JP2019052632A - Controller of in-cylinder injection type internal combustion engine - Google Patents

Abstract

To provide a controller of an in-cylinder injection type internal combustion engine capable of preventing an injection pulse width per time of multistage injection from going below a minimum injection pulse width, and also capable of maintaining the number of times for injection in the multistage injection to an optimal value.SOLUTION: A controller is configured to, in a condition that an injection pulse width TIsn per time of multistage injection goes below a minimum injection pulse width TImin when fuel pressure is basic fuel pressure, more reduce the fuel pressure than the basic fuel pressure, and perform multistage injection so that the injection pulse width TIsn per time goes beyond the minimum injection pulse width TImin.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a control device for a direct injection internal combustion engine, and more particularly to control of multi-stage injection in which fuel is injected in a plurality of times during one combustion cycle.

  In Patent Document 1, when the engine temperature is equal to or lower than a predetermined temperature, the total injection pulse width required during one combustion cycle increases as the total injection amount to be injected during one combustion cycle increases. Accordingly, there has been disclosed a fuel injection control device for a direct injection engine characterized in that the number of divided injections in one combustion cycle is increased.

Japanese Patent Laid-Open No. 2014-020211

By the way, in the cylinder injection internal combustion engine, when performing multi-stage injection in which the total fuel injection amount in one combustion cycle is divided into multiple injections, the number of injections in multi-stage injection (the number of divisions of the total fuel injection amount) is It is adapted to the number of times that the number of exhausted particulate matter PN (Particulate Number) and the amount of fuel dissolved in the engine oil (oil dilution amount) can be sufficiently suppressed.
However, depending on the change in friction in the internal combustion engine and the operating state of the auxiliary machinery, etc., if the optimal number of injections is set, the injection pulse width per multistage injection is the minimum injection pulse width that can maintain the fuel measurement accuracy. There was a possibility of falling below.
Here, if the number of injections in multi-stage injection is reduced from the optimum number in order to ensure an injection pulse width equal to or greater than the minimum injection pulse width, there arises a problem that PN and oil dilution amount deteriorate.

  The present invention has been made in view of the conventional situation, and an object of the present invention is to enable the number of injections in multistage injection while suppressing that the injection pulse width per single multistage injection is less than the minimum injection pulse width. An object of the present invention is to provide a control device for a direct injection internal combustion engine that can be maintained at an optimum value.

  According to the present invention, in one aspect thereof, when the fuel pressure is the base fuel pressure, the fuel pressure is lower than the base fuel pressure when the injection pulse width per injection in the multistage injection is less than the minimum injection pulse width. The multi-stage injection is performed such that the injection pulse width per one time exceeds the minimum injection pulse width.

  According to the above-described invention, the number of injections in multistage injection can be maintained at the optimum value as much as possible while suppressing the injection pulse width per single multistage injection from being less than the minimum injection pulse width.

It is a figure which shows the fuel-injection system of a cylinder injection type internal combustion engine. It is a block diagram which shows the fuel-injection control function of a control apparatus. It is a time chart which illustrates behavior, such as fuel pressure FP, target injection frequency Ntg, and pulse ratio PR, when processing for reducing the number of injections in multistage injection is performed. It is a diagram which shows the change of PN with respect to fuel pressure for every injection frequency of multistage injection. It is a time chart which illustrates behavior, such as fuel pressure FP, target injection frequency Ntg, and pulse ratio PR, when processing for reducing fuel pressure is performed. It is a time chart which illustrates behavior, such as fuel pressure FP, target injection frequency Ntg, and pulse ratio PR, when processing for reducing fuel pressure and processing for reducing the number of injections in multistage injection are performed. It is a time chart which illustrates behavior, such as fuel pressure FP, target injection frequency Ntg, and pulse ratio PR, when processing for reducing the injection frequency in multistage injection is performed after warm-up.

Embodiments of the present invention will be described below.
FIG. 1 is a diagram showing a fuel injection system for a cylinder injection internal combustion engine for a vehicle.
The fuel injection system of FIG. 1 includes an internal combustion engine 101, a fuel injection valve 105, and an ECU (Engine Control Unit) 109, which is a computer that performs overall control of the internal combustion engine 101 including fuel injection by the fuel injection valve 105. Have.

In FIG. 1, the intake air of the internal combustion engine 101 passes through an air flow meter 120, an electric throttle valve 119, and a collector 115 in this order, and is then sucked into the combustion chamber 121 via an intake pipe 110 and an intake valve 103 provided in each cylinder. Is done.
On the other hand, the electric low-pressure fuel pump 124 sends the fuel in the fuel tank 123 to the engine-driven high-pressure fuel pump 125.

The high-pressure fuel pump 125 boosts the fuel supplied from the low-pressure fuel pump 124 and sends it to the fuel injection valve 105 through the high-pressure fuel pipe 128. The ECU 109 adjusts the discharge amount of the high-pressure fuel pump 125. The pressure of the fuel sent to the fuel injection valve 105 (hereinafter referred to as fuel pressure) is controlled to the target fuel pressure.
The fuel tank 123, the low pressure fuel pump 124, the high pressure fuel pump 125, the high pressure fuel pipe 128, and the like constitute a fuel supply device 129 that varies the fuel pressure supplied to the fuel injection valve 105.

The fuel injection valve 105 is an electromagnetic fuel injection valve that directly injects fuel into the combustion chamber 121 (in-cylinder) of the internal combustion engine 101. The fuel injection valve 105 receives a command (injection pulse signal) from the ECU 109 and is designated by the command. By opening the valve for a predetermined time, an amount of fuel proportional to the valve opening time is injected into the combustion chamber 121.
The ECU 109 sets the total amount of fuel (total fuel injection amount) to be injected from the fuel injection valve 105 during one combustion cycle (one cycle per cylinder) based on the engine operating state, and also determines the total fuel injection based on the engine operating state. The number of injections in the multistage injection in which the amount is divided into a plurality of times in one combustion cycle (the number of divisions of the total fuel injection amount) is set, and the multistage injection by the fuel injection valve 105 is controlled.
That is, the ECU 109 functions as a total injection amount setting unit that sets the total fuel injection amount, a number setting unit that sets the number of injections in multi-stage injection, and a multi-stage injection control unit that performs multi-stage injection by the fuel injection valve 105. Prepare as software.

