JP2013083184A - Fuel injection system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change pressure of fuel injected into an intake passage in a fuel injection system for an internal combustion engine including a low-pressure fuel pump and a high-pressure fuel pump.SOLUTION: The fuel injection system for the internal combustion engine sequentially includes: the low-pressure fuel pump 1; the high-pressure fuel pump 2; a high-pressure fuel injection valve 7; a pressure reduction device 9 for reducing the pressure of the fuel to a setting pressure; and a low-pressure fuel injection valve 12. Moreover, the fuel injection system includes a communication passage 17 which communicates the low-pressure fuel pump 1 with the low-pressure fuel injection valve 12 by bypassing the high-pressure fuel pump 2, a check valve 18 which is provided in the communication passage 17 and only passes the fuel from the side of the low-pressure fuel pump 1 to the side of the low-pressure fuel injection valve, a return passage 13 which connects an upstream side and an downstream side from the low-pressure fuel pump 1, and a safety valve 14 which is provided in the return passage 13 and is opened to make the fuel flow when the pressure of the fuel at the downstream side from the low-pressure fuel pump 1 is not lower than a predetermined pressure that is higher than the setting pressure, and is closed to interrupt the flow of the fuel when the pressure is lower than the predetermined one.

Description

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

  In a fuel injection system for an internal combustion engine that directly injects fuel into a cylinder, a low-pressure fuel pump that sucks up fuel from a fuel tank, and a high-pressure fuel pump that boosts the fuel sucked up by the low-pressure fuel pump to a pressure that can be injected into the cylinder; It is known to comprise.

  Patent Document 1 describes a technique in which a low-pressure fuel pump, a high-pressure fuel pump, a high-pressure delivery pipe, and a low-pressure delivery pipe are connected in series in this order and the fuel pressure is adjusted downstream of the high-pressure delivery pipe. According to this technique, fuel is supplied from the low-pressure delivery pipe to the intake passage injector, and fuel is supplied from the high-pressure delivery pipe to the in-cylinder injector.

  However, in the configuration described in Patent Document 1, since the pressure when fuel is injected into the intake passage is fixed, the available operating states are limited. For example, if the fuel pressure is fixed at a high pressure, the fuel is injected into the intake passage at a high pressure, which may make it difficult to inject a small amount of fuel. Conversely, if the fuel pressure is fixed at a low pressure, the fuel is injected into the intake passage at a low pressure, which may make it difficult to promote atomization of the fuel.

JP 2006-144666 A JP 2006-016989 A Japanese Patent Laid-Open No. 2003-074441 JP 2010-024853 A JP 2008-231919 A

  The present invention has been made in view of the above circumstances, and an object thereof is to change the pressure of fuel injected into an intake passage in a fuel injection system of an internal combustion engine including a low pressure fuel pump and a high pressure fuel pump. There is.

In order to achieve the above object, a fuel injection system for an internal combustion engine according to the present invention comprises:
A low-pressure fuel pump that discharges fuel in the fuel tank;
A high-pressure fuel pump for boosting and discharging the fuel discharged from the low-pressure fuel pump;
A high-pressure fuel injection valve that is provided downstream of the high-pressure fuel pump and injects fuel discharged from the high-pressure fuel pump;
A pressure reducing device for reducing the pressure of the fuel to a set pressure downstream of the high pressure fuel injection valve;
A low pressure fuel injection valve that is provided downstream of the pressure reducing device and injects fuel at a lower pressure than the high pressure fuel injection valve;
A communication path that bypasses the high-pressure fuel pump and communicates the low-pressure fuel pump and the low-pressure fuel injection valve;
A check valve that is provided in the communication path and allows fuel to pass only from the low-pressure fuel pump side to the low-pressure fuel injection valve side;
A return passage connecting the fuel passage downstream from the low-pressure fuel pump and upstream from the high-pressure fuel pump and the upstream from the low-pressure fuel pump;
Provided in the return passage, and is opened when the pressure of the fuel on the downstream side of the low-pressure fuel pump and the upstream side of the high-pressure fuel pump is equal to or higher than a predetermined pressure higher than the set pressure; A safety valve that closes and shuts off the flow of fuel when less than the predetermined pressure;
Is provided.

