JP6848465B2 - Internal combustion engine fuel injection control device - Google Patents

Description

The present invention relates to an internal combustion engine fuel injection control device applied to an internal combustion engine including an in-cylinder injection valve.

As a fuel injection control device for an internal combustion engine of this type, a device that performs a split injection process that divides fuel injection by an in-cylinder injection valve in one combustion cycle into a plurality of times is known. Each of the fuel injections performed in this way is also called a split injection. In the fuel injection control device described in Patent Document 1, the lower the rotational speed of the engine output shaft, the longer the injectable period is set, and all the divided injections are completed within the same injectable period.

By the way, as the rotation speed of the engine output shaft increases, the injection possible period becomes shorter. If all the divided injections cannot be completed within the injectable period due to such shortening of the injectable period, the fuel for the required injection amount in one combustion cycle cannot be supplied to the combustion chamber. Will end up. Therefore, in the fuel injection control device described in Patent Document 1, the shorter the injectable period, the smaller the number of divisions, which is the number of divisions in one fuel cycle, so that all the divisions can be injected. I am trying to be able to complete it within.

Japanese Unexamined Patent Publication No. 2011-106350

When the rotation speed of the engine output shaft is increased or decreased, the injectable period is also increased or decreased. In the fuel injection control device described in Patent Document 1, when the injectable period fluctuates in this way, the above-mentioned increase / decrease in the number of divisions is repeated, and the combustion of the air-fuel mixture in the combustion chamber may become unstable. is there.

A fuel injection control device for an internal combustion engine for solving the above problems is applied to an internal combustion engine including an in-cylinder injection valve for injecting fuel into a combustion chamber and an ignition plug for igniting an air-fuel mixture in the combustion chamber. This fuel injection control device has an injection control unit that divides fuel injection by an in-cylinder injection valve in one combustion cycle into a plurality of times, and a case where the divided fuel injection is divided injection. When the state of the internal combustion engine satisfies the condition for performing the split injection, the fuel injection amount in any of the split injections falls below the lower limit of the fuel injection amount set for the in-cylinder injection valve. It is provided with a number determination unit for determining the number of divisions, which is the number of division injections in one combustion cycle. Then, when the state of the internal combustion engine satisfies the condition for executing the divided injection, the injection control unit causes the divided injection for the number of divisions determined by the number determination unit to be performed within one combustion cycle. .. In addition, during the period in which the state of the internal combustion engine continuously satisfies the condition for performing the divided injection, the number of times determining unit determines all the divisions as the number of divisions in one combustion cycle. Determine the number of times that is less than or equal to the minimum number of divisions.

If the fuel injection amount in at least one divided injection falls below the lower limit, there will be a discrepancy between the total fuel injection amount in one combustion cycle and the required injection amount. The "required injection amount" here is a fuel supply amount set to be supplied to the combustion chamber in one combustion cycle.

Therefore, in the above configuration, the number of divisions in one combustion cycle is determined so that the fuel injection amount in any of the division injections in one combustion cycle does not fall below the lower limit. Therefore, assuming that the number of divisions in the previous combustion cycle is maintained, when it can be determined that the fuel injection amount is below the lower limit in at least one division injection among each division injection performed in the next combustion cycle, The number of divisions in the next combustion cycle is reduced compared to in the previous combustion cycle. As a result, it is possible to suppress the discrepancy between the total fuel injection amount and the required injection amount in one combustion cycle.

On the other hand, when the number of divisions is reduced in this way during the execution of the division injection process, the number of divisions is not increased between the time when the number of divisions is reduced and the time when the condition for performing the division injection is no longer satisfied. Therefore, the number of divisions is not repeatedly increased or decreased during the period in which the condition for performing the division injection is continuously satisfied. Therefore, it is possible to prevent the combustion of the air-fuel mixture in the combustion chamber from becoming unstable during the period in which the condition for performing the split injection is continuously satisfied.

The figure which shows the functional structure of the control device which is one Embodiment of the fuel injection control device of an internal combustion engine, and the schematic structure of the internal combustion engine provided with the control device. The graph which shows the relationship between the energization time to the in-cylinder injection valve and the fuel injection amount in the internal combustion engine. A table showing the relationship between engine cooling water and injection patterns. The flowchart explaining the processing routine executed by the number-of-times determination part of the control device. The block diagram which shows the control device which is another embodiment of the fuel injection control device of an internal combustion engine, and the outline of the internal combustion engine provided with the control device.

