JP4023804B2 - Injector for internal combustion engine - Google Patents

Description

  The present invention relates to an injector for injecting high-pressure fuel into an internal combustion engine.

2. Description of the Related Art Conventionally, a pressure accumulation type fuel injection device that injects high pressure fuel accumulated in a common rail or the like from a injector into a combustion chamber of a diesel engine is known (see Patent Document 1).
The injector used in this pressure accumulation type fuel injection device includes a spring that applies a valve closing force to the needle, a control chamber that stores fuel pressure that urges the needle in the valve closing direction, and a pressure that controls the fuel pressure in the control chamber. When the fuel pressure in the control chamber is released to the low pressure side by this pressure control means, the needle is lifted and injected by the fuel pressure acting on the lower surface of the needle, and the high pressure fuel is injected into the control chamber. When stored, the needle is pushed back by the closing force of the spring, and the injection is completed.
Japanese Patent Laid-Open No. 9-32680

  In the above injector, the cross-sectional area of the needle that receives the fuel pressure in the valve closing direction (the fuel pressure in the control chamber) is equal to the cross-sectional area of the needle that receives the fuel pressure in the valve opening direction. When the high pressure fuel is stored in the control chamber after the needle is lifted by opening to the low pressure side, the fuel pressure in the valve closing direction acting on the needle balances the fuel pressure in the valve opening direction. The needle is pushed back. However, since the valve closing force of the spring is as small as several tens N, there is a problem in that secondary injection occurs when the needle bounces and restarts when the valve is closed.

Further, when pulsation occurs in the common rail that supplies high pressure fuel to the injector, the high pressure supplied to the injector fluctuates due to the influence of the pulsation. At this time, since the fuel pressure in the control chamber is introduced through the orifice, there is a response delay between the fuel pressure that urges the needle in the valve opening direction and the fuel pressure that urges the needle in the valve closing direction. Deviation occurs. As a result, the valve closing force changes and the valve closing speed changes, which causes a problem that a stable injection rate cannot be obtained.
The present invention has been made on the basis of the above circumstances, and its object is to increase the valve closing force and perform a good valve closing operation by suppressing the fuel pressure in the valve opening direction acting on the needle. An object of the present invention is to provide an injector for an internal combustion engine.

(Invention of Claim 1)
The present invention includes a body having a vertical hole formed therein and an injection hole leading to the vertical hole, a needle accommodated in the vertical hole so as to be movable in a valve opening direction and a valve closing direction, and the needle A control chamber for storing fuel pressure for biasing the valve in the valve closing direction, pressure control means for controlling the fuel pressure in the control chamber, and a needle chamber for storing fuel pressure for biasing the needle in the valve opening direction. Is an injector for an internal combustion engine that injects fuel supplied through the needle chamber from the nozzle hole during a valve opening operation in which the needle hole moves in the valve opening direction, and the needle moves in the valve hole in the valve closing direction. A pressure suppression means is provided for suppressing the fuel pressure introduced into the needle chamber so that the fuel pressure in the needle chamber is lower than the fuel pressure in the control chamber during valve operation. Further, the needle chamber is characterized by having a throttle as a pressure suppressing means between the inner peripheral surface of the vertical hole and the outer peripheral surface of the needle.

According to the above configuration, since the fuel pressure for urging the needle in the valve opening direction is lower than the fuel pressure for urging the needle in the valve closing direction, a valve closing force due to the difference between both pressures is generated. As a result, when compared with a conventional injector in which the fuel pressure that urges the needle in the valve closing direction and the fuel pressure that urges the needle in the valve opening direction are equal, a valve closing force is generated due to the difference in both pressures. Since the valve closing force increases, the resumption valve due to the bounce of the needle can be suppressed.
Further, since the fuel pressure introduced into the needle chamber is suppressed, even when the high pressure supplied to the injector fluctuates, the fuel pressure that urges the needle in the valve opening direction and the needle in the valve closing direction are urged. Since the difference in the response delay that occurs between the fuel pressure and the fuel pressure is substantially eliminated, the valve closing speed is stabilized, and variations in the injection rate can be suppressed.
In addition, by providing the throttle, the fuel pressure downstream of the throttle is suppressed, and the fuel pressure that urges the needle in the valve opening direction is reduced, so that the valve closing force is increased and a good valve closing operation is performed. Is possible.

