Fuel pump

Abstract

This fuel pump comprises a pump body, a plunger, a cam, a low-pressure fuel chamber, an auxiliary chamber, and a plurality of fuel passages. The fuel passages connect the low-pressure fuel chamber and the auxiliary chamber. The fuel passages each have a large-diameter part which is formed on the low-pressure fuel chamber side, and a small-diameter part which is connected to the large-diameter part, is formed on the auxiliary chamber side, and has an opening diameter smaller than that of the large-diameter part. When the area of a stepped part between a first portion and a second portion of the plunger is denoted as V, the angular velocity of the cam is denoted as ω, the acceleration at which the cam pushes up the plunger is denoted as ap, the number of fuel passages is denoted as n, the feed pressure is denoted as Pf, the saturated vapor pressure is denoted as Pb, and the density of fuel is denoted as ρ, the length L of the small-diameter part and the cross sectional area S of the small-diameter part are set to values satisfying formula 2.

Description

fuel pump

[0001] The present invention relates to a fuel pump that supplies fuel to an engine at high pressure.

[0002] An example of a fuel pump is described in Patent Document 1. Patent Document 1 describes a fuel pump including a plunger, a housing, and a seal. The plunger has a large diameter portion at one end and a small diameter portion at the other end, the small diameter portion having an outer diameter smaller than that of the large diameter portion, and is configured to be reciprocally movable.

[0003] The housing has a pressurized chamber in which fuel is pressurized by the large diameter portion, a low-pressure passage communicating with the pressurized chamber, and a low-pressure fuel chamber formed in the low-pressure passage. The seal portion is provided on the opposite side of the housing from the pressurized chamber and, together with the housing, forms a variable volume chamber around the small diameter portion whose volume changes with the reciprocating movement of the plunger. The first and second communication passages in the housing communicate between the low-pressure passage and the variable volume chamber.

[0004] JP 2012-127290 A

[0005] However, with the technology described in Patent Document 1, when the plunger moves, the pressure in the auxiliary chamber, which is a variable volume chamber, drops below the vapor pressure, which can cause bubbles (cavitation) to form in the auxiliary chamber. As a result, the generated bubbles (cavitation) can collapse, potentially damaging the auxiliary chamber or the plunger seal.

[0006] SUMMARY OF THE INVENTION In consideration of the above problems, an object of the present invention is to provide a fuel pump that can suppress the generation of bubbles (cavitation) in the sub-chamber.

[0007] To solve the above problems and achieve the object of the present invention, a fuel pump of the present invention includes a pump body, a plunger, a cam, a low-pressure fuel chamber, an auxiliary chamber, and multiple fuel passages. The plunger is slidably supported in the pump body and has a first portion and a second portion having an outer diameter smaller than that of the first portion. The cam reciprocates the plunger. The low-pressure fuel chamber is provided in the pump body. The auxiliary chamber is formed in the pump body and its volume varies with movement of the plunger. Multiple fuel passages communicate between the low-pressure fuel chamber and the auxiliary chamber. Each fuel passage has a large-diameter portion formed on the low-pressure fuel chamber side and a small-diameter portion formed on the auxiliary chamber side that communicates with the large-diameter portion and has an opening diameter smaller than that of the large-diameter portion. The area of ​​the stepped portion between the first and second portions of the plunger is defined as V, the angular velocity of the cam is defined as ω, and the acceleration at which the cam pushes the plunger up is defined as a. ｐ , the number of fuel passages is n, and the feed pressure is P ｆ , saturated vapor pressure is P ｂ When the density of the fuel is ρ, the length L of the small diameter portion and the cross-sectional area S of the small diameter portion are set to values ​​that satisfy the following equation 2.

[0008] According to the fuel pump having the above-described configuration, it is possible to suppress the generation of bubbles (cavitation) in the sub-chamber. Note that problems, configurations, and effects other than those described above will become apparent from the following description of the embodiment.

[0009] FIG. 1 is an overall configuration diagram of a fuel supply system using a high-pressure fuel supply pump according to a first embodiment of the present invention. FIG. 2 is a longitudinal sectional view (part 1) of a high-pressure fuel supply pump according to a first embodiment of the present invention. FIG. 3 is a horizontal sectional view, viewed from above, of a high-pressure fuel supply pump according to a first embodiment of the present invention. FIG. 4 is a longitudinal sectional view (part 2) of a high-pressure fuel supply pump according to a first embodiment of the present invention. FIG. 5 is a diagram illustrating a mechanism of cavitation occurring in a fuel passage in a conventional high-pressure fuel supply pump. FIG. 6 is an enlarged sectional view showing the periphery of a fuel passage in a high-pressure fuel supply pump according to a first embodiment of the present invention. FIG. 7 is an enlarged sectional view showing the periphery of a fuel passage in a high-pressure fuel supply pump according to a second embodiment of the present invention. FIG. 8 is a horizontal sectional view, viewed from above, of a high-pressure fuel supply pump according to a third embodiment of the present invention. FIG. 9 is a longitudinal sectional view of a high-pressure fuel supply pump according to a fourth embodiment of the present invention.

[0010] 1. First Embodiment A high-pressure fuel supply pump according to a first embodiment of the present invention (hereinafter referred to as "this embodiment") will be described below. Note that common members in each drawing are designated by the same reference numerals.

[0011] 1-1. Fuel Supply System Next, a fuel supply system using the high-pressure fuel supply pump (fuel pump) according to this embodiment will be described with reference to Fig. 1. Fig. 1 is an overall configuration diagram of the fuel supply system using the high-pressure fuel supply pump according to this embodiment.

[0012] 1 , the fuel supply system includes a high-pressure fuel supply pump (fuel pump) 100, an ECU (Engine Control Unit) 101, a fuel tank 103, a common rail 106, and a plurality of injectors 107. The components of the high-pressure fuel supply pump 100 are integrally incorporated into a pump body 1.

[0013] Fuel in a fuel tank 103 is pumped up by a feed pump 102 that is driven based on a signal from an ECU 101. The pumped up fuel is pressurized to an appropriate pressure by a pressure regulator (not shown) and sent to a low-pressure fuel intake port 51 of a high-pressure fuel supply pump 100 through a low-pressure pipe 104.