Hereinafter, an embodiment of the fuel injection control device for an internal combustion engine will be described with reference to FIGS. 1 to 4.
FIG. 1 shows an internal combustion engine 10 including a control device 50 as a fuel injection control device of the present embodiment. As shown in FIG. 1, the internal combustion engine 10 has a plurality of cylinders 11 (only one is shown in FIG. 1), and the air-fuel mixture containing fuel is burned in the region above the piston 12 in the cylinder 11. It is a combustion chamber 13 to be operated. Further, the internal combustion engine 10 is provided with an in-cylinder injection valve 14 for directly injecting fuel into the combustion chamber 13 and a spark plug 15 for igniting the air-fuel mixture. An intake passage 16 and an exhaust passage 17 are connected to the combustion chamber 13, and the intake passage 16 is opened and closed by the intake valve 18 and the exhaust passage 17 is opened and closed by the exhaust valve 19. It has come to be said.

The in-cylinder injection valve 14 is an electromagnetic injection valve that opens when energized, and is a full lift injection (hereinafter, referred to as "F / L injection") and a partial lift injection (hereinafter, "P / L injection"). It is possible to execute. The F / L injection is an injection form in which the valve body of the in-cylinder injection valve 14 is displaced to the fully open position and then the energization is stopped to stop the fuel injection, while the P / L injection is the valve of the in-cylinder injection valve 14. This is an injection form in which energization is stopped and fuel injection is stopped before the body is displaced to the fully open position.

Further, as shown in FIG. 2, the fuel injection amount Qf of the in-cylinder injection valve 14 increases as the energization time TM of the in-cylinder injection valve 14 to the electromagnetic solenoid becomes longer. In FIG. 2, the first energization time TM1 is the minimum energization time TM that can appropriately control the valve opening time of the valve body, and the second energization time TM2 starts energization to the electromagnetic solenoid. It is the energization time TM from the time when the valve body reaches the fully open position. The P / L injection is the fuel injection when the energization time TM is set to a time less than the second energization time TM2, and the F / L injection is the fuel injection when the energization time TM is set to the second energization time TM2 or more. It can be said that it is fuel injection in the case of.

In the internal combustion engine 10, the delivery fuel pressure, which is the pressure of the fuel supplied to the in-cylinder injection valve 14, can be appropriately changed. Therefore, even if the energization time TM of the in-cylinder injection valve 14 is constant, the higher the delivery fuel pressure, the larger the fuel injection amount Qf of the in-cylinder injection valve 14. That is, the minimum injection amount Qfmin shown in FIG. 2 is the fuel injection amount Qf when the energization time TM is equal to the first energization time TM1, and is a value that changes depending on the delivery fuel pressure. The slope of the solid line shown in FIG. 2 also changes depending on the delivery fuel pressure.

By the way, even if the energization time TM to the in-cylinder injection valve 14 is set to less than the first energization time TM1, fuel may be injected from the in-cylinder injection valve 14. However, in this case, since the valve opening time cannot be appropriately controlled, it is difficult to appropriately control the fuel injection amount of the in-cylinder injection valve 14. Therefore, in the present embodiment, the region of the energization time in which the energization time TM is less than the first energization time TM1 is referred to as "minimum energization region R1".

Further, in the in-cylinder injection valve 14, the valve body vibrates immediately after the valve body reaches the fully open position, and the fuel injection amount tends to be unstable. When the lower limit of the energization time TM capable of controlling the fuel injection amount Qf by F / L injection with high accuracy is set to the third energization time TM3, the energization time TM is the second energization time TM2 or more and the third energization time TM3. The region of the energization time of less than TM3 is referred to as "bounce region R2". When the energization time TM to the in-cylinder injection valve 14 is included in the bounce region R2, the fuel injection amount Qf of the in-cylinder injection valve 14 may deviate from the required injection amount.

On the other hand, the P / L injection region Rpl in which the energization time TM to the in-cylinder injection valve 14 is equal to or longer than the first energization time TM1 and less than the second energization time TM2, and the energization time TM are the third. It can be said that both of the F / L injection regions Rfl having an energization time of TM3 or more are regions in which the fuel injection amount Qf is more controllable than the above-mentioned minimal energization region R1 and bounce region R2. Therefore, in the present embodiment, when the in-cylinder injection valve 14 is to perform P / L injection, the minimum injection amount Qfmin corresponds to the lower limit of the fuel injection amount set for the in-cylinder injection valve 14. Further, when the fuel injection amount Qf when the energization time TM is equal to the third energization time TM3 is set to the minimum injection amount QfminFl at F / L, when the in-cylinder injection valve 14 is to perform F / L injection, F / The minimum injection amount QfminFl at L corresponds to the lower limit of the fuel injection amount set for the in-cylinder injection valve 14.

