JP2004084560A - Fuel supply device for internal combustion engine - Google Patents

Abstract

In an internal combustion engine that injects fuel using a high-pressure fuel pump, fuel may leak from an injector to an internal combustion engine body when the engine is stopped, resulting in deterioration of exhaust emission at startup.
When an ignition key is turned off and an internal combustion engine stop signal is transmitted to an ECU (S10), the ECU stops the high-pressure fuel pump (S12). At this time, the operation of the low-pressure fuel pump is continued. The ECU calculates the fuel injection amount required to reduce the pressure in the high-pressure fuel pipe (S14), and sets the number of injections n of the injector (S16). When the set number of injections n has been reached (Y in S20), the ECU stops fuel injection and ignition, and stops the low-pressure fuel pump (S22).
[Selection diagram] Fig. 3

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel supply device for supplying fuel to an internal combustion engine, and in particular, a fuel in a fuel tank is once supplied to a high pressure fuel pump by a low pressure fuel pump, and is further fed to a fuel injector by a high pressure fuel pump for injection. The present invention relates to a fuel supply device for supplying to a fuel supply device.
[0002]
[Prior art]
Gasoline engines of the type that directly injects fuel into cylinders (hereinafter, also referred to as "direct injection gasoline engines") are expected to be further popularized in the future due to advantages in fuel efficiency and output characteristics.
In a direct injection gasoline engine, a high pressure is required for fuel injected from an injector in order to atomize the fuel effectively. For this reason, the fuel is generally pressurized in two stages. First, the fuel in the fuel tank is pumped up by a low-pressure fuel pump, and at this time, the fuel is raised to a predetermined pressure (also referred to as a feed pressure). Next, the fuel at the feed pressure is pressurized by a high-pressure fuel pump and fed into the delivery pipe. The pressurization by the two pumps is continued during the operation of the engine. On the other hand, if the operation of stopping the engine is performed, usually, the injection operation of the injector is immediately stopped, the two pumps also stop, and the engine is stopped. Therefore, the high-pressure fuel is held in the delivery pipe even after the engine is stopped.
[0003]
Therefore, as a general problem, the high-pressure fuel in the delivery pipe leaks from the injector during the stoppage of the engine and adheres to the combustion chamber, particularly to the piston, and may cause abnormal combustion the next time the engine is started. Abnormal combustion causes deterioration of exhaust emission and knocking. In order to avoid this problem, in Japanese Patent Application Laid-Open No. H11-247734, when the internal combustion engine is stopped, the fuel injection into the delivery pipe is stopped and the injection operation of the injector is continued to perform combustion. The fuel pressure in the delivery pipe (hereinafter, also referred to as “control fuel pressure”) is reduced. Hereinafter, this injection operation is also referred to as “step-down injection”.
[0004]
[Problems to be solved by the invention]
In the above-mentioned publication, it is determined that the control fuel pressure has reached the required minimum pressure when a predetermined time has elapsed since the internal combustion engine was stopped, and the step-down injection is stopped. However, since this determination is based on estimation, the actual control fuel pressure may drop below the required minimum pressure. In this case, the injected fuel is not sufficiently atomized, and abnormal combustion occurs during the step-down injection period. May invite. That is, even if the stop timing of the step-down injection is controlled, the initial problem cannot be solved depending on the control accuracy.
[0005]
It should be noted that a direct injection gasoline engine is usually provided with a pressure sensor for measuring the control fuel pressure.Therefore, it is possible to monitor the output of this sensor and continue the step-down injection until the pressure reaches a desired pressure. The sensor is ranged for high pressure measurement and is not suitable for measuring pressure drop due to buck injection. On the other hand, if another sensor is provided for the control fuel pressure measurement at the medium and low pressures, a new high pressure seal design or the like is required, which is disadvantageous in cost.
[0006]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for reducing fuel leakage from an injector during a stop period of an internal combustion engine in which high fuel pressure is required for fuel injected from the injector. To provide. Another object of the present invention is to provide a technique for preventing abnormal combustion of fuel during pressure drop injection by controlling the control pressure not to drop too much when the pressure drop is reduced by pressure drop injection.
