JP5040588B2 - Fuel injection system - Google Patents

Description

  The present invention relates to a fuel injection system that injects fuel directly into a combustion chamber of an internal combustion engine and multiple times for one combustion.

  Pressurized fuel is supplied to an internal combustion engine, that is, a fuel injection device attached to the engine. The fuel injection device receives an injection signal from the ECU, and injects fuel during a period in which the injection signal is received.

  In order to precisely control the actual fuel injection amount that is actually injected, the relationship between the injection signal reception period and the actual fuel injection amount needs to be substantially linear. However, since the relationship between the injection signal reception period and the actual fuel injection amount is not substantially linear in the range where the injection signal reception period is equal to or less than the predetermined determination value in the fuel injection device, the injection signal reception period is controlled to achieve a desired actual value. It becomes difficult to obtain the fuel injection amount.

  In multi-injection, fuel is injected multiple times for one combustion, so that each injection signal reception period is reduced. For this reason, when the required fuel amount decreases, each injection signal reception period may become a predetermined determination value or less.

In order to solve this, a configuration is disclosed in which multi-injection is performed when the minimum injection signal reception period in multi-injection is equal to or greater than a predetermined determination value (Patent Document 1).
JP-A-10-103142

  However, even if the injection signal reception period is equal to or longer than the predetermined determination value, if the fuel pressure of the fuel supplied to the fuel injection device does not reach the predetermined target pressure, the desired actual fuel injection amount even if the multi-injection is stopped Can't get. If the desired fuel injection amount cannot be injected, the engine emission and drivability may deteriorate.

  On the other hand, the actual fuel injection amount is increased or decreased in consideration of the accelerator opening, and the actual fuel injection amount is increased as the accelerator opening increases. If the accelerator opening increases rapidly, the fuel supply to the fuel injection device cannot catch up with the increase in the actual fuel injection amount, and the fuel pressure of the fuel supplied to the fuel injection device may not reach the target pressure. Due to the decrease in the fuel pressure, a desired fuel injection amount cannot be injected in one fuel injection. If multi-injection is performed at this time, the difference between the desired fuel injection amount and the actual fuel injection amount is increased by the number of injections in the multi-injection, and the engine emission and drivability may be deteriorated.

  In view of the above problems, an object of the present invention is to provide a fuel injection system capable of suppressing deterioration of engine emission and drivability more than necessary when a desired target fuel pressure cannot be obtained.

  A fuel injection system according to a first invention of the present application includes a fuel injection unit that directly injects fuel into a combustion chamber of an internal combustion engine, and a fuel pressure measurement unit that measures an actual fuel pressure that is an actual pressure of fuel supplied to the fuel injection unit. , A fuel pressure difference detecting means for detecting a fuel pressure difference between a target fuel pressure which is a fuel pressure to be supplied to the fuel injection means and an actual fuel pressure, and a division for injecting fuel by dividing into a plurality of injections for one combustion Injection control means for causing the fuel injection means to perform injection, and the injection control means causes the fuel injection means to execute divided injection when the fuel pressure difference is less than a predetermined value, and the fuel injection means to execute divided injection. When the fuel pressure difference becomes greater than or equal to a predetermined value, the number of injections is reduced. The fuel injection means injects the fuel a plurality of times in any one or a plurality of strokes from the intake stroke to the exhaust stroke of the internal combustion engine. Thereby, even if the air-fuel ratio sensor does not function normally, predetermined performance can be obtained without deteriorating engine emission more than necessary.

  It is desirable to reduce the number of injections when a fuel pressure difference occurs due to a change in the target fuel pressure in accordance with the accelerator opening. When the target fuel pressure increases in response to a rapid increase in the accelerator opening, the fuel pressure difference may increase. Even when the fuel pressure does not reach the target fuel pressure by the user rapidly increasing the accelerator opening, a desired fuel injection amount can be injected to suppress deterioration of engine emission and drivability.

  The injection control means causes the fuel injection means to execute divided injection when a period during which the fuel pressure difference is less than a predetermined value exceeds a predetermined period, and when the fuel injection means is executing divided injection, the fuel pressure difference is greater than or equal to a predetermined value. The number of injections may be decreased when the period of time exceeds a predetermined period. As a result, even when the fuel pressure difference fluctuates in the vicinity of the predetermined value, it is possible to prevent frequent switching to the process in which the number of injections is reduced and to resume the control of the combustion injection means by the map.