(Invention of Claim 2 )
The present invention includes a body having a vertical hole formed therein and an injection hole leading to the vertical hole, a needle accommodated in the vertical hole so as to be movable in a valve opening direction and a valve closing direction, and the needle A control chamber for storing fuel pressure for biasing the valve in the valve closing direction, pressure control means for controlling the fuel pressure in the control chamber, and a needle chamber for storing fuel pressure for biasing the needle in the valve opening direction. Is an injector for an internal combustion engine that injects fuel supplied through the needle chamber from the nozzle hole during a valve opening operation in which the needle hole moves in the valve opening direction, and the needle moves in the valve hole in the valve closing direction. A pressure suppression means is provided for suppressing the fuel pressure introduced into the needle chamber so that the fuel pressure in the needle chamber is lower than the fuel pressure in the control chamber during valve operation. Further, the needle chamber has a throttle as a pressure suppressing means between the inner peripheral surface of the vertical hole and the outer peripheral surface of the needle, and the throttle is smaller when the lift amount of the needle is larger than when it is large. It is characterized in that a variable aperture that increases the aperture amount is formed.
According to this configuration, when the lift amount of the needle is small, for example, the throttle effect can be given only immediately before the needle is seated, so it is possible to suppress the reduction in the maximum injection rate due to the provision of the throttle. It is.

(Invention of Claim 3 )
The present invention includes a body having a vertical hole formed therein and an injection hole leading to the vertical hole, a needle accommodated in the vertical hole so as to be movable in a valve opening direction and a valve closing direction, and the needle A control chamber for storing fuel pressure for biasing the valve in the valve closing direction, pressure control means for controlling the fuel pressure in the control chamber, and a needle chamber for storing fuel pressure for biasing the needle in the valve opening direction. Is an injector for an internal combustion engine that injects fuel supplied through the needle chamber from the nozzle hole during a valve opening operation in which the needle hole moves in the valve opening direction, and the needle moves in the valve hole in the valve closing direction. A pressure suppression means is provided for suppressing the fuel pressure introduced into the needle chamber so that the fuel pressure in the needle chamber is lower than the fuel pressure in the control chamber during valve operation. Further, the needle chamber includes a gap formed between the inner peripheral surface of the vertical hole and the outer peripheral surface of the needle, and the passage cross-sectional area of the gap is reduced as a pressure suppressing means.
In this configuration, by adjusting the gap formed between the inner peripheral surface of the vertical hole and the outer peripheral surface of the needle, a function as a diaphragm can be provided.

(Invention of Claim 4)
The injector for an internal combustion engine according to any one of claims 1 to 3, characterized in that the pressure suppressing means is a throttle such that a ratio of a throttle area to a nozzle hole area is three times or less. This makes it possible to generate a pressure drop due to the throttle.
(Invention of Claim 5 )
In the injector for an internal combustion engine according to claim 2 , when the lift amount of the needle is small, the ratio of the throttle area to the nozzle hole area is three times or less, and when the needle lift amount is large, the variable throttle is relative to the nozzle hole area. The ratio of the aperture area is 5 times or more. Thereby, it becomes possible to suppress the fall of the maximum injection rate, and the fall of engine performance can be suppressed.
(Invention of Claim 6)
The injector for an internal combustion engine according to any one of claims 1 to 5, wherein the pressure suppressing means is a throttle provided by cutting an outer peripheral surface of a sliding portion of the needle.

  The best mode for carrying out the present invention will be described in detail with reference to the following examples.

FIG. 1 is an overall cross-sectional view of the injector 1.
An injector 1 according to the present embodiment is used, for example, in an accumulator fuel injection device (not shown) for a diesel engine. As shown in FIG. 1, a body 2 and a needle accommodated in the body 2 are used. 3. A control chamber 4 that stores fuel pressure for energizing the needle 3 in the valve closing direction (downward in FIG. 1), a pressure control means (to be described later) for controlling the fuel pressure in the control chamber 4, and the like. .

