JP2014231792A - Engine controller and engine control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine controller capable of preventing degradation in efficiency of an exhaust emission control device.SOLUTION: An engine controller (50) controlling a fuel injection device (41) to control an engine (10) to operate, comprises fuel stop means stopping fuel injection of the fuel injection device (41) on the basis of a vehicle operation state. If the fuel injection restarts after the fuel stop means stops injection of fuel to a cylinder (13), the controller (50) controls the fuel injection device (41) to inject the fuel at a fuel injection amount determined so that the engine (10) has a stoichiometric air-fuel ratio or lean burn on the basis of the vehicle operation state and controls the fuel injection device (41) to inject the fuel in a cylinder exhaust stroke.

Description

  The present invention relates to a control device and a control method for an engine mounted on a vehicle.

  A three-way catalyst and a NOx adsorption catalyst are used as an engine exhaust purification device. The NOx adsorption catalyst adsorbs NOx when the oxygen concentration in the exhaust gas is excessive, and releases NOx when the oxygen concentration decreases. By utilizing this characteristic, the three-way catalyst and the NOx adsorption catalyst are arranged adjacent to each other so that NOx is adsorbed when the air-fuel ratio is lean, and NOx is adsorbed when the air-fuel ratio becomes stoichiometric or rich. Released and purified and reduced by a three-way catalyst.

  In the control of an engine equipped with such an exhaust purification device, when fuel cut is performed at low load, the intake low temperature air is exhausted as it is. The temperature decreases and the purification performance of the catalyst decreases. In order to prevent this, when it is determined that the catalyst temperature has decreased during fuel cut, there is known an engine fuel control device (see Patent Document 1) that ends the fuel cut and controls the air-fuel ratio to be rich. ing.

JP 2002-106388 A

  In the above-described conventional technology, the air-fuel ratio is changed to rich when the fuel cut is completed for the purpose of optimizing the oxygen storage amount of the catalyst and not reducing the catalyst temperature. For this reason, the particulate matter (PM) and the particulate matter number concentration (PN) in the exhaust gas increase. Moreover, CO in exhaust gas increases because the fuel becomes rich. When these increase, there exists a problem that the purification efficiency of a catalyst falls.

  The present invention has been made in view of such problems, and in an engine that improves fuel efficiency by performing fuel cut, the catalyst purification efficiency can also be achieved when fuel cut is terminated and fuel is injected again. An object of the present invention is to provide an engine control device that does not lower the engine.

  The present invention relates to an engine provided with a catalyst for driving a vehicle and purifying exhaust gas, and a fuel injection device for injecting fuel into a cylinder. The engine controls the operation of the engine by controlling the fuel injection device. It is applied to the control device. The control device includes fuel stop means for stopping fuel injection of the fuel injection device based on a driving state of the vehicle, and restarts fuel injection after fuel injection to the cylinder is stopped by the fuel stop means. In the case where the engine is operated, the fuel is injected into the fuel injection device at an injection amount determined so that the engine is in the stoichiometric air-fuel ratio or lean combustion based on the operation state of the vehicle, and in the exhaust stroke of the cylinder, Fuel is injected into the fuel injection device.

  According to the present invention, by injecting a predetermined amount of fuel in the exhaust stroke and activating it in the catalyst, the oxygen storage amount of the catalyst that has become excessive due to fuel cut can be returned to an appropriate amount. The catalyst can be activated and the purification efficiency of the catalyst is not reduced. At this time, since the engine is driven by the stoichiometric air-fuel ratio or lean combustion, PM and PN of the exhaust gas are not increased.

It is explanatory drawing which shows the structure of the engine control system centering on the engine of embodiment of this invention. It is a flowchart of the fuel supply control which ECU of embodiment of this invention performs. It is a timing chart at the time of fuel cut and fuel cut recovery of an embodiment of the present invention. It is a timing chart at the time of the fuel cut recovery of embodiment of this invention. It is a timing chart at the time of the fuel cut recovery of embodiment of this invention. It is a timing chart at the time of the fuel cut recovery of embodiment of this invention.

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

  FIG. 1 is an explanatory diagram showing a configuration of an engine control system 1 centering on an engine 10 according to an embodiment of the present invention.

  The engine 10 includes a cylinder block 11 and a cylinder head 12. The engine 10 injects fuel into the air from the intake pipe 20 in a cylinder (cylinder) 13 and compresses and burns it to push down the piston 14 and rotate the crankshaft 15 to obtain driving force. The exhaust gas after combustion is discharged from the exhaust pipe 30. The engine 10 is, for example, a diesel engine.

  Driving of the engine 10 is controlled by an engine control unit (ECU) 50.