[0014] High-pressure fuel supply pump 100 pressurizes fuel supplied from a fuel tank 103 and sends it under pressure to a common rail 106. A plurality of injectors 107 and a fuel pressure sensor 105 are attached to common rail 106. The plurality of injectors 107 are attached in accordance with the number of cylinders (combustion chambers), and inject fuel in accordance with a drive current output from ECU 101. The fuel supply system of this embodiment is a so-called direct injection engine system in which injectors 107 inject fuel directly into the cylinders of the engine.

[0015] The fuel pressure sensor 105 outputs detected pressure data to the ECU 101. The ECU 101 calculates an appropriate fuel injection amount (target fuel injection length) and an appropriate fuel pressure (target fuel pressure) based on engine state quantities (e.g., crank angle, throttle opening, engine speed, fuel pressure, etc.) obtained from various sensors.

[0016] Furthermore, based on the calculation results of the fuel pressure (target fuel pressure) and the like, the ECU 101 controls the driving of the high-pressure fuel supply pump 100 and the plurality of injectors 107. That is, the ECU 101 has a pump control unit that controls the high-pressure fuel supply pump 100 and an injector control unit that controls the injectors 107.

[0017] The high-pressure fuel supply pump 100 has a pressure pulsation reduction mechanism 9, an electromagnetic intake valve mechanism 3 which is a variable displacement mechanism, a relief valve mechanism 4 (see FIG. 2), and a discharge valve mechanism 8. Fuel flowing in from a low-pressure fuel intake port 51 reaches an intake port 31b of the electromagnetic intake valve mechanism 3 through the pressure pulsation reduction mechanism 9 and an intake passage 10b.

[0018] The fuel that flows into the electromagnetic intake valve mechanism 3 passes through the valve portion 32 (see FIG. 2) and reaches the blocking wall 1d formed in the pump body 1. A fuel passage that communicates with the pressurizing chamber 11 is formed in the blocking wall 1d. The fuel then passes through the fuel passage provided in the blocking wall 1d and flows into the pressurizing chamber 11. A plunger 2 is inserted into the pressurizing chamber 11 so that it can reciprocate. The plunger 2 reciprocates when power is transmitted by a cam 91 (see FIG. 2) of the engine.

[0019] In the pressurizing chamber 11, fuel is drawn in through the electromagnetic intake valve mechanism 3 during the downward stroke of the plunger 2, and the fuel is pressurized during the upward stroke. When the fuel pressure in the pressurizing chamber 11 exceeds a predetermined value, the discharge valve mechanism 8 opens, and the high-pressure fuel is pumped through a discharge passage 12a to a common rail 106. The discharge of fuel by the high-pressure fuel supply pump 100 is controlled by opening and closing the electromagnetic intake valve mechanism 3. The opening and closing of the electromagnetic intake valve mechanism 3 is controlled by an ECU 101.

[0020] 1-2. High-Pressure Fuel Supply Pump Next, the configuration of the high-pressure fuel supply pump 100 will be described with reference to Figures 2 to 4. Figure 2 is a longitudinal cross-sectional view (part 1) of the high-pressure fuel supply pump 100 taken along a cross section perpendicular to the horizontal direction. Figure 3 is a horizontal cross-sectional view of the high-pressure fuel supply pump 100 taken along a cross section perpendicular to the vertical direction. Figure 4 is a longitudinal cross-sectional view (part 2) of the high-pressure fuel supply pump 100 taken along a cross section perpendicular to the horizontal direction. Note that Figure 4 is a cross-sectional view taken along line A-A' shown in Figure 3.

[0021] 2 to 4, the pump body 1 of the high-pressure fuel supply pump 100 is formed in a substantially cylindrical shape. As shown in Figures 2 and 3, the pump body 1 is provided therein with a first chamber 1a, a second chamber 1b, a third chamber 1c, and a blocking wall 1d. The pump body 1 is also in close contact with a fuel pump mounting portion 90 and is fixed thereto with a plurality of bolts (screws) (not shown).

[0022] The first chamber 1a is a cylindrical space provided in the pump body 1, and the center line 1A of the first chamber 1a coincides with the center line of the pump body 1. One end of the plunger 2 is inserted into the first chamber 1a, and the plunger 2 reciprocates within the first chamber 1a. The first chamber 1a and one end of the plunger 2 form a pressurizing chamber 11.

[0023] The second chamber 1b is a cylindrical space provided in the pump body 1, and the center line of the second chamber 1b is perpendicular to the center line of the pump body 1 (first chamber 1a). A relief valve mechanism 4 is disposed in this second chamber 1b. The diameter of the second chamber 1b is smaller than the diameter of the first chamber 1a.

[0024] The first chamber 1a and the second chamber 1b are connected to each other by a circular communication hole 1e. The diameter of the communication hole 1e is the same as the diameter of the first chamber 1a, and the communication hole 1e extends from one end of the first chamber 1a. The diameter of the communication hole 1e is larger than the outer diameter of the plunger 2. This prevents the plunger 2, which reciprocates in the pressurizing chamber 11, from colliding with the periphery of the communication hole 1e, thereby improving the durability of the plunger 2.

[0025] The center line of the communication hole 1e is perpendicular to the center line of the second chamber 1b. This allows the fuel that has passed through the relief valve mechanism 4 to pass through the communication hole 1e efficiently, and does not hinder the improvement of relief performance. Furthermore, the shape of the pump body 1 can be made simple, and the productivity of the pump body 1 and the high-pressure fuel supply pump 100 can be improved.

[0026] The diameter of the communication hole 1e is larger than the diameter of the second chamber 1b. The communication hole 1e has a tapered surface 1f, in a cross section perpendicular to the center line of the second chamber 1b, whose diameter decreases toward the second chamber 1b. This allows fuel that has passed through the relief valve mechanism 4 arranged in the second chamber 1b to flow smoothly along the tapered surface 1f and return to the pressurization chamber 11.

[0027] The third chamber 1c is a cylindrical space provided in the pump body 1 and is continuous with the other end of the first chamber 1a. The center line of the third chamber 1c coincides with the center line 1A of the first chamber 1a and the center line of the pump body 1, and the diameter of the third chamber 1c is larger than the diameter of the first chamber 1a. A cylinder 6 that guides the reciprocating motion of the plunger 2 is disposed in the third chamber 1c. This allows the end face of the cylinder 6 to abut against the step between the first chamber 1a and the third chamber 1c, preventing the cylinder 6 from shifting toward the first chamber 1a.

