JP7517214B2 - Engine Control Unit - Google Patents

Description

The present invention relates to an engine control device.

The exhaust purification catalyst installed in the exhaust passage of an internal combustion engine is in a state where the oxygen storage amount is large immediately after the engine is released from fuel cut. When the oxygen storage amount is large, there are cases where the NOx contained in the exhaust cannot be sufficiently reduced, so there is known technology for reducing the oxygen storage amount in the exhaust purification catalyst when the fuel cut is released. For example, in the fuel supply control of Patent Document 1, the fuel injection valve is made to inject fuel so that the fuel is richer than the theoretical air-fuel ratio at the timing when the fuel cut is released. This type of fuel supply control reduces the oxygen storage amount in the exhaust purification catalyst after the fuel cut is released.

JP 2003-172176 A

However, in the fuel supply control of Patent Document 1, there is a delay between when fuel is injected at the timing when the fuel cut is released and when the oxygen storage amount due to that fuel injection starts to decrease. Until that delay time has elapsed, there is a concern that NOx emissions will increase. For this reason, there is a demand for technology that can suppress NOx emissions immediately after the fuel cut is released.

The present invention was made in consideration of the above problems, and its main objective is to provide an engine control device that can appropriately suppress NOx emissions downstream of the exhaust purification catalyst immediately after fuel cut is released.

To solve the above problems, the engine control device of the present invention is applied to a vehicle engine system that is mounted on a vehicle and has an engine in which fuel injected from a fuel injection valve is burned, and an exhaust purification catalyst having oxygen storage capacity is provided in the exhaust passage of the engine, and stops fuel injection and executes a fuel cut when a predetermined fuel cut condition is met, and cancels the fuel cut and resumes fuel injection when a predetermined release condition is met during the execution of the fuel cut, and is characterized by having a timing prediction unit that predicts the release timing of the fuel cut based on vehicle driving information related to the driving of the vehicle when the fuel cut is executed, and an injection control unit that causes the fuel injection valve to inject fuel at a timing prior to the release timing when the fuel cut is executed.

When a fuel cut is released in an engine, a rich skip is generally performed to eliminate the oxygen storage state in the exhaust purification catalyst. However, there is a delay between the implementation of the rich skip and the reduction in the amount of oxygen stored in the exhaust purification catalyst, and NOx emissions downstream of the exhaust purification catalyst increase immediately after the fuel cut is released.

In this regard, in the present invention, when a fuel cut is performed while the vehicle is traveling, the timing to release the fuel cut is predicted based on vehicle travel information related to the vehicle's travel, and the fuel injection valve is made to inject fuel at a timing prior to the release timing. The vehicle travel information is considered to include information suggesting that the conditions for releasing the fuel cut are met, making it possible to predict the timing to release the fuel cut. Therefore, while taking into account the release timing of the fuel cut, it is possible to appropriately suppress NOx emissions downstream of the exhaust purification catalyst immediately after the release of the fuel cut.

FIG. 1 is a diagram showing a schematic configuration of an engine system. FIG. 4A is a diagram showing the relationship between the amount of exhaust NOx and the allowable upper limit of the amount of oxygen storage; FIG. 4B is a diagram showing the relationship between the allowable upper limit of the amount of oxygen storage and the injection amount; FIG. 4 is a diagram showing the relationship between the intake air amount and the reaction start time. FIG. 4 is a diagram showing the relationship between the injection amount and the reaction completion time. 4 is a flowchart showing a procedure of fuel injection control. 4 is a timing chart showing a fuel injection control mode. 5 is a flowchart showing a procedure for supplemental injection control. 5 is a timing chart showing a supplementary injection control mode. 4 is a flowchart showing a procedure of fuel injection control.

First Embodiment
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an engine control device according to the present invention will now be described with reference to the drawings. The engine control device according to the present invention is applied to a vehicle engine system. First, a schematic configuration of the vehicle engine system will be described with reference to FIG.

In FIG. 1, engine 50 is, for example, a multi-cylinder gasoline engine, and is mounted on a vehicle. Engine 50 also has multiple fuel injection valves 51 that inject fuel into each cylinder. An intake pipe 52 and an exhaust pipe 53 are connected to engine 50. Exhaust pipe 53, which is an exhaust passage, is provided with an exhaust purification catalyst 54 that purifies NOx and other substances contained in the exhaust gas passing through it. Exhaust purification catalyst 54 is, for example, a three-way catalyst, and has an oxygen storage capacity. When the amount of oxygen stored in exhaust purification catalyst 54 increases, the NOx reduction effect of exhaust purification catalyst 54 decreases.

