JP5716684B2 - Fuel injection control system for internal combustion engine - Google Patents

Description

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

  In a fuel supply device for an internal combustion engine that sends fuel using an electric low-pressure fuel pump to a high-pressure fuel pump driven by the internal combustion engine, and supplies fuel pressurized by the high-pressure fuel pump to the internal combustion engine. By controlling the low pressure fuel pump so as to avoid the generation of vapor due to insufficient fuel pressure (feed pressure) in the fuel path from the low pressure fuel pump to the high pressure fuel pump, the power consumption of the low pressure fuel pump is reduced. The technique to try is known (for example, refer patent document 1).

JP 2010-071224 A JP 2010-249049 A

  By the way, when a turbine pump (Wesco pump) driven by an electric motor is used as a low-pressure fuel pump, if the power consumption of the low-pressure fuel pump is reduced, the rotational speed of the low-pressure fuel pump is reduced. Torque is reduced. Therefore, when a foreign matter such as dust flows into the low-pressure fuel pump together with the fuel, if the turbine impeller bites the foreign matter, the turbine impeller may fall into a non-rotatable state (lock state). Furthermore, if the turbine impeller bites foreign matter when the power consumption of the low-pressure fuel pump is reduced, vapor is more likely to be generated, and it may be difficult to suppress the generation of vapor. In addition, when a brush motor is used as the electric motor, an insulating film is formed on the surface of the commutator, which may reduce the efficiency of the electric motor.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to increase the pressure of an electric low-pressure fuel pump for pumping fuel from a fuel tank and fuel discharged from the low-pressure fuel pump. In a fuel injection control system for an internal combustion engine that executes a process for lowering the discharge pressure of the low-pressure fuel pump, the low-pressure fuel pump while avoiding locking of the low-pressure fuel pump, a decrease in efficiency, etc. It is in the provision of the technique which can aim at reduction of the power consumption of this, and suppression of vapor.

  In order to solve the above-described problems, the present invention provides an electric low-pressure fuel pump for pumping fuel from a fuel tank, a high-pressure fuel pump for boosting fuel discharged from the low-pressure fuel pump, and a high-pressure fuel. A pressure sensor that measures the discharge pressure of the pump, and a calculation that calculates the drive signal of the high-pressure fuel pump using a proportional term and an integral term that are calculated using the deviation between the target discharge pressure of the high-pressure fuel pump and the measured value of the pressure sensor as a parameter. In a fuel injection control system for an internal combustion engine, which has a means for reducing the discharge pressure (feed pressure) of the low-pressure fuel pump in accordance with the change trend of the integral term, a discharge failure of the high-pressure fuel pump occurs Control that starts energization of the low-pressure fuel pump when the power is turned on and stops energization of the low-pressure fuel pump when a predetermined period has elapsed since the start of energization And further comprise a stage.

Specifically, the present invention includes an electric low pressure fuel pump for pumping fuel from a fuel tank;
A high-pressure fuel pump for boosting the fuel discharged from the low-pressure fuel pump;
A pressure sensor for measuring a discharge pressure of the high-pressure fuel pump;
Calculation means for calculating a drive signal of the high-pressure fuel pump using a proportional term and an integral term calculated using a deviation between a target discharge pressure of the high-pressure fuel pump and a measurement value of the pressure sensor as a parameter;
Reduction processing means for reducing the discharge pressure (feed pressure) of the low-pressure fuel pump in accordance with the change tendency of the integral term;
An internal combustion engine fuel injection control system comprising:
Control means for applying a reference voltage to the low-pressure fuel pump when a discharge failure occurs in the high-pressure fuel pump and stopping energization of the low-pressure fuel pump after a predetermined period has elapsed since the application of the reference voltage was started Was further provided.

  The “reference voltage” here is a voltage sufficiently higher than the applied voltage when a discharge failure of the high-pressure fuel pump occurs.

  When the feed pressure reduction process is performed according to the change tendency of the integral term used when calculating the drive signal of the high pressure fuel pump, the generation of vapor in the fuel path from the low pressure fuel pump to the high pressure fuel pump is suppressed. However, the feed pressure can be made as low as possible.

  By the way, when the feed pressure is made as low as possible, the fuel pressure in the fuel path from the low pressure fuel pump to the high pressure fuel pump tends to become a value near the saturated vapor pressure of the fuel. Further, when the feed pressure is made as low as possible, the applied voltage of the low-pressure fuel pump is also made as small as possible, so the rotational speed and torque of the low-pressure fuel pump are made small. Therefore, when the low-pressure fuel pump bites foreign matter, the discharge pressure of the low-pressure fuel pump tends to decrease, and the fuel pressure in the fuel path easily falls below the saturated vapor pressure.

