JP3864764B2 - Fuel injection valve - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection valve for an internal combustion engine that controls fuel injection by operating a control valve using an actuator.
[0002]
[Prior art]
One common fuel injection system for internal combustion engines is a common rail fuel injection system that uses a common rail (accumulation chamber) common to each cylinder. In a common rail fuel injection system, high pressure fuel pumped from a high pressure pump is accumulated in a common rail, and fuel is injected by driving a fuel injection valve corresponding to each cylinder at a predetermined injection timing. The fuel injection valve is configured to open and close the nozzle hole, for example, by controlling the back pressure of the nozzle needle with a hydraulic control valve. In particular, the fuel injection valve has recently been driven by a piezo actuator with good response. Have been proposed (for example, JP-A-2001-41125).
[0003]
Such a fuel injection valve includes a pump chamber whose pressure increases and decreases as the piezo actuator expands and contracts, and an operating piston that slides in the cylinder in response to the pressure. The operating piston increases and decreases the back pressure of the nozzle needle. The control valve is driven. The control valve selectively closes one of the high-pressure port communicating with the common rail and the low-pressure port communicating with the drain passage so that the pressure in the back pressure chamber that applies the valve closing force to the nozzle needle is high or low. That is, when the low pressure port is opened and the high pressure port is closed, the pressure in the back pressure chamber is reduced and fuel is injected. When the injection is stopped, if the high pressure port is opened and the low pressure port is closed, the pressure in the back pressure chamber rises, the nozzle needle descends, and the injection hole is closed.
[0004]
As shown in FIG. 4, the control valve includes, for example, a ball valve 104 for opening and closing these ports in a valve chamber 103 in which the high pressure port 101 and the low pressure port 102 are opened. In a state where the piezo actuator is contracted, the high pressure fuel flowing from the high pressure port 101 presses the ball valve 104 against the low pressure port 102, extends the piezo actuator, and when the pump chamber 105 exceeds a predetermined pressure, the operating piston 106 descends and pushes the ball valve 104 down. As a result, the fuel in the valve chamber 103 flows out from the low pressure port 102 to the low pressure passage 107, so that the pressure in the back pressure chamber communicating with the valve chamber 103 via the orifice 108 decreases, and the nozzle needle starts to lift. .
[0005]
[Problems to be solved by the invention]
However, at the same time as the working piston 106 starts moving, the ball valve 104 is separated and the fuel flows out from the low pressure port 102, so that the jet force impedes the movement of the working piston 106 that pushes down the ball valve 104. Act on. Furthermore, since the high-pressure fuel continues to flow during the injection period, the pressure in the spill chamber 109 following the low-pressure port 102 rises, acting in a direction that hinders the holding of the working piston position. Therefore, in order to operate the fuel injection valve normally in the piezo actuator, it is necessary to input extra energy corresponding to these acting forces. As a result, there has been a problem that the drive device becomes large and the cost increases.
[0006]
It is an object of the present invention to reduce the required drive energy of an actuator that drives an operating piston in a fuel injection valve configured to open and close the control valve with the operating piston, thereby enabling downsizing and cost reduction of the driving device. is there.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a fuel injection valve comprising: an operating piston driven by an actuator; a control chamber that applies hydraulic pressure to a nozzle needle; and a control valve that increases or decreases the pressure in the control chamber. The nozzle needle is raised and lowered as the valve body is driven to open and close. The control valve houses the valve body in a valve chamber having a high pressure port communicating with the high pressure passage and a low pressure port communicating with the low pressure passage, and the valve body opens the low pressure port when energy is supplied to the actuator. The high pressure port is opened and closed, and when the energy is released, the high pressure port is opened and the low pressure port is closed. Then, the working piston, accommodated in the low pressure spill chamber continuous to said low pressure port, the connection end between the spill chamber, as the passage area of the low pressure port to expand toward the spill chamber side Forming the working piston and the low pressure port.
Specifically, the connection end of the low-pressure port to the spill chamber is a taper that expands in a tapered shape toward the spill chamber, and the tip of the working piston inserted into the low-pressure port is When the rod portion has a small diameter, the passage area can be easily enlarged.