The ECU 70 is an electronic control unit mainly composed of a microcomputer including a known CPU, ROM, RAM, etc., and performs various controls of the engine 50 using detection signals from various sensors. The ECU 70 receives detection signals from an air flow meter 61 provided in the intake pipe 52 for detecting the amount of intake air, as well as detection signals from a rotation sensor 62 for detecting the rotation speed of the engine 50 and an accelerator sensor 63 for detecting the amount of accelerator operation. The ECU 70 also receives vehicle driving information related to the driving of the vehicle from other on-board ECUs (not shown). Specifically, this information includes map information, vehicle position information, operation management data, and traffic light display information. The ECU 70 performs fuel injection control of the fuel injection valve 51 based on these detection signals.

When a predetermined fuel cut condition is met in a vehicle equipped with the engine 50, the ECU 70 stops fuel injection by the fuel injection valve 51 and executes a fuel cut. Here, the fuel cut condition includes, for example, that the accelerator operation amount is zero and that the rotation speed of the engine 50 is equal to or greater than a predetermined fuel cut rotation speed (for example, 1000 rpm). In addition, when a predetermined release condition is met while the fuel cut is being executed, the ECU 70 releases the fuel cut and resumes fuel injection. The release condition includes, for example, that the accelerator operation amount becomes greater than zero.

However, when combustion in the engine 50 is stopped due to a fuel cut, the exhaust pipe 53 is filled with air. This increases the amount of oxygen stored in the exhaust purification catalyst 54, and in this state, the NOx reduction effect of the exhaust purification catalyst 54 decreases. In such a case, if fuel is burned immediately after the fuel cut is released, the exhaust purification catalyst 54 may not be able to completely reduce the NOx contained in the exhaust, and there is a risk that the amount of NOx emissions will increase.

In this embodiment, the timing to release the fuel cut is predicted when a fuel cut is performed while the vehicle is traveling, and fuel injection valve 51 injects fuel before the release timing (hereinafter, referred to as pre-release injection). The exhaust purification catalyst 54 is reduced by the fuel injected before the release timing, and the amount of oxygen stored is reduced in advance, thereby suppressing NOx emissions immediately after the fuel cut is released. Here, the prediction of the timing to release the fuel cut is performed based on vehicle traveling information. It is considered that the vehicle traveling information related to the traveling of the vehicle includes information suggesting that the fuel cut release conditions will be met.

The ECU 70 functions as a timing prediction unit to predict the timing of releasing the fuel cut based on vehicle driving information when a fuel cut is performed while the vehicle is traveling. Specifically, the ECU 70 acquires future driving route information of the vehicle equipped with the engine 50 as vehicle driving information, and predicts the timing of releasing the fuel cut according to a time-series change in engine torque that can be estimated based on the driving route information. The future driving route information of the vehicle may be information about a route from the current location of the vehicle searched by inputting a destination into a navigation device (not shown) or a mobile terminal, or may be information about roads in a section from the current location of the vehicle that does not have side roads. In other words, the future driving route information of the vehicle may be information about roads that are likely to be traveled by the vehicle in the future. The driving route information is created based on a map information database stored in the ECU 70 or an external server. Hereinafter, the predicted release timing will be referred to as the release timing RT.

The ECU 70 acquires, as driving route information, any of road gradient change information, road speed limit information, road traffic light display information, etc. Here, the road traffic light display information refers to information that indicates whether the display of the traffic light located on the road is a stop indication or a proceed indication, and also indicates the timing at which the indication changes from one indication to the other. The ECU 70 then predicts the timing RT for releasing the fuel cut according to the time-series change in engine torque that can be estimated based on the acquired information.

When ECU 70 acquires road gradient change information, it predicts the timing RT at which the vehicle will reach a road section with a steeper uphill gradient than the road section on which the vehicle is currently traveling when fuel cut is to be executed as the fuel cut release timing RT. On such road sections, there is a high possibility that engine torque will be increased, and in order to increase engine torque, the accelerator operation amount must be increased. Increasing the accelerator operation amount when fuel cut is executed indicates that the release condition is met.

Furthermore, when the ECU 70 acquires road speed limit information, it predicts the timing RT at which the fuel cut will be released, as the timing at which the vehicle will reach a road section included in the vehicle's future driving route where the speed limit is increased relative to the previous adjacent road section. In a road section where the speed limit is increased relative to the previous adjacent road section, the driver of the vehicle is likely to increase engine torque to accelerate the vehicle, and in order to increase engine torque, the accelerator operation amount must be increased. Increasing the accelerator operation amount when a fuel cut is being performed means that the release condition is met.

The time it takes for the vehicle to reach each road section from the current location is calculated based on the vehicle speed since the start of fuel cut. The vehicle speed since the start of fuel cut is estimated by subtracting the vehicle speed at the start of fuel cut according to the travel distance. The degree of subtraction may take into account the shape and gradient of each road section by referring to the travel route information, or may take into account the weight of the vehicle if it is stored in the ECU 70. The weight of the vehicle may be a value obtained by adding the weight of the average number of passengers to the weight of the vehicle itself, or may be calculated from the acceleration of the vehicle when traveling at a specified engine torque. In addition, if the vehicle is a transport vehicle, the weight of the luggage loaded at the time of departure from the collection center may be added to the weight of the vehicle itself. The weight of the luggage loaded is identified based on the operation management data.