  The low pressure fuel injection valve injects fuel at a lower pressure than the high pressure fuel injection valve. The low-pressure fuel injection valve injects fuel into an intake passage such as an intake port or an intake manifold. The high pressure fuel injection valve injects fuel into, for example, a cylinder. The fuel discharged from the low pressure fuel pump is boosted to a pressure suitable for injection from the high pressure fuel injection valve by the high pressure fuel pump. The fuel that has not been injected from the high-pressure fuel injection valve is reduced in pressure by the decompression device and supplied to the low-pressure fuel injection valve. In the pressure reducing device, the pressure of the fuel is reduced to a pressure suitable for injection from the low pressure fuel injection valve. That is, the pressure of the fuel supplied to the low pressure fuel injection valve is adjusted by the pressure reducing device.

  On the other hand, when the amount of fuel discharged from the low-pressure fuel pump is increased, the pressure of the fuel downstream of the low-pressure fuel pump and upstream of the high-pressure fuel pump (hereinafter also referred to as feed pressure) increases. When the feed pressure becomes higher than the set pressure in the pressure reducing device, the check valve opens. That is, when the feed pressure becomes higher than the set pressure, the pressure on the low-pressure fuel pump side becomes higher than the pressure on the low-pressure fuel injection valve side, so that the low-pressure fuel pump does not go through the high-pressure fuel pump. Fuel is supplied. That is, there are two paths for supplying fuel to the low-pressure fuel injection valve: a path for supplying fuel via the pressure reducing device and a path for supplying fuel via the communication path.

  And the path | route which supplies fuel to a low pressure fuel injection valve can be switched by adjusting feed pressure. The pressure of the fuel supplied by these two paths is different. That is, the pressure of the fuel supplied through the communication passage is higher than the set pressure in the decompression device. For this reason, the pressure of the fuel injected from the low pressure fuel injection valve can be changed by adjusting the feed pressure.

  Here, the safety valve opens to allow the fuel to flow when the pressure is higher than a predetermined pressure higher than the set pressure. At this time, the feed pressure becomes a predetermined pressure. That is, if the amount of fuel discharged from the low-pressure fuel pump is increased to make the feed pressure equal to or higher than the predetermined pressure, the pressure of the fuel supplied to the low-pressure fuel injection valve can be made constant at the predetermined pressure. And by supplying the fuel directly from the low pressure fuel pump to the low pressure fuel injection valve, it becomes possible to supply a relatively high pressure fuel. Can also cope with this.

  In addition, when there is a request to inject low pressure fuel from the low pressure fuel injection valve, the check valve closes if the amount of fuel discharged from the low pressure fuel pump is reduced and the feed pressure is set below the set pressure. The fuel at the set pressure is supplied to the low pressure fuel injection valve via the pressure reducing device. At this time, the power consumption of the low-pressure fuel pump may be reduced by reducing the feed pressure as much as possible. In this way, the pressure of the fuel injected from the low pressure fuel injection valve can be changed.

In the present invention, the low-pressure fuel pump operates by supplying power,
A determination unit may be provided that determines whether or not the safety valve is open based on at least one of a voltage and a current when the low-pressure fuel pump is energized.

Since the pressure of the fuel supplied to the low-pressure fuel pump is switched by adjusting the discharge amount of the low-pressure fuel pump, it is not necessary to operate the check valve or the pressure reducing device. Here, if the determination of whether or not the fuel pressure is switched is performed by detecting the fuel pressure, it is necessary to install a sensor, which increases the cost. Therefore, it is determined whether or not the fuel pressure is switched based on at least one of the voltage and current supplied to the low-pressure fuel pump. Here, the voltage and current when the low-pressure fuel pump is energized are proportional to the fuel pressure. Therefore, the fuel pressure can be estimated based on at least one of the voltage or current of electricity flowing through the low-pressure fuel pump. Thereby, it can be determined whether or not the fuel pressure is switched. For example, when the voltage or current is greater than or equal to a predetermined value, it can be determined that the check valve is open. This predetermined value can be a voltage or current value at which the feed pressure becomes the valve opening pressure of the check valve.

