaust port 126 is formed in the cylinder head 106, and an exhaust manifold 128 communicates with the exhaust port 126. The exhaust valve 130 is configured to be able to open and close the exhaust port 126, and the exhaust amount and exhaust timing of the exhaust gas from the combustion chamber 108 are controlled by the opening and closing timing of the exhaust valve 130.

  As described above, the engine 100 is composed of a plurality of cylinders, and the exhaust manifolds 128 communicating with the respective cylinders 102 are connected to collect the exhaust gas, and then led to the exhaust pipe 132 (exhaust flow path). It is burned. The exhaust pipe 132 is provided with a catalyst 134 composed of a three-way catalyst or the like that purifies a substance to be purified such as NOx, CO, and HC in the exhaust gas, and the exhaust gas is purified by the catalyst 134.

  The engine control device 140 is composed of a semiconductor integrated circuit including a central processing unit (CPU), a ROM storing programs, a RAM as a work area, and the like, and controls the entire engine 100.

  The engine control device 140 also functions as an air amount acquisition unit 142 (air amount acquisition unit) and an injection control unit 144 (injection control unit, fuel increase correction unit). The air amount acquisition unit 142 derives (acquires) the intake air amount into the combustion chamber 108 of the engine 100 based on the signal output from the air amount sensor 124. Since the intake air amount changes depending on the load of the engine 100, the load of the engine 100 can be estimated from the intake air amount.

  The injection control unit 144 controls the injection period (injection pulse width) for each fuel injection from the injector 120 based on the intake air amount. Here, since the fuel injection amount per unit time (that is, the fuel injection pressure) is fixed at a predetermined value, the fuel injection amount is controlled by the injection pulse width. Therefore, the injection pulse width corresponds to the fuel injection amount.

  FIG. 2 is a flowchart illustrating the flow of the injection pulse width determination process. As shown in FIG. 2, the air amount acquisition unit 142 derives the intake air amount based on the signal output from the air amount sensor 124 (S300).

Then, the injection control unit 144 derives a reference value Tp (S302). The reference value Tp is a value derived in the process of deriving the fuel injection period. The reference value Tp is derived from Equation 1 below, where Q is the amount of intake air, NE is the engine speed, and k is a constant.
Tp = k × Q / NE (Formula 1)

Then, the injection control unit 144 derives a correction term COEF (S304). The engine 100 performs fuel cut to stop fuel injection when a predetermined condition is satisfied in order to improve vehicle fuel efficiency. The correction term COEF is derived from Equation 2 below, where KFCR is an increase value indicating the amount of fuel increase after fuel cut recovery.
COEF = (1 + ... + KFCR + ...) (Formula 2)

The injection control unit 144 temporarily corrects the fuel injection amount by the fuel increase value KFCR when the engine 100 returns to the fuel cut state, and reduces the oxygen storage amount of the catalyst 134. Subsequently, the injection control unit 144 derives a pre-guard value TICFXL (S306). The pre-guard value TICFXL is derived from Equation 3 below, where TSDI is an invalid injection width (period) in which fuel is not substantially injected.
TICFXL = Tp × COEF + TSDI (Equation 3)

  Subsequently, the injection control unit 144 determines whether or not the derived pre-guard value TICFXL is larger than the final guard value (S308). The final guard value is a guard value that is a lower limit value of the injection pulse width, and is determined by a guard value determination process described later.

  When the pre-guard value TICFXL is larger than the final guard value (YES in S308), the pre-guard value TICFXL is set as the injection pulse width (S310). If the pre-guard value TICFXL is equal to or smaller than the final guard value (NO in S308), the final guard value is set as the injection pulse width (S312).

  And the injection control part 144 determines whether it is a fuel cut state (S314). If it is not in the fuel cut state (NO in S314), the injection pulse width determination process is terminated as it is. If it is a fuel cut state (YES in S314), the injection pulse width is set to 0 (S316), and the injection pulse width determination process is terminated.

