JP2010261363A - Internal combustion engine capable of stratificataion combustion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine capable of preventing intrusion of fuel components into an EGR layer. <P>SOLUTION: This internal combustion engine 1 includes: an intake valve 13A for opening/closing an intake port 12A relative to a combustion chamber 8; a fuel injection valve 16 capable of injecting fuel to the intake air; an EGR passage 17 connecting an exhaust passage 6 and the intake port 12A to each other; and an EGR valve 18 for opening/closing the EGR passage 17. Valve opening operation of the EGR valve 18 is controlled to lead EGR gas into the intake port 12A before opening the intake valve 13A, and after the EGR gas is led into the combustion chamber 8 from the intake port 12A with the operation for opening the intake valve 13A, and operation of the fuel injection valve 16 relative to the intake air is controlled so that an air layer L2 is left between an EGR layer L1 and an air-fuel mixture layer L3 inside the combustion chamber 8. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an internal combustion engine capable of stratifying an EGR gas and an air-fuel mixture in a combustion chamber.

  As an internal combustion engine capable of stratified combustion, it has a pair of intake ports, a swirl control valve is arranged in one intake port, and the swirl control valve and the intake valve of each intake port are closed. EGR gas is introduced downstream, and in the intake stroke, the intake valve of one intake port is first opened to form a swirl flow of EGR gas in the combustion chamber, and then the intake valve of the other intake port is opened. There is known an internal combustion engine in which a swirl flow in the opposite direction is formed above the EGR gas in the combustion chamber, and fuel is injected toward the swirl flow of the air to stratify the EGR gas and the air-fuel mixture ( For example, see Patent Document 1). In addition, Patent Documents 2 to 4 exist as prior art documents related to the present invention.

JP 2004-144052 A JP 2001-248465 A JP 2001-323828 A JP 2004-332591 A

  When the EGR layer and the air-fuel mixture layer are formed, the fuel is mixed in the inert EGR gas at the boundary between them, and the mixed fuel may not be burned but discharged as an unburned component. Accordingly, an object of the present invention is to provide an internal combustion engine capable of preventing the fuel component from being mixed into the EGR layer.

  The present invention relates to an intake valve that opens and closes an intake port for a combustion chamber, a fuel injection valve that can inject fuel to intake air, an EGR passage that connects an exhaust passage and an intake port, and the EGR passage A stratified charge combustion control device applied to an internal combustion engine having an EGR valve that opens and closes, wherein the EGR valve is opened so that EGR gas is introduced into the intake port prior to the opening of the intake valve. EGR valve control means for controlling the air, and air is introduced after EGR gas is introduced from the intake port into the combustion chamber as the intake valve is opened, and the EGR layer and the mixture layer in the combustion chamber Fuel injection control means for controlling the operation of the fuel injection valve with respect to the intake air so that an air layer remains in between.

  According to the stratified charge combustion control apparatus of the present invention, the EGR gas is introduced near the end portion of the intake port by opening the EGR valve prior to the opening of the intake valve. When the intake valve is opened, EGR gas near the end of the intake port is first introduced into the combustion chamber to form an EGR layer. Subsequently, air is introduced from the intake port into the combustion chamber, and an air layer is formed in the combustion chamber. Further, by injecting fuel from the fuel injection valve limited to a part of the air introduced following the EGR gas, an air layer remains between the EGR layer and the mixture layer in the combustion chamber. As described above, since the air layer is interposed between the EGR layer and the air-fuel mixture layer, it is possible to prevent the fuel component from being mixed into the EGR layer even if the EGR amount is increased.