  In the present invention, an upper limit setting unit that sets an upper limit value of the change rate of the pressure of the fuel downstream of the high pressure fuel pump and upstream of the pressure reducing device may be provided.

  That is, an upper limit guard is provided for the change speed of the fuel pressure. Here, when the change rate of the discharge pressure of the fuel from the high-pressure fuel pump becomes high, the change range of the fuel pressure in the low-pressure fuel injection valve becomes large. There is a possibility that the fuel ratio fluctuates. In contrast, by suppressing the change speed of the fuel pressure on the high pressure fuel pump side, the change width of the pressure of the fuel supplied to the low pressure fuel injection valve can be reduced, so that the fluctuation of the air-fuel ratio can be suppressed.

  In the present invention, the upper limit value setting unit can set an upper limit value of the change speed of the fuel pressure when there is a request to inject fuel from the low pressure fuel injection valve.

  That is, if the fuel is not injected from the low-pressure fuel injection valve, the air-fuel ratio does not fluctuate even if the pressure of the fuel on the low-pressure side fluctuates. In such a case, the pressure of the fuel injected from the high-pressure fuel injection valve can be quickly adjusted by increasing the change rate of the pressure of the fuel discharged from the high-pressure fuel pump.

  In the present invention, when the change speed of the fuel pressure downstream of the high-pressure fuel pump and upstream of the pressure reducing device exceeds a predetermined speed, fuel injection from the low-pressure fuel injection valve is performed. It is possible to provide a prohibition unit that prohibits

  By prohibiting fuel injection in this way, fluctuations in the air-fuel ratio due to fluctuations in the amount of fuel injected from the low-pressure fuel injection valve can be prevented. Since the fuel pressure stabilizes over time, fuel injection may be prohibited for a predetermined period during which the fuel pressure stabilizes. The predetermined speed may be the same value as the upper limit value.

  According to the present invention, in a fuel injection system for an internal combustion engine including a low pressure fuel pump and a high pressure fuel pump, the pressure of fuel injected into the intake passage can be changed.

It is a figure which shows schematic structure of the fuel-injection system of an internal combustion engine. It is the time chart which showed transition of the high pressure fuel pressure when the change speed of the high pressure fuel pressure exceeds the upper limit guard, and the low pressure fuel pressure for port injection. It is the time chart which showed transition of the high pressure fuel pressure and the low pressure fuel pressure for port injection when the change rate of the high pressure fuel pressure is below the upper limit guard.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of a fuel injection system for an internal combustion engine. The fuel injection control system shown in FIG. 1 is a fuel injection control system applied to an in-line four-cylinder internal combustion engine, and includes a low-pressure fuel pump 1 and a high-pressure fuel pump 2. Note that the number of cylinders of the internal combustion engine is not limited to four, and may be five or more, or may be three or less.

  The low-pressure fuel pump 1 is provided in the fuel tank 3. The low-pressure fuel pump 1 is a pump for pumping up fuel stored in the fuel tank 3 and is a turbine pump (Wesco pump) driven by electric power. One end of the low-pressure fuel passage 4 is connected to the low-pressure fuel pump 1, and the other end of the low-pressure fuel passage 4 is connected to the high-pressure fuel pump 2. The fuel discharged from the low-pressure fuel pump 1 is guided to the suction port of the high-pressure fuel pump 2 through the low-pressure fuel passage 4.

  The high-pressure fuel pump 2 is a pump for boosting the fuel discharged from the low-pressure fuel pump 1, and is a reciprocating pump (plunger pump) driven by the power of the internal combustion engine (for example, the rotational force of the camshaft). ). The amount of fuel discharged from the high-pressure fuel pump 2 (which may be the discharge pressure) is adjusted by the ECU 30 described later. One end of the high-pressure fuel passage 5 is connected to the discharge port of the high-pressure fuel pump 2. The other end of the high pressure fuel passage 5 is connected to a high pressure delivery pipe 6.

  Four high-pressure fuel injection valves 7 are connected to the high-pressure delivery pipe 6, and high-pressure fuel pumped from the high-pressure fuel pump 2 to the high-pressure delivery pipe 6 is distributed to each high-pressure fuel injection valve 7. The high pressure fuel injection valve 7 injects fuel into the cylinder of the internal combustion engine.