[0028] The cylinder 6 is formed in a cylindrical shape, and its outer periphery is press-fitted into the third chamber 1c of the pump body 1. One end of the cylinder 6 abuts against the top surface of the third chamber 1c (the step between the first chamber 1a and the third chamber 1c). The plunger 2 is in slidable contact with the inner periphery of the cylinder 6.

[0029] An O-ring 93, which is a specific example of a seat member, is interposed between the fuel pump mounting portion 90 and the pump body 1. This O-ring 93 prevents engine oil from passing between the fuel pump mounting portion 90 and the pump body 1 and leaking to the outside of the engine (internal combustion engine).

[0030] A tappet 92 is provided at the lower end of the plunger 2. The tappet 92 converts the rotational motion of a cam 91 attached to the engine's camshaft into vertical motion and transmits it to the plunger 2. The plunger 2 is biased toward the cam 91 by a spring 16 via a retainer 15, and is pressed against the tappet 92. The tappet 92 reciprocates in accordance with the rotation of the cam 91. The plunger 2 reciprocates together with the tappet 92, changing the volume of the pressurizing chamber 11.

[0031] A seal holder 17 is disposed between the cylinder 6 and the retainer 15. The seal holder 17 is formed in a cylindrical shape into which the plunger 2 is inserted, and has an auxiliary chamber 17a at its upper end on the cylinder 6 side. The seal holder 17 also holds a plunger seal 18 at its lower end on the retainer 15 side.

[0032] The plunger seal 18 is in slidable contact with the outer periphery of the plunger 2, and seals off the fuel in the auxiliary chamber 17a when the plunger 2 reciprocates, preventing the fuel from flowing into the engine. The plunger seal 18 also prevents lubricating oil (including engine oil) that lubricates the sliding parts in the engine from flowing into the pump body 1.

[0033] 2, the plunger 2 reciprocates up and down. When the plunger 2 descends, the volume of the pressurizing chamber 11 increases, and when the plunger 2 ascends, the volume of the pressurizing chamber 11 decreases. In other words, the plunger 2 is arranged to reciprocate in a direction that increases and decreases the volume of the pressurizing chamber 11.

[0034] The plunger 2 has a first portion 2a and a second portion 2b. The second portion 2b has an outer diameter smaller than that of the first portion 2a. When the plunger 2 reciprocates, the first portion 2a and the second portion 2b are located in the sub-chamber 17a. Therefore, the volume of the sub-chamber 17a increases or decreases with the reciprocating movement of the plunger 2.

[0035] The sub-chamber 17a is in communication with the low-pressure fuel chamber 10 through a fuel passage 10c (see FIG. 4). When the plunger 2 descends, fuel flows from the sub-chamber 17a to the low-pressure fuel chamber 10, and when the plunger 2 ascends, fuel flows from the low-pressure fuel chamber 10 to the sub-chamber 17a. This reduces the amount of fuel flowing into and out of the pump during the suction stroke or return stroke of the high-pressure fuel supply pump 100, thereby reducing pressure pulsations generated inside the high-pressure fuel supply pump 100.

[0036] The detailed configuration of the fuel passage 10c will be described later.

[0037] A low-pressure fuel chamber 10 is provided in the upper part of a pump body 1 of high-pressure fuel supply pump 100, and an intake joint 5 is attached to the side of pump body 1. Intake joint 5 is connected to a low-pressure pipe 104 through which fuel supplied from a fuel tank 103 (see FIG. 1) passes. The fuel in fuel tank 103 is supplied from intake joint 5 to the inside of pump body 1.

[0038] The intake joint 5 has a low-pressure fuel intake port 51 connected to the low-pressure pipe 104, and an intake passage 52 (see FIG. 6) that communicates with the low-pressure fuel intake port 51. The fuel that passes through the intake passage 52 passes through an intake filter provided inside the pump body 1 and is supplied to the low-pressure fuel chamber 10. The intake filter removes foreign matter present in the fuel and prevents the foreign matter from entering the high-pressure fuel supply pump 100.

[0039] The low-pressure fuel chamber 10 is provided with a low-pressure fuel flow path 10a and an intake passage 10b. A pressure pulsation reduction mechanism 9 is provided in the low-pressure fuel flow path 10a. When fuel that has flowed into the pressurizing chamber 11 passes through the electromagnetic intake valve mechanism 3, which is in an open state, and is returned to the intake passage 10b, pressure pulsation occurs in the low-pressure fuel chamber 10. The pressure pulsation reduction mechanism 9 reduces the pressure pulsation generated in the high-pressure fuel supply pump 100 from spreading to the low-pressure pipe 104.

[0040] The pressure pulsation reduction mechanism 9 is formed of a metal diaphragm damper made of two corrugated disk-shaped metal plates bonded together at their outer peripheries and filled with an inert gas such as argon. The metal diaphragm damper of the pressure pulsation reduction mechanism 9 absorbs or reduces pressure pulsations by expanding and contracting.

[0041] The intake passage 10b is connected to the intake port 31b (see Figure 2) of the electromagnetic intake valve mechanism 3, and the fuel that has passed through the low-pressure fuel flow path 10a reaches the intake port 31b of the electromagnetic intake valve mechanism 3 via the intake passage 10b.

[0042] 2 and 3, the electromagnetic intake valve mechanism 3 is inserted into an intake valve chamber 30 formed in the pump body 1. The intake valve chamber 30 is provided upstream of the pressurizing chamber 11 (on the intake passage 10b side) and is formed as a horizontally extending lateral hole. The electromagnetic intake valve mechanism 3 includes an intake valve seat 31 press-fitted into the intake valve chamber 30, a valve portion 32, a rod 33, a rod-biasing spring 34, an electromagnetic coil 35, and an anchor 36.

[0043] The suction valve seat 31 is cylindrical and has a seat 31a on its inner periphery. The suction valve seat 31 also has a suction port 31b that extends from the outer periphery to the inner periphery. The suction port 31b communicates with the suction passage 10b in the low-pressure fuel chamber 10.

[0044] A stopper 37 is disposed in the suction valve chamber 30, facing the seating portion 31a of the suction valve seat 31, and the valve portion 32 is disposed between the stopper 37 and the seating portion 31a. A valve biasing spring 38 is also disposed between the stopper 37 and the valve portion 32. The valve biasing spring 38 biases the valve portion 32 toward the seating portion 31a.