The fuel pressure sensor 126 detects the fuel pressure FP in the high-pressure fuel pipe 128, that is, the fuel pressure FP supplied to the fuel injection valve 105.
Then, the ECU 109 calculates a deviation ΔFP between the fuel pressure FP detected by the fuel pressure sensor 126 and the target fuel pressure FPtg set according to the engine operating conditions, and adjusts the discharge amount of the high-pressure fuel pump 125. So-called feedback control is performed in which the operation amount is set by a proportional operation, an integral operation, or the like based on the deviation ΔFP, and the fuel pressure FP is brought close to the target fuel pressure FPtg.

The internal combustion engine 101 includes an ignition device having an ignition coil 107 and an ignition plug 106.
The ECU 109 controls generation of a spark (spark) by the spark plug 106 by controlling energization to the ignition coil 107.

The air-fuel mixture in the combustion chamber 121 is ignited and burned by the spark generated by the spark plug 106, and the exhaust gas generated by the combustion is discharged from the combustion chamber 121 to the exhaust pipe 111 via the exhaust valve 104.
The exhaust pipe 111 is provided with a catalytic converter 112 that houses a three-way catalyst for purifying exhaust gas.

  The ECU 109 is a water temperature sensor 108 that measures the water temperature TW, which is the temperature of the cooling water of the internal combustion engine 101, a crank angle sensor 116 that measures the angle of the crankshaft (not shown) of the internal combustion engine 101, and the intake air flow rate QA of the internal combustion engine 101. An air flow meter 120 that measures the air-fuel ratio, an air-fuel ratio sensor 113 that detects the air-fuel ratio of the air-fuel mixture based on the oxygen concentration in the exhaust gas of the internal combustion engine 101, and an accelerator opening sensor 122 that indicates the accelerator opening ACC operated by the driver. , And a detection signal from the fuel pressure sensor 126 described above is input.

The ECU 109 calculates the required torque of the internal combustion engine 101 from the signal of the accelerator opening sensor 122 and determines whether or not the internal combustion engine 101 is in an idle operation state.
Further, the ECU 109 calculates the engine rotational speed NE based on the detection signal of the crank angle sensor 116, and determines whether or not the internal combustion engine 101 is warming up based on the detection signal of the water temperature sensor 108.

  Further, the ECU 109 calculates a target intake air amount from the above-mentioned required torque and the like, outputs an opening signal corresponding to the target intake air amount to the electric throttle valve 119, and performs total fuel injection in one combustion cycle. The amount is calculated based on the intake air amount, the engine rotational speed, etc., and the multi-stage injection is performed by the fuel injection valve 105. Further, the ignition timing is calculated according to the engine load, the engine rotational speed, etc., and the ignition coil 107 receives an ignition signal. Is output.

FIG. 2 is a functional block diagram showing the multi-stage injection control function provided in the ECU 109.
The basic injection pulse width calculation unit 200 mixes the stoichiometric air-fuel ratio when the fuel pressure FP is the reference fuel pressure FPs based on the intake air flow rate QA detected by the air flow meter 120 and the engine speed NE (engine speed rpm). A basic fuel injection pulse width TP [ms] for generating a gas is calculated.

The fuel injection pulse width calculation unit 201 (total injection amount setting unit) uses the basic fuel injection pulse width TP based on various fuel correction terms based on operating conditions such as the water temperature TW and the fuel pressure FP detected by the fuel pressure sensor 126. The total fuel injection pulse width TI in one combustion cycle is calculated with correction according to the fuel pressure correction term.
The total fuel injection pulse width TI corresponds to the total fuel injection amount injected from the fuel injection valve 105 during one combustion cycle.

The target fuel pressure map unit 202 includes, for example, a map in which the target fuel pressure FPtgm is stored for each of a plurality of combustion modes in accordance with operating conditions such as the basic fuel injection pulse width TP (engine load), engine speed NE, and water temperature TW.
The plurality of combustion modes include, for example, a stratified combustion mode, a homogeneous combustion mode, a retard mode of ignition timing during catalyst warm-up, and the like.

The multi-stage injection number map unit 203 (number-of-times setting unit) is, for example, a target injection number Ntgm (total fuel) in multi-stage injection according to operating conditions such as basic fuel injection pulse width TP (engine load), engine speed NE, and water temperature TW. The map which memorize | stored the division | segmentation number of the injection pulse width TI) is provided for every some combustion mode.
The multi-stage injection division ratio map unit 204 stores a plurality of maps storing the target division ratio SRtgm for multi-stage injection according to operating conditions such as the basic fuel injection pulse width TP (engine load), the engine speed NE, and the water temperature TW. Provided for each combustion mode and number of injections N.

Here, the target split ratio SRtgm designates what percentage of the total fuel injection pulse width TI is allocated to each injection of the multistage injection, and the sum of the split ratio (%) in each injection of the multistage injection is 100. %become.
For example, in multi-stage injection in which the total fuel injection pulse width TI is divided into two injections (target injection number Ntgm = 2), when the split ratio SR of the initial injection is specified as 25%, the total fuel injection is performed in the initial injection. 25% of the pulse width TI is injected, and 75% of the total fuel injection pulse width TI is injected in the second injection. However, the total fuel injection pulse width TI can be equally allocated to each injection in multistage injection.

The injection timing map unit 205 stores, for example, a plurality of maps that store the injection timing IT of each injection of the multi-stage injection according to operating conditions such as the basic fuel injection pulse width TP (engine load), the engine speed NE, and the water temperature TW. For each combustion mode and every number of injections Ntg.
The multi-stage injection control unit 206 receives information on the total fuel injection pulse width TI, the minimum injection pulse width TImin that can maintain the fuel measurement accuracy with the fuel injection valve 105, and the combustion mode, and the operating conditions at that time from the target fuel pressure map unit 202 The target fuel pressure FPtgm corresponding to is searched, and the target injection number Ntgm corresponding to the operation condition at that time is searched from the multistage injection number map unit 203.