  In addition, one end of a high-pressure fuel discharge passage 8 is connected to the high-pressure delivery pipe 6. The other end of the high-pressure fuel discharge passage 8 is connected to the inlet side of the decompression device 9 that reduces the fuel pressure. The decompression device 9 reduces the fuel pressure so that the fuel pressure becomes the set pressure when the fuel flows from the high-pressure fuel discharge passage 8 side to the decompression fuel passage 10 side. In this embodiment, it is assumed that the set pressure cannot be changed. One end of the decompression fuel passage 10 is connected to the outlet side of the decompression device 9. The pressure of the fuel in the high pressure fuel passage 5, the pressure of the fuel in the high pressure delivery pipe 6, the pressure of the fuel in the high pressure fuel discharge passage 8, and the pressure of the fuel injected from the high pressure fuel injection valve 7 are substantially the same. Become.

  The other end of the decompression fuel passage 10 is connected to a low pressure delivery pipe 11. Four low-pressure fuel injection valves 12 are connected to the low-pressure delivery pipe 11, and the fuel decompressed by the decompression device 9 is distributed to each low-pressure fuel injection valve 12. The low pressure fuel injection valve 12 injects fuel into an intake passage (for example, an intake port or a surge tank, an intake manifold) of the internal combustion engine.

  One end of the low pressure return passage 13 is connected to the low pressure fuel passage 4 in the middle. The other end of the low pressure return passage 13 is connected to the fuel tank 3. When the fuel passage is provided on the upstream side of the low pressure fuel pump 1, the other end of the low pressure return passage 13 may be connected to the fuel passage on the upstream side of the low pressure fuel pump 1. A low pressure safety valve 14 is provided in the middle of the low pressure return passage 13. The low-pressure safety valve 14 opens when the pressure (feed pressure) in the low-pressure fuel passage 4 exceeds a predetermined pressure. As a result, surplus fuel in the low pressure fuel passage 4 is returned to the fuel tank 3 via the low pressure return passage 13.

  One end of a high pressure return passage 15 is connected to the high pressure fuel discharge passage 8. The other end of the high pressure return passage 15 is connected in the middle of the low pressure fuel passage 4. A high-pressure safety valve 16 is provided in the middle of the high-pressure return passage 15. The high-pressure safety valve 16 allows the flow from the high-pressure fuel discharge passage 8 side to the low-pressure fuel passage 4 side and blocks the reverse flow. The high pressure safety valve 16 is opened when the pressure in the high pressure fuel discharge passage 8 (high pressure fuel pressure) exceeds a predetermined value. As a result, surplus fuel in the high-pressure fuel discharge passage 8 is returned to the low-pressure fuel passage 4 via the high-pressure return passage 15.

  In addition, one end of the communication path 17 is connected midway in the low-pressure fuel path 4. The other end of the communication path 17 is connected to the low pressure delivery pipe 11. A check valve 18 is provided in the middle of the communication path 17. The check valve 18 allows a flow from the low-pressure fuel passage 4 side to the low-pressure delivery pipe 11 side, and blocks a reverse flow. The check valve 18 opens when the fuel pressure in the low pressure fuel passage 4 becomes higher than the fuel pressure in the low pressure delivery pipe 11.

  In addition, one end of a leak throttle passage 19 is connected in the middle of the low pressure fuel passage 4, and the other end of the leak throttle passage 19 is connected in the middle of the communication passage 17 on the low pressure delivery pipe 11 side than the check valve 18. Has been. A throttle 20 is provided in the middle of the leak throttle passage 19 to allow a very small amount of fuel to flow.

  In this embodiment, the ECU 30 is provided for controlling the above-described devices. The ECU 30 is an electronic control device that includes a CPU, a ROM, a RAM, a backup RAM, and the like. The ECU 30 is electrically connected to various sensors such as a pressure sensor 31, an accelerator position sensor 32, and a crank position sensor 33.

