Fuel pump and fuel injection system

Abstract

To provide a fuel pump and fuel injection system that can pressurize a plurality of kinds of fuels in a simple structure.SOLUTION: A fuel pump 10 comprises a first piston 16, a first pressure rising chamber 11, a second piston 21, and a second pressure rising chamber 12a. The first piston 16 is reciprocated by being pushed by a cam 13. The first pressure rising chamber 11 houses a first fuel to be pressurized by the first piston 16, and comprises a first discharge hole 18 for discharging the first fuel. The second piston 21 is reciprocated by being pushed by the first fuel pressurized by the first piston 16. The second pressure rising chamber 12a houses a second fuel to be pressurized by the second piston, and comprises a second discharge hole 23 for discharging the second fuel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] TECHNICAL FIELD The disclosure herein relates to fuel pumps and fuel injection systems. [Background technology]

[0002] Patent Document 1 discloses a fuel injection device. This fuel injection device is configured to inject two types of fuel from one injection valve. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-139435 A Summary of the Invention [Problem to be solved by the invention]

[0004] The fuel injection device described in Patent Document 1 requires two fuel pumps to supply two types of fuel to the injection valve through separate paths. Here, the structure of the fuel injection system may become complicated due to the inclusion of two fuel pumps.

[0005] One disclosed object is to provide a fuel pump and a fuel injection system that are capable of pressurizing a plurality of types of fuel with a simple structure. [Means for solving the problem]

[0006] The fuel pump disclosed herein comprises: a first piston (16) that is pushed and moved by a cam (13) to reciprocate; a first boost chamber (11) for accommodating a first fuel pressurized by a first piston and having a first discharge hole (18) for discharging the pressurized first fuel; a second piston (21) that reciprocates by being pressed by the first fuel pressurized by the first piston; The second pressurizing chamber (12a) contains a second fuel pressurized by a second piston and has a second discharge hole (23) for discharging the pressurized second fuel.

[0007] According to the disclosed fuel pump, when fuel is pressurized by one piston, another fuel is also pressurized by the pressurized fuel. As a result, two types of fuel can be pressurized by pressurizing one type of fuel, so that a fuel pump with a simple structure can be provided.

[0008] The fuel injection system disclosed herein comprises: a first piston (16) that is pushed and moved by a cam (13) to reciprocate; a first main body portion (31) that forms a first pressurizing chamber (11) that contains a first fuel pressurized by a first piston and has a first discharge hole (18) that discharges the pressurized first fuel; a second piston (21) that reciprocates by being pressed by the first fuel pressurized by the first piston; a fuel pump (10) including a second body portion (32) that forms a second boost chamber (12a) that contains a second fuel pressurized by a second piston and has a second discharge hole (23) that discharges the pressurized second fuel; a first rail (4b) forming a first pressure accumulator chamber (4a) for accumulating the first fuel discharged from the first pressure booster chamber; a second rail (4d) forming a second accumulator chamber (4c) for accumulating the second fuel discharged from the second boost chamber; The fuel injection system includes an injection valve (8) that injects the first fuel distributed from the first accumulator and the second fuel distributed from the second accumulator.

[0009] According to the disclosed fuel injection system, when one fuel is pressurized using one pump, another fuel is also pressurized by the pressurized fuel. As a result, by pressurizing one type of fuel, two types of fuel can be pressurized and injected, so that a fuel injection system with a simple structure can be provided.

[0010] The various aspects disclosed in this specification adopt different technical means to achieve their respective objectives. The claims and the parenthetical symbols described in this section are merely illustrative of the corresponding relationship with the embodiments described below, and are not intended to limit the technical scope. The objectives, features, and effects disclosed in this specification will become clearer with reference to the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a fuel pump and a fuel injection system according to a first embodiment. [Diagram 2] 4 is a time chart showing the relationship between the opening and closing timing of the suction amount adjusting valve and each discharge valve and the pressure changes in each boost chamber and each pressure accumulator chamber in the first embodiment. [Diagram 3] FIG. 13 is a diagram showing a fuel pump according to a modified example. [Figure 4] FIG. 7 is a diagram showing a fuel pump and a fuel injection system according to a second embodiment. [Diagram 5] 10 is a time chart showing the relationship between the opening and closing timing of the suction amount adjusting valve and each discharge valve and the pressure changes in each boost chamber and each pressure accumulator chamber in the second embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing a schematic view of a part of an injection valve according to a second embodiment. [Figure 7] FIG. 11 is a cross-sectional view showing a state in which an injection valve according to a second embodiment is in a valve-closing operation. [Figure 8] 7 is a cross-sectional view showing a schematic diagram of a connection structure between a common rail and an injection valve according to a second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, several embodiments will be described with reference to the drawings. In addition, by assigning the same reference numerals to corresponding components in each embodiment, duplicated explanations may be omitted. When only a part of the configuration is described in each embodiment, the configuration of the other embodiment described above can be applied to the other parts of the configuration. In addition to the combination of configurations explicitly stated in the description of each embodiment, configurations of several embodiments can be partially combined together even if not explicitly stated, as long as there is no particular problem with the combination.

[0013] (First embodiment) A fuel pump 10 according to an embodiment of the present disclosure is used in a fuel injection system 1 shown in Fig. 1. The fuel injection system 1 is a system that injects two types of fuel, alcohol and diesel, into cylinders of a diesel engine of a vehicle. As shown in Fig. 1, the fuel injection system 1 includes a first fuel tank 2, a second fuel tank 3, a fuel pump 10, a common rail 4, a pressure reducing valve 7, a pressure sensor 6, an injection valve 8, and a control device 5.

[0014] A fuel pump 10 supplies two types of fuel to a common rail 4. Each type of fuel supplied from the fuel pump 10 is pressurized in the common rail 4 and then distributed to the injectors 8, from which it is directly injected into the combustion chamber of each cylinder (not shown). The fuel injection system 1 shown in FIG. 1 is based on the assumption that the engine is a direct injection engine in which one injector 8 is provided for each cylinder. A portion of the output torque of the internal combustion engine obtained by combustion is used to drive the fuel pump 10.

[0015] <First fuel tank 2 and second fuel tank 3> The first fuel tank 2 contains a first fuel. In this embodiment, the first fuel is a liquid, for example, alcohol. Alcohol is a main fuel for diesel engines. The first fuel tank 2 includes a first feed pump 2a. The first feed pump 2a is driven by an electric motor. The first feed pump 2a supplies the first fuel to the fuel pump 10 via a fuel passage A1. The first feed pump 2a may be disposed outside the first fuel tank 2. For example, the fuel pump 10 may include the first feed pump 2a built therein.

[0016] The second fuel tank 3 contains the second fuel. In this embodiment, the second fuel is liquid, for example, diesel. The diesel is used as fuel for ignition. The second fuel tank 3 includes a second feed pump 3a. The second feed pump 3a is driven by an electric motor. The second feed pump 3a supplies the second fuel to the fuel pump 10 through a fuel passage B1. The second feed pump 3a may be disposed outside the second fuel tank 3. For example, the fuel pump 10 may include the second feed pump 3a built therein.