  The cylinder head 12 includes an intake valve 25, an exhaust valve 35, a direct injection injector 41, and a spark plug 42. The cylinder block 11 is formed with a water jacket 16 through which cooling water flows, and a water temperature sensor 17 that detects the temperature of the cooling water. The crankshaft 15 is provided with a crank angle sensor 18 that detects the rotational position of the crankshaft.

  The intake pipe 20 is provided with an air filter 21, an air flow meter 22, an electric throttle valve 23, and a collector 24. The intake pipe 20 communicates with the cylinder 13 via the intake valve 25 of the cylinder head 12.

  The air filter 21 removes dust in the intake air. The air flow meter 22 detects the intake air amount Qa flowing through the intake pipe and sucked into the cylinder 13. The electric throttle valve 23 is controlled by the ECU 50 to control the intake air amount Qa. The collector 24 has a structure in which a cross-sectional area changes in the middle of the intake pipe 20, and improves the intake inertia effect.

  The exhaust pipe 30 is provided with an air-fuel ratio sensor 31, a catalyst 32, and a catalyst temperature sensor 33. The exhaust pipe 30 communicates with the cylinder 13 via the exhaust valve 35 of the cylinder head 12.

  The air-fuel ratio sensor 31 detects the oxygen concentration in the exhaust gas, and detects the air-fuel ratio AF of the engine 10 based on the detected value. The catalyst 32 purifies NOx, CO, HC, etc. in the exhaust gas into harmless nitrogen, water, carbon dioxide, etc. by oxidizing and reducing. The catalyst temperature sensor 33 detects the catalyst temperature Tcat of the catalyst 32.

The catalyst 32 includes a NOx adsorption catalyst and a three-way catalyst. The NOx adsorption catalyst has a characteristic of adsorbing NOx when the oxygen concentration in the exhaust gas is high and releasing NOx when the oxygen concentration is lowered. Utilizing this characteristic, in the catalyst 32, a NOx adsorption catalyst and a three-way catalyst are arranged adjacent to each other, and when the air-fuel ratio state is lean, NOx is adsorbed and the air-fuel ratio state becomes stoichiometric or rich. To release NOx. At this time, HC, CO, etc. in the exhaust gas react with NOx by the three-way catalyst, so that they are reduced and purified to harmless substances such as H ₂ O, N ₂ , CO ₂ .

  The ECU 50 acquires signals detected by the air flow meter 22, the water temperature sensor 17, the crank angle sensor 18, the air-fuel ratio sensor 31, the catalyst temperature sensor 33, the throttle and accelerator opening sensor 51, and the like. The ECU 50 determines the opening degree of the electric throttle valve 23, the timing of fuel injection, and the pulse width based on these acquired signals. The operation of the engine 10 is controlled by controlling the electric throttle valve 23 and the direct injection injector 41 based on this determination.

  Next, the operation of the engine control system 1 configured as described above will be described.

  The engine control system 1 according to the embodiment of the present invention also controls the engine 10 according to the catalyst temperature and the oxygen storage amount of the catalyst 32 composed of the NOx adsorption catalyst and the three-way catalyst.

  As described above, the ECU 50 controls the engine 10 based on signals from the air flow meter 22, the water temperature sensor 17, the crank angle sensor 18, the air-fuel ratio sensor 31, the catalyst temperature sensor 33, and the throttle and accelerator opening sensor 51.

  During traveling, a fuel cut is performed to stop the supply of fuel to the engine 10 in order to improve fuel consumption. For example, when the accelerator pedal is released during travel (accelerator OFF), the vehicle travels by inertia, so the driving force of the engine 10 is not necessary. When performing the fuel cut, the ECU 50 controls the direct injection injector 41 to stop the fuel supply. At this time, in the engine 10, combustion does not occur in the cylinder 13, and air is exhausted from the intake pipe 20 to the exhaust pipe 30 as it is.

  When acceleration is requested, for example, when the accelerator pedal is depressed after the fuel cut, the ECU 50 supplies the fuel again to drive the engine 10.

  During the fuel cut, the air taken in from the intake pipe 20 is exhausted to the exhaust pipe 30 as it is, so that the temperature of the catalyst 32 decreases. As the temperature of the catalyst 32 decreases, the purification efficiency of the catalyst decreases. In addition, during the fuel cut, the sucked air is exhausted as it is to the exhaust pipe 30, so that oxygen is not consumed and the oxygen storage amount of the NOx adsorption catalyst becomes excessive.

