JP2008019874A - Variable valve timing control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the startability of a cylinder injection engine by raising fuel pressure to fuel pressure suitable for starting in an early stage of start. <P>SOLUTION: In the cylinder injection engine, fuel pumped up from a fuel tank 11 by a low pressure pump 12, is pressurized by a high pressure pump 14 and is pumped to a fuel injection valve 28 since injection pressure need to be made high pressure for atomizing injected fuel. Fuel pressure need to be raised to pressure suitable for starting by the high pressure pump 14 in the early stage of start to improve startability. ECU 30 prohibits cylinder injection for a period established by elapse time, number of cycles (number of times of injection timing) or the like from cranking start, or until fuel pressure exceeds predetermined pressure at start. Consequently, cylinder injection can be started after securing sufficient fuel pressure in a short period of time and atomization of injected fuel can be accelerated from a beginning of injection start to improve startability. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel injection device for an internal combustion engine that directly injects fuel, which has been made high pressure by a high pressure pump, into a cylinder from a fuel injection valve.

  An in-cylinder injection engine that directly injects fuel into a cylinder has a shorter time from injection to combustion than an intake port injection engine that injects fuel into an intake port, and can earn enough time to atomize injected fuel. Therefore, it is necessary to atomize the injected fuel by increasing the injection pressure. Therefore, in the cylinder injection engine, the fuel pumped up from the fuel tank by the low pressure pump is increased in pressure by the high pressure pump and is pumped to the fuel injection valve. Since this high-pressure pump requires a large driving force, many of the high-pressure pumps pump fuel by reciprocating the piston of the high-pressure pump by a cam fitted to the cam shaft of the engine.

  By the way, since the high-pressure pump and the low-pressure pump are also stopped while the engine is stopped, the fuel pressure in the fuel pipe gradually decreases with time. For this reason, the fuel pressure at the time of starting is often almost 0 MPa. Therefore, at the time of start-up, it is necessary to raise the fuel pressure from the substantially 0 MPa state to the target fuel pressure, but the discharge of the high-pressure pump is performed only once or twice per one rotation of the camshaft of the engine, and the injection amount at the time of start-up As shown in FIG. 4 (a), the fuel pressure drops at each injection, the fuel pressure fluctuation at the start increases, and the injection time (injection pulse width) and the injection timing at the start are irregular as shown in FIG. It becomes. In addition, it takes time for the fuel pressure to rise to a fuel pressure suitable for starting, and during that time, injection is performed with insufficient fuel pressure, so the atomization of the injected fuel becomes insufficient and the air-fuel mixture becomes difficult to burn. Combined with the fuel pressure fluctuation at the start, the startability is deteriorated and the exhaust emission at the start is also deteriorated.

  The present invention has been made in view of such circumstances. Therefore, the object of the present invention is to quickly increase the fuel pressure to a fuel pressure suitable for starting at the time of starting, improving startability, and exhaust emission at starting. An object of the present invention is to provide a fuel injection device for an internal combustion engine that can achieve reduction.

  In order to achieve the above object, according to the fuel injection device for an internal combustion engine of claim 1 of the present invention, the fuel pressure supplied to the fuel injection valve is detected by the fuel pressure detecting means, and the detected fuel pressure at the start is equal to or lower than a predetermined pressure. Sometimes in-cylinder injection is prohibited.

  By the way, the time required to raise the fuel pressure to a fuel pressure suitable for starting at the time of starting becomes shorter as the fuel pressure at the starting time becomes higher, and the fuel pressure at the starting time varies depending on the engine stop time, and the engine stop time is short. There is little decrease in fuel pressure.

  Therefore, according to the first aspect, the in-cylinder injection prohibition period can be automatically set to the minimum necessary even if the fuel pressure at the beginning of the start is different. Therefore, for example, when restarting immediately after the engine stops (when the initial fuel pressure is kept near the target fuel pressure), in-cylinder injection is immediately started without prohibiting in-cylinder injection from the beginning. Thus, the engine can be started, and the start can be completed in a very short time.

