JP2009030515A - Fuel injection system for spark ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit variation of air current among cylinders in a cylinder direct injection spark ignition type internal combustion engine. <P>SOLUTION: A direct injection injector 19 injecting fuel in a direction intensifying tumble is provided in a cylinder. Voltage between center electrodes of a spark plug 20 is monitored in each cylinder and a condition of tumble formed in each cylinder is detected from discharge time thereof. The variation of tumble among cylinders is detected from a condition of tumble of each cylinder. The assist quantity of tumble is adjusted for each cylinder and the variation of tumble among cylinders is corrected by adjusting the quantity of fuel injected from the direct injection injector 19 of each cylinder. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel injection device for a spark ignition type internal combustion engine that uses a swirl flow such as tumble and swirl and uses direct injection in a cylinder.

In an in-cylinder direct injection spark ignition internal combustion engine, an intake air flow that swirls in the combustion chamber, such as tumble and swirl, is generated by using the inflow of air into the cylinder during intake, thereby promoting combustion. It has been known. In addition, an intake flow control valve for controlling the intake flow generated in the cylinder in the intake passage is provided, and the intake flow control is strengthened by controlling the intake flow valve during homogeneous combustion and partial load (patent) Reference 1).
JP 2005-180247 A

  However, in an in-cylinder direct injection type internal combustion engine, the state of the jet flow due to fuel injection differs in each cylinder due to the deposits etc. that block the injector nozzle. Then, the combustion conditions vary among the cylinders. Therefore, the conventional fuel injection control has a problem that torque fluctuation occurs.

  An object of the present invention is to suppress variations in airflow between cylinders in an in-cylinder direct injection spark ignition internal combustion engine.

  A fuel injection system for a spark ignition internal combustion engine according to the present invention is a fuel injection system for a spark ignition internal combustion engine having a plurality of cylinders, and includes a direct injection injector that directly injects fuel into the cylinder, and each direct injection injector Fuel injection control means for controlling the fuel injection amount to be injected and detection means for detecting the state of the swirling flow formed in each cylinder, each direct injection injector fueling in a direction to strengthen the swirling flow The fuel injection control means adjusts the fuel injection amount of each direct injection injector based on the state of the swirling flow of each cylinder detected by the detecting means, and suppresses the swirling flow variation between the cylinders. It is characterized by.

  In addition, the fuel injection system preferably includes intake port injectors disposed at the intake ports. The fuel injection control means adjusts the fuel injection amount of the direct injection injector for each cylinder by adjusting the injection ratio between the direct injection injector and the intake port injector for each cylinder, and suppresses variations in the swirling flow. As a result, the fuel injection amount of the direct injection injector can be adjusted without affecting the required air-fuel ratio, and variations in the swirling flow can be suppressed.

  Moreover, it is preferable that a detection means detects the state of the turning flow of each cylinder based on the discharge time of the spark plug provided in each cylinder. Thus, with a simple configuration, the flow velocity in the vicinity of the ignition plug of each cylinder can be monitored, and the state of the swirling flow can be accurately grasped. At this time, the fuel injection control means controls the fuel injection amount of each direct injection injector so that, for example, the discharge time of each cylinder becomes the average discharge time of all cylinders. Thereby, the variation in the swirl flow in each cylinder can be reduced quickly and appropriately.

  Further, the fuel injection system preferably includes a fuel pressure adjusting means for adjusting the pressure of the injected fuel, and the fuel pressure adjusting means is more relative in the operation mode utilizing the swirl flow than in the other operation modes. Set a high fuel pressure. Thereby, useless cooling loss can be reduced, mechanical loss of the fuel pump can be reduced, and fuel consumption can be improved.

  The fuel injection system further includes a predetermined discharge time calculating means for calculating a predetermined discharge time suitable for the operating state, and a fuel pressure correcting means for correcting the fuel pressure from the predetermined discharge time and the discharge time in an operation mode utilizing a swirl flow. It is preferable to provide. Thereby, the said effect can be acquired more effectively.

  As described above, according to the present invention, in an in-cylinder direct injection spark ignition internal combustion engine, it is possible to suppress variations in airflow between cylinders.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram schematically showing the configuration of an internal combustion engine according to an embodiment of the present invention. FIG. 1 shows only a schematic partial sectional view of one cylinder, but the internal combustion engine includes a plurality of cylinders as is well known in the art, and in this embodiment, a four-cylinder engine will be described as an example. Do.