  The injection control means decreases the number of injections when the fuel pressure difference becomes greater than or equal to the first value, and when the fuel pressure difference becomes less than the second value smaller than the first value after decreasing the number of injections. The fuel injection means is preferably configured to execute split injection. Thus, hysteresis is set to prevent frequent switching between the process of reducing the number of injections and the process of the map.

  The injection control means reduces the number of injections when the period during which the fuel pressure difference is equal to or greater than the first value exceeds a predetermined period, and after the number of injections has been decreased, the fuel pressure difference is smaller than the first value. The fuel injection unit may be configured to execute split injection when the period less than the value exceeds a predetermined period. Thus, hysteresis is set to prevent frequent switching between the process of reducing the number of injections and the process of the map.

  The injection control means desirably causes the fuel injection means to inject a constant fuel injection amount regardless of the number of injections. The same amount of fuel as before the fuel pressure difference becomes equal to or greater than a predetermined value is injected with a small number of injections to ensure the fuel injection amount necessary for the engine. By injecting a desired amount of fuel with a small number of injections, errors in the injection period and injection timing can be reduced.

  A spark ignition direct injection internal combustion engine according to a second invention of the present application is characterized by comprising the above fuel injection system. Thereby, even when the target fuel pressure cannot be obtained, it is possible to obtain a spark ignition type direct injection internal combustion engine that can suppress the deterioration of emission and drivability more than necessary.

  According to the present invention, when a desired target fuel pressure cannot be obtained, a fuel injection system capable of suppressing deterioration of engine emission and drivability more than necessary is obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  An embodiment of a fuel injection system according to the present invention will be described with reference to FIG.

  The fuel injection system is attached to a spark ignition direct injection internal combustion engine. A spark ignition direct injection internal combustion engine (hereinafter referred to as an engine) 110 sucks air sucked from an air cleaner 131 into a combustion chamber 141. Fuel is injected from the fuel injection device 111 into the combustion chamber 141. Air is mixed with fuel in the combustion chamber 141. A spark plug 142 is provided at the top of the combustion chamber 141 and ignites the fuel / air mixture in accordance with a signal from the ECU 112. After the air-fuel mixture burns, it becomes exhaust gas and is discharged to the exhaust pipe 151. The exhaust gas is purified by the exhaust gas purification catalyst 152 and then released to the atmosphere. An A / F sensor 113 is attached to the exhaust pipe 151, detects the air-fuel ratio from the exhaust gas, and transmits it to the ECU 112.

  Fuel is injected into the common rail 115 by a fuel pump 114 from a fuel tank (not shown) and pressurized. A fuel pressure sensor 117 for measuring the pressure of the fuel accumulated in the common rail 115, that is, the actual fuel pressure is attached to the common rail 115, and the fuel pressure value is transmitted to the ECU 112. The common rail 115 and the fuel injection device 111 are connected by a fuel pipe 116, and pressurized fuel is supplied to the fuel injection device 111.

  The fuel injection device 111 is provided so that the injection nozzle 118 protrudes from the cylinder head 143 to the combustion chamber 141. An opening / closing valve 120 is provided inside the injection nozzle 118, and fuel is injected into the combustion chamber 141 by opening / closing the opening / closing valve 120. An EDU (injector drive unit) 119 is connected to the fuel injection device 111. The EDU 119 energizes the fuel injection device 111 in accordance with the fuel injection signal from the ECU 112. The fuel injection device 111 injects fuel only during the energization period in which power is supplied from the EDU 119.

  The fuel injection device 111 performs multi-injection. The multi-injection is to inject fuel a plurality of times in any one of the strokes from the intake stroke to the exhaust stroke of the engine 110. By performing multi-injection when the engine is operating at a high load, the homogeneity of the fuel in the combustion chamber is improved. For example, fuel is injected at BTDC 320 °, 300 °, 280 °.

  The accelerator 160 transmits the accelerator opening to the ECU 112. The ECU 112 determines the target fuel injection amount using the accelerator opening. The target fuel injection amount is a fuel injection amount determined according to the running state of the vehicle. For example, when the accelerator opening increases, the target fuel injection amount is increased. The ECU 112 includes a map for calculating the number of fuel injections in the multi-injection from the target fuel injection amount and the actual fuel pressure, and uses this map to calculate the number of fuel injections. A fuel injection signal corresponding to the number of fuel injections is transmitted from the ECU 112 to the EDU 119.