The body 2 has an injection hole 5 for injecting fuel, a vertical hole 7 communicating with the injection hole 5 via a sack chamber 6, a high-pressure passage 8 connected to a common rail (not shown), and a fuel tank A low pressure passage 9 and the like communicating with the low pressure side is formed.
The needle 3 is inserted into the vertical hole 7 and is always urged in the valve closing direction by a spring 10, and a conical seat surface 3 a provided at the tip of the needle 3 is provided at the end of the vertical hole 7. The sheet portion 7 a is in contact with the sack chamber 6 and the vertical hole 7.

The needle 3 is integrally provided with a sliding portion 3b that slides with the inner peripheral surface of the vertical hole 7 as a guide surface, and a throttle 11 is provided on the anti-spring side of the sliding portion 3b. The throttle 11 is provided, for example, by cutting the outer peripheral surface of the sliding portion 3 b into three faces, and an annular needle chamber 12 formed around the needle 3 in the vertical hole 7, and a high-pressure passage formed in the body 2. 8 is communicated. The throttle amount (passage cross-sectional area) of the throttle 11 is constant from the closed state of the needle 3 (the seat surface 3a is seated on the seat portion 7a) to the maximum lift position of the needle 3.
The control chamber 4 is a part of the vertical hole 7, is formed above the sliding portion 3 b, and communicates with the high-pressure passage 8 through the orifice 13.

The pressure control means includes a piezo stack 14, a piezo piston 15, a valve piston 16, a ball valve 17, and the like described below.
The piezo stack 14 is configured by laminating a plurality of piezo elements (piezoelectric elements) that expand in response to an applied voltage, and is accommodated in a piezo chamber 2 a formed in the upper part of the body 2.

The piezo piston 15 is slidably inserted into a cylinder 2b formed in communication with the lower portion of the piezo chamber 2a, and a piston head 15a disposed in the piezo chamber 2a is urged by a spring 18 so as to move to the piezo stack 14. It is pressed.
The valve piston 16 is slidably inserted into a small-diameter cylinder 2c formed in communication with the lower portion of the cylinder 2b, and forms a displacement expansion chamber 2d filled with fuel between the valve piston 16 and the displacement expansion. The displacement of the piezo piston 15 is amplified and transmitted via the fuel in the chamber 2d. A low pressure passage 9 is connected to the small diameter cylinder 2c.

The ball valve 17 is accommodated in a valve chamber 2e formed in communication with the lower portion of the small-diameter cylinder 2c, and is urged upward of the valve chamber 2e by a spring 19 also accommodated in the valve chamber 2e. The communication part with the valve chamber 2e is closed.
The valve chamber 2 e communicates with the control chamber 4 via the communication passage 20 and also communicates with the high-pressure passage 8 via the branch passage 21. Therefore, when the ball valve 17 is pushed by the valve piston 16 to open the communication portion between the small diameter cylinder 2c and the valve chamber 2e, the low pressure passage 9 connected to the small diameter cylinder 2c and the communication passage 20 are connected to the valve chamber 2e. A communication with the communicating control room 4 is established.

Next, the operation of the injector 1 will be described.
When the piezo stack 14 is energized, the piezo stack 14 extends and the piezo piston 15 is pushed downward, and the displacement of the piezo piston 15 pressurizes the fuel in the displacement expansion chamber 2d. When the valve piston 16 is pushed down in the small-diameter cylinder 2c in response to the pressurized fuel pressure, the ball valve 17 is pushed by the valve piston 16 to open the communication portion between the small-diameter cylinder 2c and the valve chamber 2e. . As a result, the control chamber 4 communicates with the low-pressure passage 9 and the high-pressure fuel in the control chamber 4 is discharged to the low-pressure passage 9, thereby reducing the fuel pressure in the control chamber 4.

