JP2011058436A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device for an internal combustion engine that can reduce an exhaust amount of hydrocarbon (HC). <P>SOLUTION: The fuel injection control device is applied to an internal combustion engine 1 including a variable valve operating mechanism 6 that can change valve operating characteristics including a phase angle and a lift amount of an intake valve 5. The device includes a valve operating characteristic determining means for determining whether the valve operating characteristics of the intake valve 5 are set in a range α where a flow velocity of intake air flowing into a cylinder exceeds a predetermined threshold when the intake valve 5 is opened. The device further includes a fuel injection timing controlling means for retarding timing of starting fuel injection later than timing of opening the intake valve 5 according to a setting of the valve operating characteristics when the valve operating characteristics are determined to be set within the range α. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel injection control device for an internal combustion engine capable of controlling the start timing of fuel injection.

  An intake passage fuel injection valve for injecting fuel into the intake passage, the lift amount of the intake valve is smaller than a predetermined set amount, and the valve opening timing of the intake valve is set after the intake top dead center Of the internal combustion engine that suppresses the malfunction of the ignition plug due to a large amount of fuel adhering to the ignition plug by switching between the intake asynchronous injection and the intake synchronous injection according to the fuel property. A fuel injection control device is known (see Patent Document 1). In addition, Patent Documents 2 to 5 exist as prior art documents related to the present invention.

JP 2007-332936 A JP 2002-235580 A JP 2006-63946 A JP 2006-307784 A JP-A-5-171990

  In the fuel injection control device of Patent Document 1, when intake synchronous injection is performed, the flow rate of intake air rapidly increases due to the negative pressure in the cylinder, so that fuel adheres to the inner wall surface of the cylinder, and hydrocarbon (HC) There is a problem that the amount of emissions increases.

  Accordingly, an object of the present invention is to provide a fuel injection control device for an internal combustion engine that can reduce the amount of HC emission.

  A fuel injection control device for an internal combustion engine of the present invention is a fuel injection control device applied to an internal combustion engine provided with a variable valve mechanism that can change valve characteristics including the phase angle and lift amount of an intake valve, A valve characteristic discriminating means for discriminating whether or not the valve valve characteristic of the intake valve is set in a region where the flow velocity of the intake air flowing into the cylinder increases when exceeding the predetermined threshold when the intake valve is opened; When it is determined that the valve operating characteristic is set in the region, fuel injection timing control means for retarding the start timing of fuel injection from the valve opening timing of the intake valve according to the setting state of the valve operating characteristic; (Claim 1).

  In the fuel injection control device of the present invention, when it is determined that the valve operating characteristics of the intake valve are set in a region where the flow velocity of the intake air flowing into the cylinder when the intake valve is opened exceeds a predetermined threshold value, By delaying the start timing of fuel injection from the opening timing of the intake valve in accordance with the set state of the valve operating characteristics, it is possible to reduce the scattering of fuel to the inner wall surface of the cylinder. Thereby, the discharge amount of HC can be reduced.

  In one aspect of the control device of the present invention, the fuel injection timing control means sets the fuel injection end timing so that the fuel injection end timing does not enter the fuel injection prohibition period set at the end of the intake stroke. You may restrict | limit (Claim 2). According to this aspect, since the fuel is injected so that the end time of the fuel injection does not enter during the fuel injection prohibition period, an air-fuel mixture can be formed. Thereby, the discharge amount of HC can be reduced.

  As described above, in the fuel injection control device for an internal combustion engine according to the present invention, the valve operating characteristics of the intake valve in a region where the flow velocity of the intake air flowing into the cylinder increases beyond a predetermined threshold when the intake valve is opened. Is determined, the fuel injection start timing is retarded from the intake valve opening timing in accordance with the setting state of the valve operating characteristics, thereby reducing fuel scattering on the inner wall surface of the cylinder. be able to. Thereby, the discharge amount of HC can be reduced.

The figure which shows the outline of the principal part of the intake system of the internal combustion engine to which the fuel-injection control apparatus which concerns on one form of this invention was applied. The figure which shows the case where the lift amount of an intake valve is larger than the lift amount of FIG. The figure which shows the relationship between a crank angle, the lift amount of an intake valve, and the flow velocity of intake air. The flowchart of the fuel injection timing control which concerns on a 1st form. The flowchart of the fuel injection timing control which concerns on a 2nd form. The figure which shows the relationship between a crank angle, the lift amount of an intake valve, and the flow velocity of intake air, and the relationship between a crank angle and the discharge amount of HC. The figure which shows the relationship between the valve opening time of an intake valve, and fuel injection start time. The figure which shows the relationship of the change time of the lift amount of an intake valve, and fuel injection start time according to a driving | running state.