  The pressure sensor 31 is a sensor that is attached to the high-pressure delivery pipe 6 and outputs an electrical signal correlated with the fuel pressure in the high-pressure delivery pipe 6 (discharge pressure of the high-pressure fuel pump). According to the pressure sensor 31, the pressure of the fuel injected from the high pressure fuel injection valve 7 can be detected. The accelerator position sensor 32 outputs an electrical signal correlated with the amount of operation of the accelerator pedal (accelerator opening). The load of the internal combustion engine is detected from the output signal of the accelerator position sensor 32. The crank position sensor 33 is a sensor that outputs an electrical signal correlated with the rotational position of the output shaft (crankshaft) of the internal combustion engine. From the output signal of the crank position sensor 33, the rotational speed of the internal combustion engine is detected.

  The ECU 30 controls the low-pressure fuel pump 1 and the high-pressure fuel pump 2 based on the output signals from the various sensors described above. For example, the ECU 30 adjusts the fuel discharge amount from the high-pressure fuel pump 2 so that the detection value (actual fuel pressure) of the pressure sensor 31 converges to the target value. At that time, the ECU 30 performs proportional integral control (PI control) based on the difference between the actual fuel pressure and the target value by changing the drive duty of the high-pressure fuel pump 2 (ratio of solenoid energization time and non-energization time). Do. Further, the ECU 30 controls the fuel injection amount from the high pressure fuel injection valve 7 and the low pressure fuel injection valve 12 by controlling the energization time to the high pressure fuel injection valve 7 and the low pressure fuel injection valve 12.

Here, in this embodiment, the set pressure of the decompression device 9 is a constant value and cannot be changed. That is, when the fuel passing through the pressure reducing device 9 is injected from the low pressure fuel injection valve 12, the pressure of the injected fuel cannot be changed. By the way, when the internal combustion engine is started in a high temperature state or when the demand for atomization of the fuel is high, it is effective to inject fuel having a relatively high pressure from the low pressure fuel injection valve 12. If the set pressure of the pressure reducing device 9 is determined so as to achieve such a relatively high pressure, it becomes difficult to inject fuel at a relatively low pressure from the low pressure fuel injection valve 12. In this case, for example, the minimum amount of fuel that can be injected from the low-pressure fuel injection valve 12 (minimum injection amount) becomes large, so the opportunities for using the low-pressure fuel injection valve 12 are limited.

  On the other hand, in this embodiment, a communication passage 17 and a check valve 18 are provided. In this embodiment, the valve opening pressure (predetermined pressure) of the low-pressure safety valve 14 is set higher than the set pressure of the pressure reducing device 9. Furthermore, when there is a request to inject fuel from the low pressure fuel injection valve 12 at a relatively low pressure, the low pressure fuel pump 1 is driven so that the feed pressure is lower than the set pressure of the pressure reducing device 9. At this time, since the pressure on the low pressure delivery pipe 11 side becomes higher than the low pressure fuel passage 4 side, the check valve 18 blocks the fuel flow in the communication passage 17. The pressure of the fuel in the low pressure delivery pipe 11 becomes the pressure after being adjusted by the decompression device 9. That is, the pressure of the fuel in the low pressure delivery pipe 11 becomes equal to the set pressure of the decompression device 9. In this case, since the pressure of the fuel injected from the low pressure fuel injection valve 12 is adjusted to a relatively low pressure, the minimum injection amount can be further reduced.

  When there is a request to inject fuel from the low pressure fuel injection valve 12 at a relatively low pressure, the pressure of the fuel injected from the low pressure fuel injection valve 12 becomes the set pressure of the decompression device 9, so the feed pressure is the minimum necessary You may reduce to the value of. Note that the minimum necessary value of the feed pressure may be a lower limit value of the feed pressure at which no vapor is generated. By doing in this way, since the power consumption of the low pressure fuel pump 1 can be reduced as much as possible, the fuel consumption can be improved.

