JP3903875B2 - Injector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an injector constituting a fuel injection device.
[0002]
[Prior art]
As a fuel injection device for a diesel engine, an injector for injecting fuel into a cylinder receives a supply of fuel from a common rail that stores fuel pumped from a pump, which is known as a common rail type. The injector is an oil in which a nozzle that opens and closes a nozzle hole is slidably held at a rear end of the nozzle, and fuel from the common rail is formed on the outer periphery of the tip of the needle. Introduced into the reservoir. The introduced fuel is used as injection fuel and as control oil that generates a biasing force that acts on the needle in the seating direction. The fuel from the common rail is also introduced into a back pressure chamber having the rear end surface of the needle as a chamber wall surface, and serves as control oil that generates a biasing force that acts in the seating direction of the needle. The needle is separated when the fuel pressure in the back pressure chamber decreases and the biasing force in the separation direction with respect to the needle becomes dominant, and the fuel pressure in the back pressure chamber rises from that state and the biasing force in the seating direction becomes dominant. Sit down.
[0003]
FIG. 6 shows a structure centering on a back pressure control unit for switching the fuel pressure in the back pressure chamber inside the injector. The back pressure control unit has a valve chamber 901 that is always in communication with the back pressure chamber. A ball 902 is disposed in the valve chamber 901. The ball 902 can close the low pressure port 903 that opens to the ceiling surface of the valve chamber 901 or the high pressure port 904 that opens to the bottom surface of the valve chamber 901. The low pressure port 903 communicates with a low pressure fuel tank. The high-pressure port 904 communicates with the common rail and is at a high pressure during engine operation. A cylinder 905 is formed in the vertical direction above the valve chamber 901, and two pistons 906 and 907 having different sliding diameters are disposed in the cylinder 905. The lower piston 906 has a pin-like lower end portion 9061 protruding into the valve chamber 901 from the low pressure port 903 and can press the valve body 902, and the upper piston 907 is driven to be pressed from above by an actuator (not shown). Fuel is introduced between the pistons 906 and 907 to form a hydraulic chamber 908.
[0004]
In a state where the ball 902 is displaced downward and the low pressure port 903 is opened and the high pressure port 904 is closed, the back pressure chamber communicates with the low pressure fuel tank, and the fuel pressure in the back pressure chamber is substantially equal to the fuel pressure in the common rail ( Hereinafter, the needle is separated from the pressure value of the common rail pressure as appropriate. On the other hand, in a state where the low pressure port 903 is closed and the high pressure port 904 is opened, the back pressure chamber and the low pressure fuel tank are shut off, and the fuel pressure in the back pressure chamber becomes substantially the pressure value of the common rail pressure, and the needle is seated. . The force to raise the ball 902 with the high pressure port 904 closed is provided by the high pressure fuel from the high pressure port 904.
[0005]
[Problems to be solved by the invention]
By the way, the state of illustration is a state of an engine stop state. Therefore, although the downward driving force with respect to the upper piston 907 is released, the common rail pressure is also substantially 0 (normal pressure), so the force that keeps the low pressure port 903 closed does not act on the ball 902. Therefore, depending on the length of the engine stop state, the ball 902 and the lower piston 906 are the same as when the needle is opened, although the upper piston 907 is not displaced downward as shown in the figure. The low pressure port 903 is open because it has been lowered to the lowest position. When the ignition switch is turned on, fuel pumping to the common rail of the pump is started from this state. At this time, the ball 902 is displaced to the low pressure port 903 side so as to be in the same state as the normal needle valve closed state because the movement of the fuel ejected from the high pressure port 904 toward the ball 902 via the common rail when the pump starts operating. Pressure.
[0006]
However, since the low pressure port 903 is open, the fuel from the common rail leaks from the low pressure port 903 to the fuel tank. For this reason, the upward biasing force acting on the ball 902 by the fuel from the high pressure port 904 is due to the weight of the ball 901 and the lower piston 906, the spring force of the spring 910, and the lower piston 906 while the engine is stopped. Accordingly, the compression reaction force of the fuel flowing into the hydraulic chamber 908 from the sliding portions of the pistons 906 and 907 cannot be overcome and the ball 902 fails to rise. Eventually, the common rail pressure will not rise to the required pressure value, and the engine will fail to start.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel injection device in which the common rail pressure rises smoothly at the start of pump operation and good startability is obtained.
[0008]
[Means for Solving the Problems]
  According to the first aspect of the present invention, an injector that receives supply of fuel by a common rail that stores fuel pumped from a pump is formed with an injection hole that injects fuel supplied from the common rail, and the opening and closing of the injection hole is a needle. The back pressure that switches between the back pressure chamber and the low-pressure source in either a communication state or a shut-off state, a nozzle portion that can be switched by the above, a back pressure chamber that generates the back pressure of the needle when the fuel is introduced A control unit and a drive unit for driving the back pressure control unit;
  The back pressure control unit communicates with a valve chamber interposed between the back pressure chamber and a low pressure source, a low pressure port communicating with the low pressure source and opening in a ceiling surface of the valve chamber, and a common rail. A high pressure port that opens directly under the low pressure port to the bottom surface of the valve chamber; and the low pressure port that is disposed in the valve chamber.Or the high pressure portAnd a valve body that closes,
  The drive unit is disposed in a cylinder formed vertically above the valve chamber, and a pin-like lower end projects from the low-pressure port into the valve chamber, and a piston that can press the valve body, and the piston An actuator that generates a vertical driving force for the piston,
  In the injector configured such that the valve body is displaced downward by driving by the driving unit, and the valve chamber communicates with the low pressure source via the low pressure port.