The figure which shows the principal part of the internal combustion engine which concerns on one form of this invention in the state seen from the cylinder axial direction. The figure which shows the mode before intake valve opening. The figure which shows the mode after opening an intake valve. The figure which shows the mode at the time of intake valve closing. The flowchart which shows the driving | operation discrimination | determination routine performed in order for an engine control unit to discriminate | determine the possibility of a stratified combustion operation. The flowchart which shows the combustion control routine performed in order that an engine control unit may implement | achieve stratified combustion or homogeneous combustion selectively. The figure which shows an example of the map referred in order to determine an EGR rate by the routine of FIG. The figure which shows an example of the map referred in order to determine the valve opening time of an EGR valve in the routine of FIG. The timing chart which shows the opening / closing timing of an EGR valve and an intake valve in association with the crank angle of an internal combustion engine. The figure which shows an example of the map referred in order to determine an air rate by the routine of FIG. The figure which shows the flow volume of the intake air which passes from an intake port to a combustion chamber along a time series. The figure which divides and shows the passage flow rate of the fluid which passes an intake valve in the stratification division formed in a cylinder. The figure which shows the modification of FIG. The figure which shows an example of the map which described the relationship between the crank angle referred in order to implement | achieve the modification of FIG. 13, and valve | bulb passage flow volume. The figure for demonstrating the method of determining the fuel-injection period in the modification of FIG. The figure which shows the further modification of FIG. The figure for demonstrating the method of determining the fuel-injection period in the modification of FIG.

  As shown in FIGS. 1 to 4, an internal combustion engine (hereinafter referred to as an engine) 1 according to an embodiment of the present invention is a cylinder block 3 in which a plurality of (only one is shown in the figure) cylinders 2 are formed. A cylinder head 4 attached to the upper part of the cylinder block 3, an intake passage 5 for guiding intake air to each of the cylinders 2, and an exhaust passage 6 for guiding exhaust from the cylinder 2. A piston 7 is slidably fitted into the cylinder 2, and a combustion chamber 8 is formed between the top surface 7 a of the piston 7 and the lower surface of the cylinder head 4. The intake passage 5 is provided with a throttle valve 9 for adjusting the intake air amount. An intake manifold 10 is provided downstream of the throttle valve 9, and two branches 11 </ b> A and 11 </ b> B are extended from the intake manifold 10 toward each cylinder 2. The cylinder head 4 is formed with two intake ports 12A and 12B corresponding to each cylinder 2, and the branches 11A and 11B are connected to the intake ports 12A and 12B on a one-to-one basis. At the end of the intake ports 12A and 12B, intake valves 13A and 13B that open and close between the intake ports 12A and 12B and the combustion chamber 8 are provided. Similarly, exhaust valves 14A and 14B for opening and closing between the exhaust passage 6 and the combustion chamber 8 are provided. A spark plug 15 is provided at the center on the upper surface side of the combustion chamber 8. The intake valves 13A and 13B can be opened and closed independently from each other by a valve mechanism (not shown).

  A fuel injection valve 16 is provided in each of the intake ports 12A and 12B. One intake port 12A is connected to an EGR pipe 17 as an EGR passage. The EGR pipe 17 is connected to the intake port 12A so that EGR gas flows into the end portion of the intake port 12A along the longitudinal direction of the intake port 12A. The EGR pipe 17 is provided with an EGR valve 18 for opening and closing the EGR pipe 17. The other intake port 12B is provided with a swirl control valve 19 for opening and closing it.

  As shown in FIG. 1, the engine 1 is provided with an engine control unit (hereinafter referred to as ECU) 20. The ECU 20 is configured as a computer unit including a microprocessor and peripheral devices such as a RAM and a ROM necessary for the operation thereof, and a throttle valve 9, a fuel injection valve 16, an EGR valve 18, and a swirl control valve 19 according to a predetermined engine control program. Etc., the engine 1 is controlled to the target operating state. The ECU 20 has a water temperature sensor 21 that outputs a signal corresponding to the cooling water temperature of the engine 1 as input means for information necessary for operation control of the engine 1, and the number of rotations (rotational speed) per unit time of the engine 1. A crank angle sensor 22 that outputs a signal, an air flow meter 23 that outputs a signal corresponding to the amount of air taken into the intake passage 5, and the like are connected.

  The ECU 20 repeatedly executes each of the operation determination routine shown in FIG. 5 and the combustion control routine shown in FIG. 6 at a predetermined cycle as part of a series of processes to be executed for operation control of the engine 1. Hereinafter, these processes will be described.

