Fuel injector, and method for driving fuel injector

This fuel injector comprises: a main body portion including an inflow port into which fuel supplied from a fuel supply source flows, a flow passage through which the fuel that has flowed in from the inflow port flows, and a discharge port which is connected to the flow passage and which discharges the fuel; a valve unit at least a portion of which is formed using a magnetic body, which is disposed so as to be capable of moving in a straight-line direction between a position closing the discharge port and a position opening the discharge port, which is urged in the direction opening the discharge port by means of the pressure of the fuel flowing in from the inflow port, and to which an elastic force is imparted by an elastic member in the direction closing the discharge port; a solenoid device which includes a coil, which generates an electromagnetic force by causing a drive current to flow through the coil, and which drives the valve unit in the direction opening the discharge port, by means of the electromagnetic force; and a control portion which variably sets the value of a prescribed time period that includes a drive current supply start time point, of the drive current flowing through the coil, in accordance with a supply pressure of the fuel supplied to the inflow port.

TECHNICAL FIELD

The present disclosure relates to a fuel injector and a method for driving the fuel injector.

BACKGROUND ART

A common rail type fuel injection device that is applied to a diesel engine or the like includes a fuel pump, a common rail, and a fuel injector. The fuel pump sucks fuel from a fuel tank, pressurizes the fuel, and supplies the fuel to the common rail as high-pressure fuel. The common rail maintains the high-pressure fuel supplied from the fuel pump at a predetermined pressure. The fuel injector injects the high-pressure fuel in the common rail into a combustion chamber of the diesel engine by opening and closing an injection valve.

The fuel injector has, for example, an electromagnetic valve that includes a solenoid device that generates an electromagnetic force by causing a current to flow through a coil wound around a core and a valve unit that is formed using a magnetic body. In such an electromagnetic valve, for example, a configuration in which a fuel flow path is held down by causing an elastic force to act on the valve unit is made, and in a case where an electromagnetic force is not generated by the solenoid device, the fuel flow path is in a held down and closed state due to the elastic force. Further, in a case where the electromagnetic generated by the solenoid device, the valve unit is pulled toward the core side of the solenoid device due to the electromagnetic force, so that the valve unit is separated from the flow path to open the flow path (refer to, for example, PTL 1 and the like).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the electromagnetic valve as described above, in order to generate a large electromagnetic force, it is necessary to make a drive current flowing through the coil high. In a case where a drive current having a high value flows through the coil, the amount of heat generated in the coil increases, and a thermal load in a solenoid increases. Therefore, in the solenoid device that needs to generate a large electromagnetic force, it is necessary to separately provide a cooling mechanism that cools the coil.

The present disclosure has been made in view of the above, and has an object to provide a fuel injector and a method for driving the fuel injector, in which it is possible to suppress the amount of heat generated.

Solution to Problem

A fuel injector according to the present disclosure includes: a main body part having an inflow port into which fuel that is supplied from a fuel supply source flows, a flow path through which the fuel that has flowed in from the inflow port flows, and a discharge port that is connected to the flow path and discharges the fuel; a valve unit, at least a part of which is formed using a magnetic body, and which is disposed to be movable in a straight line direction between a position where the discharge port is closed and a position where the discharge port is opened, and is biased in a direction to open the discharge port by pressure of the fuel flowing in from the inflow port, the valve unit being applied with an elastic force in a direction to close the discharge port by an elastic member; a solenoid device that includes a coil, generates an electromagnetic force by causing a drive current to flow through the coil, and drives the valve unit in the direction to open the discharge port by the electromagnetic force; and a control unit that variably sets a value of the drive current flowing through the coil in a predetermined period that includes a drive current supply start time point, depending on a supply pressure of the fuel that is supplied to the inflow port.