  For this reason, when fuel is supplied and the driving of the engine 10 is restarted after the fuel cut, the temperature of the catalyst 32 is lowered, so the purification efficiency of the catalyst is lowered. Further, when the oxygen storage amount of the NOx adsorption catalyst becomes excessive, the NOx adsorption amount decreases, and in addition to the low activity of the catalyst 32, the NOx purification efficiency particularly decreases.

  On the other hand, the fuel at the time of fuel cut recovery can be enriched to increase the temperature of the catalyst 32 and reduce the oxygen storage amount. However, there is a possibility that PM, PN, CO and the like increase due to fuel enrichment.

  In the embodiment of the present invention, the following control is performed to improve the purification efficiency of the catalyst 32 and suppress the increase in PM, PN, CO, etc. in the fuel cut recovery after the fuel cut. did.

  FIG. 2 is a flowchart of fuel supply control executed by the ECU 50 according to the embodiment of the present invention. This flowchart is executed in a predetermined cycle (for example, 10 ms) in parallel with other processing executed in the ECU 50.

  When the flowchart shown in FIG. 2 is executed, in step S1, the ECU 50 determines the accelerator opening APO from the accelerator opening sensor 51, the intake air amount Qa from the air flow meter 22, and the engine speed from the crank angle sensor 18. Get Ne. Further, the ECU 50 acquires the air-fuel ratio AF from the air-fuel ratio sensor 31 and the catalyst temperature Tcat from the catalyst temperature sensor 33. The catalyst temperature Tcat may be estimated based on the intake air amount Qa, the engine rotational speed Ne, and the engine coolant temperature detected by the water temperature sensor 17.

  Next, in step S2, the ECU 50 calculates the basic fuel injection pulse width Tp based on the fuel injection map stored in advance based on the intake air amount Qa and the engine speed Ne. The basic fuel injection pulse width Tp is determined so that the operation of the engine 10 determined by the intake air amount Qa and the engine speed Ne becomes the stoichiometric air-fuel ratio.

  Next, in step S3, the ECU 50 calculates the oxygen storage amount OSC in the catalyst 32 based on the intake air amount Qa, the engine speed Ne, and the air-fuel ratio AF. Since the intake air amount Qa is substantially equal to the exhaust gas flow rate, the amount of oxygen flowing into the catalyst 32 or the amount of reducing agent (for example, HC, CO, etc.) that consumes the oxygen of the catalyst 32 is estimated from the exhaust gas flow rate and the air-fuel ratio AF. it can. The ECU 50 calculates the oxygen storage amount OSC by integrating the amount of oxygen in the catalyst 32 based on these values.

  Next, in step S4, the ECU 50 determines whether or not the fuel cut flag fFC is zero. The fuel cut flag fFC is set to 1 when the fuel cut is executed, and is reset to 0 when the fuel cut is not executed. Note that when the engine 10 is started, the fuel cut flag fFC is reset to zero.

  If the fuel cut flag fFC is reset (0), the process proceeds to step S5, and if 1 is set in the fuel cut flag fFC, the process proceeds to step S7.

  When the fuel cut flag fFC is reset, in step S5, the ECU 50 determines whether or not a condition for executing the fuel cut is satisfied. Specifically, if the accelerator opening APO acquired in step S1 is greater than 0, or if the engine speed Ne acquired in step S1 is smaller than the fuel cut execution permission speed Neth1, the ECU 50 performs the fuel cut. It is determined that the execution condition is not satisfied. In this case, the fuel cut flag fFC remains 0, and the process proceeds to step S6. Note that the fuel cut execution permission rotational speed Neth1 is set, for example, near the minimum rotational speed of the engine 10.

  If the accelerator opening APO is 0 and the engine rotational speed Ne is equal to or higher than the fuel cut execution permission rotational speed Neth1, the ECU 50 determines that the fuel cut execution condition is satisfied, and proceeds to step S8.

  In step S6, the engine 10 is driven without performing fuel cut. The ECU 50 calculates the fuel injection pulse width Ti by multiplying the basic fuel injection pulse width Tp acquired in step S2 by the air-fuel ratio feedback correction coefficient α.

  The fuel injection pulse width Ti is normal fuel injection performed during the intake stroke, and is the width of the drive pulse that the ECU 50 actually commands the direct injection injector 41. The air-fuel ratio feedback correction coefficient α is calculated according to the deviation between the current oxygen storage amount OSC and 50 [%] so that the oxygen storage amount OSC in the catalyst 32 becomes 50 [%]. When it is set to perform fuel injection in the exhaust stroke (exhaust stroke injection) in any cylinder of the engine 10 (when the exhaust stroke fuel injection pulse width Texh is set to other than 0), α = 1 is set.

