Patent Publication Number: US-2019178196-A1

Title: Control device for fuel pump

Description:
BACKGROUND 
     The present disclosure relates to a control device for a fuel pump. 
     An internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. 2002-242786 includes a fuel injection valve for injecting fuel into a cylinder, a fuel pipe connected to the fuel injection valve, and a fuel pump for supplying the fuel to the fuel pipe. The fuel pump includes a pump housing having a pump chamber with which a fuel suction port and a fuel discharge port communicate, and a driving member for increasing and reducing the volume of the pump chamber by being displaced. The fuel pump includes a spring for biasing the driving member in a direction of reducing the volume of the pump chamber. The fuel pump also includes an electromagnetic actuator for displacing the driving member in a direction of increasing the volume of the pump chamber against the biasing force of the spring. The fuel pump displaces the driving member by the action of the spring and the electromagnetic actuator to execute a suction operation for drawing in fuel into the pump chamber, and a discharge operation for pressurizing the fuel drawn into the pump chamber and thus discharging the fuel from the pump chamber. 
     In a control device for the fuel pump disclosed in the above-described publication, immediately after the fuel injection from the fuel injection valve is completed, the fuel pump is driven to perform fuel discharge. Thus, the fluctuations of the fuel pressure in the fuel pipe due to the fuel discharge from the fuel pump converge before the next fuel injection is started. 
     When fuel injection is performed, there are cases where multistage injection is performed, in which fuel is injected multiple times in one combustion cycle. However, the above-described publication discloses no control of the fuel pump to execute such a multistage injection. In view of this, an object of the present disclosure is to appropriately drive a fuel pump for supplying fuel to a fuel injection valve configured to execute multistage injection. 
     SUMMARY 
     In accordance with a first aspect of the present disclosure, a control device for a fuel pump is provided. The fuel pump is a motor-driven fuel pump adapted for an internal combustion engine. The internal combustion engine includes a fuel injection valve configured to execute multistage injection in which fuel is injected into a cylinder multiple times in one combustion cycle. The fuel pump is configured to supply fuel to a fuel pipe connected to the fuel injection valve. The fuel pump includes a cylinder, a mover configured to slide in the cylinder, and an electric actuator configured to move the mover. The control device comprises processing circuitry that is configured to: perform energization control on the electric actuator to reciprocate the mover so that the fuel pump draws in fuel and discharges fuel; and cause the fuel pump to discharge fuel in a period between an end of a multistage injection from the fuel injection valve and a start of a next multistage injection, and keep the fuel pump from discharging fuel in a period during which the multistage injection from the fuel injection valve is executed. 
     In accordance with a second aspect of the present disclosure, a control device for a fuel pump is provided. The fuel pump is a motor-driven fuel pump adapted for an internal combustion engine. The internal combustion engine includes a fuel injection valve configured to execute multistage injection in which fuel is injected into a cylinder multiple times in one combustion cycle. The multistage injection includes main injection in which the largest amount of fuel is injected and sub-injection in which a smaller amount of fuel than the amount in the main injection is injected. The fuel pump is configured to supply fuel to a fuel pipe connected to the fuel injection valve. The fuel pump includes a cylinder, a mover configured to slide in the cylinder, and an electric actuator configured to move the mover. The control device comprises processing circuitry that is configured to: perform energization control on the electric actuator to reciprocate the mover so that the fuel pump draws in and discharges fuel; and cause the fuel pump to start fuel discharge and end the fuel discharge in a period between a start or an end of the main injection and a start of a next main injection. 
     In accordance with a third aspect of the present disclosure, a control device for a fuel pump is provided. The fuel pump is a motor-driven fuel pump adapted for an internal combustion engine. The internal combustion engine includes a fuel injection valve configured to execute multistage injection in which fuel is injected into a cylinder multiple times in one combustion cycle. The multistage injection includes main injection in which the largest amount of fuel is injected and sub-injection in which a smaller amount of fuel than the amount in the main injection is injected. The fuel pump is configured to supply fuel to a fuel pipe connected to the fuel injection valve. The fuel pump includes a cylinder, a mover configured to slide in the cylinder, and an electric actuator configured to move the mover. The control device comprises processing circuitry that is configured to: perform energization control on the electric actuator to reciprocate the mover so that the fuel pump draws in and discharges fuel; execute a first discharge control, in which, when an injection interval between an end timing of the multistage injection from the fuel injection valve and a start timing of the next multistage injection is equal to or larger than a determination value, the processing circuitry causes the fuel pump to start fuel discharge in a period between an end of the multistage injection and a start of the next multistage injection, and keep the fuel pump from executing fuel discharge in a period during which the multistage injection from the fuel injection valve is executed; and execute a second discharge control, in which, when the injection interval is less than the determination value, the processing circuitry causes the fuel pump to start fuel discharge in a period between an end of the main injection and a start of the sub-injection that is executed after the main injection. 
     Other aspects and advantages of the present disclosure will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram showing a configuration of an internal combustion engine including a control device for a fuel pump according to a first embodiment; 
         FIG. 2  is a cross-sectional view of the high-pressure fuel pump in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view showing a state during fuel discharge in the high-pressure fuel pump in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view showing a state during fuel suction in the high-pressure fuel pump in  FIG. 2 ; 
         FIG. 5  is a functional block diagram of the control device in  FIG. 1 ; 
         FIG. 6  is a timing diagram showing an example of a manner of fuel injection from the fuel injection valve and a manner of fuel discharge from the high-pressure fuel pump; 
         FIG. 7  is a timing diagram showing an example of a manner of fuel injection from a fuel injection valve and a manner of fuel discharge from the high-pressure fuel pump according to a second embodiment; 
         FIG. 8  is a functional block diagram of a discharge start timing calculation section according to a third embodiment; and 
         FIG. 9  is a timing diagram showing an example of a manner of fuel injection from the fuel injection valve and a manner of fuel discharge from the high-pressure fuel pump according to the third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     A control device for a fuel pump according to a first embodiment will now be described with reference to  FIGS. 1 to 6 . 
     As shown in  FIG. 1 , an engine main body  11  of an internal combustion engine  10  mounted on a vehicle includes four cylinders (a first cylinder # 1  to a fourth cylinder # 4 ). To the engine main body  11 , an intake passage  12  is connected. The intake passage  12  includes an intake manifold  13  and an intake pipe  14  connected to the end of the intake manifold  13  on the intake upstream side. The intake manifold  13  includes a surge tank  13 A connected to the intake pipe  14 , an intake introduction section  13 B provided on the intake downstream side of the surge tank  13 A, and an intake branching section  13 C provided on the intake downstream side of the intake introduction section  13 B. The surge tank  13 A has a larger passage cross-sectional area than the intake pipe  14  and the intake introduction section  13 B. The intake branching section  13 C has four end portions branching on the intake downstream side, and the respective four branching end portions are connected to different cylinders. The intake pipe  14  is provided with a throttle valve  21 . By controlling the opening degree of the throttle valve  21 , the flow rate of the intake air flowing through the intake passage  12  is controlled. The air flowing from the intake pipe  14  to the intake manifold  13  is supplied to the respective cylinders # 1  to # 4 . The intake pipe  14  is provided with an air flow meter  90  that detects the flow rate of the intake air flowing through the intake passage  12  on the intake upstream side with respect to the throttle valve  21 . 
     The engine main body  11  is provided with a plurality of fuel injection valves  15 . One fuel injection valve  15  is provided for each cylinder. The fuel injection valve  15  is disposed in the cylinder to inject fuel into the cylinder. In each of the cylinders # 1  to # 4 , an ignition plug  16  is provided. In each of the cylinders # 1  to # 4 , the intake air introduced through the intake passage  12  and the fuel injected from the fuel injection valve  15  are mixed to generate an air-fuel mixture. The mass ratio of intake air to fuel in the air-fuel mixture is referred to as air-fuel ratio. The air-fuel mixture is ignited by the ignition plug  16  and combusted. 
     To the engine main body  11 , an exhaust passage  17  is connected. The exhaust passage  17  includes an exhaust manifold  18  and an exhaust pipe  19  connected to the end of the exhaust manifold  18  on the exhaust downstream side. The exhaust manifold  18  is composed of an exhaust branching section  18 A connected to the engine main body  11  and an exhaust confluence section  18 B provided on the exhaust downstream side of the exhaust branching section  18 A. The exhaust branching section  18 A has four branched ends on the exhaust upstream side, and the respective four branching end portions are connected to different cylinders. In each of the cylinders # 1  to # 4 , exhaust gas generated by combustion of the air-fuel mixture is discharged to the exhaust manifold  18 . In the exhaust passage  17 , a catalyst  20  disposed in the exhaust pipe  19  to purify the exhaust gas is provided. Further, in the exhaust pipe  19 , an air-fuel ratio sensor  91  is disposed on the exhaust upstream side of the catalyst  20 . The air-fuel ratio sensor  91  outputs an electric signal corresponding to the oxygen concentration of the exhaust gas flowing through the exhaust passage  17 , that is, the air-fuel ratio of the air-fuel mixture used for combustion. 