When the vehicle is traveling in a fuel cut state and the traffic light on the road ahead of the vehicle is displaying a stop instruction, the ECU 70 determines whether the traffic light will change from a stop instruction to a proceed instruction. If it determines that the traffic light has changed from a stop instruction to a proceed instruction, the ECU 70 predicts the timing when a predetermined time (e.g., several seconds) has elapsed since the change as the release timing RT. In other words, since it is estimated that the driver will start operating the accelerator as the traffic light changes, that is, a time-series change in engine torque will occur, the ECU 70 predicts the release timing RT based on the traffic light display information.

The ECU 70 functions as an injection control unit to perform pre-release injection by the fuel injection valve 51 at a timing prior to the release timing RT. The ECU 70 also functions as an injection control unit to set the injection amount for pre-release injection. When attempting to reduce the amount of NOx discharged downstream of the exhaust purification catalyst 54 to a predetermined standard or less, it is possible to determine the allowable upper limit of the oxygen storage amount required for the exhaust purification catalyst 54 according to the amount of exhaust NOx in the exhaust discharged from the engine 50 toward the exhaust purification catalyst 54, and it is advisable to adjust the oxygen storage amount so that it is less than the allowable upper limit. For this reason, the injection amount for pre-release injection is set according to the amount of exhaust NOx. Therefore, the ECU 70 functions as a NOx amount prediction unit to set the injection amount, and predicts the amount of exhaust NOx immediately after fuel injection is resumed in response to the establishment of the release condition based on the vehicle driving information. Then, the ECU 70 causes the fuel injection valve 51 to perform pre-release injection with the injection amount set according to the predicted amount of exhaust NOx. When the injection amount is set, the amount of oxygen storage when performing the pre-release injection is also taken into account in addition to the amount of exhaust NOx.

The ECU 70 estimates the amount of oxygen stored in the exhaust purification catalyst 54. Well-known methods can be used to estimate the amount of oxygen stored. Specifically, the amount of oxygen stored is estimated based on the amount of intake air detected by the air flow meter 61, the air-fuel ratio detected by an exhaust sensor (not shown), the rotation speed of the engine 50 detected by the rotation sensor 62, and the like. For example, the amount of oxygen stored is estimated by cumulatively calculating the amount of intake air that has passed through the exhaust purification catalyst 54 and the air-fuel ratio during that time from a predetermined reference value.

When predicting the amount of exhaust NOx, the ECU 70 acquires at least one of the vehicle speed and the vehicle weight at the time of execution of the fuel cut as vehicle driving information. The accelerator operation amount immediately after the fuel cut is released changes depending on the vehicle speed and the vehicle weight immediately before the fuel cut is released. It is also considered that the amount of exhaust NOx changes depending on the accelerator operation amount. Therefore, in order to predict the amount of exhaust NOx immediately after the fuel cut is released, the ECU 70 uses at least one of the vehicle speed and the vehicle weight at the time of execution of the fuel cut. When acquiring the vehicle speed, the vehicle speed immediately before the release timing RT is regarded as the vehicle speed immediately before the fuel cut is released, and the exhaust NOx amount is predicted. The release timing RT is predicted based on the vehicle driving information, and may differ from the timing when the fuel cut is actually released. The amount of exhaust NOx is set to be larger as the value indicating the vehicle speed or the value indicating the vehicle weight increases.

Figure 2(a) shows an example of the relationship between the amount of exhaust NOx discharged toward the exhaust purification catalyst 54 and the allowable upper limit of the oxygen storage amount. As can be seen from Figure 2(a), the allowable upper limit of the oxygen storage amount becomes lower as the amount of exhaust NOx increases, and the allowable upper limit of the oxygen storage amount is set to zero when the amount of exhaust NOx exceeds a predetermined amount.

Figure 2(b) shows an example of the relationship between the allowable upper limit of the oxygen storage amount and the injection amount when performing pre-release injection. As shown in Figure 2(b), the lower the allowable upper limit of the oxygen storage amount, the larger the injection amount when performing pre-release injection is set.

Using the settings shown in Figures 2(a) and (b), the ECU 70 calculates the allowable upper limit of the oxygen storage amount in the exhaust purification catalyst 54 immediately after fuel injection is resumed based on the predicted exhaust NOx amount, and causes the fuel injection valve 51 to perform a pre-release injection with an injection amount set based on the allowable upper limit. Therefore, the greater the exhaust NOx amount predicted by the function of the NOx amount prediction unit, the greater the injection amount in the pre-release injection, so that the oxygen storage amount of the exhaust purification catalyst 54 can be reduced by the release timing RT. Therefore, even immediately after the release timing RT, the amount of NOx emitted downstream of the exhaust purification catalyst 54 can be kept below a predetermined standard.