[0017] <Common Rail 4> The common rail 4 includes a first rail 4b forming a first accumulator chamber 4a for accumulating the first fuel pumped from the fuel pump 10, and a second rail 4d forming a second accumulator chamber 4c for accumulating the second fuel pumped from the fuel pump 10. The common rail 4 is made of metal. The first rail 4b and the second rail 4d are integrally molded. The common rail 4 distributes the accumulated first and second fuels to the injectors 8. The injectors 8 are arranged for each of the cylinders in the internal combustion engine. The injectors 8 inject high-pressure fuel from nozzle holes toward the combustion chambers in the cylinders. The first rail 4b and the second rail 4d extend in parallel to each other. The first rail 4b and the second rail 4d may be separate bodies.

[0018] <Fuel pump 10> The fuel pump 10 shown in FIG. 1 is mounted on a vehicle and is a high-pressure pump that pressurizes and discharges two types of fuel. The fuel pump 10 includes an intake metering valve 15, a first body portion 31, a second body portion 32, a cam 13, a rotating shaft 14, a first piston 16, a second piston 21, a communication passage 26, a first discharge valve 19, a second discharge valve 25, and an intake valve 20. The first body portion 31 forms a first boost chamber 11 that accommodates the first fuel. The second body portion 32 forms an accommodation space 12 that accommodates the second fuel, the second piston 21, and the first fuel. The accommodation space 12 is partitioned by the second piston 21 into a second boost chamber 12a that accommodates the second fuel and a pressurizing chamber 12b that accommodates the first fuel. The first body portion 31 and the second body portion 32 are integrally formed. The first body portion 31 and the second body portion 32 are made of metal.

[0019] The suction metering valve 15 is provided in the fuel passage A1 and switches between communication and cut-off between the first boost chamber 11 and the first feed pump 2a. The suction metering valve 15 is an electromagnetic valve that adjusts the amount of suction, and is configured to be opened and closed by the control device 5. The suction metering valve 15 opens the metering valve during the suction period to allow the first fuel to be sucked into the first boost chamber 11 through the fuel passage A1. On the other hand, during the pressurization period, the suction metering valve 15 closes the valve at a desired timing to control the timing at which the first fuel actually starts to be compressed. The suction metering valve 15 estimates the amount of fuel required from the value of the fuel pressure in the first accumulator chamber 4a and the amount of fuel consumed by the injector 8 so that the fuel pressure in the first accumulator chamber 4a becomes the target pressure, and adjusts so that the required amount of fuel is sucked in.

[0020] Here, the intake metering valve 15 may be of a type that controls the amount of fuel introduced by narrowing the flow path, or it may be of a type that draws in a larger amount of the first fuel and then expels it upstream of the intake metering valve 15 so that the amount of fuel in the first boost chamber 11 is appropriate when the first piston 16 rises.

[0021] The first piston 16 reciprocates in the first main body portion 31 to draw the first fuel into the first boost chamber 11 and compress and pressurize the drawn first fuel. Specifically, a tappet 33 is disposed between the first piston 16 and the cam 13, and the cam 13 pushes the first piston 16 via the tappet 33, so that the first piston 16 moves in a direction to compress the fuel (i.e., lifts up). Here, a first elastic member 17 is connected to the tappet 33. The first elastic member 17 is disposed so as to apply an elastic force to the tappet 33 in a direction opposite to the direction in which the first piston 16 compresses the fuel. The elastic force applied by the first elastic member 17 causes the first piston 16 to move in a direction to draw the fuel via the tappet 33 (i.e., lifts down).

[0022] A cam 13 and a driven gear (not shown) are fixed to the rotating shaft 14, and the cam 13 and the driven gear rotate integrally with the rotating shaft 14. The driven gear rotates in engagement with a driving gear (not shown), thereby rotating the rotating shaft 14. In other words, the rotational driving force of the driving gear is transmitted to the cam 13 via the driven gear and the rotating shaft 14, and becomes a driving force that lifts up the first piston 16.

[0023] The drive gear rotates using the output torque of the internal combustion engine as a drive source. Therefore, the drive gear rotates constantly while the internal combustion engine is in operation. Furthermore, the rotation speed of the drive gear fluctuates according to fluctuations in the rotation speed of the output shaft of the internal combustion engine, and therefore the rotation speed of the cam 13 also fluctuates.

[0024] A first discharge hole 18, which is a hole through which the first fuel is discharged, is provided in the first boost chamber 11. The first fuel discharged from the first discharge hole 18 flows into the first accumulator chamber 4a provided in the common rail 4 via a fuel passage A2. A first discharge valve 19, which is a check valve, is provided in the fuel passage A2 between the first discharge hole 18 and the first accumulator chamber 4a.

[0025] In the following description, the following terms will be used: the pressure of the second fuel in the fuel passage B1 will be referred to as the second pump pressure; the pressure of the first fuel in the first boost chamber 11 will be referred to as the first boost pressure; the pressure of the second fuel in the second boost chamber 12a will be referred to as the second boost pressure; the pressure of the first fuel in the first accumulator chamber 4a will be referred to as the first rail pressure; and the pressure of the second fuel in the second accumulator chamber 4c will be referred to as the second rail pressure.

[0026] The first discharge valve 19 is a check valve that opens when the first boost pressure is equal to or higher than a predetermined valve opening pressure, and closes when the first boost pressure is lower than the valve opening pressure. The first discharge valve 19 is a mechanical valve in which an elastic member applies an elastic force to the valve body toward the valve closing side to close the valve body. The valve body of the first discharge valve 19 opens against an elastic force (set load) when the pressure difference between the first boost pressure and the first rail pressure is equal to or higher than a predetermined valve opening pressure, and closes by the elastic force when the pressure difference is lower than the valve opening pressure. When the first fuel in the first boost chamber 11 is compressed and the pressure difference between the first boost pressure and the first rail pressure exceeds a set value, the check valve opens and the compressed high-pressure fuel is supplied to the first accumulator chamber 4a. That is, when the pressure difference between the first boost pressure and the first rail pressure is equal to or higher than the predetermined valve opening pressure of the first discharge valve 19, the first discharge valve 19 opens and the first fuel is supplied to the first accumulator chamber 4a.

[0027] The suction valve 20 is provided in the fuel passage B1 and switches between communication and cut-off between the second boost chamber 12a and the second feed pump 3a. The suction valve 20 is a check valve that opens when the pressure difference between the second pump pressure and the second boost pressure is equal to or greater than a predetermined valve opening pressure, and closes when the pressure difference is less than the valve opening pressure. As an example, the suction valve 20 is a mechanical valve in which an elastic member applies an elastic force to the valve body to close the valve body. The valve body of the second discharge valve 25 opens against the elastic force when the pressure difference between the second boost pressure and the second rail pressure is equal to or greater than a predetermined valve opening pressure, and closes by the elastic force when the pressure difference is less than the valve opening pressure. When the pressure difference between the second pump pressure and the second boost pressure is equal to or greater than the predetermined valve opening pressure of the suction valve 20, the suction valve 20 opens, and the second fuel is sucked into the second boost chamber 12a.