  The cylinder block 11 of the internal combustion engine 10 of the present embodiment is provided with a plurality of cylinder bores 13 in which pistons 12 are arranged, and the upper part thereof is covered with a cylinder head 14. The cylinder head 14 is provided with an intake port 15 and an exhaust port 16 that communicate with the cylinder bores 13. An intake valve 17 is provided on the intake port 15, and an exhaust valve 18 is provided on the exhaust port 16. Further, in the cylinder head 14, a direct injection injector 19 for fuel injection and a spark plug 20 for spark ignition are provided at a position that forms a substantially central top surface of the combustion chamber.

  In the present embodiment, the intake port 15 is provided with an intake port injector 21. Fuel is supplied to the direct injection injector 19 and the intake port injector 21 from the delivery pipe 22 at a predetermined fuel pressure. The fuel pressure of the delivery pipe 22 is adjusted by, for example, a fuel pump / regulator 23, and the driving of the fuel pump / regulator 23 and the driving of the direct injection injector 19 and the intake port injector 21 are controlled by the ECU 24. Further, the center electrode voltage at the spark plug 20 provided in each cylinder is monitored by the ECU 24.

  In the fuel injection control of the present embodiment, the ECU 24 determines the fuel pressure, the fuel injection amount, and the fuel injection sharing ratio between the direct injection injector 19 and the intake port injector 21 in accordance with the driver's request and operating state. The ECU 24 controls driving of the fuel pump / regulator 23 and driving of the injection valves of the direct injection injector 19 and the intake port injector 21 based on these determined values.

  The internal combustion engine 10 forms a swirl flow such as a tumble or a swirl in the combustion chamber by an air flow flowing from the intake port 15 during intake, and the nozzle of the direct injection injector 19 is in a direction to strengthen the formed swirl flow. It is set to inject fuel. In the example of FIG. 1, a forward tumble T indicated by a broken line is formed in the combustion chamber, and the direct injection injector 19 injects fuel in a direction that strengthens the forward tumble T.

  The swirl flow in the combustion chamber is generally used in lean operation, EGR operation, knock region, and the like. For example, in the knock region, a swirl flow such as tumble or swirl is formed in the combustion chamber to increase the combustion speed and retard the required ignition timing to prevent knocking. When utilizing the swirl flow, the fuel injection from the direct injection injector 19 is also used to maintain and strengthen the swirl flow. Therefore, it is preferable to set the fuel pressure higher from such a viewpoint.

  Next, fuel injection control in the present embodiment will be described with reference to the flowchart of FIG. 2 is repeatedly executed for each cycle (heat engine cycle) in the overall flow of engine system control in the ECU 24.

  In the fuel injection control of the present embodiment, first, in step S100, the operation mode of the internal combustion engine 10 is checked, and it is determined whether or not the current operation mode is an operation mode utilizing a swirl flow (for example, tumble). As described above, the operation mode utilizing the swirling flow is, for example, lean operation, EGR operation, or operation in a knock region.

  If it is determined in step S100 that the current operation mode is not an operation mode utilizing a swirling flow (tumble), an appropriate target fuel pressure is determined from the engine speed and the engine load in step S102. In step S104, the fuel pump / regulator 23 is set to the determined target fuel pressure, and then the process returns to the main process of engine system control, for example.

  In step S102, the target fuel pressure is determined with reference to, for example, a map recorded in the memory. Step S102 shows an example of a fuel pressure map when the swirl flow is not used. The horizontal axis is the engine speed, and the vertical axis is the engine load. The map has isobars corresponding to target fuel pressures of 12 MPa, 10 MPa, and 8 MPa. The ECU 24 determines the target fuel pressure from the current engine speed and engine load, for example, by linear interpolation using a constant pressure line on the map.

  On the other hand, when it is determined in step S100 that the current operation mode is an operation mode utilizing a swirl flow (tumble), a fuel pressure higher than that in the other operation modes is initially set as a target fuel pressure, and step S106 is subsequently performed. In step S118, the fuel pressure is corrected so that the swirl flow is strengthened (tumble enhancement) by the direct injection injector 19 appropriately. The initial fuel pressure is set to a predetermined value close to the maximum fuel pressure (20 MPa in the present embodiment) (may be the maximum fuel pressure).