  After the process of step S6, the process of the flowchart shown in FIG. 2 is temporarily terminated and the process returns to the other processes.

  When the fuel cut flag fFC is set to 1 in step S4, the process proceeds to step S7, and the ECU 50 determines whether or not a condition for continuously executing the fuel cut is satisfied. Specifically, when the accelerator opening APO acquired in step S1 is 0 and the engine rotational speed Ne acquired in step S1 is larger than the fuel cut recovery rotational speed Neth2, the ECU 50 continues the fuel cut. Determine to execute. In this case, the process proceeds to step S8 while the fuel cut flag is set to 1.

  When the accelerator opening APO is larger than 0, or when the engine rotational speed Ne is smaller than the fuel cut recovery rotational speed Neth2, the ECU 50 determines that the fuel cut execution condition is not satisfied. In this case, the ECU 50 determines that the fuel cut recovery condition is satisfied, and proceeds to step S10.

  The fuel cut recovery rotational speed Neth2 is set to a value larger than the fuel cut execution permission rotational speed Neth1.

  When it is determined that the fuel cut is to be continuously executed, the process proceeds to step S8, and the ECU 50 sets the fuel cut flag fFC to 1 when the fuel cut flag fFC is not set to 1. Next, the process proceeds to step S9, where the ECU 50 sets the fuel injection pulse width Ti to zero. As a result, the fuel is not injected from the direct injection injector 41 and the fuel is cut.

  After the process of step S9, the process of the flowchart shown in FIG. 2 is temporarily terminated and the process returns to the other processes.

  When it is determined in step S7 that the fuel cut recovery condition is satisfied, the process proceeds to step S10, and the fuel cut recovery process is performed. First, the ECU 50 resets the fuel cut flag fFC to 0.

  Next, in step S11, the ECU 50 calculates the OSC required increase amount pulse width Tosc based on the current oxygen storage amount OSC calculated in step S3. The OSC required increase amount pulse width Tosc is a fuel injection pulse width that defines the fuel injection amount required to return the oxygen storage amount OSC of the catalyst 32 that has become excessive due to the fuel cut to 50%. The ECU 50 refers to a map stored in advance and calculates the OSC required increase amount pulse width Tosc corresponding to the oxygen storage amount OSC.

  Next, in step S <b> 12, the ECU 50 determines whether or not the determined OSC required increase pulse width Tosc is greater than the minimum fuel injection pulse width Tmin of the direct injector 41.

  The direct injection injector 41 cannot inject an accurate amount of fuel when the fuel injection pulse width becomes shorter than the minimum fuel injection pulse width Tmin. Therefore, the ECU 50 determines whether or not the OSC required increase pulse width Tosc determined in step S11 is larger than the minimum fuel injection pulse width Tmin.

  When it is determined that the OSC required increase pulse width Tosc is larger than the minimum fuel injection pulse width Tmin, the direct injection injector 41 can accurately control fuel injection with the OSC required increase pulse width Tosc. In this case, the process proceeds to step S13. When it is determined that the OSC required increase pulse width Tosc is equal to or less than the minimum fuel injection pulse width Tmin, the direct injection injector 41 cannot accurately control fuel injection with the OSC required increase pulse width Tosc. In this case, the process proceeds to step S17.

  In step S13, the ECU 50 determines whether or not the catalyst temperature Tcat acquired in step S1 is higher than a predetermined temperature Tcatth. The predetermined temperature Tcatth is set to about 600 ° C., for example.

  In the catalyst 32, the higher the catalyst temperature Tcat, the higher the activity of the catalyst, and the exhaust purification efficiency is improved. In step S13, when the catalyst temperature Tcat is higher than the predetermined temperature Tcatth, the catalyst 32 can be sufficiently activated to cause a necessary reaction even when the exhaust temperature is low. That is, even when the fuel that has been post-injected together with the low-temperature air flows into the catalyst 32, the reaction between the fuel and storage oxygen occurs in the catalyst 32, and the oxygen storage amount OSC is set to a desired value (50 [%]). Can be returned to.

  In this case, the process proceeds to step S14, and the ECU 50 sets the exhaust stroke fuel injection pulse width Texh of the cylinder that becomes the exhaust stroke earliest after the fuel cut recovery condition is satisfied to the OSC required increase amount pulse width Tosc. Thereby, the exhaust stroke injection is executed in the exhaust stroke of the cylinder that becomes the exhaust stroke earliest after the fuel cut recovery condition is satisfied.