The multi-stage injection control unit 206 then multi-stages at the target number of injections Ntgm under the conditions of the current target fuel pressure FPtgm (base fuel pressure) based on the total fuel injection pulse width TI, the minimum injection pulse width TImin, and the target injection number Ntgm. It is determined whether or not injection is possible.
When it is assumed that the multi-stage injection control unit 206 performs multi-stage injection by dividing the total fuel injection pulse width TI equally into the target injection number Ntgm, the injection pulse width TIsn (TIsn = TI / Ntgm) in each injection of the multi-stage injection is When the minimum injection pulse width TImin is exceeded, it is determined that multi-stage injection can be performed with the target injection number Ntgm and the target fuel pressure FPtgm as preconditions.

At this time, the multi-stage injection control unit 206 sets the target injection number Ntgm as it is as the final target injection number Ntg, and uses the target injection number Ntg as will be described later for the multi-stage injection division ratio control unit 207 and the multi-stage injection timing control unit 208. In addition, the target fuel pressure FPtgm is set to the final target fuel pressure FPtg as it is, and is output to the fuel pressure control unit 209.
The fuel pressure control unit 209 performs feedback control for adjusting the discharge amount of the high-pressure fuel pump 125 based on the target fuel pressure FPtg and the fuel pressure FP detected by the fuel pressure sensor 126.

On the other hand, when it is assumed that the multi-stage injection control unit 206 performs multi-stage injection by dividing the total fuel injection pulse width TI equally into the target injection number Ntgm, the injection pulse width TIsn in each injection of the multi-stage injection is the minimum injection pulse width TImin. If it is less than, it is determined that multi-stage injection at the target number of injections Ntgm and the target fuel pressure FPtgm as the preconditions is impossible.
That is, when multi-stage injection is performed with an injection pulse width TIsn that is less than the minimum injection pulse width TImin, the fuel measurement accuracy by the fuel injection valve 105 decreases, and an amount of fuel that matches the total fuel injection pulse width TI is accurately injected. Inability to control the air-fuel ratio decreases.

Therefore, the multi-stage injection control unit 206 determines that the multi-stage injection is impossible when the multi-stage injection is performed with the injection pulse width TIsn lower than the minimum injection pulse width TImin. The conditions for multi-stage injection are changed so that injection is performed.
Specifically, the multi-stage injection control unit 206 obtains the target fuel pressure FPtg from the map according to the operation conditions at that time when the multi-stage injection is performed with the injection pulse width TIsn lower than the minimum injection pulse width TImin. By reducing it below the target fuel pressure FPtgm (base fuel pressure), the injection pulse width (valve opening time) required to inject the same amount of fuel is lengthened, and the target number of injections Ntgm is not changed. The injection pulse width TIsn is set to be equal to or greater than the minimum injection pulse width TImin.
With the control function of the multi-stage injection control unit 206, the multi-stage injection with the injection pulse width TIsn below the minimum injection pulse width TImin while maintaining the optimum target injection number Ntgm, that is, the fuel measurement accuracy of the fuel injection valve 105 is improved. Reduction is suppressed.

Further, the multi-stage injection control unit 206 may reduce the target fuel pressure FPtg to a predetermined lower limit value (limiter FPmin). If the injection pulse width TIsn in each injection of the multi-stage injection does not exceed the minimum injection pulse width TImin, the target fuel pressure The FPtg is returned to the base fuel pressure, and the target injection number Ntg is reduced from the target injection number Ntgm (base injection number) obtained from the map in accordance with the operation conditions at that time, whereby the injection pulse width TIsn in each injection of multistage injection. Is greater than or equal to the minimum injection pulse width TImin.
The control function of the multi-stage injection control unit 206 can prevent the target fuel pressure FPtg from being excessively lowered, and can perform multi-stage injection with an injection pulse width TIsn less than the minimum injection pulse width TImin, that is, fuel by the fuel injection valve 105. The decrease in weighing accuracy is suppressed.

The multistage injection division ratio control unit 207 receives information such as the target number of injections Ntg, the total fuel injection pulse width TI, the minimum injection pulse width TImin, and the combustion mode set by the multistage injection control unit 206, and receives a multistage injection division ratio map unit. A target division ratio SRtgm corresponding to the operation condition and the target injection number Ntg at that time is searched from 204.
Then, the multistage injection split ratio control unit 207 determines whether multistage injection at the target split ratio SRtgm is possible from the total fuel injection pulse width TI, the minimum injection pulse width TImin, the target injection number Ntg, and the target split ratio SRtgm. Judging.

That is, when it is assumed that the multistage injection split ratio control unit 207 divides the total fuel injection pulse width TI into the target injection number Ntg and sets the injection pulse width TIsn of each injection according to the target split ratio SRtgm. In addition, if all of the injection pulse widths TIsn of the respective injections are equal to or larger than the minimum injection pulse width TImin, it is determined that the multistage injection with the pulse width allocation according to the target division ratio SRtgm is possible.
On the other hand, when it is assumed that the multistage injection split ratio control unit 207 divides the total fuel injection pulse width TI into the target injection number Ntg and sets the injection pulse width TIsn of each injection according to the target split ratio SRtgm. In addition, if there is an injection pulse width TIsn of each injection that is less than the minimum injection pulse width TImin, it is determined that the multistage injection with the assignment of the pulse width according to the target split ratio SRtgm is impossible.

If the multistage injection split ratio control unit 207 determines that multistage injection at the target split ratio SRtgm is possible, the target split ratio SRtgm retrieved from the map is set as the final target split ratio SRtg as it is and output.
If the multistage injection split ratio control unit 207 determines that multistage injection at the target split ratio SRtgm is impossible, the multistage injection split ratio control unit 207 increases the injection split ratio SR set to the injection pulse width TIsn that is less than the minimum injection pulse width TImin. The injection pulse width TIsn greater than or equal to the minimum injection pulse width TImin is corrected and the injection pulse division ratio set to the injection pulse width TIsn greater than or equal to the minimum injection pulse width TImin is relatively set. Is reduced within a range that does not fall below the minimum injection pulse width TImin.