[0028] The second pressurizing chamber 12a is provided with a second elastic member 22 and a second discharge hole 23. The second fuel pressurized by the second feed pump 3a is drawn into the second pressurizing chamber 12a. The second pressurizing chamber 12a has a smaller volume than the first pressurizing chamber 11. The second main body portion 32 provides a stopper 24 as a bottom wall on the bottom surface of the pressurizing chamber 12b.

[0029] The fuel pump 10 is provided with a communication passage 26 through which the first fuel in the first boost chamber 11 flows into the pressurization chamber 12b. The first fuel flows from the first boost chamber 11 through the communication passage 26 into the pressurization chamber 12b.

[0030] The second piston 21 is pressed by the first fuel flowing from the communication passage 26 into the pressurized chamber 12b, and moves in a direction compressing the second fuel (i.e., lifts up). In other words, the second piston 21 reciprocates within the accommodation space 12 due to the first fuel pressurized by the lifting up of the first piston 16. By reciprocating within the accommodation space 12, the second piston 21 draws the second fuel into the second pressurized chamber 12a and compresses and pressurizes the drawn second fuel.

[0031] The direction of reciprocating movement of the second piston 21 coincides with the direction of reciprocating movement of the first piston 16. In addition, the second piston 21 and the first piston 16 are arranged coaxially so that their central axes overlap. Furthermore, the area of ​​the pressure applying surface of the second piston 21 is set smaller than the area of ​​the pressure applying surface of the first piston 16.

[0032] The communication passage 26 is disposed coaxially with at least one of the first piston 16 and the second piston 21. The passage cross-sectional area of ​​the communication passage 26 is set smaller than the area of ​​the pressurized surface of the second piston 21. The passage cross-sectional area of ​​the communication passage 26 is set smaller than the opening area of ​​the first discharge hole 18. The passage cross-sectional area of ​​the communication passage 26 may be smaller or larger than the opening area of ​​the second discharge hole 23. One end of the communication passage 26 is connected to a portion of the pressurizing chamber 12b that faces the end face of the second piston 21. The other end of the communication passage 26 is connected to a portion of the first boost chamber 11 that faces the end face of the first piston 16. The communication passage 26 has a shape that extends in a straight line.

[0033] The second elastic member 22 is provided on the inner wall of the second main body portion 32 facing the second piston 21. The second elastic member 22 is disposed in the second boost chamber 12a. The second elastic member 22 is disposed so as to apply an elastic force to the second piston 21 in a direction opposite to the direction in which the second piston 21 compresses the fuel. The elastic force applied by the second elastic member 22 causes the second piston 21 to move in a direction to suck in the fuel (i.e., lift down). The second piston 21 lifts down until it abuts against a stopper 24. The stopper 24 is provided to prevent the second piston 21 from being lifted down from a predetermined position.

[0034] The second boost chamber 12a is provided with a second discharge hole 23 through which the second fuel is discharged. The second fuel discharged from the second discharge hole 23 flows into the second accumulator chamber 4c provided in the common rail 4 via a fuel passage B2. A second discharge valve 25, which is a check valve, is provided in the fuel passage B2 between the second discharge hole 23 and the second accumulator chamber 4c.

[0035] The second discharge valve 25 is a check valve that opens when the second boost pressure is equal to or higher than a predetermined valve opening pressure, and closes when the second boost pressure is lower than the valve opening pressure. The second discharge valve 25 is a mechanical valve in which an elastic member applies an elastic force to the valve body toward the valve closing side to close the valve body. The valve body of the second discharge valve 25 opens against an elastic force (set load) when the pressure difference between the second boost pressure and the second rail pressure is equal to or higher than a predetermined valve opening pressure, and closes by the elastic force when the pressure difference is lower than the valve opening pressure. When the second fuel in the second boost chamber 12a is compressed and the pressure difference between the second boost pressure and the second rail pressure exceeds a set value and becomes high, the check valve opens, and the compressed high-pressure fuel is supplied to the second accumulator chamber 4c. That is, when the pressure difference between the second boost pressure and the second rail pressure is equal to or higher than the predetermined valve opening pressure of the second discharge valve 25, the second discharge valve 25 opens, and the second fuel is sucked into the second accumulator chamber 4c. In this embodiment, the value of the valve opening pressure of the first discharge valve 19 is set to be greater than that of the second discharge valve 25 .

[0036] <Control device 5> The control device 5 is mainly composed of a CPU 5b which is an arithmetic processing device, and a memory 5a which is a storage medium. The control device 5 is electrically connected to the intake metering valve 15, the pressure sensor 6, the pressure reducing valve 7, and each injection valve 8. The control device 5 controls the operation of the intake metering valve 15 and the pressure reducing valve 7 according to the detection value by the pressure sensor 6 and the target pressure.

[0037] <Pressure sensor 6> The pressure sensor 6 detects the pressure of the fuel accumulated in the first accumulator chamber 4a. A detection signal from the pressure sensor 6 is input to the control device 5. The value detected by the pressure sensor 6 is used to control the intake metering valve 15.

[0038] <Reducing valve 7> Pressure reducing valve 7 is an electromagnetic valve provided on first rail 4b to adjust the first rail pressure. When pressure reducing valve 7 opens, it discharges fuel in first accumulator chamber 4a to a surplus fuel pipe (not shown) to prevent the first rail pressure from rising above a predetermined value. The discharged fuel flows into first fuel tank 2 via the surplus fuel pipe. When control device 5 determines that the pressure value detected by pressure sensor 6 is equal to or higher than a predetermined value, control device 5 opens pressure reducing valve 7.

[0039] The first rail 4b has a larger volume than the second rail 4d, and the pressure reducing valve 7 is connected to the larger first rail 4b. Similarly, the pressure sensor 6 is also connected to the larger first rail 4b.

[0040] <Injection valve 8> One injector 8 is provided for each of the cylinders. Each injector 8 injects a first fuel and a second fuel into the combustion chamber in the corresponding cylinder. There is one injection port from which the injector 8 injects fuel into the cylinder, and this injection port is provided at the tip of the injector 8. The first fuel and the second fuel are mixed near the injection port, and the mixed fuel is injected from the injection port.

[0041] <Operation of the First Embodiment> Hereinafter, the operation of the first piston 16 in this embodiment from the top dead center to the bottom dead center until it rises back to the top dead center will be described in detail with reference to the time chart of FIG.

[0042] The horizontal axis of each graph in Figure 2 represents elapsed time. In graph (a), the vertical axis represents the lift amount of cam 13. Graphs (b) to (e) represent the values ​​of the first boost pressure, first rail pressure, second boost pressure, and second rail pressure, with the vertical axis representing the pressure value. Graphs (f) to (i) represent the open / closed states of suction metering valve 15, first discharge valve 19, suction valve 20, and second discharge valve 25. The solid lines in each graph in Figure 2 represent the case of normal operation, and the dashed lines represent the case where pressure reducing valve 7 is operating.