  When the operation determination routine of FIG. 5 is started, the ECU 20 first determines whether or not the elapsed time after the start of the engine 1 is longer than 30 seconds in step S1. The elapsed time after engine startup may be determined using a timer of ECU 20 after successful startup, for example. When 30 seconds or more have elapsed, the ECU 20 proceeds to step S2 and determines whether or not the cooling water temperature detected by the water temperature sensor 21 is higher than 40 ° C. When the temperature is higher than 40 ° C, the ECU 20 proceeds to step S3 and turns on the stratified EGR flag for determining whether or not the stratified EGR operation is possible, that is, the value of the stratified EGR flag is set to a value indicating a state in which the stratified EGR operation is possible. Set. On the other hand, if the condition of step S1 or S2 is negative, the ECU 20 proceeds to step S4, and turns off the stratified EGR flag, that is, sets the value of the stratified EGR flag to a value indicating a state in which the stratified EGR operation is impossible. After the process of step S3 or S4, the ECU 20 ends the current driving determination routine.

  On the other hand, when the combustion control routine of FIG. 6 is started, the ECU 20 first determines in step S11 whether or not the stratified EGR flag is on. If the flag is on, the ECU 20 proceeds to step S12 and closes the swirl control valve 19. Subsequently, the ECU 20 proceeds to step S13, and acquires the stratified EGR rate from the map shown in FIG. The map in FIG. 7 defines the EGR rate in association with the rotational speed and torque of the engine 1. In the process of step S13, the ECU 20 obtains the rotational speed of the engine 1 from the output of the crank angle sensor 22, calculates the target torque of the engine 1 from the depression amount of an accelerator pedal (not shown), etc., and the obtained rotational speed. And the EGR rate corresponding to the torque are acquired from the map of FIG.

  After acquiring the EGR rate, the ECU 20 proceeds to step S14, and acquires the valve opening time of the EGR valve 18 from the map shown in FIG. The map of FIG. 8 shows the relationship between the value obtained by dividing the intake air amount of the engine 1 by the rotational speed (air amount / rotational speed) and the opening time of the EGR valve 18 according to the EGR rate. The ECU 20 acquires the valve opening time of the EGR valve 18 from the map of FIG. 8 using the EGR rate acquired in step S13, the intake air amount acquired from the air flow meter 23, and the rotation speed acquired from the crank angle sensor 22. To do.

  After acquiring the valve opening time of the EGR valve 18, the ECU 20 proceeds to step S15 and starts operation control of the EGR valve 18 so as to open the EGR valve 18 only for the valve opening time acquired in step S14. At this time, the operation of the EGR valve 18 is controlled so that the EGR valve 18 is opened prior to the opening operation of the intake valve 13A, and the EGR valve 18 is closed when the intake valve 13A is opened. As an example, as shown in FIG. 9, when the intake valve 13A starts to open at a crank angle of 360 ° in the latter half of the intake stroke, the crank angle is traced back by the valve opening time from the crank angle of 360 ° as an end point. Thus, the opening of the EGR valve 18 is started.

  Returning to FIG. 6, in the subsequent step S <b> 16, the ECU 20 obtains the air layer ratio (air ratio) to be provided in the combustion chamber 8 from the map shown in FIG. 10. The map in FIG. 10 is determined by associating the air rate with the rotational speed and torque of the engine 1. In the illustrated example, it is uniformly set to 10%, but the air ratio may be changed in a plurality of stages within the stratified EGR region (the operation region where the stratified EGR flag is turned on). In the next step S17, the ECU 20 calculates the E fuel injection timing. For example, as shown in FIG. 11, the EGR gas introduced into the intake port 12A prior to the opening of the intake valve 13A enters the combustion chamber 8 with the start of intake (start of opening of the intake valve 13A). The intake time t1 and the time t2 when the amount of air corresponding to the air rate acquired in step S16 is sucked into the combustion chamber 8 are calculated, and the time corresponding to the sum (t1 + t2) is calculated from the start of intake. The elapsed time is determined as the fuel injection start timing, and the time t3 from the fuel injection start timing to the time when the intake valve 13A is closed is determined as the fuel injection end timing. In the intake stroke (period in which the intake valve is opened), the flow rate of the intake air passing through the crank angle and the intake port 12A to the combustion chamber 8 is determined according to the timing when each of the EGR gas, air, and air-fuel mixture is introduced into the combustion chamber 8. FIG. 12 shows the relationship with (valve passing flow rate). That is, if the intake valve 13A opens at the top dead center (TDC) and closes at the bottom dead center (BDC), EGR gas is introduced immediately after the start of intake, air is introduced, and then fuel injection is performed. Then, the air-fuel mixture is introduced.