  A biasing means for generating a biasing force for constantly biasing the valve body upward;
  In the valve body, at least a contact portion with the piston of the upper portion facing the low pressure port is a flat surface, and a spring seat protruding radially outward is provided on the outer periphery, and the spring seat And a spring serving as the biasing means between the valve chamber and the bottom surface of the valve chamber,
  When the fuel pressure of the common rail is normal and the drive unit is not driving the piston, the valve body can close the low pressure port against the downward pressing force. Set to the correct force.
[0009]
  Even when the engine is stopped, the valve body is maintained in the closed state of the low pressure port by the upward biasing force of the biasing means. Therefore, when the engine is started, the fuel pressure in the back pressure chamber rises quickly together with the fuel pressure in the common rail. Thereby, startability improves.Further, by configuring the urging means with a spring interposed between the valve body and the bottom surface of the valve chamber, it is possible to easily generate an upward urging force on the valve body, and to provide its own elasticity. Therefore, the configuration is simple.
[0010]
According to a second aspect of the present invention, in the configuration of the first aspect of the invention, the back pressure control unit is configured such that the valve chamber communicates with the back pressure chamber, and the fuel at a fuel pressure in the common rail is always in the high pressure port. A three-way valve structure is introduced that closes the high-pressure port when the valve body is displaced downward.
[0011]
When the valve body opens the low-pressure port by driving by the drive unit, the valve body reaches the bottom surface of the valve chamber and is fixed, so that the valve body vibrates even if the urging force of the urging means is not so strong. There is no. Thereby, it is possible to prevent the fuel flow from the back pressure chamber to the low pressure port in the valve chamber from becoming unstable due to vibration of the valve body.
[0012]
Further, since the urging force of the urging means does not have to be so strong, the drive energy required for the drive unit to output when the valve body is displaced downward may be small, and energy consumption can be suppressed. it can.
[0013]
Further, since the vibration of the valve body is avoided, the valve body and the piston are not worn, and the life is long.
[0014]
  The invention described in claim 3In another configuration for solving the problems of the present invention, in the injector configured as described above,
A biasing means for generating a biasing force for constantly biasing the valve body upward;
The valve body is a balance piston valve having a seat diameter and a sliding portion diameter substantially the same diameter, and at least an abutting portion of the upper portion facing the low pressure port is a flat surface, and the sliding portion is A spring chamber is provided below the high-pressure port and a spring chamber is provided below the sliding portion to accommodate the spring as the biasing means.
[0015]
  In this configuration, the same effect can be obtained, and when a pressure-balanced balance piston valve is used, the force for opening the valve can be made almost zero, so that the driving energy reduction effect is great.
[0016]
  In invention of Claim 4, in the structure of Claim 1 or 2,The valve body is a substantially spherical ball valve, and the spring seatAs above, an annular member having an inner diameter smaller than the maximum diameter of the valve body is installed from below the valve body.
[0017]
  By using a substantially spherical ball valve, the valve body configuration that is disposed in the valve chamber and performs back pressure control can be easily realized.A biasing force can be stably applied to the valve body from the biasing means to the ball-shaped valve body. As the biasing means, a spring having a relatively large diameter can be selected without being influenced by the maximum diameter of the valve body, and the degree of freedom in design is widened.
[0018]
According to a fifth aspect of the present invention, in the configuration of the first to fourth aspects of the present invention, the piston is provided with an annular protrusion for aligning with a seat of another biasing means for biasing the piston downward, and In order to prevent the piston from freely moving upward, a surface for receiving the annular protrusion is formed on the main body where the cylinder is formed above the annular protrusion.
[0019]
The position where the annular protrusion abuts the surface is the mechanical upper limit of the moving range of the piston, and it is possible to prevent an unexpected shock from being applied to the actuator that drives the piston, and the valve body has a low pressure. Even when the lower end of the piston is separated from the valve body in the closed state of the port, the gap can be suppressed to a minute amount.
[0020]
According to a sixth aspect of the present invention, in the configuration of the first to fourth aspects of the present invention, the piston is provided with an annular projection for aligning with a seat of another urging means for urging the piston downward. The annular space on the outer periphery of the piston, which stores the biasing means above the protrusion, is a damper chamber that relaxes the rising speed when the piston is raised.
