JP2008267216A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device for an internal combustion engine capablle of suppressing the adherence of fuel to the inner wall surface of a cylinder to suppress the dilution of oil. <P>SOLUTION: The fuel injection control device for an internal combustion engine comprises: a fuel injection valve 10 directly injecting the fuel in a cylinder 2 of the internal combustion engine 1; and a solenoid valve 18 adjusting the pressure of fuel injected from the fuel injection valve 10. The fuel injection control device calculates a fuel injection amount Q injected from the fuel injection valve 10 for each cycle according to the operational state of the internal combustion engine. In the fuel injection control device, when the calculated fuel injection amount Q in which a valve open period of the fuel injection valve 10 reaches a predetermined minimum valve open period Tmin is smaller than a minimum fuel injection amount Qmin, the operation of a solenoid valve 18 is controlled to decrease the pressure of fuel so as to execute split injection at which the fuel of the fuel injection amount is injected from the fuel injection valve 10 in the cylinder 2 a plurality of times, and the operation of the fuel injection valve 10 is controlled so as to execute the split injection at which the valve open period of the fuel injection valve 10 in each time reaches the minimum valve open time Tmin or longer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel injection control device for an internal combustion engine provided with a fuel injection valve that directly injects fuel into a cylinder.

  In general, in a fuel injection valve, a needle valve is urged by a spring or the like so as to block a fuel injection hole, and fuel injection from the valve is prevented, and the needle valve is moved by a solenoid or the like. The pressurized fuel guided to the inside is injected from the injection hole. In an internal combustion engine equipped with such a fuel injection valve, the fuel is injected from the fuel injection valve into the cylinder according to the operating state of the internal combustion engine, and the fuel guided to the fuel injection valve. Is controlling the pressure. For example, when the fuel injection amount required in the intake stroke injection mode in which fuel injection is mainly performed during the intake stroke cannot be injected during the intake stroke, the rest is injected in the compression stroke following the intake stroke, and the fuel during the intake stroke An in-cylinder injection internal combustion engine is known in which the injection start timing is changed based on a parameter representing the ease with which fuel adheres to the internal combustion engine (see Patent Document 1). Further, when the injection amount set by the fuel injection amount setting means is small, the discharge pressure of the fuel injection pump is lowered to lower the fuel pressure supplied to the fuel injection valve, and the injection start timing is advanced to shorten the injection period. A fuel injection control device for an internal combustion engine that is lengthened is known (see Patent Document 2). In addition, Patent Documents 3 to 6 exist as prior art documents related to the present invention.

JP 2002-13428 A Japanese Patent Laid-Open No. 9-21369 JP 2002-276402 A Japanese Patent Laid-Open No. 10-220265 Japanese Patent No. 3797278 Japanese Patent Laid-Open No. 11-22533

  When the fuel injected from the fuel injection valve adheres to the inner wall surface of the cylinder, the attached fuel is scraped off by the piston and guided to an oil pan or the like to dilute the oil. The fuel injected from the fuel injection valve is more likely to adhere to the inner wall surface of the cylinder as the penetration force of the fuel injection is stronger. This penetration force becomes stronger, for example, as the pressure of the fuel is higher and as the time during which the fuel is injected is longer. In the internal combustion engine of Patent Document 1, oil dilution is suppressed by changing the fuel injection start timing during the intake stroke. However, since the penetration force of the injected fuel is not adjusted, the fuel pressure or the fuel injection Depending on the time, the fuel tends to adhere to the inner wall surface of the cylinder. In the apparatus of Patent Document 2, the fuel pressure is controlled by lowering the discharge pressure of the fuel injection pump, that is, the pressure of the fuel introduced into the fuel injection valve, and lengthening the fuel injection period. Since it is lengthened, there is a risk that the penetrating power will not be weakened.

  Accordingly, an object of the present invention is to provide a fuel injection control device for an internal combustion engine that can suppress the adhesion of fuel to the inner wall surface of a cylinder and suppress the dilution of oil.