  In the fuel pressure correction process, first, in step S106, the discharge time of the spark plug 20 is measured from the change in the center electrode voltage of the spark plug 20. As shown in FIG. 3, there is a one-to-one relationship between the discharge time of the spark plug 29 and the flow velocity in the vicinity of the spark plug 20 (part of the swirl flow). The magnitude of the flow velocity in the vicinity of 20 decreases monotonously. Therefore, the discharge time corresponds to the strength (flow velocity) of the swirling flow in the combustion chamber. For example, if the flow velocity between the plug electrodes is U1 at the discharge time t1, the flow velocity U2 at the discharge time t2 (t1> t2). U1 <U2.

  FIG. 4 shows a time-series change in the center electrode voltage when the spark plug 20 is discharged. In FIG. 4, the solid line shows the change in the center electrode voltage when the discharge time is t1, and the broken line shows the change in the center electrode voltage when the discharge time is t2 (<t1). Discharge occurs when a constant high voltage that causes dielectric breakdown between plug electrodes is applied (capacitive discharge), and then discharge (inductive discharge) continues, but current flows between the plug electrodes as discharge occurs. The voltage between the electrodes rapidly decreases, and when the discharge is blown off by the air flow, the plug electrodes are again insulated and the voltage between the plug electrodes rapidly increases. Therefore, the discharge time can be obtained by monitoring the center electrode voltage, detecting two peaks in the time series change, and measuring the time between the peaks.

  In step S108, an appropriate discharge time corresponding to the engine operating state specified by the engine speed, the engine load, and the like is obtained. That is, a predetermined discharge time corresponding to an appropriate flow velocity in the vicinity of the plug electrode of the swirling flow (tumble) in each operation state is obtained from, for example, a map recorded in the memory. In step S108, an example of a map for obtaining a predetermined discharge time suitable for the operating state is shown. The horizontal axis represents the engine speed, the vertical axis represents the engine load, and the map shows isolines when the discharge time is 1, 0 ms, 0.8 ms, and 0.6 ms. The ECU 24 obtains an appropriate predetermined discharge time corresponding to the current engine speed and engine load based on the value of the isoline on the map, for example, using linear interpolation.

  In step S110, the actual discharge time (actual discharge time) detected from the center electrode voltage of the spark plug 20 monitored in the ECU 24 is compared with the predetermined discharge time determined from the operating state in step S108. When it is determined that the actual discharge time is less than or equal to the predetermined discharge time, that is, when the actual flow velocity in the vicinity of the plug electrode corresponding to the actual discharge time is larger than the flow velocity corresponding to the predetermined discharge time, the current discharge time is determined in step S112. The target fuel pressure is reduced by a predetermined pressure (for example, 0.1 MPa) to obtain a new target fuel pressure. That is, target fuel pressure = target fuel pressure−0.1 MPa is newly set as the target fuel pressure.

  When the target fuel pressure is updated in step S112, the process proceeds to step S120, and the variation of the turning flow velocity in each cylinder (cylinder numbers # 1 to # 4) is corrected. Thereafter, the process returns to the main process in the ECU 24. To do. Note that the processing related to the flow velocity correction of the swirling flow in each of the cylinders # 1 to # 4 (the swirling flow velocity correction processing) will be described later with reference to FIG.

  On the other hand, when it is determined in step S110 that the actual discharge time is longer than the predetermined discharge time, that is, the actual flow velocity in the vicinity of the plug electrode corresponding to the actual discharge time is smaller than the flow velocity corresponding to the predetermined discharge time. In step S114, the current target fuel pressure is increased by a predetermined pressure (for example, 0.1 MPa) to obtain a new target fuel pressure. That is, target fuel pressure = target fuel pressure + 0.1 MPa is newly set as the target fuel pressure.

  In step S116, it is determined whether or not the updated target fuel pressure is larger than a settable maximum fuel pressure (for example, 20 MPa). When the target fuel pressure is greater than the maximum fuel pressure, the target fuel pressure is set to the maximum fuel pressure of 20 MPa in step S118, and the process proceeds to step S120. If it is determined in step S116 that the target fuel pressure is equal to or lower than the maximum fuel pressure, step S120 is executed while maintaining the target fuel pressure at the updated target fuel pressure, and the process returns to the main process in the ECU 24.

  In the fuel pressure correction process in steps S106 to S118 of this embodiment, for example, the discharge time in one cylinder in the internal combustion engine 10 is detected and the fuel pressure correction is performed based on this, but the average of all cylinders is used. The discharge time may be calculated and fuel pressure correction may be performed based on the calculated discharge time.