[0008]
According to the above arrangement, since the passage area in the connection portion of the low pressure port and the spill chamber is expanded, and at the same time slow down the jet for jetting to said spill chamber, peeling, by generating eddy losses, jet energy Can be reduced .
[0010]
At this time , the radius of the low pressure port is r ₁ , the radius of the rod portion of the working piston is r ₂ , the passage area of the low pressure port is A _1, and the distance L from the proximal end portion in the flow direction of the taper portion. ₁ is defined by equation (1).
A ₁ = π · {(r ₁ ) ² − (r ₂ ) ² } = π · (L ₁ ) ² (1)
A _L1 / A ₁ ≧ 2.5 (2)
The enlargement ratio A _L1 / A ₁ of the passage area represented by the ratio of the passage area A ₁ of the passage area A _L1 and the low pressure port in the distance L ₁ is, when formed so as to satisfy equation (2), The effect of reducing the energy of the jet ejected from the low-pressure passage is high. Therefore, the acting force on the operating piston can be reduced, and the energy required for the valve element to open the low pressure port is reduced. Miniaturization and cost reduction are possible.
[0011]
As claim 2, the connection direction of the low-pressure passage connected to the spill chamber, providing thereby substantially coincident with the flow direction of the jet, the jet is directed into the low-pressure path by said communication passage. Accordingly, the fuel in the spill chamber is quickly discharged, the fuel pressure in the spill chamber acting on the operating piston is relieved, and the drive energy of the actuator required to maintain the open position of the low pressure port is reduced. can do.
[0012]
According to a third aspect of the present invention, there is provided a fuel injection valve provided with a control valve having a similar configuration, wherein the operating piston is housed in a low-pressure spill chamber continuous with the low-pressure port. A blocking wall is formed in the chamber for blocking between the flow jetted from the low pressure port to the spill chamber and the pressure receiving surface of the working piston. The blocking wall is fixed to a housing that forms the spill chamber, and is provided separately from the operating piston.
[0013]
By providing the blocking wall, it is possible to prevent the jet flow ejected from the low pressure passage from directly acting on the pressure receiving surface of the working piston. Therefore, since the energy required to drive the operating piston to open the low pressure port and maintain its position is reduced, the required drive energy of the actuator can be reduced, and the device can be reduced in size and weight. The same effect can be obtained for cost reduction.
[0014]
As in claim 4, the piston member having a larger diameter than the working piston which is driven by the actuator, the increase or decrease the hydraulic providing a pump chamber for driving the working piston by the displacement of the piston member, the actuator Therefore, a more compact and highly efficient fuel injection valve can be obtained.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1A is a diagram showing an overall configuration of a fuel injection valve 1 to which the present invention is applied. For example, the fuel injection valve 1 is suitably used in a common rail injection system of a diesel engine. The fuel injection valve 1 starts and stops fuel injection by opening and closing a nozzle hole 11 provided at the tip (lower end in the figure) of the nozzle body B by the vertical movement of the nozzle needle 12. The operation is controlled by. The nozzle hole 11 is opened when the nozzle needle 12 is at the upper end position, and is connected to the fuel reservoir 31 following the high pressure passage 3 to supply fuel, while being closed at the lower end position where the nozzle needle 12 is seated on the nozzle seat 13. Thus, the connection with the fuel reservoir 31 is cut off, and the fuel supply is stopped.
[0016]
The high-pressure passage 3 extends upward from the fuel reservoir 31 and communicates with an external common rail (not shown) through a housing H that is oil-tightly fixed to the nozzle body B. In the housing H, a drain passage 2 is formed as a low-pressure passage communicating with an external fuel tank (not shown). Above the nozzle needle 12, a control chamber 4 is formed at the abutting portion of the nozzle body B and the housing H. The nozzle needle 12 is driven by the spring force of the spring 41 disposed in the control chamber 4 and the hydraulic pressure of the control chamber 4. Always energized in the closing direction (downward).
