JP2011247150A - Fuel injection system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To have an air-fuel mixture prepared by a plurality of times of fuel injection operations stagnate at a desired position.SOLUTION: The fuel injection system for an internal combustion engine carries out a plurality of times of pilot injections prior to the main injection into a cylinder. At the plurality of the pilot injections, the fuel injection amount is reduced in a pilot injection to the latter stage with the reduction amount of the fuel injection amount is set according to the temperature in the cylinders.

Description

  The present invention relates to a fuel injection system for an internal combustion engine.

  A technique is known in which fuel injection is divided into two equal parts and fuel injection is divided to weaken the penetration force of the fuel spray so that the air-fuel mixture stays at a desired position (see, for example, Patent Document 1). .) According to this technology, even in a low speed range where the intake flow velocity is low and the tumble flow becomes weak, the balance between the fuel spray penetration force and the tumble flow strength is maintained without excessively reducing the fuel pressure, and the air-fuel mixture is reduced. It can be retained in the vicinity of the spark plug electrode as intended.

  By the way, in the case where pilot injection for injecting fuel less than the main injection is performed a plurality of times before main injection into the cylinder of the internal combustion engine, each pilot injection is affected by the previous pilot injection, It is influenced by the condition inside. For this reason, even if the pilot injection amount of each time is the same, the reaching distances may be different from each other, and it may be difficult to retain the air-fuel mixture at a desired position.

JP 2003-262146 A Japanese Utility Model Publication No. 63-090047 JP 2006-283679 A Japanese Patent Laying-Open No. 2005-042646 JP-A-2005-090401

  The present invention has been made in view of the above-described problems, and an object thereof is to retain an air-fuel mixture by a plurality of fuel injections at a desired position.

In order to achieve the above object, a fuel injection system for an internal combustion engine according to the present invention comprises:
In a fuel injection system of an internal combustion engine that performs pilot injection a plurality of times before main injection into a cylinder,
When the pilot injection is performed a plurality of times, the fuel injection amount is decreased as pilot injection is performed later, and the reduction amount of the fuel injection amount at this time is set according to the temperature in the cylinder.

That is, when pilot injection is performed a plurality of times before main injection, the initial pilot injection amount is maximized and the final pilot injection amount is minimized. Here, the spray of the pilot injection performed later has a long reach due to the airflow generated during the pilot injection performed before. For this reason, for example, by reducing the pilot injection amount by an amount corresponding to an increase in the reach distance, it is possible to prevent the spray by the previous pilot injection from overtaking the spray by the subsequent pilot injection. Incidentally, the gas temperature in the cylinder varies depending on the state of the internal combustion engine and the like. And the higher the gas temperature in the cylinder, the more easily the fuel by pilot injection evaporates, and the spray reach distance becomes shorter. This effect increases as the pilot injection amount decreases. For this reason, when pilot injection is performed a plurality of times while reducing the fuel injection amount in stages, the influence of the gas temperature increases as pilot injection is performed later. Therefore, when the fuel injection amount is decreased, if the amount of decrease in the pilot injection amount is set in accordance with the temperature in the cylinder, pilot injection can be performed in consideration of the short reach distance due to fuel evaporation. Note that the amount of decrease in the fuel injection amount may be reduced as the temperature in the cylinder is higher. That is, by increasing the pilot injection amount when the temperature in the cylinder is high than when it is low, it is possible to suppress the reaching distance from becoming too short even if the fuel evaporation amount increases. Thereby, the air-fuel mixture can be retained at a desired position. In addition, the smaller the pilot injection amount per time, the lower the accuracy of control of the injection amount. Therefore, if the pilot injection amount per time is increased and the number of injections is reduced accordingly, the combustion state is stabilized. You can also.

