JPH1150930A - Accumulator fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accelerate a pressure recovery by checking any drop in fuel pressure immediately after injection starting. SOLUTION: Both first and second fuel supply ports 27 and 28 ranging to a fuel sump chamber 18 are installed each in a nozzle body 2 and a nozzle holder, and the first fuel supply port 27 is connected to an accumulator pipeline via a filter, while the second fuel supply port 28 is connected to this accumulator pipeline as well by way of no filter. A ball 30 as a check valve is installed in a spot midway in the first fuel supply port 27, while a piston storage port 32 is installed in the midway of the second fuel supply port 28, storing a spring 34 and a piston 33. When a needle valve 7 goes up and a sealing part 24 separates from a valve seat part 17, fuel is sprayed out of a nozzle hole 19 by way of a passage 23 from the first fuel supply port 27. Immediately after the injection, if fuel pressure in this passage 23 goes down, the piston 33 is shifted to the downstream side against resilience of the spring 34, thereby making this fuel pressure in the passage 23 go up in consequence.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for an internal combustion engine, and more particularly to a pressure accumulation type fuel injection device having a pressure accumulation chamber (also called a common rail) for storing fuel pressurized by a fuel pump. It is.

[0002]

2. Description of the Related Art An accumulator type fuel injection device often used in an internal combustion engine such as a diesel engine is disclosed in JP-A-8-29.
As disclosed in Japanese Patent No. 6520 and the like, the injection hole connected to the pressure accumulation chamber via the fuel passage is opened and closed by a needle valve, and the needle valve is lifted to open the injection hole, thereby injecting fuel in the pressure accumulation chamber. It is designed to be injected from a hole.

When the behavior of the fuel pressure in the vicinity of the injection hole is examined, as shown by the broken line in FIG. 6 (G), immediately after the injection hole is opened, the fuel pressure becomes lower than when the needle valve is normally closed. Thereafter, during the fuel injection, the pressure gradually recovers, slightly rises immediately after the injection is completed, and returns to the pressure at the time of the steady valve closing again. This pressure behavior is due to the opening and closing of the injection hole.

[0004]

As described above, when the fuel pressure near the injection hole immediately after the start of the injection is reduced, the penetration force of the fuel injected at the beginning of the injection is reduced, and the injection rate is reduced. In general, in combustion in a high-speed and high-load region of an internal combustion engine, it is said that it is advantageous to reduce the generation of smoke by injecting fuel in a short time by making the injection rate pattern as rectangular as possible. The reduction of the injection rate in the initial stage is not good in that sense. Further, a decrease in the penetration force causes insufficient atomization of the fuel, making it easy to generate smoke, which is inconvenient.

Therefore, it is desirable not to lower the pressure near the injection hole during fuel injection, but this is practically impossible. One method is to set the injection pressure higher in anticipation of the fuel pressure drop at the beginning of the injection, but doing so increases the load on the fuel pump and increases the mechanical loss of the internal combustion engine, which is disadvantageous. not only,
This is disadvantageous in terms of pressure resistance and durability of the fuel injection system device, and causes an increase in cost.

Therefore, it is conceivable that the recovery of the fuel pressure after the reduction is made as fast as possible, assuming that the fuel pressure in the initial stage of the injection is not reduced. For that purpose, it is necessary to make the flow path length from the pressure accumulating chamber to the injection hole as short as possible and increase the flow path area.

However, in a multi-cylinder internal combustion engine, when distributing from one accumulator to the injection system of each cylinder,
It is practically impossible to shorten the flow path to each cylinder, and it is difficult to increase the flow path area because the size of the internal combustion engine is increased. In particular, in the case of a vehicle internal combustion engine, the installation space is limited, and it is extremely difficult to increase the flow path area.

In addition, if foreign matter is caught between the needle valve and its valve seat, there is a possibility that the fuel injection may not be completely stopped. Therefore, a filter is generally provided in the middle of the fuel passage. This contributes to delaying the recovery of fuel pressure after the resistance drops.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to suppress a decrease in fuel pressure immediately after the start of injection and to quickly recover pressure. Thus, it is intended to improve the combustion of the internal combustion engine.