[0017]
The hydraulic pressure in the control chamber 4 is controlled by a three-way valve 5 as a control valve. The three-way valve 5 has a substantially spherical valve body 52 disposed in a valve chamber 51 formed in the housing H, and the valve chamber 51 is always in communication with the control chamber 4 via the main orifice 42. The valve chamber 51 has a drain port 21 that is a low-pressure port on the top surface and a high-pressure port 32 on the bottom surface, and the valve body 52 in the valve chamber 51 moves upward or downward so that one of the two ports is Is selectively closed, the other is opened and connected to the control chamber 4. The drain port 21 communicates with the drain passage 2 via a spill chamber 22 provided above the valve chamber 51, and the high pressure port 32 communicates with the high pressure fuel passage 3.
[0018]
Therefore, when the valve body 52 opens the drain port 21 and closes the high pressure port 32, the fuel in the control chamber 4 flows out from the valve chamber 51 through the drain port 21. As a result, when the pressure in the control chamber 4 decreases and becomes equal to or lower than the valve opening pressure of the nozzle needle 12, the nozzle needle 12 moves away from the nozzle seat 13 and fuel is injected. On the other hand, when the valve body 52 opens the high pressure port 32 and closes the drain port 21, the pressure in the control chamber 4 is increased by the fuel flowing in from the high pressure port 32, and the nozzle needle 12 is lowered and seated on the nozzle seat 13.
[0019]
The control chamber 4 is always in communication with the high-pressure passage 3 without the three-way valve 5 by the sub-orifice 43 provided in communication with the lower end of the high-pressure port 32. The sub-orifice 43 has the effect of promptly closing the nozzle needle 12 by promoting the pressure rise at the end of injection by allowing fuel to flow from the high-pressure passage 3 through the sub-orifice 43 into the control chamber 4.
[0020]
Here, the top surface of the valve chamber 51 on the drain port 21 side forms a conical drain seat 53, and the bottom surface of the valve chamber 51 on the high pressure port 32 side forms a flat high pressure sheet 54. Yes. The reason why one side is made flat is to allow the axial displacement of the valve body 52. The valve body 52 closes the corresponding port by sitting on one of the seats 53, 54, but the pressure of the valve chamber 51 is always higher than the pressure of the drain port 21, so the valve body 52 is seated on the drain seat 53. What you are doing is normal.
[0021]
A piezoelectric actuator 14 serving as a driving source is accommodated in the upper end portion of the housing H, and a large-diameter piston 15 that is a large-diameter piston member is integrally provided in contact with the lower end. The piezo actuator 14 has a known configuration formed by laminating piezoelectric materials such as PZT, and is expanded by supplying energy from an external driving device D, and contracted by releasing injected energy, and has a large diameter. The piston 15 is driven. Below the large-diameter piston 15, a piezo pump chamber 16 filled with hydraulic oil and a small-diameter working piston 17 are arranged coaxially in this order, and the displacement of the large-diameter piston 15 is enlarged and transmitted to the working piston 17. To do. The displacement enlargement ratio at this time is determined according to the difference in diameter between the pistons 15 and 17. The large-diameter piston 15 is biased upward by a spring 18 accommodated in the piezo pump chamber 16 and can be displaced integrally with the piezo actuator 14.
[0022]
As shown in FIG. 1B, the working piston 17 has an upper half portion as a sliding portion, and a conical lower half portion is located in the spill chamber 22 following the drain port 21. The distal end portion of the working piston 17 is a small-diameter rod portion 17 a, and this rod portion 17 a is inserted into the drain port 21 and abuts on the valve body 52 in the valve chamber 51. A connection end portion (upper end portion) of the drain port 21 to the spill chamber 22 is a tapered portion 21 a that increases in diameter toward the spill chamber 22. The inclination of the taper surface is set so that the passage area of the drain port 21 in the taper portion 21a rapidly expands, the speed of the flow ejected from the drain port 21 is reduced, and the jet energy is reduced.
[0023]
Specifically, as shown in FIG. 2B, the drain port 21 has a radius r ₁ , the radius of the rod portion 17a of the operating piston 17 is r ₂ , and the passage area of the drain port 21 is A _1. When the distance L ₁ from the base end portion (left end portion in the figure) 6c in the flow direction of the taper portion 21a is defined by the following formula (1), the passage area A _L1 at the distance L _{1 and} the passage area of the low-pressure port magnification a _L1 / a ₁ of the passage area represented by the ratio of a ₁ is to satisfy the following expression (2).