  In the present invention, the maximum value of the fuel injection amount that does not adhere to the combustion chamber wall surface is estimated based on a physical quantity that correlates with the resistance of the gas in the cylinder to the fuel spray, and is less than or equal to the estimated maximum value of the fuel injection amount. Pilot injection can be performed so that

  Thus, if pilot injection is performed so that the fuel injection amount does not adhere to the wall surface of the combustion chamber, the fuel does not adhere to the wall surface of the combustion chamber, so that deterioration of the combustion state can be suppressed. Here, the spray reach distance varies according to the resistance of the gas in the cylinder to the fuel spray. That is, as the gas resistance increases, the spray reach distance decreases. Then, the maximum value of the fuel injection amount that does not adhere to the combustion chamber wall surface also changes in accordance with this resistance. Based on the physical quantity correlated with this resistance, the maximum value of the fuel injection quantity that does not adhere to the combustion chamber wall surface can be estimated. Further, by making the actual pilot injection amount equal to or less than the maximum value of the fuel injection amount that does not adhere to the combustion chamber wall surface, it is possible to increase the pilot injection amount per time while suppressing the fuel from adhering to the combustion chamber wall surface. can do. Note that there is a correlation between the state in the cylinder (for example, the pressure or gas density in the cylinder) and the resistance of the gas to the spray. For example, the higher the pressure in the cylinder, the greater the resistance of the gas to the spray. Therefore, since there is a correlation between the state in the cylinder (for example, the pressure or gas density in the cylinder) and the maximum value of the fuel injection amount that does not adhere to the combustion chamber wall surface, the fuel injection amount is based on the correlation. May be estimated.

  In the present invention, the fuel injection amount of each time by the pilot injection can be set within a range in which the relationship between the fuel injection amount and the spray reach distance is determined regardless of the fuel pressure.

  Here, in the fuel injection valve, when the injection amount is relatively small, the spray reach distance changes according to the fuel injection amount regardless of the fuel pressure. On the other hand, when the injection amount increases, the reach distance changes according to the fuel injection amount and the fuel pressure. Therefore, if pilot injection is performed in a region where the spray arrival distance changes according to the fuel injection amount regardless of the fuel pressure, even if the fuel pressure changes, the arrival of the spray is not considered. The distance can be obtained. This facilitates control of the fuel injection amount.

  According to the present invention, an air-fuel mixture obtained by a plurality of fuel injections can be retained at a desired position.

It is a figure which shows schematic structure of the engine by an Example. It is the time chart which showed the injection pattern of the pilot injection which concerns on an Example. It is the figure which showed the relationship between the fuel injection quantity and the reach | attainment distance of spray. It is the figure which showed the relationship between the order of the pilot injection which concerns on an Example, and the ratio of the subsequent pilot injection quantity. It is the flowchart which showed the control flow of the pilot injection which concerns on an Example.

  Hereinafter, specific embodiments of a fuel injection system for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, a case where the fuel injection system for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.

  FIG. 1 is a diagram showing a schematic configuration of an engine according to this embodiment. An engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having cylinders 2.

  The engine 1 is configured by connecting a cylinder head 1a and a cylinder block 1b.

  An intake port 4 and an exhaust port 5 are formed in the cylinder head 1a, and an intake valve 6 and an exhaust valve 7 that move up and down are provided at the boundary between the intake port 4 and the exhaust port 5 and the inside of the cylinder 2. ing. The cylinder head 1a is provided with a fuel injection valve 3 for supplying fuel into the cylinder 2. A fuel supply source 31 that supplies fuel to the fuel injection valve 3 is connected to the fuel injection valve 3. The fuel supply source 31 includes, for example, a pump and a common rail.

  When a drive current is applied to the fuel injection valve 3, the fuel injection valve 3 opens, and as a result, fuel is injected from the fuel injection valve 3 into the cylinder 2. Here, the amount of fuel injected from the fuel injection valve 3 is calculated by a map from the engine speed and the load. Further, the basic fuel injection timing is also calculated from the engine speed and load using a map. These maps are obtained in advance by experiments or the like.

  Further, the cylinder block 1 b includes a piston 10 inserted into the cylinder 2. A combustion chamber 11 that is recessed toward the center of the piston 10 is formed on the upper surface of the piston 10. A pressure sensor 13 for measuring the pressure in the cylinder 2 is attached to the cylinder head 1a.