A method for driving a fuel injector according to the present disclosure is a method for driving a fuel injector which includes a main body part having an inflow port into which fuel that is supplied from a fuel supply source flows, a flow path through which the fuel that has flowed in from the inflow port flows, and a discharge port that is connected to the flow path and discharges the fuel, a valve unit, at least a part of which is formed using a magnetic body, and which is disposed to be movable in a straight line direction between a position where the discharge port is closed and a position where discharge port is opened, and is biased in a direction to open the discharge port by pressure of the fuel flowing in from the inflow port, the valve unit being applied with an elastic force in a direction to close the discharge port by an elastic member, and a solenoid device that includes a coil, generates an electromagnetic force by causing a drive current to flow through the coil, and drives the valve unit in the direction to open the discharge port by the electromagnetic force, the method including: a step of acquiring a supply pressure of the fuel that is supplied to the inflow port; and a step of setting a value of the drive current flowing through the coil in a predetermined period that includes a drive current supply start time point, based on the supply pressure.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide a fuel injector and a method for driving the fuel injector, in which it is possible to suppress the amount of heat generated.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of a solenoid device and an electromagnetic valve of a fuel injection device according to the present disclosure will be described based on the drawings. The present invention is not limited to the embodiment. Further, components in the following embodiment include components that can be easily replaced by those skilled in the art, or components that are substantially the same.

FIG.1is a schematic configuration diagram showing an example of a fuel injection device10of the present embodiment. As shown inFIG.1, the fuel injection device10is installed in a diesel engine (internal combustion engine). The fuel injection device10includes a fuel pump11, a common rail12, and a plurality of fuel injectors13.

The fuel pump11is connected to a fuel tank14through a fuel line L11. The fuel pump11sucks fuel stored in the fuel tank14from the fuel line L11and pressurizes the fuel to generate high-pressure fuel. The fuel pump11is connected to the common rail12through a fuel high-pressure line L12. In the present embodiment, the fuel pump11is a fuel supply source from which fuel is supplied. The common rail12maintains the high-pressure fuel supplied from the fuel pump11at a predetermined pressure. The common rail12is connected to each of the fuel injectors13through each of a plurality of (in the present embodiment, four) fuel supply lines L13. The fuel injector13injects the high-pressure fuel in the common rail12into each cylinder (combustion chamber) of the diesel engine by opening and closing an electromagnetic valve.

FIG.2is a vertical sectional view showing an example of the fuel injector13. As shown inFIG.2, the fuel injector13has a shape extending in an axial direction of a central axis AX, and has a main body part20, an electromagnetic valve40, and a control unit50. Hereinafter, in describing the configuration of the fuel injector13, a fuel injection port30side in the axial direction of the central axis AX is referred to as a tip end side, and an electromagnetic valve40side is referred to as a base end side.

The main body part20has a casing21and a piston valve22. The casing21has a fuel inlet port24, an injection-side flow path25, a control-side flow path26, an injection-side pressure chamber27, a control-side pressure chamber28, a cylinder chamber29, the fuel injection port30, a fuel discharge port31, an electromagnetic valve-side pressure chamber32, and a sensor33.

The fuel from the fuel supply line L13flows into the fuel inlet port24. The injection-side flow path25connects the fuel inlet port24and the injection-side pressure chamber27. The control-side flow path26connects the fuel inlet port24and the control-side pressure chamber28.

The injection-side pressure chamber27is connected to the fuel injection port30. The fuel injection port30is disposed at an end portion on the tip end side of the casing21and injects the fuel toward each cylinder of the diesel engine.

The control-side pressure chamber28is connected to the fuel discharge port31. The fuel discharge port31is disposed at an end portion on the base end side of the casing21and connected to the electromagnetic valve-side pressure chamber32. The electromagnetic valve-side pressure chamber32is connected to the electromagnetic valve40(a space portion46dto be described later).

The cylinder chamber29is connected to the injection-side pressure chamber27and the control-side pressure chamber28. The cylinder chamber29accommodates the piston valve22. The cylinder chamber29is connected to the electromagnetic valve-side pressure chamber32through a flow path29a.

The piston valve22is accommodated in the cylinder chamber29and is provided to be movable toward the injection-side pressure chamber27side or the control-side pressure chamber28side. The piston valve22has a spring seat member22a, a control-side piston member22b, a connecting member22c, and a valve body22d. The spring seat member22a, the control-side piston member22b, and the connecting member22care integrated. The spring seat member22areceives the elastic force of an elastic member23(described later). The control-side piston member22breceives the pressure in the control-side pressure chamber28. The connecting member22cconnects the spring seat member22aand the control-side piston member22b. The valve body22dprotrudes from the spring seat member22atoward the tip end side in the axial direction of the central axis AX. The valve body22dcomes into contact with the spring seat member22adue to the resultant force of the pressure received from each pressure chamber and the elastic force. The valve body22dis formed in such a shape that its tip portion can close the fuel injection port30. The valve body22dreceives the pressure in the injection-side pressure chamber27.

