JP2762596B2 - Unit injector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a unit injector used as a fuel injection device for a diesel engine.

"Conventional technology and its problems" In a unit injector having a pump function and an injection valve function, when terminating fuel injection, the pressurizing chamber of the plunger pump is connected to the low-pressure fuel tank side by some method. At this time, the pressure in the nozzle high pressure chamber decreases, and the needle valve body closes the needle valve seat by the force of the spring in the nozzle spring chamber. As a method of connecting the pressurizing chamber to the fuel tank side, for example, a lead groove provided in a plunger or a spill valve operated by a piezoelectric laminate has been used (Japanese Patent Laid-Open Nos. 63-150070 and 62). -174561, see).

However, in the conventional structure, the state in which the injection rate is low lasts for a long time in the later stage of the injection, which causes the generation of smoke. Also, when the pressure in the engine combustion chamber is high, there is a problem that the combustion gas enters the inside of the injection nozzle and damages the needle valve seat. Therefore, in JP-A-63-230958, a sub port is formed in the plunger barrel wall of the plunger pump, and the pressure oil in the pressurizing chamber is guided to the nozzle spring chamber through the sub fuel passage to thereby achieve a peak injection rate. Disposes a unit injector that prevents the generation of smoke by shifting the injection direction to the injection end timing direction.However, since the sub-communication passage is formed in the plunger, the injection rate is easily affected by the camshaft rotation speed, and Difficulty in management of accuracy is likely to occur. Further, since the dynamic pressure of the overflow pressure oil is not actively used, the peak of the injection rate cannot be sufficiently shifted in the direction of the injection end timing, and the effect of preventing the generation of smoke is small.

In addition, the unit injector disclosed in Japanese Patent Application Laid-Open No. 63-230958 does not have any means for preventing the backflow of the combustion gas into the injection nozzle, so that the problem of damaging the needle valve seat has not been solved.

"Problems to be Solved by the Invention" The present invention has been made in order to solve the above problems, and actively uses overflow pressure oil to reduce the injection end timing from low rotation to high rotation. An object of the present invention is to provide a unit injector capable of preventing generation of smoke and backflow of combustion gas into the injection nozzle by quickly and reliably closing the injection nozzle.

[Means and Actions for Solving the Problems] A unit injector of the present invention for solving the above problems includes a reciprocating plunger driven by an engine and a pressurizing chamber for pressurizing fuel by the plunger. A unit injector for pressurizing the fuel in the pressure chamber by the plunger to feed it to an injection nozzle through a high-pressure passage and injecting the fuel from the nozzle includes a spill valve body, a valve seat chamber, and overflow limiting means. It is connected between the pressurizing chamber and the fuel tank, and when the spill valve body opens from the valve seat in the valve seat chamber, the fuel in the pressurizing chamber is transferred to the fuel tank side via the valve seat chamber and the overflow restriction means. A control valve device that overflows, a nozzle spring that urges the needle valve body of the injection nozzle toward a needle valve seat, a nozzle spring chamber that houses the nozzle spring, When the spill valve body of the control valve device is opened from a valve seat in a valve seat chamber, a back pressure port communicating the valve seat chamber with the nozzle spring chamber, and
A sub-piston provided in the nozzle spring chamber and in contact with an upper part of the needle valve body to receive an overflow pressure, wherein the diameter of the sub-piston is formed to be larger than the diameter of a sliding portion of the needle valve body; Are slidably disposed in the nozzle spring chamber in an oil-tight manner.

According to the above configuration, when the control valve device is closed, fuel injection is started from the injection nozzle by an increase in the injection pressure in the pressurized chamber of the plunger pump, and when the control valve device is opened at the end of the injection, Since the overflow pressure oil is applied to the nozzle spring chamber via the back pressure port, the needle valve body of the injection nozzle closes quickly to the needle valve seat. In other words, compared to the case where the injection nozzle is closed only by the force of the nozzle spring,
Since the lift of the needle valve body becomes zero (= 0) when the injection pressure does not decrease so much, the cutoff of the injection rate is improved, and the generation of smoke is prevented. Since the pressurized oil is applied to the nozzle spring chamber via the back pressure port for a long period of time, it is possible to prevent the backflow of the combustion gas into the injection nozzle. A sub-piston provided in the nozzle spring chamber and in contact with an upper part of the needle valve body to receive an overflow pressure; the diameter of the sub-piston is formed to be larger than the diameter of a sliding portion of the needle valve body; Is slidably disposed in the nozzle spring chamber in an oil-tight manner, so that the injection nozzle can be more quickly and reliably closed.