  The engine 1 configured as described above is provided with an ECU 12 that is an electronic control unit for controlling the engine 1. The ECU 12 controls the operating state of the engine 1 in accordance with the operating conditions of the engine 1 and the driver's request.

  In addition to the pressure sensor 13, various sensors are connected to the ECU 12 through electrical wiring, and output signals from these sensors are input to the ECU 12. On the other hand, the fuel injection valve 3 is connected to the ECU 12 via electrical wiring, and the fuel injection valve 3 is controlled by the ECU 12. The ECU 12 stores various application programs and various control maps.

When the fuel injection is performed from the fuel injection valve 3 into the cylinder 2, the ECU 12 performs a plurality of pilot injections prior to the main injection. When pilot injection is performed a plurality of times, each fuel injection amount (also referred to as pilot injection amount) is adjusted so as not to overtake the spray of fuel injected before that time. In this case, each pilot injection amount is made smaller than the pilot injection amount before that. Here, when pilot injection is performed, airflow is generated by spraying. The spray of the pilot injection performed thereafter increases the kinetic energy due to the airflow generated by the pilot injection performed previously. For this reason, since the reach distance of the fuel injected later can be longer, the fuel may adhere to the wall surface of the combustion chamber 11 unless the fuel injection amount is changed for each pilot injection. In contrast, the initial kinetic energy can be reduced by reducing the fuel injection amount at the time of the subsequent pilot injection to be smaller than the fuel injection amount at the time of the previous pilot injection. As a result, the reach of the spray by the subsequent pilot injection can be shortened, so that the spray by the pilot injection performed later overtakes the spray by the pilot injection performed before and adheres to the wall surface of the combustion chamber 11. Can be suppressed.

  Here, FIG. 2 is a time chart showing an injection pattern of pilot injection according to the present embodiment. The valve is opened when the fuel injection valve 3 is ON, and is closed when the fuel injection valve 3 is OFF. In FIG. 2, pilot injection is performed four times per cylinder per cycle. Then, from the first pilot injection to the fourth pilot injection, the fuel injection amount is sequentially decreased by shortening the ON period stepwise. The number of pilot injections, the injection amount of each injection, and the injection interval can be mapped in advance in association with the operating state of the engine 1 (for example, the engine speed and the engine load). In addition, as described later, the number of pilot injections and the injection amount of each time can be set.

  Next, FIG. 3 is a diagram showing the relationship between the fuel injection amount and the spray reach distance. FIG. 3 shows the spray reach distance with respect to the fuel injection amount when the fuel is injected from the fuel injection valve 3 only once. The solid line indicates the case where the fuel pressure is relatively high, and the alternate long and short dash line indicates the case where the fuel pressure is relatively low. Here, the relationship between the fuel injection amount and the spray reach distance varies according to the pressure in the cylinder 2. It also changes depending on the number of pilot injections. FIG. 3 shows the relationship in a preset reference state, and the relationship shown in FIG. 3 is corrected by the pressure in the cylinder 2 and the order of pilot injection.

  As shown in FIG. 3, the greater the fuel injection amount, the longer the spray reach distance. Until the fuel injection amount reaches the amount indicated by A, the relationship between the fuel injection amount and the spray reach distance is determined regardless of the fuel pressure (may be the common rail pressure), but the fuel injection amount is A If the amount exceeds the amount indicated by, the relationship between the fuel injection amount and the spray reach is affected by the fuel pressure. That is, the region where the fuel injection amount is smaller than A in FIG. 3 (the region on the left side of A in FIG. 3) is a range where the relationship between the fuel injection amount and the spray reach distance is determined regardless of the fuel pressure. I can say that. Further, it can be said that the region where the fuel injection amount is larger than A in FIG. 3 (the region on the right side of A in FIG. 3) is the range in which the spray reach distance becomes longer as the fuel pressure is higher. Note that the fuel injection amount indicated by A in FIG. 3 is determined according to the performance of the fuel injection valve 3 and can be obtained in advance by experiments or the like. Further, if the relationship between the fuel injection amount and the opening time of the fuel injection valve 3 is obtained in advance by experiments and stored in the ECU 12, the ECU 12 controls the opening time of the fuel injection valve 3. Thus, the fuel injection amount can be adjusted.

