JPS63113176A - Unit injector - Google Patents

Abstract

PURPOSE:To ensure fuel injection by determining the volume of a pressure transmission chamber with a piston to actuate a slide valve for opening and closing a fuel overflow port between a forced fuel feed chamber and a fuel injection port, and communicating said transmission chamber to the forced fuel feed chamber via a fuel filling passage. CONSTITUTION:On the way of a passage communicating a forced fuel feed chamber 18 with a fuel injection port 9, there is a slide valve 28 provided for opening and closing a fuel overflow port 29. One end of the slide valve 28 is fitted with a spring 39 for energizing the valve 28 toward an open direction and the other end thereof is connected with an actuator 44 via a rod 46. Furthermore, a pressure transmission chamber 45 and the forced fuel feed chamber 18 as divided on the motion of the piston 43 of the actuator 44 are made continuous to each other via a fuel filling passage 48. According to the aforesaid constitution, fuel filling into the pressure transmission chamber 45 can be ensured and fuel can be injected properly.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a unit injector.

[Conventional technology]

A fuel pumping chamber, a plunger driven by the engine and pressurizing fuel in the fuel pumping chamber, a fuel supply port connected to a fuel supply pump and opening into the fuel pumping chamber when the plunger is in a compression ready position, and a spring-loaded plunger. a fuel injection hole that is normally closed by a forced needle, and a fuel overflow port that is provided in a high-pressure fuel supply passage that communicates the fuel pumping chamber and the fuel injection hole and that communicates from the high-pressure fuel supply passage to a fuel overflow chamber. A unit injector is known that includes a slide valve that opens when fuel injection is stopped, and an actuator that controls the slide valve. In such a unisoto injector, the valve is defined by a spring that biases the sliding valve in the direction of opening the fuel overflow port in order to improve the responsiveness of fuel injection, and a piston driven by an actuator made of a piezoelectric element. and a rod that is driven by the fuel pressure in the pressure transmission chamber and presses the slide valve in a direction to close the fuel overflow port when the fuel pressure in the pressure transmission chamber increases. The applicant has already proposed a unit injector in which a flow chamber is connected to a pressure transmission chamber via a check valve (Japanese Patent Application No. 61-210126).
(see issue). In this unit injector, the pressure transmission chamber must be constantly filled with fuel in order to close the fuel overflow port by pressing the slide valve with the rod. Therefore, in this unit injector, the fuel overflow chamber is connected to the pressure transmission chamber via a check valve in order to supply the fuel in the fuel overflow chamber into the pressure transmission chamber when the fuel in the pressure transmission chamber leaks. There is.

[Problem that the invention seeks to solve]

However, when such a check valve is used, there is a risk that the check valve will not close completely when the fuel pressure in the pressure transmission chamber is increased for fuel injection, and in this case, the sliding valve will prevent fuel overflow. There is a problem in that fuel injection cannot be performed because the flow port cannot be closed.

[Means for solving problems]

In order to solve the above problems, the present invention includes a fuel pumping chamber, a plunger that is driven by the engine and pressurizes the fuel in the fuel pumping chamber, and a fuel pump that opens into the fuel pumping chamber when the plunger is in the compression preparation position. a supply port, a fuel injection hole normally closed by a spring-loaded needle, and a fuel overflow chamber from the high-pressure fuel supply path provided within the high-pressure fuel supply path that communicates the fuel pumping chamber and the fuel injection hole. In a unit injector equipped with a slide valve that opens a fuel overflow port leading to the fuel overflow port when fuel injection is stopped, and an actuator that controls the slide valve, a spring that biases the slide valve in a direction that opens the fuel overflow port; , a pressure transmission chamber defined by a piston driven by an actuator, and a sliding valve driven by fuel pressure in the pressure transmission chamber and oriented to close the fuel overflow port when the fuel pressure in the pressure transmission chamber increases. It includes a pressing rod and a fuel filling passage connected within the pressure transmission chamber and opening into the fuel pumping chamber when the plunger is in the compression ready position.