  However, if the low-pressure fuel pump bites foreign matter during the lowering process by the lowering processing means, the discharge pressure of the low-pressure fuel pump drops due to the biting of foreign matter even if the applied voltage of the low-pressure fuel pump increases slightly. Is difficult to eliminate, and vapor in the fuel path is also difficult to eliminate.

  On the other hand, when the discharge failure of the high-pressure fuel pump occurs, if the applied voltage of the low-pressure fuel pump is raised to the reference voltage over a predetermined period, the feed pressure is increased to a pressure sufficiently higher than the pressure that can generate vapor. To rise. As a result, the discharge failure of the high-pressure fuel pump and the decrease in discharge pressure due to the generation of vapor are eliminated.

  In addition, since the application of voltage to the low-pressure fuel pump is stopped after the predetermined period has elapsed, the feed pressure decreases with time. When the feed pressure drops below the saturated vapor pressure, defective discharge of the high pressure fuel pump occurs, so that the application of voltage to the low pressure fuel pump is resumed and the applied voltage is raised to the reference voltage.

  That is, the control means intermittently applies the reference voltage to the low-pressure fuel pump. As a result, the power consumption of the low-pressure fuel pump can be reduced as compared with the case where a low voltage such that the feed pressure is close to the saturated vapor pressure of the fuel is continuously applied to the low-pressure fuel pump.

Further, when the reference voltage is applied to the low-pressure fuel pump over a predetermined period, the rotational speed of the low-pressure fuel pump is increased and the torque is increased. As a result, it is possible to prevent the low-pressure fuel pump from becoming unable to rotate due to the foreign matter being caught. Furthermore, when a brush motor is used as the electric motor of the low pressure fuel pump, it is possible to prevent a situation where an insulating film is formed on the surface of the commutator.

  Therefore, according to the fuel injection control system for an internal combustion engine of the present invention, it is possible to reduce the power consumption of the low-pressure fuel pump and to suppress the vapor while avoiding the lock of the low-pressure fuel pump and the decrease in efficiency.

  When the drive signal of the high pressure fuel pump is calculated using proportional integral control using the deviation between the target discharge pressure of the high pressure fuel pump and the measured value of the pressure sensor (hereinafter referred to as “actual discharge pressure”) as a parameter, When vapor of fuel sucked into the high-pressure fuel pump is generated, the integral term shows an increasing tendency (a change amount of the integral term per unit time becomes larger than zero). Therefore, the control means may apply an intermittent reference voltage to the low-pressure fuel pump when the integral term shows an increasing tendency. In other words, “when the discharge failure of the high-pressure fuel pump occurs” according to the present invention may be when the integral term shows an increasing tendency. According to such a configuration, when the integral term tends to increase, the control means intermittently applies the reference voltage instead of the decrease processing means increasing the feed pressure.

  In the fuel injection control system for an internal combustion engine according to the present invention, the reference voltage may be equal to the output voltage of the battery, or the formation of an insulating film on the surface of the commutator of the low pressure fuel pump or the electric motor is avoided. It may be the lowest voltage that can be.

  When a voltage equivalent to the output voltage of the battery is used as the reference voltage, the feed pressure can be quickly increased when a discharge failure of the high-pressure fuel pump occurs, and the rotation speed and torque of the low-pressure fuel pump can be sufficiently increased. Can be increased. As a result, it is possible to more reliably prevent locking of the low-pressure fuel pump and a decrease in efficiency.

  Further, when the lowest voltage that can avoid the lock of the low-pressure fuel pump and the formation of the insulating film on the surface of the commutator of the electric motor is used as the reference voltage, the lock of the low-pressure fuel pump or the commutator of the electric motor is used. It is possible to reduce power consumption while preventing formation of an insulating film on the surface.

  In the fuel injection control system for an internal combustion engine according to the present invention, the predetermined period may be a period until the actual rotational speed of the low-pressure fuel pump increases to a rotational speed corresponding to the reference voltage. In that case, the rotational speed and torque of the low-pressure fuel pump can be reliably increased to the rotational speed and torque that can prevent the lock of the low-pressure fuel pump and the formation of an insulating film on the commutator surface of the electric motor.

  Next, the internal combustion engine fuel injection control system of the present invention may further include an accumulator disposed in the middle of a fuel path from the low pressure fuel pump to the high pressure fuel pump.

  In the configuration provided with the accumulator, when the reference voltage is applied to the low-pressure fuel pump, if the fuel pressure (feed pressure) in the fuel path becomes higher than the pressure in the gas chamber of the accumulator, Part of the fuel flows into the working chamber of the accumulator. Then, after the application of voltage to the low-pressure fuel pump is stopped, when the feed pressure becomes lower than the pressure in the gas chamber of the accumulator, the fuel in the working chamber is discharged to the path, so that the feed pressure is increased. .