     The internal combustion engine  10  is provided with a fuel supply device  30  for supplying fuel to the fuel injection valve  15  provided in the engine main body  11 . The fuel supply device  30  includes a fuel tank  31  in which fuel is stored. Inside the fuel tank  31 , a low-pressure fuel pump  32  is disposed. To the low-pressure fuel pump  32 , one end of a low-pressure fuel pipe  33  is connected. The low-pressure fuel pump  32  is a motor-driven fuel pump, pumps up the fuel in the fuel tank  31 , and discharges the fuel to the low-pressure fuel pipe  33 . To the other end of the low-pressure fuel pipe  33 , a high-pressure fuel pump  40  is connected. To the high-pressure fuel pump  40 , a high-pressure fuel pipe  34  is connected. The high-pressure fuel pipe  34  is composed of a discharge pipe  34 A connected to the high-pressure fuel pump  40  and a delivery pipe  34 B connected to the discharge pipe  34 A. To the delivery pipe  34 B, the respective fuel injection valves  15  are connected. The fuel discharged from the low-pressure fuel pump  32  to the low-pressure fuel pipe  33  is drawn into the high-pressure fuel pump  40 . In the high-pressure fuel pump  40 , the drawn fuel is pressurized and discharged to the discharge pipe  34 A. The fuel discharged to the discharge pipe  34 A is supplied to the delivery pipe  34 B and injected into the cylinder from the fuel injection valve  15 . In the delivery pipe  34 B, a pressure sensor  92  is provided on a first end portion connected to the discharge pipe  34 A. The pressure sensor  92  detects the fuel pressure Pr in the high-pressure fuel pipe  34 . In the delivery pipe  34 B, a fuel temperature sensor  93  is provided on a second end portion opposite to the first end portion. The fuel temperature sensor  93  detects the temperature of the fuel in the high-pressure fuel pipe  34 . 
     As shown in  FIG. 2 , the high-pressure fuel pump  40  includes a pump section  50  that draws in and pressurizes fuel and a casing  80  to which the pump section  50  is connected. 
     The casing  80  has a box shape. The casing  80  has a lower wall  81  and an upper wall  84  that each have a disc shape, and a peripheral side wall  82  that extends from the circumferential edge of the lower wall  81  to the circumferential edge of the upper wall  84 . At a central portion of the lower wall  81 , a columnar protruded portion  83  that protrudes in the inner space side of the casing  80  is provided. The peripheral side wall  82  is continuously provided over the entire periphery of the circumferential edge of the lower wall  81  and the upper wall  84 , and has a cylindrical shape. The upper wall  84  has a through hole  84 A at a central portion. 
     The pump section  50  includes a housing  51  fixed to the upper end surface of the upper wall  84 . The housing  51  is composed of a main body portion  52  having a cylindrical shape, a flange portion  55  disposed between the main body portion  52  and the upper wall  84 , and an insertion portion  56  extending from the flange portion  55 . The flange portion  55  has a larger diameter than the main body portion  52  and is in contact with the upper wall  84 . The insertion portion  56  extends from the flange portion  55  to the inner space of the casing  80  through the through hole  84 A. The outer diameter of the insertion portion  56  is the same as the inner diameter of the through hole  84 A. Therefore, the outer circumferential surface of the insertion portion  56  is in contact with the inner circumferential surface of the through hole  84 A of the upper wall  84 . The housing  51  has a cylinder bore  57 . The cylinder bore  57  extends from one end face (the lower end face in  FIG. 2 ) of the insertion portion  56  to the inside of the main body portion  52 . Hereinafter, the extending direction (the up-down direction in  FIG. 2 ) of the central axis L of the cylinder bore  57  is simply referred to as the axial direction. 
     The main body portion  52  has a first orthogonal hole  53  and a second orthogonal hole  54  that extend in a direction (the left-right direction in  FIG. 2 ) orthogonal to the axial direction and communicate with the cylinder bore  57 . The first orthogonal hole  53  and the second orthogonal hole  54  extend in opposite directions from the cylinder bore  57 . The first orthogonal hole  53  has a first small diameter portion  53 A that communicates with the cylinder bore  57  and a first large diameter portion  53 B that extends from the first small diameter portion  53 A to the side peripheral surface of the main body portion  52  and opens on the side peripheral surface. In the first large diameter portion  53 B, a suction valve  60  is inserted and fitted. 
     The suction valve  60  has a cylindrical shape and is attached to the main body portion  52  in a state of protruding from the main body portion  52 . In the suction valve  60 , a suction passage  61  extends through the suction valve  60  in the above-described orthogonal direction is formed. The suction passage  61  is composed of a first suction passage  61 A that is connected to the first small diameter portion  53 A, a second suction passage  61 B that is connected to the first suction passage  61 A and has a larger diameter than the first suction passage  61 A, and a third suction passage  61 C that is connected to the second suction passage  61 B and has the same diameter as the first suction passage  61 A. In the second suction passage  61 B, a first check valve  62  is disposed. The first check valve  62  is composed of a first valve body  63  and a first spring  64  for biasing the first valve body  63  toward the third suction passage  61 C. The first valve body  63  is composed of a first biasing portion  63 A that is in contact with the inner end surface of the second suction passage  61 B on which the third suction passage  61 C opens, and a first bulging portion  63 B that bulges from the central portion of the first biasing portion  63 A toward the first suction passage  61 A. The first bulging portion  63 B has a hemispherical shape. The first spring  64  has a first end that is in contact with the inner end surface of the second suction passage  61 B on which the first suction passage  61 A opens, and a second end that is in contact with the first biasing portion  63 A of the first valve body  63 . To the suction valve  60 , the low-pressure fuel pipe  33  is connected, and to the third suction passage  61 C, fuel is supplied from the low-pressure fuel pipe  33 . 
     The second orthogonal hole  54  has a second small diameter portion  54 A that communicates with the cylinder bore  57  and a second large diameter portion  54 B that extends from the second small diameter portion  54 A to the side peripheral surface of the main body portion  52  and opens on the side peripheral surface. In the second large diameter portion  54 B, a discharge valve  70  is inserted and fitted. The discharge valve  70  has a cylindrical shape and is attached to the main body portion  52  in a state of protruding from the main body portion  52 . The discharge valve  70  and the suction valve  60  are arranged side by side on the same axis extending in the above-described orthogonal direction. In the discharge valve  70 , a discharge passage  71  extending through the discharge valve  70  in the above-described orthogonal direction is formed. The discharge passage  71  is composed of a first discharge passage  71 A that is connected to the second small diameter portion  54 A, a second discharge passage  71 B that is connected to the first discharge passage  71 A and has a larger diameter than the first discharge passage  71 A, and a third discharge passage  71 C that is connected to the second discharge passage  71 B and has the same diameter as the first discharge passage  71 A. In the second discharge passage  71 B, a second check valve  72  is disposed. 
     The second check valve  72  is composed of a second valve body  73  and a second spring  74  for biasing the second valve body  73  toward the first discharge passage  71 A. The second valve body  73  is composed of a second biasing portion  73 A that is in contact with the inner end surface of the second discharge passage  71 B on which the first discharge passage  71 A opens, and a second bulging portion  73 B that bulges from the central portion of the second biasing portion  73 A toward the third discharge passage  71 C. The second bulging portion  73 B has a hemispherical shape. The second spring  74  has a first end that is in contact with the inner end surface of the second discharge passage  71 B on which the third discharge passage  71 C opens, and a second end that is in contact with the second biasing portion  73 A of the second valve body  73 . To the discharge valve  70 , the high-pressure fuel pipe  34  is connected. 
     The pump section  50  includes a plunger  75  serving as a mover that is inserted into the cylinder bore  57  and that is slidable in the cylinder bore  57 . The plunger  75  is made of a magnetic material. The plunger  75  has a columnar rod shape and is inserted into the cylinder bore  57  from the lower end opening of the insertion portion  56 . The lower end portion of the plunger  75  extends from the cylinder bore  57  to the inner space of the casing  80 . The plunger  75  has a groove  75 A at a lower end portion. The groove  75 A extends over the entire circumference in the circumferential direction. Therefore, the plunger  75  has a diameter that is partially reduced at the position in which the groove  75 A is formed. To the groove  75 A, a pedestal  76  having an annular plate shape is connected. The pedestal  76  is composed of a central portion  76 A engaged with the groove  75 A, a curved portion  76 B having a curve and extending outward in the radial direction from the central portion  76 A, and a flat portion  76 C extending outward in the radial direction from the curved portion  76 B. Between the flat portion  76 C and the insertion portion  56  of the housing  51 , a compression spring  77  is disposed. The compression spring  77  biases the pedestal  76  in a direction away from the housing  51 , that is, in a direction of pulling out the plunger  75  from the cylinder bore  57  (downward in  FIG. 2 ). The lower end surface of the plunger  75  is pressed against the upper end surface of the protruded portion  83  of the casing  80  by the biasing force of the compression spring  77 . The plunger  75  has a protrusion  75 B at a lower end portion above the groove  75 A. The protrusion  75 B extends over the entire circumference in the circumferential direction. Therefore, the plunger  75  has a diameter that is partially increased at the position of the protrusion  75 B. The diameter of the protrusion  75 B is larger than the diameter of the cylinder bore  57 . The cylinder bore  57 , the plunger  75 , the first small diameter portion  53 A, the first suction passage  61 A, the second suction passage  61 B, the second small diameter portion  54 A, and the first discharge passage  71 A constitute a pressurizing chamber  78  of the pump section  50 . 
     In the main body portion  52  of the housing  51 , a coil  85  is disposed so as to surround the periphery of the cylinder bore  57 . The coil  85  generates a magnetic field upon energization. When the coil  85  is energized, the plunger  75  is excited by the magnetic field generated around the coil  85 . 