In a case where the pressure in the injection-side pressure chamber27is smaller than the resultant force of the pressure in the control-side pressure chamber28and the elastic force of the elastic member23, the piston valve22becomes a state of being pressed toward the injection-side pressure chamber27side. In this case, the fuel injection port30becomes a closed state by the valve body22d. In this state, in a case where the pressure in the injection-side pressure chamber27becomes larger than the resultant force of the pressure in the control-side pressure chamber28and the elastic force of the elastic member23, the piston valve22becomes a state of being pressed toward the control-side pressure chamber28side. In this case, the valve body22dis separated from the fuel injection port30and the fuel injection port30becomes an open state.

The sensor33detects supply pressure which is the pressure of the fuel that is supplied to the fuel inlet port24. The sensor33may be configured to detect, for example, the pressure in the common rail12(rail pressure) as the supply pressure. The sensor33transmits the supply pressure, which is a detection result, to the control unit50.

The electromagnetic valve40has a solenoid device41and a valve unit42.FIG.3is a vertical sectional view showing an example of the electromagnetic valve40.FIG.3shows a part ofFIG.2in an enlarged manner. As shown inFIG.3, the solenoid device41drives the valve unit42along the axial direction of the central axis AX by an electromagnetic force. The solenoid device41has a core43, a coil44, a casing45, a tubular member46, and a terminal fixing member47.

The core43has a tubular portion43a, a flange portion43b, and a side surface portion43c. The tubular portion43ais formed, for example, in a cylindrical shape. The flange portion43bhas, for example, a disk shape and is disposed on the base end side of the core43. The tubular portion43aand the flange portion43bare disposed such that their central axes coincide with the central axis AX of the fuel injector13.

The side surface portion43chas a cylindrical shape that involves the tubular portion43a. The side surface portion43cis disposed to be spaced apart from the tubular portion43ain a radial direction, and extends toward the tip end side. The tubular portion43a, the flange portion43b, and the side surface portion43care formed using a magnetic body. The core43accommodates the coil44in a space surrounded by the tubular portion43a, the flange portion43b, and the side surface portion43c. In the core43, the space in which the coil44is disposed is sealed by a sealing part49. The sealing part49is formed using, for example, a resin material. Further, the terminal fixing member47is disposed between the core43and the casing45(described later) in the axial direction of the central axis AX, and fixes a terminal44athat is connected to the coil44. The terminal44apenetrates the casing45and is drawn out to the outside. The terminal fixing member47is formed using, for example, a resin material.

The coil44is disposed in a state of being wound around the tubular portion43a. The coil44penetrates the casing45(described later) and is connected to a power source part (not shown). The solenoid device41generates an electromagnetic force by causing a current to flow through the coil44.

The casing45accommodates the core43and the coil44. The casing45is formed using, for example, a resin material. The casing45has a supporting part45athat supports an elastic member48(described later).

The tubular member46is disposed on the inner periphery side of the core43. The tubular member46is formed using, for example, a metal material. The tubular member46may be metal of a non-magnetic body. The tubular member46has, for example, a cylindrical shape and is disposed such that its central axis coincides with the central axis AX of the fuel injector13. The tubular member46is disposed at a position where an end surface46bon the tip end side can come into contact with the valve unit42. In the present embodiment, the end surface46bis flush with, for example, an end surface on the tip end side of the side surface portion43cof the core43and an end surface on the tip end side of the sealing part49.

The elastic member48is accommodated on the inner periphery side of the tubular member46in a state where its end portion on the base end side is supported by the supporting part45aof the casing45. The elastic member48applies an elastic force to the valve unit42toward the tip end side in the axial direction of the central axis AX.