[0045] The valve element 32 comes into contact with the seat 31a to close the communication between the suction port 31b and the pressurizing chamber 11. When the valve element 32 closes the communication between the suction port 31b and the pressurizing chamber 11, the electromagnetic suction valve mechanism 3 is in a closed state. On the other hand, the valve element 32 comes into contact with the stopper 37 to open the communication between the suction port 31b and the pressurizing chamber 11. When the valve element 32 opens the communication between the suction port 31b and the pressurizing chamber 11, the electromagnetic suction valve mechanism 3 is in an open state.

[0046] The rod 33 passes through a cylindrical hole in the suction valve seat 31, and one end abuts against the valve portion 32. The rod biasing spring 34 biases the valve portion 32 in the valve opening direction, i.e., toward the stopper 37, via the rod 33. One end of the rod biasing spring 34 engages with the other end of the rod 33, and the other end of the rod biasing spring 34 engages with a magnetic core 39 that is arranged to surround the rod biasing spring 34.

[0047] The anchor 36 faces the end face of the magnetic core 39. The anchor 36 is engaged with a flange provided at the middle portion of the rod 33. The electromagnetic coil 35 is disposed so as to make a circuit around the magnetic core 39. A terminal member 40 is electrically connected to the electromagnetic coil 35, and a current flows through the terminal member 40.

[0048] In the non-energized state where no current flows through the electromagnetic coil 35, the rod 33 is urged in the valve-opening direction by the urging force of the rod-urging spring 34, pressing the valve portion 32 in the valve-opening direction. As a result, the valve portion 32 moves away from the seat portion 31a and abuts against the stopper 37, and the electromagnetic intake valve mechanism 3 is in the open state. In other words, the electromagnetic intake valve mechanism 3 is of a normally open type, which opens in the non-energized state.

[0049] When the electromagnetic intake valve mechanism 3 is in an open state, fuel in the intake port 31b passes between the valve portion 32 and the seat portion 31a, passes through a plurality of fuel passage holes (not shown) in the stopper 37, and the blocking wall 1d, and flows into the pressurization chamber 11. When the electromagnetic intake valve mechanism 3 is in an open state, the valve portion 32 comes into contact with the stopper 37, thereby restricting the position of the valve portion 32 in the valve opening direction. The gap that exists between the valve portion 32 and the seat portion 31a when the electromagnetic intake valve mechanism 3 is in an open state is the movable range of the valve portion 32, which is the valve opening stroke.

[0050] When current flows through the electromagnetic coil 35, the anchor 36 is attracted in the valve-closing direction by the magnetic attractive force of the magnetic core 39. As a result, the anchor 36 moves against the biasing force of the rod biasing spring 34 and comes into contact with the magnetic core 39. When the anchor 36 moves in the valve-closing direction, toward the magnetic core 39, the rod 33 with which the anchor 36 is engaged moves together with the anchor 36. As a result, the valve portion 32 is released from the biasing force in the valve-opening direction and moves in the valve-closing direction due to the biasing force of the valve biasing spring 38. When the valve portion 32 comes into contact with the seating portion 31 a of the suction valve seat 31, the electromagnetic suction valve mechanism 3 is brought into a valve-closed state.

[0051] 3, the discharge valve mechanism 8 is disposed in a discharge valve chamber 80 provided on the outlet side (downstream side) of the pressurizing chamber 11. The discharge valve mechanism 8 has a discharge valve seat 81 communicating with the pressurizing chamber 11, a valve portion 82 that moves toward and away from the discharge valve seat 81, a discharge valve spring 83 that biases the valve portion 82 toward the discharge valve seat 81, and a discharge valve stopper 84 that determines the stroke (travel distance) of the valve portion 82.

[0052] The discharge valve mechanism 8 also has a plug 85 that prevents fuel from leaking to the outside. A discharge valve stopper 84 is press-fitted into the plug 85. The plug 85 is joined to the pump body 1 by welding at a welded portion. The discharge valve chamber 80 is opened and closed by a valve portion 82. The discharge valve chamber 80 communicates with a discharge valve chamber passage 87. The discharge valve chamber passage 87 is formed in the pump body 1.

[0053] The pump body 1 is provided with a horizontal hole that communicates with the second chamber 1b (relief valve chamber) shown in Figure 2, and a discharge joint 12 is inserted into the horizontal hole. The discharge joint 12 has the above-mentioned discharge passage 12a that communicates with the horizontal hole of the pump body 1 and the discharge valve chamber passage 87, and a fuel discharge port 12b that is one end of the discharge passage 12a. The fuel discharge port 12b of the discharge joint 12 communicates with the common rail 106. The discharge joint 12 is fixed to the pump body 1 by welding.

[0054] When there is no difference in fuel pressure (fuel pressure difference) between the pressurizing chamber 11 and the discharge valve chamber 80 and discharge valve chamber passage 87, the valve portion 82 is pressed against the discharge valve seat 81 by the biasing force of the discharge valve spring 83, and the discharge valve mechanism 8 is in a closed state. When the fuel pressure in the pressurizing chamber 11 becomes greater than the fuel pressure in the discharge valve chamber 80 and discharge valve chamber passage 87, the valve portion 82 moves against the biasing force of the discharge valve spring 83, and the discharge valve mechanism 8 is in an open state.

[0055] When the discharge valve mechanism 8 is closed, the (high-pressure) fuel in the pressurizing chamber 11 passes through the discharge valve mechanism 8 and reaches the discharge valve chamber passage 87. The fuel that has reached the discharge valve chamber passage 87 is then discharged into the common rail 106 (see FIG. 1) through the fuel discharge port 12b of the discharge joint 12. With the above-described configuration, the discharge valve mechanism 8 functions as a check valve that restricts the flow direction of the fuel.

[0056] 2 is a valve that operates when a problem occurs in the common rail 106 or a component beyond it, causing the common rail 106 to exceed a predetermined pressure, and returns fuel in the discharge passage 12a to the pressurizing chamber 11. The discharge passage 12a communicates with the discharge valve chamber 80 via a discharge valve chamber passage 87. Therefore, the pressure in the discharge passage 12a is equal to the pressure in the discharge valve chamber 80.

[0057] The relief valve mechanism 4 has a relief spring 41, a relief valve holder 42, a valve portion 43, and a seat member 44. The relief valve mechanism 4 is inserted through the discharge joint 12 and disposed in the second chamber 1b. One end of the relief spring 41 abuts against the pump body 1 (one end of the second chamber 1b), and the other end abuts against the relief valve holder 42. The relief valve holder 42 engages with the valve portion 43, and the biasing force of the relief spring 41 acts on the valve portion 43 via the relief valve holder 42.