(First form)
FIG. 1 shows an outline of a main part of an intake system of an internal combustion engine to which a fuel injection control device according to one embodiment of the present invention is applied. An internal combustion engine (hereinafter may be referred to as an engine) 1 is mounted as a driving power source for a vehicle and includes a plurality of cylinders 2 (only one cylinder 2 is shown in FIG. 1). An intake passage 3 for taking intake air into the cylinder 2 is connected to the plurality of cylinders 2. The intake passage 3 includes an intake port 4 provided for each cylinder 2. The intake port 4 is provided with an intake valve 5 that opens and closes a connection portion between the cylinder 2 and the intake passage 3. The intake valve 5 is driven to open and close by a variable valve mechanism 6 that can change the valve characteristics including the phase angle and lift amount of the intake valve 5. The lift amount A1 of the intake valve 5 in FIG. 1 shows an example when the lift amount is small, and the lift amount A1 of the intake valve 5 in FIG. 2 shows an example when the lift amount in FIG. 1 is large. . The intake port 4 is provided with a fuel injection valve 7 for port injection. The fuel injection valve 7 injects fuel into the cylinder 2.

  Each of the variable valve mechanism 6 and the fuel injection valve 7 is controlled by an engine control unit (ECU) 10. The ECU 10 is configured as a computer including a microprocessor and peripheral devices such as RAM and ROM necessary for the operation of the microprocessor, and the operation state of the engine 1 based on output signals from various sensors provided in the engine 1. To control. The ECU 10 includes an air flow meter 20 that outputs a signal corresponding to the intake air amount of the engine 1, a water temperature sensor 21 that outputs a signal corresponding to the temperature of the cooling water of the engine 1, and an engine rotational speed (the number of revolutions) of the engine 1. ) Is connected to a crank angle sensor 22 or the like that outputs a signal corresponding to. In addition to this, various sensors are connected to the ECU 10, but they are not shown. ECU10 grasps | ascertains the driving | running state of the engine 1 from the numerical value acquired from various sensors, such as the airflow meter 20, the water temperature sensor 21, and the crank angle sensor 22. FIG. Thereafter, the ECU 10 determines the fuel injection amount to be injected from the fuel injection valve 7 in accordance with the operation state and the like.

  The ECU 10 determines valve operating characteristics including the lift amount of the intake valve 5 and the valve opening timing (IVO) according to the operating state. In response to this determination, the variable valve mechanism 6 drives the intake valve 5 to a predetermined lift amount and a predetermined IVO.

  FIG. 3 shows the relationship between the crank angle, the lift amount (L1 to L3) of the intake valve 5, and the flow velocity (L4 to L6) of the intake air. As a crank angle, an intake top dead center (TDC) and an intake bottom dead center (BDC) are shown. A solid line L1 in FIG. 3 indicates that the lift amount of the intake valve 5 is as small as the lift amount in FIG. 1 (hereinafter sometimes referred to as a small lift), and IVO is after the intake top dead center. That is, the intake valve 5 opens late. A solid line L4 is the flow velocity of the intake air in the case of the solid line L1. 3 is a small lift in which the lift amount of the intake valve 5 is the same as that of the solid line L1, but the IVO is further after the solid line L1. A one-dot chain line L5 is a flow velocity of the intake air in the case of the one-dot chain line L2. 3, the lift amount of the intake valve 5 is as large as the lift amount of FIG. 2 (hereinafter sometimes referred to as a large lift), and IVO is the same as the intake top dead center. A chain line L6 is the flow velocity of the intake air in the case of the chain line L3. Α indicates a region where the flow velocity of the intake air flowing into the cylinder when the intake valve 5 is opened exceeds a predetermined threshold. Furthermore, β represents a period during which fuel is injected (fuel injection period).