That is, the multistage injection split ratio control unit 207 adjusts the allocation of the total fuel injection pulse width TI to each injection time so that the injection pulse widths at each injection time do not fall below the minimum injection pulse width TImin. .
Then, the multistage injection split ratio control unit 207 outputs the target split ratio SRtgm corrected as described above as the final target split ratio SRtg.
The multi-stage injection split ratio control unit 207 determines that the total fuel injection pulse width TI is set for each injection of multi-stage injection when it is determined that multi-stage injection is not possible with the pulse width allocation according to the target split ratio SRtgm. The target division ratio SRtg to be allocated evenly can be output.

The multi-stage injection timing control unit 208 receives information on the target number of injections Ntg and the combustion mode, and searches the injection timing map unit 205 for the injection timing IT corresponding to the operating condition and the target number of injections Ntg at that time.
The fuel injection valve drive control unit 210 receives information on the target number of injections Ntg, the target split ratio SRtg, the total fuel injection pulse width TI, and the injection timing IT, and determines the injection pulse width TIsn of each injection of the multistage injection in accordance with the command. The injection pulse signal having the injection pulse width TIsn is output to the fuel injection valve 105 at a timing according to the command of the injection timing IT.

  FIG. 3 shows a target without changing the target fuel pressure FPtg as control for the ECU 109 to make the injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin when the internal combustion engine 101 is in the cold idle state. It is a time chart which illustrates behaviors, such as target injection frequency Ntg and pulse ratio PR, when implementing injection frequency control which reduces injection frequency Ntg.

The first idle means that the idling rotational speed after starting is made higher than that after warming up in order to maintain rotation, warming up and running performance after the cold starting of the internal combustion engine 101 (during warming up). This is an operating condition in which the target number of injections Ntgm is set to a relatively large number, the total fuel injection pulse width TI is short, and the injection pulse width TIsn tends to be less than the minimum injection pulse width TImin.
The pulse ratio PR is a value calculated as RP = TImin × Ntg / TI based on the target number Ntg of multistage injections, the minimum injection pulse width TImin, and the total fuel injection pulse width TI.

Therefore, when the injection pulse width TIsn when the total fuel injection pulse width TI is equally divided into the target number of injections Ntg matches the minimum injection pulse width TImin, the pulse ratio PR = 1.0, and the pulse ratio PR is equal to the total fuel injection pulse. As the injection pulse width TIsn obtained by equally dividing the width TI into the target number of injections Ntg is larger than the minimum injection pulse width TImin, the value becomes smaller than 1.0.
When the pulse ratio PR exceeds 1.0, it indicates that the injection pulse width TIsn when evenly allocated is less than the minimum injection pulse width TImin. When the pulse ratio PR is 1.0 or less, the injection pulse width when evenly allocated TIsn is equal to or greater than the minimum injection pulse width TImin, indicating that multistage injection at the target injection number Ntg is possible.

In the cold start first idle state which is the operating condition of the internal combustion engine 101 in FIG. 3, in other words, in the warm up state of the internal combustion engine 101, the target idle rotation speed is set higher than after warm up, and the ignition timing is set to warm up. In some cases, the catalyst warm-up of the catalytic converter 112 is promoted by retarding later.
When the catalyst warm-up promotion process is performed, the intake air amount of the internal combustion engine 101 is large in an idle state, and the fuel pressure FP is set to a high fuel pressure of, for example, 20 MPa or more for PN reduction. Yes, in the example of FIG. 3, the target number of injections Ntgm is set to three.
Here, in the case of the internal combustion engine 101 in which the required air amount in the first idle state is relatively small due to individual differences, the total fuel injection pulse width TI decreases as the engine rotational speed approaches the target idle rotational speed after startup, and the pulse The ratio PR gradually increases.

The determination value X shown in FIG. 3 is a threshold value of the pulse ratio PR for determining whether or not multi-stage injection at the target number of injections Ntg is impossible. For example, the determination value X is set to 1.0. The determination value X can be set to X <1.0 in consideration of variations in the valve opening characteristics of the fuel injection valve 105 and the like.
When the pulse ratio PR exceeds the determination value X at time t1, the ECU 109 determines that multistage injection at the target injection number Ntgm (map value) is impossible, and reduces the target injection number Ntg from three to two. .

When the target number of injections Ntg is changed from 3 times to 2 times, the pulse ratio PR is rapidly reduced. For example, PR = 1.034 under the conditions of TImin = 0.5 ms, TI = 1.45 ms, and Ntg = 3, whereas PR = 0.689 under the conditions of TImin = 0.5 ms, TI = 1.45 ms, and Ntg = 2. By reducing the target number of injections Ntg from three to two, multistage injection (two injections, two-part injection) can be performed with an injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin.
However, by reducing the target number of injections Ntg from three times the map value (target number of injections Ntgm), which is the optimal value, the amount of fuel adhering to the cylinder wall surface, the homogeneity of the air-fuel mixture, etc. will change. Combustion deteriorates, exhaust characteristics including PN deterioration, engine speed reduction, and the like may occur.

The determination value Y shown in FIG. 3 indicates that the target number of injections Ntg is calculated from the map value (target number of injections Ntgm) when the total fuel injection pulse width TI starts to increase due to a change in the operation region or a change in the auxiliary machine load. This is the threshold value of the pulse ratio PR for determining the timing for returning to the map value (target injection number Ntgm) from the reduced state.
This determination value Y (Y <X ≦ 1.0) takes into account the pulse ratio PR that can set the target injection number Ntgm of the map value and the fluctuation of the pulse ratio PR when the target injection number Ntg is decreased. It is set to a value that can suppress hunting of the number of injections Ntg.

At time t2 in FIG. 3, the ECU 109 determines that the pulse ratio PR has fallen below the determination value Y, and changes the target injection number Ntg from two times to the map value (target injection number Ntgm) three times, that is, at that time. The process of returning to the optimum value in the operating conditions is performed.
When the target number of injections Ntg is returned to the original three times, the amount of fuel adhering to the cylinder wall surface, the homogeneity of the air-fuel mixture, and the like are improved, and the engine speed is increased by increasing the torque due to such combustion improvement.
When the engine rotational speed increases, the total fuel injection pulse width TI decreases, and when the total fuel injection pulse width TI decreases, the pulse ratio PR starts to increase again and exceeds the determination value X. When it is determined that the pulse ratio PR exceeds the determination value X, the process of reducing the target injection number Ntg from 3 times as the map value to 2 times is performed again.