[0010]

The present invention has the following features to attain the object mentioned above. The pressure-accumulation type fuel injection device of the present invention is a pressure-accumulation type fuel injection device in which a fuel passage connecting a pressure accumulation chamber and an injection hole is opened and closed by a needle valve. The pressure accumulating chamber is connected to the pressure accumulating chamber via a bypass passage, and a piston that is movable in the bypass passage so as to balance its own longitudinal pressure is inserted.

In this pressure accumulating fuel injection device, the fuel pressure in the pressure accumulating chamber is constantly applied to the upstream side of the piston in the bypass passage regardless of the opening and closing of the needle valve. When the needle valve is opened and fuel is injected from the injection hole, the fuel pressure on the fuel passage upstream of the injection hole decreases, but the upstream side of the injection hole is connected to the piston downstream of the bypass passage, and the piston Since the pressure downstream is lower than the pressure upstream, the piston moves in the downstream direction to pressurize the downstream side, thereby trying to balance the upstream pressure and the downstream pressure of the piston. Thereby, the fuel pressure on the upstream side of the injection hole in the fuel passage is increased. Therefore, a decrease in the fuel pressure immediately after the start of the injection can be suppressed to a small value, and a quick recovery of the fuel pressure can be achieved. This makes it possible to increase the penetration force of the fuel at the beginning of the injection, and to increase the initial injection rate.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the accumulator type fuel injection device according to the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic overall system of a pressure accumulating fuel injection device (hereinafter, abbreviated as an injection device) according to a first embodiment. Fuel in a fuel tank 100 is sucked up by a fuel pump 101. Accumulation piping (accumulation chamber)
The pressure is sent to the pressure accumulating pipe 102 and stored in the pressure accumulating pipe 102 in a high pressure state. The fuel pressure in the pressure accumulation pipe 102 is
The electric signal is detected by the electronic control unit 03 and converted into an electric signal, which is input to an engine control unit (hereinafter abbreviated as ECU) 200. The fuel pump 101 is feedback-controlled based on an output signal and the like from the pressure sensor 103,
The fuel in the pressure accumulation pipe 102 is kept at a predetermined pressure.

The high-pressure fuel in the pressure accumulation pipe 102 is guided to the injector 1 of each cylinder of an internal combustion engine such as a diesel engine via the first fuel supply pipe 104, and from the injector 1 the combustion chamber of each cylinder (not shown). Is injected. Further, the injector 1 stores excess fuel in the fuel tank 10.
A return pipe 105 returning to 0 is connected. The opening and closing of the injector 1 is controlled according to the operating conditions of the internal combustion engine.
It is controlled by U200.

As shown in FIG. 2, the injector 1 includes a nozzle body 2, a nozzle holder 3, a nozzle nut 4, a holder head 5, a cap 6, a needle valve 7, a first stem 8, a second stem 9, and a control valve 10, , Electromagnetic actuator 1
1 is a main configuration.

The nozzle body 2 is arranged below the nozzle holder 3 and is fixed to the nozzle holder 3 by a nozzle nut 4. At the center of the nozzle holder 3, stem receiving holes 12a and 12b penetrating in the axial direction are continuously provided. The first stem 8 is inserted into the stem receiving hole 12a in a liquid-tight manner so as to be slidable up and down. The second stem 9 is inserted into the storage hole 12b so as to be vertically movable. The space above the upper surface of the first stem 8 in the stem housing hole 12a forms a back pressure chamber 45.

As shown in FIG. 3, the tip end of the nozzle body 2 is formed thin, and a bottomed needle valve housing hole 13 extending downward from the upper surface along the axial direction is provided at the center. The needle valve housing hole 13 is opened on the upper surface of the nozzle body 2 and the stem housing hole 12 of the nozzle holder 3 is opened.
b, a fuel passage hole 15 extending below the large diameter hole portion 14, and a small diameter hole portion 16 extending below the fuel passage hole 15. The bottom is a tapered valve seat 17. An annular fuel reservoir 18 is provided in the nozzle body 2 at the boundary between the large-diameter hole 14 and the fuel passage hole 15. Further, a plurality of injection holes 19 connected to the small-diameter hole portion 16 are provided at predetermined intervals in the circumferential direction at the distal end portion of the nozzle body 2.