[0021]
In the annular space, when the piston is raised, the discharge of fuel and the like is suppressed, and the rising speed of the piston can be suitably suppressed and controlled to an appropriate speed. Thereby, the movement of the piston becomes smooth.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 1, 2 and 3 show a common rail fuel injection device for a diesel engine to which the present invention is applied. In FIG. 3 showing the overall configuration of the fuel injection device, injectors 10 corresponding to the number of cylinders of the diesel engine are provided corresponding to each cylinder (only one injector 10 is shown in the figure), and communicated via a supply line 15. The fuel is supplied from the common rail 14 that is common to the two. The fuel in the fuel tank 11 is pumped to the common rail 14 by a high-pressure supply pump 13 that is a pump and stored at a high pressure.
[0025]
The injector 10 is controlled by an ECU 17, a drive circuit 18, a pressure sensor 19 and the like. The drive circuit 18 receives a command signal from the ECU 17 and charges and discharges a piezo stack 71 (to be described later) of the injector 10, for example, from the injector 10 to the combustion chamber of each cylinder at a required time at an injection pressure substantially equal to the common rail pressure. Fuel is injected.
[0026]
The pressure sensor 19 is provided on the common rail 14 and detects the common rail pressure. Based on the detection result, the ECU 17 controls the high-pressure supply pump 13 to adjust the fuel pumping amount to the common rail 14, and the common rail pressure is detected by other sensors. Control is performed so as to obtain an appropriate injection pressure in accordance with the operating condition known by input or the like.
[0027]
The fuel supplied from the common rail 14 to the injector 10 is used not only for injection into the combustion chamber but also as a control hydraulic pressure of the injector 10 and returns to the fuel tank 11 from the injector 10 via the low-pressure drain line 16. It is supposed to be.
[0028]
The injector 10 passes through a combustion chamber wall (not shown) of the engine and is attached so that a lower end portion in FIG. 1 protrudes into the combustion chamber. A nozzle portion 101, a back pressure control portion 102, and a drive portion 103 are configured in order from the lower end portion. The The injector 10 has a rod-like body 2 and is formed with a hole for storing the parts constituting the parts 101 to 103 and a passage through which fuel flows.
[0029]
In the nozzle portion 101, a sack portion 42 is formed at the lower end 2a of the rod-like body 2, and an injection hole 43 for fuel injection is formed through the sack portion 42 forming wall. The lower end 2 a of the rod-like body 2 is also formed with a vertical hole 21 connected to the high-pressure passage 31 leading to the supply line 15 above the sack portion 42.
[0030]
A stepped nozzle needle 61 is disposed in the upper portion of the vertical hole 21 with its tip directed downward, and is slidably held by its upper large-diameter portion 612 that is the rear end portion. An annular oil reservoir chamber 41 is formed on the outer periphery of the lower small-diameter portion 611 that is the tip of the nozzle needle 61, and the oil reservoir chamber 41 is always in communication with the high-pressure passage 31 and supplied with high-pressure fuel from the common rail 14. .
[0031]
When the nozzle needle 61 is lowered, the conical lower end is seated with the step 43a at the boundary with the vertical hole 21 at the upper end of the sac part 42 as the seat part, the sac part 42 is closed, and fuel injection from the injection hole 43 is prohibited. When the fuel is injected, the fuel is raised and is separated from the stepped portion 43a of the sac portion 42 to open the sack portion 42.
[0032]
The high pressure fuel in the oil sump chamber 41 acts upward on the step surface 61a and the conical tip surface 61b of the nozzle needle 61 to urge the nozzle needle 61 in the separating direction.
[0033]
A space 53 defined by the rear end surface 61 c and the wall surface of the vertical hole 21 above the nozzle needle 61 is introduced with fuel as control oil from the high-pressure passage 31, and a back pressure chamber that generates a back pressure of the nozzle needle 61. 53. This back pressure acts downward on the nozzle needle 61 and urges the nozzle needle 61 in the seating direction together with the spring 62 housed in the back pressure chamber 53.
[0034]
The back pressure chamber 53 is always in communication with the valve chamber 55 via the out orifice 54. The valve chamber 55 has a conical ceiling surface, and the low pressure port 22 is open at the top of the ceiling surface. The low-pressure port 22 is connected to a low-pressure passage 32 communicating with the drain line 16 through a vertical hole 23 described later, and the low-pressure passage 32 via a space 56 formed on the outer periphery of a small-diameter piston 64 described later disposed in the vertical hole 23. And always in communication.
[0035]
A front end portion of a high pressure control passage 52 communicating with the high pressure passage 31 is opened at a bottom surface of the valve chamber 55 at a position directly below the low pressure port 22 to form a high pressure port 521.
[0036]
In the valve chamber 55, a valve 63 having an upper part and a lower part cut horizontally as a substantially spherical ball valve is disposed. The valve 63 is a valve body that can move up and down. At the time of ascending, the valve seat 55 is shut off from the low-pressure passage 32 by being seated on an outer peripheral portion (hereinafter referred to as a low-pressure side seat) 551 of the low-pressure port 22 on the ceiling surface as a valve seat. As a result, the back pressure chamber 53 communicates with the high pressure passage 31 via the out orifice 54, the valve chamber 55, and the high pressure control passage 52, the back pressure of the nozzle needle 61 rises, and the nozzle needle 61 is seated.