  By the way, in the fuel cut state, combustion is not performed in the cylinder 102, and the intake air to the combustion chamber 108 is discharged as it is from the exhaust passage. As a result, oxygen is occluded excessively in the catalyst 134 and the NOx purification performance deteriorates. Therefore, when returning from the fuel cut state (recovery), it is necessary to supply a large amount of fuel and release the oxygen stored in the catalyst 134 to recover the purification performance of the catalyst 134.

  The fuel injection amount is controlled by the above-described injection pulse width. As shown in Formula 1, the injection pulse width has a reference value Tp determined on the basis of the intake air amount Q. The injection control unit 144 sets an increase value KFCR with respect to the reference value Tp and sets the injection pulse. Increasing the width increases the fuel injection amount.

  However, for example, when the accelerator is turned on to return from the fuel cut state, if the intake air amount to the engine 100 increases rapidly, the detection of the air amount sensor 124 is caused by the influence of the heat mass of the air amount sensor 124, for example. The difference between the intake air amount Q based on the value and the actual intake air amount becomes large, and the intake air amount Q is estimated smaller than the actual amount. As a result, since the increase in the injection pulse width is delayed, the increase in the fuel injection amount is delayed.

  FIG. 3 is an explanatory diagram for explaining the fuel injection amount increasing process in the comparative example. As shown in FIG. 3A, for example, it is assumed that the fuel cut flag indicating the execution of fuel cut is turned off when the elapsed time is 5 seconds. At this time, as shown in FIG. 3E, the fuel injection amount is increased by setting an increase value KFCR. Here, for comparison, an example in which the increase value KFCR is set to double in the legend indicated by the alternate long and short dash line with respect to the legend indicated by the broken line is taken as an example.

  LDATA shown in FIG. 3F is an index value indicating the engine load, which is a term of Q / NE shown in Equation 1. In the experiment, the LDATA of the broken line legend and the dashed line legend are approximately the same.

  As shown in FIG. 3D, in all the legends, the injection pulse width increases from the elapsed time of 5 seconds to 7 and 8 seconds. That is, the fuel injection amount is increased. Particularly, the legend of the alternate long and short dash line in which the increase value KFCR is doubled has a larger injection pulse width than the legend of the broken line.

  As a result, as shown in FIG. 3C, the NOx concentration in the exhaust gas is smaller in the legend of the alternate long and short dash line than in the legend of the broken line, but the emission of NOx is still not fully suppressed. Absent. Moreover, as shown in FIG. 3B, the legend of the one-dot chain line becomes extremely large in the concentration of THC (TotalHC) which is unburned fuel in the exhaust gas.

  Analyzing FIG. 3 (d), the increase width of the injection pulse width is low at the point of the alternate long and short dash line at the time of 5 seconds and then gradually increases. It is estimated that due to the response delay of the intake air amount, the injection pulse width is small and the fuel injection amount is insufficient. Therefore, in the present embodiment, by adjusting the final guard value (indicated by a three-dot chain line in FIG. 3D), which is the lower limit value of the injection pulse width, from the time when the fuel cut flag is turned off. The injection pulse width is made sufficiently large to ensure the fuel injection amount. Hereinafter, the guard value determination process will be described in detail.

  FIG. 4 is a flowchart illustrating the flow of guard value determination processing. As shown in FIG. 4, the injection control unit 144 searches a table (map) set for a normal time that is not a recovery time, and specifies a guard value corresponding to the fuel supply pressure (fuel pressure) (S400). . Hereinafter, the specified guard value is referred to as a normal time lower limit guard value (first lower limit guard value).

  Subsequently, the injection control unit 144 determines whether it is during recovery and whether or not the fuel injection amount is increased, that is, whether or not it is in the recovery state (S402). If the amount has increased (YES in S402), it is determined whether or not an attenuation flag indicating the presence or absence of an attenuation process to be described later is 1 (S404). If the attenuation flag is 1 (YES in S404), the process proceeds to attenuation process S416.

  The guard value determination process branches into three routes A, B, and C by the above two determination processes S402 and S404. Hereinafter, the routes A, B, and C will be described in order.