The overflow limiting means may be a residual pressure regulating valve that opens the valve seat chamber to the fuel tank side when the pressure in the valve seat chamber of the control valve device is equal to or higher than a predetermined value. According to this configuration,
When the control valve device is opened to stop fuel injection from the injection nozzle, the residual pressure regulating valve opens when the pressure of the overflow pressure oil is equal to or higher than a predetermined value, and when the pressure of the overflow pressure oil falls below the predetermined value. By closing the residual pressure adjusting valve, the pressure of the overflow pressure oil is maintained at a somewhat high pressure so as not to drop early.

The residual pressure regulating valve includes a spill valve body having an internal passage, a valve member capable of closing the passage, and a compression coil spring for pressing the valve member. According to this configuration, a residual pressure regulating valve that operates stably can be obtained.

The control valve device is configured to drive the spill valve body by a piezoelectric actuator via a working fluid in a cylinder chamber. According to this configuration, desired injection start timing and injection end timing can be obtained from low rotation to high rotation.

The overflow limiting means may be a throttle member provided in an internal passage of the spill valve. According to this configuration, when the control valve device is opened, when the pressure of the overflow pressure oil is high, the flow rate of the overflow flowing through the throttle member is large,
When the pressure of the overflow pressure oil decreases, the flow rate of the overflow flowing through the throttle member decreases, thereby limiting the flow rate. Therefore, the pressure is maintained at a certain high level so that the pressure does not decrease early. Further, there is an advantage that the configuration is simplified.

If the space between the sub piston and the sliding portion of the needle valve body is connected to the drain side, and the sub piston is provided with an orifice communicating between the side receiving the overflow pressure and the drain side, the orifice , The shock pressure of the overflow pressure oil applied to the pressure pin and the needle valve seat is reduced.

"Embodiment" A first embodiment of the present invention will be specifically described with reference to FIGS. 1, 2, and 3. FIG.

FIG. 3 is an enlarged view showing the injection nozzle and the nozzle spring chamber shown in FIG.

The unit injector shown in FIG. 1 includes a fuel supply device 30 that supplies fuel to a plunger pump 20, which will be described later, a plunger pump 20 that is a fuel injection pressurizing pump, and a fuel that is pressurized by the plunger pump 20. An injection nozzle 10 for spraying indoors and a control valve device 40 for controlling the operation (opening / closing) of the injection nozzle 10 are configured as main parts.

The fuel supply device 30 includes a fuel tank 31 and the fuel tank 31.
And a fuel supply pump 32 for supplying the fuel inside to the plunger pump 20. Fuel tank
The fuel in 31 is supplied to the plunger pump 20 through the flow paths 33 and 34 and the feed port 34a.
Is pressurized and returned to the fuel tank 31 via the flow paths 4, 8 and 35 in a timely manner.

The plunger pump 20 includes a reciprocating plunger 2 that moves in and out of the pressurizing chamber 3. A tappet 1 urged in a backward direction by a compression coil spring 12 is connected to a rear end of the plunger 2, and the tappet 1 is connected via a cam mechanism linked to a crankshaft (not shown) of a diesel engine. Driven. When the tappet 1 is pressed against the urging force of the compression coil spring 12 in accordance with the rotation of the crankshaft, the plunger 2 advances toward the injection nozzle 10. Tappet housing 13 is fixed to unit injector body 21,
The tappet 1 reciprocates in the tappet housing 13.

A one-way valve 100 is provided below the pressurizing chamber 3.
In the one-way valve 100, the valve body 102 is pressed against the stepped portion 101 by the spring 104. An orifice 103 is provided inside the valve body 102.

The injection nozzle 10 has a needle valve element (nozzle needle) 11 urged by a nozzle spring 93 via a pressure pin 14 in a valve chamber 91 thereof.
Opens and closes the fuel injection hole 92.