[0043] <Normal operation> First, a normal operation will be described. Time t1 is the time when the first piston 16 reaches the top dead center. After time t1, the first piston 16 is lifted down by the first elastic member 17. As a result, the first boost pressure decreases. Since the first boost pressure decreases, the first fuel flowing from the communication passage 26 into the pressurizing chamber 12b decreases, and the second piston 21 is lifted down by the second elastic member 22. The second piston 21 is lifted down until it abuts against the stopper 24. As a result, the second boost pressure also decreases.

[0044] When the first boost pressure decreases, the first discharge valve 19 closes. As a result, the first rail pressure does not change and is kept constant. Similarly, when the second boost pressure decreases, the second discharge valve 25 closes. As a result, the second rail pressure does not change and is kept constant.

[0045] While the first piston 16 is lifted down, the suction metering valve 15 opens (time t2). As a result, the first fuel pressurized by the first feed pump 2a is sucked from the first fuel tank 2 into the first boost chamber 11. The suction metering valve 15 is adjusted by an electromagnetic valve so that only the necessary amount of fuel is sucked in so that the first rail pressure becomes the target pressure. The necessary amount is estimated by the control device 5 based on the value of the pressure sensor 6 and the amount of the first fuel consumed by the injector 8.

[0046] When the second boost pressure decreases and the pressure of the second fuel boosted by the second feed pump 3a exceeds the sum of the valve opening pressure of the suction valve 20 and the second boost pressure, the suction valve 20 opens (time t2). As a result, the second fuel is sucked into the second boost chamber 12a and the second boost pressure increases. When the second boost pressure increases and exceeds a value obtained by subtracting the valve opening pressure of the suction valve 20 from the pressure of the second fuel boosted by the second feed pump 3a, the suction valve 20 closes. As a result, the suction of the second fuel into the second boost chamber 12a stops.

[0047] When the first fuel and the second fuel are injected by the injectors, the first rail pressure and the second rail pressure decrease (time t3).

[0048] When the cam 13 rotates and the operating point of the cam 13 passes the lowest point, the first piston 16 is lifted up. The first piston 16 is lifted up, and the excess amount of first fuel flows back and is discharged through the intake metering valve 15. At the timing when it is determined that the necessary amount of fuel remains in the first boost chamber 11, the intake metering valve 15 closes and the first boost pressure rises (time t4). As the first boost pressure rises, the amount of first fuel flowing in from the communication passage 26 increases, and the second piston 21 is also lifted up. This causes the second boost pressure to also rise.

[0049] The following formula is a formula for a state in which the first fuel and the second fuel are being discharged from the first delivery valve 19 and the second delivery valve 25, respectively. Pa=Par+Fkav / Sav=Pbr+Fkbv / Sbv+Fkbp / Sbp+Frbp...(1) Here, Pa represents the first boost pressure, Par represents the first rail pressure, Fkav represents the set load of the first discharge valve 19, Sav represents the pressure-receiving area of ​​the first discharge valve 19, Pbr represents the second rail pressure, Fkbv represents the set load of the second discharge valve 25, Fkbp represents the set load of the second piston 21, Frbp represents the sliding resistance of the second piston 21, Sbv represents the pressure-receiving area of ​​the second discharge valve 25, and Sbp represents the cross-sectional area of ​​the second piston 21.

[0050] When the first boost pressure Pa exceeds Par+Fkav / Sav (the valve opening pressure of the first delivery valve 19), the first delivery valve 19 opens (time t5). As a result, the first fuel is delivered to the first accumulator chamber 4a, and Par starts to rise.

[0051] On the other hand, when the first boost pressure Pa exceeds Pbr+Fkbv / Sbv (valve opening pressure of the second delivery valve 25)+Fkbp / Sbp (operating pressure difference of the second piston 21)+Frbp (sliding resistance of the second piston 21), the second delivery valve 25 opens (time t5). As a result, the second fuel is delivered toward the second accumulator chamber 4c, and Pbr starts to rise.

[0052] When the cam 13 rotates and the operating point of the cam 13 passes the highest point, the first piston 16 is lifted down and reaches the state at time t1.

[0053] In this embodiment, the first fuel pressurized in the first boost chamber pressurizes the second fuel in the second boost chamber, so that the second boost pressure also rises in conjunction with the rise in the first boost pressure. Furthermore, the second boost pressure also rises in conjunction with the rise in the first boost pressure, so that the second rail pressure also rises in conjunction with the rise in the first rail pressure.

[0054] <When the pressure reducing valve 7 operates> Next, a case where the pressure reducing valve 7 operates will be described. The same points as in the normal operation described above will not be described. Here, the pressure reducing valve 7 opens when the control device 5 determines that the first rail pressure has exceeded a predetermined value, and this predetermined value is shown as the pressure reducing valve operating pressure in Fig. 2. Also, the pressure reducing valve operating period in Fig. 2 refers to the period during which the pressure reducing valve 7 is open.

[0055] In this example, as shown by the dashed line after time t2 in graph (f), a case will be described in which the closing timing of suction metering valve 15 becomes earlier than normal. In this case, since the closing timing of suction metering valve 15 is earlier than in normal operation, the first boost pressure starts to increase earlier than in normal operation (time t4a). As the first boost pressure increases, the second boost pressure, first rail pressure, and second rail pressure also increase.

[0056] When the first rail pressure exceeds the pressure reducing valve operating pressure, the pressure reducing valve 7 operates and the first rail pressure does not increase above a predetermined value (time t6). When the increase in the first rail pressure stops, the first boost pressure and the second rail pressure also do not increase above a predetermined value due to the relationship in formula (1) while the first fuel and the second fuel are being discharged.

[0057] In this manner, in this embodiment, by providing one pressure reducing valve 7 in the first accumulator chamber 4a, it is possible to suppress an excessive increase in not only the first rail pressure but also the second rail pressure.

[0058] <Summary of the First Embodiment> According to the fuel pump 10 of this embodiment, during the discharge of the first fuel and the second fuel, the first rail pressure and the second rail pressure have a relationship of Par+Fkav / Sav=Pbr+Fkbv / Sbv+Fkbp / Sbp+Frbp. Here, the valve opening pressure (Fkav / Sav) of the first discharge valve 19 and the valve opening pressure (Fkbv / Sbv) of the second discharge valve 25 can be mechanically adjusted at the time of design. Therefore, it becomes possible to easily adjust the pressure difference between the first rail pressure and the second rail pressure mechanically.

[0059] As an example, in this embodiment, the valve opening pressure of the first delivery valve 19 is set to be higher than the valve opening pressure of the second delivery valve 25. During the delivery of the first fuel and the second fuel, the pressure difference between the first rail pressure and the second rail pressure has a relationship of Par-Pbr=Fkbv / Sbv+Fkbp / Sbp+Frbp-Fkav / Sav. In other words, by making the valve opening pressure (Fkav / Sav) of the first delivery valve 19 higher than the valve opening pressure (Fkbv / Sbv) of the second delivery valve 25, it is possible to easily make the first rail pressure and the second rail pressure equal to each other.