The valve unit42moves in the axial direction of the central axis AX due to the electromagnetic force generated by the solenoid device41. The valve unit42has an armature42a, a valve body42b, and a stepped portion42c. The armature42ais formed using a magnetic body. The armature42ahas, for example, a disk shape. The armature42ais disposed to face an end portion on the tip end side of the core43of the solenoid device41. The valve body42bextends from the armature42atoward the tip end side. The valve body42bis formed in such a shape that its tip portion can close the fuel discharge port31. The valve body42bmay be formed of a magnetic body or may be formed of a non-magnetic body. The stepped portion42cis formed in a state where the central portion of the armature42aprotrudes toward the solenoid device41side. The stepped portion42cis formed in a shape and a dimension in which it comes into contact with the end surface46bof the tubular member46when the valve unit42is drawn toward the solenoid device41side. Further, the stepped portion42creceives an elastic force from the elastic member48. The elastic force of the elastic member48is transmitted to the armature42aand the valve body42bthrough the stepped portion42c. The elastic force of the elastic member48is applied to the armature42aand the valve body42btoward the tip end side in the axial direction of the central axis AX.

The control unit50controls the operation of the solenoid device41. The control unit50has a processing device such as a central processing unit (CPU), and a storage device such as a random access memory (RAM) or a read only memory (ROM). The control unit50includes a supply pressure acquisition unit51, a drive current control unit52, and a storage unit53.

The supply pressure acquisition unit51acquires the supply pressure of the fuel that is supplied to the fuel inlet port24. The supply pressure acquisition unit51can acquire the detection result of the sensor33as the supply pressure. Further, the supply pressure acquisition unit51may be capable of acquiring an operation map indicating the operation content of the fuel injection device10from an electronic control unit (ECU) (not shown) that controls the fuel injection device10. In this case, the supply pressure acquisition unit51may be configured to extract the supply pressure, based on the acquired operation map, and acquire the extracted supply pressure.

The drive current control unit52controls a drive current that is supplied to the coil44of the solenoid device41according to the supply pressure acquired by the supply pressure acquisition unit51.FIG.4is a diagram showing an example of a profile of the drive current that is supplied to the coil44. As shown inFIG.4, a drive current I includes an inrush current I1, a pull-up current I2, and a hold current I3.

The inrush current I1flows through the coil44during an inrush period t1, which is the first period that includes a supply start time point to in a time series. For example, as shown inFIG.4, the inrush current I1is generated by a pulse signal whose period extends over the entire inrush period t1, as a control signal. The inrush current I1serves as a drive current for generating an electromagnetic force that separates the valve unit42closing the fuel discharge port31.

The pull-up current I2flows through the coil44after the inrush current I1has flowed, that is, during a pull-up period t2after the inrush period t1has elapsed. The pull-up current I2has a lower peak current value than the inrush current I1. The pull-up current I2serves as a drive current for generating an electromagnetic force that pulls the valve unit42separated from the fuel discharge port31toward the core43side. The pull-up current I2is generated by a plurality of pulse signals as a control signal.

The hold current I3flows through the coil44after the pull-up current I2has flowed, that is, during a hold period t3after the pull-up period t2has elapsed. The hold current I3is generated by a plurality of pulse signals as a control signal. The hold current I3serves as a drive current for generating an electromagnetic force that holds the valve unit42pulled toward the core43side. The hold current I3has a lower peak current value than the inrush current I1and the pull-up current I2.

The drive current control unit52variably sets the value of the drive current I in a predetermined period that includes the supply start time point to, depending on the acquired supply pressure. The drive current control unit52makes the value of the drive current I in the predetermined period smaller as the acquired supply pressure is higher, and makes the value of the drive current I in the predetermined period larger as the acquired supply pressure is lower.