The sub piston 97 is a cylindrical member having a substantially H-shaped cross section, and slides in the nozzle spring chamber 5 in an oil-tight manner.

The diameter of the sub-piston 97 is larger than the diameter of the sliding portion of the needle valve element 11 (the diameter receiving the back pressure). Therefore, at the end of the injection, the overflow pressure oil flows into the nozzle spring chamber 5, and when the pressure in the nozzle spring chamber rises, the needle valve body 11
The force for pressing the nozzle against the valve seat 90 increases, and the injection nozzle 10 can be closed more quickly and reliably. The space 5b between the sub piston 97 and the sliding portion of the needle valve element 11 is connected to the drain side to prevent oil-tight lock.

The needle valve element 11 has a stepped portion 18 at a portion where a thin front end portion and a thick rear end portion are connected to each other, and the stepped portion 18 has a high pressure passage 95, 96, 94 through the high pressure passage 95, inside the pressurizing chamber 3. When the hydraulic pressure acts, the needle valve body 11 retreats from the needle valve seat 90 against the urging force of the nozzle spring 93 in accordance with the magnitude of the hydraulic pressure, and the fuel injection hole 92 is opened. Fuel is injected.

9 is a nozzle spring holder, 15 is packing, 16 is a nozzle body, and the nozzle body 16 is fixed to the lower end of the injector body 21 by a retaining nut (not shown).

The control valve device 40 includes the spill valve 6 and a piezoelectric actuator 49 for operating a spill valve element 61 of the spill valve 6. The spill valve 6 has a spill valve body 61 formed as a tube having a plurality of small openings 63 in a peripheral wall at an intermediate portion in a longitudinal direction thereof, and the spill valve body 61 is moved backward (to the right in FIG. 1). A spill valve body is provided on a conical inner wall surface, that is, a valve seat 47, of a compression coil spring 48 for urging the spill valve body 61, a cylinder chamber 44 for accommodating the spill valve body 61 in a retractable manner, and a valve seat chamber 64.
The 61 open ends are closely and spaced apart. A rod 46 formed as a tube having one end closed is slidably and oil-tightly slidable in a cylinder 45.
In the illustrated state where the hydraulic pressure in the spill valve body 61 is relatively low compared to the urging force of the compression coil spring 48, the spill valve body 61 is at the retracted position, and the tip of the spill valve body 61 is separated from the valve seat 47. .

The residual pressure adjusting valve 7 is provided inside the spill valve body 61 and the rod 46. The residual pressure adjusting valve 7 includes a plate-shaped valve body 71 as a valve member, a compression coil spring 72, and a stopper 73. The urging force of the spring 72 pushes the valve body 71 to the left in FIG. When the pressure in the internal passage 62 of the spill valve body 61 becomes equal to or higher than a predetermined value, the valve body 71 opens to the right side in the figure due to the urging force of the spring 72, and the fuel passes through the small opening 63 and passes from the passages 8, 35 to the fuel tank 31. Reach.

The piezoelectric actuator 49 that constitutes the control valve device 40 together with the spill valve 6 stores a piezoelectric laminate 19 in which a large number of piezoelectric elements that expand and contract with good response by applying a voltage are housed in a bottomed cylindrical body. Piston 17 comprising
A compression coil spring 53 that biases 17 in the backward direction, and a piston
A cylinder chamber 50a is provided for accommodating the cylinder 17 so as to be able to advance and retreat. The fuel in the fuel tank 31 is sent by a fuel supply pump 32 through a flow path 33 into a spring chamber 50 in which a compression coil spring 53 is located. 3. Piezoelectric laminate 19
Expands (expands) quickly when a positive voltage is applied to it
Then, when a negative voltage is applied, it contracts quickly. 54 is an O-ring. The piston 17 moves forward and backward with good responsiveness due to the expansion and contraction phenomenon of the piezoelectric laminate 19. When the piston 17 advances, the hydraulic pressure (fuel oil pressure) in the cylinder chamber 50a and the back pressure chamber 43 in front thereof increases, and the rod 46 and the spill valve body 61 advance against the urging force of the compression coil spring 48. . When the fuel in the cylinder chamber 50a runs short, when the piston 17 retreats, the hydraulic pressure in the cylinder chamber 50a decreases,
A shortage of the discharge oil from the fuel supply pump 32 is sent into the cylinder chamber 50a via the flow path 84 and the one-way valve 80. 81 is a steel ball, 82 is a push rod, and 83 is a coil spring.