[0007]
[Means for Solving the Problems]
One embodiment of the present invention relates to a fuel supply device. This fuel supply device has a low-pressure fuel pump that pumps up fuel in a fuel tank, and a high-pressure fuel pump that pressurizes fuel of a predetermined pressure pumped by the low-pressure fuel pump and feeds the fuel into a high-pressure fuel pipe. A fuel supply device for an internal combustion engine that supplies fuel in a pipe to a combustion chamber of the internal combustion engine via an injector.When the internal combustion engine is stopped, the pressurizing operation of the high-pressure fuel pump is stopped and the injection operation of the injector is stopped. When the fuel pressure is reduced by continuing to lower the fuel pressure in the high pressure fuel pipe, a fuel pressure lowering means is provided for operating a low pressure fuel pump to pump fuel of a predetermined pressure into the high pressure fuel pipe.
[0008]
In this configuration, when the internal combustion engine is stopped, the pressurizing operation of the high-pressure fuel pump is stopped. Also at this time, the injection operation of the injector, that is, the step-down injection continues, and the fuel pressure in the high-pressure fuel pipe, that is, the control fuel pressure decreases. However, since the low-pressure fuel pump operates, fuel at a predetermined pressure is pumped into the high-pressure fuel pipe, and the control fuel pressure does not become lower than the predetermined pressure. Here, the “high-pressure fuel pipe” mainly indicates a fuel path including a delivery pipe from the high-pressure fuel pump to the injector.
[0009]
The predetermined pressure is preferably set to a pressure that does not cause abnormal combustion, in which case the control fuel pressure is mechanically ensured not to drop to a pressure that causes abnormal combustion. As a result, the control fuel pressure can be reduced while preventing abnormal combustion.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
FIG. 1 schematically shows an internal combustion engine 1 which is a direct injection gasoline engine provided with a fuel supply device 40 according to the embodiment. The internal combustion engine 1 further includes an engine body 15. In this embodiment, the engine body 15 has a first cylinder 16a, a second cylinder 16b, a third cylinder 16c, and a fourth cylinder 16d (hereinafter, collectively referred to as "cylinder 16" as appropriate), but this limits the present invention. It does not do. The fuel supply device 40 pressurizes the fuel pumped by the low-pressure fuel pump 3 by the high-pressure fuel pump 9 and feeds the fuel into the delivery pipe 13, and sends the high-pressure fuel to the first injector 14 a, the second injector 14 b, the third injector 14 c, The four injectors 14 d (hereinafter, collectively referred to as “injectors 14” as appropriate) directly inject the corresponding cylinders 16. An electronic control unit (hereinafter, referred to as an ECU) 30 controls the timing of pressure feeding by the high-pressure fuel pump 9 and the timing of injection by the injector 14. Hereinafter, the fuel path from the low-pressure fuel pump 3 to the high-pressure fuel pump 9 is referred to as “low-pressure fuel pipe”, and the fuel path from the high-pressure fuel pump 9 to the injector 14 is referred to as “high-pressure fuel pipe”.
[0011]
When the ignition switch 20 is turned on by the user, the ECU 30 detects a start operation of the internal combustion engine 1 and first issues a drive instruction to the low-pressure fuel pump 3. The type of the ignition switch 20 does not matter, such as a key insertion type and a wireless authentication type carried by a user. The low-pressure fuel pump 3 is an electric type driven by a battery, pumps up the fuel in the fuel tank 2, and feeds the fuel from a discharge port to a low-pressure fuel pipe. The discharge port is connected to a pressure regulator 4, and the pressure of the pumped fuel is adjusted to a predetermined feed pressure by the pressure regulator 4. When the fuel pressure exceeds the feed pressure, the pressure regulator 4 returns the fuel fed from the low-pressure fuel pump 3 to the fuel tank 2 to keep the fuel pressure in the low-pressure fuel pipe constant. The feed pressure is set to a level that does not cause abnormal combustion even if the high-pressure fuel pump 9 does not operate, and is set to, for example, 0.4 MPa. The filter 5 removes foreign matter from the fuel, and the pulsation damper 6 reduces fuel pulsation. The pumped fuel is supplied to a high-pressure fuel pump 9 through a suction pipe 7 which is a low-pressure fuel pipe.