As shown in FIG. 1, various detection systems such as a crank sensor 101, an air flow meter 102, a water temperature sensor 103, and a fuel pressure sensor 104 are electrically connected to the control device 50. The crank sensor 101 detects the engine rotation speed NE, which is the rotation speed of the crankshaft, and the air flow meter 102 detects the intake air amount, which is the amount of intake intake air introduced into the combustion chamber 13 from the intake passage 16. Further, the water temperature sensor 103 detects the water temperature TMP, which is the temperature of the engine cooling water flowing in the internal combustion engine 10, and the fuel pressure sensor 104 detects the delivery fuel pressure. Then, based on the information detected by these various detection systems, various controls are executed by the control device 50.

In the present embodiment, stratified combustion may be performed in the combustion chamber 13 when the engine is started or when the catalyst provided in the exhaust passage 17 is rapidly warmed up. The "engine start time" here is a period from the start time of the cranking operation to the time when the internal combustion engine 10 is completely detonated.

Stratified combustion realizes combustion in an extremely lean state by forming a layer having a high fuel concentration in the vicinity of the spark plug 15 in the combustion chamber 13. Then, in the internal combustion engine 10, stratified combustion can be realized by performing fuel injection by the in-cylinder injection valve 14 in a plurality of times in the cylinder 11 during the compression stroke, that is, in the combustion chamber 13. It should be noted that each of the fuel injections by the in-cylinder injection valve 14 which is divided into a plurality of times in the compression stroke is also referred to as "divided injection".

As shown in FIG. 1, the control device 50 is a number determination unit 51 and an injection control unit as functional units for dividing the fuel injection by the in-cylinder injection valve 14 in one combustion cycle into a plurality of times. It has 52. When the fuel injection is divided into a plurality of times in one combustion cycle, the number-of-times determination unit 51 determines the number of divisions N, which is the number of times the divided injection is performed in one combustion cycle. That is, the number-of-times determining unit 51 makes sure that the fuel injection amount Qf in any of the divided injections in one combustion cycle does not fall below the lower limit of the fuel injection amount Qf set for the in-cylinder injection valve 14. The number of divisions N is determined. Further, the number determination unit 51, in addition to the determination of the number of divisions N, that are also carried out the calculation of the fuel injection amount Qf of the split injection.

When the engine is started or the catalyst is warmed up, the injection control unit 52 causes the injection control unit 52 to perform a plurality of divided injections in one combustion cycle based on the determination result (division number N and fuel injection amount Qf) by the number determination unit 51. The split injection process is performed.

Note that FIG. 3 shows an example of a table used prior to carrying out the split injection process. “DI” in FIG. 3 means fuel injection by the in-cylinder injection valve 14. As shown in FIG. 3, the injection pattern including the number of divisions N and the injection form of the in-cylinder injection valve 14 is determined by the water temperature TMP of the engine cooling water detected by the water temperature sensor 103. Specifically, the first injection pattern is a pattern selected when the water temperature TMP is less than the first determination water temperature TMPTh1. When the water temperature TMP is less than the first determination water temperature TMPTh1, it can be determined that it is difficult to perform stratified combustion in the combustion chamber 13 because the water temperature TMP is extremely low. Therefore, when the first injection pattern is selected, the number of divisions N is equal to "4", and all four division injections in one combustion cycle are performed during the intake stroke. ..

On the other hand, when the water temperature TMP is equal to or higher than the first determined water temperature TMPTh1, stratified combustion can be performed in the combustion chamber 13. That is, the second injection pattern is selected when the water temperature TMP is equal to or higher than the first determination water temperature TMPTh1 and the water temperature TMP is lower than the second determination water temperature TMPTh2 higher than the first determination water temperature TMPTh1. It is a pattern. When this second injection pattern is selected, the number of divisions N is equal to "3", and all three division injections in one combustion cycle are performed during the compression stroke. Further, when the water temperature TMP is equal to or higher than the first determination water temperature TMPTh1 and the water temperature TMP is less than the second determination water temperature TMPTh2, the required injection amount, which is the amount of fuel required to be injected in one combustion cycle. Is relatively large, so all three split injections are determined to be F / L injections.

