fuel injection device

Abstract

To provide a fuel injection device capable of preventing bubbles from remaining in a channel of a fuel in an inner space of a tip end portion provided with an injection hole.SOLUTION: A fuel injection device 200 is equipped with a tapered seat portion 224 (valve seat portion), and a valve body 203. The seat portion 224 has a plurality of fuel injection holes 215. The valve body 203 is seated in or separated from the seat portion 224. The lyophilic property of an injection hole opposite region 23b opposing to the plurality of fuel injection holes 215 on a surface of the valve body 203 is higher than the lyophilic property of a conical base region 23c (tip end region) on a tip end side than the injection hole opposite region 23b.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] The present invention relates to a fuel injection device.

Background Art

[0002] Conventionally, an in-cylinder injection type internal combustion engine that directly injects fuel into a cylinder by a fuel injection device has been used. As a technology related to a conventional fuel injection device, for example, there is one described in Patent Document 1. Patent Document 1 describes a fuel injection valve that guides the flow of fuel flowing in from upstream of the seat portion toward the nozzle hole side by providing a curved surface on the surface of the valve body, thereby reducing the inflow of fuel into the sac chamber.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the fuel injection valve described in Patent Document 1, when the engine coolant temperature is low, after the fuel injection ends, the surface tension of some fuel may increase, and some fuel may not be able to flow out of the nozzle hole. As a result, some fuel remains in the internal space at the tip of the fuel injection valve.

[0005] On the other hand, air in the combustion chamber may be drawn into the nozzle hole through a nozzle hole where the fuel outflow has ended first. In this case, in the internal space at the tip of the fuel injection valve, the fuel and bubbles are mixed. If the bubbles remain between the seat portion and the nozzle hole, at the start of fuel injection in the next cycle, the remaining bubbles are injected together with the fuel. As a result, the initial shape of the spray is disturbed, and there is a risk of variation in the spray shape.

[0006] The object of the present invention is to provide a fuel injection device that can prevent air bubbles from remaining in the fuel flow path within the internal space of the tip portion where the injection holes are provided, taking into consideration the above-mentioned problems. [Means for solving the problem]

[0007] To solve the above problems and achieve the objectives of the present invention, a fuel injection device according to one aspect of the present invention comprises a tapered valve seat portion and a valve body. The valve seat portion has a plurality of injection holes. The valve body seats or separates from the valve seat portion. The hydrophilicity of the injection hole-facing region on the surface of the valve body that faces the plurality of injection holes is higher than the hydrophilicity of the tip region located on the tip side of this injection hole-facing region. [Effects of the Invention]

[0008] With the fuel injection system configured as described above, it is possible to prevent air bubbles from remaining in the fuel flow path within the internal space of the tip portion where the injection holes are provided. Furthermore, issues, configurations, and effects other than those mentioned above will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0009] [Figure 1] This is an overall configuration diagram of an internal combustion engine system equipped with a fuel injection control device according to the first embodiment. [Figure 2] This is a cross-sectional view showing an example of the internal configuration of a fuel injection system according to the first embodiment. [Figure 3] This figure shows a detailed configuration example of the drive circuit and ECU of the fuel injection control device according to the first embodiment. [Figure 4] This figure shows the drive command pulse, drive voltage, drive current, valve body displacement, and movable core displacement according to the first embodiment. [Figure 5] This is a cross-sectional view showing a cross-section perpendicular to the axial direction of the tip portion of the fuel injection control device according to the first embodiment. [Figure 6] This is a cross-sectional view along line AA shown in Figure 5. [Figure 7]It is a front view showing the surface roughness of the tip of the valve body of a conventional fuel injection device. [Figure 8] It is a cross-sectional view taken along the line B-B shown in FIG. 7. [Figure 9] It is a diagram showing the drive command pulse, drive voltage, drive current, valve body displacement and movable iron core displacement, and fuel flow rate at the nozzle exit of a conventional fuel injection device at full lift. [Figure 10] It is a cross-sectional view showing the residual bubbles on the surface of the valve body after fuel injection of a conventional fuel injection device. [Figure 11] It is a graph showing the relationship between the surface roughness and wetting angle of the surface of the valve body in a fuel and fuel injection device. [Figure 12] It is a front view showing the surface roughness of the valve body surface in the fuel injection device according to the first embodiment. [Figure 13] It is a cross-sectional view taken along the line C-C shown in FIG. 12. [Figure 14] It is a diagram showing the drive signal and injection response at full lift of the fuel injection device according to the first embodiment. [Figure 15] It is a cross-sectional view showing the residual bubbles on the surface of the valve body after fuel injection of the fuel injection device according to the first embodiment. [Figure 16] It is a graph showing the distribution of surface roughness in each region of the valve body surface of a conventional fuel injection device. [Figure 17] It is a graph showing the distribution of surface roughness in each region of the valve body surface of the fuel injection device according to the first embodiment. [Figure 18] It is a diagram showing the drive signal and injection response at half lift of the fuel injection device according to the first embodiment. [Figure 19] It is a front view showing the surface roughness of the valve body surface in the fuel injection device according to the second embodiment. [Figure 20] It is a cross-sectional view taken along the line D-D shown in FIG. 19. [Figure 21] It is a front view showing the surface roughness of the valve body surface in the fuel injection device according to the third embodiment. [Figure 22]It is a front view showing the surface roughness of the valve body surface in the fuel injection device according to the fourth embodiment.

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same function or configuration are denoted by the same reference numerals, and redundant descriptions are omitted.

[0011] 1. First Embodiment Hereinafter, the fuel injection device according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 15.

[0012] [Internal Combustion Engine System] First, a configuration example of an internal combustion engine system equipped with the fuel injection control device according to the present embodiment will be described with reference to FIG. 1. FIG. 1 is an overall configuration diagram of an internal combustion engine system equipped with the fuel injection control device according to the present embodiment.

[0013] The internal combustion engine (engine) 101 shown in FIG. 1 is a four-cycle engine that repeats four strokes of an intake stroke, a compression stroke, a combustion (expansion) stroke, and an exhaust stroke. For example, it is a multi-cylinder engine having four cylinders. The number of cylinders of the internal combustion engine 101 is not limited to four, and it may have six or eight or more cylinders.

[0014] [[ID=3,0]]The internal combustion engine 101 includes a piston 102, an intake valve 103, and an exhaust valve 104. The intake air (intake air) to the internal combustion engine 101 passes through an air flow meter (AFM: Air Flow Meter) 120 that detects the amount of inflowing air, and the flow rate is adjusted by a throttle valve 119. The air that has passed through the throttle valve 119 is sucked into a collector 115 that is a branch portion, and then is supplied to the combustion chamber 121 of each cylinder through an intake pipe 110 and an intake valve 103 provided for each cylinder (cylinder).

[0015] Meanwhile, fuel is supplied from the fuel tank 123 to the high-pressure fuel pump 125 by the low-pressure fuel pump 124, and the high-pressure fuel pump 125 increases the pressure to the level required for fuel injection. Specifically, the high-pressure fuel pump 125 moves a plunger located inside it up and down using power transmitted from the exhaust camshaft (not shown) of the exhaust cam 128, thereby pressurizing (increasing) the fuel inside the high-pressure fuel pump 125.

[0016] The intake port of the high-pressure fuel pump 125 is equipped with an on / off valve driven by a solenoid. The solenoid is connected to a control device (hereinafter referred to as "fuel injection control device 127") of the fuel injection device 200, which is located in an ECU (Engine Control Unit) 109, an example of an engine control device. The fuel injection device (fuel injection device 200) is a direct injection type fuel injection device that directly injects fuel into the combustion chamber (combustion chamber 121).

[0017] The fuel injection control device 127 controls a solenoid based on a control command from the ECU 109 and drives an on / off valve so that the pressure of the fuel discharged from the high-pressure fuel pump 125 (fuel pressure) reaches a desired pressure.

[0018] The fuel, pressurized by the high-pressure fuel pump 125, is sent to the fuel injector 200 via the high-pressure fuel piping 129. The fuel injector 200 injects fuel directly into the combustion chamber 121 based on a command from the fuel injection control device 127. The fuel injector 200 performs fuel injection by operating the valve body 203 when a drive current is supplied (energized) to the coil 208, which will be described later.

[0019] Furthermore, the internal combustion engine 101 is equipped with a fuel pressure sensor 126 that measures the fuel pressure in the high-pressure fuel line 129. Based on the measurement results from the fuel pressure sensor 126, the ECU 109 sends a control command to the fuel injection control device 127 to set the fuel pressure in the high-pressure fuel line 129 to a desired pressure. In other words, the ECU 109 performs so-called feedback control to set the fuel pressure in the high-pressure fuel line 129 to a desired pressure.