A ₁ = π · {(r ₁ ) ² − (r ₂ ) ² } = π · (L ₁ ) ² (1)
A _L1 / A ₁ ≧ 2.5 (2)
[0024]
The above equation (2) is derived as follows. In a circular spreading tube as shown in FIG. 2 (a), it is generally known that the spreading angle θ is 8 ° to 10 °, and separation of the flow from the wall surface occurs. The loss head h is represented by the following formula (3):
h∝ξ [1- (A ₁ / A ₂ )] ² (3)
In order to increase the loss head h, [1- (A ₁ / A ₂ )] ² or the coefficient ξ may be increased. In order to increase [1− (A ₁ / A ₂ )] ² , the passage area ratio, that is, the passage area A ₂ on the outlet side may be increased within a designable range with respect to the passage area A ₁ on the inlet side. . Further, it is known that the coefficient ξ has a substantially maximum value when the spread angle θ is 60 ° or more. Here, the passage area expansion rate A _L1 / A ₁ at the distance L ₁ (= r ₁ , r ₂ = 0) when θ = 60 ° is expressed by the following formula (4).
A _L1 / A ₁ = {r ₁ (1 + tan 30 °) / r ₁ } ² ≈2.5 (4)
[0025]
Therefore, if the passage area enlargement ratio A _L1 / A ₁ is 2.5 or more, peeling and vortex loss in the tapered portion 21a can be increased, and jet energy can be reduced. Therefore, it was applied to the configuration of FIG. 1 (b), so as to satisfy the above formula (2), the shape of the members, i.e., the radius r ₁ of the drain port 21, the radius r ₂ of the rod portion 17a, What is necessary is just to determine the inclination etc. of the taper part 21a.
[0026]
At this time, as shown in FIG. 1B, the jet flow 6a ejected into the spill chamber 22 through the taper portion 21a is changed in direction at the base end portion 6c, is directed obliquely upward, and is discharged from the low pressure passage 2. The low-pressure passage 2 is preferably connected to the spill chamber 22 so as to substantially coincide with the flow direction of the jet 6 a in the spill chamber 22. Thereby, it is possible to quickly discharge the jet 6a and suppress the pressure in the spill chamber 22 from increasing. The conventional fuel injection valve shown in FIG. 4 has a constant passage area ratio, so the above effect cannot be expected.
[0027]
The operation of the fuel injection valve 1 having the above configuration will be described. At the start of fuel injection, a voltage sufficient to open the drain port 21 and close the high-pressure port 32 is applied to the piezoelectric actuator 14. The piezo actuator 14 generates a displacement proportional to the voltage, moves the large-diameter piston 15 downward by the same displacement amount, and increases the hydraulic pressure of the piezo pump chamber 16. Due to the increase in the hydraulic pressure of the piezo pump chamber 16, the operating piston 17 is lowered, the valve body 52 is pushed down from the drain seat 53 and lifted, and is seated on the high-pressure seat 54. At this time, the lift of the valve body 52 is expanded by an amount corresponding to the pressure receiving area ratio of the large-diameter piston 15 and the working piston 17 with respect to the displacement of the piezoelectric actuator 14.
[0028]
As the valve body 52 is lifted, the drain port 21 opens and then the high-pressure port 32 closes, so the pressure in the valve chamber 51 decreases. When the pressure of the control chamber 4 communicating with the valve chamber 51 decreases and the oil pressure of the fuel reservoir 31 acting upward on the nozzle needle 12 exceeds the oil pressure of the control chamber 4 and the spring force of the spring 41, the nozzle needle 12 Lifts from the nozzle sheet 13 and fuel injection is started.
[0029]
Here, when the valve body 52 opens the drain port 21, the fuel in the valve chamber 51 is ejected to the spill chamber 22 through the drain port 21, but the passage area of the drain port 21 is rapidly expanded by the tapered portion 21a. At the same time as the speed of the jet 6a is reduced, the jet 6a is separated from the wall surface, and a vortex 6b is generated around it. For this reason, the energy of the jet 6a which prevents operation | movement of the action | operation piston 17 falls significantly, and the upward force which acts on the action | operation piston 17 reduces. Further, the jet 6a is directed obliquely outward along the inclination of the tapered portion 21a and flows out of the low pressure passage 2. However, since the connection direction of the low pressure passage 2 is substantially coincident with the flow direction of the jet 6a, the jet 6a Is discharged promptly. For this reason, an increase in the pressure of the spill chamber 22 is mitigated, and the pressure of the spill chamber 22 is prevented from acting upward on the working piston 17.