  Further, in the first aspect, when the in-cylinder injection prohibition state continues for a predetermined period, the in-cylinder injection prohibition is canceled and the in-cylinder injection is started even if the detected fuel pressure has not increased to the predetermined pressure. . In other words, if the in-cylinder injection is prohibited and the high-pressure pump is driven for a certain period of time, even if the detected fuel pressure does not rise to the predetermined pressure, it can be estimated that the fuel pressure has risen to that level. It starts and starts. In this way, when the in-cylinder injection prohibition state (the state where the detected fuel pressure is equal to or lower than the predetermined pressure) continues for a long time, the start-up time can be made shorter than when in-cylinder injection is continuously prohibited until the detected fuel pressure exceeds the predetermined pressure. At the same time, even if the capacity of the high-pressure pump is reduced or the fuel pressure detecting means fails, the engine can be started and the system can be provided with a fail-safe function. The predetermined pressure is a fuel pressure suitable for starting, and may be a pressure set to a pressure lower than the target fuel pressure (claim 2).

[Embodiment (1)]
Hereinafter, an embodiment (1) of the present invention will be described with reference to FIGS. A low-pressure pump 12 that pumps up fuel is installed in the fuel tank 11 that stores the fuel. The low-pressure pump 12 is driven by an electric motor (not shown) that uses a battery (not shown) as a power source. The fuel discharged from the low pressure pump 12 is supplied to the high pressure pump 14 through the fuel pipe 13. A pressure regulator 15 is connected to the fuel pipe 13, and the pressure regulator 15 regulates the discharge pressure of the low-pressure pump 12 (fuel supply pressure to the high-pressure pump 14) to about 0.3 MPa, for example. The excess is returned to the fuel tank 11 by the fuel return pipe 16.

  As shown in FIG. 2, the high-pressure pump 14 is a piston pump that sucks / discharges fuel by reciprocating a piston 19 in a cylindrical pump chamber 18. The piston 19 is fitted to a camshaft 20 of the engine. It is driven by the rotational movement of the cam 21. A fuel pressure control valve 22 made of an electromagnetic valve is provided on the suction port 23 side of the high-pressure pump 14. During the intake stroke of the high-pressure pump 14 (when the piston 19 is lowered), the fuel pressure control valve 22 is opened and fuel is sucked into the pump chamber 18, and during the discharge stroke (when the piston 19 is raised), the fuel pressure control valve. The fuel pressure (discharge pressure) is controlled by controlling the valve closing time 22. That is, when the fuel pressure is increased, the valve closing time of the fuel pressure control valve 22 is lengthened. Conversely, when the fuel pressure is decreased, the valve closing time of the fuel pressure control valve 22 is shortened.

  On the other hand, a check valve 25 for preventing the backflow of discharged fuel is provided on the discharge port 24 side of the high-pressure pump 14. The fuel discharged from the high-pressure pump 14 is sent to the delivery pipe 27 through the fuel pipe 26, and the high-pressure fuel is distributed from the delivery pipe 27 to the fuel injection valve 28 attached to the cylinder head of the engine for each cylinder. The fuel pipe 26 is provided with a fuel pressure sensor 29 (fuel pressure detecting means) for detecting the fuel pressure, and an output signal of the fuel pressure sensor 29 is input to an engine control circuit (hereinafter referred to as “ECU”) 30.

  The ECU 30 is mainly composed of a microcomputer, and reads output signals of various sensors for detecting an engine operating state such as engine speed, intake pipe pressure (or intake air amount), cooling water temperature, etc. The timing is calculated, and an injection pulse corresponding to the calculation result is output to the fuel injection valve 28 of each cylinder to execute fuel injection. Further, the ECU 30 executes the injection control program shown in FIG. 3 stored in a built-in ROM (storage medium), thereby prohibiting in-cylinder injection at the beginning of startup and quickly increasing the fuel pressure. Cancel the in-cylinder injection prohibition and switch to normal injection control.

  Hereinafter, the processing content of the injection control program of FIG. 3 which performs this injection control will be described. This program is repeatedly executed at every injection timing after the ignition switch 31 is turned on. When this program is started, first, at step 101, it is determined whether or not it is a start time based on the signal from the ignition switch 31 and the engine speed. For example, from when the ignition switch 31 is operated to the “START” position, it is determined that the engine has been started until the engine speed becomes equal to or higher than a predetermined speed. Otherwise, it is determined that the start has been completed.

  If it is determined in step 101 that the engine is started, the process proceeds to step 102, in which whether or not the number of injection timings i counted by the injection number counter from the start of cranking (starting driving of the high-pressure pump 14) is equal to or less than a predetermined number. Determine whether. Here, the predetermined number of times may be a fixed value (for example, four times) set in advance, or may be set by a map or the like according to the cooling water temperature, the intake air temperature, or the like.