As described above, when the target number of injections Ntg is reduced from the optimum value, multistage injection can be performed with an injection pulse width TIsn that is equal to or greater than the minimum injection pulse width TImin, but exhaust properties including deterioration of PN may be deteriorated. There is sex.
Therefore, the ECU 109 is configured to perform a reduction control of the target fuel pressure FPtg as a control for performing multi-stage injection with an injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin. It will be described that the control can suppress the deterioration of PN as compared with the case where the target number of injections Ntg is reduced.

FIG. 4 is a graph showing the change in PN with respect to the fuel pressure FP for each target injection number Ntg (Ntg = 1, 2, 3) of multistage injection, with the horizontal axis representing the fuel pressure FP and the vertical axis representing PN. .
When the fuel pressure FP is increased, atomization of the fuel spray is promoted, so that PN is reduced in any of the single injection (Ntg = 1), the two injections (Ntg = 2), and the three injections (Ntg = 3). Although it shows a tendency, if the fuel pressure is increased, the penetration force of the fuel spray becomes stronger and the reach distance becomes longer. Therefore, the PN that has shown a tendency to decrease according to the increase in the fuel pressure starts to increase when the fuel pressure exceeds a certain fuel pressure.

Here, even if the fuel pressure FP is the same, as the target number Ntg of multistage injections increases, in other words, as the injection pulse width TIsn per one becomes shorter, the penetration force of the fuel spray becomes weaker and the reach distance becomes shorter. Therefore, PN tends to decrease as the target number of injections Ntg increases.
Further, the fuel pressure region where the PN reduction effect can be made as large as possible varies depending on the target number of injections Ntg because of the relationship between vaporization promotion by atomization of fuel spray and the penetration force (reach distance) of the spray.

Considering such characteristics, the map values (FPtgm, Ntgm) of the target fuel pressure FPtg and the target number of injections Ntg are set to optimum values for each operation region.
For example, in the characteristics shown in FIG. 4, when the target fuel pressure FPtg = FP1 and the target number of injections Ntg = 3 are the operating conditions set as the optimum values (FPtgm, Ntgm), the injection is less than the minimum injection pulse width TImin. It is assumed that the target injection frequency Ntg is reduced from 3 times to 2 times under the condition that the pulse width TIsn is set.

In this case, the amount of increase in PN due to the reduction of the target number of injections Ntg from 3 to 2 is ΔPN, but the fuel pressure FP is maintained from 3 to 3 and the fuel pressure FP is changed from FP1 to FP2 (FP2 <FP1). The amount of increase in PN when it is lowered is the same ΔPN.
In other words, if the fuel pressure FP is adjusted between FP1 and less than FP2 while the target injection number Ntg is maintained at three times, the target injection number Ntg is set to three times if the injection pulse width TIsn is equal to or greater than the minimum injection pulse width TImin. The multistage injection with the injection pulse width TIsn equal to or larger than the minimum injection pulse width TImin can be performed while suppressing the deterioration of the PN, compared with the case where the number is reduced to twice.

Therefore, the ECU 109 reduces the target fuel pressure FPtg while maintaining the target number of injections Ntg when the injection pulse width TIsn lower than the minimum injection pulse width TImin is set. The injection pulse width TIsn is set.
However, when it is necessary to set the fuel pressure lower than the fuel pressure FP2 shown in FIG. 4 in order to set the injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin, the target injection number Ntg is reduced from 3 times to 2 times. In this case, it becomes worse than ΔPN, which is the amount of increase in PN.

Therefore, when the ECU 109 needs to reduce the fuel pressure FP to the fuel pressure FP2 in order to set the injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin, the ECU 109 reduces the fuel pressure FP to reduce the injection pulse width TIsn to the minimum injection pulse width TImin. Instead of the above, the fuel pressure FP is returned to the optimum value FP1 (target fuel pressure FPtgm which is a map value), the target number of injections Ntg is reduced from the target number of injections Ntgm (map value), and an injection pulse equal to or greater than the minimum injection pulse width TImin. The width TIsn can be set.
Further, when the ECU 109 reduces the fuel pressure FP while maintaining the target injection number Ntg at the target injection number Ntgm, which is a map value, in order to perform multi-stage injection with an injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin, When the PN change with respect to the fuel pressure fluctuation in the vicinity of the required fuel pressure FP is steep, instead of lowering the target fuel pressure FPtg from the target fuel pressure FPtgm that is the map value, the fuel pressure FP is set to the optimum value FP1 (target fuel pressure FPtgm). Returning, the target number of injections Ntg is subtracted from the target number of injections Ntgm, and an injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin is set.

In consideration of fuel pressure controllability, this is a region (for example, fuel pressure FP2 in three injections in FIG. 4) in which PN greatly changes due to fuel pressure fluctuation in order to set an injection pulse width TIsn that is equal to or greater than the minimum injection pulse width TImin. Rather than controlling the fuel pressure, the target number of injections Ntg is reduced from the target number of injections Ntgm, which is the map value, and the fuel pressure FP is in a region where the PN change due to fuel pressure fluctuation is slow (for example, the fuel pressure FP1 in the two-time injection in FIG. This is because it is desirable from the viewpoint of exhaust performance.
Therefore, the ECU 109 stores a limiter FPmin (lower limit target fuel pressure) that is a lowering limit of the target fuel pressure FPtg set in consideration of the PN deterioration allowance and the PN change characteristic, and the condition that the fuel pressure lowering below the limiter FPmin is required. Sometimes, the fuel pressure lowering process for performing the multi-stage injection with the injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin is canceled, and the target fuel pressure FPtg is returned to the optimum value (target fuel pressure FPtgm which is the map value). Ntg is subtracted from the target injection number Ntgm which is a map value.

