JP5310925B2 - Engine fuel injection control device - Google Patents

Description

  The present invention relates to an engine fuel injection control device. In particular, the present invention relates to a fuel injection control device that controls fuel injection so as to suppress torque fluctuations that occur when fuel injection returns after fuel cut.

2. Description of the Related Art Conventionally, there is a control method for an internal combustion engine that includes a cylinder injection (hereinafter referred to as direct injection) valve that injects fuel into a cylinder and a port injection valve that injects fuel into an intake passage, and selectively injects fuel. It is known (see, for example, Patent Document 1).
As shown in FIG. 6, the control method disclosed in Patent Document 1 controls an internal combustion engine having an in-cylinder injection valve and a port injection valve having a fuel injection amount per unit valve opening time smaller than that of the in-cylinder injection valve. In doing so, the total fuel injection amount TAU obtained based on the operating conditions of the internal combustion engine is obtained (step S101). Next, the TAU and the minimum fuel injection amount _QminD that can be injected by the in-cylinder injection valve are compared (step S102). If the total fuel injection amount TAU is smaller than the minimum fuel injection amount _QminD (step S102; Yes), the total fuel injection amount TAU is injected by the port injection valve (step S103, step S104).

Japanese Patent Laid-Open No. 2005-133637

Incidentally, it is known that in-cylinder injection is advantageous when it is used when high output is required of the engine. Focusing on this point, in Patent Document 1, in the range from the minimum fuel injection amount of the direct injection valve to the fuel injection amount required at the maximum output of the engine, fuel is injected from the direct injection valve. Control is performed so that fuel is injected from the port injection valve in the range from the fuel injection amount to the minimum fuel injection amount required by the engine, thereby improving the performance at high output.
Here, in-cylinder injection is to inject fuel into the direct injection cylinder, and therefore, there is an advantage over port injection in terms of responsiveness from when the fuel is injected until it burns. However, while responsiveness is advantageous, there is a disadvantage that torque shock is larger than port injection. Since Patent Document 1 does not pay attention to the point of response and torque shock, it cannot be said to be sufficient for further improving the performance of the engine.

  An object of the present invention is to provide a fuel injection control device for an engine that can suppress a torque shock at the time of fuel injection return after fuel cut.

The present invention has been made as means for solving such a problem, and includes a direct injection valve that directly injects fuel into an engine cylinder, a port injection valve that injects fuel into an intake port of the engine, and the engine. A fuel cut executing means for executing a fuel cut during the operation of the engine, and a fuel supply at the time of return necessary for keeping a torque shock generated in the engine within an allowable range upon returning from the fuel cut executed by the fuel cut executing means The direct injection valve injects a return fuel supply amount detecting means for determining the amount, a rotation speed detection means for detecting the engine speed, and a return fuel supply amount determined by the return fuel supply amount detection means. The direct injection minimum fuel injection amount and the port minimum fuel injection amount that can be injected by the port injection valve are compared, and the direct injection valve or the port injection valve is determined according to the comparison result. An injection valve control means that is selectively operated, and the injection valve control means rotates the rotation when the direct fuel injection minimum fuel injection amount and the port minimum fuel injection amount are both equal to or less than the return fuel supply amount. The port injection valve is selected and operated if the detection result of the number detection means is less than or equal to a predetermined rotation speed, and the direct injection valve is selected and operated if the detection result is greater than the predetermined rotation speed.
In this invention, at the time of return from the fuel cut by the fuel cut execution means, the fuel supply amount detection means obtains the return fuel supply amount necessary to keep the torque shock generated in the engine within the allowable range, and the return fuel supply amount. Since the direct injection valve or the port injection valve having a smaller capacity is selected by the injection valve control means to perform the fuel injection, it is possible to suppress the torque shock that occurs when the fuel injection returns after the fuel cut.
It should be noted that the return fuel supply amount can be set to a maximum value or a substantially maximum value of the fuel amount within which the torque shock is allowed.