  When the increase rate of the accelerator opening increases, the increase rate of the target fuel injection amount increases accordingly. In order to inject the target fuel injection amount, the fuel supply amount supplied to the common rail 115 by the fuel pump 114 must be increased to maintain the actual fuel pressure inside the common rail 115. The ECU 112 detects the fuel pressure difference from the actual fuel pressure and the target fuel pressure, and controls the fuel pump 114 so that the fuel pressure inside the common rail 115 becomes the target fuel pressure. When the capacity of the fuel pump 114 cannot follow the increase in the fuel supply amount, the fuel pressure inside the common rail 115 cannot be maintained, and the fuel pressure of the fuel supplied from the common rail 115 to the fuel injection device 111 does not reach the target pressure. If the fuel pressure does not reach the target pressure, a desired fuel injection amount cannot be injected even if the on-off valve 120 is opened for a predetermined period. That is, the fuel injection device 111 cannot inject a desired fuel injection amount in one fuel injection. If multi-injection is performed at this time, the difference between the desired fuel injection amount and the actual fuel injection amount increases by the number of injections in the multi-injection.

  If the multi-injection is continued when the fuel pressure inside the common rail 115 cannot be maintained, the fuel pressure inside the common rail 115 decreases every time fuel is injected, and the actual fuel pressure at the first injection and the actual fuel pressure at the last injection in the multi-injection are reduced. It will be very different. As a result, the difference between the desired fuel injection amount and the actual fuel injection amount increases. That is, there is a possibility that an optimal air-fuel ratio cannot be obtained by fuel injection using a map.

  When performing multi-injection when the actual fuel pressure has not reached the target fuel pressure, control may be performed to lengthen the actual fuel injection period in the multi-injection in order to ensure the target fuel injection amount. However, in this control, the fuel pressure inside the common rail 115 is reduced at each fuel injection to further increase the difference between the actual fuel pressure at the first injection and the actual fuel pressure at the last injection in the multi-injection. However, there is a possibility that the target fuel injection amount cannot be injected.

  Processing performed in the fuel injection system to solve this will be described with reference to FIG. In FIG. 2, the solid line 31 indicates the actual fuel pressure with respect to time, the broken line 32 indicates the target fuel pressure with respect to time, and the alternate long and short dash line 33 indicates the accelerator opening with respect to time.

  In the first period 35 of FIG. 2, the ECU 112 operates as the first control means, and performs multi-injection according to the control by the map. At this time, when the user increases the accelerator opening, the ECU 112 controls the fuel pump 114 to increase the fuel pressure to the target fuel pressure corresponding to the accelerator opening. However, the actual fuel pressure does not rise sufficiently due to a reaction delay caused by the fuel pump 114, and a fuel pressure difference d is generated between the target fuel pressure and the actual fuel pressure. When the period in which the fuel pressure difference d is equal to or greater than the first value D1 exceeds the predetermined period T1, the ECU 112 stops the control by the map and operates as the second control unit. The ECU 112 operating as the second control means reduces the number of fuel injections and divides all the fuel injection amounts immediately before stopping the map control into the reduced number of fuel injections. A period during which the number of fuel injections is decreased and fuel injection is performed is a second period 36. Since the difference between the desired fuel injection amount and the actual fuel injection amount is suppressed by reducing the number of fuel injections in this way, the fuel injection system can secure the desired fuel injection amount.

  When the increase in the target fuel pressure ends, the actual fuel pressure approaches the target fuel pressure. When the period during which the fuel pressure difference d between the actual fuel pressure and the target fuel pressure is less than the first value D1 exceeds the predetermined period T1, the ECU 112 stops the process of reducing the number of injections and operates as a first control unit. That is, the multi-injection is resumed according to the control by the map. At this time, the second period 36 ends and the third period 37 starts. As a result, the control of the fuel injection device 111 by the map can be resumed and multi-injection can be performed.

  Next, a process for reducing the number of injections will be described with reference to FIG.

  This control is executed in the ECU 112 at regular time intervals. First, in step S41, it is determined whether the period during which the fuel pressure difference d is equal to or greater than the first value D1 exceeds a predetermined period T1. If not, the process ends. If so, the process proceeds to step S42.

  In step S42, it is determined whether or not the fuel injection device 111 is performing multi-injection. This process ends when the multi-injection is not performed. When multi-injection is being performed, the second control means is executed by reducing the number of multi-injections in step S43. For example, the number of three injections is reduced to two. At this time, all the fuel injection amounts before the decrease are divided into the reduced number of fuel injections for injection.

  In the next step S44, it is determined whether the period during which the fuel pressure difference d is less than the first value D1 exceeds a predetermined period T1. If not, the determination is repeated until it exceeds. If so, the process proceeds to step S45.

  In step S45, the control of the number of fuel injections by the map as the first control means is resumed, and this process ends.