The third injection pattern is selected when the water temperature TMP is equal to or higher than the second determination water temperature TMPTh2 and the water temperature TMP is higher than the second determination water temperature TMPTh2 and lower than the third determination water temperature TMPTh3. It is a pattern. When this third injection pattern is selected, the number of divisions N is equal to "3", and all three division injections in one combustion cycle are performed during the compression stroke. Further, when the water temperature TMP is equal to or higher than the second determination water temperature TMPTh2 and the water temperature TMP is less than the third determination water temperature TMPTh3, the required injection amount in one combustion cycle is determined by the water temperature TMP as the second determination. Less than when the water temperature is less than TMPTh2. Therefore, of the three divided injections, the first divided injection and the second divided injection are determined to be F / L injections, and the third divided injection is determined to be P / L injections.

The fourth injection pattern is selected when the water temperature TMP is equal to or higher than the third determination water temperature TMPTh3 and the water temperature TMP is higher than the third determination water temperature TMPTh3 and lower than the fourth determination water temperature TMPTh4. It is a pattern. When this fourth injection pattern is selected, the number of divisions N is equal to "3", and all three division injections in one combustion cycle are performed during the compression stroke. Further, when the water temperature TMP is equal to or higher than the third determination water temperature TMPTh3 and the water temperature TMP is less than the fourth determination water temperature TMPTh4, the required injection amount in one combustion cycle is determined by the water temperature TMP as the third determination. Less than when the water temperature is less than TMPTh3. Therefore, of the three divided injections, the first divided injection is determined to be the F / L injection, and the second divided injection and the third divided injection are determined to be the P / L injection.

The fifth injection pattern is a pattern selected when the water temperature TMP is equal to or higher than the fourth determination water temperature TMPTh4. When this fifth injection pattern is selected, the number of divisions N is equal to "2", and all of the two division injections in one combustion cycle are performed during the compression stroke.

Next, with reference to FIG. 4, a processing routine in which the execution by the number-of-times determining unit 51 is started prior to the injection control unit 52 starting the execution of the divided injection process will be described.
As shown in FIG. 4, in this processing routine, the number-of-times determination unit 51 determines an injection pattern according to the water temperature TMP at the start of the split injection process using the table described with reference to FIG. 3 (step S11). .. The number of divisions N acquired by determining the injection pattern is referred to as the reference number of divisions Nb. Further, in step S11, the number-of-times determination unit 51 calculates the required injection amount in one combustion cycle based on the engine rotation speed NE and the water temperature TMP, and calculates the fuel injection amount Qf of each divided injection. Subsequently, the number-of-times determination unit 51 determines whether or not the history flag FLG, which will be described later, is set to off (step S12). When the history flag FLG is set to ON (step S12: NO), the number-of-times determination unit 51 shifts the process to step S15, which will be described later.

On the other hand, when the history flag FLG is set to off (step S12: YES), the number-of-times determining unit 51 performs split injection in which the fuel injection amount Qf is less than the lower limit in each split injection in one combustion cycle. It is determined whether or not there is (step S13). For the split injection that is the P / L injection, it is determined whether or not the fuel injection amount Qf is less than the minimum injection amount Qfmin (see FIG. 2). Further, for the divided injection which is the F / L injection, it is determined whether or not the fuel injection amount Qf is less than the minimum injection amount QfminFl at F / L (see FIG. 2).

When the fuel injection amount Qf is equal to or higher than the lower limit in any of the divided injections (step S13: NO), the number of divisions 51 makes the number of divisions N equal to the reference number of divisions Nb (step S14). Then, the number-of-times determination unit 51 shifts the process to step S16, which will be described later. On the other hand, when the fuel injection amount Qf becomes less than the lower limit in at least one divided injection among the divided injections (step S13: YES), the number-of-times determination unit 51 shifts the process to the next step S15.

In step S15, the number of times determination unit 51 equalizes the number of divisions N with the value decremented by "1" from the reference number of divisions Nb determined in step S11, and sets the history flag FLG to ON. That is, the history flag FLG is a flag that is set to off when the number of divisions N is not decreased from the reference number of divisions Nb, while is set to on when the number of divisions N is decreased from the reference number of divisions Nb. .. Further, in step S15, the number-of-times determination unit 51 performs a recalculation process of allocating the required injection amount in one combustion cycle to each divided injection. As a result, the fuel injection amount Qf in any of the divided injections does not fall below the lower limit. Then, the number-of-times determination unit 51 shifts the process to the next step S16.