〔Example〕

Referring to the drawings, a sliding valve holder 3 is fitted into the main body 2 of the unit injector 1, and the sliding valve holder 3 is fixed to the injector main body 2 together with a nozzle support 4 by a nut 5. A nozzle 6 is installed at the tip of the nozzle support 4.
is fixed by the nozzle holder 8 via the spacer 7,
A fuel injection hole 9 is formed at the tip of the nozzle 6 . Inside the nozzle 6 is a needle 1 that controls opening and closing of the fuel injection hole 9.
A compression spring 12 is inserted into the nozzle support 4 to press the needle 10 toward the fuel injection hole 9 via a pressure pin 11.

Therefore, the fuel injection hole 9 is normally closed by a needle 10. A fuel passage 13 is formed in the nozzle support 4 and communicates with a pressurizing chamber 15 around a conical pressure receiving surface 14 formed in the middle part of the needle 10. This pressurized chamber 15 is connected to the fuel injection hole 9 via an annular gap around the needle 10. When the fuel pressure in the fuel passage 13 and, therefore, the fuel pressure in the pressurizing chamber 15 increases, the needle 10 is raised against the spring force of the compression spring 12, so that high-pressure fuel flows into the fuel injection hole. It is injected from 9.

On the other hand, a plunger hole 16 extending from the upper end of the injector body 2 to the sliding valve support 3 is provided in the injector body 2.
is formed in the plunger hole 16, and a plunger 1 is inserted into the plunger hole 16.
7 is slidably inserted. Between this plunger 17 and the sliding valve support 3.

A fuel pumping chamber 18 is formed. The upper end of the plunger 17 is connected to a tappet 19, and a compression spring 20 is inserted between the tappet 19 and the injector body 2 to constantly bias the plunger 17 upward. The tappet 19 has a roller 21 rotatably mounted on the tappet 19, which roller 21 is displaced on the cam surface of an engine-driven cam 22. Therefore, when the cam 22 rotates, the plunger 1
It can be seen that 7 can be moved up and down. Sliding valve support 3
There is an annular fuel chamber 23 surrounding the sliding valve support 3.
is formed, and this annular fuel chamber 23 is connected to a fuel supply pump (not shown) via a fuel supply port 24. on the other hand,
A fuel overflow chamber 23a constituting a part of the annular fuel chamber 23 is formed on the opposite side of the fuel supply port 240 with respect to the sliding valve support 3, and this fuel overflow chamber 23a receives fuel via a constant pressure control valve (not shown). connected to the tank. Fuel fed into the annular fuel chamber 23 from the fuel supply pump through the fuel supply port 24 circulates around the sliding valve support 3 and flows into the fuel overflow chamber 23a.
is then returned to the fuel tank via the constant pressure control valve. Therefore, the fuel pressure in the annular fuel chamber 23 is maintained at a constant pressure by this constant pressure control valve. This constant pressure is, for example, l
The pressure is as low as 2 kg/cd to 2 kg/cd. As shown in the drawings, when the roller 21 is in contact with the reference circular cam surface portion of the cam 22, the plunger 17 is at the upper end position, that is, the compression preparation position. A fuel supply port 25 communicating with the annular fuel chamber 23 is formed on the inner wall surface of the fuel pumping chamber 18, and this fuel supply port 25 is connected to the plunger 1.
7 opens into the fuel pumping chamber 18 when it is in the compression preparation position. Further, the annular fuel chamber 23 communicates with the accommodation chamber of the compression spring 12 via a leakage fuel discharge passage 26 . compression spring 1
The fuel leaked into the second storage chamber is returned into the annular fuel chamber 23 via the leaked fuel discharge passage 26.

A slide valve insertion hole 27 extending laterally is provided in the slide valve support 3.
is formed, and a slide valve 28 is slidably inserted into this slide valve insertion hole 27. The sliding valve insertion hole 27 has a fuel overflow port 29 at one end thereof, which opens into the fuel overflow chamber 23a. The slide valve 28 includes an annular groove 30 extending along its entire outer peripheral surface, and an enlarged head 31 formed adjacent to the annular groove 30 and having a larger diameter than the slide valve insertion hole 27.

The enlarged head 31 is located within the fuel overflow chamber 23a, and the enlarged head 31 controls opening and closing of the fuel overflow port 29. The annular groove 30 of the slide valve 28 communicates with the fuel pumping chamber 18 via a fuel passage 32, and a pressure control valve that can flow only from the annular groove 30 into the fuel pumping chamber 18 is in this fuel passage 32. A check valve 33 is arranged. This pressure control check valve 33 consists of a ball 34 and a compression spring 35. Note that this pressure control check valve 33 does not necessarily need to be provided. Further, the annular groove 30 of the slide valve 28 communicates with the fuel passage 13 via a fuel passage 36.
A check valve 37 that allows flow only from the annular groove 30 toward the fuel passage 13 and a bar filter 38 for removing foreign matter from the fuel are inserted inside.