  If the number of injection timings i is equal to or less than the predetermined number in step 102, it is determined that the pressure (fuel pressure) of fuel supplied from the high pressure pump 14 to the fuel injection valve 28 has not increased to a fuel pressure suitable for starting. In step 103, the in-cylinder injection is prohibited, and in the next step 104, the count value i of the injection number counter is incremented by 1, and the program ends. The injection number counter is reset by an initialization program (not shown) executed when the ignition switch 31 is turned on. The processing in steps 101 to 104 serves as a start control means in the claims.

  While in-cylinder injection is prohibited, the high pressure pump 14 is driven in a state where injection is stopped, so that the fuel pressure rises quickly. When the number i of injection timings exceeds the predetermined number, it is determined that the fuel pressure has increased to a fuel pressure suitable for starting, and the routine proceeds to step 105 where the in-cylinder injection prohibition is canceled and the control is switched to normal injection control. To output an injection pulse to the fuel injection valve 28 to start in-cylinder injection.

  By the way, since the discharge of the high-pressure pump 14 is performed only once or twice per one rotation of the camshaft of the engine, and the injection amount at the time of starting is greatly increased, as in the prior art [FIG. 4 (a)]. When the injection is started from the beginning, the fuel pressure drops at every injection, the fuel pressure fluctuation at the start becomes large, and the injection time (injection pulse width) and the injection timing at the start become irregular. In addition, it takes time for the fuel pressure to rise to a fuel pressure suitable for starting, and during that time, injection is performed with insufficient fuel pressure, so the atomization of the injected fuel becomes insufficient and the air-fuel mixture becomes difficult to burn. Combined with the fuel pressure fluctuation at the start, the startability is deteriorated and the exhaust emission at the start is also deteriorated.

  On the other hand, in this embodiment (1), as shown in FIG. 4B, in-cylinder injection is prohibited from the start of cranking until the number i of injection timings reaches a predetermined number. During prohibition, the fuel pressure can be quickly raised by the high-pressure pump 14 and after the sufficient fuel pressure is secured in a short time, the in-cylinder injection can be started, and the injection fuel can be sufficiently atomized from the beginning of the injection. Can be promoted. In addition, the fuel pressure at the start can be stabilized, the injection time and the injection timing at the start can be stabilized, and the startability can be improved in combination with the atomization of the injected fuel described above. Exhaust emissions can be reduced.

  In the above embodiment (1), the period during which in-cylinder injection is prohibited in the initial stage of the start is set by the number of injection timings from the start of cranking (start of driving of the high-pressure pump 14). The in-cylinder injection prohibition period may be set based on the number of rotations) or the elapsed time.

[Embodiment (2)]
In the above embodiment (1), when the number of injection timings is less than or equal to the predetermined number of times, it is determined that the fuel pressure has not increased to a fuel pressure suitable for starting, and in-cylinder injection is prohibited. Since the time required to increase the fuel pressure varies depending on the fuel pressure at the start of the operation, the fuel pressure detected by the fuel pressure sensor 29 is taken into account in the injection control program according to the embodiment (2) of the present invention shown in FIG. In-cylinder injection is prohibited when is below a predetermined pressure.

  Specifically, first, at step 201, it is determined whether or not the engine is at the time of starting by the same method as step 101 of FIG. 3 described above. If it is at the time of starting, the process proceeds to step 202 and detected by the fuel pressure sensor 29. It is determined whether the fuel pressure is equal to or lower than a predetermined pressure. Here, the predetermined pressure is a fuel pressure suitable for starting (that is, a fuel pressure that can ensure atomization of the injected fuel necessary for starting), and is set to a pressure lower than the target fuel pressure. The predetermined pressure may be a fixed value set in advance, or may be set by a map or the like according to the cooling water temperature, the intake air temperature, or the like.

  If it is determined in step 202 that the detected fuel pressure is equal to or lower than the predetermined pressure, the process proceeds to step 203, in-cylinder injection is prohibited, and this program ends. Thereafter, when the fuel pressure exceeds the predetermined pressure, the routine proceeds to step 204 where the in-cylinder injection prohibition is canceled and the control is switched to the normal injection control, and in-cylinder injection is executed.

  In this way, even if the time required to raise the fuel pressure to a fuel pressure suitable for starting varies depending on the fuel pressure at the beginning of starting, etc., the in-cylinder injection prohibition period is automatically set to the minimum necessary accordingly. it can. Therefore, for example, when restarting immediately after the engine stops (when the initial fuel pressure is kept near the target fuel pressure), in-cylinder injection is immediately started without prohibiting in-cylinder injection from the beginning. Thus, the engine can be started, and the start can be completed in a very short time.