When the accumulator operates in this manner, the rate of increase of the feed pressure when the reference voltage is applied to the low-pressure fuel pump becomes slow, and the rate of decrease of the feed pressure after the application of voltage to the low-pressure fuel pump is stopped. Become slow. As a result, after the voltage application to the low-pressure fuel pump is stopped, it takes a long time for the feed pressure to fall below the saturated vapor pressure of the fuel. Therefore, the frequency of applying the reference voltage to the low-pressure fuel pump is reduced, and the durability of the low-pressure fuel pump can be improved. In addition, fluctuations in the discharge pressure of the high-pressure fuel pump due to intermittent energization of the low-pressure fuel pump can be reduced.

  The pressure in the gas chamber of the accumulator is the lowest feed pressure at which discharge failure of the high-pressure fuel pump cannot occur, in other words, the lowest feed pressure at which fuel vapor cannot occur in the fuel path (hereinafter referred to as “minimum feed pressure”). The pressure may be set equal to or slightly lower than the minimum feed pressure.

  In that case, if the feed pressure becomes equal to or higher than the minimum feed pressure when the reference voltage is applied to the low-pressure fuel pump, a part of the fuel in the path is stored in the working chamber of the accumulator. After the voltage application to the low-pressure fuel pump is stopped, the fuel is gradually discharged from the accumulator working chamber to the fuel path until the feed pressure falls below the minimum feed pressure. The rate of pressure drop can be made more gentle. As a result, the frequency with which the reference voltage is applied to the low-pressure fuel pump and the frequency with which the high-pressure fuel pump causes discharge failures can be more reliably reduced.

  Here, the accumulator may be arranged in the vicinity of a portion where fuel vapor is likely to be generated (hereinafter referred to as “vapor generating portion”) in the path from the low pressure fuel pump to the high pressure fuel pump. In that case, the atmospheric temperature of the gas chamber of the accumulator shows a temperature change in the same tendency as the fuel temperature of the vapor generation site. That is, when the fuel temperature at the vapor generation site increases, the ambient temperature of the gas chamber also increases. On the other hand, when the fuel temperature at the vapor generation site decreases, the ambient temperature of the gas chamber also decreases.

  The saturated vapor pressure of fuel tends to increase as the fuel temperature increases. On the other hand, the pressure in the gas chamber tends to increase as the atmospheric temperature in the gas chamber increases. Therefore, when the accumulator is disposed in the vicinity of the vapor generation site, the pressure in the gas chamber increases when the saturated vapor pressure increases as the fuel temperature increases. As a result, the flow of fuel between the working chamber of the accumulator and the fuel path (fuel inflow and discharge into the working chamber) is performed so that the fuel pressure at the vapor generation site does not fall below the saturated vapor pressure. As a result, the time from when the application of the voltage to the low-pressure fuel pump is stopped until the fuel pressure at the vapor generation site falls below the saturated vapor pressure of the fuel can be more reliably increased. In addition, since the difference between the pressure in the gas chamber and the fuel pressure at the vapor generation site is reduced, the movable range of the movable partition of the accumulator (movable partition that separates the gas chamber from the working chamber) is narrowed, and the durability of the movable partition is reduced. It can also improve sex.

  According to the present invention, an electric low-pressure fuel pump for pumping fuel from a fuel tank and a high-pressure fuel pump for boosting the fuel discharged from the low-pressure fuel pump are provided, and the discharge pressure of the low-pressure fuel pump In a fuel injection control system for an internal combustion engine that executes a process for reducing the pressure, it is possible to reduce the power consumption and the vapor of the low-pressure fuel pump while avoiding locking of the low-pressure fuel pump, a decrease in efficiency, etc. .

It is a figure which shows schematic structure of the fuel-injection control system of the internal combustion engine in a 1st Example. It is a timing chart which shows the application method of the drive voltage with respect to a low pressure fuel pump in a 1st Example. It is a flowchart which shows the process routine performed when ECU controls a low pressure fuel pump. It is a figure which shows the behavior of the integral term when the discharge pressure of a low pressure fuel pump is reduced, and the behavior of the fuel pressure in a high pressure fuel passage. It is a figure which shows schematic structure of the fuel-injection control system of the internal combustion engine in a 2nd Example. It is a timing chart which shows the application method of the drive voltage with respect to a low pressure fuel pump in a 2nd Example.

  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>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of a fuel injection control system for an internal combustion engine according to the present invention. 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. The number of cylinders of the internal combustion engine is not limited to four, but may be five or more, or may be three or less.