     As indicated by the blank arrow in  FIG. 3 , when the plunger  75  is excited, the plunger  75  moves to a first side (the upper side in  FIG. 3 ) in the axial direction against the biasing force of the compression spring  77 . The plunger  75  moves to the first side until the protrusion  75 B comes into contact with the insertion portion  56 . This movement of the plunger  75  decreases the volume of the pressurizing chamber  78  of the pump section  50  and increases the pressure in the pressurizing chamber  78 . Since the pressurizing chamber  78  is filled with fuel as described later, increasing the pressure of the pressurizing chamber  78  makes the discharge valve  70  open. Specifically, the second valve body  73  of the discharge valve  70  is subjected to the pressure in the pressurizing chamber  78  in the valve opening direction, and is also subjected to the pressure in the high-pressure fuel pipe  34  and the biasing force of the second spring  74  in the valve closing direction. When the pressure in the pressurizing chamber  78  increases and the force of biasing the second valve body  73  in the valve opening direction becomes higher than the force of biasing the second valve body  73  in the valve closing direction, the second valve body  73  is opened. When the second valve body  73  opens, fuel is discharged from the pressurizing chamber  78  to the high-pressure fuel pipe  34  as indicated by the solid line arrow in  FIG. 3 . While the fuel is discharged from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34 , the suction valve  60  is held in a closed state by the pressure in the pressurizing chamber  78 . On the other hand, when the energization to the coil  85  is stopped, the excitation of the plunger  75  is cancelled. 
     As indicated by the blank arrow in  FIG. 4 , when the excitation of the plunger  75  is cancelled, the plunger  75  moves to a second side (the lower side in  FIG. 4 ) in the axial direction by the biasing force of the compression spring  77  so that the plunger  75  is pulled out from the cylinder bore  57 . The plunger  75  moves to the second side until its lower end comes into contact with the protruded portion  83 . This movement of the plunger  75  increases the volume of the pressurizing chamber  78  and decreases the pressure in the pressurizing chamber  78 . The first valve body  63  of the suction valve  60  is subjected to the pressure in the low-pressure fuel pipe  33  in the valve opening direction, and is also subjected to the pressure in the pressurizing chamber  78  and the biasing force of the first spring  64  in the valve closing direction. When the pressure in the pressurizing chamber  78  decreases and the force of biasing the first valve body  63  in the valve closing direction becomes lower than the force of biasing the first valve body  63  in the valve opening direction, the first valve body  63  is opened. When the first valve body  63  opens, fuel is supplied from the low-pressure fuel pipe  33  to the pressurizing chamber  78  as indicated by the solid line arrow in  FIG. 4 . While the high-pressure fuel pump  40  draws in the fuel from the low-pressure fuel pipe  33 , the discharge valve  70  is held in a closed state by the pressure in the high-pressure fuel pipe  34 . 
     In this manner, the plunger  75  reciprocates in the axial direction inside the cylinder bore  57  depending on the energization state of the coil  85 . Accordingly, the coil  85  corresponds to an electric actuator for moving the plunger  75 . Each time the plunger  75  reciprocates, the high-pressure fuel pump  40  performs a suction function of drawing in the fuel and a discharge function of pressurizing and discharging the drawn fuel. Further, in the main body portion  52  of the fuel pump, a coil temperature sensor  94  is provided. The coil temperature sensor  94  detects the temperature of the coil  85 . 
     As shown in  FIG. 1 , the fuel supply device  30  includes a control device  100  for a fuel pump. Further, the internal combustion engine  10  includes a battery  120 . The battery  120  supplies electric power to the respective parts of the internal combustion engine  10 , such as the control device  100  and the electric actuator of the high-pressure fuel pump  40 . 
     To the control device  100 , output signals are input from the air flow meter  90 , the air-fuel ratio sensor  91 , the pressure sensor  92 , the fuel temperature sensor  93 , and the coil temperature sensor  94 . To the control device  100 , an output signal of a crank angle sensor  95  that detects the engine rotational speed NE, which is a rotational speed of a crankshaft of the internal combustion engine  10 , and the crank angle CA, which is a rotation phase of the crankshaft is also input. Further, to the control device  100 , output signals from various sensors such as an accelerator sensor  96  for detecting an accelerator operation amount Acc that is an operation amount of an accelerator pedal, a vehicle speed sensor  97  for detecting a vehicle speed V, etc., are also input. The control device  100  includes a CPU, a ROM, and a RAM. The control device  100  causes the CPU to execute programs stored in the ROM to control driving of the fuel injection valve  15 , and driving of the high-pressure fuel pump  40 . 
     As shown in  FIG. 5 , the control device  100  includes a target rotational speed calculation section  101 , a target torque calculation section  102 , a target fuel pressure calculation section  103 , a fuel pressure difference calculation section  104 , an injection feedback amount calculation section  105 , and a required injection amount calculation section  106 . The control device  100  also includes an injection pattern setting section  107 , a multistage injection amount setting section  108 , an injection time calculation section  109 , an injection start timing calculation section  110 , and an injection valve driving section  111 . Furthermore, the control device  100  includes a discharge start timing calculation section  112 , a target discharge amount calculation section  113 , a pump characteristics learning section  114 , and a pump driving section  115 . 
     The target rotational speed calculation section  101  calculates a target rotational speed NEt that is a target value of the engine rotational speed NE, based on the engine rotational speed NE detected by the crank angle sensor  95  and the accelerator operation amount Acc detected by the accelerator sensor  96 . 
     The target torque calculation section  102  calculates a target torque TQt that is a target value of the axial torque of the crankshaft of the internal combustion engine  10 , based on the vehicle speed V detected by the vehicle speed sensor  97  and the accelerator operation amount Acc detected by the accelerator sensor  96 . 
     The target fuel pressure calculation section  103  calculates a target fuel pressure Pt that is a target value of the fuel pressure in the high-pressure fuel pipe  34 , based on the target rotational speed NEt calculated by the target rotational speed calculation section  101  and the target torque TQt calculated by the target torque calculation section  102 . In the target fuel pressure calculation section  103 , a map indicating a relationship between a target fuel pressure Pt and each of a target rotational speed NEt and a target torque TQt is stored. This map is previously obtained by experiment and simulation. The target fuel pressure Pt is calculated so as to be higher when the target rotational speed NEt is high than when the target rotational speed NEt is low. Further, the target fuel pressure Pt is calculated so as to be higher when the target torque TQt is large than when the target torque TQt is small. 
     The fuel pressure difference calculation section  104  calculates a fuel pressure difference ΔP (ΔP=Pt−Pr), which is a value obtained by subtracting the fuel pressure Pr in the high-pressure fuel pipe  34  detected by the pressure sensor  92  from the target fuel pressure Pt calculated by the target fuel pressure calculation section  103 . 
     The injection feedback amount calculation section  105  calculates an injection feedback amount FAF for feedback control of feeding the actual air-fuel ratio detected by the air-fuel ratio sensor  91  back to the target air-fuel ratio that is a target value of the air-fuel ratio. The target air-fuel ratio is calculated based on the operating state of the internal combustion engine  10  by the control device  100 . The injection feedback amount calculation section  105  inputs a value obtained by subtracting the actual air-fuel ratio from the target air-fuel ratio to a proportional element, an integral element, and a differential element, and outputs as an injection feedback amount FAF the sum of an output value of the proportional element, an output value of the integral element, and an output value of the differential element. 
     The required injection amount calculation section  106  calculates a required fuel injection amount Qt that is a target value of the fuel amount injected from each fuel injection valve  15 . The required injection amount calculation section  106  calculates a base injection amount Qb based on the target rotational speed NEt calculated by the target rotational speed calculation section  101  and the target torque TQt calculated by the target torque calculation section  102 . The base injection amount Qb is calculated so as to be larger when the target rotational speed NEt is high than when the target rotational speed NEt is low. Further, the base injection amount Qb is calculated so as to be larger when the target torque TQt is large than when the target torque TQt is small. The base injection amount Qb is calculated as a fuel injection amount corresponding to the target air-fuel ratio. The required injection amount calculation section  106  calculates the required fuel injection amount Qt by multiplying the base injection amount Qb by the injection feedback amount FAF calculated by the injection feedback amount calculation section  105 . 
     The injection pattern setting section  107  sets an injection pattern for multistage injection based on the engine rotational speed NE detected by the crank angle sensor  95  and the accelerator operation amount Acc detected by the accelerator sensor  96 . In the multistage injection, fuel is injected multiple times in one combustion cycle. The injection pattern for multistage injection includes main injection and sub-injection to be executed during a different period from the main injection. The sub-injection includes pilot-injection and pre-injection, in which fuel is injected before the main injection, and after-injection and post-injection, in which fuel is injected after the main injection. In the main injection, the largest amount of fuel is injected, which contributes most to combustion accordingly. The injection pattern is previously obtained by experiment and simulation so as to be most suitable for the operating state of the internal combustion engine  10  based on the engine rotational speed NE and the accelerator operation amount Acc, and stored in the injection pattern setting section  107 . 
     The multistage injection amount setting section  108  calculates a target injection amount of each injection in the multistage injection, based on the injection pattern set by the injection pattern setting section  107  and the required fuel injection amount Qt calculated by the required injection amount calculation section  106 . For example, when the injection pattern set by the injection pattern setting section  107  includes the pre-injection, the main injection, and the after-injection, the multistage injection amount setting section  108  first sets as a target injection amount Qtm for the main injection an injection amount obtained by multiplying the required fuel injection amount Qt by a predetermined main ratio (for example, 90%). The main ratio is set such that the target injection amount Qtm for the main injection is maximized in one combustion cycle. The pre-injection is performed to suppress the ignition delay of fuel in the main injection so as to make combustion stable. A target injection amount Qtp for the pre-injection is calculated by multiplying the required fuel injection amount Qt by a pre-ratio (&lt;100%−the main ratio) calculated depending on the temperature in each cylinder. The main ratio and the pre-ratio are previously obtained by experiment and simulation, etc., and are stored in the control device  100 . After calculating the target injection amount Qtm for the main injection and the target injection amount Qtp for the pre-injection in this way, the multistage injection amount setting section  108  subtracts an injection amount obtained by adding the target injection amount Qtm and the target injection amount Qtp from the required fuel injection amount Qt thus to calculate a target injection amount Qta (Qta=Qt−(Qtm+Qtp)) for the after-injection. The target injection amount Qtp for the pre-injection and the target injection amount Qta for the after-injection are each smaller than the target injection amount Qtm for the main injection. 