Note that high-pressure fuel flows into the control chamber 4 from the high-pressure passage 8 through the orifice 13, but the amount of fuel flowing out of the control chamber 4 is larger than the amount of fuel flowing into the control chamber 4. The fuel pressure in the control chamber 4 gradually decreases in response to the fuel outflow from the chamber 4.
When the fuel pressure in the control chamber 4 decreases and the valve opening force exceeds the valve closing force acting on the needle 3, the needle 3 lifts in the vertical hole 7 and the needle chamber 12 and the sack chamber 6 communicate with each other. As a result, the high-pressure fuel supplied to the needle chamber 12 flows into the sac chamber 6 and is injected from the nozzle hole 5 into the combustion chamber of the internal combustion engine.

  When energization to the piezo stack 14 is completed, the piezo stack 14 contracts and the piezo piston 15 is pushed up by the reaction force of the spring 18, so that the fuel pressure in the displacement expansion chamber 2 d that has been pressurizing the valve piston 16 is increased. descend. As a result, the ball valve 17 is pushed up by the reaction force of the spring 19 and the communication portion between the small diameter cylinder 2c and the valve chamber 2e is closed, whereby the control chamber 4 and the low pressure passage 9 are disconnected. As a result, when the fuel pressure in the control chamber 4 rises and the valve closing force exceeds the valve opening force acting on the needle 3, the needle 3 is pushed back down in the vertical hole 7, and the seat surface of the needle 3 When 3a is seated on the seat portion 7a of the vertical hole 7, the communication between the needle chamber 12 and the sac chamber 6 is cut off, and the injection ends.

(Effect of Example 1)
The injector 1 is provided with the throttle 11 between the high-pressure passage 8 and the needle chamber 12, so that the fuel pressure introduced into the needle chamber 12 through the throttle 11 (the needle 3 is urged in the valve opening direction). Fuel pressure). As a result, when the energization to the piezo stack 14 is completed, the ball valve 17 is closed (the communication portion between the small diameter cylinder 2c and the valve chamber 2e is closed) and the fuel pressure in the control chamber 4 is increased. Since the fuel pressure in the needle chamber 12 is lower than the pressure, the pressure difference between the two acts as a valve closing force that pushes down the needle 3. When this valve closing force is added to the reaction force of the spring 10, the force to push down the needle 3 is increased compared to the conventional injector, so that the restart valve due to the bounce of the needle 3 can be suppressed and secondary injection can be prevented. .

  Further, since the fuel pressure introduced into the needle chamber 12 is suppressed by the throttle 11, for example, even when the high pressure supplied from the common rail to the injector 1 fluctuates, the fuel pressure in the needle chamber 12 and the fuel pressure in the control chamber 4 Is substantially eliminated, the valve closing speed of the needle 3 is stabilized, and variations in the injection rate can be suppressed.

FIG. 2 is a sectional view of the nozzle portion of the injector 1.
As shown in FIG. 2, the injector 1 of this embodiment has an annular fuel chamber 22 formed by enlarging the inner peripheral surface of the vertical hole 7 radially outward, and the high pressure passage 8 is formed in the fuel chamber 22. Is connected.
On the other hand, similarly to the first embodiment, the needle 3 is provided with a throttle 11 having an outer peripheral surface cut on the side opposite to the spring of the sliding portion 3b, and this throttle 11 forms a variable throttle with the fuel chamber 22. ing.

That is, as shown in FIG. 2, when the lift amount of the needle 3 is large, the opening area of the throttle 11 communicating with the fuel chamber 22 is increased, so that the throttle effect is reduced. Therefore, it is possible to suppress a decrease in the maximum injection rate due to the provision of the diaphragm 11.
As shown in FIG. 3, when the lift amount of the needle 3 is small, the opening area of the throttle 11 communicating with the fuel chamber 22 is small, so that the throttle effect is increased. As a result, as in the case of the first embodiment, the valve closing force of the needle 3 increases, the restart valve due to the bounce of the needle 3 can be suppressed, and the secondary injection can be prevented.