[0060] As an example, in this embodiment, a pressure reducing valve 7 for reducing the pressure of fuel is provided in the first rail 4b. This allows the first rail pressure to be reduced by the pressure reducing valve 7, and prevents the pressure from increasing excessively. Here, during the discharge of the first fuel and the second fuel, due to the relationship Par+Fkav / Sav=Pbr+Fkbv / Sbv+Fkbp / Sbp+Frbp, if the pressure of the fuel in one accumulator is reduced to prevent an excessive pressure increase, the pressure of the fuel in the other accumulator can also be prevented from increasing excessively. Therefore, the excessive pressure increase can be prevented without providing the pressure reducing valve 7 for the other rail, and the number of parts can be reduced compared to the case where the pressure reducing valve 7 is provided for both rails.

[0061] As an example, in this embodiment, a pressure reducing valve 7 that reduces the pressure of the fuel is provided in the first rail 4b. There may be cases where the second rail pressure does not increase excessively due to poor sliding of the second piston 21. For this reason, if the pressure reducing valve 7 is provided in the second rail 4d and the first rail 4b does not include the pressure reducing valve 7, there is a concern that the first rail pressure may not be prevented from increasing excessively. On the other hand, such a case does not occur with the first fuel in the first accumulator chamber 4a. Therefore, by providing the pressure reducing valve 7 in the first rail 4b, it is possible to reliably prevent the first rail pressure from increasing excessively.

[0062] <Modification> In this embodiment, the pressure sensor 6 detects the first rail pressure, but it may also be configured to detect the second rail pressure. Also, the pressure sensor 6 may be provided for each of the first rail pressure and the second rail pressure so as to detect both of them.

[0063] Pressure reducing valve 7 may be a valve that opens mechanically at a predetermined pressure. In this case, when the value of the first rail pressure becomes equal to or higher than a predetermined value, pressure reducing valve 7 opens, thereby preventing the first rail pressure from increasing above the predetermined value.

[0064] In this embodiment, the value of the opening pressure of the first delivery valve 19 is set to be greater than that of the second delivery valve 25, but the value of the opening pressure of the first delivery valve 19 may be set to be smaller than that of the second delivery valve 25, or may be set to be equal to that of the second delivery valve 25.

[0065] In this embodiment, the pressure reducing valve 7 is provided in the first rail 4b, but may be provided in the second rail 4d so as to adjust the pressure in the second accumulator chamber 4c. Moreover, the pressure reducing valve 7 may be provided in each of the first rail 4b and the second rail 4d, or in both.

[0066] In this embodiment, the intake metering valve 15 is closed at a desired timing to control the timing at which the first fuel starts to be compressed, thereby adjusting the amount of the first fuel pressurized by the first piston 16, but this is not limited to the above. The intake metering valve 15 may adjust the amount of the first fuel pressurized by the first piston 16 by adjusting the opening area of ​​the valve.

[0067] In this embodiment, the reciprocating direction of the second piston 21 coincides with the reciprocating direction of the first piston 16, but they do not have to coincide. Also, in this embodiment, the second piston 21 and the first piston 16 are arranged coaxially so that their central axes overlap, but they do not have to be arranged coaxially.

[0068] 3 shows a modified example of the fuel pump 10 in which the first piston 16 and the second piston 21 are disposed so that the reciprocating direction of the first piston 16 is different from the reciprocating direction of the second piston 21. In the modified example of FIG. 3, the central axis of the second piston 21 is perpendicular to the central axis of the first piston 16. Furthermore, the communication passage 26 is disposed coaxially with the second piston 21.

[0069] 3, the direction of reciprocating movement of the first piston 16 is perpendicular to the direction of reciprocating movement of the second piston 21. Therefore, it is possible to make the fuel pump 10 smaller in size in the direction of reciprocating movement of the first piston 16 than in a case where the direction of reciprocating movement of the second piston 21 coincides with the direction of reciprocating movement of the first piston 16, contrary to this modification.

[0070] Second embodiment A fuel pump 10 according to an embodiment of the present disclosure is used in a fuel injection system 1 shown in Fig. 4. The fuel injection system 1 is a system that injects two types of fuel, biofuel and diesel, into the cylinders of a diesel engine of a vehicle. The fuel injection system 1 according to this embodiment will be described below, focusing on the differences from the first embodiment.

[0071] <First fuel tank 2 and second fuel tank 3> The second fuel contained in the second fuel tank 3 is the biofuel described above, which is the main fuel for the diesel engine. A specific example of the biofuel is bioethanol such as alcohol. The first fuel contained in the first fuel tank 2 is the diesel fuel described above, which is the ignition fuel. By mixing diesel with the biofuel supplied to the combustion chamber of the engine, the mixture can be spontaneously ignited. In short, while in the first embodiment, the first fuel is alcohol and the second fuel is diesel, in this embodiment, the first fuel is diesel and the second fuel is alcohol.

[0072] <Common Rail 4> In the first embodiment, the first fuel accumulated in the first accumulator chamber 4a is alcohol, and the second fuel accumulated in the second accumulator chamber 4c is diesel. Therefore, the first accumulator chamber 4a is set to a larger volume than the second accumulator chamber 4c. In contrast to this, in the present embodiment, the first fuel accumulated in the first accumulator chamber 4a is diesel, and the second fuel accumulated in the second accumulator chamber 4c is alcohol. Therefore, the first accumulator chamber 4a is set to a smaller volume than the second accumulator chamber 4c.

[0073] <Fuel pump 10> In the first embodiment, the suction amount adjustment valve 15 is a solenoid valve that switches between communication and cut-off between the first pressurizing chamber 11 and the first feed pump 2a. The amount of the first fuel suctioned into the first pressurizing chamber 11 is adjusted by adjusting the timing of the switching. In contrast, in the present embodiment, the suction amount adjustment valve 15 is a solenoid valve that can continuously and steplessly adjust the degree of communication between the first pressurizing chamber 11 and the first feed pump 2a. The amount of the first fuel suctioned into the first pressurizing chamber 11 is adjusted by adjusting the degree of communication.

[0074] The communication opening of the suction metering valve 15 is controlled by the control device 5. The control device 5 does not change the communication opening during one reciprocation of the first piston 16, but fixes the communication opening. Then, the control device 5 changes the communication opening during the next and subsequent reciprocations of the first piston 16 in accordance with the difference between the target pressure and the actual pressure.

[0075] The fuel pump 10 according to this embodiment additionally includes an intake valve 20x (first intake valve) in addition to the intake valve 20 (second intake valve). The intake valve 20x is provided in a portion of the fuel passage A1 between the intake metering valve 15 and the first boost chamber 11.