  Subsequently, the ECU 20 proceeds to step S18 in FIG. 6 and controls the operation of the fuel injection valve 16 so that fuel is injected from the fuel injection valve 16 from the fuel injection start timing to the fuel injection end timing. In this case, only the fuel injection valve 16 corresponding to the intake port 12A on the side to which the EGR pipe 17 is connected is the target of fuel injection control, and the fuel from the fuel injection valve 16 corresponding to the opposite intake port 12B is fuel. Injection is prohibited.

  On the other hand, if a negative determination is made in step S11, the ECU 20 proceeds to step S21 and opens the swirl control valve 19. Subsequently, the ECU 20 sets the stratified EGR rate to 0% in step S22. Thereafter, the ECU 20 proceeds to step S23, calculates the fuel injection timing, and controls the operation of the fuel injection valve 16 so that fuel is injected from the fuel injection valves 16 of both intake ports 12A, 12B in the subsequent step S24. When fuel injection is executed in step S18 or step S24, the ECU 20 ends the current routine. In addition, the control procedures such as the valve opening timing of the fuel injection valve 16 and the fuel injection amount when steps S21 to S24 are executed may be the same as those of a known internal combustion engine when performing homogeneous combustion.

  The stratification process formed in the combustion chamber 8 as a result of controlling the operations of the EGR valve 18 and the fuel injection valve 16 during the stratified EGR as described above is shown in FIGS. First, as shown in FIG. 2, the EGR valve 18 is opened prior to the opening of the intake valve 13A, and the EGR gas 30 is introduced into the intake port 12A. As indicated by an arrow A in the drawing, the EGR gas 30 stays while swirling at the end portion of the intake port 12A. The swirl direction is a swirl formed when the EGR gas 30 is introduced into the combustion chamber 8 because the connection position of the EGR pipe 17 with respect to the intake port 12A is set to the outside of the direction in which the intake ports 12A and 12B are arranged. It coincides with the swirling direction of the flow.

  Subsequently, as shown in FIG. 3, when the intake valve 13 </ b> A is opened, the EGR gas 30 in the intake port 12 </ b> A is introduced into the combustion chamber 8. As a result, an EGR layer L1 with a swirl flow as shown by an arrow B is formed in the lower part of the combustion chamber 8. Subsequently, since the fuel injection is not started after the introduction of the EGR gas 30 until the amount of air corresponding to the air rate is introduced, an air layer L2 is formed above the EGR layer L1 in the combustion chamber 8. The air layer L2 has a swirl flow similar to that of the EGR layer L1. Then, after the formation of the air layer L2, the injection of the fuel 31 from the fuel injection valve 16 is started. As shown in FIG. 4, when the intake valve 13A is closed, an EGR layer L1, an air layer L2, and an air-fuel mixture layer L3 are formed in the combustion chamber 8 from the piston 7 upward. Since the air layer L2 remains between the EGR layer L1 and the air-fuel mixture layer L3, the fuel component of the air-fuel mixture layer L3 is prevented from being mixed into the EGR layer L1. Accordingly, it is possible to prevent the discharge of unburned components, and to obtain operational effects such as stabilization of combustion, improvement of emission, and improvement of fuel consumption rate.

  In the above embodiment, the ECU 20 functions as an EGR valve control means by executing step S15 of FIG. 6 and functions as a fuel injection control means by executing step S18.