Further, the injection valve control means, when both the direct injection minimum fuel injection amount and the port minimum fuel injection amount are less than or equal to the return fuel supply amount, the detection result of the rotation speed detection means is less than a predetermined rotation speed. If there is, the port injection valve is selected and operated, and if it is greater than the predetermined rotational speed, the direct injection valve is selected and operated.
In the case of port injection, the fuel injected is easier to vaporize than the direct injection, and it is easy to ensure the combustion stability. Therefore, port injection is used in the low engine speed range.
In addition, since a large amount of fuel is required in the high engine speed region, the engine output is improved by directly injecting the fuel into the cylinder using the direct injection valve. Response deterioration until combustion due to adhesion is improved, and responsiveness at the time of return after fuel cut is improved.

Further, the injection valve control means has an injection valve having a smaller minimum fuel injection amount when either the direct injection minimum fuel injection amount or the port minimum fuel injection amount is smaller than the return fuel supply amount. It is preferable to select and operate.
According to such a configuration, it is possible to select a fuel injection valve that is smaller than the return fuel supply amount, and thus it is possible to reliably suppress torque shock.

The direct injection minimum fuel injection amount is set to be larger than the port minimum fuel injection amount, and the injection valve control means determines that the direct injection minimum fuel injection amount and the port minimum fuel injection amount are both at the time of return. When it is larger than the fuel supply amount, it is preferable to select and operate the port injection valve.
In this case, since port injection does not directly inject fuel into the direct injection cylinder, torque shock is less likely to occur than direct injection, and fuel injection control finer than direct injection valve is possible, so a port injection valve is used. This makes it easy to suppress torque shock.

In the fuel injection control device for an engine of the present invention, it is possible to suppress a torque shock that occurs at the time of fuel injection return after fuel cut.
Moreover, the responsiveness at the time of return after fuel cut can be improved.

FIG. 1 is an explanatory diagram showing an outline of a fuel injection control device for an engine according to the present invention. FIG. 2 is an explanatory diagram showing injection timings of the direct injection valve and the port injection valve. FIG. 3 is an example of a control flowchart of the fuel injection control device for an engine according to the present invention. FIG. 4 is a graph showing the relationship between the engine speed and the engine torque when the engine coolant exceeds a predetermined temperature (in a warm state). FIG. 5 is a graph showing the relationship between the engine speed and the engine torque when the engine coolant exceeds a predetermined temperature (in the cold state). FIG. 6 is an example of a control flowchart of a conventional engine fuel injection control device.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative positions, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

FIG. 1 shows the configuration of a four-cycle gasoline engine used in an engine fuel injection control device of the present invention. As shown in the figure, an ignition plug 1 for igniting the fuel in the combustion chamber 20 is provided in the upper part of the cylinder of the engine. A direct injection valve 2 that directly injects fuel into the combustion chamber 20 is provided near the upper part of the side surface of the cylinder. An intake port 3 is formed above the direct injection valve 2, and an intake valve 4 and a port injection valve 5 for injecting fuel into the intake port 3 of the engine are provided in the intake port 3. ing.
The lower limit of the fuel amount per injection of the direct injection valve 2, that is, the direct injection minimum fuel injection amount is set larger than the minimum port fuel injection amount of the port injection valve 5.
When fuel is injected from the port injection valve 5, the fuel is sucked into the combustion chamber 20 through the intake valve 4. The fuel is sucked in as the piston 22 descends and the cylinder has a negative pressure. The direct injection valve 2 and the port injection valve 5 are controlled by the injection valve control means 113 of the engine control unit (ECU) 11.
As shown in FIG. 2, the injection timing is performed during the intake stroke in the case of the direct injection valve 2, and is performed when the port injection valve 5 is shifted from the expansion stroke to the exhaust stroke.

The fuel is pumped to the direct injection valve 2 and the port injection valve 5 shown in FIG. The feed pump 6 sucks the fuel in the fuel tank 7 and sends the fuel to the direct injection valve 2 and the port injection valve 5. The fuel cut execution unit 111 of the ECU 11 controls the operation of the feed pump 6 to execute the fuel cut. Since the direct injection valve 2 has a higher fuel injection pressure than the port injection valve 5, a high pressure pump 8 is used. Then, the solenoid valves provided in each of the direct injection valve 2 and the port injection valve 5 perform an on / off operation, whereby fuel is injected from the injection valves 2 and 5.
Further, fuel is distributed to the direct injection valve 2 and the port injection valve 5 of each cylinder of the plurality of cylinders by fuel distribution pipes 9A and 9B. Further, cooling water W for cooling the engine circulates in the cylinder, and the temperature of the cooling water W is measured using a temperature sensor 10A which is a water temperature detecting means.