     The injection time calculation section  109  calculates an injection time Fi as the execution time of each injection in the injection pattern set by the injection pattern setting section  107 , based on each target injection amount set by the multistage injection amount setting section  108  and the fuel pressure Pr detected by the pressure sensor  92 . For example, when the injection pattern includes the pre-injection, the main injection, and the after-injection, an injection time Fip of the pre-injection is calculated based on the target injection amount Qtp for the pre-injection and the fuel pressure Pr. Further, an injection time Fim of the main injection is calculated based on the target injection amount Qtm for the main injection and the fuel pressure Pr. In addition, an injection time Fia of the after-injection is calculated based on the target injection amount Qta for the after-injection and the fuel pressure Pr. 
     The injection start timing calculation section  110  calculates an injection start timing Fs of each injection in the injection pattern set by the injection pattern setting section  107 . The injection start timing Fs of each injection is calculated based on each target injection amount set by the multistage injection amount setting section  108 , each injection time calculated by the injection time calculation section  109 , the engine rotational speed NE detected by the crank angle sensor  95 . For example, when the injection pattern includes the pre-injection, the main injection, and the after-injection, the injection start timing calculation section  110  calculates an injection start timing Fsp of the pre-injection, an injection start timing Fsm of the main injection, and an injection start timing Fsa of the after-injection. 
     The injection valve driving section  111  drives the fuel injection valve  15  to execute multistage injection in which fuel is injected multiple times in one combustion cycle. Then, at the injection start timing Fs calculated by the injection start timing calculation section  110 , the injection valve driving section  111  controls driving of the fuel injection valve  15  based on the crank angle CA detected by the crank angle sensor  95  so that fuel injection from the fuel injection valve  15  is started. After the fuel injection is continued during the injection time Fi calculated by the injection time calculation section  109  from the start of the fuel injection, the injection valve driving section  111  ends the fuel injection from the fuel injection valve  15 . 
     The discharge start timing calculation section  112  calculates a discharge start timing Ts that is a point in time at which fuel discharge from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34  is started. The discharge start timing Ts is calculated based on the timing of fuel injection of the fuel injection valve  15 . In the present embodiment, the discharge start timing Ts is set to the timing at which a predetermined preparation time has elapsed from the end timing Fe of fuel injection of the fuel injection valve  15 . The end timing Fe at which the multistage injection is ended is the end timing of the last injection in the injection pattern set by the injection pattern setting section  107 . The end timing Fe of the multistage injection can be calculated based on the injection time Fi of the last injection and the injection start timing Fs of the last injection. The preparation time is set to a time required for the fuel pressure difference ΔP to become stable after the multistage injection from the fuel injection valve  15  is ended. The preparation time is previously obtained by experiment and simulation and stored in the control device  100 . 
     The target discharge amount calculation section  113  calculates a target discharge amount TPt that is a target value of the fuel discharge amount from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34 . The target discharge amount calculation section  113  calculates a base discharge amount TPb based on the required fuel injection amount Qt calculated by the required injection amount calculation section  106 . The base discharge amount TPb is calculated as an amount equal to the required fuel injection amount Qt. That is, the base discharge amount TPb increases as the required fuel injection amount Qt increases. Further, the target discharge amount calculation section  113  calculates a discharge feedback amount TK based on the fuel pressure difference ΔP calculated by the fuel pressure difference calculation section  104 . In the present embodiment, a value obtained by subtracting from the target fuel pressure Pt the actual fuel pressure Pr after fuel is discharged from the high-pressure fuel pump  40  so as to reach the target fuel pressure Pt is input to a proportional element, an integral element, and an differential element, and the sum of an output value of the proportional element, an output value of the integral element, and an output value of the differential element is calculated as the discharge feedback amount TK. The target discharge amount calculation section  113  calculates the target discharge amount TPt by multiplying the base discharge amount TPb by the discharge feedback amount TK. 
     The pump characteristics learning section  114  learns a relationship between an energization time to the high-pressure fuel pump  40  and an amount of fuel discharged from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34  as pump characteristics. The fuel discharge amount from the high-pressure fuel pump  40  is affected by the fuel temperature in the high-pressure fuel pipe  34  detected by the fuel temperature sensor  93 , the temperature of the coil  85  detected by the coil temperature sensor  94 , the battery voltage, and the like. In other words, the viscosity of the fuel is higher when the fuel temperature is low than when the fuel temperature is high. Therefore, the resistance in fuel discharge is larger when the fuel temperature is low than when the fuel temperature is high. Further, the force to move the plunger  75  toward the pressurizing chamber  78  is weaker when the temperature of the coil  85  is high than when the temperature of the coil  85  is low. In addition, the force to move the plunger  75  toward the pressurizing chamber  78  is weaker when the battery voltage is low than when the battery voltage is high. Thus, as the fuel temperature is lower, the temperature of the coil  85  is higher, or the battery voltage is lower, the amount of fuel discharged from the high-pressure fuel pump  40  tends to be smaller. The battery voltage can be obtained from a charge/discharge state of the battery  120 . The pump characteristics learning section  114  calculates a discharge amount for which the high-pressure fuel pump  40  is driven for the energization time set based on the target discharge amount TPt, based on the fuel pressure difference ΔP calculated by the fuel pressure difference calculation section  104 , and stores the discharge amount together with information of the fuel temperature, the temperature of the coil  85 , and the battery voltage. 
     The pump driving section  115  performs energization control of the high-pressure fuel pump  40  to the coil  85  at the discharge start timing Ts calculated by the discharge start timing calculation section  112 . The pump driving section  115  causes the plunger  75  to reciprocate through the energization control, thereby causing the high-pressure fuel pump  40  to execute fuel suction and fuel discharge. The pump driving section  115  ends the energization when a lift time Ti has elapsed from the start of the energization control for the high-pressure fuel pump  40 . The pump driving section  115  sets the lift time Ti such that an amount of fuel corresponding to the target discharge amount TPt is discharged, based on the pump characteristics learned by the pump characteristics learning section  114 . 
     An operation and advantages of the present embodiment will now be described with reference to  FIG. 6 . In the following description, the point in time of each operation in  FIG. 6  is indicated by t followed by three-digit numbers. However, in  FIG. 6 , the symbol t and the first digit  6  of the three digits are omitted. 
     In conjunction with the operation of the internal combustion engine  10 , multistage injection is repeatedly executed. In an example shown in  FIG. 6 , the injection pattern for multistage injection includes the pre-injection, the main injection, and the after-injection. When the multistage injection is executed, the injection valve driving section  111  first starts fuel injection at a point in time t 611  that is the injection start timing Fsp of the pre-injection calculated by the injection start timing calculation section  110 . The injection valve driving section  111  continues the fuel injection during the injection time Fip of the pre-injection calculated by the injection time calculation section  109 , and ends the pre-injection at a point in time t 612  when the injection time Fip of the pre-injection has elapsed from the point in time t 611 . After that, the injection valve driving section  111  starts fuel injection at a point in time t 613  that is the injection start timing Fsm of the main injection calculated by the injection start timing calculation section  110 . The injection valve driving section  111  continues the fuel injection during the injection time Fim of the main injection calculated by the injection time calculation section  109 , and ends the main injection at a point in time t 614  when the injection time Fim of the main injection has elapsed from the point in time t 613 . After that, the injection valve driving section  111  starts fuel injection at a point in time t 615  that is the injection start timing Fsa of the after-injection calculated by the injection start timing calculation section  110 . The injection valve driving section  111  continues the fuel injection during the injection time Fia of the after-injection calculated by the injection time calculation section  109 , and ends the main injection at a point in time t 616  when the injection time Fia of the after-injection has elapsed from the point in time t 615 . In this way, the fuel injection valve  15  executes multistage injection. 
     After the multistage injection is executed, the target discharge amount calculation section  113  calculates a target discharge amount TPt at a point in time t 617  when the preparation time described above has elapsed. The target discharge amount TPt is calculated based on a required fuel injection amount Qt for the next multistage injection calculated by the required injection amount calculation section  106  and a fuel pressure difference ΔP between the current fuel pressure Pr and the target fuel pressure Pt. The use of the fuel pressure difference ΔP when the preparation time has elapsed after the multistage injection is executed makes it possible to reduce the influence of the fluctuations of fuel pressure in the high-pressure fuel pipe  34  due to the execution of multistage injection. When the target discharge amount TPt is calculated at the point in time t 617 , the pump driving section  115  starts energization control to discharge an amount of fuel corresponding to the calculated target discharge amount TPt, and drives the high-pressure fuel pump  40 . The fuel discharge is executed during the period between the point in time t 617  and a point in time t 618  when the lift time Ti has elapsed. Thus, the target discharge amount TPt of fuel is discharged from the high-pressure fuel pump  40  following the fuel injection. 
     Then, at a point in time t 619  when a predetermined time has elapsed after the fuel discharge from the high-pressure fuel pump  40  is ended, the next multistage injection is executed. In this way, in the present embodiment, fuel is discharged during the period between the end of the multistage injection from the fuel injection valve and the start of the next multistage injection, while fuel is not discharged during the injection period in which the fuel injection is executed. Therefore, when the fuel injection is executed, the fluctuations of the fuel pressure Pr in the high-pressure fuel pipe  34  due to the fuel discharge from the high-pressure fuel pump  40  can be suppressed. Accordingly, fuel can be supplied to the high-pressure fuel pipe  34  at the timing that makes it possible to suppress the fluctuations of the fuel pressure Pr during the fuel injection period, and this provides appropriate driving of the high-pressure fuel pump  40 . 