In this embodiment, the pre-release injection is performed at a timing equal to or greater than the delay time before the release timing RT. The delay time is calculated by the ECU 70 functioning as a delay time calculation unit. The delay time corresponds to the reaction time required for the pre-release injection to reduce the amount of oxygen stored in the exhaust purification catalyst 54 during pre-release injection while fuel cut is being performed. In this embodiment, the reaction time is the sum of the reaction start time required for the pre-release injection to start reducing the amount of oxygen stored in the exhaust purification catalyst 54, and the reaction completion time required for the reaction due to the injection amount in the pre-release injection to be completed.

Figure 3 shows an example of the relationship between intake air volume and reaction start time. As shown in Figure 3, the reaction start time is set to be shorter as the intake air volume increases. The reaction start time is estimated by applying the intake air volume to a calculation map such as that shown in Figure 3.

Figure 4 shows an example of the relationship between the injection amount in pre-release injection and the reaction completion time. This injection amount is set according to the predicted amount of NOx in the exhaust. As can be seen from Figure 4, the reaction completion time is set to be shorter as the injection amount increases. The reaction completion time is estimated by applying the injection amount to a calculation map such as that shown in Figure 4. The sum of the estimated reaction start time and reaction completion time is then calculated as the delay time.

By referring to the delay time calculated using the settings shown in Figures 3 and 4, the ECU 70 sets the injection timing to a timing that is at least the delay time before the release timing RT, and then performs the pre-release injection. In this embodiment, the injection timing is set to a timing that is the delay time before the release timing RT. In other embodiments, the injection timing may be set to a timing that is the delay time plus a margin before the release timing RT.

Next, the procedure for fuel injection control in the ECU 70 will be described with reference to the flowchart in FIG. 5. This process is repeatedly executed by the ECU 70 at a predetermined interval.

When the fuel injection control process is started, the ECU 70 first determines whether or not the fuel cut condition is met (step S11). If it is determined that the fuel cut condition is not met (step S11: NO), the process ends.

On the other hand, if it is determined that the fuel cut condition is satisfied (step S11: YES), the ECU 70 acquires vehicle travel information (step S12). Here, future travel route information of the vehicle is acquired as the vehicle travel information. The travel route information includes at least one of road gradient change information, road speed limit information, and road traffic light display information. Next, the ECU 70 predicts the fuel cut release timing RT based on the travel route information acquired as the vehicle travel information (step S13). Next, the ECU 70 predicts the amount of exhaust NOx immediately after fuel injection is resumed in response to the satisfaction of the release condition (step S14). Then, the ECU 70 sets the amount of pre-release injection according to the predicted amount of exhaust NOx (step S15).

After setting the injection amount for the pre-release injection, the ECU 70 sets the injection timing for the pre-release injection (step S16). In detail, the ECU 70 calculates the delay time and then sets the injection timing for the pre-release injection. Next, the ECU 70 determines whether the injection timing has arrived (step S17). If it is determined that the injection timing has not arrived (step S17: NO), the ECU 70 temporarily ends this process.

On the other hand, if it is determined that the injection timing has arrived (step S17: YES), the ECU 70 causes the fuel injection valve 51 to perform pre-release injection with the injection amount set in step S15 (step S18). After that, the ECU 70 ends this process. In this embodiment, once the series of processes from step S12 to step S16 have been executed and the injection amount and injection timing of the pre-release injection have been set, the series of processes from step S12 to step S16 are omitted until the pre-release injection is performed (step S18) even if the positive determination of step S11 is repeated. In other embodiments, the series of processes from step S12 to step S16 may be executed each time the positive determination of step S11 is repeated, and the injection amount and injection timing of the pre-release injection may be updated.

Next, FIG. 6 shows a timing chart showing the process of FIG. 5 in more detail. At timing t11, the accelerator is released (the accelerator operation amount becomes zero), so that the fuel cut condition is met and the fuel cut is executed, and the vehicle speed starts to decrease. At this time, the injection amount becomes zero due to the execution of the fuel cut, so the oxygen storage amount of the exhaust purification catalyst 54 starts to increase. After timing t11, the exhaust pipe 53 is filled with air, and the longer the fuel cut continues, the more the oxygen storage amount of the exhaust purification catalyst 54 increases. After the fuel cut is executed, the ECU 70 acquires vehicle driving information and predicts the release timing RT, and then performs a series of processes to predict the amount of exhaust NOx immediately after fuel injection is resumed, and to set the injection amount and injection timing of the pre-release injection.

At timing t12, pre-release injection with the set injection amount is performed. Timing t12 corresponds to the timing before the release timing RT by the delay time, and timing t14 corresponds to the release timing RT. Therefore, the time from timing t12 to timing t14 corresponds to the delay time. At timing t13, the oxygen storage amount begins to decrease. That is, the time from timing t12 to timing t13 corresponds to the reaction start time described above. Then, the reaction by the injection amount injected before release at timing t12 is completed at timing t14. In FIG. 6, the allowable upper limit of the oxygen storage amount in the exhaust purification catalyst 54 immediately after fuel injection is resumed is K (>0), and at timing t14, the oxygen storage amount is reduced to K. That is, the time from timing t13 to timing t14 corresponds to the reaction completion time described above.