  Next, with reference to FIG. 5, the details of the turning flow velocity correction process (step S120) for correcting the variation of the turning flow (tumble) formed in each cylinder (#n: n = 1 to 4) will be described. Note that the variation in the swirling flow in each cylinder is caused by the influence of a deposit or the like attached to the nozzle of the direct injection injector 19, for example.

  In step S200, the average discharge time in all cylinders is calculated from the actual discharge time of each cylinder (# 1 to # 4). A variable n representing the cylinder number is initialized to 1. In step S202, it is determined whether the actual discharge time in the #n cylinder is longer than the average discharge time.

  That is, when the actual discharge time of a cylinder is longer than the average discharge time, it means that the flow velocity of the swirling flow in the cylinder is slower than the average flow velocity of the swirling flow of all the cylinders. Is shorter than the average flow velocity of the swirling flow in all cylinders (see FIG. 3). Therefore, in order to suppress the variation between cylinders, for example, in a cylinder where the flow velocity is slower than the average flow velocity, the fuel injection amount by the direct injection injector is increased to strengthen the jet flow assist, and in the cylinder where the flow velocity is faster than the average flow velocity, the direct injection injector It is effective to reduce the amount of fuel injection by weakening the jet flow assist.

  Therefore, in this embodiment, when it is determined in step S202 that the actual discharge time in the #n cylinder is longer than the average discharge time, the fuel injection of the direct injection injector 19 in the #n cylinder is increased in step S204, and the turning The flow will be further strengthened (tumble enhancement).

  Further, in this embodiment, since the fuel injection is performed using the direct injection injector 19 and the intake port injector 21, the direct injection injector 19 maintains the total amount of fuel injected from both injectors while maintaining a constant amount. It is possible to adjust the fuel injection amount from the direct injection injector 19 by increasing or decreasing the ratio of the injected fuel.

  Accordingly, in step S204, the direct injection ratio (direct injection quantity / (direct injection quantity) + intake port injector quantity) × 100) of the #n cylinder is increased by a predetermined amount, and the swirling flow is strengthened. . Specifically, for example, the direct injection ratio in the #n cylinder is updated to direct injection ratio = direct injection ratio + 0.1%.

  In step S206, it is determined whether or not the direct injection ratio of the #n cylinder set in step S204 is larger than a settable maximum value (for example, 100%). If the direct injection ratio of the #n cylinder is larger than the maximum value, the direct injection ratio of the #n cylinder is reset to the maximum value in step S208, and then the process proceeds to step S216. In this case, the process proceeds to step S216 with the set direct injection ratio.

  In step S216, it is determined whether or not the variable n corresponding to the cylinder number has reached the maximum value 4. If n is 4 or more, since the direct injection ratio is adjusted for all the cylinders # 1 to # 4 in this cycle and the correction of the turning flow velocity is completed, the turning flow velocity correction processing in this cycle is completed. To do. On the other hand, when n does not reach the maximum value 4 in step S216, the value of n is updated to n + 1 in step S218, and the same processing is repeated from step S202 on for the updated #n cylinder.

  If it is determined in step S202 that the actual discharge time of the #n cylinder is equal to or less than the average discharge time, the process proceeds to step S210, the direct injection ratio of the #n cylinder is decreased, and the direct injection injector 19 Strengthening of the swirl flow due to the fuel injection is suppressed. Specifically, for example, the direct injection ratio in the #n cylinder is updated to direct injection ratio = direct injection ratio−0.1%.

  In step S212, it is determined whether or not the direct injection ratio of the #n cylinder set in step S210 is smaller than a settable minimum value (for example, 30%). If the direct injection ratio of the #n cylinder is smaller than the minimum value, in step S214, the direct injection ratio of the #n cylinder is reset to the minimum value, and then the process proceeds to step S216. In this case, the process moves to step S216 with the set direct injection ratio.

  In step S216, as described above, it is determined whether or not the variable n corresponding to the cylinder number has reached the maximum value 4. If n ≧ 4 and correction has been completed for all the cylinders, this cycle is performed. In the other cases, the value of n is updated, the processing in step S202 and subsequent steps is repeated, and the correction for the next cylinder is executed. The turning flow velocity correction process is repeatedly executed for each cycle of the internal combustion engine 10 together with the fuel pressure correction process (steps S106 to S118).

  As described above, by performing the turning flow velocity correction process of the present embodiment, even if the same fuel pressure is applied to all the injectors, by adjusting the fuel injection amount injected into the cylinder for each cylinder, Variations in the swirling flow between the cylinders are gradually corrected, and the actual discharge time (flow velocity of the swirling flow) can be made substantially constant in all the cylinders. Thereby, the torque fluctuation | variation etc. by the difference in the combustion conditions between cylinders can be suppressed.