In step S16, the number-of-times determination unit 51 determines whether or not the execution of the split injection process is completed. When the split injection process is executed at the time of engine start, the number of times determination unit 51 determines that the execution of the split injection process is completed when the engine start is completed. Further, when the split injection process is performed during the catalyst warm-up, the number-of-times determination unit 51 determines that the split injection process is completed when the catalyst warm-up is completed.

Then, when the execution of the split injection process is not yet completed (step S16: NO), the number-of-times determination unit 51 shifts the process to step S12 described above. On the other hand, when the execution of the split injection process is completed (step S16: YES), the number-of-times determination unit 51 sets the history flag FLG to off (step S17), and ends this process routine.

Next, the action when the split injection process is carried out will be described together with the effect.
When the split injection process is performed, the number of splits N is determined so that the fuel injection amount Qf in any split injection in one combustion cycle does not fall below the lower limit. That is, when the number of divisions N is equal to the reference number of divisions Nb, it can be determined that the fuel injection amount Qf in at least one division injection among the division injections to be performed in the next combustion cycle is below the lower limit. In the next combustion cycle, the number of divisions N is reduced from the reference number of divisions Nb. As a result, as compared with the case where the number of divisions N is not reduced, the fuel injection amount Qf in each division injection is increased by the amount that the number of divisions N is reduced. As a result, an amount of fuel corresponding to the required injection amount in one combustion cycle can be supplied into the combustion chamber 13. Therefore, when the water temperature TMP is equal to or higher than the first determination water temperature TMPTh1, stratified combustion can be appropriately performed in the combustion chamber 13.

Further, in the present embodiment, when the number of divisions N is reduced in this way during the execution of the divided injection process, the number of divisions N is set between the time when the number of divisions N is reduced and the time when the execution of the divided injection process is completed. Not increased. Therefore, the increase / decrease in the number of divisions N is not repeated during the execution of the division injection process. Therefore, it is possible to prevent the combustion of the air-fuel mixture in the combustion chamber 13 from becoming unstable during the split injection process.

The above embodiment may be changed to another embodiment as described below.
-If the internal combustion engine is provided with an in-cylinder injection valve 14 and stratified combustion is performed in the combustion chamber 13 when the engine is started or the catalyst is warmed up, fuel is supplied to the intake passage 16 as shown in FIG. 5, for example. It may also be provided with a port injection valve 25 for injecting fuel.

-In the split injection process, fuel injection of any one of the plurality of split injections may be performed during the intake stroke. In this case, the difference in fuel concentration between the layer having a high fuel concentration formed in the vicinity of the spark plug 15 in the combustion chamber 13 and the layers other than the layer is smaller than that in the case of the above embodiment. However, stratified combustion (also referred to as "weak stratified combustion") can be performed.

10 ... Internal combustion engine, 13 ... Combustion chamber, 14 ... In-cylinder injection valve, 15 ... Spark plug, 50 ... Control device, 51 ... Number of times determination unit, 52 ... Injection control unit.

Claims (1)

It is applied to an internal combustion engine including an in-cylinder injection valve that injects fuel into a combustion chamber and a spark plug that ignites an air-fuel mixture in the combustion chamber.
An injection control unit that divides fuel injection by the in-cylinder injection valve in one combustion cycle into a plurality of times.
When the divided fuel injection is defined as the divided injection, when the state of the internal combustion engine satisfies the condition for executing the divided injection, the fuel injection amount in any of the divided injections is the said. A number determination unit for determining the number of divisions, which is the number of divisions in one combustion cycle, is provided so as not to fall below the lower limit of the fuel injection amount set for the in-cylinder injection valve.
When the state of the internal combustion engine satisfies the condition for executing the divided injection, the injection control unit performs the divided injection for the number of divisions determined by the number determination unit within one combustion cycle. It is supposed to be done,
During the period in which the state of the internal combustion engine continuously satisfies the condition for performing the divided injection, the number of times determining unit determines all the divided times in one combustion cycle during the period. A fuel injection control device for an internal combustion engine that determines the number of divisions that is less than or equal to the minimum number of divisions.

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