  Next, a modified example regarding control of the fuel injection timing will be described. FIG. 13 shows an example in which the fuel injection timing t4 is limited to a part of time t3 from the completion of air introduction to the end of the intake stroke. As an implementation procedure, the ECU 20 may perform the following processing as an example. That is, as shown in FIG. 14, a map in which the relationship between the crank angle and the valve passage flow rate is described in advance for each engine speed is prepared in advance, and the crank angle and valve passage corresponding to the engine speed acquired from the crank angle sensor 22 are prepared. A diagram showing the correspondence with the flow rate is specified. Subsequently, as shown in FIG. 15, an EGR amount and an air amount (an amount corresponding to the air ratio) are respectively assigned from the intake start position (TDC) to the obtained valve passage flow rate curve, and the air-fuel mixture is introduced. The period X being used is specified. Subsequently, the crank angle at which the valve passage flow rate is halved within the period X, that is, the crank angle CAx at which half the mixture is introduced with respect to the total amount of the mixture to be introduced into the combustion chamber 8 is set. Identify. The fuel injection timing is set as shown in FIG. 13 by calculating the fuel injection timing and specifying the fuel injection start time and end time with the crank angle CAx as the center so as to ensure the required fuel amount. Can do.

  FIG. 16 shows an example in which the fuel injection timing (t5 to t7) is divided into a plurality of times within the time t3 from the completion of air introduction to the end of the intake stroke. As an implementation procedure, the ECU 20 may perform the following processing as an example. First, as shown in FIG. 14, a map in which the relationship between the crank angle and the valve passage flow rate is described in advance for each engine speed is prepared in advance, and the crank angle and valve passage corresponding to the engine speed acquired from the crank angle sensor 22 are prepared. A diagram showing the correspondence with the flow rate is specified. Subsequently, as shown in FIG. 17, an EGR amount and an air amount (an amount corresponding to the air rate) are respectively assigned from the intake start position (TDC) to the obtained valve passage flow rate curve, and the air-fuel mixture is introduced. The period X being used is specified. Further, the crank angles CAx, CAy, and CAz that equally divide the valve passage flow rate by the number corresponding to the value obtained by adding 1 to the number of injections (number of injections + 1) within the period X are specified. Further, the required fuel injection amount is divided by the number of injections to calculate the injection amount per one time. Then, the fuel injection timing is calculated so that the injection amount per injection is injected around the crank angles CAx, CAy, CAz, respectively, and the fuel injection start time and end time of each time are specified. The fuel injection timing can be set as shown in FIG.

  The present invention is not limited to the form described above, and can be implemented in an appropriate form. For example, in the above embodiment, the swirl flow in the same direction is given to each of the layers L1 to L3 using the swirl control valve 19, but the airflow in each layer is controlled using other swirl forming means such as a swirl port. Also good. Further, the present invention is not limited to an example in which a swirl flow is formed, but can also be applied to an internal combustion engine that forms a stratified state using another air flow such as a tumble flow. The fuel injection valve is not limited to the port injection type, and may be a cylinder injection type.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Intake passage 6 Exhaust passage 8 Combustion chamber 13A, 13B Intake valve 16 Fuel injection valve 17 EGR piping (EGR passage)
18 EGR valve 19 Swirl control valve 20 Engine control unit (EGR control means, fuel injection control means)
30 EGR gas 31 Fuel L1 EGR layer L2 Air layer L3 Mixture layer

Claims (1)

An intake valve that opens and closes an intake port for the combustion chamber, a fuel injection valve that can inject fuel to intake air, an EGR passage that connects the exhaust passage and the intake port, and an EGR valve that opens and closes the EGR passage An internal combustion engine capable of stratified combustion with
EGR valve control means for controlling the opening operation of the EGR valve so that EGR gas is introduced into the intake port prior to the opening of the intake valve;
As the intake valve is opened, air is introduced after EGR gas is introduced from the intake port into the combustion chamber, and an air layer remains between the EGR layer and the air-fuel mixture layer in the combustion chamber. An internal combustion engine capable of stratified combustion, comprising: fuel injection control means for controlling the operation of the fuel injection valve with respect to intake air.

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