The return fuel supply amount detection means 112 for obtaining a return fuel supply amount required to keep the torque shock generated in the engine within the allowable range at the time of return from the fuel cut executed by the fuel cut execution means 111 is the engine The fuel supply amount is obtained by calculation processing based on the signal of the rotation speed detecting means 12 for detecting the rotation speed of the engine and the preset allowable torque at the time of return. The allowable torque at the time of return is stored as a map using the engine speed as a parameter as in the allowable torque characteristics at the time of fuel cut return shown in FIGS. 4 and 5. However, the allowable torque at return is detected by other means. May be.
Then, the ECU 11 uses the return fuel supply amount obtained by the return fuel supply amount detection means 112 as the direct injection minimum fuel injection amount that the direct injection valve 2 can inject and the port minimum fuel that the port injection valve 5 can inject. Compared with the injection amount, the direct injection valve 2 or the port injection valve 5 is selected and operated according to the comparison result.

FIG. 3 is a flowchart showing a control method using the fuel injection control device for an engine of the present invention. In the fuel injection control device for an engine according to the present invention, first, in step S1, the engine speed is measured by a speed detecting means. The engine rotational speed is measured based on, for example, a rotational speed signal output from a cam position sensor or an output from a crankshaft rotational speed sensor provided on the crankshaft.
Next, in step S2, the throttle opening is acquired. If the accelerator pedal is fully depressed, the throttle opening is 100%, and if the accelerator pedal is not depressed, the throttle opening is 0% and is fully closed.

Next, in step S3, it is determined whether or not this is the case when the fuel injection returns after the fuel cut. Fuel cut means that fuel injection is interrupted when the accelerator pedal is fully depressed and fully closed. In the fuel cut area, as shown in FIGS. 4 and 5, the engine speed is set in a predetermined speed area, and the fuel cut is performed when the depression of the accelerator pedal is canceled in the set area. The negative engine torque characteristic when the accelerator pedal is fully closed is shown as throttle fully closed torque in FIGS.
The time when the fuel cut is restored is when the engine is accelerated by depressing the accelerator pedal again. This determination is made by the ECU 11 based on a signal from an accelerator pedal sensor (not shown) that detects the amount of depression of the accelerator pedal. And if it does not correspond at the time of fuel injection return after fuel cut, normal control is performed in Step S4. As the normal control, for example, the required fuel injection amount is calculated from the engine speed and the accelerator pedal depression amount, and the fuel injection is controlled by the direct injection valve 2 or the port injection valve 5. A control method can be used.

On the other hand, if the ECU 11 determines in step S3 that the fuel injection returns after the fuel cut, it is determined in step S5 whether or not the temperature of the cooling water W exceeds a predetermined value by the temperature sensor 10A. Here, the predetermined value is, for example, 80 ° C. With this temperature as a boundary, the control is divided into a warm state (see FIG. 4) and a cool state (see FIG. 5). If it is determined that the temperature of the cooling water W has exceeded a predetermined value, the required fuel supply amount (Pw) at return is obtained from the allowable torque at return after fuel cut in step S6.
This allowable torque at the time of return is the limit at which a torque shock is allowed at the time of rising of the torque at the time of return from the throttle fully closed line by the test as shown as the allowable torque at the time of fuel cut entry / return in FIGS. Set as a line.
The return fuel supply amount (Pw) is calculated based on the return allowable torque with respect to the engine speed at the time of return. This return fuel supply amount (Pw) is a fuel supply amount necessary for returning without applying a torque shock.