  The low pressure fuel pump 1 is a pump for pumping up fuel stored in the fuel tank 3. The low-pressure fuel pump 1 is a turbine pump (Wesco pump) driven by a DC electric motor. The fuel discharged from the low pressure fuel pump 1 is guided to the suction port of the high pressure fuel pump 2 by 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. The high-pressure fuel pump 2 is a reciprocating pump (plunger pump) driven by the power of the internal combustion engine (for example, the rotational force of the camshaft). A suction valve 2 a for switching between conduction and blockage of the suction port is provided at the suction port of the high-pressure fuel pump 2. The suction valve 2a is an electromagnetically driven valve mechanism, and changes the discharge amount of the high-pressure fuel pump 2 by changing the opening / closing timing with respect to the position of the plunger. The base end of the high-pressure fuel passage 5 is connected to the discharge port of the high-pressure fuel pump 2. The end of the high pressure fuel passage 5 is connected to a delivery pipe 6.

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

  In addition to the in-cylinder fuel injection valve such as the fuel injection valve 7 described above, a port injection fuel injection valve for injecting fuel into the intake passage (intake port) is attached to the internal combustion engine. If so, the low pressure fuel passage 4 may be branched from the middle to supply the low pressure fuel to the port injection delivery pipe.

  A proximal end of the branch passage 8 is connected to the middle of the low-pressure fuel passage 4 described above. The end of the branch passage 8 is connected to the fuel tank 3. A pressure regulator 9 is provided in the middle of the branch passage 8. The pressure regulator 9 opens when the pressure (fuel pressure) in the low-pressure fuel passage 4 exceeds a predetermined value, so that excess fuel in the low-pressure fuel passage 4 passes to the fuel tank 3 via the branch passage 8. Configured to return.

  A check valve 10 is disposed in the middle of the high-pressure fuel passage 5 described above. The check valve 10 is a one-way valve that allows a flow from the discharge port of the high-pressure fuel pump 2 to the delivery pipe 6 and restricts a flow from the delivery pipe 6 to the discharge port of the high-pressure fuel pump 2.

  Connected to the delivery pipe 6 is a return passage 12 for returning surplus fuel in the delivery pipe 6 to the fuel tank 3. In the middle of the return passage 12, a relief valve 13 that switches between return and passage of the return passage 12 is disposed. The relief valve 13 is an electric or electromagnetically driven valve mechanism, and is opened when the fuel pressure in the delivery pipe 6 exceeds a target value.

  In the middle of the return passage 12, the end of the communication passage 14 is connected. A base end of the communication path 14 is connected to the high-pressure fuel pump 2. The communication passage 14 is a passage for guiding excess fuel discharged from the high-pressure fuel pump 2 to the return passage 12.

  Here, the fuel supply system in the present embodiment includes an ECU 15 for electrically controlling the above-described devices. The ECU 15 is an electronic control unit that includes a CPU, ROM, RAM, backup RAM, and the like. The ECU 15 is electrically connected to various sensors such as a fuel pressure sensor 16, an intake air temperature sensor 17, an accelerator position sensor 18, and a crank position sensor 19.

  The fuel pressure sensor 16 is a sensor that outputs an electrical signal correlated with the fuel pressure in the delivery pipe 6 (discharge pressure of the high-pressure fuel pump 2) Ph. The intake air temperature sensor 17 outputs an electrical signal correlated with the temperature of air taken into the internal combustion engine. The accelerator position sensor 18 outputs an electrical signal correlated with the operation amount (accelerator opening) of the accelerator pedal. The crank position sensor 19 is a sensor that outputs an electrical signal correlated with the rotational position of the output shaft (crankshaft) of the internal combustion engine.

  The ECU 15 controls the low-pressure fuel pump 1 and the intake valve 2a based on the output signals of the various sensors described above. For example, the ECU 15 adjusts the opening / closing timing of the intake valve 2a so that the output signal (actual discharge pressure) Ph of the fuel pressure sensor 16 converges to the target discharge pressure Phtrg. At that time, the ECU 15 determines the drive duty (the solenoid energization time and the non-energization time) which is the control amount of the suction valve 2a based on the difference ΔPh (= Phtrg−Ph) between the actual discharge pressure Ph and the target discharge pressure Phtrg. Ratio) Dh is feedback-controlled. Specifically, the ECU 15 performs proportional-integral control (PI control) based on the difference ΔPh with respect to the drive duty Dh of the intake valve 2a. The target discharge pressure Phtrg is a value determined according to the target fuel injection amount of the fuel injection valve 7.