"Operation of First Embodiment" The tappet 1 is pushed by the cam driven by the engine, and the plunger 2 moves downward. After the plunger 2 closes the feed port 34a, the fuel pumped by the plunger 2 passes through the flow path 4, the valve seat chamber 64, reaches the internal passage 62 of the spill valve body 61, and the valve body of the residual pressure regulating valve 7 71 is pushed open to reach the fuel tank 31 through the small opening 63 and the flow paths 8, 35. Here, the valve opening pressure of the residual pressure adjusting valve 7 (for example, 100 kgf / c
m ² ) is lower than the valve opening pressure of the injection nozzle 10 (for example, 300 kgf / cm ² ), so that no fuel is injected from the injection nozzle 10.

When a voltage is applied to the piezoelectric laminate 19 at a predetermined injection start timing as shown in FIG. 2A, the piezoelectric laminate 19 expands,
The pressure in the back pressure chamber 43 is increased, and the spill valve 6 is closed by pushing the rod 46 and the spill valve body 61 to the left in the figure and seating the spill valve body 61 on the valve seat 47. From channel 4 to internal channel 62
Is closed, the pumped fuel passes through the high-pressure passages 95, 9
After reaching the step portion 18 via 6,94, the needle valve body 11 is moved to the valve seat after a short time as shown by the solid line in FIGS. 2 (c) and 2 (d).
Injection starts from the fuel injection hole 92 by pushing up from 90. During the injection, the fuel pressure in the high-pressure portion, that is, the pressure chamber 3, the flow path 4, the valve seat chamber 64, the high-pressure passages 95, 96, 94 and the valve chamber 91 is, for example, 1000 kgf / cm.
² and high pressure.

When the voltage of the piezoelectric laminate 19 is lowered (discharged) as shown in FIG. 2A at the time of the end of the injection, the spill valve 61 moves to the right in FIG. this moment,
Part of the high-pressure fuel is rushed into the nozzle spring chamber 5 via the valve seat chamber 64 and the back pressure port 66. For this reason, the pressure in the nozzle spring chamber 5 increases, and this pressure acts in a direction to push down the needle valve element 11. Therefore,
The needle valve element 11 closes quickly and securely as shown by the solid line in FIGS. 2 (c) and 2 (d), and the fuel injection is completed. The back pressure port 66 from the valve seat chamber 64 to the end face of the needle valve body 11 is short as shown in FIG. 1, and the valve seat chamber 64 and the back pressure port 66 follow the flow of fuel. Since the pressure in the nozzle spring chamber 5 increases in a form in which the pressure component is added, the effect is even greater.

The remaining fuel passes through the valve seat chamber 64 and the internal passage 62 to push open the valve body 71 of the residual pressure regulating valve 7, and the small opening 63 and the flow passage
After returning to the fuel tank 31 via 8,35. According to the present invention,
By the operation of the residual pressure adjusting valve 7, the flow path 4, the pressurizing chamber 3, the high-pressure passage 9
Since the pressures of 5, 96, 94 and the valve chamber 91 are also maintained at a somewhat high pressure, the combustion gas passes through the fuel injection holes 92 to the valve chamber 91.
There is no backflow to the side and therefore no damage to the needle valve seat 90. Since the injection rate is good as shown by the solid line in FIG. 2 (c), the generation of smoke is suppressed.

In the conventional case in which the residual pressure adjusting valve 7 and the back pressure port 66 are not provided, the injection pressure drops rapidly as shown by the dotted line in FIG. In order to push down 11, the second injection rate
As shown by the dotted line in FIG. Also,
Since the injection pressure at the end of the injection is low, the backflow of the combustion gas from the fuel injection holes 92 easily occurs.

Next, the operation and effect of the sub piston 97 and the one-way valve 100 will be described.