[0020] Furthermore, each combustion chamber 121 of the internal combustion engine 101 is equipped with a spark plug 106, an ignition coil 107, and a water temperature sensor 108. The spark plug 106 exposes its electrode portion into the combustion chamber 121 and ignites the mixture of intake air and fuel in the combustion chamber 121 by discharge. The ignition coil 107 generates a high voltage for the discharge at the spark plug 106. The water temperature sensor 108 measures the temperature of the coolant that cools the cylinders of the internal combustion engine 101.

[0021] The ECU 109 controls the energization of the ignition coil 107 and the ignition of the spark plug 106. The mixture of intake air and fuel in the combustion chamber 121 is combusted by the spark emitted from the spark plug 106, and this pressure pushes the piston 102 down.

[0022] The exhaust gas produced by combustion is discharged into the exhaust pipe 111 via the exhaust valve 104. The exhaust pipe 111 is equipped with a three-way catalytic converter 112 and an oxygen sensor 113. The three-way catalytic converter 112 purifies harmful substances contained in the exhaust gas, such as nitrogen oxides (NOx). The oxygen sensor 113 detects the oxygen concentration contained in the exhaust gas and outputs the detection result to the ECU 109. Based on the detection result of the oxygen sensor 113, the ECU 109 performs feedback control so that the amount of fuel injected from the fuel injector 200 reaches the target air-fuel ratio.

[0023] Furthermore, the piston 102 is connected to the crankshaft 131 via a connecting rod 132. The reciprocating motion of the piston 102 is converted into rotational motion by the crankshaft 131. A crank angle sensor 116 is attached to the crankshaft 131. The crank angle sensor 116 detects the rotation and phase of the crankshaft 131 and outputs the detection result to the ECU 109. Based on the output of the crank angle sensor 116, the ECU 109 can detect the rotational speed of the internal combustion engine 101.

[0024] The ECU 109 receives signals supplied from the crank angle sensor 116, air flow meter 120, oxygen sensor 113, accelerator position sensor 122 which indicates the degree of accelerator opening operated by the driver, fuel pressure sensor 126, and the like.

[0025] The ECU 109 calculates the required torque for the internal combustion engine 101 based on the signal supplied from the accelerator pedal position sensor 122, and also determines whether or not the engine is idle. Furthermore, the ECU 109 calculates the amount of intake air required for the internal combustion engine 101 based on the required torque and outputs an opening signal corresponding to that amount to the throttle valve 119.

[0026] Furthermore, the ECU 109 has a rotational speed detection unit (not shown) that calculates the rotational speed of the internal combustion engine 101 (hereinafter referred to as "engine speed") based on a signal supplied from the crank angle sensor 116. In addition, the ECU 109 has a warm-up determination unit (not shown) that determines whether or not the three-way catalytic converter 112 is in a warmed-up state based on the temperature of the coolant obtained from the water temperature sensor 108 and the elapsed time since the start of the internal combustion engine 101.

[0027] A fuel level sensor 99 is provided inside the fuel tank 123. This fuel level sensor 99 is used to detect the remaining amount of fuel in the fuel tank 123, and is, for example, an electric type. A float 99a located inside the fuel tank 123 is connected to the electric fuel level sensor 99 via a lever 99b.

[0028] The float 99a moves up and down in response to fluctuations in the fuel level (fuel liquid height) in the fuel tank 123. The lever 99b moves in conjunction with the up and down movement of the float 99a. The fuel level sensor 99 converts the position of the lever 99b into a resistance value of a variable resistor and outputs an output signal corresponding to that resistance value to the ECU 109. The ECU 109 can detect the fuel level in the fuel tank 123 based on this output signal. Note that the configuration of the fuel level sensor 99 is not limited to the form shown in Figure 1.

[0029] Fuel is supplied to the fuel tank 123 either manually or mechanically from outside the vehicle. The amount of fuel in the fuel tank 123 is indicated by an analog or digital fuel gauge (not shown). The driver can check the amount of fuel in the fuel tank 123 by looking at the fuel gauge (not shown).

[0030] The fuel supplied to the fuel tank 123 is not necessarily limited to gasoline; for example, it may be gasoline containing alcohol. Alternatively, the fuel supplied to the fuel tank 123 may be a mixed fuel containing alcohol, synthetic fuel, and gasoline. The mixing ratio of each fuel in the mixed fuel is not necessarily the same and can vary considerably depending on the country, region, and gas station.

[0031] The fuel injection control device 127 calculates the amount of fuel (target injection amount) according to the intake air amount and outputs a corresponding fuel injection signal to the fuel injection device 200. The target injection amount is fed back to the fuel injection control device 127 based on the oxygen concentration measured by the oxygen sensor 113. The fuel injection control device 127 outputs an energization signal to the ignition coil 107 and an ignition signal to the spark plug 106.

[0032] [Fuel Injection System Configuration] Next, a detailed example of the configuration of the fuel injection system 200 shown in Figure 1 will be explained using Figure 2. Figure 2 is a cross-sectional view showing an example of the internal configuration of the fuel injection system 200.

[0033] The fuel injection device 200 of this embodiment will be described below, with reference to an electromagnetic fuel injection device for an internal combustion engine that uses gasoline or a mixed fuel as fuel.

[0034] As shown in Figure 2, the fuel injection device 200 comprises a nozzle body 201, a valve seat 202, a valve element 203, a fixed core (stator) 204, a movable core (movable element) 205, an intermediate member 206, a coil 208, and a housing 209. The fuel injection device 200 also comprises a first spring member 211, a second spring member 212, and a third spring member 213.

[0035] The nozzle body 201 is formed in a cylindrical shape. In Figure 2, the upper end of the nozzle body 201 is the rear end, and the lower end is the front end. A valve seat 202 is fixed to the front end of the nozzle body 201. The valve seat 202 has a plurality of fuel injection holes 215 that serve as fuel passages. The front end of the nozzle body 201 is inserted into an insertion hole provided in a component (cylinder block, cylinder head, etc.) that forms the combustion chamber 121 (see Figure 1).

[0036] The fixed core 204 is formed in a substantially cylindrical shape with irregularities on its outer surface. One end of the fixed core 204 is press-fitted into the rear end of the nozzle body 201. The nozzle body 201 and the fixed core 204 are joined by welding. A connector 210 is connected to the outer surface of the fixed core 204.

[0037] The nozzle body 201 and the fixed core 204 form a cylindrical nozzle 260. The other end of the fixed core 204 forms the rear end of the nozzle 260. The other end of the fixed core 204 is a fuel supply section 204a to which fuel is supplied. The fuel supply section 204a is connected to a high-pressure fuel pipe 129 (see Figure 1).

[0038] The nozzle 260, which consists of a nozzle body 201 and a fixed iron core 204, has a fuel passage formed along the central axis 200a inside so that fuel flows from the fuel supply section 204a to multiple fuel injection holes 215. The fuel injection device 200 receives fuel from the high-pressure fuel pipe 129 (see Figure 1) through the fuel supply section 204a and injects the fuel into the combustion chamber 121 (see Figure 1) from the fuel injection holes 215 of the valve seat 202.

[0039] Between the fuel supply section 204a and the valve seat 202, a valve body 203, a movable iron core 205, and an intermediate member 206 are provided. The valve body 203 is arranged to be movable along the central axis 200a. The valve body 203 is formed in a cylindrical shape. The tip of the valve body 203 seats on or off the valve seat 202. As a result, the valve body 203 opens and closes the multiple fuel injection holes 215 of the valve seat 202.

[0040] The movable core 205 is located inside the nozzle body 201. The movable core 205 is formed in a cylindrical shape with an axial hole. A small gap is formed between the outer surface of the movable core 205 and the inner surface of the nozzle body 201. One end of the movable core 205 faces the tip of the nozzle body 201.

[0041] The other end of the movable core 205 faces one end of the fixed core 204. The valve body 203 passes through the shaft hole of the movable core 205. A recess, including the shaft hole, is formed at the other end of the movable core 205. An intermediate member 206 is housed in the recess of the movable core 205. The movable core 205 also has an eccentric through-hole that communicates with the recess. This eccentric through-hole serves as a passage through which fuel passes.

[0042] The intermediate member 206 is formed in a bottomed cylindrical shape. The bottom of the intermediate member 206 faces the axial hole of the fixed iron core 204. A through hole is provided in the bottom of the intermediate member 206 through which the valve body 203 passes. An engagement flange provided on the outer surface of the valve body 203 is slidably engaged with the inner circumferential surface of the intermediate member 206. When the valve body 203 moves toward the rear end of the nozzle 260, the engagement flange engages with the bottom of the intermediate member 206. As a result, the intermediate member 206 moves toward the rear end of the nozzle 260 together with the valve body 203.