A compression spring 39 is inserted between the inner wall surface of the annular fuel chamber 23 on the opposite side to the fuel overflow chamber 23a and the slide valve 28, and the spring force of the compression spring 39 causes the slide valve 28 to close to the fuel overflow port 2.
9 is biased in the direction of opening the valve.

A rod 40 that is aligned with the slide valve 28 and abuts the enlarged head 31 of the slide valve 28 is slidably inserted into the injector body 2, and a rod drive device 41 for driving the rod 40 is connected to the injector. It is installed inside the main body 2. This rod drive device 41 includes a casing 42 fixed to the injector body 2, a piston 43 slidably supported within the casing 42, and an actuator 4 inserted between one end of the piston 43 and the casing 42.
4, a small volume pressure transmission chamber 45 defined by the other end of the piston 43, and an actuator 44 that connects the piston 43 to an actuator 44.
The outer end surface of the rod 40 is exposed in the pressure transmission chamber 45. The actuator 44 is composed of a piezoelectric element formed by laminating a large number of thin plate-like piezoelectric elements. When a voltage is applied to the piezoelectric element 44, the piezoelectric element produces longitudinal strain due to the electrostrictive effect, that is, it stretches in the longitudinal direction. For example, this amount of elongation is 5
0. Although the amount is as small as 1jm, the response time is extremely short. On the other hand, when the voltage application is stopped, the piezoelectric element 44 immediately contracts, and the response time at this time is also extremely short.

A fuel filling port 47 is formed on the inner wall surface of the fuel feeding chamber 18, and this fuel filling port 47 is communicated with the inside of the pressure transmitting chamber 45 via a fuel filling passage 48. This fuel filling port 47 opens into the fuel pumping chamber 18 when the plunger 17 is in the compression ready position. However, this fuel filling port 47 is slid relative to the fuel supply port 25 so that when the plunger 17 is lowered, the fuel supply port 25 is first closed by the plunger 17, and then the fuel filling port 47 is closed by the plunger 17. valve 2
Formed on the side closer to 8.

As mentioned above, the check valve 33 does not necessarily need to be provided, and therefore, first, the operation of the injector will be described for the case where the check valve 33 is not provided.

When the plunger 17 is in the compression preparation position, the application of voltage to the piezoelectric element 44 is stopped, and the piezoelectric element 44 is contracted. At this time, the slide valve 28 and the rod 40 move to the right, and the enlarged head 31 of the slide valve 28 opens the fuel overflow port 29. Therefore, at this time, the annular groove 3°O of the sliding valve 28 communicates with the fuel overflow chamber 23a. On the other hand, at this time, fuel is sent into the fuel pumping chamber 18 from the fuel supply port 25, and therefore the fuel pumping chamber 18 is filled with fuel. Further, a portion of the fuel sent into the fuel pressure feeding chamber 18 from the fuel supply port 25 is transferred to the fuel transfer chamber 45 via the fuel filling port 47 and the fuel filling passage 48.
The fuel transfer chamber 45 is thus also filled with fuel. At this time, the fuel transfer chamber 45, the fuel pressure feeding chamber 18
The annular grooves 30 of the slide valves 28 and 28 all communicate with the annular fuel chamber 23, so that the fuel pressure within each of these chambers or grooves is approximately equal.