     Second Embodiment 
     A control device for a fuel pump according to a second embodiment will be described with reference to  FIG. 7 . The second embodiment differs from the first embodiment in a manner in which the discharge start timing Ts is set in the discharge start timing calculation section  112 . The same constituent elements as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. 
     In the present embodiment, as in the first embodiment, a case where the injection pattern for multistage injection includes the pre-injection, the main injection, and the after-injection will be described as an example. 
     The discharge start timing calculation section  112  calculates a discharge start timing Ts as a point in time between an end timing Fem of the main injection and the injection start timing Fsa of the after-injection in the multistage injection. For example, the discharge start timing calculation section  112  calculates as the discharge start timing Ts a point in time closer to the end timing Fem of the main injection than the middle of both the timings Fem and Fsa in the period between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection. The end timing Fem of the main injection can be calculated based on the injection time Fim of the main injection and an injection start timing Fsm of the main injection. 
     An operation and advantages of the present embodiment will now be described with reference to  FIG. 7 . In  FIG. 7 , regarding a symbol t indicating the point in time of each operation and three-digit numbers following the symbol, the symbol t and the first digit  7  of the three digits are omitted. 
     In conjunction with the operation of the internal combustion engine  10 , multistage injection is repeatedly executed. When the multistage injection is executed, the injection valve driving section  111  first starts fuel injection at a point in time t 711  that is the injection start timing Fsp of the pre-injection calculated by the injection start timing calculation section  110 . The injection valve driving section  111  continues the fuel injection during the injection time Fip of the pre-injection calculated by the injection time calculation section  109 , and ends the pre-injection at a point in time t 712  when the injection time Fip has elapsed from the point in time t 711 . After that, the injection valve driving section  111  starts fuel injection at a point in time t 713  that is the injection start timing Fsm of the main injection calculated by the injection start timing calculation section  110 . The injection valve driving section  111  continues the fuel injection during the injection time Fim of the main injection calculated by the injection time calculation section  109 , and ends the main injection at a point in time t 714  when the injection time Fim has elapsed from the point in time t 713 . 
     In the present embodiment, the discharge start timing calculation section  112  calculates, as the discharge start timing Ts, a point in time between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection. Accordingly, the pump driving section  115  starts driving of the high-pressure fuel pump  40  at a point in time t 715  between when the main injection is ended at the point in time t 714  and when the after-injection is started by the injection valve driving section  111 . The discharge start timing Ts is the point in time t 715  closer to the end timing Fem (point in time t 714 ) of the main injection than a point in time t 716  that is the middle of both the timings Fem and Fsa in the period between the end timing Fem (point in time t 714 ) of the main injection and the injection start timing Fsa (point in time t 717 ) of the after-injection. The target discharge amount calculation section  113  calculates a target discharge amount TPt at the discharge start timing Ts (point in time t 715 ). The target discharge amount TPt is calculated based on a required fuel injection amount Qt for the next multistage injection calculated by the required injection amount calculation section  106  and a fuel pressure difference ΔP between the current fuel pressure Pr and the target fuel pressure Pt. 
     After energization control is executed at the point in time t 715  to start fuel discharge, the pump driving section  115  performs fuel discharge until a point in time t 719  when a lift time Ti calculated based on the target discharge amount TPt has elapsed. Thus, the target discharge amount TPt of fuel is discharged from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34 . 
     The injection valve driving section  111  starts fuel injection at the point in time t 717  that is the injection start timing Fsa of the after-injection calculated by the injection start timing calculation section  110 . The point in time t 717  is later than the discharge start timing Ts (t 715 ) of fuel discharge and is earlier than the end point in time t 719  of fuel discharge. The injection valve driving section  111  continues the fuel injection during the injection time Fia of the after-injection calculated by the injection time calculation section  109 , and ends the after-injection at a point in time t 718  when the injection time Fia of the after-injection has elapsed from the point in time t 717 . The injection time Fia of the after-injection is shorter than the lift time Ti described above, and the after-injection is ended at the point in time (t 718 ) earlier than the end point in time t 718  of fuel discharge. Accordingly, the after-injection in multistage injection is executed within a period during which fuel is discharged from the high-pressure fuel pump  40 . In addition, the fuel discharge is executed so as to overlap with only the injection period of the after-injection out of the main injection, the pre-injection, and the after-injection. 
     In this way, after the multistage injection from the fuel injection valve  15  and the fuel discharge from the high-pressure fuel pump  40  are ended, multistage injection is started from the next fuel injection valve at a point in time t 720  when a predetermined time has elapsed. 
     In the present embodiment, the discharge of fuel is started and ended in the period from the end of the main injection in the multistage injection to the start of the main injection in the next multistage injection. In the main injection, fuel contributing most to combustion is injected. In this way, the fuel discharge from the high-pressure fuel pump  40  performed while avoiding the injection period of the main injection makes it possible to suppress the fluctuations of the fuel pressure Pr during execution of the main injection and thus to ensure a combustion quality. Therefore, fuel can be supplied to the high-pressure fuel pipe at the point in time that makes it possible to suppress the fluctuations of the fuel pressure Pr during the injection period of the main injection, and this provides appropriate driving of the high-pressure fuel pump. 
     In the present embodiment, fuel discharge is started in the period between the end of the main injection and the start of the after-injection, which is executed after the main injection. Therefore, the timing of fuel discharge can be made earlier than when fuel discharge is started during execution of the after-injection as the sub-injection. As a result, it is possible to lengthen the time between the end of the fuel discharge and the start of the next multistage injection, and also to ensure a longer time to allow for convergence of the fluctuations of the fuel pressure Pr in the high-pressure fuel pipe  34  due to the fuel discharge from the high-pressure fuel pump  40 . Therefore, the fuel pressure Pr in the high-pressure fuel pipe  34  can be easily made more stable before the main injection is started in the next multistage injection. 
     As shown in  FIG. 7 , when the next multistage injection is executed, the discharge start timing calculation section  112  calculates, as a discharge start timing Ts, a point in time between the injection start timing Fsm and the end timing Fem of the main injection. Accordingly, the pump driving section  115  drives the high-pressure fuel pump  40  at a point in time t 722  between when the main injection is started by the injection valve driving section  111  at a point in time t 721  and when the main injection is ended at a point in time t 723 . The target discharge amount calculation section  113  calculates a target discharge amount TPt at the discharge start timing Ts (point in time t 722 ). The target discharge amount TPt is calculated based on a required fuel injection amount Qt for the next multistage injection calculated by the required injection amount calculation section  106  and a fuel pressure difference ΔP between the current fuel pressure Pr and the target fuel pressure Pt. 
     After energization control is executed at the point in time t 722  to start fuel discharge, the pump driving section  115  performs fuel discharge until a point in time t 724  when a lift time Ti calculated based on the target discharge amount TPt has elapsed. The point in time t 724 , at which the fuel discharge is ended, is earlier than a point in time at which the pre-injection in the next multistage injection is started. Thus, in the period from the point in time t 721  when the main injection is started to the start of the next main injection, the fuel discharge is started and ended. In this fuel discharge, the target discharge amount TPt of fuel is discharged from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34 . In this case, the after-injection in multistage injection is executed within a period during which fuel is discharged from the high-pressure fuel pump  40 . 
     In the present embodiment, fuel discharge is started in the period between the start of the main injection in multistage injection and the start of the main injection in the next multistage injection. Accordingly, in the period between the end of the fuel discharge and the start of the main injection in the next multistage injection, it is possible to ensure a time to allow for convergence of the fluctuations of the fuel pressure Pr in the high-pressure fuel pipe  34  due to the fuel discharge from the high-pressure fuel pump  40 . Therefore, the fuel pressure Pr in the high-pressure fuel pipe  34  can be easily made stable before the next multistage injection is started. As a result, variations in the fuel injection amount of the next main injection can be suppressed. 
     Third Embodiment 
     A control device for a fuel pump according to a third embodiment will be described with reference to  FIGS. 8 and 9 . The third embodiment differs from the above-described embodiments in a manner in which the discharge start timing Ts is set in the discharge start timing calculation section. The same constituent elements as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. 
     As shown in  FIG. 8 , the discharge start timing calculation section  130  includes an injection interval calculation section  131 , a necessary time calculation section  132 , a first calculation section  133 , a second calculation section  134 , and a switching determination section  135  as functional sections. 
     The injection interval calculation section  131  calculates an injection interval Int of fuel based on the end timing Fe of the multistage injection from the fuel injection valve  15 , the injection start timing Fs of the multistage injection calculated by the injection start timing calculation section  110 , and the engine rotational speed NE detected by the crank angle sensor  95 . In the present embodiment, an injection interval Int of fuel is calculated as a period of time from when the multistage injection is ended at the fuel injection valve  15  provided in any one of the cylinders to when the multistage injection is started at the fuel injection valve  15  provided in the cylinder to be ignited next. For example, in the present embodiment, the first cylinder # 1 , the third cylinder # 3 , the fourth cylinder # 4 , and the second cylinder # 2  are ignited in this order. The injection start timing Fs of the multistage injection is equal to the injection start timing of the first injection in the multistage injection, and the end timing Fe of the multistage injection is equal to the injection end timing of the last injection in the multistage injection. The injection start timing Fs of the multistage injection is the same as an injection start timing Fs calculated by the injection start timing calculation section  110  for the first injection in the injection pattern set by the injection pattern setting section  107 . The end timing Fe of the multistage injection can be calculated based on an injection time Fi calculated by the injection time calculation section  109  and an injection start timing Fs calculated by the injection start timing calculation section  110  for the last injection in the injection pattern set by the injection pattern setting section  107 . The injection interval Int of fuel tends to become shorter as the end timing Fe of the multistage injection is later, the injection start timing Fs of the multistage injection is earlier, or the engine rotational speed NE is higher. 