[0037]
When the valve 63 descends, the cut surface is seated on the outer peripheral portion of the high pressure port 521 (hereinafter referred to as a high pressure side seat) 552 as the valve seat, and the valve chamber 55 is shut off from the high pressure port 521. The back pressure chamber 53 communicates with the low pressure passage 32 via the out orifice 54, the valve chamber 55, and the low pressure port 22, and the back pressure of the nozzle needle 61 is lowered and the nozzle needle 61 is separated.
[0038]
A spring seat 66 as a seat is provided on the outer periphery of the valve 63. The spring seat 66 is a plate-like member formed in an annular shape whose inner diameter is slightly smaller than the diameter that is the maximum diameter of the valve 63, and is fitted to the valve 63 from below. Between the spring seat 66 and the bottom surface of the valve chamber 55, a valve spring 67, which is a biasing means having substantially the same diameter as the spring seat 66, is interposed, and the valve 63 is biased upward via the spring seat 66. Yes. By providing the spring seat 66, a urging force can be stably applied to the valve 63 from the valve spring 67. Therefore, a valve spring 67 having a relatively large diameter is selected regardless of the diameter of the valve 63. This increases the degree of freedom of design. The valve spring 67 is positioned by an annular recess 553 formed on the bottom surface of the valve chamber 55 on the outer periphery of the high-pressure side seat 552. The spring seat 66 has a shape such as an outer diameter so as not to obstruct the flow of fuel in the valve chamber 55. The spring force of the valve spring 67 will be described later.
[0039]
The back pressure control unit 102 is configured to switch the operating state when the valve 63 is pressed by the driving unit 103. The drive unit 103 has the vertical hole 23 that is a cylinder formed in the vertical direction above the valve chamber 55, and a small-diameter piston 64 that is a lower piston from the lower side in the vertical hole 23, a spring, and a spring 68, a disc spring 69, a large-diameter piston 65, and a piezo stack 71 are disposed. The upper end of the low-pressure port 22 is opened at the lower end surface of the vertical hole 23.
[0040]
The small-diameter piston 64 has a flange 643 that is an annular protrusion below the constant-diameter portion 644 that is in sliding contact with the wall surface of the vertical hole 23, and further below that is a conical portion 642 that decreases in diameter toward the lower side. Furthermore, there is a pressure pin 641 that passes through the low-pressure port 22 and faces the valve 63 to press the valve 63. The pressure pin 641 is formed to have a smaller diameter than the low pressure port 22.
[0041]
Of the space 56 on the outer periphery of the non-sliding portion of the small-diameter piston 64, it is defined by the downward annular step surface 231 of the rod-shaped body 2 that is the main body portion of the injector 10 that defines the upper end of the space 56, and the small-diameter piston flange 643. A spring 68 as another biasing means is disposed coaxially with the small-diameter piston 64 in the annular space 58. The spring 68 urges the small-diameter piston 64 downward to enhance the contact property between the valve 63 and the pressure pin 641.
[0042]
Further, the rod-like body 2 is formed with another annular step surface 232 which is a surface below the annular step surface 231, and the vertical hole 23 is expanded in diameter below the annular step surface 232. The annular step surface 232 faces the small diameter piston flange 643 in the vertical direction above it. The position where the flange 643 contacts the annular step surface 232 is the upper limit of the moving range of the small diameter piston 64.
[0043]
The large-diameter piston 65 is a circular member having a larger diameter than the small-diameter piston 64 and is slidably held in the vertical hole 23.
[0044]
The piezo stack 71 has a capacitor structure in which piezoelectric ceramic layers such as PZT and electrode layers are alternately laminated and has a capacitor structure. The piezo stack 71 is arranged at the uppermost portion of the vertical hole 23 with the stacking direction, that is, the expansion / contraction direction as the formation direction of the vertical hole 23. It is installed. A constant initial load is applied to the piezo stack 71 via the large-diameter piston 65 by a disc spring 69 provided below the large-diameter piston 65.
[0045]
Between the small-diameter piston 64 and the large-diameter piston 65 is filled with fuel as a hydraulic chamber 57, and when the piezo stack 71 extends and presses the large-diameter piston 65, the pressing force is passed through the fuel in the hydraulic chamber 57. It is transmitted to the small diameter piston 64. Here, since the small-diameter piston 64 has a smaller diameter than the large-diameter piston 65, the extension amount of the piezo stack 71 is expanded and converted into the vertical displacement of the small-diameter piston 64 (hereinafter, the hydraulic chamber is displaced and expanded as appropriate). Room). The displacement expansion chamber 57 is connected to the low pressure passage 32 via the check valve 104 so that sufficient fuel is always filled. The check valve 104 is provided with the direction from the low pressure passage 32 toward the displacement expansion chamber 57 as a forward direction. When the large-diameter piston 65 is pressed by the extension of the piezo stack 71, the check valve 104 is closed to confine the fuel in the displacement expansion chamber 57. It has become.