  The fuel injected in the exhaust stroke flows into the exhaust purification catalyst together with air having a low temperature. In the catalyst 32, since the catalyst temperature Tcat is higher than the predetermined temperature Tcatth, the reaction between the fuel and the storage oxygen occurs, and the oxygen storage amount OSC can be returned to a desired value (50 [%]). After performing the exhaust stroke injection, the ECU 50 resets the exhaust stroke fuel injection pulse width Texh of the cylinder to zero.

  On the other hand, in step S13, when the catalyst temperature Tcat is equal to or lower than the predetermined temperature Tcatth, the catalyst 32 is not sufficiently activated. Therefore, in order to cause a sufficient reaction in the catalyst 32, a high-temperature burned gas is sent as exhaust gas.

  In this case, the process proceeds to step S15, and the ECU 50 sets the exhaust stroke fuel injection pulse width Texh of the cylinder that burns earliest after the fuel cut recovery condition is satisfied, to the OSC required increase pulse width Tosc. Thereby, the exhaust stroke injection is executed in the cylinder that burns earliest after the fuel cut recovery condition is satisfied.

  In this case, the intake stroke injection is performed prior to the exhaust stroke injection, and the exhaust stroke injection is performed in the burned gas after the intake stroke injected fuel burns, so that the fuel is sent to the catalyst 32 together with the exhaust gas having a high temperature. It is done. Thereby, even when the temperature of the catalyst 32 is low, the catalyst 32 is activated by the exhaust gas having a high temperature. As a result, the reaction between the fuel and the storage oxygen occurs in the catalyst 32, and the oxygen storage amount OSC can be returned to a desired value (50 [%]). After performing the exhaust stroke injection, the ECU 50 resets the exhaust stroke fuel injection pulse width Texh of the cylinder to zero.

  After the process of step S14 or step S15, the process proceeds to step S16. The ECU 50 sets the fuel injection pulse width Ti to the basic fuel injection pulse width Tp. That is, the engine 10 is operated by injecting fuel corresponding to the stoichiometric air-fuel ratio into the engine 10. At this time, the ECU 50 controls to perform the exhaust stroke fuel injection with the exhaust port fuel injection pulse width Tcos set in step S11. The cylinder in which the exhaust stroke injection is performed is either the cylinder that becomes the earliest exhaust stroke or the cylinder that burns the earliest. After the process of step S16, the process of the flowchart shown in FIG. 2 is once ended and the process returns to the other processes.

  Note that, in step S16, the fuel injection pulse width Ti is determined not to be the stoichiometric air-fuel ratio (basic fuel injection pulse width Tp) but to perform lean combustion (lean combustion) based on the operating state of the vehicle. Good. Since the oxygen storage amount of the catalyst 32 can be properly returned by the exhaust stroke injection, the fuel for driving the engine 10 may be set in any way. By setting the fuel injection amount to the stoichiometric air-fuel ratio or lean combustion, it is possible to suppress the fuel enrichment at the restart of the engine 10 and to suppress the generation of PM, PN, and CO.

  If it is determined in step S12 that the OSC required increase pulse width Tosc is equal to or smaller than the minimum fuel injection pulse width Tmin, the process proceeds to step S17.

  When the OSC required increase amount pulse width Tosc is shorter than the minimum fuel injection pulse width Tmin of the injector, the injection amount cannot be accurately controlled. Therefore, the OSC required increase amount pulse width Tosc cannot be set to the exhaust stroke fuel injection pulse width Texh. Therefore, in step S17, the ECU 50 sets the exhaust stroke fuel injection pulse width Texh of all the cylinders to 0 so as not to perform the exhaust stroke injection.

  Next, in step S18, the ECU 50 calculates the fuel injection pulse width Ti by adding the OSC required increase amount pulse width Tosc to the basic fuel injection pulse width Tp. Thereby, the intake stroke injection of the cylinder that burns earliest after the fuel cut recovery condition is satisfied is increased. In this case, since the OSC required increase amount pulse width Tosc is short, the air-fuel ratio of the combustion mixture formed by the intake stroke injection does not exceed the rich limit. After the process of step S9, the process of the flowchart shown in FIG. 2 is temporarily terminated and the process returns to the other processes.

  Since PM may increase due to the enrichment of the combustion air-fuel mixture, the pulse width Tosc corresponding to the OSC required increase amount may be divided and added to a plurality of intake stroke injections.

  By such control, in the control at the time of fuel cut recovery after fuel cut, the oxygen storage amount OSC of the catalyst 32 can be quickly returned to an appropriate value (50 [%]) by exhaust stroke injection.

  At this time, since the fuel injection amount for driving the engine 10 can be the stoichiometric air-fuel ratio or lean combustion, the fuel supplied to the engine 10 does not become rich, so PM, PM, An increase in CO and the like can be suppressed.