  In this embodiment, the pilot injection amount is controlled so that the pilot injection amount is equal to or less than the fuel injection amount indicated by A in FIG. Then, the fuel injection amount indicated by A is the maximum value of the pilot injection amount, and is hereinafter referred to as the maximum pilot injection amount A. Thus, by setting the pilot injection amount to be equal to or less than the maximum pilot injection amount A, the energy given to the spray is governed only by the injected fuel amount. Even if the pressure is changed, the pilot injection amount and the kinetic energy depend only on the injection period. For this reason, the initial energy of spraying can be controlled by the fuel injection amount. That is, by setting the pilot injection amount to be equal to or less than the maximum pilot injection amount A, it is possible to eliminate the influence of the fuel pressure on the spray reach distance.

Here, the reach distance of the pilot-injected fuel changes according to the state (for example, pressure or density) in the cylinder 2. That is, since the resistance of the gas in the cylinder 2 to the spray changes according to the state (for example, pressure or density) in the cylinder 2, the reach distance of the spray changes. For example, in a highland where the air density is low, the resistance of the gas in the cylinder 2 is smaller than in a lowland where the air density is high, and therefore, the spray reach distance is long even with the same fuel injection amount. Further, the pressure in the cylinder 2 also changes depending on the crank angle. When pilot injection is performed a plurality of times during the compression stroke, the later the injection timing, the higher the pressure in the cylinder 2, and the shorter the reach distance. Therefore, in the second and subsequent pilot injections, although the reach distance becomes longer due to the airflow generated by the previous pilot injection, the higher the pressure in the cylinder 2, the smaller the degree of reach.

  On the other hand, for example, if a correction value for correcting the relationship in FIG. 3 is obtained in advance by experiments or the like according to the pressure in the cylinder 2, the relationship in FIG. 3 is corrected according to the pressure in the cylinder 2. Can do. Since the distance from the fuel injection valve 3 to the wall surface of the combustion chamber 11 is known in advance, the fuel injection amount for not reaching the wall surface of the combustion chamber 11 is calculated based on the corrected relationship shown in FIG. can do. The maximum value of the fuel injection amount that does not reach the wall surface of the combustion chamber 11 is hereinafter referred to as a maximum injection amount B. This maximum injection amount B is calculated on the premise of the relationship of the range on the left side of A in FIG. The pressure in the cylinder 2 is obtained by the pressure sensor 13. Further, since the pressure in the cylinder 2 can be estimated from, for example, the atmospheric pressure, the pressure in the intake pipe, the crank angle of the engine 1, and the like, these relationships may be stored in the ECU 12 in advance.

  Here, in a situation where it is difficult for the fuel to combust, such as at extremely low temperatures or when traveling at high altitudes, the required value of the total amount of pilot injection becomes large, so each time the pilot sprays within the range where the fuel spray does not reach the wall surface of the combustion chamber 11. It is better to increase the injection amount as much as possible. Thus, when the required value of the total amount of pilot injection is large, the first pilot injection must be performed at a relatively early time when the pressure in the cylinder 2 is low, but in the pilot injection performed after that, Since the pressure in the cylinder 2 increases, it is possible to suppress the reaching distance from increasing even if the pilot injection amount is increased. That is, the ignitability can be improved by increasing the pilot injection amount.

  Although the pilot injection amount at each time is controlled to be equal to or less than the maximum pilot injection amount A, the spray may not reach the wall surface of the combustion chamber 11 even when the maximum pilot injection amount A is exceeded. In such a case, a pilot injection amount exceeding the maximum pilot injection amount A may be set in a range where the spray does not reach the wall surface of the combustion chamber 11.