[0046]
The spring force of the valve spring 67 will be described. The spring force of the valve spring 67 is a downward biasing force of the valve 63 and the small-diameter piston 64, the spring 68 and the like when the common rail pressure is 0 and the piezo stack 71 is in a discharged state, that is, the driving unit 103 is not driven. On the contrary, the valve 63 is set to a spring force that can close the low pressure port 22. Here, when the common rail pressure is 0, when the valve 63 closes the low pressure port 22, when the inside of the valve chamber 55 is at a high pressure, the upward is defined by the seat diameter of the low pressure side seat 551 as described above. This is because even if this urging force is excluded, that is, even when the engine is stopped, the upward urging force with respect to the valve 63 is more dominant than the downward urging force.
[0047]
When the piezo stack 71 is contracted in a discharged state during normal operation in which fuel injection is sequentially performed, the spring force of the spring 68, the own weight of the small-diameter piston 64, and the like act downward with respect to the valve 63. However, the high pressure fuel in the valve chamber 55 is biased upward according to the size of the pressure receiving surface of the valve 63 defined by the seat diameter of the low pressure side seat 551, and the valve spring 67 The elastic force is biased upward. Therefore, the valve 63 is seated on the low pressure side seat 551 and the low pressure port 22 is closed.
[0048]
On the other hand, when the piezo stack 71 is charged and extended, the large-diameter piston 65 is pushed down. Here, the piezo stack 71 and the drive circuit 18 have a driving force that allows the driving force generated by the piezo stack 71 to displace the valve 63 downward against the fuel pressure in the valve chamber 55 and the upward biasing force of the valve spring 67. It is constituted so that it becomes. As a result, the downward urging force with respect to the valve 63 becomes dominant, the small-diameter piston 64 is pushed down, and the valve 63 is separated from the low-pressure side seat 551 and seated on the high-pressure side seat 552.
[0049]
The drive circuit 18 that charges and discharges the piezo stack 71 has a known configuration. For example, an in-vehicle battery is used as a power source, a DC-DC circuit, an inductor that limits a charge / discharge current to the piezo stack 71, and a charge in the piezo stack 71. It consists of a switch circuit etc. that controls the movement of. The charge holding period of the piezo stack 71 can be set by controlling the switch circuit and the like by a command signal from the ECU 17.
[0050]
The ECU 17 is composed of a microcomputer, for example, and outputs the command signal according to the calculated fuel injection timing and injection amount.
[0051]
At the start of fuel injection, first, the piezo stack 71 is charged to a predetermined charge amount, and the piezo stack 71 extends, whereby the pressure pin 641 descends and pushes down the valve 63. As a result, the valve 63 is separated from the low pressure side seat 551 and seated on the high pressure side seat 552, the fuel pressure in the valve chamber 55 is reduced, and the force acting on the needle 61 in the seating direction acts in the seating direction. The needle 61 is separated from the force, and fuel injection is started.
[0052]
On the contrary, when the injection is stopped, the piezo stack 71 is contracted by the discharge of the piezo stack 71 and the pushing force to the valve 63 is released. The fuel pressure in the valve chamber 55 is low on the ceiling surface side where the low pressure port 22 leading to the low pressure passage 32 opens, and high pressure fuel pressure is applied to the bottom surface of the valve 63 from the high pressure port 521. An upward fuel pressure acts on the valve 63 as a whole, and the release of the push-down force to the valve 63 causes the valve 63 to be separated from the high pressure side seat 552 and to be seated again on the low pressure side seat 551. Since the fuel pressure of 55 rises, the needle 61 is seated and the injection stops. Therefore, by setting the charge holding period of the piezo stack 71, fuel is injected from the injector 10 for a certain period corresponding to the charge holding period.
[0053]
The contact between the valve 63 and the pressure pin 641 is sufficient by the spring 68, and in response to the injection start command, the small diameter piston 64 is displaced while the valve 63 is seated on the low pressure side seat 551. Useless energy consumption is eliminated. Further, there is no time lag from when the small-diameter piston 64 starts to be displaced until it comes into contact with the valve 63, and the control accuracy of fuel injection is improved.
[0054]
When the charge holding period ends and the driving force of the piezo stack 71 is released, the small-diameter piston flange 643 rises and the volume of the annular space 58 is reduced. At this time, the fuel in the annular space 58 is discharged substantially only on the outer periphery of the small-diameter piston flange 643. Therefore, the annular space 58 functions as a damper chamber that relaxes the rising speed of the small-diameter piston 64. 64 is controlled to an appropriate speed. The displacement of the small diameter piston 64 becomes smooth.
[0055]
Further, since the upper limit of the displacement of the small-diameter piston 64 is defined by the annular step surface 232 that receives the flange 643, it is possible to prevent an unexpected impact from being applied to the piezo stack 71 and the like, and the valve 63 Even if the pressure pin 641 moves away from the valve 63 in the state where it is seated on the low pressure side seat 551, the gap is kept to a very small amount, and the influence of the small diameter piston 64 on the pressing start timing of the valve 63 is affected. Can be suppressed.