[0012]
The high-pressure fuel pump 9 is a mechanical type, and raises the fuel pressure in the delivery pipe 13 as a high-pressure fuel pipe to a target pressure of, for example, 12 MPa through the control of the electromagnetic valve 8. The plunger 9a of the high-pressure fuel pump 9 slides in the cylinder of the pump in synchronization with the rotation of the pump cam 10a provided on the camshaft 10. The volume of the pump chamber 9b changes with the movement of the plunger 9a. The plunger 9a is urged by a spring 9c in a direction to increase the volume of the pump chamber 9b. In the fuel discharge stroke of the high-pressure fuel pump 9, the pump cam 10a slides the plunger 9a in a direction to reduce the volume of the pump chamber 9b, and in the fuel suction stroke, the pump cam 10a conversely increases the volume of the pump chamber 9b. 9c slides the plunger 9a. The high-pressure fuel pump 9 performs two discharge strokes during one rotation of the pump cam 10a. The camshaft 10 and the crankshaft are connected via a reduction gear or the like, and the camshaft 10 makes one rotation when the crankshaft makes two rotations. Therefore, the discharge of the fuel is performed every time the fuel injection of two of the four cylinders is performed.
[0013]
The solenoid valve 8 drives the valve body 8 c based on an opening / closing instruction from the ECU 30 to open / close the suction-side opening 9 d of the high-pressure fuel pump 9. The valve element 8c is urged by a spring 8a in a direction to open the suction-side opening 9d. The electromagnetic valve 8 is opened by the biasing force of the spring 8a by demagnetizing the electromagnetic solenoid 8b during the suction stroke of the high-pressure fuel pump 9, and is closed by exciting the electromagnetic solenoid 8b during the discharge stroke. Thus, during the suction stroke, the fuel supplied from the low-pressure fuel pump 3 is sucked into the pump chamber 9b of the high-pressure fuel pump 9, and during the discharge stroke, the fuel in the pump chamber 9b is pressurized to increase the pressure. It is pumped to the fuel pipe. A check valve 11 is provided at the discharge-side opening 9e of the pump chamber 9b to restrict the flow of fuel from the pump chamber 9b toward the high-pressure fuel pipe.
[0014]
In the high-pressure fuel pipe, pressurized fuel is supplied to the delivery pipe 13 via the discharge pipe 12. The delivery pipe 13 has a sufficient volume so that the fuel pressure does not drop sharply by one fuel injection, and is designed so that the reduced pressure can be compensated for by one discharge of the high-pressure fuel pump 9. The fuel pressure sensor 17 detects the fuel pressure in the high-pressure fuel pipe, specifically, the fuel pressure in the delivery pipe 13, and transmits the detection result to the ECU 30. In general, the fuel pressure sensor 17 is set in a range for high pressure measurement from the viewpoint of cost reduction, and does not have a good sensing capability for a pressure on the low pressure side, for example, on the order of 0.1 MPa.
[0015]
The injector 14 receives an injection instruction from the ECU 30, and injects a required amount of fuel at a desired timing. The cylinder 16 is provided with an ignition mechanism, and is driven based on an instruction from the ECU 30. The ECU 30 performs feedback control of the solenoid valve 8 so that the fuel pressure in the delivery pipe 13 becomes the target pressure. Further, a water temperature sensor 21 for detecting the temperature of the cooling water is provided, and the detection result is transmitted to the ECU 30. Note that, for the sake of clarity, some broken lines indicating control from the ECU 30 to the injector 14 are omitted in the drawing.
[0016]
The return pipe 19 is provided with a relief valve 18. When the fuel pressure in the delivery pipe 13 exceeds, for example, 15 MPa, the relief valve 18 opens to return the fuel to the fuel tank 2 and acts as a high-pressure limiter for the fuel pressure in the delivery pipe 13.
[0017]
When the operation of the high-pressure fuel pump 9 and the injection operation of the injector 14 stop simultaneously, the fuel pressure in the delivery pipe 13 is maintained at the control fuel pressure at the time of the stop, as described above. The fuel pressure in the delivery pipe 13 decreases according to the amount of fuel leakage determined by the sealing characteristics of the check valve 11, the injector 14, and the relief valve 18. Generally, from the viewpoint of the discharge efficiency of the high-pressure fuel pump 9 and the feasibility of combustion, the sealing characteristic is set to a value close to zero as much as possible, so that the pressure in the high-pressure fuel pipe is maintained at a high pressure even after the internal combustion engine is stopped. Is done. For this reason, fuel leakage from the injector 14 is likely to occur, and the following step-down injection is performed.
[0018]
FIG. 2 is a timing chart showing an operation of the internal combustion engine 1 during step-down injection according to the present embodiment. FIG. 3 is a flowchart showing the procedure of the step-down injection.
[0019]
When the ignition switch 20 is turned off and a stop signal of the internal combustion engine 1 is transmitted to the ECU 30 (S10), the ECU 30 stops the high-pressure fuel pump 9 after detecting the signal (S12). That is, energization of the electromagnetic solenoid 8b of the electromagnetic valve 8 is stopped. Subsequently, the ECU 30 determines the total fuel injection required to reduce the control fuel pressure to the feed pressure based on the fuel pressure measured by the fuel pressure sensor 17, that is, the control fuel pressure, and the coolant temperature measured by the water temperature sensor 21. The amount ΔV is calculated (S14). The total injection amount ΔV is the total amount of fuel injection by the step-down injection, and can be obtained from the following equation using the control fuel pressure PH, the feed pressure PL, the volume V of the high-pressure fuel pipe, and the bulk modulus K of the fuel.
ΔV = (PH−PL) V / K
[0020]
Here, the bulk modulus K changes depending on the temperature of the fuel. Since the temperature of the cooling water has a high correlation with the temperature of the fuel, the ECU 30 calculates the bulk modulus K based on the temperature of the cooling water measured by the water temperature sensor 21 and calculates the total injection amount ΔV from the above equation. I do. However, it is not necessary to calculate the total injection amount ΔV exactly, and the total injection amount ΔV may be calculated with the bulk modulus K being a fixed value.
[0021]
Subsequently, the ECU 30 calculates the number n of step-down injections based on the calculated total injection amount ΔV (S16), and performs the step-down injection by the injector 14 according to the calculated number n of injections. That is, the injection operation of the injector 14 performed at the predetermined injection timing is continued, and the fuel is injected from the injector 14 (S18). Further, the fuel injected from the injector 14 is burned by ignition.
[0022]
The control fuel pressure in the high-pressure fuel pipe decreases from the initial value of the control fuel pressure PH every time the fuel is injected due to the step-down injection. However, at this time, the operation of the low-pressure fuel pump 3 is continued. As a result, the number of injections n is calculated as a value obtained by dividing the total injection amount ΔV by the fuel injection amount per one step-down injection. In consideration of the measurement error of the pressure sensor 17, n is set to be somewhat larger. However, the control fuel pressure does not become lower than the feed pressure PL.
[0023]
When the number of step-down injections does not reach the set value n (N in S20), the fuel injection is continued (S18), and when it reaches n (Y in S20), the control fuel pressure is equal to the feed pressure PL. Then, the ECU 30 stops the fuel injection and the ignition, and then stops the low-pressure fuel pump 3 (S22).
[0024]
As described above, according to the present embodiment, the amount of fuel leakage during the stop period of the internal combustion engine 1 can be reduced. That is, it is generally known that the amount of fuel leakage from the injector is proportional to the half power of the fuel pressure. When the control fuel pressure is reduced from 12 MPa to 0.4 MPa, for example, according to the present embodiment, the amount of fuel leakage after stopping the internal combustion engine is (0.4 / 12) ^1/2 times = about 0.18 times, that is, It decreases to 1/5 to 1/6. Further, it is possible to prevent the control fuel pressure from unnecessarily lowering due to the step-down injection. Furthermore, since the feed pressure is set to a pressure that does not cause abnormal combustion, the internal combustion engine can be stopped while maintaining a good combustion state.
[0025]
(Embodiment 2)
In the first embodiment, only the high-pressure fuel pump 9 stops at the time of the step-down injection, and the operation of the low-pressure fuel pump 3 is continued. However, the low-pressure fuel pump 3 can be temporarily stopped during the step-down injection from the viewpoint of reducing power consumption as much as possible.
[0026]
FIG. 4 is a timing chart showing the operation of the internal combustion engine 1 during the step-down injection according to the present embodiment. Simultaneously with the stop of the high-pressure fuel pump 9, the low-pressure fuel pump 3 is also temporarily stopped, and the operation of the low-pressure fuel pump 3 is restarted before the calculated number of injections n is reached, that is, before the end of the step-down injection. The timing of restarting has some margin in consideration of an error. Hereinafter, control of the fuel supply device 40 in the present embodiment can be realized by the configuration shown in the first embodiment. As described above, according to the present embodiment, power consumption can be reduced in addition to the effects of the first embodiment.
[0027]
The present invention has been described based on the embodiments. The embodiments are exemplifications, and it is understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. . Such modified examples will be described.
[0028]
In the embodiment, the total injection amount ΔV required to reduce the control fuel pressure to the feed pressure is calculated, and the number of times of the step-down injection is performed based on the calculation result. However, the present invention is not limited to this. For example, the number of step-down injections necessary to reduce the control fuel pressure to the feed pressure may be set in advance as a fixed value with some allowance, and the step-down injection may be performed the set number of times. In this case, the calculation load of the ECU 30 can be reduced.
[0029]
In the embodiment, in order to reduce the control fuel pressure to the feed pressure, the step-down injection is performed. However, the present invention is not limited to this. For example, in the fuel supply device 40 shown in FIG. 1, the amount of fuel leakage from the injector 14 may be reduced by increasing the amount of fuel leakage from the check valve 11 of the high-pressure fuel pump 9. In this case, the discharge efficiency of the high-pressure fuel pump 9 decreases, but it can be dealt with by increasing the theoretical discharge amount.
[0030]
In the embodiment, the fuel discharged from the low-pressure fuel pump 3 is fed to the high-pressure fuel pipe via the high-pressure fuel pump 9, but is not limited to this. Although not shown, there is also a fuel supply device 40 having a bypass path provided with an electromagnetic valve from the low-pressure fuel pump 3 to the high-pressure fuel pipe and having a configuration not passing through the high-pressure fuel pump 9. Also in this configuration, the fuel may be fed from the low-pressure fuel pump 3 to the high-pressure fuel pipe via this bypass path during the pressure-lowering injection. In other words, the fuel supply device 40 has a certain degree of freedom as long as the fuel at the feed pressure is supplied to the high-pressure fuel pipe at the time of step-down injection.
[0031]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the abnormal combustion at the time of a stop and start of an internal combustion engine can be suppressed. Further, fuel leakage from the injector during the stop period of the internal combustion engine can be reduced. Further, deterioration of exhaust emissions at the time of starting the internal combustion engine can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of an internal combustion engine including a fuel supply device according to Embodiments 1 and 2.
FIG. 2 is a timing chart showing an operation of step-down injection when the internal combustion engine according to the first embodiment stops.
FIG. 3 is a flowchart illustrating a procedure of step-down injection performed when the internal combustion engine according to the first embodiment is stopped.
FIG. 4 is a timing chart showing a step-down injection operation when an internal combustion engine according to a second embodiment stops.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 internal combustion engine, 2 fuel tank, 3 low-pressure fuel pump, 9 high-pressure fuel pump, 13 delivery pipe, 14 a first injector, 14 b second injector, 14 c third injector, 14 d fourth injector, 15 engine body, 16 a first cylinder 16b 2nd cylinder, 16c 3rd cylinder, 16d 4th cylinder, 17 fuel pressure sensor, 20 ignition switch, 21 water temperature sensor, 30 ECU, 40 fuel supply device.

Claims (3)

A low-pressure fuel pump for pumping the fuel in the fuel tank; and a high-pressure fuel pump for pressurizing the fuel at a predetermined pressure pumped by the low-pressure fuel pump and pumping the fuel into a high-pressure fuel pipe. A fuel supply device for an internal combustion engine that supplies the fuel into the combustion chamber of the internal combustion engine via an injector,
When stopping the internal combustion engine, stopping the pressurizing operation of the high-pressure fuel pump and continuing the injection operation of the injector to reduce the fuel pressure in the high-pressure fuel pipe, and when reducing the fuel pressure, A fuel supply device for an internal combustion engine, comprising: fuel pressure reducing means for operating a low-pressure fuel pump to pump the fuel at the predetermined pressure into the high-pressure fuel pipe. The fuel pressure reducing means, when detecting a stop operation of the internal combustion engine, sets the number of injections of the injector based on a detection result of a fuel pressure in the high-pressure fuel pipe. A fuel supply device for an internal combustion engine according to claim 1. 3. The fuel supply device for an internal combustion engine according to claim 1, wherein the fuel pressure lowering unit activates the low-pressure fuel pump at least before an end of an injection operation of the injector. 4.

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