  FIG. 3 is an explanatory diagram of the fuel cut and the fuel cut recover according to the embodiment of the present invention. 3 to 5 show examples in which the engine 10 has four cylinders.

  FIG. 3A shows a normal operation state of the engine 10 in which fuel cut is not performed. In the cylinder 1, the cylinder 2, the cylinder 3, and the cylinder 4, the intake stroke IN, the compression stroke COMP, the combustion stroke COMB, and the exhaust stroke EX are sequentially performed, respectively. In the intake stroke of each cylinder, injection is performed from the direct injection injector 41 into the cylinder 13. The fuel injection amount is controlled by the pulse width, and this pulse width is set to the fuel injection pulse width Ti as described above.

  FIG. 3B shows the operation state of the engine 10 when the fuel cut is performed.

  If it is determined in step S5 or step S7 in FIG. 2 that fuel cut is to be performed, the fuel injection pulse width Ti is reset to 0 in step S9 in FIG. Thereby, fuel is not injected into each cylinder, and fuel cut is executed.

  FIG. 3C shows the operating state of the engine 10 at the time of fuel cut recovery after fuel cut.

  At timing t1, when the fuel cut recovery condition is satisfied in step S7 in FIG. 2, the fuel cut recovery process described in steps S10 to S16 in FIG. 2 is executed. In step S11, the ECU 50 determines the OSC required increase pulse width Tosc based on the oxygen storage amount OSC. If both the determinations in steps S12 and S13 are YES, the process of step S14 is executed. That is, in the cylinder that becomes the exhaust stroke earliest (cylinder 1 in the example of FIG. 3C), the exhaust stroke fuel injection pulse width Texh is set to the OSC required increase pulse width Tosc, and the exhaust stroke injection is performed.

  At this time, the fuel injection amount of the fuel cut recovery in each cylinder is set to the basic fuel injection pulse Tp set corresponding to the stoichiometric air-fuel ratio or lean combustion. Therefore, PM, PN, An increase in CO and the like is suppressed.

  FIG. 4 is an explanatory diagram of the fuel cut recover according to the embodiment of the present invention. The example of FIG. 4 shows an example when the catalyst temperature Tcat is equal to or lower than the predetermined temperature Tcatth in step S13 of FIG.

  If the catalyst temperature Tcat is equal to or lower than the predetermined temperature Tcatth, the determination in S13 is NO and the process in step S15 is executed. That is, in the cylinder that becomes the earliest combustion stroke (cylinder 2 in the example of FIG. 4), the exhaust stroke fuel injection pulse width Texh is set to the OSC required increase pulse width Tosc, and exhaust stroke injection is performed.

  In this case, since the exhaust stroke injection is performed in the burned gas after burning in the engine 10, the fuel is sent to the catalyst 32 together with the exhaust gas having a high temperature. Thereby, even when the temperature of the catalyst 32 is low, the catalyst 32 is activated by the exhaust gas having a high temperature, and the oxygen storage amount OSC can be returned to a desired value (50 [%]).

  Also in FIG. 4, as in FIG. 3C, the fuel injection amount of the fuel cut recovery in each cylinder is set to the basic fuel injection pulse Tp set corresponding to the stoichiometric air-fuel ratio or lean combustion. An increase in PM, PN, CO and the like in the exhaust gas during fuel cut recovery is suppressed.

  FIG. 5 is an explanatory diagram of the fuel cut recover according to the embodiment of the present invention. The example of FIG. 5 shows an example when it is determined in step S12 of FIG. 2 that the OSC required increase pulse width Tosc is equal to or smaller than the minimum fuel injection pulse width Tmin.

  When the OSC required increase amount pulse width Tosc is shorter than the minimum fuel injection pulse width Tmin of the injector, the fuel injection amount cannot be accurately controlled. Therefore, the ECU 50 sets the exhaust stroke fuel injection pulse width Texh of all the cylinders to 0 so as not to perform the exhaust stroke injection.

  Then, the ECU 50 calculates the fuel injection pulse width Ti by adding the OSC required increase amount pulse width Tosc to the basic fuel injection pulse width Tp. Thereby, the intake stroke injection of the cylinder that burns earliest after the fuel cut recovery condition is satisfied is increased. With this increased amount of fuel, the oxygen storage amount of the catalyst 32 is appropriately controlled. Since the OSC required increase pulse width Tosc is short, the air-fuel ratio of the combustion mixture formed by the intake stroke injection does not exceed the rich limit, and PM, PN, and CO are suppressed from increasing.

  FIG. 6 is an explanatory diagram of the fuel cut recover according to the embodiment of the present invention. The example shown in FIG. 6 is a modification of FIG. 3C and is related to the control of the exhaust stroke injection timing.