  In the proportional integral control described above, the ECU 15 determines the control amount determined according to the control amount (feed forward term) Tff determined according to the target fuel injection amount and the difference ΔPh between the actual discharge pressure Ph and the target discharge pressure Phtrg. The drive duty Dh is calculated by adding (proportional term) Tp and a control amount (integral term) Ti obtained by integrating a part of the difference ΔPh (for example, residual deviation of proportional control).

  It should be noted that the relationship between the target fuel injection amount and the feedforward term Tff and the relationship between the difference ΔPh and the proportional term Tp are determined in advance by adaptation work using experiments or the like. In the difference ΔPh, the proportion of the amount added to the integral term Ti is also determined in advance by an adaptation operation using an experiment or the like.

Next, the ECU 15 operates the low-pressure fuel pump 1 by intermittently applying a drive voltage to the low-pressure fuel pump 1. Hereinafter, a method for applying a drive voltage to the low-pressure fuel pump 1 will be described.

  The ECU 15 starts energization of the low-pressure fuel pump 1 when a discharge failure of the high-pressure fuel pump 2 due to fuel vapor occurs, and ends energization after a predetermined period from the start of energization. Here, the voltage (reference voltage) applied to the low-pressure fuel pump 1 when the low-pressure fuel pump 1 is energized is a voltage equivalent to the output voltage of the battery. The predetermined period is a period required until the low-pressure fuel pump 1 is stabilized (steady operation) in an operation state commensurate with the applied voltage. Specifically, the predetermined period is a period required from the start of energization of the low-pressure fuel pump 1 until the rotation speed of the low-pressure fuel pump 1 is stabilized at the rotation speed corresponding to the applied voltage.

  When the low-pressure fuel pump 1 is energized by such a method, as shown in FIG. 2, when the discharge failure of the high-pressure fuel pump 2 occurs due to the generation of vapor, in other words, the discharge pressure (high-pressure fuel pump 2) When the fuel pressure (Ph) of the fuel passage 5 (Ph) decreases (t1 in FIG. 2), a reference voltage Vb equivalent to the output voltage of the battery is applied to the low-pressure fuel pump 1.

  When the reference voltage Vb is applied to the low-pressure fuel pump 1, the fuel pressure (feed pressure) Pl in the low-pressure fuel passage 4 increases, and the discharge pressure Ph of the high-pressure fuel pump 2 also increases accordingly. At this time, since the application of the reference voltage Vb is continued for a predetermined period (period T1 in FIG. 2), the feed pressure Pl continues to increase during the predetermined period T1, but the discharge pressure Ph of the high-pressure fuel pump 2 is increased. Increases until the aforementioned feedback control is reflected, and then decreases.

  When the predetermined period T1 has elapsed (t2 in FIG. 2), the voltage applied to the low-pressure fuel pump 1 becomes zero (energization is stopped). During the energization stop period of the low-pressure fuel pump 1 (T2 in FIG. 2), the feed pressure Pl gradually decreases. When the feed pressure Pl falls below the saturated vapor pressure of the fuel (t3 in FIG. 2), the application (energization) of the reference voltage Vb to the low-pressure fuel pump 1 is resumed.

  As shown in FIG. 2, when the reference voltage Vb is intermittently applied to the low-pressure fuel pump 1, the low-pressure fuel pump 1 has a lower voltage than the case where a low voltage is continuously applied to the low-pressure fuel pump 1. Power consumption can be reduced. When a low voltage is continuously applied to the low-pressure fuel pump 1, a drive circuit for adjusting the voltage applied to the low-pressure fuel pump 1 is required. According to this, there is an advantage that a driving circuit becomes unnecessary. The “low voltage” here is an applied voltage at which the feed pressure is slightly higher than the saturated vapor pressure of the fuel, for example.

  In addition, when the low voltage is applied to the low-pressure fuel pump 1, the rotational speed and torque of the electric motor are reduced, and there is a possibility that the turbine impeller enters a locked state due to biting of foreign matter. On the other hand, according to the method in which the reference voltage Vb is intermittently applied to the low-pressure fuel pump 1, during the application period (predetermined period T1) of the reference voltage Vb, the rotational speed and torque (specifically, Since the rotation speed and torque of the electric motor for rotating the turbine impeller of the low-pressure fuel pump 1 are sufficiently high, the turbine impeller is prevented from being unable to rotate (locked state) due to biting of foreign matter or the like. You can also. As a result, the feed pressure Pl can be quickly increased to a pressure higher than the saturated vapor pressure, so that it is possible to quickly eliminate the generation of vapor.