The diameter of the sub-piston 97 is larger than the diameter of the sliding portion of the needle valve element 11 (the diameter receiving the back pressure). Therefore, at the end of the injection, the overflow pressure oil flows into the nozzle spring chamber 5, and when the pressure in the nozzle spring chamber rises, the needle valve body 11
The force for pressing the nozzle against the valve seat 90 increases, and the injection nozzle 10 can be closed more quickly and reliably. The space 5b between the sub piston 97 and the sliding portion of the needle valve element 11 is connected to the drain side to prevent oil-tight lock.

In the one-way valve 100, the valve body 102 is pressed against the stepped portion 101 by the spring 104. An orifice 103 is provided inside the valve body 102. When the pressure feed of the plunger 2 starts and the spill valve 6 is closed by the piezoelectric actuator 49, the fuel pushes and opens the valve body 102 and the injection nozzle 10
Sent to the side and the injection begins. When the spill valve 6 is opened at the end of the injection, the pressure in the pressurizing chamber 3 starts to decrease. With this, the valve body
102 is pressed against the stepped portion 101. Since the pressure drop in the high-pressure passages 95, 96, 94 and the valve chamber 91 on the injection nozzle side occurs only through the orifice 103, the pressure drops slowly, and the injection pressure on the injection nozzle side is maintained for a relatively long time. (See the dashed line in FIG. 2). Therefore, the injection pressure until the needle valve element 11 is completely closed is further increased, and the effect of preventing the combustion gas from entering the valve chamber 91 is further increased.

"Other Embodiments" In the second embodiment shown in FIG. 4, the residual pressure regulating valve 7 of the first embodiment is replaced by a throttle member 75 having an orifice 74. FIG. 4 shows only the spill valve 6 and the control valve 40, and the other configuration is the same as that of the first embodiment.

The orifice 74 is provided in the internal passage 62 of the spill valve body 61. When the pumped fuel passes through the internal passage 62 of the spill valve body 61 and the orifice 74 and reaches the fuel tank 31 on the drain side, the function of the orifice 74 causes the upstream side (the internal passage 62) as in the first embodiment. The pressure in the valve seat chamber 64 and the back pressure port 66) on the near side from this part is maintained at a somewhat high pressure. By this pressure, the injection rate can be cut smoothly as in the first embodiment, the injection nozzle closes quickly, and the effect of preventing intrusion of combustion gas is obtained.

Further, since only the orifice is used instead of the residual pressure adjusting valve, the configuration is simplified.

In the third embodiment shown in FIG. 5, an orifice 97a and a fuel passage 97b are provided in the sub piston 97 of the first and second embodiments.

At the end of the injection, the overflow pressure oil flows into the nozzle spring chamber 5, but especially at high speed operation of the engine, since this pressure is applied in a shock, an excessively large force is applied to the sub piston.
97, the pressure pin 14 may be broken or the needle valve seat 90 may be damaged.

The orifice 97a is provided to reduce the impact pressure. Nozzle spring chamber 5 at the end of injection
A part of the overflow pressure oil that has flowed into the tank passes through the orifice 97a and returns to the drain side (the fuel tank 31 side) through the fuel passage 97b and the space 5b. Due to the damper effect of the orifice 97a, the impact pressure of the overflow pressure oil is reduced, and damage to the pressure pin 14 and the needle valve seat 90 can be prevented.