[0056]
Now, an operation when the ignition switch is turned on and the engine is started will be described. If the engine stop state continues, the common rail pressure is zero, and the fuel pressure in the valve chamber 55 is also substantially zero. As described above, the valve spring 67 is set to a resilient force that can resist the downward force of the valve 63 and the small-diameter piston 64 and the spring 68 when the resilient force is in the engine stop state. 63 does not separate from the low-pressure side seat 551. Therefore, when the operation of the high-pressure supply pump 13 is started, the shut-off state between the back pressure chamber 53 and the low pressure port 22 is maintained. Thereby, both the fuel pressure in the back pressure chamber 53 and the common rail pressure rise quickly.
[0057]
In addition, in the present embodiment, the back pressure control unit 102 has a three-way valve structure in which the back pressure chamber 53 communicates with either the low pressure port 22 or the high pressure port 521. Therefore, during normal operation, the piezo stack 71 is charged. When the valve 63 opens the low-pressure port 22, the valve 63 reaches the bottom surface of the valve chamber 55 and is fixed. Therefore, even if the spring force of the valve spring 67 is not so strong, the valve 63 does not vibrate with the pressure pin 641. As a result, the fuel flow from the back pressure chamber 53 toward the low pressure port 22 in the valve chamber 55 can be prevented from becoming unstable due to the vibration of the valve 63.
[0058]
Further, since the resilient force of the valve spring 67 does not have to be so strong, the drive energy required to be output by the drive unit 103 when the valve 63 is displaced downward may be small, and energy consumption is suppressed. be able to.
[0059]
Further, since the vibration of the valve 63 is avoided, the valve 63 and the small-diameter piston 64 are not worn, and the life is long.
[0060]
Further, in the configuration in which the downward biasing force is always applied from the spring to the small-diameter piston as in the present embodiment, the contact property between the valve and the small-diameter piston is improved, while FIG. As described above, the lower piston, which is a small-diameter piston, is pushed down by the spring while the engine is stopped, and acts in a direction that further prevents the valve from moving upward. In contrast, in the present embodiment, since the valve spring is provided, it is possible to prevent the upward displacement of the valve from being hindered, so that the contact property between the valve and the small-diameter piston is improved and the startability is improved. And both.
[0061]
In addition, even in an injector in which the spring for biasing the small-diameter piston downward is omitted, the small-diameter piston tends to descend by its own weight when the engine is stopped, so that the startability can be improved by providing a valve spring. it can. In this case, a small amount of spring force is sufficient for the valve spring because there is no spring for urging the valve downward.
[0064]
In this embodiment, the ball valve is used as the valve body of the back pressure control unit. However, the valve body structure is not limited to the ball valve, and other structures may be used. This embodiment is shown next.
[0065]
A second embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 4, the basic configuration of the injector of the present embodiment and the fuel injection device to which the injector is applied is the same as that of the first embodiment, and the differences will be mainly described below. In the first embodiment, the ball-shaped valve 63 is used as the valve body of the back pressure control unit 102. However, in this embodiment, the valve 72, which is a balance piston valve having a seat diameter and a sliding portion diameter that are substantially the same diameter, is used. Use. Further, in order to accommodate the valve 72, a vertical hole 24 is provided following the high pressure port 521 on the bottom surface of the valve chamber 55.
[0066]
In FIG. 5, the valve 72 has a piston shape, and has a small-diameter portion 722 that penetrates the high-pressure port 521 below the large-diameter valve portion 721 disposed in the valve chamber 55. A guide portion 723 is provided as a sliding portion that is in sliding contact with the 24 wall surfaces. The valve chamber 55 has a low-pressure port 22 and a high-pressure port 521 each having a diameter substantially the same as the diameter of the vertical hole 24 at the center portion of the ceiling surface and bottom surface which are horizontal surfaces. The valve portion 721 has a flat top surface 721a seated on the low-pressure side seat 551 at the outer peripheral portion of the low-pressure port 22, shuts off the valve chamber 55 and the low-pressure passage 32, and expands from the small diameter portion 722 upward. The conical portion 721 b is seated on the high-pressure side seat 552 on the outer peripheral portion of the high-pressure port 521 and blocks the valve chamber 55 from the high-pressure port 521.
[0067]
The tip of the high-pressure control passage 52 communicating with the high-pressure passage 31 is opened in the annular space formed around the small-diameter portion 722 of the valve 72 immediately below the high-pressure port 521, and high-pressure fuel is supplied from the common rail 14. ing.
[0068]
Inside the vertical hole 24 below the guide portion 723 of the valve 72 is a spring chamber 731 for accommodating the valve spring 73, and the valve 72 is urged upward by the valve spring 73. Note that the spring chamber 731 communicates with the low-pressure passage 32 via the communication passage 732 so as to be a closed chamber and no damper force is generated. Thereby, since the downward movement of the valve 72 is not suppressed, the valve portion 721 is quickly separated from the low-pressure side seat 551 at the start of injection.
[0069]
The spring force of the valve spring 73 will be described. Also in this embodiment, the resilient force of the valve spring 73 is set to a spring force that allows the valve 72 to close the low-pressure port 22 when the common rail pressure is 0 and the drive unit 103 is in a non-driven state. That is, when the piezo stack 71 is contracted, the elastic force of the spring 68 for bringing the small-diameter piston 64 into contact with the valve 72 or the own weight of the small-diameter piston 64 acts downward with respect to the valve 72. However, by making the spring force of the valve spring 73 larger than the downward urging force, the valve portion 721 can be seated on the low pressure side seat 551 and the low pressure port 22 can be closed even when the engine is stopped. It becomes possible.
