JP2013092159A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device that can suppress a torque step upon switching an injection mode.SOLUTION: In a fuel injection control device 11 for a spark ignition type internal combustion engine EG including a fuel injection valve 118 which directly injects fuel to a combustion chamber, a control signal for switching between a first injection mode where a first fuel injection is performed from a middle period to a latter period of an intake stroke, and a second injection mode where a fuel injection is performed only from an anterior period to a middle period of the intake stroke is outputted. The control signal for performing the fuel injection only from the middle period to the latter period of the intake stroke is outputted upon switching from the second injection mode to the first injection mode.

Description

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

  In order to improve the homogeneity of the air-fuel mixture in the high load or high rotation region, a spark ignition direct injection engine that performs fuel injection at the middle of the intake stroke and then performs at least two fuel injections after the middle of the compression stroke. Known (Patent Document 1).

JP 2005-256630 A

  However, the conventional technique has a problem that a torque step is generated when the injection mode is switched.

The problem to be solved by the present invention is to provide a fuel injection control device capable of suppressing a torque step at the time of switching the injection mode.

In the present invention, the second injection mode in which fuel is injected only during the period from the first period to the middle period of the intake stroke, the second fuel injection is performed from the first period to the middle of the compression stroke after the first fuel injection is performed from the middle period to the second period of the intake stroke At the time of switching to the first injection mode in which the second fuel injection is performed, the above problem is solved by performing the fuel injection only during the middle period to the latter period of the intake stroke.

  According to the present invention, since the fuel injection timing and the division ratio are gradually switched when switching from the second injection mode to the first injection mode, it is possible to suppress a torque step during switching of the injection mode.

1 is a block diagram showing an internal combustion engine to which an embodiment of the present invention is applied. It is a time chart which shows the fuel-injection timing of the internal combustion engine shown in FIG. 3 is a control map showing a relationship between a first injection amount and a second injection timing of the internal combustion engine shown in FIG. 1. FIG. 3 is a time chart showing fuel injection timing when switching between a first injection mode and a second injection mode of the internal combustion engine shown in FIG. 1. FIG. 2 is a graph showing a relationship between fuel injection timing and surge torque of the internal combustion engine shown in FIG. 1. 2 is a graph showing the relationship between fuel injection timing and output torque of the internal combustion engine shown in FIG. 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a spark ignition direct injection engine EG to which an embodiment of the present invention is applied. An air filter 112 and an air flow meter 113 for detecting an intake air flow rate are provided in an intake passage 111 of the engine EG. A throttle valve 114 and a collector 115 for controlling the intake air flow rate are provided.

  The throttle valve 114 is provided with an actuator 116 such as a DC motor that adjusts the opening of the throttle valve 114. The throttle valve actuator 116 electronically controls the opening of the throttle valve 114 based on the drive signal from the engine control unit 11 so as to achieve the required torque calculated based on the driver's accelerator pedal operation amount and the like. Further, a throttle sensor 117 for detecting the opening degree of the throttle valve 114 is provided, and the detection signal is output to the engine control unit 1. The throttle sensor 117 can also function as an idle switch.

  The fuel injection valve 118 is provided facing the combustion chamber 123. The fuel injection valve 118 is driven to open by a drive pulse signal set in the engine control unit 11 and injects fuel that is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator in accordance with an operation request. The fuel is directly injected into the cylinder at a predetermined timing so as to reach a quantity. Details of the fuel injection timing in this example will be described later.

  A space surrounded by the cylinder 119, the crown surface of the piston 120 that reciprocates within the cylinder, and the cylinder head provided with the intake valve 121 and the exhaust valve 122 constitutes a combustion chamber 123. The spark plug 124 is mounted facing the combustion chamber 123 of each cylinder, and ignites the intake air-fuel mixture based on an ignition signal from the engine control unit 11.

  On the other hand, the exhaust passage 125 is provided with an air-fuel ratio sensor 126 for detecting an exhaust gas by detecting a specific component in the exhaust gas, for example, oxygen concentration, and thus an air-fuel ratio of the intake air-fuel mixture. Is output. The air-fuel ratio sensor 126 may be an oxygen sensor that performs rich / lean output, or a wide-area air-fuel ratio sensor that linearly detects the air-fuel ratio over a wide area.

  The exhaust passage 125 is provided with an exhaust purification catalyst 127 for purifying the exhaust. The exhaust purification catalyst 127 oxidizes carbon monoxide CO and hydrocarbon HC in the exhaust in the vicinity of stoichiometric (theoretical air-fuel ratio, λ = 1, air weight / fuel weight = 14.7), and nitrogen oxide NOx. It is possible to use a three-way catalyst that can purify the exhaust gas by reducing the above, or an oxidation catalyst that oxidizes carbon monoxide CO and hydrocarbon HC in the exhaust gas.

  On the downstream side of the exhaust purification catalyst 127 in the exhaust passage 125, there is provided an oxygen sensor 128 that detects a specific component in the exhaust, for example, oxygen concentration, and outputs a rich / lean output, and the detection signal is output to the engine control unit 11. The Here, by correcting the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 126 based on the detection value of the oxygen sensor 128, so as to suppress a control error associated with the deterioration of the air-fuel ratio sensor 126 (so-called) Although the downstream oxygen sensor 128 is provided (for the adoption of a double air-fuel ratio sensor system), if it is only necessary to perform air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 126, the oxygen sensor 128 is Can be omitted.