FIG.5is a diagram showing an example of the drive current that is controlled by the drive current control unit52. As shown inFIG.5, the drive current control unit52can variably set the values of the drive current I, for example, in the inrush period t1and the pull-up period t2as the predetermined period that includes the supply start time point to. As shown inFIG.5, the drive current control unit52can make the values of the inrush current I1in the inrush period t1and the pull-up current I2in the pull-up period t2smaller as the acquired supply pressure is higher (a drive current IA). Further, the drive current control unit52can make the values of the inrush current I1in the inrush period t1and the pull-up current I2in the pull-up period t2larger as the acquired supply pressure is lower (a drive current IB). The values of the drive currents I, IA, and IB can be set such that the valve unit42can be pulled toward the core43side by the generated electromagnetic force. That is, the values of the drive currents I, IA, and IB can be set such that the force acting on the valve unit42toward the base end side (the elastic force from the elastic member48, or the electromagnetic force that is generated by the solenoid device41) becomes larger than the force acting on the valve unit42toward the tip end side (the pressure received from the control-side pressure chamber28). The drive current control unit52is not limited to the configuration that controls the inrush current I1and the pull-up current I2in three stages as shown inFIG.5, and may be configured to control the inrush current I1and the pull-up current I2in two stages or four or more stages.

The storage unit53stores various types of information. The storage unit53has a storage such as a hard disk drive or a solid state drive, for example. As the storage unit53, an external storage medium such as a removable disk may be used. In the present embodiment, the storage unit53stores a data table that defines the correspondence relationship between the acquired supply pressure and the drive current I.FIG.6is a diagram showing an example of the data table that is stored in the storage unit53. As shown inFIG.6, the storage unit53stores the data table in which the value of the drive current is associated with each supply pressure. The drive current control unit52described above can set the value of the drive current corresponding to the supply pressure, based on the data table stored in the storage unit53.

The operation of the fuel injector13configured as described above will be described. In a case where a current does not flow through the coil44of the solenoid device41, an electromagnetic force is not generated in the solenoid device41. In this case, in the valve unit42, the valve body42bpresses the fuel discharge port31toward the tip end side due to the elastic force of the elastic member48. In this way, the fuel discharge port31becomes a closed state.

In a state where the fuel discharge port31is closed, the resultant force of the pressure in the control-side pressure chamber28and the elastic force of the elastic member23becomes larger than the pressure in the injection-side pressure chamber27. Therefore, the piston valve22presses the fuel injection port30and the fuel injection port30becomes a closed state.

Further, in a case where a current flows through the coil44of the solenoid device41, an electromagnetic force is generated in the solenoid device41.FIG.7is a vertical sectional view showing an example of the operation of the electromagnetic valve40.FIG.7shows an example in a case where a current flows through the coil44. As shown inFIG.7, in a case where an electromagnetic force is generated in the solenoid device41, in the valve unit42, the armature42ais pulled toward the core43side by the electromagnetic force, and the valve body42bis separated from the fuel discharge port31. In this way, the fuel discharge port31becomes an open state.

The fuel discharge port31is opened, whereby the pressure in the control-side pressure chamber28is lowered. In a case where the resultant force of the pressure received from the control-side pressure chamber28and the elastic force of the elastic member23becomes smaller than the pressure received from the injection-side pressure chamber27, the piston valve22moves toward the control-side pressure chamber28side. In this case, the valve body22dof the piston valve22is separated from the fuel injection port30and the fuel injection port30becomes an open state. In a case where the fuel injection port30is in an open state, the fuel that has flowed from the fuel inlet port24into the injection-side pressure chamber27through the injection-side flow path25is injected from the fuel injection port30.

In the above operation, in a case where the valve unit42is pulled toward the core43side by the electromagnetic force of the solenoid device41, the stepped portion42cof the valve unit42comes into contact with the end surface46bof the tubular member46, as shown inFIG.7. In this case, the tubular member46functions as a stopper that restricts the movement of the valve unit42toward the base end side.

Further, in the above operation, the pressure in the control-side pressure chamber28changes depending on the supply pressure of the fuel that is supplied to the fuel inlet port24of the fuel injector13. That is, the larger the supply pressure, the larger the pressure in the control-side pressure chamber28becomes, and the smaller the supply pressure, the smaller the pressure in the control-side pressure chamber28becomes. When the pressure in the control-side pressure chamber28is large, the force biasing the valve unit42toward the core43side becomes large. Further, when the pressure in the control-side pressure chamber28is small, the force biasing the valve unit42toward the core43side becomes small.