FIG. 4 is a cross-sectional view of the nozzle portion of the injector 1.
The injector 1 of the present embodiment is an example in which a throttle 11 is provided in the high-pressure passage 8 connected to the fuel chamber 22 as shown in FIG. In this case, since it is only necessary to provide an orifice as the throttle 11 in the high-pressure passage 8, it is easy to form the throttle 11, and it is possible to suppress an increase in cost due to the provision of the throttle 11. In the present embodiment, since one high pressure passage 8 is branched and connected to the control chamber 4 and the fuel chamber 22, the throttle 11 is provided between the branch point of the high pressure passage 8 and the fuel chamber 22. Can be provided.

FIG. 5 is a cross-sectional view of the nozzle portion of the injector 1.
As shown in FIG. 5, the injector 1 of the present embodiment is an example in which the aperture 11 is formed by reducing the gap between the inner peripheral surface of the vertical hole 7 and the outer peripheral surface of the needle 3. In this case, the gap between the vertical hole 7 and the needle 3 is reduced, the pressure loss is increased, and the fuel pressure acting on the seat surface 3a of the needle 3 is reduced, whereby the valve closing force can be increased.

FIG. 6 is a graph showing the pressure drop rate of the high-pressure fuel with respect to the ratio between the throttle area and the nozzle hole area, and FIG. 7 is the flow rate drop rate of the fuel flowing out from the nozzle hole with respect to the ratio between the throttle area and the nozzle hole area. FIG.
As a result of simulating the pressure drop rate of the high-pressure fuel with respect to the ratio of the passage sectional area of the nozzle hole 5 (referred to as the nozzle hole area) and the passage sectional area of the throttle 11 (referred to as the throttle area), as shown in FIG. It has been clarified that the pressure drop rate gradually increases when the ratio of the throttle area to the hole area is three times or less. Therefore, in this embodiment, the ratio of the throttle area to the nozzle hole area is set to 3 times or less. As a result, a pressure drop in the needle chamber 12 can be generated when the needle 3 is closed, so that the fuel pressure in the needle chamber 12 is lower than the fuel pressure in the control chamber 4, and the pressure difference between them is the needle 3. Acts as a closing force that pushes down.

Further, when the variable throttle described in the second embodiment is employed, it is necessary to suppress the pressure drop of the high-pressure fuel caused by the throttle 11 when the lift amount of the needle 3 is large. On the other hand, according to the simulation result shown in FIG. 6, if the ratio of the throttle area to the nozzle hole area is 5 times or more, the pressure drop rate of the high-pressure fuel can be suppressed to about 3%. Here, as a result of simulating the rate of decrease in the flow rate of the fuel flowing out from the nozzle hole 5 with respect to the ratio between the throttle area and the nozzle hole area, as shown in FIG. 7, the ratio of the throttle area to the nozzle hole area is 5 times or more. Then, it was found that the rate of decrease in the flow rate of the fuel was in a negligible range of about 1.5%.
Therefore, when the lift amount of the needle 3 is large, the ratio of the throttle area to the nozzle hole area is 5 times or more, and when the lift amount of the needle 3 is small, the ratio of the throttle area to the nozzle hole area is three times or less. It is desirable to configure a variable aperture.

(Modification)
In the first embodiment, the piezo stack 14 is used as an actuator for driving the ball valve 17, but a solenoid actuator (for example, an electromagnetic valve) may be employed as the pressure control means of the present invention.

1 is an overall cross-sectional view of an injector according to Embodiment 1. FIG. It is sectional drawing of the nozzle part (the lift amount of a needle: large) of the injector concerning Example 2. FIG. It is sectional drawing of the nozzle part (the lift amount of a needle: small) of the injector concerning Example 2. FIG. 6 is a cross-sectional view of a nozzle portion of an injector according to Embodiment 3. FIG. It is sectional drawing of the nozzle part of the injector concerning Example 4. FIG. (Example 5) which is a figure which shows the pressure fall rate of a high pressure fuel with respect to the ratio of an aperture area and a nozzle hole area. (Example 5) which is a figure which shows the flow velocity fall rate of the fuel which flows out out of a nozzle hole with respect to the ratio of a throttle area and a nozzle hole area.