[0043] The housing 209 is formed in a bottomed cylindrical shape. A through hole is formed in the bottom of the housing 209 through which the nozzle body 201 passes. The opening edge of the through hole in the housing 209 and the outer surface of the nozzle body 201 are welded, for example, all the way around. The cylindrical portion of the housing 209 covers the joint between the nozzle body 201 and the fixed iron core 204.

[0044] The coil 208 is positioned between the outer surface of the fixed core 204 and the inner surface of the housing 209. The fixed core 204, coil 208, and housing 209 constitute an electromagnet. The beginning and end ends of the coil 208 are connected to the power supply terminals 210a of the connector 210 via wiring (not shown).

[0045] The first spring member 211 is positioned within the cylindrical bore of the fixed core 204. One end of the first spring member 211 abuts against a spring engagement flange provided at the rear end of the valve body 203. The other end of the first spring member 211 abuts against a spring engagement portion 216 provided within the cylindrical bore of the fixed core 204. The first spring member 211 biases the valve body 203 toward the valve seat 202 (the tip side of the nozzle 260). A passage for fuel is formed in the spring engagement portion 216.

[0046] The valve body 203 passes through the second spring member 211. One end of the second spring member 211 abuts against the bottom of the intermediate member 206. The other end of the second spring member 211 abuts against the engagement flange of the valve body 203. The second spring member 211 biases the movable iron core 205 toward the valve seat 202 (the tip side of the nozzle 260) via the intermediate member 206.

[0047] The third spring member 213 is positioned inside the cylindrical bore of the nozzle body 201. The valve body 203 passes through the third spring member 213. One end of the third spring member 213 abuts against a spring engagement portion 217 provided inside the cylindrical bore of the nozzle body 201. The other end of the third spring member 213 abuts against one end of the movable core 205. The third spring member 213 biases the movable core 205 toward the fixed core 204 side (the rear end side of the nozzle 260). A passage for fuel is formed in the spring engagement portion 217.

[0048] When the coil 208 is not energized, the force obtained by subtracting the biasing force of the third spring member 213 from the biasing forces of the first spring member 211 and the second spring member 212 biases the valve body 203 toward the valve seat 202 (in the valve closing direction). As a result, the tip of the valve body 203 contacts (seats) the valve seat 202 and closes the multiple fuel injection holes 215. This state is called the valve closed stable state (valve closed standby state). In the valve closed stable state, the movable iron core 205 is positioned in the valve closed position with contact with the intermediate member 206. The valve body 203 is driven via the transmission surface 219 that transmits the load from the movable iron core 205.

[0049] In the stable closed valve state, the intermediate member 206 is biased toward the valve seat 202 side (valve closing direction) by the second spring member 212 and is in contact with the engagement flange of the valve body 203, remaining stationary. The movable core 205 is biased toward the fixed core 204 side (valve opening direction) by the third spring member 213 and is in contact with the intermediate member 206. Since the biasing force of the second spring member 212 is greater than that of the third spring member 213, a gap 250 is created between the valve body 203 and the movable core 205.

[0050] When the coil 208 is energized, magnetic flux flows through the magnetic circuit, which includes the fixed core 204, the movable core 205, the nozzle body 201, and the housing 209. A magnetic attractive force is then generated in the fixed core 204 that attracts the movable core 205. When the magnetic attractive force of the fixed core 204 exceeds the force obtained by subtracting the biasing force of the third spring member 213 from the biasing forces of the first spring member 211 and the second spring member 212, the movable core 205 moves toward the fixed core 204. The movable core 205 moves until it collides with the fixed core 204.

[0051] As the movable core 205 moves toward the fixed core 204, it engages with the engagement flange of the valve body 203. As a result, the valve body 203 moves toward the fixed core 204 together with the movable core 205. When the valve body 203 moves toward the fixed core 204, the tip of the valve body 203 separates from the valve seat 202. This causes the valve body 203 to open the multiple fuel injection holes 215 of the valve seat 202. Consequently, the fuel injector 200 enters an open state.

[0052] The fuel injection system 200 is connected to a fuel injection control device 127 and an ECU 109. The ECU 109 includes a CPU (Central Processing Unit) 501, as shown in Figure 3, which will be described later. The fuel injection control device 127 has a circuit that receives a drive command pulse from the ECU 109 and supplies a drive current (drive voltage) to the fuel injection system 200. The ECU 109 and the fuel injection control device 127 may be configured as a single component. At least the fuel injection control device 127 is a device that generates the drive voltage for the fuel injection system 200, and may be integrated with the ECU 109 or configured as a standalone unit.

[0053] The ECU 109 receives signals indicating the status of the internal combustion engine 101 from various sensors and calculates the appropriate drive command pulse width and injection timing according to the operating conditions of the internal combustion engine 101. The drive command pulse output from the ECU 109 is input to the fuel injection control device 127 via the signal line 142.

[0054] The fuel injection control device 127 controls the drive voltage applied to the coil 208 and supplies the drive current. The ECU 109 communicates with the fuel injection control device 127 through the communication line 141. The ECU 109 can switch the drive current generated by the fuel injection control device 127 according to the fuel pressure and operating conditions supplied to the fuel injector 200. The fuel injection control device 127 can change its control constants through communication with the ECU 109, and the current waveform changes according to the control constants.

[0055] [Configuration of fuel injection control system] Next, the configuration of the fuel injection control device 127 will be explained using Figure 3. Figure 3 shows a detailed configuration example of the drive circuit of the fuel injection control device 127 and the ECU 109.

[0056] The CPU 501, built into the ECU 109, receives various signals indicating the engine status from the fuel pressure sensor 126, air flow meter 120, oxygen sensor 113, crank angle sensor 116, etc. Based on these signals, the CPU 501 calculates the drive command pulse width and injection timing to control the amount of fuel injected from the fuel injector 200 according to the operating conditions of the internal combustion engine 101.

[0057] Furthermore, the CPU 501 calculates the appropriate pulse width and injection timing of the drive command pulse according to the operating conditions of the internal combustion engine 101, and outputs the drive command pulse to the drive IC (Integrated Circuit) 502 (labeled "IC" in the diagram) of the fuel injector 200 via the signal line 142. The amount of fuel injected is determined by the magnitude of the pulse width of the drive command pulse. Subsequently, the drive IC 502 switches the energization of the switching elements 505, 506, and 507 to supply drive current to the fuel injector 200.

[0058] The switching element 505 is connected between a high-voltage source higher than the voltage source VB input to the drive circuit of the fuel injection control device 127 and the high-voltage terminal of the coil 208 of the fuel injection device 200. The switching elements 505, 506, and 507 are composed of, for example, FETs (Field Effect Transistors) or transistors. The switching elements 505, 506, and 507 can switch the power supply to the fuel injection device 200 on and off.

[0059] The boosted voltage VH, which is the initial voltage value of the high-voltage source, is, for example, 65V, and is generated by boosting the battery voltage using a boost circuit 514. The boost circuit 514 consists of, for example, a coil 530, a transistor 531, a diode 532, and a capacitor 533.

[0060] In the boost circuit 514, when transistor 531 is turned ON, the battery voltage VB flows to the ground potential 534 side. On the other hand, when transistor 531 is turned OFF, the high voltage generated in coil 530 is rectified through diode 532, and charge is accumulated in capacitor 533. Then, the ON or OFF of this transistor is repeated until the boost voltage VH is reached, increasing the voltage across capacitor 533. Transistor 531 is connected to a drive IC 502 or CPU 501, and the boost voltage VH output from the boost circuit 514 is detected by the drive IC 502 or CPU 501. Note that the boost circuit 514 may also be configured using a DC / DC converter or the like.

[0061] Switching element 507 is connected between the low voltage source and the high voltage terminal of coil 208. The low voltage source VB is, for example, the battery voltage, and its voltage value is approximately 12-14V. Switching element 506 is connected between the low voltage terminal of fuel injection device 200 and ground potential 515.

[0062] The drive IC 502 detects the value of the current flowing through the fuel injector 200 using current-sensing resistors 508, 512, and 513, and switches the energization or de-energization of switching elements 505, 506, and 507 according to the detected current value to generate the desired drive current. Diodes 509 and 510 apply a reverse voltage to the coil 208 of the fuel injector 200, rapidly reducing the current supplied to the coil 208.

[0063] The CPU 501 communicates with the drive IC 502 through the communication line 141. The CPU 501 can switch the drive current generated by the drive IC 502 according to the fuel pressure and operating conditions supplied to the fuel injector 200. The ends of resistors 508, 512, and 513 are connected to the A / D conversion port of the drive IC 502. The drive IC 502 detects the voltage across the ends of resistors 508, 512, and 513.

[0064] [Fuel injection system operation] Next, the operation of the fuel injection system 200 under the control of the fuel injection control device 127 will be explained using Figure 4. Figure 4 shows the drive command pulse, drive voltage, drive current, valve body displacement, and movable core displacement.