Next, in step S7, the direct injection minimum fuel injection amount per injection in the case of direct injection and the port minimum fuel injection amount per injection in the case of port injection are both the return fuel supply amount (Pw). Judge whether to satisfy. That is, it is determined whether or not both the direct injection minimum fuel injection amount and the port minimum fuel injection amount are equal to or less than the return fuel supply amount (Pw).
In step S7, in the case of NO, both the case where both the direct injection minimum fuel injection amount and the port minimum fuel injection amount are not satisfied and the case where one of them is not satisfied are included.
When one of them does not satisfy, the torque shock can be surely suppressed by using the injection valve that satisfies the condition, that is, the injection valve that can inject the minimum fuel injection amount equal to or less than the return fuel supply amount (Pw). This case is not shown in the flowchart of FIG.
If both are not satisfied, port injection (MPI) is performed by the port injection valve 5 in step S8. Since the port injection does not directly inject fuel into the direct injection combustion chamber 20, torque shock is less likely to occur than direct injection, and finer fuel injection control than the direct injection valve 2 is possible. It becomes easy to suppress a torque shock by using.

  On the other hand, if YES in step S7, that is, if any of the injection valves 2, 5 satisfies the return fuel supply amount (Pw), the process proceeds to step S9, and whether or not the engine speed is greater than a predetermined value. To be judged. If the engine speed is in the low speed range smaller than the predetermined value, the process proceeds to step S9, and the recovery after the fuel cut is performed by port injection. This is because the port injection is easier to vaporize the injected fuel than the direct injection, and it is easier to ensure the combustion stability.

  On the other hand, when the engine speed exceeds the predetermined value, the process proceeds to step S10, and the recovery after the fuel cut is performed by direct injection. This is because a large amount of fuel is required in the high engine speed range, so that direct injection valve 2 is used to inject fuel directly into combustion chamber 20 to improve engine output and port injection. This is because the deterioration of the response to the combustion due to the fuel port adhesion in the fuel is improved, and the response at the time of return after the fuel cut is improved.

  Here, the predetermined value of the engine speed refers to the value at the boundary B between the port injection return and the direct injection return shown in FIG. In this direct injection return zone, the direct injection minimum fuel injection amount torque and port minimum fuel injection amount torque lines are below the allowable torque line at the time of fuel cut entry and return, and the direct injection valve 2 is used. Even if the port injection valve 5 is used, a shock due to torque fluctuation is not applied, but as described above, direct injection return is performed for the following reason. First, since a large amount of fuel is required in the high engine speed range, the engine output can be improved by directly injecting the fuel into the combustion chamber 20 using the direct injection valve 2. . Secondly, there is no problem that the injected fuel generated when the port injection valve 5 is used adheres to the intake port 3. When the fuel adheres to the intake port 3, it is necessary to introduce the fuel in anticipation of the amount of the intake port 3 attached, resulting in complicated control.

  If the temperature of the cooling water is equal to or lower than the predetermined value in step S5, the process proceeds to step S10, and fuel cut return is performed by direct injection (DI) by the direct injection valve 2. This case corresponds to the cold state shown in FIG. This is a case where the temperature of the cooling water W (shown in FIG. 1) is low, for example, when the cooling water W is 80 ° C. or lower. When the detection result of the temperature sensor 10 </ b> A is below a temperature at which it is difficult to vaporize the fuel in the intake port 3, fuel vaporization by the port injection valve 5 cannot be expected, and liquid fuel adheres to the intake port 3. This problem can be avoided by injecting the fuel directly into the combustion chamber 20 by the direct injection valve 2. Here, the temperature at which it is difficult to vaporize the fuel in the intake port 3 refers to a temperature at which liquid fuel adheres to the intake port 3 and hinders fuel atomization. The predetermined value may be set to this temperature.

  The throttle full-close torque graph of FIG. 5 has a negative torque width that is wider as the engine torque moves in the negative direction than the throttle full-close torque graph of FIG. This is because when the coolant temperature is low, engine friction is large and negative torque is large. Therefore, the difference between the allowable torque at the time of fuel cut entry / return and the fully closed torque increases.