[0070]
Further, in the present embodiment, the diameter of the low pressure side seat 551 (low pressure seat diameter) that shuts off the valve chamber 55 and the low pressure passage 32 and the diameter of the high pressure side seat 552 that shuts off the valve chamber 55 and the high pressure passage 31 (high pressure). Sheet diameter) and the diameter (guide diameter) of the vertical hole 24 in which the guide portion 723 of the valve 72 slides are substantially the same diameter. Therefore, in the state where the valve portion 721 of the valve 72 closes the low pressure port 22, The force with which the high-pressure fuel in the chamber 55 biases the valve portion 721 of the valve 72 upward and the force with which the guide portion 723 is biased downward are substantially balanced. Therefore, it is possible to reduce the driving force required to push down the valve portion 721 of the valve 72 and separate the seat from the low-pressure side seat 551 during fuel injection.
[0071]
In practice, however, the diameter of the low pressure side seat 551 (the diameter of the low pressure seat) is set to the diameter of the vertical hole 24 in which the guide portion 723 slides in order to reliably shut off the valve chamber 55 and the low pressure passage 32 during non-injection. It is better to make it slightly larger than (guide diameter). At this time, upward biasing force acting on the valve 72 (= (π / 4) · {(low-pressure seat diameter))²-(Guide diameter)²} × pressure of high pressure fuel + elastic force of valve spring 73) is larger than downward urging force such as elastic force of spring 68 of small diameter piston 64, so valve portion 721 is seated on low pressure side seat 551. The state can be maintained.
[0072]
Further, the diameter of the high-pressure side seat 552 (high-pressure seat diameter) is slightly larger than the diameter of the vertical hole 24 (guide diameter) through which the guide portion 723 slides so as to ensure the return force of the valve 72 at the end of injection. is there. At this time, in a state where the valve portion 721 is seated on the high-pressure side seat 552, the force by which the high-pressure fuel in the high-pressure port 521 pushes up the valve portion 721 becomes dominant over the force pushing the guide portion 723 down. Separate from the high-pressure side sheet 552.
[0073]
The operation of the present embodiment is the same as that of the first embodiment. At the start of fuel injection, the piezo stack 71 extends and pushes down the large-diameter piston 65, thereby increasing the pressure in the displacement expansion chamber 57 and causing the small-diameter piston 64 to move. The valve 72 is pushed down. Then, the valve portion 721 of the valve 72 is separated from the low pressure side seat 551 and then seated on the high pressure side seat 552, and the fuel pressure in the valve chamber 55 is reduced. As a result, the fuel in the back pressure chamber 53 escapes to the low pressure passage 32 via the out orifice 54, the valve chamber 55, and the low pressure port 22, so that the back pressure is lowered and the nozzle needle 61 is separated, and fuel injection is performed. Made.
[0074]
Conversely, when the piezo stack 71 contracts and the pressing force to the valve 72 is released, the upward biasing force of the valve spring 73 and the high fuel pressure of the high pressure port 521 acting upward on the valve portion 721 The valve portion 721 is separated from the high pressure side seat 552 and then seated on the low pressure side seat 551. Accordingly, high pressure fuel from the valve chamber 55 flows into the back pressure chamber 53 through the out orifice 54, and high pressure fuel from the high pressure passage 31 flows into the back pressure chamber 53 through the in orifice 51, and the back pressure chamber. Since the pressure of 53 rises, the needle 61 is seated and injection stops.
[0075]
Also in this embodiment, as in the first embodiment, the valve spring 73 is provided, so that the valve 72 is seated on the low pressure side seat 551 even when no high pressure is applied. It is possible to prevent the pumped fuel from leaking to the low pressure side. Therefore, it is possible to improve both the contact property between the valve 72 and the small diameter piston 64 and the startability.
[0076]
In this embodiment, a pressure balance type three-way valve structure is adopted, and the low pressure seat diameter, the high pressure seat diameter, and the guide diameter are substantially the same. Therefore, the valve 72 is in a pressure balance state, and the force necessary for opening the valve is obtained. Can be almost zero. Therefore, the driving energy can be further reduced as compared with the structure using the ball valve as in the first embodiment.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an injector according to a first embodiment to which the present invention is applied.
FIG. 2 is an enlarged cross-sectional view of the injector of the first embodiment.
FIG. 3 is a configuration diagram of a fuel injection device including the injector according to the first embodiment.
FIG. 4 is a cross-sectional view of an injector according to a second embodiment to which the present invention is applied.
FIG. 5 is an enlarged cross-sectional view of an injector according to a second embodiment.
FIG. 6 is a partial cross-sectional view of a conventional injector.