  The fuel injection control device for an internal combustion engine according to the present invention includes a fuel injection valve that directly injects fuel into a cylinder of the internal combustion engine, a fuel pressure adjusting unit that can adjust a pressure of fuel injected from the fuel injection valve, and the internal combustion engine. A fuel injection amount calculating means for calculating an amount of fuel to be injected from the fuel injection valve per cycle in accordance with an operating state of the engine; Is less than the minimum fuel injection amount at which the opening period of the fuel injection valve is a predetermined minimum valve opening period, the amount of fuel calculated by the fuel injection amount calculation means is the fuel injection amount. The operation of the fuel pressure adjusting means is controlled to reduce the pressure of the fuel injected from the fuel injection valve so that the divided injection injected into the cylinder in a plurality of times from the valve can be executed, and the split Squirt And an operation control means for controlling the operation of the fuel injection valve so that the valve opening period of the fuel injection valve at each time of the divided injection becomes equal to or longer than the minimum valve opening period. This problem is solved (claim 1).

  According to the fuel injection control device of the present invention, when the valve opening period of the fuel injection valve is less than the minimum fuel injection amount that is the minimum valve opening period, the pressure of the fuel injected from the fuel injection valve is reduced and split injection is performed. Therefore, the penetration force of the fuel injected from the fuel injection valve at each time of the divided injection can be weakened. Therefore, it is possible to suppress the dilution of oil by suppressing the adhesion of fuel to the inner wall surface of the cylinder. Further, as is well known, a fuel injection valve has a lower limit value of a valve opening period in which the amount of fuel injected from the fuel injection valve can be appropriately controlled. In the fuel injection control device of the present invention, each time during divided injection, Since the valve opening period is set to be equal to or longer than the minimum valve opening period, it is possible to prevent the metering accuracy of the fuel injection valve from deteriorating by appropriately setting the minimum valve opening period.

  In one form of the fuel injection control device of the present invention, a lower limit value of a valve opening period range in which the control accuracy of the fuel amount injected from the fuel injection valve can be maintained may be set in the minimum valve opening period. (Claim 2). By setting the minimum valve opening period in this way, the amount of fuel injected from the fuel injection valve can be properly controlled even if the valve opening period of the fuel injection valve is set to the minimum valve opening period.

  In one form of the fuel injection control device of the present invention, the operation control means limits a decrease in fuel pressure so that the pressure of fuel injected from the fuel injection valve is equal to or higher than a predetermined lower limit pressure. Means may be provided (claim 3). As is well known, the average particle size of the injected fuel increases as the pressure of the fuel injected from the fuel injection valve decreases. In this embodiment, since the fuel pressure reduction is restricted by the fuel pressure reduction limiting means, the average particle size of the fuel can be prevented from becoming excessively large. Therefore, it is possible to appropriately atomize the injected fuel and suppress the adhesion to the inner wall surface of the cylinder.

  In this embodiment, the lower limit pressure may be set to a lower limit value of a pressure range in which atomization of the fuel injected from the fuel injection valve is promoted (Claim 4). By setting the lower limit pressure in this way, the fuel injected from the fuel injection valve can be appropriately atomized even during divided injection.

  In one form of the fuel injection control device of the present invention, the operation control means is a cold start time in which the temperature at the start of the internal combustion engine is a predetermined low temperature range, and is calculated by the fuel injection amount calculation means. When the fuel amount is less than the minimum fuel injection amount, the operation of the fuel pressure adjusting means is controlled so that the split injection can be executed to reduce the pressure of the fuel injected from the fuel injection valve, and the split The operation of the fuel injection valve may be controlled so that the fuel injection valve opening period is equal to or longer than the minimum valve opening period at each time of the divided injection. When the internal combustion engine is cold and cold, the fuel adhering to the inner wall surface of the cylinder is difficult to vaporize, so that the adhering fuel is scraped off by the piston and easily mixed with oil. Therefore, in such a case, the fuel pressure is reduced and split injection is performed to suppress oil dilution.