[0058] The valve portion 43 is pressed by the urging force of the relief spring 41 to block the fuel passage of the seat member 44. The movement direction of the valve portion 43 (relief valve holder 42) is perpendicular to the reciprocating direction of the plunger 2. The center line of the relief valve mechanism 4 (center line of the relief valve holder 42) is perpendicular to the center line of the plunger 2.

[0059] The seat member 44 has a fuel passage facing the valve portion 43, and the side of the fuel passage opposite the valve portion 43 communicates with the discharge passage 12a. The movement of fuel between the pressurizing chamber 11 (upstream side) and the seat member 44 (downstream side) is blocked when the valve portion 43 comes into contact (close contact) with the seat member 44 to block the fuel passage.

[0060] When the pressure in the common rail 106 and the components beyond it increases, the fuel on the seat member 44 side presses against the valve portion 43, moving the valve portion 43 against the biasing force of the relief spring 41. As a result, the valve portion 43 opens, and fuel in the discharge passage 12a returns to the pressurizing chamber 11 through the fuel passage of the seat member 44. Therefore, the pressure that opens the valve portion 43 is determined by the biasing force of the relief spring 41.

[0061] The movement direction of the valve portion 43 (relief valve holder 42) in the relief valve mechanism 4 is different from the movement direction of the valve portion 82 in the above-described discharge valve mechanism 8. That is, the movement direction of the valve portion 82 in the discharge valve mechanism 8 is a first radial direction of the pump body 1, and the movement direction of the valve portion 43 in the relief valve mechanism 4 is a second radial direction different from the first radial direction of the pump body 1. This allows the discharge valve mechanism 8 and the relief valve mechanism 4 to be disposed in positions where they do not overlap each other in the up-down direction, making it possible to effectively utilize the internal space of the pump body 1 and reduce the size of the pump body 1.

[0062] 1-3. Operation of the High-Pressure Fuel Pump Next, the operation of the high-pressure fuel pump according to this embodiment will be described with reference to FIGS.

[0063] In Figure 2, if the electromagnetic intake valve mechanism 3 is open when the plunger 2 descends, fuel flows into the pressurization chamber 11 through an opening in the blocking wall 1d. Hereinafter, the stroke in which the plunger 2 descends will be referred to as the intake stroke. On the other hand, if the electromagnetic intake valve mechanism 3 is closed when the plunger 2 ascends, the fuel in the pressurization chamber 11 is pressurized and is pumped through the discharge valve mechanism 8 to the common rail 106 (see Figure 1). Hereinafter, the process in which the plunger 2 ascends will be referred to as the upstroke.

[0064] As described above, if the electromagnetic intake valve mechanism 3 is closed during the ascending stroke, the fuel drawn into the pressurization chamber 11 during the intake stroke is pressurized and discharged toward the common rail 106. On the other hand, if the electromagnetic intake valve mechanism 3 is open during the ascending stroke, the fuel in the pressurization chamber 11 is pushed back toward the blocking wall 1d and is not discharged toward the common rail 106. In this way, the discharge of fuel by the high-pressure fuel supply pump 100 is controlled by opening and closing the electromagnetic intake valve mechanism 3. The opening and closing of the electromagnetic intake valve mechanism 3 is controlled by the ECU 101.

[0065] During the intake stroke, the volume of the pressurization chamber 11 increases, and the fuel pressure in the pressurization chamber 11 decreases. This reduces the fluid pressure difference between the intake port 31b and the pressurization chamber 11 (hereinafter referred to as the "fluid pressure difference across the valve portion 32"). When the biasing force of the rod biasing spring 34 becomes greater than the fluid pressure difference across the valve portion 32, the rod 33 moves in the valve-opening direction, the valve portion 32 separates from the seat portion 31a of the intake valve seat 31, and the electromagnetic intake valve mechanism 3 enters the valve-open state.

[0066] When the electromagnetic intake valve mechanism 3 is in an open state, fuel in the intake port 31b passes between the valve portion 32 and the seat portion 31a and through a plurality of fuel passage holes (not shown) in the stopper 37, and flows into the pressurization chamber 11. When the electromagnetic intake valve mechanism 3 is in an open state, the valve portion 32 comes into contact with the stopper 37, thereby restricting the position of the valve portion 32 in the valve opening direction. The gap that exists between the valve portion 32 and the seat portion 31a when the electromagnetic intake valve mechanism 3 is in an open state is the movable range of the valve portion 32, which is the valve opening stroke.

[0067] After the intake stroke is completed, the valve moves to the upstroke. At this time, the electromagnetic coil 35 remains de-energized, and no magnetic attractive force acts between the anchor 36 and the magnetic core 39. The valve portion 32 is subjected to a biasing force in the valve-opening direction corresponding to the difference in biasing forces between the rod biasing spring 34 and the valve biasing spring 38, as well as a force in the valve-closing direction due to a fluid force generated when fuel flows back from the pressurizing chamber 11 to the low-pressure fuel flow path 10a.

[0068] In this state, the difference in the biasing forces of the rod biasing spring 34 and the valve biasing spring 38 is set to be greater than the fluid force so that the electromagnetic intake valve mechanism 3 maintains the open state. The volume of the pressurization chamber 11 decreases as the plunger 2 rises. Therefore, the fuel that was drawn into the pressurization chamber 11 passes between the valve portion 32 and the seat portion 31a and is returned to the intake port 31b, and the pressure inside the pressurization chamber 11 does not increase. This stroke is called the return stroke.

[0069] In the return stroke, when a control signal from the ECU 101 (see FIG. 1) is applied to the electromagnetic intake valve mechanism 3, a current flows through the electromagnetic coil 35 via the terminal member 40. When a current flows through the electromagnetic coil 35, a magnetic attraction force acts between the magnetic core 39 and the anchor 36, and the anchor 36 (rod 33) is attracted to the magnetic core 39. As a result, the anchor 36 (rod 33) moves in the valve closing direction (direction away from the valve portion 32) against the biasing force of the rod biasing spring 34.

[0070] When the anchor 36 (rod 33) moves in the valve closing direction, the valve portion 32 is released from the biasing force in the valve opening direction and moves in the valve closing direction due to the biasing force of the valve biasing spring 38 and the fluid force caused by the fuel flowing into the intake passage 10b. When the valve portion 32 comes into contact with the seating portion 31a of the intake valve seat 31 (the valve portion 32 seats on the seating portion 31a), the electromagnetic intake valve mechanism 3 is brought into a valve closed state.