Plunge 17 then descends to first close fuel supply port 25 and then close fuel fill port 47. Then, even if the plunger 17 further descends, the fuel in the fuel pumping chamber 18 only flows out into the fuel overflow chamber 23a through the fuel passage 32 and the annular groove 30 of the sliding valve 28, so that the fuel in the fuel pumping chamber 18 Pressure does not increase. Next, when it is time to start fuel injection, a voltage is applied to the piezoelectric element 44, and as a result, the piezoelectric element 44 extends, causing the piston 43 to move to the left. At this time, fuel filling port 4
7 is closed by the plunger 17, the pressure within the pressure transmission chamber 45 immediately rises. As a result, the rod 40 moves to the left, causing the slide valve 28 to move to the left against the spring force of the compression spring 39, such that the enlarged head 31 of the slide valve 28 moves into the fuel overflow port 29. will be closed. When the fuel overflow port 29 is closed, the pressure inside the fuel feeding chamber 18 immediately increases, and at the same time, the high pressure fuel passages from the fuel feeding chamber 18 to the fuel injection holes 9, that is, the fuel passage 32, the annular groove 30, and the fuel passage 36 , 13 and the pressure inside the pressurizing chamber 15 also rise immediately. As a result, the needle 10 rises and fuel injection begins. Plunger 17 then continues to descend, allowing fuel injection to continue. When the fuel injection completion time comes, the application of voltage to the piezoelectric element 44 is stopped, and the piezoelectric element 44 contracts. As a result piston 4
3 moves to the right, the pressure within the pressure transmission chamber 45 immediately decreases. When the pressure in the pressure transmission chamber 45 decreases, the slide valve 28 and rod 40 move to the right by the spring force of the compression spring 39, and the enlarged head 31 of the slide valve 28 opens the fuel overflow port 29. . As a result, the pressure in the fuel pumping chamber 18 and the high-pressure fuel passage decreases, so that the needle 1
0 closes the fuel injection hole 9, thus stopping the fuel injection action. Incidentally, since the injector according to the present invention has extremely good responsiveness, when the sliding valve 28 opens the fuel overflow port 29, the fuel pressure in the high pressure fuel passage immediately decreases.

However, if the fuel pressure in the high-pressure fuel passage suddenly drops before the needle 10 completely opens the fuel injection hole 9, there is a risk that combustion gas will be sucked in from the fuel injection hole 9. Therefore, a check valve 37 is provided to prevent combustion gas from being sucked in in this way. That is, when such a check valve 37 is provided, when the fuel pressure in the high-pressure fuel passage starts to decrease, the check valve 39 opens, and thus the pressure in the fuel passage 13 and the pressurizing chamber 15 decreases. - It is possible to prevent combustion gas from being inhaled because the temperature does not become low.

Next, when the plunger 17 starts its upward movement, the check valve 3
3 is not provided, fuel is sent into the fuel pumping chamber 18 from the fuel passage 32.

Then, when the plunger 17 rises again to the compression preparation position, fuel is replenished into the fuel feeding chamber 18 from the fuel supply port 25, and at the same time, the pressure transmission chamber 45 is replenished with fuel.

In this way, in the present invention, the pressure transmission chamber 45 is replenished with fuel each time the plunger 17 moves up and down, so that the pressure transmission chamber 45 is reliably filled with fuel before voltage is applied to the piezoelectric element 44. It turns out. In addition, the piezoelectric element 4
Since the fuel filling port 47 is completely closed by the plunger 17 when a voltage is applied to the pressure transmission chamber 45, the pressure inside the pressure transmission chamber 45 can be reliably increased, and thus fuel injection can be performed reliably. .

As mentioned above, the fuel pressure in the annular fuel chamber 23 is l kg
/ c- to 2 kg/a (low pressure), therefore, the engine speed becomes high and the opening time of the fuel filling port 47 by the plunger 17 is short (there is a risk that sufficient fuel will not be supplied into the pressure transmission chamber 45). To avoid such a risk, it is preferable to provide a check valve 33 in the fuel passage 32 that opens at a constant pressure as shown in the drawings.

That is, as described above, when the plunger 17 starts to move downward, the fuel supply port 25 is first closed, and then the fuel filling port 47 is closed, but a check valve 33 is provided which opens at a constant pressure. As soon as the plunger 17 closes the fuel supply port 25, the compression action of the fuel in the fuel pumping chamber 18 starts, and the fuel pressure in the fuel pumping chamber 18 increases. This fuel pressure is applied to the fuel filling port 47 in the fuel pumping chamber 1.
Since the pressure increases considerably while communicating with the inside of the pressure transmission chamber 45, high-pressure fuel is sent into the pressure transmission chamber 45. By providing the check valve 33 in this way, high pressure fuel can be transferred to the pressure transmission chamber 45.
Since the fuel is fed into the pressure transmission chamber 45, the pressure transmission chamber 45 can be completely filled with fuel even if the engine speed becomes high.