     The necessary time calculation section  132  calculates a necessary time Tnes required for the high-pressure fuel pump  40  to discharge fuel of a target discharge amount TPt calculated by the target discharge amount calculation section  113 . The necessary time calculation section  132  calculates, as the necessary time Tnes, an energization time required for the high-pressure fuel pump  40  to discharge the target discharge amount TPt of fuel to the high-pressure fuel pipe  34 , based on a relationship between the pump characteristics of the high-pressure fuel pump learned by the pump characteristics learning section  114 , that is, the energization time for the high-pressure fuel pump  40 , and an amount of fuel to be discharged from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34 . 
     The first calculation section  133  calculates a discharge start timing Ts that is a start timing at which fuel discharge from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34  is performed. The discharge start timing Ts is calculated based on the timing of fuel injection from the fuel injection valve  15 . In the present embodiment, the first calculation section  133  calculates, as the discharge start timing Ts, the end timing Fe at which the multistage injection from the fuel injection valve  15  is ended. As described above, the end timing Fe of the multistage injection can be calculated based on the injection time Fi of the last injection in the injection pattern set by the injection pattern setting section  107  and the injection start timing Fs of the last injection. 
     The second calculation section  134  calculates the discharge start timing Ts as a point in time within a period between an end timing Fem of the main injection in the multistage injection and an injection start timing Fss of the sub-injection executed after the main injection. The second calculation section  134  calculates, as the discharge start timing Ts, a point in time closer to the end timing Fem of the main injection than the middle of both the timings Fem and Fss in the period between the end timing Fem of the main injection and the injection start timing Fss of the sub-injection. The end timing Fem of the main injection can be calculated based on the injection time Fim of the main injection calculated by the injection time calculation section  109  and the injection start timing Fsm of the main injection calculated by the injection start timing calculation section  110 . The injection start timing Fss of the sub-injection is the same as the injection start timing of the injection to be executed immediately after the main injection, out of the injection start timings calculated by the injection start timing calculation section  110 . 
     The switching determination section  135  switches the calculation section to calculate the discharge start timing Ts to one of the first calculation section  133  and the second calculation section  134 , based on the injection interval Int of fuel calculated by the injection interval calculation section  131  and the necessary time Tnes calculated by the necessary time calculation section  132 . When the injection interval Int is equal to or longer than the necessary time Tnes (Int Tnes) and the injection interval Int is long, the switching determination section  135  sets the first calculation section  133  as the calculation section to calculate the discharge start timing Ts. Accordingly, if the fuel discharge from the high-pressure fuel pump  40  can be completed within the injection interval Int, the discharge start timing Ts is set to the end timing Fe at which the multistage injection from the fuel injection valve  15  is ended. Further, when the injection interval Int is shorter than the necessary time Tnes (Int&lt;Tnes) and the injection interval Int is short, the switching determination section  135  sets the second calculation section  134  as the calculation section to calculate the discharge start timing Ts. Accordingly, if the fuel injection from the high-pressure fuel pump  40  cannot be completed within the injection interval Int, the discharge start timing Ts is set to a point in time between the end timing Fem of the main injection in the multistage injection and the injection start timing Fss of the sub-injection executed after the main injection. 
     The pump driving section  115  performs energization control of the high-pressure fuel pump  40  to the coil  85  at the discharge start timing Ts calculated by the discharge start timing calculation section  130 . That is, when the switching determination section  135  sets that the discharge start timing Ts is to be calculated by the first calculation section  133 , the pump driving section  115  performs the energization control at the discharge start timing Ts calculated by the first calculation section  133 . In this case, a first discharge control is executed in which fuel discharge is performed in the period between the end of the multistage injection and the start of the next multistage injection but fuel discharge is not performed in the period during which the multistage injection is performed. The first calculation section  133  and the pump driving section  115  function as a first execution section configured to execute the first discharge control. Further, when the switching determination section  135  sets that the discharge start timing Ts is to be calculated by the second calculation section  134 , the pump driving section  115  performs the energization control at the discharge start timing Ts calculated by the second calculation section  134 . In this case, a second discharge control is executed in which fuel discharge is started in the period between the end of the main injection and the start of the sub-injection executed after the main injection. The second calculation section  134  and the pump driving section  115  function as a second execution section configured to execute the second discharge control. The discharge control of the high-pressure fuel pump  40  is switched between the first discharge control and the second discharge control by the switching determination section  135 . 
     The pump driving section  115  causes the plunger  75  to reciprocate through the energization control, thereby causing the high-pressure fuel pump  40  to execute fuel suction and fuel discharge. The pump driving section  115  ends the energization when a lift time Ti has elapsed from the start of the energization control for the high-pressure fuel pump  40 . The pump driving section  115  sets the lift time Ti such that an amount of fuel corresponding to the target discharge amount TPt is discharged, based on the pump characteristics learned by the pump characteristics learning section  114 . The lift time Ti is equal to the necessary time Tnes. 
     An operation and advantages of the present embodiment will now be described with reference to  FIG. 9 . In  FIG. 9 , regarding a symbol t indicating the point in time of each operation and three-digit numbers following the symbol, the symbol t and the first digit  9  of the three digits are omitted. A case where the injection pattern for multistage injection includes the pre-injection, the main injection, and the after-injection will be described below as an example. 
     In conjunction with the operation of the internal combustion engine  10 , multistage injection is repeatedly executed. In the multistage injection, the pre-injection, the main injection, and the after-injection are executed in this order. When this fuel injection is executed, the required injection amount calculation section  106  first calculates a required fuel injection amount Qt before the fuel injection is executed. After that, the multistage injection amount setting section  108  calculates the target injection amount of each injection in the multistage injection based on the required fuel injection amount Qt, and the injection time calculation section  109  calculates the injection time Fi of each injection. In addition, the injection start timing calculation section  110  calculates the injection start timing Fs of each injection in the multistage injection based on the required fuel injection amount Qt. 
     In the present embodiment, before a first multistage injection executed at a point in time t 912 , an injection time Fi and an injection start timing Fs of each injection in the first multistage injection are calculated. Further, at a point in time t 911  that is a little earlier than the point in time t 912 , at which the first multistage injection is started, an injection time Fi and an injection start timing Fs of each injection in a second multistage injection to be executed after the first multistage injection are calculated. In the period between when the injection time Fi and the injection start timing Fs of each injection in the second multistage injection are calculated and when the first multistage injection is started (point in time t 911  to point in time t 912 ), a discharge start timing Ts at which fuel discharge from the high-pressure fuel pump  40  to the high-pressure fuel pipe  34  is started is calculated. That is, when the injection time Fi and the injection start timing Fs of each injection in the second multistage injection are calculated at the point in time t 911 , the injection interval calculation section  131  calculates an injection interval Int( 1 ) of fuel for the multistage injection based on the injection time Fi and the injection start timing Fs. The injection interval Int( 1 ) of fuel is an interval between the end timing (t 917 ) of the first multistage injection and the start timing (t 920 ) of the second multistage injection. 
     Further, when a required fuel injection amount Qt for the first multistage injection is calculated by the required injection amount calculation section  106 , the target discharge amount calculation section  113  calculates a target discharge amount TPt based on the required fuel injection amount Qt and a fuel pressure difference ΔP between the current fuel pressure Pr and the target fuel pressure Pt. That is, the target discharge amount TPt is calculated before the point in time at which the discharge start timing Ts is calculated. The necessary time calculation section  132  calculates a necessary time Tnes required for the high-pressure fuel pump  40  to discharge fuel of a target discharge amount TPt calculated by the target discharge amount calculation section  113 . In this way, when the injection interval Int( 1 ) is calculated at the point in time t 911  after the necessary time Tnes is calculated, the switching determination section  135  determines which one of the first calculation section  133  and the second calculation section  134  is used to calculate the discharge start timing Ts. In the example shown in  FIG. 9 , the injection interval Int( 1 ) between the first multistage injection and the second multistage injection is longer than the necessary time Tnes. Accordingly, in the period between the point in time t 911  and the point in time t 912 , the switching determination section  135  sets that the discharge start timing Ts is to be calculated by the first calculation section  133 . Even before the point in time t 911 , the switching determination section  135  sets that the discharge start timing Ts is to be calculated by the first calculation section  133 . Accordingly, the discharge control of the high-pressure fuel pump  40  is set to the first discharge control before the first multistage injection is executed. 
     After that, the injection valve driving section  111  starts fuel injection at a point in time t 912  that is an injection start timing Fsp of the pre-injection in the first multistage injection calculated by the injection start timing calculation section  110 . Thus, the first multistage injection is started. The injection valve driving section  111  continues the fuel injection during an injection time Fip of the pre-injection in the first multistage injection calculated by the injection time calculation section  109 , and ends the pre-injection at a point in time t 913  when the injection time Fip of the pre-injection has elapsed from the point in time t 912 . After that, the injection valve driving section  111  starts fuel injection at a point in time t 914  that is an injection start timing Fsm of the main injection in the first multistage injection calculated by the injection start timing calculation section  110 . The injection valve driving section  111  continues the fuel injection during an injection time Fim of the main injection in the first multistage injection calculated by the injection time calculation section  109 , and ends the main injection at a point in time t 915  when the injection time Fim of the main injection has elapsed from the point in time t 914 . After that, the injection valve driving section  111  starts fuel injection at a point in time t 916  that is an injection start timing Fsa of the after-injection in the first multistage injection calculated by the injection start timing calculation section  110 . The injection valve driving section  111  continues the fuel injection during an injection time Fia of the after-injection in the first multistage injection calculated by the injection time calculation section  109 , and ends the after-injection at a point in time t 917  when the injection time Fia of the after-injection has elapsed from the point in time t 916 . Thus, the first multistage injection is ended. In this way, the first multistage injection from the fuel injection valve  15  is executed. 