Further, when a brush-type electric motor is used as the electric motor of the low-pressure fuel pump 1, if the low voltage is continuously applied to the low-pressure fuel pump 1, an insulating film is formed on the surface of the commutator of the electric motor. The resistance between the brush and the commutator could be large. In that case, the efficiency of the electric motor may decrease and the power consumption may increase. On the other hand, according to the method in which the reference voltage Vb is intermittently applied to the low-pressure fuel pump 1, the predetermined period T1.
Since a reference voltage Vb sufficiently higher than the low voltage is applied to the electric motor, an insulating film is hardly formed on the surface of the commutator. Therefore, it is possible to prevent a reduction in the efficiency of the electric motor and to suppress an increase in power consumption accompanying a reduction in the efficiency of the electric motor.

  Hereinafter, the control procedure of the low-pressure fuel pump 1 in this embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing a processing routine executed when the ECU 15 controls the low-pressure fuel pump 1. This processing routine is a routine that is stored in advance in the ROM or the like of the ECU 15 and is a routine that is periodically executed by the ECU 15.

  In the processing routine of FIG. 3, the ECU 15 first determines in S101 whether or not a discharge failure of the high-pressure fuel pump 2 has occurred. For example, the ECU 15 determines whether or not a discharge failure of the high-pressure fuel pump 2 has occurred based on a change tendency of the integral term Ti used when feedback controlling the drive duty Dh of the high-pressure fuel pump 2.

  The integral term Ti shows an increasing tendency when vapor is generated in the low pressure fuel passage 4, in other words, when the fuel pressure in the low pressure fuel passage 4 is lower than the saturated vapor pressure of the fuel. FIG. 4 is a diagram showing the behavior of the integral term Ti and the fuel pressure in the high-pressure fuel passage 5 (actual discharge pressure of the high-pressure fuel pump 2) Ph when the feed pressure Pl is continuously reduced. In FIG. 4, when the feed pressure Pl falls below the saturated vapor pressure (t10 in FIG. 4), the integral term Ti shows a moderate increasing tendency. Thereafter, when the feed pressure Pl is further reduced, a suction failure or a discharge failure of the high-pressure fuel pump 2 occurs (t20 in FIG. 4). When the suction failure or the discharge amount of the high-pressure fuel pump 2 occurs, the rate of increase of the integral term Ti increases and the fuel pressure Ph in the high-pressure fuel passage 5 decreases. Therefore, the ECU 15 can determine that a discharge failure of the high-pressure fuel pump 2 has occurred when the rate of increase of the integral term Ti increases.

  Therefore, the ECU 15 subtracts the previous integral term Tiold from the latest integral term Ti to calculate the integral term difference ΔTi (= Ti−Tiold). If the difference ΔTi is equal to or greater than the threshold value α, the high pressure fuel You may make it determine with the discharge failure of the pump 2 having generate | occur | produced. The threshold value α is a value obtained in advance by an adaptation process using an experiment or the like, and is a value stored in a ROM or the like of the ECU 15. The threshold value α may be a fixed value, but may be a variable value that is changed according to the fuel injection amount per unit time. When the fuel injection amount per unit time is large, the rate of decrease of the feed pressure Pl is faster than when the fuel injection amount is small. Therefore, the discharge pressure Ph of the high-pressure fuel pump 2 may rapidly decrease when vapor is generated. Therefore, the threshold value α may be set to a smaller value when the fuel injection amount per unit time is large than when the fuel injection amount is small.

  Here, returning to the processing routine of FIG. 3, if the ECU 15 makes a negative determination in S101, the execution of this routine is once terminated. On the other hand, when a positive determination is made in S101, the ECU 15 proceeds to S102.

  In S102, the ECU 15 applies a reference voltage Vb equivalent to the output voltage of the battery to the low-pressure fuel pump 1. Subsequently, the ECU 15 starts a timer in S103. The timer measures an elapsed time C from the time when application of the reference voltage Vb to the low-pressure fuel pump 1 is started.

  In S104, the ECU 15 determines whether or not the measurement time C of the timer is equal to or longer than a predetermined period T1. As described above, the predetermined period T1 is a period required from the start of energization of the low-pressure fuel pump 1 until the operation state of the low-pressure fuel pump 1 is stabilized in an operation state commensurate with the applied voltage. This is the period determined by the process.

  If a negative determination is made in S104 (C <T1), the ECU 15 repeatedly executes the process of S104. On the other hand, if a positive determination is made in S104 (C ≧ T1), the ECU 15 proceeds to S105.

  In S105, the ECU 15 stops applying the reference voltage Vb to the low-pressure fuel pump 1 (stops energization). Next, the ECU 15 proceeds to S106 and resets the measurement time of the timer.