  As a result, even if a fuel pressure difference occurs between the actual fuel pressure and the target fuel pressure, it is possible to achieve an optimal air-fuel ratio while securing the amount of fuel necessary for combustion of the engine 110. By realizing the optimum air-fuel ratio, it is possible to keep the fuel in a good combustion state, prevent the emission from deteriorating more than necessary, and allow the engine 110 to exhibit a predetermined performance.

  In step S43, the number of fuel injections may be one. At this time, all the fuel injection amounts before the decrease are injected at one time. As a result, it is possible to realize an optimal air-fuel ratio while securing the amount of fuel necessary for combustion of the engine 110.

  In step S41, it is determined only whether the fuel pressure difference d is greater than or equal to the first value D1, and in step S44, only whether the fuel pressure difference d is less than a second value D2 that is smaller than the first value D1. May be determined. It is possible to make a quick decision by setting the hysteresis to reduce the number of fuel injections and preventing the map from switching frequently and omitting the judgment of whether or not the predetermined period has been exceeded. It becomes.

  Further, in step S44, the predetermined value may be a second value D2 smaller than the first value D1, and the predetermined period may be T2. By setting the hysteresis, it is possible to prevent frequent switching between the process for reducing the number of fuel injections and the process using the map.

  In addition, although the case where the actual fuel pressure cannot follow the change of the target fuel pressure has been described, when the difference between the actual fuel pressure and the target fuel pressure becomes larger than the predetermined value due to the change of the actual fuel pressure when the target fuel pressure does not change, The process may be executed. Even when the desired actual fuel pressure cannot be obtained due to a failure in the fuel system or the like, it is possible to obtain an optimal air-fuel ratio and suppress deterioration of engine emission and drivability more than necessary.

It is the figure which showed typically the fuel-injection system connected to the spark ignition type direct injection internal combustion engine. It is the graph which showed the relationship between target fuel pressure and actual fuel pressure. It is the flowchart which showed the process in a fuel-injection system.

Explanation of symbols

110 Engine 111 Fuel injection device 112 ECU
113 A / F sensor (air-fuel ratio meter)
114 Fuel Pump 115 Common Rail 117 Fuel Pressure Sensor 118 Injection Nozzle 119 EDU (Injector Drive Unit)
120 On-off valve

Claims (8)

Fuel injection means for directly injecting fuel into the combustion chamber of the internal combustion engine;
Fuel pressure measuring means for measuring an actual fuel pressure which is an actual pressure of fuel supplied to the fuel injection means;
Wherein the fuel pressure difference detecting means for detecting a fuel pressure difference between the target fuel pressure and the actual fuel pressure when not reached the target fuel pressure is a fuel pressure to the actual fuel pressure is supplied before Symbol fuel injection means,
Injection control means for causing the fuel injection means to execute divided injection for injecting fuel divided into a plurality of injection times for one combustion,
The injection control means causes the fuel injection means to execute divided injection when the fuel pressure difference is less than a predetermined value, and the fuel pressure difference becomes equal to or greater than a predetermined value when the fuel injection means is executing divided injection. A fuel injection system that reduces the number of injections in the event of an accident.   The fuel injection system according to claim 1, wherein the fuel pressure difference is caused by a change in the target fuel pressure.   The fuel injection system according to claim 2, wherein the target fuel pressure changes according to an accelerator opening.   The injection control means causes the fuel injection means to execute divided injection when a period during which the fuel pressure difference is less than a predetermined value exceeds a predetermined period, and the fuel pressure when the fuel injection means is executing divided injection. 2. The fuel injection system according to claim 1, wherein the number of injections is decreased when a period in which the difference is equal to or greater than a predetermined value exceeds the predetermined period.   The injection control means decreases the number of injections when the fuel pressure difference becomes equal to or greater than a first value, and after reducing the number of injections, the fuel pressure difference is less than a second value that is smaller than the first value. 2. The fuel injection system according to claim 1, wherein the fuel injection unit performs split injection when the fuel injection means becomes.   The injection control means reduces the number of injections when the period in which the fuel pressure difference is equal to or greater than a first value exceeds a predetermined period, and after reducing the number of injections, the fuel pressure difference is less than the first value. 2. The fuel injection system according to claim 1, wherein when the period that is less than the small second value exceeds the predetermined period, the fuel injection unit performs divided injection. 3. The fuel injection system according to claim 1, wherein the injection control unit causes the fuel injection unit to inject a constant fuel injection amount regardless of the number of injections.   A spark ignition direct injection internal combustion engine comprising the fuel injection system according to claim 1.

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