[0065] As shown in Figure 4, when the drive command pulse Ti is input at time Ts, a drive voltage 304 is applied from a high-voltage source that has been boosted to a voltage higher than the battery voltage VB, and the supply of current to the coil 208 (see Figure 2) begins.

[0066] After energizing the coil 208, a magnetomotive force is generated by the electromagnet formed by the fixed core 204, the coil 208, and the housing 209. This magnetomotive force causes a magnetic flux to flow around the magnetic path formed by the fixed core 204, the housing 209, and the movable core 205, which surrounds the coil 208. At this time, a magnetic attractive force acts between the movable core 205 and the fixed core 204, causing the movable core 205 and the intermediate member 206 to displace toward the fixed core 204. Subsequently, the movable core 205 displaces to a position 334 where the transmission surface 219 of the valve body 203 and the transmission surface 218 of the movable core 205 come into contact. The valve body 203 continues to maintain contact with the valve seat 202.

[0067] When the movable core 205 is displaced by the gap 250 between the valve body 203 and the movable core 205, and the transmission surface 219 of the valve body 203 collides with the transmission surface 218 of the movable core 205, the valve body 203 is pulled upstream by the energy of the movable core 205, and the valve body 203 separates from the valve seat 202. This creates a gap between the valve body 203 and the valve seat 202, opening the fuel passage. As a result, fuel is injected from multiple fuel injection holes 215. The valve body 203 is displaced rapidly by the movable core 205, which has kinetic energy. When the movable core 205 is displaced to position 335, the valve body 203 is in a full-lift state.

[0068] The fuel injection control device 127 applies a high drive voltage 304 and supplies a drive current 308 to the coil 208 from time Ts until time T31 (valve opening start timing), when the movable core 205 and the valve body 203 collide and the valve body 203 separates from the valve seat 202. This generates a sufficient magnetic attraction force between the movable core 205 and the fixed core 204, allowing the movable core 205 to respond quickly. By allowing the movable core 205 to respond quickly, even if the gap 250, which serves as the pre-stroke, varies from unit to unit, the influence of this variation on the injection amount can be reduced.

[0069] The fuel injection control device 127 sets the drive voltage 304 so that the drive current 308 reaches its peak current value Ip at the valve opening start timing. Then, when the drive current 308 reaches its peak current value Ip, the fuel injection control device 127 turns off the voltage. Figure 4 shows how the voltage is turned off when the drive current 308 reaches its peak current value Ip. In this way, the fuel injection control device 127 can turn off the voltage at a timing that can suppress excessive acceleration of the movable iron core 205.

[0070] The application time of the drive current 308 until the peak current value Ip is reached according to this embodiment can be determined based on the valve opening start timing. For example, if the magnetic attraction force generated before the valve opening start timing is weak, the fuel injection control device 127 may configure the drive current 308 to reach the peak current value Ip after the valve opening start timing. Alternatively, the fuel injection control device 127 may apply a reverse voltage when the drive current 308 reaches the peak current value Ip.

[0071] After time T31, the drive voltage 304 rapidly decreases, reducing the drive current 308 and decreasing the magnetic attractive force acting between the movable core 205 and the fixed core 204. This decrease in magnetic attractive force suppresses excessive acceleration of the movable core 205 and reduces the collision energy when it collides with the fixed core 204. In other words, the fuel injection control device 127 suppresses excessive acceleration of the movable core 205 and reduces the collision energy when the movable core 205 collides with the fixed core 204 by applying a reverse voltage before the movable core 205 collides with the fixed core 204.

[0072] After the collision between the movable core 205 and the fixed core 204, the valve body 203 is displaced upstream, and the movable core 205 is displaced downward. When the fixed core 204 and the movable core 205 collide, the valve body 203 and the movable core 205 separate, and the movable core 205 is displaced downstream, but eventually comes to rest and stabilizes at the target lift position. This state is defined as the valve open stable state.

[0073] After a high drive voltage 304 is applied, when the drive current 308 reaches a first current value Ih1 that can hold the valve open, the fuel injection control device 127 continues to apply the drive voltage 305 until time Te. The drive voltage 305 alternates between applying the battery voltage VB and 0V. As a result, the fuel injection control device 127 flows a first hold current 331 (drive current) to maintain the first current value Ih1.

[0074] The fuel injection control device 127 maintains the first hold current 331 for a predetermined time, and then reduces the current value of the drive current 308. When the drive current 308 reaches a second current value Ih2 that can hold the valve open, the fuel injection control device 127 applies a drive voltage 305. As a result, the fuel injection control device 127 flows a second hold current 332 (drive current) to maintain the second current value Ih2.

[0075] The predetermined time is set according to the time it takes for the magnetic flux to saturate, etc. The first hold current 331 and the second hold current 332 are drive currents for maintaining the valve body 203 in an open state (open valve holding state).

[0076] Next, when the drive command pulse Ti turns OFF at time Te, the fuel injection control device 127 applies the drive voltage in the reverse direction (i.e., applies a reverse voltage). This cuts off the current supply to the coil 208, eliminating the magnetic flux generated in the magnetic circuit and causing the magnetic attractive force to disappear. As a result, the movable iron core 205, having lost its magnetic attractive force, is pushed back to the closed position where the valve body 203 contacts the valve seat 202 by the load of the first spring member 211 and the force due to the fuel pressure.

[0077] [Detailed structure of valve seat and valve body] Next, the detailed configuration of the valve seat 202 and the tip portion 23 of the valve body 203 according to this embodiment will be described with reference to Figures 5 and 6. Figure 5 is a cross-sectional view of the tip of the fuel injection device 200, perpendicular to the axial direction. Figure 6 is a cross-sectional view along line AA shown in Figure 5.

[0078] As shown in Figure 5, the valve seat 202 has a cylindrical portion 222 that is press-fitted into the inner wall surface of the nozzle body 201, and a seat portion 224 that is continuous with the tip side of the cylindrical portion 222 in the axial direction Da.

[0079] A tip-side sliding portion 231, provided on the tip portion 23 of the valve body 203, slides on the inner circumferential surface 221 of the cylindrical portion 222. In addition, multiple (four in this example) flow path forming portions 223 are formed in the cylindrical portion 222. The multiple flow path forming portions 223 are arranged at equal intervals in the circumferential direction on the inner circumferential surface 221 of the cylindrical portion 222. Flow paths FC (FC1 to FC4) through which fuel passes are formed between the flow path forming portions 223 and the tip-side sliding portion 231. Flow paths FC extend toward the seat portion 224.

[0080] The seat portion 224 is formed continuously with the tip of the cylindrical portion 222 and closes the opening on the tip side of the cylindrical portion 222. The seat portion 224 is formed in a roughly hemispherical cup shape that protrudes toward the tip. Inside the seat portion 224, a seat surface 224a is formed which the spherical portion 230 of the valve body 203 (described later) contacts and separates from. The seat surface 224a is formed in a frustoconical shape (tapered) that decreases in diameter toward the tip. Multiple (six in this example) fuel injection holes 215 are formed toward the tip side of the seat surface 224a of the seat portion 224.

[0081] Furthermore, a sac chamber 225 is formed inside the seat portion 224. The sac chamber 225 is a substantially hemispherical recess located towards the tip of the multiple fuel injection holes 215. The sac chamber 225 is also formed at a position that coincides with the central axis AX1 of the fuel injection device 200. At least a portion of the convex portion 233 provided on the spherical portion 230 of the valve body 203, which will be described later, is inserted into this sac chamber 225.

[0082] The tip portion 23 of the valve body 203 has a spherical portion 230 and a tip-side sliding portion 231.

[0083] The tip-side sliding portion 231 slides against the inner circumferential surface 221 of the cylindrical portion 222 of the valve seat 202. The spherical portion 230 is formed continuously with the tip-side sliding portion 231 in the axial direction Da towards the tip. The spherical portion 230 is formed in a substantially hemispherical shape. The spherical portion 230 has a valve body-side seat surface 232 and a convex portion 233.

[0084] The valve body-side seat surface 232 faces the seat surface 224a of the seat portion 224 and moves closer to and further away from the seat surface 224a. When the valve body-side seat surface 232 contacts the seat surface 224a, the flow path FC leading to the fuel injection hole 215 is closed. When the valve body-side seat surface 232 and the seat surface 224a come into contact, a portion of the protrusion 233 is inserted into the sac chamber 225. When the valve body-side seat surface 232 moves away from the seat surface 224a, a flow path FC through which fuel passes is formed between the valve body-side seat surface 232 and the seat surface 224a, and fuel is injected from the fuel injection hole 215.

[0085] As shown in Figure 6, the fuel injection hole 215 is formed in a three-stage shape, consisting of an orifice hole 215a for forming the spray, a counterbore hole 215b, and a surface press hole 215c for forming a flat surface.