[0030]
When stopping the fuel injection, the voltage of the piezoelectric actuator 14 is made zero by releasing the electric charge of the piezoelectric actuator 14. During this time, the piezo actuator 14 contracts by the amount of displacement at the time of voltage application and returns to its original length, and the large-diameter piston 15 is raised by being biased by the spring 18. Along with this, the hydraulic pressure of the piezo pump chamber 16 decreases, and the operating piston 17 loses the force to press the valve body 52 against the high pressure of the high pressure port 32 against the high pressure seat 54 and rises together with the valve body 52.
[0031]
When the valve body 52 is seated on the drain seat 53 again and the lift position returns to the initial state, the high pressure port 32 is opened, and then the drain port 21 is closed, so that the pressure in the valve chamber 51 and the control chamber 4 is restored. . When the pressure in the control chamber 4 rises and the force acting downward on the nozzle needle 12 exceeds the oil pressure in the fuel reservoir 31, the nozzle needle 12 descends and seats on the nozzle seat 13 again to stop fuel injection. .
[0032]
As described above, in the configuration of the present embodiment, during the fuel injection, the valve body 52 opens the drain port 21 and further reduces the drive energy of the piezo actuator 14 required to hold the closed position of the high-pressure port 32. Therefore, it is possible to reduce the size and cost of the apparatus.
[0033]
FIG. 3A shows a second embodiment of the present invention. The basic configuration of the present embodiment is substantially the same as that of the first embodiment, and is different in that a blocking wall 7 is provided in the spill chamber 22 instead of changing the shape of the drain port 21. Yes. The blocking wall 7 is installed so as to partition the spill chamber 22 in the vertical direction, and protects the pressure receiving surface 17b of the working piston 17 located above the blocking wall 7. The rod portion 17 a passes through a through hole 71 provided in the center of the blocking wall 7 and reaches the drain port 21. The upper and lower chambers of the spill chamber 22 partitioned by the blocking wall 7 communicate with the low-pressure passages 23 and 24, respectively.
[0034]
Here, the pressure receiving surface 17b of the operating piston 17 indicates a bottom surface of the sliding portion of the operating piston 17 and a tapered surface that decreases in diameter from the bottom surface to the rod portion 17a. The clearance between the rod portion 17a and the through hole 71 at the center of the blocking wall 7 is set to a clearance that does not prevent the rod portion 17a from moving up and down and can prevent the intrusion of the jet.
[0035]
In the above configuration, when the valve body 52 opens the drain port 21, the fuel in the valve chamber 51 is ejected to the spill chamber 22 through the drain port 21, but the blocking wall 7 is provided so as to protect the pressure receiving surface 17b of the working piston. Since the jet 6 a is disposed, the jet 6 a collides with the blocking wall 7 to change the flow direction and is discharged from the low-pressure passage 24. For this reason, since it is possible to prevent the jet 6a from acting directly on the operating piston 17, the same effect of reducing the driving energy required for the piezo actuator 14 can be obtained, and the apparatus can be reduced in size and cost.
[0036]
In addition, as shown in FIG. 3B, the configuration of the first embodiment and the second embodiment is combined, and the connection end of the drain port 21 to the spill chamber 22 is a tapered portion 21a. Of course, the blocking wall 7 can be disposed in the spill chamber 22. As a result, the jet energy can be reduced and the pressure receiving surface 17b of the operating piston 17 can be protected by the blocking wall 7. Therefore, the upward acting force on the operating piston 17 can be reduced, and the driving energy of the piezo actuator 14 can be reduced. The effect to do becomes higher.
[0037]
In the above embodiment, the piezoelectric actuator is used. However, the present invention is not limited to this, and any actuator may be used as long as the actuator generates a displacement by energization, such as a magnetostrictive actuator using a magnetostrictive element. Further, it is not necessary to use a three-way valve as the control valve, and a configuration in which the nozzle needle is opened and closed by another method such as a two-way valve may be used.