[Embodiment (3)]
In the embodiment (3) of the present invention, the injection control program of FIG. 6 is executed. The injection control program of FIG. 6 is characterized in that step 101a is added between step 101 and step 102, and other than this, it is exactly the same as the injection control program of FIG.

  In the present embodiment (3), the conditions for prohibiting in-cylinder injection at the time of starting are that the fuel pressure detected by the fuel pressure sensor 29 is a predetermined pressure or less (step 101a), and the number i of injection timings is a predetermined number or less. (Step 102), and in-cylinder injection is prohibited only when these two conditions are satisfied simultaneously (Step 104). Therefore, even if the detected fuel pressure is equal to or lower than the predetermined pressure, if the number i of the injection timing exceeds the predetermined number, the in-cylinder injection prohibition is canceled and the normal injection control is switched to start in-cylinder injection (step 105). . That is, if the high-pressure pump 14 is driven for a certain period while prohibiting in-cylinder injection, it can be estimated that the detected fuel pressure has increased to a fuel pressure close to that even if the detected fuel pressure has not increased to a predetermined pressure. Is started and started.

  In this way, when the in-cylinder injection prohibition state (the state where the detected fuel pressure is equal to or lower than the predetermined pressure) continues for a long time, the start-up time can be made shorter than when in-cylinder injection is continuously prohibited until the detected fuel pressure exceeds the predetermined pressure. . Moreover, even if the capacity of the high-pressure pump 14 is reduced or the fuel pressure sensor 29 is broken, the engine can be started, and the system can be provided with a fail-safe function, thereby improving the reliability of the system.

[Embodiment (4)]
Next, Embodiment (4) of this invention is demonstrated based on FIG. 7 thru | or FIG. In the present embodiment (4), as shown in FIG. 7, the fuel injection valve 28 for in-cylinder injection is attached to the upper part of each cylinder of the in-cylinder injection engine 40, and the intake port 41 of each cylinder has intake air. A fuel injection valve 42 for port injection is attached. As shown in FIG. 8, the fuel injection valve 42 for the intake port injection of each cylinder is attached to the delivery pipe 43, and the fuel discharged from the low pressure pump 12 is supplied to the delivery pipe 43 through the fuel pipes 13 and 44. The fuel is distributed from the delivery pipe 43 to the fuel injection valve 42 for the intake port injection of each cylinder. Other system configurations are the same as those in FIG. 1 described in the first embodiment.

  In the present embodiment (4), the injection control program shown in FIG. 9 is repeatedly executed at each injection timing after the ignition switch 31 is turned on, and the intake port injection by the fuel injection valve 42 for intake port injection is performed according to the fuel pressure at the start. And in-cylinder injection by the in-cylinder fuel injection valve 28 are switched as follows.

  First, in steps 301 and 302, if the fuel pressure is equal to or lower than the predetermined pressure at the start, the process proceeds to step 303, and in-cylinder injection by the in-cylinder fuel injection valve 28 is prohibited. The ECU 30 outputs an injection pulse to the fuel injection valve 42 for intake port injection to execute intake port injection. Intake port injection has a longer time from injection to combustion than in-cylinder injection, and can earn time to atomize the injected fuel, so even injected fuel can be atomized and burned even at low fuel pressure A simple air-fuel mixture can be formed. Thereby, it is also possible to complete the start-up by the intake port injection during the in-cylinder injection prohibition period.

  Thereafter, when the fuel pressure exceeds a predetermined pressure, the routine proceeds to step 305, and after prohibiting intake port injection, it is determined at step 306 whether or not a predetermined period has elapsed since the end of intake port injection. Here, the predetermined period is a period until the wet fuel adhering to the inner wall or the like of the intake port 41 evaporates and decreases due to the intake port injection. The elapsed time from the end of the intake port injection, the number of cycles (the rotation of the crankshaft) The number of times may be set. In step 306, if the predetermined period has not yet elapsed, the program is terminated without executing in-cylinder injection. During this period, the air-fuel ratio of the air-fuel mixture is ensured by the evaporated amount of wet fuel.

  Thereafter, when a predetermined period has elapsed, it is determined that the evaporative gas of the wet fuel sucked into the cylinder has decreased, and the routine proceeds to step 307 where an injection pulse is output from the ECU 30 to the fuel injection valve 28 for in-cylinder injection. Then, in-cylinder injection is started. Thereafter, in-cylinder injection is continued even after the start is completed.

