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A fuel injection controller includes an increase control portion applying the boost voltage to the coil to increase a coil current to a first target value, and a constant current control portion applying a voltage to the coil to hold the coil current to a second target value. A threshold is an energ

A fuel injection controller includes an increase control portion applying the boost voltage to the coil to increase a coil current to a first target value, and a constant current control portion applying a voltage to the coil to hold the coil current to a second target value. A threshold is an energization time period that is necessary to reach a boundary point between a seat throttle area of a property line and an injection-port throttle area of the property line from an energization start time point. An initial-current applied time period is from the energization start time point that the boost voltage starts to be applied to the coil to a time point that the coil current is decreased to the second target value. The increase control portion controls the coil current such that the initial-current applied time period is less than the threshold.

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1. A fuel injection controller for a fuel injector injecting fuel used in a combustion of an internal combustion engine by a valve-opening operation of a valve body according to an electromagnetic attractive force generated by an energization of a coil, the fuel injection controller controlling an i

1. A fuel injection controller for a fuel injector injecting fuel used in a combustion of an internal combustion engine by a valve-opening operation of a valve body according to an electromagnetic attractive force generated by an energization of a coil, the fuel injection controller controlling an injection state of the fuel injector by controlling a coil current flowing through the coil, the fuel injection controller comprising: a boost circuit boosting a battery voltage to a boost voltage; andan increase control portion controlling the boost voltage to be applied to the coil, so as to increase the coil current to be equal to or greater than a first target value, whereinthe increase control portion executes an increase control to control the coil current such that an initial-current applied time period is less than a threshold, wherein the initial-current applied time period corresponds to a time period from an energization start time point that the boost voltage starts to be applied to the coil to a time point that the coil current is decreased to a second target value, and the threshold corresponds to an energization time period that is necessary for a position of the valve body to reach 50% of a maximum valve-opening position. 2. A fuel injection controller for a fuel injector injecting fuel used in a combustion of an internal combustion engine by a valve-opening operation of a valve body according to an electromagnetic attractive force generated by an energization of a coil, the fuel injection controller controlling an injection state of the fuel injector by controlling a coil current flowing through the coil, the fuel injection controller comprising: a boost circuit boosting a battery voltage to a boost voltage; andan increase control portion controlling the boost voltage to be applied to the coil, so as to increase the coil current to be equal to or greater than a first target value, whereinan energization time period of the coil and an injection amount of the fuel are set to have a relationship therebetween in a property line that has (i) an injection-port throttle area in which the injection amount is determined by a flow-throttling degree at an injection port of the fuel injector, and (ii) a seat throttle area in which the injection amount is determined by the flow-throttling degree at a seating surface of the valve body, andthe increase control portion executes an increase control to control the coil current such that a boost energization stop time point that the boost voltage applied to the coil is terminated is ahead of a time point that the injection amount reaches a turning point, wherein the injection-port throttle area has the turning point that a second derivative value of the property line is the maximum. 3. A fuel injection controller for a fuel injector injecting fuel used in a combustion of an internal combustion engine by a valve-opening operation of a valve body according to an electromagnetic attractive force generated by an energization of a coil, the fuel injection controller controlling an injection state of the fuel injector by controlling a coil current flowing through the coil, the fuel injection controller comprising: a boost circuit boosting a battery voltage to a boost voltage; andan increase control portion controlling the boost voltage to be applied to the coil, so as to increase the coil current to be equal to or greater than a first target value, whereinan energization time period of the coil and an injection amount of the fuel are set to have a relationship therebetween in a property line that has (i) a seat throttle area in which a flow-throttling degree at a seating surface of the valve body is greater than the flow-throttling degree at an injection port of the fuel injector, and (ii) an injection-port throttle area in which the flow-throttling degree at the injection port of the fuel injector is greater than the flow-throttling degree at the seating surface of the valve body, andthe increase control portion executes an increase control to control the coil current such that an initial-current applied time period is less than a threshold, wherein the initial-current applied time period corresponds to a time period from an energization start time point that the boost voltage starts to be applied to the coil to a time point that the coil current is decreased to a second target value, and the threshold corresponds to an energization time period that is necessary to reach a boundary point between the seat throttle area of when the valve-opening operation of the valve body is executed and the injection-port throttle area of when the valve-opening operation of the valve body is executed from the energization start time point. 4. A fuel injection controller according to claim 3, further comprising a pre charge control portion controlling the battery voltage to be applied to the coil before the boost voltage is controlled to be applied to the coil by the increase control portion. 