FIG. 5 is a diagram for explaining a fuel pressure lowering process for performing multi-stage injection with an injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin, and shows a cold fast idle state of the internal combustion engine 101 (idle operation during warm-up). ) Represents an example of behavior such as the target fuel pressure FPtg.
Note that the pulse ratio PR, determination value X, and determination value Y shown in FIG. 5 are the same as those described with reference to FIG.

The determination value A (first determination value) is a threshold value of the pulse ratio PR for determining the timing for starting the control for reducing the target fuel pressure FPtg, and is a determination for determining whether or not to decrease the target number of injections Ntg. The value is lower than the value X (second determination value) (determination value A <determination value X ≦ 1.0).
This takes into account the response delay until the actual fuel pressure FP changes due to the fuel pressure control, starts the process of reducing the fuel pressure FP before the pulse ratio PR reaches the determination value X, and during the transient response of the fuel pressure FP lowering This is to prevent the injection with the injection pulse width TIsn below the minimum injection pulse width TImin.

  The determination value B is a threshold value of the pulse ratio PR for determining the timing for starting the control to increase the target fuel pressure FPtg to return to the target fuel pressure FPtgm (base fuel pressure) that is the map value, and is the same as the determination value A. Further, in consideration of the response delay of the fuel pressure FPn, a value higher than the determination value Y (third determination value) is set (determination value Y <determination value B <determination value A <determination value X ≦ 1.0).

The time t1 in FIG. 5 is the start timing of the internal combustion engine 101, and from time t1 to time t2 when the pulse ratio PR reaches the determination value A, the target fuel pressure FPtg is held at the target fuel pressure FPtgm, which is a map value. The target number of injections Ntg is held at the map value of 3 times.
The period from time t2 to time t3 in FIG. 5 is a period during which the ECU 109 decreases the fuel pressure FP because the pulse ratio PR exceeds the determination value A.

When the pulse ratio PR exceeds the determination value A, the ECU 109 decreases the target fuel pressure FPtg by a predetermined pressure every predetermined time with the target fuel pressure FPtgm (base fuel pressure) as a map value as an initial value, and gradually decreases the fuel pressure FP. Let Note that the ECU 109 can variably set the amount of decrease (decrease rate) in the target fuel pressure FPtg according to the deviation between the pulse ratio PR and the determination value A.
Further, a limiter FPmin is provided for the process of reducing the target fuel pressure FPtg, and the ECU 109 sets the target fuel pressure FPtg until the pulse ratio PR becomes lower than the determination value A or until the target fuel pressure FPtg reaches the limiter FPmin. Decrease gradually.

The limiter FPmin is set between the fuel pressures FP1 and FP2 in FIG. 4 (FP2 <FPmin <FP1). Further, the ECU 109 can calculate the limiter FPmin as a function of the target fuel pressure FPtgm (base fuel pressure).
When the target fuel pressure FPtg (actual fuel pressure FP) is decreased, the injection pulse width for injecting the same amount of fuel increases, so that the pulse ratio PR decreases, and the pulse ratio PR becomes the determination value A at time t3. Until the target fuel pressure FPtg is lowered.

From time t3 to time t4 in FIG. 5, the target fuel pressure FPtg is a target when the pulse ratio PR reaches the determination value A in a period in which the pulse ratio PR is a value between the determination value A and the determination value B. The fuel pressure FPtg is held, and the target number of injections Ntg is held at 3 times that is a map value.
Between time t4 and time t5 in FIG. 5, the period during which the pulse ratio PR decreases to the determination value B and the ECU 109 performs processing to return the target fuel pressure FPtg to the target fuel pressure FPtgm (base fuel pressure) that is a map value. It is.

When the pulse ratio PR reaches the determination value B, the ECU 109 increases the target fuel pressure FPtg by a predetermined pressure every predetermined time toward the target fuel pressure FPtgm (base fuel pressure) that is a map value, and the target fuel pressure FPtg becomes the target fuel pressure FPtgm. At the time of return (time t5 in FIG. 5), the process of gradually increasing the target fuel pressure FPtg is stopped.
The ECU 109 can variably set the amount of increase (increase speed) of the target fuel pressure FPtg in accordance with the deviation between the pulse ratio PR and the determination value B.

FIG. 6 shows that the pulse ratio PR exceeds the determination value X even when the ECU 109 reduces the target fuel pressure FPtg to the limiter FPmin when the internal combustion engine 101 is in the cold first idle state (warming up), and the ECU 109 maps the target number of injections Ntg. An example of the behavior of the pulse ratio PR, the target fuel pressure FPtg, the target number of injections Ntg, etc. in a situation where the process of reducing the value from 3 to 2 is performed is shown.
The pulse ratio PR, determination value X, determination value A, determination value B, and determination value Y shown in FIG. 6 are the same as those in FIG. 3 and FIG.

Since the pulse ratio PR exceeds the determination value A at time t1 in FIG. 6, the ECU 109 starts a process of gradually decreasing the target fuel pressure FPtg from the target fuel pressure FPtgm (base fuel pressure) that is the map value, and at the time t2, the target fuel pressure FPtg. Has reached the limiter FPmin, the process of gradually decreasing the target fuel pressure FPtg is stopped, and the target fuel pressure FPtg is held in the limiter FPmin.
Even after the target fuel pressure FPtg reaches the limiter FPmin, the pulse ratio PR increases, and the pulse ratio PR exceeds the determination value X at time t3. Therefore, the ECU 109 changes the target injection number Ntg from three times, which is a map value. At the same time, the process of returning the target fuel pressure FPtg from the limiter FPmin to the target fuel pressure FPtgm that is the map value is started.

By reducing the target injection number Ntg from 3 times, which is the map value, to 2 times, the pulse ratio PR starts to decrease after time t3, and the pulse ratio PR falls below the determination value Y at time t4. Determines that the condition (total fuel injection pulse width TI) that allows setting of the injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin even when the target injection number Ntg is restored to the map value (target injection number Ntgm) The number of injections Ntg is returned from 2 times to 3 times that is the map value.
As described above, the ECU 109 basically controls the pulse ratio PR so that the pulse ratio PR does not exceed the determination value X by reducing the target fuel pressure FPtg. However, even if the target fuel pressure FPtg is reduced to the limiter FPmin, the pulse ratio PR is determined to be the determination value X. Is exceeded, the target fuel pressure FPtg is returned to the map value, and the target injection number Ntg is subtracted from the target injection number Ntgm, which is the map value, to eliminate the state where the pulse ratio PR exceeds the determination value X.