[0086] The orifice hole 215a extends from the sheet surface 224a toward the outer peripheral surface 220. The counterbore hole 215b is formed so as to surround the orifice hole 215a. The counterbore hole 215b extends from the end of the orifice hole 215a on the outer peripheral surface 220 toward the outer peripheral surface 220. The surface press hole 215c is a recess that is recessed from the outer peripheral surface 220 toward the counterbore hole 215b. The surface press hole 215c is formed so as to surround the periphery of the counterbore hole 215b.

[0087] The fuel injection port 215 is formed in the hemispherical seat portion 224 of the valve seat 202. Therefore, the fuel injection port 215 is provided with a counterbore hole 215b to adjust the length of the orifice hole 215a.

[0088] The ratio of the length to the diameter of the orifice hole 215a is a factor that determines the straightness of the fuel spray flow. Therefore, the orifice hole 215a is designed so that the ratio of the length to the diameter is a predetermined value. The diameter of the orifice hole 215a is determined according to the engine specifications (fuel flow rate requirements). Therefore, the ratio of the length to the diameter of the orifice hole 215a is set by adjusting the length. The length of the orifice hole 215a is then adjusted by adjusting the depth of the counterbore hole 215b.

[0089] In this embodiment, the fuel injection port 215 has a three-stage shape, but the shape of the fuel injection port according to the present invention is not limited to this. The fuel injection port according to the present invention may have, for example, four or more stages, or it may have a single-stage shape consisting only of an orifice hole.

[0090] [Surface roughness of the valve tip of a conventional fuel injection system] Next, the surface roughness of the tip portion 23 of the valve body 203 in a conventional fuel injection system will be described with reference to Figures 7 and 8. Figure 7 is a front view showing the surface roughness of the tip of the valve body in a conventional fuel injection system. Figure 8 is a cross-sectional view along the BB line shown in Figure 7.

[0091] As shown in Figures 7 and 8, the surface of the tip portion 23 of the conventional valve body 203 is divided into a seat portion opposing region 23a, a pre-processed region 23t, and a conical region 23r. The seat portion opposing region 23a, the pre-processed region 23t, and the conical region 23r are each subjected to surface processing to have different surface roughness.

[0092] The seat-facing region 23a is formed in an annular shape, including the valve body-side seat surface 232 (see Figure 6). The seat-facing region 23a needs to contact the seat surface 224a of the valve seat 202 to reliably seal the fuel. Therefore, the seat-facing region 23a is surface-treated to have a smooth surface with low surface roughness. The surface roughness of the seat-facing region 23a is set, for example, to a maximum height of less than 0.2 micrometers.

[0093] The pre-processing area 23t is the area where pre-processing is performed when surface processing is applied to the sheet portion opposing area 23a. The pre-processing area 23t is located towards the tip of the sheet portion opposing area 23a and is formed in an annular shape adjacent to the sheet portion opposing area 23a. The surface roughness of the pre-processing area 23t is greater than that of the sheet portion opposing area 23a. The surface of the pre-processing area 23t is processed to have a relatively rough surface. The surface roughness of the pre-processing area 23t is set, for example, to a maximum height of 0.2 micrometers or more and less than 0.5 micrometers.

[0094] The conical region 23r encompasses the entire area towards the tip, beyond the pre-processed region 23t. Since the conical region 23r is an area that does not come into contact with other components, there is no need to reduce its surface roughness. The conical region 23r has a greater surface roughness than the pre-processed region 23t. The conical region 23r is surface-processed to have a relatively rough surface. The surface roughness of the conical region 23r is set, for example, to a maximum height of 0.5 micrometers or more and less than 1.0 micrometer.

[0095] Furthermore, the tip of the valve body may be configured such that the seat portion opposing region 23a and the conical region 23r are adjacent to each other, without providing a pre-processing region 23t.

[0096] [Conventional residual behavior of bubbles] Next, the residual behavior of bubbles after fuel injection in conventional fuel injection systems will be explained using Figures 9 and 10. Figure 9 shows the drive command pulse, drive voltage, drive current, valve body displacement, movable core displacement, and fuel flow rate at the fuel injection port outlet of a conventional fuel injection system at full lift. Figure 10 is a cross-sectional view showing residual bubbles on the valve body surface after fuel injection is complete in a conventional fuel injection system.

[0097] The operation of the drive command pulse, drive voltage, drive current, valve body displacement, and movable core displacement shown in Figure 9 is the same as in Figure 4. When fuel injection ends at time Te, a voltage for closing the valve is applied to the fuel injector. As a result, the drive current 308 stops, and the displacement of the valve body 203 begins to decrease. Then, at time Tb, when the displacement of the valve body 203 becomes zero and the valve body side seat surface 232 (see Figure 6) seats on the seat portion 224, the fuel supply to the fuel injection hole 215 stops.

[0098] The fuel present in the internal space at the tip of the valve seat 202 is discharged out through the fuel injection port 215 due to residual pressure and inertia. However, when the engine coolant temperature is low, such as immediately after starting, the surface tension of the fuel increases. As a result, some of the fuel present in the internal space of the valve seat 202 after fuel injection is not able to flow out through the fuel injection port 215 and remains in the internal space of the valve seat 202.

[0099] At that time, air from the combustion chamber is drawn into the fuel injection port 215 through the fuel injection port 215, from which the fuel outflow has already ended. As a result, a mixture of fuel and air bubbles 24 remains in the internal space of the valve seat 202 (see Figure 10).

[0100] The residual bubbles 24 include, for example, residual bubbles 24h near the nozzle, residual bubbles 24r on the valve body tip side, and residual bubbles 24s in the sac chamber. Residual bubbles 24h near the nozzle are bubbles that remain between the seat portion 224 and the fuel injection hole 215. Residual bubbles 24r on the valve body tip side are bubbles that remain between the seat portion 224 and the convex portion 233 of the valve body 203. Residual bubbles 24s in the sac chamber are bubbles that remain inside the sac chamber 225.

[0101] When fuel injection in the next cycle begins, the fuel that first passes through the seat section 224 collides with the residual bubbles 24h near the nozzle. As a result, the initial shape of the spray may become turbulent, potentially leading to variations in the spray shape.

[0102] The volume of residual bubbles 24h near the nozzle is small compared to the volume of fuel being injected, and therefore has almost no effect on the displacement of the valve body 203. However, at the Tbubble, which is the timing when residual bubbles 24h near the nozzle pass through the fuel injection hole 215, disturbance occurs in the fuel injection rate (see the fifth row of Figure 8).

[0103] Immediately after the valve opens and the fuel injection rate is low, the pressure and flow rate of the fuel passing through the fuel injection port 215 are low and the flow is weak, making the spray shape easily unstable due to disturbances. Residual bubbles 24h near the injection port enter the fuel injection port 215 along with the fuel after the valve opens, so they pass through the fuel injection port immediately after the valve opens. Therefore, residual bubbles 24h near the injection port are likely to destabilize the spray shape.

[0104] Thus, in conventional fuel injection systems, when fuel injection starts in the next cycle, the fuel collides with residual air bubbles, causing turbulence in the initial shape of the spray. Alternatively, if the fuel flow rate is low and the flow is weak, residual air bubbles are injected, causing turbulence in the initial shape of the spray. As a result, there was a risk of variations in the spray shape.

[0105] [Hydrophilicity and surface roughness] Here, we will explain the hydrophilicity and surface roughness using Figure 11. Figure 11 is a graph showing the relationship between the fuel, the surface roughness of the valve body 203 in the fuel injection device 200, and the wetting angle.

[0106] The inventors focused on the hydrophilicity of the tip portion 23 of the valve body 203 as a means of controlling the residual position of the bubbles 24. Hydrophilicity is determined by the balance of the surface tensions of the liquid, solid, and gas in contact. That is, hydrophilicity is expressed by equation (1), which represents the wetting angle θ, which is the angle that the surface of a droplet attached to a flat plate makes with the flat plate. [Mathematics 1] θ=(γSV−γSL) / γLV (1)

[0107] Note that equation (1) is Young's equation, where γSV is the surface tension of a solid relative to a gas, γSL is the surface tension of a solid relative to a liquid, and γLV is the surface tension of a liquid relative to a gas.

[0108] Surfaces with a θ greater than 90° are classified as hydrophilic, and surfaces with a θ less than 90° are classified as hydrophobic. In this embodiment, the fuel injector 200 is made of stainless steel, and the fuel is gasoline. Stainless steel is a hydrophilic surface with respect to gasoline. Other types of fuel may be used as long as they are within the range of contact between hydrophilic and gasoline surfaces.