  On the other hand, when the internal combustion engine is started in a high temperature state or when there is a high demand for atomization of fuel, there is a request to inject fuel from the low pressure fuel injection valve 12 at a relatively high pressure. When there is such a request, the low-pressure fuel pump 1 is driven so that the feed pressure becomes higher than the set pressure of the pressure reducing device 9. At this time, the check valve 18 is opened because the pressure on the low pressure delivery pipe 11 side is lower than the pressure on the low pressure fuel passage 4 side. Then, the fuel flows from the low pressure fuel passage 4 side to the low pressure delivery pipe 11 side through the communication passage 17. At this time, the pressure of the fuel in the low pressure delivery pipe 11 becomes the same as the feed pressure, and the pressure of the fuel in the low pressure delivery pipe 11 is adjusted by manipulating the discharge amount of the low pressure fuel pump 1. The feed pressure may be increased until the low pressure safety valve 14 is opened. Then, the pressure of the fuel in the low pressure delivery pipe 11 becomes a predetermined pressure that is the valve opening pressure of the low pressure safety valve 14. Thus, since the pressure of the fuel injected from the low pressure fuel injection valve 12 is adjusted to a relatively high pressure, atomization of the fuel can be promoted.

  Thus, by manipulating the amount of fuel discharged from the low-pressure fuel pump 1, the fuel pressure in the low-pressure delivery pipe 11 can be adjusted to one of the set pressure or the feed pressure of the decompression device 9. That is, fuels having different pressures can be injected from the low pressure fuel injection valve 12. The amount of fuel discharged from the low-pressure fuel pump 1 can be adjusted by operating the drive duty of the low-pressure fuel pump 1. Further, the amount of fuel discharged from the low-pressure fuel pump 1 may be adjusted by operating the power supplied to the low-pressure fuel pump 1.

The feed pressure when the feed pressure is set higher than the set pressure of the decompression device 9 may be set according to the required value of the pressure of the fuel injected from the low pressure fuel injection valve 12. Further, when fuel of a relatively high pressure is injected from the low pressure fuel injection valve 12, the pressure of the fuel injected from the low pressure fuel injection valve 12 may be adjusted by operating the feed pressure. Alternatively, the discharge amount of the low-pressure fuel pump 1 may be increased so that the feed pressure increases so that the low-pressure safety valve 14 can be opened, and fuel at a relatively high pressure may be injected from the low-pressure fuel injection valve 12. In this case, the predetermined pressure which is the valve opening pressure of the low-pressure safety valve 14 becomes the fuel pressure in the low-pressure delivery pipe 11. At this time, if the low-pressure fuel pump 1 is driven so as to open the low-pressure safety valve 14, the pressure of the fuel in the low-pressure delivery pipe 11 becomes constant, so that fine control of the discharge amount of the low-pressure fuel pump 1 becomes unnecessary. .

  By making the pressure at which the low pressure safety valve 14 opens higher than the set pressure of the pressure reducing device 9, it is possible to prevent the low pressure safety valve 14 from opening before the check valve 18 is opened. The pressure at which the low-pressure safety valve 14 opens may be determined in consideration of the durability of the device while being higher than the set pressure of the pressure reducing device 9.

  Since the low pressure delivery pipe 11 is not provided with a pressure sensor, it is not possible to directly detect what value the actual fuel pressure is. In contrast, in this embodiment, the state of the fuel pressure in the low-pressure delivery pipe 11 is estimated based on at least one of a voltage and a current when the low-pressure fuel pump 1 is energized.

  Here, the voltage or current applied to the low-pressure fuel pump 1 when power is supplied to the low-pressure fuel pump 1 is proportional to the feed pressure. In particular, the current value has a high correlation with the fuel pressure. In this embodiment, an experiment is performed in advance using the low-pressure fuel pump 1 in a state where the fuel discharge capacity is reduced to the lower limit of the allowable range, and the voltage and current when the low-pressure safety valve 14 is opened are measured as threshold values. Keep it. Then, it is possible to determine whether or not the low-pressure safety valve 14 is open by comparing the actual voltage or current with the threshold value. That is, it can be determined whether or not the fuel pressure in the low pressure delivery pipe 11 is relatively high. Further, the relationship between the voltage or current and the feed pressure may be obtained in advance through experiments or the like and stored in the ECU 30. In this embodiment, the ECU 30 that determines whether or not the low-pressure safety valve 14 is open corresponds to the determination unit in the present invention.

  As described above, according to the present embodiment, a relatively high pressure fuel and a relatively low pressure fuel can be injected from the low pressure fuel injection valve 12. That is, the pressure of the fuel injected into the intake passage can be changed. Thereby, the driving | running state which can use the low pressure fuel injection valve 12 can be expanded.