  Thus, when the ECU 15 executes the processing routine of FIG. 3, the control means according to the present invention is realized. As a result, the reference voltage Vb is intermittently applied to the low-pressure fuel pump 1. Therefore, it is possible to reduce the power consumption and the vapor of the low-pressure fuel pump 1 while preventing the low-pressure fuel pump 1 from being locked and reducing the efficiency.

<Example 2>
Next, a second embodiment of the fuel injection control system for an internal combustion engine according to the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  The difference between the first embodiment and the present embodiment is that an accumulator 11 is disposed in the middle of the low pressure fuel passage 4. FIG. 5 is a diagram showing a schematic configuration of a fuel injection control system for an internal combustion engine in the present embodiment. In FIG. 5, an accumulator 11 is disposed in the middle of the low pressure fuel passage 4. The accumulator 11 is a pressure accumulator having a gas chamber and a working chamber separated by a movable partition. When the fuel pressure (feed pressure) Pl in the low-pressure fuel passage 4 exceeds the pressure in the gas chamber, the accumulator 11 is low-pressure. When a part of the fuel in the fuel passage 4 flows into the working chamber and the feed pressure Pl falls below the pressure in the gas chamber, the fuel in the working chamber is discharged to the low pressure fuel passage 4.

  According to the fuel injection control system for an internal combustion engine configured as described above, the feed pressure Pl exceeds the pressure in the gas chamber of the accumulator 11 during the period (predetermined period) T1 when the reference voltage Vb is applied to the low-pressure fuel pump 1. When this happens, a part of the fuel in the low-pressure fuel passage 4 flows into the working chamber of the accumulator 11. Further, after the application of the reference voltage Vb to the low-pressure fuel pump 1 is stopped, the fuel is discharged from the working chamber of the accumulator 11 to the low-pressure fuel passage 4 when the feed pressure Pl falls below the pressure of the gas chamber of the accumulator 11. Will be.

  When the accumulator 11 operates in this way, as shown in FIG. 6, the rate of increase of the feed pressure Pl in the period (predetermined period) T1 during which the reference voltage Vb is applied to the low pressure fuel pump 1, and the energization stop of the low pressure fuel pump 1 The rate of decrease of the feed pressure Pl in the period T2 is gentle compared to the case where the accumulator 11 is not provided (see, for example, FIG. 2). As a result, after the energization of the low-pressure fuel pump 1 is stopped, the time taken for the feed pressure Pl to fall below the saturated vapor pressure of the fuel, in other words, the time taken for the high-pressure fuel pump 2 to cause a discharge failure is long. Become. Therefore, the energization frequency of the low pressure fuel pump 1 is reduced, and the durability of the low pressure fuel pump 1 can be improved. Furthermore, the fluctuation range of the discharge pressure of the high-pressure fuel pump 2 due to intermittent energization of the low-pressure fuel pump 1 can also be suppressed.

Since the rate of increase of the feed pressure Pl when the reference voltage Vb is applied to the low-pressure fuel pump 1 is gentler than when the accumulator 11 is not provided, the length of the predetermined period T1 is provided with the accumulator 11. It is assumed that it is set longer than the case where there is no such as (T1 in FIG. 2). The length of the predetermined period T1 at that time is a length required for the feed pressure Pl to rise to a sufficiently high pressure with respect to the saturated vapor pressure, and is a length determined in advance by an adaptation process using an experiment or the like. Shall be set to

  In addition, when the atmospheric temperature of the accumulator 11 is normal temperature and the working chamber is empty, the pressure of the gas chamber (minimum operating pressure) causes a discharge failure of the high-pressure fuel pump 2 when the fuel temperature is normal temperature. The lowest feed pressure that cannot be obtained, in other words, may be set to a pressure that is equal to or slightly lower than the lowest feed pressure at which fuel vapor cannot be generated (minimum feed pressure).

  In that case, when the feed pressure Pl becomes equal to or higher than the minimum feed pressure in the predetermined period T1, a part of the fuel in the low pressure fuel passage 4 flows into the working chamber of the accumulator 11, so that the feed pressure Pl becomes the minimum feed pressure. The rate of increase of the feed pressure Pl after becoming Pl or higher can be made gentler, and a rapid increase in the discharge pressure of the high-pressure fuel pump 2 can be suppressed. In addition, since the fuel is gradually discharged from the working chamber of the accumulator 11 to the low pressure fuel passage 4 during a period until the feed pressure Pl falls below the minimum feed pressure after the energization of the low pressure fuel pump 1 is stopped, the feed pressure Pl decrease rate can be made more gentle. As a result, the energization frequency of the low-pressure fuel pump 1 is further reduced, and the durability of the low-pressure fuel pump 1 is further improved.