[0071] After the electromagnetic intake valve mechanism 3 is closed, the fuel in the pressurizing chamber 11 is pressurized as the plunger 2 rises, and when the pressure reaches a predetermined level, the fuel passes through the discharge valve mechanism 8 and is discharged into the common rail 106 (see FIG. 1). This stroke is called the discharge stroke. That is, the upward stroke of the plunger 2 from its lower starting point to its upper starting point consists of a return stroke and a discharge stroke. The amount of high-pressure fuel discharged can be controlled by controlling the timing of energization of the electromagnetic coil 35 of the electromagnetic intake valve mechanism 3.

[0072] If the timing of energizing the electromagnetic coil 35 is advanced, the proportion of the return stroke during the ascending stroke decreases and the proportion of the discharge stroke increases. As a result, less fuel is returned to the intake passage 10b and more fuel is discharged at high pressure. On the other hand, if the timing of energizing the electromagnetic coil 35 is delayed, the proportion of the return stroke during the ascending stroke increases and the proportion of the discharge stroke decreases. As a result, more fuel is returned to the intake passage 10b and less fuel is discharged at high pressure. In this way, by controlling the timing of energizing the electromagnetic coil 35, the amount of fuel discharged at high pressure can be controlled to the amount required by the engine (internal combustion engine).

[0073] 1-4. Cavitation Generation Mechanism Here, the mechanism by which cavitation occurs in the fuel passage of a conventional high-pressure fuel supply pump will be described with reference to Fig. 5. Fig. 5 is a diagram showing the mechanism by which cavitation occurs in the fuel passage of a conventional high-pressure fuel supply pump.

[0074] As shown in Figure 5, a pump body 201 of a conventional high-pressure fuel supply pump is formed with a fuel passage 210c that connects the auxiliary chamber with the low-pressure fuel chamber 10. The opening diameter of this fuel passage 210c is set to be uniform from the auxiliary chamber to the low-pressure fuel chamber 10. When the plunger 202 descends to just before bottom dead center during the intake stroke, fuel pushed out from the auxiliary chamber passes through the fuel passage 210c. Therefore, an inertial force 251 directed from the auxiliary chamber to the low-pressure fuel chamber 10 is generated in the fuel passage 210c and the auxiliary chamber by the fuel pushed out from the auxiliary chamber.

[0075] The pressure in the fuel passage 210c and the auxiliary chamber becomes negative due to inertial force 251. When the plunger 202 reaches the bottom dead center, the pressure in the fuel passage 210c and the auxiliary chamber has dropped below the vapor pressure, causing bubbles (cavitation) 250 to form in the fuel passage 210c and the auxiliary chamber.

[0076] Furthermore, when the plunger 202 passes bottom dead center and transitions to the pressurizing stroke, an inertial force 252 from the low-pressure fuel chamber 10 to the auxiliary chamber is generated in the fuel passage 210c and the auxiliary chamber by the fuel flowing from the low-pressure fuel chamber 10 to the auxiliary chamber. This inertial force 252 causes bubbles 250 generated in the fuel passage 210c and the auxiliary chamber to collapse. As a result, the conventional high-pressure fuel supply pump has a problem in that the generation and collapse of bubbles 250 can damage the auxiliary chamber 17a and the plunger seal 18.

[0077] Here, the area of ​​the stepped portion between the first portion 2a and the second portion 2b of the plunger 2 is V, the angular velocity of the cam 91 is ω, and the acceleration at which the cam 91 pushes up the plunger 2 is a ｐ , the length of the fuel passage is L, the cross-sectional area of ​​the fuel passage is S, and the number of fuel passages is n. Then, the feed pressure of the high-pressure fuel supply pump is P ｆ , saturated vapor pressure is P ｂWhen the density of the fuel is ρ, the following equation 1 must be satisfied in order to suppress the generation of bubbles (cavitation) 250. The units of the parameters shown in Equation 1 are, for example, length L (m), cross-sectional area S (m ２ ), pressure P ｆ , P ｂ (Pa), angular velocity ω (rad / s), fuel density ρ (kg / m ３ ), and Va (m / rad ２ )

[0078] 1-5. Configuration of the Fuel Passage Next, the configuration of the fuel passage 10c in the high-pressure fuel supply pump 100 of this embodiment will be described with reference to Figures 3, 4, and 6. Figure 6 is an enlarged cross-sectional view showing the fuel passage 10c and its surroundings.

[0079] As shown in Figures 3 and 4, the pump body 1 is formed with a plurality of fuel passages 10c (two in this example). By providing a plurality of fuel passages 10c in this way, the flow velocity of fuel flowing through the fuel passages 10c can be reduced. As shown in Figure 3, the two fuel passages 10c are arranged with the plunger 2, which slides in the pump body 1, sandwiched between them. The two fuel passages 10c are also arranged on either side of the axis of the rod 33 of the electromagnetic intake valve mechanism 3, with the axis sandwiched between them.

[0080] In this way, by arranging the two fuel passages 10c apart, fuel can be supplied evenly to the low-pressure fuel chamber 10 and the auxiliary fuel chamber 17a, which makes it possible to distribute the pressure acting on the low-pressure fuel chamber 10 and the auxiliary fuel chamber 17a.

[0081] As shown in Figure 6, the fuel passage 10c has a large diameter portion 21, a small diameter portion 22, and a connecting portion 24 that connects the large diameter portion 21 and the small diameter portion 22. The large diameter portion 21 is formed on the low-pressure fuel chamber 10 side of the fuel passage 10c, and the small diameter portion 22 is formed on the sub-chamber 17a side of the fuel passage 10c. The opening diameter of the large diameter portion 21 is set larger than the opening diameter of the small diameter portion 22. By dividing the fuel passage 10c into the large diameter portion 21 and the small diameter portion 22, the length of the small diameter portion 22, which is prone to large inertial forces, can be shortened.

[0082] The connecting portion 24 is formed so that the opening diameter continuously increases from the small diameter portion 22 toward the large diameter portion 21. In other words, the connecting portion 24 is formed in a tapered shape.