The needle valve 7 is housed in the needle valve housing hole 13 of the nozzle body 2 so as to be vertically movable, and has a large-diameter portion 20 slidable in a liquid-tight manner in the large-diameter hole portion 14 of the needle valve storage hole 13. , A small diameter portion 21 inserted into the fuel passage hole 15, and a fuel reservoir chamber 1 formed between the large diameter portion 20 and the small diameter portion 21.
8 and a tapered portion 22 located inside the tapered portion 8.

A passage 23 through which fuel can flow is provided between the inner peripheral surface of the fuel passage hole 15 and the outer peripheral surface of the small diameter portion 21.
The passage 23 and a first fuel supply hole 27 described below constitute a fuel passage in this embodiment. Needle valve 7
The tip of the small-diameter portion 21 is a seal portion 24 which can be seated on and separated from the valve seat portion 17 of the nozzle body 2.
The flow of fuel to the valve seat 9 is prevented.
When it is separated from 7, fuel can flow from the passage 23 to the injection hole 19. That is, the fuel passage is opened and closed by the needle valve 7.

The projection 25 at the upper end of the needle valve 7 is connected and fixed to the lower end of the second stem 9, and the second stem 9 is urged downward by a spring 26 housed in the stem housing hole 12b. Accordingly, the needle valve 7 is biased in the valve closing direction.

The nozzle body 2 and the nozzle holder 3
A first fuel supply hole 27 and a second fuel supply hole (bypass passage) 28 having one end connected to the fuel reservoir chamber 18 and the other end opened to the outer surface of the nozzle holder 3 are provided. First
The fuel supply hole 27 is connected to the pressure accumulation pipe 102 via the first fuel supply pipe 104, and the second fuel supply hole 28 is
The fuel supply pipe 106 is connected to the pressure accumulating pipe 102.

First fuel supply hole 2 in nozzle holder 3
7 is provided with a filter 44. Nozzle body 2
In the middle of the first fuel supply hole 27 in FIG.
The check valve housing hole 29 accommodates a ball 30 as a check valve and a spring 31 for urging the ball 30 in the valve closing direction.

On the other hand, a piston housing hole 32 is provided in the middle of the second fuel supply hole 28 in the nozzle body 2, and the piston housing hole 32 is provided in the piston housing hole 32.
And a spring 34 for urging the piston 33 upstream of the second fuel supply hole 28 are housed. The piston 33 moves so as to balance the pressure before and after the piston 33 in the second fuel supply hole 28, that is, the pressure on the upstream side and the pressure on the downstream side with the piston 33 as a boundary. That is, when the pressure downstream of the piston 33 in the second fuel supply hole 28 becomes smaller than the pressure upstream of the piston 33, the piston 33 moves downward in the piston housing hole 32 against the urging force of the spring 34, Pressurize the downstream side to equilibrate the pressure.

Holder head 5 and electromagnetic actuator 11
Is located above the nozzle holder 3 and is fixed to the nozzle holder 3 by a cap 6. Plates 36 and 37 are sandwiched between the nozzle holder 3 and the holder head 5.

The holder head 5 is provided with a control valve housing hole 38, and the holder head 5 and the plates 36 and 37 are provided with a back pressure passage 39 for communicating the control valve housing hole 38 with the back pressure chamber 45. The holder 3 and the plate 36 are provided with a third fuel supply hole 40 for communicating the first fuel supply hole 27 and the back pressure passage 39, and one end of the holder head 5 and the cap 6 is connected to the control valve housing hole 38. End is return pipe 105
The nozzle holder 3 and the plates 36 and 37 are provided with a pressure guiding hole 42 communicating the stem housing hole 12b and the return passage 41.