[0109] Furthermore, hydrophilicity changes depending on the surface roughness of the solid. The relationship between surface roughness and wetting angle is expressed by Wenzel's equation. That is, in a plane with wetting angle θ, the wetting angle θ' when the surface roughness is multiplied by r is expressed by equation (2). [Math 2] cosθ' = r × cosθ ···(2)

[0110] As shown in Figure 16, on a hydrophilic surface, the smaller the surface roughness of the solid surface (the surface of the valve body 203), the larger the wetting angle, and the closer it approaches a surface that is difficult to wet. Conversely, the larger the surface roughness, the smaller the wetting angle, and the closer it approaches a surface that is easily wetted.

[0111] The aforementioned hydrophilicity describes the behavior of liquid droplets adhering to a solid surface in a gaseous environment. However, the opposite relationship holds true for bubbles adhering to a solid surface in a liquid environment. That is, on a hydrophilic surface, the smaller the surface roughness of the solid surface, the less easily it is wetted by the liquid, and the more easily bubbles adhere. Conversely, the larger the surface roughness, the easier it is to wet, and the less easily bubbles adhere. In the fuel injection device 200 according to the first embodiment, the surface roughness of the tip portion 23 of the valve body 203 is determined based on this principle.

[0112] [Surface roughness of the valve tip portion of the fuel injection device according to the first embodiment] Next, the surface roughness of the tip portion 23 of the valve body 203 according to the first embodiment will be described with reference to Figures 12 and 13. Figure 12 is a front view showing the surface roughness of the tip of the valve body according to the first embodiment. Figure 13 is a cross-sectional view along the CC line shown in Figure 12.

[0113] As shown in Figures 12 and 13, the surface of the tip portion 23 of the valve body 203 in the first embodiment is divided into a seat portion opposing region 23a, a nozzle opposing region 23b, a conical base region 23c, and a conical apex region 23d. The seat portion opposing region 23a, the nozzle opposing region 23b, the conical base region 23c, and the conical apex region 23d each have a set surface roughness.

[0114] The seat-facing region 23a is formed in an annular shape, including the valve body-side seat surface 232 (see Figure 6). The seat-facing region 23a needs to contact the seat surface 224a of the valve seat 202 to reliably seal the fuel. Therefore, the seat-facing region 23a is surface-treated to have a smooth surface with low surface roughness. The surface roughness of the seat-facing region 23a is set, for example, to a maximum height of less than 0.2 micrometers.

[0115] The nozzle-facing region 23b is located towards the tip of the seat-facing region 23a and is formed in an annular shape adjacent to the seat-facing region 23a. As shown in Figure 13, the nozzle-facing region 23b includes regions facing multiple fuel injection holes 215. The nozzle-facing region 23b is surface-treated to have a relatively rough surface. The nozzle-facing region 23b has a greater surface roughness than the seat-facing region 23a. The surface roughness of the nozzle-facing region 23b is set, for example, to a maximum height of 0.2 micrometers or more and less than 0.5 micrometers.

[0116] The conical base region 23c is located towards the tip of the nozzle-facing region 23b and is formed in an annular shape adjacent to the nozzle-facing region 23b. As shown in Figure 13, the conical base region 23c includes a region on the inner surface of the valve seat 202 that is towards the tip of the multiple fuel injection holes 215. The conical base region 23c is surface-machined to have a relatively smooth surface. The surface roughness of the conical base region 23c is less than that of the nozzle-facing region 23b. The surface roughness of the conical base region 23c is set to, for example, less than 0.2 micrometers in maximum height.

[0117] The conical apex region 23d encompasses the entire area towards the tip of the cone, compared to the conical base region 23c. As shown in Figure 13, the conical apex region 23d faces the sac chamber 225. The conical apex region 23d is surface-treated to have a relatively rough surface. The surface roughness of the conical apex region 23d is greater than that of the nozzle-facing region 23b. The surface roughness of the conical apex region 23d is set, for example, to a maximum height of 0.5 micrometers or more and less than 1.0 micrometer.

[0118] [Residual behavior of bubbles in the first embodiment] Next, the residual behavior of bubbles after fuel injection is completed in the fuel injection device 200 of the first embodiment will be explained using Figures 14 and 15. Figure 14 shows the drive command pulse, drive voltage, drive current, valve body displacement, movable core displacement, and fuel flow rate at the outlet of the fuel injection port of the fuel injection device 200 of the first embodiment when it is at full lift. Figure 15 is a cross-sectional view showing residual bubbles on the surface of the valve body after fuel injection is completed by the fuel injection device 200 of the first embodiment.

[0119] The operation of the drive command pulse, drive voltage, drive current, valve body displacement, and movable core displacement shown in Figure 13 is the same as in Figure 4. When fuel injection ends at time Te, a voltage for closing the valve is applied to the fuel injector. As a result, the drive current 308 stops, and the displacement of the valve body 203 begins to decrease. Then, at time Tb, when the displacement of the valve body 203 becomes zero and the valve body side seat surface 232 (see Figure 6) seats on the seat portion 224, the fuel supply to the fuel injection hole 215 stops.

[0120] The fuel present in the internal space at the tip of the valve seat 202 is discharged out through the fuel injection port 215 due to residual pressure and inertia. However, when the engine coolant temperature is low, such as immediately after starting, the surface tension of the fuel increases. As a result, some of the fuel present in the internal space of the valve seat 202 after fuel injection is not able to flow out through the fuel injection port 215 and remains in the internal space of the valve seat 202.

[0121] At that time, air from the combustion chamber is drawn into the fuel injection port 215 through the fuel injection port 215, from which the fuel outflow has already ended. As a result, a mixture of fuel and air bubbles 24 remains in the internal space of the valve seat 202 (see Figure 15).

[0122] The nozzle-facing region 23b has a relatively higher surface roughness than the adjacent regions (sheet-facing region 23a and cone base region 23c), resulting in a smaller wetting angle. Therefore, bubbles 24 are less likely to adhere to the nozzle-facing region 23b. Figure 15 shows an example where bubbles 24 do not adhere to the nozzle-facing region 23b.

[0123] On the other hand, the conical base region 23c has a lower surface roughness and a larger wetting angle than the nozzle-facing region 23b. In other words, the hydrophilicity of the nozzle-facing region 23b is higher than that of the conical base region 23c. Therefore, bubbles 24 are more likely to adhere to the conical base region 23c than to the nozzle-facing region 23b.

[0124] In this way, by increasing the surface roughness of the areas where bubble adhesion 24 is to be suppressed and decreasing the surface roughness of the areas where bubble adhesion is to be promoted, the area to which bubbles 24 adhere can be controlled. That is, while suppressing the increase of residual bubbles 24h near the nozzle remaining in the nozzle-facing region 23b, bubbles 24 can be preferentially attached to the conical base region 23c, thereby increasing the proportion of residual bubbles 24r on the valve body tip side.

[0125] Most of the residual bubbles 24r on the valve tip side and residual bubbles 24s in the sac chamber flow around the internal space of the sac chamber 225 after the valve opens before entering the fuel injection port 215. Therefore, the time at which residual bubbles 24h and 24r reach the fuel injection port 215 is later than the time at which residual bubbles 24r on the valve tip side reach the fuel injection port 215. In other words, as residual bubbles 24h near the injection port decrease and the proportion of residual bubbles 24r on the valve tip side and residual bubbles 24s in the sac chamber increase, the arrival time Tbubble, when bubbles 24 reach the fuel injection port 215, becomes later.

[0126] When the arrival time Tbubble of the bubble 24 to the fuel injection hole 215 is delayed, the valve body displacement at the time of arrival of the bubble 24 becomes larger, and the fuel pressure and fuel flow rate are stabilized. Therefore, the later the arrival time of the bubble 24 to the fuel injection hole 215, the smaller the variation in spray shape caused by the bubble 24 passing through the fuel injection hole 215 can be.

[0127] [Surface roughness distribution] Next, the surface roughness distribution of the valve body 203 of the first embodiment and the conventional valve body will be described with reference to Figures 16 and 17. Figure 16 is a graph showing the distribution of surface roughness in each region of the surface of a conventional valve body. Figure 17 is a graph showing the distribution of surface roughness in each region of the surface of the valve body 203 according to the first embodiment.

[0128] In the closed valve state, the seat portion opposing region 23a contacts the seat surface 224a of the valve seat 202 (Figure 6a). Therefore, no air bubbles 24 remain in the seat portion opposing region 23a. The region where air bubbles 24 can remain (hereinafter referred to as the "air bubble retention region") is located on the tip side (to the right in Figures 16 and 17) of the seat portion opposing region 23a.

[0129] As shown in Figure 16, in conventional valve bodies, the pre-processed region 23t has the smallest surface roughness among the regions where bubbles can remain, making it easy for bubbles 24 to adhere. Furthermore, a portion of the pre-processed region 23t faces multiple fuel injection holes 215. As a result, in the fuel injection of the next cycle, the time at which bubbles 24 reach the fuel injection holes 215 is shortened, causing turbulence in the initial shape of the spray.