[Explanation of symbols]
10 Injector
101 Nozzle
102 Back pressure control unit
103 Piezo actuator (drive unit)
11 Fuel tank (low pressure source)
13 High-pressure supply pump (pump)
14 Common rail
22 Low pressure port
232 Annular step surface
41 Oil sump chamber
43 nozzle hole
521 High pressure port
53 Back pressure chamber
55 Valve chamber
58 Annular space
61 Nozzle needle (needle)
63 Valve (Valve)
64 Small-diameter piston (piston)
641 Pressure pin (lower end)
66 Spring seat (annular member)
67 Valve spring (biasing means)
68 Spring (another biasing means)
71 Piezo stack
72 Valve
721 Valve
722 Small diameter part
723 Guide part (sliding part)
73 Valve spring (biasing means)
731 Spring chamber

Claims (6)

An injector that receives supply of fuel by a common rail that stores fuel pumped from the pump, and has a nozzle portion that injects fuel supplied from the common rail, the nozzle portion being openable and closable by a needle; and A back pressure chamber in which the fuel is introduced to generate a back pressure of the needle, a back pressure control unit that switches between the back pressure chamber and the low pressure source between the communication state and the cutoff state, and the back pressure control A drive unit for driving the unit,
The back pressure control unit communicates with a valve chamber interposed between the back pressure chamber and a low pressure source, a low pressure port communicating with the low pressure source and opening in a ceiling surface of the valve chamber, and a common rail. A high pressure port that opens to the bottom surface of the valve chamber directly under the low pressure port, and a valve body that is disposed in the valve chamber and closes the low pressure port or the high pressure port ,
The drive unit is disposed in a cylinder formed vertically above the valve chamber, and a pin-like lower end projects from the low-pressure port into the valve chamber, and a piston that can press the valve body, and the piston An actuator that generates a vertical driving force for the piston,
In the injector configured such that the valve body is displaced downward by driving by the driving unit, and the valve chamber communicates with the low pressure source via the low pressure port.
A biasing means for generating a biasing force for constantly biasing the valve body upward;
In the valve body, at least a contact portion with the piston of the upper portion facing the low pressure port is a flat surface, and a spring seat protruding radially outward is provided on the outer periphery, and the spring seat And a spring serving as the biasing means between the valve chamber and the bottom surface of the valve chamber,
When the fuel pressure of the common rail is normal and the drive unit is not driving the piston, the valve body can close the low pressure port against the downward pressing force. Injector characterized by the fact that it is set to a strong force.   2. The injector according to claim 1, wherein the back pressure control unit is configured such that the valve chamber communicates with the back pressure chamber, fuel at a fuel pressure in a common rail is constantly introduced into the high pressure port, and the valve body is displaced downward. An injector with a three-way valve structure that sometimes closes the high-pressure port. An injector that receives fuel supplied by a common rail that stores fuel pumped from a pump, and has a nozzle portion that injects fuel supplied from the common rail, and a nozzle portion that can be opened and closed by a needle; and A back pressure chamber in which the fuel is introduced to generate a back pressure of the needle, a back pressure control unit that switches between the back pressure chamber and the low pressure source between the communication state and the cutoff state, and the back pressure control A drive unit for driving the unit,
  The back pressure control unit communicates with a valve chamber interposed between the back pressure chamber and a low pressure source, a low pressure port communicating with the low pressure source and opening in a ceiling surface of the valve chamber, and a common rail. A high pressure port that opens to the bottom surface of the valve chamber directly under the low pressure port, and a valve body that is disposed in the valve chamber and closes the low pressure port or the high pressure port,
  The drive unit is disposed in a cylinder formed vertically above the valve chamber, and a pin-like lower end projects from the low-pressure port into the valve chamber, and a piston that can press the valve body, and the piston An actuator that generates a vertical driving force for the piston,
  In the injector configured such that the valve body is displaced downward by driving by the driving unit, and the valve chamber communicates with the low pressure source via the low pressure port.
  A biasing means for generating a biasing force for constantly biasing the valve body upward;
  The valve body is a balance piston valve whose seat diameter and sliding part diameter are substantially the same diameter, and at least the abutting part of the upper part facing the low pressure port is a flat surface,
  The sliding part is disposed below the high-pressure port, and a spring chamber is provided below the sliding part to accommodate a spring as the urging means,
  When the fuel pressure of the common rail is normal and the drive unit is not driving the piston, the valve body can close the low pressure port against the downward pressing force. Injector characterized by the fact that it is set to a strong force. 3. The injector according to claim 1, wherein the valve body is a substantially spherical ball valve, and an annular member having an inner diameter smaller than the maximum diameter of the valve body is installed from below the valve body as the spring seat. An injector characterized by   5. The injector according to claim 1, wherein the piston is provided with an annular projecting portion to be used as a seat of another urging means that urges the piston downward, and the piston freely moves upward. An injector in which a surface for receiving the annular protrusion is formed above the annular protrusion in the main body where the cylinder is formed in order to suppress movement.   5. The injector according to claim 1, wherein the piston is provided with an annular projecting portion that serves as a seat for another urging means that urges the piston downward, and the attaching portion is provided above the annular projecting portion. An injector in which the annular space on the outer periphery of the piston, which stores the biasing means, is a damper chamber that relaxes the rising speed when the piston is raised.

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