A control valve 10 having a ball 10a for opening and closing the upper opening of the back pressure passage 39 is housed in the control valve housing hole 38 so as to be vertically movable. The control valve 10 is urged downward by a spring (not shown), and is opened and closed by ON / OFF of the electromagnetic actuator 11. That is, when the electromagnetic actuator 11 is turned on, the control valve 10 is pulled upward by the armature 43 against the urging force of the spring, and the ball 10a separates from the upper opening of the back pressure passage 39 as shown in FIG. Is communicated between the back pressure passage 39 and the return passage 41. On the other hand, when the electromagnetic actuator 11 is turned off, the control valve 10 is pushed down by the spring, and the ball 10a closes the upper opening of the back pressure passage 39 and shuts off the back pressure passage 39 and the return passage 41 as shown in FIG. .

Next, the operation of this device will be described. First fuel supply hole 27 and second fuel supply hole 28 of injector 1
Is always supplied with fuel in the pressure accumulation pipe 102, and the fuel pressure in the pressure accumulation pipe 102 is applied.

When the electromagnetic actuator 11 is OFF, the ball 10a of the control valve 10 closes the upper opening of the back pressure passage 39 to cut off the back pressure passage 39 and the return passage 41. 3 The fuel supplied to the back pressure passage 39 through the fuel supply hole 40 flows into the back pressure chamber 45 without flowing to the return passage 41, and the fuel pressure in the pressure accumulation pipe 102 is applied to the upper surface of the first stem 8. This produces a force that pushes down the first stem 8, which is transmitted to the needle valve 7 via the second stem 9.

In this state, the force acting on the needle valve 7 to lower the first stem 8 by the fuel pressure in the back pressure chamber 45 acting on the first stem 8 and the spring 26 acting on the second stem 9 And force to push down the needle valve 7 downward,
The fuel pressure in the fuel storage chamber 18 acts on the tapered portion 22 of the needle valve 7 to apply a force for pushing the needle valve 7 upward, but the force for pushing the needle valve 7 downward is greater than the force for pushing the needle valve 7 upward. , The needle valve 7 is pushed down. As a result, the sealing portion 24 of the needle valve 7
Is seated on the valve seat 17 of the nozzle body 2, the injector 1 is closed, and the electromagnetic actuator 11 is turned off.
As long as it is in the state, the injector 1 is kept in the valve closed state.

When the electromagnetic actuator 11 is turned on,
The control valve 10 is lifted upward, and the ball 10a is separated from the upper opening of the back pressure passage 39 to connect the back pressure passage 39 and the return passage 41. Therefore, the first fuel supply hole 27 to the third fuel supply hole The fuel supplied to the back pressure passage 39 through the fuel tank 40 and the fuel in the back pressure chamber 45 flow out to the return passage 41 and are returned to the fuel tank 100 via the return pipe 105.
Is discharged. As a result, the fuel pressure in the back pressure chamber 45 decreases, the pressure balance holding the needle valve 7 in the closed state is broken, and the force for pushing the needle valve 7 upward is superior to the force for pushing the needle valve 7 downward. The needle valve 7 moves up together with the first stem 8 and the second stem 9 to separate the seal portion 24 from the valve seat portion 17 and open the valve. Then, the fuel supplied to the first fuel supply hole 27 pushes down the ball 30 as a check valve, and the fuel reservoir chamber 18 and the passage 2
3 and is injected from the injection hole 19.

The needle valve 7 continues to rise until the upper surface of the first stem 8 hits the lower surface of the plate 36. While the injector 1 is open, a part of the fuel supplied to the first fuel supply hole 27 passes through the third fuel supply hole 40, the back pressure passage 39, the return passage 41, and the return pipe 105 while a small amount. And is continuously discharged to the fuel tank 100.

Meanwhile, at the same time when the seal portion 24 of the needle valve 7 is separated from the valve seat portion 17, the fuel pressure in the passage 23 drops. However, the injector 1 has the second fuel supply hole 28 and the piston 33, and the fuel pressure in the pressure accumulating pipe 102 is constantly applied upstream of the piston 33, so that the fuel pressure in the passage 23 decreases. When a pressure difference equal to or greater than a predetermined value is generated between the upstream and downstream of the piston 33, the piston 33 moves downstream against the elasticity of the spring 34 to balance the pressure, and pressurizes the downstream.