At timing t14, the accelerator is turned on (the accelerator operation amount becomes greater than zero), which satisfies the release condition, the fuel cut is released, and the vehicle speed begins to increase. At this time, the injection amount also increases due to the release of the fuel cut. After timing t14, the oxygen storage amount gradually approaches zero from the value indicated by K. In Figure 6, the release timing RT predicted based on the vehicle driving information is the same as the timing when the fuel cut is actually released.

In FIG. 6, the oxygen storage amount and injection amount in a comparative example where pre-release injection is not performed at timing t12 are shown by dashed lines DL1 and DL2. As shown by dashed line DL2, if pre-release injection is not performed at timing t12, fuel injection is not performed from when fuel cut begins at timing t11 until fuel cut is released at timing t14. Therefore, in the comparative example, as shown by dashed line DL1, the oxygen storage amount of exhaust purification catalyst 54 continues to increase even after timing t13.

Then, at timing t14, the fuel cut is released, and fuel injection is performed for the first time. However, since the amount of oxygen stored is high immediately after the fuel cut is released, the NOx contained in the exhaust may not be sufficiently reduced. On the other hand, in this embodiment, when the fuel cut is performed, pre-release injection is performed by the fuel injection valve 51 at a timing prior to the release timing RT, so that the amount of oxygen stored immediately after the fuel cut is released can be made lower than in the comparative example.

The first embodiment described above provides the following excellent effects:

When a fuel cut is performed while the vehicle is traveling, the fuel cut release timing RT is predicted based on vehicle travel information related to the vehicle's travel, and the fuel injection valve 51 is made to perform pre-release injection at a timing prior to the release timing RT. The vehicle travel information is considered to include information suggesting that the fuel cut release conditions will be met, making it possible to predict the fuel cut release timing RT. Therefore, while taking into account the fuel cut release timing RT, it is possible to appropriately suppress NOx emissions downstream of the exhaust purification catalyst 54 immediately after the fuel cut is released.

In addition, during pre-release injection while fuel cut is being performed, the reaction time required for the injected fuel to reduce the amount of oxygen stored in the exhaust purification catalyst 54 is calculated as a delay time, and the pre-release injection is performed at a timing that is at least this delay time before the release timing RT. The reaction time is the sum of the reaction start time required for the pre-release injection to start reducing the amount of oxygen stored in the exhaust purification catalyst 54, and the reaction completion time required for the reaction to be completed by that injection amount.

As a result, when a pre-release injection is performed at a timing earlier than the release timing RT, it is possible to prevent the release timing RT from arriving before the start of the decrease in the amount of oxygen stored due to the pre-release injection. Also, if the reaction completion time required for the reaction due to the pre-release injection to complete is included, the reaction due to the pre-release injection is completed at the release timing RT. Therefore, compared to a case in which the pre-release injection is performed at a timing shorter than the delay time before the release timing RT, it is possible to suppress NOx emissions downstream of the exhaust purification catalyst 54 immediately after the release of the fuel cut.

In addition, future vehicle travel route information is acquired as vehicle travel information, and the release timing RT is predicted according to the time series change in engine torque that can be estimated based on the travel route information. There is a high probability that the fuel cut release condition will be met at the timing when the engine torque increases in the time series change in engine torque. Therefore, with this configuration, the fuel cut release timing RT can be properly predicted according to the time series change in engine torque, and thus pre-release injection can be properly performed.

In addition, as driving route information, any of road gradient change information, road speed limit information, and road traffic light display information is acquired, and the release timing RT is predicted according to the time series change in engine torque that can be estimated based on that information. Road gradient change information, road speed limit information, and road traffic light display information are all considered to suggest changes in engine torque. Therefore, it is possible to predict the release timing RT of the fuel cut according to the time series change in engine torque that can be estimated based on any of this information. As a result, pre-release injection can be performed appropriately.

In addition, when fuel cut is performed, the amount of exhaust NOx immediately after fuel injection is resumed due to the establishment of the release condition is predicted based on the vehicle driving information, and the fuel injection valve 51 is caused to inject fuel at an injection amount set according to the predicted amount of exhaust NOx at a timing prior to the release timing RT.

The amount of exhaust NOx immediately after fuel injection is resumed varies depending on the vehicle's running state at the time of resumption of fuel injection. If it is desired to reduce the amount of NOx emissions downstream of the exhaust purification catalyst 54 to a predetermined standard or less, it is possible to determine the allowable upper limit of the amount of oxygen storage required for the exhaust purification catalyst 54 according to the amount of exhaust NOx at the time of resumption of fuel injection, and it is advisable to adjust the amount of oxygen storage so that it is less than the allowable upper limit. Therefore, by predicting the amount of exhaust NOx and performing pre-release injection with an injection amount according to the amount of exhaust NOx, it is possible to reduce the amount of NOx emissions to a predetermined standard or less immediately after fuel injection is resumed. In addition, if pre-release injection is performed with an injection amount that brings the amount of oxygen storage to the allowable upper limit, it is possible to prevent the injection amount from being excessive or insufficient in the fuel injection aimed at reducing the amount of NOx emissions to a predetermined standard or less.