(Route A)
If the attenuation flag is not 1 (NO in S404), has the injection control unit 144 passed a preset update time since the last time the recovery time lower limit guard value (second lower limit guard value) was updated? It is determined whether or not (S406). Here, the lower limit guard value at the time of recovery is the lower limit value of the injection pulse width applied at the time of recovery.

  If the update time has not elapsed (NO in S406), the process proceeds to guard value determination process S414. When the update time has elapsed (YES in S406), the injection control unit 144 specifies a temporary recovery time lower limit guard value corresponding to the fuel pressure from the recovery time table (S408). The recovery time table is a table set for recovery time. Referring to the recovery time table, a guard value corresponding to the engine speed and the throttle opening is specified. Hereinafter, the guard value specified by the recovery time table is referred to as a temporary recovery time lower limit guard value.

  Then, the injection control unit 144 determines whether or not the specified provisional recovery lower limit guard value is greater than the previous value of the recovery lower limit guard value (S410).

  If the temporary recovery lower limit guard value is less than or equal to the recovery lower limit guard value (NO in S410), the process proceeds to guard value determination processing S414 as it is. If the temporary recovery lower limit guard value is larger than the recovery lower limit guard value (YES in S410), the temporary recovery lower limit guard value is substituted into the recovery lower limit guard value (S412).

  In this way, the fuel cut flag is turned off by updating the recovery lower limit guard value with the temporary recovery lower limit guard value acquired from the recovery time table according to the latest fuel pressure at each update time. It becomes possible to reflect the change of the operating condition of the subsequent engine 100 to the recovery time lower limit guard value.

  Then, the injection control unit 144 determines whether or not the recovery time lower limit guard value is larger than the pre-guard value TICFXL derived by the above Equation 3 (S414). If the recovery-time lower limit guard value is larger than the pre-guard value TICFXL (YES in S414), 0 is substituted for the attenuation flag (S420), and the process proceeds to the normal-time lower limit guard value determination process S422. When the recovery time lower limit guard value is equal to or less than the pre-guard value TICFXL (NO in S414), the route B is merged.

(Route B)
The injection control unit 144 performs a guard value attenuation process (S416). In the guard value attenuation process, a process of subtracting a constant from the recovery time lower limit guard value is executed. The injection control unit 144 then assigns 1 to the attenuation flag (S418).

  Here, when the attenuation flag is set to 1, since the process proceeds to the route B in the determination process S404, the attenuation process is repeated until it is determined in the determination process S402 that the recovery state is not established. Decrease the hour lower guard value to zero.

  Thereafter, processes S422 to S426 common to the route A and the route B are performed. Specifically, the injection control unit 144 determines whether or not the recovery time lower limit guard value is larger than the normal time lower limit guard value (S422). When the recovery time lower limit guard value is equal to or lower than the normal time lower limit guard value (NO in S422), the normal time lower limit guard value is substituted for the final guard value (S424), and the guard value determination processing is terminated.

  If the recovery-time lower limit guard value is larger than the normal-time lower limit guard value (YES in S422), the recovery-time lower limit guard value is substituted for the final guard value (S426), and the guard value determination process is terminated.

(Route C)
In the increase determination process S402, when the fuel injection amount is not increased (NO in S402), 0 is substituted for the attenuation flag (S428), and the normal time lower limit guard value is substituted for the recovery time lower limit guard value (S430). ). Then, the normal lower limit guard value is substituted for the final guard value (S432), and the guard value determination process is terminated.

  According to the flowchart of FIG. 4, the process of route C is performed in the normal time that is not the recovery time, and the injection control unit 144 substitutes the normal time lower limit guard value for the final guard value (S432).

  Then, as shown in FIG. 2, if pre-guard value TICFXL exceeds the final guard value (here, the normal time lower limit guard value) (YES in S308), engine 100 is passed over the period indicated by the pre-guard value. If fuel is injected and the injection pulse width is the normal time lower limit guard value (NO in S308), the fuel is injected into engine 100 over the period indicated by the normal time lower limit guard value.

  That is, the injection control unit 144 sets the injection pulse width of the injector 120 so that it does not fall below the normal time lower limit guard value during steady operation of the engine 100.