  When the lift amount of the intake valve 5 is a small lift and the IVO is after intake top dead center, for example, during a cold start when the engine 1 is started when the temperature of the engine 1 is equal to or lower than the outside air temperature. It hits. Further, when the lift amount of the intake valve 5 is a large lift and IVO is the same as the intake top dead center, for example, the operating state corresponds to a high load.

  Next, the ECU 10 determines the start timing (fuel injection start timing) for injecting fuel from the fuel injection valve 7 according to the lift amount of the intake valve 5 and the valve operating characteristics of the IVO. The ECU 10 controls fuel injection by switching between intake synchronous injection in which fuel is injected while the intake valve 5 is open and intake asynchronous injection in which fuel is injected before the intake valve 5 is opened. . The ECU 10 controls whether or not the intake synchronous injection is executed and the fuel injection start timing when the intake synchronous injection is executed according to the flowchart shown in FIG.

  In FIG. 4, the ECU 10 acquires the operating state of the engine 1, the lift amount of the intake valve 5, and IVO at the “start” of step S <b> 1. As the operating state of the engine 1, the temperature of the cooling water of the engine 1 is acquired. In the next step S2, the ECU 10 determines whether or not it is during cold start from the operating state acquired in step S1. If not, the control of this flowchart is not executed.

  On the other hand, in the case of the cold start, the process proceeds to step S3, and the ECU 10 determines whether or not the lift amount is a small lift from the lift amount of the intake valve 5 acquired in step S1. When the lift amount is a large lift, the control of this flowchart is not executed.

  On the other hand, if the lift amount is a small lift, the process proceeds to step S4, and the ECU 10 determines whether or not the IVO acquired in step S1 is after TDC. When IVO is before TDC, the control of this flowchart is not executed.

  On the other hand, if the IVO is after TDC, the process proceeds to step S5, where the ECU 10 calculates the fuel injection start timing X1, and sets the fuel injection start timing X1 obtained by the calculation. The fuel injection start timing X1 is calculated by the following equation (1), where α is a region in which the flow velocity of the intake air flowing into the cylinder when the IVO and the intake valve 5 are opened exceeds a predetermined threshold. .

  X1 = IVO + α (1)

  Next, in step S5, the ECU 10 sets the fuel injection start timing X1 obtained by calculation. Then, the control of this flowchart ends.

  After performing the above control, the ECU 10 injects fuel from the fuel injection start timing X1 during the fuel injection period β. When the control of the flowchart of FIG. 4 is not executed, fuel is injected by intake asynchronous injection. As described above, the ECU 10 determines whether or not the valve operating characteristics of the intake valve 5 are set in the region α in which the flow velocity of the intake air flowing into the cylinder when the intake valve 5 is opened exceeds a predetermined threshold. When the valve characteristic determination means and the valve characteristic are determined to be set in that region, the fuel that delays the start timing of fuel injection from the valve opening timing of the intake valve 5 according to the setting state of the valve characteristics It functions as an injection timing control means.

  As shown in FIG. 3, the lift amount of the intake valve 5 is smaller and the IVO is after the intake top dead center than when the lift amount of the intake valve 5 is the large lift and IVO is before the intake top dead center (L6). In the case of (L4 and L5), the flow rate of the intake air flowing into the cylinder from the opening to the closing of the intake valve 5 is generally increased. Further, when the lift amount of the intake valve 5 is a small lift and the IVO is after the intake top dead center (L4 and L5), the fuel injection start timing X1 is delayed from the opening timing of the intake valve 5, and the region α Can be done after.

  According to the first mode, since the flow rate of the intake air flowing into the cylinder from the opening to the closing of the intake valve 5 is substantially increased, the formation of the air-fuel mixture can be promoted. Further, since the fuel injection is started after the region α has passed, the scattering of the fuel to the inner wall surface of the cylinder 2 can be reduced. Thereby, the discharge amount of HC can be reduced.

(Second form)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 shows a flowchart of fuel injection timing control according to the second embodiment. Controls (S1 to S4) common to the flowchart of FIG. 4 are denoted by the same reference numerals (S1 to S4) in FIG. Moreover, FIG. 1 is referred about the whole structure of this form.

  The flowchart of FIG. 5 will be described. Since steps S1 to S4 in FIG. 5 are common to steps S1 to S4 in FIG. 4, the ECU 10 performs the same control as in FIG. Therefore, in step S4, when IVO is before TDC, the control of the flowchart of FIG. 5 is not executed.