In a case where an electromagnetic force is not generated by the solenoid device41, the elastic force from the elastic member48and the pressure in the control-side pressure chamber28act on the valve unit42. The elastic member48is configured to apply an elastic force, which is larger than the received pressure that may be generated in the control-side pressure chamber28, to the valve unit42so as to be able to maintain a state where the valve unit42closes the fuel discharge port31in this state.

In recent years, during the operation of the fuel injection device10, it has been required to operate the fuel injection device10by increasing the maximum value of the supply pressure in the common rail12, that is, to increase the pressure in the common rail12. In a case where the pressure in the common rail12is increased, in order to prevent the fuel discharge port31from being opened due to the supply pressure, it is necessary to make the elastic force of the elastic member48that acts on the valve unit42large in response to the maximum value of the supply pressure.

On the other hand, in a case of operating the fuel injection device10, there is a period during which the fuel injection device10is operated with the supply pressure lowered, for example. In a case where the supply pressure is low, the pressure in the control-side pressure chamber28becomes low. Since the elastic force of the elastic member48is set in response to the maximum value of the supply pressure, it is necessary to generate a larger electromagnetic force in order to separate the valve unit42from the fuel discharge port31. That is, it is necessary to cause a larger current to flow through the coil44.

In a case where a drive current having a large value flows through the coil44as described above, the amount of heat generated by the coil44increases, and a thermal load in the solenoid device41increases. In the solenoid device41that needs to generate such a large electromagnetic force, a separate cooling mechanism for cooling the solenoid device41is required.

On the contrary, in the fuel injection device10according to the present embodiment, by adjusting the drive current flowing through the coil44according to the supply pressure of the fuel that is supplied to the fuel inlet port24, it is possible to suppress the amount of heat generated in the coil44. The control unit50variably sets the value of the drive current flowing through the coil44in a predetermined period that includes the drive current supply start time point to, depending on the supply pressure of the fuel that is supplied to the fuel inlet port24.

FIG.8is a flowchart showing an example of the operation of the fuel injection device10according to the present embodiment. As shown inFIG.8, the supply pressure acquisition unit51of the control unit50acquires the supply pressure of the fuel that is supplied to the fuel inlet port24(step S10). The supply pressure acquisition unit51acquires at least one of the detection result of the sensor33and the supply pressure that is extracted from the operation map of the ECU (not shown).

Next, the drive current control unit52selects the drive current I corresponding to the supply pressure from the data table stored in the storage unit53, based on the acquired supply pressure (step S20). After the drive current I is selected, the drive current control unit52controls such that the selected drive current I flows through the coil44(step S30).

By this control, it is possible to cause the drive current to flow through the coil44such that the minimum electromagnetic force required for pulling the valve unit42toward the core43side is generated, depending on the supply pressure of the fuel that is supplied to the fuel inlet port24. Therefore, the amount of heat generated in the coil44is reduced compared to a configuration of the related art in which a constant drive current is supplied regardless of the supply pressure.

As described above, the fuel injector13according to the present embodiment includes: the main body part20having the fuel inlet port24into which the fuel that is supplied from the fuel pump11flows, flow paths (the injection-side flow path25and the control-side flow path26) through which the fuel that has flowed in from the fuel inlet port24flows, and the fuel discharge port31that is connected to the flow paths (25,26) and discharges the fuel; the valve unit42, at least a part of which is formed using a magnetic body, and which is disposed to be movable in a straight line direction between a position where the fuel discharge port31is closed and a position where the fuel discharge port31is opened, and is biased in a direction to open the fuel discharge port31by the pressure of the fuel flowing in from the fuel inlet port24, the valve unit42being applied with an elastic force in a direction to close the fuel discharge port31by the elastic member48; the solenoid device41that includes the coil44, generates an electromagnetic force by causing a drive current to flow through the coil44, and drives the valve unit42in the direction to open the fuel discharge port31by the electromagnetic force; and the control unit50that variably sets a value of the drive current flowing through the coil44in a predetermined period that includes a drive current supply start time point to, depending on the supply pressure of the fuel that is supplied to the fuel inlet port24.