[Effect of the Invention] As described above, the unit injector of the present invention includes a reciprocating plunger driven by an engine and a pressurizing chamber for pressurizing fuel by the plunger, and the fuel in the pressurizing chamber is supplied by the plunger. In a unit injector that pressurizes and feeds to an injection nozzle through a high-pressure passage and injects from the nozzle, the unit injector includes a spill valve body, a valve seat chamber, and an overflow restricting means, and is provided between the pressurizing chamber and the fuel tank. A control valve device that is connected between the valve and a valve that causes fuel in the pressurized chamber to overflow to the fuel tank through the valve seat chamber and the overflow restricting means when the spill valve element is opened from the valve seat in the valve seat chamber. A nozzle spring for urging a needle valve body of an injection nozzle toward a needle valve seat, a nozzle spring chamber accommodating the nozzle spring, and a spill valve body of the control valve device When the valve is opened from the valve seat in the valve seat chamber, a back pressure port communicating the valve seat chamber with the nozzle spring chamber, and the back pressure port provided in the nozzle spring chamber, contact the upper part of the needle valve body to reduce the overflow pressure. A receiving sub-piston, the diameter of the sub-piston is formed larger than the diameter of the sliding portion of the needle valve body, and the sub-piston is disposed in the nozzle spring chamber so as to be slidable in an oil-tight manner. The generation of smoke can be reliably prevented, and further, the backflow of the combustion gas into the injection nozzle can be prevented, and there is an excellent effect that the needle valve seat is not damaged.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a unit injector of the present invention, FIG. 2 is a characteristic curve diagram for explaining the operation of the first embodiment, and FIG. 3 is an injection nozzle and a nozzle spring shown in FIG. FIG. 4 is an enlarged view showing a chamber, FIG. 4 is a sectional view showing a second embodiment, and FIG. 5 is a sectional view showing a third embodiment. 2 ... reciprocating plunger, 3 ... pressurizing chamber, 5 ... nozzle spring chamber, 7 ... residual pressure adjusting valve, 10 ... injection nozzle,
11 Needle valve element, 31 Fuel tank, 40 Control valve device, 43 Back pressure chamber, 47 Valve seat, 49 Piezoelectric actuator, 50a Cylinder chamber, 61 Spill valve Body, 62 ...
... internal passage, 64 ... valve seat, 66 ... back pressure port, 71 ...
A plate-shaped valve element (as a valve member), 72, a compression coil spring,
74 orifice, 75 throttle member, 90 needle valve seat, 91 valve chamber, 92 fuel injection hole, 93 nozzle spring, 94, 95, 96 high-pressure passage, 97 Sub piston,
97a… orifice, 97b… fuel passage.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-81950 (JP, A) JP-A-2-161136 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) F02M 47/00 F02M 57/02 310 F02M 57/02 330

Claims (6)

(57) [Claims] 1. A reciprocating plunger driven by an engine and a pressurizing chamber for pressurizing fuel by the plunger. The fuel in the pressurizing chamber is pressurized by the plunger, so that the fuel is supplied to an injection nozzle through a high-pressure passage. In a unit injector for pressure-feeding and injecting from the nozzle, a spill valve body, a valve seat chamber, and an overflow limiting means are connected between the pressurizing chamber and the fuel tank, and the spill valve body is provided inside the valve seat chamber. A control valve device for allowing fuel in the pressurized chamber to overflow to the fuel tank via the valve seat chamber and the overflow restricting means when the valve is opened from the valve seat; and urging the needle valve body of the injection nozzle toward the needle valve seat. A nozzle spring chamber for accommodating the nozzle spring, a valve seat chamber and the nozzle split when the spill valve element of the control valve device opens from a valve seat in the valve seat chamber. A back pressure port communicating with the needle chamber; and a sub-piston provided in the nozzle spring chamber and in contact with an upper part of the needle valve body to receive an overflow pressure. A unit injector having a diameter larger than the diameter of the sub-piston and slidably disposed in the nozzle spring chamber in an oil-tight manner. 2. The overflow limiting means is a residual pressure regulating valve which opens the valve seat chamber to the fuel tank side when the pressure in the valve seat chamber of the control valve device is equal to or higher than a predetermined value. Item 2. The unit injector according to Item 1. 3. The residual pressure regulating valve according to claim 1, further comprising an internal passage provided in the spill valve body, a valve member capable of closing the passage, and a compression coil spring pressing the valve member in a closing direction. The unit injector according to claim 2, wherein 4. The unit according to claim 1, wherein the control valve device drives the spill valve body by a piezoelectric actuator via a working fluid in a back pressure chamber. Injector. 5. A unit injector according to claim 1, wherein said overflow restricting means is a throttle member provided in an internal passage of said spill valve body. 6. A space between the sub-piston and a sliding portion of the needle valve body is connected to a drain side, and the sub-piston is provided with an orifice communicating between a side receiving the overflow pressure and the drain side. The unit injector according to claim 1, wherein: