JP4066744B2 - Fuel supply device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel supply device for supplying fuel to an internal combustion engine, and in particular, the fuel in a fuel tank is once supplied to a high-pressure fuel pump by a low-pressure fuel pump, and further pumped and injected to an injector by a high-pressure fuel pump. The present invention relates to a fuel supply device to be supplied to
[0002]
[Prior art]
Gasoline engines that directly inject fuel into the cylinder (hereinafter also referred to as “direct-injection gasoline engines”) are expected to become more popular in the future because of their merit in fuel efficiency and output characteristics.
In a direct injection gasoline engine, a high pressure is required for the fuel injected from the injector in order to atomize the fuel effectively. For this reason, generally, the pressurization of the fuel has a two-stage configuration. First, the fuel in the fuel tank is pumped up by the low-pressure fuel pump, and at this time, the fuel is pulled up to a predetermined pressure (also referred to as feed pressure). Next, the fuel at the feed pressure is pressurized with a high-pressure fuel pump and pumped into the delivery pipe. The pressurization by the two pumps is continued during the operation of the engine. On the other hand, if the engine is stopped, the injection operation of the injector is usually stopped immediately, the two pumps are stopped, and the engine is stopped. For this reason, 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 engine stop period and adheres to the combustion chamber, particularly the piston, and can cause abnormal combustion the next time the engine is started. Abnormal combustion causes exhaust emission deterioration and knocking. In order to avoid this problem, in Japanese Patent Application Laid-Open No. 11-247734, when the internal combustion engine is stopped, the injection operation of the injector is continued to perform combustion in a state where the pumping of fuel into the delivery pipe is stopped, 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 publication, it is determined that the control fuel pressure has reached the required minimum pressure when a predetermined time has elapsed since the stop operation of the internal combustion engine was performed, and the step-down injection is stopped. However, since this determination is based on estimation, the actual control fuel pressure may be lower than the required minimum pressure. In this case, the injected fuel is not sufficiently atomized and abnormal combustion occurs during the step-down injection period. There is a possibility of inviting. That is, even if the stop timing of the step-down injection is controlled, the initial problem is not solved depending on the control accuracy.
[0005]
In addition, since a direct-injection gasoline engine is usually provided with a pressure sensor that measures the control fuel pressure, there is an idea to monitor the output of this sensor and continue the step-down injection until a desired pressure is reached. The range of the sensor is set for high pressure measurement, and is not suitable for measuring the pressure reduced by the pressure drop injection. On the other hand, if a separate sensor is provided for medium and low pressure control fuel pressure measurement, a new high-pressure seal design or the like is required, which is disadvantageous in terms of cost.
[0006]
The present invention has been made in view of the present situation, and an object of the present invention is to reduce the leakage of fuel from the injector during the stop period of an internal combustion engine of a type in which high fuel pressure is required for the fuel injected from the injector. It is to provide. Another object is to provide a technique for preventing abnormal combustion of fuel during step-down injection by controlling the control fuel pressure so as not to decrease too much when the control fuel pressure is reduced by step-down injection.
[0007]
[Means for Solving the Problems]
One embodiment of the present invention relates to a fuel supply apparatus. The fuel supply device includes 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 up by the low pressure fuel pump and pumps 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, and stops the pressurization operation of the high-pressure fuel pump and stops the injection operation of the injector when the internal combustion engine is stopped. A fuel pressure lowering means is provided for continuously lowering the fuel pressure in the high-pressure fuel pipe and operating the low-pressure fuel pump to pump fuel of a predetermined pressure into the high-pressure fuel pipe when the fuel pressure is lowered. The predetermined pressure is set so as not to cause abnormal combustion in the combustion chamber. The fuel pressure lowering means performs an injection operation of the injector so that the fuel pressure does not fall below a predetermined pressure.
[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 of a predetermined pressure is pumped into the high-pressure fuel pipe, and the control fuel pressure does not become less than the predetermined pressure. Here, the “high pressure fuel pipe” refers to a fuel path mainly 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 this case, the control fuel pressure is mechanically ensured not to decrease to a pressure that causes abnormal combustion. As a result, the control fuel pressure can be reduced while preventing abnormal combustion.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 schematically shows an internal combustion engine 1 that is a direct injection gasoline engine provided with a fuel supply device 40 according to an embodiment. The internal combustion engine 1 further includes an engine body 15. In this embodiment, the engine main body 15 includes 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), which limits the present invention. Not what you want. The fuel supply device 40 pressurizes the fuel pumped up by the low-pressure fuel pump 3 by the high-pressure fuel pump 9 and pumps it 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 and the second Each of the four injectors 14d (hereinafter collectively referred to as “injector 14” as appropriate) is directly injected into the corresponding cylinder 16. The pressure feeding timing by the high-pressure fuel pump 9 and the injection timing by the injector 14 are controlled by an electronic control unit (hereinafter referred to as ECU) 30. 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 ignition switch 20 may be of any type such as a key insertion type or a wireless authentication type carried by the user. The low-pressure fuel pump 3 is electrically driven by a battery, pumps up the fuel in the fuel tank 2 and feeds it from the discharge port to the 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 height that does not cause abnormal combustion even when the high-pressure fuel pump 9 does not operate, for example, 0.4 MPa. The filter 5 removes foreign matters from the fuel, and the pulsation damper 6 reduces fuel pulsation. The pumped fuel is supplied to the high pressure fuel pump 9 through the suction pipe 7 which is a low pressure fuel pipe.
[0012]
The high-pressure fuel pump 9 is mechanical, and boosts the fuel pressure in the delivery pipe 13 that is 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 pump cylinder in synchronization with the rotation of the pump cam 10a provided on the camshaft 10. The volume of the pump chamber 9b changes depending on 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 by the high-pressure fuel pump 9, the pump cam 10a slides the plunger 9a in the direction to reduce the volume of the pump chamber 9b, and in the fuel suction stroke, the spring in the direction to increase the volume of the pump chamber 9b. 9c slides the plunger 9a. The high pressure fuel pump 9 performs two discharge strokes while the pump cam 10a makes one rotation. The camshaft 10 and the crankshaft are connected via a reduction gear or the like, and the camshaft 10 is configured to rotate once when the crankshaft rotates twice. Therefore, the fuel is discharged every time the fuel injection of two cylinders out of the four cylinders is performed.
[0013]
The electromagnetic valve 8 drives the valve body 8c based on an opening / closing instruction from the ECU 30 to open / close the suction side opening 9d of the high-pressure fuel pump 9. The valve body 8c is biased by the spring 8a in the 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 in the intake stroke of the high-pressure fuel pump 9, and is closed by exciting the electromagnetic solenoid 8b in the discharge stroke. Thereby, during the intake 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 and pressurized. Pumped to fuel piping. A check valve 11 is provided in the discharge side opening 9e of the pump chamber 9b, and restricts the flow of fuel from the pump chamber 9b to 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 suddenly by a single fuel injection, and the pressure reduction is compensated for by a single discharge amount 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 for a 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 predetermined 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 electromagnetic valve 8 so that the fuel pressure in the delivery pipe 13 becomes the target pressure. Further, a water temperature sensor 21 that detects the temperature of the cooling water is provided, and the detection result is transmitted to the ECU 30. For ease of viewing, a part of broken lines indicating control from the ECU 30 to the injector 14 is omitted in the drawing.
[0016]
The return pipe 19 is provided with a relief valve 18. The relief valve 18 opens when the fuel pressure in the delivery pipe 13 exceeds, for example, 15 MPa, returns the fuel to the fuel tank 2, and acts as a high-pressure side 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 are stopped at the same time, the fuel pressure in the delivery pipe 13 is held 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 fuel leakage amount determined by the seal characteristics of the check valve 11, the injector 14, and the relief valve 18. In general, from the viewpoint of the discharge efficiency of the high-pressure fuel pump 9 and combustion feasibility, the seal characteristics are set to a value close to zero, so that the pressure in the high-pressure fuel pipe remains high 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 pressure-down injection is performed.
[0018]
FIG. 2 is a timing chart showing the operation of the internal combustion engine 1 during the step-down injection according to the present embodiment. FIG. 3 is a flowchart showing the procedure of step-down injection.
[0019]
When the ignition switch 20 is turned off and a stop signal for 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 solenoid valve 8 to the solenoid 8b is stopped. Subsequently, the ECU 30 performs the total 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 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 volume elastic modulus K of the fuel.
ΔV = (PH−PL) V / K
[0020]
Here, the bulk modulus K varies 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 volume elastic 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. To do. However, it is not necessary to calculate the total injection amount ΔV strictly, and the total injection amount ΔV may be calculated using the bulk modulus K as a fixed value.
[0021]
Subsequently, the ECU 30 calculates the step-down injection number n based on the calculated total injection amount ΔV (S16), and performs the step-down injection by the injector 14 according to the calculated injection number n. That is, the injection operation of the injector 14 performed at a predetermined injection timing is continued, and 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 fuel injection is performed by step-down injection. However, at this time, the operation of the low-pressure fuel pump 3 is continued. Thus, the number of injections n is calculated as a value obtained by dividing the total injection amount ΔV by the fuel injection amount per step-down injection, but n is set somewhat larger in consideration of the measurement error of the pressure sensor 17. However, the control fuel pressure does not become lower than the feed pressure PL.