Further, a method for driving the fuel injector13according to the present embodiment is a method for driving a fuel injector which includes the main body part20having the fuel inlet port24into which fuel that is supplied from the fuel pump11flows, the injection-side flow path25and the control-side flow path26, through which the fuel that has flowed in from the fuel inlet port24flows, and the fuel discharge port31that is connected to the injection-side flow path25and the control-side flow path26and injects the fuel, the valve unit42which is formed using a magnetic body, is disposed to be movable in a straight line direction between a position where the fuel discharge port31is closed and a position where the fuel discharge port31is opened, is biased in a direction to open the fuel discharge port31by the pressure of the fuel flowing in from the fuel inlet port24, the valve unit42being applied with an elastic force in a direction to close the fuel discharge port31by the elastic member48, and the solenoid device41that includes the coil44, generates an electromagnetic force by causing a drive current to flow through the coil44, and drives the valve unit42in the direction to open the fuel discharge port31by the electromagnetic force, the method including: a step of acquiring a supply pressure of the fuel that is supplied to the fuel inlet port24; and a step of setting a value of the drive current flowing through the coil44in a predetermined period that includes a drive current supply start time point to, based on the supply pressure.

According to this configuration, it is possible to set the drive current that flows through the coil44such that the minimum electromagnetic force required for pulling the valve unit42toward the core43side is generated, depending on the supply pressure of the fuel that is supplied to the fuel inlet port24. In this way, it becomes possible to suppress the amount of heat generated in the coil44.

In the fuel injector13according to the present embodiment, the control unit50makes the value of the drive current in the predetermined period smaller as the supply pressure is higher, and makes the value of the drive current in the predetermined period larger as the supply pressure is lower. According to this configuration, it is possible to more reliably generate the minimum electromagnetic force required for pulling the valve unit42toward the core43side.

In the fuel injector13according to the present embodiment, the drive current includes the inrush current I1that flows through the coil44during the inrush period t1, which is the first period that includes the supply start time point to in a time series, the pull-up current I2that flows during the pull-up period t2after the inrush current I1has flowed, and the hold current I3that flows during the hold period t3after the pull-up current I2has flowed, and the control unit50makes the values of the inrush current I1and the pull-up current I2smaller as the supply pressure is higher, and makes the values of the inrush current I1and the pull-up current I2larger as the supply pressure is lower. According to this configuration, it is possible to efficiently generate the minimum electromagnetic force required for pulling the valve unit42toward the core43side.

In the fuel injector13according to the present embodiment, the fuel injector13further includes the sensor33that detects the supply pressure, and the control unit50sets the value of the drive current in a predetermined period, based on the detection result of the sensor33. According to this configuration, it is possible to flexibly set the value of the drive current according to the detection result of the sensor33.

In the fuel injector13according to the present embodiment, the control unit50is capable of acquiring an operation map indicating the operation content of the fuel pump11, extracts the supply pressure based on the acquired operation map, and sets the value of the drive current in a predetermined period, based on the extracted supply pressure. According to this configuration, by extracting the supply pressure, based on the operation map, it is possible to set the value of the drive current according to the operation situation.

In the fuel injector13according to the present embodiment, the fuel injector13further includes the storage unit53that stores a data table that defines the correspondence relationship between the supply pressure and the drive current, and the control unit50sets the drive current in a predetermined period corresponding to the supply pressure, based on the data table stored in the storage unit53. According to this configuration, it is possible to efficiently set the drive voltage corresponding to the supply pressure.

The technical scope of the present invention is not limited to the above-mentioned embodiments, and can be appropriately changed without departing from the scope of the present invention. For example, in the embodiment described above, a configuration in which the electromagnetic valve40is provided in the fuel injector13of the fuel injection device10has been described as an example. However, the example is not limited thereto. The electromagnetic valve40may be provided at another portion of the fuel injection device10.

Further, the embodiment of the fuel injection device10or the embodiment of the fuel pump11is not limited to the embodiment described above. For example, the number of common rails12or fuel injectors13, the connection position of the fuel pump11, and the like can be appropriately set.

Further, in the embodiment described above, a case where the inrush current I1and the pull-up current I2of the drive current I can be variably set has been described as an example. However, the example is not limited thereto. For example, the hold current I3may be capable of being variably set. Further, only the inrush current I1may be capable of being variably set.

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