<Example 2>
In this embodiment, an upper limit value is set for the change rate (change amount per unit time) of the discharge pressure of the high-pressure fuel pump 2 (hereinafter referred to as high-pressure fuel pressure). That is, it guards with an upper limit (provides an upper limit guard). The high pressure fuel pressure is the pressure of the fuel in the high pressure fuel passage 5, the pressure of the fuel in the high pressure delivery pipe 6, the pressure of the fuel in the high pressure fuel discharge passage 8, or the fuel injected from the high pressure fuel injection valve 7. It is good also as a pressure. Since other devices are the same as those in the first embodiment, the description thereof is omitted.

  Here, the high-pressure fuel pressure varies, for example, from about 4 to 12 MPa depending on the operating state. This change in the high-pressure fuel pressure is detected by the pressure sensor 31 and the energization time of the high-pressure fuel injection valve 7 is corrected. For this reason, even if the high pressure fuel pressure changes, fluctuations in the amount of fuel injected from the high pressure fuel injection valve 7 are suppressed.

  However, the fuel pressure of the low pressure fuel injection valve 12 is generally adjusted by a mechanical relief valve, for example, a pressure of 300 to 400 kPa. In this case, there is no correction of the fuel injection amount by the pressure sensor. Here, in the configuration where the pressure reducing device 9 reduces the pressure to the set pressure, when the high pressure fuel pressure fluctuates, the pressure reducing device 9 cannot remove the fuel pressure fluctuation, so the fuel pressure in the pressure reducing fuel passage 10 is also reduced. Will fluctuate. For this reason, if there is no mechanism for adjusting the pressure of the fuel injected from the low pressure fuel injection valve 12 or means for correcting the fuel injection amount, the air-fuel ratio fluctuates, the engine performance decreases, There is a possibility that many harmful substances are contained in the exhaust.

  On the other hand, in the present embodiment, since the upper limit guard is provided for the change speed of the high-pressure fuel pressure, the change speed of the high-pressure fuel pressure can be suppressed below the upper limit guard. The upper limit guard is used as an upper limit value of the change speed of the high pressure fuel pressure so that the fluctuation of the fuel pressure in the low pressure delivery pipe 11 (hereinafter also referred to as port injection low pressure fuel pressure) is within an allowable range. It asks by. The change rate of the high-pressure fuel pressure can be lowered by, for example, reducing the drive duty of the high-pressure fuel pump 2 or limiting the change rate of the target high-pressure fuel pressure.

  Here, FIG. 2 is a time chart showing the transition of the high pressure fuel pressure and the low pressure fuel pressure for port injection when the change speed of the high pressure fuel pressure exceeds the upper limit guard. FIG. 3 is a time chart showing the transition of the high pressure fuel pressure and the low pressure fuel pressure for port injection when the rate of change of the high pressure fuel pressure is equal to or lower than the upper limit guard. As shown in FIG. 3, when the upper limit guard is provided, the increasing speed and decreasing speed of the high-pressure fuel pressure are lower than in the case shown in FIG. For this reason, the fluctuation of the low pressure fuel pressure for port injection is smaller in the case shown in FIG. 3 than in the case shown in FIG.

  Thus, since the change of the low pressure fuel pressure for port injection can be suppressed by the change of the high pressure fuel pressure, the change of the air-fuel ratio can be suppressed. In this embodiment, the ECU 30 that sets the upper limit guard for the change rate of the high-pressure fuel pressure corresponds to the upper limit setting unit in the present invention.

  Note that the upper limit guard may be provided for the change speed of the high pressure fuel pressure only when there is a request to inject fuel from the low pressure fuel injection valve 12. This may be limited to when fuel is injected from the low pressure fuel injection valve 12. That is, if fuel is not injected from the low pressure fuel injection valve 12, there is no problem even if the low pressure fuel pressure for port injection fluctuates. Moreover, if the upper limit guard is not provided for the change speed of the high-pressure fuel pressure, the high-pressure fuel pressure can be changed quickly, so that the high-pressure fuel pressure can be quickly adjusted to the target value.