  In FIG. 1, reference numeral 129 denotes a muffler.

  The crankshaft 130 of the engine EG is provided with a crank angle sensor 131, and the engine control unit 11 counts a crank unit angle signal output from the crank angle sensor 131 in synchronization with the engine rotation for a predetermined time, or By measuring the cycle of the crank reference angle signal, the engine speed Ne can be detected.

  The cooling jacket 132 of the engine EG is provided with a water temperature sensor 133 facing the cooling jacket, detects the cooling water temperature Tw in the cooling jacket 131, and outputs this to the engine control unit 11.

  Now, as mentioned in the background section, the homogeneity of the air-fuel mixture is poor and the combustion fluctuation is large in the low-rotation and high-load region of the direct injection engine.

  In the plot of “Δ” shown in FIG. 5, the throttle valve 114 is fully opened, and the stoichiometric (excess air ratio λ = 1) at intervals of 10 ° in the range of the crank angle CA of 0 to 230 ° ATDC in the intake stroke and the compression stroke. It is a graph which shows the result of having measured the surge torque when the fuel of 1) is injected once.

  According to this, in the low rotation and high load region, it is understood that the fuel injection is the smallest in the period of CA = 40 to 50 ° ATDC indicated by P1, and the operability is good, but indicated by P2. It was confirmed that even if fuel was injected during the period of CA = 90 to 130 ° ATDC, the same surge torque was obtained. This is because the period from the middle stage to the latter stage of the intake stroke such as CA = 90 to 130 ° ATDC is considered to be a sufficiently high region that does not break the tumble flow in the cylinder.

  It was also confirmed that the surge torque was reduced even when fuel was injected during the CA = 190-220 ° ATDC period indicated by P3. This is because the period from the first to the middle of the compression stroke of CA = 190 to 220 ° ATDC is considered to be a region where the mixing volume of air and fuel is large and the homogeneity is high because the cylinder volume is large.

  Therefore, the present inventor performs the first fuel injection (stoichiometric) at the time of CA = 90 ° ATDC (fixed), and then the second time at intervals of 10 ° in the range of CA = 160 to 260 ° ATDC. The surge torque when fuel injection was performed was measured. The division ratio between the first fuel injection amount and the second fuel injection amount was 7: 3. The plot of “◯” shown in FIG. 5 is a graph showing this result.

  According to this, for the first fuel injection performed at CA = 90 ° ATDC, CA = 180 to 240 ° ATDC, more preferably CA = 200 to 230 ° ATDC, and even more preferably CA = 210 to P4. It was confirmed that the surge torque is reduced by about 25% when the second fuel injection is performed during the period of 220 ° ATDC. This is because, as described above, the period from the first half to the middle of the compression stroke of CA = 180 to 240 ° ATDC is considered to be a region where the mixing volume of air and fuel is large and the homogeneity is high because the cylinder volume is large. .

  Therefore, after the first fuel injection is performed in the middle to late period of the intake stroke of CA = 90 to 130 ° ATDC in the low rotation and high load region, from the first half of the compression stroke of CA = 180 to 240 ° ATDC. When the second fuel injection is performed in the middle period, that is, by performing the fuel injection twice at a timing at which homogeneous combustion is performed, the surge torque is reduced and the drivability is improved.

  Further, such control of the fuel injection timing contributes not only to improvement of surge torque, that is, combustion fluctuation, but also to improvement of output. That is, in the low rotation high load region, since the knock margin is smaller than that in the high rotation region, the ignition timing is set at a time away from the minimum ignition advance value MBT. For this reason, there is a problem that not only the combustion fluctuation increases but also the output decreases, but by performing the first and second fuel injections at the above timing, not only the combustion fluctuation but also the output is improved.

  The plot of “Δ” shown in FIG. 6 indicates that the throttle valve 114 is fully opened and the stoichiometric air excess ratio λ = 1 at intervals of 10 ° in the range of the crank angle CA of 50 to 250 ° ATDC in the intake stroke and the compression stroke. It is a graph which shows the result of having measured the output torque when richer fuel is injected once.

  According to this, it has been confirmed that when the fuel injection is performed at the time of CA = 100 ° ATDC, the output torque is maximized. Therefore, after the first fuel injection timing is performed at CA = 100 ° ATDC (fixed) In the range of CA = 150 to 260 ° ATDC, the output torque when the second fuel injection was performed at 10 ° intervals was measured. The division ratio between the first fuel injection amount and the second fuel injection amount was 7: 3. The plot of “◯” shown in FIG. 6 is a graph showing this result.

  According to this, it was confirmed that when the second fuel injection is performed at CA = 180 to 240 ° ATDC indicated by P5, the output torque is improved by about 5%.

  Based on the above knowledge, the following control is executed in this example.