In addition, based on the predicted amount of exhaust NOx, the allowable upper limit of the amount of oxygen stored in the exhaust purification catalyst 54 immediately after fuel injection is resumed is calculated, and the fuel injection valve 51 performs pre-release injection with an injection amount set based on this allowable upper limit. The predicted amount of exhaust NOx is used as the standard for calculating the allowable upper limit of the amount of oxygen stored, and the injection amount of the pre-release injection is set based on this allowable upper limit. Therefore, it is possible to set the injection amount necessary to make the predicted amount of exhaust NOx equal to or less than a predetermined standard. As a result, the pre-release injection can be performed appropriately.

In addition, at least one of the vehicle speed and vehicle weight when fuel cut is performed is acquired, and the amount of exhaust NOx immediately after fuel injection is resumed is predicted based on that information. The accelerator operation amount when fuel injection is resumed changes depending on the vehicle speed and weight while fuel cut is being performed. And the amount of exhaust NOx also changes depending on the accelerator operation amount. Therefore, based on information indicating at least one of the vehicle speed and vehicle weight, it is possible to predict the amount of exhaust NOx when fuel injection is resumed. Furthermore, by performing pre-release injection with an injection amount according to the amount of exhaust NOx, the amount of oxygen stored in the exhaust purification catalyst 54 can be kept below the allowable upper limit.

Second Embodiment
The second embodiment will be described below with respect to differences from the first embodiment. In the second embodiment, the ECU 70 functioning as a timing prediction unit acquires, as vehicle travel information, vehicle distance information with respect to a preceding vehicle traveling ahead of the vehicle, instead of or in addition to travel route information, unlike the first embodiment. When the ECU 70 acquires the vehicle distance information, it predicts the release timing RT according to a time-series change in engine torque that can be estimated based on the vehicle distance information.

A vehicle equipped with the engine control device of the second embodiment detects the distance from the vehicle ahead based on images captured by a stereo camera and the detection results of a millimeter wave radar or laser radar. The ECU 70 then predicts the timing RT at which the distance between the vehicles will decrease and then start to increase after the start of fuel cutoff as the timing RT at which the fuel cutoff will be released. At this time, if the detection results include the relative speed between the vehicle ahead and the vehicle ahead, the ECU 70 may predict the timing RT at which the fuel cutoff will be released by referring to the relative speed instead of or in addition to the distance between the vehicles.

The processing procedure for the fuel injection control in the second embodiment is the same as the processing procedure for the fuel injection control in the first embodiment (shown in FIG. 5), except that when vehicle distance information is acquired as vehicle driving information in step S12, the timing RT for releasing the fuel cut is predicted based on the vehicle distance information in step S13.

The change in the distance from the preceding vehicle makes it possible to quickly detect when the vehicle is transitioning from a fuel cut state to a fuel injection state, i.e., when the driver notices an increase in the distance between the vehicles and accelerates. Therefore, according to the second embodiment described above, the timing RT for releasing the fuel cut can be accurately predicted based on the distance information between the vehicles, and pre-release injection can be appropriately performed.

Third Embodiment
The third embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. The ECU 70 performs supplemental injection control in addition to the fuel injection control described in the first embodiment (described in Figs. 5 and 6). If the release condition is not met and the fuel cut is not released at timing t14 (Fig. 6), which is the release timing RT, the oxygen storage amount increases again after timing t14. Therefore, the ECU 70 functions as a supplemental injection control unit, and causes the fuel injection valve 51 to inject fuel with a predetermined injection amount every time a predetermined time has elapsed during the fuel cut from the release timing RT.

The procedure for the supplemental injection control in the ECU 70 will be explained using the flowchart in FIG. 7. This process is executed by the ECU 70 at a predetermined interval while fuel cut is being performed.

When the supplemental injection control process is started, first, the ECU 70 determines whether or not the release timing RT has arrived (step S21). If it is determined that the release timing RT has not arrived, that is, if the release timing RT has not arrived yet (step S21: NO), the process ends.

On the other hand, if it is determined that the release timing RT has arrived, that is, if the release timing RT has arrived (step S21: YES), the ECU 70 determines whether or not a predetermined time has elapsed since the release timing RT during the fuel cut (step S22). If the predetermined time has not elapsed (step S22: NO), the process ends. On the other hand, if the predetermined time has elapsed (step S22: YES), the ECU 70 causes the fuel injection valve 51 to inject fuel at a predetermined injection amount (step S23). The ECU 70 then ends the process. Note that in step S22 after the supplementary injection control is started and step S23 is performed once, the start point of the calculation of the fuel cut duration is the point at which the last fuel cut duration elapsed the predetermined time.