[0083] Here, the area of ​​the stepped portion between the first portion 2a and the second portion 2b of the plunger 2 is V, the angular velocity of the cam 91 is ω, and the acceleration at which the cam 91 pushes up the plunger 2 is a ｐ , the length of the small diameter portion 22 is L, the cross-sectional area (opening diameter) of the small diameter portion 22 is S, and the number of fuel passages is n. Then, the feed pressure of the high-pressure fuel supply pump is P ｆ , saturated vapor pressure is P ｂ When the density of the fuel is ρ, the small diameter portion 22 is set to satisfy the following equation 2. The units of the parameters shown in Equation 2 are, for example, length L (m), cross-sectional area S (m ２ ), pressure P ｆ , P ｂ (Pa), angular velocity ω (rad / s), fuel density ρ (kg / m ３ ), and Va (m / rad ２ )

[0084] In this way, the small diameter portion 22 of the fuel passage 10c is set to satisfy the relationship of the above-mentioned equation 2, so that it is possible to sufficiently reduce the inertial force generated when the plunger 2 moves. As a result, it is possible to prevent the pressure in the auxiliary chamber 17a from becoming smaller than the vapor pressure, and it is possible to prevent cavitation from occurring in the auxiliary chamber 17a and the fuel passage 10c.

[0085] Note that the occurrence of cavitation can be suppressed by increasing the cross-sectional area S of the small diameter portion 22. However, the constricted portion of the pump body 1, the cylinder 6, etc. are arranged around the small diameter portion 22. Therefore, the cross-sectional area S of the small diameter portion 22 is set to a value that satisfies the following equation 3 with respect to the minimum wall thickness k around the plunger 2 in the pump body 1. Note that the ratio of the circumference of a circle to its circumference is π.

[0086] Here, the minimum thickness k is defined as r0, where r1 is the outer diameter of the constricted portion of the pump body 1, and r2 is the inner diameter of the pump body 1 around the sub chamber 17a. If r1<r2, the minimum thickness k is r1-r0. On the other hand, if r1>r2, the minimum thickness k is r2-r0.

[0087] In this way, by satisfying the above-mentioned equation (3), it is possible to set the cross-sectional area S of the small diameter portion 22 taking into consideration the minimum wall thickness k of the pump body 1. As a result, it is possible to set the size of the small diameter portion 22 to an appropriate size. Furthermore, by satisfying the equation (3), it is possible to prevent the wall thickness of the pump body 1 from becoming too thick.

[0088] 2. Second Embodiment Next, a high-pressure fuel supply pump according to a second embodiment will be described with reference to Fig. 7. Fig. 7 is a cross-sectional view showing the configuration of the fuel passage and its surroundings in the high-pressure fuel supply pump according to the second embodiment.

[0089] The high-pressure fuel supply pump 100B according to the second embodiment differs from the high-pressure fuel supply pump 100 according to the first embodiment in the configuration of the fuel passages. Therefore, the same reference numerals are used to designate parts common to the high-pressure fuel supply pump 100 according to the first embodiment, and redundant explanations will be omitted.

[0090] 7, a fuel passage 10cB is formed in the pump body 1 of the high-pressure fuel supply pump 100B, connecting the low-pressure fuel chamber 10 and the sub-chamber 17a. The fuel passage 10cB has a large diameter portion 21, a small diameter portion 22, a connecting portion 24, a second large diameter portion 23, and a second connecting portion 25.

[0091] The configurations of the large diameter portion 21, the small diameter portion 22, and the connecting portion 24 are the same as those of the large diameter portion 21, the small diameter portion 22, and the connecting portion 24 according to the first embodiment, and therefore a description thereof will be omitted.

[0092] The second large diameter portion 23 is formed in the fuel passage 10c closer to the low-pressure fuel chamber 10 than the large diameter portion 21. The opening diameter of the second large diameter portion 23 is set larger than the opening diameter of the large diameter portion 21. The second large diameter portion 23 and the large diameter portion 21 are connected via a second connecting portion 25 formed in a tapered shape.

[0093] By providing the second large diameter portion 23, which is larger than the large diameter portion 21, the length of the small diameter portion 22 can be made shorter than the small diameter portion 22 according to the first embodiment. Furthermore, the amount of fuel flowing through the fuel passage 10cB can be increased compared to the fuel passage 10c of the high-pressure fuel supply pump 100 according to the first embodiment. Furthermore, the total passage area of ​​the fuel passage 10cB can be increased, further reducing the flow velocity of the fuel flowing through the fuel passage 10cB. As a result, the inertial force generated in the fuel passage 10cB can be reduced, and the pressure drop in the auxiliary chamber 17a due to the inertial force can be reduced.

[0094] The other configurations are the same as those of the high-pressure fuel supply pump 100 according to the first embodiment described above, and therefore a description thereof will be omitted. The high-pressure fuel supply pump 100B according to the second embodiment also provides the same functions and effects as those of the high-pressure fuel supply pump 100 according to the first embodiment described above.

[0095] In addition, in the high-pressure fuel supply pump 100 according to the first embodiment, the fuel passage 10c is changed in two stages, and in the high-pressure fuel supply pump 100B according to the second embodiment, the fuel passage 10cB is changed in three stages, but this is not limitative. The opening diameter of the fuel passage may be changed in four or more stages.

[0096] 3. Third Embodiment Next, a high-pressure fuel supply pump according to a third embodiment will be described with reference to Fig. 8. Fig. 8 is a horizontal cross-sectional view of a high-pressure fuel supply pump 100 according to the third embodiment, seen from a cross section perpendicular to the vertical direction.

[0097] The high-pressure fuel supply pump 100C according to the third embodiment differs from the high-pressure fuel supply pump 100 according to the first embodiment in the number of fuel passages. Therefore, the same reference numerals are used to designate parts common to the high-pressure fuel supply pump 100 according to the first embodiment, and redundant explanations will be omitted.

[0098] 8, three fuel passages 10c are formed in the pump body 1 of the high-pressure fuel supply pump 100B. Two of the three fuel passages 10c are located closer to the electromagnetic intake valve mechanism 3 than the plunger 2. This shortens the travel distance of the fuel during intake and spill, and makes it possible to evenly distribute the pressure applied to the low-pressure fuel chamber 10 and the sub-chamber 17a.

[0099] By increasing the number of fuel passages 10c, the amount of fuel flowing can be increased compared to the fuel passages 10c of the high-pressure fuel supply pump 100 according to the first embodiment. The total passage area of ​​the fuel passages 10c can be increased, and the flow velocity of the fuel flowing through the fuel passages 10c can be further reduced. As a result, the inertial force generated in the fuel passages 10c can be reduced, and the pressure drop in the auxiliary chamber 17a due to the inertial force can be reduced.