[0023]
When the number of times of step-down injection does not reach the set value n (N in S20), fuel injection is continued (S18), and when it reaches n (Y in S20), the control fuel pressure is equal to the feed pressure PL. The ECU 30 stops fuel injection and 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 fuel pressure 1/2 power. 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 drops to 1/5 to 1/6. In addition, it is possible to avoid a decrease in the control fuel pressure that is more than necessary due to the low pressure 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 is stopped and the operation of the low-pressure fuel pump 3 is continued during the low-pressure injection. However, the low-pressure fuel pump 3 can be temporarily stopped during the step-down injection from the viewpoint of reducing the 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 again before reaching the calculated injection number n, that is, before the end of the step-down injection. The timing of resumption takes some margin into account. Hereinafter, the 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 will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. . Examples of such modifications are given.
[0028]
In the embodiment, the total injection amount ΔV required to reduce the control fuel pressure to the feed pressure is calculated, and the step-down injection is performed the number of times based on the calculation result, but the present invention is not limited to this. For example, the number of step-down injections required to reduce the control fuel pressure to the feed pressure may be set in advance as a fixed value with some margin, and the step-down injection may be performed for the set number of times. In this case, the calculation load on the ECU 30 can be reduced.
[0029]
In the embodiment, the pressure-lowering injection is performed in order to reduce the control fuel pressure to the feed pressure. 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, although the discharge efficiency of the high-pressure fuel pump 9 is lowered, 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 the present invention is not limited to this. Although not shown, there is also a fuel supply device 40 that has a bypass path in which an electromagnetic valve is provided from the low pressure fuel pump 3 to the high pressure fuel pipe and does not pass through the high pressure fuel pump 9. Even in this configuration, the fuel may be fed from the low-pressure fuel pump 3 to the high-pressure fuel pipe via the bypass path at the time of the step-down injection. That is, as long as the fuel at the feed pressure is supplied to the high-pressure fuel pipe at the time of the step-down injection, the configuration of the fuel supply device 40 is flexible.
[0031]
【The invention's effect】
According to the present invention, it is possible to suppress the occurrence of abnormal combustion when the internal combustion engine is stopped and started. Further, fuel leakage from the injector during the stop period of the internal combustion engine can be reduced. Furthermore, it is possible to suppress the deterioration of exhaust emission when starting the internal combustion engine.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of an internal combustion engine provided with a fuel supply device according to Embodiments 1 and 2. FIG.
FIG. 2 is a timing chart showing the operation of step-down injection when the internal combustion engine according to Embodiment 1 stops.
FIG. 3 is a flowchart showing a procedure of step-down injection performed when the internal combustion engine according to Embodiment 1 is stopped.
FIG. 4 is a timing chart showing the operation of step-down injection when the internal combustion engine according to Embodiment 2 stops.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion engine, 2 Fuel tank, 3 Low pressure fuel pump, 9 High pressure fuel pump, 13 Delivery pipe, 14a 1st injector, 14b 2nd injector, 14c 3rd injector, 14d 4th injector, 15 Engine main body, 16a 1st 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 that pumps up fuel in a fuel tank; and a high-pressure fuel pump that pressurizes and pumps fuel at a predetermined pressure pumped up by the low-pressure fuel pump into a high-pressure fuel pipe. In a fuel supply device for an internal combustion engine that supplies fuel to the combustion chamber of the internal combustion engine via an injector,
When the internal combustion engine is stopped, the pressurization operation of the high-pressure fuel pump is stopped and the injection operation of the injector is continued to reduce the fuel pressure in the high-pressure fuel pipe, and when the fuel pressure is reduced, A fuel pressure lowering means for operating a low-pressure fuel pump to pump the fuel of the predetermined pressure into the high-pressure fuel pipe ;
The predetermined pressure is set so as not to cause abnormal combustion in the combustion chamber,
The fuel supply device for an internal combustion engine, wherein the fuel pressure lowering means performs an injection operation of the injector so that the fuel pressure does not fall below the predetermined pressure . The fuel pressure reducing means is a total injection required to reduce the fuel pressure to the predetermined pressure based on a detection result of the fuel pressure in the high-pressure fuel pipe when a stop operation of the internal combustion engine is detected. 2. The fuel supply device for an internal combustion engine according to claim 1, wherein an amount of fuel is calculated and the number of injections of the injector is set based on the calculated total injection amount .   3. The fuel supply device for an internal combustion engine according to claim 1, wherein the fuel pressure lowering unit puts the low-pressure fuel pump into an operating state at least before an end of an injection operation of the injector.

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