  Further, the accumulator 11 may be disposed at a position where vapor is likely to be generated in the low pressure fuel passage 4 (vapor generation site), for example, in the vicinity of the intake valve 2 a of the high pressure fuel pump 2. In that case, the atmospheric temperature of the gas chamber of the accumulator 11 shows a temperature change in the same tendency as the fuel temperature of the vapor generation site. That is, when the fuel temperature at the vapor generation site increases, the atmospheric temperature of the gas chamber also increases. On the other hand, when the fuel temperature at the vapor generation site decreases, the ambient temperature of the gas chamber also decreases.

  The saturated vapor pressure of fuel tends to increase as the fuel temperature increases. On the other hand, the pressure in the gas chamber tends to increase as the atmospheric temperature in the gas chamber increases. Therefore, when the accumulator 11 is disposed in the vicinity of the vapor generation site, the pressure in the gas chamber increases when the saturated vapor pressure increases as the fuel temperature increases. As a result, the flow of fuel between the working chamber of the accumulator 11 and the vapor generation site (fuel inflow and discharge into the working chamber) is performed so that the fuel pressure in the vapor generation site does not fall below the saturated vapor pressure. It will be.

  As a result, it is possible to further increase the time from when the power supply to the low-pressure fuel pump 1 is stopped until the fuel pressure at the vapor generation site falls below the saturated vapor pressure of the fuel. Further, since the difference between the pressure in the gas chamber and the fuel pressure in the vapor generation site is reduced, the movable range of the movable partition of the accumulator 11 is narrowed, and the durability of the movable partition can be enhanced.

  In the first and second embodiments described above, an example in which the reference voltage Vb is set to be equal to the output voltage of the battery has been described. However, the turbine impeller is locked due to foreign object biting or the commutator of the electric motor. The lowest voltage that can avoid the formation of the insulating film on the surface may be set to the reference voltage Vb. In this case, it is possible to further reduce the power consumption of the low-pressure fuel pump 1 while preventing the low-pressure fuel pump 1 from being locked and lowering the efficiency. In addition, the minimum voltage that can avoid the lock of the turbine impeller due to the foreign object biting and the formation of the insulating film on the commutator surface of the electric motor can be experimentally obtained in advance.

DESCRIPTION OF SYMBOLS 1 Low pressure fuel pump 2 High pressure fuel pump 2a Suction valve 3 Fuel tank 4 Low pressure fuel passage 5 High pressure fuel passage 6 Delivery pipe 7 Fuel injection valve 8 Branch passage 9 Pressure regulator 10 Check valve 11 Accumulator 12 Return passage 13 Relief valve 14 Communication passage 15 ECU
16 Fuel pressure sensor

Claims (5)

An electric low pressure fuel pump for pumping fuel from the fuel tank;
A high-pressure fuel pump for boosting the fuel discharged from the low-pressure fuel pump;
A pressure sensor for measuring a discharge pressure of the high-pressure fuel pump;
Calculation means for calculating a drive signal of the high-pressure fuel pump using a proportional term and an integral term calculated using a deviation between a target discharge pressure of the high-pressure fuel pump and a measurement value of the pressure sensor as a parameter;
Reduction processing means for reducing the discharge pressure of the low-pressure fuel pump in accordance with the change tendency of the integral term;
An internal combustion engine fuel injection control system comprising:
Control that applies a reference voltage to the low-pressure fuel pump when discharge failure of the high-pressure fuel pump occurs, and stops energization of the low-pressure fuel pump after a predetermined period has elapsed since the application of the reference voltage was started In addition example Bei means,
The lowering processing means lowers the discharge pressure of the low-pressure fuel pump when the integral term does not tend to increase, and increases the discharge pressure of the low-pressure fuel pump when the integral term tends to increase. ,
A fuel injection control system for an internal combustion engine , wherein when the discharge failure of the high-pressure fuel pump occurs, the integral term shows an increasing tendency . Oite to claim 1, wherein the reference voltage is the internal combustion engine fuel injection control system is the lowest voltage low-pressure fuel pump is not fall unrotatable when the elaborate foreign matter bite into the low-pressure fuel pump. Oite to claim 1 or 2, wherein the predetermined period of time, the internal combustion engine fuel injection control system for a period in which the rotational speed is required until the rotational speed that matches the reference voltage of the low-pressure fuel pump. The fuel injection control system for an internal combustion engine according to any one of claims 1 to 3 , wherein an accumulator is disposed in the middle of a fuel path from the low pressure fuel pump to the high pressure fuel pump. Oite to claim 4, the pressure of the accumulator gas chamber, the high-pressure fuel pump minimum feed pressure and the internal combustion engine fuel injection control system that is set equal to or smaller than the ejection failure can not occur in the.

Images