Explanation of symbols

1 Injector for internal combustion engine 2 Body 3 Needle
3b Sliding part 4 Control chamber 5 Injection hole 7 Vertical hole 8 High pressure passage 11 Restriction (pressure suppression means)
12 Needle chamber 14 Piezo stack (pressure control means)
17 Ball valve (pressure control means)

Claims (6)

A body having a vertical hole formed therein and a nozzle hole leading to the vertical hole;
A needle accommodated movably in the valve opening direction and the valve closing direction in the longitudinal hole;
A control chamber for storing fuel pressure for urging the needle in the valve closing direction;
Pressure control means for controlling the fuel pressure in the control chamber;
A needle chamber for storing fuel pressure for urging the needle in the valve opening direction;
An injector for an internal combustion engine that injects fuel supplied through the needle chamber from the nozzle hole during a valve opening operation in which the needle moves in the valve opening direction in the vertical hole,
During the valve closing operation in which the needle moves in the valve closing direction in the longitudinal hole, the fuel pressure introduced into the needle chamber is suppressed so that the fuel pressure in the needle chamber is lower than the fuel pressure in the control chamber. Pressure suppression means ,
The injector for an internal combustion engine , wherein the needle chamber has a throttle as the pressure suppressing means between an inner peripheral surface of the vertical hole and an outer peripheral surface of the needle . A body having a vertical hole formed therein and a nozzle hole leading to the vertical hole;
A needle accommodated movably in the valve opening direction and the valve closing direction in the longitudinal hole;
A control chamber for storing fuel pressure for urging the needle in the valve closing direction;
Pressure control means for controlling the fuel pressure in the control chamber;
A needle chamber for storing fuel pressure for urging the needle in the valve opening direction;
An injector for an internal combustion engine that injects fuel supplied through the needle chamber from the nozzle hole during a valve opening operation in which the needle moves in the valve opening direction in the vertical hole,
During the valve closing operation in which the needle moves in the valve closing direction in the longitudinal hole, the fuel pressure introduced into the needle chamber is suppressed so that the fuel pressure in the needle chamber is lower than the fuel pressure in the control chamber. Pressure suppression means,
The needle chamber has a throttle as the pressure suppressing means between the inner peripheral surface of the vertical hole and the outer peripheral surface of the needle,
2. The injector for an internal combustion engine according to claim 1, wherein the throttle forms a variable throttle in which the throttle amount increases when the needle lift amount is smaller than when the needle lift amount is large . A body having a vertical hole formed therein and a nozzle hole leading to the vertical hole;
A needle accommodated movably in the valve opening direction and the valve closing direction in the longitudinal hole;
A control chamber for storing fuel pressure for urging the needle in the valve closing direction;
Pressure control means for controlling the fuel pressure in the control chamber;
A needle chamber for storing fuel pressure for urging the needle in the valve opening direction;
An injector for an internal combustion engine that injects fuel supplied through the needle chamber from the nozzle hole during a valve opening operation in which the needle moves in the valve opening direction in the vertical hole,
During the valve closing operation in which the needle moves in the valve closing direction in the longitudinal hole, the fuel pressure introduced into the needle chamber is suppressed so that the fuel pressure in the needle chamber is lower than the fuel pressure in the control chamber. Pressure suppression means,
The needle chamber includes a gap formed between an inner circumferential surface of the vertical hole and an outer circumferential surface of the needle, and the passage cross-sectional area of the gap is reduced as the pressure suppressing means. Injector for engine. The injector for an internal combustion engine according to any one of claims 1 to 3,
An injector for an internal combustion engine , wherein the pressure suppressing means is a throttle such that a ratio of a throttle area to a nozzle hole area is three times or less . The injector for an internal combustion engine according to claim 2 ,
In the variable throttle, when the lift amount of the needle is small, the ratio of the throttle area to the nozzle hole area is three times or less, and when the needle lift amount is large, the ratio of the throttle area to the nozzle hole area is five times or more. an internal combustion engine injector characterized by comprising. The injector for an internal combustion engine according to any one of claims 1 to 5 ,
The injector for an internal combustion engine , wherein the pressure suppressing means is a throttle provided by cutting an outer peripheral surface of a sliding portion of the needle .

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