  FIG. 2 is a time chart showing the fuel injection timing of the direct injection engine EG of this example, and the first injection mode and the second injection mode are selected and switched according to the operating state. As described with reference to FIGS. 5 and 6, the first injection mode shown in the upper part of the figure performs the first fuel injection in the middle period to the latter period of the intake stroke, and starts from the first half of the subsequent compression stroke. This is a mode in which the second fuel injection is performed in the middle period, whereby homogeneous combustion is performed.

  This first injection mode is executed, for example, under the operating condition of low rotation and high load. In other words, the execution of the first injection mode is prohibited under operating conditions other than low rotation and high load. As a result, the first injection mode is prohibited under the operating conditions in which the first injection mode cannot necessarily suppress the combustion fluctuation or the output torque is improved, and the combustion fluctuation or the output torque is improved. For example, the second injection mode is executed under operating conditions other than the low rotation and high load that prohibit the first injection mode.

  The division ratio between the first fuel injection amount and the second fuel injection amount in the first injection mode can be appropriately set according to the operating conditions. In this example, as shown in FIG. The second fuel injection timing is retarded as the division ratio of the fuel injection amount is increased. FIG. 3 is a control map showing the relationship between the first injection amount and the second injection timing of the direct injection engine EG.

  This may reduce the homogeneity due to the increased amount of the first fuel, but retarding the second injection suppresses the deterioration of the homogeneity of the fuel because both injection intervals are increased. be able to.

  On the other hand, for example, the second injection mode shown in the lower part of FIG. The second injection mode is a mode in which fuel injection is performed only once during the period from the previous period to the middle period of the intake stroke, whereby homogeneous combustion is performed.

  When switching from the first injection mode to the second injection mode, or when switching from the second injection mode to the first injection mode, the fuel injection timing can be switched directly as shown in FIG. In order to suppress the torque step at the time of switching, control is performed as shown in FIG.

  FIG. 4 is a time chart showing the fuel injection timing at the time of switching between the first injection mode and the second injection mode of the direct injection engine EG, and the top shows the fuel injection timing in the second injection mode. The bottom shows the fuel injection timing in the first injection mode.

  And, for example, when switching from the second injection mode to the first injection mode, as shown in the second and third from the top, the timing of the one-time fuel injection that is performed from the first period to the middle period of the intake stroke Is retarded until the first injection timing in the first injection mode, and then, as shown in the fourth from the top, after the first fuel injection is performed in the intake stroke as in the first injection mode, in the compression stroke A second fuel injection is performed. At this time, if there is no change in the fuel injection amount, the division ratio of the second fuel injection amount is gradually increased.

  Conversely, when switching from the first injection mode to the second injection mode, the division ratio of the second fuel injection amount is gradually decreased as shown in the second from the bottom and the bottom, and the third from the bottom. Thus, after shifting to the same one-time fuel injection as in the second injection mode, the one-time fuel injection timing in the intake stroke is advanced as shown in the fourth and top from the bottom.

  In this way, by gradually switching the first injection mode and the second injection mode with respect to the fuel injection timing and the division ratio, it is possible to suppress the occurrence of a torque step at the time of switching.

  As described above, according to the direct injection engine EG of this example, the homogeneity of the air-fuel mixture particularly at a low rotation and high load is increased, the surge torque is reduced, and the drivability is improved. Further, knocking is improved and output torque is also improved.

  The engine control unit 11 corresponds to control means according to the present invention.

EG ... Engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 11 ... Engine controller 111 ... Intake passage 112 ... Air filter 113 ... Air flow meter 114 ... Throttle valve 115 ... Collector 116 ... Throttle valve actuator 117 ... Throttle sensor 118 ... Fuel injection valve 119 ... Cylinder 120 ... Piston 121 ... Intake valve 122 ... Exhaust Valve 123 ... Combustion chamber 124 ... Spark plug 125 ... Exhaust passage 126 ... Air-fuel ratio sensor 127 ... Exhaust purification catalyst 128 ... Oxygen sensor 129 ... Muffler 130 ... Crankshaft 131 ... Crank angle sensor 132 ... Cooling jacket 133 ... Water temperature sensor 134 ... Temperature Sensor

Claims (3)

In a fuel injection control device for a spark ignition internal combustion engine having a fuel injection valve for directly injecting fuel into a combustion chamber,
The first injection mode in which the first fuel injection is performed during the middle to late period of the intake stroke and the second fuel injection is performed during the first to middle period of the compression stroke, and the first to middle period of the intake stroke Control means for outputting a control signal for switching between the second injection mode for performing fuel injection only at
The control means is a fuel injection control device that outputs a control signal for injecting fuel only during a middle period to a late period of the intake stroke when switching from the second injection mode to the first injection mode. The fuel injection control device according to claim 1,
In the first injection mode, the control means performs the first fuel injection during a crank angle of 90 to 130 ° ATDC and the second fuel during a crank angle of 180 to 240 ° ATDC. A fuel injection control device that outputs a control signal for performing injection. The fuel injection control device according to claim 1 or 2,
The control means retards the second fuel injection timing as the division ratio of the first fuel injection amount to the second fuel injection amount is increased in the first injection mode. A fuel injection control device that outputs a control signal.

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