  Further, instead of providing an upper limit guard for the change speed of the high pressure fuel pressure, fuel injection from the low pressure fuel injection valve 12 may be prohibited when the change speed of the high pressure fuel pressure exceeds a predetermined speed. The predetermined speed here can be set to the same value as the upper limit guard. In this way, by prohibiting fuel injection from the low-pressure fuel injection valve 12, it is possible to suppress fuel injection when the fluctuation of the low-pressure fuel pressure for port injection exceeds the allowable range. Can be suppressed. The low pressure fuel pressure for port injection is stabilized over time due to the effect of the throttle 20. Therefore, fuel injection from the low pressure fuel injection valve 12 may be prohibited only during a period until the low pressure fuel pressure for port injection is stabilized. During this period, an optimum value can be obtained by experiments or the like. In the period during which fuel injection from the low pressure fuel injection valve 12 is prohibited, the fuel shortage can be compensated by injecting that much fuel from the high pressure fuel injection valve 7. In the present embodiment, the ECU 30 that prohibits fuel injection from the low-pressure fuel injection valve 12 corresponds to a prohibition unit in the present invention.

DESCRIPTION OF SYMBOLS 1 Low pressure fuel pump 2 High pressure fuel pump 3 Fuel tank 4 Low pressure fuel passage 5 High pressure fuel passage 6 High pressure delivery pipe 7 High pressure fuel injection valve 8 High pressure fuel discharge passage 9 Pressure reduction device 10 Pressure reduction fuel passage 11 Low pressure delivery pipe 12 Low pressure fuel injection valve 13 Low pressure return passage 14 Low pressure safety valve 15 High pressure return passage 16 High pressure safety valve 17 Communication passage 18 Check valve 19 Leak restrictor passage 20 Restrictor 30 ECU
31 Pressure sensor 32 Accelerator position sensor 33 Crank position sensor

Claims (5)

A low-pressure fuel pump that discharges fuel in the fuel tank;
A high-pressure fuel pump for boosting and discharging the fuel discharged from the low-pressure fuel pump;
A high-pressure fuel injection valve that is provided downstream of the high-pressure fuel pump and injects fuel discharged from the high-pressure fuel pump;
A pressure reducing device for reducing the pressure of the fuel to a set pressure downstream of the high pressure fuel injection valve;
A low pressure fuel injection valve that is provided downstream of the pressure reducing device and injects fuel at a lower pressure than the high pressure fuel injection valve;
A communication path that bypasses the high-pressure fuel pump and communicates the low-pressure fuel pump and the low-pressure fuel injection valve;
A check valve that is provided in the communication path and allows fuel to pass only from the low-pressure fuel pump side to the low-pressure fuel injection valve side;
A return passage connecting the fuel passage downstream from the low-pressure fuel pump and upstream from the high-pressure fuel pump and the upstream from the low-pressure fuel pump;
Provided in the return passage, and is opened when the pressure of the fuel on the downstream side of the low-pressure fuel pump and the upstream side of the high-pressure fuel pump is equal to or higher than a predetermined pressure higher than the set pressure; A safety valve that closes and shuts off the flow of fuel when less than the predetermined pressure;
A fuel injection system for an internal combustion engine. The low-pressure fuel pump operates by supplying power,
2. The fuel injection system for an internal combustion engine according to claim 1, further comprising a determination unit that determines whether or not the safety valve is open based on at least one of a voltage and a current when the low-pressure fuel pump is energized.   3. The fuel injection system for an internal combustion engine according to claim 1, further comprising an upper limit value setting unit that sets an upper limit value of a change speed of the pressure of the fuel downstream of the high-pressure fuel pump and upstream of the pressure reducing device. .   The fuel injection system for an internal combustion engine according to claim 3, wherein the upper limit value setting unit sets an upper limit value of a change speed of the pressure of the fuel when there is a request to inject fuel from the low pressure fuel injection valve.   A prohibition unit that prohibits fuel injection from the low-pressure fuel injection valve when the rate of change of the pressure of the fuel downstream of the high-pressure fuel pump and upstream of the decompression device exceeds a predetermined speed; The fuel injection system for an internal combustion engine according to claim 1 or 2.

Images