[0130] On the other hand, as shown in Figure 17, in the valve body 203 according to the first embodiment, the conical base region 23c has the smallest surface roughness among the regions where bubbles can remain, making it easier for bubbles 24 to adhere. Furthermore, since the conical base region 23c is located closer to the tip than the multiple fuel injection holes 215, the time it takes for bubbles 24 to reach the fuel injection holes 215 is delayed, and the initial shape of the fuel spray is stabilized. As a result, variations in the spray shape can be reduced.

[0131] [Half-lift control] Next, the drive signal and injection response of the fuel injection system 200 according to the first embodiment during half-lift will be described with reference to Figure 18. Figure 18 shows the drive signal and injection response of the fuel injection system 200 according to the first embodiment during half-lift.

[0132] As shown in Figure 18, the first stage is the injection command pulse, the second stage is the voltage applied to the fuel injector, the third stage is the drive current flowing through the fuel injector, the fourth stage is the displacement of the valve body, and the fifth stage is the fuel flow rate at the outlet of the fuel injection hole. The fuel injection of the fuel injector described above was explained using the full-lift operation of the valve body 203 as an example. However, the fuel injector according to the present invention may also perform fuel injection by performing a half-lift operation of the valve body 203.

[0133] Even in this case, the bubbles 24 can be more easily attached to the conical base region 23c of the bubble retention area. This delays the time it takes for the bubbles 24 to reach the fuel injection hole 215, stabilizing the initial shape of the spray. Therefore, even when fuel injection is performed by operating the valve body 203 in half-lift mode, variations in the spray shape can be reduced.

[0134] 2. Second Embodiment Next, a fuel injection device according to a second embodiment of the present invention will be described.

[0135] The fuel injection system according to the second embodiment has the same configuration as the fuel injection system 200 according to the first embodiment. The difference between the fuel injection system according to the second embodiment and the fuel injection system 200 according to the first embodiment is the region that defines the surface roughness of the valve body 203. Therefore, the surface roughness of the valve body 203 according to the second embodiment will be described here, and the description of redundant components will be omitted.

[0136] [Surface roughness of the valve tip portion of the fuel injection device according to the second embodiment] The surface roughness of the tip portion 23 of the valve body 203 according to the second embodiment will be described with reference to Figures 19 and 20. Figure 19 is a front view showing the surface roughness of the tip of the valve body according to the second embodiment. Figure 20 is a cross-sectional view along the line DD shown in Figure 19.

[0137] As shown in Figures 19 and 20, the surface of the tip portion 23 of the valve body 203 in the second embodiment is divided into a seat portion opposing region 23a, a nozzle opposing region 23b, a conical base region 23c, a conical apex region 23d, a highly hydrophilic region 23e, and a lowly hydrophilic region 23f. The seat portion opposing region 23a, the nozzle opposing region 23b, the conical base region 23c, the conical apex region 23d, the highly hydrophilic region 23e, and the lowly hydrophilic region 23f each have a set surface roughness. The seat portion opposing region 23a, the nozzle opposing region 23b, and the conical base region 23c are the same as in the first embodiment.

[0138] The highly hydrophilic region 23e is located towards the tip of the conical base region 23c and is formed in an annular shape adjacent to the conical base region 23c. As shown in Figure 20, the highly hydrophilic region 23e faces the region on the inner surface of the valve seat 202 that is towards the tip of the multiple fuel injection holes 215. The highly hydrophilic region 23e is surface-treated to have a relatively rough surface. The surface roughness of the highly hydrophilic region 23e is set to be the same as the surface roughness of the injection hole opposing region 23b. That is, the surface roughness of the highly hydrophilic region 23e is set to, for example, a maximum height of 0.2 micrometers or more and less than 0.5 micrometers.

[0139] The low-hydrophilic region 23f is located further forward than the high-hydrophilic region 23e and is formed in an annular shape adjacent to the high-hydrophilic region 23e. As shown in Figure 20, the low-hydrophilic region 23f is located on the inner surface of the valve seat 202, in the region further forward than the multiple fuel injection holes 215 and opposite the sac chamber 225. The low-hydrophilic region 23f is surface-treated to have a relatively smooth surface. The surface roughness of the low-hydrophilic region 23f is set to be equivalent to the surface roughness of the conical base region 23c. That is, the surface roughness of the low-hydrophilic region 23f is set to, for example, a maximum height of less than 0.2 micrometers.

[0140] The conical apex region 23d is the entire area on the tip side of the low-hydrophilic region 23f. As shown in Figure 20, the conical apex region 23d faces the sac chamber 225. The conical apex region 23d is surface-treated to have a relatively rough surface. The conical apex region 23d has a greater surface roughness than the nozzle-facing region 23b and the high-hydrophilic region 23e. The surface roughness of the conical apex region 23d is set, for example, to a maximum height of 0.5 micrometers or more and less than 1.0 micrometer.

[0141] In the second embodiment, the conical base region 23c is sandwiched between the nozzle-facing region 23b and the highly hydrophilic region 23e. The highly hydrophilic region 23e is sandwiched between the conical base region 23c and the low-hydrophilic region 23f. In other words, regions with high hydrophilicity and regions with low hydrophilicity are arranged alternately. As a result, when a bubble 24 attempts to move from a region with low hydrophilicity (where bubbles easily adhere) to a region with high hydrophilicity (where bubbles are less likely to adhere), the radial movement speed of the valve body 203 in the bubble 24 can be reduced at the boundary. Consequently, the radial movement of the valve body 203 in the bubble 24 can be further suppressed, and the generation of residual bubbles 24h near the nozzle can be further suppressed.

[0142] Furthermore, multiple highly hydrophilic regions 23e and low hydrophilic regions 23f may be provided and arranged alternately. In this case, the surface roughness of the multiple highly hydrophilic regions 23e does not need to be the same; it may vary as long as it is more hydrophilic than the adjacent low hydrophilic region 23f. Similarly, the surface roughness of the multiple low hydrophilic regions 23f does not need to be the same; it may vary as long as it is less hydrophilic than the adjacent highly hydrophilic region 23e.

[0143] 3. Third Embodiment Next, a fuel injection system according to a third embodiment of the present invention will be described.

[0144] The fuel injection system according to the third embodiment has the same configuration as the fuel injection system 200 according to the first embodiment. The difference between the fuel injection system according to the third embodiment and the fuel injection system 200 according to the first embodiment is the region that defines the surface roughness of the valve body 203. Therefore, the surface roughness of the valve body 203 according to the third embodiment will be described here, and the description of redundant components will be omitted.

[0145] [Surface roughness of the valve tip portion of the fuel injection device according to the third embodiment] The surface roughness of the tip portion 23 of the valve body 203 according to the third embodiment will be described with reference to Figure 21. Figure 21 is a front view showing the surface roughness of the tip portion of the valve body according to the third embodiment.

[0146] As shown in Figure 21, the surface of the tip portion 23 of the valve body 203 in the third embodiment is divided into a seat portion opposing region 23a, a nozzle opposing region 23b, a conical base region 23c, and a conical apex region 23d. The surface roughness of the seat portion opposing region 23a, the nozzle opposing region 23b, the conical base region 23c, and the conical apex region 23d is the same as in the first embodiment.

[0147] A slit 25 is provided in the nozzle-facing region 23b. The slit 25 extends radially across the valve body 203. Since the nozzle-facing region 23b does not require fuel sealing performance, it does not necessarily need to be formed as a closed region with an annular shape. The slit 25 is formed by applying a C-shaped lapping process to the surface of the valve body 203, creating an area where lapping has not been applied.

[0148] A slit 26 is provided in the conical base region 23c. The slit 26 extends radially across the valve body 203. Since the conical base region 23c does not require fuel sealing performance, it does not necessarily need to be formed as a closed region with an annular shape. The slit 26 is formed by applying a C-shaped lapping process to the surface of the valve body 203, creating an area where lapping has not been applied.

[0149] The width and depth of the slits 25 and 26 should preferably be set to a size that prevents the bubbles 24 from moving along the surface of the valve body 203 along the slit 25. The width and depth of the slits 25 and 26 should be set, for example, within the range of 0.3 micrometers to 1.0 micrometer.

[0150] This makes it possible to suppress the radial movement of the bubbles 24 on the valve body 203, even with the presence of slits 25 and 26. Therefore, in the fuel injection system according to the third embodiment, the attachment position of the bubbles 24 can be controlled, and spray variations can be suppressed.

[0151] 4. Fourth Embodiment Next, a fuel injection system according to a fourth embodiment of the present invention will be described.