  Further, when recovering, if the fuel injection amount is increasing and the guard value attenuation process has not started, the process of route A is performed. As a result, when the recovery time lower limit guard value is larger than the guard previous value or the normal time lower limit guard value, the recovery time lower limit guard value becomes the final guard value.

  That is, the injection control unit 144 sets the lower limit guard value at the time of recovery larger than the lower limit guard value at normal time as the lower limit value of the injection pulse width for a predetermined period from the start of fuel increase.

  Here, the injection pulse width before correction by the lower limit guard value at the recovery time, that is, the pre-guard value TICFXL becomes equal to or greater than the lower limit guard value at the recovery time until the attenuation process is started for the predetermined period. It is a period.

  Then, after the predetermined period has elapsed (after the pre-guard value exceeds the recovery time lower limit guard value), once the attenuation process is started, the attenuation process of the route B is repeated thereafter. As a result, when the recovery-time lower limit guard value is smaller than the normal-time lower limit guard value, the normal-time lower limit guard value becomes the final guard value. As described above, the second lower limit guard value converges to the first lower limit guard value by the predetermined attenuation control after the elapse of the predetermined period.

  FIG. 5 is an explanatory diagram for explaining the fuel injection amount increasing process in the present embodiment. In FIG. 5, the legend indicated by the two-dot chain line is obtained by performing the guard value determination process shown in FIG. 4, and the other legends (the legend indicated by the broken line and the legend indicated by the one-dot chain line) are shown in FIG. The normal lower limit guard value is the guard value.

  As shown in FIG. 5E, the fuel injection amount is increased by setting the increase value KFCR. Here, for comparison, an example in which the increase value KFCR is set to double in the legend indicated by the alternate long and short dash line with respect to the legend indicated by the alternate long and two short dashes line and the legend indicated by the broken line.

  In FIG.5 (d), the part of the circle A is extracted and shown in the enlarged partial view B. In FIG. 5D, a three-dot chain line indicates the final guard value. As the final guard value, immediately after the fuel cut flag is turned off as a result of the processing of the route A described above, a recovery lower limit guard value larger than the normal lower limit guard value is substituted.

  As described above, in the fuel cut state, the injection control unit 144 sets the injection pulse width to the recovery-time lower limit guard value that is larger than the normal-time lower limit guard value from the start of fuel supply to the engine 100.

  As a result, as shown in the partially enlarged view B, the legend indicated by the two-dot chain line indicates that the injection pulse width is the final guard value immediately after the fuel cut flag is turned off, and the legend and the one-dot chain line indicated by the broken line. It is larger than the legend shown in.

  In this way, by increasing the final guard value, the delay of the rising part of the increase in the injection pulse width due to the response delay of the intake air amount is avoided, and the behavior close to that when there is no response delay of the intake air amount is realized. Yes. As a result, as shown in FIG. 5C, the NOx concentration in the exhaust gas is smaller in the two-dot chain line with a larger guard value than in the legend of the broken line or the one-dot chain line.

  Further, since the legend indicated by the two-dot chain line is half the legend indicated by the one-dot chain line for the increase value KFCR, the maximum value of the injection pulse width is not as great as the legend indicated by the one-dot chain line. Therefore, as shown in FIG. 5 (b), the THC concentration in the exhaust gas is suppressed without extremely increasing the legend indicated by the alternate long and two short dashes line like the legend of the alternate long and short dash line.

  As described above, the engine control device 140 according to the present embodiment can suppress the increase in the NOx concentration in the exhaust gas by forcibly increasing the fuel injection amount and recovering the performance of the catalyst 134 early during recovery. it can. At the same time, it is possible to suppress an increase in the concentration of CO and HC in the exhaust gas.

  The final guard value starts to attenuate by the processing of the route B from the timing when the broken line legend exceeds the legend of the two-dot chain line, and finally converges to the normal time lower limit guard value. That is, the injection control unit 144 continues the process of setting the lower limit value of the injection pulse width as the recovery-time lower limit guard value as cut recovery control until the legend of the broken line exceeds the legend of the two-dot chain line.