     The first calculation section  133  sets the discharge start timing Ts to the same point in time as the end timing Fe at which the first multistage discharge is ended. Accordingly, at the point in time t 917  when the first multistage discharge is ended, the pump driving section  115  starts energization control to discharge the calculated target discharge amount TPt of fuel, and drives the high-pressure fuel pump  40 . The fuel discharge is executed during the period between the point in time t 917  and a point in time t 918  when the lift time Ti has elapsed. As a result, the target discharge amount TPt of fuel is discharged from the high-pressure fuel pump  40 . 
     After that fuel discharge is performed, at a point in time t 919  earlier than the injection start timing Fs of the second multistage injection (point in time t 920 ), an injection time Fi and an injection start timing Fs of each injection in a third multistage injection to be executed after the second multistage injection are calculated. Then, in the period between the point in time t 919  and the injection start timing Fs of the second multistage injection, the switching determination section  135  determines which one of the first calculation section  133  and the second calculation section  134  is used to calculate the discharge start timing Ts based on an injection interval Int( 2 ) between the second multistage injection and the third multistage injection. In the example shown in  FIG. 9 , since the injection interval Int( 2 ) between the second multistage injection and the third multistage injection is longer than the necessary time Tnes, the switching determination section  135  sets that the discharge start timing Ts is to be calculated by the first calculation section  133 . Thus, the first discharge control is continued. 
     After that, the injection valve driving section  111  starts fuel injection at the point in time t 920  that is an injection start timing Fsp of the pre-injection in the second multistage injection calculated by the injection start timing calculation section  110 . Thus, the second multistage injection is started. When the pre-injection is ended, the injection valve driving section  111  sequentially executes the main injection and the after-injection. The injection valve driving section  111  ends the after-injection at a point in time t 921 . Thus, the second multistage injection is ended. After the second multistage injection is executed, at the point in time t 921  when the second multistage discharge is ended, the pump driving section  115  starts energization control to discharge the target discharge amount TPt of fuel, and drives the high-pressure fuel pump  40 . 
     When the operating state of the internal combustion engine  10  changes and the rotational speed of the internal combustion engine thus increases, the injection interval Int decreases. In the example shown in  FIG. 9 , an injection interval Int( 3 ) between the third multistage injection and a fourth multistage injection to be executed after the third multistage injection is short. In this case, first, an injection time Fi and an injection start timing Fs of each injection in the fourth multistage injection are calculated at a point in time t 922  after the fuel discharge is ended at the point in time t 921  and before the third multistage injection is started. Then, in the period between the point in time t 921  and the injection start timing Fs (point in time t 923 ) of the third multistage injection, the switching determination section  135  determines which one of the first calculation section  133  and the second calculation section  134  is used to calculate the discharge start timing Ts based on an injection interval Int( 3 ) between the third multistage injection and the following fourth multistage injection. In the example shown in  FIG. 9 , the injection interval Int( 3 ) between the third multistage injection and the fourth multistage injection is shorter than the necessary time Tnes. For this reason, the switching determination section  135  sets that the discharge start timing Ts is to be calculated by the second calculation section  134 . Thus, the discharge control of the high-pressure fuel pump  40  is switched from the first discharge control to the second discharge control in the period between the point in time t 922  and the point in time t 923 . 
     The injection valve driving section  111  starts fuel injection at the point in time t 923  that is an injection start timing Fsp of the pre-injection in the third multistage injection calculated by the injection start timing calculation section  110 . Thus, the third multistage injection is started. The injection valve driving section  111  continues the fuel injection during an injection time Fip of the pre-injection in the third multistage injection calculated by the injection time calculation section  109 , and ends the pre-injection at a point in time t 924  when the injection time Fip of the pre-injection has elapsed from the point in time t 923 . After that, the injection valve driving section  111  starts fuel injection at a point in time t 925  that is an injection start timing Fsm of the main injection in the third multistage injection calculated by the injection start timing calculation section  110 . The injection valve driving section  111  continues the fuel injection during an injection time Fim of the main injection in the third multistage injection calculated by the injection time calculation section  109 , and ends the main injection at a point in time t 926  when the injection time Fim of the main injection has elapsed from the point in time t 925 . 
     The second calculation section  134  sets the discharge start timing Ts to a point in time between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection. Accordingly, the pump driving section  115  drives the high-pressure fuel pump  40  at a point in time t 927  between when the main injection is ended at the point in time t 926  and when the after-injection is started by the injection valve driving section  111 . The discharge start timing Ts is calculated as the point in time t 927  closer to the end timing Fem (point in time t 926 ) of the main injection than a point in time t 928  that is the middle of both the timings Fem and Fsa in the period between the end timing Fem (point in time t 926 ) of the main injection and the injection start timing Fsa (point in time t 929 ) of the after-injection. After energization control is executed at the point in time t 927  to start fuel discharge, the pump driving section  115  performs fuel discharge until a point in time t 931  when a lift time Ti calculated based on the target discharge amount TPt has elapsed. As a result, the target discharge amount TPt of fuel is discharged from the high-pressure fuel pump  40 . 
     Further, after the fuel discharge is started by the pump driving section  115 , the injection valve driving section  111  starts the after-injection at the injection start timing Fsa (point in time t 929 ) of the after-injection in the third multistage injection calculated by the injection start timing calculation section  110 . The injection time Fia of the after-injection in the third multistage injection is shorter than the lift time Ti described above, and the after-injection is ended at a point in time (t 930 ) earlier than the end point in time t 931  of fuel discharge. Accordingly, the after-injection in the third multistage injection is executed within a period during which fuel is discharged from the high-pressure fuel pump  40 . Executing the after-injection in this way, the third multistage injection is ended. 
     After that third multistage injection and the fuel discharge are performed, at the following point in time t 932 , an injection time Fi and an injection start timing Fs of each injection in a fifth multistage injection to be executed after the fourth multistage injection are calculated. Then, in the period between the point in time t 932  and the injection start timing Fs (point in time t 933 ) of the fourth multistage injection, the switching determination section  135  sets which one of the first calculation section  133  and the second calculation section  134  is used to calculate the discharge start timing Ts based on an injection interval Int( 4 ) between the fourth multistage injection and the fifth multistage injection. In the example shown in  FIG. 9 , since the injection interval Int( 4 ) between the fourth multistage injection and the fifth multistage injection is shorter than the necessary time Tnes, the switching determination section  135  sets that the discharge start timing Ts is to be calculated by the second calculation section  134 . Thus, the second discharge control is continued. 
     After that, if the operating state of the internal combustion engine  10  changes and the rotational speed of the internal combustion engine thus decreases, the injection interval Int(n) between the end timing of the multistage injection and the start timing of the next multistage injection becomes longer than the necessary time Tnes required for discharging fuel. In this case, at a point in time t 934  before a multistage injection is started, the switching determination section  135  sets that the discharge start timing Ts is to be calculated by the first calculation section  133 . Accordingly, the discharge control of the high-pressure fuel pump  40  is switched from the second discharge control to the first discharge control. As a result, fuel discharge is performed at a point in time t 935 , at which the multistage injection is ended. 
     In the present embodiment, when the injection interval Int between the end timing Fe of the multistage injection and the injection start timing Fs of the next multistage injection is equal to or longer than the necessary time Tnes required for discharging fuel, the first discharge control is executed. Specifically, fuel discharge is performed in the period between the end of the multistage injection and the start of the next multistage injection but fuel discharge is not performed in the period during which the multistage injection is performed. In other words, if the injection interval Int is long and the fuel discharge can be completed within the injection interval Int, the fuel discharge is started within the injection interval Int, and fuel discharge is not performed in the injection period during which the fuel injection is executed. Therefore, when the fuel injection is executed, the fluctuations of the fuel pressure Pr in the high-pressure fuel pipe  34  due to the fuel discharge from the high-pressure fuel pump  40  can be suppressed. 
     Further, when the injection interval Int is less than the necessary time Tnes, the second discharge control for starting the fuel discharge is executed in the period between the end of the main injection and the start of the after-injection to be executed after the main injection. In other words, if the injection interval Int is short and the fuel injection cannot be completed within the injection interval Int, the fuel discharge is performed at time avoiding the main injection which most contributes to combustion but at time as close to the main injection as possible after the main injection. That fuel discharge from the high-pressure fuel pump  40  performed while avoiding the injection period of the main injection makes it possible to suppress the fluctuations of the fuel pressure Pr in the high-pressure fuel pipe  34  during execution of the main injection and thus to ensure a combustion quality. In addition, earlier start of fuel discharge than the start of fuel discharge during execution of the after-injection makes it possible to lengthen the time from the completion of fuel discharge to the start of the next multistage injection, and also to ensure a longer time to allow for convergence of the fluctuations of the fuel pressure Pr in the high-pressure fuel pipe  34  due to the fuel discharge from the high-pressure fuel pump  40 . Thus, the fuel pressure Pr in the high-pressure fuel pipe  34  can be easily made more stable before the main injection is started in the next multistage injection. Therefore, fuel can be supplied to the high-pressure fuel pipe  34  at the point in time that makes it possible to suppress the fluctuations of the fuel pressure Pr during the injection period of the fuel injection. 