[Brief description of the drawings]
1A and 1B show a first embodiment of the present invention, in which FIG. 1A is a cross-sectional view showing an overall configuration of a fuel injection valve, and FIG.
FIGS. 2A and 2B are diagrams for explaining a method of setting a passage area at a connection end of a drain port. FIGS.
3A is an enlarged cross-sectional view of the main part of the fuel injection valve in the second embodiment, and FIG. 3B is an enlarged cross-sectional view of the main part of the fuel injection valve in which the configurations of the first and second embodiments are combined. FIG.
FIG. 4 is an enlarged cross-sectional view of a main part of a conventional fuel injection valve.
[Explanation of symbols]
H Housing B Valve body 1 Fuel injection valve 11 Injection hole 12 Nozzle needle 13 Nozzle seat 14 Piezo actuator (actuator)
15 Large diameter piston (piston member)
16 Piezo pump room (pump room)
17 Working piston 2 Drain passage (low pressure passage)
21 Drain port 22 Spill chamber 3 High pressure passage 31 Fuel reservoir 32 High pressure port 4 Control chamber 5 Three-way valve (control valve)
51 Valve chamber 52 Valve body 53 Drain seat 54 High pressure seat 6a Jet 7 Shut-off wall

Claims (4)

An operating piston driven by an actuator, a control chamber that applies hydraulic pressure to the nozzle needle, and a control valve that increases and decreases the pressure in the control chamber are provided, and the operating piston opens and closes the valve body of the control valve. A fuel injection valve for raising and lowering the nozzle needle, wherein the valve body of the control valve is housed in a valve chamber provided with a high-pressure port communicating with a high-pressure passage and a low-pressure port communicating with a low-pressure passage. The valve body opens the low pressure port to close the high pressure port, and when the energy is released, the valve body opens and closes the low pressure port, and the operating piston is connected to the low pressure port. accommodated in the low pressure spill chamber for continuous, the connection end portion to said spill chamber of the low pressure port, toward the spill chamber side tape A tapered portion for diameter expansion to Jo, the distal end of the working piston to be inserted into the low-pressure port as a rod of small diameter, the radius of the low pressure port r _1, the radius of the rod portion of the hydraulic piston r _{2. When} the passage area of the low-pressure port is A ₁ and the distance L ₁ from the base end in the flow direction of the tapered portion is defined by the following formula (1),
A ₁ = π · {(r ₁ ) ² − (r ₂ ) ² } = π · (L ₁ ) ² (1)
A _L1 / A ₁ ≧ 2.5 (2)
Magnification A _L1 / A ₁ of the passage area represented by the ratio of the passage area A ₁ of the passage area A _L1 and the low pressure port in the distance L ₁ is, fuel and satisfies above formula (2) Injection valve. The fuel injection valve according to claim 1 , wherein a connection direction of the low-pressure passage connected to the spill chamber is substantially matched with a flow direction of the jet flow . An operating piston driven by an actuator that generates displacement by energization, a control chamber that applies hydraulic pressure to the nozzle needle, and a control valve that increases or decreases the pressure in the control chamber, and the operating piston controls the valve body of the control valve. A fuel injection valve that raises and lowers the nozzle needle as it is opened and closed, and the valve body of the control valve is accommodated in a valve chamber provided with a high-pressure port that communicates with a high-pressure passage and a low-pressure port that communicates with a low-pressure passage The valve element opens the low pressure port to close the high pressure port when energy is supplied to the actuator, and opens the high pressure port to close the low pressure port when the energy is released. A piston is housed in a low-pressure spill chamber continuous with the low-pressure port, and the spill chamber is formed in the spill chamber. Is fixed to the managing, interrupting the connection between the said low pressure port of the pressure receiving surface of the flow and the hydraulic piston for ejecting the said spill chamber, a fuel injection valve, characterized in that the formation of the blocking wall of the actuating piston and another member . 4. A piston member having a diameter larger than that of the operating piston driven by the actuator, and a pump chamber for driving the operating piston by increasing or decreasing the hydraulic pressure by displacement of the piston member . Fuel injection valve.

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