  As described above, according to the fuel injection control device of the present invention, when the valve opening period of the fuel injection valve is less than the minimum fuel injection amount that is the minimum valve opening period, the pressure of the fuel injected from the fuel injection valve In addition, the split injection is performed, so that the penetration force of the injected fuel can be weakened to suppress the fuel from adhering to the inner wall surface of the cylinder. Therefore, dilution of oil can be suppressed.

  FIG. 1 shows a main part of an internal combustion engine in which a fuel injection control device according to one embodiment of the present invention is incorporated. An internal combustion engine (hereinafter also referred to as an engine) 1 in FIG. 1 is configured as a spark ignition type internal combustion engine that is mounted on a vehicle as a driving power source and in which a plurality of cylinders 2 are arranged in an appropriate layout. Yes. In FIG. 1, only one cylinder 2 is shown. An intake passage 3 and an exhaust passage 4 are connected to each cylinder 2. A piston 5 connected to a crankshaft (not shown) via a connecting rod 6 is inserted into each cylinder 2 in a state where it can reciprocate. Each cylinder 2 is provided with a spark plug (not shown) on a substantially center line of the cylinder 2 so that its electrode portion protrudes. The intake passage 3 includes an intake port 3 a provided for each cylinder 2, and the exhaust passage 4 includes an exhaust port 4 a provided for each cylinder 2. The intake port 3 a and the exhaust port 4 a communicate with the combustion chamber 7. An intake valve 8 opens and closes the intake port 3 a and the combustion chamber 7, and an exhaust valve 9 opens and closes the exhaust port 4 a and the combustion chamber 7. The intake valve 8 and the exhaust valve 9 are opened and closed by a known valve mechanism. Further, an oil pan is provided at the bottom of the engine 1 to store oil supplied to each part of the engine 1, but the illustration thereof is omitted. In addition, since these may be the same as a well-known engine, detailed description is abbreviate | omitted.

  Further, in order to supply fuel to each cylinder 2, the internal combustion engine 1 includes a fuel injection valve 10 that directly injects fuel into the cylinder 2. That is, the engine 1 is a so-called in-cylinder direct injection engine. The fuel injected from the fuel tank 11 by the fuel pump 12 and further pressurized by the high-pressure fuel pump 13 and accumulated in the delivery pipe 14 is sent to the fuel injection valve 10. The fuel injection valve 10 may be a well-known one that drives a needle valve with a solenoid and a spring, and therefore a detailed description thereof is omitted. The high-pressure fuel pump 13 may be a well-known pump that is driven by rotation of the crankshaft or camshaft of the engine 1, and thus detailed description thereof is omitted. As shown in FIG. 1, the delivery pipe 14 is connected with a return passage 15 for returning the fuel to the fuel tank 11. The return passage 15 is provided with a relief valve 16 that opens when the pressure of the fuel in the delivery pipe 14 exceeds a predetermined pressure (hereinafter sometimes referred to as normal pressure) Pf1. As shown in FIG. 1, the return passage 15 is provided with a bypass passage 17 that bypasses the relief valve 16, and the bypass passage 17 is provided with an electromagnetic valve 18 as fuel pressure adjusting means for opening and closing the passage. . The pressure of the fuel in the delivery pipe 14, that is, the pressure of the fuel sent to the fuel injection valve 10 and injected from the fuel injection valve 10 is controlled by the relief valve 16 and the electromagnetic valve 18. For example, when the fuel pressure in the delivery pipe 14 exceeds the normal pressure Pf1, the relief valve 16 is opened and the fuel is returned to the fuel tank 11, so that the fuel pressure in the delivery pipe 14 is maintained at the normal pressure Pf1 or lower. In addition, since the fuel can be returned from the delivery pipe 14 to the fuel tank 11 by opening the electromagnetic valve 18, the pressure of the fuel in the delivery pipe 14 can thereby be reduced.

  Operations of the fuel injection valve 10 and the electromagnetic valve 18 are controlled by an engine control unit (ECU) 20. The ECU 20 is configured as a computer including a microprocessor and peripheral devices such as RAM and ROM necessary for the operation of the microprocessor, and controls the operating state of the engine 1 based on various sensors provided in the engine 1. Computer unit. As sensors connected to the ECU 20, as shown in FIG. 1, a crank angle sensor 21 that outputs a signal corresponding to the engine rotational speed (rotation speed) of the engine 1, and an air flow meter 22 that outputs a signal corresponding to the intake air amount. And a fuel pressure sensor 23 that outputs a signal corresponding to the pressure of the fuel supplied to the fuel injection valve 10. In addition, illustration of other various sensors was abbreviate | omitted.

  An outline of control of the fuel injection valve 10 by the ECU 20 will be described. The ECU 20 calculates the basic injection amount of the fuel based on the rotational speed specified from the output signal of the crank angle sensor 21 and the intake air amount specified from the output signal of the air flow meter 22, and calculates the basic injection amount to various values. Correcting according to the information, the final fuel injection amount Q per cycle is calculated, and based on the fuel injection amount Q, the fuel injection time of the fuel injection valve 10, that is, the valve opening for opening the fuel injection valve 10 is opened. Control the period. Since the fuel injection amount Q is calculated in this way, the ECU 20 corresponds to the fuel injection amount calculation means of the present invention. Further, the ECU 20 controls the fuel injection valve 10 so that the divided injection in which the calculated fuel injection amount of fuel is injected in a plurality of times (for example, twice) is performed. Note that during split injection, the operation of the fuel injection valve 10 is controlled so that, for example, the first fuel injection is performed during the intake stroke and the second fuel injection is performed during the compression stroke following the intake stroke.

  As is well known, the fuel injection valve 10 has a valve opening period range in which the amount of fuel to be injected can be appropriately controlled, and the valve opening period is referred to as a lower limit value of the valve opening period range (hereinafter referred to as a minimum valve opening period). If it is less than Tmin, the control accuracy of the needle valve of the fuel injection valve 10 is deteriorated, and the metering accuracy of the fuel injection valve 10 is deteriorated. As is well known, the amount of fuel injected from the fuel injection valve 10 has a correlation with a value obtained by integrating the pressure of the fuel injected from the fuel injection valve 10 and the valve opening period. Therefore, the valve opening period can be lengthened by reducing the pressure of the fuel supplied to the fuel injection valve 10. When the valve opening period of the fuel injection valve 10 is less than the minimum valve opening period Tmin, the pressure of the fuel supplied to the fuel injection valve 10, that is, the pressure of the fuel in the delivery pipe 14 is decreased to open the fuel injection valve 10. Is adjusted to be longer than the minimum valve opening period Tmin. Further, when the valve opening period of the fuel injection valve 10 is less than the minimum valve opening period Tmin, the ECU 20 performs divided injection to suppress the fuel injected from the fuel injection valve 10 from adhering to the inner wall surface of the cylinder 2. Therefore, the ECU 20 can execute divided injection when the valve opening period of the fuel injection valve 10 is less than the minimum valve opening period Tmin, and the valve opening time of each time of this divided injection becomes longer than the minimum valve opening period Tmin. Thus, the fuel pressure in the delivery pipe 14 is reduced. Hereinafter, the pressure of the fuel after the reduction is sometimes referred to as a target pressure Pf2. Further, the control for executing the split injection by reducing the fuel pressure in this way may be referred to as low fuel pressure split injection control.

  An example of low fuel pressure split injection control will be described with reference to FIG. 2 is a diagram showing the relationship between the pressure of the fuel injected from the fuel injection valve 10 and the valve opening time of the fuel injection valve 10 at that pressure, and the upper diagram of FIG. 2 reduces the fuel pressure. FIG. 2 shows the relationship before, that is, the normal pressure Pf1, and the lower diagram in FIG. 2 shows the relationship after the fuel pressure is lowered, that is, the target pressure Pf2. As shown in the upper diagram of FIG. 2, when the valve opening time of the fuel injection valve 10 becomes less than the minimum valve opening period Tmin at the normal pressure Pf1, the fuel injection valve 10 is supplied as shown in the lower diagram of FIG. The fuel pressure to be reduced is reduced to a target pressure Pf2 lower than the normal pressure Pf1, and divided injection is executed in which the valve opening time of each time is equal to or longer than the minimum valve opening period Tmin.

  FIG. 3 shows a fuel injection control routine that is repeatedly executed at a predetermined cycle during operation of the engine 1 in order for the ECU 20 to control the fuel injection valve 10 described above. By executing this control routine, the ECU 20 functions as the operation control means of the present invention. In the control routine of FIG. 3, the ECU 20 first acquires the operating state of the engine 1 in step S11. As the operating state of the engine 1, for example, the rotational speed of the engine 1 and the intake air amount are acquired. In subsequent step S12, the ECU 20 calculates the fuel injection amount Q. The fuel injection amount Q may be calculated by the known calculation method described above.

  In the next step S13, the ECU 20 determines whether or not the calculated fuel injection amount Q is less than a preset minimum fuel injection amount Qmin. In the minimum fuel injection amount Qmin, a fuel injection amount is set such that the opening period of the fuel injection valve 10 becomes the minimum valve opening period Tmin when the pressure of the fuel supplied to the fuel injection valve 10 is the normal pressure Pf1. Therefore, when the fuel injection amount Q is less than the minimum fuel injection amount Qmin, it can be determined that the valve opening period of the fuel injection valve 10 is less than the minimum valve opening period Tmin. When it is determined that the fuel injection amount Q is equal to or greater than the minimum fuel injection amount Qmin, the process proceeds to step S14, where the ECU 20 controls the fuel injection valve 10 by normal control in which fuel is injected from the fuel injection valve 10 at the normal pressure Pf1. Thereafter, the current control routine is terminated. In this normal control, fuel of the fuel injection amount Q may be divided, that is, injected multiple times, or fuel of the fuel injection amount Q may be injected by one injection.

  On the other hand, when it is determined that the fuel injection amount Q is less than the minimum injection fuel amount Qmin, the process proceeds to step S15, and the target pressure Pf2 is set. The target pressure Pf2 is set so that the divided injection can be executed as described above, and the valve opening time of each time of the divided injection is equal to or longer than the minimum valve opening period Tmin. The target pressure Pf2 is set to a pressure equal to or higher than a predetermined lower limit pressure Pb. As is well known, when the pressure of the fuel supplied to the fuel injection valve 10 is lowered, the average particle diameter of the fuel injected from the fuel injection valve 10 increases. FIG. 4 shows an example of this relationship. If the average particle size of the fuel injected into the cylinder 2 becomes large, the fuel is difficult to vaporize in the cylinder 2, so that the fuel may adhere to the inner wall surface of the cylinder 2 or the combustion state may deteriorate. Therefore, the ECU 20 reduces the fuel pressure so that the average particle size of the fuel injected from the fuel injection valve 10 falls within the range of the average particle size at which the fuel injected from the fuel injection valve 10 is appropriately vaporized in the cylinder 2. Limit. Then, the fuel pressure corresponding to the lower limit value of the average particle diameter range is set to a predetermined lower limit pressure Pb. In addition, since the pressure of such fuel changes according to a fuel injection valve, you may change suitably according to the performance of the fuel injection valve provided in the engine 1, a structure, etc. By limiting the decrease in the fuel pressure in this way, the ECU 20 functions as the fuel pressure decrease limiting means of the present invention.

  In the next step S16, the ECU 20 controls the operation of the electromagnetic valve 18 to adjust the fuel pressure in the delivery pipe 14 to the target pressure Pf2. In the subsequent step S17, the ECU 20 executes low fuel pressure split injection control. Thereafter, the current control routine is terminated.

  Thus, when the fuel injection amount Q is less than the minimum fuel injection amount Qmin, the low fuel pressure split injection control is executed, so that the penetration force of the fuel injected from the fuel injection valve 10 can be weakened. Further, since the target pressure Pf2 set during the low fuel pressure split injection control is limited to the lower limit pressure Pb or more, the injected fuel can be appropriately atomized. Thus, since the penetration force can be weakened while maintaining atomization of the fuel, it is possible to suppress the fuel from adhering to the inner wall surface of the cylinder 2. Therefore, dilution of oil can be suppressed. Moreover, since the value more than the minimum valve opening period Tmin is set in each valve opening period at the time of low fuel pressure division | segmentation injection control, it can suppress that the metering precision of the fuel injection valve 10 deteriorates.

  The present invention is not limited to the above-described form and can be implemented in various forms. For example, the present invention is not limited to a spark ignition engine internal combustion engine, but may be applied to a diesel engine. The number of injections at the time of low fuel pressure split injection control is not limited to two, and the injection may be divided into three or more times. At this time, the valve opening times may be different from each other.

  As is well known, when the engine temperature is low, the fuel is less likely to vaporize in the cylinder, and the fuel tends to remain on the inner wall surface of the cylinder. Therefore, even if the low fuel pressure split injection control is executed when the engine is cold-started when the engine temperature is lowered to about the outside air temperature and the fuel injection amount Q is less than the minimum fuel injection amount Qmin. Good. As described above, by performing the low fuel pressure split injection control at the cold start, the dilution of the oil is suppressed.

The figure which shows the principal part of the internal combustion engine in which the fuel-injection control apparatus which concerns on one form of this invention was integrated. The figure which shows the relationship between the pressure of the fuel injected from a fuel injection valve, and the valve opening time of the fuel injection valve in the pressure. The flowchart which shows the fuel-injection control routine which ECU performs. The figure which shows an example of the relationship between the pressure of the fuel supplied to a fuel injection valve, and the average particle diameter of the fuel injected from the fuel injection valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 10 Fuel injection valve 18 Solenoid valve (fuel pressure adjustment means)
20 Engine control unit (fuel injection amount calculating means, operation control means, fuel pressure drop limiting means)

Claims (5)

A fuel injection valve for directly injecting fuel into the cylinder of the internal combustion engine, a fuel pressure adjusting means capable of adjusting the pressure of the fuel injected from the fuel injection valve, and the fuel injection valve per cycle according to the operating state of the internal combustion engine A fuel injection control device for an internal combustion engine, comprising: a fuel injection amount calculating means for calculating a fuel amount to be injected from the fuel injection valve;
When the fuel amount calculated by the fuel injection amount calculating means is less than the minimum fuel injection amount at which the valve opening period of the fuel injection valve is a predetermined minimum valve opening period, the fuel amount calculated by the fuel injection amount calculating means The pressure of the fuel injected from the fuel injection valve is controlled by controlling the operation of the fuel pressure adjusting means so that the divided injection in which the fuel is injected into the cylinder in a plurality of times from the fuel injection valve can be executed. And an operation control means for controlling the operation of the fuel injection valve so that the valve opening period of the fuel injection valve is equal to or longer than the minimum valve opening period at the same time that the split injection is performed and the split injection is performed each time. A fuel injection control device for an internal combustion engine, comprising:   2. The internal combustion engine according to claim 1, wherein a lower limit value of a valve opening period range in which control accuracy of the amount of fuel injected from the fuel injection valve can be maintained is set in the minimum valve opening period. Fuel injection control device.   The said operation control means is provided with the fuel pressure fall restriction | limiting means which restrict | limits the fall of the pressure of fuel so that the pressure of the fuel injected from the said fuel injection valve may become more than predetermined | prescribed lower limit pressure. 3. A fuel injection control device for an internal combustion engine according to 1 or 2.   The fuel injection control device for an internal combustion engine according to claim 3, wherein a lower limit value of a pressure range in which atomization of fuel injected from the fuel injection valve is promoted is set as the lower limit pressure.   The operation control means is a cold start where the temperature at the start of the internal combustion engine is a predetermined low temperature range, and the fuel amount calculated by the fuel injection amount calculation means is less than the minimum fuel injection amount The operation of the fuel pressure adjusting means is controlled so that the divided injection can be executed to reduce the pressure of the fuel injected from the fuel injection valve, and the divided injection is executed and at each time of the divided injection. The fuel of the internal combustion engine according to any one of claims 1 to 4, wherein an operation of the fuel injection valve is controlled so that a valve opening period of the fuel injection valve becomes equal to or longer than the minimum valve opening period. Injection control device.

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