[0152] The fuel injection system according to the fourth embodiment has the same configuration as the fuel injection system 200 according to the first embodiment. The difference between the fuel injection system according to the fourth embodiment and the fuel injection system 200 according to the first embodiment is the region that defines the surface roughness of the valve body 203. Therefore, the surface roughness of the valve body 203 according to the fourth embodiment will be described here, and the description of redundant components will be omitted.

[0153] [Surface roughness of the valve tip portion of the fuel injection device according to the fourth embodiment] The surface roughness of the tip portion 23 of the valve body 203 according to the fourth embodiment will be described with reference to Figure 22. Figure 22 is a front view showing the surface roughness of the tip portion of the valve body according to the fourth embodiment.

[0154] As shown in Figure 22, the surface of the tip portion 23 of the valve body 203 in the fourth embodiment is divided into a seat portion opposing region 23a, a nozzle opposing region 23b, a conical base region 23c, and a conical apex region 23d. The surface roughness of the seat portion opposing region 23a, the nozzle opposing region 23b, the conical base region 23c, and the conical apex region 23d is the same as in the first embodiment.

[0155] Micro-slits 27 are formed on the surfaces of the nozzle-facing region 23b and the conical base region 23c as scratches that occurred during processing. The nozzle-facing region 23b and the conical base region 23c are not required to have fuel sealing performance. Therefore, it is possible to tolerate slight scratches (micro-slits 27) that occur during processing in the nozzle-facing region 23b and the conical base region 23c.

[0156] In the case of accidental scratches such as the micro-slits 27, they are of a size that prevents the bubbles 24 from moving. As a result, even with the micro-slits 27, the movement of bubbles 24 in the radial direction of the valve body 203 can be suppressed. Therefore, in the fuel injection system according to the fourth embodiment, the attachment position of the bubbles 24 can be controlled, and spray variations can be suppressed.

[0157] 5. Summary (1) As described above, the fuel injection device 200 according to the first embodiment comprises a tapered seat portion 224 (valve seat portion) and a valve body 203. The seat portion 224 has a plurality of fuel injection holes 215. The valve body 203 seats on or away from the seat portion 224. The hydrophilicity of the injection hole facing region 23b on the surface of the valve body 203 that faces the plurality of fuel injection holes 215 is higher than the hydrophilicity of the conical base region 23c (tip region) that is located towards the tip of the injection hole facing region 23b. This allows bubbles 24 to adhere to the conical base region 23c rather than the nozzle-facing region 23b. As a result, bubbles 24 can be prevented from remaining in the fuel flow path. Furthermore, since the conical base region 23c is located closer to the tip than the multiple fuel injection holes 215, the time it takes for the bubbles 24 to reach the fuel injection holes 215 is delayed. Therefore, the initial shape of the fuel spray can be stabilized, and variations in the spray shape can be reduced.

[0158] (2) The nozzle-facing region 23b according to the first embodiment described above is formed to form an annular closed region on the surface of the valve body 203. This makes it possible to suppress or prevent bubbles 24 from adhering to the region facing the fuel injection hole 215. It also makes it possible to suppress or prevent bubbles 24 from moving from the conical base region 23c to the region facing the fuel injection hole 215.

[0159] (3) The surface roughness of the nozzle-facing region 23b according to the first embodiment described above is greater than the surface roughness of the cone base region 23c (tip region). This makes it possible to make the hydrophilicity of the nozzle-facing region 23b higher than that of the conical base region 23c.

[0160] (4) The surface roughness of the nozzle-facing region 23b according to the first embodiment described above is set to a maximum height within the range of 0.5 to 1.0 micrometers. This makes it easier to perform surface processing to reduce the surface roughness of the conical base region 23c compared to the nozzle-facing region 23b. However, if the surface roughness of the nozzle-facing region 23b is too low, it becomes more difficult to perform surface processing on the region where the surface roughness needs to be reduced even further.

[0161] (5) The surface roughness of the cone base region 23c (tip region) according to the first embodiment described above is set to a maximum height of less than 0.5 micrometers. This makes it easy to perform surface processing to make the surface roughness of the cone base region 23c smaller than the surface roughness of the nozzle-facing region 23b.

[0162] (6) A cone apex region 23d is formed on the tip side of the cone base region 23c (tip region) according to the first embodiment described above, and has a surface roughness equal to or greater than that of the nozzle-facing region 23b. This eliminates the need to perform surface processing on the entire area beyond the nozzle-facing region 23b to a surface roughness lower than that of the nozzle-facing region 23b. Therefore, the area that needs to have a surface roughness lower than that of the nozzle-facing region 23b (the conical base region 23c) can be reduced, and the time required for surface processing can be shortened.

[0163] (7) On the surface of the valve body 203 according to the second embodiment described above, a highly hydrophilic region 23e, which has the same hydrophilicity as the nozzle-facing region 23b, and a low hydrophilic region 23f, which has the same hydrophilicity as the cone-base region 23c, are formed adjacent to each other in the radial direction of the valve body 203 on the tip side of the cone base region 23c (tip region). As a result, when the bubbles 24 attempt to move from the low-hydrophilic region 23f to the high-hydrophilic region 23e, the movement speed of the bubbles 24 in the radial direction of the valve body 203 can be reduced at the boundary. Consequently, the movement of bubbles 24 in the radial direction of the valve body 203 can be suppressed, and the generation of bubbles 24 adhering to the nozzle-facing region 23b (residual bubbles 24h near the nozzle) can be prevented.

[0164] The embodiments of the fuel injection device of the present invention, including their operation and effects, have been described above. However, the fuel injection device of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the gist of the invention as described in the claims.

[0165] Furthermore, the embodiments described above are explained in detail for the purpose of clearly illustrating the present invention, and are not necessarily limited to those comprising all the described configurations. It is also possible to replace parts of the configuration of one embodiment with those of another embodiment, and to add configurations from other embodiments to the configuration of one embodiment. Additionally, it is possible to add, delete, or replace parts of the configuration of each embodiment with those of other embodiments.

[0166] In this specification, although terms such as "parallel" and "orthogonal" are used, these do not mean only strictly "parallel" and "orthogonal," but may also refer to states that are "approximately parallel" or "approximately orthogonal," which include "parallel" and "orthogonal" and are within a range in which they can perform their functions. [Explanation of symbols]

[0167] 23...tip, 23a...seat-facing region, 23b...nozzle-facing region, 23c...cone base region, 23d...cone apex region, 23e...highly hydrophilic region, 23f...lowly hydrophilic region, 23r...cone region, 23t...pre-processed region, 24...bubble, 24h...residual bubble near nozzle, 24r...residual bubble on valve body tip side, 24s...sack chamber residual bubble, 25,26...slit, 27...fine slit, 101...internal combustion engine, 109...ECU (Engine Control Unit), 121...combustion chamber, 200...fuel injection device, 200a...central axis, 201...nozzle body, 202...valve seat, 203...valve body, 204...fixed iron core, 204a...fuel supply section 205...Movable core, 206...Intermediate member, 208...Coil, 209...Housing, 210...Connector, 210a...Terminal, 211...First spring member, 212...Second spring member, 213...Third spring member, 215...Fuel injection hole, 215a...Orifice hole, 215b...Counterbore hole, 215c...Surface press hole, 216,217...Spring engagement part, 218,219...Transmission surface, 220...Outer peripheral surface, 221...Inner peripheral surface, 222...Cylindrical part, 223...Flow path forming part, 224...Seat part, 224a...Seat surface, 225...Sack chamber, 230...Spherical part, 231...Tip side sliding part, 232...Valve body side seat surface, 233...Convex part 250... Gap, 260... Nozzle

Claims

1. A tapered valve seat portion having multiple nozzles, The valve comprises a valve body that seats or separates from the valve seat portion, The hydrophilicity of the nozzle-facing region on the surface of the valve body that is opposite to the nozzle is higher than that of the tip region located further forward than the nozzle-facing region. Fuel injection device.

2. The nozzle-facing region is formed to form an annular closed region on the surface of the valve body. The fuel injection device according to claim 1.

3. The surface roughness of the region facing the nozzle is greater than the surface roughness of the tip region. The fuel injection device according to claim 1.

4. The surface roughness of the area facing the nozzle is set to a maximum height within the range of 0.2 to 0.5 micrometers. The fuel injection device according to claim 3.

5. The surface roughness of the aforementioned tip region is set to a maximum height of less than 0.2 micrometers. The fuel injection device according to claim 4.

6. On the surface of the valve body, a top region is formed that has a surface roughness greater than or equal to the surface roughness of the region facing the nozzle, on the tip side of the tip region. The fuel injection device according to claim 1.

7. On the surface of the valve body, a highly hydrophilic region having the same hydrophilicity as the nozzle-facing region and a low hydrophilic region having the same hydrophilicity as the tip region are formed adjacent to each other in the radial direction of the valve body, closer to the tip region than the tip region. The fuel injection device according to claim 1.

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