On the other hand, in order to stop the fuel injection action with good response when the voltage application to the piezoelectric element 44 is stopped or stopped, the spring force of the compression spring 39 that biases the slide valve 28 in the valve opening direction is made as strong as possible. It is necessary to study. However, if the spring force of the compression spring 39 is made too strong, the pressing force acting on the rod 40 when voltage is applied to the piezoelectric element 44 will not be able to press the sliding valve 28 in the valve closing direction. However, if high-pressure fuel is sent into the pressure transmission chamber 45, the sliding valve 2 can be reliably closed even if the spring force of the compression spring 39 is increased. That is, when high-pressure fuel is sent into the pressure transmission chamber 45, the piezoelectric element 44 contracts slightly, but the pressure transmission chamber 45 is filled with high-pressure fuel. However, the piezoelectric element 44 has a property that it always expands by a certain amount regardless of the pressure inside the pressure transmission chamber 45 when a voltage is applied. Therefore, even if the pressure transmission chamber 45 is filled with high-pressure fuel, the volume reduction rate in the pressure transmission chamber 45 when voltage is applied to the piezoelectric element 44 is sufficiently large, and the pressure transmission chamber 45 before the volume reduction
Since the pressure inside is high pressure, the pressure transmission chamber 45 after volume reduction
The pressure inside becomes quite high. Therefore, by feeding high-pressure fuel into the pressure transmission chamber 45, the sliding valve 28 can be reliably closed even if the spring force of the compression spring 39 is increased.

By sending high-pressure fuel into the pressure transmission chamber 45 in this manner, the spring force of the compression spring 39 can be increased, so that the responsiveness of stopping fuel injection can be improved. Note that if the check valve 33 is provided, fuel will not be supplied from the fuel passage 32 into the fuel pumping chamber 18 when the plunger 17 rises, so the pressure in the fuel pumping chamber 18 will decrease, and the plunger 17 will close the fuel filling port 47. When the pressure transmission chamber 45 is opened, part of the fuel in the pressure transmission chamber 45 flows out into the fuel pressure transmission chamber 18, but when the plunger 17 descends, high pressure fuel is pumped into the pressure transmission chamber 45 again, so no problem occurs. .

〔Effect of the invention〕

The pressure transmission chamber can be reliably filled with fuel, and when voltage is applied to the piezoelectric element, the plunger completely blocks the outflow of fuel from the pressure transmission chamber, so when voltage is applied to the piezoelectric element. In this way, the fuel pressure within the pressure transmission chamber can be reliably increased, and thus fuel injection can be performed reliably.

[Brief explanation of the drawing]

The figure is a side sectional view of the unit injector. 9...Fuel injection hole, 10...Needle,
17...Plunger, 18...Fuel pressure feeding chamber,
23... Annular fuel chamber, 23a... Fuel overflow chamber, 25... Fuel supply port, 28... Sliding valve, 2
9... Fuel overflow port, 30... Annular groove, 40...
...Rod, 43...Piston, 44.
...Actuator, 45...Pressure transmission chamber, 47.
...Fuel filling port, 48...Fuel filling passage. 45...Pressure transmission chamber 48...Fuel filling passage

Claims (1)

[Claims] A fuel pumping chamber, a plunger driven by the engine and pressurizing the fuel in the fuel pumping chamber, a fuel supply port that opens into the fuel pumping chamber when the plunger is in the ready compression position, and a spring-loaded needle that normally The closed fuel injection hole and the fuel overflow port, which is provided in the high-pressure fuel supply path that communicates the fuel pumping chamber and the fuel injection hole and communicates from the high-pressure fuel supply path to the fuel overflow chamber, are opened when fuel injection is stopped. A unit injector comprising a sliding valve that controls the sliding valve and an actuator that controls the sliding valve, wherein the unit injector includes a spring that biases the sliding valve in a direction to open the fuel overflow port, and a piston that is driven by the actuator. a pressure transmission chamber defined therein; a rod driven by fuel pressure within the pressure transmission chamber and urging the sliding valve in a direction to close the fuel overflow port when fuel pressure within the pressure transmission chamber increases; A unit injector comprising a fuel filling passage connected to a pressure transmission chamber and opening into the fuel pumping chamber when the plunger is in a compression ready position.