In FIG. 5, the direct injection minimum fuel injection amount torque that has exceeded the allowable torque in the port injection return zone of FIG. 4 becomes less than the allowable torque. That is, since the direct injection minimum fuel injection amount torque and the port minimum fuel injection amount torque are both equal to or less than the allowable torque in the fully closed fuel cut region, either the direct injection valve 2 or the port injection valve 5 is selected. Good. However, as described above, the response to combustion is faster than when the port injector 5 is selected, and there is no problem of adhesion of injected fuel to the intake port 3 that occurs when the port injector 5 is used. Considering this point, the direct injection valve 2 is selected. Further, in addition to these points, atomization of fuel at the intake port 3 is not sufficient in the cold state, and harmful exhaust gas can be reduced by performing direct injection that is excellent in microparticulation.
4 and 5, the fuel is not cut in a region where the engine speed is lower than the fully closed fuel cut region.

  The processes in steps S1 to S10 described above are always performed as an infinite loop while the vehicle is running, and are terminated when, for example, the engine key is turned off. Then, after the engine is started again, the above process is started from step S1.

  In the embodiment described above, at the time of return from fuel cut by the fuel cut execution means 111, the return fuel supply amount detection means 112 requires a return fuel supply amount (Pw) required to keep the torque shock generated in the engine within an allowable range. Since the ECU 11 selects the direct injection valve 2 or the port injection valve 5 having a capacity smaller than the fuel supply amount (Pw) at the time of return and performs fuel injection, a torque shock is applied at the time of fuel injection return after the fuel cut. In addition, if the torque shock is within an allowable range, the responsiveness at the time of return can be improved by performing the injection using the direct injection valve 2 having high engine responsiveness.

  Although the present invention has been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that other various modifications are possible without departing from the essence thereof.

  According to the present invention, torque shock can be suppressed at the time of fuel injection return after fuel cut, and therefore, it can be applied to an engine fuel injection control device.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Direct injection valve 3 Intake port 4 Intake valve 5 Port injection valve 6 Feed pump 7 Fuel tank 8 High pressure pump 9A, 9B Fuel distribution pipe 10A Temperature sensor 11 Engine control unit (ECU)
DESCRIPTION OF SYMBOLS 111 Fuel cut execution means 112 Fuel supply amount detection means at the time of return 113 Injection valve control means 12 Rotation speed detection means 20 Combustion chamber 22 Piston 100 Spark plug 101 Direct injection valve 102 Port injection valve 103 Fuel tank 104 Feed pump 105 High pressure pump B Boundary

Claims (3)

A direct injection valve that directly injects fuel into the cylinder of the engine;
A port injection valve for injecting fuel into the intake port of the engine;
Fuel cut execution means for executing fuel cut during operation of the engine;
A return fuel supply amount detection means for obtaining a return fuel supply amount necessary for keeping a torque shock generated in the engine within an allowable range upon return from the fuel cut executed by the fuel cut execution means;
A rotational speed detection means for detecting the rotational speed of the engine;
The return fuel supply amount obtained by the return fuel supply amount detection means is compared with the minimum direct fuel injection amount that can be injected by the direct injection valve and the minimum port fuel injection amount that can be injected by the port injection valve, An injection valve control means for selecting and operating the direct injection valve or the port injection valve according to a comparison result, and
When the direct fuel injection minimum fuel injection amount and the port minimum fuel injection amount are both equal to or less than the return fuel supply amount, the injection valve control means determines that the detection result of the rotation speed detection means is equal to or less than a predetermined rotation speed. A fuel injection control device for an engine, wherein the port injection valve is selected and operated, and the direct injection valve is selected and operated when the rotational speed is greater than the predetermined rotational speed. The injection valve control means includes
When either the direct injection minimum fuel injection amount or the port minimum fuel injection amount is smaller than the return fuel supply amount, an injection valve having the smaller minimum fuel injection amount is selected and operated. The fuel injection control device for an engine according to claim 1. The direct injection minimum fuel injection amount is set larger than the port minimum fuel injection amount,
The injection valve control means includes
The port injection valve is selected and operated when both the direct injection minimum fuel injection amount and the port minimum fuel injection amount are larger than the return fuel supply amount. Engine fuel injection control device.

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