  In the present embodiment (4) described above, the intake port injection that can be started even at a low fuel pressure is performed until the fuel pressure exceeds a predetermined pressure at the time of start, thereby speeding up the start. Since there is a lot of wet adhering to the inner wall of the intake port 41 and the like, this wet fuel gradually evaporates and is sucked into the cylinder. Can be supplied with fuel. In consideration of this, in the present embodiment (4), as shown in FIG. 10, since the in-cylinder injection is started after a lapse of a predetermined period from the end of the intake port injection at the time of start-up, there is little evaporation of wet fuel. In-cylinder injection can be started, and the air-fuel ratio of the air-fuel mixture after switching from intake port injection to in-cylinder injection can be prevented from becoming excessively rich due to evaporation of wet fuel. Can be reduced.

  In the present embodiment (4), the intake port injection period at the time of starting is set until the fuel pressure exceeds a predetermined pressure. This intake port injection period is the same as the in-cylinder injection prohibition period in the embodiment (1). Alternatively, it may be set according to the elapsed time from the start of cranking, the number of cycles (number of injection timings), or the like.

[Embodiment (5)]
In the above embodiment (4), in-cylinder injection is started after a lapse of a predetermined period from the end of intake port injection in consideration of the presence of wet due to intake port injection. In the embodiment (5), in-cylinder injection is started immediately after the intake port injection is completed. At this time, the injection amount (injection pulse width) after the start of in-cylinder injection is gradually increased in response to the gradual decrease in the amount of evaporation of wet fuel after the intake port injection ends. In this way, the air-fuel ratio of the air-fuel mixture can be made constant even if wet fuel remains after the start of in-cylinder injection, and the air-fuel mixture after the start of in-cylinder injection is the same as in the embodiment (4). It is possible to prevent the air-fuel ratio of the fuel from becoming excessively rich due to the evaporation of the wet fuel.

The figure which shows schematic structure of the whole fuel-injection system in Embodiment (1). High-pressure pump configuration diagram The flowchart which shows the flow of a process of the injection control program in embodiment (1). (A) is the time chart which shows the behavior of the injection control at the time of the conventional start, (b) is the time chart which shows the behavior of the injection control at the time of start of embodiment (1). The flowchart which shows the flow of a process of the injection control program in embodiment (2). The flowchart which shows the flow of a process of the injection control program in embodiment (3). The longitudinal cross-sectional view of the principal part of the cylinder injection engine in Embodiment (4) The figure which shows schematic structure of the whole fuel-injection system in Embodiment (4). The flowchart which shows the flow of a process of the injection control program in embodiment (4). Time chart explaining timing of switching between intake port injection and in-cylinder injection at start-up in embodiment (4) Time chart explaining timing of switching between intake port injection and in-cylinder injection at start-up in embodiment (5)

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Fuel tank, 12 ... Low pressure pump, 14 ... High pressure pump, 15 ... Pressure regulator, 19 ... Piston, 20 ... Cam shaft, 21 ... Cam, 22 ... Fuel pressure control valve, 25 ... Check valve, 27 ... Delivery pipe, DESCRIPTION OF SYMBOLS 28 ... Fuel injection valve for in-cylinder injection, 29 ... Fuel pressure sensor (fuel pressure detection means), 30 ... ECU (starting control means), 31 ... Ignition switch, 40 ... In-cylinder injection engine, 41 ... Intake port, 42 ... Intake Fuel injection valve for port injection, 43 ... delivery pipe.

Claims (2)

In a fuel injection device for an internal combustion engine in which fuel is made high pressure by a high pressure pump and supplied to a fuel injection valve for in-cylinder injection, and fuel is injected into the cylinder from the fuel injection valve.
Fuel pressure detecting means for detecting the pressure of fuel supplied to the fuel injection valve (hereinafter referred to as “fuel pressure”);
Starting control means for prohibiting in-cylinder injection by the fuel injection valve when the fuel pressure detected by the fuel pressure detecting means at the time of starting is below a predetermined pressure,
The start control means cancels the in-cylinder injection prohibition and starts the in-cylinder injection when the in-cylinder injection prohibition state continues for a predetermined period.   2. The fuel injection device for an internal combustion engine according to claim 1, wherein the predetermined pressure is a fuel pressure suitable for starting, and a pressure set to a pressure lower than a target fuel pressure.

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