[0076] The suction valve 20x switches between communication and cut-off between the first boost chamber 11 and the first feed pump 2a. The suction valve 20x is a check valve that opens when the pressure difference between the downstream pressure of the suction metering valve 15 and the first boost pressure is equal to or greater than a predetermined valve opening pressure, and closes when the pressure difference is less than the valve opening pressure. As an example, the suction valve 20x is a mechanical valve in which an elastic member applies an elastic force to the valve body to close the valve. The function of the suction valve 20x is to prevent fuel in the first boost chamber 11 from flowing back toward the first feed pump 2a.

[0077] In this embodiment, the second elastic member 22 according to the first embodiment is omitted. The second piston 21 is actuated by the pressure difference between the pressure of the alcohol in the second pressurizing chamber 12a and the pressure of the diesel fuel in the pressurizing chamber 12b.

[0078] Specifically, when the first piston 16 is lifted down and the pressure in the first boost chamber 11 drops, if the suction valve 20 is closed, the pressure in the pressurizing chamber 12b also drops, and the second piston 21 is lifted down. As a result, the pressure in the second boost chamber 12a drops and the suction valve 20 opens. Thereafter, when the second piston 21 continues to be lifted down and abuts against the stopper 24, the pressure in the second boost chamber 12a rises as fuel flows into the second boost chamber 12a. As a result, the suction valve 20 closes.

[0079] When the first piston 16 is lifted up and the pressure in the first boost chamber 11 rises, if the intake valve 20 is closed, the pressure in the pressurizing chamber 12b also rises, and the second piston 21 is lifted up. As a result, the pressure in the second boost chamber 12a rises and the second discharge valve 25 opens. In other words, the alcohol pressurized by the fuel pump 10 is pumped to the second accumulator chamber 4c.

[0080] <Leak part 7x> As shown in Fig. 4, in the fuel pump 10 according to this embodiment, the pressure reducing valve 7 according to the first embodiment is eliminated and a leak portion 7x is newly provided. Whereas the pressure reducing valve 7 is provided on the first rail 4b, the leak portion 7x is provided on the second rail 4d. Whereas the pressure reducing valve 7 is an electromagnetic valve and is driven and controlled by the control device 5, the leak portion 7x is a throttle valve that constantly leaks fuel from the second accumulator chamber 4c and is not driven and controlled by the control device 5. The fuel leaked from the leak portion 7x is returned to the second fuel tank 3.

[0081] The leak section 7x is set to leak a minute amount of fuel. Therefore, during normal operation of the engine and the fuel pump 10, the pressure drop in the second accumulator chamber 4c due to the leak is negligible. On the other hand, when the engine and the fuel pump 10 are stopped, the pressure in the second accumulator chamber 4c drops over time due to a minute amount of leak.

[0082] <Fuel pump operation> Hereinafter, the operation of the first piston 16 in this embodiment from the top dead center to the bottom dead center until it rises back to the top dead center will be described in detail with reference to the time chart of FIG.

[0083] The horizontal axis of each graph in Figure 5 represents elapsed time. Graph (a) shows the lift amount of cam 13. Graph (b) shows the lift amount of second piston 21. Graph (c) shows the first boost pressure and the second boost pressure. Graph (d) shows the first rail pressure and the second rail pressure. Graphs (e) to (h) show the open / closed states of suction metering valve 15, first suction valve (suction valve 20x), second suction valve (suction valve 20), first discharge valve 19 and second discharge valve 25.

[0084] After time t1 when the first piston 16 reaches the top dead center, the first piston 16 is lifted down by the first elastic member 17. Accordingly, the first boost pressure decreases. Because the first boost pressure decreases, the first fuel flowing from the communication passage 26 into the pressurizing chamber 12b flows back, and the second piston 21 is lifted down. The second piston 21 is lifted down until it abuts against the stopper 24, and the second boost pressure also decreases.

[0085] When the first boost pressure decreases, the first discharge valve 19 closes. As a result, the first rail pressure does not change and is kept constant. Similarly, when the second boost pressure decreases, the second discharge valve 25 closes. As a result, the second rail pressure does not change and is kept constant.

[0086] While the first piston 16 is lifted down, the first fuel pressurized by the first feed pump 2a from the first fuel tank 2 is sucked into the first boost chamber 11 through the suction metering valve 15. The suction metering valve 15 is adjusted by an electromagnetic valve so that only the necessary amount of fuel is sucked in so that the first rail pressure becomes the target pressure. The necessary amount is estimated by the control device 5 based on the value of the pressure sensor 6 and the amount of fuel consumed by the injection valve 8. The control device 5 does not change the opening degree of the electromagnetic valve during one reciprocating motion of the first piston 16, but keeps the opening degree fixed.

[0087] When the second boost pressure decreases and the pressure of the second fuel boosted by the second feed pump 3a exceeds the sum of the valve opening pressure of the suction valve 20 and the second boost pressure, the suction valve 20 opens (time t2). As a result, the second fuel is sucked into the second boost chamber 12a and the second boost pressure increases. When the second boost pressure increases and exceeds a value obtained by subtracting the valve opening pressure of the suction valve 20 from the pressure of the second fuel boosted by the second feed pump 3a, the suction valve 20 closes. As a result, the suction of the second fuel into the second boost chamber 12a stops.

[0088] When the first fuel and the second fuel are injected by the injector 8, the first rail pressure and the second rail pressure decrease (time t3).

[0089] When the cam 13 rotates and the operating point of the cam 13 passes the lowest point, the first piston 16 is lifted up. When the first piston 16 is lifted up and the air bubbles generated by the negative pressure in the first boost chamber 11 are crushed, the first boost pressure increases (time t4). Since the first boost pressure increases, the first fuel flowing in from the communication passage 26 increases, and the second piston 21 is also lifted up. As a result, the second boost pressure also increases.

[0090] The following formula is a formula for a state in which the first fuel and the second fuel are being discharged from the first delivery valve 19 and the second delivery valve 25, respectively. Pa=Par+Fkav / Sav=Pbr+Fkbv / Sbv+Frbp...(1) Here, Pa represents the first boost pressure, Par represents the first rail pressure, Fkav represents the set load of the first discharge valve 19, Sav represents the pressure-receiving area of ​​the first discharge valve 19, Pbr represents the second rail pressure, Fkbv represents the set load of the second discharge valve 25, Frbp represents the sliding resistance of the second piston 21, and Sbv represents the pressure-receiving area of ​​the second discharge valve 25.

[0091] When the first boost pressure Pa exceeds Par+Fkav / Sav (the valve opening pressure of the first delivery valve 19), the first delivery valve 19 opens (time t5). As a result, the first fuel is delivered to the first accumulator chamber 4a, and Par starts to rise.

[0092] On the other hand, when the first boost pressure Pa exceeds Pbr+Fkbv / Sbv (the valve opening pressure of the second delivery valve 25)+Frbp (the sliding resistance of the second piston 21), the second delivery valve 25 opens (time t5). As a result, the second fuel is delivered toward the second accumulator chamber 4c, and Pbr starts to rise.

[0093] When the valve opening pressure of the second discharge valve 25 is set higher than the valve opening pressure of the first discharge valve 19, the first rail pressure becomes higher than the second rail pressure in the period from time t3 to time t5. However, this pressure difference is so small that it can be ignored, and is therefore not shown in the graph in FIG. 5(d).