Figure 8 shows a timing chart when supplemental injection is performed. In Figure 8, the time from timing t14 to timing t15 and the time from timing t15 to timing t16 correspond to the predetermined time. The fuel injections at timings t15 and t16 correspond to fuel injections with a predetermined injection amount. The predetermined injection amount is set to increase according to the length of the predetermined time. When the release condition is met at timing t17 and the fuel cut is released, fuel injection is resumed and the oxygen storage amount gradually approaches zero.

According to the third embodiment described above, even if the fuel cut is not released at the release timing RT, it is possible to suppress an increase in the amount of oxygen stored in the exhaust purification catalyst 54 after the release timing RT has passed. Therefore, it is possible to appropriately suppress NOx emissions downstream of the exhaust purification catalyst 54 immediately after the fuel cut is released.

Fourth Embodiment
The fourth embodiment will be described below with respect to differences from the first embodiment. In the fourth embodiment, unlike the first embodiment, pre-cancellation injection is not performed, and fuel injection is resumed after the cancellation condition is satisfied. In the fourth embodiment, the ECU 70 sets the injection amount in the fuel injection when it is resumed. As in the first embodiment, the ECU 70, which functions as a NOx amount prediction unit, predicts the amount of exhaust NOx immediately after fuel injection is resumed in response to the satisfaction of the cancellation condition based on the vehicle driving information, and then sets the injection amount according to the predicted NOx amount. In detail, the ECU 70 uses the predicted exhaust NOx amount and the relationship shown in Figures 2(a) and (b) to calculate the allowable upper limit of the oxygen storage amount in the exhaust purification catalyst 54 immediately after fuel injection is resumed, and sets the injection amount based on the allowable upper limit. In the fourth embodiment, the ECU 70 obtains the vehicle speed at the time when the fuel cut is executed as the vehicle driving information, and predicts that the larger the value indicating the speed, the larger the amount of exhaust NOx immediately after fuel injection is resumed.

Next, the processing procedure for fuel injection control in the ECU 70 of the fourth embodiment will be described with reference to the flowchart in FIG. 9. This processing is repeatedly executed by the ECU 70 at a predetermined interval.

When the fuel injection control process is started, the ECU 70 first determines whether or not the fuel cut condition is satisfied (step S31). If it is determined that the fuel cut condition is not satisfied (step S31: NO), the process ends.

On the other hand, if it is determined that the fuel cut condition is met (step S31: YES), the ECU 70 acquires vehicle driving information (step S32). Here, the vehicle driving information acquired is information indicating the vehicle speed at the time when the fuel cut was performed. Next, the ECU 70 predicts the amount of exhaust NOx immediately after fuel injection is resumed in response to the satisfaction of the cancellation condition (step S33). Then, the ECU 70 sets the injection amount to be injected when fuel injection is resumed according to the predicted amount of exhaust NOx (step S34).

After setting the injection amount at the time of restart, the ECU 70 determines whether the cancellation condition is met (step S35). If it is determined that the cancellation condition is not met (step S35: NO), the ECU 70 temporarily ends this process. On the other hand, if it is determined that the cancellation condition is met (step S35: YES), the ECU 70 determines that fuel injection has been restarted and causes the fuel injection valve 51 to inject fuel at the injection amount set in step S34 (step S36). The ECU 70 then ends this process.

The amount of exhaust NOx immediately after fuel injection is resumed varies depending on the running state of the vehicle at the time of resuming fuel injection. If it is desired to reduce the amount of NOx emissions downstream of the exhaust purification catalyst 54 to a predetermined standard or less, it is possible to determine the allowable upper limit of the amount of oxygen storage required for the exhaust purification catalyst 54 according to the amount of exhaust NOx at the time of resuming fuel injection, and it is advisable to adjust the amount of oxygen storage so that it is less than the allowable upper limit. According to the fourth embodiment described above, the amount of exhaust NOx is predicted, and fuel is injected at the time of resuming with an injection amount according to the amount of exhaust NOx, so that the amount of NOx emissions after fuel injection is resumed can be reduced to a predetermined standard or less. In addition, if fuel is injected at the time of resuming with an injection amount that brings the amount of oxygen storage to the allowable upper limit, it is possible to suppress excess or deficiency in the injection amount in the fuel injection aimed at reducing the amount of NOx emissions to a predetermined standard or less.

In addition, based on the predicted amount of exhaust NOx, the allowable upper limit of the amount of oxygen stored in the exhaust purification catalyst 54 immediately after fuel injection is resumed is calculated, and when fuel injection is resumed, the fuel injection valve 51 is made to inject fuel at an injection amount set based on this allowable upper limit. The predicted amount of exhaust NOx is used as the basis for calculating the allowable upper limit of the amount of oxygen stored, and the injection amount at the time of resuming injection is set based on this allowable upper limit. Therefore, it is possible to set the injection amount necessary to keep the predicted amount of exhaust NOx at or below a predetermined standard. As a result, fuel injection at the time of resuming injection can be performed appropriately.