  Further, in the present embodiment, by adopting a dual injection system using a direct injection injector and an intake port injector, the direct injection injector is adapted to variations in the swirling flow between the cylinders without affecting the air-fuel ratio. The amount of fuel injection by can be adjusted.

  Furthermore, in this embodiment, since the fuel pressure is set to be relatively high in the operation state utilizing the swirl flow such as tumble and swirl, and the fuel pressure is set to be relatively low in the other operation states, the combustion by the swirl flow is performed. This makes it possible to reduce the cooling loss due to direct injection when no improvement is required, and to shorten the period during which the fuel pressure is set high, thereby reducing the mechanical loss of the fuel pump and improving the fuel consumption.

  Further, in the present embodiment, even in an operation state utilizing the swirl flow, the strength of the swirl flow in the combustion chamber is monitored by finely adjusting the fuel pressure by monitoring the discharge time, so that the fuel pressure is more than necessary. Therefore, the above effect can be further enhanced.

  In the present embodiment, the amount of fuel injection by direct injection is increased in the cylinder considered to be slower than the average flow velocity, and the fuel injection amount by direct injection is reduced in the cylinder considered to be faster than the average flow velocity. It is also possible to increase the direct injection fuel injection amount of the other cylinders according to the cylinder, or decrease the direct injection fuel injection amount of the other cylinders according to the minimum cylinder. In this embodiment, the state of the swirling flow in each cylinder is estimated from the discharge time of the spark plug provided in each cylinder and the variation is corrected. However, the state of the swirling flow is evaluated by other methods. Is also possible.

1 is a block diagram schematically showing the configuration of an internal combustion engine that is an embodiment of the present invention. It is a flowchart for demonstrating the fuel-injection control in this embodiment. It is a graph which shows the relationship between the discharge time of a spark plug, and the flow velocity between plug electrodes. It is a graph which shows the discharge waveform of the spark plug with respect to two flow rates. It is a flowchart of the turning flow velocity correction process in the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11 Cylinder block 12 Piston 13 Cylinder bore 14 Cylinder head 15 Intake port 16 Exhaust port 17 Intake valve 18 Exhaust valve 19 Direct injection injector 20 Spark plug 21 Intake port injector 22 Delivery pipe 23 Fuel pump / regulator 24 ECU

Claims (6)

A fuel injection system for a spark ignition internal combustion engine having a plurality of cylinders,
A direct injection injector that injects fuel directly into the cylinder;
Fuel injection control means for controlling the fuel injection amount injected from each direct injection injector,
Detecting means for detecting the state of the swirling flow formed in each cylinder,
Each of the direct injection injectors injects fuel in a direction in which the swirl flow is strengthened, and the fuel injection control unit is configured to perform the direct injection on the basis of the swirl flow state of each cylinder detected by the detection unit. A fuel injection system for a spark ignition type internal combustion engine, wherein the fuel injection amount of the injector is adjusted to suppress variations in swirling flow between the cylinders.   An intake port injector disposed in each intake port, and the fuel injection control means adjusts an injection ratio between the direct injection injector and the intake port injector for each cylinder, thereby fueling the direct injection injector The fuel injection system for a spark ignition type internal combustion engine according to claim 1, wherein an injection amount is adjusted for each cylinder to suppress variations in the swirling flow.   2. The fuel injection of the spark ignition type internal combustion engine according to claim 1, wherein the detection means detects a state of a swirling flow of each cylinder based on a discharge time of a spark plug provided in each cylinder. system.   4. The spark ignition type according to claim 3, wherein the fuel injection control unit controls a fuel injection amount of each direct injection injector so that a discharge time of each cylinder becomes an average discharge time of all cylinders. A fuel injection system for an internal combustion engine.   Fuel pressure adjusting means for adjusting the pressure of the injected fuel is provided, and the fuel pressure adjusting means sets a fuel pressure relatively higher in the operation mode utilizing the swirl flow than in the other operation modes. The fuel injection system for a spark ignition type internal combustion engine according to claim 3.   A predetermined discharge time calculating means for calculating a predetermined discharge time suitable for the operating state; and a fuel pressure correcting means for correcting the fuel pressure from the predetermined discharge time and the discharge time in an operation mode utilizing the swirl flow. The fuel injection system for a spark ignition type internal combustion engine according to claim 5.

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