5. A fuel injection controller according to claim 4, wherein a pre charge control executed by the pre charge control portion is permitted in a condition that a pressure of the fuel supplied to the fuel injector is greater than or equal to a predetermined pressure. 6. A fuel injection controller according to claim 3, wherein the first target value is set lower when a pressure of the fuel supplied to the fuel injector is lower. 7. A fuel injection controller according to claim 3, further comprising a constant current control portion controlling a voltage to be applied to the coil, so as to reduce the coil current that is increased by the increase control portion and to hold the coil current applied to the coil at the target value, whereinthe second target value is set lower when a pressure of the fuel supplied to the fuel injector is lower. 8. A fuel injection controller according to claim 3, further comprising a constant current control portion controlling a voltage to be applied to the coil, so as to reduce the coil current that is increased by the increase control portion and to hold the coil current applied to the coil at the second target value, whereinthe coil current is prohibited from flowing in the opposite direction during a decreasing time period that the coil current is decreased to the second target value. 9. A fuel injection controller according to claim 3, further comprising: an adjacent member being adjacent to the coil; anda non-adjacent member being not adjacent to the coil, whereinthe adjacent member and the non-adjacent member generate a magnetic circuit through which a magnetic flux generated according to an energization of the coil flows, andthe adjacent member has an electrical resistivity greater than that of the non-adjacent member. 10. A fuel injection controller according to claim 3, wherein a magnetic circuit through which a magnetic flux generated according to an energization of the coil flows has a part including a sintered material that is made of a metal. 11. A fuel injection controller according to claim 3, wherein the fuel injector has a stator core generating a part of a magnetic circuit as a passage of a magnetic flux generated according to an energization of the coil wherein the stator core generates an electromagnetic force,a movable core being slidable with respect to the valve body wherein the movable core is moved together with the valve body by the electromagnetic force,a main spring applying an elastic force to the valve body in a valve-closing direction, anda sub spring applying an elastic force to the valve body in a valve-opening direction via the movable core. 12. A fuel injection controller according to claim 11, wherein a pressure-bounce property curved line represents a relationship between a bounce amount of the movable core relative to the stator core and a pressure of the fuel supplied to the fuel injector, andthe increase control is executed by the increase control portion at a pressure greater than a pressure where a second derivative value of the pressure-bounce property curved line is the maximum. 13. A fuel injection controller according to claim 11, wherein a limit of a pressure of the fuel supplied to the fuel injector which is able to open the valve body 12 is referred to as an injection limit pressure, andthe increase control is executed by the increase control portion when the pressure of the fuel supplied to the fuel injector is greater than or equal to 50% of the injection limit pressure. 14. A fuel injection controller according to claim 3, wherein the fuel injector is inserted into an attachment hole disposed at a predetermined position of the internal combustion engine, and has a housing receiving the coil,the housing is cylinder-shaped and generates a part of a magnetic circuit through which a magnetic flux generated according to an energization of the coil flows,the housing has a coil portion accommodating the coil,the attachment hole has an inner peripheral surface, andan outer peripheral surface of at least a part of the coil portion is surrounded by the inner peripheral surface over the whole periphery. 15. A fuel injection controller according to claim 3 being applied to a combustion system having a fuel pump, the fuel pump driven by the internal combustion engine and generating a pressure of the fuel supplied to the fuel injector, wherein the increase control is executed by the increase control portion, when the internal combustion engine is operating in an idle operation. 16. A fuel injection controller according to claim 3, wherein the increase control is executed by the increase control portion, when a multi-injection in which fuel is divided to be injected for multiple times in a single combustion cycle is executed. 17. A fuel injection controller according to claim 3, further comprising a constant current control portion controlling a voltage to be applied to the coil, so as to reduce the coil current that is increased by the increase control portion and to hold the coil current applied to the coil at the second target value, whereinthe constant current control portion controls the battery voltage to be applied to the coil so as to hold the coil current applied to the coil at the second target value. 18. A fuel injection controller according to claim 3, wherein an integrated value of the coil current flowing according to the increase control portion is referred to as an initial energy applied amount, andthe increase control portion executes the increase control to control the coil current such that a differential amount of the initial energy applied amount generated due to a variation in a coil temperature is less than a predetermined value. 19. A fuel injection controller according to claim 18, wherein the increase control portion executes the increase control to control the coil current such that a peak value of the coil current flowing according to the increase control portion decreases in accordance with the coil temperature. 20. A fuel injection controller according to claim 18, wherein the boost circuit has a condenser and a switching member, and the boost circuit boosts the voltage by switching the switching member to charge or discharge the condenser, andthe switching member has a discharge capacity greater than a predetermined capacity. 21. A fuel injection system comprising: the fuel injection controller according to claim 3; andthe fuel injector.