The above embodiment may be modified, for example, as follows:

- In the above embodiment, any of road gradient change information, road speed limit information, and road traffic light display information is acquired as driving route information and the fuel cut release timing RT is predicted, but this is not limited to the above. For example, information on a road section registered as having a high probability of satisfying the release conditions may be acquired as driving route information and the fuel cut release timing RT may be predicted. In such a case, if the vehicle passes through that road section while a fuel cut is being performed, the passing timing is predicted as the fuel cut release timing RT.

- In the above embodiment, examples of the timing set as the injection timing of the pre-release injection include a timing that is earlier than the release timing RT by the delay time, and a timing that is earlier than the release timing RT by the delay time plus a margin, but this is not limited to this. For example, the past average value of the time difference between the release timing RT and the injection timing of the pre-release injection is stored in the ECU 70, and a timing that is earlier than the release timing RT by the time difference of that average value may be predicted as the injection timing of the pre-release injection.

- In the above embodiment, the vehicle speed immediately before the release timing RT is assumed to be the vehicle speed immediately before the fuel cut is released, and the amount of NOx in the exhaust is predicted, but this is not limited to the above. For example, the amount of NOx in the exhaust may be predicted based on the driving tendencies of the vehicle driver. In such a case, for example, the driving tendencies of the vehicle driver are stored in the ECU 70, and the amount of NOx in the exhaust may be predicted according to the driving tendencies. Here, the driving tendencies refer to the tendency that appears when increasing the accelerator operation amount (whether to increase gradually or rapidly).

- In the above embodiment, the reaction time used as the delay time is the sum of the reaction start time and the reaction completion time, but this is not limited to this. For example, the reaction time may be a time that includes only one of the reaction start time and the reaction completion time.

The control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more dedicated computers configured by combining a processor and a memory programmed to execute one or more functions with a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transient tangible recording medium as instructions executed by the computer.

50...engine, 51...fuel injector, 52...intake pipe, 53...exhaust pipe, 54...exhaust purification catalyst, 70...ECU

Claims (3)

An engine control device (70) is applied to a vehicle engine system having an engine (50) mounted on a vehicle and in which fuel injected from a fuel injection valve (51) is combusted, and an exhaust purification catalyst (54) having an oxygen storage capacity is provided in an exhaust passage of the engine, the engine control device (70) stops fuel injection and executes a fuel cut when a predetermined fuel cut condition is satisfied, and releases the fuel cut and resumes fuel injection when a predetermined release condition is satisfied during the execution of the fuel cut,
a timing prediction unit which, when executing the fuel cut while the vehicle is traveling, acquires any one of road gradient change information, road speed limit information, and road traffic light display information, and, when the gradient change information is acquired, predicts as the timing to cancel the fuel cut the timing when the vehicle will reach a road section where the upward gradient of the road becomes larger, when the speed limit information is acquired, predicts as the timing to cancel the fuel cut the timing when the vehicle will reach a road section where the speed limit of the road increases, when the speed limit information is acquired, and predicts as the timing to cancel the fuel cut the timing when the traffic light display ahead of the vehicle changes from a stop instruction to a proceed instruction, when the traffic light display information is acquired ;
a NOx amount prediction unit that obtains at least one of the speed and weight of the vehicle when the fuel cut is executed, and predicts the amount of NOx in the exhaust gas discharged from the engine toward the exhaust purification catalyst immediately after fuel injection is resumed in response to the establishment of the release condition, so that the amount of NOx increases as the speed of the vehicle increases or the weight of the vehicle increases;
an injection control unit that sets a pre-release injection amount, which is an injection amount before the release of the fuel cut, in accordance with the NOx amount predicted by the NOx amount prediction unit when the fuel cut is performed, and causes the fuel injection valve to inject fuel at the pre-release injection amount at a timing prior to the release timing,
the injection control unit uses a relationship in which the greater the amount of NOx in the exhaust, the lower the allowable upper limit of the oxygen storage amount in the exhaust purification catalyst, and calculates the allowable upper limit immediately after fuel injection is resumed in accordance with the amount of NOx predicted by the NOx amount prediction unit, and calculates the pre-release injection amount using a relationship in which the lower the allowable upper limit, the larger the pre-release injection amount, and performs fuel injection with the pre-release injection amount at a timing prior to the release timing . a delay time calculation unit that calculates, as a delay time, a reaction time required for an oxygen storage amount to be reduced in the exhaust purification catalyst by an injected fuel when the fuel cut is being executed,
The engine control device according to claim 1 , wherein the injection control unit performs fuel injection at a timing that is at least the delay time before the release timing. 3. The engine control device according to claim 1, further comprising a supplemental injection control unit that, when the fuel cut is not released at the release timing, causes the fuel injection valve to inject a predetermined injection amount of fuel every time a predetermined time elapses during the duration of the fuel cut from the release timing .

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