  The ECU 50 controls the direct injection injector 41 to perform intake stroke injection and exhaust stroke injection. These injection timings are determined based on a control timer executed inside the ECU 50.

  The intake stroke injection and the exhaust stroke injection are individually executed at similar timings. Therefore, in the example shown in FIG. 6, the exhaust stroke injection is performed at the same timing (timing tx) as the intake stroke injection of the other cylinders 13.

  In order to control the fuel injection timing, a control timer is required. The ECU determines the fuel injection timing in each cylinder 13 based on a control timer. At this time, as long as only the intake stroke injection is performed, the fuel injection timings of the different cylinders 13 do not overlap, so that the fuel injection timings of all the cylinders 13 can be controlled by one control timer.

  On the other hand, in the exhaust stroke injection, the fuel injection timing is close between the intake stroke injection of one cylinder and the exhaust stroke injection of another cylinder, so the intake stroke injection and the exhaust stroke injection are controlled by different control timers. There is a need to. However, since the exhaust stroke injection is not frequently performed in the engine 10 and the intake stroke injection and the exhaust stroke injection are performed at close timings, the intake stroke injection and the exhaust stroke injection may be performed at the same time. .

  With this configuration, the control timer in the ECU 50 can be reduced, the control can be simplified, and the cost can be reduced.

  As described above, in the embodiment of the present invention, in the engine 10 provided with the catalyst 32 that drives the vehicle and purifies the exhaust, and the direct injection injector 41 as the fuel injection device that injects fuel into the cylinder 13. The present invention relates to an ECU 50 as an engine control device that controls the operation of the engine 10 by controlling the direct injection injector 41.

  The ECU 50 is configured as a fuel stop unit that stops the fuel injection of the direct injector 41 based on the driving state of the vehicle (accelerator opening APO, engine rotational speed Ne, etc.). When the fuel injection is restarted after the fuel injection to the cylinder 13 is stopped by the fuel stop means, the injection determined so that the engine 10 becomes the stoichiometric air-fuel ratio or lean burn based on the operation state of the vehicle. The direct injection injector 41 is made to inject fuel in an amount (fuel injection pulse Ti). At this time, a predetermined amount of fuel (OSC required increase amount pulse width Tosc) is injected into the direct injection injector 41 in the exhaust stroke of the cylinder 13.

  As described above, after performing fuel cut, by performing exhaust stroke injection during the fuel cut recovery process in which fuel is injected to drive the engine 10, the oxygen storage amount of the catalyst 32 in which the oxygen storage amount becomes excessive during the fuel cut. Can be returned properly. Thereby, the catalyst 32 of the fuel cut recover can suppress a decrease in purification efficiency.

  At this time, the fuel injection amount for driving the engine 10 is the stoichiometric air-fuel ratio or lean combustion. Thereby, it is possible to suppress the generation of harmful substances such as PM, PN and CO in the exhaust gas without enriching the fuel at the time of fuel cut recovery.

  The ECU 50 is configured as catalytic oxygen storage amount detection means for calculating the oxygen storage amount OSC in the catalyst 32 based on the intake air amount Qa, the engine speed Ne, and the air-fuel ratio AF. Based on the oxygen storage amount OSC (oxygen storage amount) of the catalyst 32 detected by the catalyst oxygen storage amount detection means, the ECU 50 determines the exhaust stroke injection amount (OSC required increase amount pulse width Tosc) of the fuel to be injected in the exhaust stroke of the cylinder. ). The ECU 50 causes the direct injection injector 41 to inject the fuel of the determined exhaust stroke injection amount.

  As described above, since the exhaust stroke injection amount of the exhaust stroke injection is determined based on the oxygen storage amount of the catalyst 32, the oxygen storage amount of the catalyst 32 can be promptly made appropriate and extra fuel is injected. There is no. Thereby, NOx emission can be suppressed.

  The ECU 50 is configured as catalyst temperature detection means for detecting the catalyst temperature Tcat of the catalyst 32. When the catalyst temperature Tcat is higher than the predetermined temperature Tcatth, the ECU 50 performs the exhaust stroke injection in the exhaust stroke of the cylinder 13 that becomes the exhaust stroke the earliest.

  As described above, when the temperature of the catalyst 32 is sufficiently high, the catalyst 32 is activated, so that the oxygen storage amount of the catalyst 32 can be made appropriate by performing the exhaust stroke injection at the earliest possible timing. . Thereby, NOx emission can be suppressed.