  Here, the above-mentioned maximum injection amount B is calculated according to the relationship on the left side of A in FIG. 3, and thus the fuel pressure is not taken into consideration. For this reason, when the maximum injection amount B is larger than the maximum pilot injection amount A, the maximum injection amount B cannot be used as it is. For this reason, when the maximum injection amount B is larger than the maximum pilot injection amount A, the fuel spray reaches the wall surface of the combustion chamber 11 based on the fuel pressure according to the relationship of the region on the right side of A in FIG. The amount of fuel injection to be performed is obtained. The fuel injection amount obtained in this way is set as the maximum injection amount C, and the actual pilot injection amount is obtained. Thus, if more fuel than the maximum pilot injection amount A can be injected, the ignitability can be further improved by injecting more fuel than the maximum pilot injection amount A.

  In addition, when the upper limit value of the allowable range of the initial pilot injection amount (hereinafter referred to as the initial allowable maximum injection amount) is set in advance and the calculated pilot injection amount exceeds the initial allowable maximum injection amount, Let the amount of fuel injected at the initial allowable maximum injection amount. Here, if the amount of pilot injection per time is too large, when the spray evaporates, heat is taken away by latent heat, so the temperature of the air-fuel mixture becomes too low. As a result, the ignitability may be deteriorated, so that the pilot injection amount is set so that the ignitability is not deteriorated. That is, the initial allowable maximum injection amount is an upper limit value of the injection amount that does not deteriorate the ignitability, and is obtained in advance through experiments or the like. The initial allowable maximum injection amount is set to a value larger than the maximum pilot injection amount A.

In the present embodiment, the subsequent pilot injection amount is increased as the temperature in the cylinder 2 is higher. That is, the amount of decrease when the subsequent pilot injection amount is decreased from the previous pilot injection amount is made smaller as the temperature in the cylinder 2 is higher. Here, when the temperature in the cylinder 2 is high, such as when the engine 1 has been warmed up or when a high-load operation has been performed, the spray by the pilot injection evaporates during movement, so that the spray reach distance Becomes shorter. Therefore, in the second and subsequent pilot injections, although the reach distance becomes longer due to the air flow generated by the previous pilot injection, the higher the temperature in the cylinder 2, the smaller the degree that the reach distance becomes longer.

  Then, the influence of this evaporation is larger as the subsequent pilot injection with a smaller injection amount is performed. Therefore, the influence can be canceled by increasing the subsequent pilot injection amount accordingly. Further, since the accuracy of the injection amount increases as the pilot injection amount per time increases, the combustion state becomes more stable when the pilot injection amount is increased to reduce the number of pilot injections.

  FIG. 4 is a diagram illustrating a relationship between the order of pilot injection according to the embodiment and the ratio of the subsequent pilot injection amount. FIG. 4 shows the pilot injection amount of each time when four pilot injections per one cylinder are performed as a ratio to the first pilot injection amount with the first pilot injection amount as a reference (1.0). Represents. A solid line indicates a case where the temperature in the cylinder 2 is relatively high, and a one-dot chain line indicates a case where the temperature in the cylinder 2 is relatively low. This relationship is set so as not to overtake the previous spray by the pilot injection. This relationship can be obtained in advance through experiments or the like. Thus, the higher the temperature in the cylinder 2, the higher the ratio of the subsequent pilot injection amount. Further, the later the pilot injection order, the lower the ratio of the subsequent pilot injection amount. That is, when pilot injection is performed a plurality of times, the fuel injection amount is decreased as pilot injection is performed later, and the decrease amount of the fuel injection amount at this time is set according to the temperature in the cylinder 2. Thereby, the spray by the subsequent pilot injection is suppressed from overtaking the spray by the previous pilot injection while canceling out the influence due to the evaporation of the fuel.

  FIG. 5 is a flowchart showing a control flow of pilot injection according to the present embodiment. This routine is executed by the ECU 12 every predetermined time.