  On the other hand, if IVO is after TDC, the process proceeds to step S10. First, the ECU 10 calculates the fuel injection end timing Y. The fuel injection end timing Y is expressed by the following formula (IVO), where α is a region where the flow velocity of the intake air flowing into the cylinder when the intake valve 5 is opened exceeds a predetermined threshold value, and β is the fuel injection period. 2).

  Y = IVO + α + β (2)

  Next, the ECU 10 calculates whether or not the fuel injection end timing Y enters the fuel injection prohibition period. A fuel injection prohibition period in which the end timing of fuel injection is set at the end of the intake stroke will be described with reference to FIG. In FIG. 6, the solid line L1 and the solid line L4 shown in FIG. 3 are shown, and the relationship between the crank angle and the HC discharge amount is shown by the solid line L7. As shown in FIG. 6, the amount of HC emission increases rapidly in the region A2. Further, the HC discharge amount between the predetermined crank angle θ and the BDC is larger than that in the region α (HC1 in FIG. 6). The crank angle θ to BDC is the fuel injection prohibition period γ.

  Returning to FIG. 5, the description of the flowchart will be continued. The ECU 10 calculates whether or not the fuel injection end timing Y enters the fuel injection prohibition period γ. This is determined by whether or not the fuel injection end timing Y calculated by the above equation (2) satisfies the following equation (3) when the BDC and the fuel injection inhibition period are γ.

  Y ≦ BDC−γ (3)

  If the above equation (3) is satisfied, the process proceeds to step S11, and if not, the process proceeds to step S12. The case where it progresses to step S11 previously is demonstrated. The ECU 10 calculates the fuel injection start timing X2, and sets the fuel injection start timing X2 obtained by the calculation. As in the above equation (1), when the fuel injection start timing X2 is α, a region in which the flow rate of the intake air flowing into the cylinder when the IVO and the intake valve 5 are opened exceeds a predetermined threshold value is α. It is calculated by the following formula (4).

  X2 = IVO + α (4)

  Next, in step S11, the ECU 10 sets the fuel injection start timing X2 obtained by calculation. Then, the control of this flowchart ends.

  Subsequently, when the above equation (3) is not satisfied, the process proceeds to step S12. That is, the fuel injection end timing Y is in the fuel injection prohibition period γ. The ECU 10 calculates the fuel injection start timing X3 and sets the fuel injection start timing X3 obtained by the calculation. The fuel injection start timing X3 is calculated by the following equation (5), where BDC, the fuel injection period is β, and the fuel injection prohibition period is γ.

  X3 = BDC−β−γ (5)

  Next, in step S12, the ECU 10 sets the fuel injection start timing X3 obtained by calculation. That is, the ECU 10 limits the fuel injection end timing Y so that the fuel injection end timing Y does not enter the fuel injection prohibition period γ. Then, the control of this flowchart ends.

  After performing the above control, the ECU 10 injects fuel from the fuel injection start timings X2 and X3 during the fuel injection period β. When the control of the flowchart of FIG. 5 is not executed, fuel is injected by intake asynchronous injection. Thus, the ECU 10 functions as the fuel injection timing control means of the present invention.

  According to the second mode, the ECU 10 can limit the fuel injection end timing Y so as not to enter the fuel injection prohibition period γ. Therefore, the air-fuel mixture can be formed by the flow rate of the intake air flowing into the cylinder. Thereby, the discharge amount of HC can be reduced.

  This invention is not limited to each form mentioned above, It can implement with a various form. FIG. 7 shows the relationship between the valve opening timing of the intake valve and the fuel injection start timing. As shown in FIG. 7, during the fuel injection period β1, the fuel injection end timing Y does not enter the fuel injection prohibition period γ even if fuel is injected from the fuel injection start timing X4. However, the fuel injection period β1 may increase due to a decrease in fuel injection pressure or the use of fuel such as ethanol. For example, as shown in FIG. 7, when the fuel injection period β2 is reached for the above reason, if fuel is injected from the fuel injection start timing X4, the fuel injection end timing Y enters the fuel injection prohibition period γ. In such a case, the fuel injection start timing X4 is retarded according to the fuel injection period β so that the fuel injection end timing Y does not enter the fuel injection prohibition period γ, and fuel is injected from the fuel injection start timing X5. May be. That is, the maximum value of the retard amount related to the fuel injection start timing may be limited by the ECU 10 in accordance with the fuel injection period β2 so as not to enter the fuel injection prohibition period γ. The ECU 10 functions as fuel injection timing control means. According to this aspect, even when the fuel injection period β1 increases, the fuel injection end timing Y does not enter the fuel injection prohibition period γ. Therefore, the air-fuel mixture can be formed by the flow rate of the intake air flowing into the cylinder. Thereby, the discharge amount of HC can be reduced.