  On the other hand, when the catalyst temperature Tcat is lower than the predetermined temperature Tcatth, the ECU 50 performs the exhaust stroke injection in the exhaust stroke of the cylinder 13 that becomes the combustion stroke earliest.

  Thus, when the temperature of the catalyst 32 is low and the catalyst 32 is not activated, the exhaust stroke injection is performed together with the exhaust gas having a high temperature after combustion. Thereby, the temperature of the catalyst 32 can be quickly raised to activate the catalyst, and the oxygen storage amount of the catalyst 32 can be made appropriate. Thereby, NOx emission can be suppressed.

  If it is determined that the OSC required increase pulse width Tosc, which is the exhaust stroke injection amount, is equal to or less than the minimum fuel injection pulse width Tmin in the direct injection injector 41, the injection amount cannot be controlled accurately. In this case, the ECU 50 is set not to perform the exhaust stroke injection, and calculates the fuel injection pulse width Ti by adding the OSC required increase amount pulse width Tosc to the basic fuel injection pulse width Tp. Thereby, the intake stroke injection is increased to the rich side, the oxygen storage amount of the catalyst 32 can be made appropriate, and NOx emission can be suppressed.

  In the above-described embodiment of the present invention, the vehicle in which the engine 10 is mounted and performs fuel cut is described as an example, but the present invention is not limited to this. For example, a hybrid vehicle driven by a motor and an engine 10 may be applied to a vehicle that performs hybrid traveling by driving the engine 10 again after stopping the operation of the engine 10 and performing electric traveling.

10 Engine 13 Cylinder
17 Water temperature sensor 18 Crank angle sensor 23 Electric throttle valve 25 Intake valve 30 Exhaust pipe 31 Air-fuel ratio sensor 32 Catalyst 33 Catalyst temperature sensor 35 Exhaust valve 41 Direct injection injector 50 Engine control unit (ECU)
51 Accelerator position sensor

Claims (6)

In an engine provided with a catalyst for driving a vehicle and purifying exhaust and a fuel injection device for injecting fuel into a cylinder, the engine control device controls the operation of the engine by controlling the fuel injection device. And
The controller is
Fuel stop means for stopping fuel injection of the fuel injection device based on the driving state of the vehicle;
When fuel injection is resumed after the fuel injection into the cylinder is stopped by the fuel stop means,
Injecting the fuel into the fuel injection device at an injection amount determined so that the engine becomes a stoichiometric air-fuel ratio or lean combustion based on the driving state of the vehicle,
An engine control device that causes the fuel injection device to inject fuel during an exhaust stroke of the cylinder. The controller is
Based on the oxygen storage amount of the catalyst, determine the exhaust stroke injection amount of fuel to be injected in the exhaust stroke of the cylinder,
2. The engine control device according to claim 1, wherein in the exhaust stroke of the cylinder, fuel of the determined exhaust stroke injection amount is injected into the fuel injection device. 3. The fuel injection device is capable of injecting fuel into each of a plurality of cylinders,
The controller is
Comprising catalyst temperature detecting means for detecting the temperature of the catalyst;
When the temperature of the catalyst detected by the exhaust temperature detection means is higher than a predetermined temperature,
3. The engine control device according to claim 1, wherein fuel is injected into the fuel injection device in an exhaust stroke of the cylinder that becomes an exhaust stroke earliest among the plurality of cylinders. 4. The controller is
When the temperature of the catalyst detected by the exhaust temperature detection means is lower than a predetermined temperature,
The engine control device according to claim 3, wherein fuel is injected into the fuel injection device during an exhaust stroke of the cylinder that becomes the earliest combustion stroke among the plurality of cylinders. The fuel injection device controls a fuel injection amount by a fuel injection pulse,
The controller is
When the injection pulse width corresponding to the determined exhaust stroke injection amount is smaller than the minimum injection pulse width of the fuel injection device,
Adding the determined fixed injection amount to the injection amount determined to be the stoichiometric air-fuel ratio, and causing the fuel injection device to inject fuel at the added injection amount in the intake stroke of the cylinder; The engine control device according to claim 2. In an engine equipped with a catalyst for driving a vehicle and purifying exhaust gas and a fuel injection device for injecting fuel into a cylinder, the engine control method controls the operation of the engine by controlling the fuel injection device. There,
Based on the driving state of the vehicle, stop fuel injection into the cylinder by the fuel injection device,
When fuel injection is resumed after fuel injection into the cylinder is stopped,
Injecting the fuel into the fuel injection device at a fuel injection amount determined so that the engine becomes a stoichiometric air-fuel ratio or lean combustion based on the driving state of the vehicle,
A method for controlling an engine, wherein fuel is injected into the fuel injection device during an exhaust stroke of the cylinder.

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