     The above-described embodiments may be modified as follows. The above-described embodiments and the following modifications can be combined as long as the combined modifications remain technically consistent with each other. 
     In the first embodiment, the discharge start timing calculation section  112  calculates a point in time at which the predetermined preparation time has elapsed from the end timing Fe of the multistage injection as the discharge start timing Ts. Calculation of the discharge start timing Ts can be changed as appropriate. For example, the same point in time as the end timing Fe of the multistage injection may be calculated as the discharge start timing Ts, without taking into consideration the preparation time. In this case, the fuel discharge is started at the point in time at which the multistage injection is ended. 
     In the first embodiment, the injection pattern for multistage injection including the pre-injection, the main injection, and the after-injection is exemplified, but the injection pattern for multistage injection is not limited thereto. For example, as the injection pattern for multistage injection, an injection pattern including the pre-injection and the main injection but not including the after-injection may be employed. In this case, the discharge start timing Ts is set between the end timing of the main injection in the current multistage injection and the start timing of the pre-injection in the next multistage injection. Further, as the injection pattern for multistage injection, an injection pattern including the main injection and the after-injection but not including the pre-injection can be employed. In this case, the discharge start timing Ts is set between the end timing of the after-injection in the current multistage injection and the start timing of the main injection in the next multistage injection. In addition, as the injection pattern for multistage injection, an injection pattern including the pilot-injection or the post-injection can be employed. 
     In the second embodiment, the discharge start timing calculation section  112  calculates, as the discharge start timing Ts, a point in time closer to the end timing Fem of the main injection than the middle of both the timings Fem and Fsa in the period between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection. Instead of this configuration, the discharge start timing calculation section  112  may calculate, as the discharge start timing Ts, the midpoint of both the timings Fem and Fsa in the period between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection. In addition, the discharge start timing calculation section  112  may calculate, as the discharge start timing Ts, a point in time closer to the injection start timing Fsa of the after-injection than the middle of both the timings Fem and Fsa in the above period. Further, the discharge start timing Ts may be the same point in time as the end timing Fem of the main injection. In this case, the fuel discharge is started immediately after the main injection is ended. 
     In the second embodiment, the injection pattern for multistage injection including the pre-injection, the main injection, and the after-injection is exemplified, but the injection pattern for multistage injection is not limited thereto. For example, as the injection pattern for multistage injection, an injection pattern including the main injection and the after-injection but not including the pre-injection can be employed. Further, as the injection pattern for multistage injection, an injection pattern including the main injection and the post-injection but not including the after-injection can be employed. In this case, it is possible to provide a configuration in which the fuel discharge is started in the period between the end of the main injection and the start of the post-injection. 
     In the second embodiment, the discharge start timing calculation section  112  is configured to set the discharge start timing Ts to a point in time between the end timing Fem of the main injection and the discharge start timing Fsa of the after-injection, or a point in time between the discharge start timing Fsm and the end timing Fem of the main injection. The discharge timing of fuel is not limited to this. For example, the discharge start timing Ts can be set to a point in time in the period during which the sub-injection to be executed after the main injection is executed. Since the fuel discharge is started during execution of the sub-injection, this configuration can make the discharge start timing Ts earlier than the configuration in which the fuel discharge is started after the end of the sub-injection. Further, the discharge start timing Ts can be set to a point in time after the end of the main injection and the after-injection and before the injection start timing Fsp of the pre-injection of the next multistage injection. In this configuration, it is possible to execute fuel discharge so that it overlaps with only the pre-injection injection period among the main injection, the pre-injection, and the after-injection. 
     In the third embodiment, the first calculation section  133  calculates, as the discharge start timing Ts, the end timing Fe at which the multistage injection from the fuel injection valve  15  is ended, but calculation of the discharge start timing Ts is not limited thereto. For example, the first calculation section  133  can calculate, as the discharge start timing Ts, a point in time when the preparation time has elapsed from the end timing Fe at which the multistage injection from the fuel injection valve  15  is ended. 
     In the third embodiment, the second calculation section  134  calculates, as the discharge start timing Ts, a point in time closer to the end timing Fem of the main injection than the middle of both the timings Fem and Fsa in the period between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection. Instead of this configuration, the second calculation section  134  may calculate, as the discharge start timing Ts, the midpoint of both the timings Fem and Fsa in the period between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection. In addition, the second calculation section  134  may calculate, as the discharge start timing Ts, a point in time closer to the injection start timing Fsa of the after-injection than the middle of both the timings Fem and Fsa in the above period. Further, the discharge start timing Ts may be the same point in time as the end timing Fem of the main injection. In this case, the fuel discharge is started immediately after the main injection is ended. 
     In the third embodiment, the injection pattern for multistage injection including the pre-injection, the main injection, and the after-injection is exemplified, but the injection pattern for multistage injection is not limited thereto. For example, as the injection pattern for multistage injection, an injection pattern including the main injection and the after-injection but not including the pre-injection can be employed. Further, as the injection pattern for multistage injection, an injection pattern including the main injection and the post-injection but not including the after-injection can be employed. In this case, the second calculation section  134  may start fuel discharge in the period between the end of the main injection and the start of the post-injection. 
     In the third embodiment, the second calculation section  134  is configured to set the discharge start timing Ts to a point in time between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection. The discharge timing of fuel is not limited to this. For example, the discharge start timing Ts can be set to a point in time between the start and the end of the main injection, a point in time in the period during which the sub-injection to be executed after the main injection is executed, etc. That is, for example, if the injection pattern for multistage injection includes the main injection, the after-injection, and the post-injection, the second calculation section  134  can set the discharge start timing Ts to a point in time in the period during which the main injection is executed, a point in time between the end timing Fem of the main injection and the injection start timing Fsa of the after-injection, a point in time in the period during which the after-injection is executed, a point in time between the end timing Fea of the after-injection and the injection start timing of the post-injection, or a point in time in the period during which the post-injection is executed. In order to lengthen the time between the completion of the fuel discharge from the high-pressure fuel pump  40  and the start of the next multistage injection, it is desirable to calculate a point in time close to the end timing Fem of the main injection as the discharge start timing Ts. In these configurations, since the fuel discharge is started during execution of the sub-injection, the discharge start timing Ts can be made earlier than that in the configuration in which the fuel discharge is started after the end of the sub-injection. 
     In the third embodiment, the fuel discharge is executed so that it overlaps with only the injection period of the after-injection. However, the fuel discharge may be executed in a period overlapping with both the injection period of the after-injection and the injection period of the following pre-injection. 
     In the third embodiment, if the injection interval Int is equal to or longer than the necessary time Tnes (Int Tnes) and the injection interval Int is long, the switching determination section  135  executes the first discharge control; if the injection interval Int is shorter than the necessary time Tnes (Int&lt;Tnes) and the injection interval Int is short, the switching determination section  135  executes the second discharge control. Switching of the discharge control in the switching determination section  135  is not limited to this. For example, even if the injection interval Int is shorter than the necessary time Tnes (Int&lt;Tnes), the switching determination section  135  may determine that the injection interval Int is long and execute the first discharge control when the difference between the injection interval Int and the necessary time Tnes is relatively small. In this case, when the injection interval Int is shorter than the necessary time Tnes and the difference between the injection interval Int and the necessary time Tnes becomes relatively large, the switching determination section  135  can determine that the injection interval Int is short and execute the second discharge control. That is, a determination value for the switching determination section  135  to determine the switching of the discharge control is not limited to the necessary time Tnes. As the determination value, a value smaller or larger than the necessary time Tnes can be used. 
     The fuel in the fuel tank  31  may be drawn in by the high-pressure fuel pump  40 . In this case, the low-pressure fuel pump  32  and the low-pressure fuel pipe  33  can be omitted. 
     The configuration of the high-pressure fuel pump  40  can be changed as appropriate. For example, the plunger  75  may be composed of a round bar portion that is made of a material different from magnetic material and is inserted in the cylinder bore  57 , and a magnetic portion that is connected to one end of the round bar portion and is made of a magnetic material. Furthermore, a configuration may be provided in which the plunger  75  is displaced by moving the magnetic portion by a magnetic field generated by energizing the coil  85  so that the volume of the pressurizing chamber  78  is changed. In other words, as long as the fuel pump can reciprocate the plunger  75  by energization and has a suction function of drawing in fuel by reciprocating the plunger  75  and a discharge function of pressurizing and discharging the drawn fuel, the same control device as that in each of the above-described embodiments can be adapted for the fuel pump. 
     The control device  100  for a fuel pump has a function of controlling driving of the fuel injection valve  15 . This function may be included in a control section different from the control device  100  for the fuel pump. In this case, the control device  100  may be configured to communicate with the control section to transmit and receive necessary information to and from each other so that the driving of the fuel pump is controlled in the same manner as in each of the above-described embodiments. 
     The control device is not limited to a device that includes a CPU, a ROM, and a RAM and executes software processing. For example, a dedicated hardware circuit (such as an ASIC) may be provided that executes at least part of the software processes executed in each of the above-described embodiments. That is, the controller may be modified as long as it has any one of the following configurations (a) to (c). (a) A configuration including a processor that executes all of the above-described processes according to programs and a program storage device such as a ROM that stores the programs. (b) A configuration including a processor and a program storage device that execute part of the above-described processes according to the programs and a dedicated hardware circuit that executes the remaining processes. (c) A configuration including a dedicated hardware circuit that executes all of the above-described processes. A plurality of software processing circuits each including a processor and a program storage device and a plurality of dedicated hardware circuits may be provided. That is, the above processes may be executed in any manner as long as the processes are executed by processing circuitry that includes at least one of a set of one or more software processing circuits and a set of one or more dedicated hardware circuits.