When the ECU 109 returns the target fuel pressure FPtg to the target fuel pressure FPtgm, which is a map value, the ECU 109 sets the target fuel pressure FPtg so that the measurement accuracy of the fuel injection valve 105 can be prevented from deteriorating due to rapid fluctuations in the fuel pressure FP. Increase gradually toward fuel pressure FPtgm.
Further, the ECU 109 returns the target fuel pressure FPtg to the map value when the target number of injections Ntg is decreased, as shown in FIG. 4, at the target fuel pressure FPtg in the region where the change in PN with respect to the fuel pressure FP fluctuation is small. This makes it possible to stably control the PN to a small state even if there is a variation in the control of the fuel pressure FP.
The ECU 109 performs control of the target fuel pressure FPtg based on the pulse ratio PR described in accordance with FIGS. 5 and 6 described above, in a cold state where the influence on the exhaust gas and PN is large when the target injection number Ntg is decreased. The present invention can be implemented only during the catalyst warm-up, that is, during the warm-up of the internal combustion engine 101.

FIG. 7 shows the behavior of the target number of injections Ntg in the idle state after the catalyst warm-up is completed in the configuration in which the control of the target fuel pressure FPtg based on the pulse ratio PR described above is performed on the condition that the catalyst is warmed up. It is an example.
Note that the pulse ratio PR, determination value X, determination value A, determination value B, and determination value Y shown in FIG. 7 are the same as those in FIG. 3, FIG. 5, and FIG.

When the ECU 109 determines that the catalyst warm-up is completed at time t1 in FIG. 7, that is, the catalyst temperature has reached the activation temperature, normal ignition is performed from the control for retarding the ignition timing for catalyst warm-up by switching the combustion mode. Control is shifted to timing control, and the target idle rotation speed is lowered from a high rotation for catalyst warm-up to a target idle rotation speed corresponding to the water temperature TW. By such control, the internal combustion engine 101 shifts to an operation region where the required air amount is small.
In addition, with the catalyst warm-up completion determination (combustion mode switching determination) at time t1 in FIG. 7, the ECU 109 switches the map for searching for the target injection number Ntgm, so that the target injection number Ntg is 3 to 2 times. Changed to

At the subsequent time t2, the pulse ratio PR exceeds the determination value A, but since the catalyst warm-up, which is a condition for not performing the control of the target fuel pressure FPtg based on the pulse ratio PR, is completed, the ECU 109 determines that the pulse ratio PR is Even if the judgment value A is exceeded, the control for reducing the target fuel pressure FPtg is not performed.
When the friction of the internal combustion engine 101 is relatively small and the total fuel injection pulse width TI is calculated to be shorter than the standard, the pulse ratio PR further increases after time t2.

When the pulse ratio PR exceeds the determination value X at time t3, the ECU 109 decreases the target number of injections Ntg from two times that is the map value to one time, and sets an injection pulse width TIsn that is equal to or greater than the minimum injection pulse width TImin. In other words, the pulse ratio PR is adjusted to the target injection number Ntg that can be made equal to or less than the determination value X.
After the target number of injections Ntg has been reduced from two to one, the total fuel injection pulse width TI increases to a value that allows the target number of injections Ntg to be doubled due to changes in the operating range and operating conditions of the auxiliary machinery. As a result, the pulse ratio PR becomes lower than the determination value Y at time t4.

However, when the target number of injections Ntg is reduced based on the pulse ratio PR in the idle state after the catalyst warm-up is completed, the ECU 109 next until the idle condition is not satisfied (until the internal combustion engine 101 is accelerated and exits the idle state). ), The target number of injections Ntg reduced from the map value (target injection number Ntgm) is maintained.
When the target number of injections Ntg decreases or increases (returns), the combustion state changes due to changes in the amount of fuel adhering to the cylinder wall surface, the homogeneity of the air-fuel mixture, etc. In the idle region where the engine rotational speed is low, rotational speed fluctuations due to combustion changes tend to be noticeable.

For this reason, the ECU 109 is in an operating state in which the influence of exhaust gas and PN due to the decrease in the target injection number Ntg from the map value (target injection number Ntgm) is relatively small, or after the catalyst warm-up determination or the water temperature, oil temperature, etc. Only in the idle region of a predetermined temperature or higher, even if the pulse ratio PR falls below the judgment value Y, the target injection number Ntg reduced from the map value is maintained, and the occurrence of rotational fluctuations accompanying the return of the target injection number Ntg is maintained. Deter.
Then, when the idle state in which the target injection number Ntg is decreased from the map value is released (in other words, the ECU 109 shifts from the idle state in which the target injection number Ntg is decreased from the map value to the non-idle state). ) Increase the target injection number Ntg so as to return to the map value.

Although the embodiment of the present invention has been described in detail above, the parameters for controlling the fuel pressure and the number of injections of multistage injection are the minimum injection pulse width TImin and the total fuel injection pulse width TI per combustion cycle described above. It goes without saying that the same operation is possible even if a new parameter that can estimate the injection pulse width and the injection pulse width is used in addition to this ratio.
In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  In the control function of the ECU 109 shown in FIG. 2, the ECU 109 searches the map for a standard target fuel pressure FPtgm corresponding to the operating condition of the internal combustion engine 101, a standard target injection number Ntgm corresponding to the operating condition of the internal combustion engine 101, and the like. However, the ECU 109 can calculate the target fuel pressure FPtgm (base fuel pressure) and the target number of injections Ntgm (base injection number) based on a function whose operating conditions are variables.