[0094] When the cam 13 rotates and the operating point of the cam 13 passes the highest point, the first piston 16 is lifted down and reaches the state at time t1.

[0095] In this embodiment, the first fuel pressurized in the first boost chamber pressurizes the second fuel in the second boost chamber, so that the second boost pressure also rises in conjunction with the rise in the first boost pressure. Furthermore, the second boost pressure also rises in conjunction with the rise in the first boost pressure, so that the second rail pressure also rises in conjunction with the rise in the first rail pressure.

[0096] <Injection valve 8> As shown in Fig. 6, the injector 8 includes a body 81, a valve element 82, and a sliding seal 83. The injector 8 further includes an electromagnetic valve 84 shown in Fig. 4, etc. The injector 8 is attached to the cylinder head of the engine, and injects a first fuel (diesel) and a second fuel (alcohol) into the combustion chamber. The injector 8 injects a mixture of the two types of fuel into the combustion chamber.

[0097] The body 81 forms a fuel passage therein and accommodates the valve element 82 therein. The body 81 has a generally cylindrical shape centered on a central axis C1. The valve element 82 is accommodated inside the body 81 in a state in which it can move in a direction along the central axis C1. The lift-up movement of the valve element 82 corresponds to the valve-opening operation of the injection valve 8, and the lift-down movement corresponds to the valve-closing operation. The sliding seal 83 is in the shape of a ring assembled to the body 81. The sliding seal 83 is disposed between the valve element 82 and the body 81, and seals the gap between the body 81 and the valve element 82 as it moves.

[0098] The fuel passages formed inside the body 81 include a diesel passage R11, an alcohol passage R21, an alcohol annular passage R22, and a mixing passage R30. A fuel passage is also formed inside the valve body 82, and the fuel passages include a communication passage R12, a main passage R13, and a throttle R14. The alcohol annular passage R22 and the mixing passage R30 are formed between the inner peripheral surface of the body 81 and the outer peripheral surface of the valve body 82.

[0099] The alcohol supplied from the second accumulator 4c to the supply port R20 of the injection valve 8 (see FIG. 8) flows through the alcohol passage R21, the alcohol annular passage R22, and the mixing passage R30 in this order, and is injected from the injection hole R31. The diesel fuel supplied from the first accumulator 4a to the supply port R10 of the injection valve 8 flows through the diesel fuel passage R11, the communication passage R12, the main passage R13, the throttle R14, and the mixing passage R30 in this order, and is injected from the injection hole R31. That is, the alcohol and the diesel fuel are mixed in the mixing passage R30, and are injected from the injection hole R31 in the mixed state. The sliding seal 83 separates the alcohol annular passage R22 from the diesel fuel passage R11.

[0100] A seat surface 82a is formed at the tip of the valve body 82, and a valve seat 81a is formed in a portion of the body 81 facing the seat surface 82a. As shown in Fig. 7, when the valve body 82 is lifted down and the seat surface 82a is seated on the valve seat 81a, the mixing passage R30 is closed and fuel injection is stopped. On the other hand, when the valve body 82 is lifted up and the seat surface 82a is separated from the valve seat 81a as shown in Fig. 6, the mixing passage R30 is opened and fuel is injected.

[0101] As shown in Fig. 8, the common rail 4 is formed with a recess 41 communicating with the first accumulator chamber 4a and a recess 42 communicating with the second accumulator chamber 4c. A portion of a body 81 of the injection valve 8 in which a light oil supply port R10 is formed is inserted into the recess 41. A portion of the body 81 in which an alcohol supply port R20 is formed is inserted into the recess 42. An O-ring 43 is disposed in each of the recesses 41 and 42. The O-ring 43 provides a seal between the body 81 and the common rail 4.

[0102] Furthermore, the body 81 defines a control chamber (not shown) therein. Light oil flows into the control chamber through a passage branched off from the light oil passage R11. The pressure of the light oil in the control chamber is called the control pressure. The control pressure is applied to the valve element 82 in a direction to close the valve element 82. The light oil that generates the control pressure acting in the valve closing direction corresponds to the valve closing working fluid.

[0103] On the other hand, a portion of the alcohol branched off from the alcohol passage R21 is applied to the valve element 82 in a direction that opens the valve element 82. The alcohol that generates a pressure (valve opening pressure) acting in this manner on the valve opening side corresponds to a valve-opening working fluid.

[0104] When the pressure difference between the valve-closing working fluid and the valve-opening working fluid is equal to or greater than a predetermined value, the valve element 82 is closed by the control pressure. When the control pressure decreases and the pressure difference falls below the predetermined value, the valve element 82 is opened by the valve-opening pressure.

[0105] The solenoid valve 84 shown in Fig. 4 controls the control pressure by controlling the inflow or outflow of diesel to the control chamber. For example, the solenoid valve 84 opens and closes a passage through which diesel flows out from the control chamber. When the control device 5 drives the solenoid valve 84 to open, diesel flows out of the control chamber and the control pressure drops. This opens the valve body 82. When the control device 5 drives the solenoid valve 84 to close, the outflow of diesel from the control chamber is stopped, while the control pressure rises due to the inflow of diesel from the diesel passage R11 into the control chamber. This closes the valve body 82.

[0106] <Summary of the second embodiment> According to the fuel pump 10 of this embodiment, during the discharge of the first fuel and the second fuel, the first rail pressure and the second rail pressure have a relationship of Par+Fkav / Sav=Pbr+Fkbv / Sbv+Frbp. Here, the valve opening pressure (Fkav / Sav) of the first discharge valve 19 and the valve opening pressure (Fkbv / Sbv) of the second discharge valve 25 can be mechanically adjusted at the time of design. Therefore, it becomes possible to easily adjust the pressure difference between the first rail pressure and the second rail pressure mechanically.

[0107] As an example, in this embodiment, the valve opening pressure of the second delivery valve 25 is set to be higher than the valve opening pressure of the first delivery valve 19. During the delivery of the first fuel and the second fuel, the pressure difference between the first rail pressure and the second rail pressure has a relationship of Par-Pbr=Fkbv / Sbv+Frbp-Fkav / Sav. In other words, by making the valve opening pressure (Fkav / Sav) of the first delivery valve 19 lower than the valve opening pressure (Fkbv / Sbv) of the second delivery valve 25, it is possible to easily make the first rail pressure higher than the second rail pressure.

[0108] Furthermore, in this embodiment, the valve is closed when the pressure difference between the valve-closing working fluid and the valve-opening working fluid is equal to or greater than a predetermined value, and is opened when the pressure difference is less than the predetermined value. Here, the following comparative structure contrary to this embodiment will be described. In the comparative structure, the force of the electromagnetic actuator is directly applied to the valve body 82 to open and close the valve body 82. In this case, when the pressure of the fuel supplied to the injector 8 is high, the force required of the electromagnetic actuator is large. This leads to an increase in the size of the electromagnetic actuator, and therefore to an increase in the size of the injector 8. In contrast, in this embodiment, the valve body 82 is opened and closed by the pressure difference of the working fluid, so that the size of the injector 8 can be suppressed even when the fuel pressure is high.