As a result, the decrease in fuel pressure near the injection hole 19 immediately after the start of fuel injection is reduced, the pressure recovery is faster than before, the actual injection pressure is increased, and the fuel penetration force at the beginning of injection is increased. The fuel atomization is promoted. Further, the fuel injection rate in the early stage of the injection also increases. Therefore, the combustion of the internal combustion engine can be improved, and the suppression of smoke generation in a high-speed and high-load region, the improvement of startability at low temperatures, and the suppression of white smoke can be achieved.

When the upstream pressure and the downstream pressure are balanced, the piston 33 is pushed upward by the elasticity of the spring 34, and is usually located at the upstream end in the piston receiving hole 32.

FIG. 6 is a characteristic diagram of the injector.
(A) is a diagram showing a drive pulse waveform, (B) is a back pressure chamber 45
(C) is a diagram showing a change in the flow rate of fuel supplied to the first fuel supply hole 27, and (D) is a diagram showing a change in the flow rate of fuel discharged from the return passage 41. (E) is a diagram showing a change in the lift amount of the needle valve 7,
(F) illustrates a change in the fuel injection rate, and (G) illustrates the passage 23.
FIG. 5 is a diagram showing a change in fuel pressure in the inside. (E),
In (F) and (G), the solid line shows the characteristic of the injector 1 in this embodiment, and the broken line shows the characteristic of the conventional injector, and (A), (B), (C),
(D) is the same in this embodiment and the conventional one.

6 (E), 6 (F), and 6 (G), the injector 1 has a smaller fuel pressure drop near the injection hole 19 immediately after the start of injection than the conventional injector, and has a smaller pressure recovery than the conventional injector. It can be seen that the fuel injection rate is higher than before and the fuel injection rate in the early stage of the injection is increased.

[0037]

As described above, according to the pressure-accumulation type fuel injection device of the present invention, in the pressure-accumulation type fuel injection device in which the fuel passage connecting the pressure accumulation chamber and the injection hole is opened and closed by the needle valve, A portion of the passage upstream of the valve seat of the needle valve is connected to the pressure accumulating chamber via a bypass passage, and a piston that is movable in the bypass passage so as to balance its own longitudinal pressure is inserted. The fuel pressure drop in the vicinity of the injection hole immediately after the start of injection can be reduced, the actual injection pressure increases, the penetration force of the fuel in the initial stage of injection increases, the fuel can be atomized, and the injection rate can be increased. can do. Therefore,
It is possible to improve the combustion of the internal combustion engine, to suppress the generation of smoke in a high-speed and high-load range, to improve the startability at low temperatures, and to suppress the generation of white smoke.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall system of a pressure accumulating fuel injection device according to the present invention.

FIG. 2 is an overall longitudinal sectional view of an injector in one embodiment of the accumulator type fuel injection device of the present invention.

FIG. 3 is an enlarged longitudinal sectional view of a nozzle body of an injector in one embodiment of the accumulator type fuel injection device of the present invention.

FIG. 4 is an enlarged longitudinal sectional view of a main part near a control valve when the injector is closed in one embodiment of the pressure accumulating fuel injection device of the present invention.

FIG. 5 is an enlarged longitudinal sectional view of a main part near a control valve when an injector is opened in an embodiment of the pressure accumulating fuel injection device of the present invention.

FIG. 6 is a characteristic diagram of an injector.

[Explanation of symbols]

 7 Needle valve 17 Valve seat 19 Injection hole 23 Gap (fuel passage) 27 First fuel supply hole (fuel passage) 28 Second fuel supply hole (bypass passage) 33 Piston 102 Pressure accumulation pipe (pressure accumulation chamber)

Claims (1)

[Claims] 1. A pressure accumulating fuel injection device in which a fuel passage connecting a pressure accumulating chamber and an injection hole is opened and closed by a needle valve, wherein a portion of the fuel passage upstream of a valve seat of the needle valve and the pressure accumulating chamber are formed. A pressure-accumulation type fuel injection device which is connected via a bypass passage, and in which a piston which is movable to balance its own longitudinal pressure is inserted.