  FIG. 8 shows the relationship between the change amount of the lift amount of the intake valve and the fuel injection start time according to the operating state. For example, if there is a request for rapid acceleration by the driver of the vehicle even during cold start, the load must be shifted to a high load (the lift amount of the intake valve 5 is increased to increase the intake amount) In this case, driving responsiveness and smoothness are required. Therefore, the air-fuel ratio is deteriorated due to the lift amount (intake amount) of the intake valve 5 and the fuel injection start timing (the timing of switching between intake-synchronous injection and intake-asynchronous injection), particularly the lift amount of the intake valve 5 and the fuel injection start timing. It is necessary to suppress simultaneous changes.

  When the driver's request is switching from a low load to a high load, control may be performed as shown on the left side of FIG. 8 (low load → high load switching). The timing for changing the lift amount of the intake valve 5 and the fuel injection start timing in this case will be described below. From t1 to t2 until the load is switched from the low load to the high load, the lift amount of the intake valve 5 is set to a small lift, and the intake synchronous injection is performed. Next, during a certain period from t2 to t3, the lift amount of the intake valve 5 is changed from a small lift at t2 to a large lift at t3. Therefore, the intake valve 5 is driven by the variable valve mechanism 6 so that the lift amount gradually increases. Subsequently, from t3 when the lift amount of the intake valve 5 becomes a large lift, the ECU 10 changes from intake synchronous injection to intake asynchronous injection. When the load is high at t4, the lift amount of the intake valve 5 is a large lift and the intake asynchronous injection is performed. According to the above control, it is possible to suppress the rough air-fuel ratio. Thereby, the discharge amount of HC can be suppressed.

  Further, when the driver's request is switching from a high load to a low load, the control may be performed as shown on the right side of FIG. 8 (from high load to low load). The timing for changing the lift amount of the intake valve 5 and the fuel injection start timing in this case will be described below. From t6 to t7 until the load is switched from the high load to the low load, the lift amount of the intake valve 5 is set to a large lift and the intake asynchronous injection is performed. Next, in a certain period from t7 to t8, the ECU 10 changes from intake asynchronous injection to intake synchronous injection. Subsequently, the lift amount of the intake valve 5 is changed from a large lift at t8 to a small lift. Therefore, the intake valve 5 is driven by the variable valve mechanism 6 so that the lift amount gradually decreases. When the load is low at t9, the lift amount of the intake valve 5 is a small lift and intake synchronous injection is performed. In the case of switching from a high load to a low load, if the lift amount of the intake valve 5 is made smaller than a predetermined amount and then switched to intake synchronous injection, the air-fuel ratio becomes rough. According to the above control, it is possible to suppress the rough air-fuel ratio. Thereby, the discharge amount of HC can be suppressed.

2 cylinder 4 intake port 5 intake valve 6 variable valve mechanism 7 fuel injection valve 10 engine control valve (ECU, valve characteristic discriminating means, fuel injection timing control means)

Claims (2)

A fuel injection control device applied to an internal combustion engine having a variable valve mechanism capable of changing valve characteristics including a phase angle and a lift amount of an intake valve,
A valve characteristic discriminating means for discriminating whether or not the valve valve characteristic of the intake valve is set in a region where the flow velocity of the intake air flowing into the cylinder when the intake valve is opened exceeds a predetermined threshold; and
Fuel injection timing control means for retarding the start timing of fuel injection from the valve opening timing of the intake valve according to the set state of the valve timing when it is determined that the valve timing characteristic is set in the region; ,
A fuel injection control device for an internal combustion engine.   2. The internal combustion engine according to claim 1, wherein the fuel injection timing control means limits the end timing of the fuel injection so that the end timing of the fuel injection does not enter a fuel injection prohibition period set at the end of the intake stroke. Fuel injection control device.

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