[0109] Furthermore, in this embodiment, the rail that accumulates the valve-opening working fluid out of the first rail 4b and the second rail 4d is provided with a leak portion 7x that leaks the valve-opening working fluid. Therefore, when the engine and the fuel pump 10 are stopped, the pressure in the accumulator chamber (second accumulator chamber 4c) of the valve-opening working fluid decreases over time due to a small amount of leakage. Therefore, when the engine is stopped, the concern of unintended fuel injection, such as the pressure difference of the working fluid decreasing and the valve body 82 opening, can be reduced. For example, if the leak portion 7x is eliminated contrary to this embodiment, there is a risk that the light oil pressure will decrease more quickly than the alcohol pressure immediately after the engine is stopped. In that case, the pressure difference of the working fluid will decrease and the valve body 82 will open, and there is a concern of unintended fuel injection. This concern is reduced by providing the leak portion 7x.

[0110] Furthermore, in this embodiment, the leak portion 7x constantly leaks the valve-opening working fluid regardless of whether the fuel pump 10 is in operation. Therefore, the valve-opening working fluid can be leaked with a simple configuration without using a solenoid valve.

[0111] Furthermore, in this embodiment, the pressure sensor 6 for detecting the fuel pressure is provided on the rail (first rail 4b) that accumulates the valve-closing working fluid out of the first rail 4b and the second rail 4d. Therefore, it is possible to quickly detect a situation in which the valve-closing working fluid pressure drops significantly below the target pressure. This makes it possible to prevent problems such as the valve body 82 opening due to a drop in the pressure difference of the working fluid that accompanies the above situation.

[0112] Here, the first fuel is directly pressurized by the first piston 16, and therefore the pressure of the first fuel is increased more quickly and reliably than that of the second fuel. In consideration of this point, in this embodiment, the injector 8 is configured so that the first fuel functions as a valve-closing working fluid. Therefore, it is possible to further reduce the concern of unintended fuel injection, such as the valve body 82 opening due to a decrease in the pressure difference of the working fluid.

[0113] <Modification> The leak part 7x is not limited to a structure that constantly leaks, and may be a check valve that opens when the fuel pressure reaches or exceeds a set pressure, or may be an electromagnetic valve. The leak part 7x is not limited to being provided in the common rail 4, and may be provided in the injection valve 8 or the fuel pump 10.

[0114] Pressure sensor 6 is not limited to being provided on first rail 4b, and may be provided on second rail 4d. In each of the above embodiments, two types of fuel are injected from one injector 8. However, an injector for injecting the first fuel and an injector for injecting the second fuel may be provided separately.

[0115] The injector 8 is not limited to a configuration in which the first fuel functions as the valve-closing working fluid, and may be a configuration in which the second fuel functions as the valve-closing working fluid. Also, the injector 8 is not limited to a configuration in which the valve body 82 is opened and closed by the differential pressure of the working fluid, and may be a direct acting type in which the force of an electromagnetic actuator is directly applied to the valve body 82 to open and close it.

[0116] The disclosure in the specification and drawings is not limited by the claims. The disclosure in the specification and drawings includes the technical ideas described in the claims, and extends to more diverse and broader technical ideas than the technical ideas described in the claims. Therefore, various technical ideas can be extracted from the disclosure in the specification and drawings without being bound by the claims. [Explanation of symbols]

[0117] 1... fuel injection system, 2... first fuel tank, 2a... first feed pump, 3... second fuel tank, 3a... second feed pump, 4... common rail, 5... control device, 6... pressure sensor, 7... pressure reducing valve, 7x... leak portion, 8... injection valve, 10... fuel pump, 11... first booster chamber, 12... accommodation space

Claims

1. a first piston (16) that is pushed and reciprocated by a cam (13); a first boost chamber (11) for accommodating a first fuel pressurized by the first piston and having a first discharge hole (18) for discharging the pressurized first fuel; a second piston (21) that reciprocates by being pushed by the first fuel pressurized by the first piston; a second boost chamber (12a) for accommodating a second fuel pressurized by the second piston and having a second discharge hole (23) for discharging the pressurized second fuel; A fuel pump comprising:

2. a first discharge valve (19) that functions as a check valve and is provided between the first discharge hole and a first accumulator chamber (4a) that accumulates pressure in the first fuel discharged from the first discharge hole; 2. The fuel pump according to claim 1, further comprising: a second discharge valve (25) that functions as a check valve and is provided between a second accumulator chamber (4 c) that accumulates pressure in the second fuel discharged from the second discharge hole and the second discharge hole.

3. 3. The fuel pump according to claim 2, wherein an opening pressure of the first delivery valve is greater than an opening pressure of the second delivery valve.

4. a first piston (16) that is pushed and reciprocated by a cam (13); a first body portion (31) that forms a first boost chamber (11) that contains a first fuel pressurized by the first piston and has a first discharge hole (18) that discharges the pressurized first fuel; a second piston (21) that reciprocates by being pushed by the first fuel pressurized by the first piston; a second body portion (32) that forms a second boost chamber (12a) that contains a second fuel pressurized by the second piston and has a second discharge hole (23) that discharges the pressurized second fuel; a first rail (4b) forming a first accumulator chamber (4a) for accumulating the first fuel discharged from the first boost chamber; a second rail (4d) forming a second accumulator chamber (4c) for accumulating the second fuel discharged from the second boost chamber; an injection valve (8) for injecting the first fuel distributed from the first accumulator and the second fuel distributed from the second accumulator; A fuel injection system comprising:

5. 5. The fuel injection system according to claim 4, further comprising a pressure reducing valve (7) for reducing the pressure of fuel in one of the first rail and the second rail.

6. 6. The fuel injection system of claim 5, wherein the pressure reducing valve is provided in the first rail.

7. one of the first fuel and the second fuel is a valve-opening working fluid, and the other fuel is a valve-closing working fluid; 5. The fuel injection system according to claim 4, wherein the injector is configured to perform a valve closing operation when a pressure difference between the valve-closing working fluid and the valve-opening working fluid is equal to or greater than a predetermined value, and to perform a valve opening operation when the pressure difference is less than the predetermined value.

8. 8. The fuel injection system according to claim 7, wherein one of the first rail and the second rail, which accumulates the valve-opening working fluid, is provided with a leak portion (7x) for leaking the valve-opening working fluid.

9. 9. The fuel injection system according to claim 8, wherein the leak portion constantly leaks the valve-opening actuation fluid regardless of whether the fuel pump is in operation or not.

10. 8. The fuel injection system according to claim 7, further comprising a pressure sensor (6) for detecting a fuel pressure, the rail that accumulates the valve-closing operating fluid among the first rail and the second rail.

11. A fuel injection system according to any one of claims 7 to 10, wherein the injector is configured such that the first fuel acts as a valve closing actuation fluid.

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