[0100] The number of fuel passages 10c is not limited to two or three, but may be four or more.

[0101] The other configurations are the same as those of the high-pressure fuel supply pump 100 according to the first embodiment described above, and therefore a description thereof will be omitted. The high-pressure fuel supply pump 100C according to the third embodiment can also achieve the same functions and effects as those of the high-pressure fuel supply pump 100 according to the first embodiment described above.

[0102] 4. Fourth Embodiment Next, a high-pressure fuel supply pump according to a fourth embodiment will be described with reference to Fig. 9. Fig. 9 is a vertical cross-sectional view of the high-pressure fuel supply pump according to the fourth embodiment, taken along a cross section perpendicular to the horizontal direction.

[0103] The high-pressure fuel supply pump 100D according to the fourth embodiment differs from the high-pressure fuel supply pump 100 according to the first embodiment in the configuration of the small diameter portion of the fuel passage. Therefore, the same reference numerals are used here to designate parts that are common to the high-pressure fuel supply pump 100 according to the first embodiment, and duplicated explanations will be omitted.

[0104] Three fuel passages 10cD are formed in the pump body 1 of the high-pressure fuel supply pump 100D. Each fuel passage 10cD has a large diameter portion 21 and a small diameter portion 22D. The large diameter portion 21 has an axial direction parallel to the center line 1A of the pump body 1. In contrast, the small diameter portion 22D has an axial direction inclined relative to the center line 1A of the pump body 1. In other words, the axial direction of the small diameter portion 22D is inclined relative to the axial direction of the plunger 2.

[0105] By inclining the small diameter portion 22D in this manner, the length of the small diameter portion 22D can be made shorter than that of the small diameter portion 22 in the first embodiment. This reduces the inertial force generated in the fuel passage 10cD, and reduces the pressure drop in the auxiliary chamber 17a due to the inertial force.

[0106] The other configurations are the same as those of the high-pressure fuel supply pump 100 according to the first embodiment described above, and therefore a description thereof will be omitted. The high-pressure fuel supply pump 100D according to the fourth embodiment can also achieve the same functions and effects as those of the high-pressure fuel supply pump 100 according to the first embodiment described above.

[0107] The above describes the embodiments of the fuel pump of the present invention, including their functions and effects. However, the fuel pump of the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the invention as defined in the claims. Furthermore, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to a configuration including all of the described configurations.

[0108] In this specification, the words "parallel" and "orthogonal" are used, but these do not mean only "parallel" and "orthogonal" in the strict sense, but also include "parallel" and "orthogonal" and may also mean a "substantially parallel" or "substantially orthogonal" state within a range in which the functions can be exerted.

[0109] DESCRIPTION OF SYMBOLS 1...Pump body, 1a...First chamber, 1b...Second chamber, 1c...Third chamber, 1d...Blocking wall, 1e...Communicating hole, 1f...Tapered surface, 1A...Center line, 2...Plunger, 3...Electromagnetic intake valve mechanism, 4...Relief valve mechanism, 5...Intake joint, 6...Cylinder, 8...Discharge valve mechanism, 9...Pressure pulsation reduction mechanism, 10...Low-pressure fuel chamber, 10c, 10cB, 10cD...Fuel passage, 11...Pressure chamber, 12...Discharge joint, 17a...Sub-chamber, 21...Large diameter portion, 22, 22D...Small diameter portion, 23...Second large diameter portion, 31...Intake valve seat, 31a...Seat portion, 31b...Intake port, 32...Valve portion, 33...Rod, 35...Electromagnetic coil, 36...Anchor, 37...Stopper, DESCRIPTION OF SYMBOLS 39...Magnetic core, 40...Terminal member, 42...Relief valve holder, 43...Valve portion, 44...Seat member, 81...Discharge valve seat, 82...Valve portion, 84...Discharge valve stopper, 85...Plug, 100, 100B, 100C, 100D...High-pressure fuel supply pump (fuel pump), 101...ECU, 102...Feed pump, 103...Fuel tank, 104...Low-pressure piping, 105...Fuel pressure sensor, 106...Common rail, 107...Injector

Claims

1. A pump comprising: a pump body; a plunger slidably supported on said pump body and having a first portion and a second portion having an outer diameter smaller than that of said first portion; a cam for reciprocating said plunger; a low-pressure fuel chamber provided in said pump body; an auxiliary chamber formed in said pump body and having a volume that varies with movement of said plunger; and a plurality of fuel passages communicating said low-pressure fuel chamber with said auxiliary chamber, said fuel passages having a large diameter portion formed on the low-pressure fuel chamber side, and a small diameter portion communicating with said large diameter portion, formed on said auxiliary chamber side, and having an opening diameter smaller than that of said large diameter portion; wherein V is the area of ​​a stepped portion between said first portion and said second portion of said plunger, ω is the angular velocity of said cam, and a is the acceleration at which said cam pushes up said plunger. ｐ , the number of fuel passages is n, and the feed pressure is P ｆ , saturated vapor pressure is P ｂ When the density of the fuel is ρ, the length L of the small diameter portion and the cross-sectional area S of the small diameter portion are set to values ​​that satisfy the following equation 2: Fuel pump.

2. The cross-sectional area S of the small diameter portion is set to a value that satisfies the following equation 3 with respect to the minimum wall thickness k around the plunger in the pump body:

2. The fuel pump of claim 1.

3. A fuel pump according to claim 1, wherein the pump body is provided with an electromagnetic intake valve mechanism, and the plurality of fuel passages are arranged on both sides of the axis of the rod of the electromagnetic intake valve mechanism, sandwiching the plunger therebetween when the pump body is viewed from a direction perpendicular to the axial direction of the plunger.

4. The fuel pump according to claim 3, wherein two of the plurality of fuel passages are disposed closer to the electromagnetic intake valve mechanism than the plunger.

5. The fuel pump according to claim 4, wherein three fuel passages are formed in the pump body.

6. A fuel pump according to claim 1, wherein the fuel passage has a second large diameter portion formed closer to the low-pressure fuel chamber than the large diameter portion and having an opening diameter larger than that of the large diameter portion.

7. A fuel pump according to claim 1, wherein the axial direction of the small diameter portion is inclined with respect to the axial direction of the plunger.

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