  In step S101, a required pilot total amount that is a total amount of required pilot injection amount is calculated. The required pilot total amount is the total amount of pilot injection required per one cylinder cycle, and is determined according to the operating state of the engine 1. For example, the relationship between the engine speed, the engine load, and the required pilot total amount is obtained in advance through experiments or the like and stored in the ECU 12.

  In step S102, the correction value of the spray reach distance at the time of the first pilot injection is calculated. In this step, a correction value for correcting the spray reach distance based on the gas resistance in the cylinder 2 is calculated. The first pilot injection time is a time when pilot injection is first performed among pilot injections that are injected every cycle of one cylinder. This timing changes according to the required pilot total amount calculated in step S101, and the relationship between the required pilot total amount and the timing when the first pilot injection is performed is stored in the ECU 12 in advance. Since the correction value has a correlation with the pressure in the cylinder 2, the relationship between the correction value and the pressure in the cylinder 2 is obtained in advance through experiments or the like and stored in the ECU 12.

  In step S103, the first pilot injection amount is calculated. In this step, a pilot injection amount at which fuel does not adhere to the wall surface of the combustion chamber 11 is calculated according to the relationship of FIG. 3 and FIG. Note that, as described above, the pilot injection amount exceeding the maximum pilot injection amount A may be set in a range in which fuel does not adhere to the wall surface of the combustion chamber 11.

  In step S104, the second pilot injection amount that does not overtake the spray by the first pilot injection is calculated. This second pilot injection amount is smaller than the first pilot injection amount. Here, the reach of the second pilot injection becomes longer due to the airflow generated by the first pilot injection. However, since the pressure in the cylinder 2 is higher at the time of the second pilot injection than at the time of the first pilot injection, the resistance of the gas to the spray becomes larger, so that the reach distance of the second pilot injection is shorter accordingly. Become. Further, the higher the temperature in the cylinder 2, the easier the fuel evaporates, so the reach distance of the pilot injection becomes shorter. Taking these into account, the second pilot injection amount is calculated. In each case, a map for obtaining a correction value for correcting the relationship of FIG. 3 may be stored, and the second pilot injection amount may be calculated based on the correction value.

  In step S105, the remaining number of pilot injections and the amount of pilot injection for each time are calculated. That is, in the same manner as the second pilot injection, the third and subsequent pilot injection amounts are calculated. In addition, the number of pilot injections that satisfy the required pilot total amount is calculated.

  In step S106, pilot injection is performed using the calculated pilot injection amount.

  As described above, according to the present embodiment, the reach of the fuel spray can be controlled with high accuracy. As a result, the fuel can be prevented from adhering to the wall surface of the combustion chamber 11 and the air-fuel mixture can be retained at a desired position.

1 Engine 1a Cylinder head 1b Cylinder block 2 Cylinder 3 Fuel injection valve 4 Intake port 5 Exhaust port 6 Intake valve 7 Exhaust valve 10 Piston 11 Combustion chamber 12 ECU
13 Pressure sensor 31 Fuel supply source

Claims (3)

In a fuel injection system of an internal combustion engine that performs pilot injection a plurality of times before main injection into a cylinder,
A fuel for an internal combustion engine characterized in that when the pilot injection is performed a plurality of times, the fuel injection amount is decreased as pilot injection is performed later, and the reduction amount of the fuel injection amount at this time is set according to the temperature in the cylinder Injection system.   Based on the physical quantity that correlates with the resistance of the gas in the cylinder to the fuel spray, the maximum value of the fuel injection amount that does not adhere to the combustion chamber wall surface is estimated, and the pilot is set to be equal to or less than the maximum value of the estimated fuel injection amount. 2. The fuel injection system for an internal combustion engine according to claim 1, wherein injection is performed.   3. The fuel for an internal combustion engine according to claim 1, wherein the fuel injection amount at each time by the pilot injection is set within a range in which the relationship between the fuel injection amount and the spray reach distance is determined irrespective of the fuel pressure. Injection system.

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