  In addition, the ECU 109 replaces the configuration for determining whether or not the conditions allow the multistage injection with the injection pulse width TIsn equal to or greater than the minimum injection pulse width TImin based on the pulse ratio PR (RP = TImin × Ntg / TI). The minimum injection pulse width TImin is compared with the shortest injection pulse width TImin among the injection pulse widths TIsn in each injection specified based on the total fuel injection pulse width TI, the target number of injections Ntgm, and the target split ratio SRtgm. It is possible to determine whether or not the conditions allow multistage injection with an injection pulse width TIsn equal to or greater than the injection pulse width TImin.

Further, when the ECU 109 determines that the shortest injection pulse width TIsn in each injection corresponding to the target division ratio SRtgm is less than the minimum injection pulse width TImin, the ECU 109 keeps the target division ratio SRtgm within a predetermined range. If all the injection pulse widths TIsn at each injection time can be made equal to or greater than the minimum injection pulse width TImin by changing in step S1, the target split ratio SRtgm is changed and the target split ratio SRtgm is changed within a predetermined range. The target fuel pressure FPtg can be reduced when the injection pulse width TIsn at each injection time cannot be all made equal to or greater than the minimum injection pulse width TImin.
Further, the ECU 109 does not change the target split ratio SRtgm when determining that the shortest injection pulse width TIsn of the injection pulse widths TIsn in each injection corresponding to the target split ratio SRtgm is less than the minimum injection pulse width TImin. In addition, all of the injection pulse widths TIsn at the respective injection times can be made equal to or greater than the minimum injection pulse width TImin by decreasing the target fuel pressure FPtg.

Further, even after the internal combustion engine 101 is warmed up, the ECU 109 performs a process of reducing the target fuel pressure FPtg from the base fuel pressure in order to make all the injection pulse widths TIsn at each injection time equal to or greater than the minimum injection pulse width TImin. be able to.
Further, the ECU 109 can change the level of the determination value A in accordance with the increasing rate of the pulse ratio PR, and the control for decreasing the fuel pressure FP by decreasing the level of the determining value A as the increasing rate of the pulse ratio PR increases. By accelerating the start of the fuel pressure control, it is possible to prevent the fuel pressure FP from being excessively controlled while preventing the injection pulse width TIsn from becoming less than the minimum injection pulse width TImin due to the response delay of the fuel pressure control.

  DESCRIPTION OF SYMBOLS 101 ... Internal combustion engine, 105 ... Fuel injection valve, 109 ... ECU (control apparatus), 129 ... Fuel supply apparatus, 201 ... Fuel injection pulse width calculating part (total injection amount setting part), 203 ... Multistage injection frequency map part (Number of times) Setting unit), 206... Multistage injection control unit

Claims (11)

A control device applied to a direct injection internal combustion engine comprising a fuel injection valve that directly injects fuel into a cylinder of the internal combustion engine and a fuel supply device that varies a fuel pressure supplied to the fuel injection valve. And
A total injection amount setting unit for setting a total fuel injection amount to be injected from the fuel injection valve during one combustion cycle;
A number-of-times setting unit for setting the number of injections in multi-stage injection in which the total fuel injection amount is injected in a plurality of times during one combustion cycle;
When the fuel pressure is the base fuel pressure, when the injection pulse width per injection in the multistage injection is less than the minimum injection pulse width, the fuel pressure is reduced below the base fuel pressure, and the injection per injection A multi-stage injection control unit that performs multi-stage injection so that a pulse width exceeds the minimum injection pulse width;
A control apparatus for a direct injection internal combustion engine.   The multi-stage injection control unit is configured such that the number of injections is Ntg, the minimum injection pulse width is TImin, and the total fuel injection pulse width corresponding to the total fuel injection amount is TI when the fuel pressure is the base fuel pressure. 2. The control device for an internal combustion engine according to claim 1, wherein, when TImin × Ntg / TI is a condition that is equal to or less than a first determination value (<1.0), multistage injection is performed at the base fuel pressure.   The multi-stage injection control unit is configured such that the number of injections is Ntg, the minimum injection pulse width is TImin, and the total fuel injection pulse width corresponding to the total fuel injection amount is TI when the fuel pressure is the base fuel pressure. , TImin × Ntg / TI is a condition that is greater than the first determination value (<1.0), the fuel pressure is reduced from the base fuel pressure to a fuel pressure at which TI / Ntg is equal to or greater than the minimum injection pulse width TImin. The control apparatus for an internal combustion engine according to claim 1 or 2.   The multi-stage injection control unit directs the fuel pressure toward the base fuel pressure when TImin × Ntg / TI is smaller than the first determination value in a state where the fuel pressure is lower than the base fuel pressure. The control device for an internal combustion engine according to claim 3, wherein the control device is raised.   The control device for an internal combustion engine according to claim 3 or 4, wherein the multi-stage injection control unit changes the fuel pressure within a predetermined range.   The multi-stage injection control unit reduces the number of injections when the injection pulse width per one time is less than the minimum injection pulse width even if the fuel pressure is reduced to a predetermined fuel pressure lower than the base fuel pressure. The control apparatus for an internal combustion engine according to claim 1, wherein fuel injection is performed such that a single injection pulse width exceeds the minimum injection pulse width.   The multi-stage injection control unit reduces the number of injections by reducing the number of injections when TImin × Ntg / TI when the fuel pressure is the base fuel pressure exceeds a second determination value that is larger than the first determination value. The control apparatus for an internal combustion engine according to claim 3, wherein the multi-stage injection is performed such that the injection pulse width per revolution exceeds the minimum injection pulse width.   The multi-stage injection control unit maintains the state where the number of injections is reduced when TImin × Ntg / TI in a state where the number of injections is reduced exceeds a third determination value which is smaller than the first determination value. 8. The control apparatus for an internal combustion engine according to claim 7, wherein the number of injections is increased when TImin × Ntg / TI falls below the third determination value.   The control device for an internal combustion engine according to claim 6 or 7, wherein the multi-stage injection control unit increases the fuel pressure when reducing the number of injections.   The control apparatus for an internal combustion engine according to claim 1, wherein the multi-stage injection control unit reduces the fuel pressure while the internal combustion engine is warmed up.   The said multistage injection control part increases the said frequency | count of injection when the said idling state is cancelled | released when the said frequency | count of injection is reduced in the idling state after warm-up of the said internal combustion engine. Control device for internal combustion engine.