  Here, in the legend of the two-dot chain line, the lower limit guard value at the time of recovery is not set, and the pre-guard value is used as the injection pulse width. That is, the injection control unit 144 sets the lower limit value of the injection pulse width as the recovery-time lower limit guard value for a period until the pre-guard value becomes equal to or greater than the final guard value (recovery-time lower limit guard value).

  This corresponds to a period from when the process moves from the route A to the route B in the above flowchart until the attenuation process of the recovery time lower limit guard value is started. In other words, in the flowchart of FIG. 4, the predetermined period is the guard value determination process S <b> 414 until the recovery time lower limit guard value is equal to or lower than the pre-guard value (NO in S <b> 414). Thereafter, the lower limit guard value at the time of recovery is attenuated, and the final guard value becomes smaller as indicated by a three-dot chain line.

  The injection control unit 144 performs cut recovery control and performs normal control after a predetermined trigger. As described above, when the recovery lower limit guard value is equal to or less than the pre-guard value, the fuel injection amount is increased by the recovery lower limit guard value only after the recovery from the fuel cut state by terminating the cut recovery control. . Thereafter, even if the injection pulse width is reduced, only the increase in fuel injection amount by the normal time lower limit guard value smaller than the recovery time lower limit guard value is obtained, and the increase in the THC concentration can be suppressed small.

  In addition, the period until the lower limit guard value at the time of recovery falls below the pre-guard value is set as a predetermined period for performing the process of setting the injection pulse width to the lower limit guard value at the recovery time, so that the identification immediately after returning from the fuel cut state Can be performed easily and accurately.

  Also provided are a program that causes the computer to function as the engine control device 140 and a storage medium such as a computer-readable flexible disk, magneto-optical disk, ROM, CD, DVD, or BD on which the program is recorded. Here, the program refers to data processing means described in an arbitrary language or description method.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Is done.

  For example, in the above-described embodiment, the case where the final guard value is provided also in a state other than the recovery state, that is, the case where the normal time lower limit guard value is set as the final guard value has been described. However, the final guard value may be provided only in the recovered state after returning from the fuel cut state. In this case, the normal time lower limit guard value is set to 0, and the recovery time lower limit guard value is an arbitrary value larger than 0.

  Further, in the above-described embodiment, the case where the injection amount for each fuel injection is controlled by the injection pulse width has been described. However, when the fuel pressure is variable, the fuel injection amount for each fuel injection is only the fuel pressure, Or you may control by a fuel pressure and an injection pulse width.

  Note that the injection pulse width determination process and the guard value determination process in this specification do not necessarily have to be performed in time series in the order described in the flowchart, and are performed in parallel or by a subroutine. May be included.

  The present invention can be used in an engine control device that performs fuel cut control.

100 Engine 128 Exhaust manifold (exhaust flow path)
132 Exhaust pipe (exhaust flow path)
134 Catalyst 140 Engine control device 142 Air amount acquisition unit (air amount acquisition means)
144 Injection control unit (injection control means, fuel increase correction means)

Claims (4)

A catalyst for purifying exhaust gas provided in the exhaust system of the engine;
An air amount acquisition means for acquiring an intake air amount of air sucked into the engine;
Injection control means for setting an injection pulse width of the fuel injection valve so as not to fall below a first lower limit guard value based on the intake air amount during steady operation of the engine;
A fuel increase correction means for temporarily increasing the fuel injection amount at the time of fuel cut recovery of the engine and reducing the oxygen storage amount of the catalyst;
With
The injection control means sets a second lower limit guard value larger than the first lower limit guard value as a lower limit value of the injection pulse width for a predetermined period from the start of fuel increase by the fuel increase correction means. A characteristic engine control device.   The engine control apparatus according to claim 1, wherein the second lower limit guard value is updated according to a fuel pressure.   The predetermined period is a period until the injection pulse width before correction by the second lower limit guard value is equal to or greater than the second lower limit guard value. 2. The engine control device according to 2.   The engine according to any one of claims 1 to 3, wherein the second lower limit guard value converges to the first lower limit guard value by predetermined attenuation control after the predetermined period has elapsed. Control device.

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